JPH0724838B2 - Method of composting organic sludge - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for composting organic sludge generated from a human waste treatment plant or the like by aerobic fermentation.

[Conventional technology and its problems]

Aerobic fermentation is the deposition of organic sludge and the like under aerobic conditions and the decomposition of organic matter by the action of aerobic microorganisms into a safer and more stable substance. This aerobic fermentation can be roughly divided into two stages, primary fermentation and secondary fermentation. In the primary fermentation, easily degradable organic substances (low molecular weight carbohydrates, fats, proteins, etc.) having a relatively simple structure are produced. It is mainly decomposed, and then secondary fermentation decomposes hardly-decomposable organic substances having a complicated structure (polymeric hemicellulose, cellulose, etc.). When organic substances are decomposed, carbon dioxide (CO ₂ ) is eventually
And ammonia gas (NH ₃ ) is generated.

By the way, in the aerobic fermentation, the temperature in the fermenter rises to a high temperature of 60 to 80 ° C. due to the heat of fermentation in the stage of the primary fermentation, but conventionally, the fermentation was carried out in the high temperature state.

The high-temperature fermentation has the advantage that a product with a low water content can be obtained because the sterilization can be performed and the water evaporation rate becomes large, but it has the following drawbacks.

First, high temperature fermentation has a problem that the fermentation temperature is slow. This is because even a thermophilic degrading microorganism has a markedly attenuated activity at a temperature of 70 ° C or higher and hardly appears at a temperature of 75 ° C or higher.

Second, high temperature fermentation has a problem that the odor of NH ₃ gas is terrible. This is because the NH ₃ gas generated by the decomposition is once dissolved in the water in the raw material in the form of NH ₄ ⁺ ions, but when the temperature becomes high, it is released again in the form of NH ₃ gas.

Therefore, the present invention is intended to provide a fermentation method capable of increasing the fermentation rate of the primary fermentation and suppressing the emission of NH ₃ gas.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention is configured such that the primary fermentation is carried out in two stages of a low temperature fermentation process at 60 ° C or lower and a high temperature fermentation process at 60 ° C or higher.

[Action]

As mentioned above, when low temperature fermentation is performed at a temperature of 60 ° C or lower,
Since the activity of microorganisms is active, the fermentation rate is fast, and the decomposition of easily decomposable organic substances is almost completed in the low temperature fermentation process.

Therefore, the high temperature fermentation process performed after the low temperature fermentation process may be a short period of time as a process for sterilization.
It is possible to minimize the emission of NH ₃ gas.

〔Example〕

 Examples of the present invention will be described below.

According to the present invention, primary fermentation in aerobic fermentation is divided into two steps, a first step and a second step, and the first step accelerates the fermentation rate and operates a low odor by low-temperature fermentation at 60 ° C or lower, and then 60% for sterilization. High temperature fermentation is performed at a temperature of ℃ or higher.

The adjustment of the fermentation temperature in the fermenter is performed by the amount of air blown into the fermenter. That is, oxygen is required for aerobic fermentation, and air is blown into the fermenter as a carrier gas for evaporating water by the heat of fermentation, so the amount of air blown is large in the low-temperature fermentation process. By doing so, the fermentation temperature is lowered. In the low-temperature fermentation step, the amount of blown air is adjusted to be higher or lower so that the fermentation temperature is 60 ° C. or lower, preferably 40 to 50 ° C. ~ 20 times. On the other hand, the amount of air blown in the high temperature fermentation step is preferably as small as possible within the range where the oxygen deficiency state is not caused, because heat is not taken out by air and the temperature becomes high. When the decomposition rate of organic substances in the low-temperature fermentation process is high and the temperature is difficult to rise in the high-temperature fermentation process, the exhaust gas from the low-temperature fermentation zone in the fermenter is blown directly into the high-temperature fermentation zone, or the air blown by a heat exchanger is used. Should be raised.

The number of days of fermentation in the low temperature fermentation step may be 3 to 5 days, which is about 1/3 of the number of days required for the conventional primary fermentation, because the activity of microorganisms is higher and the fermentation rate is faster than in the conventional method. Further, the number of fermentation days in the high temperature fermentation step may be about 2 days since this step is for sterilization.

Next, an example in which the present invention is incorporated into a human waste treatment system will be described with reference to the drawings.

In this human waste treatment system, human waste 1 is removed by a residue removal process 2
Using a fine screen (1 mm between the eyes) and a centrifugal dehydrator, not only impurities but also floating organic substances in human urine 1 are collected as much as possible before the biological treatment step 3 to reduce the load of the biological treatment step 3. On the other hand, the residue 4 which contains a large amount of easily decomposable organic matter generated and has a high calorific value is decomposed in an aerobic fermentation tank. Further, in the aerobic fermenter, excess sludge generated in the biological treatment step 3 is dehydrated in the dehydration step 5 together with the above-mentioned sludge.
The cake 6 that has been dehydrated in is added as a raw material. Then, in the aerobic fermenter, the primary fermentation step 7 is performed in two stages of low temperature fermentation and high temperature fermentation, and then the secondary fermentation step 8 is performed to obtain compost.

In addition, in the above-mentioned human waste treatment system, the removal step 2
It is effective to add a coagulant and collect a larger amount of organic pollutants. This is because the higher the collection rate of organic pollutants in the residue removal process 2, the higher the biological treatment process 3
This is because the amount of excess sludge generated in 1 is reduced, and at the same time, it is possible to supply the fermenter with a raw material that easily generates aerobic and has a high calorific value.

〔effect〕

As described above, according to the present invention, the primary fermentation in the aerobic fermentation is performed in two stages of low-temperature fermentation and high-temperature fermentation. Therefore, the fermentation rate is fast, the fermentation days can be shortened, and NH ₃ gas Emissions are small and odor control is easy.

The results of the comparative test between the present invention and the conventional method are shown in Table 1.

In the above comparative test, a small fermenter was used, and human waste was removed by a centrifuge, and the remaining residue (solid content) was mixed with 2 dehydrated cakes of excess sludge and 2 returned composts to ferment them. The initial water content of the raw material was 55%. In this comparative test, the organic matter decomposition rate of the present invention is higher,
The water content of the product was low, and a product superior to the conventional method was obtained. In addition, NH ₃ gas with a high concentration of 1000 ppm is emitted over a long period of 14 days in the conventional method, but in the present invention, it is very low as 50 ppm for 4 days in the low temperature fermentation process and as high as 1500 ppm in the high temperature fermentation process. However, since the process is only for 2 days, the emission amount of NH ₃ gas is extremely smaller than that of the conventional method as a whole.

[Brief description of drawings]

The drawing is a flow sheet of a human waste treatment system incorporating the present invention. 7 ... Primary fermentation process, 8 ... Secondary fermentation process.

Claims (1)

[Claims] 1. A method of composting organic sludge by performing primary fermentation in an aerobic fermenter followed by secondary fermentation, wherein the primary fermentation is performed at a low temperature fermentation step of 60 ° C. or lower and at a temperature of 60 ° C. or higher. A method for composting organic sludge, which is characterized in that the high temperature fermentation process is performed in two stages.