Upflow anaerobic sludge blanket (UASB) treatment of supernatant of cow manure by thermal pre-treatment

Upflow anaerobic sludge blanket (UASB) methane fermentation treatment of cow manure that was subjected to screw pressing, thermal treatment and subsequent solid–liquid separation was studied. Conducting batch scale tests at temperatures between 140 and 180 °C, the optimal temperature for sludge settling and the color suppression was found to be between160–170 °C. UASB treatment was carried out with a supernatant obtained from the thermal treatment at the optimal conditions (170 °C for 30 minutes) and polymer-dosed solid–liquid separation. In the UASB treatment with a COD_Cr loading of 11.7 kg/m³/d and water temperature of 32.2 °C, the COD_Cr level dropped from 16,360 mg/L in raw water to 3,940 mg/L in treated water (COD_Cr removal rate of 75.9%), and the methane production rate per COD_Cr was 0.187 Nm³/kg. Using wastewater thermal-treated at the optimal conditions, also a methane fermentation treatment with a continuously stirred tank reactor (CSTR) was conducted (COD_Cr in raw water: 38,000 mg/L, hydraulic retention time (HRT): 20 days, 35 °C). At the COD_Cr loading of 1.9 kg/m³/d, the methane production rate per COD_Cr was 0.153 Nm³/kg. This result shows that UASB treatment using thermal pre-treatment provides a COD_Cr loading of four times or more and a methane production rate of 1.3 times higher than the CSTR treatment.