FR2890653A1 - Preparing a compost of wood fibers coming from the industrial products, useful for plants, comprises forming a mixture made up of wood fibers, adding water for composting and fermenting obtained mixture to give a composite - Google Patents

Abstract

Preparing a compost of wood fibers coming from industrial products comprises forming a mixture made up of wood fiber paste of urea and bark tree and excluding additional source of nitrogen, adding water for composting and fermenting the obtained mixture to give a compost. An independent claim is included for compost obtained by the process.

Description

The present invention relates to a method for manufacturing a support for

  growing plants from wood fibers derived from industrial by-products.

  The subject of the present invention is also a plant growing medium consisting essentially of the product of composting glued wood fibers in the presence of tree bark.

  BACKGROUND OF THE INVENTION For the purposes of the present invention, the term "industrial by-products" means glued wood fibers which are not used immediately for the manufacture of medium-density fiberboard (MDF), and which thus represent industrial by-products. normally considered non-reusable. Glued wood fibers are potential sources of pollution.

  Glued wood fibers used for the manufacture of MDF panels have the same physical characteristics as natural fibers, with the major disadvantage of containing more or less toxic chemical additives.

  The term "chemical additives" means glues and synthetic resins used for the manufacture of wood panels, which belong to the following categories: - thermosets: these resins polymerise when hot; it is in particular ureaformaldehyde (UF) or phenol-formaldehyde (PF), - thermoplastics: the term refers to neoprene-type glues, polyamides and other synthetic resins, - emulsion glues: mainly the vinyl glues, and - hot-melt glues based on wax or paraffin.

  Synthetic glues based on urea-formaldehyde, among others, cause fumes that can be harmful.

  Formaldehyde is a colorless, strong-smelling gas that already exists naturally in wood. Its fumes are therefore even more important when the fibers, particles or wood chips are bonded using a synthetic urea formaldehyde-based adhesive; moreover, emissions increase with increasing temperature and with the degree of humidity of the air.

  Phenol-formaldehyde or phenol-resorcinol resins, less toxic and more expensive than urea-formaldehyde (UF), are commonly used in the manufacture of MDF boards.

  The glued wood fibers used according to the process of the present invention are obtained, before sizing, by grinding, according to a method of the prior art perfectly known to those skilled in the art. Thus the glued wood fibers comprise about 90% by weight of organic materials (of which about 45% of cellulose and 45% of lignin, but also tannins, pectin, starch, etc.), and mineral salts . They have the following characteristics at the time of their production: * pH: between about 4 and about 5.5 * Moisture content: about 20 to 40% * Water retention: on the order of 550 to 800 mI / I The MDF panels are obtained by treatment of wood fibers according to an industrial process known to those skilled in the art with the addition of glues and synthetic resins and gluing in press at high temperature.

  MDF panels contain about 10% by weight of glue or synthetic resins.

  The wood industry produces large quantities of by-products soiled by chemical additives whose depollution entails significant logistics and high costs.

  Glued wood fibers can be burnt off in incinerators. On the other hand, there are few solutions to recycle this waste.

  Furthermore, it is already known from French Patent No. FR 2 793 487 a method for manufacturing culture media based on a small amount of natural wood fibers transformed by fermentation.

  This method of the prior art uses only natural wood fibers and does not propose treatment of glued fibers for recycling.

  SUMMARY OF THE INVENTION The Applicant has surprisingly discovered and it is the object of the present invention to compost glued wood fibers or wood fibers from MDF panels contaminated with resins and glues containing a source. Nitrogen, especially in the form of urea, makes it possible to depollute these materials and to recover them in the form of non-toxic agricultural products.

  Indeed, not only the method described below allows certain microorganisms to survive in a medium initially toxic because too rich in ammonia (from the degradation of urea), but also to obtain a product devoid of formaldehyde (with the exception of the one residing in the natural state in wood) while it contains significant amounts (of the order of 800 mg / kg of dry product) before treatment.

  The present invention therefore aims to provide a method that is both simple and inexpensive, which makes it possible to obtain a culture support substantially free of toxic products initially present in glued wood fibers and MDF panels.

  Composting of glued wood fibers alone is not working well. In fact, the quantity of ammoniacal nitrogen released during the first weeks of storage of the glued wood fibers becomes a limiting or inhibitory factor for the development of microorganisms.

  In addition, the composting of materials with high carbon content and low nitrogen content, such as tree bark, requires a nitrogen supply to feed the micro-organisms and thus allow the fermentation process.

