IMPROVEMENTS IN RELATION TO WASTE TREATMENT

Abstract

A method of removing phosphates from water in a continuous process, the method comprising the steps of: (a) passing the water through a first zone in which the pH is adjusted; and (b) passing the water through a second zone in which the water is contacted with magnesium ions; wherein the water is contacted with ammonia in the first zone and/or in the second zone.

Claims

1. A method of removing phosphates from water in a continuous process, the method comprising the steps of: (a) passing the water through a first zone in which the pH is adjusted; and (b) passing the water through a second zone in which the water is contacted with magnesium ions; wherein the water is contacted with ammonia in the first zone and/or in the second zone.

2. The method according to claim 1, wherein the water is waste water from an industrial or environmental process.

3. The method according to claim 1, wherein the water provided is from a sewage treatment process; preferably from a sewage treatment process which includes an enhanced biological phosphate removal step.

4. The method according to claim 1, wherein the pH is increased in step (a).

5. The method according to claim 1, wherein a pH adjustment agent is added in step (a); preferably wherein the pH adjustment agent comprises sodium hydroxide.

6. The method according to claim 1, wherein a gas is bubbled through the water in step (a); preferably wherein the gas is air.

7. The method according to claim 1, wherein the pH of the water passing through the first zone is increased by the addition of an organic ash.

8. The method according claim 1, wherein the ammonia is provided as an ammonia solution.

9. The method according to claim 1, wherein the ammonia is provided by a waste stream rich in ammonia; preferably from an anaerobic digester digestate dewatering process.

10. The method according to claim 1, wherein the magnesium ions are provided by magnesium oxide and/or magnesium sulfate.

11. The method according to claim 1, which further includes a step passing the water through a third zone in which gas is bubbled through the water.

12. The method according to claim 1, which includes a heating step between step (b) and step (c) and/or during step (c).

13. The method according to claim 1, which includes a step (d) of collecting particles of struvite which form during the process.

14. The method according to claim 1, which includes a step before step (b) of determining the concentration of phosphate ions present in the water.

15. The method according to claim 14, wherein in step (b) the ammonia and magnesium ions are added in sufficient amounts to react with substantially all of the phosphate ions present to produce struvite.

16. An apparatus for removing phosphates from water, the apparatus comprising: water inlet means; water outlet means; a conduit to carry water from the inlet means to the outlet means; and a means for collecting solid materials; wherein the conduit is configured to carry water through at least two zones in which: a first zone is provided with means for adjusting the pH of water passing through that zone; and a second zone is provided with means for delivering magnesium ions into water passing through that zone; wherein the first zone and/or the second zone is provided with means for delivering ammonia into that zone.

17. The apparatus according to claim 16, wherein the means for adjusting the pH in the first zone comprises means for delivering a pH adjustment agent to water passing through that zone and/or means for bubbling gas through water passing through that zone.

18. The apparatus according to claim 16, which further comprises a third zone is provided with means for bubbling gas through water passing through that zone

19. The apparatus according to claim 18, which includes heating means configured to provide heated water to the third zone.

20. The apparatus according to claim 17, wherein the means for collecting solid materials comprises a movable belt or wherein the means for collecting solid materials comprises a screw conveyor.

21. (canceled)

Description

[0155] This invention will now be further described with reference to the accompanying drawings in which:

[0156] FIG. 1 shows an apparatus of the second aspect which includes a third zone;

[0157] FIG. 2 is an enlarged view of the ammonia recovery unit show in FIG. 1;

[0158] FIG. 3 is a cross sectional view of the second zone B of the apparatus of FIG. 1; and

[0159] FIGS. 4 to 19 are photographs of an apparatus of the invention in use.

[0160] Water is directed into the apparatus of the invention includes via the water inlet means 1. This may be closable by a tap or valve.

[0161] The water 4 passes along the conduit 2 and exits via the water outlet means 3.

[0162] The water passes through the conduit through a first zone A, a second zone B and a third zone C.

[0163] A movable belt 5 extends along the conduit. The flow of water into the conduit is controlled to ensure a headspace 6 for air and other gases.

[0164] Air is blown into the first zone A via pipe 7.

[0165] The water then passes into the second zone B.

[0166] Ammonia solution is dosed into the water via pipe 8 and magnesium oxide is delivered via inlet 9. This leads to the formation of struvite particles 10 which precipitate and settle onto belt 5.

[0167] A part of this zone of the apparatus is shown in cross section in FIG. 3. Struvite particles 10 settle on belt 5. Rubber seals 51 stop the water from leaking below the belt. The walls of the conduit include cut out overflow portions 50 through which water in the upper region of the zone can drain as indicated by arrows 52. This water is collected and recirculated into zone B, for example via addition to pipe 9.

[0168] The water is heated by heating coil 11 from about 20° C. when it is in the second zone to about 45° C. in the third zone C. In the third zone C air is bubbled through the water via pipe 12. The struvite carried on the belt is lifted out of the water after the third zone and deposited in receptable 13.

[0169] Ammonia and nitrogen or air in the headspace are directed via outlet 14 and pipe 15 into the ammonia recovery unit 16 which removes ammonia from the nitrogen and air giving a stream 17 that may be recirculated back through zone C; and ammonia solution 19 via pipe 18. The ammonia solution may also be reused in the process.

[0170] Water exiting may be directed to a water course via outlet 20 or to the ammonia recovery unit via valve 21.

[0171] The ammonia recovery unit shown in FIG. 2 includes a conduit 30 through which water flows entering by inlet 31 and exiting via outlet 32.

[0172] The water is chilled to around 15° C. by chiller coil 41. There is a headspace 33 for gases. This is divided into sections by partitions 34 which extend across the headspace but not fully through the depth of the water.

[0173] Ammonia enriched air from the headspace 6 in the struvite formation apparatus is directed into a first section I via pipe 35. The pipe is configured to provide bubbles having a diameter of 1 to 100 microns, preferably 1 to 25 microns. These pass through the liquid. Gases from the headspace above section I are compressed using compressor 36.

[0174] The compressed gases X are then directed into pipe 37 which delivers bubbles having a diameter of 1 to 100 microns, preferably 1 to 25 microns into section II. A second compressor 38 delivers gases Y into a third section III via pipe 39.

[0175] Clean air exits via outlet 40 and an approximately 20% ammonia solution is provided via outlet 32.

[0176] The skilled person will appreciate that the number of sections in the ammonia recovery unit may be varied.

[0177] FIG. 4 is a photograph of an apparatus of the invention including first and second zones. The first zone is closest to the camera in FIG. 5 and the belt can be seen rising out at the end past the second zone.

[0178] FIG. 6 is a photograph of the second zone and FIG. 7 shows the means for collecting the struvite.

[0179] FIG. 8 shows an overflow slot in the side of the wall of the second zone.

[0180] FIG. 9 shows struvite settled on the belt and FIG. 10 shows collected struvite which has been dried in an oven.