Chapter 5: Other Advanced Wastewater Treatment Processesbaiyu/ENGI 9605 files/lecture-5 .pdf ·...

Chapter 5:

Other Advanced Wastewater

Treatment Processes

Winter 2011Faculty of Engineering & Applied Science

ENGI 9605 – Advanced Wastewater Treatment

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1. Suspended solids left in wastewater after

conventional treatments

5.1 Suspended solids removal

(Viessman et al., Water Supply and Pollution Control, 2009 )2

Removal of suspended solids from the effluent of a

conventional treatment plant necessary to reduce the

organic content or to pretreat the wastewater from

subsequent processing

Effective disinfection requires removal of suspended

solids that can harbour and protect pathogenic

bacteria and viruses from the oxidizing action of

chlorine or ozone

Carbon adsorption columns are preceded by filtration

to prevent fouling of the granular activated carbon

medium

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2. Suspended solids removed through granular-

media filtration

(UNEP., Water and Wastewater Reuse , 2008)4

Tertiary wastewater treatment processes

(Al-Malack, Water Supply and Wastewater Engineering, 2007 )5

A typical granular filter system

(Shanahan, Water and Wastewater Treatment Engineering, 2006 )

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Typical layout of a biological treatment plant with tertiary granular-media filters

(Viessman et al., Water Supply and Pollution Control, 2009 )

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Example 5-1 Four granular-media filters are designed for

suspended-solids removal from a trickling-filter plant effluent.

The average daily flow is 18.2 mgd (68,900 m3/d) and the

maximum wet-weather flow for a 4-hr period is 31.0 mgd

(117,000 m3/d). Data from a pilot-plant study are plotted in the

figure followed. Filters are dual-media, gravity-flow beds,

downtime for backwashing is 30 min, and water usage equals

150 gal/ft2 (6.1 m3/m2). Assume a nominal filtration rate of 3

gpm/ft2 (54 m3/m2 × d), the inflow with SS of 30 mg/l and the

outflow with SS of 5 mg/l. (1) Compute the area of granular-

media filters required for suspended-solids removal; (2)

calculate the quantity of suspended solids removed from the

filtration; and (3) check the peak rate with one filter cell out of

service.

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1. Dissolved organics left in wastewater after


5.2 Dissolved organics removal


Tertiary wastewater treatment processes

(Al-Malack, Water Supply and Wastewater Engineering, 2007 )11


2. Dissolved organics removed through granular-

carbon adsorption

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A GAC tank

Contact time 7 to

20 minutes in typical

water treatment plant

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1. Pathogen left in wastewater after conventional

treatments

5.3 Pathogen removal

Many infectious diseases are transmitted by fecal wastes and the pathogens encompass all categories of microorganisms viruses, bacteria, protozoa and helminths

Although disinfection (e.g., chlorination) is effective in killing bacteria and inactivating enteric viruses these pathogens can be protected in suspended and colloidal solids if the wastewater has not been filtered first for turbidity (solids) removal (Suspended and colloidal solids act as a shield for microorganisms from chlorine)

Cysts of protozoa and helminth eggs are resistant to chlorine they need to be physically removed by effective chemical coagulation and granular-media or membrane filtration

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2. Pathogen removal through chemical coagulation-

granular media filtration-disinfection

(UNEP., Water and Wastewater Reuse , 2008)15

3. Pathogen removal through micro-ultra filtration

Membrane filtrations can be classified, according to the size of materials removed, as followed

Microfiltration (MF) membrane has pores of 0.1-1μm in diameter is effective against bacteria, cysts, and oocysts

Ultrafiltration (UF) membrane has smaller pores (0.01-0.1μm) can remove particles and large molecules, including bacteria and viruses

Nanofiltration (NF) membrane is similar to RO with lower operation pressure and salt rejection rate

Reverse Osmosis (RO) membrane can remove even smaller ionic solutes such as salts resulting in almost mineral-free water, based on sieving and electrochemical interaction between molecules and membrane remove metal ions

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(NanoSense., Nanofiltration , 2008)

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(UNEP., Water and Wastewater Reuse , 2008)

MF-UF membrane filtrations is a promising alternative technology for a large sedimentation pond or a coagulation process using chemicals filtering achieves the removal of bacteria and viruses contribute to minimizing health risk

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Microfiltration

(NanoSense., Nanofiltration , 2008)20

Ultrafiltration

(NanoSense., Nanofiltration , 2008)21

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Membrane filtration in Winsor Lake, St. John’s

(Niblock, Water Treatment Plants in St. John’s , 2010 )

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(Niblock, Water Treatment Plants in St. John’s , 2010 )

