Methods and system for removal of contaminants from a gas

Abstract

In certain aspects, the invention is related to methods and systems for concomitant removal of H2S, siloxanes and volatile organic compounds (VOCs) in a way that leverages humidity management and ferromagnetic separation with sequential slag filtration columns.

Description

[0001]Attorney Docket. No.205948-7156WO1 (00432) TITLE OF THE INVENTION Methods and System for Removal of Contaminants from a Gas CROSS-REFERENCE TO RELATED APPLICATION This application claims the benefit of priority to U.S. Provisional Patent Application Serial No.63 / 538,654 entitled "METHODS AND SYSTEM FOR CONCOMITANT REMOVAL OF CONTAMINANTS FROM A GAS," filed September 15, 2023, the disclosure of which is incorporated herein by reference in its entirety. BACKGROUND OF THE DISCLOSURE Copious amounts of biogas are produced by wastewater treatment plants and anaerobic digesters worldwide. This distributed methane source is experiencing a period of rapid development for an expanding role in renewable energy markets. As an emerging commodity, however, biogas is facing challenges that can limit its integration into commercial and residential energy systems. While biogas is rich in methane (CH4), it also contains unwanted fractions of hydrogen sulfide (H2S) and siloxanes; both gases have oxidation products that cause serious damage to energy recovery infrastructure. While conventional “scrubbing” technologies have been successfully applied to remove sulfur and siloxane impurities from biogas, their operational complexity and associated capital costs render biogas less competitive as a viable source for renewable natural gas (RNG). No single sorbent is currently available that can purify biogas into RNG; instead, multiple sorbents are used in combination with other treatment methods (i.e., membranes, cryogenic approaches, etc.). Current biogas scrubbing practices rely on specialty activated carbon columns, along with proprietary zeolites, mesoporous silicas, and / or organo‐ metallic frameworks (e.g., iron “sponges”). Raw biogas is nearly saturated with humidity and many of these specialty sorbents must be protected from water vapor to be effective (adding operational complexity and cost). Therefore, there is need in the art to develop operationally simple and cost-effective technologies for removal of contaminants from biogas. The present invention addresses this unmet need. BRIEF SUMMARY OF THE INVENTION In one aspect, provided herein is a method of filtering or sorbing a gas. The method of filtering also includes contacting a gas may include hydrogen sulfide (H2S) and siloxanes with granulated steel slag; where the grain-size distribution of the granulated steel slag is - 1 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) from about 0.5 mm to about 3.0 mm, and where the contacting concomitantly removes at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) from the gas to yield a filtered or sorbed gas. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods. In another aspect, a system for filtration or sorption of a gas is provided. The system also includes a filtration or sorption module may include a granulated steel slag, where the grain-size distribution of the granulated steel slag ranges from about 0.5 mm to about 3.0 mm; where the system is configured and adapted to sequester at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) from the gas to yield a filtered or sorbed gas. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods. BRIEF DESCRIPTION OF THE DRAWINGS The following detailed description of exemplary embodiments of the invention will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, non-limiting embodiments are shown in the drawings. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities of the embodiments shown in the drawings. FIGs.1A-1B each depict experimental set-up of a filtration system in accordance with the embodiments of the present invention. FIG.1A depicts an experimental set-up as integrated into existing biogas system at the Boulder Water Resource Recovery Facility (WRRF). The thick arrows indicate the existing pipeline within the Boulder WRRF biogas network, while the thinner arrows indicate the newly installed piping for the BOF slag sorption system. The raw anaerobic digester biogas flowed bottom-up of the packed bed column, ID = 1.5 cm, containing 50 g of BOF slag (0.84 – 1.4 mm) with an average packed bed height of 16 cm. Effluent H2S and siloxane concentrations were monitored and recorded every 15 minutes and hour, respectively. FIG.1B is a photograph of the experimental set-up at the WRRF. FIGs.2A-2B show H2S and siloxane (D4, D5, D6, corresponding to the most common Si- containing contaminant gasses) breakthrough curves when the filtration system was challenged with real anaerobic digester biogas at the WRRF with FIG.2A) 0.6 ft3 / hr and - 2 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) FIG.2B) 0.45 ft3 / hr biogas flow rates. FIGs.2A-2B illustrate simultaneous H2S and siloxane removal. Siloxanes D4, D6 and H2S were completely removed (100% removal rates) at least for the first 20 hours during the slow biogas flow rate experiments. Overall, the slower flow rate (FIG.2B) resulted in extended breakthrough times. FIG.3 is a graph depicting the results from a bench‐scale biogas treatment demonstration, challenging (0.05 kg) granulated slag columns with 200 mL / min of raw biogas. This proof‐of‐concept feasibility studies with granulated steel slag achieved near complete biogas contaminant removal. Results suggest a 100x materials cost‐savings could be realized with granulated discarded steel slags as compared conventional sorbents. FIG.4 is a schematic of pilot scrubbing / filtration according to the embodiments of the present invention, showing the system fitted with 5 kg activated slag columns treating 1.2 m3biogas / hr. This configuration separates magnetic (iron) and non‐magnetic slag fractions to minimize competitive sorption and optimize sulfide and siloxane removal with humidity management. FIGs.5A-5B are graphs showing breakthrough curves for filtering H2S and siloxanes from biogas. Flow rates: H2S –7.5 mL / min and siloxanes –0.45 ft3 / hr. FIG.6 shows the structure of siloxanes D4, D5, and D6 that can be removed according to the methods described