FR2824548A1 - Waste water treatment plant biological reactor has cylinders made from thin plastic discs separated by cellular material with micro-organisms - Google Patents

Abstract

The plant has a biological treatment reactor with a rotating shaft (62) carrying cylindrical elements for cultivating aerobic or anaerobic microorganisms used to break down organic matter in the effluent. The cylinders are separated by a cellular material (74). The plant has a biological treatment reactor with a rotating shaft (62) carrying cylindrical elements for cultivating aerobic or anaerobic microorganisms used to break down organic matter in the effluent. The cylinders are in the form of thin discs (60-1, 60-2, 60-3), each made from two parallel plates (70, 72) separated by a cellular material (74) with open cells and with the outer surfaces of the plates acting as supports for the microorganism cultivation. The reactor is located after a pretreatment unit in which floating and sunken materials are removed from the effluent, and before a clarifier.

Description

according to one of claims l to 6.

  The present invention relates to a pre-

  treatment of domestic wastewater collected by pipes and conduits in sewage treatment plants located downstream from the municipalities which carry out the pre-treatment and treatment of the collected water and aim to purify this water before it is discharged into the environment. The present invention relates in particular to a system of

  pre-treatment of wastewater in a treatment plant.

  Treatment plants generally include a pretreatment set located upstream of the treatment resector where the first stage of treatment takes place

  proper effluent thanks to a physico-

  chemical or biological process.

  In traditional purification processes, the aim of pre-treatment is to remove the coarsest materials and the elements likely to interfere with the subsequent stages from the treatment process. The pretreatment generally includes three operations: dogrillagetamisage, desanding and stripping, the role of which is to remove bulky waste, sands, oils and hydrocarbons from the effluent. During the screening-sieving operation,

  the effluent passes through a grid in order to be filtered.

  A basin receives the filtered effluent for the sand removal operation which consists in allowing the suspended solids to settle by decantation. Another tank receives the effluents from the sanding tank for the last pre-treatment operation, deoiling, which consists of recovering the fats, oils and hydrocarbons which

  float and remove them from the effluent.

  At the end of this pre-treatment, the effluent is ready to be treated biologically in the biological reactor. The main drawback of the pretreatment method described above lies in the management of the by-products generated, such as screen refusal products, sands and greases. Indeed, these sub

  products constitute the residues of the pre-

  processing and must be transformed, thereby processing other energies. A large part of these by-products must go through the incineration stage, since the law on waste does not authorize any more from 2002, that the landfill of so-called "ultimate" waste. The processing of by-products is generally carried out by a company

  specializing outside the treatment plant. Money-

  products are compacted on site using a compacting device or are moved to a specialized site and are then transported to a center for incineration or landfill. These operations for handling and transporting by-products require daily maintenance of the equipment and generate

a significant odor nuisance.

  In addition, the sands recovered during the sanding operation must be washed several times in order to keep only the recoverable fraction of this waste and these successive washes require a significant amount of water. Paradoxically, this water then returns to

the processing unit.

  The management of by-products therefore represents a significant cost which is added to the operating and maintenance costs of the treatment plant and

  is the responsibility of the local authorities.

  This is why the main object of the invention is to provide a system for pre-treating domestic waste water which accepts all of the effluent brought to

the treatment plant.

  Another object of the invention is to propose a system which brings together on the same site, the purification station itself, the operations of pre-treatment of the effluent and dogradation of by-products without having to remove them from the sector. pre-treatment using the effluent itself to degrade

these matters.

  According to the invention, these aims are achieved by means of a pretreatment system in a wastewater treatment plant.

  wastewater comprising at least one set of pre-

  treatment responsible for eliminating the floating parts of waste water such as grease and foam and the falling parts such as sand, solid or heavy matter, at least one treatment reactor responsible for treating the effluent resulting from the assembly pre-treatment to clean up the effluent and a clarifier responsible for removing sludge from the treatment reactor. According to a main characteristic of the invention, the pre-treatment system comprises a single pre-treatment tank divided into a first tank receiving the untreated wastewater and a second tank sending the pre-treated effluent to the treatment reactor, the two basins being separated by a permeable wall allowing the passage of the used water freed from the floating parts and the falling parts from the first basin to the second basin, and pre-treatment means allowing the elimination of the floating parts and the falling parts without having to remove them from the

pre-treatment tank.

