WO2013093155A1

WO2013093155A1 - Biofilter comprising black slag from an electric arc furnace and uses thereof

Info

Publication number: WO2013093155A1
Application number: PCT/ES2012/070874
Authority: WO
Inventors: Ana ELÍAS SÁENZ; Astrid BARONA FERNÁNDEZ; Luis GURTUBAY BUSTINDUY; Gorka Javier Gallastegui Ruiz De Gordoa; Naiara ROJO AZÁCETA
Original assignee: Universidad Del País Vasco
Priority date: 2011-12-19
Filing date: 2012-12-18
Publication date: 2013-06-27
Also published as: ES2409156B1; ES2409156A1

Abstract

The invention relates to a biofilter comprising black slag from an electric arc furnace as a filler material and micro-organisms capable of breaking down one or more pollutant substances such as volatile organic compounds (VOCs), hydrogen disulphide (H₂S), carbon sulphide (CS₂) and any combination of same. The invention also relates to a method for purifying a gas stream containing at least one biodegradable gaseous pollutant by means of biofiltration in which the gas stream containing at least one biodegradable gaseous pollutant is made to pass through the biofilter.

Description

BIOFILTER THAT INCLUDES BLACK ESCORIA OF ELECTRIC ARC OVEN AND ITS APPLICATIONS

FIELD OF THE INVENTION

The present invention relates, in general, to the purification of contaminated gases with biodegradable gaseous pollutants. In particular, the invention relates to a biofilter comprising black slag from an electric arc furnace as filler material, to eliminate or reduce the content of biodegradable gaseous pollutants present in a polluted gaseous stream containing at least one of said pollutants, thus as with a biofiltration method comprising the use of said biofilter.

BACKGROUND OF THE INVENTION

The increasing emission of pollutants into the environment and the consequent deterioration of the latter has led to legal control over their emission. There are countless gases that are released into the atmosphere and that can be qualified as pollutants; such as, for example, hydrogen sulfide, carbon disulfide, volatile organic compounds, ammonia etc.

Hydrogen sulfide (H ₂ S) is extremely harmful to health, 20-50 ppm in the air is enough to cause acute discomfort that leads to suffocation and can lead to death from overexposure.

Carbon disulfide (CS ₂ ) constitutes a highly dangerous pollutant due mainly to its harmful effects on human health. Prolonged exposure to CS ₂ vapors causes symptoms of intoxication ranging from reddening of the face and euphoria to loss of consciousness, coma and breathing paralysis. Chronic intoxication causes headache, loss of sleep, impaired vision, memory and hearing, nerve inflammation and vascular damage.

Volatile organic compounds (VOCs) constitute a type of highly hazardous contaminants. The American Protection Agency Environmental (US EPA) defines VOCs as any organic compound that has a vapor pressure greater than 0.1 mm Hg under standard conditions (25 ° C and 760 mm Hg). Thus, under this definition, VOCs encompass a wide range of chemical compounds, including aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, aldehydes, ketones, ethers, acids and alcohols, many of which may have adverse effects on the human or animal health, as well as the environment in general, in the short or long term. Likewise, VOCs have been identified as one of the main sources in the formation of photochemical smog by reacting with other air pollutants (for example, nitrogen oxides) and with sunlight, which can cause respiratory problems, eye irritation, pain head, etc., and damage to flora and animal life.

Therefore, it has been necessary to develop processes aimed at controlling the emission of this type of pollutants into the environment. Most of these processes are based on physical-chemical principles. However, these processes have several drawbacks since they generally require various equipment for the complete separation and elimination of the contaminant, which makes them expensive and with high energy requirements, and, sometimes, they are inefficient, particularly when the contaminant is in Low concentrations and large flows. Therefore, none of the traditional physicochemical technologies (thermal oxidation, thermocatalytic processes, incineration, hydrogenation, hydrolysis, condensation, adsorption, etc.) currently represents an appropriate option for the treatment of such contaminants (H ₂ S, CS ₂ and / or VOCs).

Over the last few years, biological technologies for the purification of contaminated gaseous streams have gained strength as an alternative to physical-chemical technologies, since they are cleaner and cheaper processes, eliminating many of the disadvantages associated with physical-chemical systems. traditional, for example, generation of new waste, etc., and are especially useful when the flows to be treated are large and the concentrations of pollutants (eg, H ₂ S, CS ₂ and / or VOCs) are low. The foundation of all biological processes is based on the ability of some microorganisms to degrade contaminants and transform them into products that are harmless or less harmful to human or animal health and / or the environment. Biological technologies are based on a series of reactions Microbiological metabolics that lead to the degradation of pollutants present in the gas stream. Through oxidative and, to a lesser extent, reductive reactions, pollutants can be transformed into by-products such as C0 ₂ , water vapor, nitrates, sulfates and new biomass, among other products.

Although there are a large number of different configurations, the most commonly used biological gas purification systems can be classified into three large groups: biolavadores ("bioscrubber"), drained bed bioreactors ("biotrickling filter") and fixed bed biofilters (" biofilter ") [Delhomenie, MC. et al. 2005. Biofiltration of Air: A Review. Review! Reviews in Biotechnology, 25: 53-72]. The basic mechanisms for removing the contaminant are similar in all cases, differing from each other in the presence or absence of a support, the nature of the support used, the presence or absence of a mobile liquid phase, and / or the ability to treat Different pollutants

Specifically, conventional fixed-bed biofilters employ microorganisms that are fixedly adhered in a porous medium to degrade contaminants present in a gaseous stream that flows through the bed. Said microorganisms grow in a biofilm supported on the surface of the medium. When the gas passes through the bed, the contaminants of the gas phase are absorbed in the biofilm that surrounds the environment, where they are biodegraded. Therefore, biofilters basically consist of a compartment that contains a filler or support material (filter material) that serves as a carrier of the biomass responsible for the biodegradation of contaminants. Despite their name, they are not "filtration" units in the strict sense of the word, but instead encompass a combination of several basic processes: absorption, adsorption, biodegradation and desorption. The absence of a mobile aqueous phase makes these bioreactors ideal for the treatment of contaminants that are not very soluble in water.

The selection of the support material is a fundamental factor for the proper functioning of conventional biofilters, since it influences both the ability to remove the contaminant (microbial activity) and the final cost of the biofiltration system (replacement frequency of the depleted support and its subsequent management, load losses associated with bed compaction, etc.). Likewise, at The biomass responsible for the degradation of pollutants must be developed on its surface, certain important physical-chemical characteristics must be taken into account: high specific surface area, high porosity, low apparent density, high water retention capacity and availability of essential nutrients for correct development of microbial metabolism.

