FR2989078A1 - Treating industrial or urban effluents, by subjecting effluents to first aerobic activated sludge treatment followed by second treatment with membrane filtration, where first treatment is treatment in mixed cultures with bacteria supports - Google Patents

Abstract

The method comprises subjecting effluents to a first aerobic activated sludge treatment followed by a second treatment with filtration by membranes (8a, 8b), where the first treatment is a treatment in mixed cultures with mobile bacteria supports (4) under a weak mass load and with maintenance of a sludge age. The mass load is lower than 0.3 kg biochemical oxygen demand after 5 days of incubation (BOD 5)/kg MES.day. The sludge age in the first treatment, is higher than 10 days of free biomass and 20 days of fixed biomass. The method comprises subjecting effluents to a first aerobic activated sludge treatment followed by a second treatment with filtration by membranes (8a, 8b), where the first aerobic treatment is a treatment in mixed cultures with mobile bacteria supports (4) under a weak mass load and with maintenance of a sludge age. The mass load is lower than 0.3 kg biochemical oxygen demand after 5 days of incubation (BOD 5)/kg MES.day. The sludge age in the first treatment, is higher than 10 days of free biomass and 20 days of fixed biomass. The membranes are external with a first reactor (2) ensuring the first treatment. The two treatments are carried out in separate reactors, where the effluent having undergone the first treatment is sent to a second reactor for the second treatment. The membranes are immersed in the second reactor carrying out the second treatment. The first treatment in mixed cultures is carried out in a reactor of type Meteor (RTM: Compact integrated fixed-film activated sludge biological process). The reactor of the type Meteor (RTM: Compact integrated fixed-film activated sludge biological process) is coupled with an organic membrane bioreactor of type Ultrafor (RTM: Biological wastewater treatment process-combining ultra filtration membrane purification and clarification). An independent claim is included for an installation for the application of a method of waste treating.

Description

METHOD AND PLANT FOR TREATING BIODEGRADABLE POLLUTION EFFLUENTS. The invention relates to a process for the treatment of effluents with biodegradable pollution, in particular of industrial or urban effluents, a process according to which the effluent is subjected to a first aerobic activated-sludge treatment, followed by a second filtration treatment. on membrane. By biodegradable effluent is meant an effluent in which the pollution has a COD / BOD5 ratio of less than 3.5 (COD = chemical oxygen demand, BOD5 = biochemical oxygen demand after 5 days of incubation). WO 2011/06 55 20 shows a process in which both treatments are carried out in the same tank, the aerobic treatment taking place in the lower part while the membrane filtration is carried out in the upper part, separated from the lower part by a screen leaving a narrow passage between the two compartments. It is desirable to reduce the carbon footprint and footprint of water and sludge from such an effluent treatment process. It is desirable to be able to discharge the treated water directly into the receiving medium via the rainwater network, which implies complying with a more stringent discharge standard than in the case where the discharge of the treated water is carried out in a network. urban community. Thus, the object of the invention is, above all, to provide a process which makes it possible to achieve high yields of elimination of carbon pollution, in particular to obtain a purification efficiency equal to or greater than 98% of removal of carbon pollution. According to the invention, the biodegradable effluent treatment method comprises a first aerobic activated sludge treatment to which the effluent is subjected, followed by a second treatment by membrane filtration, and is characterized in that the first Aerobic treatment is a mixed culture treatment with mobile bacteria supports, under a low mass load and with a high sludge age. Preferably, the mass load is less than 0.3 kg DB05 / kgMES.day. The age of the sludge in the first treatment is advantageously greater than 10 days for the free biomass and greater than 20 days for the fixed biomass. The membranes may be external to a reactor providing the first treatment.

The two treatments can be carried out in separate reactors, the effluent having undergone the first treatment being sent to the reactor of the second treatment. The membranes can be immersed in the second reactor carrying out the second treatment.

