Comparison Of Active Chlorine Generation In Situ And Carbamazepine Degradation On Ti/RuO₂ And Platinum Electrode

The reverse osmosis concentrate?ROC?from the sewage treatment plant usually contains trace organic pollutants which are difficult to be degraded by microorganisms,and the ROC has a high salinity and poor biodegradability,so the advanced oxidation process is generally applied to treat ROC.Due to the high concentration of chlorine ion in ROC,oxidizing substances such as hypochlorous acid can be generated in situ by electrochemical oxidation for indirect oxidation,which is used to oxidize organic substances in wastewater.However,ROC contains not only chloride ions,but also inorganic substances such as sulfates,nitrates,carbonates,and ammonia nitrogen.Most of the previous studies focused on the active chlorine generation and the organic matter removal in the single NaCl electrolyte system,but there are few studies about the influence of inorganic ions in solution on the active chlorine generation and carbamazepine degradation.In this study,the effects of current density,chloride ion concentration and inorganic ions on the active chlorine generation and carbamazepine degradation in Ti/RuO₂ coated electrode and platinum electrode system were studied.The effects of current density,chloride ion concentration,temperature and inorganic ions on the active chlorine generation and carbamazepine degradation in the Ti/RuO₂electrode and Pt electrode system were studied.The current density was 80 mA and the chloride ion concentration was 15 mM in the Ti/RuO₂ electrode system,when 30 mM sodium sulfate,20 mM sodium bicarbonate,2 mM ammonium chloride and 5 mM sodium nitrate were added to the solution,the carbamazepine removal efficiency was decreased from 96.8%to 88.9%,36.5%,90.7%,96.6%respectively.When two kinds of ions coexist,except for the increase of carbamazepine removal efficiency when nitrate coexist with sulfate and bicarbonate,the coexistence of the other two kinds of ions will reduce carbamazepine removal efficiency.The more kinds of ions coexist,the lower carbamazepine removal efficiency will be obtained..It may be because the presence of ions reduces the active chlorine generation in the system.The current density was 15 mA/cm²and the chloride ion concentration was 15 mM in the Pt electrode system,when 30 mM sodium sulfate,20 mM sodium bicarbonate,2 mM ammonium chloride and 5 mM sodium nitrate were added to the solution,the carbamazepine removal efficiency was decreased from 95.8%to 88.9%,60.4%,92.6%,89.1%,respectively.When bicarbonate coexists with three other ions,the removal efficiency of carbamazepine increased,while when the other two ions were combined,the removal efficiency of carbamazepine decreased.No big difference was found on carbamazepine removal between three and four ions coexist.It may be because the hydroxyl radical and electrochemical oxidation directly contribute significantly to the carbamazepine removal.Mechanism analysis of the two electrode systems were compared subsequently.The linear voltammetry test showed that no direct oxidation reaction of inorganic ions occurred on the the anode surface.The results of free radical quenching experiments show that there is no hydroxyl radical involved in the carbamazepine degradation in the presence of sodium chloride alone in the Ti/RuO₂ electrode system.For the Pt electrode system,the addition of t-butanol and nitrobenzene in the presence of sodium chloride alone reduced the carbamazepine removal efficiency,indicating that the system has hydroxyl radicals involved in the carbamazepine degradation.The ion coexistence experiment showed that the effect of carbamazepine removal efficiency of Pt electrode system was smaller than that of Ti/RuO₂ electrode.It can be seen that when the wastewater component is more complicated,it is feasible to use Pt electrode for electrochemical degradation.