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Slime eating paints |
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| Incorporating slime-eating bacteria or enzymes into paint products sounds like a pool boy's dream, but researchers are hoping this 'living paint' technology will become a reality for the shipping industry. |
Biological fouling (biofouling) is a universal problem that occurs on surfaces ranging from ship hulls, to house walls, to the interior of water pipes. Not only does biofouling result in corrosion, degradation of materials and buildings, and the transport of introduced pests, it can harbour pathogens.
That sliminess on pool surfaces that keeps pool vacuums busy? You guessed it: biofouling.
A major problem for many industries is marine biofouling, the colonisation of submerged surfaces by living organisms. The barnacles that collect on submerged ship hulls are an obvious example of marine biofouling.
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Common marine fouling organism Bryozoan (Bugula neritina). These organisms attach themselves to submerged surfaces to breed (Photo courtesy of the Centre for Marine Biofouling and BioInnovation, UNSW)
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Dr. Lachlan Yee, from the University of NSW, explained that "the major focus of fouling and antifouling technologies has been in the marine shipping industry, where fouling is estimated to cost the industry more than $5 billion per year."
With a team from the Environmental Biotechnology Cooperation Research Centre (EBCRC), Lachlan is using biotechnology to develop new approaches for controlling unwanted biofouling and corrosion on submerged surfaces and building walls. These methods incorporate metabolically active bacteria or enzymes into coatings.
"Other than repeated cleaning of surfaces, by far the most common commercial approach to fouling control is to coat surfaces with antifouling paints that use heavy metals such as copper, zinc or tin as the killing agents," he said.
Environmental effects of the heavy metals released from these coatings are such a concern that the International Maritime Organisation is in the process of banning tri-butyl tin based coatings, the most commonly used paints in the marine environment. Copper based paints are prohibited in some parts of Europe. (House paints typically contain toxic antibacterial or antifungal compounds to inhibit microbial fouling.)
Traditional paints' environmental effects highlight the importance of the EBCRC's work. Bacteria in the paint release natural products that prevent the organisms that cause fouling from adhering to the surface. Enzymes are capable of catalysing the reaction to degrade any attaching organisms or fouling species.
The paint containing the living bacteria or enzymes will possess an active surface. This means it's capable of breaking down initial compounds that allow the first wave of organisms to colonise. Anti-bacterial compounds may also destroy these attachment bacteria. This is important because marine fouling is a multistage process.
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Most work to date is in the lab. Some field tests have been done in Sydney harbour to see how long paint polymers last in the water.
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Lachlan and his team are making good progress. "At present we have a few working polymer models that contain bacteria and are showing bacteria living for periods of up to 120 days," he said. "We are in the process of applying the technology to the field in an effort to obtain a working model in an actual real life biofouling situation".
Enzymes are an expensive raw material for use in any product, and if highly purified enzymes are required costs escalate enormously. A Macquarie University team directed by leading biotechnologist Professor Peter Bergquist is preparing novel enzymes to reduce costs and provide effective results.
Research activity is focussing on methods of delivering bacteria or enzymes to the coating system so that they are stable before the coating is applied but will deliver a cost effective and worthwhile benefit during the entire life of the final coating.
The scope for replacing current biocidal additives is enormous. It ranges across the current market of coatings to cleaners and surface preparation products that tend to utilise harmful toxic chemicals. Biofouling slurping paints that employ naturally derived alternatives present in bacteria and enzymes suggest an environmentally-friendly future.
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