FR2762597A1 - Compost production from pig slurry and straw or waste wood - Google Patents

Abstract

Liquid pig slurry (14) is spread over a solid medium (17)and mixed to help impregnation. The mixture is allowed to ferment and become compost. Mixing and fermentation takes place in two parallel enclosures (3 and 5), separated by a third enclosure (4) where the mixture is held for maturation. All three enclosures have sealed floors (10) and are under cover (2).

Description

 The present invention relates to a process for composting from a stream of liquid raw material comprising pig manure and an installation for implementing said process.

 The known composting methods which use pig manure as fermentable material consist of an aerobic fermentation of said manure which is spread beforehand on a solid structuring agent of the straw type.

 The mixture intended to be fermented also comprises an adjuvant which is intended, on the one hand, to constitute a nutrient for the bacteria inherent in fermentation and, on the other hand, to ensure satisfactory adhesion between the pig manure and said agent structuring, in order to facilitate the absorption of slurry by the latter and the compactness of the swath formed by said mixture. The adjuvants used for example consist of sulphite detergents or modified starch products. Sulphite detergents have the particular advantage of promoting the multiplication of microorganisms and they have a deodorant action on the compost.

 The known composting processes based on pig manure are often carried out outdoors. A representative example of such methods will be described below.

 Firstly, the fermentable mixture consisting of pig manure and said adjuvant, which is stirred for several hours, is prepared. Then spread the straw directly on the ground and in one go, so as to obtain a layer of straw of substantially constant height.

 Subsequently, the slurry is spread several times on the straw using a slurry spreader and each time the straw is thoroughly mixed with slurry using a tooth or blade rotor. The frame on which said rotor is mounted is hitched transversely to the rear of a towing vehicle, by means of a three-point hitch system. As for said rotor, it is rotated by the PTO of said vehicle.

 The mixture obtained is then left to stand for a variable duration, for example from two to three weeks, then the abovementioned cycle of spreading slurry on the straw and restarting the straw and spreading slurry is repeated.

 After a further period of rest, the said spreading and mixing cycle is repeated.

 As an indication, approximately 15 m3 of slurry are treated per tonne of straw following the implementation of the above process, for a quantity of straw close to 25 kg / m2 of ground surface. As for the duration of aerobic fermentation, it is around two months.

 At the end of these two months, the fermented mixture is moved to a storage location where it is grouped in heaps and covered with a tarpaulin for its maturation.

 A major drawback of known composting methods using pig manure as a fermentable material lies in the relatively high cost of their implementation, which is in particular due to the use of said adjuvant and to the time spent in brewing and storage operations of the mixture during fermentation.

 An object of the present invention is to provide a method of composting from a stream of liquid raw material comprising pig manure and at least one solid structuring agent, of the type consisting successively in spreading said manure over said at least one structuring agents, to return the mixture obtained so as to impregnate said or each manure structuring agent and to allow said inverted mixture to stand for its maturation, which overcomes the aforementioned drawback.

 To this end, the composting method according to the invention consists in using only pig manure for said stream of liquid raw material, and in carrying out the abovementioned composting steps on a sealed soil and under shelter.

 According to a first example of implementation of said method, it consists in using only straw for said structuring agent.

 According to a variant of said first example, said method consists in using a mixture of straw and wood bark for said structuring agents, in respective mass proportions close to 20% and 80%.

 According to a second example of implementation of said method, it consists in using either a mixture of sawdust and wood bark for said structuring agents, in substantially identical mass proportions, or a mixture of platelets, forest chips or green waste.

 Advantageously, said method consists in recycling into said stream of liquid raw material the excess of spilled slurry which has not impregnated said structuring agent or agents.

 Another object of the present invention is to provide a composting installation allowing the implementation of said process.

 A composting installation according to the invention comprises, on the one hand, two parallel lateral spans which are respectively intended to receive said mixture for its fermentation and, on the other hand, a median span adjacent to said lateral spans which is intended to receive said mixing at the end of fermentation with a view to its maturation, the bottom of each bay being made up of said sealed soil.

 According to another characteristic of the invention, said installation is such that the bottom of each lateral span is provided along its length with means for the diffusion of air in an upward or downward direction.

