Aerated Biological Filtration Process for Water Treatment with a View to Reducing the Nitrogen Content (NGL) of Said Water with Reduction of Carbon-Source and Aeration Requirements

Abstract

The present invention relates to a biological filtration process for water loaded with nitrogenous pollutants in order to reduce the global nitrogen content of said water, characterised in that it comprises a first step of nitritation and filtration carried out in a first aerated biological reactor, a second step of deammonification, denitrification and filtration carried out in a second non-aerated biological reactor, and a step of evaluation of the ratio of the nitrite content to the ammoniacal nitrogen content of the water at the outlet of the first reactor. When this ratio is greater than a predetermined stoichiometry value, the process according to the invention comprises a step of addition of water to be treated to the water originating from the first reactor so as to obtain, at the inlet of the second reactor, a mixture having a ratio of the nitrite content to the ammoniacal nitrogen content that is close to the stoichiometric ratio of the Anammox reaction.

Claims

1-11. (canceled)

12. A method of biologically treating water containing nitrogenous pollutants and reducing the concentration of ammoniacal nitrogen (NH4.sup.+) in the water, the method comprising: directing at least a portion of the water into a first aerated biological reactor and subjecting the water to nitritation and filtration; passing the water through the first aerated biological reactor where ammonium oxidizing bacteria (AOB) converts a portion of the ammoniacal nitrogen to nitrites; filtering the water passing through the first aerated biological reactor with filtering material contained in the first aerated biological reactor; wherein the water leaving the first aerated biological reactor is rich in nitrites and includes some ammoniacal nitrogen and nitrates; after treating the water in the first aerated biological reactor, directing the water leaving the first aerated biological reactor into a second non-aerated biological reactor and subjecting the water to deammonification, denitrification and filtration in the second non-aerated biological reactor; in the second non-aerated biological reactor, contacting the water with a media having anammox bacteria and heterotrophic bacteria supported thereon; wherein through an anammox reaction, the anammox bacteria in the second non-aerated biological reactor, via deammonification, converts ammoniacal nitrogen and nitrites in the water to molecular nitrogen and some nitrates; wherein the heterotrophic bacteria in the second non-aerated biological reactor via denitrification converts nitrates in the water in the second non-aerated biological reactor to nitrites; calculating a first ratio of nitrite content to ammoniacal nitrogen content in the water leaving the first aerated biological reactor; and if said first ratio is greater than a pre-determined stoichiometric value, the method includes adjusting the ratio of the nitrite content to the ammoniacal nitrogen content in the directed into the second non-aerated biological reactor by mixing another portion of the water with the water directed into the second non-aerated biological reactor such that the water directed into the second non-aerated biological reactor includes a second ratio of nitrite content to ammoniacal nitrogen content that is approximately the stoichiometric ratio of the anammox reaction.

13. The method of claim 12 wherein said pre-determined stoichiometric value is between 1 and 2.5.

14. The method of claim 12 wherein said nitrite content of the water leaving the first aerated biological reactor is measured at the outlet of the first aerated biological reactor.

15. The method of claim 12 wherein said ammoniacal nitrogen content of said water leaving the first aerated biological reactor is measured at the outlet of the first aerated biological reactor.

16. The method of claim 12 wherein said AOB in the first aerated biological reactor is supported on the filter material.

17. The method of claim 12 wherein said first aerated biological reactor includes first and second stages with the first stage including moving media having AOB thereon and the second stage containing said filter material.

18. The method of claim 17 wherein the filter material in the first aerated biological reactor is a fixed bed of particles of a particle size between 2 and 6 mm and a bulk density between 15 and 100 kg/m.sup.3.

19. The method of claim 12 wherein mixing said another portion of the water with the water directed into the second non-aerated aerated biological reactor makes available an additional carbon source that promotes the activity of the heterotrophic bacteria responsible for the denitrification that takes place in the second non-aerated biological reactor.

20. The method of claim 12 wherein the nitritation and the filtration takes place simultaneously in the first aerated biological reactor.

