Conversion of organic solid waste to hydrogen and methane by two-stage fermentation system with reuse of methane fermenter effluent as diluting water in hydrogen fermentation

In this study, a two-stage system converting organic solid waste (food waste+sewage sludge) to H₂ and CH₄ was operated. In the first stage of dark fermentative hydrogen production (DFHP), a recently proposed method that does not require external inoculum, was applied. In the second stage, anaerobic sequencing batch reactor (ASBR) and an up-flow anaerobic sludge blanket reactor (UASBr) were followed to treat H₂ fermenter effluent. (H₂+CH₄-ASBR) system showed better performance in terms of total biogas conversion (78.6%), while higher biogas production rate (2.03L H₂/L_system/d, 1.96L CH₄/L_system/d) was achieved in (H₂+CH₄-UASBr) system. To reduce the alkali addition requirement in DFHP process, CH₄ fermenter effluent was tested as a diluting water. Both the ASBR and UASBr effluent was effective to keep the pH above 6 without CH₄ production. In case of using ASBR effluent, H₂ production dropped by 15%, but alkali addition requirement was reduced by 50%.