Water Treatment Method for Simultaneous Abatement of Carbon, Nitrogen and Phosphorus, Implemented in a Sequencing Batch Moving Bed Biofilm Reactor

Abstract

Water treatment method for simultaneous abatement of carbon, nitrogen and phosphorus, implemented in a sequencing batch moving bed biofilm reactor (SBMBBR) comprising carriers suitable for the development of a biofilm. The method comprises sequences of successive treatments, each treatment sequence comprising:

an initial phase of anaerobic treatment,

said initial phase of anaerobic treatment being followed by at least one aerobic/anoxic cycle consisting of: an aerobic treatment phase so as to obtain an ammonium ion concentration that does not pass below a threshold concentration of ammonium ions; and

a phase in which the biofilm is placed, at least locally, under anoxic conditions, this phase being concomitant with or posterior to said aerobic treatment phase; the threshold concentration of ammonium ions being calculated to allow the development of Anammox microorganisms during the phase in which the biofilm is placed, at least locally, under anoxic conditions.

Claims

1. Water treatment method for simultaneous abatement of carbon, nitrogen and phosphorus, implemented in a sequencing batch moving bed biofilm reactor (SBMBBR) comprising carriers suitable for the development of a biofilm, said method comprising sequences of successive treatments, each treatment sequence comprising: an initial phase of anaerobic treatment, said initial phase of anaerobic treatment being followed by at least one aerobic/anoxic cycle comprising: an aerobic treatment phase so as to obtain an ammonium ion concentration that does not pass below a threshold concentration of ammonium ions; and a phase in which the biofilm is placed, at least locally, under anoxic conditions, this phase being concomitant with or posterior to said aerobic treatment phase; the threshold concentration of ammonium ions being calculated to allow the development of anammox microorganisms during the phase in which the biofilm is placed, at least locally, under anoxic conditions.

2. Method according to claim 1, wherein the threshold concentration of ammonium ions is ≥1 mg N/L.

3. Method according to claim 1 wherein, for each treatment sequence the SBMBBR has a volume exchange ratio (ERV) between 90% and 100%.

4. Method according to any one of claim 1, wherein for each biological treatment cycle, the anaerobic treatment phase lasts from 30 minutes to 5 hours and the at least one aerobic/anoxic cycle lasts from 1 hour to 10 hours.

5. Method according to any one of claim 1, wherein for each cycle of the at least one aerobic/anoxic treatment cycle, the phase in which the biofilm is placed under anoxic conditions is posterior to the aerobic phase, and the ratio between the duration of the aerobic phase and the total duration of the aerobic-anoxic phase is between 0.2 and 0.8.

6. Method according to claim 1, wherein said carriers are capable due to their geometry to remain in close proximity to each other when the aeration intensity is moderate, thus forming local anoxic conditions during an aerobic treatment phase.

7. Method according to claim 1, wherein there is no pre-seeding with anammox microorganisms and denitrifying polyphosphate accumulative organisms (DPAOs).

8. Method according to any one of claim 1, wherein there is no addition of an external source of carbon and/or there is no addition of an external source of metal salts.

9. A method of biologically treating water containing carbon, nitrogen and phosphorus and removing carbon, nitrogen and phosphorus from the water, comprising: directing the water into an SBMBBR containing biofilm carriers; subjecting the water to sequences of successive treatments in the SBMBBR, each treatment sequence comprising: an initial phase of aerobic treatment; after the initial phase of aerobic treatment, subjecting the water in the SBMBBR to at least one aerobic/anoxic cycle comprising: an aerobic treatment phase that maintains an ammonium ion concentration in the water greater than a threshold concentration; and a phase in which the biofilm carriers are maintained, at least locally, under anoxic conditions with this phase occurring in the aerobic treatment phase or after the aerobic treatment phase; and wherein the threshold concentration of ammonium ions is set to allow the development of anammox microorganisms during the phase in which the biofilm carriers are maintained, at least locally, under anoxic conditions.

10. The method of claim 9 wherein the method gives rise to DPAOs and wherein the method includes utilizing the DPAOs to accumulate polyphosphates in the water being treated.

11. The method of claim 10 wherein the method is performed without pre-seeding the water with anammox or DPAO microorganisms.

12. The method of claim 11 wherein the method is carried out without any addition of an external source of carbon or an external source of metal salts.

