Enhancing methane production during anaerobic digestion of municipal organic solid wastes by ethanol-type fermentation pretreatment coupled with biochar addition

Nowadays, the main mechanism of traditional anaerobic digestion relies on interspecific hydrogen transfer (IHT). However, IHT is highly dependent on mass transfer and diffusion rates, which can be hindered during the treatment of municipal organic solid wastes (MOSW), mainly including food waste and waste activated sludge. This hindrance leads to stagnation of methane production. Direct interspecific electron transfer (DIET) has a low dependence on these rates, making it a promising alternative to IHT for methane production in MOSW anaerobic digestion. Currently, ethanol-type fermentation pretreatment and the addition of carbon-based conductive materials are used to promote DIET. In this study, we used municipal organic solid wastes as the substrate to explore the enhancement of anaerobic methane production performance through ethanol-type fermentation pretreatment coupled with biochar addition. The results showed that: (1) Optimal cultivation conditions were achieved for brewing yeast by optimizing the cultivation time, inoculation ratio, and medium composition. The optimal conditions were as follows: cultivation time of 21.17 hours, inoculation ratio of 15%, and medium composition per 30 mL liquid medium of 3.00 g glucose, 0.12 g peptone, 0.12 g yeast extract powder, and trace elements. (2) The best process conditions for ethanol-type fermentation pretreatment were determined by optimizing the temperature and inoculation ratio of brewing yeast. The optimal conditions for ethanol-type fermentation were at temperature of 37 ℃ and a brewing yeast inoculation ratio of 20 mL/ L. (3) A semi-continuous flow anaerobic digestion experiment was designed to investigate the effect of ethanol-type fermentation pretreatment coupled with biochar on methane production and substrate removal of MOSW. Compared to the control group, the ethanol-type fermentation pretreatment (inoculated with 20 mL/L brewing yeast) coupled with biochar (2 g/L) group increased methane production by 102.5% and substrate removal rate by 16.2%. (4) Microbial community analysis revealed that ethanol fermentation pretreatment coupled with biochar increased the relative abundance of Metanosaeta. This study optimized the culture conditions of yeast and determined the optimal pretreatment temperature and inoculation ratio of ethanol fermentation to reduce economic costs. By employing ethanol-type fermentation pretreatment coupled with biochar addition, DIET was established to enhance methane production and improve the resource utilization and reduction during MOSW anaerobic digestion.