Water recycling for beneficial use

7/29/2019 Water recycling for beneficial use

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Water recycling for beneficial use

Adam Eaton

Nick Kelley

Elias Potts

Yiwen Zhang

CVEN 664

Dr. Kelly Brumbelow

December 10, 2013


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Water recycling for beneficial use 2

Introduction

Water scarcity is becoming a larger concern for many people throughout the world. The

world's supply of fresh water is limited to a fixed amount. About 2.5% of all the water in the

world is fresh water, with only about 31% of that being in a usable form as groundwater or

surface water (USGS 2012). Water is considered a renewable resource but is often treated as an

unlimited resource. Many areas in the world withdraw fresh water resources faster than they can

be replenished, resulting in unsustainable practices that lead to water shortages. Recycling water

can help mitigate the demand of water from the natural supply. If water of a lower quality can be

used in place of drinking-quality water, then more potable water will be available for human

consumption.

According to the United States Environmental Protection Agency (EPA), water recycling

is defined as "[] reusing treated wastewater for beneficial purposes such as agricultural and

landscape irrigation, industrial processes, toilet flushing, and replenishing a ground water basin

[]" (US EPA 2012). Recycled water, also known as reused or reclaimed water, can be

introduced and used in a water system in one of two ways. The first way is indirect use, in which

the reused water is put into a natural water body or system before being used by humans. General

examples of this method include adding reused water into a surface reservoir, or allowing the

water to infiltrate into an aquifer. The second method of introduction is direct use where the

recycled water is put to beneficial use immediately after being treated. With direct use, there are

no natural systems involved prior to using the water and the recycled water may be introduced

into a municipal water system directly from the wastewater treatment plant (WWTP).

Uses of Recycled Water


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The most common uses of recycled water are for non-potable purposes. These include

agriculture, landscape, public parks, golf course irrigation, cooling water for power plants and oil

refineries, processing water for mills and plants, toilet flushing, dust control, construction

activities, concrete mixing, and artificial lakes (US EPA).

Aside from saving fresh water for human consumption, recycling water also promotes

environmental benefits. Recycling water decreases the amount of water taken from sensitive

ecosystems, as well as decreasing wastewater discharge and pollution into those ecosystems.

Recycled water can also be introduced into wetlands and riparian habitats, enhancing the existing

ecology or even creating new ecosystems (US EPA).

Recycling water on-site or nearby saves energy and money that would otherwise be spent

transporting the water longer distances. This not only includes the cost and energy of physically

transporting the water but the infrastructure needed to do so. Keeping water sourced locally

reduces the need for importing water from far away or having to pump water from greater depths

in a depleting aquifer. Establishing different grades of recycled water and specific purposes for

those grades also saves energy during treatment. Rather than using potable water for cooling a

power plant, lower-grade water can be used in its place since the cooling water is considered

non-contact water and does not require the same level of treatment as drinking water. This

lower-grade water would therefore require less energy to create than potable water.

Why Recycle Wastewater?

In earlier days, when water quality standards were practically non-existent, water that

was considered fit enough to drink was drinking water and water that wasn't was considered

wastewater. The concept of "grades" of water with varying levels of contaminant concentrations


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and treatment standards did not exist. But as technology and health standards have increased, so

too have the problems associated with them.

One of the main drivers for the increase in recycled water use is climate change. The

changing climate has shifted water distribution patterns and behaviors. Areas that are normally

dry are getting drier, receiving less than average levels of precipitation. The inhabitants of these

areas must rely more on groundwater and importing water from other regions as local surface

water sources become depleted. And areas that are normally wet are getting wetter, but not in a

good way. Storms are becoming more intense, unloading large amounts of rain in short periods

of time, often resulting in flooding. The seasonal timing of rainfall events also appears to be

shifting, with rainfall occurring earlier in the year when it can't be used for irrigation, or no

rainfall occurring at all, causing droughts during times when the water is needed most.

Exacerbating the problems of climate change is population growth. With many regions of

the world seeing less water available for their inhabitants, increasing populations further strain

these shortages and put increased demand on already limited water supplies. Alongside

groundwater and surface water, recycled water adds a third source of water identification.

