Biological columns sprinkling filters

Biological columns are large-sized concrete or masonry structures, usually round with a gridded base. They are filled with filtration packing through which treated wastewater flows downstream (Fig. 4.25). 

At a high volume loading the microorganisms can reproduce to such a degree that the flow-rate capacity of the column seriously decreases and the column becomes flooded. However, it should be noted that increased thickness of the microbial coat above the optimum limit does not result in increased efficiency of the column. At a high hydraulic surface loading the 

The efficiency of a biological column is expressed in per cent of removed BOD5  

An efficiency of 95% has been achieved experimentally, but an efficiency of 85% BOD is considered to be good. 

Biological columns are classified according to the degree of loading, the construction, operation, etc. The most frequently used types can be categorized as follows  

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