METHOD FOR CLEANING DIALYSATORS USED IN WATER FILTRATION

Description

FIELD AND BACKGROUND OF THE INVENTION

[0001] The present disclosure relates to water filtration and to reuse, in water filtration systems, of medical filters discarded from medical use, and a connection thereof to water filtration systems and, more particularly, but not exclusively, to dialyzers discarded from medical use.

[0002] Waste water, surface water, storm water, ground water and sea water are frequently contaminated with the fecal material of man or other animals. Cryptosporidium oocysts (protozoan infections), E. coli and Vibrio cholerae (bacterial infections), and Hepatitis A (viral infections) are but a few examples of contaminants. Water filtration and water purification are required in many situations. In addition, contaminated water may include colloidal materials, which can destroy expensive Reversed Osmosis ("RO") membranes used in water purification and particularly in desalinization. Fouling of such expensive membranes can be prevented by pretreatment of water before undergoing reversed osmosis treatment.

[0003] Ultra-filtration ("UF") can be used, for example, for production of tertiary effluent from secondary effluent in municipal waste water treatment plants, such as for "polishing" sand filter tertiary effluent and, for example, for water pretreatment in reversed osmosis applications such as the desalination of sea water and brackish water. Ultra-filtration is a separation process using filter membranes having pore sizes in the range of 0.1 micron (100 nanometer) to 0.001 micron (1 nanometer). UF membranes are used to treat surface water, storm water, ground water, seawater and waste water as either primary treatment or as pretreatment in reversed osmosis desalination plants, or other types of desalinization plants. In these and other applications, UF filters are used in water filtration to remove high molecular-weight substances, colloidal materials, organic and inorganic polymeric molecules, and pathogens.

[0004] However, UF water filters are expensive.

[0005] Large water treatment plants typically use 500-1000 UF filters at a cost of many millions of dollars (including support systems). One such filter typically costs more than a thousand dollars. For example, at retail prices current at the time of filing of this application, Applied Membrane Model M-UB8040PES 8"×40" UF PES Membrane 10,000 MWCO (Molecular Weight Cut Off) cost is $1544, without a pressure tank). A Hydranautics Hydracap UF filter sells for $2550.

[0006] Apart from UF membranes per se, water filtration apparatus requires various tubes and couplings (e.g. quick release) as used in the industry or described in publications such as US 4,923,226, US 2009 / 227954, and WO 2007 / 049053.

[0007] Additional background art includes: Published PCT Patent Application WO 2010 / 143184 of Yoram Lass or US2011 / 056894A1SUMMARY OF THE INVENTION

[0008] The present disclosure relates to water filtration and to reuse, in water filtration systems, of medical filters discarded from medical use, and a connection thereof to water filtration systems and, more particularly, but not exclusively, to dialyzers discarded from medical use.

[0009] The invention is defined in claim 1 and concerns a method of cleaning one or more dialyzers in a water filtration system and comprising more than one dialyzer for water filtration, providing clean water from a clean water output of one or more first dialyzers, through a fluid connection, to a clean water output of one or more second dialyzers, to backwash the second dialyzers, wherein a number of first dialyzers is not greater than a number of second dialyzers.

[0010] Further aspects of the invention are defined in the dependent claims.

[0011] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and / or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0012] Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

[0013] In the drawings: FIGURE 1A is a simplified line drawing illustration of a cross section of a dialyzer according to prior art; FIGURE 1B is an image of a dialyzer connected to flexible tubing according to prior art; FIGURE 2 is a graph showing filtration efficacy of a dialyzer, when used as a water filter according to an example embodiment, relative to various fluid purification filters; FIGURE 6A is a simplified line drawing illustration of a flow path of clean water from an output of a first dialyzer and a second dialyzer, both dialyzers used to filter water according to an example embodiment of the invention; FIGURE 6B is a simplified line drawing illustration of a flow path of clean water from an output of a first dialyzer used to clean a second dialyzer by backwashing according to an example embodiment of the invention; FIGURE 7A is a simplified line drawing illustration of a flow path of clean water from an output of several dialyzers, the dialyzers used to filter water according to an example embodiment of the invention; FIGURE 7B is a simplified line drawing illustration of a flow path of clean water from an output of a first group of dialyzers used to clean a second group of dialyzers by backwashing, according to an example embodiment of the invention; and FIGURE 8 is a simplified diagrammatical illustration of a water filtration unit according to an example embodiment of the invention. DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0014] The present disclosure relates to water filtration and to reuse, in water filtration systems, of medical filters discarded from medical use, and a connection thereof to water filtration systems and, more particularly, but not exclusively, to dialyzers discarded from medical use.Overview

