Biological nitrate removal from wastewater of a metal-finishing industry

Abstract

An upflow packed bed reactor at laboratory scale has been operated for a continuous period of 5 months to investigate the technical feasibility of biological nitrate removal applied to the effluent of the coagulation–sedimentation wastewater of a metal-finishing industry. The reactor was fed with industrial wastewater in a five-fold dilution to reproduce the global spill in the factory (20/80, industrial wastewater/domestic wastewater) with a concentration of nitrate between 141 and 210 g NO 3-N/m 3. Methanol was added as a carbon source for denitrification. Inlet flow rate was progressively increased from 9 to 40 L/day (nitrogen input load from 45 to 250 g NO 3-N/(m 3 h)). The highest observed denitrification rate was 135 g NO 3-N/(m 3 h) at a nitrate load of 250 g NO 3-N/(m 3 h), and removal efficiencies higher than 90% were obtained for loads up to 100 g NO 3-N/(m 3 h). A mass relation between COD consumed and NO 3-N removed around 3.31 was observed. Better results were achieved in a previous stage using tap water with nitrate added as a sole pollutant as a synthetic feed (critical load of 130 g NO 3-N/(m 3 h) and denitrification rate of 200 g NO 3-N/(m 3 h) at a nitrate load of 250 g NO 3-N/(m 3 h)). This fact could indicate that the chemical composition of the industrial source hinders to some extent the performance of the biological process. Whatever case, results demonstrated the viability of the denitrification process for the global industrial wastewater. A simple model based on Monod kinetics for substrate consumption, and constant biomass concentration was applied to model the industrial wastewater treatment, and a reasonably good fitting was obtained.