USE OF REVERSE OSMOSIS TO RECOVER WATER …3961/datastream/OBJ/...USE OF REVERSE OSMOSIS TO RECOVER...

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USE OF REVERSE OSMOSIS TO RECOVER WATER FROM A NUTRIENT SEPARATION SYSTEM FOR

DAIRY MANURE MANAGEMENT

By

John Stephen Budaj

A THESIS

Submitted to Michigan State University

in partial fulfillment of the requirements for the degree of

Biosystems Engineering - Master of Science

2016

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ABSTRACT

USE OF REVERSE OSMOSIS TO RECOVER WATER FROM A NUTRIENT SEPARATION SYSTEM FOR DAIRY MANURE MANAGEMENT

By

John Stephen Budaj

Manure storage is sometimes limited and over application of manure on fields is dangerous

to the environment, especially ground water. Filtration systems using reverse osmosis (RO), are one

alternative approach to reusing waste water and eliminating risk for manure spills or harming the

environment. There are various challenges involved when trying to optimize this system, one of

which is membrane fouling upon the RO filters. The rapid increase in pressure and reduced

permeate generation due to fouling is problematic. To address this issue, antiscalant was added to

the feed and the feed stream was pH adjusted using sulfuric acid or hydrochloric acid. In order to

determine what foulants were present on the membrane, some of the membranes were dissected

and tested using scanning electron microscopy (SEM), energy dispersive x-ray (EDX), chromatic

elemental imaging (CEI), Fourier transform infrared technology (FTIR), and effervescing. Testing

indicated organic and silcate scaling were present under all operating conditions. In addition, there

was a greater degree of scaling using non pH adjusted feed versus pH adjusted. The use of air

stripped water processed through the RO system was used for all the experiments at the pH of 5.5,

6.5, 7.5 and 8. Sulfuric acid and hydrochloric acid were used to lower the pH of the air stripped

water (normal pH of 8) and the various acid runs were compared in the study. After optimizing the

system, and using permeate production as a gauge, the system performed best at a feed pH of 6.5

using sulfuric acid and an appropriate dose of antiscalant, determined by the Avista Advisor

modeling software. The use of hydrochloric acid was very expensive when pH adjusting versus the

use of sulfuric acid for pH adjustment. Operational costs and capital costs were also determined.

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ACKNOWEDGEMENTS

I would like to acknowledge and thank my major professor Dr. Saffron, my mentor Jim

Wallace, my committee member Dr. Safferman, and the great staff in the Biosystems department at

MSU for all their input and assistance during my project.

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TABLE OF CONTENTS

LIST OF TABLES ...................................................................................................................................... vi

LIST OF FIGURES ................................................................................................................................... vii

KEY TO ABBREVIATIONS ......................................................................................................................... x

Chapter 1 - Overview .............................................................................................................................. 1 1.1 Introduction ................................................................................................................................ 1 1.2 Problem Statement ..................................................................................................................... 1 1.3 Objective ..................................................................................................................................... 5

Chapter 2 – Literature Review ................................................................................................................ 6 2.1 History ......................................................................................................................................... 6 2.2 Applications ................................................................................................................................. 7 2.2.1 Desalination of Sea Water ...................................................................................................... 8 2.2.2 Reverse Osmosis Treating Municipal Wastewater ................................................................. 9 2.2.3 Reverse Osmosis in Food Processing .................................................................................... 10 2.2.4 Reverse Osmosis in Manure Management ........................................................................... 10 2.3 Reverse Osmosis Knowledge Needed for Manure Management ............................................. 12 2.4 Reverse Osmosis Membranes ................................................................................................... 14 2.5 Pretreatment ............................................................................................................................ 17 2.6 Antiscalants ............................................................................................................................... 18 2.7 Membrane Fouling .................................................................................................................... 20 2.7.1 Calcium Carbonate Scale ....................................................................................................... 20 2.7.2 Calcium, Barium, Strontium, and Sulfate Scale .................................................................... 20 2.7.3 Calcium Phosphate Scale ...................................................................................................... 21 2.7.4 Metal Oxide/ Hydroxide Foulants ......................................................................................... 21 2.7.5 Polymerized Silica Scale ........................................................................................................ 21 2.7.6 Colloidal Foulants .................................................................................................................. 21 2.7.7 Dissolved Natural Organic Matter (NOM) Foulants .............................................................. 22 2.7.8 Soluble Microbial Products (SMP) and Microbial Deposits .................................................. 22 2.8 Membrane Fouling in Manure Management ........................................................................... 22 2.9 Dynamics of Membrane Fouling ............................................................................................... 23 2.9.1 Concentration Polarization ................................................................................................... 24 2.9.2 Fouling Mechanisms ............................................................................................................. 24 2.9.3 Stages of Fouling ................................................................................................................... 26 2.10 Foulants of interest ................................................................................................................... 27 2.10.1 Silica ...................................................................................................................................... 28 2.10.1.1 Silica’s Chemical Properties .............................................................................................. 29 2.10.1.2 Silica Scaling and Fouling .................................................................................................. 32 2.10.1.3 Carbonate .......................................................................................................................... 34 2.10.1.4 Carbonate’s Chemical Properties ...................................................................................... 35 2.10.1.5 Carbonate Scale ................................................................................................................ 38 2.10.2 Organics (EfOM) .................................................................................................................... 39 2.10.2.1 Humus (Humic substances) ............................................................................................... 40 2.10.3.1 NOM fouling ...................................................................................................................... 42 Chapter 3 – Initial Observations ........................................................................................................... 44

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3.1 Initial Observations ......................................................................................................................... 44 3.2 Hypothesis ....................................................................................................................................... 47 3.3 Materials and Methods ................................................................................................................... 47 3.3.1 Analytical Testing ......................................................................................................................... 47 3.3.2 Modeling Software ....................................................................................................................... 48 3.3.3 Pilot RO System ............................................................................................................................ 48 3.3.4 Scanning Electron Microscopy (SEM) .......................................................................................... 48 3.3.5 Energy Dispersive X-ray (EDX) ...................................................................................................... 49 3.3.6 Chromatic Elemental Imaging (CEI) ............................................................................................. 49 3.3.6 Fourier Transform Infared Technology (FTIR) .............................................................................. 49 3.3.7 Effervescing .................................................................................................................................. 50 3.4 Avista Autopsy and Analysis (membrane run with pH adjusted feed) ........................................... 50 3.4.1 Results of the Salt Passage, Fujiwara Analysis, Dye Testing ........................................................ 51 3.4.2 Results of the Microscopy Testing ............................................................................................... 52 3.4.3 Results of the Fourier Transform Infared Technology (FTIR) Analysis ......................................... 53 3.4.4 Results of Effervescing ................................................................................................................. 53 3.4.5 Cleaning Study ............................................................................................................................. 53 3.5 Confirmation of the Avista Microscopy Testing at the MSU SEM Facility ...................................... 55 3.5.1 SEM Images .................................................................................................................................. 56 3.5.2 EDX Mapping ................................................................................................................................ 58 3.6 SEM analysis (membrane run without pH adjusted feed) .............................................................. 61 3.6.1 SEM Images .................................................................................................................................. 62 3.6.2 EDX Mapping ................................................................................................................................ 63 Chapter 4 – Optimization ...................................................................................................................... 69 4.1 Permeate Production over Time ............................................................................................... 71 4.2 Flux over time ................................................................................................................................. 72 4.3 Pressure increase over time............................................................................................................ 74 4.4 Feed Quality .................................................................................................................................... 75 4.5 Permeate Quality ............................................................................................................................ 77 4.6 Concentrate Quality ........................................................................................................................ 78 4.7 Ammonia Balance ........................................................................................................................... 81 4.8 Membrane Cleaning ........................................................................................................................ 81 4.8.1 Cleaning Routines ........................................................................................................................ 83 4.8.2 Cleaning Frequency ...................................................................................................................... 84 4.8.3 Cleaning Costs .............................................................................................................................. 84 4.9 Economic evaluation ....................................................................................................................... 85 4.9.1 Electrical Costs ............................................................................................................................. 85 4.9.2 Capital Costs ................................................................................................................................. 85 4.9.3 Operating Costs ............................................................................................................................ 85 Chapter 5 – Conclusion and Future Recommendations ....................................................................... 86 REFERENCES .......................................................................................................................................... 88

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LIST OF TABLES

Table 1 - Calssification of hardness by carbonate concentration (MacAdam, 2004) ........................... 38 Table 2 - Air stripped water analytes. ................................................................................................... 46 Table 3 – Average analytical results of the 9 EDX scans (membrane run with pH adjustment) .......... 60 Table 4 - Average analytical results of the 9 EDX scans (membrane run without pH adjustment) ...... 67 Table 5 - Air stripped water analytes. ................................................................................................... 70 Table 6 - pH range and temperature limits for Filmetc membranes. (DOW Form No. 609-23010-0211) .............................................................................................................................................................. 82 Table 7 - List of chemical cleaning solutions used for the various foulant types. ................................ 82 Table 8 - Example of a cleaning cycle at Car-Min-Vu Dairy addressing organic and silicate fouling (high pH) and inorganic scale (low pH). ......................................................................................................... 83

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LIST OF FIGURES

Figure 1 - Poor waste management leads to manure or silage spills that can be extremely harmful to local aquatics. (Dohr, 2014) .................................................................................................................... 2 Figure 2 - Manure storage can be limited or expensive to construct. (Fulhage, 2012) .......................... 3 Figure 3 - Demonstration of manure applied to fields. (Patz, 2014) ...................................................... 3 Figure 4 - McLanahan Nutrient Separation System processing sand and solid separated dairy manure. ................................................................................................................................................................ 4 Figure 5 - Membrane types and their rejection limits. (McGowan, 2001) ............................................. 8 Figure 6 - Cut out of a reverse osmosis membrane ("Membrane Construction," 2015)...................... 15 Figure 7 - A demonstration of various fouling by adsorption, cake layer formation, pore blocking, and depth fouling (Adams, 2012). ............................................................................................................... 25 Figure 8 - Flux decline as a consequence of fouling for four experimental runs. ................................. 26 Figure 9 – Monosilicic acid (Ning, 2011) ............................................................................................... 30 Figure 10 - Solubility of silica from temperatures rangning from 0 to 80 ⁰C (Zuhl, 2013).................... 31 Figure 11 – Concentration of dissolved silica between pH of 2 to 11 (Amjad, 1997) ........................... 32 Figure 12 - This displays how dispersants act on compounds such as silica. (Demadis, 2004) ............ 33 Figure 13 - The structural relationships of the carbonate mineral (Keener, 2011) .............................. 35 Figure 14 - Schematic representation of crystallographic unit cells for (a) calcite and (b) isostructural dolomite, as well as (c) aragonite and (d) vaterite. (Xu, 2014) ............................................................. 36 Figure 15 - Solubility of the carbonate mineral (Moles) at a pH of 4 to 12 (Javid, 2011) ..................... 37 Figure 16 - Graph of non pH adjusted AS water (displayed over a time of 24 hours to see the drastic drop in permeate production) .............................................................................................................. 44 Figure 17 - SEM photo at x5000 revealed a granular foulant noticed upon the membrane surface ... 45 Figure 18 - Effervessing performed on a calcium carbonate scaled membrane (“Calcium Carbonate Scale,” 2015) ......................................................................................................................................... 50 Figure 19 - Display of the SEM image (left) and CEI (right) analysis showing foulants due to sulfur, silica, carbon, magnesium, and calcium ............................................................................................... 52 Figure 20 - FT-IR spectral image of foulant that was removed from membrane surface .................... 53 Figure 21 - Membrane prior to cleaning ............................................................................................... 54

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Figure 22 - Membrane after cleaning ................................................................................................... 55 Figure 23 - Foulant observed on the membrane at x500 magnification showing a mixture of organic material, silica, and minor traces of inorganics .................................................................................... 56 Figure 24 – Foulant observed on the membrane at x5000 magnification showing a mixture of organic material, silica, and minor traces of inorganics .................................................................................... 57 Figure 25 - Granular foulant observed on the membrane at x5000 magnification showing a mixture of organic material, silica, and minor traces of inorganics ................................................................... 57 Figure 26 – Image of the membrane sample (run at low pH conditions) used for EDX mapping ........ 58 Figure 27 - EDX mapping portraying large amounts of carbon, oxygen, silica, and sulfur. Also showing very minor amounts calcium ................................................................................................................ 59 Figure 28 - EDX mapping demonstrating very minor amounts of iron and copper .............................. 60 Figure 29 – The foulant inspected at x500 magnification revealing a mixture of organic and inorganic material ................................................................................................................................................. 62 Figure 30 –The x1500 magnification shows bolus’ representing inorganic calcium carbonate scale, and random white regions representing silicate scale upon a layer of organic foulant. ..................... 62 Figure 31 - The x5000 magnification shows the detailed inorganic calcium carbonate scale (shown as round bolus’). The image also shows the depth of the fouling. ........................................................... 63 Figure 32 - Image of the membrane sample (run without acid addition) used for EDX mapping ........ 64 Figure 33 - EDX mapping portraying large amounts of carbon, oxygen, and silica. Nitrogen, calcium, magnesium were also present in significant amounts. ........................................................................ 65 Figure 34 - EDX mapping displaying small amounts of sulfur, sodium, chlorine, postassium, and iron. .............................................................................................................................................................. 66 Figure 35 - Comparison of foulant upon the membrane run with acid addition versus the membrane run without acid addition. Displayed in the graph are the elements which are most likely to cause issues with fouling. ................................................................................................................................ 67 Figure 36 - Experimental design ........................................................................................................... 70 Figure 37 – Displays the comparison of flux decline as a negative slope at the various operating conditions using sulfuric, hydrochloric, or no acid at various pH ranges. ............................................ 72 Figure 38 - A display of the UF permeate versus air stripped water at pH 6.5. There is essentially no difference in performance. ................................................................................................................... 73 Figure 39 - The flux rate of the experiments performed at various pH ranges using sulfuric acid, hydrochloric acid, and no acid addition is displayed. At a pH of 6.5 there were replicate experiments performed for hydrochloric and sulfuric runs. ..................................................................................... 74

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Figure 40 - Pressure increase shown as a positive slope is displayed in the graph. The runs with

sulfuric, hydrochloric and, and no acid addition at various pH ranges is graphed. .............................. 75

Figure 41 - This graph displays the feed water quality in units of COD for the hydrochloric and sulfuric runs at the various pH ranges. .............................................................................................................. 76 Figure 42 - This graph displays the feed water quality in units of ammonia concentration (mg/L) for the hydrochloric and sulfuric runs at the various pH ranges. ............................................................... 76 Figure 43 - This graph displays the permeate quality in units of COD for the hydrochloric and sulfuric runs at the various pH ranges. .............................................................................................................. 77 Figure 44 - This graph displays the permeate quality in units of ammonia concentration (mg/L) for the hydrochloric and sulfuric runs at the various pH ranges. ............................................................... 78 Figure 45 - This graph displays the concentrate quality in units of COD for the hydrochloric and sulfuric runs at the various pH ranges. ................................................................................................. 80 Figure 46 - This graph displays the concentrate quality in units of ammonia concentration (mg/L) for the hydrochloric and sulfuric runs at the various pH ranges. ............................................................... 80

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KEY TO ABBREVIATIONS

Abbreviation Full Word

RO Reverse Osmosis

SEM Scanning Electron Microscopy

EDX Energy Dispersive X-ray

CEI Chromatic Elemental Imaging

FTIR Fourier Transform Infrared Technology

GFD Gallons per square Foot per Day

GPD Gallons Per Day

UN United Nations

TDS Total Dissolved Solids

BWRO Brackish Water Reverse Osmosis

UF Ultrafiltration

NF Nanofiltration

SMP Soluble Microbial Products

NOM Natural Organic Matter

EfOM Effluent Organic Matter

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Chapter 1 - Overview

1.1 Introduction

The use of RO has grown immensely over the past 40 years (Baker 2012). Reverse osmosis

provides a means of reclaiming purified water fairly inexpensively. One reason RO has become more

popular is due to the scarcity of fresh water in many areas such as dry lands, densely populated areas,

and isolated islands (Mohamed, 2004). According to the United Nations about 85% of the world lives in

regions with inadequate fresh water supply and 783 million people do not have access to clean water

(“Water Cooperation,” 2015). On Earth, water management has become a concern in growing

populations since less than 1% of water is available for human use (“Water Sense,” 2015). Forty states in

the USA expect water shortages within the next decade (“Water Sense,” 2015). The scarcity of water

within the USA is typically caused by increasing populations, increased industry, and climate change

(WWDR4, 2012). Clean water reclamation has become a reality and a priority in the USA and in the

world.

1.2 Problem Statement

Membrane technology is a fairly inexpensive way to reuse and reclaim water from waste water

applications. The cost to desalinate sea water and brackish water has dropped from $1 per 250 gallons

to around $0.5 per 250 gallons in 5 years (Henley, 2013). Water reclamation and nutrient recovery are

important aspects in today’s world to protect the fragile environment. Livestock agricultural is a

significant contributor to waste generation (USDA, 2006). Due to the need for more dairy and hog

operations, the production of wastes from hog and dairy processing, meat processing, and manure

management has increased (USDA, 2012). For example, large-scale dairy operations have increased from

564 farms in 1992 to 1807 in 2012, a 45% increase in 10 years (MacDonald, 2014). The shift to larger

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dairy operations is driven by higher profits from larger heard sizes (MacDonald, 2014). Manure

management has become a significant issue as farmers struggle to store (see Figure 2), transport, and

land apply manure (see Figure 3) (USDA, 2006). Manure spills have had disastrous effects to humans and

wildlife (portrayed in Figure 1). An example of this is when an eight-acre hog-waste lagoon in North

Carolina burst, spilling 25 million gallons of manure into the New River, killing around 10 million fish and

shutting down shellfishing in 364,000 coastal acres in 1996 (NRDC, 2015). In some cases over excessive

land application of nutrient-rich manure has been performed as a last resort to get rid of the waste

(USDA, 2006). A great example from a recent study displayed that some larger dairy operations apply

manure to crops at rates that are three times greater than smaller farms (MacDonald, 2009). Often

times manure storage volume dictates the timing of manure land application. In turn, this can result in

excess manure application and increase the potential to negatively impact surface water due to runoff.