Numerous microorganisms capable of degrading H ₂ S belonging to the genera Acidthiobacillus (eg, A. thiooxidans strain AZ11, etc.), Beggiatoa, Macromonas, Pseudomonas (eg, P. acidovorans strain DMR-11; P. putida strain CH11, are known, etc.), Sulfolobus (eg, S. Metallicus, etc.), Thiobacterium, Thiobacillus (eg, T. sp., T. denitrificans; T. novellus strain CH3; T. thioparus strain CH11, T. thioparus strain DW44, etc. .), Thiomicrospira, Thiomonas, Thiospira, Thiosphaera, etc.

Among the microorganisms capable of degrading CS ₂ are microorganisms of the genus Paracoccus (P. denitrificans, etc.), Thioalkalimicrobium (eg, T. aerophilum, T. sibericum, etc.), Thioalkalivibrio (eg, T. versutus, T. nitratis, T. denitrificans, etc.), Thiobacillus (eg, Thiobacillus strain TJ330; T. thioparus strain TK-m; T. sp. strain DSM 8985, etc.), Thiomonas, Thiothrix (eg, T. ramose, etc. ), etc.

On the other hand, the treatment of gaseous streams contaminated with VOCs by means of biofilters filled with various types of support is known. By way of illustration, Dorado et al. [A comparative study based on physical characteristics of suitable packing materials in biofiltration. Environ. Technol 31 (2) (2010): 193-204] compare ten materials commonly used as biofiltration support, both organic in nature (for example, coconut fiber, pine leaves, compost, etc.) and inorganic or synthetic (for example , polyurethane foam, lignite, lava rock, etc.). Among other features, its ability to adsorb toluene from a gas stream is evaluated. However, despite the different types of filler material known, it is convenient to have a greater range of such filler materials in order to have more resources when selecting the most appropriate material based on the particular characteristics of purification (contaminants present, concentration, etc.).

On the other hand, Chou et al. [Treatment of 1,3-butadiene in an air stream by a biotrickling filter and a biofilter. J. Air & Waste Manage. Assoc. 48 (1998): 711-720; Treatment of styrene-contaminated airstream in biotrickling filter packed with slags. J. Environ. Eng. 124 (9) (1998): 844-850; Treatment of toluene in an air stream by a biotrickling filter packed with slags. J. Air & Waste Manage. Assoc. 49 (1999): 386-398] have used blast furnace slags as a bed of a laboratory-scale biopercolator filter for the independent treatment of various contaminants: toluene [yield greater than 90% for contaminant ingress loads greater than 30 gm ^"3 h ^{" 1} and 3 minutes of residence time], styrene [yield greater than 95% for contaminant inlet loads less than 30 gm ^"3 h ^{" 1} and 1.07 minutes of residence time] or 1.3 -butadiene [elimination capacity less than 5 gm ^"3 h ^{" 1} for contaminant inlet charges less than 25 gm ^"3 h ^{" 1} and residence times around 1.89-5.04 minutes]. A disadvantage associated with these systems is that they require proper management of the liquid medium that is continuously recirculated through the filling material. Additionally, many authors have shown that drained filter bioreactors or "biotrickling filters" result in excessive accumulation of biomass, which leads to a loss of filtration efficiency. Also, the conjunction of relatively high operational costs and restrictions regarding the solubility of VOCs is a clear drawback compared to biofilters.

Therefore, there is still a need to find alternative methods for treating gaseous streams contaminated with biodegradable gaseous pollutants, for example, VOCs, H ₂ S, CS ₂ , etc., simple and reliable, which, preferably, solve at least some of the problems of the biofiltration methods of gaseous streams contaminated with said contaminants described in the prior art.

SUMMARY OF THE INVENTION

The authors of the present invention have developed a fixed bed biofiltration method to purify (ie, eliminate or reduce) the amount of biodegradable gaseous pollutants present in a gaseous stream contaminated with at least one of said pollutants efficiently; Illustrative, non-limiting examples of such biodegradable gaseous pollutants include VOCs, H ₂ S, and CS ₂ . This method is based on the use of black slag from an electric arc furnace or EAFS [of English, "Electric Are Furnace Slag"] as a biofilter filler, and in the use of microorganisms capable of degrading such contaminants, and provides various advantages over traditional methods and with other biological methods described in the state of the art, mainly due to its physical-chemical characteristics that allow continuous operation for long periods of time without suffering erosion and / or deterioration. After a previous stage of inoculation with microorganisms capable of degrading the contaminant or contaminants, this residue (EAFS) adequately serves as support for them, which form a biofilm of microorganisms around it, thus enabling the purification of the contaminated gas stream.

Thus, in one aspect, the invention relates to a biofilter comprising black arc furnace slag (EAFS) as filler material ("biofilter of the invention"). For commissioning, said biofilter also comprises microorganisms capable of degrading the biodegradable gaseous pollutant that it is desired to eliminate, for example, one or more VOCs, H ₂ S, CS ₂ , etc. Said microorganisms are inoculated into the filler material (EAFS) of the biofilter.

In another aspect, the invention relates to an installation for the purification of gaseous streams contaminated with at least one biodegradable gaseous pollutant comprising at least one biofilter of the invention.

In another aspect, the invention relates to a method for purifying a gaseous stream containing at least one biodegradable gaseous pollutant, by means of biofiltration, which comprises passing said gaseous stream containing at least one biodegradable gaseous pollutant through a biofilter of the invention which also comprises microorganisms capable of degrading said biodegradable gas contaminant (s).

In another aspect the invention relates to the use of black arc furnace slag (EAFS) as a filler material in a fixed bed biofilter for the purification of gaseous streams, in particular, gaseous streams contaminated with at least one gaseous pollutant. biodegradable.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 represents a particular embodiment of a continuous acclimatization system for obtaining inoculum for starting a biofilter of the invention.

Figure 2 is a schematic representation of a particular embodiment of an installation suitable for the implementation of a biofiltration method of biodegradable gaseous pollutants, for example, VOCs, according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Biofilter of the invention

In one aspect, the invention relates to a fixed bed biofilter, hereinafter "biofilter of the invention", which comprises black arc furnace slag (EAFS) as filler material. The biofilter of the invention can be used to purify contaminated gases containing at least one biodegradable gaseous pollutant (eg, a chemical compound that can be decomposed by the action of biological agents), for example, a volatile organic compound (VOC), hydrogen disulfide (H ₂ S), carbon sulfide (CS ₂ ), etc. In a particular embodiment, the biofilter of the invention is used to purify gases contaminated with one or more VOCs, H ₂ S and / or CS ₂ , by biofiltration, that is, to eliminate or reduce the amount of VOCs, H ₂ S and / or CS ₂ , present in a gas stream containing VOCs, H ₂ S and / or CS ₂ . In another particular and preferred embodiment, the biofilter of the invention is used to purify, by biofiltration, gases contaminated with one or more VOCs.

