Research On Removal Of Nitrogenous Contaminants In Wastewater By Electrochemical Catalytic Oxidation

With the fast development of social economy, industrial production of nitrogenous contaminants discharged into water was increasing. The concentration of NH3-N and TN in effluent was hard to meet the discharge standards by regular biochemical technology. Meanwhile, some industrial wastewater with high NH3-N concentration, poor biodegradability and high salt which easily lead to secondary pollution treated by the conventional ammonia-stripping technology. (NH4)2SO4 as a by-product is very difficult to sell as chemical intermediate product which is. Electrochemical catalytic oxidation with its high efficiency and without secondary pollution had the incomparable advantage other wastewater treatment processes.In this paper, electrochemical catalytic oxidation technology was studied. The electrode characteristic was analyzed. The influence mechanism of wastewater of low NH3-N was studied which was treated by electro-catalytic oxidation technology. Meanwhile, the degradation mechanism of NH3-N was explored, the optimum operating parameters were obtained and the BAF effluent was treated by electro-catalytic oxidation technology. Furthermore, the influence mechanism of wastewater with high NH3-N was studied which was treated by electro-catalytic oxidation technology. The optimum operating parameters were obtained and the high salty, high copper-ammonia complex wastewater water was treated by electrolytic oxidation technology. The influence mechanism of electro-catalytic oxidation in the degradation of DMA was studied and the degradation mechanism of DMA was explored.The SEM and EDX graph of electrode showed that the electrode was stable and its surface with few cracks. The Ti/TiO2-RuO2 anode had high oxygen evolution overpotential and low chlorine evolution overpotential. The existed Tafel region of electrode indicated that oxygen evolution reaction and chlorine evolution reaction of electrodes were controlled by the electrochemical polarization function.The optimum operating parameters of wastewater with low concentration of NH3-N treated by the electrochemical oxidation technology was:the removal rate of NH3-N reached 100% when the NH3-N concentration of 300mg/L, the current density of 20 mA/cm2, the initial Cl- of 5000 mg/L, the plate separation of 1 cm, the initial pH of 10 and electrolysis time of 50 min; the degradation of NH3-N mainly controlled by indirect oxidation of anode, it was oxidized to HClO at the anode and NH3-N can be oxidated by HClO to N2 when the solution contained Cl-. The BAF effluent from wastewater of chemical engineering was treated by the electrochemical oxidation technology under the optimum operating parameters, and the results showed that the removal rate of NH3-N reached 100% and TN of 20 mg/L, under the electrolysis times of 45 min, wastewater can be effectively degraded to meet the discharged standard, the energy consumption is 48 KW·h/Kg(NH3-N).The optimum operating parameters of wastewater with high concentration of NH3-N treated by electrochemical oxidation technology was:the removal rate of NH3-N reached 100% when the current density of 35 mA/cm, the initial Cl-of 30000 mg/L, the plate separation of 3 cm, pH during the electrolysis process was adjusted to 8, electrolysis time of 3.5 h. The high salty and high copper-ammonia complex wastewater was treated by electrolytic technology, the results showed that electrolysis time of 8h, the removal rate of NH3-N reached 45%, the removal rate of CODCr reached 25%, the Cu2+ could be removed from the wastewater by plated at the cathode, the energy consumption of 19 KW·h/Kg(NH3-N);in the further treatment, pH during the electrolysis process was adjusted to stable 8, electrolysis time of 7h, NH3-N was completely degraded, the removal rate of CODCr reached 48% up to the local discharged standard, the energy consumption is 32 KW·h/Kg(NH3-N).The optimum operating parameters of wastewater with DMA treated by the electrochemical oxidation technology was the current density of 15 mA/cm2, the Cl- of 2000 mg/L, electrolysis time of 75min, the removal rate of TKN reached 93%, the removal rate of TOC reached 75%. The degradation of DMA mainly controled by indirect oxidation of anode, it was oxidized to HClO at the anode and DMA can be oxidated by HClO to N2, HCOOH, CO2 when the solution contained Cl-.In terms of low nitrogen concentration wastewater for advanced treatment and high ammonia concentration wastewater with high salt for pretreatment, the eletrochemical catalytic oxidation technology had obvious advantage.