阅读说明：本技术 用于通过淘洗从废水中回收尺寸选定营养物的方法和设备 (Method and apparatus for recovering size-selected nutrients from wastewater by elutriation ) 是由 赛奇·洛巴诺夫 于 2020-08-14 设计创作，主要内容包括：本公开提供方法和设备,用于通过淘洗将溶解物类以尺寸选定沉淀物形式从废水流中回收。所述方法例如可进行控制而使得回收的尺寸选定固体采取相对不可溶的植物营养物的形式,如鸟粪石。被提取的营养物例如可包括磷和/或氮和/或钾的固体物类。(The present disclosure provides methods and apparatus for recovering dissolved species from a wastewater stream as a size-selected precipitate by elutriation. The process may be controlled, for example, such that the recovered size-selected solids take the form of relatively insoluble plant nutrients, such as struvite. The extracted nutrients may for example comprise solids of phosphorus and/or nitrogen and/or potassium.)

1. A method for removing dissolved species from an aqueous influent stream, the dissolved species comprising dissolved nitrogen and/or dissolved phosphorus and/or dissolved potassium species, the method comprising:

dividing the aqueous influent stream into a plurality of reactor influent streams and directing the plurality of reactor influent streams upward into the floor of a reaction conduit section in a reactor vessel to form a turbulent upward stream in the reaction conduit;

injecting a precipitating agent into the base of the reaction conduit while maintained in the reaction conduit to provide a supersaturated concentration of a reaction product of the precipitating agent to react with the dissolved species to provide the reaction product having a saturation index of at least 2, the reaction product forming a solid precipitate species entrained in an upward reaction conduit fluid stream;

directing the upward reaction conduit fluid flow to an adjacent purifier section of the reactor, the purifier section of the reactor being dimensionally adapted to reduce an upward flow velocity of the upward reaction conduit fluid flow and maintain a flow velocity of an upward purification fluid flow in the purifier to allow entrained solid precipitate species to settle in the purifier section of the reactor and return to the reaction conduit as a purification discharge fluid flow continues to flow upward out of the purifier section of the reactor;

maintaining conditions in the reactor to allow gradual aggregation of the precipitate species to form aggregated particles sufficient in size and density to settle toward the base of the reaction conduit when the turbulent upward reaction conduit fluid flow is present;

injecting an upwardly channeled fluid stream through a channel in fluid communication with the base of the reaction conduit, the channel being dimensionally adapted to allow metering of the upwardly channeled fluid stream to allow aggregated particles of a selected size and density to settle through the channel while returning unselected precipitate species upwardly back to the reaction conduit, thereby separating a size selected solid particulate product by elutriation, the size selected solid particulate product settling through the channel into an adjacent pellet hopper, the pellet hopper being dimensionally adapted to contain a quantity of the size selected solid particulate product in a settling amount.

2. The method of claim 1, further comprising:

periodically restricting the upward channel fluid flow in the channel and releasing the contents of the hopper downward to collect the desired solid particulate product.

3. The method of claim 1 or 2, further comprising:

recirculating a portion of the purge fluid flow from the purge to the hopper to mediate the upward channel fluid flow through the channel.

4. The method of any of claims 1 to 3, further comprising:

providing an upward hopper fluid flow in the hopper to mediate an upward channel fluid flow in the channel, and sizing the hopper such that the upward hopper fluid flow is less than the upward channel fluid flow.

5. The method of any of claims 1 to 4, further comprising:

splitting the aqueous influent stream into a plurality of reactor influent streams in a manifold in fluid communication with the reaction conduit.

6. The method of any one of claims 1 to 5,

the precipitating agent comprises: base, magnesium salt, MgCl₂、MgSO₄、MgO、Mg(OH)₂Magnesia, brucite, combustion bottom ash or fly ash.

7. The method of any one of claims 1 to 6,

desirable solid particulate products include one or more of the following: struvite, K-struvite, ammonium calcium phosphate CaNH₄PO₄And/or hydroxyapatite Ca₅(PO₄)₃(OH), brushite CaHPO₄·2H₂O, MgHPO of magnesium phosphorus stone₄·3H₂O, and/or magnesium phosphate Mg₃(PO₄)₂。

8. The method of any one of claims 1 to 7,

the inflow stream comprises: suspended solids up to 1%, 2%, 3%, 4% or 5% by weight;

optionally, wherein 50-95% of the suspended solids in the influent stream pass through the reactor to the purified effluent fluid stream.

9. The method of any one of claims 1 to 8,

the channel has an average channel cross-sectional area C_XareaSaid pellet hopper having an average pellet hopper cross-sectional area PH_XareaAnd the reaction conduit has an average conduit cross-sectional area RC_XareaWherein, C_Xarea＜PH_XareaAnd C is_Xarea＜RC_Xarea。

10. The method of any of claims 1 to 9, further comprising:

collecting said solid particulate product of selected size on a screen;

optionally further washing said selected size solid particulate product on said sieve;

optionally drying the size selected solid particulate product on the screen.

11. The method of any one of claims 1 to 10,

the desired solid particulate product is at least 70%, 75%, 80%, 90% or 95% pure.

12. The method of any one of claims 1 to 11,

the flow rate of the upflow channel fluid stream is maintained at about 10%, optionally in the range of 5-50%, of the flow rate of the upflow reaction conduit fluid stream.

