METHODS AND APPARATUS FOR NUTRIENT AND WATER RECOVERY FROM WASTE STREAMS

Abstract

The present invention is directed to equipment, systems and methods for recovering nitrogen, potassium, phosphates and water from wastewater effluents. More particularly the invention discloses methods and equipments for treating waste streams to produce water that can be discharged to the environment and concentrated potassium ammonium struvite solid fertilizers.

Claims

1. A method for recovering nitrogen, phosphorus, and potassium from wastewater and producing low nutrient water comprising: adding external phosphoric acid to the wastewater A having total alkalinity of (AL1) and initial concentrations of ammonium (N), phosphate (P), and potassium (K) to increase the phosphate concentration to (P2) at AL1/P2 mass ratio exceeding 4; adding air to the wastewater to remove dissolved carbon dioxide and increase the pH to the extent that pH stays constant; adding external magnesium salt to the wastewater at Mg/P2 molar ratio of 0.8-1.2; mixing and/or aerating the said wastewater to remove residual dissolved CO2, reaching pH of at least 7 which results in formation of ammonium potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O), then separating precipitated solids containing NPK from liquid to produce low nutrient water and high NPK solids.

2. A method according to claim 1 wherein no external alkali source is used for struvite formation.

3. A method for recovering nitrogen, phosphorus, and potassium from wastewater by combined ammonia stripping and struvite formation comprising addition of phosphoric acid to wastewater (A) containing initial concentrations of ammonium (N1), phosphate (P1), and potassium (K1) to increase the phosphate concentration of the said wastewater to P2 wherein P2/K1 molar ratio<5.5; then adding and mixing external alkalinity source to the said wastewater to increase the pH and; adding magnesium chloride solution at Mg/P2 ratio of 0.8-1.2; mixing and/or aerating the said wastewater to simultaneously remove dissolved CO2 and ammonia, and formation of ammonium potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O); continuing the aeration until ammonia concentration remains constant; separating solids from liquid to produce water containing low concentrations of nitrogen, phosphorus and potassium (low NPK water) and high NPK solids.

4. A method according to claim 3 wherein external alkalinity source is sodium carbonate or sodium hydroxide.

5. A method according to claim 3 wherein pH is kept between 9 to 11.

6. A process for producing low nutrient water and biosolids containing high concentrations of nitrogen, potassium, and phosphorus according to claims 1 to 5 wherein the said wastewater (A) is a digestate slurry and high NPK solids are mixture of organics and ammonium potassium struvite.

7. A process for precipitation and granulation of nutrients in wastewater (A) containing ammonium, phosphate, potassium, and alkalinity comprising: continuously transferring and mixing of the said wastewater with magnesium containing solution in a fluidized bed reactor having an elongated lower tubular section connected to an elongated upper tubular section with a relative diameter of upper section to lower section between 1.378 and 1.598, and most preferably about 1.516, wherein mixing and precipitating nutrients take place in the lower section of the reactor and precipitates are fluidized by a recycle flow from a recycle port from the upper section to the lower section; and the effluent wastewater (B) exits the upper section of the reactor from an effluent port in the upper tubular section of the reactor.

8. A process according to claim 7 wherein the total height of the said fluidized bed reactor is at least 3 meters and the distance between the said recycle port and effluent port is at least 1.5 meters.

9. A process according to claim 7 wherein fine precipitated particles accumulate in the said elongated upper tubular section between the said recycle port and effluent port; recycle back to the lower section of the fluidized bed reactor via a first recycle pump.

10. A process according to claims 7, 8 and 9 wherein the said fine precipitated particles recycle back to the lower section of the fluidized bed reactor via a recycle pump to grow in size and accumulate in the lower section of the reactor for harvesting.

11. A process according to claim 7 wherein the said effluent wastewater (B) is further aerated in a multifunctional reactor vessel coupled to an external clarifier wherein ammonia and carbon dioxide are stripped out of the effluent wastewater (B) to produce wastewater effluent (C) and fine particles are settled in the external clarifier.

