Water treatment process using activated sludge

Abstract

The present invention relates to a method for the biological treatment of wastewater comprising a biological treatment step, a step of separating a mixed liquor leading to the production of purified water on the one hand and sludge on the other hand, a step of recirculating a portion of the sludge 21, a step of extracting the sludge, a step of thickening the extracted sludge 3, a selection step applied to a portion 32 of the thickened extracted sludge leading to the production of at least two sludge fractions of different densities and / or sizes, namely a fraction 52 of sludge having a higher density and / or size and a fraction 51 of sludge having a lower density and / or size, a treatment step 4 applied to another portion 31 of the thickened extracted sludge, and a step of recirculating the sludge fraction having a higher density and / or size 52. Figure 1

Description

Title of the invention: Water treatment process using activated sludge Technical field

[0001] The field of the invention is that of the biological treatment of wastewater.

[0002] More specifically, the invention relates to wastewater treatment processes and installations using activated sludge. The innovation relates to a specific operating configuration applied to the aerobic, anoxic or anaerobic process for treating water using activated sludge, making it possible to improve its performance. Prior art

[0003] Various biological wastewater treatment processes are currently used, such as activated sludge water treatment. These processes involve a biological effluent treatment step to reduce carbon pollution and / or nitrogen compound levels and / or phosphorus compound levels, followed by a separation step to separate the biological sludge from the treated water.

[0004] The biomasses are thus implemented in one or more treatment basins, under different conditions (anoxic, aerobic, anaerobic, etc.) suitable for their metabolism which can be autotrophic or heterotrophic or mixed. The biomasses develop in the form of free biological sludge (activated sludge process) or in the form of biofilm (biomass supported by biofilm supports or self-supported, i.e. granular sludge).

[0005] Activated sludge processes are the most widespread to date and involve recirculation of the activated sludge.

[0006] Biological processes, regardless of the biomass used, lead to the production of sludge which is extracted and treated by the sludge treatment process. These treatments aim to limit its volume and to reduce the pollution it contains. This sludge can thus be dehydrated, dried and / or subjected to thermal lysis or digestion.

[0007] It has also been proposed in the prior art to carry out a selection of activated sludge by implementing a selector, for example at the level of recirculation of activated sludge. Such a method is described in patent EP2925676B1.

[0008] The selector may be a hydrocyclone or other separation technique, and allows the selection of the densest activated sludge which is returned to the biological reactors. The less dense sludge constitutes the extracted sludge to be treated on the sludge treatment line.

[0009] However, according to this technique, the sludge volumes in the selector are high and consequently the capacities of the selector are large, which increases the overall installation and operating costs.

[0010] Another disadvantage is the recovery of sands with dense flocs during recirculation in biological reactors. Objectives of the invention

[0011] The objective of the invention is to propose a method and an installation making it possible to overcome these drawbacks of the prior art.

[0012] More specifically, an objective of the invention is to propose a device for biological treatment of wastewater using activated sludge and a device for enriching biomass based on an activated sludge selector placed after a sludge thickening step. This makes it possible to work with a smaller selector, with lower operating costs and offering the possibility of extracting and not returning the sand to the biological reactors, in whole or in part.

[0013] The present invention makes it possible to reduce the costs of implementing, operating and maintaining such a method and such an installation. Presentation of the invention

[0014] These objectives, as well as others which will appear subsequently, are achieved using a biological wastewater treatment process comprising the following steps:

[0015] - a biological treatment step within at least one treatment basin biological in which said wastewater is brought into contact with activated sludge;

[0016] - a step of separating a mixed liquor coming from said at least one basin of biological treatment implemented in a separator leading to the production of purified water on the one hand and sludge on the other, the separator being either integrated into the biological treatment basin or external to said biological treatment basin;

[0017] - if the separator is external to said biological treatment basin, a recycling step circulation of a portion of the sludge towards said at least one biological treatment basin;

[0018] the treatment method being characterized in that it comprises the following additional steps:

[0019] - a step of extracting the sludge from the separator or the recycling line culture;

[0020] - a step of thickening the extracted sludge within a thickener leading to obtain thickened sludge with a concentration of between 5 and 200 g MES / L and preferably between 10 and 50 g MES / L;

[0021] - a selection step applied to a portion of said thickened sludge within a selector leading to the production of at least two sludge fractions of different densities and / or sizes, namely a sludge fraction having a higher density and / or size and a sludge fraction having a lower density and / or sludge size,

[0022] - a treatment step applied to another part of said extracted sludge thickened;

[0023] - a step of recirculating said fraction of sludge having a density and / or a higher size towards said at least one biological treatment basin.

