JPS6397299A - Anaerobic digestion method for organic sludge - Google Patents

Abstract

PURPOSE:To make high-speed anaerobic digestion of org. sludge by adding a flocculating agent to the org. sludge after acid fermentation thereof, subjecting the sludge to a solid-liquid sepn., subjecting the separated liquid to methane fermentation and drying the solid-liquid separated sludge by a digesting gas from said methane fermentation stage. CONSTITUTION:After the org. sludge such as sewer sludge 1 is subjected to the acid fermentation in an acid fermentation tank 2, the flocculating agent 4 such as cation polymer is added to the sludge and the sludge is subjected to the solid-liquid sepn. by a sludge dehydrator 5, by which the sludge is separated to the sludge 6 and the separated liquid 7. The separated liquid 7 is subjected to the methane fermentation by utilizing the methane bacteria immobilized in a methane fermentation tank 8 [e.g., upward counter current anaerobic sludge blanket method (UASB method)]. Hot air 17 generated from a hot air generating furnace 16 using the digesting gas 14 from the tank 8 as fuel is blown to a drying machine 8 to dry the sludge 6. As a result, the rational and high-speed anaerobic digestion of the org. sludge is executed and the drying of the sludge 6 with the less energy is permitted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a novel anaerobic digestion process that can perform methane fermentation of organic sludge such as sewage sludge at high speed, and can dehydrate and dry the sludge with significant energy savings. It is something.

[Conventional technology]

In the field of sewage sludge treatment, anaerobic digestion has been used for a long time because of the following advantages.

(b) Large quantities of dilute organic slurry at low cost? Stabilization (S
(tabilization) possible.

(b) The amount of sludge to be disposed of can be reduced.

(c) Pathogens are sterilized.

) Digested sludge can be used as a soil conditioner.

(e) It has the advantage of being able to convert organic carbon in sludge into gas whose main component is methane.

Despite these numerous advantages, conventional anaerobic digestion processes have not reached the stage where they can fully realize their potential. This is due to the following reasons.

(a) insufficient research has been conducted on the physical, chemical, and biochemical interactions in the methane fermentation process; and (b) the design and operation of the anaerobic digestion process is tied to conventional methods. thing.

The present invention was completed as a result of conducting studies based on this awareness of the problem, and is based on the two-phase digestion method (two-phase acid fermentation and methane fermentation process) proposed by Ash (USA) in 1975. Method of anaerobic digestion with clear separation into phases)
- By introducing a new perspective, we aim to provide a new process that can rationally and rapidly anaerobically digest organic sludge and dry digested sludge in an extremely energy-saving manner.

[Problem to be solved by the invention]

The two-phase digestion method proposed by Go eh (J, W, P, 0.1
PVo1.47. The major problem with conventional anaerobic digestion methods for sewage sludge, including No. This is a phenomenon in which SS is returned to the sewage treatment process. In other words, SS that no longer has gas generation potential from the anaerobic digestion sludge sedimentation separation tank
This is a vicious cycle in which the sludge flows out and flows into the primary settling tank for sewage treatment where it is sedimented and separated, and this settled sludge is again supplied to the anaerobic digestion process.

Even in the two-phase digestion method proposed by Gosh, he adopted the flow -m-OkaO←i-crack-1])-, thereby avoiding the trouble of 8-day carryover from the settling tank. That is difficult. In particular, methane-producing sludge often has poor sedimentation and separation properties.

The first problem of the present invention is to solve this problem of SS backflow. Next, in the conventional sewage sludge anaerobic digestion method, there has been insufficient consideration given to the rational treatment of digested sludge, and the digested sludge is simply dehydrated using a customary method and then the dehydrated cake is disposed of. There wasn't. In other words, none of the conventional methods has established a total process that takes into account the rational disposal of digested sludge.

The second objective of the present invention is to establish a total process including a rational method for treating digested sludge.

[Means for solving problems]

The present invention involves acid fermenting organic sludge, then adding a flocculant such as a cationic polymer to perform solid-liquid separation, and using fixed methane-producing bacteria to perform methane fermentation on the separated liquid. This is an anaerobic digestion method characterized by drying the solid-liquid separated sludge using digestion gas generated from the fermentation process.

An embodiment of the present invention will be described in detail below with reference to the drawings, taking an example of application to sewage sludge.

Sewage sludge 1 is concentrated as necessary and then subjected to acid fermentation [2
The temperature was 35-37°C and the pH was 5.0-5.8.
Under conditions of residence time of 1 to 3 days, acid fermentation bacteria (Acid f.
(orming bacteria), the solubilization of sludge solids and the production reaction of volatile organic alcohol proceed.

After the sludge 5 flowing out from the acid fermenter is added with a flocculant 4 such as a cationic polymer, it is introduced into a sludge dewatering machine 5 such as a centrifugal dewatering machine or a belt press, and solid-liquid separation is performed into a dehydrated cake 6 and dehydrated separated water 7. be done. The dehydrated separated water 7 contains a high concentration of organic alcohols such as acetic acid and butyric acid produced in the acid fermentation tank, and contains almost no p or ss. in this way,
In the present invention, a flocculant such as a cationic polymer is added to the acid fermentation sludge to flocculate and separate SS, so the removal rate of 88 is high, and the subsequent methane fermentation tank 8 always has an SS concentration number IQ.
Can supply liquid with low SS concentration of Q mW/L or less.

This point is particularly important, especially in high-concentration sewage sludge, etc.
This makes it possible to effectively apply methane fermentation methods using immobilized microorganisms (CUA, B, etc.) which are difficult to apply to liquids containing 8.

The most suitable methane fermentation method is the UASB method, which utilizes the self-immobilization effect of methane-producing bacteria, but the anaerobic fluidized bed method and anaerobic fixed bed method, which use microorganism-attached carriers such as granular ceramics and granular activated carbon, are also used. It is also suitable to do so.

