MXPA00010900A - Method for regulating aeration during waste water biological treatment - Google Patents

Abstract

The invention concerns a method characterised in that it consists of the following steps:continuously evaluating the treated medium oxidation-reduction, for actuating the aerating means or not;during the aerating phases, measuring the oxygen concentration and using its value, jointly with those of the oxidation-reduction for:maintaining aeration if the oxygen concentration corresponds to a set value range;decreasing aeration if the oxygen concentration is less than the set range and, producing a self-adaptation of the oxygen set point values by comparing, during the"partial nitrification/total nitrification"transition of the oxidation-reduction potential, the real oxygen concentration, with the system set value range and by adjusting the set value based on said system real oxygen requirement.

Description

PROCEDURE FOR REGULATING AERATION DURING THE BIOLOGICAL TREATMENT OF WASTEWATER Description of the invention The present invention relates to a process for regulating the aeration of a biological treatment plant for waste water, with a view to the elimination of carbonated and nitrogenous contaminations. It is known that sanitation of wastewater is a major problem. It is in this way that the European Union has issued a directive (No. 91/271 / CEE) related to the treatment of urban wastewater that determines the limits of the rejections, in the natural environment, of untreated wastewater. In this way, each treatment unit will affect a precise objective as far as the quality of the water treatment is concerned, being able to give rise to the fact of not reaching such objective, to penalties of the financial or even criminal order. Most of the urban wastewater treatment facilities put the activated sludge process into operation. A The important phase of the process lies in the elimination of the carbon and nitrogen contained in the wastewater, by sequencing the periods of aeration. In fact, it is known that the main problem found in wastewater treatment facilities is to adapt the treatment to variations in the flow or expense of the water to be purified and its pollutant load, in order to obtain a constant quality of purified water and the minimum regulatory amount of pollutant rejects to the natural environment. With this objective, the elimination of carbon and nitrogen requires a very strict and precise control of aeration since this elimination must meet two requirements. According to the first, a sufficient total aeration duration per day must be ensured in order to carry out the oxidation of the carbon components of the wastewater and the stabilization of the sludge; the second is more directly linked to the daily distribution of the aeration phases to provide good nitrogen removal. On the one hand, it is necessary to respect a sufficient duration of a maintenance in aerobic condition for the sludge to carry out the nitrification and on the other hand In part, denitrification requires an appropriate residence time of the effluent in anoxic condition. With this objective, in the low-load activated sludge processes, put into operation in a single aeration pond, the elimination of the nitrogen compounds results from a strict control of the alternation of the aerated and non-aerated sequences. Any lack of regulation or operation of the oxygen supply devices results in a malfunctioning of the purification or purification of wastewater stations, with the repercussions on the quality of the treated effluent, the balance of the purifying biomass and the characteristics of the sludge produced. A mismatch of the aeration sequences thus has short-term effects on the quality of the water obtained, which may therefore contain nitrogenous nitrogenous compounds if the aeration periods are not long enough, or nitrates if the periods of anoxia are very short. On the other hand, when the aeration periods are very long, the effluent to be treated finds anaerobic conditions that must be absolutely avoided. In fact, the anaerobiosis phenomena in the treatment pond, linked to a suboxidation of certain zones, involve in the long term the appearance of filamentous bacteria and these microorganisms induce a modification of the structure of the floccule and a decrease in its aptitude for decantation, which, of course, has an unfavorable impact on the quality and cost of the treatment. Another consequence of an accumulated duration of insufficient aeration refers to the quality of the sludge and, in particular, conditions its stability. It is understood that the regulation of aeration is one of the key points of such a water treatment process. Various regulatory procedures have been put into operation. Among them, the following techniques can be mentioned: 1) the most rustic technique in the field of aeration of biological ponds is the clock that, according to a program defined by the user, allows the oxygen to be distributed at certain moments of the day, without any correlation with the real needs of the installation. - - *. -sJSgfeftE. ) a slightly improved technique is the decision of the aeration as a function of a high threshold and a low threshold of the oxide-reduction potential (Redox potential) measured on the installation: the decision is made on an information at the moment T, the information that can be denied a few seconds later,) a more rigorous technique has been put to the point by the present owner (FR-A-2 724 646). This procedure takes into account various Redox potentials, the derivative of the variation of this Redox potential and the history of the purification station, thus approaching the notion of the expert system,) other logical regulating devices rely on the measurement of the concentration of oxygen in the water to be purified; this notion that does not really make sense, after the phases of non-aeration of the ponds, the measurement of the concentration of oxygen is then replaced by a clock that will allocate a time of non-aeration (period of anoxia), for example 40 to 60 minutes, followed by a period in which the regulation will be effected effectively on the oxygen setpoint, for example with a progressive stop of the aeration turbines, one by one, 5) Certain attempts of regulation have been made in relation to the measurement of the concentration of ammonia and nitrate compounds in the aeration tank, characterizing the efficiency of nitrification and denitrification and, consequently, the oxygen needs of the purification station. The putting into operation of the various techniques of the prior art mentioned above reveals the numerous drawbacks that attest to their limitations. Among these drawbacks, the following will be cited: 1) Subjection or slavery to a time clock does not take into account the