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)

Applications Claiming Priority (3)

Publications (1)

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ID=32039603

Family Applications (1)

Country Status (7)

Cited By (1)

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Family Cites Families (7)

• 2002
  • 2002-10-10 FR FR0212593A patent/FR2845682B1/fr not_active Expired - Lifetime
• 2003
  • 2003-10-02 WO PCT/FR2003/050075 patent/WO2004033371A2/fr not_active Ceased
  • 2003-10-02 BR BRPI0315210-3A patent/BR0315210B1/pt active IP Right Grant
  • 2003-10-02 EP EP03780287A patent/EP1554222A2/de not_active Ceased
  • 2003-10-02 AU AU2003288372A patent/AU2003288372A1/en not_active Abandoned
  • 2003-10-02 CA CA 2501387 patent/CA2501387A1/fr not_active Abandoned
  • 2003-10-02 US US10/530,850 patent/US7335304B2/en not_active Expired - Lifetime

Non-Patent Citations (1)

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