Eradication of algae in ships' ballast water by electrolyzing

Joumal of Marine Science and Application, VolL.5, No.4, December 2006, pp.58-61Eradication of algae in ships' ballast water by electrolyzingDANG Kun', SUN Pei-ting', XIAO Jing-kun', and SONG Yong-xin'1. Marine Engineering College, Dalian Maritime University, Dalian 116026,China2. Environmental Science and Technology College, Dalian Maritime Universit, Dalian 116026,ChinaAbstract: In order to verify the effectiveness of electrolytic treatment on ships’ ballast water,experiments are carried out by a pilot system in laboratory. The raw seawater and seawater with differentconcentrations of different algae are simulated as ships' ballast water. The algae in the raw seawater canbe klled if it is treated by electrolysis with an initial residual chlorine concentration of5 mg/L. If theseawater with one kind of algae Nitzschia closterum, Dicrateria spp， or Pyramidomonnassp.10Cell/mL) is treated by electrolysis with an initial residual chlorine concentration of 5 mg/L, thealga can be sterilized. If the seawater with one kind of algae (Dunalella sp.. Platymonas or Chlorella spp.)is directly treated by electrolyzing with an initial residual chlorine concentration of 4 mg/L, the instantmortality changes with the concentration of dfiferent algac. However, after 72 hours, in all treatedsamples, there are no live algal cells found.Keywords: ships' ballast water; electrolysis; algacCLC number: U664.5 Document code: AArticle ID: 1671-9433(2006)04-058-041 Introductionseawater with different concentrations of Artemiasalinal".The introduction of invasive marine species into newenvironments by ships' ballast water, attached to2 Experimental systemships' hulls and via other vectors, has been identifiedby the Global Environment Facility (GEF) as one ofThe experimental system is ilustrated in Fig.1. Thehe four greatest threats to the world's oceans". Theexperimental system mainly consists of:other three are land-based sources of marine pollution,1) One storage tank 2.0 mx1.0 mx1.0 m;over-exploitation of living marine resources an2) One electrolytic unit. AC 440V, 50A (Applied DCphysical alteration/destruction of marine habitat.0V~12V), rated treatment capacity 2.5 m'/h.3) One portable submerged pump, centrifugal type,There are many technologies underdeveloped to treatwith a rated capacity of 3.0m'/h and a rated waterships ballast water, such as exchange at seal2 ,head of 2.5m;filtration(4,5),. heatingo, UV treatment', O3 treatment8!4) One floater type flowmeter with a measurementPeraclean@ Ocean treatment9), Seakleen treatment [10.scale of 0.1~3.0 m'/h;The work presented in this paper is from item 1B4C5) Large barrels, 4x120 L;(Electrolytic Treatment of Ships' Ballast Water and the6) Sample receivers.Development of a Ballast Water Treatment Unit) ofChina activities as part of Global Ballast WaterWhen experiments are being carried out, the seawaterManagementProgramme(GloBallastwill be pumped into the system by the submergedhtp://globallat.imo.org). The Project 1B4C waspump in the large barrel (simulated as ballast tank). Infinancially supported by GloBallast and China Oceanord'1e concentration, two中国煤化工、Shipping Company (COSCO Group). Before thmregulate the appliedpaper presented here, some experiments had beenvolYHCNMHGandthereare4gearsdone by directly electrolyzing raw seawater andon the control panel, which can be adjusted andregulated with applied voltage from 0V to 12V. AndReceived date: 2006-07-28.Foundation item: Supported by GloBallast. China Ilem 1B4C.another is to throttle the outlet valve before theDANG Kun, et al: Eradication of algae in ships' ballast water by electrolyzing59flowmeter. This is suitable for centrifugal pumps but2HO 2e- >H2o*o,on no account used for a displacement pump. The20- +O2.heater is used to sterilize seawater before thesurrogates are put into the ballast tank'. AIll flasks forThe oxygen molecules disperse to the cathode,holding water samples are sterilized before using. Andreacting with water and producing ions of hydrogenall water samples are taken in the midst of processperoxide.after the system running steadily.O2+H2O+2e- +HO2" +HO.The ions of hydrogen peroxide have strong power in*killing bacteria, but it is unstable and works for a very空short time. It will produce activated oxygen freeradicals if it