Abstract
Recently, harmful ion, nitrate nitrogen, is contained so much in wastewater such as an agricultural effluent. If this ion flows into a river etc., it causes a serious social problem such as water pollution and a bad influence to an ecological system. Therefore, development of the effective technology for removing nitrate ion is desired. Generally, the removal of nitrates ion is based on the reduction by hydrogen donor reagent, but it is difficult to control the degree of reduction because of its complicated reaction mechanism. The reactions of nitric compounds are governed by standard oxidation-reduction potentials of each species. The reduction of nitrates ion favorably proceeds under low pH, on the contrary, the formation of nitrogen gas is desired to keep the reaction condition at high pH. In this paper, we proposed a new method to convert nitrates ion into nitrogen gas via nitrous acid and ammonium ions. 10 ppm of nitrates ion and several organic acids were reacted at 200 to 350 °C under 18 MPa to examine an optimum condition to reduce the nitrates ion. It was found that nitrates ion was converted completely into the equivalent mixture of nitrous acid and ammonium ions using 1000ppm of citrate acid as an additive. Thus converted mixture was reacted for 70 s under 7 of pH at 340°C in 18MPa of pressure, and these ions were successfully converted into nitrogen. Thus, it was found that the proposed method is effective for removing nitrates ion at short contact time.
