A hydrogenotrophic denitrification system was evaluated in removing nitrate from synthetic aquaculture wastewater for recirculation purposes. Two membrane bioreactor (MBR) systems, namely, aeration-denitrification system (ADS) and denitrification-aeration system (DAS) were studied with 50 mg/L of influent concentrations for both organic matter and nitrate nitrogen. The DAS achieved better removal efficiency of 91.4% total nitrogen (T-N) and denitrification rate of 363.7 mg/L.day at a HRT of 3 It compared to ADS. Further, there was no nitrite accumulation in the DAS effluent. The nitrite accumulation in ADS effluent was lesser when CO2 was used as buffer rather than K2HPO4 and KH2PO4. Estimation of kinetic parameters of hydrogenotrophic bacteria indicated lesser sludge production compared to heterotrophic denitrification. In the DAS, membrane fouling was nonexistent in the aeration reactor that was used to produce the recirculating effluent. On the contrary, membrane fouling was observed in the denitrification reactor that supplied hydrogen to the mixed liquor. Thus, this study demonstrated DAS capability in maintaining the acceptable water quality appropriate for aquaculture, in which a closed recirculating system is typically used. (C) 2008 Elsevier Ltd. All rights reserved.