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URBAN WASTEWATER URBAN WASTEWATER URBAN WASTEWATER URBAN WASTEWATER TREATMENT TREATMENT TREATMENT TREATMENT TECHNOLOGIES TECHNOLOGIES Statistical, Economic and Social Research and Training Centre for Islamic Countries Higher Council for
Statistical, Economic and Social Research and Training Centre for Islamic Countries Higher Council for Environment and Natural Resources “Water Resources Management” Water Resources Management 23rd-24th November, 2011 Khartoum,Sudan
Waste-water originates predominantly from water usage by residences and commercial and industrial establishments, together with groundwater, surface water and storm water.
Ph i l h i l Physical, chemical and biological methods are used to remove contaminants from waste-water. In order to achieve different levels of contaminant removal, individual waste- water treatment procedures are combined into a variety of systems, classified as primary, secondary, and tertiary waste-water treatment.
Biological processes are usually used in conjunction with physical and chemical processes with the main objective of reducing the organic chemical processes, with the main objective of reducing the organic content and nutrient content of waste-water. Bi l i l d f t t t t t b l ifi d Biological processes used for waste-water treatment may be classified under five major headings: (a) Aerobic processes; (b) Anoxic processes; (c) Anaerobic processes; ( ) (d) Combined processes; (e) Pond processes. These processes are further subdivided, depending on whether the treatment takes place in a suspended-growth system an attached-growth system or a combination of both
So far it is the most widely used biological process for the treatment of municipal and industrial wastewaters the treatment of municipal and industrial wastewaters in developed countries. Mi bi l it ( ti t d l d ) i hi hl Microbial community (activated sludge) is highly diverse and competitive
Liquid-solids separation occurs in sedimentation tank
separation unit back to the reactor to maintaining a high concentration of cells
gravity settling Basic activated sludge process flow sheet Basic activated sludge process flow sheet
Advantages
(except very small ones)
p parameters (SS,COD, N, P);
Small area required Disadvantages
y g p
regular monitoring regular monitoring
always easy to control (bulking sludge) always easy to control (bulking sludge)
Nitrogen Nitrogen and and phosphorus phosphorus are are the the principal principal nutrients nutrients of
concern in in waste waste-
water discharges discharges. . Discharges Discharges containing containing nitrogen nitrogen and and phosphorus phosphorus may may accelerate accelerate the the eutrophication eutrophication of
lakes and and reservoirs reservoirs and and stimulate stimulate the the growth growth of
algae and and rooted rooted aquatic aquatic plants plants in in shallow shallow streams streams. . g g q p
A/O Process (Mainstream Phosphorus Removal) A/O Process (Mainstream Phosphorus Removal) ( p ) ( p ) The proprietary A/O process is The proprietary A/O process is used combined carbon oxidation and phosphorus removal from wastewater The A/O process is a
single-sludge suspended-growth system that combines anaerobic d bi ti i and aerobic sections in sequence. “In A/O Processes there is no nitrification, and the anaerobic detention time is 30 min to 1h for biological phosphorus removal. SRT (solid retention time) of the aerobic zone mixed liquor is 2 to ( ) q 4 d, depending on temperature.”
PhoStrip Process (Sidestream Phosphorus Removal) PhoStrip Process (Sidestream Phosphorus Removal)
In fact fact PhoStrip PhoStrip Process Process consists consists of
In fact fact PhoStrip PhoStrip Process Process consists consists of
biological biological and and chemical chemical process process. .
part of
the return return activated activated sludge sludge i i t t d t t d t bi bi is is transported transported to to an an anaerobic anaerobic stripper stripper tank tank. . The The retention retention time time in in this this tank tank ranges ranges from from 8 8 to to 12 12 hours hours. . A ti A ti id id i fl t i fl t i i dd d dd d t
Acetic acid acid or
influent is is added added to to stripper stripper tank tank to to supply supply phosphorus phosphorus release release. . The The phosphorus phosphorus released released in in the the stripping stripping tank tank passes passes out
in in the the stripping stripping tank tank passes passes out
the the tank tank in in the the supernatant, supernatant, and and the the phosphorus phosphorus-
poor activated activated sludge sludge is is returned returned to to the the aeration aeration tank tank is is returned returned to to the the aeration aeration tank tank.
The phosphorus phosphorus-
rich supernatant supernatant is is treated treated with with lime lime
another another coagulant coagulant in in a separate separate tank tank So So coagulant coagulant in in a separate separate tank
So phosphorus phosphorus will will be be removed removed in in chemical chemical sludge sludge. .
