Study On The Removal Of Dissolved Nitrate In Water With Fe/C-Pd-Cu Microelectrolysis

In recent years,the use of pesticides and fertilizers in agriculture and the continuous discharge of chemical and non-chemical pollutants by industries have led to a significant decline in the proportion of potable fresh water,and the global environmental technology market for water purification and treatment has developed rapidly.Nitrate is a pollutant that widely exists in surface water and groundwater.It is of practical significance to remove soluble nitrate in water economically and efficiently.Among many processing methods,economical and easy-to-operate iron-carbon micro-electrolysis technology has gradually attracted attention.At present,due to its advantages of low treatment cost and no need for additional chemicals,iron carbon micro electrolysis technology has gradually attracted attention in the removal of nitrate in water.Nitrate is mainly removed by reduction through adsorption on the surface of activated carbon,but the adsorption performance of general activated carbon for nitrate in water is poor,and without adding catalyst.High conversion rate of ammonia nitrogen and low conversion rate of nitrogen in iron carbon micro electrolysis limits the removal effect of nitrate in micro electrolysis.In this study,reduced iron powder and shrimp shell activated biochar supported with palladium copper bimetal catalyst were used as raw materials to constitute a micro-electrolysis system.The removal effect of iron-carbon micro-electrolysis on soluble nitrate in water was studied.Zn Cl₂ was used to activate shrimp shell biochar,to increase the adsorption of nitrate by activated carbon in the micro-electrolysis system,and then promote the reduction of nitrate on its surface.The effects of process parameters such as Fe/C dosing ratio,Fe/C dosing amount,initial p H value,initial dissolved oxygen DO value,and Pd/Cu dosing ratio on the micro-electrolytic removal effect were investigated,and a palladium-copper bimetal catalyst was supported on the bioactive carbon to improve the iron-carbon micro selectivity of the electrolysis system to N₂.It was found through experiments that the activated biochar accelerated the reduction rate of nitrate concentration in the micro-electrolysis system in the early stage of the reaction,and the selectivity of N₂ was significantly increased after the addition of the bimetal catalyst,which promoted the reduction reaction of nitrate on the surface of the carbon electrode.The main results obtained from the study are as follows:（1）Shrimp shell-based biochar was activated at different temperatures and Zn Cl₂impregnation conditions.Comprehensive analysis of material characterization proved the successful activation of Zn Cl₂ shrimp shell biochar.After activation,the specific surface area and pore volume of biochar increased significantly,reaching a maximum of 1506.5m2·g^-1 and 0.8331cm³·g^-1;the surface of activated biochar was changed from uneven to smooth with pores by SEM;Infrared spectroscopy found that the treatment of shrimp shells at 400℃increased the calcium carbonate content greatly,and after the second high temperature activation,CO₃^2-was converted into C=O in lipids and CO in alcohols;XRD analysis showed that A large amount of Ca CO₃ existing in the original shrimp shell was transformed into Ca O after a high temperature treatment and then completely decomposed.（2）The activation of shrimp shell biochar by activator Zn Cl₂ can increase its adsorption capacity for nitrate in water.Shrimp shell-based bioactive carbon at different impregnation ratios and activation temperatures showed different nitrate adsorption capabilities.The best adsorption effect was C-400-2,that is,the activation temperature was 400℃,and the impregnation ratio was Zn Cl₂:C=2:1.Under this activation condition,the unit adsorption of biochar can reach 5.09 mg·g^-1.The adsorption kinetics of shrimp shell-based bioactive carbon on nitrate in water meets the quasi-first-order adsorption kinetics and quasi-second-order adsorption kinetics,and the quasi-first-order fitting effect is more suitable.（3）The removal rate of nitrate in water by the micro-electrolysis system composed of reduced iron powder and ordinary activated carbon is greater than the sum of the separate removal rates of reduced iron powder and shrimp shell biological activated carbon for nitrate,which proves that the iron-carbon micro-electrolysis reaction system was successfully constructed.And at Fe/C=3:1,the dosage is 10g·L^-1,initial NO₃^-concentration is 20 mg·L^-1,DO<0.5mg·L^-1,initial p H is neutral,temperature under the experimental conditions of 25℃,the nitrate concentration in the water decreased from20mg·L^-1 to 2.2 mg·L^-1 after 350min reaction,and the removal rate was 89%.The change of nitrate concentration during the reaction accorded with the quasi-first-order adsorption kinetic model.（4）The Fe/C-Pd-Cu microelectrolysis system consisting of shrimp shell-based bioactive carbon and reduced iron powder supporting Pd-Cu bimetal catalyst has a higher removal rate of nitrate in water than the microelectrolysis system consisting of unsupported catalyst bioactive carbon and reduced iron powder.It is significantly reduced and the selectivity of N₂ is greatly improved,which proves that the palladium-copper bimetallic catalyst promotes the conversion of nitrate nitrogen to nitrogen.At p H neutral,DO<0.5mg·L^-1,Fe/C dosing ratio is 3:1,dosing amount is 10g·L^-1,and Pd-Cu loading ratio is 2:1.The micro-electrolysis system composed of reduced iron powder can remove nitrate up to 100%and the N₂ conversion rate is 86.67%.The micro-electrolysis system is less affected by the concentration of dissolved oxygen in water,but the coexisting anions still have a greater impact on the removal rate.