JPH11277098A - Dephosphorizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform sufficient dephosphorization without obstructing methane fermentation. SOLUTION: Liquid org. waste is successively introduced into an anaerobic biological treatment process #3 and an aerobic biological treatment process #4 not only to decompose org. matter but also to perform denitrification and phosphorus discharged from the org. waste is excessively taken by bacteria held under an aerobic condition and generated phosphorus-containing excess sludge 6 is guided to a dehydration process #7 along with the digested sludge 9 generated in an anaerobic fermentation process #7 and flocculants 10, 11 are added to both sludges and these sludges are dehydrated to be separated as dehydrated sludge 12. By this method, it is unnecessary to pass the flocculants through the anerobic fermentation process #6 and, therefore, a proper amt. of the flocculants large in phosphorus removing effect can be added without considering the obstruction of methane fermentation and phosphorus is certainly removed to be discharged out of the system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing phosphorus when treating organic waste.

[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. 2. 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 decomposed by BOD and denitrified if necessary in the biological treatment step # 33, and the suspended solids are removed in the solid-liquid separation step # 34. COD, pigment components, iron and iron are removed in the advanced treatment step # 35. It removes heavy metals such as manganese and disinfects it to produce 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]

However, since night soil and septic tank sludge contain a relatively large amount of phosphorus,
Normally, phosphorus is transferred to the dewatered sludge 32 by adding a flocculant in the solid-liquid separation step # 32.
In the latter stage of the anaerobic fermentation step # 37 in which 2 is supplied, the coagulant is added again to the digested sludge 34 to transfer phosphorus to the dehydrated sludge 35 side, and is discharged out of the system as fertilizer or the like, or the dehydrated filtrate 36 The phosphorus is recovered by performing a crystallization method or the like.

However, when the coagulant is added in the solid-liquid separation step # 32, for example, an aluminum-based or iron-based coagulant inhibits methane fermentation, so the type and amount of the coagulant must be considered. Therefore, if a sufficient coagulation effect is not exerted, phosphorus may migrate to the liquid waste 31 side and may be discharged.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to enable sufficient dephosphorization without inhibiting methane fermentation.

[0008]

In order to solve the above problems, the method for removing phosphorus according to the present invention is a method for removing organic waste having different properties and concentrations, such as human waste, septic tank sludge, and garbage, into liquid organic waste. A biological treatment step of biologically treating the substance, and an organic waste containing solids is subjected to anaerobic fermentation under anaerobic conditions by a anaerobic fermentation step of recovering methane gas by a treatment system having a anaerobic fermentation step. In the treatment process, liquid organic waste is sequentially introduced under anaerobic and aerobic conditions to decompose and denitrify organic substances, and to remove phosphorus released from organic waste under aerobic conditions. Excessive ingestion by the lower microorganisms, the generated phosphorus-containing excess sludge, together with the digested sludge generated in the anaerobic fermentation step, is led to a dehydration step, a coagulant is added, dewatered, and separated as dewatered sludge. Was

According to the above configuration, the liquid organic waste is successively introduced under anaerobic and aerobic conditions, so that the microorganisms present in this biological treatment step are B
It releases phosphorus in the body under OD-rich and anaerobic conditions and becomes phosphorus-starved, and ingests excess phosphorus when moved to aerobic conditions with organic waste.

Therefore, the phosphorus-containing surplus sludge generated in the biological treatment step is led to the dehydration step together with the digested sludge generated in the anaerobic fermentation step, and a coagulant is added thereto for dehydration. It can be transferred to sludge and separated, and phosphorus can be efficiently removed from the treatment system.

In this case, the coagulant does not pass through the anaerobic fermentation step, and conversely, in the coagulation membrane separation step, an appropriate amount of the coagulant having a large phosphorus removing effect without considering the inhibition of methane fermentation. Since it can be added, it is possible to surely remove phosphorus and prevent phosphorus from being mixed into the discharge water.

