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23 Cards in this Set
- Front
- Back
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what are the aims of waste water treatment?
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to reduce BOD by removing or destroying microorganism and pathogens
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What is primary treatment of waste water? what is the aim and outcome?
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Aims: Reduces BOD by 25-45% and bacteria by 25-75%
Process: put in sedimentation tank to allow 40-70% of suspended solids to settle Flocculating chemicals may be added Primary sludge is driend and incinerated or digested by microorganisms Outcome: Decreased BOD and bacteria content May be discharged to water ways or go under secondary treatment |
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What is secondary treatment of water?
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Aerobic digestion of remaining waste in water
Two methods: Trickling Filter Activated Sludge Sludge remaining needs to be treated also |
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What is the Trickling Filter method?
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secondary treatment of waste water
waste is sprayed over bed of rocks or plastic honey comb organisms form biofilm and oxidize any organic matter in sewage BOD reduced by 80-95% and bacteria reduced by 90-95% |
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What is the Activated Sludge Method?
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Secondary treatment of waste water
air is blown through water. Increased aeration allows slime forming bacteria to grow, oxidize organic matter, and clump to form flocs (aka activated sludge) Material is then passed to settling tank where sludge is removed and treated BOD reduced by 80-95% and bacteria by 90-98% |
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What is sludge and how is it treated?
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remains from secondary treatment of waste water. Is high in cellulose and other organic compounds.
is treated by microbial digestion under anaerobic condition. Ch4 produced can be burned and used to power plant (source of CO2) BOD is reduced by 90% and remaining material is incinerated or burned... |
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What is 3rd level of treatment of waste water? outcomes?
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involves a combination of
1. Biological treatment 2. flocculation 3. filtration 4. chemical and ozonation Final liquid effulent can be suitable for drinking water if coliforms and fecal coliforms low enough |
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How do trickling filter and activated sludge methods differ? how are they the same?
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both use microorganisms to oxidize organic matter in sewage and reduce BOD and bacteria significantly BUT
Trickling filter allows oxidizing organisms to form biofilm on material in which water is trickled over Activated sludge increases the oxygen concentrations in water so slime forming microbes (that oxidize the organic matter) can grow easier and clump to form flocs of activated sludge |
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What is a septic tank and how does it work?
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Settling tank for domestic use -- only primary treatment (domestic waste contains high water content)
after settled, top water is distributed over tile/leeching field of a large area. sand and soils naturally filter sludge Reduced BOD by 60% and thus protects near by waterways and ground water |
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What are two indicators of contamination?
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Coliforms and fecal coliforms
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How do coliforms and fecal coliforms differ?
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Temperature and primary origin
Coliforms = 35 C not all are of intestinal origin non-spore forming Fecal coliforms= 44.5 C (excdpt E. coli O157: H7) ALL of intestinal origin of warm blooded animals form cyst |
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Coliform
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faculative aerobes, gram - neg, non spore forming
ferment lactose with gas formation at 35 C variety of different bactera--not all of fecal orgin |
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Fecal coliform
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grow at 44.5 C (except e. coli O157:H7)
derived from intestines of warm blooded animals -- indication of fecal contamination (especially e. coli) BUT absence doesn't mean good quality because cyst may still be present (ex. cryptosporidium parvum) |
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Most Probably Numebr (MPN)
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test for coliforms (incubated at 35 C)
done by innoculating lactose broth and preforming serial dilution and then incubating gas bubbles = positive for lactose fermenting coliforms compare results to stat stable to determine MPN |
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Membrane Filtration
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Faster and easier than MPN
Non-fecal and fecal coliforms can be tested for depending on incubation test run large volume of water through filter (and put on EMB agar) |
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What are the aims of Water Treatment (4)?
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1. Remove Pahogens
2. Improve Clarity 3. Remove compounds of bad taste and smell 4. Soften water (remove metal ions) |
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What are the four steps of water treatment?
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1. Sedimentation
2. Flocculation 3. Filtration 4. Disinfection |
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What is the first step of water treatment?
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Sedimentation
remove large debris by allowing water to settle in tank for long period of time |
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What is Flocculation? What are flocs?
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2nd step in water treatment, after sedimentation.
Coagulating agents are added and left to settle and form FLOCS Flocs are large flacky precipitates carrying other small particles, organisms and chemicals still suspended in water after sedimentation 80% of bacteria, color and particles removed BUT water may still have cysts!!!!!!!!!! |
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What happens during Filtration?
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Water is passed over sand to remove remaining particles and any G, lamblia cyste
98-99% of bacteria removed BUT c. parvum cyste may still be present |
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What are the two methods of Disinfection?
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4th/final step of water treatment
1. Chlorination 2. Ozone |
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Why is chlorination done, what is the problem?
Why is there residual? |
Chlorination kills remaining microorganism and neutralizes most chemicals that give bad taste and odor.
BUT some are resistant to chlorine (ex. C. parvum cysts) Residual chlorine is left in water after treatment to protect water from re-contamination during water distribution |
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Why and when is ozonation done?
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More effective than chlorine to kill microorganisms (such as C. parvum cysts) BUT has short half life and cannot protect water during distribution
usually ozone is added to kill all microorganism and then treated with chlorine to protect during distribution |