[0015] Above-mentioned Published PCT Patent Application WO 2010 / 143184 of Yoram LASS describes water filtration using recycled medical filters, or medical filters discarded from medical use for some reason.

[0016] An aspect of some embodiments of the invention involves using clean water output from one dialyzer to clean by reverse flow (backwash) through another dialyzer.

[0017] Dialyzers are constructed of capillary tube membrane where the membrane material is especially smooth, allowing a dialyzer to be cleaned with water output of another dialyzer.

[0018] In some embodiments, filtered output water of one dialyzer is used to backwash one other dialyzer.

[0019] In some embodiments, a water filtration system having two dialyzers uses filtered output water of one dialyzer to backwash one other dialyzer.

[0020] In some embodiments one or more valves are built into the water filtration system so that at one position or positions the valve(s) are set to have input water flow into inputs in the two dialyzers and produce clean filtered water output from both the dialyzers, and at other position(s) the valve(s) are set to have input water flow into an input in a first one of the dialyzers, produce clean filtered water output from the first dialyzer, and direct the clean filtered water in reverse flow through a second one of the dialyzers, backwashing the second dialyzer.

[0021] For purposes of better understanding some embodiments of the present invention, as illustrated in Figures 2 and 6-8 of the drawings, reference is first made to Figure 1A, which is a simplified line drawing illustration of a dialyzer according to prior art.

[0022] Figure 1A depicts a dialyzer 100, including blood input / output ports 102a 102b, and dialysate fluid input / output ports 103a 103b. Figure 1A, being a cross section, depicts a simplified line drawing illustration of capillary membrane tubes 106.

[0023] Reference is also made to Figure 1B, which is an image of a dialyzer connected to flexible tubing according to prior art.

[0024] Figure 1B depicts a dialyzer 100, including blood input / output ports 102a 102b, and dialysate fluid input / output ports 103a 103b. Figure 1B also shows blood input and output tubes 107a 107b, connected by prior art connectors 108a 108b. Figure 1B also shows dialysate fluid input and output tubes 109a 109b, connected by prior art connectors 110a 110b.

[0025] The blood input / output ports 102a 102b, and the dialysate fluid input / output ports 103a 103b are typically of a standard size and shape. The connectors 108a 108b to the blood input / output ports 102a 102b, and the connectors 110a 110b to the dialysate fluid input / output ports 103a 103b typically connect to an end of a flexible blood tube 107a 107b and / or dialysate fluid tube 109a 109b by a clip-on connector or by a Hansen connector or by a Luer taper. The prior art connectors typically connect into the end of the flexible tubes by a plastic tip which expands the flexible tube to press on the tip.Introduction

[0026] A dialyzer is used for medical purpose as a device to remove waste from the blood by diffusion. To that purpose the dialyzer uses a membrane filter with a membrane material and pore sizes especially suitable for such diffusion.

[0027] In some embodiments of the invention, it is realized that the membrane of a hemodialyzer is useful for filtering, and one or more dialyzers built for medical use are re-purposed and used as a filter, to filter unclean water and provide filtered water.

[0028] A dialyzer comprises two blood input / output ports, to insides of tubes of a set of capillary tube membranes, and two dialysate fluid input / output port, to outsides of tubes of the capillary tube membranes.

[0029] A dialyzer is originally designed, built, proofed and quality tested as a medical device. The dialyzer can provide absolute filtration corresponding to pore sizes of 30 nm (nanometers) and nominal filtration corresponding to pore sizes of 3.3 nm.

[0030] The dialyzer has a smooth membrane surface, relative to industrial filters, which potentially enables low fouling and makes the membrane surface easy to clean.

