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Acid mine drainage (AMD) in the coal mining industry is recognized as one of the major sources of environmental damage. The active treatment of AMD involves adding alkaline reagents to wastewater so as to raise pH and to precipitate dissolved metals in the form of oxides/hydroxides. Studies have shown that yellow pigment (goethite) can be produced from the iron present in AMD. However, the presence of other metals can prevent the formation of pigment. Therefore, this paper seeks to evaluate several processes for purifying iron sludge so as to obtain raw material that can be recovered from AMD and thereby obtain a good quality of yellow pigment. The experiments were carried out by causing precipitation with strong and weak bases and removing other metals from the sludge by washing and filtering the sludge or by centrifugation. The results show that the color, type and morphology of the compounds changed, depending on the number of contaminants, and that these factors are strongly dependent on the type of reagent and less dependent on the separation process and the repetition of washes.

A techno-economic evaluation of a lignocellulosic bioethanol facility that uses acid mine drainage for the pre-treatment of weeping love grass (Eragrostis curvula) was performed. Both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) reactor configurations were evaluated. Results were compared to an evaluation of the same process with biomass pre-treated with dilute H2SO4. Capital and operating costs were estimated and a simple economic evaluation was conducted. It was found that all scenarios made a loss except for biomass pre-treated with H2SO4 in the SHF reactor configuration, although the high capital cost resulted in a payback period of 80.7 years, which is unfeasible. SHF was found to produce more ethanol at a lower capital cost than SSF, indicating that it is more economically feasible. Incorporating the remediation of AMD into a simultaneous process could help improve process economics. It is thus recommended that a techno-economic evaluation be conducted on a process that produces bioethanol through SHF and simultaneously remediates AMD.

The objective of this study was to evaluate performance of a co-treatment method of industrial acid mine drainage (I-AMD) and municipal wastewater (MWW) by dual-chamber microbial fuel cells (DC-MFC). Sewage sludge and MWW were used as inoculum-fuel in anodic chamber. I-AMD was fed to the cathode side of the chamber. A 100 Ω resistor was used to externally connect the anode to the cathode (DC-MFC-A). A second cell was operated at the open circuit potential (DC-MFC-B). In both cells, the efficiency of organic matter removal was ~15% and the wastewater alkalinity was reduced by more than 50% in both cells. On the other hand, the physicochemical characteristics and composition of I-AMD were modified. The pH increased from 2.50 to 4.12 ± 0.6. The S O 4 2 − concentration was reduced ca. 20 and 8% for the DC-MFC-A and DC-MFC-B, respectively. N O 3 − Concentration decreased in both cells by >90%. Different heavy metals (HMs) and metalloid removal values were observed in the cells: 42, 84, 71, 77, 55 and 42% for Cd, Cu, Fe, Al, Pb and As, respectively. Finally, a maximum volumetric power of 14,000 mW/m3 was reached by DC-MFC-A. The DC-MFCs achieved simultaneous treatment of MWW, partial neutralization of I-AMD, HMs removal, and bioelectricity generation. Hence, DC-MFCs seem to be an encouraging alternative for bioremediation of both MWW and I-AMD.

The high levels of sulfate and the metals in acid mine drainages generate important environmental problems. This paper describes the synergistic combination of a biosorption process and a new sulfate removal process. The treatment for the elimination of metals by biosorption with a Bacillus strain allowed reducing the high metal concentrations that had a toxic effect on the sulfate-reducing bacteria (SRB). On the other hand, the sulfate removal process used a microbial sulfate-reducing halotolerant consortium, which was able to reduce the sulfate concentration using low-cost organic substrates such as spirulina, cellulose and industrial starch. Independent of substrate present in the culture medium, the SRB was the predominant group. The sulfate-reducing consortium was cultured on a bench-scale upflow anaerobic packed bed bioreactor filled with Celite R-635. It was possible to reduce the concentration of sulfate in the culture medium in batch or semi-continuous operation. This integrated process is an inexpensive alternative for the elimination of metals by biosortion and the elimination of sulfate using a sulfate-reducing consortium.

Portland cement is an effective but expensive option for source control of acid mine drainage (AMD); the cost could be reduced by blending the cement with cheap waste materials such as fly ash from coal combustion and sludge produced from neutralization of acid mine drainage with lime. To test how these two additives affect cement performance in reducing AMD generation, blended cement slurries were applied to sulfidic waste rocks from Brukunga, South Australia, in leaching columns monitored for around 1 year. Acidity, metal and sulfate loads decreased greatly (by 80–95%) for all cement applications but the effect varied, depending mostly on the depth of penetration of the cement in the column (a function of slurry viscosity). The fly ash-blended cements penetrated further into the columns than the more viscous surface-capping sludge-blended cements, causing a greater decrease of leachate acidity loads and sulfide oxidation due to better coverage of the waste rocks and more acidity neutralization by cement dissolution. The AMD sludge showed no evidence of releasing its adsorbed heavy metals, but the fly ash released some Si, indicating that it is not chemically stable in the cement. There was little secondary mineral growth in the blended cements; the ettringite in the AMD sludge-blended cement formed from bassanite present in the sludge rather than exposure to acid mine drainage. Overall analysis of the long-term effectiveness of the blended cement applications shows that cement placed as a surface cap on top of the waste rock provides more value, because the slower cement dissolution rates ensure continued effectiveness for many years. Scaling up the results from the laboratory study to the field scale at the Brukunga mine site suggests that benefit/cost ratios in the order of 20–30 might be achieved compared to the present use of lime neutralization for AMD treatment.

Novel application of alkaline waste materials from the alumina industry (Bayer precipitates) to both neutralize and remove dissolved metals from acid mine drainage (AMD) has been demonstrated. The hypothesis was that Bayer precipitates could not only economically treat a wide range of AMD compositions but also do this in an environmentally acceptable manner. Therefore, the aim was to synthesise a range of Bayer precipitates and test their remediation effectiveness with a variety of real AMD samples. Thermal activation of Bayer precipitate at 380 °C produced a material which required the least mass to neutralize AMD and removed greater amounts of problematic species such as manganese (e.g. 74 to 82.8% reduction for Bayer precipitate and 83.7 to 91.6% reduction for thermally activated Bayer precipitate). The presence of an amorphous mixed magnesium/aluminium oxide and lack of carbonate species in the thermally activated Bayer precipitate was proposed to explain the improved performance. The resultant sludge was composed of hydrotalcite and possibly calcium sulphate and calcium carbonate, with precise quantities dependent upon the AMD tested. Exposure of sludge to water promoted the dissolution of a fraction of the hydrotalcite which enhanced concentrations of Mg and Ca in solution; albeit, contact of the sludge with AMD resulted in further removal of dissolved metals and raised the pH of the AMD. In summary, this study has developed a new process using two industrial waste products to solve a critical environmental problem. Future research should investigate the commercial feasibility.

