WO2012056081A1 - Biofilter and biofiltration-based method for the purification of a gas stream containing carbon disulfide - Google Patents

Abstract

The invention relates to a biofilter comprising a filler material and microorganisms capable of degrading CS₂, in which the filler material comprises a compost that can be obtained by means of the aerobic-anaerobic decomposition of a mixture containing (i) 30-70 wt.-% animal waste and (ii) 70-30 wt.-% plant waste. The invention also relates to a method for purifying a gas stream containing CS₂ by means of biofiltration, in which the gas stream is made to pass through said biofilter.

Description

 BIOFILTER AND METHOD TO CLEAN THROUGH A BIOFILTRATION A GASEOUS CURRENT CONTAINING CARBON DISULFIDE

FIELD OF THE INVENTION

The present invention relates, in general, to the purification of gases contaminated with a contaminant, and, in particular, with a bio filter to eliminate or reduce the content of carbon disulfide (CS ₂ ) present in a gas stream contaminated by that compound, as well as with the corresponding bio filtration method.

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. Specifically, carbon disulfide (CS ₂ ), a volatile, colorless and very easily flammable liquid, constitutes a highly dangerous pollutant due mainly to its harmful effects on human health. Prolonged exposure to carbon sulfide vapors causes symptoms of intoxication ranging from redness 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.

Therefore, it has been necessary to develop processes aimed at controlling the emission of said pollutant (CS ₂ ) 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 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 CS ₂ .

Over the past few years, biological technologies for cleaning contaminated gas streams have gained strength as an alternative to physicochemical technologies, since they are cleaner and more economical processes, which eliminate many of the disadvantages associated with physical systems. traditional chemicals, and are especially useful when the flow rates to be treated are large and the concentrations of pollutants (eg, CS ₂ ) are low.

 Biological gas stream purification systems can be classified into three main groups: biolavadores ("bioscrubber"), drained bed bioreactors ("biotrickling") and fixed bed biofilters [Delhomenie, MC. et al. 2005. Biofiltration of Air: A Review. Critical Reviews in Biotechnology, 25: 53-72].

The biolavadores ("bioscrubber") constitute a technology of treatment in two stages. In the first, the contaminated gas comes into contact with a liquid phase that absorbs the contaminants. After the contaminants have been absorbed, the liquid is treated by a traditional biological process (for example, by an activated sludge process). Biolavadores have as their main drawback their inability to treat poorly soluble compounds, so they are not good candidates in the case of CS ₂ .

Drained bed bioreactors ("biotrickling filters") require the continuous feeding of a liquid medium onto a bed of inorganic support material (eg, polyethylene, polypropylene, PVC or lava rock). This technology is mainly controlled by the mass transfer between the gas phase and the liquid phase, which is a disadvantage because the gaseous CS ₂ is very poorly soluble in water. Another disadvantage associated with continuous liquid feeding consists in obtaining a liquid medium that must be properly managed. In addition, the inorganic nature of the support material forces the system to be inoculated with the appropriate biomass for biodegradation. US patents US 4968622, US 5747331 and US 5236677 describe drained bed bioreactors for the biological degradation of CS ₂ . Biofilters ("fixed bed bioreactors") constitute, in Europe, the most used biological gas treatment technology for the elimination of odors and volatile organic compounds (VOCs) and sulphides (VSCs). 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. Basically, biofilters 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.

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. In the specific case of CS ₂ , degradation occurs according to the following sequence of reactions [Smith, NA et al. (1988). Oxidation of carbon disulphide as the solé source of energy for the autotrophic growth of Thiobacillus thioparus strain TK-m. J. Gen. Microbiol, 134: 3041-3048]:

1. S = C = S + H ₂ 0 → 0 = C = S + H ₂ S

2. 0 = C = S + H ₂ 0 → C0 ₂ + H ₂ S

3. H ₂ S + 20 ₂ → H ₂ S0 ₄ + Energy

Other authors, Revah et al. [Revah et al. (1994). Air biodesulphurisation in process plants. In: Bioremediation: The TOKYO '94 Workshop, OECD Publishing, Paris] and Alcántara et al. [Alcantara et al. (1999) Carbon disulfide oxidation by a microbial consortium from a tricking filter. Biotechnol Lett., 21: 815-819] propose other additional intermediate steps in the subsequent degradation of hydrogen sulfide:

