High-concentration Nitrogen Removal in Industrial Wastewater Combining Biological Nitrite Reactions and Subcritical Hydrothermal Reactions

The removal of high-concentration nitrogen using subcritical hydrothermal reactions of equivalent mixtures of NO2－ converted from the original NH4＋ and NH4＋ without a catalyst was studied. This reaction was carried out in a pressure bottle shaken for 1h with three kinds of initial substrate concentrations: 1,500, 3,000, and 5,000 ㎎/L of either NH4-N or NO2-N while setting the temperature at 140, 160, 180, or 200℃. In the cases where the reaction temperatures were 180 and 200℃, over 90％ of the total nitrogen successfully decomposed at the initial concentrations in the artificial water. Even if the reaction temperature was lowered to 140℃, over 90％ was removed when the concentration of NH4-N and NO2-N were over 5,000 ㎎/L. On the other hand, it was necessary to achieve above a 90％ total nitrogen decomposition value when the initial concentration of NO2-N was 1.6 to 2.2 times higher than that of NH4-N when biologically treated water were used. The combined treatment of a subcritical hydrothermal reaction followed by a biological nitrite reaction, can effectively remove high concentrations of nitrogen in industrial wastewater.