Efficient degradation of polyacrylamide using a 3-dimensional ultra-thin SnO2-Sb coated electrode

Highlights: • A new type of 3D electrode with ultra-thin SnO₂-Sb catalytic layer was prepared. • The 3D electrode performed raised OH·generation by 20%. • The 3D electrode showed improved service life by 16.3 times. • A 99.3% of mineralization efficiency of PAM solution was achieved. • Biodegradability of PAM solution was raised with BOD₅/COD ratio from 0.05 to 0.41. Polyacrylamide (PAM) is widely used in polymer flooding processes to increase oil recovery while the byproduct of PAM-containing wastewater is a serious environmental issue. In this study, electrochemical oxidation process (EAOP) was applied for treating PAM wastewater using a new type of 3-dimensional ultra-thin SnO₂-Sb electrode. Nano-sized catalysts were evenly dispersed both on the surface and inside of a porous Ti filter forming nano-thickness catalytic layer that enhances the utilization and bonding of catalysts. This porous Ti electrode showed 20% improved OH· production and 16.3 times increased accelerated service life than the planar Ti electrode. Using this electrode to treat 100 mg L⁻¹ PAM, the TOC removal efficiency reached over 99% within 3 h under current density of 20 mA cm⁻². The EAOP could fastly break the long-chain PAM molecules into small molecular intermediates. With the porous electrode treating 5 g L⁻¹ PAM under current density of 30 mA cm⁻², EAOP reduced 94.2% of average molecular weight in 1 h and 92.0% of solution viscosity in 0.5 h. Moreover, the biodegradability of PAM solution was significantly improved as the solution BOD₅/COD ratio raised from 0.05 to 0.41 after 4 h treatment. The degradation pathway of PAM was also investigated.