Project highlights

  • This project addresses an emerging issue associated with closed landfill sites where plastics degradation and their release are important carriers of environmental pollutants
  • Microplastics discharged from these sites may pose greater risks to human and environmental health due to adsorbed toxic and persistent hazardous chemicals.
  • Knowledge is still scarce on the factors influencing the release of microplastics from landfills, and characterisation tools and technology responses must be developed to mitigate this source of microplastics
  • This project will develop new insights into the behaviour of plastics as they break down, their pollution potential and their role in mobilising other pollutants, such as metals. This also presents an opportunity for innovative metal recovery through leachate treatment facilities.

Overview

There is a significant legacy of landfills in the UK, with an estimated 24,000 sites of varying sizes, most of which are now closed; 4,000 of these sites operated with a permit, thus those pre-dating the 1974 Control of Pollution Act are termed ‘historic’ sites. More modern landfill sites (post 1994) were largely engineered with the use of impervious lining material, such as plastic or clay, and will manage the leachate produced.

Previous work has demonstrated the degradation of plastics in landfill conditions (Canopoli et al, 2020).  This research aimed to understand the recycling opportunities for plastics extracted from closed landfills under the enhanced landfill mining approach.  The formation of microplastics during the degradation of plastics within a landfill site, either through physical, chemical or biological degradation, is inevitable with emerging research developing methods to detect microplastics in landfill soils (Siva Naga Sai Goli and Narain Singh, 2022).  Metal sorption to microplastics has been observed, however in wetland environments (Jian et al, 2022).  Therefore, it is known that plastics degrade in a landfill site, that microplastics can absorb metals and that no work to date has assessed the formation of microplastics and the contribution to metal mobility in a landfill environment.  This will present opportunities for the recovery of metals through landfill leachate treatment systems should the metal to microplastic mechanisms be further understood.  It will also a more complete understanding of the human and environmental risks posed by landfill leachate and its mitigation.

The proposed PhD project will develop new understanding in the mechanisms of plastic degradation within a landfill site, the products of degradation and how these products contribute to metal mobility within a landfill site.   The products of degradation will go beyond micro and nano plastics, developing new chemical understanding of fingerprint compounds present in leachate which could inform site operators of the status of contained plastics and how to control/limit/enhance metal mobility.

Diagram showing cross-section of ground and text outlining the outcomes of plastics interacting with metals

Figure 1: Illustration of plastics to micro and nano plastics, absorption of metals available within the landfill site and mobilisation of metals.

Host

Cranfield University

Theme

  • Climate and Environmental Sustainability
  • Organisms and Ecosystems

Supervisors

Project investigator

Dr Stuart Wagland, Cranfield University ([email protected])

Co-investigators

Professor Frederic Coulon, Cranfield University ([email protected])

Dr Darren Beriro, British Geological Survey ([email protected])

How to apply

Methodology

The PhD researcher will work with samples extracted from closed landfill sites to determine the main composition of the waste, the extent of plastic degradation, products of degradation and the distribution of microplastics and metals bound to soil media and/or microplastic.

Phase 1: State of the art: Knowledge gaps about the mechanisms of plastic breakdown in landfill environments and likely degradation products.

Phase 2: Characterisation: Develop techniques to determine the breakdown products of plastics (XRF, FTIR, TGA-GCMS), including smaller fragments of plastics (micro/nano plastics) and other organic compounds formed during the breakdown of polymeric bonds.

Phase 3: Metal and pollutant binding behaviour: Determine metal contribution, distribution and chemical binding characteristics.  This may include leaching tests. It will also involve ICP-MS, XRF and FTIR techniques.

The researcher will need to characterise a range of extracted landfill samples, working with the industrial sponsor to plan the sampling campaign.  Samples of landfill leachate should also be characterised to assess the presence of any plastic degradation products.

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

This studentship will provide a wide range of technical and soft skills training throughout the PhD.  This includes research skills, such as writing scientific papers, formulation of scientific hypotheses and presenting work at conferences.  The researcher will be required to join one of the Cranfield Communities of Practice where they will meet other researchers and academic staff working in similar areas and have further opportunities to present and discuss their work.  The researcher will work closely with the industrial sponsor and will spend significant time at landfill sites and leachate treatment facilities, enhancing their industrial experience.

