Effects of microaeration on hydrogen and methane production from cassava wastewater using a two-stage UASB system

Abstract

In this work, a two stage up flow anaerobic sludge blanket (UASB) system was used to produce separately hydrogen and methane from cassava wastewater under mesophilic temperature (37 ℃) with a recycle ratio of 1:1 (final effluent flow rate: feed flow rate) and a constant pH of 5.5 in the hydrogen UASB unit. The liquid working volumes of the hydrogen and methane UASB units were 4 and 24 L, respectively. For the first part without micro aeration, For the first part without micro aeration, the optimum COD loading rate was found to be 6 kg˙m-3˙d-1 based on the methane UASB volume to provide the highest process performance, the produced gas contained 34 %H2, 65 %CO2, 1 %CH4, the hydrogen yield of 45 mL˙kg-1COD removed and the COD removal of 37% for the hydrogen UASB volume. For the methane UASB volume was compose of 63 %CH4, 36.6 %CO2, 0.4 %H2, the methane yield of 652.6 mL˙kg-1COD removed and the COD removal of 52.0%. At this optimum COD loading rate, the system was operated at different oxygen supply rate (ranging from 5.2 to 7.9 mL O2˙L-1wastewater˙d-1), the optimum oxygen supply rate of 6.1 mL O2˙L-1 wastewater˙d-1 was found to provide the highest improvement of process performance in terms of the highest methane content of 67%, the highest methane yield of 682.3 mL˙kg-1COD removed and the highest COD removal of 57.7%. Moreover, the addition of oxygen was found to eliminate completely H2S in the produced gas from the methane UASB unit.