Biohydrogen production from cassava wastewater using an anaerobic sequencing batch reactor

Abstract

Hydrogen is an alternative energy resource that is increasingly used instead of fossil fuels to reduce the emission of greenhouse gases. Biohydrogen production is of great interest because it can be produced from renewable resources, including wastes and wastewaters, under ambient conditions. In this study, hydrogen production from cassava wastewater by dark fermentation process using anaerobic sequencing batch reactors (ASBR) was investigated. The seed sludge taken from an anaerobic lagoon treating cassava wastewater was boiled at 95°C for 15 min before being added to the ASBR as the anaerobic seed sludge. The ASBR systems were operated at the chemical oxygen demand (COD) loading rate of 10 to 25 kg/m³d with 5 kg/m³d increments and 15 to 37.5 kg/m³d with 7.5 kg/m³d increments at 4 cycles per day and 6 cycles per day, respectively, under a mesophilic temperature of 37°C, a controlled pH of 5.5, and a 24 h HRT in order to determine the optimum COD loading rate and number of cycles per day. The results showed that the COD loading rate of 30 kg/m³d at 6 cycles per day provided the maximum hydrogen production. The maximum specific hydrogen production rate (SHPR) and hydrogen yield of 388 ml H₂/g VSS d (3,800 ml H₂/L d) and 186 ml H₂/g COD removed, respectively, were obtained. The effect of nutrient supplementation was also studied by adding NH₄HCO₃ into the system at the COD:N ratios of 100:2.2, 100:3.3, and 100:4.4 under the COD loading rate of 30 kg/m³d and 6 cycles per day. The SHPR and hydrogen yield of 524 ml H₂/g VSS d (5,680 ml H₂/L d) and 438 ml H₂/g COD removed, respectively, were maximum at the optimum COD:N ratio of 100:2.2.