WO2015036629A1

WO2015036629A1 - Method for eliminating nitrogen anaerobically on a plastic support

Info

Publication number: WO2015036629A1
Application number: PCT/ES2013/070631
Authority: WO
Inventors: Carme PÉREZ VIZUETE; Cristina HERNÁNDEZ ROMERO; Carlos RODRÍGUEZ LÓPEZ; Luís LARREA URCOLA; Ion IRIZAR PICÓN
Original assignee: Acciona Agua S.A.
Priority date: 2013-09-12
Filing date: 2013-09-12
Publication date: 2015-03-19
Also published as: ES2547023B1; ES2547023A1

Abstract

The invention relates to a method for the elimination of nitrogen from wastewater, comprising the following steps: a) partial nitrification of the ammonium by means of autotrophic ammonia-oxidising bacteria; and b) anaerobic elimination of the inorganic nitrogen from the water obtained in (a) by means of autotrophic anaerobic bacteria; said method being characterised in that the autotrophic ammonia-oxidising bacteria of step (a) and the autotrophic anaerobic bacteria of step (b) are in the form of a biofilm on a support; and in that steps (a) and (b) are carried out in different tanks.

Description

NITROGEN ELIMINATION PROCEDURE BY ANAEROBIC ROUTES ON PLASTIC SUPPORT

The present invention relates to a process for treating wastewater with high nitrogen contents by means of different autotrophic biomass. Therefore, the invention could be framed in the technical sector of wastewater treatment procedures.

STATE OF THE TECHNIQUE

Currently, the most innovative technologies for removing nitrogen from sludge liquor are based on the existence of two biochemical reactions by bacteria:

(1) NH ₄ ⁺ + 1, 50 ₂ → N0 ₂ ^" + H ₂ 0 + 2H ⁺

(2) NH ₄ ⁺ + 1, 32N0 ₂ ^"+ 0,066HCO _^3" + 0, 13H ⁺ → 1, 02N ₂ + 0,26NO ₃ ^"+ 2,03H ₂ O +

The first reaction called "Partial Nitritation" is carried out by ammonium oxidizing bacteria (XNH) and the high ammonium of the liquor is partially transformed into nitrite, therefore requiring a lower oxygen consumption, compared to total nitrification. In the second reaction, carried out by anaerobic autotrophic bacteria (XAN), the ammonium and nitrite resulting from the first reaction are fundamentally transformed into nitrogen gas and a small fraction of nitrate. The set of the two reactions is called "deamonification".

To carry out these reactions, the market basically offers 3 technologies:

1) Procedure with biomass in granular biofilm, the two reactions can be carried out either in 2 separate reactors or tanks (Sharon®-Anammox®, described in US6383390B1) or in a single reactor where both biomass and reactions interact (Anammox®, described in WO9807664A1)

2) DEMON® procedure with suspended biomass in a single reactor, described in US2009272690A1; Y

3) Anita-mox® procedure with biofilm biomass on plastic support in a single reactor. The implementation of these technologies in urban wastewater treatment plants (WWTPs) is still not very widespread, which is attributed to their complexity. In order to save investment costs due to the high price of the landfill used, we try to keep the two mandatory steps of the process in a single biofilm (instead of two differentiated as the object of this invention), that is, on the same landfill In a single tank an attempt is made to generate a biofilm that in its outer layer is colonized by nesting microorganisms (ammonium oxidizers), which is where aerobic conditions are needed, and in its inner layers (where oxygen does not reach) anaerobic autotrophic bacteria develop . Maintaining this balance requires very fine control of the operating conditions so as not to unbalance this development of multi-population biofilm.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the removal of nitrogen from wastewater, by means of a technology characterized by being simple and robust, thanks to the fact that it is based on the following aspects:

one . Biomass are developed in biofilm and suspension, instead of only biomass in suspension (Demon procedure) since this allows operating with dissolved oxygen concentrations in the liquid (1 -2 mg / l) not as low as in other methods (0.2 mg / l in Demon) and control systems of dissolved oxygen (OD) and pH less complicated or sophisticated. There is also Keep in mind that both ammonium oxidizing bacteria (XNH) and anaerobic autotrophic bacteria tend to generate biofilms naturally, that is, if there is a support, the bacteria generate biofilms. .

