From yard waste to leachate treatment: Dual function of biochar as nutrient amendment and adsorbent under real...

This study uniquely integrates nutrient release characterization, multiscale adsorption evaluation, and transport modeling using locally derived yard waste biochar and real landfill leachate to demonstrate material-level dual functionality under wetland-relevant conditions. This case study evaluated locally produced yard waste biochar for dual use in constructed wetland leachate treatment: (1) as a nutrient amendment and (2) as an adsorbent for influent contaminants. It represents an assessment tailored to local landfill conditions and biochar characteristics. Using a modified EPA 1314 Leaching Environmental Assessment Framework (LEAF) method, we quantified nutrient release of total organic carbon (TOC), biochemical oxygen demand (BOD), total nitrogen (TN), and inorganic nitrogen species. Biochar produced at 300 °C released the highest TOC (2.1 mg/g), while 500-700 °C biochar released less due to carbon stabilization. Aged feedstock enhanced nutrient release, with aged biochar (A-YW-300) yielding the highest TN (∼0.1 mg/g). BOD/TOC ratios indicated both bioavailable and refractory carbon fractions. Adsorption tests showed yard waste biochar achieved equilibrium TDS removals comparable to commercial activated carbon, reaching 15-30% removal from real leachate. Kinetic modeling followed pseudo-second-order behavior (R² = 0.66-0.72, moderate fit), with activated carbon equilibrating faster (∼3 h) than aged biochar (∼12 h). Fixed-bed column studies confirmed strong TDS retention (R > 1). Overall, biochar produced at moderate pyrolysis temperatures (300-500 °C) provided balanced nutrient release and competitive adsorption performance, demonstrating its potential as an amendment for biochar-enhanced constructed wetlands.