Treatment of wastewater containing phosphate and methods for controlling fine particles.

Abstract

Wastewater treatment containing phosphate and methods for controlling fine particles. Methods and apparatus for precipitating dissolved materials from an aqueous solution are provided. In one embodiment, the method comprises: introducing the aqueous solution into a reactor and introducing a magnesium (mg) source into the reactor in a sufficient quantity to cause the dissolved materials to precipitate into crystals. The mg source is introduced into the reactor in the form of particles of a mg-containing material. The mg source has a solubility in the aqueous solution less than about 1 g / L. Alternatively, the mg concentration in the reactor is less than about 0.03 mol / L. In another embodiment, the apparatus comprises a reaction tank having an inlet and an outlet and a hydration tank associated with the reaction tank and configured to hydrate a mg source in an aqueous solvent and introduce the mg source as a hydrated fluid paste into the reaction tank.

Description

"TREATMENT OF WASTEWATER CONTAINING PHOSPHATE AND METHODS FOR CONTROLLING FINE PARTICLES" Technical Field

[001] The invention relates to apparatus and methods for precipitating dissolved materials. Some embodiments provide apparatus and methods for crystallizing materials, such as struvite, from aqueous solutions, such as wastewater or process water. For example, some embodiments relate to apparatus and methods for precipitating dissolved materials to form crystals while controlling fine particles. Background

[002] Reactors in general, and fluidized bed reactors in particular, have been used to remove and recover phosphorus from solutions such as wastewater and process water. Aqueous solutions from some sources contain significant concentrations of phosphorus, usually in the form of phosphate. These aqueous solutions can come from a wide variety of sources. This includes sources such as landfill leachate, agricultural runoff, industrial process effluents, industrial process water, municipal wastewater, animal manure, phosphogypsum tank water, and the like. These aqueous solutions, if released into the environment without treatment, can result in excessive levels of phosphorus in receiving waters.

[003] There are several technologies for phosphorus removal and recovery. Some of these technologies provide fluidized bed reactors for the removal of phosphorus from aqueous solutions by producing struvite (MgNI I.|PO.|·6I FO) or a struvite analogue or a phosphate compound in granular form. Magnesium can be added to the reactor to form struvite. Struvite can be formed by the reaction: Mg2++ NH4+ + PO43-+ 6H2O θ MUNI I J'O-6112O

[004] Koch et al., Fluidized Bed Wastewater Treatment, US Patent Petition 870210068203, dated 07 / 27 / 2021, page 7 / 61 / 46 No. 7622047 describes examples of reactors and methods that can be applied to remove and recover phosphorus from aqueous solutions.

[005] A difficulty sometimes exhibited in crystallization reactions is that the particle sizes produced by the reaction may not be desirable. For example, under certain operating conditions, a reactor may produce a large quantity of very small crystals (“fine particles”), where larger crystals are desired. Excessive production of fine particles can result in low phosphate uptake, since fine particle production can be carried out with effluent from a crystallization reactor. Crystal sizes are affected by a wide range of factors, including flow conditions, chemical composition, temperature, etc. For example, if the feed (i.e., the mass of phosphorus (PO4-P) added to a reactor (or portion thereof) per unit time) is too high, then undesirable fine particles will be formed.Load limitations impact the volume of aqueous solution that can be treated per unit of time, thus impacting struvite production as a function of time.

[006] References describing various crystallization processes include: US8245625; US7942939; WO2006082341; US6946572; US6364914; WO9837938; US4666527; US3419899; US2209019; US4159194; US4263010; US5124265; US6660049; US5663456; AU2004320909; WO2012022099; WO2012134255.

[007] There remains a need for effective reactors and methods for removing and recovering dissolved materials from solutions. There remains a particular need for effective reactors and suitable methods for preparing large particles of marginally soluble substances such as struvite, struvite analogues and calcium phosphate.

[008] The preceding examples of the related technique and the limitations associated therewith are intended to be illustrative and not exhaustive. Other limitations of the related technique will become apparent to those skilled in the art. Petition 870210068203, dated 07 / 27 / 2021, page 8 / 61 / 46 in the technique after reading the descriptive report and studying the drawings. Summary

[009] The following embodiments and aspects thereof are described and illustrated together with apparatus, systems, tools and methods which are intended to be exemplary and illustrative, without limiting the scope. In several embodiments, one or more of the problems described above have been reduced or eliminated, while other embodiments are directed to other improvements.

[0010] Aspects of the present invention relate to apparatus and methods for precipitating dissolved materials. The apparatus and methods have exemplary application to the growth of crystals of materials such as struvite, struvite analogues and calcium phosphate.

[0011] Apparatus and methods according to some embodiments operate to grow particles, avoiding or minimizing the production of fine particles, by injecting a fluid aqueous paste of a low-solubility magnesium (Mg) source. By maintaining a low concentration of fine particles, the growth rates of larger particles can be intensified and the loss of phosphorus through fine particles can be minimized or eliminated.

[0012] Some aspects of the invention provide methods in which a reactor is operated under high growth conditions. For example, the high growth conditions may correspond to the loading conditions for a substance being produced. In some embodiments, the loading is above a threshold to achieve a high crystal growth rate. For example, in some embodiments, the loading may be 5 g of PO4P / min / m3 or more or 50 g of PO4-P / min / m3 or more or 100 g of PO4-P / min / m3 or more or 250 g of PO4-P / min / m3 or more in a reactor (or a portion of the reactor).

[0013] In some embodiments, a reason for Petition 870210068203, dated 07 / 27 / 2021, p. 9 / 61 / 46 supersaturation (ratio of the product of the concentrations of the constituents of the substance to the product of concentrations corresponding to equilibrium) is above a threshold to achieve a high crystal growth rate. For example, in some embodiments, the supersaturation ratio for struvite or other material being crystallized may be 2 or more, or 3 or more, or 5 or more in the reactor. In some embodiments, the substance is moderately soluble in aqueous solution. The concentration of fine particles can be maintained below a threshold, thus maintaining a growth rate of larger particles, by injecting an aqueous fluid paste of a low-solubility magnesium (Mg) source into the reactor (or portion of the reactor), as described in this document.

[0014] In some embodiments, the method for precipitating dissolved materials from an aqueous solution involves introducing the aqueous solution containing the dissolved materials into a reactor and introducing a magnesium (Mg) source into the reactor. The Mg source is introduced in a sufficient quantity to cause the dissolved materials in the aqueous solution to precipitate into crystals. The Mg source may, for example, be in the form of particles of a material containing Mg. The Mg source may, for example, have a solubility in the aqueous solution less than about 1 g / L and / or the concentration of Mg in the reactor that is available for the reaction to produce struvite (including solids in the particles of Mg-containing material) may be less than about 0.03 mol / L.

[0015] In some embodiments, the Mg source is introduced into the reactor as a fluid paste. The fluid paste can be prepared by adding water to the Mg source and soaking the Mg source for a hydration time before introducing the hydrated fluid paste into the reactor. The Mg source may, for example, have a solubility in aqueous solvent of about 5 mg / L to about 500 mg / L, or about 5 mg / L to about 150 mg / L. The concentration of Mg in the reactor may be from about 0.1 mmol / L to about 0.03 mol / L after the Petition 870210068203, dated 27 / 07 / 2021, p. 10 / 61 / 46 introduction of the fluid paste. The Mg source may, for example, have a particle size smaller than 50 μm, or about 10 μm to about 30 μm, or about 100 mesh to about 400 mesh, or about 17SGN to 100 SGN, for example.

[0016] In some embodiments, the method additionally includes maintaining the aqueous solution at a pH greater than about 7. In some embodiments, the pH of the aqueous solution is maintained by adding an acid or a base to the hydrated fluid paste. In some embodiments, the pH of the aqueous solution is maintained by controlling the amount of the Mg source present in the aqueous solution.The amount of Mg source present in the aqueous solution can be controlled by the following steps: measuring the pH of the aqueous solution in real time, comparing the measured pH with a target pH (or pH “set point”), and adjusting the pH by introducing the Mg source into the aqueous solution so that the pH of the aqueous solution is controlled to be equal to or close to the target pH. In some embodiments, the Mg source is introduced into the reactor at a predefined time interval, such as intervals of about 30 seconds to about 5 minutes.

[0017] In some embodiments, the Mg source is a low-solubility Mg source. The low-solubility Mg source may, for example, be MgO, Mg(OH)2, or a magnesium carbonate. Examples of magnesium carbonate may include one or more of anhydrous magnesite salts (MgCOs), barringtonite (MgCOs^2H2O), nesquehonite (MgCOs^3H2O), lansfordite (MgCOs^5H2O), arinite (MgCOs^Mg(OH)2^3H2O), hydromagnesite (4MgCOsMg(OH)2^4H2O), dippingite (4 MgCO3Mg(OH)2^5H2O), dolomitic lime, and limestone.

[0018] In some embodiments, the low-solubility source of Mg is MgO. MgO can be prepared in any suitable manner. In some embodiments, MgO is prepared at a calcination temperature for a period of time sufficient to produce MgO particles. The calcination temperature may, for example, be in the range of about Petition 870210068203, dated 07 / 27 / 2021, page 11 / 61 / 46 from 600 °C to approximately 1200 °C. The time period used to produce MgO particles can, for example, be in the range of about 1 to 3 hours. The hydration time can be, for example, between about 15 minutes and about 36 hours.

[0019] In some embodiments, an acid is added to the hydrated fluid paste before introducing the hydrated fluid paste into the reactor. The acid may, for example, be added in about 0.4:1 molar equivalents. The acid may be a strong acid, such as any of hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3). In some embodiments, the acid is a weak acid, such as any of acetic acid, citric acid, or oxalic acid.

[0020] In some embodiments, the Mg source reacts with the aqueous solution for a reaction time of about 30 minutes to about 60 minutes.

[0021] In some embodiments, the aqueous solution has a phosphorus concentration in the range of about 40 mg / L to about 10,000 mg / L.

[0022] In some embodiments, a highly soluble Mg source, such as MgCl2 or MgSO4, is introduced into the reactor in addition to the introduction of the low-solubility Mg source. The highly soluble Mg source and the low-solubility Mg source may be introduced into the reactor at the same time.

[0023] Some aspects of the invention provide a fluidized bed reactor for precipitating dissolved materials from an aqueous solution. The fluidized bed reactor may comprise a reaction tank and a hydration tank. The reaction tank may include an inlet and an outlet. The hydration tank may be associated with the reaction tank and configured to hydrate a magnesium (Mg) source in an aqueous solvent and introduce the Mg source as a hydrated fluid paste into the reaction tank. In some embodiments, the reactor additionally includes a control valve. Petition 870210068203, dated 07 / 27 / 2021, page 12 / 61 / 46 The control valve can be configured to control the flow of hydrated fluid paste from the hydration tank to the reaction tank. In some embodiments, the reactor additionally includes a recycle path. The recycle path can be configured to take a solution from one part of the reaction tank and return at least part of the removed solution to another part of the reaction tank. The recycle path may optionally include a fine particle treatment tank. In some embodiments, a solids separation device is upstream of the fine particle treatment tank. The solids separation device can be configured to separate solids from liquid in the recycle path.