  According to the method of the invention, glued wood fibers are mixed with a material rich in carbon, preferably tree bark in order to rebalance the carbon / nitrogen ratio of said fiber / bark mixture necessary for composting.

  The expression fiber / bark mixture used in the present description is understood to mean the mixture of glue-like wood fibers containing a sufficient quantity of nitrogen source in the form of urea and tree bark according to the present invention.

  Detailed description of the invention

  The implementation of the method according to the invention is particularly simple since it boils down to the manufacture of a compost, an operation well known to those skilled in the art.

  Thus, according to a first aspect of the invention, the method is characterized in that the following steps are carried out: a) a mixture of glue-containing wood fibers containing urea with bark of trees without additional source of nitrogen, b) a sufficient amount of water is added to the composting, c) the said fiber / bark mixture is fermented until a compost is obtained.

  The glued wood fibers that may be used in the context of the invention are advantageously chosen from hardwood fibers such as birch, beech, and charm and from softwood fibers.

  The barks that may be used in the context of the invention are advantageously chosen from conifer bark such as pines, fir, spruce, and maritime pine.

  According to the method of the invention, three types of fiber / bark mixtures will advantageously be chosen: Type 1: 100% barks from softwoods (particles of an average size of 1 to 15 mm) / fibers made up of 80% of essences of softwood (particles with an average size of 5 to 25 mm) Type 2: 100% softwood bark (particles with an average size of 1 to 15 mm) / 100% hardwood fibers (particles with an average size of 1 to 10 mm) Type 3: 100% Maritime Pine bark (particles with an average size of 1 to 10 mm) / 100% hardwood fibers (particles with an average size of 1 to 10 mm) It is nevertheless possible to choose all species used by the fibreboard industry.

  Said fiber / bark mixture according to the invention generally contains from 30% to 70% by volume of glued wood fibers, and preferably from 50% to 70% by volume of glued wood fibers.

  Glued wood fibers and bark are in the form of particles with a particle size of between 1 mm and 35 mm and preferably between 5 mm and 15 mm.

  The granulometry of the bark is preferably close to that of the glued wood fibers. The fermentation process of the fiber / bark mixture is all the more effective as the attack surface of the microorganisms is higher. Homogeneity of the particles of the fiber / bark mixture may also make it possible to economize on final sieving of the mixture. However, particles of bark more or less coarse allow to provide some natural ventilation.

  The glued wood fibers come directly from the manufacturing circuit of MDF panels. The glued wood fibers used according to the present invention contain UF glues with a high nitrogen content in the form of urea and optionally glues and / or resins chosen from the group comprising phenol-formaldehyde (PF), glues of neoprene type, polyamide glues, vinyl glues, hot melt glues based on wax or paraffin.

  In addition the glued wood fibers can come partly from the grinding of MDF panels.

  The ratio of glued wood fibers / glued wood fibers from the grinding of MDF panels according to the invention is preferably between 10: 1 and 2: 1 by volume, and preferably 6: 1 by volume.

  Fermentation of said fiber / bark mixture is not accompanied by any bacterial and / or fungal seeding. It is not necessary to add additional nitrogen because of the presence of UF-type glue in the glued wood fibers.

  Both bark and wood fiber are fermentable.

  The biological process of degradation of organic matter is ensured by the bacteria and fungi present in the bark. The process of development of microorganisms is mainly done on the carbon support by consuming the nitrogen of the fibers.

  Composting is faster as the amount of bark is important. However, the object of the present invention being to treat glued wood fibers, their proportion preferably remains the majority.

  It is nevertheless preferable that a maximum of 70% by volume of glued wood fibers be respected to allow favorable composting conditions.

  According to the present invention, a sufficient amount of water is added to bring the water retention of said fiber / bark mixture between 50% and 80% of its maximum retention capacity at -10kPa.

  By water retention is meant the capacity of a substrate to retain water and in the specific case of the invention, the water retention of a substrate at -10 kPa is the amount of water that the substrate retains at most. after draining the gravity water when the substrate has been immersed. It is then considered that the suction force of 10 kPa exerted on the substrate is equivalent to the gravitational force. A volume of water equal to the water retention of the substrate at -10 kPa (or pFl) is then recovered. The water retention is expressed in mi / I or in% of the dry weight.

  The sufficient amount of water at the start of fermentation of the fiber / bark mixture is between 100 and 200 L / m3 and preferably 150 L / m3 of said mixture. The said fiber / bark mixture is then allowed to ferment, either in a circulating air fermenter or by forming windrows in an open environment.

  Advantageously, the volume of the water supply is between 10 and 40% relative to the volume of said fiber / bark mixture.

