The Study Of Sulfate-radical Based Advanced Oxidation Processes For The Degradation Of Typical Organic Compounds

Chloroanilines such as aniline and p-chloroaniline （PCA） are common water pollutantswhich are widely used in many industries such as dye manufacturing, pesticides, rubberchemicals, antioxidants, pharmaceuticals, pesticides and herbicides. PCA and aniline areconsidered to be toxic and carcinogenic to animals and human beings. These hazardousproperties of PCA and aniline require the treatment of contaminated wastewater to preventany deleterious effect to the environment.Advanced oxidation processes based on the generation of sulfate radicals （SO₄^-） is oneof the most effective ways to remove the nonbiodegradable organic pollutants. Due to its highoxidation ability, SO₄^-is getting more and more attention for the treatment of wastewater.Persulfate activation is a promised technique to produce SO₄^-due to the simplicity of methodand mildness of reaction conditions. In this study zero valent iron （ZVI） was used to activatepersulfate for the degradation of PCA and aniline in wastewater. Zero valent iron （ZVI） canactivate persulfate to generate sulfate free radicals which are a strongest oxidant to degradeorganic pollutantsThe degradation of p-chloroaniline （PCA） by persulfate (S₂O₈^2-) activated with zero-valent iron （ZVI） was investigated through batch experiments. Effects of pH, temperature anddosages of ZVI on PCA degradation were also examined. The degradation of PCA increasedwith higher dosage of ZVI due to increased activation of persulfate by zero-valent iron whichgenerates strong oxidizing species （sulfate radicals） in aqueous solution. The PCAdegradation was higher under acidic conditions （pH2.0and4.0） when compared to alkalineconditions. Complete degradation of PCA was obtained by ZVI-activated persulfate at pH4.0in12minutes. PCA mineralization was significant, where69%TOC removal efficiency wasachieved within30min. TOC removal efficiency increased with increasing time, so that94%TOC was removed after3h reaction time at pH4.0. An increase in reaction temperature from15to50℃significantly enhanced the PCA degradation. The aniline, N-（4-chlorophenyl）-p-phenylene di-imine,1-（4-chlorophenyl）-3-phenylurea and5-chloro-2-（4-chlorophenyl diazenyl） phenol were identified as the major intermediates of PCA oxidationby persulfateThe oxidative degradation of aniline in aqueous solution by persulfate activated withzero valent iron was studied under laboratory conditions. Batch experiments were conductedto investigate the effects of different parameters such as pH, ZVI concentration, aniline concentration, persulfate concentration and reaction temperature on aniline degradation. Theresults showed that aniline degradation increased with increasing temperature. The optimumdosage of ZVI was0.4g/L, and85%aniline degradation was observed. Maximum anilinedegradation was observed at pH4.0, whereas at pH above or below4.0, aniline degradationefficiency was decreased. In persulfate-ZVI system, the apparent energy of activation foraniline degradation was14.85kJ mol^-1. The existence of persulfate radicals and hydroxylradicals produced during the degradation of aniline were identified with scavenger ethanoland tert-butyl alcohol. The reaction intermediates nitrobenzene, nitroso-benzene and p-benzoquinone were detected by gas chromatography–mass spectrometry. Based on theseintermediates observed a probable pathway of aniline degradation has been proposed.