The filler material (support) contained in the biofilter of the invention, black slag from an electric arc furnace (EAFS), is a waste from the steel industry legally considered as an inert waste [Official Gazette of the Basque Country (BOPV), 1994 ; No 239, Decree 423/1994] and is obtained as an unwanted by-product during the manufacture of steel from scrap iron and / or steel as raw material in electric arc furnaces. Steel productions, worldwide and European, in 2008 were 1,327 and 198 million tons (mt), respectively, while Spanish production in 2009 was 14.4 mt. This steel manufacturing generates a large amount of industrial waste that represents between 15% and 20% of the total steel production [150-200 kg of slag per ton produced of steel], the black slag being an electric arc furnace (EAFS) the quantitatively most important industrial by-product in the manufacture of common steels. Due to the high generation and accumulation in outdoor deposits of these black slags (EAFS), their use has been authorized as a final product on roads and public or private roads of traffic as one of the structural layers, as raw material in the cement manufacturing and as aggregate for structural concrete. It has now been found that it can also be used as a filler material in biofilters intended for the purification, by means of biofiltration, of gaseous streams contaminated with at least one biodegradable gaseous pollutant, whereby the present invention also contributes to solving the problem generated for the excess of these slags (EAFS), proposing a novel application for that residue.

Mineralogically, the black slag of electric arc furnace (EAFS) mainly comprises calcium silicates, ferrites and metal oxides. In general, the main mineralogical phases present are dicalcium silicate (lamite, β- Ca ₂ Si04), dicalcium ferrite (2CaOFe ₂ 03) and wustite (iron oxide (II), FeO). In addition to these mineralogical phases, common minerals may also be present, such as olivine (Mg ₂ Si04), mervinite (Ca ₂ Mg (Si04) ₂ ), tricalcium silicate (3CaOSi0 ₂ ), brown millerite (NiS), etc., as well as various oxides, for example, free calcium oxide (CaO), free magnesium oxide (MgO), silica (Si0 ₂ ), ferrous oxide (FeO), aluminum oxide or alumina (A1 ₂ 0 ₃ ), manganese oxide ( MnO), phosphorus pentoxide (P ₂ 0 ₅ ), etc. In a particular embodiment, said EAFS comprises CaO (35-60%), Si0 ₂ (9-20%), FeO (15-30%), MgO (5-15%), A1 ₂ 0 ₃ (2-9% ), MnO (3-10%) and P ₂ 0 ₅ (0, 1-2%)), where the% are percentages by weight with respect to the total. However, the person skilled in the art will understand that the chemical composition of the EAFS that can be used in the biofilter of the invention may vary depending on the starting materials used in the production of steel, the type of steel manufactured, the conditions of the oven, cooling system, etc.

Black slags of electric arc furnace (EAFSs) have been commonly used as aggregates for road construction, as raw material in the Cement manufacturing process, as landfill in forest tracks, and, currently, are used in structural concrete for construction with 80% of the steel aggregate.

Therefore, the use of EAFS as a filler or support material for fixed bed biofilters for the treatment of contaminated gaseous streams, which contain at least one biodegradable gaseous pollutant, for example, VOCs, H ₂ S, CS ₂ , etc. , supposes a new application for this waste of the steel industry. Said EAFS, moreover, can be used as it is produced, that is, without the need for any prior conditioning except prior screening of EAFS particles to use the appropriate / desired size fraction.

The use of EAFS in fixed-bed biofilters, to purify gaseous streams contaminated by biofiltration has numerous advantages, among which it is worth noting its stability against long periods of operation in a continuous regime, its inert character compared to the different gaseous streams at treat, its ability to regulate pH due to its chemical composition, in particular, its CaO content, its minimum cost and its high availability. In addition, its use contributes to the revaluation of a very abundant residue.

The size of EAFS particles can vary within a wide range; however, in a particular embodiment, at least 50%, typically at least 60%, advantageously at least 70%, preferably at least 80%, more preferably at least 90%, even more preferably at least 95 %, and even more preferably, 96%, 97%, 98% 99% or 100% of the EAFS particles have an average diameter equal to or less than 20 mm, typically equal to or less than 10 mm, usually between about 4 mm and approximately 7 mm, preferably between approximately 5 mm and approximately 6.5 mm.

As mentioned above, the implementation of the biofiltration method provided by this invention requires the inoculation of EAFS with microorganisms capable of degrading the contaminant or biodegradable contaminants that it is desired to be removed. The term "microorganism" as used herein includes bacteria, fungi, yeasts, protozoa, etc. Numerous microorganisms capable of degrading biodegradable contaminants, possibly present in gaseous streams, are known, for example, VOCs, H ₂ S, CS ₂ , etc. In a particular embodiment, the biodegradable gaseous pollutant present in the gaseous stream is a VOC. In the sense used in this description a "volatile organic compound" or "VOC", according to the US EPA definition, is an organic compound that has a vapor pressure greater than 0.1 mm Hg under standard conditions (25 ° C and 760 mm Hg), and encompasses a wide range of chemical compounds, including aliphatic hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, aldehydes, ketones, ethers, acids and alcohols, many of which may have adverse effects for human or animal health, as well as the environment in general, in the short or long term. Illustrative, non-limiting examples of VOCs include benzene, chlorobenzene, ethylbenzene, toluene, styrene, xylene, pentane, ethylene, ethanol, phenol, butylacetate, ethyl acetate, dichloromethane, dimethyl sulfide, etc. When the biodegradable gaseous pollutant present in the gaseous stream is a VOC, the biofilter of the invention comprises a microorganism capable of degrading VOCs. In the sense used in the present invention, a "microorganism capable of degrading VOCs" is a microorganism that has the ability to use a VOC as a source of energy and transform it into a harmless or less harmful product for human or animal health and / or For the enviroment. Said microorganism can be a bacterium, a fungus, a yeast, a protozoan, etc. Illustrative, non-limiting examples of microorganisms capable of degrading VOCs include fungi and yeasts of the genera Exophiala, Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, Fusarium or Phanerochaete Chrysosporium (García-Peña et al, 2009. Dynamic numerical reconstruction of a fungal biofiltration system using differential neural network. J. Process Control. 19, 1103-1110; Zhao et al., 2010. Isolation and identification of black yeasts by enrichment on atmospheres of monoaromatic hydrocarbons. Microb. Ecol. 60, 149-156), bacteria from genera Acinetobacter, Alcaligenes (eg, A. xylosoxidans strain Y234, etc.), Bacillus (eg, B. sphaericus, etc.), Burkholderia (eg, B. vietnamiensis strain G4, etc.), Corynebacterium, Hyphomicrobium, Pseudomonas (eg , P. aeruginosa; P. putida strain Fl; etc.), Rhodococcus (eg, R. fascians, R. pyridinovoran, R. rhodochrous, etc.), or Xanthobacter (Malhautier et al., 2005. Biofiltration of volatile organic compounds , Appl. Microbiol. Biotechnol 68, 16-22), etc. Additional examples of microorganisms capable of degrading VOCs, and therefore useful in the context of the present invention, include the microorganisms mentioned by Delhomenie et al. [Delhomenie et al, 2005. Biofiltration of Air: A Review. Review! Reviews in Biotechnology, 25: 53-72 (see Table 3)]. In a particular embodiment, the biofilter of the invention contains microorganisms capable of degrading VOCs belonging to a single genus or to a single species of microorganisms capable of degrading VOCs; alternatively, in another particular embodiment, the biofilter of the invention contains microorganisms capable of degrading VOCs belonging to different genera and / or species of microorganisms; In a particular embodiment, said microorganisms form a consortium of microorganisms.