13. The method of any one of claims 1 to 12,

the initial saturation index SI of the reaction product at the base of the reaction conduit is maintained in the range of 2.0 to 3.0, alternatively about 2.5.

14. The method of any one of claims 1 to 13,

the flow rate of the upward reaction conduit fluid flow is maintained between 20 and 80 cm/min, alternatively about 50 cm/min.

15. The method of any one of claims 1 to 14,

the hydraulic hold time in the reaction conduit is maintained between 1 and 10 minutes, optionally between 2 and 5 minutes.

16. The method of any one of claims 1 to 15,

the flow rate of the upward stream of purge fluid is maintained at about 1-5 cm/min, alternatively about 2 cm/min.

17. The method of any one of claims 1 to 16,

the purifier is a truncated cone shaped purifier;

optionally wherein the frusto-conical shaped purifier comprises a sloped wall having an angle of inclination of about 45-85 °, optionally about 60-70 °.

18. The method of any one of claims 1 to 17,

the removing of the one or more dissolved species from the aqueous influent stream to provide a purified effluent stream is at least 60%, 70%, 80%, or 89%.

19. The method of any one of claims 1 to 18,

the size selected solid particulate product has an average product size of from about 1mm to about 2 mm.

20. The method of any one of claims 1 to 19,

the size selected solid particulate product has a product purity of at least about 60%, 70%, 80%, 90%, or 96%.

21. A reactor system operable to remove dissolved species including dissolved nitrogen and/or dissolved phosphorus and/or dissolved potassium species from an aqueous influent stream, the reactor system comprising:

a manifold that divides an aqueous influent stream into a plurality of reactor influent streams that are directed upward into a base of a reaction conduit segment in a reactor vessel in fluid communication with the manifold to form a turbulent upward flow in the reaction conduit;

a precipitant inlet port in fluid communication with the base of the reaction conduit adapted to inject a precipitant into the base of the reaction conduit under control of the reactor system controller to provide a supersaturated concentration of a reaction product of the precipitant reacting with the dissolved species, the reaction product providing a saturation index of at least 2, the reaction product forming a solid precipitate species entrained in an upward reaction conduit fluid flow;

a clarifier section of the reactor, upwardly adjacent to the reaction section, the clarifier section of the reactor being dimensionally adapted relative to the reaction section to reduce an upward flow velocity of an upward reaction conduit fluid flow directed from the reaction section into the clarifier, operable under control of a clarifier system controller to maintain a flow velocity of an upward flow of a clarifying fluid in the clarifier, thereby allowing entrained solid precipitate species to settle in the clarifier section of the reactor and return to the reaction conduit as a flow of a clarifying effluent fluid continues to flow upward out of the clarifier section of the reactor;

wherein the reactor system controller is operable to maintain conditions in the reactor to allow gradual aggregation of the precipitate species to form aggregated particles sufficient in size and density to settle the aggregated particles toward the base of the reaction conduit when the turbulent upward reaction conduit fluid flow is present;

a channel in fluid communication with the base of the reaction conduit, having a channel fluid source to provide an upward channel fluid flow through the channel into the base of the reaction conduit, the channel being dimensionally adapted to allow metering of the upward channel fluid flow to allow aggregate particles of a selected size and density to settle through the channel while returning unselected precipitate species upward back to the reaction conduit, thereby separating a size selected solid particulate product by elutriation, the size selected solid particulate product settling through the channel into an adjacent pellet hopper, the pellet hopper being dimensionally adapted to contain a settling amount of the size selected solid particulate product.

22. The reactor system of claim 21, further comprising:

an inflow pump upstream of the manifold providing a pressurized aqueous inflow stream.

23. The reactor system of claim 21 or 22, further comprising:

a sleeve on the purifier configured to collect the purified exhaust fluid stream.

24. The reactor system as recited in any one of claims 21 to 23, further comprising:

an injection nozzle directing the plurality of reactor influent streams upwardly into the base of the reaction conduit;

optionally, wherein the injection nozzle is elevated above a bottom portion of the reaction conduit;

optionally, wherein there are at least 2, 3, 4, 5 or 6 injection nozzles;

optionally, wherein the injection nozzles are substantially evenly distributed in a cross-sectional area at the base of the reaction conduit;

optionally wherein the upper flow surface velocity provided in each nozzle is between 5 and 15m/s, or about 10 m/s.

25. The reactor system as recited in any one of claims 21 to 24, further comprising:

a screen positioned in the aqueous influent stream prior to the aqueous influent stream entering the manifold;

optionally, wherein the screen has a mesh smaller than a diameter of the injection nozzle.

26. The reactor system of any one of claims 21 to 25,

the precipitant is fed in the immediate vicinity of the injection nozzle.

27. The reactor system of any one of claims 21 to 26, for performing the method of any one of claims 1 to 20.

Technical Field

Innovations in the field of water chemistry are disclosed, including methods and apparatus for removing dissolved species from wastewater as size-selected precipitates.

Background

Dissolved phosphorus, nitrogen, potassium species are often discharged into wastewater, particularly agricultural wastewater. This can have the adverse effects of: is beneficial to the growth of algae and other organisms in water, and can further cause the occurrence of eutrophication which is harmful to the environment in natural water bodies. This reverse process of the nutrient cycle involves the use of metered amounts of phosphorus, nitrogen, potassium species as agricultural fertilizers. Thus, efficient recycling of nutrients from wastewater to fertilizer is not satisfactory.