Acid mine Drainage (AMD) is a low pH, sulphate and heavy metal rich leachate that is produced from oxidation of sulphide bearing minerals commonly found in the host rocks of some mineral ores. The pH augmentation, and sulphate and metal removal in AMD is often achieved by adding alkaline reagents in it. CaCO3 and/or its derivatives are commonly used for this purpose due to their abundance and affordability as compared to other neutralizing reagents. The problems associated with the use of this naturally occurring reagent do not only include the emission of greenhouse gases and ecological disturbances but also include a disastrous implication of depleting their reserves. To avoid these predicaments, green liquor dregs (GLD) from two Kraft pulp manufactures in South Africa were used as alternative alkaline reagents to neutralize AMD originating from Witwatersrand goldfields in Johannesburg. These GLD samples were referred to as GLD A and B. CaCO3 was used as a reference material. The GLD samples had neutralizing values that are comparable to that of CaCO3. Thus, CaCO3, GLD A, and GLD B had a neutralizing value of, 26.0, 21.2, and 21.0% CaO respectively. Different dosages 1, 2, 6, 10, and 20 g/L of these neutralizing reagents were used to neutralize the AMD. Results of this study showed that raising the pH of AMD was possible even at a low dosages of 1 g/L. At this dosage, the acidity of the AMD sample changed from 183.36 to 21.7, 36.4, and 48.72 mg/L CaCO3, and changed the pH from 5.6 to 8.84, 8.21, and 8.0 respectively. However, the SO42− and Ec had increased from 2093 to 2360, 2538, and 2407 mg/L and from 3.6 to 4.0, 4.3, 4.2 mS/cm respectively, indicating that caution should be taken to keep these values low by keeping the reagent dosage low and being cognizant of the carbonate mineral present in GLD. The x-ray diffraction patterns of the reacted samples confirmed the presence of metal oxides and Ca and Mg compounds that were depicted by SEM/EDX micrographs. In conclusion, the results from this study showed that the pH of AMD can be raised to optimum pH process value and reduce the acidity at a low dosage, a competitive advantage over commercial CaCO3. The proposed concept can be adopted by both the mining and pulp and paper industries, for the upscaling of co-disposing GLD and AMD contaminants as an eco-friendly alternative for the CaCO3.

In this study, eggshell (ES) powder was evaluated as a cheap and biocompatible waste material for the pre-treatment of acid mine drainage (AMD) leachate from coal dump. First, the composition of the AMD and physiochemical properties of the ES powder were determined using various standard characterization techniques. Then the removal efficiency of the target metal contaminants and the acid-neutralisation effect were explored in batch and kinetic set-ups. Thereafter, the settling rate of sludge formed after separately reacting ES and limestone powders with AMD was explored. Results revealed that the AMD leachate was highly acidic and contaminated with both cations and anions. Thermogravimetric analysis (TGA) and X-ray fluorescence (XRF) analyses demonstrated that ES powder was thermally stable up to 700 °C and CaO was the main component, respectively. Scanning electron microscopy (SEM) and EDX spectra confirmed the removal of contaminants. Both the decrease in particle size and increase in mass of ES enhanced the treatment efficiency. Although complete Fe and Al removal was achieved, Mn and sulphates posed a challenge as they were partially removed. Meanwhile, ES demonstrated superior acid-neutralizing effect to limestone and the mine water clarity and pH were shifted to acceptable levels. Both Fe and Al removal proceeded through an exothermic process while it was opposite for Mn. Kinetics were rapid and the sludge from ES powder settled faster compared with that from limestone powder. Cost analysis indicated that significant financial savings can be realised by substituting limestone with ES material. The findings suggest that ES waste could be an efficient and cheap material in the pre-treatment of AMD effluents.

Acid mine drainages (AMD) are the most harmful and chemically complex aqueous waste produced by the mining industry, causing contamination of fresh water sources, affecting human communities and the environment surrounding the mine facilities. Nowadays, AMD treatments use a high amount of reagents that produce a considerable quantity of waste, limiting the opportunity for recovering valuable metals. AMD typically can contain high quantities of copper that could be potentially recovered as a saleable product. Accordingly, this study proposes a novel combination of metal sulfide precipitation with membrane microfiltration process to clarify and separate those previously formed metal sulfide, focused on enhancing the copper recovery and the performance of clarification, evaluated in terms of turbidity of treated solution and separation rate. Three synthetic AMD were assessed, varying the copper content in a mono tubular ceramic membrane of 0.14 µm pore size. Results were promising: flux values were higher than 0.1 L/m2s, at least one order of magnitude higher with respect to other matrices. Copper recoveries were closer to 100% and turbidity values in the treated solution were lower than 2 NTU for sulfide stoichiometric dosages of 120%. Hence, this method could be an excellent alternative to efficiently recover copper from AMD.

This paper considers the evaluation of the performance of the biological sulphate reduction in continuous mode using grass cutting. Initially the reactor was operated in batch mode for 26 days, followed by a change to a continuous feeding mode at a Hydraulic Retention Time (HRT) varying from 8 to 2 days. At the start of the experimental period the bioreactor was filled with 89 kg of ceramic rings as support medium for Sulphate Reducing Bacteria (SRB) and 50 L SRB (COD = 852 mg/L and SO 4 2 = 600 mg/L) obtained from an existing biological sulphate reducing bioreactor. Rumen fluid was collected from a slaughterhouse and added to the bioreactor. Grass cuttings (10 kg) were added to the bioreactor as a carbon and energy source. The results showed that from day 59–106 the bioreactor was operated in continuous mode and the percentage SO 4 2− reduction efficiencies were 73%, 85% and 71%, corresponding to the HRT of 8, 6 and 4 days respectively.

The present study discusses the potentiality of using anaerobic Packed Bed Bioreactor (PBR) for the treatment of acid mine drainage (AMD). The multiple process parameters such as pH, hydraulic retention time (HRT), concentration of marine waste extract (MWE), total organic carbon (TOC) and sulfate were optimized together using Taguchi design. The order of influence of the parameters towards biological sulfate reduction was found to be pH > MWE > sulfate > HRT > TOC. At optimized conditions (pH - 7, 20% (v/v) MWE, 1500 mg/L sulfate, 48 h HRT and 2300 mg/L TOC), 98.3% and 95% sulfate at a rate of 769.7 mg/L/d. and 732.1 mg/L/d. was removed from the AMD collected from coal and metal mine, respectively. Efficiency of metal removal (Fe, Cu, Zn, Mg and Ni) was in the range of 94–98%. The levels of contaminants in the treated effluent were below the minimum permissible limits of industrial discharge as proposed by Bureau of Indian Standards (IS 2490:1981). The present study establishes the optimized conditions for PBR operation to completely remove sulfate and metal removal from AMD at high rate. The study also creates the future scope to develop an efficient treatment process for sulfate and metal-rich mine wastewater in a large scale.

