Performance of anaerobic membrane bioreactor during digestion and thickening of aerobic membrane bioreactor excess sludge

In this study, we evaluated the performance of an anaerobic membrane bioreactor in terms of digestion and thickening of excess sludge from an aerobic membrane bioreactor. A digestion reactor equipped with an external polytetrafluoroethylene tubular microfiltration membrane module was operated in semi-batch mode. Solids were concentrated by repeated membrane filtration and sludge feeding, and their concentration reached 25,400 mg/L after 92 d. A high chemical oxygen demand (COD) removal efficiency, i.e., 98%, was achieved during operation. A hydraulic retention time of 34 d and a pulse organic loading rate of 2200 mg-COD/(L-reactor) gave a biogas production rate and biogas yield of 1.33 L/(reactor d) and 0.08 L/g-CODinput, respectively. The external membrane unit worked well without membrane cleaning for 90 d. The transmembrane pressure reached 25 kPa and the filtration flux decreased by 80% because of membrane fouling after operation for 90 d.