JPH11228267A - Production of fertilizer from organic sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sanitarily and efficiently produce a fertilizer from an organic sludge with a high moisture content by charging a fly ash as a dehydrating assistant and a deodorizer into the organic sludge, sufficiently mixing both, then dehydrating the resultant mixture and further mixing the sludge after the dehydration with wheat or barley straws, etc., as a fermentation assistant. SOLUTION: A fly ash with >=4 wt.% content of unburned carbon is preferably used. The amount of the charged fly ash based on the organic sludge at a low concentration before dehydration is regulated so as to provide 60-75 wt.% moisture content of a sludge cake after the dehydration and >=50 and <=200 wt.% based on the sludge solid matter expressed in terms of addition ratio based on the organic sludge. After charging the fly ash into the organic sludge, a polymeric flocculant is added thereto. The amount thereof added is preferably 0.3-2.0 wt.% (based on the sludge solid matter). After the dehydration, a fermentation assistant such as wheat or barley straws is mixed so as to afford 55-73 wt.% moisture content of the sludge after the dehydration. The sludge after the mixing is aerobically fermented by a field heaping method, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fertilizer from an organic sludge having a high water content, such as sewage sludge, marine sludge or livestock sludge, in a sanitary and efficient manner.

[0002]

2. Description of the Related Art The amount of sewage sludge generated in Japan is increasing year by year as sewerage spreads, and the amount of sewage sludge is expected to further increase due to the spread of sewerage and promotion of advanced treatment in the future. .

About 99% of sewage sludge is water, and when it is disposed of, it is disposed of after reducing the amount of water by removing water. Generation of the sludge except those incinerated, in one year 1993 is up to about 200 million m ^3. In recent years, sludge has been reduced by incineration and drying, but the amount of dewatered cake has been increasing.

[0004] Currently, about 50% of sewage sludge is disposed of by landfill, but it is increasingly difficult to secure disposal sites especially in large cities. Reduction of sludge by incineration is necessary to extend the life of the disposal site, but it will eventually reach its limit. Rather than disposing of sludge as unneeded matter, regenerating it and using it effectively is not only from the viewpoint of disposal sites but also from the viewpoint of global environmental conservation.・ It will contribute to energy saving. For this reason, there is a strong demand for a method of effectively utilizing sludge.

[0005] As one method of effective utilization, a method of utilizing sludge as a raw material of an organic fertilizer has been known for a long time. This has attracted attention as a recycling farming method.

However, even if sewage sludge, marine sludge or livestock sludge is subjected to dehydration treatment using a polymer flocculant, the water content of the dewatered sludge is as high as 80% or more. The adjustment of water content to lower the water content is an important step. Conventionally, wheat straw, rice husk, rice straw, sawdust, bark
(Bark) etc. have been used. However, since the water content of the dewatered sludge is too high, it has been difficult to adjust the water content suitable for fermentation even with the addition of these water conditioning materials. As a result, aerobic fermentation did not progress and good composting was not achieved in some cases. Therefore, in order to solve this problem, a method for improving the sludge dewatering rate has been desired. In addition, the odor inherent in sludge and the strong odor generated during composting are environmentally
It has become a work problem and this improvement has been desired at the same time.

[0007] Coal is an important energy that accounts for about 30% of the world's primary energy, and has abundant resources,
Due to its economic efficiency, its use is increasing year by year, and the demand for steam coal in 2000 alone is expected to be about 80 million tons in Japan alone. If the ash generation rate at that time is calculated as 16%, the amount of coal ash generation reaches 12.8 million tons. Fly ash accounts for 80 to 90% of the total coal ash. At present, 40 to 45% of coal ash generated by thermal power generation is effectively used, but the rest is landfilled, and it is increasingly difficult to secure landfill sites. In addition, since landfill disposal of coal ash is against the global trend of environmental protection, the development of technology for effective utilization of coal ash is desired as soon as possible. Fortunately, the use of coal ash as a soil conditioner or as a special fertilizer for the supply of essential trace elements such as boron and molybdenum is being established, albeit modestly.

