Removal of Microcystin-LR in Water by Chlorine Dioxide

734Joumal of Donghua University(Eng. Ed. ) Vol 24, No 6(2007)Removal of Microcystin-LR in Water by Chlorine DioxideJI Ying(季颖), HUANG Jun-li(黄君礼), FU Jiao(付娇), wU Ming-song(吴明松), SU Li-qiang苏立强)2, CUI Chong-wei(崔崇威)I School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China2 School of Chemistry and Chemical Engineering, Qiqihar University, Qiqihar, Heilongjiang 161006, ChinaAbstract: Microcystins( MCs are well known as tumor promoters. Since cyanobacterial blooms which producehepatotoxins produced by blooms of toxic cyanobacteria microcystins have been extensively found in drinking water(blue-green algae abundant in surface water used asreservoirs of many countries such as Australia], Japan[5Jdrinking water resource and have drawn attention of Argentina [o, German SootlandaJ, Switzerland t3environmentalists world over by leading to adverse health China [io] and so on, it is widely suspected that manyeffects.A study on efficiency and reaction kinetics of conventional water treatment methods are ineffectual innicrocystin-LR( MC-LR)degradation by Cio was removing then a. These water treatment plants are requiredperformed. Experimental results indicated that MC-LR wasto guarantee the drinking water quality according to theremoved by CIO effectively and the residual concentration of respective national drinking water guidelines,the WorldMC-LR could meet the national guideline (GB5749-2006)Health Organization CIJ(WHO, 1998)has set a provisional(1.0 ug.L>, the efficiency of removal was in positiveguideline value for Microcystins-LR(MC-LR)(L: lysinecorrelation to CIo, dosage and reaction time and in negativecorrelation to initial concentration of MC-LR and ph valueR: arginine)of 1.0 Ag. L-in drinking water. Nowadaysthere are many researches on methods of cyanobacterialwhereas it was affected by temperature slightly. Clodosage was the most important reaction factor on base of thetoxins removal, such as photocatalytic system of Uv/orthogonal test results. The reaction was second orderH O2/TiO, 4123, UV-radiation 133, activated carbonoverall and first order with respect to both CIO and mcadsorption[i4. 15], biodegradationL1d-18), ozonation [19 ironLR, and had an activation energy of 78. 81 kJ. mol ". The (I)chloride 2o and chlorination[2, and so on. However,reaction rate constant was 4.74X 10 L/(mol, min) at these methods have some disadvantages and are in phase of10 C. Therefore oxidation of CIO could be taken as an research without using widely. Therefore, looking for neweffective technology for removing MC-LR from drinkingmethods of removing MC-Lr in drinking water is stillwater resources in traditional drinking water suppliesimportant and urgent. Research about chlorine dioxideKey words: CLO2; microcystin, the efficiency of degradation microcystinsremoul, reaction kineticssystematically yet. Chlorine dioxide, a new kind of waterCLC number: X 524 Document code: Atreatment chemical and a potent oxidant used widelyArticle:;1672-5220(200706-0734-06brings no harmful byproducts in reactions with someorganic contaminants[ 21,223. MC- LR is the most commonlymicrocystins in blooms of toxic cyanobacteria in the surfaceIntroductionwater of the world [233. In this research, the degradation ofMC-LR was investigated in detail using chlorine dioxideBlooms of toxic cyanobacteria(blue-green algae) havethe effects of reaction factors were discussed respectivelybecome increasingly common in the surface water of theworld Cr. They potentially threaten human health and areand kinetics parameters were confirmed, and the results ofincreasing the world-wide interest in the health riskexperiments showed that the removal efficiencies wereassociated with cyanobacterial toxinslz. Of the knownsatisfactory.toxins produced by cyanobacteria, the microcystins are themost significant threat to human and animal healthi.McsExperimentalare potent and highly specific hepatotoxins 33, andtumor-promoting activity through inhibition of protein1.1 Chemicalsphosphatases l and 2A [23. Mcs are also well known as liverHPLC-grade MC-Lr mw995. 