No abstract

An anaerobic membrane bioreactor (AnMBR) treating swine waste was operated over 300 days to evaluate the effect of high shear in the external membrane unit on process efficiency. The reactor had a successful startup at the initial loading rate of 1 g volatile solids (VS)/L/day. However, after a two-fold increase in loading rate followed by a sudden, two-fold increase in flow velocity through the membrane module on day 75, the performance of the AnMBR deteriorated as measured by volatile fatty acid (VFA) accumulation, decrease in pH, and biogas production. The archaeal population dynamics in the reactor were monitored with terminal restriction fragment length polymorphism (T-RFLP). The results indicated the presence of five methanogenic populations. Methanogens belonging to the order of Methanomicrobiales (hydrogen utilizing methanogens) increased during decreased performance. The reactor performance recovered after addition of NaHCO 3 and termination of feeding for two weeks. The loading rate was increased to 3 g VS/L/day on day 186 and the performance was generally good at this higher loading rate.