JP2003320394A - Treatment apparatus and treatment method for organic waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the digestion efficiency of dehydrated sludge returned to a digestion tank and to promote the volumetric reduction of sludge and the production of gas, in the anaerobic treatment of organic waste by dehydrating digested sludge by a dehydrator to return the dehydrated sludge to the digestion tank. <P>SOLUTION: The organic waste is anaerobically digested in the digestion tank 1 and the digested sludge is dehydrated by the dehydrator 2. The dehydrated sludge is finely divided in a finely dividing tank 3 and the finely divided sludge is returned to the digestion tank 1. Moisture is supplied to the finely divided dehydrated sludge to adjust the concentration of the sludge. The returned sludge is uniformly dispersed in the digestion tank 1 and efficiently brought into contact with acid producing bacteria or a hydrolyzing enzyme to be decomposed by the same digestion efficiency as the sludge in the tank. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to high-concentration organic wastewater such as human waste, septic tank sludge, sewage sludge, food factory wastewater, chemical factory wastewater, surplus sludge from biological treatment processes, food waste, livestock excrement, and raw materials. The present invention relates to a treatment device and a treatment method for anaerobically digesting organic waste such as solid waste such as garbage, and particularly, to enhance the anaerobic digestion efficiency of the organic waste to promote the volume reduction of digested sludge and methane gas. The present invention relates to a treatment device and a treatment method for organic waste, which aims to increase the amount of generation.

[0002]

2. Description of the Related Art As a method for treating organic waste, there is an anaerobic digestion method in which organic waste is subjected to methane fermentation in the presence of anaerobic bacteria. In the case of anaerobic digestion of organic waste, if the main component is easily biodegradable, it can be decomposed in a short residence time and the amount of methane gas generated will increase. On the other hand, in the case of sewage sludge or solid waste that is hardly biodegradable and has a slow decomposition rate, a long retention time is required to obtain a high volume reduction rate and methane production amount, and the digester tank volume is growing.

As a method of suppressing the increase in the digestion tank volume and ensuring a long residence time, the digested sludge is drawn out from the digestion tank,
A method has been proposed in which this is concentrated by solid-liquid separation and concentrated, and the concentrated sludge is returned to the digestion tank. By returning the concentrated sludge to the digestion tank in this way, the SRT (solids retention time) can be set longer while the HRT (hydraulic retention time) remains unchanged, and the decomposition rate in organic waste can be increased. It is possible to decompose even a slow solid content, and a high volume reduction rate and a high methane production amount can be obtained.

Conventionally, as a method for concentrating this digested sludge,
The general method is the precipitation method, the membrane separation method, or the centrifugation method. However, these methods are applied only when the concentration of the digested sludge (solids (SS) concentration) is low and it is difficult to decompose, so the SRT is lengthened by returning the sludge. Therefore, it cannot be applied to anaerobic digestion of sewage sludge, etc., where sludge is highly concentrated in the tank.

That is, in the solid-liquid separation by the precipitation method or the membrane separation, if the digested sludge concentration exceeds 3%, good solid-liquid separation cannot be performed. It is impossible. In particular, in the case of membrane separation, if the digested sludge concentration is high, it is necessary to wash the membrane frequently due to clogging of the membrane, which is practically unusable.

From the above, the sludge concentration in the digestion tank cannot be increased to 3% or more by the conventional solid-liquid separation method, and the concentration ratio can hardly be increased even in the membrane separation. The digestion sludge is returned to the digestion tank with almost no concentration by the separating means, and a large capacity digestion tank is required.

In addition, the precipitation method and the centrifugal method use S in digested sludge.
It is not possible to collect S as much as possible.
Since is discharged to the outside of the system together with the separated water or as a sludge residue, there is also a drawback that the volume of sludge cannot be sufficiently reduced.

Therefore, in order to reduce the volume of sludge and promote the production of methane gas, the digested sludge is highly concentrated to recover the SS content as much as possible, and the SS content is returned to the digestion tank again to be anaerobic. For digestion, it is considered most effective to dehydrate digested sludge with a dehydrator. If it is a dehydrator,
Even if the digested sludge has a high concentration, it can be surely highly concentrated and the outflow of SS into the separated water can be prevented.

