Acid Mine Drainage Treatment Systems Research Articles

Determination and prediction of micro scale rare earth element geochemical associations in mine drainage treatment wastes

Acid mine drainage (AMD) has been proposed as a novel source of rare earth elements (REE), a group of elements that includes critical metals for clean energy and modern technologies. REE are sequestered in the Fe–Al–Mn-rich precipitates produced during the treatment of AMD. These AMD solids are typically managed as waste but could be a REE source. Here, results from AMD solids characterization and geochemical modeling are presented to determine the minerals/solid phases that are enriched in REE and identify the mechanism(s) of REE attenuation.AMD solids collected from limestone-based AMD treatment systems were subjected to sequential extraction and synchrotron microprobe analyses to characterize the binding nature of the REE. The results of these analyses indicated REEs were mainly associated with Al or Mn phases. Only selected REE (Gd, Dy) were associated with Fe phases, which were less abundant than Al and Mn phases in analyzed samples. The sequential extractions demonstrated that acidic and/or reducing extractions effectively mobilize REE from the AMD solids evaluated. The observed element associations in solids are consistent with geochemical model results that indicate dissolved REE can be effectively attenuated by adsorption on freshly precipitated Fe, Al, and Mn oxides/hydroxides. The model, which simulates dissolution of CaCO3 and the precipitation of Fe, Al, and Mn oxides with increased pH, accurately predicts the pH dependent accumulation of dissolved REE with Al, Mn, and Fe oxides/hydroxides in the studied AMD treatment systems.The methods and results presented here can be used to identify conditions favorable for accumulation of REE-enriched AMD solids and possible passive or active treatment(s) to extract REE from AMD. This information can be used to design AMD treatment systems for the recovery of REE and is an opportunity to transform the challenges of addressing polluted mine drainage into an environmental and economic asset.

Sulfur disproportionation realizes an organic-free sulfidogenic process for sustainable treatment of acid mine drainage

Biological sulfidogenic processes (BSPs) have been considered effective biotechnologies for the treatment of organic-deficit acid mine drainage (AMD) and heavy metal recovery. However, high-rate sulfide production relies on the continuous addition of exogenous organic substrates as electron donors to facilitate dissimilatory sulfate reduction, which substantially increases the operational cost and CO2 emission and also limits the wide application of BSPs in AMD treatment. In this study, we proposed a novel chemoautotrophic elemental sulfur disproportionation (SD) process as an alternative to conventional BSPs for treating AMD, in which sulfur-disproportionating bacteria (SDB) disproportionates sulfur to sulfide and sulfate without organic substrate supplementation. During the 393-day lab-scale test, we observed that the sulfur-disproportionating reactor (SDR) achieved a stable high-rate sulfide production, with a maximal rate of 21.10 mg S/L-h at an organic-substrate-free condition. This high rate of sulfide production suggested that the SD process could provide sufficient sulfide to precipitate metal ions from AMD. Thermodynamics analysis and batch tests further revealed that alkalinity rather than sulfate was the critical factor influencing the SD process, suggesting that the abundant sulfate present in AMD would not inhibit the SD process. The critical condition of SD in the SDR was therefore determined. Microbial community analysis showed that Dissulfurimicrobium sp. was the dominant SDB during the long-term operation regardless of dynamic sulfate and/or alkalinity concentrations, which provides evidence that SDB can be employed for sustainable and high-rate sulfide production for engineering purposes. A multi-stage AMD treatment system equipped with a SDR removed over 99% of the influent metals (i.e., Fe, Al, Zn, Cu, Pb) from AMD except for Mn. This study demonstrated that the novel SD process is a green and promising biotechnology for the sustainable treatment of organic-deficient metal-laden wastewater, such as AMD.

Analysis of the development and effects of a combined treatment system for acid mine drainage via bio-oxidation and carbonate rock neutralization

A unique acid mine drainage treatment system for simultaneous biological oxidation and carbonate neutralization was designed for use prior to the carbonate rock neutralization process.

