FR2686814A1 - Method for treating and upgrading animal waste obtained by soilless industrial farming, such as liquid manure - Google Patents

Abstract

The invention relates to a method for treating and upgrading animal waste, such as liquid manure, characterised in that it comprises the steps consisting in: - receiving (1) the said waste in a storage tank; - flocculating (2) essentially the fermentable material contained in the said waste; - separating (3) the flocculated essentially fermentable materials from the essentially unfermentable materials so as to obtain an essentially organic solid S1 and waste water E1; - precipitating (4) the nitrates and the phosphates contained in the said waste water E1 in the form of magnesium ammonium phosphate so as to obtain an essentially inorganic solid S2 and weakly loaded waste water E2; - separating (5) the said precipitated essentially inorganic solid S2 from the weakly loaded waste water E2.

Description

 Process for the treatment and recovery of animal manure obtained in off-ground industrial farming, such as slurry.

 The agricultural economy of the industrialized countries has for many years been oriented towards the intensive breeding of animals destined either for slaughter or reproduction. The concept of intensive breeding to meet the important needs of the market has revolutionized production techniques and has led to the practice of breeding outside traditional natural surfaces, so as to control more easily the parameters involved in the growth or growth. animal reproduction. This type of farming, called above-ground farming, is now very commonly used both in the poultry sector and in the field of pig or cattle breeding.

 Above-ground industrial farming, although leading to productivity values much higher than those obtained by traditional farming techniques, is not without posing certain problems among which we find the production of manure. These techniques have indeed contributed to the modification of the animal manure compositions, due to the evolution of the nutrients used but especially to the localized concentration of these excrements.

 The problems posed by the concentration of manure of animal origin are particularly increased in the context of the industrial breeding of pigs. Manure is indeed a source of nuisance and, although constituting an excellent fertilizer, it can not be sold in its entirety by this way of valorization.

 Among the nuisances caused by manure, the main consists of the smell that emanates and is likely to prevent the establishment of pig farms near homes. The micro-organisms content of slurry is also a possible source of bacteriological pollution.

 The liquid nature of the slurry and its physicochemical constitution have led to the use of the spreading on the cultivable soils surrounding the production units, as a way of recovery. This technique makes it possible to improve the fertility of the treated soils in a non-negligible way. However, the quantities of materials thus distributed can exceed the acceptance capacities of the grounds and lead to more or less long term to harmful consequences on the environment.

 Pork manure is an intimate mixture of faeces, bristles and food reflux. Slurry may also contain rainwater added to its composition during storage. The volume of manure rejected by a pig depends essentially on the age of the animal and its type of feed. On average, each pig discharges 1 m3 of manure, which leads on average to 2.5 m3 per square meter per year in intensive industrial farms. The physicochemical composition of manure is highly variable and depends, in addition, on the diet and the presentation of food. The physiological stage of development of the animal, however, does not play a very important role, contrary to the nature of the diet. In order to obtain manure that is easier to use, it has been proposed, among other solutions, to modify the nature of the feeds brought to the breeding pigs. It has thus been proposed to reduce the level of phosphates of these foods in order to obtain a slurry less rich in this compound. However, this type of method quickly shows its limits related to the imperatives concerning animal nutrition.

Table 1 shows the average dry matter, total nitrogen and phosphorus contents of pigs and pigs.

<Tb>

<SEP> Parameters <SEP> Sows <SEP> pregnant <SEP> Piglets <SEP> weaned
<tb> Material <SEP> dry <SEP> g / l <SEP> 10.4 <SEP> 8.9 <SEP>
<tb> Nitrogen <SEP> total <SEP> gfl <SEP> 6.5 <SEP> 6.3
<tb> P205 <SEP> g <SEP> 6.5 <SEP> 5.6
<Tb>
Table 1
The amounts of phosphorus and nitrogen are unequally distributed between the solid phase of slurry and the liquid phase. Thus, the average samples of pig manure show that 87% of the total phosphorus is present in the solid phase while 85% of the total nitrogen is present in the liquid phase.

 The physico-chemical composition of slurry varies during storage: the organic matter is degraded and the percentage of mineral matter, relative to the dry matter increases; the amount of ammonium nitrogen increases relative to the amount of total nitrogen.

