Studies On The Adaptability Of Combined Processes Based On Ultrafiltration To Treatment Of Micro-polluted Minjiang River

Current water environmental situation and drinking water safety problem are still not optimistic in China at present.The restriction of conventional water treatment process in waterworks is becoming apparent.Under such circumstances,ultrafiltration(UF)process is continuously developing and improving.It is widely accepted that hybrid process combined UF with other technologies as the pretreatment before the membrane can effectively enhance removal of pollutants that are hard to remove completely by conventional water treatment procedures and reduce the membrane fouling at the same time.However,the applications of UF technology in large and medium-sized waterworks in Fujian are yet very few.Thus the adaptability of combined processes based on UF to the treatment of Minjiang River is unknown,resulting in a lack of corresponding running and management experiences.In view of this problem,this paper brings forward several suitable combined forms of the hybrid process based on UF corresponding to discussed water quality levels,and their adaptability to Minjiang River were evaluated.In addition,optimum selection of membrane materials and operational modes,and the optimization of overall operation parameters of the hybrid process were conducted to improve the adaptability of those combined processes.Finally,the practical applications of the combined process based on UF were evaluated by assessing the treatment performance and operation stability of UF in emergency water supply in Fujian.The integrated device of multiple agent filtration-UF-reverse osmosis(RO)can be used to treat Minjiang River with high-salinity level,the average chloride ion concentration in the effluent was 14.4 mg-L-1,with an average removal rate of 96.89%,the desalinization rate was over 97%with low operation cost,the integrated device of UF+RO can be used to solve the problem of brackish water caused by seawater intrusion.The integrated device of coagulation-sedimentation-ozone-granular activated carbon(GAC)-UF can be used to treat Minjiang River with high concentration of organic substance,the removal rates of CODMn,UV254 and UV410 were 53.42%,64.88%and 84.17%,respectively,which showed effective removal of organics,the GAC process placed before membrane and the induction of ozone process can effectively relieve membrane fouling by removing the pollutants that effect the membrane fouling greatly.The integrated device of adsorption+UF and UF pre-coating process,using coagulation and sedimentation as the pre-treating process,can be used to treat Minjiang River with high concentration of ammonia nitrogen,the powdered zeolite can be used as absorbing materials,in addition,the powdered zeolite or powdered zeolite coupled with kaolin clay can be used as the coating material,actually,the effluent reached the standard with powdered zeolite dosage of 70 mg·L-1 when ammonia nitrogen in raw water was in the range of 0.6 to 0.7 mg·L-1.The inside-out PES module,outside-in PVDF module and outside-in PAN module did not showed significant difference of the removal efficiency of turbidity,CODMn and ammonia nitrogen.The inside-out PES module has its advantages such as higher membrane specific flux,and lower operating pressure and energy consumption,for the treatment of Minjiang River in a good water quality period,the inside-out PES membrane module would be the preferred choice.As for the optimization of overall operation parameters of the hybrid process,results showed that The major factors in membrane fouling were the tryptophan protein-like substances and the soluble microbial products(SMP).By numerical optimization,the optimal preparation conditions for SF decay rate in a single filtration cycle can be obtained:the agitator rotational velocity:40 rpm,NaCIO dosage:0 mg·L-1 and operating flux:100 LMH.In addition,the optimal preparation conditions for organics removal:the agitator rotational velocity:41.79 rpm,NaCIO dosage:1.40 mg·L-1 and operating flux:82.26 LMH.The hybrid process based on UF presented good water outlet quality with low trans-membrane pressure and operating pressure during half a month's continuously operational and stable period in emergency water supply in Fujian,providing drinkable water for people in the disaster areas.The better treatment performance and higher operation stability of hybrid process based on UF compared with conventional water treatment procedures provide further evidences that the combined process based on UF has well adaptability for treating micro-polluted Minjiang River.