Anaerobic Bioremediation of Acid Mine Drainage using Emulsified Soybean Oil

Abstract  Batch incubation and flow-through column experiments were conducted to evaluate the use of emulsified soybean oil for in situ treatment of acid mine drainage. Addition of soybean oil, soluble substrates, and a microbial inoculum to the batch incubations resulted in complete depletion of SO₄, 50% reduction in Fe, and an increase in pH to >6. A one time injection of emulsified soybean oil, lactate, yeast extract, and a microbial inoculum stimulated SO₄ and metal ion reduction for ≈300 days in laboratory columns packed with mine tailings receiving influent solutions with a pH≈3 and≈5. In all emulsion treated columns, SO₄ and Fe were reduced, pH increased to >6, and Al, Cu and Zn removal efficiency was 99% or greater. Cu, Fe, Mn and Zn were removed as metal sulfides and/or carbonates with removal efficiency decreasing with increasing metal sulfide solubility. The low pH and high heavy metals concentrations did not significantly inhibit biological activity. However, SO₄ removal with associated precipitation of metal sulfides may have been limited by the short hydraulic retention time (6-7 days) of the columns. There was a significant hydraulic conductivity loss in one of the four treated columns, indicating that hydraulic conductivity loss may be an issue under certain conditions.     

Acid Mine Drainage Flowing from Abandoned Gas Wells

Abstract  In northwestern Pennsylvania (USA), numerous abandoned natural gas wells are producing artesian flows of Fe-contaminated water. The origin of the polluted water has been generally assumed to be brines from the gas-producing sands. We sampled 20 artesian discharges where iron staining was conspicuous. The waters were not brines, but were more characteristic of acid mine drainage (AMD). The dominant cations were Fe, Ca, and Mg, while the dominant anion was sulfate. The study area has a long history of coal mining in the lower Allegheny formation; however, the coal beds are generally at higher elevations than the discharges. We propose that AMD formed in the coal mines is infiltrating into lower aquifers, moving outside the lateral limits of mining, and using abandoned gas wells as conduits to the surface. While flowing through the underlying sandstones, the AMD chemistry is modified by contact with siderite, the dominant carbonate mineral in this stratigraphy. This would suggest that current remediation strategies that emphasize plugging the pollution-producing gas wells may be ill-advised because the source of the polluted water is more shallow than currently assumed.     

A Bench-scale Assessment of a Combined Passive System to Reduce Concentrations of Metals and Sulphate in Acid Mine Drainage

Abstract  Passive treatment of acid mine drainage (AMD) requires a combined strategy to minimize the effect of climatic variability on the treatment performance of the system. A vertical-flow combined passive treatment system was developed and evaluated in a bench-scale laboratory test for a 290-day period. The combined system consisted of four components with specific treatment functions: an oxidation/precipitation basin for excess iron removal; a peat biofilter for heavy metal sorption and the establishment of anoxic conditions; a bioreactor for alkalinity generation and sulphate reduction; and an anoxic limestone drain for alkalinity addition. The benchscale system was dosed with moderate strength synthetic AMD at a surface loading of 95 L/m²/d, and operated under continuous flow conditions. Removal efficiencies were 99.7%, 99.9%, 99.9%, 98.6%, 98.2%, and 99.9% for Fe, Al, Zn, Mn, Ni, and Cu, respectively, while Cd remained more mobile with a removal efficiency of 66.5%. Sulphate concentrations were reduced from 3030 mg/L to 814.9 mg/L and the acidic drainage was neutralized to an effluent pH of 7.2 and an alkalinity of 1353.6 mg/L (as CaCO₃).     

Performance of a Natural Wetland Treating Acid Mine Drainage in Arid Conditions

Abstract  A wetland naturally formed in the discharge from a copper mine tailing impoundment in Rajasthan, India. The wetland is abundantly vegetated. This study investigated changes that occurred in the seepage as it travelled 180 and 380 m (P₁ and P₂) through the wetland. The pH increased from 6.17 to 7.10 at P₁ and 7.34 at P₂ in the pre-monsoon season, 6.53 to 7.36 at P₁ and 7.77 at P₂ in the post-monsoon season, and from 6.20 to 6.63 at P₁ and 6.89 at P₂ in the winter. Contaminant removal at P₂ ranged from 40 to 95%.     

