Evaluating carbon footprint of municipal solid waste treatment: Methodological proposal and application to a case study

Abstract

Abstract This paper applies the Life Cycle Assessment methodology to develop a simple method to calculate the carbon footprint of the municipal solid waste treatment stage. This simple and structured methodological procedure takes into account: i) direct greenhouse gas emissions produced in waste treatment, taking place within the city boundary (scope 1 of international carbon footprint standards); ii) indirect greenhouse gas emissions related to the use of grid-supplied electricity, as well as fuel production and distribution (scopes 2 and 3 emissions as per international carbon footprint standards); and iii) avoided greenhouse gas emissions as a result of the products obtained (if any) that can replace other products or the raw materials used to produce them. Madrid City (a representative European city), the capital of Spain, was used as a case study to prove the validity and usefulness of the proposed methodology. In this city, 344 kg of municipal solid wastes were produced per inhabitant in 2013. These wastes were collected separately in different fractions (packaging, glass, paper/cardboard and mixed waste, including organic material). Mixed waste and packaging fractions were processed at the Valdemingomez Technology Park. The current treatment stage was compared with several alternative scenarios which describe hypothetical management routes for the different waste fractions. The carbon footprint for the current situation is equal to 224 kg CO2 eq/twaste. In comparison to the worst situation, corresponding to the scenario in which municipal wastes were landfilled without energy recovery, the current scenario reduces its carbon footprint by 1597 kg CO2 eq/twaste (a reduction of 88%). Improvements in the material separation and recovery processes, along with the implementation of biological treatments for the organic fraction, clearly contribute to reducing the carbon footprint of the municipal solid wastes handled in the city of Madrid. According to the obtained results, the scenarios based on a total recovery of valuable materials and waste-to-energy or anaerobic digestion treatments present the lowest carbon footprint because burden avoided is more important than direct and indirect emissions from treatments. In addition, the consumption of electricity and the emissions derived from its generation (mix of generation), can increase the carbon footprint of power-intensive treatments.