Performance of UASB reactors at 6 to 32°C in municipal wastewater treatment

The feasibility of using a high-rate upflow anaerobic sludge blanket (UASB) system for the treatment of low-strength municipal wastewater at 6 to 32 degrees C was investigated for temperate climate applications. UASB reactors could be started up successfully in about 60 days at 20 degrees C. Under stable conditions, the removal of GOD, BOD and SS ranged from 38 to 90%, 47 to 91% and 50 to 92%, respectively, for a temperature range of 6 to 32 degrees C. Sulfate reduction ranged from 10 to 90%, showing a decreasing trend with a decrease in temperature at each HRT. The average biogas production and methane content ranged from 167 to 199 mt CH4/g-CODremoved and 65 to 86%, respectively. The recovery of methane in the gas phase was very low compared with soluble COD removals, especially during operation at lower temperatures (6 to 15 degrees C). Digital image analysis and scanning electron microscopy results indicated the aggregation of biomass in the form of flocs and small granules. The mean size of aggregated sludge particles increased from 0.2 to 3.0 mm,with a sludge volume index of 18 +/- 2 mL/g during the operation.