Cost-effective desulfurization of acid mine drainage with food waste as an external carbon source: A pilot-scale and long-term study

Sulfate reduction process can be a promising method for simultaneously removing sulfate , metals and metalloids from acid mine drainage (AMD). However, organic matter in AMD is far from enough for sulfate reduction, and an additional carbon source is required, which increases operation costs for AMD treatment. In this study, a two stage AMD treatment system was established (chemical precipitation - sulfate reduction), and food waste hydrolysate was utilized as a carbon source for AMD treatment. Simultaneous removal of sulfate, organics, metals and metalloids was observed in a pilot-scale (10 m 3 ) upflow anaerobic sludge bed (UASB) for over 400 days. Introducing of food waste hydrolysate (FWHS) was not harmful for sulfate reducers in UASB. Decomposition of refractory organic matter in AMD was enhanced after FWHS addition, which led to decreasing of COD concentration (50%) in effluents of UASB. Ten out of 17 organic matter in effluents was no longer detected after FWHS addition. Metals and metalloids from both AMD and FWHS were efficiently removed during the sulfate reduction process (97.7–100%). Volatile fatty acids (acetic and valeric acids) produced during the food waste hydrolysis could be utilized as carbon source for AMD treatment. Interactions among fermentative microbes , sulfate reducers, denitrifiers and methanogens enhanced carbon, sulfur and nitrogen removal in the UASB. Therefore, a cost-effective method for AMD and food waste cotreatment (3.6 kgSO 4 2− /kgTS food waste) was established in this study by reducing carbon source addition (100%), biomass production (93%), VFA production (54.5%) and sulfide emission (50%), which might be applied for AMD recycling at mining sites. • a two-step fermentation and sulfate reduction coupling process was established. • Food waste was used as carbon and nutrients source for acid mine drainage treatment. • Sulfate, carbon, metals and metalloids were efficiently removed (87.3–100%). • The established technology might be used for acid mine drainage treatment in mines.

Changes in the prokaryotic diversity in response to hydrochemical variations during an acid mine drainage passive treatment

Acid mine drainage (AMD) causes major environmental problems and consequently, several treatments are proposed, favoring the passive systems because of their many advantages. The main goal of these procedures is the neutralization and removal of potentially toxic elements (PTE), yet little is known about the changes in the microbial assemblages in response to the hydrochemical variations during the treatments. Therefore, the main objective of this research was to determine the changes in the diversity and structure of the prokaryotic assemblages in a hybrid abiotic and biological (wetland) passive treatment system. The 16S rRNA gene survey showed that the AMD coming from the mine (pH 2.6) was mainly composed of acidophilic genera such as Acidithiobacillus, Leptospirillum, Ferritrophicum, and Cuniculiplasma (up to 76 % relative abundance). In the abiotic treatment, Acidiphilium was dominant in the sections with limestone filters (pH 2.2–4.8), followed by Limnobacter in the subsequent dolomite/limestone and phosphoric rock filters (pH 5.2–5.8). In these abiotic passive treatment sections, the microbial assemblage showed a limited diversity and richness. However, when the treated AMD reached the two final wetlands (pH ~6.8), the microbial diversity and richness increased, suggesting that further bioattenuation mechanisms might be occurring. Limnobacter and Novosphingobium were the main bacterial genera in the water samples of the wetland sections (Arundo donax). These changes in the composition of the microbial assemblages were highly correlated with the pH and Eh values during the treatment (p-value <0.001); however, the concentration of metal(loid)s such as Al, Cd, Fe, Mn, Ni, and Zn were also significantly related (p-value <0.05). In conclusion, the studied passive AMD treatment system enhanced the chemical quality of the treated AMD, showing high removal efficiencies for Al and Fe (> 99 %), and increasing the microbial diversity and richness in the effluent.

Neutralization and uptake of pollutant cations from acid mine drainage (amd) using limestones and zeolites in a pilot-scale passive treatment system

The exploration and beneficiation of mineral coal involve managing acid mine drainage (AMD), the acidic and metallic ion composition of which requires adequate treatment for disposal. In the present work, a passive pilot-scale AMD treatment system was developed using open channels of calcitic (CL-I and CL-II) and dolomitic (DL-I and DL-II) limestone beds and mixtures with natural zeolites (NZ) and functionalized zeolites (FZ). Investigated parameters include pH, electrical conductivity, total acidity, total alkalinity, and concentrations of aluminum, iron and manganese ions. DL-I, CL-II and mixtures of CL-II/NZ and CL-II/FZ increased pH levels from 3.3 to 7.9, 8.2, 7.9 and 7.6, respectively; increased total alkalinity levels from 0 mgCaCO3.L-1 to 20, 107, 42 and 34 mgCaCO3.L-1, respectively; and reduced total acidity levels by 95, 91, 90 and 90%, respectively. All beds promoted the removal of aluminum, iron and manganese ions, but the CL-II/FZ mixture was the most efficient due to both neutralization and a higher uptake of manganese ions (roughly 99%), which are pollutants that are typically difficult to remove. The study results reveal ways to transform passive treatment systems using limestone beds and unconventional materials such as zeolites, combine neutralization and adsorption mechanisms in the same operation, ensure a simple maintenance and operational system and improve the economic and environmental sustainability of related processes.

