Experimental Study On Membrane Process For The Treatment Of Slightly-Polluted Luan River Water

With the development of society and the increase of life standard, demand for drinking water is stricter and stricter. Ultrafiltration technology, as a new process for the assurance of drinking water quality, is more and more emphasized and concerned by many water treatment investigators. The aim of this thesis is to establish an UF membrane process for drinking water with three hollow fiber UF membranes used to treat polluted Luan River water and supply theorial and practical base for membrane process applied to drinking water plant. The research contents of this thesis contain two aspects followed. Firstly, to study comparablely the pollution removal effect by three UF membranes and optimize the operational parameters of membrane process, and put forward a technical scheme for improving the removal of organics during different water quality periods. Secondly, to analysis the influencing factor of column membrane and immersed membrane such as raw water, pretreatment condition and operational parameters and study the cleaning method and measures controlling membrane fouling, and put forward the measures reducing membrane fouling and cleaning methods restoring efficiently membrane flux.Luan River water, as the main source in Tianjin, has obvious seasonal characteristics such as high-algea and low-turbidity and low-temperature so as to possess larger differences in three water quality periods. The results show that turbidity, particle count and organics of permeate by each membrane all meet the demand of water quality. UF membrane has fine removal effect on turbidity with below 0.14 NTU in the whole year; the difference in particle count is larger which declares that pore size is the major factor of removal effect; smaller pore size, higher organics removal rate, but pore size of UF membrane has minor influence on the removal of dissolved organic matters. The DOC removal ability of UF membrane with smaller pore size is high whenever coagulation is used as pretreatment. During normal water quality period, 36.5～41.6% of permanganate index can be better removed adding 4mg/L of FeCl as coagulant. During low-turbidity and low-temperature water quality period, the decrease of temperature increases water viscosity and reduces the chances of collision between the particles which takes disadvantage of the growth of compact large-size coagulationflocculation, so the dosages should be increased to guarantee the removal oforganics. During high-algae and high-temperature water quality period, membranefouling is rather serious due to higher content of algae, so pre-chlorination (2-3mg/L of residual chlorine) before coagulation step should be executed for effectiveremoval of algae to assure the steady operation of membrane process and improvethe removal ability of organics.Pilot research for drinking water treatment on optimization of runningparameters, organic removal and membrane fouling prevention by coagulation/UFprocess with immersed cluster membrane first applied in an internal plant willsupply an indicative action for its coming wide application in a plant. The researchresults show running parameters and raw water quality are main factors formembrane fouling, among which water quantity, filtration cycle and backwashmethod all affect the stable operation of membrane process, as well as organicconstituent in raw water and low-temperation. Organics with MW less than 1 kDaoccupying above 44% of sum are hard to be removed, while organics with MWgreater than 30 kDa is major factor for membrane fouling. During low-temperatureperiod, the filtration performances of used several UF membranes all decrease indifferent degree, but the operation is rather stable by immersed membrane with thesame parameters as other water quality periods, so there is a certain practicalsignificance that immersed cluster membrane is applicable for low-temperaturecondition.The research results show that pretreatment is an important method reducingmembrane fouling. During high-algae period, pre-chlorination/coagulation andPPC/coagulation can improve the removal of algae as well as relieve the burden ofUF membrane. Though the addition of pretreatment agents such as FeClB3B and PAClall relieve membrane fouling, the operation by the membrane with differentmaterials is obvious different with different coagulants. With material of PVC, theoperational effect is better adding FeClB3B than PACl. With material of PVDF, theremoval rate of permanganate index, UVB254B and DOC adding PACl are higher thanFeClB3B, especially UVB254B, and the operational effect is better than FeClB3B. Besides,PAC as pretreatment before membrane opponently aggravates membrane foulingdue to the action between PAC particles and membrane surface. The chemical cleaning effect is better with the combination with hydrochloric acid, sodium hydroxide and sodium hypochlorite for material of PVC and PVDF, and water temperature, agent dosage and cleaning time are important factors determining the effect. To assure the long-term steady operation in higher flux for immersed cluster membrane, an effective cleaning method restoring membrane flux is advanced. EFM with 1200 mg/L of sodium hypochlorite after every 48 filtration cycles is executed for etiminating organic fouling; when TMP is higher, addition of hydrochloric acid (1.5%) can contribute to lower the TMP in a large degree. With the cleaning method above, the cycle of chemical cleaning can maintain three months.The comparison between UF membrane process and conventional process shows that membrane process will inevitably possess wide application prospect due to good water quality, relative simplicity of installation and operation.