FR2825997A1 - PROCESS AND PLANT FOR PURIFYING AT LEAST PARTIALLY BIODEGRADABLE EFFLUENTS - Google Patents

Abstract

The process for purifying effluents at least partially biodegradable and free from toxic products, comprises a biological, aerobic and / or anaerobic treatment of said effluents which results in the formation of sludge. It comprises the following stages: a) a stage of recovery of the sludge either mixed with the treated effluents or mixed with a liquid supply, b) at least a stage of filtration of the mixture for elimination of particles greater than or equal to approximately 140 m and, c ) a step of feeding the mixture thus filtered under pressure into a micro-irrigation network of an area planted with plants, of which it constitutes a growth fertilizer.

Description

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PROCESS AND! NSTALLAT) ON OF EPURAHON OF AT LEAST EFLUENTS
PARTIALLY BIODEGRADABLE The present invention relates to the purification of effluents at least partially biodegradable and free of toxic products. It relates in particular to a process which combines both the aerobic or anaerobic biological purification technique, causing the formation of sludge, and the micro-irrigation technique. It also relates to an installation specially designed for the implementation of such a process.

 Among the various effluent purification techniques, biological purification is known in particular, which relates to effluents which are totally or partially biodegradable. According to this technique, the biodegradable polluting compounds present in the liquid effluents are transformed into mud, under the action of bacteria. This sludge is separated from the effluent treated by decantation and then dried by pressing. They are then eliminated by spreading, landfilled or incinerated.

 This biological purification technique concerns effluents from most food manufacturers, but also from other industries such as the paper, cardboard and cosmetic industries.

 The major drawback of this biological purification technique lies in the problem of eliminating sludge. Incineration is expensive. Landfill is highly regulated and will likely be prohibited. As for spreading, it is particularly regulated and is faced with the reluctance of farmers to accept sludge which may appear suspicious and risk contaminating crops, or even return to the food chain.

 Another technique is currently being developed which implements a natural treatment of effluents which combines the purifying power of the soil, the absorption capacities of certain plants and irrigation technology.

The effluents are injected into the soil through a micro-irrigation network, a sort of drip. The effluents provide materials in

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suspension which are retained in the first centimeters of the ground. The organic matter thus provided degrades slowly, releasing mineral elements. The mineral elements contained in the effluents penetrate into the soil with the water which contains them and become fixed there except for nitrates and chlorides which remain in solution. The plants that are chosen to be implanted in the irrigated area have the capacity to absorb and capture all of the elements and trace elements such as nitrates, phosphates, chlorides, etc. The soil micro-organisms act on organic matter and certain minerals, which completes the purifying action of plants. The periodic harvest of plants that have been fertilized by these effluents, allows a part of the captured mineral elements to be exported, while producing low-polluting renewable energy that can be used in automated boiler rooms.
According to this technique, therefore, very short rotation coppice willows have already been set up, called TTCR.

 However, this new natural purification process is only suitable for certain limited types of effluent. The aim of the present invention is to propose a method which makes it possible to overcome the drawbacks of biological purification while benefiting from the advantages of fertigation.

 The process of the invention is a process for purifying effluents at least partially biodegradable and free from toxic products. It comprises, in known manner, a step of a biological, aerobic and / or anaerobic treatment, of said effluents resulting in the formation of sludge.

 Characteristically according to the invention, said method comprises the following steps: a) a step of recovery of the sludge either mixed with the treated effluents or mixed with a liquid supply, b) at least one step of filtering the mixture for removal of the upper particles or equal to about 140 µm and,

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 c) a step of feeding under pressure the mixture thus filtered into a micro-irrigation network of an area planted with plants, of which it constitutes a growth fertilizer.

 Document FR 2 782 508 discloses an effluent treatment which comprises a step of biological treatment using a bacterial bed, followed by the elimination of the materials in suspension in the effluent thus treated and simultaneously a treatment sludge by filtration-composting on filters planted with reeds. However, in this process, which combines biological and plant treatment, a sludge is obtained which is certainly stabilized and non-fermentable but which must nevertheless be eliminated for use such as making embankments.

 The merit of the present invention is to completely eliminate the production of sludge while benefiting from the advantages of biological purification and by combining these advantages with those of fertigation.

 The filtered mixture must have a sufficient liquid content to be usable in the micro-irrigation network. This content can vary according to the dimensions of the drippers and the pressure used.

 It is generally at least 80%, which corresponds to a dryness or dry matter content of at most 20%.

 Preferably there are two operations of filtration of the mixture obtained, namely a first operation for the elimination of coarse particles, greater than 1 to 3 mm, for example by screening, and a second operation of fine filtration by elimination of the upper particles. or equal to about 140 µm. Of course one can be satisfied with the second fine filtration operation when the mixture does not contain coarse particles.