S + H ₂ 0 + 3/2 0 ₂ ^ H ₂ S0 ₄

In spite of the different configurations of the biological reactors, the biomass or population of microorganisms capable of degrading the contaminant constitutes, in all cases, a decisive element for the effective functioning of the system. Its biodiversity depends on the composition of the fed gas, the bed. support and, in general, environmental conditions. Microorganisms capable of degrading CS ₂ are not as abundant as microorganisms capable of degrading other pollutants (eg, hydrogen sulfide (H ₂ S)), possibly due to the fact that CS ₂ possesses fungicidal properties since the breakage of its double bonds require more energy [Yang, Y. et al. (1997). Biofiltration for control of carbon disulfide and hydrogen sulfide vapors, for presentation at the "Air and waste management association's 90th annual meeting &exhibition", Toronto, Canada]. In fact, as the following list reflects, the number of strains capable of degrading CS ₂ is very limited:

Thiobacillus TJ330 [Hartikainen, T. et al. (2000). Physiology and taxonomy of Thiobacillus strain TJ330, which oxidizes carbon disulphide (CS ₂ ). J. Appl.

Microbiol 89: 580-586];

 Thiothrix ramosa [Odintsova, E.V. et al. (1993). Chemolithoautotrophic Growth of Thiotrix Ramosa. Archives of Microbio logy, 160: 152-157];

 - an unidentified strain of the Thiobacillus species [Pías, C. et al. (1993).

 Degradation of carbon disulphide by a Thiobacillus isolate. Appl. Microbiol

Biotechnol 38: 820-823];

 Thiobacillus thioparus TK [Smith, N.A. et al. (1988). Oxidation of carbon disulphide as the solé source of energy for the autotrophic growth of Thiobacillus thioparus strain TK-m. J. Gen. Microbiol. 134: 3041-3048];

 - Paracoccus denitrificans KS1, KS2 and KS2 [Jordán, S.L. et al. (nineteen ninety five). Novel eubacteria able to grow on carbon disulfide. Arch. Microbiol. 163: 131-137; Jordán, S.L. et al. (1997). Autotrophic growth on carbon disulfide is a property of novel strains of Paracoccus denitrificans. Arch. Microbiol. 168: 225-236];

Thioalkalivibrio [Sorokin, D.Y. et al. (2001). Thioalkalimicrobium aerophilum gene. nov., sp. Nov. and Thioalkalimicrobium sibericum sp. nov., and

Thioalkalivibrio versutus gen. nov., sp. Nov., Thioalkalivibrio nitratis sp. Nov. and Thioalkalivibrio denitrificans sp. Nov., novel obligately alkaliphilic and obligately chemolithoautotrophic sulfur-oxidizing bacteria from soda lakes. Int. J. Syst. Evol Microbiol 51: 565-580]; Y

- Thiomonas [Pol, A. et al. (2007). Isolation of a carbon disulfide utilizing Thiomonas sp. and its application in a biotrickling filter. Appl. Microbiol Biotechnol 74: 439-446].

 On the other hand, the nature of the support material of the microorganisms is also a fundamental factor for the proper functioning of the bioreactors, since it influences both the ability to eliminate the contaminant and the cost of the system. The ideal support should meet various characteristics such as, for example, having a high moisture and biomass retention capacity, a high contact surface, a suitable bed porosity (to avoid load losses and system collapse), low economic cost , long life time, etc. In addition, once exhausted, it should be easy to manage to avoid generating an added problem.

 Although biofilters with specially designed inorganic supports have been described, the use of supports of an organic nature provides several advantages, among which it is worth noting the possibility of containing indigenous biomass (bacteria, fungi, protozoa, algae, etc.) and nutrients, although, on the other hand, this type of supports undergoes greater degradation over time than some of the synthetic materials. Among the naturally occurring support materials of biofilters are compost [Yang, Y. et al. (1994). Oxidative destruction of carbon disulfide vapors using biofiltration In: Air & Waste Management Association's 87th Annual Meeting & Exhibition, Cincinnati, Ohio], peat [Hartikainen, T. et al. (2001). Carbon Disulfide and Hydrogen Sulfide Removal with a Peat Bio filter. J Air & Waste Manag. Assoc, 51: 387-392], acid peat [US 5747331], pine bark or a mixture of compost, sawdust and perlite [Vaith, K. et al. (1997). Comparison of Biofilter Performance for Hydrogen Sulfide, Methyl Mercaptan, Carbon Disulfide, and Dimethyl Disulfide Removal. In proceedings of Control of odors and VOC emissions specialty conference, Houston].

Many of the gas stream biofiltration systems containing CS ₂ proposed to date require a previous stage of inoculation of the support material with logically pure microbe cultures of microorganisms capable of degrading CS ₂ to make the system degrade CS ₂ . Other limitations of known CS ₂ biofiltration systems, which complicate their operation and increase the cost associated with them, include the requirements related to maintenance (pH adjustment, reagent consumption, irrigation, etc.) as well as the deterioration of the support material.

