WO2002102721A1

WO2002102721A1 - Method and installation for purifying effluents that are at least partially biodegradable

Info

Publication number: WO2002102721A1
Application number: PCT/FR2002/002071
Authority: WO
Inventors: Christian Cuingnet; françois COLLETTE
Original assignee: Bionis Environnement
Priority date: 2001-06-18
Filing date: 2002-06-14
Publication date: 2002-12-27
Also published as: FR2825998B1; FR2825998A1

Abstract

The invention relates to a method of purifying effluents which are at least partially biodegradable and which are exempt from toxic products comprising the aerobic and/or anaerobic biological treatment of said effluents which causes the formation of sludge. The inventive method consists of the following steps: a) recovery of the sludge that has been mixed either with the treated effluents or with a liquid feed; b) at least one step involving the filtration of the mixture in order to eliminate particles that are greater than or equal to 140νm approximately; and c) supplying under pressure the mixture thus filtered to a micro-irrigation network in an area planted with vegetables in which said mixture constitutes a growth fertiliser.

Description

PROCESS AND PLANT FOR THE PURIFICATION OF AT LEAST PARTIALLY BIODEGRA DRAIN EFFLUENTS

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 or fertigation technique. It also relates to an installation specially designed for the implementation of such a process. 0 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. These sludges are separated from the effluent treated by decantation and then possibly dried by passing through a press. They are then eliminated by spreading, landfilled or incinerated.

This biological purification technique concerns effluents from most food manufacturers, but also 0 from other industries such as the paper, cardboard, cosmetic industry, as well as effluents from communities, livestock, etc. ..

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 uses a natural treatment of effluents which combines the purifying power of the soil, the absorption capacities of certain plants and irrigation technology. According to this so-called micro-irrigation technique, the effluents are injected in the ground by a fixed network laid on or buried in the ground, pipes comprising micro-perforations. The effluents bring suspended matter which is retained in the first centimeters of the soil. 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 which 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, coppices with very short rotation of willows have already been set up, called TTCR.

However, this new natural purification process is only suitable for certain limited types of effluents. 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 approximately 130 μm and. 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 matters 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.

Document US.3.844.481 discloses an effluent treatment implementing an irrigation step, but it is an aerial spraying of the effluent by an aerial, mobile spreader, provided with nozzles large size, step not comparable to the technique of fixed micro-irrigation, by pipes laid on or under the ground and provided with calibrated orifices of very small size.

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 approximately 130 μm. Of course we can be content 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 having to subsequently reprocess this water from the decantation.

The liquid supply can also consist of a supply of other effluents of the liquid type, such as pig manure or of other animals, manure juice, slurry, leaching juice, juice or liquid leaving a septic tank. In this case, this liquid supply generates additional pollution which is taken into account in the micro-irrigation stage. Preferably the fine filtration is carried out with a backwashing with pure water, or liquid coming from the filtration step, or possibly with water coming 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 the sludge at the outlet of the biological treatment device and on the other hand 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 130 μm approximately, 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.

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. Preferably the micro-irrigation network is buried, and advantageously in this case it is buried at a depth of 10 to 60 cm.

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

The effluents of the food industries, which can either be treated by the process of the invention or intervene as a liquid supply concern all the branches of the food industries namely vegetables, fruits, chocolate, confectionery, dairy industry, cold cuts, eggs, wines, alcohols , fruit juices, pasta, rice, cereals, ready meals, sugar and also:

- meat industries (slaughterhouses and workshops for processing cattle, sheep, goats, and more generally all animals), - fish and shellfish processing industry,

- breeding: pig, cattle, sheep manure and more generally all animals etc., - farms: manure juice, liquid manure juice, all leaching juice ...,

- sludge from industrial, urban and rural, collective and individual treatment plants. What all of these industries have in common 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 above effluents 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 for treating this sludge has been indicated, namely, after drying by passing through a press or by any other method, elimination by spreading, discharging or incineration.

Typically, according to the invention, the sludge from the decanter, optionally after drying by passage through a press or by any other technique, is mixed in a conventional mixer, with a liquid supply, a supply which can at least partly come from 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 or other effluents considered as liquids such as liquid manure. pigs or other animals or manure, slurry or leaching juice or juice or liquids from a septic tank.

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 transporting it 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 backwash 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.