13. The method of claim 9 wherein the threshold of ammonium ion concentration is set at 1 mg N/L or higher.

14. The method of claim 9 wherein during the phase in which the biofilm carriers are maintained, at least locally, under anoxic conditions, the anammox and DPAO microorganisms transforms NH.sub.4.sup.+NO.sub.2.sup.− and NO.sub.3.sup.− into nitrogen without requiring an external source of carbon and at the same time the DPAOs also remove phosphorus from the water by accumulation.

15. The method of claim 9 wherein in each treatment sequence, the SBMBBR has a volume exchange ratio (ERV) between 90% and 100%.

16. The method of claim 9 wherein for each biological treatment cycle, the anaerobic treatment phase lasts from 30 minutes to 5 hours and at least one aerobic/anoxic cycle lasts from 1 hour to 10 hours.

17. The method of claim 9 wherein said biofilm carriers include a particular geometry that is configured to cause the biofilm carriers to remain in close proximity to each other during aeration in the SBMBBR so as to form local anoxic conditions during the aerobic treatment phase.

Description

LIST OF FIGURES

[0049] The invention, as well as its various advantages, will be more readily understood with the following description of two non-restrictive embodiments thereof, as well as one embodiment of a conventional method that is not part of the invention, with reference to the following figures:

[0050] FIG. 1 is a graph showing the nitrogen concentration of the ammonia ion (NH.sub.4.sup.+) at the input of the SBMBBR (left-y-axis; mg N/L), the soluble global nitrogen (soluble NGL=soluble TKS+NO.sub.2−+NO.sub.3.sup.−) concentration at the output of the SBMBBR (left-y-axis; mg N/L) and the soluble global nitrogen removal efficiency (right-y-axis; %) as a function of the operating days in a conventional SBMBBR method. The soluble global nitrogen content of the water to be treated is mainly ammonia nitrogen, the nitrite (NO.sub.2) and nitrate (NO.sub.3.sup.−) content being negligible at the input of the SBMBBR.

[0051] FIG. 2 is a graph showing the nitrogen concentration of the ammonia ion (NH.sub.4.sup.+) at the input of the SBMBBR (mg N/L), the soluble global nitrogen (soluble NGL) concentration at the output of the SBMBBR (mg N/L) and the soluble global nitrogen removal efficiency (%) as a function of the operating days in a method implemented according to the invention where the application of anoxic conditions is posterior to the aerobic phase. The soluble global nitrogen content of the water to be treated is mainly ammonia nitrogen, the nitrite (NO.sub.2.sup.−) and nitrate (NO.sub.3.sup.−) content being negligible at the input of the SBMBBR.

[0052] FIG. 3 is a graph showing the nitrogen concentration of the ammonia ion (NH.sub.4.sup.+) at the input of the SBMBBR (mg N/L), the global nitrogen (soluble NGL) concentration at the output of the SBMBBR (mg N/L) and the nitrogen removal efficiency (%) as a function of the operating days in a method implemented according to the invention where the application of anoxic conditions is concomitant with the aerobic phase. The soluble global nitrogen content of the water to be treated is mainly ammonia nitrogen, the nitrite (NO.sub.2.sup.−) and nitrate (NO.sub.3.sup.−) content being negligible at the input of the SBMBBR.

[0053] FIG. 4 is a graph showing the number of NOB bacteria in the biofilm (left-y-axis; NOB bacteria/m.sup.2 of biofilm carrier) and the number of Anammox bacteria in the biofilm (right-y-axis; Anammox bacteria/m.sup.2 of biofilm carrier) as a function of the test days and for the three implementations of the SBMBBR (conventional implementation on the left, implementation according to the invention where the application of anoxic conditions is posterior to the aerobic phase in the middle, implementation according to the invention where the application of anoxic conditions is concomitant with the aerobic phase on the right).

[0054] FIG. 5 is a graph showing the phosphate (PO.sub.4) concentration in the SBMBBR (left-y-axis; mg P/L), the nitrogen concentration of the ammonia ion (NH.sub.4.sup.+) in the SBMBBR (left-y-axis; mg N/L) and the nitrogen concentration of the nitrite ion (NO.sub.2.sup.−) in the SBMBBR (right-y-axis; mg N/L) during a single treatment cycle that took place during the implementation of the SBMBBR method according to the invention, where the application of anoxic conditions is posterior to the aerobic phase.

[0055] FIG. 6 is a graph showing the phosphate (PO.sub.4) concentration in the SBMBBR (left-y-axis; mg P/L), the nitrogen concentration of the ammonia ion (NH.sub.4.sup.+) in the SBMBBR (left-y-axis; mg N/L) and the nitrogen concentration of the nitrite ion (NO.sub.2.sup.−) in the SBMBBR (right-y-axis; mg N/L) during a single treatment cycle that took place during the implementation of the SBMBBR method according to the invention, where the application of anoxic conditions is concomitant with the aerobic phase.

