Mechanisms of metal removal by manures and cellulosic waste in anaerobic passive systems

摘要

In the present paper, the performance of manures and cellulosic waste as substrates for anaerobic passive systems designed to treat acid mine drainage (AMD) is presented. Their performance is based on the activity of sulphate reducing bacteria (SRB). By oxidation of simple organic material, SRB are able to generate hydrogen sulphide and bicarbonate alkalinity, thus producing reducing conditions and circumneutral pH. Under these conditions, precipitation of dissolved metals from acidic mine waters will take place in the form of sulphides, carbonates or hydroxides; in addition, complexation and ion exchange of metals may occur with the organic substrate. In the present paper it was shown that fresh and aged cow manures, individually or in mixture with cellulosic waste, are effective in removing Fe~(2+), Fe~(3+), Zn~(2+) and Mn~(2+) from acidic solutions (pH chemical bounds 2.6). In contrast, pure cellulosic waste substrates were rather inefficient. Speciation analysis of the metals retained in the substrate revealed that iron was bound in stable species, mainly in the oxidisable and reducible fractions. Zine was retained in less stable reducible and carbonate forms. Finally Mn was retained in the least stable exchangeable and carbonate forms.