JP2006026461A - Method and apparatus for controlling anaerobic water treatment plant generating methane gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control apparatus having a control method for promptly judging whether the performance of a reactor is good or not in a methane fermentation plant, and promptly performing quantitative treatment when a performance deterioration is detected. <P>SOLUTION: In the control method, when water containing biodegradable organic matter continuously discharged from processes is supplied to a plant generating gas mainly comprising methane, actual COD volume loading of feed water supplied to the plane is compared to the target value of COD volume loading calculated from the volume of gas generated from the plant assuming that the plant is operated in good condition, and from the comparison result, it is judged whether the activity of methane generation is good or not. The control apparatus comprises equipment for generating the gas mainly comprising methane, a device for measuring the volume of the gas generated from the plant, a flowmeter for measuring a supply flow rate to the plant, and devices located at the inlet and outlet of the plant for automatically obtaining COD or TOC. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, when performing an operation of generating methane gas from water containing biodegradable organic matter to perform water treatment and recovery of valuable gas mainly composed of methane, the amount of gas generated and the load of biodegradable substances in the treated water are reduced. A method for controlling anaerobic water treatment equipment that generates methane gas that performs load control sensitively to performance deterioration; The present invention relates to a control device.

  Conventionally, specific methane production activity has been used for performance determination in methane fermentation. This is calculated as the amount of methane produced per unit sludge. Industrially, it is calculated by dividing the methane production rate per unit volume generated from the unit by the sludge concentration.

  In methane fermentation, the reaction proceeds in three steps: hydrolysis of the substrate, acetylation of the degradation product, and methane gasification of acetic acid, and each cell is undertaken by the reaction. Progresses. However, especially methane gasification of acetic acid tends to be rate-determining because the growth of bacteria is slow, and it is known that acetic acid changed from the substrate accumulates in the system and damages the bacteria when excessively loaded. Damaged bacteria should be avoided not only because of the reduced generation of methane gas, but also because it takes a long time to recover. In other words, it is desirable to determine the current reactor capacity and to quickly reduce the load and avoid overload as much as possible when an excessive load is applied.

  However, since the allowable load changes every moment due to the activity of the sludge inherent in the reactor, the amount of methane gas generated per unit sludge also changes to determine the performance.

  On the other hand, as shown in Patent Document 1, a control device that performs control using an index called specific methane conversion activity has been proposed as an automatic control index.

  This is obtained by dividing the specific methane production activity by the COD volumetric load, and assuming the activity that should be sludge by the volumetric load, using it as a reference value, and comparing it to determine the quality of the activity.

  According to this, it is possible to quickly detect a deviation from the actual state of the methane fermentation facility and to promptly reduce the load.

  However, the control method according to this method requires a measuring device for volatile suspended solids (VSS) and methane gas concentration, which is cumbersome and expensive, and this index is difficult and difficult to manage in actual control. There was a problem of being.

  On the other hand, removal performance of COD (chemical oxygen demand) and TOC (Total organic carbon) in and out of the reactor is a simple performance management index, but the response is poor due to the size of the reactor, There was a problem that it was difficult to detect a rapid deterioration in performance.

  Therefore, as a result of repeated studies, it was possible to supply water containing biodegradable organic matter continuously discharged from the process, and to make methane without having to enter and exit the facilities necessary for the generation of methane gas during operation. If a reactor that does not supply or withdraw sludge is used for the equipment (reactor) that generates gas containing as the main component, the increase in the amount of sludge that is filled is extremely small, so there is little need to calculate the amount of sludge. The methane gas concentration was found to be unnecessary when a continuous wastewater from a continuously operated process is treated, for example, and therefore a measuring device as described in Patent Document 1 is unnecessary.

We also found that the deterioration of reactor performance can be detected quickly by monitoring and controlling the relationship between the measured amount of biogas generation and the supply load to the reactor.
Japanese Patent Laid-Open No. 11-253149

  The object of the present invention is to quickly determine the quality of the reactor (methane fermentation facility) performance in the methane fermentation facility, and when it is recognized that the reactor performance is deteriorated, it can be promptly linked to a quantitative action. Another object of the present invention is to provide a control method and a control device for an anaerobic water treatment facility that generates methane gas.