[0009]

However, according to the study by the present inventors, when the dehydrated sludge obtained by dehydrating the digested sludge with a dehydrator is returned to the digestion tank, the digestion efficiency of the dehydrated sludge is improved. Poorly, it was found that the volume reduction of sludge and the improvement of methane gas production efficiency could not be achieved.

The present invention enhances the digestion efficiency of the dehydrated sludge returned to the digestion tank and reduces the volume of the sludge in the anaerobic treatment of the organic waste which is dehydrated by the dehydrator and returned to the digestion tank. It is also an object of the present invention to provide an organic waste treatment device and a treatment method for promoting the production of methane gas.

[0011]

The apparatus for treating organic waste according to the present invention dehydrates the anaerobic digestion tank for anaerobic digesting the organic waste and the digested sludge discharged from the anaerobic digestion tank. It is characterized by having a dehydrator, a subdivision means for subdividing the dehydrated sludge from the dehydrator, and a returning means for returning the sludge subdivided by the subdivision means to the anaerobic digestion tank.

When the high-concentration digested sludge is dehydrated, the obtained dehydrated sludge becomes cake-like mass, which is larger than the sludge in the digestion tank. In particular, when a coagulant is used for this dehydration, the SS particles in the sludge are bound by the coagulant to form a very large lump of dehydrated sludge.

On the other hand, the decomposition of solid organic matter by anaerobic bacteria is carried out by a part of acid-producing bacteria producing a hydrolase which is an extracellular enzyme, and this hydrolase is used. Therefore, in order to accelerate the hydrolysis, it is necessary to increase the contact efficiency between the organic particles and these bacteria or enzymes.

However, as described above, the sludge after dehydration is a large lump, has a small surface area, and the contact efficiency with bacteria and enzymes is poor, so that it is more difficult to decompose than the sludge before dehydration.
Therefore, if the digested sludge is simply dehydrated and returned to the digestion tank, the SRT becomes longer, but the improvement of the digestion efficiency cannot be achieved. Further, when returning such a large lump of dehydrated sludge, the SS concentration in the digestion tank becomes high, the stirring becomes insufficient, and the sludge is not sufficiently dispersed in the digestion tank,
As a result, digestion efficiency may also be reduced by causing a decrease in effective volume.

In the present invention, since the dehydrated sludge is subdivided and returned to the digestion tank, the returned sludge is uniformly dispersed in the digestion tank and efficiently contacts with acid-producing bacteria and hydrolytic enzymes, It will be decomposed with the same digestion efficiency as the sludge in the tank. For this reason, the increase in SRT by returning sludge effectively functions in the sludge digestion efficiency, and it is possible to promote volume reduction of sludge and increase the amount of methane gas production.

In the present invention, the concentration of digested sludge is high,
If the dehydrated sludge also has a high concentration, the sludge has poor fluidity and is difficult to transfer or subdivide.
In addition, a problem such as a large amount of fragmentation energy may occur. Therefore, it is preferable to supply water to the dewatered sludge before the subdivision so as to adjust the sludge concentration so that the sludge can be easily transferred or subdivided.

Further, in order to further improve the digestion efficiency of the sludge in the digestion tank, the returned sludge and / or the digested sludge may be modified.

The method for treating organic waste of the present invention comprises an anaerobic digestion step of anaerobic digesting the organic waste, a dehydration step of dehydrating digested sludge from the anaerobic digestion step with a dehydrator, After the moisture is supplied to the dehydrated sludge from the dehydration step to adjust the concentration thereof, it is provided with a fragmentation step of fragmentation, and a return step of returning the sludge fragmented in the fragmentation step to the anaerobic digestion step. By dewatering the digested sludge, adjusting the concentration of the dehydrated sludge, subdividing it, and then returning it to the digestion tank, the conventional HRT, that is, without increasing the digestion tank volume, SRT The sludge can be lengthened to accelerate the volume reduction of sludge and the production of methane gas.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the apparatus and method for treating organic waste of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a system diagram showing an embodiment of an organic waste treatment apparatus of the present invention.