[0008] The present invention is a technique for producing a high value-added product in a sanitary and efficient manner by combining wastes which are increasing more and more. As an example of producing fertilizer using both, as disclosed in JP-A-63-185881, JP-A-57-42785 or JP-A-59-3089, fly ash is added to organic sludge. Alternatively, there is a method of mixing fly ash coarse powder. However,
In these methods, sludge is dehydrated to a water content of about 80%, and then fly ash is charged and mixed. According to this method, the mixing of the sludge and the fly ash becomes uneven, the odor is not sufficiently removed, and the mixing of the fly ash does not exert sufficient power even in composting.
Japanese Patent Publication No. 1-27036 discloses a method of mixing fly ash coarse powder having a low unburned content (unburned carbon content) into a part of dewatered sludge as a dewatering aid, and then adding the rest after dewatering. It has been disclosed. In this invention as well, although the water content is sufficient, there is a possibility that sufficient aerobic fermentation does not occur because fly ash inhibits air permeation into the sludge. Other problems are that the operation is complicated because fly ash is added in two parts, and that fly ash is a fine powder, and when it is added to sludge after dehydration, it generates violent dust. . Japanese Patent Application Laid-Open No. 61-186277 discloses a method in which deodorized sludge (dewatered cake) and fly ash are mixed to remove odor, but the method of adding fly ash to dehydrated sludge results in insufficient mixing. Odors are not uniformly dispersed throughout, so the odor removal is incomplete.

[0009]

[Problems to be solved by the present invention] The present invention aims at increasing the water content of dehydrated sludge, which has been a problem in the conventional method for producing organic fertilizer using organic sludge and fly ash, as described above. An object of the present invention is to produce an effective fertilizer in a short period of time by solving the problem of malodor generation during and after fermentation.

[0010]

Means for Solving the Problems As a result of various studies for achieving the above object, the present inventors have found that fly ash containing 4 to 13% by weight of unburned carbon is added to organic sludge before dehydration as a dewatering aid and The present invention was found to be able to solve the above-mentioned problems by adding as a deodorant, mixing well, and then dewatering, and further mixing the dewatered sludge with wheat fertilizer, rice straw, sawdust, bark (bark), etc. as fermentation aids. Was completed.

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to various organic sludges containing high water content, which are generated in connection with the treatment of wastewater from sewage treatment plants, marine and livestock products or other food processing processes, ie, primary sludge and activated sludge. Applies to mixed sludge, and these digested sludges. The concentration of these sludges in the present invention is preferably from 0.1 to 5% by weight from the viewpoints of transfer, mixing, stirring, etc. Be adaptable.

Next, the fly ash to be mixed with these is ash generated from a pulverized coal boiler or a coal fluidized bed boiler and collected by an electric dust collector, and contains unburned carbon. The unburned carbon content in fly ash is
1% to 40% by weight, depending on the locality and composition of the coal used, the shape at burning (particle size, etc.), or the type of boiler, and the burning conditions (air ratio, burning temperature, etc.) in the boiler Is known to exist. In the present invention, it is preferable to use, of these fly ashes, those having an unburned carbon content in the ash of 4% by weight or more. When the unburned carbon content of fly ash is less than 4% by weight, the control of offensive odor is unstable and incomplete. On the other hand, the upper limit of the unburned carbon content in fly ash is not particularly limited, but if it is 15% by weight or less, it is generated from an extremely common boiler that does not require a special structure or special combustion conditions. However, it is preferable because it can be easily obtained.
In addition, coal ash containing bottom ash or incinerated ash discharged from general incineration equipment may be used if the unburned carbon content in the ash is 4% by weight or more, and the particle size is several mm to several cm. It is possible to apply by separating coarse ones.

The amount of fly ash added to the low-concentration organic sludge before dehydration is such that the moisture content of the sludge cake after dehydration is 60%.
７５75% by weight, and the addition rate to the organic sludge is 50% by weight or more and 200% by weight per sludge solid content.
The following are preferred. If the addition ratio of fly ash to the organic sludge is less than 50% by weight, the moisture content of the dewatered sludge cake becomes 75% by weight or more, causing problems such as handling due to an increase in fluidity and sufficient deodorization of the sludge. And the stench remains. On the other hand, when the addition ratio of fly ash to the organic sludge is 200% by weight or more, the efficiency of the fermentation process after the addition of a fermentation aid to the dehydrated sludge is reduced, so that the compost in a good condition is reduced. This is not preferable because not only the conversion is not performed, but also the amount of dewatered sludge cake to be handled increases.

