FR2632808A1 - Process for the depolluting treatment of liquid manures - Google Patents

Abstract

The present invention describes a process for the treatment of liquid livestock effluents which ensures the deodorisation, sterilisation, removal of antibiotics and pharmaceutical products, flocculation and separation of the solid parts, as well as the reduction in the phosphorus and nitrogen content of the clear liquid part discharged. The clear effluents may be discharged into the natural environment. The sludges may be used for the preparation of compost optionally by mixing with agricultural waste. The process consists in an oxidising treatment of the liquid manures by means of air containing between 0.1 and 5% by volume of nitrogen oxides.

Description

Industrialized pig, sheep and cattle farms, as well as certain fur animals such as mink, pose effluent elimination problems that are all the more difficult to solve as the number of farms increases in number. heads.

The present invention provides an original solution for eliminating pollution from slurry. The present invention provides deodorization, precipitation of solid particles, elimination of mucilage and results in a significant reduction in the chemical oxygen demand. The rejection into the natural environment of the aqueous part of the effluents treated according to the present invention becomes possible because it is sterile, limpid, odorless and poor in fermentable organic matter.

It is known to treat manure by aerobic biological fermentation to ensure the oxidation of foul smelling combinations. It is also known to treat manure in an anaerobic environment to ensure the production of biogas. These operations are carried out in installations similar to those used for wastewater and urban waste.

It is also known to treat fermentable and foul-smelling waste with oxidizing agents, hydrogen peroxide, hypochlorites and even nitrogen oxides.

French patents n07590692 of Nov. 23, 1933 and 784196 of January 15, 1935 describe the action of nitrogen oxides on wet hydrocarbon materials in the presence of phosphate ores.

The same is true for British Patent No. 424,260 dated Feb. 18. 1935 which describes a process for the manufacture of phosphate fertilizer by attacking organic waste and ground phosphate. (French patent application n ° 74 35202 dated Oct. 18.

1974.) French patent n ° 501 668 dated July 16, 1919 indicates the possibility of sterilizing the slushes of the cities using gases containing nitrous gases; French Patent No. 76,135 dated April 30, 1976 recommends the addition of "oxygenated acids H2SO4, - H3 PO4 and HNO3 to organic and mineral materials intended for the preparation of compost. This resulting from aerobic fermentation of the mixture thus acidified. French Patent No. 1,332,433 dated June 4, 1963 mentions the destruction of putrid compounds contained in household waste using gases containing nitrogen oxides. French Patent Application No. 2,574 390 dated December 12, 1984 adds to the sterilizing and deodorizing function of nitrogen oxides that of solubilizing phosphates added to compost.

All these patents relate to the treatment of solid and, if necessary, humidified products. The present invention relates to the treatment of liquid effluents containing less than 20% of dry matter in suspension
The aforementioned patents aim at the preparation of fertilizers or composts. The aim of the present invention is the destruction of the -polluting combinations contained in certain effluents from 'afro industry.

These effluents are particularly polluting and cannot be stored without gene for the neighborhood because of their pestilential odor.

The present invention provides a solution to the odor problem by deodorizing the effluent continuously, as it is produced.

The present invention therefore allows the storage of these effluents for the purpose of treatment or subsequent use without gene for the neighborhood.

The present invention ensures effective separation of the suspended parts because, thanks to a treatment with nitrogen oxides combined with a contribution of salts, the flocculation of the mucilages and excellent coagulation of the sludges are obtained.

These sludges, deodorized and sterilized by the treatment in accordance with the present invention can be used as an agricultural amendment after possible addition of mineral elements intended to improve it. fertilizing power. They can be treated according to the process described in the French patent application nt 84 18966 dated t2 dec. 1984 by nitrogen oxides in the presence of natural phosphates in order to prepare an organomineral nitro-phosphate fertilizer. This sludge can also be treated in biogas generators in order to recover methane. The treatment of effluents according to the present invention has the advantage of destroying all or almost all of the pharmaceutical and veterinary compounds such as residues hormonal and especially antibiotics. Experience shows that industrial farms protect themselves against epizootics by the massive use of antibiotics ;, these products are found in very large quantities in effluents and interfere with aerobic and anaerobic fermentations, often delaying destruction very significantly biological polluting organic constituents.

The clarified effluent, which contains only a small amount of dissolved organic matter, consisting essentially of sugars, has a very low chemical oxygen demand compared to that of the starting effluent. It is, moreover, freed from a large part of the soluble phosphates and of the urea and ammoniacal nitrogen compounds. It is then possible to reject it without damaging the environment in the natural environment.