The purpose of the fine filtration operation is to remove particles equal to or greater than approximately 130 μm, which corresponds to the size of the orifices of the micro-irrigation network.

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 or automated.

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 control system. The pressure used is of the order of 2 to 6.10 ⁵ Pa (2 to 6 bars), on average of the order of 4.10 ⁵ Pa. A micro-irrigation network is made up of irrigation pipes comprising drippers which are passage openings of the order of 130 μm. Irrigation pipes can be laid on the ground but are preferably buried at a depth of 10 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 can 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 a plant growth fertilizer. Said plants are regularly cut and generate biomass themselves, which is a positive element to be taken into account in the overall cost of the treatment of effluents.

Conventionally, the pipes are buried to limit the evaporation of irrigation water by the sun, and incidentally to prevent theft of the pipes. In the case of the present invention, the micro-irrigation network is buried on the one hand to prevent the spread of odors due to effluents and on the other hand, at a depth of 10 to 60 cm, to allow the purifying action. of the soil, all year round and whatever the climatic conditions, in particular in the event of moderate frost or heavy rain. In fact, contrary to what is sought in irrigation, the primary objective is not to feed the plant but to eliminate and purify effluents, even when the plant is living in slow motion. This objective is achieved thanks to the microorganisms contained in the soil. The effluents brought in by the micro-irrigation network diffuse into the soil. The effluents bring suspended matter which is retained in the first centimeters of the soil under the micro-irrigation network. The organic matter thus provided is slowly degrade by releasing mineral elements. Soil microorganisms act on organic matter and certain minerals. Part of the nitrogen can, for example, be lost in gaseous form, completing the purifying action of the coppice. The upper burial threshold, preferably of the order of 10 cm, is desirable to avoid moderate frost and to avoid heavy rain which tends to leach the ground on the surface. This threshold can be variable depending on regions and soil types. The lower burial threshold of the order of 60 cm is desirable to allow the activity of microorganisms, depending on the nutrients contained in the effluents. Beyond this depth, the quantity of soil microorganisms decreases.

The micro-irrigation network is formed by an alignment of pipes, composed for example, over one hectare, of twenty pipes 100 meters long spaced from each other by 5 meters and comprising a micro-perforation every meter, i.e. around 2000 micro-perforations per hectare. The land on which the plantations are carried out, and irrigated by micro-irrigation networks, is served by paths allowing the work of the soil and the crops. These paths, generally covered with grass, can be used to spread the sludge in a conventional manner. 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 / 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

1. A 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 sludge recovery step either mixed with the treated effluents or mixed with a liquid supply, b) at least one step of filtering the mixture to remove particles greater than or equal to about 130 μm and, c) a feeding step under pressure of the mixture thus filtered in a micro-irrigation network of an area planted with plants, of which it constitutes a growth fertilizer.

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 claim 3 characterized in that the supply of liquid, for the preparation of the mixture with the sludge consists at least in part in other liquid effluents, in particular pig manure or other animals, manure juice , slurry or leaching juice.

6. Method according to one of claims 1 to 5 characterized in that it comprises two operations for filtering 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 approximately 13O μm.

7. Method according to claim 6 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.

8. Method according to claim 7 characterized in that the waters charged with backwashing are reintroduced into the effluents having undergone the biological treatment, possibly before decantation.

9. Method according to one of claims 1 to 8 characterized in that the pressure supply of the filtered mixture in the micro-irrigation network is carried out under flow and pressure regulation.

10. Method according to one of claims 1 to 9 characterized in that the pressurized supply of the micro-irrigation network is carried out while it is buried in the ground at a depth of 10 to 60 cm.

1 1. Installation designed for the implementation of the effluent purification process according to one of claims 1 to 8 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 approximately 130 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.

12. Installation according to claim 11 characterized in that it comprises a screen for the elimination of coarse particles, greater than 1 to 3 mm and a self-cleaning filtration device with backwashing for the elimination of the remaining upper particles or equal to about 130 micrometers.

13. Installation according to one of claims 11 or 12 characterized in that the mixture circulation pump is equipped with a pressure and flow regulator.

14. Installation according to one of claims 11 to 13 characterized in that the micro-irrigation network is buried, at a depth of 10 to 60 cm.

15. Installation according to claim 14 characterized in that the micro-irrigation network comprises of the order of 2000 micro-perforations per hectare.