Activated Sludge Process produced biomass in inffluant by the growth of microorganisms in aeration tank in presence of dissolve oxygen.
Hello, reders, today i m going to explain about Activated sludge process.
What is activated sludge?
This is biomass produced in effluent by the growth of microorganisms in aeration tank in the presence of dissolve oxygen. the term activated comes from the fact that sludge is rich of bacteria and many other living organisms which can be fed on organic matter in incoming effluent.
Major constituent of activated sludge is bacteria along with small fungi and protozoan’s.
Becteria…….. Heterotrophic is major constituent and breaths organic matter.
Principal of activated sludge process.
1. The effluent is first mixed with air in aeration tank to decompose the organic matter by microorganisms.
2. This effluent enters the clarifier Or settler where activated sludge is settled.
3. The part of this activated sludge is returned to aeration tank for treatment of fresh effluent.
Analysis of activated sludge
The sequence of operations in activated sludge process.
1. Aeration Of Effluent
(a) Diffused Aeration
Effluent liquor is run into deep tank where air is pumped at bottom through blocks in form of bubbles. For example – (fish tank).
These bubble also cause stirring action. Strong effluent oxygen may be used in place of air. the compressors are used to blow the air.
(b) Mechanical Agitation
It creates turbulence on the air liquid interface which helps air to enter effluent. For example, (high speed impellers).
In the aeration tank the effluent is mixed with port of activated sludge. the bacteria consume dissolved organic matter as food to live, grow and multiply.
Heterotrophic bacteria are in major quantity and derive their food from organic matter.
Their food is bacteria itself and particulate matter. they are present in small quantity. It is on type of biological indicater of the condition of activated sludge.
They are excellent indicater of aerobic conditions. they are also indicator of toxic substance in effluent as are more sensitive to toxic substances then bacteria.
fungi; In small quantity can break ammonium compounds to nitrate.
Clerifier Or Settler
When effluent is oxidized for 1-2 days the organic matter is broken down by microbes. this effluent is now collected in clerifier or settler hence activated sludge is settled in 1-2 hours. Part of sludge is returned to aeration tank.
Returned activated sludge and remaining is sent for their treatment and disposal. For example; Surplus activated sludge.
High quality effluent – high cost
Reduction of 90% BOD – sensitive to shock load
– Sensitive to toxic wast
– The success depends on mixed community of microbes present that will consume verity of organic wastes.
Activated Carbon Absorption
A form of carbon that has been processed to make it extremely porous and then have large surface area available for adsorption.
1. Activated sludge process reduce BOD by 90-95 but in case of COD, it is not reduced.
2. Activated carbon process can remove many finishing chemicals and dyes reducing COD.
3. Overall maintenance is cheaper such as capital cost, operational cost.
4. It is cheaper process compare with reverse osmosis process.
5. Sometimes effluent after primary treatment is directly subjected to activated carbon process without biological treatment (activated sludge process).
1. Effluent is passed over a bed of activated carbon.
2. If the chemical molecules come in contact with surface of carbon and if held there by week vanderwall’s forces.
3. Treatment efficiency is affected if a suspended solid exceeds 50mg/l which is collected in carbon bed. hence, before passing through carbon bed the suspended solids should be less then 50mg/l.
4. The surface are of activated carbon is about 100m2/g. the poor structure and high surface area is very important.
The first stage of sludge treatment is to reduce its volume. in case of sludge, it is difficult to manage without thickening. the volume of sludge is reduced by 50% with the help of this process.
Sludge thickening can be done by:
(a) Gravity thickening
(b) Dissolves air flotation.
• it consists of a circular type tank, it is same as sedimentation tank with conical shape at bottom.
• The sludge is allowed to enter this tank which is provided with vertical pickets to stir the sludge properly.
• This stirring action opens up channels of water and sludge settles down and is withdrawn from conical bottom.
• The finely water is returned to primary setting tank.
it is slow process
(b) Dissolves air flotation method:
• In this method, some amount or small quantity of effluent is subjected to aeration under pressure of 60lb/in2.
• this pressurized effluent is released at bottom to tank and depressurized to atmospheric pressure.
• the air is release in the form of bubbles (small bubbles) that entraps the sludge particles, carrying them at top.
• the thickened sludge is skimmed off from the top of tank, where as water is removed at bottom.
1. Treatment and disposal of sludge is not easy it is very complex and important job.
2. It may contain many objectionable materials.
3. 40% of total effluent cost is for sludge disposal.
Characteristic of sludge
1. Sludge contain 90-95% of effluent BOD.
2. It become anaerobic within some hours and must be isolated to prevent nuisance problem.