Method and arrangement for processing nitrogen-concentrated effluents in a sequential fractionated cycle biological reactor

[0001] The subject of the invention is a method of treating wastewater with a high nitrogen content, realizing the oxidation of ammonium nitrogen to nitrites (nitrates

III), followed by the transformation of nitrite (nitrates III) to gaseous nitrogen in a biological sequential reactor, in which the reaction phases are divided into fractions, in a process in which the volume of wastewater to be treated is poured into a reactor containing nitrifying bacteria, with the operating conditions being designed to stimulate the action of nitrifying bacteria I, and to maximally inhibit the action of nitrifying bacteria II, they include treatment cycles with at least one oxygenation phase to induce nitrification followed by a phase in which oxygenation is stopped and a carbon source is introduced into the reactor to convert nitrite (nitrite III) into nitrogen.

[0002] More specifically, the invention relates to a waste water treatment process in which the nitrogen concentration is higher than 100 mg N / L.

Waste water treatment process with high nitrogen content [0003] Many installations for the treatment of pollution encounter in receiving environments increasing problems regarding the control and processing of nitrogenous waste, mainly ammonia. Ammonia can cause environmental damage, such as reducing the oxygen content in the aquatic environment, toxicity to fish or causing eutrophication. In order to limit the adverse impact on the environment, the regulations impose more and more stringent limits on sewage disposal, which often leads to costly works related to the reconstruction of existing treatment plants.

[0004] One of the main methods of nitrogen processing is the biological nitrification / denitrification process, in which ammonium nitrogen is oxidized in two stages under oxygenation conditions, first to nitrites (nitrates III) and then to nitrates, and then reduced to nitrogen gas under conditions hypoxia. In the case of concentrated wastewater, by controlling various parameters, it is possible to shorten the biological process by partial nitrification to nitrites (nitrates III), which are then directly denitrified. This process, also called "bypass process

[Shunt] nitrates', has already been described in patents EP-A-826639 and WO 00/05176, and theoretically may reduce the need for oxygen for nitrification by

25% and the demand for biodegradable coal for denitrification by 40%, as well as reducing the production of heterotopic sludge.

[0005] Wastewater treatment plants equipped with anaerobic digesters generate discharged wastewater with a high content of ammoniacal nitrogen (in the order of 1000 mg N / l) in the sludge treatment process, which, after being re-transferred to the beginning of the installation, can constitute up to 20% of the total nitrogen load. The specific process of their processing would allow, in many cases, to avoid costly work related to the reconstruction of the main wastewater treatment line in order to meet the requirements related to the limits for discharged wastewater. In addition, more and more stations are forced to process generated waste or gaseous wastewater, generating condensates with a high content of ammoniacal forms, which must be obligatorily limited. Ultimately, waste perlate is the third type of wastewater for which ammonium is one of the main sources of pollution. [0006] All types of wastewater generally contain very little biodegradable carbon, which means that biological processing equipment can be dimensioned almost exclusively as nitrogen treatment equipment. Biological processing, bypassing nitrates, would reduce significant costs over the conventional nitrification / denitrification process.

Bypass nitrates in the SBR configuration (sequential biological reactor) [0007] Fux C., Lange K., Faessler A., ​​Huber P., Grueniger B. and Siegrist H.

(2003), in an article titled "Nitrogen removal form digester supernatant via nitrite-SBR or SHARON?", Which appeared in Water Science and Technology Review, Volume 48, No. 8, pp. 9-18 (2003), showed the benefits of the use of a sequential biological reactor (SRB) consisting of feed, reaction (oxygenation + hypoxia), deposition and removal phases to introduce a nitrate bypass process from wastewater with a high nitrogen content. In fact, the SRB configuration allows the use of significant volumetric charges through biomass retention in the same reactor, as opposed to the SHARON process

EP 1 910 233 B1 (patent EP-A-826639), in which the lack of biomass retention allows for specific leaching of the biomass responsible for the oxidation of nitrites (nitrates III) to nitrates (V). According to the SRB Fux process & al. the volume of wastewater to be processed in the full cycle is transferred to the reactor according to consecutive volume fractions, the entire processing cycle is divided into successive sub-cycles, each sub-cycle contains a volume phase supply, then an oxygenation phase to nitrification, followed by an anaerobic phase during which oxygenation is stopped, and a carbon source is introduced into the reactor to convert nitrites (nitrates III) into nitrogen.

