Ecology and Resilient Infrastructure (2018) 5(3): Online ISSN: ORI

Ecology and Resilient Infrastructure (2018) 5(3): 111-117 https://doi.org/10.17820/eri.2018.5.3.111 http://www.seie.or.r/ Online ISSN: 2288-8527 ORIGINAL ARTICLE Special feature: Special Issue of Yonsei Univ. Creative Human Resources Center for Resilient Infrastructure (II) 이산화염소를이용한선박평형수내지표미생물불활성화 Inactivation of Indicating Microorganisms in Ballast Water Using Chlorine Dioxide 박종훈 1 ㆍ심영보 2 ㆍ강신영 3 ㆍ김상현 4 * 1 고려대학교건축사회환경공학부박사과정, 2 연세대학교사회환경시스템공학부석사과정, 3 대구대학교환경공학과석사과정, 4 연세대학교사회환경시스템공학부교수 Jong-Hun Par 1, Young-Bo Sim 2, Shin-Young Kang 3 and Sang-Hyoun Kim 4 * 1 Department of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Korea 2 School of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Korea 3 Department of Environmental Engineering, Daegu University, Gyeongsan 38453, Korea 4 School of Civil and Environmental Engineering, Yonsei University, Seoul 03722, Korea Received 21 June 2018, revised 30 July 2018, accepted 3 August 2018, published online 30 September 2018 ABSTRACT: Disinfection of ballast water using chlorine dioxide was investigated under various initial microorganism contents, dose concentrations and ph values. Kinetics of microorganism inactivation and byproduct generation of chlorine dioxide treatment were compared with the chlorine treatment. Results of treatments with chlorine dioxide concentrations of 0 to 10 mg Cl 2 /L showed that The optimum concentration of chlorine dioxide required for disinfection of ballast water was 1 mg/l. The difference among the second order reaction constants for bacterial disinfection at ph 7.2 to 9.2 for chlorine dioxide was less than 5% for both bacteria. This result implied that the bactericidal effects of chlorine dioxide was independent of the ph in the examined range. On the other hand, the inactivation inetics of chlorine for E. coli and Enterococcus decreased by 17% and 25%, respectively, when ph increased from 7.2 to 9.2. The bactericidal power of chlorine dioxide was superior to sodium hypochlorite above ph 8.2, the average ph value of sea water. Furthermore, treatments of chlorine dioxide gened less harmful byproducts than chlorine and had a long-term disinfection effect on bacteria and phytoplanton from the results of experiment for 30 days. Chlorine dioxide would be a promising alternative disinfectant for ballast water. KEYWORDS: Bacteria, Byproducts, Disinfection, ph, Phytoplanton 요약 : 선박평형수처리에의적용을목적으로다양한미생물농도, 소독제주입량, ph 조건에서이산화염소의소독효과를조사하였다. 살균반응속도및소독부산물생성여부는선박평형수처리에일반적으로사용되는소독제인염소와비교평가하였다. 