The first treatment in mixed cultures is advantageously carried out, under low mass loading, in a MBBR reactor (Moving Bed Biofilm Reactor), in particular a reactor of the type known under the name METEOR® from the Degrémont Company. This reactor can be coupled to an organic membrane bioreactor (BRMO), in particular of the type known under the name ULTRAFOR® from the Degrémont Company. The movable supports are advantageously constituted by plastic elements comprising rings and radial extensions inwards and / or outwards, these supports having a density slightly less than that of water, in particular of about 0 , from 9 to 0.98. The mobile supports are retained in the reactor by means of a static grid or a strainer whose spacing between bars is adapted to the material. The invention also relates to an installation for the implementation of the effluent treatment method defined above, this installation comprising at least one bioreactor for a first aerobic activated sludge treatment and membranes for providing filtration treatment of the effluent after it has undergone the first treatment, this facility being characterized in that the bioreactor for aerobic activated sludge treatment comprises mobile supports of bacteria for treatment in mixed cultures. The plant may comprise two separate reactors assigned respectively to each treatment, the membranes being immersed in the second reactor. Alternatively, the membranes may be external. According to another variant, the membranes may be immersed in the bioreactor comprising mobile supports of bacteria. The movable supports are advantageously constituted by plastic rings of a density lower than that of water, specially designed to allow a durable and stable colonization by the bacteria. The bioreactor for aerobic treatment in mixed cultures comprises means for supplying supercharged air to ensure, on the one hand, the supply of oxygen necessary for the bacteria and, on the other hand, the suspension of the mobile supports. The invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed hereinafter with regard to exemplary embodiments described with reference to the appended drawing. but which are in no way limiting. In this drawing: FIG. 1 is a diagram of an installation implementing the treatment method of the invention with external membranes. Fig. 2 is a diagram of a variant of the plant with two separate reactors to provide both treatments and FIG. 3 is an enlarged diagram of an example of a mobile support for mixed cultures processing. Referring to Fig. 1, it can be seen that the plant for the treatment of industrial effluent that arrives via a pipe 1 comprises a bioreactor 2 into which the effluent is discharged. The effluent to be treated is biodegradable with a COD / BOD5 ratio of less than 3.5. By way of example, the sizing parameters for an effluent to be treated are as follows: flow rate: 40 m3 / day COD: 1200 kg / day BOD5: 800 kg / day which, in this case, corresponds to a COD / ratio BOD5 equal to 1.5. The purifying efficiencies targeted to respect the norms of rejection in the natural environment are very high: superior to 99% in mass of elimination of the carbon pollution. An example of the objective of treatment of industrial water for a discharge in a natural environment is the following for the treated water: COD: 125 mg / L BOD5: 30 mg / L MES: 35 mg / L (MES = suspended solids) ) T ° C <30 ° C The aerobic treatment in the reactor 2 is obtained by blowing air in the lower part using a ramp 3 to supply oxygen to the bacteria. The aerobic treatment is performed in low mass load, less than 0.3 kgDBO5 / kgMES.day.

The reactor 2 is of the MBBR (moving bed bioreactor) type, comprising mobile supports 4 on which the bacteria develop. The continuous or discontinuous aeration of the effluent in the reactor 2 further ensures the suspension of the mobile supports 4. As can be seen in FIG. 3, these supports 4 are advantageously made in the form of plastic rings. of a density slightly lower than that of water, for example density of 0.90 to 0.98, and are designed with radial and / or longitudinal extensions to allow a stable and stable colonization of bacteria.

A static grid or strainer 5 is provided in the reactor to retain the supports 4. The treatment is carried out by maintaining a high sludge age in the biological reactor 2 to allow a thorough degradation of the organic matter and a reduced production of sludge. excess. The age of sludge is advantageously at least equal to 5 days. Preferably, the age of the sludge, in the first treatment, is greater than 10 days for the free biomass and greater than 20 days for the fixed biomass. The mixed cultures reactor 2 is advantageously of the METEOR® type from the Degrémont Company.

