Abstract
In this study, two strains of Aspergillus sp. and Lysinibacillus sp. with remarkable abilities to degrade low-density polyethylene (LDPE) were isolated from landfill soils in Tehran using enrichment culture and screening procedures. The biodegradation process was performed for 126 days in soil using UV- and non-UV-irradiated pure LDPE films without pro-oxidant additives in the presence and absence of mixed cultures of selected microorganisms. The process was monitored by measuring the microbial population, the biomass carbon, pH and respiration in the soil, and the mechanical properties of the films. The carbon dioxide measurements in the soil showed that the biodegradation in the un-inoculated treatments were slow and were about 7.6% and 8.6% of the mineralisation measured for the non-UV-irradiated and UV-irradiated LDPE, respectively, after 126 days. In contrast, in the presence of the selected microorganisms, biodegradation was much more efficient and the percentages of biodegradation were 29.5% and 15.8% for the UV-irradiated and non-UV-irradiated films, respectively. The percentage decrease in the carbonyl index was higher for the UV-irradiated LDPE when the biodegradation was performed in soil inoculated with the selected microorganisms. The percentage elongation of the films decreased during the biodegradation process. The Fourier transform infra-red (FT-IR), x-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine structural, morphological and surface changes on polyethylene. These analyses showed that the selected microorganisms could modify and colonise both types of polyethylene. This study also confirmed the ability of these isolates to utilise virgin polyethylene without pro-oxidant additives and oxidation pretreatment, as the carbon source.
Highlights
Synthetic plastics, such as polyethylene, are used extensively in packaging and other industrial and agricultural applications
The data obtained from the respiration and microbial population measurements showed significant differences between the inoculated and un-inoculated treatments with the selected microorganisms
The Fourier transform infra-red (FT-IR), x-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses demonstrated the ability of the selected microorganisms to modify and colonise both types of PE as the carbon source, and demonstrated the important role of these isolates in the PE biodegradation process
Summary
Synthetic plastics, such as polyethylene, are used extensively in packaging and other industrial and agricultural applications. The UV irradiation (photo-oxidation) and, thermal and chemical oxidation of PE prior to its exposure to a biotic environment enhances biodegradation [2] These pretreatments increase surface hydrophilicity of the polymer by the formation of additional groups such as carbonyl groups that can be utilised by microorganisms [3,4,5]. In this study, selected microorganisms were isolated from a typical aged landfill and were identified as Aspergillus niger (designated F1) and Lysinibacillus xylanilyticus XDB9 (T) strain S7–10F. The ability of these isolates to degrade LDPE films in soil was investigated
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