OXYGEN TRANSFER AND CONSUMPTION IN A BIOLOGICAL AERATED FILTER
Abstract:The gas/liquid mass-transfer coefficient was measured over a wide range of gas and liquid flow rates in a submerged-media biological aerated filter under both abiotic and biotic conditions. A bench-scale unit was used to determine the mass-transfer coefficient without biological activity and a pilot-scale unit was used to evaluate oxygen transfer under nitrifying conditions. Abiotic liquid-side, mass-transfer coefficients (KLa) measured using a nitrogen gas stripping method, were found to increase as both gas and liquid superficial velocities increase, with values ranging from approximately 40 to 380 h−1. The overall effect of variables including gas and liquid velocities, dirty water to clean water ratios, and liquid temperature, was correlated to within ± 20% of the experimental KLa value. The nitrifying biological aerated filter pilot unit operated for 5 months at a domestic wastewater treatment facility under varying hydraulic and pollutant loadings. Endogenous respiration contributed to only 2 to 7% of the total oxygen demand with regions of biomass activity changing with respect to the applied loading conditions. The biotic KLa values inferred using an overall oxygen balance ranged between 64 and 158 h−1 for the experimental conditions evaluated. Comparing abiotic and biotic mass-transfer coefficients suggests that an apparent biological oxygen transfer enhancement may occur in the biologically active pilot. The enhancement could be accounted for by either an increase in KLa or the associated concentration driving force.
Document Type: Research Article
Publication date: January 1, 2003
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