The addition of the polymer flocculant to be added after the fly ash is added to the organic sludge before dewatering is preferably from 0.3 to 2.0% by weight (solid content relative to sludge) from the viewpoint of economy and effectiveness. . In addition to polymeric flocculants, calcium-based,
An iron-based or aluminum-based inorganic coagulant, waste paper, or the like can be used in combination.

The stirring after the addition of fly ash to the low-concentration organic sludge may be performed to such an extent that the unevenness of the concentration of the mixed slurry is eliminated, and a conventional paddle-type, turbine-type, or propeller-type stirrer can be used.

When the above-mentioned calcium-based, iron-based, and aluminum-based inorganic coagulants and waste paper are used in combination, there is no particular limitation on the timing of their addition, and fly ash to be added to low-concentration organic sludge can be used. It may be either before or after. Regarding the timing of adding the polymer flocculant, it is preferable that fly ash or the like is added to the low-concentration organic sludge and then added after stirring and mixing in terms of the performance of the polymer flocculant.

The dehydration treatment after the addition of fly ash includes a vacuum dehydration filtration device, a pressure filtration device, a centrifugal dehydration device,
Any of a belt press dehydrator, a screw press dehydrator, a multi-disc dehydrator and the like can be applied.

As fermentation aids to be mixed, wheat straw,
There are zeolite, granulated fly ash, and kiln ash in addition to organic matter such as rice husk, rice straw, sawdust, bark (bark), and wood chips. Among these, organic substances that reduce the volume after fermentation, especially from the fact that there are few inorganic components and morphological characteristics,
Wheat straw, rice straw, sawdust, bark and the like, which are easily decomposed themselves, are preferred. These fermentation aids are mixed so that the water content of the sludge after dehydration is 55 to 73% by weight. Although the screw conveyor type was used for mixing the dewatered sludge and the fermentation aid, any other mixing machine for compost may be used.

The sludge mixed with the fermentation aid is subjected to aerobic fermentation by a method using various fermenters such as a rotary kiln type, a multi-stage type, a silo type, an auger type and a bottle type, in addition to the open stacking method. During fermentation, the oxygen concentration in the sludge void is maintained at 2 to 15% by turning back or forced ventilation. 2%
If it is less than 15%, the period required for fermentation will be long. On the other hand, if it exceeds 15%, the energy cost required for ventilation will increase, which is not preferable. There is no particular problem as long as the fermentation temperature is in the range of 40 to 80 ° C, but in order to maintain the composting reaction rate at a high level, 50 to 70 ° C is suitable. In addition, fermentation period, the type of organic sludge and dehydration aid,
Alternatively, depending on the mixing ratio, sludge moisture before fermentation, and fermentation method, in the case of aerobic fermentation, a short one is used.
Although it is about 60 days for a long one, it is not particularly limited because it is necessary to determine an appropriate range according to the situation of fertilization. In addition, anaerobic fermentation can be applied as a simpler method, but in this case, a fermentation period of six months to one year is required.

[0020]

According to the present invention, fly ash is added to low-concentration organic sludge before dehydration, mixed uniformly by stirring, and then dehydrated. Dehydration efficiency is improved by the added fly ash, and at the same time, unburned carbon having deodorizing performance, which is contained in the fly ash by 4% by weight or more, is uniformly dispersed in organic sludge which is a source of offensive odor. Removal is achieved very efficiently. Furthermore, by adding a fermentation aid such as wheat straw after dehydration, a void structure that allows air to sufficiently penetrate into the sludge is formed.
Thereby, the subsequent aerobic fermentation can be stably continued, and the effect of the unburned matter in the fly ash added in the previous step is also combined, and composting in a good state without odor generation is achieved. It is considered something.

