In the most general sense, biological purification is to remove the organic materials which cannot be disposed in waste water by means of physical and chemical processes from the waste water as the microorganisms use thme as nutrition and energy source. 

At the end of the bio-chemical processes, organic materials are converted by microorganisms to CO2 and H2O. Nutritive materials such as nitrogen and phosphor are remove with biological purification as well as organic materials. 

The purpose is to dispose of organic or inorganic components in industrial waste water. 

Due to the fact that some components in the industrial waste water are toxic for microorganisms, preliminary purification should be applied before discharging industrial waste water into the household sewage system. 

Classical Activated Sludge Systems:
The most common method is activated sludge systems in case of oxygen in biological purification. It is a purification method to remove the organic contamination by means of mircoorganisms kept sustained. 

Various biological purification technics are utilized in household and industrial waste water purification. Various parameters are effective in biological purification of such waste water, and these parameters must be between determined values. Purification performance will be high if the parameters such as F/M rate, dissolved oxygen amount, detention period are selected correctly. 

In this regard, biological purification processes will be correct option for you if you aim to remove the contaminants such as nitrogen, phosphor, organic material, particular material etc. from waste water.