The World Health Organization (WHO) drinking water guideline is 10mg/L and the U.S. Geological Survey

found that 15% of shallow groundwater sampled below agricultural and urban areas had nitrate levels

higher than 10mg/L (Payal, 2000).

Figure 1 - Poor waste management leads to manure or silage spills that can be extremely harmful to

local aquatics. (Dohr, 2014)

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Figure 2 - Manure storage can be limited or expensive to construct. (Fulhage, 2012)

Figure 3 - Demonstration of manure applied to fields. (Patz, 2014)

Nutrient separation systems have become of interest to prevent pollution and meet various

environmental standards. However, nutrient recovery has its own challenges as manure is a very

complex waste and should be studied under pilot projects, analyzed, and optimized. Only a few projects

have used membrane technology to process dairy manure waste streams. Some of these projects are

listed in the articles written by Masse and Gou, where they discuss challenges and lack of research in

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identifying potential foulants, optimizing filtration systems for dairy manure waste, calculating the costs

associated with processing dairy manure through filtration systems. Masse and Gou expressed that

fouling of the membrane technology is a major issue in the dairy industry and should be researched to

determine the foulants involved. Fouling leads to a host of problems so the knowledge of the foulants

involved would decrease operational and maintenance costs, since there would be less irreversible

fouling, less down time for cleaning, less use of chemicals for cleaning, and less frequent membrane

replacement. One example of a comprehensive nutrient separation system was developed by the

McLanahan Corporation. Prior to nutrient separation, manure is sand and solid separated, leaving

behind a liquid manure slurry. This slurry is sent to an anaerobic digester coupled to an ultrafiltration

(UF) system. The phosphorus rich slurry is returned to the digester, where it is concentrated, and the

volatile ammonia in the ultrafiltered permeate is air stripped and stabilized by the absorber, as

ammonium sulfate. Finally, the RO system processes either air stripped water or non-air stripped water

to produce clean water and concentrate that is rich in potassium. A schematic of the process is shown in

Figure 4.

Figure 4 - McLanahan Nutrient Separation System processing sand and solid separated dairy manure.

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1.3 Objective

Nutrient separation systems offer a treatment alternative to enhance the environmental

standing of large animal agriculture operations. As stated earlier, nutrient recovery provides a

mechanism to segregate nutrients and produce clean water but it has its own challenges. RO membrane

technology is one method used to produce water but is prone to fouling and scaling if improper

pretreatment and maintenance is not established. Specifically, RO membranes are particularly sensitive

to carbonate fouling, organic fouling, and silicate fouling in waste water applications dealing with

agriculture. In order to limit the fouling potential, tests for carbonate, organics, and silicates should be

performed. After analyzing the potential for fouling and scaling, pretreatment strategies can be put into

place, and optimization of the system can be performed so that nutrients are concentrated and clean

water is produced efficiently.

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Chapter 2 – Literature Review

RO is currently used to purify water from sea water, brackish water, and waste water (Baker).

Approximately 70% of the Earth is covered in water and 97% of that coverage is sea water, so

desalination with use of RO is momentous (Perlman, 2014). In June 2011, 15,988 desalination plants

were producing 17.6 billion gallons of water per day, and supplying 300 million people worldwide with

that water (Henthorne, 2012). According to the article "Desalination industry enjoys growth spurt as

scarcity starts to bite," water retrieved from desalination increased to 20.7 billion gallons in 2013.

Reclamation of high quality water has also become prevalent in waste water applications, preventing

the pollution of groundwater and natural aquatics due to discharge of waste water. “RO membranes

have proven to successfully treat such waste water and provide water that exceeds reuse quality

requirements (Bartels, 2015).” Industrial and agricultural facilities have been able to treat waste water

using RO.

2.1 History

As the book “Reverse Osmosis Industrial Applicarions and Processes” by Jane Kucera states, the

earliest record of thin film semipermeable membranes was in 1748, discovered by Abbe Nollet, while

observing the phenomena of osmosis. Over the years this finding evolved, and by 1959, at the University

of Florida, C.E. Reid and E.J. Breton demonstrated that a cellulose acetate film could act to desalinate

water. Next was the commercialization of the cellulose acetate filters by optimizing the flux rate and

durability of the membrane. The flux rate is calculated from the amount of clean water produced per

day by the RO system. In 1960 Loeb and Srinivasa researched how to use this cellulose acetate

membrane under water pressure, and made RO commercially viable since it significantly improved flux.

The flux rated of the improved cellulose acetate membrane was about ten times greater than that of

other known membrane materials. Shortly then after, the first brackish water RO facility was

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constructed, using wound filtration membranes, in Coalinga CA. The wound membranes became quite

popular and are currently used today, with some new improvements. Innovations keep growing and the

use of the spiral wound membranes exceeded expectations for desalinating sea water and brackish

water. This has been due to the modification of the membranes by the use of various polyamide or

cellulose membranes, different configurations of design within the membrane, and increased surface

area. Over time, enhancements allowed certain membranes to operate at higher pressure, from 1000

psi to 1200 psi. One of the current advancements is the nanotechnology membrane which has been

designed to reject 95% sodium chloride and 99.3% calcium chloride. Membrane technology continues to

evolve just as RO progresses and operates among other sources of water like industrial and municipal

waste streams. (Kucera, 2010)

2.2 Applications

Water reclamation by RO has become very popular especially due to the advancement in

membrane technology, less frequent membrane replacement, and prices of membranes have become

relatively inexpensive (Baker, 2012). The price to desalinate sea water and brackish water has been

reduced from $1 per 250 gallons to around $0.5 per 250 gallons in 5 years (Henley, 2013). RO is one of

the best water purification methods available today since it rejects most dissolved solids and suspended

solids by separating small solutes from water. The RO operation rejects material around 10-4 microns

(Figure 5). The rejected solids can collect on the membrane surface and foul the membrane.

Sometimes it is required to pretreat the feed water to the RO system with antiscalant and either

acid or base in order to minimize fouling and scaling of the membrane surface. Occasionally it is also

required to perform mandatory cleanings on the membranes, depending on the quality of the

concentrated water being treated. RO systems are primarily used in industrial settings but there are also

small-scale systems that have been used in homes, yachts, ocean liners, and remote regions. The

primary role of RO is to extract nutrients and other compounds from water, specifically sodium, out of

the feed stream to produce potable water (Kershner, 2008). As interest in RO grew, it has been applied

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to other industries. The large diversity of applications have been able to reclaim and purify water

effectively and cost-efficiently. Some examples of where RO technology has proven to be effective is in

the treatment of municipal waste water and hazardous waste, extraction of specific compounds in the

food and beverage industry, and the retrieval of organic and inorganic materials from chemical

operations. Each field has its own set of challenges depending on the water being treated. The following

industries listed are currently using RO.

2.2.1 Desalination of Sea Water

RO technology was initially designed to separate sodium and other minerals from salt water. RO

technology is mostly used in this industry. Christopher Gasson from Global Water Intelligence stated

roughly 1% of the world population is dependent on desalination processes and by 2025 the UN

projected that 14% of the world’s population will be faced with scarcity of water ("Desalination industry

Figure 5 - Membrane types and their rejection limits. (McGowan, 2001)

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enjoys growth spurt as scarcity starts to bite"). There are currently between 15,000 to 20,000

desalination plants worldwide producing water at a rate of more than 5.3 million gallons per day (GPD).

This shows the immense effectiveness of desalination and proves that continuous efforts have been

made to the advancements of this membrane technology.

2.2.2 Reverse Osmosis Treating Municipal Wastewater

RO systems processing municipal wastewater are typically located in regions that lack water

resources. Membrane treatment of municipal wastewater has proven to be a cost effective way of

reclaiming water. RO membranes have also proved that they are worthy in this field by significantly

reducing total dissolved solids, heavy metals, organic pollutants, viruses, bacteria, and other dissolved

contaminants. A few of the municipal RO plants include the 13.2 million GPD (gallons per day) plant in

West Basin, CA, the 10.6 million GPD plant in Singapore, and the 8.5 million GPD Bedok plant in

Singapore (Chilekar, Hydronautics). Some plants that process far more waste water than mentioned

before include the 71.3 million GPD plant in Orange County, California and the 100 million GPD plant for

Sulayabia, Kuwait (Bartels, Hydronautics). In the USA only 10% of water is used for drinking and cooking,

and the rest is flushed down the toilet or drain. California currently uses recycled water for toilet

flushing currently lowering its need for water by a quarter ("Indoor Water Use in the United States,”

2013). Also, San Diego is currently using recycled water from municipal waste water treatment plants

because it imports 85% of its drinking water from Northern California and the Colorado River, which are

currently in a drought crisis (Cho, 2011). These waste water RO plants demonstrate the importance of

recovering water and the acceptance that this technology has gained over the years.

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2.2.3 Reverse Osmosis in Food Processing

Due to the disproportioned ratio of food production versus the growth of the world population,

nutrient recovery and water recovery has become very valuable. The application of membranes in the

food and beverage industry has increased dramatically since the 1980’s to recover and reuse as much

water as possible (Ganorkar, 2012). These industries include fruit and vegetable processing, animal

products, various beverages, sugar refining, and grain products (Ganorkar, 2012). Soybean processing

plants have been using nanofiltration-RO systems (NF) developed to recover water from soybean

soaking water (Guu, 1997). The article named “Reverse Osmosis System Cuts Food Plant’s Eco Footprint”

stated that a plant in Wisconsin recently started using RO to soften water for the boiling process and, in

turn, has also increased the efficiency of the boilers because of reduced alkalinity. The article also

mentioned that the treated boiler water is used in the canning process for carrots, green beans, and

potatoes. Low flow RO can also be used to treat bottle washing water producing drinkable water or

discharge water in the beverage industry (Mavrov, 2000). One of the beverage industries that utilizes

ultrafiltration and RO is the dairy industry. The dairy industry generates about 10 gallons of pollutant per

gallon of processed milk (Vourch, 2008). Additionally, it takes about 35 gallons of water to produce 1

cup of yogurt, 42 gallons to produce 1 scoop of ice cream, 50 gallons to produce two slices of cheese, 90

gallons to produce 1 cup of Greek yogurt, and 109 gallons of water to produce 1 stick of butter (Lurie,

2014). In these cases RO is highly regarded as a means to recycle water and concentrate nutrients.

2.2.4 Reverse Osmosis in Manure Management

In recent years manure management has become very important in the agricultural settings. A

few study’s in the year 2009 and 2011 found that the majority of large-scale dairies applied manure to

croplands at a rate of about 3 times more than small-scale farms (Macdonald, 2009). The loss of

phosphorus, nitrogen, and potassium to the environment during manure management is highly possible.

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Normally manure is temporarily stored for a certain period of time (usually over the winter months and

when crops are growing) and then land applied as crop fertilizer. These techniques are typically suitable

for small-scale farms, or if the manure storage and application is agronomically correct and

environmentally friendly on large-scale farms (“Nutrient Recovery,” 2010). Sometimes this is not the

case. According to the website “Facts about Pollution from Livestock,” California identified that the

major source of nitrate pollution was from livestock agriculture, polluting over 100,000 square miles of

groundwater. The article also stated that in 1993, poor plant management practices at a dairy

contributed to the contamination of Milwaukee’s drinking water, killing over 100 people, and made

400,000 sick. Over application of manure leads to diminished crop yields and can lead to nitrogen

filtering into groundwater (Cogger, 2004). It is obvious that in recent years there has been greater

awareness in managing the dispersal of nutrients efficiently with minimal runoff (“Nutrient Recovery,”

2010). Producers are also interested in adding value to operations by generating electricity or placing a

value on concentrated nutrients (“Nutrient Recovery,” 2010). Mechanical wastewater treatment is one

way to concentrate the nutrients from manure. Ultrafiltration and RO are mechanical filtration methods

that can segregate nutrients such as phosphorus, potassium, and nitrogen. RO can also produce clean

water that may be suitable for direct discharge or land irrigation. The methods to recover nutrients and

produce clean water is a great way to prevent pollution due to livestock agriculture (“Nutrient

Recovery,” 2010).

With the innovative solutions to manure management come advanced challenges. Some

challenges are from the engineering design of systems, cost of systems, and the waste that needs to be

treated. In this study the manure is the waste that needs to be treated using membrane technology. The

greatest challenge is membrane fouling because the RO systems operate to produce clean water at the

molecular level. The fouling can be due to various elements that adhere to the membrane surface. RO is

still an attractive method for many industries since clean water is produced for reuse or is discharged.

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Another benefit to using RO is the better environmental footprint RO systems leave behind by reducing

the discharge of waste into the environment, satisfying communities, meeting certain regulations, and

providing a positive influence to stay green and clean. There are also new innovations to RO technology

in order to address many of the challenges associated with the various applications.

2.3 Reverse Osmosis Knowledge Needed for Manure Management

As RO continues to expand, it has grown from primarily processing sea water, to reclaiming water in

the food and beverage industry, and has evolved to process waste water, or manure, in agriculture. RO

systems used in manure applications have been studied, but not entirely. Both Masse and Gou stated

that further controlled studies are required to develop a viable and economical technology for the use

of RO to process a downstream manure slurry (Masse, 2007, Gou, 2014). Masse and Gou also

mentioned that the following areas should be researched (Masse, 2007, Gou, 2014):

– Pretreatment:

A pretreatment strategy is needed in order to optimize system performance and keep costs low.

The effect of acid addition on transmembrane flux, reversible and irreversible fouling, cleaning

frequency, chemical requirements, permeate quality, and maximum volume reduction is also not

understood.

– Relationship between System Performance:

Various relationships with the following parameters are needed to better understand the

operation of the system to maximize performance. Masse and Gou recommended that the

following should be tabulated and compared: flux, fouling rate, concentrate characteristics,

volume reduction, permeate quality, pressure, and temperature.

13

– Major Types of Fouling

Masse and Gou emphasized the importance of understanding the fouling of the RO system.

Specifically, organic, inorganic, and biological fouling should be studied to understand what

compounds may be the primary cause for fouling. Once the components of fouling are

understood then a cleaning strategy and routine can be configured.

– Ammonia Volatilization

In order to document the volatilization of ammonia, a mass balance of ammonia across the RO

system is needed. Feed, concentrate, and permeate samples should be tested to observe the

amount of ammonia present in each stream and confirm the mass balance.

– Reuse of RO Permeate and RO Concentrate

In some cases the RO permeate may be suitable for disposal, otherwise it may be used

somewhere on the farm, for land irrigation, washing, cow cooling, used in a boiler system, or

possibly as animal drinking water. The concentrate would typically be stored and land applied

since it is rich in potassium and minor traces of phosphorus. It could also be dried in an

evaporator, to a solid form, extracting more water, for land application or commercial sale.

– Economic Evaluation

In order to understand the economics, all the capital costs and operational costs need to be

calculated and presented. This includes the acid addition, antiscalant addition, chemical cleaning

costs, costs associated with energy usage, replacement membranes, and the price of the entire

RO skid.

14

2.4 Reverse Osmosis Membranes

As previously stated, the RO system is a membrane based demineralization technique which

separates dissolved solids and suspended solids from solution for numerous source waters (Kucera,

2010). The suspended solids are typically known to foul the RO membrane (Roque, 2012). The most

common types are the thin film, cellulose acetate, composite membranes, which provide high rejection

and low operating pressure (Roque, 2012). If the source water has a high organic content, then the

cellulose acetate membranes are commonly recommended because they provide the least fouling rates

and shorter down time for cleaning (Roque, 2012).

RO membranes have evolved quite dramatically and new generations of membranes have been

produced offering adaptability to numerous applications (Roque, 2012). The hollow fiber modules used

to be quite popular for membrane filtration (Roque, 2012). These membranes are very sensitive to pH

change, pressure, and temperature (Roque, 2012). The hollow fiber membranes also became outdated

due to their high potential for fouling and scaling however, are sometimes used in applications with low

suspended solids content (Roque, 2012). More recently, the spiral wound membranes are preferred in

many fields of water treatment (Kucera 2010). The spiral wound RO membranes have multiple flat sheet

membrane leaves wrapped around a perforated permeate collection tube (Baker, 2004). Feed flows in

on one side of the membrane while the permeate passes the membrane on the other side and is

collected within the collection tube (see Figure 6). Each manufacturer has engineered various models for

different treatment applications.

15

Figure 6 - Cut out of a reverse osmosis membrane ("Membrane Construction," 2015).

RO membranes are typically made of cellulose acetate, cellulose diacetate, polysulfone,

polyethersulfone or polyamide material (Kucera, 2010). Cellulose acetate has been the most popular

(Kucera, 2010). All the membranes have a relatively smooth surface which potentially prevents fouling

(Kucera, 2010). Most of the membranes exhibit a neutral charge (Kucera, 2010). Depending on the

manufacturer, the maximum operating temperature is 113 degrees Celsius and the operating pH is

typically 4 to 7 (Kucera, 2010). Operating pressure is limited up to about 400 psig to prevent membrane

16

compaction (Kucera, 2010). The polyamide membranes were engineered to improve the performance of

the cellulose acetate membranes (Kucera, 2010). The chemical compositions of the membranes vary

between manufacturers and, depending on the process, one material may be favored over another to

maintain optimal permeate flux rates at minimized fouling potentials (Kucera, 2010).

