WO2005075367A1

WO2005075367A1 - The method of water treatment and the device for water treatment

Info

Publication number: WO2005075367A1
Application number: PCT/PL2005/000008
Authority: WO
Inventors: Andrzej Panuszewski; Tadeusz Kozak
Original assignee: Andrzej Panuszewski; Tadeusz Kozak
Priority date: 2004-02-03
Filing date: 2005-02-01
Publication date: 2005-08-18
Also published as: PL364737A1; PL211231B1

Abstract

Water is initially oxidized and disinfected with the first agent added in an amount of 10 to 100 ppm, followed by mechanical filtration and the purification process on filtration columns connected in series. The first column is used to carry out a removal of iron and manganese with the residual mechanical impurities. The second column with a porous cation exchange resin is used to carry out a removal of calcium Ca2 + and magnesium Mg2+, ammonia and heavy metals. The third column with a porous cation exchange resin is used to carry out a removal of heavy metals and the rest of cations. The fourth column with a blend of anion exchange resins is used to carry out a removal of remaining organic contaminants, nitrates, nitrites, phosphates and other anions. The purified water is admixed with a second agent with a remineralizating activity in an amount sufficient to reach potable water hardness of 60 to 100 ppm CaCO3; followed by passing water through an activated carbon bed to remove any remaining organic impurities and reagents from the purification steps; and optionally disinfection of water with a UV source. The invention provides also a device for carrying out the method.