Acid mine drainage is formed from the oxidation and hydro-geo-chemical weathering of sulphide bearing minerals. These minerals originate from mining and natural processes. This has led to the formation of a very acidic mine drainage enriched with Al, Fe, Mn and sulphate. The low pH of mine water promotes the leaching of residual toxic and hazardous chemical species from the surrounding parent rocks. Due to the potency of AMD to harm the environment and degrade its intrinsic values, this mine effluent requires a prudent management and an effective treatment option prior release to different receiving compartments of the environment. The present study was therefore designed with the aim of evaluating the efficiencies of different alkaline generating agents for acid mine drainage (AMD) treatment. To fulfil the goals of this study, a comparative study was undertaken using limestone, lime, hydrated lime, magnesite, periclase, brucite, soda ash and caustic soda. Bench scale laboratory studies were undertaken. The experiments were done at 60 mins of mixing, 1 g: 100 mL S/L ratios, and ± 25 °C room temperature and mixing at 650 rpm using overhead stirrers. The experimental results revealed that the pH of AMD increased after contacting different neutralizing agents. Chemical species were also removed from an aqueous system using different agents. Using pH as an indicator, the neutralisation efficiencies varied as follow: caustic soda ≥ hydrated lime ≥ lime ≥ cryptocrystalline magnesite ≥ periclase ≥ soda ash ≥ brucite ≥ limestone. This study advised on the best and effective pre-treatment agents and options that can be used by different mining houses.

Cement has been little investigated as a control for acid mine drainage, despite having advantages over cheaper alternatives. Leaching column experiments (set up in triplicate) investigated the effect of applying Portland cement slurries with three different water/cement (w/c) ratios (0.8, 1.0, 1.2) to pyrite-bearing waste rock from Brukunga mine in southeastern Australia. After application of the cement, leachate from the cemented columns showed a reduction in acidity compared to the control columns of ∼85% and 100% for w/c ratios of 0.8 and both 1.0 and 1.2 respectively. This was due to direct neutralisation of acidity by cement dissolution and encapsulation of the pyrite-bearing rock fragments by the cement (as shown by a reduction in oxygen consumption rates of up to 70%). In columns with the higher w/c ratios (1.0, 1.2), the cement slurry penetrated to the base of the columns and greatly decreased the permeability. The greater coverage of the waste rock by the cement and increased contact time between the leachate and cement meant that no acid drainage leached from these columns (pH 7–8, Fe, Al, Mn, Zn and Cu concentrations rarely above detection limits). In columns with a w/c ratio of 0.8, the cement slurry was mostly retained in the upper 30–50% of the waste rock, leaving a large fraction of the waste rock below without any cement coverage. Leachate drained relatively quickly from these columns, probably through a small number of pathways through the cement plug and carried relatively small loads of acidity and metals from uncemented waste rock beneath the cement. Thus cement may be a viable method for controlling acid mine drainage generation from waste rock dumps, and could be applied with both lower and higher w/c ratios could be used to achieve an optimal balance between deep penetration and surficial retention.

Dispersed alkaline substrate (DAS) is a matured passive remediation technology that has shown very high performances treating acid mine drainages (AMD). However, this remediation approach needs to improve its environmental footprint as well as to ensure almost complete water sulfate removals for longs periods of time. The present study improves the use of witherite (BaCO3) as a reagent on DAS-type treatments to induce highwater sulfate removals in the context of Andean AMD. Also, three CaCO3-rich residues from the agri-food industry were tested as alternatives to the current use of limestone. Two sets of column experiments were developed with various flow rates (1.5–5.4 L/day), net acidities (202 and 404 mg/L as CaCO3 eq.) and reactive agents (calcite, eggshells, seashells and witherite). Seashells were validated as a perfect limestone substitutes on the CaCO3-DAS stages. Malachite was observed, for the first time within these columns, as a mineral phase actively involved in Cu water removal. The BaCO3-DAS columns achieved values under 500 mg/L of sulfate at the output of the system for up to 6 months (initial sulfate concentration ranged 1234–2468 mg/L). Upscaling calculations of the present results support the feasibility of using this technology at a full field scale, especially as a wastewater treatment for abandoned mine sites, although some strategies to reduce witherite costs are recommended.

Three different iron oxide-based sorption media samples were tested for removal of phosphorus (P) from fish hatchery effluents using fixed bed processing. Two of the media samples were derived from residuals produced by the treatment of acid mine drainage, which were then compared to granular ferric hydroxide (GFH), a commercially available sorption medium. All of the media types removed from 50 to 70% of the P from the incoming aquaculture wastewater over 70–175 days of operation without regeneration. In some of the sorption trials, the GFH media showed superior adsorption in the earlier stages of the trial, but the GFH appeared to reach saturation more quickly, so that media performance was similar – at about 60% removal of P – over a longer time period of 175 days. Media regeneration tests were also conducted for both the commercial and mine drainage media, and demonstrated longer term performance, with overall P removal of 50–55%, over 223 days of total operation, with the advantages of phosphorus recycle and media reuse.

A laboratory-scale sulfate-reducing fluidized bed reactor at a controlled mesophilic condition of ±28 °C examined the biotreatment process of real acid mine drainage and hospital wastewater. In an attempt to substitute the carbon source, the study used the hospital wastewater in this regard. In this study, there was no supplement of carbon source during the treatment, but only the hospital wastewater provided the dissolved organic carbon. The process evaluated a biological treatment efficiency in stepwise phases, monitoring the effect of retention time, influent pH, and sulfates. The overall removal for the effluent COD concentrations and sulfate were between 39.5 mg/l and 42 mg/l at COD/SO42− ratio of 0.68 and hydraulic retention time of 8 h. The overall COD oxidation and sulfate reduction performance of the reactor was recorded as an average of 96 % and 97 %, correspondingly. The sulfide concentration averaged 235 mg/l, and the alkalinity generated in sulfidogenic organic from hospital wastewater neutralized the acid in mine water. The metal removal efficiencies documented at HRT of 8 h, were all above 98 %. The biological treatment further recorded the removal efficiencies of 44 % for naproxen and 55 % for ibuprofen pharmaceutical compounds as an additional advantage to the system.

