Method for producing suspension fertilizer

A high analysis suspension fertilizer containing predetermined amounts of nitrogen and other inorganic plant nutrients is produced from a low plant nutrient-containing organic material, such as animal manure or sewage sludge, by first preparing an aqueous initial suspension of the organic material by admixing with a sufficient amount of water for the organic material to be uniformly dispersed throughout the initial suspension and admixing with the initial suspension a sufficient amount of an acid, such as sulfuric acid, for reacting with the organic material and transforming it into colloidal form, the weight ratio of the acid to the total weight of the organic material in the initial suspension being within the range of about 0.2 to about 2 and the weight ratio of the acid to the total dry weight of the organic material being within the range of about 0.5 to 5. An ammoniacal compound, such as anhydrous or aqueous ammonia, and supplemental compound or compounds for providing the other desired inorganic plant nutrients are added to and admixed with the acidified suspension to produce a finished suspension fertilizer having the desired analysis.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates to methods for producing fertilizers from low plant 
nutrient-containing organic materials and, more particularly, to methods 
for producing liquid, slurry or suspension fertilizers from such 
materials. 
Organic materials and wastes, such as animal manure, sewage sludge, 
industrial organic waste and the like, have been used as fertilizers. Such 
fertilizers contain both inorganic plant nutrients, such as nitrogen and 
phosphorous, and organic materials capable of being broken down to form a 
humus which contains humic acid, fulvic acid and humin, and is desirable 
for conditioning the top layer of soil. For example, the humus enhances 
the capability of the soil to absorb and retain moisture, produces a soft, 
friable soil which improves penetration of air and water into the root 
zone and creates an environment for supporting large population of 
beneficial soil organisms. 
The plant nutrient value of such organic materials and wastes usually is 
quite low, the total amount of inorganic plant nutrients being as low as 
1-5% in some cases. Also, the natural biological process for decomposing 
the organic materials into the desired humus requires a relatively long 
time. Because of the low plant nutrient value and the time required for 
the natural decomposition of the organic materials, synthetic inorganic 
fertilizers are much more widely used. Some of the inorganic materials can 
be leached from synthetic fertilizer during rain or irrigation. In 
addition to not being available as to serve as a plant nutrient, the 
leached inorganic materials can be carried into and pollute waterways. 
II. Prior Art 
Processes for treating organic materials and wastes to accelerate break 
down of the organic material and add inorganic nutrients to form a higher 
analysis fertilizer are known. Wilson U.S. Pat. No. 3,050,383 discloses a 
process for producing a high analysis granular fertilizer from a low 
analysis organic waste material, such as sewage sludge and animal manure, 
by simultaneously admixing with the waste material sulfuric or phosphoric 
acid and an aqueous ammoniacal solution and tumbling the resulting 
reaction mass to form granules. 
O'Neill et al. U.S. Pat. No. 3,966,450 discloses a process for 
simultaneously controlling the odor and increasing the plant nutrient 
value of an animal waste slurry by admixing therewith an aqueous hydrogen 
peroxide solution, adjusting the pH to 4-8 by adding a mineral acid and 
mixing the slurry until the animal waste odor is no longer objectionable 
and ammonia is converted to an ammonium salt. 
O'Donnell U.S. Pat. No. 3,942,970 discloses a process for treating sludge 
filter cake to produce a granular, high nitrogen fertilizer by introducing 
comminuted, partially dried sludge filter cake into a reactor, adding an 
acid to decrease the pH to 3-5 and reacting an alkaline N-methylol-urea 
aqueous prepolymer solution with the partially-dried, acidified sludge, 
while vigorously mixing the sludge particles to complete the reaction and 
conversion of the prepolymer, to produce a granular reaction product 
comprising the condensed polymer and dried sludge. 
Trocino U.S. Pat. No. 3,929,446 discloses a process for producing a 
fertilizer from Douglas fir bark by extracting wax and removing the cork 
from the bark and then blending a water soluble nutrient, such as urea, 
ammonium nitrate or super phosphate, with the remaining matrix. 
Applicant's earlier patent, Robinson U.S. Pat. No. 4,743,287, discloses a 
process for producing a granular or slurry fertilizer product from organic 
materials and wastes by sequentially blending an acid material and a base 
material with the organic material in a sealed reactor and maintaining the 
pressure in the reactor up to 30 psi. A reactor capable of withstanding 
such pressure can be quite expensive to manufacture and maintain 
operational. It also can be difficult to maintain pressure seals at the 
material inlet and outlet and the inlets for the acid and base materials. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a simple and cost effective method 
for producing a high analysis suspension fertilizer from low plant 
nutrient-containing organic materials and wastes. 
