The Study On Adsorption And Coadsorpiton Of Atrazine And Degrading Bacterium Onto Adsorbents

Atrazine was one of most commonly used s-triazine herbicides, which was of strongtoxicity and difficult to be biodegraded. This article mainly studied the adsorption behaviorof atrazine and degrading bacterium onto several common adsorbents—montmorillonite,attapulgite, bamboo-charcoal and charcoal. And the coadsorption of atrazine and thedegrading bacterium onto adsorbents were preliminarily studied. The effects of pH andionic strengths were also investigated. Meanwhile, the Zeta potentials of these adsorbentsand the bacterium were analysed. The results would be helpful to understand theadsorption mechanism of organic pollutions onto adsorbents, and these would provide thetheory for remediation of pesticide pollution in farmland. The results will also providecertain basis for the adsorption mechanism of bacteria on adsorbents. The main contentsand results were as follows:1. The adsorption of atrazine onto montmorillonite, attapulgite, bamboo-charcoaland charcoal were studied using adsorption equilibrium experiments. The results suggestedthat the adsorption of atrazine onto these adsorbents were well fitted by the Freundlichisotherm and adsorption of atrazine onto these adsorbents increased with increasingconcentration. The adsorption capacity of adsorbents for atrazine followed the order:charcoal> bamboo-charcoal> attapulgite> montmorillonite, and bamboo-charcoal andcharcoal had much higher adsorption capacity to atrazine than montmorillonite andattapulgite. The effects of pH and ionic strength were investigated. The results showed thatthe adsorption quantity of atrazine onto adsorbents decreased with increasing pH andincreased with increasing ionic strength of bulk solution.2. The Zeta potentials of the adsorbents after biological conditioning with thedegrading bacterium were analysed. The results showed that when the pH of bulk solutionranging from3to8, the Zeta potentials of montmorillonite, attapulgite, bamboo-charcoaland charcoal suspensions possessed negative values, indicating the pHiep(isoelectric point)of the above adsorbents less than3. Meanwhile, the Zeta potentials became less negativewith decreasing pH and increasing ionic strengths of bulk solution. When ionic strength iscertain, after conditioning with degrading bacterium the changes of the Zeta potentials ofall of adsorbents were not significant with increasing pH. And with increasingconcentration of atrazine, the Zeta potentials of the adsorbents also did not changedobviously. 3. Adsorption kinetics and adsorption isotherms of the degrading bacterium ontoadsorbents were studied, and the effects of pH and ionic strength were investigated. Theexperimental results suggested that with the extension of adsorption time, the adsorptioncapacity of the degrading bacterium increased. When the adsorption time reached30-40min, the adsorption quantity reached maximum, after that, the adsorption quantity did notchange significantly. The adsorption of the degrading bacterium onto these adsorbents waswell fitted by the Langmuir equation and the adsorption capacity onto these adsorbentsincreased with increasing cell concentration. The adsorption capacity of adsorbents for thedegrading bacterium followed the order: charcoal> bamboo-charcoal> montmorillonite>attapulgite. The adsorption capacity increased with decreasing pH and increasing ionicstrength.4. With the changing of pH and ionic strength, the results of Zeta potential values ofthe degrading bacterium showed that the Zeta potential values became more negative withincreasing pH, and its pHiepwas around pH2.7. With increasing ionic strength, the Zetapotentials of the degrading bacterium became less negative, that was to say, the valuesshifted to the positive. But the pHiepwas not changed. Through comparing the Zetapotentials of absorbents, before and after conditioning with the degrading bacterium, thesewere concluded that the Zeta potential values of adsobents became less negative.Electrostatic interactions were existed between adsorbents and the degrading bacterium.5. The coadsorption of atrazine and degrading bacterium onto several adsorbentswere preliminarily investigated. Through the results of residual rate of atrazine and theadsorption amount of the degrading bacterium onto adsorbents, we could find that theeffect of coadsorption was better than the role of the degrading bacterium independently toatrazine.