JPH1119692A - Sewage sludge treatment method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To add a water conditioner and an organic substance as a calorie source to a dewatered cake of sewage sludge and perform fermentation treatment.
Efficient fermentation treatment is performed by easily controlling the amount of input material to the fermenter. SOLUTION: A water conditioner and an organic substance are added to a dewatered cake of sewage sludge having a water content of 75 to 85%, the temperature is maintained at 60 to 80 ° C in a fermenter 1, and the air pipe 3 is stirred by a stirrer 2. Ferment with aeration from. The addition amount is controlled so that the BOD tank capacity load becomes 8 kg-BOD / m ³ · day or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fermenting sewage sludge, and more particularly to a method for treating sewage sludge which is improved so that the fermentation reaction proceeds efficiently.

[0002]

2. Description of the Related Art As a method of fermenting sludge, there is known a method of mixing sludge with sawdust to control the water content and increasing the porosity to promote the growth of aerobic bacteria, thereby performing fermentation treatment (Japanese Patent Application Laid-Open No. Sho. 55-90494).

In such a method for treating sludge, a method for preventing a decrease in the fermentation reaction rate due to an insufficient amount of organic substances and improving the efficiency of fermentation treatment is described in US Pat.
Sawdust 10 per 100 parts by weight of dewatered cake of 5% sewage sludge
To 50 parts by weight and 5 to 30 parts by weight of an organic substance serving as a calorie source such as rice bran, and the temperature is adjusted to 60 to 80 in the fermenter.
A method has been proposed in which fermentation is performed while maintaining the temperature at 0 ° C (JP-A-9-85300).

In the method of treating sewage sludge described in Japanese Patent Application Laid-Open No. 9-85300, an organic substance serving as a calorie source such as rice bran is added, so that even if the decomposition of the organic substance in the sewage sludge progresses, By utilizing the added organic substance as a nutrient source of the microorganism, the heat of the decomposition reaction of the organic substance of the microorganism is sufficiently generated, the temperature in the fermenter is maintained at 60 to 80 ° C., and the rapid decomposition reaction of the sewage sludge is performed. Can be continued. As a result, the volume of sewage sludge can be significantly reduced by a short-time treatment, and it becomes possible to efficiently produce fertilizer using sewage sludge as a raw material.

[0005] Rice bran used as an organic substance serving as a calorie source usually has a high BOD of about 300 mg / g, and this BOD is derived from the oil content in the rice bran and is easily decomposable. In addition, since the bulk specific gravity is about 0.3 and the water content is as low as about 10 to 15%, it is well mixed with the dewatered cake and has an effect of loosening the dewatered cake.

[0006]

In the method of fermenting by adding an organic substance serving as a calorie source such as rice bran, the amount of the organic substance to be added has an optimum range. In some cases, efficient fermentation cannot be performed, and fermentation inhibition may occur.

[0007] For example, if the amount of rice bran added is insufficient, the rice bran cannot function as a nutrient source for microorganisms in the fermenter, so that the temperature in the fermenter does not rise and decomposition of the dehydrated cake does not progress. Conversely, if it is excessively added, microorganisms in the fermenter ingest rice bran to generate decomposition heat and raise the temperature in the fermenter. By deviating from the appropriate growth temperature range, decomposition of the dehydrated cake does not proceed. In addition, surplus rice bran increases the organic matter in the compost product and when applied to soil,
It acts as a fast-acting fertilizer for plants and may inhibit growth. In addition, excessive addition of rice bran naturally leads to a rise in rice bran cost and, consequently, a processing cost.

As described above, since there is a suitable range for the amount of the organic substance added as a calorie source, it is important to exhibit the maximum effect with the minimum amount of addition. Therefore, control of the amount of addition of the organic substance is an important management item in the fermentation treatment. For the same reason, the amount of the dewatered cake and other additives added to the fermenter is also an important management item in the fermentation process.

By the way, in the fermentation treatment of the dehydrated cake, the water content, the C / N ratio, the BOD concentration, and the like after the addition can be considered as indices for controlling the amount of the input to the fermenter. For example, the water content is preferably around 60%. For a dehydrated cake having a high water content, a large amount of additives are added to adjust the water content.
May be insufficient and fermentation may not proceed. Also, C / N
When the ratio (C: total carbon content of easily decomposable organic substance and hardly decomposable organic substance, N: nitrogen) is used as an index, since the substance to be decomposed in fermentation is an easily decomposable organic substance, /
It is necessary to analyze the ratio of the easily decomposable organic substance in the C value of the N ratio, but there is no appropriate analysis method, and it is difficult to control by the C / N ratio. Further, the BOD concentration serves as an index of the mixing ratio between the dehydrated cake and the additive, but does not serve as an index of the input amount.