  The volume of water to be added is even higher than the percentage (%) of wood fiber glued the mixture is high. The water retention capacity of bark is lower than that of wood fiber.

  This water supply allows the hydrolysis of urea and other additives initially contained in the wood fibers and the obtaining of conditions necessary for the development of microorganisms.

  Composting is an aerobic process. Thus said fiber / bark mixture must be returned if it is constituted by static windrows, or ventilated by blowing, suction or continuous agitation when said fiber / bark mixture is stored in a closed environment, for example, in a fermenter.

  The quality of the compost can be determined throughout the progress of the fermentation process of said fiber / bark mixture, by monitoring several physicochemical characteristics including pH, electrical conductivity and the determination of carbon and nitrogen. as well as the germination rate of a test plant to control the absence of phytotoxicity.

  The general fermentation and maturation process of the fiber / bark mixture according to the invention, in the form of windrows or in a closed medium such as a fermenter takes place over several months following the process, the proportions of the fiber / bark mixture and tree species used.

  When the composting is carried out in an open environment, the windrows are turned several times to ensure a suitable aeration, and preferably at a higher frequency at the beginning of the fermentation. For example, we will return windrows once every fortnight for about 2 months and then once a month.

  The fermentation time of the mixture is adjusted according to the ratio fiber% / bark%. In general, this duration is less than or equal to 8 months and depends mainly on the evolution of composting.

  We can abstain from returning windrows when their temperature does not vary anymore and that their pH remains stable.

  In all cases, the temperature is monitored so as not to exceed about 70 ° C, the threshold beyond which the risk of developing incandescent fires increases and bacteria and fungi no longer play their role.

  The method according to the present invention also makes it possible to use an alternative source of carbon-rich material, for example vegetable waste relatively nitrogen-deficient, such as pruning wood, in place of tree bark, or a mixture of bark and peel. 'trees / vegetable waste.

  According to another aspect of the invention, it also relates to the plant culture support obtained by the method described above. The growing medium is characterized in that it is obtained by composting a mixture of glued wood fibers and tree bark or vegetable waste, said mixture is substantially free of pollutant and toxic residue such as formaldehyde .

  Such a support proves to be a culture support that perfectly satisfies the various physicochemical conditions required of a substrate for the cultivation of plants.

  The excess nitrogen provided by the urea of the sized fibers is hydrolysed substantially in the form of ammonia which is converted to nitric nitrogen or organic nitrogen by the microorganisms.

  The culture medium has no trace of formaldehyde as evidenced by the liquid chromatography assay.

  The glued wood fibers are thus cleaned up and recovered.

  The culture support according to the present invention has a higher water retention than the initial fiber / bark mixture. Advantageously, the culture medium has a water retention of between 500 and 750 ml / l.

  In general, the culture medium is characterized by a compost obtained from the fermented mixture of a) glued wood fibers advantageously chosen from hardwood fibers such as birch, beech, and hornbeam and from softwood fibers. and (b) tree bark advantageously selected from softwood bark such as pines, fir, spruce, and maritime pine.

  The growing medium is also characterized in that the compost comprises between 30% and 70% by volume of fermented sized wood fibers.

  The culture support according to the present invention can be used as such for the cultivation of plants.

  The culture support according to the present invention can also be completed at the time of its use, with one or more compounds chosen from the group comprising: barks; peat; -of the earth; - manure type compost; nutrients such as ternary fertilizers or any other compound used in the composition of a carrier for growing plants.

  The culture support obtained according to the process of the present invention makes it possible to form a base for culture supports characterized by physicochemical properties comparable to those obtained by using mainly sphagnum peat moss, its advantage being that it is more economical and more economical. ecological in that it recycles products considered normally non-reusable. The proportion of the compounds used in the fiber / bark mixtures will be chosen by those skilled in the art according to the initial contents of said mixtures of glued wood fibers and bark and according to the desired final substrate type.

  The culture support obtained by the process according to the present invention has a set of particularly favorable characteristics for its use in agriculture.

  This support is easily manageable and can be easily used in all types of containers, for example a bucket, a pot, or a container.

  The culture support obtained by the process according to the present invention is of pleasant appearance and odor, has good stability, and can be stored without inconvenience and without deterioration.

  In order to better describe the invention, an embodiment is given by way of non-limiting example of the invention.

Example 1

  Compost Lot Fiber and Bark (CFE) The following mixture is placed in windrows which are returned 8 times during the total fermentation period which is 8 months: * 35% by volume of maritime pine bark * 65% by volume of hardwood fibers bonded with urea formaldehyde resin.