herein, in accordance with various embodiments. FIG.7 shows a schematic of an apparatus used to observe the removal of H2S by BOF slag consisted of a glass column with ID of 0.6 cm, packed with 2 g of BOF slag (0.42 – 0.60 mm), and a bed height of 6 cm. N2served as the carrier gas that flowed through an impinger filled with water to create saturated gas conditions. After diluting concentrated H2S gas (2.5%) to a desired H2S concentration, the gas flowed bottom-up through a BOF packed bed reactor. The effluent H2S concentrations were continuously monitored and recorded every 15 minutes. FIG.8 shows a schematic of an apparatus used to observe the removal of D5 siloxanes by BOF slag consisted of a glass column with ID of 0.6 cm, packed with 2 g of BOF slag (0.42 – 0.60 mm), and a bed height of 6 cm. N2 served as the carrier gas that flowed through an impinger filled with liquid D5 siloxanes, after mixing with an additional N2line in the mixing chamber, D5 siloxanes were challenged to removal in a BOF packed bed reactor. The effluent siloxanes concentrations were continuously monitored and recorded every hour. FIGs.9A-9B show breakthrough behavior of 1,000 ppm inlet H2S concentrations: FIG.9A) under saturated gas conditions and various gas flow rates: 7.5 mL / min (diamonds), 15 mL / min (circle), 30 mL / min (triangles), and 50 mL / min (squares); and FIG.9B) 15 - 3 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) mL / min flow rate experiments under dry (triangle) and saturated (circle) gas conditions. FIGs.10A-10B show aspects of the BOF slag-grain surface. FIG 10A shows SEM imaging (left) and EDS analysis (right) of an unadulterated BOF slag grain surface.50 ^m magnification is used as a scale. The largest and most abundant peaks represent the most dominant elements present, which include calcium, iron, and oxygen. FIG.10B shows SEM imaging (left) and EDS analysis (right) of an unadulterated BOF slag grain surface.100 ^m magnification is used as a scale. The largest and most abundant peaks represent the most dominant elements present, which include calcium, iron, and oxygen. Insert of elements of interest: Si and their associated elemental percentage. FIG.11 shows breakthrough behavior of D5 siloxane experiments and BOF slag packed bed columns challenged with 7.39 mg D5 / m3and 5.25 mg D5 / m3inlet concentrations. These inlet concentrations correlated to flow rates (and mass loading rates) of 190 mL / min (triangle) and 200 mL / min (circle), respectively. FIGs.12A-12B show aspects of the BOF slag-grain surface. FIG.12A) SEM imaging (left) and EDS analysis (right) of an unadulterated BOF slag grain surface.100 ^m magnification is used as a scale. The largest and most abundant peaks represent the most dominant elements present, which include calcium, iron, and oxygen. Insert of elements of interest: Si and their associated elemental percentage. FIG.12B) SEM imaging (left) and EDS analysis (right) of a BOF slag grain surface that has been exposed to siloxane gas.100 ^m magnification is used as a scale. The largest and most abundant peaks represent the most dominant elements present, which include calcium, iron, and oxygen. Insert of elements of interest: Si and their associated elemental percentage. FIGs.13A-13B show breakthrough curve behavior of H2S and siloxanes (D4, D5, D6) removal by BOF slag challenged with real anaerobic digester biogas at the Boulder WRRF. Different biogas flow rates were tested FIG.13A) 0.30 and FIG.13B) 0.45. Insert show a close-up of the first few hours of each experimental run isolating D4 and D5 breakthrough behavior. FIGs.14A-14B show aspects of the BOF slag-grain surface. FIG.14A) SEM imaging (left) and EDS analysis (right) of an unadulterated BOF slag grain surface.500 ^m magnification is used as a scale. The largest and most abundant peaks represent the most dominant elements present. Insert of elements of interest: S, Si, and Fe and their associated elemental percentages. FIG.14B) SEM imaging (left) and EDS analysis (right) of a BOF slag grain surface that has been exposed to raw anaerobic digester biogas from the Boulder - 4 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) WRRF.500 ^m magnification is used as a scale. The largest and most abundant peaks represent the most dominant elements present. Insert of elements of interest: S, Si, and Fe and their associated elemental percentages. DETAILED DESCRIPTION OF THE DISCLOSURE The present disclosure is related to cost‐effectively reclaiming high quality methane from the (untapped) abundance of raw gas (such as, for example, raw biogas) generated by wastewater facilities, anaerobic digesters, and landfills across the nation (and the world). This technology enhancement is based on well‐characterized sorption and surface‐reaction principles. The most common corrosive contaminants that otherwise prevent direct biogas reuse as a renewable natural gas (RNG) are hydrogen sulfide (H2S) and volatile siloxanes (SixOx[CH3]2x); these contaminants can be passively removed with granulated steel‐slag. The activation of steel slag into a cost‐effective biogas purification process would substantially improve the availability of RNG sources, which remain underutilized because current biogas treatment costs are not competitive with conventional natural gas prices. Therefore, in one aspect, described herein is a sustainable alternative to current biogas scrubbing practices, wherein steel-making residuals, commonly referred to as “slags” are be engineered to reliably remove reduced sulfur, silicon and other metalloids from biogas, with high efficiency. The steelmaking industry generates 10-15 million tons of steel slag every year in the U.S. alone. Steel slags are stockpiled at steel plants and eventually sent to slag disposal sites or used as low-value geotechnical aggregates. However, the chemical, mineralogical, and morphological properties of steel slag illustrate potential technically sound uses in environmental engineering applications. Steel slags have a high specific surface area, and unique sorption and reactivity characteristics that can be suited for reduced sulfur and siloxane removal. Specifically, basic oxygen furnace (BOF) slags are predominately composed of calcium, silicates, and iron oxides, including both amorphous and crystalline phases. Thus, in one aspect, novelty of the presently disclosed methods and system lies in a new approach for engineering steel-making residuals for the specific purpose of biogas purification and biomethane recovery, thereby establishing a new and synergist path for the beneficial reuse of slags in the next generation energy portfolio. Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will - 5 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter. Throughout this document, values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y," unless indicated otherwise. Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z," unless indicated otherwise. In the methods described herein, the acts can be carried out in any order, except when a temporal or operational sequence is explicitly recited. Furthermore, specified acts can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed act of doing X and a claimed act of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process. Definitions The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range, and includes the exact stated value or range. In this document, the terms "a," "an," or "the" are used to include one or more than one unless the context clearly dictates otherwise. The term "or" is used to refer to a nonexclusive "or" unless otherwise indicated. The statement "at least one of A and B" or "at least one of A or B" has the same meaning as "A, B, or A and B." In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section. All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. As used here, the term “filtration”, "scrubbing" or "sorption" refers to a process by - 6 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) which particulate and / or vapor contaminants / pollutants are removed from a fluid. As used herein the term "scrubber" refers to an installation configured to remove a particulate and / or a vapor contaminant from a gas stream. As used herein the term, "column", "sorption column" or "scrubbing column" refers to a scrubbing tower packed with a bed comprising, for example, steel slag or a fraction thereof and is specifically designed for the removal of contaminants from a fluid, such as, for example a biogas. As used herein, the term "steel-slag" refers to a by-product of steel making that is produced during the separation of the molten steel from impurities in steel-making furnaces. The slag occurs as a molten liquid melt and is a complex solution of silicates and oxides that solidifies upon cooling. As used herein, the term "in series" means that two or more devices or parts of a device are placed along a flow line such that a fluid stream being treated moves from one device / part of the device to the next of while maintaining a substantially constant flow in a downstream direction. Throughout this disclosure, various aspects of the disclosure can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosure. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range. Methods of Gas Filtration / Purification In one aspect, the invention provides a method for filtering a gas, wherein the method comprises the steps of contacting an unfiltered / raw gas containing at least one of hydrogen sulfide (H2S), siloxanes, and / or VOCs (volatile organic compounds) with granulated steel slag, wherein the contacting concomitantly removes at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) from the unfiltered gas to yield a filtered gas. In certain embodiments, the method removes at least about, greater than, or equal to about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or about100% of H2S - 7 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) and / or siloxanes form the unfiltered / raw gas. In various embodiments, the unfiltered / raw gas also contains volatile organic compounds (VOCs) and at least about, greater than, or equal to about 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or about100% of the VOCs are removed using the method. In certain embodiments, the unfiltered / raw gas contains H2S and no VOCs or siloxanes. In certain embodiments, the unfiltered / raw gas contains siloxanes and no H2S or VOCs. In certain embodiments, the unfiltered / raw gas contains VOCs and no siloxanes or H2S. In certain embodiments, the unfiltered / raw gas contains VOCs and siloxanes and no H2S. In certain embodiments, the unfiltered / raw gas contains siloxanes and H2S and no VOCs. In certain embodiments, the unfiltered / raw gas contains VOCs and H2S and no siloxanes. The method described herein can thus remove any combination of H2S, siloxanes, and / or VOCs, from the unfiltered / raw gas whether present or absent. There is no limitation on the type of siloxane that can be removed, and both linear, branched, and cyclic siloxanes, or mixtures thereof, can be removed by the systems and methods described herein. For example, siloxanes having a molecular weight of at least about, equal to, or greater than 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 g / mol, can be removed by the methods and systems described herein. In one non-limiting embodiment, siloxanes such as D4, D5, and / or D6, and mixtures thereof, can be removed as described herein. The structures of siloxanes D4, D5, and D6 is shown in FIG.6. Likewise, there is no limitation on the type of VOCs that can be removed by the methods and systems described herein. The VOCs can be any carbon-containing compound(s) that is / are at least partly in the gas phase at a temperature of about 30-40 ºC. In one non-limiting embodiment, the VOCs are C1-C6fatty acids, C1-C6fatty aldehydes, or C1- C6 fatty acid esters, including linear and branched derivates thereof, and mixtures thereof. In certain embodiments, the grain-size distribution of the granulated steel slag ranges from about 0.5 mm to about 3.0 mm. In certain embodiments, the characteristic length grain- size of the granulated steel slag is about 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3 mm. In certain embodiments, the grain-size distribution of the granulated steel slag ranges from about 0.84 mm to about 1.4 mm. The grain-size of the granulated steel slag can be determined in accordance with ASTM D422-63 (ASTM 2007c). In certain embodiments, the granulated steel slag has a bulk porosity of about 30% to about 80%. In certain embodiments, the granulated steel slag has a bulk porosity of at