Comparison Of Two Fluorescent Tracers’ Degradation And Cytotoxicity In Circulating Cooling Water

At present,the discharge of circulating cooling water in industry lack the restriction of corresponding standards and relevant laws,enterprises would treat it as general industrial sewage.However,some components(bactericides and algicides)and high-salt in circulating cooling water were not very friendly to the biological methods,which made it difficult for traditional wastewater treatment plants to effectively degrade the waste water treatment agents.In this article,advanced oxidation processes(AOPs)based on UV/H2O2 method were adopted to treat two fluorescent tracers HPTS and PTSA in circulating cooling water wastewater as the target pollutants for degradation and effective results were obtained.The degradation kinetics,degradation pathways,degradation efficiency,and cytotoxicity of HPTS and PTSA were investigated.The main research contents were as follows:UV-Vis spectrophotometry was used to measure HPTS and PTSA,and the effectiveness of the method was analyzed.The effect of different initial concentrations of HPTS and PTSA on the degradation of themselves was investigated.The results showed that the degradation efficiency of HPTS and PTSA gradually decreased with the increase of initial concentration under UV irradiation only,and the degradation efficiency of PTSA was much lower than that of HPTS under the same condition,which was caused by the complex interference factors(mass transfer process,intermediate products,etc.)during the photodegradation process and the difference of their electrophilic reaction to hydroxyl radical.The formation rate of hydroxyl radical could increase by adding hydrogen peroxide,when the concentration of hydrogen peroxide was increased to 3 mg/L,the removals of HPTS and PTSA(20 mg/L)were 97.6%and 97.5%under UV irradiation for 1 h,and the degradation data fitted pseudo-first-order kinetics models with kinetics constants of 0.0588 min-1 and 0.0614 min-1 respectively,the effects of interference factors and two tracers themselves on photodegradation process could be ignored.The pH value of circulating cooling water usually fluctuated in the range of 6-9,at same time a large number of inorganic ions existed,so it was necessary to investigate the effect of these factors on the degradation of the two fluorescent tracers.The experimental results showed that:under different pH conditions,chloride ions(250 mg/L)and sulfate ions(250 mg/L)had no significant effect on the degradation,while nitrate ions(20 mg/L)made the degradation rates of HPTS and PTSA gradually decreased with the increase of pH.It was explained that the oxidation process was prolonged due to the intermediate electron transfer reaction.Gaussian software was used to analyze the natural charge distribution of HPTS and PTSA under stable configuration,then surface electrostatic potential of HPTS and PTSA could be obtained by Multiwfn and VMD software.The solutions of HPTS and PTSA before and after reaction were characterized by NMR and HPLC-MS.Through these,the degradation pathways of HPTS and PTSA were speculated as follows:Firstly,hydroxyl radical attacked the carbon atom with higher charge density on pyrene ring to remove the sulfonic group and formed pyrene-phenol.Secondly,pyrene-phenol was further oxidized to pyrene quinone,and then the ring opened and formed the intermediate product 1,4,5,8-naphthalenetracarboxylic acid.Finally,after a series of oxidation,1,4,5,8-naphthalenetracarboxylic acid was generated into small molecules of carbon dioxide and water.The TOC removal and fluorescence removal of HPTS and PTSA were investigated.The results showed that when the initial concentrations of HPTS and PTSA were 20 mg/L under the conditions of 3 mg/L H2O2 concentration and UV irradiation for 1 h,the TOC removals of HPTS and PTSA were 46.07%and 35.45%,respectively,which were much higher than those of traditional biological methods.The fluorescence of the degraded solution disappeared through 3D fluorescence spectra,indicating that the substances with large conjugated structures in the solution had been degraded.The cytotoxicity of HPTS and PTSA at different initial concentrations on mice hepatocytes was compared.The results showed that with the increase of initial concentration,PTSA had no significant cytotoxicity and remained unchanged,while the cytotoxicity of HPTS increased gradually.The reason was that PTSA was stable and not easy to participate in the metabolic process in vivo,while HPTS might be easier to participate in the metabolic process in vivo,and the intermediate products generated had high toxicity.