EP1360149A1

EP1360149A1 - Self-adaptive method for regulating an effluent treating plant, in particular for waste water

Info

Publication number: EP1360149A1
Application number: EP02703656A
Authority: EP
Inventors: Patrice Chatelier; Gilles Carrand; Jean-Marc Audic
Original assignee: Ondeo Services
Current assignee: Ondeo Services
Priority date: 2001-02-12
Filing date: 2002-02-05
Publication date: 2003-11-12
Also published as: SK9962003A3; AR032670A1; MXPA03007180A; US20040089614A1; CZ20032124A3; CN1494514A; CA2437637A1; FR2820732B1; US6916422B2; ZA200306084B; AU2002237349B2; FR2820732A1; CN1257112C; HUP0303872A2; HUP0303872A3; WO2002064514A1

Abstract

The invention concerns a method for regulating an effluent treating plant, in particular for waste water or sludge derived from that type of treatment, using in particular ponds and cells provided with aerating means, for eliminating carbonaceous, nitrogenous, phosphate pollutants and a regulating automaton operating on the analysis of the evolution of predetermined operating parameters of the plant. The invention is characterised in that: the automaton uses periods during which the station is under-loaded to impose on it abnormal operating conditions, and the automaton analyses the response of the plant to said abnormal operating conditions to update and optimise the plant operating parameters for heavy-load periods, by automatically adjusting the parametering of the automaton logic. In the implementing example, the method is used for controlling the aeration of a purification plant.

Description

Self-adaptive method for regulating an effluent treatment plant, in particular wastewater

The present invention relates to a self-adaptive method for regulating effluent treatment stations, in particular waste water or sludge which results from this type of treatment. The invention can be applied in particular to such treatment stations in which various pollutions, in particular carbonaceous, nitrogenous or phosphatic, are eliminated. It is known that these installations use treatment basins or cells provided with aeration means and that they generally comprise an aeration regulation system designed so as to allow corresponding pollution elimination yields to be obtained. to the maximum that can be reached by the capacity of the station.

Examples of embodiments of such regulation systems are described in FR-A-2 724 646 and 2 765 210.

In these treatment stations, it is necessary to carry out a physico-chemical phosphate removal for which reagents such as in particular ferric chloride are used, which leads to a modification of the values of the redox potential of the wastewater. being processed. This type of interference is detrimental to any regulatory system taking into account the evolution of the oxidation-reduction potential for the management of the aeration of the treatment basins, as is the case for the systems described in the cited publications. above. In this case, the thresholds of the original logic of the regulatory system are unsuitable for the treatment of elimination of nitrogen pollution (nitrification and denitrification) and it is then necessary to reposition these values.

Indeed, the presence of a reagent for the simultaneous physico-chemical phosphate removal in the aerated sludge of the wastewater treatment stations leads to a modification of the oxidation-reduction equilibria. These reagents are powerful oxidants and their addition to sludge (for example in the form of ferric chloride or aluminum salts) generates an increase in the redox values obtained, which is variable depending on the amount of reagents injected into the sludge. In addition, it appears in practice that the redox values increase with difficulty appreciable depending on the reagent used and the operating conditions of the station (for example modification of the load or the treatment rate, breakdown of the reagent dosing pump). Such sensitivity to changes in operating conditions in operation requires regular adaptation of the thresholds in the logic of the regulatory system. The generalization of the phosphate removal treatment of wastewater, required by national and European regulations, leads to a repetition of this type of problem on existing treatment plants and the present invention has set itself the objective of providing a solution . To this end, it appeared to the present holder that, firstly, it was necessary to link the redox reference values to measurable operating parameters on the sites and to define new threshold values according to the conditions of exploitation linked, for example to simultaneous physico-chemical dephosphatation. In a second step, it seemed desirable to develop an automated logic allowing the predefined redox thresholds to be varied in the logic of the regulation system, in order to get rid of manual interventions of resetting of the thresholds of the station management logic. processing (including ventilation) for any modification of operating conditions. This self-adaptation of the redox thresholds of the regulation automaton must be able to be carried out whatever the type of reagent used and whatever the operating conditions of the station. This should make it possible to ensure the performance of the treatment of nitrogen pollution (nitrification and denitrification) in a sustainable manner whatever the operating context.

