In the present study, the performance of compound flocculants composed of different concentrations of polyaluminum chloride (PAC) and cationic polyacrylamide (CPAM), the influencing mechanism of the flocculation process and the effects of temperature, settling time, and speed and time of stirring were investigated. The results show that the poor water quality with high concentrations of oil, suspended solids (SS) and polymer greatly increases the oily wastewater emulsion stability and the difficulty of the flocculation treatment process. The compound flocculant in oily wastewater treatment can achieve best results at optimum conditions of temperature 45 °C, settling time 60 min, and two stirring stages, 250 r·min−1 for 3 min followed by 100 r·min−1 for 7 min. At the PAC dosage of 80 mg·L−1 and the CPAM dosage of 0.8 mg·L−1, the turbidity of oily wastewater is reduced from 153.8 NTU to 11.2 NTU, and the turbidity removal rate reaches 92.69%. Through further measurements, oil content and SS content are less than 10 mg·L−1, which meets the requirement of the Daqing oilfield re-injection standard.

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