12. A process according to claims 11 and 7 wherein the stetted particles in the external clarifier are pumped back to the lower tubular section of the said fluidized bed reactor via a second recycle pump.

13. A process according to claim 11 wherein the minimum hydraulic retention time of aerated reactor vessel is six hours.

14. A process according to claim 7 wherein magnesium solution is added to the reactor at minimum magnesium to phosphate molar ratio of 0.8.

15. A process according to claim 7 wherein the pH of wastewater in the upper section of the reactor is at least 6.9.

16. A process according to claim 11 wherein the multifunctional reactor vessel is converted to a biological reactor by adding mixture of Anammox bacteria and nitrifying bacteria to the said reactor and controlling the dissolved oxygen in the reactor below 2 mg/L and the content of said external clarifier is recycled back to the multifunctional tank via a pump.

17. A process according to claim 16 wherein the residual ammonium in the wastewater effluent is removed in the said multifunctional tank by the Anammox and nitrifying bacteria.

18. A process for precipitation and granulation of nutrients from wastewater and producing low nutrient water according to process of claims 7 to 17 and the method of claim 1 wherein the said wastewater A having initial alkalinity of AL1 is mixed with phosphoric acid in a feed tank to increase the phosphate concentration of said wastewater to (P2) so that AL1/P2 mass ratio exceeds 4 before transferring that wastewater to the said fluidized bed reactor to be mixed with a magnesium chloride solution to co-precipitate ammonium and potassium struvite.

19. A process for precipitation and granulation of nutrients from wastewater and producing low nutrient water according to process of claim 7 to 17 and the method of claim 3 wherein wastewater A is mixed with external phosphoric acid and alkaline solution in a feed tank to increase the phosphate concentration of the said wastewater to P2 wherein P2/K1 molar ratio<5.5; transferring and mixing the said wastewater with magnesium containing solution in the lower section of said fluidized bed reactor to precipitate to co-precipitate ammonium and potassium struvite.

20. A process according to claims 18, 19 wherein magnesium chloride solution is added to the lower section of the fluidized bed reactor at Mg.sup.2+ to P2 molar ratio of 0.8 to 1.2.

21. A process according to claim 19 wherein alkaline solution is added to the said wastewater A in the feed tank to increase the pH to 9-11.

22. A process according to claims 18 19 and 11 wherein the effluent wastewater (C) is a dischargeable water with low concentrations of ammonium, phosphate and potassium.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0051] The present invention is described in conjunction with reference to the following drawings which illustrate embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way.

[0052] FIG. 1 is a schematic of an up flow reactor apparatus for phosphorus, nitrogen and potassium recovery from wastewater.

[0053] FIG. 2 is a schematic of a waste slurry treatment process to produce low nutrient water and organic biosolids fertilizer.

DETAILED DESCRIPTION OF EMBODIMENTS

[0054] According to a first preferred aspect of the present invention, there is provided an upflow fluidized bed reactor apparatus for phosphorus, nitrogen, and potassium recovery from wastewater.

[0055] In reference to FIG. 1, a schematic of nutrient recovery system is shown comprising a feed tank (1) for feed preparation, fluidized reactor vessel (5) for the precipitation and granulation of nutrients including phosphate, ammonium and potassium in wastewater, and a multifunctional external tank (25) for polishing the wastewater effluent from the fluidized reactor vessel.

[0056] The feed tank (1) is equipped with a valve (2), an air pump (3) for removing dissolved carbon dioxide and increasing pH of the untreated wastewater, an alkalinity pump (35) for adding external alkalinity source to the untreated wastewater to increase the alkalinity, and a chemical dosing pump (4) for adding the phosphoric acid to the untreated wastewater for increasing the phosphate concentration.

