AU2015283717A1

AU2015283717A1 - Method and facility for aerobic biological treatment of urban or industrial wastewater

Info

Publication number: AU2015283717A1
Application number: AU2015283717A
Authority: AU
Inventors: Laure Graveleau; Marie SECONDAT
Original assignee: Suez International SAS
Current assignee: Suez International SAS
Priority date: 2014-06-30
Filing date: 2015-06-29
Publication date: 2017-01-19
Anticipated expiration: 2035-06-29
Also published as: CN106536423A; EP3160910B1; ES2802379T3; AU2015283717B2; EP3160910A1; WO2016001823A1; FR3022902B1; MX2016017096A; FR3022902A1; CN106536423B

Abstract

The invention relates to a method for aerobic biological treatment of urban or industrial wastewater, for removing the biodegradable carbonaceous matter and oxidising the nutriment (carbon and/or NH4), according to which the water to be treated flows in a plug flow between an inlet (2) and an outlet (3), and air vents (5) are distributed under the water flow and supplied by at least one air source (A), the flow rate of said source being modulated according to at least one treatment parameter; the concentration of nutriment (carbon and/or NH4) in the water to be treated is measured (16) continuously at the inlet (2), and the flow rate of the air vents is modulated according to the measured concentration of nutriment (carbon and/or NH4). The facility comprises a plug-flow reactor, the water to be treated flowing between an inlet (2) and an outlet (3) and air vents being distributed below the water flow and supplied by at least one air source (A). The facility comprises at the inlet of the reactor/pond, a sensor (16) enabling the concentration of nutriment (carbon only or carbon and NH4) in the water to be continuously estimated, and a processing unit (17) receiving the information from the sensor (16) and capable of controlling the flow rate of the air vents.

Description

WO 2016/001823 1/24 PCT/IB2015/054868

METHOD AND FACILITY FOR AEROBIC BIOLOGICAL TREATMENT OF URBAN OR INDUSTRIAL WASTEWATER

The invention relates to a method for the biological treatment of urban or industrial wastewater via the aerobic pathway, for the elimination of biodegradable carbonaceous matter and the oxidation of ammonium.

Treatment via the aerobic pathway is ensured by virtue of a supply of air or of oxygen. Hereinafter, for simplification, only a supply of air will be mentioned, but this expression is to be understood to also encompass a supply of oxygen.

The invention relates to a method, according to which the water to be treated flows in plug flow between an inlet and an outlet, and the air supplies are distributed under the flow of water and are supplied by at least one source of air, the flow of this source being modulated according to at least one treatment parameter.

The plug flow treatment configuration gives rise to a concentration gradient of carbonaceous pollution and of ammonium between the inlet and the outlet of a biological tank or reactor, generally of an elongated rectangular shape, in which the treatment is carried out. There is a notable difference to a treatment with complete mixing, in which the concentration at any point in the tank is identical.

Conventional regulation of the air supply for a plug flow configuration is not entirely satisfactory and needs to be improved. The regulation is often carried out on the basis of the residual oxygen concentration measured at the outlet of the treatment zone.

Optimally, the total air supply provided during the treatment time must correspond to the air requirements to ensure treatment. In the majority of the treatment zone, all the oxygen supplied is consumed by the biomass, thus ensuring the elimination of carbon and the oxidation of ammonium. Residual oxygen at the end of the treatment is a guarantee that the air supply was sufficient and that all the oxidizable matter was able to be treated.

The difficulty arises from the fact that the amount of oxidizable matter varies continuously, such that the amount of air to be provided must be adjusted WO 2016/001823 2/24 PCT/IB2015/054868 continuously. The oxygen concentration at the end of treatment, conventionally used to regulate the air supply, is a parameter which is highly variable over time, since as soon as the oxidizable matter has been totally treated, the oxygen concentration goes from a value close to 0 to 8 mg/l in a few tens of minutes.

