The treatment of sewage by microorganisms especially bacteria.
The discharge of sewage into a fresh water source is a biological treatment process.
Both aerobic and anaerobic bacteria play a major role in the biological treatment.
PRINCIPLES OF BIOLOGICAL TREATMENT
Large porous surface is needed for the aerobic bacteria to perform their functions.
When sewage is passed through the beds, where aerobic activity is there the following action takes place.
The colloidal and putrecible organic compounds are absorbed within few minutes in the trickling filters.
The bacteria feed the organic matter necessary for their growth.
The bacteria feed on organic matter and convert them into stable inorganic forms by oxidizing them.
The nitrates,Co2 and sulphates remain in the sewage. The gases escape in the atmosphere
TRICKLING FILTERS
These are used for the biological treatment of domestic sewage and industrial which are amenable to aerobic biological process.
This process is preceded by primary sedimentation so that settelable solids do not clog the filter.
This process is followed by final settling tank with skimming devices
As the sewage trickle through the filter media a biological slime of aerobic bacteria and other biota build up a surface and makes filter ready for use.
Organic material is absorbed by the slime and increases the thickness.
Scouring of slime is done periodically and this is known as sloughing or unloading.
UNDER – DRAINAGE SYSTEM
Consists of V-shaped or half round channels cast in concrete.
These drains are covered by concrete blocks.
The floor is given a slope.
Compressed air is passed through this drainage lines through vertical pipes.
This under-drainage must be self-cleansing.
VENTILATION
Ventilation increases the efficiency.
As the dose increases more quantity of air is required.
If the temperature difference is 6˚C, the air gets displaced at rate of 0.3 m3/m2/sec.
If the temperature difference is 1.9˚C, there is no air displacement.
Usually 6˚C temperature difference is sufficient to supply the required quantity of air.
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