Another object of the invention is to provide such a method which can be 
operated at ambient pressure and with relatively short reaction times. 
A further object of the invention is to provide such a method in which the 
suspension fertilizer product contains inorganic plant nutrients which are 
physically and/or chemically attached to the organic material in a manner 
to provide a slow release and resistance to being leached away from the 
organic nucleus when exposed to water. 
Other objects, aspects and advantages of the invention will become apparent 
to those skilled in the art upon reviewing the following detailed 
description and the appended claims. 
The invention provides a method for producing a high analysis suspension 
fertilizer containing predetermined amounts of nitrogen and one or more 
other inorganic plant nutrients from low plant nutrient-containing organic 
materials. An aqueous suspension of a low plant nutrient-containing 
organic material is first prepared by admixing such an organic material 
with a sufficient amount of water to permit the organic material to be 
substantially uniformly dispersed throughout the suspension. The initial 
suspension is admixed with a sufficient amount of an acid, such as 
concentrated sulfuric acid, for reacting with and transforming the organic 
material into a colloidal form and to provide a weight ratio of the acid 
to the total weight of the initial suspension within the range of about 
0.2 to about 2 and a weight ratio of the acid to the total dry weight of 
the organic material within the range of about 0.5 to about 5. The 
reaction of the acid with the organic material is allowed to proceed for a 
time period sufficient for at least a substantial portion of the organic 
material to be transformed into a colloidal form and remain substantially 
suspended in the acidified suspension. An ammoniacal compound, such as 
anhydrous or aqueous ammonia, and one or more supplemental compounds for 
providing inorganic plant nutrients other than nitrogen, such as 
phosphate, potash, calcium, magnesium and other desired micronutrients 
(trace elements) are admixed with the acidified suspension to provide the 
desired analysis in the finished suspension fertilizer. If required, 
sufficient amount of water is added to the acidified suspension to provide 
an amount of organic material, as dry solids, in the finished suspension 
fertilizer within the range of about 2 to about 20 weight %, based on the 
total weight of the finished product after completion of acid reaction. 
The additional water can be added prior to addition of either the 
supplemental compounds or the ammoniacal compound, along with either the 
supplemental compounds or the ammoniacal compound and/or after addition of 
both the supplemental compounds and ammoniacal compound. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
As used herein, the term "low plant nutrient-containing organic material" 
means organic materials capable of being broken down to form a humus and 
employed as an organic plant fertilizer, but containing only small amounts 
of available nitrogen and other inorganic plant nutrients such as 
phosphate, potash and sulfate. Representative examples of such organic 
materials include various types of animal manure, such as cattle, horse, 
swine, sheep and poultry manure, sewage sludge, industrial organic wastes, 
such as waste from vegetable and fruit canning plants, whey, cotton gins 
and paper pulping plants, fish scraps, dried blood, bone meal and other 
materials such as coal, peat, lignite, leonardite, humates, spent mushroom 
compost, soybean meal, peanut hulls, tobacco stems, cocoa shells and the 
like. The method of this invention is particularly effective for treating 
animal manures, either composted or relatively fresh, and various types of 
sewage sludge. 
As used herein, the term "high analysis suspension fertilizer" means a 
fertilizer made from a low plant nutrient-containing organic material and 
having a higher nitrogen content, and in some cases a higher content of 
other inorganic plant nutrients, than the starting organic material. As 
used herein, the term "suspension" means a pumpable liquid containing 
uniformly dispersed colloidal particles of an organic material (with 
nitrogen, and in some cases other inorganic plant nutrients, attached 
after processing in accordance with the invention), which particles may 
settle if the liquid remains quiescent for an extended time period, but 
can be readily returned into a relatively stable dispersed condition by 
recirculating or otherwise agitating the liquid. Thus, the term 
"suspension" does not necessarily mean either a true suspension or a true 
suspension by traditional definitions. 
The organic material is first made into an initial aqueous suspension by 
admixing with a sufficient amount of water to permit the organic material 
to be substantially uniformly dispersed throughout the initial suspension. 
The amount of organic material used is that required to provide a total 
dry weight of organic solids in the finished suspension fertilizer within 
the range of about 2 to about 20, preferably about 3 to about 9, based on 
the total weight of the finished suspension fertilizer. 