Performance Evaluation of Fe-Al Bimetallic Particles for the Removal of Potentially Toxic Elements from Combined Acid Mine Drainage-Effluents from Refractory Gold Ore Processing

Acid mine drainage (AMD) is a serious environmental issue associated with mining due to its acidic pH and potentially toxic elements (PTE) content. This study investigated the performance of the Fe-Al bimetallic particles for the treatment of combined AMD-gold processing effluents. Batch experiments were conducted in order to eliminate potentially toxic elements (including Hg, As, Cu, Pb, Ni, Zn, and Mn) from a simulated waste solution at various bimetal dosages (5, 10, and 20 g/L) and time intervals (0 to 90 min). The findings show that metal ions with greater electrode potentials than Fe and Al have higher affinities for electrons released from the bimetal. Therefore, a high removal (&gt;95%) was obtained for Hg, As, Cu, and Pb using 20 g/L bimetal in 90 min. Higher uptakes of Hg, As, Cu, and Pb than Ni, Zn, and Mn also suggest that electrochemical reduction and adsorption by Fe-Al (oxy) hydroxides as the primary and secondary removal mechanisms, respectively. The total Al3+ dissolution in the experiments with a higher bimetal content (10 and 20 g/L) were insignificant, while a high release of Fe ions was recorded for various bimetal dosages. Although the secondary Fe pollution can be considered as a drawback of using the Fe-Al bimetal, this issue can be tackled by a simple neutralization and Fe precipitation process. A rapid increase in the solution pH (initial pH 2 to &gt;5 in 90 min) was also observed, which means that bimetallic particles can act as a neutralizing agent in AMD treatment system and promote the precipitation of the dissolved metals. The presence of chloride ions in the system may cause akaganeite formation, which has shown a high removal capacity for PTE. Moreover, nitrate ions may affect the process by competing for the released electrons from the bimetal owing to their higher electrode potential than the metals. Finally, the Fe-Al bimetallic material showed promising results for AMD remediation by electrochemical reduction of PTE content, as well as acid-neutralization/metal precipitation.

Economic Performance of Active and Passive AMD Treatment Systems Under Uncertainty: Case Studies from the Brunner Coal Measures in New Zealand

Acid mine drainage (AMD) often requires management long after mining operations have ceased. Cost-effective long-term passive treatment systems (PTS) are required for closure of mine sites. However, PTS research seldom defines well-constrained operational and financial parameters to enable confident decision making by mining companies. PTS are generally assumed to be a lower-cost alternative to active systems when used in favorable circumstances, but there is little objective information to define when they are more suitable than active treatment. Instead, general ‘rules-of-thumb’ for flow rates or acid loads are used to determine when PTS are best used. We used well-characterized AMD from multiple historic and active coal mine sites in New Zealand to test these rules-of-thumb from a financial perspective by modelling capital and operational costs over a 100 year timeframe. We present static and uncertainty-based cost assessments of a mussel shell reactor PTS compared to typical active AMD treatment systems at six mine drainage sources from the Brunner Coal Measures. We show that for expected AMD characteristics and duration of treatment, savings on operational costs with PTS can exceed the higher initial capital costs. In addition, the financial advantage of PTS over time may be achieved at flow rates and acidity loads that exceed the industry rules-of-thumb PTS limits. However, in some circumstances, cost projections for high up-front capital costs of purchasing all treatment media for the life span of the PTS is less favorable than discounted treatment media in active treatment systems over time. Understanding financial models of AMD treatment options during mine site design can help reduce the costs of operating and closing mine sites.

Crab shell amendments enhance the abundance and diversity of key microbial groups in sulfate-reducing columns treating acid mine drainage.