2. Biofilm is used on plastic support, since the tanks are geometrically much simpler compared to the granular process that requires special hydrodynamics, since it requires that the tanks (or reactors) have elongated geometry. In addition to forming such granules, very special stirring conditions are necessary.

3. Two tanks are used in front of a single tank used in the state of the art in order to have greater flexibility for automatic control based on online sensors. This provides greater stability of the biofilm and the operation of each of the tanks and therefore a greater robustness of the global system due to the logical variations in the characteristics of the return liquor.

4. It saves 60% of oxygen consumption and 100% of the carbon source with respect to conventional pre-denitrification-nitrification.

Therefore, the advantages of the process of the present invention are:

- The process produces less oxygen consumption than in conventional processes.

- No organic matter is necessary to remove the oxidized nitrogen species.

- The implementation of this system in an existing plant is easy since it is an element outside the main process.

- A large part of the bacteria that participate in the different processes are fixed on a mobile biofilm, which causes them to be retained in their respective tanks before any eventuality of the process, whether hydraulic, chemical or biological.

Therefore, a first aspect of the present invention relates to a process for the removal of nitrogen from wastewater comprising the following steps: a) partial nitrification of the ammonium from the wastewater by autotrophic ammonoxidant bacteria; b) anaerobic removal of inorganic nitrogen from the waters from (a) by anaerobic autotrophic bacteria; characterized in that the autotrophic ammonium-oxidizing bacteria of stage (a) and the anaerobic autotrophic bacteria of stage (b) are in the form of biofilm on a support and; characterized in that stages (a) and (b) are carried out in different tanks.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the present invention relates to a process for the removal of nitrogen from wastewater comprising the following steps: a) partial nitrification of the ammonium from wastewater by autotrophic ammonium oxidizing bacteria; b) anaerobic removal of inorganic nitrogen from the waters from (a) by anaerobic autotrophic bacteria; characterized in that the autotrophic ammonium-oxidizing bacteria of stage (a) and the anaerobic autotrophic bacteria of stage (b) are in the form of biofilm on a support and; characterized in that stages (a) and (b) are carried out in different tanks.

"Wastewater" (also called effluents with high nitrogen content) means drained obtained in dehydration of anaerobically digested sludge, where the concentration of ammonia can reach levels of up to 1000 mg / l. In the case where the concentrations were higher than 1000 mg / l, there could be a previous stage in which the wastewater is diluted with water, to adjust the concentration of the inlet. This dilution can be carried out in the retention tank.

The term "partial nitrite" means the oxidation of ammonium to nitrite, where the state of nitrogen oxidation varies from -3 to 3.

The step (a) of partial nitritation which aims to partially transform the concentration of ammonium from the return liquor into nitrite nitrogen by means of ammoniaxidant bacteria (XNH) both in suspension within the tank liquid and (mostly) adhered in the form of Biofilm to a plastic support. Nitroxidant bacteria (XNO) are removed by washing, to minimize the oxidation of nitrite to nitrate. Under the conditions of the process of the invention, the concentration of nitrate in the tank where step (a) is carried out is from 40 mg / l to 100 mg / l, preferably from 60 mg / l to 80 mg / l.

In order to achieve proper operation, the degree of transformation of ammonium must be 60% accurately and in a stable and robust manner. For this, the tank is equipped with an automatic control system based on OD, NH ₄ ⁺ and NO3 ^" online sensors. The BOD (demand biological oxygen) from the return liquor is eliminated in this same tank by its transformation into CO ₂ and heterotrophic bacteria that grow in suspension and biofilm. The control system allows to minimize the inhibition of ammonium oxidizing bacteria by BOD.

