Research On Wastewater Denitrification Technology Based On Three-dimensional Electrocatalysis Of Suspended Particles

In the study of wastewater denitrification,it is difficult to remove nitrate because it is easily soluble in water.When the concentration is low,the use of biological nitrification-denitrification requires an additional carbon source which increases the cost.When the concentration is high,the chemical reduction method is used.The sludge output is large,which is easy to cause secondary pollution.In the conventional electrochemical process,the electrode plate is usually seriously corroded,the denitrification product have many intermediate product,and the total nitrogen removal rate is low.In this project,surface-modified Ti/RuSn electrodes are used to continuously transform intermediate products through anodic oxidation,and particle electrodes are prepared to form a three-dimensional electrocatalytic system with a self-designed electrode reactor.Potassium nitrate is used as a pollutant to carry out research.An iron cathode with high electroreduction performance for nitrate was screened out,and a two-dimensional electrocatalytic system was formed with the screened surface-modified titanium-based Ti/RuSn anode.The removal of intermediate product ammonia is strengthened.In a 120 m L electrolytic cell,with iron as the cathode,under the static operating conditions of constant voltage 20 V,electrolysis time 2.5 h,and NaCl concentration of 833 mg/L,The removal rate of nitrate by different anodes（Ti/RuSn anode,iron anode,aluminum anode,titanium anode）are:96.07%,95.46%,94.75%,and 45.38%,respectively.The Ti/RuSn anode-Fe cathode combination has the highest total nitrogen removal rate of 69.08%,while other electrode combinations have low total nitrogen removal rate and The product is mainly ammonia,and this electrode combination has the lowest electrolysis sludge mass,which is 22.3 mg/L.The SEM characterization and surface element analysis of the Ti/RuSn anode prove that the surface of the electrode plate has wrinkles and depressions,the reaction area is large,and the surface morphology and surface element content change little after use,and it has good stability.A three-dimensional electrocatalytic system was constructed in a 120 m L electrolyzer and subjected to univariate analysis.In order to reduce energy consumption,the experiment adopts a constant voltage of 10 V and static electrolysis for 2.5 hours.Under the experimental conditions of initial nitrate nitrogen concentration of 300mg/L,NaCl concentration of 833 mg/L,and particle electrode addition amount of 41.52 g/L,The removal rates of NO₃^--N and TN were the highest,which were 75.92%and 70.08%,respectively.Compared with the two-dimensional electrocatalytic system,the three-dimensional electrocatalytic system achieved a higher total nitrogen removal rate at a lower voltage.The addition of particle electrodes further promoted the conversion of intermediate products,and at the same time verified the adaptability of the particle electrode to low concentration（30 mg/L）nitrate nitrogen wastewater.A three-dimensional electrocatalytic system was constructed in a self-designed reactor with an effective volume of 2.6 L and a single factor analysis was performed.The influence of the particle electrode dosage was re-explored.When the hydraulic retention time was 1.5h,the particle electrode dosage was 9.62 g/L,and the p H was6.98,the removal rates of NO₃^--N and TN were:91.05%and 76.85%,respectively.Compared with the two-dimensional electrocatalytic system under the same conditions,the NO₃^--N and TN removal rates were increased by 24.30%and 19.91%,respectively.The reaction results also showed that the particle electrode further enhanced the conversion of intermediate products.The particle electrodes were characterized,and the performance and mechanism of the three-dimensional electrocatalytic system were investigated.SEM characterization showed that the loading of the catalyst caused wrinkles and depressions on the surface of the plastic electrode,and a small part of the catalyst was detached after use.XRD shows that the catalyst is a bimetallic Pd-Sn catalyst composed of graphene-supported Pd,Sn,and Ru,a Ru-Sn catalyst and a Pd oxide,and the crystal structure of the catalyst changes little before and after use.The removal rate of nitrate nitrogen still reached 85.01%after the particle electrode was recycled for 6times.And it is verified that the system has good applicability to the actual wastewater.Kinetic analysis showed that the degradation process of nitrate conformed to the second-order kinetic law.Under the optimal conditions,the energy consumption of the three-dimensional electrocatalytic system for nitrate nitrogen degradation under dynamic operating conditions is calculated to be 0.062 k Wh·g^-1.The presence of hydrogen radicals and chloride ions played an important role during the reaction.