Recovery of Hydrogen and Methane from Wastewater Using a Two-Stage UASB System

Biological hydrogen and methane production from a sucrose-containing synthetic wastewater was setup in a two stage up-flow anaerobic sludge blanket (UASB) system. Thermally pretreated UASB granule was used as an inoculated seed in a 1 L hydrogenogenic reactor (first stage) whereas non thermally pretreated UASB granule was used as the inoculated seed in a 1.5 L methanogenic reactor (second stage). All experiments were conducted under the room temperature (30 +/- 3 degrees C) and fixed influent pH of 5.5 for the hydrogenogenic reactor and that of 7.0 for the methananogenic reactor. The hydrogenogenic reactor was operated at varied hydraulic retention time (HRT) and organic loading rates (ORL) whereas the methanogenic reactor was operated at fixed hydraulic retention time of 12 hr and OLR dependent on the COD effluent from the hydrogenogenic reactor. In the hydrogenogenic stage, hydrogen productivity, production rate and COD removal efficiency of 21.87 mM g(-1) COD, 1.8 L d(-1) and 49.23% were optimally achieved at operational condition of HRT 6 h with OLR of 6.5 g COD d(-1). Methane productivity, production rate and COD removal efficiency of 96.00 mM g(-1) COD, 2.9 Ld(-1) and 87.40%, respectively were observed in the methanogenic stage. Overall performance of combined two stage system is 90% with respect to COD removal efficiency.