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

Pre-magnetized Fe 0 /persulfate (pre-Fe 0 /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-Fe 0 and 1 mM PS. The increase of PS concentration and pre-Fe 0 dosage was conducive to the degradation. The coexistence of Cl − , NO 3 − and SO 4 2− accelerated the removal, however the presence of HCO 3 − 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., SO 4 − , OH, O 2 − ), which could be continuously formed via the Fe 2+ /Fe 3+ cycle in solution and on pre-Fe 0 surface. In pre-Fe 0 /PS system, SO 4 − in solution, surface-bound SO 4 − , OH, OH in solution, O 2 − 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-Fe 0 /PS and Fe 0 /PS pretreatments both reduced the generation of C-DBPs except for chloral hydrate, while increased the formation of N-DBPs except for trichloroacetamide.