FR2913419A1 - Biological process for the treatment of wastewater in which organic matters are degraded by bacterial activity, comprises performing an extensive or intensive biological treatment of wastewater slightly or strongly filled with pollution - Google Patents

Abstract

The invention relates to a biological process for the treatment of wastewater in which the organic materials are degraded by the activity of bacteria.According to the invention, the method consists, for waters with low pollution, in a biological treatment step extensive, based on the principle of natural phenomena of self-purification inherent to shallow water bodies, implemented in a lagoon scrubber (1) comprising at least one lagoon (2), on the bottom (3) of which are sludge concentrated in bacteria, and from which water is taken low pollution and filtered in a well (7) opening above the bed of sludge through submerged membranes (4), including capillaries or According to a particular embodiment for the treatment of waste water heavily loaded with pollution, the process will also have a prior biological treatment step intended to reduce the pollution. concentration of pollutions in water. The invention will also concern a lagoon scrubber suitable in particular for carrying out the process.

Description

The invention relates to a biological process for the treatment of

  waters in which organic matter is degraded by the activity of bacteria. The invention will also relate to a lagoon scrubber suitable for carrying out this process. The aquatic natural environment, river, pond and other bodies of water have their own purification capacities. This faculty is based in particular on the principle of self-purification phenomena inherent to the shallow water body. However, this natural purification requires sufficient oxygen consumption to degrade the biodegradable materials in the water. An aquatic environment, too heavily loaded with organic pollution, thus sees its oxygen concentration decrease, favoring, over time, the development of algae and the asphyxiation of fish species. The treatment of wastewater is thus indispensable for the preservation of the natural environment. Wastewater from agglomerations, industries or other polluting activities is thus collected by the sewerage network to be transported to so-called sewage treatment plants. The wastewater treatment then consists of reducing the pollutant concentrations in the water to an acceptable degree so that the discharged water does not degrade the natural environment. Today, in wastewater treatment plants, wastewater treatment consists of a succession of stages, grouped under three levels: pretreatments, essentially mechanical processes, such as screening, grinding, sandblasting, and degreasing / deoiling, - primary treatments, intended to remove by settling suspended solids, - secondary treatments for the removal of soluble and / or colloidal materials.

  The biological process and the lagoon scrubber according to the invention are part of this third level of treatment, namely that of the secondary treatments, which, for most of them, are based on biological treatments in which the organic materials are degraded by the presence of bacteria. These biological treatments are of two types, either of extensive type relying on the natural phenomena of self-purification of shallow water bodies, or of intensive type, that is to say using a bacterial culture.

  Today, extensive biological treatments, called natural, are in the form of lagoon systems. The lagooning is a substantially surface treatment, and not volume, the removal of organic matter present in the water taking place at the liquid interface / lagoon bottom, through the bacteria concentrated in sludge. The lagoon waters are indeed low in bacteria. The oxygen required by bacteria for the removal of organic matter is provided by gas exchange with the atmosphere at the water level and by the action of photosynthesis of microalgae.

  Document BE 1.007.470 is also known, an improved extensive biological treatment for which the lagoon waters are more aerated and put into circulatiion. The intensive biological treatments, gather, meanwhile, various techniques whose common point is the use of a bacterial culture. This bacterial culture can be fixed on supports, for example granular type, or be free in the water to be treated, for example in a so-called activated sludge treatment. In an activated sludge plant, the bacterial culture is maintained in an aerated pond and stirred by the same aeration system. The biological treatment is voluminal, unlike lagooning, the bacteria being present in water at high concentration.

  After a residence time, the water is then conveyed to a clarifier, also called secondary clarifier, and whose purpose is to separate the water concentrated sludge bacteria. Part of this sludge is then rerouted to the basin, the other part, superabundant, being evacuated, used especially for spreading. Recently, also known activated sludge plants using membrane processes. Concretely, the membranes are immersed in the ventilated basin and brewed. The clarifier is no longer needed and is therefore superseded. The fineness of the filtrations of these membranes makes it possible to filter the water by retaining the bacteria which can not cross the membranes. Document WO 03/053552 discloses a device with capillary membranes that can be used in an activated sludge basin in which these membranes are placed in the path of the rising gas flow of the aeration and stirring system in order to limit their clogging. However, because of the high concentrations of bacteria in the water, these membranes clog rather quickly requiring frequent maintenance and a high operating cost of the installation.

  The object of the present invention is to provide a biological wastewater treatment process, ensuring a high quality water sanitation while allowing to be more energy efficient and maintenance than the previous processes. The invention will also relate to a lagoon scrubber 25 for carrying out this method. Other objects and advantages of the present invention will become apparent from the description which follows, which is given for information only, and which is not intended to limit it. The invention relates to a biological process for the treatment of wastewater in which organic materials are degraded by the activity of bacteria.

