Cost-benefit analysis of of technologies for microplastics removal and prevention

Microplastics (MPs) are defined as plastic particles with dimensions ranging between 1 µm and 5 mm, originating from a variety of sources located in the inland, seas and oceans, and air. Their release in the environment and the consequent pollution of soil, water, and the atmosphere can represent a serious threat to marine ecosystems and human health. When they are dispersed in air, their presence could even impact climate change, due to MPs property of interfering with the equilibrium of radiative forcing. Reducing their presence in the environment is by now clearly urgent, and it can be carried out through either removal or prevention methods, or a combination of both. The present work examines three technologies – one for MPs removal and two for MPs prevention – through a cost-benefit analysis (CBA), a method in which advantages and disadvantages of one or more processes or assets are evaluated, to understand if a given goal is worth achieving, and which is the best solution to do so. In this thesis, the CBA was performed considering the results of an operation time of one year, and for each technology it included the device costs, the environmental costs, and the qualitative benefits. For each case study, a cost-benefit ratio was calculated: for the removal case study, the ratio was defined as the annual cost of the technology over the amount of MPs yearly removed; for the prevention case studies it was defined as the annual cost of the technology over the amount of plastics yearly avoided to be dispersed in the environment. The first case study examines a filtration technology that retains MPs through a silicon carbide membrane, and its cost-benefit ratio resulted equal to €70.04 per kg of retained MPs. The second case study focuses on a technology used to clean rivers, consisting of a barrier that stops the floating litter and moves it towards the riverbanks, where it is collected. This was considered as a prevention method because the plastics collection from the river would prevent their degradation to MPs in water. This case study also includes the cost of transportation of the litter and the landfill costs; the resulting cost-benefit ratio was €4.67 per kg of collected plastics. The third and last case study deals with dehumidifiers that produce drinking water from air, which leads to a saving of plastic bottles resulting in a cost-benefit ratio of €4.75 per kg of plastics avoided to be dispersed in the environment every year. The results seem to show that the river cleaning method is more efficient than the dehumidifiers, since the collection of macroplastics would impede a higher MPs dispersion than the one coming from the saved plastics of the third case study; however, the amount of collected plastics is highly location dependent, and the difference in the cost-benefit ratio is so little that producing plastic-free drinking water could be in the long term more beneficial than having to remedy to the already dispersed plastics. Concerning the filtration technology, the efficiency results are strongly location dependent as well, and the different definition of its CBA ratio does not allow a comparison with the prevention options; also, no benchmark value was provided to assess the goodness of the technology alone. Despite the limitations and the uncertainties of the analysis, this work provides a first example of how CBA can be used to quantify and compare alternative technologies, and to encourage the commitment to reducing the presence of plastics in the environment.