선박평형수배출규제항목인 E. coli 와 Enterococcus의이산화염소에의한사멸효과는유사 2차반응으로모사하였다. 선박평형수처리를위한최적이산화염소투입농도는 1 mg/l 으로나타났다. ph 7.2-9.2 범위에서이산화염소의살균반응속도상수의변화폭이 5% 이내였던데비해같은유효염소농도에서의염소의살균반응속도상수는 E. coli 기준 17%, Enterococcus 기준 25% 감소하여약염기성인선박평형수의소독에이산화염소가염소에비해효과적임을확인하였다. 또한생태계를교란할수있는소독부산물생성에있어서도염소에비해현격히낮은결과를보였다. 소독후장기보관시 30 일까지는지표세균및플랑크톤의재증식은발견되지않았다. 이산화염소는선박평형수에적합한소독제로판단된다. 핵심어 : 세균, 부산물, 소독, ph, 식물성플랑크톤 *Corresponding author: sanghim@yonsei.ac.r, ORCID 0000-0003-3835-4077 c Korean Society of Ecology and Infrastructure Engineering. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original wor is properly cited. 111

112 J. Par et al. / Ecology and Resilient Infrastructure (2018) 5(3): 111-117 1. 서론선박평형수 (Ballast water) 란선박에화물을적하시부력에의해무게중심이높아져선박안정성이낮아지는것을방지하기위해선박의밑부분에채우는물로써, 해로를통한선박이동이대부분이므로주로해수가사용되며국제적인무역량이증가함에따라선박평형수의사용량도증가하는추세이다. 국제해사기구 (International Maritime Organization, IMO) 에서는선박평형수로세계에서매년 30-50 억톤이상의바닷물이이동하고있으며, 7000종이상의수중생물이선박평형수와함께이동하고있다고보고하였다 (Latarche 2014). 선박평형수로이동된생물이새로운환경에서정착하여생존할확률은낮으나, 정착에성공했을경우토착생물의생존을위협하며생태계교란을일으킬수있다. 이에따라 IMO는 2004년에 선박평형수처리기준 을제시하여, 우리나라를비롯하여세계의모든선박은 2017년부터선박평형수처리장치를의무적으로장착하고있다. 한편, IMO의규정이명문화되기이전부터선박평형수이동양이많은캘리포니아와뉴욕등은선박평형수를규제관리해왔으며, 현재는 IMO 규정보다최대 1000배강화된규정을적용중이다. 특히캘리포니아주의경우세계최고수준의선박평형수처리기준을지 향하여, 장기적으로선박평형수내미생물불검출을목표로하고있다. 또한뉴욕주의경우는 2013년 8월부터모든선박이규제대상이되고, 2012년에는미국해안경비대 (USCG) 에서선박평형수배출기준을제시하였으며, 2013년 12월 1일이후제조되는모든선박은이를만족해야한다 (Table 1). 이처럼선박평형수처리에관해여러기준들이생겨남에따라세계적관심이높아지고있으며, 국제기준을제시하는 IMO는앞으로보다강력한규제를할것으로예상된다. 현재상용화된선박평형수처리기술은대부분약품주입또는전기분해로생성된염소 (Cl 2 ) 를이용한살균에바탕을두고있다. 그러나, 염소를이용한처리기술은 ph가높을경우효율이급격히저하되며, Trihalomethanes (THM) 등과같은해양생태계에유해한부산물이생성될가능성이높다는한계가있다 (Maranda et al. 2013, Simon et al. 2014). 본연구에서는강력한산화제로알려져있는이산화염소 (ClO 2 ) 의해수내미생물사멸능력을염소와비교평가하여선박평형수처리에대한적용가능성을타진하였다. 선박평형수를모사한다양한미생물농도, 소독제주입량, ph 조건에서이산화염소의소독효과를조사하고, 살균반응속도및소독부산물생성여부를선박평형수처리에일반적으로사용되는소독제인염소와비교평가하였다. Table 1. Criteria for ballast water discharge (IMO 2004) Organism category Planton, >50 µm in minimum dimension Planton, 10-50 µm IMO US coast guard legislation California NY (CWA401) Phase-1 Phase-2 (SB497) 2012 (all ships) 2013 (new ships) <10 cell/m 3 <10 cell/m 3 <1 cell/100 m 3 0 <1 cell/10 m 3 0 <10 cells/ml <10 cells/ml <1 cell/100ml <0.01/mL <1 cell/10 m 3 <0.01/mL Planton, 10 µm N/A N/A Toxicogenic Vibrio cholera (O1 and O139) Escherichia coli Intestinal Enterococci <1 CFU/ <250 CFU / <100 CFU / <1 CFU/ <250 CFU / <100 CFU / <1,000 bacteria/ <10,000 virus/ <1,000 bacteria/ <10,000 virus/ N/A <1,000 bacteria/ < 10,000 virus/ <1 CFU/ <1 CFU/ <1 CFU <1 CFU/ <126 CFU / <126 CFU / <126 CFU / <126 CFU /100 ml <33 CFU / <33 CFU / <33 CFU / <33 CFU /