[0008] For wastewater such as the supernatant (top layer above the sludge) from the anaerobic digestion chamber, condensates from gas processing and waste peroclates, it is particularly difficult to optimize the reactions of nitrite production and reduction (nitrates III) for two main reasons:

• These wastewater are subject to significant fluctuations in ammonium nitrogen intensity and content, which necessitates constant adaptation of the operating criteria in order to provide wastewater of consistent quality.

• Environments with a high salt content and a variety of ionic compounds, such as those listed in the invention, can have a negative impact on the performance of the probes (contamination of the sulfur-reducing oxidation reactors) and cause deviations that cause the equipment to immediately switch to a temporary mode with poorer performance .

[0009] In view of the above, it is desirable to design a robust wastewater management system in order to increase the reliability of nitrogen processing from wastewater with its high content by bypassing nitrates in the SBR reactor. [0010] The present invention assumes the elimination of nitrogen from wastewater with its high content through a nitrification / denitrification process in a biological sequential reactor (SBR) in which the sequence comprises several feed / oxygenation / hypoxic phases of individual volume fractions. The amount and duration of individual phases, as well as the introduction of the carbon reagent, are adjusted thanks to a series of measurements made in real time on the treated wastewater, in the effluent and in the biological reactor.

[0011] The wastewater treatment process with a high nitrogen content according to the invention, in the type described above, in which the volume of wastewater to be processed in the full cycle is transferred to the reactor according to successive volume fractions, the full processing cycle being divided for subsequent sub-cycles, each of the sub-cycles contains a volume fraction feed phase, then an oxygenation phase to induce nitrification, then an anaerobic phase, during which oxygenation is stopped and a carbon source is introduced into the reactor to convert nitrites (nitrates III) into nitrogen, it is characterized by a series of measurements in real time on the processed wastewater, in the effluent and in the biological reactor, the nitrogen volume charge to be processed in the wastewater is assessed and the minimum number of full cycle feed phases depending on this nitrogen charge and the minimum fluid volume in the reactor is determined based on the following formula:

<img file="PL1910233T3_D0001.tif" />

where:

Nzasilmin: minimum number of power cycles

FNH4J: daily nitrogen load [NH4⁺] eff: concentration of ammonium ions in the effluent effluent from the reactor

Vmin: minimum liquid volume (after discharge and before feeding)

NRBS: number of complete SBR cycles per day [NH4⁺]: concentration of ammonium ions inhibiting nitrifying biomass in such a way that the concentration of nitrogen in the volume fraction entering the reactor is diluted in the volume of fluid remaining in the reactor, which avoids inhibiting the action of nitrifying bacteria, but the nitrogen charge in the volume fraction is, however, sufficient providing "portion" or peak of ammonium ion in the reactor when transferring each fraction, which promotes the development of nitrite-producing biomass (III nitrates).

[0013] Preferably, the process estimates the volumetric nitrogen load for processing contained in the wastewater by measuring the conductivity (X) and the flow (Q) of the wastewater.

[0014] Preferably, the dissolved oxygen concentration in the reactor is measured and controlled to keep the values ​​low enough while reducing the duration of the oxygenated phases and adjusting the amount of oxygen input to the charge for processing.

[0015] The minimum Nbiolmin number of aerobic / anaerobic sub-cycles may be determined so as not to exceed the total duration of the biological reaction chosen to limit the variation in dissolved oxygen concentration in the range of 0 to 2 mg O2 / I.

[0016] The pH indicator inside the reactor is measured and pH autoregulation is ensured by exchanging similar nitrification and denitrification phases, limiting pH oscillations between 6.5 and 8.5, and a preferred limitation between 7 and 8.

[0017] "Aerobic / anaerobic" biological cycles with fixed duration of aerobic and anaerobic phases are defined in advance, with the total tC duration of these reaction phases being calculated as a function of the number of NC cycles:

^{tC = (t}RBS ^{- vol}Enrich^{- vol}sedym ^{- vol}extract^{) / NC} where:

tRBS: duration of the full cycle SBR tzasil: duration of the full feed (not split into fractions) tsedym: duration of the sedimentation phase text: duration of the extraction phase [0018] The "aerobic / anaerobic" biological cycle actually used is the cycle whose oxygenation duration corresponds as accurately as possible to the theoretical oxygenation time calculated on the basis of the input charge, configuration of the reactor oxygenation system and reaction kinetics. The duration of anaerobic phases is limited to a degree that reduces the risk of anaerobic conditions.

[0019] The introduction time of the carbon source in the anaerobic phase is determined on the basis of measuring the introduced nitrogen load. Preferably, the nitrogen elimination efficiency is calculated and compared to the minimum efficiency, while the introduction of the carbon source in the anaerobic phase is optimized depending on

EP 1 910 233 B1 from the results of the comparison, by adjusting the factor input to the input for processing.

