Energy recovery from agro-industrial wastewaters through biohydrogen production: Kinetic evaluation and technological feasibility

Biohydrogen production from cassava, dairy and citrus processing wastewaters (WWs) without nutritional supplementation was evaluated in anaerobic single-batch reactors at 37 °C for 70 h. Hydrogen production from cassava, dairy and citrus WW was 31.41, 37.25 and 28.95 mL g−1 of chemical oxygen demand (COD). The kinetic parameters indicated that H2 production rates for cassava processing WW (0.32 mL h−1) and dairy WW (0.31 mL h−1) were similar, whereas citrus processing WW exhibited the highest value (0.59 mL h−1). The carbohydrate degradation rate (k1App) was highest for dairy WW (0.045 h−1), but the most efficient overall conversion of organic matter to H2(k2App) was observed with cassava WW (0.014 h−1). The rate of conversion of the organic matter of the cassava WW together with its ready availability resulted in a recovery of 0.59 109 MJ year−1, the highest in this study. Cassava WW showed the highest hydrogen production potential (97.9 mL), when compared with dairy (76.1 mL) and citrus WW (66.6 mL). The economic estimation based on the gasoline energetic equivalent indicated that a single process of H2 production allowed the maximum economic yield of US$ 0.009 cents L−1 WW. Alternatively, a sequential hydrogen and methane process could increase energy recoveries and economic yields to values near 10.48 kJ g−1 COD and US$ 0.61 cents L−1 WW (US$ 6.10 m−3 WW).