Water treatment method to generate potable water and a fertilization or fertigation product

Abstract

A water treatment method is provided to generate potable water and a fertilization or fertigation product. This includes steps of a] regenerating a strong base anion resin (10, 10', 10'') using an amount of potassium chloride solution of between 0.25 and 1.0 mols / L of resin at a concentration of less than or equal to 1.0M and 5 at a flow rate of less than or equal to 1 bed volumes / hour; b] rinsing the strong base anion resin (10, 10', 10''); c] passing a raw water stream to be treated through the regenerated strong base anion resin (10, 10', 10''); d] collecting between 100 bed volumes and 150 bed volumes of an output stream from the strong base anion resin as a high-nitrate-concentration fertilization or fertigation 10 output; and e] subsequently collecting between 300 bed volumes and 500 bed volumes of the output stream from the strong base anion resin (10, 10', 10'') as low-nitrate-concentration potable water.

Description

[0001] Water Treatment Method To Generate Potable Water And A Fertilization Or Fertigation Product

[0002] The present invention relates to a water treatment method to generate potable water and a fertilization or fertigation product.

[0003] Nitrate contamination in drinking water is a major global concern, and typically occurs from industrial effluent and fertilizer run-off from agricultural practices. Historically, nitrate contamination has been attributed to farming activities mainly through the development of cheap fertilizers in the 1950’s leading to overuse, resulting in significant nitrate run-off. Animal waste is also a contributing factor. Nitrate contamination levels are consistently higher in areas of high agricultural activity. Fertigation, that is, the application of fertilizer in liquid solution, is acknowledged as best practice for fertilizer addition due to the efficiency of both water and fertilizer along with minimal run-off and environmental impact. Fertigation is therefore being utilised on an increasing basis, particularly in areas with water supply problems; Israel has a fertigation take-up rate of 50%, compared with just 5% take-up in the UK versus solid fertilizer.

[0004] The two most common methods of reducing nitrate levels in drinking water are ion exchange and reverse osmosis, with ion exchange being regarded as the superior technology due to the lower waste volumes produced.

[0005] A strong base anion resin will typically comprise a nitrate-selective core of its matrix, provided in the form of beads, and an outer layer of mixed-ion-selectivity having a radius of between 10% and 50% of that of the nitrate-selective core. Typically, there will also be a very small outermost layer which is phosphateselective, suspected as being due to hydrogenation of the surface. Such a strong base anion bead is shown in Figure 1 A at 10.

[0006] Other types of resin are known. Nitrate-selective resins are similar to strong base anion resins, but the nitrate-selective core is much larger; the outer layer or layers are generally less than 5% of the radius of the matrix, as shown in Figure 1 B at 10’. Shallow shell technology resins are also known, in which approximately 40% of the diameter of the bead is chemically inert. This reduces the salt required to regenerate the resin compared with strong base anion resins. This is shown in Figure 1 C at 10”.

[0007] Regeneration of a strong base anion resin is commonly performed via a segmented regeneration, that is, by applying a weak chloride solution followed by a strong chloride solution to ensure that both the nitrate-selective core and the outer layer of mixed-ion-selectivity are regenerated fully. A graph of the regeneration process is illustrated in Figure 2; bicarbonate and sulphate ions are removed first, within the first 3 bed volumes of regenerant being applied, with nitrate removal only really being seen thereafter once there is a much greater concentration of chloride ions.

[0008] The present invention seeks to provide a method of making use of the reaction kinetics of regeneration to provide discrete high-nitrate and low-nitrate product outputs for use in fertilization or fertigation and potable water respectively.