 In particular, manure application poses problems of contamination of surface water and groundwater. Studies have shown that nitrogen leaching losses in various forms ranged from 5% for 25% spring application to fall or winter application. In regions with a very high incidence of manure spreading, it has also been shown that the spreading operations contribute to the aggravation of the air pollution phenomenon. These studies have led to the regulation of the spreading operations, especially according to the seasons, in order to avoid that these cause an excessive increase of nitrate levels in the environment and of olfactory genes.

 The valuation of slurry as a fertilizer therefore knows limitations due to its nature but also to the quantities produced, often extremely important. Although frequently practicing parallel crops, hog producers generally do not have enough arable land to sell all the manure produced by their livestock.

These producers are therefore faced with a problem of development and management of surplus manure, problems that are reflected at the regional level when the regions practice abundantly intensive industrial livestock above-ground pigs. In order to manage these surpluses, regional slurry banks have been set up to promote regional and inter-regional trade between slurry producers, ie farmers, and users, that is to say growers. The quantities "exported" slurry however remain random and depend on the willingness of the recipients.

 The excrement is a source of nuisance including olfactory and microbiological, so we sought different ways to eliminate or transform the excess quantities of slurry or to purify.

 The first way that can be used to get rid of these surpluses is to destroy them thermally. However, the destruction of such materials leads to energy consumption and possible atmospheric pollution.

 Under the leadership of the competent authorities in the field of agriculture and the environment, other techniques have recently been developed in order to exhaust and / or recover economically the excess quantities of manure.

 These recovery techniques must meet strict standards for discharges into the environment and lead to a richest possible residue of nutrients (nitrogen, potassium, phosphorus) in order to give this residue a significant market value. Their development required the precise study of the manure constitution.

 One of the known manure processing techniques is to ferment the manure so as to draw a gas that can be used to make either steam or electricity and hot water. According to this method, the slurry undergoes a first step of methane fermentation in anaerobic environment. This fermentation step leads to obtaining the gas. The residue resulting from this fermentation is then subjected, for example, to centrifugation so as to obtain a liquid phase and a solid phase. The liquid phase can be purified by biological means while the solid phase undergoes a thermal drying leading to the production of a pulverulent dry residue containing the initial fertilizer elements of the slurry. This technique has the advantage of leading to solid and liquid deodorized residues. However, the energy produced in the form of gas does not cover the needs necessary for the evaporation and drying stages; the treatment is therefore energetically deficit. In addition, this technique, essentially based on biological processes uses voluminous and expensive installations.

 Another technique envisaged for treating excess slurry consists in causing evaporation of the water contained in this manure using a carrier fluid constituted by paraffin. This technique consists in acidifying the slurry to a pH close to 5 so as to render the ammonia it contains non-volatile. The manure thus treated is for example mixed with paraffin. The method then consists of proceeding with the re-incorporation of the water contained in this mixture and then separating the paraffin from the solid by centrifugation. The fog resulting from the evaporation operations can be condensed and the liquid obtained biologically purified. The solid phase obtained consists of dehydrated raw slurry.

 This slurry heat treatment technique has the disadvantage of being a big consumer of energy and requiring large installations.

In addition, it induces the use of paraffin whose total recycling is not ensured, which contributes to increase its cost. Moreover, the dry residue obtained at the end of treatment is not deodorized. It can therefore pose problems of use and constitute a source of nuisance.

 The object of the present invention is to propose a non-destructive method for the treatment and recovery of animal dung obtained in off-ground industrial farming, such as slurry, which does not have the drawbacks of those of the state of the art. In particular, one of the aims of the invention is to propose a non-destructive method for the treatment and recovery of animal dung leading to the production of a waste water freed from most of the phosphorus, nitrogen and suspended matter such as, in particular, micro-organisms.

 The object of the invention is also to propose such a method that can be implemented both in the context of localized units, for example mobile units, comprising a small number of producers, and in the context of centralized units comprising a number of important producers.

 In particular, one of the objectives of the invention is to provide a process that consumes little energy while ensuring the production of readily recoverable by-products.

 Yet another object of the invention is to describe such a process which does not involve any micropollutant treatment and does not lead to the production of any new chemical.