[0024] In some embodiments, the reactor additionally includes a pH probe. The pH probe can be configured to measure the pH of the aqueous solvent in the reaction tank. In some embodiments, a controller can be configured to receive an input from the pH probe. The controller can be configured to control the opening and closing of the control valve in response to a deviation of the pH of the aqueous solvent in the reaction tank from a desired pH setpoint.

[0025] In some embodiments, the hydration tank includes a first acid injector. The first acid injector can be configured to dose an acid in a controlled manner into the fluid slurry in the hydration tank. In some embodiments, the reactor includes a second acid injector. The second acid injector can be configured to dose an acid in a controlled manner into the solution stream in the recycle path. The reactor may also include a base injector. The base injector can be configured to dose a base in a controlled manner into the solution stream in the reaction tank. In some embodiments, the base injector is located downstream of the acid injector in the recycle path.

[0026] Another aspect provides a method for preparing struvite or an analogue of struvite. The method comprises providing a reactor vessel in which, Petition 870210068203, dated 07 / 27 / 2021, page 13 / 61 / 46 in at least one portion of the reactor vessel, a cross-sectional area of ​​the reactor vessel increases with elevation, maintaining a fluidized bed segregated by granule size in the portion of the reactor vessel flowing a solution comprising phosphate upwards through the portion of the reactor. An upward fluid velocity of the flowing solution decreases with elevation in the reactor portion. The method introduces fine particles from a low-solubility magnesium source into the reactor and allows the fine particles to disperse in the fluidized bed. Some of the granules are removed from the fluidized bed. The fine particles may comprise, for example, magnesium oxide. The fine particles may, for example, have sizes of SGN 100 or less. The fine particles may, for example, have diameters of 0.1 mm or less.

[0027] In this method, the pH can be maintained at a pH setpoint that is equal to or greater than pH 7.5 in at least part of the reactor vessel. The pH set point may be at least pH 8 in some cases.

[0028] The method may involve recycling the solution in the reactor vessel via a recycle path extending from an elevation in the reactor vessel above the fluidized bed to an elevation in the reactor vessel that is below the fluidized bed. Optionally, the method includes capturing or redissolving struvite particles in the recycle path.

[0029] Fine particles from a low-solubility magnesium source can be introduced into the reactor vessel as a fluid paste of fine particles. The fluid paste can be hydrated before being introduced into the reactor vessel. Hydration can be performed by mixing the fine particles with aqueous solvent (e.g., water) and allowing the particles to remain in contact with the water for a period of at least a few minutes before introducing the fluid paste into the reactor vessel. The fluid paste can be injected into the reactor vessel at a location below the fluidized bed. In some cases, an acid is mixed with the fluid paste before introducing the fluid paste into the reactor vessel. A pH at a location in the reactor vessel. Petition 870210068203, dated 07 / 27 / 2021, page 14 / 61 / 46 can be controlled by the controlled addition of fluid paste. In some cases, fluid paste buffers at an alkaline pH (e.g., at least pH 7.5 or at least around pH 8).

[0030] In addition to the aspects and forms of embodiment described above, other aspects and forms of embodiment will become evident by reference to the drawings and by studying the following detailed descriptions. Brief description of the Drawings

[0031] Exemplary embodiments are illustrated in the referenced figures of the drawings. The embodiments and figures disclosed in this document are intended to be considered illustrative rather than restrictive.

[0032] FIG. 1A is a schematic diagram of an example reactor apparatus according to one example embodiment. FIG. 1B is a schematic diagram of an example reactor apparatus according to another example embodiment.

[0033] FIG. 2 is a flowchart of a method according to an example embodiment.

[0034] FIG. 3 is a graph showing the relationship between phosphorus (P) removal (%) and reaction time for an aqueous solution treated with Mg sources.

[0035] FIG. 4 is a graph showing the effect of temperature on the hydration of an aqueous fluid paste of MgO.

[0036] FIG. 5 is a graph showing the effect of aqueous fluid pastes of Mg sources on P removal (%).

[0037] FIG. 6 is a graph showing the effect of aqueous fluid pastes of Mg sources on the final Mg concentration.

[0038] FIG. 7 is a graph showing the relationship of P removal (%) as a function of hydration time for aqueous fluid pastes of Mg sources. Petition 870210068203, dated 07 / 27 / 2021, page 15 / 61 / 46

[0039] FIG. 8 is a graph showing the effect of hydration temperature on P removal (%) by aqueous fluid pastes of a light burnt magnesium oxide product derived from natural magnesite ore.

[0040] FIG. 9 is a graph showing the effect of hydration temperature on P removal (%) by aqueous flowable pastes of a synthetically derived light burnt magnesium oxide product.

[0041] FIG. 10 is a graph showing the P removal rate (%) as a function of reaction time for aqueous fluid pastes from Mg sources.

[0042] FIG. 11 is a graph showing the P removal rate (%) as a function of pH for aqueous fluid pastes from Mg sources.

[0043] FIG. 12 is a graph showing the relationship between P removal (%) and reaction time for aqueous fluid pastes of Mg sources. Description

[0044] Throughout the following description, specific details are set forth in order to provide a fuller understanding for persons skilled in the art. However, well-known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Consequently, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0045] This invention relates to the crystallization of materials from solution. Embodiments provide crystallization reactors and methods, as well as apparatus and methods for reducing the concentration of fine particles in crystallization reactors. Other embodiments provide crystallization reactors and methods for the growth of crystals of materials that have low solubility (of which struvite, struvite analogs, and calcium phosphate are examples). The invention can be applied to control fine particles in the crystallization of any of a wide range of chemical substances from solution. The precipitation of struvite from aqueous solutions is used in this Petition 870210068203, dated 07 / 27 / 2021, page 16 / 61 / 46 disclosure as a non-limiting example of an application of the invention.

[0046] Some embodiments of the invention described below relate to crystallization reactors and methods in which magnesium is added to precipitate phosphorus in wastewater in the form of struvite or struvite analogues or a phosphate compound. For example, some embodiments provide crystallization reactors and methods in which magnesium is added to precipitate phosphorus from wastewater in the form of struvite (MgNI I.|P('V6I PO)) according to the following reaction: Mg2+ + NH4+ + PO43· + 6H2O θ MENU J'O-61 PO)

[0047] Struvite can be in the form of granules. The granules can, for example, have sizes from about 0.1 mm to 3 mm or more. These examples coincide with embodiments having significant commercial utility. The scope of the invention, however, is not limited to these examples.

[0048] The term “aqueous solution” or “solution” is used in the following description and claims to include aqueous solutions such as industrial and municipal wastewater, industrial process water, bleach, runoff, animal waste, effluents, phosphogypsum reservoir water, or the like. Some embodiments provide methods for treating municipal sewage and / or animal waste. Some embodiments provide methods for treating other types of wastewater. Some embodiments provide methods for crystallizing materials using feedstock other than wastewater.

[0049] The term “charge” or “loading” is used in the following description(s) and claims to mean the mass of phosphorus (PO4-P) added to a reactor (or portion of the reactor) per unit time.

[0050] The term “saturation” is used in the following description and claims to mean a solution at its equilibrium point that cannot dissolve more of one solute under the present conditions.

[0051] The term “supersaturation” is used in the following description and claims to mean a solution at its equilibrium point that cannot dissolve more of one solute under the present conditions. Petition 870210068203, dated 07 / 27 / 2021, p. 17 / 61 / 46 claims to mean a solution containing more of a dissolved solute than could be dissolved by the solvent under the present conditions.

[0052] One aspect of the invention relates to apparatus and methods for precipitating dissolved materials, such as struvite, struvite analogues, calcium and phosphate. Some aspects of the invention relate to apparatus and methods for operating a reactor under high growth conditions.

[0053] In some embodiments, the reactor comprises a fluidized bed reactor. An example of a fluidized bed reactor 12 is shown in FIG. 1. The reactor 12 comprises an inlet 14, an outlet 16, and a reaction tank 18. An aqueous solution is introduced into the reaction tank 18 through the inlet 14. The inlet 14 is below the outlet 16. The tank 18 is constructed so that the flow of the aqueous solution in the reactor 12 is generally upward. The crystals that may form in the reactor 12 will be propelled upward and against the force of gravity by the fluid flow in the reactor 12. The crystals may grow by adhesion and / or further crystallization. Where the flow rate decreases with elevation in the tank 18, the composite particles of crystallization product tend to be sorted by size, with the larger particles tending to be located in the lower parts of the tank 18 and the smaller particles tending to be higher in the tank 18.

[0054] The aqueous solution flows into the reaction tank 18 through the inlet 14 and flows out of the reaction tank 18 through the outlet 16. In some embodiments, the reactor 12 comprises a plurality of inlets and / or outlets.

[0055] Inlet 14 may be located, for example, at or near the lower portion of reaction tank 18. Outlet 16 may be located, for example, at or near the upper portion of reaction tank 18. In some embodiments, inlet 14 is oriented to face upwards and a solution flow introduced from inlet 14 into reaction tank 18 is Petition 870210068203, dated 07 / 27 / 2021, page 18 / 61 / 46 directed upwards.

[0056] In some embodiments, a method for preparing a crystalline product includes providing at least one ionic species that reacts to form the crystalline product from a material that produces the ionic species when dissolved where the material has low solubility. The material may be provided in the form of fine particles. For example, when the product is struvite, the ionic species may be magnesium ions (Mg+2) and the material may be magnesium oxide (MgO) which has low solubility in water. The MgO may be provided in the form of a fluid paste of fine particles.

[0057] Reactor 12 comprises a hydration tank 40. A low-solubility Mg source is introduced into the hydration tank 40 through inlet 42. An aqueous solvent (e.g., water) is introduced into the hydration tank 40 through inlet 44. The low-solubility Mg source is hydrated with the aqueous solvent for a period of time sufficient to hydrate the Mg source to provide a hydrated fluid paste comprising free Mg+2 ions available in solution for struvite production in reaction tank 18. The hydrated fluid paste is dispensed from the hydration tank 40 to reaction tank 18 through inlet 46. Inlet 46 may be located, for example, within or near the lower portion of reaction tank 18. In some embodiments, inlet 46 is directed upwards and the flow of a hydrated fluid paste introduced from inlet 46 to reaction tank 18 is directed upwards.

[0058] Under the correct reaction conditions, crystals (e.g., struvite crystals or other phosphorus-containing compounds in some embodiments) form in the reaction tank 18 by precipitation of materials dissolved in the solution (e.g., wastewater solution in some embodiments). The crystals can grow over time and can be classified according to size by differences in fluid velocities in different regions within the reaction tank. By Petition 870210068203, dated 07 / 27 / 2021, page 19 / 61 / 46 example, in some embodiments, the fluid flows upwards in the reaction tank with a velocity that increases with depth in the reaction tank (decreases with elevation). This can be achieved, for example, by providing a reaction tank having a cross-sectional area that increases with elevation above the inlet and / or providing recycle paths (described elsewhere in this document) having outlets at different depths in the reaction tank 18.