21. The method of claim 12 including mixing said another portion of water with the water directed into the second non-aerated biological reactor such that the second ration of nitrite content to ammoniacal nitrogen content is approximately 1.3.

22. A method of biologically treating water containing nitrogenous pollutants and reducing the concentration of ammoniacal nitrogen (NH4.sup.+) in the water, the method comprising: splitting the water into first and second streams; directing the first stream of water into a first aerated biological reactor and subjecting the water to nitritation and filtration; passing the first stream of water through the first aerated biological reactor where ammonium oxidizing bacteria (AOB) converts a portion of the ammoniacal nitrogen to nitrites; filtering the water passing through the first aerated biological reactor with filtering material contained in the first aerated biological reactor; wherein the first stream of water leaving the first aerated biological reactor is rich in nitrites and includes some ammoniacal nitrogen and nitrates; mixing the first stream of water leaving the first aerated biological reactor with the second stream of water to form a third stream of water; directing the third stream of water into a second non-aerated biological reactor and subjecting the third stream of water to deammonification, denitrification and filtration in the second non-aerated biological reactor; in the second non-aerated biological reactor, contacting the third stream of water with a media having anammox bacteria and heterotrophic bacteria supported thereon; wherein through an anammox reaction, the anammox bacteria in the second non-aerated biological reactor, via deammonification, converts ammoniacal nitrogen and nitrites in the third stream of water to molecular nitrogen and some nitrates; wherein the heterotrophic bacteria in the second non-aerated biological reactor, via denitrification, converts nitrates in the third stream of water to nitrites; and wherein the method includes mixing a sufficient amount of the second stream of water with the first stream of water leaving the first aerated biological reactor such that the ratio of the nitrite content to the ammoniacal nitrogen content in the third stream of water is approximately the stoichiometric ratio of the anammox reaction.

23. The method of claim 22 wherein ratio of the nitrite content to the ammoniacal nitrogen content in the third stream of water directed into the second non-aerated biological reactor is approximately 1.3.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0054] FIG. 1 shows a diagram of a facility suitable for implementing the process according to the invention.

[0055] FIG. 2 shows a diagram of another facility suitable for implementing the process according to the invention.

[0056] FIG. 3 schematically shows the process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0057] The inventors have highlighted that it was also possible to improve the existing processes for treating water loaded with nitrogenous pollutants, particularly making them more economical. Indeed, the inventors have shown, ingeniously, that it was possible to use water loaded with nitrogenous pollutants (water to be treated) to adjust the nitrite and ammoniacal nitrogen stoichiometry of the Anammox reaction before the entry into the reactor wherein the Anammox reaction takes place. In addition, water loaded with nitrogenous pollutants contains carbon sources that advantageously make it possible to promote the activity of the heterotrophic bacteria responsible for the denitrification while limiting the exogenous supply of carbon sources, or even by preventing any exogenous supply of carbon sources. Thus, thanks to the process according to the invention, the oxygen consumption may be reduced up to 55% and the exogenous carbon source consumption may be reduced up to 100% in relation to the processes currently implemented.

[0058] The process according to the invention is a process for biological filtration of water loaded with nitrogenous pollutants with a view to reducing the global nitrogen content (NGL for N Global) of said water.

[0059] The process of the invention will be described in more detail, by referring to the figures for illustration purposes only, the object of these references not being to limit the scope of the present invention.

First Reactor

[0060] The process according to the invention comprises a first step of nitrification 101 and filtration 102 that occurs in a first aerated biological reactor 10 having a bed of a filter medium 12. Such a reactor may comprise known means for injecting oxygen, particularly air, such as a ramp located in the lower portion of the first reactor.

[0061] The water to be treated 100 is brought 100a by a pipe 1 to the inlet 13 of the first reactor 10.

[0062] According to one embodiment, such as schematically shown in FIG. 1, the water passes into the first reactor 10 according to an ascending flow and passes through a filtration and nitrification area containing an autotrophic biomass predominantly consisting of AOB fixed on a bed of a filter medium 12.