2, Cs H4 No O2Received date: 2006-04-27Foundation item the National Nanure Science Foundation of China (No. 50178022)and the National 863 Projects(No. 2006AA06Z309).CorrespondenceshouldbeaddressedtoJiYing,Dr.,E-mail;jiyingdoctor@126.comTHaNI万方数括Joumal of Donghua University(Eng. Ed. Vol 24, No 6(2007) 735purity 96%)standard was purchased from ALEXIS and dissolved with 0. 2 mL HPLC-grade methanol beforeBiochemicals(San Diego, USA). All other chemicals used being analyzedwere analysis-grade or HPLC-grade. All the solutions were 1. 5 Experiments of degradationprepared in Milli-Q water Millipore, H2O- MQ)The MC-LR stock solution was obtained by dissolvingChlorine dioxide purity 98%)was generated in HPLC-grade MC -LR in H2O-MQ. Experiments oflaboratorychlorine dioxide degeneration MC-LR were performed in1. 2 Generation and analysis of chlorine dioxide an airtight amber glass bottles in dark place. The operatingaqueous)parameters such as chlorine dioxide dosage, pH valueGeneration and analysis of chlorine dioxide weretemperature, initial concentration of Mc-Lr and reactionaccording to the method described by Huang Jun-li [21, 22)time were changed, respectively. The reactions were1. 2. 1 Generation of chlorine dioxide(aqueousquenched with a drop of Sodium thiosulfate solution ata solution of 25% Naclo2 was introduced bypredefined times. The concentrations of residual MC-LRpumping it at a feed rate of 2-3 mL. min i into a gas in the reaction mixture were analyzed by the hPlc methodgenerating bottle containing 25% H2SO. This bottleescribed abovwas connected to a chlorine scrubber bottle containing a10% solution of NaC1O The scrubber was connected to 2 Results and Discussiona chlorine dioxide collection bottle filled with de-ionizeddistilled water. At the end of the series, an additional 2.1 Effect of reaction timechlorine dioxide trap bottle with 10% KI was present toDegradation efficiencies of MC-Lr at differenttrap any remaining chlorine dioxide. The stock solution reaction time were shown in Fig. 1. Results indicated thatof chlorine dioxide was of an averaged purity of 98% and there was a positive correlation between the degradationstored in the closed container at 4c in the dark to efficiency of Mc -lr by CiO2 and the reaction time.prevent light decomposition of the ClOzBecause of high concentration of reactants the reaction1.2.2 Analysis of chlorine dioxide (aqueous)rate was fast at the initial stage It could be observed thatContinuous iodometric method was used to analyze the 64. 86% Mc-LR could be removed within 30 min andoncentration of ClO2, Ck, ClOz and CIO in water by 95. 2% MC-LR removal occurred within 60 minchanging pH valueExtended reaction times to 75 min and 90 min, the1.3 Analysis of MC-LRdegradation efficiencies were 96. 42% and 96. 88%MC-LR was analyzed using Shimadzu LC-10A respectively and no obvious effect of further degradationHPLC(LC--10ATVP Plus, UV-VIS Detector, CLASSwas shown owing to decreased reactants and increasedVP Workstation ) reversed-phase Hypersil BDS C18 products. Based on result above and conditions ofcolumn (5 Am, 4.6X250 mm). The HPLC conditions werereaction, the reaction time of 60 min was determined asfollows, the uv absorbance detection was set to 238 the optimal for efficiency of removal and evaluating othernm,the mobile phase was methanol0.1%arametersPatrifluoroacetic acid (TFA)(70 30, v/v) with a flow-rateof 1.0 mL. min", a 50 FL sample was manually injectedthe column temperature was held at 25C. The limit of8070determination of Mc-lr by Solid-Phase Extraction (SPE)60is less than1g·L11.4 Solid-phase extractionThe samples should be pre-concentrated by SPe due2010to the trace concentration of MC-LR. The pe0153045607590105cartridges( Solute SPE columns, 1 g of C18(EC)/6 mL) were conditioned with 10 mL of methanolfollowed by 10 mL of Milli-Q water. The samplesFig 1 Effect of time on the degradation efficiency of MCLR( CO(MC-LR=100g·L1yClO2 dosage=5mg·were applied via Teflon tubes at a flow rate ofL-1;pH=6.48;T=10℃)3 mL. min. Then the cartridge was rinsed with10 mLof 10% methanol of aqueous solution and then 2. 