The invention relates to a process for the treatment and recovery of animal dung obtained in off-ground industrial farming, such as slurry. The method according to the invention is characterized in that it comprises the steps of: - receiving said droppings in a storage tank; essentially flocculating the fermentable material contained in said droppings; separating essentially flocculated fermentable materials from essentially non-fermentable materials so as to obtain an essentially organic solid Sl and a wastewater E; precipitating the ammonium ions and phosphates contained in said waste water E1 in the form of ammoniaco-magnesium phosphate so as to obtain an essentially mineral solid S2 and a waste water with little charge Ez .; separating said precipitated essentially inorganic solid S2 from the waste water E2
The known precipitation method of ammonium-magnesium phosphate used in the process is summarized by the following reaction:
Mg2 + + NH4 + + PQ ======> MgNH4PO4
According to STUMM and MORGAN, which studied the precipitation conditions of ammonium-magnesium phosphate in water with zero ionic strength, the precipitation of MgNH4PO4 is favored in alkaline solution and the solubility product of this compound reaches its minimum at pH = 10, 7. According to the law of mass action this reaction must be conducted in the presence of an excess of ammonia or phosphorus.

 The essentially organic solid S1 obtained during the process can be used by the farmer as an amendment on the farmland.

 The S2 solid, almost exclusively mineral, is not fermentable. It contains most of the phosphorus and manure nitrates and can be used as a fertilizer in deficit regions or as a basic component in synthetic fertilizers. Its low moisture content makes it shovelable, storable in silo and granular.

 Preferentially, said step of essentially flocculating the fermentable material contained in said droppings is carried out by adding to said droppings a flocculant in the form of a cationic polymer.

 Also preferably said cationic polymer is selected from the group consisting of polyethylenamines and polyvinylamines.

 Advantageously, said step of separating the essentially mineral solid from the waste water Ez is immediately preceded by a second flocculation step.

 Also advantageously, said second flocculation step is carried out by addition to said effluent water El of a flocculant in the form of an anionic polymer.

 Although it may be envisaged, to carry out the precipitation of ammonium-magnesium phosphate to use any reagent that can serve as a source of magnesium and any source of phosphorus in order to meet the law of In order to produce the reaction, said precipitation step is particularly advantageously carried out by the addition, in basic medium, of magnesium sulphate or magnesium oxide and decadmized phosphoric acid.

Preferably, said ammonia-magnesium phosphate precipitation step is conducted in the presence of lime
The wastewater EZ can be managed with return to the operating soil or, in an interesting way, the process can comprise a complementary step consisting in purifying said wastewater that is not heavily loaded by so-called activated sludge treatment or by lagooning.

 Preferably, said separation steps are carried out on a drip table or filter press. It should be noted that in the case of installations for the centralized implementation of the invention, these separation steps may be carried out by other means, for example centrifugation.

The invention also relates to an installation for carrying out the process characterized in that it comprises a single drip table used to carry out said separation steps on the one hand of the essentially organic solid S1 of the wastewater Et and on the other hand of the essentially mineral solid S2 of the waste water Ez
The invention will be more easily understood from the following description of non-limiting embodiments of the invention with reference to the drawings in which: - Figure 1 represents the flow chart of the treatment process and recovery of animal waste exits industrial breeding according to the invention, in the context of a localized processing unit; FIG. 2 represents a schematic diagram of the process according to the invention including a process for the purification of the wastewater obtained in order to allow their rejection in nature, in the context of a centralized treatment unit.

Example 1
With reference to FIG. 1, the process according to the invention can be carried out at the level of a localized manure treatment and recovery unit made available to a limited number of breeders. This unit can for example be mobile and move from breeding to breeding.

The course of the process, for example for a ton of slurry, is as follows. Slurry is received (1) in a storage tank. The composition of the raw slurry is given in Table 2:

<tb><SEP> Parameters <SEP> Quantity
<tb><SEP> Phosphate <SEP> (P2O5 <SEP> g / kg) <SEP> 2.95
<tb><SEP> Nitrogen <SEP> (N.NH4 + <SEP><SEP> g / kg) <SEP> 6,11
<tb><SEP> Nitrogen <SEP> total <SEP> J <SEP><SEP> g / kg) <SEP> 9.25
<tb> DCOg / kg <SEP> COD <SEP> 84 <SEP>
<tb><SEP> Dry <SEP> Material <SEP> g / kg <SEP> 91
<Tb>
To the raw manure is added a quantity of a cationic flocculating agent: the polymer
Z 78 FS40 sold by the company BETZ Industrie S.As The polymer is diluted to 2 per thousand in the network water or possibly in the wastewater E2 from the ammonia-magnesium phosphate precipitation step (see below). ), which can be recycled. The flocculation step (2), allowing the separation of the fermentable materials from the nonfermentable materials of the binding is carried out by adding to the slurry the diluted solution of the polymer at a rate of 20 ml per 100 g of initial mixture.

