Denitrification of high-strength nitrate wastewater using fluidized-bed biofilm reactors

The removal of nitrogen compounds from wastewater before disposal to water bodies has relevance with respect to a number of ecological and public health effects including eutrophication of surface water bodies and infant methemoglobinemia. The denitrification of high-strength nitrate wastewater is a major problem for many industries, especially for those involved in the production of petrochemicals, explosives, fertilizers, pectin and many metal finishing industries. Municipal wastewater treatment plants are also facing the same challenge with high nitrate concentrations in side-stream wastewaters such as nitrified sludge decants.; In this research, the biological denitrification characteristics of high strength nitrate wastewater was investigated using two laboratory-scale high performance fluidized-bed biofilm reactors (FBBRs) with specific emphasis on two main operational parameters: the nitrogen loading rate and the superficial velocity (V_s).; The results demonstrated that the FBBR system is capable of efficiently handling a high nitrate concentration of 1000 mg-N/L. At a loading rate of 6.3 kg-N/m3_bed·d, almost complete denitrification was achieved. The maximum efficient loading rate (L.R_max) at which the U.S. drinking water nitrate standard concentration of 10 mg-N/L would be exceeded was found to be a function of the applied V _s. The L.R_max was 12 kg-N/m 3_bed·d at a V_s value of 45 m/h. As V_s was increased to 55 m/h and 65 m/h, the optimum L.R_max dropped to 9.5 kg-N/m 3_bed·d and 8 kg-N/m3_bed·d, respectively.; The average biomass concentration in the FBBR decreased with an increase in V_s at all the applied nitrogen loadings. Reported correlations by other researchers for predicting the biomass concentration in the FBBR were examined for their validity in comparison with the experimental results of this study, and an applicable set of correlations was recommended. A correlation between the biofilm dry density and the biofilm thickness was produced from the results of this study.; A simplified model of the denitrification kinetics of high performance FBBRs was developed based on Monod kinetics. The engineering value of this model was illustrated by proposing a simplified design procedure of FBBRs for denitrification purposes.