Mitigating suspended solids interference in COD analysis: Optimized homogenization for reliable landfill leachate characterization

Accurate chemical oxygen demand (COD) determination in landfill leachate is critical for pollution assessment and treatment design but is severely compromised by heterogeneous suspended solids. Conventional filtration pretreatments improve precision but only quantify the soluble fraction, inherently underestimating the total organic load. This study introduces and systematically optimizes a novel mechanical homogenization protocol to overcome this limitation. We demonstrate that homogenizing leachate with a blender for 30 s, followed by 30-40 min of settling, effectively disperses solids into a stable, representative suspension. This optimized approach yields total COD values 26.7%–35.3% higher than filtration-based methods, with superior precision (RSD < 5%) and accuracy (spike recovery 93%–111%). Turbidity monitoring confirmed the stability of the homogenized system. Our work advances COD pretreatment practice by providing a standardized, reliable method for quantifying the total oxidizable pollutant load, ensuring data representativeness for accurate process design and environmental monitoring of landfill leachate. gravity filtration