The Influence Mechanism Of Sludge Flocs On The Catalytic Ozonation Process And The Study Of The Nano-catalytic System

The petrochemical industry is a pillar industry of the national economy.However,the petrochemical industry will produce a large amount of petrochemical wastewater with a high concentration of organic pollutants,strong toxicity,and large fluctuations in water quality and quantity,so there are potential risks to the ecological environment.Biological treatment is the most widely used wastewater technology in petrochemical wastewater treatment,but the biochemical effluent of petrochemical wastewater usually contains a large amount of refractory organic pollutants,which cannot meet the relevant discharge standards.The catalytic ozonation process is one of the most widely used advanced treatment technologies,but the traditional catalytic ozonation technology has the problem of low efficiency.Therefore,this thesis takes the biochemical effluent of comprehensive wastewater in the petrochemical industrial park as the research object,then systematically analyzes the water quality,and studies the influence mechanism of sludge flocs from the secondary sedimentation tank on the traditional catalytic ozonation system.And based on the preparation of high-efficiency nano-catalysts and the construction of nano-catalytic systems,the pollutant removal effect during the treatment process,the change of wastewater toxicity and the degradation path of characteristic organic pollutants are explored,aiming to provide theoretical support for the process improvement of advanced oxidation technology for advanced treatment of petrochemical wastewater.The main research contents and conclusions are as follows:（1）Analysis of the water quality characteristics of the secondary effluent of petrochemical wastewater.The water quality and sludge floc characteristics of the secondary effluent of petrochemical wastewater were analyzed through routine water quality index testing,organic matter hydrophilicity and hydrophobicity analysis,organic molecular weight classification test,three-dimensional fluorescence test,and electron microscope detection.The test results show that the B/C value of the biochemical effluent of petrochemical wastewater is only 0.05,and the COD is about 85.7±25.5 mg/L.The water quality fluctuates greatly and cannot meet the standard stably for a long time.The characteristic organic compounds in the secondary effluent of petrochemical wastewater are mostly alkane compounds,benzene compounds,and ester compounds.The order of the content of hydrophilic and hydrophobic organic matter from high to low is hydrophilic neutral organic matter（Hi N）>hydrophobic acidic organic matter（Ho A）>hydrophilic basic organic matter（Hi B）>hydrophobic basic organic matter（Ho B）>hydrophobic neutral organic matter（Ho N）>hydrophilic acidic organics（Hi A）.By ultrafiltration membrane fractionation,it was found that about 77%of the organic matter had an apparent molecular weight less than 1 k Da.The fluorescence peaks of organics present four main components:component 1（Ex/Em=280/350 nm）is tryptophan or proteoids,component 2（Ex/Em=330/410 nm）and component 3（Ex/Em=370/450 nm）is humic substances,and component 4（Ex/Em=270/380 nm,270/280 nm）is aromatic proteins.The morphology of the sludge flocs was observed using a fluorescence electron microscope,and it was found that the sludge flocs had a loose structure and small flocs,and the biological phase of swimming flagellates and a large number of free bacteria could be observed.Bdelloid rotifers,rose rotifers and polychaetes pilgrims co-exist in the flocs,indicating that the biochemical effluent treatment effect is better,but the sludge flocs are older.（2）The influence mechanism of sludge flocs on the traditional catalytic ozonation systemThe influence of different concentrations of suspended solids on ozone consumption in the catalytic ozonation system was analyzed.The COD removal efficiency indicated that the presence of floc particles would significantly increase ozone depletion.When the system does not contain floc particles,the amount of ozone used to degrade 1 mg COD is 1.16 mg,and when the SS concentration is 30 mg/L,the ozone consumption increases to 1.66 mg O₃/mg COD.Since the floc particles react with O₃,the available O₃ and hydroxyl radicals（·OH）for COD removal are reduced.When the SS concentration was30±0.96 mg/L,the O₃ dosage below 10 mg/L did not cause changes in particle size and surface properties.As the O3 dosage increased to 26 mg/L,the extracellular polymeric substance（EPS）reacted with O₃/·OH in varying degrees.Dissolved organic matter（DOM）had the highest consumption reaction rate,followed by loose EPS（LB-EPS）and compact EPS（TB-EPS）.The average reaction rate constants of the three components were 1.44,0.212,and 0.079 mg·L/min,respectively.