Method and apparatus for the recovery of nutrients of a certain size from wastewater by hydrocyclone

Abstract

Methods and apparatus are provided for recovering dissolved species from wastewater streams in the form of a sized precipitate by elutriation. These methods can be controlled, for example, so that the sized solids recovered are in the form of relatively insoluble plant nutrients, such as struvite. The extracted nutrients can include, for example, solid species of phosphorus, and / or nitrogen, and / or potassium.

Description

Technical Field

[0001] Technological innovations in the field of aqueous chemistry are disclosed, including methods and apparatuses for removing dissolved species from wastewater as precipitates of a defined size.

Background Art

[0002] Dissolved phosphorus, nitrogen, and potassium species are often discharged into wastewater, particularly wastewater of agricultural origin. This can have a detrimental effect of promoting the growth of algae and other organisms in water, which in turn can lead to harmful eutrophication of natural water bodies. The reverse components of this nutrient cycle involve the metered use of phosphorus, nitrogen, and potassium species as fertilizers in agriculture. Thus, the need for effective recycling of nutrients from wastewater to fertilizers is not being met.

[0003] There are many nutrient recovery technologies based on crystallization processes. Some of these technologies extract phosphorus and other nutrients in the form of fine crystals or powders as either struvite, calcium phosphate, or some other sparingly soluble compound. This causes problems in the separation of the recovered product from wastewater and other suspended solids. Fine materials can be difficult, costly to dewater, dry, and process. Many of the substances recovered as powders need further treatment before they can be used as fertilizers. Thus, alternative processes for recovering valuable materials from wastewater in a physical form convenient for later use are still sought.

[0004] Some sparingly soluble phosphate compounds, such as struvite, are effective slow-release fertilizers because of their relatively low solubility. This is in contrast to typical water-soluble fertilizers, such as monoammonium phosphate and diammonium phosphate, which can only be partially absorbed by crops, while a significant portion of such fertilizers may be washed from the soil into the environment. Struvite dissolves very slowly, thereby improving the loss of nutrients from the soil and providing effective nutrition to plants. Such fertilizers have a relatively low solubility and also help prevent the "burning" of plant roots by the high salinity that may be caused by more water-soluble fertilizers. Since many agricultural, urban, and industrial wastewaters contain large amounts of nutrients, especially phosphorus and nitrogen, there is a possibility that struvite can be recovered from these waste streams.

Summary of the Invention

Problems to be Solved by the Invention

[0005] For example, there are many processes for recovering phosphorus from waste streams in the form of struvite and other phosphate compounds. Many existing struvite recovery processes extract it in the form of very small powdery particles that are very difficult to dry and separate from impurities, which is a significant drawback for the final fertilizer product. Therefore, there is a need for a process that can produce high-quality struvite fertilizer products in the form of small granules or pellets that can be easily separated from wastewater and other impurities and can also be easily dried, transported, and stored.

Means for Solving the Problems

[0006] A method and apparatus for recovering dissolved species from a wastewater stream in the form of a precipitate of a certain size are disclosed. For example, a method for removing dissolved species from an aqueous influent stream is provided, and the dissolved species include dissolved nitrogen and / or dissolved phosphorus and / or dissolved potassium species. These methods can include separating the aqueous influent into a flow directed into a reactor, and a precipitant is also injected into the reactor. The precipitant can be provided, for example, in a separate material stream, for example as a solid or a liquid, or the precipitant can be present in one or more of the aqueous influent streams.

[0007] The aqueous influent stream can be separated, for example, within a manifold in fluid communication with a reaction tube, for example into a plurality of reactor influent streams. The plurality of reactor influent streams can create upward turbulent flow within the reaction tube as they are directed upward into the base of a reaction tube segment within the reactor vessel.

[0008] For example, under conditions maintained within the reaction tube, a precipitant can be injected into the base of the reaction tube to provide a supersaturated concentration of the reaction product of the precipitant reacting with the dissolved species. The precipitant (either a solid or a liquid, for example) can be, for example, any one or more of an alkali (caustic soda, caustic potash, lime, ammonia), a magnesium salt (MgCl2, MgSO4, MgO, Mg(OH)2), magnesite, brucite, combustion bottom ash, or fly ash. These reactor conditions can be controlled, for example, to provide a desired saturation index for the reaction product, for example at least 2 (optionally 2.0 - 3.0, optionally 2.5), and the reaction product forms solid precipitant species that are entrained in the upward reaction tube fluid flow.

[0009] The upward reaction tube fluid flow can then be directed towards an adjacent clarifier segment of the reactor. The upward reaction tube fluid flow rate can be maintained, for example, between 20 - 80 cm / min, optionally at about 50 cm / min. The clarifier segment of the reactor can be dimensioned, for example, to reduce the upward flow rate of the upward reaction tube fluid flow. The clarifier can be, for example, a frustoconical clarifier, for example the frustoconical clarifier includes inclined walls having an inclination angle of about 45 - 85°, optionally about 60 - 70°.

[0010] The upward purification fluid flow rate can be maintained in the purifier such that the captured solid precipitant species descend within the purifier segment of the reactor and return to the reaction tube, while the purified effluent fluid flow can continue to flow upward from the purifier segment of the reactor. The upward purification fluid flow rate can be maintained, for example, between about 1 and 5 cm / min, optionally about 2 cm / min. For example, conditions can be maintained within the reactor to substantially remove dissolved species from the aqueous influent flow to provide a purified effluent fluid, such that the removal of dissolved species from input to output is, for example, at least 60%, 70%, 80%, or 89%.