The present invention relates to the use of nitrogen oxides as an "oxidation, flocculation catalyst and as a bactericidal agent. The present invention relates to the use of very small quantities of these oxides, quantities which can be generated in small equipment dimension, easy to transport and install. It appeared in fact, during research carried out by the inventors, that it was not necessary to use very large quantities of nitrous gas to ensure the treatment of slurry. Low proportion when mixed with air, the nitrogen oxides generated by catalytic oxidation of ammonia, activate the oxygen in the air and make it aggressive with respect to the organic and mineral combinations contained in the slurries.

Treatment of raw slurry with nitrogen weights of the order of 100 ppm already ensures very effective momentary deodorization.

Unlike the previously described methods, there is no need to ensure oxidation, sterilization by the sole effect of oxygen combined with nitrogen. the presence of very small proportions of active oxides in a medium containing nearly 18% of atmospheric oxygen is sufficient to ensure complete treatment of the most foul-smelling organic waste, to deodorize it, to sterilize it and to ensure flocculation.

In addition, the present invention can be oriented, depending on the goal, either on the preparation of a clear effluent, very poor in elements capable of causing eutrophication, or for the preparation of a fertilizing effluent intended for spreading on crops.

Description of the process.

Nitrous gases are prepared by catalytic oxidation by air drawn in by a fan, gaseous ammonia coming from a tank in a catalytic micro-burner. The nitrous gases obtained are diluted 10 to 20 times in a volume of air and brought into contact with the liquid effluents to be treated.

 This contact can be ensured by bubbling in a multicellular pit directly placed at the outlet of the breeding block or, by spraying in a column with trays. This immediate treatment of slurry, before any storage, has several advantages: it ensures decontamination and deodorization, it increases the speed of sedimentation of solid elements. It ensures the destruction or coagulation of most of the colloidal substances, which generate persistent mosses, and it lowers the level of soluble phosphates.

Oxidation is very rapid and the foul odor disappears even before the pH of the material to be treated has started to drop. Used to treat raw and alkaline manure, -Nitrogen oxides deplete these in ammoniacal and urea nitrogen by
simultaneous decomposition of the nitrites formed, into molecular nitrogen. in water and carbon dioxide come from urea. This nitrogen depletion will be sought when the clarified effluents have to be discharged into the natural environment. This depletion will reduce the eutrophication of the rivers receiving the effluents.

It is however possible to neutralize the free alkalinity of the slurry with a cheap mineral acid (hot, H2S04) and not leaving pollutant residues or eutrophication generators The amount of acid necessary for neutralization is of the order of 5 to 8 kg HCI per tonnes of slurry The increase in the saline concentration of clarified effluent which results from it remains too small to be considered as polluting, but in this case, the destruction of the nitrogen, urea, ammonia and amino combinations is less rapid. and this will be used if the manure is to be spread on crops.

The effluents treated and thickened by natural decantation can be mixed with straws or any other absorbent organic waste, sawdust, peat, oil cake, cereal glumes, etc. so as to prepare a compost for market gardening use. This production of compost will be carried out after addition of thermophilic microorganisms according to a known process. The sterilization undergone by the effluents, at the exit of the breeding block, ensures perfect sterility of the product and the absence of any pathogenic germ. It should be noted here that the present invention, by avoiding the accumulation of large quantities of effluents which could contain pathogenic germs, protects farms against epizootics.

The solution which consists in mixing the treated effluents with straw will be chosen for small farms (example 1), in particular for farms combined with grain farms.

The present invention also provides a solution to the treatment of industrial farms which today frequently reach 50,000 heads and which even reach 250,000 stalls for pigs.

Such farms are, under current effluent treatment conditions, extremely polluting and can cause real ecological disasters. A farm of 200,000 pigs produces 83 m3 per hour of slurry or 2,000 m3 per day. The most efficient treatment facilities currently in existence can only remove a third of the pollutants contained in these effluents.

The present invention consists in treating the effluents immediately as and when they are produced (Example 2) in a column comprising three or four # treatment stages. In this column, the slurry is sprayed at the top - by a pump and collected in the tray located below the column. It is taken up by the pump of this tray and recycled by spraying. This maintains a mist of fine droplets of slurry. The quantity of slurry corresponding in volume to the initial supply overflows tray by tray towards the interior tray where it is taken up by pump and sprayed below the previous tray. The gaseous atmosphere is supplied with a gas containing 0.5% of nitrogen oxides. This gas is prepared in the catalytic oxidation furnace from ammonia stored in a bottle and air blown by the fan. The weight of nitrogen oxides injected is calculated so as to bring the pH of the suspension during treatment to a value close to 3. The slurry collected at the bottom of the column is sterilized and becomes odorless or slightly smells organic acids, it has lost much of the original ammonia and urea nitrogen. An addition of the flocculating salts, generally the salts of trivalent cations, is carried out during treatment.

 The treatment column is maintained in slight depression thanks to the fan. It is also this depression which allows the suction of the dilution air. The gases discharged to the atmosphere by the exhaust fan lost any foul odor because they followed all the phases of the treatment by crossing the column by cocurrent with the materials to be treated.

