Mechanisms of metal removal by manures arid cellulosic waste in anaerobic passive Systems

摘要

In the present paper, the performance of manuresand cellulosic waste as substrates for anaerobic passive systemsdesigned to treat acid mine drainage (AMD) is presented. Theirperformance is based on the activity of sulphate reducingbacteria (SRB). By oxidation of simple organic material, SRBare able to generate hydrogen sulphide and bicarbonatealkalinity, thus producing reducing conditions and circumneutralpH. Under these conditions, precipitation of dissolved metalsfrom acidic mine waters will take place in the form of sulphides,carbonates or hydroxides; in addition, complexation and ionexchange of metals may occur with the organic substrate. In thepresent paper it was shown that fresh and aged cow manures,individually or in mixture with cellulosic waste, are effective inremoving Fe~(2+), Fe~(3+), Zn~(2+) and Mn~(2+) from acidicsolutions (pH=2.6). In contrast, pure cellulosic waste substrateswere rather inefficient. Speciation analysis of the metals retainedin the substrate revealed that iron was bound in stable species,mainly in the oxidisable and reducible fractions. Zinc wasretained in less stable reducible and carbonate forms. Finally Mnwas retained in the least stable exchangeable and carbonate forms.