Denitrification in anaerobic digesters: possibilities and influence of wastewater COD/N-NO_X ratio

Laboratory-scale completely-stirred anaerobic digesters were fed with synthetic wastewaters containing nitrate and nitrite and with glucose as the only source of organic carbon in order to investigate and compare the denitrification potentials of anaerobic digesters in the presence of nitrate and nitrite. Varying the input nitrate and nitrite concentration at fixed COD and HRT, methane production without denitrification occurred at COD/N-NO_X > 53; denitrification and methane production at 8.86 ≤ COD/N-NO_X≤ 53 and only denitrification at COD/N-NO_X <8.86. At COD/N-NO_X > 53, ammonification appeared to be the main nitrate and nitrite reduction pathway. The successful competition of ammonia formers over the true denitrifiers at high ratios was attributed to the low initial nitrate and nitrite concentrations.