MXPA00004316A - Novel methods and apparatus for improved filtration of submicron particles - Google Patents

Abstract

The subject invention pertains to novel methods of filtration, novel methods for production of filters, and novel filters, for the efficient filtration of particles. The materials and methods of the subject invention are particularly advantageous for the filtration of submicron particles, for example, nanoparticles, and can utilize the electrostatic attraction between particles and the fibers of microporous filters, for example, polypropylenefilters. The subject methods of filtration can lower the energy barrier between the particles and the filter surface and thus increase the deposition of particles on the surface of the filter. The methods and apparatus of the subject invention can be used to filter particles from many fluids including water and air. Advantageously, the subject surface modified filters can result in increased fluid flow, for the same pressure drop, compared to conventional filters.

Description

METHODS AND APPARATUS FOR IMPROVED FILTRATION OF SUBMICRATIC PARTICLES The present invention was carried out with the support of the US government. under a research project supported by the Concession No. EEC-94-02989 of the National Science Foundation. The government of the U.S.A. You have certain rights in this invention.

BACKGROUND OF THE INVENTION Water-borne gastroenteritis is a major public health problem in both developed and developing countries (Payment et al 1991a, Payment et al 1991b, Rao 1976). Many cases of human infections caused by waterborne enteric pathogens have occurred in the United States and around the world. At the end of the 1980s, more than 50 outbreaks of waterborne diseases were reported (Levine et al.). Between 1991 and 1992, 17 states and territories in the United States reported 34 outbreaks related to drinking water. These outbreaks caused approximately 17,464 people to become ill (Moore et al., 1993). In 1993, there was an outbreak of waterborne cryptosporidiosis in Milwaukee. During this outbreak more than 400,000 people had intestinal disease (MMWR, June 16, 1995). A recent report by the Academy of Microbiology (Colwell, R.R., 1996) indicated that our surface and drinking waters are no longer safe from the microbiological point of view. According to the report, there has been an increase in waterborne diseases around the world. The annual social costs of mild gastrointestinal diseases transmitted by water in the United States have been estimated to be over 22 billion dollars. The cases of diseases reported annually in the United States attributed to contacts with waterborne pathogens were estimated at a minimum of one million and a maximum of seven million (staff of ENEWS, 1998). Deaths were estimated between 1000-1200 per year. The most common disease of water-related diseases is gastroenteritis; other diseases include hepatitis, typhoid fever, mycobacteposis, pneumonia, and dermatitis (Levine et al., 1991, Payment et al., 1994, Sherris et al, 1990). More efforts and improvements are needed in the drinking water treatment procedures to improve and maintain the quality and quantity of drinking water nowadays. Deep bed filtration through formed particle media is a commonly used method to remove particles from water (Bitton, 1994). This filtration process may not be effective in removing microorganisms and is based either on the addition of flocculants to the incoming water or on the development of a biofilm on the surface of the filter media. Metal hydroxide flocs (ferric hydroxide and aluminum hydroxide) have been used to treat water and wastewater for many years (Bitton, 1994). These flocs adsorb microorganisms and remove them from the water followed by sedimentation or filtration. However, combining flocculation with filtration has had limited success in producing flow-through filters to remove microorganisms from large volumes of water. There are potential drawbacks to this approach; the flocs may not be retained by the filters or clog the filters and restrict the flow of water enough, thus requiring frequent backwash (Bitton 1994). Several studies have examined the possibility of modifying the formed particulate media for filtration to improve their capacity to eliminate microorganisms. The use of efficient filtration materials to eliminate microorganisms improves the aesthetics and chemical quality of water and reduces the need for subsequent disinfection. These modifications include coating of diatomaceous earth filters or microporous with cationic polymers (Brown et al., 1974, Preston et al. 1988), impregnation of coal with metal hydroxides (Chaudhuri and Sattar, 1986), addition of positive charges to silica using an organosilane derivative (Zerda et al., 1985), incorporation of metal hydroxides in and on the surfaces of solid materials using in situ precipitation of metal hydroxides (Farrah et al., 1985, Lukasik et al., 1996), adsorption of metallic flocs on surfaces (Edwards and Benjamín, 1989), and incorporation of metal peroxides in microporous filters (Gerba et al., 1988) or diatomaceous earth (Farrah et al 1991).

There have been numerous reports of disease transmission associated with bathing in recreational waters (D 'Alessio et al., 1981, Hawley et al., 1973. Kee et al. Lenway et al, 1989, MMWR 1997, and Turner et al., 1987). The etiological agents responsible could be viral, bacterial or protozoal and the symptoms include diarrhea, nausea, vomiting and abdominal pain. It is likely that many cases of milder infections are not reported. Disinfection and filtration are common methods used to control pathogens in pool water. Diatomaceous earth and sand filters are commonly used for swimming pools. Diatomaceous earth filters have the advantage of efficiently eliminating microorganisms (Brown et al 1974), but they are subject to frequent obstruction, restriction of flow, and their use can often give rise to health concerns. These health concerns are related to the possible role of diatomaceous earth particles in lung diseases. Sand filters have been widely used in water filtration procedures (Bitton, 1994). These filters remove relatively small numbers of pathogenic microorganisms from the water. Its performance can be improved by allowing the development of a biofilm in the sand. Also, efficient elimination of microbes can be carried out using coagulants, (polymeric compounds or metal hydroxides). These procedures, although useful for the treatment of water and wastewater, may not be practical for swimming pools. Swimmers can oppose the presence of coagulants and long maturation periods for filters may not be possible. Pool filtration is usually combined with disinfection. Chlorine is the most common disinfectant used in water treatment; It is effective in killing a wide range of microorganisms. However, its use is limited to low concentrations since it is caustic and can produce toxic byproducts by reaction with organic materials. The elimination of particulate pollutants is very important for many applications including, for example, water recovery, potable water treatment, water purification in microelectronics and pharmaceutical industries, and other point of use filters where ultra water is required pure The efficiency of the filtration of particulate pollutants depends on several factors including the particle size, physicochemical properties of the particles, and the collectors or filter media. For example, due to their large pore sizes, conventional filters can not be used to filter submicron / nanoparticle particles or biological particles such as bacteria and viruses. Although large particles can be filtered by entrapment mechanisms, as the particle size decreases, the removal of particles becomes more difficult and therefore other techniques for efficient filtration may be necessary. In particular, techniques that increase the interaction between the particles and the collectors can be used to increase the efficiency of the filtration.

The deposition of submicron particles in collectors has captured the interest of many researchers over the years (Fitzpatrick et al. [1973]; Clint ef al. [1973]; Spielman ef al [1994]; Rajagopalan et al. [1977a]; Rajagopalan ef al. [1977b]; Onorato et al. [1980]; Oak ef al. [1985] Shields ef al. [1986]; Russell ef al. [1989]; Sisson ef al. [nineteen ninety five]; Johnson ef a /. [nineteen ninety six]; Chang et al. [1990]). These investigations have focused mainly on the interactions between the particles and the collectors. Polypropylene is commonly used to make prefilters and filters since it is inexpensive and very inert. A technique that could alter the polypropylene filters to increase the interaction between the particles and said filters would increase the filtering efficiency of said filters.

BRIEF DESCRIPTION OF THE INVENTION The present invention relates to novel filtration methods, novel method for the production of filters, and novel filters, for the efficient filtration of impurities. Such impurities include, but are not necessarily limited to, particles and chemical species. The materials and methods of the present invention are particularly favorable for the filtration of submicron particles, for example nanoparticles, and can utilize electrostatic attraction between the particles and the microporous filter matrix. The filtration methods of the present invention can reduce the energy barrier between the particles and the filter surface and thus increase the deposition of particles on the filter surface. The methods and materials of the present invention can be used to filter particles and chemical contaminants dissolved from many fluids including water and air. Advantageously, the modified surface filters of the present may result in increased fluid flow, for the same pressure drop, compared to unmodified filters. In a specific embodiment, because most of natural materials are negatively charged (Rosen, MJ, 1988), a monomolecular layer of cationic surfactant to a filter microporous polypropylene to give the filter surface load is added positive. Advantageously, the adsorption of negatively charged and / or neutral particles in these surface modified filters and the resulting filtration efficiency are improved. These modified surface filters can be useful for removing bacteria, viruses, and nanoparticles in the treatment of wastewater, and may also be useful in resource recovery procedures. In an alternative embodiment, a monomolecular layer of anionic surfactant can be added to a filter microporous polypropylene to give the filter surface a negative charge, resulting filtration efficiency improved for particles with positive and / or neutral charge. In a further embodiment, a monomolecular layer of nonionic surfactant can be added to a microporous polypropylene filter, resulting in improved filtration efficiency for positive, negative and / or neutral particles. In another embodiment, the modified surface filters of the present may be stacked, resulting in a further increase in filtration efficiency. Specifically, the modified filter surface having a positive charge, negative charge, or neutral charge can be stacked in a variety of combinations to filter more efficiently target particles, for example negative, positive, and neutral particles simultaneously. Filters made of materials that are not polypropylene microporous can also be modified by the addition of surfactants or polymers according to the present invention. The present invention also relates to novel methods for coating filter media, novel filter media, for the efficient filtration of chemical and biological fluid contaminants. The materials and methods of the present invention are particularly favorable for the filtration of ions, materials formed from particles, bacteria, viruses, protozoan parasites, fungi, yeasts and other submicron particles of aqueous and gaseous systems. The coatings herein can be applied to a variety of filter media, for example woven fabrics or filters. nonwovens, fiberglass, fiberglass air filters, polypropylene, cellulose, sand, diatomaceous earth, fine sand, gravel, and any filter media formed of particles.