[0009] According to a first aspect of the invention, there is provided a water treatment method to generate potable water and a fertilization or fertigation product, the water treatment method comprising the steps of: a] regenerating a strong base anion resin using an amount of potassium chloride solution of between 0.25 and 1 .0 mols / L of resin at a concentration of less than or equal to 1 ,0M and at a flow rate of less than or equal to 1 bed volumes / hour; b] rinsing the strong base anion resin; c] passing a raw water stream through the regenerated strong base anion resin; d] collecting between 100 bed volumes and 150 bed volumes of an output stream from the strong base anion resin as a high-nitrate-concentration fertilization or fertigation output; and e] subsequently collecting between 300 bed volumes and 500 bed volumes of the output stream from the strong base anion resin as low-nitrate-concentration potable water.

[0010] The principle of the present invention is that a slow and dilute regeneration of a strong base anion resin will only regenerate the outer functional sites of the resin matrix, which exhibit 1 :1 reaction kinetics. This means that bicarbonate is flushed from the resin early on during the regeneration process. When the interstitial fluid is rinsed from the ion exchange column prior to re-use of the strong base anion resin, nitrate and sulphate ions will replace some of the chloride ions in the outer functional sites, which will elute on eventual re-use of the ion exchange column. This creates an initial fertilization or fertigation product. Once this is retrieved, then subsequent outputs will form a potable water product, up until the point at which nitrate breakthrough on resin occurs. This technique allows for significantly increased retrieval of nutrients from water sources, which may otherwise not have been viable as potable water sources. A significantly reduced amount of salt is also required to regenerate the ion exchange column.

[0011] Optionally, during step a], the potassium chloride solution may be provided in an amount of between 0.75 and 1.0 mols / L of resin. During step a], the potassium chloride solution may be provided in an amount of 0.86 mols / L of resin.

[0012] Preferably, the strong base anion resin may comprise a matrix having a nitrateselective core and an outer mixed-ion-selectivity region.

[0013] Optionally, the method may be restarted at step a] following completion of step d].

[0014] The method may further comprise a step f] subsequent to step e] of collecting an amount of the output stream from the strong base anion resin as a further high- nitrate-concentration fertilization or fertigation output.

[0015] Once nitrogen breakthrough occurs on the ion exchange column, that is usually a sign ifier that the column needs regeneration. However, once the output stream ceases to be potable, there will be a high nitrate concentration output which can be collected to increase the amount of fertilization or fertigation product from the system.

[0016] Preferably, the strong base anion resin may be provided in a system having a single ion exchange column.

[0017] Alternatively, the strong base anion resin may be provided in a system having a plurality of ion exchange column in parallel with one another. Where parallel columns are provided, they can be loaded out of phase with one another, which allows for better selection of the ratio of potable water to fertilization or fertigation product to be achieved.

[0018] Optionally, during step a] the potassium chloride solution may be less than or equal to 0.5M. More preferably, during step a] the potassium chloride solution may be less than or equal to 0.3M.

[0019] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0020] Figure 1A shows a pictorial representation of a strong base anion resin matrix, as known within the state of the art;

[0021] Figure 1 B shows a pictorial representation of a nitrate-selective resin matrix, as known within the state of the art;

[0022] Figure 1 C shows a pictorial representation of a shallow-shell technology resin matrix, as known within the state of the art;

[0023] Figure 2 shows a graph indicating the concentrations of effluent ions and conductivity of an output of a strong base anion resin ion exchange column being regenerated using a segmented regeneration process known in the art; and

[0024] Figure 3 shows a graph indicating the concentration of nitrate ions and conductivity of an output of a strong base anion resin ion exchange column being regenerated via a water treatment method in accordance with the first aspect of the invention.

[0025] The present invention relates to a method of treating water to generate both potable water and a fertilization or fertigation product, using a strong base anion resin 10, specifically.

[0026] As shown in Figure 1A, the strong base anion resin 10 has a nitrate-selective core 12, an outer layer 14 of mixed-ion-selectivity, and an outermost layer 16 which displays phosphate selectivity. When a new strong base anion resin 10, all of the functional sites of the nitrateselective core 12, outer layer 14 of mixed-ion-selectivity, and outermost layer 16 are occupied by chloride ions.