[0059] In such embodiments, particles composed of crystals can move downwards as they grow in size (e.g., through accretion and / or aggregation with other crystals). The particles can ultimately enter a harvest zone in the reaction tank 18, from which they can be removed for use as fertilizer or other applications.

[0060] In some embodiments, the reaction tank 18 comprises a substantially vertically oriented conduit having a harvest section and two or more sequential sections vertically above the harvest section. The cross-sectional area of ​​the conduit may increase, moving from the bottom of the reaction tank 18 towards the top of the reaction tank 18. For example, the cross-sectional area may increase between adjacent sections. The number of sections in the conduit may be varied. In some embodiments, the cross-sectional area increases gradually. In some embodiments, the cross-sectional area increases smoothly. In some embodiments, the reaction tank 18 is cone-shaped or horn-shaped or otherwise configured to have a cross-sectional area that increases smoothly with elevation above the bottom of the reaction tank 18. The tank 18 may be round in cross-section, but it is not necessarily so.Entry 14 may be located within or below the harvesting section, for example.

[0061] Some embodiments of the present invention may Petition 870210068203, dated 07 / 27 / 2021, p. 20 / 61 / 46, comprises a fluidized bed reactor of the type described in Britton, publication WO No. 2012 / 119260, entitled “Reactor for Precipitating Solutes from Wastewater and Associated Methods” and / or of the type described in Britton, et al., publication WO No. 2015 / 003265, entitled “Reactor Apparatus and Methods for Fines Control” and / or of the type described in Koch et al., US Patent No. 7622047, entitled “Fluidized Bed Wastewater Treatment”, which are hereby incorporated by reference in their entirety for all purposes.

[0062] It has been determined that, in some applications, it is desirable to be able to maintain control over the size of the product crystals (e.g., struvite crystals, struvite analogues, or other phosphorus-containing compounds) that form in the reactor through precipitation of dissolved materials. For example, it may be desirable to selectively precipitate and harvest relatively large product crystals and / or granules (e.g., crystals and / or granules with a diameter >1 mm), where the product crystals aggregate to form product granules.

[0063] One aspect of the invention relates to apparatus and methods that provide for the control of fine particles (fine particles are very small crystals, for example, crystals with a diameter <100 μm can be described as “fine particles”) in a reactor. Many fine particles in a reactor can have sizes in the range of about 1 pm to about 10 pm.

[0064] Fine particles can have an extremely large surface area to mass ratio compared to larger crystals. Where a large number of fine particles are present in a crystallization reactor, a high proportion of crystal growth can occur on the surface of the fine particles, thus reducing the growth rates of larger crystals. It has been observed that the production of fine particles in a reactor can result from zones of high supersaturation (exceeding metastable limits and resulting in primary or secondary nucleation) or from the accumulation of previously formed crystals within the reactor. The production of fine particles can be reduced. Petition 870210068203, dated 07 / 27 / 2021, page 21 / 61 / 46 operating a reactor with very low supersaturation. However, crystals may grow slowly under such conditions. It is desirable to be able to control the accumulation of fine particles within the reactor, especially product crystal sizes (e.g., >1 mm) when large crystal sizes are desired.

[0065] It has been observed that a reactor can be operated under increasing loading conditions by increasing the concentrations of one or more of the constituents of the struvite product, struvite analogue, or another phosphorus-containing compound. For example, increasing the concentration of free Mg+2 ions can intensify crystal growth.

[0066] During the operation of the struvite crystallizer, and especially when operating with feed solutions with high phosphate concentrations (feed loads > 100 mg / L PO4-P and particularly > 2,000 mg / L PO4-P), and / or extended hydraulic retention times (> 1 hour and particularly > 12 hours) in a fluidized bed reactor (such as reactor 12), it has been observed that fine particles (crystals with a diameter < 100 µm) tend to accumulate in the reactor. In some cases, within a period of 6 to 12 hours of operation, almost all crystal formation / growth can occur as fine particles, either by primary / secondary nucleation, or due to growth occurring mainly on the surface of existing fine particles retained in the reactor.It is believed that this phenomenon may occur as a result of a combination of increased secondary nucleation in the presence of high levels of fine particles combined with the overwhelming majority of the crystal surface area in the reactor being on the surface of fine particles (which have much higher surface area to volume ratios than larger, more desirable crystals with diameters of, for example, 1-5 mm).

[0067] The rate at which fine particles accumulate can be controlled to some extent (and the period before which uncontrolled fine particle production begins can be extended) by reducing the reaction rate of Petition 870210068203, dated 07 / 27 / 2021, page 22 / 61 / 46 crystallization and / or supersaturation ratio and / or loading and / or concentration of magnesium added to the reactor. However, if significant quantities of fine particles (e.g., > 5 mg / L of sedimented fine particles as measured in the reactor recycle path flow, or turbidity > 500 NTU) were present in the reactor, a further increase in crystal size distribution or the growth of large crystals could be significantly hampered by the presence of a large number of fine particles.

[0068] Typically, struvite crystal recovery processes use soluble Mg sources, such as magnesium chloride (MgCl2) and / or magnesium sulfate (MgSÜ4), as a source of free Mg+2 for struvite production. Due to the high solubility of these Mg sources (MgCl2 has a water solubility of approximately 54 g / L), the introduction of MgCl2 and / or MgSÜ4 almost immediately leads to an increase in the concentration of free Mg+2 ions, increasing the supersaturation ratio in the localized area where the Mg source was introduced. Thus, zones of high supersaturation can occur in the reactor (or portions of the reactor), producing fine particles, as described elsewhere in this document. For example, when the Mg source is MgCl2, a portion (e.g., about 10-50%) of the struvite crystals produced may be present as fine particles (i.e., <20 gm in diameter).These fine particles are too small to settle effectively and be retained in the reactor, and are therefore removed by washing the reactor and lost with the treated effluent (i.e., loss of fine particles).

[0069] It has been empirically determined that when a Mg source with lower solubility than conventional soluble magnesium sources (e.g., MgCl2 and / or MgSÜ4) is used, the production of fine particles is eliminated or reduced, even under increased loading. Consequently, one aspect of the invention provides methods comprising injecting a low-solubility Mg source into the reactor. Petition 870210068203, dated 07 / 27 / 2021, page 23 / 61 / 46 for the recovery of struvite crystal.

[0070] In some embodiments, the methods comprise a hydration step of a low-solubility Mg source before injecting the resulting hydrated fluid paste into the reactor (or portion of the reactor). Thus, free Mg+2 ions are available to react to form struvite in the reactor. For example, the methods may operate by forming an aqueous fluid paste from a source that releases Mg+2 ions as it dissolves. The Mg source may be mixed with an aqueous solvent for a period of time (i.e., the hydration time).

[0071] In some embodiments, the hydrated fluid slurry is circulated from a fluid slurry tank around a mesh and back to the fluid slurry tank. The fluid velocity in the mesh can be kept high enough to prevent sedimentation of fluid slurry particles in the mesh. The mesh can be arranged to pass close to the reactor. Injection of the hydrated fluid slurry into the reactor may comprise diverting some of the hydrated fluid slurry flowing in the mesh into the reactor, for example, by means of a valve.

[0072] FIG. 2 is a flowchart of a method 100 according to an exemplary embodiment of the invention. The method 100 comprises step 110 of hydrating a low-solubility Mg source in an aqueous solvent, and step 120 of injecting the resulting hydrated fluid paste into a reactor (or a portion of the reactor) to precipitate dissolved materials (including phosphorus (PO4-P)) from an aqueous solution to form crystals.

[0073] In some embodiments, the source of Mg is magnesium oxide (MgO). As shown by the reaction below, in hydration, MgO forms an MgOH+ complex on the surface of the MgO particle and ultimately results in the formation of 2 mol of OH-(aq): MgO(surface) + H (aq)>MgOH (surface) + OH-(aq) ^ MgOH+^OH-(surface) ^ Mg2+(aq) + 2OH-(aq) « Mg(OH)2(s) Petition 870210068203, dated 07 / 27 / 2021, page 24 / 61 / 46

[0074] The formation of 2OI Ι-ι:.1ψ increases and / or maintains the pH of the solution in the reactor at a level suitable for crystal formation and growth and, in some embodiments, reduces and / or eliminates the overall consumption of caustic agent for crystal precipitation in the reactor. In some embodiments, the use of a low-solubility Mg source, such as MgO or Mg(OH)2, can replace the need for caustic agent (e.g., NaOH), reducing or eliminating pH / supersaturation peaks at a caustic agent injection site in the reactor (or portion of the reactor). This can reduce capital and / or total operating costs by eliminating or reducing the need for a separate pH control reagent and the need for associated storage and dosing systems. Additionally, by eliminating or reducing pH / supersaturation peaks, the production of fine particles can be reduced or eliminated.In some embodiments, hydrated fluid paste buffers at alkaline pH. For example, it has been empirically determined that a hydrated fluid paste formed by hydrating MgO in an aqueous solvent buffers at a pH of about 8.1.

[0075] Suitable sources of low-solubility Mg may include: MgO, Mg(OH)2, magnesium carbonates (such as anhydrous magnesite salt (MgCOs), barringtonite di-, tri- and pentahydrate (MgCOs · 2H2O), neskeonite (MgCOs · 3H2O) and lansfordite (MgCOs · 5H2O), respectively, arinite (MgCOs^Mg(OH)2^3H2O), hydromagnesite (4 MgCO3sMg(OH)2MH2O), dippingite (4 MgCO3 / Mg(OH)2MH2O), dolomitic lime or limestone with adequate Mg content). Such sources are typically cheaper than conventionally used soluble Mg sources (e.g., MgCH4 and MgSO4). In some embodiments, the low-solubility Mg source has a solubility in water (from about 25 °C to about 30 °C) of less than about 1 g / L.

[0076] In some embodiments, the low-solubility source of Mg has solubility in water (at about 25 °C to about 30 °C) in Petition 870210068203, dated 07 / 27 / 2021, page. 25 / 61 / 46 range of: about 5 mg / L to about 1 g / L, about 5 mg / L to about 500 mg / L, about 5 mg / L to about 150 mg / L, about 5 mg / L to about 100 mg / L, about 5 mg / L to about 90 mg / L, about 5 mg / L to about 80 mg / L, about 5 mg / L to about 70 mg / L, about 5 mg / L to about 60 mg / L, about 5 mg / L to about 50 mg / L, about 5 mg / L to about 40 mg / L, about 5 mg / L to about 30 mg / L, about 5 mg / L to about 20 mg / L, or about 5 mg / L to about 10 mg / L. For example, MgO has a water solubility of about 86 mg / L (at 30 °C). Mg(OH)2 has a water solubility of about 6.4 mg / L (at 25 °C). MgCO3 has a water solubility of about 139 mg / L (at 25 °C).

[0077] Those skilled in the art will recognize that some variability in solubility is common and that the solubility of a Mg source may differ depending on the provider of that Mg source. For example, the solubility of a Mg source may differ depending on the calcination temperature and / or calcination time used to prepare the Mg source, as described elsewhere in this document.