The amount of water used for forming the initial aqueous suspension varies 
considerably depending upon the type, consistency and moisture content of 
the organic material being treated and to some extent on the type of 
mixing equipment used. The same criteria is, for the most part, true for 
the particle size of the organic material. Generally, only enough water to 
permit the organic material to be uniformly dispersed throughout the 
initial suspension is used because the reaction time for the acid to 
transform the organic material into colloidal form decreases with an 
increase in solids content of the initial suspension. For example, 
uncomminuted composted cattle manure can be mixed with water in a tank by 
a recirculating suspension pump or a conventional paddle type mixer to 
form a uniformly dispersed suspension having a solids content of about 30 
weight % or more. On the other hand, relatively fresh cattle manure 
usually must be diluted to a solid content in the vicinity of 13 weight % 
before a uniformly dispersed suspension can be formed. Generally, the dry 
solids content of the initial suspension is about 5 to about 50 weight %. 
Harder, more dense organic materials may have to be ground, shredded or 
otherwise comminuted so they can be uniformly dispersed as a suspension. 
After the initial suspension has been formed, an acid capable of reacting 
with the organic material and transforming it into colloidal form is added 
to and blended with the initial suspension, preferably while the initial 
suspension is being agitated. As used herein, the term "colloidal form" 
means that the organic material is broken down into humus and the chemical 
and/or physical properties are changed in a manner to make it capable of 
remaining substantially suspended in water and also receptive to 
attachment with nitrogen and other inorganic plant nutrients subsequently 
added to the acidified suspension. While the specific mechanism of this 
attachment is not fully understood at this time, it appears that some sort 
of bonding or complexing occurs because nitrogen and other inorganic plant 
nutrients remain attached to the organic material in a manner which 
minimizes their movement through the soil after application of the 
fertilizer. 
The acid can be injected into the suspension by a plurality of spargers or 
introduced through a pipe or conduit extending to the bottom of a tank or 
the like. The acid addition can take place in the same tank or container 
in which the initial suspension is formed or in a separate tank or 
container. In either case, the tank or container preferably is vented to 
the atmosphere so that the reaction is carried out at substantially 
ambient pressure, thereby eliminating costs associated with a sealed 
reactor vessel. 
The acid preferably is a mineral acid, such as sulfuric, phosphoric, nitric 
or hydrochloric acid and mixtures thereof. Sulfuric acid is preferred and 
it preferably has a concentration between about 90 and about 98%. The 
amount of acid added is sufficient to transform substantially all organic 
material into a colloidal form. 
To accomplish the desired transformation of the organic material to a 
colloidal form, the weight ratio of the acid to the total weight of the 
initial suspension is within the range of about 0.2 to about 2, preferably 
about 0.4 to about 1.5, and most preferably about 0.7 to about 0.9 and the 
weight ratio of the acid to the total dry weight of the organic material 
is within the range of about 0.5 to about 5, preferably about 1 to about 
3. Generally, at weight ratios of the acid to the initial suspension below 
about 0.2, the reaction time for the acid to transform the organic 
material to a colloidal form is excessively long and at ratios above about 
2, the organic material is adversely degraded and no longer capable of 
providing the desired soil conditioning. Also, at weight ratios of acid to 
the total dry weight of the organic material above about 5, the excess 
acid tends to react with the subsequentially added ammoniacal compound to 
form salts and/or degrade the organic material and, at ratios lower than 
about 0.5, substantial amounts of the organic material are not transformed 
to a colloidal form. 
The reaction of the acid with the organic material is exothermic. The time 
interval for adding the acid varies depending on the particular acid, 
injection system and pump used and the amount of acid added. The 
temperature of the suspension during the addition of the acids usually 
increases to a temperature in the vicinity of 120.degree.-200.degree. F. 
While the temperature of the suspension preferably is controlled by rate 
of acid addition, it is within the scope of the invention to either cool 
or heat the suspension during acid addition. The pH of the suspension 
after adding the acid usually is below 1 and may decrease to about 0.5 and 
even lower. 
After the acid has been added, the reaction of the acid with the organic 
material, with or without mixing, is allowed to proceed for a period of 
time sufficient for all, or at least a substantial portion, of the organic 
material to be transformed to a colloidal form. This usually can be 
determined by observing the acidified suspension to detect when the 
organic material appears to be substantially uniformly suspended 
throughout the acidified suspension. This reaction time varies depending 
on the type and amount of acid used and the type and concentration of the 
organic material in the initial suspension. Generally, the acid reaction 
time is at least 5 minutes, preferably at least 15 minutes and can be up 
to several hours. For example, for an initial suspension containing 
composted cattle manure at a solids content of about 30 weight %, the acid 
reaction time can be about 15 minutes or less. An initial suspension 
containing relatively fresh cattle manure at a solids content of about 13% 
may require an acid reaction time of 24 hours or more. 