[0027] As water to be treated is passed across the strong base anion resin 10, the functional sites will be loaded, with the nitrate-selective core 12 binding to nitrate ions, and a varied selection of ions present in the outer layer 14 of mixed-ion- selectivity. Typically it would be expected that chloride, bicarbonate, nitrate, sulphate, and phosphate ions would be found in the outer layer 14 of mixed-ion- selectivity.

[0028] Segmented regeneration of the strong base anion resin 10 affects all functional sites in the nitrate-selective core 12, outer layer 14 of mixed-ion-selectivity, and outermost layer 16. However, some of the nitrate ions ejected from the nitrateselective core 12 will be reabsorbed by the nitrate-selective core 12 and the outer layer 14, and when the ion exchange column is put back into service, there will be an initial nitrate leakage observed due to incoming sulphate and bicarbonate ions in the raw water, displacing nitrate ions absorbed in the outer layer 14.

[0029] The present invention seeks to actively prevent regeneration of the nitrateselective core 12, instead only regenerating the outer layer 14 of mixed-ion- selectivity the outermost layer 16. When the strong base anion resin 10 is rinsed with water, interstitial liquid in the ion exchange column will be flushed across the strong base anion resin 10. This interstitial liquid will primarily comprise nitrate and sulphate ions, since bicarbonate ions will have been removed early on in the regeneration process and will not have remained in the interstitial liquid. Some of the nitrate and sulphate ions will become loaded into outer layer 14 of mixed-ion- selectivity.

[0030] Because the labile sites in the outer layer 14 of mixed-ion-selectivity now include nitrate loading, when raw water to be treated is passed across the ion exchange column, bicarbonate and sulphate in the water will displace the nitrate, giving a large nitrate peak in the output liquid. In one specific embodiment of the invention, it has been found that the desirable effects can be achieved by the use of a regenerant having an amount of potassium chloride solution of 0.86 mols / L of resin at a concentration of less than or equal to 0.3M and at a flow rate of less than or equal to 1 bed volumes / hour. One example of such an ion exchange resin is the Purolite (RTM) A600e / 9149, supplied by Purolite Ltd of Unit D, Llantrisant Business Park, Llantrisant, Rhondda Cynon Taff, CF72 8LF, United Kingdom.

[0031] Collecting between 100 bed volumes and 150 bed volumes of the output product from the ion exchange column will yield a desirable fertilization or fertigation product. Thereafter, the next 300 to 500 bed volumes of output product will have eliminated the early nitrate peak, and will be suitable for use as potable water. The specific regenerant embodiment described has been tested, and the nitrate concentration and conductivity of the output product during the potable water production period is illustrated in Figure 3.

[0032] In this regeneration method, it has been determined that the interstitial fluid will comprise approximately 5% chloride (measured at 676mg / L), 17% nitrate (measured at 2,710mg / L) and 78% sulphate (12,200mg / L). This was measured for a volume of 3.85 bed volumes. The bicarbonate content was measured as being negligible. It is the absence of the bicarbonate which permits the reabsorption of monovalent nitrate ions onto the outer layer 14 of mixed-ion- selectivity, which would otherwise be occupied by chloride ions with a conventional or segmented regeneration. The nitrate ions are then displaced by bicarbonate or sulphate ions once raw water is introduced. In the present experiment, 135 bed volumes of fertilization or fertigation product were collected, with a nitrate content of approximately 20mg / L. The subsequent potable water was collected from bed volumes 135 to 572, with an average nitrate content of 3mg / L.

[0033] It is anticipated that a potassium chloride solution of between 0.75 and 1 .0 mols / L of resin will be viable to produce the same effect, and also of between 0.25 and 1 .0 mols / L of resin. It is also anticipated that somewhat higher concentrations of potassium chloride solution might be viable without indirectly regenerating the nitrate-selective core 12. A concentration of less than or equal to 0.5M may be viable, and furthermore a concentration of less than or equal to 1 ,0M may also be viable.

