EP1554222A2 - Method for reducing sludge of a biological ozone treatment system - Google Patents

Method for reducing sludge of a biological ozone treatment system

Info

Publication number
EP1554222A2
EP1554222A2 EP03780287A EP03780287A EP1554222A2 EP 1554222 A2 EP1554222 A2 EP 1554222A2 EP 03780287 A EP03780287 A EP 03780287A EP 03780287 A EP03780287 A EP 03780287A EP 1554222 A2 EP1554222 A2 EP 1554222A2
Authority
EP
European Patent Office
Prior art keywords
ozone
effluent
gas
ozone gas
sludge
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP03780287A
Other languages
German (de)
French (fr)
Inventor
Philippe Campo
Jérôme Cluzeau
Christian Jalbert
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Original Assignee
Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Air Liquide SA, LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude filed Critical Air Liquide SA
Publication of EP1554222A2 publication Critical patent/EP1554222A2/en
Ceased legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F3/00—Biological treatment of water, waste water, or sewage
    • C02F3/02—Aerobic processes
    • C02F3/12—Activated sludge processes
    • C02F3/1205—Particular type of activated sludge processes
    • C02F3/1221—Particular type of activated sludge processes comprising treatment of the recirculated sludge
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/72—Treatment of water, waste water, or sewage by oxidation
    • C02F1/78—Treatment of water, waste water, or sewage by oxidation with ozone
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00—Technologies for wastewater treatment
    • Y02W10/10—Biological treatment of water, waste water, or sewage