[0024] Thus, according to the invention, the thickening step upstream of the selector allows the use of a selector with smaller hydraulic capacity and less electricity consumption.

[0025] Furthermore, the thickening step allows for better control of the variability of the sludge concentrations entering the selector. The selector will therefore not have to undergo the more variable operation of the biological treatment.

[0026] At the outlet of the selector, the sludge fraction having lower particle sizes and / or sludge density joins the sludge treatment process which may be, for example and without limitation, thermal lysis, digestion, dehydration, drying. The second fraction from the selector has higher particle sizes and / or density. It is returned to at least one biological treatment tank.

[0027] According to a preferred characteristic of the invention, the selection step is a hydrocycloning step.

[0028] According to a variant of the invention, the hydrocycloning step is implemented using a two-phase hydrocyclone and leads to the production of said at least two sludge fractions of different densities and / or sizes.

[0029] According to another variant of the invention, the hydrocycloning step is carried out using a three-phase hydrocyclone and leads to the production of said at least two sludge fractions of different densities and an essentially mineral fraction.

[0030] Thus, in order to limit the accumulation of sand in the biological treatment basin(s), the invention uses a three-phase hydrocyclone. This three-phase hydrocyclone makes it possible to divide the sludge into three fractions:

[0031] - a mineral fraction, containing sands and the heaviest particles which is eliminated for treatment in a specific sector;

[0032] - a light fraction, not or only slightly flocculated, having particle sizes and / or a lower density(ies), which may be rich in oils and fats, which is sent to the sludge treatment process (thickening and / or digestion and / or dehydration);

[0033] - a sludge fraction having particle sizes and / or a density greater high, consisting of flocculated or even granulated biomass, which is recycled to the biological treatment basin(s) to densify the active biomass.

[0034] The three-phase hydrocyclone therefore makes it possible not to accumulate sand in the biological treatment basins and to recirculate only the active biomass with the highest size and / or density characteristics, allowing for optimized sludge and biomass management within the facility.

[0035] According to another aspect of the invention, the selection step can also be implemented using a three-phase separator-classifier.

[0036] Preferably, the biological treatment step is chosen from the group consisting of conventional activated sludge processes, SBR (Sequenced Batch Reactor) processes, hybrid processes, granular processes and / or processes using a membrane bioreactor.

[0037] Thus, the invention may comprise any type of biological treatment using activated sludge coupled or not with biofilm technologies. This thus concerns, in a non-exhaustive manner, conventional activated sludge processes, SBR (Sequencing Batch Reactor) processes or activated sludge processes in batch configuration, membrane bioreactors (membranes installed in the activated sludge basin or in a separate structure), hybrid processes called IFAS (Integrated Fixed Film Activated Sludge) coupling activated sludge and biofilm, the biofilm being able to be supported by any type of support or being able to be self-supported (MBBR - "Moving Bed Bio Reactor", MABR - "Membrane Aerated Biofilm Reactor", aerobic granules, etc.).

[0038] According to an advantageous preferred characteristic of the invention, the method also comprises a step of controlling and regulating the recirculation flow rate of the sludge from the selector, depending on the pollution to be treated in the biological treatment basin.

[0039] In order to optimize the quantity of biomass within the biological treatment basin, the method according to the invention proposes to regulate the different recirculated flow rates at the inlet of the biological treatment basin(s). Thus, in the case where a significant quantity of sludge is required, the activated sludge at the outlet of the separator and / or the thickener would be preferentially directed towards the biological treatment basin(s) and / or the selector, respectively. Whereas in the case where a small quantity of sludge is required, the activated sludge at the outlet of the separator and the thickener would be preferentially directed towards the treatment means. This operating mode makes it possible to adapt the quantity of biomass to the quantity of pollution to be treated, thus contributing to the optimization of the process and its associated energy consumption.

