JP2002361293A - Method and apparatus for reducing volume of organic sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new technique for reducing the volume of organic sludge such as waste sludge produced in an organic sewage biologically treating step at high speed in high efficiency with saved energy. SOLUTION: The method for reducing the volume of organic sludge comprises a step to acid-ferment the organic sludge, a step to subject the acid-fermented organic sludge to solid-liquid separation, a step to solubilize the sludge separated by the solid-liquid separation and a step to digest the solubilized sludge anaerobically. The liquid separated by the solid-liquid separation can bye methane-fermented by immobilized methane bacteria or supplied to an anaerobic part or an oxygenless part of the step to treat organic sewage biologically or to a tank where the solubilized sludge is digested anaerobically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an energy-saving and high-speed organic sludge such as excess sludge and sewage-mixed raw sludge generated from a process of biologically treating organic sewage such as sewage and industrial wastewater. On new technologies that can reduce weight.

[0002]

2. Description of the Related Art A large amount of organic sludge (excess sludge, raw sludge, etc.) is generated daily from activated sludge treatment facilities such as sewage, industrial wastewater, human waste, and landfill wastewater. More than 10 million tons. Treatment and disposal of excess sludge has become the biggest environmental problem.
That is, surplus sludge is very hard to dehydrate among these organic sludges, so a large amount of a dehydration aid (polymer, etc.) is added, and the sludge dewatering machine is used to dewater to about 85% moisture, and the dewatered cake is landfilled. Or incineration, but suffers from many problems, such as the cost of dehydrating aids, lack of landfills for dewatered cakes, lack of disposal sites for incinerated ash, high incineration equipment costs, and high cost of heavy oil for incineration. ing.

[0003] In order to solve such a problem, a patent publication discloses a "method of reducing excess sludge using ozone". This technology, from the activated sludge treatment process of wastewater,
This is a method in which an activated sludge having a larger amount than the generated excess sludge is drawn out, oxidized with ozone, and returned to the activated sludge treatment step as it is.

[0004] In addition, a method of improving the biodegradability of activated sludge by hydrolyzing activated sludge with an alkaline agent, and a method of heating activated sludge to destroy cells (Journal of the Japan Society on Water Environment, Vol. 21, No. 6, p. 360: Activated sludge process that does not generate excess sludge using thermophilic microorganisms), method of crushing activated sludge with a mill, sludge provided at high-pressure pump discharge port 1-2 m
Water jet method in which high-speed injection is performed on a plate from a nozzle of about m (Aso et al .; Basic study of sludge reduction system; 37th Sewerage Research Presentation Lectures, p482-484, 20
2000), adding excess ozone to the sludge or irradiating it with ultrasonic waves, solubilizing the sludge, and then performing anaerobic digestion (No. 41 of the Japan Society of Civil Engineers).
Annual Scientific Lecture, November 1986, p915-) is known.

[0005]

However, the conventional technology requires a large amount of aeration power in order to reduce the amount of solubilized sludge by aerobic organisms, so that there is a problem of high energy consumption. Even when the amount of the solubilized sludge is reduced by the anaerobic digestion treatment, there is a problem that the time required for the anaerobic digestion treatment is long, and a considerable amount of digestion residue that cannot be digested remains. The present invention has been made in view of such conventional problems, and reduces organic sludge such as surplus sludge generated from a biological treatment process of organic wastewater at a high speed and energy saving with a high weight loss efficiency. It is an object to provide new technologies that can be developed.

[0006]

The present invention has solved the above-mentioned problems by the following means. (1) Organic sludge is subjected to acid fermentation treatment, followed by solid-liquid separation, solubilization of the separated sludge obtained by the solid-liquid separation, and anaerobic digestion of the solubilized sludge obtained by the solubilization treatment. A method for reducing organic sludge, comprising: (2) whether the separated liquid separated by solid-liquid separation after the acid fermentation treatment is subjected to methane fermentation treatment with immobilized methane bacteria, or supplied to an anaerobic part or an oxygen-free part in a biological treatment step of organic wastewater; The method for reducing organic sludge according to claim 1, wherein the sludge is supplied to an anaerobic digestion tank for solubilized sludge. (3) The method for reducing organic sludge according to claim 1, wherein the digested sludge generated in the anaerobic digestion is sent back to the solubilization treatment of the separated sludge as digested sludge.