Substrate amendments composed of crab shell (CS) waste materials have been shown to significantly improve the longevity and performance of acid mine drainage (AMD) treatment systems containing spent mushroom compost (SMC), yet the development of key microbial populations within these systems has not been investigated. To better understand the effects of CS on microbial dynamics in these systems, clone libraries and real-time quantitative PCR (qPCR) were performed on materials from a laboratory-scale AMD treatment system containing SMC and 0 to 100% CS substrate after receiving a continuous flow of AMD for 148 days (428 pore volumes). The proportion of CS in the substrate positively correlated with the diversity of sulfate-reducing bacteria (SRB) and archaeal clones, but negatively correlated with fungal diversity. CS also impacted microbial community structure, as revealed in Unifrac significance and principal coordinate analysis tests. The column containing 100% CS substrate supported 7 different genera of SRB-the most ever observed in an AMD treatment system. Moreover, the copy numbers of functional genes representing fermenters, sulfate reducers, and chitin degraders increased with increasing proportions of CS. These observations agree well with the chemical performance data, further validating that by supporting more abundant key microbial groups, chitinous substrates may provide benefits for improving both the longevity and performance of AMD treatment systems, and may provide similar benefits for the treatment of other environmental contaminants that are amenable to anaerobic bioremediation.Key points• Crab shell improves the longevity and performance of acid mine drainage treatment.• The diversity of sulfate-reducing bacteria is enhanced with crab shell amendments.• Crab shell supports more abundant key microbial groups than spent mushroom compost.

Removal of heavy metals using a novel sulfidogenic AMD treatment system with sulfur reduction: Configuration, performance, critical parameters and economic analysis

A novel sulfidogenic acid mine drainage (AMD) treatment system with a sulfur reduction process was developed. During the 220-d operation, >99.9% of 380-mg/L ferric, 150-mg/L aluminum, 110-mg/L zinc, 20-mg/L copper and 2.5-mg/L lead ions, and 42.6–44.4% of 100-mg/L manganese ions in the synthetic AMD were step-by-step removed in the developed system with three pre-posed metal precipitators and a sulfur reduction reactor. Among them, zinc, copper and lead ions were removed by the biogenic hydrogen sulfide that produced through elemental sulfur reduction; while ferric, aluminum and manganese ions were removed by the alkali precipitation. Compared with the reported sulfate reduction reactors, the sulfur reduction reactor significantly reduced the chemical cost by 25.6–78.9% for sulfide production, and maintained a high sulfide production rate (1.12 g S2-/L-d). The pH level in the sulfidogenic reactor driven by sulfur-reducing bacteria posed a significant effect on the sulfide production rate. Under a nearly neutral condition (pH 7.0–7.5), elemental sulfur dissolved into polysulfide to increase the bioavailability of S0. At acidic conditions (pH < 6.0), polysulfide formation was limited and sulfate reduction became dominant. Therefore, maintaining the sulfidogenic reactor driven by sulfur-reducing bacteria at neutral condition is essential to realize high-rate and low-cost AMD treatment. Moreover, the escape of residual hydrogen sulfide from the system was eliminated by employing a 17% recirculation from effluent to the sulfidogenic reactor.

Freezing/thawing effects on geochemical behavior of residues from acid mine drainage passive treatment systems

Passive systems are promising for the treatment of acid mine drainage (AMD) but generate metal-rich solids or residues. In subarctic climate, freezing/thawing (F/T) cycles may influence the chemical stability of waste, including residues from AMD passive treatment. The objective of this study was to assess and better understand the effect of F/T cycles on contaminants (metal and sulfates) leaching from AMD post-treatment residues. To do so, samples of residues WA50 (50 % wood ash and 50 % wood chips), PBR (30 % inorganic materials and 70 % organic substrate) and C50 (50 % calcite and 50 % wood chips) were collected from a laboratory tri-unit passive treatment system for iron-rich AMD (Fe-AMD) operated for over 1-year. To better understand the effect of freezing upon contaminant leaching, kinetic tests in weathering cells under wetting/drying (W/D) and F/T cycles were performed. Results showed that F/T cycles are likely to enhance the potential of metal leaching from post-treatment residues. The Fe leaching was 1.6-(for WA50), 3.2-(for C50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles. Similarly, Zn leaching was 2.4-(for WA50), 4.9-(for PBR) and 5-(for C50) times higher under F/T cycles compared to the W/D cycles. Finally, Mn leaching was 2.4-(for WA50) and 5.2-(for PBR) times higher under F/T cycles relative to the W/D cycles but no difference in Mn concentration was observed for C50 residues. These findings suggest that during snow melt or early spring significant metal concentrations could be released while disposing AMD passive treatment residues.