The drawing shows UASB@ as an example.

Therefore, the dehydrated separated water 7 is a sludge dehydrated cake 6 which will be described later.
The dehydrated separated water 7 is brought into direct contact with the dry exhaust gas 10 discharged from the dryer 9 in the scrubber 11, and is heated by the latent heat of condensation of the dry exhaust gas. The heated and dehydrated separated water 12 is introduced into the UA8B reactor in an upward flow, and is subjected to methane fermentation at a high rate by methane-producing bacteria forming a high concentration of blanket in the reactor.

Methanobacter granules with a particle size of approximately 2 to 3 cm are forming a blanket 8' in the U18B reactor (according to scanning electron microscopy, the inside of the granules is composed of a high density of methane bacteria belonging to the genus Methanothrlx; The concentration of the surface (covered with mucilage secreted by the methane bacteria themselves) is maintained at an extremely high concentration of 75,000 to 80,000 mf/L, and this is thought to be the reason why high-speed methane fermentation is possible. It will be done.

According to the experimental results of the present inventor, it is possible to carry out a significantly high load of about a o kg 0 ODcr/m'' in the U5B B reactor, and the sewage mixed raw sludge with a p1 solids concentration of 3% can be mixed with the When using anaerobic digestion,
It was found that one day is sufficient for the required residence time in the mesotemperature digestion UA8B reactor at 35 to 37°C, even if a margin is considered. The total required residence time for the acid fermenter 2 and UAAEIBIJ Actor 8 is 2 to 4 days, which can be significantly reduced compared to the 20 to 30 days required for conventional processes. there were. 13 is a digestion gas collector, 14 is a digestion gas, and 15 is a gas tank.

Hot air 17 generated from a hot air generating furnace 16 using digestion gas 14 as fuel is blown into the sludge dewatering cake dryer 9.
The dehydrated cake 6 with a water content of about 80 parts is dried to become a dried cake 18 with a water content of 20 parts or less.

Drying of the dehydrated cake can be done only by the heat of the digestion gas generated in the UA8B reactor, and heavy oil,
Purchased fuel such as city gas is not required. This effect is
This is one of the important effects of the present invention.

A suitable type of dryer 9 is a granulation dryer that simultaneously performs drying and granulation using the action of an agitated fluidized bed.

This is because a granulation dryer based on an agitated fluidized bed has high heat utilization efficiency, and the dry exhaust gas has a temperature of 70 to 80°C and a humidity of 10°C.
This is because it has a very convenient characteristic for recovering the latent heat of condensation, as it is expressed as a wet bulb temperature like 0.

The dry exhaust gas 10 is brought into direct contact with the dehydrated separated water 7 to recover the latent heat of condensation as described above, and a portion of the exhaust gas 10'
Another preferred embodiment is a method in which the latent heat of condensation is recovered by diffusing air into the acid fermenter 2 and bringing it into direct contact with the slurry in the acid fermenter 2.

19.20 is the dry exhaust gas from which the latent heat of condensation has been recovered,
It is led to a deodorizing process (not shown) and deodorized.

The dehydrated cake of sludge flowing out from the acid fermenter 2 is generally H
Since it has a 2S odor and an organic acid odor, there is a problem that if it is disposed of directly in a landfill, it will emit a bad odor.However, in the present invention, the bad odor in the dehydrated cake 6 is removed by drying it using digestive gas generated from within the process system. It is possible to volatilize the ingredients. As a result, the dried material 18 hardly generates any bad odor and can be disposed of or effectively utilized without causing any odor problems.

〔Effect of the invention〕

According to the present invention, the following IL-important effects can be obtained.

1. Organic sludge can be processed at extremely high speeds (required residence time: 2 to 4 days)
As a result of being able to perform anaerobic digestion, the installation area and equipment construction costs can be reduced compared to conventional methods.

2. Sludge dewatering cake can be dried without using purchased fuel such as heavy oil.

As a result, the amount of sludge to be disposed of can be significantly reduced.

5. The odor of sludge dewatering cake can be removed at low cost.

Table: To recover the latent heat of condensation from dry exhaust gas, there is no need for an indirect heating heat exchanger, which requires scale removal work, is troublesome to maintain, and has high equipment costs.

a Since a low BS liquid can be reliably supplied to the methane fermentation process using immobilized methane-producing bacteria such as the UA day B method, UABB@ can be operated without trouble. (If a large amount of 8B flows in, it becomes difficult to generate granules using the UASB method, and moreover, it causes problems with scum generation.)

[Brief explanation of the drawing]

FIG. 1 is a process diagram for explaining the method of the present invention. 1... Sewage sludge, 2... Acid fermentation tank, 4...
Dehydration aid, 5... Sludge dehydrator, 6... Dehydrated cake, 8... Methane fermentation tank, 9... Dryer,
1o...Dry exhaust gas, 11...Scrubber 13...Digestion gas collector,

Claims (1)

[Claims] 1. After acid fermenting organic sludge such as sewage sludge,
A flocculant is added to separate solid and liquid into sludge and separated liquid,
A method for anaerobic digestion of organic sludge, characterized in that the separated liquid is subjected to methane fermentation using immobilized methane bacteria, and the separated sludge is dried using digestion gas generated in the methane fermentation process as fuel. 2. The anaerobic digestion method according to claim 1, which uses an upflow anaerobic sludge blanket method (UASB method) as the methane fermentation step using the immobilized methane bacteria. 3. The anaerobic digestion method according to claim 1 or 2, wherein the dry exhaust gas discharged from the sludge drying step is brought into direct contact with the solid-liquid separation liquid to recover the latent heat of condensation of the dry exhaust gas. .