Biodegradable plastics are plastics that can be decomposed by microbes into water, carbon dioxide, and biomass. For example, PLA (poly-lactic acid), is one of the most common material in biodegradable plastics. PLA can be decomposed in composts with high temperature, high humidity and microbes in a relatively short time span. However, the information about how fast and the effectiveness of biodegradable plastics’ decomposition in composts are still quite rare in Taiwan. Thus, the purpose of this project “The Feasibility Study about the Decomposition of Biodegradable Plastic Bags and Containers in Commercial Composting Systems” includes: 1. Testing the effectiveness of biodegradation of certificated compostable bags and containers, in commercial composting systems. 2. Examining the composting results if meet the requirements of fertilizer protocol. 3. Searching for the safe microorganisms which can accelerate PLA’s biodegradation.
The result of this study shows that in the experiments of two commercial composting yards, all compostable products including bags, containers, and straws decomposed into pieces 45 days after treatment. All samples wholly decomposed visually within 60 days. This was because it would produce high temperature environment during composting. The final composts have been tested and certified that no biotoxin found in seed germination and vegetable growth experiments. Additionally, the final composts meet the requirements of fertilizer protocol under Taiwan’s regulation.
In lab scale quantitative experiments, we collected various of soil samples and commercial compost products as decomposition medium. The purpose of soil medium was investigated the decomposition of biodegradable plastics in landfill. We also investigated the decomposing of biodegradable plastics in different commercial compost products’ medium which can provide variety of decomposing environment by microbial diversity. We found the compostable bags buried in soil medium, within 60 days, show decomposing by 20-35% weight-loss. In compost medium, the bags show better decomposing effect with 25-60% weight-loss. Moreover, we found the PLA containers have no significant decomposition without high temperature. Once providing 40-50℃ temperature treatment for 2-4 weeks, PLA containers decomposed increasingly to 63-87% weight-loss, within 60 days.
From the various medium (soils and composts) used in this study and the final composts of the mentioned experiments in commercial composting yards, we collected microorganism samples and looked for which one can accelerate the biodegradation of PLA. After purification and species identification, we got 4 safe strains (Agromyces mediolanus, Arthrobacter chlorophenolicus, Microbacterium bakeri, and Streptomyces diastaticus) belong to Risk Group 1. From them, we found Microbacterium barkeri having the best performance, causing 27.59% weight-loss on the PLA testing sample within 7 days, much better than the blank controller, only decomposed by 9.89% weight-loss.