The performance of a partly aerated submerged filter in treating high nitrogenous wastewaters such as industrial effluents after anaerobic treatment was investigated in this study. The filter was operated without effluent recycling and its response to various test conditions of aeration rates, hydraulic loads, COD/N ratios and hydraulic retention times was evaluated. Results indicated that for an influent concentration of 250 mg N/L and for a loading rate of 0.7 kg N/m3.d, 60% of the nitrogen can be removed. For a reduced loading rate of 0.25 kg N/m3.d, nitrogen removal efficiency could reach 86%. Denitrification was hypothesized to have taken place inside the support media in the aerated zone of the filter where oxygen was lacking as well as at locations immediately below the air diffuser where an anoxic zone was formed with the back-flowing nitrified substrate.

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