Performance of Three Aquatic Plant Species in Bench-scale Acid Mine Drainage Wetland Test Cells

Abstract  We investigated pollutant removal from acid mine drainage (AMD) by three different aquatic plant species (Typha angustifolia, Desmostachya bipinnata, and Sacharum bengalense) in bench-scale wetland test cells of 1 m³. AMD was generated in the laboratory using chalcopyrite, galena, and sphalerite ore. A substrate containing 75% soil, 20% powdered goat manure, and 5% wood shavings was used in each cell. The performance of the system was evaluated for different water column heights (100, 150, and 200 mm) and for different retention periods (24, 48, 72, 96, and 168 hrs). The performance of the plant species was different for the various metals of AMD; therefore, multi-species plantings should be considered in constructed wetlands.     

Injection of Fluidized Bed Combustion Ash into Mine Workings for Treatment of Acid Mine Drainage

Abstract  A demonstration project was conducted to investigate treating acid mine water by alkaline injection technology (AIT). A total of 379 t of alkaline coal combustion byproduct was injected into in an eastern Oklahoma drift coal mine. AIT increased the pH and alkalinity, and reduced acidity and metal loading. Although large improvements in water quality were only observed for 15 months before the effluent water chemistry appeared to approach pre-injection conditions, a review of the data four years after injection identified statistically significant changes in the mine discharge compared to pre-injection conditions. Decreases in acidity (23%), iron (18%), and aluminum (47%) were observed, while an increase in pH (0.35 units) was noted. Presumably, the mine environment reached quasi-equilibrium with the alkalinity introduced to the system.     

Treatment of Mine Water by a Microbial Mat: Bench-scale Experiments

Abstract.   We investigated the treatment of acid mine drainage (AMD) by a blue-green algae-microbial consortium and substrate (containing powdered goat manure, wood chips, and soil) in 1 m³ bench scale biological treatment test cells. The microbial mat resulted from the interaction of bacteria and filamentous blue-green algae (predominantly Oscillatoria spp). The experiments were carried out for different water column heights, and were evaluated for 24, 48, 72, 96, and 168 hours of retention. Within 24 hours of retention, the pH increased from 2.93 to 6.78 as net alkalinity went from -125 mg/L to 197 mg/L as CaCO₃. Turbidity decreased by 33–54%, sulphate decreased by 23–29%, and hardness decreased by 19 to 26%. We also observed that: 95% of the Fe, 79–97% of the Cu, 84–86% of the Zn, 88% of the Pb, 59–83% of the Co, 22–62% of the Ni, and 28–45% of the Mn were removed. A blue-green algae/microbial mat consortium may be a cost–effective treatment technique for removing metals from AMD.     

Waste from Biodiesel Manufacturing as an Inexpensive Carbon Source for Bioreactors Treating Acid Mine Drainage

Abstract.  Alcohol-fed, semi-passive bioreactors have been used to support the growth of sulfate-reducing bacteria (SRB) for treatment of acid drainage from mine sites. An alcohol source not previously examined for use in these reactors is the glycerol-methanol waste remaining after the production of biodiesel fuel. In the laboratory, rock-filled columns were used to investigate biodiesel waste (BDW) as a carbon source for SRB. Columns were provided with water containing 900 mg/L sulfate, and fed reagent-grade glycerol or BDW in sufficient quantity to reduce 50% of the sulfate. Addition of 246 mg/L of reagent-grade glycerol resulted in 50% sulfate reduction and production of up to 59 mg/L of soluble sulfide, while the equivalent of 246 mg/L of glycerol provided as BDW resulted in 55% sulfate reduction and the production of up to 92 mg/L of soluble sulfide. During the initial stages of acclimation, propionic, acetic, formic, and lactic acids were observed. Acid concentrations were reduced over time in the effluent, and organic carbon in the BDW was nearly completely converted to carbon dioxide.     

