From Waste to Resource

Converting Harmful Plastic into a Useful By-Product

Modern agriculture uses large amounts of plastics along the production chain to grow, process and store agricultural products. Due to a lack of engineering solutions, agricultural plastic waste has become a source of soil, surface water, groundwater and air pollution. Moreover, the linear-sequence of 'manufacture-use-dispose' ignores the potential economic value of used plastics. This BARD-funded study by Israeli researchers Dr. Roy Posmanik, a BARD postdoctoral alumni (ARO), and Prof. Yael Dubowski (of the Technion Institute), together with the American researchers Dr. Jillian Goldfarb (of Cornell University) and Dr. Deborah Sills (of Bucknell University), will develop a sustainable process to valorize agricultural plastic waste. By adopting advanced thermochemical processes, enhanced polymer degradation will generate valuable compounds required for re-production of "new plastic" with properties similar to the original polymer. While current plastic recycling usually "downgrades" the raw plastic, turning it into its monomeric substances. Researchers hope studies like this may provide an opportunity to create a new platform to re-generate plastic material.

The study will advance the utilization of plastic waste from agricultural systems where it usually contains mix of different polymers together with soil and crop residues. If successful, this research could improve the sustainability of agricultural systems and contribute to creating a circular economy for agricultural plastic waste. The Israeli team at ARO led by Dr. Posmanik will study the conversion of selected polymers in a lab-scale hydrothermal reactor into valuable monomeric products that can be efficiently turned back into a renewable plastic. In parallel, the U.S. team at Cornell will study the pyrolysis process of plastic waste and will focus specifically on the non-degraded plastics from hydrothermal treatment (shipped from ARO) as a source of renewable fuel. All degradation products of the processes will be characterized using a variety of chromatography, spectroscopy and microscopy methods together with x-ray and molecular weight analyses.

Specific attention will be given to the potential for atmospheric pollution from the thermochemical conversion of plastic. Both investigated processes are known to produce mostly CO2 with trace amounts of CO, CH4 and C1-C4 valuable compounds.  However, in “real-life” situations where agricultural plastic waste is combined with insecticides, fertilizers and biomass residues, processes might also generate toxic volatile organic compounds (VOC) such as formaldehyde, petrochemicals such as benzene, toluene, ethylbenzene and xylene (BTEX), furan and dioxins. The exhaust gases from the hydrothermal and pyrolysis units will be trapped in sorption tubes and then extracted and analysed.

The U.S. team at Bucknell University will use the experimental results obtained by both the ARO and Cornell teams, to construct a modeling framework that includes energy and material flow, life cycle assessment, techno-economic analysis, and a comprehensive uncertainty analysis comparing the proposed treatment approach with existing recycling scenarios. At the end of the project, final model results will quantify the tradeoffs inherent in valorizing plastic waste.