Drinking water production by ultrafiltration of Songhuajiang River with PAC adsorption

Available online at www. sciencedirect.comJOURNAL OFENVTRONMENTAL。ScienceDirectSCIENCESISSN 1001-0742JES,CN11-2629/XJournal of Environnental Sciences 19(2007) 536 -539www.jesc.ac.cnDrinking water production by ultrafiltration of Songhuajiang Riverwith PAC adsorptionXIA Shengji+*, LIU Ya-nan2, LI Xing', YAO Juan-juan'1. State Key Laboratory of Plluion Control and Resources Reuse, Tongi University, Shanghai 20092, China, E-mail: xiashengji@ yahoo.com2. School of Environmental Science and Engineering, Dong Hua University, Shanghai 201620, China3. School of Architecture and Civil Engineering, Bejing University of Technology, Bejing 100083, ChinaReceived 29 May 2006; revised 8 September 2006; accepted 18 September 2006AbstractIn recent years, membrane ultrafiltration (UF) of surface water for drinking water treatment has become a more atractive technologyworldwide as a possible altermative treatment to conventional clarification. To evaluate the performance of ultrafilration membranesfor treatment of surface water in North China, a 48-m2 low pressure hollow fiber membrane utrafiltration pilot plant was constructed.Utrafiltration was operated in cos-Aow and with powdered activated carbon (PAC) adsorption. Turbidity was almost completelyremoved to less than 0.2 NTU (below Chinese standard 1 NTU). It was found that PAC addition enhanced organic matter removal. Thecombined process of PAC/UF allowed to 41% removal of CODMo, 46% removal of DOC and 57% decrease in UV2s4 absorbance. Theelimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PACconcentration was below 30 mg/L, backwashing could recovery the membrane fux with backwash intera/backwashing duration of1/30.Key words: surface water; drinking water treatmnent; ultrafltration; powdered activated carbonIntroductionactivated carbon (PAC) adsorption.As the economic conditions improve and the livingIn South Africa, aiming at the rural and pre-urbanstandard rises every year in China, people are more andcommunities, altemnative process for water purification tomore concerned about food and drinking water quality.conventional water treatment was investigated. Botes etHowever, the tap water quality is not as satisfactory asal. (1998) has taken evaluation of a ultrafiltration (UF)other aspects because of the poor quality of raw water duepilot plant for potable water production. The results ofto unfit soil and water conservancy; therefore, advanceda 15-m2 UF membrane have shown the removals, >95%water treatment should be constructed to replace theturbidity, 92%- 97% apparent color, 97%- 99% iron, andconventional clarification. In recent years, ultrafiltration60%-80% natural organic matters. All fecal and otherprocess applied to water treatment has become a morecoliform bacteria were also removed. A 15%- 20% averageattractive technology worldwide to produce potable water.specific fux loss was observed, and the membrane life wasCompared to the conventional treatment, ultrafiltrationestimated to be more than 5 years.process seems to have many advantages such as smallerFor the design and construction of a membrane waterspace requirements, invariable quality of produced water,potabilization facility, Arual et al. (2002) carried out somesavings of water purification chemicals and operationtests with a UF plant to analyze the UF performance.cost and easy automation (Wiesner and Chellam, 1992;The plant has an ultrafiltration module equipped with aLahoussine-Turcaud et al, 1990). However, an importantpolisulfone spiral wound membrane with a cut-off of 100obstacle to further incorporation of membrane processkDa. According to the results, it can be said that membraneinto water treatment plants is the problem of membraneperformance is very satisfactory; especially bearing infouling, especially in case of using surface water. Controlmind that the water used in those tests has very unfavorableof fouling is of utmost importance. A technique for foulingcharacteristics. The rejection of test UP membrane to thealleviation is pretreatment of feed water with powderedmicr(中国煤化工Vas gtten to 100%.Tofound that the appli-catioC N M H Gfective in the removalProject supported by the Hi-Tech Ressarch and Development ProgramTH(863) of China (No. 2002AA601140), the Science and Technologyof organte suDstances wIn DoUn I0W and high molecularCommission of Shanghai Municipality (No, 052312008) and the Na-weights. Humic acids were removed in about 90% andtional Eleven Five Year Scientific and Technical Support Plans (No.phenol was removed completely for the same PAC dosage2006BAJ08B06, 2006BAJ08B02).