Another constraint which the invention had to hold

10 account is that of avoiding any additional addition of material to the treatment installation, in order to be able to implement the method which is the subject of the invention on regulation systems produced in accordance with the prior art mentioned above.

15 Consequently, the present invention relates to a method for regulating an effluent treatment station, in particular waste water or sludge which results from this type of treatment, implementing in particular basins or cells provided with means

20. aeration, in particular with a view to eliminating carbon, nitrogen and phosphate pollution and a regulation automaton operating on the analysis of the evolution of the station's operating parameters, chosen in advance, this process being characterized in that:

25 - the PLC uses the periods during which the station is underloaded to impose abnormal operating conditions on it and

- the automaton analyzes the station's response to these abnormal operating regimes to update and optimize

30 the operating parameters of the station for periods of high load, by automatically adjusting the configuration of the logic of the PLC.

Thus, the method which is the subject of the invention ensures repositioning of the threshold values of the oxidative potential.

35 reference reduction used in the regulation machine according to the prior art specified above above so as to maintain the guarantee of the results of treatment of carbonaceous and nitrogenous pollution in the presence of a simultaneous physico-chemical phosphorous removal. The operation of this logic allows the controller to automatically adapt to all operating conditions.

Thus, according to the invention, the maximum oxidation level reached by the sludge in the aeration tank is determined in order to automatically adapt the thresholds 10 predefined in the logic of the regulation automaton.

According to an embodiment of the invention:

- the values of the redox potential are recorded during an aeration forcing period, this period corresponding to a period during which the station is

15 underloaded;

- the maximum level of the redox potential is detected as well as its stabilization resulting in the presence of a redox plate;

- we measure the value of this redox plate and store it; 20. - the operation is repeated over a fixed period, for example of the order of a week;

the average of the redox plateau over the measurement periods of the latter is calculated and said average is used to obtain an update of the redox potential thresholds, by comparison with the original redox potential thresholds, the automaton then operating at from these new thresholds.

We will now describe, in detail, an embodiment of the process which is the subject of the invention, applied to a treatment station comprising a physico-chemical dephosphatation simultaneous with treatments for eliminating carbon and nitrogen pollution. As will be explained below, this is only a non-limiting example of implementation, the method according to the invention being capable of receiving other applications. The conditions forcing the aeration during the underload period of the wastewater treatment plant, the conditions for recording the forcing value, the conditions for calculating the average of the values and obtained, the comparison between the average thus calculated and the original redox thresholds and the authorized translation of the redox thresholds of the logic of the regulation automaton.

Conditions for forcing and stopping ventilation

The objective of forcing the aeration is to make the redox evolve to high values and to detect a stabilization thereof during the night period, characteristic of underloaded periods.

In this exemplary implementation of the method of the invention, the forcing of the aeration corresponds to the commissioning for a maximum duration of 2 hours of all the aeration organs available during the night period between 2:00 and 8:00 in the morning. The start of forcing must correspond to the first start on a regulation cycle between 2h00 and 8h00, the maximum ventilation is then requested. There can be only one and only forcing during the period considered. The maximum ventilation time allowed here will be 2 hours. If after 2 hours the redox has not stabilized, the ventilation will stop automatically. Stopping the ventilation after forcing will correspond to a return to service of the regulation system, i.e. 2 hours maximum shutdown.

In accordance with the process which is the subject of the invention, the forcing of the aeration must be carried out during underloaded periods. The night slot 2h00 to 8h00 chosen in the example of implementation described here, is representative of the conditions linked to urban waste water. The forced period can be modified in contexts precise (case of regular nocturnal rejection), without departing from the scope of the invention.

Detection of a redox plateau during forcing

5

The detection of what should be called a redox plate (defined below) will be used to determine the maximum level of oxidation of the sludge reached in the presence of the dephosphating reagent.

10 The redox value recorded for the detection of the redox plateau will be the average over one minute of the values scanned by the automaton, this in order to limit the effect of variation of the redox.

