SEWAGE TREATMENT:

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By-

VIJAY KARHALE

SHANKAR DHADAM

AKASHAY ZENDE

SHAILESH BANGAR

GAJANAN GUTTHE

Sewage:

It is an domestic sewage comprises spent water from kitchens ,bathrooms, lavatories etc.

Sewage is nearly 99.9% water and 0.1% waste matter.

It is this small amount of effluents that bring about grossly polluted conditions.

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Sewage CharacteristicsPhysical Characteristics

Chemical Characteristics

Biological Characteristics

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Sewage Characteristics Table:

Item Range Of Value Contributed in Waste Water(mg/l)

BOD5 170-250

COD (1.6-1.9) BOD5

Total Solids 600-800

Suspended Solids 400-600

Grit 20-55

Oil and Grease 60-120

Phosphorus 03-15

Nitrogen 40-80

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Pollutional Effects Of SewageThe Following materials can cause pollution

1) Organic Matter

2) Suspended Solids

3) Oils and Greases

4) Micro Organisms

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Treatment Of SewagePreliminary Treatment

Primary Treatment

Secondary Treatment

Tertiary Treatment

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Preliminary Treatment

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It consists of Screens and Grit Chambers units.

1) Screens

Coarse Screens(50mm to 75mm)

Medium Screens(20mm to 50mm)

Fine Screens(Less than 20mm)

2) Grit Chambers

It removes sand, gravel, silt, cinders, broken glass, inorganic solids, eggshells, bone chips, etc.

Primary Treatment

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The tanks are used to settle sludge while grease and oils rise to the surface and are skimmed off.

Fig. Primary Sedimentation tank.

Primary Sedimentation Tank:BOD removal is 30 to 35 %

Suspended solids removal 50 to 60 %

Detention Time 2 to 2.5 hours

Average Over flow Rate is 35 to 50 m3/m2/D

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Secondary TreatmentIt consists of Activated sludge process and Secondary Sedimentation.

Activated sludge process:

It is an aerobic process, in which oxygen is supplied from outside.

In this process microorganism convert or reduce organic content of sewage.

1) Oxidation:

COHNP + O2 + Microorganism CO2+ H2O + NH3 + End Products +

(Organic Matter) +Energy

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Activated Sludge Process2) Synthesis:COHNP + O2 C5H7O2N

(Organic Matter) (Bacteria)

3) Auto Oxidation:C5H7O2N + O2 CO2 + H2O + NH3 + End Products + Energy(Bacteria)

Design Parameters:f/m=0.2 to 0.4, MLSS= 1500-3000mg/l, HRT= 4-8 Hours, Qr/Q=0.25-0.5, O2 required= 1 Kg/Kg Of BOD destroyed, Efficiency= 85-92%

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Activated Sludge Process

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Anaerobic DigesterAnaerobic digestion is a collection of processes by which microorganism

break down organic material in the absence of oxygen.

In this process there are two processes as follows:

1) Standard rate digester

2) High rate digester

Following activities takes place in anaerobic digester

1) Hydrolysis

2) Acid Formation

3) Alkaline Fermentation

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Standard and high rate Anaerobic Process

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Sludge Drying Bed

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Sludge is dewatered to reduce the volumes so that it is easy for transportation to disposal site.

ChlorinationThe purpose of chlorination in the treatment of waste water is to substantially reduce the number of microorganisms in the water to be discharged back into the environment for the later use of drinking, bathing, irrigation, etc.

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Flow Diagram For Sewage Treatment

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References:Sewage manual

http://nzic.org.nz/ChemProcesses

http://water.worldbank.org/shw-resource-guide/infrastructure/menu-technical-options/wastewater-treatment

http://www.fao.org/docrep/t0551e/t0551e05.htm

http://www.actew.com.au/Water%20and%20Sewerage%20Systems/ACT%20Sewerage%20System/What%20is%20sewage/Sewage%20Treatment%20Process.aspx

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