A Pilot Study On External Circular Continuous Filtration-Ultrafiltration Process For Songhua River Water Treatment

In recent years,with the increasing water pollution and the continuous improvement of drinking water standards in China,traditional drinking water treatment technology is difficult to meet the safety requirements of drinking water at present.Therefore,with ultrafiltration as the core,the third generation drinking water treatment technology emerged as the times require and developed rapidly.However,most of the application of ultrafiltration in China is to combine with the traditional technology simply,which have the complex process and the excessive dependence on chemical agents.In this article,with the Songhua River as the the object of treatment and the external circular continuous filtration as the pretreatment process,the pilot study of external circular continuous filtration-ultrafiltration process has been performed to support for the development of the ultrafiltration-based green water purification process with short process and low chemical dosage.Firstly,to research and optimize the operating parameters of continuous filtration.The results indicates that increasing the thickness of filter layer,decreasing the filtration rate and prolonging the backwash cycle can improve the treatment effect of continuous filtration.The increase of head loss accelerates with the increase of the filtration rate,but excessive filtration rate will cause the head loss to decrease.The backwash cycle has no significant effect on head loss,and the backwash cycle within 6h can effectively control the pollution of filter layer.The effect of backwash intensity of 16L/(m2·s)is the same as that of 20L/(m2·s),which can finish washing in 8min.The optimum condition of continuous filtration are determined as follows: the thickness of filter layer is 1.0m,the filtration rate is 4m/h,the backwash cycle is 6h,the backwash intensity is 16L/(m2·s),and the backwash duration is 8min.Then,to research the operating parameters of ultrafiltration by small-scale device.The results indicates that decreasing the membrane flux,increasing the backwash pressure,prolonging backwash cycle and shortening filtration cycle can reduce the membrane fouling rate.And changing operating parameters has no or only slight effect on the treatment effect of ultrafiltration.Take the results of the small-scale experiment as a reference,the optimum condition of ultrafiltration are determined as follows: the membrane flux is 20L/(m2·h),the backwash pressure is 3.5m,the backwash cycle is 2min,and the filtration cycle is 120 min.In addition,to compare the effect of combined process and direct ultrafiltration.The results indicates that the removal rate of CODMn,UV254 and ammonia nitrogen by combined process are 9.97%,7.02% and 33.84% higher than that of direct filtration respectively.And the membrane fouling rate of combined process is much less than that of direct ultrafiltration.Continuous filtration pretreatment can not only improve the removal efficiency of organic matter and ammonia nitrogen,but also alleviate ultrafiltration membrane fouling effectively.Finally,to investigate the treatment efficiency and membrane fouling characteristics of combined process in long-term operation and optimum condition.The results indicates that the removal rates of turbidity,CODMn,UV254,DOC and ammonia nitrogen by combined process are 99.75%,32.21%,17.12%,15.27% and 70.77% respectively.Due to the organic matter in Songhua River is mostly small or medium-sized,the combined process has the poor removal effect on them.Because the continuous filtration and ultrafiltration can form microbial degradation in long-term operation,the combined process shows the outstanding and steady removal effect on ammonia nitrogen.Although the removal of microorganisms by combined process is significant,the effluent has not achieved the microbial standard yet.The combined process has excellent effects on the removal of Al,Fe and Mn,which are mainly colloidal or particulate,while it has no significant effect on the removal of Mg and Ca,which are mainly ionic.In the early stage,the rate of membrane fouling is slow,and it become faster after the 15 th day.At last,the transmembrane pressure increase to the superior limit of 50.3k Pa on the 50 th day.In this experimental conditions,the chemical cleaning cycle of ultrafiltration membrane is about 50 days.Humic acid organic compounds and tryptophan proteins are the main irreversible pollutants for ultrafiltration membrane.Continuous filtration pretreatment can effectively alleviate ultrafiltration membrane fouling by removing large particles,macromolecular organics and tryptophan proteins.In conclusion,taking Songhua River as the treatment object,the external circular continuous filtration-ultrafiltration process shows good treatment efficiency in long-term operation and optimum condition.The effluent can basically achieve the standard of drinking water,and the ultrafiltration shows steady operation and low fouling rate.Compared with the direct ultrafiltration,the combined process has obvious advantages in treatment efficiency and membrane fouling control,which provides reference for research and development of the ultrafiltration-based green water purification process with short process and low chemical dosage.