Definitions

  • the present invention relates to methods of treating aqueous effluents using a biological step.
  • Aerobic biological treatments of effluents generally consist in bringing these effluents into contact with a biomass (microorganisms) which degrades the pollution contained in them by transforming organic molecules into minerals: this is the step commonly called aeration of biological basins.
  • the implementation of such treatments leads to a progressive increase in the quantity of biomass and to the need to evacuate the excess biomass commonly called "excess sludge”.
  • Excess sludge To deal with the constantly increasing quantity of this excess biological sludge and its disposal, different solutions have been proposed.
  • a first family of processes consists in withdrawing this excess sludge at the end of the biological treatment and either finding a suitable outlet for it or treating it during a specific degradation step. They can thus be used as fertilizer in agriculture (spreading).
  • solutions consist in carrying out a partial lysis of the sludge, that is to say destroying a part of the microorganisms which make up the sludge by making it partially soluble.
  • the products from this lysis which contain at least partially soluble organic compounds can then be sent to the top of the effluent treatment to undergo the biological treatment, during which the microorganisms will treat the products from the lysis.
  • a first known lysis technique consists in exerting a mechanical action on the sludge coming from the biological treatment basin which causes the bursting of part of the cells of the micro- organisms constituting excess sludge. It can be a mechanical grinding, compression / expansion technique, sonochemistry, ...
  • a second lysis technique is a basic or acid attack using chemical agents possibly coupled with a rise in temperature, but this technique requires the pH of the solution obtained to be readjusted before it is reinjected into the aeration tank.
  • the disadvantage of this solution is that it increases the salinity of the hydrolyzed sludge which can lead to a dysfunction of the biological treatment stage.
  • a third lysis technique is based on the action of oxidizing agents such as: ozone, air, hydrogen peroxide or oxygen under pressure.
  • the object of the present invention is to propose a new implementation of ozone for the reduction of excess sludge conventionally produced during a biological treatment of water not presenting the implementation difficulties defined above.
  • the invention relates to a method for reducing the sludge formed during the biological treatment of an aqueous effluent, said treatment comprising at least one step during which the effluent is brought into contact with microorganisms in a aeration, a process in which an ozone gas comprising at least 2.5 mg of ozone per liter of gas is injected into the aeration tank by means of an apparatus producing an emulsion of the ozone gas in the effluent.
  • the invention relates to any type of effluent treatment process in which the effluent is subjected to a biological treatment step.
  • This mud generally includes living and dead microorganisms, cellular debris, organic absorbents and colloids, organic corpuscles and / or mineral particles.
  • an ozone gas is injected into the aeration tank so as to obtain aeration of the tank and a lysis of the microorganisms contained in the biological mud and thus reduce the formation of excess mud.
  • the term ozone gas is understood to mean a gas comprising at least ozone and oxygen.
  • a first essential characteristic of the invention is that the ozone gas is injected directly into the aeration tank.
  • a second essential characteristic concerns the composition of the ozone gas which must comprise at least 2.5 mg of ozone per liter of gas.
  • this ozone gas comprises at most 300 mg of ozone per liter of gas.
  • the ozone gas is injected directly into the aeration tank by means of a device producing an emulsion of the ozone gas in the effluent.
  • a device producing an emulsion of the ozone gas in the effluent will be used.
  • the use of these devices generally makes it possible to transfer almost all of the ozone in the effluent and thus to have no environmental risk of rejection of ozone to the atmosphere. This is due to the fact that the solubility of ozone in water is approximately ten times higher than that of oxygen and its reactivity in the effluent very fast (during the tests, no residual ozone was detected on the mixture of effluent and biological sludge leaving the aeration tank).
  • the means for transferring the ozone gas into the effluent may be composed of a venturi supplied by a pump and comprising a means for injecting gas into the narrow part of the venturi.
  • the pump makes it possible to circulate the effluent from the aeration tank in the venturi and the gas injection means injects the ozone gas into the effluent stream created by the venturi and the pump.
  • An ozone gas / liquid effluent emulsion then occurs which is diffused in the aeration tank. This diffusion can be improved by means of nozzles and ejectors placed after the venturi in the direction of the flow of the effluent.
  • the means for transferring the ozone gas into the effluent may be composed of a turbine and of a means for injecting gas into the turbine.
  • this device is composed of a self-aspirating turbine and a propeller, said self-aspirating turbine and said propeller being carried by the same hollow drive shaft, and said hollow shaft ensuring the supply of ozone gas of the turbine. More specifically, this type of device comprises a drive device placed above the liquid to be agitated and provided with a shaft equipped at its lower end with at least one axial flow mobile immersed in the liquid.
  • the shaft also carries the self-aspirating turbine immersed in the liquid and which can be driven by the shaft.
  • the shaft is wrapped coaxially by a cylinder linked at its upper end in a sealed manner to the drive device and the lower end of which opens into the turbine.
  • the upper end of the cylinder is pierced with an ozone gas injection opening in an annular interval delimited by the shaft and the cylinder.
  • the liquid is stirred by the turbine. By turning, it sucks the ozone gas through the annular space of the shaft and diffuses it into the liquid at the level of the turbine.
  • the gas / liquid dispersion thus created is very widely distributed in the aeration tank via the turbine and the propeller generally placed under said turbine.
  • This injection means is described in application EP-A1 -0 995485. This type of device is marketed by Air Liquide under the reference Turboxal ® .
  • the means for transferring the ozone gas into the effluent have the advantage of exhibiting very good transfer yields and an effect of partial destructuring of the biological flocs (disaggregation of the flocs, or even destruction of the cell walls of the microorganisms). This destructuring effect of the flocs increases the efficiency of ozone for the reduction of biomass.
  • the ozone gas can come directly from an ozone generator or from another step in the effluent treatment process which also uses an ozone gas.
  • the ozone gas can be the residual ozone gas coming from a gas vent (recycling). Due to the very rapid decomposition of ozone in aqueous effluents and its high solubility in these effluents, the transfer of ozone in these effluents is close to 100% and the formation of ozone at the surface of the basins. ventilation is avoided.
  • the method according to the invention has the advantage of combining in a single step: the at least partial aeration of the biological basin by means of oxygen from the ozone gas and sludge reduction by means of the high amount of ozone in the ozone gas.
  • a basin 9 m deep and 6000 m 3 in volume is aerated using two Ventoxal devices. Each Ventoxal device injects 53 Nm 3 / h of oxygen corresponding to the hourly need for ventilation.
  • the production of excess organic sludge extracted each day to keep the concentration of sludge in the aerated tank constant is 460 kg / d.
  • the oxygen from one of the two Ventoxal devices is doped with 17 mg / l of ozone.
  • Daily sludge production drops to 320 kg / d, a reduction of 30%.
  • An improvement in the sludge index is also observed as well as an ease of dewatering of the excess of remaining sludge.

