Experimental study on flocculation performance of Chitosan-Based Flocculant using a Novel Jar Tester

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1 v Engineering Group Journl of ivil Engineering nd Environmentl Sciences DOI: ISSN: X y Kzuhiro Fujiski* Senior cdemy of Kyushu Institute of Technology, Kitkyushu, Jpn Received: 24 Septemer, 28 ccepted: 3 Octoer, 28 Pulished: 4 Octoer, 28 *orresponding uthor: Kzuhiro Fujiski, Senior cdemy of Kyushu Institute of Technology, Kitkyushu, Jpn, E-mil: Keywords: hitosn; Floccultion window; Floccultion rte process; Microdose; Novel jr tester Reserch rticle Experimentl study on floccultion performnce of hitosn-sed Flocculnt using Novel Jr Tester strct The effectiveness of chitosn s flocculnt ws tested with novel experimentl pprtus. Using newly developed floccultion tester, lrge numer of floccultion rte processes were mesured. The novel jr tester included photocoupler nd switching timer. Mixing ws pused for period nd the floc-settling velocity nd residul turidity were mesured during this period. The reltion etween the turidity of the superntnt (i.e., the residul turidity) nd chitosn dose ws mesured over wide rnge of initil turidities. The chitosn showed two windows for the optimum dose: () dose close to tht used with ordinry inorgnic flocculnts, t which the residul turidity showed complicted ehvior under the influence of vrious fctors, nd (2) n optimum dose in the order of 4 of the initil turidity. The ltter optimum-dose rnge is very nrrow, nd simple chrgeneutrliztion plys n importnt role in the floccultion. Introduction Mterils nd Methods hitosn is liner copolymer tht is produced y decetyltion of chitin, which is the second-most undnt iopolymer in the world fter cellulose. Owing to its unique properties, chitosn is used in mny industril pplictions []. hitosn hs lso ttrcted significnt mount of reserch ttention s promising cogulnt nd flocculnt, (hereinfter, floccultion is used insted of cogultion/ floccultion, s well s flocculnt insted of cogulnt/ flocculnt ) owing to its environment friendly properties. lthough mny floccultion experiments hve een conducted using chitosn nd excellent reviews hve een reported so fr [, 2], the mechnism of floccultion y chitosn hs not een sufficiently clrified. This study ims to investigte the chrcteristics of chitosn when used s flocculnt. For this purpose, floccultion rte process nd residul turidity were mesured with vrious chitosn doses over wide rnge of initil turidities. novel floccultion tester ws used for the mesurement of these floccultion processes. This device includes photocouplers ttched to oth sides of eker. The floccultion experiments were conducted y intermittent mixing. When mixing ws pused, the settling velocity of the floc nd the residul turidity of the solution were mesured y light trnsmission. Floccultion windows, which indicte the effective rnge of flocculnt doses, were demonstrted for wide rnge of initil turidities. In ddition, the floccultion rte processes re lso discussed. Experimentl setup The experimentl setup is shown in figure. Photocouplers (I) nd switching timer (F) re ttched to conventionl jr tester. The photocouplers re ttched to oth sides of the eker for mesuring the turidity of the suspension (Figure ). lthough severl pprtuses for opticl mesurements of floccultion processes hve een reported [3-7], they hve ll dopted suction nd continuoussmpling methods. In the proposed study, residul turidity ws mesured y pusing mixer nd llowing flocs to settle in the eker [8], which is unique function of the novel jr tester. The photocouplers were composed of 68-nm-wvelength red ) H D F E G Figure : Experimentl setup ) Generl ssemly nd ) close up of eker with photo-coupler. 38 ) I I ittion: Fujiski K (28) Experimentl study on floccultion performnce of hitosn-sed Flocculnt using Novel Jr Tester. J ivil Eng Environ Sci 4(2): DOI:

2 light-emitting diode (LED) lsers nd fier-type nlog opticl sensors (F7RN Tkenk Denshi o., Ltd., Jpn). lirtion curve nd smple powder Figure 2 shows the reltionship etween the solids concentrtion, or turidity, nd the output voltge of the turidity meter developed for these tests. The verticl nd horizontl xes represent the concentrtion of grde- kolin powder introduced to the suspension nd the output voltge of the turidity-meter sensor, respectively. Regent-grde kolin powder ws not used in the floccultion experiment, ecuse it is expensive nd ecuse we hd to conduct very lrge numer of trils. However, the solid prticles/flocs concentrtions could ll e expressed s equivlent kolin prticle concentrtions using this clirtion curve. Figure 2 shows tht it is possile to mesure prticle concentrtions from to mg/l using this device. White cly powder for pinting ( Shiroetuchi sok ermic Mteril o., Ltd., Jpn), with properties like those of stndrd kolin powder, ws used in this study. The ignition loss of this powder is 2.5%, nd the min constituents re 47.6% SiO 2, 38.5% l 2 O 3,.52% Fe 2 O 3,.5% O,.22% MgO,.42% K 2 O,.