There are a variety of nutrient recovery techniques based on crystallization processes. Some of these techniques extract phosphorus and other nutrients as struvite, calcium phosphate, or other poorly soluble compounds in the form of fine crystals or powders. This leads to separation problems of the products recovered from the waste water from other suspended solids. Fine materials can be difficult to handle and expensive to dewater, dry and process. Many materials recovered as powders require further processing before they can be used as fertilizers. Thus, there remains a need for alternative methods for recovering useful materials from wastewater in a physical form that is convenient for subsequent use.

Some poorly soluble phosphate compounds (e.g., struvite) are effective slow release fertilizers due to their relatively low solubility. This is unlike typical water-soluble fertilizers, such as monoammonium phosphate and diammonium phosphate, which are only partially assimilated by the crop, and a substantial portion of these fertilizers may be washed from the soil into the environment. Struvite dissolves very slowly, thereby mitigating nutrient loss from the soil and providing efficient nutrition to the plant. The relatively low solubility of this fertilizer also helps prevent "burn-out" of the plant roots due to high salinity (which may be due to more water-soluble fertilizer). Since many agricultural, municipal and industrial waste water streams contain large amounts of nutrients, particularly phosphorus and nitrogen, it is possible to recover struvite from these waste streams.

For example, there are various methods for recovering phosphorus from waste streams in the form of struvite and other phosphate compounds. Many existing struvite recovery processes extract struvite in the form of small powdered particles that are difficult to dry and separate from impurities, which is a significant drawback for the final fertilizer product. Thus, there is a need for a high quality struvite fertilizer product that can be produced in small granular or pellet form, that can be easily separated from wastewater and other impurities, and that can be easily dried, transported and stored.

Disclosure of Invention

Methods and apparatus for recovering dissolved species from a wastewater stream as a size-selected precipitate are disclosed. For example, methods are provided for removing dissolved species from an aqueous influent stream, the dissolved species including dissolved nitrogen and/or dissolved phosphorus and/or dissolved potassium species. These methods may include the steps of: the aqueous influent stream is split into streams that are directed into a reactor into which a precipitant is injected. The precipitating agent may be provided, for example, in different material streams (e.g., as a solid or liquid), or the precipitating agent may be present in one or more of the aqueous stream streams.

The aqueous influent stream may be divided into a plurality of reactor influent streams, such as in a manifold in fluid communication with the reaction conduits, for example. The multiple reactor influent streams may be directed upwardly into the floor of a reaction conduit section in the reactor vessel to create a turbulent upward flow in the reaction conduit.

The precipitating agent may also be injected into the base of the reaction conduit, for example, while maintained in the reaction conduit, to provide a supersaturated concentration of reaction product for the precipitating agent to react with the dissolved species. The precipitating agent (e.g., solid or liquid) may be, for example, any one or more of the following: alkali (caustic soda, caustic potash, alkaline water, ammonia), magnesium salt (such as MgCl)₂、MgSO₄、MgO、Mg(OH)₂) Magnesium carbonate, brucite, combustion bottom ash or fly ash. These reactor conditions may be controlled, for example, to provide a desired saturation index of the reaction product, for example at least 2 (alternatively 2.0 to 3.0, alternatively 2.5), with the reaction product forming solid precipitate species entrained in the upward reaction conduit fluid stream.

The upward reaction conduit fluid flow may then be directed to an adjacent purifier section of the reactor. The flow rate of the upward reaction conduit fluid flow may be maintained, for example, between 20 and 80 cm/min, alternatively about 50 cm/min. The reactor purifier section may, for example, be dimensionally adapted to reduce the upward flow velocity of the upward reaction conduit fluid flow. The purifier may for example be a truncated cone purifier, for example, wherein the truncated cone purifier comprises inclined walls having an inclination angle of about 45-85 °, optionally about 60-70 °.

The flow rate of the upward purge fluid stream in the purifier may be maintained to allow entrained solid precipitate species to settle in the purifier section of the reactor and return to the reaction conduit as the purge effluent fluid stream continues to flow upward out of the purifier section of the reactor. The flow rate of the upward stream of purge fluid may be maintained, for example, at about 1-5 cm/min, alternatively about 2 cm/min. For example, conditions may be maintained in the reactor to substantially remove dissolved species from the aqueous influent stream to provide a purified effluent stream, e.g., such that at least 60%, 70%, 80%, or 89% of the dissolved species are removed from the input to the effluent.

Conditions may be maintained in the reactor to allow gradual aggregation of the precipitate species, for example to form aggregated particles sufficient in size and density to settle the aggregated particles towards the base of the reaction conduit, as has surprisingly been demonstrated: the conditions may be arranged such that this settling occurs when there is turbulent upward reaction conduit fluid flow. The hydraulic holding time in the reaction conduit may be, for example, 1 to 10 minutes, alternatively 2 to 5 minutes.

The upflow channel fluid stream may be injected into the reactor through a channel in fluid communication with the base of the reaction conduit. The channels may, for example, be dimensionally adapted to allow for metering of an upward channel fluid flow to allow for the settling of aggregated particles of a selected size and density through the channels while returning unselected precipitate species upward back to the reaction conduit. The flow rate of the up channel fluid flow may for example be maintained at about 10%, optionally in the range of 5-50%, of the flow rate of the up reaction conduit fluid flow.