Description

The method of water treatment and the device for water treatment

The invention relates to a method of water treatment and to a device for water treatment. Quality of water for potable, household, and industrial uses is strictly regulated by law, and must also meet user requirements. Available raw water sources, like surface waters and wells, often do not meet potable water standards. Therefore, water treatment is necessary. A problem of water treatment arises often in emergency situations, such as ecological disaster (e.g. flood, contamination from a chemical plant etc.), terrorist attack, etc., when potable water sources become polluted or contaminated. Waters of natural origin contain inorganic and organic pollutants. Depending on the origin and local conditions, the contents of dissolved solids (TDS index - Total Dissolved Solids) varies from tenths to thousands of mg/liter. Usually water contains the following cations: calcium Ca^{2 +}, magnesium Mg^{2 +}, sodium Na⁺, and less abundant potassium K⁺ and ammonium NrLj⁺, as well as anions: bicarbonate HCO₃ ^~, chloride Cl^", sulphate SO₄ ^2", nitrate NO₃ ^" and phosphate PO ³\ Other cations and anions are usually present in trace amounts and testify for the presence of industrial contamination. In water from deep wells, except brines and mineral waters, the absolute dominants are cations of calcium and magnesium as well as a bicarbonate anion. Other contaminants present in water are organic substances, mainly humic and fulvic acids, as well as byproducts of household and industrial human activity, like detergents, phenols, and pesticides. The goal of a water treatment is to remove mechanical contaminants like slurries and suspensions, organic and inorganic contaminants, including iron and manganese, as well as another undesirable and even toxic constituents like heavy metal cations (e.g. iron Fe²⁺, manganese Mn ⁺, lead ?b² cadmium Cd²⁺, mercury Hg²⁺ etc.) or various detrimental anions (e.g. fluoride F, sulphide S^2", chromate CrO₄ ^2", nitrate NO₃ ^" and nitrite N0₂ ^"). The first known water treatment process is water filtration, usually combined with iron and manganese removal. Water filtration aims at a removal of mechanical contaminants, i.e. solid particles, in a form of suspensions, slurries etc. Appropriate filters are used to this end, from typical mesh filters to filters with appropriate beds, such as sand and gravel. Filtration is usually combined with iron and manganese removal. Iron and manganese are almost always present in natural waters. Their removal is based on oxidation of divalent cations of iron Fe²⁺ and manganese Mn²⁺ to higher oxidation levels. Precipitated hydroxides of these metals (of oxidation level +3) are then filtered off. Traditional oxidation is effected by aeration of water. Another known method is based on filtration through appropriate oxidizing beds, such as green- sand zeolites. To oxidize cations, chemical oxidizing agents are also admixed with water. Examples of oxidizing agents are typically: sodium hypochlorite NaCIO, potassium permanganate KMnO₄, and gases like chlorine Cl , chlorine dioxide ClO₂, and ozone O₃. In adition, chemical oxidation beneficially effects water disinfection, or killing or deactivation of all microorganisms present in water. Mechanically treated water may be potable only in the absence of excessive contamination, like detrimental anions and cations, or too high chemical oxygen requirement (ChZT). Moreover, often iron and manganese levels still exceed standard levels. Disinfection level is rather low and any excessive bacteria and viruses levels remain after the treatment. Oxidation helps to attain a higher water purity level, but still some detrimental cations and anions remain in water. After removal of mechanical contaminants, iron and manganese, water may contain organic and inorganic contaminants. Organic contaminants comprise organic compounds of natural origin or introduced by household an industrial activities of men. Natural contaminants are products of metabolic processes of living organisms: plants, animals and microorganisms, as well as residues from their de- cay, as in rot processes. Among others, humic and fulvic acids, which form complexes with iron and manganese and render their removal difficult, are present. Such contaminants can degrade the taste and odour of water, but are otherwise rather harmless for men's health. Much more detrimental are man made contaminants. Pesticides, detergents, chlorinated hydrocarbons from raw oil and other chemical agents introduced into the environment from sewage and industrial wastes, e.g. phenols. As the sole practical process for removing organic contaminants, the water is filtered through activated carbon as a filter bed. A drawback of such activated carbon beds is their disposable nature, because the bed cannot be regenerated after saturation and must be replaced. Organic synthetic absorbents (ion exchange resins of cationic, anionic or neutral nature) are also used to remove organic pollutants. Sometimes, organic contaminants are removed in an oxidation process using oxidizing agents, like permanganate, hypochlorite, chlorine gas, etc., which cause degradation of even complex molecular organic compounds. Inorganic water contaminants have mainly an ionic character. Especially harmful are heavy metal cations, particularly lead, mercury, cadmium. Contaminated water can contain harmful anions like chromates, cyanides, nitrites. To remove inorganic contaminants, ion exchange resins and membrane techniques are mainly used. Ion exchange techniques on resins are used to soften water, i.e. to remove calcium and magnesium cations, to selectively remove nitrates, as well as heavy metals, fluorides and sulphides. Membrane techniques are very efficacious in removing almost all water contaminants, but suffer also from some drawbacks. Water must be deeply mechanically purified, and freed of iron, manganese, and softened, before being processed on membrane. The reverse osmosis technique leads to a deep water demineralization (with almost 95% of dissolved materials removed), which is rather unbeneficial for living organisms. Thus water from reverse osmosis must be additionally mineralized to be potable. Polish patent No. 178415 describes water treatment process comprising simultaneous removal of excessive manganese with autocatalytic oxidation and sorption, and ammonia nitrogen removal in a biological nitrification process. According to this method, manganese compounds and ammonia nitrogen are removed simultaneously by continuous water filtration on a pirolusite bed with a strictly defined particle size range and bed height. The filtration process is carried out in a reactor in a direction from the bottom to the top, with simultaneous introduction of compressed air in a cocurrent or countercurrent mode. Polish patent No. 164523 teaches a method for simultaneous demineralization and deoxidation of natural waters. The method comprises passing pre-decationized (on a highly acidic cation ex- changer resin) and desorbed free of