Syntrophic Propionate Degradation Response to Temperature Decrease and Microbial Community Shift in an UASB Reactor

Propionate is an important intermediate product during the methane fermentation of organic matter, and its degradation is crucial for maintaining the performance of an anaerobic digester. In order to understand the effect of temperature on propionate degradation, an upflow anaerobic sludge blanket (UASB) reactor with synthetic wastewater containing propionate as a sole carbon source was introduced. Under the hydraulic retention time (HRT) of 10 h and influent propionate of 2,000 mg/l condition, propionate removal was above 94% at 30-35 degrees C, whereas propionate conversion was inhibited when temperature was suddenly decreased stepwise from 30 degrees C to 25 degrees C, to 20 degrees C, and then to 18 degrees C. After a long-term operation, the propionate removal at 25 degrees C resumed to the value at 30-35 degrees C, whereas that at 20 degrees C and 18 C was still lower than the value at 35 degrees C by 8.1% and 20.7%, respectively. Microbial community composition analysis showed that Syntrophobacter and Pelotomaculum were the major propionate-oxidizing bacteria (POB), and most FOB had not changed with temperature decrease in the UASB. However, two FOB were enriched at 18 degrees C, indicating they were low temperature tolerant. Methanosaeta and Methanospirillum were the dominant methanogens in this UASB and remained constant during temperature decrease. Although the FOB and methanogenic composition hardly changed with temperature decrease, the specific CODpro removal rate of anaerobic sludge (SCRR) was reduced by 21.4%-46.4% compared with the control (35 degrees C) in this system.