2 Effect of CIO2 dosagedried under nitrogen flow for half an hour. MC-LRFig. 2 showed that the dosage of CIO2 had anwas then eluted out from the cartridge using 5 mL of important influence on the degradation of MC-LR andHPLC-grade methanol under vacuum at a flow rate of the relationship between them was presented nonlinearly1 mL. minI. The eluate was dried in nitrogen flow positive correlation. The degradation efficiency of MCTHaNI万方数括736Joumal of Donghua University(Eng. Ed. )Vol 24, No 6(2007)LR increased with increasing ClOz dosage, it was 2.4 Effect of temperature87. 04% with 0. 5 mg. L-I of C102 dosage and couldig. 4 showed the effect of reaction temperature onobtain 94% removal when raising C1O dosage tothe degradation of MC-LR. It could be observed that2. 5 mg.L-1. However, the removal efficiency the temperature had a slight influence on the removalincreased indistinctively when raising the dosage of CIO2 efficiency of MC-LR on the whole. The degradationto high concentration continuously, it increased only efficiencies were 92. 79%-95.9%in the range of1. 2% and 3. 25%with the CIOz dosage of 5 and5-25℃8 mg. L-1. Considering the cost of ClOz and theappearance of harmful byproducts, it is very important toconfirm the dosage of CIO2 in practice projects. Thefeasible dosage of CIOz was ascertained as 2.5 mg. Laccording to the experimental results above909490T/℃Fig 4 Effect of temperature on the degradation efficiencyf MC-LR (CockminlsCIO do2.5mg·LH=6.48)80234567892.5 Effect of initial MC-LR concentrationCIO2 dosage/(mL min")The influence of initial MC-LR concentration onFig 2 Effect of CIO2 dosage on the degradation efficiencythe degradation was presented in Fig. 5. TheofMC-LR《 CO(MC-LR=100阳gL-1t=60mi;concentration of CiO2 was 2.5 mg.L, and thepH=648;T=10)initial MC-LR concentrations were 100, 250 and 375ug.L-l and the corresponding degradation efficiencies2. 3 Effect of ph valuewere 94%,88%,83, 82%respectively with reactionThe effect of pH on the degradation of MC-Lr wastime of 60 min. The degradation efficiencies wereillustrated in Fig 3. Here wide range of ph was researcheddecreased while the initial concentration of MC-Lrfrom 1. 25 to 10, 56. It could be observed that ph was anincreased, and they were in negative correlation, theinfluencing factor on the removal efficiency. When the pH relationship between the removal efficiency andvalues were1.25,3.08,5.07,6.47,8.53and10.56,thereaction time was also accorded with the results showedremoval efficiencies were 99. 99%, 94. 86%,94. 38%,in Fig. 194%,93.14%and 91. 17%, respectively. The degradationefficiencies of MC-LR were slightly increased as the phvalues decreasing in the range of 3 to 11. The resultsshowed that CIO could be effective in a wide range of phvalue. In summary, the satisfactory degradation can be100gLobtained under the conventional water treatment pH要呈250ggcondition→375μgL45751/minFig. 5 Effect of initial MC-LR concedegradation efficiency of MC-LR(CIOz dosage2.5 mg.L60 min, pH2.6 The result and analysis of orthogonal te80456789101112Ly(3)was taken in the orthogonal test. The fourfactors were CIO2 dosage (mg. L-I),time( min)Fig 3 Effect of pH on the degradation efficiency of MC℃)14)d theLR(Co(MC-LR= 100 Pg.L-l, (=60 min CIO2corresponding three levels were 2. 5-5sage=2.5mg“L-l;T=10℃)mg·Ll),60-75-90(min),5-15-25(C)THaNIJoumal of Donghua University( Eng. Ed. )Vol 24, No 6(2007) 737and 4.51-6.. 53 respectively. The results were 2.7 Degeneration kineticsshown in Table 12. 