The role of beneficial microorganisms in an anoxic-oxic (AO) process for treatment of ammonium-rich landfill leachates: Nitrogen removal and excess sludge reduction

Abstract This study comprehensively investigated the performances of the anoxic-oxic processes with (AO-M) and without the beneficial microorganisms (AO-N) for the treatment of the ammonium-rich landfill leachates. Although the AO-M had the lower concentrations of the mixed liquor suspended solids (MLSS, 3230 mg L-1) and mixed liquor volatile suspended solids (MLVSS, 2480 mg L-1) compared to the AO-N process (MLSS = 7790 mg L-1; MLVSS = 5260 mg L-1), dissolved organic compounds and nitrogen species could be more effectively removed using the AO-M process (removal efficiency of dissolved organic carbon (DOC) = 99.0%; removal efficiency of total nitrogen (TN) = 79.2%) than the AO-N process (removal efficiency of DOC = 98.6%; removal efficiency of TN = 75.1%). Moreover, the excess sludge production was also less pronounced for the AO-M process than the AO-N process since the enhanced endogenous respiration and relative enzyme activity of microorganisms in the oxic bioreactor of the AO-M process via the inoculation of the beneficial microorganisms reduced the excess sludge production significantly. These observations suggest that the variations in the relative abundances of microorganisms through the inoculation of the beneficial microorganisms into the sludge digestion tank might enhance the removal of nitrogen species and the reduction of the excess sludge production during the during the treatment of the ammonium-rich landfill leachates.