Abstract
Bioelectrochemical systems are emerging technologies for the reduction in CO2 in fuels and chemicals, in which anaerobic chemoautotrophic microorganisms such as methanogens and acetogens are typically used as biocatalysts. The anaerobic digestion digestate represents an abundant source of methanogens and acetogens microorganisms. In a mixed culture environment, methanogen’s inhibition is necessary to avoid acetate consumption by the presence of acetoclastic methanogens. In this study, a methanogenesis inhibition approach based on the thermal treatment of mixed cultures was adopted and evaluated in terms of acetate production under different tests consisting of hydrogenophilic and bioelectrochemical experiments. Batch experiments were carried out under hydrogenophilic and bioelectrochemical conditions, demonstrating the effectiveness of the thermal treatment and showing a 30 times higher acetate production with respect to the raw anaerobic digestate. Moreover, a continuous flow bioelectrochemical reactor equipped with an anion exchange membrane (AEM) successfully overcomes the methanogens reactivation, allowing for a continuous acetate production. The AEM membrane guaranteed the migration of the acetate from the biological compartment and its concentration in the abiotic chamber avoiding its consumption by acetoclastic methanogenesis. The system allowed an acetate concentration of 1745 ± 30 mg/L in the abiotic chamber, nearly five times the concentration measured in the cathodic chamber.
Highlights
The increase in CO2 generation is bound to further increase as a result of the economic growth and urbanization [1]
The anion exchange membrane (AEM) membrane guaranteed the migration of the acetate from the biological compartment and its concentration in the abiotic chamber avoiding its consumption by acetoclastic methanogenesis
The hydrogenophilic tests were conducted to test the effectiveness of the thermal treatment of the anaerobic digestate as previously reported [23]
Summary
The increase in CO2 generation is bound to further increase as a result of the economic growth and urbanization [1]. Technologies that allowed the CO2 capture and conversion into valuable products has been named carbon capture and utilization chain (CCU) [2] In this context, biological CCU approaches, which allows for the CO2 fixation in liquid [7], solid [8], gaseous [9] fuels represent an effective strategy towards a sustainable zero-emission economy. Removing the acetate from the cathode compartment and concentrating it in an abiotic compartment represents an effective solution to the coexistence between producers and competitors’ microorganisms In this way the simultaneous production and extraction of the acetate in a combined device is achieved according to the recent “In situ product recovery” consisting in the integration of the biological production and product extraction the same reactor [26]
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