J. Par et al. / Ecol. Resil. Infrastruct. (2018) 5(3): 111-117 113 2. 재료및방법 2.1 선박평형수를모사한인공해수제조대표성이있는해수제조를위해 ASTM (2013) 에서제안한해수조성에따라인공해수를제조하였으며 (Table 2), 이때 ph는 8.2로측정되었다. 사용한시약은모두덕산약품 ( 대한민국 ) 에서구입하였고미량물질의영향을최소화하기위하여희석수로는초순수를사용하였다. E. coli, Enterococcus, 종속영양세균의농도는 G시소재하수처리장유입수를투입하여조절하였으며, 이때의종속영양세균 (heterotrophic bacteria) 농도는 IMO가제시하는 ml당 10 4 colony forming unit (CFU) 이상조건을만족하였다 (Latarche 2014). 추가로식물성플랑크톤 (phytoplanton) 의대표적인종인 Tetraselmis suecica를식종하였다 (Creswell 2010). 각미생물의초기농도는해수에대한기존문헌을참고하여설정하였다 (Maranda et al. 2013). 에서이산화염소및염소투입후 42일간실험을수행하여미생물재성장여부및소독부산물생성을검증하였다. 2.3 화학분석이산화염소및염소농도는 Standard Methods (APHA 1998) 의 DPD ferrous titrimetric method (4500-Cl-F) 로측정하였다. E. coli, Enterococcus, heterotrophic bacteria 농도는 IDEXX laboratories Inc. (Maine, USA) 의 Colilert18, Enterolert, HPC it를이용하여분석하였다. Tetraselmis suecica의배양및계수는 Standard methods (APHA, 1998) 및 Creswell (2010) 을참고하였다. THMs 항목은 Gas chromatography/mass spectrometry (GC/MS, Bruer 320MS, USA) 를활용하여측정하였다 (Lee and Lee 2015). 타분석항목은 Standard Methods (APHA, 1998) 을준용하여분석하였다. 2.2 살균실험세균초기농도 (E. coli 572-8,704 CFU/, Enterococcus 122-1,951 CFU/), 이산화염소농도 (0-10 mg/l), ph (7.2-9.2) 를변화하면서 8-12 hr 동안살균실험을수행하였다. Tetraselmis suecica 초기농도, 온도, 용존유기탄소농도는각각 6,000 cell/ml, 20 C, 5 mg/l으로고정하였다. ph 영향고찰시동일한유효염소량의염소 (Cl 2 ) 를투입하여미생물사멸효율을비교평가하였다. 또한도출된최적조건 3. 결과및고찰 3.1 살균반응속도해석미생물살균반응의동력학적해석을위해세균의초기농도를달리하여온도 20 C, ph 8.2, 이산화염소 5 mg/l에서이산화염소를이용한살균실험을수행하였다. 세균초기농도는하수처리장유입수의투입량을통해조절하였다. 시간에따른세균및플랑크톤의농도변화는 1차식 Eq. 1 또는 2차식 Eq. 2로해석하였다. Table 2. Characteristics of artificial seawater (ASTM 2013) Chemical Concentration salt (g/l) Percentage in salt (%) NaCl 24.53 0.681 MgCl 2 5.2 0.144 Na 2 SO 4 4.09 0.114 CaCl 2 1.16 0.0322 KCl 0.695 0.0193 NaHCO 3 0.201 0.00558 KBr 0.101 0.0028 H 3 BO 3 0.027 0.000749 SrCl 2 0.025 0.000694 NaF 0.003 0.0000833

114 J. Par et al. / Ecology and Resilient Infrastructure (2018) 5(3): 111-117 Table 3. Disinfection of E. coli and Enterococcus by chlorine dioxide at various initial bacterial contents Species E. coli (CFU /) Enterococcus (CFU /) Initial conc. 572 885 1,847 4,674 8,704 122 197 450 1,095 1,951 (CFU /) Time (hr) 1st-order constant 2nd-order constant 0 572 885 1,847 4,674 8,704 122 197 450 1,095 1,951 2 505 773 1,453 3,524 7,556 119 185 433 995 1,710 4 461 698 1,299 2,938 5,298 108 171 405 901 1,599 6 414 663 1,135 2,242 4,083 107 166 377 846 1,442 8 377 552 976 1,887 3,223 105 153 347 780 1,273 12 335 480 753 1,696 1,894 95 145 307 688 1,146 (hr -1 ) 0.0469 0.052 0.0757 0.1021 0.1269 0.0206 0.0268 0.0328 0.0396 0.0464 R 2 0.9849 0.9837 0.9838 0.9621 0.9867 0.9483 0.9722 