Cascade hydrogen production from butyrate-type straw fermentation effluent using a microbial electrolysis cell

In order to solve the problem that butyric acid is difficult to be degraded in butyrate-type fermentation effluent, corn straw was used as a substrate for dark fermentation to produce hydrogen, and different substrates (butyric acid, acetic acid, and fermentation effluent) were used to enrich the bioanode of the microbial electrolysis cell (MEC). The effects of the anode enrichment method, substrate concentration and applied voltage on hydrogen production from butyrate-type straw fermentation effluent were investigated. The microbial community structure was analysed by high-throughput sequencing. The results showed that the maximum hydrogen yield and hydrogen production rate reached 943 mL g^-1 and 3.62 m³ m^-3 d^-1, respectively, when the bioanode enriched with butyric acid was used to treat the straw fermentation effluent at 0.6 V applied voltage. Compared with the enrichment of fermentation effluent, the degradation rate of butyric acid and the removal rate of chemical oxygen demand (COD) increased by 35.1% and 25%, respectively. The anode enriched with butyric acid had higher species richness and diversity, and the abundance of butyric acid oxidizing bacteria Syntrophomonas was as high as 8.7%. It is speculated that butyric acid is first oxidized to acetic acid, and then hydrogen is produced by electrogenic bacteria. Butyric acid oxidation is the rate-limiting step of hydrogen production. The two-stage cascade hydrogen production process significantly improved the straw conversion rate and hydrogen production efficiency, and realized the simultaneous purification of hydrogen fermentation effluent, which provided a reference for the large-scale biological hydrogen production of straw.