FR2575455A1 - Process for biological purification of waste water and activated sludge tank for its implementation - Google Patents

Abstract

Biological purification techniques. The process is characterised in that the sludge to be recycled entering the regeneration is divided into two parts 19, 20 and 21, 22, the part 19, 20 going directly to the regeneration, while the part 21, 22 is thickened and then mixed with the first part 19, 20 of the sludge to be recycled for their simultaneous regeneration, such that in the first purification stage 2 the ratio of the organic contaminants in the waste water 1 arriving at the purification to the activated sludge 3, 4 remains constant. The invention applies especially to the total biological purification of concentrated industrial waste water containing organic contaminants which are difficult to oxidise.

Description

 The present invention relates to the purification of waste water loaded with organic pollutants, and in particular relates to a process for the purification of waste water by activated sludge, as well as a tank with activated sludge for its implementation.

 The invention can be applied with maximum efficiency to the total biological purification of concentrated industrial fallow deer water containing organic pollutants which are difficult to oxidize, when the arrival of wastewater for purification is irregular, both in quantity and in composition.

 The invention can also be applied to the total biological purification of urban waste water in the case of common sewer systems, when all the waste water - domestic, industrial and rainwater - is discharged by a common network of conduits and canals beyond the city limits.

 The invention can also be applied to the total biological treatment of urban waste water in the case of separate sewer systems, when rainwater and conventionally clean industrial water are evacuated by a network of conduits and canals. , and polluted domestic and industrial wastewater is discharged through one or more other networks, as well as in the case of combined sewer systems.

 The processes for the biological purification of waste water by activated sludge are based on the ability of aerobic microorganisms to use various materials as nutrients, and, first of all, the organic materials present in the waste water, by oxidizing them. during their activity of living organisms. In this way, artificially developed microorganisms, whose concentrate is called "activated sludge", rid the wastewater of pollutants by meeting their energy needs and ensuring the growth of biomass. Biologically, it is possible to treat (oxidize) a very large number of diverse organic matter and coraplexes. Also treated are certain mineral compounds: hydrogen sulfide, ammonia, nitrites, etc. However, wastewater also contains materials that do not oxidize or only partially oxidize biologically. Biological purification is said to be total if the total biochemical oxygen demand (BOD) of the purified water is less than 20 rng / l, and it is said to be incomplete If your DFO is greater than 20 mg / l. Such a minas determination is, to a certain extent, conventional, because, even in the case of total biological purification, the water still contains a determined quantity of impurities.

 Biological treatment is usually carried out in reinforced concrete tanks, called activated sludge tanks. In activated sludge tanks, a mixture of sludge with a concentration usually between -1.5 and 2.5 g / l is subjected to continuous aeration by an oxygenated gas (air), supplied by a disperser, during its journey from the start of the basin to its exit, then the activated sludge is separated from the purified waste water and is recycled in the basin.

 According to the hydrodynamic structure of the bacterial mixture flows, a distinction is made between displacement activated sludge tanks, in which waste water and activated sludge are admitted and discharged at their ends, and activated mixer sludge tanks, in which the Accepted wastewater mixes almost instantly with the entire volume of the tank's contents. It has been established that activated displacement sludge tanks are advantageous for the thorough purification of wastewater with low treatment loads, whereas qe sludge tanks. activated mixers, which do not give a thorough purification, are capable of operating with high treatment loads and of maintaining longer the stability of the treatment when the waste water contains toxic constituents.

 At the present time, the basins having received the most extension are the activated single-stage sludge basins and the activated two-stage sludge basins with regenerators. Compared to the others, the activated sludge basins on a single stage are relatively simple to operate, but their field of application is limited. The purification in a single stage in the activated sludge basins presents a series of notable drawbacks. In such basins, the purification of effluents cannot be intensified by increasing the mass of activated sludge. Furthermore, during peak flows of waste water containing toxic impurities, activated sludge can lose its quality or even be destroyed. regenerator tanks, in which the mixture of waste water and activated sludge is aerated for a minimum time, sufficient to obtain the required yield of BOD purification, then the sludge to be recycled, after its separation in the decanter, -are pumped into the regenerator, where the processes of oxidation of the adsorbed pollutants 5 'complete and the initial properties are restored to the sludge The activated sludge tank with regenerator requires a structure of much lower useful volume, and, moreover, if the activated sludge in the tank is altered as a result, for example, of the arrival of toxic impurities, the activated sludge from the regenerator constitutes a safe reserve. of activated sludge tanks with two floors lies in the fact that on each floor there are "specialized" activated sludges11 # so it becomes possible to carry out total biological purification of high concentration waste water containing organic pollutants hardly oxidizable.

 The organic pollutants brought in by the wastewater arrive at the purification works on an irregular basis during the day, this irregularity having two components: irregularity in the quantity of water arriving at the purification and irregularity in the concentration of pollutants . The coincidence in time of the said irregularities means that, during determined periods of operation of the activated sludge tanks, lgs treatment loads exceed the average values by 3 to 5 times, and even more in certain cases. with activated sludge is determined by a series of conditions, to which # they relate: the composition and properties of the waste water, the hydrodynamic conditions for mixing the treatment medium, the proportion between the quantity of pollutants supplied and the concentration of activated sludge , as well as the oxygen regime of the pelvis. In real conditions, under the effect of sudden fluctuations in the charge, which are not tolerated by any living cell, the activated sludge is "affected by disease", loses its oxidative properties and its derangement, which can cause only a strong deterioration in the quality of treatment, but even a total disruption of the operation of the structure. In order to make the operation of activated sludge tanks less sensitive to fluctuations in the treatment load, the useful volume of the structures and the consumption of electrical energy for aeration must be significantly increased. For example, in real conditions of urban wastewater treatment, the contact of wastewater with activated sludge in basins lasts on average 6 to 8 hours, and the specific consumption of air according to the pollution of the wastewater s pupil at 5-15 m3 per cubic meter of purified water. For a wastewater flow of 50,000 m3 / d, corresponding to a medium-sized unit, the volume of activated sludge tanks is 20,000- 25,000 m3, and the daily consumption of electrical energy for ventilation is 7,000 to 10,000 kWh, a significant part of these volumes and this energy being used in an inefficient manner.

 There is a known process for the biological purification of waste water by activated sludge in a single-stage activated sludge tank (Japanese patent application No. 57 "28316, Int. Cl. C 02 F 3/12), in which the waste water is purify are mixed with, the activated sludge, the bacterial medium is aerated, then the sludge to be recycled is separated from said bacterial medium and readmitted for mixing with the waste water arriving at the purification, while the purified waste water is transmitted to the treatment subsequent, for example to sterilization with chlorine. The control of the progress of the process under conditions of fluctuations in the load of pollutants supplied is carried out by measuring the concentration of activated sludge and the quantity of oxygen absorbed and the maintenance the proportion between the organic pollutants in the waste water arriving at the treatment plant and the activated sludge at a constant optimal level is achieved by varying the concentration of the sludge activated in the system, obtained by regulating the surplus of activated sludge discharged.

 This process ensures reliable and quality treatment only for wastewater with a relatively simple composition of pollutants, when the fluctuations in the treatment load are of insignificant amplitude and progressive in character.

 However, such conditions of service are rare in practice. In the most widespread cases, when the waste water contains organic pollutants of complex composition and the load fluctuations over a period of a few hours are significant, the application of this process has no appreciable effect.

 In addition, the gravimetric separation of the bacterial medium concentrated in sludge to be recycled and treated wastewater is accompanied by an increased entrainment of suspended particles, which greatly reduces the purification yield. In case of use, after biological purification, of advanced purification works (sand or carbon filters, ozonization plants, filters with ion exchangers, etc.), these are, as a general rule, quickly put out of use when the content of suspended matter in the water to be treated exceeds 15 to 20 mgfl.

 There are also known processes in two stages of biological purification of waste water by elimination of organic pollutants by means of activated sludge (application RFA nt 2 936 884A I, Cl. Int. C 02 F 3/12), in which, at the first stage, the bacterial medium is aerated, then separated, the activated sludge is then regenerated, and at the second stage, the medium is aerated, then the remains of activated sludge are removed.

 This process makes it possible to purify highly concentrated waste water (BOD of more than 1000 mg / l), containing industrial pollutants that are difficult to oxidize.

 However, the scope of this procedure, although covering industrial waste water, remains limited. As a result of fluctuations in the treatment load in the first stage of biological purification, operating at a constant concentration of activated sludge, there occur during the day frequent deviations from the optimal ratio of the quantity of organic pollutants supplied to the concentration of sludge activated. The overloads are particularly strong in the initial areas of the first treatment stage; it follows that the quality of water treatment becomes unstable, the sludge tends to swell, its settling deteriorates and a significant quantity of pollutants which have not been oxidized on the first treatment stage begins to pass to the second, with excess suspended matter. This' drives the operation of the second stage and large quantities of pollutants that are difficult to oxidize escape to the treated water.

