Methods for microbial in-situ remediation for the sustainable immobilization of inorganic pollutants in contaminated waters

Abstract

Method for microbial in-situ treatment and in-situ remediation for the sustainable immobilization of inorganic pollutants in contaminated waters, surrounding aquifer areas and zones, and extraction residues by sequencing and controlling activated natural mineral formation processes, characterized in that a buoyant reactive material is introduced into the contaminated waters, surrounding aquifer areas and zones, and extraction residues as bulk material and / or by controlled flushing as a solid-water mixture via naturally occurring hydraulic connections and / or engineered inlets and outlets with technical systems and equipment, wherein the reactive material consists of a buoyant solid carrier material in the form of a foam glass substrate made of glass powder and blowing agent.with a silicate coating consisting of hydrogen-releasing and / or sulfate-reduction-promoting substances and at least one additive homogeneously embedded in the silicate coating, and the silicate coating of the reactive material stimulates the metabolic processes of autochthonous sulfate-reducing microorganisms by reducing site-specific and / or supplied sulfate to sulfide, and sulfide formation and gradual surface oxidation of formed sulfides occur on the floating reactive material through oxygen present from inflowing groundwater or through the gradual supply of oxygen via technical systems and facilities for the formation of pyrites and iron oxides through gradual surface oxidation on the floating reactive material, wherein hydrogen is released at rates of 0.0005 mol / kg*d to 0.0005 mol / kg*d during contact of the reactive material with the polluted waters.0.5 mol / kg*d is released and autotrophic microbial sulfate reduction is stimulated with reduction rates of 0.75 mg / l*d to 70 mg / l*d.

Description

[0001] The invention relates to a method for microbial in-situ remediation for the sustainable immobilization of inorganic pollutants in contaminated waters by sequencing and controlling activated natural mineral formation processes through in-situ treatment and in-situ remediation of the contaminated waters and the surrounding aquifer areas and zones as well as the extraction residues by metered introduction of a buoyant reactive material, consisting of a buoyant solid carrier material in the form of a foam glass base body with a silicate coating of hydrogen-releasing and / or sulfate-reduction-promoting substances and at least one additive, as bulk material before flooding and / or by controlled flushing as a solid-water mixture during flooding to influence the material conversions of autochthonous sulfate-reducing microorganisms and to form pyrites and iron oxides.

[0002] During the extraction of mineral resources, particularly through acid leaching, acidic, oxidizing waters are generated on a large scale due to acid deposition and natural pyrite weathering. Primarily in tailings deposits after mining operations and water management have ceased, inorganic pollutants, mainly metals, heavy metals, and naturally occurring radionuclides, are mobilized from the rock and dissolved in the water by acidification, depending on the geological conditions. These contaminated waters accumulate in the tailings, remaining mine workings, the surrounding rock formations, and the leached aquifer. These disturbances of the natural hydro- and geochemical environment impair the chemical condition of the aquifers and groundwater, which are generally not improved by natural self-purification processes or only over very long periods.Furthermore, such sources of damage often lead to contamination of connected, unaffected groundwater aquifers and surface waters, as well as remaining or remediated underground facilities and post-mining landscapes, so that without technical measures, long-term damage to the environment and public goods will result.

[0003] When dealing with widespread water contamination, remediation of the source of the contamination is often not possible for geological, technical, or cost reasons.

[0004] According to current technology, contaminated water is collected and treated on-site using conventional water treatment plants (pump-and-treat). The treated water is then either discharged into the receiving water body or the groundwater aquifer, or returned to the source of the contamination; if necessary, clean water is added for a process known as washing.

[0005] Pump-and-treat processes require complex technical systems, such as extraction wells, pumps, pipeline systems, and extensive downstream water treatment facilities (exsite plant). Operating a water treatment plant is also associated with high operating costs and relatively labor-intensive due to the continuous consumption of energy and chemicals. Furthermore, the water treatment process constantly generates residues that typically require costly disposal and the provision of land.

