Strong enhancement of trichloroethylene degradation in ferrous ion activated persulfate system by promoting ferric and ferrous ion cycles with hydroxylamine

The persulfate (PS) activated by ferrous ion (Fe(II)) system could generate reactive oxygen species capable of degrading refractory organic contaminants trichloroethylene (TCE). Nevertheless, the slow conversion from ferric ion (Fe(III)) back to Fe(II) limits its widespread practical application. Therefore, different reducing agents, i.e., hydroxylamine (HA), sodium thiosulfate, ascorbic acid, sodium ascorbate and sodium sulfite, were added into PS/HA system for accelerating the Fe(II) regeneration, and HA was most efficient in TCE degradation. The effects of HA, Fe(II) and PS concentrations were also evaluated in PS/Fe(II)/HA system. The results indicated that a proper HA and Fe(II) concentrations were needed in practical application, too low or too high dosages were adverse to TCE degradation. Moreover, TCE degradation was increased with the increasing of PS dosage over the tested range. The radical scavenging tests confirmed that the primary reactive oxygen species were sulfate radicals (SO4−), hydroxyl radicals (OH) and superoxide radical (O2−) in PS/Fe(II)/HA process. Both inorganic anions (Cl−, HCO3−, SO42−, NO3− ions) and natural organic matter had inhibitory effects on TCE removal, and the suppressive effects of inorganic anions can be ranked in an ascending order of NO3− < SO42− < Cl− < HCO3− in PS/Fe(II)/HA system.