[0063] In this configuration, the nitrification 101 and the filtration 102 take place at the same level in the reactor, and occur simultaneously. With reference to FIG. 3, the water to be treated 100 is led 100a to the inlet of the first reactor 10, wherein the steps of nitrification 101 and filtration 102 will be carried out simultaneously, and leading it 101a from one stage to the other in the first reactor is not necessary.

[0064] According to another embodiment, such as schematically shown in FIG. 2, the water passes into the first reactor 10 according to an ascending flow and passes through a first stage containing moving media 11, whereon is fixed an autotrophic biomass predominantly consisting of AOB capable of carrying out the nitrification 101. The water is subsequently led 101a into the second stage containing the filter medium bed 12 to make it possible to filter 102 the water. The autotrophic biomass may also develop on the filter medium bed in this second stage. In this case, the filtration 102 is accompanied with a nitrification activity.

[0065] Generally, the first reactor 10 may contain other autotrophic bacteria such as NOB. However, the conditions inside the first reactor, such as the pH, the aeration, the load applied and/or the temperature, are adapted in such a way as to promote the development predominantly of AOB within the autotrophic biomass, according to known techniques of the prior art. Maintaining a low level of density of the NOB type bacteria limits the conversion of nitrites into nitrates, according to the nitrate shunt principle. Thus, during the first step, some of the ammoniacal nitrogen contained in the water to be treated is predominantly converted into nitrites by AOB. The water obtained at the outlet 14 of the first reactor 10, at the end of the first step, is rich in nitrites and poor in nitrates.

[0066] The first reactor 10 may also contain a heterotrophic bacterial biomass contributing to the reduction of most of the dissolved organic carbon contained in the water to be treated (oxidation of the dissolved organic carbon into CO.sub.2).

[0067] It should be noted that the heterotrophic and autotrophic bacteria may develop, within the first reactor, on the bed of a filter medium 12 and, if applicable, on the moving media 11.

[0068] The fixed bed of filter particles 12 makes it possible to retain the organic matter and the suspended particles present in the water during the first step of the process according to the invention.

[0069] The water rich in nitrites and poor in nitrates reaches 102a the outlet 14 of the first reactor 10. The ratio of the nitrite content to the ammoniacal nitrogen content of the water on leaving 14 the first reactor 10 is then evaluated 103.

Second Reactor

[0070] The water is led 103a by a pipe 2 towards the inlet 23 of the second non-aerated biological reactor 20. The second step of deammonification, denitrification and filtration of the process according to the invention occurs in the second reactor 20. The water at the inlet 23 of the second reactor 20 passes through the second reactor 20 according to an ascending flow. It passes through a first stage 21 containing moving media receiving a bacterial biomass consisting of Anammox bacteria and of heterotrophic bacteria. In this first stage 21, the deammonification and the denitrification occur together 104 thanks to the presence of a carbon source. Another portion of the ammoniacal nitrogen, the nitrites originating from the first reactor and the nitrites produced by the heterotrophic bacteria are predominantly converted into molecular nitrogen and into a small amount of nitrates by the Anammox bacteria (deammonification). At the same time, in the first stage 21, the nitrates originating from the first reactor and the small amount of nitrates produced by the Anammox bacteria are converted into nitrites by the heterotrophic bacteria (denitrification). These nitrites are then used by the Anammox bacteria.

[0071] The water at the outlet of the first stage 21 thus mainly contains molecular nitrogen. It then passes 104a into the second stage 22, containing a bed of a filter medium, and there undergoes a step of filtration 105. It should be noted that the bacterial biomasses may also develop on the filter bed of the second stage, making it possible for the deammonification and the denitrification to continue simultaneously with the filtration in the second stage.

Media

[0072] Preferably, the moving media of the first and/or of the second reactor have a density between 900 and 1200 kg/m.sup.3, preferably between 920 and 980 kg/m.sup.3, and comprise a surface protected from the collision with the surface of other moving media. Such moving media are for example the moving media described in the patent application published under the number WO2012/136654.

