Implementación y verificación del ensayo demanda química de oxigeno mediante la técnica colorimétrica de reflujo cerrado en aguas residuales

Abstract

The reliable determination of Chemical Oxygen Demand (COD) is essential for operational control and environmental monitoring of wastewater treatment processes. This study aimed to implement and verify the closed reflux colorimetric method in accordance with Standard Methods 5220 D and ASTM D1252-06, ensuring its suitability under the specific operating conditions of a process control laboratory in Guayaquil, Ecuador. An applied, quantitative, and experimental research approach was adopted to evaluate key analytical performance parameters, including selectivity, limits of detection and quantification, linearity, analytical sensitivity, trueness, precision, measurement uncertainty, and robustness through a factorial design. The results demonstrated appropriate linear behavior within the working range, compliance with statistical acceptance criteria for precision and recovery, and expanded uncertainty values consistent with EURACHEM guidelines and ISO/IEC 17025 requirements. The robust assessment confirmed method stability under controlled variations in digestion temperature, reaction time, and digestion equipment. Finally, the application of the verified method to real influent monitoring confirmed its metrological reliability, supporting its routine implementation and potential accreditation within the laboratory quality management system. Keywords: Chemical Oxygen Demand, method verification, measurement uncertainty, closed reflux, analytical quality control.