Pilot Study On Ultrafiltration Membranes Treatment Technology In City Waterwork

Since the pollution of the surface water has been more and more serious in China,the conventional water treatment process has been unable to meet the requirements ofthe drinking water quality standards which becomes more and more stringent recently. Itis necessary to develop some new water treatment technologies. Since the membranetechnology has developed rapidly, it is found that the low-pressure membranes,including microfiltration membrane and ultrafiltration membrane (UF), have a goodperformance on drinking water treatment. The ultrafiltration membrane has a betterwater quality, and the UF has a wider range of potential applications because of itslarger filter area and it is easy to install. Different types of surface water have differentwater quality characteristics. It is necessary to carry out pilot experiments befor theultrafiltration membranes are used in the drinking water treatment in order to test itswater treatment effects as well as membrane fouling and operating parameters.This study selected two submerged ultrafiltration membranes that produced by twomanufacturers in China. They are numbered I, II. The pilot scale experiment was carriedout in the Third Waterworks in Mianyang City, Sichuan Province. Based on thevariation of Fujiang water in one year, this experiment is divided into three phases: thelow turbidity period in winter, high turbidity period in summer and ultra-high turbidityperiod in rainstorm time. This paper studied the treatment effects and membranepollution changes of the two ultrafiltration membranes in the three periods. The mainresults are as follows:1) Both of the two ultrafiltration membranes has a goodperformance in the removal of turbidity during three periods, with an average effluentturbidity in0.15NTU, which is considered satisfactory for drinking water monitoring;2)In the period of the low turbidity influent in winter, both of the two ultrafiltrationmembranes have low CODMnremoval rates. Besides in conditions of high turbidityperiod in summer and ultra-high turbidity period in rainstorm, the influents have veryhigh CODMnvalues. There are a lot of particles in the membrane influents during thetwo periods. Most of the organic compounds are adsorbed on these particles, so theultrafiltration membrane can remove them easily. The CODMnvalues of the membraneeffluents remain stable. Besides the CODMnvalues of the two membranes differs little;3)During the three periods the UV254values in influents of the two ultrafiltrationmembranes change a little, but the UV254values of the two effluents don’t change asfollowed, and both of them differs little;4) The microorganisms in the effluents of the two membranes are occasionally detected. In theory, the ultrafiltration membranes havealmost100%rejection of the microorganisms. But in practical applications, because ofthe pollution of pipelines, or the backwash water bringing in some microorganisms,sometimes there are amounts of microorganisms existing in the influents. Therefore, inorder to ensure the quality and safety of the drinking water, there must be a disinfectionunit after the membrane treatment process;5) The transmembrane pressure is effected alot by the turbidity rising in the effluent. During the low turbidity period in winter, thetransmembrane pressure rising rate of the No. I ultrafiltration membrane is less than theNo. II ultrafiltration membrane’s. During the high turbidity periods in the summer andthe heavy rain period, the transmembrane pressure rising rate of the No. I membrane ishigher than the No. II membrane’s;6)The specific flux (SF) is related to the membranequality and water quality of the influent. During the whole three periods, the specificflux of No. I membrane is always greater than the SF of No. II membrane. It shows thatit is easier for water to go through the No. I ultrafiltration membrane than the No. IImembrane, and thus in the practical application, the higher the SF is, the lower theenergy consumption whould be. So the energy consumption of the No. I ultrafiltrationmembrane should be lower. Considering about the descending rate of SF, during thethree periods the No. I ultrafiltration membrane is higher than No. II membrane,indicating that No. I ultrafiltration membrane is more liable to the affections of changesin water quality;7) Comparing the recovery rates of the three chemical cleanings duringthe whole experiment, the No. I ultrafiltration membrane is lower than the No. IIultrafiltration membrane, indicating that the antipollution ability of No. II ultrafiltrationmembrane is better than the No. I ultrafiltration membrane;8) The higher the waterturbidity is, the greater the resistance of membrane and membrane resistance increasingrate would be. In the winter when the water turbidity is low, the total membraneresistance constitutes mainly by the membrane resistance itself. During the high waterturbidity in summer and heavy rains, the membrane resistance constitutes mainly by thedeposition layer resistance. In the low water turbidity period in winter, the concentrationpolarization resistance can be negligible. But in the high water turbidity periods insummer and heavy rains, the concentration polarization resistance increasessignificantly, and cannot be ignored.