JP2003200198A - Method and apparatus for treating sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for treating sludge which can increase the amount of methane generated in the anaerobic digestion treatment of sludge and reduce sludge volume. <P>SOLUTION: In this sludge treatment method where the sludge generated in a water treatment process is treated by anaerobic digestion, a concentration process of the digested sludge is performed in a membrane filtration tank 12 installed after an anaerobic digestion process in a methane fermentation tank 11, the digested sludge thickened by the concentration process is circulated and introduced into the methane fermentation tank 11 through a thickened sludge circulation path 13 to be anaerobically digested again, and at least a part of the digested sludge introduced into the anaerobic digestion process is introduced into an ultrasonic irradiation means 14, where the sludge is treated by ultrasonic irradiation. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sludge treatment method and apparatus, and more specifically, to sludge generated in a water treatment process for treating wastewater such as sewage, industrial wastewater, and livestock wastewater by anaerobic digestion treatment in a methane fermentation tank. A method and apparatus for performing and processing.

[0002]

2. Description of the Related Art Generally, biological treatment is used for treating wastewater such as sewage, industrial wastewater, and livestock wastewater, and a large amount of excess sludge is discharged along with the removal of biological BOD components. However, due to soaring costs of surplus sludge treatment and shortage of final disposal sites, anaerobic digestion treatment, in which surplus sludge is subjected to methane fermentation as an organic resource, is drawing attention.

The anaerobic digestion process of sludge is intended to reduce the amount of organic substances and the amount of sludge by utilizing the decomposition action of microorganisms in an anaerobic state, and to treat organic waste such as food residues and human waste treatment. Widely used. However, compared to these organic wastes, excess sludge generally has poor digestion efficiency. It is said that the excess sludge contains a large amount of microorganism-derived persistent components protected by cell walls.
Therefore, in the conventional excess sludge fermenter, the digestion efficiency is only about 30%, and the contribution to sludge reduction is not sufficient. In addition, the water quality of the digestive juice obtained after anaerobic digestion is poor, and there is a problem that the treatment is difficult.

On the other hand, it has been reported that the sludge generated in the water treatment process is irradiated with ultrasonic waves to improve the properties of the sludge and improve the efficiency of methane fermentation. This method is to improve the methane fermentation efficiency by irradiating sludge with ultrasonic waves to cause dispersion of sludge flocs and destruction of cell walls.

[0005]

However, if the whole amount of sludge is irradiated with ultrasonic waves, there is a problem that the treatment equipment becomes large. Moreover, if ultrasonic irradiation is applied to the entire amount of sludge, a large amount of energy for generating ultrasonic waves is required,
There is also a drawback that the running cost becomes high. Furthermore, because ultrasonic waves indiscriminately act on easily degradable components,
There is also a problem that the utilization efficiency of ultrasonic waves is low.

[0006] Therefore, an object of the present invention is to provide a sludge treatment method and apparatus capable of improving the efficiency of anaerobic digestion treatment combined with ultrasonic irradiation, and increasing the amount of methane generation and reducing the amount of sludge.

[0007]

In order to achieve the above object, the sludge treatment method of the present invention is a method for treating sludge generated in a water treatment step by an anaerobic digestion step, wherein the digested sludge concentration step is performed after the anaerobic digestion step. The digestive sludge concentrated in the concentration step is circulated and introduced into the anaerobic digestion step for reprocessing, and a part of the digested sludge to be introduced into the anaerobic digestion step is subjected to ultrasonic irradiation. There is.

The sludge treatment apparatus of the present invention is a sludge treatment apparatus equipped with a methane fermentation tank for anaerobically digesting sludge generated in a water treatment process, wherein digested sludge concentrating means is installed in the latter stage of the methane fermentation tank, A route for circulating and introducing the digested sludge concentrated by the digested sludge concentrating means into the methane fermentation tank was provided, and an ultrasonic irradiation means for performing ultrasonic irradiation treatment on a part of the digested sludge introduced into the methane fermentation tank was provided. It is characterized by that.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a system diagram of a sludge treatment device showing a first embodiment of the present invention. This sludge treatment device
A methane fermentation tank 11 that performs an anaerobic digestion process for initial sludge and surplus sludge generated in a water treatment process, and a membrane filtration tank as a sludge concentrating means that is provided at a subsequent stage of the methane fermentation tank 11 and performs a digestion sludge concentration process. 12, a concentrated sludge circulation path 13 for circulating and introducing the digested sludge concentrated in the membrane filtration tank 12 into the methane fermentation tank 11, and an ultrasonic wave irradiation means 14 provided in parallel with the concentrated sludge circulation path 13. Has been formed.

