Environmental Engineering Reference
In-Depth Information
3.4.7 The pH (Chemical Environment, Electrolytes)
The measure of alkalinity (acidity) is pH. A pH value of 7 is considered to be neutral,
values below 7 are acidic and those above 7 are alkaline. Typically natural seawater
has an approximate pH ranging from 7.4-8. When carbon dioxide (CO 2 ) is absorbed
by seawater, it reduces the seawater pH. The pH of sea water is affected at sites near
sea water desalination plants because of the discharge of large quantities of solid
and liquid wastes from the membrane ilters. Reaction rates of many processes are
determined by the pH, and they get altered because of the changes in pH. Reaction
rates of esters are affected by a shift in pH, at times by an order of magnitude [37].
Biodegradation may be either acid or base catalysed. The effect of pH on most of
the biodegradable polymers has been studied by many researchers using polymers
such as polyglycolic acid and poly(lactic- co -glycolic acid). The pH of the medium
plays a major role in the degradation process, and the breaking strength of the
bonds in the polymer depends on the pH and is found to be highest at a neutral pH.
The degradation rate of poly[bis( p -carboxyphenoxy) propane anhydride] cylinders,
could be increased by a factor of 10 by increasing the pH of the medium from 7.4
to 10 [38]. Polymers such as poly( ortho -esters) degrade faster at an acidic pH when
compared to those degraded at a neutral pH, and they are resistant at a basic pH.
Thus, the degradation rate of the same polymer may vary in different marine locations
because of changes in the pH.
3.4.8 Bio-fouling Community (Bioilm)
Katsanevakis and co-workers [39] reported that in the marine environment, the
marine debris at the bottom of the sea can be highly dense and can have an impact
on benthic communities by providing a shelter to mobile species such as algae and
bacteria. The unwanted accumulation of bacteria, microorganisms, algae or even
animals on underwater structures is a common phenomenon. Any material immersed
in aqueous environments or under high humidity conditions are rapidly covered by
biofouling which ultimately leads to biodegradation. Over 4,000 organisms are related
to biofouling in the marine environment [40]. They are divided according to their
size: microorganisms (bioilm) include bacteria, slime and micro-fouling, macrofouling
includes barnacles, hydroides, algae, bryozoans, mussels, and polychaetes. As can be
seen from the Figure 3.5 and Figure 3.6 the biofouling depends on the type of material.
For example not much fouling is seen on syntactic foam compared to polyester.
 
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