Ozone Oxidation And Enhanced Biodegradability For Chloronitrobenzenes Wastewater

Chloronitrobenzenes(ClNBs),as a large class of aromatic compounds that contain chloro- and nitro- groups,are widely used as intermediates for the chemical synthesis of medicines,dyes and pesticides,and are also declared to be the priority persistent toxic and difficult degraded organic pollutants by the EPA of USA,EEC and China.Due to their mass production and uses for a long time,many rivers,lakes,farmlands and even groundwater in China have been polluted at different levels,which becomes a serious threaten to human health and water environment.Therefore,it is of impendence to develop highly-efficient and cost-effective innovative processes for wastewaer treatment and pollution remediation.Ozonation,catalytic ozonation of ClNBs and catalytic ozonation-biological coupling for the treatment of high concentrations of ClNBs-producing wastewater were investigated in this thesis,and the main results are as follows:1.Selecting ortho-,recta- and para-chloronitrobenzene(respectively denoted o-ClNB, m-ClNB and p-ClNB) as the model pollutants,the steady-state kinetics and mechanism of the degrdation of the pollutants in aqueous solution by ozone alone were investigated. Through studying the effect of pH and gas flowrate on mass transfer coefficient of ozone, steady-state conditions of ClNBs ozonation were determined.Afterwards,the effect of initial pollutant concentration,pH and radical scavenger(tertiary butyl alcohol,TBA) on ClNBs removal were investigated.Results demonstrated that the decomposition of ClNBs was a pseudo-first-order reaction with respect to the pollutant concentration and overall rate constant increased with an increase in the pH,however declined with an increase in the pollutant and radical scavenger concentration.Removal rate of ClNBs followed the order of o-ClNB＜m-ClNB＜p-ClNB,stoichiometric ratios of ozone and ClNBs were 1.0, reaction constants of o-ClNB,m-ClNB and p-ClNB reacting directly with ozone were 6.342×10^-3,3.890×10^-2 and 6.442×10^-2 L·mol^-1·s^-1,respectively.The reaction rate constants of o-ClNB,m-ClNB and p-ClNB with·OH,measured by means of a competition kinetics,were 2.037×10⁹,2.398×10⁹ and 3.869×10⁹ L·mol^-1·s^-1,respectively. More than 95%of ClNBs removal in ozonation system was due to hydroxyl radical oxidation at pH≥7.Results of GC-MS,LC or LC-MS show that main intermediate products of ClNBs were aromatic phenolic substances and nonaromatic acyclic substances.In the ozonation process of p-ClNB,-Cl and -NO₂ could be replaced by·OH,chlorophenol and nitrophenol were formed meanwhile.But in the ozonation process of o-ClNB and m-ClNB,neither nitrophenol nor chlorophenol was detected.The hydrogen on the phenyl of all these three ClNBs could be replaced by·OH,thus nitrochlorophenol was produced. The difference of the substitutional place of-Cl or -NO₂ on the phenyl could lead to the difference of the electron cloud density of carbon,the probability of the reaction between·OH and the hydrogen on the phenyl has some relationship with electron cloud density of carbon.The reaction between·OH and ClNBs is probably similar to the electrophilic substitution reactions of aryl.2.Efficiency and possible mechanism of homogeneous catalytic ozonation of ClNBs in aqueous solution by seven kinds of metallic ions and their combinations were compared, it was focus on the effects of pH,catalyst dosage and radical scavenger in above-mentioned system.Ozone consumption in terms of pollutant degradation and TOC elimination was also compared under the same operating conditions.Experimental results indicated that these single metallic ion and metal combinations can accelerate the rates of ClNBs removal and TOC elimination.In single metallic ion systems,increasing the catalyst concentration increased the removal rate of ClNBs;However,further increasing the catalyst concentration caused no further significant increase.When 0.4 mM catalyst was added,the effective factors at pH 2.0 followed the order Co²⁺＞V⁴⁺＞Fe²⁺＞Fe³⁺＞Zn²⁺＞Ni²⁺＞Mn²⁺ and those at pH 5.0 followed the order Co²⁺＞Ni²⁺＞Zn²⁺＞V⁴⁺＞Mn²⁺＞Fe³⁺＞Fe²⁺,suggesting that catalytic ozonation was strongly influenced by reaction media pH.In metal combination systems,the coexistence of Mn²⁺ and V⁴⁺ reduced the removal of CINBs.Considering ozone consumption during ozonation,O₃/Mn²⁺-Co²⁺ system showed the highest removal efficiency.The negative effect of the radical scavenger on the catalytic ozonation processes suggests that the degradation reaction in catalytic