WO2003037826A1

WO2003037826A1 - Fertiliser

Info

Publication number: WO2003037826A1
Application number: PCT/GB2002/004983
Authority: WO
Inventors: Robert Silvestri; Robert Pitour; Paul Llau; Didier Champol
Original assignee: I.T.E. Services Limited
Priority date: 2001-11-02
Filing date: 2002-11-01
Publication date: 2003-05-08
Also published as: AR037174A1

Abstract

A method for producing fertiliser from putrescible waste is disclosed. The method comprises the steps of drying animal waste, collecting the effluent, adding non-animal putrescible waste to the dried waste, grinding the waste mixture, extracting metal particles, analysing the waste mixture, optionally adding the effluent, breaking up biomolecules and rendering heavy metals insoluble in water by mixing the waste with selected additives, removing and washing the vapours generated to form an aqueous solution and adding the aqueous solution to the reaction mixture as desired, screening the waste to obtain waste particles having a predetermined particle size, analysing the resulting product to determine the amounts of selected chemicals therein, and optionally adjusting the amounts of effluent and additives according to the results of the analysis. The biomolecules may be broken up by heat generated by the exothermic chemical reaction of quicklime with water.

Description

FERTILISER

The present invention relates to fertiliser, in particular a method for producing fertiliser from waste materials.

Many natural waste products contain materials which are useful as fertilisers, in particular materials which are sources of nitrogen, phosphorous, potassium and magnesium. Such waste materials include, for example, green and household waste, pig slurry, cattle and sheep manure, shellfish and poultry droppings. A number of methods for processing waste are known, including compost manufacture, liquid/solid separation techniques, acidification, worm digestion, furnace drying, fermentation, mineralisation and denitrification. The nitrogen (N) , phosphorous (as P₂0₅) , and potassium (as K₂0) content of some types of waste materials are shown in Table 1 below:

The term "poultry manure" refers to poultry waste which includes straw, whereas the term "poultry droppings" refers to poultry waste which does not include straw.

Nitrogen promotes foliage growth in plants, phosphorous root and flower development, and potassium resistance to adverse environmental conditions, insects, and disease, and taste in fruit. Other elements which facilitate plant growth and development are, in lesser amounts, magnesium, calcium, sulphur, boron, chlorine, iron, manganese, zinc and cobalt.

Synthetic chemical fertiliser usage and waste management are increasingly becoming topics of public and political concern, with increasing emphasis being placed on natural (so-called "organic") fertilisers and waste recycling.

The present invention seeks to provide a method for producing fertiliser which contains soil enriching chemicals for enhancing plant growth and development, which fertiliser has improved environmental impact and is produced from putrescible waste. Herein "putrescible waste" comprises waste selected from green and household waste, guano, poultry droppings, peat moss, and animal manure and slurry.

According to the present invention in a first aspect there is provided a method for producing fertiliser from putrescible waste, which method comprises the steps of: a) drying animal waste in a dryer by evaporation by blowing gas therethrough under pressure at ambient temperature or higher; b) collecting gaseous and liquid effluent, and removing the dried waste; c) adding non-animal putrescible waste to the dried waste obtained from step b) in a grinder; d) grinding the waste mixture of step c) in the grinder; e) extracting metal particles or objects from the ground waste mixture from step d) ; f) analysing the waste mixture from step e) to determine levels of humidity, and amounts of selected chemicals present in the waste mixture; g) optionally adding liquid effluent collected in step b) according to results of the analysis in step f) ; h) breaking up biomolecules and rendering heavy metals present in the waste insoluble in water by mixing the waste with selected additives and reacting with the same at a temperature and for a time sufficient to break up the biomolecules and render the heavy metals insoluble in water; i) removing vapours generated during the reaction of step h) , and washing the same and/or gaseous effluent removed in step b) to form an aqueous solution, and adding the aqueous solution to the reaction mixture of step h) as desired; j) screening the waste from step i) to obtain waste particles having a predetermined particle size; and k) analysing the resulting product to determine the amounts of selected chemicals therein, and optionally adjusting the amounts of liquid effluent and additives added in steps g) , and h)and i) respectively according to the results of the analysis.

