Degradation Of Salicylic Acid In Aqueous Solution By Micro-Electrolysis Combined With Ozonation

With the rapid development of the chemical industry,toxic substances in wastewater had a serious impact on the environment.Iron-carbon microelectrolysis has the characteristics of low running cost and simple operation.Some of the organic pollutants that are difficult to biodegrade can be decomposed into small molecules which biodegraded easily through iron-carbon microelectrolysis.Iron-carbon microelectrolysis has been widely employed for treatment of wastewater,but the degradation efficiency was not high and the speed of reaction was slow.Ozonation has been widely used in disinfection,odor removal and sterilization of drinking water because that it has advantages such as safety,high efficiency and lack of secondary pollution.However,the application of ozonation has been limited in the treatment of toxic and difficult-to-degrade organic pollutants because of its a high processing cost and selective oxidation.Studies have found that micro-electrolysis combined with ozonation can make ozone produce more·OH and other free radicals.These free radicals are more oxidizing than ozone and have no selectivity in the oxidation of organics pollutants.In addition,these free radicals can increase the efficiency of degradation in organic pollutants and mineralization of wastewater.So far,only a small amount of research has been reported due to the complexity of the micro-electrolysis combined with ozonation.Thus,we need further research to promote the industrial application of the micro-electrolysis combined with ozonation.Salicylic acid?SA?,as an important industrial raw material,is widely used and causes pollution to the environment at the same time.The reaction between SA and ozone molecules is very slow(the constant of rate is 600 L×mol^-1×s^-1),and reacts rapidly with·OH(the constant of rate is 2.2×10¹⁰ L×mol^-1×s^-1),so it is often used as determination of·OH probes.In this paper,we had studied the influencing factors,efficacy,stability,kinetics and biological toxicity of SA simulated wastewater by micro-electrolysis combined with ozonation,then we speculated the mechanism,which could be divided into five aspects as follow:?1?Degradation of SA in aqueous solution by iron-carbon micro-electrolysis,ozonation and micro-electrolysis combined with ozonation respectively showed that the effect of the micro-electrolysis combined with ozonation was significant.?2?Micro-electrolysis combined with ozonation was employed for degration of salicylic acid?SA?in aqueous solution.The primary influencing factors on the degradation rate of SA including pH conditions,initial SA concentration,ozone concentration and temperature were investigated.p H was the decisive factor influencing the degradation effect.When pH was from 4 to 11,the degradation rate was firstly increased then decreased,and the optimal condition was obtained when pH was 8.Within the range of experimental conditions,the degradation rate of SA was increased with the decrease of c₀,and the degradation rate was increased the increase of ozone concentration and temperature,but the increase is relatively small.The optimum operating parameters were determined experimentally:pH was 8,c₀ was400 mg·L^-1,ozone concentration was 17.2 mg·L^-1,and the temperature was 298 K.The degradation rate of SA was 99.93%under the optimizing condition after 30 minutes of reaction.The performance and stability of the degradation of SA were studied.Under the optimal conditions,six groups of parallel experiments were carried out.The degradation rate of SA was above 98.98%after 30 minutes of reaction,respectively.The relative standard deviation of the degradation of SA rate was 0.36%,and the degradation efficiency of SA is very stable.?3?The kinetics of the degradation of SA by micro-electrolysis combined with ozonation was investigated.The degradation of SA followed pseudo-first-order kinetics under the experimental conditions,and the kinetic model was established by power index equation:?4?The removal rate of COD was 79.34%and the toxicity characterized by the relative inhibition rate decreased from 99.68%to 23.68%under optimizing conditions after 60 min.?5?The intermediates of SA were analyzed and identified.Three intermediates were identified,and the mechanism of micro-electrolysis combined with ozonation was speculated.