Environmental assessment of shredder residue management

Metal recycling from automobiles, appliances and scrap steel occurs at dedicated metal shredding operations. Shredder residue (SR) consists of glass, rubber, plastics, fibers, dirt, and fines that remain after ferrous and nonferrous metals have been removed. The over 3 million tonnes of SR generated in the U.S. each year are managed by landfilling. Material recovery or energy recovery alternatives to landfilling can be beneficial because of conservation of non-renewable resources and reduction of waste disposal. In this study, the human health and environmental impacts of landfilling and three recovery options (supplemental fuel and mineral feed for cement manufacturing, hydrolysis to light fuel oil, and material recovery for recycling) were quantified and characterized using a life-cycle assessment (LCA) approach. Comparisons were carried out after characterization of emissions relative to potential impact categories of global warming, freshwater aquatic toxicity, acidification, eutrophication, human toxicity, photochemical oxidant creation, and terrestrial ecotoxicity. SR recovery in cement manufacturing could result in 1 million tonnes of coal conservation each year for the U.S. Compared to landfilling, recovery of the fuel and mineral value of SR in cement manufacturing provides net benefits for all environmental impact characteristics considered primarily due to avoided coal mining and landfilling impacts. As much as 750,000 tonnes of recyclable materials could be recovered from SR. Material recovery system impact results were very sensitive to process energy requirements as well as the assumptions of percent recovery and the specific material types recovered. Hydrolysis of SR could produce 250 million gallons of light fuel oil equivalent per year. The hydrolysis process requires a significant amount of electricity, the impacts of which are somewhat offset by the avoided impacts of producing fuels from crude oil resources. Primarily due to high electricity consumption, both the hydrolysis and material recovery scenarios yielded trade-offs (some net benefits and some net higher impacts) compared to landfilling. The results of this end-of-life impact assessment showed that the supplement for cement manufacturing option was environmentally beneficial to the current practice of landfilling and appears better in comparison to the other management methods studied.