Method for preparing granular fertilizer from manure

The invention relates to a method for preparing a granular fertilizer from manure, comprising the steps of: PA1 i) acidifying the manure; PA1 ii) dehydrating the acidified manure and evaporating the carrier liquid; and PA1 iii) forming granules from the fertilizer obtained. Preferably the manure is acidified using a mixture of nitric acid and sulphuric acid, wherein in the mixture the nitric acid to sulphuric acid ratio is 30-50:70-50. The granulate comprises: ______________________________________ NH.sub.4 --N 1-3% by weight NO.sub.3 --N 1,5-3,5% by weight N-total 5-9% by weight P.sub.2 O.sub.3 -total 2-5% by weight K.sub.2 O-total 3-10% by weight ______________________________________

The present invention relates to a method for preparing a granular 
fertilizer from manure. 
In the conversion processes of manure it is important that at much as 
possible valuable products are separated from the manure. In these 
conversion processes most attention is paid to the separation of solids 
from the manure, which solids after drying may be used as a substitute for 
artificial fertilizer. 
A known manure converting process is the so called Promest process, wherein 
first the manure is fermented in a fermentation installation, in order to 
produce biogas. Subsequently solids are removed from the manure fermented, 
which solids form after drying as manure cake a valuable product. Due to 
the fermentation the manure cake comprises a relative low amount of 
organic compounds. These organic compounds in combination with the mineral 
nutrients, nitrogen, phosphorus and potassium, incorporated in the 
fertilizer result in a positive difference of the fertilizer over 
artificial fertilizer. 
OBJECT OF THE INVENTION 
The invention has for its object to provide a fertilizer which is 
agronomically improved over artificial fertilizer, so that as will be 
illustrated below the dose of fertilizer, may be reduced to that of 
artificial fertilizer. 
SUMMARY OF THE INVENTION 
According to the invention this is obtained in that the method according to 
the invention for preparing a granular fertilizer from manure, comprises 
the steps of: 
i) acidifying the manure; 
ii) dehydrating the acidified manure and evaporating the carrier liquid; 
and 
iii) forming granules from the fertilizer obtained.

DETAILED DESCRIPTION OF THE INVENTION 
According to the invention this is obtained in that the method according to 
the invention for preparing a granular fertilizer from manure, comprises 
the steps of: 
i) acidifying the manure; 
ii) dehydrating the acidified manure and evaporating the carrier liquid; 
and 
iii) forming granules from the fertilizer obtained. 
By acidifying the manure, preferably already at the farm, the biological 
degradation of the organic substances present in the manure, is 
substantially avoided. Accordingly the fertilizer according to the 
invention will comprise a relatively high percentage of organic 
substances, generally more than 30 to 40%, preferably about 50% organic 
substances. Next to this the emission of ammonia is strongly reduced. 
For example the manure may be acidified using nitric acid. But for safety 
reasons sulphuric acid is preferred, whereby the formation of ammonium 
nitrate that might be explosive, is avoided. In using sulphuric acid in 
the acidification the composition of the active nutrients nitrogen, 
phosphorus and potassium in the fertilizer is 9-3-6. Using sulphuric acid 
in the acidification, the composition of these active nutrients nitrogen, 
phosphorus and potassium is 6-3-6. An agronomical study showed, that the 
fertilizer possess a phosphate effect which is equal to that of artificial 
fertilizer, whereas the nitrogen effect (mineral and organic nitrogen) is 
about 70% of that of artificial fertilizer. 
Preferably the acidification is carried out using a mixture of nitric acid 
and sulphuric acid because under particular conditions the acidification 
using this mixture improves the agronomical value of the fertilizer. For 
example the acidification may be carried out using a mixture of which the 
nitric acid to sulphuric acid ratio is 30-50:70-50. More preferably the 
nitric acid to sulphuric acid ratio is 35-45:65-55. 
Dependent on the type of manure and on the solid content of the manure, the 
amount of acid added is generally sufficient to result in a pH increase of 
3.5-5.5, more preferably to 4-5, particularly to 4.1-4.3. Generally the 
amount of acid added is 1-10% by weight based on the weight of the manure. 
