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Barton, C. D., & Karathanasis, A. D. (1997). Aerobic and anaerobic metal attenuation processes in a constructed wetland treating acid mine drainage. In AAPG Eastern Section and the Society for Organic Petrology joint meeting; abstracts (1545). 81: AAPG Bulletin.
Abstract: The use of constructed wetlands for acid mine drainage amelioration has become a popular alternative to conventional treatment methods, however, the metal attenuation processes of these systems are poorly understood. Precipitates from biotic and abiotic zones of a staged constructed wetland treating high metal load (approx. equal to 1000 mg L (super -1) ) and low pH (approx. 3.0) acid mine drainage were characterized by chemical dissolution, x-ray diffraction, thermal analysis and scanning electron microscopy. Characterization of abiotic/aerobic zones within the treatment system suggest the presence of crystalline iron oxides and hydroxides such as hematite, lepidocrocite, goethite, and jarosite. At the air/water interface of initial abiotic treatment zones, SO (sub 4) /Fe ratios were low enough (<2.0) for the formation of jarosite and goethite, but as the ratio increased due to treatment and subsequent reductions in iron concentration, jarosite was transformed to other Fe-oxyhydroxysulfates and goethite formation was inhibited. In addition, elevated pH conditions occurring in the later stages of treatment promoted the formation of amorphous iron oxyhydroxides. Biotic wetland cell substrate characterizations suggest the presence of amorphous iron minerals such as ferrihydrite and Fe(OH) (sub 3) . Apparently, high Fe (super 3+) activity, low Eh and low oxygen diffusion rates in the anaerobic subsurface environment inhibit the kinetics of crystalline iron precipitation. Some goethite, lepidocrocite and hematite, however, were observed near the surface in biotic areas and are most likely attributable to increased oxygen levels from surface aeration and/or oxygen transport by plant roots. Alkalinity generation from limestone dissolution within the substrate and bacterially mediated sulfate reduction also has a significant role on the mineral retention process. The formation of gypsum, rhodochrocite and siderite are by-products of alkalinity generating reactions in this system and may have an impact on S, Mn, and Fe solubility controls. Moreover, the buffering of acidity through excess alkalinity appears to facilitate the precipitation and retention of metals within the system.
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Kepler, D. A., & Mc Cleary, E. C. (1994). Successive Alkalinity-Producing Systems (SAPS) for the Treatment of Acid Mine Drainage. Proceedings, International Land Reclamation and Mine Drainage Conference, 1, 195–204.
Abstract: Constructed wetland treatment system effectiveness has been limited by the alkalinity-producing, or acidity-neutralizing, capabilities of systems. Anoxic limestone drains (ALD's) have allowed for the treatment of approximately 300 mg/L net acidic mine drainage, but current design guidance precludes using successive ALD's to generate alkalinity in excess of 300 mg/L because of concerns with dissolved oxygen. “Compost” wetlands designed to promote bacterially mediated sulfate reduction are suggested as a means of generating alkalinity required in excess of that produced by ALD's. Compost wetlands create two basic needs of sulfate reducing bacteria; anoxic conditions resulting from the inherent oxygen demand of the organic substrate, and quasi-circumneutral pH values resulting from the dissolution of the carbonate fraction of the compost. However, sulfate reduction treatment area needs are generally in excess of area availability and/or cost effectiveness. Second generation alkalinity-producing systems demonstrate that a combination of existing treatment mechanisms has the potential to overcome current design concerns and effectively treat acidic waters ad infinitum. Successive alkalinity-producing systems (SAPS) combine ALD technology with sulfate reduction mechanisms. SAPS promote vertical flow through rich organic wetland substrates into limestone beds beneath the organic compost, discharging the pore waters. SAPS allow for conservative wetland treatment sizing calculations to be made as a rate function based on pH and alkalinity values and associated contaminant loadings. SAPS potentially decrease treatment area requirements and have the further potential to generate alkalinity in excess of acidity regardless od acidity concentrations.
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Dempsey, B. A., & Jeon, B. - H. (2001). Characteristics of sludge produced from passive treatment of mine drainage. Geochem.-Explor. Environ. Anal., 1(1), 89–94.