 To increase the stability of the treatment, it is necessary to give the first stage of purification a greater inertia, that is to say that it is necessary to increase by 2 to 3 times the useful volume of the works, hence the increase - sowing construction costs and locauping a large area. At the same time, the operating costs increase sharply and, first of all, the ventilation costs, because, in order to avoid destruction of the activated sludge due to a lack of oxygen, it proves necessary to ensure the regime corresponding to the maximum load. In periods of reduced load, for example at night, excess ventilation fragments the activated sludge, which, in the event of insufficient nutrients, easily divides into particles decantable. The fragmented activated sludge is caught by separate air bubbles and entrained on the surface, where it forms a "float" mass or foam. The appearance of such a foam disturbs the sludge separation process, lowers the quality of the purified water and causes a large reduction in the concentration of activated sludge in the system. Usually this happens at night, when visual control of the treatment is made difficult.

 In the known method which has just been described, the regulation of the ventilation intensity as a function of the load is carried out by variation of the number of blowers in service, which does not allow ventilation and a degree use of sufficiently uniform oxygen.

 It was therefore proposed to create a biological purification process for waste water and an activated sludge tank for its implementation, in which, thanks to the immediate regulation of the concentration of activated sludge at the first stage of purification by variation of the quantity of oxygenated gas and change of the hydrodynamic structure of the flow of bacterial medium, the ratio between the organic pollutants of the waste water arriving at the purification and the activated sludges would have constantly an optimal value.

 This object is achieved by the fact that, in the process of biological purification of redundant water, of the type in which organic pollutants are eliminated in two stages by means of activated sludge, at the first of which the waste water arriving at the purification is mixed with the activated sludge, the bacterial medium thus obtained is aerated, then the sludge to be recycled is separated from the bacterial medium in the terminal zone of this stage, regenerated and readmitted in the initial zone of this stage for mixing with the waste water arriving during purification, while in the second stage, the sludge water, obtained after separation of the sludge to be recycled from the bacterial medium, is aerated, then rid of the remains of activated sludge, according to the invention the sludge to be recycled admitted during regeneration are divided into two parts, one going directly to regeneration, and the other being thickened, then mixed with the first part of sludge to be recycled for their simultaneous regeneration, of te This ensures that the ratio between the organic pollutants in the waste water arriving at the treatment plant and the activated sludge remains constant at the first stage of treatment.

 The division of the flow of sludge to be recycled going to the reeration into two parts, one of which is thickened before the regeneration, makes it possible to reduce the duration of separation of the sludge to be recycled from the bacterial medium to 15-30 min instead of 60 to 90 min usually necessary, which reduces their stay in anaerobic conditions to a minimum and ensures better conservation of their activity. The increase in the concentration of sludge to be recycled increases the efficiency of use of the useful volume regenerators and oxygenated gas necessary for regeneration Finally, the increase in the concentration of activated sludge in regenerators causes, due to the increase in the average concentration of activated sludge in the system, an increase in the concentration of sludge activated in the first stage of purification, which increases the oxidizing power, increases stability when the treatment loads are increased and ensures the maintenance of an optimal ratio co between the organic pollutants in the waste water arriving at the treatment plant and the activated sludge.

 This makes it possible to accelerate the separation of the sludge from 3 to 4 times, to reduce by 1.5 to 2 times the volume of the sludge to be recycled going to the regeneration, to reduce the aeration period from 1.1 to 1.3 times sludge activated at the first stage, as well as reducing from 8 to 12 the quantity of oxygenated gas (air) admitted to the regeneration of sludge.

 It is advantageous that the part of the sludge to be recycled subjected to thickening is substantially from 0.2 to 0.8 of the total mass of the sludge to be recycled going to regeneration.

 The concentration of sludge to be recycled going to regeneration depends on its thickening and settling capacity (sedimentation properties) and can oscillate over a wide range. The sedimentation properties of the sludge, determined by their bacterial composition and by the physiological state of the microorganisms, depend primarily on the nature of the wastewater, as well as on a whole series of factors, determining the physico-chemical conditions of The variation of the part of the sludge to be recycled subject to thickening within a range of, appreciably, 0.2 to 0.8 of the total mass of the sludge to be used makes it possible to maintain the average concentration of the sludge to be recycled at a constant value, corresponding to the level prescribed for different sedimentation properties of activated sludge.

 It is recommended, in the event of increased arrival of residual water, to premix part of the flow of residual water) # - # res arriving at the first stage with the regenerated active sludge going to the first stage and to perform additional aeration by admitting oxygenated gas, then mixing the bacterial medium obtained with the rest of the waste water going to the initial zone of the first stage, and then, after the treatment in the first stage, returning part of the flow of bacterial medium from the zone terminal to the initial zone of the first stage, which is achieved by mixing it with the sludge to be recycled going to regeneration, the quantity of oxygenated gas blown in for the additional aeration being such that it ensures an energetic longitudinal mixing of the bacterial medium of the first stage by recirculation of this medium between the terminal zone and the initial zone of the first stage.

 The implementation of additional ventilation during the increased arrival period ensures the introduction of the necessary quantity of oxygen.

 In order for oxygen to be used as fully as possible during the additional aeration, it is desirable that part of the waste water flow arriving on the first stage is premixed with the regenerated activated sludge going to the first stage, which increases the oxygen consumption speed and prepares the sludge for treatment loads from the regeneration stage.

 The effective longitudinal mixing of the bacterial medium between the terminal zone and the initial zone of the shoreline, caused by the additional aeration1 changes the hydrodynamic structure of its flow from the displacement regime to the total mixing regime, which contributes to a uniform distribution. rapid pollutants.

The gradients of concentration of organic pollutants, dissolved oxygen and activated sludge according to the flow of bacterial medium are then minimal. The proportional increase in the concentration of activated sludge necessary on the first stage in the period of increased arrival is ensured. thanks to the rapid reciprocal homogenization of regenerated activated sludge and bacterial medium flows.

 The indicated treatment operations increase the oxidizing power of the first purification stage by several times, without lowering the quality of the purified water, this being obtained with a minimum level of energy expenditure and without increasing the useful volumes of the system, although the arrival may increase from 1.5 to 2 times, and the processing load from 3-5 times.

 A favorable effect is obtained when the oxygenated gas for additional aeration is admitted in a quantity ensuring, between the rate of recirculation of the bacterial medium and the rate of waste water arriving at the purification, a ratio lying substantially in the range of 3 to 10.

 The oxygenated gas introduced into the bacterial medium during additional aeration fulfills two functions simultaneously. The first is to create a hydrodynamic structure of the flow close to the total mixing regime, when the oxygenated gas ensures the recirculation of the bacterial medium between the terminal zone and the initial zone of the first stage. The second function is to introduce an additional quantity of dissolved oxygen into the bacterial medium, which is necessary for the course of the oxidation ensuring the purification of waste water.

 When the wastewater arriving at the treatment plant has low concentrations of BOD pollutants (up to 150 mg / l), the determining function is the first, and the ratio between the recirculation rate of the bacterial medium and the rate of waste water arriving at purification is minimal, equal to 3. When the concentrations of organic pollutants in waste water arriving at J. tLpuration are high, it is the second function which is decisive, and the ratio between the recirculation flow of bacterial medium and the flow of waste water arriving at the purification is maximum, equal to 10.

 This makes it possible, during periods of increased arrival, as well as during so-called peak loads, to maintain energy consumption at an optimal level, thanks to a more complete use of the oxygenated gas admitted, both for transport only for oxidation.

 A favorable effect is obtained when the flow of waste water going to the premix with the regenerated sludge is substantially between 1/3 and 2/3 of the flow of waste water arriving at the purification.

 The range of practically possible fluctuations in the arrival of wastewater ranges from 1.3 to 3 times the average arrival. In other words, during periods of increased arrival of wastewater for treatment, the additional quantity of wastewater arriving for treatment is 1/3 to 2/3 of the flow rate. For the purification to remain stable on the first stage, it is advantageous to subject the additional quantity of water to additional aeration and to mix it with the activated sludge regenerated.

 The limits indicated are optimal, because their exceeding towards lower values would increase the oxygen losses at the atmosphere, and their exceeding towards higher values would make appear in the zone of action of the complementary aeration a lack of dissolved oxygen, which would have an unfavorable effect on the treatment of waste water.

 It is advantageous that the water formed as a result of the thickening of a part of the sludge to be recycled going to regeneration, is admitted to the second stage and subjected to aeration, and that the activated sludge separated after the second stage is mixed with sludge to be recycled going to regeneration.

 The sludge water formed during the thickening of the sludge to be recycled contains a significant amount of suspended particles which are difficult to settle, which, before final settling, are advantageously subjected to aerocoagulation by blowing small quantities of oxygenated gas. This increases the electrostatic charge on the surface of the mud flocs, which increases their mutual attraction and accelerates decantation.Moreover, certain pollutants which are difficult to oxidize sometimes pass from the first stage to the second, where their oxidation is completed by the bacterial medium, the second stage operating under a low treatment load regime.

 The total amount of sludge carried by the sludge water to the second purification stage can exceed the amount of excess activated sludge. In addition, in certain periods of operation, it is advantageous that part of the activated sludge withdrawn after the second stage is mixed with the sludge to be recycled going to regeneration, in order to maintain high concentrations of activated sludge in the purification system. .

 Thanks to the treatment operations thus carried out, it becomes possible to ensure a stable and thorough purification of the wastewater when its arrival is irregular, with minimal energy expenditure and a reduction of the civil engineering of the system from 1.5 to 2 times.