(4) An acid fermenter for acid fermentation by introducing organic sludge, a solid-liquid separator for introducing acid fermentation sludge from the acid fermenter and separating it into separated sludge and a separated liquid, and the solid-liquid separator Organic sludge reduction characterized by having a solubilization treatment tank for introducing and separating solubilized sludge from, and an anaerobic digestion tank for anaerobic digestion by introducing solubilized sludge from the solubilization treatment tank. Device. (5) Upstream anaerobic sludge blanket device of the separated liquid from the solid-liquid separation device at the subsequent stage of the acid fermentation tank, or oxygen-free or anaerobic portion in the biological treatment process of organic wastewater, or solubilization 5. The organic sludge reduction apparatus according to claim 4, further comprising a supply pipe to the anaerobic digestion tank for sludge.
Note that an ultrasonic wave is defined as a sound wave or an elastic wave having a frequency (about 10 KHZ or more) exceeding the audible frequency of the human ear.

[0008]

FIG. 1 is a block diagram showing a configuration example in which the present invention is applied to the reduction of excess activated sludge generated from an activated sludge treatment facility for organic wastewater. That is, FIG.
Here, an apparatus for reducing sludge 1 as surplus activated sludge from an activated sludge treatment facility (not shown) is shown. The acid fermentation tank 2 and the acid fermentation tank perform an acid fermentation treatment using an acid fermentation bacterium. A solid-liquid separation device 4 for solid-liquid separation of the acid fermentation sludge 3 is provided at a stage subsequent to the step 2. The solubilized sludge 9 is solubilized by a solubilization treatment tank 7 for solubilization, and the solubilized sludge 9 is further digested by being placed in an anaerobic digestion tank 10 at a later stage, and generated digestion gas 14 is discharged out of the system from the top of the tank 10. At the same time, the digestion-desorbed liquid flows out of the system as the membrane permeated water 12 by the membrane separation unit 11 installed in the anaerobic digestion tank 10, and at the same time, the solubilized concentrated sludge that is difficult to digest is taken out as digested sludge 13. Partly returned as sludge 15 Comprising a pipe for returning to the processing tank 7, only the undigested residual traces discharged from the system as waste digested sludge 16, whereas the separated liquid 6 leaving the solid-liquid separator 4,
Upflow anaerobic sludge blanket device (hereinafter “UAS”)
B ") or treated to be discharged out of the system as digested gas 19 and treated water 18 by fixed methane bacteria of 17 or to an anaerobic section or anoxic section 20 in a biological treatment step of organic wastewater. It is configured to be supplied back through a pipe or supplied to an anaerobic digestion tank 10 for solubilized sludge 9.

In the present invention, an activated sludge treatment step for purifying sewage water with aerobic microorganisms (including a method with an anaerobic part such as a biological dephosphorization method and a biological nitrification denitrification method)
A part of the settled sludge in the settling tank is withdrawn and supplied to the acid fermenting tank 2 for performing the acid fermentation treatment by the acid fermenting bacterium (passive bacterium), and is kept for a required time. The main components constituting the cell wall of activated sludge are polysaccharides and proteins, but polysaccharides are hardly anaerobically digested. However, when activated sludge is subjected to acid fermentation, polysaccharides are converted into monosaccharides, lower fatty acids, and organic acids such as acetic acid. Proteins are converted into peptides, amino acids, and fatty acids.

Next, the acid fermentation sludge 3 flowing out of the acid fermentation tank 2 is subjected to solid-liquid separation. The solid-liquid separator 4 employs various kinds of separation means such as centrifugal separation, flotation separation, sedimentation separation, and membrane separation.
Next, the separated sludge 5 is supplied to the solubilization tank 7. As the means for solubilizing the sludge in the solubilization treatment tank, ultrasonic treatment, ozone oxidation, sludge grinding with a mill or the like, alkali treatment, destruction of known excess sludge biological cell walls such as heat treatment, that is, solubilization means, Especially ultrasonic 8
The solubilizing means is preferable since it has the lowest solubilization cost and the apparatus is simple and small.

