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Review of Passive Systems for Acid Mine Drainage Treatment

A passive acid mine drainage treatment pond.

When appropriately designed and maintained, passive systems can provide long-term, efficient and effective treatment for many acid mine drainage sources. Passive AMD treatment relies on natural processes to neutralize acidity and to oxidize or reduce and precipitate metal contaminants. Passive treatment is most suitable for small to moderate AMD discharges of appropriate chemistry, but periodic inspection and maintenance, plus eventual renovation, are generally required. 

Passive treatment technologies can be separated into biological and geochemical types. Biological passive treatment technologies generally rely on bacterial activity and may use organic matter to stimulate microbial sulfate reduction and adsorb contaminants. Constructed wetlands, vertical flow wetlands and bioreactors are all examples of biological passive treatment technologies. Geochemical systems place alkalinity-generating materials, such as limestone, in contact with AMD (direct treatment) or with fresh water upgradient of the AMD. 

Most passive treatment systems employ multiple methods, often in series, to promote acid neutralization and oxidation and precipitation of the resulting metal flocs. Before selecting an appropriate treatment technology, the AMD conditions and chemistry must be characterized. Flow, acidity and alkalinity, metal and dissolved oxygen concentrations are critical parameters. This paper reviews the current state of passive system technology development, provides results for various system types, and provides guidance for sizing and effective operation.

Read the full article at SpringerLink