Development of a simple nitrate removal reactor using biofilm-electrode.

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Denitrification rates of a biofilm-electrode system were first analyzed based on a mathematical biofilm model. The model takes into cinsideration the mass transfer rates in the electric field, biological reaction rates, and electrochemical reaction rates. Calculation results from the model showed that the response of the denitrification rates to applied electric current can be divided into three regions ; linear, and declined regions. From a view point of process design and control as well as a long term performance of laboratory-scale reactors, the biofilm-electrode system can be operated in the linear region. On the other hand, a novel multi-polar electrode system using metal electrodes was developed for enhanced denitrification and a multi biofilm electrodes reactor (Multi BER) was designed and constructed. Continuous experiments with the Multi BER demonstrated that nitrate in groundwater was stably and quickly removed by an application of electric current and at the same time the treated water was aerated by oxygen produced from anode. Furthermore, it was also demonstrated that nitrate and pesticide were removed concurrently by BER but other major constituents such as SO_4^<2->, Cl^-, and Ca^<2+> were almost the same in the influent and effluent.