[0057] The fluidized reactor vessel (5) is comprised of a tubular lower section (6) having a diameter of d1 and a larger upper section (7) configured as tube or cone connected to the lower section (6) having a most upper section diameter of d2 where the d2/d1 is preferebly 1.516. The lower section (6) is equipped with a liquid inflow pump (8) connected to an inflow pipe (9) and valve (10) for transferring the untreated wastewater into the lower section (6), a chemical feed pump (11) connected to an inflow pipe (9) and valve (12) for injecting a magnesium solution into the lower section (6) of the reactor (5); a recycle pump (13) connected to an inflow pipe (9) and valve (14) for recycling the content of the upper section (7) to the lower section (6); an outflow pipe (15) and a sample valve (16) for withdrawing agglomerated phosphate containing crystals out of the lower section (6).

[0058] The upper section of the reactor (7) is comprised of an outflow recycle port (17) and an outflow effluent port (18) for transferring the treated wastewater out of the reactor (5). The vertical distance between outflow effluent port (18) and outflow recycle port (17) in the upper section (7) is at least 1.5 meters, but preferably 3-4, m to provide adequate retention time to the section above the recycle line. The outflow recycle port (17) is connected to a valve (19) on the outside of the upper section (7) and a recycle inflow pipe (20) with a funnel (21) at its end, located inside the upper section (7), for collecting the liquid and fine particles in the reactor's upper section (7). The untreated wastewater, magnesium solution and recycle flow are mixed in the lower section (6) of the reactor vessel (5) where precipitation of struvite occurs. The upper section (7) is equipped with a pH monitoring device (22). The outflow effluent port (18) is connected to a flow splitting device (23) and a valve (24) for directing a proration of effluent flow to the multifunctional external tank (25). The multifunctional external tank (25) may be operated as a seed injection tank, a biological reactor for removing organics and left over nutrients from the effluent of the fluidized reactor (5) The multifunctional external tank (25) is equipped with an effluent pipe (26) an air pump (27) for injecting air into the tank (25), an overflow pipe (28) for transferring the tank content to the clarifier section (29), recycle outflow port (30), and a pump (31) connected to a flow splitting device (34) and a valve (33) for directing a proration of flow to the inflow pipe (9) and valve (32) that transfers the content of the clarifier (29) to the lower section (6) and/or back to the multifunctional external tank (25).

[0059] According to a second preferred aspect of the present invention, there is provided a method for co-precipitation and granulation of ammonium and potassium struvite (NH4KMgPO4.6H.sub.2O) described in the first aspect of the invention in reference to FIG. 1.

[0060] The method comprises of pumping a seed material via a multifunctional external tank (25) to the lower section (6) of the fluidized bed reactor (5) wherein the seed material is fluidized by a recycle pump (13). Mixing of the untreated wastewater with phosphoric acid via a chemical dosing pump (4) to the wastewater having total alkalinity of A and initial concentrations of ammonium (N), phosphate (P), and potassium (K) to increase the phosphate concentration to P2 so that A/P2 mass ratio exceeds 4. Adding air to the solution to remove dissolved carbon dioxide and increasing the pH in the feed tank (1). Pumping the wastewater to the lower section (6) of the reactor (5), injecting magnesium solution to the lower section (6) of the said reactor (5), and adjusting the concentration of Mg so that the molar ratio of the wastewater nutrients has a Mg/P2 0.8.-1.2. This will result in precipitation of NH.sub.4KMgPO.sub.4.6H.sub.2O in the fluidized bed reactor (5) and production of reactor effluent. The reactor effluent is transferred to a multifunctional external tank (25) wherein the said reactor effluent is aerated by air pump (27) to strip out carbon dioxide and dissolved ammonia gas. The content of the multifunctional external tank (25) is transfer to the clarifier section (29) via an overflow pipe (28) wherein the fine struvite particles are captured and transferred to the lower section (6) of the fluidized bed reactor (5) wherein they are granulated to large particles having at least 1 mm in diameter.