[0078] In some embodiments, the low-solubility Mg source has a concentration in the reactor of less than about 0.03 mol / L. In some embodiments, the low solubility source of Mg has a concentration in the reactor in the range of: about 0.1 mmol / L to about 0.03 mol / L, about 0.1 mmol / L to about 0.02 mol / L, about 0.1 mmol / L to about 4 mmol / L, about 0.1 mmol / L to about 2.5 mmol / L, about 0.1 mmol / L to about 2.2 mmol / L, about 0.1 mmol / L to about 2.0 mmol / L, about 0.1 mmol / L to about 1.7 mmol / L, about 0.1 mmol / L to about 1.5 mmol / L, about 0.1 mmol / L to about 1.2 mmol / L, about 0.1 mmol / L to about 1.0 mmol / L, about 0.1 mmol / L to about 0.7 mmol / L, approximately 0.1 mmol / L to approximately 0.5 mmol / L, or approximately 0.1 mmol / L to approximately 0.25 mmol / L. For example, when the low-solubility Mg source is MgO, the Mg concentration in the reactor may be approximately 2.1 mmol / L or less. Petition 870210068203, dated 07 / 27 / 2021, p. 26 / 61 / 46

[0079] When the low-solubility Mg source is Mg(OH)2, the Mg concentration in the reactor can be about 0.1 mmol / L or less. When the low-solubility Mg source is MgCO3, the Mg concentration in the reactor can be about 1.6 mmol / L or less.

[0080] In some embodiments, the extent of hydration of the low-solubility Mg source correlates with phosphorus removal (e.g., struvite crystal production). The extent of hydration can be controlled by one or more of the following: the duration of the hydration time, heating of the Mg source and aqueous solvent mixture, and the concentration of the hydrated fluid paste. For example, where the Mg source is MgO, the hydration time can be controlled to prevent or minimize the formation of solid Mg(OH)2. Mg(OH)2(s) can accumulate on the surface of the MgO particles, thus decreasing the rate of release of free Mg+2 and reducing crystal formation in the reactor.

[0081] Since Mg(OH)2(s) is less soluble than MgO(s), the time period to redissolve Mg(OH)2(s) in an aqueous solvent to provide free / dissolved Mg+2 for crystal formation is longer. In some embodiments, the hydration time for a low-solubility Mg source is controlled to improve crystal production. For example, it has been empirically demonstrated that hydrating MgO in an aqueous solvent for about 20 hours resulted in a struvite yield about 4-8% better than a hydration time of about 15 minutes or about 36 hours. In some embodiments, the desired hydration time for MgO is between about 15 minutes and about 36 hours.

[0082] In some embodiments, the hydration time for MgO is between approximately 15 minutes and 1 hour. In some embodiments, the hydration time for MgO ranges from approximately 15 minutes to several hours (e.g., 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours). Petition 870210068203, dated 07 / 27 / 2021, page 27 / 61 / 46 hours, 18 hours, 19 hours, 20 hours).

[0083] Those skilled in the art will understand that the hydration time can be influenced by the reaction conditions and / or the Mg source. For example, temperature and / or pressure and / or the presence of other solutes in an aqueous solvent can impact the release of free Mg+2 and / or the formation of Mg(OH)2(s) when the low-solubility Mg source is MgO. For example, an aqueous fluid paste of MgO heats up as hydration proceeds, especially when acid is added to the fluid paste. This heating can impact the hydration time. Thus, the hydration time of MgO can be greater than 36 hours or less than 15 minutes.

[0084] In some embodiments, when the low-solubility Mg source is a substance other than MgO, the desired hydration time is greater than 15 minutes. In some embodiments, the hydration time is between about 15 minutes and several hours (e.g., 15 minutes to 20 hours). Some examples of non-limiting hydration times are 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours, 35 hours, 36 hours.

[0085] To prepare the hydrated fluid paste, an aqueous solvent (e.g., water) is added to the low-solubility Mg source. In some embodiments, the hydrated fluid paste contains about 5% to about 30% Mg by weight. In some embodiments, the hydrated fluid paste contains less than about 10% Mg by weight. As MgO absorbs water during hydration, the hydrated fluid paste can become “thick” if too little aqueous solvent is used. Consequently, a hydrated fluid paste of MgO with about 25% to about 30% Mg by weight may be too dry and / or viscous and / or thick to mix easily and pump into the reactor (or Petition 870210068203, dated 07 / 27 / 2021, p. 28 / 61 / 46 part of the reactor). In some embodiments, the amount of soluble Mg in the hydrated fluid paste is less than about 5 mg / L. In some embodiments, the amount of soluble Mg in the hydrated fluid paste is about 0.5 mg / L.

[0086] If the weight percentage of Mg in the hydrated fluid paste is too low, this can reduce crystal production and / or increase production times and / or consume excess water, thus increasing production costs. In some embodiments, the hydrated fluid paste is more effective when the fluid paste is relatively dilute (e.g., the fluid paste contains less than about 10% Mg by weight). For example, crystal production can be increased when the hydrated fluid paste of Mg(OH)2 is dilute (e.g., contains less than about 5% Mg by weight).

[0087] In some embodiments, Mg(OH)2 is used as the low-solubility Mg source and is in the form of a fluid paste. Since the Mg(OH)2 form is already hydrated, no further hydration time is required. Because Mg(OH)2 is less soluble than MgO, the use of Mg(OH)2 as a magnesium source may require thinner fluid pastes to achieve performance equivalent to MgO fluid pastes. Consequently, Mg(OH)2 may be a less effective Mg source than MgO in terms of struvite recovery and / or loading.

[0088] Magnesium carbonates can be used as a source of Mg. However, the hydration of magnesium carbonates can result in the production of carbon dioxide (CO2) gas, which can cause foaming problems and / or affect the pH of the fluid paste. CO2 gas is acidic, and consequently, a caustic agent may be necessary to neutralize the excess acid. Dolomitic lime or limestone can be used as a source of Mg. However, these Mg sources contain calcium (Ca), which can interfere with struvite production and / or contaminate the resulting product with Ca. These products may more readily precipitate in wastewater, but they can also be... Petition 870210068203, dated 07 / 27 / 2021, p. 29 / 61 / 46 less desirable as a fertilizer than struvite. However, since MgO, Mg(OH)2, magnesium carbonates, lime, and limestone are relatively inexpensive, they may be an attractive source of low-solubility Mg for struvite production.

[0089] In some embodiments, the particle size of the low-solubility Mg source is controlled to prevent or minimize the hydrated fluid paste from clogging reactor orifices or tubes, such as collector orifices or the like. If the particle size exceeds a desired size, the hydrated fluid paste may clog the buffer tubes to the point where flow is impeded and / or causes damage to the pumping equipment. In some embodiments, the particle size of the low-solubility Mg source is in the range of: about 100 to about 400 mesh, about 100 to about 350 mesh, about 100 to about 300 mesh, about 100 to about 250 mesh, about 100 to about 200 mesh, about 150 to about 200 mesh, about 200 to about 400 mesh, about 250 to about 400 mesh, about 300 to about 400 mesh, or about 350 to about 400 mesh. In some embodiments, MgO has a particle size of about 200 mesh.In some embodiments, MgO has a particle size of about 400 mesh. In some embodiments, the low-solubility source of Mg is a fine powder having a particle size in the range of about 10 to about 50 gm, about 10 to about 40 gm, or about 12 to about 30 gm. In some embodiments, MgO has a particle size in the range of about 17 SGN to about 100 SGN (size guide number). In some embodiments, MgO has a particle size in the range of about 17 SGN to about 30 SGN.

[0090] Those skilled in the art will recognize that the mesh size of the low-solubility Mg source can be affected by the calcination temperature and / or the calcination time to prepare the Mg source. For example, MgO can be prepared by calcining magnesium carbonate. Petition 870210068203, dated 07 / 27 / 2021, pages 30 / 61 / 46 In some embodiments, the calcination temperature is less than about 1200 °C. In some embodiments, the calcination temperature is in the range of about 600 °C to about 1200 °C. In some embodiments, the calcination time is less than about 3 hours. In some embodiments, the calcination time is in the range of about 1 to 3 hours. In some embodiments, the calcination time is about 2 hours.

[0091] By optimizing the conditions for the preparation of the low-solubility Mg source, particle size, specific surface area, and reactivity can be controlled. For example, in some embodiments, a particle size of about 200 mesh is desirable. Such particles can be ideally retained by the reactor without clogging the system used to dispense the low-solubility Mg source to the reactor and / or without the need for high-flow pumps.

[0092] Without being tied to any particular theory, it is believed that employing a low-solubility Mg source can prevent or reduce the production of fine particles due to the longer retention time of slowly dissolving low-solubility Mg sources compared to conventional soluble Mg sources (e.g., MgCl2 and / or MgSO4). Low-solubility Mg sources slowly release free Mg+2 ions into the solution so that the distribution of Mg+2 ions throughout the reactor (or portion of the reactor) is substantially uniform. In this way, crystallization is promoted throughout the reactor (or part of the reactor), and localized areas where the Mg concentration is significantly high can be minimized or avoided. Thus, the slow dissolution rate of low-solubility Mg sources can prevent or minimize areas where the supersaturation ratio is high enough to cause the production of a large number of fine particles.

[0093] Another theory is that the presence of a low-solubility Mg source helps any fine particles that are produced in the reactor (or Petition 870210068203, dated 07 / 27 / 2021, page 31 / 61 / 46 a portion of the reactor) adhering to or other particles present in the solution. The effluent treated by adding a low-solubility Mg source to the aqueous solution in a fluidized bed reactor was tested at loading rates between 5 and 250 g PO4-P / min / m3 and no fine particles or MgO particles were observed in the effluent or recycle fluid. If the reduction or elimination of fine particles was due solely to a longer retention time, the observation of the low-solubility Mg source would be expected in the treated effluent and / or recycle fluid. Since the treated effluent and recycle fluid were empirically observed to be free of the low-solubility Mg source, it is possible that the low-solubility Mg source “adheres” to the struvite crystals present in the reactor.

[0094] Thus, in some embodiments, the low-solubility Mg source (e.g., MgO) is introduced into a fluidized bed. The particles in the fluidized bed may comprise struvite, an analog of struvite, or monoammonium phosphate, for example. The low-solubility Mg source may be provided in the form of particles that would be removed by washing the reactor for certain fluid flow rates in the reactor. The interaction between the small MgO particles (or other low-solubility source such as an ionic species) may retain the small particles in the fluidized bed so that the particles provide Mg+2 (or other ionic species) throughout all or large parts of the fluidized bed. The distributed small particles may replenish the available Mg+2 (or other ionic species) as the available Mg+2 is consumed in the production of struvite or other product.

