The effects of pH and temperature on the acetate production and microbial community compositions by syngas fermentation

Syngas fermentation into acetate by mixed cultures is considered as a promising biotechnology. The effects of pH and temperature on the conversion efficiency, product composition, selectivity and microbial community composition during syngas fermentation are investigated in this work. The maximum total volatile fatty acids and ethanol concentrations can reach 3400 and 3100 mg/L both at pH 9 under mesophilic and psychrophilic conditions, respectively. The highest ratio of acetate to total volatile fatty acids and ethanol are also obtained at pH 9 and reach 91 and 90% under mesophilic and psychrophilic conditions, respectively. Although the production and selectivity are higher under mesophilic condition than psychrophilic condition, it's also found that the activity of methanogens can be better inhibited under psychrophilic condition than mesophilic condition. The high-throughput sequencing analysis of 16S rRNA genes shows the abundance of genus Clostridium and Acetobacterium, containing several homoacetogens, are enriched in initial pH of 9 under both mesophilic condition and psychrophilic conditions, which may be related with the conversion of CO and H-2 into acetate.