Method, System and Stable for Phosphate Recovery from a Waste Stream

Abstract

The invention relates to a method and system for phosphate recovering from a waste stream, such as an animal manure waste stream. The method comprises the steps of: - providing a tank reactor, 5 - providing acidogenic bacteria and/or acetogenic bacteria and the waste stream to the tank reactor, - hydrolysing the waste stream, forming a reaction mixture; - providing a gas flow to the reaction mixture for removing carbon dioxide from the reaction mixture; 10 - providing the reaction mixture to an anaerobic sludge reactor, - removing a compound comprising phosphate from the reaction mixture within the anaerobic sludge reactor, and - removing gas from the reaction mixture within the anaerobic sludge reactor.

Claims

1. A method for phosphate recovery from a waste stream, such as an animal manure waste stream, comprising the steps of: providing a tank reactor; providing acidogenic bacteria and/or acetogenic bacteria and providing the waste stream to the tank reactor; hydrolysing the waste stream, and forming a reaction mixture with a compound comprising phosphate; providing a gas flow to the reaction mixture for removing carbon dioxide from the reaction mixture; providing the reaction mixture to an anaerobic sludge reactor; removing the compound comprising phosphate from the reaction mixture within the anaerobic sludge reactor; and removing gas from the reaction mixture within the anaerobic sludge reactor.

2. The method according to claim 1, wherein the waste stream is an animal manure waste stream.

3. The method according to claim 1, further comprising the step of adding a compound comprising calcium to the tank reactor.

4. The method according to claim 1, further comprising the step of adding a compound comprising calcium to the anaerobic sludge reactor.

5. The method according to claim 1, further comprising the step of separating the waste stream into a thick fraction and a thin fraction prior to the providing the waste stream to the tank reactor step, and wherein the thin fraction is provided to the tank reactor.

6. The method according to claim 5, wherein the step of separating comprises sieving the waste stream, wherein the sieving is preferably performed using a drum sieve.

7. The method according to claim 1, further comprising the step of providing a gas flow to the anaerobic sludge reactor prior to and/or in the step of removing a compound comprising phosphate from the reaction mixture within the anaerobic sludge reactor, wherein the gas flow provided to the anaerobic sludge reactor comprises gas from the step of providing a gas flow to the reaction mixture for removing carbon dioxide from the reaction mixture.

8. The method according to claim 1, further comprising the step of adding hydrogen gas to the anaerobic sludge reactor prior to and/or in the step of removing the compound comprising phosphate from the reaction mixture within the anaerobic sludge reactor.

9. The method according to claim 1, wherein the gas flow provided to the tank reactor comprises gas from the step of removing gas from the reaction mixture within the anaerobic sludge reactor, and/or wherein the reaction mixture within the tank reactor has a DH in the range of 4 to 7, preferrably a pH in the range of 4 to 6, and most preferably a pH in the range of 5 to 6. and wherein the reaction mixture within the anaerobic sludae reactor comDrises a pH of at least 6, preferably a pH of at least 7, and most preferably a DH of at least 7.5.

10. (canceled)

11. The method according to claim 1, further comprising the step of heating the waste stream prior to the step of hydrolysing waste stream, wherein the waste stream is heated to at least 45° C., preferably to at least 50° C., and most preferably to at least 55° C.

12. The method according to claim 1, wherein the step of providing the waste stream to the tank reactor is performed at an organic loading rate in the range of 2 to 7 kg COD/m3 .Math.d, preferably at an organic loading rate in the range of 3 to 6 kg COD/m3 .Math.d.

13. The method according to claim 1, further comprising the step of removing a compound comprising nitrogen and/or the step of removing a compound comprising sulphur after and/or during the step of removing gas from the reaction mixture within the anaerobic sludge reactor.

14. The method according to claim 1, wherein the acidogenic bacteria and/or acetogenic bacteria is one or more selected from the group of: Thermoplasmatales, MBA03 of the class Clostridia, Hydrogenispora sp., Halocella sp., Fermentimonas sp., Proteiniphilum sp., Candidatus Methanoplasma sp., Methanoculleus ssp., Methanobrevibacter sap., Sphaerochaeta ssp..

15. A system for phosphate recovering from a waste stream, such as an animal manure waste stream, comprising: a tank reactor for performing hydrolysis with acidogenic bacteria and/or acetogenic bacteria comprising: a gas inlet; a gas outlet; a waste stream inlet; and a reaction mixture outlet; and an anaerobic sludge reactor, comprising: a reaction mixture inlet, which is operatively coupled to the reaction mixture outlet of the tank reactor; a gas inlet; a particle outlet; a gas outlet; and a liquid outlet.