degrades, or produces hydroxide ions,which have no action on disinfection.HO2*- +HO+ O,HO2* +2e+H2O- +3HO.6As to the effect of electric field, if the voltage appliedon the cell membrane is greater than the limit, then thecell will break or the enzyme delivery channel of the[]cell will be destroyed and in turn leads to the death of1.heater; 2ectrolytic unit; 3.flowmeter;the algal cell [121.4. filter; 5.sample receiver; 6.ballast tank; 7.pump.Fig.1 The experimental system4 Experiments, testing methods and results3 Mechanisms of electrolytic treatment4.1 The electrolyzing experiments of raw seawaterand seawater with individual alga (qualitativeHypochlorous acid is a powerful disinfectant, which isanalysis)as strong as 50~80 times of hypochlorous acid radicalThe raw seawater from Xinghai Bay was simulated aswith respect to disinfection capability.ships' ballast water and treated by electrolysis. Theseawater with one kind of alga was treated and testedThe mechanisms of direct electrolysing lie in twoby the following method:aspects. One is that many oxidants including Cl2,CIO*, OH, O, HO2 are produced during electrolysisThe seawater was heated in the heater to 100°C atof seawater. They work together to kill organisms andatmospheric pressure and allowed to cool to roomhave a synergistic effect, which is more powerful thantemperature (about 25°C). Then the selected algaeany individual one. The other aspect is the effect of(Nitzschiaclosterum,DicrateriaSPP., orelectric field.Pyramidomonnas sp.) were each put into the seawaterseparately. The density of each alga in the ballast tankThe basic reactions are:is about 10'cells/mL. After that, the seawater wasanode: 2CI- +Cl2↑+2e,treated by electrolysis with an initial residual chlorinecathode: 2H* +2e-→H2↑,concentrations of 5, 8, or 25 mg/L respectively.hydrolyzation of chlorine:Samples were taken as 2x200 mL in conical flasks.Cl2+H2O=CIO+CT+2H*.Then each sample was added with requiredHowever, different reactions will take place at anodenutrimental salt liauid and cultured under light.as electrolytic potentialvaries, and different中国煤化工substances will be produced, especially someAfter|YHCN MH Gnples there was nopowerful oxidants such as free radicals, peroxides, etc.algae growth and all control samples had algaeActivated oxygen free radical will be producedgrowing in them (the colour turned to green or becamethrough the following reactions:brown). The results are shown in the following tables:6(Journal of Marine Science and Application Vol.s, No.4, December 2006Table 1 Electrolysing conditions and initial residual chlorineGear PositionIIIVoltage/V.8Current/A142855Temperature/rC252:Flowrate/m'h-'1.Initial residual chlorine/mg:L-1.08.025.0Fig.5 AIll samples cultured under lightTable 2 Results of the electrolysing treatment (individual4.2 The electrolyzing experiments of seawater withalga and raw seawater)individual alga (quantitative analysis)SamplesColour Colour ColourThe sea water was heated in the heater to 100'C atInitial residual chlorine/ mg:L~5.025.atmospheric pressure and allowed to cool to roomRaw seawater-CAppear Appear Appeartemperature (about 25°C). Then the selected algaNitzschia closterum-CGreen Green Green(Dunaliella sp.,Platymonas or Chlorella spp.) wereDicrateria spp. -CBrown Brown Browneach put into the seawater separately. After that, thePyramidomonnas sp. -CGreenseawater was treated by electrolysis with an initialNOAll treated samplesresidual chlorine concentration of 4 mg/L respectively.Note: c stands for control groups.The density of the alga was inspected under themicroscopeat 40x16 times.PhytoplanktonPictures of water samples are shown in Fig.2 to Fig.5.enumerating volume (0.1 mL) was adopted for thenumber counting of the alga. The number of eyeshot is25 for each sample.Table 3 The etrolyzing parameters(quantitative analysis)1.81Temperaturer*C24Fig.2 Nitzschia closterum treatment-I and control groupsFlowrate/ m'h-'2.0Initial residual chlorine/ mg:L-'4.0Table 4 Density inspection resultsBefore After M-rate M-rate72hx108 x108 Instan/% 48h/%Dualella sp.7.689.592.1 NilChlorellaspp.1.6 0.662.587.5 NilPlatymonas1.2 0.1587.593.4 NilFig.3 Pyramidomonnas sp.treatmentI and control groupsNote: M-MortalityModality observation:1) After treatment, the green Dunalella sp. turned tolight yellow. Part of the green colour has beenremoved. It indicates