Also, as a function of the load of oxidizable matter, there is a risk of having oxygen concentration profiles, according to the length of the treatment tank, which are unsatisfactory. In a situation of low load, the air supply may be too high, which may result in a high oxygen concentration over more than half of the treatment zone; there is then useless expenditure on providing air.

In a situation of high load, the air supply may be too low, which does not make it possible to measure a residual oxygen concentration at the end of the treatment zone. This treatment was insufficient, and did not make it possible to eliminate the majority of the oxidizable matter.

It therefore appears that the regulation generally used is not entirely satisfactory insofar as the air supply is adjusted as a function of the residual oxygen concentration, observed at the end of treatment. This is a regulation a posteriori which does not make it possible to foresee variations in the load to be treated. The air flow is adjusted as a function of the residual oxygen observed at the outlet water. The high variation in oxygen concentration at the end of treatment moreover gives rise to significant variations in the required air flows, which is a phenomenon which leads to surges in the production or distribution of the air, particularly in the case in which several treatment lines are supplied with air from a common source.

The aim of the invention is above all to provide a biological plug flow treatment method which no longer has, or has to a lesser extent, the drawbacks recalled above, and which especially makes it possible to better manage the variations in air supply to ensure the elimination of biodegradable carbonaceous matter and the oxidation of ammonium. The cost of carrying out the method must also remain acceptable compared to the cost of a conventional method.

According to the invention, the method for the biological treatment of urban or industrial wastewater via the aerobic pathway, for the elimination of WO 2016/001823 3/24 PCT/IB2015/054868 biodegradable carbonaceous matter and the oxidation of ammonium, according to which method the water to be treated flows in plug flow between an inlet and an outlet, and air supplies are distributed under the flow of water and are supplied by at least one source of air, the flow of this source being modulated according to at least one treatment parameter, is characterized in that: the nutrient (carbon and/or ammonium) concentration of the water to be treated is measured continuously at the inlet, and the flow of the air supplies is modulated according to the nutrient (carbon and/or ammonium) concentration.

Preferably, the nutrient (carbon and/or ammonium) concentration of the water during treatment is measured at a point in the course of the treatment, in particular at the halfway point, so as to integrate the degree of elimination effectively achieved to modulate the air flow.

The air flow may be calculated according to a formula (D1) taking into account the nutrient (carbon and/or ammonium) concentration at the inlet of the plug flow Nutrlnlet and at a point of the treatment NutrCourse, especially in the middle, D1 Qair = Qmin + B*Nutrlnlet + C (NutrCourse - E*Nutrlnlet) with, nutrient (carbon and/or NH4) concentration in mg/l,

Qmin in Nm3/h,

Qmin being between 2 and 6 Nm3/h/m2 * surface of aerated tank in m2, B in Nm3/h/mg/l, B being between 400 and 1000, advantageously equal to 700 (for a treatment based on the nitrogen measurement and an urban wastewater in Europe), C in Nm3/h/mg/l, C being between 150 and 600 in Nm3/h/mg/l, according to the configuration (for a treatment based on the nitrogen measurement and an urban wastewater in Europe), E being unitless, between 0.5 and 0.8.

The air flow may also be calculated according to another formula (D2) taking into account on the one hand the flow of air Qair-1, applied at the time t-1, and on the other hand the variation (pNutrlnlet) in nutrient (carbon and/or NH4) concentration as a function of time, at the inlet of the plug flow, and the variation WO 2016/001823 4/24 PCT/IB2015/054868 in the degree of nutrient (carbon and/or NH4) elimination over a point in the course, in particular over the first half of the plug flow, D2 -> Qair = Qair-1 + F*pNutrlnlet+ G*p(NutrCourse - E*Nutrlnlet) with

Qair-1 equal to the air flow applied at t-1 (t-1 minute, generally equal to 10 minutes), pNutrlnlet, the variation in nutrient (carbon and/or nitrogen) concentration at the inlet of the plug flow, p(NutrCourse - E*Nutrlnlet), the variation in the degree of nutrient (carbon and/or nitrogen) elimination at a point in the course, especially over the first half of the plug flow, F in Nm3/h/mg/l/min, F being between 6000 and 12 000, advantageously equal to 8000 (for a treatment based on the nitrogen measurement and an urban wastewater in Europe), G in Nm3/h/mg/l/min, G being between 1 and 10, advantageously equal to 5 (for a treatment based on the nitrogen measurement and an urban wastewater in Europe), E being unitless, between 0.5 and 0.8.

