Research On Removal Of Ammonia In Wastewater By Electrochemical Oxidation Based On Circulated Electrolytic Cell

Along with the increasingly serious eutrophication problem and gradually stricter ammonia discharge standard, the advanced technology of ammonia wastewater treatment has recently attracted a great deal of attention by scholars around the world. In order to make the treatment process more stable and more efficient, this work studied effects of different operating parameters on ammonia treatment and kinetic model of electrochemical degradation of ammonia to make the low concentration of ammonia wastewater reach the discharge standard, moreover, this work also studied the specific electro-activity on ammonia among three DSA electrodes.The FESEM, oxygen and chlorine evolution potential curves and linear sweep voltammetry under different pH values and electrolytes were used to compare the specific electro catalytic properties, surface morphologies and the superiority of electrodes among three DSA electrodes:the Ti/RuO2-IrO2, the Ti/IrO2-Ta2Os and the Ti/RuO2. From the experiment, the Ti/RuO2-IrO2and the Ti/RuO2electrodes were chlorine electrodes which electro-oxidized ammonia mainly through indirect electro-oxidation mechanism, moreover, the Ti/RuO2-IrO2electrode had higher oxygen evolution potential than the Ti/RuO2which could effectively reduce the incidence of side reaction, and Ti/IrO2-Ta2O5was oxygen electrode which was less suitable to remove ammonia in the wastewater containing chlorine ions. Linear sweep voltammetry tests under different pH values and different electrolytes expressed that the Ti/RuO2-IrO2electrode was little affected by the pH than the other two and well adaptability in pH changes, therefore it could electrolyze Cl" and generated active chlorine compounds efficiently. The degradation of ammonia was mainly through the indirect mechanism rather than the direct pathway with the Ti/RuO2-IrO2electrode due to the week effect of direct oxidation. The experiments also verified that the NH3-N was easier to be oxidized than the NH4+-N. Above all, the Ti/RuO2-IrO2electrode was more suitable to treat the ammonia wastewater containing chlorine ions with tiny and uniform crystals, the less cracks produced through the electrochemical process and well electrochemical stability.The experiments studied the effects of four operating parameters including the current density, the chlorine ions concentration, the initial pH and the initial ammonia concentration with the Ti/RuO2-IrO2electrode. It was found that the ammonia degradation rate growd linearly with the current density and chlorine ions concentration, but when the current density increased from16.7to20.6mA/cm2there was little difference in the ammonia oxidation efficiency, and there was also little increase in ammonia removal rate from the300mg/L to400mg/L of chlorine ions, and the ammonia was seldom removed in the wastewater without chlorine ions. The Ti/RuO2-IrO2presented a well performance in wide pH ranges. The relative differences were not large varied with different pH values, and the ammonia degradation efficiency and rate reached the peak when the pH was9to11, but at higher pH (above12), the ammonia was seldom removed. It could be conclusion that the optimal parameters of treating40mg/L ammonia wastewater were as follows:the current density16.7mA/cm2, the chlorine ions concentration300mg/L, the initial pH kept neutral or weak alkaline, which were combined with the indexes of ammonia removal efficiency, ammonia oxidation rate, energy consumption and current efficiency.The results showed that the degradation of ammonia followed pseudo zero-order kinetics and greatly related to chloride ions concentration and current density when the ammonia concentration below80mg/L aside from initial pH values which did little effect on ammonia degradation rate. The kinetic constant expressed as d[NH4+-N]/dt=0.00513[Cl-]j+0.75771.This research showed that the electrochemical oxidation technology could remove ammonia in waste water efficiently. Metals like Ir, Ru and Ta could oxidize ammonia to nitrogen effectively with excellent electro catalytic properties. The Ti/RuO2-IrO2electrode had better electro catalytic properties and well stability than the other two which laid the theoretical foundation for the industrial application of this electrode.