WO2007017864A2

WO2007017864A2 - Decontaminating system for drinking water

Info

Publication number: WO2007017864A2
Application number: PCT/IL2006/000907
Authority: WO
Inventors: Abraham J. Domb; Haim Wilder
Original assignee: H 2 Q Water Industries Ltd.
Priority date: 2005-08-05
Filing date: 2006-08-06
Publication date: 2007-02-15
Also published as: WO2007017864A3

Abstract

A system for disinfecting and detoxifying water using a filter unit loaded with a layer of resinous matrix having biocidal and contaminant accumulating properties. In addition, the system is capable of preventing components of the resinous matrix from being released into the disinfected water.

Description

DECONTAMINATING SYSTEM FOR DRINKING WATER

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority to US Provisional Patent Application Serial Number 60/706,1 16, filed August 5, 2005, entitled "DECONTAMINATING SYSTEM FOR DRINKING WATER ". The aforementioned application is hereby incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a water disinfection and detoxification filtration elements. More specifically the invention relates to composite microbiocidal materials and absorbing composites for loading into a filter are used for the treatment of raw water by gravimetrically passing through the filter.

BACKGROUND ART

Drinking water from different sources may contain various toxic and harmful components which include biological species such as bacteria, fungi, parasites, worms, and viruses or toxic soluble chemicals including heavy metal ions, nitrates and organic molecules that may drift into drinking water by human contamination or naturally from the source of supply. In various communities the water supply is contaminated by certain bacteria, fungi or parasites or contains toxic ions. The most common disinfection methods for drinking water employ activated carbon materials and ion exchange resins with bactericidal compounds, such as iodine, bromine and silver. The strong bactericidal properties of iodine and silver make them ideal disinfectants for small scale water supply systems.

For the simultaneous disinfecting and purification of drinking water it is known to use a composition of coarse and fine carbon fibers, including carbon fibers activated with metal salts; for instance, silver in an amount of 0.01 to 8% deposited thereon as a bactericidal additive (Swiss Patent 556,680). The disinfection of drinking water by passing it through the above described activated materials, which were treated with silver salts, was not sufficiently efficient due to the fact that the improvement in the bactericidal properties was effected by silver ions released into water in the course of the treatment. To ensure longevity of the bactericidal properties, it is necessary to treat materials with concentrated silver salt solutions, which may adversely affect human health if imbibed. U.S. Patent 4,555,347 teaches the use of filtration material in the form of activated carbon and iodine crystals for water disinfection. However, the method based on releasing iodine into water, can not be used for continuous consumption and may adversely affect human health. Anion-exchange resin treated with silver nitrate solution is disclosed in U.S. Patent 2,434,190, and the use of a cation exchange resin treated with a silver salt solution is described in U.S. Patent 2,692,855. U.S. Patent 3,817,860 discloses a water disinfection method by which water is brought into contact with layers of an iodine containing resin and additionally the water is treated by silver salts. U.S. Patent 5,366,636 and the Journal of Water Chemistry and Technology, USSR, 1989, vol. 11 , No. 2 disclose methods whereby the water passes through layers of iodine and silver containing ion- exchange resins. In these cases, iodine is released into the water in the course of the drinking water disinfection.

U.S. Patent 5,366,636 discloses a system whereby water passes through a porous, granular, iodine containing anion-exchange resin. As water forms a contacts with the resin, the iodine is released into the water. Subsequently the treated water passes through the porous granules of a chelating Ag resin, which contains iminodiacetate groups and bound silver ions. The silver ions react with the iodide ions forming insoluble silver iodide. This method is disadvantageous, due to the large amounts of iodine that must be released into the water from the anion-exchange resin to be effective. Subsequently, this method necessitates trapping of the iodine in the subsequent layers of adsorbents. The process of disinfection of water performed by passing it successively through layers of anion exchange resin containing iodine, synthetic activated carbon and macroporous strong acid cation exchange resin treated with silver nitrate solution allows to efficiently disinfect water of microorganisms (E. CoIi for example). However, it implies the use of high concentrations of bactericidal components (Journal of Water Chemistry and Technology, USSR, 1989, vol. 11 , No. 2). There is also known in the art a method of water disinfection using filtering material composed of an ion-exchange resin mixture. The essence of the method is in passing water through the mixture of ion-exchange resins (99%) and bacteriostatic resin (1 %). The bacteriostatic properties of the resin are related to the metallic silver grains present on the surface and inside the granules of the resin. The mixture of resins prevents biomass development in the ion-exchange filter and the infiltration of bacteria into the water ("Eau et Ind.", 1981 , No. 58, 88- 90). However, despite the mentioned merits of the method, the silver ions are gradually washed out of the resin, accumulating in the water, thereby potentially adversely affect human health.

