Abstract
The stoichiometry and kinetics of biological denitrification of water using an anoxic up flow filter were investigated. The feasibility and potential of the process were also evaluated. The anoxic filter was operated at nitrate loadings of 60 to 270 g(N)/m3 and an empty bed hydraulic retention time of 8.7 hours. High denitrification efficiencies (86-90%) were achieved for nitrate loadings of 60-200 g(N)/m3 d. The effect of nitrate loading was not found to be significant on nitrate removal efficiency when nitrate loading was varied within this range. Slight decreases in the denitrification efficiency (76%) were observed when nitrate loadings were increased to 270 g(N)/m3 d. Denitrification rates as high as 0.22 kg(N)/m3 d could be achieved using an anoxic up flow filter with methanol as a substrate. It was also found that a methanol to nitrate ratio of 0.56 should be used to minimize methanol concentrations in the effluent and to achieve effective denitrification. Analysis of reactor kinetics showed that higher detention times, or column depths, are needed for high nitrate loadings in order to reach a point where the rate of nitrite reduction exceeds the rate of nitrite formation. The half order rate model was found adequate to describe the process.