A2 2/O /O Process Process A2 2/O /O process process is is a a modification modification of
the A/O A/O process process and and provides provides an an anoxic anoxic zone zone for for denitrification denitrification. . The The detention detention time time in in the the anoxic anoxic zone zone is is approximately approximately one
hour.
Bardenpho Process (five Bardenpho Process (five-
stage) B d h i i i i l bi h PAO B d h i i i i l bi h PAO k d k d
Bardenpho process contains an initial anaerobic zone where PAOs Bardenpho process contains an initial anaerobic zone where PAOs take up and take up and store VFAs that are either present in the influent wastewater or store VFAs that are either present in the influent wastewater or produced produced by by fermentation in this zone. fermentation in this zone. Effluent from the anaerobic zone flows into an anoxic Effluent from the anaerobic zone flows into an anoxic zone where nitrate zone where nitrate-
rich mixed liquor from the downstream aerobic zone (mixed mixed liquor from the downstream aerobic zone (mixed liquor recycle, MLR) is liquor recycle, MLR) is added to provide nitrate added to provide nitrate-
nitrogen to allow denitrification to occur.
Biodegradable organic matter, present in the influent wastewater, provides the Biodegradable organic matter, present in the influent wastewater, provides the carbon source to drive a rapid rate of denitrification. carbon source to drive a rapid rate of denitrification.
Effluent from the anoxic zone Effluent from the anoxic zone flows to the first aerobic zone where oxygen is added flows to the first aerobic zone where oxygen is added to allow nitrification to occur. to allow nitrification to occur. PAOs also oxidize the VFAs stored in the anaerobic zone. Effluent from the first PAOs also oxidize the VFAs stored in the anaerobic zone. Effluent from the first aerobic zone flows into the second anoxic zone where additional denitrification aerobic zone flows into the second anoxic zone where additional denitrification
The effluent from the second anoxic zone flows to the second aerobic zone The effluent from the second anoxic zone flows to the second aerobic zone where nitrogen gas formed in the upstream anoxic zone is stripped from the mixed where nitrogen gas formed in the upstream anoxic zone is stripped from the mixed liquor prior to following to the secondary clarifier. liquor prior to following to the secondary clarifier.
UCT (University of Cape Town) Process UCT (University of Cape Town) Process Negative effects of nitrate recycle to anaerobic stage have been observed. Negative effects of nitrate recycle to anaerobic stage have been observed.
g y g g y g On On the the basis basis of
these observations,
UCT process process was was developed developed changing changing A A2 2/O /O process process. . There There are are two two differences differences between between A A2 2/O /O process process and and UCT UCT process process. . First First difference difference is is that that return return activated activated sludge sludge is is returned returned to to anoxic anoxic stage stage instead instead
anaerobic stage stage. . Second Second difference difference is is that that an an internal internal recycle recycle from from anoxic anoxic stage stage to to anaerobic anaerobic stage stage is is added added. . By By returning returning the the activated activated sludge sludge to to the the anoxic anoxic stage, stage, the the introduction introduction of
the g , g , nitrate nitrate to to the the anaerobic anaerobic stage stage is is eliminated, eliminated, thereby thereby improving improving the the release release of
phosphorus in in the the anaerobic anaerobic stage stage. . The The internal internal recycle recycle feature feature provides provides for for increased increased
utilization utilization in in the the anaerobic anaerobic stage stage. . The The mixed mixed liquor liquor from from the the anoxic anoxic stage stage contains contains substantial substantial soluble soluble BOD BOD but but little little nitrate nitrate. . The The recycle recycle of
the anoxic anoxic i d i d li li id id f ti l ti l mixed mixed liquor liquor provides provides for for
conditions conditions for for fermentation fermentation uptake uptake in in the the anaerobic anaerobic stage stage. .