The construction and design of certain RO membranes can also vary. A common difference in

design of membranes is the thickness of the feed spacer. A thin feed spacer may be recommended in

certain applications where fouling is not a major concern (Kucera, 2010). A large feed spacer is used for

applications that are at risk for high fouling (Kucera, 2010). Low fouling RO membranes use large feed

spacers (about 31 to 34 millimeters), exhibit the same throughput as most generic RO membranes, and

are neutrally charged (Kucera, 2010). Generic RO membranes are negatively charged and 28 millimeters

thick (Kucera, 2010). Another type of construct is a larger membrane square footage. Typically, a single

generic RO membrane has about 365 square feet of surface area, while the high productivity

membranes have 400 to 440 square feet of surface area allowing for a higher permeate recovery

(Kucera, 2010). Lastly, there are sanitary membranes which can be used in dairy, pharmaceutical, and

biological processing. The sanitary membranes can be sanitized for short periods at 185 degrees

Fahrenheit and are constructed without a brine seal to eliminate stagnant areas within the module

where bacteria may grow (Kucera, 2010). Brine seals are o-rings at the end of the element to prevent

feed from passing by the outside of the element casing. Even with the advancements in membrane

construction to limit fouling, pretreatment strategies are still needed to optimize clean water production

and prevent scaling.

17

2.5 Pretreatment

Membrane scaling and fouling is the major concern for RO systems as it leads to a higher than

normal pressure drop, higher operating pressure, and reduced permeate generation. Pretreatment is

especially important to maintain optimal operation of the RO system.

If there is inadequate pretreatment an RO system will require frequent cleaning intervals and

membrane life will be short. Increased cleaning intervals, increased shut down, and frequent

replacement of membranes increase costs and reduces efficiency. Optimization of the pretreatment

stage is necessary to enhance the operation of the RO.

Numerous forms of pretreatment are classified as mechanical, chemical, mechanical plus

chemical, and sequenced. Mechanical pretreatment contains the use of clarifiers, multimedia pressure

filters, high efficiency filters, carbon filters, ultraviolet irradiation, and UF or NF membranes. Clarifiers

can be designated as mechanical plus chemical systems if the clarifier incorporates a chemical

pretreatment of coagulation and/or flocculation. Typically chemical pretreatment includes the addition

of acid or base like concentrated hydrochloric acid, sulfuric acid, or concentrated sodium hydroxide.

Sometimes ozone is added during pretreatment to address microbes, total organic carbon, odor, and

color. The chemical pretreatment, excluding coagulation, is used to chemically reduce, remove, destroy

or inhibit bacteria, hardness scale, and oxidizing agents. Antiscalants are another form of pretreatment

that are used to minimize scale formation on the surface of RO membranes. Antiscalants work to keep

supersaturated salts in solution, change the shape of crystals to move through the membrane, and

impart a high negative charge to various crystals to prevent propagation. (Baker, 2012)

In most applications, acid addition is the most cost effective pretreatment technique. Acid

reduces the pH of the RO feed. Normally, fouling due to crystallization and precipitation on the

membranes is minimized with increased doses of acid and therefore the performance of the membrane

is increased (DOW Filmtech, 2000). The acids break down carbonate ions by removing one of the

18

reactants necessary for calcium carbonate precipitation, specifically reducing the crystallization of

calcium carbonate (Kucera, 1997). Sulfuric acid and hydrochloric acid are the standard pH adjustment

acids used for RO treatments. Sulfuric acid is used quite often since it is relatively inexpensive compared

to hydrochloric acid. Currently, in the year 2015, PAR Technology stated the cost of 98% sulfuric is

$0.09/lb and 32% hydrochloric is $0.25/lb (if shipped in 55 gallon drums). When using sulfuric acid the

formation of sulfate scale increases, such as barium sulfate, calcium sulfate, and strontium sulfate. Also,

from performing simulations using the Avista Advisor and ROSA software, it has been shown that the

amount of hydrochloric acid needed to lower pH is about 1/4 less than the amount needed to lower pH

using sulfuric acid. The reason less HCl is needed is because it is a stronger acid than H2SO4, meaning it

has a higher tendency to release hydrogen ions in an aqueous solution. A strong acid completely splits

its hydrogen apart to give ions in solution (100% dissociation) where weak acids only slightly dissociate

in solution. By comparing the dissociation reactions and the pKa values it shows how hydrochloric acid

dissociates in solution versus sulfuric acid. The lower �� value signifies a stronger acid as shown

below.

• Hydrochloric �� + �� → �� + � � �� = −6.3

• Sulfuric 1. �� + �� → ��

� + � � �� = −3

2. �� + �� → ��

�� + � � �� = 2

2.6 Antiscalants

In the 1800’s antiscalants started to be used in boiler systems to prevent scale buildup, now

they are used in RO systems for the same purpose (Darton, 2000). Antiscalants contain surface active

minerals that interfere with the precipitation reactions of various compounds by threshold inhibition,

crystal modification, and dispersion (Lenntech, 2015). Threshold inhibition prevents sparingly soluble

salts to supersaturate, crystal modification distorts the shape of crystals and prevents scale growth, and

19

dispersion acts to neutralize the positive charges on the scale with negatively charged elements from

the antiscalant, disrupting the electronic balance necessary to promote crystal growth (Lenntech, 2015).

After the antiscalant interferes with the crystals, the crystals take on a round shape and are less

compact so that the crystals are less likely to combine and block the membrane pores. Dispersion is a

method where high anionic charges are made because the antiscalant adsorbs onto the crystal or

colloids (Lenntech, 2015). This tends to keep crystals or colloids separated and the high anionic charge

also splits particles from secured anionic charges on the membrane surface (Lenntech, 2015).

Some antiscalants contain organophosphonate, polyphosphate or polymer type compounds

(Greenlee, 2009). Most generic antiscalants will include ingredients such as acrylic polymer dispersants

and chelating agents. Some examples of chelators include ethylenediaminetetraacetate (EDTA),

nitrilotriacetate (NTA), and polyelectrolytes such as polyacrylic acid (PAA) and polyethylenimine (PEI)

(Seungkwan, 1997). Dispersants are either a non-surface active polymer or a surface-active substance

(surfactants) added to solutions including colloids to improve the separation of particles and to prevent

settling or clumping (Seungkwan, 1997). Cationic-based copolymers are normally effective silica

polymerization inhibitors (Amjad, 2008). Proper dosing of the antiscalants is critical, typically around 10

mg/L and no more than 35mg/L (Boffardi, 1997). If dosing is not managed appropriately the antiscalants

themselves can become foulants at excessive concentrations (Rahardianto, 2006). Antiscalants have

certain limitations, especially when containing ingredients like polyacrylic acid or hexametaphosphate

(Hydronautics, 2003). Polyacrilic acid can foul membranes in the presence of high iron, and

hexametaphosphate can hydrolyze in the presence of air (Hydronautics, 2003). High concentrations of

antiscalant can also promote biological growth (Malekar, 2005). Most antiscalant dosages are

determined by the manufacturer using modeling software such as the Avista Advisor program by Avista

Technologies. Even though the antiscalants won’t completely prevent precipitation at high ion

concentrations (Greenlee, 2009), they are a simple way to lower costs associated with pretreatment by

20

preventing crystallization, and keep most compounds that could potentially foul the RO membrane in

solution.

2.7 Membrane Fouling

Fouling occurs when substances accumulate upon the membrane or within the membrane pores

(AWWA, 1992). Ultimately, this reduces the performance and degrades the membrane (AWWA, 1992).

RO fouling is sometimes called a “surface layer,” or a “dynamic membrane,” which is formed on the

membrane surface during operation (Lenntech TSB107.21, 2011). This layer regulates the permeate

generation rate, permeate quality, and the selectivity of the material that passes by (Lenntech

TSB107.21, 2011). This foulant layer limits membrane performance, reduces the permeability (flux rate)

of the membrane, and increases cleaning costs (Verberk, 2005). Numerous studies have shown to

reduce fouling but it cannot be eliminated. In most cases it is more expensive to pretreat the RO feed to

limit membrane fouling so frequent cleaning routines are used instead.

Lenntech’s technical service bulletin, TSB107.21, lists eight categories of foulants (a. through h.

listed below). These foulants are:

2.7.1 Calcium Carbonate Scale

This is a mineral scale and can be inhibited by use of antiscalant or dispersant. It can also be

reduced by lowering the pH of the wastewater. Crystalization of calcium carbonate will easily form on

the membrane surface if preventative measures are not taken.

2.7.2 Calcium, Barium, Strontium, and Sulfate Scale

When using sulfuric acid, the sulfate scale is more prevalent and according to Lenntech, it is a

much harder mineral scale than calcium carbonate and is therefore harder to remove from the RO

membrane. Antiscalant is necessary in these cases to prevent crystallization on the active membrane

21

layers. In particular, barium and strontium sulfate scale is very difficult to remove and are insoluble in

some cleaning solutions.

2.7.3 Calcium Phosphate Scale

This scalant is present in municipal waters or nutrient rich water. Calcium phosphate was not a

concern until RO started being used in municipal waste water treatment. Due to water shortages

municipalities started using more RO systems to reuse water. If the majority of foulant is due to calcium

phosphate then the scale can be removed by an acidic cleaning solution.

2.7.4 Metal Oxide/ Hydroxide Foulants

Iron, zinc, manganese, copper and aluminum are the most common in this category. The

presence of these compounds could be due to pretreatment strategies that include iron- and aluminum-

based coagulants, or could be introduced into the water by corrosion of pipes or tanks. They could also

appear in the waste stream due to oxidation of soluble metal ions with air, chlorine, ozone, or potassium

permanganate.

2.7.5 Polymerized Silica Scale

Super-saturation and polymerization of soluble silica forms a gel coating and is very difficult to

remove. Silica can be removed by use of sodium dodecyl sulfate and or NaOH.

2.7.6 Colloidal Foulants

Colloidal foulants are suspended in the water and will not settle due to gravity. These colloids are a mix

of inorganic or mixed inorganic/organic compounds.

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2.7.7 Dissolved Natural Organic Matter (NOM) Foulants

Decomposed vegetable material cause well water to have a high concentration of dissolved

NOM. The major components of NOM are humic acids and fulvic acids.

2.7.8 Soluble Microbial Products (SMP) and Microbial Deposits

These complexes are found in biological wastewater treatment processes from substrate

metabolism. This fouling could also be due to bacterial slimes, fungi, molds, and other microbes.

Biocides are typically used to clean membranes and inhibit microbial growth with SMP and microbial

deposits.

In order to optimize an RO system the constituents and degrees of membrane fouling must be

understood. The RO system parameters for performance, cleaning protocols and pretreatment

strategies must be made to maximize production of high quality permeate.

2.8 Membrane Fouling in Manure Management

In the dairy industry, in order for a cow to produce one gallon of milk it produces two gallons of

manure (Dicktrell, 2014). Concentrating nutrients at milk processing plants with use of membrane

filtration has become very valuable and important and it is just as important to concentrate nutrients in

manure management to minimize pollution and agricultural runoff. The major nutrients are nitrogen,

phosphorus, potassium, calcium and magnesium, while the micronutrients are copper, iron, manganese,

and zinc (Yang, 2007). Organic material, in the form of humus substances, is also present. Additionally,

there are varying concentrations of boron, carbonate, and silica (Eriksson, 2001). The mineral content

mainly depends on the location of the farming operation, the feed ration, and the quality of water which

the cattle drink. The various compounds incorporated prior to downstream processing, specifically

related to membrane fouling should be considered. The processing of manure wastewater treatment is

23

quite similar to municipal wastewater treatment as similar treatment strategies are used, such as

anaerobic digestion, dissolved air flotation, clarification, centrifugation, ultrafiltration, microfiltration,

nanofiltration, and RO . Biological, organic, and inorganic fouling has been observed with membrane

technology processing manure wastewater (Masse, 2007). The biological constituents are usually

microbial matter, the organics are typically from humus substances or soluble microbial byproducts, and

the inorganic fouling is usually from carbonate or other inorganic constituents from the feed,

groundwater, or pretreatment. Just as brackish water, municipal wastewater, and milk processing

experience fouling or scaling from pretreatment, there may be additional compounds like aluminum,

iron, lime, sulfur, and polyelectrolytes from manure pretreatment that can cause scaling or fouling (Lin,

2013). There are numerous challenges from fouling that must be overcome when using RO. Once

optimized, the RO system would be able to operate efficiently at an acceptable flux rate and minimized

fouling rate. With nutrient recovery systems that incorporate polymers for coagulation before RO, there

may be major risks with irreversible fouling and deterioration of spiral wound membranes (Juang, 2001).

When using a nutrient recovery system that incorporates ultrafiltration and air stripping as

pretreatment to RO there is a low total solids content (about 0.7 wt %), no microbes or bacteria, lower

amount of volatile ammonia, and the only concern would be the compounds that could cause scaling or

fouling. The majority of these compounds are colloidal natural organic material, carbonate salts, and

possibly some elements from pretreatment.

2.9 Dynamics of Membrane Fouling

The fouling of the membrane system is influenced by the membrane type, quality of feed, and

fluid dynamics of the system (Adams, 2012). The most important concept of the fouling mechanism is

the concentration polarization.

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2.9.1 Concentration Polarization

The dynamic accumulation of feed solids at the membrane surface due to the balanced

convective transport toward a membrane and the rate of diffusion away from the membrane is

concentration polarization (Cheryan, 1998). Balanced convective transport is the convection due to an

induced pressure gradient force (Frye 1913). The gel layer is a boundary which results from the

accumulation of the solids on the membrane surface. This occurs from supersaturation of the reject

(concentrate) that may result from increasing viscosity due to filtration forming the gel like boundary

layer (Adams, 2012). The gel layer then prevents the passage of permeate and osmotic pressure builds

up at the membrane surface acting against the trans membrane pressure (Adams, 2012). This is very

important in RO processes, but not as important in larger pore size systems such as ultrafiltration and

mediafiltration (Adams, 2012). Concentration polarization naturally occurs in membrane systems due to

the hydrodynamic conditions, and is not caused by the membrane itself (Marshall, 1993). Flux rate lost

to concentration polarization can be completely or partially restored when either the trans membrane

pressure is decreased, feed concentration is decreased, or cross-flow velocity in increased (Cheryan,

1998).

2.9.2 Fouling Mechanisms

Fouling occurs by four mechanisms after concentration polarization is in effect. These

mechanisms are adsorbtion, pore blocking, cake layer formation, and depth fouling (See Figure 7)

(Brans, 2004).

In dairy settings, proteins from milk production adsorb to polymeric, non-cellulosic membranes

under static conditions so some adsorption and fouling may occur well before concentration

polarization starts (Adams, 2012).

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Figure 7 - A demonstration of various fouling by adsorption, cake layer formation, pore blocking, and

depth fouling (Adams, 2012).

On most occasions fouling is reversible by performing membrane cleaning, however, irreversible

fouling can sometimes occur and cleaning will not be able to restore full membrane performance.

Absorption occurs when foulant adheres to the membrane and may occur on the membrane surface or

within the pores (Adams, 2012). Absorbtion in the pores prevents passage of permeate and hence

reduces the flux (Adams, 2012). Cake layering is formed when foulants adsorb onto the surface of the

membrane or when particles agglomerate and bridge over sections of the porous membrane surface

(Adams, 2012). Compression of particulate that becomes caught in the bridging or piling of various

foulants can also occur adding additional layers that prevent and resist the passage of permeate

(Adams, 2012). Pore blocking occurs when particles that are larger than the pore become lodged at the

pore entrance (Adams, 2012). Another form of blocking is depth fouling and it occurs when a large

particle is forced deep into a pore through which it would not normally pass (Adams, 2012). This occurs

when there is an excessive trans-membrane pressure and therefore reduces membrane permeability

26

(Adams, 2012). Typically fouling can be cleaned from the membrane, however irreversibly bound

foulant, such as depth fouling, limits membrane performance and its lifespan (Renner, 1991).

2.9.3 Stages of Fouling

After concentration polarization and fouling, the resistance from these mechanisms increases

contributing to higher trans-membrane pressure (Fritsch, 2008). The concentration polarization and

fouling can be 10 to 50 times the resistance contributed by the membrane itself in the filtration process

(Hanemaaijer 1989). The trend of flux decline in cross-flow RO membrane processes is depicted in Figure

8:

Figure 8 - Flux decline as a consequence of fouling for four experimental runs.

Concentration polarization promotes fouling and is often called stage I flux decline (Marshall,

1993). Very early in RO process, during stage 1, the membrane flux rapidly drops, within seconds or

minutes. Immediate foulant adsorption also adds to this rapid flux decrease, as adsorption of protein to

the membrane surface occurs without concentration polarization (Tong, 1988). Since many polymeric

0

1

2

3

4

5

6

7

8

9

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Flu

x (G

FD)

Time (hrs)

27

varieties of membranes are deformable, membrane compaction may also be responsible for the

resistance of permeation and decrease in flux during the initial stage (Marshall, 1993). Stages II and III of

membrane systems flux decline are due to fouling. The drop in flux during stage II occurs by the initial

deposition of foulant onto the membrane and is a less dramatic decline compared to concentration

polarization (Marshall, 1995). Finally, stage III is an asymptotic decline and can be due to the additional

deposition and compaction of the foulant layer (Marshall, 1995). After solutes and colloidal particles

become adsorbed onto the membrane surface, cake layers or monolayers are formed (Belfort, 2004).

These monolayers start overlapping and form multilayers, then the multilayers are compacted under the

system’s trans-membrane pressure (Belfort, 2004). The RO process is quite simple, however, the fouling

mechanisms and concentration polarization can be complex and it is recommended that the stages of

fouling are understood when trying to evaluate the effectiveness of a membrane filtration system.

