JPH09110570A - Production of organic fertilizer and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an organic fertilizer by mixing organic matter to be treated such as sewage sludge with an acidic solution to maintain the pH level of the mixture at pH <7 followed by drying it under heating to retain the effective nitrogen therein, reduce ammonia-nitrogen in wastewater and mitigate the load on a water treatment installation. SOLUTION: First, organic matter to be treated such as dehydrated sludge cake is mixed with an acidic solution in a mixer to adjust the pH value of the mixture to <7. Subsequently, the mixture is dried under heating by use of a dryer to produce the objective organic fertilizer. The steam discharged from the dryer is condensed by a condenser and fed via an effluent tank to a water treatment installation to dispose of the ammonia contained in the condensed water, and the resultant water is discharged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic fertilizer manufacturing method and apparatus for manufacturing organic fertilizer from an object to be treated such as sewage sludge.

[0002]

2. Description of the Related Art Sewage sludge and industrial waste are generally dumped in the ocean or used for landfill after incineration. However, such ocean dumping and incineration pollute the global environment and cause pollution, which is becoming unacceptable.

Therefore, the applicant of the present application tried to produce an organic fertilizer by drying dehydrated sludge by heat treatment for the purpose of utilizing sludge such as sewage sludge on agricultural land.

[0004]

However, during the drying process by the above heat treatment, ammonia nitrogen in sludge is easily released to the gas phase, and the amount of ammonia nitrogen remaining in the sludge after drying is reduced, so that it is effective as a fertilizer component. However, there is a problem that it is not possible to effectively use ammonia nitrogen in a form that is easy for plants to use.

Further, in order to transfer the ammonia nitrogen released in the vapor phase in the drying process of the above-mentioned heat treatment to the condensed water after evaporating from the sludge and drain the condensed water to a river, etc. It is necessary to remove ammonia nitrogen, which is a chemical substance. However, since it is difficult to remove the ammonia nitrogen from the waste water, there is a problem that the load on the water treatment facility becomes large. Nitrogen in the wastewater is an item that has recently been regulated together with phosphorus, and a technique for removing nitrogen in the wastewater is still in the process of being established.

[0006] Therefore, an object of the present invention is to provide an organic fertilizer manufacturing method and apparatus capable of retaining effective nitrogen of an object to be treated and reducing the amount of ammonia nitrogen in waste water to reduce the load of water treatment equipment. To provide.

[0007]

In order to achieve the above object, the method and apparatus for producing organic fertilizer according to claim 1 mix an object to be treated and an acidic solution to obtain the object to be treated and the acidic solution. The method is characterized by comprising a step of adjusting the pH value of the mixture to 7 or less and a step of drying the mixture by heating.

According to the method for producing an organic fertilizer according to the above-mentioned claim 1, in an object to be treated such as sewage sludge, ammonia and ammonium ions are in a dissociation equilibrium state, and p
When the H value exceeds 7, by mixing an acidic solution with the object to be treated and setting the pH value of the mixture to 7 or less,
Since the dissociation constant increases and the amount of ammonium ions increases, the amount of ammonia decreases, so that even if the mixture is dried by heating, almost no ammonia is released into the gas phase. Therefore, to prevent the reduction of ammonia nitrogen in the material to be treated, among organic nitrogen and ammonia attitude nitrogen that are separated as nitrogen components in the fertilizer, treatment after drying the ammonia nitrogen in a form that is easy for plants to utilize. Can be reserved for things. Further, in the drying treatment, less ammonia is released from the mixture to the gas phase, and the amount of ammonia nitrogen transferred to the condensed water after evaporation from the mixture is reduced, so that water for removing ammonia nitrogen is reduced. The load on processing equipment can be reduced.

The organic fertilizer manufacturing apparatus according to a second aspect of the present invention is an apparatus for supplying an object to be processed for supplying an object to be processed, an apparatus for supplying an acidic solution for supplying an acidic solution, and the object to be processed from the apparatus for supplying an object to be processed. And the acidic solution from the acidic solution supply device to form a mixture,
It is characterized by comprising a mixing device for adjusting the pH value to 7 or less, and a drying device for drying the above mixture from the above mixing device by heating.

According to the organic fertilizer producing apparatus of the second aspect, the mixture is mixed with the object to be treated from the object supplying apparatus and the acidic solution from the acidic solution supplying apparatus to form a mixture, The pH value of the mixture is 7 or less. Then, the mixture from the above-mentioned mixing device is heated by a drying device to evaporate water contained in the object to be processed and dry it. At this time, since the pH value of the mixture is set to 7 or less, the dissociation constant increases and the ammonium ion increases, while the ammonia decreases, and the ammonia is hardly released to the gas phase during the drying treatment. Therefore, preventing the decrease of ammonia nitrogen in the above-mentioned processed material,
Ammonia nitrogen can be retained in the dried product. Further, in the drying treatment, the amount of ammonia released from the mixture to the gas phase is reduced, and the amount of ammonia nitrogen transferred to the condensed water after evaporation from the mixture is reduced, so that a water treatment for removing ammonia nitrogen is performed. The load on the equipment can be reduced.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing an organic fertilizer and the apparatus therefor according to the present invention will be described in detail below with reference to the embodiments shown in the drawings.

