Thermophilic and mesophilic anaerobic fermentation of swine manure

The effects of temperature (35° and 55°C), influent Volatile Solids (VS) concentration (So = 50·4 and 62·5 kg VS m−3) and hydraulic retention time (HRT = 5, 10, 15 and 25 days) on methane (CH4) production from swine manure were evaluated using 3-dm3 laboratory scale fermentors. The highest CH4 production rate achieved was 3·12 m3 CH4 per m3 fermentor per day at 55°C, 5-day HRT and So = 50·4 kg VS m−3. Batch fermentations showed an ultimate CH4 yield (B0) of 0·49 m3 CH4 kg VS fed. Extreme fermentation instability was experienced by the thermophilic (55°C) fermentors at 25-day HRT and S0 = 62·5 kg VS m−3. This instability was attributed to free-ammonia and influent-substrate inhibitions. After a significant period for adaptation (over 170 days), the thermophilic fermentors adapted to the high free-ammonia concentrations and operated satisfactorily.