2.10 Foulants of interest

The specific foulants of interest are silica, carbonate, and natural organic material because they

are assumed to cause complications with this specific project, and are known to be challenging for many

waste water applications that use RO. The applications section, Section 2.2, provided great insight about

the various compounds that could be of interest. Silica was chosen because it is found in manure at

concentrations around 100 mg/L and is a common concern in many RO applications (Amjad, 2008).

Natural organic matter is also of interest since manure organics are commonly found in manure at high

concentrations. Carbonate scale is also problematic in many RO settings, but can be addressed by

pretreatment much easier than silica and natural organic material. Combined, these inorganic and

organic foulants can drastically reduce the efficiency of RO systems.

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2.10.1 Silica

Silica is found in sand and plants, can constitute 2-5% of dry leaf mass in plant matter (Massey,

Ennos and Hartley, 2006) and is indigestible to many animals (Saha, 2010). Silicic acid is one of the major

constituents in the soil solution which becomes deposited in plant roots (Epstein, 1994). Typically, the

organic matter in flooded soil causes a higher mobility of silica due to the ferric hydrous oxides that also

releases the silicic acid (Kabata-Pendias , 2001). The silica is taken up by plants as an essential

micronutrient to support the shoot of the plant (Epstein, 1994). “Plants deprived of Si are often weaker

structurally and more prone to abnormalities of growth, development and reproduction and it is the

only nutrient which is not detrimental when collected in excess” (Epstein, 1999). Silica is also very

prevalent in sand. Sands contain small quantities of heavy rock forming minerals (“Sand,” 2015). Quartz,

a form of silica, is the most common element in all types of sand because of silica’s abundance in rocks

(“sand,” 2015). Quartz can be defined as the complete dehydrated form of silicic acid (Ning, 2003). As

rocks erode they produce silica enriched sand (“sand,” 2015). The silicic acid in the sand then

depolymerizes by re-hydration when contacted with a water stream and becomes a soluble form of

silicic acid (Ning, 2003). The concentrations may vary depending on the exposure to geologic material.

The forms of the silica mineral (silicon dioxide) are quartz, tridymite, cristobalite, coesite,

stishovite, lechatelierite, and chalcedony (“silica mineral,” 2015). Tridymite, cristobalite, and the

hydrous silica mineral opal are quite uncommon (“silica mineral,” 2015). Vitreous silica, coesite, and

stishovite, are even more uncommon than the latter, and are considered extremely rare (“silica

mineral,” 2015). Silica is the group of minerals composed of silicon and oxygen, which are the most

copious elements in the earth's crust (“silica mineral,” 2015). About 28% of the Earth’s crust contains

silica minerals (“silica mineral,” 2015). Silica is commonly found in well water, as the vitreous form, and

can reach values of 60 parts per million (Peairs, 2007). Water collected near volcanic activity or oil fields

can have silica concentrations as high as 300 parts per million (Meyers, 1975). Enormous amounts of

29

silica are carried away in solution from weathering rocks and soils every year (“silica mineral,” 2015).

Silica is also prevalent in surface waters that contain biological activity (Peairs, 2007). Certain algal

microorganisms, like diatoms, integrate reactive silica to construct a protective shell made of silicon

dioxide crystals (Peairs, 2007). When the algal microorganisms decompose, the silica is released into the

environment as reactive silica (Peairs, 2007). The interaction of biological organisms also creates the

colloidal silicates which are prevalent in most surface waters (Peairs, 2007). There are high

concentrations of reactive silica in well water and some surface water since the water is in contact with

dissolving rock (Peairs, 2007). Silica is prevalent on the earth and is present in essentially all forms of

water.

2.10.1.1 Silica’s Chemical Properties

“Silica has historically created problems for water treatment because of its stability as an un-

ionized compound, making it difficult to remove using ion-exchange processes, and is in fact one of the

least preferred anions to treat (Peairs, 2007).” The bonding of silicon is very similar to that of carbon,

with its four valence electrons, however, it is an inert element (Myshli︠a︡ eva, 1974). Crystalline silica has a

very similar composition to silicon dioxide where 46.75 % by weight is silicon and 53.25 % by weight is

oxygen (“silica mineral,” 2015). Crystalline silica has a very low solubility (6 mg/L) in water compared to

amorphous forms of silica (100 to 140 mg/L) (Amjad, 2008). All silicate compounds, except for stishovite,

are crystallographic structures (“silica mineral,” 2015). These structures are three-dimensional arrays of

linked tetrahedrons, each consisting of a silicon atom coordinated by four oxygen atoms (“silica

mineral,” 2015). The tetrahedrons contain silicon-oxygen bond distances of 1.16±0.002 Å and the main

differences between the silicate compounds is the geometry of the tetrahedral linkages (“silica mineral,”

2015). The stishovite structures are octahedrons where silicon atoms bond with 6 oxygen atoms (“silica

mineral,” 2015). Silicon has a high affinity to oxygen and it is quite problematic to separate silicon

30

dioxide, SiO2 (“silica mineral,” 2015). All of the silicate compounds have a specific gravity around 2 to

2.7 g/L (“silica mineral,” 2015). The solubility increases with increased temperature (“silica mineral,”

2015). The solubility also increases in the presence of �� groups and � �� (“silica mineral,” 2015).

Quartz is the least soluble out of all the silica compounds. In pure water, at 25°C, the solubility of quartz

is 6 parts per million (“silica mineral,” 2015).

The compound SiO2 bonds with itself and can form a tetrahedral, crystalline forming a lattice, or

can be in a non-crystalline form and is classified as reactive (dissolved), colloidal, or suspended

particulate (Ning, 2011). Reactive silica is much smaller than the colloidal form and can be distinguished

as monosilicic acid, disilicic acid and polysilicic acid (Ning, 2011). The reactive form dissolves in water

and forms monosilicic acid (Figure 10) (Ning, 2011).

Figure 9 – Monosilicic acid (Ning, 2011)

Monosilicic acid is unionized at natural pH levels, 10% ionized at a pH of 8.5, and 50% ionized at

a pH range of 9 to 10 (Peairs, 2007). The silicate colloids are generally thought to be either silicon that

has polymerized with numerous elements of silicon dioxide, or silicon that formed bonds with organic

compounds or other complex inorganic compounds (Peairs, 2007). When silica forms anhydrides from

the reaction of silicic acid and organic compounds, silica scale is increased and therefore limits recovery

rates of filtration systems (Ning, 2011). At higher temperatures the compounds which bond to silica are

usually aluminum and calcium oxide structures, increasing the solubility of silica (Peairs, 2007). Silica can

also interact with compounds such as nitrogen, sulfur, phosphorus, aluminum, iron, and some halides

31

(Kabata-Pendias, 2001). When silica is present in acidic conditions within the soil, silica and phosphate

ions can form insoluble precipitates (Kabata-Pendias, 2001). Finally, particulate silica is larger in size and

mostly comprised of sand, like quartz, or suspended solids in water (Ning, 2011).

Silica and metal silicate-based salts are the most problematic foulants in industrial wastewater

systems. When silica forms anhydrides from the reaction of silicic acid and organic compounds, silica

scale is increased and, therefore, limits recovery rates of filtration systems (Ning, 2011). Notice the

trough in the solubility graph, Figure 12, between the pH range of 7 to 7.5 where the solubility is

extremely low. Also, as temperature increases the solubility of silica increases as seen in Figure 11.

Figure 10 - Solubility of silica from temperatures rangning from 0 to 80 ⁰C (Zuhl, 2013)

32

Figure 11 – Concentration of dissolved silica between pH of 2 to 11 (Amjad, 1997)

2.10.1.2 Silica Scaling and Fouling

Fouling due to silica will occur at low pH ranges and low temperatures (see Figures 11 and 12).

“Silica solubility is well known to be both pH and temperature dependent (Amjad, 1997).” At low pH,

and if metal ions are present (ions such as aluminum, iron, calcium, and magnesium), then the fouling

due to silica is exacerbated (Amjad, 2008). Silica becomes more soluble at high pH, so acidifying does not

help. However, it is highly soluble at higher temperatures, above 80 degrees Fahrenheit. The silica

solubility is also limited if certain compounds such as sodium chloride or magnesium chloride are

present (Hamrouni, 2001). This can be challenging when trying to solubilize silica. Silicate fouling can

occur due to condensation of monomeric silicic acid on solid substrates containing hydroxyl groups (-

OH), polymerization of silicic acid or colloidal deposition, and biogenic amorphous silica by living

33

organisms (Amjad, 2009). Fouling due to precipitation occurs when monomeric silica, also called silicic

acid, polymerizes on the RO membrane surface (Amjad, 2008). Particulate fouling occurs when colloids

accumulate during the polymerization process onto the RO equipment and membranes. Depending on

the structure of the silica layer, transport of solutes can be convective or diffusive. If the layer is colloidal

or particulate then solutes transport through the layer dominated by convective flow, but if the silica

layer is made up of polymerized silica then the solutes transport via diffusion (Amjad, 1997).

Prevention of silica fouling is best addressed by using dispersants and high temperature (Peairs,

2007). “The results of a pilot RO study showed that deposition of silica and magnesium silicate on

membrane surface can be prevented by the use of a polymeric dispersant (Amjad, 1997).” Antiscalants

containing dispersants can prevent silica polymerization and scatters fine particles of amorphous silica

once they have formed (Gill, 1990). Dispersion is defined as a method to finely divide a substance in

solution (“Terminology of Polymers,” 2011). The appropriate dosing of antiscalant is necessary and can

be calculated by using antiscalant simulation software, such as the Avista Advisor from Avista

technologies, which contains models constructed by Avista Technologies. Figure 13 displays how

dispersion works, it prevents the agglomeration and adhesion of silicon dioxide onto the membrane

surface.

Figure 12 - This displays how dispersants act on compounds such as silica. (Demadis, 2004)

34

2.10.1.3 Carbonate

Carbonate is derived from either carbonic acid or carbon dioxide. Carbonates can also be

classified as inorganic or organic forms ("carbonate,” 2015). Inorganic carbonates are made from

carbonic acid salts (H2CO3) which contain the carbonate ion (CO ��) and metals such as calcium and

sodium ("carbonate,” 2015). The hard shells of many marine invertebrates are made from inorganic

carbonate ("carbonate,” 2015). Another inorganic form is the carbonate mineral and is the most widely

distributed within the Earth’s crust ("carbonate mineral,” 2015). Organic carbonates, esters, contain the

carbon group ethyl (C2H5), which takes the place of hydrogen atoms of carbonic acid ("carbonate,”

2015). Fifty percent of the carbonate and bicarbonate salts that exist in natural water can be due to

weathering (Chapman 1996). The concentration of carbonate and bicarbonate in surface waters is

generally less than 500 mg/L and more commonly less than 25 mg/L (Chapman 1996). Groundwater is

sometimes more alkaline with concentrations of carbonate or bicarbonate of up to 10 mg/L while

surface waters generally contain lesser amounts of carbonate because their pH rarely exceeds 9

(Chapman 1996). Carbonate salts are also contained in some of the livestock’s feed, but most salts

entrained in manure are from the water supply (Johnson, 2006).

There are over eighty known forms of the carbonate mineral, which are constituents of certain

rocks, and the most common varieties of carbonate are calcite, dolomite, and aragonite (“carbonate

mineral,” 2015). Calcite is the principal mineral of limestone and marble (“carbonate mineral,” 2015).

However, when there is an excess amount of dolomite in limestone, the rock is typically named

dolomite (“carbonate mineral,” 2015). Aragonite is found in calcareous skeletons, within the shells of

organisms and also found in some sediment (“carbonate mineral,” 2015). Some other carbonate

minerals are found in metal ore and the most common are siderite, rhodochrosite, strontianite,

smithsonite, witherite and cerussite (“carbonate mineral,” 2015).

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2.10.1.4 Carbonate’s Chemical Properties

The carbonate ion has a trigonal symmetry which allows most carbonate minerals to form

crystal like structures (“carbonate mineral,” 2015). The carbon atom within the carbonate mineral is

centrally located and surrounded by oxygen atoms (“carbonate mineral,” 2015). The anion within the

carbonate mineral then bonds with compounds such as aluminum, barium, calcium, copper, iron, lead,

manganese, sodium, uranium, and zinc (“carbonate mineral,” 2015). The structure of carbonate changes

as protons are removed and changes from carbonic acid to bicarbonate to the carbonate ion (Figure 14).

The structural relationship is also dependent on pH, shown in Figure 17. This is important to understand

since when pH adjusting the carbonate ion can be in the form of primarily one structure or 2 structures,

and the structure can be fully or partially soluble at various pH ranges (Figure 16).

Figure 13 - The structural relationships of the carbonate mineral (Keener, 2011)

Typically most of the rocks that contain carbonate are either structured by calcite or aragonite

(“carbonate mineral,” 2015). The calcite is structured very similarly to that of sodium chloride in a

rhomohedral form. In this case the sodium and chloride groups become calcium and carbonate groups,

respectively. Within the calcite structure CO3 groups lay in parallel and horizontal layers and CO3 groups

in adjacent layers point in opposite directions. The calcium atoms bond with 6 oxygen atoms and the

36

calcium atom is distributed one each from three CO3 groups in a layer above and three from CO3 groups

in a layer below. Dolomites structure is similar to that of calcite, except that there is an extra

magnesium, and a lower symmetry. The aragonite structure is orthorhombic and like the calcite

structure, the cation in the aragonite structure is surrounded by 6 carbonate groups, however, they are

rotated about an axis perpendicular to their plane and the cation is matched with nine oxygen atoms

rather than six. Bicarbonate is formed when half the acidic hydrogen in carbonate is replaced by a metal,

such as calcium (MacAdam, 2004). Hydrated carbonates, bicarbonates, and compound carbonates

containing other anions in addition to carbonate are some other forms of carbonate minerals

(MacAdam, 2004). Figure 15 illustrates the various structures carbonate can form when clustered

together. These structures are calcite and isostructural dolomite, as well as aragonite and vaterite

(Figure 15)

Figure 14 - Schematic representation of crystallographic unit cells for (a) calcite and (b) isostructural

dolomite, as well as (c) aragonite and (d) vaterite. (Xu, 2014)

The natural alkalinity of groundwater, earths buffering system, is comprised primarily of bicarbonate,

37

carbonate, and hydroxide ions. The buffering occurs when small doses of strong acid, for example acid rain, react with the alkalinity in water. The acid converts carbonate to bicarbonate, converts bicarbonate to carbon dioxide, and this all occurs with a minor change in the pH of the water. During buffering the dissolved CO2 may react with water to form a weak acid called carbonic acid. In the pH range of 4.2 to 4.5, or 8.2 to 8.4, carbon dioxide and bicarbonate are balanced. The alkalinity is in the form of carbon dioxide at a pH of 4.2 to 4.5 while at a pH of 8.2 to 8.4 most alkalinity is in the bicarbonate form with not much carbon dioxide present. At a pH around 8.2 or 9.6 there can be a balance of carbon dioxide and bicarbonate. Typically, at a pH of 9.6, no carbon dioxide or bicarbonate is present, and the majority of alkalinity is carbonate. When the pH of water is above 9.6 alkalinity occurs due to the presence of hydroxyls, the presence of the hydroxide ion. Natural water sources can have a pH in the range of 6 to 8.4 and the presence of hydroxides is predominantly due to human impacts. Alkalinity can be measured using chemical indicators and reported as M-Alkalinity and P-Alkalinity in terms of “ppm as calcium.” M- Alkalinity is normally called the Total Alkalinity and measures the amount of carbonate, bicarbonate, and hydroxide present. The P-Alkalinity measures the concentration of hydroxyl and carbonate alkalinity. (Bates, 2015)

Figure 15 - Solubility of the carbonate mineral (Moles) at a pH of 4 to 12 (Javid, 2011)

38

2.10.1.5 Carbonate Scale

Before delving into the details of carbonate scale, harness of water should be understood.

Hardness occurs when divalent metal cations bond to anions, like carbonate and sulfate, to form a

precipitate (MacAdam, 2004). Total hardness is usually quantified by the concentration of magnesium

and calcium cations (MacAdam, 2004). Temporary harness is measured by the concentration of

bicarbonate and carbonate salts. The classification of hardness is shown in Table 1.

Table 1 - Calssification of hardness by carbonate concentration (MacAdam, 2004)

Concentration (�� as �� ) Degree of hardness

0-50 Soft

50-100 Moderately soft

Table 1 (cont’d)

100-150 Slightly hard

150-250 Moderately hard

250-350 Hard

350+ Excessively hard

In order to limit carbonate scale the RO unit must be run under acidic conditions, below a pH of seven

(Mullin, 2001). Calcium carbonate crystallization occurs in three phases called supersaturation,

nucleation, and crystal growth. During supersaturation, there is an induction period where the first

nucleus is formed (Mullin, 2001). Post supersaturation, calcium ions and carbonate ions begin to cluster

and form a stable nuclei during the nucleation step (Mullin, 2001). This cluster continues to cultivate and

becomes the crystal growth phase (Mullin, 2001). In some cases, temperature influences crystallization

39

where low temperature increases heterogeneous precipitation and high temperature induces

homogeneous precipitation (Mullin, 2001). Scaling occurs when the foulant is transferred from bulk

solution and binds to surface. The scale can increase strength by recrystallizing and also withstands

erosion. At high pH ranges bicarbonate becomes carbonate, which allows for more carbonate fouling to

exist (Andritsos, 1999).