% N 2 O,.28% TiO 2. The settling-velocity distriution of the smple powder is shown in figure 3. The verticl xis of figure 3, cumultive finer, is the mss-rtio of the prticles moving slower thn the settling velocity on the horizontl xis to the totl prticles in the suspension. Flocculnt nd other experimentl conditions The flocculnt tested in this study ws commercilly ville chitosn-sed flocculnt (FUJI len KT-25, Fuji Engineering o., Ltd., Jpn). Hereinfter, chitosn is used in plce of chitosn-sed flocculnt. It hs een reported tht the moleculr weight of this chitosn powder flocculnt is on the order of 6 nd tht its degree of decetyltion is out 6%. Household well wter ws used, with temperture in the rnge of 5 25 nd ph = 6.5, respectively. The mixing conditions were stndrdized s follows: strong mixing t 25 rpm (G = 5 s ) for 4 min, performed twice (totl 8 min = 48 s) nd, fter tht, slow mixing t 6 rpm (G = 35 s ). The photocoupler ws locted 2.4 cm elow the wter surfce. totl of 25 ml suspension contining the smple powder nd flocculnt ws introduced to the 3-mL eker. The suspension is initilly stirred for 3 minutes. The mixing nd pusing steps oth lsted for 4 min. The residul turidity is defined s the turidity of superntnt contining prticles whose settling velocities elow. cm/s (i.e., 2.4 cm/24 s). The output voltge corresponding to trnsmitted light ws recorded continuously on computer vi dt-logger. Results nd Discussion Exmples of experimentl results Figure 4 plots the temporl vrition in the suspension turidity. The horizontl nd verticl xes represent the time (s) elpsed from the strt nd the residul turidity of the suspension, s mesured 2.4 cm elow the suspension surfce. During the mixing periods, the turidities were high nd vried little, wheres during the intermittent puses the floc concentrtion rpidly declined due to settling. For the nlysis of floccultion processes, the mesured results shown in figure 4 cn e divided into two prts, periods for mixing (Figure 5) nd still conditions (Figure 6). Figure 5 excludes the settling periods shown in figure 4. Thus, the horizontl xis in figure 5 represents the net mixing time. The gry curves with origins shifted y 2 s in figure 5 represent the results from continuous-mixing trils, which hd no puses. Since the two curves nd their residul turidity mostly mtch, the effectiveness of the intermittent mixing method is confirmed. Figure 6 shows only the dt from the intermittent puses. With incresing mixing time, the flocs grow, so the settling speed increses, which increses the slopes of these curves. The distriution of flocsettling velocities cn e otined y differentiting these curves. lso, y connecting the tops of these curves, we find rte t which the residul turidity decresed, s discussed elow. Output voltge (v) Figure 2: Reference curve. Figure 3: Settling velocity distriution of whitecly smple nd kolin powder. Turidity Turidity :2mg/L : 4mg/L : 6mg/L Time (s) Figure 4: Exmple of vrition in residul turidity over time. 39 ittion: Fujiski K (28) Experimentl study on floccultion performnce of hitosn-sed Flocculnt using Novel Jr Tester. J ivil Eng Environ Sci 4(2): DOI:

3 Ordinry dose floccultion window For vrious initil turidities, the influence of chitosn dose on residul turidity is plotted in figure 7. The horizontl xis represents the chitosn dose nd the verticl xis represents the residul turidity (turidity of the superntnt). The solid nd roken lines indicte residul turidities mesured fter 32 min nd 64 min of mixing. These mixing durtions were chosen s temporry stndrds for short- nd longterm mixing, respectively, to llow comprison of floccultion processes mesured under identicl mixing conditions. Usully, the centrl regions of such windows show the optiml dose, since floccultion decreses with either underor over-dosing. Thus, the windows usully show U-shped residul turidity curves. However, in this experiment, s shown in figure 7, the curves were not monotonic. When the dose ws incresed ove the optiml dose, floccultion deteriorted [-3]. However, further incresing the dose promotes floccultion [9]. hitosn flocculnt seems to hve the unique chrcteristic tht wveform ppers in the floccultionwindow curve. In ddition, these windows show the unique fetures corresponding to ech initil turidity. For the initil turidity 5 mg/l (Figure 7), if the dose rnge is 2 mg/l or more (except ner 5 mg/l), the