 It is advantageous to implement the process which is the subject of the invention in an activated sludge tank comprising a mixing tank forming part of a first stage, equipped with compressed air dispersers and comprising an initial zone in which there are devices for entering waste water and activated sludge into the tank, as well as a terminal zone in which the outlet for bacterial medium is located, placed in communication with a sludge separator suitable for separating the sludge to be recycled from the bacterial medium, this separator having an outlet for purified waste water, placed in combination with a displacement tank forming part of a second stage, equipped with compressed air dispersers and a sludge separator, as well as a sludge outlet to be recycled placed in communication with a regeneration chamber comprising compressed air dispersers, the outlet of this chamber being placed in communication with the inlet device for s activated sludge regenerated in the tank on the first stage, a basin which, according to the invention, is equipped with a sludge thickener, suitable for increasing the concentration of sludge to be recycled and comprising an inlet which is placed in communication with the outlet for sludge to be recycled from the sludge separator, as well as two outlets, one for the sludge to be recycled, placed in communication with the inlet of the regeneration chamber, and the other, for the sludge water, communicating with the entrance to the second stage displacement tank.

The use of a sludge thickener suitable for increasing the concentration of sludge to be recycled, in combination with a short period of sludge separation, not only increases the amount of microor
active systems ensuring the purification of waste water, but also, thanks to the thickening under aerobic conditions, of maintaining the oxidizing properties of activated sludge at the highest level.

 this results in a significant increase in the rate of oxidation of the pollutants, which makes it possible to substantially reduce the volume of the activated sludge tanks.

 It is desirable that the activated sludge tank is also equipped with a prechamber comprising compressed air dispersers and interposed between the outlet of the regeneration chamber and the device for entering the activated tanks in the tank of the first stage, This prechamber being also placed in communication with the Petrée device for waste water in the tank of the first pledge, and the regeneration chamber being put in communication with the terminal area of the tank on the first stage.

 The actual diagram of the fluctuations in the load of the purification works as a function of the hours of the day generally includes two zones of extreme (maximum) values: morning and evening. The unproductive expenditure of electrical energy is all the lower and the technological and economic performances all the higher as the staircase diagram of the controlled oxidizing power of the activated sludge tank is compared to the diagram of the load of waste water This is obtained by an appropriate choice of the number of pre-chambers and their flow. From the point of view of the convenience of the control, while obtaining optimum technical and economic performance, it is advantageous for the activated sludge tank to be equipped with a main prechamber and an additional prechamber.

 A favorable effect is obtained when the outlet of activated bottles from the second stage sludge separator is brought into communication with the inlet of the regeneration chamber.

 The possibility of transmitting the activated sludge leaving the sludge separator of the second stage to the regeneration chamber1 which can be considered as being a periodic recycling of the activated sludge from the second purification stage to the first, makes it possible to maintain the necessary concentrations of sludge activated on the first treatment stage during peak loads. This also makes it possible to adjust the ratio between the activated sludges circulating in the system to the desired value: purification and the activated excess sludges to be removed from the system.

It is recommended that the activated sludge tank include a longitudinal tank open at its upper part, divided by a transverse partition into two compartments, in the first of which are placed longitudinal partitions, which form, on the one hand, along the axis longitudinal of the tank, the first stage tank, inside which oxygenated gas dispersers are mounted, and which, on the other hand, form, with the walls of the tank, the main regeneration chamber and the additional chamber of regeneration, located on either side of the tank of the first stage and comprising transverse partitions dividing them into cells, in each of which is placed a disperser of oxygenated ga #, thus closes longitudinal and transverse partitions arranged near the initial zone of the tank, inside the longitudinal partitions, so as to form a main prechamber and an additional prechamber, placed in communication with the chambers main and additional res regeneration by
sns high baffles, and with the tank, by thresholds, and equipped with oxygenated gas dispersers, and in the second of which, along its axis, is mounted a horizontal gravity type sludge separator, placed in communication with the tank of the first stage by a siphoid passage and forming with the walls of the second compartment the reservoir of the second stage, vertical mud thickeners of the gravity type being mounted near the transverse partition of the tank and placed in communication with the main and additional regeneration chambers , and the sludge separator being equipped with means of ascent to the air ("airlifts") for the supply of sludge to be recycled with increased concentration in the main and additional regeneration chambers.

 The arrangement of all the main structures in a single tank has several objectives at the same time. Such a solution makes it possible to reduce the consumption of building materials on the surface of the ground necessary, thanks to the extensive use of dividing partitions and to the reduction of the length of the distribution devices and of the dimensions of the input devices.

For a series of works, such an arrangement proves to be radical. For example, the combination of regeneration chambers and pre-chambers with the mixing tank of the first purification stage, operating during the increased arrival period, according to the principle of communicating vessels, makes it possible to reduce expenditure to a minimum. energy for water recirculation.

 Gravity separators and thickeners make it possible, at minimum cost, and without disturbing the structure of the sludge flock, to maintain a high concentration of sludge to be recycled.

 The use of means of ascent to the air for the transfer of activated sludge from the separator to the thickener, as well as from the thickener to the regeneration chambers, is the simplest solution under real conditions, and allows at the same time saturating the activated sludge with dissolved oxygen during their thickening, which contributes to the conservation of their useful properties.

invention will be better understood and other objects, details and advantages thereof will appear better on reading the explanatory description which will follow of different embodiments given solely by way of nonlimiting examples, with references to the nonlimiting drawings upset in which:
- Figure 1 schematically represents the sequence of operations of the biological purification process in the case of the average arrival of waste water, according to one invention;
- Figure 2 shows the variation of the concentration of the thickened part of the sludge to be recycled (a2) as a function of the time (t) of stay in the thickener;
- Figure 3 shows said sequence of operations in case of increased arrival of waste water, according to one invention;
FIG. 4 represents said sequence of operations when the arrival of residual water is maximum, according to the invention; ;
- Figure 5 shows the variation of the hydrodynamic structure of the flow of bacterial medium (D / IU) as a function of the recirculation ratio (R);
- Figure 6 shows an overview of an activated sludge tank according to the invention;
- Figure 7 shows section 7-7 of Figure 1;
- The figure shows section 8-8 of Figure 1;
- Figure 9 shows section 9-9 of Figure 1;
- Figure 10 shows the diagram of the variations in the quantity of oxygen admitted as a function of the hours of the day, resulting from the operation of the main and additional pre-chambers.

The proposed process of biological purification of waste water by activated sludge consists essentially of the following. The waste water 1 (FIG. 1) to be treated is admitted to the first treatment stage 2, where it mixes with the regenerated activated sludge 3, 4 at a concentration of approximately 8 g / l, arriving from the regenerators 5, G, and the bacterial medium obtained, at a sludge concentration of 1.5 5 2.5 g / l, is aerated by an oxygenated gas 7, for example air During aeration by bubbling with fine bubbles, the oxygen of the gas bubbles dissolve in the liquid, which ensures aerobic conditions for the microorganisms of activated sludge carrying out water purification On the first stage 2 of purification, the flocks of activated sludge adsorb the organic pollutants supplied and partially oxidize them, then the sludge to be recycled at a concentration of 4 to 7 g / i is separated from the bacterial medium 8 in the terminal zone of the first stage 2, for example by gravity, using the separator 9 for sludge from the first stage 2
In order to restore to the activated sludge of the terminal zone of the first stage 2 their initial activity, this decreasing as the organic pollutants are adsorbed, these sludges are subjected to aerobic stay regeneration for more than their hours - during from which the activated sludge found in the regenerators 5, 6 metabolizes the adsorbed pollutants and is aerated by oxygenated gas 10, 11. The activated sludge obtained is readmitted to the mixture with the waste water 1 arriving in the initial zone of the first stage 2 , and the treatment process repeats.

 When separating the sludge to be recycled from the bacterial medium 8 from the terminal area of the first stage, under conditions of short-term contact (15 to 30 minutes), water 12 of sludge is formed, formed by waste water purified at least 90% and activated sludge entrained, mainly those which are difficult to detect at a concentration of 0.2 to 0.5 g / l.

In order to rid them of the suspension which is difficult to decant or contain, as well as to complete the oxidation of the remains of organic pollutants, these waters 12 are admitted to the second stage 13 of purification, where they are subjected to aeration 14. During from the aeration on the second stage 13, the flocs of activated sludge grow larger and consequently become heavier as a result of their biecoagulation, after which the charged water 15 from the second stage 13 is separated for 1 to 1.5 hours, in the separator 16 of the second stage, in activated sludge and in waste water 17 completely purified (DS0 = 10 to 15 mg / l), which are evacuated from the basin and transmitted, for example, to disinfection, before being discharged into a body of water .

 Activated sludge 18 in excess, resulting from the growth of recycled activated sludge from the first stage, settles and thickens in the sludge separator 16 from the second stage to a concentration of 9 to 12 g / l, and is discharged for further processing or recovery.

 According to the invention, the sludge to be recycled is divided into two parts, one of which, part 19, 20, goes directly to the regenerators1 and the other, part 211 22, undergoes before regeneration a preliminary thickening. (i.e. an increase in their concentration) in thickeners 23, 24, and it is only after this treatment that the thickened sludges 25, 26 are remixed with the first part 19, 20 of the sludges to recycle for their simultaneous regeneration.