  The aims, objects and characteristics of the invention

  will appear more clearly on reading the description

  which follows made with reference to the drawings in which, FIG. 1 is a block diagram of a treatment plant incorporating a pretreatment system according to the invention, FIG. 2 is a sectional view of the pretreatment tank showing the two tanks separated by a permeable partition, FIG. 3 represents a transverse section of the pre-treatment tank, represented in FIG. 3, along the axis AA of FIG. 2, FIG. 4 represents a biological treatment reactor which can be used in combination with a system

  pre-treatment according to the invention.

  A wastewater treatment plant in accordance with the invention shown diagrammatically in FIG. 1, includes a pre-treatment unit 10 allowing the dissolution or degradation into fine particles of the solid materials contained in the effluent arriving from the collector 11, a physicochemical or biological reactor 12 in which the effluent is treated and a clarifier 14 intended to separate by sedimentation the sludges from the reactor from the treated water. The station also includes a sludge silo 16, the outlet of which consists of a liquid part recycled at the inlet of the pre-treatment tank and a part containing the sludge to be removed. The effluent is sent from the pretreatment assembly to the resector by a line 13 and from the reactor to the clarifier by a line 15. From the clarifier 14, the purified water is discharged into nature through the outlet 17, and from the silo to sludge 16, the

  thickened sludge is removed through outlet l9.

  Referring to Figure 2, the set of pre-

  treatment according to the invention is a tank 10 preferably masonry, flat bottom and whose dimensions vary according to the amount of domestic waste water to manage. It is separated into two basins 22 and 24, by a vertically centered partition. The partition is composed, from bottom to top, of a first fixed and waterproof partition 26, of a permeable and movable wall 28 and of a second fixed and waterproof partition 30. The three parts which make up the central partition each represent approximately a third of the

total height of the partition.

  The effluent containing the domestic wastewater arrives in the basin 22 through a collector ll. The materials contained in the effluent have different densities and therefore the high density materials such as sands and heavy materials tend to settle in the lower part of the basin while the low density materials such as greases and foams go up in the upper part of the basin. The major part of the effluent is therefore in the central part of the basin 22 and migrates towards the basin 24 via the permeable wall 28. The effluent being in the basin 22 is evacuated towards the biological reactor by means of a hydraulic pump 32 and conduits 34 and 13. This pumping therefore naturally creates a flow of effluent from the basin 22 towards

  the basin 24 through the permeable wall 28.

  Since the composition and the volume of the effluent vary according to the hours of the day, it is necessary to have a flow control system in order to maintain in the tank an amount of effluent such as the surface of the effluent is always located at the level of the second fixed and watertight partition 30. The equation for the crime consists in returning to the basin 22 a portion of the effluent from the basin 24 by means of the hydraulic pump 32 and the conduits 34 and 40 while another portion of the effluent pumped by means of the hydraulic slurry 32 (or of another pump) is sent to the reactor by the conduit 13. This recycling therefore constitutes a reflux of the effluent from the basin 24 to the basin 22 which attenuates the flows from basin 22 to basin 24 through the permeable wall 28 and which contributes to the homogenization of the effluent. It should be noted that an electromechanically adjusted valve 38 makes it possible to stop the return of the effluent from the basin 24 to the basin 22 and therefore to adjust the flow rate during a sharp increase in the rate of incoming effluent. In addition, this valve is adjusted in order to leave a lapse of time between the reflux in the first tank 22 and the suction towards the treatment reactor thus allowing the non-dograded materials.

  to find their place in the basin 22.

  The actual delicting system comprises a programmable electronic control system 44 connected to at least one level sensor 42 of the mercury sensor type for example, to the hydraulic pump (s) 32 and to the solenoid valve 38. Safety level contacts can also be connected to the control system in order to prevent any malfunction of the device, breakdown of a pump for example. The electronic control system 44 can act by means of an automaton, therefore without human intervention, according to a certain number of instructions such as the time of the day, the season, the quantities of effluent entering and / or transferred to the sles following steps from the processing ... The request system is programmed in such a way as to receive the parameters inherent in the treatment plant to be checked by means of previously established printed cards.

according to the needs of the municipality.

