Bioconversion of de-oiled Jatropha Waste (DJW) to hydrogen and methane gas by anaerobic fermentation: Influence of substrate concentration, temperature and pH

Cellulosic materials-based de-oiled Jatropha Waste (DJW) was fermented to H₂ and CH₄ using sewage sludge inoculum. Batch assays were performed at various substrate concentrations (40-240 g/L), temperatures (25-65°C) and pHs (5.5-7.5). The peak hydrogen production rate (HPR) and hydrogen yield (HY) of 744.0 ± 11.3 mL H₂/L-d and 10.6 ± 0.2 mL H₂/g VS obtained when the optimal substrate concentration, pH, temperature were 200 g/L, 6.5, 55°C, respectively. The peak methane production rate (MPR) of 178.4 ± 5.6 mL CH₄/L-d obtained while DJW concentration, pH, temperature were 200 g/L, 7.0, 45°C, however, peak methane yield (MY) of 23.3 ± 0.1 mL CH₄/g VS obtained at 40 g/L, 7.0 and 55°C, respectively. Effect of substrate concentration on HPR and MPR was elucidated using Monod model. Butyrate and acetate were the main soluble metabolic products. Maximal carbohydrate removal and COD reduction were achieved as 51.7 ± 0.7% and 68.3 ± 1.6%, respectively.