Treatment of polyacrylamide-containing wastewater by ionizing radiation: Efficient reduction of viscosity and degradation of polyacrylamide

Polyacrylamide is one of the most widely used polymer to enhance oil recovery in oilfield, leading to generation of partially hydrolyzed polyacrylamide (HPAM)-containing wastewater, with large amount, high viscosity and emulsification, making the oil droplets and particles in the wastewater stable and difficult to remove. In present work, ionizing radiation was applied to decompose HPAM, thus to reduce the viscosity of HPAM-containing wastewater. During radiation, the viscosity of HPAM solution declined rapidly and the reduction extend was affected slightly by the initial HPAM concentration and pH. The viscosity decreased from 5.2 to 12 mPa s to 1.1–1.6 mPa s at the absorbed dose of 1.0 kGy, while the absolute value of zeta potential also declined rapidly from 116 mV to 79 mV. The removal efficiency of HPAM was 62–78% at 10 kGy at the initial concentrations of 250–1000 mg/L. The molecular weight of HPAM declined from 12,000 kDa–320 kDa at 5 kGy. Gamma radiation might destroy hydrogen bonds of intermolecular and intramolecular HPAM molecules preferentially, leading to the destruction of the curling network structure, thus the reduction of viscosity. The attacks on C–N bond, C–C skeleton, amide and carboxyl groups were also occurred, resulting in the formation of intermediate products, such as aliphatic hydrocarbon, ammonium, ketone, etc. In summary, ionizing radiation is a promising alternative to treat HPAM-containing oilfield wastewater.