0.992 0.9906 0.9831 ( CFU -1 hr -1 ) 1 7.71 6.06 3.54 2.18 20 20 8.45 4.55 3.09 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 10-5 R 2 0.9973 0.9839 0.9924 0.9908 0.9406 0.9513 0.9829 0.9821 0.9986 0.9914 Table 4. Disinfection of Tetraselmis suecica by chlorine dioxide Time (hr) cells/ml 0 6,000 2 2,000 4 1,000 6 0 8 0 1st-order constant, (hr -1 ) Tetraselmis suecica R 2 for the 1st-order constant 2nd-order constant, (ml cells-1 hr -1 ) R 2 for the 2nd-order constant 0.5255 0.9930 0.0002 0.9722 (Eq. 1) (Eq. 2) 여기서 C 0 는미생물초기농도 (CFU/ for bacteria, cells/ml for phytoplanton), C는시간에따른미생물농도 (CFU/ for bacteria, cells/ml for phytoplanton), 는살균반응속도상수 (1차반응의경우 hr -1, 2차반응의경우 CFU -1 hr -1 for bacteria, ml cells -1 hr -1 for phytoplanton), t는살균시간 (hr) 이다. E. coli는초기개체수 572, 885, 1,847, 4,674, 8,704 CFU/ 조건에서, Enterococcus는초기개체수 122, 197, 450, 1,095, 1,951 CFU/ 조건에서실험을진행하였으며, 결과를 Table 3에도시하였다. E. coli 및 Enterococcus 반응해석최적화를위한모델링 결과 2차반응의반응상수 () 및결정계수 (R 2 ) 가 1차반응의반응상수및결정계수에비해반응해석에적합한것으로판단되어차후실험결과해석은 Eq. 2를이용하여세균농도에대한 2차반응으로해석하였다. 한편 E. coli, Enterococcus 모두초기개체수가많을수록 2차살균반응속도 가감소하는형태를보여미생물농도에있어완전한 2차반응이아닌유사 2차식인것으로나타났다. 이는이산화염소에의한세균의소독반응이단순한 1차또는 2차반응이아닌여러단계로구성된다소복잡한기작에의해진행되기때문인것으로사료된다 (Benarde et al. 1967). 반면 Tetraselmis suecica의경우 1차반응의반응상수 () 및결정계수 (R 2 ) 가 2차반응의반응상수및결정계수에비해반응해석에적합한것으로판단되어차후실험결과해석은 1차반응으로해석하였다 (Table 4).

J. Par et al. / Ecol. Resil. Infrastruct. (2018) 5(3): 111-117 115 Fig. 1. Time-dependent decrease of E. coli and Enterococcus with the treatment of chlorine dioxide up to 1 mg/l. Fig. 2. Time-dependent decrease of E. coli and Enterococcus with the treatment of chlorine dioxide from 1 to 10 mg/l. 3.2 이산화염소농도영향이산화염소투입농도를 0, 0.1, 0.5, 1 mg/l로변화시키면서 8시간동안살균실험을수행한결과, 대조군에비해이산화염소투입시미생물의농도가확연히줄어들고, 이산화염소농도의증가에따라살균반응속도가향상됨을효율이향상됨을확인하였다 (Fig. 1). 이에추가적으로이산화염소의농도를 1, 3, 5, 8, 10 mg/l로달리하여 8시간동안살균실험을진행하였으며, 1 mg/l 이상에서는이산화염소농도증가에따른살균증대효과가미미한것을확인하였다 (Fig. 2). 이산화염소제조에소요되는비용을절감하고해수방류시이산화염소에의한생태계 2차교란을방지하기위하여, 추후살균조건도출실험은최적이산화염소농도인 1 mg/l에서진행하였다. 3.3 ph 영향과염소와살균력비교해수의 ph 농도및소독제종류에따른 E. coli 및 Enterococcus의살균반응속도를비교하는실험을수행하였다. 염소와의살균영향을대조하기위해환원반응식 (Eqs. 3 and 4) 을참조하여유효염소농도를동 일하게하였으며 ( 이산화염소 1 mg/l, 염소 2.63 mg/l), ph에따른세균농도및살균반응해석결과를각각 Tables 5 and 6에나타내었다. ClO 2 + 5e - + 4H + Cl - + 2H 2 O (Eq. 3) 0.5Cl 2 + e - Cl - (Eq. 4) ph 7.2에서의살균력은이산화염소와염소가유사하였지만, ph 8.2와 9.2에서는이산화염소가염소에비해우수한살균효과가있음을확인하였다. 해수의 ph가통상적으로 8.0 이상임을감안할때, 동일한유효염소농도에서이산화염소가염소에비해우수한세균살균력을보일것으로판단된다. 이는염소의경우차아염소산이온 (OCl - ) 에비해살균력이 100배정도높은차아염소산 (HOCl) 의비율이 ph가증가할수록감소하나 (MetCalf and Eddy 2014), 이산화염소의경우 ph에따른이온화가진행되지않기때문인것으로판단된다. HOCl H + + OCl - (pka: 7.58 at 20 C) (Eq. 5)