In steps a) and b) of the first aspect of the present invention, animal waste is dried by evaporation, gaseous and liquid effluent are collected, and dried waste is removed. Drying of the animal waste is conveniently achieved by introducing the waste into a drier, for example a hopper, and blowing gas therethrough at ambient temperature or higher. The gas is preferably air, and may conveniently be injected into the drier through openings in the lower part thereof.

Gaseous effluent is conveniently extracted at the upper part of the drier, and passed to a washer for use in the aqueous additive of step i) . The gaseous effluent will typically comprise, for example, ammonia, amines, and mercaptans. The liquid effluent is conveniently collected at the bottom of the drier, by running down into a suitable collector, for possible use as an additive in step g) .

The dried waste is preferably collected and removed from the drier to storage using an extruder. The extruder is preferably placed in a lower part of the drier to collect and remove successive layers of waste as it dries under action of the pressurised gas.

In steps c) and d) , the dried waste collected from step b) is introduced into a grinder, together with non-animal putrescible waste, for example household and green waste, and peat moss. The grinder grinds the waste mixture to a desirable particle size, suitable methods for which are known to those skilled in the art. The ground waste preferably has a particle size of substantially 50mm or less.

In step e) , metal particles or objects are extracted from the ground waste mixture from step d) . Metal particles and objects may contaminate the fertiliser produced by the present method, and may cause damage to or malfunctions of the apparatus used to perform the present method. Any conventional method for extracting metal particles or objects, both magnetic and non- magnetic, may be used in step e) , for example eddy current techniques, electromagnetic techniques, a chute or drum separator, a perma or lifting plate, or an overband.

The waste is preferably passed through a second grinder between steps e) and f) , for example to obtain a waste particle size of substantially between 5 and 10mm.

In step f) , the waste resulting from step e) is analysed to determine levels of humidity (i.e. water content), and amounts of selected chemicals therein. In particular, the amounts of carbon, nitrogen, hydrogen, oxygen, sulphur, phosphorous, potassium, chlorine and calcium present in the waste are preferably measured. The measured amounts of the selected chemicals in the waste are compared to the desired amounts of the selected chemicals in the resulting fertiliser, and in step g) liquid effluent collected in step b) can be added and mixed with the waste to adjust the amounts of the selected chemicals in the resulting fertiliser if desirable.

In step h) , the waste from step g) passes to a reactor to chemically react the waste with additives to break up biomolecules and trap heavy metals present in the waste.

Biomolecules as defined herein includes proteins , peptides , fats , carbohydrates , polysaccharides , glycerophospholipids , DNA, RNA, and other molecules which participate in the natural processes of living tissues found in putrescible waste . The biomolecules are broken down in order to avoid bacterial development .

The biomolecules are preferably broken down by hydrolysis at elevated temperature up to 105 °C, more preferably by means of an exothermic reaction . A preferred exothermic reaction is that between calcium oxide (quicklime) and residual water contained in the waste :

CaO + H₂0 -> Ca (OH) ₂ ΔH = -15 . 4 kcal

The energy evolved by this reaction heats the waste and residual water, which breaks down biomolecules. The amount of quicklime required for the reaction is determined by the amount of residual water contained in the waste, which is measured in step f) . The energy emitted by this reaction, and the consequent amount of water vaporised, can be calculated from the enthalpy of reaction for the reaction given above, the specific heat of the waste (approximately 1 cal/g/°C) , and the enthalpy of vaporisation of water (9.726 kcal/mol), as will be apparent to those skilled in the art. Of course, any suitable unstable chemical reagent which is able to perform an exothermic reaction with the waste may be employed; however, quicklime is preferred due to its effectiveness and low cost.

