Degradation Mechanism Of Trimethoprim By Different Ways Of Activated Sodium Persulfate

Trimethoprim?TMP?,a medical antibacterial drug,was used in large amounts,and was difficult to degrade when it remained in the water.The conventional sewage treatment plant had limited to degrade TMP.TMP maintained a low concentration in the water for a long time.Studies havd shown that TMP in water inhibited the growth of freshwater microalgae,and remained in aquatic organisms,and enriched in body through the food chain,bring health risks to humans.Therefore,it is of great theoretical and practical significance to study the method and mechanism of degradation of TMP.The advanced oxidation technology based on sulfate radicals could effectively treat organic pollutants and had obvious advantages in engineering applications.Sulfate radical?SO₄·^-?had stronger oxidation capacity,longer half-life than hydroxyl radical?·OH?.Transition metal ions could activate persulfate to produce SO₄·^-at room temperature,which is easy to operate,fast to react,and does not consume external energy.Fe²⁺activated PDS system was conducted to study the effect of Fe²⁺,PDS,pH on the degradation of TMP.Then the effects of interfering ions Cl^-,HPO₃^2-,HCO₃^-,NO₂^-,and humic acid on the degradation of TMP were studied.The results showed that TMP had the highest degradation rate at 25°C,pH=3 and Fe²⁺:PDS:TMP=15:200:1.Increasing PDS concentration,the degradation rate of TMP increased first and finally stabilized.Increaseing of PDS/Fe²⁺molar ratio,the degradation rate of TMP increased.The slow reaction phase of TMP met the pseudo first-order reaction kinetics.The low concentration of HPO₃^2-and HCO₃^-in natural water promoted degrading TMP,and the high concentration showed an inhibitory effect.The low concentration of HA produced an inhibitory effect,and the high concentration showed a promoting effect.NO₂^-only produced an inhibitory effect,Cl^-only produced enhancement.TOC experiments showed that the extension of the reaction time could significantly increase the mineralization rate of TMP.Under acidic and neutral conditions,SO₄·^-was the main oxide species of the system,but under basic conditions,·OH played a dominant role on degrading TMP.Citric acids/Fe²⁺/PDS system was conducted to determine determine the optimum conditions at different citric acid?CA?concentration,Fe²⁺concentration,PDS concentration,and pH value.The effects of different organic acids?citric acid,EDTA,oxalic acid,and sodium pyrophosphate?on degrading TMP were compared,and the effect of organic acids on degrading TMP was investigated under different complexing ratios and pH conditions.The results showed that in the citric acid system,increasing the PDS could significantly increase the degradation rate of TMP,and SO₄·^-was the main active species.CA and PDS had a significant impact on degrading of TMP,and pH has a significant impact on degrading of TMP.Five intermediates were identified by employing liquid chromatography-mass spectrometry?LC/MS?techniques,and it was speculated that the degradation pathways of TMP involved hydroxylation,demethylation and cleavage.Under the same conditions,the order of the influence of different organic acids on the degradation rate of TMP is:citric acid>EDTA>sodium pyrophosphate>oxalic acid.In the same complexing system,the influence of different complexing ratios on degrading TMP had a high similarity under different pH conditions.However,the effect of this complexation ratio was different in different complexing agent systems due to the complexing ability of the complexing agent.