H2 production from coal by enriching sugar fermentation and alkane oxidation with hyperthermophilic resistance microbes in municipal wastewater

Anaerobic hydrogen production from coal provides an alternative to achieve clean energy and zero greenhouse gas emissions. However, the recalcitrant structure of coal is the barrier for microorganisms to access, leading to inefficient hydrogen production. Municipal wastewater contains rich microbial resources with high degradability and a broad tolerance range to temperature, which was herein used to drive hydrogen production from coal at 35, 55 and 65 °C. The result showed the total hydrogen production (1.02 mL/g TS) at 65 °C was 34.0 and 51.0 times the 35 °C and 55 °C, respectively. For 65 °C, the decomposability of C-H linkage and aromatic ring structures in coal was the best; sugar fermentation and alkane oxidation pathways were effectively enriched, leading to the highest concentration of volatile fatty acids and alkanes. Which resulted in a shift of dominant bacteria from the lactate- and hydrogen-producing bacterium Bacillus at 35 °C and 55 °C to the hydrogen-producing bacterium Thermoanaerobacterium at 65 °C. Moreover, a gradient temperature cultivation from 35 to 65 °C (gradient increase temperature, GIT) based on the domestication concept was conducted. It is surprising that the GIT group displayed significantly lower hydrogen production (0.14 mL/g TS) compared to 65 °C group, because bacteria can adapt from mesophilic to hyperthermophilic temperatures, including Bacillus, Fonticella, Lysinibacillus, Ureibacillus, Microbacterium, and Geobacillus, inhibiting the Thermoanaerobacterium in the GIT group by producing lactic acid and competing for living space. This study proposes an alternative for efficient hydrogen production from coal. In the future, hydrogen production can be further enhanced through both substrate pretreatment and inoculum domestication, the related core mechanism will also be focus on.