In the coagulation membrane separation step, an aluminum-based coagulant such as bansulfate, aluminum chloride, aluminum sulfate, and TK floc, polyiron, ferrous sulfate, ferric sulfate,
An iron-based coagulant such as ferric chloride, an inorganic coagulant such as magnesium chloride and slaked lime are added. In the dehydration step, the same inorganic coagulant as in the coagulation membrane separation step and an organic polymer such as an amphoteric polymer and a cationic polymer are used. The phosphorus removal effect is high when the coagulant is added sequentially.

[0013]

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.

[0014] 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. 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, or a concentration screen or a gravity concentration tank according to a desired sludge moisture content. It can be omitted if it is not necessary.

The separation liquid 4 (or the liquid organic waste 1 ') is introduced into the anaerobic biological treatment step # 3 and the anaerobic biological treatment step # 4 sequentially, and circulated from the step # 4 to the step # 3. In addition, BOD decomposition and denitrification are performed, and microorganisms moving from anaerobic to aerobic conditions are caused to excessively ingest phosphorus. The biologically treated water 5 is discharged or reused through a downstream treatment step (not shown), and the excess sludge 6 containing phosphorus is treated as described later due to the low methane fermentation rate.

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 / separating step #
Crush in step 5 and separate plastic bags and trays.

The crushed material 7 obtained by crushing and separation is mixed with the above-mentioned dewatered sludge 3, and the TS (total evaporation residue) concentration is adjusted.
In the anaerobic fermentation step # 6, methane fermentation is performed in the fermenter, and the generated methane gas 8 is collected. At this time,
The crushed material 7 and the dehydrated sludge 3 are efficiently mixed with components different from each other, for example, trace elements (Fe, Ni, Co, etc.), and are efficiently methane fermented in a short number of days.

Digested sludge 9 generated in anaerobic fermentation step # 6
To the dehydration step # 7, the excess sludge 6 from the biological treatment step # 3 is appropriately extracted and led to the dehydration step 7, mixed with each other, and added with the inorganic flocculant 10 and the organic polymer flocculant 11 while adjusting the pH. Then, dewatering is performed by a dehydrator such as a centrifugal dehydrator, a belt press dehydrator, a filter press, a rotating disk dehydrator, or the like.

Since the separated dewatered sludge 12 contains phosphorus from the digested sludge 9 and the excess sludge 6, the dewatered sludge 12 is carried out through a composting step (not shown) or the like, or is directly carried out of the system to be dewatered. The filtrate 13 is returned to the aerobic biological treatment step # 4 for further processing.

In the aerobic biological treatment step # 4, if an external pressure type membrane separation device having a membrane element such as a ceramic tubular membrane or a flat organic membrane is immersed in a treatment tank, microorganisms can be held efficiently. This is convenient because clear biologically treated water 5 can be obtained during biological treatment, but the biologically treated water 5 may be led out by overflow and solid-liquid separation may be performed outside the treatment tank.

The pretreatment of the organic waste to be supplied to the anaerobic fermentation step # 6 is not limited to the above-mentioned method, but can be appropriately changed according to the properties of the object to be treated. However, in the crushing / sorting step # 5, 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 20 with a single-shaft 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 very 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 # 6 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.

[0025]

As described above, according to the present invention, phosphorus is generated biologically by introducing liquid organic waste sequentially under anaerobic and aerobic conditions. The excess sludge contained is led to the dehydration step together with the digested sludge generated in the anaerobic fermentation step, and the coagulant is added and dewatered. The type and amount of addition can be selected,
Phosphorus can be reliably transferred to the dewatered sludge side and removed from the treatment system.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a dephosphorization method according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating a conventional method for treating organic waste.

[Description of Signs] 6 Excess sludge 8 Methane gas 9 Digested sludge 10 Inorganic coagulant 11 Organic polymer coagulant 12 Dehydrated 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, in the biological treatment step, the liquid organic waste is subjected to anaerobic conditions and aerobic conditions. In order to decompose the organic matter, denitrify, and let the microorganisms under aerobic conditions ingest the phosphorus released from the organic waste excessively,
A dephosphorization method, wherein the generated phosphorus-containing excess sludge is led to a dehydration step together with a digested sludge generated in the anaerobic fermentation step, a coagulant is added, dewatered, and separated as dehydrated sludge.