When supplied to an ultrasonic irradiation tank and irradiated with ultrasonic waves 8, sludge 1 is solubilized to effectively destroy sludge cell walls. When the suitable ultrasonic frequency is too high, the sludge solubilizing effect is found to be deteriorated.
KHZ, more preferably 15 to 50 KHZ, is suitable. The ultrasonic irradiation energy for solubilizing sludge is preferably 2 to 10 Kwh / kg · SS. In the solubilization method using ultrasonic waves 8, there was an optimum range for the solid concentration, and a proper range was a concentration of 1.5 to 4%.
At the sludge solid concentration in this range, it was recognized that the sludge cell destruction effect at the same ultrasonic output, in other words, the sludge solubilization effect was improved.

If the concentration exceeds 4%, the concentration becomes too high, the viscosity of the sludge slurry becomes too high, and the fluidity deteriorates, so that the effect of ultrasonic irradiation on the sludge becomes uneven. In addition, when the solid concentration is less than 1.5%, the solid concentration is too low, and the energy of the ultrasonic wave is wasted in addition to the solubilizing action of the solid. The time of ultrasonic irradiation is very short and sufficient, and may be several minutes or less. Therefore, the ultrasonic irradiation tank volume can be very small. When irradiating ultrasonic waves,
Since the ultrasonic energy is finally converted into heat and the temperature of the sludge rises, the temperature rise effect of the ultrasonic irradiation can be advantageously used for the medium-temperature methane fermentation treatment in which a liquid temperature of about 35 ° C. is suitable.

When the excess sludge 1 is solubilized by ozone, the separated sludge 5 after the acid fermentation tank 2 is previously aerated with an oxygen-containing gas to increase the oxidation-reduction potential (ORP) and then oxidize with ozone. Other reducing substances such as hydrogen sulfide are reduced, and the amount of ozone required for solubilizing sludge can be reduced. As described above, the ozone injection rate for solubilizing acid-fermented sludge in an aerobic state with ozone may be 20 to 60 g ozone per 1 kg of sludge solid weight.

When the acid-fermented sludge is solubilized, the particle system of the acid-fermenting bacteria and the activated sludge that could not be liquefied by the acid-fermenting bacteria becomes finer and the cell wall is destroyed, so that the anaerobic digestive bacteria can be easily utilized. Become. Next, the separated liquid 6 after acid fermentation
The organic components of UA are mainly composed of organic acids.
By the methane fermentation method using immobilized methane bacteria such as SB17, it is decomposed into methane gas and carbon dioxide gas at a very high speed. In the UASB method, high concentrations of S in raw water
Although the S content is an obstacle, in the present invention, the solid-liquid separated SS
Therefore, there is no such an obstacle because a small amount of separation liquid can be supplied. The acid fermentation sludge separation liquid 6 may be supplied to the anaerobic digestion tank 10 for solubilized sludge and subjected to anaerobic digestion together. Alternatively, the separated liquid 6 after the acid fermentation tank 2 is supplied to the oxygen-free or anaerobic part 20 in the biological treatment process of the organic wastewater, and an organic carbon source for facilitating the expulsion of phosphorus from the biodephosphorus bacteria. Or as an organic carbon source for biological denitrifying bacteria.

In the UASB device 17, the solid matter concentration of the methane bacteria granules forming the blanket is very high, 75,000 to 90000 mg / liter, so that the organic matter load is about 30 kg COD.
may take a significantly higher load of cr / m ^3.
Therefore, the solid-liquid separation liquid 13 after solubilization of excess sludge of the present invention is used.
In the case of treating, the residence time of the UASB device 17 can be sufficient methane fermentation treatment in a short time of several hours at a temperature of 35 ° C.

As a method using immobilized methane bacteria,
The UASB method utilizing the self-fixation (self-granulation) phenomenon of methanogens is optimal, but the anaerobic fluidized bed method using a microorganism-adhered carrier such as granular ceramic, granular activated carbon, and granular zeolite, and the anaerobic fixed bed method May be applied. FIG. 1 illustrates the UASB method.

The sludge solubilized by ozone or ultrasonic waves 8 has an increased biodegradability by anaerobic bacteria. Advances. The anaerobic digestion tank 10 in FIG. 1 is stirred, and a membrane separation unit 11 is installed inside. The sludge from the anaerobic digestion tank 10 is supplied to the membrane separation unit 11
, And the digested and separated liquid flows out as the membrane permeated water 12. In the present invention, when the solubilized sludge is subjected to anaerobic digestion, three days at a temperature of 35 ° C. are sufficient. As a result, the total processing speed is greatly improved as compared with the conventional method, and the entire processing tank volume is reduced.

