Study On The Control Of Ultrafiltration Membrane Fouling By Filtration Pretreatment

Ultrafiltration has been considered as a promis ing alternative to the traditional drinking water treatment process. However, membrane fouling which caused a series of problems, such as the decrease of effic iency of water production, the increase of operating pressure and the increase of operating cost, is the main obstacle to the application of low pres sure. Therefore, various pretreatment methods are combined with the ultrafiltration process to slow down the membrane fouling. The purpose of this paper is to study on the control of ultrafiltration membrane fouling by filtration pretreatment.In this study, we first explore the control of membrane fouling by physical filtration pretreatment,and the specific approach is to filter raw water of Songhua River Raw Water by different filter media including fly ash, quartz sand and granular activated carbon,then the effluent is used as the influent of ultrafiltration system.In this process, we detect the water quality of water samples,such as conventional water quality indicators, transmembrane pressure and three-dimensional fluorescence data.The experimental results show that the physical pre- filtration has a certain effect on the ultrafiltration membrane fouling. However, different filter materials’ s role on ultrafiltration membrane fouling is different.The filter media which has Large particle size(The diameter is of 1~ 2mm) have a worse removal effect of UV254 and DOC than the small one(The diameter is of 0.5~1mm),the possible reason is that the small particle size filter media has a greater specific surface area to contact solut ion, thus resulting in a bette r adsorption effect. Both the big and small particle size filter media have the advantage in turbidity removal effects, and the difference between them is not obvious. After running 24 hours,irreversible membrane fouling is dominant in membrane fouling.It was found that the membrane irreversible fouling resistance was the least after the granular activated carbon filter, followed by fly ash, and the quartz sand was the biggest.The effect of particle size of quartz sand and fly ash on the irreversible resistance of the membrane is not so obvious as that of the activated carbon.By using three dimensional fluorescence parallel factor analysis,we obtained three components of the fluorescent image in water samples and the corresponding fluorescent contour peak position:component 1(Ex / Em: 230((275) nm / 306 nm) was identifed as tyrosine- like protein; component 2(Ex / Em: 230(290)nm / 410nm)was identifed as microbial-derived humus- like substances;component 3 was identifed as terrestrial--derived humus- like substances.We then studided on the control of membrane fouling by biological filtration pretreatment.We runned the pre filtration device for thirty- five days, and the corresponding filter column which plus 0.1% sodium azide solut ion to inhibit bacterial growthwas as a contrast. Every five days,the effluent of filtration pretreatment was taken as the influent of UF,and the water quality indexes were detected.The results showed that the whole filtering process is gradually transition from the init ial physical filtration to physical and biological filtration together with running of the reactor.Granular activated carbon pre filtrationis is easier to hang membrane success than the other two kinds of filter.The transmembrane pressure of the influent of UF after the three filter pre filter has a peak value,and the difference is that the transmembrane pressure peak of granular activated carbon appeared in the 15 to 25 days, and quartz sand and fly ash appeared between 20 to 25 days. During the whole stage of the reacto r, the reversible fouling resistance and irreversible fouling resistance showed the same trend as the first increasing and then decreasing. In addition, compared with the irreversible and reversible membrane fouling, the irreversible fouling played a leading role in membrane fouling during the operation cycle. The value of TOC and turbidity of the three kinds of filter media showed a weak correlation with the irreversible fouling resistance, while the value of UV254 was not significantly correlated. The value of TOC and turbidity of the effluent of activated carbon pre filtration showed a certain correlation with the reversible fouling of membrane, but the other two kinds of filter media showed no correlation. In the light polluted area, the correlation between component 1 and membrane irreversible fouling is most obvious, and component 2 and 3 showed showed no correlation.; in the heavy polluted area, component1, 2 and 3membrane showed no correlation with irreversible fouling.Possible reason was that pr otein adsorped to membrane surface in the process of protein separation which caused the irreversible membrane fouling in the early days of the ultrafiltration, along with the aggravation of pollut ion a cake layer gradually formed, thus UF was seriously polluted, irreversible fouling of membranes caused by synergistic pollution of various pollutants, so solely component 1 ’s pollut ion effect is not obvious. In addition, component 1, 2 and 3showed showed no correlation with reversible fouling.