Therefore, there is still a need to find alternative methods for treating gaseous streams contaminated with CS ₂ , simple and reliable, which, preferably, solve at least some of the problems of the biofiltration methods of gaseous streams contaminated with CS ₂ described in the state of the art

SUMMARY OF THE INVENTION

The authors of the present invention have developed a fixed bed biofiltration method to efficiently purify (eliminate / reduce) the amount of CS ₂ present in a gaseous stream contaminated with said compound (CS ₂ ). Said method, based on the use as filler material of the biofilter of a product commonly used as compost, provides several advantages over traditional methods and other biological methods described in the state of the art, mainly due to its physical characteristics. -chemistry.

Thus, in one aspect the invention relates to a biofilter comprising a filler material and microorganisms capable of degrading CS ₂ , wherein said filler material comprises 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.

In another aspect the invention relates to a method for purifying a gas stream containing CS ₂ by biofiltration comprising passing said gas stream containing CS ₂ through said biofilter.

In another aspect the invention relates to an installation for the purification of a gaseous composition comprising CS ₂ comprising at least one of said bio filters.

In another aspect, the invention relates to a method for acclimatizing to CS ₂ microorganisms capable of degrading CS ₂ contained in a compost, wherein said compost is obtainable by aerobic-anaerobic decomposition of a mixture that It comprises (i) 30-70% by weight of animal waste, and (ii) 70-30%> by weight of plant waste, which comprises contacting said compost containing microorganisms capable of degrading CS ₂ with a gaseous stream that it comprises CS ₂ in an amount less than about 100 ppmv, with a residence time of less than about 120 seconds, continuously, for at least 100 days.

In another aspect, the invention relates to a method for generating a population of microorganisms capable of degrading CS ₂ which comprises combining: a) a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70%) in weight of animal waste and (ii) 70-

30% by weight of vegetable waste, comprising microorganisms capable of degrading CS ₂ CS ₂ acclimatized by the method defined above acclimation (acclimatized compost), with

 b) a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70%> by weight of animal waste and (ii) 70-

30% or by weight of vegetable waste (fresh compost),

in a proportion (acclimatized compost): (fresh compost) between approximately 1: 1 and approximately 5: 1, by weight.

BRIEF DESCRIPTION OF THE FIGURES

 Figure 1 is a photograph showing 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 , in the form of pellets.

Figure 2 is a schematic representation of a particular embodiment of an installation suitable for the implementation of the CS ₂ biofiltration method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

 Bio filter of the invention

In one aspect, the invention relates to a biofilter of carbon disulfide (CS ₂ ), hereinafter "biofilter of the invention", which comprises a filler material and microorganisms capable of degrading CS ₂ , wherein said filler material comprises 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. Said biofilter of the invention can be used to purify gases contaminated with CS ₂ by bio filtration, that is, to reduce the amount of, or eliminate, the amount of CS ₂ present in a gaseous stream containing CS ₂ .

The filler material present in the biofilter of the invention comprises a product of an organic nature, in particular, a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising from 30%> to 70%> by weight of animal waste and of the 70%> to 30%> by weight of plant waste. Illustrative, non-limiting examples of animal residues suitable for the production of compost used in the biofiltration method of the invention, include pig purines, poultry residues, cattle residues, etc., and combinations thereof. Illustrative, non-limiting examples of plant residues include leaves, branches, pieces of wood, sawdust, etc., and combinations thereof. The authors of the present invention have found that a product commonly used for agricultural purposes (fertilizer) can also be used advantageously as filler material (filter material) in a CS ₂ biofilter due, among other reasons, to its characteristics physicochemical such as, for example, high moisture retention capacity, high porosity, high contact surface, good ability to regulate pH, adaptable and diverse biomass, low investment cost and long duration (mechanically resistant and chemically inert and stable). Said filler material (compost) of the biofilter of the invention serves as support for microorganisms capable of degrading CS ₂ and provides the necessary nutrients for the metabolism of said microorganisms capable of degrading CS ₂ although, at times, it may be necessary to make a contribution additional nutrients for the maintenance and growth of the microorganisms present in said filler material.

The compost used as filler material of the biofilter of the invention can be used without compacting, that is, in the form of more or less loose granules of different granulometry, or, advantageously, in compacted form. In a particular embodiment, said compost is in the form of compacted particles, preferably in the form of pellets (Figure 1). The size of said pellets may vary within a wide range; however, in a particular embodiment, said compost pellets have an average diameter between about 5 mm and about 12 mm, preferably between about 6 mm and about 8 mm. The size of the compost pellets together with the high porosity of the compost, provide a large surface area that favors the contact of microorganisms capable of degrading CS ₂ with said contaminant. Likewise, the morphological regularity of the compost pellets constituting the biofilter filler material of the invention ensures a very homogeneous distribution of the filler material in the biofilter of the invention, which minimizes the development of preferential paths that limit the contact time. actual between the gas stream containing CS ₂ to be treated and the active surface of the filler material comprising the microorganisms capable of degrading CS ₂ .

