Waste to Resource: Processing Agricultural Waste into Novel Sustainable Materials for Iron and Manganese Removal in Remote Community Drinking Water Systems

Iron (Fe) and manganese (Mn) are common drinking water contaminants, posing health risks and causing aesthetic issues. Conventional treatments are effective, but often too costly or impractical for remote areas. This study tested six biochars (BC) and six phosphoric acid-activated carbons (AC), from agricultural residues, as low-cost adsorbents for Fe and Mn removal in regional Queensland drinking water conditions. Batch adsorption experiments were conducted using 10 mg/L Fe and 10 mg/L Mn, with results interpreted through isotherm and kinetic modelling. Activated carbons demonstrated superior performance, with Fe removal efficiencies of 85–99% and Mn removal efficiencies of 85–98%. Maximum adsorption capacities (qₘ) reached 8.01 mg/g for Fe and 4.67 mg/g for Mn. Adsorption followed Langmuir isotherms (R² up to 0.9954 for Fe and 0.9169 for Mn). Kinetic modelling showed that Fe adsorption followed a pseudo-second order (PSO) mechanism, whereas Mn adsorption adhered to pseudo-first order (PFO) kinetics. Biochar exhibited more variable performance, with Fe removal ranging from 48 to 99% and Mn removal from 31 to 97%, alongside lower qₘ values (1.24–3.25 mg/g for Fe and 0.27–2.85 mg/g for Mn). Langmuir R² values for BCs ranged from 0.7182 to 0.9541 for Fe and 0.1998 to 0.8624 for Mn. Overall, ACs are recommended for centralised treatment systems due to their high performance, while biochar offer a promising, low-cost, and sustainable alternative for decentralised and rural applications. These findings highlight the potential of developing of waste-derived adsorbents as field-ready solutions to improve drinking water quality in underserved communities.