（3）Research on the construction of nano catalytic systems and the effect of sludge flocs on their degradation efficiencyThree kinds of magnetic nanocomposite catalysts,Zn O/Fe₃O₄,Cu O/Fe₃O₄,and Cu O/Zn O/Fe₃O₄,were prepared by the co-precipitation method.The performance of the catalyst was characterized and evaluated,the degradation effects of different catalytic oxidation systems on target pollutants were compared,and the influence of sludge flocs on each catalytic system was analyzed.According to the detection results of liquid chromatography（HPLC）,Cu O/Zn O/Fe₃O₄ has the best degradation effect on pollutants,and the optimal dosage is 0.5 g/L.It is worth noting that the catalyst contains Zn O,an ultraviolet light-driven characteristic component,and Cu O,which can activate persulfate with a narrow band gap.In addition,Cu,Fe,and Zn can all play a role in the heterogeneous catalytic ozonation system as transition metals.Catalyst characterization results show that Cu O/Zn O/Fe₃O₄ magnetic nanocatalyst has more hydroxyl groups on its surface and has a larger specific surface area than the other two catalysts.It is a photocatalytic,ozone catalytic performance and persulfate activation performance of magnetic nanocomposite catalysts.Cu O/Zn O/Fe₃O₄ particles combined with O₃,persulfate（PMS）and UV can constitute three new nano-catalytic oxidation systems:nano-catalytic ozone oxidation,nano-catalyst activated persulfate and nano-ultraviolet photocatalytic oxidation system.The degradation effects of aniline in the three newly constructed nano-catalytic oxidation systems are all good.Except for the nano-photocatalytic oxidation system,aniline can achieve 100%degradation in the other two systems.The average degradation rate of three different systems within 1 hour was 94%.The average degradation rates of dibutyl phthalate（DBP）and diethyl phthalate（DEP）in different systems within 1 hour can reach 67%and 24.3%,respectively.By analyzing the influence of sludge flocs on the three nano-catalytic oxidation systems,it was found that the presence of sludge flocs had a great influence on the degradation of micro-pollutants in the UV-driven nano-photocatalytic oxidation system.When flocs existed,the degradation efficiencies of aniline,DBP,and DEP decreased by 16.8%,50.5%,and49.8%,respectively.The nano-catalytic ozonation system has the best degradation effect on the three refractory organic pollutants.（4）Research on the degradation of characteristic organic compounds by nano-catalytic ozonation systemTaking DBP-containing wastewater as the research object,the toxicity of wastewater treated with ozone alone,catalyst adsorption,and catalytic ozonation was analyzed.It was found that the specific oxygen uptake rate（SOUR）values in the activated sludge showed a downward trend in the initial stage（down to 4.859±0.804 mg/L）.The lag phases of catalytic ozonation,adsorption,and ozone alone are 6.67,7.09,and 7.89 hours,respectively,and the corresponding SOUR values at the end of the lag phase are 5.194,5.663,and 4.056 mg O₂/g MLVSS·h.This indicated that the degree of residual toxicity was the highest in the single ozonation system,the detoxification effect of the nanocatalytic ozonation system on DBP was the best,followed by the adsorption system.The results of the toxicity test verified that the catalyst has good performance and can play the role of adsorption and catalysis at the same time.The analysis results of ultra-high performance liquid chromatography quadrupole time-of-flight mass spectrometer（UHPLC-QTOF-MS）and total ion chromatogram（TIC）showed that DBP was degraded by O₃,·OH,and superoxide radicals(·O^2-)to generate intermediate products,this process mainly undergoes reactions such as shortening of the alkyl chain,hydroxylation of the benzene ring,ring opening of the benzene ring,etc.,and also undergoes the degradation reaction of the alkane substituent generated by the electrophilic substitution reaction of lipids through·OH.All intermediate products can be further oxidized or even mineralized to CO₂ and H₂O.In summary,based on the analysis of the biochemical effluent quality of petrochemical wastewater,this thesis explores the mechanism of the influence of sludge flocs on the heterogeneous catalytic ozonation system.The new nanocatalytic systems were constructed for the tertiary treatment of biotreated effluent from petrochemical wastewater.And this thesis explores the degradation path of the target organic pollutant DBP by the nano-catalytic ozonation system.The above research is of great significance for the realization of the standard discharge of petrochemical wastewater,especially the degradation and removal of the characteristic organic pollutants in the new standard.