  A characteristic of the pre-treatment system according to the invention is to treat the effluent as much as possible to make it as homogeneous as possible. This is what allows the conduit 50 for returning the effluent (from the conduit 40) illustrated in FIG. 3, the outlet of which is located in the lower part of the basin 22. This creates a vortex which stirs the heavy parts or high density solids located in zone 54 and reduces them to fine particles in order to dissolve or to be easily entrained in the liquid effluent by crossing the wall 23. Note that second return conduit 52 (from conduit 40) to the basin 22 at its outlet located in the upper part of the basin 22 this in order to create a swirl in the floating materials being in the zone 56. A part of the floating materials thus stirred , like mosses, flows to the bottom. Greases, oils and hydrocarbons, by their nature and by the effect of the hydraulic movement created by the ebb and flow, are deposited on the walls of the pre-treatment tank, thus forming an insulating film preventing any penetration of oxygen and promoting anacrobic fermentation and therefore the progress of the various stages leading to methanogenesis, that is to say the transformation of lipid organic matter into

methane and carbon dioxide.

  The effluent resulting from the pre-treatment tank (also called liquor) is sent via the hydraulic pump, to the treatment reactor 14. With reference to FIG. 4, the treatment reactor is a basin in which a certain number of discs 60-1 to 60-3 half immersed in the effluent 64 to be treated rotate slowly around an axis 62 at a speed of the order of 1 to 2 revolutions per minute. The discs, about 2m in diameter, are preferably formed from two circular plates 70 and 72 substantially parallel and separated by a cellular material 74 with open cells allowing the effluent to be stirred and thus to be oxygenated and homogenized. In fact, the ambient air trapped in the disc cells enters the effluent in large quantities. At the interface of the two air / effluent fluids, the effluent becomes saturated with oxygen, the diffusion of oxygen then begins towards the deeper layers of

  the effluent. In addition, a quantity of effluent circulates

  even in the disc sockets and is all the more

brewed and oxygenated.

  The discs can have a shape other than circular without departing from the scope of the invention. According to a preLerated embodiment, the discs are made of polypropylene. This material has, among other things, the following two advantages: its low density which reduces its weight

  and its low thermal conductivity which contributes to the non

  heat dispersion. In addition, the hollow structure of

  discs also lightens the support considerably.

  The effluent arrives on one side of the reactor via the conduit 13 and leaves the opposite side of the reactor via the outlet 15 by gravity, the outlet 15 being situated substantially at the level of the axis 62 of the discs in order to

  keep the level of effluent in the reactor constant.

  Thus, the effluent inlet and outlet create a flow

  effluent from one end of the reactor to the other.

  The two faces of the discs serve as a support for microorganisms, in particular aorobic and anaorobic bacteria which will then feed on the pollutant load of effluent 64. This technique of "culture

  fixed "uses the capacity that most micro-

  organisms to produce exo-polymers allowing their fixation on very diverse supports to form a biofilm. The colonization of a disc begins on a certain number of privileged sites, these sites gradually extending until forming a bio-film which develops continuously until covering of the total surface of the two faces of the disc by a layer single cell. From this moment, the growth is continuous by production of new layers which come to cover the initial layer. There is therefore a stratification of a certain number of culture layers in such a way that the oxygen which diffuses through the thickness of the biofilm does not reach the deepest layer. In the end, the faces of the disc are therefore covered with a layer of

  Anaerobic bacteria and a layer of acrobatic bacteria.

  In an aorobic environment, part of the organic matter contained in the effluent to be treated is consumed thanks to the oxygen dissolved in the effluent by bacteria

  aerobic and dograded in biomass and carbon dioxide.

  In anaorobic environment, another part of the organic matter contained in the effluent is consumed away from oxygen by anaorobic bacteria and dograded in biomass, methane and carbon dioxide. The microorganisms that make up the layer of aerobic bacteria consume oxygen for their energy needs, their reproduction by cell division called bacterial synthesis and their endogenous respiration. These oxygen requirements are met in part by the rotation of the half-immersed discs which allow the aorobic bacteria to come into contact alternately with the organic matter to be dograder then with the oxygen present in the ambient air. They are also provided by the honeycomb shape of the discs which allows the oxygenation of the effluent. Note that the mixing of the effluent by the discs takes place substantially in vertical planes parallel to the discs and therefore perpendicular to the crossing flow of

effluent.