2.10.2 Organics (EfOM)

Effluent organic matter (EfOM) is a form of wastewater effluent and when introduced to the RO

membrance can contribute to fouling (Barker, 2000). The organic compounds associated with EfOM are

polysaccharides, proteins, aminosugars, nucleic acids, humic and fluvic acids, organic acids, and other

cell compounds (Barker, 2000). These intricate compounds are classified into two groups: soluble

microbial products (SMP) and natural organic matter (NOM) (Drewes, 1999). Decomposed vegetable

material cause well water to have a high concentration of dissolved NOM. In solution NOM is a

multifarious mix of particulate and soluble components of both inorganic and organic origin that vary

from one source to another (Howe, 2002). Natural organic matter is primarily humic substances which

can represent about 60 to 90% dissolved organic carbon in natural waters (Choi, 2003). The major

components of NOM are humic acids and fluvic acids. Humic substances are refractory anionic

macromolecules that contain both aromatic and aliphatic components with carboxylic and phenolic

functional groups (Hong, 1997). These humic substances are negatively charged at the pH of natural

water (Hong, 1997). Humic substances can be divided into humic acid and fulvic acids (Yamauchi, 1984).

Fluvic acid is the lighter portion of the humic substance and is soluble under both acidic and alkaline

conditions (Yamauchi, 1984). Fulvic acids are typically found in nutrient rich ground water and

specifically in agricultural environments (Yamauchi, 1984). Soluble microbial products (SMP) and

40

microbial deposits are found in biological wastewater treatment processes from substrate metabolism.

This fouling could also be due to bacterial slimes, fungi, molds, and other microbes.

2.10.2.1 Humus (Humic substances)

Humus is very important for plant growth and nutrition because it contains large amounts of carbon

and nitrogen, and lesser amounts of calcium, iron, magnesium, and phosphorus (Waksman, 1936).

Humus is a natural body or a composite entity from plants, animals, and microbial substances. Due to

the many materials that contribute to its formation, humus is very chemically complex (Waksman,

1936). Some properties of humus are listed below (Waksman, 1936):

1. It is possesses a dark aggregate brown or black amorphous color.

2. Humus is essentially insoluble in water even though part of it may become colloidal. For the

most part humus can dissolve in alkaline conditions, especially upon boiling when the color

becomes darker. The majority of this dark water precipitates in the presence of mineral acids.

Sometimes humus constituents dissolve in acidic conditions and are precipitated at the

isoelectric point, a pH of 4.8.

3. The carbon content of humus is quite high, around 55%.

4. Humus continuously gives off carbon dioxide and ammonia during its decomposition.

Humus is also recognized as four varieties (Waksman, 1936). The first is the brown variety which is

found in living vegetation, fallen litter, peat, shore side sea weed, and fungi (Waksman, 1936). The

second is called the black variety (Waksman, 1936). This humus variety is found in, deep layers of soil,

decomposing leaves and wood in forests, animal manure, peat of swamps, and mud (Waksman, 1936).

Number three is the humus transference variety which is contained in rivers, lakes, springs, and rain

water (Waksman, 1936). The 4th type is the humus in fossil conditions which are in the form of lignite,

41

brown-coal and other carbonaceous deposits, and some minerals like hydrated ores of iron and

manganese (Waksman, 1936).

Fulvic acid and humic acid can be extracted from humus in certain organic rich environments, such as

animal manure. According to Moral et al., animal manure contains more fulvic acid than humic acid

(Moral, 2005). Humic and fulvic acid are the two classes of natural acidic organic polymers that can be

extracted from humus ("humic acid,” 2015). The breakdown of humus is not very well understood, but

the majority of studies believe that it accumulates as a residue from the metabolism by microorganisms

("humic acid,” 2015).

The chemical formula for humic acid is �!"#�!"$"%&%�! and is insoluble in strong acid. Humic

acid is characterized as a loose assembly of aromatic polymers with various acidity and reactivity

("humic acid,” 2015). The ratio of hydrogen and carbon is 1:1 and is indicative of benzene rings and

therefore gives the substance an aromatic character ("humic acid,” 2015). The oxygen to carbon ratio is

low, indicating a lower amount of acidic functional groups ("humic acid,” 2015). The compounds which

react strongly with humic acid are transition and heavy metals as well as aromatic and hydrophobic

chemical structures ("humic acid,” 2015).

The Latin word fulvus indicates it is yellow in color ("fulvic acid,” 2015). Fulvic acid is very soluble

in strong acid ("fulvic acid,” 2015). Its chemical formula is �! '�!"�%'&'�� and it contains a hydrogen

to carbon ration of 1:1 also indicating an aromatic character, just like humic acid ("fulvic acid,” 2015). In

contrast to humic acid, its oxygen to carbon ratio is greater than 0.5:1 indicating a more acidic character

than humic acid ("fulvic acid,” 2015). Fulvic acid contains a loose arrangement of aromatic organic

polymers containing carboxyl groups (COOH) that release hydrogen ions ("fulvic acid,” 2015). It tends to

favor reactions with aluminum, copper, and iron. After the reactions occur the solubility increases in

solution ("fulvic acid,” 2015).

42

2.10.3.1 NOM fouling

Humus causes fouling problems in membrane filtration applications more than any other NOM

because of its adsorptive capacity on the membrane surface (Wiesner, 1996). Humus can form a glue

like film on the membrane surface allowing inorganic constituents to bind to it (Mallevialle, 1989).

Studies have also shown that treatment water with high concentrations of organic material and

inorganic calcium lead to high fouling rates (Mo, 2003). Humic substances are the most problematic and

research has shown that humic substances can cause irreversible fouling (Mo, 2003). A study by Shafer

determined that humic acid caused a 78% flux decline and fulvic acid caused a 15% flux decline in a RO

membrane system (Schafer, 2003). This suggests humic acid can cause a greater impact on the

membrane performance than fulvic acid. The cause of higher fouling potential could be due to the

humic acids high aromaticity properties, adsorptive behavior, hydrophobia, and a greater molecular

weight (Lahoussine-Turcaud, 1990). Apparently, a lower pH causes NOM to have a high ionic strength

and increased divalent cation concentration, allowing the NOM to increase in molecular weight and

surface area (Braghetta, 1995). Low pH and high ionic strength contribute to the reduced intermolecular

electrostatic repulsion of NOM (Braghetta, 1997). Humic substances have an increased hydraulic

resistance at low pH and in the presence of calcium ions (Cho, 2000). The agglomeration of this humic

NOM is increased and the solubility is decreased (Cho, 2000).

A complete understanding of the types of potential foulants is of upmost importance to

determine to enhance the pretreatment stage, cost effectively. Tests for organic, inorganic, and

biological fouling should be performed (Masse, 2007, Gou, 2014). Once the foulant analysis is performed

then the pretreatment and cleaning strategies can be studied to optimize system performance and

efficiency. The performance of the RO system should be well understood, such as permeate production

and the increase in pressure due to fouling. Ammonia volitalization should also be studied in order to

43

understand how much ammonia the streams in the RO process will contain. After this is all complete,

costs can be calculated to determine the capital, and operational costs for the RO system.

44

Chapter 3 – Initial Observations

Within the manure nutrient separation system, there are three main processes prior to RO. In Figure 4

the first step is anaerobic digestion of sand and solid separated manure, followed by ultrafiltration, and

air stripping of the ultrafiltered permeate. The air stripped ultrafiltered permeate is then run through

the RO system. Without pretreatment, the fouling rate of the RO membranes is high resulting in a low

permeate rate. Pretreatment with acid and antiscalant is highly recommended to increase the flux rate

of permeate and decrease the fouling rate.

3.1 Initial Observations

The high fouling rate caused by the feed stream proves to be quite challenging since sustained

runs are not possible without pretreatment (see Figure 18). Throughout various runs, fouling was

observed creating a layer over the membrane surface that precludes the flow of permeate. This was also

confirmed by scanning electron microscopy, SEM (Figure 19), and after cleaning. After cleaning with high

pH and EDTA coffee colored water discharged that was suspected to be organic foulant (Waksman,

1936).

Figure 16 - Graph of non pH adjusted AS water (displayed over a time of 24 hours to see the drastic

drop in permeate production)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00 22.00 24.00

Pe

rme

ate

Ge

ne

rati

on

Ra

te (

GP

M)

Time (hrs)

UF Permeate Air Stripped Water

45

SEM was performed at Michigan State University’s Center for Advanced Microscopy. The scanning

electron microscopy revealed a granular foulant upon the surface of the membrane.

Figure 17 - SEM photo at x5000 revealed a granular foulant noticed upon the membrane surface

Cleaning methodology: Initially, the RO membranes were cleaned with low pH, 2.5, using citric

acid. This only slightly cleaned the membranes since only inorganic scale was addressed. After further

literature research and discussions with DOW Filmtec and Avista Technologies, a more refined cleaning

protocol was made. High pH cleaning was incorporated to the cleaning routine and proved to be a

success. This was because a large amount of dark coffee colored water was discharged when the pH was

brought up to around 12.5, suggesting the removal of some inorganic and organic material. The high pH

cleaning was followed by a low pH cleaning to remove layers of foulant soluble at high pH and low pH. It

is important to cycle high pH and low pH because during operation of the spiral wound membrane

system layers of organic foulant followed by inorganic scale pile one on top of another (Sangyoup,

2006). The organic fouling is cleaned with high pH while inorganics are cleaned by low pH (Sangyoup,

2006).

46

The analytical results of the air stripped ultrafiltered permeate revealed some information that

could be related to fouling and scaling. Bicarbonate as CaCO3 is by far the most prevalent in the sample.

This shows that inorganic carbonate scale will most likely deposit on the RO membrane surface, in the

absence of pretreatment. The calcium and magnesium values also suggest there may be inorganic

carbonate scale. Silica also poses a fouling related problem, from previous research, when silica is

typically above 100 mg/L there may be issues related to silicon dioxide fouling (Koo, 2001). Organic

fouling will obviously be present since manure is a highly organic material. The COD of 7800mg/L

suggests the waste water is highly organic. The ultrafilter will prevent passage of microbial matter but

cannot prevent passage of natural organic material (NOM). The alkaline cleaning solution will remove

organic foulant by hydrolysis and solubilization (Ang, 2006).

Table 2 - Air stripped water analytes.

Analyte Result (mg/L) Analyte Result (mg/L)

Aluminum Non-detectable Strontium Non-detectable Barium Non-detectable Bicarbonate as CaCO3 5000 Boron Non-detectable Chloride 490 Calcium 120 Flouride Non-detectable Iron Non-detectable Sulfate 85 Magnesium 280 Nitrate Non-detectable Potassium 1400 Phosphate as PO4 31 Silica as SiO2 150 Ammonia 990 Sodium 600 COD 7800

The analytical data presented above in Table 3 shows what the RO system is faced with

processing without pretreatment. Carbonate must be addressed first, most likely by pH adjustment.

Pretreatment by pH adjustment and antiscalant addition is necessary to enhance the gallons produced

per square foot of membrane per day (GFD). Optimization of the system is necessary in order to

determine the proper dosing rate of acid, best pH range, and antiscalant. For pH adjustment, sulfuric

acid or hydrochloric acid could be used to decrease the fouling potential. From the analytical results of

47

the feed, Avista Technologies has recommended their Vitec 4000 antiscalant, since it had the highest

recovery rate in the Avista Advisor model. The Antiscalant is also used to limit fouling and scaling.

3.2 Hypothesis

From previous literature, by observing the waste water analytical results, and inspecting the

SEM image of the membrane, inorganic constituents (silica, carbonate) and organic material (such as

humic acid and fulvic acid) are responsible for fouling this RO system.

3.3 Materials and Methods

3.3.1 Analytical Testing

The analytical tests on the waste water were performed at TestAmerica Laboratories and

Fibertec. The concentrations of elements analyzed by TestAmerica were determined by Inductivly

Coupled Plasma Mass Spectroscopy, ICP-MS (Thomas, 2001). The plasmas used in the spectrochemical

analysis are electrically neutral, with each positive charge on an ion balanced by a free electron

(Thomas, 2001). Almost all the positive ions within the plasma are all single charged and there are few

negative ions, meaning there are nearly equal amounts of ions and electrons in each volume of plasma

(Thomas, 2001). Cones within the machine extract the ions from the plasma into a mass spectrometer

(Thomas, 2001). The ions are then separated based on the mass-to-charge ratio and a detector receives

an ion signal proportional to the concentration (Thomas, 2001).

The COD testing at Fibertec was performed with the Hach test. The test uses a chemical oxidant

in an acid solution and heat to oxidize organic carbon to CO2 and H2O (Boyles, 1997). The measured

amount of oxidant consumed using titrimetric or photometric methods determined the oxygen demand

(Boyles, 1997). The Hach COD test measures the oxygen demand of a combination of organic substances

(Boyles, 1997).

48

3.3.2 Modeling Software

The modeling software used was the Avista Advisor and the Reverse Osmosis System Analysis,

ROSA. The ROSA software allows the user to input concentrations of ions in the feed water, select the

type of Filmtec membrane, and input numerous membrane configurations. ROSA performs all the

mathematical calculations and produces a complete report predicting the fouling potential, water

quality, flow rate, energy use, and chemical use. In order to address fouling, the Avista Advisor software

will recommend a type of Vitec antiscalant based on the concentrations of ions in the feed. Both of

these programs use algorithms that the companies have designed based off of current research and

literature.

3.3.3 Pilot RO System

The experimental trials were performed on a 4 GPM pilot RO system using four Filmtech SW30

HRLE 40-40 membranes. The configuration consisted of two trains of the Filmtec RO membranes. Each

train consisted of two elements, equaling a total of four membranes. The membranes were

recommended by the ROSA modeling software and discussions with Dynatec Systems. Dynatec Systems

from New Jersey provided the RO skid.

3.3.4 Scanning Electron Microscopy (SEM)

In SEM imaging, an image is produced by scanning a sample with a focused beam of electrons

(Atteberry, 2009). The sample's surface topography and composition is created after the electrons

interact with atoms in the sample, producing various signals that can be detected by the SEM

(Atteberry, 2009). This technique can achieve resolutions better than 1 nanometer (Atteberry, 2009).

Specimens can be observed in a high or low vacuum, in wet conditions, and a wide range of

temperatures (Atteberry, 2009).

49

3.3.5 Energy Dispersive X-ray (EDX)

EDX analysis is conducted in combination with the scanning electron microscopy (SEM) to

identify the foulant constituents (“surface analysis,” 2015). The electron beam in the microscope causes

specimens to emit x-rays including those from the k, l and m atomic shells (“surface analysis,” 2015). The

mass spectrometer counts these x-rays, and characterizes the elements present in the specimen. EDX

can determine the quantitative measurement of compounds on the sample (“surface analysis,” 2015).

3.3.6 Chromatic Elemental Imaging (CEI)

The CEI analysis is essentially a mapping technique coupled with the EDX analysis. Every element

has its own unique atomic shell, so the element’s electron emission from its atomic shell produces an X-

ray spectrum that allows for its identification ("A New Approach to Membrane Separations,” 2015). Each

element is assigned a color by the CEI and displays a high quality image of their exact location in a

sample ("A New Approach to Membrane Separations,” 2015). The color intensity of each element in a

Chromatic Elemental Image is influenced by its concentration in the foulant sample; the greater the

concentration of elements will be have a greater intensity in the image ("A New Approach to Membrane

Separations,” 2015). This technique also shows the location of different elements in a sample ("A New

Approach to Membrane Separations,” 2015).

3.3.6 Fourier Transform Infared Technology (FTIR)

This is an analytical technique where spectra are collected based on measurements of the temporal

coherence of a radiative source, using time-domain measurements of the electromagnetic radiation or

other type of radiation (Griffiths, 2007). The FT-IR analysis recognizes the functional groups of organic

and inorganic foulant components which will reveal what is present on the membrane surface (Griffiths,

2007).

50

3.3.7 Effervescing

Effervescing is a technique used to see if there is carbonate present. Dilute hydrochloric acid is

dropped onto the foulant and if it fizzes then there is carbonate present (King, 2015). Carbonate

minerals are unstable in contact with hydrochloric acid. When acid begins to fizz, or effervesce, on a

sample a reaction takes place (King, 2015). Shown below is the reaction that occurs when hydrochloric

acid is added to calcium carbonate.

�(� + 2�� → �� + �� + �(�� + ��

Figure 18 - Effervessing performed on a calcium carbonate scaled membrane (“Calcium Carbonate

Scale,” 2015)

3.4 Avista Autopsy and Analysis (membrane run with pH adjusted feed)

At Avista Laboratories, one of the membranes was sent there to be tested, dissected, and

analyzed for performance and foulant analysis. The autopsy was performed there since Avista

Laboratires used specialized equipment, could assess what damage may have been made and what

foulants are present on the RO membrane. To address the fouling issue, the RO system was run under

various low pH conditions (a pH range between 5.5 and 7.5 using sulfuric acid), and with the Vitec 4000

51

antiscalant recommended by Avista’s modeling software, the Avista Advisor. At this point in time

cleaning was not well understood and the membrane was run for over 20 hours under low pH

conditions (pH around 5 to 7.5) without cleaning. An initial "wet" test or flux test was performed and

compared that to the manufacturer specifications. After the wet test, the technicians dissected the

membrane. Once dissected, the membrane sheets were excised and examined using advanced

microscopy techniques and other analyses to determine what fouling was prevalent on the membrane

surface. Once the whole analysis was complete, a necessary cleaning protocol was determined by

cleaning multiple sheets of the dissected membrane with the P111 Avista product. Once cleaned, the

sheets were then tested for salt passage and compared with the membrane

manufacturer specifications.

The imaging and analytical techniques performed to determine some of the fouling were

Scanning Electron Microscope (SEM), Energy Dispersive X-ray (EDX), and Avista’s mapping procedure

called Chromatic Elemental Imaging (CEI). Effervescing and Fourier Transform Infared Technology (FTIR)

was also performed on the membrane sample.

3.4.1 Results of the Salt Passage, Fujiwara Analysis, Dye Testing

Before disassembling the membrane, the performance of the membrane was tested and

determined that the permeate flow rate was 0.2GPM. This confirmed fouling on the membrane since

the manufacturer specifications state the permeate generation rate should be between 0.9 to 1.3 GPM.

