Abstract: The generation and release of acidic drainage containing high concentrations of dissolved metals from decommissioned mine wastes is an environmental problem of international scale. A potential solution to many acid drainage problem is the installation of permeable reactive walls into aquifers affected by drainage water derived from mine waste materials. A permeable reactive wall installed into an aquifer impacted by low-quality mine drainage waters was installed in August 1995 at the Nickel Rim mine site near Sudbury, Ontario. The reactive mixture, containing organic matter, was designed to promote bacterially mediated sulfate reduction and subsequent metal sulfide precipitation. The reactive wall is installed to an average depth of 12 feet (3.6 m) and is 49 feet (15 m) long perpendicular to ground water flow. The wall thickness (flow path length) is 13 feet (4 m). Initial results, collected nine months after installation, indicate that sulfate reduction and metal sulfide precipitation is occurring. Comparing water entering the wall to treated water existing the wall, sulfate concentrations decrease from 2400 to 4600 mg/L to 200 to 3600 mg/L; Fe concentration decrease from 250 to 1300 mg/L to 1.0 to 40 mg/L, pH increases from 5.8 to 7.0; and alkalinity (as CaCO<inf>3</inf>) increases from 0 to 50 mg/L to 600 to 2000 mg/L. The reactive wall has effectively removed the capacity of the ground water to generate acidity on discharge to the surface. Calculations based on comparison to previously run laboratory column experiments indicate that the reactive wall has potential to remain effective for at least 15 years.

Abstract: The aim of this investigation was to assess the potential of activated sludge for the remediation of sulphur-rich wastewaters. A pilot-scale activated sludge plant was acclimatised to a low load of sulphide and operated as a flow-through unit. Additional sludge samples from different full-scale plants were compared with the acclimatised and unacclimatised sludges using batch absorption tests. The effects of sludge source and acclimatisation on the ability of the sludge to biodegrade high loads of sulphide were evaluated. Acclimatisation to low-sulphide concentrations enabled the sludge to degrade subsequent high loads which were toxic to unacclimatised sludge. Acclimatisation was seen to be an effect of selection pressure on the biomass, suggesting that the treatment capability of activated sludge will develop after acclimation, indicating potential for treatment of acid mine drainage (AMD) by a standard wastewater treatment process. Existing options for biological treatment of AMD are described and the potential of activated sludge treatment for AMD discussed in comparison with existing technologies. (C) 2002 Elsevier Science Ltd.

Abstract: When designing wetland treatment systems for trace metal removal, both aerobic and anaerobic processes can be incorporated into the final design. Aerobic processes such as adsorption and ion exchange can successfully treat neutral drainage in overlandflow systems. Acid drainage can be treated in anaerobic systems as a result of sulfate reduction processes which neutralize pH and precipitate metals.Test work on both aerobic and anaerobic systems has been conducted in Minnesota. For the past three years, overland flow test systems have successfully removed copper, cobalt, nickel and zinc from neutral mine drainage. Nickel, which is the major contaminant, has been reduced around 90 percent from 2 mg/L to 0.2 mg/L. A sulfate reduction system has successfully treated acid mine drainage for two years, increasing pH from 5 to over 7 and reducing concentrations of all metals by over 90 percent.Important factors to consider when designing wetlands to remove trace metals include not only the type of wetlandrequired but also the size of the system and the residence time needed to achieve the water quality standards.