The air flow may be calculated according to the two formulae (D1) and (D2), chosen by the operator, the formula D2 enabling better adjustment of the air flow supplied.

Advantageously, the oxygen concentration of the water is measured at the end of treatment and the regulation of the air flow is supplemented by adding a correction factor based on this oxygen concentration. A range of oxygen concentration may be determined (Oxygmin / Oxygmax) and when the measured value of the oxygen concentration is outside this range (O2 measured > Oxygmax or O2 measured < Oxygmin), the air flow Qair calculated is corrected:

When the air flow (Qair) is calculated according to the formula (D1), a correction factor of O.Ox may be applied incrementally, in particular to each measurement in which the concentration of O2 measured < Oxygmin, O.Ox increment is added WO 2016/001823 5/24 PCT/IB2015/054868 to the correction factor k, the air flow thus becoming

Qair = k [Qmin + B*Nutrlnlet + C(NutrCourse - E*Nutrlnlet)] with initial k = 1 k being unitless

In the case in which O2 measured > Oxygmax, the correction factor k is decremented by O.Ox.

When the air flow (Qair) is calculated according to the formula (D2), a fixed correction factor may be applied to each measurement of oxygen concentration, in particular, to each measurement in which the concentration of O2 measured < Oxygmin, a correction of (1+0.Ox) is applied, and to each measurement in which O2 measured > Oxygmax, a correction of (1-0.0x) is applied, the air flow thus becoming:

Qair = (1+0.0x)(or 1-0.0x)*[Qair-1 + F*pNutrlnlet + G*p(NutrCourse - E*Nutrlnlet)] with x being unitless.

If the air flow calculated (according to D1 or D2) is equal to Qmin, a decrement is not applied and similarly, if the air flow calculated is equal to Qmax, the correction factor is not incremented.

The invention also relates to a facility for the biological treatment of urban or industrial wastewater via the aerobic pathway, for carrying out the method as defined above, comprising an aerobic pathway plug flow reactor, for the elimination of biodegradable carbonaceous matter and the oxidation of the ammonium, the water to be treated flowing between an inlet and an outlet, and air supplies being distributed under the flow of water and supplied by at least one source of air, the flow of this source being modulated according to at least one treatment parameter, characterized in that it comprises, at the inlet of the reactor/tank, a sensor enabling continuous estimation of the nutrient (carbon and/or NH4) concentration of the water, and a computation unit receiving the information from the sensor and able to control the flow of the air supplies. WO 2016/001823 6/24 PCT/IB2015/054868

Preferably, the facility comprises, over the course of the plug flow, in particular at the halfway point, a sensor enabling continuous estimation of the nutrient (carbon and/or NH4) concentration of the water at this point in the course, the sensor being connected to the computation unit so as to integrate the degree of elimination effectively achieved to modulate the air flow.

Advantageously, the computation unit is programmed to calculate the air flow according to at least two formulae D1, D2.

Preferably, the facility comprises, at the outlet of the plug flow, a probe for measuring the oxygen concentration in the water, this probe being connected to the control unit, in order for the regulation of the air flow to be supplemented by adding a correction factor (k) based on this oxygen concentration.

The sensors for sensing the nutrient (carbon and/or NH4) concentration may be ISE sensors.

The invention makes it possible to ensure a priori regulation of the aeration of the plug flow based on the load to be treated.

In particular, the development of ISE (ion-selective electrode) sensors enables continuous estimation of the nutrient (carbon and/or NH4) concentration of the water. The use of this information makes it possible to predict part of the load to be treated (nitrogenous load) and is used for the regulation of the air. Any other continuous or semi-continuous means of measuring the nutrient (carbon and/or NH4) may be used.