 Once the flocculation is complete, the mixture undergoes a separation step (3) so as to obtain a substantially organic solid phase S1 containing the fermentable materials and a waste water E1. The separation takes place on a drip table having a porosity of about 400 μm.

 The treatment of one ton of manure leads to 380 kg of solid S1. This solid phase S1 obtained at the end of this separation can be advantageously used by the producer as an amendment material or be stabilized by composting and / or incorporated into a commercial amendment formulation.

 Waste water E1 has a nitrogen content of 4.53 gAl and a P205 phosphorus content of 1.49 g / l. This waste water is then brought into a reactor in order to undergo a precipitation step (4) ammonium phosphate magnesium in basic medium.

 The precipitation reaction takes place in the presence of an excess of magnesium and an excess of phosphorus. The magnesium source used is magnesia (magnesium oxide) and the phosphorus source is decadmized phosphoric acid H3PO4. 32 kg of phosphoric acid corresponding to 7.5 kg of phosphorus are added to the waste water El, 10 kg of quicklime CaO making it possible to fix the pH of the medium at 9.2 and 19 kg of magnesium oxide. All these reagents are readily available on the market. The pH of 9.2 used reduces the amount of lime to be added to the medium, while allowing the ammonia-magnesium phosphate precipitation reaction to occur. We can choose to use a compound other than quicklime to increase the pH of the medium, such as slaked lime, potash or soda. Other sources of magnesium such as magnesium chloride and other sources of phosphorus such as potassium hydrogen phosphate or dipotassium phosphate, industrial phosphorus residues or station sludge may also be considered. biological dephosphatation especially in the case of tertiary chemical dephosphatation.

 The precipitation reaction (4) is followed by a flocculation step (6) to promote the separation of ammonia-magnesium phosphate precipitated from the medium. This flocculation step (6) is carried out using a flocculant in the form of an anionic polymer.

 The set of reagents must advantageously be added slowly, in particular to prevent the occurrence of foaming.

The mixture obtained after the flocculation can then be easily separated into an essentially inorganic solid mixture 5z and into a waste water with little charge. This final separation step (5) leads to obtaining, for an initial ton of manure, 620 liters of effluent water with low Ex content and from 230 kg to 22% dry matter of essentially mineral solid S2. The composition of the light waste water is given in Table 3.

<tb><SEP> Parameters <SEP> Quantity
<tb> Phosphates <SEP> (P295 <SEP> mgl) <SEP> 50
<tb><SEP> (PYO4 <SEP> izg) <SEP> 22
<tb><SEP> Nitrogen <SEP> (N.NH4 + <SEP>) <SEP> 0.4 <SEP> to <SEP> 0.8
<tb><SEP> Nitrogen <SEP> total <SEP> gas <SEP> 1,02 <SEP>
<tb><SEP> COD <SEP> g / kg <SEP> 15 <SEP> to <SEP> 28
<Tb>

Table 3
The essentially inorganic solid S2 consists mainly of ammonium-magnesium phosphate. Its content of ammonia nitrogen, total nitrogen and phosphate is given in Table 4

<tb><SEP> Parameters <SEP> Quantity
<tb> Nitrogen <SEP> (N.NH4 <SEP> + <SEP> g / kg) <SEP> 10.1
<tb> Nitrogen <SEP> total <SEP> (N <SEP> akg) <SEP> 12.3
<tb> Phosphorus <SEP> P94 <SEP> g / kg <SEP> 22.9
<Tb>
Table 4
Thus the waste water E2 low content contains ammonia nitrogen and phosphates less than 90% to the initial content of the slurry.

This waste water can be easily reused on farms and, as part of the process, can be used to carry out the dilutions of the flocculating polymers. The S2 solid is a recovery product that can for example be used as fertilizer. This solid can be collected and for example exploited outside the surplus zone, or be transformed to be in the form of granules and keep for a long time since it contains only little organic matter, which further increases its field of application.

Example 2
Although it can be reused on a farm, wastewater E2 is still too much to be discharged into the natural environment. In the case of fixed centralized units to which a large number of farmers regularly contribute their slurry production, this wastewater can not be used directly and must therefore be purified. With reference to FIG. 2, the method according to the invention includes, in the same way as the process described in example 1, a stage for receiving slurry (1), followed by a flocculation and separation step (2). ), to obtain an essentially organic solid S and a waste liquid El, then a precipitation step (4) coupled to a flocculation and separation to obtain a waste water
Ex and an essentially mineral solid S2.

