Environmental Engineering Reference
In-Depth Information
biofouling because of the ability of various marine species to reproduce and grow at
a faster rate than at low temperatures. The interaction between the various fouling
species is also an important factor in biofouling [3].
Biofouling not only affects metal surfaces immersed in the sea but also polymer surfaces.
Polymers and composites that are used in marine industry include polyurethanes
(PU), glass fibre reinforced polymers (GFRP), polyester resins, polyethylene
terephthalate (PET), silicone polymers, luoropolymers, rubbers and so on. PU are
extensively used in fabrication of selectivity grids, oceanographic appliances including
fenders in underwater antenna protection and tubing on underwater vehicles [6].
GFRP are used as lightweight materials in ships, boats, patrol boats, underwater
sea pipes and ishing gear. Polyester resins are mostly used with glass ibres and in
reinforced composite structures [7]. Polymers are also used as coating materials for
anti-fouling surfaces. The surface characteristics of these polymers inluence fouling.
Anti-fouling paints and coatings have also been used for many years to inhibit fouling
of surfaces by marine organisms. Prior to the 18
th
century, lead sheathings were
commonly used for protection from fouling. Most of the anti-fouling paints used for
many years were based on copper and tin. Tributyltin (TBT) self-polishing copolymer
(SPC) paints have been the most successful in ighting biofouling. Unfortunately, TBT
paints adversely affect the environment. In October 2001 regulations were passed
at the
Anti-fouling Systems Convention
by the International Maritime Organization
to ban the use of TBT paints on ships from 2003 and banned the presence of
TBT paints on ships from 2008 [2]. Currently, copper-based paints are used as
alternatives to the TBT paints. To these paints, booster biocides are also added to
enhance the anti-fouling effects, which include copper pyrithione or isothiazolone [2].
These booster biocides are also under scrutiny because of environmental issues [8].
This has led the researchers to focus on the replacement of toxic biocides with natural
non-toxic biocides, which includes microbial secondary metabolites and enzymes.
Another non-toxic biofouling control approach involves designing polymer surfaces
that can minimise the adhesion strength of the settling organisms [2, 9, 10]. These
include self-polishing (SP) or foul release surfaces.
2.2 Bioilms
Bioilms can be deined as settlement and attachment of communities of microorganisms
on wet surfaces [11]. The formation of bioilm begins when the microbes sense
favorable environment conditions including nutrition, temperature, osmolarity, pH,
iron and oxygen which activate the switch from a planktonic to a community-based
bioilm state [11].