[0095] It has been empirically determined that the resulting struvite crystals can be relatively pure, with little or no excess Mg observed in the product samples. Therefore, it is believed that the low-solubility Mg source can be essentially completely dissolved and used to form struvite crystals. Further tests were carried out in which the reactor was fed with essentially phosphate-free tap water. Petition 870210068203, dated 07 / 27 / 2021, page 32 / 61 / 46 ammonia, and a fluid paste of hydrated MgO, resulting in the injection and dilution of the fluid paste of MgO in water, but without a struvite formation reaction. In this case, a substantial portion of the injected fluid paste of MgO was observed in the reactor recycle and effluent. The experiment was repeated with and without a fluidized bed of struvite particles present in the reactor, with the same results. This indicates that the occurrence of the struvite formation reaction is necessary for the hydrated fluid paste particles of MgO to adhere to the fluidized bed.

[0096] Without being bound to any particular theory, it is believed that the formation of a fluid paste by hydrating a low-solubility Mg source before the source is added to the reactor (or portion of the reactor) can result in the uniform distribution of Mg+2 ions throughout the reactor volume (or portion of the reactor volume), thus increasing loading limitations and / or increasing struvite production and / or reducing fine particle production. For example, the limited solubility of the low-solubility Mg source may allow the localized supersaturation ratio around the Mg+2 injection point to remain relatively low compared to cases where conventional highly soluble Mg sources (e.g., MgCl2 and MgSO4) are injected into a similar reactor.

[0097] In some embodiments, method 100 comprises an optional step 130 of adding an acid to the hydrated fluid paste. The acid can be added to the tank in which the fluid paste from the low-solubility Mg source is hydrated or stored. The addition of acid can increase the struvite yield in the treatment of high-concentration wastewater (e.g., wastewater containing large amounts of fats, oils, and greases (FOG) or other organic components). The addition of a molar ratio of approximately 0.4:1 of H+ to Mg has been found to be effective in increasing the struvite yield. When the low-solubility Mg source Petition 870210068203, dated 07 / 27 / 2021, page 33 / 61 / 46 solubility is MgO, the acid provides H+(aq) to drive the formation of the MgOH+ complex in the first step of the hydration mechanism described elsewhere in this document.

[0098] It has been empirically determined that adding an appropriate amount of acid to the hydrated fluid paste can increase the struvite crystal production rate and / or overall struvite conversion efficiency, thus resulting in a higher struvite crystal yield and / or allowing for increased reactor loading.

[0099] For example, the addition of an acid in a molar equivalent ratio of 0.2:1 of H+:Mg increased the struvite crystal yield by about 10-20%. In some embodiments, a quantity of acid is added to the hydrated flow paste to neutralize about 20% of any hydroxide formed by the hydration of the low-solubility Mg source. Suitable acids include strong acids such as hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), etc., and weak acids such as acetic acid, citric acid, oxalic acid, etc. Acids that interfere with struvite production (e.g., phosphoric acid (H3PO4)) and / or acids that are too weak to break down MgO particles (or other low-solubility Mg source particles) are avoided in some embodiments.

[00100] In one embodiment, the acid comprises sulfuric acid. For example, the acid may be 93%–98% sulfuric acid. Sulfuric acid is readily available from wet-process phosphoric acid plants and is therefore convenient to use when operating this method in or near a wet-process phosphoric acid plant. Sulfuric acid is generally one of the most economically available commercially.

[00101] In another embodiment, the acid comprises acetic acid (or another volatile fatty acid or combination of volatile fatty acids), which is useful as a source of volatile fatty acids needed for absorption. Petition 870210068203, dated 07 / 27 / 2021, pp. 34 / 61 / 46, regarding phosphate in wastewater treatment plants using enhanced biological phosphorus removal. Therefore, the application of acetic acid or volatile fatty acids to wastewater in the recycle pathway creates an additional level of synergy.

[00102] In some embodiments, in step 120, the acid is dosed into the hydrated fluid paste. For example, the acid can be added in liquid form to a fluid paste hydration tank. Weak acids, such as citric acid, which are available in dry form, can be added as a powder to the hydration tank, or premixed with MgO before hydration.

[00103] In some embodiments, in step 110 and / or step 120, the pH of the hydrated fluid paste is controlled by adding an appropriate amount of acid.

[00104] The reactor configuration and / or reaction conditions may impact fine particles and / or struvite production and / or operating economies when the Mg source is a low-solubility source. For example, in some embodiments, the hydrated fluid paste is injected near the bottom of the reactor (or portion of the reactor), as described elsewhere in this document.

[00105] Since hydrated fluid pastes, such as hydrated fluid pastes of MgO, can be prone to fouling and clogging, a recycle path can be used to adjust fluid flow rates within the hydrated fluid paste mixture and pumping system. The relatively high fluid velocity in the recycle path can prevent or minimize fouling and clogging by the source of low-solubility Mg.

[00106] In the embodiment illustrated in FIG. 1A, reactor 12 comprises a recycle path 30. Not all fluidized bed reactors have a recycle path. However, a recycle path 30 can be advantageous as it provides a way to adjust fluid flow rates within the reactor. Petition 870210068203, dated 07 / 27 / 2021, page 35 / 61 / 46 reactor 12, without altering the rate at which the aqueous solution is introduced into the reaction tank 18 at inlet 14. The recycle path 30 is connected to receive or remove solution from the reaction tank 18 and to return the solution to the reaction tank 18. Reactors according to some embodiments may provide a plurality of recycle paths 30.

[00107] The illustrated recycle path 30 has an inlet end 30A and an outlet end 30B. In the embodiment of FIG. 1, the outlet 16 connects to the inlet end 30A of the recycle path 30, although in other embodiments, the inlet end 30A of the recycle path 30 may be separated from the outlet 16. The outlet 16 may connect to an effluent piping system 20. The inlet 14, the outlet 16, the recycle path 30 and the effluent piping system 20 each comprise one or more valves that allow them to be switched on or off.

[00108] Recycle path 30 is connected to remove the solution from reaction tank 18 and to return the solution to reaction tank 18. In some embodiments, recycle path 30 returns the solution to reaction tank 18 below a location where the solution is received from reaction tank 18. In some embodiments, recycle path 30 shares inlet 14 and / or outlet 16 (for example, inlet end 30A of recycle path 30 is in direct fluid communication with outlet 16 and / or outlet end 30B of recycle path 30 is in direct fluid communication with inlet 14). In other embodiments, recycle path 30 has one or more inlet ends separate from outlet 16 and / or one or more outlet ends in reaction tank 18 separate from inlet 14.

[00109] When the solubility of a substance being precipitated is pH dependent, the reactor 12 may comprise an acid injector 32 to apply an acid to the solution stream. The acid may be injected, for example, into the recycle path 30. The acid injection reduces the pH of the solution in the path of Petition 870210068203, dated 07 / 27 / 2021, page 36 / 61 / 46 recycle 30 or in reactor 12 as a whole. A recycle path 30 with an acid injector 32 can act as a fine particle destruction mesh, selectively dissolving fine particles that are small enough to be kept in suspension in the reactor recycle path flow. Most of the larger crystals remain in the reaction tank 18 (e.g., in the fluidized bed in the reaction tank).

[00110] In some embodiments, the acid applied in recycle path 30 may reduce the pH not only in recycle path 30 but also in reaction tank 18. It is possible that the pH reduction locally in recycle path 30 may be greater than the pH reduction in reaction tank 18, which is farther from the acid injector 32. Because fine particles have a high surface area to volume ratio compared to larger crystals, fine particles tend to dissolve faster in a % mass base than larger crystals. In some embodiments, the pH is increased in the recycle path (e.g., by neutralizing the acid by injecting a base) before the recycle path rejoins tank 18.

[00111] In some embodiments, the reaction tank 18 may comprise a base injector that injects a base (e.g., a substance that increases the concentration of OH- ions in the solution and / or increases the pH of the solution) into the solution in the reaction tank 18 to increase or maintain the pH of the solution. An example base injector 40A is schematically illustrated in FIG. 1A. The base injector 40A may be connected to a controller and a measuring device (e.g., a pH probe).

[00112] In some embodiments, the pH of the solution in reaction tank 18 is maintained at a relatively high pH (compared to some previous struvite precipitation processes – for example, a pH > 7 or > 7.5). In some cases, a pH of 8 or 9 or higher is maintained throughout, or part of, the reaction tank. It has been determined that maintaining certain formation reactions Petition 870210068203, dated 07 / 27 / 2021, page 37 / 61 / 46. Increasing the pH of struvite at a higher pH can help drive the equilibrium reaction to completion. This, in turn, improves the effectiveness of phosphate removal. Specifically, it has been found that increasing the pH of the reaction using MgO as the Mg source in the struvite formation reaction can achieve near-complete (98%) phosphate removal effectiveness from a given wastewater sample. The typical phosphate removal effectiveness using conventional struvite formation reactions is significantly lower.

[00113] The rate of addition of hydrated fluid paste to the reaction tank can impact the effectiveness of phosphate removal. It has been found that the pH of the solution in reaction tank 18 can be used as an indicator of the amount of hydrated fluid paste (or specifically the concentration of the low-solubility Mg source) present in the reactor solution at a given time. In some embodiments, the pH is maintained by adjusting the flow rate of hydrated fluid paste in reaction tank 18 (or, conversely, the injection of hydrated fluid paste into the reaction tank is controlled based on the pH in reaction tank 18). It is also possible to control the addition of hydrated fluid paste to maintain a desired molar ratio of Mg:P in the reactor.

[00114] In some embodiments, the pH of the solution in reaction tank 18 is controlled by the addition of hydrated fluid paste. In some embodiments, the reactor 12 comprises a control valve 31 between the reactor tank 18 and the hydration tank 40. The control valve 31 controls the flow of hydrated fluid paste out of the hydration tank 40 and into the reaction tank 18. In some embodiments, the control valve 31 is connected to a controller 35. The controller 35 may receive input from a pH probe 33. The pH probe 33 measures the pH of the solution in reaction tank 18. The controller 35 may control the opening and closing of the control valve 31 in response to the pH of the solution in reaction tank 18. In some embodiments, the pH probe 33 transmits measurements of Petition 870210068203, dated 07 / 27 / 2021, page 38 / 61 / 46. Real-time pH of the solution in reaction tank 18 for controller 35. Control valve 31 can open to allow the flow of hydrated fluid paste into reaction tank 18 in response to a deviation in the solution pH from a target pH. In some embodiments, the target pH is at a higher pH than that conventionally maintained in struvite precipitation processes. In these embodiments, control valve 31 can open to allow the flow of hydrated fluid paste into reaction tank 18 in response to a decrease in the solution pH from the target pH. The increase in hydrated fluid paste flowing through the fluidized bed of reaction tank 18 results in an increase in the solution pH. In some embodiments, control valve 31 can be set to open at intervals of about 30 seconds to about 5 minutes.

