Study On Treatment Of Simulated Pva Wastewater By Advanced Oxidation Processes In Rotating Packed Bed

The textile industry is an important civilian production industry in China.Sizing and desizing are two main processes in the textile industry.Large amounts of textile wastewater containing polyvinyl alcohol(PVA)will be discharged from these two processes.The composition of this wastewater is complex and recalcitrant,and such wastewater can make seriously harms to the environment.Recent research results show that advanced oxidation processes(AOPs)are an effective way to treat recalcitrant organic wastewater,providing a feasible route for PVA wastewater.Ozone-based AOPs is a type of gas-liquid two-phase reaction.The key factor that affects the progress of this type of reaction is the effect of mass transfer between gas and liquid.High-gravity technology is an effective method to increase the contact area and enhance the mass transfer between phases.In this study,a combination of these two technical processes was used to effectively promote the absorption of O3 in the reaction system so as to enhance the treatment effect of PVA wastewater.The high-gravity equipment selected in this work was the rotating packed bed(RPB).Four different AOPs including O3,O3/H2O2,O3/Fe2+,and O3/Fenton were used with RPB to treat simulated PVA wastewater.The products structure and kinetics of PVA degradation were also investigated.The conclusions are shown as follows:(1)The O3 and O3/H2O2 processes were employed to treat the simulated PVA wastewater in RPB.It was found that the increase of RPB rotation speed and O3 concentration improved the degradation percentage of PVA to a certain extent.Increasing reaction temperature and wastewater flow rate kept the PVA degradation percentage decreaing.As the H2O2 concentration increased,the degradation percentage of PVA first went up and then declined in the O3/H2O2 process.As the pH of the solution increased,the degradation percentage of PVA increased in the O3 process,but first rose and then decreased in the O3/H2O2 process,and the degradation percentage of PVA reached the optimal value of 83.6%at pH 10 in the O3/H2O2 process.According to the analysis results of infrared spectroscopy,the structures of the PAV's degratation products were similar in the above two processes.The carbon-carbon double bonds in PVA were broken by the reaction,which may produce trans-olefin di-substituted products and some long-chain alkanes.(2)The O3/Fe2+ and O3/Fenton processes were used to treat the simulated PVA wastewater in RPB.The degradation of PVA by both processes reached the best effect at pH 2.With the increase of O3 concentration,the degradation percentage of PVA sowed an overall upward trend.In the O3/Fe2+ process,as the RPB rotation speed and reaction temperature increased,the degradation effect of PVA was continuously improved.As the Fe2+ concentration increased,the degradation effect of PVA was first rose and then decreased.In the O3/Fenton process,as the RPB rotation speed and Fe2+/H2O2(mole ratio)increased,the degradation percentage of PVA first increased and then declined.As the reaction temperature increased,the degradation percentage of PVA first increased and then remained largely unchanged.The O3/Fenton process demonstrated the best PVA degradation effect.When the initial pH was 5.7;the gas phase O3 concentration was 30 mg/L;the H2O2 concentration was 35 mg/L;the Fe2+ concentration was 0.8 mmol/L;the RPB rotation speed was 1000 r/min;the liquid flow rate was 30 L/h;the gas flow rate was 90 L/h;the reaction tempreture was 25?;the PVA concentration was 200 mg/L,the degradation percentage of PVA reached 94.8%.The PVA degradation products in the above two processes had similar infrared spectrums.It can be found from the analysis that the degradation products include carboxylic acids,and the presence of aldehydes cannot be ruled out.In addition,there may be hydrocarbons containing methyl branches in the products.(3)The kinetic study of the degradation of PVA wastewater by the O3/Fenton process was carried out,and the reaction was determined to be a first-order reaction.The apparent activation energy of the reaction was 42.9 kJ/mol,suggesting that it is a relatively easy reaction.Akinetic model of the reaction was established as follows:.k=1.645 × 106 × e(-42879/R0T0)×[Fe2+]2336[H2O2]2346[PVA0]-0.7017[O3]1.135The model can predict the apparent reaction rate constant undercertain conditions.Based on the absolute value of the reaction sub-order of every factor,it can be deduced that the influence of these factors on the kinetic process of PVA degradation follows the following order:O3 concentration>Initial PVA concentration>H2O2 concentration ? Fe2+ concentration.