[0040] The invention also relates to a biological wastewater treatment plant comprising:

[0041] - means for supplying waste water;

[0042] - means for biological treatment of wastewater using sludge activated;

[0043] - separation means receiving a mixed liquor from said separation means biological treatment allowing the production of purified water on the one hand and sludge on the other, the separation means being either integrated into the biological treatment means or external to the biological treatment means;

[0044] - if the separation means are external to the biological treatment means, a recirculation pipeline for part of the sludge from the separation means to said biological treatment means;

[0045] characterized in that it further comprises:

[0046] - means for extracting sludge from the separation means or from the ca recirculation finalization;

[0047] - means for thickening the extracted sludge allowing sludge to be obtained thickened with a concentration between 5 and 200 g MeS / L and preferably between 10 and 50 g MeS / L;

[0048] - a selector receiving a portion of the thickened extracted sludge from said thickening means enabling at least two sludge fractions of different densities and / or sizes to be obtained, namely a sludge fraction having a higher density and / or size and a sludge fraction having a lower density and / or sludge size,

[0049] - treatment means receiving another part of said extracted sludge thickened;

[0050] - means for recirculating said fraction of sludge having a higher density raised towards said at least one biological basin.

[0051] According to a preferred characteristic of the invention, said selection means comprise a hydrocyclone.

[0052] According to a preferred variant of the invention, said hydrocyclone is a two-phase hydrocyclone.

[0053] According to an even more preferred variant of the invention, said hydrocyclone is a three-phase hydrocyclone.

[0054] According to another preferred characteristic of the invention, said selection means comprise a three-phase separator-classifier.

[0055] According to a preferred characteristic of the invention, said thickening means are chosen from a draining table, a centrifugation system, a gravity thickener, a drum.

[0056] According to an advantageous characteristic of the invention, the installation comprises an algorithm, sensors and automatons regulating the flow rate of sludge from the selector, depending on the pollution to be treated. Presentation of figures

[0057] Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and non-limiting example and described with reference to the following drawing:

[0058] [Fig.l] represents a device for biological treatment of wastewater, according to an exemplary embodiment of the invention.

[0059] [Fig.2] represents a device for biological treatment of wastewater, according to another exemplary embodiment of the invention, in which the separator is integrated into the biological treatment basin.

[0060] [Fig. 3] represents a device for biological treatment of wastewater, according to another exemplary embodiment of the invention, in which the selector is three-phase. Detailed description of the invention

[0061] 1. General description

[0062] The technique of the invention is based on the development of a wastewater treatment system using activated sludge.

[0063] Thus, in relation to [Fig.l], the present invention implements a method for the biological treatment of wastewater comprising: one or more biological treatment basins 1 containing activated sludge, a separator 2, separating the sludge from the purified water, and a recirculation 21 of the sludge from the separator 2, towards the inlet of the biological treatment basin(s) 1, means for extracting sludge from the separator and / or from the recirculation line (or pipeline) 21, a thickener 3 for thickening the extracted sludge, at the outlet of which a portion 31 of the thickened extracted sludge is conveyed to a treatment system 4, while the other portion 32 of the thickened extracted sludge is conveyed to a selector 5, this selector making it possible to recover a dense fraction 52 of sludge, and which is transferred to the biological treatment basin(s) 1, in order to densify active biomass.

[0064] 2. Biological treatment basin(s) 1

[0065] The installation according to the invention comprises at least one biological treatment basin 1, the latter being supplied with water to be treated which may be wastewater. The water to be treated is thus brought into contact with an activated sludge in order to obtain a mixed liquor.

[0066] The biological treatment basin(s) allow the implementation of biological treatments using activated sludge, which may in particular be bio-sludge. free logic, or hybrid biological sludge called IFAS (“Integrated Fixed Film Activated Sludge”) with fixed film coupling activated sludge and biofilm.

[0067] Thus, the processes used for this biological treatment step can be conventional activated sludge processes, SBR processes (“Sequenced Batch Reactor”), i.e. activated sludge processes in discontinuous configuration (“batch”), processes using a bioreactor with submerged or non-immersed membrane(s), hybrid processes called IFAS (“Integrated Fixed Film Activated Sludge”) coupling activated sludge and biofilm, the biofilm being able to be supported by any type of support or being able to be self-supporting (MBBR - “Moving Bed Bio Reactor”, MABR - “Membrane Aerated Biofilm Reactor”, aerobic granules.

[0068] Air supply means may be provided in at least part of these basins.

[0069] According to an exemplary embodiment, the biological treatment basin(s) comprise autotrophic, heterotrophic or mixed bacteria.

