Psychrophilic and mesophilic anaerobic treatment of synthetic dairy wastewater with long chain fatty acids: Process performances and microbial community dynamics

•Biomass acclimation to cold condition is necessary for efficient treatment at 15 °C.•Putative syntrophic fatty acid bacteria were the key player of the microbiome.•Methanocorpusculum was the dominant archaea at 37 °C and 15 °C.•Fungal-bacterial biofilm was essential for efficient psychrophilic treatment.