Evaluating substrates in the biological treatment of acid mine drainage

Acid mine drainage (AMD) contains high concentrations of sulphates and meta ls at low pH. biological treatment of AMD via the sulphate reduction pathwa y seems promising. To make this treatment method economical, the availabili ty of a suitable low cost organic substrate in the vicinity of the mine sit e is essential. The objectives of this study were: (1) to try and predict t he degradability of three organic materials using the Forage Fibre Analysis (FFA) technique, BOD/COD ratio, protein and carbohydrate contacts and C/N ratio, and (2) to evaluate the suitability of these organic materials to pr ovide substrate for the sulphate reducing bacteria (SRB) in the anaerobic t reatment of AMD. All four tests indicated that activated sludge would be th e 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 s uitable material followed by digested sludge. But, the protein and carbohyd rate contacts and the C/N ratio pointed to digested sludge as the second mo st suitable material followed by rabbit pellets. None of the four tests alo ne was found to be sufficient to predict the biodegradability of organic ma terials. To assess the degradability of the three materials a series of ana erobic reactors was operated at room temperature with the different organic materials spiked with potassium sulphate. For comparison, ethanol, a readi ly degradable substrate, was included in the anaerobic assessment process. Of the three organic materials examined, activated sludge was found to be t he most suitable material to provide substrate for SRB followed by rabbit p ellets and digested sludge. The disparity in predicted and actual assessmen t results is discussed.