Oil Separation Performance of Transformer Accident Oil Under Different Degreasing Methods

This study investigates the separation performance of transformer oil–water mixtures using gravity separation and chemical demulsification. The synthetic emulsion had an initial oil concentration (C0) of approximately 246,000 mg/L. For gravity separation, the effects of compartment volume ratio, influent flow rate, initial water level, and oil discharge strategy were systematically evaluated. Under optimal conditions (volume ratio 2:1:1, flow rate 0.0055 L/s, initial water level 5 cm), the effluent oil concentration was reduced to as low as 0.020 mg/L, corresponding to a removal efficiency higher than 99.99%. For chemical demulsification, polyaluminum chloride (PAC), polyferric sulfate (PFS), polyacrylamide (PAM), and an organosilicon polyether demulsifier (MCL-D) were tested. The effects of pH, dosage, and temperature on demulsification efficiency (DE) and dehydration rate (DR) were investigated. Under optimal conditions (pH 3–5, dosage 300 mg/L, temperature 50 °C), MCL-D achieved the best performance, with a DE of 95.09% and a DR of 99.50%. Overall, gravity separation is effective for removing free and dispersed oil with low operational cost, whereas chemical demulsification is more suitable for treating stable emulsified oil. The combination of these two methods provides an efficient strategy for the treatment of transformer oil-containing wastewater.