JPH11285698A - Biological dephosphorization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the addition of a flocculant, to diminish the the generation of sludge and to prevent the inhibition of methane fermentation at the time of treating org. waste in the treating system having a biological treating stage and an anaerobic fermentation stage. SOLUTION: A part of the excess sludge 5a generated in a biological treating stage #3 is introduced into an anaerobic fermentation stage #5 and transferred to an aerobic nitrification stage #6 along with digestion sludge 8, hence phosphorus is ingested by the facultative anaerobe contained in the excess sludge 5a, and the excess sludge 11 contg. the facultative anaerobe is separated. As a result of such biological dephosphorization, the addition of a flocculant in the subsequent stage of the anaerobic fermentation stage #5 and the generation of sludge are reduced, and fermentation is not inhibited by the returned flocculant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for recovering useful substances by treating a plurality of types of organic wastes having different properties and concentrations in a treatment system having a biological treatment step and an anaerobic fermentation step. The present invention relates to a biological dephosphorization method.

[0002]

2. Description of the Related Art Conventionally, organic waste has been recycled. For example, Japanese Patent Application Laid-Open No. Hei 9-201699 discloses that human waste, septic tank sludge, sewage sludge, agricultural sludge, livestock manure, garbage and foods are disclosed. Organic waste with different properties and concentrations, such as waste, is treated in the same system to collect useful substances,
A method for recycling is disclosed.

This method is as shown in FIG. 3. In this method, human waste, septic tank sludge, agricultural sludge, sewage sludge, and livestock manure are removed in a removing step # 31, and a solid-liquid separation step # 3 is performed.
In 2, the liquid waste 31 and the dewatered sludge 32 are separated,
The liquid waste 31 is subjected to BOD decomposition and denitrification as necessary in the biological treatment step # 33, and suspended matter is removed in the solid-liquid separation step # 34. COD, pigment components, iron and manganese are removed in the advanced treatment step # 35. Heavy metals such as are removed and disinfected for effluent or reused water.

On the other hand, garbage and food waste are crushed in a crushing / separating step # 36, plastic bags and trays are separated, and then mixed with the above-mentioned dewatered sludge 32.
In the anaerobic fermentation step # 37, methane fermentation is performed, and the generated methane gas 33 is collected and used in the form of electricity or heat in the power generation step # 38 and the like, and the digested sludge 34 is converted into dehydrated sludge 35 in the dehydration step # 39. And sent to the composting process # 40, etc. to collect it as fertilizer, solid fuel or dry sludge.
3 to be processed.

[0005]

By the way, phosphorus contained in garbage and food waste is removed from the anaerobic fermentation step # 3.
7, the coagulant is added to the digested sludge 34 to transfer it to the dewatered sludge 35 side and to be taken out of the system. However, the coagulant treatment increases the amount of the dewatered sludge 35 generated. Problem.

Further, the dehydrated filtrate 36 is subjected to a biological treatment step # 33.
Is usually contained in excess sludge introduced from the biological treatment step # 33 through the solid-liquid separation step # 32 into the anaerobic fermentation step # 37, and the flocculant is added to the anaerobic fermentation step # 37. A with high phosphorus aggregation effect
In the case of l-type or Fe-type flocculants, there is a problem that methane fermentation is inhibited.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to reduce the amount of a flocculant added, to reduce the amount of sludge generated, and to prevent the inhibition of methane fermentation.

[0008]

Means for Solving the Problems To solve the above problems, the biological dephosphorization method of the present invention is a method for removing organic waste having different properties and concentrations, such as human waste, septic tank sludge, and garbage.
Treated with a treatment system that has a biological treatment process for biologically treating liquid organic waste and an anaerobic fermentation process for recovering methane gas by methane fermentation of organic waste containing solids under anaerobic conditions In doing so, a part of the sludge generated in the biological treatment step is introduced into an anaerobic fermentation step, and digested sludge generated in the anaerobic fermentation step is subjected to aerobic denitrification under aerobic conditions. Transfer to the process, decompose part of the organic matter contained in the digested sludge, and in a state of denitrification, let the facultative anaerobic bacteria contained in the sludge introduced from the biological treatment process take up phosphorus, and Excess sludge containing anaerobic bacteria is separated.