Reusing water instead of discharging it in a way that loses the water to the environment reduces

the demand put on natural groundwater and surface water sources.

Types of Wastewater

Building upon the concept of water quality grades, wastewater has its own grades as well,

with wastewater generally falling into one of four categories: gray water, black water, industrial

effluent, and storm water.


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Gray water is defined as "[] water that has been used for washing dishes, laundering

clothes, or bathing. Essentially, any water, other than toilet wastes, draining from a household is

greywater" (NMSU 1996). Gray water is typically defined in the context of domestic water use,

though the exact definition of gray water is not entirely clear as the quality of the water depends

on what is going down the drains. In some states, water from kitchen sinks, garbage disposals,

and dishwashers is considered black water whereas other states consider it gray water (CSU

Extension 2012). Most states have their own rules and regulations regarding the use of gray

water but universally, gray water is of a lower quality than drinking water and higher quality

than black water.

If gray water is any water draining from a house that is not toilet waste, then black water

could be defined as any water draining from a house that is not gray water, i.e., toilet waste. In a

broader context, black water is sewage or any water containing human waste. For obvious

reasons, black water is considered the lowest quality.

The third category of wastewater is industrial effluent. Industrial effluent is considered as

any wastewater produced by industrial activities. Industrial activities are considered to be any

process that creates an object or service for profit (Bio-Systems SA 2012). Such activities

include manufacturing, commercial businesses, mining, agricultural production and processing,

and wastewater from cleanup of petroleum and chemical contaminated sites (Florida DEP

industrial 2012). Due to the diversity of existing industries, industrial effluent can contain a

myriad of contaminants such as pesticides, fertilizer, sediment, organic matter, nutrients, oil,

acids, and dioxin (ExtoxNet 1997).

The final category is storm water, which is usually defined as surface runoff with regards

to precipitation events, but can include water captured directly as rain or snow. Storm water is


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sort of a catchall category for water that cannot be clearly defined as gray water or black water as

storm water is often contains non-point source contaminants. The main issue with storm water is

the uncertainty of its quality. Rainfall captured directly is often considered fairly clean, while the

quality of surface runoff depends on the surfaces it contacts. Surface runoff can contain oil,

fertilizers, pesticides, sediment, debris, animal waste, toxic metals, organic compounds, bacteria,

and viruses (Washington State DOE 2012).

Treatment

Each category of wastewater requires different levels of treatment. The poorer the water

quality, the more it needs to be treated to reach a high standard. The specific use of the recycled

water must also be taken into consideration when evaluating treatment methods. Along with

classifying recycled for direct or indirect use, there is also the consideration of contact and non-

contact use.

There are no federal regulations regarding the use of recycled water, leaving states to

define their own regulations. However, the EPA has created guidelines for certain reuses,

categorizing them as either contact, or limited/non-contact. Contact uses include irrigation for

public areas such as parks and golf courses, and agricultural irrigation for food crops that will not

be commercially processed or will be eaten raw. Limited or non-contact uses include the

irrigation of restricted areas such as sod farms and silviculture (forestry), and agricultural

irrigation for food crops that will be commercially processed, and non-food crops and pastures

(Haering 2009).

Within these general categories are specific criteria that define contact and non-contact

water uses. The criteria include the level of treatment of the water (secondary, disinfection, etc.),


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water quality (pH, BOD, NTU, fecal coliforms, residual chlorine), setback distances, and

monitoring timescales. For example, for recycled water to be used in a public contact purpose it

must have less than 10 mg/L BOD, be at least 50 feet from a potable water well, and be

monitored daily for fecal coliforms.