Heavy metal pollutants, for example mercury and cadmium, in particular heavy metal oxides, typically enter the food chain by virtue of their solubility in leaching water. In the present method, these metals are rendered insoluble, thus trapping them in the waste. Preferably, complexes of the heavy metals are crystallised in aluminosilicates, for example a heavy metal complex can be enclosed in a matrix obtained by crystallisation with a silicic acid derivative. Thus, heavy metals are not removed from the waste in the method of the first aspect of the present invention, but are prevented from entering the water table by leaching water by being rendered insoluble, i.e. effectively rendered non-toxic.

In step i) , noxious vapours generated during the reactions of step h) are removed from the reactor. These vapours may be eliminated by reaction with additive reagents, or may be washed to form an aqueous solution and added to the reaction mixture of step h) . Additionally or alternatively, the gaseous effluent removed in step b) may be washed to form the aqueous solution. Sulphur-containing noxious gasses, for example, such as hydrogen sulphide and sulphur dioxide, may be eliminated by reaction with calcium hydroxide (lime) to form calcium sulphate (gypsum) . In addition, ammonia may be reacted with sulphuric acid to form an aqueous solution of ammonium sulphate. Ammonium sulphate is used as a fertiliser and can hence be used as an additive to further enrich the waste.

The amounts of reagents and additives used in steps h) and i) can be varied so as to adjust the pH of the fertiliser, according to the intended use of the fertiliser. For example, barley and sugar beet require a soil pH of 6.8 to 8, wheat 6 to 7.5, potatoes and oats 5 to 7, and rye 4.5. The additives used in steps h) and i) will also depend upon the N, P and K content of the waste resulting from steps b) and c) . The basic amounts of N, P and K present in the waste are largely determined from steps b) and c) . For example, poultry manure contains high amounts of N, P₂0₅ and K₂0 compared to putrescible household waste. Thus, additional additives are may not be required, or may be added in lesser amounts, for the former compared to the latter, other than for the purposes of obtaining the desired pH for the product fertiliser.

The reactions of steps h) and i) will typically be performed for 1 to 4 hours, preferably 2 to 3 hours, and preferably at a temperature of up to 105°C.

In step j ) , the waste is screened to obtain particles having a predetermined particle size. The screening is preferably performed in two stages, a first stage to separate the lighter fractions from the heavier fractions (for example, 10mm particle diameter or less) , and a second stage to obtain a particle size of predetermined size (for example 5mm diameter or less) . Screening may be performed by such methods as are conventional in the art, for example rotary and mesh screening.

In step k) , the resulting product from step j) is analysed to determine the amounts of selected chemicals therein. In particular, the nitrogen, phosphorous, potassium, and magnesium content of the product is measured. The analysis results are used to adjust the amounts of liquid effluent and additives used in steps g) , and h) and i) respectively, in order to obtain a product having particular chemical characteristics. The analysis results are preferably fed into a managing computer, which automatically adjusts the amounts of said additives added to the waste during the present method according to predetermined additive mixtures.

According to the present invention in a second aspect there is provided a method for rendering heavy metals present in a fertiliser water insoluble to prevent in use the heavy metals from entering the water table via leaching water, which method comprises crystallising complexes of the heavy metals in aluminosilicates.

The present invention will now be described in detail by way of example, with reference to the accompanying drawings, in which:

Figure 1 is side view of a drier for use in the method of the first aspect of the present invention.

Figure 2 is a cross-sectional view through line b-b in Figure 1.

Figure 3 is a flow diagram of the method of the first aspect of the present invention. - sa in step a) of the method of the first aspect of the present invention, animal waste is dried in a dryer by evaporation by blowing gas therethrough under pressure at ambient temperature or higher. A preferred dryer is shown in Figures 1 and 2.

Referring to Figure 1, the dryer 1 has an opening 4 through which the animal waste to be dried is introduced into the dryer 1. Pressurised air at ambient temperature or higher is injected into the dryer 1 through openings 8 and 9 in a lower part of the drier 1. The drier 1 has a further opening 5 in the upper part thereof for collecting and removing effluent gasses, for example ammonia, amines and mercaptans. The lower part of the drier 1 has a collector 10 for collecting and removing liquid effluent. The dried animal waste is collected and removed from the dryer 1 by an extruder 6, 7, further details of which are shown in Figure 2. Figure 2 is a cross- sectional view through line b-b of Figure 1, and shows the extruder 6, 7 to comprise a central screw 7 and a series of transverse screws 6. The extruder 6, 7 removes dried waste in successive layers as the waste is dried by the pressurised air injected into the dryer 1 through openings 8 and 9.