The Use of Measured and Calculated Acidity Values to Improve the Quality of Mine Drainage Datasets

Abstract:  The net acidity of a water sample can be measured directly by titration with a standardized base solution or calculated from the measured concentrations of the acidic and basic components. For coal mine drainage, the acidic components are primarily accounted for by free protons and dissolved Fe²⁺, Fe³⁺, Al³⁺, and Mn²⁺. The base component is primarily accounted for by bicarbonate. A standard way to calculate the acidity for coal mine drainage is: Acid^calc = 50*(2*Fe²⁺/56 + 3*Fe³⁺/56 + 3*Al/27 + 2*Mn/55 + 1000*10^-pH)—alkalinity, where acidity and alkalinity are measured as mg/L CaCO₃ and the metals are mg/L. Because such methods of estimating acidity are derived by independent laboratory procedures, their comparison can provide a valuable QA/QC for AMD datasets. The relationship between measured and calculated acidities was evaluated for 14 datasets of samples collected from mine drainage discharges, polluted receiving streams, or passive treatment systems, containing a total of 1,484 sample analyses. The datasets were variable in nature, ranging from watersheds where most of the discharges contained alkalinity to ones where all of the discharges were acidic. Good relationships were found to exist between measured and calculated acidities. The average acidity measurement was 239 mg/L CaCO₃ and the average acidity calculation was 226 mg/L CaCO₃. Linear regressions were calculated for individual datasets and for the entire dataset. The linear regression for the entire dataset was: Acid^calc = 0.98 * Acid^meas – 8, r² = 0.98. The good correlation between calculated and measured acidity is the basis for an easy and inexpensive QA/QC for AMD data. Substantial variation between measured and calculated acidities can be used to infer sampling or analytical problems.     

Improving the Accuracy of Geochemical Rock Modelling for Acid Rock Drainage Prevention in Coal Mine

Abstract.   The results of static tests are used to geochemically model the distribution of potentially acid and non-acid forming materials and plan mining excavation and overburden dumping to prevent or minimize the generation of acid rock drainage (ARD). The accuracy of the model depends very much on the amount and validity of the available pre-mine data and how the data is interpreted in both lateral and vertical directions. This results of such modelling was compared with subsequent overburden information provided by analysis of blast hole drill cuttings. We found that the model overestimated the amount of potentially acid forming material, but that it was still useful in ARD prevention.     

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Youghiogheny River Basin,Pennsylvania, USA

Abstract.  Nighttime high-resolution airborne thermal infrared imagery (TIR) data were collected in the predawn hours during Feb 5-8 and March 11-12, 1999, from a helicopter platform for 72.4 km of the Youghiogheny River, from Connellsville to McKeesport, in southwestern Pennsylvania. The TIR data were used to identify sources of mine drainage from abandoned mines that discharge directly into the Youghiogheny River. Image-processing and geographic information systems (GIS) techniques were used to identify 70 sites within the study area as possible mine drainage sources. The combination of GIS datasets and the airborne TIR data provided a fast and accurate method to target the possible sources. After field reconnaissance, it was determined that 24 of the 70 sites were mine drainage. This paper summarizes: the procedures used to process the TIR data and extract potential mine-drainage sites; methods used for verification of the TIR data; a discussion of factors affecting the TIR data; and a brief summary of water quality.     

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Kettle Creek and Cooks Run Basins,Pennsylvania, USA

Abstract.  High-resolution airborne thermal infrared (TIR) imagery data were collected over 90.6 km² (35 mi²) of remote and rugged terrain in the Kettle Creek and Cooks Run Basins, tributaries of the West Branch of the Susquehanna River in north-central Pennsylvania. The purpose of this investigation was to evaluate the effectiveness of TIR for identifying sources of acid mine drainage (AMD) associated with abandoned coal mines. Coal mining from the late 1800s resulted in many AMD sources from abandoned mines in the area. However, very little detailed mine information was available, particularly on the source locations of AMD sites. Potential AMD sources were extracted from airborne TIR data employing custom image processing algorithms and GIS data analysis. Based on field reconnaissance of 103 TIR anomalies, 53 sites (51%) were classified as AMD. The AMD sources had low pH (<4) and elevated concentrations of iron and aluminum. Of the 53 sites, approximately 26 sites could be correlated with sites previously documented as AMD. The other 27 mine discharges identified in the TIR data were previously undocumented. This paper presents a summary of the procedures used to process the TIR data and extract potential mine drainage sites, methods used for field reconnaissance and verification of TIR data, and a brief summary of water-quality data.     