Water pollution from acid mine drainage (AMD) has received extensive attention in recent years. However, previously used active treatment methods have many problems, such as high cost, difficult maintenance, and a large amount of sludge production. This study presented a novel process that combined dolomite aeration and an oxidation filter bed. The acidic water generated from coal mine drainage water was the object of research. First, the effects of important operating factors (such as particle size, initial pH, aeration rate, and flow rate) to neutralize acidity and remove contaminants from real mine effluents were studied. Based on these results, the treatment efficiency and sludge performance under repeated treatment were compared between the dolomite and limestone processes. Then the treatment effect under recycling condition was also compared between dolomite and limestone processes. Finally, the application and economic benefits of this combined process in the practical treatment project were evaluated. It was revealed that the Fe(II), total Fe removal efficiency all could reach nearly 100%, and the sulfate removal efficiency and pH could reach 96.2% and 6.53, respectively, after 3 h reaction under optimal conditions (dolomite particle size 0.5–1 cm, initial pH 4, aeration rate 10 L/min, flow rate 100 mL/min). The comparison results show that the dolomite process could achieve good effects while the neutralization agent consumption rate was at least 3 times slower than limestone. Meanwhile, the effluent quality was stable, and the sludge quantity was only one-third that of the sludge quantity produced from the limestone process. The setting capacities of sludge in the dolomite process were better than the limestone process. Additionally, the consumption of dolomite was better than that of limestone. The findings indicated that important cost reduction could be realized by substituting the limestone process with the dolomite aeration oxidation filter bed process, and has good performance in the engineering application.

Basic Oxygen furnace slag (BOFS) based geopolymers with open porosity ranging from 21%–57 % and density between 1255 kg/m3-2432 kg/m3 were synthesized. The synthesized geopolymers potential; to be used as attenuators for metal removal and neutralization of Acid Mine Drainage (AMD); were assessed and evaluated through column test studies conducted over a period of 133 days. The results show that BOFS based geopolymer composites can be used as attenuators as over 99 % metals were removed during the first 50 days. The results also revealed that higher porosity promoted greater neutralizing ability by dissolution of soluble salts from the BOFS based geopolymer; which improves the removal efficiencies of sulphates, metals and neutralization of AMD. Characterization of the composites after contact with AMD revealed that gypsum was the main mineral phase in the geopolymers indicating that precipitation was the major mechanism that enhanced metal and sulphates removal. BOFS based geopolymers can be used to replace armoring neutralizing agents such as limestone. The research contributes to sustainable development by addressing the environmental pollution posed by AMD and utilization of BOFS as a medium for remediation of AMD. The utilization of BOFS for remediation of AMD mitigates and responds to the environmental problems and demands associated with such waste

Residues from passive treatment of acid mine drainage (AMD) have variable chemical stability and could regenerate contaminated drainage. Stabilization/solidification (S/S) can prevent contaminant leaching. Residues were collected from a tri-step AMD field passive treatment system, operated for 6 years at the reclaimed Lorraine mine site, Quebec, Canada. General Use Portland cement (GU), blended binders based on GU with pozzolanic additives (ground-granulated blast-furnace slag; GGBFS and fly ash type C; FAC) were used as hydraulic binders, in proportions (w/w %) of 100GU, 20GU/80GGBFS, and 50GU/50FAC, respectively. Residues were mixed with wood ash (35%) and sand (25%), while reference samples (100% sand) were also prepared. Prior to S/S, raw materials were characterized. The S/S effectiveness was assessed mineralogically and mechanically (unconfined compressive strength; UCS). Environmental behavior assessment (static vs semi-dynamic leaching tests) was also performed. UCS results showed that strength increase with age. At 56 days, GU- (1.3 MPa) and GU/GGBFS (0.7 MPa) satisfied Quebec's strength requirements for landfill disposal (0.7 MPa), but not GU/FAC (0.6 MPa), while all samples satisfied USEPA criteria (0.35 MPa). The semi-dynamic test showed that all elements can be immobilized successfully in GU- and GU/GGBFS. The GU binder had the best stabilizing performance. Based on USEPA requirements, S/S using GU, GGBFS, and FAC can be also considered for contaminant immobilization in AMD passive treatment residues. Finally, the comparison between replicates using Student's t-test indicated good reproducibility of S/S treatment.

The high levels of metals and sulfate ions in acid mine drainage (AMD) constitutes a severe risk to the environment. Our study evaluated at pilot-scale the operational conditions of actual AMD nanofiltration (NF) to recover water and subsequent recovery of copper from the concentrated retentate solution by a solvent extraction (SX) process. NF showed a high copper concentration capacity (0.6 to 2.4 g/L) and good total rejection of species (~82%). While NF treatment allowed a high water recovery of 80%, the polarization resistance could limit its performance. A 1.1 g/L copper retentate solution was selected for use in the SX study to prevent membrane fouling in a possible in-series process (NF-SX). Equilibrium isotherms and McCabe-Thiele diagrams obtained using LIX 84-IC as the extractant indicated that using two countercurrent extraction stages and one stripping stage, it could be recovered 97% of the copper. The use of antiscalants and CaSO4 precipitates formed during NF had a negligible effect on the copper extraction yield by SX. The combined NF-SX results showed that a high recovery of water and copper from AMD is possible. This technology can have an impact on the reduction of freshwater consumption and wastewater treatment costs of mining, and its development is the subject of further research work.

Acid mine drainage represents a major cause of environmental impact associated with the activity of mineral extractive industries. In this study, we evaluated the treatment of this wastewater through an anaerobic sequencing batch reactor at 15, 30, and 55 °C with a sludge of sulfidogenic and methanogenic origin. The operation at 30 °C with sulfidogenic sludge showed the highest average removal of sulfate (80 %), while the highest average removal of COD (92 %) occurred at 30 °C with methanogenic sludge. The sulfidogenic phases showed lower apparent kinetic constants (Kap), compared at the same temperature, with the methanogenic phases, according to the first-order kinetic adjustment, considering residual concentration. The sulfate-reducing bacteria reproduced at 15 °C, according to growth enumeration by the most probable number method, which demonstrates its contribution to the growth of communities present in the inoculum due to the environmental conditions.

The biggest challenge that the mining and metallurgic industry faces is overcoming the contradictions between this activity benefits and environmental costs. One of the steps that causes the greatest damage to the environment and human health refers to acid mine drainage (AMD) and pickling solutions, which is a result of certain sulfide minerals oxidation. This process causes water acidification as well as the considerable increase in metals and sulfate concentrations on aqueous matrices restricting its use. Thus, it is necessary to adopt cleaner production methods to meet increasingly restrictive environmental legislation and, moreover, allow the possibility to recover these sub-products, generating operational economic savings. In this scenario the membrane distillation (MD) application, which is based on the vapor pressure difference between the two sides of hydrophobic membrane surfaces, stands out. Among the MD process the direct contact membrane distillation (DCMD) is highlighted, it has several advantages, such as its ability of 100% (theoretical) macromolecules rejection, in addition to non-volatile compounds and inorganic ions. Moreover, MD operates at relatively low temperature and lower operating pressures when compared to the classical membrane separation processes (MSP), producing high-quality water. These MD characteristics prove that this method is able to treat the AMD and pickling solutions.