[00115] In an exemplary embodiment, as illustrated in FIG. 1B, the reactor 12 includes a fluid paste mesh 48. The fluid paste mesh 48 circulates the hydrated fluid paste into and out of the hydration tank 40. The hydration tank 40 may comprise a mixer 41 for continuously mixing the hydrated fluid paste. The fluid paste mesh 48 may be in fluid connection with the inlet 46. This allows the hydrated fluid paste to flow out of the fluid paste mesh 48 and into the reaction tank 18. In some embodiments, the hydrated fluid paste is continuously circulated out of the hydration tank 40 and into the reaction tank 18 through the fluid paste mesh 48. In some embodiments, the flow of the hydrated fluid paste from the fluid paste mesh 48 to the reaction tank 18 is controlled by the valve 31.It was determined that circulating the hydrated fluid paste within a fluid paste mesh maintains the flow of the hydrated fluid paste within the reactor at a desired rate that prevents sedimentation of the Mg source particles.

[00116] In some embodiments, a source of soluble Mg (e.g., MgCl2) may be injected into the reaction tank 18, in addition to introducing Petition 870210068203, dated 07 / 27 / 2021, page 39 / 61 / 46, refers to a hydrated fluid paste containing a low-solubility Mg source. The soluble Mg source can optionally be injected into reaction tank 18 simultaneously with the hydrated fluid paste. The soluble Mg source can be injected into reaction tank 18 through the same inlet or a different inlet from the injection of the low-solubility Mg source.

[00117] Reaction time can impact struvite and / or fine particle production and / or operational economies when the Mg source is a low-solubility source. Due, at least in part, to the limited solubility of a low-solubility Mg source, reaction times to achieve the desired phosphorus removal are generally longer than those observed for conventional soluble Mg sources (e.g., MgCl₂ and MgSO₄). The low solubility of the low-solubility Mg source allows the Mg source to slowly release free Mg⁺² ions over time. For example, reaction times of about 6 minutes are typical for soluble Mg sources. For low-solubility Mg sources, reaction times of about 30 to about 60 minutes may be required to achieve the desired phosphorus removal.

[00118] The reaction time can be controlled by decreasing the flow rate of the aqueous solution into the reactor. By increasing the reaction time, the low-solubility Mg source may be able to distribute itself uniformly throughout the reactor volume (or portion of the reactor volume). This can allow the localized supersaturation ratio around the hydrated fluid paste injection point to remain relatively low compared to conventional soluble Mg sources (e.g., MgCl2 and MgSO4), while maintaining a relatively high supersaturation over a substantial portion of the reactor (or portion of the reactor) as the particles of the low-solubility Mg source continue to dissolve, thus replenishing the free Mg+2 concentration throughout the fluidized bed.

[00119] Loading may impact struvite production and / or Petition 870210068203, dated 07 / 27 / 2021, page 40 / 61 / 46 formation of fine particles and / or operational economies when the Mg source is a low-solubility source. For example, a fluidized bed reactor can be operated under high growth conditions (i.e., high loading conditions) when a low-solubility Mg source is added to an aqueous solution in the reactor (or portion of the reactor). In some embodiments, the loading is above a threshold to achieve a high crystal growth rate. For example, it has been empirically observed that the loading can be 5 g PO4-P / min / m3 or more, or 50 g PO4-P / min / m3 or more, or 100 g PO4-P / min / m3 or more, or 250 g PO4-P / min / m3 or more in a reactor (or a portion of the reactor).In some cases, the loading of PO4-P can be increased by a multiple of 2, 5, 7, 10, 17, 20, 25 or more, while producing commercially acceptable struvite particles, by changing from injecting a highly soluble Mg source to injecting a less soluble Mg source, as described in this document (e.g., when a 10% by weight aqueous MgO flowable paste is used) compared to a similar case where conventional soluble Mg sources (i.e., MgCl2 or MgSO4) are used (typically as 1% to 32% solutions of MgCl2 or MgSO4). Consequently, the loading can be increased very significantly, for example, by a multiple of 5 or more, or 10 or more, or 25 or more times, by employing a less soluble Mg source, as described in this document, compared to a case where a highly soluble Mg source is used.

[00120] In some embodiments, an aqueous solution having a relatively high concentration of phosphorus (i.e., about 2,000 to about 10,000 mg / L of PO4-P) can be fed to the reactor at a relatively low flow rate to maintain reactor loading. In some embodiments, an aqueous solution having a lower concentration of phosphorus (i.e., about 40 to about 600 mg / L of PO4-P) can be fed to the reactor. In some embodiments, the reactor (or a portion of the reactor) Petition 870210068203, dated 07 / 27 / 2021, page 41 / 61 / 46, has a hydraulic limitation (i.e., a maximum upward flow velocity and / or a minimum hydraulic retention time (HRT)) that may limit the maximum loading. For example, in some embodiments, the reaction tank 18 of reactor 12 comprises a substantially vertically oriented conduit having a harvesting section and two or more sequential sections vertically above the harvesting section. In these embodiments, the reactor may be operated at an upward flow velocity of about 250 cm / minute in a harvesting section of the reaction tank and 60 cm / minute in one or more of the vertically sequential sections above the harvesting section.In some embodiments, fine particles can be separated from the solution in a recycle path and concentrated by sedimentation, filtration, centrifugation, or other solids separation techniques, and the concentrated fine particle solids are sent to a fine particle treatment tank where they are dissolved in a reduced pH solution (e.g., an acidic solution) before returning to the reaction tank and / or the recycle path. The fine particle treatment tank can be operated at an upward flow rate of about 7 cm / minute. The fine particle treatment tank can be used to capture fine particles and / or particles from the low-solubility Mg source and return the low-solubility Mg source to the reaction tank and / or the recycle path to be dissolved for crystal production.Where the low-solubility source of Mg particles sediments quickly enough to be retained in the reactor, or is otherwise agglomerated into growing struvite particles, then the low-solubility source of Mg can be retained for a period of time that is longer than the HRT of aqueous solution flowing through the reactor, possibly eliminating or reducing HRT as a limiting factor in reactor loading and leaving the upward flow rate as the limit. Example 1 - Phosphorus removal with various Mg sources Petition 870210068203, dated 07 / 27 / 2021, pages 42 / 61 / 46

[00121] Aqueous solution samples (liquids removed from anaerobic digesters of municipal wastewater treatment plants) reacted with various low-solubility Mg sources to determine the impact of the type of low-solubility Mg source on phosphorus (P) removal (%) as a function of reaction time (minutes). The test results are shown in FIG. 3. The samples were prepared as described in Table 1.

[00122] In each case, a 10% solution of fluid MgO paste was prepared. If acid was used, then 93% sulfuric acid was dosed to the fluid MgO paste at a 0.4:1 mol H per mol Mg ratio. The fluid MgO paste was then allowed to hydrate for 15 minutes before being measured at a 1:1 Mg:P ratio in a water removal liquor flask. The flask was allowed to react for 60 minutes, and then the soluble concentrations in the flask were recorded to determine the removals. After 20 hours of hydration, another flask of water removal liquor was dosed with the fluid MgO paste at a 1:1 Mg:P ratio, allowed to react for 60 minutes, and then the soluble concentrations in the flask were recorded. Table 1 - Phosphorus removal with various Mg sources Source of Mg Hydration Time Mg:P (mol:mol) Acid Base pH LOCAL 1 aqueous fluid paste of Mg(OH)2 at 10% 1:1 LOCAL 1 aqueous fluid paste of Mg(OH)2 at 0.57% 1.5:1 LOCAL 2 aqueous fluid paste of Mg(OH)2 at 10% 0.25 h 1:1 LOCAL 2 aqueous fluid paste of Mg(OH)2 at 10% 0.25 h 1.25:1 LOCAL 2 aqueous fluid paste of Mg(OH)2 at 10% 1:1 LOCAL 2 by weight of MgCl2 at 32% 1:1 LOCAL 1 fluid paste 1.25:1 Petition 870210068203, dated 07 / 27 / 2021, pp. 43 / 61 / 46 aqueous slurry of Mg(OH)2 at 10% LOCAL 1 aqueous slurry of Mg(OH)2 at 0.23% 1:1 LOCAL 2 aqueous slurry of MgO at 10% 0.25 h 1:1 Yes 0.4:1 mol of H+:mol of Mg LOCAL 2 aqueous slurry of 10% MgO 0.25 h 1:1 Yes 0.4:1 mol H+:mol Mg NaOH added >8 Example 2 - Effect of Acid and Hydration Time on Struvite Recovery

[00123] The following hydrated fluid pastes were prepared in water: (i) 10 wt% MgO, hydration time = 20 hours; (ii) 10 wt% MgO, hydration time = 15 minutes; (iii) 10 wt% MgO with 0.2:1 mol H2SO4:MgO, hydration time = 19 hours; and (iv) 10 wt% MgO with 0.2:1 mol H2SO4:MgO, hydration time = 15 minutes. Each hydrated fluid paste was added to a sample of an aqueous fluid paste (water removal liquors from anaerobic digesters of a municipal wastewater treatment plant) and the solutions were mixed for 60 minutes.

[00124] The solutions were analyzed for P, N, and Mg content. At least 80% of the phosphorus (P) content of each aqueous solution was removed by the hydrated fluid pastes, as indicated in Table 3. The removal of P (%) was greater where the hydrated fluid paste contained 0.2:1 mol of H2SO4:MgO (i.e., fluid pastes (iii) and (iv)) and where the fluid paste had a longer hydration time (i.e., fluid pastes (i) and (iii)). Analysis of Mg content indicated that less Mg was available for P removal for fluid pastes (ii) and (iv). Table 3 - Effect of Acid and Hydration Time on Struvite Recovery Fluid Paste Hydration time (hours) H2SO4:MgO (mol:mol) Mg:P (mol:mol) P removal (%) Petition 870210068203, dated 07 / 27 / 2021, pp. 44 / 61 / 46 i 19 0 1:1 90 ii 0.25 0 1:1 84 iii 20 0.2:1 1:1 91 iv 0.25 0.2:1 1:1 87 Example 3 - Effect of Acid on the Concentration of Free Mg2+ Ions

[00125] Acid was added to the hydrated fluid pastes of MgO prepared in Example 2. The final ratios were as follows: (i) 0.49:1 mol H2SO4:MgO; (ii) 0:1 mol H2SO4:MgO; (iii) 0.20:1 mol H2SO4:MgO; and (iv) 0.94:1 mol H2SO4:MgO. Each hydrated fluid paste was added to a sample of an aqueous solution (water removal liquors from anaerobic digesters of a municipal wastewater treatment plant). Additional acid was added to the samples with hydrated fluid pastes (i) and (iv) to lower the pH below 9.

[00126] Without being tied to any particular theory, it is believed that additional acid was needed to lower the pH because the mechanism for producing Mg(OH)2 from MgO includes the intermediate production of Mg+2(aq) and OH-(aq). The Mg+2(aq) ions are available for crystal production and the OH-(aq) ions remain free in the solution available to form MgOH+OI H (surface) and promote the further production of Mg+2(aq) and OH-(aq), causing the pH to continue to rise until Mg(OH)2(s) is formed.