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In a specific embodiment, the in situ precipitation of metal hydroxides and / or metal oxides can be used to coat the filter media. Coated filter media can be useful to eliminate, for example, bacteria, viruses, protozoan parasites, fungi, organic and inorganic chemicals, and / or dust. The materials and methods herein can be used in, for example, water purition devices for survival or personal, home water filters, air filters, filter media for water recovery, water maintenance procedures, soil maintenance, filters to eliminate viruses, and / or protective clothing.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to novel filtration methods, novel methods for the production of filters, and novel filters, for the efficient filtration of impurities in a fluid. The materials and methods of the present invention are particularly favorable for the filtration of submicron particles, for example nanoparticles, and can utilize electrostatic attraction between the particles and the matrix of a filter. The filtration methods of the present invention can reduce the energy barrier between the particles and the filter surface and thus increase the deposit of particles on the filter surface. The methods and apparatus of the present invention can be used to filter impurities from many fluids including ^^^^^^ gs ^ gtegjWj ^ jj ^^^^^^ water and air. Advantageously, the modified surface filters of the present may result in increased fluid flow, for the same pressure drop, compared to unmodified filters. In a specific embodiment, because most of the natural particles have a negative charge (Rosen, MJ, 1988), a thin layer of cationic surfactant is added to a microporous polypropylene filter to give the filter surface a charge positive. In a specific embodiment, this layer can be monomolecular. Advantageously, the adsorption of negatively charged and / or neutral particles on these surface modified filters and the resulting filtration efficiency are improved. These modified surface filters are useful for removing bacteria, viruses, and nanoparticles in wastewater treatment, and are also useful in resource recovery procedures. In an alternative embodiment, a thin layer of anionic surfactant can be added to a microporous polypropylene filter to give the filter surface a negative charge, resulting in improved filtration efficiency for positively charged and / or neutral particles. In a further embodiment, a thin layer of nonionic surfactant can be added to a microporous polypropylene filter, resulting in improved filtration efficiency for neutral particles. These layers can be monomolecular. Thus, in alternative embodiments, cationic polymers can be used to coat filter surfaces, resulting in increased filtration efficiency of negative and / or neutral particles; Anionic polymers can be used to coat filter surfaces, resulting in increased filtration efficiency of positive and / or neutral particles; and nonionic polymers can be used to coat filter surfaces, resulting in increased filtration efficiency of negative, positive, and / or neutral particles. The present invention can be applied to many types of prefilters and filters, including polymeric filters. In a preferred embodiment, the filters herein are micro-porous polypropylene filters, which are inexpensive and very inert. Advantageously, the methods and apparatus of the present invention allow for the monitoring of charge neutralization of the filter surface to determine when it is necessary to replace the filter. This monitoring can be carried out, for example, by measuring the zeta potential of a filter using, for example, a current potential apparatus. The surfactants and polymers that can be used in the present invention include the following: Cationic surfactants C20 -C26 , where TAB is trimethylammonium bromide Anionic surfactants Dicetilphosphate Phosphatidic acid Cationic polymers Poly (4-vinylpyridine) Poly (d-glucosamine) chitosan Polyethyleneimine Polymers anionic Poly (acrylic) acid Poly ( butyl acrylate) / poly (acrylic acid) Other Hydrophobically modified cationic polymers Hydrophobically modified anionic polymers Zwitterionic surfactants (groups as well as +) such as lecithin (Soya lecithin) Nonionic polymers Polyvinyl alcohol although, it is understood that other surfactants and polymers can also be used within the scope of the present invention. In another embodiment, the modified surface filters of the present may be stacked resulting in a further increase in filtration efficiency. Specifically, the modified filter surface having a positive charge, negative charge, or neutral charge can be stacked in a variety of combinations to filter more efficiently target particles, for example, negative, positive and neutral particles simultaneously. Filters made of materials that are not polypropylene Z:?.?. ^ - .- Z, ^ z * - - ^ & ^ ^ may also be modified microporous by addition of surfactants or polymers according to the present invention. The present invention also relates to novel methods for coating filter media, and novel filter media, for the efficient filtration of chemical and biological fluid contaminants. The materials and methods of the present invention are particularly favorable for the filtration of chemical species, materials formed from particles, bacteria, viruses, protozoan parasites, fungi, yeasts, and other submicron particles from aqueous and gaseous systems. The coatings of the The present invention can be applied to a variety of filter media, for example filters or woven and non-woven fabrics, fiberglass, fiberglass air filters, polypropylene, cellulose, sand, diatomaceous earth, fine sand, gravel, activated carbon, and any filter media formed of particles. The present invention also relates to the precipitation of (hydr) metal oxides in a filter matrix, the resulting filters, and a method for filtering a fluid using said filter. In a specific embodiment, the in situ precipitation of metal hydroxides and / or metal oxides can be used to coat filter media. The coated filter media can be useful for removing, for example, bacteria, viruses, parasites protozoa, fungi, organic and inorganic chemical substances, and / or dust. The materials and methods herein can be used in, for example, water purification devices for survival or personal, home water filters, air filters, filter media for water recovery, water maintenance procedures, soil maintenance procedures, filters to eliminate viruses, and / or protective clothing. To precipitate (hydr) metal oxides in a filter matrix, where (hydr) metal oxides refer to metal hydroxides and / or metal oxides, the filter matrix may, for example, be first moistened with a metal chloride solution. Other solutions can also be used, such as a metal sulfate solution. Once the moistened filter matrix dries, a basic solution can be applied. Examples of such basic solutions include ammonium hydroxide, sodium hydroxide, and potassium hydroxide. Other concentrated base solutions that raise the pH can also be used. Preferably, the pH of said basic solution is at least pH 9, and preferably at least pH 11. Once the filter matrix dries again, the filter medium having a coating of (hydr) oxides on metal the surface is ready to be used. In a preferred method for applying the metal chloride and ammonium hydroxide solutions, the particles of the filter media of the present are preferably heated to an elevated temperature. Applying the coatings while the filter media is at elevated temperatures is particularly favorable for sand, diatomaceous earth and filter media formed from particles. For example, on a scale of 60 ° C to 100 ° C, preferably 70 ° C to 95 ° C, and preferably 75 ° C to 85 ° C, and most preferably about 80 ° C. Also, preferably the means The filter can also be stirred mechanically, for example on a vibrating platform. The agitation helps promote the uniformity of the coating to be applied. The heating method may comprise the use of, for example, infrared radiation, blowing hot air into the vibrating particles, microwaves, or any other heating mechanism that may be incorporated with the coating method herein without interference. Once the media is heated, and preferably while stirring, a metal chloride solution can be applied to the surface of the media. In a specific embodiment, a preheated solution at approximately the same temperature of the filter media (eg, about 80 ° C) of 0.25 M ferric chloride and 0.5 M aluminum chloride in a solution of water is atomized onto the vibrating particles. 50% ethanol. Preferably, the solution is atomized in short applications to avoid excessive wetting of the surface and to allow a uniform drying. The heating and stirring can continue throughout the atomization process. The atomization preferably continues until the surface of the solid substrate is uniformly treated and completely coated with the metal chloride solution. It should be mentioned that a variety of methods can be used to apply the metal chloride solution. Then the coating is allowed to dry. To allow the coating to dry quickly and evenly, heating and stirring can continue. Excessive heating should be avoided to avoid the corresponding metal oxides. The coated material tends to acquire a yellowish coloration when properly coated. The solid materials can then be coated, for example atomized or exposed to saturated vapors of ammonium hydroxides, by a 3.0 M solution of ammonium hydroxide. A 3.0 M solution of ammonium hydroxide is preferred. Again, the coating is preferably applied while the media is heated and stirred. This forms the precipitate of corresponding (hydr) metal oxides on the surface. The coated solid materials can then be rinsed in deionized water and dried. The filter media is ready to be used. The metal chloride solution can have a scale of molarities. Preferably the ferric chloride is in the range of 0.1 M to 2.0 M, preferably 0.2 M to 0.4 M, and most preferably about 0.25 M, while the aluminum chloride is preferably in the range of 0.1 M to 2.0 M, preferably 0.2 M to 0.8 M and most preferably approximately 0.5 M. The metal (hydr) oxide coating herein can be produced using metal sulfates, such as aluminum sulfate and / or ferrous sulfates. The metal chloride solution may be in, for example, 100% water, however preferably ethanol is added to accelerate the drying process. It was found that 50% ethanol - 50% water worked well. As mentioned, the heating was stopped after the metal chloride solution was dried to prevent the coating from going to the oxide. A dark brown or black color may indicate rust formation.

