JPS6054794A - Anaerobic digesting method of organic waste - Google Patents

Abstract

PURPOSE:To reduce the cost of equipment and operation needed for the agitation by adding a specified amt. of humic acid in digesting anaerobically the sludge of organic waste. CONSTITUTION:The high-viscosity concd. sewage sludge 4 and 1/50-1/600 times as much humic acid 5 such as nitrohumic acid which is dissolved in an aq. alkaline soln. of NaOH, etc. are charged into a mixing tank 1. And the digesting sludge 7 from a digesting tank 3 is added to the liquid mixture of sludge and humic acid to decrease the viscosity and to regulate the pH to 6-8. The mixture is then charged into the digesting tank 3 by a pump P1, and digested anaerobically. The formed gas is blown into the tank 3 with a compressor C. The digesting sludge taken out from the bottom of the digesting tank 3 is returned and circulated to the upper part of the tank 3 by a pump P2 to mix uniformly the content of the tank 3. The viscosity of the digesting sludge in the digesting tank 3 is remarkably decreased, and the cost of the equipment and operation of the pump P2 and the compressor C can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for anaerobically digesting waste in a low viscosity state.

Conventional Technology Conventionally, methane gas has been recovered from organic wastes such as sewage sludge, human waste, and municipal waste through anaerobic digestion. In the anaerobic digestion process, organic matter introduced into the digestion tank is liquefied by facultative anaerobic bacteria into volatile fatty acids, which are then decomposed into methane, carbon dioxide, etc. by obligate anaerobic bacteria. A portion of the generated gas will be used as an energy source for heating the digester, and excess gas will be recovered as secondary energy.

In order to improve digestion efficiency, the digestive fluid in the tank is stirred to increase the frequency of contact between the input organic matter and the digestive teeth. Stirring methods are broadly classified into pump circulation methods, mechanical stirring methods, and gas stirring methods. In the pump circulation method, the digested sludge deposited at the bottom of the tank is pulled out by a pump and returned to the top of the tank, and in the mechanical stirring method, the digestive fluid is stirred using stirring impellers installed on the premises or an axial flow pump.
In addition, in the gas stirring method, a part of the generated gas is blown into the digestive fluid in the tank by a blower to stir the digestive fluid. In either stirring method, power is required to drive the pump or the prower.

In general, the number of days required for digestion is as long as 20 to 40 days, and the tank capacity is 100,771" or more even for a small-scale digester, and a large capacity of 10,000 m" or more for a sewage sludge digester.

In order to stir such a large amount of digestive fluid, a large-capacity pump or the like is required, and the operating cost thereof increases.

By the way, in recent years, many improvements have been made to improve digestive efficiency. One method is to increase the concentration of digested sludge in the digestion tank and perform anaerobic digestion. In high-temperature fermentation, it is said that the organic matter load increases in proportion to the 0.41 power of the digested sludge concentration. In the anaerobic digestion of sewage sludge, excess sludge or raw sludge is concentrated in a settling tank to a solid content concentration of 1 to 2 g, and then is fed into an anaerobic digestion tank. The viscosity of this input sludge is as low as 50 to 100 centipoise (hereinafter referred to as cp). In the highly concentrated digestion method that has been adopted in recent years, the solid content concentration of input sludge is 5 to 6%.
Therefore, the viscosity of the input sludge is between 2000 and 4000.
C7).

In addition, the viscosity of the digested sludge in the digestion tank is 20 to 30 Cp when the solid content concentration of the input sludge is 2 to 6 Cp, but 30 Cp when the solid content concentration of the input sludge is 5 to 6 Cp.
to 40-OCp.

Thus, in the highly concentrated digestion method, the construction and operating costs of the sludge supply pump increase. As for the digester tank, the increased viscosity of the digested sludge increases the power required for pumps, melors, mechanical stirring motors, etc. necessary for stirring the digested sludge, increasing the construction and operating costs thereof.

OBJECTS OF THE INVENTION An object of the present invention is to provide an anaerobic digestion method that significantly reduces the viscosity of input sludge or digested sludge and reduces construction and operating costs required for charging sludge and stirring digested sludge. .

Summary of the Invention: The present invention is a method for anaerobic digestion of organic waste in the presence of heptaminic acid.