[0011] Conditions can be maintained within the reactor to allow for the progressive aggregation of the precipitant species, for example, to form aggregated particles, such that the size and density of the aggregated particles are sufficient to cause the aggregated particles to settle towards the base of the reaction tube. It has been demonstrated that surprisingly, the conditions can be adjusted such that this settling occurs in the presence of an upward turbulent reaction tube fluid flow. The hydraulic residence time within the reaction tube can be maintained, for example, between 1 and 10 minutes, optionally between 2 and 5 minutes.

[0012] An upward flow path fluid flow can be injected into the reactor through a flow path that is in fluid communication with the base of the reaction tube. The flow path can be sized, for example, such that aggregated particles of a selected size and density descend through the flow path while non-selected precipitant species can be returned upward to the reaction tube, allowing for the metering of the upward flow path fluid flow. The upward flow path fluid flow rate can be maintained, for example, in the range of about 10% of the upward reaction tube fluid flow rate, optionally between 5 and 50%.

[0013] The flow path can be sized, for example, to have an average flow path cross-sectional area C Xarea while the pellet hopper can similarly have an average pellet hopper cross-sectional area PH Xarea and the reaction tube can have an average tube cross-sectional area RC Xarea and these dimensions are such that C Xarea < PH Xarea and C Xarea < RC XareaIt can be adjusted to be such.

[0014] In this way, solid particle products of a certain size are separated by elutriation, and this product thus descends through the flow path. This product of a certain size can be collected into an adjacent pellet hopper that is sized, for example, to accommodate the sedimentation volume of the solid particle product of a certain size. In the selected embodiment, this method may involve periodically restricting the upward flow path fluid flow in the flow path and discharging the contents of the pellet hopper downward to collect the desired solid particle product. The solid particle product of a certain size can be collected, for example, on a sieve, washed on the sieve, and then dried. The solid particle product of a certain size can have, for example, an average product size, and the average product size can be, for example, about 1 to 2 mm. The granular product can have, for example, a desired product purity of at least about 60%, 70%, 80%, 90%, or 96%.

[0015] The desired solid particle product can be, for example, one or more of struvite, K-struvite, calcium ammonium phosphate CaNH4PO4, and / or hydroxyapatite Ca5(PO4)3(OH), brushite CaHPO4·2H2O, newberyite MgHPO4·3H2O, and / or magnesium phosphate Mg3(PO4)2. In the selected alternative embodiment, the purity of the desired solid particle product can be, for example, at least 70%, 75%, 80%, 90%, or 95%.

[0016] In one aspect, the method may involve recirculating a portion of the purified fluid flow from the purifier to the hopper and using this recirculated fluid flow to mediate the upward flow path fluid flow through the flow path. For example, an upward hopper fluid flow in the hopper that mediates the upward flow path fluid flow in the flow path can be provided, and the hopper can be sized such that the upward hopper fluid flow is less than the upward flow path fluid flow.

[0017] One aspect of the selected embodiments of the present method is the ability to handle influent streams having relatively high levels of suspended solids. For example, the influent stream can contain up to 1%, 2%, 3%, 4%, or 5% suspended solids by weight. In some embodiments, 50 - 95% of the suspended solids in the influent stream pass through the reactor and reach the purified effluent fluid stream.

[0018] The method can be carried out in a reactor equipped with a control system that constitutes a reactor system operable to remove dissolved species (dissolved species including dissolved nitrogen and / or dissolved phosphorus and / or dissolved potassium species) from an aqueous influent stream. One or more screens can be placed in the aqueous influent stream before it enters the manifold, and these screens can have a mesh smaller than, for example, the diameter of the injection nozzles placed inside the reactor.

[0019] This reactor system can include a manifold that separates the aqueous influent stream into a plurality of reactor influent streams and directs the plurality of reactor influent streams upward into the base of the reaction tube segments within the reactor vessel, for example, to create upward turbulent flow within the reaction tubes. A water intake pump can be placed, for example, upstream of the manifold to provide a pressurized aqueous influent stream. A precipitant inlet port can be provided in fluid communication with the base of the reaction tube, which is adapted to inject a precipitant into the base of the reaction tube under the control of a reactor system control adapted to maintain conditions within the reaction tube, for example, to provide a supersaturated concentration of the reaction product of the precipitant that reacts with the dissolved species. The precipitant can be introduced in proximity to the injection nozzles that direct the input fluid into the reactor. In this way, for the reaction product, as described above, at least two saturation indices can be maintained, for example. The reaction product thus forms solid precipitant species that are incorporated into the upward reaction tube fluid flow.

[0020] The purifier segment of the reactor, which is adjacent to the reaction segment upward, can be sized to reduce the upward flow rate of the upward reaction tube fluid flow directed from the reaction segment into the purifier, under the control of a purifier system control operable to maintain the upward purifying fluid flow rate in the purifier such that, for example, the entrained solid precipitant species descends in the purifier segment of the reactor and returns to the reaction tube while the purified effluent fluid flow continues to flow upward from the purifier segment of the reactor. A jacket configured to collect the purified effluent fluid flow can be provided on the purifier.

