Improved microbial conversion of de-oiled Jatropha waste into biohydrogen via inoculum pretreatment: Process optimization by experimental design approach

In this study various pretreatment methods of sewage sludge inoculum and the statistical process optimization of de-oiled jatropha waste have been reported. Peak hydrogen production rate (HPR) and hydrogen yield (HY) of 0.36 L H₂/L-d and 20 mL H₂/g Volatile Solid (VS) were obtained when heat shock pretreatment (95 °C, 30 min) was employed. Afterwards, an experimental design was applied to find the optimal conditions for H₂ production using heat-pretreated seed culture. The optimal substrate concentration, pH and temperature were determined by using response surface methodology as 205 g/L, 6.53 and 55.1 °C, respectively. Under these circumstances, the highest HPR of 1.36 L H₂/L-d was predicted. Verification tests proved the reliability of the statistical approach. As a result of the heat pretreatment and fermentation optimization, a significant (~ 4 folds) increase in HPR was achieved. PCR-DGGE results revealed that Clostridium sp. were majorly present under the optimal conditions.