7.1 Determination of reaction order of MC-lr and aoTable 1 Analysis of orthogonal test resultsAccording to the method of the law of isolatedParameter described by pilling[26], determination ofreaction order was proposed The initial concentration ofTimeemoval efficiencyL-1) /min T/cNo. /(mgof MC-LR/%MC-LR was 100 Fg.L, the dosages of CIO were 810, 15 and 20 mg .L-, which were over-dose in thedegradation reaction so as to be considered as a constant2.56.48Results shown in Table 3 indicated that the correspondin22.5correlation coefficient R2 was more than 0. 97 and there2.54.596.98was a linear relation between In(Co/c)and reaction time4.51t, so the degradation process was fitted with pseudo-first7596.4order rate equation well, and the reaction orders of mC68.53LR was first order. Rate constant ki of the pseudo-first-order rate equation increased along with increasing of84.5197.41concentration of CIO25In Fig. 6, the experimental data were fitted with linearequation, the corresponding correlation coefficient R wasK194.5495.4595.1495.811 and the relationship of In ki-In[CIO2 Jo was similarlyK296.1996.196.5496.05linear, the slope which was the reaction order of CIO2 wasK398.0397.2297.0896.90close to 1, so the reaction order of clo was first order andR,3.491.771.931.09the total reaction order was second order.Table 3 Parameters of pseudo-first-order kinetics atFrom the analysis ofR, IR;= max(Ki )-min(K ))indifferent initial CIO, concentrationsTable l, it could be concluded that the significance rank of(pH=6.48;t=60min;MC-LR=100g·L-1;T=10℃)the four factors affecting degradation efficiency was theCIO dosage, temperature, time, pH. CIo dosage was No [CIO2 Jo/(mg·L1)Rate equationmore important than pH value, temperature and reactiontime affecting the degradation efficiency, so CIO dosagehn(co/c)=0057t-0.1430.0570.9886hould be optimized in order to improve the removal2ln(co/c)=0.071r-0.2440.0710.9950efficienciesln(co/c)=0.105t-0.6730.1050.9747In water body of our nation used as drinking water420ln(co/c)=0.139t-0.5250.1390.9810resource, the actual concentration of mc -lr is less than10]g.L-1L24, 23. Results of removal efficiency of 5 AgL1McC- LR with1.0mg· L- CIO and10g·LMcLR with 2.0 Hg.L CIO were shown in Table 2, residualy=09715r-48838concentrations of mcLR were both less thanR=11.0Ag.L,which met the requirement of therecommended value of who. It was taken as basis of2.5theory in practical water treatmentTable 2 Results of ClO2 degradation low concentration2.53.5MC-LR(t= 60min; pH=6. 48)In[CIO2]oFig 6 Determination of reaction order of CIO2InitialResidua[CO2Jo concentratioconcentration2.7.2 Determination of reaction rate constants k/(mg·L-l)ofMC-LRof mc-LR/("g·L-1)/(g·L-1)In the practical engineering, the reaction rate constantk of C102 degradation MC-Lr is also an important<1.0parameter, and the second order reaction rate constants k21.015<1.0could be obtained from the equation of k2 =k1/[CIO2 Jo2.0<1.0The dosages of CIO were 8, 10, 15 and 20 mg.L-,and2.015<1.0corresponding k were listed in Table 4, so the calculated10average of k2 was 4.74 X10 L/(mol. min)THaNI万方数括738Joumal of Donghua University(Eng. Ed. )Vol 24, No 6(2007)Table 4 Determination of reaction rate constants kSynthetase System[J]. Chemistry& Biology, 2000, 7(10)1753-764Average ofk2×1022 Tsuji K, Watanuki T, Kondo F, et al. 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The dosage of CIO affected the removal seriouslyOrganization, Geneva, 1998: 95-110.proved by the orthogonal test results.[12] Qiao R P, Li N, Qi X H, ef al. Degradation of2)The kinetics of MC-lr degradation by CIOMicrocystin-RR by UV Radiation in the Presence offollowed second order reaction equation, reaction orders ofHydrogen Peroxide[J]. Toxicon, 2005, 45: 745-752the CIO, and MC-LR were first order respectively, the [13] Alam M B, Otaki M, Furumai H, et al. Direct andreaction rate constant was 4. 74 X102 L/(mol min)andIndirect Inactivation of Microcystis Aeruginosa by UVactivation energy was 78.81 k. mol. In conclusion,Radiation[J]. Water Research, 2001, 35(4): 1008-1014[14] Pendleton P, Schumann R, Wong S H. Microcystin-LRoxidation of CIO could be taken as an effective technologyAdsorption by Activated CarbonLJ]. 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