 The separation of the flow of sludge to be recycled going to regeneration into two parts, one of which, the part 21, 22 is thickened before the regeneration, which results in an increase in the average concentration of sludge to be recycled, makes it possible to to solve a series of technical problems: to reduce the separation time of the sludge to be recycled from the waste water 8 to 15-30 min instead of the 60 to 90 min ordinarily necessary, and thus to better maintain its activity, because its length of stay under anaerobic conditions is reduced to a minimum; to increase by 50 to 100% the efficiency of the useful volume of the regenerators 10, il and to increase by at least 3 to 4% the degree of use of the oxygen admitted to the generators 10, 11 for aeration , which, in turn, increases the use of oxygenated gas by 15 to 20%; increase the concentration of activated sludge in the first treatment stage up to 2.5 to 3 g / l, which increases the stability of the treatment process by maintaining the ratio between the organic pollutants of the waste water arriving at purification and activated sludge a constant optimal level when the treatment loads are increased.

 The ratio of organic pollutants from waste water arriving at treatment to activated sludge is expressed in BOD per gram of activated sludge and per unit of time (day). The optimal ratios depend on the nature of the waste water and the nature of the treatment. , the degree of purification required and, in each specific case, are determined experimentally. It can be assumed that for urban waste water and industrial waste water which are close to them in composition, the optimal ratio between the organic pollutants of the waste water arriving at treatment and the activated sludge for the first treatment stage biological is approximately between 0.8 and 1 BOD / g of activated sludge per day. This ratio, with which a practically total biological purification is obtained, must be considered to be optimal, because, at lower values, although the quality of the purification is preserved, the oxidizing louse or even of activated sludge is not completely used, and at higher values, activated sludge tends to swell, which affects water purification and causes serious operating difficulties.

 So that the concentration of sludge to be recycled going to regeneration does not depend on their sedimentation properties, it is advantageous that the part of the sludge to be recycled subject to the preliminary thickening is substantially equal to 0.2-0.8 of the total mass sludge to recycle going to regeneration.

This makes it possible to maintain on the first stage of purification of the activated sludge tanks a concentration of activated bc "a" of up to 3 g / l, which ensures the stability of the treatment at increased loads. The concentration of activated sludge "a" on the first treatment stage and the concentration of activated sludge to regenerate ao are linked to each other by the relationship:
# ao
a = 1 + #
1 + # being the fraction of sludge to be recycled compared to
I1 waste water intake adopted for the calculations,
equal to 0.5-0.6.

1 + 0,60,5-0,6.So we have:

1 + 0.60.5-0.6.

 ------- = 8 g / l.

q1 et q2 étant les quantités de boues à recycler non
épaissies et épaissies, respectivement, exprimées
en fractions d'unité. 0.6
In turn, the quantity aO is linked to the concentration of sludge to be recycled which is not thickened a1 and thickened a2 by the relation:

q1 and q2 being the quantities of sludge to be recycled not
thickened and thickened, respectively, expressed
in fractions of unit.

The quantities a1 and a2 depend on the character of the wastewater, as well as on a number of other factors, determining the ability of the sludge to settle and thicken. It follows that for sludge settling well a1 = = 7 g / l, q1 = 0.8 and a2 = 12 g / l, q2 = 0.2, and for sludge settling badly a1 = 4 g / i, q1 = 0.2 and a2 = 9 g / l, @ 2 = 0.8. It is easy to ensure the accuracy of the selected reports as follows:
for sludge settling well
7.0.8 + 12.0.2
ao = ----------- = 8 g / l,
0.8 + 0.2 for sludge settling badly:
4.0.2 + 9.0.8 ao = ---------- = 8 g / l.

0.2 + 0.8
ba regeneration of activated sludge at a concentration greater than 8 g / l is irrational, because, in this case, the mixing of the bacterial medium, the resistance to transfer of oxygen to the liquid increases, the formation of moss intensifies and the pumping sludge becomes more difficult.

 In FIGS. 1, 3, which represent the sequence of operations of the biological purification process, the broken lines indicate the flows of waste water to be treated and treated, the solid lines indicate the flows of regenerated activated sludge, to be recycled and excess at a concentration of 4 g / l and above, the mixed lines indicate the flows of bacterial medium originating from the terminal areas of the first and second stages and of sludge water originating from the separation and thickening of the sludge.

 FIG. 2 represents the variation, obtained experimentally, of the concentration a2 of the thick part q2 these sludges recycle in g / l as a function of the time t expressed in hours of stay in the thickener for the activated sludges settling hien ( curve A) and settling ma '(curve B).

The time interval O to 2 hours is in fact the area of aerobic thickening of the sludge to be recycled, when the active microorganisms do not lose their functional properties. After a stay of more than 2 hours, the sludge to be recycled continues to concentrate up to 20-30 gjl, but this is now done under an anaerobic regime, when their activity is largely lost and can only be restored by prolonged treatment. The curves t. and Bdata show that, for sludges to be recycled having different sedimentation properties, the concentrations calculated a2 (9 and 12 g / l respectively) can be reached by thickening in aerobic regime.

In the period of increased arrival of waste water and increase in the concentration of organic pollutants in waste water, or when the factors indicated appear simultaneously, the optimal value of the ratio between organic pollutants of waste water arriving at treatment and the activated sludge is exceeded on the first stage of biological purification by 1.5 times and even more. In order that, in the increased arrival period, said ratio remains maintained at a level close to the optimum value, the concentration of activated sludge in the bacterial medium must also be immediately increased by 1.5 times and more. must receive an additional quantity of oxygen and the hydrodynamic structure of the flow of bacterial medium must be compared to the total mixing regime, in order to ensure the consistency of the purification parameters from the initial zone to the terminal zone of the first stage of purification
For this (FIG. 3), when the arrival of waste water increases, part of the flow 27 of waste water arriving on the first floor is premixed with the regenerated activated sludge going to the first floor, and subjected to additional aeration 28 by admitting oxygenated gas, then the bacterial medium obtained is mixed with the rest of the waste water admitted into the initial zone of the first stage 2 and, after treatment on the first stage, part 29 of the flow of bacterial medium from the terminal zone of the first stage 2 is returned to the initial area of the first stage, this being achieved by mixing it with the sludge 19, 25 to be recycled, going to regeneration.

 The increase in the concentration of activated sludge on the first purification stage, necessary in the increased arrival period and in proportion to the increasing load, is ensured thanks to the rapid reciprocal homogenization. Of the flows of regenerated activated sludge coming from the regenerator 5 and bacterial medium. As the concentration of regenerated activated sludge 3 is in fact 8 g / l, and the concentration of activated sludge in bacterial medium 8 is on average 2 g / l, taking into account the possible volumes of regenerator 5 and the mixing tank of the first purification stage 2, the working concentration of the activated sludge during the increased arrival period will be on average 4 g / l. This means that the implementation of the indicated treatment device ensures that the ratio between the organic pollutants supplied and the activated sludge is maintained at an optimal level under the conditions of a rapid variation in the treatment load which can go at least up to 'twice.

 So that, during the additional aeration 28, the oxygen is used as completely as possible, the part 27 of the waste water flow arriving at the first stage is advantageously premixed with the regenerated activated sludges 3 going to the first stage starting from the regenerator . This increases the degree of oxygen use up to 10 to 12%, thanks to the increase. the speed of its consumption, and ensures the adaptation of the sludge to the treatment loads from the final stage of regeneration.

 Oxygenated gas for additional aeration 28 must be admitted in sufficient quantity, not only to maintain the increased speed of oxidation of pollutants, but also to ensure longitudinal energetic mixing of the bacterial medium of the first stage by rec.irsularion 29 30 of this environment between the termin zones: - # and initial, respectively, of the first floor.

The increased quantity of pollutants brought in during the increased period of arrival at the first biological purification stage creates a tendency to local overload of the activated sludge, as well as to a reduction in the concentration of dissolved oxygen in the bacterial medium to a value less than 2 mgll in the initial area of the first floor. Such a situation is completely undesirable, because it disturbs the stability of the process of thorough purification of residual water by activated sludge. So that this does not happen, it is necessary to maintain the recirculation rate 29, 30 of the water charged between the terminal and initial zones of the first stage 2 at a determined level, corresponding to the increased amount of organic pollutants arbi.

to treatment. This is obtained by additional admission of oxygenated gas 28, in an amount such that the hydrodynamic structure of the flow of bacterial medium remains close to the total mixing regime, and that the concentrations of activated sludge, organic pollutants and dissolved oxygen remain practically constant along the length. of the first stage 2 of purification.

 In certain periods of operation, when the increased arrival of wastewater reaches the maximum values, the increase in the concentration of activated sludge at the first propping upstay up to 4 g / l will be insufficient for maintaining the proporition. between the Orpanic pollutants and the activated sludge has an optimal value. This can happen, for example, when the load of organic pollutants increases not twice, but by 3.

For the quality of purification of the waste water under the conditions of a maximum arrival remains high, together with 1 aeration of the recirculation flow 29, 30, an additional aeration 31 (FIG. 4) is subjected by the gas o, Sygéne the recirculation flow 32, 33 of bacterial medium 8 from the terminal zone of the first stage 2 to the regenerator 6 and from the regenerator 6 to the initial zone of the first stage, respectively, where one admits part 34 of the waste water arriving at the The 35 personable part of the wastewater is admitted to the first treatment stage. Thanks to the reciprocal homogenization of flows of activated sludge regenerated at a concentration of.% G / l coming from the regenerators, and of bacterial medium, the working concentration of activated sludge on the first purification stage is on average 6 g / This indicates that the implementation of the indicated treatment devices ensures that the ratio between the organic pollutants supplied and the activated sludge is maintained at an optimal level under the conditions of a rapid variation in the treatment load of at least three times, as well as the additional introduction of the quantity of dissolved oxygen necessary for the proper functioning of the action of aerobic microorganisms.