Aside from the provisions described above, the invention consists of a certain number of other provisions, of which mention will more explicitly be made hereinafter with regard to an entirely nonlimiting exemplary embodiment described with reference to the appended drawings. On these drawings:

Fig.1 is a schematic plan view of a biological wastewater plug flow treatment tank.

Fig.2 is a diagram illustrating the variation in the carbonaceous pollution and nutrient (carbon and/or NFI4) concentration, plotted on the y axis, as a function of the course of the plug flow between the inlet and the outlet, plotted on the x axis. WO 2016/001823 7/24 PCT/IB2015/054868

Fig.3 is a diagram of a facility carrying out the method of the invention.

Fig.4 is a diagram illustrating the method of the invention and the variation in the nutrient (carbon and/or NH4) concentration at the inlet of treatment, in the oxygen concentration at the end of treatment, in the calculated air flow and in the supplied air flow, plotted on the y axis, as a function of time, plotted on the x axis.

Fig.5 is a diagram similar to that of fig.4, but in the case of a conventional regulation based on the oxygen concentration at the end of treatment.

Fig.6 is a diagram illustrating the variation in the concentration of oxidizable matter plotted in the y axis as a function of the course of the plug flow, plotted on the x axis, and also the variation in the oxygen concentration in the case of a sufficient supply of air.

Fig.7 is a diagram similar to that of fig.6, in the case of too high a supply of air, and

Fig.8 is a diagram similar to that of fig.6, in the case of a high load of oxidizable matter, with too low a supply of air.

With reference to fig.1 of the drawings, a schematic representation of a tank 1, generally of elongated rectangular shape, for biological plug flow treatment via the aerobic pathway of urban or industrial wastewater can be seen. The water to be treated enters the tank 1 via an inlet 2 and is discharged via an outlet 3, as indicated by arrows. The course of the water in the tank 1 is essentially rectilinear as indicated by the arrow 4, the current lines all being parallel to this arrow, the cross sections moving parallel to one another, as in the case in which the fluid is pushed by a piston, without there being mixing between zones staggered along the longitudinal direction of the tank 1.

Air supplies are distributed under the plug flow, in the bottom of the tank 1 as illustrated in fig.3 by nozzles 5 distributed along the length of the tank. The nozzles 5 are connected in parallel to one and the same pipe 6, oriented along the length of the tank and supplied by a pipeline 7 for air originating from a source A, especially a booster. Regulation of the air flow from the pipeline 7 is provided. This regulation may be ensured by a valve 8 controlled in an appropriate way. As a variant, the regulation could be ensured by modulating the flow from the source A.

The regulation is ensured globally for all the nozzles 5, since separate control of WO 2016/001823 8/24 PCT/IB2015/054868 each of the nozzles 5 would lead to a complex facility and complex use, which is too costly.

The carbonaceous pollution and ammonium concentration in the water, which moves in the tank 1 between the inlet and the outlet, changes as schematically illustrated by the curve 9 of fig.2, on which the pollution concentration is plotted on the y axis while the position along the length of the tank is plotted on the x axis. The concentration, at its maximum at the inlet 2, decreases gradually under the effect of the aerobic treatment by virtue of the supply of air which enables the elimination of the biodegradable carbonaceous matter and the oxidation of the nutrient (carbon and/or NH4). In the plug flow treatment, a concentration gradient is therefore observed between the arrival point of the water and the outlet as illustrated by the curve 9.

The difficulty with a plug flow treatment is ensuring the treatment of all the pollution, regardless of the load of the wastewater at the inlet of the tank 1, while avoiding an excess air supply leading to useless expenditure. The signal of the end of the pollution treatment corresponds to an increase in the oxygen concentration in the water. Indeed, as soon as the oxidizable matter has been totally treated, the oxygen concentration goes from a value close to 0, to 8 mg/l in a few tens of minutes. This is illustrated by the diagram of fig.6 on which the variation in the pollution concentration, plotted on the y axis, is represented by the curve 10 as a function of the position along the length of the reactor 1 according to the curve 10. The variation in the oxygen concentration of the water is illustrated by the curve 11.

