Study On Strengthing Effect Of Nitrate Reduction By Electrochemical Methods Using Organics

Groundwater plays an important role in the planet’s hydrological cycle, and it serves as an important source of drinking water in various parts of the word. However, due to the increased use of fertilizers in intensive agriculture, industrial and municipal effluent discharge,nitrate contamination in groundwater is now widespread. The worldwide pollution represents a risk on human health. For this reason, effective treatment measures should be taken to tackle the problem of nitrate contamination. Electrochemical reduction of nitrate is receiving more and more attention due to its high efficiency, low investment cost, easy operation and environmental friendliness, compared to the traditional physicochemical and biological methods. However, this electrochemical methods is limited in use due to its high energy consumption, low current efficiency and fouling problems. Thus optimization and modification of the process is needed to improve the nitrate reduction.The efficiency of nitrate reduction is maily limited by catalytic characteristics of the cathode materials, ammonia oxidation characteristics of the anode materials, the electrode spacing, the current density and the electrolyte characteristics during the process of electrochemical nitrate treatment. In this research, the cathode materials, Na Cl concentration, the current density and the electrode spacing were studied; and we obtained the optimum condition of nitrate reduction: Ti/Ir O2-Pt as anode, Cu-Zn as cathode, setting the electrode spacing at 20 mm, the current density to 20 m A/cm2, adding 0.5 g/L Na Cl and 1.5 g/L Na2SO4. In this condition, the nitrate removal efficiency could reach to 72.1% and the ammonia was nearly oxidized, what’s more, no nitrite was detected in the final treated solution in all experiments.In this study, two ways which could improve the efficiency of nitrate reduction were presented in electrolysis process:(1) Enhancing electrochemical denitrification, in which the produced hydrogen was acted as electron acceptor and the cathodic reduction was promoted;(2) Fading anodic oxidation, in which the produced hydroxyl radicals was captured by salicylic acid and the nitrate reduction was not limited by hydroxyl radicals any more. A Ti/Ir O2-Pt plate was employed as the anode and a Cu-Zn plate as the cathode in this study. Methanol or salicylic acid was added into the electrochemical cell in order to increase the hydrogen production or capture the hydroxyl radicals, respectively. In the presence of 0.0067 g/L methanol(100 mg/L COD), the nitrate decreased from 50 mg/L to 3.2 mg/L at 180 minutes. More 16.5% nitrate was reduced than the result with the absence of methanol. Moreover, the selectivity of nitrate reducing to nitrogen gas was improved with the presence of methanol. More 14.4% nitrate was reduced when 0.0316 g/L salicylic acid(20 mg/L COD) was added. Although ammonium and nitrite, the by-products, were produced during the electrolysis, neither of them was detected in the final treated solution in all experiments. Both the nitrate and the added organic compound could be removed completely in electrolysis process, which meant that the electrochemical technology presented in this study was suitable for advanced treatment of water contaminated by nitrate.