JP3303906B2 - Biological treatment of garbage and organic wastewater - 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 biologically treating garbage, and more particularly, to a method for garbage that is subjected to anaerobic digestion treatment of garbage and to biologically denitrify the treated liquid together with organic wastewater. It relates to the biological treatment of organic wastewater.

[0002]

2. Description of the Related Art Conventionally, most garbage is incinerated and landfilled together with other general garbage. On the other hand, in order to reduce and recycle garbage, at present, the promotion of composters for households and the separate collection of kitchen waste are being carried out. Since nitrogen in wastewater is a problem as a cause of eutrophication in closed water bodies, some wastewater is treated by biological nitrification denitrification. In the incineration of general garbage, garbage causes a change in the calorific value, and there is a concern that chlorine in the garbage may generate dioxins. Anaerobic digestion is one of the garbage disposal technologies. Research and development of anaerobic digestion of garbage has been conducted in Japan for a long time, but it has not been put to practical use because of the problem with the treatment of anaerobic digestion wastewater, which is relatively high-concentration wastewater.

[0003] Methane bacteria involved in anaerobic digestion are inhibited by free ammonia, and are inactivated at higher concentrations. Although garbage contains various animal and plant organic matter, when the ratio of animal garbage increases, ammonia that is solubilized and eluted in the anaerobic digestion tank accumulates at a high concentration, causing anaerobic digestion. Will not progress. When the methane bacterium plays an important role in the anaerobic digestion treatment, when the ammonia concentration is high, the activity of the methane bacterium decreases due to its toxicity. Therefore, in order to perform the anaerobic digestion efficiently, the ammonia nitrogen concentration is 1500 mg / mg. Not more than 1 liter, preferably 1
000 mg / liter or less, desirably a lower concentration is better. Ammonia in water exists in equilibrium with ammonia ion (NH ₄ ⁺ ) and free ammonia (NH ₃ ) as shown in equation (1). By moving the equilibrium state to the left, the free ammonia concentration can be reduced, but there is a problem that the cost of chemicals increases. ^{_{NH 4 + + OH - ⇔ NH}} 3 + H 2 O (1)

[0004] Nitrogen in wastewater not only inhibits anaerobic digestion but also is strongly demanded to be removed as a causative substance of eutrophication in a water system to be discharged. At present, almost all of the nitrogen removal of wastewater is performed by biological nitrification and 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, so that it is not necessary to inject a valuable reducing agent for denitrification. 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 garbage digestion / desorption solution becomes insufficient for denitrification, and the garbage digestion / desorption solution is economically denitrified. There was a problem that it was not possible.

[0005]

DISCLOSURE OF THE INVENTION In view of the above-mentioned prior art, the present invention relates to a food waste and organic waste that can efficiently perform anaerobic digestion of food waste and economically perform a denitrification treatment from separated water. It is an object to provide a biological treatment method for wastewater.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, according to the present invention, when garbage having a solid content adjusted by injecting dilution water is anaerobically digested in an anaerobic digestion tank,
The suspended solids (SS) are separated from the effluent of the anaerobic digestion tank in a solid-liquid separation step, and the separated effluent is introduced into a biological denitrification step together with organic wastewater to be subjected to nitrification denitrification, A biological treatment method for garbage and organic wastewater, wherein the treated water subjected to denitrification is used as dilution water to be injected into the garbage.

[0007]

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 biological treatment method of the present invention. In FIG. 1, garbage 1
Is crushed and sorted in the pretreatment step 2, introduced into the dilution adjustment tank 4 as sorted garbage 3 and adjusted to an SS (suspended solids) concentration of 10 to 15% by injecting dilution water 16 to perform anaerobic digestion. It is introduced into the tank 5. The organic matter in the influent flowing into the anaerobic digestion tank 5 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. The digester effluent 9 is introduced into the sludge dewatering step 10,
Separated into dewatered sludge 11 and dewatered separated water 12, and separated water 12
Is a biological nitrification and denitrification process 14 with organic wastewater 13
And a part of the treated water 15 is injected as dilution water 16 into the dilution adjustment tank 4, and the remaining part 15 is discharged or further treated.

The garbage 1 is one that is discharged from general households, food service centers, restaurants, food processing factories, and the like. For households, sorted garbage is desirable. The pretreatment step 2 is a step of removing non-biodegradable plastics, metals, and the like, and is a step of automatically separating foreign substances by a machine such as a garbage bag breaker, a soft or hard plastic separator, or a magnetic separator of irons. In addition, hand sorting is performed as needed. It is desirable that the garbage be crushed and pulverized before or after sorting so that the garbage can be easily decomposed. The kitchen waste introduced into the dilution adjustment tank 4 has a water content of about 70 to 80% and does not have fluidity necessary for anaerobic digestion.
To make the SS concentration 10-15% (water content 85-90%).
%) And inject steam etc. to adjust the water temperature to 50-
Let stay at 55 ° C for 1-2 days. As a result, the microbial acid fermentation proceeds and the SS is solubilized, thereby facilitating gasification by anaerobic digestion.