*Corresponding author.equal to 100 mg PACI (powdered activated CI). In the UFE-mail: xiashengji@ yahoo.com.No.5Drinking water production by ultrafitration of Songhuajiang River with PAC adsoption537process conducted without PAC addition only 40% of HAreactor unit, a cross-flow UF unit with a recirculation andwere rejected, while the total amount of phenol passedpermeate backwashing. PAC was added as pretreatmentthrough a membrane.for membrane filtration. Suficient and rapid mixing isIn this paper we report the results of UF experimentsprovided by a static mixer, The reactor tank was 1 m3 andwith modified polyvinyl chloride (PVC) membranes. Our the reacting time was 10 min. Water was prefiltrated to 200eartier study (Xia et al.2004a, 2004b), a capacity of 100pum, and then injected in the circulation loop by the feedLh, has shown ultrafiltration was very efficient to producepump. In the ultrafiltration phase, the water was filtrateddrinking water with a raw water in North China. In thisfrom inside to outside of the hollow fiber with a constantresearch, a capacity of 5 m'/h ulrafltration process wastransmembrane pressure 0.12 MPa. In the backwash phase,constructed. This paper presents results concerning thethe washing water was sent to pressurize from the outsidepilot plant investigation.about 0.2 MPa to the inside of the hollow fiber. Pressuregauges and electromagnetic flow meters were used to1 Materials and methodscontrol the operating performances. The raw water used1.1 Membranes and PACwas Songhuajiang River water nearby Harbin in NorthUtrafiltration membranes (from Lisheng Co. Ltd.) madeChina. A and B were the points of water sampling whichof PVC were used in the experiments. The nominal molec-indicated the raw water and ultrafiltrated water.ular weight cut off of these membranes as reported by1.3 Analytical methodsthe manufacture is 80000 Dalton. Characteristics of theAll water samples were analyzed for chemical oxygenmembranes are shown in Table 1. The powdered activateddemand (CODM), UV absorbance at 254 nm and dis-carbon was obtained from Ninde Xinsen Co. Ltd. Itssolved organic carbon (DOC) concentration. CODMn wascharacteristics are given in Table 2.determined according the method described in USEPA1.2 Ultrafiltration test apparatus and procedure(1983). DOC was analyzed on fitered samples (0.45 um)Fig.1 shows a schematic diagram of the UF exper-in a TOC analyzer (Shimadzu TOC-Vcpn). UV absorbanceimental facility. The system consists of three parts: awas measured in an UV/Vis spectrophotometer (Leng-guang 752N), also on filtered samples (0.45 um). QuartzTable 1 Membrane characteristis datacuvette with a path length of 1 cm was used. The turbidityParameterUF membraneswas measured with the help of the HACH turbid meter,model 2100AN. Particle counting was done with a PCXTypeHollow fiber2200 (HACH). The particle counter has 8 channels from 2MaterialMolecular weight cut off (Da)80000um to 750 um.Hollow fiber internal diameter (mm)9Hollow fiber extemal diameter (mm)1.52 Results and discussionMembrane surface area (m2)482.1 Efect of PAC added on permeate fluxpH-range of operation2-13Temperature-range (°C)0- 40Variations of the permeate fux for different carbondosages are presented in Fig.2. The ultrafiltration fuxTable 2 Characteristics of powdered activated carbondecreased from approximately 90- 65 L/(m2h) after 60Descriptionmin. There is no difference between them with diferentPAC concentration. These results were consistent withlodine number (mg/L)1000-1400the results by Tomaszewska and Mozia (2002). It can beMethylene blue (ml/g, 0.12%)200-270Moisture content (% max)5-10explained by a relatively loose structure and high porosityBET surface area (m2/g)840of PAC cake deposited on the membrane. The thicknessreatmg)Iron content (% max)0.05-0.1of the PAC cake was probably independent on the PACChloride content (% max)0.05- -0.2dosage applied because the outer layer of the cake wasDischargc,PrefilterPemcatePACMembrane| Static mixermoduletank40000-Raw water中国煤化工pumpReactorMHCNMHGsackwasnngFeed pumpFig. 1 Schematic flow diagram of the experiment.538XIA Shengji et al.Vol. 19100r 8(QUF图 PACUFE14(+ 10 mg/L0f昂20+3omgL20-1 PACUF1030CODmaDOCTime (min)AvVwFig. 