[0021] The reactor system control can be fabricated to be operable to maintain conditions in the reactor that allow for the progressive aggregation of the precipitant species to form aggregated granules, the size and density of which are sufficient to cause the aggregated granules to settle towards the base of the reaction tube in the presence of the upward turbulent reaction tube fluid flow.

[0022] A flow path in fluid communication with the base of the reaction tube can be connected to a flow path fluid source to provide an upward flow path fluid flow leading into the base of the reaction tube through the flow path. The flow path is sized to allow for the metering of the upward flow path fluid flow such that aggregated granules of a selected size and density descend through the flow path while non-selected precipitant species are returned upward to the reaction tube, thereby allowing for the separation by decantation of a constant-size solid granule product that descends through the flow path into an adjacent pellet hopper sized to accommodate the sedimentation volume of the constant-size solid granule product.

[0023] An injection nozzle can be provided to direct a plurality of reactor influent flows upward into the base of the reaction tube. The injection nozzle can be raised, for example, above the bottom of the reaction tube. For example, there may be at least 2, 3, 4, 5, or 6 injection nozzles. The injection nozzles can be distributed substantially uniformly over the entire cross-sectional area at the base of the reaction tube. In a selected embodiment, a superficial upward flow velocity between 5 and 15 m / s, or about 10 m / s, can be maintained inside each nozzle.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

DETAILED DESCRIPTION OF THE INVENTION

[0025] Methods and apparatuses are disclosed for recovering dissolved species from wastewater streams in the form of a precipitate of a certain size by decantation. In some embodiments, the solids recovered can be, for example, plant nutrients. The nutrients extracted can include, for example, solid species of phosphorus (P), and / or nitrogen (N), and / or potassium (K). These methods can be carried out on a wide range of aqueous feeds from wastewater streams of various origins, such as, for example, agricultural (manure), municipal (sewage), or other industrial origins.

[0026] In selected embodiments, the nutrients are extracted through a crystallization process of phosphates containing insoluble compounds. Such compounds can include, but are not limited to, for example, struvite (magnesium ammonium phosphate, MAP), K-struvite (magnesium potassium phosphate, MKP), and other insoluble phosphate compounds. In one aspect of the process, the nutrients migrate from an aqueous liquid (e.g., wastewater) to a solid (e.g., crystal) as a result of creating supersaturation in the wastewater of the reaction product of the precipitant and the dissolved species, i.e., the compound to be extracted from the aqueous influent stream. The crystallization process is caused by the supersaturation conditions. Supersaturation can be created in many ways, including by adding a precipitant to the wastewater or by mixing together different wastewater streams where the precipitant is provided in one of these streams. The solid material obtained during the precipitation process can then be separated from the liquid.

[0027] The method disclosed herein provides for the recovery of nutrients from wastewater in a form in which the compounds to be extracted can be provided as relatively large spherical granules (pellets). These granules generally represent aggregates of smaller crystals produced in a crystallization device (reactor). As disclosed herein, the chemical and hydrodynamic conditions inside the reactor can be controlled in such a way that the rate of crystal aggregation is relatively high. As a result, the granules grow quickly, enabling more efficient extraction of nutrients from the wastewater. At the same time, it has been demonstrated that the method can be controlled so that the granules can be grown to a size sufficient to be separated from the wastewater and other suspended solids. In selected embodiments, the method thereby facilitates the recovery of high-purity products from liquid streams, which can be achieved, for example, with influent streams having relatively large amounts of suspended solids, such as up to 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by weight, or in an alternative embodiment, up to 5% by weight of suspended solids. In selected embodiments, the relatively high efficiency of the treatment process enables a smaller plant footprint and promotes economical energy consumption.

[0028] In one illustrated embodiment, there are two main components of the apparatus used to implement the present method, namely a crystallization reactor and a wastewater injection system. The crystallization reactor as illustrated is an upright fluidized bed reactor as shown in FIG. 1. The reactor consists of three main parts, namely a reaction tube (1), a purifier (2), and a pellet hopper (3). The purifier is continuous with and directly adjacent to the reaction tube and is disposed above it. The cross-sectional area of the purifier gradually increases from the bottom to the top in the illustrated embodiment, and thus the purifier is in the shape of a frustum of a cone. The cross-sectional contours of the reaction tube and the purifier can be, for example, circular, rectangular, or polygonal. The top of the purifier may be open, and the bottom of the reaction tube is closed except at the locations where various input ports are disposed. A pellet hopper (3) providing a container for the bulk pellets of the recovered product can be disposed below the reaction tube, which can advantageously be tapered downward so as to facilitate discharging the recovered product at the bottom of the hopper. The top of the pellet hopper is connected to the bottom of the reaction tube through a vertical pipe or any other flow path, which can have a cross-sectional area substantially smaller than that of the pellet hopper and the reaction tube as illustrated.

[0029] A specific wastewater injection process is facilitated by the presently disclosed apparatus. As illustrated, the injection system consists of one or more sets of the following: a pump (4), a manifold (5), and an injection nozzle (6). Each set is available for a separate wastewater stream to be processed within the apparatus. This can be particularly advantageous when individual wastewater streams should not be mixed with each other prior to the treatment process. In each set, the pump conveys the wastewater to be processed into the manifold, thereby creating an elevated pressure inside it. The manifold (5) can be adapted, for example, to distribute the wastewater substantially evenly among the nozzles (6) connected to it. The nozzle outlets are disposed at the bottom or base of the reaction tube (1). These can be directed substantially upward and slightly raised above the surface of the bottom of the reaction tube. The total number of nozzles from all injection sets can be, for example, at least three, and the nozzles can be evenly distributed over the entire cross-sectional area at the bottom of the reaction tube.

