Treatment of acid mine drainage by sulphate-reducing bacteria using low cost matrices

This paper reports a laboratory-scale investigation concerning the use of sulphate-reducing bacteria (SRB) in a semi-continuous process, where column packed-bed type bioreactors were used for the treatment of acid mine drainage (AMD). The use of different materials as solid matrices was tested and the performance of the bioremediation processes was discussed in terms of sulphate and metals removal and acid neutralization. The behaviour of a reactor filled with acidic soil from a mining area and organic wastes was compared with other three reactors where coarse sand, glass spheres and cereal straw were used as packaging materials. Batch experiments showed the presence and growth of SRB from the acidic soil in different pH conditions and the effect of the absence or presence of several added carbon sources: lactate, ethanol and lactose. The data showed that it is possible to grow SRB using the acidic soil as source of inocula, in the absence and in the presence of the carbon sources tested, since the pH of the media was previously increased to values of 5 or higher. When acidic soil from the mining area and organic wastes were utilised as column matrices, it is possible to remove the metals and to neutralise the acidity of AMD, although an inefficient sulphate removal was observed. When coarse sand or glass spheres were utilised, efficient metals sulphate removal were achieved. However, the incapacity of both systems to generate enough alkalinity does not allow maintaining their good performances in terms of iron removal and sulphate reduction. As a result, the incorporation of materials with neutralizing and buffer capacity to the matrix is recommended. Due to its low density, cereal straw was not suitable to obtain an anaerobic environment inside the column for SRB activity.