La gestione integrata dei rifiuti urbani: analisi economica di scenari alternativi

A critical assumption of studies assessing comparatively waste management options is the consideration of a constant average cost for selective collection regardless the Source Separation Level (SSL) reached, and to neglect the mass constraint. In the literature, most often technologies are compared with each other (eg incineration vs. recycling or composting), while costs and benefits, either financial or external, are usually referred to individual facilities and technologies rather than to integrated waste management scenarios. The present study compares alternative waste management scenarios through the development of a desktop model that tries to remove the above limits. Several alternative scenarios based on different combinations of energy and materials recovery are applied to two imaginary areas modeled in order to represent a typical Northern Italian setting. External costs and benefits implied by scenarios are also considered. Scenarios are compared on the base of the full cost for treating the total waste generated in the area. The model investigates the factors that influence the relative convenience of alternative scenarios. Finally, a sensitivity analysis is provided in order to clarify the criticalness of assumptions made in the scenarios. The study emphasizes the need to consider waste management alternatives as complementary parts of an integrated strategy, rather than alternatives. In this light, it emerges quite clearly that both materials recycling and energy (and heat) recovery through incineration of residual waste are needed in order to minimize the waste flow addressed to landfill. The study also demonstrates that there are diminishing returns in the recovery of materials: a rate of material recycling beyond 50% implies higher costs, and these are not justified by positive externalities. It also emerges that after accounting for positive externalities (displaced energy sources), incineration can very well compare with recycling also in terms of social cost/benefit.