More preferably the amount added is 1-5% by weight, conventionally 3% by 
weight. 
Additives may be added to the fertilizer in order to adjust the composition 
of the active nutrients and nitrogen, phosphorus and potassium to the 
fertilization advice, the additives comprise sulphates, nitrates and 
potassium salts. 
Because usually the fertilizer obtained is in a powder form, it is 
preferred to granulate the fertilizer. In principle the fertilizer 
granulates spontaneously, but the granulation may be carried out within 
narrow granulate-sized distributions when preferably granulation promoting 
agents are added. These granulation promoting agents comprise for instance 
chalk, molasses, carboxymethyl cellulose and bentonite. In fact these 
additives are binders which bind the fertilizer granules to an 
agglomerate. 
In order to avoid the emission of large volumes of air when the agglomerate 
formed is dried, it is preferred to dry the agglomerate using vacuum 
cooling. Accordingly it is possible to safe significantly on the amount of 
air to be discharged, if necessary the air must be purified, but moreover 
the odour emission is substantially reduced, and the condensation water 
formed may be purified at relatively low costs prior to discharge. 
Preferably the manure is dehydrated according to the so called Greenfield 
process (U.S. Pat. No. 3,855,079, U.S. Pat. No. 4,270,974 and U.S. Pat. 
No. 4,608,120). According to this known process a non-volatile oil is 
added to the manure and the oil slurry formed is dehydrated by evaporation 
using heat, whereafter the oil is removed from the solids by evaporation 
at a temperature of 140.degree.-160.degree. C. Due to this high 
evaporation temperature weed seeds present in the manure are killed, and a 
sterilization takes place which allows a longterm storage of the 
fertilizer or fertilizer granules. Another important advantage is that 
germs containing manure, such as swine fever, may be processed because all 
germs are killed in the sterilization step. 
In this respect it is an additional advantage, that after granulation hair 
which may be present in the manure may be easily removed by sieving. 
The granulate formed has a solid content of more than 80% preferably more 
than 85%, more preferably more than 90%. Generally the granulate 
comprises: 
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NH.sub.4 --N 1-3% by weight 
NO.sub.3 --N 1,5-3,5% by weight 
N-total 5-9% by weight 
P.sub.2 O.sub.3 -total 
2-5% by weight 
K.sub.2 O-total 
3-10% by weight 
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The method according to the invention may be used with many types of 
manure, such as manure which originates from cattle farm, swine farm, 
poultry farm and the like. Generally the manure may have a solid content 
of more than 7%, but the method according to the invention is particularly 
suitable for manure having a higher solid content, such as preferably at 
least 10%, and more preferably to more than 14%. Accordingly the advantage 
is obtained, that in a central manure processing a smaller amount of 
manure is to be transported. Moreover the addition of acid at the farm 
results in a remarkably reduced emission of ammonia. 
Hereafter the method according to the invention will be illustrated further 
with reference to an embodiment in which also the agronomical value of the 
fertilizer prepared is compared to that of artificial fertilizer. 
Bulky waste is removed by sieving from swine manure which prior to storage 
is acidified using nitric acid or a mixture of nitric acid and sulphuric 
acid (40/60) (w/w), whereby the pH of the manure is lowered to pH 4.2. The 
manure acidified was mixed with a water insolvable, liquid paraffin having 
a boiling point of about 180.degree. C. This mixture of manure and 
paraffin was dehydrated by evaporation. The vapor formed was condensated 
in a condensor. The concentrated liquid mixture of manure and paraffin was 
added to a heating vessel, in which at a temperature of about 
180.degree.-190.degree. C. the paraffin was removed by evaporation. If 
necessary remainder paraffin may be removed from the fertilizer obtained 
by steam stripping. After drying the fertilizer obtainer has a residual 
moisture content of about 1.5% and a fineness such that about 28% of the 
fertilizer has a particle size smaller than 100 .mu.m. The bulk weight is 
about 500 g/l. 
Subsequently the fertilizer is granulated. Thereto the fertilizer, if 
necessary additives and granulation promoting agent are added to a 
granulation drum, in which the fertilizer is granulated to a granulate 
having a particle size distribution which very subsequently within 0.5-8 
mm. 