116 J. Par et al. / Ecology and Resilient Infrastructure (2018) 5(3): 111-117 3.4 소독제의장기영향및 THM 생성비교평형수처리소독제투입시기를결정하기위해, 이산화염소주입시 E. coli, Enterococcus, Total coliforms, Tetraselmis suecica 대한영향을 42일동안관찰하였다 (Table 5). 실험결과, 42일이후 E. coli의농도는각각 855 CFU/에서 82 CFU/로감소하였 고, Enterococcus의농도는 637 CFU/에서 75 CFU/로감소하여 IMO기준에따른개발목표치인 <200 및 <80 CFU/를달성함을보여주었다. 그러나, 시간에따른 E. coli 및 Enterococcus 농도변화를살펴보면 30일이후조금씩농도가증가함을볼수있다. 소독제처리후장기보관시세균의재증식은 Maranda et al. (2013) 등기존문헌에서도보고된바있 Table 5. Effect of ph on the disinfection of E. coli and Enterococcus by chlorine dioxide Time (hr) 2nd-order equation Species E. coli (CFU /) Enterococcus (CFU /) ph 7.2 8.2 9.2 7.2 8.2 9.2 0 4,674 4,674 4,674 1,214 1,214 1,214 2 3,174 3,257 3,174 1,060 1,085 1,085 4 2,513 2,575 2,577 956 975 976 6 2,025 2,042 2,091 882 884 881 8 1,731 1,671 1,769 826 829 829 ( CFU -1 hr -1 ) 4.67 10-5 4.59 10-5 4.47 10-5 5.02 10-5 4.94 10-5 4.96 10-5 R2 0.9987 0.9989 0.9971 0.9927 0.9983 0.9978 Table 6. Effect of ph on the disinfection of E. coli and Enterococcus by chlorine Time (hr) 2nd-order equation Species E. coli (CFU /) Enterococcus (CFU /) ph 7.2 8.2 9.2 7.2 8.2 9.2 0 4,674 4,674 4,674 1,214 1,214 1,214 2 3,151 3,241 3,325 1,085 1,112 1,169 4 2,646 2,638 2,789 956 1,020 1,057 6 2,042 2,071 2,277 885 916 955 8 1,732 1,768 1,948 826 861 890 ( CFU -1 hr -1 ) 4.52 10-5 4.39 10-5 3.77 10-5 5.03 10-5 4.29 10-5 3.77 10-5 R 2 0.9944 0.998 0.9961 0.9949 0.9954 0.9684 Table 7. Time-dependent in concentrations of E. coli, Enterococcus, Tetraselmis suecica, and heterotrophic bacteria with chlorine dioxide at 1 mg/l Species Time (days) E. coli (CFU /) Enterococcus (CFU /) Tetraselmis suecica (cells /ml) Heterotrophic bacteria (CFU /) 0 855 637 6,000 178,000 4 368 197 0 3,873 8 96 84 0 1,872 14 116 90 0 1,054 24 52 50 0 873 30 41 51 0 719 36 61 72 0 581 42 82 75 0 560

J. Par et al. / Ecol. Resil. Infrastruct. (2018) 5(3): 111-117 117 Table 8. Trihalomethane, dichlorobromo methane, dibromochloro methane, tribromomethane concentrations after 42 days treatment of Cl 2 and ClO 2 Chemicals Trichloro methane (µg/l) Dichlorobromo methane (µg/l) Dibromochloro methane (µg/l) Tribromomethane (µg/l) Control N.D 1.57 N.D N.D Cl 2 4.55 1.82 N.D N.D ClO 2 N.D 1.58 N.D N.D 는현상이며, 평형수의경우 30일이상의보관은적절치않은것으로판단된다. 한편, Tetraselmis suecica은 4 일이후전혀발견되지않았다. 한편, 42일이후이산화염소처리군, 염소처리군, 대조군에서의 THM (trichloromethane, dichlorobromomethane, dibromochloromethane, tribromomethane) 을분석한결과를 Table 6에나타내었다. 이산화염소실험군의경우, dichlorobromomethane 만 1.58 µg/l 검출되었으나, 이는대조군에서도 1.57 µg/l으로검출된물질이었다. 1 mg/l의이산화염소를이용한평형수처리는 THM 생성을유발하지않을것으로사료된다. 