variations in the pollutant load inflicted on the station due to the irregularity of the contributions of water to be treated, 2) The method of the ORP thresholds does not take into account the historical facts of the purification station, such as temporary overloads, random equipment failures, etc. ) The procedure according to the French patent FR-A-2 724 646 allows to ensure effective decontamination, on carbon contamination, in the nitrification plan and in the denitrification plan. However, the objective of this procedure is to ensure sufficient aeration, which is in fact translated, always due to an excess of oxygen supply. Now, this excess can be penalizing from an economic point of view. On the other hand, from the point of view of the water, the aeration phase is affected since it starts in the presence of a relatively high proportion of oxygen, from 7 to 8 mg / l, which is going to be eliminated before starting to use oxygen from nitrates. For the same denitrification duration, the aeration stop phase will be longer, and the effective treatment time is reduced by one day. ) The putting into operation of the technique based on a simple measurement of the concentration of oxygen in the water to be purified, does not allow controlling the progress of the denitrification reactions that take place in activated sludge ponds, since There is a need for a zero concentration of oxygen for the achievement of this phase. In addition, the oxygen concentrations necessary to ensure nitrification can evolve in a range from 3 to 7 mg / l, mainly as a function of the oxidation state of the sludge present in the biological reactor. 5) The technique based on the measurement of the concentration of ammonia and nitrate compounds in the aeration pond is not significant more than in the large stations, taking into account the high prices of the equipment. On the other hand, this technique never takes into account the oxidation state of the sludge since a measurement of the oxidation reduction potential according to FR-A-2 724 646 allows to evaluate the physiological state of the sludge. The drawbacks of the solutions according to the prior art mentioned above, lead then to look for the means that allow to optimize the different reactions in the ponds ..., of aeration of the purification or purification station, always administering more judiciously the oxygen contributions to the latter. This is the problem solved by the present invention. The object of the invention is therefore a process for regulating aeration in a biological treatment plant for waste or used water, which operates a carbon removal stage, a nitrification stage and a denitrification stage, characterized in that it includes the following stages: 1) continuously measure the value of the oxidoreduction potential of the treated medium, allowing the aeration means to be activated or not, 2) in the course of the aeration phases, measure the concentration of oxygen and exploit its value, together with those of the oxide-reduction potential to: maintain aeration if the oxygen concentration corresponds to a setpoint limit; decrease aeration if the oxygen concentration is higher than the setpoint limit and, increase the aeration if the oxygen concentration is lower than the setpoint limit and, 3) carry out a self-adaptation of the oxygen slogans comparing, at the moment of the transition of the oxide-reduction potential "partial nitrification / total nitrification", the actual oxygen concentration, with the setpoint limit of the system and adjusting the setpoint value according to the actual oxygen requirement of said system. According to the present invention, when the Redox transition "partial nitrification / total nitrification" intervenes in the lower area of the oxygen concentration setpoint, the value of this setpoint is reduced. According to the invention, when the value of the redox transition "partial nitrification / total nitrification" is not reached for the setpoint value of the oxygen concentration, the latter is increased. It is understood that the objective method of the present invention constitutes a combination of a process as defined in FR-A-2,724,646, which includes a tracking of the derivative of the variation of the oxide-reduction potential, with a tracking of the signal of "oxygen concentration" only in the course of the aeration phase. Schematically, the analysis of the values of the oxidation-reduction potential allows defining the duration of the sequence of running and stopping the installation, and the analysis of the values of the concentration of oxygen allows to control the power before being put into play. in the course of the aeration phases. According to the invention, the combination of the ORP potential measurement plus the measurement of the oxygen concentration in absolute value [Q2] / the continuous comparison of said parameters allows the deduction and confirmation of the coherence of the information received on this combination. the station. In this way, thanks to the operation of the procedure according to the invention, there is access to various information and possibilities of primary interventions related to the station's state, mainly such as: - control of the reliability of the collectors of the station. Redox potential and oxygen concentration; the control of the reliability of the equipment or the identification of pollution overloads; the finest analysis of the biological state of the sludge; the possibility of readjusting the setpoint values of the oxygen concentration, depending on the operation of the sludge; and addressing the denitrification phase with a relatively small proportion of residual oxygen and ensuring a rapid start of the denitrification phase. Other features and advantages of the invention will emerge from the description made later with reference to the accompanying drawings in which: Figure 1 is a diagram that highlights the different steps of the method of the invention as defined above, Figure 2 is a scheme that allows to understand the putting into operation of the method of the invention and, - Figure 3 is a curve illustrating the variations of the threshold of oxygen concentration as a function of time, taken on an industrial installation. As mentioned above, the different steps of the method of the invention, illustrated by the scheme of figure 1 can be summarized as follows: First, at the time of the start phase, maximum aeration of the possibilities of the installation, in order to make a massive contribution of oxygen: experience shows that this massive contribution is useful for the proper functioning of the purification: Stage 1: Measured in a continuous way the value of the Redox potential (EH) of the treated medium, allowing the aeration means to be activated or not (suppressor of the aeration).

