Biofouling: A ‘Gluey Constrictor’

Garware’s V2 technology has built-in antifouling properties

The famous phrase by Captain Haddock in Tintin’s ‘Billions of Blue Blistering Barnacles!’ would be one of the first introductions to biofouling species in our childhood. Any surface submerged in water is susceptible to the growth of aquatic species: both micro and macro, and this effect is known as biofouling. Each year, the control of biofouling on various marine industries such as shipping, oil & gas and aquaculture costs billions of dollars.

A growing global population, combined with factors such as changing socioeconomics, will place increased pressure on the world’s resources to provide not only more but also different types of food. The world population is projected to reach more than nine billion by 2050. With a third more mouths to feed by 2050, and most of the land-based resources being overexploited, ocean-based farming shows great promise for meeting the growing protein demand. Fish is a vital source of food for people. It is man’s single most important source of high-quality protein, providing ∼16% of the animal protein consumed by the world’s population, according to the Food and Agriculture Organization.

Marine aquaculture is one of the fastest growing industries in the food sector and contributes significantly to the national economy of many countries. Globally, commercial marine aquaculture has evolved into one of the most developed sectors in the food industry over the last decade. However, marine aquaculture is plagued by problems such as biofouling, sea lice infestation, diseases, harsh environmental conditions, and predators leading to heavy losses.

Typical aquaculture farms use nylon or polyester nets to farm fish like salmon, trout, sea bass, sea bream, etc. Both micro and macro fouling stick on the nets and start ‘constricting’ the mesh leading to reduced water exchange in the aquaculture cage. Additionally, biofouling on nets leads to increased drag and load on the mooring system. The additional drag leads to reduction in effective volume of the cage net, which is detrimental to the fish. Biofouling can be very aggressive in summer times and the settlement on nets in winter times is generally very low in the salmon farming countries. In some parts of the world, biofouling can be observed year round and the cost to control can be sizeable.

Two major strategies are used to control biofouling growth on the nets: i) antifouling paints and ii) in-situ cleaning of nets. Antifouling paints chip off and sink causing elevated copper levels in the sediment. Elevated levels of copper can be toxic to the benthic organisms. Nylon nets are often treated with cuprous oxide based antifouling paints. The paint lasts for 3-9 months depending on the geography and time of the year. Therefore, the nets may need to be coated twice in one production cycle. The biocides (copper oxide) leach into the environment over a period and remain toxic to non-target species.

Nylon nets suffer from a major problem i.e., nylon absorbs water and subsequently the strength drops after absorbing. More recently, polyolefin nets such as high-density polyethylene (HDPE) netting have been introduced into the fish farming industry. HDPE does not absorb water and hence does not show the same level of reduced strength. However, high-density polyethylene nets have some drawbacks. Due to the low surface energy of HDPE, it is hard to bind antifouling paints to the HDPE nets. Therefore, HDPE nets require frequent in-situ washing to assist in maintaining dissolved oxygen levels inside the pen. The same attribute also results in easy cleaning of this type of net.

Garware Technical Fibres, the world’s largest manufacturer and supplier of salmon cage nets, has come up with an innovative composite yarn called V2 that has a built-in antifouling property. The highly specialized extrusion technology involves the formation of a composite yarn by an extrusion process involving HDPE along with metallic copper. In the case of nets made of V2 yarn, biofouling resistance is achieved by the slow release (corrosion) of copper ions from the surface of the copper present in the V2 composite net, when immersed in seawater.

The V2 net has gone through a full production cycle of 13 months and the feedback received from the fish farmer was that on an average they are observing up to 50% reduction in in-situ cleaning frequency on the most recent versions. Additionally, the V2 net has been recognised by the Aquaculture Stewardship Council (ASC) and can be used at ASC certified sites as per ASC guidelines.

www.garwarefibres.com

Captions:
Above: A simple laboratory experiment shows that after spinning a V2 net in seawater for 3 days, no sedimentation was observed.