J. of Marine Env. Eng., Vol. 7, pp. 217-230 Reprints available directly from the publisher Photocopying permitted by license only
© 2004 Old City Publishing, Inc. Published by license under the OCP Science imprint, a member of the Old City Publishing Group.
Ballast Water Heating Offers a Superior Treatment Option G E O F F R I G B Y 1 * , G U S TA A F H A L L E G R A E F F 2 A N D A L A N TAY L O R 3 1Reninna
Pty Limited, 36 Creswell Avenue, Charlestown NSW 2290, Australia
Tel: +61 2 4943 0450, Fax: 61 2 4947 8938, Email:
[email protected] 2University
of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
Tel: +61 3 6226 2623, Fax: +61 3 6226 2698, Email:
[email protected] 3Alan
H Taylor & Associates, 59 Hillcrest Drive, Templestowe, Victoria 3106, Australia
Tel/Fax: +61 3 9846 2650, Email:
[email protected]
Ballast water regulations in place in many parts of the world to minimise the risks associated with the introduction and establishment of nonindigenous organisms into ports around the world currently require ship’s Masters to undertake a range of approved management procedures, primarily based on exchanging the water at sea during the voyage. Limitations associated with ocean exchange have prompted significant research and development into alternative treatment techniques that will offer enhanced biological effectiveness and make practical implementation, ship’s safety and cost more attractive. At a Diplomatic Conference in February 2004 the International Maritime Organisation adopted the International Convention for the Control and Management of Ships’ Ballast Water and Sediments (which includes Performance Standards and provisions for incorporating improved treatment
techniques). Heating the ballast water to 4045°°C is sufficient to kill or inactivate most ballast water organisms (except bacteria) that have the potential to initiate new invasions by inactivating their metabolic processes. Heating to lower temperatures for longer periods of time can be effective and the relationship between time and temperature for a wide range of marine organisms is reviewed. A variety of practical shipboard design options utilizing waste heat from the engine cooling system in conjunction with other heat sources available on the ship are examined in a number of case studies and other suggested operational concepts based on optimizing the heat availability, different voyage conditions, sea temperatures and other operating parameters (including higher treatment temperatures for bacteria, if required. Full scale shipboard
____________________ *Corresponding author: Email:
[email protected]
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trials utilising one of the options involving only waste heat from the cooling system in a combined flushing/heating mode has demonstrated high levels of biological and cost effectiveness with a superior performance to typical ballast water exchange and other treatment options currently available. Keywords: Ballast water, heating, invasions, marine organisms, translocation, treatment.
BACKGROUND AND INTRODUCTION Mandatory reporting and regulations now exist in many parts of the world for the management and control of ballast water to minimize the risks of translocating harmful organisms around the world (Rigby and Taylor 1993). The International Maritime Organisation’s (IMO) Maritime Environmental Protection Committee (MEPC) Ballast Water Management Convention was adopted at a Diplomatic Conference in February 2004. This Convention requires each ship to have on board and implement a Ballast Water Management Plan (BWMP) that uses an approved management procedure. At the present time this generally involves the use of an accepted form of Ballast Water Exchange (BWE). In addition to BWE most Guidelines/Regulations (including the new IMO Convention) have provision for the use of an alternative treatment option that complies with the approved standard for efficacy. BWE significantly reduces the number of organisms from the ballasting port being discharged into the receiving environment and hence is a step in the right direction in reducing the risk of the establishment of new inoculations establishing. In general, the BWE
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regulations stipulate that a water exchange replacement efficiency of at least 95% be achieved. However for many ships and/or voyages, although this level of water exchange is achieved (or exceeded) the biological replacement efficiency for e.g. zooplankton may be considerably less than 95%. Furthermore, for some voyages, BWE can significantly increase the risk of possible establishments of harmful aquatic organisms as a result of taking on new organisms during the exchange process that may be more detrimental than those in the originally ballasted water (Rigby 2001). Even though insufficient information is currently available to estimate with certainty what constitutes a minimal viable inoculum for a biological establishment, it is widely recognized that the ultimate long term goal for ballast water treatment should be a 100% removal or inactivation of harmful organisms. A variety of alternative technologies have been tested (Rigby and Taylor 2001) and new options are continually being proposed as possible candidates. However at the present time, only limited success has been achieved in achieving superior performance to that available from BWE. One of the difficulties in comparing the performance of alternative technologies arises from the fact that no definitive comprehensive standard for biological efficiency currently exists. The IMO Convention includes preliminary standards for Ballast Water Exchange (D-1) and Ballast Water Performance (D-2) for treatment other than by exchange. Refinements and clarification of both standards will continue so that definitive guidlines can ultimately be issued. The most promising treatment option iden-