The biofilter filler material of the invention has a good water retention capacity, which is very favorable since microorganisms require a significant amount of water to grow and the process is exothermic. Although the moisture content of the filler material can vary over a wide range, in a particular embodiment, the moisture content of the biofilter filler material of the invention is between 30% and 70%, preferably between 35% o and 50% or A low moisture content in the filler material reduces the thickness of the biofilm and adversely affects the activity of microorganisms capable of degrading CS ₂ , and, consequently, the activity of the biofilter. On the other hand, a high degree of humidity can create saturation, causing anaerobic areas or increase the loss of load. The biofilter of the invention comprises, in addition to said filler material, microorganisms capable of degrading CS ₂ . In the sense used in the present invention, a microorganism capable of degrading CS ₂ 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 the environment, for example, in sulfate [see, for example, Smith, NA et al. (1988); Revah et al. (1994); Alcantara et al. (1999), cited above]. Said microorganism capable of degrading CS ₂ 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 (eg, P. denitrificans, etc.), Thioalkalimicrobium (eg, T. aerophilum, T. sibericum, etc.), Thioalkalivibrio (eg, T. denitrificans, T. nitratis, T. versutus, etc.), Thiobacillus (eg, Thiobacillus TJ330, T. thioparus, etc.), Thiomonas, Thiothrix (eg, T. ramosa, etc.), etc. In a particular embodiment, the biofilter of the invention contains microorganisms capable of degrading CS ₂ belonging to a single genus or to 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.

Some of said microorganisms capable of degrading CS ₂ useful for the implementation of the present invention are commercially available or in crop collections. However, the person skilled in the art knows that, in general, microorganisms that tolerate the contaminant in question (CS ₂ ) live in samples from sites contaminated with said contaminant, for example, areas or facilities where gas streams are used or generated containing CS ₂ , etc .; therefore, by selecting the cultures of the microorganisms present in said samples it is possible to find strains of microorganisms capable of degrading the contaminant in question (CS ₂ ). Therefore, due to the diversity of waste used in the preparation of the filler material used in the biofilter of the invention, said filler material (compost) contains microorganisms of a very diverse nature, and, among said microorganisms there are microorganisms capable of degrading CS ₂ which can be identified and isolated by conventional methods of selecting microorganisms known to those skilled in the art. Indeed, the biomass Indigenous (native microorganisms) of the compost that constitutes the biofilter filler material of the invention is adaptable, since in contact with gaseous streams containing CS ₂ , advantageously moistened previously with water, the population of microorganisms present in said compost is self- regulated to proliferate microorganisms capable of degrading CS ₂ and incapable of degrading microorganisms are repressed CS _2. Therefore, in a particular embodiment, the implementation of the bio filtration method provided by this invention does not require initial inoculation with microorganisms capable of degrading CS ₂ since these are present in the filler material (compost) of the biofilter used in said bio filtration method; however, if desired, in a particular embodiment, said compost can be inoculated with a culture of microorganisms capable of degrading CS ₂ .

The ability of a microorganism to degrade CS ₂ can be determined by any conventional procedure, known to those skilled in the art, which allows to know if a microorganism uses CS ₂ , for example, by contacting a culture of said microorganism with CS ₂ and incubating under appropriate conditions; Under these conditions, the detection of hydrogen sulfide, an intermediate product of the oxidation of CS ₂ , or the production of sulfate, a final product of the oxidation of CS ₂ , is indicative that the analyzed microorganism is capable of degrading CS ₂ ; if desired, the microorganism may be supported on a filler material of the type used in the biofilter of the invention (compost) and the CS ₂ may be contained in a stream of air, preferably moistened with 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 CS _{2 are found} , as well as means for entering the gas stream containing CS ₂ , optionally moistened previously, and means for the output of the gas stream totally or partially discharged from CS ₂ . Optionally, if desired, devices can be included to measure the inlet temperature of the gas stream containing CS ₂ to be treated since it can affect the metabolic process of microorganisms capable of degrading CS ₂ , or to measure the pH since During the operation of the bio filtration method provided by this invention, acid products can be generated that can adversely affect the activity of the biofilter. The bio filter of the invention can be designed in various shapes and dimensions, using the appropriate materials for it.

The structural simplicity of the bio filter 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 bio filter 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 to each other, 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, so similarly, the outlet gas stream of said second bio filter of the invention is introduced into the third of the biofilters of the invention, and so on until the final exit of the total or partially discharged gas stream of CS ₂ .

Invention Method

As previously mentioned, the bio filter of the invention can be used to purify gases contaminated with CS ₂ by bio filtration.