As described above, conventionally, in a method of treating sewage sludge in which a moisture control material and an organic substance as a calorie source are added to a dewatered cake and fermented, an effective index for determining an amount to be fed into a fermenter. There was no.

The present invention solves the above-mentioned conventional problems, and adds a water conditioner and an organic substance serving as a calorie source to a dewatered cake of sewage sludge having a water content of 75 to 85%, and raises the temperature in a fermenter to 60%. Provided is a method for treating sewage sludge that enables easy control of the amounts of dewatered cake, moisture regulator, and organic substance in a method of fermenting while maintaining the temperature at 〜80 ° C., thereby enabling efficient fermentation. The purpose is to:

[0012]

The method for treating sewage sludge of the present invention comprises the steps of:
In a method for treating sewage sludge in which a water conditioner and an organic substance serving as a calorie source are added and fermentation is performed in a fermenter while maintaining the temperature at 60 to 80 ° C., the BOD tank capacity load of the fermenter is set at 8 kg- BOD / m ³ · day or more (preferably 8 to 1
5 kg-BOD / m ³ · day).

The BOD tank capacity load of the fermenter is 8 kg-BO
The inside of the fermenter is controlled to optimal conditions for fermentation by adjusting the amounts of the dehydrated cake, the water regulator, and the organic substance as a calorie source to the fermenter so as to be at least D / m ³ · day. be able to.

[0014]

Embodiments of the present invention will be described below in detail.

First, a method for calculating the BOD tank capacity load according to the present invention will be described.

In order to determine the capacity load of the BOD tank, first, a dewatered cake to be fed into the fermentation tank, a moisture adjusting material such as sawdust, and an organic substance such as rice bran (hereinafter, these may be referred to as "inputs"). ) And the contents of the fermenter before the introduction of these inputs (hereinafter, may be referred to as “contents before input”). The total BOD amount of the input per day is calculated by the following method.

[0017]

(Equation 1)

Calculated total BOD of input per day
By dividing the amount [B] (kg) by the fermenter capacity (m ³ ) after input, the BOD tank capacity load (kg-BOD /
m ³ ) is required.

In the present invention, the BOD determined in this way is
The input amount of each input is controlled so that the tank capacity load is 8 kg-BOD / m ³ · day or more. This value is 8kg-BO
If it is less than D / m ³ · day, a sufficient fermentation decomposition rate cannot be obtained.
However, the capacity load of the BOD tank is 20 kg-BOD / m ³
Since the fermentation decomposition rate decreases after more than one day, the BOD tank capacity load is 8 to 20 kg-BOD / m ³ · day, especially 8 to
It is preferably 15 kg-BOD / m ³ · day.

In the present invention, the water content [C] (%) of the content after charging calculated by the following method is preferably used as an index of control together with the BOD tank capacity load. Is preferably controlled so that the water content is 50 to 70%, particularly about 60%.

[0021]

(Equation 2)

In the present invention, the sewage sludge contains water 7
Use a dehydrated cake dehydrated to 5 to 85%.
If the water content is higher than 85%, the amount of the water conditioning material added becomes excessive, which is not preferable. Further, making the water content lower than 75% is not preferable because the dewatering treatment cost increases.

As the moisture adjusting material, sawdust, rice husk,
Used paper and the like can be used. Of these, sawdust includes conifers such as cedar, pine, toga, and hinoki, cherry, beech, shii, chestnut,
Broad-leaved trees such as zelkova, katsura, camphor, paulownia, rice, northern timber, lauan,
Various kinds of wood sawdust such as southern lumber such as red lauan, white lauan and yellow lauan can be used.

As organic substances serving as calorie sources, rice bran and oily scum such as rapeseed oil scum, cottonseed oil scum, soybean oil scum, herring sardine, sardine sprouts, silkworm oil scum and the like are suitable. Particularly preferably, rice bran is used.