Neutralizing Coal Mine Effluent with Limestone to Decrease Metals and Sulphate Concentrations

Abstract.   This paper describes pilot scale tests of a novel process for the neutralisation of acidic mine water. Leachate from a waste coal dump was neutralised with limestone, and iron, aluminium, and sulphate were removed. Specific aspects studied were: the process configuration; the rates of iron oxidation, limestone neutralisation, and gypsum crystallisation; the chemical composition of the effluents before and after treatment; the efficiency of limestone utilisation; and the sludge solids content. The acidity was decreased from 12,000 to 300 mg/L (as CaCO₃), sulphate from 15,000 to 2,600 mg/L, iron from 5,000 to 10 mg/L, aluminium from 100 to 5 mg/L, while the pH increased from 2.2 to 7.0. Reaction times of 2.0 and 4.5 h were required under continuous and batch operations respectively for the removal of 4 g/L Fe (II). The iron oxidation rate was found to be a function of the Fe (II), hydroxide, oxygen, and suspended solids (SS) concentrations. The optimum SS concentration for iron oxidation in a fluidised-bed reactor was 190 g/L. Up-flow velocity had no influence on the rate of iron oxidation in the range 5 to 45 m/h. Sludge with a high solids content of 55% (m/v) was produced. This is high compared to the typical 20% achieved with the high density sludge process using lime. It was determined that neutralisation costs could be reduced significantly with an integrated iron oxidation and limestone neutralisation process because limestone is less expensive than lime, and a high-solids-content sludge is produced. Full scale implementation followed this study.     

Long-term Performance of Passive Acid Mine Drainage Treatment Systems

Abstract.   State and federal reclamation programs, mining operators, and citizen-based watershed organizations have constructed hundreds of passive systems in the eastern U. S. over the past 20 years to provide reliable, low cost, low maintenance mine water treatment in remote locations. While performance has been reported for individual systems, there has not been a comprehensive evaluation of the performance of each treatment type for a wide variety of conditions. We evaluated 83 systems; five types in eight states. Each system was monitored for influent and effluent flow, ph, net acidity, and metal concentrations. Performance was normalized among types by calclating acid loading reductions and removals, and by converting construction cost, projected service life, and metric tonnes of acid load treated into cost per tonne of acid treated. Of the 83 systems, 82 reduced acid load. Average acid load reductions were 9.9 t/yr for open limestone channels (OLC), 10.1 t/yr for vertical flow wetland (VFW), 11.9 t/yr for anaerobic wetlands (AnW), 16.6 t/yr for limestone leach beds (LSB), and 22.2 t/yr for anoxic limestone drains (ALD). Average costs for acid removal varied from $83/t/yr for ALDs to $527 for AnWs. Average acid removals were 25 g/m²/day for AnWs, 62 g/m²/day for VFWs, 22 g/day/t for OLCs, 28 g/day/t for LSBs, and 56 g/day/t for ALDs. It appears that the majority of passive systems are effective but there was wide variation within each system type, so improved reliability and efficiency are needed. This report is an initial step in determining passive treatment system performance; additional work is needed to refine system designs and monitoring.     

Limestone Drain Design Parameters for Acid Rock Drainage Mitigation

Abstract.  Limestone drains are an integral component of some of the most efficacious passive systems for the treatment of acid rock drainage (ARD). A critical design parameter for a limestone drain is the mass of limestone that will be required for effective treatment. This in turn depends on the flow rate, limestone dissolution rate, and associated hydraulic detention time necessary to achieve a certain effluent alkalinity for a given design life. Rates of alkalinity generation and limestone dissolution, and the quality of the limestone in terms of weight fraction of CaCO₃ and percentage CaCO₃ available must be known to determine the required mass of limestone. These parameters were experimentally determined for a natural and synthetic suite of ARD waters. The experimental results show that the empirical change in the alkalinity over time cannot simply be modeled as a first-order process. During the initial stage, the concentration increase is extremely fast, giving a linear and steep rise in the alkalinity. Alkalinity concentrations peaked at elapsed times of 90 to 180 minutes and then declined to a nearly constant value. The decline in alkalinity corresponds with a decline in concentrations of dissolved iron and aluminum, implying that the consumption of alkalinity by the hydrolysis of these metals is faster than the rate of alkalinity production by the dissolution of limestone, so that the reaction appears zero order in the early stage and pseudo-first order later. Because the changes in concentration were complex, considerable uncertainty exists in the rate constants for estimating alkalinity concentration. This causes problems in design equations based solely on a limestone dissolution rate that is estimated from alkalinity generation rates. A more applicable design procedure, combining the kinetics of alkalinity production and consumption with the hydraulics and chemical equilibrium of the system, is illustrated. Research was conducted while the first and third authors were with Ecology and Environment, Inc, Dallas, TX, USA;     