Other coatings may be applied, such as magnesium peroxide, silver chloride, and manganese oxide. As can also be described in other examples, the metal chloride and ammonium hydroxide coatings can be applied in a variety of ways, for example dipping the filter media into appropriate solutions or contacting the filter media with saturated vapors. It was found that atomization provides a uniform coating, but other application techniques, for example immersion, may be more practical for large volumes. In a specific modality, fiberglass filter media can be precipitated with (hydr) metal oxides. This embodiment is particularly favorable for porous filters where the atomization can sufficiently wet the filter matrix. Hot air can be passed through the filters to raise the temperature of the substrates to be coated at approximately 80 ° C. A preheated solution (approximately 80 ° C) of 0.25 M of ferric chloride and 0.5 M of aluminum chloride in a 50% ethanol solution can be sprayed onto the filter surface. Other combinations of chlorides and / or metal sulfates may also be used. The hot air can be blown continuously while the solution is atomized. Preferably the solution is atomized uniformly and sporadically to allow uniform drying. The heating can continue throughout the atomization process. The surface of the solid substrate can be treated uniformly and completely coated with a dry film of, for example, the metal chloride or FtßjS &D? Tjtteiaun sulfate metal. Again, excessive heating should be avoided to prevent the formation of the corresponding metal oxides. The coated material may have a yellowish brown coloration when sufficiently coated. Then a basic solution can be applied. For example, the solid materials can be applied by atomization of a 3.0 M solution of ammonium hydroxide or exposed to saturated vapors of ammonium hydroxide while heating. This forms the precipitate of corresponding (hydr) metal oxides on the surface. The drying by hot air pass can continue until the filter is dry. The coated solid materials can then be rinsed in deionized water and dried. After drying, they are ready to be used. The coating methods herein can also be applied to wool fiber filters such as those used under a sink to filter water from the tap. Often these filters are made from dense filter media such as cellulose, where the atomization may not be adequate to wet the filter matrix. For this type of filter, the substrates can be heated preferably to approximately 80 ° C. A preheated solution (approximately 80 ° C) of 0.25 M of ferric chloride and 0.5 M of aluminum chloride in a 50% ethanol solution can be passed through the filter. Preferably the filter is saturated with the solution. A contact time of 10 minutes allows sufficient contact, although longer or shorter periods can also be used. The heating can continue during the contact time. Hot air can be passed to through the filter to clean the excess solution. The passage of hot air can continue until the filter is completely dry. Now the filter should be treated uniformly and fully coated with a dry film of metal chloride. Excessive heating should be avoided to avoid the corresponding metal oxides. The coated material may have a yellowish brown coloration when sufficiently coated. A solution of 3.0 M of ammonium hydroxide preheated to about 80 ° C can then be passed through the filter quickly or saturated vapors of ammonium hydroxides can pass through the filters while they are heated. This forms the corresponding precipitate of metal hydroxides on the surface. Then warm air can be passed through the filter to remove excess liquid and dry the filter. The coated solid materials can be rinsed in deionized water and dried. Once the coated solid materials are dry they are ready to be used. The following examples illustrate procedures for practicing the invention: These examples should not be considered as limiting. All percentages are by weight and all proportions of solvent mixture are by volume unless otherwise indicated. d ^^^^^ ^? ^^? ^ EXAMPLE 1 Nanoparticle filtration with polypropylene filters treated with surfactants The filters used in this example are melt blown microporous polypropylene disk filters with a diameter of 25 mm (Millipore, MA). The average pore sizes are 0.6 μm (AN06), 1.25 μm (AN12), 2.5 μm (AN25), 5.0 μm (AN50), and 10.0 μm (AN1 H). These filters were treated with a two-tailed water-insoluble cationic surfactant, dimethyldioctadecylammonium bromide (DDAB), by first dissolving the surfactant in methanol and then soaking the filters in the methanol solution (4 ml per filter) for 3 hours. After the 3 hour treatment, the filters were dried under vacuum overnight. Before using them for filtration experiments, the filters were cleaned with 30 ml of distilled water to remove excess surfactants and / or loose surfactants from the surface of the filter. The average pore diameters were supplied by the manufacturer. Dimethyldioctadecylammonium bromide was purchased from Sigma Chemical Company (St. Louis, MO) and used without further purification. The nanoparticles were purchased from Bangs Labs, Inc. (Carmel, IN). The negatively charged particles, P (S / A? / - COOH), are composed of polystyrene, an acrylic polymer (not specified), a vinyl group (polymerizable group not specified), and a functional carboxylate group. The average diameter and surface charge density of these nanoparticles are 60 + 3.6 nm and 365 μeq / g, respectively, and 197 nm (standard deviation is not given) and 141 μeq / g, respectively. The positively charged particles are modified quaternary ammonium polystyrene (P (S / Ammonium Cuat)) particles with an average diameter of 200 nm and a surface charge density of 121 μeq / g, particle concentrations (% by weight) of solids) were measured by absorbance of UV light with an 8453 spectrophotometer from Hewlett Packard at a wavelength of 255 nm. The qualitative comparison of the degree of DDAB coating on the filters was made through contact angle measurements. The AN06 filters (0.6 μm) were treated with different concentrations of DDAB according to the aforementioned procedure. After the filters were rinsed with 30 ml of distilled water, they were cut into four strips. The strips were then immersed in a rectangular piece of PMMA (4 mm thick) in a 50 ml beaker (Pyrex No. 1000) containing 20 ml of distilled water. One drop, approximately 1.5 μl of 1, 2,2-tetrabromoethane was placed on top of the filter with a microsyringe. After the drop was allowed to spread on the filter for 1.5 minutes, the contact angle of the drop was measured with a contact angle goniometer. Six readings were taken at different places on the filter surface with each of the filters to obtain an average contact angle value. The zeta potential of the filters was measured with the Brookhaven Electrokinetic Analyzer B1-EKA that is provided for equipment evaluation (Brookhaven Instruments Corporation, New York). For particle adsorption experiments, the untreated and treated AN06 filters were rinsed with 30 ml of deionized distilled water. Then each filter was soaked in 25 ml of a particle suspension containing 0.012% by weight of solids (2.8 × 10 10 particles / ml) of 197 nm of P (S / A / V-COOH) or 200 nm of P (S / Ammonium Cuat) for 30 minutes. The filter was then removed from the suspension and rinsed in 100 ml of distilled water and then dried under vacuum overnight before being coated with gold for scanning electron microscopy. The SEM images were taken with an S4000 Field Emission Scanning Electron Microscope from Hitachi (Tokyo, Japan). The particle analysis was performed on a Macintosh computer using the NIH imaging program of the public domain (developed at the National Institutes of Health in the United States and available on the Internet at http://rsb.info.nih.gov/nih -image /). Filtration was carried out using a stainless steel filter holder, a 12ml glass syringe and a syringe pump with variable speed control (Dual Infusion / Withdrawal Pump, model 944, Harvard Apparatus Co., Millis, Mass. ). For each experiment, 10 ml of the particle suspension was filtered through each filter at a constant flow rate of 9 ml / minute. The filtered product was collected in an 11ml glass flask and then transferred to the UV / VIS cell for concentration measurement.

The microporous polypropylene filters were coated with a monomolecular layer of dimethyldioctadecylammonium bromide (DDAB) to give them a positively charged surface. The DDAB was chosen because of the two hydrocarbon chains that can bind hydrophobically to the surface 5 of the polypropylene and render this surfactant insoluble in water. The contact angle was used as a measure of the amount of DDAB adsorption on the surface of the filters. For flat, non-porous and smooth solid materials, contact angle measurements can be made easily by placing a drop of liquid such as carbon tetrachloride 10 on the surface of the substrate and measuring the angle using a microscope adapted with a goniometer eyepiece. Nevertheless, for polypropylene filters, contact angle measurements are a bit more difficult. First, carbon tetrachloride should not be used because it is too hydrophobic and is absorbed into the fibers upon contact. A preferred liquid that is suitable for this material is 1,1-2,2-tetrabromoethane. Second, the surface of a microporous filter is not smooth. The roughness of the surface can increase or decrease the contact angle. For wetting surfaces,? <90 °, the roughness of the surface reduces the contact angle, but increases for surfaces that are not wetting (Davies ef al., 1961). For this reason, an average of six readings were taken in different places on the surface of the filter. A high contact angle may indicate that the surface is hydrophilic. On the contrary, an angle of riai ^. ^ ^^^^, __ - ^^^^^^^^^^^ jiijfltffc ^^ flfflai ^^^^ teh low contact may mean that the surface is hydrophobic. The average contact angle for untreated filters was approximately 25 °. The filters treated with 5 mM DDAB solution had the lowest contact angles between the treated filters, and the filters treated with 10 mM DDAB had the highest contact angles. Because the standard deviation of this measurement was very large, the difference in filters treated with 10 and 20 mM DDAB was not very significant. Therefore, treatment with 10 mM was chosen as the standard treatment method for the filters. The adsorption concentration of the cationic surfactant was tested by cleaning the treated filters with different amounts of water and then measuring the contact angles. The amount of water pumped through the filters did not have a significant effect on the contact angle, which indicated that the surfactant was not being removed. The outflows were collected for surface tension measurements. The results indicated that the surfactant was not being removed as detected by surface tension measurements. From previous experiments, it has been shown that 2.5x10 5 mol / L of the surfactant in water decreased the surface tension of water from 72.4 to 43.9 dynes / cm.Thus, the surface tension method is able to detect the DDAB On the micromole scale per liter of water, since both the filters and the particles are not conductive, they were coated with gold before taking the scanning electron micrographs, due to the limitation of the method and the availability of The particles, the adsorption of particles of larger sizes (197 nm and 200 nm) than those used in the experiments, were studied. of real filtration (60 nm). The zeta potential of the untreated filters indicated that the filters had a slight negative charge. The untreated AN06 filters treated with 10 nM DDAB were manufactured by a meltblowing process and were fibrous. Since the untreated filters had a slight negative charge, the negatively charged particles will not adsorb onto the surface due to electrostatic repulsion, but the positively charged particles will be absorbed due to electrostatic attraction. The results of the experiment confirm this. Only a few negatively charged particles adhered to the surface of the untreated filter, while significantly more positively charged particles adhered. The zeta potential of the filters treated with surfactants presented a positive charge for the entire pH scale. In this case, an insignificant number of the positively charged particles were adsorbed on the surface. However, negatively charged particles were irresistibly attracted to the surface. The adsorption of particles is also a function of the suspension concentration. By increasing the suspension concentration, more particles will spread to the filter surface and adsorb onto the surface. The effects of the concentrations of 0.020% by weight of solid materials at 0.050% by weight of solid materials show that the number of particles adsorbed on the filter surface increases with their concentration in the aqueous phase.

The filtration efficiency or elimination percentage improved significantly with the DDAB treatment. For untreated filters, the filtration efficiency varied from 5% to 10%, but after the filters were treated with 10 mM DDAB, the filtration efficiency increased to 50% or 60% for the initial concentration range more low. The increase in capture efficiency was mainly due to the electrostatic attraction between the negatively charged particles and the positively charged polar head of the surfactant molecules on the filter surface. Since the average pore size was 0.6 μm, the increase in capture efficiency was due in part to the smaller pore size in certain regions of the filters due to the adsorption of the surfactant in clusters. However, examining the results for filtration at pH 10.0, it is evident that the increase due to entrapment was not very significant since the filtration efficiency of the treated and untreated filters was very similar. If entrapment is the main mechanism, then the filtration efficiency would not depend on the pH of the suspension unless pH-induced flocculation was occurring. However, if pH-induced flocculation was taking place, then the capture efficiency of the untreated filters would have increased as the pH was reduced. This was not observed experimentally. In addition, the apparently elastic light scattering measurements showed that the average particle size did not increase with decreasing suspension pH, indicating an absence of flocculation at a lower pH.