 According to another characteristic of the invention, said installation comprises at least one turning device which is designed to move longitudinally in each lateral span so as to turn said mixture during fermentation.

 According to another characteristic of the invention, said turning device comprises a tooth or blade rotor which is provided with an inverter provided for reversing its direction of rotation, so that it can rotate in the direction of advance of the towing vehicle and also in reverse.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being made in relation to the accompanying drawings, among which:
Fig. I is a front view of a composting installation according to the invention,
Fig. 2 is a top view and a cutaway of said installation,
Fig. 3 is a side view of a turning device for said installation according to a first embodiment of the invention,
Fig. 4 is a diagram illustrating the composting method according to the invention.

 The composting facility I shown in FIG. I is delimited externally by a roof construction 2. This construction is advantageously of the greenhouse type, and it consists of an assembly of translucent walls in whole or in part. It has two lateral fermentation spans 3 and 5 and a middle maturing span 4. These three spans 3, 4 and 5 are parallel and each of them is delimited by two longitudinal walls 6, 7 of reduced height. In addition, said spans 3, 4 and 5 have in common the longitudinal walls 6 and 7 of the maturing span 4.

 As can be seen in Fig. 2, the installation I has a rectangular shape. There is shown in this FIG. two longitudinal rows of posts 8 provided to support the construction 2. The posts 8 are mounted on the longitudinal walls 6 and 7 of the maturing span 4 (only the first post 8 of each row is visible in FIG. 1). In addition, the construction 2 is mounted by each of its longitudinal edges 9 on the longitudinal wall 6 or 7 externally delimiting each fermentation span 3, 5.

Preferably, the installation 1 is closed at its longitudinal sides 1a and possibly at its rear and front ends 1b and 1c, which are visible at the
Fig. 1. Each of said ends 1b and 1c can advantageously be provided with opening panels (not shown) on at least part of its surface.

 The soil 10 of each span 3, 4, 5 is made of a waterproof material, for example concrete or a waterproof coating covered by clay. In addition, the soil 10 of each fermentation span 3, 5 is provided along its length with air diffusion means 11.

 In this exemplary embodiment, said air diffusion means 11 consist of pierced pipes which are designed to generate air currents in an upward direction. The pipes 1 1 are respectively mounted in longitudinal gutters 12 spaced across the width of each fermentation span 3, 5 (see Fig. 1). These pipes 11 are connected to blowing means (not shown) for the emission of forced air, for example.

 One could however provide at the bottom of each fermentation span 3, 5 air diffusion means 11 which generate air currents in a downward direction. Such diffusion means It could for example be made up of fans designed to draw ambient air towards the ground 10 of said spans 3, 5.

 Along each fermentation span 3, 5, means 13 for spraying liquid 14 are mounted on a ramp 15 which is provided with the construction 2 at regular intervals (the ramp 15 is shown in Fig. 2, only one means spray 13 is visible for each fermentation span 3, 5 in Fig. 1).

A composting installation I according to the invention also comprises at least one turning device 16 which is designed to move longitudinally in each fermentation span 3, 5 (see arrows A in Fig. 2), so as to turn the swath 1 7 to be composted which is deposited in said bay 3, 5
According to a first embodiment of the invention, the composting installation 1 comprises one or two turning devices 16 (see FIG. 3). Said or each turning device 16 consists of a rotor 18 with teeth or radial blades 19, the frame 20 of which is coupled to a tractor vehicle 21 by a three-point coupling system 22. The rotor 18 is rotated in the direction of advancement of the wheels 21a of the towing vehicle 21 by a power take-off 23 which is provided with the latter. Advantageously, the rotor 18 is provided with an inverter 24 provided to reverse its direction of rotation, so that it can rotate in the direction of advance of the towing vehicle (see arrow B) and also in the opposite direction (see arrow VS).

 As an indication, the surface area on the ground 10 of each fermentation span 3, 5 is approximately 200 m2, for a quantity of slurry 14 produced by a breeding comprising a hundred sows, for example. In addition, the height of each longitudinal wall 6 of the maturing span 4 is close to 1 m.

