Mechanism of microbial involvement in nitrogen conversion affecting methane production in dry anaerobic digestion

Abstract

Nitrogen conversion is driven by different microorganisms, which plays a crucial role in methane (CH4) production during dry anaerobic digestion (AD). However, the effect of nitrogen conversion on the metabolic mechanisms of methanogens network remains unclear. Batch AD experiments were carried out using chicken manure and rice husk as substrates. Biogas slurry was added as the inoculum. In a 40-day AD experiment, the initial operating conditions of the AD system: the temperature was 37 °C, C/N ratio was 20 ± 2.5, total solid was 25 ± 0.2%. After AD, total organic nitrogen relative content varied from 1.35% to 2.05%, ammonia nitrogen content varied from 600.31 to 1028.88 mg/kg, nitrate nitrogen content varied from 649.83 to 86.51 mg/kg and nitrite nitrogen content varied from 33.63 to 11.61 mg/kg. High-throughput sequencing results showed that partial Clostridiales promoted the dissimilatory nitrate reduction to ammonia, increased ammonia nitrogen content, and further increased the abundance of partial Methanomicrobiaceae by 310%, leading to an increase in CH4 yield (0–22.03 std m3 kg−1 VS (Volatile Solids) added). This study explored the relationship between nitrogen conversion and microorganisms in the three stages of AD to propose possible mechanisms affecting CH4 yield. The results provide a theoretical basis for the identification of key microorganisms that nitrogen conversion affects methanogenesis during dry AD.