Denitrification of concentrated industrial wastewater: Microorganism selection and kinetic studies

This study was carried out to find a bacterial system to allow a complete denitrification of an industrial wastewater. The average nitrate concentration was 600 mM NO3 (about 37 g NO3 l), and there was no nitrite. The carbon substrate used wits the acetic acid. Batch and continuous cultures were chosen as culture modes in stirred anaerobic reactors. The bacteria were selected from the microorganisms in the ponds of the industrial plant where the wastewater was stored, using a selective denitrifying bacteria medium. Two strains were selected (Pseudomonas cepacia, and Staphylococcus hominis). Complete denitrification was possible, even with a high nitrate concentration. A batch culture on concentrated medium showed that the microorganisms could tolerate high nitrate concentrations. The specific growth rates were 0.08 and 0.06 h(-1) respectively for the strain S1 and S2. The first strain (Pseudomonas cepacia) appeared to reduce the nitrates to nitrites stage (with a ratio of 44%), and into gaseous nitrogen. The second strain (Staphylococcus hominis) changed the nitrites into gaseous nitrogen. The continuous experiment showed that development and denitrification with the two strains successfully processed the industrial wastewater under continuous conditions. This experiment confirmed the kinetic parameters determined in the batch experiment (mu(max) below 0.1 h(-1)).