There are three levels of treating wastewater: primary treatment, secondary treatment,

and tertiary or advanced treatment. Primary treatment is the first stage of treatment and involves

removing solids and particulate. The water is filtered through screens to remove large debris and

particles. The water is then placed in sedimentation tanks or ponds where heavier particles and

wastes sink to the bottom while lighter constituents float to the top and are removed. Secondary

treatment involves the use of microorganisms to remove organic and inorganic solids. This

process also includes more sedimentation. Tertiary treatment includes refined levels of inorganic

compound removal, removal of nutrients such as nitrogen and phosphorus, enhanced filtration,

and disinfection. (Sydney Water 2012)

The level of quality the water needs to attain after treatment, as well as the quality of the

water before treatment, dictates how much treatment is required. For example, according to the

EPA's guidelines, both contact and non-contact uses require water to be treated to the secondary

level, but contact water needs to be filtered and disinfected while non-contact water only needs

to be disinfected (Haering 2009).

Irrigation

One of the main uses of recycled water is for irrigation. Since irrigation water usually

does not need to meet the quality standards of drinking water, depending on the crops being

irrigated, most applications can save potable water by using recycled water instead.


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The city of El Paso, Texas, began using recycled water for irrigation purposes in 1963.

The majority of El Paso's water is supplied by El Paso Water Utilities (EPWU). Located in an

arid environment, El Paso relies on recycled water to mitigate their use of surface water from the

Rio Grande River, and groundwater from local aquifers. EPWU operated the first WWTP in the

world to meet drinking water standards for recycled water. Currently, El Paso uses around 6

billion gallons per day of recycled water, with 39% of that irrigating golf courses, city parks,

school grounds, apartment landscapes, and 40% being used for industrial applications (EPWU

2007).

China has one of the lowest per capita water supply availability in the world. As such,

they have increased their use of recycled water in the face of growing water demand. China first

started using recycled water to irrigate crops in the 1940's, and since 1985 have steadily

increased their resources towards recycling wastewater. In 2004, the Ministry of Water

Resources reported that agriculture used 2.3 trillion m3water, which accounted for 77% of the

total water usage in the country. In 2008, the Ministry of Construction reported that 8% (1.6

billion m3) of total treated municipal wastewater in the country was used, primarily for

agricultural irrigation and recreational/environmental enhancement (Yi 2011).

Managed Aquifer Recharge

Another big use for recycled water is managed aquifer recharge (MAR). MAR is the

intentional storage of water in aquifers. MAR is also known as enhanced recharge, water

banking, and sustainable underground storage (Dillon 2005). There are many specific techniques

and definitions of MAR, including aquifer storage and recovery, bank filtration, infiltration

ponds, and soil aquifer treatment. The main goal of MAR is to store water in underground


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reservoirs where there is less loss of water due to evaporation compared to surface reservoirs.

MAR uses two main methods of recharge: direct injection and infiltration.

Direct injection is typically performed where low-permeability soils or limited surface

area for infiltration exist (Bouwer 2002). Direct injection methods include aquifer storage and

recovery (ASR) and aquifer storage transfer and recover (ASTR). ASR involves injecting water

into a well for storage that also allows for recovery of the water through the same well (Dillon).

These wells are often used for seasonal storage of drinking water or good-quality raw water

supplies when in surplus. The water is then recovered when it is needed (Bouwer). ASTR is

similar to ASR in that it involves injecting water into a well for storage, but it uses different

wells to recover the water (Dillon). Using different wells to store and recover the water allows

the water to flow through the substrate of the aquifer, utilizing the substrate as a natural filter

which provides additional treatment of the water.

Recycled water, referred to as treated sewage effluent (TSE) in the world of MAR, can

also be injected into aquifers. Typically, TSE is injected into confined aquifers, particularly in

arid regions such as North Africa, China, Australia, USA, and the Middle East, where

groundwater depletion and the high cost of desalination facilitate the need for alternate water

sources. In many areas, seasonal variations in water demand and supply produce excess TSE that

can be stored and used later when demand increases (Maliva 2011).

The second method of MAR is infiltration, where water is typically allowed to naturally

infiltrate into an aquifer. This process has the added bonus of filtering the water as it infiltrates

which reduces the need to treat the water to as high a quality before storing it. Infiltration

methods include bank filtration, dune filtration, infiltration ponds, percolation tanks, rainwater

harvesting, and soil aquifer treatment (Dillon).


