Environmental Engineering Reference
In-Depth Information
3.4.4 Salinity
Salinity refers to the saltiness or the presence of dissolved salt (calcium sulfate,
magnesium or sodium chloride) content in the ocean water. Salinity in oceanography
is expressed as parts per thousand (ppt), which is approximately grams of salt
per kilogram of solution. The plants and organisms, which are adapted to saline
environments are called halophytes and extremophiles or halophiles. An increase
in the salinity of the water decreases the solubility of carbon dioxide. Salinity has
signiicant effects on survival, larval duration and life of many organisms [34].
Marine benthic invertebrates can tolerate up to 5 ppt. Salinity of the marine
environment decreases during the rainy season.
3.4.5 Humidity
High humidity plays a major role in accelerating the rate of degradation of plastics
[35] and the 'plasticising' action of small quantities of absorbed water increases the
access of the polymer matrix to oxygen or causes leaching out of additives from the
formulation.
3.4.6 Amount of Available Water
The biodegradation process cannot proceed without water in dry condition.
The process of hydrolysis is a bimolecular reaction where water and the functional
group having the labile bond are involved. The reaction velocity of polymer
biodegradation is determined by the concentration of both reaction partners.
The degradation velocity rate of lipophilic polymers decreases, thus, it is not able to
take up large quantities of water [36], whereas hydrophilic polymers take up large
quantities of water thereby increasing their degradation rates. The degradation rate of
polymers is also dependent on the amount and quality of the water. Many researchers
have studied the comparative biodegradation analysis of polymeric substances in
fresh water and salt water environments. The rate of biodegradation in the marine
environment is mostly affected by the water temperature and in cold water the
polymer retains its own structure and properties and the original form could endanger
marine life for an extended period of time. The initial research trials carried out by
Plastral Fidene (Australia), using a blend of starch-PCL, found that the blend took
20 weeks to degrade in Queensland water and it was found to degrade in 30 weeks
in South Australian water whereas it was found to fully degrade in 20-30 days in
acompostingenvironment.Normallytemperaturesareveryhighinacomposting
environment. Therefore, seasonal and climatic effects on the rate of biodegradation
need to be considered in speciic applications.
 
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