Treatment of a Domestic Wastewater with UASB Reactors

Abstract

This study investigated a feasibility of employing pilot-scale upflow anaerobic sludge blanket (UASB) reactors to treat a domestic (or relatively low-strength) wastewater. Four 30-1 UASB reactors, each with a 0.15-m inner diameter and 2-m height were used in this study which was conducted at an average ambient temperature of 30°C. Three reactors were inoculated with different types of seed sludge, namely: sludge from a facultative waste stabilization pond, anaerobically digested sludge and sludge from a UASB reactor treating a distillery wastewater. The fourth reactor was started without inoculum and was studied for possible self inoculation. Domestic wastewater was mixed with a stock glucose solution to increase the influent COD concentrations to about 600 mg/l. All four reactors were started with a hydraulic retention time (HRT) of 24 h, and this HRT was later reduced to 12, 6 and 3 h, consecutively, corresponding to the organic loading rates (OLR) of 0.4-0.6, 0.9-1.4, 1.8-2.8 and 3.6-6.0 kg COD/(m3.d), respectively. At the highest OLR or shortest HRT, there was about 90% removal of the influent COD in Reactors 1-3 while the methane (CH4) production rate was found to be 150 N1/kg COD removed with a methane (CH4) content of 75%. Reactor 4, without inoculation, could not develop sufficient amount of biomass to withstand the high OLR and its performance deteriorated at the HRT of 3 and 6h. The scanning electron microscopic (SEM) examinations of the sludge floc revealed the predominance of Methanothrix-like bacteria in all reactors. The experimental results obtained have suggested a technical feasibility of employing UASB reactors to treat domestic wastewaters. The facultative waste stabilization pond sludge and anaerobically digested sludge were found to be suitable inoculum sources for the UASB reactors treating this low-strength wastewater.