This study aimed to investigate the effects of
nitrate on the ultraviolet (UV) treatment of simulated washing wastes containing Trion X-100 (TX-100)
surfactant and
4,4'-dibromodiphenyl ether (BDE-15)
pollutant. The presence of
nitrate accelerated the photodegradation of BDE-15 and
TX-100, because they reacted with
reactive oxygen species (ROS) produced from conversion between
nitrate and
nitrite. Due to
nitrite having a stronger radical quenching property than
nitrate,
nitrite hindered
TX-100 decay while the photodegradation rate of BDE-15 was similar to that in the presence of
nitrate. This indicated that
nitrate/
nitrite affected BDE-15 photodegradation by
photosensitization and
TX-100 loss by ROS attack. An increased
TX-100 concentration increased the loss of total inorganic
nitrogen possibly owing to an increase in organic
nitrogen formation through
TX-100 nitration reactions. At pH < 7 HOONO rapidly isomerized to NO3-, and at pH = 7-9 it homolyzed to ONOO-, which increased
OH production to decay the BDE-15 and
TX-100 and also increased NO2- formation. BDE-15 mainly underwent debromination, and some rearrangement, ring formation, nitration and hydroxylation products were detected, indicating that the produced
OH and NO2 attacked the BDE-15 and products. Furthermore, broken-chain, carboxylation, hydroxylation and nitro products were detected by Liquid chromatography high resolution mass spectrometry (LC-HRMS). Escherichia coli was used to assess the toxicity of washing waste containing
nitrate: the presence of
nitrate will increase the wastes' toxicity during UV treatment. Therefore, the presence of
nitrate is deleterious to the UV treatment of washing wastes, and it is important to remove
nitrates and
nitrites from washing waste before UV irradiation.