EFECTO DEL COBRE PARA LA REMOCIÓN DE SULFATO EN UN REACTOR DE LECHO FIJO

Mining of sulfide-rich pyritic ores produce acid mine drainage (AMD), which contains high metal concentrations and have acid pH, causing major environmental problems. Over the last 20 years a variety of passive AMD treatment systems, like anaerobic wetlands, bioreactors and permeable reactive barriers, have been studied. Under controlled conditions bioreactors employ inoculants of sulfate-reducing bacteria (SRB) to treat effluents and capture commercial grade metals. The objective of this research was to evaluate the effect of Cu on the removal efficiency of sulfate in a fixed bed reactor. During 28 d the fixed bed reactor maintained a hydraulic residence time (HRT) of 12 h and an influent rate of 0.67 gCOD/gSO 4 2– . Phase I (synthetic solution with 50 mg Cu/L) lasted 7 d, allowing Cu removal of 99.59 ± 0.43 % and sulfide production of 39.29 mg S 2- /L∙d. Sulfate-reducing activity (SRA) was not affected (40.25 mg S 2- /L∙d) during Phase II (21 d without Cu). Results showed no significant alteration in sulfate and COD removal, as well as sulfur production after the addition of Cu. It is concluded that SRB can be used for AMD treatment.

Preliminary Assessment of Ferrate Treatment of Metals in Acid Mine Drainage.

We report a preliminary assessment of ferrate [Fe(VI)] for the treatment of acid mine drainage (AMD), focused on precipitation of metals (i.e., iron [Fe] and manganese [Mn]) and subsequent removal. Two dosing approaches were studied to simulate the two commercially viable forms of Fe(VI) production: Fe(VI) only, and Fe(VI) with sodium hydroxide (NaOH). Subsequent metal speciation was assessed via filter fractionation. When only Fe(VI) was added, the pH remained <3.6, and the precipitation of Mn and Fe was <30 and <70%, respectively, at the highest, stoichiometrically excessive Fe(VI) dose. When NaOH and Fe(VI) were added simultaneously, precipitation of Mn was much more complete, at doses near the predicted oxidation stoichiometric requirement. The optimal dosage of Fe(VI) for Mn treatment was 25 μM. The formation of Mn(VII) was noted at Fe(VI) dosages above the stoichiometric requirement, which would be problematic in full-scale AMD treatment systems. Precipitation of Fe was >99% when only NaOH was added, indicating that oxidation by Fe(VI) did not play a significant role when added. The Fe(III) and Al(III) particles were relatively large, suggesting probable success in subsequent removal through sedimentation. Resultant Mn-oxide particles were relatively small, indicating that additional particle destabilization may be required to meet Mn effluent goals. Ferrate seems viable for the treatment of AMD, especially when sourced through onsite generation due to the coexistence of NaOH in the product stream. More research on the use of Fe(VI) for AMD treatment is required to answer extant questions.

Dynamics of Mn removal in an acid mine drainage treatment system over 13 years after installation

Acid mine drainage (AMD) from abandoned and active mines continues to pose a serious threat to the environment. Metal-rich fluids may emerge from abandoned mine works for hundreds of years, so the long-term performance of treatment systems must be evaluated to minimize the environmental impacts of AMD. A two-step process consisting of an aerobic wetland and a limestone bed is being used to treat coal mine-derived AMD in the Huff Run watershed of eastern Ohio, USA, and has been in operation for over 13 years. In 2002, the water was acidic (3.66 pH). From 2004 to 2014, water entering the treatment system had a pH of ~ 5.7 that increased to 7.25 by the time it exited the limestone bed. Since 2004, the effluent Al, Mn, and Fe concentrations have been between 0.05 and 0.12 mg/L, 0.04 and 0.25 mg/L, and 0.05 and 0.34 mg/L, respectively, with the majority of Fe and Al removal occurring in the wetland along with partial Mn removal. Subsequently, further Mn removal occurs as AMD flows through a limestone bed that was inoculated with a consortium of Mn(II)-oxidizing bacteria at the time of construction. An evaluation of historical system performance and current conditions indicate that effective metal removal has been sustained for over 13 years. While Mn(II)-oxidizing bacteria were most abundant in the limestone bed, they were detected throughout the system, indicating that indigenous Mn(II)-oxidizing microorganisms may be contributing to Mn removal well after the inoculation of the system.