[0031] A dialyzer is robust - a dialyzer used experimentally as a water filter has been used for more than 3 years of continuous operation, and is still performing.

[0032] In some embodiments of the invention a dialyzer is constructed as a water filter with water input through one or two input port on one side of a hemo-dialyzer membrane, and water output from another side of the hemo-dialyzer membrane. One side of the membrane optionally provides only water output, at least during use as a water filter. In some embodiments the output side may optionally have water input when being washed. Such washing is optionally achieved by using valves and / or plugs to redirect water flow.

[0033] In some embodiments of the invention a dialyzer is constructed as a water filter with water input through one or two blood inputs, and water output through both dialysate fluid ports.

[0034] In some embodiments of the invention a dialyzer is constructed as a water filter with water input through one or two blood inputs, and water output through one dialysate fluid port, and the other dialysate fluid port is plugged shut.

[0035] In some embodiments a dialyzer may be constructed as a water filter with an advance mechanical filter for particles of approximately 200 µ.

[0036] In some embodiments the dialyzer(s) may optionally be in line steam sterilized, based on the membranes being resistant to high temperature.

[0037] In some embodiments the dialyzer(s) may optionally be dialyzer(s) built to medical specifications but never packaged or never used as such.

[0038] Dialyzer availability is potentially abundant, as dialyzers are used to treat millions of patient per year.

[0039] Water filters using dialyzers as water filters potentially enable reuse of wasted elements, potentially saving disposal of medical waste.

[0040] Water filters using dialyzers as water filters potentially enable recycling polluted water: using no chemicals; potentially requiring little energy expenditure; potentially at low operational costs.

[0041] Reference is now made to Figure 2, which is a graph showing filtration efficacy of a dialyzer, when used as a water filter according to an example embodiment of the invention, relative to various fluid purification filters.

[0042] Figure 2 illustrates that when the membrane material of a hemodialyzer, designed for diffusion of blood waste from the blood, is compared to conventional filters, the capabilities of a hemodialyzer, repurposed as a filter, fall in a range overlapping capabilities categorized as nano-filtration and ultra-filtration.

[0043] Figure 2 depicts: a third row 203 which is a logarithmic scale of particles blocked by the various fluid purification filters; a first row 201 which lists how a particle of a size described in the third row 203 may be viewed or detected; a second row 202 which lists terms describing the size described in the third row 203; a fourth row 204 which lists common materials having the size described in the third row 203; and a fifth row 205 which lists names used for classifying filters for blocking particles having the size described in the third row 203.

[0044] A block 200 in the fifth row 205 depicts a range of sizes which a dialyzer, when used as a filter, may be used for filtering.

[0045] The position of the block 200 depicts that a dialyzer, when used as a fluid filter, provides performance at a high end of the ultra-filtration range, and into the nano-filtration range. It is noted that when dialyzers which are discarded from medical use, whether after having been used or without having been used, a water filter of excellent performance may be produced at a low cost, benefiting from low cost of an expensive product discarded from its initially intended expensive use.Cleaning a dialyzer by backwashing

[0046] Water filters are sometimes cleaned by backwashing, that is, providing plenty of clean water flowing through the water filter in reverse, so as to wash out and clean a clogged water filter. However, a typical prior art water filter requires plenty of water to unclog or clean by backwashing, and the clean water of several water filters is required for backwashing a single prior art water filter, or the clean water of a large number of water filters is required for backwashing a smaller number of prior art water filters.

[0047] A dialyzer used as a water filter may also become dirty, less efficient, or even clogged.

[0048] In some embodiments of the invention, clean water from an output of a first dialyzer may be directed to an output of a second dialyzer, and flow in a reverse direction, backwash, through the second dialyzer. Such a reverse flow potentially cleans the second dialyzer. The clean water from the first dialyzer flows into the clean side of the second dialyzer, and unclean water flows back through the unclean side of the second dialyzer.

[0049] Capillary membranes of dialyzers, being designed for blood flow on an inside of the capillary membranes, are especially smooth, resist fouling, and are easier to clean than typical ultra-filtration filters.

[0050] In some embodiments of the invention, a single dialyzer is sufficient to provide clean water to clean another single dialyzer by backwashing.

