The O <sub> 3 </ Sub> / H <sub> 2 </ Sub> O <sub> 2 </ Sub> System For Removal Of High-stability Organic

Advanced oxidation processes have been the subject of many studies in recent yearsin view of their potential ability to produce HO·radical, which enhances thedegradation of organic pollutants in water. Therefore we choose O₃/H₂O₂ process toinvestigate the removal of some aromatic compounds from the water. We studied theremoval efficiency of O₃/H₂O₂ process toward 3-chlorophenol, nitrobenzene and2,4-dichlorophenoxy acetic acid. TOC removal was investigated in this research as well.We also studied the effect of the molar ratio of hydrogen peroxide and ozone, pH value,temperature and water background on the oxidation process. We analyzed thedegradation products through GC-MS and LC-MS and confirmed the presence of somedegradation intermediates in the oxidation process. Based on above the possibledegradation pathways were also proposed for these compounds.It was found that the presence of hydrogen peroxide highly enhanced the removal ofall three compounds by ozone. The proper H₂O₂/O₃ molar ratio was related with thecorresponding chemical structure. The experimental results showed that the solutionTOC could be removed efficiently by O₃/H₂O₂ process compared with ozone alone. Andthe ozonation of 2,4-dichlorophenoxyacetic acid was found to follow apseudo-first-order kinetic. A model was proposed to predict the preudo-first-order rateconstants of the decay of 2,4-dichlorophenoxyacetic acid.With the increasing of pH value, the removal efficiency of the compounds alsoincreased in O₃/H₂O₂ process. However, very high pH value could inhibit the oxidationreaction. Tert-butanol, a typical free radical inhibitor, significantly decreased theremoval rate of all three compounds. However, HCO₃^-, a usually found inhibitor innatural waters, could enhance O₃/H₂O₂ process and inhibit O₃ process. It was also foundthat the presence of HA at certain concentration enhanced the removal of the organicsfrom the water. While overdose of HA decreased the efficiency of the O₃/H₂O₂ oxidationprocess. Some metal ions in the water such as sodium/potassium/magnesia/calcium/copper/zinic/aluminium ions have no influcnce toward the removal of theorganic from the water under this experiment condition. Other metal ions such as cobalt/nickel/cadmium/chromium/iron/maganese ions could enhance the removal of theorganic from the water when they are in proper concentration. Iron(â…¡,â…¢) andmanganese(â…¢) ions exhibited better catalytic activity toward ozonation. And Iron(â…¢)and manganese(â…¢) ions could also enhance the TOC removal of three compounds. Itwas found that the pH value of 3-chlorophenol and 2,4-dichlorophenoxyacetic acidsolution decreased greatly after catalyzed ozonation. It was proposed that hydrochloricacid may form during the 3-chlorophenol and 2,4-dichlorophenoxyacetic acid oxidationprocess by hydroxyl radical. The corresponding mechanism was also proposed.It was also found that high pH value of solution enhanced the ozone transferredefficiency. And at the same time, ozone and hydrogen peroxide resiudal in the waterdecreased. The cobalt/nickel/cadmium/chromium/iron/maganese ions which couldcatalyze ozonation were also found to have similar effect. Through GC-MS and LC-MSanalysis we analyzed both the degradation intermediates and final products of3-chlorophenol, nitrobenzene and 2,4-dichlorophenoxyacetic acid by O₃/H₂O₂ oxidationprocess. It was concluded that the benzene ring could only be broken through apolyhydroxy benzene process although different substitution group attached to benzenering.