JP2000005797A - Method for recovering metahne from organic solid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover methane gas even from the excess sludge having a high content of difficult-to-decompose org. matter with high efficiency in the same way as for garbage by promoting the solubilization of the excess sludge by the heat, ultrasonic wave and lytic enzyme at the preceding stage to the stage of mixing the excess sludge with garbage and then mixing the solubilized sludge with garbage. SOLUTION: Excreta and septic-tank sludge are freed from the residue (S1) and then biologically treated by an activated-sludge device (S2), and the supernatant liq. is subjected to such complete treatment as flocculation and separation/ activated-carbon treatment and then discharged. Meanwhile, the excess sludge settled and removed by the biological treatment is concentrated in a concentration tank (S3), then the molecular weight lowering and solubilization of the cellulose, etc., contained in the excess sludge are promoted by the heat or ultrasonic wave by decomposing them to the org. acid or the like. Subsequently, the excess sludge and the crushed garbage obtained by crushing the garbage (S4) are charged into a mixing tank (S5) to mix the excess sludge and garbage and methane-fermented (S6). The produced methane is used to generate electric power (S7), and the digested sludge is composted (S9).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to methane fermentation by mixing a plurality of types of organic wastes having different properties and concentrations (human waste, septic tank sludge, sewage sludge, livestock wastewater sludge, and raw garbage and fish ash). The present invention relates to an organic solid matter methane recovery method for performing methane fermentation in a tank and recovering useful substances such as methane, and in particular, performs night soil, septic tank sludge, sewage sludge, livestock wastewater sludge (hereinafter referred to as night soil and sludge), and the like. After removing the residue, the organic wastewater is subjected to biological treatment, and the excess sludge generated by the biological treatment is mixed with kitchen waste such as garbage and fish ash, and then subjected to methane fermentation to recover useful substances such as methane. Methane recovery method.

[0002]

2. Description of the Related Art Conventionally, the above-mentioned human waste and sludge are subjected to organic wastewater biological treatment after removing the residue, and excess sludge generated by the biological treatment is mixed with kitchen waste such as garbage and fish ash. An organic solid methane recovery method for performing methane fermentation and recovering useful substances such as methane is disclosed in
It is disclosed in U.S. Pat.

[0003] The methane recovery process will be described with reference to Fig. 4. First, after excrement of human waste and septic tank sludge is removed using a screen or the like (S1), the activated sludge is formed of an aeration tank and a sedimentation tank. Biological treatment (S2) is performed by a sludge device, and the supernatant is discharged after performing advanced treatment (not shown) such as coagulation separation / activated carbon treatment. On the other hand, the excess sludge settled and removed by the biological treatment is concentrated in a concentration tank (S3), and then put into a mixing tank together with crushed kitchen garbage obtained by crushing kitchen garbage such as garbage and fish ash (S4).
In the mixing tank (S5), the concentrated excess sludge and the garbage are sufficiently mixed and then methane fermented in a methane fermentation tank (S6).

[0004] Digested gas such as methane gas gasified by the methane fermentation (S6) is supplied to power generation (S7) and used as electric power in the treatment plant, and digested sludge after the methane fermentation (S6) is dewatered. (S8), the dewatered dewatered cake is composted (S9) and used for compost or the like, while the dewatered filtrate is returned to a biological treatment tank such as an activated sludge apparatus.

[0005]

However, surplus sludge after biological treatment (S2) and kitchen waste greatly differ in the ease of decomposing organic substances. More specifically, surplus sludge that is difficult to decompose in surplus sludge is used. Because of the high proportion of methane gas, simply mixing excess sludge and garbage in the first stage of the methane fermentation tank means that the amount of methane gas recovered from kitchen waste is high, but the amount of gas generated from excess sludge is low. Had issues.

On the other hand, when mainly decomposing garbage or the like is mainly treated in a methane fermentation tank, the sludge concentration in the methane fermentation tank is reduced, thereby causing troubles such as rancidness due to organic acid generation in the methane fermentation tank. Tends to occur.

