Microbial Dynamics and Acetic Acid Production in Anaerobic Sludge Exposed to CO2 and Zero-Valent Iron

This laboratory investigation explores the impact of carbon dioxide and zero-valent iron on the microbial dynamics within anaerobic sludge, aiming to enhance the production of acetic acid, a key intermediary in methane production processes within bioreactors. A variety of sludge types were employed as inocula, including River-SL from the Germasogia River, Wetland-SL from Choletria constructed wetland, AnGr-SL anaerobic granular sludge from an upflow anaerobic sludge blanket reactor processing cheese whey, Comp-SL a compost mixture of organic materials, Anaer-SL and Activ-SL from a municipal wastewater treatment plant, and Dr.Cuts-SL from industrial waste treatment.The experiments were conducted in 500 mL serum vials, each supplemented with 80 g/L ZVI and filled to a working volume of 250 mL with growth medium, under stringent anoxic conditions using high-purity carbon dioxide and nitrogen gases. The research was structured over two 56-day cycles, distinguished by varying carbon dioxide feeding regimes to simulate environmental changes, and the microbial community dynamics were analyzed using 16S rRNA gene sequencing.Results:Acetobacterium Proliferation: Marked growth of Acetobacterium was observed across all systems, particularly in those inoculated with river and wetland sludge. Initial exposure to carbon dioxide and ZVI led to Acetobacterium constituting 27 to 71 of the microbial community in these systems by day 56, significantly enhancing acetic acid production.Firmicutes Dominance: By the end of the second cycle, Acetobacterium and other Firmicutes represented 58 to 87 of the microbial community across various setups, reflecting a substantial shift towards this phylum over time due to the imposed environmental conditions.Enhanced Acetic Acid Production: The highest acetic acid production was observed in systems with a dominant presence of Acetobacterium, particularly those inoculated with River-SL and Wetland-SL, reaching up to 300 mg L day. This underscores the efficacy of carbon dioxide in enhancing ZVI-mediated acetic acid generation.Conclusion: The findings highlight the potential of optimizing anaerobic conditions to favor acetic acid production, with significant implications for wastewater treatment and renewable energy production. The prominent role of Acetobacterium in transforming environmental inputs into valuable biochemical outputs, using only carbon dioxide and ZVI as substrates, underscores its importance in industrial bioprocesses. This comprehensive analysis illuminates the adaptive capabilities of microbial communities under varied environmental stresses and their potential applications in biotechnology.