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.

[5] With fuel typically comprising up to half of marine transport costs, antifouling methods save the shipping industry a considerable amount of money.

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 (hard) fouling organisms include barnacles, encrusting bryozoans, mollusks such as zebra mussels, and polychaete and other tube worms.

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 (e.g. Vibrio alginolyticus, Pseudomonas putrefaciens) 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 (e.g. Enteromorpha intestinalis, Ulothrix) and protozoans (e.g. Vorticella, Zoothamnium sp.)

[2][8] 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.

[11][citation needed] Medical devices often include fan-cooled heat sinks, to cool their electronic components.

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.

[16] Consequently, stock affected by biofouling can experience reduced growth, condition and survival, with subsequent negative impacts on farm productivity.

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 (250–280 nm) equipment that can detect biofouling buildup, and can even prevent it.

[1] 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 dependence of effectiveness on vessel speed prevents use of PDMS on slow-moving ships or those that spend significant amounts of time in port.

They rely on high amounts of hydration in order to increase the energetic penalty of removing water for proteins and microorganisms to attach.

Plasma pulse technology is effective against zebra mussels and works by stunning or killing the organisms with microsecond-duration energizing of the water with high-voltage electricity.

[8] Similarly, another method shown to be effective against algae buildups bounces brief high-energy acoustic pulses down pipes.

[27] Regimens to periodically use heat to treat exchanger equipment and pipes have been successfully used to remove mussels from power plant cooling systems using water at 105 °F (40 °C) for 30 minutes.

[31] An Aramaic record dating from 412 BC tells of a ship's bottom being coated with a mixture of arsenic, oil and sulphur.

There is dispute whether many of these treatments were actual anti-fouling techniques, or whether, when they were used in conjunction with lead and wood sheathing, they were simply intended to combat wood-boring shipworms.

[citation needed] From about 1770, the Royal Navy set about coppering the bottoms of the entire fleet and continued to the end of the use of wooden ships.

[24] As an alternative to organotin toxins, there has been renewed interest in copper as the active agent in ablative or self polishing paints, with reported service lives up to 5 years; yet also other methods that do not involve coatings.

Modern adhesives permit application of copper alloys to steel hulls without creating galvanic corrosion.

[39] Study of biofouling began in the early 19th century with Davy's experiments linking the effectiveness of copper to its solute rate.

[42] Materials research into superior antifouling surfaces for fluidized bed reactors suggest that low wettability plastics such as polyvinyl chloride (PVC), high-density polyethylene and polymethylmethacrylate ("plexiglas") demonstrate a high correlation between their resistance to bacterial adhesion and their hydrophobicity.

The resolution to this problem may come from understanding the mechanisms by which mussels adhere to solid surfaces in marine environments.