( f ) ( f )
VIP process (VIP stands for the Virginia Initiative Plant) VIP process (VIP stands for the Virginia Initiative Plant) VIP process is similar to UCT process, with one exception. There is VIP process is similar to UCT process, with one exception. There is anaerobic, anaerobic, anoxic, aerobic tanks in VIP process are divided parts anoxic, aerobic tanks in VIP process are divided parts , , p p , p p
JOHANNESBURG JOHANNESBURG
The The process process is is an an alternative alternative to to standard standard and and modified modified UCT UCT processes processes to to minimize minimize nitrate nitrate feeding feeding to to the the anaerobic anaerobic zone zone. . The The return return activated activated sludge sludge is is directed directed to to an an anoxic anoxic zone zone that that has has g sufficient sufficient detention detention time time to to reduce reduce the the nitrate nitrate in in the the mixed mixed liquor liquor before before it it is is fed fed to to the the anaerobic anaerobic zone zone . . Compared Compared to to the the UCT UCT process process a higher higher MLSS MLSS concentration concentration can can be be maintained maintained in in the the process process a higher higher MLSS MLSS concentration concentration can can be be maintained maintained in in the the anaerobic anaerobic zone zone which which has has a a detention detention time time of
about 1 1 h h. .
An
An aerated aerated lagoon lagoon is is a a basin basin between between 1 1 and and 4 4 meters meters in in depth depth
The
The microbiology microbiology involved involved in in this this process process is is similar similar to to that that of
the activated activated-
sludge process process. . However, However, differences differences arise arise because because the the large large surface surface area area of
lagoon may may cause cause more more temperature temperature effects effects than than are are ordinarily
encountered in in conventional conventional activated activated-
sludge processes processes. .
Waste
Waste-
water is is oxygenated
by surface, surface, turbine turbine or
diffused aeration aeration. .
The trickling filter is the most commonly encountered aerobic attached-
growth biological treatment biological treatment process used for the removal of organic matter from waste process used for the removal of organic matter from waste-
water water. water.
It consists of a bed of highly permeable medium to which organisms are attached, medium to which organisms are attached, forming a biological slime layer, and through which waste forming a biological slime layer, and through which waste-water is water is percolated. The
forming a biological slime layer, and through which waste forming a biological slime layer, and through which waste water is water is percolated. The
filter medium usually consists of rock or plastic packing material. filter medium usually consists of rock or plastic packing material.
The organic material present in the waste present in the waste-
water is degraded by adsorption on to the biological slime layer. In the outer portion of biological slime layer. In the outer portion of that layer, it is degraded by aerobic that layer, it is degraded by aerobic micro micro-
As the micro-
slime layer increases and the
. An An anaerobic environment is thus established near the surface of anaerobic environment is thus established near the surface of the filter medium. the filter medium.
As the slime layer increases in thickness, the organic matter is degraded before it in thickness, the organic matter is degraded before it reaches the micro reaches the micro-organisms near the surface of the
medium Deprived of their reaches the micro reaches the micro-organisms near the surface of the
external organic source of nourishment, these micro external organic source of nourishment, these micro-
washed
Advantages
p y p
Di d t Disadvantages
removal (85%)
the effluent (20 to 30 mg/l) ( g )
control
A rotating rotating biological biological contractor contractor (RBC) (RBC) is is an an attached attached-
growth biological biological process process that that consists consists of
more basins basins in in which which large large closely closely-spaced spaced circular circular disks disks g y mounted mounted on
horizontal shafts shafts rotate rotate slowly slowly through through waste waste-
water The disks are partially submerged in the waste water so that a bacterial slime layer waste-water, so that a bacterial slime layer forms on their wetted surfaces. As the disks rotate the bacteria are As the disks rotate, the bacteria are exposed alternately to waste-water, from which they adsorb organic matter, and to air from which they absorb oxygen air, from which they absorb oxygen. Organic matter is degraded by means of mechanisms similar to those operating in mechanisms similar to those operating in the trickling filters process. Partially submerged RBCs are used for carbonaceous BOD removal, combined carbon oxidation and nitrification, and nitrification of secondary effluents. Completely submerged RBCs are used for denitrification.
A stabilization stabilization pond pond is is a a relatively relatively shallow shallow body body of
waste-
water contained contained in in an an earthen earthen basin basin using using a completely completely mixed mixed biological biological process process without without solids solids return return earthen earthen basin, basin, using using a completely completely mixed mixed biological biological process process without without solids solids return return. Mixing Mixing may may be be either either natural natural (wind, (wind, heat heat
fermentation) fermentation)
induced induced (mechanical (mechanical or
diffused aeration) aeration). . Stabilization Stabilization ponds ponds are are usually usually classified classified as as aerobic, aerobic, anaerobic, anaerobic, or
aerobic-
anaerobic. . , , The bacterial population oxidizes organic matter, producing ammonia, carbon dioxide sulfates water and other end dioxide, sulfates, water and other end products, which are subsequently used by algae during daylight to produce
Waste-water retention time ranges b t 30 d 120 d Thi i between 30 and 120 days. This is a treatment process that is very commonly found in rural areas because of its low t ti d ti t construction and operating costs.