Subsequently the granulate is sieved in order to remove hair and the like. 
Finally the granulate is classified. 
The granulate formed generally has a moisture content of 25-35%, preferably 
32-36%. The temperature of the granulate is dependent on the granulation 
process used, but for instance lies between 80.degree.-100.degree. C. 
Subsequently the granulate is added to a vacuum cooling unit, in which the 
moisture access is readily evaporated by reducing the pressure to about 20 
mBar, and the temperature of the granulate decreases. If the granulate to 
be dried has a temperature which is not sufficiently high, the granulate 
may be conditioned by adding an extra amount of steam. 
Using this vacuum cooling technique the amount of air necessary for drying 
the granulate is substantially reduced, whereas the granulate has an 
optimal abrasion resistance, hardness and capability. It is noted that for 
a sufficient fast drying of the granulate, it is preferred that the 
granulate has a diameter which lies between 1 and 8 mm. Finally if 
necessary, the granulate may be post-dried. 
The table below shows a number of granulation experiments using fertilizer 
which is acidified using a mixture of 40/60 nitric acid/sulphuric acid. 
The fertilizer granulates obtained from manure that is acidified with 
nitric acid (hereafter referred to as fertilizer N) and acidified using a 
mixture of 40/60 nitric acid/sulphuric acid (hereafter referred to as 
fertilizer S) are studied for their agronomical value, using artificial 
fertilizer as a reference. 
Table 2 shows the composition of the fertilizer granulates used. 
The experiments are performed on clay soil and on sand soil. On clay soil 
the crop was consumption potatoes and on sand soil the crop was industrial 
potatoes. 
For each type of soil five fertilizers-N-steps were used, which varied from 
0 to 280 kg nitrogen/ha pro year. Based on a soil test the fertilization 
advice for clay soil was 220 kg nitrogen and for sand soil 210 kg 
nitrogen. 
During the growth season the crop showed very rapidly remarkable 
differences in color. Crop grown on fertilizer products had a color which 
on average was comparable to crop fertilized with 140 kg nitrogen/ha. 
FIGS. 1 and 2 show the results of the field experiments on clay soil for 
the nitrogen content (in % solids) and nitrogen uptake (in kg/ha) at a 
nitrogen dose using artificial fertilizer (0-280 kg/ha) and by 
N-fertilizer and S-fertilizer. The FIGS. 3 and 4 show similar results in 
field experiments on sand soil. 
From these results it is apparent that a mineral nitrogen dose of 100 kg/ha 
in the form of fertilizer corresponds to a nitrogen dose of 140 kg/ha in 
the form of artificial fertilizer. Accordingly the mineral load of the 
soil is lower. 
In the experiments on clay soil using consumption potatoes it was apparent 
that using the N-fertilizer and S-fertilizer the yield of potatoes in 
ton/ha in comparison to that using artificial fertilizer (59.1 ton/ha) is 
increased to 42.2 and 67.2 ton/ha, respectively. 
For industrial potatoes on sand soil the yield in comparison to that using 
artificial fertilizer (46.0 ton/ha) is increased to 48.4 en 48.5 ton/ha, 
respectively. The weight of crop paid for was, in comparison to 67.6 
ton/ha using artificial fertilizer, 67.8 and 66.8 ton/ha, respectively. 
These experiments further show that nitrogen present in the fertilizer is 
remarkably active, whereby not only mineral nitrogen but also organic 
nitrogen is active. This may explain the lower dose of fertilizer 
according to the invention compared to that of artificial fertilizer, in 
order to obtain similar yield results. 