 Organized recirculation of the flows 29, 30, 32, 33 of bacterial medium of variable values from the terminal zone of the first stage 2 of treatment to the initial zone is the simplest means from the technical point of view and, at the same time, , the most effective for controlling the wastewater treatment process in the activated sludge tank. Such a system ensures in the initial zone, which is the busiest zone on the first stage, not only the hydraulic dilution of the waste water arriving at the treatment by the treated waste water, but also their biological dilution by the powerful recirculation flows. 29, 30, 32, 33 of fresh activated sludge. To ensure favorable conditions for the course of the process of biological oxidation of organic pollutants in a wide range of variation in the treatment load, the oxygenated gas for additional aeration 28, 31 is admitted in a quantity ensuring, between the rate of recirculation of the bacterial medium and the rate 1 of waste water arriving at the purification, a ratio comprised substantially between 3 and 10.

 The lower limit. the ratio between the recirculation flow rate of the bacterial medium and the flow rate of waste water arriving at the purification, or else the non-dimensional recirculation ratio R, can be illustrated using the diagrams represented in FIG. carried the non-dimensional values of the diffusion criterion D / Ul, characterizing the hydrodynamic structure of the flow of bacterial medium, D being the diffusion coefficient in m2 / sr U, the speed of the flow in m / s, and X r the linear dimension of the basin in m.

The diagram obtained experimentally shows that, when D / UL>, 0.5-, the. regime is close to the total mixing regime in the flow of bacterial medium, as soon as R approaches 3.

 In the case of treatment of urban waste water or industrial waste water close to them in composition, a value of the parameter R of between 3 and 5 is usually sufficient to provide the treatment, during the period of increased loads, the additional quantity of oxygen, which is introduced by the bacterial medium in recirculation.

 The maximum value of parameter R 10 is valid for the treatment of highly concentrated waste water (BOD>) 1000 mg / l), when the determining objective is the introduction, in the initial zone of the first stage d purification, of an additional quantity of dissolved oxygen excluding the limitation of the respiratory functions of the microorganisms present in the activated sludge.

 Since the range of possible fluctuations of the increased arrival of waste water is between 1.3 and 3 times the average flow, the excess parts 27134 of the total flow of waste water 1 admitted to the premix with the regenerated sludge 3,4 (FIGS. 3, 4>, coming from the regenerators 5,6, amount substantially to a value between 1/3 and 2/3 of the total flow of waste water arriving at the treatment plant.

 Such a treatment device solves several problems at once: it facilitates the action of activated sludge in the initial zone of the first stage, allows oxygen to be used more completely (up to 10-12%) additional aeration 28.31, thanks to its accelerated consumption by the mixture of regenerated activated sludge and waste water arriving at the purification, adapts the activated sludge to the treatment loads.

 The water 36a 37 of sludge forming in the thickeners 23, 24 during the thickening of the sludge to be recycled, for example by gravity, contains a significant quantity (up to 2 g / l) of materials in suspension with difficulty decantable. It is advantageous to admit them to the second stage 13 of purification and to subject them to aeration 14, as well as to return the flow 38.39 of activated sludge, separated downstream of the second stage 13 of purification, to mix it with sludge 19, 20, 25, 26, recycle going to regeneration.

 The concentration of activated sludge in the second purification stage 13 amounts to 1-1.5 g / l, which makes it possible, thanks to aeration 14, not only to improve the sedimentation properties of the activated sludge before their admission into the separator 16 of the second stage, but also to rid the residual water of certain pollutants hardly oxidizable arriving from the first stage 2 of purification.

 The total quantity of sludge entrained by the water 36, 37 of sludge on the second stage 13 of purification generally exceeds the quantity of activated sludge in excess 18 having to be evacuated. This is why, in the periods of increased and maximum arrival of waste water, the evacuation of excess activated sludge 18 is temporarily stopped, and the activated sludge coming from the separator 16 of the second stage, at a concentration of 8 to 12 g / l, in an amount equal to 0.1-0.2 of the total waste water flow rate, are sent regenerator 5 only or to the two regenerators 5,6, respectively (Figures 3,4). This ensures the implementation of the necessary quantity of activated sludge in the system, and, moreover during the peak load period, contributes to maintaining higher concentrations of activated sludge on the first purification stage.

 The activated sludge tank, for the implementation of the biological purification process of waste water by activated sludge, being the object of the invention, compares a longitudinal mixing tank 40 (FIG. 6) of a first stage. , equipped with dispersers 41 of oxygenated gas and comprising an initial zone and a terminal zone, which are respectively determined by the locations where the devices for entering the waste water and activated sludge in the tank and the outlet from the bacterial medium are located.

The biological purification of waste water takes place, for example, in reinforced concrete tanks, in which, during continuous aeration by oxygenated gas admitted through the dispersers, aerobic microorganisms, including the concentrate is called "activated sludge", metabolize organic pollutants; by adsorbing them and partially oxidizing them as a result of their activity as living organisms. In activated sludge tanks, the mixture of waste water and regenerated activated sludge, known as "bacterial medium", has a concentration of 1 .5 to 2.3 gfl in the minimum pollutant arrival period
A ~ 7n to restore their oxidizing power, the sludge to be recycled with a concentration of 4 to 7 g / l, obtained at the end of the separation of the water from sludge d 3 with the bacterial medium, is first admitted in a regenerator
In the regenerator, which is continuously aerated, the pollutants adsorbed by the activated sludge blurs are oxidized, which ensures the restoration of the initial properties of the sludge and their transformation into regenerated activated sludge, which is readmitted in the basin. The regenerated activated sludge is thus brought into contact with a new portion of wastewater arriving at the treatment, and the process of biological oxidation of organic pollutants is repeated.
The devices for entering the wastewater into the reservoir 40 include a channel 42 for distributing the wastewater with a rotating flap 43, central orifices 44 and lateral orifices 45 and 46 arranged higher than the orifices 44. The medium outlet bacterial for its separation into sludge to recycle and sludge-water is carried out through a partition 47 of soothing and a weir 48, which communicates with a sludge separator 49. The function of the separator 49 is to separate the sludge to recycle from the bacterial medium.

 It is planned for a duration of stay of 15 to 20 min.

Separator 49 co -:% uorte an outlet of purified waste water with a concentration of suspended matter up to 0.5 g / l, analogous to the outlet of bacterial medium; that is to say constituted by a weir 50 and a soothing partition 51, the weir being placed in communication with a displacement tank 52, 53 of the second stage, which is equipped with dispersers 54, 55 of oxygenated gas, longitudinal partitions 56 t 57 dividing it into flow lanes 58, 59, as well as a sludge separator (not shown by convention in FIG. 6).

 The two-stage treatment makes it possible to carry out the total biological treatment of highly concentrated wastewater; contained pollutants that are difficult to oxidize, thanks to their additional oxidation by microorganisms of a specific nature specific to each of the purification stages.

 The outlet 60 of sludge to be recycled from the separator 49 communicates with a regeneration chamber 61, comprising dispersers 62 of oxygenated gas. The outlet 63 of the chamber 61 communicates with the input device for activated sludge regenerated in the tank 40 of the first stage.

 The regenerated activated sludge entry device comprises a high baffle 64 (FIG. 73 and a threshold 65.

In addition, the activated sludge tank is equipped with a sludge thickener 66 (fiqure 6), intended to increase the concentration of part of the activated sludge to be recycled separated by the separator 49. The separation of the flow of sludge going to the regeneration in two parts, one of which is thickened additionally before the regeneration, makes it possible to reduce the separation time of the sludge recycle from the bacterial medium to 15-20 min, instead of the 60-90 min ordinarily necessary, this which minimizes the duration of their stay under anaerobic conditions and contributes to the conservation of their activity. In this case, the average concentration of activated sludge going to regeneration can be brought up to 4.5-5 g / l, which, in turn, increases the efficiency of use of regenerators and oxygenated gas and increases the average concentration of activated sludge in the system of the first purification stage up to 2.5-3 g / l. In this way, it becomes possible to maintain the relationship between, on the one hand, the organic pollutants of the waste water arriving at the treatment plant and, on the other hand, the activated sludge, at a constant optimal value, as well as the system stability in the presence of fluctuating processing loads
The sludge thickener 66 has an inlet 67 communicating with the outlet 68 of sludge to be recycled from the separator 49, and outlets 69, 70, respectively, for the sludge to be recycled and for the sludge water, the first being in communication with the entrance to the regeneration chamber, and the second, with the entrance to the second stage displacement tank. The clarified water from the additional thickening of the activated sludge to be recycled is called 'sludge water' 8 and contains a significant amount of suspended matter (up to 2 g / l), which is discharged to the second stage of purification.

 On the other hand, the activated sludge tank is equipped with a prechamber 71, comprising dispersers 72 of compressed air. This prechamber 71 is connected between the outlet 63 of the regeneration chamber 61 and the device for entering the activated sludge in the tank 40 of the first stage, comprising a high baffle 64 (FIG. 7) and a threshold 65. In addition , the regeneration chamber 61 (FIG. 6) communicates with the reservoir 40, in its terminal zone, by a circulation channel 73.