[0006] When using pump-and-treat methods, an initially intensive but short phase of highly concentrated discharges (first flush) occurs, followed by a long period of only low-concentration discharges. Consequently, successful remediation of contaminated water requires decades of operation for the plants and equipment. Conventional pump-and-treat methods are particularly ineffective during the period of low-concentration discharges and unsuitable for the promising remediation of contaminated water. With this method, the mining-altered hydro- and geochemical conditions only very slowly approach their original in-situ state. During the indeterminate duration of the process, in addition to unsatisfactory remediation results, further releases of pollutants and their accumulation in the water continue.

[0007] To minimize the operating costs and duration of pump-and-treat methods, intensive work is underway on the development of in-situ remediation techniques. Combinations of pump-and-treat methods with passive barriers downstream of the source of contamination, or funnel-and-gate systems, which belong to the category of passive technologies, are already known. When using funnel-and-gate systems, cutoff walls (funnels) are installed to focus the water flow, while permeable walls (gates) are installed perpendicular to the flow direction in the wastewater stream to treat the water flowing through. For example, pollutants are immobilized in absorber walls or degraded in reaction walls. The effectiveness of the passive barriers used depends primarily on the cost of the reactive material and the installation of the barriers, as well as the time required for the active removal of pollutants from the water.If pollutants are separated by precipitation, the precipitates clog the pores of the reactive material, rendering it impermeable to water and thus ineffective for its intended purpose. If pollutants are separated by adsorption, the available surface area, i.e., the particle size distribution of the material used, is crucial. Here, the precipitation of water-insoluble carbonates or sulfates in the reactive material usually presents a limitation that jeopardizes the feasibility of the process. On the one hand, if the reactive material is too fine, permeability is no longer guaranteed after a short time; on the other hand, if the pore volume is too small, the adsorption capacity of the reactive material for pollutants becomes unacceptably low.However, it has also become apparent that only certain substances or groups of substances can be treated by the walls, which can be a significant disadvantage, especially in cases of complex contamination. Another drawback is the extensive construction work required for the installation of reactive walls or funnel-and-gate systems, which becomes increasingly costly the deeper the aquifer to be treated lies and the more extensive and widespread the contamination.

[0008] Active remediation measures are also known, which, for example, attempt to stimulate or further accelerate in-situ pollutant degradation via injection lances or infiltration wells by supplying oxygen or pumping in nutrient solutions. However, the weakness of these measures lies in the efficiency of mixing the contaminated water with the injected substances. It takes a very long time for the slow-flowing, laminar groundwater to mix with the introduced substances, and particularly in heterogeneous aquifers with preferential flow paths, mixing is often insufficient.

[0009] Established reactive zone technologies are not applicable in flooded mines. Commonly used reactive materials cannot serve as substrates for native microorganisms and precipitated mineral phases because they are either not present in particulate form, cannot be transported by the water flow in flooded mine workings, or their composition can lead to the mobilization of pollutants, for example, through the release of pollutant-complexing molecules. Furthermore, conventional reactive materials do not react gradually and permanently. They do not guarantee reliable immobilization under changing environmental conditions. Moreover, conventional reactive materials usually introduce substances foreign to the groundwater, which complicates their large-scale application from a regulatory perspective.

[0010] Document US 6,719,902 B1 discloses a method and apparatus for the remediation of contaminated aquifers. This document discusses the prior art, in which, on the one hand, abiotic processes using, for example, Fe(O)₂ are employed to remove dissolved oxygen and increase the pH of the water, both of which are used to accelerate the chemical reduction of chromium and uranium and to immobilize these materials. Furthermore, reference is made to biotic processes used in the prior art, in which microbes indirectly contribute to metal reduction, for example, to the production of S₂S from sulfate ions (SO₄). 2-) and can be used to produce Fe(II) from Fe(III). The production of hydrogen during Fe(0) corrosion promotes the growth of beneficial anaerobic bacteria. In contrast, dissolved oxygen, which is present in some aquifers, is toxic to anaerobic bacteria and can inhibit their activity. However, oxygen is rapidly consumed during the aerobic corrosion of Fe(0).