The channels may for example dimensionally have an average channel cross-sectional area C_XareaAnd the pellet hopper similarly has an average pellet hopper cross-sectional area PH_XareaThe reaction conduit also has an average conduit cross-sectional area RC_Xarea: these dimensions may be arranged such that C_Xarea＜PH_Xarea，C_Xarea＜RC_Xarea.12。

In this way, the solid particulate product of selected size is separated by elutriation, which correspondingly settles through the channels. This size selected product may be selected into an adjacent pellet hopper, for example, sized to hold a quantity of the size selected solid particulate product. In select embodiments, the method may include: periodically restricting upward channel fluid flow in the channel and releasing the contents of the pellet hopper downward to collect the desired solid particulate product. The size-selected solid particulate product may be collected on a sieve, for example, and may be washed on the sieve, and may then be dried. The size-selected solid particulate product may, for example, have an average product size, and the average product size may, for example, be in the range of about 1mm to about 2 mm. The particulate product, for example, can have a desired purity, e.g., at least about 60%, 70%, 80%, 90%, or 96%.

The desired solid particulate product may, for example, comprise one or more of the following: struvite, K-struvite, ammonium calcium phosphate CaNH₄PO₄And/or hydroxyapatite Ca₅(PO₄)₃(OH), brushite CaHPO₄·2H₂O, MgHPO of magnesium phosphorus₄·3H₂O, and/or magnesium phosphate Mg₃(PO₄)₂. In select alternative embodiments, the desired solid particulate product may be at least 70%, 75%, 80%, 90%, or 95% pure, for example.

In one aspect, a method may comprise: a portion of the stream of purge fluid from the purge is recycled to the hopper, and this recycled fluid stream is used to mediate the upward channel fluid stream through the channel. For example, upward hopper fluid flow in the hopper may be provided to mediate upward channel fluid flow in the channel; the hopper may be sized such that upward hopper fluid flow is less than upward channel fluid flow.

One aspect of select embodiments of the method is: an influent stream having a relatively high level of suspended solids can be treated. For example, the influent stream may include up to 1%, 2%, 3%, 4%, or 5% by weight suspended solids. In some embodiments, 50-95% of the suspended solids in the influent stream pass through the reactor to the purge effluent fluid stream.

The method may be performed in a reactor by a control system constituting 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 may be positioned in the aqueous influent stream prior to its entry into the manifold, the screens having a mesh size that may be smaller than the diameter of an injection nozzle positioned within the reactor, for example.

The reactor system may include: a manifold that divides the aqueous influent stream into a plurality of reactor influent streams and directs the plurality of reactor influent streams upwardly into the floor of the reaction conduit section in the reactor vessel, e.g., to create a turbulent upward flow in the reaction conduit. An influent pump may be located upstream of the manifold, for example, to provide a pressurized aqueous influent stream. The precipitant inlet port can be disposed in fluid communication with the base of the reaction conduit and adapted to inject a precipitant into the base of the reaction conduit (e.g., under control of a reactor system controller, wherein the reactor system controller is adapted to maintain conditions in the reaction conduit) to provide a supersaturated concentration of reaction products of the precipitant reacting with the dissolved species. The precipitant may be fed in the immediate vicinity of the injection nozzle (directing the input fluid into the reactor). In this way, the saturation index may be maintained for the reaction product, as previously described, e.g., at least 2. The reaction products are accordingly entrained in the upward reaction conduit fluid flow as solid precipitate species are formed.

The purifier section of the reactor (upwardly adjacent the reaction section) may be dimensioned relative to the reaction section to reduce the upward flow rate of the upward reaction conduit fluid flow directed from the reaction section into the purifier, for example under the control of a purifier system controller (operable to maintain the flow rate of the upward purification fluid flow in the purifier) to allow entrained solid precipitate species to settle in the purifier section of the reactor and return to the reaction conduit as the purification discharge fluid flow continues to flow upward out of the purifier section of the reactor. A sleeve may be disposed on the purifier configured to collect the purified effluent fluid stream.

The reactor system controller may be operable to maintain conditions in the reactor to allow gradual aggregation of the precipitate species to form aggregated particles that are sufficient in size and density to settle toward the base of the reaction conduit when turbulent upward reaction conduit fluid flow is present.

The channel (which is in fluid communication with the base of the reaction conduit) may be connected to a channel fluid source to provide an upward channel fluid flow through the channel into the base of the reaction conduit. The channels may be dimensionally adapted to allow metering of the upward channel fluid flow to allow aggregate particles of a selected size and density to settle through the channels while returning unselected precipitate species upward back to the reaction conduit, thereby separating the size selected solid particulate product by elutriation, the size selected solid particulate product settling through the channels into an adjacent pellet hopper, the pellet hopper being dimensionally adapted to contain a settling amount of the size selected solid particulate product.

Injection nozzles may be provided to direct a plurality of reactor influent streams up into the base of the reaction conduit. The injection nozzle may, for example, be raised above the bottom portion of the reaction conduit. For example, there may be at least 2, 3, 4, 5 or 6 injection nozzles. The injection nozzles may be substantially evenly distributed in the cross-sectional area at the base of the reaction conduit. In select embodiments, the upper flow surface velocity within each nozzle may be maintained between 5 and 15m/s, or about 10 m/s.

Drawings

Fig. 1 is a schematic elevation view of an apparatus for performing the methods disclosed herein.

Fig. 2 is a schematic elevation view of an alternative apparatus for performing the methods disclosed herein.