TEKNOLOGI PENGOLAHAN AIR ASAM TAMBANG BATUBARA “Alternatif Pemilihan Teknologi”

Acid Mine Drainage (AMD) treatment systems can be broadly categorised as either active or passive systems, which differ according to their ability to handle Acidity, flow rate and Acidity Load of the influent AMD. Most passive and active systems utilise aggregate carbonate to neutralise the pH and encourage precipitation of metals as hydroxides or sulphide minerals. In addition, passive treatment systems often use organic matter to provide alkalinity and create reducing conditions which favour the precipitation of metal sulphides.Active treatment systems can be engineered to accommodate essentially any acidity, flow rate and acidity load. Active treatment of AMD can be achieved using fixed plants or portable equipment for in-situ treatment. Passive treatment systems are almost invariably used for post closure treatment scenarios, and are best suited to AMD with low Acidity and low flow rates. The key factors in selection and design of active and passive AMD treatment systems are water chemistry including pH, metals, sulphate levels and redox state and flow rate of influent AMD, and the objectives of AMD treatment. Other important factors include capital and operating costs, availability of suitable treatment reagents or materials and sludge management issues. Keywords: Acid Mine Drainage, Active Treatment, Passive Treatment, Coal Mining.

A preliminary study to design a floating treatment wetland for remediating acid mine drainage-impacted water using vetiver grass (Chrysopogon zizanioides).

Acid mine drainage (AMD) is extremely acidic, sulfate-rich effluent from abandoned or active mine sites that also contain elevated levels of heavy metals. Untreated AMD can contaminate surface and groundwater and pose severe ecological risk. Both active and passive methods have been developed for AMD treatment consisting of abiotic and biological techniques. Abiotic techniques are expensive and can create large amounts of secondary wastes. Passive biological treatment mainly consists of aerobic or anaerobic constructed wetlands. While aerobic wetlands are economical, they are not effective if the pH of the AMD is <5. Anaerobic wetlands use organic-rich substrates to provide carbon source to iron- and sulfate-reducing bacteria. The efficiency of these systems declines overtime and requires continuous maintenance. Our objective is to develop an alternative, low-cost, and sustainable floating wetland treatment (FWT) system for AMD for the abandoned Tab-Simco coal mining site in Illinois using vetiver grass (Chrysopogon zizanioides). Tab-Simco AMD is highly acidic, with mean pH value of 2.64, and contains high levels of sulfate and metals. A greenhouse study was performed for a 30-day period in order to screen and optimize the necessary parameters to design a FWT system. Water quality and plant growth parameters were continuously monitored. Results show significant SO42- removal, resulting in increased pH, particularly at higher planting densities. Vetiver also helped in metal removal; high amounts of Fe, Zn, and Cu were removed, with relatively lower amounts of Pb, Al, and Ni. Iron plaque formation on the root was observed, which increased metal stabilization in root and lowered root to shoot metal translocation. Vetiver was tolerant of AMD, showing minimal change in biomass and plant growth. Results obtained are encouraging, and a large scale mesocosm study is now in progress, as the next step to develop the vetiver-based system for AMD treatment.

Year-Round Performance of a Passive Sulfate-Reducing Bioreactor that Uses Rice Bran as an Organic Carbon Source to Treat Acid Mine Drainage

The development of compact and cost-effective passive treatment systems is of critical importance for acid mine drainage (AMD) remediation in Japan. The purpose of this study was to construct an AMD treatment system comprising a sulfate-reducing bioreactor using rice bran as a carbon source for sulfate-reducing bacteria (SRB) and to demonstrate its stable operation for at least a year in terms of continuous sulfate reduction and metal removal. Our 35 L bioreactor comprised a packed inoculum layer of a mixture of rice husks, limestone, and field soil, which was covered with rice bran. During operation, the AMD input flow rate was adjusted to 11.7 mL/min (hydraulic retention time, HRT; 50 h). Throughout the year, physicochemical analyses of system input and output AMD samples revealed that both pH and oxidation–reduction potential values were consistent with the process of sulfate reduction by SRB, although this reduction was observed to be stronger in summer than in winter. Efficient metal removal was observed, with concentrations at the outlet port of <0.33 mg/L Zn, <0.08 mg/L Cu, and <0.005 mg/L Cd, more than meeting Japan’s national effluent standards. Illumina sequencing of 16S rRNA genes revealed that Desulfatirhabdium butyrativorans-related species, which belong to a lineage within Deltaproteobacteria, were dominant (39–48% of the total SRB population) within the bioreactor.

