Addition of electron shuttling compounds and different pH conditions for hydrogen production by a heat-treated sludge

Abstract In the present work, the effect of anthraquinone-2-sulfonate (AQS) and its reduced form anthrahydroxyquinone-2-sulfonate (AH2QS), and different pH values were evaluated during a dark fermentation process using heat-treated anaerobic granular sludge for hydrogen production. The highest maximum hydrogen production (1.99 mmol) was obtained by adding the reduced electron shuttling compound (AH2QS) at pH 6. This experimental condition also reflected the highest substrate consumption efficiency and the lowest lag phase in relation to the AQS and the control (only sludge). In contrast, the lag phase and maximum hydrogen production were not impacted by AH2QS addition at initial pH of 6.4 and 7.8. Regardless of the initial pH value, the hydrogen production rate was increased after the addition of the electron shuttling compounds, which could be attributable to the performance of either the oxidized and reduced form of the electron shuttling compound. These findings demonstrate the feasibility of AH2QS addition during dark fermentation at pH 6.4 for improving the hydrogen production rate. Exoelectrogenic microorganisms identified in the inoculum could be responsible to improve the dark fermentation process in assays with electron shuttling compounds.