Anaerobic Bioreactor Technology (ABT) for the Treatment of Acid Mine Drainage (AMD)

Acid mine drainage (AMD) is considered as a widely spread environmental problem that affects several countries involved in mining activities. Because of its high acidity as well as high metal(loid)s content generating environmental and health toxicity, AMD poses a threat to the surrounding ecosystems. Generally, when exposed to air and water, sulfide minerals undergo oxidative dissolution, which results in formation of AMD. Treatment of AMD at source is regarded to be an effective option; however, this might not be possible at all the sites. Technologies for treating AMD can be governed through the application of various physical, chemical, and biological processes to defuse acidity and remove metal(loid)s from the liquid streams. However, the physicochemical techniques are intended to achieve process viability and cost-effective when the treatment stream is of high volume and sulfate rich. In contrast to this, biological processes are economical to run and do not require a high concentrations of sulfate in the targeted stream. The present chapter critically reviews the state-of-the-art on available aerobic and anaerobic bioreactor technologies with an emphasis on anaerobic bioreactors for the treatment of AMD. In the remediation of AMD, the anaerobic process is a type of biological remediation that relies on neutralizing acidity and precipitating the metal contaminants by natural microbial consortia preferably the sulfate-reducing bacteria (SRB). However, as the AMD is associated with low organic matter, a supply of source of an external factor carbon that is required to complete the remediation process. Anaerobic bioreactors, such as membrane bioreactors, continuous stirred tank reactors, bioelectrochemical systems, up-flow sludge blanket reactors, are suitable bioreactor processes for the treatment of AMD wherein the syntrophic activity of both SRBs and other fermentative and few methane forming bacteria takes place. These anaerobic reactors through the application of SRBs are paving its path in the treatment of AMD because of its efficacy and cost-effectiveness. However, adding of external organic substances are required during the treatment of AMD with SRB which could play a pivotal role in determining the cost of the technology. This chapter describes briefly about the aerobic reactors and detailed information on the different types of anaerobic bioreactors available that can be made suitable for AMD treatment. Comparing the passive and active SRB-based alternatives, their substrate choice, and the recent advances in the anaerobic treatment of AMD along with future perspectives as an alternative to conventional techniques are discussed.