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 CH(4)-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 CH(4)g VS(-1) fed for days 1-183 and 0.174 vs. 0.130 l CH(4)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 degrees C.