In another particular embodiment, the biodegradable gaseous pollutant present in the gaseous stream is H ₂ S; in that case, the biofilter of the invention comprises a microorganism capable of degrading H ₂ S. In the sense used in the present invention, a "microorganism capable of degrading H? S" is a microorganism that has the ability to use H ₂ S as a source of energy and transform it into a harmless or less harmful product for human or animal health and / or for the environment. Said microorganism can be a bacterium, a fungus, a yeast, a protozoan, etc. Illustrative, non-limiting examples of microorganisms capable of degrading H ₂ S include microorganisms of the genus Acidthiobacillus (eg, A. thiooxidans strain AZ11, etc.), Beggiatoa, Macromonas, Pseudomonas (eg, P. acidovorans strain DMR-11; P Putida strain CH11, etc.), Sulfolobus (eg, S. Metallicus, etc.), Thiobacterium, Thiobacillus (eg, T. sp., T. denitrificans; T. novellus strain CH3; T. thioparus strain CH11, T. thioparus strain DW44, etc.), Thiomicrospira, Thiomonas, Thiospira, Thiosphaera, etc. (Omri et al, 2011. H2S gas biological removal efficiency and bacterial community diversity in biofilter treating wastewater odor. Bioresour. Technol. 102, 10202-10209; Aroca et al., 2007. Comparison on the removal of hydrogen sulfide in biotrickling filters inoculated with Thiobacillus thioparus and Acidithiobacillus thiooxidans. EJB. 10 (4), 514-520). In a particular embodiment, the biofilter of the invention contains microorganisms capable of degrading H ₂ S belonging to a single genus or to a single species of microorganisms capable of degrading H ₂ S; alternatively, in another particular embodiment, the biofilter of the invention contains microorganisms capable of degrading H ₂ S belonging to different genera and / or species of microorganisms; In a particular embodiment, said microorganisms form a consortium of microorganisms.

In another particular embodiment, the biodegradable gaseous pollutant present in the gaseous stream is CS ₂ ; in that case, the biofilter of the invention comprises a microorganism capable of degrading CS ₂ . In the sense used in the present invention, a "microorganism capable of degrading CS?" It is a microorganism that has the ability to use CS ₂ as a source of energy and transform it into a harmless or less harmful product for human or animal health and / or for the environment. Said microorganism can be a bacterium, a fungus, a yeast, a protozoan, etc. Illustrative, non-limiting examples of microorganisms capable of degrading CS ₂ include microorganisms of the genera Paracoccus (P. denitrificans, etc.), Thioalkalimicrobium (eg, T. aerophilum, T. sibericum, etc.), Thioalkalivibrio (eg, T. versutus, T. nitratis, T. denitrificans, etc.), Thiobacillus (eg, Thiobacillus strain TJ330; T. thioparus strain TK-m; T. sp. strain DSM 8985, etc.), Thiomonas, Thiothrix (eg, T. ramose, etc.), etc. (Pol et al, 2007. Isolation of a carbon disulfide utilizing Thiomonas sp. And its application in a biotrickling filter. Appl. Microbiol. Biotechnol. 74, 439-446).

In a particular embodiment, the biofilter of the invention contains microorganisms capable of degrading CS ₂ belonging to a single genus or a single species of microorganisms capable of degrading CS ₂ ; alternatively, in another particular embodiment, the biofilter of the invention contains microorganisms capable of degrading CS ₂ belonging to different genera and / or species of microorganisms; In a particular embodiment, said microorganisms form a consortium of microorganisms.

The person skilled in the art will understand that the microorganisms to be inoculated in the biofilter filler material of the invention will be chosen according to the biodegradable pollutant present in the gas stream to be purified. Such microorganisms will have the potential capacity to degrade said biodegradable contaminants.

Some of said microorganisms capable of degrading biodegradable contaminants useful for the implementation of the present invention are commercially available or in crop collections. Likewise, the person skilled in the art can find and identify, by conventional methods, other microorganisms capable of degrading said biodegradable contaminants from various sources. Indeed, the person skilled in the art recognizes that microorganisms that tolerate the biodegradable contaminant in question (eg, VOCs, H ₂ S, CS ₂ , etc.) can live in samples from sites contaminated with said contaminant, for example, areas or facilities wherein gaseous streams containing said biodegradable contaminants, soils contaminated with said contaminants, activated sludge, composting, etc .; are used or generated. therefore, by selecting the cultures of the microorganisms present in said samples and / or a period of acclimatization to the contaminant it is possible to find strains of microorganisms capable of degrading the biodegradable contaminant in question.

The ability of a microorganism to degrade a biodegradable pollutant, for example, VOCs, H ₂ S, CS ₂ , etc., can be determined by any conventional procedure, known to those skilled in the art, that allows to know if a microorganism uses said contaminant biodegradable, for example, by contacting a culture of said microorganism with said biodegradable contaminant (eg, one or more VOCs, H ₂ S, CS ₂ , etc.) and incubating under appropriate conditions for the development and growth of the microorganism in question; Under these conditions, the decrease in the amount of said biodegradable contaminant (eg, one or more VOCs, H ₂ S, CS ₂ , etc.) is indicative that the analyzed microorganism is capable of degrading said biodegradable contaminant. The amount of biodegradable contaminant can be determined by conventional methods, for example, by chromatography (eg, gas chromatography, etc.). If desired, the microorganism may be supported on a filler material of the type used in the biofilter of the invention (EAFS) and the biodegradable contaminant may be contained in a stream of air, preferably saturated with water vapor in water before contacting it with the microorganism.