Therefore, in another aspect, the invention relates to a method for purifying a gas stream containing CS ₂ by bio filtration, hereinafter "biofiltration method of the invention", which comprises passing said gas stream containing CS ₂ to through a biofilter of the invention, that is, a biofilter comprising a filler material and microorganisms capable of degrading CS ₂ , wherein said filler material comprises 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.

In the sense used in this description, the expression "purify gases contaminated with CS ₂ " includes both the almost total elimination of CS ₂ present in a gaseous stream containing CS ₂ and the reduction of the amount of CS ₂ present in a gaseous stream It contains CS ₂ up to levels permitted by legislation or that are not harmful to human or animal health, and / or to the environment. The amount of CS ₂ present in said gaseous stream containing CS ₂ can vary within a wide range; however, in a particular embodiment the amount of CS ₂ present in said gaseous stream to be treated by the bio filtration method of the invention is comprised between approximately 50 parts per million by volume (ppmv) [1 ppmv = 1 μg x ml ¹ ] and approximately 250 ppmv. The gaseous stream containing CS ₂ to be treated by the biofiltration method of the invention can come from various polluting sources, for example, from process facilities that use or generate CS ₂ , such as the cellulose fiber manufacturing sectors, industry synthetic wrap food, etc.

The biofiltration method of the invention comprises passing said gas stream containing CS ₂ through a biofilter of the invention, the characteristics of which have already been mentioned previously. The amount of CS ₂ present in said gaseous stream to be treated may vary within a wide range, as can the residence time or average amount of time that the gaseous stream containing CS ₂ to be treated remains in contact with the filling material. . However, in a particular embodiment, said gaseous stream to be treated contains CS ₂ in an amount between about 50 ppmv and about 250 ppmv and the residence time is between about 10 seconds and about 80 seconds Measuring the concentration of CS ₂ a The output of the biofilter can be checked for the operation of the filler material and of the microorganisms capable of degrading CS ₂ so that, in the event that the efficiency of the biofilter decreases, in the first instance it would be enough to water the filler material with a solution of nutrients, as mentioned below, to restore normalcy.

In practice it is convenient that the gaseous stream comprising CS ₂ to be treated is wet, or previously moistened, since the humidity of said gaseous stream itself 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 gaseous stream containing CS ₂ to be treated, for which said gaseous stream is contacted with an aqueous medium, for example, water, before being introduced into the biofilter. The aqueous medium used at 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 gaseous stream containing CS ₂ the necessary humidity, located before the bio filter. 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 humidification of the gas stream containing CS ₂ to treat and minimize system maintenance. In a particular embodiment, the relative humidity of the gas stream containing CS ₂ entering the bio filter is equal to or greater than 90%, preferably equal to or greater than 95%, even more preferably equal to or greater than 99%. Thus, the use of a compost with a moisture content of between 35% and 50% as a filler material of the bio filter of the invention used in the biofiltration method of the invention offers good results.

During the biofiltration process, the gaseous stream containing CS ₂ to be treated passes through the filler material that supports the growing microorganisms capable of degrading CS ₂ . The degradation of CS ₂ occurs, in general, after transferring the gas stream containing CS ₂ to a liquid medium where it is used as a source of carbon and energy. The use of said contaminant (CS ₂ ) implies the partial or total oxidation of CS ₂ and the production of biomass (microorganisms capable of degrading CS ₂ ) and with which the biofiltration process of the invention results in a practically complete decomposition of the CS ₂ generating non-hazardous (harmless) products for human or animal health and / or the environment and a total or partially discharged gas stream in CS ₂ .

Although it is not strictly necessary, it can sometimes be advantageous, before passing the gas stream containing CS ₂ to be treated through the biofilter of the invention, subjecting the microorganisms initially contained in the compost used as filler material of the biofilter of the invention used in the biofiltration method of the invention, at a previous stage of acclimatization to CS ₂ .