DESCRIPTION OF DETAILED EMBODIMENTS OF THE INVENTION

[0056] Tests were carried out according to two embodiments of the invention and compared to the results obtained by another test implementing the “conventional” method in a SBMBBR that is not part of the invention.

[0057] Test 6.1-Conventional implementation of the “SBMBBR” used for comparison purposes and not being part of the invention.

[0058] For this implementation, “conventional” carriers were used, such as “K5” carriers from Anoxkaldnes™. These carriers are perfectly fluidised when the aeration required to achieve aerobic conditions is applied.

[0059] The “conventional” SBR cycles consists of two phases: an anaerobic phase followed by an aerobic phase.

[0060] The carriers are not seeded with Anammox bacteria before the start of the tests.

[0061] Their oxygen content in the reaction medium during the aerobic phase are maintained at values comprised between 4 and 5 mg O.sub.2/L.

[0062] With reference to FIG. 1, under these operating conditions, the soluble global nitrogen (soluble NGL) removal is comprised between 33 and 67%, thus reaching soluble global nitrogen concentrations in the treated water close to 25 mg N/L and always above 20 mg N/L over the 600 days of testing.

[0063] With reference to FIG. 4 (left part of the graph), the number of NOB bacteria per m.sup.2 of carrier is high and in the order of 10.sup.8 per m.sup.2 of carrier. The one of Anammox bacteria remains low, in the order of 10.sup.8 per m.sup.2 of carrier corresponding to the quantification limit of the analytical method.

[0064] Test 6.2-Implementation of a method according to the invention with the introduction of an anoxic phase posterior to the aerobic phase.

[0065] For this implementation, “conventional” carriers were used, such as “K5” carriers from Anoxkaldnes™. These carriers are perfectly fluidised when the aeration required to achieve aerobic conditions is applied.

[0066] The carriers were not seeded with Anammox bacteria before the start of the tests. Until day 350, the SBMBBR operates in a conventional manner, with treatment cycles alternating between a 2-hour anaerobic phase and a 6-hour aerobic phase. This period corresponds to a seeding of the biofilm with dephosphating and nitrifying bacteria.

[0067] From day 350, an anoxic phase is added after the aerobic phase. Typically, the duration of the different operating phases is 2 to 3 hours for the anaerobic phase, 4 to 5 hours for the aerobic phase, and 1 to 2 hours for the anoxic phase. The aeration conditions (duration and oxygen content) of the aerobic phase are adjusted to reach an ammonia (NH.sub.4.sup.+) content in the reaction medium greater than or equal to 1 mg N/L before the anoxic phase. The oxygen content in the reaction medium is comprised between 4 and 5 mg O.sub.2/L for the aerobic phase, and 0 mg O.sub.2/L for the anoxic phase.

[0068] With reference to FIG. 2, until day 350 before the implementation of the invention, the abatement of soluble global nitrogen (mg N/L) is comprised between 25 and 45% to reach a content in the treated water comprised between 30 and 45 mg N/L. After the implementation of the invention by adding an anoxic phase posterior to the aerobic phase, where the aeration conditions are adjusted to reach an ammonium (NH.sub.4.sup.+) content higher than 1 mg N/L, a progressive increase of this abatement is observed, that reaches 80% with a soluble global nitrogen content in the treated water comprised between 10 and 25 mg N/L.

[0069] With reference to FIG. 4 (middle part of the graph), the number of NOB bacteria per m.sup.2 of carrier is high and in the order of 10.sup.9 before day 350 of operation. After seeding the biofilm with nitrifying bacteria and achieving complete nitrification, this number is in the same order of magnitude as for the conventional implementation described in paragraph 6.1. After the implementation of the anoxic phase, the number of NOBs decreases to one log less. NOB bacteria lose the competition for nitrites against Anammox bacteria and DPAOs and are gradually eliminated from the biofilm.

[0070] Before day 350 and until the implementation of the invention, the number of Anammox bacteria remains low, in the order of 10.sup.8 per m.sup.2 of carrier corresponding to the quantification limit of the analytical method.

[0071] After implementing the invention by adding an anoxic phase posterior to the aerobic phase, where the aeration conditions are adjusted to reach an ammonium ion (NH.sub.4.sup.+) content of more than 1 mg N/L, the number of Anammox bacteria increases progressively to reach 10.sup.11 Anammox bacteria/m.sup.2 of carrier. This number of bacteria is considered high and representative of proven Anammox activity in the biofilm.

