Enhancing the biodegradation rate of poly(lactic acid) films and PLA bio-nanocomposites in simulated composting through bioaugmentation. (August 2018)

• Record Type: Journal Article
• Authors: Castro-Aguirre, E.; Auras, R.; Selke, S.; Rubino, M.; Marsh, T.
• Is Part Of: Polymer degradation and stability. Volume 154(2018)
• Page Start: 46
• Page End: 54
• Publication Date: 2018-08
• Subjects: Polylactide -- MMT -- Nanoclay -- Geobacillus -- Biofilm -- Degradation -- Compostability; Polymers -- Deterioration -- Periodicals; Stabilizing agents -- Periodicals; Polymères -- Dégradation -- Périodiques; Stabilisants -- Périodiques; 668.9
• DOI: 10.1016/j.polymdegradstab.2018.05.017
• Languages: English
• ISSNs: 0141-3910

Abstract

Abstract: Biodegradable polymers provide an opportunity to divert plastic waste from landfills, with composting as an alternative disposal route. However, some biodegradable polymers, such as poly (lactic acid) (PLA), do not biodegrade as fast as other organic wastes during composting, affecting their general acceptance in industrial composting facilities. Bioaugmentation, the addition of specific microbial strains, is a promising technique to accelerate the biodegradation of compostable plastics, so that they biodegrade in comparable time frames with other organic materials. In this study, we evaluated the effect of bioaugmentation on the biodegradation of PLA and PLA bio-nanocomposites (BNCs) in simulated composting conditions. PLA, PLA with 5% organo-modified montmorillonite (PLA-OMMT5), and PLA with 0.4% surfactant (PLA-QAC0.4) films were produced and fully characterized. PLA-degrading bacteria were isolated through an enrichment technique with PLA as the sole carbon source at 58 °C. Isolates were identified as Geobacillus using 16 S rRNA gene sequencing and the NCBI database, and further used to study the effect of bioaugmentation on the biodegradation rate of PLA and BNCs in solid environments. The biotic and abiotic degradation was assessed in compost, inoculated vermiculite, and uninoculated vermiculite at 58 °C by analysis of evolved CO2 using an in-house built direct measurement respirometer. Size exclusion chromatography was also used to measure and to monitor the change in molecular weight of the film samples retrieved every week during the biodegradation test. The microbial attachment on the surface of PLA of the isolated microbial strain and other microorganisms present in the compost was evaluated by a biofilm forming assay in wells incubated at 58 °C. Bioaugmentation with Geobacillus increased the evolution of CO2 and accelerated the biodegradation phase of PLA and BNCs when tested in compost and inoculated vermiculite with compost mixed culture. Bioaugmentation could commercially be used to accelerate the biodegradation of PLA in compost environments. Graphical abstract: Image 1 Highlights: Geobacillus thermoleovorans was identified as the microbial strain present in compost capable of degrading PLA at 58 °C. Bioaugmentation with Geobacillus increased the evolution of CO2 and shortened the lag phase. Geobacillus inoculated alone in vermiculite did not produce significant mineralization of either PLA or PLA-OMMT5 films. Geobacillus was able to form biofilm and attach to the surface of PLA. The biodegradation rate of PLA and PLA-based products can be enhanced through bioaugmentation.