Degradation of sulfadimethoxine by permanganate in aquatic environment: Influence factors, intermediate products and theoretical study

The excess sulfadimethoxine (SDM) in the environment could lead to antibiotic resistance by microorganisms and may do harm to many aquatic organisms. In this work, the removal of SDM by potassium permanganate (KMnO4) was comprehensively studied. The influence of various factors, including the pH, oxidant doses, and temperature, on SDM removal were investigated. The optimal reaction conditions were determined to be pH 5.0, T = 25 degrees C and [KMnO4](0) = 200 mu mol L-1. Anions (Cl-, SO42 -, HCO32-, and NO3-) and cations (K+, Ca2+, Mg2+, and NH4+) had no significant influence on the removal of SDM. However, H2PO4- improved the efficiency of SDM removal by KMnO4. Humic acid (0-10 mg L-1) promoted the removal of SDM, which was attributed to the generation of in situ MnO2. Meanwhile, the degradation of SDM in various water matrices was studied, and the removal order was ultrapure water > Jiuxiang river water approximate to synthetic water > secondary clarifier effluent. According to ten intermediate products identified and a frontier electron densities (FED) calculation, several pathways were proposed that involve the oxidation of amidogen, the cleavage of C-S and S-N bonds, and an oligomerization reaction. The predicted toxicity assessment indicated that most of the degradation products were not harmful to aquatic organisms except SDM dimers (connection by -HN=NH-), suggesting that byproducts, such as dimers, formed during the oxidation of SDM and other sulfonamides should be taken into consideration. In sum, KMnO4 has the potential to remove SDM from the aquatic environment. (C) 2019 Elsevier B.V. All rights reserved.