[0073] According to a preferred embodiment, the filter medium of the first and/or of the second reactor consists of a fixed bed of particles of particle size between 2 and 6 mm and of bulk density between 15 and 100 kg/m.sup.3. Such particles make it possible to retain the particulate pollution. In addition, their density lower than that of water makes it possible to wash the particles under gravity. Preferably, these particles are made of polystyrene. According to one variant, these particles are made of expanded polystyrene.

Treated Water

[0074] The water that leaves 105a the second reactor 20 is treated water 106. This treated water is led from the outlet 24 of the second reactor 20 by a pipe 3. This treated water may be brought to a storage area, an additional treatment area or a distribution area in view of its use.

Bypass

[0075] When the ratio of the nitrite content to the ammoniacal nitrogen content of the water, evaluated 103 at the outlet 14 of the first reactor 10, is greater 103b than a predetermined stoichiometry value, water to be treated 100 is added 103c to said water originating from said first reactor 10 thanks to a so-called bypass pipe 4. This makes it possible to obtain, at the inlet 23 of the second reactor 20, a mixture having a ratio of the nitrite content to the ammoniacal nitrogen content that is close to the stoichiometric ratio of the Anammox reaction.

[0076] According to one embodiment, the bypass 4 is a pipe that connects the pipe 1 for bringing the water to be treated 100 into the first reactor 10 to the pipe 2 for bringing the water coming from the first reactor 10 into the second reactor 20. The bypass 4 may be equipped with a valve (not shown) for controlling the entry of the water to be treated at the pipe 1, and/or with a valve (not shown) for controlling the exit of the water to be treated at the pipe 2.

[0077] Thus, in the process according to the invention, the water at the outlet 14 of the first reactor 10 may be different from the water at the inlet 23 of the second reactor 20.

[0078] The conditions in the first reactor 10 are adjusted according to known means to enable the effective conversion of the ammoniacal nitrogen mainly into nitrites by the biomass. These known means are for example the ammoniacal nitrogen aeration and applied load in the first reactor 10. The adjustment of the conditions in the first reactor 10 is necessary when the nitrite content of the water becomes too low in relation to the ammoniacal nitrogen content, particularly when the ratio of the nitrite content to the ammoniacal nitrogen content becomes significantly lower than a predetermined stoichiometry value.

[0079] As previously indicated, the predetermined stoichiometry value may be between 1 and 2.5, preferably between 1.1 and 2, more preferably between 1.2 and 1.5. In particular, the predetermined stoichiometry value may be approximately 1, approximately 1.1, approximately 1.2, approximately 1.3, approximately 1.4, approximately 1.5, approximately 1.6, approximately 1.7, approximately 1.8, approximately 1.9, approximately 2.0, approximately 2.1, approximately 2.2, approximately 2.3, approximately 2.4 or approximately 2.5.

[0080] As the water to be treated 100 contains carbon sources, its addition 103c to the water coming from the first reactor 10 also makes it possible to supply the carbon sources necessary for the activity of the heterotrophic bacteria of the first stage 21 of the second reactor 20. Thus, the process according to the invention is implemented with an exogenous supply of carbon source that is reduced as much as possible or even zero. As shown in the examples, the carbon consumption is significantly reduced thanks to the process of the invention, in relation to known processes. Another advantageous consequence of the process according to the invention is that the amount of sludges formed by the exogenous supply of carbon sources is also reduced. However, it may be desired to supply an exogenous carbon source, for example when the water to be treated does not contain enough of said carbon source to enable a satisfactory activity of the heterotrophic bacteria. In order to make this supply possible, the second reactor 20 may advantageously be provided with a pipe bringing a carbon source to the first stage 21. Carbon source means easily biodegradable carbon substrates, such as methanol.

[0081] The evaluation 103 of the ratio of the nitrite content to the ammoniacal nitrogen content is performed from measured values of the nitrate and nitrite contents. This evaluation may be performed thanks to a known calculation apparatus, such as for example a calculation tool implemented by a computer. Such a computer may advantageously control the opening and the closing of the valve(s) that may equip the bypass 4, when they are present.

