Methods of biological treatment

There are two methods of biological treatment aerobic and anaerobic (217). The aerobic systems use free oxygen dissolved in the wastewater to convert wastes in the presence of microorganisms to more microorganisms, energy required for their existence, and carbon dioxide. The anaerobic process occurs in the absence of free oxygen and converts the waste to methane and carbon dioxide, generally in deep tanks or basins, and can produce odor problems when sulfides or sulfates are present in the wastewater. 

At present, the most frequently used method of biological treatment is activation of wastewaters [1,3,6, 7]. In the activation tank, water is mixed with activated sludge. Whereas in the biological columns water flows through immobile microbial growth, in this case the activated component of the treatment, i.e. microorganisms, are dispersed in water in the form of acti-... 

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