Because the particles have more negative charge at higher pH values due to a higher degree of ionization, the higher filtration efficiency was expected in the higher pH range. However, the results showed the opposite trend. The capture efficiency was higher in the lower pH range. This tendency could be due to one of the following two effects. Either the surfactant was being removed in the higher pH range or a competitive ion adsorption was taking place. To determine if the surfactant was being removed, the treated filters were cleaned with a pH 10.0 solution. The outflows were collected for surface tension measurements. If the DDAB was being removed, the surface tension of the outflows should have been lower than the pure water due to surfactants on the surface. The results indicated that there was no change in the surface tension of the outflows. The contact angle measurements offered additional proof that the surfactants were not being removed. Even with a wash with 200 ml of pH 10.0 solution, the average contact angle of the surface, 70.7 ± 12.7 degrees, remained approximately the same as those that were cleaned with 30 ml of distilled water. Finally, the filters were rinsed with 30 ml of pH 10.0 solution, followed by 20 ml of distilled water, and then used to filter particles at pH 4.0. The results indicated that the filters were as effective as those that were rinsed with distilled water, which is another indication that the surfactant was not being removed at the higher pH values. Since the surfactants were not being removed, the only explanation was that the hydroxide ions were competing with the negatively charged particles for the places of the positively charged surfactant. At pH 10.0, for example, due to the high number of hydroxide ions and due to their higher mobility due to their smaller size, they spread to the filter surface much faster than the large negatively charged particles. It is believed that it was the competitive adsorption mechanism of low and high suspension pH values, where the adsorption of the hydroxide ions protected the charge of the surfactants from the particles, and therefore, the particles were not adsorbing to the surface of the filters.

EXAMPLE 2 Novel method for coating filter media with precipitates of metal hydroxides and / or metal oxides and the resulting coated filter media The present invention relates to a novel method for coating filter media with precipitates of metal hydroxides and / or metal oxides and the resulting coated filter media. The resulting coated filter media can be used in, for example, devices for water purification for survival or personal, home water filters, air filters, filter media for water recovery, water maintenance procedures, soil maintenance procedures, filters to eliminate viruses, and protective clothing. Glass fiber air filters, woven and non-woven fabrics or filters, sand, and diatomaceous earth were coated in this experiment, as mentioned above. Their elimination efficiencies were determined for the individual pollutants studied.

EXAMPLE 3 Filtration of microbes with polypropylene filters treated with surfactants This example refers to the use of polypropylene filters treated with surfactants for the filtration of bacteria and bacteriophages. Two different types of bacteria and three different types of bacteriophages were chosen for experiments to determine the effectiveness of said filtration. The two bacteria were Staphylococcus aureus (ATCC 12600), a Gram-positive bacterium, and Escherichia coli (ATCC 15597), a gram-negative bacterium. The bacteriophages were used as substitutes for human pathogens. Three widely studied phages were chosen to represent a wide range of properties that human pathogens may have. The phages and their respective hosts were MS2 (Escherichia coli C-3000), fX-174 (Escherichia coli KC) and PRD-1 (Salmonella typhimurium). A comparison between MS2 and PRD-1 can help delineate the effect of virus size and the comparison between MS2 and fX-174 can help reveal the effect of the isoelectric point or load characteristic. All calculations of filtration efficiency and filter coefficient are based on the number of viable bacteria and bacteriophages. Therefore, it should be noted that although the term "adsorption" or "adhesion" is used to explain the differences between the number of bacteria in the inflow and outflow, some of these differences may be due to the fact that the coatings Surface or shear or transport procedure kill bacteria or bacteriophages. The filter coefficient, in essence, explains all the microbial reduction mechanisms in the solution. Throughout this application the terms "bacteriophage", "phage", and "virus" will be used interchangeably. The microporous polypropylene filters can be treated as described above in example 1. For the filtration of bacteria and phages, AN25 filters having an average pore diameter of 2.5 μm were used. By using larger pore size filters, the pressure drop can be reduced and leaks in the filter holders can be minimized. In microbial filtration, multiple layers of filters can be used. The bacteria used for the experiments were grown overnight in a 3% tryptic soy broth and then diluted by a factor of 1000 in a pH buffer made of 0.02 M of midazole and 0.02 M of glycine and adjusted with HCl at pH 7.0. This gives the approximate initial concentrations of 2x105 for S. aureus and 1x105 for E. coli. The filtration apparatus consisted of a variable speed Infusion-Withdrawal Syringe Pump (Harvard Apparatus Co., MA), six 25 mm stainless steel filter holders (Fisher Scientific) connected in series, and plastic valves and connectors for sampling ports. Each filter holder contained a polypropylene filter layer. The filters were oriented vertically and the direction of flow was upwards so that no air bubbles remained trapped in the filters or in the line. The flow rate was maintained at a constant flow of 10 ml / minute. A total of 120 ml of contaminated water was pumped through the filters. After approximately 20 ml of contaminated water had passed through the filters, the first sample was taken starting from port 1 at the bottom. After all the samples from the different ports were taken, a second sample was taken from each port in the reverse order, and then a third sample from each port was taken starting from the lower port. The samples were diluted with a solution containing 1% tryptic soy broth. Bacterial concentration was measured within 12 hours using the smear plate method (Gerhardt, 1994) using Mannitol Salt Agar for E. aureus and MacConkey Agar for E. coli. Each sample was plated in duplicate.

The same apparatus and procedures were used in bacteriophage filtration experiments. The initial phage concentrations were approximately 3x105, 3x106 and 6x104 PFU / ml for MS2, PRD-1 and fX-174, respectively. Phages were analyzed immediately after filtration using the soft agar shell method described by Snudstad and Dean (1971). In bacteria filtration, S. aureus and E. coli were mixed together in a solution before being used in the experiment. Similarly, in the bacteriophage filtration, all three phages were added to the buffer solution at the same time. This was done to reduce the number of experiments required. Because both bacteria were tested at the same time, the preferential adsorption of the bacteria can also be determined from the results. Similarly, the preferential adsorption of phages can also be observed. The information on the selective adsorption of a microbe on the others is important since in real life situations, contaminated water always contains more than one type of microorganism. The untreated polypropylene filter has a negative charge in the range of pH 4.0 to 10.0, wherein the filter treated with 10 mM DDAB, on the one hand, has a positive charge in the same pH range. The results of the filtration of both E. coli and S. aureus are shown. The filters treated with 10 mM surfactants removed the bacteria much better than the untreated filters. The data points are adjusted to the following equation to obtain the filter coefficient: ? _ C ^ entry - C ^ exit _ i ~ ^ L "entered (3-1) where? Is the filtration efficiency or elimination percentage, Centered is the initial concentration in colony forming units per milliliter (CFU / ml) for bacteria and plaque forming units (PFU / ml) for phages, Csaiida is the final concentration, L is the length of the filter in units of number of layers, and? is the filter coefficient with units of 1 / filter layer. It is advisable to convert the results to filter coefficients to compare the effectiveness of the different coatings for bacteria removal.The filter coefficients and linear regression coefficients are shown in Table 3-2.The linear regression coefficient indicates how well the adjust the information points to the filtration equation, with a value of 1.0 as a perfect fit.The filter coefficients of the untreated filters are 0.485 and 0.353 [1 / number of filters] in the filtration of S. Aure us and E. coli, respectively. The filter coefficients of the filters treated with 10 mM DDAB are 1039 and 0.896 in the filtration of S. aureus and E. coli, respectively. From the filtration equation, it is obvious that the higher the filter coefficient, the better the filtration efficiency. The filter coefficients as defined in this application have units of 1 / number of filters. In the filtration of S. Aureus, there is an improvement of 114% in the filter coefficient. In other words, to obtain the same percentage of elimination of S. Aureus, the untreated filters would require 114% more filter layers than the filters treated with surfactants. For the filtration of E. coli, the improvement in the filtration coefficient is even more significant than the improvement for S. Aureus. The improvement for E. coli filtration was 154%.

TABLE 3-2 Filter coefficient (?) And linear regression coefficient (R2) for untreated AN25 treated with 10 mM DDAB for different bacteria Because bacteriophages are much smaller than bacteria, the filtration efficiency or percent removal of both untreated and treated with surfactant filters is not expected to be as high as the kill percentage for bacteria. The results for both untreated filters and treated filters have a high degree of dispersion or standard deviation. The data for the untreated filters have a very poor R2 setting of 0.28 to 0.38 when they fit equation 3-1. Isoelectric points (IEP), the pH at which the zeta potential is zero, of the bacteriophages MS2, PRD-1 and FX-174 are 3.9, 4.2 and 6.6, respectively. At pH values below the isoelectric points, the phages have positive charges and at a pH above the isoelectric points, they have a negative charge. Although no zeta potential data is available as a function of pH, it can be inferred from the isoelectric point that in the neutral pH range most likely MS2 has a higher negative charge density than PRD-1 and FX-174. With an IEP of 6.6, FX-174 has only a slight negative charge at pH 7.0 of the experiment. Coating with positively charged surfactants in the polypropylene filters greatly improved the filtration efficiency of the filters for the bacteriophages MS2 and PRD-1, but was not as effective for the elimination of the bacteriophage FX-174. The filter coefficients for the untreated polypropylene filters are 0.062, 0.069 and 0.069 for the filtration of MS2, PRD-1 and FX-174, respectively. As expected, the filter coefficients are very low because the phages are much smaller than the bacteria. Also, the filter coefficients for filtering the three different phages for the untreated filters are the same because the removal is negligible and probably due to deformations or entrapment mechanism.

For filters treated with surfactants, the filter coefficients are 0.345, 0.269 and 0.084 for the filtration of MS2, PRD-1 and FX-174, respectively. In the MS2 filtration, there is a 458% improvement in the filter coefficient. In the filtration of PRD-1, there is an improvement of 288% in the filter coefficient, and in the filtration of phage FX-174 an improvement of 22% is obtained. This small improvement is within the standard deviation and therefore, surface modifications based on columbian interaction may not be useful in phage FX-174 filtration. This is possibly due to the fact that the phage is very close to its isoelectric point (ie pH 6.6). The bacteriophage MS2 has the lowest isoelectric point and the highest filter coefficient. These results reinforced the idea that electrostatic attraction is an important factor in bacterial and viral adsorption to surfaces.