TABLE 1 
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Fertilizer granulates according to the invention 
0 1 2 3 4 5 6 
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Fertilizer (kg) 
-- 2,5 2 2 25 25 25 
Binder (kg) 
-- -- -- 
chalk 30% H.sub.2 O 2,85 
molasse 1,74 
CMC 2 
Bentonite 2,5 
Water (l) -- 1,4 1,23 
0,87 
17,5 11.2 15 
Moisture (%) 
1,5 32,5 36,4 32,4 31 31,4 33,2 
Granulate 
distribution (%) 
8 mm -- -- -- -- 0,9 -- 6,3 
6 mm -- 1,5 -- 0,6 8 3 7,7 
5 mm -- 8 0,9 1,4 19 10 12 
3 mm -- 28 6,5 15 39 29 59 
2 mm 0,2 53 42 72 54 75 82 
1 mm 2 89 93 96 84 84 93 
0,5 mm 22 99,3 99,1 99,4 98,5 96,3 99,1 
&lt;0,5 mm -- 0,7 0,9 0,6 1,5 3,7 0,9 
0,2 mm 58 -- -- -- -- -- -- 
0,1 mm 72 -- -- -- -- -- -- 
&lt;0,1 mm 27 -- -- -- -- -- -- 
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TABLE 2 
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Analysis N-Fertilizer 
S-Fertilizer 
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Dry matter 84,3 97,2 
NH.sub.4 --N 1,76 2,60 
NO.sub.3 --N 3,03 2,10 
N-total 6,90 7,81 
P.sub.2 O.sub.5 -total 
2,80 3,39 
K.sub.2 O-total 5,28 7,99 
Organo-chloropesticides (mg/kg) 
&lt;10 &lt;10 
Polychlorobiphenyls (mg/kg) 
&lt;10 &lt;10 
Cadmium (mg/kg) &lt;1 &lt;1 
Chromium (mg/kg) 39 47 
Copper (mg/kg) 225 245 
Mercury (mg/kg) 0,1 0,1 
Nickel (mg/kg) 21 14 
Lead (mg/kg) &lt;10 &lt;10 
Zinc (mg/kg) 340 345 
Arsenic (mg/kg) 1,1 0,8 
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I claim: 1. Method for preparing a granular fertilizer from manure, 
consisting essentially of the steps of: 
i) acidifying the manure by using a mixture of nitric acid and sulfuric 
acid in the ratio of 30-50:70-50, to achieve a pH of 3.5-5.5 and further 
to an extent necessary to prevent biological degradation of the organic 
substances present in the manure, to generate an acidified manure; 
ii) treating the acidified manure with an organic carrier liquid to form a 
slurry; 
iii) dehydrating said slurry and then evaporating said organic carrier 
liquid; and 
iv) granulating the material remaining after the slurry is dehydrated and 
evaporated. 2. Method as claimed in claim 1, wherein the nitric acid to 
sulfuric acid ratio is 35-45:65-55. 3. Method as claimed in claim 1, 
wherein 1-10% by weight acid is added to the manure. 4. Method as claimed 
in claim 3, wherein 1-5% by weight acid is added to the manure. 5. Method 
as claimed in claim 3, wherein 3% by weight acid is added to the manure. 
6. Method as claimed in claim 1, wherein the manure is acidified to a pH 
of 4-5. 7. Method as claimed in claim 6, wherein the manure is acidified 
to a pH of 4.1-4.3 shortly after its production. 8. Method as claimed in 
claim 1, wherein at least one additive selected from the group consisting 
of sulphates, nitrates and potassium salts is added to the granular 
fertilizer. 9. Method as claimed in claim 1, wherein at least one 
granulation promoting agent is added during step iv). 10. Method as 
claimed in claim 9, wherein said granulation promoting agent is selected 
from the group consisting of chalk, molasses, carboxymethyl cellulose and 
bentonite. 11. Method as claimed in claim 1, wherein the dry manure 
content of the granular fertilizer is more than 80%. 12. Method as claimed 
in claim 1, wherein the dry manure content of the granular fertilizer is 
more than 85%. 13. Method as claimed in claim 1, wherein the dry manure 
content of the granular fertilizer is more than 90%. 14. Method as claimed 
in claim 1, wherein the granular fertilizer includes the following 
constituents: 
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NH.sub.4 --N 1-3% by weight 
NO.sub.3 --N 1,5-3,5% by weight 
N-total 5-9% by weight 
P.sub.2 O.sub.3 -total 
2-5% by weight 
K.sub.2 O-total 
3-10% by weight 
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