The use of halogens, including iodine, to clean or disinfect water is well known. However, problems exist regarding purification levels, particulate matter and the amount of time the disinfectant must interact with the water to purify a volume of water. Iodine has long been recognized as an effective disinfectant for waterborne bacteria. It is equal to or better than chlorine for reduction of pathogenic species that are known to contaminate potable water sources. Chang and Morris (1952, cited in Block, 1977) showed that waterborne microbial contamination was reduced by 7 logs or greater when using 3 - 4ppm for 12 min at 24 degrees C, however, the antimicrobial agent, iodine, remains in the processed water. DISCLOSURE OF THE INVENTION

Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The present invention provides a method and means for disinfecting and detoxifying water. The invention relates to antimicrobial and toxicant accumulating media loaded in a filter to implement an effective decontamination filtration system used for the treatment of water passing through a filter, deactivating common bacteria, fungi or parasites present in drinking water as well as removing toxic ions such as heavy metal ions, nitrates, cyanates and organic molecules. The treatment takes effect as the water passes through a filter of the invention, obtaining an effective decontamination of water containing as high as about 100,000 microbial species per ml to a level of less than 1000 species per ml, preferably less than 100 per ml. The filter may contain media compositions with specific affinity and high capacity of removing certain contaminants such as arsenic ions, Pb, mercury, palladium, nitrates, chlorates, peroxides and other toxic ions.

Two major classes of bacteriocidal agents are used in accordance with the present invention; in the first class of agents the active moiety is complexed to a matrix carrier such as polyamines. The active biocidal agent, typically iodine, is consumed by interacting with bacteria. In the second class are included resins with inherent biocidal activity, accessible by microorganisms which then intact with them. These agents are described in more detail below.

The first class of agents is characterized by controlled release of active agents. Iodine is the most common example. The iodine is complexed onto a polymer matrix. Typical polymers that are capable of trapping iodine while retaining the antimicrobial activity of the iodine are polyamines; some exemplary polymers are based on aminomethyl styrene, poly(ethylene imine), polyvinyl amine), poly(allyl amine), polyvinyl pyridine) and, polyvinyl pyrrolidone). In addition, some polysaccharides which possess high affinity to iodine, such as amylose, are suitable. Other polymers having antimicrobial activity can be prepared by complexing reducing biocidal agents such as borane onto a polyamine as described above. The borane-polyamine complex has antimicrobial activity due to its strong reducing capacity. These borane polymer complexes can be used for the reduction of silver ions onto the polymer in order to obtain silver coated polymer that possess antimicrobial activity.

The agents of the second class are polymers having active sites that kill microbes upon contact, without releasing any active agent. First subclass of the second class agents contains polymers containing a high proportion of quaternary ammonium groups having at least one alkyl chain of four methylenes or more. These polymers are prepared by alkylating polyamines with long chain alkyl halides followed by alkylation with methyl or ethyl halides. Polymers possessing tertiary amines, such as pyridine based polyamines, are quaternized by alkylation with a long chain alkyl halide. Polymers possessing primary amines such as polyethylene imine, polyallyl amine or chitosan can be alkylated by reductive amination using alkanals, followed by alkylation with short chain alkyl halides. Alternatively, vinyl monomers possessing antimicrobially active quaternary amines are polymerized or copolymerized to form a polymer having quaternary ammonium side group. The second subclass of antimicrobial polymer agents possessing reactive groups that interact with the microbe rendering it inactive are polymers having aldehyde groups which are stable in water but have a strong capacity of reacting with amine groups. Harmful organisms affected by such agents are bacteria, viruses, and protein based contaminants that may react with the aldehyde groups and being entrapped with the polymer matrix carrying the reactive aldehyde groups. Such polyaldehyde agents are easily prepared from the oxidation of natural polysaccharides such as cellulose, amylose, dextran and other polymers having terminal hydroxyl groups. The oxidation step is taking place in water at room temperature using periodate as oxidizing agent.

A hybrid class expressing both aspects of the two classes described above can be used as well in a filter unit of the invention. Purodine™ - by Purelite Co consists of iodine complexed on resinous matrix possessing quaternary ammonium residues. Such hybrid agents are active as a result of both the active iodine and the matrix itself. The advantage in this case is that the matrix can be loaded with a lesser amount of releasable active agent, namely iodine, thus when and if depleted it can still provide with a disinfecting potential.