two curves show similr shpes, which suggests tht the floccultion performnce is similr in this dose rnge. With mixing for 32 min, wveform clerly ppers in the windows of mg/l (Figure 7) nd 6 mg/l (Figure 7d) nd the two curves show similr trends. On the contrry, in the 64-min mixing window shown in figure 7 nd 7d, the curves show quite different shpes. In ddition, in the cse of 2 mg/l (Figure 7c), the window wveform resemles the 5 mg/l cse (Figure 7) more thn the others (Figure 7,7d). Since vrious fctors influence the dsorption of chitosn on the prticle surfces, these wveforms provide useful initil dt for detiled study of the complex mechnisms of floccultion using chitosn. Smll-dose floccultion window Figure 8 shows the influence of smll dose of chitosn on residul turidity figure 8. Is n expnsion version of the smlldose region of figure 7, with the horizontl xis expnded on logrithmic scle. lerly, the chitosn strongly encourges floccultion, even t very smll doses figure 8. Shows tht the optiml dose rnge is very nrrow nd the residul turidity is less thn in the ordinry dose cse (Figure 7). Furthermore, the floccultion rte is lso very high. In figure 8, the floccultion is nerly complete fter 32 min of mixing. When normlized vlues re compred, mening we convert oth xes to reltive vlues y dividing them y the respective initil turidity, the four curves resemle ech other (Figure 9), indicting tht the floccultion mechnisms re similr in this very-smll-dose region. The results lso indicte tht the vlue of the optimum reltive dose is (.2 2) -4. The following mechnisms hve een considered to explin floccultion y chitosn: simple chrge neutrliztion, chrge Turidity Time (s) Figure 5: Finl stge of floccultion. Turidity ptching, dsorption, ridging, nd sweeping [,2,,]. In the cse of the microdose (Figure 8), chrge neutrliztion seems predominnt, since the optimum dose is proportionl to the initil turidity [2,5], while t higher doses, e.g., lrger thn mg/l (Figure 7), other mechnisms seem to e involved in complicted mnner. hitosn hs een reported to hve ' ' ' Time (s) Figure 6: Time vrition of settling velocity. Residul tueidity Residul turidity Residul turidity turidity Residul mg/L mg/l 2mg/L d 6mg/L 4 > Flocculnt dose Figure 7: Floccultion windows ordinry dose-. c ittion: Fujiski K (28) Experimentl study on floccultion performnce of hitosn-sed Flocculnt using Novel Jr Tester. J ivil Eng Environ Sci 4(2): DOI: 4

4 highly efficient floccultion effect even t smll doses [, 9-, 2-4]. The experimentl results shown in Figure 8 confirm the results of previous reserch. To check the influence of eker contmintion, lnk experiment with no chitosn dose ws performed, nd confirmed the vlidity of the present experimentl results. Floccultion rte processes The floccultion rte processes with different doses re compred in figure. The horizontl nd verticl xes represent the net mixing time nd the residul turidity, respectively. The initil turidity ws mg/l in ll trils. lerly, the vrition in floccultion rte processes depended on the dose. For exmple, in the /L dose cse, floccultion ends fter. mg only 2 min (72 s) of mixing. On the other hnd, when the dose ws. mg/l, flocks lso rpidly grew, ut then repeted cycles of rekge nd refloccultion occurred. t other doses such s.5, 2, nd 4 mg/l, the floccultion seemed to hve pused despite continuous mixing. To investigte which phenomen occurred during this puses, simultneous mesurements of chitosn dsorption nd the zet potentil on the prticle surfces re necessry. To fcilitte more-detiled discussion of the floccultion rte processes shown in figure, the timevritions of flocsettling velocity distriutions re shown in figure. In the erly stges of floccultion, very smll, reltively uniform-size flocs were produced with ll three doses. For the. mg/l dose, floccultion ws lmost finished fter only very short mixing period, 48 s. On the other hnd, for the.5 mg/l dose, the flocs mixed for s did not significntly grow during mixing, while for the 4 mg/l dose, the flocs mixed for time rnge s showed remrkle growth during mixing. These findings re consistent with the corresponding floccultion rte processes shown in figure. For the. nd.5 mg/l dose, the floc-settling velocities were round.6 cm/s. For the 4 mg/l dose, despite reltively high flocsettling velocity,.3 cm/s, the residul turidity ws rther high. In this cse, the floc-size distriution is rod, so smll flocs remined in the suspension for long time. Figure 2 shows the floccultion rte processes for vrious initil turidities. The horizontl xis represents the net mixing time, nd the verticl xis represents the reltive turidity, tht is, the residul turidity divided y the initil turidity. The