Landscapes

  • Life Sciences & Earth Sciences (AREA)
  • Biodiversity & Conservation Biology (AREA)
  • Microbiology (AREA)
  • Hydrology & Water Resources (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Treatment Of Water By Oxidation Or Reduction (AREA)
  • Treatment Of Sludge (AREA)

Abstract

The invention concerns a method for treating an effluent comprising at least one biological treatment step leading to the production of biological sludge, a step during which the effluent is contacted with micro-organisms in a tank, wherein ozone-containing gas is injected into said tank comprising at least 2.5 mg of ozone per litre of gas.

Description

Procédé de réduction des boues d'un traitement biologique de l'eau mettant en œuvre de l'ozone. Process for reducing sludge from biological water treatment using ozone.
La présente invention concerne les procédés de traitement d'effluents aqueux mettant en œuvre une étape biologique.The present invention relates to methods of treating aqueous effluents using a biological step.
Les traitements biologiques aérobie d'effluents consistent généralement à mettre en contact ces effluents avec une biomasse (micro-organismes) qui dégrade la pollution contenue dans ceux-ci en transformant les molécules organiques en minéraux : il s'agit de l'étape appelée communément aération des bassins biologiques. La mise en œuvre de tels traitements conduit à une augmentation progressive de la quantité de biomasse et à la nécessité d'évacuer la biomasse en excès communément appelée "boues en excès". Pour faire face à la quantité sans cesse croissante de ces boues biologiques en excès et de leur évacuation, différentes solutions ont été proposées. Une première famille de procédés consiste à soutirer ces boues en excès à l'issue du traitement biologique et soit leur trouver un débouché adapté soit les traiter lors d'une étape spécifique de dégradation. Elles peuvent ainsi être utilisées comme engrais dans l'agriculture (épandage). Toutefois, le respect des normes sur l'environnement et la présence possible de micropolluants ou de métaux lourds dans les boues conduisent à réduire cette utilisation. Une autre solution consiste à soutirer ces boues et à les incinérer ; il faut alors les transporter vers un incinérateur ce qui implique un coût. De plus, les difficultés pour implanter de nouveaux incinérateurs freinent le développement de cette solution. Une autre solution consiste à réaliser une oxydation par voie humide des boues en excès : les boues sont alors minéralisées. Une seconde famille de procédés consiste à réduire la production de boues lors du traitement biologique. Ces solutions consistent à utiliser des moyens permettant de réduire la production de boues au cours du processus biologique de dépollution des eaux. Ces solutions consistent à réaliser une lyse partielle les boues, c'est-à-dire détruire une partie des micro-organismes qui composent les boues en les rendant partiellement solubles. Les produits issus de cette lyse qui contiennent des composés organiques au moins partiellement solubles peuvent alors être renvoyés en tête du traitement d'effluents pour subir le traitement biologique, au cours duquel les microorganismes vont traiter les produits issus de la lyse. Une première technique de lyse connue consiste à exercer une action mécanique sur les boues provenant du bassin de traitement biologique ce qui provoque l'éclatement d'une partie des cellules des micro- organismes constituant les boues en excès. Il peut s'agir d'un broyage mécanique, de technique de compression/détente, de sonochimie, ... Cette technique est généralement simple à mettre en œuvre mais présente l'inconvénient de ne réduire que faiblement la production des boues en excès. En outre, le coût énergétique est important. Une deuxième technique de lyse est une attaque basique ou acide à l'aide d'agents chimiques éventuellement couplée à une élévation de température, mais cette technique nécessite le réajustement du pH de la solution obtenue avant sa réinjection dans le bassin d'aération. L'inconvénient de cette solution est qu'elle augmente la salinité des boues hydrolysées ce qui peut conduire à un dysfonctionnement de l'étape de traitement biologique. Une troisième technique de lyse est basée sur l'action d'agents oxydants tels que : l'ozone, l'air, le peroxyde d'hydrogène ou l'oxygène sous pression. L'inconvénient de l'air, du peroxyde d'hydrogène et de l'oxygène est qu'ils ne sont pas assez efficaces seuls : ils doivent être associés à un chauffage et/ou un catalyseur, ce qui augmente également le coût de ces techniques. Quant à l'ozone, son utilisation nécessite la mise en place d'un dispositif particulier. En effet, dans son