[0051] In some embodiments, a first group of dialyzers, being made of especially smooth capillary membranes, may optionally be cleaned with a flow of clean water from a second group of dialyzers, with the number of dialyzers in the first group not lesser than the number of dialyzers in the second group.

[0052] In some embodiments, dialyzers, being made of especially smooth capillary membranes, may optionally be cleaned with a flow of clean water from one or more dialyzers possessing a total membrane area equal or even lesser than a total membrane area of the dialyzers being cleaned.

[0053] Reference is now made to Figure 6A, which is a simplified line drawing illustration of a flow path of clean water from an output of a first dialyzer and a second dialyzer, both dialyzers used to filter water according to an example embodiment of the invention.

[0054] Figure 6A depicts an example embodiment for filtering water. Water inputs 601a 601b provide water to dialyzers 602a 602b, and the dialyzers 602a 602b filter the water, producing outputs 603a 603b of filtered water. The outputs 603a 603b may provide filtered water separately, as separate outputs 603a 603b, and, in some embodiments the outputs 603a 603b may connect to a single output 604. In some embodiments the outputs 603a 603b may connect to the single output 604 via a valve 605.

[0055] It is noted that when a dialyzer is used as a water filter, in some example embodiments of the invention one dialyzer port may be used for water input, and in some example embodiments of the invention two dialyzer ports may be used for water input.

[0056] It is noted that when a dialyzer is used as a water filter, in some example embodiments of the invention one dialyzer port may be used for water output, and in some example embodiments of the invention two dialyzer ports may be used for water output.

[0057] Reference is now made to Figure 6B, which is a simplified line drawing illustration of a flow path of clean water from an output of a first dialyzer used to clean a second dialyzer by backwashing according to an example embodiment of the invention.

[0058] Figure 6B depicts an example embodiment for cleaning the second dialyzer by backwashing with clean water from the first dialyzer. A water input 601a provides water to a first dialyzer 602a, the dialyzer 602a filters the water, producing output 603a of filtered water. The filtered water is fed via a valve 605 to output 603b of a second dialyzer 602b, and flows through the second dialyzer 602b, backwashing and cleaning the second dialyzer 602b, exiting from the second dialyzer 602b via the water input 606b.

[0059] It is noted that in some embodiments no water flows out from the output 604 when the first dialyzer 602a is being used to backwash the second dialyzer 602b.

[0060] It is noted that when a first dialyzer is being cleaned by backwash, in some example embodiments of the invention one dialyzer port may be used for water input, and in some example embodiments of the invention two dialyzer ports may be used for water input.

[0061] It is noted that when a dialyzer is being cleaned by backwash, in some example embodiments of the invention one dialyzer port may be used for water output, and in some example embodiments of the invention two dialyzer ports may be used for water output.

[0062] In some embodiments of the invention, in a water filtration system comprising dialyzers for water filtration, a method of cleaning a dialyzer includes providing clean water from a clean water output of one first dialyzer to a clean water output of one second dialyzer, to backwash the second dialyzer.

[0063] In some embodiments of the invention the providing clean water from a clean water output includes providing clean water from a clean water output of first group of dialyzers to a clean water output of a second group of dialyzers, to backwash the second group of dialyzers.

[0064] In some embodiments the number of dialyzers in the first group of dialyzers is not greater than the number of dialyzers in the second group of dialyzers.

[0065] Reference is now made to Figure 7A, which is a simplified line drawing illustration of a flow path of clean water from an output of several dialyzers, the dialyzers used to filter water according to an example embodiment of the invention.

[0066] Figure 7A depicts an example embodiment for filtering water. Water inputs 701a ... 701d ... 701k ... 701x ... 701z provide water to dialyzers 702a ... 702d ... 702k ... 702x ... 702z, and the dialyzers 702a ... 702d ... 702k ... 702x ... 702z filter the water, producing outputs 703a ... 703d ... 703k ... 703x ... 703z of filtered water. The outputs 703a ... 703d ... 703k ... 703x ... 703z may provide filtered water separately, as separate outputs 703a ... 703d ... 703k ... 703x ... 703z, and, in some embodiments the outputs 703a ... 703d ... 703k ... 703x ... 703z may connect to one or more output(s) 704. In some embodiments the outputs 703a ... 703d ... 703k ... 703x ... 703z may connect to the one or more output(s) 704 via one or more valve(s) 705.