Therefore, in a particular embodiment, the biofiltration method of the invention comprises performing a previous stage of acclimatization to CS ₂ of the microorganisms initially contained in said compost. This step is particularly interesting when the corresponding microorganisms initially contained in the compost used as filler material of the biofilter of the invention used in the bio-filtration method of the invention are to be used as microorganisms capable of degrading CS ₂ ; in fact, this stage of previous acclimatization could be avoided if the compost was inoculated with microorganisms capable of degrading standardized CS ₂ . Said acclimatization can be carried out in any appropriate installation, for example, in the biofilter of the invention itself, or, alternatively, in a laboratory or in a pilot plant, and, in general, comprises contacting said compost, which contains a population of indigenous microorganisms (indigenous biomass), some of which are capable of degrading CS ₂ , with a gaseous stream containing CS ₂ . The amount of CS ₂ present in said gaseous stream containing it may vary within a wide range; however, in practice it is usually started using a gas stream containing CS ₂ in a relatively low amount, generally equal to or less than 100 ppmv, typically between 20 and 100 ppmv. The amount of CS ₂ present in said gaseous composition can be reduced, if desired, as the acclimatization of the microorganisms to CS _{2 increases} . The person skilled in the art can generate, by conventional methods, gaseous streams containing different concentrations of CS ₂ , and select that which provides a better acclimatization of the microorganisms present in the compost to CS ₂ . The conditions for acclimating to the CS ₂ the microorganisms initially contained in the compost used as filler material in the biofilter of the invention used in the implementation of the bio-filtration method of the invention depend, in general, on various factors, for example, of the content in CS ₂ in the gas stream used, the residence time, the duration of the treatment, etc. In this sense, although the conditions for acclimatizing to CS ₂ the microorganisms initially contained in the compost present in the biofilter filler material of the invention used in the implementation of the bio-filtration method of the invention can vary widely, in one embodiment. in particular, said acclimatization comprises treating said compost with a gas stream comprising CS ₂ in an amount equal to or less than about 100 ppmv, with a residence time equal to or less than about 120 seconds, continuously, for approximately at least 100 days, preferably approximately 200 days. In an even more particular embodiment, said step of acclimatization to the CS ₂ of the microorganisms initially contained in the compost used as a filler material of the bio filter of the invention used in the biofiltration method of the invention is carried out with a gas stream comprising CS ₂ in an amount between about 25 ppmv and about 100 ppmv, the residence time being between about 20 seconds and about 120 seconds, continuously, for at least 100 days.

In general, during the acclimatization stage, colored fungi are initially developed on the compost, which are primarily responsible for the degradation of CS ₂ . Subsequently, the coloration of the fungi disappears from the surface, and then the bacteria appear to be responsible for the degradation of CS ₂ . As of that moment, the compost is prepared to receive increasing concentrations of CS ₂ and degrade it efficiently.

During this stage of previous acclimatization (if applicable) it may be necessary to provide the compost with a nutrient solution, such as the one mentioned previously, in order to maintain the metabolism of microorganisms capable of degrading CS ₂ . The contribution of said nutrient solution to the compost can be done by irrigation, as previously mentioned.

After the acclimatization period, the biomass developed on the compost, which comprises microorganisms capable of degrading CS ₂ , can be used as inoculum of other bio filters, for example, bio filters of the invention, thus obtaining very fast starts with high debugging efficiencies (elimination or reduction) of CS ₂ practically from startup.

The person skilled in the art will understand that the biofiltration method of the invention includes the possibility of passing the gas stream containing CS ₂ through one or more bio filters of the invention. Thus, in a particular embodiment, the biofiltration method of the invention comprises passing the gaseous stream containing CS ₂ to be treated through a single biofilter of the invention. In another particular embodiment, the biofiltration method of the invention comprises passing the gas stream containing CS ₂ to be treated through two or more biofilters of the invention, for example, 2, 3, 4, or even more, operatively connected to each other; in this case, the gaseous stream containing CS ₂ to be treated is passed through the first of the biofilters of the invention and the gaseous outflow of said first bio filter of the invention, which will be at least partially discharged into CS ₂ , is passed through the second bio filter of the invention, and, similarly, the gaseous stream of said second bio filter of the invention, which will be even more shameless in CS ₂ , is passed through the third bio filter of the invention, and so on until the final exit of the total or partially discharged gas stream of CS ₂ . Therefore, the bio filtration method of the invention allows to achieve a removal efficiency of CS ₂ of 100%, or very close to 100%, in relation to the amount of CS ₂ present in the gaseous stream containing CS ₂ to be treated .

Although the filler material present in the biofilter of the invention can supply the nutrients necessary for the metabolism of microorganisms capable of degrading CS ₂ , during the performance of the bio filtration method of the invention, the stable operation of the biofilter of the invention can require the 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; a quantity of 5 cm ³ of 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 is added -4H ₂ 0.60 mg / dm ³ of CuCl ₂ , 50 mg / dm ³ of ZnCl ₂ , 50 mg / dm ³ of H ₃ BO 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 the metabolism (growth and maintenance) of microorganisms capable of degrading CS ₂ , with this irrigation the sulfate (S0 ₄ ^{2 ~} ) generated as a product of the degradation reaction of CS _{2 is carried away} . In any case, the good pH regulatory characteristics as well as the Good characteristics for retaining moisture by the compost used as a filler material of the bio filter used in the bio filtration method of the invention minimize the need for watering very continuously. Although the period of time between two consecutive irrigations can vary within a wide range, depending on numerous factors (eg, need to provide nutrients, need to moisten the compost, etc.), in a particular embodiment, the period of time between two consecutive waterings is approximately 60 days, typically approximately 40 days.