[0011] In US patent application 6,719,902 B1, the use of a composition of Fe(0) and microorganisms for the remediation of aquifers is proposed. Fe(0) can be iron, an iron alloy, or an iron bimetal in various forms, including powder. The metal can be immobilized in a matrix or other medium, used in combination with one or more zeolites or minerals, or embedded. The metal can also be immobilized on glass. The bacteria are described as hydrogenotrophic bacteria that form a composition with Fe(0). In one embodiment, the iron and bacteria are uniformly distributed within a reactive wall. The contaminated water flows through the iron- and bacteria-containing reactive, permeable wall, where chemical reduction reactions occur and pollutants are bound.The walls used can be permeable or semipermeable. Furthermore, flow-through reactors, flooded bed reactors, flow-through tubes, and sediment tanks are proposed.

[0012] The object of the invention is to develop an effective, cost-efficient, and low-equipment method for microbial in-situ remediation for the sustainable immobilization of inorganic pollutants, primarily metals, heavy metals, and natural radionuclides, in contaminated waters, which controls the immobilization of pollutants by sequencing and controlling activated natural mineral formation processes and guarantees long-term effective in-situ remediation. - negative impacts on natural hydro- and geochemical conditions, and thus further disturbances of groundwater, surface water and the environment with pollutants, are significantly reduced and prevented in the long term, and pre-mining conditions are actively developed. - already mobilized inorganic pollutants immobilized at the source of the contamination itself - to prevent further release of inorganic pollutants from the rock matrix and long-term discharge of mobile pollutants into the waters - the only reaction products remaining in the water are substances that already occur naturally and are not pollutants. - Long-term, costly measures and expenditures, including conventional water treatment, disposal and landfilling, can be limited in time or avoided. - legal requirements, official regulations and water law provisions regarding the reduction of concentrations of metals, heavy metals and natural radionuclides are safely met and guaranteed, and the waters can be discharged into receiving waters with official approval or can flow away naturally.

[0013] According to the invention, the problem is solved by a method for microbial in-situ remediation for the sustainable immobilization of inorganic pollutants, primarily metals, heavy metals and natural radionuclides, in contaminated waters and for suppressing ongoing pollutant mobilizations by sequentially and controlling activated natural mineral formation processes in a reactive zone, wherein, for in-situ treatment and in-situ remediation of the contaminated waters and the surrounding aquifer areas and zones as well as the extraction residues, a buoyant reactive material, consisting of a buoyant solid carrier material in the form of a foam glass base body with a silicate coating of hydrogen-releasing and / or sulfate-reduction-promoting substances, is introduced in a time- and / or spatially controlled manner as bulk material and / or by controlled flushing as a solid-water mixture.Solved. The controlled flushing of the buoyant reactive material for in-situ treatment and in-situ remediation of the contaminated water is carried out via naturally occurring hydraulic connections and / or technically constructed inlets and outlets with technical systems and equipment.

[0014] The buoyant solid carrier material in the form of a foam glass base body with a silicate coating of hydrogen-releasing and / or sulfate-reduction-promoting substances and at least one additive homogeneously embedded in the silicate coating influences the material conversions of autochthonous sulfate-reducing microorganisms by reducing naturally occurring and / or supplied sulfate and contributes to the formation of pyrites and iron oxides through gradual surface oxidation on the buoyant reactive material by oxygen present from inflowing groundwater and / or gradual supply of oxygen via technical systems and equipment in the source of the contamination.

