Valorization of Fruit Peel Waste via Microwave-Assisted Co-Pyrolysis: Dual-Optimized Biochar Production for Soil Amendment and Pollutant Adsorption

The valorization of fruit peel waste through microwave-assisted co-pyrolysis (MACP) offers a sustainable pathway for producing high-performance functional materials. This study employed a Central Composite Design (CCD) and multi-objective desirability function to engineer biochars tailored for soil amendment (BCop-bf) and pollutant adsorption (BCop-ads). Synergistic effect analysis provided empirical evidence of the superiority of biomass blending, showing significant gains in nitrogen (15.77%), phosphorus (14.29%), and oxygen-containing functional groups (15.44%) compared to theoretical additive values. Optimization for BCop-bf (212.3 °C) maximized macronutrient retention (7.93% N, 7.62% K), while BCop-ads (259.4 °C) yielded a matrix with high surface functionality (3.44 mmol/g of OFG). Thermogravimetric analysis (TGA/DTG) of the optimized products confirmed high thermal recalcitrance, with residual masses exceeding 50% at 800 °C, ensuring long-term carbon stability. Although the BET surface area was modest (10.84 m²/g), textural analysis revealed a predominantly mesoporous structure (pore size of 2.94 nm) that, combined with a versatile point of zero charge (pHpzc = 8.0), facilitates mass transfer and multi-mechanism adsorption. This dual-optimization strategy validates MACP as a robust technology for converting environmental liabilities into application-specific resources for the circular bioeconomy.