[0021]

EXAMPLES The deodorizing performance of fly ash having different unburned carbon contents was measured. The unburned carbon content in the fly ash was determined by a method of pyrolyzing a sample in oxygen to produce carbon dioxide (Maruzen, 4th edition Experimental Chemistry Lecture 15, pages 167 to 172). In addition, JIS A-6201
An approximate value of the unburned carbon content can also be obtained by the method of measuring the ignition loss of the present invention, and the method can be effectively utilized as a fixed simple method.

(Deodorizing performance of fly ash) 2 ml of a 0.1% methyl mercaptan standard solution was placed in a 500 ml gas-cleaning bottle, and one port was connected to a 12 cmφ U-shaped tube.
The concentration of mercaptan was measured by sucking gas with a gas detector tube (manufactured by Gastec). At this time, 3g
Was packed in a U-shaped tube and its deodorizing performance was measured (see FIG. 1).

The results are shown in Table 1 and FIG. clearly,
It can be seen that fly ash having an unburned carbon content of 4% or more has excellent deodorizing performance. In the following Examples and Comparative Examples, fly ash having an unburned carbon content of 4.2% shown in Table 1 was used.

[Example 1] A dewatering test of digested sludge (solid content concentration: 1.7% by weight) was performed in a terminal treatment plant. Here, the effect of fly ash as a dewatering aid and deodorant was confirmed. 11 for solid content of digested sludge
After adding 8% by weight of fly ash, 0.84% by weight of polymer flocculant (based on sludge solids) was added. Subsequently, it was dewatered by a belt press. The water content of the dehydrated cake is 73.
At 6% by weight, there was almost no odor. Table 2 shows the results.
Shown in

Next, 5000 kg of this dewatered sludge and a water content of 1 kg
500 kg of 0 wt% wheat straw was mixed by a screw conveyor type mixer to prepare a composted sample.

The composting test was carried out using a test box (2 m ^{3 in} capacity) whose periphery was covered with a heat insulating material. The composted sample was put into a test box and composted.
Truncation was performed on days 25, 67, and 88, respectively. The temperature of the sample was measured over 100 days. The water content was measured five times during the test. The odor concentration was measured at the beginning and at the end of composting. The results are shown in FIGS.

[Comparative Example 1] A composting test was conducted by a method in which fly ash, which is usually performed in a final treatment plant, was not added during dehydration. First settled sludge (solids concentration 4.0% by weight) to digested sludge (solids concentration 1.7% by weight)
Was added thereto, and a polymer coagulant was added thereto at 0.78% by weight (based on sludge solid content), followed by dehydration with a belt press. The water content of the dehydrated cake was 80.9%, and the odor was not completely removed. Table 2 shows the results.

5,000 kg of the same dewatered sludge as in Comparative Example 1, 500 kg of fly ash and 500 kg of wheat straw having a moisture content of 10% by weight were mixed by a screw conveyor type mixer to prepare a composted sample (Table 3).

The test for composting was carried out using the same test box as in Example 1, and the test was repeated, and the measurement of temperature, moisture content, and odor concentration was performed at the same interval days as in Example 1. The results are shown in FIGS.

[Comparative Example 2] A composting test was performed using the same composting sample as in Comparative Example 1 (Table 3).

Next, 5000 kg of the dewatered sludge and a water content of 1 kg
500 kg of 0 wt% wheat straw was mixed by a screw conveyor type mixer to prepare a composted sample.

The composting test was carried out using the same test box as in Example 1, and the temperature, water content, and odor concentration were measured at the same interval days as in Example 1. The results are shown in FIGS.

Example 2 A dehydration test was performed using the same digested sludge as in Example 1 (solids concentration: 1.7% by weight). After adding 88% by weight of fly ash to the solid content of the digested sludge, 0.87% by weight of a polymer flocculant (solid content relative to sludge) was added. Subsequently, it was dewatered by a belt press. The water content of the dehydrated cake was 73.2% by weight, and the offensive odor was considerably reduced. Table 2 shows the results.

A composting test was carried out in the same manner as in Example 1, and the fermentation was successful, and a high-quality compost was obtained. There was no odor after fermentation.