[0072] With reference to FIG. 5, the consumption of ammonium ions (NH.sub.4.sup.+) and the accumulation of nitrite ions (NO.sub.2.sup.−) during the aerobic phase are notably observed, followed by a simultaneous consumption of ammonium ions (NH.sub.4.sup.+) and nitrite ions (NO.sub.2.sup.−) during the anoxic phase. At the end of the treatment cycle by the activity of Anammox bacteria, the soluble global nitrogen content is 11 mg N/L, comprising respectively ammonium ion (NH.sub.4.sup.+) content of 1 mg N/L, nitrite ion (NO.sub.2.sup.+) content of 2 mg N/L and nitrate ion (NO.sub.3.sup.−) content of 8 mg N/L. The PO.sub.4 concentration in the treated water is also less than 0.5 mg P/L, corresponding to an abatement of PO.sub.4 of more than 90% for the cycle in question without the addition of chemicals.

[0073] It has therefore been shown that the embodiment with an anoxic phase posterior to the aeration phase is more effective in removing nitrogen than the conventional method. Indeed, after the implementation of the “anoxic” strategy around day 350, the nitrogen removal efficiencies (soluble NGL) increased rapidly and stabilised at 75-80% over more than 200 days (day 450 to day 650). The soluble NGL content at the output of the reactor decreased significantly to less than 15 mg N/L over the same period. Before the implementation of the “anoxic” strategy, the measurements of Anammox bacteria by qPCR did not allow the detection of Anammox bacteria (quantities below the quantification limit in the order of 5.10.sup.8). From the implementation of the “anoxic” strategy around day 350, the quantities increased rapidly and significantly to reach values in the order of 1.10.sup.11. The development and activity of Anammox bacteria largely explain the good nitrogen removal efficiencies.

[0074] 6.3-Implementation of a method according to the invention where the creation of anoxic zones is concomitant with the aerobic phase.

[0075] For this implementation, “corrugated” carriers were used, such as “Z” carriers from Anoxkaldnes™. These carriers favour the creation of local anoxic zones during the aeration phases.

[0076] The implemented operation consists of a 2-hour anaerobic phase followed by a 6-hour aerobic phase. The dissolved oxygen content during the aerobic phase is comprised between 4 and 5 mg O.sub.2/L.

[0077] The “Z” carriers used, due to their geometry, can remain in close proximity to each other, thus forming local anoxic conditions during the aerobic treatment phase.

[0078] With reference to FIG. 3, the implementation of the invention comprising an anaerobic phase followed by an aerobic phase during which the ammonium ion concentration is greater than 1 mg N/L and for which the biofilm is placed under anoxic conditions locally, an abatement of soluble global nitrogen NGL comprised between 70 and 90% is observed, to reach on average a content in the treated water in the order of 10 mg N/L.

[0079] With reference to FIG. 4 (right part of the graph), the mean number of NOB bacteria per m.sup.2 of carrier is in the order of 10.sup.8 for the entire duration of the tests. Furthermore, the average number of Anammox bacteria per m.sup.2 of carrier is in the order of 10.sup.13, which is a very high number for a method whose treatment objectives do not exclusively concern the abatement of global nitrogen by Anammox bacteria.

[0080] With reference to FIG. 6, despite a dissolved oxygen concentration of 5 mg O.sub.2/L in the liquid throughout the aerobic phase, the soluble global nitrogen (NGL) concentration in the treated water reached 10 mg N/L comprising respectively an ammonium ion (NH.sub.4.sup.+) concentration of 0.1 mg N/L, a nitrite ion (NO.sub.2) concentration of 0.9 mg N/L and a nitrite ion (NO.sub.3.sup.−) concentration of 9 mg N/L. The PO.sub.4 concentration in the treated water is also equal to 0.1 mg P/L, corresponding to an abatement of PO.sub.4 of more than 95% for the cycle in question without the addition of chemicals.

[0081] With reference to FIG. 3, it has been shown that by establishing local “anoxic” conditions concomitant with the aerobic phase, the development of species such as Anammox bacteria and the performance of nitrogen treatment are greatly improved while ensuring a satisfactory carbon and phosphorus removal. The soluble global nitrogen (SGN) content at the output of the reactor fluctuated between 10 and 15 mg N/L with a number of Anammox bacteria in the biofilm in the order of 10.sup.12-10.sup.13/m.sup.2 of carrier.