Structurally, the biofilter of the invention comprises a reservoir, in which the filler material and microorganisms capable of degrading the biodegradable pollutant (s) (eg, one or more VOCs, H ₂ S, CS ₂ , etc.) are located. .) as well as means for the entry of the gas stream containing said contaminant or contaminants, suitably saturated in water vapor previously, and means for the exit of the gas stream totally or partially discharged from said or said biodegradable contaminants. The biofilter is also preferably provided with irrigation means to periodically provide nutrients to the microorganisms. Optionally, if desired, devices can be included to measure the inlet temperature of the gas stream containing the biodegradable contaminants to be treated since it can affect the metabolic process of microorganisms capable of degrading said biodegradable contaminants, or to measure the pH since during the operation of the biofiltration method provided by this invention acid products can be generated that can adversely affect the activity of the biofilter. Additionally, load loss meters can be included, since excess biomass can fill up and render the biofiltration system useless. The biofilter of the invention can be designed in various shapes and dimensions, using the appropriate materials for it.

The structural simplicity of the biofilter of the invention facilitates the design of bioreactors containing one or more biofilters of the invention. Thus, in a particular embodiment, the invention contemplates the development of a bioreactor comprising a single biofilter of the invention, while, in another particular embodiment, the invention contemplates the development of a bioreactor comprising two or more biofilters of the invention, for example, 2, 3, 4 or even more, operatively connected in series, so that the gaseous outflow of the first of said biofilters of the invention is introduced into the second of the biofilters of the invention, and, similarly , the gaseous outflow of said second biofilter of the invention is introduced into the third of the biofilters of the invention, and so on until the definitive exit of the gaseous stream totally or partially discharged from biodegradable contaminant. Biofiltration method of the invention

The biofilter of the invention can be used to purify gases contaminated with one or more biodegradable contaminants by biofiltration. Therefore, in another aspect, the invention relates to a method for purifying a gas stream containing at least one biodegradable gaseous pollutant by biofiltration, hereinafter "biofiltration method of the invention", which comprises passing said gas stream containing at least one biodegradable gaseous pollutant through a biofilter of the invention, that is, a biofilter comprising black arc furnace slag (EAFS) as filler material and microorganisms capable of degrading said biodegradable pollutant.

In the sense used in this description, the expression "purifying a gaseous stream containing at least one biodegradable gaseous pollutant" includes both the virtually total elimination of the biodegradable gaseous pollutant (or pollutants) present in a gaseous stream containing said pollutant as reducing the amount of said biodegradable gaseous pollutant (or pollutants) present in a gaseous stream that contains said pollutant to levels permitted by legislation or that are not harmful to human or animal health and / or the environment.

The term "biodegradable", as used herein, refers to a chemical compound that can be decomposed by the action of biological agents, for example, a microorganism, etc. Therefore, a "biodegradable gaseous pollutant" is a chemical compound considered as a pollutant, in a gaseous state, which can be decomposed by the action of biological agents, for example, a microorganism. Illustrative, non-limiting examples of biodegradable gaseous pollutants include volatile organic compounds (VOCs), hydrogen disulfide (H ₂ S), carbon sulphide (CS ₂ ), etc.

The biofiltration method of the invention can be used to purify a gaseous stream contaminated with one or more biodegradable gaseous pollutants. In a particular embodiment, the biofiltration method of the invention is used to purify a gaseous stream contaminated with a single gaseous pollutant. biodegradable. In another particular embodiment, the biofiltration method of the invention is used to purify a gaseous stream contaminated with two or more biodegradable gaseous pollutants.

Although practically the biofiltration method of the invention can be used to purify a gaseous stream contaminated with any biodegradable gaseous pollutant, that is, with any gaseous pollutant that can be decomposed by the action of a biological agent, such as a microorganism capable of degrading said Gaseous pollutant, in a particular embodiment, said biodegradable gaseous pollutant is selected from the group consisting of VOCs, H ₂ S, CS ₂ , and any combination thereof. Therefore, in a particular embodiment, said polluted gaseous stream to be purified comprises one or more VOCs. In another particular embodiment, said contaminated gas stream to be purified comprises H ₂ S. In another particular embodiment, said contaminated gas stream to be purified comprises CS ₂ . In another particular embodiment, said polluted gaseous stream to be purified comprises one or more VOCs, and a biodegradable gaseous pollutant selected from H ₂ S and CS ₂ . In another particular embodiment, said polluted gas stream to be purified comprises at least one biodegradable gaseous pollutant selected from H ₂ S and CS ₂ , and, optionally, one or more VOCs. In another particular embodiment, said polluted gas stream to be purified comprises one or more VOCs, H ₂ S and CS ₂ .

In a particular embodiment, the biofiltration method of the invention comprises performing a previous step of inoculating the EAFS (biofilter filler material of the invention) with microorganisms capable of degrading the biodegradable contaminant (s) to be treated, with the aim of forming a biofilm of said microorganisms on the biofilter filler material of the invention that enables the purification of the contaminated gaseous stream to be purified. The inoculation of the EAFS can be carried out directly with microorganisms capable of degrading the standardized biodegradable pollutant (s) or pollutants (s), or with an inoculum obtained preliminary by acclimatization of a given biomass to the contaminant or contaminants to be treated. Said acclimatization can be carried out in any suitable installation, for example, in the biofilter of the invention itself, or, alternatively, in a laboratory or in a plant pilot, using a continuous or discontinuous acclimatization reactor. In general, acclimatization comprises contacting a biomass rich in microorganisms, such as biological sludge from a wastewater treatment plant (WWTP), with a gaseous stream containing the biodegradable pollutant (s) to treat, so that an optimal population of microorganisms capable of degrading said contaminant (s) is developed. The amount of biodegradable gaseous pollutant (s) present in said gaseous stream can vary within a wide range; however, in practice it is usually started using a gaseous stream containing the biodegradable pollutant (s) to be treated in a relatively low amount, generally equal to or less than 100 parts per million by volume (ppmv) [ 1 ppmv = 1 μg x mi ^-1 ], typically between 25 and 100 ppmv. The amount of biodegradable gaseous pollutant (s) present in said gaseous stream can be increased, if desired, as the acclimatization of the microorganisms to said biodegradable gaseous pollutant (s) increases ( s). The person skilled in the art can generate, by conventional methods, gaseous streams containing different concentrations of pollutant or biodegradable pollutant (s) to be analyzed, and select the one that provides a better acclimatization of the microorganisms present in the biological medium chosen at pollutant or contaminants. Likewise, flows of said gaseous stream that provide a residence time [in English, "EBRT" (empty bed residence time), which relates the flow of the gaseous stream with the size of the biofilter according to the formula EBRT = V _f / Q, where V _f is the volume of the empty biofilter and Q is the flow rate of the gas stream, and gives an idea of the treatment time] equal to or less than 3 minutes, typically, approximately 2 to 3 minutes, are usually adequate during the stage acclimatization The conditions for acclimatizing the microorganisms initially contained in the biomass to said biodegradable pollutant (s) or pollutants (s) depend, in general, on various factors, for example, on the biodegradable gaseous pollutant or pollutant content (s) (s) in the gas stream used, residence time, duration of treatment, etc. During this stage of previous acclimatization, as during the biofiltration itself, it may be necessary to provide a nutrient solution in order to favor Metabolism of microorganisms capable of degrading said pollutant (s) or biodegradable gaseous pollutant (s). The contribution of said nutrient solution can be carried out by irrigation in the case of acclimatization in the biofilter or by addiction / replacement to the liquid medium in the case of acclimatization in an acclimatization reactor.