least, greater than, or equal to about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%% or - 8 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) about 80%. In certain embodiments, the granulated steel slag has a porosity of about 50%. In certain embodiments, the granulated steel slag comprises a magnetic fraction and a non-magnetic fraction. In certain embodiments, the magnetic fraction is separated from the non-magnetic fraction. In certain other embodiments, the magnetic fraction and the non- magnetic fractions are not separated. In certain embodiments, the magnetic fraction and the non-magnetic fractions are mixed together. In certain embodiments, the magnetic fraction and the non-magnetic fractions are each present as individual layers. In certain embodiments, the steel slag is selected from the group consisting of blast- furnace slag, a steel-furnace slag, a basic-oxygen-furnace (BOF) slag, an electric-arc-furnace (EAF) slag, a ladle slag, and any combination thereof. In certain embodiments, the steel slag is a BOF slag. In certain embodiments, basic oxygen furnace (BOF) slags are composed of calcium, silicates, and iron oxides. At least in part because of their iron content, at least or about 50% of slag mass can be separated by a simple magnet (i.e., an iron rich fraction, from a silica rich fraction). Unlike other sorbents, slags’ sorption potential is not labile to humidity; in certain embodiments water vapor can significantly improve sulfide sequestration performance. In certain embodiments water vapor can affect siloxane sequestration performance. In certain embodiments, when the magnetic and non-magnetic fractions are separated, the magnetic fraction is contained in a first column and the non-magnetic fraction is contained in a second column. The columns can be any suitable column that can hold solid media such as the magnetic and non-magnetic BOF slag fractions described herein, and through which the unfiltered / raw gas can pass through. The first and second columns can have suitable packed bed heights to achieve a desired flow rate while ensuring that the appropriate amount of the H2S, siloxane, and / or VOC impurity is removed from the unfiltered gas. In certain embodiments, the relative humidity in the column containing the magnetic fraction of the steel slag is at least, greater than, or equal to about 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100%. In certain embodiments, the relative humidity in the column containing the non-magnetic fraction of the steel slag is at least, greater than, or equal to about 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or 1%. In certain embodiments, the relative humidity in the column containing the non- magnetic fraction of the steel slag is less than about 50%. In certain embodiments, the magnetic fraction of the steel slag sequesters H2S. In certain embodiments, the non-magnetic fraction of the steel slag sequesters siloxanes and - 9 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) volatile organic compounds (VOCs). In certain embodiments, the method further comprises detecting, monitoring, and comparing the levels of H2S and siloxanes in the unfiltered and in the filtered gas. In certain embodiments, the gas is a biogas or a gas emanating at least partly from a biogenic process. The methods and systems described herein can find use in a variety of settings, including, but not limited to, dairy farms, animal feeding operations, landfills, biowaste disposal sites, water purification sites, and the like. System for Gas Filtration / Purification In another aspect, the invention provides a system for filtration or sorption of an unfiltered / raw gas, wherein the system comprises a filtration and / or a sorption module comprising a granulated steel slag, wherein the grain-size distribution and the porosity of the granulated steel slag are in the ranges as specified elsewhere herein. In certain embodiments, the system is configured and adapted to sequester at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) from an unfiltered / raw gas to yield a filtered and purified gas, as a result of both purification mechanisms: filtration and sorption. In various embodiments, the terms “filtration” and “purification” include a mechanical process that specifically includes the chemical processes of absorption and adsorption of H2S, siloxanes, and / or VOCs. The sum of absorption and adsorption can be operationally defined as "sorption. " In certain embodiments, filtration includes removal of particulate matter from the unfiltered / raw gas and sorption includes absorption and / or adsorption of H2S, siloxanes, and / or VOCs in the unfiltered / raw gas. In certain embodiments, when the granulated steel slag is separated into a magnetic fraction and a non-magnetic fraction, the system further includes: a first column containing the magnetic fraction, wherein the first column is configured to sequester hydrogen sulfide (H2S); a second column containing the non-magnetic fraction, wherein the second column is configured to sequester siloxanes. In certain embodiments, the system includes a H2S sensor configured to determine the amounts of H2S comprised in the unfiltered and the filtered (sorbed) gas. In certain embodiments, the system further includes a siloxane sensor configured to determine the siloxanes comprised in the filtered and the unfiltered gas. In certain embodiments, the system further includes a humidity management system. In certain embodiments, the humidity management system includes a condenser, which is operatively connected to the first and the second columns. - 10 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) In certain embodiments, the first column, the humidity management system, and the second column are installed in succession in a series. In certain other embodiments, the first and the second columns are integrated into a single continuous column. In certain embodiments, the system further includes a plurality of control valves for regulating the flow of the gas to and from each of columns and the humidity management system. In certain embodiments, the system further comprises a data collection module, wherein the data collection module is configured to monitor the amounts of H2S and siloxanes in the unfiltered gas and the filtered gas. The filtration module and the data collection module are operatively connected to each other. With reference to FIG.1A, FIG.1A is a schematic of the apparatus employed for conducting continuous slag sorption tests. Dynamic sorption experiments were conducted at room temperature (20 ± 2°C) with single-pass plug-flow glass columns and N2carrier gas. Glass columns with an internal diameter (ID) of 0.6 cm were utilized as the packed bed reactor. 