Resins containing amino groups of specific structure are effective in complexing and absorbing toxic ions. For example, triethylammoniummethyl polystyrene has a specific affinity to arsenic with high capacity for removal of heavy metals. This resin is capable of removing nitrates and chlorates.

The object of this invention is to provide compact filters that are loaded with resin compositions that are capable of removing high concentrations of toxic ions from drinking water as well as deactivating harmful biological species.

Examples:

Example 1 : Preparation of antimicrobial particles containing quaternary ammonium groups:

This example relates to water insoluble polymeric particles composed of aliphatic and aromatic quaternary ammonium sites having antimicrobial activity. The particles are made from a water insoluble amino containing aliphatic polymer quatemized with alkyl group of 1-15 methylene groups. The polymers are aliphatic or aromatic polyamines such as polyethylene imine, polyvinyl pyridine or polyvinyl amine or a natural polysaccharide such as chitosan or a polyamine made form amination of a polysaccharide. The polyamine is crosslinked or hydrophobized rendering it insoluble in aqueous media and having a particle size ranging from about 0.2 mm to about 5 mm. The polyamine quaternization is done by either alkylation of the amino groups with activated alkanes such as alkyl halides.

Crosslinkinq of polyethyleneimine (PEO with dibromopentane

Aqueous solution of PEI was lyophilized to dryness before use. PEI (18.65 g, 0.434 mol) of the 1 ,000,000-600,000 Da was dissolved in 186 ml of absolute ethanol. Dibromopentane (17.35 mrnol, 2.4 ml) was added at 1 :0.04 mole ratio (PEI monomer/dibromopentane). Crosslinking reaction was carried out at reflux conditions for 24 hours. The reaction was continued at the same conditions for additional 24 hours. After cooling to room temperature, the resulting residue was purified from NaBr by gravitational filtration. Filtrate was evaporated to dryness under reduced pressure to yield yellow viscous residue which upon mixing in ethanol forms a fine powder; with yield of 75 % w/w

The degree of crosslinking with dibromopentane was determined by microanalysis and found to be 100%; the results of microanalysis %C=48.05, %N=21.20.

Alkylation of crosslinked PEI-based particles with bromooctane

Crosslinked PEI (1.9 g, 45 mmol) was dispersed in 20 ml of absolute ethanol. 7.73 ml of bromooctane (45 mmol, 1 equimolar) was added to a suspension containing 1 equimolar amount of the crosslinked PEI particles. Alkylation reaction was carried out at reflux conditions for 24 hours. After cooling to room temperature, the resulting residue was purified from NaBr by washing with water and isolation of the particles by filtration or decantation.

The same procedure was repeated with various alkylbromides including bromobutane, bromohexane, bromooctane, bromodecane and bromohexadecane. Compounds based on alkylation with longer alkylbromides such as bromodecane and bromohexadecane were purified by precipitation in methanol; with yield of 90% w/w. The degree of alkylation with bromoalkanes was determined by microanalysis and found to be 80%.

Synthesis of pyridinium-type based particles

Suspension polymerization of the 4-vinylpyridine (4-VP)

The polymerization reaction of 4VP and divinylbenzene (DVB) (1-30% mol/mol to 4VP) was carried out in a three-necked round bottom flask equipped with a nitrogen inlet and reflux condenser. 1.08 ml (9.9mmol) of 4VP and DVB (0.01 equimolar, 0.099 mmol or higher amount as given in the table below) were dissolved in 0.5 ml of N-methylpyrrolydone. Polymerization was carried out in 5 ml of DDW (doubly distilled water) using 10mg of AIBN (azo bis iso buyro nitrile) as a radical chain initiator and polyvinyl alcohol (0.1%) as a dispersing agent at 8O⁰C in dark under a nitrogen atmosphere. White suspension was obtained within 7 hours. The polymerized crosslinked particles were collected by filtration followed by washing with ethanol to remove N-methylpyrrolydon and DDW to remove polyvinyl alcohol. Average yield was 60% w/w. FT-IR (KBr): 1418cm^"1 (symmetric C-N stretching vibration) and 825cm^"1 (C-H out of plane bending vibration).

