| Ultrafiltration is now increasingly used as a technology for surface water purification,as its stable water quality safety and biological safety.UF can effectively remove particles,microorganisms and some viruses.Nevertheless,the main drawbacks of this technology are membrane fouling and low rejection of small organic molecules,which are two major obstacles to the widespread application in water and wastewater treatment.In surface water applications coagulation are employed to lower the resistance of the particle cake deposited on the membrane during filtration.In this work,a hybrid coagulation–ultrafiltration process was used to treat micro-polluted surface water.The effects of the coagulant dosage,on the process performance were investigated.Then the relationship between aggregates characteristic and membrane foulling was analyzed.Lastly,the cakelayer formed by aggerates was applied to remove organic matter.The hybrid coagulation-ultrafiltration process was used treat the micro-polluted surface water with phosphate and ammonia.After 20 days operation,the anti-fouling properties of a membrane and optimization of the operational conditions has a certain influence on membrane fouling.Coagulation as a pretreatment process can effectively remove inorganic particles and organic pollutants with the removal rate of 90% and 35% respectively.The removal efficiency of dissolved phosphorus up to 95%,however,the removal efficiency of ammonia nitrogen(about 30%)and nitrate nitrogen(only 6%)is limited.The membrane fouling results showed that coagulation was a good approach for membrane fouling control,reducing the irreversible membrane fouling.Malvern laser particle size analyzer and micro-scale ultrafiltration unit were used to investigate membrane fouling caused by the flocs formed by coagulants(i.e.Aluminium polychlorid(PACl),ferric trichloride(Fe Cl3))and aid-coagulant(polyacrylamide(PAM)).Most inorganic particles and a small amount of small organic molecules can be removed by coagulants,meanwhile,cake layer deposited on the membrane archived more porous and amorphous.The membrane flux(0.696)improved significantly and the resistance of cake layer(0.34×10-11 m-1)increased slowly with an appropriate dosage of coagulants.However,adding the dose up to 8 mg/L,the flux(0.331)decreased significantly with the cake layer resistance(1.74×10-11 m-1)increased sharply.The floc size exhibited an obviously increase trend up to 1000 ?m combined with PAM as a coagulant aid.The results indicated that when the PAM dosage was in the range of 1.0-15 mg/L,specific membrane flux decreased significantly to 0.585,while cake resistance increased to 0.62×10-11 m-1.The results demonstrated that cake layer was the dominant fouling mechanism under different conditions and membrane pore blocking are severe in the case of higher PAM dosage.Micro-scale ultrafiltration unit were implemented to investigate the removal rate of antibiotics and HA by cake layer formed on membrane surface under two different coagulants coupled with coagulant aid polyacrylamide(PAM)in coagulation process.The original membrane structure parameters and performance parameters,to a certain extent which affected the pollutant entrapment ability in the process of membrane filtration changed because of the alter of the interfacial interaction among membrane surface,cake layer and pollutants.The results show that the change of coagulant type,dosage and volume contribute the highest removal rate less than 5% of sulfamethazine and sulfamethoxazole with coating cake layer by pre-filtering coagulation suspension on the origin membrane.With the highest removal rate up to 53.4 %,the result indicated that HA mainly removed by coagulants,while PAM did not play a significant role.The mechanism for HA removal by cake layer was steric hindrance. |
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