[0020] The process is preferably used to purify supernatants from anaerobic digestion chamber or to process condensates from gas treatment, or to process waste perlate.

[0021] The invention also relates to installations for the treatment of wastewater with a high nitrogen content, especially containing more than 100 mg N / l, which oxidize the amount of ammonium ions to nitrites (nitrates III), followed by the conversion of nitrites (nitrates III) to gas nitrogen a sequential biological reactor in which the reaction phases are divided into fractions, which reactor contains nitrifying bacteria, the operating conditions of which have been anticipated to stimulate the action of nitrifying bacteria (I) and maximally inhibit the action of nitrifying bacteria (II), the volume of wastewater for processing in the full cycle is transferred to the reactor according to successive volume fractions, the full processing cycle is divided into successive sub-cycles , each of the sub-cycles contains the phase of feeding by volume fraction, then the oxygenation phase to induce nitrification, then the anaerobic phase, during which oxygenation is stopped and a carbon source is introduced into the reactor to convert nitrites (nitrates III) into nitrogen, this installation is characterized by the fact that it consists of devices for assessing the volume of nitrogen charge for processing in wastewater, in particular a conductivity probe ( X) and a flow meter measuring the flow rate (Q) of wastewater, and devices for calculating and controlling the number of full-cycle feed phases depending on this nitrogen load and the minimum volume of fluid in the reactor, such that the concentration of nitrogen in the volume fraction entering the reactor is diluted in the volume of fluid remaining in the reactor, which avoids bacterial inhibition nitrifying, however, the nitrogen charge in the volume fraction is, however, sufficient to ensure in the reactor "portions" or peaks of the ammonium ion charge when transferring each fraction, conducive to the development of nitrite-producing biomass (nitrates III).

[0022] The installation consists of a conductivity probe and a flow meter placed on the sewage outlet and other sensors in the

In the reactor, in particular conductivity sensors, dissolved oxygen concentration, reducing oxidation potential and pH, all probes and sensors are associated with a controller to enable continuous monitoring of the evolution of wastewater treatment and control of corrective actions.

[0023] Preferably, the installation comprises a carbon source and a metering pump controlled by a controller regulating the duration of metering the carbon source during the anaerobic phase, the metering time being determined based on measurements of the nitrogen load introduced.

[0024] The installation consists of oxygenation means controlled by a controller based on measurements of dissolved oxygen concentration.

[0025] The invention allows, by optimized division into fractions of the feed phase, oxygenation phase and anaerobic phase of a given SBR cycle in several stages, to produce beneficial effects in relation to nitrogen processing by bypassing nitrates:

a) "portioning" the ammonia charge [0026] In a continuous feed system, for example according to patent EP 0 826 639, the concentration of substrates in the reactor is equal to the concentration measured at the reactor outlet. Given that the concentration of ammonia directly determines the kinetics of nitrite (III nitrate) production, it is very difficult to obtain both high speed and processing efficiency.

[0027] In SBR, the fact that a division into successive volume or reservoir fractions is used allows the concentration of ammonium at the beginning of the sub-cycles and stimulation of the action of nitrifying bacteria (I) by inhibiting the action of nitrifying bacteria (II), and thus achieving significant reaction speed. However, given the high concentration of ammonia in the environment, the individual "portions" of charge should be divided into fractions in order to dissolve them in the reactor and to avoid inhibiting nitrite producing biomass.

[0028] The process described in the invention allows for an optimal division into feed fractions, allowing maximization of the ammonium nitrogen conversion rate while avoiding inhibition of biomass.

EP 1 910 233 B1

b) limited oxygenation management [0029] The SBR configuration allows biomass retention. Accordingly, the choice of nitrite-producing biomass (III nitrates) by limiting the age (period of activity) of the sediments (process principle according to patent EP 0 826 639) is not applicable. Maintaining a low concentration of dissolved oxygen in a biological pool during the oxygenation phase is necessary to ensure the formation of nitrites (nitrates III) while avoiding the formation of nitrates.

[0030] Due to the strong variability of the type of wastewater for treatment, there is a risk of incorrect adjustment of the supplied oxygen, both due to a quantitative deficiency or incorrect distribution of oxygen during the aerobic / anaerobic sequence.