[0061] According to other aspects of the present invention, the multifunctional external tank (25) is used as a biological reactor to remove more ammonia from the wastewater. This is achieved by turning off the pump (31), adding a mixture of anammox bacteria and nitrifying bacteria seed to the multifunctional external tank (25), and turning on the air pump (27). Aeration in the multifunctional external tank (25) provides the condition of biological ammonium removal by anammox bacteria wherein the dissolved oxygen concentration is kept below 2 mg/L.

[0062] According to a third preferred aspect of the present invention, there is provided a process for co-precipitation and granulation of ammonium and potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O) and production of dischargeable water described in the first aspect of the invention in reference to FIG. 1.

[0063] The process comprises of adding phosphoric acid via chemical dosing pump (4) to wastewater stored in the feed tank (1) having total alkalinity of A and initial concentrations of ammonium (N), phosphate (P), and potassium (K) to increase the phosphate concentration of the said wastewater to P2 wherein P2/K molar ratio<5.5.

[0064] Then, adding and mixing alkalinity via an alkalinity pump (35) to the said wastewater in the feed tank (1) to increase the pH to 9-11. Transferring the feed to the lower section (6) of the fluidized bed reactor (5) where the wastewater is mixed with external magnesium salt solution (Mg), particularly MgCl.sub.2, at Mg/P2 molar ratio of 0.8-1.2.

[0065] Treating the said wastewater in the fluidized bed reactor (5) to remove residual dissolved CO2 and strip ammonia, maintaining pH at 9-11, which results in formation of ammonium and potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O) and alkalinity removal during struvite formation; then, separating precipitated solids containing NPK from liquid in the upper section (7) of the fluidized bed reactor (5) followed by further polishing the treated wastewater in the multifunctional external tank (25). The content of the multifunctional tank (25) is transferred to the clarifier section (29) via an overflow pipe (28) wherein the fine struvite particles are captured and transferred to the lower section (6) of the fluidized bed reactor (5) wherein they are granulated to large particles.

[0066] In reference to FIG. 2, a schematic of a waste slurry treatment process to produce low nutrient water and organic biosolids fertilizer is provided.

[0067] The process comprises of transferring the waste slurries (42) to a precipitation tank (36) that is equipped with an inflow pipe (37) for transferring the waste slurries into the tank (36), mixing device (38), an aeration device (39) for injecting air into the precipitation tank (36), an outflow pipe (40) connected to a solids separation device (41) for transferring the content of the tank (36) to the solids separation device (41). The solids separation device (41) separates the waste slurries into low NPK water and high NPK biosolids that exit the solids separation device (41) via two separate discharge ports: solids discharge port (50) and liquid discharge port (49).

[0068] The waste slurries having total alkalinity of A and initial concentrations of ammonium (N), phosphate (P), and potassium (K) is mixed with phosphoric acid (43) to increase the phosphate concentration to P2 so that A/P2 mass ratio exceeds 4. Adding air via aeration device (39) to the mixture in the precipitation tank (36) to remove dissolved carbon dioxide and increase the pH.

[0069] Adding external magnesium (Mg) salt (44) to the precipitation tank at Mg/P2 molar ratio of 0.8-1.2.

[0070] Mixing and/or aerating the said waste slurries to remove residual dissolved CO2, reaching pH of at least 7 which results in the formation of ammonium and potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O) and alkalinity removal during struvite formation. Separating solids from the liquid using a solids separation device (41) separates the waste slurries into low NPK water (45) and high NPK biosolids (46). The high NPK biosolids (46) are further dried and pelletized (47). The described system can be incorporated as part of the conventional solids separation systems such as dissolved air flotation, centrifuge, screw press, or rotary press systems where the sludge premixing tank is retrofitted to add magnesium and phosphoric acid ports.

