Micro-organisms:

The micro-organisms mixed up in aerobic absorption and their activities are the same as those found in nature. The organic compounds are oxidised to H₂O and CO₂, and nitrogenous elements and biomass are also created. However in waste water, the organic materials are present in much larger concentrations than in nature. so, the microbial population and activities are gained accordingly by (i) giving large surface for bio film creation and O₂ exchange in fixed film structures, basically trickling filters, and (ii) returning a type of the operated sludge to the digester vessel and creating effective aeration arrangements.