Fully assembled rack in Winsor Lake at St. John’s

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1. Toxic water pollutants

5.4 Toxic substance removal

Numerous organic chemicals and several inorganic ions, mostly heavy metals are classified as toxic water pollutants

A typical list of toxic pollutants heavy metals, cyanide, polynuclear aromatic hydrocarbons, aromatics, phenols, aliphatics, phthalates, pesticides

Their toxicity to aquatic life related either to acute or chronic effects on the organisms or to humans by biological accumulation in seafood

Their toxicity to humans related to either carcinogenicity or chromic disease through long term consumption of contaminants

Currently over 100 substances are listed as priotity toxic water pollutants

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2. Toxic substance left in wastewater after


The general goal of municipal wastewater treatment with

pretreatment of industrial wastewaters is to reduce the

discharge of toxic pollutants to an insignificant level

Heavy metals are partially removed by entrapment and

adsorption onto settled solids or biological floc

nevertheless, a portion appears in the effluent up tp 70%

removal of Cd, Cr, Cu, Pb, Ni and Zn

Organic toxic compounds maybe biologically

decomposed or entrapped in settled solids or volatilized

very little data are available on the removal rates

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3. Toxic substance removed through nanofiltration

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Nanofiltration

Typical pore size: 0.001 micron (1 nm)

Low to moderate pressure

Removes toxic or unwanted bivalent ions (ions with 2 or more charges), such as

Lead

Nickel

Mercury (II)


Nanofiltration water cleaning serving Mery-sur-Oise, a suburb of Paris, France

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The active ingredient of the filter media is a nano alumina fiber, only 2 nm in diameter The nano fibers are highly electropositive

Separate particles by charge, not size pores are large (2 microns)

The filter retains all types of particles by electroadsorption including silica, natural organic matter, metals, bacteria, DNA and virus

NanoCeram® filters


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Nanomembranes can be

uniquely designed in

layers with a particular

chemistry and specific

purpose insert

particles toxic to bacteria

Embed tubes that “pull”

water through and keep

everything else out

signal to self-clean

Image of a nanomembrane

New nanomembranes -I


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Embed “tubes” composed

of a type of chemical that

strongly attracts (“loves”)

water

Weave into the membrane a

type of molecule that can

conduct electricity and repel

oppositely charged particles,

but let water through

Water-loving tubes

Electricity moving

through a membrane

New nanomembranes -II


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4. Toxic substance removed through engineered wetlands

Disadvantages of CWs

artificial designed and constructed

utilize natural processes involving wetland vegetation, soils, and their associated microbial assemblages to assist in waste treatment

satisfy the exponentially increasing demands of human expansion and resource exploitation

performance inconsistent due to environmental changes e.g. wetland treatment efficiencies may vary seasonally in response to rainfall/drought and temperature

chemical/biological components sensitive to toxic chemicals e.g. ammonia and pesticides

flushes of pollutants may temporarily reduce treatment effectiveness

Constructed wetlands (CWs)

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Water level above ground surface

Water flow primarily above ground

Surface Flow CWs

Water level below ground

Water flow through a sand/gravel

bed

Subsurface Flow CWs

(Zhang et al., Phytoremediation in Engineered Wetlands, 2010)

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special and advanced kinds of CWs operating conditions are more actively monitored, manipulated and controlled all EWs CWs, but not all CWs EWs

Engineered wetlands (EWs)

Phytotransformation direct uptake of organic contaminants and metabolites into the plant tissue

Rhizosphere bioremediation release of exudates and enzymes to stimulate microbial activity and the resulting biodegradation of organics in the rhizosphere

Phytoextraction uptake and recovery of metals into above-ground biomass

Rhizofiltration filter metals from water onto root systems

Phytostabilization stabilize wastes by erosion control and evapotranspiration of large quantities of water

Five processes of phytoremediation in EWs

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Design modifications Aeration in/under substrate beds to increase

aerobic biodegradation rates

Use of engineered SSF substrates in place of

gravel to adsorb contaminants and control

hydraulic loading

Process additions Chemical and energy addition (eg. low grade

heat)

Alkaline streams

Vegetation changes Plant harvesting for nutrient removal

Phytoremediating plants, stress resistant

species

Advanced operation

methods

Recycle of effluents, intermediate streams

Separation of competing reactions into

different cells

Ways to "Engineer" a Constructed Wetland


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Phytotransformation and rhizosphere bioremediation of

organic contaminants by plants in EWs

Source: Suthersan, 1997

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Phytoextraction of heavy metals in EWs

Source: Suthersan, 1997

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Appleton/Glenwood EW Treatment System in NL


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Chapter 5: Other Advanced Wastewater Treatment Processesbaiyu/ENGI 9605 files/lecture-5 .pdf ·...

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