Detailed Description

Methods and apparatus are disclosed for recovering dissolved species from a wastewater stream in the form of a precipitate sized by elutriation. In some embodiments, the recovered solids may be, for example, plant nutrients. The extracted nutrients may for example comprise solids of phosphorus (P) and/or nitrogen (N) and/or potassium (K). The method may be performed for a wide range of aqueous feeds, such as wastewater streams from various sources, such as agricultural (fertilizer), municipal (sewage), or other industrial sources.

In the selected examples, the nutrients are extracted by a process of crystallization of phosphate containing small amounts of soluble compounds. Such compounds may include, for example, but are not limited to: struvite (magnesium ammonium phosphate, MAP), K-struvite (magnesium potassium phosphate, MKP), and other small soluble phosphate compounds. In one aspect of the method, nutrients are converted from an aqueous liquid (e.g., wastewater) to a solid (e.g., crystals) due to supersaturation in the wastewater of the reaction products of the precipitate and dissolved species, i.e., compounds are extracted from the aqueous influent stream. The supersaturated state thereby triggers the crystallization process. Supersaturation can be formed in a number of ways, including: by adding a precipitating agent(s) to the waste water or by mixing different waste water streams together, wherein a precipitating agent is provided into one of these streams. The solid material obtained in the precipitation process can then be separated from the liquid.

The methods disclosed herein enable the recovery of nutrients from wastewater in a form that can provide the extracted compounds as relatively large spherical particles (pellets). These particles generally present aggregates of smaller crystals produced in the crystallization equipment (reactor). As disclosed herein, the chemical and hydrodynamic conditions within the reactor can be controlled by: the crystal aggregation rate is relatively high. This causes the particles to grow rapidly and allows for more efficient extraction of nutrients from the wastewater. At the same time, it has been demonstrated that the process can be controlled so that the particles can grow large enough to be separated from the wastewater and other suspended solids. In select embodiments, the process thus facilitates recovery of high purity products from the liquid stream, such as may be achieved by an influent stream having a relatively high amount (e.g., up to 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% by weight) of suspended solids (or up to 5% by weight suspended solids in alternative embodiments). In the selected examples, the relatively high efficiency of the process allows for a smaller plant footprint and contributes to economic energy consumption.

In the illustrated embodiment, there are two main components of the device for implementing the method: a crystallization reactor and a waste water injection system. The crystallization reactor is exemplified as a vertical fluidized bed reactor as shown in fig. 1. The reactor comprises three main components: a reaction conduit (1), a purifier (2), and a pellet hopper (3). The purifier is adjacent to and immediately above the reaction conduit. In the illustrated embodiment, the cross-sectional area of the purifier gradually increases from bottom to top; the shape of the purifier is thus in the form of a truncated cone. The cross-sectional profiles of the reaction conduit and the purifier may be circular, rectangular or polygonal, for example. The top of the purifier may be open and the bottom of the reaction conduit closed except where the various input ports are located. A pellet hopper (3) may be located below the reaction conduit, providing a container for bulk pellets of the recovered product; it may advantageously be tapered downwardly to facilitate discharge of the recovered product at the bottom of the hopper. The top of the pellet hopper is connected to the bottom of the reaction conduit by a vertical pipe or any other passageway (which as shown may have a significantly smaller cross-sectional area than the pellet hopper and the reaction conduit).

The apparatus disclosed herein facilitates a particular wastewater injection process. As shown, the injection system includes one or more of the following components: a pump (4), a manifold (5), and an injection nozzle (6). Each set may be used for a different wastewater stream to be treated in the plant. This may be particularly advantageous in case the different waste water streams should not be mixed with each other prior to the treatment process. In each group, a pump delivers the wastewater to be treated into the manifold, thereby creating a higher pressure within the manifold. The manifold (5) may for example be adapted to distribute the waste water substantially equally in each nozzle (6) connected thereto. The nozzle outlet is located at the bottom or base of the reaction conduit (1). They may be directed generally upward and slightly above the surface of the bottom of the reaction conduit. The total number of nozzles for all injection groups may be, for example, at least 3; the nozzles may be evenly distributed in the cross-sectional area at the bottom of the reaction conduit.

In the apparatus shown, the wastewater is injected into the reactor at the bottom of the reaction conduit (1) through nozzles (6) in such a way that the upper flow surface velocity inside each nozzle is between 5 and 15m/s, preferably 10 m/s. This forms a plurality of jets directed generally upwardly; the jets produce high turbulence at the bottom of the reaction conduit. The size (or diameter) of the nozzles depends on their number and the flow rate of the waste water and can be determined by a person skilled in the art. The nozzle (6) typically has a circular cross-sectional area, but may also be rectangular, polygonal, etc. Prior to entering the manifold, the wastewater stream may pass through an optional screen to separate any particulate material larger than the nozzle size (diameter) to prevent possible nozzle clogging.

The reactor shown is operated in continuous upflow mode. In operation, all parts of the reactor may be filled with crystals of compounds extracted from the wastewater; each part of the reactor accommodates crystals of different sizes. As mentioned before, the wastewater to be treated is injected into the reaction conduit (1) from the bottom through the injection nozzle (6). At the same time, the precipitant(s) can be fed at the bottom of the reaction conduit (1) in the immediate vicinity of the injection nozzle (6), where it is immediately mixed with the wastewater, thereby forming a supersaturated chemical state.

