L-cysteine boosted Fe(III)-activated peracetic acid system for sulfamethoxazole degradation: Role of L-cysteine and mechanism

•The addition of L-cysteine effectively boosted Fe(III)/PAA system for SMX removal.•The added L-cysteine promoted the redox cycle and the stability of Fe(III)/Fe(II).•FeIVO2+ and HO were primary reactive species responsible for SMX degradation.•SMX was degraded to less toxic small molecules via four degradation pathways.•The satisfactory degradations of SMX were obtained in three real waters.