Study On Advanced Removal Of Typical Organics In Secondary Effluent From The Chemical Industry Park By Catalytic Ozonation/coagulation Process

The wastewater in sewage plant of the chemical industry park contains many refractory and toxic organic pollutants,bringing difficulties and challenges to the traditional biochemical method.Nowadays,it is urgent for sewage plant effluent of the chemical industrial park to reach the discharge standard.However,due to the limited space for reconstruction,it is effective to strengthen or optimize the advanced treatment process on the basis of current wastewater treatment process.Catalytic ozonation/coagulation for advanced treatment of secondary effluent can offer the synergistic removal of refractory organics by direct or indirect interactions among ozone,catalysts,organics and coagulants.The results of its application indicate that the removal efficiency of organics primarily depends on characteristics of effluent organic matter(EfOM).EfOM mainly consists of synthetic organics(SOC),soluble microbial products(SMP)and humic acids(HA).The typical EfOM(eg.benzotriazole et al.)of the fine chemical park in Huaihe River Basin have been selected as target pollutants.The removal characteristics and mechanisms of benzotriazole(BTA)by catalytic ozonation(FeCeAC/O3)were systematically investigated.The removal behaviors of EfOM in FeCeAC/O3,coagulation and catalytic ozonation/coagulation(FeCeAC/O3/PAC)systems were compared.The insight mechanisms of enhanced EfOM removal by FeCeAC/O3/PAC could be elucidated.Meanwhile,an integrated device of catalytic ozonation/coagulation for advanced treatment of secondary effluent from the chemical industry park was designed.The main conclusions are as follows:(1)Catalytic ozonation with FeCeAC removed 75.15%of TOC compared to 45.33%by single ozonation.The exhausted FeCeAC was regenerated by thermal regeneration,and FeCeAC still retained stable catalytic activity after five cycles.The prediction model of rate contants of BTA degradation in FeCeAC/O3 process was established as affected by ozone concentration,BTA concentration,pH,and catalyst dosage.Quenching experiments and electron paramagnetic resonance spectra demonstrated that both O2·-and·OH were involved in the removal of BTA.The degradation efficiency of BTA was mainly affected by O3 and O2·-,while the mineralization efficiency of organics was mainly affected by·OH.The removal mechanisms were manifested by analyses of X-ray photoelectron spectroscopy and pyridine-infrared spectroscopy.There were different mechanisms for the two active components(Fe,Ce)to promote O3 decomposition to ·OH.Fe could serve as Lewis acid sites(α-Fe2O3)and surface hydroxyl groups(FeOOH),while Ce could supply the oxidation-reduction reaction between Ce(Ⅲ)and Ce(Ⅳ)to initiate the decomposition of O3.In addition,FeCeAC/O3 could be widely applied to remove other heterocyclic compounds(5-methyl-1Hbenzotriazole and benzothiazole)and humic acids with the TOC removal efficiency up to 66.52%.(2)The removal efficiency of UV254 and TOC in FeCeAC/O3/PAC process were increased by 13.52%and 12.11%,respectively,when compared with that in conventional coagulation+catalytic ozonation process.It can be seen that there is an obvious synergistic effect between FeCeAC/O3 and coagulation process.The COD removal efficiency of secondary effluent from the chemical industry park was increased to 44.19%,and the COD of FeCeAC/O3/PAC effluent could be reduced to 48.10 mg/L,which met the discharge standard(GB 18918-2002).EEM-PARAFAC model was used to quantify the typical fluorescent components in EfOM,including HA,SMP and hydrophobic humic acids(HOA).Their relative fluorescence intensities were also compared and sorted as HA>SMP>HOA.The removal efficiency of HA,SMP and HOA by FeCeAC/O3/PAC in 30 minutes was 95.26%,94.51%and 92.86%,respectively.The degradation rate constants of fluorescent components were with the order of HA(0.118 min-1)>SMP(0.101 min-1)>HOA(0.097 min-1).The rate constants of HA,SMP and HOA increased by 11.32%,55.38 and 4.30%,respectively,when compared to that in FeCeAC/O3 system.These results indicated that FeCeAC/O3 can not only react with HA and HOA preferentially through FeCeAC/O3 process,but also remove SMP effectively through coagulation process.The dynamic and static quenching models displayed that the number of binding sites(1.68)and the binding constant(4.90×105 L/mol)between SMP and Al3+in FeCeAC/O3/PAC system were higher than those of single coagulation system.It is because that the FeCeAC/O3 process increased the content of oxygen-containing functional groups of SMP,and then enhanced the affinity between SMP and Al3+,which made the coagulation process easy to form A13+-SMP complexes.Furthermore,the mechanisms of enhanced EfOM removal in FeCeAC/O3/PAC system were elucidated with electron paramagnetic resonance spectra and particle size analyses.FeCeAC and PAC promoted O3 decomposition to generate·OH,thereby increasing ·OH yield rate.The complexes were formed between PAC and fluorescent components through static quenching,thereby forming larger-sized flocs.(3)The toxicity of secondary effluent was evaluated by the zebrafish.The toxicity of FeCeAC/03/PAC effluent was reduced by 21.20%.(4)According to the theoretical research mentioned above,an integrated device for advanced treatment of scondary effluent from the chemical industry park was designed.It included three functional zones:oxidation zone,coagulation zone and sedimentation zone.The oxidation zone was used to remove most SOC and HA,and the coagulation zone and sedimentation zone mainly enhanced SMP removal.The device could save land area and improve ozone utilization,catalyst utilization,and the removal efficiency of organics.Conclusively,this work could provide a technical support for upgrading process of sewage plant from the chemical industry park.