In order to accelerate the biofilter startup, it is preferred that the acclimatization takes place outside the biofilter itself, and, in particular, in a continuous acclimatization system. In this sense, although the conditions for acclimatization can vary widely, in a particular embodiment, said acclimatization comprises the bubbling on a liquid medium rich in microorganisms in constant agitation (for example, a sludge from an WWTP) of a gas stream comprising one or more biodegradable gaseous pollutants in an amount equal to or less than about 100 ppmv, typically between 25 ppmv and 100 ppmv, continuously, with a flow rate that provides a residence time equal to or less than 3 minutes, typically between 2 and 3 minutes approximately, for at least 30 days, preferably for approximately 60 days. A particular embodiment of a continuous acclimatization system for obtaining inoculum for starting the biofilter of the invention provided with: (1) gaseous current inlet, (2) sampling point, (3) is shown in Figure 1. liquid medium under stirring, (4) sampling point and (5) gaseous current outlet.

Once the microorganisms capable of degrading said biodegradable pollutant (s) have been developed, a "activated" liquid medium is obtained, that is, a liquid medium containing the microorganism or microorganisms capable of degrading the contaminant or biodegradable gas contaminants (s) in question, which is used to inoculate the SAIs. Preferably, the inoculation is carried out in the biofilter itself, previously loaded with the filler material, for example, by irrigation with said "activated" liquid medium. After successive irrigation, the biofilm of microorganisms is formed, so that the biofilter is now ready for the purification of gaseous streams contaminated with the biodegradable pollutant (s) in question. In a variant of the invention, it is contemplated that the acclimatization process initiated outside the biofilter continues in the biofilter itself. To do this, after inoculating the biofilter previously loaded with filler material, it is fed for a short period (typically 2 weeks) with currents with low pollutant concentrations, normally not exceeding 100 ppmv.

In another alternative embodiment, it is contemplated that the entire acclimatization process takes place in the biofilter itself. Thus, the watering of the filler material contained in the biofilter with a liquid medium that presents various populations of microorganisms, such as biological sludge from an WWTP, together with the passage of a gas stream containing at least one biodegradable gaseous pollutant, preferably in a relatively low amount also leads to the formation of the biofilm of microorganisms on the filler material, responsible for purification.

Various acclimatization strategies useful in conventional biofilters are described in the prior art [Elias, A. et al. (2010). J. Air & Waste Manage. Assoc. 60: 959-967].

The biofiltration method of the invention comprises passing said gas stream containing at least one biodegradable gaseous pollutant through a biofilter of the invention. The amount or concentration of biodegradable pollutant (s) or pollutant (s) present in said gaseous stream to be purified may vary within a wide range. However, in a particular embodiment, said gaseous stream to be purified contains at least one biodegradable gaseous pollutant in an amount between about 50 ppmv and about 250 ppmv. Since the contaminated gaseous stream to be purified may contain one or more biodegradable gaseous pollutants, in the present invention, unless otherwise indicated, the amounts or concentrations of biodegradable gaseous pollutant expressed refer to total amounts or concentrations of biodegradable gaseous pollutant. , so that if there is more than one biodegradable gaseous pollutant in the polluted gaseous stream to be purified, the total amount or concentration results from the sum of the amounts or concentrations of each of them. Also, the residence time, or average amount of time that the gaseous stream can remain that contains at least one biodegradable gaseous pollutant to be cleaned in contact with the filler material (EAFS) of the biofilter of the invention can vary over a wide range. . However, in a particular embodiment, said residence time is between about 10 seconds and about 80 seconds, typically about 60 seconds. By measuring the concentration of the biodegradable gaseous pollutant (s) in question at the exit of the biofilter of the invention, the operation of the filler material and the microorganisms capable of degrading said gaseous pollutant (s) can be checked ( s) biodegradable (s), so that, if the effectiveness of the biofilter declines, take appropriate measures to increase the effectiveness, for example, watering the filler material with a nutrient solution, as mentioned below. , to recover normalcy.

The gaseous stream containing at least one biodegradable gaseous pollutant to be purified by the biofiltration method of the invention can come from various pollutant sources, for example, from process facilities that use or generate said pollutants, such as fiber manufacturing facilities. of cellulose, synthetic wrap food industry, pharmaceutical industry, chemical industry, paint manufacturing, etc.

In practice, it is convenient that the gas stream containing at least one biodegradable pollutant gas to be purified is moist, or saturated in water vapor, since the humidity of said gas stream contributes to the proper development of the microorganisms present in the Biofilter filler material of the invention. Therefore, in a particular embodiment, the biofiltration method of the invention comprises a step of humidifying the gas stream containing at least one biodegradable pollutant to be purified, for which said gas stream is contacted with an aqueous medium. , for example, water, before being introduced into the biofilter. The aqueous medium used in this stage may be present in a humidification system, such as, for example, one or more columns of aqueous medium (eg, water), which yields (n) to the gas stream containing at least one contaminant. biodegradable gas the necessary humidity, located before of the biofilter. In a particular embodiment, said humidification system comprises a single column of aqueous medium (eg, water); in another particular embodiment said humidification system comprises at least two, for example, 2, 3, 4 or even more, columns of aqueous medium (eg, water), in order to guarantee a correct saturation of the gas stream containing the less a biodegradable gaseous pollutant to purify and minimize system maintenance. In a particular embodiment, the relative humidity of the gas stream containing at least one biodegradable gaseous pollutant entering the biofilter of the invention is equal to or greater than 70%, usually equal to or greater than 80%, advantageously equal to or greater than 90% , preferably equal to or greater than 95%, even more preferably equal to or greater than 99%.

During the biofiltration process, the gaseous stream containing at least one biodegradable pollutant to be purified passes through the filler material that supports the growing microorganisms capable of degrading said gaseous pollutant (s). biodegradable (s). The degradation of said pollutant (s) occurs, in general, after transferring the gas stream containing at least one biodegradable gaseous pollutant to a liquid medium where it is used as a source of carbon and / or energy. The use of said contaminant implies a series of chemical reactions that lead to the decomposition or degradation of the contaminant, for example, to its partial or total oxidation, as well as the production of biomass capable of degrading said contaminant (s), with what the biofiltration method of the invention results in a practically complete degradation of the biodegradable pollutant or gaseous pollutants (s) generating non-hazardous (harmless) products for human or animal health and / or the environment and a current Total or partially discharged gas in said pollutant (s) or biodegradable gaseous pollutant (s).