The sludge extracted from the water treatment process and flowing in from the sludge inflow route 21 joins the concentrated sludge circulating in the concentrated sludge circulation route 13 and flows into the methane fermentation tank 11.
Anaerobic digestion of sludge is performed in this methane fermentation tank 11,
Due to the action of microorganisms, the amount of organic matter is reduced, sludge is reduced, and methane is generated. The generated methane is recovered as methane gas from the methane recovery route 22 and used as fuel.

Digested sludge in the methane fermentation tank 11 is route 2
4 is introduced into the membrane filtration tank 12 through
The digested sludge is concentrated at. The treated water separated by the membrane filtration is sent to the water treatment process through the path 25, and the concentrated digested sludge is extracted to the concentrated sludge circulation path 13. Then, at least a part of the digested sludge passing through the concentrated sludge circulation path 13 is branched to the ultrasonic wave irradiation path 26 provided with the ultrasonic wave irradiation means 14, and after the ultrasonic wave irradiation processing is performed by the ultrasonic wave irradiation means 14. , Again concentrated sludge circulation route 13
Then, it is mixed with the sludge flowing in from the sludge inflow route 21 and is circulated and introduced into the methane fermentation tank 11.

The amount of digested sludge to be subjected to ultrasonic wave irradiation by the ultrasonic wave irradiation means 14 can be set in consideration of the scale of the sludge treatment amount and the property of the sludge. For example, the sludge inflow route 21
It may be set according to the amount of newly inflowing sludge from the above and the amount of concentrated digested sludge passing through the concentrated sludge circulation route 13, and ultrasonic irradiation processing is performed on all the amount of concentrated digested sludge passing through the concentrated sludge circulation route 13. May be.

If solid components such as inorganic matter that cannot be digested are accumulated in the methane fermentation tank 11, a part of the digested sludge in the methane fermentation tank 11 may be removed from the sludge withdrawal route 23, if necessary. , It is taken out from the concentrated sludge circulation path 13 and sent to the outside of the system. The withdrawal amount and frequency at this time may be appropriately set according to the properties of the sludge.

FIG. 2 is a system diagram of a sludge treatment device showing a second embodiment of the present invention. In this sludge treatment device, the ultrasonic irradiation means 14 is provided in the path after the concentrated digested sludge circulated from the membrane filtration tank 12 through the concentrated sludge circulation path 13 and the new inflow sludge flowing in from the sludge inflow path 21 are mixed. The ultrasonic wave irradiation paths 26 provided with are connected in parallel. That is, in this embodiment, a part of the sludge in which the concentrated digested sludge and the new inflow sludge are mixed is branched to the ultrasonic wave irradiation path 26, and ultrasonic wave irradiation is performed after ultrasonic wave irradiation is performed by the ultrasonic wave irradiation means 14. It is arranged to be introduced into the methane fermentation tank 11 after being combined with sludge that is not used.

In both of the embodiments, the amount of digested sludge branched to the ultrasonic irradiation route 26, that is, the ratio of the amount of digested sludge to be subjected to ultrasonic irradiation treatment to the total amount of digested sludge circulated varies depending on the properties of the sludge. Generally, 20% or more, preferably 30% or more is suitable, and if the amount of sludge irradiated with ultrasonic waves is too small, the modifying effect may be weakened and desired treatment results may not be obtained.

As described above, when the sludge discharged from the water treatment step is subjected to anaerobic digestion treatment in the methane fermentation tank 11, the digested sludge concentrated in the membrane filtration tank 12 in the latter stage is treated in the methane fermentation tank 1
Methane fermenter 1
The amount of methane generated in 1 can be increased, and the amount of sludge can be reduced. In addition, by performing ultrasonic irradiation treatment on a part of the sludge introduced into the methane fermentation tank 11,
Sludge flocs that could not be digested can be dismantled, cell walls can be damaged, cell destruction can be accelerated, the methane generation rate in the methane fermentation tank 11 can be improved, and the utilization efficiency of ultrasonic waves is also improved. Can be made.

