Application of a cadmium-free continuous flow analysis system to industrial wastewater: Interference evaluation and environmental impact assessment

• Cadmium-free CFA validated for nitrogen analysis in industrial wastewater. • High recovery (≥90 %) and accuracy (≥95 %) confirmed under interference conditions. • Copper–zinc reduction coil showed high durability in continuous wastewater analysis. • Life cycle assessment revealed major reductions in environmental and health impacts. • Provides a robust and sustainable alternative to cadmium-based CFA methods. Building on our previous work with natural waters, this study evaluates a cadmium-free copper–zinc reduction continuous flow analysis (CFA) system for the determination of nitrogen species—nitrate-nitrogen, ammonia-nitrogen, and total nitrogen—in industrial wastewater. A key novelty is the systematic investigation of interference from common coexisting substances in industrial effluents, such as heavy metals and organic compounds, which often compromise colorimetric detection in complex matrices. We conducted controlled spike-recovery experiments and validated results with reference materials to assess analytical robustness. The cadmium-free CFA system demonstrated analytical accuracy of ≥95 % when tested with reference materials and maintained recovery rates above 90 % in actual industrial wastewater samples across all nitrogen species, even under high-interference conditions, matching the performance of conventional cadmium-based methods. Additionally, a life cycle assessment (LCA) revealed substantial reductions in environmental and human health impacts by replacing cadmium with zinc and phenol with salicylic acid, with significant improvements in toxicity and resource-related categories. These findings demonstrate that the proposed CFA method provides both analytical reliability and environmental sustainability, confirming its suitability as a robust and eco-friendly alternative for accurate nitrogen monitoring in complex industrial matrices.