Agricultural waste valorization: field application of rice straw-derived carboxymethyl cellulose for irrigation water reuse

This study developed a sustainable bio-adsorbent derived from rice straw carboxymethyl cellulose (CMC) and evaluated its efficiency in improving canal water quality for agricultural reuse. The synthesized CMC exhibited high solubility with a degree of substitution of 0.67. Batch adsorption experiments identified optimal conditions for manganese (Mn²⁺) removal at pH 6, 2.0 g L⁻¹ dosage, and 10 min contact time, achieving 97.0% removal efficiency and an adsorption capacity of 10.54 mg g⁻¹. The adsorption process followed the Freundlich model (R² = 0.9501), indicating heterogeneous multilayer adsorption. To assess field applicability, a pilot-scale multi-stage filtration system - comprising sand, activated carbon, and CMC columns - was operated for 101 days at the Rangsit Prayurasak Canal. The system effectively reduced BOD₅ (85.4% ± 4.5%), Mn²⁺ (81.5% ± 3.6%), chloride (48.7% ± 3.68%), and salinity (46.3% ± 9.8%), producing treated water that met Thailand's Type III surface water standard for agricultural reuse. This work is the first to demonstrate the field-scale use of rice straw-derived CMC in a modular filtration system under actual canal conditions. The results highlight the dual benefits of agricultural waste utilization and practical water quality improvement, offering a technically feasible and low-cost solution for decentralized water treatment in agricultural communities.