utilisation pour la réduction du volume de boues en excès, l'injection d'ozone est dissociée de l'étape d'aération des bassins d'aération. Le gaz ozone est injecté au sein d'un réacteur séparé des bassins d'aération. C'est un inconvénient, car l'installation est coûteuse et la mise en œuvre sur des unités existantes est compliquée. Le document US-A-5,573,670 évoque la possibilité d'injecter un gaz ozone très faiblement concentré en ozone (0,01 à 0,16 % en poids d'03 par rapport à 02) dans un bassin d'aération d'une unité de traitement biologique d'effluents aqueux uniquement dans les buts d'éviter la formation de bactéries filamenteuses et de faire chuter le Carbone Organique Total (COD) de manière significative. Aucune influence de cette injection directe de gaz à faible taux d'ozone sur le taux de boues en excès n'a pu être constatée.Aerobic biological treatments of effluents generally consist in bringing these effluents into contact with a biomass (microorganisms) which degrades the pollution contained in them by transforming organic molecules into minerals: this is the step commonly called aeration of biological basins. The implementation of such treatments leads to a progressive increase in the quantity of biomass and to the need to evacuate the excess biomass commonly called "excess sludge". To deal with the constantly increasing quantity of this excess biological sludge and its disposal, different solutions have been proposed. A first family of processes consists in withdrawing this excess sludge at the end of the biological treatment and either finding a suitable outlet for it or treating it during a specific degradation step. They can thus be used as fertilizer in agriculture (spreading). However, compliance with environmental standards and the possible presence of micropollutants or heavy metals in the sludge leads to a reduction in this use. Another solution is to extract this sludge and incinerate it; they must then be transported to an incinerator, which involves a cost. In addition, the difficulties in setting up new incinerators are hampering the development of this solution. Another solution consists in carrying out a wet oxidation of the excess sludge: the sludge is then mineralized. A second family of processes consists in reducing the production of sludge during biological treatment. These solutions consist in using means making it possible to reduce the production of sludge during the biological process of water pollution control. These solutions consist in carrying out a partial lysis of the sludge, that is to say destroying a part of the microorganisms which make up the sludge by making it partially soluble. The products from this lysis which contain at least partially soluble organic compounds can then be sent to the top of the effluent treatment to undergo the biological treatment, during which the microorganisms will treat the products from the lysis. A first known lysis technique consists in exerting a mechanical action on the sludge coming from the biological treatment basin which causes the bursting of part of the cells of the micro- organisms constituting excess sludge. It can be a mechanical grinding, compression / expansion technique, sonochemistry, ... This technique is generally simple to implement but has the disadvantage of only slightly reducing the production of excess sludge. In addition, the energy cost is important. A second lysis technique is a basic or acid attack using chemical agents possibly coupled with a rise in temperature, but this technique requires the pH of the solution obtained to be readjusted before it is reinjected into the aeration tank. The disadvantage of this solution is that it increases the salinity of the hydrolyzed sludge which can lead to a dysfunction of the biological treatment stage. A third lysis technique is based on the action of oxidizing agents such as: ozone, air, hydrogen peroxide or oxygen under pressure. The disadvantage of air, hydrogen peroxide and oxygen is that they are not effective enough alone: they must be combined with a heating and / or a catalyst, which also increases the cost of these techniques. As for ozone, its use requires the installation of a specific device. In fact, in its use for reducing the volume of excess sludge, the injection of ozone is dissociated from the aeration step of the aeration basins. The ozone gas is injected into a reactor separate from the aeration tanks. This is a disadvantage, because the installation is expensive and the implementation on existing units is complicated. Document US-A-5,573,670 mentions the possibility of injecting an ozone gas very weakly concentrated in ozone (0.01 to 0.16% by weight of 0 3 relative to 0 2 ) in an aeration tank of a biological treatment unit for aqueous effluents only for the purpose of preventing the formation of filamentous bacteria and significantly lowering the Total Organic Carbon (DOC). No influence of this direct injection of low-ozone gas on the rate of excess sludge could be observed.