The composting process according to the invention, which is implemented by means of installation I, can be broken down into several phases 100, 200 and 300 (see
Fig. 4).

 The first phase 100 essentially consists of a fermentation with several loads of slurry 14 over a period of approximately two months, and it is subdivided into at least three composting steps 110, 120 and 130.

 A first step 110 consists in impregnating slurry 14 with at least one solid structuring agent 30 during the first day, and in allowing the mixture 17 obtained to ferment for two to three weeks.

 More specifically, it consists first of all in spreading a predetermined quantity of at least one solid structuring agent 30 in at least one of the fermentation spans 3, s, in spraying pig manure 14 with the said structuring agent (s) 30, to return the mixture 17 obtained by means of said or each turning device 16 in each fermentation bay 3, 5 so as to aerate it, and to repeat this sequence of operations ten times during said first day.

 According to a first example of implementation of the composting method according to the invention, one can provide a single structuring agent 30 consisting of straw, or several agents 30 consisting of a mixture of straw and wood bark according to respective mass proportions of 20% and 80%.

 From the initiation of this sequence of operations and this for two to three weeks, the mixture 17 is aerated by means of said diffusion means 11. This has the effect of accelerating the drying and aerobic fermentation of said mixture 1 7.

 As for the pig manure 14, it is subjected to a homogenization treatment 40 prior to its spraying. In addition, it is such that its dry matter content is greater than 6.5%.

 As an indication, an average of 8 to 9 m3 of slurry 14 is sprayed per ton of structuring agent 30 during said first day, in the case where said structuring agent 30 consists only of straw. On the other hand, on average 2 to 3 m3 of slurry are sprayed 14 per tonne of structuring agents 30 when the latter consist of said mixture of straw and wood bark.

 As an indication, the mixture 17 can reach temperatures close to 70 ° C. during the fermentation which takes place following the first day of impregnation.

 A second composting step 120 consists, on the one hand, of impregnating the slurry 14 with the mixture 1 17 obtained at the end of said first step 110 during a first day following this one and, on the other hand, allowing said impregnated mixture 117 to ferment over the next two or three weeks.

 More precisely, it consists first of spraying slurry 14 satisfying the conditions of homogeneity and dry matter content mentioned above, said mixture 11, the latter being optionally added to the preload with a given quantity of structuring agents 30 (see dotted in Fig. 4), then to return the assembly by means of said or each device 16 so as to ventilate it, and to repeat this sequence of operations during said first day.

Following this first day and this for the above two to three weeks, the mixture 117 loaded with slurry and turned over is left to stand. Experience shows that the temperature of the latter decreases rapidly over time, which makes its fermentation much less active.
At the end of said second step 120, said mixture 117 has dried up considerably and has a compact appearance.

 It will be noted that the volume of slurry sprayed on said mixture 117 is less than that used for the first step 110.

 As an indication, an average of 3 to 4 m3 of slurry 14 is sprayed per ton of structuring agent 30 present in said mixture 117 during the first day of the second step 120, in the case where said structuring agent 30 consists solely of straw . On the other hand, on average I spray 2 to 3 m3 of slurry 14 per tonne of structuring agents 30 when the latter consist of said mixture of straw and wood bark.

 A third composting step 130 consists, on the one hand, of impregnating the slurry 14 with the mixture 127 obtained at the end of said second step 120 during a first day following this and, on the other hand, allow the said impregnated mixture 127 to ferment for the next two or three weeks.

 More specifically, it consists first of spraying slurry 14 satisfying the conditions of homogeneity and dry matter content mentioned above, said mixture 127, the latter being optionally added beforehand with a given quantity of structuring agents 30, then return the assembly by means of said or each device 16 so as to ventilate it, and to renew this sequence of operations during said first day.

 Following this first day and this for the above two or three weeks, the mixture 127 loaded with slurry and returned is left to stand, which has the effect of prolonging the lowering of the temperature of said mixture 127 loaded and returned. This results in an additional slowing down of its fermentation.

 It will be noted that the volume of slurry 14 sprayed on the mixture 127 is less than that used for the second step 120.