CO₂ water, in a continuous manner, through two layers of a highly alkaline anion exchanger resin, upper in a sulphite form and lower in a hydroxide form. Polish patent application No. P-339630 discloses an apparatus for the treatment and dosing of water, comprising a casing and supply means, and an inlet of raw unfiltered water, an outlet of purified water, replaceable filter with deep filter layers and icroporous membrane arranged be- tween said inlet and outlet. The apparatus also comprises means to drive water through filter in a constant rate, means to count time from installation of a fresh filter and means to monitor an amount of filtered water and keep a constant flow rate. The apparatus also comprises a control element to alert on exceeding allowable threshold parameters based on measured values. In a preferred embodiment, the apparatus includes means to automatic blocking of water flow through the filter on exceeding desired water purity levels. Polish patent No. 339610 describes a device for water purification and dosing, having an enclosure, dosing elements, a raw water inlet, and a treated water outlet. It uses deep filtering beds and a micro-porous membrane. It has elements for passing the water through the filter at a constant flow rate, a filter change timer, and sensors for monitoring water quality. It has a controller that displays measured parameters, and warns when parameters are out of range. It blocks water flow through the filter automatically if parameters of water purity are out of range. Polish patent No. 157120 describes a microstation for water treatment comprising at least three columns, with the first two being filtration or sorption columns, and the third a disinfection column connected in series to the first two columns, said disinfection column comprising a UV radiator disposed above a water level. A casing of the disinfection column has an inner reflective wall, and inside the column, baffles are arranged in a relatively shifted manner and perpendicular to the water stream flow. Container arrangements for water treatment are known. One such arrangement is disclosed in a Polish patent application No. P-329183 and is designed to remove volatile chlorine compounds and phenols. The device is in part put together of known assemblies to provide successive phases of potable water treatment. In a column with a polymer packing, above a spraying nozzle, a de- mister and an activated carbon filter with a sucking ventilator are arranged. A polymer packing is filled into layers of baskets with a free space between them. A container arrangement for water treatment of a Polish patent application No. P-349615 comprise a sink pump and a pressure tank connected to an assembly of serially arranged initial purification filters. The filter assembly comprise a sedimentation filter, an iron removal filter and a sedimentation-carbon filter. The filter assembly is connected to a filter for a water disinfection in a form of a bacteria removing sterilizer. The output of the arrangement is provided with an osmotic filter. No known method for water treatment is effective enough in the case of treatment of very polluted water, with various contaminants. In most cases, a method is adapted to the specific kind of water to be treated. Meanwhile, in an emergency case, like a flood, an universal method of the efficacy independent on the kind of pollutants contained in water is desired. It seems that the universal character of the method can be provided by combining several known methods, and such attempts were made in the art. But serious problems are encountered here. Ion exchange resins used in the art are rather selective and are not too useful as universal packings to remove various cations and anions with an equal efficacy. One must use many various ion exchange packings to remove any potential impurity. Moreover, combining in an individual arrangement many elements employing various purification methods must in consequence lead to a significant increase of its dimensions. Another problem is a rather long duration of processes for removal of some impurities. This is the case of ammonia, which is removed by oxidizing with hypochlorite NaClO. An acceptable amount of the oxidant from the point of view of water parameters is rather small, thus the process is rather slow. This results in the lack of synchronization between the steps of the treatment which are either slow or rapid. Another problem is a non- uniform rate of consumption of different packings, depending on different and rather unpredictable water properties. The object of the invention is to provide an efficient and fast water treatment system for treating water from extremally contaminated sources. Another object is to provide an arrangement in a highly compact form, that is highly efficient, easy to transport, install and regenerate, for use especially in emergency situations. The method of the invention is based on following steps: water is first oxidized and disinfected by dosing with a composition comprising an oxidizing agent, zinc salt and organic or inorganic acid, most preferably a mixture of potassium permanganate KMnO₄, zinc sulphate ZnSO and an organic acid. The first agent is added in an amount of 10 ppm to 100 ppm. Then, water is subjected to a mechanical filtration, and it is passed through an array filtration columns in series. On the first column packed with greensand zeolite water is subjected to iron and manganese removal, with simultaneous removal of the mechanical residues. On the second column with a porous cation exchange resin packing, calcium cations Ca²⁺ and magnesium cations Mg²⁺ are re- moved, and on the third column with a porous cation exchange resin packing, heavy metal and other cations are removed, and on the fourth column with a blend of anion exchange resins packing the rest of organic contaminants, nitrites, nitrates, phosphates and other anions are removed. The thus purified water is admixed with another agent with a mineralizing activity in an amount to reach treated water hardness of 60 to 100 ppm CaCO₃, and then water is loaded onto the bed of activated coal to remove the residual organic contaminants and reagents added in the purification process. After the active coal filtering, water is disinfected with UV radiation. The mechanical filtration process is preferably carried out in two steps: the first step comprises removing of mechanical contaminants of the size above 90 μm, and the second step comprises removing of mechanical contaminants of the size above 30 μm. It is preferable to carry out one initial step of mechanical filtration before pumping. The second column is preferably packed with a strongly acidic porous cation exchange resin in a form of sodium Na⁺ salt. The third column is preferably packed with a weakly acidic porous cation exchange resin in a form of sodium Na⁺ salt. The fourth column is preferably packed with a blend of two strongly alkaline anion exchange resins in a 2:3 ratio. The first agent comprises an oxidizing agent, preferably potassium permanganate, in an amount