Production of biogas from cassava wastewater using a three-stage upflow anaerobic sludge blanket (UASB) reactor.

Abstract In this study, a three-stage upflow anaerobic sludge blanket (UASB) system was developed and tested for hydrogen (H 2) and methane (CH 4) production from cassava wastewater with an emphasis on CH 4 production. The experiment was carried out at mesophilic temperature (37 °C) at different chemical oxygen demand (COD) loading rates from 5 to 18 kg/m3d (based on total liquid holding volume) with a recycle ratio of the final effluent to both the first and second bioreactors at a constant 1: 1 flow rate ratio of feed: final effluent. The first bioreactor was maintained pH at 5.5 while those of the other two bioreactors were not controlled. At an optimum COD loading rate of 15 kg/m3d, the system provided the highest COD removal level (92.5%) and the highest H 2 and CH 4 yields of 0.43 mL H 2 /g COD applied, and 328 mL CH 4 /g COD applied, respectively. The very high productivity of CH 4 with the very low H 2 productivity resulted from the recycled methanogen sludge from the third bioreactor to the first and second bioreactors. The process performance of the three-stage UASB system in terms of optimum COD loading rate and total energy yield was much higher than those of single and two-stage anaerobic processes. Graphical abstract Image Highlights • The three-stage UASB provided a high optimum COD loading rate with a high energy yield. • The high CH 4 yield with very low H 2 yield resulted from the recycled methanogenic sludge. • The recycled effluent could provide proper pH values in both first and second bioreactors with a minimum NaOH consumption. [ABSTRACT FROM AUTHOR]