Le but de la présente invention est de proposer une nouvelle mise en œuvre de l'ozone pour la réduction des boues en excès produites classiquement lors d'un traitement biologique des eaux ne présentant pas les difficultés de mise en œuvre définies ci-dessus.The object of the present invention is to propose a new implementation of ozone for the reduction of excess sludge conventionally produced during a biological treatment of water not presenting the implementation difficulties defined above.
Dans ce but, l'invention concerne un procédé de réduction des boues formées lors du traitement biologique d'un effluent aqueux, ledit traitement comprenant au moins une étape au cours de laquelle l'effluent est mis en contact avec des microorganismes dans un bassin d'aération, procédé dans lequel on injecte dans le bassin d'aération un gaz ozone comprenant au moins 2,5 mg d'ozone par litre de gaz au moyen d'un appareil produisant une émulsion du gaz ozone dans l'effluent. L'invention se rapporte à tout type de procédé de traitement d'effluent dans lequel l'effluent est soumis à une étape de traitement biologique. Au cours de cette étape de traitement biologique, l'effluent est mis en contact avec des micro-organismes (biomasse) et une boue biologique est générée. Cette boue comprend généralement des micro-organismes vivants et morts, des débris cellulaires, des absorbats et colloïdes organiques, des corpuscules organiques et/ou des particules minérales.To this end, the invention relates to a method for reducing the sludge formed during the biological treatment of an aqueous effluent, said treatment comprising at least one step during which the effluent is brought into contact with microorganisms in a aeration, a process in which an ozone gas comprising at least 2.5 mg of ozone per liter of gas is injected into the aeration tank by means of an apparatus producing an emulsion of the ozone gas in the effluent. The invention relates to any type of effluent treatment process in which the effluent is subjected to a biological treatment step. During this biological treatment step, the effluent is brought into contact with microorganisms (biomass) and a biological sludge is generated. This mud generally includes living and dead microorganisms, cellular debris, organic absorbents and colloids, organic corpuscles and / or mineral particles.
Selon l'invention, on injecte un gaz ozone dans le bassin d'aération de manière à obtenir une aération du bassin et une lyse des micro-organismes contenus dans la boue biologique et réduire ainsi la formation d'excès de boue. Selon l'invention, on entend par gaz ozone, un gaz comprenant au moins de l'ozone et de l'oxygène. Une première caractéristique essentielle de l'invention tient à ce que le gaz ozone est directement injecté dans le bassin d'aération. Une deuxième caractéristique essentielle concerne la composition du gaz ozone qui doit comprendre au moins 2,5 mg d'ozone par litre de gaz. De préférence, ce gaz ozone comprend au plus 300 mg d'ozone par litre de gaz.According to the invention, an ozone gas is injected into the aeration tank so as to obtain aeration of the tank and a lysis of the microorganisms contained in the biological mud and thus reduce the formation of excess mud. According to the invention, the term ozone gas is understood to mean a gas comprising at least ozone and oxygen. A first essential characteristic of the invention is that the ozone gas is injected directly into the aeration tank. A second essential characteristic concerns the composition of the ozone gas which must comprise at least 2.5 mg of ozone per liter of gas. Preferably, this ozone gas comprises at most 300 mg of ozone per liter of gas.
Selon l'invention, le gaz ozone est injecté directement dans le bassin d'aération au moyen d'un appareil produisant une émulsion du gaz ozone dans l'effluent De façon avantageuse, les appareils connus pour posséder un taux de transfert élevé en oxygène dans les effluents aqueux seront utilisés. En effet, l'utilisation de ces appareils permet en général de transférer la quasi-totalité de l'ozone dans l'effluent et ainsi de n'avoir aucun risque environnemental de rejet d'ozone à l'atmosphère. Cela vient du fait que la solubilité de l'ozone dans l'eau est approximativement dix fois plus élevée que celle de l'oxygène et sa réactivité dans l'effluent très rapide (au cours des essais, aucun ozone résiduel n'a été détecté