Recent Advances in Understanding the Role of Wastewater …
9
1.4.6 Chemical Bonding
The chemical linkages and bonding in polymers can influence the rate of degradation in plastics. Head-to-head and tail-to-tail addition of monomer units during
addition polymerization can form weak joints which make thermoplastics more
prone to degradation [19]. Thermal degradation and photodegradation increases with
branching in the polymer chain and decrease with crosslinking as it averts lamellar
unfolding.
1.4.7 Effect of Stress
Stress can have a major influence on polymer disintegration. The rate of photodegradation increases with increase in tensile stress and decreases with compressive stress.
The morphology of the plastic polymer can be studied to infer the consequence of
stress on degradation rates. The straightening of the polymer chains in the amorphous
regions can be observed when high stress is being subjected on the polymers. Stressed
polymer chains had an increased rate of crack development and hence underwent a
higher degree of degradation as compared to unstressed state [20].
1.4.8 Environmental Conditions
Biodegradation of polymer depends upon environmental settings like pH, temperature, amount of moisture, oxygen content, and required population of microorganisms [21]. The rate of polymer degradation by the microorganisms increases with
increase in relative humidity ideally above 70%. The combined effect of temperature and moisture demonstrates a significant degree of photodegradation of the
polymeric materials. Higher temperatures and high humidity have been studied to
cause an increase in the photo-damage in thermoplastic polymers [22].
2 Biological Treatment of Wastewater Containing Plastic
Derived Nitrogen Compounds
2.1 Heterotrophic Nitrification
It involves the use of chemoorganotrophic microorganisms which oxidize ammonia
[23], organic nitrogen compounds [24] and hydroxylamine [25] to nitrite and
nitrate. Commonly used heterotrophic nitrifiers are bacteria [26], algae [27] and
fungi [28]. Nitrification rate of heterotrophic nitrifiers are low when compared to
autotrophic nitrifiers [29], therefore heterotrophic nitrification is preferentially used
9
1.4.6 Chemical Bonding
The chemical linkages and bonding in polymers can influence the rate of degradation in plastics. Head-to-head and tail-to-tail addition of monomer units during
addition polymerization can form weak joints which make thermoplastics more
prone to degradation [19]. Thermal degradation and photodegradation increases with
branching in the polymer chain and decrease with crosslinking as it averts lamellar
unfolding.
1.4.7 Effect of Stress
Stress can have a major influence on polymer disintegration. The rate of photodegradation increases with increase in tensile stress and decreases with compressive stress.
The morphology of the plastic polymer can be studied to infer the consequence of
stress on degradation rates. The straightening of the polymer chains in the amorphous
regions can be observed when high stress is being subjected on the polymers. Stressed
polymer chains had an increased rate of crack development and hence underwent a
higher degree of degradation as compared to unstressed state [20].
1.4.8 Environmental Conditions
Biodegradation of polymer depends upon environmental settings like pH, temperature, amount of moisture, oxygen content, and required population of microorganisms [21]. The rate of polymer degradation by the microorganisms increases with
increase in relative humidity ideally above 70%. The combined effect of temperature and moisture demonstrates a significant degree of photodegradation of the
polymeric materials. Higher temperatures and high humidity have been studied to
cause an increase in the photo-damage in thermoplastic polymers [22].
2 Biological Treatment of Wastewater Containing Plastic
Derived Nitrogen Compounds
2.1 Heterotrophic Nitrification
It involves the use of chemoorganotrophic microorganisms which oxidize ammonia
[23], organic nitrogen compounds [24] and hydroxylamine [25] to nitrite and
nitrate. Commonly used heterotrophic nitrifiers are bacteria [26], algae [27] and
fungi [28]. Nitrification rate of heterotrophic nitrifiers are low when compared to
autotrophic nitrifiers [29], therefore heterotrophic nitrification is preferentially used