[0030] In the illustrated apparatus, the waste water is injected into the reactor at the bottom of the reaction tube (1) through the nozzle (6) in such a way that the surface upflow velocity inside each nozzle is between 5 and 15 m / s, preferably 10 m / s. Thereby, a substantial number of upward jets are generated, and the jets cause a great deal of turbulence at the bottom of the reaction tube. The size (or diameter) of the nozzle depends on these numbers and the flow rate of the waste water and can be determined by anyone skilled in the art. The nozzle (6) usually has a circular cross-sectional area, but it can also be rectangular, polygonal, etc. Before entering the manifold, the waste water stream can pass through any screen to separate any particulate material larger than the size (diameter) of the nozzle to prevent possible clogging of the nozzles.

[0031] The reactor as illustrated operates in a continuous upflow mode. During operation, the crystals of the compound extracted from the waste water can fill all parts of the reactor, and different parts of the reactor contain crystals of different sizes. As described above, the waste water to be treated is injected into the reaction tube (1) through the injection nozzle (6) from the bottom. At the same time, a precipitant can be introduced in the vicinity of the injection nozzle (6) at the bottom of the reaction tube (1), where it is immediately mixed with the waste water, thus creating supersaturated chemical conditions.

[0032] A precipitant is usually a substance that reduces the solubility of the substance to be extracted in wastewater. For example, if the substance to be extracted is struvite, the precipitant can be an alkali, a magnesium salt, or any combination thereof. The precipitant can be injected through one or more inlet ports installed vertically, horizontally, or diagonally. The precipitant can be, for example, either a liquid or a slurry, which can be continuously fed in a controlled manner using a metering pump, a pH controller, etc. to maintain a specific level of supersaturation in the reaction tube with respect to the compound to be extracted from the wastewater. Alternatively, supersaturation can be created by mixing various wastewater streams together without adding a precipitant, but instead by using separate injection systems set for each of the wastewater streams to achieve the desired supersaturation.

[0033] In a selected embodiment, the pH value can be controlled within the reactor, for example, maintained to achieve a desired saturation index. Similarly, the temperature within the reactor can be controlled with the expectation of setting the temperature within the reactor to achieve the desired saturation index. In a selected embodiment, if struvite is the desired product, the pH of the reactor can be controlled, for example, between 7 and 10, and the expected temperature range will be, for example, between 10 and 40 °C, or up to 60 °C.

[0034] Supersaturation causes the formation of crystals inside the reactor and promotes their growth and aggregation. The crystals remain suspended in the liquid upflow in all sections of the reactor. When crystals are formed, nutrients are extracted from the liquid phase. Conditions can be maintained such that relatively small crystals then settle downward in the clarifier (2) and return to the reaction tube, while the purified wastewater flows out from the top of the clarifier, and the suspended solids originally present in the influent stream can also be adjusted to flow out from the top of the clarifier. The reactor effluent thus contains a significantly reduced amount of nutrients and represents the treated wastewater stream. At the same time, crystals aggregate inside the reaction tube (1), which is surprisingly promoted by the turbulent flow generated by the injection, thereby forming granules, or pellets (which can be, for example, approximately spherical). As shown in the examples of this specification, it has been discovered that conditions can be adjusted such that pellets grown to the desired or selected size settle to the bottom of the reaction tube (1) and then further into the pellet hopper (3).

[0035] The pellet hopper (3) facilitates the continuous separation of pellets from aggregates and crystals ( "non - selected" precipitates) that have not yet reached the desired size and are therefore not selected to be extracted from the reactor. At the same time, by continuously removing the pellets from the reaction tube (1), over - densification of crystals at the bottom of the tube, which could have an adverse effect on the process, is prevented.

[0036] Pellet separation is achieved through the principle of hydraulic classification. As described above, the bottom of the reaction tube (1) is connected to the top of the pellet hopper (3) through a pipe or flow path (7), which can be a tube with a cross-sectional area smaller than both the reaction tube and the pellet hopper. The cross-sectional area of the flow path (7) can be, for example, circular, rectangular, or polygonal. An upward flow of liquid, i.e., an upward flow path fluid flow, opposite to the sedimentation direction of the pellets, is generated within the flow path. The upward flow is maintained such that larger pellets can sediment or be suspended therein, while smaller pellets and other crystals are carried upward by the upward flow and returned into the reaction tube. Larger particles finally sediment into the pellet hopper (3), where the hopper has a cross-sectional area larger than that of the flow path (7), and thus the upward flow velocity is not high enough to keep the pellets suspended, so they do not remain suspended.

[0037] The pellets are periodically discharged from the pellet hopper (3) by using a shut-off valve (8) and simultaneously opening a discharge valve (9) at the bottom of the pellet hopper (3) to isolate the pellet hopper (3) from the reaction tube. The pellets can be discharged over a sieve, where the liquid and any suspended solids therein are easily discharged through the remaining pellets on the sieve. After removing the pellets from the hopper, the discharge valve (9) is closed, the hopper is filled with liquid, and then the shut-off valve (8) is opened again to enable collection of the next batch of pellets. The pellet hopper (3) usually has a large capacity so as to accommodate a large amount of bulk pellets to avoid the need for frequent discharging. The pellets on the sieve can be washed with water to remove any impurities from their surfaces and then dried in air, in a low-temperature oven, or by any other means known in the art. The fertilizer pellets represent the final product that is ready for market without any further treatment required. In the selected embodiment, the purity of the final fertilizer product can exceed, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%.