ozonation systems proceeds by mainly radical-type mechanisms.3.Diatomite supported MnO_x-CoO_x catalysts were prepared by the incipient impregnation method,its activity was investigated through catalytic degradation of nitrobenzene(NB) and p-ClNB by simultaneous use of it and ozone.The catalyst was characterized by SEM,XRD,FTIR and XPS.Results demonstrated that the effects of molar ratio of active components,roast temperature and time are significant;At the same time,FTIR analysis indicated that the supported metals mainly existed as multivalence mixtures and the abundant surface hydroxyl led to high dispersion of MnO_x-CoO_x; Combination of XRD and XPS analyses indicated that the supported metals were present on catalyst surface as forms of well dispersed divalent,trivalent and tetravalent oxides; The study of performance and mechanism of catalytic ozonation of NB and p-ClNB by diatomite supported bimetallic catalysts showed that addition of 1 g/L catalyst accelerated pollutants removal,especially TOC removal,enhanced TOC increments in case of pH 3.0 and pH 7.0 were 46-57%and 35-40%,respectively.Further study observed that catalytic ozonation accelerated formation of intermediate phenolic aromatics,Cl^-,NO₃^- and oxidation of acetic acid and oxalic acid,low concentrations of H₂O₂ was generated in reaction system meantime;TBA addition distinctly inhibited the proceeding of oxidation reaction,EPR experiments also showed that the existence of·OH in catalytic ozonation process,and the concentration of·OH is much higer than that in ozone alone,which is possible reason why there was enhanced pollutants removal and mineralization in catalytic system.Based on experimental results,a synergistic menchanism of catalytic ozonation was presented.4.Integrative Mn-Co modified porous diatomaceous ceramic filling catalysts were prepared,the degradation performance of production wastewater in three different processes(ozonation + unmodified porous filling,ozonation alone and catalytic ozonation) was compared.The results showed that the COD and TOC removal rates in the production wastewater through ozonation were improved by employing porous filling and Mn/Co modified porous filling,the increments in TOC and COD removal were respective 2-11%and 2.5-24%for the former while the ones for the latter were 35%and 38%, respectively.The highest increase in TOC and COD removal efficiency was achieved in the presence of ozonation/Mn-Co modified porous filling and the modification process can improve the catalytic activity of porous filling for ozonation of the production wastewater.Afetr 2 h catalytic ozonation treatment,the color of the wastewater was almost removed,the biodegradability was significantly enhanced(BOD₅/COD increased from 0.02 to 0.5 or so) and the acute toxicity inhibition on photobacteria decreased by about 25 times.From this point of view,the coupling of catalytic ozonation with sequential biological treatment processes proved quite promising.5.Single biological and a combined catalytic ozonation process(COP) / biological treatment were evaluated for the treatment of production wastewater containing toxic and refractory chlorinated nitroaromatic compounds(CNACs).The results demonstrated that single biological treatment could remove main pollutants present in production wastewater,however,due to its poor performance in color,ammonia,TOC and COD removal,the treated effluent still did not satisfy the soecific discharge standard.COP with Mn/Co modified ceramic catalysts can be successfully used as a pre-treatment process to biocompatibilize the wastewater.With prolonged reaction time,the wastewater became decolorized and more biodegradable,as well as reaching a higher oxidation state. Moreover,the catalyst preserved its catalytic properties after 70 times of reuse,displaying good durability and stability.An integrated treatment system consisting of 1 h catalytic ozonation and subsequent 10 h biological treatment was investigated and the performance of the system was measured for 30 days.The results showed that under conditons of influent COD concentrations of 2840-3120 mg/L,average effluent concentrations of NH₃-N,COD,BOD₅,TOC and color were 10 mg/L,128 mg/L,27.5 mg/L,25.0 mg/L and 20-multiple,respectively,with corresponding average removal efficiencies are about 80%, 95.8%,93.8%,97.6%and 99.3%,respectively.It is thus concluded that the integrated catalytic ozonation/biological process is a promising and economically viable technology for the treatment of production wastewater containing recalcitrant CNACs.