Impact of temperature on performance, microbiological, and hydrodynamic aspects of UASB reactors treating municipal wastewater.

The present study examined the feasibility of treating municipal wastewater by a UASB system under low-temperature conditions. Two reactors were started-up at 20 degrees C and subsequently operated at temperatures of 32, 20, 15, 11, and 6 degrees C applying several hydraulic retention times (HRTs) ranging from 48 to 3 h during an operational period of approximately 900 days. Chemical oxygen demand (COD) removal efficiency ranged from 70 to 90% up to an HRT of 6 h and 11 degrees C. The performance of the reactor was not very satisfactory during 6 degrees C operation (average COD removal 40%). Sulfate reduction played an important role in COD reduction. Digital image analysis and scanning electron microscopic observations of sludge samples revealed aggregation of biomass in the form of irregular shaped granules (mean size ranged from 1.5 to 3.0 mm). The hydraulic regime in the reactor was impacted by the change in operating temperature. This study demonstrated that the UASB system could be applied successfully for pre-treatment/treatment of municipal wastewater under low-temperature conditions.