The diagram of fig.6 illustrates the aim to be achieved regardless of the load: the oxygen concentration only increases in the vicinity of the outlet of the plug flow, and the concentration of oxidizable matter has reached a value considered to be minimal. In this case, the air supply was just sufficient to treat all the pollution.

The diagram of fig.7 illustrates the case in which the air supply was too high, for example due to a low load of oxidizable matter in the wastewater to be treated. The curve 12 represents the variation in the pollution concentration, while the curve 13 represents the variation in the oxygen concentration. The oxygen concentration increases roughly at the halfway point of the tank, whereas the WO 2016/001823 9/24 PCT/IB2015/054868 pollution concentration has practically reached its minimum value. In this case, the too high supply of air leads to useless expenditure.

Fig.8 illustrates the case in which the air supply is insufficient for the treatment of the pollution to be complete at the outlet of the plug flow tank. The pollution concentration curve 14 remains at a relatively high level at the outlet of the tank while the oxygen concentration curve 15 remains at a level close to 0 due to the fact that not all the oxidizable matter has been treated. This situation may correspond to a case of a high load of oxidizable matter.

By way of indication, the water to be treated passes through the tank or reactor 1 in a few hours.

According to the invention, a sensor 16 enabling continuous estimation of the nutrient (carbon and/or NH4) concentration of the water is installed at the inlet 2 of the plug flow tank. The information provided by the sensor 16 makes it possible to predict part of the load to be treated (nitrogenous load) and is used for the regulation of the air. Any other continuous or semi-continuous means of measuring the nutrient (carbon and/or NH4) may be used. The sensor 16 is advantageously of ISE (ion-selective electrode) type. According to the invention, the air supply is regulated a priori by being based on the load to be treated.

The information provided by the sensor 16, as illustrated in fig.3, is sent to a computation unit 17, in particular a controller or a microcomputer, which outputs 18 an instruction sent to a circuit 19 converting the information originating from the output 18 into a signal for controlling the valve 8, for regulation of the air supply.

Preferably, another sensor 16a for sensing the nutrient (carbon and/or NH4) concentration of the water is arranged in the tank 1 on the treatment course, at a distance from the inlet 1, roughly halfway through the treatment, that is to say at the halfway point of the tank 1. The nutrient (carbon and/or NH4) concentration measured at this point by the sensor 16a makes it possible to integrate the degree of elimination effectively achieved.

The control unit 17 is programmed to determine a priori the necessary air flow. WO 2016/001823 10/24 PCT/IB2015/054868

The parameters used are as follows: - nutrient concentration at the inlet (mg/l): Nutrlnlet, - nutrient concentration at a point of the course (mg/l): NutrCourse, - oxygen concentration at the outlet (mg/l), - applied air flow (Nm3/h): Qair.

The unit 17 is programmed to use at least two modes of calculating the necessary air flow.

Depending on the case, this a priori determination of the air requirements may be supplemented by an a posteriori correction based on the oxygen concentration of the water measured at the end of treatment by a probe 21 arranged in the vicinity of the outlet 2. The information from the probe 21 is sent to the unit 17 in the form of an oxygen concentration setting 22.

The two calculation modes which may be used to determine a priori the necessary air flow Q are described below.

According to a first formula D1: D1 Qair = Qmin + B*Nutrlnlet + C (NutrCourse - E*Nutrlnlet) with,

Qmin (minimum flow) in Nm3/h, B in Nm3/h/mg/l, C in Nm3/h/mg/l, E being unitless.

According to a second formula D2: D2 Qair = Qair-1 + F*pNutrlnlet+ G*p(NutrCourse - E*Nutrlnlet) with Qair-1 the airflow applied att-1 (t-1 minute, generally 10 minutes), pNutrlnlet, the variation in nutrient concentration at the inlet of the plug flow, pNutrlnlet corresponds to the slope, i.e. the tangent of the gradient angle a (fig.4) of the curve illustrating the variation in concentration at the inlet as a function of time, p(NutrMiddle - E*Nutrlnlet), the variation in the degree of NH4 nutrient elimination (carbon and/or NH4) over a first course of the plug flow, F in Nm3/h/mg/l/min, WO 2016/001823 11/24 PCT/IB2015/054868 G in Nm3/h/mg/l/min, E being unitless.