In this implementation example, the stabilization of the

15 Redox is governed as follows: during the maximum 2 hours of aeration, if the redox does not increase or decrease by more than 20 mV for a time of 15 minutes, then the ventilation stops. These conditions correspond to the appearance of stabilization corresponding to

20 the appellation “redox plateau”. The maximum value recorded during the 15 minutes of stabilization will be memorized and stored in the PLC. This value will correspond to the D-day redox plate.

If no redox plateau could be detected, then the

25 forced ventilation will end after 2 hours. No forced redox value will be memorized for this specific day.

Conditions for calculating the average redox forcings

30

The calculation of the mean of the redox forcings will serve to dampen the possible fluctuations of these values, so as to initiate actions in a time representative of the inertia of the mud and reactive mixing system. 35. A calculation of the average of the redox forcing values recorded will be requested every 7 days, in this example of implementation. For this, conditions must be met before authorizing the controller to average the values.

These conditions essentially concern the number of values:

- if the number of forcing values recorded (trays reached) over the 7 days is greater than or equal to 4, then the average of the values can be calculated;

- conversely, if the number of forcing values is strictly less than 4, then the mean of the values is meaningless and should not be calculated. The average will not update and will remain the same as the previous week. This absence of a new mean value will be listed. The average forcing value of the week will be used for comparison with the current threshold values of the regulation system, so as to determine their relevance under the updated operating conditions. If the calculation of the weekly average could not be carried out, this will inform of a significant beat of the measurement, which can be linked to a problem with the redox electrode, unusual nocturnal consecutive events, ...

Use of the weekly average redox forcings

The average value obtained will be compared with the value of the high threshold 2 (see the table below) in progress in the logic of the regulation system. The high threshold 2 corresponds in fact to the maximum value that it is possible to reach when the oxidation of the sludge is satisfactory on the station. This comparison will serve to determine the relevance of the thresholds used, and modify them if necessary. This comparison used to update the thresholds will be carried out for example once a week. The weekly average value will be used as follows.

- If Threshold 2 high present - average value> + 25 mV then drop by one level in all the redox thresholds of the logic of the regulation system.

- If Threshold 2 high present - average value <- 25 mV then increase by one level of all the redox thresholds of the logic of the regulation system.

- If Threshold 2 high present - average value <+ 25 mV and> - 25 mV then no action is requested and the regulation system continues to operate with the thresholds preceding this calculation.

These comparative tests will make it possible to determine the difference existing between the values of the thresholds of the logic of the regulation system used and the current redox values. An update of the thresholds will be requested if the calculated difference exceeds 25 mV. If the difference is greater than +25 mV then a decrease in the thresholds is requested, conversely if the difference is greater than -25 mV then an increase in the thresholds is necessary.

Request to translate the thresholds of the control system logic

The thresholds will evolve according to the criteria of a predefined table. This table will allow the redox thresholds to be changed in steps of 25 mV for most of the regulation system thresholds, depending on the case in steps of 50 mV for the low restart threshold. The table below shows the translation of the thresholds. BOARD

Evolution of redox thresholds in the logic of the regulatory system

This table indicates a translation of the redox thresholds in steps of 25 mV for thresholds 1, 2 and 3, and in most cases for the low threshold of the logic of the regulation system. A single translation step is authorized after each weekly average calculation. These steps correspond to a slow evolution of the system and indicate a nonetheless significant change in the redox balance within the activated sludge of the installation.

Changes in authorized thresholds are limited to a maximum of 600 mV, corresponding to very strong redox measurements and rarely reached on sanitation stations. Beyond this threshold, no increase is authorized and an alarm informs of this excess.

In low values, the redox thresholds are bounded by the original thresholds of the logic of the regulation system

(level n-3). This makes it possible to cope with a stop of the injection of dephosphating reagent taking into account the inertia of the system. Indeed, one to three months approximately are necessary for the total disappearance of dephosphating reagent within the sludge (inertia relative to more than three ages of sludge). The decrease in steps of 25 mV will thus gradually reach the thresholds of the logic of the regulation system. This minimum threshold corresponding to the logic threshold of the regulation system makes it possible to manage the disappearance of dephosphating reagent and to continue to regulate the aeration on known bases without faulting the automatic

10 regulation.