[0038] The upward liquid flow in the flow path (7) connecting the pellet hopper (3) to the reaction tube (1) can be achieved, for example, by pumping a part of the reactor effluent from the purifier (2) into the pellet hopper using an additional pump (10). Using the reactor effluent has the advantage of keeping the pellets in the mother liquor, thereby preventing their dissolution, and at the same time maintaining a constant volume of wastewater that would otherwise increase if additional external liquid were used for that purpose. By controlling the upward flow velocity in the flow path (7), it becomes possible to selectively separate specific pellet sizes and maintain the desired crystal size distribution of the harvested pellets. The cross-sectional area and flow rate through the flow path (7) can be selected, for example, so as not to significantly affect the desired hydrodynamic and chemical conditions inside the reaction tube (1). The flow rate can be maintained, for example, at about 10% of the total flow rate in the reaction tube.

[0039] In one aspect of the method, the method is carried out while maintaining a specific, relatively constant level of initial supersaturation with respect to the extractable compound in the reaction tube (1). This operating parameter is advantageous for controlling the process efficiency. The supersaturation can be maintained, for example, by controlling the flow rate of the precipitating agent. Alternatively, in embodiments where more than one wastewater stream is treated in the apparatus, the supersaturation can be maintained, for example, by controlling the mixing ratio of the wastewater streams.

[0040] In this specification, the supersaturation of a liquid with respect to a substance is expressed as the saturation index SI, which is the common logarithm of the ratio between the activity product of the ionic species constituting the substance and the thermodynamic solubility product of the substance. For example, in the case of struvite (magnesium ammonium phosphate, MgNH4PO4·6H2O), the SI would be expressed as follows.

[0041]

Equation

[0042] Here, {Mg 2+}, {NH4 +}, {PO4 3-} are the activities of magnesium, ammonium, and orthophosphate ions, respectively, K sp(struvite) is the thermodynamic solubility product of struvite.

[0043] The saturation index can be determined by using this equation as part of the control system of the present method. The activities of the relevant ionic species can be either directly measured by using standard analytical methods or mathematically derived from the measured concentrations of the relevant ionic species. The activity coefficients of the species, as well as the solubility products of the extraction compounds, will be available from widely available literature sources.

[0044] The initial saturation index SI at the bottom of the reaction tube (1) for the extraction compound can be maintained, for example, in the range of 2.0 to 3.0, optionally 2.5. This saturation index associated with the very high turbulence within the reaction tube has surprisingly been found to cause rapid crystal nucleation. At the same time, this also provides a surprisingly high crystal aggregation rate, such that the newly formed small crystals can rapidly aggregate into larger granules (pellets). By establishing and maintaining conditions such that the crystal aggregation rate is greater than the crystal formation rate, the number of small crystals can be reduced and the number and size of the larger aggregates can be increased. This enables the control of the crystal size distribution and population density within the reactor and, ultimately, the rapid formation of large granules of the extraction compound. In addition, it has been found that the specific hydrodynamic and chemical conditions within the reaction tube (1) can be selected to promote the affinity of the crystals for each other rather than for other suspended solids present in the wastewater stream. As a result, it has been shown that the extraction compound of high purity can be obtained with relatively little contamination by solid impurities in the wastewater. In the selected embodiment, it has been found that the present method is capable of treating a liquid stream as high as 2% of total suspended solids without substantially impairing the quality of the recovered fertilizer product.

[0045] The implementation of the process with the above saturation index has been found to provide a relatively low residual concentration of nutrients in the reactor effluent, perhaps by substantially completing the chemical reaction before the wastewater stream exits the reactor. In the selected embodiment, when the reaction occurs within the reaction tube (1), the saturation index rapidly decreases to a level between 0.1 and 1.0. This may thus prevent the formation of new crystals and instead promote the growth of existing ones. This condition can be adjusted to occur in the upper section of the reaction tube. In particular, it has been found that conditions can be provided such that large pellets generally settle to the bottom of the reaction tube while some of the much smaller crystals remain suspended throughout its volume. As soon as the crystals grow large enough and no longer remain suspended by the upflow, they settle into the bottom of the reaction tube and aggregate into pellets.

[0046] In the selected embodiment, in order to promote the sedimentation of small and medium-sized crystals, the surface upflow velocity within the reaction tube (1) can be maintained, for example, between 20 and 80 cm / min, or at about 50 cm / min. The hydraulic residence time within the reaction tube can be maintained, for example, between 1 and 10 minutes, or between 2 and 5 minutes, where these conditions provide sufficient time for the chemical reaction to be substantially completed. The physical dimensions of the reaction tube (1) can be designed based on these requirements.