The invention allows better control at a low level of dissolved oxygen concentration by limiting the duration of the oxygenation phases and by adjusting the amount of oxygen supplied to the charge to be purified.

c) autoregulation of the ambient pH value [0032] The maintenance of the pH value between 6.5 and 8.5 avoids the inhibition of ammonium nitrogen producing biomass. In contrast, the SBR process used in the nitrate bypass process may increase the impact of ammonia charges in relation to the biomass oxidizing ammonium nitrogen at the beginning of each charge and indirectly lead to lower pH values ​​in the oxygenation phase. In fact, protons are released during nitrite (III nitrate) production, while hydroxyl ions are released during denitrification. Their impact on the pH of the environment is much greater if they can accumulate during the stage of covering the tank.

[0033] The invention allows better self-regulation of the ambient pH by replacing similar phases of nitrification and denitrification.

d) optimized anaerobic phase control

[0034] Maintaining the extended duration of the anaerobic phase under low-charge conditions can lead to anaerobic conditions that degrade the proper operation of the process and can lead to contamination of the sensors used.

[0035] The invention reduces the risk of anaerobiosis by limiting the duration of anaerobic phases.

[0036] Furthermore, during the anaerobic phase, availability of biodegradable carbon must be ensured to complement denitrification. Considering that the waste water in question usually contains very small amounts of biodegradable carbon, it should usually be introduced from an external source at the denitrification stage. It is very important to optimize the amount of factor added, which is one of the main cost points of the process. Usually a suitable constant average dosage is used depending on the previously determined average nitrogen load, based on the theoretical stoichiometric coefficient or a coefficient established on the basis of experiments.

[0037] The invention allows to optimize the addition of biodegradable carbon by adjusting the amount of agent added to the load to be processed.

[0038] The invention consists, in addition to the above assumptions, a number of other assumptions, which will be discussed in more detail in the following embodiment with reference to the attached drawings; however, these assumptions are not restrictive in any way.

[0039] The subject of the invention is illustrated in a drawing in which:

Fig. 1 is a schematic diagram of a plant with a sequential biological reactor for applying the process according to the invention,

Fig. 2 - graph showing level variations in the reactor, depending on time, during the processing cycle,

Fig. 3 shows successive full cycle phases and sub-cycles,

Fig. 4 - synoptic diagram of the installation operating according to the process,

Fig. 5 - graph showing fluctuations in the reactor:

EP 1 910 233 B1

- water height, expressed in meters (m),

- dissolved oxygen concentration expressed in mg / l,

- pH

- conductivity X expressed in mS / cm (millisiemens per centimeter),

- and the ammonium nitrogen concentration expressed in mgN / l represented on the ordinate, depending on the time, expressed in hours, represented on the coordinate axis, and

Fig. 6 - graph showing fluctuations in ammonia concentration expressed in mgN / l and flow rate expressed in m³/ day depicted on the ordinate axis, depending on the time shown on the coordinate axis.

[0040] The diagram of Figure 1 shows a sewage treatment plant with ammonium nitrogen content in which the nitrogen concentration exceeds 100 mgN / L (100 mg nitrogen / liter). This plant consists of a sequential biological reactor 1 filled, for a full cycle, by volume or tank fractions and removed after processing. Waste water poured into reactor 1 is also called "inlet waste water". In the reactor 1, the minimum volume of fluid Vmin remains after its removal, the level of this fluid is indicated by a horizontal line 2 in Fig. 1.

[0041] The sequential biological reactor, abbreviated SBR, contains nitrifying bacteria I, which contain nitrate-promoting bacteria (oxidizing ammonium nitrogen to nitrite) and nitrifying bacteria II (oxidizing nitrite to nitrate). The operating conditions were designed to stimulate the nitrifying bacteria and oxidizing ammonium nitrogen to nitrite (nitrite III) and to inhibit nitrifying bacteria II, oxidizing nitrite to nitrate maximally.

[0042] The open buffer tank 3 was placed upstream of the reactor 1. The supply of the reactor 1 to the wastewater for treatment is guaranteed by a pump 4 installed on the pipe 5 led out of the open buffer tank 3. The removal is ensured by, for example, the pump 6 and the pipe 7 forming the chamber nipple up to level 2. Carbon source 8, for example

A methanol tank was provided to allow the metering pump 9 to inject methanol or another carbon source into the reactor during the anaerobic phase. Oxygenation devices 10 are provided at the bottom of the reactor 1, e.g. perforated ducts connected to a source of compressed air, e.g. a hydrophore 11, via a solenoid valve 12.