The purpose of this research is to examine the neutralization performances of CaO-rich industrial waste products (IWPs) in the sulphide-rich environment of cemented paste backfill (CPB). A total of 205 CPB samples were prepared by using four different IWPs (type-C fly ash (C-FA), blast furnace slag (BFS), calcitic limestone (CL) and dolomitic limestone (DL)) as 5, 10 and 15 wt% substitute for sulphide-rich tailings. These CPB samples were cured and subjected to the acid (pH) and sulphate (SO42−) tests during 7–360 days of curing periods. MIP and XRD tests were also carried out to understand the generation of acid and sulphate and their effect on CPB stability at 28 and 180 days. The findings indicated that the utilisation of IWPs in CPB mixtures mitigated the acid (up to 58.9% higher pH values) and sulphate (up to 72.1% lower SO42− ion release) production, and enhanced the microstructure (12.43% lower total porosity) of CPBs owing to the neutralization potential, pore-filling effect, pozzolanic and partially binding characteristics of IWPs. It can be inferred from these findings that the IWPs can be suitably utilised as neutralization materials in CPB of sulphide-rich tailings. This in turn allows the mitigation of potential disposal/pollution problems associated with these IWPs.

Many industries and industrial processes, such as electroplating, acid mine drainage, the pharmaceutical industry, and industries that use phosphorous, produce large volumes of acidic wastewater that must be treated before discharge. Generally, a large quantity of an alkali, such as lime, caustic soda, or soda ash is used to neutralize the acidic wastewater and it is a costly treatment process. Therefore, new self-releasing alkali materials were studied. This research proposed the synthesis of sustainable porous alkali-activated materials (porous AAMs) by a simple method for acidic wastewater treatment. Industrial wastes, i.e., fly ash and bottom ash from a power plant, were employed to produce porous AAMs using sodium silicate solution as a foaming agent. The test results showed that fly ash and bottom ash AAMs had the potential to be used as pH modifiers. 0.001 M HCl solution (pH of 3) was selected as the representative acidic wastewater, and the pH of the solution fell to within the allowable discharge pH range of 5.5–9.0 according to the effluent discharge standard of Thailand. The retention time was three days for a solid-to-solution ratio of 1:500 w/v (g/ml). Porous AAMs present an attractive way of utilizing waste coal ashes compared to a cost-effective method for acidic wastewater treatment.

A novel application of acid mine drainage (AMD) for biomass recovery of two morphologically different microalgae species with respect to AMD dosage, microalgal cell density and pH of medium was investigated. Optimal flocculation of Scenedesmus obliquus and Chlorella vulgaris occurred with 10% dosage of AMD at an initial pH 9 for both 0.5 and 1.0 g/L cell density. The flocculation efficiency was 89% for S. obliquus and 93% for C. vulgaris. Zeta potential (ZP) was increased from -10.66 to 1.77 and -13.19 to 1.33 for S. obliquus and C. vulgaris, respectively. Scanning electron microscope with energy-dispersive X-ray of the microalgae floc confirmed the sweeping floc formation mechanism upon the addition of AMD. Application of AMD for the recovery of microalgae biomass is a cost-effective method, which might further allow reuse of flocculated medium for algal cultivation, thereby contributing to the economic production of biofuel from microalgal biomass.

Two enrichment cultures (one iron oxidizing and one sulfur oxidizing) obtained from an acid mine drainage were physiological and molecular characterized; the first of them showed 99% 16S rRNA gene sequence similarity with Leptospirillum ferrooxidans, while the sulfur oxidizing species was highly related to Acidithiobacillus ferrooxidans and Acidithiobacillus ferrivorans sequences although, unlike them, the species in the enrichment culture does not seem to be able to oxidize iron. The consortium constituted by both enrichment cultures achieved a successful biooxidation of Hualilan ore allowing the increase of gold recovery up to 96.4 % in the best culture condition (low pulp density in 1K medium). At the same time, this condition showed an effective zinc bioleaching (up to 86 %) although the recovery was much higher in cultures with initially supplemented iron; kinetics studies suggested that bioleaching rate in 1K medium at low pulp densities is controlled by diffusion through a layer mainly constituted by jarosite (rather than sulfur) which was detected in X-ray diffraction diagrams. The recovery of zinc as subproduct of the pretreatment to optimize gold recovery would also allow decrease the metallic charge of the leachates from the biooxidation tanks which is an environmental advantage., Centro de Investigación y Desarrollo en Fermentaciones Industriales

Acid mine drainage (AMD) treatment remains a virgin area for extensive research owing to the limitations of the existing and proposed AMD treatment technologies. Hence, the current study aims to apply crushed sea shells as an efficient and cost effective adsorption medium for AMD treatment in batch and column studies. The metal–adsorption medium interaction was characterized using FTIR and XRF analyses. The effects of adsorbent mass and solution pH were investigated in batch studies whilst initial concentration, flow rate and adsorbent bed mass were considered during fixed bed column studies. A close analysis of all parameters varied showed that initial metal concentration had the greatest effect on metal removal from AMD, with lower initial concentration resulting in more water being treated at breakthrough point. The experimental breakthrough curves for the removal of iron from AMD were fully described by the Yoon-Nelson and Thomas models. The preliminary results showed that sea shell derived adsorbent has a great potential as an alternative low cost material in the treatment of AMD.

Zinc can be removed from natural acid rock drainage by clinoptilolite, a natural sorbent, in a slurry bubble column. Afterwards, the clinoptilolite can be regenerated. This paper investigates the regeneration of clinoptilolite after it has been used for zinc removal and assesses the effects of regeneration time, regenerant concentration, pH, solution/sorbent ratio, water quality and uptake capacity of the regenerated clinoptilolite. Satisfactory treatment was achieved using 20 g L − 1 NaCl solution in distilled water, adjusted to a pH of 3. Good regeneration was achieved for 1 h agitation in the slurry bubble column, with a regenerant/sorbent ratio of 10 g g − 1 . Tests with the regenerated clinoptilolite revealed promising Zn removal capacity.

Bioleaching of copper from the flue dust of the Sarcheshmeh copper smelter has been investigated. A series of continuous tests were carried out in two-stages of airlift bioreactors inoculated with the acidophilic, iron and sulfur oxidizing bacteria, initially derived from acid mine drainage. The effects of different parameters such as pulp density, retention time and temperature on the mesophile bioleach performance of the copper sulfide rich dust were evaluated after pre-leaching with dilute acid. Pulp densities of 2% and 4% gave the same oxidation–reduction potential in both reactors. However, increasing the average pulp density to 7% generated an unstable oxidation–reduction potential in the first bioreactor at 34 °C. Overall copper extractions calculated for 2%, 4% and 7% pulp densities were 90%, 89% and 86% with mean retention times of 2.7, 4 and 5 days, respectively. The process is net acid consuming and has the potential for further development and feasibility studies.

