The mining industry is the major producer of acid mine drainage (AMD). The problem of AMD concerns at active and abandoned mine sites. Acid mine drainage needs to be treated since it can contaminate surface water. Constructed wetlands (CW), a passive treatment technology, combines naturally-occurring biogeochemical, geochemical, and physical processes. This technology can be used for the long-term remediation of AMD. The challenge is to overcome some factors, for instance, chemical characteristics of AMD such a high acidity and toxic metals concentrations, to achieve efficient CW systems. Design criteria, conformational arrangements, and careful selection of each component must be considered to achieve the treatment. The main objective of this review is to summarize the current advances, applications, and the prevalent difficulties and opportunities to apply the CW technology for AMD treatment. According to the cited literature, sub-surface CW (SS-CW) systems are suggested for an efficient AMD treatment. The synergistic interactions between CW components determine heavy metal removal from water solution. The microorganism-plant interaction is considered the most important since it implies symbiosis mechanisms for heavy metal removal and tolerance. In addition, formation of litter and biofilm layers contributes to heavy metal removal by adsorption mechanisms. The addition of organic amendments to the substrate material and AMD bacterial consortium inoculation are some of the strategies to improve heavy metal removal. Adequate experimental design from laboratory to full scale systems need to be used to optimize equilibria between CW components selection and construction and operational costs. The principal limitations for CW treating AMD is the toxicity effect that heavy metals produce on CW plants and microorganisms. However, these aspects can be solved partially by choosing carefully constructed wetlands components suitable for the AMD characteristics. From the economic point of view, a variety of factors affects the cost of constructed wetlands, such as: detention time, treatment goals, media type, pretreatment type, number of cells, source, and availability of gravel media, and land requirements, among others.
Development of the data-driven models for accessing the impact of design variables on heavy metal removal in constructed wetlands