반면, 동일한유효농도의염소를사용한경우 trichloromethane 4.55 µg/l, dichlorobromomethane 1.82 µg/l가검출되어, 이산화염소를이용한선박평형수살균이상대적으로해양생태계에미치는잠재적인부작용이낮은방안이라는것을확인하였다. 4. 결론 선박평형수를모사한인공해수를이용한실험에서이산화염소가동일함량의유효염소량의염소에비하여미생물사멸효과가크고소독유해부산물생성량이적었다. 일반적으로이산화염소의생산단가가염소보다높지만투입요구량이낮고해양생태계에미치는부작용이적다는측면에서이산화염소를이용한선박평형수처리가타당할것으로판단된다. References American Public Health Association (APHA), American Water Wors Association (AWWA), and Water Environment Federation (WEF) 1998. Standard Methods for the Examination of Water and Wastewater, 20th Edition. United Boo Press, Inc., Baltimore, MD, USA. American Society for Testing and Materials (ASTM) 2013. Standard Practice for the Preparation of Substitute Ocean Water, ASTM D1141-98. West Conshohocen, PA, USA. Benarde, M.A., Snow, W.B., Olivieri, V.P., and Davidson, B. 1967. Kinetics and mechanism of bacterial disinfection by chlorine dioxide. American Society for Microbiology 15(2): 257-265. Cha, H.-G., Seo, M.-H., Lee, H.-Y., Lee, J.-H., Lee, D.-S., Shin, K.-S., and Choi, K.-H. 2015. Enhancing the efficacy of electrolytic chlorination for ballast water treatment by adding carbon dioxide. Marine Pollution Bulletin 95(1): 315-323. Creswell, L. 2010. Phytoplanton Culture for Aquaculture Feed. Pub. No. 5004, Southern Regional Aquaculture Center (SRAC), USA. International Maritime Organization (IMO) 2004. International Convention for the Control and Management of Ships Ballast Water and Sediments. Document BWM/CONF/36, 16 February 2004. IMO, London, UK. Latarche, M. 2014. Ballast Water Treatment: A Guideline to Regulation and Technology. ShipInsight, Surrey, UK. Lee, K. and Lee, W. 2015. Effects of ph, water temperature and chlorine dosage on the formation of disinfection byproducts at water treatment plant. Journal of Korean Society of Environmental Engineers 37(9): 505-510. (in Korean) Maranda, L., Cox, A.M., Campbell, R.G., and Smith, D.C. 2013. Chlorine dioxide as a treatment for ballast water to control invasive species: Shipboard testing. Marine Pollution Bulletin 75: 76-89. Metcalf and Eddy. 2014. Wastewater Engineering Treatment and Reuse, 5th ed., McGraw-Hill, Singapore. Simon, F.X., Berdalet, E., Gracia, F.A., Espana. F., and Llorens, J. 2014. Seawater disinfection by chlorine dioxide and sodium hypochlorite. A comparison of biofilm formation. Water, Air, & Soil Pollution 225: 1921-1. Waite, T.D., Kazumi, J., Lane, P.V.Z., Farmer, L.L., Smith, S.G., Smith, S.L., Hitchcoc, G., and Capo, T.R. 2003. Removal of natural populations of marine planton by a large-scale ballast water treatment system. Marine Ecology Progress Series 258: 51-63.