Biofouling

Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that cause degradation to the primary purpose of that item. Such accumulation is referred to as epibiosis when the host surface is another organism and the relationship is not parasitic. Since biofouling can occur almost anywhere water is present, biofouling poses risks to a wide variety of objects such as boat hulls and equipment, medical devices and membranes, as well as to entire industries, such as paper manufacturing, food processing, underwater construction, and desalination plants.
Anti-fouling is the ability of specifically designed materials to remove or prevent biofouling.
The buildup of biofouling on marine vessels poses a significant problem. In some instances, the hull structure and propulsion systems can be damaged. The accumulation of biofoulers on hulls can increase both the hydrodynamic volume of a vessel and the hydrodynamic friction, leading to increased drag of up to 60%. The drag increase has been seen to decrease speeds by up to 10%, which can require up to a 40% increase in fuel to compensate. With fuel typically comprising up to half of marine transport costs, antifouling methods save the shipping industry a considerable amount of money. Further, increased fuel use due to biofouling contributes to adverse environmental effects and is predicted to increase emissions of carbon dioxide and sulfur dioxide between 38% and 72% by 2020, respectively.

Biology

Biofouling organisms are highly diverse, and extend far beyond the attachment of barnacles and seaweeds. According to some estimates, over 1,700 species comprising over 4,000 organisms are responsible for biofouling. Biofouling is divided into microfouling—biofilm formation and bacterial adhesion—and macrofouling—attachment of larger organisms. Due to the distinct chemistry and biology that determine what prevents them from settling, organisms are also classified as hard- or soft-fouling types. Calcareous fouling organisms include barnacles, encrusting bryozoans, mollusks such as zebra mussels, and polychaete and other tube worms. Examples of non-calcareous fouling organisms are seaweed, hydroids, algae, and biofilm "slime". Together, these organisms form a fouling community.

Ecosystem formation

Marine fouling is typically described as following four stages of ecosystem development. Within the first minute the van der Waals interaction causes the submerged surface to be covered with a conditioning film of organic polymers. In the next 24 hours, this layer allows the process of bacterial adhesion to occur, with both diatoms and bacteria attaching, initiating the formation of a biofilm. By the end of the first week, the rich nutrients and ease of attachment into the biofilm allow secondary colonizers of spores of macroalgae and protozoans to attach themselves. Within two to three weeks, the tertiary colonizers—the macrofoulers—have attached. These include tunicates, mollusks, and sessile cnidarians.

Impact

Governments and industry spend more than US$5.7 billion annually to prevent and control marine biofouling.
Biofouling occurs everywhere but is most significant economically to the shipping industries, since fouling on a ship's hull significantly increases drag, reducing the overall hydrodynamic performance of the vessel, and increases the fuel consumption.
Biofouling is also found in almost all circumstances where water-based liquids are in contact with other materials. Industrially important impacts are on the maintenance of mariculture, membrane systems and cooling water cycles of large industrial equipment and power stations. Biofouling can occur in oil pipelines carrying oils with entrained water, especially those carrying used oils, cutting oils, oils rendered water-soluble through emulsification, and hydraulic oils.
Other mechanisms impacted by biofouling include microelectrochemical drug delivery devices, papermaking and pulp industry machines, underwater instruments, fire protection system piping, and sprinkler system nozzles. In groundwater wells, biofouling buildup can limit recovery flow rates, as is the case in the exterior and interior of ocean-laying pipes where fouling is often removed with a tube cleaning process. Besides interfering with mechanisms, biofouling also occurs on the surfaces of living marine organisms, when it is known as epibiosis.
Medical devices often include fan-cooled heat sinks, to cool their electronic components. While these systems sometimes include HEPA filters to collect microbes, some pathogens do pass through these filters, collect inside the device and are eventually blown out and infect other patients. Devices used in operating rooms rarely include fans, so as to minimize the chance of transmission. Also, medical equipment, HVAC units, high-end computers, swimming pools, drinking-water systems and other products that utilize liquid lines run the risk of biofouling as biological growth occurs inside them.
Historically, the focus of attention has been the severe impact due to biofouling on the speed of marine vessels. In some instances the hull structure and propulsion systems can become damaged. Over time, the accumulation of biofoulers on hulls increases both the hydrodynamic volume of a vessel and the frictional effects leading to increased drag of up to 60% The additional drag can decrease speeds up to 10%, which can require up to a 40% increase in fuel to compensate. With fuel typically comprising up to half of marine transport costs, biofouling is estimated to cost the US Navy alone around $1 billion per year in increased fuel usage, maintenance and biofouling control measures. Increased fuel use due to biofouling contributes to adverse environmental effects and is predicted to increase emissions of carbon dioxide and sulfur dioxide between 38 and 72 percent by 2020.
Biofouling also impacts aquaculture, increasing production and management costs, while decreasing product value. Fouling communities may compete with shellfish directly for food resources, impede the procurement of food and oxygen by reducing water flow around shellfish, or interfere with the operational opening of their valves. Consequently, stock affected by biofouling can experience reduced growth, condition and survival, with subsequent negative impacts on farm productivity. Although many methods of removal exist, they often impact the cultured species, sometimes more so than the fouling organisms themselves.

