The first stage in the treatment process is screening. Screening iscarried out using a static stainless steel retaining screen. Removal of solids isessential and results in higher treatment efficiencies for downstream biologicalsystem. Screening also ensures safety for transfer pumps which otherwisewould ultimately clog. The wastewater after screening enters an aeratedequalization tank.
The equalization tank is aerated by fine pore subsurface diffusers to preventsettling of solids and also to build up the dissolved oxygen level in thewastewater. Aeration ensures complete mixing of the wastewater and thesolids are maintained in suspension. Settling of solids could lead toaccumulation and stagnation, leading to anaerobic and septic conditions, theresult being strong odor problems. Aeration also aids in maintaining a residual dissolved oxygen level in the wastewater, which aids in treatmentefficiency.
Equalization pumps (one operating and one-100% standby) transferwastewater from the equalization tank to the extended aeration tank. Air-liftpumps are used for equalization pumps, up to a flow of 10,000gal/day. Theextended aeration process is a suspended growth biological treatmentprocess wherein the micro-organisms grow in the suspended form. A higherlevel of micro-biological population is maintained in the tank. The aerationtank is continuously aerated with fine pore subsurface AIRMAX diffusers. Theentire process is aerobic in nature.
Micro-organisms in their endogenous phase of respiration receive less food incomparison to the food available. This process is more popularly termed as“cannibalism”. Micro-organisms eventually consume themselves when notadequate food is available. The organic matter is consumed and biologicallydegraded to stable end products.
Extended aeration processes are very popular for sewage treatmentapplications. Waterworks has EA systems operating around the globe for thisapplication in remote camp sites, hotels, hospitals and resorts.Wastewater after extended aeration treatment flows by gravity to thesecondary clarifier. The biomass settles by gravity and the supernatantoverflows the weirs to the adjoining chlorine contact tank.
The settled biomassis air-lifted and recycled to the extended aeration tank to maintain thepopulation of biomass. The extended aeration tanks is operated at a MLSSlevel of 3000 to 3500 mg/L.
The food to micro-organism ratio is maintainedbetween 0.1 and 0.15 When the biomass concentration exceeds the required MLSS level in theextended aeration tank, sludge is wasted to the sludge holding tank.
Thesludge tank is an aerated tank where the waste biomass is held and aeratedcontinuously. In the absence of any organic matter entering the sludge tank,the biomass digests itself thereby concentrating and thickening itself.
The chlorine contact tank is a baffled tank to promote contact and mixing fordisinfection. The treated wastewater exits the chlorine contact tank.
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