Biogas potential of high strength municipal wastewater treatment in laboratory scale up-flow anaerobic slugde blanket (UASB) reactors

Abstract

The main focus of this study is investigating the effectiveness of anaerobic treatment of municipal wastewater for converting organic matter to methane production in anaerobic granular sludge reactors. In-house designed laboratory scale, up-flow anaerobic sludge blanket (UASB) reactor systems were set up for treating of high strength municipal wastewater treatment i.e. below 1200 mg COD/l under mesophilic condition (20 – 25 °C). Three UASB reactors were set up in the study; one reactor (Reactor A) used inactive granular sludge; and two reactors (Reactor I and Reactor II) used active granular sludge. Hydraulic retention time (HRT) applied was between 24 – 1.4 hours in Reactor A and 5.6 – 1.4 hours in Reactor I and Reactor II. Organic loading rate (OLR) was increased gradually from 1.0 g COD/l.d to 15.0 g COD/l.d. The obtained results indicate a significant COD removal efficiency and methane production in UASB reactors. Methane production rate increased with OLR, proportional to the amount of organic matter removed in the UASB reactors. However, in general, COD removal efficiency and methane yield decreased with increasing OLR and decreasing HRT. COD removal efficiency reached a maximum of above 70% in UASB reactors. At the lowest HRT applied (1.4 h) with 15.0 g COD/l.d of OLR, the COD removal efficiency was in the range of 48 – 65%. The optimum biogas potential was occurred in Reactor II; 70% COD removal efficiency was achieved at 3.3 h of HRT with 6.0 g COD/l.d of OLR and 3.0 g COD/l.d of COD removed was converted to methane. Overall methane yields obtained were 0.226 l CH4/g COD, 0.224 l CH4/g COD, and 0.286 l CH4/g COD in Reactor A, Reactor I and Reactor II, respectively, at operating condition. Under these conditions, approximately 22.5 MWh/d of electricity and 121500 MJ/d of heat could be recovered at IVAR Grødaland which has approximately 5000 m3/d of average hydraulic loading and an OLR of 6.0 g COD/l.d. Anaerobic treatment systems using UASB reactor for treating high strength municipal wastewater represents a feasible and an attractive alternative as pre-treatment for SBR units at IVAR Grødaland by reduction of the SBR inlet total COD to about 300-400 mg/l and conversion organic matter into economically valuable products as methane with 1.3 l CH4/d of specific volume methane production.