Aeration System

Once the tank geometry, water depth and oxygen requirements have been determined then number, design form and arrangement of the multi-path ejectors can be adapted to the case in question. Their mounting can be affected quite simply by two flanges in the pipelines for motive flow and compressed air.

Installation of compact units on the tank floor guarantees comprehensive aeration and complete intermixture of the waste water.

The ejector is made of stainless steel and is mounted “through-the-wall“. Its connections for motive flow and compressed air are located outside the aeration tank.

These comparatively large units are equipped with a second downstream mixing zone in which additional liquid is sucked in, so intensifying the intermixing action in the tank.

If required, the ejector can be equipped with a shut-off device downstream of the motive nozzle so that the motive nozzle can be checked at any time without having to empty the tank. This equipment option allows for a permanent application of the oxygen transfer system, even with extreme concentrations of calcium carbonate in the waste water.

At the usual entrance depths of 5 to 8 m it is possible to achieve an oxygen efficiency OC20 in clean water of 11 g O2/Nm3 • m. In partial load operation – at a reduced air amount – the oxygen efficiency can be boosted above this value as far as 14 g O2/Nm3 • m. Depending on entrance depth and oxygen requirements approx. 400 - 500 Nm3/h of compressed air can be injected into the tank by one single ejector.

Increase the volume of return sludge & ensure that the required bio sludge is being conveyed to aeration system & less flow going to sludge drying bed. If the MLSS does not still attain the desirable level, the incoming effluent has to be analyzed for ppm ratio of Nitrogen, phosphorous, carbon and any toxic material.

Check for environmental conditions. When sludge is being recycled & no appreciable increase in MLSS is witnessed, this is because of insufficient food in the waste. Add externally, fresh cow dung (or) domestic waste to increase the MLSS level (if required).

The amount of oxygen transferred in the aeration tank theoretically equals the amount of oxygen required by microorganisms in activated sludge process to oxidize the organic matter as well as to maintain residual dissolved oxygen operating levels. The DO level in aeration tank should be at about 1.0 to 1.5 mg/lit. When DO is less, oxygen limits the growth of microorganisms. Filamentous organisms may occur and cause sludge bulking leading to poor quality and settle-ability of sludge. DO levels above 2 mg/l do not improve the operation considerably, but increase the power requirement to the biological system. Therefore in order to conserve energy maintaining high DO is not advisable.

The extended aeration system is designed under aeration mode in which microorganisms are in endogenous phase. This results in rapid growth of microorganisms and consequently good quality of treated effluent and settle-ability of bio-sludge. F/M ratio under extended aeration mode ranges from 0.1 to 0.15 kg BOD applied/kg MLVSS.

Low F/M ratio may encourage the growth of certain filamentous organisms.

High F/M ratio may result in formation of floc forming bacteria, which can be rectified by increasing sludge wasting rate, when F/M ratio is low, increase BOD load to the system if available or sludge wasting can be reduced.