Optimization of and mechanism for the coagulation–flocculation of oil-field wastewater from polymer flooding

Abstract

Oil-field wastewater from polymer flooding (OWPF) is difficult to deal with because it contains a high concentration of partially hydrolyzed polyacrylamide (HPAM), which stabilizes the wastewater. Coagulation–flocculation with polyepicholorohydrin–dimethylamine (EPI-DMA) and polymeric aluminum ferric chloride (PAFC) was used to optimize the treatment of OWPF. HPAM and COD removal were optimized using the response surface method (RSM), based on the Box–Behnken design (BBD). The variables EPI-DMA dose, PAFC dose, and pH were selected as the factors in the RSM to investigate their individual and interaction effects on the response values, HPAM and COD removal efficiencies. The results showed that HPAM and COD removal efficiencies of 95.4 and 85.7%, respectively, could be reached using 0.65 mg/L EPI-DMA, 924 mg/L PAFC, and pH 5.51. Fourier transform infrared spectroscopy, zeta potential, particle size analysis, scanning electron microscopy, and energy dispersive spectroscopy were used to study the mechanism of the coagulation–flocculation process. The results indicated that the main functions of the EPI-DMA and PAFC in the coagulation–flocculation process were electric neutralization, adsorption, and sweeping.