A laboratory-scale anaerobic-aerobic-membrane system was operated with and without aerobic effluent recycle at 24∼27°C. The anaerobic H2-producing bioreactor was inoculated with heat-shocked anaerobic digester sludge, and operated at pH 5.5 and hydraulic retention time (HRT) equal to solids retention time (SRT) of 10 hours. The aerobic membrane bioreactor (MBR), with HRT of 10 hours and SRT of 4 days, was operated at pH 7.0 or 7.5.At an MBR pH of 7.5, 16% and 4% reductions in NaOH and HCl consumption, respectively, were realized with recycle. Recycle also reduced hydrogen recovery by 28% while increasing the system organic loading rate. Volatile fatty acid and alcohol concentrations were not significantly affected. The MBR effectively polished the anaerobic effluent with a chemical oxygen demand (COD) removal efficiency greater than 90%. A sequential anaerobic-aerobic-membrane system is potentially useful for recovering hydrogen while complying with wastewater treatment discharge criteria.