The performance of anaerobic membrane bioreactors (AnMBRs) at psychrophilic temperatures commonly observed in temperate climates (10–24°C) was assessed. A unique aspect of the research was operation at controlled SRT with regular membrane cleaning. COD removal and permeate VFA concentrations were similar at 15 and 24°C and deteriorated at 10°C. As temperature decreased, the COD mass flow to methane decreased and COD mass flows in the permeate and waste sludge increased. At 24°C, rapid membrane TMP increases were not observed while at 15 and 10°C rapid increases occurred at 11.7 ± 0.46 and 7.6 ± 0.45 days, respectively, indicating a greater fouling propensity of the mixed liquor at lower temperatures. When the temperature was reduced from 15°C to 10°C in a transient test, CH₄ production was reduced and VFA concentrations increased. A 2–3 SRT lag in the responses suggested that the delayed response was due to long‐term changes in microbial population. The permeate VFA content in a PAC‐dosed reactor was lower than that without PAC dosing, and PAC addition increased the time to rapid TMP development to 11.3 ± 0.46 days from 7.4 ± 0.49 days. The primary benefit of PAC addition at low temperatures is enhanced membrane performance.

Practitioner points

• AnMBRs can produce high‐quality effluents at temperatures of 15°C
• Membrane fouling increases as temperature decreases
• Bioreactor performance was sustained for 2–3 SRTs after temperature decrease
• PAC addition reduced the permeate VFA concentrations
• Membrane fouling at 10°C was reduced through PAC addition