Sulfate or sulfuric acid is generated during the biofiltration method of the invention; however, in general, it is not necessary to use additional reagents to neutralize sulfuric acid from the oxidation of CS ₂ .

 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 in a continuous regime have shown that the compost used in the preparation of the filler material of the bio filter used in the biofiltration method of the invention, due to its good physical-chemical characteristics, does not suffer deterioration ( or erosion) significant after more than 12 months of operation and is expected to exceed 24 months. Therefore, the present invention provides a stable and durable method for the purification (elimination or reduction of the amount) of the CS ₂ contained in a gaseous stream containing said contaminant.

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 moisture) gas stream containing CS ₂ is passed through the material of filler contained in the biofilter of the invention wherein CS ₂ is degraded by microorganisms capable of degrading CS ₂ . Briefly, a gaseous stream containing CS ₂ (2) from a contaminating source (1) is introduced into a humidification system (3) that contains water in order to moisten said gaseous stream containing CS ₂ before entering a bioreactor (5). The humidified gas stream containing CS ₂ (4) is introduced into said bioreactor (5) which contains 3 biofilters of the invention (6a, 6b and 6c); each of which comprises a filler material and microorganisms capable of degrading CS ₂ , wherein said filler material comprises a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70% by weight of waste from animals and (ii) 70-30% by weight of plant residues. The 3 biofilters of the invention (6a, 6b and 6c) are arranged vertically and operatively connected to each other so that the output current of the first bio filter (6a) feeds the second bio filter (6b) and the output current of said Second bio filter (6b) feeds the third bio filter (6c) from which the gaseous stream practically discharged from CS ₂ (7) comes out. If necessary, the nutrients contained in the nutrient store (8) are supplied to the biofilters of the invention by irrigation in order to maintain the metabolism of microorganisms capable of degrading CS ₂ .

Installation of the invention

The bio filtration method of the invention can be carried out in a suitable installation comprising at least one bio filter of the invention, that is, a bio filter comprises a filler material and microorganisms capable of degrading CS ₂ , wherein said filler material It comprises 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. 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 whose characteristics have been previously defined. Therefore, in a particular embodiment, the installation of the invention comprises a single bio filter 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 this case, the gaseous stream containing CS ₂ to be treated is passed through the first bio filter of the invention and the gaseous stream of said first bio filter of the invention is passed through the second bio filter of the invention, and, similarly, the gaseous outflow of said second Biofilter of the invention is passed through the third biofilter of the invention, and so on until the final exit of the total or partially discharged gas stream of CS ₂ .

The modular design of the installation of the invention allows biofilters farther from the entrance of the gas stream containing CS _{2 to} receive very low concentrations of CS ₂ but sufficient for the adaptation of microorganisms capable of degrading CS ₂ . Likewise, the modular design allows the biodegradation of CS ₂ in the first biofilter while the remaining biofilters can act as a reserve, which guarantees the efficiency of the system even with sudden increases in pollutant load (CS ₂ ).

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 CS ₂ the necessary humidity, located before the biofilter of the invention. Additionally, the installation of the invention includes suitable means for transporting the gas stream 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 CS ₂ 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 CS ₂ to be treated, means for measuring the pH inside the biofilter. , and means for measuring the amount of CS ₂ present in the gas stream of the biofilter.

Inoculation of microorganisms capable of degrading CS?

As previously mentioned, the invention contemplates that, after the acclimatization period, the biomass developed on the compost, which comprises microorganisms capable of degrading CS ₂ , is used as inoculum of other biofilters, for example, biofilters of the invention, thus obtaining very fast starts with high purification efficiencies (elimination or reduction) of CS ₂ practically from the start. The acclimatization to the CS ₂ of the microorganisms capable of degrading CS ₂ can be carried out by means of a treatment comprising contacting the compost that contains a population of native microorganisms (indigenous biomass), some of which are capable of degrading CS ₂ , with a gas stream containing CS ₂ , as previously mentioned in relation to the implementation of the bio filtration method of the invention.

Therefore, in another aspect, the invention relates to a method for generating a population of microorganisms capable of degrading CS ₂ which comprises combining: a) 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, which comprises microorganisms capable of degrading CS ₂ acclimatized to CS ₂ according to the acclimatization method defined above (acclimatized compost), with

 b) a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70%) by weight of animal waste and (ii) 70-30% or by weight of plant waste (fresh compost),

in a proportion (acclimatized compost): (fresh compost) between approximately 1: 1 and approximately 5: 1, preferably by weight, approximately 3: 1.