[0067] Reference is now made to Figure 7B, which is a simplified line drawing illustration of a flow path of clean water from an output of a first group of dialyzers used to clean a second group of dialyzers by backwashing, according to an example embodiment of the invention.

[0068] Figure 7B depicts an example embodiment for cleaning the second group of dialyzers by backwashing with clean water from the first group of dialyzers. Water inputs 701a ... 701d provide water to a first group of dialyzer 702a ... 702d, the first group of dialyzers 702a ... 702d filter the water, producing outputs 703a ... 703d of filtered water. The filtered water is fed via a valve 705a to outputs 703k ... 703x of a second group of dialyzers 702k ... 702x, and flows through the second group of dialyzers 702k ... 702x, backwashing and cleaning the second group of dialyzer 702k ... 702x, exiting from the second group of dialyzers 702k ... 702x via the water inputs 706k ... 706x.

[0069] It is noted that in some embodiments no water flows out from an output 704a when the first group of dialyzers 702a ... 702d are being used to backwash the second group of dialyzer 702k ... 702x.

[0070] It is noted that in some embodiments water may flow out from a third group of dialyzers 702z, optionally through the same valve 704a, or through a different 704b, when the first group of dialyzers 702a ... 702d is being used to backwash the second group of dialyzers 702k ... 702x.

[0071] Reference is now made to Figure 8, which is a simplified diagrammatical illustration of a water filtration unit according to an example embodiment of the invention.

[0072] Figure 8 depicts a water filtration unit 800, which includes two dialyzer modules 801a 801b, each of which includes 40 dialyzers. Backwashing of one of the dialyzer modules 801a 801b happens from time to time using clean water produced by another one of the dialyzer modules 801a 801b.

[0073] A simplified description of backwashing in the water filtration unit 800 is provided below.

[0074] Water is provided at a water input 802. In some embodiments the water is provided at a pressure of 3 atmospheres, although a range of pressures of 0.2-10 atmospheres is optionally contemplated.

[0075] In some embodiments a pressure pump (not shown) is included as part of the water filtration unit 800 to provide water pressure to water being input at the water input 802.

[0076] In some embodiment the water provided at the water input 802 is provided at a rate of 43 cubic meters per hour, although a range of water provision rates of 0.5-10,000 cubic meters per hour is optionally contemplated.

[0077] The water supplied is filtered through the dialyzer modules 801a 801b.

[0078] In some embodiments the dialyzer modules 801a 801b operate in a dead-end configuration, where the water provided at the water input 802 does not exit the dialyzer modules 801a 801b.

[0079] Filtered water is optionally provided to a water output 803.

[0080] In some embodiments the water output 803 optionally supplies the filtered water to a reverse osmosis unit (not shown), as the degree of filtration is potentially good enough to supply a reverse osmosis unit, for example for desalinization, without additional filtering.

[0081] In some embodiments the water is also optionally chlorinated by a chlorination tank 804. In some embodiments the chlorinated water is optionally neutralized by a SMBS dosing unit (not shown).

[0082] In some embodiments the SMBS dosing unit (not shown) is optionally controlled by a Redox controller (not shown).

[0083] In some embodiments the water filtration unit 800 includes 2 skids, each skid with 3 modules of 80 dialyzers.

[0084] In some embodiments a backwash operation of 60 seconds, where a skid provides filtered water to another skid for backwashing, is performed once every 2 hours.

[0085] In some embodiments a first skid filters water and provides the filtered water for backwashing a second skid. Later, the second skid filters water and provides the filtered water for backwashing the first skid.

[0086] In some embodiments the frequency and duration of backwashing is optionally variable, determined by physical and / or microbiological load in the input water. In some embodiments the frequency of backwashing may optionally be selected between once every 5 minutes and up to once a week. In some embodiments a typical backwash time may vary from 30 seconds up to 10 minutes.

