MICROBIOLOGY OF

SEWAGE AND SEWAGE

TREATMENT

Pro. F. Tahir12/2/2014 1MCB 503 - ENVIRONMENTAL MICROBIOLOGY

Sewage or Wastewater Treatment• Introduction

Sewage is waste matter carried in sewers or drains. Itis a “mixture of water and solids separated fromvarious types of water as a result of natural orartificial processes”.

Sewage could be sludge or wastewater from:

–Domestic used water and toilet wastes

–Rainwater (surface runoffs)

– Industrial effluent

–Agricultural wastes12/2/2014 2MCB 503 - ENVIRONMENTAL MICROBIOLOGY

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 3MCB 503 - ENVIRONMENTAL MICROBIOLOGY

Nature and Characteristics of Sewage• The properties of sludge resulting from urban sewage

wastewater treatment differ from place to place anddepend on the structure of the population and its eatinghabits, season, diversity of industrial and agricultural unitswhich overflow the wastewater into the urban sewage, onthe way of its treatment in the purification plant, etc.

• Sewage is 99.9% water and 0.02-0.04% solids and sewagesludge is formed at the wastewater sewage treatmentplants by being evacuated through the sewage system. Itcontains mineral, organic, and biological impurities andmicroorganisms in soluble, insoluble and colloidal forms.

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MICROBIOLOGY4

• The important physical, chemical and biologicalcharacteristics 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)

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Nature and Characteristics of Sewage continued

Microorganisms found in sewageBACTERIA

Salmonella typhimuriumVibrio cholerae

Clostridium botulinumEscherichia coli

Etc.

VIRUSESPROTOZOA

Giardia lambliaEntomoeba histolyticaCryptosporidium parvumEtc.

NEMATODESSchistosomes, Guinea worm,

Tapeworm, Ascaris etc.

12/2/2014 6MCB 503 - ENVIRONMENTAL MICROBIOLOGY

B.O.D. EffectsBiochemical 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/literNatural water BOD: 5-10mg/L

If you dump raw sewage into“receiving water”, the dissolved O2can be quickly depleted by microbes

12/2/2014 7MCB 503 - ENVIRONMENTAL MICROBIOLOGY

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 digesterand disposed of

12/2/2014 8MCB 503 - ENVIRONMENTAL MICROBIOLOGY

Primary (1°) Treatment

Filter & settle steps remove ~50% of solids & 25% of BOD

12/2/2014 9MCB 503 - ENVIRONMENTAL MICROBIOLOGY

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

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Secondary (2°) Treatment

• Eliminates most of remaining BOD

• Microbial degradation of organic material

• 4 different options

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2° Treatment cont.

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Tertiary or Advanced TreatmentPhysical, 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 13MCB 503 - ENVIRONMENTAL MICROBIOLOGY

Disinfection

Performed before effluent is discharged.

•Chlorine

•Ozone

•Ultraviolet light

Purpose: reduce numbers of microorganisms and viruses

12/2/2014 14MCB 503 - ENVIRONMENTAL MICROBIOLOGY

THANK

YOU

FOR LISTENING12/2/2014 15MCB 503 - ENVIRONMENTAL MICROBIOLOGY