[0071] In another aspect of the waste slurry treatment process, the NPK removal from the slurry is maximized through simultaneous struvite formation and ammonia stripping. The method comprises of simultaneously removing NPK from waste slurry by adding external alkalinity, phosphoric acid (P2), and magnesium (Mg) to the waste slurry containing initial concentrations of ammonium (N1), phosphate (P1), and potassium (K1). The method comprises of adding phosphoric acid to waste slurry first to increase the phosphate concentration of the said waste slurry to P2 wherein P2/K molar ratio<5.5.

[0072] Then adding and mixing alkalinity (48) to the said waste slurry to increase the pH and alkalinity. Adding magnesium chloride (Mg) solution at Mg/P2 molar ratio of 0.8-1.2; mixing and/or aerating the said waste slurry to simultaneously remove dissolved CO2 and ammonia, which results in formation of ammonium and potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O) and alkalinity removal during struvite formation. Separating precipitated solids containing NPK from the liquid using a solids separation device (41) produces low NPK water (45) and high NPK biosolids (46). The described system can be incorporated as part of the conventional solids separation systems such as dissolved air flotation, centrifuge, screw press, or rotary press systems where the sludge premixing tank is retrofitted to add magnesium, phosphoric acid, and alkalinity ports.

Example 1

[0073] A method for removal of ammonium, potassium, and phosphate from wastewater streams without additional external alkaline source and addition of phosphoric acid is described in the following example.

[0074] 25 mL of food waste digestate with initial ammonium, phosphate, potassium (K), and alkalinity (A1) concentrations of 2260 ppm N, 39 ppm P, 1208 ppm K, and 12500 ppm CaCO3 respectively was spiked with phosphoric acid (75% concentration) to increase the phosphate (P2) concentration to 3110 ppm P so that the P2/K molar ratio becomes 2.97 and the A1/P2 mass ratio exceeds 4. Then, air was added to the wastewater for 60 minutes to remove dissolved carbon dioxide and increase the pH from 7.91 to 8/1. After, magnesium chloride (Mg) was added to the solution at Mg/P2 molar ratio of 0.8. The solution was mixed and aerated to remove residual CO2 and maintain the pH of at least 7 for 10 min which resulted in the formation of ammonium potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O). Struvite was separated from the treated food waste digestate using a centrifuge; the food waste digestate had a final ammonium, phosphate, and potassium concentrations of 1122 ppm N, 61 ppm P, and 1127 ppm K respectively. The ammonium, phosphate, and potassium removal rates were determined to be 50%, 98%, and 14% respectively.

TABLE-US-00001 Initial Sample Final Sample Removal Rates (ppm) (ppm) (%) Ammonium 2260 1122 50 Phosphate 39 61 98 Potassium 1316 1127 14 Alkalinity 12500 875 93

Example 2

[0075] An improved method for removal of ammonium, potassium, and phosphate from wastewater streams with addition of phosphoric acid and external alkaline source is described in the following example.

[0076] 50 mL of food waste digestate with initial ammonium, phosphate, and potassium (K) concentrations of 1030 ppm N, 250 ppm P, and 1472 ppm K respectively was spiked with phosphoric acid (75% concentration) to increase the phosphate (P2) concentration to 5865 ppm P so that the P2/K molar ratio becomes 5.01. Then, the food waste digestate was mixed with 5N sodium hydroxide (external alkalinity source) so that the alkalinity increased from 4500 ppm CaCO3 to 14089 ppm CaCO3 and the pH increased from 8.13 to 11.56. After, magnesium chloride (Mg) was added to the solution at Mg/P2 molar ratio of 0.8. The solution was mixed and aerated to remove residual CO2 and maintain the pH of at least 11 for 30 min which resulted in the formation of ammonium potassium struvite (NH.sub.4KMgPO.sub.4.6H.sub.2O) and simultaneously stripping the residual ammonia. Struvite was separated from the treated food waste digestate using a centrifuge; the food waste digestate had a final ammonium, phosphate, and potassium concentrations of 151 ppm N, 70 ppm P, and Oppm K respectively. The ammonium, phosphate, and potassium removal rates were determined to be 85%, 99%, and 100% respectively.

