Aeration System in Wastewater Plant

Aeration System is typically constructed for use in wastewater plant to treat sewage coming from municipalities. It is the core of biological treatment process using oxygen consuming bacteria similar just like the unit processes taking place in an aerobic digester or if large area of land is available, a treatment lagoon can be used instead. The system is usually designed to be able to hold huge volume of wastewater and it is quite common to have a system which is capable of having detention time of up to 60 days.

Aeration system using medium sized basin usually have much lower capacity with detention time that goes up to only 12 to 48 hours and thus the F/M ratio is much lower. Typical design using diffusers must be able to supply at least 2 to 3 lb of oxygen and same goes if surface aerators are installed instead. Another type of system which is a variation of the aeration basin is known as oxidation ditch. One of the main advantages of this is that basically it can support higher F/M loading ratio but however, when it comes to reduction in organic matter, oxidation ditch is considered less effective compared to treatment lagoons.

One of the main aspects involved in every biological process is the generation of sludge. In any aeration system, where food in the form of phosphate is available, bacteria will start to multiply and the buildup in the biomass contributes to the increase in the quantity of sludge. As the amount increases, it will finally reach an equilibrium with the amount of foods available and the generation of new cells will be halted. In a typical municipality system, desluging is often carried out in order to control generation of sludge and to remove out the dead bacteria. This will ensure a balanced system whereby the new bacteria will have chance to propagate and replace the aging ones.

Wastewater going into treatment plant will usually first subjected to grit removal in a grit chamber and then the diverted to a primary clarifier, also called sedimentation basin. During this step, a well controlled setup should have the BOD level reduced by about 30%. The water carry over from this unit will then flow to aeration basin and the expected range for the MLSS (Mixed Liquor Suspended Solid) should be around 2500 to 3500mg/L. After a certain detention time depending on the size of the aeration system, the overflow water will go into final clarifier whereby the unit will allow the generated sludge to be removed by settling. Finally what follows next is disinfection step using Ozone so that safer standard of water discharge is maintained.

Recommended Engineering Books