A product such as dephosphating reagents acts on the redox electrode as a strong oxidant. This effect is especially predominant at low redox values corresponding to the resumption of aeration. For this, a

15 additional increase in the redox restart threshold compared to the other thresholds is necessary in order to limit the ventilation downtime. The low threshold was defined at 225 mV for the reference translation level n. A regular pitch of 25 mV cannot include all of the

20 translations, a step of 50 mV has been defined between thresholds 2 of 400-450 mV, in order to be able to reach the low threshold corresponding to the predefined threshold in the logic of the regulation system.

To facilitate commissioning and expertise

25 which may follow, the translation n represented in bold in the table above will correspond to the redox values during the initialization of the logic. Indeed, the sites encountered until now in condition of simultaneous physico-chemical phosphate removal, were functioning

30. with maximum redox values of around 500 mV / H2 during aeration. This makes it possible to reach the boundaries of the redox thresholds established in the translation table, within a maximum of three weeks.

For practical reasons of writing the program,

35 the values entered in the table above will be theoretical values. Indeed, it will be accepted every values of the thresholds of the control system logic ending differently from 0 or 5. Programming of threshold 2 high and threshold 2 low will automatically update the other thresholds of this logic. In this way, we can find all units between 0 and 5, but always with a constant differential between the different thresholds corresponding to said logic.

Parameter initialization

Before the PLC is put into service, the initialization values must be configured. The main initialization values concern the redox thresholds of the logic of the control system at the start of the program. These must be at level n described in the table above.

The intermediate level of these thresholds in the number of translation, makes it possible to start the automaton in any initial redox conditions. In addition, this level corresponds to the thresholds commonly encountered on physico-chemical phosphate removal sites. One week is enough for the automaton to position itself at 25 mV higher or lower and three weeks are necessary to reach the imposed limits.

The example of implementation above related to the adaptation of the predefined thresholds in the logic of the automatic regulation machine to the case of sites with simultaneous physico-chemical dephosphating. In this adaptation, the automaton uses periods when the station is underloaded to impose abnormal operating regimes on it (here the automaton forces ventilation for a period of 1 day when this is not necessary). The automaton analyzes the response of the installation to these abnormal operating regimes to adjust its operating parameters. It will therefore be perfectly configured to make the most of the installation during periods of high load. Thus, according to the process which is the subject of the invention, the automaton uses periods when the installation is under load to adjust its configuration for periods of high load.

The idea underlying the present invention therefore consists in using a reactor or a machine, during a period of underload, to optimize the parameters for periods of overload. In the example of implementation described above, it was applied to the control of the aeration of a treatment plant. Other applications are possible without departing from the scope of the invention. Some examples are given below.

- Controlling the ventilation of underloaded or variable load stations: in these two types of operation, the operation of regulation systems using redox potential thresholds can pose problems. These thresholds are characteristic of a state of the station for a given load. If this load changes, the threshold values must be adjusted. Likewise, thresholds programmed for a usual charge must be modified when installing the automation on a station with very low load. The device implemented above automatically performs this adjustment of the redox thresholds of the automation.

Optimization of a flocculant dosage in sludge treatment: this is for example the case of units where a thickening grid is coupled to a band filter. For a few moments, the mass flow of sludge to be treated can be limited while varying the flocculant flow rate and by measuring the water flow drained by the thickening grid. It is thus possible to adjust (taking into account the quality of the sludge to be treated) the flow rate of flocculant relative to the flow rate of water drained by the thickening grid. During this operation, the operation of the grid is not optimal. This deficiency must be compensated by the band filter, which is quite possible given the limitation of the mass load to be treated during this phase.

- There are also known methods for measuring the total amount of sludge contained in a biological wastewater treatment plant. In this regard, reference may be made to FR-A-2 769 305. This technique is applicable to installations the charge level of which is low enough to produce an effluent the quality of which is compatible with European regulations. For these load levels, normal operation of the installation automatically implies that the mass of biomass contained in the clarifier of the treatment station is negligible during periods of hydraulic underload (usually at night). This condition is necessary and sufficient - so that this method of measuring the total mass of sludge contained in an installation can be implemented.