 In a preferred embodiment, the addition of liquid, for the preparation of the mixture with the sludge, consists at least in part in water coming from the settling of the effluents having undergone aerobic and / or anaerobic biological treatment; this avoids

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 to have to later reprocess this water from decantation.

 Preferably the fine filtration is carried out with a backwash, optionally with water from the settling of the effluents having undergone the biological treatment. Certainly filtration with backwashing generates charged water; advantageously, these are reintroduced into the effluents having undergone the biological treatment, possibly before decantation.

 The pressurized supply of the filtered mixture to the micro-irrigation network is carried out under flow and pressure regulation.

 It is another object of the invention to propose an installation specially designed for the implementation of the abovementioned effluent purification process. This installation comprises: a) an aerobic and / or anaerobic biological treatment device, b) optionally a decanter intended to separate at the outlet of the biological treatment device, on one side the sludge and on the other side the liquid effluents, c ) optionally a mixer capable of mixing the sludge from the decanter and a liquid supply, in particular liquid effluents leaving the decanter, d) at least one filtration device capable of allowing the elimination of particles greater than or equal to approximately 140 μm , e) a circulation pump, f) a micro irrigation network, made up of micro perforated pipes placed on the ground or buried in an area planted with plants.

 Preferably, the installation also includes a screen for removing coarse particles, greater than 1 to 3 mm.

 The mixture circulation pump is advantageously equipped with a pressure and flow regulator.

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 When the micro-irrigation network is buried, it is preferably buried at a depth of 20 to 60 cm.

 The present invention will be better understood on reading the description which will be given of a process for the purification of effluents from the food industry, illustrated by the appended drawing, the single figure of which is a diagrammatic representation of the various stages of said process. .

 The effluents of the food industries, which can be treated by the process of the invention concerns all the branches of said industries namely vegetables, fruits, chocolate, confectionery, dairy industry, meat, cold meats, eggs, fish, wines, alcohols, juice fruit, pasta, rice, cereals, ready meals, sugar ... The point common to all these industries is that the effluents are totally or partially biodegradable and do not contain toxic products such as heavy metals, chemicals or hydrocarbons .

 Of course, the invention is not limited to the treatment of effluents from the food industry but to all the effluents which have said characteristics, in particular the effluents from the paper, cardboard or cosmetic industries. It can also be effluents from small and medium-sized communities, from 100 to 10,000 Eh (equivalent-inhabitant).

 The raw effluents, after having possibly undergone a screening, are first treated by an aerobic or anaerobic biological treatment process which in known manner, under the action of bacteria transforms into biodegradable polluting compounds which are present in the liquid effluents . Such biological treatment and the corresponding device is well known elsewhere and will not be described more precisely. It is up to the person skilled in the art to determine the appropriate operating conditions and equipment according to the effluents.

 The assembly consisting of the treated effluents and the sludge produced during the abovementioned biological treatment is subjected to a decantation operation in an equally conventional decanter which allows the separation of the sludge and the treated liquid effluents. In the figure the usual circuit of

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 treatment of this sludge, namely, after drying by pressing, elimination by spreading, landfilling or incineration.

 Typically, according to the invention, the sludge from the decanter, optionally after drying by pressing, is mixed in a conventional mixer, with a liquid supply, supply which may at least partly come from the treated effluents leaving the decanter; for the rest, the treated effluents are subjected to a final purification treatment before returning to the natural environment.

 The liquid supply can come from liquids other than the effluents from the decanter, whether it is process water, raw water or drinking water.

 Of course it is preferable that the sludge leaving the decanter is taken up immediately for the preparation of the mixture. However, depending on the type of installation, it could possibly be necessary to carry out a press pass to partially dry the sludge, with a view to its transport to the mixing station. The mixture is then subjected to a screening operation, in a screen where the mesh size is between 1 to 3 mm, having the effect of removing coarse particles.

The mixture thus screened is then subjected to a fine filtration operation, on a filtration device with self-cleaning filter against backwashing. Part of the treated effluent leaving the decanter or possibly other liquids can be used as backwashing liquid.
As for the backwashing return, this liquid can itself be recycled with the treated effluents and the sludge leaving the biological treatment, in particular at the top of the decanter.

ou supérieures à 140 um environ. The purpose of the fine filtration operation is to remove even particles

or greater than about 140 µm.

 In the automated backwashing system which allows optimum filtration efficiency to be maintained, said backwashing is preferably controlled by a fouling measurement by differential pressure. It can also be controlled by periodic triggering adjustable by the operator.

