Optimatization of two-stages UASB system for H2 and CH4 production from cassava wastewater with added cassava residue

Abstract

In this research, hydrogen and methane production from cassava wastewater with added cassava residue by using a two stage up flow anaerobic sludge blanket (UASB) system was investigated under thermophilic temperature (55 °C). The two stage UASB system was operated at different cassava residue concentrations (ranging from 300 to 1,500 mg/1 under a COD loading rate of 12 kg/m3d based on the methane bioreactor or 72 kg/m3d based on the hydrogen bioreactor without added cassava residue). The recycle ratio of the effluent from the methane bioreactor to the feed flow rate was fixed at 1:1. In addition, the solution pH was controlled at 5.5 in the hydrogen bioreactor while the methane bioreactor was not controlled. Under the optimum cassava residue concentration of 1,200 mg/1, the produced gas contained 43 % H2, 55 % CO2, and 2 % CH4 for the hydrogen bioreactor and 70.5 % CH4, 28 % CO2, and 1.5 % H2 for the methane bioreactor. Apart from hydrogen and methane production performance, the two stage UASB system could significantly break down the cellulosic fraction. Under the optimum cassava residue concentration of 1,200 mg/1 and the COD loading rate of 12 kg/m3d of the cassava wastewater, the degradation performance of cellulose and hemicellulose were 42.1 % and 20.7 %, respectively for the hydrogen bioreactor and 35.2 % and 17.8 % for the methane bioreactor.