Insights into methanogenesis of mesophilic-psychrophilic varied anaerobic digestion of municipal sludge with antibiotic stress.

Methane production through anaerobic digestion (AD) of municipal sludge is economic and eco-friendly, which is commonly affected by temperature and pollutants residues. However, little is known about methanogenesis in psychrophilic AD (PAD) with temperature variations that simulating seasonal variations and with antibiotic stress. Here, two groups of AD systems with oxytetracycline (OTC) were operated with temperature maintained at 35 °C and 15 °C or variation to explore the influence to methanogenesis. The acetic acid was noticeably accumulated in OTC groups initially (P < 0.001). Methane production was noticeably inhibited initially in PAD with OTC, but had been stimulated later at 35 °C. The dominant acetoclastic methanogens Methanosaeta gradually decreased to 15.48% and was replaced by methylotrophic Methanomethylovorans (73.43%) in PAD with OTC. Correspondingly, the abundances of functional genes related to methylotrophic methanogenesis were also higher in these groups. Besides, genes involving in methane oxidation had over 50 times higher abundances in PAD with OTC groups in the second phase. Further investigation is essential to understand the main dynamics of methanogenesis in PAD and to clear the related molecular mechanism for future methane production regulation in sludge systems.