16. The system according to claim 15, wherein the gas outlet of the anaerobic sludge reactor is operatively coupled to the gas inlet of the tank reactor.

17. The system according to claim 15, wherein the system further comprises a screw press which is operatively coupled with the waste stream inlet of the tank reactor, and is configured to separate the waste stream into a thick fraction and a thin fraction, wherein the thin fraction is provided to the tank reactor, and/or wherein the anaerobic sludge reactor further comprises at least one pneumatic valve which is configured to add a compound comprising calcium in a controlled manner.

18. (canceled)

19. The system according to claim 15, wherein the system further comprises heating means, wherein the heating means are operatively coupled to the tank reactor to heat the waste stream.

20. The system according to claim 15, wherein the system further comprises a nitrogen removal reactor for removing a compound comprising nitrogen, and/or wherein the system further comprises a sulphur removal reactor for removing a compound comprising sulphur, wherein the sulphur removal reactor is aerated.

21. (canceled)

22. The system according to claim 15, further comprising a manure pit, wherein the manure pit is operatively coupled to the tank reactor.

23. A stable for phosphate recovering from a waste stream, such as an animal manure waste stream, comprising the system according to claim 15.

Description

[0159] FIG. 1 shows a schematic overview of the method according to the present invention; [0160] FIG. 2 shows an embodiment of the system capable of performing the method described in the description; [0161] FIG. 3 shows the liberation of phosphorus into solution; and [0162] FIG. 4 shows the effect of addition of a calcium chloride to the anaerobic sludge reactor.

[0163] Method 2 (FIG. 1) for phosphate recovering from a waste stream follows a sequence of different steps.

[0164] In the illustrated embodiment method 2 may start with step 10 of separating the waste stream into a thick fraction and a thin fraction prior to the providing the waste stream to the tank reactor step.

[0165] Step 12 of providing a tank reactor is followed by step 14 of providing acidogenic bacteria and/or acetogenic bacteria and the waste stream to the tank reactor, wherein the thin fraction of step 10 is used as waste stream. The waste stream is treated in step 16 of hydrolysing the waste stream, and forming the reaction mixture.

[0166] In an alternative embodiment according to the invention, step 18 of adding a compound comprising calcium prior to and/or in the step of hydrolysing the waste stream is performed before step 16.

[0167] In another alternative embodiment according to the invention or in addition to the previous embodiment, the step of heating the waste stream prior to the step of hydrolysing waste stream, wherein the waste stream is heated to at least 45° C., preferably to at least 50° C., and more preferably to at least 55° C. 32 is performed before step 16.

[0168] Step 16 is performed together with or followed by step 20 of providing a gas flow to the reaction mixture for removing carbon dioxide from the reaction mixture.

[0169] In an alternative embodiment the gas is the removed gas from the reaction mixture within the anaerobic sludge reactor.

[0170] Step 20 is then followed by step 22 of providing the reaction mixture to an anaerobic sludge reactor. From the anaerobic sludge reactor the compound comprising phosphate may be removed in step 24 of removing a compound comprising phosphate from the reaction mixture within the anaerobic sludge reactor.

[0171] In an alternative embodiment the step of adding a compound comprising calcium after the step of providing the reaction mixture to the anaerobic sludge reactor 25 may be performed before step 24.

[0172] In another alternative embodiment according to the invention or in addition to any one of the previous embodiments hydrogen gas is added to the anaerobic sludge reactor by step 30 of adding hydrogen gas to the anaerobic sludge reactor.

[0173] Step 24 is followed by step 26 of providing a gas flow to the anaerobic sludge reactor.

[0174] Preferably, the gas flow provided to the anaerobic sludge reactor comprises gas from step 20. From the anaerobic sludge reactor gas is removed by step 28 removing gas from the reaction mixture within the anaerobic sludge reactor. The removed gas may be used in step 20.

[0175] Preferably the reaction mixture is then provided to the nitrogen removal reactor and/or sulphur removal reactor by step 34 of providing the reaction mixture to the nitrogen removal reactor and/or sulphur removal reactor. The recovery/removal of the compound comprising nitrogen and/or compound comprising sulphur is performed by step 36 of removing a compound comprising nitrogen and/or step 38 of removing a compound comprising sulphur after the step of removing gas from the reaction mixture within the anaerobic sludge reactor.

[0176] System 50 (FIG. 2) comprises tank reactor 52 for performing hydrolysis with acidogenic bacteria and/or acetogenic bacteria. Tank reactor 52 comprises gas inlet 54, gas outlet 56, waste stream inlet 58, and reaction mixture outlet 60. Waste stream inlet 58 and reaction mixture outlet 60 preferably comprise a valve (not shown) to control the input and output of tank reactor 52. Tank reactor 52 further comprises stirring means 62 enabling to continuously stir reaction mixture 64.

