Evaluation of mechanical pretreatments and mineral amendments on the degradation of municipal solid waste using digestive bales

The global increase in urban solid waste generation demands efficient and decentralized management alternatives. This study compared seven bale configurations — an unmodified control, two mechanical pretreatments, a mineral amendment, inoculation with mature compost and two wetting regimes — in terms of organic matter degradation and biofertilizer quality in digestive bales, a low-cost technology for treating the organic fraction of municipal solid waste (OFMSW). The experiment was conducted under tropical conditions for 87 days, monitoring temperature, pH, height reduction, and the volatile solids to total solids ratio (VS/TS). All treatments reduced their VS/TS ratio relative to the initial value of the corresponding bale, with changes ranging from 27.70% (control) to 46.59% (rock powder). Rock powder addition showed the largest observed change, achieving the highest compaction kinetic constant (k = 0.086 d⁻ 1 ) and greatest VS/TS reduction, while mature compost inoculation produced the greatest final height reduction (52.2%), a measure of settlement rather than of degradation. Particle size reduction improved initial degradation rates, whereas the wetting treatments limited thermophilic activity. All treatments except full wetting reached hygienization conditions (>50 °C). Principal Component Analysis revealed a mineral-organic gradient as the main axis of variation among final biofertilizers. These results indicate that digestive bales stabilize the OFMSW without turning or active aeration, and that mechanical pretreatment was the most consistent intervention among those tested.