FIG. 1 is a schematic configuration diagram of an organic fertilizer manufacturing apparatus according to an embodiment of the present invention, in which 1 is a sludge receiving hopper as a processed material supply apparatus for supplying a dehydrated sludge cake obtained by dehydrating sewage sludge. A sulfuric acid tank storing a sulfuric acid solution for pH adjustment, 3 is a kneading machine as a mixing device for mixing the dehydrated sludge cake from the sludge receiving hopper 1 and the sulfuric acid solution from the sulfuric acid tank 2, and 4 is the kneading machine 3 And vegetable oil from the oil tank 7 described below (hereinafter referred to as oil)
And a stirring adjustment tank 5 for stirring and a hydraulic decompression type drying device as a drying device for drying the mixture and oil from the stirring adjustment tank 4 by heating, and 6 a heat treatment by the oil temperature decompression type drying device 5. A centrifuge for separating the sludge and oil that has been separated, 7 stores the oil separated by the centrifuge 6, and the stirring adjustment tank 4 and the oil temperature decompression type drying device 5
Is an oil tank for supplying oil to the pump by a pump 22. Further, 8 is a condenser for cooling the steam from the oil temperature decompression type drying device 5, 9 is a cooling tower for cooling the water circulating in the condenser 8, and 10 is the condenser 8
A pump for draining the condensed water inside, 11 is the condenser 8
A drainage tank for storing water discharged from the pump 10 through the pump 10, a water treatment facility 12 for treating the drainage water from the drainage tank 11, and 13 at atmospheric pressure in the oil temperature decompression type drying device 5 via the condenser 8. It is a vacuum pump that reduces the pressure below.

In the organic fertilizer producing apparatus having the above-mentioned structure, the dehydrated sludge cake is put into the kneading machine 3 from the sludge receiving hopper 1, and the sulfuric acid solution is supplied from the sulfuric acid tank 2 by the pump 21 to form the dehydrated sludge cake in the kneading machine 3. Mix the sulfuric acid solution and adjust the pH value of the mixture to about 6.5. The mixture from the kneader 3 is stirred and adjusted in the tank 4
After that, the mixture and the oil sent from the oil tank 7 by the pump 22 are agitated.

Then, the mixture of sludge and oil from the agitation adjustment tank 4 is introduced into an oil temperature decompression type drying device 5, and the mixture is heated to about 110 ° C. under reduced pressure below atmospheric pressure.
As a result, the water contained in the mixture evaporates and replaces the oil, and the sludge is dried.

Next, the sludge containing the oil discharged from the oil temperature decompression type drying device 5 is deoiled by the centrifugal separator 6.
The dried sludge discharged from the centrifugal separator 6 becomes organic fertilizer, while the oil separated by the centrifugal separator 6 is collected in the tank 7 and reused.

Further, in the oil temperature decompression type drying device 5, the vapor from the oil temperature decompression type drying device 5 is cooled by the condenser 8 and condensed, and the condensed water in the condenser 8 is pumped.
Is drained to the drainage tank 11. Then, the drainage from the drainage tank 11 is treated by the water treatment facility 12.

Ammonia contained in the dehydrated sludge cake before the above treatment maintains dissociation equilibrium as shown in the following formula.

Embedded image For example, when the OH ⁻ ion concentration in the aqueous solution becomes high, that is, when the pH value of the aqueous solution exceeds 7, the equilibrium between the ammonium ion NH ₄ ⁺ and the ammonia NH ₃ in the aqueous solution is biased to the right, and the ammonium ion NH ₄ ⁺ The ratio of ammonia NH ₃ to Furthermore, the water temperature rises, the dissociation constant k is increased, since the equilibrium is biased to the right, ammonia N for ammonium ion NH ₄ ⁺
The proportion of H ₃ increases. Further, when the ammonia NH ₃ is released into the gas phase and is lost, the lost ammonia N 3
Equilibrium is biased to the right to compensate for H ₃ . Moreover, the ammonia NH ₃ solubility in the ammonium ion NH ₄ ⁺ than water since it is low enough equilibrium tilts right, that is, as ammonia NH ₃ is large proportion of ammonia NH ₃
Is released into the gas phase. Therefore, the heat treatment increases the proportion of ammonia NH ₃ and increases the amount of ammonia nitrogen released into the gas phase.