Partners and collaboration

The team is uniquely placed to manage a highly impactful PhD. Dr Wagland is a Reader in Energy and Environmental Chemistry, has a significant track record in landfill chemistry and coordinates the UK Enhanced Landfill Mining network. Dr. Beriro, is a senior geoscientist at BGS, NERC Knowledge Exchange Fellow and has a strong pre-academic background in applied geoscience. Prof. Coulon is an internationally recognised environmental chemist with expertise in landfill chemistry.

Additional partners have shown an interest, with discussions ongoing about additional financial support.  Dr Beriro is seeking a £4,000 contribution from BGS to cover experimental work.

Further details

If you wish to apply to the project, applications should include:

  • A CV with the names of at least two referees (preferably three and who can comment on your academic abilities)

Applications to be received by the end of the day on Wednesday 11th January 2023. 

Possible timeline

Year 1

Review existing literature to understand mechanisms of plastic degradation in landfills and publish review article on microplastics and metal mobilisation within landfill environment.  The researcher will be expected to complete experimental design, carry out laboratory training on techniques in readiness for collecting excavated landfill samples.

 

 

Year 2

Commence basic characterisation of excavated landfill samples, including physical composition, micro/nano plastic content and total metals.  Setup experimental design to determine metal absorption/adsorption potential of microplastics, concluding which microplastic has greatest affinity for metal mobilisation, and which metals are most likely to be absorbed/adsorbed.  Publication of first technical paper and presentation of findings at a peer-reviewed international conference.

Year 3

Further characterisation of landfill samples to understand plastic degradation products beyond micro/nano plastics.  Develop the theory of plastic degradation mechanisms.  Publish further technical paper and write-up PhD thesis.

Further reading

  • Siva Naga Sai Goli, V., Narain Singh, D. (2022) ‘Extraction and Characterization of microplastics in landfill-mined-soil-like-fractions: a novel methodology’, Chemical Engineering Journal. https://doi.org/10.1016/j.cej.2022.139217
  • Pastre G., Griffiths Z., Val J., Tasiu A.M., Camacho-Dominguez V., Wagland S., Coulon F. (2018) ‘A decision support tool for enhanced landfill mining’. Detritus. 01: 91-101. http://dx.doi.org/10.26403/detritus/2018.5
  • Emkes H., Coulon F., Wagland S. (2015) ‘A decision support tool for landfill methane generation’. Waste Management. 43: 307-318. https://doi.org/10.1016/j.wasman.2015.07.003
  • Dino, G.A., Rossetti, P., Perotti, L., Alberto, W., Sarkka, H., Coulon, F., Wagland, S., Griffiths, Z., Rodeghiero, F. (2018) ‘Landfill mining from extractive waste facilities: The importance of a correct site characterisation and evaluation of the potentialities. A case study from Italy’. Resources Policy. 59: 50-61. https://doi.org/10.1016/j.resourpol.2018.04.012
  • Canopoli, L., Coulon, F., Wagland, S.T. (2020) ‘Degradation of excavated polyethylene and polypropylene waste from landfill’. Science of The Total Environment. 698: 134125.  https://doi.org/10.1016/j.scitotenv.2019.134125
  • Lee, H., Coulon, F., Wagland, S.T. (2022) ‘Influence of pH, depth and humic acid on metal and metalloids recovery from municipal solid waste landfills’. Science of The Total Environment. 806. 1. 150332. https://doi.org/10.1016/j.scitotenv.2021.150332
  • Lee, H., Coulon, F., Beriro, D.J., Wagland, S.T. (2022) ‘Recovering metal(loids) and rare earth elements from closed landfill sites without excavation: Leachate recirculation opportunities and challenges’. Chemosphere. 292: 133418. https://doi.org/10.1016/j.chemosphere.2021.133418

COVID-19

The researcher will be handling samples extracted from landfill sites, which will pose health and safety risks.  Landfill samples may contain asbestos fibres, dust and toxic metals; the in-house risk assessment Cranfield uses for these samples will be applied to minimise exposure and mitigate against risks.  The risk assessment for such material involves using good laboratory practice, P100 face masks, disposable suit and gloves in an isolated laboratory.  Samples are sent to a third party laboratory for asbestos screening, with negative results allowing the researcher to proceed with sample characterisation.