Dark fermentation of starch factory wastewater with acid- and base-treated mixed microorganisms for biohydrogen production

Abstract

Biohydrogen (Bio-H2) can be produced from starch factory wastewater and mixed microorganisms using dark fermentation. Acidic and basic chemicals were used to treat the microorganisms to select the hydrogen (H2)-producing culture. The experiment used a 120 mL bioreactor at 35 °C and the operation commenced with the initial pH level of wastewater in the pH range 4–7 in batch mode. The bacteria:chemical oxygen demand (COD) ratio was 0.2. The initial pH level of the wastewater in the fermentation process affected the H2 yield and the specific hydrogen production rate (SHPR). For acid-treated bacteria, the maximum H2 yield and SHPR were produced at an initial pH of 6.5. The maximum H2 yield and SHPR were 138 mL/g COD degraded and 7.42 mL/g cells‧h, respectively. For the base-treated bacteria, the maximum H2 yield and SHPR were produced at initial pH of 6.5 and pH 7, respectively. The maximum H2 yield and SHPR were 182 mL/g COD degraded and 25.60 mL/g cells‧h, respectively. The COD degradation efficiency levels were 16 and 20% for acid- and base-treated bacteria, respectively. The digested wastewater remained acidic at pH 4.79–4.83. Throughout the study, no methane gas was observed in the gas mixture produced.