[0047] Crystals that are too small to remain in the reaction tube (1), as well as suspended solids originally present in the wastewater, are carried by the upward flow into the purifier (2). In the illustrated embodiment, the purifier has a gradually increasing cross-sectional area that gradually reduces the upward flow velocity of the fluid therein, i.e., the upward purification fluid flow. As a result, in the selected embodiment, small crystals, for example, about 50 microns in size, can be retained inside the reactor without any substantial loss of the extracted compound associated with the effluent. The surface upward flow velocity at the top of the purifier can be maintained, for example, between 1 and 5 cm / min, optionally about 2 cm / min, to retain the crystals inside the purifier (2). The inclination angle of the frustum of the purifier in the selected embodiment can be, for example, between 45 and 85°, optionally between 60 and 70°. The physical dimensions of the purifier (2) can be designed, for example, based on these requirements. In an exemplary embodiment, the frustum shape of the purifier creates a small turbulence at the attachment point between the purifier and the reaction tube (1) together with the bulk crystals that settle from the purifier against the flow. This does not create something new but can further help promote the growth of existing crystals. By implementing the aforementioned conditions, the purifier (2) can be made to contain a suspension bed of small crystals. This bed is generally dynamic as it continuously exchanges crystals with the reaction tube (1), and crystals that grow large enough will settle, but some of the newly formed fine crystals are carried upward with the flow. Consequently, the bed functions as a "filter" that captures the fine crystals and prevents them from escaping from the reactor. At the same time, the suspended solids originally present in the wastewater stream usually have a much smaller size and lower density than the crystals. As a result, they freely pass through the bed and are carried away from the purifier by the effluent stream, thereby preventing their accumulation in the purifier (2). The constant volume of the bed can be controlled by the initial saturation index and the hydrodynamic conditions at the bottom of the reaction tube. By accurately controlling the operating parameters, it is prevented that the bed overflows and loses fine crystals with the effluent. The top of the purifier may have an overflow weir (11) to uniformly disperse the outflow over a large surface area to minimize the resuspension of the settled crystals, as shown in FIG. 1.The effluent from the reactor will then overflow into an external purifier (12) designed as a jacket of the reactor purifier. The jacket (12) can further minimize the loss of fine crystals associated with the effluent. [Example]

[0048] The exemplified method was implemented in an apparatus as shown in Figure 2. The wastewater stream to be treated was anaerobic digested chicken manure that had undergone a solid separation process. The wastewater had the following characteristics on average, namely total suspended solids - 2.0%, pH - 8.4, conductivity - 18 mS / cm, alkalinity - 30,000 mg / L as CaCO3, soluble orthophosphate P - PO4 - 205 mg / L, soluble ammonia nitrogen N - NH3 - 5050 mg / L, soluble magnesium Mg - 5 mg / L, soluble calcium Ca - 50 mg / L. The wastewater was continuously pumped from the storage tank into the manifold at an average flow rate of 200 m 3 / day by a pump. Before entering the manifold, the wastewater passes through a screen with a 5 mm opening. The differential pressure inside the manifold is maintained at 0.1 MPa. The manifold distributes the wastewater among four identical circular nozzles. The superficial upward flow velocity inside each nozzle was maintained at 9 m / s.

[0049] The wastewater enters a cylindrical reaction tube where it is immediately mixed with a precipitant introduced at the bottom of the reaction tube. The precipitant is a concentrated solution of a water-soluble magnesium salt. The salt solution is continuously fed by a metering pump in a controlled manner such that the molar ratio between soluble magnesium and soluble orthophosphate in the reaction tube is about 1. When the precipitant is mixed with the wastewater, the reaction between magnesium, ammonia, and orthophosphate occurs essentially immediately, and struvite crystals are formed inside the reaction tube. The initial saturation index of struvite in the reaction tube is about 2.3. The superficial upward flow velocity inside the reaction tube was 47 cm / min. The pH value at the top of the reaction tube was monitored by a pH meter, which showed a value of about 8.3. The superficial upward flow velocity at the top of the purifier was 5 cm / min. The purifier had an overflow weir and a jacket. The treated wastewater (effluent) overflows into the jacket and exits the reactor through a port installed in the jacket.

[0050] The effluent had an average concentration of the following, namely soluble orthophosphate P-PO4 - 22 mg / L, soluble ammonia nitrogen N-NH3 - 4800 mg / L, soluble magnesium Mg - 14 mg / L, and soluble calcium Ca - 48 mg / L. The removal efficiency of soluble orthophosphate was thus 89%. A part of the effluent from the jacket was pumped into the pellet hopper at a flow rate of 23 m 3 / day. The pellets of struvite formed in the reaction tube continuously settled into the pellet hopper through a vertical pipe. The surface upflow velocity in the pipe was maintained at 415 cm / min. This upflow velocity made it possible to separate struvite pellets larger than 1 mm in size from the rest of the crystals in the reaction tube. The pellets were discharged from the pellet hopper once every two days by closing the shut-off valve between the reaction tube and the pellet hopper and opening the discharge valve at the bottom of the pellet hopper. The pellets were discharged into a container equipped with a sieve at the bottom together with the liquid. The opening size of the sieve was 0.5 mm. The liquid was discharged through the sieve while the struvite pellets remained on it. The pellets were then rinsed with clean water and dried outdoors. The weight of the dried struvite crystals extracted per harvest was approximately 500 kg. The struvite pellet size ranged between 1 - 2 mm. The purity of the struvite product was approximately 96%.

