Copper load to the marine environment.
GLOBAtech Australia
Manufacturer of environmentally friendly ultrasonic Bio-fouling prevention ENVSonic, CleanAHull & HullSonic.
“If you can’t measure it, you can’t manage it” – part 2.
The use of Tributyltin (TBT) started in the 1960s as a biocide in antifouling paints.? Although very effective, it turned out to be toxic for non-targe species and persist in the marine environment for long periods. Use of TBT has been banned by IMO.? The next best thing to TBT that has been found, which is now the most common biocide currently in use, is copper.?? One topic that is rarely mentioned is the shear amount of copper that anti-fouling coating and ICAF systems disperses into the environment.?
Fig. 1. The modern dilemma of biofouling control – historical development and future trends. On the one hand, biofouling causes problems that are not tolerable.? On the other hand, the commercially available biofouling control coatings still have significant drawbacks. The future in this field lies in biofriendly solutions.? Source:? Functional polymer materials for modern marine biofouling control
?Copper does occur naturally in the marine environment in small amounts.? It is an essential trace element needed for the growth of many marine organisms.? At larger doses, it is quite effective at the prevention of settlement and growth of marine organism, particularly during their rather sensitive early life such as larval and juvenile stages.? There are differences in the mode of action for copper between fish/invertebrates and plants/algae.? On land, copper commonly used as active ingredient for fungicide and herbicide.
Environmental water quality guidelines
In May 2023, Water Quality Australia (QQG) published a draft technical brief for dissolved copper in marine water, which closed for stakeholder review and comment on 17 August 2023.? This brief is a part of a series of toxicant default guideline values for aquatic ecosystem protection.? Separate draft technical briefs for Copper in freshwater and Ammonia in freshwater are open for public comment until 20 December 2023.
Toxicant DGVs for zinc in marine water was published on 29 October 2020.
?
DGVs guideline values are provided for 99, 95, 90 and 80% species protection.? The DGV that is applicable to your situation depends on the current or desired condition of the ecosystem and the associated level of protection that is assigned. In most cases:
Shipping ports and sections of harbours serving coastal cities are examples of highly disturbed systems that have measurably degraded ecosystems of lower ecological value.
?
The ‘level of protection’ is defined as the degree of protection afforded to a water body based on its ecosystem condition.? The level of protection informs the acceptable water/sediment quality for a waterway.
Refer to Level of protection for additional guidance on determining an ecosystem condition and associated level of protection.
The Default Guideline Values (DGV) for dissolved copper in marine water varies depending on the concentration of Dissolved Organic Carbon (DOC).? DOC is defined as the organic matter that can pass through a filter, generally range in size between 0.7 and 0.22 μm.?? Conversely, Particulate Organic Carbon (POC) is that carbon that is too large and is filtered out of a sample.? DOC and POC are important components in the carbon cycle and serve as a primary food sources for aquatic food webs.? Among others, DOC forms complexes with trace metals, creating water-soluble complexes which can be transported and taken up by organisms.
A DOC (in mg/L) of 0.5 mg/L is representative of most New Zealand and Australian marine waters and where bio-availability and toxicity would be highest.? At this DOC level, toxicant Default Guideline Values (DGV’s) for dissolved copper in marine water as per Australian and New Zealand Guidelines for Fresh and Marine Water Quality website (ANZG 2018) is as follows:
Level of species protection (%) ???????????????? DGV for copper in marine water (μg/L) a, b
99 ???????????????????????????????????????????????????????????????????????? ?0.12
95 ????????????????????????????????????????????????????????????????????????? 0.40
90 ????????????????????????????????????????????????????????????????????????? 0.72
80 ????????????????????????????????????????????????????????????????????????? 1.4
The DGV values for copper in marine water for higher DOC levels can be found in Copper marine DGV draft Technical brief, appendix C, Table C 2 Default guideline values, dissolved copper in marine water, varying DOC concentrations.
Different organisms can withstand different concentrations of copper.? Some organisms are quite happily growing in water with copper concentrations as high as 100 μ/L, which is extremely high and not often seen in the natural environment unless it is in a highly polluted area.? This also explains why copper based anti-fouling biocides or coatings aren’t fully effective against the whole suite of organisms.
领英推荐
Copper marine DGV draft Technical brief, appendix F, Figure?F?4 Species sensitivity distribution, final dataset for dissolved copper.
Anti-fouling hull coating.
For the prevention of biofouling, it is the copper concentration leaching out from the paint, that is important for the effects on different organism.? The release of Cu (and Zn for that matter) is paint specific.? There are different anti-fouling paint systems available, depending on product type (ablative/non-ablative, biocidal/non-biocidal), class (substrate suitability), grade (vessel speed/activity) and application (docking cycle).?
Research has shown that the leaching increases with higher salinity. ??There is not generic formula or model that can be used to calculate the copper load to the environment.? The concentration known to be effective against barnacles is a leach rate of 10 μg/cm2 per day.? The datasheet for the anti-foul paint system used for the vessel provides the relevant release rate. ?Based on this, along with the wetted hull area, the copper load to the environment of the anti-fouling paint system for a particular vessel can be calculated.?
Marine Growth Protection Systems (MGPS)
Niche areas such as sea chests and internal seawater systems provide additional challenges.? Biofouling growth can block the intake and passage of critical cooling water in the ship seawater system, impairing the heat transfer system, overheating water-cooled machinery, increasing corrosion, and reducing piping flow rate, resulting in overall reduction in vessel operating efficiency, running speed and safety.?? In addition to the use of anti-fouling coating on the vessel sea chest, other Marine Growth Prevention Systems (MGPS) are uses as a preventative strategy for trying to stop biofouling from establishing in niche areas.?
