Electrochemical Catalytic Reduction For Nitrate Removal From Water

Nitrate pollution has caused widespread concern because of its global and carcinogenicity, and domestic and foreign researchers have proposed a number of methods to remove nitrate pollution. Some researches obtained the high efficiency nitrate removal, however, the total nitrogen (TN) removal rate was still low accompanied with the ammonia nitrogen byproduct generated. In this work, the electrochemical catalytic system with graphite or carbon nanotube-graphite electrodes cathodes, titanium based oxide mateial as anode was used for the reduction of NO3-using nitrate simulated wastewater. The main results obtained are as follows.Firstly, the reduction potential of NO3-was studied by linear sweep voltammetry. On the base of the above study, the removal of NO3-was investigated using graphite cathode and various anodes. It was found that graphite, Ti/IrO2, Ti/TiO2-IrO2, Ti/SnO2-Sb2O5-IrO2, this four electrodes could be used as auxiliary electrode coordinating graphite cathode for the catalytic reduction of NO3-. Contrastly, Ti/SnO2-Sb2O5-IrO2has the preferable denitration effect, the lowest selectivity to ammonia and high catalytic activity. It is the preferred anode material used for the removal of NO3-.The results of NO3-removal by the electrochemical reduction using Ti/SnO2-Sb2O5-IrO2anode and graphite cathode or carbon nanotube-graphite cathode show that cathodic potential and initial pH have remarkable effect on the removal of NO3-and the selectivity of ammonia nitrogen generation. It was found that as the cathode potential became negative shift, the removal rate of NO3-and NH4+generating rate showed a trend of first increasing and then decreasing, and became maximum at-1.4V (SCE).The NO3-removal of69.69%and the total nitrogen removal of42.62%with the current efficiency of18.08%were achieved by the treatment of240min using graphite as the cathode. Contrastly, the NO3-removal of80.97%and the total nitrogen removal of52.36%with the current efficiency of30.40%were achieved by the treatment of120min using nanotube-graphite as the cathode. Additionally, the two cathodes in neutral and alkaline solution are not beneficial to the removal of NO3-.Using indirect electrochemical oxidation method to remove the ammonia nitrogen of acidic solution was carried out. The results showed that ammonia nitrogen removal was able to be enhanced by the increase of chloride ions concentration, and the total nitrogen removal was significantly enhanced. Ammonia nitrogen was completely removed and the total nitrogen removal rate reached to87.09%accomping with39.58%of current efficiency by the treatment of240min under the conditions of3000mg/L chloride ion, the anode potential of1.6V. Ammonia nitrogen was mainly oxidized to N2by active chlorine along with electrochemical process.In this work, a better removal of NO3-and the total nitrogen has been achieved by the electrochemical catalytic reduction, which can present the theory supporting for its application in deal with the pollution caused by nitrate.