Stage 2: Examination of this ORP potential: if the value of this potential is high, nitrification and removal of carbon is done well; If the value of the ORP is low, this is due to insufficient nitrification and carbon removal, which necessitates an examination of the oxygen component of the regulation.

Stage 3: Proceed to a measurement of the oxygen concentration of the treated medium and to the examination of this concentration (see figure 2). The following cases may occur: a) whether the oxygen concentration value [02] is in the area of the figure 2 called "Oxygen Setpoint Limit", the aeration power must be maintained, b) whether the oxygen concentration value [02] is located in the area designated by reference 2 in Figure 2 (ie below the setpoint of [02]: it is necessary to increase the oxygenation power or, in the absence of this, maintain the aeration suppressors to the maximum of their operation in order to provide the necessary amount of oxygen, c) either that the value of [02] is located in the area designated by reference 3 in figure 2 (ie above the setpoint limit of [02]), the ORP potential may be insufficient but the oxygen setpoint is exceeded: aeration is reduced or, in the absence of this, aeration suppressors are maintained at their minimum operation. d) Whether the value of [02] is located in the area designated under reference 1 in figure 2 (Redox potential and very low oxygen concentration) this situation may correspond to an overload of the station (strong respiration of the sludge) or a deficiency of the equipment or sensors: in this case, the invention provides for the activation of an alarm and, e) whether the value of [02] is located in the area designated by reference 4 in the Figure 2: the simultaneity of a high proportion of oxygen with an average Redox potential can indicate a lack of sensors or even intoxication of the biomass (weak respiration of the sludge): in this case, the invention also foresees the activation of an alarm .

