Long-term effect of seasonal and constant low temperatures on mesophilic biomass treating sewage in continuously stirred tank anaerobic granular reactor

• Published in: Bioresource technology Vol. 386; p. 129471
• Main Authors: Gupta, Rohan, Sethi, Shradhanjali, Sahu, Rojalin, Bharshankh, Ankita, Biswas, Rima
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-10-2023
• Subjects: Carbon diversion; Dissolved methane; Gene mapping; Methanol; Psychrotolerant methanogenic community; Dissolved methane; Psychrotolerant methanogenic community; Carbon diversion; Gene mapping; Methanol
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2023.129471

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•CSAGR treating domestic sewage was studied for 1733 days at low temperature.•Effect of seasonal low temperature and prolonged low temperature was evaluated.•Granular biomass adapted to seasonal low temperatures quickly.•Biomass underwent functional changes at prolonged exposure to temperatures ≤ 15 °C.•Community shifted its focus from energy metabolism to cellular repair and transport.
A Continuously Stirred Tank Anaerobic Granular Reactor seeded with mesophilic biomass was studied for 1733 days analysing the impact of seasonal (12–23 °C) and controlled (8–15 °C) low temperatures on anaerobic treatment of sewage. Aided by intermittent dosing of 0.04% (v/v) methanol, the microbiota quickly adapted to temperature fluctuations. Chemical oxygen demand (COD) removal efficiency was high but low temperatures affected methane production. Under low-temperature stress, the Methanomythylovorans and Methanosaeta-dominated methanogenic community shifted focus to cellular repair and transport, with carbon diversion towards assimilative pathways, thereby decreasing methane yields. Specific methanogenic activity at 15 °C and 30 °C increased by five and four times, respectively, from their initial values indicating microbiota retained its mesophilic properties. Despite lower methane yield, stable and high COD removals, along with low dissolved methane and volatile fatty acids indicated that low-temperature anaerobic sewage treatment using mesophilic biomass in the long run is sustainable.