Uncertainty analysis in the environmental assessment of an integrated management system for restaurant and catering waste in Spain

Abstract

[EN] Purpose The goal of this study is to analyze the environmental improvement brought about by an alternative system for waste management proposed by the Integral-b project, funded by the European Union (EU). Its aim is to treat both used cooking oil (UCO) and organic waste from the restaurant and catering sector in Spain, by biodiesel production and anaerobic digestion, respectively. A cogeneration engine adapted to use glycerin as a fuel is implemented.

Methods The functional unit (FU) is the management of the UCO and organic waste from restaurants and catering produced per person and year in Spain. The system proposed (scenario A) is compared to a system consisting of the prevailing management options for the same kind of waste (scenario B). Apart from including biodiesel production from the UCO, this reference scenario assumes that the organic waste is allocated to different streams, according to Spanish statistics. The systems under study generate different coproducts and as such are complex; therefore, system expansion is performed. Different scenario formulations are set to analyze the influence of assumptions regarding co-product credits in the results. Finally, Monte Carlo simulations are carried out to analyze parameter uncertainty.

Results and discussion The environmental benefits caused by scenario A are conditional on the choices regarding coproduct credits. Scenario A causes a reduction of the impact (43-655 %) in most of the scenario formulations when the current levels of UCO collection are considered. However, when higher levels of UCO collection are taken into account for the definition of the FU, scenario B performs better for half of the scenario formulations, due to the increase in the environmental credits from glycerin production. The only impact categories for which scenario A performs unconditionally better than scenarioBare global warming and photochemical ozone creation. Parameter uncertainty appears to influence the comparative results to a lesser extent, mainly caused by the parameters involved in avoided processes.

Conclusions Although system expansion appears as an option for dealing with the multifunctionality of waste management processes, uncertainty caused by choices must be assessed. Under our scenario assumptions, re-using the glycerol in the system proposed by Integral-b can be detrimental, and the reference scenario results in higher avoided burdens in some scenario formulations. Including glycerin valorization in scenario B should be considered if the biodiesel production keeps increasing in Spain. Analyzing parameter uncertainty helps to provide reliable results.