JPH091194A - Excess sludge treatment method - Google Patents

Abstract

(57) [Summary] [Purpose] Providing an excess sludge treatment method that requires a short number of days for treatment and low chemical and energy input costs. [Structure] Excess sludge treated with alkali without addition of alkali or with an alkali concentration of 0.02 N or less is heated under anaerobic conditions to obtain a solubilized solution, which is then treated with an upflow anaerobic sludge bed method (Upflow Anaerobic Sludge).
A method for treating surplus sludge, which comprises performing high-speed methane fermentation treatment by Blanket Process).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating surplus sludge generated when treating activated sludge.

[0002]

2. Description of the Related Art Excess sludge, which is produced in large quantities when waste water is treated with activated sludge, is treated as industrial waste. Currently, excess sludge is being used as a soil improving material and a composting material, but development of a cheaper treatment method and reduction of sludge generation are important issues. Several sludge reduction methods have been reported, including those already in practical use. Anaerobic digestion is the most widely used method. This is to decompose organic matter in sludge by the action of anaerobic microorganisms containing methane bacteria and convert it into methane and carbon dioxide. This method is an excellent method in that it can reduce the amount of sludge and recover energy at the same time, but it has a drawback that the number of days required for digestion is as long as 35 days and thus a large digestion tank is required. There is also a method of reducing the amount of sludge by improving the dehydration property of the sludge or by drying it, but it is close to the technical limit for dehydration, and drying is effective because it takes too much energy. Absent. On the other hand, solubilize sludge by various methods,
A method for reducing the weight has also been reported. Many have been studied as a pretreatment method for improving the efficiency of the above-described anaerobic digestion method, and examples thereof include anaerobic autolysis, heat treatment, microbial treatment, and ultrasonic treatment. Also, assuming aerobic treatment,
Aerobic autolysis (50 to 87% solubilization by aeration at 25 to 45 ° C) is also reported as a method of solubilizing with an alkali and mixing, and a method of requiring no post-treatment. However, these methods have problems such as long treatment days, high costs of chemicals and input energy, and are not practical.
Patent applications relating to the treatment of excess sludge include Japanese Patent Publication No. 56-42995, Japanese Patent Application Laid-Open No. 53-58377, and Japanese Patent Application Laid-Open No.
2-97698, JP-A-4-326998 and the like.
Japanese Examined Patent Publication No. 56-42995 "Anaerobic digestion method of organic waste" discloses a method of digesting an organic waste (excess activated sludge etc.) by adding an alkali. JP-A-53-
58377 "Method for producing organic fertilizer", the excess sludge in an alkaline solution of 0.5-40% by weight 40-1
It is disclosed that the fertilizer is processed under the condition of 00 ° C. In JP-A-62-97698 "Method of reconstructing and converting sludge", organic sludge having a pH of 10 to 13 and 20 to 90 ° C is used.
The method of converting organic sludge into useful substances by adjusting the above is disclosed. Furthermore, in Japanese Unexamined Patent Publication No. 4-326998 "Method for treating organic sludge", the organic sludge is made alkaline and
A method of treating at 0-100 ° C is disclosed. As a result of examining the techniques of these prior applications, a method of performing alkali treatment at high temperature is disclosed, but the treatment period takes about 10 to 20 days and there is a time problem. Further, there is a problem that it is necessary to use a large amount of alkali treatment liquid of 0.1 N or more even if the same alkali treatment is performed.
Further, there is no disclosure about a comprehensive treatment method of how the solubilized liquid obtained by treating the organic sludge at high temperature with an alkali can be used thereafter.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide an excess sludge treatment method which requires a short treatment time and a low cost of chemicals and input energy.

[0004]

