Degradation Of Sulfadiazine By Electrochemical Oxidation Process In Aqueous Solution

Sulfadiazine is synthetic antimicrobial agents, which are used in aquacultrure, animal husbandry and human medicines commonly. As a result of their antibacterial natrue, antibotic residues cannot be effectively destructed by traditional biological methods. Sulfadiazine which residues in environmental is harmful to human health and ecological system. The electrochemical technology has attracted a great deal of atteniion recently, mainly because of its spceial advantage.In this thesis, sulfadiazine is chosen as target pollutants. Various process conditions affecting the removal of sulfadiazine in electrochemical reactor are investigated. The electrochemical oxidation mechanism is elucidated.The electrode of Ti/RuO2-IrO2, which has been used in chlor-alkali industry, is employed as anode, and Ti as cathode. Physical characterization and electrochemical performance test were conducted. The results showed that ruthenium oxide and iridium oxide were well loaded on the surface of titanium substrate. The anode of Ti/RuO2-IrO2had oxygen evolution over-potential of about1.3V and showed good catalytic oxidation performance in the sulfadiazine solution containing chloride ion.In Na2SO4system, electro-catalytic oxidation was effective to remove sulfadiazine in aqueous solutions. The optimal treatment process in the controlled test was determined as follows:the pH value of7; the Na2SO4concentration of0.05mol·L-1; the current density of10mA·cm-2; the initial sulfadiazine mass concentration of50mg/L; the electrode distance of2cm. Higher current density, initial sulfadiazine concentrations and electrode distance could enhance the decay rate of sulfadiazine. Lower pH values were preferable while higher pH values might partly inhibit the degradation. The concentration of Na2SO4as electrolyte was negatively correlated with the decay rate of sulfadiazine. The degradation mechanism was based on-OH oxidation to form mainly4-[2-iminopyrimidine-1(2H)-yl]aniline as intermediate product. Degradation procedure was in accordance with the first-order kinetic model.In NCI system, The removal rate of sulfadiazine was90.12%after10minutes treatment, and the TOC concentration significantly decreased66%after4hours; After4h treatment, the removal rates of TOC at pH3,4,8,8.5,10and12were29%,46%,55%,61%,52%and47%, respectively, the peak of removal rate appeared at8.5; The removal rate of TOC could be enhanced through increasing the current density and the NaCl concentration, decreasing the initial sulfadiazine mass concentration. The optimal treatment process was determined as follows:the pH value of8.5; the NaCl concentration of0.025mol·L-1; the current density of20mA·cm-2; the initial sulfadiazine mass concentration of100mg/L. The degradation mechanism was based on the·OH-induced oxidation and strong oxidant CIO" to form mainly p-aminobenzene sulfonic acid,2-pyrimidinamine,1-2-benzenediol, m-dihydroxybenzene, benzoquinone and some small organic acids as intermediate product. And then these are completely oxidized and mineralizatied into carbon dioxide, water and inorganic salt such as nitrate.