The organic waste is introduced into the digestion tank 1 and subjected to anaerobic digestion treatment. A part of the digested sludge in the digestion tank 1 is extracted and dehydrated by the dehydrator 2. The dehydrated sludge of the dehydrator 2 is sent to the subdivision tank 3 to be subdivided, and the subdivided sludge is returned to the digestion tank 1.

The dehydrator 2 for dehydrating the digested sludge is not particularly limited, and a filter cloth type dehydrator, a press dehydrator, a filter press, a centrifugal separator and the like can be used.

At the time of dehydration in the dehydrator 2, a coagulant, preferably a polymer coagulant, is added to remove S from the digested sludge.
Aggregating the S component is preferable because the SS recovery rate can be increased. As such a polymer flocculant, a nonionic, cationic, amphoteric polymer flocculant or the like can be used, and the addition amount thereof is 0.5 to 1.
It is preferably about 0% by weight. When the coagulant is added to the digested sludge, the coagulant may be injected into the digested sludge transfer line, added to the dehydrator, or a coagulation tank may be separately provided for the coagulation treatment.

When anaerobic digestion of hardly decomposable organic waste such as sewage sludge, the sludge concentration in the digestion tank is 4 to 8%.
It is preferable to increase it to a certain degree, and therefore, in the dehydrator 2,
It is preferable to dehydrate the digested sludge having an SS concentration of about 4 to 8% extracted from the digestion tank 1 to obtain a dehydrated sludge of about 15 to 25%.

As the subdivision tank 3, a mixer (rotary blade), a jet nozzle, or a stirrer capable of strong stirring can be used. In addition to such a subdivision tank, a crushing pump or the like can be used as a subdivision means for the dehydrated sludge.

This crushing means does not require a strong crushing force to destroy sludge particles, and when the lumps of dehydrated sludge are crushed and returned to the digestion tank 1, they are not lumps but liquid in the tank. It is sufficient that it is evenly dispersed in it.

The dehydrated sludge obtained by the dehydrator 2 is usually 1 to
Although it is a lump of about 50 cm, it is preferable to subdivide such a lump of dehydrated sludge into a particle size of 2 mm or less, preferably about 1 mm or less by a fragmentation means such as a fragmentation tank 3.

By the way, the high-concentration dewatered sludge obtained by the dewatering machine 2 has low fluidity as it is and is difficult to transfer, or is difficult to be subdivided, or requires great energy for subdivision. In many cases, it is preferable to supply water to the dehydrated sludge to adjust the sludge concentration to have fluidity, preferably to an SS concentration of about 5 to 10%.

The water supplied to the dehydrated sludge for adjusting the concentration may be the desorbed liquid of the dehydrator 2 or the digested sludge. It may also be organic waste to be treated. When using the desorbed liquid for concentration adjustment,
A part of the desorbed liquid discharged from the dehydrator 2 is collected in the line (3) and supplied to the subdivision tank 3. When digested sludge is used, a part of the digested sludge extracted from the digestion tank 1 through the system shown in FIG. 1 is supplied to the subdivision tank 3. As water for adjusting the sludge concentration, industrial water, city water, treated water of other processes, etc. may be supplied from outside the system.

In FIG. 1, the water is directly supplied to the subdivision tank 3 to adjust the sludge concentration and the subdivision at almost the same time. However, dehydration is performed between the dehydrator 2 and the subdivision tank 3. The concentration may be adjusted by supplying water to the sludge. In this case, water may be supplied to the dewatered sludge transfer line, or a separate adjustment tank for adjusting the sludge concentration may be provided.

The sludge subdivided by the subdivision means such as the subdivision tank 3 is returned to the digestion tank 1. In the present invention, a sludge reforming means is provided between the subdivision tank 3 and the digestion tank 1. By reforming the subdivided sludge and returning it to the digestion tank 1, the digestion efficiency of the sludge can be further enhanced, which is preferable.

The sludge reforming is to modify and destroy the sludge cells into a form that is easily assimilated by microorganisms, and any method commonly known as a sludge reforming method can be adopted. Various methods such as ozone treatment, chemical treatment with strong oxidizing power such as hydrogen peroxide, acid, alkali, etc., ultrasonic treatment, physical treatment such as milling, thermal treatment, etc. Can be used alone or in combination of two or more.

