Defining the maximum reliable threshold for separate waste collection: a multi-dimensional analysis and empirical validation in Campania, Italy

In this study we propose a method to determine the maximum reliable threshold for separate waste collection (SWC) at the municipal level, grounded on the quantification of the residual fraction (i.e. non-recyclable and non-compostable) generated by an average citizen. Using the Junker app, we compiled an inventory of 225 residual items and, for each item, estimated the number of users, annual consumption (with ±20% variability around the mean) and average weight. Summing contributions across items yields a national average residual of 50.20 kg/inhabitant/year (range: 40.16–60.24), implying a reliable SWC rate of 88–92% given 502.15 kg/inhabitant/year of municipal solid waste (MSW). Considering biodegradable/compostable substitutes where available (91 out of 225 items), the residual drops to 23.80 kg/inhabitant/year, consistent with a 95.26% SWC under a “zero-waste” behavioral profile. The threshold was also derived for Italian macro-areas and for Campania and its provinces. An empirical survey in 32 high-performing municipalities (634 valid responses; 2.61 items/response) confirmed the plausibility of the theoretical ranking of key residuals. This framework provides a replicable and evidencebased benchmark that can be used by policy makers and waste managers to set realistic targets, prioritize interventions on critical waste streams, and verify the credibility of reported SWC performances.