Enriching Acidophilic Fe(II)-oxidizing Bacteria in No-flow, Fed-batch Systems.

Low-pH microbial Fe(II) oxidation occurs naturally in some Fe(II)-rich acid mine drainage (AMD) ecosystems across so-called terraced iron formations. Indigenous acidophilic Fe(II)-oxidizing bacterial communities can be incorporated into both passive and active treatments to remove Fe from the AMD solution. Here, we present a protocol of enriching acidophilic Fe(II)-oxidizing bacteria in no-flow, fed-batch systems. Mixed cultures of naturally occurring microbes are enriched from the fresh surface sediments at AMD sites using a chemo-static bioreactor (Eppendorf BioFlo®/Celligen® 115 Fermentor) with respect to constant stirring speed, temperature, pH and unlimited dissolved oxygen. Ferrous sulfate is discontinuously added to the reactor as the primary substrate to enrich for acidophilic Fe(II)-oxidizing bacteria. Successfully and efficiently enriching acidophilic Fe(II)-oxidizing bacteria helps to exploit this biogeochemical process into AMD treatment systems.

Role of Arsenic During the Aging of Acid Mine Drainage Precipitates

Iron-rich sediments cover the riverbeds affected by acid mine drainage (AMD) resulting from sulfide mineral oxidation. Precipitates are mainly composed of schwertmannite, which is a poorly-crystalline Fe-oxyhydroxysulfate that recrystallizes over a short-time period to goethite. Schwertmannite precipitation has a strong capacity for removal of some toxic elements like As. This study examines the influence of the initial As(V) concentration on the kinetics of precipitation and transformation of schwertmannite by means of batch experiments. A set of schwertmannites were synthetized with different As concentrations, and solid-solution interactions were allowed at 60°C during different time periods (from 1h to 75 d). The increase of the initial As concentration notably the precipitation of schwertmannite and its transformation to goethite. Moreover, the transformation of schwertmannite into goethite entails the release of sulfate and, at a longer time scale, of part of the previously retained As. Thus, As acts as a retardant for schwertmannite transformation; however, this toxic element is released from the precipitates once the schwertmannite is transformed, which is per se an environmental paradox. Furthermore, schwertmannite precipitation also plays an important role in the AMD treatment systems; hence, the long-term behavior of these precipitates should be considered for the solid waste management.

Impacts of detrital nano- and micro-scale particles (dNP) on contaminant dynamics in a coal mine AMD treatment system

Pollutants in acid mine drainage (AMD) are usually sequestered in neoformed nano- and micro-scale particles (nNP) through precipitation, co-precipitation, and sorption. Subsequent biogeochemical processes may control nNP stability and thus long-term contaminant immobilization. Mineralogical, chemical, and microbiological data collected from sediments accumulated over a six-year period in a coal-mine AMD treatment system were used to identify the pathways of contaminant dynamics. We present evidence that detrital nano- and micron-scale particles (dNP), composed mostly of clay minerals originating from the partial weathering of coal-mine waste, mediated biogeochemical processes that catalyzed AMD contaminant (1) immobilization by facilitating heterogeneous nucleation and growth of nNP in oxic zones, and (2) remobilization by promoting phase transformation and reductive dissolution of nNP in anoxic zones.We found that dNP were relatively stable under acidic conditions and estimated a dNP content of ~0.1g/L in the influent AMD. In the AMD sediments, the initial nNP precipitates were schwertmannite and poorly crystalline goethite, which transformed to well-crystallized goethite, the primary nNP repository. Subsequent reductive dissolution of nNP resulted in the remobilization of up to 98% of S and 95% of Fe accompanied by the formation of a compact dNP layer. Effective treatment of pollutants could be enhanced by better understanding the complex, dynamic role dNP play in mediating biogeochemical processes and contaminant dynamics at coal-mine impacted sites.