Abstract: In the 1994 paper by Brown, Skousen & Renton it was argued that settleability and wet-packing density were the most important physical characteristics of sludge from treatment of mine drainage. These characteristics plus zeta-potential, intrinsic viscosity, specific resistance to filtration, and coefficient of compressibility were determined for several sludge samples from passive treatment sites and for several sludge samples that were prepared in the laboratory. Sludge from passive systems had high packing density, low intrinsic viscosity, low specific resistance to filtration and low coefficient of compressibility compared to sludge that was produced after addition of NaOH.
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Demchak, J., Morrow, T., Skousen, J., Donovan, J. J., & Rose, A. W. (2001). Treatment of acid mine drainage by four vertical flow wetlands in Pennsylvania Evolution and remediation of acid-sulfate groundwater systems at reclaimed mine-sites. Geochemistry – Exploration, Environment, Analysis, 1(1), 71–80.
Abstract: Acid mine drainage (AMD) is a serious problem in many watersheds where coal is mined. Passive treatments, such as wetlands and anoxic limestone drains (ALDs), have been developed, but these technologies show varying treatment efficiencies. A new passive treatment technique is a vertical flow wetland or successive alkalinity producing system (SAPS). Four SAPS in Pennsylvania were studied to determine changes in water chemistry from inflow to outflow. The Howe Bridge SAPS removed about 130 mg l (super -1) (40%) of the inflow acidity concentration and about 100 mg l (super -1) (60%) iron (Fe). The Filson 1 SAPS removed 68 mg l (super -1) (26%) acidity, 20 mg l (super -1) (83%) Fe and 6 mg l (super -1) (35%) aluminium (Al). The Sommerville SAPS removed 112 mg l (super -1) (31%) acidity, exported Fe, and removed 13 mg l (super -1) (30%) Al. The McKinley SAPS removed 54 mg l (super -1) (91%) acidity and 5 mg l (super -1) (90%) Fe. Acid removal rates at our four sites were 17 (HB), 52 (Filson1), 18 (Sommerville) and 11 (McKinley) g of acid per m (super 2) of surface wetland area per day (g/m (super 2) d (super -1) ). Calcium (Ca) concentrations in the SAPS effluents were increased between 8 and 57 mg l (super -1) at these sites. Equilibrators, which were inserted into compost layers to evaluate redox conditions at our sites, showed that reducing conditions were generally found at 60 cm compost depths and oxidized conditions were found at 30 cm compost depths. Deeply oxidized zones substantiated observations that channel flow was occurring through some parts of the compost. The Howe Bridge site has not declined in treatment efficiency over a six year treatment life. The SAPS construction costs were equal to about seven years of NaOH chemical treatment costs and 30 years of lime treatment costs. So, if the SAPS treatment longevity is seven years or greater and comparable effluent water quality was achieved, the SAPS construction was cost effective compared to NaOH chemical treatment. Construction recommendations for SAPS include a minimum of 50 cm of compost thickness, periodic replacement or addition of fresh compost material, and increasing the number of drainage pipes underlying the limestone.
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Mustikkamaki, U. - P. (2000). Metallipitoisten vesien biologisesta kasittelysta Outokummun kaivoksilla. Metal content treated with biological methods at the Outokummun operation. Vuoriteollisuus = Bergshanteringen, 58(1), 44–47.
Abstract: Acid mine drainage (AMD) is one of the most serious environmental problems in the metal-mining industry. AMD is formed by the chemical and bacterial oxidation of sulphide minerals, and it is characterized by low pH values and high sulphate and metals content. The most common method to treat AMD is chemical neutralization. The chemical treatment requires high capital and operating costs and its use is problematic at the closed mines sites. Outokumpu has studied and used sulphate reducing bacteria (SRB) as an alternative method for the treatment of AMD. SRB existing in many natural anaerobic aqueous environments can reduce sulphate to sulphide which precipitates metals as extremely insoluble metal sulphides. Full scale experiments were begun in summer 1995 in the Ruostesuo open pit (depth 46 m) by adding liquid manure as a source of bacteria and press-juice as a growth substrate. The average Zn content of the whole column has decreased from 3,5 mg/l to 0,8 mg/l and below 25 m zinc is 0 mg/l. Similar results have been reached with nickel in the Kotalahti old nickel mine, where bacteria were brought in 1996. We have found that the same bacterial mechanism acts in peat-limestone filters, which Outokumpu has built at several mine sites since 1993.
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