JP3276138B2 - Organic waste treatment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating organic waste, and more particularly, to an anaerobic digestion treatment of organic waste such as garbage and a biological denitrification treatment of a digested and desorbed liquid. About the law.

[0002]

2. Description of the Related Art Conventionally, most organic substances such as garbage are incinerated and landfilled together with other general garbage. However, in recent years, due to waste reduction and recycling,
Efforts are being made to promote the use of household posters, separate collection of kitchen waste, and composting. Further, since nitrogen in wastewater is a problem as a cause of eutrophication in closed water bodies, some wastewater is treated by a biological denitrification method. In the incineration of general garbage, garbage causes a change in calorific value, and there is a concern that dioxin may be generated due to chlorine in the garbage. Furthermore, there is anaerobic digestion method as one of the garbage disposal technology. Research and development of anaerobic digestion of garbage has been conducted in Japan for a long time, but anaerobic digestion is a relatively high concentration wastewater. Since there is a problem in the treatment of the desorbed liquid, it has not been put to practical use.

[0003] Nitrogen in wastewater is strongly required to be removed as a causative substance of eutrophication in the water system to which it is discharged.
Anaerobic digestion has no nitrogen removal function. At present, almost all nitrogen removal of wastewater is performed by biological denitrification. The most widespread method in this treatment is a nitrification liquid circulation system. In this method, nitric acid generated by nitrification of ammonia can be denitrified by using BOD components (organic pollutants) in wastewater, and the amount of valuable reducing agent injected for denitrification is extremely small. It is economical and has the advantage that BOD components can be treated simultaneously with denitrification. However, in the anaerobic digestion treatment, since the BOD component is gas-treated, the amount of BOD remaining in the digestion and desorption solution of garbage becomes insufficient for denitrification, and the denitrification treatment cannot be performed economically. was there.

[0004]

DISCLOSURE OF THE INVENTION In view of the above prior art, the present invention provides a method for treating an organic waste capable of efficiently and inexpensively denitrifying an anaerobic digestion solution of an organic waste. The task is to provide.

[0005]

In order to solve the above problems, according to the present invention, an organic waste is solubilized in an acid fermentation step and then anaerobic digested in an anaerobic digestion step. In a method for treating an organic waste in which an effluent is treated in a biological denitrification step, a part of the lysate from the acid fermentation step is injected into a biological denitrification step and denitrified together with the digestion step effluent. It is to be processed. In the method for treating organic waste, the solubilized solution in the acid fermentation step is preferably subjected to solid-liquid separation and the separated solution is injected into the biological denitrification step,
The effluent from the anaerobic digestion step is also preferably subjected to solid-liquid separation, and the separated liquid is subjected to a biological denitrification step.

[0006]

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall process diagram for carrying out the processing method of the present invention. In FIG. 1, garbage 1 as organic waste is crushed and sorted in a pretreatment step 2, and sorted garbage 3 is introduced into an acid fermentation tank 4 under anaerobic conditions, and is usually injected by diluting water 20. It is adjusted to an SS (suspended solids) concentration of 10 to 15% for easy stirring, and is introduced into the anaerobic digestion tank 5 after the acid fermentation has progressed. If the stirrer in the acid fermentation tank is compatible with high concentration, the SS concentration is necessarily 15%
There is no need to: In the acid fermenter 4, since the biodegradable organic matter is anaerobically decomposed and the organic acid that facilitates methane fermentation accumulates to lower the pH, the acid fermenter must be constructed of a corrosion-resistant material. Acid fermentation tank 4 Effluent is anaerobic digestion tank 5
And the organic matter in the influent is decomposed into biogas 6 under anaerobic conditions. The biogas 6 is stored in a gas tank 8 via a desulfurization device 7, and is used according to the application. Although not shown, the digestion tank 5 is subjected to mechanical stirring or gas stirring.

[0007] The digestion / elimination liquid (digestion tank effluent) 9 is introduced into a sludge dewatering step 10, where dewatered sludge 11 and dewatered separated water 12 are removed.
The separated water 12 flows into a denitrification step 13 which is a biological treatment apparatus, and is subjected to a denitrification treatment. A part 14 of the liquid in the acid fermentation tank 4 is directly introduced into the denitrification step 13 without passing through the digestion tank 5. The BOD source mainly composed of the organic acid in the liquid 14 serves as a nitric acid reducing agent. The organic acid is a very excellent reducing agent for denitrification (biological decomposition of nitric acid). SS for liquid 14
In the case of a large amount, the amount of excess sludge 15 in the denitrification step 13 is increased. To prevent this, the SS is separated by a solid-liquid separator 16 such as a centrifuge or a membrane separator, and separated. The liquid 17 is introduced into the denitrification step 13 and separated sludge 18
May be returned to the acid fermenter 4. The excess sludge 15 can be reduced in volume and gasified by being introduced into the anaerobic digestion tank 5.

[0008] The amount of the acid fermentation liquor to be injected into the denitrification step may be set approximately according to the following equation. Q = 3Q ′ · N ′ (X-3N) ⁻¹ Q: Acid fermentation liquid injection amount (m ³ / day), X: Acid fermentation liquid BOD concentration (mg / liter), N: Acid fermentation liquid nitrogen concentration (mg) / L), Q ': Separated water amount (m ³ / day), N': Separated water nitrogen concentration (mg / L) In the denitrification step 13, the BOD component in the organic wastewater can be used as a reducing agent for denitrification. A known biological denitrification method such as an economic nitrification liquid circulation system or a batch system can be used.