sur le mélange d'effluent et de boues biologiques en sortie du bassin d'aération).According to the invention, the ozone gas is injected directly into the aeration tank by means of a device producing an emulsion of the ozone gas in the effluent. Advantageously, devices known to have a high oxygen transfer rate in aqueous effluents will be used. Indeed, the use of these devices generally makes it possible to transfer almost all of the ozone in the effluent and thus to have no environmental risk of rejection of ozone to the atmosphere. This is due to the fact that the solubility of ozone in water is approximately ten times higher than that of oxygen and its reactivity in the effluent very fast (during the tests, no residual ozone was detected on the mixture of effluent and biological sludge leaving the aeration tank).
Selon une première mise en œuvre, le moyen de transfert du gaz ozone dans l'effluent peut être composé d'un venturi alimenté par une pompe et comprenant un moyen d'injection de gaz dans la partie étroite du venturi. La pompe permet de faire circuler l'effluent du bassin d'aération dans le venturi et le moyen d'injection de gaz assure l'injection du gaz ozone dans le courant d'effluent créé par le venturi et la pompe. Il se produit alors une émulsion gaz ozoné/effluent liquide qui est diffusée dans le bassin d'aération. Cette diffusion peut être améliorée par l'intermédiaire de tuyères et d'éjecteurs placés après le venturi dans le sens du courant de l'effluent. Ce type d'appareil est commercialisé par Air Liquide sous la référence Ventoxal®. Selon une deuxième mise en œuvre, le moyen transfert du gaz ozone dans l'effluent peut être composé d'une turbine et d'un moyen d'injection de gaz dans la turbine. Selon une variante préférée, ce dispositif est composé d'une turbine autoaspirante et d'une hélice, ladite turbine auto-aspirante et ladite hélice étant portées par un même arbre d'entraînement creux, et ledit arbre creux assurant l'approvisionnement en gaz ozone de la turbine. Plus précisément, ce type de dispositif comprend un dispositif d'entraînement placé au-dessus du liquide à agiter et pourvu d'un arbre équipé à son extrémité inférieure d'au moins un mobile à flux axial immergé dans le liquide. L'arbre porte également la turbine auto-aspirante immergée dans le liquide et pouvant être entraînée par l'arbre. L'arbre est enveloppé coaxialement par un cylindre lié à son extrémité supérieure de manière étanche au dispositif d'entraînement et dont l'extrémité inférieure débouche dans la turbine. L'extrémité supérieure du cylindre est percée d'une ouverture d'injection du gaz ozone dans un intervalle annulaire délimité par l'arbre et le cylindre. Lors du fonctionnement de ce dispositif, le liquide est brassé par la turbine. En tournant, celle-ci aspire le gaz ozone à travers l'espace annulaire de l'arbre et le diffuse dans le liquide au niveau de la turbine. La dispersion gaz/liquide ainsi créée est diffusée très largement dans le bassin d'aération par l'intermédiaire de la turbine et de l'hélice placée généralement sous ladite turbine. Ce moyen d'injection est décrit dans la demande EP-A1 -0 995485. Ce type d'appareil est commercialisé par Air Liquide sous la référence Turboxal®.According to a first implementation, the means for transferring the ozone gas into the effluent may be composed of a venturi supplied by a pump and comprising a means for injecting gas into the narrow part of the venturi. The pump makes it possible to circulate the effluent from the aeration tank in the venturi and the gas injection means injects the ozone gas into the effluent stream created by the venturi and the pump. An ozone gas / liquid effluent emulsion then occurs which is diffused in the aeration tank. This diffusion can be improved by means of nozzles and ejectors placed after the venturi in the direction of the flow of the effluent. This type of device is marketed by Air Liquide under the reference Ventoxal ® . According to a second implementation, the means for transferring the ozone gas into the effluent may be composed of a turbine and of a means for injecting gas into the turbine. According to a preferred variant, this device is composed of a self-aspirating turbine and a propeller, said self-aspirating turbine and said propeller being carried by the same hollow drive shaft, and said hollow shaft ensuring the supply of ozone gas of the turbine. More specifically, this type of device comprises a drive device placed above the liquid to be agitated and provided with a shaft equipped at its lower end with at least one axial flow mobile immersed in the liquid. The shaft also carries the self-aspirating turbine immersed in the liquid and which can