JPS61287497A - Anaerobic digester - Google Patents

Abstract

PURPOSE:To obtain high treating efficiency by measuring the generation rate of a digestion gas to estimate the progress of the digestion, estimating the amt. and activity of microbes retained in a digestion tank and judging and controlling the amt. of org. wastes to be charged. CONSTITUTION:Org. wastes are intermittently charged into digestion tanks 2 and 4 in an aerobic digester. The generation rate of a digestion gas from the digestion tanks is measured by a measuring device 12, an output from the measuring device immediately before org. wastes are charged into the digestion tank is compared with the preset value by an arithmetic unit 13, the amt. of org. wastes to be charged into the digestion tank is calculated on the basis of the deviation and the amt. of org. wastes to be charged into the digestion tank is controlled by a controller 14 receiving the output from the arithmetic unit. Consequently, the digester can be operated under an appropriate load of org. wastes and high treating efficiency can be obtained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an anaerobic digestion device for treating organic waste generated in factory wastewater treatment facilities, sewage treatment plants, etc. Regarding input and control.

[Technical background of the invention and its problems]

Anaerobic digestion has been used for a long time as a method for treating organic sludge. In recent years, with the deterioration of the energy situation, this anaerobic digestion method has attracted attention.
:It has become to. This method has the advantage that it is possible to obtain a large amount of methane-based digestion gas that can be used as energy, and that it does not require large amounts of aeration as in aerobic treatment methods.

This anaerobic digestion method is a method of decomposing organic matter using the action of anaerobic microorganisms. It consists of a two-step reaction in which acid is mainly decomposed into carbon dioxide and methane. Bacteria that perform the liquefaction reaction are called acid-producing bacteria, and bacteria that perform the gasification process are called methane bacteria.

Figure 5 shows a general systematic diagram of the anaerobic digestion method.

Organic sludge is introduced into a primary digestion tank 2 via a pipe 1. Generally, the injection is not carried out continuously, but intermittently several times a day. In primary digestion tank 2, organic sludge is
It is allowed to stay for about 5 to 20 days, and is finally decomposed into 6-nimethane, carbon dioxide, etc. through the liquefaction and gasification reactions described above. In order to maintain high bacterial activity, the primary digestion tank 2 contains 30 to 40
Generally, it is heated to about ℃ (the heating device is not shown). Further, in order to uniformly mix the introduced organic sludge and bacteria, the generated digestion gas is circulated by a blower 9 or the like to agitate the inside of the primary digestion tank.

The digested sludge that has undergone the digestion process is sent to the secondary digestion tank 4 via the transfer pipe 3. The secondary digestion tank 4 is provided mainly for the purpose of sedimentation and concentration of digested sludge. For this reason, heating devices and stirring devices are usually not installed.

The separated supernatant liquid is discharged into a river or the like via pipe 5 or is returned to a water treatment process. The concentrated digested sludge accumulated in the lower part of the tank is sent to the next sludge treatment step via a pipe 6. Primary Digestion Tank 2. Digestion gas generated from the secondary digestion tank 4 is stored for one day in a gas tank 8 via a pipe 7, and then used as energy for heating the primary digestion tank 2.

Since the anaerobic digestion process is carried out by the action of microorganisms, the amount of organic waste input into the primary digestion tank 2 is an important management factor. In other words, if organic waste is added in excess of the processing capacity of the microorganisms held in the primary digestion tank 2, volatile fatty acids will accumulate, the pH will decrease, and the processing activity of the microorganisms will become extremely low. It may drop and become impossible to process. On the other hand, if the amount of organic waste to be input is small, the digestion tank equipment will not be used effectively.

Conventionally, the amount of organic waste input into the primary digestion tank 2 has been controlled using a widely used method.

That is, one method is to always feed a fixed amount of organic waste into the primary digestion tank 2, which is used in the majority of treatment facilities. This is listed on page 437 of "Sewerage Facility Design Guidelines and Explanations" (Japan Sewage Works Association).1. Approximately 3
This is a method of controlling the amount of organic waste input so that the hydraulic retention time is 12 days. Usually, the input pump is turned on and off by a timer or the like, and a predetermined amount of organic waste is input. Such conventional methods have the following drawbacks.

First, if the concentration of organic matter in the input organic waste changes, the amount of organic matter loaded onto microorganisms will also change, leading to a decrease in treatment efficiency. In this way, the amount of organic matter load fluctuates, and as a result, as mentioned above, if more organic waste is input than the processing capacity of microorganisms, the processing activity of microorganisms will decrease, and in the worst case, processing will not be possible. become. On the other hand, if the input amount of organic waste is too small, it means that the treatment facility is not being utilized effectively.

Second, organic waste is input without regard to the state of the digestion tank, i.e., the progress of the digestive reaction, the amount of microorganisms, and even its activity, so it may be processed under conditions that deviate from the appropriate processing conditions. This may lead to a decrease in processing efficiency.

In addition, other conventional methods include a method of controlling the weight of input organic waste to a constant level (for example, Japanese Patent Application Laid-Open No. 58-15
(See No. 9900). This method is a two-control method in which the product of the flow rate of organic waste to be input and the solids concentration is constant. If the solids concentration of organic waste is high, the input flow rate is reduced. , conversely, when the solid concentration of organic waste is low, the input flow rate is increased. Since this method can stabilize the organic matter load to the digestion tank, it is possible to perform stable treatment with better treatment efficiency than the first conventional method described above. However, since this method also inputs organic waste without regard to the progress of the digestive reaction, the amount of microorganisms, or its activity, the activity of microorganisms may fluctuate depending on changes in the composition of the organic waste. If overload 1
; This may lead to a decrease in processing efficiency.