The dewatered separated water 12 and the denitrified water 19 can be used as dilution water 20 in the acid fermentation tank 4. Organic waste includes garbage from households, catering centers, restaurants, etc., waste from food processing plants (okara, juice grounds, beer grounds, shochu lees, etc.), expired foods, distribution process Foods that can be basically decomposed by microorganisms, such as spoiled foods, surplus compost, spent mushroom culture beds, agricultural and livestock wastes, etc. It may be solid, slurry, or liquid such as suspension. The garbage 1, which is an organic waste, is intended to be discharged from households, catering centers, restaurants, food processing factories, and the like. From households, garbage collected separately is desirable. The pre-treatment step 2 is a step for removing non-biodegradable plastics, metals, and the like, and includes automatic separation of foreign substances by a machine such as a garbage bag breaker, a soft or hard plastic separator, or a magnetic separator of irons. Hand sorting is performed as needed. It is desirable that the garbage is crushed and pulverized so that it can be easily decomposed before or after sorting.

The garbage introduced into the acid fermentation tank 4 has a water content of about 70 to 80% and does not have the fluidity required for anaerobic digestion. 1
While adjusting to 0 to 15% (water content 85 to 90%),
Steam is injected to keep the water temperature at 50 to 55 ° C for 1 to 2 days. Thereby, the microbial acid fermentation proceeds and the SS is solubilized, so that gasification by anaerobic digestion becomes easy. In the main tank 4, acid fermentation proceeds smoothly by gentle mechanical agitation, and foreign substances having a relatively large specific gravity settle at the bottom. In addition, sedimentation and separation of fine sand or the like adhering to the solid matter is facilitated by dilution and solubilization of the solid matter. In the influent into the anaerobic digestion tank 5, organic matter is gasified at a water temperature of about 55 ° C. and a staying number of 10 to 15 days.

In the dewatering step 10, in order to obtain a dewatered sludge 11 having a low water content, a sludge dewatering polymer is injected at about 1.0% of SS, and a conventional dewatering apparatus such as a centrifugal dewatering machine, a belt press, and a screw is used. It is desirable that the water content is adjusted to 80% or less, preferably about 70% by a dehydrator such as a press or a filter press. If the properties of the digested sludge are good, the injection amount of the polymer can be reduced or not added. Next, another embodiment of the processing method of the present invention will be described with reference to FIG. In FIG. 2, a part 14 of the liquid in the acid fermenter 4 is introduced into the dehydration step 10 and dehydrated,
Since the liquid component containing the organic acid therein is introduced into the denitrification step 13 together with the dewatered and separated water 12, economical denitrification can be easily performed. This method may be applied to the liquid 14 in which the biodegradable organic matter is sufficiently solubilized and the relatively non-biodegradable SS is relatively turbid.

[0012]

The present invention will be described below in more detail with reference to examples. Example 1 An example in which the present invention was performed according to the process charts of FIGS. Sorted garbage: 5 t / day, acid fermentation tank (dilution adjustment tank: vertical screw stirrer, attached to sediment discharge pipe), effective volume: 10 m ³ , water temperature: 55 ° C., injection amount of dewatered separated water: 5 m ³ / day, Anaerobic digestion tank (with gas stirrer), Effective volume: 100m ³ , Water temperature: 55 ° C,

Dehydrator (screw press dehydrator), cationic polymer injection amount (for sludge), based on SS: 0.3 to 1.0%, dehydrated separated water NH ₃ -N: 1000 mg / liter, biological denitrification Treatment method: nitrification liquid circulation type membrane separation method, total effective volume: 20 m ³ , treatment water temperature: 35 ° C., liquid distribution amount from acid fermentation tank, method of FIG. 1: 1.8 m ³ / day, method of FIG. 2: 1.8 m ³ / day, Comparative example: 0.0 m ³ / day

[Processing result] Table 1 shows the processing result. As a comparative example, a case where the liquid from the acid fermentation tank is not introduced into the denitrification step is also shown. According to the present invention, a high-rate nitrogen treatment can be performed without using methanol as a reducing agent for denitrification. In the comparative example, the nitrogen removal rate when methanol was not used was only 16%.

[Table 1]

[0015]

Industrial Applicability According to the present invention, high-rate biological denitrification of an anaerobic digestion / desorption solution can be carried out without using a valuable reducing agent such as methanol or the like with little or no use. Can be.

[Brief description of the drawings]

FIG. 1 is an overall process diagram for implementing a processing method according to an example of the present invention.

FIG. 2 is an overall process diagram for implementing another example of the processing method of the present invention.

[Explanation of symbols]

1: garbage, 2: pretreatment step, 3: sorted garbage, 4: acid fermentation tank, 5: anaerobic digestion tank, 6: biogas, 7: desulfurization unit, 8: gas tank, 9: digestion desorption liquid , 10: sludge dewatering step, 11: dewatered sludge, 12: dewatered separated water, 13: denitrification step, 14: acid fermentation liquid, 15: surplus sludge, 16: solid-liquid separation device, 17: separation liquid, 18: separation Sludge, 19: denitrified water, 20: dilution water

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B09B 3/00 C02F 3/34 101 C02F 11/04

Claims (3)

(57) [Claims] An organic waste obtained by solubilizing an organic waste in an acid fermentation step, anaerobic digestion in an anaerobic digestion step, and treating an effluent from the digestion step in a biological denitrification step. 3. The method for treating organic waste according to claim 1, wherein a part of the lysate from the acid fermentation step is injected into a biological denitrification step and denitrified together with an effluent from the digestion step. 2. The method for treating organic waste according to claim 1, wherein the solubilized solution in the acid fermentation step is subjected to solid-liquid separation, and the separated solution is injected into a biological denitrification step. 3. The organic waste according to claim 1, wherein the effluent from the anaerobic digestion step is subjected to solid-liquid separation and the separated liquid is treated in a biological denitrification step. Processing method.