Electrochemical Enhancement And Degradation Mechanism Of Pyridine Contaminated Wastewater

With the acceleration of the global industrialization process,the discharged industrial organic wastewater has caused serious pollution to the environment.Among them,the pyridine-containing wastewater is a great threat to the ecological environment and human health due to its"three-induced"?carcinogenic,teratogenic and mutagenic?characteristics.Electrochemical method has the advantages of high removal efficiency,simple processing equipment,and environmental friendliness,which has received wide attention.However,the traditional electrochemical techniques have the disadvantages of high energy consumption and low current efficiency.Therefore,it is very necessary to optimize the traditional electrochemical system to overcome the above-mentioned shortcomings.The objective of this study was to establish an iron net-enhanced electrochemical system to treat pyridine-containing wastewater.By altering the current density and other influence factors,the optimal operating conditions and the influence of each factor on the treatment effect were obtained.The response surface methodology?RSM?was conducted to optimize the current density,plate distance and NaCl concentration,and the mechanism of the reaction process was investigated under optimal operating conditions.The results showed that:?1?After the enhancement,the removal efficiency of pyridine increased by 11.3%,while the energy consumption decreased by 14.2%.?2?A removal efficiency of 90.2%for pyridine was obtained after 240 min electrolysis under the conditions of pyridine concentration 100 mg/L,current density 100 mA/cm²,electrolyte?NaCl?concentration 10.0 g/L,and plate distance 3 cm.?3?Using the Ti/RuO₂ as anode had a better removal effect.With the increased current density,the plate distance and NaCl concentration were conducive to the degradation of pyridine.Lower initial pH and pyridine concentration of the solution would increase the removal efficiency of pyridine.Co-existing ions NO₃^-,SO₄^2-,HCO₃^-and F^-in water had the inhibitory effect on pyridine removal.?4?The optimum operating conditions were obtained by RSM to degrade pyridine in this electrochemical system,which were 99.45 mA/cm² of current density,3 cm of plate distance,and 8.78 g/L of NaCl concentration,respectively.The removal efficiency of pyridine could achieve 98.15%.?5?Through the detection of reactive oxidizing substances in the system,it was proved that both·OH and effective chlorine were present,and the content of effective chlorine greatly exceeded than·OH.High performance liquid chromatography?HPLC?showed that pyridine had a ring-opening reaction and was degraded into small molecules of organic acid.?6?Fumaric acid,maleic acid,formic acid,and malonic acid have been identified as the major intermediate products in the pyridine degradation process and NO₂^-/NO₃^-were also detected in aqueous solution.Based on these,It was deduced that the possible degradation pathway of pyridine was due to the mineralization of pyridine with a small amount of·OH adsorbed on the surface of the plate.Simultaneously,the pyridine in the solution reacts with Cl₂,HClO,and ClO₂^-and opens at the C-N bond of pyridine to form a small organic acid.The organic acid of the molecule,in this process,pyridine nitrogen forms NO₂^-/NO₃^-and is reduced to N₂ by the action of metallic iron,and the intermediate product is further mineralized into CO₂ and H₂O.