The precipitating agent is typically a substance that reduces the solubility of extracted substances in the wastewater. For example, if the extracted material is struvite, the precipitating agent may be an alkali, a magnesium salt, or any combination thereof. The medicament may be injected through one or more inlet ports (mounted vertically, horizontally, or at an angle). The precipitant may be, for example, a liquid or slurry; which can be continuously fed in a controlled manner using metering pumps, pH controllers, etc. to maintain a certain degree of supersaturation in the reaction conduit for compounds extracted from the wastewater. Alternatively, supersaturation may be formed without addition of precipitating agent(s) instead by: the individual wastewater streams are mixed together to achieve the desired supersaturation by using a separate set of injection systems for each wastewater stream.

In select embodiments, the pH may be controlled in the reactor, for example, it may be maintained to achieve a desired saturation index. Similarly, the temperature in the reactor (again for a desired value of the set temperature in the reactor) can be controlled to achieve a desired saturation index. In select embodiments, if struvite is the desired product, the reactor pH may be controlled, for example, between 7-10, with contemplated temperature ranges being, for example, 10-40 ℃, or alternatively as high as 60 ℃.

Supersaturation triggers crystal formation within the reactor and promotes its growth and aggregation. In all reactor options, the crystals are suspended in the liquid upflow. As crystals form, nutrients are extracted from the liquid phase. The conditions may be maintained such that the relatively small crystals then settle down in the purifier (2) and return to the reaction conduit as the purified wastewater exits the top portion of the purifier, or may be arranged such that suspended solids originally present in the influent stream also move out of the top portion of the purifier. The reactor effluent accordingly contains a significantly smaller amount of nutrients and is presented as a treated wastewater stream. At the same time, aggregates of crystals (which surprisingly benefit from the turbulence generated by the jet) within the reaction conduit (1) thus form particles or pellets (which may for example be substantially spherical). It has been found (as shown in the examples herein): the conditions may be arranged such that pellets that have grown to the desired or selected size settle to the bottom of the reaction conduit (1) and then settle further into the pellet hopper (3).

The pellet hopper (3) facilitates continuous separation of pellets from aggregates and crystals ("unselected" sediment) that have not yet achieved the desired size and are therefore not selected for extraction from the reactor. At the same time, the continuous removal of the pellets from the reaction conduit (1) prevents an excess of crystals at the bottom of the conduit (which may have a potential negative impact on the process).

The separation of the pellets is achieved by the elutriation principle. As previously mentioned, the bottom of the reaction conduit (1) is connected to the top of the pellet hopper (3) by a pipe or channel (7), which may be a tube having a smaller cross-sectional area than the reaction conduit and pellet hopper. The cross-sectional area of the channel (7) may be circular, rectangular, or polygonal, for example. An upflow of liquid (i.e., an upflow channel fluid stream) is created in the channel, opposite the settling direction of the pellets. The upstream is maintained such that: it enables the larger pellets to fall suspended therein while the smaller pellets and other crystals are carried back up into the reaction conduit with the upflow. The larger particles eventually settle into the pellet hopper (3) where they no longer remain suspended because the hopper has a larger cross-sectional area than the passage (7) and the upflow velocity is no longer high enough to keep the pellets suspended.

The pellets are periodically discharged from the pellet hopper (3) by: the pellet hopper (3) is isolated from the reaction conduit using a shut-off valve (8) while a discharge valve (9) at the bottom of the pellet hopper (3) is opened. The pellets may be discharged onto a screen where the liquid, and any suspended solids therein, are readily drained past the pellets retained on the screen. After unloading of the pellets from the hopper, the discharge valve (9) is closed and the hopper is filled with liquid, after which the shut-off valve (8) is opened again so that the next batch of pellets can be collected. The pellet hopper (3) typically has a large capacity capable of holding a large number of stacked pellets without the need for frequent discharge. The pellets on the screen may be washed with water to remove any impurities from their surface and then dried in air, in a low temperature oven, or by any other means known in the art. The fertilizer pellets are presented as a final product ready for supply to the market without any further treatment. In select embodiments, the purity of the final fertilizer product may exceed, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%.

The liquid upflow in the channel (7) connecting the pellet hopper (3) to the reaction conduit (1) can be achieved, for example, by: an additional pump (10) is used to pump a portion of the reactor effluent from the purifier (2) into the pellet hopper. The use of reactor effluent has the following advantages: keeping the pellets in the mother liquor to prevent their dissolution; and keeping the amount of wastewater constant (otherwise the amount of wastewater would increase if additional extraneous liquid was used for this purpose). Control of the upflow velocity in the channel (7) allows selective separation of specific pellet sizes and maintenance of the desired crystal size distribution of the harvested pellets. The cross-sectional area and flow rate through the channel (7) may for example be selected such that it does not significantly affect the desired hydrodynamic and chemical state within the reaction conduit (1). The flow rate may be maintained at about 10% of the total flow rate in the reaction conduit, for example.

In one aspect of the method, the method is performed while maintaining a particular relatively constant level of initial supersaturation with respect to the compound being extracted in the reaction conduit (1). This operating parameter is advantageous for controlling process efficiency. Supersaturation may be maintained, for example, by controlling the flow rate of the precipitating agent(s). Alternatively, in embodiments where more than one wastewater stream is treated in the plant, supersaturation may be maintained, for example, by controlling the mixing ratio of the wastewater streams.