FIG. 2 shows the abundance ratios of ammonia NH ₃ and ammonium ion NH ₄ ^{+ to} the pH value, whereas the ratio of ammonium ion NH ₄ ⁺ to ammonia NH ₃ decreases as the temperature of the aqueous solution increases. As the pH value of the aqueous solution decreases, the ratio of ammonium ion NH ₄ ⁺ to ammonia NH ₃ increases.

Table 1 shows that the pH values in FIG. 2 are 8.5 and 6.
Ammonia NH ₃ and ammonium ion NH _{4 at 0}
^When the sludge at 20 ° C. is heated to 100 ° C., ammonium ion NH ₄ ⁺ is 100% to 96%, ammonia NH ₃ is 0% when the pH value is 6.0.
%, The pH value is 8.5, and the ammonium ion NH ₄ ⁺ changes significantly from 90% to 8% and the ammonia NH ₃ changes from 10% to 92%.

[Table 1] Therefore, in the above-mentioned organic fertilizer manufacturing apparatus, a sulfuric acid solution is mixed with a weakly alkaline dehydrated sludge cake to adjust the pH value of the mixture to about 6.5. The ratio of ammonia NH _{3 to 4} ⁺ becomes about 10% or less at 100 ° C., and in the heat treatment using the oil temperature decompression dryer 5,
Suppress release of ammonia NH _{3 into} the gas phase.

Below, the results of experiments in the organic fertilizer producing apparatus with and without addition of the sulfuric acid solution to the dehydrated sludge cake will be described. The pH value of the mixture of the dehydrated sludge cake and the sulfuric acid solution was set to about 6.5.

Table 2 shows the amount of ammonia nitrogen in the dehydrated sludge cake before the treatment, the fertilizer after the treatment and the condensed water when the sulfuric acid was added (average value after 11 treatments). In addition, the amount of ammonia nitrogen in the condensed water in Table 2 is 20 minutes, 35 minutes, 50 minutes, 65 minutes after the oil temperature decompression type drying treatment is started.
It represents the amount of ammonia nitrogen transferred to the condensed water after a minute. The unit of numerical values in Table 2 is mg / kg.

[Table 2] Further, Table 3 shows the amount of ammonia nitrogen in the dehydrated sludge cake before the treatment, the fertilizer and the condensed water after the treatment when sulfuric acid was not added (average value after 12 treatments). The amount of ammonia nitrogen in the condensed water in Table 3 represents the amount of ammonia nitrogen transferred to the condensed water after 20 minutes, 35 minutes, 50 minutes, and 65 minutes from the start of the oil-temperature reduced-pressure drying treatment. The unit of numerical values in Table 3 is mg / kg.

[Table 3] Based on Tables 2 and 3 above, FIG. 3 shows changes in the amount of ammonia nitrogen in the dehydrated sludge cake and the fertilizer after the treatment when sulfuric acid was added and when sulfuric acid was not added. As can be seen from the change in the amount of ammonia nitrogen shown in FIG. 3, the decrease in ammonia nitrogen in the fertilizer when sulfuric acid is added is significantly suppressed as compared with when sulfuric acid is not added.

Table 4 shows the retention rate of ammonia nitrogen in the fertilizer obtained from Tables 2 and 3 above, and Table 5 shows the retention rate of ammonia nitrogen in condensed water obtained from Tables 2 and 3 above. The release rate.

[Table 4]

[Table 5] Based on Table 5 above, FIG. 4 shows the change in the amount of ammonia nitrogen with respect to the elapsed time from the start of the oil temperature reduced pressure drying process. From the change in the amount of ammonia nitrogen shown in FIG. 4, it can be seen that when sulfuric acid is added, the amount of ammonia nitrogen released is small regardless of the elapsed time.

As described above, by mixing the dehydrated sludge cake with a sulfuric acid solution and setting the pH value of the mixture to about 6.5, the dissociation constant becomes large, and the ammonia NH ₃ ⁺ to the ammonium ion NH ₄ ⁺ is increased. The rate decreases.
Therefore, even if the mixture of the dehydrated sludge cake, the sulfuric acid solution, and the oil is heat-treated by the oil-temperature reduced-pressure drying device 5,
Since the amount of ammonia NH ₃ released into the gas phase is reduced, the dry fertilizer deoiled after the heat treatment should be separated into the organic nitrogen and ammonia nitrogen that are separated as nitrogen components in the fertilizer.
Ammonia nitrogen in a form that can be easily used by plants can be reserved. Further, in the heat treatment by the oil temperature decompression type drying device 5, the amount of ammonia released from the mixture into the gas phase is reduced, and the amount of ammonia nitrogen in the condensed water after evaporation is reduced. The load on the processing facility 12 can be reduced.

Further, since the oil temperature decompression type drying device 5 heats the mixture in the oil, the water in the mixture replaces the oil and the water in the sludge can be efficiently evaporated.