The present invention has been made in view of the above problems, and provides an organic solid matter methane recovery method capable of efficiently recovering methane gas from excess sludge containing a large amount of hardly decomposable organic substances such as cellulose as well as kitchen waste. The purpose is to:

Another object of the present invention is to improve the efficiency of the methane fermentation tank and to return a part of the undigested sludge of the methane fermentation tank to the tank to prevent a decrease in the solid concentration in the tank. An object of the present invention is to provide an organic solid methane recovery method that can effectively prevent the occurrence of troubles such as rancidity due to organic acid generation in a fermenter.

[0009]

According to the first aspect of the present invention,
After mixing excess sludge generated from organic wastewater biological treatment with kitchen garbage, methane fermentation is performed, and in an organic solid methane recovery method for recovering useful materials such as methane, in the previous stage of mixing the excess sludge with kitchen garbage. After the solubilization is promoted by solubilizing means using heat, ultrasonic waves, a lytic enzyme or a combination thereof, the mixture is mixed with the garbage.

According to the invention, the excess sludge is hardly degraded by applying heat, ultrasonic waves, or reacting with a lytic enzyme to reduce the molecular weight and solubilize it. In methane fermentation after mixing solubilized surplus sludge with kitchen waste, methane gas can be recovered with high efficiency. That is, methane fermentation is a method in which organic substances such as carbohydrates and proteins contained in the excess sludge and kitchen waste are decomposed into lower fatty acids and the like by acidophilic bacteria, and further decomposed to methane gas and carbon dioxide gas by methane bacteria. In addition, since the decomposability of the hardly decomposable organic matter in the excess sludge is improved by the acid bacteria, methane gas can be recovered with high efficiency as in kitchen garbage.

According to a second aspect of the present invention, after mixing surplus sludge generated from organic wastewater biological treatment with kitchen waste, methane fermentation (S6) is performed in a methane fermentation tank to recover useful substances such as methane. In the method for recovering a solid methane, the digested sludge discharged from the methane fermentation tank is dewatered, and a part of the dewatered sludge is returned to the methane fermentation facility.

In this invention, as a countermeasure against troubles such as rancidity due to organic acid generation in a methane fermentation tank, a part of the dewatered sludge is returned to supply solid matter. Thus, troubles such as rancidity due to organic acid generation in the methane fermentation tank can be prevented. The invention of claim 2 may be used alone, but the effect of the present invention can be more effectively achieved by combining with the invention of claim 1.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.

FIG. 1 shows a methane recovery process according to a first embodiment of the present invention. In FIG. 1, firstly, night soil and septic tank sludge are subjected to residue removal (S1) using a screen or the like. After that, biological treatment (S2) is performed by an activated sludge device including an aeration tank and a sedimentation tank, and the supernatant is subjected to advanced treatment (not shown) such as coagulation separation / activated carbon treatment and then discharged. The residue removed in the residue removal (S1) step is sent to an incinerator (S10).

On the other hand, the excess sludge settled and removed by the biological treatment is concentrated in a concentration tank (S3), and then the cellulose or the like contained in the excess sludge is decomposed into organic acids by heat or ultrasonic waves (S11). Reduce the molecular weight and solubilize. In this case, the heat may be heated to 50 to 60 ° C. or higher, and the oscillation intensity of the ultrasonic wave may be enough to loosen the molecular structure of cellulose or the like.

The excess sludge, which has been reduced in molecular weight and solubilized, is put into a mixing tank (S5) together with crushed garbage obtained by crushing garbage such as garbage and fish ash (S4). Mixing tank (S
In 5), the concentrated excess sludge and the garbage are sufficiently mixed and then methane fermented in a methane fermentation tank (S6).

In the methane fermentation tank, since the excess sludge has a molecular structure equivalent to that of kitchen waste, its degradability in methane fermentation is improved, and methane gas can be recovered with high efficiency.

The digested gas such as methane gas gasified by the methane fermentation (S6) is supplied to power generation (S7) and used as electric power in the treatment plant, and the digested sludge after the methane fermentation (S6) is dewatered. (S8), the dewatered dewatered cake is composted (S9) and used for compost or the like, while the dewatered filtrate is returned to a biological treatment tank such as an activated sludge apparatus.