Last stage: It has been seen above that the invention provides for an additional step that lies in the autoadaptation of the slogans of oxygen concentration. At the moment of the transition of the oxidoreduction potential from the zone of "partial nitrification" to the zone of "total nitrification", the invention provides for a measurement of the oxygen concentration of the system in order to modify the values of the setpoints of oxygen, which allows to reassess the real needs of oxygen, necessary for the achievement of the nitrification reactions and for the complete oxidation of the constituents of the sludge. If this Redox transition intervenes in the zones 1 6 2 (Figure 2) the oxygen concentration values, the oxygen requirement required by the biomass is small and, according to the invention, the oxidation setpoint is reduced, which allows favor an economy of energy relative to aeration. On the contrary, when the value of the Redox transition can not be regularly reached under the proposed oxygen concentration setpoint conditions, there is a significant need for oxygen and it is therefore necessary to increase the value of the setpoint [02]. This increase makes it possible to ensure procedure and favor in this case a reoxygenation of the sludge. In figure 3 of the attached drawings, the evolution of the oxygen concentration threshold, as a function of time, has been represented, allowing this figure to resurface how, by putting into operation the method of the invention, a self-adaptation of the thresholds of the slogan [02]. This figure 3 represents the evolutions of the oxygen thresholds over the duration of the study period (noticeably 1 year). The so-called B-points of real value represent the concentrations of dissolved oxygen reached when the Redox potential indicates a step from "partial nitrification" to "complete nitrification" in "PHASE 3". The continuous and more stable line represents the oxygen setpoint defined by the management logic, based on real values. The variations are here damped, so as to limit the modifications of the instructions, always facilitating the procedure. The important to note the range of variation of this value of the slogan [02] that translates the important evolution of the real needs of biomass (rejuvenation of populations). In fact, the curve in Figure 3 teaches that the biological system can work very well in total nitrification with a dissolved oxygen ratio of the order of 2 to 3 mg / l (case of "aged" sludge), while in certain cases (more "young" sludge); a proportion of 5 to 6 mg / l will be proven to be insufficient to ensure total nitrification. The invention makes it possible to overcome this difficulty and this leads to a self-adaptation of the operating conditions. In the following table, the comparative results have been indicated, obtained in three installations that put into operation respectively a biological wastewater treatment procedure without automatic regulation (A), with an automatic regulation of the Redox potential EH only (B), and with an automatic regulation of the Redox potential EH and concentration of oxygen according to the present invention (C). This table makes clear the advantages, mainly economic, brought about by the operation of the process, object of the present invention.

D Among the advantages provided by the process object of the invention, the following can be mentioned mainly: Modulation of the aeration power provided, necessary for the achievement of the reactions of treatment of the carbon and nitrogen pollutants; The possibility of verification of the coherence of the received information and of detection of the limiting events, that occur in the purification station and, The possibility, by a finer experience of the needs of the sludge, of carrying out a self-adaptation of the own slogans of system regulation with a view to its reliability. It is understood that the present invention is not limited to the embodiments described and / or mentioned above, but it encompasses all variants that come within the scope of the appended claims.

Claims (5)

1. Aeration regulation procedure in a biological wastewater treatment facility, which puts into operation a carbon removal stage, a nitrification stage and a denitrification stage, characterized in that it includes the following stages: 1) continuous measurement the value of the oxide-reduction potential of the treated medium, allowing the aeration means to be activated or not; 2) in the course of the aeration phases, measure the concentration of oxygen and exploit its value, together with those of the oxide-reduction potential to: maintain aeration if the concentration of oxygen corresponds to a setpoint limit; decrease aeration if the oxygen concentration is higher than the setpoint limit and, increase the aeration if the oxygen concentration is lower than the setpoint limit and, 3) carry out a self-adaptation of the oxygen slogans comparing, at the moment of the transition of the oxide-reduction potential "partial nitrification / total nitrification", the actual oxygen concentration, with the system setpoint limit and ^ * | «S ^ í ^^ 5g ^^^ =? TA | a by adjusting the value of the slogan according to the real need for oxygen in said system.

2. Process according to claim 1, characterized in that, when the transition from the oxide-reduction potential of the partial nitrification zone to the total nitrification zone is involved in the lower zone of the setpoint value of the oxygen concentration, it is reduced to value of this slogan.

3. Process according to claim 1, characterized in that, when the value of the transition of oxide-reduction potential of the zone: partial nitrification to the total nitrification zone is not reached for the setpoint value of the oxygen concentration, this last is increased.

4. Method according to claim 1, characterized in that, when the value of the oxygen concentration is very low as well as the oxide-reduction potential, an alarm is triggered.

5. A method according to claim 1, characterized in that at the moment of a simultaneity of one, a high proportion of oxygen and a weak dioxide-reduction potential, an alarm is triggered.