[0070] 3. Separator 2

[0071] The separator 2 can be integrated into the biological treatment tank as illustrated by [Fig.2], or can be external to it as illustrated by [Fig.l]. It is supplied with mixed liquor from the biological treatment tank(s), and therefore implements a step of separating the mixture from the biological tank(s). It thus makes it possible to separate, on the one hand, sludge, and on the other hand, purified water.

[0072] This separator can take the form of a flotation system, a filter, a membrane integrated into the biological treatment basin, or even a decanter external to the biological treatment basin.

[0073] The purified water can undergo post-treatment (for example filtration, etc.) or be used directly at the outlet of the separator, or even discharged into the natural environment.

[0074] A portion of the separated sludge is recirculated in the biological treatment tank(s) 1, while another portion can be extracted from the separator by extraction means.

[0075] According to an exemplary embodiment, the concentration of the separated sludge is preferably between 5 and 20 g MES / L (grams of suspended matter per liter).

[0076] 4. Thickener 3

[0077] The thickener 3 receives the sludge extracted by the extraction means 211, 212, coming from the separator 2 and / or from the recirculation line (pipeline) 21. Thickener 3 implements a thickening step for this extracted sludge by increasing its concentration. The sludge thickener can be static (gravity) or dynamic. This thickener can, for example, be in the form of a drainage table, a centrifugation system, a gravity thickener, a drum or even a flotation unit.

[0078] At the outlet of the thickener, the concentration of the thickened sludge is between 5 g MES / L and 200 g MES / L, and preferably between 10 g MES / L and 50 g MES / L (grams of suspended matter per liter).

[0079] At the outlet of the thickener, a portion 31 of the thickened sludge is directed towards treatment means 4, while the other portion 32 is sent to a selector 5. According to a discontinuous operating mode of the treatment line, all or part of the sludge can be directed either towards treatment means 4 or towards the selector 5. The thickening step makes it possible to have more concentrated sludge at the inlet of the selector 5 and to reduce the total volume to be passed through this selector. It is therefore possible to work with a selector of smaller hydraulic capacity. This leads to a reduction in energy consumption and a reduction in space requirements.

[0080] This also allows better control of the concentration at the inlet of the selector 5 (lower variability), without having to undergo the potentially random operation of the biological treatment within the basin(s) 1. Consequently, this allows better control of the biomass densification process.

[0081] 5. Means of sludge treatment 4

[0082] The treatment means 4 are fed with a portion 31 of the thickened sludge coming from the thickener. In certain cases, the flow rate of this sludge may be zero. These means may be in the form of a thermal hydrolyzer, a digester, dehydration equipment such as centrifuges, belt filters, filter presses, followed or not by chemical (liming) and / or biological (composting) stabilization and / or thermal drying and / or incineration.

[0083] 6. Selector 5

[0084] The selector 5 may advantageously be in the form of a hydrocyclone. However, it may be in the form of a sieve or a classifier. It implements a selection step by size and / or by density, and is fed by the other part 32 of the thickened sludge coming from the thickener 3 (which is not sent to the treatment means 4). The selector 5 makes it possible to obtain at least two fractions of sludge of different densities and / or sizes, that is to say, a fraction 52 of sludge having a higher density and / or size and a fraction 51 of sludge having a lower density and / or size.The sludge having a higher density and / or size 52 is then recirculated to the biological treatment tank(s) 1; while the fraction of sludge having a lower density and / or size is directed to the sludge treatment line 4 in order to be thickened and / or digested and / or dehydrated. The selector 5 can be bi-. phasic or triphasic.

[0085] Thus, in the case where the presence of sand is not very significant, the installation of a conventional (two-phase) hydrocyclone as illustrated by figures 1 and 2 is sufficient.

[0086] However, according to an advantageous embodiment described in relation to [Fig.3], the selector 5 is a three-phase hydrocyclone. Indeed, this makes it possible to take into account the risk of accumulation of mineral matter (for example sand) in the biological treatment basin(s) due to the recirculation of the densified / granulated sludge, thus making it possible to limit the presence of sand in the biological treatment basin(s). The three-phase separation of the sludge is carried out in the same equipment, in a single treatment step. The three-phase selector thus makes it possible to separate, in addition to the floaters, the mineral fraction (sand) from the organic fraction. Thus, the three-phase selector makes it possible to separate the sludge into three fractions

[0087] - a very dense fraction 53 comprising sands or other minerals, which is eliminated towards the sand treatment line;

[0088] - a light fraction 51, unflocculated or with light flocs, which may be rich in oils and greases or filamentous microorganisms, which is sent to the sludge treatment line (thickening and / or digestion and / or dehydration);

[0089] - a dense fraction 52 consisting of active biomass possibly in the form granular, which is recycled to the biological treatment basin(s) to densify the active biomass.

