chapter 5: other advanced wastewater treatment processesbaiyu/engi 9605 files/lecture-5 .pdf ·...
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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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(Viessman et al., Water Supply and Pollution Control, 2009 )9
1. Dissolved organics left in wastewater after
conventional treatments
5.2 Dissolved organics removal
(Viessman et al., Water Supply and Pollution Control, 2009 )10
Tertiary wastewater treatment processes
(Al-Malack, Water Supply and Wastewater Engineering, 2007 )11
(Shanahan, Water and Wastewater Treatment Engineering, 2006 )
2. Dissolved organics removed through granular-
carbon adsorption
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(Shanahan, Water and Wastewater Treatment Engineering, 2006 )
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
(Viessman et al., Water Supply and Pollution Control, 2009 )16
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
conventional treatments
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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(NanoSense., Nanofiltration , 2008)
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)
(NanoSense., Nanofiltration , 2008)
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
(NanoSense., Nanofiltration , 2008)
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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
(NanoSense., Nanofiltration , 2008)
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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
(NanoSense., Nanofiltration , 2008)
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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
(Zhang et al., Phytoremediation in Engineered Wetlands, 2010)
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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
(Zhang et al., Phytoremediation in Engineered Wetlands, 2010)
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