2 g of BOF slag (Cleveland Cliffs, Inc.) #40 x #30 (0.42 - 0.595 mm) were carefully packed into the column resulting in an average packed bed height of 6 cm. The average bulk density ( ^bulk) was determined to be 1.28 g / mL ^ 0.04 g / mL) and porosity (determined by volume of water / slag volume) was 0.55. FIG.1A illustrates H2S specific experiments where inlet gas concentrations to these columns were controlled by combining 2.5% v / v H2S diluted in dry nitrogen (Airgas) with a pure carrier gas, N2, using mass flow controllers (Alicat, Tucson, AZ). Inlet and effluent H2S concentrations were monitored using an online H2S sensor (Unisense, Denmark). With reference to FIG.1B, FIG.1B illustrates siloxane specific experiments Inlet siloxane concentration was controlled with a mass flow controller (Alicat, Tucson, AZ) bubbling dry, ultrapure nitrogen through an impinger filled with liquid siloxane (Sigma Aldrich, CAS Number 541-02-6). The impinger effluent line met with another dry ultrapure nitrogen flow also controlled with a mass flow controller (Alicat, Tucson, AZ). Both the nitrogen and siloxane gas lines met in a mixing chamber that was continuously stirred with a stir bar, prior to entering the packed bed column. The effluent from the mixing chamber was introduced to the column packed with slag; siloxane concentration in the column effluent was continuously measured (every hour) with an in-line gas chromatograph and ion mobility spectrometer (GC-IMS-SILOX) specific for siloxanes (Ohio Lumex, Solon, OH). - 11 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) With reference to FIG.4, FIG.4 is a schematic of the apparatus installed at the Boulder Water Resource Recovery Facility in Boulder, CO. Pilot-scale experiments were conducted utilizing 50g of milled BOF slag (Cleveland Cliffs, Inc.), #20 x #14, 0.84 – 1.4 mm, which were continually challenged with actual anaerobic digester biogas. The slag was carefully packed in glass columns with an ID = 1.5 cm and reached an average packed bed height of 16 cm. The average bulk density ( ^bulk) was determined to be 1.11 g / mL ^ 0.009 g / mL) and porosity (determined by volume of water / slag volume) was 0.5. The biogas H2S and siloxane content were measured for 24 hours between each experiment, to determine long term average concentration in the column influents. The two biogas flow rates that were tested under these field conditions were 0.30 and 0.45 ft3 / hr (141 and 212 mL / min, respectively). The biogas humidity was assumed to be saturated throughout these studies, given the typical conditions in anerobic digester headspace at water resource recovery facilities (RH > 95%). It is to be understood that wherever values and ranges are provided herein, all values and ranges encompassed by these values and ranges, are meant to be encompassed within the scope of the present disclosure. Moreover, all values that fall within these ranges, as well as the upper or lower limits of a range of values, are also contemplated by the present application. The following examples further illustrate aspects of the present disclosure. However, they are in no way a limitation of the teachings or disclosure of the present disclosure as set forth herein. EXPERIMENTAL EXAMPLES The disclosure is further described in detail by reference to the following experimental examples. These examples are provided for purposes of illustration only, and are not intended to be limiting unless so specified. Thus, the invention should in no way be construed as being limited to the following examples, but rather, should be construed to encompass any and all variations which become evident as a result of the teaching provided herein. The following working examples therefore are not to be construed as limiting in any way the remainder of the disclosure. Example 1: - 12 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) The proof‐of‐concept biogas scrubbing demonstrations were executed using slag with a narrow grain size distribution; this was defined by a mean grain diameter D50=1.5 mm, where the minimum “scrubbing” column diameter was at least 10 x D50 and minimum bed depth was at least 10 x the column diameter. It was decided that using granulated steel‐slag, a pilot demonstration would be executed that scales up the proof‐of concept operations by at least a factor of 100 as follows: The proposed series of pilot scale experiments would reduce the averaged diameter of the slag (sorbent) grain size distribution to near the pressure loss tolerance accepted for gas scrubbing in wastewater cogeneration practice (ca. < 250 Pa). All of the pilot‐scale tests will be conducted at the City of Boulder Wastewater Treatment Facility and executed under the following conditions: in an enclosed warehouse with temperature control (18 °C < Tambient< 23 °C); saturated humidity (RH > 90%); and, where protected from vibration and sunlight. Table 1 shows inlet concentrations of contaminants, according to various embodiments. Table 1. Inlet concentrations of the contaminants of interest at the Boulder WRRF.