of 10 to 80 g, a zinc salt, preferably zinc sulphate, in an amount of 10 to 150 g, an organic or inorganic acid in an amount of 0,1 to 50 g for each 1 dm³ of treated water. Preferably as the organic acid, adipic acid is used. The second agent comprises preferably magnesium salts or a blend of calcium and magnesium salts. The first and second agents are preferably admixed with a dye, to constantly monitor the efficiency of activated coal column. The packings filling the columns can be regenerated periodically in a countercurrent manner. The first column packings are back washed with water, and the second, third and fourth column packings are back washed with aqueous sodium chloride or sodium bicarbonate. The device for water treatment of the invention comprise a mechanical filter, preferably two mechanical filters connected in series with an optional initial filter, a first column packed with greensand zeolite, a second column packed with a porous cation exchange resin, preferably strongly acidic in nature, a third column packed with a porous cation exchange resin, preferably weakly acidic in nature, a fourth column packed with a blend of anion exchange resins, and a fifth column packed with an activated coal. The water conduct for purified water provided with an initial filter leads to a supply pump; the conduct is also connected with a pump for dosing a first agent solution; between the forth and fifth column a pump for dosing a second agent solution is provided; the outlet is provided with an UV radiation source. The device is also provided with tanks to store both first and second agent, and an electric unit to provide a power source to drive mechanisms and feed light sources. The device is contained in an enclosure with an inlet and outlet openings, and preferably a mobile mechanism. This method of water treatment carried out in the device for water treatment of the invention is very effective; a flow rate reaches 900 dm^/h. This throughput is significantly higher than the throughput for techniques and devices known in the art. Such throughput was achieved by combining column processes for water purification with carefully selected packings and particular formulations of {wo agents added to the water stream in the process of water treatment. The first agent is highly oxidative. A particular formulation allows for the following functions: microorganism deactivation, oxidation of divalent iron and manganese to higher oxidation levels, oxidation of organic contaminants, ammonia complexing. The latter function is of particular importance - converting ammonia to a complex moiety enables its removal in a subsequent stage on a cation exchange column with a much faster rate matching the overall rate of the process. Use of potassium permanganate in the agent in a quantity according to the invention permits to effectively conduct an oxidation process, and any excess amount regenerates the zeolite bed of the first column, to provide a continuous operation of the process. An organic acid increases the effective- ness of permanganate action and corrects pH value. The second agent exerts a mineralizing action. It comprises a magnesium salt or a mixture of calcium and magnesium salts. Since the second column softens water, or removes calcium and magnesium ions, and potable water should have a minimal hardness, treated water must be enhanced with these cations. A sequence of operation according to the invention and a site of dosing agents to water circulation comprise fundamental features of the water treatment process. The initial step in water treatment processes is its softening, inasmuch as hard water definitely lowers efficacy of a filtration process and manganese removal. According to the invention, a step of water softening is carried out after a filtration step and a removal of manganese and iron. In the inventive process, by a dosing of the first solution, a continuous and simultaneous removal of iron and manganese, and an initial disinfection, and a partial oxidation of organic moieties, and ammonia complexing, and an additional mechanical filtration of particles greater than 30 μm, is carried out. The complexed ammonia is removed rapidly on the first column along with heavy metals. The sequence of operation of the invention takes into consideration interactions between water contained impurities and their interactions with beds contained in columns. Conversion of some impurities into more readily removable forms or forms not preventing a removal of other impurities, by utilizing specially selected compositions added on specified process steps and a sequence of steps arising therefrom are the novel and non-obvious features of the inventive solution. The method of the invention comprise an universal water treatment system. The system pro- vides a simultaneous removal of mechanical impurities, cations, including heavy metal cations, anions, including nitrates, nitrites, phosphates, chromates, sulphides, fluorides, as well as ammonia and organic pollutants. The method of the invention provides removal of detrimental cations and anions, by a ion exchange into sodium salts and bicarbonates. Chloride and sulphate levels are lowered, calcium and magnesium levels (i.e. water hardness) are stabilized, and bacteria and other organisms are removed. In this way, the method of the invention finds utility in a treatment of water from highly polluted sources. After the treatment, water becomes potable. Another beneficial feature is a possibility of water treatment efficacy by a constant monitoring of colour of treated water. Any discoloration clearly shows that water is purified insufficiently. This is achieved by admixing water with some dye compounds of various colors. The dyes are added along with the first agent and the second agent. The device is small - it can be constructed in shape of a cuboid with the longest edge not exceeding 1,5 m. All elements of the device can be mounted in a stiff enclosure to facilitate transport and use thereof in any suitable place. A beneficial feature is also the possibility of column regeneration after use, without any need for a replacement. The regeneration can be carried out by a final user. The device can be equipped with a kit of test papers or analytical means to quickly determine a hardness of initial and processed water to asses a ion exchange efficiency of the device. The device can be very useful in emergency situations, e.g. flood, local water poisoning, as well as a local water treatment plant for any potable and household needs, or industrial/technological purposes. The basic use of the device is a use thereof in emergency situations. Instead of transporting water from the outside, it would be enough to supply the device and use it to produce potable water. The device would be also useful in power shortage situations, inasmuch as it is adapted to be powered by a generator. The device can be used as a local water treatment unit, in a small settlement as well as a small-scale factory, hotel or restaurant. A unit throughput amounts to 20,000 1/24 h to 200,000