that the chlorophyll that formshe |中国煤化工aged evidently. UnderInalella sp. appears aslarlYHCNMH Gnt and congregates .together.Fig.4 Dicrateria spp. treatment-I and control groups2) After treatment, the colour of Platymonas changedgreatly. Before treatment, it is a fresh green and afterDANG Kun, et al: Eradication of algae in ships' bllas water by electrolyzing6treatment, no any colour is shown. The whole sampleNo.2). [R].Canberra: Australian Government Publishingbecomes clear and transparent. At the bottom of theService,1993.container of the sample, there was a floc formation of[3RIGBY G, HALLEGRAEFF G M. The transfer andcontrol of harmful marine organisms in shipping ballastdamaged Platymonas.water: behaviour of marine plankton and ballast water3) After treatment, the individuality of Platymonasexchange trials on the MV“Iron Whyalla"[J]. J Mar Envlost its mobility. It became still and obviously had noEng, 1994,1: 91-1 10.colour.[4] HIROSHI T. Progress report on the “Special PipeSystem”as a potential mechanical treatment for ballastwater[A]. 2nd Intermational Ballast water Treatment R&D4.3 Measurement of residual chlorinesymposium[C]. London , 2003.The DPD colour comparison method is adopted to[5ITAY K. The temary effect for ballast water treatment[A] .measure the residual chlorine concentration in water2nd International Ballast water Treatment R&Dsamples by means of residual chlorine indicator. 1%Tolidinedihydrochloride(C14H16N2.2HCl 0) [6BOLCH C J S. Ballast water and harmful algalsolution is used as reagent.blooms- current research and future directions[A]. Reportof the ICES/IOC/IMO Study Group on Ballast Water andSediments[C]. La Tremblade, France, 1997:13-14 .5 Conclusions[7WRIGHT D A, DAWSON R. Shipboard trials of ballastwater treatment systems in the United States[A]. 2ndIf the sea water with one kind of algae (NitzschiaInternationalBallastwater Treatment R&Dclosterum, Dicrateria spp., or Pyramidomonnas sp.symposium[C]. London, 2003.about 10 cells/mL) is treated by electrolysis with an[8REYNOLDS G L, MEKRAS C, PERRY R,initial residual chlorine concentration of 5 mg/L, theGRAHAM N. Alternative disinfectant chemicalsalga can be killed.for trihalomethane control-a review [J].Environ.Technol. Lett, 1989,10: 591-600.If raw seawater is directly treated by electrolyzing with[9RAINER F. Peraclean@Ocean_ a potential treatmentan initial residual chlorine concentration of 5 mg/L, theoption for ballast water[A]. The 2nd Intermational Ballastalgae in the seawater can be extinguished.water Treatment R&D symposium[C]. London, 2003.[10]CUTLER S J. SeaKleen-a potential product forcontrolling aquatic pests in ships' ballast water[A]. TheIf the seawater with one kind of algae (Dunalella sp.,Platymonas or Chlorella spp. About 10'cells/mL) issymposium[C]. London,2003.directly treated by electrolyzing with an initial[11]DANG Kun, YIN Peihai, SUN Peiting, XIAO Jingkun,residual chlorine concentration of 4 mg/L, the instanceSONG Yongxin. Application study of ballast waterof mortality changes with the concentration oftreatment by electrolyzing seawater[A]. The SecondBallast waterTreatmentR&Ddifferent algae. However, after 72 hours, in all treatedSymposium[C]. London, 2003.samples, no living algal cells are found.[12]FENGYujie.Application of electrochemicaltechnologies to environmental engineering[M]. Beijing:AcknowledgementChemical Press, 2002.We would like to express our appreciation to theDANG Kun was born in Deccember 1965. He is anGloBallast Programme Coordination Unit (PCU), GEF,Associate Professor and a Doctor of MarineUNDP, COSCO and China SMA. We are grateful toEngineering at Dalian Maritime University. Hiscurrent research interest is ships' ballast waterMr. Zhao Dianrong for his coordination between PCUtreatment. Dang has 6 books to his credit, oneand the implementation team for our project.patent proclaimed and two patents granted anregistered. More than 10 of his technical papershave been published. At present, he works as aReferences:visiting scholar at School of Engineering in James中国煤化工1] STEVE R. Report for the GEF/UNDP/IMO global ballastwater management programme (GloBallast)[R].TYHCNMHGLondon :The Institute of Marine Engineering, 2002.[2]RIGBY G， HALLEGRAEFF G M. Ballast waterexchange trials and marine plankton distribution on theMV“Iron Whyalla" (AQIS Ballast Water Series Report