The effluent exits the reactor 2, at the bottom, through a pipe 6 on which one or two pumps 7 are installed, and is sent to a filtration membrane unit 8a, 8b. According to the example of FIG. 1, the membranes are external to the reactor. The two membranes are supplied in parallel by the effluent from the reactor 2. The filtrate, or permeate, leaving the membrane 8a is sent to the inlet of the second membrane 8b. The filtrate outlet of the membrane 8b is collected by a pipe 9. The membranes constitute a total barrier which guarantees the absence of sludge feeds into the filtrate so that the pipe 9 can be directed towards a natural receiving medium while ensuring a perfect respect for the environment.

Part of the retentate of each membrane is recycled via a line 10 to the reactor 2. The other fraction of the sludge is directed by a line 11 to a sludge treatment plant. The membranes 8a, 8b can be placed in a housing. They can be used in so-called tangential filtration.

The mixed culture provided by the reactor 2 provides stability of biological processes and good resistance to variations and surges of charge, while filtration membranes provide excellent separation of biomass and treated water. Membrane processes are modular processes that allow easy adaptation to a possible increase in production by the addition of membranes in an existing biological basin. The implementation of membrane filtration, a real physical barrier, ensures a constant quality of water treated and independent of sludge settling ability. It makes it possible to overcome, among other things, malfunctions linked to the proliferation of filamentous bacteria frequent in a very highly biodegradable medium. Advantageously, the filtration membranes are membranes of Zenon ZeeWeed 500c and 500d. These membranes are pre-integrated at the factory, with molded collectors; they ensure a great robustness of the operation of the system on the applications of wastewater treatment. They guarantee a very good quality of the effluent (physical disinfection), allowing the reuse of treated water, for example for watering green areas. According to the variant embodiment of FIG. 2, the membrane filtration unit (s) 8c is placed in a second reactor 12 separated from the first 2, the membrane (s) 8c being immersed in the effluent that has been previously treated in the reactor 2. The elements of the scheme of FIG. 2 identical or having the same function as elements described in connection with FIG. 1 are designated by the same reference numerals without their description being repeated. According to another embodiment not shown, the membrane 8c could be immersed in the biological reactor 2, the membrane being then protected to prevent the media from bumping. The organic membrane bioreactor may be of the ULTRAFOR® (BRMO) type from the Degrémont Company. The coupling of a reactor in mixed cultures, with mobile supports 4, and filtration membranes 8a, 8b or 8c, preferably immersed in an organic membrane bioreactor, makes it possible to improve the quality of the treated water by eliminating the total biodegradable pollution through the development of a specific fixed biomass which requires a significant residence time (obtained with sufficient sludge age) for its development and which is activated in the presence of a pollution that is difficult to biodegrade. This coupling also makes it possible to increase the filtration rate of the membranes because the concentration of materials and free biomass is reduced in the biological reactor 2 and because of the rheological quality of the free biomass in the presence. The reduction of the residual soluble COD is also a factor favorable to the increase of the filtrate flow rate of the membranes. The mixed culture reactor 2 makes it possible to concentrate the fixed biomass, while the membrane separation makes it possible to concentrate the free biomass, allowing high volume loads, in particular of the order of 4 kg BOD5 / m 3 day, while maintaining low mass loads, especially less than 0.3 kgDBO5 / kgMES.day. Coupling according to the invention of a mixed culture reactor 2 and filtration membranes makes it possible to reduce the volume of the biological reactor by 25 to 70% compared to a conventional free culture membrane bioreactor. The membrane surface can also be reduced by 20 to 30% compared to a conventional free culture membrane bioreactor. The method and the installation of the invention have many advantages: compactness and modularity; - installation with low footprint; - mixed-culture biological reactor contributing to the modularity of the station by accepting increases in the polluting load; - filtration membranes allowing an increase in the hydraulic load; - reduction of the carbon footprint. The process ensures an excellent quality of the treated water and a maximum elimination of the pollution (carbon, nitrogen, phosphorus, detergents, substances extractable with hexane, AOX, suspended matter and micropollutants, ...). The process also provides a reduction in organic sludge production of 25 to 35%, compared to a conventional free culture membrane bioreactor method and a 35 to 60% reduction over a mixed-culture method alone, thus reducing the operating time of the sludge dewatering plant, the consumption of reagents (coagulants, polymers, dilution water, lime) and the evacuation constraints of dewatered sludge. The process allows final composting of agricultural upgrading sludge. Compared to sludge spreading, this solution makes it possible to avoid the construction of a storage silo and regularly evacuate the dewatered sludge. Reuse of the treated water is possible, for example for: - washing of the dehydration plant, 35 - secondary dilution of a flocculant, - booster water after reverse osmosis, - watering, cooling tower, - robustness and reliability of use.