Table I. A summary of the relation between the ratio of DVB reacted with 4VP and particle size of the product

Quaternization of the pyridine rings

Quaternization of tertiary amine groups of the pyridine rings was carried out with excess of bromooctane. 0.2gr (1.9mmol) of the polymerized 4VP was dispersed in 1 ml of absolute ethanol and 2.85mmol (1.5 equimolar) of bromooctane was added. Reaction was carried out at reflux conditions with vigorous mixing for 48 hours. The product was collected by filtration followed by washing with ethanol to remove unreacted bromooctane and water. Average yield was 95%. The degree of quaternization with bromooctane was determined by microanalysis (%Br) and found to be >80%. FT-IR (KBr): 1418cm^"1 (symmetric C-N stretching vibration) and 1637cm^"1 (quaternized pyridine rings).

Table II: A summary of the relation between the ratio of DVB reacted with 4VP and and the degree of quaternization

The filter unit

The active polymers can be either crosslinked to form water insoluble particles such as porous granules or beads having a high internal surface area. The particles are loaded into the filter, or they can be absorbed onto an inert carrier such as carbon granules, synthetic polymer beads such as polypropylene or polystyrene beads. They can also be grafted onto a carrier such as carbon particles, polysaccharide beads, or vinyl polymer beads. Alternatively, these polymers can be fabricated into porous sponges, non-woven or woven fabrics, collection of fibers or any configuration that allows efficient passage and decontamination of water through the media. Small particles, having size of less than 50 micron, are not recommended as these particles may escape the filter media into the drinking water. To avoid passage of small particles, a non-woven fabric or membrane may be disposed at the bottom of the cartridge to collect any small particle.

A schematic presentation of a filter of the invention is shown in

Figs 1A- B. In Fig. 1A the disinfecting filter appendage 10 is disposed at the bottom of the purifying filter 12. Body 14 of the disinfecting filter appendage contains the disinfecting material. At the bottom of the disinfecting filter appendage a sieve 16 is optionally disposed for blocking particles from exiting the disinfecting filter appendage water flow. In Fig. 1 B a schematic sectional view in a disinfecting filter appendage is shown. To water purification filter 24 a disinfecting appendage 25 is joined such that all the water coming out of the filter as in the direction designated by arrow 26, flow through. In upper disinfecting layer 28 a disinfecting resin is packed, typically in porous beads, such that the water passing through is not blocked yet form contact with the resin. A lower resinous layer 30 functions as trap layer for released active groups flowing downstream. In between the layers, in space 32 a fabric can be disposed to keep the resinous beads of upper layer from draining downstream. If the resin in upper layer 28 does not release any material, the lower resinous layer is redundant. The trapping layer is typically used to trap iodine released from the upper disinfecting layer, in such cases where the complexed iodine is used for disinfection.

The trapping layer consists of particles made of insoluble resin having affinity to the active agent released from the upper disinfection layer. Typically, iodine or other oxidizing agents are used such as chlorine, chloroxide, iodates, and peroxides. For each such agent a specific trapping resin is to be provided. Antibacterial effect

Example 2: The antibacterial effect of the previously described PEI nanoparticles at the various amounts (%w/w). Preparation of the bacteria:

Streptococcus mutants (ATCC#27351 ) were used in the study. Bacteria were cultured overnight in 5 ml of brain-heart infusion broth (BHI) (Difco, Detroit, Ml., USA), at 37^QC. To avoid large bacterial aggregates or long streptococcal chains, the top 4ml of the undisturbed bacterial culture were transferred into a new test tube and centrifuged for 10 min at 3175xg. Supernatant was discarded and the bacteria were resuspended in 5ml phosphate buffered saline (PBS) (Sigma, St. Louis, MO., USA) and vortexed gently for 10 sec. Each bacterial suspension was adjusted to an optical density 1 at 650 nm. Ten microliters from ten fold serial dilutions were plated on BHI agar to determine colony-forming units per milliliter. BHI and PBS were supplemented with bacitracin 0.0625gr/ml (Sigma, St. Louis, MO., USA), to minimize external contamination.

