Kinetics and microbial community analysis of sludge anaerobic digestion based on Micro-direct current treatment under different initial pH values

The effects of Micro-direct current treatment (Micro-DC) on the performance of sludge anaerobic digestion under different initial pH values were investigated in this study. Biogas production and VS removal rate tests were conducted to determine the optimum initial pH value based on the Micro-DC treatment, and the evolution of archaeal community was also investigated through high-throughput sequencing method to reveal its mechanism. Furthermore, three different models were employed to reveal the principle kinetics of methane production. The results showed that the optimum initial pH was 9.0 with the Micro-DC treatment of 0.6 V, simultaneously the methane production could be greatly upgraded to 224 mL CH4/g-VS as well as a VS removal rate of 38.07% after 32 days digestion. The archaeal community analysis illustrated that Methanosaeta dominated in the treatments with initial pH between 5.0 and 9.0, while they were Methanobacterium and Methanoculleus in the treatments at initial pH values of 3.0 and 11.0, respectively. Positive correlations were found between Methanosaeta relative abundance and biogas production. Model simulation presented that the Cone model fitted the experiment data better and the calculated parameters indicated that anaerobic digestion of sludge at near-neutral pH had shorter lag phase and higher hydrolysis rate.