[0090] An alternative to the three-phase hydrocyclone would be a three-phase classifier separator, the principle being to separate the particles into three fractions in an ascending fluidized bed. The sands 53 are extracted at the low point, the dense granulated sludge 52 is extracted at the intermediate point to be sent to the biological basin 1 and the low-density non-flocculated sludge 51 is discharged as an overflow to the sludge treatment line 4. The efficiency of the separation depends on the fluidization speed. The separator-classifier is less compact than a hydrocyclone but it is less energy-intensive.

[0091] According to an exemplary embodiment, the fraction 52 of the sludge recycled to the biological treatment basin(s) 1 has a Mohlman index (SVI, “sludge volume index”) of less than 120 mL / g.

[0092] 7. Management of biomass in the biological treatment basin(s)

[0093] Advantageously, a regulation algorithm is integrated into the installation according to the invention, to control the quantity of biomass in the biological treatment basin(s) 1 as a function of the quantity of pollution to be treated. The algorithm makes it possible to adjust the quantity of hydrocycloned thickened sludge 52 from the selector 5 to be sent to the biological treatment basin(s) 1.

[0094] Advantageously, this management of the quantities of sludge from the selector 5 is carried out using an algorithm, sensors, and automatons regulating the flow rate of the sludge 52 from the selector 5. Thus, this management of the biomass makes it possible to preferentially feed the biological treatment basin(s) 1 and / or the thickener 3 at the outlet of the separator 2; and / or to preferentially feed the treatment means 4 and / or the selector 5, at the outlet of the thickener 3.

[0095] It is thus possible to optimize biological treatment while optimizing energy consumption. The mass load (ratio between pollution to be treated and biomass) can thus be kept constant regardless of the water quality.

Claims

1.

2.

3. Claims Biological wastewater treatment process comprising the following steps: - a biological treatment step within at least one biological treatment basin (l) in which said wastewater is brought into contact with activated sludge; - a step of separating a mixed liquor from said at least one biological treatment basin implemented in a separator (2) leading to the production of purified water on the one hand and sludge on the other hand, the separator being either integrated into the biological treatment basin or external to said biological treatment basin; - if the separator (2) is external to said biological treatment basin (1), a step of recirculating part of the sludge (21) to said at least one biological treatment basin (1); the treatment method being characterized in that it comprises the following additional steps: - a step of extracting the sludge from the separator (2) or from the recirculation line (21); - a step of thickening the extracted sludge (211, 212) within a thickener (3) leading to the production of thickened sludge having a concentration of between 5 and 200 g MES / L and preferably between 10 and 50 g MES / L; - a selection step applied to a portion (32) of said thickened sludge within a selector (5) leading to the obtaining of at least two fractions of sludge of different densities and / or sizes, namely a fraction (52) of sludge having a higher density and / or size and a fraction (51) of sludge having a lower density and / or size of sludge, - a treatment step (4) applied to another part (31) of said thickened extracted sludge; - a step of recirculating said fraction of sludge having a higher density and / or size (52) towards said at least one biological treatment basin 1. Method according to claim 1 characterized in that said selection step is a hydrocycloning step. Method according to claim 2 characterized in that said hydrocycloning step is carried out using a two-phase hydrocyclone and leads to the obtaining of said at least two sludge fractions of different densities.

4. Method according to claim 2 characterized in that said hydrocycloning step is carried out using a three-phase hydrocyclone and leads to the production of said at least two sludge fractions of different densities and an essentially mineral fraction.

5. Method according to claim 1 characterized in that said selection step is implemented using a three-phase separator-classifier and leads to the obtaining of said at least two sludge fractions of different densities and an essentially mineral fraction.

6. Method according to one of claims 1 to 5, characterized in that said biological treatment step is chosen from the group of conventional activated sludge methods, SBR (Sequenced Batch Reactor) methods, hybrid methods, granular methods and / or methods using a membrane bioreactor.

7. Method according to one of claims 1 to 6, characterized in that it implements a step of controlling and regulating the flow rate of sludge (52) from the selector (5), depending on the pollution to be treated in the biological treatment basin.

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