TABLE 3-3 Filter coefficient and linear regression coefficient for untreated AN25 and treated with 10 mM DDAB for different bacteriophages Because the concentrations used in the experiments were too low to see the bacteria on the filter surface under increased magnification, the filters were soaked in a solution containing high concentrations (Ix 107 CFU / ml) of E. Coli and S. aureus for 30 minutes. 5 After soaking in the solution for 30 minutes, the filters were completely washed 3 times with deionized water. They were then placed in a container containing osmium tetraoxide vapor for 2 days to fix the cells so that they would not burst, break or shrink in the drying step. The filters were then air dried and covered with gold for SEM analysis. When observing the wetting capacity of the filters, it was observed that the wetting capacity of the filter was not uniform throughout the filter. Bacterial adsorption on the filter surface was not uniform throughout the filter surface. When studying the adsorption of S. aureus and 5 E. coli on the polypropylene filter treated with 10 mM DDAB, it was shown that a large part of the microbial adsorption occurred in the central region of the filter. The areas around the edges have some bacteria but not as high a concentration as in the central region. For the untreated filter, only few S. aureus and E. coli cells were found on the filter surface 0. On the other hand, the filter treated with surfactant, attracted many more bacteria to the filter surface, especially in localized areas. There was an important difference between the adsorption of bacteria on the filters treated with surfactant and untreated. The spherical particles A-ajfc ^ jaB- -eiW! they are S. aureus bacteria and the bar-type particles are E. coli bacteria.

EXAMPLE 4 5 Microdenier Polyester treated with surfactant Polyester yarn has many industrial and consumer uses, which include clothing, strings of tires for tires, conveyor belts, waterproof tarpaulins and fishing nets. The Microdenier polyester fabric is selected for the filtration of nanoparticles and biological particles because it is readily available and to which it is tenacious. Therefore, it can handle high flow rates and high pressure drops. In addition, since it is textured and woven, it increases the flow path sinuosity and therefore increases the probability that the particles collide with the surface of the filters. The thread used to make the fabric, as described in the next section, is a microdenier thread, but the term "microdenier polyester" and "polyester" will be used interchangeably throughout the discussion of the experimental result in this application since only a type of thread was tested. Other terms, which will have the same meaning in this context are bacteriophages, phages and viruses. Bacteriophages or phages are specific host viruses. Therefore, they will be used interchangeably.

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The microdenier polyester fabric used in the experiments in question consists of an S twill of 2 x 2, weighing approximately 186.48 g / m2 and constructed of a microdenier textured 1/140/200 polyester yarn, Type 56T Dacron® from DuPont in the warp direction and a microdenier 1/150/100 textured polyester yarn, Type 56T Dacron® from DuPont in the weft direction. The construction of the fabric was 76 passes in the weft direction and 176 ends in the warp direction. The fabric was cut in 25 mm circles with a die cutter before the surfactant treatment was applied. Once the filters were cut in circles, they were treated with a 10 mM solution of DDAB using previously described procedures. Before using the filters in the experiments, they were washed with 120 ml of deionized water. The filtration apparatus used for these experiments is the same as described and shown in example 3. The filtration and sampling procedures are the same as those used for example 3 with the exception that each filter holder contained 4 layers of these cloth filters instead of a layer. The zeta potentials of the microdenier polyester filters treated with 10 mM DDAB and untreated were measured with a potential current device. Six layers of the fabric were used in each measurement. The untreated filters are negatively charged from pH 4 to pH 9.0 while the polyester filters treated with surfactant are positively charged at the same pH scale.

Z¡S £. S & - ^^ s- ^ - ^ * * For the pressure drop experiment, the apparatus is the same as for filtration experiments. The flow velocity was maintained at a constant speed of 268.22 m / sec. and the pressure in each port was measured with a digital pressure indicator. From these pressures, the pressure drop for each filter holder (4 layers of fabric filters) was calculated. For untreated filters, standard deviations are greater than filters treated with surfactant. For untreated filters, pressure drops range from 0.04921 kg / cm2 per 4 filter layers to 0.21793 kg / cm2 per 24 filter layers. However, for the filters treated with surfactant, the pressure drop is much lower due to the increase in wettability of the fabric. The pressure drops of the filters treated with surfactant are 0.01406 kg / cm2 and 0.07733 kg / cm2 for 4 layers and 24 layers of the fabric filters, respectively. The decrease in pressure drop with the surfactant treatment is beneficial because it requires less energy to pass the liquid through the filters. Essentially, for the same pressure drop, more yields can be achieved. Two different types of bacteria were used in these experiments. The gram-positive bacteria was E. coli and the gram-negative was S. aureus. These bacteria were prepared according to the procedures described in Example 3. Filtration was carried out at pH 7.0 using a pH regulator of 0.02 M imidazole-glycine. The initial concentrations of the bacteria were approximately 1x105 CFU / ml for both bacteria. The flow rate was maintained at a constant speed of 268.22 m / sec with the use of a syringe pump. Samples were collected in 3 separate times and each sample was plated in duplicate. In general, the standard deviations of the untreated filters are greater than those of the filters treated with surfactant. In addition, the results of the first four layers always have a greater degree of dispersion when compared to the rest of the filters. This is a common problem in filtration experiments, probably due to the fact that the flow has not been fully developed at the entrance of the system. The results show that untreated polyester cloth filters removed more S. aureus than E. coli. One possible explanation is that E. coli is more negatively charged than S. aureus (Sonohara et al., 1995), and therefore the repulsion between the filter surface and the bacterium is greater. In their study of bacterial adhesion to different fabrics, Hsieh and Merry (1986) also found that S. aureus has a stronger affinity for polyester [untreated] than E. coli. The polyester filter treated with surfactant, on the other hand, eliminated the same percentage of both bacteria coming from the aqueous streams. It has been shown that for small particles (Spielman and Friedlander, 1973; Ruckenstein and Prieve, 1973; Li and Park, 1997), the procedure is limited to diffusion once the repulsive energy barrier has been removed. In this case, because the surface is positively charged and the bacteria are negatively charged, there does not appear to be any significant barrier to the adhesion or adsorption process. The rate of bacterial adsorption / adhesion to the filter surface is possibly limited by the transport of the bacteria to the surface and / or the collision of the bacteria with the filter surface. Therefore, because the bacteria are of approximately the same size, the elimination is expected to be similar for E. coli and S. aureus, which was observed experimentally.

TABLE 4-1 Filter coefficient and linear regression coefficient for untreated polyester cloth filter and treated with 10 mM DDBA for different bacteria The filter coefficients of untreated polyester cloth filters are 0.085 and 0.055 [1 / filter] for the filtration of S. aureus and E. coli, respectively. For untreated filters, the process is not limited to diffusion or transport due to the repulsive barrier between the bacteria and the filter surface. Since there is a difference in the filter coefficient or filter efficiency of the untreated filters, factors other than the Columbian interaction are likely to be involved. It is possible that hydrophobic interactions or other specific interactions are involved. For filters treated with DDAB, the filter coefficients are 0.251 and 0.238 for the filtration of S. aureus and E. coli. Within experimental errors, these two numbers can be considered identical. The treatment with surfactant improved the filter coefficient in 195% for the filtration of S. aureus and 330% for the filtration of E. coli. The same apparatus and procedure was used in the bacteriophage filtration experiments. The initial phage concentration was approximately 3x105, 6x104 and 3x106 PFU / ml for MS2, FX-174 and PRD-1 respectively. The phages were analyzed immediately after filtration using the soft agar cover method described by Snudstad and Dean (1971). For the MS2 filtration, only about 20% of the phage in the inflow could be removed with 24 layers of untreated polyester filter. These elimination efficiencies are much lower than those of the bacteria because the phages are about 10 times smaller than the bacteria. The surfactant treatment significantly increased the filtration efficiency of MS2. With 24 layers of the treated filters, about 98% of MS2 was removed in the inflow. Similar trends were observed for the filtration of PRD-1, with 24 layers of treated filters eliminating about 97% of the phage in the inflow. In the filtration of bacteriophage FX-174, the results are very different. The filters treated with surfactant were not as effective by eliminating FX-174 as they were when removing MS2 and PRD-1. Even with 24 layers of filters, less than 40% of the phage in the inflow was removed. All the data points were adjusted to an exponential damping equation described in example 3. The filter coefficient 5 of the untreated filters for the filtration of MS2, PRD-1 and FX-174 are 0.008, 0.005 and 0.009, respectively. Due to the large dispersion of data for untreated filters, the coefficients are statistically the same. Viruses or phages are not expected to adsorb to the surface of untreated filters. Therefore, it is possible that the elimination is due to voltage or entrapment of the particles in the structure of the filters. However, for filters treated with surfactant, the results of the various phages are very different. The filter coefficients are 0.268, 0.158 and 0.018 for the filtration of MS2, PRD-1 and FX-174, respectively. There is a strong correlation between the isoelectric point (IEP), the pH at which the zeta potential is zero and the filtration coefficients and therefore the filtration efficiency. The isoelectric point of bacteriophage MS2, PRD-1 and FX-174 are 3.9, 4.2 and 6.6, respectively. Seeing these numbers, MS2 has the lowest isoelectric point, followed by PRD-1 and then FX-174. Due to low IEP, MS2 should be the phage more negatively loaded in the experiment condition, followed by PRD-1 and FX-174. Due to this high charge density, MS2 has the highest adsorption for the filter. The treatment with surfactant increases the filter coefficient by 3300%, which means that to obtain the same percentage of elimination of MS2, the length (filter number in this case) of the untreated filters must be 33 times greater than the treated filters. The filter coefficient improves by 2800% in the filtration of phage PRD-1. In the FX-174 filtration, the filter coefficient is improved by only 98%. This improvement is rather insignificant because the standard deviation is definitely high. Due to its high IEP of 6.6, the phage is only slightly negatively charged at the experimental pH of 7.0. Other researchers have shown that FX-174 is one of the most difficult phages to remove from aqueous streams and air due to its poor adhesion to surfaces. To verify that the bacteria were attracted to the surface of the filters, the first layer was examined with a scanning electron microscope after having passed through it a bacterial solution of 1.0 L containing S. aureus (approximately 1x105 CFU / ml ) and E.coli (approximately 1x105 CFU / ml). The filter was then rinsed with deionized water in a beaker to remove loose bacteria from the surface. The wet sample was prepared for SEM analysis by placing the contaminated filter in a chamber saturated with osmium tetraoxide vapor for 2 days. Then the filter was removed and allowed to dry overnight. Once the sample was dried, it was covered with a thin layer of gold. SEM analysis was performed with a Hitachi S4000 Field Emission Scanning Electron Microscope (Tokyo Japan). The amount of bacteria on the surface of the filters is very small. These descriptions are not representative of the surface of the filters. The bacterial concentration in these filtration studies is only about 1x105 CPU / ml. Therefore, it is not expected to find many bacteria in such a small surface area, due to the increase required to see the microorganisms. It is also possible that many of the bacteria did not survive the SEM preparation procedure. Some of the cells may have died and broken before they could be fixed with the osmium tetraoxide vapor. In an effort to show that the surfaces of the treated filters are actually more active than the untreated filter, solutions containing a higher concentration of bacteria were used. In this study, each filter was soaked in a solution containing a mixture of 2.0 ml of S. aureus and E. coli for 30 minutes. Bacterial solutions were taken directly from the growth broth without dilution. Their concentrations were approximately 1x107 CPU / ml after soaking for 30 minutes, the filters were rinsed with deionized water three times before they were fixed with osmium tetraoxide vapor and analyzed according to the procedure previously described. Bacterial adhesion (S. aureus and E. coli) to the surface of the untreated polyester cloth filter is shown in Figure 4-12. Only a few bacteria are seen in these drawings. Untreated filters are negatively charged and therefore can actually repel bacteria instead of attracting them. On the other hand, the filters treated with surfactant are positively charged and therefore, it is likely that bacteria will be attracted to the filter surface. Significantly more bacteria, S. aureus and E. coli, were adsorbed to the treated filter surface. It appears that surface charge modification can substantially increase the number of bioparticles that adhere to the filter surface and therefore increase the filtration efficiency.

