Research Chair on Abandoned Mine Site Rehabilitation

Sulphate-reducing passive bioreactors have received much attention lately as alternating technologies for acid mine drainage (AMD) treatment. The long-term efficiency is sometimes limited because they rely on the activity of sulphate-reducing bacteria (SRB) which is primarily controlled by the reactive mixture composition. Our review shows that the most important mixture component is the organic carbon source. Several studies conducted to find the best mixture of natural organic substrates for SRB showed that a combination of organic carbon sources is preferable than a unique source. In addition to metal sulphide precipitation, which is the main metal removal mechanism, other mechanisms including adsorption and precipitation of metal carbonates and hydroxides occur in passive bioreactors. The more successful designs allow the flow to be reversed between upward and downward modes. Pilot and field-scale passive bioreactors filled with mixtures of organic and cellulosic wastes were installed in Canada and USA and efficiently removed sulphate and metals for periods up to 5 years. Additional work needs to be done to properly assess the long-term efficiency of reactive mixtures and the metal removal mechanisms. Furthermore, toxicity assessment of treated effluent from on-site passive bioreactors has yet to be performed on a regular basis