B A L L A S T WAT E R H E AT I N G O F F E R S A S U P E R I O R T R E AT M E N T O P T I O N
tified by the US National Research Council review for successful shipboard treatment was constant backwash filtration (NRC 1996). Extensive research and demonstration studies have been undertaken internationally using this and other filtration systems to assess the effectiveness of this option. From work carried out so far, mean particle size count efficiencies of 91% have been achieved for particles above 50 µm (using a screen filter) and 91.6% for particles above 100 µm (disk filter) with wide variations in removal efficiencies for organisms with a mean of 90% for zooplankton (50 µm filter) and 50%-around 95% for phytoplankton (Parsons and Harkins 2002; Cangelosi 2002). Like BWE, filtration, which is based on a physical separation process, is not directly linked to biological destruction but rather relies on the efficiency of size separation and the relationship between size and organism species for removal. Clearly this option has limitations in achieving what may be regarded as an acceptable level of biological efficiency. Likewise very few other treatment options have demonstrated an ability to achieve desirable results, especially at the scale of operations that will be required for many vessels (2000 to 20,000 m3/h ballast water-or an equivalent total quantity of 25,000 to 200,000 m3). Heating ballast water to kill or inactivate ballast water organisms, although not yet formally accepted by IMO or any National Authority as an approved treatment option (although the flushing-heating option described in Case Study 1 has been approved by the Australian Quarantine and Inspection Service based on the fact that it can achieve the specified 95% water exchange criterion) has been demonstrated in some full on-board
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at sea trials to be capable of destroying virtually all of the phytoplankton and zooplankton present in the ballast water, and as such offers a superior treatment option in cases where it can be used. This paper reviews the current status of heat treatment research and development and recommends its acceptance as one of the superior options for future implementation.
RESEARCH METHODS AND REVIEW OF STUDIES TO DATE The biological basis of heat to kill or inactivate marine organisms. High temperatures induce denaturation of key proteins and compromise cell membrane structures through increased mobility of molecules, thereby inactivating metabolic processes vital to all known living organisms. As a general rule, the smallest organisms such as bacteria tend to be most heat resistant, because their minute protoplasm volume allows for less damage from heat-induced mobility of molecules. Enterobacteria such as Salmonella, Campylobacter and Escherichia, which are adapted to living within warm blooded animals, require heat treatments of 60-70oC for complete inactivation. It has been well established that effective heat treatment is a probability function of both temperature and treatment time, e.g. milk pasteurisation can equally be achieved by 15 seconds at 72 oC (“flash” pasteurisation) or 30 min at 63-66 oC (“holding method”). There is no evidence that heat treatment has any cumulative effect on cells (Brock and Madigan 1994). Among the enterobacteria, species that produce highly resistant endospores (e.g. Clostridium botulinum)
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TABLE 1 Summary of Lethal Temperatures for Marine Organisms.
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FIGURE 1 Relationship between treatment time (plotted on a logarithmic scale; in minutes) and lethal temperatures (°C) for a wide range of marine organisms. The solid lines for dinoflagellate cysts (D), seaweeds (W), starfish (S) and molluscs (M) are based on Mountfort et al. (1999) supplemented by data for vegetative stages of microalgae (A), crustaceans (C) and rotifers (R) as specified in Table 1. The overwhelming majority of marine organisms can be killed utilising temperatures of 40-45 °C in combination with treatment times of 100-1000 mins.
are the most heat resistant. Autoclaving procedures widely used to sterilise laboratory and hospital equipment utilize heat treatment of 10-15 min at 121oC. Table 1 lists lethal temperatures for a wide range of marine organisms, from bacteria, microalgae, seaweed spores, molluscs, starfish, brineshrimp to rotifers. A striking conclusion (Figure 1) is that most marine organisms, at least in a hydrated stage, can be killed at temperatures of 40-45 oC, that is
well below temperatures used in food treatment technology. The only exceptions are marine bacteria (commonly requiring 45-55 oC), the smallest (