Resistivity Level Runs to Detect Water-filled Mine Voids between Drill Holes

Abstract.  Resistivity level runs are collected by lowering a current source down one well and measuring the resulting voltage at the same depth in another well. Mine voids between the wells that contain acid water appear as conductive anomalies on the resulting apparent resistivity profiles. Resistivity level runs can be collected rapidly and without lowering expensive equipment down holes of unknown stability. The data can be interpreted on-site, and are relatively insensitive to positioning errors. The method is well suited to sites where several drill holes have failed to intersect a known mine void. We demonstrated the feasibility of resistivity level run profiling at an abandoned mine complex in central Pennsylvania, where resistivity level runs were successfully used to locate haulage ways containing mine water.     

The Potential Importance of Mine Sites for Biodiversity

Abstract  Abandoned mine sites are typically viewed as environmental problems due to their negative impacts on local ecosystems. This paper presents an alternative viewpoint providing evidence of the potential importance of mine sites for supporting rare and threatened species from many of the major taxonomic orders. The potential importance of these species in remediation of polluted environments is also highlighted.     

Microbial Alkalinity Production to Prevent Reacidification of Neutralized Mining Lakes

Abstract.  Microbial alkalinity production was evaluated as a method to prevent reacidification of neutralized mining lakes by acidic ground and seepage water. We used 60 L mesocosms to represent the sediment and water column of a shallow acidic mine lake. To enhance alkalinity production, acidic and neutralized lake waters were treated with either phosphorus (controlled eutrophication) or organic matter (controlled saprobization). Controlled eutrophication could not produce enough autochthonous biomass as substrate for microbial alkalinity production to change the acidity of the water. Chemical pre-neutralization of the acidic water caused the inorganic carbon concentration to increase, but at the same time, hindered algae growth by reducing the availability of phosphate by sorption to the freshly precipitated iron hydroxide. This effect was so strong that even high phosphorus additions could not increase the algae biomass production. In contrast to controlled eutrophication, controlled saprobization produced significant alkalinity. Despite inhibition of the most important alkalinity producing process, namely microbial sulfate reduction, by low pH values, the microbial alkalinity production rate was not affected by pre-neutralization of the water column. Other alkalinity producing processes raised the pH in the reactive zone until sulfate reduction was no longer inhibited.     

Studies on Microbial Heavy Metal Retention from Uranium Mine Drainage Water with Special Emphasis on Rare Earth Elements

Abstract.  Microbial heavy metal retention was studied using seepage water sampled from a former uranium mining site in Eastern Thuringia, Germany. The seepage water has a low pH and contains high concentrations of metals, including uranium, rare earth elements (REE), and other heavy metals. Microbial influence on sorption and/or active uptake of heavy metals was studied using REE patterns. Incubation of seepage water with the bacterium Escherichia coli caused sorption of heavy metals to biomass. Incubation with the fungus Schizophyllum commune, however, had a much more pronounced effect, including significant fractionation of REE, pointing to the possibility of a specific active uptake mechanism. Extraction factors and fractionation coefficients are given to show the capacity of the presented bioextraction for future applications.     

Pollution of Water and Stream Sediments Associated with the Vale De Abrutiga Uranium Mine,Central Portugal

Abstract.   The Vale de Abrutiga uranium deposit, located in Central Portugal near the Aguieira dam reservoir, was surface mined. Low-grade ore and waste rock were deposited on permeable ground, close to the mine, and were not revegetated. A lake has formed in the open pit. Surface waters draining the mine site are acidic, have high conductivity, and high concentrations of U, SO42-, Zn, Fe, Mn, Ra, Cu, Th, and Pb. The groundwater and the water from the reservoir cannot be used for human consumption or irrigation. The sampled waters show higher contaminant concentrations in winter than in summer. Stream sediments have high geoaccumulation indices for U, Fe, Ag, Zn, Cr, Co, and Pb. In general, sediments bordering the dam reservoir have higher metal contents in winter than in summer.