Microbiology of sewage and sewage treatment
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Sewage or wastewater contains water and solids separated from various sources like domestic, industrial, and stormwater runoff. It contains pathogens and organic material. Treatment aims to remove solids, reduce biochemical oxygen demand (BOD), and eliminate pathogens through primary, secondary, and sometimes tertiary processes. Primary treatment removes 50% of solids and 25% of BOD through settling. Secondary treatment further reduces BOD through microbial degradation. Sludge from primary treatment is anaerobically digested by microbes to produce methane and reduce pathogens before disposal or reuse. Disinfection with chemicals or UV light is sometimes applied before releasing the treated water.
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Microbiology of sewage and sewage treatment
- 1. MICROBIOLOGY OF SEWAGE AND SEWAGE TREATMENT Pro. F. Tahir 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 1
- 2. Sewage or Wastewater Treatment • Introduction Sewage is waste matter carried in sewers or drains. It is a “mixture of water and solids separated from various types of water as a result of natural or artificial processes”. Sewage could be sludge or wastewater from: – Domestic used water and toilet wastes – Rainwater (surface runoffs) – Industrial effluent – Agricultural wastes 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 2
- 3. Purpose of treatment –Eliminate potential pathogens and toxins –Decrease nutrient content (reduce microbial growth) –Remove odour and chemical contaminants –Reduce B.O.D. 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 3
- 4. Nature and Characteristics of Sewage • The properties of sludge resulting from urban sewage wastewater treatment differ from place to place and depend on the structure of the population and its eating habits, season, diversity of industrial and agricultural units which overflow the wastewater into the urban sewage, on the way of its treatment in the purification plant, etc. • Sewage is 99.9% water and 0.02-0.04% solids and sewage sludge is formed at the wastewater sewage treatment plants by being evacuated through the sewage system. It contains mineral, organic, and biological impurities and microorganisms in soluble, insoluble and colloidal forms. 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 4
- 5. Nature and Characteristics of Sewage continued • The important physical, chemical and biological characteristics of sewage are: Temperature The pH Colour and Odour Solids Nitrogen and Phosphorus Chlorides Toxic Metals and Compounds Organic Material • Biochemical Oxygen Demand (BOD) • Chemical Oxygen Demand (COD) 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 5
- 6. Microorganisms found in sewage BACTERIA Salmonella typhimurium Vibrio cholerae Clostridium botulinum Escherichia coli Etc. NEMATODES Schistosomes, Guinea worm, Tapeworm, Ascaris etc. VIRUSES PROTOZOA Giardia lamblia Entomoeba histolytica Cryptosporidium parvum Etc. 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 6
- 7. B.O.D. Effects Biochemical oxygen demand (BOD): Amount of oxygen required for microbial decomposition of organic matter in sample • Oxygen is removed from water when organic matter is consumed by bacteria. • Low oxygen conditions may kill fish and other organisms. Raw sewage BOD: 300 to 400 mg/liter Natural water BOD: 5-10mg/L If you dump raw sewage into “receiving water”, the dissolved O2 can be quickly depleted by microbes 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 7
- 8. Large Scale Wastewater Treatment Multi-series process • Primary (1°) treatment • Secondary (2°) treatment (4 methods) • Advanced treatment (3o treatment) Effluent (treated liquid) is discharged into water bodies Sludge (solid) is further treated in anaerobic digester and disposed of 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 8
- 9. Primary (1°) Treatment Filter & settle steps remove ~50% of solids & 25% of BOD 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 9
- 10. Anaerobic Sludge Digestion • Anaerobic organisms act on solids (sludge) • Various populations act sequentially Organic matter organic acids, CO2, H2 Organic acids acetate, CO2, H2 Acetate, CO2, H2 methane • Remaining sludge dehydrated • Disposal: incineration, landfill, fertilizer 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 10
- 11. Secondary (2°) Treatment • Eliminates most of remaining BOD • Microbial degradation of organic material • 4 different options 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 11
- 12. 2° Treatment cont. 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 12
- 13. Tertiary or Advanced Treatment Physical, chemical or biological processes Increased expense over 1° and 2 ° treatment Removal of ammonia, nitrates and phosphates • Ammonia stripping: Liberates gaseous ammonia from water • Denitrification: use of bacteria (creation of N2 gas) • Chemical precipitation: phosphate removal 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 13
- 14. Disinfection Performed before effluent is discharged. • Chlorine • Ozone • Ultraviolet light Purpose: reduce numbers of microorganisms and viruses 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 14
- 15. THANK YOU FOR LISTENING 12/2/2014 MCB 503 - ENVIRONMENTAL MICROBIOLOGY 15
Editor's Notes
- Higher BOD-large amounts of degradable materials present
- Bacteria: typhoid, cholera (photo), leigeonella, botulism Protozoa: giardia (photo), entomoeba, cryptosporidium (diarrhea, bad in HIV+) Worms: schistosome (photo), guinea worm, tapeworm, ascaris Viruses: rotavirus (photo), hepatitis A, polio
- Sludge is removed for sludge digestion Liquid sent for secondary treatment Sludge digestion?
- (Fermentation & TCA cycle Many treatment plants use generated methane to power equipment Organic acids: Lactic acid, Acetic acid, citric acid May have concentrated heavy metals
- Can be used in combo Look up ozone antimicrobial activity: )3 made by passing O2 across UV light, made on site and bubbled through water, highly reactive because unstable (like H2O2)