The passive co-treatment of municipal wastewater and acid mine drainage is an ecological engineering approach that has recently shown promise for the sustainable remediation of common liquid wastes. In order to investigate a possible regeneration technique and illuminate further treatment possibilities, four replicate columns containing limestone overlain with inert biofilm media that had been processing a passively pre-treated mixture of high-strength acid mine drainage and raw municipal wastewater were pulled offline, kept filled, sealed and incubated. The incubation period (91 d) was presumed to far exceed that required to reach a pseudo-steady state to drive reactions closer to completion than the standard residence time (42-h and 18-h in the inert media and limestone stages of the columns, respectively). Further nitrate reduction, alkalinity generation, and pH increase resulted. Further Al, Mn, and Zn removal was observed. Dissolved Fe increased from 45.3 to 147 mg/L, a likely result of Fe-reducing bacterial activity, indicating that accumulated Fe in solid phases could be transformed, remobilized, and flushed from the unit process. This phenomenon could serve to passively regenerate treatment cells by removing accumulated solids to avoid clogging and preferential flowpaths. Phosphate and other trace metals (e.g., As, Cd, Pb) associated with solid phases were not released into solution, indicating the stability of the phosphate-related solids formed during standard operation or the availability of further re-sorption sites. Overall, results revealed that most anaerobic treatment reactions were near completion under the previous treatment regime, that further Zn processing was likely practical, and a possible passive media regeneration technique, thus illuminating further options regarding high-strength acid mine drainage and raw municipal wastewater passive co-treatment.

In this study, the microalgae culture system to combined active treatment system and pipe inserted microalgae reactor (PIMR) was investigated. After pretreated AMD in active treatment system, the effluent load to PIMR in order to Nephroselmis sp. KGE 8 culture. In experiment, effect of iron on growth and lipid accumulation in microalgae were inspected. The 2nd pretreatment effluent was economic feasibility of microalgae culture and lipid accumulation. The growth kinetics of the microalgae are modeled using logistic growth model and the model is primarily parameterized from data obtained through an experimental study where PIMR were dosed with BBM, BBM added 10 mg L−1 iron and 2nd pretreatment effluent. Moreover, the continuous of microalgae culture in PIMR can be available. Overall, this study indicated that the use of pretreated AMD is a viable method for culture microalgae and lipid accumulation.

One of the best available technologies for the removal of metals from water is in the form of metal sulphides. Metal removal by sulphide precipitation is a well-known process that is characterised by compact residues and very high removal efficiencies. Compared to neutralisation alone the sludge volume is 6 to 10 times lower and the toxic metals are removed to a 0.01–1 ppm level. Furthermore, selective metal precipitation is possible, allowing for separate recovery of valuable metals like copper, nickel, cobalt and zinc from nuisance metals like arsenic and antimony. However, the cost of reagent (NaHS or H 2 S gas) and safety aspects are often prohibitive. This paper describes a novel biological process for safe and cost effective production of sulphide from elemental sulphur, waste sulphuric acid or sulphate present in effluents. With this technology, gaseous or dissolved H 2 S is produced on-site and on-demand in an engineered, high rate bioreactor. Experience with industrial applications at metal processing plants will be presented. The technology can serve to selectively recover metals from e.g. bleed streams, leach liquor, effluent streams and acid mine drainage. Lower overall costs and increased safety (no transport or storage of sulphide, production on-demand and at ambient pressure) are the main advantages of this new process compared to its alternatives.

High rate sulfate reducing bioreactors can be effectively used in the treatment of acid mine drainage (AMD), The main disadvantage of sulfate reducing bioreactors is the requirement of a suitable carbon source and electron donor as the dissolved organic carbon content of AMD is usually quite low. In this study, a landfill leachate was used as a low-cost carbon source for sulfate reducing bacteria in a fluidized-bed (FBR) reactor for the treatment of synthetic AMD. Ethanol was replaced with leachate in the feed of FBR operated longer than 150 days at 35 degrees C. Although sulfate reduction rates decreased appreciably when ethanol (3.44 g sulfate/L/d) was replaced with leachate (0.90 g sulfate/L/d), leachate-fed FBR still performed well as the pH increased to neutral values, soluble metal removals were 82-99.9%, and total metal removals were 80-99.9%. In the case of leachate, electron flow to sulfate reduction decreased significantly. Higher performance may be achieved at chemical oxygen demand (COD)/sulfate ratios higher than 1.0. This study showed that leachate may be used as a low-cost soluble substrate for sulfate reducing bacteria in high rate bioreactors for AMD treatment. (c) 2012 Elsevier Ltd. All rights reserved.

In this work a pilot scale sulfidogenic bioreactor was used to treat acid mine drainage (AMD) from Zijinshang copper mine. In this process, S 2− produced in the Up-flow Anaerobic Sludge Bed (UASB) reactor were recycled in the two precipitation tanks for copper and iron precipitation, activated sludge from local waste water treatment plant was used as the carbon source. The reactor were steady operated in acid condition (with no pH control) for 4 month, AMD with a copper concentration of 100–120 mg/L, iron concentration of 170–200 mg/L, sulfate concentration of 2000–2500 mg/L and pH of 2.34–2.56, were feeding into the reactor under a feed rate of 1 m 3 /days and HRT of 3 days, copper and iron removal were 60.95%, 97.83% respectively. The precipitant in the precipitation tank containing 15.7% Cu and 22.66% Fe, thus indicating a recovery possibility of copper by pyrometallurgy process. From these results we can conclude that an SRB process would be a viable method of treating Zijinshan AMD.

In order to treat acid mine drainage (AMD) effectively using sulfate-reducing bacteria (SRB) at high concentration of sulfate and heavy metals, Fe0 was added to enhance the activity of SRB. When AMD was treated by SRB and Fe0 at 25 °C, more than 61% of sulfate was removed and the effluent pH was improved from 2.75 to 6.20 during the operation. Cu2+ was removed effectively with the removal efficiency at 99%, while only 86% of Fe2+ was removed during the AMD treatment, without conspicuous change of Mn2+ in the effluent in the process.

The focus of this study is to investigate efficiency of the sulphate reducing passive bioreactors for the treatment of acid mine drainage. The performance of locally available substrates (manures, woodchips, millet fodders and sugarcane waste) were examined for the treatment of acid mine drainage. The manures showed efficient removal of metals and other pollutants. With cow manure, buffalo manure and goat manure pH increased from initial 2.70 to 6.25, 7.10 and 7.50. All cellulosic wastes also raised pH in a range of 4.83–5.32. Significant reduction was observed in Eh, acidity and sulphate concentration also. It was observed that: 51.49–99.32% of Fe, 84.95–99.97% of Cu, 35.11–99.78% of Zn, 17.87–99.14% of Ni, 63.55–99.02% of Co and 12.68–73.86% of Mn were removed in maximum retention period of 10 days. Thus manures can be cost effective as a single substrate in a passive treatment method for removal of metals from AMD in bioreactors. Also chemical makeup of substrate provided an insight on the ability of sulphate reduction and metal removal.

