Efficient treatment of polyacrylamide wastewater by cascade heterogeneous Fenton and magnetic flocculation process

Abstract

A large quantity of polyacrylamide containing wastewater is generated during polymer flooding every year and it poses great threats to the environment. As highly efficient technology for polyacrylamide wastewater treatment with potential for engineering application is rare, magnetic flocculation represents a promising alternative. It usually takes minutes for complete sedimentation to occur. However, we found in experiments that viscosity reduction in advance was essential to improve the performance of magnetic flocculation. So, a cascade of heterogeneous Fenton and magnetic flocculation process was proposed. Effect of Fe3O4 dosage, flocculants type and dosage, flocculation pH, stirring conditions and flocculation methods on the removal efficiency of PAM was investigated. The cascade process turned out to be one of the most efficient technologies and achieved 92% PAM removal rate in the shortest time (45 min) for 500 mg/L of PAM when Fe3O4 dosage was 1.5 g/L, AlCl3 dosage was 100 mg/L and flocculation pH was 8.0 under optimized stirring conditions. Nano-Fe3O4 exhibited good stability after at least 3 successive runs. The water quality of polymer flooding wastewater from Nanyang Oilfield reached the required standards for reinjection after treatment by the cascade process. The study provides a new and highly efficient technology for PAM wastewater treatment with promising potential for engineering application.