[0051] References Ghosh, S., Lobanov, S., Lo, V.K. (2019) Impact of supersaturation ratio on phosphorus recovery from synthetic anaerobic digester supernatant through a struvite crystallization fluidized bed reactor. Environmental Technology, 40(15), 2000 - 2010.

[0052] Ghosh, S., Lobanov, S., Lo, V.K. (2019) An overview of technologies to recover phosphorus as struvite from wastewater: advantages and shortcomings. Environmental Science and Pollution Research, 26(19), 19063-19077.

[0053] Peng, L., Dai, H., Wu, Y., Peng, Y., Lu, X. (2018) A comprehensive review of phosphorus recovery from wastewater by crystallization processes. Chemosphere, 197, 768-781.

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[0084] The citation of references in this specification does not admit that such references are prior art to the present invention. All priority documents, including but not limited to patents and patent applications cited in this specification, and all publications, as well as all documents cited in such documents and publications, are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated herein by reference and were fully described herein. Although various embodiments of the present invention are disclosed herein, many adaptations and modifications can be made within the scope of the present invention in accordance with the common general knowledge of those skilled in the art. Such modifications include replacing any aspect of the present invention with known equivalents to achieve substantially the same method and the same result. Terms such as "exemplary" or "illustrated" are used herein to mean "serving as an example, instance, or illustration". Any embodiment described herein as "exemplary" or "illustrated" should not necessarily be construed as preferred or advantageous over other embodiments, and all such embodiments are independent embodiments. Unless otherwise specified, numerical ranges include the numbers defining the range, and the numerical values are necessarily approximations of the given decimal numbers. The word "comprising" is used herein as an open-ended term substantially equivalent to the phrase "including but not limited to", and the word "comprises" has the corresponding meaning. As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to "a thing" includes more than one such thing. The present invention includes substantially all embodiments and variations as described above and with reference to the examples and drawings.

Claims

1. A method for removing dissolved species including dissolved nitrogen and / or dissolved phosphorus and / or dissolved potassium species from an aqueous influent stream, comprising: separating the aqueous influent stream into a plurality of reactor influent streams and directing the plurality of reactor influent streams upwardly into the base of a reaction tube segment within a reactor vessel, thereby creating an upward turbulent flow within the reaction tube segment; injecting a precipitant into the base of the reaction tube segment under conditions maintained within the reaction tube segment, thereby providing a supersaturated concentration of a reaction product of the precipitant that reacts with the dissolved species and providing at least two saturation indices for the reaction product, wherein the reaction product forms solid precipitant species that are entrained in an upward reaction tube fluid flow; directing the upward reaction tube fluid flow toward an adjacent clarifier segment of the reactor vessel, wherein the clarifier segment of the reactor vessel is sized to reduce the upward flow rate of the upward reaction tube fluid flow by increasing the cross-sectional area of the clarifier segment relative to the cross-sectional area of the upward reaction tube; maintaining an upward clarifying fluid flow rate within the clarifier segment such that entrained solid precipitant species descend within the clarifier segment of the reactor vessel and return to the reaction tube segment while a clarified effluent fluid flow continues to flow upwardly from the clarifier segment of the reactor vessel; maintaining conditions within the reactor vessel that allow progressive agglomeration of the precipitant species to form agglomerate particles having a size and density sufficient to cause the agglomerate particles to settle toward the base of the reaction tube segment in the presence of the upward turbulent reaction tube fluid flow, i.e., maintaining the fluid surface upflow velocity within the reaction tube; Injecting an upward flow path fluid flow through a flow path in fluid communication with the base of the reaction tube segment, wherein the flow path has a cross-sectional area dimension such that agglomerated particles of a selected size and density descend through the flow path while non-selected precipitant species can be returned upward to the reaction tube segment, and thereby the upward flow path fluid flow can be metered, and the solid particulate product of a certain size descends through the flow path into an adjacent pellet hopper sized to accommodate the sedimentation volume of the solid particulate product of a certain size, and separating the solid particulate product of a certain size by elutriation, including the step of The saturation index is the common logarithm of the ratio between the activity product of the ionic species constituting the reaction product and the thermodynamic solubility product of the reaction product. The method.

2. Further comprising periodically restricting the upward flow path fluid flow in the flow path and discharging the contents of the hopper downward to collect the solid particulate product. The method according to claim 1.

3. Further comprising recirculating a portion of the purified fluid flow from the purifier segment to the hopper to mediate the upward flow path fluid flow through the flow path. The method according to claim 2.

4. Further comprising providing an upward hopper fluid flow in the hopper to mediate the upward flow path fluid flow in the flow path, and sizing the hopper such that the upward hopper fluid flow is less than the upward flow path fluid flow. The method according to claim 3.

5. Further comprising separating an aqueous inflow into a plurality of reactor inflows within a manifold in fluid communication with the reaction tube segment. The method according to claim 4.

6. The sedimentation agent contains an alkali, a magnesium salt, MgCl ２ , MgSO ４ , MgO, Mg(OH) ２ , magnesite, brucite, combustion bottom ash or fly ash The method according to claim 5.

7. The solid particle product includes struvite (magnesium ammonium phosphate hexahydrate, MgNH₄PO₄·6H₂O), K-struvite (magnesium potassium phosphate hexahydrate, MgKPO₄·6H₂O), calcium ammonium phosphate CaNH ４ PO ４ , and / or hydroxyapatite Ca ５ (PO ４ ) ３ (OH), brushite CaHPO ４ ·2H ２ O, newberyite MgHPO ４ ·3H ２ O, and / or magnesium phosphate Mg ３ (PO ４ ) ２ , including one or more of the following: The method according to claim 6.

