Sludge transfer point of a UASB-digester system: key to efficient low temperature anaerobic sewage treatment

The up flow anaerobic sludge bed (UASB)-digester system is one promising low temperature anaerobic process for sewage treatment. In this study, the effects of height of UASB sludge transfer (HUST) on performance of a UASB-digester system treating sewage at 15°C were studied. The studied HUSTs were 27, 47 and 67 cm in the UASB sludge bed of 70 cm, from which sludge was transferred to the digester. The biogas production in the UASB reactor increased with a higher HUST. Suspended chemical oxygen demand (COD) removal efficiency and total COD removal efficiencies increased from 52 to 65% and from 30 to 38%, respectively, when increasing the HUST from 27 to 67 cm. Increased HUST resulted in a high VSS concentration of the UASBdigester system. Methanogenic capacity at 15°C of the UASB sludge bed also increased from 9.4 to 11.7 g CH4 COD/d as HUST increased from 27 to 47 cm.