A bench-scale Upflow Anaerobic Sludge Blanket (UASB) reactor was used to study the treatment of acid mine drainage through the biological reduction of sulfate. The reactor was fed with acid mine drainage collected at the Osamu Utsumi uranium mine (Caldas, MG, Brazil) and supplemented with ethanol as an external carbon source. Anaerobic granular sludge originating from a reactor treating poultry slaughterhouse wastewater was used as the inoculum. The reactor's performance was studied according to variations in the chemical oxygen demand (COD)/ SO 4 2 − ratio, influent dilution and liquid-phase recirculation. The digestion of a dilution of the acid mine drainage resulted in a 46.3% removal of the sulfate and an increase in the effluent pH ( COD / SO 4 2 − = 0.67). An increase in the COD / SO 4 2 − ratio to 1.0 resulted in an 85.6% sulfate reduction. The reduction of sulfate through complete oxidation of the ethanol was the predominant path in the reactor, although the removal of COD was not greater than 68% in any of the operational stages. The replenishment of the liquid phase with tap water positively affected the reactor, whereas the recirculation of treated effluent caused disequilibrium and decreased efficiency.

Passive co-treatment of municipal wastewater and synthetic acid mine drainage in a laboratory-scale, four-stage continuous flow reactor system was examined for changes in fecal indicator bacteria (FIB) counts. Raw municipal wastewater (MWW) from the City of Norman, Oklahoma was mixed at a 2:1 ratio with high-strength synthetic acid mine drainage and introduced to the system. The MWW contained varying concentrations of total coliforms (TC), fecal coliforms (FC), Escherichia coli, and fecal streptococci (FS). Initial concentrations ranged from 6 to 13, 0.6 to 6, 3 to 5, and 0.1 to 0.7 million cfu/100 mL, for TC, FC, E. coli, and FS, respectively. During the 6.6-day system residence time, a 100% reduction of all FIB was observed. However, FIB exhibited evidence of sub-lethal injury with slower colony formation rates on standard growth media after 81 h of retention. Extending standard incubation periods resulted in higher concentrations of all FIB in each treatment stage, except the final stage where only E. coli and TC counts increased. Although this co-treatment regime reduced FIB concentrations more effectively than conventional active or passive MWW treatment systems, further work can be done to optimize the efficiency of treating these wastes simultaneously.

Marble stone powder (calcite tailing) is a residual material resulting from the cutting and polishing of marble stone. Its use as adjuvant for the biologic treatment of acid mine drainage is studied. The performance of a combined chemical/biologic packed bed reactor containing a sulphate-reducing bacteria inoculum and calcite tailing as neutralising agent was compared with the individual neutralisation and biologic steps. Unlike the individual steps, the combined column is efficient in terms of metals and sulphate removal and acidity neutralisation, producing treated water suitable for irrigation. This work emphasizes on the key role played by waste calcite tailing in the inlet of the reactor. By thus adjusting pH to values adequate for sulphate-reducing bacteria water suitable for irrigation can be obtained in a single equipment with low energy demand. This goal would be impossible without the neutralisation action.

Biological treatment of sulfate and metal-containing wastewater (such as acid mine drainage) is a viable option due to lower cost and better sludge quality compared to conventional chemical treatment. Although several substrates can be used as carbon source, a low-cost substrate is required for large scale applications. This study was conducted to investigate the suitability of waste sludge as a carbon and seed source for sulfate reduction at 8 °C in batch bioassays. Around 7 mmol of sulfate was reduced when the waste sludge mixture (WS) (6700 mg SS l−1) from primary and secondary settling tank was supplemented as a carbon and seed source. However, only 1.6 mmol of sulfate was reduced with anaerobic digester effluent (ADS) (5300 mg SS l−1). The produced H2S from 1 g VSS l−1 WS and ADS oxidation can theoretically precipitate around 90 and 35 mg Fe2+, respectively. Both WS and ADS oxidized ethanol to acetate at similar rates. It appears that WS is a good candidate for carbon and start-up seed source of sulfate reduction at 8 °C, whereas sulfidogenic acetate oxidation was the limiting step. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes showed that both sludge sources contain Desulfomicrobium apsheronum strain.

Sulfate-reducing passive bioreactors have proved to be an effective technology for the treatment of acid mine drainage (AMD) contaminated waters over relatively short periods of time (1–5 a). However, long-term efficiency can be limited by several factors including problems related to the hydraulic properties of the reactive mixture. In this study, the effect of two hydraulic retention times (HRTs) of 7.3 d and 10 d on the performance of passive bioreactors was evaluated over an 11-month period for the treatment of a highly contaminated AMD. Evolution of the porosity and hydraulic conductivity of the reactive mixture was also evaluated during the 15-month operation of two bioreactors. Results indicated that bioreactors were effective at both HRTs for increasing the pH and alkalinity of contaminated water and for SO4 and metal removal (60–82% for Fe and up to 99.9% for Cd, Ni and Zn). Although the quality of treated effluent was significantly improved with the 10 d HRT compared to the 7.3 d HRT, results showed that the higher HRT reduced the porosity and the permeability of the reactive mixture which might lead to hydraulic related problems and, eventually, to limited efficiency in long-term operation compared to a shorter HRT. The choice of HRT for a passive bioreactor must therefore consider both the desired quality of treated effluent and the potential for deterioration of hydraulic properties in the reactive mixture.

In a study of the 29 operating passive systems for acid mine drainage (AMD) treatment, 19 systems showed various performance problems. Some systems showed very low efficiency even without visible leakage or overflow. Though systems show fairly good efficiency in metal removal (mainly iron) and pH control, sulfate removal rates were very low which indicates the possibility of very poor sulfate reductions by Sulfate Reducing Bacteria (SRB). As an alternative method, In-Adit-Sulfate-Reducing System (IASRS), the method of placing the SAPS inside the adit, to have temperature constant at about 15 degrees C, was suggested. Lab-scale model experiments of IASRS were carried out. The models 1 and 2 were run at 15 degrees C and 25 degrees C, respectively. The model 1 contained about a half of COD in the beginning of the operation than that of model 2. Metal removal ratios were higher than 90% in both systems. Both systems showed the sulfate removal ratios of 23% and 27%, respectively, which were still considerably low, even though higher than those of presently operating systems. However, since the synthetic AMD used was very low in pH (2.8) and very high in sulfate concentration, if some suggested modifications were applied to the standard design, it is presumed that the sulfate removal ratio would have increased.

Over the last few decades, the use of sulfate-reducing bacteria (SRB) in the treatment of heavy-metal containing wastewaters including acid mine drainage has become a topic of scientific and commercial interest. However, technical difficulties such as the sensitivity of SRB to toxic metals and high effluent COD limit the widespread use of SRB in high heavy-metal containing wastewater. The aim of this study was to clarify the reasons why the immobilized SRB sludge with inner cohesive carbon source (ISIS) process can endure high metal toxicity and decrease effluent COD. The ISIS process can physically set apart SRB and free the system of external influences such as the surrounding toxic metallic ions, as well as form inner carbon sources to avoid high effluent COD. Metal toxicity and bead durability are the two major factors which influence the regeneration and reuse of gel beads. Reuse of suspended SRB sludge and beads crosslinked with boric acid were unsuccessful due to metal toxicity and agglomeration of beads, respectively. However, beads crosslinked with ammonium sulfate prevented agglomeration of beads allowing successful bead regeneration and reuse. The result of four cyclic trials showed that over 99% of zinc was removed in each trial using these beads.