[0015] The buoyant solid carrier material, in the form of a foam glass substrate made of glass flour and blowing agent, with a silicate coating of hydrogen-releasing and / or sulfate-reduction-promoting substances and at least one additive homogeneously embedded in the silicate coating, releases hydrogen at rates of 0.0005 mol / kg*d to 0.05 mol / kg*d during contact with contaminated water and stimulates autotrophic microbial sulfate reduction with reduction rates of 0.75 mg / l*d to 70 mg / l*d. The metered and / or controlled flushing of this buoyant reactive material is used for the in-situ treatment and remediation of contaminated water. It is a foam glass substrate with a particle size of 1 mm to 50 mm and a density of 0.2 g / cm³. 3 up to 1 g / cm² 3and the silicate coating, consisting of hydrogen-releasing and / or sulfate-reducing substances made of water glass with a mass fraction of 20% to 50% by weight and a powdered iron-carbon alloy with a particle size of 10 µm to 500 µm, homogeneously embedded in the water glass and with a mass fraction of 5% to 40% by weight, and at least one additive with a mass fraction of 5% to 10% by weight based on the buoyant solid foam glass substrate, is introduced. To improve convection and throughput, water can be selectively extracted from and / or added to the contaminated water at suitable points.

[0016] The in-situ treatment and in-situ remediation of the contaminated waters and the surrounding aquifer areas and zones, as well as the extraction residues, is carried out by sequencing and controlling activated natural mineral formation processes or by inducing sequences of mineral formation reactions, consisting of sulfide precipitation, pyritization and gradual surface oxidation of iron sulfides, through the introduction of buoyant reactive material with a silicate coating of hydrogen-releasing and / or sulfate-reduction-promoting substances.

[0017] Autotrophic microbial catalyzed sulfate reduction is achieved by stimulating the metabolic processes of autochthonous sulfate-reducing microorganisms through the reduction of naturally occurring, site-specific, and / or added sulfate by the silicate coating consisting of hydrogen-releasing and / or sulfate-reduction-promoting substances. Natural self-cleaning processes are stimulated and supported.

[0018] Pyritization and gradual surface oxidation of the formed sulfides occurs through locally occurring oxygen and / or through the gradual supply of oxygen via technical systems and facilities, after sulfide formation has taken place at a defined rate over a defined period of time.

[0019] Stimulated microbial sulfate reduction converts sulfate present at the source of pollution and / or introduced into sulfide, which reacts with cations present at the source or introduced to form sulfide minerals, preferably iron sulfides. This microbial sulfate reduction process consumes hydrogen ions. Dissolved inorganic pollutants are immobilized by precipitation or co-precipitation (e.g., zinc, arsenic), sorption, or surface reduction (e.g., uranium). The stimulated autochthonous sulfate-reducing microorganisms also cause direct microbial uranium reduction. Furthermore, the sulfides formed are used as redox buffers, for example, by reducing dissolved oxygen. Contact with oxidizing agents is controlled to form iron(II) hydroxides, during whose crystallization the inorganic pollutants, primarily metals and heavy metals, are encapsulated.The formation of crystalline iron (hydr)oxides on the coatings prevents the oxidative release of reductively bound inorganic pollutants and acts as a sorbent for these pollutants. This enables the sustained immobilization of inorganic pollutants even after the introduction of the floating reactive material has ceased, thus stimulating the metabolic activity of native sulfate-reducing microorganisms. Through the described microbial in-situ remediation process, the stimulated microbial sulfate reduction within a reactive zone is made applicable for the sustained immobilization of inorganic pollutants by sequentially and controllably activating natural mineralization processes.

[0020] By introducing a buoyant reactive material as bulk material and / or by controlled flushing as a solid-water mixture into the source of contamination for microbial in-situ remediation and the sustainable immobilization of inorganic pollutants, the following essential reactions occur in contact with contaminated water. x / 2 SiO2 + x H + → Si(OH) x pH buffering to the range > 4.5 by dissolving basic mineral components Fe 0 + 2 H2O → Fe 2+ + H2 + 2 OH- Release of elemental hydrogen and reduction of the redox potential to < 500 mV SO4 2- + H + + 4 H2 → HS - + 4 H2O Microbiologically catalyzed sulfate reduction (microbial colonization of the reactive material) Me 2+ + HS - → MeS↓ + H + Metal sulfide precipitation 2 FeS + 0.5 H2O + 0.75 O2 → FeS2 + FeOOH Pyrite formation FeS2 + 3 H2O + 6 Fe 3+ → 7 Fe 2+ + S2O3 2- + 6 H + Surface oxidation of pyrite Fe 2+ + 2 H2O → Fe(OH)2 + 2 H + Surface precipitation of Fe(OH)2 The following pollutant reactions occur: uranium reduction, precipitation of pollutant sulfides, arsenic co-precipitation in iron sulfide, and pollutant sorption to Fe(OH)₂ and FeOOH. Key processes include the release of hydrogen through the reaction of elemental iron with polluted waters, as well as buffer reactions that, in the long term, shift the hydro- and geochemical environment towards neutral, intermediate conditions. The improvement of the hydro- and geochemical environmental conditions is, in turn, a prerequisite for the significant progression of heterotrophic sulfate reduction processes.