Example 5 Removal of microorganisms from water by sand covered with ferric and aluminum hydroxides.

The source of sand was "All Purpose Sand" by Pebble Junction, Division of Delaware Valley Landscape Stone, Inc., Sandford, Florida. The sand was sieved in a size less than 100 meshes before use. To cover, the sand was soaked in one of the following solutions: aluminum chloride or ferric chloride (Fisher Scintific, Pittsburgh, PA) in concentrations of 0.05 M, 0.1 M, 0.5 M, or 1.0 M. In some tests, a combination was used of 1.0 M ferric chloride and 1.0 aluminum chloride. The coating was applied with heat and agitation similar to the temperatures and agitation described in examples 2 and 6. Sufficient solution was used to completely cover the sand. After 30 minutes, the solution was removed and the sand allowed to dry. Occasional stirring was used to dissolve the lumps that formed and ensure that the sand dried completely. Then, the sand was added to two 3M volumes of ammonium hydroxide and left to soak for 10 minutes. The ammonium hydroxide was removed, the sand dried again with occasional stirring. The dried sand was rinsed and stored at room temperature until use. Escherichia coli (ATCC 13607) was obtained from the American Type Culture Collection and used in column and batch adsorption experiments. Escherichia coli was routinely grown in Tryptic Soy Broth (Difco Labs, Detroit, Ml) and analyzed using MacConkey agar (Difco Labs, Detroit, Ml). A strain 124 of Vibrio cholera isolated from Chillón River, Lima, Peru, was supplied by Dr. Tamplin of the Department of Food Science at the University of Florida. 10 It was developed in Tryptic Soy Broth and analyzed using Tryptic Soy Agar plate (Difco Labs, Detroit Ml) containing 1% sodium chloride (PH7). Poliovirus 1 (strain LSc-2ab) was developed in green buffalo monkey (BGM) cells and analyzed as plaque forming units (PFU) using a cover technique with agar (Smith and Gerba, 1982). The bacteriophage MS-2 was developed in Escherichiacoli C-300 (ATCC 15597) and analyzed by soft agar cover (Snustad and Dean, 1971). All tap water used in this study was dechlorinated by the addition of sodium thiosulfate, residual chlorine was determined using O-tolidine (American Public Health Association, 1995). The water in the dechlorinated key was then impregnated with bacteria or viruses. Raw sewage was collected from the sewage treatment plant at the University of Florida and used the same day.

The untreated or modified sand was packed in columns of different sizes. The sizes of columns used and the weight of dry sand added were as follows: A. girl: 10 x 2.5 cm with 80 g of sand; B: Large: 35 x 5 cm, with 1 kg of sand. Glass wool (Fisher Scientific, Pittsburgh, PA) was placed at the base of each column. Before being used in the experiments, deionized water was passed through the columns until the unbound metal hydroxide was removed and the column outlet flows were transparent and free of precipitates. Samples were passed through the columns using gravity flow (small size columns) or under positive pressure by pressurized nitrogen gas (large size columns). In the small size columns, 160 ml of samples were passed separately through the columns. Samples of 40 ml were collected and analyzed. The initial samples, the column exit flows and the rinse were analyzed to determine the elimination efficiency. In the large size columns, four liters of sample were passed at 450 ml / min. After the passage of the first 500 ml, the column output flows were analyzed. Both the initial samples and the column output streams were analyzed for bacteria or viruses. Four liters of tap water were dechlorinated by the addition of sodium thiosulfate (0.0002% final concentration) and passed through the columns (35.0 x 5.0 cm) containing one kilogram of modified sand (with 1.0 M aluminum chloride and 1.0 M ferric chloride) or unmodified at a rate of 450 ml / min. daily for 48 days. Once a week, 4 liters of water were impregnated from the dechlorinated key with E.coli KC, and MS-2, passed through the columns at the same flow rate and collected. Initially and after the passage of 120 liters of water through the filters (29 days), the columns were attacked with polyvirus in addition to two other microorganisms. This was repeated after the passage of 198 L of water (48 days). Both the initial samples and the column exit flows were analyzed for the three microorganisms. At the end of the study, 192 liters of water had passed through each of the sand columns. After the adsorption experiments were performed with small columns (10 x 2.5 cm, 80 g) as described above, 40 ml of rinse water was collected and passed through the column, then 160 ml of 3% were passed of beef extract at pH 7 (Becton Dickinson, Cockeysville, MD) to elute the adsorbed microorganisms. The microorganisms in the initial sample, the column exit flow, the rinse and the column elution were analyzed for bacteria or viruses to determine the elimination and recovery efficiencies. Water from the dechlorinated key by sodium thiosulfate was passed through the columns containing untreated or modified sand columns (10 x 2.5 cm, 80 g). The output streams of the column and a water control of the tap were impregnated with microorganisms. The samples were analyzed initially and after three hours of incubation at temperature rr- '~ z¿nuaßr? environment to determine the effect of column exit flows on the survival of microorganisms. Modified or unmodified sand (5 g) was mixed with 7 ml of one of each of the following pH regulators that had been impregnated with E. coli or MS-2: A: 0.02M imidazole and 0.02M glycine, pH 7; B: pH regulator A + 0.1 M sodium citrate, pH 7; C: pH regulator A + 0.1% tween 80, pH 7; D: pH regulator A + 0.1 M sodium citrate, 0.1% tween 80, pH 7). The samples were mixed on a rotary shaker at approximately 100 rpm for 15 minutes. The initial and final supernatants were analyzed. Microorganisms were also added to the pH-free pH-regulator samples as controls. Modified or unmodified sand (5 g) was stirred with 7 ml of pH buffer (0.02M imidazole and 0.02M glycine pH 7) which had been impregnated with E. coli MS-2 at approximately 100 rpm for 15 minutes. After this period of adsorption, the supernatant was removed and analyzed. Then, 7 ml of each of the following pH regulators were added: A: 0.02M imidazole and 0.02M glycine, pH 7; B: pH regulator A + 0.1 M sodium citrate, pH 7; C: pH regulator A + 0.1% tween 80, pH 7; D: pH regulator A + 0.1 M sodium citrate, 0.1% tween 80, pH 7; E: 3% beef extract, pH 7). The samples were stirred for another 15 minutes at 100 rpm in a New Brunswick scientific orbit agitator. The impregnated initial pH regulator, the supernatant sample from the adsorption step and the supernatant samples from the elution steps were analyzed. As controls, the sand-free pH regulator samples were impregnated with E. coli and MS-2 and shaken for 15 minutes to observe their effects on the test organisms. The standard deviations, inclinations, correlation and general probabilities of t-test were determined using PSI-Plot software (Poly Software International, Salt Lake City, Utah). Inlet flows and column outflows were analyzed by Argon Coupled Induction Spectroscopy. The effects of the different concentrations of ferric chloride and aluminum, used to modify the sand, in the adsorption of microorganisms to sand columns (10 x 2. 5 cm., 80 g of sand) are shown in Table 5-1. . The greater the concentration of chemicals added to modify the sand, the greater the elimination of microorganisms. There was a linear correlation between the concentration of the salt used to treat the sand and the logio elimination of the tested microorganisms, r > 0.8. Columns that contain modified sand using 0. 1 M FeCl3 reduced E. coli and MS-2 by more than 99.9%. Equivalent eliminations were obtained using sand modified with 0.05M aluminum chloride. Columns containing modified sand with higher concentrations of metal chloride reduced concentrations of E. coli and MS-2 by more than 5 log-io. In contrast, columns containing untreated sand only eliminated 0.53 log-io of MS-2 and less than 0.62 log of Escherichia coli. The flow velocity of the treated and untreated sand columns was approximately 90 ml / min. The pressure drop across the treated and untreated sand columns was similar (data not shown). The columns (10x2.5 cm., 80 g of sand) containing sand 5 modified using 0.1 M ferric chloride and 0.1 M aluminum chloride reduced MS-2, Escherichia coli, and Vibrio cholera in 7.7 log-io, 5.3 log- io, and 2.2 logio, respectively (Table 5-2). The combination of both chemicals to modify sand used in the filters had a synergistic effect. The increase in the concentration of both salts used to modify the sand at 1.0 M produced a small change or no change in the elimination of MS-2 but significantly increased the elimination of E. coli and V. cholera. Sand modified with the combination of 1 M ferric chloride and 1 M aluminum chloride was used in additional studies on elimination of microorganisms from water. 15 Large columns with modified sand reduced the number of E. coli in 5 Logio (99.999% removal) after the passage of 28 liters of water. After the passage of 172 liters of tap water, the columns removed more than 90% of E. coli. However, with the passage of more water, the columns with modified sand showed a capacity decreased to eliminate E. coli. At the end of the test, the columns containing either treated or untreated sand were similar in their ability to eliminate E. coli. In contrast, columns containing modified sand reduced the number of MS-2 by more than 5 logio after passage of 148 liters of tap water. After 192 liters of water passed through the columns, they were able to eliminate 99.9% of MS-2. The columns containing modified sand could reduce the level of polio 1 in 4.1 logio units on day 1. A reduction of more than 3 logio was obtained after the passage of 120 liters of water, while the columns containing untreated sand eliminated less than 1 log? 0 of polio 1 of the tap water impregnated throughout the experiment. After the passage of 192 liters the columns removed approximately 90% polio 1 from the tap water. The raw sewage impregnated with MS-2 passed through the columns (10.0 x 2.5 cm, 80 g) at different temperatures. The modified sand columns reduced more than 4 log-io of coliform bacteria from the raw sewage at room temperature. The elimination capacity was related to the temperature, while a better elimination was observed at higher temperatures. Columns containing modified sand removed more than 3 log-? 0 of MS-2 at each of the three temperatures tested. More MS-2 was removed at 25 ° C and 37 ° C than at 4 ° C. The untreated columns at all temperatures tested had a logio elimination of less than 0.3 and 1.0 for MS-2 and E. Coli, respectively. In the column-adsorption-elution experiments, modified sand columns removed more than 99.9% of E. coli and MS-2 from water (Table 5-3). None of the microorganisms adsorbed to the modified sand columns could be detected in the water rinse of the dechlorinated key. However, more than 10% of the retained microorganisms could be washed from the columns containing untreated sand. When 3% beef extract was passed with 0.1 M sodium citrate at pH 7 through the columns, a higher percentage of microorganisms was eluted from the modified and untreated sand columns. Nevertheless, in the case of E. coli, the total recovery of the columns with modified sand was only about 5%. A greater percentage of E. coli was eluted from the columns containing unchanged sand even though these columns had a lower elimination efficiency. It was possible to explain 74% of E. coli that was initially applied to the columns. The majority of MS-2 (66%) adsorbed to the columns containing modified sand could be eluted. It was possible to explain about 90% of the MS-2 inflow in the columns containing untreated sand. The outflows of columns containing the modified sand did not deactivate E. coli or MS-2 when impregnated with these and incubated at room temperature for 3 hours (data not shown). In the batch adsorption experiments (Table 5-4), Tween 80 was found to interfere with the adsorption of E. coli, but had a small effect on the adsorption of MS-2. Sodium citrate decreased the adsorption of E. coli, and completely eliminated MS-2 adsorption. The combination of Tween 80 and sodium citrate reduced the adsorption of E. coli and MS-2 as much as did citrate alone.