Acid mine drainage is an environmental problem produced when sulphide in mine tailings dams comes in contact with O 2 , bacteria and water. Oxidation occurs and a succession of reactions is responsible for producing acid and metals in the environment. One solution proposed is to use red mud bauxite (RMB) that is very alkaline to neutralise acidic tailings. Previous experiments showed that RMB has a good neutralisation capacity for a short time, but the long-term neutralisation potential is uncertain. So brine was added to RMB to verify if it can improve long-term alkalinity retention of RMB. Some authors have presented results where seawater or other natural or artificial Ca- and Mg-rich brines were used with RMB to convert the basicity (mainly NaOH) and other soluble alkalinity into low solubility hydroxide, carbonate and hydroxycarbonate minerals. Results showed that neutral pH conditions were maintained over the entire test for RMB and a mixture of RMB with brine. Addition of brine to RMB slightly lowered the pH compared to RMB alone. RMB alone lost a lot of dissolved alkalinity at the beginning of the test. Most of the alkalinity was lost in water after a few flushes for RMB samples. The addition of brine helped to keep neutralisation potential over more cycles of leaching.

The acid mine drainage of a closed iron sulphide mine in northern Japan was treated on-site using a continuous flow bench scale plant. In the bench scale plant of the two-step neutralization ferrite-formation process, magnesium oxide or calcium carbonate was used during the first neutralization step to raise the pH to around 4.8 to produce aluminium hydroxide sludge. In the second neutralization step sodium hydroxide was applied to reach a pH of 8.5 to produce ferrite sludge. Initial settling rates of the produced aluminium and ferrite sludge were from 1.2 to 4.8 times higher than the initial settling rates of the sludge produced by the treatment plant currently operated at the mine. The suspended solids (SS) concentration in the sludge ranged from 1.0 to 11.8 times higher than the SS concentration in the sludge produced by the current facility. The sludge volume index (SVI) of aluminium sludge was 11 and 36 mL/g when produced with magnesium oxide or calcium carbonate, respectively. The SVI of ferrite sludge was 4 mL/g regardless of the type of neutralizer used in the first neutralization, while the same parameter (SVI) of the sludge produced by the current facility is 70 mL/g, which indicates that the two-step neutralization ferrite-formation process generates sludge with much higher density. In addition, the process effectively reduced the concentration of toxic heavy metals from above 800 ppb, 13 ppm, and 15 ppm to as low as 1.4 ppb, 0.02 ppm and 0.2 ppm for arsenic, copper, and zinc, respectively.

The current approach of the biological treatment of acid mine drainage by means of a passive remediation system involves the choice of an appropriate organic substrate as electron donor for sulphate reducers. Nowadays this selection is one of the critical steps in the performance of such treatment, as this depends to a great extent on the degradability of the organic substrate. Thus, a prior characterisation of the organic substrate predicting its biodegradability would be desirable before embarking on an extensive large-scale application. The aim of this study was to correlate the chemical composition (lignin content) of four different natural organic substrates (compost, sheep and poultry manures, oak leaf) and their capacity to sustain bacterial activity in an attempt to predict biodegradation from chemical characterisation. The results showed that the lower the content of lignin in the organic substrate, the higher its biodegradability and capacity for developing bacterial activity. Of the four organic materials, sheep and poultry manures and oak leaf evolved reducing conditions and sustained active sulphidogenesis, which coupled with the decrease in sulphate concentration indicated bacterial activity. Sheep manure was clearly the most successful organic material as electron donor (sulphate removal >99%), followed by poultry manure and oak leaf (sulphate removal of 80%). Compost appeared to be too poor in carbon to promote sulphate-reducing bacteria activity by itself. Column experiments emphasised the importance of considering the residence time as a key factor in the performance of continuous systems. With a residence time of 0.73 days, sheep manure did not promote sulphidogenesis. However, extending residence time to 2.4 and 9.0 days resulted in an increase in the sulphate removal to 18% and 27%, respectively.

An upflow anaerobic digestor was fed dried algal biomass as a carbon source to establish the feasibility of using micro-algal biomass as the sole carbon source for biological sulphate reduction. The effect of the COD:SO4 ratio on substrate consumption and sulphate removal efficiencies were assessed by varying the organic carbon content of the media. Similar COD removal efficiencies were obtained irrespective of the influent COD:SO4 ratios, which were 8.1, 11.2 and 15.0. However, the rates of COD removal did differ with influent COD:SO4 ratios. The percentage sulphate removed decreased as the ratio of COD:SO4 increased. Not all of the COD was used for sulphate reduction, with only 31% being accounted for.

Sulfate-reducing reactive walls installed in situ in the path of acid mine drainage contaminated groundwater, present a promising passive treatment technology. However, a rigorous and methodical selection of the most appropriate reactive mixture composition still needs to be investigated. The aim of this study was the selection of the most reactive medium using a multiple factor design and the modeling of the sulfate-reduction rate. Reactivity of 17 mixtures was assessed in batch reactors (in duplicates) using a synthetic AMD. Results indicate that within 41 days, sulfate concentrations decreased from initial concentrations of 2,000-3,200 mg/l to final concentrations of

The aim of this work was to produce a poly-alumino-iron sulphate coagulant from acidic coal mine drainage. Precipitating the iron and aluminium at pH 5.0, followed by dissolution in sulphuric acid, produced a coagulant consisting of 8.7% iron and 3.3% aluminium. Water treatment tests proved that this coagulant was as efficient as the coagulant chemicals conventionally used in water treatment plants. The process can be easily incorporated into conventional AMD treatment plants, thereby reducing sludge waste issues and producing a valuable chemical reagent.

Organic waste materials were tested as the electron donors for sulphate reducers in treating acid mind drainage. They are oak chips (OC), spent oak from shiitake farms (SOS), spent mushroom compost (SMC), sludge from a wastepaper recycling plant (SWP) and organic-rich soil (ORS). The materials were placed in column reactors, which were inoculated by anaerobic digester fluid. The number of sulphate-reducers increased to 108–109 cells/ml in 2 weeks in the reactors. The reactors were continuously fed with simulated mine drainage for 35 weeks to determine sulphate reduction and metal removal. SOS, SMC and SWP served better as electron donors than OC and ORS. Metal removal efficiency of the reactor with OC was lower than those with SOS, SMC and SWP at the beginning, but became comparable at a later stage. The solvent extractable of OC inhibited the growth of sulphate-reducers. Cellulose polysaccharides were the main components of the waste materials consumed in the reactors.