Embodiments of the Invention The heptaminic acid used in the present invention can be obtained in large quantities and at low cost by oxidative decomposition or alkali extraction of coal. Humic acid is a brown to black amorphous acidic organic substance whose structure is mainly polyhydric phenol. An example of the chemical structure of humic acid is shown below. Nitrohumic acid is a suitable amino acid in the present invention. Nitrohumic acid may be added directly to the anaerobic digestion tank, but it may also be added to the input sludge in advance. good. When stirring the digestion tank using a pump circulation method, a method of injecting humic acid into the circulation line may be used.

Since humic acid is highly acidic, the addition of humic acid lowers the pH of the digested sludge. In this case, alkali is added as appropriate to keep the pH of the digested sludge neutral.

The optimal amount of humic acid to be added varies depending on the type of organic waste to be treated, its solid content concentration, the number of days for digestion, the temperature of the digestion tank, etc., but it is 1150 to 1/1500 of the weight of the input waste.
is preferable, and when digesting sewage sludge, V2O to 1
/600 is suitable.

FIG. 1 is a flow sheet showing a preferred embodiment of the present invention. Concentrated sewage sludge and humic acid are supplied to mixing tank 1 and mixed. Since humic acid is generally insoluble in water, humic acid is converted into an alkaline aqueous solution in the humic acid addition device 2. Alternatively, humic acid in the mixing tank 1 may be solubilized by adding an alkali such as caustic soda to the mixing tank 1. Mixing tank 1 also serves as a pH adjustment tank, and the pH of the mixture of sludge and humic acid is
Adjust H to 6 to 8. This mixture is put into the digestion tank 6 via line 6 by pump P. Digested sludge in the digestion tank is mixed uniformly by gas agitation by blowing generated gas into the tank by compressor C and pump circulation in which digested sludge pulled from the bottom of the digestion tank is returned to the top of the tank by pump P2. . When the digestion tank starts operating or when the humic acid concentration in the digested sludge decreases, the digested sludge is sent to the mixing tank 1 through the line 7, and the digested sludge and finic acid are rapidly mixed.

According to the present invention, since the viscosity of digested sludge is significantly reduced, the construction cost and operating cost of pump P2 and compressor C can be reduced.

By the way, the mechanism of viscosity reduction due to the use of 7-minic acid has not been fully elucidated. The properties of amine acids include strong reducing properties, high acidity, high molecular weight (molecular weight 1000 to 500), water-insoluble and water-soluble forms depending on the form, and ion exchange properties. This has been known for a long time. Moreover, by utilizing the properties of humic acid, it is possible to use it as a soil improvement agent or
Aminic acids are used as H buffering agents and the like. but,
The viscosity reduction according to the present invention cannot be derived from these conventional findings. According to the inventor's inspection, sludge-
When humic acid is mixed with sludge, the amine acid is adsorbed on the surface of the solid content of the sludge, and the function of humic acid as a surfactant is imparted to the surface of this solid content. It is presumed that the viscosity of the sludge decreases due to this action. This mechanism is schematically shown in FIG.

Example 1 7Mic acid 2I was added to N/IQ KOH aqueous solution to adjust the pH.
An aqueous solution of 7 minic acid was prepared. After mixing this humic acid aqueous solution with 500 cc of surplus sludge, the viscosity of the surplus sludge was measured and the results are shown in FIG. From this, 1 for the amount of sludge
It can be seen that the addition of humic acid of /250 reduces the viscosity by about 25 inches.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing the method of the present invention, FIG. 2 is a schematic diagram showing the mechanism of viscosity reduction by the method of the present invention, and FIGS. 6 and 4 are diagrams showing changes in viscosity over time. 1.--Mixing tank, 2.--Humic acid addition device, 3.-.
・Digestion tank, 21...solid content, 22...humic acid. Patent Applicant: Shinryo Refrigeration Industry Co., Ltd. (4 others) Parent/Kimi 2 Zukei Tsukyu vl (hh) Koma ('FJ)

Claims (1)

[Claims] 1. A method for anaerobic digestion of organic waste, characterized by adding humic acid and performing anaerobic digestion. 2. The amount of humic acid added is 115% of the amount of input organic waste.
2. A method according to claim 1, which is between 0 and 1/600. 3. The method according to claim 1, wherein the humic acid is nitrofumic acid. 4. The method according to claim 1, wherein the organic waste is surplus sludge.