A Study On Ozone Post-treatment Of Chloronitrobenzene Manufacture Wastewater From Changshan Chemical Plant

Chloronitrobenzenes, as important building blocks for synthesis of industrial chemicals, are quite recalcitrant and toxic. They have been declared to be the priority persistent toxic substances(PTS) by the EPA of USA, EEC and China, and great interest is taken in the remediation technique. Chloronitrobenzenes are mainly produced in China and then supplid to the world. Chloronitrobenzene manufacture wastewater is generally treated by a pretreatment combined with biological treatment process. Performances of wastewater treatment system of Changshan Chemical Plant, one of the main chloronitrobenzene manufacturers, during the year 2004 and 2005 were evaluated. In order to decolorize the effluent of the wasterwater treatment system, ozone was applied for a post-treatment of the industrial effluent. Besides, removal of p-chloronitrobenzene and p-nitrophenol, the main pollutants of the wastewater by ozone was also investigated. The following results were achieved.1. Fe/C-A/O process was employed to treat chloronitrobenzene manufacture wasterwater from Changshan Chemical Plant. Operating results during the year of 2004 and 2005 indicated that this treatment system exhibited well performance for high concentrations of organic pollutants removal, and strong toelrance against fluctuating loadings. The results demonstrated that effluent quality from integrated process could meet the second standard of GB8978-96 with a removal effiency of 91.35% COD, 96.38% nitrobenzenes and 98.75% anilines. The main problem was that the effluent of the wastewater treatment system was still fairly colored.2. Rate constants of reaction of ozone with p-nitrophenol was found to increase with increasing solution pH.and ozone dosage but decrease with increasing the p-nitrophenol initial concentration. Temperature and radical scavenger has little effect on p-nitrophenol degradation. Direct ozone oxidization was predominant to indirect radical oxidation reaction during the degradation process of p-nitrophenol. Rate constants of reaction of ozone with p-chloronitrobenzene also increased withincreasing solution pH.and ozone dosage but decrease with increasing the p-chloronitrobenzene initial concentration.But indirect oxidization of radical was predominant to direct oxidation reaction during the degradation process of p-chloronitrobenzene. The difference of the reaction mechanism was probably due to the difference between the dissociation property of two reactants.3.Color could be efficiently removed by ozone as a result of the decomposition of main pollutants in effluent from Fe/C-A/O process of Chanshan Chemical Plant. Effluent quality could be improved by increasing ozone dosage and hydraulic retention time. Comparing with other ozonized decolorization reactors, the counterflow packed column reactor presented the best decolorization performances. Complete decolorization was achieved at ozone dosage of 100 mg/min and hydraulic retention time of 4 minutes with a removal efficiency of 89.3%. Operation cost for effluent decolorization was about 0.6 ~ 0.8 RMB/t wastewater. These results demonstrated that ozonized decolorization process exhibite the potential of full-scale application.