Anaerobic Treatment of Sugary Wastewater by the UASB Process.

Abstract

High strength sugary wastewater was continuously treated in a 12.5l UASB reactor operated at 37°C for 440 days. This included 350 days of loading rate study during which volumetric loading rate (VLR) was increased from 0.3 to 24 g-TOC/l·d and 90 days of investigation at a stable loading rate of 8 g-TOC/l·d. The UASB reactor achieved 80-98% TOC reduction at VLRs up to 16 g-TOC/l·d. Mass balance calculations revealed that 46% and 49% of TOC removed was converted to CO2 and CH4, respectively while the rest was converted to biomass with an average observed sludge yield of 0.094 g-VSS/g-TOC. The C: N: P ratio in the wastewater, pH, volatile fatty acid (VFA) concentration of the effluent and hydraulic retention time (HRT) were all correlated with the removal efficiency of the reactor. For achievement of effective TOC removal efficiencies, these parameters must be maintained at C: N: P=350: 10: 2; pH, 6.8-7.2; VFAs, less than 1000mg/l; and HRT, greater than 12 hr. The microbial structure of the granules was elucidated and microorganisms resembling the Methanobacterium and Methanobrevibacter genera were found to be dominant in the granular sludge cultivated during the period of loading rate increases. However, Methanothrix-like methanogens were found to be dominant in granular sludge cultivatedduring the period with a stable loading rate of 8 g-TOC/l·d. And loading rate is a majoroperational parameter in a UASB reactor for selection of granular sludge with better characteristics such as granule size, settling velocity, MLSS and VSS concentration.