The acidified suspension preferably is maintained in a substantially 
quiescent condition during the reaction period following addition of the 
acid. 
After the acid reaction period, a sufficient amount of an ammoniacal 
compound is added to the acidified suspension to provide the desired 
nitrogen content in the finished suspension fertilizer and also adjust the 
pH thereof to an acceptable level. Suitable ammoniacal compounds include 
anhydrous or aqueous ammonia, nitrogen-containing inorganic compounds, 
such as ammonium nitrate, ammonium chloride, ammonium sulfate and ammonium 
phosphate, and organic nitrogen-containing compounds such as urea. 
Anhydrous and aqueous ammonia are the preferred ammoniacal compounds. 
Nitrogen-containing inorganic and organic compounds can be added either in 
a solid form or as a solution. A mixture of one or more ammoniacal 
compounds can be used. When anhydrous or aqueous ammonia is used, it 
preferably is injected into the acidified suspension through one or more 
perforated pipes located near the bottom of a tank holding the suspension. 
This, coupled with the vigorous reaction of ammonia with the acid and 
organic material, usually provides sufficient agitation of the suspension 
to obtain a homogenous mixing of ammonia with the suspension. Solutions of 
inorganic and organic nitrogen-containing compounds can be added in a 
similar manner. 
While the reaction temperature of the suspension during addition of the 
ammoniacal compound is not particularly critical, the ammoniacal compound 
preferably is added at a rate sufficiently slow to maintain the 
temperature of the acidified suspension below about 220.degree. F. so as 
to minimize evaporation. However, this temperature can be allowed to 
increase to a higher level. The rate at which the ammoniacal compound is 
added depends on the particular ammoniacal compound, injection system and 
pump used, the batch size of the suspension and the amount of ammoniacal 
compound added. Generally, this time interval for adding the ammoniacal 
compounds ranges from a few minutes up to one or more hours. 
When anhydrous ammonia is used as the ammoniacal compound, the suspension 
may partially gel during addition. When this occurs, the suspension can be 
agitated to break down the gel and addition of ammonia continued 
thereafter. 
The ammoniacal compound addition can take place in the same tank or 
container in which the initial suspension is acidified for a batch 
operation or in a separate tank or container for a continuous operation. 
In either case, the tank or container preferably is vented to the 
atmosphere so that the reaction of the ammoniacal compound with the 
acidified suspension is carried out at substantially ambient pressure, 
thereby eliminating costs associated with a sealed reactor. 
As mentioned above, the amount of the ammoniacal compound added is 
sufficient to provide the desired available nitrogen content in the 
finished suspension fertilizer and also control the pH of the finished 
suspension fertilizer. This can be determined by calculations and/or 
routine experimentation. In some cases, the nitrogen content of the 
starting organic materials is so low that it can be ignored when 
determining the amount of ammoniacal compound to add. However, for organic 
materials having a nitrogen content of about 2% or more, the amount of the 
existing nitrogen should be taken into account when making such a 
determination. 
The pH of the finished suspension fertilizer can be within the range of 
about 3.5 to about 7, preferably about 6.5 to about 6.8. When the pH is 
below about 3.5, the finished suspension fertilizer usually will not 
contain the desired amount of available nitrogen. When the pH is higher 
than about 7 and anhydrous ammonia is used as the ammoniacal compound, 
free ammonia evolves from the reaction mixture and is wasted. For some 
operations, the appropriate amount of ammonia can be determined by 
detecting for the odor of ammonia above the reaction mixture, measuring 
the pH or adding a measured amount of ammonia. 
