- Title
- Evaluation of biodegradability of polystyrene materials in the managed landfill and soil
- Creator
- Ho, Thanh Ba
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Polystyrene is a widely used plastic in many aspects of human life and industrial products due to its useful characteristics. The demand for polystyrene is continuously growing, and the amount of polystyrene waste also continuously increasing. However, polystyrene is very stable and extremely hard to degrade in the environment after disposal. The scarcity of landfill space, hazards of waste incineration and increasing costs of disposing of solid wastes have led to investigations into additives that are believed to help promote the decomposition of polystyrene. Some researchers have reported that additives do help promote the decomposition of plastics, but these tests have been carried out in laboratory conditions. In summary, evaluations of polystyrene biodegradation have been carried out in vitro, and no comprehensive research has been carried out in the real situation of commercial landfills. In this project, the biodegradability of a patented (Patent US 20120301648A1) novel polystyrene cup, where the surface of pre-expanded polystyrene beads had been electrostatically coated with starch, was investigated. This product was believed to be biodegradable in laboratory tests but no data was available on the breakdown of the product when placed in a commercial waste disposal landfill facility. Therefore, the research was conducted in the landfill, where most polystyrene wastes end up. The in situ investigation was followed by further tests in laboratory conditions with leachate organisms from the landfill. A comparison was also made between landfill and soil biodegradation. Microorganisms in the landfill capable of decomposing polystyrene were isolated and identified. The present research is the first report on biodegradability of polystyrene in a managed landfill. The landfill test was conducted at the Summerhill Waste Management Centre (SWMC), Newcastle, NSW, Australia, a solid waste landfill managed by City of Newcastle. The site is licensed by the NSW Environment Protection Authority (EPA) to receive a wide variety of 'General Solid Waste (Putrescible and Non-putrescible) and Special Waste'. The test samples were installed inside the landfill at 11 meters depth for test time up to 1 year. The samples were analysed after incubations of 76 days, 165 days, 257 days and 356 days. The lab tests using leachate from the landfill were performed in the laboratory for 90 days at 46 & 28 degrees Celsius. The test with garden soil was done for six months. The biodegradability of polystyrene was analysed by FTIR, FESEM, GPC, NMR, GC-MS, gas measurement, visual observation and weight loss. Bacteria from the landfill and leachate were isolated and investigated for their ability to biodegrade polystyrene. The results showed that microorganisms could degrade polystyrene in the landfill and soil. However, in general, the biodegradability of polystyrene was very slow. FESEM showed changes in surface of the test samples such as scabrous or rough surface and forming cracks or holes compared to smooth surface of control. Also, FTIR and NMR showed slight changes in peak intensities in their spectra indicated that the chemical structure of polystyrene had been affected considerably in both regions of aliphatic chains and aromatic rings. These changes were interpreted as signs of depolymerisation. However, in other tests no evolved gas was found, and only a slight decrease in molecular weight was measured indicating that the decomposition process is very slow. Intermediate products of biodegradation also were found as styrene oxide, phenylacetaldehyde and 2-phenyl ethanol in culture solution with isolated bacteria and modified polystyrene as a sole source of carbon. There were eight bacteria strains isolated from the landfill by culturing over 90 days in mineral salt medium with polystyrene as the sole source of carbon. It was shown that these organisms were able to degrade polystyrene in laboratory tests but to varying extents. Next-generation sequencing and bioinformatics analyses showed that they belonged to the Bacillus genus and the Brevibacillus genus. Due to time constraints these pure cultures were not further characterised. Bioinformatics analysis of landfill and leachate also revealed the vast diversity of microbial communities present in the landfill and leachate. The work described in this thesis supports the hypothesis that modified polystyrene as per US Patent 20120301648A1 is able to be degraded by organisms present in landfill but to a limited extent. Further work is needed to characterise the organisms isolated and indeed to look further into the existence of other candidate organisms in the landfill before commercially viable organisms can be employed in the fight to reprocess polystyrene in landfill.
- Subject
- polystyrene; landfill; polystyrene biodegradation; leachate
- Identifier
- http://hdl.handle.net/1959.13/1397916
- Identifier
- uon:34373
- Rights
- Copyright 2019 Thanh Ba Ho
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 14 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 210 KB | Adobe Acrobat PDF | View Details Download |