After the adsorption of microorganisms in batch experiments, the solutions were tested for their ability to elute the adsorbed microorganisms (Table 5-5). PH regulator solutions alone or pH regulator with Tween 80 did not elute any of the adsorbed microorganisms. A portion of E. coli and MS-2 adsorbed was eluted by solutions of sodium citrate, sodium citrate + Tween 80, and beef extract. Neither the pH regulator nor the eluents deactivated MS-2 or E. coli, except for sodium citrate which deactivated 90% E. coli after three hours (data not shown). No deactivation was observed in the 20 minutes duration of the test. Columns containing modified sand removed more microorganisms than columns containing untreated sand at each tested pH (pH 5, pH 7, and pH 9) (Table 5-6). The best eliminations were observed at pH 7 for E. coli and MS-2. The outflows and column inlet flows contained less than 0.01 μg / ml of ferric or aluminum when tested by Induction Coupled Argon Plasma Spectroscopy.

Ma ^ ^^^^^ fa ^ É ^^^^^ TABLE 5-1 The effect of the concentration of aluminum or ferric salt used to modify sand in the elimination of microorganisms by means of modified sand columns * * The columns (10.0 x 2.5 cm) containing 80 g of 100-mesh sand modified with FeCI5 and AICI5 values represent the average and standard deviation of series in triplicate.

TABLE 5-2 The elimination of microorganisms by means of filters containing said modified sand by a combination of FeC and AIC Notes: The values represent the mean and standard deviation for elimination by means of three columns (10.0 x 2.5 cm, 80 g of 100-mesh sand). In each row, values with the same letter were not significantly different from P > 0.05.

TABLE 5-3 Elution of Escherichia coli and MS-2 adsorbed to sand filters Notes: An initial sample of 160 ml of water from the dechlorinated key was impregnated with approximately 5x106 PFU / ml of MS-2 or 1x106 PFU / ml of Escherichia coli and passed through 10.0x2.5 cm of columns containing 80 g of 100-mesh sand Afterwards, 40 ml of water from the dechlorinated key was passed through without impregnation through the columns. Then, 160 ml of 3% 1.0 M sodium citrate res extract was passed through the columns. The percentages for MS-2 and E. coli in the outflow d column, wash and elution were determined based on the number in the initial sample. The values represent the mean and standard deviation. It will give the DOG columns triDlicated.

TABLE 5-4 Effect of salt and detergent on the adsorption of Escherichia coli and MS-2 for modified sand 15 The adsorption was performed in the presence of the pH regulator containing 5.93 + 0.15 logio cfu / ml E. coli and 5.28 + 0.48 log10 pfu / ml. MS-2 PH regulators: 0.02M imidazole and 0.02 M glycine, pH 7; all chemical solutions were made in this pH regulator and adjusted to pH 7. The values represent the mean and standard deviation for triplicate determinations (5 g of 100-mesh sand treated with 1M FeCIs + 1M AICI5). For each column, the values followed by the same letter were not significantly different at the P > 0.05.

TABLE 5-5 Effect of salt and detergent on the elution of MS-2 and E. coli previously adsorbed from modified sand The adsorption was carried out in the presence of the pH regulator containing 5.93 ± 0.15 log ™ cfu / ml. E co / i and 5.28 ± 0.48 long10 pfu / ml. MS-2 PH regulators: 0.02 M midazole and 0.02 M glycine, pH 7; all chemical solutions were made in this pH regulator and adjusted to pH 7. The values represent the mean and standard deviation for triplicate determinations (5 g of 100-mesh sand treated with 1 M FeCI5 + 1 M AICI5).

For each column, the values followed by the same letter were not significantly different at the P > 0.05.

TABLE 5-6 Effect of pH on the elimination of microorganisms by sand filters The values represent the mean and standard deviation of triplicate columns (10.0x2.5 cm, 80 g of 100-mesh sand). The E. coli titration was 6.06, 5.52, and 5 94 log-? 0 CFR / ml in pH regulators of pH 5.7, and 9, respectively. The MS2 titration was 5.66, 6.19, and 6.49 logio PFU / ml in pH regulators of pH 5.7, and 9, respectively.

EXAMPLE 6 Elimination of microorganisms through a filter containing sand coated with metal hydroxides Modification of sand. Silica sand (Oglebay Norton, Brady TX) was purchased at a local pool supply store. To coat, the sand was soaked in a solution containing 0.2 M ferric chloride and 0.4 M aluminum chloride. After 30 minutes, the excess solution was removed and the sand allowed to dry at 80 ° C. Occasional stirring may be used to dissolve the lumps that formed and ensure that the sand has completely dried. Then, the sand (still warm) was added to 2 volumes of 3 M ammonium hydroxide and left to soak for 10 minutes. The ammonium hydroxide was removed, and the sand was dried again with occasional stirring at 80 ° C. The dried sand was rinsed and stored at room temperature until used.

Bacterial cultures The following bacterial strains were used in elimination studies: Escherichiacoli C-3000 (ATCC 15597), which was routinely cultured in Tryptic Soy Broth (TSB) and analyzed using MacConkey Agar (Difco Labs, Detroit, Ml); and Staphylococcus aureus (ATCC 12600), which was grown in TSB and analyzed in Mannitol Salt Agar (Difco Labs. Detroit, Ml).

Viral and virus analyzes. Polio virus 1 (strain Lsc), Echo virus 1, and Coxsackie virus B5 were cultured in buffalo monkey green cells (BGM) and analyzed as plaque forming units (PFUs) using an agar-coated technique (Smith and Gerba, 1982). Rotavirus SA11 was cultured with serum-free media in MA 104 cells and analyzed using the Most Probable Number software (Environmental Protection Agency, 1994). The following bacteriophages and their host bacteria were used: MS2 (Escherichia coli C-3000 ATCC 15597); fX 174 (Escherichia coli, ATCC 13607); PRD-1 (Salmonella typhimurium, ATCC 19585). The baceriophages were cultured in their respective hosts and analyzed by soft agar cover (Snustad and Dean, 1971).

Protozoan parasites Viable oocysts of Cryptosporidium parvum were obtained from Waterbome Inc. (New Orleans, LA). For enumeration, Cryptoglow ™ staining was used according to the manufacturer's instructions and the oocysts (Waterbome, New Orleans, LA) were visualized and counted under a fluorescence microscope.

Filter system and water samples. Two identical filtration systems were used; one contained modified sand as described above and the other contained unmodified sand. Each filter system consisted of a commercial pool filter Porpoise 180 (Porpoise, Jacksonville, FL) that operated by an electric pump controlled with a stopwatch at 151.41 It / min. connected to a water container of 378.53IL Each filter contained 220 kg of sand in an area of 0.05M3. The tap water circulated through the filter for 5 hours a day during the 170 days of the test period. A total chlorine residual of 2 ppm was maintained in the water tanks while the filters operated. Ten times that residue was used for super chlorination at monthly intervals to simulate pool treatment practices. The tank water was changed frequently and samples were taken for metal analysis. Before impregnating with bacteria or viruses, the tanks were dried and filled with water that had been dechlorinated by the addition of sodium thiosulfate. Chlorination was carried out through the addition of household bleach. Residual chlorine was determined using O-tolidine (American Public Health Association, 1989).

Elimination of microorganism. During the entire test period, Cryptosporidium bacteria, viruses and oocysts were added to 378.53 I of water from the dechlorinated key to obtain an initial concentration of approximately 105 / ml. The tanks were mechanically shaken for 15 minutes and the samples were taken before filtration. They were then passed through each filter and 189.26 lbs. Of the impregnated water was collected. The samples of inflow and outflows in triplicate were analyzed and used to determine the percentage of elimination of the different microorganisms. In separate experiments, 378.53 It of water was impregnated with microorganisms and the water circulated through the filter for 1 hour. The samples were dried in triplicate before and after circulation and the percentage of elimination of the test microorganisms was determined.

Statistic analysis. The standard deviations, correlations and general probabilities of t test were determined using PSI-Plot software (Poly Software International, Salt Lake City, Utah).

