| Sodium dodecyl benzene sulfonate (DBS) is widely used in industryand life. DBS discharged into the natural water affects the stability of themicroenvironment and destroys the balance of the water environment,thus causing the pollution. Biofilms, common complex systems in naturalwater, have effect on heavy metals and organic matter in water such asenrichment, adsorption and transformation as There exists relatedresearches about light and diurnal variation effect on the degradation oforganic matter by biofilms, and preliminary researches found that thestrong oxidizing reactive oxygen species (ROS) produced fromphotosynthesis may accelerate the degradation of organic matter.However, it’s not clear about the mechanism of the production of ROSfrom chlorella photosynthesis and the degradation of organic matter inlighting conditions. In this study, we considered from the perspective ofthe iron and manganese as components of biofilms with biofilm/watersystem to simulate the natural water and DBS to simulate organicpollutants, then investigated the influence of different biofilm quantities,different forms and proportion of Fe and Mn on DBS degradation at thepresence of natural biofilms and chlorella biofilms in lighting conditions.On this basis, the Fe and Mn influence mechanism on the degradation ofDBS was analyzed and the role of ROS represented by H2O2in DBSdegradation was inferred. Researches on biofilm degradation effect oforganic matter in lighting conditions would contribute to furtherunderstanding and researching the rule of degradation and transformation of organic matter in natural water and provide references for the removaland purification of organic pollutants in natural water.The results showed that the greater the amount of biofilms was, thegreater the concentration of H2O2and the amount of DBS degradationwere. The degradation of DBS of natural biofilms was greater thanchlorella biofilms for the same quantity of biofilm. pH and DO valueincreased and the change of two parameters indirectly proved that theROS had impacts on the system microenvironment. Chlorella contents ofchlorella biofilms were much greater than the natural biofilms for thesame amount of biofilms; however the degradation of DBS of naturalbiofilms was greater than the chlorella biofilms. It showed that thechemical changes of other substances in the system such as iron oxideand manganese oxide indirectly influenced the types and contents of ROSwith the increment of biofilms, and then affected the biofilm degradationof DBS.Three forms of iron and manganese played a catalytic role ondegradation of DBS and production of H2O2in the natural biofilm systemand chlorella biofilm system, and the degree of influence was ionicstate> complexing state>oxidation state with certain changes on pH andDO. Ionic state of iron and manganese had the most significant impact onnatural biofilms and so as complexing state of iron on chlorella biofilms.Rather, oxidation state of iron and manganese showed no significantinfluences on two kinds of biofilm systems. The degradation and H2O2concentration in chlorella biofilm system were lower than those in naturalbiofilm system. Nevertheless, DBS and H2O2variation in chlorellabiofilm system after adding iron and manganese were greater than those of natural biofilms. The influence degree of three forms of iron andmanganese on degradation of DBS may depend on whether they wereconducive to process of biofilm photosynthesis and whether they wereeffectively metabolic to promote the production of H2O2and the otherROS.Iron expressed a much greater effect on degradation of DBS andproduction of H2O2in biofilm systems than manganese. For all the Fe andMn concentrations, the influences degree to biofilm degradation of DBSand production of H2O2were2:1>1:0>1:2>1:1>0:1>0:0. When the ironand manganese concentration ratio was2:1, both the concentration ofH2O2and DBS degradation in biofilm systems were greater than othersystems. Effects of iron was a predominant factor when iron andmanganese had the same total concentrations for the ratio of1:0,1:1and0:1. The degradation of DBS was the lowest with neither iron normanganese in the biofilm systems. |
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