Degradation of polyacrylamide-containing wastewater by ultraviolet-activated iron-carbon micro-electrolysis and potassium persulfate

Polyacrylamide (PAM) is a commonly used straight-chain organic polymer with good shear resistance, flocculation, dispersibility, and drag-reducing effect. It is mainly used in soil improvement, medicine, petrochemical industry, and environmental protection. By 2030, fossil fuels and renewable energy are projected to remain the primary energy sources (67.8×1016 J in total, with fossil fuels accounting for 78% of the total energy consumption). Over the past 40 years, polymer flooding technology has been applied in marginal oil fields and has proven effective in many cases. Most polymer flooding projects have employed partially hydrolyzed PAM and petroleum sulfonates. However, PAM can naturally degrade into aromatic amide monomers, which are highly toxic to humans. The purification methods of PAM-containing wastewater mainly include physical methods (flocculation, thermal degradation, mechanical shear degradation, and membrane separation), biological methods, and chemical methods. Among them, iron/carbon (Fe/C) micro-electrolysis, one of the widely used water treatment technologies in advanced oxidation processes, has been demonstrated as an efficient and low-cost method to treat various types of wastewaters and contaminated soils, including dye wastewater, organic wastewater, arsenic-containing, and fluoride-containing wastewater. Using ultraviolet (UV)-activated Fe/C micro-electrolysis, the study determined the chemical oxygen demand (COD) removal rates of PAM solution under different pH values, reaction times, K2S2O8 concentrations, and UV powers. The experimental results showed that the COD removal rate under 365 nm UV irradiation was higher than that under 395 nm and 405 nm. Based on the measurements of the COD removal rate and the mass of iron oxide precipitates, the K2S2O8 dosage fluctuation range was determined to be 1 mmol/L. The central composite design (CCD) approach-based response surface methodology (RSM) analysis showed that pH, reaction time, K2S2O8 concentration, and UV power had significant effects on COD removal rate. The regression model yielded a coefficient of determination (R2) of 0.778 9, indicating good agreement between the model and experimental results. The optimal conditions for PAM solution degradation were identified as pH 3.01, a reaction time of 3 h, a K2S2O8 concentration of 1.4 mmol/L, and a UV power of 30 W. Under these conditions, the COD removal rate reached 90.2%, achieving effective removal of PAM.