Preferably, for D1 and D2, NutrCourse is measured in the middle of the passage and becomes NutrMiddle.

Depending on requirements, this a priori determination of the air requirements may be supplemented by an a posteriori correction based on the oxygen concentration measured at the end of treatment. The aim of the regulation is to determine a priori the air requirements and to adjust this estimation as a function of the residual oxygen - the values chosen for the coefficients of regulation, corresponding to the different letters of formulae D1 and D2, are adapted to this aim.

The choice of mode for calculating the air flow to be applied is made by the operator, formula D2 giving a better adjustment of the air flow supplied. A range of oxygen concentration is determined as a function of the aeration conditions necessary for the treatment (Oxygmin / Oxygmax), for example a minimum concentration at treatment outlet of 0.75 mg/l and a maximum desired concentration of 2 mg/l) and when the measured value of the oxygen concentration is outside this range (O2 measured > Oxygmax or O2 measured < Oxygmin), the air flow Qair calculated (according to one of the two formulae above, D1, D2) is corrected in this way: - If Qair is calculated according to the formula D1, a correction factor is applied incrementally. For example, to each measurement in which the concentration of O2 measured < Oxygmin, O.Ox increment is added to the correction factor k. The air flow thus becomes

Qair = k [Qmin + B*Nutrlnlet + C(NutrCourse - E*Nutrlnlet)j with initial k = 1 k being unitless.

If the concentration of O2 measured > Oxygmax, O.Ox is subtracted as a decrement from the correction factor k. WO 2016/001823 12/24 PCT/IB2015/054868 -If Qair is calculated according to the formula D2, a fixed correction factor is applied to each measurement of oxygen concentration.

For example, to each measurement in which the concentration of O2 measured < Oxygmin, a correction of (1+0.Ox) is applied, and to each measurement in which O2 measured > Oxygmax, a correction of (1-0.0x) is applied. The air flow thus becomes:

Qair= (1+0.0x)(or 1-0.0x)*[Qair-1 + F*pNutrinlet + G*p(Nutrcourse - E*Nutrinlet)] with x being unitless.

Tests were carried out on an existing plant at 15eC, treating an urban wastewater at 190 mg/l BOD and a mean value of 36 mg/l TKN (Kjeldahl nitrogen). The volume of one treatment zone is 1700 m3 composed for 1/3 of the volume of an anoxic zone and for 2/3 of the volume of an aerated zone. The mean flow permitted over the zone is 2700 m3/h of raw water and the SM (suspended matter) concentration is 4 g/l.

The following parameters were used for the regulation according to the first calculation mode:

Qmin = 9000 Nm3/h corresponding to the air requirement to maintain the biomass in suspension. It is of the order of 2 to 6 Nm3/h/m2 of aerated tank, B = 700 is determined as a function of the project data (permitted load and volume of the works) - its value is between 400 and 1000 according to the configurations retained, C = 400 is determined as a function of the project data (permitted load and volume of the works) - its value is between 150 and 600 according to the configurations retained, and WO 2016/001823 13/24 PCT/IB2015/054868 E = 0.8 corresponds to the portion of the nutrient (carbon and/or NFU) not treated in the first part of the plug flow. It is determined as a function of the project data [permitted load (concentration and COD/TN or total nitrogen ratio) and volume of the works]; its value is between 0.5 and 0.8 according to the configurations retained, x = 0.02, i.e. a 2% modulation of the air flow calculated a priori, and a variation of the order of 200 Nm3/h at each measurement of the oxygen at the end of treatment.