[0082] The measurement of the nitrite content may be carried out by any known means. According to one embodiment, the measurement of the nitrite content is carried out by a probe 31. The use of a probe 31 is advantageous because it makes it possible to continuously take measurements of the nitrite content in the water. Such probes are commercially available, such as for example the OPUS Nitrite probe marketed by Trios.

[0083] The measurement of the ammoniacal nitrogen content may be carried out by any known means. According to one embodiment, the measurement of the ammoniacal nitrogen content is carried out by a probe 32. The use of a probe is advantageous because it makes it possible to continuously take measurements of the ammoniacal nitrogen content in the water. An example of probe suitable for measuring the ammoniacal nitrogen content according to the invention is the ammonium analyser marketed under the AMTAX brand by Hach.

[0084] According to one embodiment, the process according to the invention further comprises measuring the ammoniacal nitrogen content of the water to be treated 100. This measurement may be carried out by any known means. In a particular embodiment, this measurement is carried out using a probe 33 located upstream of the first reactor 10, for example on the pipe 1. An example of probe suitable for measuring the ammoniacal nitrogen content according to the invention is the ammonium analyser marketed under the AMTAX brand by Hach.

[0085] According to a particular embodiment, the process according to the invention also comprises measuring the nitrate content in the water at the outlet of the first reactor 10. This measurement may be performed by any known means, in particular by a probe (not shown) placed at the outlet of the first reactor, for example on the pipe 2. This measurement makes it possible to rapidly detect nitrates, and thus reduce the supply of air in the first reactor in order to limit the development of the bacterial biomass of the NOB type.

[0086] It is possible to subject the water to be treated to one or more preliminary treatments, before bringing it into the first reactor 10. In particular, in order to reduce the amount of suspended particles in the water to be treated before its entry into the first reactor, the process according to the present invention may comprise a preliminary step of passing the water to be treated into a settler.

Examples

[0087] Other features and advantages of the invention will become more apparent from the following examples, given for illustrative and non-limiting purposes.

[0088] A water treatment plant is arranged in order to implement the process according to the invention. In particular, a first aerated biological reactor followed by a second non-aerated biological reactor are installed, connected by a pipe provided with probes for measuring the nitrite and ammoniacal nitrogen content. The pipe bringing the water to be treated into the first reactor is modified in such a way as to also communicate with a bypass pipe. The bypass pipe joins the pipe connecting the two reactors together upstream of the inlet into the second reactor.

[0089] The first aerated biological reactor 10 contains an autotrophic biomass predominantly consisting of AOB fixed on a filter medium 12. It also contains a heterotrophic biomass making it possible to reduce the dissolved organic carbon. The second non-aerated biological reactor 20 has a first stage containing moving media 21 receiving a bacterial biomass consisting of Anammox bacteria and heterotrophic bacteria, and a second stage containing a bed of a filter medium 22, whereon the bacterial biomasses may also be fixed.

[0090] Water loaded with nitrogenous pollutants 100 is brought 100a into the first reactor 10, wherein the nitrogen aeration and loading conditions are configured in such a way as to promote the nitrification of the ammoniacal nitrogen. At the outlet 14 of the first reactor, the water is rich in nitrites and poor in nitrates. The nitrite and ammoniacal nitrogen contents of the water at the outlet of the first reactor are measured thanks to probes 31, 32. The mole ratio of the nitrite content to the ammoniacal nitrogen content is measured and, when the value of this ratio is greater than 1.7, water to be treated 100 is injected 103c into the bypass 4. The water to be treated is mixed with the water coming from the first reactor 10, upstream of the inlet 23 of the second reactor 20, in such a way that the mixture has a ratio of the nitrite content to the ammoniacal nitrogen content that is close to the stoichiometric ratio of the Anammox reaction.

[0091] The oxygen consumption and the carbon source consumption are measured, correlated to the amount of nitrogen treated, and compared to the values obtained by conventional processes.

REFERENCES

[0092] Strous M, Kuenen J G, Jetten M S. Key physiology of anaerobic ammonium oxidation. Appl Environ Microbiol. 1999 July; 65(7):3248-50. doi: 10.1128/AEM.65.7.3248-3250.1999. PMID: 10388731; PMCID: PMC91484.