Preparation of the microtiter plate:

Twenty two samples of various synthesized quaternary polymers were added to microtiter plate (96-wells flat bottom Nunclon, None, Copenhagen, Denmark). 10μl of bacterial suspension (ca.10⁶ bacteria) were placed on each tested material sample in a set of 7 wells, and the plate was incubated for 1 hr at 37⁰C. During this incubation period, the suspension's liquid evaporated and a thin layer of bacteria was achieved ensuring direct contact between all bacteria and the tested surface as demonstrated by scanning electron microscopy (data not shown). The plate was then placed horizontally and 220 μl of brain-heart infusion broth were added to each well containing the material. All wells loaded with quaternary polymeric particles killed all bacteria while the control plates loaded with the same polymer particles but without quaternary groups did show propagation of bacteria like the wells without any additive. Example 3: Iodine-polymer complexes loaded in a filter

The crosslinked polymeric particles of Example 1 before quaternization or after quaternization were added to excess 5% w/w KI/I2 solution and mixed for 5 hours at room temperature. The dispersion was filtered and washed with water to yield brown dark particles loaded with 5% to 20% w/w active iodine complexed in the polymer. The complexes did not release detectable amount of iodine when dispersed in drinking water while were capable of disinfecting contaminated water with 100,000 E. CoIi per ml when passing through a filter loaded with these particles.

Filter loaded with active carbon, chitosan and ion exchanger with or without a layer of antimicrobial agent was tested for ability to reduce amount of bacterial (E. CoIi) contamination in water. The tests were performed with different levels of contamination - 4X10² - 4X10⁴ CFUs/ml (colony forming units/ml) before using the filters and after 100 liters of water passed through the filters. The effect was measured by seeding the water samples on semisolid agar and counting the spots after incubation.

Results:

The filter without the antimicrobial agent layer reduced about 15% of bacterial contamination in water. The filter with the layer of antimicrobial agent, Purodine™ -by Purelite Co, an iodine complex onto a polystyrene quaternary ammonium, fount to reduce 100% of bacterial contamination in water in the first passing. There were no live bacteria found in the first wash.

Example 4: Filter components assayed in agar plates.

The filter components were tested for their antibacterial properties in semi-solid agar containing E. CoIi bacteria (>105 CFUs/mL). The effect was measured by radius of "clean ring" around the component after 24 hrs incubation at 37⁰C. Results:

Carbon, chitosan and ion exchanger have no antibacterial effect in semi-solid agar.

Purodine has anti-bacterial effect in semi-solid agar. The "clean ring" with radius of 0.5-2 cm found around 50-200 mg of Purodine. The effect is proportional to amount.

Quaternary polyethylene imine has anti-bacterial effect on semisolid agar. The "clean ring" with radius of 0.2-0.5 cm found around 50-200 mg of PEI-particles. This effect is also proportional and weaker then effect of Purodine.

Flow rate

The effectiveness of the disinfecting agent is positively correlated with the interaction time it is allowed with the disinfecting filtering agent.

It will be appreciated that the present invention is not limited by what has been described hereinabove and that numerous modifications, all of which fall within the scope of the present invention, exist. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims which follow:

Claims

1. A system for disinfecting and detoxifying water, comprising:

■ a filter unit loaded with least one layer of resinous matrix having biocidal and contaminant accumulating properties, and wherein said resinous material is packed in porous particles;

■ means for preventing components of said matrix from being released into the disinfected water.

2. A system for disinfecting water as in claim 1 wherein said means for preventing said release of components is a second trapping layer consisting of a trapping resin.

3. A system for disinfecting water as in claim 1 wherein said resinous matrix is a complexing matrix for small biocidal molecules.

4. A system for disinfecting water as in claim 3 wherein said biocidal molecules are iodine molecules.

5. A system for disinfecting water as in claim 3 wherein said biocidal molecules are borane molecules.

6. A system for disinfecting water as in claim 1 wherein said resinous matrix is a polymer incorporating biocidal monomers.

7. A system for disinfecting water as in claim 6 wherein said biocidal monomers are quaternary amines.

8. A system for disinfecting water as in claim 7 wherein said quaternary amines are alkylated by at least one alkyl group consisting of 4 - 15 methylene groups.

9. A system for disinfecting water as in claim 6 wherein said polymer incorporates reducing monomers.

10. A system for disinfecting water as in claim 9 wherein said polymer is a polyaldehyde.

11. A system for disinfecting water as in claim 1 wherein said toxicant accumulating layer is also a biocidal layer.

12. A system for disinfecting water as in claim 1 wherein said toxicant accumulating layer is contains monomers containing amino groups.

13. A system for disinfecting water as in claim 12 and wherein said toxicants are heavy metals.

14. A system for disinfecting water as in claim 12 and wherein said toxicants are any anions selected from the list containing: cyanates, nitrites, chlorates.

15. A system for disinfecting water as in claim 12 and wherein said toxicants are arsenic containing compounds.