^ H2S Siloxane D4 Siloxane D5 Siloxane D6 continuous removal of the following contaminants from raw, anaerobic digester biogas to levels that are in compliance with RNG direct reuse standards in the US and European Union (2021): H2S < 4 ppmv; ∑ siloxanes SixOx[CH3]2x <6.5 ppbv; ∑VOCs<5 ppmv Example 2: Pilot-scale studies - 13 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) Pilot-scale studies confirmed the use of BOF slags to serve as a potent biogas scrubbing media in a series of experiments conducted at the Boulder Water Resource Recovery Facility (WRRF), Colorado, USA. This study used a single pass, plug-flow column containing milled slag granules, characteristic length between 0.84 – 1.4 mm, which were continually challenged with actual anaerobic digester biogas. FIGs.1A-1B illustrate the pilot-scale set-up, which was integrated into the existing biogas system at the Boulder WRRF. During experimental run times, the main valve of the existing raw (untreated / unfiltered) biogas was closed in order for the biogas to flow through the experimental set-up. The biogas flow rate was regulated with a highly sensitive bonnet needle valve (Swagelok) and confirmed with a rotameter that was in-line after the sorption column. Effluent H2S and siloxane concentrations were continuous measured and recorded with an H2S sensor (Unisense, Denmark) and a specialized gas chromatography (GC) to measure the full range of siloxane species, GC-IMS-SILOX (Ohio Lumex, USA). The average inlet concentrations of H2S and (D4, D5, and D6) siloxanes were measured for 24 hours between each experiment and determined to be 150 ppmv H2S, 7.8x10-2ppmv (0.95 mg / m3) D4, 2.7x10-1ppmv (4.2 mg / m3) D5, and 5.3x10-3ppmv (0.1 mg / m3) D6. 50 g of steel slag were added to the single-pass column for each experiment with a grain-size distribution of 0.84 – 1.4 mm, 50% bulk porosity, and biogas flow rates that were tested were 0.45 and 0.6 ft3 / hr. As shown in FIGs.2A-2B simultaneous H2S and siloxane removal was achieved. There were no significant findings that D4 and D6 were removed by the BOF slag, but D5 and H2S were completely removed (100% removal rates) at least for the first 20 hours during the slow biogas flow rate experiments. Overall, the slower flow rate (FIG.2B) resulted in extended breakthrough times. Thus, for the very first time, the simultaneous H2S and siloxane removal utilizing BOF slag and real anaerobic digester biogas is demonstrated herein. This pilot-scale study also demonstrated that slag activated in this application can deliver engineering performance competitive with conventional scrubbing technologies but is markedly cheaper. This approach will likely have immediate impact in the biogas recovery industry, such that it can be easily scaled in a “plug and play” scenario with current gas treatment infrastructure in a sustainable environmental paradigm. Example 3 The present systems and methods overcome the limitations of existing biogas scrubbing practices. Given similar contaminant sorbent capacity, steel slags are abundant - 14 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) industrial aggregates that are orders of magnitudes cheaper than their closest competitor (activated carbon) in this application, on a mass basis (ca. $54 vs $2700 metric ton (2022, USGS est.)); proprietary sorbents are even more expensive. Unlike their proprietary counterparts, the chemical, mineralogical, and morphological properties of steel slag are publicly available, consistent and well‐characterized. Relevant to biogas scrubbing, basic oxygen furnace (BOF) slags are predominately composed of calcium, silicates, and iron oxides; because of their iron content, about 50% of slag mass can be separated by a simple magnet (i.e., an iron rich fraction, from a silica rich fraction). And unlike other sorbents, slags’ sorption potential is not labile to humidity; in fact, water vapor can significantly improve sulfide sequestration performance. While slags have been recognized for their ability to immobilize sulfide, the novelty demonstrated in this proposed approach, is the concomitant removal of H2S, siloxanes and VOCs in a way that leverages humidity management and ferromagnetic separation with sequential slag “scrubbing” columns (FIG. 4). Example 4 The technology described herein would have the following impacts on biogas scrubbing practices: first and foremost, slag activated in this application has immediate cost, operational, and life cycle benefits. Even without optimization, recent bench‐scale results suggest some steel slags may prove to have superior sequestration capacity than existing biogas scrubbing media(s). Most existing biogas scrubbers in the US and EU are packed with activated carbon and / or other (relatively expensive) “proprietary media(s)”. The more expensive “designer” sorbents currently used for biogas scrubbing, can be feasibly substituted with milled steel slag grains, through a “plug‐and‐play” scenario in our existing wastewater treatment infrastructure. The steel tariffs imposed in the past decade have prompted substantive increases in domestic steel production, which in‐turn dictate marked increases in slag stockpiles distributed across the US. Steel slags are already orders of magnitude cheaper (> 10‐(2)$ / ton) than the sorbents currently used to purify biogas. The American Infrastructure Act and Buy America Act, as well as tariff‐associated steel production increases, will only serve to drive residual steel slag prices lower. Further, “spent” slag from biogas scrubbing operations presents unique opportunities for sustainable reuse, as a desirable characteristic of their terminal disposal path. Beneficial reuse of the “spent” slag from biogas scrubbing operations includes the following scenarios: (i) upcycling “spent” slag as an environmentally compatible agricultural sulfur and silicon - 15 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) amendment; and (ii) upcycling “spent” slag a phosphorus sequestering agent that can be added directly to anaerobic digesters and disposed of with dried biosolids. Example 5 FIGs.9A-9B illustrate the breakthrough behavior of the H2S lab-scale experiments against various operating conditions. FIG.9A illustrates the breakthrough behavior in response to varying influent gas flow rates (7.5, 15, 30, and 50 mL / min) at saturated RH conditions and 1,000 ppmvinfluent H2S. Changes in flow rate significantly impacted the time to initial breakthrough. The sorption capacities (calculated at breakthrough) were 16.4, 15.5, 12.3, and 9.95 mg H2S / g BOF slag, respectively. Sorption capacity was shown to incrementally decrease with increasing flow rate. FIG.9B illustrates the impact on the H2S breakthrough when humidity is isolated as a process variable. These experiments were challenged with dry and saturated gas conditions under otherwise identical operating parameters (15 mL / min flow rate and 1,000 ppmvH2S inlet concentration). Experiments under dry conditions experienced breakthrough much sooner (within 2 hours) compared to experiments under saturated gas conditions (22 hours). The sorption capacities (calculated at breakthrough) were 4.56 and 15.5 mg H2S / g BOF