Circularity, Cost and Life Cycle Impact: Accounting for Trade-Offs in Choosing Plastic Grocery Bags and Waste Management Strategies

With the onus of waste mitigation and elimination of oceanic plastics, it is essential to establish Circular Economy for Plastics. This work aims to develop a theoretical framework for the assessment and design of alternative plastic products while accounting for Circularity, Impact and Costs. A holistic network is developed to link various modules in life-cycles of five different types of plastic bags that can be used by a household. A Multi-objective non-linear optimization problem is solved to find the globally optimal pathway in this network. Optimization criteria include - Degree of Circularity, Global Warming Potential and Cost. A novel metric captures the restored value in down-scaling of waste plastic and loss of natural capital due to littering, thereby describing the economic circularity of the network. Decision variables are the fraction of each bag type used, preferred collection method and waste management strategies.

Two stake holders are considered for the objectives, namely - Individual Households and Society, corresponding to Bag costs and Life-Cycle Costs respectively. Pareto fronts for three objectives are plotted and an optimal set of decisions is proposed, which, from Societal perspective is the uptake of reusable low-density polyethylene (LDPE) bags and single-use high-density polyethylene (HDPE) bags, with curbside collection and combination of recycling and incineration. Whereas, the decisions from perspective of consumers shift towards using a fraction of bags which are biodegradable (poly-lactic acid - PLA), and partial waste management by composting. Numerous additional insights are obtained from the study, including sensitivity of results towards re-usability of bags.