  According to the control method of the present invention, the raw material continuously discharged from the process is generated in the facility that generates gas mainly composed of methane without entering and leaving the microorganisms necessary for generating methane gas to the facility during operation. When supplying water containing degradable organic matter, the actual COD is calculated by dividing the product of the amount of water supplied to the facility and the converted COD concentration calculated from the COD concentration or TOC concentration of the supplied water by the effective volume of the facility. Obtain the volumetric load and obtain the COD volumetric load target value calculated from the amount of gas generated from the equipment as being well operated, and compare these COD volumetric load and COD volumetric load target value. And the quality of the activity of methane production is judged from the comparison result.

  In addition, the control device of the present invention can supply water containing biodegradable organic matter continuously discharged from the process without newly entering and leaving microorganisms necessary for generating methane gas to the facility during operation. In a facility that generates a gas mainly composed of methane, a device that measures the amount of gas generated from the facility with a flow meter, a flow meter that measures the flow rate supplied to the facility, and an inlet and an outlet of the facility A device that automatically obtains COD or TOC is installed, and the product of the amount of water supplied to the equipment and the converted COD concentration calculated from the supplied COD concentration or TOC concentration is divided by the effective volume of the equipment. Compare the actual COD volumetric load to obtain the COD volumetric load and the COD volumetric load target value calculated from the amount of gas generated from the equipment that the equipment is operating well. Determining the quality of methane production activity Characterized by comprising a means.

  According to the present invention, in a methane fermentation facility, it is possible to quickly determine whether the performance of the reactor (methane fermentation facility) is good or not, and when it is recognized that the performance of the reactor is deteriorated, it is possible to quickly connect to a quantitative action. It becomes.

Hereinafter, the present invention will be described in detail.
In methane fermentation, BOD (biochemical oxygen demand) components in wastewater are reacted in the presence of specific cells in an anaerobic atmosphere, and the BOD components are volatilized as methane gas and removed from the wastewater. Technology that makes it possible to reduce excess sludge that has been generated as industrial waste when treated with aerobic treatment, and to reduce costs by using methane gas as an alternative energy source. It is.

  The BOD component is decomposed into methane gas through a hydrolysis reaction, then an acetic acid production reaction, and finally a reaction for generating methane gas from acetic acid, all of which are handled by separate cells stored in the reactor. This series of reactions is called methane fermentation.

  FIG. 1 shows a typical process flow. The flow does not limit the technology. One or more kinds of waste water 1 having a BOD load is received in a buffer tank 2 and mixed and homogenized raw water 3 passes through a flow meter 4 and a TOC meter or COD meter 6 and then supplied to a regulating tank 8 in a certain amount. . In the adjustment tank 8, the temperature and pH are adjusted and mixed with the treated water 14, and then supplied as reactor supply water 9 to the reactor 10. From the reactor 10, a biogas 11 from the reactor is generated. This gas passes through the gas flow meter 12 and is then effectively used as a fuel for a combustion furnace or the like as the biogas 13. The treated water 14 that has been treated is returned to the adjustment tank 8, but a supply amount corresponding to the treated water 14 is discharged out of the system via the TOC meter or the COD meter 17 as out-of-system drain water 18.

  Next, the basic concept of control will be described.

  It is most reliable to judge whether methane gas generation corresponding to the supplied BOD load is performed as to whether the methane fermentation reaction is being performed satisfactorily.

  The amount of methane gas generated increases as the supplied BOD load increases, but if the drainage composition changes, the methane concentration in the reactor output biogas 11 slightly changes. However, wastewater discharged from the equipment that operates continuously at a nearly constant composition and concentration, and wastewater that has been smoothed in composition and concentration by having a specific buffer tank even for wastewater discharged in batches, That is, if it is the waste water from a continuous process, the composition is considered to be constant, and even if it does not measure the methane gas concentration, there is no big trouble in using it as an index for judging the quality of the gas using the gas generation flow rate.

  On the other hand, the supply load to the methane fermentation reaction tank should originally be represented by the product of the BOD concentration and the supply flow rate. However, since BOD requires a long time of 5 days for analysis, it cannot be continuously monitored. Usually, it can be continuously estimated by monitoring using a COD or TOC meter that is alternatively used to manage the drainage load. Basically, BOD, COD, and TOC are often correlated with each other, and therefore, are often used in wastewater monitoring because they often show a substantially direct correlation with the amount of gas generated. However, it is more preferable to use CODCr, which measures COD using chromic acid as an oxidizing agent, as an index.