The dilution adjusting tank 4 has a role of adjusting the solid concentration so as to facilitate anaerobic digestion. However, the dilution water 16 is generated in the process in order to save water and limit the amount of discharged water. It is desirable to use water with a low solids concentration. As described above, methane bacteria involved in anaerobic digestion are inhibited by ammonia. Therefore, the anaerobic digestion reaction can be smoothly advanced by diluting the solid concentration and the ammonia with the denitrification-treated water 15 from which the ammonia has been removed, instead of the dewatered and separated water 12. In the main tank 4, the acid fermentation proceeds smoothly by gentle mechanical stirring, and the foreign matter 13 having a relatively large specific gravity is deposited on the bottom, so that it is preferable to periodically discharge the foreign matter 13. 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. Since the pH of the material of the main tank 4 decreases due to acid fermentation, a corrosion-resistant material such as stainless steel is preferably used.

The influent flowing into the anaerobic digestion tank 5 has a water temperature of 55 ° C.
Organic matter is gasified in about 10 to 15 days. In the dewatering step 10, in order to obtain the dewatered sludge 11 having a low water content, a sludge dewatering polymer is injected at about 1.0% of SS, and a conventional dewatering device such as a centrifugal dewatering machine, a belt press, a screw press, and a filter is used. With a dehydrator such as a press, the water content is desirably 80% or less, preferably around 70%. The biological nitrification denitrification step 14 comprises
It is possible to use a well-known nitrification denitrification method of a digestive juice circulation system or a batch system in which the BOD component in the organic wastewater 13 can be used as a reducing agent for denitrification. Organic wastewater 1
As No. 3, wastewater having a higher BOD concentration than nitrogen, for example, night soil, septic tank sludge, sewage, food processing wastewater, livestock wastewater, and the like can be used.

[0011]

The present invention will be described below in more detail with reference to examples. Example 1 An example of processing in which the present invention is performed according to the process diagram of FIG. 1 will be described. Sorted garbage: 5 t / day (animal meat residue 25%, vegetable waste 75%), organic nitrogen-containing wastewater (human waste): 5 m ³ / day, dilution adjustment tank (acid fermentation tank: vertical screw stirrer, sediment discharge) Attached to pipe), Effective volume: 15m ³ , Water temperature: 55 ° C, Injection amount of denitrification water: 10m ³ / day,

Anaerobic digestion tank (with gas stirring equipment), effective volume: 150 m ³ , water temperature: 55 ° C., dehydrator (screw press dehydrator), cationic polymer injection amount (for sludge), SS: 1.0% , Biological nitrification denitrification treatment method, nitrification liquid circulation type membrane separation method, total effective volume: 200m ³

[Results] The results of the present invention are shown in Table 1. As a comparative example, an example is shown in which separated water obtained by centrifuging an effluent from an anaerobic digestion tank is directly injected into a dilution adjustment tank as dilution water. The digester effluent of the comparative example had more fine colloidal suspensions than the present invention. Centrifuged water B of Comparative Example
It is for this reason that the OD is high. Further, it is considered that the reason why the water content of the comparative example is high is that the aggregation effect of the cationic polymer was small due to the large amount of suspended colloid.

[0014]

[Table 1]

[0015]

According to the present invention, the toxicity of ammonia in anaerobic digestion can be reduced, so that the quality of centrifuged water can be improved, the moisture content of dewatered sludge can be reduced, and the amount of biogas generated can be increased. Further, the biological denitrification treatment of the anaerobic digestion / desorption liquid can be economically performed.

[Brief description of the drawings]

FIG. 1 is an overall process chart for carrying out a biological treatment method of the present invention.

[Explanation of symbols]

1: garbage 2: pretreatment step 3: sorted garbage 4: dilution adjustment tank, 5: anaerobic digestion tank, 6: biogas, 7: desulfurizer, 8: gas tank, 9: digestion tank effluent , 10: sludge dewatering step, 11: dewatered sludge, 12: dewatered separated water, 1
3: organic wastewater, 14: biological nitrification denitrification step, 1
5: treated water, 16: dilution water

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-13091 (JP, A) JP-A-7-115862 (JP, A) Takayuki Suzuki, Yoshiyuki Ichiki, Koichi Kiriyama, Methane fermentation method Sludge treatment and resource / energy recovery, environmental management, Japan Industrial Environmental Management Association, July 10, 1997, Vol. 33, No. 7, pp. 26-34 (58). ⁷ , DB name) B09B 3/00 C02F 11/04 C02F 3/30

Claims (1)

(57) [Claims] When garbage having a solid content adjusted by injecting dilution water is subjected to anaerobic digestion in an anaerobic digestion tank, suspended solids (SS) are solidified from the effluent of the anaerobic digestion tank. Separated in the liquid separation step, the separated effluent is introduced into the biological denitrification step together with the organic wastewater and subjected to nitrification denitrification, and the denitrified treated water is used as dilution water to be injected into the garbage. A biological treatment method for garbage and organic wastewater.