Analysis of metals in water. The metals in the water were analyzed before and after filtration, by means of Argon Plasma Spectroscopy Coupled by Induction. ~? *? a? *? Ukl ii ~ *. ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ At the beginning of the study, both the one-step experiments and the recirculation tests in water were carried out for 1 hour (Table 6). -1 ). After one step through the filter, the average removal of all viruses by the filter containing untreated sand was only about 5-20%. In contrast, after a passage through the filter with modified sand, the average viral elimination of all viruses was 60%. By allowing the water to circulate through the filter for 1 hour, the average elimination of all the viruses was 99.5% through a filter with modified sand. The filter with unmodified sand eliminated only about 30% of the viruses test. When the filters were attacked with the bacteria, an average removal of 78% was obtained with the filter containing modified sand. In comparison, the filter with the unmodified sand eliminated 40% of the bacteria. The Cryptosporidium oocysts were reduced by 51% in one-step and 95% experiments following recirculation through the sand-containing filter treated. Under the same conditions, percentages of reductions of 21% and 37% of Cryptosporidium oocysts were obtained by means of filters containing unmodified sand. ^ l¡ ^^! g ^^ j giggg | TABLE 6-1 Elimination of microorganisms by Porpoise filters containing coated and uncoated sand. The one-step experiments and water circulation through the filter * are shown * The data represents the triplicate average. In all cases, the differences between elimination through filters containing unmodified sand and filters containing modified sand are statistically significant (P <0.05).

The elimination percentage of several microorganisms did not decrease significantly over the length of the test period. Each virus was analyzed in triplicate on day 170, the filter containing modified sand reduced the number of bacteriophage by 2.4 log-io units as compared to 3.0 log-? 0 units. The filter output streams always contained less than 0.01 mg / l of aluminum or iron ions at a time when 189.2611 of water were circulated through the filter for 50 hours. a-aa «& EXAMPLE 7 Uncontrolled precipitation of mixed iron oxides in polyester cloth filters The precipitation of metal hydroxides in fibrous and sand media has been studied by many researchers. In this example, an in situ precipitation method can be used to coat iron oxides in polyester fabric filters. Different processes have been used to treat the polyester fabric. A preferred procedure involves soaking the polyester filters in FeC, dry the filters overnight and then precipitate the iron oxides, for example, with a strong solution of ammonium hydroxide. The filters can then be dried in a vacuum oven. The preferred concentration of FeC was determined at approximately 0.4 M. The preferred concentration of NH 4 OH used was about 2 M. These concentrations were selected to allow the maximum amount of coating to be deposited on the filter surface without plugging the filters. The selection of the aforementioned concentration was also based on visual observation of the uniformity of the treated filters. It seems that the filters treated with 0.4 M FeCI3 are the most uniform. Filtration was performed using the apparatus and procedures described in Example 3, with the exception that each filter holder had 4 layers of the filters in place of a layer due to the high permeability of the fabric filters. The initial concentrations of S aureus and E. coli were approximately 2x105 and 1x105 CFU / ml, respectively. The initial concentrations of the bacteriophages were 1x105, 1x106 and 1x104 CFU / ml for MS2, PRD-1, and FX-174, respectively. The zeta potential of the filters coated with iron oxide is positive below pH 4. The isoelectric point of the treated filters is about 4.5. At the experimental pH, the treated filters are slightly less electronegative than the untreated filters. The treated filters were more wetted than the untreated filters. The pressure drop of the untreated filters was 0.05624 kg / cm2 through 4 filter layers and 0.23199 kg / cm2 through 24 filter layers. The pressure drop of the filters treated with iron oxide, on the other hand, was only 0.00703 kg / cm2 through 4 layers of filters and 0.08436 kg / cm2 through 24 layers of filters. The pressure drop of the treated filters was significantly lower than the untreated filters. The results of the filtration of S aureus and E. coli showed that the filter coefficient of the filters coated with iron oxide improves by only 18%, from 0.085 to 0.100 to the filtration of S aureus. In the filtration of E. coli, the treated filters do not seem to show any improvement. The treated filters have better performance in bacteriophage filtration. In the MS2 filtration, the filtration efficiency of the precipitated iron oxide coated filters is significantly higher than that of the untreated filters. The treatment or coating improved the filter coefficient by 500%.

In the filtration of PRD-1, the coating increased the filter coefficient by 516%. In the filtration of FX-174, the filter coefficient is even higher. The filter coefficient of the filters treated in the filtration of FX-174 is 0.08, which is an improvement over the untreated filters of 1.388%. It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes will be suggested in view thereof to those skilled in the art and will be included within the spirit and scope of this application.

Claims (38)

1. NOVELTY OF THE INVENTION CLAIMS 1. - A method for filtering a fluid, comprising the following steps: applying a surfactant or polymer to a filter matrix; and placing the filter matrix in contact with a fluid, wherein the removal of an impurity from the fluid is improved by applying the surfactant to the filter matrix. 2. The method according to claim 1, further characterized in that said impurity is selected from the group consisting of: particles, dissolved chemical contaminants, particles, particulate materials, bacteria, viruses, protozoan parasites, fungi, yeast, particles of submicras, chemical species, organic chemicals, inorganic chemicals and dust. 3. The method according to claim 1, further characterized in that said surfactant or polymer is a surfactant or cationic polymer. 4. The method according to claim 1, further characterized in that said surfactant or polymer is a surfactant or anionic polymer. 5. - The method according to claim 1, further characterized in that said surfactant or polymer is a surfactant or nonionic polymer. 6. The method according to claim 1, further characterized in that a monomolecular surfactant or polymer is applied to the filter matrix. 7. The method according to claim 1, further characterized in that the filter matrix comprises at least one material selected from the group consisting of woven fabric, nonwoven fabric, glass fiber, polypropylene, cellulose, sand, diatomaceous earth , fine sand, gravel and media of particulate materials. 8. The method according to claim 1, further characterized in that said fluid is selected from the group consisting of: water and air. 9. The method according to claim 3, further characterized in that said polymer or cationic surfactant is selected from the group consisting of: C20 -C2β , wherein TAB is trimethylammonium bromide, Poly (4-vinylpyridine), (Poly (d-glucosamine) of chitosan, polyethyleneimine, cationic hydrophobically modified polymers and surfactants -zwiteriónicos (group +) 10. The method according to claim 4, further characterized in that said polymer or anionic surfactant is selected from the group consisting of: dicetyl phosphate, phosphatidic acid, poly (acrylic) acid, poly (butyl acrylate) / poly (acrylic acid), hydrophobically modified anionic polymers and surfactants - zwitterionic 11.- The method according to claim 5, further characterized in that said polymer or nonionic surfactant is polyvinyl alcohol 12.- The method of compliance with the claim 1, further characterized in that a plurality of surfactants or polymers are applied to a corresponding plurality of filter matrices and wherein each matrix of the plurality of filters is brought into contact with the fluid. 13. The method according to claim 12, further characterized in that at least one of the pluralities of surfactants or polymers is cationic and at least one of the pluralities of surfactants or polymers is anionic. 14. A method for filtering a fluid, consisting of the following steps: precipitate in situ at least one (hydr) metal oxide to the filter matrix; and placing the filter matrix in contact with a fluid, wherein the removal of at least one impurity from the fluid is improved by the application of at least one (hydr) metal oxide to the filter matrix. 15. The method according to claim 14, further characterized in that the filter matrix is heated at an elevated temperature during the step of in situ precipitation of at least one (hydr) metal oxide to the filter matrix. 16. - The method according to claim 15, further characterized in that the elevated temperature is between 60 ° C and approximately 100 ° C. 17. The method according to claim 15, further characterized in that the elevated temperature is between about 70 ° C to about 95 ° C. 18. The method according to claim 15, further characterized in that the elevated temperature is between about 75 ° C to about 85 ° C. 19. The method according to claim 15, further characterized in that the elevated temperature is about 80 ° C. 20. The method according to claim 14, further characterized in that the step of precipitation in situ of at least one (hydr) metal oxide to a filter matrix consists of the steps of: applying at least one of the group consisting of : metallic chloride and metal sulphate; dry the filter matrix; apply a base solution to the filter matrix; and dry the filter matrix. 21. The method according to claim 20, further characterized in that at least said metal chloride selected from the group consisting of ferric chloride and aluminum chloride is applied to the filter matrix. 22. - The method according to claim 21, further characterized in that the filter matrix is heated to an elevated temperature during the application of at least one metal chloride. 23. The method according to claim 22, further characterized in that the filter matrix is agitated during the application of at least one metal chloride. 24. The method according to claim 22, further characterized in that at least said metal sulfate selected from the group consisting of: ferric sulfate and aluminum sulfate is applied to the filter matrix. 25. The method according to claim 24, further characterized in that the filter matrix is heated to an elevated temperature during the application of at least one metal sulphate. 26. The method according to claim 25, further characterized in that the filter matrix is agitated during the application of at least one metal sulphate. 27. The method according to claim 21, further characterized in that at least said metal chloride is atomized in the filter matrix. 28.- The method according to claim 24, further characterized in that at least said metal sulphate is atomized in the filter matrix. ^ ^ - ^ i 29. The method according to claim 20, further characterized in that said base is selected from the group consisting of: ammonium hydroxide, sodium hydroxide and potassium hydroxide. 30. The method according to claim 20, further characterized in that at least one of the drying steps is carried out at an elevated temperature. 31. The method according to claim 20, further characterized in that at least said metal chloride consists of ferric chloride and aluminum chloride. The method according to claim 31, further characterized in that the ferric chloride is in the range of 0.1 M to 2.0 MN. 33.- The method according to claim 31, further characterized in that the ferric chloride is in the range of 0.
2. 2 M to 15 4.0 MN. 34.- The method according to claim 31, further characterized in that the ferric chloride is approximately 0.25 M. The method according to claim 31, further characterized in that the aluminum chloride is in the scale of 0.1. to 2.0 MN. 36. - The method according to claim 31, further characterized in that the aluminum chloride is in the range of .02 M to 0.8 MN. 37.- The method according to claim 31, further characterized in that the aluminum chloride is about 0.5 M. 38. The method according to claim 20, further characterized in that the metal chloride solution consists of water and ethanol.