Biogas production and microbial profile estimation in bioreactor landfills

This study investigated the municipal solid waste (MSW) biodegradation process, simulating landfill conditions using a bioreactor. A core objective was to identify key markers in leachate that could forecast the methane (CH₄) generation process during anaerobic digestion (AD). To further understand the causes of CH₄ production inhibition and to propose strategies for enhancing AD system performance, we aimed to compare the microbial community structures in leachate from different reaction periods and in solid MSW samples.

A bioreactor was utilized to replicate the landfill's MSW biodegradation process. Research workers analyzed the relationship between the methanogenic process and the properties of leachate from anaerobic digestion. To investigate the underlying causes of inhibition, we compared the features and differences in the microbial community structure of leachate samples from different reaction periods and solid samples (end-state MSW and cover layer).

The biogas production potential was found to be 74.36 L kg^-1, and the rate constant for MSW digestion gas production was 0.0359 days^-1. A correlation was observed between the leachate's pH, TOC/TN ratio, and the CH₄ generation process, though the correlation between pH variation and methanogenesis showed a clear lag, indicating pH alone is not a sufficient predictive signal. The system became unstable due to ammonia buildup, with a TOC/TN value below 13 coinciding with minimal gas output. Microbial analysis showed that the genetic similarity between leachate and MSW samples was inversely related to the length of the reaction period. A key observation was the absence of Nitrospirain leachate, which likely interrupts the nitrogen conversion cycle. The nitrification process was found to primarily occur in the cover layer. Decreased CH₄ generation was mostly caused by ammonia inhibition, which reduced the activity of acetate-utilizing methanogenic archaea. The intermediate cover layer acted as a biochemical reaction zone with greater microbial diversity.

The findings indicate that due to ammonia buildup, the fermentation system became unstable when the TOC/TN value fell below 13. The absence of Nitrospirain leachate is identified as a critical factor disrupting the nitrogen cycle. Therefore, inoculation with Nitrospira-containing agents is proposed as crucial for maintaining system stability and enhancing treatment efficiency. The intermediate cover layer, harboring greater microbial diversity, contributed to enhanced anaerobic digestion and supported increased system stability, functioning as a vital biochemical reaction zone. These insights provide recommendations for enhancing the AD system's CH₄ production capacity.