In 2018, the global annual consumption of polyethylene terephthalate (PET) bottles was about 27.64 million tons, with one million plastic bottles being sold worldwide every minute. The rapid rise in the consumption of PET bottles has been flagged as a critical international issue that must be dealt with urgently. The problem of PET plastic starts when it enters the ecosystem as unmanaged waste. Unmanaged PET bottles abandoned in the ecosystem adversely impact human health and the ecosystem. Hence, this thesis has three main goals: (1) To review available sustainable resource management tools, namely the circular economy (CE), industrial ecology (IE), and the energy-water-food (EWF) nexus. (2) To assess the sustainability of eight PET bottle waste processing alternatives. (3) To design an optimal collection system for waste PET bottles. To address the first objective, we conducted a systematic review of the literature to determine how tools have been used in resource management in general and plastic waste in particular. In addition, we present a comprehensive list of methods, performance indicators, and applications to lay the scientific foundation for the development of an optimal framework for the sustainable management of PET waste.
To achieve the second goal, we developed a holistic multi-criteria decision-making (MCDM) approach that combines the technique for order of preference by similarity to an ideal solution (TOPSIS), the analytic hierarchy process (AHP), and the coefficient of variation (COV). To the best of our knowledge, TOPSIS combined with COV has not been used in waste management. We compared eight different PET waste treatment methods which are: closed-loop recycling, open-loop (mechanical recycling), open-loop (semi-mechanical recycling), landfill, incineration with heat recovery, incineration with heat and power recovery, glycolysis, and pyrolysis. These methods were assessed
using twelve performance criteria representing the pillars of sustainability i.e. environmental, economic, and social. Our analysis indicates that closed-loop recycling is the optimal alternative for treating PET waste bottles. As for the third goal, we suggest an analytical, single-objective approach that minimizes the total annual cost at a tactical level of the collection network for PET waste. We proposed and compared three different design options to determine the optimal design and location of a recycling facility for a post-consumer PET waste collection network. The first design option, which is called "local bins with recycling company collection," requires consumers to deposit their used PET bottles in the nearest dedicated bin, and recycling company vehicles to collect the waste. The second model, called "retailer bins with recycling company collection", requires consumers to deposit their used PET bottles in dedicated bins located at retailers while shopping. Recycling company vehicles collect the used bottles. The third model, called "retailer bins with collection by a manufacturing company", is similar to the second in that consumers are required to deposit used PET bottles in the bins located at retailers, but with the notable difference that in this case the bottled water manufacturers/distributors are responsible for collecting the waste from retailers. Hence, this latter option can be seen as a reverse logistics design. The three designs were analyzed in detail and compared using data from a case study in the State of Qatar. For each design, and each recycling rate, we computed the optimal location of the recycling facility, as well as the optimal number and capacity of the dedicated bins, and the optimal capacity and size of the vehicle fleet. The numerical results show that the reverse logistics option is by far the most economical, being about three times cheaper than the first and half as expensive as the second. Furthermore, the results suggest that Messaieed is the optimal location for the recycling center facility, and recommend the use of larger capacity vehicles (22 tons).
In addition, our study highlighted the fact that the contribution of all entities (i.e., consumers, manufacturers, government, and retailers) is essential to achieve the desired economic and environmental benefits.
| Date of Award | 2022 |
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| Original language | American English |
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| Awarding Institution | - HBKU College of Science and Engineering
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