[0043] During the processing sub-cycle, after feeding the volume fraction, in the first aerobic phase, the oxygenation of the reactor 1 is ensured by pumping air into the conduits 10 and generating bubbles in the waste water in the reactor to convert ammonium nitrogen into nitrite under the action of nitrifying bacteria (AND). In the next anaerobic phase, oxygenation is stopped, a carbon source, e.g. methanol, is introduced into the rector 1 by means of a metering pump 9 to convert nitrites (nitrates III) into nitrogen. Together, the oxygenation phase and the anaerobic phase form the biological cycle of the sub-cycle.

[0044] The term "full cycle" refers to all operations carried out to process a volume corresponding to the capacity of the reactor between maximum level 13 and minimum level 2 of fluid. At the beginning of the full cycle, the level is minimal, then the reactor is filled up to the maximum level 13, and after processing the liquid is removed from the rector until the minimum level 2 is reached.

[0045] Reactor 1 is fed with successive volume fractions for the full cycle. The volume of sewage supplied to each fraction is only part of the reactor capacity, so that the concentration of nitrogen in the sewage is dissolved in the content of the reactor and remains at an acceptable level to avoid inhibition of nitrifying bacteria by too high a nitrogen content. And so, subsequent fractions of wastewater introduced into the reactor will cause the fluid level to rise according to successive stages 14, 15, 16 and 13 (Fig. 2) or by four stages as in the analyzed example. If the introduced sewage has a concentration significantly exceeding the concentration inhibiting the activity of nitrifying bacteria, which should not be exceeded, the division into supply fractions dilutes the filled fraction in the volume of fluid already present in reactor 1, which avoids exceeding the inhibitory concentration.

[0046] At the beginning of the injection of each volume fraction, a "portion" or peak P (Fig. 5) of an ammonia charge is generated, favoring the development of nitrifying biomass to the detriment of nitrate-producing biomass despite the retention of sludge specific to reactor 1. Most preferably peak P is maintained at a level exceeding 125% of the concentration of ammonia that characterizes the end of a given sub-cycle, for a period of time equal to at least a quarter of the duration of the sub-cycle.

[0047] Measuring probes and sensors are provided at various installation locations. The sewage conductivity measuring probe 17 and flow meter 18 are provided on the sewage supply line. The measurement results are transmitted in the form of electronic signals to electronic computing and control devices consisting of a computer or a C controller with a microprocessor. Measurements of conductivity and flow rate allow the controller C to determine the nitrogen load, which is introduced to the rector 1 in a given time period. A conductivity probe 19 and a flow meter 20 are provided on the removal line; the measurement results are also transferred to the C controller. In the reactor fluid 1, which is a biological reservoir, a probe 21 for measuring dissolved oxygen, probe 22 for measuring the reduction of oxidation potential and probe 23 for measuring the pH coefficient, as well as a temperature sensor 24 are provided. All these probes and sensors are connected to the C controller, which controls the start or stop of pumps 4, 6 and 9, as well as the opening or closing of the solenoid valve 12, as well as the operation or suspension of the hydrophore 11.

[0048] As shown schematically in the lower part of Fig. 3, the full cycle comprises several successive sub-cycles, while each of the sub-cycles comprises the following stages:

- supplying the volume fraction,

- and a biological cycle with an oxidation phase to convert the aerobic nitrification process and an anaerobic phase to convert nitrites (nitrates III) to nitrogen. The full cycle ends with a stage of sedimentation and then removal. The times of individual phases and stages may fluctuate.

EP 1 910 233 B1

The upper part of Figure 3 schematically shows the "portions" or P-peaks of the ammonia charge [NH4 +] expressed in mgN / L, elicited by the feed at the beginning of each sub-cycle. The P-peaks are shown in more detail in the graph in Fig. 5. [0049] In order to adapt the operation of the process to the variability of wastewater for treatment, the determination of the number and duration of phases, as well as the addition of carbonaceous factor 8 is performed by the controller C, according to the program introduced to the controller, based on real-time measurements on three levels:

1) in raw wastewater to determine the nitrogen load at the input and clarify the number of sub-cycles "supply / oxygenation / anaerobic cycle", duration of oxygenation and addition of carbon source,

2) in outflows to determine the processing efficiency and allow retroactive adjustment of the process,

3) in a biological reactor to control the proper course of biological processes during aerobic and anaerobic cycles.

[0050] In the following, the individual components of the process according to the invention are described in detail.

1) Utilization of wastewater measurements for processing [0051] The nitrogen load introduced for a given time is determined by, for example, measuring the conductivity made using probe 17 and flow rate using a flow meter 18 or using special sensors • Optimal distribution into supply fractions during the general SBR cycle is carried out so as to increase the kinetics of nitrite production (III nitrates) by impacts with ammonia concentration, but while avoiding deterioration of bacterial activity.