[0177] System 50 further comprises anaerobic sludge reactor 66. Anaerobic sludge reactor 66 comprises reaction mixture inlet 68, gas inlet 70, particle outlet 72, gas outlet 74, and liquid outlet 76. Anaerobic sludge reactor 66 enables formation of particles 88.

[0178] Reaction mixture inlet 68 is operatively coupled to reaction mixture outlet 60 via pipe 75. Pipe 75 comprises valve 80, wherein valve 80 controls the mixing of the reaction mixture with stream 82. Stream 82 may comprise additional waste stream, additives, solvent, and the like.

[0179] In an alternative embodiment gas inlet 54 and gas outlet 74 are operatively connected via pipe 86. In another alternative embodiment gas inlet 70 and gas outlet 56 are operatively coupled via pipe 84.

[0180] Pipe 84 comprises valve 85 to control the gas flow from tank reactor 52 and may provide additional gas to anaerobic sludge reactor 66.

[0181] Pipe 86 comprises valve 100 to control the gas stream from anaerobic sludge reactor 66.

[0182] In order to control the addition of a compound comprising calcium to tank reactor 52 and/or anaerobic sludge reactor 66, tank reactor 52 and/or anaerobic sludge reactor 66 may comprise pneumatic valve 90 and/or pneumatic valve 92 respectively. Pneumatic valve 90 is operatively connected to tank 91 and pneumatic valve 92 is operatively connected to tank 93.

[0183] Furthermore, tank reactor 52 and/or anaerobic sludge reactor 66 may comprise heating means 94 and/or heating means 96 respectively. The heating means may heat the waste stream and/or reaction mixture in order to increase the reactions within tank reactor 52 and/or anaerobic sludge reactor 66.

[0184] System 50 further comprises screw press 98 which is operatively coupled with waste stream inlet 58 and nitrogen removal tank 102. Screw press 98 is configured to separate the waste stream in a thick fraction and thin fraction, and wherein the thin fraction is provided to tank reactor 52.

[0185] Liquid outlet 76 is operatively to nitrogen removal reactor 102 via pipe 104 and 106. Pipe 104 provides the reaction mixture to nitrogen removal reactor 102 and pipe 106 may provide gasses via inlet 108 to anaerobic sludge reactor 66. Such gasses may be for example hydrogen.

[0186] System 50 further comprises sulphur removal tank 110 which is operatively coupled with nitrogen removal tank 102 via pipe 112. Sulphur removal tank 110 is aerated and further comprises outlet 114.

[0187] System 50 further comprises manure pit 116 which is operatively coupled to screw press 98 to provide a waste stream to tank reactor 52. Such waste stream may be animal manure.

[0188] In an alternative embodiment nitrogen removal tank 102 and sulphur removal tank 110 are swapped.

[0189] Optionally, a buffer tank may be arranged between tank reactor 52 and anaerobic sludge reactor 66, wherein said buffer tank is operatively coupled with tank reactor 52 and anaerobic sludge reactor 66.

[0190] Experiments show that the liberation of phosphorus into solution provides good results (FIG. 3). The soluble phosphate and phosphorus concentrations are plotted against final measured pH for manure of a cow at 25° C. The lines TP and SP represent total phosphorus (TP) and soluble phosphorus (SP). The x-axis comprises pH, the y-axis comprises phosphate concentration (mg/L) and phosphorus concentration (mg/L). The square represents the phosphate mean and the tringle represents the phosphorus mean.

[0191] Further experiments show that a lab pilot provides good results for the recovery of phosphate (FIG. 4). FIG. 4 proves that the method and system according to the invention provide efficient and effective recovery of phosphate. It can be concluded that the addition of a compound comprising calcium increases the phosphorus removal. The compound comprising calcium was in this particular case CaCO.sub.3.The x-axis represents the operation time in days (d) and the y-axis represents the phosphorus removal (%).

[0192] Further experiments show the influence of a calcium composition addition, wherein the addition of the calcium composition was tested in two 45 Litre anaerobic sludge reactors for 455 days (Table 1). The process and reaction conditions in both reactors were the same, except that to the first reactor the calcium composition was added and to the second reactor no compound comprising calcium was added.

[0193] It is noted that the composition comprising calcium did not include any phosphorus.