124 h, depending on the size of filtration columns and amount of column packings. If any other non-potable water parameters are needed, the device can be easily accommodated to the require- ments by a proper choice of filtration beds. The device of the invention is shown in one embodiment on the drawings, wherein fig. 1 shows the block system of a device, and fig. 2 the device draft. All arrays and component elements of the device are mounted in an enclosure 16 based on a metal frame. Walls are made of sheet metal or grillwork. The enclosure is mounted on casters 17 and wheels 18. Raw water from any source is drawn into a flexible vacuum hose. The hose has a filter sponge on the inlet to protect from injecting of particles greater than 150 μ, that can block the hose, and it is attached to a check valve 20 mounted on the wall of enclosure 16. A water circuit 19 is connected to the check valve outlet for routing the water through the treating system. Water flow is produced by a pump 1 with an electric motor, small water/pressure tank, and a pressure activated switch. The first agent comprising potassium permanganate in an amount of

10 g/d , zinc sulphate in an amount of 30 g/dm^ and adipic acid in an amount of 40 g/drn^ is added to the raw water. The agent has intense violet colour. The agent is added to circuit 19 from a tank 8 by a dosing pump 7 controlled by a contact water meter. The agent is added at the rate of approximately 1 dm^/m- of water. Next, the water in the circuit 19 passes through initial filter 2 that removes suspensions >90 μm, and a fine filter 4 that removes suspensions > 30 μm. The water is then routed, through a water meter 3, to an array of filtration columns ϋ, 12, J_3, 14, 15, wherein the essential purification of treated water is realized. The columns are bottle-shaped elements, each equipped with a water inlet and outlet valve. Column H contains a bed of manganese zeolite of a "greensand" type (e.g. Relite M-50 or Purolite MZ 10). Column JJ, removes manganese and iron hydroxides and oxidizes and removes any remaining unprecipitated iron and manganese and mechanical impurities. Column 12 contains strongly acidic porous cation exchange resin bed in a sodium Na⁺ salt form (e.g. Relite CFZ, Amberlite MR200). Column 12 removes organic contaminants and calcium and magnesium ions by exchange with sodium ions, i.e. water softening. Column 13 contains weakly acidic porous cation exchange resin bed (e.g. Amberlite IRC 86 or Lewatit CNP, or Relite CNS, or Relite CND, or Wofatit CA20). Column removes heavy metals and other cations. Column H contains a blend of two anion exchange resins (e.g. one of Amberhte IRA 900 or IRA 910, Relite 3AZ or D-182, or IMAC HP 661, with one of Relite A 490 or A 502E or IMAC 555). Column 14 removes detrimental anions. Column 15 contains activated carbon (e.g. Relite P60) and removes residual contaminants. Between columns H and 15, a second agent, being a mixture of magnesium chloride and calcium chloride, of intense yellow color is injected into the water in an amount of 1,0 dm- m^ of treated water. This preparation mineralizes the water to a desired hardness level. It is dosed from a tank 6 using a dosing pump 5 in an amount of 1 ,0 dm- n water. After column 15 the water flows through the conduct 19 to an ultraviolet lamp 10 for treated water disinfection. The device is equipped with safe electric power and control wiring with a leakage current breaker, and a protective system for the feeding pump I, dosing pumps 5 and 6, the water meter 3. A distribution panel of the electric system is mounted in the enclosure 16. The method and the device was examined in the Instytut Ochrony Srodowiska (Environment Protection Institute) (a research topic 70-OW-BW-7083). The device was supplied with a polluted water at a linear rate of about 30 m/h. Parameters of the raw water supplied to the device and parameters of water purified by the method of the invention are presented in Table. Table