Different treatment methods are available with Impressed Current Anti Fouling (ICAF) being one of the most common one.? Chlorine dosing is another method, typically used on larger ocean-going vessels.? ICAF relies on electrolytic release of copper ions into the sea chest and seawater pipework.? As mussel larvae are sensitive to copper ions, the method is efficient to prevent growth inside the pipes.? Note, ICAF systems require seawater as an electrolyte and therefore ICAF systems do not work in fresh water.
ICAF for open-loop seawater cooling systems
Studies have revealed that the actual copper emissions from ICAF for open-loop seawater cooling systems are significantly higher.? One study showed a median value of over 42 μ/L, considerably higher than the concentration of 2 μ/L indicated by manufacturers.? It is likely that this high concentration is related to the variable raw water flow rate for open-loop seawater cooling systems.? When in port, there is a lower demand for cooling and a lower flow rate of cooling water is required.? However, often ICAF systems are set to a fixed – maximum - release of copper ions, disproportional to the actual requirements to protect the seawater pipework.? The study showed that the environmental load of copper from ICAF for these open-loop systems was ranging from 74-182 % of the load from the vessels’ anti-fouling paint.? Shipowners will know the actual consumption rate for the vessel since they will have to order periodically replacement copper anodes.
ICAF for Boxcoolers
Box coolers are U-shaped bundles of metal tubes fitted in a so-called sea chest, allow hot engine water to exchange heat with cold seawater.? Many box coolers are fabricated from aluminium brass tubes that require a protective coating.? This coated insulation layer is necessary to provide the box cooler tubes with the required corrosion resistance and protects the unit and the vessel from galvanic corrosion and stray currents.? In turn, these coated bundles require ICAF to release copper ions into the water inside the sea chest, to discourage biological growth settling on the coated tube bundles.
The annual copper consumption for these ICAF systems varies between vessels and depends on the number and size of box coolers, as well as other conditions, such as location.? A typical anode consumption requirement is 0.6 kg/m2 cooling surface per year.?? As an example, a PSV (Platform Supply Vessel) that has 4 off 1800 kW Diesel Generator sets, Auxiliary Cooling for Converters, Transformers, DC Motors, etc. has some 422 m2 of box cooler tubes.? This means 253 kg of copper anodes is required per year, or 1,266 kg of copper anodes for a 5-year Docking Schedule.? Shipowners will know the actual consumption rate for the vessel since they will have to order periodically replacement copper anodes.
Environmental Impact
Regulation of shipping subsystems for different on-board operations are set separately, e.g., in the MARPOL Annexes (Table 1), and often based on type approval of emissions from a single subsystem on board.? However, the total amount of one specific contaminant from a single ship may originate from several subsystems.? For example, copper emitted from a ship may originate from antifouling paints, cooling-, bilge- and scrubber water.?
Whilst there are regulations on the maximum allowed copper concentration in antifouling paints (e.g., EU Biocidal Product Regulation BPR 528/2012); there are no regulations for the other subsystems. ??As such, most contaminants emitted from shipping are not routinely monitored hence excluded in assessments of status, pressure, and impacts.
?
The environmental impact of a ship can be measured by several different methods.? Life cycle assessment (LCA) is a method that evaluates the environmental impacts of a product or service throughout its life cycle, from cradle to grave lifetime of a system.? LCA can help you compare different design options, materials, fuels, and operational strategies for a ship.? LCA can also help you identify the most critical stages and aspects of a ship's environmental performance, such as energy consumption, emissions, waste generation, and resource use.?
Other methods that can be used to measure the environmental impact of a ship are the use of environmental performance indicators (EPIs), environmental impact assessment (EIA), eco-labelling and certification and environmental management systems (EMS).?
Summary
Ports and harbour waters visited by vessels often are known to have high levels of pollution and toxins (e.g., copper).? The copper load caused by ICAF (used for box coolers and raw water cooling) must be accounted for when considering the emissions caused by ships.? Given the large amount of copper discharged into the marine environment, further study analysing and sampling the total emission and reaction (and indirectly toxicity) of copper is warranted.
Copper as a biocide will stay with us for many more years to come.? Because of the wide variety of biofouling species that exist out there, there is no one single solution – or ‘silver bullet’ – that can address or prevent biofouling.?? A wide range of anti-fouling paint systems is available, and no doubt new ones will enter the market.? Selecting the right coating for the application, one that meets the performance requirements and is environmentally sustainable, is only part of solution.? It is very well possible to take a more environmentally friendly design approach.? For example, one can substitute an inboard heat exchanged cooling system by using a externally mounted GRIDCOOLER Keel Cooler unit. Another solution could be selecting box cooler constructed from 90/10 CuNi. Because its remarkable resistance against corrosion from clean seawater, a protective coating on tubes typically not required. And because of the natural antifouling capabilities of 90/10 CuNi, these box coolers do not require an ICAF system.
Another solution is selecting Ultrasonic Antifouling (UA) as a MGPS, that works alongside with the coating system and is part of a tailor-made solution.? UA is becoming more common, also due to its environmentally friendly approach, with no release of copper.
?
Globatech Australia is playing its role in addressing this global issue of biofouling by providing environmentally sound Ultrasonic Antifouling solutions, that do not release biocides into the environment.
?
?