The present invention makes it possible to extend the field of application of the method for measuring the total mass of sludge contained in an installation in accordance with the French publication mentioned above FR-A-2 769 305.

In the case where, even during a period of hydraulic underload, the mass of biomass contained in the clarifier is not negligible, the present invention can be applied, by imposing maximum values of the recirculation flow rate. This unusual attitude in those skilled in the art will result in the emptying of the clarifier and will allow the measurement of the total sludge mass contained in the installation.

- The aeration basins of treatment plants are usually stirred. The purpose of this mixing is to homogenize the concentration of materials in these basins. Those skilled in the art therefore keep this mixing system in action as far as possible. It is also necessary (see FR-A-2 784 093) in an automation system to measure the ability of the sludge to settle. This measurement is carried out by a manual decantation test in a test tube. The present invention makes it possible to avoid this manual measurement.

It is therefore necessary to stop the device during a period of non-aeration, and this, for a limited limited time (for example one hour), then to monitor the concentration of suspended matter at a given depth of the basin (for example 50 centimeters). Analysis of this curve gives those skilled in the art a measure of the ability of the sludge to settle. In order to avoid any malfunction of the installation, it is necessary to stop the agitation during periods of underload of the treatment unit.

It remains to be understood that the present invention is not limited to the embodiments and / or applications described and shown above, but that it encompasses all variants thereof.

Claims

1 - Method for regulating an effluent treatment station, in particular waste water or sludge which results from this type of treatment, using in particular basins or cells provided with aeration means, with a view to elimination of carbonaceous, nitrogenous and phosphatic pollution and a regulation automaton operating on the analysis of the evolution of

10 operating parameters of the station chosen in advance, characterized in that: the automaton uses the periods during which the station is underloaded to impose abnormal operating modes on it and

15 - the automaton analyzes the response of the station to these abnormal operating regimes in order to update and optimize the operating parameters of the station for periods of high load, by automatically adjusting the configuration of the logic of the automaton.

20. 2 - Method according to claim 1, applied in particular to the simultaneous treatment of carbonaceous, nitrogenous and phosphatic pollution, characterized in that the automaton forces aeration during a period during which the station is underloaded and it analyzes the response of the

25 station at this abnormal operating speed to adjust the operating parameters of the station by optimizing them for periods of overload.

- 3 - Method according to claim 2, characterized in that:

30 - the values of the redox potential are recorded during an aeration forcing period, this period corresponding to a period during which the station is under-loaded; - the maximum level of the redox potential is detected as well as

35 its stabilization resulting in the presence of a redox plateau; - we measure the value of this redox plate and store it;

- the operation is repeated over a determined period, for example of the order of a week;

- the average redox plateau is calculated over the measurement periods of the latter and

- Said average of the redox plateau is used to obtain an update of the redox potential thresholds, by comparison with the original redox potential thresholds, the automaton then operating on the basis of these new thresholds.

4 - Method according to claim 1, applied to the dosing of flocculant in sludge treatment, in particular on units implementing a thickening grid coupled to a band filter, characterized in that: - for a determined period, we limit, the mass flow of the sludge to be treated, while varying the flocculant flow rate; the water flow drained by the thickening grid is measured; and - the flocculant flow rate is adjusted relative to the water flow drained by the thickening grid.

5 - Method according to claim 1, applied to the measurement of the total mass of sludge contained in a biological treatment plant, characterized in that, during periods of under hydraulic load, maximum values of the sludge recirculation flow are imposed , which results in the emptying of the clarifier from the station and the total mass of sludge contained in the station is measured.

6 - Process according to claim 1, applied to the measurement of the capacity of the sludge to settle in a treatment plant comprising a mixing of the aeration tanks in order to ensure the homogenization of the concentration of suspended solids in the sludge , characterized in that:

- stirring is stopped during periods of underload; - we follow the evolution of the concentration of suspended matter at a determined depth of the aeration tank;

- the curve obtained is analyzed and - the ability of the sludge to settle is deduced therefrom.