When the ozone treatment means is adopted as the sludge reforming means, an ozone treatment tank is provided between the subdivision tank 3 and the digestion tank 1, and the subdivision sludge is introduced into the ozone treatment tank to contact with ozone. Good. As a method of contacting with ozone, a method of introducing subdivided sludge into an ozone treatment tank and blowing in ozone, a method of mechanical stirring, a method of utilizing a packed bed, and the like can be adopted. As ozone, in addition to ozone-containing gas, ozone-containing water can be used, and the amount of ozone used is usually 0.0
_{1~0.3g-O 3 / g-VSS} , preferably 0.03
It is a _{~0.2g-O 3 / g-VSS} .

In the above example, the sludge reforming means is used as the subdivision tank 3
The sludge reforming means may be provided in the subdivision layer 3 to simultaneously subdivide the sludge and reform it with ozone or the like. The sludge may be reformed not on the returned sludge but on the digested sludge in the digestion tank 1. In this case, the digestion tank and the sludge reforming means are connected by a supply path for sending the digested sludge to the reforming means and a return path for returning the modified sludge to the digestion tank, and a part of the digested sludge in the digestion tank is modified. It can be easily digested by sending it to a quality means for modification and then returning it to the digestion tank.

In this way, a part of the digested sludge in the digestion tank 1 is extracted and dehydrated by the dehydrator 2, and the dehydrated sludge is subdivided and returned to the digestion tank 1, thereby increasing the SRT without changing the HRT. be able to.

The amount of digested sludge extracted from the digestion tank 1 is not particularly limited, but is 1/30 to 1 of the retained sludge in the digestion tank 1.
Approximately / 10 is drawn out, dehydrated, circulated and then circulated, so that the SRT can be extended at least about 3 times as long as when such sludge circulation is not performed, and it is a biodegradable organic substance. Even with waste, it is possible to promote volume reduction of sludge and increase the amount of methane gas produced.

Further, in the present invention, it is preferable to operate the dehydrator and the subdivision tank in a state of being shielded from the atmosphere. For example, by contacting the sludge with oxygen by dehydrating with the dehydrator closed. When it is limited, the anaerobic bacteria can be returned to the digestion tank while being kept alive, and the number of viable bacteria in the digestion tank can be easily maintained and increased, and the digestion efficiency can be improved.

[0038]

EXAMPLES The present invention will be described more specifically below with reference to experimental examples, examples and comparative examples.

Experimental Example 1 Digested sludge with a VSS concentration of 28,000 mg / L discharged by anaerobic digestion of excess sludge (SS content 4%) at a sewage treatment plant was dehydrated with a centrifugal dehydrator to obtain an SS concentration of 18%. I got dehydrated sludge. Tap water was added to this dehydrated sludge to adjust the SS concentration to 7%. The diameter of this sludge mass was 10 to 50 mm.

A part of the sludge adjusted to have an SS concentration of 7% was subdivided with a mixer to have a particle diameter of 1 mm or less.

A part of the fragmented sludge was treated with ozone at an ozone usage amount of 0.03 g-O ₃ / g-VSS.

After the dehydrated digested sludge was dehydrated, the sludge having an SS concentration of 7% (7% dehydrated sludge), the sludge subdivided (dehydrated, subdivided sludge), and the sludge further subjected to ozone treatment (dehydrated, Each of the subdivided and ozone-treated sludge) was put into a digestion tank, and the decomposability of the sludge was examined from the increase in the amount of methane gas produced over time, and the results are shown in FIG.

As is clear from FIG. 2, dehydrated and fragmented sludge has twice as much sludge decomposability as compared to undivided 7% dehydrated sludge, and dehydrated, fragmented and ozone-treated. Sludge has four times the sludge degradability.

Therefore, if the digested sludge is dehydrated and returned to the digestion tank as it is, the decomposability is lowered. Therefore, the dehydrated sludge is subdivided to restore the original decomposability of the digested sludge and then returned to the digestion tank. In addition, it is preferable that the fragmented sludge is treated with ozone and returned to the digestion tank, which can improve the digestion efficiency.

