Electron flow of biological H₂ production by sludge under simple thermal treatment: Kinetic study

Mixed culture sludge has been widely used as a microbial consortium for biohydrogen production. Simple thermal treatment of sludge is usually required in order to eliminate any H₂-consuming bacteria that would reduce H₂ production. In this study, thermal treatment of sludge was carried out at various temperatures. Electron flow model was then applied in order to assess community structure in the sludge upon thermal treatment for biohydrogen production. Results show that the dominant electron sink was acetate (150-217 e- meq/mol glucose). The electron equivalent (e- eq) balances were within 0.8-18% for all experiments. Treatment at 100 °C attained the highest H₂ yield of 3.44 mol H₂/mol glucose from the stoichiometric reaction. As the treatment temperature increased from 80 to 100 °C, the computed acetyl-CoA and reduced form of ferredoxin (Fd_red) concentrations increased from 13.01 to 17.34 e- eq (1.63-2.17 mol) and 1.34 to 4.18 e- eq (0.67-2.09 mol), respectively. The NADH₂ balance error varied from 3 to 10% and the term e-(Fd↔NADH₂) (m) in the NADH₂ balance was NADH₂ consumption (m = -1). The H₂ production was mainly via the Fd:hydrogenase system and this is supported with a good NADH₂ balance. Using the modified Gompertz model, the highest maximum H₂ production potential was 1194 mL whereas the maximum rate of H₂ production was 357 mL/h recorded at 100 °C of treatment.