The anaerobic digestion tank 10 accumulates residues that are hardly digested by the anaerobic digestion of the solubilized concentrated sludge. The residue is appropriately extracted, returned to the solubilization treatment tank 7 and solubilized. Becomes anaerobic digestible,
It is decomposed in the anaerobic digester 10. As a result, the amount of undigested residue decreases, and almost no undigested residue is generated. According to experiments by the present inventors, when excess activated sludge is reduced by the present invention, the amount of sludge that must be finally disposed of outside the system is 0.07 to 0.09 kg per 1 kg of input excess activated sludge. It was only.

[0019]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Example 1 A test was conducted on surplus activated sludge discharged from a sewage activated sludge treatment facility. Table 1 shows the test conditions.

[0021]

[Table 1]

As a result of operating under the above conditions, the amount of sludge that had to be discarded out of the system from the anaerobic digestion tank was 46 g · SS / d on a solid basis. Since the excess sludge treatment amount is 700 g SS / d, the sludge reduction rate is 93%.
And was excellent. The quality of UASB treated water is BOD150
mg / l, the desorbed liquid quality of the sludge anaerobic digestion tank is 23
It was as good as 0 mg / liter.

[0023]

According to the present invention, the following (1) to (3)
The effect was obtained. (1) Organic sludge such as surplus activated sludge can be highly reduced with high speed and energy saving. (2) Therefore, the sludge dewatering / incineration process is greatly streamlined. (3) Since power can be generated using the generated methane gas as fuel, the obtained power can be used as power for generating ultrasonic waves for sludge solubilization and power for an ozone generator, and the power purchased from outside can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an organic sludge reduction apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sludge (excess activated sludge) 2 Acid fermentation tank 3 Acid fermentation sludge 4 Solid-liquid separation apparatus 5 Separation sludge 6 Separation liquid 7 Solubilization means 8 Ultrasonic 9 Digestion gas 10 Anaerobic digestion tank 11 Membrane separation unit 12 Membrane permeation liquid 13 Digested sludge 14 Digested gas 15 Return digested sludge 16 Waste digested sludge 17 UASB 18 Treated water 19 Digested gas 20 Anaerobic or oxygen-free part in biological treatment process of organic wastewater

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Akira Watanabe 11-1 Haneda Asahimachi, Ota-ku, Tokyo F-term in Ebara Corporation (reference) 4D040 AA01 AA04 AA31 AA34 4D059 AA04 AA05 BA13 BA21 BC02 BE31 BE38 BE41 BE42 BE46 BE49 BF02 BF14 BK11 BK12 BK22 CA28 CA29 DA01 DA43

Claims (5)

[Claims] An organic sludge is subjected to acid fermentation treatment, followed by solid-liquid separation, solubilization of the separated sludge obtained by the solid-liquid separation, and anaerobic digestion of the solubilized sludge obtained by the solubilization treatment. A method of reducing organic sludge. 2. The separated liquid separated by solid-liquid separation after the acid fermentation treatment is subjected to methane fermentation treatment with immobilized methane bacteria or supplied to an anaerobic part or an oxygen-free part in a biological treatment step of organic wastewater. The method for reducing the amount of organic sludge according to claim 1, wherein the organic sludge is treated by supplying it to an anaerobic digestion tank for solubilized sludge. 3. The method for reducing the amount of organic sludge according to claim 1, wherein the digested sludge generated in the anaerobic digestion is sent back to the solubilization treatment of the separated sludge as digested sludge. 4. An acid fermentation tank for introducing an organic sludge and performing acid fermentation, a solid-liquid separation device for introducing an acid fermentation sludge from the acid fermentation tank and separating it into a separated sludge and a separated liquid, Organic sludge reduction characterized by having a solubilization treatment tank for introducing and separating solubilized sludge, and an anaerobic digestion tank for performing anaerobic digestion by introducing solubilized sludge from the solubilization treatment tank. apparatus. 5. An upflow anaerobic sludge blanket device of a separated liquid from a solid-liquid separation device at a subsequent stage of the acid fermentation tank, an oxygen-free portion or an anaerobic portion in a biological treatment process of organic wastewater, or The organic sludge reduction apparatus according to claim 4, further comprising a supply pipe for supplying the solubilized sludge to the anaerobic digestion tank.