Life Cycle Assessment of Energy and Energy Carriers from Waste Matter – A Review

The development of economic growth, population, and rapid urbanization is increasing the pace of energy consumption and waste production. These trends, if left unchecked, will lead to massive environmental degradation. Waste-to-energy (WtE) conversion is one way of alleviating the twin problems of fossil fuel use and solid waste disposal, and their related problems (climate change, pollution etc). Life Cycle Assessment (LCA) is a useful tool for assessing the environmental performances of WtE systems. Over fifty LCA studies on various WtE systems are reviewed, comprising different waste sources, energy products, and including countries from six continents. A variety of waste types, such as agricultural residues, used cooking oil, manure, municipal solid waste, and waste wood were studied. The review found that a large majority of WtE has lower greenhouse gas emissions when compared to fossil fuels. However, some WtE studies showed an increase in environmental impacts such as acidification and eutrophication, compared to fossil fuel extraction and use. This is due to the use of chemicals (fertilizers, pesticides) in agriculture and the allocation of these impacts to the use of the agricultural waste for energy conversion. Other problems with LCA are also highlighted, including allocation issues, definition of reference systems and functional units.