The person skilled in the art will understand that the biofiltration method of the invention includes the possibility of passing the gas stream containing at least one biodegradable gaseous pollutant through one or more biofilters of the invention. Thus, in a particular embodiment, the biofiltration method of the invention comprises passing the gaseous stream containing at least one biodegradable gaseous pollutant to be purified through a single biofilter of the invention. In other Particular embodiment, the biofiltration method of the invention comprises passing the gas stream containing at least one biodegradable gaseous pollutant to be purified through two or more biofilters of the invention, for example 2, 3, 4, or even more, operationally connected to each other; in this case, the gaseous stream containing at least one biodegradable pollutant to be purified is passed through the first of the biofilters of the invention and the gaseous outlet of said first biofilter of the invention, which will be at least partially discharged in said biodegradable gaseous pollutant (s), it is passed through the second biofilter of the invention, and, similarly, the gaseous outflow of said second biofilter of the invention, which it will be even more discharged in said biodegradable gas contaminant (s), is passed through the third biofilter of the invention, and so on until the final exit of the total or partially discharged gas stream from said biodegradable gaseous pollutant (s). Therefore, the biofiltration method of the invention allows to achieve an efficiency of elimination of said biodegradable pollutant (s) of 100%, or very close to 100%, in relation to the amount of said biodegradable gaseous pollutant (s) present in the gaseous stream containing at least one biodegradable gaseous pollutant to be purified.

During the realization of the biofiltration method of the invention, the stable operation of the biofilter of the invention may require irrigation of the filler material with a nutrient solution. Appropriate macronutrients must contain N, P, K, completed to a lesser extent with micronutrient elements such as Fe or Ni, among others [Barona, A., et al. (2007). Additional determinations in a potential support material for toluene biofiltration: adsorption and partition in the nutrient solution. Chem. Biochem. Eng. Q. 21 (2): 151-157]. In a particular embodiment, the nutrient solution contains 100 mg of KH ₂ P0 ₄ , 400 mg of K ₂ HP0 ₂ , 27 mg of MgS0 ₄ -7H ₂ 0, 10 mg of CaS0 ₄ -2H ₂ 0, 10 mg of FeS0 ₄ 7H ₂ 0 and 500 g of (NH ₄₎ ₂ S0 ₄ in 1 L of water; an amount of 5 was added ³ micronutrient solution containing 2 g / dm ³ of FeCl ₂ -4H ₂ 0, 2 g / dm ³ of CoCl ₂ -6H ₂ 0, 0.5 g / dm ³ of MnCl ₂ -4H ₂ 0.60 mg / dm ³ of CuCl ₂ , 50 mg / dm ³ of ZnCl ₂ , 50 mg / dm ³ of H ₃ B0 ₃ , 2 g / dm ³ of HC0 ₃ Na, 90 mg / dm ³ (ΝΗ ₄₎ ₆ ₇ 0 ₂₄ · Μο 4Η ₂ 0, 1 g / dm ³ etilentetraaminodiacético acid (EDTA), 0, 1 g / dm ³ of Na ₂ SE0 _3, 50 mg / dm ³ of NiCl ₂ -H ₂ 0. In addition to providing nutrients to promote metabolism (growth and maintenance) of microorganisms capable of degrading the biodegradable gas contaminant (s) to be treated, with such irrigation the buffering (buffer effect) of the pH of the biofilm where the microorganisms reside is favored and carry potential degradation intermediates (acids) generated as unwanted by-products of the degradation reaction of said biodegradable gas contaminant (s). In any case, the good pH regulating characteristics as well as the good characteristics for retaining moisture by the SAIs used as a biofilter filler material used in the biofiltration method of the invention minimize the need for watering very continuous Although the period of time between two consecutive irrigations may vary within a wide range, depending on numerous factors (eg, need to provide nutrients, need to moisten the support, etc.), in a particular embodiment, the period of time between two consecutive waterings is between approximately 1 and 5 days, typically between approximately 1 and 2 days.

Although during the operation of the biofiltration method of the invention, carbon dioxide / carbonic acid could be generated, for example, when the biodegradable gaseous pollutant comprises a VOC, in practice, in general, it is not necessary to use additional reagents to neutralize said acid. from the oxidation of said contaminants.

On the other hand, the generation of leachate associated with the implementation of the biofiltration method of the invention is minimal and, in general, of little or no environmental impact, so it is not necessary to perform any management with said leachate.

Tests carried out by the inventors on a continuous basis have shown that the SAIs used in the preparation of the biofilter filler material used in the biofiltration method of the invention, due to their good physical-chemical characteristics, do not suffer deterioration (or erosion) significant after more than 12 months of operation and is expected to reach even 10 years. Therefore, the present invention provides a stable and durable method for the purification (elimination or reduction of the amount) of one or more gaseous pollutants. biodegradable contained in a gas stream containing said contaminant (s).

An illustrative scheme of a particular embodiment of the biofiltration method of the invention is shown in Figure 2, in which it can be seen that a moistened (eg, saturated with moisture) gas stream containing at least one biodegradable gaseous pollutant is passed, for example, one or more VOCs, H ₂ S, CS ₂ , etc., or combinations thereof, through the filler material contained in the biofilter of the invention wherein said gaseous pollutant (s) (s) ) biodegradable (s) is / are degraded by microorganisms capable of degrading said contaminant (s). Briefly, a gaseous stream containing at least one biodegradable gaseous pollutant (2) from a pollutant source (1) is introduced into a humidification system (3) containing water in order to moisten said gaseous stream containing at least one biodegradable gaseous contaminant before entering a bioreactor (5). The moistened gaseous stream containing at least one biodegradable gaseous pollutant (4) is introduced into said bioreactor (5) which contains 2 biofilters of the invention (6a and 6b); each of which comprises a filler material and microorganisms capable of degrading said biodegradable gaseous contaminant (s), wherein said filler material comprises EAFS. The 2 biofilters of the invention (6a and 6b) are arranged vertically and operatively connected to each other so that the output current of the first biofilter (6a) feeds the second biofilter (6b) from which the practically discharged gas stream from said ( s) biodegradable gas contaminant (s) (7). If necessary, the nutrients contained in the irrigation system (8) are supplied to the biofilters of the invention by irrigation in order to maintain the metabolism of microorganisms capable of degrading said gaseous pollutant (s) (s) biodegradable (s).

Installation of the invention

The biofiltration method of the invention can be carried out in a suitable installation comprising at least one biofilter of the invention, that is, a biofilter comprising black electric arc furnace slag (EAFS) as filler material and microorganisms capable of degrading the biodegradable pollutant or gaseous pollutants to be eliminated, such as VOCs, H ₂ S, CS ₂ , etc. Said installation, hereinafter "installation of the invention", constitutes an additional aspect of this invention.