Referring to Figure 3, the dried animal waste is removed from the drier 1 by the extruder 6,7 into a storage tank 102. The liquid effluent collected from dryer 1 is removed to storage tank 104. From storage tank 102, the dried animal waste is introduced into a first grinder 105. Also introduced into the grinder 105 is non-animal putrescent waste, in particular household and green waste from storage tank 103. The mixture of dried animal waste and non-animal waste is ground in the grinder 105 to a desired particle size. Grinding of the waste mixture increases the surface area of the waste, and hence improves the efficiency of chemical reactions performed later in the present method.

From the grinder 105, the ground waste is transferred on a conveyer belt through a metal remover 106 and an eddy current stand 107, to remove ferrous and non-ferrous metal particles and objects. Metal particles and objects in the waste not only contaminate the fertiliser produced by the present method, but may cause damage to or malfunctions of the apparatus used to perform the method.

The waste is then passed by the conveyer belt into a second grinder 121 to obtain waste having a particle size of between substantially 5 and 10mm.

From the second grinder 121, the conveyer belt then feeds the waste into a first buffer hopper 108 into which liquid effluent can be added from storage tank 104. The waste is mixed in the first buffer hopper 108 for approximately 15 to 20 minutes, and samples of the waste from first buffer hopper 108 are taken for analysis by analyser 115. The samples are tested for humidity (water content) , and amounts of selected chemicals therein, in particular carbon, nitrogen, hydrogen, oxygen, sulphur, phosphorous, potassium, chlorine and calcium. The measured amounts of the selected chemicals in the waste are compared to predetermined desired amounts of the chemicals in the waste, and the liquid effluent in storage tank 104 can be added and mixed with the waste in first buffer hopper 108 to adjust the levels of the chemicals in the waste if desirable. The liquid effluent in storage tank 104 comprises manure, natural putrescible waste, slurry, and effluent from leaching of ground and/or putrescible waste storage percolating water. The humidity of the waste is measured in order to calculate the amount of chemical additive required at a later stage of the process which reacts with the residual water in the waste.

The waste is then passed to a second buffer hopper 109, where chemical additives 116, 117, 118 and 122 are added and mixed with the waste over a period of approximately 15 minutes. Additive 116 comprises CaO (in an amount of 16kg per 800kg of waste), additive 117 comprises CaC0₃ (1/800), Al₂0₃ (2/800) and Si(ONa)₄ (3/800), additive 118 comprises (NH₄)₂S0₄ (in varying amounts), and additive 122 comprises Si(OK)₄ (1/800), H₃P0₄

(5/800), (NH₂)₂CO (urea, 10/800), and HN0₃ (3/800). The compounds of additive 122 may be premixed and added to the waste as a mixture, or may be added to the waste separately.

The additives 116, 117, 118 and 122 adjust the waste to pH 8. The waste is then passed to reactor 110 where it is allowed to react with the additives 116, 117, 118 and 122 for approximately 2 hours. The chemical reactions between the additives 116, 117, 118 122 and the waste break down biomolecules in the waste, and trap heavy metals in the waste. Vapours, mainly ammonia, produced by the chemical reaction are drawn off from the reaction 110 by a ventilator to a two-stage washer 112. Sulphuric acid 119 is added to the washer 112 to react with the ammonia and thus form ammonium sulphate, i.e. additive 118, which can be recycled back into the second buffer hopper 109 to further enrich the waste.

It should be noted that additive 122, or combinations of the compounds included in additive 122, is optional and may not always require adding to the waste. The inclusion or otherwise of additive 122, and amount thereof if included, will depend upon the N, P and K content of the waste, for example as present in storage tank 102, and grinder 105 when mixed with non-animal putrescent waste from storage tank 103. The mixture of waste from storage tanks 102 and 103 determines the basic amounts of N, P and K present in the waste, together with other natural organic waste which enriches the waste from storage tank 104.