Detection

Shipping companies have historically relied on scheduled biofouler removal to keep such accretions to a manageable level. However, the rate of accretion can vary widely between vessels and operating conditions, so predicting acceptable intervals between cleanings is difficult.
LED manufacturers have developed a range of UVC equipment that can detect biofouling buildup, and can even prevent it.
Fouling detection relies on the biomass' property of fluorescence. All microorganisms contain natural intracellular fluorophores, which radiate in the UV range when excited. At UV-range wavelengths, such fluorescence arises from three aromatic amino acids—tyrosine, phenylalanine, and tryptophan. The easiest to detect is tryptophan, which radiates at 350 nm when irradiated at 280 nm.

Regulations and guidelines

In 2023, the International Maritime Organization adopted 'Guidelines for the control and management of ships' biofouling to minimize the transfer of invasive aquatic species'.
In April 2025, the IMO agreed to develop a legally binding framework for controlling and managing ships’ biofouling to reduce the accumulation of marine organisms on the hulls of ships and thereby reduce the transfer of invasive aquatic species. Controlling ship's biofouling also improves the environmental efficiency of ships by reducing drag resistance.

Prevention

Antifouling

Antifouling is the process of preventing accumulations from forming. In industrial processes, biodispersants can be used to control biofouling. In less controlled environments, organisms are killed or repelled with coatings using biocides, thermal treatments, or pulses of energy. Nontoxic mechanical strategies that prevent organisms from attaching include choosing a material or coating with a slippery surface, creating an ultra-low fouling surface with the use of zwitterions, or creating nanoscale surface topologies similar to the skin of sharks and dolphins, which only offer poor anchor points.

Coatings

Non-toxic coatings

Non-toxic anti-sticking coatings prevent attachment of microorganisms thus negating the use of biocides. These coatings are usually based on organic polymers.
There are two classes of non-toxic anti-fouling coatings. The most common class relies on low friction and low surface energies. Low surface energies result in hydrophobic surfaces. These coatings create a smooth surface, which can prevent attachment of larger microorganisms. For example, fluoropolymers and silicone coatings are commonly used. These coatings are ecologically inert but have problems with mechanical strength and long-term stability. Specifically, after days biofilms can coat the surfaces, which buries the chemical activity and allows microorganisms to attach. The current standard for these coatings is polydimethylsiloxane, or PDMS, which consists of a non-polar backbone made of repeating units of silicon and oxygen atoms. The non-polarity of PDMS allows for biomolecules to readily adsorb to its surface in order to lower interfacial energy. However, PDMS also has a low modulus of elasticity that allows for the release of fouling organisms at speeds of greater than 20 knots. The dependence of effectiveness on vessel speed prevents use of PDMS on slow-moving ships or those that spend significant amounts of time in port.
The second class of non-toxic antifouling coatings are hydrophilic coatings. They rely on high amounts of hydration in order to increase the energetic penalty of removing water for proteins and microorganisms to attach. The most common examples of these coatings are based on highly hydrated zwitterions, such as glycine betaine and sulfobetaine. These coatings are also low-friction, but are considered by some to be superior to hydrophobic surfaces because they prevent bacteria attachment, preventing biofilm formation. These coatings are not yet commercially available and are being designed as part of a larger effort by the Office of Naval Research to develop environmentally safe biomimetic ship coatings.