title: The effect of sludge recirculation rate on a UASB-digester treating domestic sewage at 15 °C.
abstract: The anaerobic treatment of low strength domestic sewage at low temperature is an attractive and important topic at present. The upflow anaerobic sludge bed (UASB)-digester system is one of the anaerobic systems to challenge low temperature and concentrations. The effect of sludge recirculation rate on a UASB-digester system treating domestic sewage at 15 °C was studied in this research. A sludge recirculation rate of 0.9, 2.6 and 12.5% of the influent flow rate was investigated. The results showed that the total chemical oxygen demand (COD) removal efficiency rose with increasing sludge recirculation rate. A sludge recirculation rate of 0.9% of the influent flow rate led to organic solids accumulation in the UASB reactor. After the sludge recirculation rate increased from 0.9 to 2.6%, the stability of the UASB sludge was substantially improved from 0.37 to 0.15 g CH₄-COD/g COD, and the bio-gas production in the digester went up from 2.9 to 7.4 L/d. The stability of the UASB sludge and bio-gas production in the digester were not significantly further improved by increasing sludge recirculation rate to 12.5% of the influent flow rate, but the biogas production in the UASB increased from 0.37 to 1.2 L/d. It is recommended to apply a maximum sludge recirculation rate of 2-2.5% of the influent flow rate in a UASB-digester system, as this still allows energy self-sufficiency of the system.
authors.affiliation: Sub-department of Environmental Technology, Wageningen University, The Netherlands.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Tim L G
authors.initials: TL
authors.lastname: Hendrickx
authors.forename: Christel
authors.initials: C
authors.lastname: Kampman
authors.forename: Grietje
authors.initials: G
authors.lastname: Zeeman
authors.forename: Hardy
authors.initials: H
authors.lastname: Temmink
authors.forename: Weiguang
authors.initials: W
authors.lastname: Li
authors.forename: Cees J N
authors.initials: CJ
authors.lastname: Buisman
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D057919:Biological Oxygen Demand Analysis; D019149:Bioreactors; D003102:Colloids; D005191:Family Characteristics; D008697:Methane / Q000378:metabolism; D010865:Pilot Projects; D012212:Rheology; D012722:Sewage / Q000737:chemistry*; D013696:Temperature; D014835:Volatilization; D014865:Waste Disposal, Fluid; D018508:Water Purification / Q000295:instrumentation*
chemical_list: D003102:Colloids; D012722:Sewage; D008697:Methane