Study On Operation Characteristics Of Urban Large-scale Ultrafiltration Water Plant

The water environment pollution in China is increasingly serious. The latest national standard for drinking water quality has been fully implemented and hence the existing water treatment process comprehensively being upgraded and reformed. Ultrafiltration(UF) technology in recent years has had a rapid development and more general application, but in a large town the applicability of the drinking water treatment process and membrane pollution control technology still need a long-term in-depth study.Based on the first 100 000 tons/day large-scale water treatment plant in China, this study focus on the the conventional process-UF process for urban drinking water, including the performance of the UF combination process on water purification, membrane fouling and process characteristics. Another task is investigating the newly-built short process-ultrafiltration process, including the debugging operation process, the characteristics of UF operation condition and comparing the two kinds of UF combination processes in terms of operation performance and features.The results show that the conventional process – UF combination process in the long-term run can keep good performance on water clean, ensuring the stability of the water quality. The periodical hydraulic backwashing can effectively control membrane fouling, sustaining membrane flux and trans-membrane pressure. Basically, the chemical cleaning is not required. The long-term operation would lead to membrane wire fracture, whose number has a positive correlation with the amount of water particles. Thus, the amounts of particles in permeated water can be detected by the rate of membrane fracture for ensuring the quality of treated water.Short process – UF process can achieve good performanceon on water purifaction, but the high concentration of foulant in UF membrane pool has a negative effect on membrane fouling and increases the frequency of cleaning. Sludge backflow would aggravate membrane fouling. The membrane fouling rate of short process-UF process without sludge backflow is 2.5 times the figure for the conventional process – UF combination process; When operating the sludge backflow process, it would be 4.5 times the figure for the conventional process- UF process, but the effect of removing organic foulants are improved.Water temperature is an important factor of membrane flux and transmembrane pressure. According to the results of the long-term run of conventional process-UF process, water temperature, in different seasons, has a significant impact on membrane flux and transmembrane pressure. Incresing the the backwashing water temperature can effectively reduce the irreversible membrane fouling resistance, decrease the membrane backwash resistance and improve the cleaning efficiency of backwash.The results of the comparison of the two UF combination processes show that the conventional process-UF process has been stably operated for more than five years. The performance and membrane fouling control are comprehensively good. By contrast, the short process-UF process is still required to adjust operating conditions and the mitigation of membrane fouling should be optimized further.