slag, for dry and saturated gas conditions, respectively. The results of comparing the dry and saturated gas condition experiments reveal the impact and possible presence of a thin water layer that facilitates chemical reactions at the surface of BOF slag, which have been further verified in literature. Example 6 SEM coupled with EDS analysis examined the surface properties and elemental characterization of the unadulterated and exposed to H2S BOF slag samples. SEM / EDS analysis showed obvious changes in the morphological characteristics and elemental composition of the BOF slag surface in response to H2S exposure as illustrated in FIGs.10A- 10B. The analysis revealed significant differences between these two states, supporting iron- sulfur complexes participate in the BOF surface transformations induced by H2S exposure. The significant increase in sulfur (0.5 to 21.7 weight %) and morphological changes (more structured and crystalline) can be attributed to H2S removal and iron-sulfide complexation during these experimental runs. These observations align closely with the possibility that sulfur removal is chiefly attributed to the distribution of iron-containing mineralogy of BOF slag. - 16 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) Enumerated Embodiments Embodiment 1 provides a method of filtering or sorbing a gas, wherein the method comprises: contacting a gas comprising at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) with granulated steel slag; wherein the grain-size distribution of the granulated steel slag is from about 0.5 mm to about 3.0 mm; and wherein the contacting concomitantly removes at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) from the gas to yield a filtered or sorbed gas. Embodiment 2 provides the method of embodiment 2, wherein the grain-size distribution of the granulated steel slag ranges from about 0.84 mm to about 1.4 mm. Embodiment 3 provides the method of any one of embodiments 1-2, wherein the granulated steel slag has a bulk porosity of about 30% to about 80%. Embodiment 4 provides the method of any one of embodiments 1-3, wherein the granulated steel slag comprises a magnetic fraction and a non-magnetic fraction. Embodiment 5 provides the method of any one of embodiments 1-4, wherein the magnetic fraction sequesters H2S. Embodiment 6 provides the method of any one of embodiments 1-5, wherein the non- magnetic fraction sequesters siloxanes and / or volatile organic compounds (VOCs). Embodiment 7 provides the method of any one of embodiments 1-6, wherein the magnetic fraction is separated from the non-magnetic fraction. Embodiment 8 provides the method of any one of embodiments 1-7, wherein the magnetic fraction is comprised in a first column, wherein the relative humidity is at least about 80%. Embodiment 9 provides the method of any one of embodiments 1-8, wherein the non- magnetic fraction is comprised in a second column, wherein the relative humidity is less than about 50%. Embodiment 10 provides the method of any one of embodiments 1-9, wherein the steel slag is selected from the group consisting of blast-furnace slag, a steel-furnace slag, a basic-oxygen-furnace (BOF) slag, an electric-arc-furnace (EAF) slag, a ladle slag, and any combination thereof. - 17 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) Embodiment 11 provides the method of any one of embodiments 1-10, wherein the method further comprises detecting, monitoring, and comparing the levels of H2S and siloxanes in the gas and in the filtered or sorbed gas. Embodiment 12 provides a system for filtration or sorption of a gas, wherein the system comprises: a filtration or sorption module comprising a granulated steel slag, wherein the grain-size distribution of the granulated steel slag ranges from about 0.5 mm to about 3.0 mm; wherein the system is configured and adapted to sequester at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) from the gas to yield a filtered or sorbed gas. Embodiment 13 provides the system of embodiment 12, wherein the grain-size distribution of the granulated steel slag ranges from about 0.84 mm to about 1.4 mm. Embodiment 14 provides the system of any one of embodiments 12-13, wherein the granulated steel slag has a bulk porosity of about 30% to about 80%. Embodiment 15 provides the system of any one of embodiments 12-14 wherein the system further comprises a data collection module, wherein the data collection module is configured to monitor the amounts of H2S and siloxanes in the gas and the filtered gas, wherein the filtration module and the data collection module are operatively connected to each other. Embodiment 16 provides the system of any one of embodiments 12-15, wherein the granulated steel slag is separated into a magnetic fraction and a non-magnetic fraction, and wherein the system further comprises: a first column comprising the magnetic fraction, wherein the first column is configured to sequester hydrogen sulfide (H2S); a second column comprising the non-magnetic fraction, wherein the second column is configured to sequester siloxanes; and a humidity management system. Embodiment 17 provides the system of any one of embodiments 12-16, wherein the first column, the humidity management system, and the second column are arranged in succession in a series. Embodiment 18 provides the system of any one of embodiments 12-17, wherein the first column and the second are optionally integrated into a single continuous column. - 18 - 52990416.1 Attorney Docket. No.205948-7156WO1 (00432) Embodiment 19 provides the system of any one of embodiments 12-18, wherein the humidity management system comprises a condenser. Embodiment 20 provides the system of any one of embodiments 12-19, wherein the relative humidity in the first column is at least about 80%. Embodiment 21 provides the system of any one of embodiments 12-20, wherein the relative humidity in the second column is less than about 50%. Other Embodiments The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety. While this disclosure has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this disclosure may be devised by others skilled in the art without departing from the true spirit and scope of the disclosure. The appended claims are intended to be construed to include all such embodiments and equivalent variations. - 19 - 52990416.1