The parameters F and G in the case of the use of formula D2 will take the values of F = 8000, determined as a function of the project data (permitted load and volume of the works) - its value is between 6000 and 12 000 according to the configurations retained, and G = 5, determined as a function of the project data (permitted load and volume of the works) - its value is between 1 and 10 according to the configurations retained.

The results for the example under consideration are represented in fig.4. The curve 23 corresponds to the change in the ammonium NH4 concentration at the inlet of the reactor. The ammonium concentration is plotted on the left-hand y-axis scale in mg/l. The time plotted on the x axis is expressed in minutes. The lower curve 24 corresponds to the oxygen concentration at the outlet of the reactor 1, also expressed in mg/l.

The curve 25 corresponds to the air flow supplied expressed in Nm3/h, according to the right-hand y-axis scale, and the dashed curve 26 corresponds to the air flow calculated by the regulation according to the invention.

It is noted that the regulation makes it possible to correctly monitor the variations in the load to be treated without generating surges in the air requirements, since the variations are smoothed.

Fig.5 illustrates, for the same example of water to be treated, the curves WO 2016/001823 14/24 PCT/IB2015/054868 obtained with a conventional regulation based on the oxygen concentration of the water at the outlet 3 of the treatment tank. The curve 23 of the change in the ammonium concentration is identical to that of fig.4. On the contrary, the curve 25a of the air flow shows abrupt variations, corresponding to surges in the form of peaks 27 and troughs 28, 29. The curve 24a of the oxygen concentration at the outlet of the reactor also has surges corresponding substantially to those of the curve 25a.

Such abrupt variations are detrimental to the facility and also to the treatment, and the invention makes it possible to avoid them.

The solution of the invention especially offers the following advantages: • Simplicity of installation and of start-up - a limited number of parameters have to be determined on the basis of the dimensioning data, • The air requirements change gradually, which makes it possible for the air production equipment (booster, regulation valves, air compressor) to operate easily by limiting situations of blockage or excess pressure and reduced pressure, mainly when several lines are operating in parallel and draw from this equipment in a “disordered” manner, • The air requirements are determined on the load to be treated (a priori regulation) which makes it possible to anticipate the requirements and hence limit flow surges and the energy consumed.

Claims

1. A method for the biological treatment of urban or industrial wastewater via the aerobic pathway, for the elimination of biodegradable carbonaceous matter and the oxidation of ammonium, according to which method the water to be treated flows in plug flow between an inlet (2) and an outlet (3), and air supplies are distributed under the flow of water and are supplied by at least one source of air (A), the flow of this source being modulated according to at least one treatment parameter, characterized in that: - the nutrient concentration (carbon only) of the water to be treated is measured (16) continuously at the inlet (2), - and the flow of the air supplies is modulated according to the nutrient (carbon and/or NH4) concentration measured.

2. The method as claimed in claim 1, characterized in that, aside from the carbon only, the concentration of NH4is measured.

3. The method as claimed in either of claims 1 and 2, characterized in that the nutrient (carbon only or carbon and NH4) concentration of the water during treatment is measured (16a) at a point in the course of the treatment, in particular at the halfway point, so as to integrate the degree of elimination effectively achieved to modulate the air flow.

4. The method as claimed in claim 3, characterized in that the air flow is calculated according to a formula (D1) taking into account the nutrient (carbon only or carbon and NH4) concentration at the inlet of the plug flow Nutrlnlet and at a point of the treatment NutrCourse, especially in the middle,

with, nutrient concentration in mg/l, Qmin in Nm3/h, Qmin being between 2 and 6 Nm3/h/m2 * surface of aerated tank in m2, B in Nm3/h/mg/l, B being between 400 and 1000, advantageously equal to 700 C in Nm3/h/mg/l, C being between 150 and 600 in Nm3/h/mg/l, according to the configuration, E being unitless, between 0.5 and 0.8.