[0087] In some embodiments, the backwashing is initiated automatically, by way of a non-limiting example by sensing water pressure at an input of a dialyzer of group of dialyzers, and / or by sensing a water pressure differential between input and output of a dialyzer or group of dialyzers.

[0088] In some embodiments backwash is manually ended by an operator seeing that backwash water is clear.

[0089] In some embodiments backwash is automatically ended by a sensor providing an ending signal when the backwash water clarity is above a specific value, and / or the backwater opacity is below a specific value.

[0090] In some embodiments the backwash operates without providing additional pressure for backwash water.

[0091] In some embodiments the backwash operates without providing a vessel for collecting clean water for backwashing, based on providing clean water for backwashing from one or more dialyzers or dialyzer groups operating under water pressure and / or water flow rate similar or equal to water pressure and / or flow rate used for filtering water for non-backwash purposes.

[0092] In some embodiments the backwash operates with a pressure booster pump which maintains a desired backwash pressure, without a vessel for collecting clean water for the backwashing. In some embodiments the pressure booster operates to add pressure, and a pressure relief valve optionally relieves pressure.

[0093] In some embodiments backwash water is optionally provided at a range of pressures between 0.4 and 6 bars.

[0094] The above features of operating backwash optionally without a water pressure pump for backwash use, and / or without a vessel for collecting clean water for backwash potentially provides an advantage over typical ultra-filtration units which require such a vessel or pressure supply for performing backwash.

[0095] The above features of operating backwash optionally without a water without a vessel for collecting clean water for backwash potentially provides an advantage over typical ultra-filtration units which do use such a collection vessel, and then need to chlorinate water in the collection vessel, since it is standing water during all non-backwash periods.

[0096] In some embodiments chlorinated water is optionally used for backing, thereby providing Chemically Enhanced Backwash.

[0097] It is expected that during the life of a patent maturing from this application many relevant dialyzers will be developed and the scope of the term dialyzer is intended to include all such new technologies a priori.

[0098] As used herein the term "approximately" refer to ± 25 %.

[0099] The terms "comprising", "including", "having" and their conjugates mean "including but not limited to".

[0100] The term "consisting of" is intended to mean "including and limited to".

[0101] The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

[0102] As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a unit" or "at least one unit" may include a plurality of units, including combinations thereof.

[0103] The words "example" and "exemplary" are used herein to mean "serving as an example, instance or illustration". Any embodiment described as an "example or "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and / or to exclude the incorporation of features from other embodiments.

[0104] The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". Any particular embodiment of the invention may include a plurality of "optional" features unless such features conflict.

[0105] Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0106] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging / ranges between" a first indicate number and a second indicate number and "ranging / ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

Claims

1. A method of cleaning one or more dialyzers in a water filtration system, comprising more than one dialyzer for water filtration: providing clean water from a clean water output of one or more first dialyzers, through a fluid connection, to a clean water output of one or more second dialyzers, to backwash the second dialyzers, wherein a number of first dialyzers is not greater than a number of second dialyzers.

2. The method of claim 1, wherein a single first dialyzer provides clean water to backwash a single second dialyzer.

3. The method of any one of claims 1 and 2, wherein a total membrane area of the first dialyzers is not greater than a total membrane area of the second dialyzers.

4. The method of any one of claims 1-3 wherein the backwashing is performed without a vessel for collecting clean water for the backwashing.

5. The method of any one of claims 1-4 wherein the method comprises, switching from backwashing the second dialyzers using output of clean water from the clean water output of the first dialyzers to backwashing the first dialyzers using output of clean water from the clean water output of the second dialyzers.

6. The method of any one of claims 1-5 wherein the backwashing is performed at a duration between 30 seconds and 10 minutes.

7. The method of any one of claims 1-6 wherein the backwashing is performed at a frequency between once every 5 minutes and once every week.

8. The method of any one of claims 1-7 wherein the frequency and duration of the backwashing is variable, determined by physical and / or microbiological load in the input water.

9. The method of any one of claims 1-8 wherein the backwashing is initiated automatically.

10. The method of any one of claims 1-9 wherein the backwashing operates without providing additional pressure for backwashing water.