| Natural biofilms and dissolved organic matter (DOM) coexist in natural watersand both of them influence obviously the fate of trace heavy metals. Few study hasconsidered the effect of coexisting DOM on the adsorption of trace metals ontobiofilms. Therefore, polyacrylic acid (PAA) and ethylenediamine tetraacetic acid(EDTA) were chosen as the model DOM and cadmium (Cd) was chosen as the modelheavy metal in the study. Then we studied the effect of DOM on the adsorption of Cdonto biofilms for better understanding the effect laws, the environmental behavior ofheavy metals and the action of biofilms in the realistic aquatic environment. Resultsare shown below.Higher concentration of DOM usually resulted in more significant decrease inthe adsorption of Cd onto the biofilms. This result could be attributed to that higherconcentration of DOM has the stronger competition with the biofilms for Cd, moresignificant conversion of Cd speciation and more effective dissolution of Mn oxides.This inhibition on the adsorption was more significant in the conditions of higherpH than lower pH. This result could be attributed to that the dissolution of Mn oxideswas more significant and the complex formed by DOM and Cd was adsorbed muchheavily by the biofilms in higher pH conditions.The influence of adsorption sequence on the effect of DOM was insignificant inlower pH range, while the adsorption usually decreased in the order of Cd onlyadsorption> Cd first adsorption> EDTA first adsorption≈simultaneous adsorption inhigher pH range. Besides, contrasted to the PAA with higher molecular weight, thesuppression of EDTA with lower molecular weight on the adsorption was slightlysignificant under the same conditions. The effect of DOM on the Cd adsorption ontothinner biofilms was more significant than that onto thicker biofilms.In general, DOM decreased the adsorption of Cd onto the biofilms and the effect was determined by concentration of DOM, solution pH, adsorption sequence and thequantity of biofilms. |
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