Generally, the sludge generated in the biological treatment step contains facultative anaerobic bacteria, and the facultative anaerobic bacteria are B-type anaerobic bacteria.
It releases phosphorus in the body under anaerobic conditions rich in OD, and has the property of ingesting excessive phosphorus under aerobic conditions. On the other hand, facultative anaerobic bacteria do not usually exist in the anaerobic fermentation step in which methane fermentation is performed.

[0010] Therefore, when the sludge generated in the biological treatment step is introduced into the anaerobic fermentation step, the facultative anaerobic bacteria contained in the sludge are phosphorus-starved, and the phosphorus-starved facultative anaerobic bacteria are: In a subsequent aerobic denitrification step, phosphorus introduced by digested sludge is taken in excessively. Therefore, phosphorus can be removed from the treatment system by separating the excess sludge containing the facultative anaerobic bacteria.

According to such a biological dephosphorization method,
The amount of coagulant added and the amount of sludge generated in the latter stage of the anaerobic fermentation process can be reduced, and the inhibition of methane fermentation caused by the returned coagulant can be prevented.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, organic waste in the form of slurry, such as night soil, septic tank sludge, sewage sludge, agricultural sludge, livestock manure, etc., is subjected to an appropriate screen according to the size of the sediment contained in the sediment removal step # 1. Remove the residue. This residue removal step # 1 is performed for protection of a dehydrator and the like at a later stage, and can be omitted when unnecessary.

[0013] Solid-liquid separation step #
2, and depending on the properties, an organic polymer flocculant 2 is added to perform solid-liquid separation to obtain a dehydrated sludge 3 and a separated liquid 4. here,
The solid-liquid separation step # 2 is performed by a dehydrator such as a centrifugal dehydrator, a belt press type dehydrator, a filter press, a rotating disk type dehydrator, etc., or a concentration screen or a gravity concentration tank according to a desired sludge moisture content. And can be omitted if not necessary.

The separation liquid 4 (or the liquid organic waste 1 ') is introduced into the biological treatment step # 3, BOD is decomposed and, if necessary, denitrified. Lead to processing.

[0015] On the other hand, other organic wastes containing non-fermentable substances such as plastics, such as garbage and food waste, or being heterogeneous, are subjected to a crushing / separation step #.
Crush in step 4 and separate plastic bags and trays.

The crushed material 6 obtained by crushing and separation is mixed with the above-mentioned dewatered sludge 3 to adjust the concentration of TS (total evaporation residue), introduced into the anaerobic fermentation step # 5, and introduced into the fermenter 10 to 15 minutes. The methane fermentation is performed in a state where the methane gas is retained for a day, and the generated methane gas 7 is collected.

At this time, a part of the excess sludge 5a generated in the biological treatment step # 3 is passed through the inside of the inner cylinder immersed and installed in the fermentation tank so that the number of days of stay in the tank is 1-2 days. . Then, the digested sludge 8 (substantially liquid) discharged out of the tank including the excess sludge 5a is diluted with a dehydrated filtrate 9 described below and transferred to the aerobic denitrification step # 6, where the microorganisms are removed under aerobic conditions. In a state where the water-soluble organic matter is decomposed and denitrified by the action of, the facultative anaerobic bacteria in the surplus sludge 5a ingest phosphorus. The denitrified water 10 is treated in the same manner as the biologically treated water 5.

Excess sludge 11 containing the facultatively anaerobic bacteria ingested with phosphorus is appropriately extracted and led to a dehydration step 7, where an inorganic coagulant 12 and an organic polymer coagulant 13 are added, and a centrifugal dehydrator, a belt press The dewatered sludge 14 and the above-mentioned dehydrated filtrate 9 are separated by dewatering with a dehydrator such as a mold dehydrator, a filter press, and a rotating disk dehydrator. The dewatered sludge 14 is treated in the same manner as in the prior art.

According to the above-described biological dephosphorization method, the amount of the inorganic coagulant 12 and the amount of the organic polymer coagulant 13 added and the amount of dewatered sludge 14 generated can be reduced. Alternatively, if biological treatment step # 3 is configured to perform aerobic denitrification, digested sludge 8 may be introduced into biological treatment step # 3, as shown in FIG. .

In this case, by performing biological dephosphorization,
The amount of the inorganic flocculant 12 and the organic polymer flocculant 13 and the amount of the dewatered sludge 14 can be reduced in the same manner as described above. Since it is not necessary to add a large amount of a substance having a high dephosphorizing effect as described above, even if the dehydrated filtrate 9 is returned to the biological treatment step # 3, there is little possibility that a flocculant that inhibits anaerobic fermentation will be introduced. The excess sludge 5a of # 3 can be introduced into the anaerobic fermentation step # 5 as described above. The dehydrated filtrate 9 can also be used as dilution water for adjusting the concentration in the anaerobic fermentation step # 5 and adjusting the pressure in the crushing / sorting step # 4.