This fractionation is obtained by starting or stopping the pump 4.

• The daily oxygen demand, as well as the duration of the oxygenation phase necessary to meet this demand, is determined in

EP 1 910 233 B1 depends on the installed oxygenation capacity and the number of oxygen / anaerobic cycles used.

• The demand for biodegradable coal is determined on the basis of theoretical or experimental factors, and then the operating time of the pump 9 dosing the carbon medium during the anaerobic phase is determined. Pump 9 operation is controlled by the C controller.

[0052] The minimum number of feeding phases Nzasilmin (or the number of consecutive volume fractions) of the full SBR cycle is determined by the controller C depending on the volume charge of nitrogen to be processed (a larger charge causes an increase in the number of cycles) so as to avoid inhibition by ammonia concentrations. The following formula can be used to calculate the minimum fractions to be used for daily charge:

<img file="PL1910233T3_D0002.tif" />

where:

Nzasilmin: minimum number of feed cycles (or volume fractions) FNH4, j: daily nitrogen load [NH4⁺] eff: concentration of ammonium ions in the effluent effluent from the reactor

Vmin: minimum liquid volume (after discharge and before feeding)

NRBS: number of complete SBR cycles per day [NH4⁺]: concentration of ammonium ions inhibiting nitrifying biomass; depends on the pH coefficient and the temperature of the environment and the concentration of [NH3] inhibitory ammonia inhibit the population of bacteria present in the reactor as:

<img file="PL1910233T3_D0003.tif" />

[0053] Concentrations of only 10 mg N-NH3 / L can be toxic to nitrifying bacteria.

[0054] Controller C determines the minimum number of Nbiolmin aerobic / anaerobic sub-cycles so as not to exceed the total duration

In a given biological reaction selected in such a way as to avoid fluctuations in dissolved oxygen concentration and too high a pH level and prolonged anaerobic periods.

[0055] In order to maintain robustness and proper processing, the amount of feed fractions should be combined with the number of aerobic / anaerobic sub-cycles in such a way that one sub-cycle "feed / aerobic / anaerobic" is used. The number of NCs actually used for the sub-cycles will therefore be the largest between Nzasilmin and Nbiolmin.

[0056] After determining the number of "feed / aerobic / anaerobic" sub-cycles, a number of "aerobic / anaerobic" sub-cycles are pre-determined in which the duration of the oxygen phase and the anaerobic phase is determined. The total duration of tC of these reaction phases will be determined depending on the number of NC sub-cycles:

<img file="PL1910233T3_D0004.tif" />

[[057] An "aerobic / anaerobic" sub-cycle effectively used is one whose oxygenation length best corresponds to the theoretical length calculated by controller C based on the input charge, reactor oxygenation system configuration and reaction kinetics. Similarly, the operating time of the methanol 9 metering pump will be able to be calculated by the C controller based on the input nitrogen load measurements.

[0058] The calculation of the average nitrogen load is made during an appropriate period, for example during the duration of the biological cycle, the feed period, the hydraulic retention time or the length of the day, because, given the significant variability of the types of processed wastewater, too short a time range can lead to system instability, and too long a time range can lead to the determination of oxygenation levels and / or the addition of a carbon source generally not adapted to the amount of waste water to be processed.

2) The use of measurements for discharged wastewater [0059] It is possible to improve the oxygenation process by introducing an automatic retroactive fit depending on

The nitrogen elimination efficiency in biological treatment calculated by C on the basis of measurements at the inlet and outlet lines of reactor 1.

[0060] In order to optimize the addition of carbonaceous agent, it is possible to establish an automatic backward adjustment system of the dosing pump 9 based on measurements at the inlet (17, 18) and the outlet (19, 20) of the biological tank. If the nitrogen elimination capacity calculated by the C controller is higher than the previously specified minimum capacity, the C controller gives the command to shorten the operation time of the dosing pump 9 in order to reduce the amount of added carbon (initially calculated depending on the load introduced). In the event of deterioration of the quality of treated wastewater at the outlet of reactor 1, the first corrective action recommended by controller C will be to restore the initial working time of the dosing pump 9. The periodicity of this adaptation should take place after at least 3 periods of sludge activity in order not to introduce too much system disturbance. It is recalled that the age (period of activity) of the sludge is the ratio between the mass of sludge present in the reactor and the daily mass of sludge extracted from the reactor.

