Biomedical Engineering Reference
In-Depth Information
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TD-LDPE run 1 (75 mg/g soil)
TD-LDPE run 2 (35 mg/g soil)
Docosane
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Incubation time (days)
Figure 16.4
Mineralization profi les of thermally oxidized LDPE fi lms and cellulose in a soil
burial respirometric test.
In this connection, by using the materials retrieved from different abiotic degrada-
tion tests, several biometric respirometric tests have been carried out. The aim
was to assess the susceptibility to mineralization under test conditions representa-
tive of soil, compost, and river water environments of LDPE that had reached
different degrees of oxidation during the abiotic degradation stage.
Highly reproducible results have been obtained from several biodegradation
tests carried out in soil burial biometer fl asks aimed at assessing the biodegrada-
tion behavior of thermally oxidized LDPE fi lm samples [42]. In all cases, the
mineralization in soil of thermally oxidized samples does not show appreciable
lag phases but it tends to a fi rst plateau at about 5-7% mineralization in a few
weeks (Figure 16.4). After that, a prolonged stasis (4-6 months) in the microbial
conversion to CO
2
of the carbon in the samples has been observed repeatedly
before further and markedly exponential increases in the biodegradation rate.
Fairly high (55-65%) degrees of mineralization are observed after 18-24 months
of incubation at room temperature. This two-step biodegradation behavior of
thermally oxidized LDPE samples has been observed also in mature compost
biodegradation tests. Therefore, in contrast to previous studies [41, 43] showing
only limited and slow conversion to CO
2
of UV-irradiated LDPE samples, samples
with no preaging and additive-free LDPE samples in natural soils, very large
degrees of mineralization have been recorded although these were obtained over
a relatively long time frame ranging between 22 and 30 months [42].
The fi rst exponential phase, occurring during the fi rst days of incubation in the
biodegradation of thermally oxidized LDPE in soil, could be attributed to the fast
assimilation by soil microorganisms of low- molecular - weight oxidized intermedi-
ates whose formation on the fi lm surfaces has been demonstrated by the increased
