Anaerobic digestion of brewery primary sludge to enhance bioenergy generation: A comparison between low- and high-rate solids treatment and different temperatures

Anaerobic digestion of brewery wastewater solids in the form of primary sludge was investigated for its potential as a source of energy (methane). We operated a low-rate (hydraulic retention time (HRT) = solids retention time (SRT)) continuously stirred anaerobic digester (CSAD) and a high-rate (SRT > HRT) anaerobic sequencing batch reactor (ASBR) in parallel for 250 days. We found that high-rate anaerobic digestion was beneficial for solids-rich waste flows even during a long-term operating period that included a shock load of nonbiodegradable total solids. The ASBR biomass achieved a higher specific methanogenic activity compared to the CSAD biomass (0.257 ± 0.043 vs. 0.088 ± 0.008 g CH4-COD g−1 VSS d−1), which aided in stability during the shock load with total solids. The methane yield for the ASBR was 40–34% higher than for the CSAD (0.306 vs. 0.219 l CH4 g VS−1 fed for days 1–183 and 0.174 vs. 0.130 l CH4 g VS−1 fed for days 184–250, respectively). Finally, we operated an ASBR for an additional 295 days to evaluate the effect of temperature variation on system stability. A stable performance was achieved between the operating temperatures of 22–41 °C.