5. The method as claimed in claim 3 or 4, characterized in that the air flow is calculated according to a formula (D2) taking into account on the one hand the flow of air Qair-1, applied at the time t-1, and on the other hand the variation (pNutrlnlet) in nutrient (carbon and/or NH4) concentration as a function of time, at the inlet of the plug flow, and the variation in the degree of nutrient (carbon and/or NH4) elimination over a point in the course, in particular over the first half of the plug flow,

with Qair-1 equal to the air flow applied at t-1 (t-1 minute), pNutrlnlet, the variation in nutrient concentration at the inlet of the plug flow, p(NutrCourse - E*Nutrlnlet), the variation in the degree of nutrient (carbon and/or NH4) elimination at a point in the course, especially over the first half of the plug flow, F in Nm3/h/mg/l/min, F being between 6000 and 12 000, advantageously equal to 8000, G in Nm3/h/mg/l/min, G being between 1 and 10, advantageously equal to 5, E being unitless, between 0.5 and 0.8.

6. The method as claimed in claims 4 and 5, characterized in that the air flow is calculated according to the two formulae (D1) and (D2), chosen by the operator, the formula D2 enabling better adjustment of the air flow supplied.

7. The method as claimed in any one of the preceding claims, characterized in that the oxygen concentration of the water is measured (21) at the end of treatment and the regulation of the air flow is supplemented by adding a correction factor (k) based on this oxygen concentration.

8. The method as claimed in claim 7, characterized in that a range of oxygen concentration is determined (Oxygmin / Oxygmax) and when the measured value of the oxygen concentration is outside this range (O2 measured > Oxygmax or 02 measured < Oxygmin), the air flow Qair calculated is corrected:

9. The method as claimed in all of claims 4 and 8, the air flow (Qair) being calculated according to the formula (D1), characterized in that a correction factor of O.Ox is applied incrementally, in particular to each measurement in which the concentration of O2 measured < Oxygmin, O.Ox increment is added to the correction factor k, the air flow thus becoming

with initial k = 1 k being unitless in the case in which O2 measured > Oxygmax, the correction factor k is decremented by O.Ox.

10. The method as claimed in all of claims 5 and 8, the air flow (Qair) being calculated according to the formula (D2), characterized in that a fixed correction factor is applied to each measurement of oxygen concentration, in particular, to each measurement in which the concentration of O2 measured < Oxygmin, a correction of (1+0.Ox) is applied, and to each measurement in which 02 measured > Oxygmax, a correction of (1-0.0x) is applied, the air flow thus becoming:

with x being unitless.

11. A facility for the biological treatment of urban or industrial wastewater via the aerobic pathway, for carrying out the method as claimed in claim 1 or 2, comprising an aerobic pathway plug flow reactor, for the elimination of biodegradable carbonaceous matter and the oxidation of the nutrient (carbon only or carbon and NH4), the water to be treated flowing between an inlet (2) and an outlet (3), and air supplies being distributed under the flow of water and supplied by at least one source of air (A), the flow of this source being modulated according to at least one treatment parameter, characterized in that it comprises, at the inlet of the reactor/tank, a sensor (16) enabling continuous estimation of the nutrient (carbon only or carbon and NH4) concentration of the water, and a computation unit (17) receiving the information from the sensor (16) and able to control the flow of the air supplies.

10. The facility as claimed in claim 11, characterized in that it comprises, over the course of the plug flow, in particular at the halfway point, a sensor (16a) enabling continuous estimation of the nutrient (carbon only or carbon and NH4) concentration of the water at this point in the course, the sensor (16a) being connected to the computation unit (17) so as to integrate the degree of elimination effectively achieved to modulate the air flow.

13. The facility as claimed in claim 10 or 11, characterized in that the computation unit (17) is programmed to calculate the air flow according to at least two formulae (D1, D2).

14. The facility as claimed in any one of claims 11 to 13, characterized in that it comprises, at the outlet (3) of the plug flow, a probe (21) for measuring the oxygen concentration in the water, this probe being connected to the control unit (17), in order for the regulation of the air flow to be supplemented by adding a correction factor (k) based on this oxygen concentration.

15. The facility as claimed in any one of claims 11 to 14, characterized in that the sensors for sensing the nutrient (carbon and/or NH4) concentration are ISE sensors.