Assessment of bimetallic and trimetallic iron-based systems for persulfate activation: Application to sulfamethoxazole degradation

• Sulfamethoxazole is fully degraded in Fe0/PS systems at room temperature.
• PS activation by iron particles minimizes the formation of by-products.
• Plated systems AgFe, CoFe, AgCoFe and CoAgFe maintain PS in solution longer time.
• Bimetallic and trimetallic systems improve the RSE in disturbed systems.
• AOPs based on Fe0 and plated Fe0 PS activation decreased the formation of sludge.

This work investigated the potential of different iron-based systems to activate persulfate (PS) into sulfate radicals (SRs) through catalytic electron transfer. SRs were then used to degrade sulfamethoxazole (SMX) in water. PS activators like Fe2+, Fe0, AgFe and CoFe (bimetallics), AgCoFe and CoAgFe (trimetallics) were tested on SMX solution (39.5 μM) spiked with PS (1.0 mM). Results on SMX degradation showed better kinetics and efficiency in case of non-plated iron particles used compared to bimetallic and trimetallic systems as well as Fe2+ at early stage of the reaction. Direct and sequential addition of Fe2+ resulted in better reaction stoichiometric efficiency (RSE) however did not yield full SMX degradation in contrast to metallic particles. Bimetallic and trimetallic systems showed higher RSE than Fe0 initially due to less PS consumption while maintaining acceptable SMX degradation rate. Smooth corrosion was responsible of progressive release of iron corrosion products for SRs production. However, in case of improved corrosion, generated SRs were quenched by an excess of iron-based activators which negatively affected the RSE. SMX mineralization was greatly improved in oxic solution rather than in anoxic medium. This work demonstrated the potential of iron-based systems to sustain PS longer in oxic solutions without the production of heavy sludge or formation of transformation products that can burden the treatment process.