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| The effects of Micro-direct current treatment (Micro-DC) on anaerobic digestion of sludge 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, First-order kinetics, Transfer function model and Cone model were employed to reveal the principle kinetics of methane production from waste activated sludge (WAS). The results showed that the optimum initial pH was 9.0 with the Micro-DC treatment of 0.6 V, with which the methane production could be greatly upgraded with a value of 224 mL CH4/g-VS as well as a VS removal rate of 38.07% after 32 days digestion. Micro-DC treatment with an initial pH value of 9.0 enhanced the microbial activities and avoided the accumulation of volatile fatty acids (VFAs) and free ammonia ([NH3]) and subsequent inhibition, inducing a stable digestion environment. The archaeal community analysis showed that Methanosaeta dominated in the treatments with initial pH values between 5.0 and 9.0, while they were Methanobacterium and Methanoculleus in the treatments at initial pH values of 3 and 11, respectively. 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 values has shorter lag phase and higher hydrolysis rate. Furthermore, positive correlations were found between Methanosaeta relative abundance and biogas production. |
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| Keywords:Micro-direct current treatment; Sludge anaerobic digestion; Initial pH value; Kinetic analysis; Archaeal community |
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