Example 3 A dehydration test was performed using the same digested sludge as in Example 1 (solids concentration: 1.7% by weight). After adding 176% by weight of fly ash to the solid content of the digested sludge, 0.72% by weight of polymer flocculant (solid content relative to sludge) was added. Subsequently, it was dewatered by a belt press.
The water content of the dehydrated cake was 71.0% by weight, and there was almost no odor. Table 2 shows the results.

A composting test was carried out in the same manner as in Example 1, and the fermentation was successful and a good quality compost was obtained. There was no odor after fermentation.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

[0042]

When the first embodiment is compared with the first and second comparative examples,
Again, the decrease in the water content during the composting period was greatest in Example 1 and Comparative Example 2 was the second. In Comparative Example 1 to which fly ash was not added, the decrease in water content was small even after 100 days of the test (see FIG. 3). Thus, fly ash was also effective in changing the water content due to composting (FIG. 3).

Regarding the odor, the data on the fourth day of composting (Table 4) show that the fly ash was used during dehydration (Example 1) as compared with the one without fly ash (Comparative Example 1). Had the lowest odor concentration, and the mixture containing fly ash after dehydration (Comparative Example 2) also showed a large decrease in odor concentration. By causing fly ash to act on the sludge in this way, the odor inherent in the sludge could be reduced.

When the odor concentration was measured in the same manner after the completion of the composting test (see Table 5), the odor concentrations of Comparative Examples 1 and 2 were considerably lower than those at the beginning of composting. In Example 1, the odor concentration was higher than those in Comparative Examples 1 and 2. However, the odor of Example 1 was an odor generated from actinomycetes unique to compost, indicating that composting was completely achieved.

From these test results, it was found that the composting of sewage sludge was superior to the conventional one by adding fly ash as a dewatering aid during the dewatering of sewage sludge.

As described above, in the method of adding fly ash of the present invention in an amount of 50 to 200% by weight based on the solid content of sludge,
The dewatering property was improved and the water content of the dewatered cake was reduced by about 10% as compared with the usual method of adding the initial settled sludge. Further, the odor was also significantly reduced as compared with the usual method, and although very small amount remained when 88% by weight of fly ash was added, it was completely removed by adding 118% by weight and 176% by weight. Further, in the subsequent composting test, good results were obtained by adding fly ash during dehydration and adding a fermentation aid during fermentation.

As described above, according to the method of the present invention, efficient and good organic fertilizer can be obtained from organic sludge.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 1, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Added

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a diagram showing an apparatus used for deodorization performance measurement.

FIG. 2 is a graph showing the relationship between the unburned carbon content (% by weight) in fly ash and deodorizing performance.

FIG. 3 is a graph showing a temperature change of a sample in a composting test. Also, a graph of the temperature change during the test period is shown.

FIG. 4 is a graph showing a change in water content of a sample in a composting test. ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] April 1, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction contents]

[0042]

When the first embodiment is compared with the first and second comparative examples,
Again, the decrease in the water content during the composting period was greatest in Example 1 and Comparative Example 2 was the second. With respect to Comparative Example 1 to which fly ash was not added, the decrease in the water content was small even after the test for 100 days (see FIG. 4 ). Thus, fly ash was also effective in changing the moisture content due to composting (FIG. 4 ).

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masaaki Kobayashi 2-1-47 Tottori-Minami, Kushiro-shi, Hokkaido Nippon Paper Industries Co., Ltd. Kushiro Mill

Claims (2)

[Claims] 1. A method for producing a fertilizer from organic sludge, comprising the steps of (1) adding fly ash to the organic sludge before dehydration in an amount of 50 to 200% by weight per solid content of the organic sludge, stirring and mixing; 2) Next, a polymer coagulant is added to the mixed sludge in an amount of 0.3 to 2.0% by weight based on the solid content of the mixed sludge, and the mixture is stirred and dehydrated to a water content of 60 to 75% by weight. A step of adding wheat straw, rice straw, sawdust, bark (bark) and the like as fermentation aids to the dehydrated sludge so that the water content of the sludge becomes 55 to 73% by weight, mixing, and fermenting. A method of producing fertilizer from organic sludge. 2. The method for producing fertilizer from organic sludge according to claim 1, wherein the unburned carbon content in fly ash is 4% by weight or more.