be driven by the shaft. The shaft is wrapped coaxially by a cylinder linked at its upper end in a sealed manner to the drive device and the lower end of which opens into the turbine. The upper end of the cylinder is pierced with an ozone gas injection opening in an annular interval delimited by the shaft and the cylinder. During the operation of this device, the liquid is stirred by the turbine. By turning, it sucks the ozone gas through the annular space of the shaft and diffuses it into the liquid at the level of the turbine. The gas / liquid dispersion thus created is very widely distributed in the aeration tank via the turbine and the propeller generally placed under said turbine. This injection means is described in application EP-A1 -0 995485. This type of device is marketed by Air Liquide under the reference Turboxal ® .
Pour ces deux mises en œuvre, ies moyens de transfert du gaz ozone dans l'effluent ont l'avantage de présenter de très bons rendements de transfert et un effet de déstructuration partielle des flocs biologiques (désagrégation des flocs, voire destruction des parois cellulaires des microorganismes). Cet effet de déstructuration des flocs accroît l'efficacité de l'ozone pour la réduction de la biomasse.For these two implementations, the means for transferring the ozone gas into the effluent have the advantage of exhibiting very good transfer yields and an effect of partial destructuring of the biological flocs (disaggregation of the flocs, or even destruction of the cell walls of the microorganisms). This destructuring effect of the flocs increases the efficiency of ozone for the reduction of biomass.
Le gaz ozone peut provenir directement d'un générateur d'ozone ou d'une autre étape du procédé de traitement des effluents qui met également en œuvre un gaz ozone. Ainsi, le gaz ozone peut être le gaz ozone résiduel provenant d'un évent gazeux (recyclage). Du fait de la décomposition très rapide de l'ozone dans les effluents aqueux et de sa grande solubilité dans ces effluents, le transfert de l'ozone dans ces effluents est proche de 100 % et la formation d'ozone à la surface des bassins d'aération est évitée.The ozone gas can come directly from an ozone generator or from another step in the effluent treatment process which also uses an ozone gas. Thus, the ozone gas can be the residual ozone gas coming from a gas vent (recycling). Due to the very rapid decomposition of ozone in aqueous effluents and its high solubility in these effluents, the transfer of ozone in these effluents is close to 100% and the formation of ozone at the surface of the basins. ventilation is avoided.
Le procédé selon l'invention présente l'avantage de combiner en une seule étape : l'aération au moins partielle du bassin biologique au moyen de l'oxygène du gaz ozone et la réduction de boues au moyen de la quantité élevée d'ozone dans le gaz ozone.The method according to the invention has the advantage of combining in a single step: the at least partial aeration of the biological basin by means of oxygen from the ozone gas and sludge reduction by means of the high amount of ozone in the ozone gas.
EXEMPLE - Oxygénation pour l'aération et l'ozonation pour la réduction de la production de boues simultanée d'un bassin biologique.EXAMPLE - Oxygenation for aeration and ozonation for the reduction of simultaneous sludge production in a biological basin.
Un bassin de 9 m de profondeur et de 6000 m3 de volume est aéré à l'aide de deux appareils Ventoxal. Chaque appareil Ventoxal injecte 53 Nm3/h d'oxygène correspondant au besoin horaire en aération. La production de boues biologiques en excès extraite chaque jour permettant de maintenir constante la concentration en boues dans le bassin aérée est de 460 kg/j.A basin 9 m deep and 6000 m 3 in volume is aerated using two Ventoxal devices. Each Ventoxal device injects 53 Nm 3 / h of oxygen corresponding to the hourly need for ventilation. The production of excess organic sludge extracted each day to keep the concentration of sludge in the aerated tank constant is 460 kg / d.
Sur une filière de traitement parallèle et identique, l'oxygène d'un des deux appareils Ventoxal est dopé par 17 mg/l d'ozone. La production de boues journalière passe à 320 kg/j soit une réduction de 30 %. Une amélioration de l'indice de boues est également observée ainsi qu'une facilité de déshydratation de l'excès de boues restantes. On a parallel and identical treatment system, the oxygen from one of the two Ventoxal devices is doped with 17 mg / l of ozone. Daily sludge production drops to 320 kg / d, a reduction of 30%. An improvement in the sludge index is also observed as well as an ease of dewatering of the excess of remaining sludge.