The term "autotrophic ammonium-oxidizing bacteria" (XNH) means prokaryotic microorganisms that obtain energy for their metabolism from the oxidation reaction of ammonium with oxygen (such as nitrosomones, for example). It is clear to any expert in the field which bacteria are ammonium-oxidizing autotrophs. The most common are bacteria of the genus nitrosomonas or nitrosococcus.

The term "anaerobic nitrogen removal" means the removal of nitrogen through biological processes in which there is an absence of molecular oxygen.

The anaerobic elimination of nitrogen aims to transform ammonia and nitrite outgoing from the partial nitrite tank into nitrogen gas, using anaerobic autotrophic bacteria both in suspension within the liquid of the tank and (mostly) in biofilm of a plastic support. To prevent the inhibition of these bacteria by nitrite, the tank is equipped with an automatic control system based on an online NH ₄ ⁺ sensor, thus allowing stable, robust and reliable operation.

The term "anaerobic autotrophic bacteria" refers to prokaryotic microorganisms that obtain energy for their metabolism from the oxidation of ammonium in conditions of absence of oxygen (such as platomycetes). It is clear to any expert in the field which bacteria are anaerobic autotrophs. The most common is Canditatus Brocadia anammoxidans, which usually develops mostly. The term "biofilm" means a conglomerate of microorganisms that are generated on surfaces exposed to the activity of microorganisms. It is usually composed of bacteria and other types of microfauna (protozoa, etc.) together with products of secretion of these (exopolymers) and other types of both organic and inorganic compounds (embedded in exopolymers). The biofilm is fixed on plastic supports, preferably mobile, which are retained in the tanks by means of the corresponding retention devices at their exits.

In an embodiment of the first aspect of the present invention, the support is mobile. This support can have different geometries and compositions. Preferably the support is formed of a plastic material, with a density lower than water so that the operation in the aeration system is easier to float.

In another embodiment of the first aspect of the present invention, the autotrophic ammonium-oxidizing bacteria of step (a) and the anaerobic autotrophic bacteria of step (b) are also in suspension.

In another embodiment of the first aspect of the present invention, the concentration of ammonium in the wastewater at the inlet of the tank where step (a) is carried out is 400 mg / 1000 mg / l, preferably 600 mg / l. 800 mg / l As previously mentioned, if the wastewater had an ammonium concentration greater than 1000 mg / l, a previous stage of dilution of said waters would be necessary before introducing them into the tank where stage (a) is carried out.

In the context of the invention, by concentration of a compound at the entrance of a stage x (or the tank in which stage x takes place) means the concentration of the inlet flow, before stage x takes place. By concentration in stage x (or in the tank in which stage x takes place) means the concentration within the tank, once the stage x. This last concentration will obviously coincide with the concentration of said compound at the exit of stage x (or of the tank in which stage x takes place).

In another embodiment of the first aspect of the present invention, the tank where step (a) is carried out is an aerated taque. Preferably, the concentration of dissolved oxygen in the tank where step (a) is carried out is 1.3 mg / l to 3.0 mg / l.

In another embodiment of the first aspect of the present invention, the NO ₂ ^" / NH ₄ ⁺ ratio in the tank where step (a) is carried out is 1 to 1, 5, preferably the ratio Νθ ₂ ^" ΝΗ ₄ ⁺ in the tank where stage (a) is carried out is 1, 3. This is the ideal ratio for the reaction of step (b) to be carried out efficiently.

In another embodiment of the first aspect of the present invention, the pH in the tank where step (a) is carried out is 6 to 8, preferably 6.5 to 7.5.

In another embodiment of the first aspect of the present invention, step (a) is carried out at a temperature of 20 ° C to 40 ° C, preferably 30 ° C to 35 ° C.

In another embodiment of the first aspect of the present invention, the concentration of nitrate in the tank where step (b) is carried out is from 130 to 80 mg / l.

In another embodiment of the first aspect of the present invention, the pH in the tank where step (b) is carried out is from 7 to 9.5, preferably 7.5 In another embodiment of the first aspect of the present invention, when the concentration of nitrite in the tank where stage (b) is carried out is greater than 80 mg / l, the tank where stage (b) is carried out is feeds directly from wastewater.

