Urban solid waste plant treatment in Brazil: Is there a net emergy yield on the recovered materials?

Disposal alternatives of urban solid waste (USW) are being considered one of the main topics on the political agenda worldwide due to high concerns related to economic, social and environmental issues. In São Paulo Municipality, Brazil, the Sorting and Composting Waste Treatment Plant (SCWTP) is suggested as an appropriated way to manage the 14,000 Mg of USW generated daily by 11 million inhabitants in 2010. The argument is that recovering materials from USW is aligned to sustainable development concept, however there is a lack of a deeper sustainability assessment, raising doubts about the benefits received by society on recovering materials. In this sense, emergy accounting (spelled with “m”) suggests to be a good alternative when assessing these benefits under a global scale. The aim of this work is to assess the São Paulo's SCWTP using Emergy Accounting. Results shown that currently there is an emergy balance by sorting paper (ratio of recovered by invested emergy of 0.97), and an emergy benefit for iron&steel (2.65), plastic (2.91) and compost (2.57). However, there is an emergy cost by sorting glass (0.23) and aluminum (0.20). A plausible scenario by increasing the recovering efficiency of glass from current 11.6% to 52.9%, and aluminum from 4.7% to 24.7% (both in wet weight), results in an emergy benefit for all materials. The Net Emergy Benefit indicates the SCWTP as a better alternative when the total net emergy return to society is the focus, because while it makes available about 3.13E+14 seJ/Mg of treated USW, the landfills have an average emergy deficit of −3.39E+13 seJ, indicating that landfill uses more emergy than makes available. Results indicates that SCWTP must receive political incentives due to its good emergy performance and others social beneficial aspects, however, aiming to improve the overall performance, each individual citizen must collaborate with waste reduction and the separation of non-organic material from the organic ones at origin.

► An alternative system for recovering materials from solid urban waste is presented. ► The net emergy benefit to society by recovering materials is evaluated. ► Currently, there is a benefit by recovering paper, iron&steel, plastic and compost, but a cost for glass and aluminum. ► The alternative system has better net emergy performance than landfills. ► Separating abiotic from biotic materials at origin is the key to reach better emergy performance.