Study On The Removal Of Typical PPCPs Pollutants And The Control Of By-product Formation By UV/CL Hybrid Process

Pharmaceuticals and personal care products is a kind of emerging contaminants,detected frequently in drinking water sources and other water bodies.PPCPs in water are getting more and more attention from people because of the negative environmental effects.PPCPs generally has strong polarity and are difficult to be volatilized.Conventional water treatment process of coagulation,sedimentation,filtration can't effectively remove PPCPs in water.They penetrate the front of the water plant and enter the disinfection unit,where a series of chemical changes produce complex by-products that threaten the safety of the water.Ultraviolet and chlorine as commonly used disinfectants are widely used in water disinfection.Based on the typical PPCPs,diclofenac sodium?DS?as the research object,using chemical methods and biological methods,to investigates efficiency of the degradation mechanism of the DS by UV,chlorine and UV/Cl processes,in order to provide basic data and theoretical support for the safety of drinking water.Using UV/ClO₂ disinfection system,the degradation for DS in separate UV,ClO₂and UV/ClO₂ system was contrasted,and the reaction kinetics and influencing factors on the removal of DS were studied.The contribution of main free radicals was discussed,too.The change of the acute toxicity and genetic toxicity were evaluated in the degradation process of DS solution.comparing the way of dosing in UV/ClO₂disinfection system and analyzing the possibility of the UV/Cl O₂ in practical application were carried out in the meantime.The results showed that the combination of UV and ClO₂ could produce syneresis,and UV/ClO₂ could effectively remove DS in the water,and the degradation of DS in separate UV,ClO₂ and UV/ClO₂ was consistent with the pseudo first-order reaction kinetics model.The degradation rate in the UV/ClO₂ system was 0.02963s^-1,which was 41 times and 1.88 times of the separate UV and separate ClO₂.The main factors of the degradation of the DS is chlorine dioxide and·OH,and the contribution of·OH and·O₂^-are 18.6%and 5.4%separately;In the experiment,the reaction rate increases linearly with the increase of ClO₂ from 0.00072s^-11 to 0.0403s^-1.The pH value has little influence on the UV/ClO₂ system in the range of 4.50 to 8.50;It was found that humic acid show a significant inhibitory effect on DS degradation,and the degradation rate was reduced from 100%to 70%,when humic acid concentration was increase from 0 to 7 mg·L^-1.The effect of bicarbonate on the UV/ClO₂ disinfection system was little.One-time addition of chlorine dioxide is better for the degradation of DS.It has been found that that toxicity effect of the medium product in the degradation process is greater than that of DS,and the toxicity effect of the DS degradation process by UV irradiation and chlorine dioxide is always obvious.UV/Cl O₂ can not only degrade the DS effectively,but also can control the toxicity of the non-controlled by-product in the solution effectively,so as to ensure the safety of drinking water.The removal rate was 95%in actual wate when the concentration of DS is 550?g·L^-1,pH is 6.8,the initial ClO₂ concentration is 0.4 mg·L^-1.The degradation of DS are studied in UV/NaCl O system,and the efficiency of degradation was investigated and compared in UV,NaClO and UV/NaClO.The main contribution of free radicals in the reaction process was discussed.The main influence factors,such as the quantity of NaClO dosing,pH,humic acid,bicarbonate root and the way adding were investigated,The assessing the change of toxicity in DS solution,as well as analyzing the possibility of the UV/NaClO in practical application was carried out.The results showed that UV/NaClO could also effectively degrade DS in water bodies,and the reaction still follows the pseudo-first-order reaction kinetics model.The pseudo first rate constants of UV irradiation,NaClO and UV/NaClO are 0.0331min^-1,0.00075 min^-11 and 0.0721min^-1,separately.Different from UV/ClO₂ system,Hydroxyl radical?·OH?is the main free radical in the process of DS degradation by UV/NaClO system with the contribution of 44.43%,O₂^-also has a promoting effect with the contribution of 16.10%.and.The degradation rate of DS increased linearly with the increase of dosage of sodium hypochlorite.The pH has obvious influence on the UV/NaClO system,the pseudo first order reaction rate constant decreases gradually with the increase of pH.When the pH increased from 5 to 8,the rate constant decreases from 0.0797 min^–11 to 0.0445 min^–1;Humic acid and bicarbonate root had significant inhibitory effect on the removal of DS.When the humic acid concentration reached 7 mg·L^-11 and the bicarbonate concentration reached 100 mg·L^-1,the removal effect of DS was reduced by 69%and 24%respectively.In the experiment,one-time addition of chlorine dioxide is better for the degradation of DS,and mutually quenching was not observed when the coexistence of large amount of free radicals.Through UV/NaClO disinfecting system,acute toxicity in the process of DS degradation presented fluctuations in increase or decrease,finally the toxicity is lower than the initial solution toxicity.Genetic toxicity reduced after first increases,and in the end the solution presented no obvious toxicity effect;When DS concentration in actual wate is 550?g·L^-1,pH=6.8,initial concentration of free chlorine is 7 mg·L^-1,removal rate can reach 99%in 75 minutes.