Fate of organic carbon in UAFB treating raw sewage: impact of moderate to low temperature.

The anaerobic biological treatment of raw sewage under low ambient temperatures was investigated in an up-flow anaerobic fixed bed (UAFB) reactor, over a 220-day trial period. The operating temperature was lowered stepwisely from 35 to 25, 20 and 15°C. Obvious accumulation of acetic acid was observed in the effluent as the temperature dropped, which almost tripled at 15°C compared to that at 35°C. An interesting psychrophilic-forward-shift trend of methane production rate following the decrease of temperature was discovered. The methane yield at each trial was 169, 201, 256 and 269 L(STP) CH(4)/kg COD(removed). For each temperature trial, about 32.6%, 28.3%, 34.4% and 34.9% were removed in form of methane. Based on PCR-DGGE results, the band corresponded to Methanosphaera spp. only showed up on 15°C profile. Analysis of both methane production and DGGE results indicated that psychro-tolerant microorganisms dominated the archaeal populations in the UAFB under low-temperature.