The integrity of the membrane was confirmed to be in great condition. After the exterior inspection and

performance test, the membrane was carefully disassembled and additional testing was performed on

the membrane leafs.

Finally, Avista concluded that flat sheet samples produced higher than normal salt passage that

was observed after cleaning (691% of normal). The Fujiwara analysis tested negative for the presence of

52

halogens like chlorine in the membrane structure. Dye testing was also performed to identify any

damage and revealed substantial dye uptake across the membrane surface, primarily between the feed

spacer contact points. Additionally, pinhole sized areas were observed on the membrane backing

indicating severe damage to the active membrane surface. Based on these findings it was determined

that the high salt passage was due to damage to the active membrane surface which was exposed after

the foulant material was removed. Through communication with the Avista technicians, Avista’s

technicians proposed the pinholes could be caused from oxidation near the feed spacers of the

membrane or from starting and stopping the RO system causing the spacers to move back and forth.

Oxidation could not have occurred because no oxidizers, like chorine, were present in the feed stream,

so it was assumed that the pinholes were due to the more than frequent starting and stopping of the

system during testing.

3.4.2 Results of the Microscopy Testing

The SEM scan revealed there was a granular foulant coating the vast majority of the membrane.

EDX and CEI identified silicon as the primary inorganic contributor to the surface foulant material (Figure

21). Lesser amounts of magnesium, calcium, copper, aluminum and iron were also detected.

Figure 19 - Display of the SEM image (left) and CEI (right) analysis showing foulants due to sulfur,

silica, carbon, magnesium, and calcium

53

3.4.3 Results of the Fourier Transform Infared Technology (FTIR) Analysis

The FTIR testing was also performed the fouled membrane and determined that peaks

representing organic fouling were present. Specifically peaks associated with C-N, N-H, C-C, C=C, H-C-

OH, N-H-C=O, and C-O-C.

Figure 20 - FT-IR spectral image of foulant that was removed from membrane surface

3.4.4 Results of Effervescing

There was no effervescing present when dilute hydrochloric acid was dropped onto the foulant

sample. Even though the EDX and CEI image revealed there was some inorganic fouling, there was no

indication by effervessing that there was major inorganic fouling on the membrane surface.

3.4.5 Cleaning Study

After the foulant analysis the membrane samples underwent a cleaning study. The cleaning

involved the use of a cleaning agent, Avista P111, which is a proprietary blend of ingredients that Avista

54

put together in order to achieve the highest efficiency for cleaning, at a pH around 11. This soluble

product was added to 95°F water, at 2% by weight, and the cleaning solution was circulated by passing

the solution over the harvested sample of the membrane. This membrane cleaning was performed for

about 2 hours. Avista reported that over 90% of the visual foulant material was cleaned off of the

membrane and water passage was restored to within the manufacturer's specified range (see Figure 23

and Figure 24).

Figure 21 - Membrane prior to cleaning

55

Figure 22 - Membrane after cleaning

3.5 Confirmation of the Avista Microscopy Testing at the MSU SEM Facility

In order to replicate the imaging Avista had performed, and make significant conclusions using

multiple samples, the same membrane samples tested by Avista were saved and sent to Michigan State

University’s Center for Advanced Microscopy. To reiterate, the sacrificed membrane was run under

various low pH conditions, for over 20 hours without cleaning. Three membrane samples were tested.

One was very dark colored, one was a brown color (mix of dark and light), and one was a light colored

sample. Each of the 3 samples were inspected 3 times for a total of 9 scans. Each of the 9 scans were

tested at x500, x1500, and x5000 magnification plus a point and ID to study various structures of foulant

on the membrane. Mapping was also performed on each sample, and quantitative results were

recorded from each test. The SEM technicians also mentioned organic and inorganic material would be

56

seen on the membrane when using SEM-EDX, so FTIR was not needed. FTIR was also not performed

since it did not fit the budget of the project.

Analytical results showed that the Avista findings were correct, silica was present as one of the

major contributors as it was evenly spread out on the membrane surface, organic material was

definitely present since there was nitrogen and a large amount of carbon. Organic fouling can be

concluded because a study by Rabiller-Baudry confirmed that when nitrogen and carbon are present in

an SEM EDX analysis the fouling is due to organics (Rabiller-Baudry, 2012). Inorganics were minimal

because of low calcium and magnesium values, most likely since the runs were performed at low pH

conditions where inorganic scale is soluble. Please see the results of the SEM and EDX testing in section

3.4.1.

3.5.1 SEM Images

Figure 23 - Foulant observed on the membrane at x500 magnification showing a mixture of organic

material, silica, and minor traces of inorganics

57

Figure 24 – Foulant observed on the membrane at x5000 magnification showing a mixture of organic

material, silica, and minor traces of inorganics

Figure 25 - Granular foulant observed on the membrane at x5000 magnification showing a mixture of

organic material, silica, and minor traces of inorganics

58

The images above (Figure 25, Figure 26, Figure 27) confirm Avista’s findings that there was a

granular foulant upon the membrane surface. After performing advanced microscopy EDX mapping the

primary contributor to the fouling was organic material, followed by silica and sulfur. Traces of inorganic

material were also seen. Sulfuric scale was one of the inorganic materials present upon the membrane

surface primarily due to the use of sulfuric acid during pH adjustment. These findings were identical to

the Avista autopsy results. Please see section 3.4.2 for the EDX results.

3.5.2 EDX Mapping

Figure 26 – Image of the membrane sample (run at low pH conditions) used for EDX mapping

59

Figure 27 - EDX mapping portraying large amounts of carbon, oxygen, silica, and sulfur. Also showing

very minor amounts calcium

60

Figure 28 - EDX mapping demonstrating very minor amounts of iron and copper

Table 3 – Average analytical results of the 9 EDX scans (membrane run with pH adjustment)

Element Avg wt.%

C 41.98

N 3.98

O 30.70

Mg 0.14

Si 13.95

P 0.11

S 8.00

K 0.08

Cl 0.09

Ca 0.23

Fe 0.46

Cu 0.83

The EDX mapping illustrated a fairly homogenous mixture of organic and inorganic material

present upon the membrane surface (Figure 29 and 30). According to the EDX maps (Figure 29 and

Figure 30) and analytical results (Table 3), the main sources of fouling were organic material, followed by

silica and sulfur. Minor amounts of iron, calcium, magnesium, and phosphorus representing inorganic

scale were noticed.

61

3.6 SEM analysis (membrane run without pH adjusted feed)

A membrane was taken out of the RO system after running without pH modification, meaning

no addition of acid. This membrane was run until there was virtually no permeate produced, therefore

the membrane was fully fouled. This membrane was dissected and sent to the SEM Facility at Michigan

State University for qualitative and a quantitative analysis. Three samples from the same membrane

were tested at three random locations per sample. This equaled a total of nine microscopy scans from

the RO membrane. SEM was performed in conjunction with EDX to see what type of foulant and scale

was present on the membrane. The SEM image determined there was some type of granular layer

present on the membrane. After further analysis, with EDX mapping, it was concluded that there was

inorganic scale by calcium carbonate, organic fouling (noticed by significant amounts of carbon and

nitrogen), and silicate fouling. In comparison with the analysis performed at Avista Laboratories, there

was a significantly larger amount of inorganic calcium carbonate scale, 2.81wt% versus 0.23wt% on the

membrane run under the high pH condition. Again, the organic fouling was confirmed because of the

higher than normal nitrogen values. The study by Rabiller-Baudry confirms that when nitrogen and

carbon are present in an SEM EDX analysis the fouling is due to organics (Rabiller-Baudry, 2012). Please

see the SEM and EDX results in Section 3.5.1.

62

3.6.1 SEM Images

Figure 29 – The foulant inspected at x500 magnification revealing a mixture of organic and inorganic

material

Figure 30 –The x1500 magnification shows bolus’ representing inorganic calcium carbonate scale, and

random white regions representing silicate scale upon a layer of organic foulant.

63

Figure 31 - The x5000 magnification shows the detailed inorganic calcium carbonate scale (shown as

round bolus’). The image also shows the depth of the fouling.

The three images, Figure 31, Figure 32, and Figure 33, are captured via SEM at 500x, 1500x, and

5000x magnification to understand how the foulant layer looks. The round protrusions were determined

to be calcium carbonate scale through the EDX analysis. The calcium carbonate is spread out in random

clusters among the membrane surface. Silica is represented by the granular white regions and the dark

regions are typically the organic foulant (Figure 34). The microscopy is also great way to see the depth of

the foulant.

3.6.2 EDX Mapping

The images (Figures 35 and 36) and analytical results (Table 4) are the outcome from the EDX

mapping. Carbon is fairly evenly spread out with slightly higher concentrations on the left and right side

of the sample. Silica and oxygen are somewhat concentrated in the same area, confirming the silicon

dioxide scaling. This is seen dead center of the sample, in a diagonal from, the bottom left corner of the

64

membrane to the top right corner of the membrane. Sulfur is also present in the bottom right portion.

The most interesting observation is the calcium scale, in the form of calcium carbonate, which forms the

small balls dispersed on the membrane surface. The nitrogen is also seen in this sample indicating

organic fouling. The rest of the analytes are dispersed among the sample in low concentrations, which

slightly contribute to the scaling of the membrane.

Figure 32 - Image of the membrane sample (run without acid addition) used for EDX mapping

65

Figure 33 - EDX mapping portraying large amounts of carbon, oxygen, and silica. Nitrogen, calcium,

magnesium were also present in significant amounts.

66

Figure 34 - EDX mapping displaying small amounts of sulfur, sodium, chlorine, postassium, and iron.

67

Table 4 - Average analytical results of the 9 EDX scans (membrane run without pH adjustment)

Element Avg wt.%

C 40.74

N 3.97

O 33.02

Na 0.37

Mg 1.26

Si 12.84

P 1.35

S 2.34

K 1.10

Cl 0.53

Ca 2.81

Fe 0.34

Figure 35 - Comparison of foulant upon the membrane run with acid addition versus the membrane

run without acid addition. Displayed in the graph are the elements which are most likely to cause

issues with fouling.

Both membrane samples have revealed that they contain the same large amounts of carbon and

some traces of nitrogen, indicating organic fouling (seen in Figure 35). The analysis also showed that

there is a large amount of silicon dioxide fouling in both samples represented by silica and oxygen. The

0.00

10.00

20.00

30.00

40.00

50.00

60.00

Carbon Nitrogen Oxygen Magnesium Silica Calcium Sulfur

Co

nce

ntr

atio

n (

wt%

)

Element

No Acid Addition (high pH) Acid Addition (low pH)

68

sample run at low pH had more sulfur than the sample run at high pH indicating that the sulfuric acid

contributed to some fouling when the RO system was run at low pH conditions. Calcium, chlorine, iron,

magnesium, phosphorus, and potassium values were greater in the sample taken off the membrane run

without pH adjusted material. These results suggest that acidification is necessary to prolong the

production of RO permeate (clean water). The results show that there is evidence of organic and

inorganic fouling. Now that the foulants are understood the engineering section provides information

on how to address fouling using proper pretreatment to optimize the performance of the RO system.

69

Chapter 4 – Optimization

In order to address the main problem of fouling on the RO membranes, experimental runs were

performed, at various doses of sulfuric acid or hydrochloric acid, to find which cases were the most

sustainable, produced the most high quality permeate with the least ammonia and COD in 24 hours.

Masse and Gou suggested that the first step is to determine the best pretreatment technique to

concentrate nutrients and produce clean water by RO. In this nutrient separation system, designed by

James Wallace at McLanahan, the best way to treat a manure slurry is to put it through anaerobic

digestion followed by UF, taking the tea water (UF permeate) through an air stripper system to remove

ammonia, add antiscalant, and finally pH adjust the air stripped water using acid. The air stripped,

pretreated UF permeate is then processed through the RO system, which uses sea water elements from

Dow Filmtec. UF permeate could be run through the RO system, however, the data determined that

there was essentially no difference between running air stripped water versus ultrafiltered permeate

through the RO system except for the ammonia values which were lower in the RO permeate that was

generated from air stripped water trials. So the study focused on testing air stripped water through the

RO system. However, certain sites may not be concerned about ammonia removal which is another

reason optimization experiments were performed on processing the non-air stripped ultrafiltered

permeate through RO. The experiments were typically run at 90 – 100 degrees Fahrenheit, the feed

adjusted to a specific pH range using sulfuric acid or hydrochloric acid, followed by the addition of

antiscalant (Figure 38).

The compounds and their adjusted proportions in the air stripped water are in Table 5. This data

has been used in the RO simulators available from DOW Filmtech and Avista Technologies to predict

fouling (ROSA and Avista Advisor). According to the simulators (ROSA and Avista Advisor), silica fouling

limits the RO system from achieving a high recovery rate. The expected recovery rate is around 70% or

more at 5GFD (Gallons per square Foot of membrane per Day) or greater.

70

Figure 36 - Experimental design

Table 5 - Air stripped water analytes.

Analyte Result (mg/L) Analyte Result (mg/L)

Aluminum Non-detectable Strontium Non-detectable Barium Non-detectable Bicarbonate as CaCO3 5000 Boron Non-detectable Chloride 490 Calcium 120 Flouride Non-detectable Iron Non-detectable Sulfate 85 Magnesium 280 Nitrate Non-detectable Potassium 1400 Phosphate as PO4 31 Silica as SIO2 150 Ammonia 990 Sodium 600 COD 7800

Masse and Gou stressed that pretreatment is important since membrane scaling and fouling is

the major concern for RO systems. A high fouling rate leads to higher than normal pressure drop, higher

operating pressure, and reduced permeate generation. Pretreatment is crucial in order to maintain

operation of a RO system in a challenging waste water environment.

If there is an inadequate pretreatment routine, an RO system will require frequent cleaning

intervals and membrane life will be short. Determining a cost effective pretreatment will reduce the

intensity of cleaning and may enhance membrane life. The pretreatment that was chosen for this

71

project chemical based where acid and antiscalant were batch fed to a tank prior to processing through

the RO system. The acids that were compared were concentrated hydrochloric acid and concentrated

sulfuric acid. As discussed earlier, the acids are used to chemically reduce, remove, destroy or inhibit

bacteria, hardness scale, and oxidizing agents. The antiscalant used in the process is called Vitec 4000,

which is primarily used for waters containing high concentrations of silica but also prevents carbonate

and sulfate scale. As stated earlier, antiscalants work to keep supersaturated salts in solution, change

the shape of crystals to move through the membrane, and impart a high negative charge to various

crystals to prevent propagation. For this particular project the acid addition and use of antiscalants was

the most cost effective pretreatment technique.

Sulfuric acid is typically cheaper than hydrochloric but both were compared to test their

effectiveness on the reduction of membrane fouling. In theory, when using sulfuric acid, the formation

of sulfate scale increases, such as barium sulfate, calcium sulfate, and strontium sulfate. Also, according

to the Avista Advisor and ROSA modeling software less hydrochloric is needed to lower pH compared to

sulfuric acid. Since less HCl is necessary for pH adjustment it may seem beneficial to use HCl instead of

H2SO4 depending on the economics and if HCl can perform better than sulfuric acid on reducing

membrane fouling.

4.1 Permeate Production over Time

The following graph (Figure 39) displays the permeate production and flux over time at the various

feed pH ranges, pH = 5.5, 6.5, 7.5, and no pH adjustment (pH = 8). The feed pH of 6.5 was the best

performer, since the slope of permeate production (minor axis in Figure 39) was the least and produced

the most permeate in a 24 hour period, compared to the rest. The performance of the system was

determined by the amount of permeate generated in a 24 hour period. Since the pH of 6.5 was the best

overall, replicate experiments were executed to confirm its performance. Also, surprisingly, the RO

system performance was pretty much the same using hydrochloric acid verses sulfuric acid. Sulfuric acid

72

was the preferred acid to use since it is much cheaper to use than hydrochloric acid and it allows the RO

system to work efficiently (more permeate generated in 24 hours). The use of acid also enhanced the

longevity of the run, indicating there was less membrane fouling when acid was used and resulting in

less frequent membrane cleaning. With sulfuric acid used for pretreatment, the UF permeate at a pH of

6.5 processed through the RO system produced a similar amount of RO permeate as the air stripped

water processed through the RO system at a pH of 6.5, but had a higher ammonia concentration,

therefore only air stripper runs were performed for this study.

Figure 37 – Displays the comparison of flux decline as a negative slope at the various operating

conditions using sulfuric, hydrochloric, or no acid at various pH ranges.

4.2 Flux over time

The flux is the gallons of permeate produced per square foot of membrane per day. On this

specific RO system, the total area of all the membranes combined was 340 square feet. The declining

flux rate per hour had the same trend as the permeate generation rate per hour. According to Figure 41,

the pH at 7.5 showed to have a high flux but a poor permeate quality according to ammonia levels

0

0.05

0.1

0.15

0.2

0.25

0.3

pH = 5.5 pH = 6.5 pH = 7.5 pH = 8

Slo

pe

(N

eg

ati

ve

)

Sulfuric

Hydrochloric

Non pH Adjusted

73

(Figure 45). At the pH of 5.5 the flux rate was also high, however, the permeate quality was not very

good, according to the COD values (Figure 45). Again, the experiment using air stripped water pH

adjusted with sulfuric acid at a pH of 6.5 proved to be the best contender, since it had the second

highest flux rate, and better permeate quality. The same repeated trials with air stripped water at pH 6.5

were executed to confirm the performance using sulfuric and hydrochloric acid. There were five

experiments using air stripped water adjusted with sulfuric to a pH of 6.5, two experiments using air

stripped water adjusted with hydrochloric to a pH of 6.5, and two experiments using UF permeate

adjusted with sulfuric to a pH of 6.5. The error bars, standard deviation, for air stripped water at pH 6.5

using sulfuric was 1.67 and 0.43 when using hydrochloric (Figure 40). Also, the UF permeate processed

through the RO system had the same or similar flux as the air stripped water processed through the RO

system at the pH of 6.5 using sulfuric acid (Figure 40). The standard deviation for UF permeate was 0.57

and 1.17 for air stripped water at a pH of 6.5 using sulfuric acid (Figure 40).