The process is stable under large load variations. The installation is tolerant to disturbances. A very rapid recovery of the biological treatment is carried out after major disturbances (load shocks, variability of the composition of the effluents ...).

There is no clogging of the reactors, nor risks of sludge swelling. The method and the installation have good flexibility. The technology is suitable for other types of effluents from the agri-food, pharmaceutical, chemical, petrochemical and paper industries, as well as urban wastewater. The process and installation provide an ease of future developments and extensions. In some cases, the process makes it possible to dispense with tertiary treatment of the effluent. Existing tanks for the bioreactor can be used, and many reactor forms can be used.

Claims (12)

REVENDICATIONS1. Process for the treatment of effluents with biodegradable pollution, in particular of industrial or urban effluents, according to which the effluent is subjected to a first aerobic activated sludge treatment, followed by a second treatment by membrane filtration, characterized in that the first aerobic treatment is a mixed culture treatment with mobile supports (4) of bacteria, under a low mass load and with a high sludge age. 2. Method according to claim 1, characterized in that the mass load is less than 0.3 kg BOD5 / kgMES.day. 3. Method according to claim 1 or 2, characterized in that the sludge age, in the first treatment, is greater than 10 days for free biomass and 20 days for the fixed biomass. 4. Method according to any one of the preceding claims, characterized in that the membranes (8a, 8b) are external to a reactor (2) providing the first treatment. 5. Method according to any one of claims 1 to 3, characterized in that the two treatments are carried out in separate reactors (2, 12), the effluent having undergone the first treatment being sent to the reactor of the second treatment. 6. Method according to claim 5, characterized in that the membranes (8c) are immersed in the second reactor (12) performing the second treatment. 30 7. Process according to any one of the preceding claims, characterized in that the first treatment in mixed cultures is carried out in a METEOR® type reactor. 8. Process according to claim 7, characterized in that the METEOR® type reactor is coupled to an organic membrane bioreactor (BRMO) of the ULTRAFOR® type. 9. Installation for carrying out an effluent treatment process according to any one of the preceding claims, comprising at least one bioreactor for a first aerobic activated sludge treatment and membranes to provide a filtration treatment of the effluent. effluent after undergoing the first treatment, characterized in that the bioreactor (2) for aerobic activated sludge treatment comprises mobile supports (4) of bacteria for treatment in mixed cultures. 10. Installation according to claim 9, characterized in that it comprises two separate reactors (2, 12) respectively assigned to each treatment, the membranes being immersed in the second reactor (12). 11. Installation according to claim 9, characterized in that the membranes are immersed in the bioreactor comprising mobile supports (4) of bacteria. 12. Installation according to any one of claims 9 to 11, characterized in that the movable supports (4) are constituted by plastic elements having rings and radial extensions inwards and / or outside, these carriers having a density slightly lower than that of water, particularly about 0.9-0.98.