  * Supply of water: 150L / m3 Final results: Parameters measured Initial Final (after mixing and water supply) Humidity 63% 56% Organic matter (% of 85% 83% dry weight) pH 5.5 7.2 according to standard NF EN 13037 CE (ms / m) 22 17 according to standard NF EN 13038 NO3 (mg / l of substrate) 0 10 according to standard NF EN 13652 NH4 + (mg / l of substrate) 34 30 according to standard NF EN 13652 formaldehyde ( mg / kg dry) 400 1 Water retention pFl 500 699 according to standard NF EN 13041 Retention in air at pFl 240 190 according to standard NF EN 13041 C / N 14 25 N TOTAL (% on dry weight) 2.8 1, 66

Example 2

  Final average characteristics of composts types 1 to 3: Type 1 Type 2 Type 3 Organic matter 70 -80 70 -85 70 -85% Dry% Dry matter% 30 - 40 30 - 40 30 - 40 Retention capacity 480 - 650 550 - 700 550 700 pFl pH 7-8 7-8 6.5 -7.5 Conductivity 0.2 -0.6 0.5 0.7 0.3-0.8 Formaldehyde / / 1 (mg / kg of material dried)

Claims (20)

  1. A method of manufacturing a culture support from wood fibers derived from industrial by-products, characterized in that the following steps are carried out: a) forming a mixture consisting of glued wood fibers containing the urea with tree bark without additional source of nitrogen, (b) a sufficient amount of water is added to the composting, (c) the mixture is allowed to ferment until a compost is obtained.   2. Method according to claim 1, characterized in that in step a) the fibers of said mixture are selected from hardwood fibers such as birch, hornbeam and beech, and conifers.   3. Method according to claim 1 or 2, characterized in that in step a) the barks of said mixture are selected from conifer bark such as pines, fir, spruce, and maritime pine.   4. Method according to any one of claims 1 to 3, characterized in that in step a) the mixture comprises between 30% and 70% by volume of glued wood fibers.   5. Method according to one of claims 1 to 4, characterized in that in step a) the mixture preferably comprises between 50% and 70% by volume of glued wood fibers.   6. Method according to any one of claims 1 to 5, characterized in that in step a) the glued wood fibers and the barks have a particle size of between 1 mm and 35 mm and preferably between 5 mm and 5 mm. 15 mm.   7. Method according to any one of claims 1 to 6, characterized in that in step a) the glued wood fibers contain UF glues with a high nitrogen content in the form of urea and optionally glues and or resins chosen from the group comprising phenol formaldehyde (PF), neoprene-type glues, polyamide-type glues, vinyl glues, hot-melt glues based on wax or paraffin.   8. Method according to any one of claims 1 to 7, characterized in that in step a) the mixture comprises glued wood fibers from the grinding of MDF panels.   9. Method according to claim 8, characterized in that the ratio of glued wood fibers / glued wood fibers from the grinding of MDF panels in said mixture is preferably between 10: 1 and 2: 1 by volume.   10. Process according to any one of claims 1 to 9, characterized in that in step b) a volume of water is added to bring the water retention of the fiber / bark% mixture between 50% and 80%. its maximum holding capacity at -10kPa.   11. Process according to any one of claims 1 to 10, characterized in that in step b) a volume of water of between 100 and 200 L / m 3 and preferably 150 L / m 3 is added. fiber / bark mixture.   12. Method according to any one of claims 1 to 11, characterized in that after step c) the mixture is returned several times during composting.   13. Method according to any one of claims 1 to 12, characterized in that the composting time is less than or equal to 8 months.   14. Method according to any one of claims 1 to 13, characterized in that the temperature of the composting does not exceed about 70 C.   15. Method according to any one of claims 1 to 14, characterized in that in step a) the mixture comprises instead of tree bark, plant waste or a mixture of tree bark / waste plants.   16. Culture support, characterized in that it is obtained according to the method described in claims 1 to 15.   17. Culture support according to claim 16, characterized in that it consists of a compost substantially free of pollutant and toxic residue.   18. Culture support according to one of claims 16 and 17, characterized in that the compost comprises between 30% and 70% by volume of composted wood glue fibers.   19. Culture medium according to any one of claims 16 to 18, characterized in that the water retention of the compost is between 500 and 750 ml / l.   20. Culture support according to any one of claims 16 to 19, characterized in that it further comprises one or more compounds selected from the group consisting of bark, peat, soil, compost type manure and / or nutrients such as ternary fertilizers.