[0061] This application is particularly useful for wastewater treatment with a high nitrogen content to which the process of the present invention applies, for which alternative autotrophic denitrification processes have been written, leading to virtually zero demand for biodegradable carbon.

[0062] To recommend appropriate corrective action, it is often useful to combine this information with information provided by sensors that determine the state of the system in the biological tank, i.e., the fluid in reactor 1.

3) Use of measurements for the biological tank [0063] The process can use information provided by individual sensors installed in the biological tank, such as conductivity sensor 21, dissolved oxygen concentration 22, reducing and oxidizing potential 23 and pH 24,

EP 1 910 233 B1 connected to the controller C, which will allow continuous monitoring of the evolution of purification and recommending corrective actions. Temperature sensors are also foreseen: the temperature in the reactor is measured and then the temperature is controlled so as to keep it between 5 and 45 ° C.

[0064] The length of the aerobic and anaerobic phases initially determined depending on the nitrogen load to be processed and, optionally, the nitrogen elimination efficiency can thus be changed by the controller C depending on the set values ​​or conductivity thresholds, the dissolved oxygen concentration, the redox potential and / or pH . And so, the operation of the 10.11 oxygenator can be:

- adjustable depending on the dissolved oxygen setpoint and / or derivative of the redox potential and / or conductivity.

- stopped or resumed depending on the levels of dissolved oxygen and / or reduction and oxidation potential and / or pH through the controller C, recommending starting or stopping the operation of the hydrophore 11, by opening or closing valve 12.

[0065] The choice of sensors and the type of oxygenation control will be determined depending on the specific technical and economic constraints of the system.

[0066] The diagram in Fig. 4 shows a complete management system based on measurements of the flow rate Q and conductivity X at the inlet and outlet of reactor 1 and the measurements of dissolved oxygen concentration 02, pH, ORP reduction and oxidation potential and conductivity X in the reactor biological 1. Measurement of the charge at the entrance to the reactor allows determining the number of NC sub-cycles with the duration of tC, and the duration of the oxygen phases (t aer) and anaerobic phases (t anox). The modification with the option smaller C (x-1) or larger C (x + 1) is made depending on the capacity calculations (R) and measurements on the line in the biological reactor.

Example [0067] The average nitrogen load of the supernatant from the centrifugation of fermented sludge is 150 kg N / day at an average concentration of 600 mg N-NH4⁺/ l but

EP 1 910 233 B1 variables between 400 and 1000 N-NH4⁺/ L. It is also assumed that the power supply was stopped for a period of three days as a result of failure of the centrifuges around the twentieth day, which resulted in zero flow (Fig. 6).

[0068] This nitrogen load is processed in a 450 m sequential biological reactor (SBR)³where the fluid height varies between 3 and 4 meters, in 3 complete cycles of 8 hours / day. The minimum supply fraction (Nalimmin) in 4 phases was calculated taking into account the following assumptions: [NH4⁺] eff = 50 mg N / l, [NH3] inhib = 10 mg N-NH3 / l, pH = 8.3, T = 25 ° C. The resulting biological time tC was coherent with the minimum specified by the system. Therefore, four "feeding / aerobic / anaerobic" sub-cycles were used before the sedimentation and removal steps to avoid inhibition by concentration of the highest pH ammonia to apply a sufficient oxygenation period and to avoid prolonged anaerobic periods. In this configuration, five biological reaction periods (oxygenation / anaerobic phase) were determined (Table 1).

Table 1: Full cycles and biological cycles (sub-cycles) of the SBR reactor used to process nitrogen from wastewater in the anaerobic fermentation chamber by bypassing nitrates.

<td>Number of SBR cycles / day</td><td> 3</td>

<td>Cycle time SBR</td><td>8 hours</td>

<td>Power period</td><td>60 min</td>

<td>Sedimentation period</td><td>30 minutes.</td>

<td>Extraction period</td><td>30 minutes.</td>

<td>Number of cycles biological / cycle SBR</td><td> 4</td>

<td>Duration cycle biological / SBR cycle</td><td>90 min</td>

EP 1 910 233 B1

<td rowspan="2">Cycle biological</td><td colspan="2">min./cykl</td><td colspan="2">godz./dzień</td>

<td>oxygenation</td><td>phase anaerobic</td><td>oxygenation</td><td>phase anaerobic</td>