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 The liquid effluents thus filtered are transported under pressure to the irrigation networks thanks to a pump which is itself equipped with a flow and pressure regulation system. A micro-irrigation network is made up of irrigation pipes comprising drippers which are passage openings of the order of 130 μm. The irrigation hoses can be laid on the ground or buried, preferably at a depth of 20 to 60 cm. The irrigation area is itself planted with plants which complement the purifying action of the soil. These plants can be very short rotation coppice (TTCR) of willows, short rotation coppice (TCR) of poplars, eucalyptus or any other hardwood adapted to the climate of the country where this system was established. These plants can also be rhysophites. In addition, the area in which said plants are planted may also include peat beds. In the case of very short rotation willow coppices or short rotation of poplars, eucalyptus or other hardwoods, the effluents which contain nutrients act as fertilizers for plant growth. Said plants are regularly cut and generate biomass themselves, which is a positive element to be taken into account in the overall cost of effluent treatment.

 It should be noted that, unlike certain spreading practices on crops, the effluents treated according to the method of the invention do not enter the food chain.

 In the description which has just been made, the sludges leaving the decanter are mixed with a liquid supply before undergoing the screening and fine filtration operations, in order to be injected with flow and pressure regulation, into the network of micro irrigation.

However, the use of this mixture is not strictly compulsory.

 For certain types of biological treatment and certain types of effluents, all the treated effluents and sludge leaving the biological, aerobic or anaerobic treatment, may have desirable characteristics of the mixture without the need for settling and then for additional liquid supply.

 In general, it is estimated that the decanted sludge mixture must be

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 / liquid intake or treated sludge / effluent must have a liquid content of at least 80%, this content being determined according to the micro-irrigation network, in particular the size of the passage orifices and drippers and the injection pressure.

Claims (12)

 CLAIMS 1. Process for purifying effluents at least partially biodegradable and free from toxic products, comprising a biological, aerobic and / or anaerobic treatment, of said effluents causing the formation of sludge, characterized in that it comprises the following steps: a) a step of taking up the sludge either mixed with the treated effluents or mixed with a liquid supply, b) at least one step of filtering the mixture for removing particles greater than or equal to approximately 140 μm and, c) a step of pressure feeding of the mixture thus filtered in a micro-irrigation network of an area planted with plants, of which it constitutes a fertilizer for growth. 2. Method according to claim 1 characterized in that the filtered mixture has a moisture content of at least 80%. 3. Method according to one of claims 1 or 2 characterized in that the recovery of the sludge is done after a settling and separation operation of the sludge and the treated liquid effluents. 4. Method according to claim 3 characterized in that the supply of liquid, for the preparation of the mixture with the sludge consists at least in part in water from the settling of effluents having undergone aerobic biological treatment and / or anaerobic.  5. Method according to one of claims 1 to 4 characterized in that it comprises two operations of filtration of the mixture obtained, namely a first operation for the removal of coarse particles, greater than 1 to 3 mm, for example by screening, and a second fine filtration operation by elimination of the remaining particles greater than or equal to about 140 μm.  6. Method according to claim 5 characterized in that the fine filtration is carried out with a backwash, optionally with water from the settling of the effluents having undergone the biological treatment. <Desc / Clms Page number 10> 7. Method according to claim 6 characterized in that the waters loaded with backwashing are reintroduced into the effluents having undergone the biological treatment, possibly before decantation. 8. Method according to one of claims 1 to 7 characterized in that the pressure supply of the filtered mixture to the micro-irrigation network is carried out under flow and pressure regulation. 9. Installation designed for the implementation of the process for purifying the aforementioned effluents according to one of claims 3 to 7 comprises: a) an aerobic and / or anaerobic biological treatment device, b) optionally a decanter intended to separate into outlet from the biological treatment device, on the one side the sludge and on the other side the liquid effluents, c) optionally a mixer capable of mixing the sludge from the decanter and a liquid supply, in particular liquid effluents leaving the decanter , d) at least one filtration device capable of eliminating particles greater than or equal to about 140 μm, e) a circulation pump, f) a micro-irrigation network, composed of micro-perforated pipes placed on the ground or buried in an area planted with plants.  10. Installation according to claim 9 characterized in that it comprises a screen for the removal of coarse particles, greater than 1 to 3 mm and a self-cleaning filtration device with backwashing for the removal of the remaining upper particles or equal to about 140 micrometers.  11. Installation according to one of claims 9 or 10 characterized in that the mixture circulation pump is equipped with a pressure and flow regulator.  12. Installation according to one of claims 9 to 11 characterized in that the micro-irrigation network is buried, at a depth of 20 to 60 cm.