Home » A Greener Solution to Deter Marine Biofouling
The process of growth and accumulation of barnacles, mussels, algae and various organisms on ship hulls and other submerged structures, known as marine biofouling, is a long-standing problem closely related to the efficiency and safety of human activities and properties in marine environments. The problem is ubiquitous and can be easily found on large cargo vessels, commercial fishing boats, naval vessels, recreational yachts and small craft, aquaculture gear, ocean sensors, UUVs, marine hydrokinetic structures, and so on. The adverse effects of marine fouling on these properties include a significant increase in hydrodynamic drag and associated additional fuel consumption, and increased emissions, corrosion and damage to the structure, spreading of non-indigenous species and diseases disturbing the marine ecosystems and causing significant economic loss. It is estimated that heavy calcareous fouling on ship hulls such as barnacle attachment can reduce fuel efficiency by up to 85%.
Even light (or heavy) slime coverage can cause about a 9% (or 17%) increase in total hydrodynamic resistance, which can cause up to 18% shaft power penalties.
Approximately 2% (~13 Quads) of the world’s energy is currently used in the commercial marine shipping industry, consisting of nearly 100,000 commercial cargo ships, which also contributes to 1.1 billion tonnes of carbon emissions.
To put this in a different context, globally $60 billion/yr in fuel cost alone can be saved if we can successfully address the marine biofouling problem on ship hulls (Figure 1).
Traditional solutions to address the hull fouling problem typically involve the application of toxic substances (biocides) to kill the organisms. The rise of self-polishing paints containing tributyltin (TBT) in the late 1970s seemed to have permanently solved this long-standing problem. They were highly effective in maintaining a clean hull for a long enough time. Nevertheless, these highly toxic tin compounds resulted in widespread environmental harm from damage to non-target organisms and surrounding ecosystems, and were gradually phased out. Eventually, the International Maritime Organization (IMO) placed a global ban on TBT-based paints in 2008, forcing the paint manufacturers to go back to copper-based compounds such as cuprous oxide (Cu
O) or copper pyrithione. Despite the advancement of the self-polishing copolymer (SPC) binder technologies to control the release rate of copper-based biocides, these paints are less effective than TBT-based paints due to the reduced toxicity of copper. Moreover, recent studies show growing resistance to copper from an increasingly prevalent species in the United States such as Balanus amphitrite (barnacle).
With increasing awareness of the environmental impact of toxic chemicals and microplastics leaching from marine paints and due to documented negative effects of copper biocides on the marine environment, there is mounting regulatory pressure from U.S. federal and state agencies to reduce the use of such toxic coatings in the market today. In 2017, Washington State passed a ban to limit the use of copper-based paints on recreational vessels in significant part due to their concern over the effect on salmon aquaculture, making the development of an alternative, non-biocidal solution even more important.