The concentration (MLSS) of digested sludge to be subjected to ultrasonic treatment by the ultrasonic irradiation means 14 is usually 5000 m.
g / L or more, preferably 10000 mg / L or more, and particularly preferably 20000 mg / L or more. If the sludge concentration is too low, the efficiency of ultrasonic waves will be low, and the desired treatment results may not be obtained.

The frequency of the ultrasonic wave in the ultrasonic wave irradiation means 14 is 15 to 50 kHz, preferably 15 to 40 kHz.
z, especially 20-30 kHz is suitable. If this frequency is too low, it may not be possible to obtain sufficient processing effects.
If it is too high, the wear of the ultrasonic oscillator becomes extremely severe, and frequent replacement may be required.

The intensity of ultrasonic waves is set appropriately according to the amount and concentration of sludge to be irradiated.
Generally, 5-100 kWs / L, preferably 10-
80 kWs / L, especially 20-60 kWs / L is suitable. If the ultrasonic wave intensity is too low, a sufficient effect may not be obtained, and if it is too high, an effect proportional to the intensity may not be obtained.

Each of these conditions, that is, the sludge concentration, ultrasonic frequency, ultrasonic intensity, and ultrasonic irradiation sludge amount, is an element of each condition, and the cost of treatment, treatment time, etc. are taken into consideration. The conditions can be changed as appropriate to improve efficiency.

As the ultrasonic wave irradiating means, a container having a sludge inflow port and a sludge outflow port is provided in the middle of the ultrasonic wave irradiating flow path, and an ultrasonic oscillator is installed in the container. It is possible to use a device in which an ultrasonic wave oscillator is installed in a pipe forming a part or all of the flow path, and a known product such as a general commercial product can be used by appropriately setting the sludge treatment amount.

Further, as the methane fermentation tank 11 and the membrane filtration tank 12, it is possible to use well-known ones conventionally used in this kind of apparatus, for example, the methane fermentation tank 11
Any of room temperature, medium temperature, and high temperature can be used for this.
Further, a hydrolysis tank may be provided before the methane fermentation tank 11. As the sludge concentrating means, known means such as membrane filtration, gravity settling, centrifugal dehydration, pressure dehydration and the like can be selected. Of these, concentration by membrane filtration is preferable, and microfiltration, ultrafiltration, etc. can be used for the filtration membrane, but ultrafiltration is particularly suitable.

[0023]

As described above, according to the present invention,
The amount of methane gas generated during anaerobic digestion of sludge can be increased, the energy can be recovered as effective energy, and the amount of sludge can be reduced.

[Brief description of drawings]

FIG. 1 is a system diagram of a sludge treatment device showing a first embodiment example of the present invention.

FIG. 2 is a system diagram of a sludge treatment device showing a second embodiment of the present invention.

[Explanation of symbols]

11 ... Methane fermentation tank, 12 ... Membrane filtration tank, 13 ... Concentrated sludge circulation path, 14 ... Ultrasonic irradiation means, 21 ... Sludge inflow path, 22 ... Methane recovery path, 23 ... Sludge extraction path, 26
… Ultrasonic irradiation route

Claims (2)

[Claims] 1. A method for treating sludge generated in a water treatment step by an anaerobic digestion step, wherein a digestion sludge concentration step is performed after the anaerobic digestion step, and the digested sludge concentrated in the concentration step is circulated and introduced into the anaerobic digestion step. Sludge treatment method, wherein a part of the digested sludge to be introduced into the anaerobic digestion step is subjected to ultrasonic irradiation treatment. 2. A sludge treatment device equipped with a methane fermentation tank for anaerobically digesting sludge generated in a water treatment step, wherein digestive sludge concentrating means is installed in the latter stage of the methane fermentation tank and concentrated by the digestive sludge concentrating means. A sludge treatment device provided with a path for circulating and introducing digested sludge into the methane fermentation tank, and ultrasonic wave irradiation means for performing ultrasonic irradiation treatment on a part of the digested sludge to be introduced into the methane fermentation tank. .