Environmental Engineering Reference
In-Depth Information
The main limitation of the natural isolates is that a metabolite, which is able to
inhibit attachment of one organism may not be as effective against the adhesion of
other organisms such as mussels, barnacles, bacteria and so on. This is because of
the range of adhesion mechanisms and the variation of chemical sensitivity to toxins
found in fouling organisms [2, 78]. Incorporation of natural metabolites in a paint
matrix should not alter their activity. Production of these metabolites at a large
enough scale to be used in paints is another bottleneck in the process. Also several
metabolites in small quantities may act synergistically and may not be effective when
used alone in a paint matrix. A synthetic derivative of the natural metabolite could
well be an alternative.
2.5.3 Alternative Non-toxic Anti-fouling Paints
2.5.3.1 Enzyme Technology
Biological methods also involve using a variety of enzymes secreted by microorganisms
that can inhibit the growth of others. The application of enzymes as anti-fouling
agents has recently generated interest among researchers. Several types of enzymes
have been investigated including oxidoreductases, transferases, hydrolase, lyase,
isomerase and ligase [8]. Enzyme anti-fouling coatings can either be direct or indirect
( Figure 2.18 ). Indirect refers to the use of enzymes to release an active biocide with
anti-fouling activity. For direct anti-fouling, numerous patents have been granted,
and its commercial production has been initiated. However, the main drawback has
been that an eficient broad spectrum enzyme-based anti-fouling coating has not yet
been developed [79].
Enzymes can function by: (i) degrading the adhesives used for settlement, (ii) degrading
the polymers in the bioilm matrix, (iii) releasing anti-fouling compounds such as
deterrents/biocides from surfaces, and (iv) interfering with intercellular communication
[8, 62].
Serine protease inhibits the attachment of barnacles and Ulva spores by reducing the
eficiency of the cyprid adhesives [80]. These proteases act on peptide-based adhesive
compounds that are mainly produced by macrofoulers. A single protease or a mixture
of proteases can be used for this purpose. Enzymic degradation of polysaccharide
adhesives is carried out by glycosylases such as agarase, amylase, cellulase, chitinase,
chitosanase, collagenase, endoglucanase, fructan hydrolase, galactosidase, glucanase,
glucosaminidase, glucosidase, hyaluronidase, isoamylase, lysozyme, mannosidase,
pectinase, pullulanase, and xylanase. They work by hydrolysing the ester-bonds in
the polysaccharides [8].
 
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