Coffea arabica husk flour as a low-cost bioadsorbent for mercury removal from river water
Description
Introduction. Mercury-contaminated river water requires low-cost treatments connected with agro-industrial residue valorisation. Objetives. This study evaluated Coffea arabica husk flour as a bioadsorbent for total mercury removal from a severe-contamination river-water matrix. Materials and Methods. Coffee husk was washed, oven-dried, milled and sieved to 300 µm. The material underwent proximate characterisation and infrared spectroscopy. Batch assays followed a completely randomised 4 x 3 factorial arrangement with four doses, three contact times and two replicates. Residual mercury, removal percentage and adsorption capacity were analysed by factorial analysis of variance and a quadratic response-surface model. Results. The initial mercury concentration was 1.568 ± 0.028 mg L⁻¹. The flour contained mainly carbohydrates, protein, ash and moisture, with hydroxyl, aromatic and carbon-oxygen signals. Dose and contact time significantly reduced residual mercury. The best observed condition was 12 g L⁻¹ for 90 min, which reduced mercury to 0.120 ± 0.024 mg L⁻¹ and achieved 92.35 ± 1.55% removal. The model showed high fit and predicted an optimum near 12 g L⁻¹ and 88.18 min. Conclusions. Coffee husk flour acts as a low-cost primary abatement material, although strict water-quality targets require complementary polishing.