Example 1 Using the apparatus for treating organic waste shown in FIG. 1, anaerobic digestion treatment of mixed sludge (SS content 4%) at a sewage treatment plant was performed at a treatment amount of 2.4 g / day (SS conversion) and HRT. = It took 30 days.
A centrifugal dehydrator was used as the dehydrator 2, and a household mixer was used as the subdivision tank 3.

VSS concentration from digestion tank 1 of 28,000 m
3.2 g (SS conversion) of g / L digested sludge was extracted and dehydrated by the dehydrator 2 to obtain a dehydrated cake having an SS concentration of 18%.
In the dehydration, 0.5% by weight of SS was added to the digested sludge as a coagulant, a cationic polymer coagulant. The desorbed liquid of the dehydrator 2 was SS: 0.5% and was discharged to the outside of the system.

The dewatered sludge is then placed in the subdivision tank 3 to have a particle size of 1 m.
It was subdivided into m or smaller. In this subdivision, digested sludge was supplied as water to adjust the concentration of the subdivided sludge to 7%. The fragmented sludge was returned to the digestion tank 1.

In this way, by dewatering the digested sludge and then subdividing it and returning it to the digestion tank, it was possible to secure 120 days or more of SRT.

The TVS removal rate and the amount of methane produced in the digester at this time were investigated, and the results are shown in Table 1.

Example 2 Sewage sludge was subjected to anaerobic digestion in the same manner as in Example 1 except that the subdivided sludge was ozone-treated and then returned to the digestion tank, and the TVS removal rate and the amount of methane produced were examined. Is shown in Table 1. The ozone treatment was 0.03 g-O.
It carried out by the ozone usage amount of ₃ / g-VSS.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the digested sludge was not dehydrated, subdivided and returned, and HRT = SRT = 30 days. The results are shown in Table 1.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the digested sludge was dehydrated and then returned to the digestion tank without being subdivided, and the TVS removal rate and the methane production amount were examined. Is shown in Table 1.

[0053]

[Table 1]

As is clear from Table 1, in Example 1,
The TVS removal rate and the methane gas production amount increased 1.3 times as compared with Comparative Example 1 due to the extension of the SRT by dewatering the digested sludge and then fragmenting it and returning it to the digestion tank. Further, according to Example 2 in which the fragmented sludge was subjected to ozone treatment and returned to the digestion tank, the TVS removal rate and the methane gas production amount were further improved, and were 1.5 times those in Comparative Example 1.

Even if the dehydrated sludge is returned, in Comparative Example 2 in which the dehydrated sludge is directly returned without being subdivided, the TVS removal rate and the methane production amount are not improved.

[0056]

As described in detail above, according to the apparatus and method for treating organic waste of the present invention, the organic waste is efficiently treated in the anaerobic digestion treatment of the organic waste. It is possible to further reduce the volume of sludge and increase the amount of methane gas produced.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of an organic waste treatment apparatus of the present invention.

FIG. 2 is a graph showing the results of Experimental Example 1.

[Explanation of symbols]

1 digestion tank 2 dehydrator 3 subdivision tanks

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B09B 3/00 D

Claims (4)

[Claims] 1. An anaerobic digester for anaerobically digesting organic waste, a dehydrator for dehydrating digested sludge discharged from the anaerobic digester, and a subdivision for subdividing the dehydrated sludge from the dehydrator. An apparatus for treating organic waste, comprising: a liquefying means and a returning means for returning the sludge subdivided by the subdividing means to the anaerobic digestion tank. 2. The apparatus for treating organic waste according to claim 1, further comprising a water supply unit for adjusting the sludge concentration of the dehydrated sludge subdivided by the subdivision unit. 3. The organic substance according to claim 1, further comprising a sludge reforming unit for reforming sludge returned to the anaerobic digester and / or digested sludge in the anaerobic digester. Equipment for toxic waste. 4. An anaerobic digestion step of anaerobically digesting organic waste, a dehydration step of dehydrating digested sludge from the anaerobic digestion step with a dehydrator, and supplying water to the dehydrated sludge from the dehydration step. After adjusting the concentration of the organic waste, it is provided with a subdivision step of subdividing, and a returning step of returning the sludge subdivided in the subdivision step to the anaerobic digestion step. Method.