Environmental assessment of the integrated municipal solid waste management system in Porto (Portugal)

Abstract This paper presents the results of the environmental evaluation of the waste treatment processes occurring at LIPOR (the Inter-municipal Waste Management System of Greater Porto – Portugal) in the period 2007–2011. To this aim two methodologies are applied, namely the Energy and Material Flow Analysis (EMFA) and the Ecological Footprint (EF). The benefits of their joint application are explored, as well as the usefulness of the indicators derived to guide the company in the identification of the hot spots and in the improvement of their management practices. The Integrated Waste Management System (IWMS) at LIPOR includes several units, specifically the separation of several materials for valorization (namely, packaging materials -as metals and plastics-, glass and paper and cardboard), the incineration of waste with energy recovery, composting of the organic fraction and the landfilling of pre-treated waste. From the EMFA, it can be highlighted that the electricity generated in the energy recovery plant is the most important energy flow and that it largely exceeds the energy demands from the LIPOR system. According to the net EF results, the composting and energy recovery units were found as very beneficial in terms of resources savings. Despite the fact that the composting plant has the largest gross EF (0.28 ± 0.02 gm 2  kg −1 in average for the period analyzed, where gm 2 refers to global square meters), a significant counter footprint effect associated with the production of the compost was calculated (−1.51 ± 0.10 gm 2  kg −1 of waste composted). The energy recovery plant shows the lower gross EF (0.05 ± 0.01 gm 2  kg −1 of waste combusted), but also an important contribution to the counter footprint (−0.78 ± 0.01 gm 2  kg −1 in average). These individual results are reported to 1 kg of waste treated at each facility. Meanwhile, the EF for the overall IWMS reaches −0.49 ± 0.12 gm 2  kg −1 , where this result is reported to the total wastes treated at LIPOR. The negative value means that, in terms of the EF, the global system is environmentally beneficial because of the recovery of resources such as the compost and electricity.