Research Of Application Of Ultrafiltration In Reconstruction Of Traditional Drinking Water Plant

The contradiction between improved drinking water quality standard and thedeterioration of raw water quality poses serious challenge to the processing ability oftraditional drinking water treatment plants, reconstruction of traditional water treatmentplants has become an urgent need. Effluent of different stages of traditional drinkingwater treatment units had been chosen as the influent of ultrafiltration membranes tostudy the possible way of combination between ultrafiltration membrane andpretreatments, backwashing of ultrafiltration membrane and operating conditions hadbeen studied on this basis.The pilot experiments firstly took effluent of sedimentation tank and sand filtrationtank of an drinking water treatment plant in Shaoguan city as influent of ultrafiltrationmembranes, the results showed that turbidity of the two ultrafiltration membraneseffluent was both below1NTU with a guaranteed rate of100%, total iron was less than0.05mg/L, chroma was less than5degree, without disinfection, total bacteria count ofeffluent was in line with the National Hygienic Standard for Drinking Water, total E.coli had never been found, the two combined ultrafiltration membranes processes couldboth assure biological security perfectly. When the influent was sand filtration effluent,no attenuation of membrane flux had been found during four operational cycles, and noincrease of membrane inlet pressure had been found during four chemical cleaningcycles, ultrafiltration membrane ran stably. When the influent was sedimentationeffluent, attenuation of membrane flux could be as more as1.7L/（m2·h） in a singleoperational cycle, membrane inlet pressure could be restored by chemical cleaning afterfour chemical cleaning cycles, however, variation in turbidity, UV₂₅₄and COD_Mnofbackwashing water related to time showed that residual contamination had been lefteven after completely restoration of membrane inlet pressure, long-term operation couldeasily result in irreversible pollution of ultrafiltration membrane. The second period ofthe pilot experiments took sand filter and carbon filter as the pretreatment ofultrafiltration, the results showed that the effluent of ultrafiltration fluctuated with theinfluent, so it is helpful for stable operation of ultrafiltration membrane and removal oforganic matter, inhibiting membrane fouling with the pretreatment of carbon filter, theremoval rate of UV₂₅₄and COD_Mnprocessed by coagulation–sedimentation–carbonfilter–ultrafiltration could be as more as72.7%and57.2%, respectively. Thebackwashing experiments of ultrafiltration membrane showed that under the same watercapacity, backwashing effect in a high-frequency and low-flow way is better than that ina low-frequency and high-flow way; Increase of backwashing strength above a certainflux contributed to the recovery of membrane flux; extended backwashing time ishelpful for contributing the recovery of membrane flux; extended air rinse stage alone enhanced backwashing effect limited.The combined process of replacing sand filter with carbon filter and increasingultrafiltration could avoid the contact between membrane and floc in effluent ofsedimentation, ensure the stable operation of the ultrafiltration membrane, increase theorganic matter removal on this basis, protect the water quality comprehensively, it is anideal way of reconstruction. The research of this paper has been put in application, ancoagulation–sedimentation–carbon filter–ultrafiltration process drinking water treatmentplant with the maximum capacity of36000m³/d is about to build. The new treatmentprocess can not only promote the security assurance of water quality, but also providereference to the reconstruction of similar scale drinking water plants.