[0021] The described process achieves hydro- and geochemical improvement, pollutant fixation, sulfate reduction, and suppression of ongoing pollutant mobilization at the source of the contamination, while preventing the introduction of foreign or poorly degradable substances or pollutants into the groundwater. The reaction products remaining in the aquifer, surrounding aquifer areas and zones, and extraction residues are iron oxides and sulfides, the mineral carrier material (silicates), and metal oxides and sulfides. These substances occur naturally in ore bodies and aquifers. Example of implementation

[0022] This exemplary implementation describes a pilot test for the process-based treatment of acidic, highly oxidizing floodwater from an underground mine. Following the cessation of uranium leaching, the mine has been undergoing controlled flooding for several years. The hydrochemical environment of the floodwater is currently acidic and oxidizing. A natural decrease in pollutant concentrations in the floodwater is occurring only very slowly through dilution and leaching. The floodwater is currently collected in its entirety and treated in a conventional water treatment plant, a process that is complex in terms of equipment, cost, and personnel. According to available forecasts, the pollutant concentrations in the floodwater are decreasing only very slowly, so considerable expenses for water treatment are expected and budgeted for over many years.

[0023] The pilot test is conducted in a column filled with 25 kg of sandstone granules (< 3 mm) and 4.5 kg of iron hydroxide sludge from the quarry, as well as 2.4 kg of reactive material consisting of a buoyant, solid foam glass substrate, glass powder (preferably recycled glass), and an expanding agent, with a silicate coating composed of 40% sodium silicate, 30% gray cast iron powder (45 µm), and 9% Portland cement (CEM I 52.5) ​​based on the foam glass substrate. The 1.45 m long column, with a total volume of 65.6 l, was gassed with N₂ after filling with the solids and supplied with 8.0 l of acidic, oxidizing floodwater from the quarry. The column is subjected to saturated flow conditions. The untreated floodwater is characterized by the following parameters: - PH value 2,9 - Redox potential 770 mV - iron 67.7 mg / l - arsenic 31 µg / l - zinc 6.7 mg / l - uranium 8.9 mg / l.

[0024] For the experiment, the residence time of the flooding water in the column was determined based on the conditions in the flooded pit. The average flow rate through the column was 0.25 l / d. Therefore, the average residence time of the flooding water in the column was approximately 1 month.

[0025] The experimental column was operated for 270 days. After approximately one month of testing, no pollutants were detected in the column effluent at pH values ​​of 9 to 10 and redox potentials of approximately 330 mV, and the following values ​​were achieved: - iron < 0.04 mg / l - uranium < 5 µg / l - zinc < 50 µg / l - arsenic < 10 µg / l.

[0026] The pollutants in the solids (rock granules and iron hydroxide sludge) as well as all pollutants introduced with the flooding water were retained in the column. Analysis of the reactive material after the experiment revealed microbial colonization, the presence of pyrite, and the accumulation of uranium and zinc (pollutants with the highest concentrations in the flooding water) on the material surfaces. The predominant form of pollutant binding was determined to be in poorly crystalline iron (hydr)oxides.

