Nitrogen removal in a submerged filter with no effluent recirculation

The performance of a partly aerated submerged filter in treating high nitro genous wastewaters such as industrial effluents after anaerobic treatment w as investigated in this study. The filter was operated without effluent rec ycling and its response to various test conditions of aeration rates, hydra ulic loads, COD/N ratios and hydraulic retention times was evaluated. Resul ts indicated that for an influent concentration of 250 mg NIL and for a loa ding rate of 0.7 kg N/m(3).d, 60% of the nitrogen can be removed. For a red uced loading rate of 0.25 kg N/m(3).d, nitrogen removal efficiency could re ach 86%. Denitrification was hypothesized to have taken place inside the su pport media in the aerated zone of the filter where oxygen was lacking as w ell as at locations immediately below the air diffuser where an anoxic zone was formed with the back-flowing nitrified substrate.