Experimental Study On Advanced Treatment Of Secondary Biochemical Effluent From A Chemical Plant By Ozone Catalytic Oxidation

The petrochemical industry is my country's pillar industry,and a large amount of petrochemical wastewater will inevitably be generated during the production of chemical products.After the traditional secondary biochemical treatment of petrochemical wastewater,the COD value is usually about 120mg/L,of which refractory organic pollutants contribute most of the COD value,the biodegradability is extremely poor and the water quality composition is extremely complex.The"Petrochemical Industry Pollutant Discharge Standards"?GB31571-2015?,which has been in effect since 2015,requires the COD of effluent to be less than 60mg/L,and the COD emission value should not exceed 50mg/L in areas with high environmental protection requirements.Therefore,it is an urgent need of the petrochemical industry to carry out in-depth treatment of the secondary biochemical tail water of petrochemical enterprises to meet the above discharge standards.Based on the above background,this article uses homogeneous and heterogeneous catalytic ozone oxidation technology to treat the secondary biochemical tail water of a petrochemical plant in East China:?1?The experiment selected four transition metals of iron,manganese,copper and nickel as homogeneous catalysts,and explored the six factors of reaction pH,ozone flow rate,reaction time,reaction temperature,type of medium added,and amount of medium added to the homogeneous phase.The influence of the catalytic oxidation process.The experiment shows that all six factors have an effect,and the degree of influence is in the order of reaction pH>dosing medium type>reaction time>medium dosing amount>ozone flow rate>reaction temperature.The optimal reaction conditions are:pH:9,ozone flow rate:0.5 L/min,reaction time:60 min,reaction temperature:30°C,type of dosing medium:NiSO₄;medium dosing amount:0.0262 mol/L.The homogeneous catalytic oxidizing capacity of metal ions is Ni²⁺>Cu²⁺>Fe²⁺>Mn²⁺.Under the optimal reaction conditions,the COD effluent was57.09mg/L,and the removal rate reached 56.71%.?2?In this paper,granular activated carbon with coconut shell texture is selected as a heterogeneous catalyst carrier.At the same time,on the basis of this,the catalytic ozone oxidation treatment effect when using activated carbon alone as a catalyst is studied,and different modification methods?HNO₃,H₂O₂,Ammonia?,modified solution concentration,reaction pH,reaction time,ozone flow rate and other conditions on the effect of activated carbon catalytic ozone oxidation.The Boehm titration method was used to determine the effect of different modification methods on the surface functional groups of activated carbon.Tests show that the degree of influence of each factor is:modification mode>reaction pH>reaction time>modification solution concentration>ozone flow rate.Among them,a large amount of acidic functional groups such as carboxyl groups and phenolic hydroxyl groups were added to the surface of the activated carbon after oxidation modification,and the basic functional groups on the surface of activated carbon were mainly increased by reduction modification.A large amount of phenolic hydroxyl groups were added to the surface of the granular activated carbon modified by 15%H₂O₂ solution.At the same time,more mesopores and macropores were etched on the surface of the activated carbon,and the catalytic performance was optimal.Under optimal conditions,the COD removal rate of the petrochemical secondary biochemical tail water can reach 26.61%.?3?Using granular activated carbon as a carrier,four kinds of transition metal ions of Ni²⁺,Cu²⁺,Fe²⁺,Mn²⁺are selected as active components to prepare activated carbon-supported metal catalyst by impregnation method.Taking the concentration of impregnating solution,pH of impregnating solution,impregnating temperature,impregnating time,roasting temperature and roasting time as the influencing factors of catalyst preparation,taking the COD removal rate of wastewater as an indicator,a seven-factor mixed level orthogonal table was designed to explore the optimal type of catalyst and its Preparation conditions.The degree of influence of various factors on the test surface is:dipping temperature>roasting time>metal type>immersion time>immersion liquid concentration>roasting temperature>immersion liquid pH.Under the optimal conditions for catalyst preparation,that is,the concentration of CuSO₄ impregnating solution is 0.04mol/L,pH is 2,the impregnation time is 10h,and the Cu²⁺/AC catalyst prepared under the condition of calcination at 100?for 4h catalyzes ozone oxidation for 60min.The effluent COD is42.90mg/L and COD removal rate reached 65.43%,which meets the emission requirements in"Petrochemical Industry Pollutant Emission Standards"?GB31571-2015?.Compared with single ozone oxidation,activated carbon+O₃ catalytic ozone oxidation,and Cu²⁺homogeneous catalytic ozonation,the average removal rate of COD increased by 40.16%,31.85%,and 12.23%,respectively.On this basis,the prepared Cu²⁺/AC catalyst was characterized by SEM,EDS,active component loading and so on.Various characterization results show that this catalyst preparation method can successfully support Cu²⁺on granular activated carbon,with a Cu²⁺loading of 5.79×10^-3mol/g.After the catalyst was used six times,the COD removal rate remained stable at more than 60%,and the effluent COD was less than50mg/L.?4?To explore the influence of inorganic salts on the ozone oxidation process,sodium sulfate,sodium carbonate,and sodium phosphate were selected as the investigation objects,and the COD removal rate of the petrochemical secondary biochemical tail water was evaluated.Tests show that sulfate will not be captured and can react with it.When the pH is greater than 10,most of the free radicals of sulfate are converted into hydroxides,thereby promoting ozone oxidation;and sodium carbonate and sodium phosphate will oxidize ozone The process produces different degrees of inhibition.Among them,sodium carbonate is a quencher of hydroxyl radicals,which can react quickly and greatly reduce the ozone oxidation efficiency.Therefore,the treatment effect is worse than when sodium phosphate is added.The degree of influence of the type of inorganic salt on the inhibition of ozone oxidation is:sodium carbonate>sodium phosphate>sodium sulfate.At the same time,for the simulated high salt content?adding 25000mg/L sodium carbonate to the petrochemical wastewater sample?,a pretreatment method?dosing CaO?was proposed.The results showed that:The COD removal rate of the water sample was 22.79%higher than the water sample without pretreatment.