8. The inflow contains up to 5% suspended solids by weight, and 50-95% of the suspended solids in the inflow pass through the reactor vessel and reach the purified discharge fluid flow. The method according to claim 7.

9. The flow path has an average flow path cross-sectional area C Ｘａｒｅａ The pellet hopper has an average pellet hopper cross-sectional area PH Ｘａｒｅａ The reaction tube segment has an average tube cross-sectional area RC Ｘａｒｅａ C Ｘａｒｅａ < PH Ｘａｒｅａ and C Ｘａｒｅａ < RC Ｘａｒｅａ is satisfied The method according to claim 8.

10. Further comprising collecting the solid particulate product of a certain size on a sieve, and further washing and drying the solid particulate product of a certain size on the sieve. The method according to claim 9.

11. The purity of the solid particulate product is at least 90%. The method according to claim 10.

12. The upward flow path fluid flow rate is maintained in the range of 5-50% of the upward reaction tube fluid flow rate. The method according to claim 11.

13. The initial saturation index SI at the base of the reaction tube segment for the reaction product is maintained in the range of 2.0 to 3.0, The method according to claim 12.

14. The upward reaction tube fluid flow rate is maintained between 20 and 80 cm / min, The method according to claim 13.

15. The hydraulic residence time in the reaction tube segment is maintained between 1 and 10 minutes, The method according to claim 14.

16. The upward purification fluid flow rate is maintained between 1 and 5 cm / min, The method according to claim 15.

17. The purifier segment is a frustum-shaped purifier, and the frustum-shaped purifier includes an inclined wall having an inclination angle of 45 to 85°, The method according to claim 16.

18. The removal of one or more of the dissolved species from the aqueous inflow stream providing the purified effluent fluid stream is at least 60%, The method according to claim 17.

19. The solid particulate product of a certain size has an average product size, and the average product size is 1 to 2 mm, The method according to claim 18.

20. The solid particulate product of a certain size has a product purity of at least 80%, The method according to claim 19.

21. A reactor system operable to remove dissolved species including dissolved nitrogen and / or dissolved phosphorus and / or dissolved potassium species from an aqueous inflow stream, A manifold that separates the aqueous inflow stream into a plurality of reactor inflow streams, and directs the plurality of reactor inflow streams upward into the base of a reaction tube segment within a reactor vessel in fluid communication with the manifold, thereby creating an upward turbulent flow within the reaction tube segment, the manifold, A water intake pump that provides a pressurized aqueous inflow stream upstream of the manifold, An injection nozzle that directs the plurality of reactor inflow streams upward into the base of the reaction tube segment, the injection nozzle rising above the bottom of the reaction tube segment, and a surface rising flow rate between 5 and 15 m / s is provided inside each nozzle, the injection nozzle, A screen disposed in the aqueous inflow stream before the aqueous inflow stream enters the manifold, the screen having a mesh smaller than the diameter of the injection nozzle, the screen A precipitant inlet port in fluid communication with the base of the reaction tube segment, adapted to inject a precipitant into the base of the reaction tube segment under the control of a reactor system control adapted to maintain conditions within the reaction tube segment, thereby providing a supersaturated concentration of the reaction product of the precipitant that reacts with the dissolved species, providing at least two saturation indices for the reaction product, and the reaction product forming solid precipitant species that are entrained in the upward reaction tube fluid flow, the precipitant inlet port and, A clarifier segment of the reactor vessel that is adjacent to the reaction tube segment in an upward direction, the cross-sectional area of the clarifier segment being increased relative to the cross-sectional area of the upward reaction tube to reduce the upward flow rate of the upward reaction tube fluid flow directed from the reaction tube segment into the clarifier segment under the control of a clarifier system control operable to maintain an upward clarifying fluid flow rate within the clarifier segment such that the entrained solid precipitant species descend within the clarifier segment of the reactor vessel and return to the reaction tube segment while the clarified effluent fluid flow continues to flow upward from the clarifier segment of the reactor vessel, the clarifier segment of the reactor vessel and, A jacket on the clarifier segment configured to collect the clarified effluent fluid flow, The reactor system control is operable to allow progressive aggregation of the precipitant species to form aggregated granules, the size and density of which are sufficient to cause the aggregated granules to settle towards the base of the reaction tube segment in the presence of the upward turbulent reaction tube fluid flow, i.e., to maintain the fluid surface upflow velocity within the reaction tube, The reactor system further comprises, A flow path that is in fluid communication with the base of the reaction tube segment and has a flow path fluid source that provides an upward flow path fluid flow into the base of the reaction tube segment through the flow path, wherein aggregated particles of a selected size and density descend through the flow path while non-selected precipitant species can be returned upward to the reaction tube segment, and the cross-sectional area of the flow path is dimensioned such that the upward flow path fluid flow can be metered, whereby the reaction tube segment descends through the flow path into an adjacent pellet hopper sized to accommodate the sedimentation volume of solid particle products of a constant size, and the solid particle products of the constant size are separated by elutriation, and the flow path is provided with The saturation index is the common logarithm of the ratio between the activity product of the ionic species constituting the reaction product and the thermodynamic solubility product of the reaction product. The reactor system.

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