Industrial wastewaters such as mining effluents and landfill leachate may contain
metal ions in higher concentrations than those for which the regulatory standards require a
treatment for their removal/reduction. Chemical precipitation/settling is the most common
method used for removal/reduction of metal ions (e.g. iron, lead, copper, nickel, zinc,
aluminum, manganese, etc.). Separation of metalloids (e.g. arsenic, selenium, molybdenum,
antimony, etc.) can be achieved by co-adsorption onto iron or aluminum. Thiosalts,
incomplete anoxysulphur compounds and cyanide often require the addition of a strong
oxidation reagent. Biological nitrification and denitrification are conventional methods for
removal of ammonia and nitrate. Respectively as industry accepts and often prefers to use
conventional methods as proven and best available technology economically achievable
(BATEA), depending on the site conditions and requirements. Emerging technologies such
as membrane technologies (e.g. nanofiltration, reverse osmosis, etc.) have only been recently
applied to many sites. Innovative approaches, such as snow making, are also used to separate
ammonia and metal ions from wastewaters. Innovations have progressed on developing
either new technologies or new approaches for mode of application of known technologies.
Mode of application could vary from active methods, where pumps and pipes are used and
the process takes place in reactors under controlled conditions, or passive methods, where
the use of pipes and pumps is eliminated or limited. Wetlands (natural or engineered) and
peat filters are often considered as passive methods. Conventional, emerging and innovative
separation technologies and application of passive and active methods as well as capabilities
and limitation of processes are discussed.
Keywords: Heavy metals, Metalloids, Ammonia-nitrate removal, Cyanide
destruction, Thiosalts, Landfill leachate treatment, Mining effluents, Acid mine
drainage, High density sludge process, BATEA, Chemical precipitation, Lime
neutralization, Passive treatment, Biological treatment, Sulphate reducing bacteria,
Wetland, Peat filter, Waste management, Ion exchange, Membrane technologies.
