Technical substitutability of recycled materials in life cycle Assessment: A comprehensive review and framework for quantification

In evaluating environmental sustainability with methodologies like life cycle assessment (LCA), recycling is usually credited for avoiding impacts from virgin material production. Consequently, the LCA results are influenced by the manner in which the substitutability of virgin by recycled materials is estimated. This study reviews how the scientific community assesses the technical substitutability of recycled materials in LCA. Accordingly, 49 peer-reviewed papers were in-depth analysed, considering aspects such as materials studied, type of substitution, recycled material (rMaterial) application, and life cycle stages (LCSs) where substitution was evaluated. The results show that 49% of the papers investigated material substitutability through technical and economic aspects. 51% of the articles did not consider the final application of the rMaterial. Plastics were the most studied material, and mass was the most used property to quantify technical substitutability. Certain materials were more analysed in specific LCSs (e.g., metals in the natural resource extraction stage). As 51% of the papers developed a new approach for substitutability calculation, this shows that substitutability is still a concept in development. It was noticed in 33% of the papers that substitutability values were taken from external sources, and in some cases were used without considering whether they were representative for a specific case. Aspects such as harmonization, transparency, and consideration of the application of recycled materials, therefore, require more attention in substitutability evaluation. Based on the results, a step-wise framework to measure technical substitutability at different LCSs was developed to guide researchers in including substitutability in LCA studies.

Environmental Benefits of Air Emission Reduction in the Waste Tire Management Practice

Montenegro faces serious challenges in terms of waste tire management. The main goal of our paper is to consider the financial and economic justification of the implementation of the first phase of the project of collection, takeover and transport, sorting, and storage of waste tires from the three municipalities in Montenegro. The financial feasibility analysis pointed out the need to organize the second phase of the project and the production of commercially usable and energy efficient products. That phase would lead to the desired commercial effects and will probably ensure the financial sustainability of the project. The economic feasibility analysis of the project included an assessment of the socio-economic benefits from the emission reduction of the first group of pollutants (PM, SOX, NOX, VOC, CO) as a consequence of the waste tires’ destruction, predominantly by combusting them. Unit values of pollution costs by types of gases, adjusted for Montenegro, were defined in the interval from 192 EUR/t for CO to 24,294 EUR/t for PM. We proved that the direct socio-economic benefits of this project are savings in the cost of environmental pollution. The total present value of discounted costs in the observed time period was calculated at the level of EUR 1,620,080, while the total present value of the positive socio-economic effects was estimated at EUR 1,991,180. Dynamic justification indicators suggest that this investment has a satisfactory socio-economic justification, i.e., the economic rate of return is higher than the opportunity cost of capital (ERR = 15.82%), the economic net present value is greater than 0 (ENPV = 371,100 EUR), and the benefit–cost ratio is greater than 1 (B/C ratio = 1.23).

Resource and environmental assessment of pyrolysis-based high-value utilization of waste passenger tires

Carbon black and fuel oil as the products of conventional pyrolysis are limited in application owing to their low quality. This paper presents a pyrolysis-based high-value utilization process of waste passenger tires (WPTs). A comparison of the life cycle assessment (LCA) between this process and a conventional pyrolysis process was carried out. Moreover, a comprehensive evaluation index of the ratio of economic profit to environmental cost (PCR) was established. The results show that the increase in economic profits brought about by the high-value utilization process is higher than the increase in environmental costs, and the pyrolysis-based high-value utilization of WPTs has more positive benefits than conventional pyrolysis. Reducing the consumption of electricity and natural gas in the high-value utilization process has a significant effect on the decline of the main environmental impacts. Compared with the production of conventional pyrolytic products, this has the dual advantages of resource saving and environmental protection. Also, the environmental loads of ozone layer depletion (ODP) and human toxicity (HTP) are reduced by over 90%, and the loads of abiotic depletion (ADP) of minerals and fossil fuels are reduced by over 84%. Sensitivity analyses show that both the production cost and the price of carbon black significantly influence the PCR. The replacement of coal-fired power generation with renewable energy generation has a positive effect on improving the resource and environmental performance for the high-value utilization process of WPTs.