<td>Cycle 1</td><td> 15</td><td> 75</td><td> 6</td><td> 18</td>

<td>Cycle 2</td><td> 30</td><td> 60</td><td> 9</td><td> 15</td>

<td>Cycle 3</td><td> 45</td><td> 45</td><td> 12</td><td> 12</td>

<td>Cycle 4</td><td> 60</td><td> 30</td><td> 15</td><td> 9</td>

<td>Cycle 5</td><td> 75</td><td> 15</td><td> 18</td><td> 6</td>

[0069] The introduced nitrogen load is calculated by the controller C once a day based on the average conductivity measurements transmitted by the probe 17 and the measurements of the flow fraction supplied by the flow meter 18. The conductivity / ammonia ratio has been previously established for the above-mentioned wastewater. The theoretical periods of oxygenation and anaerobic phase are calculated on the basis of the charge to be processed in relation to the oxygen demand (relative to the nitrite intermediary), while checking whether the reaction kinetics are not limiting. In this way, the closest of the five pre-defined time options is used. At the same time, the operating time of the methanol 9 metering pump is determined depending on the demand for biodegradable carbon (relative to the nitrite intermediary) of the charge being introduced, while checking that the reaction kinetics are not limiting.

[0070] Fig. 5 shows typical changes in the supervisory and control parameters of reactor 1 during four full sub-cycles

8 hour cycle:

• Dissolved oxygen concentration

The dissolved oxygen measuring probe 22 allows oxygenation to be regulated between 1 and 2 mg O2 / L setpoints; a longer duration of the oxygen phase would cause more frequent stops and restart of the hydrophore 11.

EP 1 910 233 B1

The curve consisting of dashes 02 in Fig. 5 shows fluctuations in concentration 02, which increases in the aerobic phase and decreases or disappears in the anaerobic phase.

• pH

The pH curve represents oscillations of the pH coefficient, which decreases in the aerobic phase and increases in the anaerobic phase. The pH remains between 6.5 and 8.5, practically 7 and 8.

If the feed would not be divided into fractions, the pH would probably be lowered during the aerobic phases up to the value inhibiting the activity of ammoniacal nitrogen oxidizing bacteria.

• Conductivity

The X (conductivity) curve shows the decrease in conductivity during the anaerobic denitrification phase as a result of the transition of nitrogen ionic forms into nitrogen gas. At the end of the period, the conductivity derivative approaches zero, reflecting full denitrification.

NH4 curve⁺ shows P-peaks of ammonia concentration or ammonia "charge portions" at the beginning of the feed of each volume fraction, relative to the levels of the H curve of the water level. P-peaks reach 100 mgN / L and exceed 65 mgN / L (125% of 52 mg N / L measured at the end of the cycle) only at a time less than a quarter of the duration of the sub-cycle.

[0071] The elimination of ammoniacal nitrogen from the system takes place by bypassing nitrates, with the oxidation of ammoniacal nitrogen to nitrites (nitrates III) in the aerobic phase and reduction of nitrites to gaseous nitrogen during the anaerobic phase due to the added carbon. The pressure exerted by the ammonia charge portions at the beginning of each biological sub-cycle, combined with the maintenance of a low dissolved oxygen concentration in the oxygenation phase, allows the selective development of nitrifying biomass to the detriment of biomass contributing to the formation of nitrates, despite the retention of sludge specific to the SBR reactor.

[0072] The measurement of conductivity at the end of the purification process, through probe 19, allows the nitrogen elimination efficiency to be correctly determined, and serves as an alarm to correct any system deviations. And so, with a set minimum capacity of 80%, it was reduced to 70% when using Biological Cycle # 2. Controller C stated that the dissolved oxygen concentration did not exceed 1 mg / l during the oxygen phase during the day, reflecting incomplete oxygenation of the ammonia charge, then cycle 3 was recommended, including the longer oxygen phase. Measurement of conductivity by sensor 21 in a biological reactor may also be useful. And so, a few days later, again a reduction in efficiency was observed, while the derivative of the conductivity measurements in the anaerobic phase did not approach the value 0, reflecting incomplete denitrification. The consequent action was the application of cycle No. 2.

[0073] A circuit for re-adjusting methanol dosing has been installed so as to limit the operation time of the dosing pump every 15 days. In the event of a reduction in the nitrogen elimination capacity below the set minimum value, the operating time of the pump 9 is reset to the previous value.

[0074] The process according to the invention allows for significant savings in relation to aeration energy (25%), addition of carbon medium (40% minimum) and production of sludge (about 30%), while constantly providing sufficient amounts of air and coal to process the load contaminated in a sequential biological reactor. This configuration allows the use of larger volumetric charges compared to other reactors with constant feed, previously described as part of the process of nitrogen processing by bypassing nitrates.

EP 1 910 233 B1