The Effects Of Reactive Oxygen Species On Degradation Of Sodium Dodecyl Benzene Sulfonate In Natural Biofilm Systems Under Illumination

Natural water biofilm,as a composite microbial community,will affect the characteristics of surrounding microenvironment,which can change the migration and transformation of organic pollutants in natural water by enrichment,adsorption and transformation.The related studies have shown that active substances such as reactive oxygen species（ROS）produced through photosynthesis of algae can promote the degradation of organic pollutants.There are many kinds of ROS released from alage to natural water,and the effects of ROS on the degradation of organic pollutants are different so that the degradation mechanism isn’t clear.In order to explore the role of ROS produced by natural water biofilm on the degradation of organic pollutants deeply,a simulation experiment system was constructed with sodium dodecyl benzene sulfonate（SDBS）as representative of organic pollutants.The specific ROS were cleared away by the appropriate reactive oxygen scavenger（FRS）to determine theirroles in the SDBS degradation process.Common FRS were for experiments,then the optimum concentration of FRS was determined in H₂O₂ systems,SDBS systems and H2O₂^-SDBS systems.The ROS clearance was calculated with fluorescence intensities of the fluorescence probe of ·O₂^-,·OH,¹O₂ to select the FRS which were fit for experimental systems while the effects of feeding time on activities of FRS were verified.Summing up to above,the service conditions of FRS could be determined.Four representative kinds of ROS,·O₂^-,H₂O₂ ·OH and ¹O₂ were used for experiments.The effect of single ROS on the degradation of SDBS was studied in direct and indirect ways by clear it away orleave it alone in the water-biofilm systems.Other influence factors on the degradation of SDBS were investigated by removing all ROS or oxygen free radicals.In addition,certain two of four kinds of ROS were removed for further studies.The results indicated that the optimum concentrations of each FRS selected for experiments in H₂O₂ systems and SDBS systems were as follows: Vc and thiourea were 0.5 mg/L,CAT and IPA ware 0.7 mg/L,L-GSH,SOD,mannitol,histidine and diphenylamine were 1.0 mg/L.The fluorescence intensities of fluorescent probe indicated that the ROS in water-biofilm systems could be effectively removed.By comparing the clearance rates,SOD,CAT,mannitol and histidine were respectively used as scavengers of ·O₂^-,H₂O₂,·OH and ¹O₂.Experiments in the water-biofilm systems demonstrated that the residence time of FRS in the systems didn’t affect their activities.Changes of SDBS degradation amounts with removing or retaining certain ROS indicate that the four kinds of ROS will participate directly or indirectly in the SDBS degradation process.High concentration and stability of H₂O₂ result in a major role in the degradation process.·OH and ·O₂^-also play a crucial part in SDBS degradation respectively for their high activity and the earliest generated time.The degradation of SDBS by ¹O₂ is relatively weak.In addition to ROS,there are other factors in the water-biofilm systems which promote the degradation of SDBS,such as microbial effects on biofilms.As the conversion relationship among ROS is more complex,The correlation experiments between the two kinds of ROS futher prove that ROS can promote the degradation of SDBS.The degradation of SDBS isn’t caused by a certain single ROS’s effect,but the result of a variety of ROS interactions.ROS can be converted to each other in complicated processes.