Influence of temperature and COD loading on biological nitrification–denitrification process using a trickling filter: an empirical modeling approach

To cut down aeration power for nitrification, we constructed a biological nitrification–denitrification process with a trickling filter for nitrification and an anaerobic biological filter for denitrification. The influences of temperature and chemical oxygen demand (COD) loading on the nitrification and denitrification performance of the process are discussed in this paper through experimental and empirical modeling approaches. The model constants were determined by the experimental data of the process using municipal wastewater in Ryukoku University. Then, the influences of temperature and COD loading were estimated by the model. The COD levels required for NO3–N removal depended on both, the temperature and influent COD/NO3–N ratio. A lower temperature and higher influent COD/NO3–N ratio increased the COD requirement, because of the different responses between denitrifying bacteria and heterotrophic bacteria against temperature, COD, and NO3–N concentrations. In addition, our experimental system could satisfy the Japanese effluent standard at temperatures higher than 12 °C. The dissolved nitrogen (DN) concentration in the final effluent was more strongly affected by the NH4–N discharged from the trickling filter than it was by the residual NO3–N in the effluent from the denitrification tank. Therefore, the enhancement of the nitrification efficiency in the trickling filter was inferred to enhance the nitrogen removal efficiency. To prevent a low nitrogen removal efficiency at temperatures lower than 15 °C, it was necessary to set the low hydraulic loading.