Claims

Attorney Docket. No.205948-7156WO1 (00432) CLAIMS What is claimed is:

1. A method of filtering or sorbing a gas, wherein the method comprises: contacting a gas comprising at least one of hydrogen sulfide (H2S), siloxanes, and VOCs (volatile organic compounds) with granulated steel slag; wherein the grain-size distribution of the granulated steel slag is from about 0.5 mm to about 3.0 mm; and wherein the contacting concomitantly removes at least a portion of the at least one of hydrogen sulfide (H2S), siloxanes, and VOCs from the gas to yield a filtered or sorbed gas.

2. The method of claim 1, wherein the grain-size distribution of the granulated steel slag ranges from about 0.84 mm to about 1.4 mm.

3. The method of claim 1, wherein the granulated steel slag has a bulk porosity of about 30% to about 80%.

4. The method of claim 1, wherein the granulated steel slag comprises a magnetic fraction and a non-magnetic fraction.

5. The method of claim 4, wherein the magnetic fraction sequesters H2S.

6. The method of claim 4, wherein the non-magnetic fraction sequesters siloxanes and / or VOCs.

7. The method of claim 4, wherein the magnetic fraction is separated from the non- magnetic fraction.

8. The method of claim 7, wherein the magnetic fraction is comprised in a first column, wherein the relative humidity is at least about 80%.

9. The method of claim 7, wherein the non-magnetic fraction is comprised in a second column, wherein the relative humidity is less than about 50%. - 20 - 52990416.1Attorney Docket. No.205948-7156WO1 (00432) 10. The method of claim 1, wherein the steel slag is selected from the group consisting of blast-furnace slag, a steel-furnace slag, a basic-oxygen-furnace (BOF) slag, an electric-arc-furnace (EAF) slag, a ladle slag, and any combination thereof.

11. The method of claim 1, wherein the method further comprises detecting, monitoring, and comparing the levels of the at least one of H2S, siloxanes, and VOCs in the filtered or sorbed gas.

12. A system for filtration or sorption of a gas, wherein the system comprises: a filtration or sorption module comprising a granulated steel slag, wherein the grain-size distribution of the granulated steel slag ranges from about 0.5 mm to about 3.0 mm; wherein the system is configured and adapted to sequester at least a portion of at least one of hydrogen sulfide (H2S), siloxanes, and VOCs from the gas to yield a filtered or sorbed gas.

13. The system of claim 12, wherein the grain-size distribution of the granulated steel slag ranges from about 0.84 mm to about 1.4 mm.

14. The system of claim 12, wherein the granulated steel slag has a bulk porosity of about 30% to about 80%.

15. The system of claim 12 wherein the system further comprises a data collection module, wherein the data collection module is configured to monitor the amounts of H2S and siloxanes in the gas and the filtered gas, wherein the filtration module and the data collection module are operatively connected to each other.

16. The system of claim 12, wherein the granulated steel slag is separated into a magnetic fraction and a non-magnetic fraction, and wherein the system further comprises: a first column comprising the magnetic fraction, wherein the first column is configured to sequester hydrogen sulfide (H2S); a second column comprising the non-magnetic fraction, wherein the second column is configured to sequester siloxanes and / or VOCs; and - 21 - 52990416.1Attorney Docket. No.205948-7156WO1 (00432) a humidity management system.

17. The system of claim 16, wherein the first column, the humidity management system, and the second column are arranged in succession in a series.

18. The system of claim 16, wherein the first column and the second are optionally integrated into a single continuous column.

19. The system of claims 16, wherein the humidity management system comprises a condenser.

20. The system of claim 16, wherein the relative humidity in the first column is at least about 80%.

21. The system of claim 16, wherein the relative humidity in the second column is less than about 50%. - 22 - 52990416.1

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