  According to the invention, the process consists, for waters with a low pollution load, in an extensive biological treatment step, based on the principle of the natural phenomena of self-purification inherent in shallow bodies of water, implemented in a lagoon scrubber comprising at least one lagoon on the bottom of which rests sludge concentrated in bacteria, and from which water is taken and filtered in a well opening above the bed of sludge, through membranes immersed, especially capillary or flat. According to a particular embodiment of the method provided for the treatment of waters heavily loaded with pollution, the process will have at least one prior stage of biological treatment of wastewater, intended to reduce the concentration of pollution in the water, in which the organic matter is degraded by the activity of bacteria present in the water, the preliminary treatment stage being in the form of an extensive biological treatment, based on the principle of the natural phenomena of self-purification inherent in the shallow water, or intensive biological treatment, using a bacterial culture. The invention will also relate to a lagoon scrubber, the principle of which is based on the natural self-purification phenomena inherent to shallow water bodies, comprising at least one lagoon on the bottom of which sludge concentrated in bacteria rests. . According to the invention, the lagoon scrubber has a well, opening out above the sludge bed, inside which a membrane bundle is immersed, said membranes, in particular capillary or flat membranes being open on a permeate collection zone. . The invention will be better understood on reading the following description accompanied by the appended drawings in which: FIG. 1 is a diagrammatic perspective view of a lagoon purifier suitable for carrying out the process according to the invention; - Figures 2 and 3 are respectively sectional views according to two embodiments of a well provided under the lagoon bottom of a lagoon scrubber according to the invention. The invention is based on the idea of an extensive, rather than intensive, biological finishing treatment using membranes with low micro-organisms concentration in order to be more energy efficient and maintenance. The invention relates to a biological process for the treatment of wastewater, particularly heavily polluted, having at least a first stage of biological treatment in which the organic materials are degraded by the activity of bacteria. The first stage of biological treatment, a preliminary stage of treatment, is in the form of either an extensive biological treatment, based on the principle of the natural phenomena of self-purification inherent to shallow water bodies, or a intensive biological treatment, using a bacterial culture. The first biological treatment can be extensive, lagoon type, consisting of one or more basins in series. Alternatively, the first biological treatment may be intensive, using bacterial cultures, in particular be constituted by: a fixed culture installation, where the bacterial culture rests on a support such as pebbles, granular media or the like; free culture, especially activated sludge type. The activated sludge plant may consist of an aerated and stirred tank followed by a clarifier. According to the invention, the biological process also has an extensive finishing treatment step, based on the principle of the natural self-purification phenomena inherent to shallow water bodies, used in a lagoon scrubber. 1 comprising at least one lagoon 2. On the bottom 3 of the lagoon lie sludge concentrated in bacteria. The lagoon is removed from the water slightly polluted, and filtered in a well 7 opening above the bed of sludge through submerged membranes 4, including capillary or flat. The first stage of intensive or extensive biological treatment allows the discharge of some of the organic pollutants, soluble or colloidal. The treated water is then conveyed to the lagoon scrubber of said finishing treatment according to the invention where they undergo a final biological treatment, extensive, and filtration through the capillary membranes. Advantageously, the water treated in the lagoon treatment of the finishing treatment is thus poorly loaded with suspended solids and organic soluble pollutants, thus ensuring a low clogging of the membranes during filtration. Low pollution waters, for example, means a five-day biochemical oxygen demand (BOD) of less than 250 mg / l. Also, according to a particular embodiment, in particular for the production of drinking water, in the case of wastewater initially low in pollution (BOD <500 mg / I), the prior stage of biological treatment, also called first biological treatment step, can be suppressed, the method according to the invention consisting only in the biological treatment step and in the filtration step implemented in the lagoon scrubber 1. Advantageously, the biological treatment step Extensive, especially finishing, implemented in the lagoon scrubber 1 may further provide, in whole or in part: -the aeration of water in the lagoon scrubber 1 by injection of a stream of air, - the putting into circulation the waters of said lagoon scrubber,

  The fact that the membranes 4 are subjected to an upward gas flow in order to limit their colrnatage. Advantageously, according to a particularly advantageous embodiment of the treatment step, the water is aerated in the lagoon scrubber 1 by means of an air injection device 5 provided in the well 7 and whose flow In addition to the water oxygenation function, the generated rising gas combines a function for the circulation of water in the lagoon 2 and a function for the declogging of the capillary membranes 4.

  Apart from the. replacement of the membranes 4, the maintenance of the lagoon purifier 1 according to the invention will be limited to remove the superabundant sludge resting on the bottom of the lagoon 2. These sludge may be used in particular, after treatment, for their agricultural application .

  The invention will also relate to a lagoon purifier 1, particularly suitable for carrying out the biological process according to the invention, the purification principle of which is based on the natural phenomena of self-purification inherent in shallow bodies of water. comprising at least one lagoon 2 on the bottom 3 of which are sludge concentrated in bacteria. According to the invention, the lagoon purifier 1 has a well 7, opening above the sludge bed, within which a bundle of capillary membranes 4 is immersed. The said membranes 4 are open on a zone 6 for collecting the permeate.