Claims

[1] Methods for microbial in-situ treatment and in-situ remediation for the sustainable immobilization of inorganic pollutants in contaminated waters, surrounding aquifer areas and zones, and extraction residues by combining and controlling activated natural mineralization processes, characterized by, that a buoyant reactive material is introduced into the contaminated waters, surrounding groundwater areas and zones, and extraction residues as bulk material and / or by controlled flushing as a solid-water mixture via naturally occurring hydraulic connections and / or engineered inlets and outlets with technical systems and equipment, wherein the reactive material consists of a buoyant solid carrier material in the form of a foam glass base body made of glass flour and blowing agent, with a silicate coating of hydrogen-releasing and / or sulfate-reduction-promoting substances and at least one additive homogeneously embedded in the silicate coating,and the silicate coating of the reactive material stimulates the metabolic processes of autochthonous sulfate-reducing microorganisms by reducing site-specific and / or added sulfate to sulfide, and sulfide formation and gradual surface oxidation of the formed sulfides occur on the floating reactive material through oxygen present from incoming groundwater or through the gradual supply of oxygen via technical systems and facilities, leading to the formation of pyrites and iron oxides through gradual surface oxidation on the floating reactive material, whereby hydrogen is released at rates of 0.0005 mol / kg*d to 0.05 mol / kg*d during contact of the reactive material with the polluted waters, and autotrophic microbial sulfate reduction is stimulated at reduction rates of 0.75 mg / l*d to 70 mg / l*d. [2] Method according to claim 1, characterized bythat in stimulated microbial sulfate reduction, dissolved inorganic pollutants are immobilized by precipitation or co-precipitation, sorption or surface reduction. [3] Method according to claim 2, characterized by that the inorganic pollutants are metals, heavy metals and / or natural radionuclides. [4] Method according to claim 2, characterized by that the inorganic pollutants are zinc and / or arsenic. [5] Method according to claim 1, characterized by that the stimulated autochthonous sulfate-reducing microorganisms cause the formation of iron sulfide. [6] Method according to at least one of the preceding claims, characterized by , that microbial uranium reduction is caused by the stimulated autochthonous sulfate-reducing microorganisms. [7] Method according to at least one of the preceding claims, characterized bythat the sulfides formed are used as redox buffers through reaction with dissolved oxygen. [8] Method according to at least one of the preceding claims, characterized by that pollutant sorption to Fe(OH)2 and / or FeOOH takes place on the reactive material. [9] Method according to at least one of the preceding claims, characterized by , that the following reactions occur through contact of the floating reactive material with the polluted waters: x / 2 SiO2 + x H + → Si(OH) x pH buffering to the range > 4.5 by dissolving basic mineral components, Fe 0 + 2 H2O → Fe 2+ + H2 + 2 OH - Release of elemental hydrogen and sen- Redox potential rise < 500 mV, SO4 2- + H + + 4 H2 → HS - + 4 H2O Microbiologically catalyzed sulfate reduction (microbial colonization of the reactive material), Me 2+ + HS - → MeS↓ + H + 2 FeS + 0.5 H2O + 0.75 O2 → FeS2 + FeOOHFeS2 + 3 H2O + 6 Fe 3+ → 7 Fe 2+ + S2O3 2 - + 6 H + and Metal sulfide precipitation, pyrite formation, surface oxidation of pyrite Fe 2+ + 2 H2O → Fe(OH)2 + 2 H + Surface precipitation of Fe(OH)2. [10] Method according to at least one of the preceding claims, characterized by , that the buoyant reactive material for the in-situ treatment and in-situ remediation of contaminated waters is in the form of a foam glass substrate with a grain size of 1 mm to 50 mm and a density of 0.1 g / cm³ 3 up to 1 g / cm² 3and is coated with a silicate coating of hydrogen-releasing and sulfate-reducing substances, comprising water glass with a mass fraction of 20% to 50% by weight, a powdered iron-carbon alloy with a grain size of 10 µm to 500 µm homogeneously embedded in the water glass at a mass fraction of 5% to 40% by weight, based on the buoyant solid foam glass base body, and at least one additive with a mass fraction of 5% to 10% by weight, based on the buoyant solid foam glass base body. [11] Method according to at least one of the preceding claims, characterized by , that water is selectively extracted and / or added to the polluted waters at suitable locations to improve convection and throughput.