In step (b) nitrite and ammonium are removed. However, an increase in the concentration of nitrite in step (b) irreversibly inhibits the anaerobic nitrogen removal process. Therefore, when the control system detects that the nitrite concentration in stage (b) is greater than 80 mg / l, the first system is activated to restore balance: the feeding of the tank where it is carried is started. carry out stage (b) with wastewater (the same as those used at the entrance of stage (a)). In this way, the concentration of ammonium in step (b) is increased and the N0 ₂ 7NH ₄ ⁺ ratio necessary for anaerobic nitrogen removal is restored.

In another embodiment of the first aspect of the present invention, the process further comprises a step (c) of separation of the suspended biomass from the treated waters from stage (b).

The term "suspended biomass" means biomass not associated with the biofilm and which is immersed in the liquid inside the tanks. This biomass comprises the total of the autotrophic living organisms that participate in the process of which the invention is subject, as well as heterotrophic bacteria that also exist in the environment. Autotrophic biomass is formed by anaerobic autotrophic bacteria.

This separation allows storing the anaerobic autotrophic bacteria that can be returned to the denitrification tank to instantly absorb abrupt variations in the characteristics of the incoming water in it. This provides an additional degree of control and robustness of the global system. That is, in another embodiment of the first aspect of the present invention, when the concentration of nitrite in the tank where step (b) is carried out is greater than 80 mg / l, the biomass separated in step (c) is recirculate to stage (b).

When, due to a concentration of nitrite in stage (b) greater than 80 mg / l, the sewage feed to the tank where stage (b) is carried out has begun, and if this was not sufficient to restore the N027NH ₄ ⁺ ratio necessary for anaerobic nitrogen removal, a separate recirculation of the biomass would be carried out in stage (c) towards stage (b), in order to increase activity.

In another embodiment of the first aspect of the present invention, there is a retention reservoir prior to the tank of step (a). This retention tank limits the discontinuous flow of wastewater from drains that may have very different models from one installation to another. In this way, the flow to the tank in which the reaction to (Q fed) is carried out is continuous and is regulated by the automatic control system. The retention reservoir also serves as a settler to remove suspended solids.

Following the diagram in Figure 1, the automatic control system involves the following strategies, taking into account that the system's automatic control system is based on the use of (N-NH ₄ ⁺ (ammonium-shaped nitrogen) and N -NO3 ^" (nitrate-shaped nitrogen)) as nutrient analyzers, based on sensors placed throughout the system, preferably in reactors or tanks (T _a , T _b ):

- according to the automatic control of dissolved oxygen (C _b ) in the ammonium partial nitrification tank or ÑIPAR (T _a ), the air flow (Q _a ) is automatically manipulated according to the discrepancies between the value for adjusting dissolved oxygen and measurements of dissolved oxygen in the ÑIPAR reactor (T _a );

Automatic regulation of the dissolved oxygen adjustment value: the dissolved oxygen adjustment value is automatically modified according to:

- A pre-adjustment value for the relationship between NO2 ^" and N-NlV concentrations in the ÑIPAR reactor (T _a ) [adjustment value of N-N0 ₂ 7 N-NH ₄ ⁺ ]

- The measurement of N-NH ⁺ in the ÑIPAR reactor (C _b )

- Indirect estimation of the concentration of N-NO2 ^" in the ÑIPAR reactor (T _a ) from the direct measurements of N-NH ₄ ⁺ in the retention tank (D) and the feed rate (Q _to i¡¡ m);

Automatic control of N-NH ₄ ⁺ (C _c ) in the anaerobic nitrogen removal tank (ANAMMOX) (T _b ): The fraction of the feed flow that is diverted to the ANAMMOX tank (T _b ) (F _a i¡ _m ) and the Qr (sludge recirculation flow) are automatically manipulated according to:

- An adjustment value of N-NH ₄ ⁺ in the anaerobic nitrogen removal tank reactor;

- Indirect estimation of the concentration of N-NO2 ^" in the anaerobic nitrogen removal tank (T _b ) from direct measurements of N-NH ₄ ⁺ and N-NO3 ^" (C _c ) in the tank anaerobic nitrogen removal.

Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and figures are they are provided by way of illustration, and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Diagram of the procedure. W: wastewater; D: retention deposit; C _a : Control a, NH ₄ ⁺ ; Q _to ii _m: feed rate; F i¡ _m: fraction of the feed stream is diverted to tank b; T _a : Tank a (ÑIPAR); Q _a : air flow; Ct .: Control b, dissolved oxygen and ammonium; T _b : Tank b (anaerobic nitrogen removal or ANAMMOX); Q _r : recirculation flow from the settler to tank b; C _c : Control c, ammonium and nitrates; S: settler.

EXAMPLES

The invention will now be illustrated by tests carried out by the inventors, which demonstrates the effectiveness of the process of the invention.

Example 1. Example of embodiment of the process of the invention

The process of the invention begins with a retention tank (D) of 2m ³ where the anaerobically digested sludge dehydration liquor containing an ammonium concentration of 750 mg / l is collected. In this retention tank there is a control system (C _a ) that takes a reading of the concentration of ammonium.

This liquor is fed with a flow of 83 l / h to the partial nitrification tank (ÑIPAR), tank a, T _a ) of 2m ^3, so the hydraulic retention time (HRT) is 1 day. This reactor is filled in 50% of the volume with a mobile plastic support that has a specific surface area of 500 m ² / m ³ , where ammonium oxidizing bacteria (XNH) grow that also flow into the liquid in the form of suspended solids. The pH is maintained at 6.4 without the addition of chemical reagents is required. By means of an automatic control of the dissolved oxygen in 2.6 mg / l (adjustment value), carried out through the regulation of the air flow (Q _a ) and the measurement of NH ₄ ⁺ and of the dissolved oxygen (C _b ) , a nitrite / ammonium (Νθ2 ^" / ΝΗ ₄ ⁺ ) ratio of 1, 3 (NH ₄ ⁺ = 308 mg / l, N0 ₂ ^" = 398 mg / l) and nitrate (N0 ₃ ^{") is} achieved ) of 36 mg / l.

The effluent liquid from the partial nitrification tank (T _a ) is fed with a flow rate of 77 l / h to the anaerobic nitrogen removal tank (tank b, T _b ) of 1, 6 m ^3, so that the HRT is 0.9 days The excess flow (6 l / h) is discharged into a sump. The anaerobic nitrogen removal tank (T _b ) is filled in 50% of the volume with a plastic support that has a specific surface area of 500m ² / m ³ , where anaerobic autotrophic bacteria grow that also detach into the liquid form of suspended solids. In this tank b there is a control system (C _c ) that takes a reading of the concentration of ammonium and nitrate. Since the incoming liquid has an N02 ^" / NH ₄ ⁺ ratio of 1, 3 and NO ^ of 36 mg / l; a high and balanced elimination of ammonium and nitrite is achieved, reaching NH ₄ ⁺ values = 15 mg / l, N0 ₂ ^" = 10 mg / l.

Nitrate increases from 36 to 100mg / L. In short, the nitrogen removal performance (NH ₄ ⁺ ¡ _n f -N _T oT, ef) / NH ₄ ⁺ INF in the global system is 83%.

When the ammonium influences the global system increases gradually and slowly from 750 mg / l to 1000 mg / l the global control system acts so that the adjustment value of dissolved oxygen varies gradually until it reaches a value of 3mg / l. Under these conditions, the effluent ammonium from the partial nitrification tank (ÑIPAR, tank a) is 417 mg / l and the NO2 ^"is 550 mg / l, so that the ratio N02 ^" / NH ₄ ⁺ is maintained at 1, 3. Nitrate (N-NO3 ^" ) decreases to 26 mg / l. In the anaerobic nitrogen removal tank (tank b) the ammonium (15 mg / l) and nitrite (10mg / l) values are maintained. Nitrate (N-NO3 ^" ) reaches a value of 1,114 mg / L.