[00127] Without being bound to any particular theory, it is believed that the sample containing hydrated fluid paste (iii) does not require additional acid, since the MgO likely converted completely to Mg(OH)2 and consequently the pH of the solution was controlled by the dissolution of Mg(OH)2 and precipitation of struvite. The sample containing hydrated fluid paste (iv) required additional acid because the hydrated fluid paste likely formed an initial layer of Mg(OH)2 and additional Mg+2(aq) and OH-(aq) ions were released into the solution as MgOH+OH-(surface) was formed. The sample containing hydrated fluid paste (i), which is believed to have been less hydrated than the sample containing hydrated fluid paste (iii), required acid. Petition 870210068203, dated 07 / 27 / 2021, p. 45 / 61 / 46 additional. It is likely that some unreacted MgO was hydrating during struvite production. Since the hydrated fluid paste (ii) did not contain acid, was hydrated for a shorter period of time (i.e., 15 minutes) and the temperature was maintained at room temperature, it is believed that the water did not have sufficient time to diffuse within the MgO particles. Consequently, the initial surface layer of Mg(OH)2 could still be forming and would be available to react with the struvite. Once the struvite reaction was complete, a number of unreacted MgO sites would have remained (which would explain the low final Mg concentration observed). Example 4 - Removal of P (MgCh)

[00128] A 32% by weight aqueous solution of MgCh was prepared and added to an aqueous solution (water removal liquors from anaerobic digesters of a municipal wastewater treatment plant) so that the Mg:P (mol:mol) ratio was 1:1. The pH of the resulting solution was increased to 7.9 by the addition of 0.5 mL of NaOH(aq), and the solution was mixed for 60 minutes. The pH rose to 8.24 during the 60-minute mixing time. The removal of P was 92%, and the solution contained 32 mg / L of Mg, 10.8 mg / L of P, and 621 mg / L of NH3-N. Example 4A - Alternative sources of MgO

[00129] The differences in reactivity between different MgO sources were compared. FIG. 5 shows the % removal of P and FIG. 6 shows the final Mg concentration for various samples prepared using MgO from a first supplier (Supplier 1) and MgO from a second supplier (Supplier 2). The hydrated fluid pastes of MgO from the two sources were prepared as follows: Source of MgO Acid Hydration Time Supplier 2 Yes 0.2 mol H2SO4: mg ~20 hours Supplier 1 Yes 0.2 mol H2SO4: mg ~20 hours Supplier 2 Yes 0.2 mol H2SO4 mg <15 minutes Supplier 1 Yes 0.2 mol H2SO4: mg <15 minutes Petition 870210068203, dated 07 / 27 / 2021, page 46 / 61 / 46 Supplier 2 0 ~20 hours Supplier 1 0 ~20 hours Supplier 2 0 <15 minutes Supplier 1 0 <15 minutes

[00130] Each hydrated fluid paste was added to a sample of an aqueous solution (water removal liquors from anaerobic digesters of a municipal wastewater treatment plant) and the P removal (%) was determined. The P removal (%) was higher for MgO from Supplier 2 compared to MgO from Supplier 1. This indicates that the hydrated fluid pastes of MgO from Supplier 2 were likely limited in Mg and that the MgO source from Supplier 1 is likely less reactive than the MgO source from Supplier 2. However, the MgO source from Supplier 1 was more sensitive to hydration time and added acid. The % P removal was higher where the hydration time was longer (i.e., ~20 hours vs. <15 minutes). The % P removal was higher where acid was added to the fluid paste of MgO.It is important to note that the fluid MgO pastes from Supplier 1 were all hydrated at a lower temperature than the fluid MgO pastes from Supplier 2, since the heat of reaction of Supplier 2's MgO and water was greater than that of Supplier 1's fluid MgO pastes. Furthermore, the final pH of Supplier 1's fluid MgO paste and the aqueous solution mixture was approximately 0.1 lower than the pH of Supplier 2's fluid MgO paste and the aqueous solution mixture. Consequently, secondary acid addition was not necessary for the mixtures containing Supplier 1's fluid MgO paste. This may imply the presence of fewer MgOH+ sites for the reaction and / or that Supplier 1's fluid MgO paste particles have a smaller surface area than Supplier 2's fluid MgO paste particles.Since excess pH appears to be of less concern when using a fluid paste of MgO from Supplier 1, MgO from Supplier 1 may be preferable for use in struvite recovery. Petition 870210068203, dated 07 / 27 / 2021, pages 47 / 61 / 46 Example 5 - Effect of Hydration Time

[00131] Aqueous fluid pastes of MgO from Supplier 2 and MgO from Supplier 1 were prepared and subjected to various hydrations. An aqueous fluid paste of MgO that was hydrated for 48 hours appeared dry, indicating that the MgO had likely converted entirely to Mg(OH)2(s). Aqueous fluid pastes of MgO from Supplier 2 and MgO from Supplier 1 were prepared with the following hydration times: 15 minutes, approximately 20 hours, and 36 hours. Each fluid paste was added to a sample of an aqueous solution containing P (water removal liquors from anaerobic digesters of municipal wastewater treatment plants) and the P removal (%) was compared. The results are shown in Figure 7. The fluid pastes of MgO that hydrated for 36 hours were less effective at removing P than the fluid pastes of MgO that hydrated for 20 hours. Fluid MgO pastes that hydrated for 15 minutes were less effective at removing P.Fluid MgO pastes prepared with acid achieved greater P removal than fluid MgO pastes prepared without acid. Example 6 - Effect of temperature

[00132] The effect of temperature on hydration was tested by heating aqueous fluid pastes of MgO prepared from Supplier 2 MgO and Supplier 1 MgO in the presence and absence of acid. The hydration time was 15 minutes. As shown in FIGS. 11 and 12, increasing the ambient temperature to more than 55 °C had little effect on P removal (i.e., Flasks 4, 13, 9, and 15). The addition of acid improved P removal (%) at ambient temperature (i.e., Flasks 2 and 7). Example 7 - Effect of Retention Time

[00133] The effect of reaction time on P removal (%) was tested for aqueous fluid pastes of MgO from Supplier 2 and MgO from Supplier 1 prepared with and without acid (10% fluid pastes of MgO with and without dose). Petition 870210068203, dated 07 / 27 / 2021, page 48 / 61 / 46 molar of 0.2:1 H2SO4:MgO). A fluidized bed reactor of the type described in Britton, publication WO 2012 / 119260, entitled “Reactor for Precipitating Solutes from Wastewater and Associated Methods”, was used. The reactor had a volume of approximately 168 m3 to the bottom of the recycle collector. As shown in FIG. 10, the P removal (%) was determined after reaction times of 6.5 minutes (which is the HRT of the reactor), 15 minutes, and 60 minutes. FIG. 11 shows the pH of each aqueous solution. The removal of P (%) was greater for the 15-minute sample than for the 6.5-minute sample, which may be related to the observed increase in pH of 0.2 after the longer reaction time.

[00134] NaOH was added to raise the pH of each mixture above 8, and the removal of P (%) was determined after reaction times of 6.5 minutes, 15 minutes, and 60 minutes. The Mg:P ratio (mol:mol) was 1.25:1 for each sample. The removal of P (%) was also determined for a sample of MgCl2 with NaOH added to raise the pH above 8. The results are shown in FIG. 12.

[00135] Fluid MgO pastes showed increased P removal performance with increased reaction time and acid addition; approaching the performance of soluble Mg sources (MgCl2) and caustic agents at 60 minutes reaction time. Example 8 - Full-scale demonstrations

[00136] Commercial full-scale fluidized bed reactors were used to test the use of a low-solubility Mg source, specifically MgO, in wastewater precipitation. Two full-scale demonstration experiments were performed. Different MgO sources were used in the two experiments. In the first experiment, the MgO source was a fine powder of calcined magnesite with a particle size distribution in which approximately 90% of the particles were smaller than 75 µm. A target MgO concentration of approximately 12 wt% was maintained in the Petition 870210068203, dated 07 / 27 / 2021, page 49 / 61 / 46 reaction tank. The loading was approximately 65 kg of PO4-P per day. The pH of the solution in the reaction tank was in the range of approximately 7.5 to approximately 8.1. The flow of the hydrated fluid paste of MgO in the reaction tank was controlled by maintaining a molar ratio of Mg:P in the reaction tank. Samples from the reaction tank were collected and analyzed to determine the amount of solids produced in the reaction and the amount of dissolved Mg that remained in the sample supernatant. The percentage of total solids and the amount of dissolved Mg detected in the collected samples were 18.75% and 0.566 mg / L, respectively.

[00137] In the second experiment, the MgO source was a fine powder of calcined magnesite with a particle size of approximately 200 mesh (with approximately 96% passage). A target MgO concentration of approximately 20% by weight was maintained in the reaction tank. The loading rate was approximately 195 kg of PO4-P per day. The flow rate of the hydrated fluid paste of MgO into the reaction tank was controlled by maintaining the pH at approximately 7.9 to approximately 8. Samples from the reaction tank were collected and analyzed to determine the amount of solids produced from the reaction and the amount of dissolved Mg remaining in the sample supernatant. The percentage of total solids and the amount of dissolved Mg detected in the collected samples were 30.21% and 1.36 mg / L, respectively.

[00138] The results of these experiments illustrate that low amounts of free Mg are present when the reaction is complete. This suggests that most of the Mg that was added to the reaction tank was used to form struvite.

[00139] Although a number of aspects and embodiments of example have been discussed above, those skilled in the art will recognize certain modifications, permutations, additions, and subcombinations thereof. It is therefore intended that the following appended claims and claims set forth below be interpreted to include all Petition 870210068203, dated 07 / 27 / 2021, pp. 50 / 61 / 46 these modifications, permutations, additions, and subcombinations that are consistent with the broader interpretation of the specification as a whole. Interpretation of Terms

[00140] Unless the context clearly requires otherwise, throughout the description and claims: • “Approximately” a declared value means a range of values ​​that is within plus or minus 10% of the declared value (for example, “approximately 10” means in the range of 9 to 11); • “Compreende”, “compreendendo” and similar terms should be interpreted in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is, in the sense of “including, but not being limited to”; • When used to describe this descriptive report, the terms “in this document,” “above,” “below,” and words of similar significance should refer to this descriptive report as a whole, and not to any particular portions of this descriptive report; • “or”, when referring to a list of two or more items, encompasses all of the following interpretations of the word: any of the items in the list, all the items in the list, and any combination of the items in the list; • The singular forms “um”, “uma”, and “o” and “a” also include the meaning of any appropriate plural forms.

[00141] Specific examples of systems, methods, and apparatus have been described in this document for illustrative purposes only. These are merely examples. The technology provided in this document can be applied to systems other than the example systems described above. Many alterations, modifications, additions, omissions, and permutations are possible within the practice of this invention. This invention includes variations on the embodiments described that would be evident to a skilled practitioner, including variations obtained by: substituting resources, elements, and / or acts with equivalent resources, elements, and / or acts; mixing and combining resources, elements, and / or acts of Petition 870210068203, dated 07 / 27 / 2021, pp. 51 / 61 / 46 different forms of implementation; combination of resources, elements and / or acts of forms of implementation as described in this document with resources, elements and / or acts of another technology; and / or omission of combination of resources, elements and / or acts of the forms of implementation described.