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

EXAMPLE 1

 Design of a CS2 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 3 biofilters (6a, 6b and 6c), placed vertically, with an approximate total volume of 4.5 L, built in chloride polyvinyl (PVC) and with downward gas flow; the biofilters (6a, 6b and 6c) are operatively connected to each other and, inside, there is the filling material comprising a compost in the form of pellets (supplied by the company SLIR), which acts as a support material on the The biomass responsible for the degradation of CS ₂ (microorganisms capable of degrading CS ₂ ) is developed. Said compost has been obtained 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. Table 1 shows some physicochemical properties of the pelletized compost used.

Table 1

 Physicochemical properties of the compost used

 [ufe: colony forming units]

 [σ Standard deviation]

In an initial stage of acclimatization in a pilot laboratory plant, indigenous compost biomass feeds on gaseous streams contaminated with CS ₂ and saturated in moisture (> 90%) generated in the laboratory, with concentrations not greater than 100 ppmv of CS ₂ approximately and with a residence time of less than approximately 120 seconds, continuously, for 24 hours a day. This period does not require any additional compost treatment (eg, inoculation of microorganisms capable of degrading CS ₂ ).

 Once the active biomass is acclimatized (microorganisms capable of degrading

CS ₂ ), this can be used to treat gaseous streams containing CS ₂ (bio-filter feed stream), with an amount of CS ₂ between approximately 50 ppmv and approximately 250 ppmv, with residence times of approximately 10 seconds to approximately 80 seconds. The maintenance of moisture in the filling material of the bio-filter (compost) is achieved by monthly irrigation with the nutrient solution required for the metabolism of active biomass.

The effectiveness of the treatment of purification of CS ₂ is greater than 90% in the first third of design volume [bio-filter (6a)], with the remaining 2/3 parts [bio filters (6b and 6c)] being the reserve system by that pass very low concentrations of CS ₂ , which guarantee its acclimatization and potential purification activity of CS ₂ . Therefore, said reserve system can be used as inoculum to start up new bioreactors for the purification of gaseous streams containing CS ₂ as a contaminant.

The process of purification of said gaseous stream containing CS ₂ as a contaminant does not generate leachates in the system, which eliminates the need for subsequent treatment.

Claims

A method for purifying a gas stream containing CS ₂ by bio filtration comprising passing said gas stream containing CS ₂ through a biofilter, said biofilter comprising a filler material and microorganisms capable of degrading CS ₂ , wherein said material The filling comprises 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. Method according to claim 1, wherein the relative humidity of said gaseous stream containing CS ₂ is equal to or greater than 90%>, preferably equal to or greater than 95%. Method according to claim 1, comprising the acclimatization prior to CS ₂ of microorganisms capable of degrading CS ₂ . Method according to claim 3, wherein said acclimatization comprises treating the compost with a gas stream comprising CS ₂ in an amount less than about 100 ppmv, with a residence time of less than about 120 seconds, continuously, for approximately at least 100 days  Method according to claim 1, wherein the animal residues are selected from the group consisting of pig purines, poultry residues, cattle residues, and combinations thereof; and / or organic vegetable waste is selected from the group consisting of branches and pieces of wood, sawdust, and combinations thereof.  Method according to claim 1, wherein said compost is in the form of compacted particles.  Method according to claim 1, wherein said compost is in the form of pellets. Method according to claim 1, wherein said gas stream comprises CS ₂ in an amount between about 50 ppmv and about 250 ppmv. 9. Method according to claim 1, further comprising watering said bio filter with a nutrient solution. 10. A bio filter comprising a filler material and microorganisms capable of degrading CS ₂ , wherein said filler material comprises a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70% by weight of waste of animals, and (ii) 70-30% by weight of plant waste.  11. An installation comprising at least one biofilter according to claim 10. 12. A method for acclimating to CS ₂ microorganisms capable of degrading CS ₂ contained in a compost, wherein said compost is 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 residues, comprising contacting said compost containing microorganisms capable of degrading CS ₂ with a gaseous stream comprising CS ₂ in an amount less than about 100 ppmv, with a residence time of less than about 120 seconds, continuously, for at least 100 days. 13. A method for generating a population of microorganisms capable of degrading CS ₂ comprising combining: c) a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70%) by weight of animal waste and (ii) 70-30% or by weight of plant waste, which comprises microorganisms capable of degrading CS ₂ acclimatized to CS ₂ according to the previously defined acclimatization method (acclimatized compost), with  d) a compost obtainable by aerobic-anaerobic decomposition of a mixture comprising (i) 30-70%> by weight of animal waste and (ii) 70-30% or by weight of plant waste (fresh compost),  in a proportion (acclimatized compost): (fresh compost) between approximately 1: 1 and approximately 5: 1, by weight.