After the reaction has completed, the waste is transferred to a rotary screen 111, to separate the light fractions from the heavy fractions, using a 10mm particle diameter cut-off. Separation of light fractions from heavy fractions is completed by then screening the waste against a mesh screen 113, to obtain a granulometry of 5mm or less and provide the product fertiliser of the present method.

Samples of the final product fertiliser are sampled and analysed by analyser 120, and the results are fed into a managing computer, which can automatically adjust the amounts of liquid effluent 104, and additives 116, 117, 118, and 122 added to the waste during the present method if desired. In particular, the nitrogen, phosphorous, potassium, and magnesium content of the product is measured.

Claims

1. A method for producing fertiliser from putrescible waste, which method comprises the steps of: a) drying animal waste in a dryer by evaporation by blowing gas therethrough under pressure at ambient temperature or higher; b) collecting gaseous and liquid effluent, and removing the dried waste; c) adding non-animal putrescible waste to the dried waste obtained from step b) in a grinder; d) grinding the waste mixture of step c)in the grinder; e) extracting metal particles or objects from the ground waste mixture from step d) ; f) analysing the waste mixture from step e) to determine levels of humidity, and amounts of selected chemicals present in the waste mixture; g) optionally adding liquid effluent collected in step b) according to results of the analysis in step f) ; h) breaking up biomolecules and rendering heavy metals present in the waste insoluble in water by mixing the waste with selected additives and reacting with the same at a temperature and for a time sufficient to break up the biomolecules and render the heavy metals insoluble in water; i) removing vapours generated during the reaction of step h) , and washing the same and/or gaseous effluent removed in step b) to form an aqueous solution, and adding the aqueous solution to the reaction mixture of step h) as desired; j) screening the waste from step i) to obtain waste particles having a predetermined particle size; and k) analysing the resulting product to determine the amounts of selected chemicals therein, and optionally adjusting the amounts of liquid effluent and additives added in steps g) , and h)and i) respectively according to the results of the analysis.

2. A method according to claim 1 wherein the gas in step a) is pressurised air.

3. A method according to claim 1 or 2 wherein the gaseous effluent collected in step b) comprises ammonia, amines, and/or mercaptans .

4. A method according to any one of claims 1, 2 or 3 wherein the dried waste is removed from the drier by an extruder.

5. A method according to any preceding claim wherein metal particles and/or objects are removed from the waste in step e) by apparatus which comprises an eddy current stand.

6. A method according to any preceding claim wherein the waste is ground in a second grinder between steps e) and f) .

7. A method according to any preceding claim wherein the biomolecules in step h) comprise proteins, peptides, fats, carbohydrates, polysaccharides, glycerophospholipids, DNA and/or RNA.

8. A method according to any preceding claim wherein the biomolecules are broken up by heat generated by an exothermic chemical reaction.

9. A method according to claim 8 wherein the exothermic reaction is that between quicklime and residual water contained in the waste.

10. A method according to any preceding claim wherein the heavy metals in step h) are crystallised.

11. A method according to any preceding claim wherein the heavy metals are crystallised in aluminosilicates.

12. A method according to any preceding claim wherein the vapours removed in step i) include ammonia.

13. A method according to claim 12 wherein the ammonia is washed with sulphuric acid to form ammonium sulphate.

14. A method according to any preceding claim wherein the additives in steps h) and/or i) are added to the waste to adjust of the amounts of nitrogen, phosphorous and potassium present in the waste, and the pH of the waste resulting from steps f) and g) .

15. A method according to any preceding claim wherein the waste from step j) has a particle size of substantially 5mm or less.

16. A method for rendering heavy metals present in a fertiliser water insoluble to prevent in use the heavy metals from entering the water table via leaching water, which method comprises crystallising complexes of the heavy metals in aluminosilicate .