[00142] It is therefore intended that the following appended claims and claims introduced hereafter be interpreted as including all modifications, permutations, additions, omissions and subcombinations that may reasonably be inferred. The scope of the claims should not be limited by the preferred embodiments presented in the examples, but should receive the broadest interpretation consistent with the description as a whole.

Claims

1. A method for precipitating struvite or a struvite analogue from an aqueous solution, characterized in that it comprises: introducing the aqueous solution containing the dissolved materials into a reactor; and introducing a magnesium (Mg) source into the reactor in an amount to maintain the concentration of Mg available for precipitation in the reactor less than 0.03 mol / L and to precipitate the dissolved materials in the aqueous solution into crystals, wherein the Mg source is introduced into the reactor in the form of particles of a material containing Mg, and wherein the Mg source has a solubility in the aqueous solution less than 1 g / L; or wherein the Mg source is introduced as a hydrated fluid paste; and wherein an acid is added to the hydrated fluid paste before introducing the hydrated fluid paste into the reactor.

2. Method according to claim 1, characterized in that it further comprises preparing the hydrated fluid paste by adding water to the Mg source and soaking the Mg source for a hydration time before introducing the hydrated fluid paste into the reactor.

3. Method according to claim 1 or 2, characterized in that the Mg source has a solubility in aqueous solvent of 5 mg / L to 500 mg / L.

4. Method according to claim 1 or 2, characterized in that the Mg source has a solubility in aqueous solvent of 5 mg / L to 150 mg / L.

5. Method, according to any one of claims 1 to 4, characterized in that it comprises maintaining the concentration of Mg in the reactor in the range of 0.1 mmol / L to 0.03 mol / L.

6. A method according to any one of claims 1 to 5, characterized in that the Mg source has a particle size smaller than 50 Lim.

7. Method, according to any one of claims 1 to 5, characterized in that the Mg source has a particle size in the range of 10 pm to 30 µl.

8. A method according to any one of claims 1 to 5, characterized in that the Mg source has a particle size in the range of 100 mesh to 400 mesh.

9. A method according to any one of claims 1 to 8, characterized in that it further comprises maintaining the pH of the aqueous solution at a pH greater than 7.

10. Method according to claim 9, characterized in that the pH of the aqueous solution is maintained by adding an acid or a base to the hydrated fluid paste.

11. Method according to claim 9, characterized in that the pH of the aqueous solution is maintained by controlling the amount of the Mg source present in the aqueous solution.

12. Method according to claim 11, characterized in that the amount of Mg source present in the aqueous solution is controlled by: measuring the pH of the aqueous solution in real time; comparing the measured pH with a target pH; adjusting the pH by introducing the Mg source into the aqueous solution so that the pH of the aqueous solution is changed towards the target pH.

13. Method according to claim 12, characterized in that the target pH is greater than 7.

14. Method, according to any of the claims 1 Petition 870260052251, dated 05 / 29 / 2026, page 19 / 26 3 / 9 to 13, characterized in that it further comprises introducing the Mg source into the reactor at a predefined time interval.

15. Method according to claim 14, characterized in that the predefined time interval is from 30 seconds to 5 minutes.

16. Method, according to any one of claims 1 to 15, characterized in that the Mg source comprises a low-solubility Mg source, the low-solubility Mg source comprising one or more of: MgO, Mg(OH)2 and a magnesium carbonate.

17. Method according to claim 16, characterized in that the magnesium carbonate comprises one or more anhydrous salts of magnesite (MgCO3), barringtonite (MgCO.^21 FO), neskeonite (MgCO3^3H2O), lansfordite (MgCO3^5H2O), arinite (MgCO3^Mg(OH)2^3H2O), arinite (4 MgCOAkíOI F-41 FO), dippingite (4 MgCO3Mg(OH)2^5H2O), dolomitic lime and limestone.

18. Method according to claim 16, characterized in that the low-solubility Mg source comprises MgO.

19. Method according to claim 18, characterized in that MgO is prepared at a calcination temperature for a period of time sufficient to produce MgO particles and the calcination temperature is in the range of 600 °C to 1200 °C.

20. Method according to claim 19, characterized in that the time period is in the range of 1 to 3 hours.

21. Method according to claim 2, characterized in that the hydration time is between 15 minutes and 36 hours.

22. A method according to any one of claims 1 to 21, characterized in that 0.4:1 molar equivalents of the acid are added to the hydrated fluid paste.

23. Method, according to any one of claims 1 to 22, characterized in that the acid is a strong acid. Petition 870260052251, dated 05 / 29 / 2026, page 20 / 26 4 / 9 24. Method according to claim 23, characterized in that the acid is one or more of: hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid.

25. A method according to any one of claims 1 to 22, characterized in that the acid is a weak acid.

26. Method according to claim 25, characterized in that the acid is acetic acid, citric acid or oxalic acid.

27. A method according to any one of claims 1 to 26, characterized in that the Mg source reacts with the aqueous solution in a reaction time of less than 60 minutes.

28. Method, according to any one of claims 1 to 26, characterized in that the Mg source reacts with the aqueous solution for a reaction time of 30 minutes to 60 minutes.

29. A method, according to any one of claims 1 to 28, characterized in that the loading is 5 g of PO4-P / min / m3 or more into the reactor tank.

30. A method, according to any one of claims 1 to 28, characterized in that the loading is 50 g of PO4-P / min / m3 or more into the reactor tank.

31. A method, according to any one of claims 1 to 28, characterized in that the loading is 250 g of PO4-P / min / m3 or more into the reactor tank.

32. Method, according to any one of claims 29 to 31, characterized in that the aqueous solution has a phosphorus concentration in the range of 40 mg / L to 10,000 mg / L.

33. Method according to claim 1, characterized in that the Mg source comprises a highly soluble Mg source and a low-soluble Mg source, the highly soluble Mg source comprising MgCl₂ or MgSO₄ and the low-soluble Mg source comprising one or more of: MgO, Mg(OH)₂ and a magnesium carbonate.

34. Method according to claim 33, characterized in that the high-solubility Mg source and the low-solubility Mg source are introduced into the reactor simultaneously.

35. Fluidized bed reactor for carrying out the method for precipitating dissolved materials from an aqueous solution, as defined in any one of claims 1 to 34, the reactor characterized in that it comprises: a reaction tank having an inlet and an outlet; a hydration tank associated with the reaction tank and configured to hydrate a magnesium (Mg) source in an aqueous solvent and introduce the Mg source as a hydrated fluid paste into the reaction tank; and wherein the hydration tank comprises a first acid injector configured to controllably dose an acid into the hydrated fluid paste in the hydration tank.

36. Reactor, according to claim 35, characterized in that it further comprises a control valve configured to control a flow of hydrated fluid paste from the hydration tank to the reaction tank.

37. Reactor, according to claim 35 or 36, characterized in that it further comprises a recycle path associated with the reaction tank and configured to remove solution from one part of the reaction tank and return at least a portion of the removed solution to another part of the reaction tank.

38. Reactor, according to any one of claims 35 to 37, characterized in that it further comprises a pH probe for measuring the pH of the aqueous solvent in the reaction tank.

39. Reactor, according to claim 38, characterized in Petition 870260052251, dated 05 / 29 / 2026, page 22 / 26 6 / 9 by the fact that it further comprises a controller connected to the pH probe and the control valve, the controller controlling the opening and closing of the control valve in response to a change in the pH of the aqueous solvent in the reaction tank.

40. Reactor, according to claim 39, characterized in that the reactor comprises a second acid injector that is configured to dose an acid in a controlled manner into the solution stream in the recycle path.

41. Reactor according to claim 40, characterized in that the reactor comprises a base injector that is configured to dose a base in a controlled manner into the solution stream in the reaction tank.

42. Reactor according to claim 41, characterized in that the base injector is located downstream of the acid injector.

43. Reactor, according to any one of claims 37 to 42, characterized in that the recycle path comprises a fine particle treatment tank.

44. Reactor, according to claim 43, characterized in that it further comprises a solids separation device upstream of the fine particle treatment tank.

45. Reactor, according to claim 44, characterized in that the recycle path comprises a solids separation device upstream of the fine particle treatment tank, and the solids separation device is configured to separate solids from the liquid in the recycle path.

46. ​​Reactor, according to claim 35, characterized in that it further comprises a fluid paste mesh configured to circulate the hydrated fluid paste into and out of the hydration tank.

47. Reactor, according to claim 46, characterized by the fact that it comprises an inlet connecting the fluid paste mesh to the reaction tank. 48.A method according to claim 1, characterized in that: in at least one portion of the reactor, a cross-sectional area of ​​the reactor increases with elevation; maintaining a fluidized bed segregated by granule size in the reactor portion, flowing the aqueous solution containing the dissolved materials, wherein the dissolved materials comprise phosphate, upwards through the reactor portion, wherein an upward fluid velocity of the flowing solution decreases with elevation in the reactor portion; introducing fine particles of the magnesium source into the reactor and allowing the fine particles to disperse in the fluidized bed; removing some of the granules from the fluidized bed; wherein the introduction of fine particles of the magnesium source into the reactor comprises the introduction of the hydrated fluid paste of the fine particles into the reactor; and mixing the acid with the hydrated fluid paste before introducing the hydrated fluid paste into the reactor, wherein the precipitated material comprises struvite.

49. Method according to claim 48, characterized in that the fine particles comprise magnesium oxide.

50. Method according to claim 48 or 49, characterized in that the fine particles have sizes of SGN 100 or less.

51. Method according to claim 48 or 49, characterized in that the fine particles have diameters of 0.1 mm or less.

52. Method, according to any of the claims 48 Petition 870260052251, dated 05 / 29 / 2026, pp. 24 / 26 8 / 9 to 51, characterized in that it comprises maintaining a pH at a pH setpoint equal to or greater than 7.5 in at least a part of the reactor.

53. Method according to claim 52, characterized in that the pH set point is at least pH 8.

54. A method according to any one of claims 48 to 53, characterized in that it comprises recycling the solution in the reactor through a recycle path extending from an elevation in the reactor above the fluidized bed to an elevation in the reactor that is below the fluidized bed.

55. Method according to claim 54, characterized in that it comprises capturing or redissolving struvite particles in the recycle path.

56. Method according to claim 55, characterized in that it comprises preparing the hydrated fluid paste by mixing the fine particles with water and allowing the particles to remain in contact with the water for a period of at least a few minutes before introducing the hydrated fluid paste into the reactor.

57. Method, according to claim 55 or 56, characterized in that it comprises injecting the hydrated fluid paste into the reactor at a location below the fluidized bed.

58. A method according to any one of claims 48 to 57, characterized in that it comprises controlling a pH at a location in the reactor by adding hydrated fluid paste.

59. Method, according to any one of claims 48 to 58, characterized in that the hydrated fluid paste is buffered to an alkaline pH.

60. Method, according to claim 59, characterized in that the hydrated fluid paste is buffered to a pH of at least 7.

5.

61. Method according to claim 60, characterized in that the hydrated fluid paste is buffered to a pH of 8.

62. A method, according to any one of claims 48 to 61, characterized in that the solution comprises municipal or agricultural wastewater.

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