cption, for exmple, 5:. mens tht the initil turidity ws 5 mg/l nd chitosn flocculnt dose ws. mg/l. The sme nottion is used for the cptions in figure 3. In figure 2 nd 2, for ech initil turidity, the dose tht shows norml or reltively good floccultion performnce is selected. For lrge doses (Figure 2), ll the curves show preprtory or puse period, in which the floccultion speed slows to ner zero; fter this intervl, floccultion resumes. lthough the durtion of this period vries depending on the initil turidity, the puses tended to egin round 2 s. For smll doses (Figure 2), the reltive residul turidities decresed to / of the initil turidities within 6 s of mixing, except when the initil turidity ws 5 mg/l. Residulturidity turidity Residul turidity Residul 2 Residulturidity Flocculnt dose 2 d 6mg/L c 5mg/L mg/l 2mg/L >. Flocculnt dose Figure 8: Floccultion window smll dose-. residul turidity/initil turidity ( -).E+.E-.E-2.E-3.E-4 mixing mg/l E-5 chitosn dose/ini l turidity (-) Figure 9: omprison of windows with normlized scle. Figure : Floccultion rte process. This rpid decrese indictes tht the chitosn encourges floccultion remrkly well, even t smll doses. In ddition, some of the curves showed similr shpes, suggesting tht similr phenomen took plce during floccultion. ittion: Fujiski K (28) Experimentl study on floccultion performnce of hitosn-sed Flocculnt using Novel Jr Tester. J ivil Eng Environ Sci 4(2): DOI: 4

5 Furthermore, for up to out 5 s of mixing, the curves were lso close to liner, mening tht the floccultion kinetics cn e pproximted s first-order chemicl rection. Figure 3, shows the floc-settling velocity distriutions for vrious initil turidities figure 3. ompres the floc-settling velocities chieved with smll chitosn doses nd for the short mixing time of 48 s. When the initil turidity ws reltively low (i.e., in the rnge 5 mg/l), lthough the floc sizes were nerly uniform, the settling velocities were slow since the floc size is lso smll. Figure 3, compres the settling velocities chieved with lrge chitosn dose nd long mixing time of 92 s. In this cse, the settling-velocity distriutions were roder nd the settling velocities were severl times higher with the lrge doses thn they were with the smll ones. It should e noted tht this figure is presented only for the ske of comprison. lerly, some of the smples mixed for 92 s were still flocculting t the end of the tests. In figures 3, the floccultion rte processes under vrious conditions re depicted. The chrcteristics of chitosn floccultion re clerly shown in these figures. Therefore, the present experimentl dt provides importnt informtion for the dvnced nlysis of floccultion mechnism with chitosn. The vrince in the mesured turidities ws generlly within 5%, the dt, however, sometimes showed lrge scttering in the dose rnge where the curves of floccultion window hd steep slopes. detiled study is currently ongoing to understnd this process etter. onclusions This study demonstrtes tht chitosn encourges floccultion vi different mechnisms depending on the dose. The optimum doses for chitosn flocculnt fll into two optiml Reltive vle of residul turidity ( -) Reltive vlue of residul turidity ( -).. lrge mount of dose. Figure 2 Floccultion 2rte processes 3 4 Mixing time (s).. : 3 2 : 5 4 : 4 6 : 2 8 : 4 smll mout of dose 5 :. :. 2 :. 4 : 8 :. 5 Mixing time (s) Figure 2: Floccultion rte process. Reltive frequency ( -) Reltive frequency ( -) s mixing 5:. :. 2:. 4: 8: Settling velocity (cm/s) 92s mixing.5 Settling velocity (cm/s) :3 2:5 4:4 8:4 Figure 3: Time vritions of floc settling velocity. c windows. t very smll doses, microdose, on the order of 4 of the initil turidity nd the second ws pproximtely 3 of the initil turidity, which is on the sme scle s the dose used for usul inorgnic flocculnts. In this norml-dose regime, the residul turidity curves re not U-shped, ut fluctute with incresing chitosn dose. In the microdose window, on the other hnd, floccultion proceeds quickly nd the residul turidity is low. These unique results reflect inherent properties of iopolymer flocculnt chitosn. Thus, the ove results my prove useful in further studies on floccultion mechnisms of chitosn relted flocculnts. In ddition, the novel experimentl photocoupler pprtus proves to e useful nd inexpensive tool for floccultion studies. cknowledgements Figure : Time vrition of floc settling. The chitosn flocculnt used in these tests ws donted y Fuji Engineering o. Ltd, for which the uthor is grteful. 42 ittion: Fujiski K (28) Experimentl study on floccultion performnce of hitosn-sed Flocculnt using Novel Jr Tester. J ivil Eng Environ Sci 4(2): DOI:

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