 The load of organic pollutants on the purification works is irregular during the day, and the irregularity consists of two components: the irregularity of the quantity of water arriving at the purification and the irregularity of the concentration in pollutants. In specific periods of operation of the activated sludge tanks (usually in the morning and in the evening), the treatment loads exceed the average values by 3 to 5 times.

Under conditions of sudden load fluctuations, activated sludge, which is extremely sensitive to overloads, loses its oxidizing properties, its settleability, which results in a reduction in the quality of treated water. In order to ensure the stability of the purification bed, it is necessary to oversize the works. In addition, the ventilation intensity is determined in pa; have conditions of the maximum load, also, of the periods of reduced loads, the intensity of aeration is it much greater than that required. It follows unproductive expenses of electrical energy, the fragmentation of the flocs of activated sludge and, consequently, the increase in the quantity of suspended matter entrained out of the basin and the formation of foam.

To resolve the contradictions between the dynamically varying load and the reaction inertia of the structure, the purification process must be controlled, i.e. intervening in real time on the quantity of dissolved oxygen, the concentration of activated sludge and the hydrodynamic structure of the flow
The prechamber takes the bacterial medium at the terminal zone of the activated sludge tank, saturates it with dissolved oxygen and returns it to the initial, most charged zone of the tank, and also ensures primary biological purification of part of the flow. waste water arriving at the activated sludge tank, when the value of this flow is increased.

 The aeration system ensuring the operation of the prechamber is said to be additional 11, # while the aeration system of the permanently functioning activated sludge tank provided for the minimum load, is said to be basic.

 It is advanced that the second stage sludge separator (not shown by convention in FIG. 6) is put in communication by its activated sludge outlet with the inlet 74 of the chamber 61 of regeneration.

 The possibility of admitting activated sludge from the second stage separator into chamber 61 of rO-'gene-.raL-ion maintains the necessary concentration of activated sludge on the first purification stage during periods of maximum load. As a result of the metabolism of the microorganisms in the activated sludge, their increase is observed, known as "activated sludge in excess". The device which has just been described ensures the necessary ratio between the active sludge circulating in the purification system and the activated sludge in excess in front be extracted from the system for later recovery.

 The activated sludge tank according to the invention comprises a longitudinal tank 75 open at its upper part, shared by a transverse partition 76 in two compartments. Longitudinal partitions 77 and 78, placed in the first compartment, form along the longitudinal axis of the tank 75 the reservoir 40 of the first stage, inside which are dispersed dispersers 41 of oxygenated gas.

 The longitudinal partitions 77 and 78 form with the walls of the tank 75 the main and additional chambers 61 and 79 for regeneration, respectively.

 The regeneration chambers 61 and 79 are located on either side of the reservoir 40 on the first floor and have main and additional transverse partitions 80 and 81, respectively, dividing the regeneration chambers 61 and 79 into cells. In the cells are arranged dispersers 62 and 82. of main and additional oxy genet gases respectively.

 Next to the initial zone of the reservoir 40, at lte: xtE-- rieur of the # Longitudinal partitions 77 and 78, there are provided longitudinal and transverse main partitions 83 and # 4, respectively; and additional longitudinal and transverse partitions 85 and 86, respectively, which form the main and additional pre-chambers 71 and 87, respectively, placed in communication with the main and additional chambers 6s and 7g of regeneration by the main and additional high baffles 88 and 64, as well as with the reservoir 40 via the main and additional thresholds S 89 and 65. The main and additional pre-chambers 71 and 87 are equipped with main and additional dispersers 72 and 90, respectively.

 In the actual diagram of the load fluctuations on the treatment works during the daylight hours, three periods can be distinguished: minimum load up to 2000 g BOD / m3. j, increased load up to 5000 g DP0 / m3.j, and maximum load, exceeding 5000 g BOD / m3 + j.

The control of the oxidizing action of the activated sludge tank according to the diagram of the fluctuations in the supply of pollutants can be carried out by successively putting the main and additional pre-chambers into service, the main and additional regeneration chambers being respectively put into service . This device makes it possible to obtain optimum technical and economic performance, thanks to the reduction in the oxidation power of the activated sludge tank at minimum loads, achieved by operating the basic aeration system at its minimum intensity, sufficient to keep the activated sludge in suspension, and increase the oxidation power of the activated sludge tank at increased and maximum loads, achieved by successively putting the main and additional pre-chambers into service.

 In the second compartment, along its axis, is installed a separator 49 of sludge, for example horizontal, of the gravity type, placed in communication with the reservoir 40 of the first stage by the weir a8 and the partition 47 of evacuation, and forming with the walls of the second compartment, the reservoir 52, 53 of the second stage, equipped with dispersers 54, 55 of oxygenated gas.

Near the transverse partition 76 of the tank 75 are mounted thickeners 66 (FIG. 8) and 91 # of main and additional sludge, for example vertical, of the gravity type
The separator 49 is equipped with liftsl92, which put the mud hoppers 93 of the separator 49 in communication with the channels 94 and 95 for discharging the sludge, soothing partitions 47 (FIG. 9), 51 (FIG. 6) and weirs 48 (figure 9), 50 (figure 6)
The main and additional thickeners 66 (Figure 8), 91 have conical bottoms 96, 97, respectively; and are fitted with central tubes 98 and 99, discharge pipes 100 and 101, connected respectively to the channels 94 and 95 for discharging the sludge from the separator 49 and introduced into the central tubes: 98 and 99 of the thickeners 66 and 91, means of air ascent ("airlifts") 102 (FIG. 6) and 103 of sludge to be recycled of increased concentration, placed respectively in communication with the main and additional chambers 61 and 79 of regeneration, and of peripheral channels 104 and 105 , putting the thickeners 66 and 91 in communication with the reservoir 52, 53 of the second stage.

 The design adopted for the sludge separator ensures uniform separation of activated sludge along the length of the structure, reduces operating costs related to collecting the deposit, thanks to the renouncement of mechanical scraping devices, and increased 'water clarification effect, due to the absence of levitation of the deposit. In addition, gravity sludge separators and thickeners maintain a high concentration of activated sludge in the system without disturbing the structure of the bacterial flock. The use of air ascent means for the transfer of activated sludge separated from the separator to the thickener, as well as thickeners to the regeneration chambers, ensures, together with the main function, the saturation of the activated sludge in dissolved oxygen.

 It should be noted that the dispersers 62 and 82 of the main and additional chambers 61 and 79 of rege aeration, as well as the dispersers 41 of the tank 40 of the first c - # age and the dispersers 54 and 55 of the tank- see @@@ 53 of the second stage, are connected by pipes 106 under pressure, assigned the same reference number due to their identical function, to the blowers sCi of the basic aeration system, while the dispersers 72 and 90 of the main prechamber and additional 71 and 87 are respectively connected by pressure lines 108 and 109 to the blowers 110 and 111 of additional ventilation. In addition, the dispersers 72 and 90 are connected to the blowers 107 of the basic aeration system by connection tubes 112 and 113 comprising non-return valves 114 and 115.

 In addition, the activated G-sludge basin is equipped with lateral channels 116 and 117 for the waste water, disposed at the periphery of the basin and having overflow thresholds 118 and 119 and inlet orifices 120 and 121, putting them in communication with the initial zone of the main and additional chambers 61 and 79 of regeneration, of lateral channels 122 and 123 for the thickened sludge, comprising orifices 74 and 124, putting them in communication with the initial zone of the main and additional chambers 61 and 79 of regeneration, of vertical guiding walls 125 and 126, arranged perpendicular to the transverse partition 76, of baleen form of circulation channels 73 and 127, as well as of longitudinal partitions 56 and 57, arranged in the tank 52, 53 of the second stage, which they share in flow corridors 58, 59, which lead to an outlet orifice 128.

The arrangement of the main structures in a single tank makes it possible to reduce the consumption of building materials and the need for land for construction, thanks to the extensive use of adjoining partitions, by reducing the length of the distribution and dimensions of input devices; the connection of the regeneration chambers and the pre-chambers to the mixing tank of the first purification stage, ensuring their operation according to the principle of communicating vessels during the period of increased loads, makes it possible to reduce the costs of recirculation of the medium to a minimum, to preserve its activity and its structure; the relative arrangement of the sludge separator and the sludge thickeners reduces the costs of transferring the thickened activated sludge to be recycled, reduces to a minimum the duration of their stay under anaerobic conditions (without the arrival of oxygen), and the use of air ascent means on as transfer devices allows to keep the structure of the bacterial flock and to increase its activity thanks to the additional oxygen saturation
The activated sludge tank which is the subject of the invention operates as follows.

 In the minimum load period, up to 2000 g DB0 / m3 d; when the rotary shutter 43 is in its intermediate position, the waste water arriving in the distribution channel 42 passes through the central orifices 44, the level of which is lower than that of the lateral orifices 45 and 46 and q # ui are provided for continuous passage of the minimum flow, and enter the low sir. mixing 40 of the first stage, where they mix with the activated sludge arriving from chambers 61 and 79 of regeneration passing through the pre-chambers 71 and 87, thanks to the effect of ascension to air. The effect of ascent to air esc obtained in the pre-rooms 71 and 87 by admitting the air from the basic ventilation system, supplied by the blowers 107! to the dispersers 62 and 82 of said pre-chambers 71 and 871 via the connecting tubes 112 and 113. The valves 114 and lids of non-retc-ur mounted on the connecting tubes 112 and 113, exclude the possibility of passage of the air from the supple.enta-re ventilation system, supplied by the blowers 110 and 111, to the basic system, supplied by the blowers 107, but does not prevent the reverse circulation of air.