[Structure] The inventors have paid attention to the above problems,
With a smaller amount of alkaline solution than before, for a short time (2-3
To produce a solubilized liquid with an increased organic acid production rate by solubilizing excess sludge, and then use the upflow anaerobic sludge bed method to perform high-speed methane fermentation using the solubilized liquid with an increased organic acid production rate. The problem was to develop a method that can treat excess sludge efficiently by treating with a small amount of alkali and energy as a whole. That is, the present invention
Excess sludge that has been alkali-free or alkali-conditioned with an alkali concentration of 0.02 N or less is heated at 40 to 80 ° C., and the resulting solubilized liquid is subjected to an upflow anaerobic sludge bed method (U
pflow Anaeroic SludgeBla
The present invention relates to a method for treating surplus sludge, which is characterized by performing a high-speed methane fermentation treatment by an nket process. The surplus sludge referred to in the present invention is an organic sludge containing carbon, nitrogen, phosphorus, sulfur components and the like, which is discharged from factories such as foods and chemicals, and sewage treatment plants. The amount of alkali added to the excess sludge is such that no alkali is added to the entire excess sludge to be treated or 0.02 N or less, preferably 0.01 N. Alkaline condition is 0.02
If it exceeds N, the self-digestion reaction is hindered, and the organic acid production rate sharply decreases. The type of the alkali used in the present invention is not particularly limited, but for example, sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and the like can be used. Of these, sodium hydroxide and potassium hydroxide are particularly effective. These alkalis are preferably added in the form of an aqueous solution or a solid. The heating temperature after addition of the alkali is preferably 40 to 80 ° C, more preferably 60 ° C or higher.
If the heating temperature is lower than 40 ° C, the solubilization rate of the excess sludge required to achieve the object of the present invention cannot be achieved, and heating to a temperature higher than 80 ° C will lead to thermal economy and self-heating. It is not preferable from the viewpoint of a decrease in the organic acid production rate due to the inhibition of the digestive reaction. Therefore, it is preferable that the solubilization rate and the organic acid production rate required to achieve the object of the present invention are obtained, and the heating energy required for heating is around 60 ° C., which requires a minimum amount of thermal energy. Further, the heating treatment time is usually about 1 to 5 days, though it varies depending on the alkaline conditions or the heating temperature, the type of excess sludge, and the desired solubilization rate and organic acid production rate, but 60 ° C. In order to obtain a desired solubilization rate with a heating time of about 2 days, about 2 days are preferable.

The heating treatment after the alkali addition can be carried out under aerobic or anaerobic conditions, but the reaction is promoted more under anaerobic conditions. In order to subject the solubilized liquid obtained as described above to a high-speed methane fermentation treatment by the UASB method, the solubilization rate is preferably 30% or more and the organic acid production rate is preferably 15% or more. Solubilization rate is 30%
If the amount is less than 1, the organic acid is not sufficiently produced, and if the organic acid production rate is less than 15%, the methane production in the UASB treatment may not be efficiently performed unless the obtained supernatant is sufficiently acid-fermented. . Under the conditions of the present invention, the solubilization rate and the organic acid production rate slightly change depending on the pH treatment conditions and the heating treatment temperature, but the solubilization rate is usually 20% or more and the organic acid production rate is 10% or more. . Of these, U as described above
A solubilization solution having a solubilization rate of 30% or more and an organic acid production rate of 15% or more suitable for high-speed methane fermentation treatment by the ASB method is, for example, 0.01 N as an alkali addition amount (as a final concentration), and a heat treatment. It can be performed by heating the excess sludge at a temperature of 60 to 80 ° C. for a heat treatment time of 2 days. The solubilization rate as referred to in the present invention indicates the ratio of the weight of organic carbon in the supernatant fraction after pH adjustment and heat treatment to the total weight of organic carbon of sludge, which is expressed by the following formula. A numerical value that is calculated. Solubilization rate (%) = organic carbon weight (TOC) of supernatant fraction /
Total organic carbon weight of sludge × 100 In addition, the organic acid production rate is the organic acid such as acetic acid, propionic acid, butyric acid, and valeric acid in the supernatant fraction after pH adjustment and heating treatment of sludge. It shows the ratio of carbon weight,
It is calculated by the following formula. Organic acid production rate (%) = carbon weight of organic acids such as acetic acid in the supernatant fraction / total organic carbon weight of sludge × 100 The solubilizing liquid is supplied to the methane fermentation treatment apparatus after solid-liquid separation. As the apparatus used for the methane fermentation treatment in the present invention, the apparatus conventionally used for the high-speed methane fermentation treatment by the UASB method can be used.

