Evaluating Substrates in the Biological Treatment of Acid Mine Drainage

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Abstract
Acid mine drainage (AMD) contains high concentrations of sulphates and metals at low pH. Biological treatment of AMD via the sulphate reduction pathway seems promising. To make this treatment method economical, the availability of a suitable low cost organic substrate in the vicinity of the mine site is essential. The objectives of this study were: (1) to try and predict the degradability of three organic materials using the Forage Fibre Analysis (FFA) technique, BOD/COD ratio, protein and carbohydrate contents and C/N ratio, and (2) to evaluate the suitability of these organic materials to provide substrate for the sulphate reducing bacteria (SRB) in the anaerobic treatment of AMD. All four tests indicated that activated sludge would be the most suitable material. However, the results of the tests for predicting the biodegradability of the other two materials, were inconsistent. The FFA method and the BOD/COD ratio indicated rabbit pellets as the second most suitable material followed by digested sludge. But, the protein and carbohydrate contents and the C/N ratio pointed to digested sludge as the second most suitable material followed by rabbit pellets. None of the four tests alone was found to be sufficient to predict the biodegradability of organic materials. To assess the degradability of the three materials a series of anaerobic reactors was operated at room temperature with the different organic materials spiked with potassium sulphate. For comparison, ethanol, a readily degradable substrate, was included in the anaerobic assessment process. Of the three organic materials examined, activated sludge was found to be the most suitable material to provide substrate for SRB followed by rabbit pellets and digested sludge. The disparity in predicted and actual assessment results is discussed.

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