Nitrogen and residual organic matter removal from anaerobic reactor effluent in a fixed‐bed reactor with biogas for denitrification

BACKGROUND This paper describes an evaluation of a fixed-bed aerobic/anoxic reactor (AAFBR) for the post-treatment of effluent from an up-flow anaerobic sludge blanket (UASB) reactor treating domestic sewage. This is a new reactor configuration comprising an upper aerobic nitrification chamber fed with effluent from the UASB reactor. The nitrified effluent flows downwards to an anoxic chamber that is fed synthetic biogas (CH4, CO2 and H2S) from the bottom for denitrification. RESULTS The AAFBR removed organic matter at efficiencies higher than 90% for hydraulic detention times (HDT) of 7.5 and 5.0 h. The average nitrogen removal efficiencies were higher than 70% under conditions of excess H2S in the synthetic biogas. At an HDT of 5.0 h and with synthetic biogas of a similar composition to that in UASB reactors treating domestic sewage, the average N removal was approximately 50%. Under these conditions, the reactor achieved hydrogen sulfide and methane removal efficiencies of 100% and 60%, respectively. CONCLUSIONS The results obtained for the denitrifying activity indicated the coexistence of both autotrophic and heterotrophic denitrification in the anoxic chamber. The AAFBR exhibited additional ability as a gas cleanup system. The results demonstrate the potential of AAFBR as an alternative for the tertiary treatment of domestic wastewater. © 2014 Society of Chemical Industry