The installation of the invention may contain one or more biofilters of the invention. Thus, in a particular embodiment, the installation of the invention comprises a single biofilter of the invention. In another particular embodiment, the installation of the invention comprises two or more biofilters of the invention, for example, 2, 3, 4, or even more, operatively connected to each other (in series); in this case, the gas stream containing at least one biodegradable gaseous pollutant (eg, one or more VOCs, H ₂ S, CS ₂ , etc., or combinations thereof) to be purified is passed through the first biofilter of the invention and the gaseous outflow of said first biofilter of the invention is passed through the second biofilter of the invention, and, similarly, the gaseous outflow of said second biofilter of the invention is passed through of the third biofilter of the invention, and so on until the definitive exit of the total or partially discharged gas stream of said biodegradable gas contaminant (s).

The modular design of the installation of the invention allows the biofilters of the invention further away from the entrance of the gaseous stream containing at least one biodegradable gaseous pollutant to receive very low concentrations of said gaseous pollutant (s). biodegradable (s) but sufficient for the adaptation of microorganisms capable of degrading said gaseous pollutant (s) biodegradable (s). Likewise, the modular design allows biodegradation of said biodegradable gaseous pollutant (s) in the first biofilter of the invention while the remaining biofilters can act as a reserve, which guarantees the efficiency of the system even with sudden increases in pollutant load.

The installation of the invention advantageously includes, if desired, a humidification system, such as, for example, one or more columns of aqueous medium (eg, water), which yields (n) to the gas stream containing at least a biodegradable gaseous pollutant the necessary moisture, located before the biofilter of the invention. Additionally, the installation of the invention includes suitable means for transporting the gas stream to be purified, and, if desired, a source of nutrients in case it is necessary to contribute to the biofilter of the invention to maintain the metabolism of microorganisms capable of degrading said Biodegradable gaseous contaminant (s) present in the biofilter of the invention.

Likewise, if desired, the installation of the invention may include means for measuring and / or controlling the inlet temperature to the biofilter of the invention of the gas stream containing at least one biodegradable gaseous pollutant to be purified, means for measuring the pH in inside the biofilter, and means for measuring the amount of biodegradable gaseous pollutant (s) present in the gaseous outflow of the biofilter of the invention.

The installation of the invention, in addition to at least one biofilter of the invention, may contain one or more different biofilters in which the biofilter filler material is not EAFS but another material of an inorganic nature or of an organic nature for example, compost , peat, acid peat, pine bark, a mixture of compost, sawdust and perlite, or a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70% by weight of animal waste, and (ii ) 70-30% by weight of plant waste.

The following example illustrates the invention and should not be considered in a limiting sense thereof.

EXAMPLE 1

Design of a toluene biofiltration system

Figure 2 shows a schematic representation of an installation suitable for the implementation of the biofiltration method of the invention. As can be seen, said installation basically consists of a humidification system (3) and a bioreactor (5) containing 2 biofilters (6a and 6b), placed vertically, with an approximate total volume of 4.5 L, built in polyvinyl chloride (PVC) and with downward gas flow; the biofilters (6a and 6c) are operatively connected to each other and, inside, is the filling material comprising EAFS, which acts as a support material on which the biomass (microorganisms) responsible for the degradation of toluene (biodegradable gaseous pollutant contained in the polluted gaseous stream to be purified) is developed.

The inoculum was obtained from the biological sludge of a wastewater treatment plant (WWTP). The acclimatization process of the biomass contained in the mud was carried out in an acclimatization reactor built in PVC

4.5 L), as shown in Figure 1. In this initial stage of acclimation, feeding with gaseous streams containing toluene, with toluene concentrations between 25 and less than 100 ppmv, and, with residence times of approximately 3 minutes, which bubbled over the sample of sludge while stirring, it was possible to obtain, after about 30 days, the liquid medium necessary for the inoculation of the black slag of electric arc furnace (EAFS).

The EAFS was introduced into the modular bioreactor (Figure 2) and irrigated with the acclimatized inoculum, forming a biofilm containing the active biomass, that is, the microorganisms capable of degrading toluene.

The utility of the system was evaluated with a gas stream with a toluene content of approximately 50-150 ppmv. With this current the efficiency of the treatment of purification of toluene was greater than 90% for residence times of approximately 60 s. The maintenance of moisture in the biofilter filler material (EAFS) was achieved by daily irrigation with the nutrient solution required for active biomass metabolism.

The purification process of said gaseous stream containing toluene as a pollutant did not generate leachates in the system, which eliminated the need for subsequent treatment.

Claims

1. A fixed bed biofilter comprising black electric arc furnace slag (EAFS) as filler material.

2. Biofilter according to claim 1, further comprising microorganisms capable of degrading at least one biodegradable gaseous pollutant.

3. Biofilter according to claim 2, wherein said biodegradable gaseous pollutant is selected from the group consisting of volatile organic compounds (VOCs), hydrogen disulfide (H ₂ S), carbon sulfide (CS ₂ ), and any combination thereof. same.

4. An installation comprising at least one biofilter according to any one of claims 1 to 3.

5. A method for purifying a gaseous stream containing at least one biodegradable gaseous pollutant by means of biofiltration comprising passing said gaseous stream containing at least one biodegradable gaseous pollutant through a biofilter according to claim 1, said biofilter, in addition to black arc furnace slag (EAFS) as filler material, microorganisms capable of degrading said at least one biodegradable gaseous pollutant.

6. The method of claim 5, wherein said biodegradable gaseous pollutant is selected from the group consisting of volatile organic compounds (VOCs), hydrogen disulfide (H ₂ S), carbon sulphide (CS ₂ ), and any combination thereof. same.

7. A method according to claim 5 or 6, wherein said gas stream contains at least one biodegradable gaseous pollutant in an amount between about 50 parts per million by volume (ppmv) and about 250 ppmv.

A method according to any one of claims 5 to 7, wherein the flow rate of said gaseous stream containing at least one biodegradable gaseous pollutant is selected such that the residence time is between about 10 s and about 80 s.

9. A method according to claim 5, comprising prior inoculation of the biofilter filler material with microorganisms capable of degrading at least one biodegradable gaseous pollutant.

10. The method according to claim 9, wherein said inoculation comprises the previous acclimation of a sample of a biological sludge.

11. The method according to claim 10, wherein said biological sludge sample is from a wastewater treatment plant (WWTP).

12. A method according to any of claims 10 or 11, wherein said acclimatization comprises the treatment of biological sludge with a gaseous stream containing at least one biodegradable gaseous pollutant in an amount equal to or less than about 100 ppmv, continuously, with a flow rate that provides a residence time equal to or less than 3 minutes, for at least 30 days.

13. Use of black arc furnace slag (EAFS) as a biofilter filling material for biofiltration in fixed bed systems of gaseous streams contaminated with at least one biodegradable gaseous pollutant.