COD balance and nitrogen removal in a biofilter pilot plant

Biological nitrogen removal from wastewater depends on nitrogen incorporation and on denitrification. Both processes strongly depend on the degradation of COD. On the hand of operational data from a biofilter pilot plant, the relation between COD-removal and nitrogen removal is shown. Mass balances for the two parameters COD and N are the base of this consideration, as they are excellent tools for the evaluation of WWTPs (large scale plants as well as pilot plants) in order to estimate the fluxes of these substances and to draw conclusions of general validity. When applying the results from the pilot scale investigation to the whole treatment process (which includes sludge stabilisation), reject water must be taken into account. Therefore, the N removal efficiency was calculated both for the process with and without return liquor.