  Usually, in methane fermentation, COD volumetric load is used as an index representing load. In the case of the TOC, it can be read and used.

(COD volumetric load) = (Raw water COD concentration) × (Raw water flow rate) / (Reactor volume)
The amount of biogas generated is generated in proportion to the removed COD load.
(Biogas generation amount) = ((Raw water COD concentration) − (Treated water COD concentration)) × (Raw water flow rate) × C1 (Coefficient)
Therefore, the following equation (a) is established between the COD volumetric load and the biogas generation amount.
(Biogas generation amount) = (COD volumetric load) × (COD removal rate) × (reactor volume) × C1 (a)
However, (COD removal rate) = ((raw water COD concentration) − (treated water COD concentration)) / (raw water COD concentration)

  Good performance means that the COD removal rate is high. In that case, it may be judged by measuring COD or TOC of the reactor. However, the reactor for methane fermentation has a very large capacity, and it takes a long time for the residence time to reach 3 to 10 hours and the concentration at the outlet, so the amount of biogas generated with a quick response should be used as an index. It is. By monitoring the correlation with the amount of biogas generated that immediately responds to the COD volumetric load, it is possible to quickly evaluate the performance without delay time.

  Next, a method for detecting performance will be described with reference to FIG. In FIG. 1, the feed water flow rate is measured by the flow meter 4, the COD or TOC is measured by the COD or TOC meter 6 at the point where the raw water supplied to the methane fermentation facility enters the adjustment tank 8, and the COD (TOC) is measured by the volume load calculator 19. Supply amount and volume load can be obtained. On the other hand, as shown above, the amount of biogas generated can be measured by the gas flow meter 12. As a result, installing a COD (TOC) meter in the treated water is effective for knowing the state of the treatment, but as mentioned earlier, taking this delay into account, this value is taken into account for quick performance. Not suitable for ascertaining.

  On the other hand, in this system, the bacteria used to generate methane gas are filled exclusively in the reactor, so there is no need to supply or withdraw, and the amount of bacteria hardly grows, so that the reactor capacity is constant. Basically, the amount of cells can be considered the same.

  From these, assuming that the methane fermentation reactor has good performance, that is, the COD removal rate is a certain set value, if the biogas generation amount is determined, the COD volumetric load value that should be present can be expressed by the above formula (a ) Is calculated by the desired volume load calculator 20 (COD volume load target value). The volume load calculator 19 is compared with the volume load calculator 20 that should be, and the volume load comparison calculator 21 compares the volume load calculator 19 and the deviation is calculated. When the deviation exceeds the set ratio, the alarm 22 notifies the abnormality immediately.

  A conceptual diagram of the control is shown in FIG. The horizontal axis represents the COD volumetric load, and the vertical axis represents the biogas generation amount. The position of the measured gas generation amount G and the measured volume load F is represented by the measured volume load 24. From the relationship of the formula (a), the gas generation amount and the volume load show a proportional relationship. The slope represents the removal rate. The larger the slope, the higher the removal rate. At this time, when the desired removal rate is indicated by a line 25, the current desired volume load F 0 is at a point indicated by 26. Here, when the volume load 24 measured from the set lower limit removal rate 27 deviates to the right side, it indicates that the load on the reactor is too much for the amount that the reactor can actually handle. Therefore, in this case, it is necessary to warn to reduce the load from the measured volume load 24 to the current desired volume load 26 immediately.

  Further, in the second invention, the flow rate is converted by the flow rate converter 23 of FIG. 1 so as to act by the volume load difference between the measured volume load 24 calculated as described above and the current volume load 26 which should be, and the flow meter 4 is adjusted. By doing so, it is possible to avoid an overload condition quickly and automatically. When the flow rate is reduced by the flow meter 4, the balance of the buffer tank 2 becomes unbalanced, but it may be dealt with by overflowing the waste water in the buffer tank 2.

(Example)
As biodegradable organic substances, raw water containing acetic acid, terephthalic acid, and p-toluic acid with a total CODcr concentration of 8500 mg / L to 13000 mg / L, and 11 tons of granules with a solid content of 5.6% according to the flow shown in FIG. The charged 550 m ³ IHI reactor was supplied. At this time, the total mixing amount of terephthalic acid and p-toluic acid was 2500 mg / L or less in terms of CODcr. The raw water supply flow rate was up the raw water supply flow rate after a lapse of 12 hours after the start of the test as shown in Table 1 to ^{39m 3 / h → 45m 3 /} h. Table 1 shows changes in biogas generation amount, calculated volumetric load value, CODcr concentration of raw water and treated water, and removal rate with time.