Further, since the mixture is heated under the reduced pressure of atmospheric pressure or less by the oil temperature decompression type drying device 5, evaporation of water in the sludge can be promoted at a relatively low temperature. In addition, since organic matter in sludge is not burned, it is possible to produce high-quality organic fertilizer rich in nutrients.

In the above embodiment, in the oil temperature decompression type drying device 5 as the drying device, the sludge as the object to be treated is heated and dried in oil, but the heating and drying method by the drying device is not limited to this. Convection heat transfer (warm air) drying, conduction heat transfer drying, radiation conduction drying, etc. may be used.

Further, in the above embodiment, the dehydrated sludge cake and the sulfuric acid solution are mixed, and the pH value of the mixture is about 6.
The pH value of the mixture was adjusted to 5 so that the ratio of ammonia NH ₃ to ammonium ion NH ₄ ⁺ was 100.
It may be an appropriate value of 7 or less, which is about 20% or less at ° C.

Further, in the above-mentioned embodiment, the sulfuric acid solution as the acidic solution was mixed with the sludge as the material to be treated, but the acidic solution is not limited to this, and inorganic acid, organic acid (eg citric acid)
It doesn't matter.

In the above embodiment, the sewage sludge is treated as the object to be treated, but the object to be treated is not limited to this, and may be garbage, manure, industrial waste or the like.

[0030]

As is apparent from the above, in the method for producing organic fertilizer according to the first aspect of the invention, the pH value of the mixture of the material to be treated and the acidic solution is 7 by mixing the material to be treated and the acidic solution. Since it is set as follows, the dissociation constant of ammonia and ammonium ions in the dissociation equilibrium state in the mixture becomes large, and the ammonium ions increase while the ammonia amount decreases. Then, when the above mixture is heated, the amount of ammonia released into the gas phase is reduced, so that the reduction of ammonia in the mixture is prevented. Therefore, even if the above mixture is dried by heating, almost no ammonia is released into the gas phase, so that reduction of ammonia nitrogen is prevented and effective nitrogen is retained in the dried product. Further, in the drying treatment, the amount of ammonia nitrogen contained in the condensed water after being evaporated from the mixture is reduced, so that the load on the water treatment equipment for removing ammonia nitrogen can be reduced.

Further, in the organic fertilizer manufacturing apparatus of the invention of claim 2, the mixing apparatus mixes the object to be treated from the object supplying apparatus and the acidic solution from the acidic solution supplying apparatus to generate a mixture, and After adjusting the pH value of the mixture to 7 or less,
The mixture from the above mixing device is heated by a cooker to evaporate the water contained in the material to be treated to produce an organic fertilizer. At this time, since the pH value of the mixture is set to 7 or less, the dissociation constant increases and ammonium ions increase, while ammonia decreases and the amount of ammonia released into the gas phase during the drying process decreases. Therefore, it is possible to prevent the decrease of ammonia nitrogen in the mixture during the heat treatment and to retain the available nitrogen in the dried fertilizer. Further, since the amount of ammonia nitrogen transferred to the condensed water after being evaporated from the mixture in the drying treatment is small,
It is possible to reduce the load on the water treatment facility for removing ammoniacal nitrogen.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an organic fertilizer manufacturing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing the abundance ratios of ammonia and ammonium ions with respect to pH values.

FIG. 3 is a diagram showing the amount of ammonia nitrogen when sulfuric acid is added and when sulfuric acid is not added, based on the results of experiments by the organic fertilizer manufacturing apparatus of the above embodiment.

FIG. 4 is a diagram showing the amount of ammonia nitrogen in the condensed water for each elapsed time from the start of the oil temperature decompression type drying process, based on the experimental results by the organic fertilizer manufacturing apparatus.

[Explanation of symbols]

1 ... Sludge receiving hopper, 2 ... Sulfuric acid tank, 3 ... Kneader,
4 ... Stirring adjustment tank, 5 ... Oil temperature decompression type drying device, 6 ... Centrifuge, 7 ... Oil tank, 8 ... Condenser, 9 ... Cooling tower, 10, 21, 22 ... Pump, 11 ... Drainage tank, 12 ... Water Processing equipment.

Claims (2)

[Claims] 1. A step of mixing a material to be treated with an acidic solution so that a pH value of the mixture of the material to be treated and the acidic solution is 7 or less; and a step of drying the mixture by heating. A method for producing an organic fertilizer, comprising: 2. An object-supplying device for supplying an object to be processed, an acidic-solution supplying device for supplying an acidic solution, the object to be processed from the object-supplying device and the object to be supplied from the acidic-solution supplying device. A mixing device for mixing the acidic solution and the mixture to form a mixture, the pH value of the mixture being 7 or less, and a drying device for drying the mixture from the mixing device by heating are provided. Characteristic organic fertilizer manufacturing equipment.