  The membranes 4 may be, for example, capillaries or flat. They are marketed by various specialists such as ZENON, KUBOTA, or MITSUBISHI. The well 7 opens above the bed of sludge in the water volume of the lagoon 2: according to an exemplary embodiment, the surface of the body of water is 1 m 20 from the bottom of the lagoon, the well 7 opening to 0.5 m from the bottom. Superabundant sludge must be removed before

  8 do not reach the level of the mouth of the well 7, in particular to prevent their fall. Advantageously, as illustrated according to the example of FIG. 1, the lagoon scrubber 1 forms a closed circuit for a fluid stream 20.

  At least a portion of said fluid stream passes through the well 7. For this purpose, the well 7 is provided with a supply duct 9 communicating, on the one hand, with the lagoon, at an opening 10 of sampling liquid, and secondly, with the well 7 at its lower end 11. As illustrated, the liquid withdrawal opening 10 is located above the sludge bed, in the volume of lagoon water 2, especially at a level comparable to that of the mouth of the well 7, to prevent sludge falling in the conduit 9. Advantageously, according to the illustrated example, the well 7 integrates, in addition to the beam 8 of membranes 4, an air injection device 5, in particular provided on the lower part of the well. Advantageously, said membranes are positioned in the path of the upward gas flow generated by the air injection device 5. The device 5 of air injection ensures the oxygenation of water, the circulation of water, and the unclogging of the membranes.

  According to the illustrated examples, the capillary membranes are each in the form of a tubular, having a closed free end, in particular an upper end, and a lower end secured to the plumb and above the air injection device 5 , open on the permeate collection zone 6.

  In addition, the lagoon 2 may have a partition 12 positioned between said withdrawal opening 10 of said supply duct and said well 7. This partition may be provided to force the flow of fluid to pass through said supply duct 9 of the well 7. The upper end of the well 7 may be provided with a deflector 13, designed to deflect the upward fluid flow generated in the well 7 into a fluid stream 20 of substantially horizontal direction in said lagoon 2. Of course, other embodiments or implementation could have been envisaged without departing from the scope of the invention defined by the claims below.

Claims (11)

  A biological process for the treatment of wastewater in which the organic matter is degraded by the activity of bacteria, characterized in that the process consists, for wastewater with a low pollution load, in an extensive biological treatment step, based on the principle of the natural phenomena of self-purification inherent to shallow water bodies, mils implemented in a lagoon scrubber (1) comprising at least one lagoon (2) on the bottom (3) of which rests sludge concentrated in bacteria, and from which water is taken and filtered in a well (7) opening above the sludge bed, through submerged membranes (4), in particular capillary or flat.   2. Biological process according to claim 1, intended in particular for wastewater heavily polluted, having at least one prior stage of biological treatment of wastewater, intended to reduce the concentration of pollution in water, in which organic matter. are degraded by the activity of bacteria present in the water, the previous stage of biological treatment being in the form of an extensive biological treatment, based on the principle of the natural self-purification phenomena inherent in the water treatment plans. shallow water, which is an intensive biological treatment, using a bacterial culture.   3. Method according to claim 1 or 2, wherein the water is aerated in the lagoon scrubber (1) by injecting a stream of air.   4. Method according to one of claims 1 to 3, wherein circulates the waters of said lagoon scrubber (1).   5. Method according to one of claims 1 to 4, wherein the membranes (4) are subjected to an upward gas flow to limit clogging.   6. Method according to claims 3, 4 and 5, wherein the water is aerated in the lagoon scrubber (1) via an air injection device 11 (5) provided in the well (7). ), whose combined upward gas flow combines, in addition to the water oxygenation function, a function for the circulation of water in the lagoon (2) and a function for the declogging of the capillary membranes (4).   7. Method according to one of claims 1 to 6, wherein, expiry (s), is removed superabundant sludge resting on the bottom (3) of the lagoon (2) of said lagoon scrubber (1).   8. Lagoon scrubber (1) whose principle of purification is based on the natural phenomena of self-purification inherent to shallow water bodies comprising at least one lagoon (2) on the bottom (3) of which sludge is based concentrated bacteria characterized in that the lagoon purifier (1) has a well (7) opening above the sludge bed, inside which a membrane bundle (4) is immersed, said membranes (4), in particular capillaries or plates, being open on a zone (6) for collecting the permeate.   9. lagoon scrubber (1) according to claim 8, forming a closed circuit for a fluid stream (20), a portion of said stream of fluid at least passing through the well (7), said well (7) being provided with a supply duct (9) communicating, on the one hand, with the lagoon (2), at a liquid withdrawal opening (10), and on the other hand, with the well (7) at the its lower end (11), said well (7) integrating, in addition to the membrane bundle (4), a device (5) for injecting air, said membranes (4) being positioned in the path of the gas flow ascending generated by said device (5) for injecting air.   10. lagoon purifier (1) according to claim 9, wherein the lagoon (2) has a partition (12) positioned between said sampling opening (10) of said supply duct (9) and said well (7), said partition (12) being provided to force the flow of fluid to pass through said supply duct (9) of the well (7).   The lagoon scrubber (1) according to claim 9 or 10, wherein the upper end of the well (7) is provided with a deflector (13) provided to deflect the upward fluid flow generated in said well (7) by a fluid stream (20) of substantially horizontal direction in said lagoon (2).