 As a guide, an average of 2 to 3 m3 of slurry 14 is sprayed treated in the aforementioned manner per tonne of structuring agent 30 during said first day of step 130, in the case where said structuring agent 30 consists solely of straw. On the other hand, on average 1 to 2 m3 of slurry are sprayed 14 per tonne of structuring agents 30 when the latter consist of said mixture of straw and wood bark.

 Concerning said second and third step 120 and 130, it will be noted that the additional spreading of the structuring agent (s) 30 which precedes the slurry spray 14 promotes, on the one hand, the homogeneity and the density of the mixture 117, 127 in progress fermentation and, on the other hand, its fermentation by increasing the temperature in its heart.

 It will also be noted, in accordance with a second example of implementation of the composting method according to the invention, that it is possible to use structuring agents which consist of a mixture of forest residues not comprising straw . Such a mixture can advantageously consist of sawdust and wood bark, in identical mass proportions. Said mixture can also consist of chips or forest chips or green waste.

In these specific cases, the aforementioned first phase 100 comprises, in addition to the three steps 110, 120 and 130, two additional impregnation and fermentation steps which are similar to said step 120 or 130.

 Regarding the turning operations inherent in said first phase 100 of the method according to the invention, the device 16 is first actuated so that the corresponding rotor 18 brews each element of a swath 17, 117, 127, 217 in a given direction (for example in the direction of advance B of the wheels 21a of the tractor vehicle 21 to which it is coupled). Then the direction of rotation of said rotor 18 is reversed by means of the reverser 24, so that said rotor 18 mixes each element previously encountered in the opposite direction (arrow B). This has the effect of reducing the compaction of the part of the swath 17, Il 7, 127, 217 which is between the working end of each tooth or blade 19 of the rotor 18 and the soil 10 of the fermentation span 3 , 5 corresponding, and therefore to optimize said reversal.

 The second phase 200 of the composting process according to the invention essentially consists in prolonging the fermentation of the mixture 137 obtained at the end of the first phase without refilling slurry, and this for approximately two months. This second phase 200 comprises the following two steps 210 and 220.

The first step 210 of said second phase 200 consists of going up in a heap and leaving said mixture 137 to stand for about fifteen days so as to allow, on the soil 10 of each fermentation span 3, 5, the flow of slurry
14 which has not impregnated the structuring agent (s) 30 following the first phase 100.

This flow is commonly called rewetting by a person skilled in the art. This results in drying of said mixture 137.

 Advantageously, the drying juices 214 can be used in addition to the slurry 14 for the impregnation of the structuring agent or agents 30, during the first step 110 of the first phase 100 (see the dotted lines in FIG. 4).

The second step 220 of said second phase 200 first consists in moving the mixture 217 obtained at the end of said first step 210, from the or each fermentation span 3, 5 into the central span 4 (see the arrows A of the
Fig. 2) by means of an apparatus known as a tractor-loader (not shown), for example.

This movement is intended to further complete the fermentation of said mixture 217, which is left to stand for approximately six to eight weeks in said central span 4
It will be noted that the reduced height of the longitudinal walls 6 and 7 of said central span 4 saves time for the delivery of the mixture at the end of fermentation 217 to the maturation zone, compared with the composting installations of the prior art.

 The third phase 300 of the composting process according to the invention, or maturation phase of the fermented mixture 227 obtained at the end of said second phase 200, consists in allowing said fermented mixture 227 to stand for approximately two months in said maturation bay 4.

 Due to the above-mentioned drying which took place in said second phase 200, the fermented mixture 227 does not have a pasty or sticky character during its maturation, contrary to the prior art.

 It will be noted that the ventilation of the composting installation 1 can be modified during the implementation of the method according to the invention, as a function of the internal temperature and humidity rate, so as to optimize the aerobic fermentation of the windrows 17 , 117, 127, 137, 217.

