Simultaneous methanogenesis and acetogenesis from the greenhouse carbon dioxide by an enrichment culture supplemented with zero-valent iron

The microbial reduction of CO2 into value-added products is gaining considerable attention and can play a significant role in the field of environment and energy research. A novel strategy for biotransformation of CO2 was tested with zero valent iron (ZVI) and enrichment cultures for methane and acetate production under anaerobic conditions at room temperature. The favorable performance of CO2 conversion (81.67% of conversion rate) was achieved in ZVI-amended treatments by enhanced methanogenesis and acetogenesis simultaneously. The enrichment consortium of microorganisms containing Methanosarcina spp. and Clostridiaceae was responsible for methane and acetate production, and accounted for 25.89% and ∼4.83% of CO2 conversion, respectively. Scanning electron microscopy (SEM) observation and mass balance analysis of hydrogen detected in the headspace indicated that direct electron transfer and utilization possibly occurred with these microbes, especially methanogens. Interestingly, X-ray Photoelectron Spectroscopy (XPS) confirmed carbonation mineral (FeCO3) as the major strategy of CO2 consumption under the experimental conditions. These observations collectively revealed that supplementation of ZVI can be a favorable electron donor to stimulate and accelerate the biotransformation of CO2 into methane and acetate by the enrichment culture of microorganisms, and the information presents available alternative biochemical pathways for energy recovery from greenhouse gas under anaerobic conditions.