TABLE-US-00001 TABLE 1 influence of addition of compound comprising calcium Time No calcium addition Calcium addition (days) Pt in sd Pt out sd Pt in sd Pt out sd 27 527 1 482 4 514 11 442 1 34 529 8 442 7 543 8 384 7 41 504 13 468 11 502 8 350 4 49 484 0 378 8 471 5 219 1 55 538 4 411 1 540 0 415 6 62 542 3 429 1 403 1 311 2 69 475 24 388 7 488 4 164 2 76 505 2 360 3 508 1 142 2 81 490 7 304 1 487 0 195 1 90 489 0 241 8 485 14 115 0 96 502 7 412 2 523 28 136 1 104 473 6 448 4 480 4 106 0 109 471 0 353 7 467 1 118 7 118 488 6 435 1 501 17 97 1 125 476 7 408 8 494 12 185 4 132 492 6 436 6 531 3 123 0 139 497 10 444 4 503 6 191 2 146 497 5 410 1 487 6 150 0 153 464 1 459 5 469 1 198 3 160 472 0 460 2 585 10 215 1 168 531 3 403 13 552 6 129 2 176 518 5 339 9 585 3 187 3 183 545 4 433 1 526 9 204 1 189 494 24 382 1 477 25 96 1 195 548 3 415 8 549 27 138 2 202 472 8 398 5 499 2 307 4 209 492 6 344 9 532 9 241 5 216 464 9 204 3 610 0 96 3 223 492 16 120 1 488 2 92 2 230 438 4 116 3 483 8 96 1 237 471 11 92 3 519 6 101 1 244 391 7 96 3 496 4 106 8 251 362 1 104 2 383 3 110 3 258 392 25 105 5 406 11 226 1 265 455 7 122 1 523 8 114 1 272 419 5 102 0 481 1 101 1 279 386 16 92 1 411 4 110 1 286 437 26 101 8 448 12 125 4 320 451 94 1 477 99 0 336 83 2 81 1 356 654 30 146 3 606 8 132 3 369 591 0 585 6 546 9 141 1 404 529 4 504 1 529 4 379 1 456 563.75 11.25 223 7 564 11 223 3

[0194] In Table 1 Pt refers to total phosphorus present as solid or aqueous species. Pt in refers to the phosphorus entering the reactor as (diary) manure in mg/L, and Pt out refers to the phosphorus leaving the reactor in the effluent in mg/L. Furthermore, sd is the standard deviation of the analysis of two samples taken from the influent/effluent.

[0195] Table 1 shows that the addition of calcium helps to retain phosphorus in the anaerobic sludge reactor and to recover it form said reactor. Furthermore, this shows that calcium binds to phosphorus and forms solids which are separate by gravimetric induced separation. Calcium has also a positive effect on the retention of other solids, such as biomass, by bridging between negatively charged sites of different compounds with its divalent positive charge. This may induce agglomeration, which is enhancing gravimetric separation and retention in the anaerobic sludge reactor. Therefore, Table 1 shows that Pt out is affected by the addition of calcium.

[0196] Further experiments show that calcium addition may be performed to increase the concentration of calcium and therefore to increase the concentration of calcium ions.

[0197] In this experiment the set up according to FIG. 2 was used. The effluent of the tank reactor was continuously pumped to the anaerobic tank reactor. The initial pH in the tank reactor was 5. This pH provides favouring conditions for acidogenic and acetogenic reactions over methanogenic reactions. To provide low starting pH (pH=5) different acids were tested, for example acetic acid, citric acid, and hydrogen chloride. It was found that the acetic acid provided sufficient recovery of phosphorus comprising compounds.

[0198] Preferably, the retention time in the tank reactor and/or anaerobic sludge reactor is long enough to keep the acid production higher than or equal to the acid consumption. Said conditions inhibit methanogens.

[0199] For example, the size of the tank reactor relative to the anaerobic sludge reactor may vary, such that a difference in loading of the reactor is achieved.

[0200] Further experiments showed that the system according to FIG. 2 enables sufficient production of organic acids in the tank reactor through degradation of organic matter. Furthermore, it was found that when an initial pH of about 5 and temperature between 45° C. and 80° C. of the waste stream provides effective and efficient degradation of organic matter. Furthermore, these conditions prevented further degradation of the organic acids. Furthermore, experiments showed that the preservation of the organic acids in the tank reactor was even more efficient when a buffer tank was used. Said buffer tank enables to condition the effluent of the tank reactor before it is provided to the anaerobic sludge reactor.

[0201] Further experiments showed that the addition of starch may steer the production of volatile fatty acids (VFA) and that this may keep the acidity level in the tank reactor at the desired pH of about 5. Furthermore, it was found that the addition of starch resulted in an increase of the VFA and H.sub.2 production.

[0202] The present invention is by no means limited to the above described preferred embodiments and/or experiments thereof. The rights sought are defined by the following claims within the scope of which many modifications can be envisaged.