Optimization of Denitrification Process

A denitrification system composed of a completely stirred tank reactor (CSTR) followed in series with a plug flow reactor (PFR) was tested in order to minimize the disadvantages of each process when used separately. High efficiency of NO₃-N removal and good process control can be achieved with the series treatment system using 25% of the volume required with a single CSTR reactor. Most influent NO₃-N concentrations were greater than 1000 mg/l, and these usually result in effluent concentrations less than 50 mg/l. The effluent NO₃-N concentration was reduced to less than 0.5 mg/l with a total hydraulic detention time of 1.7 hr when the influent NO₃-N concentration was 80 mg/l. Design conditions which would minimize treatment volume requirements would include microbial mass loadings (g NO₃-N g VSS/ day in the CSTR and PFR of 2.0 day^-¹, and 0.2 day^-¹, respectively, resulting in a 40% removal efficiency in the CSTR reactor and greater than 95% NO₃-N removal efficiency in the total system. The microbial yield averaged 0.11 g VSS synthesized per g of COD removed.