The supersaturation of a liquid with respect to a substance is expressed herein as the saturation index SI, which is the ion constituting said substanceThe common logarithm of the ratio of the activity product of a sub-species to the thermodynamic solubility product of the substance. For example, struvite (magnesium ammonium phosphate, MgNH)₄PO₄·6H₂O), SI will be expressed as:

wherein: { Mg²⁺}、{NH⁴⁺}、{PO₄ ^3-The activities of magnesium, ammonium, orthophosphate ions, respectively; k_sp(struvite)Is the thermodynamic solubility product of struvite.

The saturation index may be determined by using this formula as part of the control system of the method. The activity of the ionic species of interest can be measured directly or mathematically obtained using standard analytical methods based on the measured concentration of the ionic species of interest. The activity coefficient of the species and the solubility product of the extracted compound will be available from widely available literature sources.

The initial saturation index SI at the bottom of the reaction conduit (1) with respect to the compounds extracted may be kept, for example, in the range of 2.0-3.0, alternatively 2.5. It has been surprisingly found that this saturation index, together with the high turbulence in the reaction conduit, leads to a high rate of crystal nucleation. At the same time, it also provides a surprisingly high rate of aggregation of the crystals, so that the newly formed small crystals can rapidly aggregate into larger particles (pellets). By establishing and maintaining such a state (where the rate of crystal aggregation is greater than or equal to the rate of crystal formation), the number of small crystals can be reduced, while the number and size of larger aggregates can be increased. This allows control of the crystal size distribution and population density within the reactor and ultimately the rapid formation of large particles of the extracted compound. In addition to this, it has been found that: the particular hydrodynamic and chemical states in the reaction conduit (1) may be selected to facilitate the affinity of the crystals for each other over other suspended solids present in the wastewater stream. This has been shown to result in the formation of highly pure extracted compounds, which are hardly contaminated by solid impurities in the waste water. In select examples, it has been found that: the process is capable of handling up to 2% of the total suspended solids in a liquid stream without significantly compromising the quality of the recovered fertilizer product.

It has been found that: the practice of a process having the above saturation index provides relatively low residual concentrations of nutrients in the reactor effluent, admittedly by substantially completing the chemical reaction before the wastewater stream exits the reactor. In a select embodiment, once the reaction occurs in the reaction conduit (1), the saturation index is rapidly reduced to a level of 0.1-1.0. This may correspondingly hinder new crystal formation, but favor existing crystal growth. This condition can be carefully planned to develop in the upper region of the reaction conduit. In particular, it has been found that: the states may be set such that: the large pellets essentially settle to the bottom of the reaction conduit while some much smaller crystals remain suspended within their volume. As long as the crystals grow large enough that they no longer remain suspended by the upflow, they settle down into the bottom portion of the reaction conduit and aggregate into pellets.

In the chosen embodiment, the upper surface velocity in the reaction conduit (1) may be maintained, for example, at 20-80 cm/min, or about 50 cm/min, to facilitate settling of small and medium size crystals. The hydraulic holding time in the reaction conduit may be kept, for example, between 1 and 10 minutes, or between 2 and 5 minutes, wherein these conditions provide sufficient time for the chemical reaction to be substantially complete. The physical dimensions of the reaction conduit (1) may be designed based on these requirements.

Crystals too small to be retained in the reaction conduit (1), and suspended solids originally present in the wastewater, are carried upstream into the purifier (2). In the illustrated embodiment, the purgers have progressively increasing cross-sectional areas, which progressively reduce the upflow velocity of the fluid therein (i.e., upward purge fluid flow). As a result, in select embodiments, crystals as small as 50 microns, for example, may remain in the reactor without any substantial loss of extracted compounds with the effluent. In order to retain the crystals within the purifier (2), the upflow surface velocity at the top of the purifier may be maintained, for example, at 1-5 cm/min, alternatively about 2 cm/min. In a concentrating embodiment, the angle of inclination of the purifier truncated cone may be, for example, 45-85 °, alternatively 60-70 °. The physical dimensions of the purifier (2) can be designed, for example, on the basis of these requirements. In the shown embodiment, the truncated cone shape of the purifier, and the block crystals descending counter-current from the purifier, create a slight turbulence at the attachment point between the purifier and the reaction conduit (1). This can further be used to promote the growth of existing crystals in preference to the production of new crystals. For carrying out the aforementioned conditions, the purifier (2) can be made to contain a suspended bed of small crystals. This bed is dynamic as a whole, since it continuously exchanges crystals with the reaction conduit (1): the crystals grow large enough to settle down, while some newly formed fine crystals are carried upwards with the flow. As a result, the bed acts as a "filter" to capture fine crystals and prevent them from escaping the reactor. At the same time, suspended solids initially present in the wastewater stream typically have much smaller sizes and lower densities than the crystals. As a result, they can pass freely through the bed and be 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 state of the bottom of the reaction conduit. Precise control of the operating parameters prevents the bed from overflowing and losing fine crystals with the effluent. The top of the purifier may optionally have a weir (11), as shown in fig. 1, for distributing the outflow evenly over a wide surface area to minimize resuspension of the crystals. The effluent from the reactor will then overflow into an external purifier (12) designed as a jacket of the reactor purifier. The jacket (12) further minimizes fine crystal loss with the effluent.