It will be noted that the composting method according to the invention can be implemented without the use of an adjuvant thanks to the composting installation I in particular, unlike the methods of the prior art which use pig manure 14 as fermentable material and necessarily an adjuvant, while obtaining good adhesion between the slurry 14 and the structuring agent or agents 30
It will also be noted that the high temperature characterizing the mixture during fermentation 17, 117, 127 during said first phase 100 of the process according to the invention makes it possible to sanitize it satisfactorily, insofar as the germs which would be pathogenic for the environment during the spreading of the compost 3 17 finally obtained are gradually destroyed, because of said temperature which is greater than or equal to 55C C for several days.

 The composition, the high dry matter content, the homogeneity and the fine particle size of the compost 317 obtained at the end of the two months of maturation are such that it constitutes a good amendment.

 In addition, the compost 3 1 7 obtained by the process according to the invention is almost odorless. By way of indication, the mass quantity of total nitrogen present in said compost 3 17 is reduced by more than 50% relative to said quantity present in the pig manure 14 initially used.

 It will also be noted that the composting installation I according to the invention is such that no infiltration occurs in the surrounding soil, due to the sheltered and leaktight nature of the soil 10 and the recovery of the drying juices 214 .

 It will also be noted that the total quantity of straw 30 which is spread in accordance with said first example of implementation of the method according to the invention is greater than that which is spread according to existing composting methods. As an indication, it can be close to 50 kg per m2 of floor space 10. With a substantially identical composting surface, the height of each swath 17, 117, 127, 137, 217, 227 is therefore greater than that of the swaths arranged in known installations.

 As a result, the structuring agent or agents 30 are weakened to a lesser extent by the slurry spray 14, compared to the structuring agents spread in existing installations, which improves the homogeneity and consistency of the compost 3 17 obtained.

 In addition, this large height of structuring agents 30 promotes the increase in temperature at the core of the heap 17, 117, 127, 137, 217 during fermentation, hence an acceleration of the latter.

 It also follows from this significant height a better yield from the above-mentioned turning operations, with an identical composting surface.

Claims (10)

 1) A method of composting from a stream of liquid raw material comprising pig manure (14) and at least one solid structuring agent (30), of the type consisting successively in spreading said manure (14) on said or said structuring agents (30), to invert the mixture (17) obtained so as to impregnate said or each structuring agent (30) with slurry (14) and to allow said mixture (17) returned to stand for its maturation, characterized in that 'It consists in using only pig manure (14) for said stream of liquid raw material, and in that it consists in carrying out the above-mentioned composting steps on a sealed soil (10) and under shelter.  2) A composting method according to claim 1, characterized in that it consists in using only straw for said structuring agent (30).  3) A composting method according to claim 1, characterized in that it consists in using a mixture of straw and wood bark for said structuring agents (30). according to respective mass proportions close to 20% and 80%.  4) A composting method according to claim 1, characterized in that it consists in using a mixture of sawdust and wood bark for said structuring agents (30), in substantially identical mass proportions.  5) A composting method according to claim 1, characterized in that it consists in using a mixture of chips, forest chips or green waste for said structuring agents (30).  6) A composting method according to one of claims I to 5, characterized in that it consists in recycling in said stream of liquid raw material the excess liquid manure (14) which has not impregnated said agent or agents structuring (30).  7) Composting installation (1) for implementing the method according to one of the preceding claims, characterized in that it comprises, on the one hand, two parallel lateral spans (3 and 5) which are respectively intended for receiving said mixture (17. 117, 127, 137, 217) for its fermentation and, on the other hand, a median span (4) adjacent to said lateral spans (3 and 5) which is intended to receive the mixture at the end of fermentation (217) with a view to its maturation, the bottom of each span (3, 4, 5) consisting of said sealed floor (10).  8) Composting installation (1) according to claim 7, characterized in that the bottom (10) of each lateral span (3, 5) is provided over its length with means (11) of air diffusion in an upward direction or descending.  9) Composting installation (l) according to claim 7 or 8, characterized in that it comprises at least one turning device (16) which is intended to move longitudinally in each lateral span (3, 5) so as to return said mixture (1 7, 117, 127, 217) during fermentation.  10) Composting installation (1) according to claim 9, characterized in that said turning device (16) comprises a rotor (18) with teeth or blades (19) which is provided with an inverter (24) provided for reverse its direction of rotation, so that it can turn back and forth.