A relatively rapid increase in influential ammonium from 750 to 1000 mg / L may not be absorbed by the amount of ammonium oxidizing biomass present in the partial nitrification tank (tank a), which may require temporary modification of the feed flow (F _a ), whereby a fraction of the influent flow is diverted directly to the anaerobic nitrogen removal tank or Anammox (tank b) in order to maintain the N0 ₂ 7NH ₄ ⁺ ratio at 1, 3. Similarly, the increase in nitrogen load to the anaerobic nitrogen removal tank or Anammox may not be assimilated by the amount of biomass present, which may require the temporary activation of the biomass feed accumulated in the settler (S ) through the flow of the recirculation pump (Q _r ).

When the ammonium influences the global system gradually decreases from 750 mg / l, the control system acts so that the dissolved oxygen (OD) gradually decreases so that the nitrate does not increase significantly but the ratio 1 cannot be achieved, 3. This is only possible by progressive increase in pH, which can be automatically controlled by the appropriate addition of chemical reagents. Thus, for an influential ammonium of 500 mg / l the ratio 1, 3 is achieved by automatic control of pH at 6.8 and OD at 1.5 mg / l.

Claims

one . - Procedure for the removal of nitrogen from wastewater comprising the following stages: a) partial nitrification of ammonia from wastewater by autotrophic ammonium oxidizing bacteria; b) anaerobic removal of inorganic nitrogen from the waters from (a) by anaerobic autotrophic bacteria; characterized in that the autotrophic ammonium-oxidizing bacteria of stage (a) and the anaerobic autotrophic bacteria of stage (b) are in the form of biofilm on a support and; characterized in that stages (a) and (b) are carried out in different tanks.

2. - The method according to the preceding claim characterized in that the support is mobile.

3. - The method according to any of the preceding claims, characterized in that the autotrophic ammonium-oxidizing bacteria of step (a) and the anaerobic autotrophic bacteria of step (b) are also in suspension.

4. - The method according to any of the preceding claims wherein the concentration of ammonia in the wastewater at the entrance of the tank where step (a) is carried out is 400 mg / 1000 mg / l, preferably 600mg / 800 mg / l

5. - The method according to any of the preceding claims, wherein the tank where stage (a) is carried out is an aerated tank.

6. - The method according to the preceding claim, wherein the concentration of dissolved oxygen in the tank where step (a) is carried out is 1.3 mg / l to 3.0 mg / l.

7. - The method according to any of the preceding claims, wherein the ratio N0 ₂ 7NH ₄ ⁺ in the tank where step (a) is carried out is 1 to 1, 5.

8. - The method according to the preceding claim, wherein the ratio N0 ₂ ^" / NH ₄ ⁺ in the tank where step (a) is carried out is 1, 3.

9. - The method according to any of the preceding claims wherein the pH in the tank where step (a) is carried out is from 6 to 8, preferably from 6.5 to 7.5.

10. - The method according to any of the preceding claims wherein step (a) is carried out at a temperature of 20 ° C to 40 ° C, preferably from 30 ° C to 35 ° C.

eleven . - The method according to any of the preceding claims wherein the concentration of nitrate in the tank where step (b) is carried out is from 130 to 80 mg / l.

12. - The method according to any of the preceding claims wherein the pH in the tank where step (b) is carried out is from 7 to 9.5, preferably from 7.5 to 8.5.

13. - Method according to any of the preceding claims, characterized in that when the concentration of nitrite in the tank where it is stage (b) is carried out is greater than 80 mg / l, the tank where stage (b) is carried out is fed directly from wastewater.

14. - The method of any of the preceding claims, characterized in that it further comprises a step (c) of separation of the suspended biomass from the treated waters from stage (b).

15. - Method according to the preceding claim, characterized in that, when the concentration of nitrite in the tank where stage (b) is carried out is greater than 80 mg / l, the biomass separated in stage (c) is recirculated to stage (b).

16. - The method according to any of the preceding claims, characterized in that there is a retention tank prior to the tank of step (a).