When it is desired to reject the clarified effluents (example 2), the fluid part is set aside for settling. The settling system can be static or dynamic. In the static system, the treated slurry is brought into a settling volume constituted by
several tanks placed in series and of a sufficient volume so that all the sludge has time to settle. The treatment of the slurry by the present invention makes it possible to shorten the duration of the settling. Generally after 48 hours a clear phase appears. This rapid decantation allows treatment with relatively small volumes of equipment.

The laird party may, if the environmental rules require it. undergo aerobic biological treatment by lagooning after sowing with selected ferments: saccharomyces, yeasts, etc., with mechanical oxygenation followed by lagooning with aquatic vegetation. It will then be rejected in a natural environment where it will only cause a tolerable increase in BOD.

Mechanical decantation will use centrifugal thickeners which will allow a clear effluent to flow. The sludge collected, both in mechanical separation and in separation by natural settling, can be used for the preparation of composts for agricultural, horticultural and market gardening according to known techniques.

Example 1 (plank)
A farm farm of 250 pigs delivers 2,500 to 3,000 liters per day of slurry (1).

this is treated in a container with a capacity of 6 m3 consisting of several cells placed in series, by bubbling a gaseous mixture containing 1% of nitrogen oxides generated continuously with a micro ammonia burner (5 ). supplied with air by the fan (3) and the ammonia bottle (4). The duration of treatment reaches 24 hours. The treated effluent is at a pH of 3.5 and it turns out to be odorless and sterile. The exhausted nitrogen oxide gases are released to the atmosphere in (6). The treated effluent is withdrawn by gravity or by pump. It is then mixed with chopped straw # (8) in a screw mixer (9) and swathed (10) to undergo aerobic fermentation. The chopped straw is mixed with a small amount of compost resulting from a previous operation in order to ensure the seeding in ferments. The time necessary for the formation of the compost varies with the ambient temperature but does not exceed a few weeks. The fermentation is favored by the aspiration of air through the reaction mass thanks to perforated pipes placed at the bottom of the swath and put under vacuum using a fan according to a known process.

Example 2 (Plate 2)
An industrial farm of 50,000 places of pigs and 40,000 cattle produces 1000 m3 of slurry each day containing on average 4 to 5% of dry matter. The slurry collected by washing the pens is collected in a pit (1) from where it is pumped (2) to the top of a column (7) in masonry coated internally with epoxy resin.

This column has a dimension of 10 meters in diameter and twenty meters in height.

This column comprises three stages (8), (10), (12) of treatment constituted by trays comprising pump recoveries and overflows. The pumps, one per stage (9), (11), (13) have a nominal flow rate of 300 m3 per hour and spray the product by nozzles arranged laterally so as to ensure a uniform dispersion of the suspension in the empty volume. The product circulates by overflowing from one floor to another. the treatment gases, consisting of air supplemented with nitrogen oxides coming from a continuous ammonia oxidation station comprising: an ammonia stock (4), a blowing fan (3), a catalysis oven (5). These gases are admitted to the upper part of the column after having added air (6). The waste gases, odorless and depleted of NOx, are discharged to the atmosphere by an extractlon fan (14). Salts of trivalent iron and alumina cations are added during treatment; (15) so as to accelerate the coagulation of the mucilages.

The effluent taken up by the last recycling pump (13) is continuously withdrawn and sent to a centrifugal thickener (16). The thick phase is sucked up by the slurry pump (17 and sent to composting (20). The clear phase overflows into the foot pan (18) from where the pump (19) sends it into the natural environment.

The weight of nitrogen required to treat these effluents is 2.5 tonnes per day. or less than 30 grams per head of cattle per day.

Claims (3)

ftevenolsstlons  1) Process for treating agricultural liquid manure, characterized by the oxidizing treatment of  these slurries using air containing quantities of nitrogen oxides between 0.1 and  5% by volume of NOx.  2) Method according to claim 1) characterized in that the effluents thus treated  are deodorized and stripped of their pharmaceutical constituents.  during or immediately after the oxidative treatment.  3) Procedure according to 1) and 2) characterized in that flocculating salts are added to the  of the clear part.  easily flocculate which allows an efficient and fast separation of the solid part and  -4) Process according to 1), 2) and 3) characterized in that the effluents thus treated  clear is depleted in nitrogen and soluble phosphate compounds.  5) Processes according to claims 1), 2), 3) and 4) characterized in that 'effluent  aerobic decomposition of residual organic matter.  the clear effluent can be inoculated with ferments chosen to accelerate the  6) Method according to claims 1), 2), 3), 4) and 5) characterized in that  7) Apparatus for the treatment of slurry according to claims 1), 2),  3), 4), 5) and 6) characterized by the fact that they use as an oxidation activator  nitrogen oxides produced by catalytic oxidation of ammonia and diluted in a  sufficient amount of air.