Study On The Treatment Of Nitrobenzene Wastewater By Microelectrolysis-Catalytic Ozonation-biodegradation

Nitrobenzene compounds, an important chemical material, is widely used in the area of dyestuff and pharmacy, etc. With the development of chemical industry, nitrobenzene has entered people’s living environment. Nitrobenzene has its nature of high toxicity, chemical stability, difficulty to biodegradation, and long-term maintenance of pollution in water, etc. Therefore, the investigation of treatment technology on nitrobenzene wastewater is very urgent and necessary. This paper aimed to study the degradation effect of nitrobenzene wastewater treatment combining pretreatment with biochemical technology. With a series of experimental researches carried out, the route and appropriate conditions of process for nitrobenzene wastewater treatment were preliminarily proved, which would provide theory basis and practical guidance for practical engineering design and application.During the investigation for nitrobenzene wastewater by microelectrolysis reduction, it was found that the microelectrolysis packing of Fe/C was better than that of Fe/Cu on the degradation effect for nitrobenzene wastewater. After the pretreatment of Fe/C microelectrolysis, more than92%nitrobenzene was reduced to aniline, which made the treatment of nitrobenzene wastewater transform into that of aniline wastewater. Through the single factor variable experiment, the optimum conditions were found for the reaction of microelectrolysis:the volume ratio of Fe/C was1.5:1; the particle size of packing was6mm; the pH of influent was3.0; the influent flow was250mL-min-1; the influent load was designed for300mg·L-1.MnO2-CuO-CeO2/zeolite compound supported catalyst was prepared. Under its effect, the treatment efficiency of aniline wastewater was obvious by ozonation. The removal efficiency of aniline reached90%, and that of COD was over45%, which made aniline wastewater transform into organic wastewater containing a lot of organic acid, and greatly enhanced the biodegradability of wastewater. Through the single factor variable experiment, the best conditions were found for the process:the dosing quantity of catalyst was5g·L-1; the particle size of catalyst was3mm; the ozone flow was16mg·min-1; the pH of influent was7.0; the influent load was200mg-L"1.To further study degradation mechanism of aniline by catalytic ozonation, the degradation efficiency of aniline by ozonation alone was compared with catalytic ozonation. The results indicated that the catalyst of MnO2-CuO-CeO2/zeolite could effectively improve the degradation rate of aniline by ozonation, that the removal efficiency of aniline increased from75%to89%after20min when original aniline concentration was200mg·L-1; At last, COD respectively kept stable at261.87mg·L-1230.63mg·L-1by ozonation alone and catalytic ozonation when original COD of aniline wastewater was490.12mg·L-1; The catalyst of MnO2-CuO-CeO2/zeolite could shorten the time by ozonation alone from150min to90min. Two oxidation processes presented a series of changes of colors: colorless-brown-tan-brown-yellow-colorless, and pH decreased from7.03to2.00.The degradation pathway of aniline in the effect of ozonation was learned, and four new metabolites were detected by LC-MS. P-benzoquinonimine、p-benzoquinone、maleic acid and oxalic acid were successfully detected and identified based on mass spectrum analysis and transformation between metabolite accumulation. A chemical degradation pathway of aniline was proposed, aniline firstly was decomposed into p-benzoquinonimine, then p-benzoquinonimine hydrolyzed and was oxidized into p-benzoquinone, further p-benzoquinone was oxidized and decomposed as maleic acid, and maleic acid was degraded into oxalic acid, last partial organics were mineralized to CO2and H2O.With the pretreatment of Fe/C microelectrolysis and catalytic ozonation, nitrobenzene wastewater was transformed into organic wastewater containing a lot of organic acid, and various indexes had not met the Sewage Comprehensive Discharge Standard. SBR system was used in the further biological treatment for nitrobenzene wastewater which was pretreated, which achieved the final treatment goal of nitrobenzene wastewater. In the research, it was found that the effect of SBR system running was best when the pH of influent was7.0; the best hydraulic retention time of process system was24h, containing0.5h of influent,22h of reaction,1h of precipitation,0.5h of effluent; At the same time, the highest influent load that SBR biochemical system could endure was850mg·L-1of COD.