Abstract
Laboratory-scale UASB reactors were started-up successfully at 20°C and operated at temperatures of 32, 20, 15, 11, and 6°C applying several hydraulic retention times (HRTs) ranging from 48 to 3 h during an operational period of approximately 900 days. Changes in temperature and HRTs impacted the reactor performance. However, overall reactor performance (70 to 90 % COD removal) was found to be stable up to an HRT of 6 h and temperature of 11°C. The performance of UASB reactor was not very stable during 6°C operation, even though 30 to 50% of COD removal could be achieved. Biomass aggregation in the form of granules/bio-pellets (mean size ranged from 1.8 mm to 3.0 mm) could be achieved during 20°C operation. The impact of temperature on morphology, surface structure, and shape of bio-pellets was explored. Morphological and elemental composition analyses showed the possible mechanism of biomass aggregation in UASB reactors. This study demonstrated that the UASB process could be applied successfully with some minor adjustment for the treatment of municipal wastewater in temperate and cold regions (average summer temperature 11-25°C).
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