According to this embodiment, methane gas can be efficiently recovered from excess sludge containing a large amount of hardly decomposable organic substances such as cellulose as well as kitchen waste.

FIG. 2 shows a methane recovery process according to a second embodiment of the present invention. The difference from FIG. 1 will be mainly described. Excess sludge settled and removed by the biological treatment is concentrated. Concentrated (S3), then lysed enzyme (S12)
Thus, cellulose and the like contained in the excess sludge are subjected to acid fermentation and decomposed into organic acids to reduce the molecular weight and solubilize. The excess sludge, which has been reduced in molecular weight and solubilized, is fed into the mixing tank (S5) together with the crushed garbage obtained by crushing garbage such as garbage and fish ash (S4). The following steps are the same as in the above embodiment.

FIG. 3 shows a methane recovery process according to a first embodiment of the present invention, wherein heat, ultrasonic waves, lytic enzymes or a combination thereof are used at the stage before mixing the excess sludge with kitchen garbage. The present invention is applicable when a solubilizing means may be provided or when no solubilizing means is provided.

That is, in the present embodiment, the excess sludge generated from the biological treatment of organic wastewater is reduced in molecular weight and solubilized (S11, S12) by a solubilizing means as required,
Mixing with the crushed kitchen waste in the mixing tank (S5), further performing methane fermentation (S6) in the methane fermentation tank, and dewatering the digested sludge discharged from the methane fermentation tank until the dewatered sludge is dewatered. 1 or the embodiment shown in FIG. 2, but a part of the dehydrated sludge is returned (S1) as a countermeasure in case of trouble such as rancidity due to organic acid generation in the methane fermentation tank.
3) to supply solids.

According to this embodiment, it is possible to prevent troubles such as rancidity due to the production of organic acids in the methane fermentation tank, and the digested sludge discharged from the methane fermentation tank is subjected to repeated return, for example, of excess sludge. Even hardly decomposable organic substances such as cellulose are sufficiently digested, and undigested sludge from the methane fermentation tank can be composted (S9) without sufficiently discharging sludge to the outside of the system.

[0024]

As described above, according to the first aspect of the present invention, methane gas can be efficiently recovered from surplus sludge containing a large amount of hardly decomposable organic substances such as cellulose as well as kitchen waste. According to the second aspect of the present invention,
Along with increasing the efficiency of the methane fermentation tank, it is possible to effectively prevent the occurrence of troubles such as rancidity due to organic acid generation in the methane fermentation tank.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a methane recovery process according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a methane recovery process according to a second embodiment of the present invention.

FIG. 3 is a flowchart showing a methane recovery process according to the first embodiment of the present invention.

FIG. 4 is a flowchart showing a methane recovery process according to the related art.

[Explanation of symbols]

(S2) Organic wastewater biological treatment step (S5) Mixing tank for excess sludge and kitchen waste (S6) Methane fermentation step (S11) Heat and ultrasonic application step (S12) Lytic enzyme step (S13) Part of dehydrated sludge Process of returning to methane fermentation equipment

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Nakamura 12 Nishikicho, Naka-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. Yokohama Works (72) Inventor Hiroaki Sudo 1-8-1, Koura, Kanazawa-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd. 4D059 AA01 AA02 AA03 AA05 AA07 AA08 BA12 BA25 BA26 BA56 BE00 BF02 BJ00 BK11 BK12 BK22 CA01 CA11 CA28 CC01 CC03

Claims (2)

[Claims] 1. An organic solid methane recovery method for mixing garbage with garbage after mixing excess sludge generated from organic wastewater biological treatment with garbage, wherein the excess sludge is mixed with garbage. Before mixing, heat, ultrasonic,
A method for recovering organic solid methane, comprising: promoting solubilization by a lytic enzyme or a solubilizing means obtained by combining them; 2. An organic solid matter methane recovery method for mixing surplus sludge generated from biological treatment of organic wastewater with kitchen garbage and then performing methane fermentation in a methane fermentation tank to recover useful substances such as methane. A method for recovering organic solid methane, comprising dewatering digested sludge discharged from a methane fermentation tank and returning a part of the dehydrated sludge to a methane fermentation facility.