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A prime example of infiltration storage is in Orange County, Florida, where roughly 15

million gallons of highly treated wastewater are pumped into rapid infiltration basins. The rapid

infiltration basins contain a sinkhole that allows water to flow at 1000 gallons per minute directly

into the Floridan aquifer. The water infiltrates first through a sand layer before reaching the

limestone aquifer below. The sand filtration further treats the water, keeping the water quality of

the aquifer high and decreasing the need for extensive treatment when the water is pumped back

out (Florida DEP 2012).

Environmental Use

Recycled water is also used for the benefit of ecosystems. Along with utilizing soil

substrate as a natural filter, there are many places that discharge treated effluent into nearby

wetlands. The wetlands help filter and clean the water even further while at the same time

providing habitat for wetland organisms. Using and maintaining wetlands also provides a buffer

zone for flooding. In West Palm Beach, Florida, treated wastewater is pumped directly from the

WWTP into a nearby 2000 acre wetland. The wetland acts primarily as a water filter, treating the

wastewater as it passes through to the aquifer before being pumped out again on the other side.

This process takes about two years for the water to cycle through the wetlands, which also act as

a nature preserve (Florida DEP).

Treated wastewater can also be used to sustain and augment stream flows. In San

Antonio, Texas, recycled water is used to augment the flow of the San Antonio River in the

River Walk area. The San Antonio River Walk is a popular attraction consisting of a network of

walkways along the San Antonio River (Paseo del Rio 2012). In March 2000, the San Antonio

Water System began supplying recycled water to the San Antonio River. Water in the river had


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previously been supplied by wells withdrawing from the Edwards aquifer, which provided the

entire stream flow during dry seasons. Utilizing recycled water instead allows less water to be

taken from the aquifer and saved for more beneficial uses.

Industrial Uses

In many areas, industrial uses can comprise a significant portion of water consumption.

Since much of the water used in industrial applications is often discharged as effluent, there is

great potential for recycling this water rather than letting it go. Recycling industrial effluent also

lessens the need for using potable water in industrial applications, which often do not require

drinking-quality water.

About 12% of all the water used in Sydney, Australia, is used in industry. Sydney Water,

Sydneys primary water provider, operates one ofthe largest industrial wastewater recycling

programs in Australia. Treated wastewater is sent from water recycling plants to nearby

industries such as BlueScope Steel, replacing 7.3 billion liters of drinking water per year, and the

Port Kembla Coal Terminal, replacing 1.4 million liters of drinking water per day (Sydney

Water: recycling 2012). Also in Australia, the Eraring Power Station uses off-site effluent in

their boilers, cooling systems, and for cleaning, while Oceanic Coal uses off-site effluent for coal

washing, dust suppression, irrigation of mine sites, and fire fighting (Recycled Water in Australia

2012).

There is also potential for reusing wastewater more efficiently on-site. Many facilities

that use water for cooling purposes utilize recirculating cooling systems that reuse the same

water several times. In thermal power plants, recycling boiler blowdown (wastewater expelled to

limit the buildup of dissolved solids) could conserve up to 50% of water used in the plant (Al


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Smadi 2010). Recycled water also has great potential in the production of concrete, which is one

of the largest water-consuming industries in the world. It requires 150 liters of water to produce

one cubic meter of concrete mix (Silva 2010). In Germany, most ready-mix concrete plants

recycle water from unset and discarded concrete, as well as wash water used to clean mixer

trucks, concrete pumps, and other equipment. Other countries have studied the potential for using

recycled water in concrete production including Indonesia, Saudi Arabia, and Kuwait.

Issues and Risks

While technologies and methods involved in water recycling have evolved over the past

decades, the risks associated with reused water have remained the same. The most significant

issue is that of water quality. Wastewater can contain many contaminants with varying degrees

of adverse effects on human and environmental health. The effect that these contaminants will

have depends on the intended use of the recycled water and the amount of contaminant in the

water.