Claims

REVENDICATIONS
1. Procédé de réduction des boues formées lors du traitement biologique d'un effluent aqueux, ledit traitement comprenant au moins une étape au cours de laquelle l'effluent est mis en contact avec des microorganismes dans un bassin d'aération, caractérisé en ce qu'on injecte dans le bassin d'aération un gaz ozone comprenant au moins 2,5 mg d'ozone par litre de gaz au moyen d'un appareil produisant une émulsion du gaz ozone dans l'effluent.1. Method for reducing the sludge formed during the biological treatment of an aqueous effluent, said treatment comprising at least one step during which the effluent is brought into contact with microorganisms in an aeration tank, characterized in that 'An ozone gas comprising at least 2.5 mg of ozone per liter of gas is injected into the aeration tank by means of an apparatus producing an emulsion of the ozone gas in the effluent.
2. Procédé selon la revendication 1, caractérisé en ce que le gaz ozone comprend au plus 300 mg d'ozone par litre de gaz.2. Method according to claim 1, characterized in that the ozone gas comprises at most 300 mg of ozone per liter of gas.
3. Procédé selon la revendication 1 ou 2, caractérisé en ce que l'appareil produisant une émulsion du gaz ozone dans l'effluent est composé d'un venturi alimenté par une pompe et comprenant un moyen d'injection de gaz dans la partie étroite du venturi.3. Method according to claim 1 or 2, characterized in that the apparatus producing an emulsion of the ozone gas in the effluent is composed of a venturi supplied by a pump and comprising a gas injection means in the narrow part venturi.
4. Procédé selon la revendication 1 ou 2, caractérisé en ce que l'appareil produisant une émulsion du gaz ozone dans l'effluent est composé d'une turbine et d'un moyen d'injection de gaz dans la turbine.4. Method according to claim 1 or 2, characterized in that the apparatus producing an emulsion of the ozone gas in the effluent is composed of a turbine and a means of injecting gas into the turbine.
5. Procédé selon la revendication 4, caractérisé en ce que l'appareil produisant une émulsion du gaz ozone dans l'effluent est composé d'une turbine auto-aspirante et d'une hélice, ladite turbine auto-aspirante et ladite hélice étant portées par un même arbre d'entraînement creux, et ledit arbre creux assurant l'approvisionnement en gaz ozone de la turbine. 5. Method according to claim 4, characterized in that the apparatus producing an emulsion of the ozone gas in the effluent is composed of a self-aspirating turbine and a propeller, said self-aspirating turbine and said propeller being carried by the same hollow drive shaft, and said hollow shaft ensuring the supply of ozone gas to the turbine.
EP03780287A 2002-10-10 2003-10-02 Method for reducing sludge of a biological ozone treatment system Ceased EP1554222A2 (en)

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FR0212593A FR2845682B1 (en) 2002-10-10 2002-10-10 METHOD OF REDUCING SLUDGE OF BIOLOGICAL TREATMENT OF WATER USING OZONE
FR0212593 2002-10-10
PCT/FR2003/050075 WO2004033371A2 (en) 2002-10-10 2003-10-02 Method for reducing sludge of a biological ozone treatment system

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US7335304B2 (en) 2008-02-26
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WO2004033371A3 (en) 2004-07-15
FR2845682B1 (en) 2004-11-19
CA2501387A1 (en) 2004-04-22
FR2845682A1 (en) 2004-04-16
WO2004033371A2 (en) 2004-04-22
AU2003288372A1 (en) 2004-05-04
AU2003288372A8 (en) 2004-05-04
US20060086661A1 (en) 2006-04-27

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