METHODS OF DEALING WITH CO-PRODUCTS IN A LIFE-CYCLE ASSESSMENT OF BIODIESEL FUEL PRODUCED FROM WASTE COOKING OIL

Biodiesel fuel has received considerable attention as a more sustainable alternative to traditional fuel. This paper presents a life cycle assessment (LCA) for producing biodiesel fuel from waste vegetable oil (WVO). Comparisons are made for different methods of dealing with additional products. The LCA is a cradle to fuel model that includes the following unit processes: soybean farming, soy meal and soy oil extraction, processing of soy oil, cleaning/drying waste oil, transesterification to produce useful biodiesel and transportation to various sites. Metrics evaluated to determine sustainability include global warming potential (GWP) and cumulative energy demand (CED). Values are obtained using GREET1. Credits for additional products must be applied in the LCA. WVO is a byproduct of oil produced for cooking fried products. We account for oil consumed in the cooking process using two approaches. In the first approach, the amount of oil consumed in the cooking process is credited to the WVO. All the cooking oil is considered WVO. In the second approach, the WVO is considered a "free" product. This means only the CED and GWP associated with WVO transportation, processing and fransesterification are included in the LCA. Other co products are considered applying two fraditional methods used in LCA: mass-based allocation and displacement. In mass-based allocation, CED and GWP are adjusted considering the mass fraction of soy oil produced from soybeans and the mass fraction of biodiesel produced from WVO in the transesterification process. In the displacement method, soymeal is considered to displace soybeans as animal feed and glycerin displaces synthetic glycerin. The CED and GWP of the displaced products are subtracted as credits. LCA results for the various approaches to additional products are compared. We demonstrate a wide range of results are possible. These results should provide useful information for dealing with additional products in determining the sustainability of producing biodiesel fuel from waste vegetable oil.