Wetlands are inundated land areas with water Wetlands are inundated land areas with water depths typically less than 2 ft depths typically less than 2 ft (0.6 m) that support (0.6 m) that support the the growth of emergent plants such as cattail, growth of emergent plants such as cattail, bulrush, reeds and sedges. The vegetation bulrush, reeds and sedges. The vegetation provides surfaces for the provides surfaces for the attachment of bacteria attachment of bacteria films, aids in the filtration and adsorption of films, aids in the filtration and adsorption of waste waste-
water constituents, transfers oxygen into
the water column, and controls the growth of the water column, and controls the growth of algae by restricting the penetration of sunlight. algae by restricting the penetration of sunlight. There are several types of constructed wetlands: surface flow wetlands, subsurface flow wetlands, and hybrid systems that incorporate surface and subsurface flow wetlands. Constructed tl d t l b bi d wetland systems can also be combined with conventional treatment technologies.
A subsurface subsurface flow flow (SSF) (SSF) wetland wetland consists consists of
a sealed sealed basin basin with with a a
porous porous substrate substrate of
rock or
gravel. . The The water water level level is is designed designed to to remain remain below below the the top top of
the substrate substrate. . In In most most of
the systems systems in in the the U it d U it d St t St t th th fl fl th th i i h i t l h i t l lth h lth h E United United States, States, the the flow flow path path is is horizontal, horizontal, although although some
European systems systems use use vertical vertical flow flow paths paths. .
Inlet and outlet zone with coarse gravel or rocks for better distribution of wastewater
Water Hyacinth Water Lettuce - Duckweed Irıs Pseudacorus Reed Mace (Typhia latifolia) Irıs Pseudacorus Reed Mace (Typhia latifolia)
Cyperus alternifolius Sedge
Scirpus Juncus species
Ad t f CTW Ad t f CTW
Advantages of CTW Advantages of CTW
medium investment cost
–unskilled labour unskilled labour
Disadvantages: Disadvantages:
up problems
Space requirement Space requirement
L ti L ti
For Human Use; recreation walking, fishing, art (photography) g g (p g p y)
Anaerobic digestion digestion involves involves the the biological biological conversion conversion of
and inorganic inorganic matter matter in in the the absence absence of
molecular oxygen
to a a variety variety of
end-
yg yg y products products including including methane methane and and carbon carbon dioxide dioxide. .
The two most widely used types of anaerobic digesters are standard two most widely used types of anaerobic digesters are standard-
rate d hi h d hi h t I th t d d t I th t d d t di ti th t t f th di ti th t t f th and high and high-rate. In the standard
rate digestion process, the contents of the digestion process, the contents of the digester are usually unheated and unmixed, and are retained for a digester are usually unheated and unmixed, and are retained for a period period ranging from 30 to 60 days. In the high ranging from 30 to 60 days. In the high-
rate digestion process, the contents f th di t h t d f th di t h t d d i d l t l d t i d t i ll d i d l t l d t i d t i ll
and mixed completely, and are retained, typically, for a period of 15 days or less. for a period of 15 days or less.
Advantages Advantages
Advantages Advantages
Production of
energy-
rich methane methane
No energy energy demand demand for for aeration aeration
No removal removal
nitrogen nitrogen and and phosphorus phosphorus (this (this is is an an advantage advantage if if effluent effluent is is to to be be reused reused in in agriculture) agriculture)
High organic
loading rates rates can can be be applied applied
Suitable for for high high-strength strength wastewater wastewater Limitations Limitations treating treating domestic domestic sewage sewage
Not effective effective in in removing removing nutrients nutrients
Suitable for for high high strength strength wastewater wastewater (high (high BOD) BOD)
Low production production of
excess sludge sludge; ; the the digestate digestate is is highly highly stabilized stabilized and and can can
Only partially partially effective effective in in removing removing pathogens pathogens
Difficulties in in removing removing finely finely dispersed dispersed lid lid digestate digestate is is highly highly stabilized stabilized and and can can easily easily be be dewatered dewatered solids solids
Low activity activity at at temperatures temperatures < < 10 10-
15 ° °C C
At low low temperatures temperatures the the hydrolysis hydrolysis rate rate
particulate matter matter becomes becomes the the rate rate
particulate matter matter becomes becomes the the rate rate limiting limiting step step