Research On Electrocatalytic Degradation Of Phenol-containing Wastewater In Coal Chemical Industry By Modified SnO₂ Electrod

The coal chemical industry produces a large number of toxic,harmful and inbiodegradable pollutants every year,which will seriously damage the ecological environment even human health if discharged without treatment.At present,China has raised the environmental protection requirements and sewage discharge standards,consequently the traditional biochemical treatment of coal chemical wastewater cannot meet criteria.Electrochemical oxidation technology is very suitable for the upgrading of wastewater system because of its advantages such as no need to add chemicals,no secondary pollution,mild reaction conditions and high degree of automation.It can deeply treat biochemical tail water and meet the zero discharge and reuse standard of wastewater.The electrochemical degradation of ammonia nitrogen and COD in wastewater by modified SnO₂ electrode(ESIX-SnO₂)was carried out to achieve zero waste water discharge.The electrochemical properties of ESIX-SnO₂electrode and Ti/SnO₂ electrode were compared,and the effects of current density,initial pH and initial Cl^-concentration of wastewater on the electrocatalytic degradation of ammonia nitrogen and COD in wastewater were investigated.The results showed that the grain size of ESIX-SnO₂ electrode decreased,the oxygen evolution potential and accelerating life were significantly improved,and the electrode surface roughness,total voltammetry charge and outer voltammetry charge were also significantly improved.In the actual catalytic oxidation process,more hydroxyl radicals with strong oxidability were generated on the surface of the ESIX-SnO₂,which can rapidly oxidize ammonia nitrogen and organic matter,achieved rapid and harmless removal of pollutants.Under the best conditions(current density 30 mA·cm^-2,initial pH=11,and initial Cl^-concentration is 600 mg·L^-1),the removal rates of ammonia nitrogen and COD were 100%and 90%respectively after 30 min of electrolysis of ESIX-SnO₂ electrode,and the effluent quality meets the first-level standard of DB14/1928-2019 of Shanxi Province.In order to further investigate the mechanism of organic degradation in coal chemical wastewater,ESIX-SnO₂-Sb electrode was used to electrochemically oxidize phenol in simulated wastewater.The effects of the initial concentration of phenol and electrolyte,current density on the degradation efficiency of phenol were investigated.In addition,the effect of pulse frequency and duty cycle ratio on electrocatalytic degradation and the degradation mechanism of phenol were analyzed.The experimental results show that the removal rate of phenol decreases with the increase of initial concentration of phenol,and the degradation of phenol can be promoted with the increase of NaCl concentration and current density of electrolyte.The removal rate(98.3%)of phenol degradation by pulse power supply is higher than that of direct current power supply.In addition,pulse mode has low energy consumption and high current efficiency.Active chlorine was found to play a major role in the degradation of phenol,and benzoquinone intermediates were produced during the degradation of phenol.ESIX-SnO₂ electrode electrocatalyzes the degradation of coal chemical wastewater,realizing the rapid and efficient removal of pollutants.The effluent quality meets the first-level discharge standard.It has great application potential in realizing zero discharge and reuse of wastewater.In addition,in the electrocatalytic degradation experiment of phenol,the pulsed power supply can improve the pollutant removal rate and current efficiency,and reduce energy consumption.It is also found that active chlorine plays a major role in the removal of pollutants in the chloride ion system.This experiment has guiding significance for the industrialization application of electrocatalytic technology.