As an apparatus for the biological treatment step # 3 or the aerobic denitrification step # 6, an external pressure type membrane separation apparatus having a membrane element such as a ceramic tubular membrane or a flat organic membrane is installed in the biological treatment tank. The immersion-installed type is advantageous because it can maintain microorganisms at a high concentration, obtain clear treated water, and eliminate the need for a solid-liquid separation step using a subsequent sedimentation basin or the like, but can be variously modified.

In the anaerobic fermentation step # 5, the crushed material 6 and the dewatered sludge 3 are composed of components different from each other, for example, trace elements (F
e, Ni, Co, etc.), and the methane fermentation can be performed efficiently in a short number of days due to the effect of mixing. However, these pretreatments are not limited to the above-described methods, but may be performed according to the properties of the object to be treated. It can be changed as needed. However, in the crushing / separation step # 4, it is preferable that the organic waste is coarsely crushed by a coarse crusher such as a uniaxial crusher and then compressed and crushed by a compression crusher at a high pressure of 200 to 250 kg / cm ^2. . In this case, not only garbage and food waste, but also the residue separated in the residue removing step # 1 may be mixed, and the above-described dewatered sludge 3 may be mixed at this stage.

According to this method, the organic wastes and the plastics accompanying the organic wastes have a particle size of 20 to 200 with a uniaxial crusher.
After being coarsely crushed to 100 mm or less, the crushed material is compressed and crushed by a compression crusher at a high pressure, and has a particle size of 1 corresponding to the diameter of the crushing discharge hole.
Fine particle crushed material of ~ 2 mm or less, and non-crushable residue
It is automatically classified as unsuitable for fermentation such as plastics, metals, stones and sand.

The separated crushed material is reduced to fine particles and the cell membrane is partially destroyed, so that the biodegradability becomes extremely large. In addition, the organic waste that has been removed by being adhered to the unsuitable fermentation material may be included in the crushed material, and the recovery rate of organic components such as methane gas becomes extremely high.

The concentration of the organic waste in the anaerobic fermentation step # 5 may be such that the fluidity can be maintained in the fermentation tank. The methane bacteria concentration is increased by concentrating with a filtration membrane and the like and returned to the fermenter (residual), or solubilized by maintaining the dehydrated sludge 3 at about 70 to 80 ° C. for 3 days. If you do, the fermentation efficiency will increase.

[0026]

As described above, according to the present invention, a part of the sludge generated in the biological treatment step is introduced into the anaerobic fermentation step, and the digested sludge generated in the anaerobic fermentation step is removed from the aerobic denitrification step. Dephosphorization can be carried out by effectively utilizing the properties of microorganisms, and the amount of coagulant added at the later stage of the anaerobic fermentation process can be reduced compared to conventional dephosphorization methods using coagulants However, the amount of sludge generated can be reduced, and the amount of coagulant brought into the anaerobic fermentation step by return can be reduced, so that methane fermentation can be prevented from being inhibited.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a biological phosphorus removal method according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating a biological dephosphorization method according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing a conventional organic waste treatment flow.

[Explanation of symbols]

 5a Excess sludge 7 Methane gas 8 Digested sludge 11 Excess sludge

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Shibata 2-47 Shishitsu Higashi, Naniwa-ku, Osaka-shi, Osaka Kubota Corporation

Claims (1)

[Claims] An organic waste having different properties and concentrations, such as night soil, septic tank sludge, and garbage, a biological treatment step of biologically treating a liquid organic waste, and an organic waste containing solids. When treating in a treatment system having an anaerobic fermentation step of recovering methane gas by methane fermentation under anaerobic conditions, a part of the sludge generated in the biological treatment step is introduced into the anaerobic fermentation step, Along with the digested sludge generated in the fermentation process, it is transferred to the aerobic denitrification process where biological denitrification is performed under aerobic conditions, in which some of the organic matter contained in the digested sludge is decomposed and denitrified. A method of biologically removing phosphorus, comprising ingesting phosphorus into facultative anaerobic bacteria contained in sludge introduced from a biological treatment step, and separating excess sludge containing the facultative anaerobic bacteria.