[0006]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 (1) Effect on solubilization rate and organic acid production rate by adjusting pH of excess sludge treatment To 100 ml of excess sludge generated by activated sludge treatment, alkali-free or sodium hydroxide shown in Table 1 was added. The mixture was added under alkaline conditions to replace the gas phase in an anaerobic glove box, then tightly sealed, placed in an incubator, and kept at 50, 60, 70, 80 ° C. for 2 days. Then, the solubilized solution after heating was filtered with a 0.45 μm membrane filter, and the solubilization rate and the organic acid production rate of the obtained supernatant were examined. As a control, the same excess sludge as above was added with the acids shown in Table 1 and treated under the same conditions, and then the solubilization rate and the organic acid production rate were examined. The solubilization rate is TOC manufactured by Shimadzu Corporation.
The organic acid production rate was measured with an analyzer (TOC-5000) by Shimadzu Corporation HPLC (LC-10 organic acid analysis system). The results are shown in FIGS. 1 and 2, and it can be seen that pH adjustment in which the solubilization rate is high and the organic acid production rate is good is an alkali-free condition or a low alkali concentration up to 0.02N.

[Table 1]

(2) Solubilization of Excess Sludge and Methane Fermentation In this example, the excess sludge was solubilized and the methane fermentation property of the supernatant obtained by solid-liquid separation was examined. First, according to (1) of Example 1, 0.01N sodium hydroxide was added to make alkaline conditions, and excess sludge left to stand anaerobically at 60 ° C. for 2 days was subjected to solid-liquid separation, and the solubilized liquid supernatant was obtained. Obtained. Next,
To 300 ml of this supernatant, 700 ml of anaerobic treated water and 4 g VSS of anaerobic sludge were added (COD load 0.5 g, pH 6.
8), agitated at 35 ° C. by the device shown in FIG.
The volume was measured after 5 hours. On the other hand, as a control, excess sludge added with 0.03 N sodium hydroxide under alkaline conditions was treated and reacted in the same manner as above.
As a result, the recovery rate of each methane based on the theoretically generated methane volume (175 ml) from sodium acetate having the same COD amount is shown in Table 2.

[Table 2]

(3) UASB treatment of solubilized liquid According to the method of (1) of Example 1, 0.01 was added to excess sludge.
Add sodium hydroxide (N) at 60 ° C under anaerobic condition 2
The supernatant obtained by allowing to stand for a day and solid-liquid separation was subjected to UASB treatment under the conditions shown in Table 3 using the apparatus shown in FIG.

[Table 3] Reaction tank volume 500 ml Raw water TOC 350-500 mg / L Flow rate 2.2 L / d TOC load 1.5-2.2 kg / L / d Temperature 35 ° C. HRT 5.5 h TOC load 2.2 kg / L / d Average TO for 4 days
The C removal rate was 88%. Original data of FIG. 1 Conditions: anaerobic state, standing for 2 days Numbers represent solubilization rate (%).

[Table 4] Original data of FIG. 2 Conditions: The same as in the case of FIG. 1 The numbers represent the organic acid production rate (%).

[Table 5]

[0010]

By carrying out the present invention, excess sludge is solubilized in a short time (1 to 5 days) with a smaller amount of alkaline solution than before, and organic acid is produced in the solubilized solution produced under the above conditions. By increasing the rate and combining UASB high-speed methane fermentation, excess sludge can be efficiently treated with a small amount of alkali as a whole.

[Brief description of the drawings]

FIG. 1 is a diagram showing the influence of pH and temperature on the solubilization rate in a batch system (second day).

FIG. 2 is a diagram showing the influence of pH and temperature on the organic acid production rate.

FIG. 3 is a schematic diagram showing a methane fermentation operation of Example 1 (2).

FIG. 4 is a schematic diagram showing a methane fermentation operation of a solubilized solution using UASB.

[Explanation of symbols]

 A HCl, 0.03N (pH 2.4) B HCl, 0.02N (pH 3.6) C HCl, 0.01N (pH 6.1) D No pH adjustment (pH 7.7) E NaOH, 0.01N (pH 10) .1) F NaOH, 0.02N (pH 11.3) G NaOH, 0.03N (pH 11.7)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chikako Iwabuchi 2-13-1, Omorikita, Ota-ku, Tokyo Asahi Biru Co., Ltd. Alcoholic Beverage Development Laboratory (72) Inventor Seiji Imabayashi 2-Omorikita, Ota-ku, Tokyo 13-1 Asahi Biru Co., Ltd. Liquor Development Laboratory

Claims (1)

[Claims] 1. An upflow anaerobic sludge bed method (Upflow) is carried out using a solubilized liquid obtained by heating excess sludge that has been alkali-free with an alkali concentration of 0.02 N or less under an anaerobic condition. Anaeroic Slud
ge Blanket Process, UAS
Also called B method. ) Is used for high-speed methane fermentation treatment.