  The homogenization of the effluent ensured by the rotation of the discs ensures intimate contact between the polluting elements and the bacteria. In addition, the oxygen supply also ensured by the rotation of the discs avoids additional equipment of the compressor or aorator type or any other system allowing stirring, or a cascade or trickling process. Indeed, the low oxygenation of the effluent would cause the formation of nitrates and the accumulation of phosphates, which would involve additional stages of denitrification and dephoophatation since these products with high

doses are very toxic.

  The load variations of organic materials to be dograder are smoothed by the principle of homagenization and

  the regulation system of the pre-treatment tank.

  However, in the case of a very large increase in delIT and therefore in the organic load, the biological film in activity on the discs has the property of absorbing a load ten times greater than the load

  normal, without altering the quality of the water leaving.

  The so-called "normal" load is evaluated by a preliminary design made from a certain number of parameters for the installation of each treatment plant. The biological mass present on the discs is also able to absorb and digest the complex molecules that are hydrocarbons, fats

  and other fats not absorbed by the pre-

  treatment. These moleaules arriving in the reactor are condemned to deposit on the discs during their rotation, which allows the bacteria in activity on the discs to feed in optimal proportion of this pollution. The bladder resistor treatment system 1 0 according to the invention is capable of absorbing up to 100 mg of fat per liter of effluent while the proportions estimated in household discharges never exceed 40

at 60 mg per liter.

  At the end of the treatment phase in the biological reactor, the decontaminated effluent is loaded with sludge

  made up of dead bacteria and inert matter.

  It is transferred by means of the outlet 15 into a basin or clarifier 14 where it is subjected to a natural decantation allowing the separation of the sludge and the purified water. Thus, decantation allows the clarification of the effluent and the thickening of the mud. Biological sludge is generally fluffy and has a density very close to that of water, and therefore, the duration of decantation is a parameter to take into account in the design of the treatment plant. The capacity of the effluent to settle, depends on a number of factors such as: the presence of industrial waste, the dissolved oxygen content, the variation in composition of the organic load of the effluent, the temperature, etc. The measurement of the ascent speed (or speed of ascent of the water relative to the mud) is a common parameter in clarification tanks. The guide values for domestic effluents vary on average over a day depending on whether the organic load is low or high between 0.3 m / h and 1.25 m / h. The treatment system according to the invention makes it possible to accept all of the effluent arriving at the station, to smooth the variations in charge of organic matter by the principle of homogenization and the prequlation system of the pre tank. -treatment and therefore to control the production of sludge in the reactor and to provide a large amount of dissolved oxygen thanks to the biological disk reactor. Thanks to these purification conditions carried out on all the pre-treatment and treatment, the upward speed of the sludge in the clarifier is greatly increased compared to traditional treatment plants and reaches 1 1 2 at 2.5 m / h. This significant upward speed of the mud makes it possible to reduce the volume of the clarifier and in particular to decrease its surface area, which represents a non-negligible impact on the investment cost, both in terms of civil engineering and that of the right-of-way. land. At the end of the clarifier, the purified water is discharged into the environment while the sludge is placed in a closed sludge silo 16 while awaiting their evacuation and / or their liquefaction. The sludge can have several final destinations such as agricultural recovery, incineration or landfill. Their elimination from traditional treatment plants represents, all

  about three months, a significant transport cost.

  The sludge from the treatment plant according to the invention undergoes liquefaction due to the composition

  even sludge. Indeed, the combination of the pre-

  treatment and the reactor as described here produces sludge whose composition is not comparable to the sludge produced in traditional treatment plants. In fact, in addition to dead bacteria and inert materials, the sludge from the treatment plant according to the invention contains compounds in small quantities such as nitrates, phosphates, inorganic and organic materials which together continue to undergo an anaerobic dogradation. Thus, the frequency of withdrawal of sludge from silo 16 is reduced compared to

a traditional process.

  In order to increase the capacity of the treatment plant, it is possible to increase the volumes of

  pools carrying out the pre-treatment and treatment.