Supplemental compounds for providing inorganic plant nutrients, other than 
nitrogen, can be added to the acidified suspension prior to, concurrently 
with or after addition of the ammoniacal compound. Representative suitable 
supplement compounds for providing inorganic plant nutrients include 
phosphoric acid, urea (when necessary to supplement the available nitrogen 
added by the ammoniacal compound), superphosphates (18-20% P.sub.2 
O.sub.5), triple phosphate (45-50% P.sub.2 O.sub.5), ground phosphate 
rock, such as apatite, potash materials, such as muriate of potash (50-60% 
K.sub.2 O), kainite (12.5% K.sub.2 O), calcium, magnesium and compounds of 
trace elements, such as iron, zinc, copper, molybdenum and manganese in 
water soluble form. Like nitrogen, the amounts of other inorganic plant 
nutrients in some organic materials are so low that they can be ignored 
when determining the amounts of supplemental compounds to add. Also like 
nitrogen, the amounts of inorganic plant nutrients in starting organic 
materials may be high enough to require the existing amount to be taken 
into account when determining how much of each supplemental compound to 
add. 
As mentioned above, the amount of water used to form the initial suspension 
preferably is kept to a minimum in order to minimize the acid reaction 
time. Thus, the suspension usually must be diluted with additional water 
to provide the desired amount of organic material, as dry solids, in the 
finished suspension fertilizer. When water must be added to provide such a 
solids content, it is added after completion of the acid reaction. All or 
part of the additional water can be added prior to addition of either the 
supplemental compounds or the ammoniacal compound, along with either the 
supplemental compounds or the ammoniacal compound and/or after addition of 
both the supplemental compounds and the ammoniacal compound. When 
anhydrous ammonia is used, the additional water preferably is added prior 
to the addition of ammonia so as to increase the volume of the reaction 
medium and thereby decrease the time interval for introducing the ammonia. 
The finished suspension fertilizer can be applied in any suitable manner, 
such as by spraying on the surface of the ground in the vicinity of the 
plants to be fertilized, sub-surface injection or spraying on the plant 
foliage. 
After the addition of the ammoniacal compound and the supplemental 
compounds, the resulting suspension may contain unreacted particulate 
materials, such as straw or the like, which are large enough to plug 
passages in the application equipment, such as spray nozzles. In that 
case, such materials can be removed in any suitable manner, such as by 
passing the finished suspension fertilizer through an appropriate size 
screen or other suitable filtering means to remove particles larger than 
the smallest opening in the application equipment. Also, grit and sand can 
be introduced with the starting organic material, particularly animal 
manure. This can be removed by passing the suspension through a strainer 
or grit channel.

The following example is intended to exemplify a preferred embodiment of 
the invention and is not to be construed as a limitation thereof. 
EXAMPLE 
The following formulation is used to prepare 2000 lbs of a 4-4-0(N-P-K) 
suspension fertilizer from a composted cattle manure having a moisture 
content of 17.6 weight % to provide a product containing 4.35 weight % 
organic material as dry solids, based on the total weight of the finished 
suspension. 
______________________________________ 
Formulation for 4-4-0 Suspension 
Fertilizer - Composted Cattle Manure 
Amount, wt %, Based 
Ingredient on total weight of finished product 
______________________________________ 
Dry organic material 
4.35 
Water 68.15 
Sulfuric acid 
12.3 
Phosphoric acid 
7.0 
Soft rock phosphate 
3.5 
Ammonia 4.7 
100.00 
______________________________________ 
105.6 lbs of the composted cattle manure and 184.4 lbs of water are mixed 
together in a tank by recirculation with a suspension pump for 
approximately 2-5 minutes to form an initial suspension with the manure 
substantially uniformly dispersed throughout and containing approximately 
30 weight % dry solids. 246 lbs of 93% sulfuric acid are added to and 
mixed with the initial suspension. 
Mixing is terminated and the reaction mixture allowed to stand for 
approximately 15 minutes or more for the sulfuric acid to complete 
transformation of the organic materials in the manure to a colloidal form. 
Following this reaction period, 140 lbs of phosphoric acid, 70 lbs of soft 
rock phosphate and 1178.6 lbs of water (remaining amount required to 
provide desired dilution) are added to and mixed with the acidified 
suspension. 94 lbs of anhydrous ammonia is injected to the bottom of the 
tank and bubbled into the acidified suspension over a period of 
approximately 20-30 minutes. The weight ratio of sulfuric acid to initial 
suspension is 246/290=0.85 and the ratio of sulfuric acid to dry organic 
solids is 246/87=2.83. The pH of the finished suspension fertilizer is 
6.5-6.8. 
The resulting product can be passed through an appropriate size screen for 
removing unreacted materials, such as a straw, which could clog spray 
nozzles of application equipment and then through a grit channel to remove 
sand and grit introduced with the manure. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of the invention and, without departing from 
the spirit and scope thereof, make various changes and modifications to 
adapt it to various usages.