[0034] At this point, it may be possible to regenerate the strong base anion resin 10 according to the method herebefore described. However, nitrate leakage will begin to occur at some point once the strong base anion resin 10 is overloaded, and there may be a viable product output which can still be used for fertilization or fertigation products, either separately or in conjunction with the first said fertilization or fertigation product output.

[0035] Various system configurations could be considered to run the present method. For example, a two-column ion exchange system could be used which allows the proportion of fertilization or fertigation product to potable water product to be varied. Alternatively, a plant could be produced to create a requisite quantity of h igh-n itrate irrigation water to support a low run-off commercial greenhouse crop, such as tomatoes. A single ion exchange column could be constructed as well with the aim to maximise the production of nutrient products and vary the proportion of irrigation water to potable water production. Equally, a two column system could be considered to produce the lowest achievable levels of nitrate in the potable water output with minimized production of nutrients.

[0036] Segmentation of the regenerant could also be considered to produce a high potassium bicarbonate based foliar spray, for powdery mildew treatment, along with lower bicarbonate levels in the nutrient feed.

[0037] Further treatment of the nutrient product may be feasible to alter the ion content therein.

[0038] The present invention provides a means of yielding both fertilization and / or fertigation product output from otherwise poor water sources. This may allow for restoration of previously abandoned wells, and encourages efficient use of nutrients and water, whilst also reducing soil nitrate emissions. Such reuse of resources has a much smaller carbon footprint when compared with industrial fertilizer production via the Mannheim or Haber processes, for instance.

[0039] The regeneration process therefore uses a weak regenerant at a low flow rate to preferentially regenerate only the outer functional sites of the strong base anion resin. Rinsing the interstitial liquid following regeneration in this manner encourages preferential reloading of nitrate and sulphate onto the labile outer sites.

[0040] The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0041] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

[0042] The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

Claims1 . A water treatment method to generate potable water and a fertilization or fertigation product, the water treatment method comprising the steps of: a] regenerating a strong base anion resin using an amount of potassium chloride solution of between 0.25 and 1 .0 mols / L of resin at a concentration of less than or equal to 1 ,0M and at a flow rate of less than or equal to 1 bed volumes / hour; b] rinsing the strong base anion resin (10, 10’, 10”); c] passing a raw water stream to be treated through the regenerated strong base anion resin (10, 10’, 10”); d] collecting between 100 bed volumes and 150 bed volumes of an output stream from the strong base anion resin (10, 10’, 10”) as a high- nitrate-concentration fertilization or fertigation output; and e] subsequently collecting between 300 bed volumes and 500 bed volumes of the output stream from the strong base anion (10, 10’, 10”) resin as low-nitrate-concentration potable water.

2. A method as claimed in claim 1 , wherein, during step a], the potassium chloride solution is provided in an amount of between 0.75 and 1 .0 mols / L of resin3. A method as claimed in claim 2, wherein, during step a], the potassium chloride solution is provided in an amount of 0.86 mols / L of resin.

4. A method as claimed in any one of the preceding claims, wherein the strong base anion resin (10, 10’, 10”) comprises a matrix having a nitrateselective core and an outer mixed-ion-selectivity region.

5. A method as claimed in any one of the preceding claims, wherein the method is restarted at step a] following completion of step e],6. A method as claimed in any one of claims 1 to 4, further comprising a step f] subsequent to step e] of collecting an amount of the output stream from the strong base anion resin (10, 10’, 10”) as a further high-nitrate-concentration fertilization or fertigation output.

7. A method as claimed in any one of the preceding claims, wherein the strong base anion resin (10, 10’, 10”) is provided in a system having a single ion exchange column.

8. A method as claimed in any one of claims 1 to 6, wherein the strong base anion resin (10, 10’, 10”) is provided in a system having a plurality of ion exchange column in parallel with one another.

9. A method as claimed in any one of the preceding claims, wherein during step a] the potassium chloride solution is less than or equal to 0.5M.

10. A method as claimed in claim 9, wherein during step a] the potassium chloride solution is less than or equal to 0.3M.

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