Examples of the invention

The exemplary method is performed in a device as shown in fig. 2. The wastewater stream to be treated is anaerobically digested chicken manure which has been subjected to a solids separation treatment. The wastewater had the following average characteristics: 2.0% of total suspended solids; the pH was 8.4; a conductivity of 18 mS/cm; alkalinity of 30,000mg/L (e.g., CaCO)₃) (ii) a Soluble orthophosphate P-PO₄205 mg/L; soluble ammonia nitrogen N-NH₃Is 5050 mg/L; the soluble magnesium Mg is 5 Mg/L; the soluble calcium Ca is 50 mg/L. Wastewater was continuously pumped from the storage tank to the manifold by a pump at an average flow rate of 200m³The day is. Before entering the manifold, the wastewater passed through a screen with 5mm openings. The pressure differential in the manifold was maintained at 0.1 MPa. ManifoldThe wastewater was distributed between 4 identical circular nozzles. The upper flow surface velocity in each nozzle was kept at 9 m/s.

The wastewater enters the cylindrical reaction conduit where it is immediately mixed with the precipitant fed at the bottom of the reaction conduit. The precipitant is a concentrated solution of a water soluble magnesium salt. The salt solution is continuously fed in a controlled manner by means of a metering pump so that the molar ratio between soluble magnesium and soluble orthophosphate in the reaction conduit is about 1. Once the agent is mixed with the wastewater, the reaction between magnesium, ammonia and orthophosphate occurs substantially immediately and struvite crystals form in the reaction conduit. The initial saturation index of struvite in the reaction conduit is about 2.3. The upper flow surface velocity in the reaction conduit was 47 cm/min. The pH at the top of the reaction conduit was monitored by a pH meter, indicating a value of about 8.3. The upper flow surface velocity at the top of the purifier was 5 cm/min. The purifier has an overflow weir and a jacket. The treated wastewater (effluent) overflows into the jacket and leaves the reactor through a port installed in the jacket.

The effluent had the following average concentrations: soluble orthophosphate P-PO₄Is 22 mg/L; soluble ammonium nitrogen ammonia N-NH₃4800 mg/L; the soluble magnesium Mg is 14 Mg/L; the soluble calcium Ca is 48 mg/L. The removal of soluble orthophosphate was correspondingly 89%. A portion of the effluent from the jacket was pumped by an additional pump into the pellet hopper at a flow rate of 23m³The day is. Struvite pellets formed in the reaction conduit are continuously lowered through vertical piping into a pellet hopper. The surface velocity of the water flow in the pipe was maintained at 415 cm/min. This upflow velocity enables struvite pellets of a size greater than 1mm to be separated from the remaining crystals in the reaction conduit. Pellets are discharged from the pellet hopper every two days by closing a shut-off valve between the reaction conduit and the pellet hopper and opening a discharge valve at the bottom of the pellet hopper. The pellets, as well as the liquid, are discharged into a vessel having a screen at its bottom. The size of the opening of the sieve is 0.5 mm. The liquid drains through the screen while the struvite pellets remain on the screen. The pellets were then rinsed with clean water and dried in open air. The weight of the extracted dry struvite crystals per harvest was about 500 kg. Struvite pellets range in size from 1 to 2 mm. Purity of struvite productThe degree is about 96%.

Reference to the literature

Ghosh, S., Lobanov, S., Lo, V.K. (2019) Effect of supersaturation ratio on phosphorus recovery from the surface of synthetic anaerobic digesters by a struvite crystallization fluidized bed reactor environmental technologies, 40(15), 2000-.

Summary of the technology for recovering struvite phosphorus from wastewater (2019): environmental science and pollution research, 26(19), 19063-.

Peng, L., Dai, H., Wu, Y., Peng, Y., Lu, X. (2018) review of phosphorus recovery from wastewater by crystallization methods Chemosphere, 197, 768 781.

US10266433(2019)

US8999007(2015)

US7922897(2011)

US7622047(2009)

US7005072(2006)

US6994782(2006)

US2012003135(2012)

US4389317(1983)

US3869381(1975)

FR2962433(2012)

US8017019(2011)

CN209242807U(2019)

CN107445266A(2017)

CN106512465A(2017)

CN106430506A(2017)

CN206255878U(2017)

CN204298122U(2015)

CN104129769A(2014)

CN103935974A(2014)

WO2017194997(2017)

KR20170014793A(2017)

EP3112320A1(2017)

ES2455740(2014)

JP4505878B2(2010)

JP3883222B2(2007)

JP3649471B2(2005)

JP3344132B2(2002)

JPH11267665A(1999)

JP2576679B2(1997)

US4946653(1990)

Citation of documents herein is not an admission that such documents are prior art to the present invention. Any and all prior documents and publications (including but not limited to patents and patent applications) cited in this patent document, and all documents cited in these documents and publications, are hereby incorporated by reference herein, as if each individual publication were specifically and individually indicated to be incorporated by reference and were set forth in its entirety herein. Although various embodiments of the invention are disclosed herein, various adaptations and modifications may be made within the scope of the invention by the common general knowledge of those skilled in the art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Terms such as "exemplary" or "instantiated" are used herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" or "exemplified" should accordingly be considered as not necessarily preferred or advantageous over other embodiments, all such embodiments being separate examples. Unless otherwise indicated, numerical ranges include the numbers defining the range, and numbers are necessarily approximations for the given decimal. The word "comprising" is used herein as an open-ended term, substantially equivalent to the expression "including, but not limited to," with the word "comprising" having a corresponding meaning. As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "an item" includes more than one of such item. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.