Claims

1. A method of water treatment, comprising the step of mechanical filtration and the ion ex- change process and potassium permanganate oxidating agent treatment, wherein the method comprises the steps of: initial oxidation and disinfection by the first agent added in amounts of 10 to 100 ppm; mechanical filtration; purification process on a series of filtration colums, the first column for carrying out a removal of iron and manganese with the residual mechanical impurities, the second column with a porous cation exchange resin for carrying out a removal of calcium Ca ⁺ and magnesium Mg²⁺, ammonia and heavy metals, the third column with a porous cation exchange resin for carrying out a removal of heavy metals and the rest of cations, the fourth column with a blend of anion exchange resins for carrying out a removal of remaining organic contaminants, nitrates, nitrites, phosphates and other anions; admixing such treated water with a second agent with a remineralization activity in an amount sufficient to reach potable water hardness of 60 to 100 ppm CaCO3; and passing water through an activated carbon bed to remove any remaining organic impurities and reagents from the purification steps; and optionally disinfection of water with a UV source.

2. The method according to claim 1, whereb the process of mechanical filtration is carried out in at least two steps.

3. The method according to claim 2, wherein in the first step of mechanical filtration mechanical impurities of sizes greater then 150 μm are removed, and in the second step me- chanical impurities of sizes greater then 90 μm are removed, and in the third step mechanical impurities of sizes greater then 30 μm are removed.

4. The method according to claim 1, wherein the first column is packed with manganese zeolite of a "greensand" type.

5. The method according to claim 1, wherein the second column is packed with strongly acidic porous cation exchange resin bed in a sodium Na⁺ salt form.

6. The method according to claim 1, wherein the third column is packed with weakly acidic porous cation exchange resin in a sodium Na⁺ salt form.

7. The method according to claim 1, wherein the fourth column is packed with a blend of two strongly basic anion exchange resins.

8. The method according to claim 7, wherein the anion exchange resins are used in a ratio of2:3.

9. The method according to claim 1, wherein the first agent comprises an oxidizing agent in an amount of 10 to 80 g/dm- of treated water, a zinc salt in an amount of 10 to 150 g/dm3 of treated water, and organic or inorganic acid in an amount of 0,1 to 50 g/dm^ of treated water.

10. The method according to claim 9, wherein the first agent comprises potassium perman- ganate KMnO zinc sulphate ZnSO4 ^an(^ ^an organic or inorganic acid.

11. The method according to claim 10, wherein the first agent comprises potassium permanganate in an amount of 10 to 50 g, zinc sulphate in an amount of 10 to 150 g, and organic acid in an amount of 0,1 to 50 g/dm^ of solution.

12. The method according to claim 11 , wherein the organic acid is adipic acid.

13. The method according to claim 1, wherein the second agent comprises magnesium salts or a blend of calcium and magnesium salts.

14. The method according to claim 13, wherein the magnesium salt is magnesium sulphate.

15. The method according to claim 13, wherein the blend of calcium and magnesium salts comprises magnesium chloride and calcium chloride.

16. The method according to claim 1, wherein the first and/or second agent is admixed with dye materials.

17. A water treatment device, with an enclosure, water inlet and outlet, a mechanical filter and columns with ion exchange packings, wherein the device comprises at least one me- chanical filter, the first column with "greensand" type zeolite, the second column with a porous cation exchange resin, the third column with a porous cation exchange resin, the fourth column with a blend of anion exchange resins, the fifth column with the activated carbon bed; and a conduct for the treated water is connected to the feeding pump, then to the dosing pump for the first agent, and between the fourth and fifth column another pump for dosing for the second agent, and the outlet is provided with an optional UV source; said device including tanks for the first and second agent and the electric power system to deliver electric power to drive mechanisms and feed light sources.

18. The device according to claim 17, wherein the mechanical filter comprise at least two filters in series.

19. The device according to claim 17, wherein the initial filter is adapted to remove impuri- ties greater than 150 μm.

20. The device according to claim 17, wherein the first filter is adapted to remove impurities greater than 90 μm.

21. The device according to claim 17, wherein the second filter is adapted to remove impurities greater than 30 μm.

22. The device according to claim 17, wherein the second column contains strongly acidic porous cation exchange resin bed in a sodium Na⁺ salt form.

23. The device according to claim 17, wherein the third column contains weakly acidic porous cation exchange resin bed in a sodium Na⁺ salt form.

24. The device according to claim 17, wherein the fourth column preferably contains a blend of two strongly basic anion exchange resins.

25. The method according to claim 24, wherein the anion exchange resins are used in a ratio of2:3.