Figure 38 - A display of the UF permeate versus air stripped water at pH 6.5. There is essentially no

difference in performance.

0

1

2

3

4

5

6

UF Permeate Air Stripped Water

Flu

x R

ate

(G

FD

)

74

Figure 39 - The flux rate of the experiments performed at various pH ranges using sulfuric acid,

hydrochloric acid, and no acid addition is displayed. At a pH of 6.5 there were replicate experiments

performed for hydrochloric and sulfuric runs.

4.3 Pressure increase over time

The pressure increase over time was monitored to investigate the fouling rate. As pressure

increases the membrane becomes scaled over and pores become blocked. When the pores become

blocked, the pressure increases and the permeate generation rate decreases. The minor axis in Figure 42

is the slope of the pressure as it increases over time. The slope is positive and the greater the slope the

greater the overall pressure resulting from a high fouling rate. The run with sulfuric acid and a pH of 6.5

proved to be one of the better runs since the slope was less than one, while the rest of the trials had a

slope above one (Figure 42). The run with a feed pH of 7.5 by use of hydrochloric acid was at a slope of

one and very similar to the run using sulfuric acid at a pH of 6.5, however the permeate quality at the pH

7.5 was lower than that of the sulfuric run at pH 6.5 (Figure 46). For the most part the other trials had a

pressure increase above one. The most significant pressure increase was when no pH adjustment was

0

1

2

3

4

5

6

pH = 5.5 pH = 6.5 pH = 7.5 pH = 8

Flu

x R

ate

(G

FD

)

Sulfuric

Hydrochloric

Non pH Adjusted

75

made, at a slope of 14 in Figure 42. The rest of the trials were comparable, but the run with sulfuric at a

pH of 6.5 was best.

Figure 40 - Pressure increase shown as a positive slope is displayed in the graph. The runs with

sulfuric, hydrochloric and, and no acid addition at various pH ranges is graphed.

4.4 Feed Quality

The feed stream to the RO system has high COD and high ammonia values. This can be seen in

the graphs below (Figure 43 and 44). Figure 43 also shows very little differences for COD and ammonia

values between the 3 pH adjustment targets (pH of 5.5, 6.5, and 7.5). The reason the ammonia

concentration for the permeate was higher at pH 5.5 in this graph is because at the time, the air stripper

system was being optimized and unfortunately this run had produced a higher ammonia value. The

ammonia value for numerous runs using sulfuric acid at a pH of 6.5 had shown to be one of the best

since it was consistently lower, around 335mg/L (Figure 44). Replicates were gathered at the pH of 6.5.

Three samples at a pH of 6.5 using sulfuric acid and two samples at a pH of 6.5 using hydrochloric acid

were used for COD and Ammonia in Figure 43 and 44. For COD, the standard deviation error bars were

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

pH = 5.5 pH = 6.5 pH = 7.5 pH = 8

Slo

pe Sulfuric

Hydrochloric

Non pH Adjusted

76

378 for use with sulfuric and 71 for use with hydrochloric. The ammonia concentration had SD error bars

that were 78 for sulfuric and 127 for hydrochloric.

Figure 41 - This graph displays the feed water quality in units of COD for the hydrochloric and sulfuric

runs at the various pH ranges.

Figure 42 - This graph displays the feed water quality in units of ammonia concentration (mg/L) for the

hydrochloric and sulfuric runs at the various pH ranges.

0

500

1000

1500

2000

2500

3000

3500

4000

4500

pH = 5.5 pH = 6.5 pH = 7.5

CO

D (

mg

/L)

Sulfuric

Hydrochloric

0

100

200

300

400

500

600

700

800

pH = 5.5 pH = 6.5 pH = 7.5

Am

mo

nia

Co

nce

ntr

ati

on

(m

g/L

)

Sulfuric

Hydrochloric

77

4.5 Permeate Quality

Again, there was a total of three trials using sulfuric acid and two trials using hydrochloric at a

pH of 6.5, since the trials at 6.5 performed the best (produced the most permeate) at the lowest cost

and best permeate quality. The permeate quality was determined by COD and ammonia values. For this

reason the COD and ammonia values were gathered, averaged and graphed (See Figure 45 and 46

below). The RO permeate had a fairly low COD, ~20mg/L, and low ammonia concentration, ~60mg/L,

when using sulfuric at a pH of 6.5. When using hydrochloric, similar results are displayed however it

costs more to pH adjust so it is not recommended. In Figure 45 the standard deviation at the pH of 6.5

using sulfuric was 29 and 16 when using hydrochloric. The standard deviation in Figure 46 is 52 for

sulfuric and 32 for hydrochloric. The feed at a pH of 7.5 using sulfuric and hydrochloric had produced the

same COD result (between 20 and 30mg/L) as the pH of 6.5 however the ammonia value was quite high

(between 160 and 180mg/L). At a pH of 5.5 the permeate COD was over 100mg/L. If the permeate

meets EPA and other government standards it could be reused for cow drinking, barn washing, direct

discharge or possibly other uses at the facility.

Figure 43 - This graph displays the permeate quality in units of COD for the hydrochloric and sulfuric


0

10

20

30

40

50

60

70

80

90

100

110

pH = 5.5 pH = 6.5 pH = 7.5

CO

D (

mg

/L)

Sulfuric

Hydrochloric

78

Figure 44 - This graph displays the permeate quality in units of ammonia concentration (mg/L) for the

hydrochloric and sulfuric runs at the various pH ranges.

4.6 Concentrate Quality

The concentrate quality is listed below and contains the remainder amount of ammonia, COD,

and retains essentially all of the remaining nutrients, especially potassium. The COD and ammonia data

values are portrayed in Figure 47 and 48. The results show that for feed with sulfuric dosing, the COD is

very high, 12000 mg/L, in concentrate at the lowest pH, 9833 mg/L at the pH 6.5, and 7400 mg/L for the

pH 7.5. The results show that the feed adjusted with H2SO4 had concentrate ammonia values highest at

the pH of 5.5 (2100 mg/L) and values about the same at the pH 6.5 (1757 mg/L) and 7.5 (1200 mg/L).

The standard deviation for the COD data at pH 6.5 was 1401 for sulfuric and 566 for hydrochloric. The

feed adjusted with hydrochloric revealed that the concentrate COD was about the same at pH levels of

5.5, 6.5, and 7.5 (7800 to 8800 mg/L). The concentrate of the feed adjusted with hydrochloric showed

that the ammonia values were lowest at pH of 5.5 (1027 mg/L) and highest at the pH of 7.5, 1400mg/L.

The pH level of 6.5 using hydrochloric had an ammonia value of 1115 mg/L. The standard deviation of

0

20

40

60

80

100

120

140

160

180

200

pH = 5.5 pH = 6.5 pH = 7.5

Am

mo

nia

Co

nce

ntr

ati

on

(m

g/L

)

Sulfuric

Hydrochloric

79

the ammonia concentrations at pH 6.5 was 1205 for sulfuric and 262 for hydrochloric. Finally, the

concentrate is high in potassium which is an essential nutrient for various crops. This is a highly

concentrated form of potassium and could be sold or used on the farm as a fertilizer.

80

Figure 45 - This graph displays the concentrate quality in units of COD for the hydrochloric and sulfuric


Figure 46 - This graph displays the concentrate quality in units of ammonia concentration (mg/L) for

the hydrochloric and sulfuric runs at the various pH ranges.

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

11000

12000

13000

pH = 5.5 pH = 6.5 pH = 7.5

CO

D (

mg

/L)

Sulfuric

Hydrochloric

0

500

1000

1500

2000

2500

3000

3500

pH = 5.5 pH = 6.5 pH = 7.5

Am

mo

nia

Co

nce

ntr

ati

on

(m

g/L

)

Sulfuric

Hydrochloric

81

4.7 Ammonia Balance

The average ammonia balance was calculated from two of the runs performed using sulfuric acid for pH

adjustment at a pH of 6.5. The mass balance, of ammonia, revealed that both of the runs had a

consistent 90% ammonia removal efficiency.

4.8 Membrane Cleaning

Cleaning should be performed when there is evidence of fouling. Membrane cleaning is

important to maintain permeability of the RO process. Fouling is evident when normalized permeate

flow has decreased less than 10% from the starting flow, normalized permeate quality has decreased

less than 10% from the starting quantity, and normalized pressure drop between feed and concentrate

increases about 15% from the starting pressure (Hydronautics TSB107.21, 2011). It is also important to

clean the RO membranes when they are lightly fouled rather than heavily fouled. In some cases,

frequent cleaning is mandatory and membrane replacement will most likely occur every year or every

few years. In certain applications membranes can be cleaned once a day and in more extreme cases

sometimes a 30 second cleaning every 30 minutes (DOW Form No. 609-00306-800, 2000). Chemical

cleaning of the RO membranes removes deposits by chemical reactions including hydrolysis, peptization,

solubilization, dispersion, chelation, sequestering, and suspending (Tragardh, 1989). This restores the

capacity as well as separation characteristics of the system. Selecting the correct cleaning products and

cleaning procedure greatly depends on the assortment of foulants present upon the membrane (DOW

Form No. 609-00306-800, 2000). Chemical cleaning with acid and base reacts with deposits to dissolve

foulants and keep the foulants dispersed and in solution. Low pH is used to clean inorganic material and

high pH is used to clean organic material that adheres to the membrane. DOW recommends cleaning

their Filmetec membranes with an alkaline cleaning solution first. Most Filmtec polyamide membranes

82

can be safely cleaned at the pH range of 1 to 12 according to appropriate temperature range shown in

Table 6. (DOW Form No. 609-23010-0211)

Table 6 - pH range and temperature limits for Filmetc membranes. (DOW Form No. 609-23010-0211)

The process of adding alkaline chemicals elevates the solubility and negative charge on the organic

based foulant (Ang, 2009). DOW Filmtec’s “Cleaning and Sanitation” technical bulletin mentioned that

using EDTA (disodium ethylenediaminetetraacetate) and SDS (sodium dodecyl sulfate) can increase the

cleaning efficiency on the RO membranes. EDTA is a metal chleating agent that is used to remove

organic material that contain divalent cations (Ang, 2009). Anionic surfactants, such as SDS, have

hydrophilic and hydrophobic groups, are semi soluble in organic and aqueous solvents, and are used to

remove foulants by solubilizing macromolecules by forming micelles around them (Ang, 2009). Inorganic

scale due to metal oxides, carbonates and sulfates are normally cleaned by using acids such as

hydrochloric acid or citric acid. Acids will dissolve precipitants that are lodged on the membrane surface

(Arnal, 2011). Below is a chart, Table 7, which displays chemical agents that are responsible of removing

various foulants.

Table 7 - List of chemical cleaning solutions used for the various foulant types.

Fouling due to Chemical Solutions

Carbonate scale HCl, EDTA, SDS

Sulfate scale HCl, EDTA

Phosphate scale HCl

Metal oxide scale Citric acid, HCl, Na2SO4

Silicate scale NaOH

83

Table 7 (cont’d)

Colloids NaOH, EDTA, SDS

NOM (Natural Organic Material) NaOH, EDTA, SDS

Biofilms NaOH, EDTA, SDS, Disinfectants

4.8.1 Cleaning Routines

A general cleaning sequence includes numerous stages such as product removal by rinsing with

clean water, chemical cleaning in a series of steps, and finally rinsing again with water. Filmtec

recommends using chlorine-free water such as RO permeate or deionized water for rinsing. Softened

water is recommended if RO permeate or deionized water is not available. Depending on the foulants,

the chemical cleaning may involve multiple rinses with high or low pH and circulation with various

cleaning solutions. Rinsing and cleaning should be pumped at a low flow rate, around 40 psi, and certain

solutions may be heated as per membrane specs. Soaking is optional and effective but may conflict with

mandatory operational time. To determine a successful cleaning, the permeate generation rate should

be higher and the concentrate pressure lower than those used during normal operation (Tragardh,

1989). The permeate rate should be the same or close to the manufacturer specifications under certain

operating conditions to determine whether or not a cleaning cycle has been effective. An example of a

typical cleaning at Car-Min-Vu dairy, using the four membrane pilot system, addressing mostly organic

and silica fouling is shown in Table 8.

Table 8 - Example of a cleaning cycle at Car-Min-Vu Dairy addressing organic and silicate fouling (high

pH) and inorganic scale (low pH).

Method (high pH)

Chemical

Vol.

(gal)

Water

(gal)

Prev. Soln.

(%)

pH Temp.

(°F)

Circ.

time

Clean water rinse - - 50 - 7 ~70 -

High pH rinse 50% NaOH 0.09 50 - 12 95 -

High pH rinse and circulate 50% NaOH 0.08 50 20 12 95 45

High pH rinse and circulate 50% NaOH 0.08 50 20 12 95 45

Avista P111 rinse and circulate 50% NaOH Avista P111

0.03 3lbs

50 - 12 95 45


84

Table 8 (cont’d)

Clean water flux test - - - - 7 85 -

Method (low pH)

Chemical

Vol.

(mL)

Water

(gal)

Prev. Soln.

(%)

pH Temp.

(°F)

Circ.

time


Low pH rinse 50% HCl 50 - 1.5 70 -

High pH rinse and circulate 50% HCl 0.08 50 20 12 95 45

High pH rinse and circulate 50% HCl 0.08 50 20 12 95 45

Avista P111 rinse and circulate 50% HCl Avista P303

0.03 3lbs

50 - 12 95 45


Clean water flux test - - - - 7 85 -

4.8.2 Cleaning Frequency

Without pH adjustment the pilot RO system would have to be cleaned about every four hours

due to a rapid flux decline (Table 8). With use of acid and antiscalant the RO system does not need to be

cleaned as often. From the trials performed on this pilot system, and using the preferred pH of 6.5 using

sulfuric acid, the recommended cleaning frequency of the membrane system is once a day. This could

potentially be extended to one and a half days or two days if the trials were to be replicated for 48 hour

runs.

4.8.3 Cleaning Costs

The chemical costs to clean the RO is the largest cost operation. For this pilot membrane system

50% NaOH, 32% HCl, and Avista ROclean P111 would be needed (in bulk). In order to clean a 20 element

system every day it would cost $2.82 for 50% NaOH, $7.44 for 32%HCl, and $42.68 for the Avista P111.

The total daily cost to clean the RO is $94.17.

85

4.9 Economic evaluation

4.9.1 Electrical Costs

The average electrical cost is $0.10/kWh, according to the US Department of Energy. According

to the ROSA simulation software the amount of energy required to process 1000 gallons of feed is

2.28kWh. The total electrical cost to run a 20 element system is approximately $0.2/kgal or $0.0002/gal.

4.9.2 Capital Costs

Membranes cost about $550 per module according to the local distributor (Purchase

Advantage). The total cost, including the membrane cost, for an RO skid is $3100 per module. Each

module has a filtration area of 400 square feet. A 20 element system would process dirty water over

8000 square feet of membrane and the capital cost would be roughly $62000.

4.9.3 Operating Costs

Essentially, there are three main aspects to the operating costs. These are primarily chemical

costs. One chemical cost is for pretreatment, the other chemical cost is for daily cleaning. Finally, a labor

cost of $25 an hour at 0.35 full time equivalents (FTE) is necessary, for cleaning and maintenance. If

hydrochloric was used to pretreat the feed stream from a pH around 8 to a pH of 6.5 the cost would be

$0.0119/gallon versus using sulfuric which would cost $0.0032/gallon to adjust air stripped water. The

total cost for cleaning chemicals is $94.17 a day.

86

Chapter 5 – Conclusion and Future Recommendations

The RO systems have come a long way from initially specializing in rejecting salt and minerals

from salt water to treating some of the most challenging waste streams such as municipal waste and

agricultural waste (manure slurry). This project determined what types of elements from a manure

slurry may pose problems due to fouling and scaling on the spiral wound membranes of the RO system.

The main foulants are organic material (such as humic acid and fulvic acid) and inorganic constituents

(carbonates and silica). The organic fouling can be inhibited by using antiscalants that include chelating

agents such as EDTA salts and the inorganic fouling due to carbonates and silica can be inhibited by pH

modification and addition of antiscalant. The FTIR and SEM – EDX imaging proved that organic fouling is

always present. The imaging analysis showed that when no pH adjustment is made there is more

inorganic foulant present. Less inorganic foulant is present when there is pH adjustment, using acid. By

using these tools the RO system was optimized to fit this system, and sulfuric acid was the

recommended acid used for pretreatment. By adjusting the pH of the feed to 6.5 and completing the

pretreatment stage with proper use of antiscalant, and performing at its best, the RO system can

effectively produce permeate at around 1GPM and a flux rate of about 4.3GFD (Figure 41) . Ammonia

and COD was tracked throughout the study and also confirmed that the most stable and best quality

permeate was delivered using sulfuric acid to pH adjust air stripped water at a pH of 6.5. Finally the

cleaning study determined the appropriate timing for cleaning as well as chemicals required to clean the

RO system. Concentrated NaOH, HCl, and Avista ROClean P111 were used to clean the system with a

recommended cleaning protocol. The costs to use each chemical for cleaning and pH adjustment were

gathered and included in the operational costs. The capital costs were also calculated. Also, the

permeate and concentrate samples were frequently tested during the course of the study to determine

the ammonia mass balance and the permeate quality from this particular RO system. At a pH of 6.5 the

ammonia removal efficiency was 90%.

87

A highly replicated study is recommended to determine the exact elements, especially organics,

that are the culprits for the RO fouling. By knowing which organic elements are fouling the RO system

the pretreatment strategy could be modified to enhance the efficiency, permeate production, of the

system. This is particularly difficult since every location is different and will have diverse analytical,

water chemistry data, depending on the water and food provided to the cows for drinking and eating.