As described above, the moisture adjusting material and the organic substance
It is added so that the capacity load of the BOD tank is 8 kg-BOD / m ³ · day or more, preferably 8 to 15 kg-BOD / m ³ · day, and the water content of the content is about 50 to 70% after being charged. In a normal case, the mixing ratio of the moisture adjusting material is preferably 5 to 50 parts by weight, particularly preferably 8 to 30 parts by weight, per 100 parts by weight of the dewatered cake. If the amount of the water conditioning material is smaller than this range, the water content of the object to be treated is too large, and is not suitable for the propagation of microorganisms. On the other hand, if the water content exceeds 50 parts by weight, the cost is high and the water content is too low, which is not suitable for the propagation of microorganisms. In addition, the mixing ratio of the organic substance serving as a calorie source such as rice bran is 5 to 3 with respect to 100 parts by weight of the dehydrated cake.
0 parts by weight, especially 5 to 20 parts by weight, is suitable. If this organic substance is less than 5 parts by weight, the fermenter will need
If it cannot be maintained at 0 to 80 ° C. and exceeds 30 parts by weight, on the contrary, it takes time to decompose the organic substance, and the material cost increases.

In the present invention, the dehydrated cake, the water conditioner and the organic substance serving as a calorie source are charged into the fermenter, and the mixture is stirred while being ventilated, thereby allowing the decomposition reaction by the microorganisms to proceed. As this fermenter, various types equipped with a stirring device and an air blowing device can be used.

When the volume in the fermenter is 100 parts by volume, the mixture of the dewatered cake, the water conditioner and the organic substance is 1 part.
It is preferable to introduce these into the fermenter intermittently (preferably at a rate of about once every 1 to 3 days) so as to be about 0 to 40 parts by volume.

Basically, the amount of ventilation into the tank is adjusted so that the temperature in the tank is maintained at 60 to 80 ° C. and the water content is maintained.

[0029]

The present invention will be described more specifically with reference to the following examples.

Example 1 A sewage sludge dewatered cake was treated using the vertical scoop fermentation apparatus shown in FIG. In this vertical scoop fermentation apparatus, a rotary agitator 2 is movably installed in a steel plate or concrete fermentation tank (deposition height 1.5 to 2.5 m) 1. The stirrer 2 is moved in the horizontal direction while supplying air from the air pipe 3 to mix the material in the tank 1.

The dewatered cake used was obtained by subjecting sewage sludge of the oxidation ditch method to belt press dehydration. The water content and the BOD amount are as shown in Table 1.

Sawdust (broadleaf tree (Nara)) and rice bran having a water content and a BOD amount shown in Table 1 were used as the moisture regulator and the organic substance, respectively.

Table 1 shows the water content and the BOD content of the tank contents before the introduction of these materials.

[0034]

[Table 1]

Dewatered cake, sawdust and rice bran were charged from the upper part of the tank 1 at 400 kg, 40 kg and 40 kg, respectively. The content before charging was 700 kg.

Switching was performed at a rate of 2 to 3 times / day, and removal was performed by carrying out a part of the processing while carrying out the switching. Aeration rate is 100 to 200 L / m
in (per 1 m ^{3 of} fermentation tank).

At this time, the capacity load of the BOD tank is 8 kg-B
OD / m ³ · day, water content of the contents is 55%
Met.

Thus, the temperature in the fermenter could be maintained at 60 to 80 ° C.

The same procedure was followed except that the BOD tank capacity load was changed as follows, and the BOD tank capacity load and organic matter decomposition rate (decomposition rate of dry matter in the input material per day (% / day)
Was replaced by ) Was obtained, and the results are shown in FIG.

Examples 2 to 6 and Comparative Example 1 For comparison, the same procedure as in Example 1 was carried out except that the amounts of dehydrated cake, sawdust and rice bran were changed and the BOD load shown in Table 2 was used. As shown in FIG.

[0041]

[Table 2]

As is clear from FIG. 2, the maximum value of the dry matter decomposition rate was obtained around the capacity load of the BOD tank of 8 kg−BOD / m ³ · day. Value.

[0043]

As described above, according to the method for treating sewage sludge of the present invention, the amounts of the dewatered cake, the water regulator and the organic substance as a calorie source to the fermentation tank can be easily controlled to increase the efficiency. Fermentation treatment can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a vertical scoop fermentation apparatus.

FIG. 2 is a graph showing the results of Examples 1 to 6 and Comparative Example 1.

[Explanation of symbols]

 Reference Signs List 1 fermenter 2 rotary stirrer 3 air pipe

Claims (1)

[Claims] 1. A dewatered cake of sewage sludge having a water content of 75 to 85%, to which a water conditioner and an organic substance serving as a calorie source are added, and the temperature is maintained at 60 to 80 ° C. in a fermentation tank for fermentation. In the method for treating sewage sludge, the BOD tank capacity load of the fermentation tank is set to 8 kg-BOD / m ^3.
A method for treating sewage sludge, wherein the treatment time is at least one day.