Degradation of p-arsanilic acid by pre-magnetized Fe0/persulfate system: Kinetics, mechanism, degradation pathways and DBPs formation during subsequent chlorination

Pre-magnetized Fe0/persulfate (pre-Fe0/PS) process was innovatively employed for controlling the pollution of p-arsanilic acid (p-ASA). This process showed favorable removal performance, achieving almost complete elimination of 10 mg/L p-ASA within 30 min at the reaction conditions of 0.2 g/L pre-Fe0 and 1 mM PS. The increase of PS concentration and pre-Fe0 dosage was conducive to the degradation. The coexistence of Cl−, NO3− and SO42− accelerated the removal, however the presence of HCO3− and HA presented the opposite trend. The p-ASA degradation decelerated gradually with increasing pH from 5 to 9. Its removal was caused by the attack of reactive oxygen species (i.e., SO4−, OH, O2−), which could be continuously formed via the Fe2+/Fe3+ cycle in solution and on pre-Fe0 surface. In pre-Fe0/PS system, SO4− in solution, surface-bound SO4−, OH, OH in solution, O2− in solution and Fe(IV) contributed to the p-ASA degradation. A plausible transformation route related to the break of C-N and As-C bonds, the substitution of OH group was put forward. More importantly, the released inorganic arsenic during p-ASA decomposition could be effectively controlled through multiple functions including the precipitation, co-precipitation and sorption, which was well confirmed by XPS, FTIR and XRD analysis. Pre-Fe0/PS and Fe0/PS pretreatments both reduced the generation of C-DBPs except for chloral hydrate, while increased the formation of N-DBPs except for trichloroacetamide.