[Purpose of the invention]

An object of the present invention is to provide an anaerobic digestion apparatus that allows organic waste to be constantly fed into the digester in accordance with the amount of microorganisms held in the tank and their activity.

[Summary of the Invention] The present invention relates to an anaerobic digestion device in which organic waste is intermittently introduced into a digestion tank, and includes a measuring device for measuring the generation rate of digestion gas generated from the digestion tank, and a A device that compares the output from the measuring device immediately before the introduction of organic waste into the tank with a scheduled setting value and calculates a lid for introducing the organic waste into the digestion tank based on the deviation, and this calculation device. The system is equipped with a control device that controls the amount of organic waste input into the digester based on the output from the digester, and the amount of microorganisms stored in the digester and their activation status can be determined from the rate of generation of the digestion gas. Then, the corresponding amount of organic waste is put into the digestion tank.

[Embodiments of the invention]

First, two basic concepts of the present invention will be explained.

As mentioned above, the input organic waste is decomposed into digestion gas whose main components are methane and carbon dioxide. That is, since digestive gas is a foreshadowing product of microorganisms, the progress of the digestive reaction at that time can be estimated by measuring the rate of digestive gas generation.

Here, in the anaerobic digestion process, organic waste is generally input intermittently. For this reason, the rate of digestion gas generation follows a pattern in which it gradually increases after organic waste is introduced, reaches a maximum value, and then gradually decreases again (see Figure 2). Therefore, if the input amount of organic waste is appropriate for the bacterial cell cage held in the primary digestion tank 2, the starvation pattern of the digestion gas generation rate will be as shown in Figure 3, Reiji. The next time organic waste is introduced, the rate of digestion gas generation gradually decreases to around the baseline unique to each treatment facility. On the other hand, the amount of microorganisms 4 retained in the primary digestion tank 2
On the other hand, when the amount of organic waste input is excessive, as shown in FIG. 4, the digestion gas generation rate does not decrease to near the baseline even when organic waste is input next time. This means that untreated organic matter still remains in the primary digestion tank 2, and if operation and management continue as is,
Volatile organic acids accumulate in the primary digestion tank 2, lowering the pH and causing a decrease in digestion efficiency.

Based on the above information, measure the rate of digestion gas generation just before inputting organic waste, compare it with the planned setting value to determine whether it has decreased to near the baseline unique to the treatment facility, and check the deviation. By obtaining this information, it is possible to estimate the progress of the digestive reaction based on the amount of microorganisms and their activity at that time. Therefore, on the basis of this deviation value, it is possible to control the amount of organic waste to be input so that the amount of organic matter load is appropriate for the amount of microorganisms and their activation state.

The present invention will be described below based on an illustrated embodiment. FIG. 1 is a schematic block diagram showing one embodiment of the present invention.

In the figure, a gas pipe line 7 is provided with a measuring device for measuring the rate of digestion gas generation, that is, a gas flow meter 12. The flow meter 12 outputs the organic waste input schedule determined by each treatment facility, as well as the measured value G of the digestion gas generation rate immediately before the start of input.
given to 3. Based on the measured value Gl2, the arithmetic device 13 calculates a target value Qin for the next input amount of organic waste using arithmetic number 2. This can be done, for example, by finding the variation ΔQin of Qin using the following equation 12.

△Qjn 2K (Go G) (Qin)n+t=(Qin)n+△Qtn where G.

is a predetermined setting value, and K is a predetermined coefficient, which can be determined for each processing facility. Also (Q l
n) n+t is the amount of organic waste to be input next time,
(Qin)n indicates the amount of organic waste input last time.

The output of the arithmetic unit 13 obtained in this way is given to a control device 141, and by controlling the operation time of the dosing pump 11, the target amount of input is achieved.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to measure the digestive gas generation rate and estimate the progress of the digestive reaction.
The system estimates the microorganisms held in the digestion tank and their activity, determines whether the amount of organic waste input is appropriate, and controls the next organic waste storage to be input. General rule: It can be operated with an appropriate amount of organic matter load and high treatment efficiency can be achieved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the anaerobic digestion device according to the present invention, Figs. It is a flow diagram of an anaerobic digestion device. 2...Primary digestion tank 4...Secondary digestion tank 11...
・Dosing pump 12...Gas velocity measuring device 13...
・Arithmetic device 14...Control device (7317)
Agent: Patent attorney Kensuke Chika (and 1 other person)

Claims (1)

[Scope of Claims] An anaerobic digestion device in which organic waste is intermittently introduced into a digestion tank, comprising: a measuring device for measuring the generation rate of digestion gas generated from the digestion tank; a calculation device that compares the output from the measuring device immediately before inputting the organic waste with a scheduled set value and calculates the amount of organic waste to be input into the digestion tank based on the deviation; and an output from the calculation device. An anaerobic digestion device comprising: a control device for controlling the amount of organic waste input into the digestion tank in accordance with the received organic waste.