 The bacterial medium is aerated by the oxygen gas dispersers 41, which are connected by the pressure lines 106 of the base aeration system to the blowers 107. During the aeration and the routing of the mixture of waste water and activated sludge in the tank 1 of the first stage, the microorganisms of the activated sludge carry out the biological oxidation of the pollutants.

 In the sludge separator 49, receiving the biochemically purified waste water through the soothing partition 47 and the weir 48, and provided for a settling time of 15 to 20 min, the main mass of the activated sludge is collected in the hoppers 93 to sludge, from where it is transmitted by the air ascent means 92 to the channels 94 and 95 for sludge removal.

The sludge arriving in the channels 94 and 95 goes to the central tubes 98 and 99 of the main and additional thickeners 66 and 91, respectively passing through the discharge pipes 100 and 101.

 The activated sludge to be recycled of increased concentration settling on the conical bottoms 96 and 97 of the thickeners 66 and 91, provided for a duration of thickening of 1 to 1.5 hours, is taken up there by the means of ascent to the air. 102 and 103 which transmit them to the main and additional chambers 61 and 79 for regeneration. Such a method of thickening the activated sludge requires volumes 2 to 3 times smaller than in the case of the ordinary process using secondary decanters, and such a relative arrangement of the separator 49 and the thickeners 66 and 91 makes it possible to reduce the expense of energy for the transfer of the sludge to be recycled. In addition, the twice contact of the sludge to be recycled with the oxygen of the air during its transfer by the means of ascent to the air- excludes the appearance of conditions anaerobic and contributes to their thickening.

 The clarified water, containing activated sludge at a level equal to 10 202 of the initial concentration, goes to the reservoir 52, 53 of the second stage, to which are also admitted the sludge water leaving by the peripheral channels 104 and 105 of the main thickeners and additional 66 and 91, respectively. In the reservoir 52, 53 of the second stage, the remaining pollutants undergo additional biochemical oxidation D and the sedimentation properties of the activated sludge improve there, thanks to the bubbling produced by the dispersers 54 and 55 connected by the pressure lines 106 to the blower 107 of the basic ventilation system.

 The suspension coagulated with the purified waste water passes through the outlet port 128 and goes to the second purification stage, where the remaining pollutants undergo additional oxidation in a lowered concentration of activated sludge (0.5 to 1.5 g / l), the activated sludge is separated and excess activated sludge is removed from the system.

 At this operating speed of the activated sludge tank, i.e. at loads not exceeding 2000 g BOD / m3.d, the concentration of activated sludge in the structure is between 1.5 and 2.5 g / l, the concentration of sludge to be recycled being 6 to 7 g / l.

 The regeneration chambers 61 and 79 are supplied by the activated sludge coming from the separator 49, at a concentration of 4 to 6 g / l, and, moreover, by the thickened activated sludge coming from the thickeners 66 and 91, at a concentration of 8 to 10 girl, in a quantity equal to 0.2-0.8 of the sludge to be recycled from the separator 49. 'Such a ratio of the sludge flow rates ensures the maintenance of a concentration of the activated sludge of 6 to 10 g / l in chambers 61 and 79 for regeneration, and 1.5 to 2.5 girl, in the system.

 In the period of increased arrival of waste water, when the load on the tank reaches 5000 g BOD / m3.d, the rotating flap 43 occupies one of the extreme positions.

The constant flow of waste water through the part of the central orifices 44 which are open arrives in the reservoir 40 of the first stage, while the main mass of the water passes through the lateral orifice 45 or 46 to go to the prec * main or additional amber 71 or 87, respectively. Since the pressure of the waste water at the part of the central orifices 44 operating at this speed is greater, the flow of water which they admit remains constant and equal to the flow admitted by all the central holes 44 when the level of the waste water is minimal in channel 42 of distribution.

 When the tank is operating at this speed, the blowers 110 or 111 of the additional aeration system are activated. The air delivered is transmitted through the pressure lines 106 to the dispersers 72 or 90 of the pre-chamber ~ ncipale or additional 71 or 87.

 As a result of the increase in back pressure in the additional ventilation system, one of the non-return valves 114 and 115 in service, mounted respectively on the connecting tubes 112 and 113, closes, insulating the air flows of the basic aeration system and of the additional aeration system, thanks to the air supply to the prechamber 71 or 87 by the dispersers 72 or 90, the water circulate from bottom to top and the mixture of regenerated sludge and waste water passing through the respective high chicane 64 or 88 rises from this the main or additional chamber 61 or 79 of rege- tion towards the threshold 65 or 89, and pours into the reservoir 40 of the first stage The transverse flow of the bacterial medium passing through the partition 47 dVaisement and through the weir 48 of the sludge separator 49 goes to clarification, while the recirculation flow of the bacterial medium, from 3 to 5 times greater than the ferry speed, is transmitted by the channel 73 or 127 for circulation to the respective main or additional chamber 61 or 79 for regeneration.

 In order to minimize the energy expenditure to generate the controlled flow of recirculation of the bacterial medium when the water level in the prechamber 71 or 87 rises above the working level in the tank 40 of the first stage from 0.1 to 0.5 me the reservoir 40 and the regeneration chamber 61 or 79 work according to the principle of communicating vessels The pumping of a predetermined quantity of bacterial medium from the regeneration chamber 61 or 79 to the reservoir 40 of the first stage by the intermediary of the respective prechamber 71 or 87 conditions the return of the same quantity of water from the end of the reservoir 40 to the inlet of the regeneration chamber 61 or 79, which generates a recirculation rate of the bacterial medium from 3 to 5 times greater than the wastewater flow, with a concentration of activated sludge of 4.5 to 5 g / l, in which the biochemical oxidation of organic matter is intensified.

 To increase the degree of use of oxygen up to 8-10 t, that is to say 1.5 times when a single prechamber 71 or 87 is operating, part of the waste water flow, amounting to 1 / 3-1 / 6 of the total flow, is admitted directly to the prechamber, without passing through the tank 40.

 When the system is operating at this speed, the excess activated sludge is not evacuated from the second purification stage, and the activated sludge separated at the second purification stage, at a concentration of 8 to 12 gXl and in an amount equal to 0.1-0.2 of the total wastewater flow, are returned to the Initial zone of the main or additional chamber 61 or 79 for regeneration, respectively via the side channel 122 or 124 of thickened sludge, to through inlet ports 74 or 124. In this case, the working concentrate in activated sludge in the "first stage tank-regeneration chamber" system reaches 4.5 to 5 g / l, which maintain an optimal ratio between the biomass and the nutrient medium under the conditions of an increased arrival of waste water. Biochemical oxidation in the aerated stream with an activated sludge concentration of 4.5 to 5 g / l is intensified by the temporary reduction in the size of the bacterial flock, by the uniformization of the load on the sludge according to the length of the stream. , as well as by increasing the degree of use of air oxygen in the pre-room, in which the main mass of the initial pollutants from the wastewater is rapidly metabolized.

 The organized recirculation of the sludge mixture from the terminal zone of the first stage reservoir to its initial zone is the parameter which is technically best suited to adjustment for controlling the biochemical process in activated sludge tanks, making it possible to ensure not only dilution hydraulics of the wastewater arriving at the purification, but also their "biological" dilution by the fresh activated sludge.

 In the period of even greater increase in the load, reaching values 4 to 5 times greater than the average value, the flap 43 again occupies its intermediate position, the constant flow of waste water arrives in the tank 40 from the first stage passing through the central orifices 44, while the main body of water is distributed in equal quantities between the two pre-chambers 71 and 87.

 The tilting of the non-return valves 114 and 115 and the operation of the pre-chambers 71 and 87 take place in a similar manner. The bacterial mixture cross-flow goes to clarification, and the bacterial mixture recirculation flow, which exceeds by 6 to 10 times the cross-flow, passes through circulation channels 73 and 127 and goes to the main chambers 61 and additional 79 regeneration. In this case, it forms in the tank system 40 of the first stage and pre-chambers 71 and 87 two aerated flows looped with conservation of the conditions of intensification of biochemical oxidation of organic pollutants.

 The implementation of the recirculation of the bacterial mixture in the basin makes it possible to greatly reduce the zone with an insufficient quantity of oxygen dissolved in the waste water and to regulate its quantity in the initial zones, the most loaded in the basin. This gives the possibility of reducing the intensity of the basic aeration and calculating it starting from the conditions of minimum load at the head of the structure and the maintenance of the activated sludge in suspension, that is to say so maintain the homogeneity of the bacterial mixture according to the height of the basin. When the charge increases, additional oxygen is introduced with the recirculation mixture, the quantity of which is controlled by varying the number of pre-chambers in service. Since the charge is calculated according to the concentration of pollutants at the head of the he structure, which decreases during recirculation, the maximum intensity of the additional aeration is much lower than in the case of the calculation of the ordinary activated sludge tank. The increase in the number of pre-shades in service is followed by a decrease in the time intervals during which the most intense aeration takes place and, consequently, by a reduction in the quantity of air admitted to the aeration.

 In order to increase the degree of use of oxygen up to 11-15%, that is to say twice during the operation of the two pre-chambers, part of the waste water flow, rising 2/3 of the total flow, the pre-room is admitted directly.

