Ammonium changes the pathway of tetrabromobisphenol S degradation by sulfate radical oxidation

Sulfate radical (SO 4 •- )-based advanced oxidation processes (SR-AOPs) show great potential in the elimination of organic pollutants in wastewater treatment and groundwater remediation . Tetrabromobisphenol S (TBBPS) as an emerging contaminant can be effectively degraded in SR-AOPs. However, the present study found that SO 4 •- also reacted with ammonium (NH 4 + ), a ubiquitous inorganic nitrogen species in aquatic environments, thus markedly affected the rates and pathways of TBBPS degradation in SR-AOPs. TBBPS underwent β-scission and debromination upon SO 4 •- attack, leading to various transformation products . The released bromide (Br - ) underwent further oxidation by SO 4 •- to form free bromine which reacted with certain TBBPS intermediates, generating disinfection byproducts (DBPs). When NH 4 + was present in such system, the abatement of TBBPS was apparently suppressed. Meanwhile, NH 4 + was oxidized by SO 4 •- to nitrogen dioxide radical (NO 2 • ) which coupled with certain radical intermediates of TBBPS oxidation, yielding nitrophenolic products including 2,6-dibromo-4-nitrophenol (DBNP) and mono-nitro substituted TBBPS. When 10 μM TBBPS was treated by heat activated peroxydisulfate with 1 mM NH 4 + , the molar yield of DBNP reached 22% in 2 h. More importantly, NH 4 + scavenged the in situ formed free bromine to form monobromamine (NH 2 Br), decreasing regulated DBPs formation but leading to highly toxic dibromoacetonitrile (DBAN). This study broadens the understanding of interactions between the transformation of halogens and NH 4 + during SO 4 •- oxidation. It also reveals the potential environmental risks when SR-AOPs are employed for the organohalogen pollutants degradation in realistic environments where NH 4 + is present.