 The effluent wastewater Ex is then subjected to a biological treatment to improve the purification by removing residual oxidizable charges (COD), fayote and phosphorus it still contains. This activated sludge stage (7) is carried out by diverting the waste water towards a ventilation tank at which it undergoes alternating nitrifying and denitrifying stages. At the end of this treatment, a solid S3 and a waste water E3 are obtained which has a COD 40 times lower than that of the effluent water Ex and which can then undergo a lagooning stage (8), consisting of this wastewater should be kept in a suitable area for a period of time long enough to allow the natural removal of most of the remaining nitrogen and phosphorus in the effluent. The effluent obtained E4 following this lagooning step has an extremely low nitrogen content of the order of 0.02 kg / m3, a phosphorus level of the order of 0.002 kg / m3 and a COD of about 0.12 kg / m3. It can be rejected in the natural environment.

 The examples described here can not in any case be considered as limiting the invention. It can be envisaged to make multiple modifications without departing from the scope of the invention. In particular, other flocculants as well as other magnesium or phosphoric reagents or other compounds for alkalinizing the medium may be used.

 It should be noted that the invention has the advantage of reducing the germs contained in the treatment discharges, in particular the waste water E2, because this has a pH of the order of or greater than 9, which does not is not conducive to the development of flora.

 It has also been found that the process reduces odors, in particular due to the extraction at the top of the fermentable materials, because of the trapping of ammonia in the ammonia-magnesium phosphate precipitation step, and the fact that the pH is maintained around 9.2, which reduces the stripping and evaporation of ammonia (the pK of NH3 and NH4 + is of the order of 9.2).

Claims (13)

1. Process for the treatment and recovery of animal dung obtained in off-ground industrial farming, such as manure characterized in that it comprises the steps of: - receiving (1) said dung in a storage tank; - flocculating (2) essentially the fermentable material contained in said droppings - separating (3) essentially fermentable materials flocculated substantially non-fermentable materials so as to obtain an essentially organic solid Si and a waste water E1; precipitating (4) the ammonium ions and the phosphates contained in said waste water E1 in the form of ammoniaco-magnesium phosphate so as to obtain an essentially inorganic solid S2 and a waste water with little charge E2 .; separating (5) said precipitated essentially inorganic solid S2 from the waste water E2.  2. A method of treating and recovering animal waste according to claim 3, characterized in that said step (2) of essentially flocculating the fermentable material contained in said droppings is carried out by adding to said droppings a flocculant. presenting in the form of a cationic polymer.  3. Method for treating and recovering animal waste according to claim 2 characterized in that said cationic polymer is selected from the group consisting of polyethylenamines and polyvinylamines.  4. A method for treating and recovering animal dung according to one of claims 1 to 3 characterized in that said step (5) of separating the essentially mineral solid waste water E2 lightly filled is immediately preceded by a second flocculation step.  5. Process for the treatment and recovery of animal waste according to claim 4 characterized in that said second flocculation step (6) is carried out by adding to said effluent water El a flocculant in the form of a anionic polymer.  6. Process for treating and recovering animal dung according to one of claims 1 to 5 characterized in that said precipitation step is carried out by adding, in basic medium, sulfate or magnesium oxide and phosphoric acid. décadmié.  7. A method of treating and recovering animal waste according to one of claims 1 to 6 characterized in that said step (4) for precipitation of ammonia-magnesium phosphate is conducted in the presence of lime.  8. Method according to any one of claims 6 and 7 characterized in that the basic medium is maintained at a pH of about 9.2.  9. A method according to claim 6 characterized in that the decadmitated phosphoric acid is replaced in whole or in part by potassium hydrogen phosphate or dipotassium phosphate, industrial phosphorus residues, or sludge biological dephosphatation station.  10. A method for treating and recovering animal dung according to one of claims 1 to 9 characterized in that it comprises a complementary step of purifying said waste water low E2 by said treatment of activated sludge (7) and / or by lagooning (8).  11. A method for treating and recovering animal dung according to one of claims i to 10 characterized in that said separation steps (3, 5) are conducted on a drip table and / or press filters and / or centrifugal .  12. Installation for carrying out the process according to claim 11 characterized in that it comprises a single separation plant used to carry out said separation steps (3,5) on the one hand part of the essentially organic solid S1 of the waste water E1 and secondly essentially mineral solid S2 of the waste water E2.  13. Use of solid and / or liquid residues from the process according to any one of claims 1 to 11 as products usable for the agricultural land amendment.