There may also be an influence with the bedding used for the cows, whether it be sand (rich in silica),

manure solids, or fresh hay. Further analytical testing should be performed once more systems are in

place to determine the differences in water quality prior to the RO system and determine what analytes

may cause fouling issues to the RO system. A highly replicated study to compare various cost effective

pretreatment strategies is also recommended.

The RO system can run without supervision, with use of a proper automated pretreatment

routine, and needs mandatory cleaning every day. Further research could also be performed to verify

that a 48 hour run or maybe a 32 hour run is sustainable to save money on operational, cleaning, and

maintenance costs. The RO system is an extremely important aspect in the nutrient separation system

to ensure the highest quality water is permeated and reused somewhere in the dairy. RO is a step

forward in closing the sustainability loop and bringing water back to the beginning of the dairy industry

cycle.

88

REFERENCES

89

REFERENCES

"The 4 C’s of Manure Spill Response." Michigan State University Extension. Web. 2 July 2014. "Calcium Carbonate Scale." Avista. Web. 02 August 2015. "Carbonate." Encyclopedia Britannica Inc. Web. 29 June 2015. "Carbonate Mineral." Encyclopædia Britannica Inc. Web. 29 June 2015. "Chromatic Elemental Imaging." Color Imaging Fundamentals and Applications (2008): n. pag. Avista.

Avista, Aug. 2013. Web. "Desalination Industry Enjoys Growth Spurt as Scarcity Starts to Bite." Global Water Intel. Web. 01 June

2015. "Facts About Pollution from Livestock Farms." NRDC 21 February, 2013. Web. 17 August 2015. "Indoor Water Use in the United States." EPA. United States Environmental Protection Agency, 2013.

Web. "Membrane Construction." AvistaTechnologies. Web. 22 July 2015. "Nutrient Recovery: State of Knowledge." WERF. December 2010. Web. 17 August 2015. "Reverse Osmosis System Cuts Food Plant's Eco Footprint." Environmental Leader RSS 27 August, 2013.

Web. 21 July 2015. "Scale Control." DOW, Filmtec August, 2000. Web. "Silica Mineral." Encyclopedia Britannica Inc. Web. 16 June 2015. "Surface Analysis." Encyclopædia Britannica Inc. Web. 01 August 2015. "Ultrafiltration Water Purification, Microfiltration Membranes." Meco. Web. 22 July 2015. "Water Sense - Statistics & Facts." Environmental Protection Agency. Web. 01 June 2015. Adams, Michael Corey. "Examination of Methods to Reduce Membrane Fouling During Dairy

Microfiltration and Ultrafiltration." Cornell University, 2012. Print. Alexander, GB. "The Preparation of Monosilicic Acid." Journal of the American Chemical Society 75.12

(1953): 2887-88. Print. Alghoul, MA, et al. "Review of Brackish Water Reverse Osmosis (Bwro) System Designs." Renewable and

Sustainable Energy Reviews 13.9 (2009): 2661-67. Print.

90

Amjad, Z, and RW Zuhl. "An Evaluation of Silica Scale Control Additives for Industrial Water Systems." NACE International, New Orleans (2008). Print.

Amjad, Z. Silica Control in Industrial Water Systems with a New Polymeric Dispersant. AWT 2009 Annual Convention, Hollywood, FL. 2009. Print.

A New Antifoulant for Controlling Silica Fouling in Reverse Osmosis Systems. IDA World Congress on Desalination and Water Reuse, Madrid. 1997. Print.

Andritsos, N, and AJ Karabelas. "The Influence of Particulates on Caco3 Scale Formation." Journal of heat

transfer 121.1 (1999): 225-27. Print. Ang, Wui Seng, Sangyoup Lee, and Menachem Elimelech. "Chemical and Physical Aspects of Cleaning of

Organic-Fouled Reverse Osmosis Membranes." Journal of membrane science 272.1 (2006): 198-210. Print.

Atteberry, Johnathan. "How Scanning Electron Microscopes Work" 21 April 2009.

HowStuffWorks.com Baker, Richard W. Membrane Technology and Applications. West Sussex, United Kingdom: John Wiley

and Sons Ltd, 2012. Print. Bartels, Craig R. "Reverse Osmosis Membranes for Wastewater Reclamation." Nitto Hydronautics. Web.

2015 2 June. Bates, Wayne. "Ro Water Chemistry." Hydronautics 2015. Web. Batista-Garcia, Valerie. "Treating Brackish Groundwater in Texas: A Comparison of Reverse Osmosis and

Nanofiltration." US Department of the Interior May 2015. WebTreating Brackish Groundwater in Texas: A Comparison of Reverse Osmosis and Nanofiltration

Belfort, Georges, Robert H Davis, and Andrew L Zydney. "The Behavior of Suspensions and

Macromolecular Solutions in Crossflow Microfiltration." Journal of Membrane Science 96.1 (1994): 1-58. Print.

Boyles, Wayne. "The science of chemical oxygen demand." Technical information series, Booklet 9 (1997) Brans, GBPW, et al. "Membrane Fractionation of Milk: State of the Art and Challenges." Journal of

Membrane Science 243.1 (2004): 263-72. Print. Chapman, Deborah V, and World Health Organization. "Water Quality Assessments: A Guide to the Use

of Biota, Sediments and Water in Environmental Monitoring." (1996). Print. Cheryan, Munir. Ultrafiltration and Microfiltration Handbook. CRC press, 1998. Print. Chilekar, Satish. "Production of High Purity Water for Semi-Conductor Industry Using City Sewage by

Public Utility Board of Singapore: A Case Study." (2015). Print.

91

Cho, Renee. "From Wastewater to Drinking Water." State of the Planet. Earth Institure, Columbia University, 4 Apr. 2011. Web.

Cogger, Craig. "Manure on Your Farm: Asset or Liability?" Livestock and Poultry Environmental

Stewardship (n.d.): n. pag. Washington State University. 2 Dec. 2004. Web. Demadis, Konstantinos D, and Eleftheria Neofotistou. "Inhibition and Growth Control of Colloidal Silica:

Designed Chemical Approaches." Materials performance 43.4 (2004): 38-42. Print. Dickrell, Jim. "From Liquid Manure to Drinkable Water." AgWeb, Dairy Today 09 June, 2014. Web. 11

September 2015. Epstein, Emanuel. "The Anomaly of Silicon in Plant Biology." Proceedings of the National Academy of

Sciences 91.1 (1994): 11-17. Print. "Silicon." Annual review of plant biology 50.1 (1999): 641-64. Print. Eriksson, Jan. Concentrations of 61 Trace Elements in Sewage Sludge, Farmyard Manure, Mineral

Fertiliser, Precipitation and in Oil and Crops. Vol. 5159: Swedish Environmental Protection Agency Stockholm, Sweden, 2001. Print.

Fritsch, JACIM, and CI Moraru. "Development and Optimization of a Carbon Dioxide-Aided Cold

Microfiltration Process for the Physical Removal of Microorganisms and Somatic Cells from Skim Milk." Journal of dairy science 91.10 (2008): 3744-60. Print.

Fulhage, Charles D, Donald L Pfost, and John Feistner. Storage Tanks for Liquid Livestock Manure.

University of Missouri--Columbia, Extension Division., 2002. Print. Ganorkar, Pravin, Anil Nandane, and Ajay Tapre. "Reverse Osmosis for Fruit Juice Concentration–a

Review." Research & Reviews: Journal of Food Science & Technology 1.1 (2012). Print. Greenlee, Lauren F, et al. "Reverse Osmosis Desalination: Water Sources, Technology, and Today's

Challenges." Water research 43.9 (2009): 2317-48. Print. Griffiths, P. ; de Hasseth, J.A. "Fourier Transform Infrared Spectrometry " Wiley-Blackwell 18 May 2007.

Web. 01 August 2015. Guo, Xuejun, and Xin Jin. "Purification of Uf-Treated Anaerobically Digested Manure Wastewater by

Two-Pass Reverse Osmosis." Desalination and Water Treatment 52.16-18 (2014): 3027-34. Print. Guu, Yuan-Kuang, Chiu-Hsia Chiu, and Jing-Kun Young. "Processing of Soybean Soaking Water with a Nf-

Ro Membrane System and Lactic Acid Fermentation of Retained Solutes." Journal of Agricultural

and Food Chemistry 45.10 (1997): 4096-100. Print. Hamrouni, B, and M Dhahbi. "Analytical Aspects of Silica in Saline Water—Application to Desalination of

Brackish Waters." Desalination 136.1 (2001): 225-32. Print. Henley, Will. "The New Water Technologies That Could Save the Planet." The Guardian (2013). Print.

92

Hong, Seungkwan, and Menachem Elimelech. "Chemical and Physical Aspects of Natural Organic Matter (Nom) Fouling of Nanofiltration Membranes." Journal of membrane science 132.2 (1997): 159-81. Print.

Hydronautics. "Chemical Pretreatment for Ro and Nf." 111. Nitto October 2013. Web.

A Comparison of Conventional Treatment Methodsand Vsep, a Vibrating Membrane Filtration System. Proceedings of the El Paso Desalination Conference, El Paso Texas. 2006. Print.

Juang, Ruey-Shin, and Chwei-Huann Chiou. "Feasibility of the Use of Polymer-Assisted Membrane

Filtration for Brackish Water Softening." Journal of Membrane Science 187.1 (2001): 119-27. Print.

Kabata, Alina, and H Pendias. "Trace Elements in Soils and Plants." CRC, Washington, DC (2001). Print. King, Hobart. "The "Acid Test" for Carbonate Minerals and Carbonate Rocks." Geology.com. N.p., n.d.

Web. 19 Apr. 2015. Kershner, Kate. "How Reverse Osmosis Works." HowStuffWorks.com (2008). Print. Khan, Muhammad Tariq, et al. "How Different Is the Composition of the Fouling Layer of Wastewater

Reuse and Seawater Desalination Ro Membranes?" Water research 59 (2014): 271-82. Print. Koo, T, YJ Lee, and R Sheikholeslami. "Silica Fouling and Cleaning of Reverse Osmosis Membranes."

Desalination 139.1 (2001): 43-56. Print. Kucera, J. "Reverse Osmosis Design, Processes, and Applications for Engineers, 2010." Co-published by

John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem,

Massachusetts. Print. Kucera, Jane. "Properly Apply Reverse Osmosis." Chemical engineering progress 93.2 (1997). Print. Lenntech. Foulants and Cleaning Procedures for Composite Polyamide RO Membrane Elements (ESPA,

ESNA, CPA, LFC, NANO and SWC) Http://www.lenntech.com/Data-sheets/tsb107-L (2011): n. pag. Lenntech. Nitto Hydronautics, Oct. 2011. Web.

Lenntech. "Scaling and Antiscalants." Web. 30 August 2015. Lin, Hongjun, et al. "A Review on Anaerobic Membrane Bioreactors: Applications, Membrane Fouling

and Future Perspectives." Desalination 314 (2013): 169-88. Print. Lurie, Julia. "It Takes How Much Water to Make Greek Yogurt?!" Mother Jones 10 March 2014. Web. 21

July 2015. MacDonald, James, and Doris Newton. "Milk Production Continues Shifting to Large-Scale Farms."

Amber Waves (2014). 1E.

93

MacDonald, J.M., and W. D. McBride. "The Transformation of U.S. Livestock Agriculture: Scale, Efficency, and Risks." U.S. Department of Agriculture, Economic Research Service (2009). Electronic Information Bulletin No.EIB43.

MacAdam, Jitka, and Simon A Parsons. "Calcium Carbonate Scale Formation and Control." Re/Views in

Environmental Science & Bio/Technology 3.2 (2004): 159-69. Print. Marshall, AD, PA Munro, and G Trägårdh. "The Effect of Protein Fouling in Microfiltration and

Ultrafiltration on Permeate Flux, Protein Retention and Selectivity: A Literature Review." Desalination 91.1 (1993): 65-108. Print.

Masse, L, DI Masse, and Y Pellerin. "The Use of Membranes for the Treatment of Manure: A Critical

Literature Review." Biosystems engineering 98.4 (2007): 371-80. Print. Massey, Fergus P., A. Roland Ennos, and Sue E. Hartley. "Silica in Grasses as a Defence against Insect

Herbivores: Contrasting Effects on Folivores and a Phloem Feeder." Journal of Animal Ecology

75.2 (2006): 595-603. Print. Mavrov, V, and E Bélières. "Reduction of Water Consumption and Wastewater Quantities in the Food

Industry by Water Recycling Using Membrane Processes." Desalination 131.1 (2000): 75-86. Print.

McGowan, Wes. "Water Processing, 3rd Ed." Water Quality Association 2000. Web. Meyers, Peter. "Behavior of Silica in Ion Exchange and Other Systems." IWC 99 (1975): 64. Print. Mullin, John William. Crystallization. Butterworth-Heinemann, 2001. Print. Myshli︠a︡ eva, Lidii︠a︡ Vasil′evna, and Valencn Vasil′evich Krasnoshchekov. Analytical Chemistry of Silicon.

Halsted Press, 1974. Print. Ning, Robert Y. "Discussion of Silica Speciation, Fouling, Control and Maximum Reduction." Desalination

151.1 (2003): 67-73. Print. Ning, Robert Y, and Thomas L Troyer. "Colloidal Fouling of Ro Membranes Following Mf/Uf in the

Reclamation of Municipal Wastewater." Desalination 208.1 (2007): 232-37. Print. Okazaki, Minoru, et al. "Water Recycling Using Sequential Membrane Treatment in the Electronics

Industry." Desalination 131.1 (2000): 65-73. Print. Peairs, David. "Silica over-Saturation, Precipitation, Prevention and Remediation in Hot Water Systems."

Cal Water (2007). Print. Pinnau, I, and BD Freeman. "Formation and Modification of Polymeric Membranes: Overview."

Membrane Formation and Modification 744 (2000): 1-22. Print.

94

Rabiller-Baudry, M, et al. "Coupling of Sem-Edx and Ftir-Atr to (Quantitatively) Investigate Organic Fouling on Porous Organic Composite Membranes." Chapter in Current Microscopy

Contributions to Advances in Science and Technology, Formatex, Badajoz, Spain (2012). Print. Railsback, L Bruce. "Some Fundamentals of Mineralogy and Geochemistry." On-line book, quoted from:

www. gly. uga. edu/railsback (2006). Print. Renner, Edmund, and MH Abd-El-Salam. Application of Ultrafiltration in the Dairy Industry. Elsevier

Science Publishers Ltd., 1991. Print. Roque, Jennifer C. "Evaluation of an on-Line Device to Monitor Scale Formation in a Brackish Water

Reverse Osmosis Membrane Process." University of Central Florida Orlando, Florida, 2012. Print. Sangyoup Lee, Wui Seng Ang, Menachem Elimelech, Fouling of reverse osmosis membranes by

hydrophilic organic matter: implications for water reuse, Desalination, Volume 187, Issues 1–3, 5 February 2006, Pages 313-321, ISSN 0011-9164

Sampat, Payal. "Groundwater Shock." World Watch 13.1 (2000): 10-22. Print. Slomkowski, Stanislaw, et al. "Terminology of Polymers and Polymerization Processes in Dispersed

Systems (Iupac Recommendations 2011)." Pure and Applied Chemistry 83.12 (2011): 2229-59. Print.

Thomas, Robert. "A beginner’s guide to ICP-MS." Spectroscopy 16.4 (2001): 38-42. Tong, PS, DM Barbano, and MA Rudan. "Characterization of Proteinaceous Membrane Foulants and Flux

Decline During the Early Stages of Whole Milk Ultrafiltration." Journal of Dairy Science 71.3 (1988): 604-12. Print.

UNICEF. "Managing Water under Uncertainty and Risk, the United Nations World Water Development

Report 4, Un Water Reports, World Water Assessment Programme." UNESCO, Paris, France, 2012. Print.

USDA. "Agricultural Waste Management Field Handbook." Chapter 4, Agricultural Waste Characteristics.

USDA Natural Resources Conservation Service 12 December 2006. Web. "Facts About Pollution from Livestock Farms." USDA National Agricultural Statistics Service. 2012 Census

of Agriculture. Web. 30 August 2015. Visser, J, and Th JM Jeurnink. "Fouling of Heat Exchangers in the Dairy Industry." Experimental Thermal

and Fluid Science 14.4 (1997): 407-24. Print. Vourch, Mickael, et al. "Treatment of Dairy Industry Wastewater by Reverse Osmosis for Water Reuse."

Desalination 219.1 (2008): 190-202. Print. Waksman, Selman A. "Humus Origin, Chemical Composition, and Importance in Nature." Soil Science

41.5 (1936): 395. Print.

95

Wilf, Mark, and Steven Alt. "Application of Low Fouling Ro Membrane Elements for Reclamation of Municipal Wastewater." Desalination 132.1 (2000): 11-19. Print.

Williams, M. "A Review of Wastewater Treatment by Reverse Osmosis." EET Corporation and Williams

Engineering Services Company Inc (2003). Print. Xu, Ben, and Kristin M Poduska. "Linking Crystal Structure with Temperature-Sensitive Vibrational

Modes in Calcium Carbonate Minerals." Physical Chemistry Chemical Physics 16.33 (2014): 17634-39. Print.

Yang, J, et al. "Mechanistic Evidence and Efficiency of the Cr (Vi) Reduction in Water by Different Sources

of Zerovalent Irons." Water Science & Technology 55.1-2 (2007): 197-202. Print. Zuhl, Robert W, and Zahid Amjad. "10 Solution Chemistry Impact on Silica Polymerization by Inhibitors."

Mineral Scales in Biological and Industrial Systems (2013): 173. Print.

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