Abstract
Digesters at water resource recovery facilities (WRRFs) operating at different temperatures within the mesophilic and thermophilic temperature range is a flexibilization concept to contribute to heat management. Four 25 L digesters were fed with sewage sludge from a municipal WRRF and were operated at 37, 43, 47 and 53 °C, respectively, to describe changes in the overall process performance and the microbiota. Specific methane yield and COD degradation rates were the highest at 47 °C, only being up to 7% higher compared with at 37 °C. The increase in pH and concentrations of NH4-N and PO4-P above 43 °C were statistically significant. The effect on the microbial community was strong, indicating both a constant specialization towards thermophilic organisms as well as a change from acetoclastic to hydrogenotrophic/methylotrophic methanogenesis. The influence of temperature on process-engineering and physicochemical aspects was rather small compared with the changes in the microbiota.
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