Probably the most significant threat to human health is microorganisms. Pathogens such

as viruses, bacteria, protozoa, and parasites can be difficult to treat. Some pathogens are resistant

to certain disinfection processes and any WWTP that does not use sufficient disinfection

methods may introduce these pathogens into the environment. Other contaminants, such as trace

organic compounds and heavy metals, may be even more difficult to remove and often require

higher levels of treatment

Other risks associated with wastewater reuse, in the context of ecological effects, include

temperature and salinity. Water used for cooling is oftentimes released into a nearby water

system at a higher temperature than the natural water, which can affect the organisms living in


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that water. Even small increases in average water temperature can kill some organisms and

disrupt behaviors that rely on changes in water temperature to act as an external cue. Recycled

water used for irrigation containing high salinity concentration can affect soil chemistry,

resulting in degradation of the soil for crops, and increased runoff which can transport more

nutrients and other chemicals off-site. (Toze 2006).

Health risks are not the only issues involved with using recycled water. Another concern

is that of pricing structure. Some distributors charge less for recycled water compared to drinking

water, while others charge more. Charging more for recycled water would help recoup costs of

investment and operation, but it may also dissuade people from using it. Charging less would

promote use of the water, but initial investment and operational costs would have to be covered

elsewhere. Many municipalities that provide recycled water do not have well-defined pricing

structures.

There are also cultural issues concerning recycled water. Many people don't understand

the process involved in creating their drinking water, or where it even comes from to begin with.

A common example is that of cities getting their drinking water from a nearby river where

upstream users have already discharged their effluent into that river. At that point in the river,

that water is essentially wastewater.

Many people who hear of the concept of recycled water, or the term "toilet to tap", think

that the water is still dirty and contaminated and that it couldn't possibly be as clean as drinking

water. But there are many examples of recycled water meeting or even exceeding drinking water

standards. El Paso, TX, for example, operates WWTPs whose effluent quality surpasses drinking

water quality requirements. The main issue with spreading the use of recycled water is public


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awareness and making people realize that recycled water can be just as clean as their drinking

water (or cleaner).

In the Middle East, cultural concerns regarding the use of recycled water are stronger due

to the religious ties that water has. In the Islamic religion, water is defined as having two distinct

uses (Farooq 1983). The first is mundane use, which includes drinking, cooking, washing dishes

and clothes, and any other non-religious activity. The second use is for religious purposes, such

as cleansing oneself or any object that has been defiled by impurity.Apart from these uses are

three categories in which water is placed: thur, thir,and mutanajjis. Each of these categories

describes the purity of water, with thurbeing the purest water fit for religious or mundane use,

clean thirthat may only be used for mundane uses, and defiled mutanajjis that is unfit for any

use other than irrigation. In Islamic tradition, impure water can be purified through dilution,

treatment, or the passage of time. In 1978, the Council of Leading Islamic Scholars in the

Kingdom of Saudi Arabia issued afatw, or juristic ruling, stating that recycled water can be

used for ablution (religious cleansing) provided that the water is sufficiently treated (Maliva

2011). From an Islamic perspective, recycled water can be acceptably used for mundane uses,

however negative sentiment may still permeate through the publics perception of such water.

Future

The future of recycled water seems to be bright. An increasing number of cities and

countries are adopting water recycling programs and enacting their own regulations and policies.

There is, however, still the potential for advancement in the area of water recycling. The issue of

treating wastewater has been, for the most part, well addressed and acted upon. Right now, the


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main components concerning the future of recycled water are public awareness and better

management, including developing defined pricing structures and regulations.

The advancement of technology used in water and wastewater treatment is important for

attaining higher levels of efficiency and standards. However, the political and socioeconomic

components of wastewater recycling need to advance as well, and in some cases, catch up to the

technology side. Water is an important component of many aspects of our world and as the lines

of water quality begin to blur, peoples awareness must expand along with the issues. Political

institutions will have to work to define standards and regulations involving treated wastewater.

Water utilities will have to continue informing the public and increasing the acceptance of

recycled water. Many recycled water programs will require better planning and management,

taking into consideration the future uses and expansion of the role of recycled water in our lives,

as well as how to economically sustain it.


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