  It is also possible to carry out in parallel several pre-treatment and resector sets of

  treatment in the same treatment plant.

  Although the pretreatment system according to the invention is preferably used with a biological resector as described above, it is also possible that the treatment of the effluent, at the outlet of the pretreatment, is carried out in a resector physicochemical type without departing from the scope of the invention. The advantages and performances of the system according to the invention are numerous and are clear from the

  description just given, in particular:

  the pollution produced upstream of pre-treatment by traditional processes is almost eliminated, the pre-treatment system for wastewater performs all of the operations necessary for biological pretreatment and by eliminating conventional operations

  screen, desanding and oil removal.

Claims (12)

  1. Pre-treatment system in a wastewater treatment plant comprising at least one pre-treatment assembly (10) responsible for eliminating the floating parts of the used water such as greases and foams and the falling parts such that the sands, solid or heavy materials, at least one treatment reactor (l 2) responsible for treating the effluent resulting from said pre-treatment assembly for depolluting the effluent and a clarifier (l4) responsible for eliminating the sludge resulting from said treatment reactor; said system being characterized in that it comprises a single pre-treatment tank which divides into a first tank (22) receiving the untreated wastewater and a second tank (24) sending the pre-treated effluent to said treatment reactor , the two basins being separated by a permeable wall (28) allowing the passage of waste water rid of floating parts and falling parts of said first basin to said second basin and, pre-treatment means allowing the elimination of floating parts and falling parts without having   to withdraw them from the pre-treatment tank (10).   2. Pretreatment system according to claim 1, in which said tank is separated into two basins by a partition, constituted from bottom to top of a first sealed part (26), of said permeable wall (28) and of a second sealed part (30), creating a flow of effluent from the basin (22) to the basin (24) through said permeable wall (28).   3. Pretreatment system according to claim 1 or 2, wherein the pretreatment tank has a flow rate equation system in order to maintain in said tank an amount of effluent such as the surface of the effluent is always located at said second sealed portion (30), regardless of the flow rate and the composition of the incoming effluent.   4. Pretreatment system according to claim 1, 2 or 3, further comprising a conduit (34,40) for returning by means of at least one hydraulic quench (32) and via a solenoid valve (38), a portion of the effluent from the basin (24) to the basin (22), the operation of said pump and the opening of said solenoid valve being under the control of said equation system. 5. Pre-treatment system according to one of   claims 1 to 4, wherein the conduit (34,40) of   returning the effluent from the basin (24) to the basin (22) is divided into two conduits (50) and (52) in the basin (22), the outlet of said conduit (52) being located at the height of said first part sealed (26) and the outlet of said conduit (50) being located at the height of said second waterproof part (30).   6. Pre-treatment system according to one of   claims 1 to 5, wherein said system of   litigation reqlation includes a programmable electronic control system (44) connected to a sensor (42) for detecting the level of effluent in the tank. 7. Pre-treatment system according to one of   claims 4 to 6, wherein a portion of the effluent   in the tank is sent to the reactor by   a conduit (34,13) by means of said hydraulic pump.   8. Treatment plant including a pre-treatment system   treatment according to one of claims 1 to 7, of a   biological treatment resector (12) comprising a set of discs (60-1 to 60-3) fixed on a rotating axis (62), partly immersed in the pretreated effluent (64) required by said pre-set treatment, and the faces of which comprise aerobic and anserobic microorganisms for the degradation of organic matter contained in the effluent, each of said discs being formed from two substantially parallel plates (70 and 72) separated by a cellular material (74) with open cells allowing the oxygenation of the effluent,   oxygenation of microorganisms and contact of micro-   organisms with organic matter from the effluent.   9. Treatment plant according to claim 8, in which the disks of said treatment reactor   IS biological (12) are made of polypropylene.   10. Treatment plant according to claim 8 or 9, in which the effluent at the outlet of said reactor is placed in a clarifier (14) where it is subjected to a natural decantation allowing the separation of sludge and purified water.   11. Treatment plant according to claim 10, in which the sludge from said clarifier (14) 2s is placed in a sludge silo for their liquefaction and their evacuation.   12. Treatment plant according to claim 11, in which the liquefied sludge is reintroduced at the inlet.