TABLE-US-00002 Initial Sample Final Sample Removal Rates (ppm) (ppm) (%) Ammonium 1030 151 85 Phosphate 250 70 99 Potassium 1472 0 100

Example 3

[0077] A method for removal and granulation of ammonium and phosphate from wastewater streams without additional external alkaline source and phosphoric acid in the fluidized bed reactor is described in the following example.

[0078] Struvite seeds were initially seeded to the fluidized bed reactor (FIG. 1) by pumping the seed material via the multifunctional external tank to the lower section of the fluidized bed reactor via the pump. Municipal centrate was fed to the lower section of the fluidized bed reactor via the liquid inflow pump with initial ammonium and phosphate (P) concentrations of 838 ppm N and 144 ppm P respectively at a rate of 300 mL/min. The solution in the upper section was recycled back to the lower section via a recycle pump that was set at a minimum of 2000 mL/min to provide fluidization. 0.5M magnesium chloride (Mg) was added to the lower section of the fluidized bed reactor at a rate of 3.4 mLlmin so that the Mg/P molar ratio was 1.2. Then, struvite granulated to large particles over 100 hours and was separated from the treated municipal centrate through the sample valve at the bottom of the lower section; the treated municipal centrate exited the fluidized bed reactor through the outflow effluent port located in the upper section of the reactor and had a final ammonium and phosphate concentrations of 749 ppm N and Oppm P respectively. The ammonium and phosphate removal rates were determined to be 11% and 100% respectively.

TABLE-US-00003 Initial Sample Final Sample Removal Rates (ppm) (ppm) (%) Ammonium 838 749 11 Phosphate 144 0 100

Example 4

[0079] A method for removal and granulation of ammonium, phosphate, and potassium from wastewater streams with additional external alkaline source and phosphoric acid in the fluidized bed reactor is described in the following example.

[0080] Struvite seeds were initially seeded to the fluidized bed reactor (FIG. 1) by pumping the seed material via the multifunctional external tank to the lower section of the fluidized bed reactor via the pump. 280 mL of phosphoric acid (75% concentration) and was added to 200 L of digestate stored in the feed tank having total alkalinity of 4500 mg/L CaCO3 and initial ammonium, phosphate, and potassium (K) concentrations of 619 ppm N. 144 ppm P, and 1520 ppm K to increase phosphate (P2) concentration of the municipal centrate to 777 ppm P wherein P2/K molar ratio is 0.64. Then, 880 g of sodium hydroxide was added to the 200 L of the said solution to increase the pH to 9.85. The said municipal centrate was fed to the lower section of the fluidized bed reactor via the liquid inflow pump at a rate of 31 mL/min. 0.5M magnesium chloride (Mg) was added to the lower section of the fluidized bed reactor at a rate of 1.8 mL/min so that the Mg/P2 molar ratio was 1.2. Then, struvite granulated to large particles over 24 hours and was separated from the liquid through the sample valve at the bottom of the lower section. The liquid exited the fluidized bed reactor through the outflow effluent port located in the upper section of the reactor into the multifunctional external tank where the fine struvite particles were captured in the clarifier section and were recycled back to the lower section via the pump that was set at a minimum of 1800 mL/min to provide fluidization. The treated municipal centrate exited the multifunctional external tank via the effluent pipe and had a final ammonium, phosphate, and potassium concentrations of 60 ppm N, Oppm P, and 992 ppm K respectively. The ammonium, phosphate, and potassium removal rates were determined to be 87%, 100%, and 35% respectively.

TABLE-US-00004 Initial Sample Final Sample Removal Rates (ppm) (ppm) (%) Ammonium 619 60 87 Phosphate 144 0 100 Potassium 0 992 35