 When the system works at this speed, the activated sludge separated on the second purification stage is returned by the side channels 122 and -123 of thickened sludge to the two regeneration chambers 61 and 79, in an amount equal to 0.2-0 , 3 of the total waste water flow, with a concentration of 8 to 2 gases in this case, the average working concentration of activated sludge in the "first stage tank - main regeneration chamber and" first floor tank - additional regeneration chamber "reaches 5.5 to 6.5 g / l, which maintains the optimal ratio between the biomass and the nutrient medium under the conditions of maximum load.

 In the eventuality of exceeding the maximum load, the excess waste water crosses the overflow thresholds 118 and 119, flows into the side channels 116 and 117 of waste water, passes through the orifices 120 and 121 of entry into the cells of the regeneration @@@@@@@ 61 and 79 most distant from the pre-chambers 71 and 87. This device makes it possible to keep the degree of purification of waste water at the required level without additional expenditure, thanks to the increase in their average route length.

 The main difficulties encountered in obtaining the optimal regime for the biological purification of wastewater in a traditional activated sludge tank are due to the large fluctuations in the load, making - e the proportion between the concentrations of wastewater in pollutants, activated sludge and dissolved oxygen do not deny constant and deviate from the optimal level.

 The device resold # for the implementation of the biological purification process, is free from this drawback1 which allows maximum use of the oxidizing power of activated sludge in the presence of practically any fluctuations in the charge.

 FIG. 10 represents the diagram of variation of the load as a function of the hours of the day (curve C) superimposed on the diagram of operation of the basic and additional ventilation systems (broken line D).

On the ordinate, the load of BOD and the quantity of oxygen introduced, expressed in relative units, were carried.

 The lower level of the broken line D corresponds to the operating speed of the basic aeration system, the average level of the line D corresponds to the increased period of waste water arrival when the main prechamber is activated, and the upper level of line D corresponds to the period in which the arrival of waste water reaches the maximum values and the additional pre-chamber is activated.

 The higher the precision with which the diagram of variation of the oxidizing power of the activated sludge tank fits into the diagram of the fluctuating load on the tank, the lower the unproductive expenditure of electrical energy and the more the technological and economic performances. of the purification system are high. This is obtained by an appropriate choice of the number of pre-chambers in service and their throughput.

 it is advantageous, during peak load hours, to combine the action of the main prechamber with that of the additional prechamber. The periods of activation of the pre-chambers are determined, for example, according to the indications of a limnimeter mounted in the waste water distribution channel, with correction of their operation according to the indications of an oxygen sensor. dissolved, mounted at critical points on the first stage tank

Claims (10)

R E V E N D I C A T I O N S  1. Process for the biological purification of wastewater, of the type in which it is freed of organic pollutants by means of activated sludge and in two stages, namely: a first stage (2) where the wastewater (1) arriving at the purification are mixed with the activated sludge (3, 4), the bacterial medium thus obtained is aerated, then the sludge to be recycled (19, 20) is separated from the bacterial medium (8) in the terminal zone on this floor. (2), regenerated (5, 6) and readmitted in the initial zone of this stage (2 days to be mixed with the waste water (1) arriving at the purification, and a second stage (13) or the sludge water ( 12) obtained after separation of the sludge to be recycled (19, 20) from the bacterial medium are aerated, then freed from the remains of activated sludge (18), characterized in that the sludge to be recycled admitted for regeneration is divided into two parts (19 , 20) and (21, 22), the part (19, 20) going directly to regeneration, while the part (21, 22) is thickened, then mixed with the first part (19, 20) of the sludge to be recycled for their simultaneous regeneration, by ensuring that the audit between the first stage (2) of the treatment and the ratio between the organic pollutants of the waste water (1) arriving at the treatment and the activated sludge (3, a) remains constant  2 Method according to claim 1, characterized in that the part (21, 22) of the sludge to be recycled which is subjected to thickening constitutes substantially 0.2 to 0.8 of the total mass of the sludge to be recycled (19, 20 , 25, 26) going to regeneration.  3. Method according to one of claims 1 and 2, characterized in that, in the event of increased arrival of waste water (1), a portion (27, 34) of waste water (1) arriving at the first stage (2 ) is premixed with the regenerated activated sludge (3, 4) going to the first stage (2), and that an additional aeration is carried out by admission of oxygenated gas, then the bacterial medium obtained is mixed with the rest (35) of the waters waste going to the initial zone of the first stage 12), and, after the treatment on the first stage (2), part (29, 32) of the bacterial medium is brought back from the terminal zone to the initial zone of the first stage (2) by mixing it with the sludge to be recycled, going to regeneration, the quantity of oxygenated gas (28, 31) admitted for the additional aeration being chosen so as to ensure a longitu so-called energetic mixing of the bacterial medium of the first stage (2) by re-ircuJa +; lo. of this medium between the terminal zone and the initial zone of the first stage (2).  4 method according to claim 3, characterized in that the amount of oxygenated gas admitted for additional aeration is chosen so that the ratio between ..e recirculation flow of the bacterial medium and the flow of waste water (i) arriving at treatment is mainly in the range of 3 to 10.  5 Method according to one of claims 3 and 4, characterized in that the flow (27, 34) of the waste water going to the premix with the regenerated sludge (3, 4) is essentially between 1/3 and 2/3 of the waste water flow arriving at purification.  6. Method according to one of the preceding claims, characterized in that the sludge water (36, 37) forming as a result of the thickening of part of the recycling sludge (21, 22) going to regeneration are admitted to the second stage (13) and subjected to aeration, and that the activated sludge (38, 39) separated after the second stage (13) is mixed with the sludge (19, 20, 25, 26) recycled during regeneration .  7. Activated sludge tank for biological purification  waste water, of the type comprising a long-term inal tank for mixing (40) a first purification stage (equipped with oxygenated gas dispersers (41) and comprising an initial zone in which devices are arranged (42, 43, 44, 45, 46) inlet of the waste water (1) and the activated sludge (3, 4) into the tank (40), as well as a terminal zone in which there is an outlet for the bacterial medium, placed in communication with a separator of sludge (49) suitable for separating the recycling sludge from the bacterial medium, this separator (49) comprising an outlet (50, 51) for the purified waste water, placed in communication with a displacement tank (52, 53) a second purification stage, equipped with oxygenated gas dispersers (54, 55) and a sludge separator (9), as well as an outlet (60) for the sludges to be recycled, placed in communication with a regeneration chamber - (61) comprising oxygenated gas dispersers (62), the outlet (63) of this chamber being placed in communication with a device (64, 65) for entering the regenerated activated sludge into the tank (40) of the first stage, characterized in that it is equipped with a sludge thickener (66) adapted to increase the concentration of recycling sludge and comprising an inlet (67) communicating with the outlet (68) of the recycling sludge from the sludge separator (49), as well as two outlets (69, 70), the outlet (69) recycling sludge being placed in communication with Igeate of the regeneration chamber (61), and the outlet (70) of the sludge water, with the inlet of the displacement tank (52) of the second stage.  8. Activated sludge tank according to claim 7, characterized in that it is equipped with a prechamber (71) comprising dispersers (72j of air equipped and interposed between the outlet (63) of the regeneration c-chamber (61) and the device (64, 65) for entering the activated sludge into the tank (40) of the first stage, this prechamber (71) being placed in communication with the device (45)  of waste water entering the reservoir (40) of the  first stage, and the regeneration chamber (64) being  put in communication with your terminal area of the  see v40) on the first floor  9. Activated sludge tank according to one of the  claim 7 and 8, characterized in that the outlet  activated sludge from the sludge separator (16) of the second  floor is connected to entry t74) of  the regeneration chamber (61) -.  10. Activated sludge tank according to claim 7,  characterized in that it comprises a longitudinal tank  (75) open at its upper part, shared by a  transverse partition (76) in two compartments, in the  first of which are placed longitudinal partitions (77, 78) which form, along the longitudinal axis of the tank (75), the tank (40) of the first stage, inside which are mounted the oxygenated gas dispersers 141) let which also form, with the walls of the tank (75), the main regeneration chamber (61) and an additional regeneration chamber (79) located on either side of the tank (40) on the first stage and comprising transverse partitions (80, 81) dividing them into cells, in each of which is placed a disperser. oxygenated gas (62, 82), as well as longitudinal and transverse partitions (83, 84, 85, 86) arranged near the initial zone of the tank (40), outside the longitudinal partitions (77, 78), so to form a main prechamber l71) and an additional prechamber (87) placed in communication with the main and additional regeneration chambers (Ç1, 79) by high baffles (64, 88), and with the reservoir (-40), by thresholds (65, 89), and equipped with oxygenated gas dispersers (72, 90) 1 while in the second compartment is mounted, along the axis thereof thereof sludge separator  (49) horizontal, of the gravity type, connected  with the reservoir (40) of the first stage by a passage  siphoid (47, 48) and forming with the walls of said second  compartment the tank (52, 53) of the second stage,  vertical sludge thickeners (66, 91), of the gravity type entering mounted near the transverse partition (76) of the tank (75) and placed in communication with the main and additional regeneration chambers (61, 79), the separator of sludge (49) being equipped with means of ascent to the air (92) for bringing (94, 95) recycling sludge, of increased concentration, into the main and additional regeneration chambers (61, 79) .