2 Permeate fux decline with dfferent PAC.Fig. 4 Organic matter removal with UF and PAC/UF.continuously removed by flowing retentive. According towere removed. The combined process of PAC/UF alowedSylwia and Tomaszewska (2004), the porosity of the PAC to 41% removal of CODMn, 46% removal of DOC and 57%cake formed on the membrane surface was much greaterdecrease in Avs. Comparing CODMn, DOC to UVzs4than the maximum pore size of the membrane, which was rejection, a higher rejection of UV absorbing compoundsthe reason that the PAC cake structure should not afect thewas observed, this indicated a preferential removal ofprocess performance.larger and more aromatic compounds. UV254 measures2.2 Turbidity reduction during experimental timemostly molecules with conjugated double bonds like aro-matics. DOC measures all total dissolved organic carbon,In this study, turbidity was used to monitor the mem-therefore, more small molecules are not probably retained.brane separation efficiency. Turbidity is a qualitativeCODMn again measures even inorganic material, which canmeasurement of the amount of dissolved solids in a processbe oxidized, and therefore retention according to CODMnstream and is measured in nephelometric turbidity unitsis low with UF membranes.(NTU). Fig.3 shows a sharp reduction in the turbidity:2.4 Removal of particles by ultrafiltrationmore than 99% of turbidity is eliminated. The permeateturbidity is usually around 0.15 NTU and below 0.5 NTUIn addition to the measurement of turbidity and organicunder all experimental conditions studied.matters, particle retention per ml was determined in thetest. The raw water was pumped in from the Songhuajiang1000River. Typical particle distribution by number percentageis shown in Fig.5. The specific distribution (Fig.5) wasbased on average 60 measurements during one run. As wasexpected, fine particles larger than 2 um were signifcantlyremoved by membrane filtration. Particles between 2-3◆Rawwntar- + AfterUfμm occupied approximately 53% in the raw water, andwere 56.3% in the permeated. The percentage of particles0.14u屹p岫岭的公个between 3- 6 pum in the permeated were less than those inthe raw water imply that those particles had a tendencyto be removed. Particles larger than 7 pum were almost04-Jm24Jm14J元3-Augcompletely removed through qualitative analysis. As canDatcbe seen, around 99.8% of the counted number of particlesFig, 3 Turbidity reduction during experimental time.was found in the range of 2-8 pum in the raw water. Anexample of the particle number (particle size >2 um) in2.3 UF and PAC/UF on organics removalraw water, and ultrafiltrated water with two operations runAn improvement of UF permeated quality in the com-bination of powdered activated carbon with UF process10000空Rawwater。。Uhas been observed in several studies (Lin et al, 2000;F Rawwater(%) 子UF (%)+8Hagen, 1998; Krystyna and Grzegorz, 2002). The mem-brane provides a physical barrier preventing the passageof the PAC, and therefore retaining the organic commandst 60100 tabsorbed on the PAC, which otherwise would be trappedby the membrane. In Fig.4 the effectiveness of the removal- 40of CODMa, DOC and UV2s4 absorbance (Auvzs) during中国煤化工UF and PAC/UF progress were presented. The PAC dosaget2was equal to 30 mg/L with raw water of CODMn 4.20MYHCNMHGmg/L, DOC 9.31 mg/L and UV254 0.154 cm-'. It was .0.01found that PAC addition enhanced organics removal. When2-3 3-4 4-5 5-66-7 7-8 8-750the UF process was conducted without PAC addition, 30%Particle size (um)of CODMn, 35% of DOC and 43% of UV254 absorbanceFig. 5 Particle distribution of raw water and permeate water.No.5Drinking water production by ulrafilration of Songhuajiang River with PAC adsorption539Table 3 Effect of backwashing on the fAux recovery ([L/(m2 :b))Backwash intervalPAC 10 mg/LPAC 30 mgLPAC 50 mg/LBefore washingAfter washing20 min73.4)074.19279.49140 min69.068.389.573.18760 min67.13966.288.68is given in Fig.6. The elimination of particles, from averageResults showed that turbidity was almost completely12000/L in the raw water to approximately 15/ml in theremoved to about 0.15 NTU independent of raw waterpermeated, was observed. The number of particles in thequality. It was found that PAC addition enhanced organicUF filtrate is about 100 count/ml just after the backwashmatter removal. The combined process of PAC/UF reachedand decrease rapidly to the level of 10 -20 count/ml. Thisto 41% removal of CODMn, 46% removal of DOC and 57%confirms that the membrane was not damaged during thedecrease in UV254 absorbance. Comparing CODMn, DOCtest period.to UV254 rejection, a higher rejection of UV absorbingcompounds was observed. The particles between 3 and 600000μm seemed to have a tendency to be eficiently removed.10000In China, for surface water of high turbidity and fairlyvariable quality, PAC adsorption prior to UF should be1000considered.AfterUF00 kReferences0fAmal J M, Femandez M s, Martin G V et al, 2002. Design andconstruction of a water potabilization membrane facility300120and its application to the third world countries PreliminaryTime (min)tests[J]. Desalination, 145: 305- -308.Fig. 6 Removal of particles by ulriftration.Botes J P, Jacobs E P, Bradshaw S M, 1998. 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