A Practical Approach for Measuring Chemical Oxygen Demand (COD) of Fats, Oils, and Grease (FOG) Using Tween 80 in Wastewater

This study aims to estimate the organic load of oily wastewater by using Chemical Oxygen Demand (COD) measurements, addressing the analytical challenges posed by the hydrophobic, nonpolar, and often emulsified nature of Fats, oil and grease (FOG). This study established a reproducible and practical methodology for measuring COD in wastewater containing FOG at a laboratory scale, utilizing the nonionic surfactant T80 as a solubilizing and emulsifying agent. Precise gravimetric methods were employed to measure the mass of T80 (indirectly from volume (100–1400 µL/L)) added, and its correlation with COD was established. A strong linear relationship (R2 = 0.993–0.998) between T80 concentration and COD confirmed its stability and suitability as a calibration standard. Experiments with sunflower (1–4 mL/L) and rapeseed oils (1–3 mL/L) showed that COD increased linearly with oil concentration and stabilized after prolonged mixing (96–120 h), indicating complete emulsification and micellar equilibrium. Even under T80 overdose conditions, COD retained linearity (R2 > 0.99), though absolute values were elevated due to excess surfactant oxidation. Temperature variation (5 and 20 °C) and mild heating of coconut fat (30–32 °C) showed no significant effect on COD reproducibility, indicating that mixing time and surfactant dosage are the dominant factors influencing measurement accuracy. Overall, the study establishes T80 as a reliable surfactant for solubilizing oily matrices, providing a consistent and repeatable approach for COD assessment of wastewater containing FOG. The proposed method offers a practical basis and a step towards environmental monitoring and process control in decentralized and industrial wastewater treatment systems.