  As can be seen from Table 1, as a result of increasing the load at the 12th hour, the amount of gas generated should be the volume load that should follow the 16th hour because the biogas generation amount suddenly decreased at the 20th hour. The flow rate was reduced to a level corresponding to. As a result, the amount of biogas generated at the 27th hour was maintained at the level before the load increase.

(Comparative example)
As biodegradable organic matter, raw water equivalent to that in the example was supplied to the same methane fermentation reactor as in the example by the same flow. The raw water supply flow rate was up the raw water supply flow rate after the elapse of the start of the test after 7 hours as shown in Table 1 to ^{42m 3 / h → 52m 3 /} h. Table 2 shows changes over time in the amount of biogas generated, the calculated volumetric load, the CODcr concentration of raw water and treated water, and the removal rate. Similarly, an example of biogas generation amount and volumetric load transition when the reactor COD amount rapidly increases is shown. As a result of increasing the flow rate at the 7th hour, the gas generation amount followed up to the 24th hour, but the gas generation decreased thereafter, and the COD removal rate decreased to 41% at the 58th hour.

It is a figure which shows the flow and control system of a methane fermentation installation. It is a figure which shows the concept of control by the relationship between a volume load and a gas generation amount.

Explanation of symbols

1 Wastewater 2 Buffer tank 3 Raw water 4 Flow meter 6 TOC meter or COD meter 8 Preparation tank 9 Reactor supply water 10 Reactor 11 Reactor biogas 12 Gas flow meter 13 Biogas 14 Treated water 17 TOC meter or COD meter 18 Outside the system Discharged water 19 Volumetric load calculator 20 Desired volumetric load calculator 21 Volumetric load comparison calculator 22 Alarm 23 Flow rate converter 24 Measured volumetric load 25 Desired removal rate 26 Desired volumetric load 27 Lower limit removal rate

Claims (4)

During operation, water containing biodegradable organic matter continuously discharged from the process is added to the facility that generates methane-based gas without entering and exiting the microorganisms necessary for generating methane gas to the facility. When supplying, the product of the amount of water input supplied to the equipment and the converted COD concentration calculated from the COD concentration or TOC concentration of the supplied water is divided by the effective volume of the equipment to obtain the actual COD volume load, Obtain the COD volumetric load target value calculated from the amount of gas generated from the equipment, assuming that the equipment is operating well, and compare these COD volumetric load and COD volumetric load target value. A method for controlling an anaerobic water treatment facility for producing methane gas, characterized by determining whether methane production activity is good or bad. Compare the obtained COD volumetric load target value with the actual COD volumetric load, and if the COD volumetric load target value is smaller than the actual COD volumetric load over a certain percentage, the actual COD volumetric load and the COD volumetric load are 2. The method for controlling anaerobic water treatment equipment for producing methane gas according to claim 1, wherein the supply load is controlled to be reduced by a difference between the target values. Supplying water containing biodegradable organic matter continuously discharged from the process, and generating gas mainly composed of methane without entering and leaving microorganisms necessary for generating methane gas to the facility during operation Equipment that measures the amount of gas generated from the equipment with a flow meter, a flow meter that measures the flow rate supplied to the equipment, and COD or TOC automatically at the entrance and exit of the equipment. Install the equipment to obtain, and obtain the COD volumetric load by dividing the product of the amount of water input supplied to the equipment and the converted COD concentration calculated from the COD concentration or TOC concentration of the supplied water by the effective volume of the equipment. The COD volumetric load is compared with the COD volumetric load target value calculated based on the amount of gas generated from the equipment that the equipment is operating well, and the quality of the methane production activity is judged from the comparison result. Characterized by having means Control device for anaerobic water treatment facility for generating that methane gas. Compare the obtained COD volumetric load target value with the actual COD volumetric load, and if the COD volumetric load target value is smaller than the actual COD volumetric load over a certain percentage, the actual COD volumetric load and the COD volumetric load are 4. The control apparatus for anaerobic water treatment equipment for producing methane gas according to claim 3, further comprising means for controlling the supply load to be reduced by a difference between the target values.

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