JP6432226B2 - Method and apparatus for anaerobic digestion of sewage treatment sludge - Google Patents

Description

  The present invention relates to a method and an apparatus for anaerobic digestion treatment of sewage treatment sludge, and more particularly to an anaerobic digestion method and apparatus for sewage treatment sludge capable of increasing the generation amount of resource gas such as methane gas.

  In the sewage treatment plant, the first sedimentation basin for precipitating solids contained in the inflowing sewage, an air tank (aeration tank) for purifying organic substances in water by the activity of aerobic microorganisms, and sludge mixed water that has been purified in the air tank are precipitated. In general, a final sedimentation basin is provided to recover sludge floc containing aerobic microorganisms and to obtain clear water.

  The sludge that settled in the first sedimentation basin is called the first sedimentation sludge (or raw sludge). This initial sedimentation sludge is not reused in the water treatment system and is appropriately discharged out of the system.

  Part of the sludge that has settled in the final sedimentation basin is returned to the air tank and reused, but excess sludge is appropriately discharged out of the system. This discharged sludge is called surplus sludge.

  The initial settling sludge and surplus sludge are increased in concentration by gravity concentration tanks and mechanical concentrators, then sent to a dehydrator, the water content is reduced by dehydration, and then incinerated, landfilled, and farmland It is used for reduction.

  In order to reduce the volume of primary sludge and excess sludge, an anaerobic digester is installed, and sludge is decomposed by the activity of anaerobic microorganisms to reduce the volume. In this anaerobic digester, digestion gas (carbon dioxide gas or methane gas) is generated by decomposition of organic matter. Since this methane gas is flammable and has a high calorie, it may be used as fuel for boilers, supplied to a generator for use as fuel for power generation, or may be sold after purification of the gas.

  An anaerobic digester can process a large amount of organic matter by preparing its environment, but its activity is slow and it takes time to consume the organic matter. This is because anaerobic microorganisms do not decompose organic matter taken into water and carbonic acid by themselves like an aerobic microorganism, but there are multiple stages in the anaerobic digestion process in the anaerobic digestion tank (anaerobic process) This is because a group of microorganisms responsible for each process is mixed, and the digestion process is composed of a chain system that decomposes decomposition by-products while relaying them.

  In this chain system, acetic acid is produced by an acid production reaction by acid producing bacteria. From this acetic acid, methane gas is produced by methanogenic bacteria.

  In order to speed up the reaction of this chain system, the inside of the digestion tank is kept at a high temperature to increase the digestion rate and to reduce the size of the equipment. That is, the methanogen (seed) grows efficiently in a medium temperature zone near 37 ° C or a high temperature zone near 55 ° C. Therefore, the temperature of the anaerobic tank is kept at a medium temperature around 37 ° C or a high temperature around 55 ° C.

  Conventionally, the generated methane gas is combusted for this temperature increase, but in recent years, the gas has been effectively used as described above. For this reason, not only a large amount of methane gas is generated but also its quality has been demanded. For example, for a power generation gas engine, it has been required to increase the methane concentration or stabilize the concentration.

  For this reason, anaerobic digesters installed in sewage treatment plants are required to maintain the activity of methanogenic bacteria stably at a high level. Moreover, it is calculated | required to raise the acid production ability of the organic substance supplied to an anaerobic digester. Even if the methanogen has high activity, if the acid generation process in the previous stage in the anaerobic process is not successful, the amount of methane gas generated will not be obtained as expected, and the anaerobic process will gradually increase as the relay stagnates. It may worsen and lead to long-term malfunctions in processing.

  It is known that the growth of anaerobic bacteria is slow. For example, when the ability is reduced in sewage treatment, it takes a long time to recover the performance of a method that relies on the self-healing of the bacteria.

  For this reason, there is a demand for a management method that increases the activity of bacteria involved in acid production while maintaining the activity of methanogenic bacteria, and allows the anaerobic process to be performed without delay.

  However, the conventional method aims to keep the activity of the methanogen in the anaerobic digester well, and this alone does not lead to stabilization of the acid production process, and as a result, the expected amount of methane generation is obtained. The methane concentration (partial pressure) in the generated gas is often low.

  In order to efficiently perform acid generation, it is necessary to prepare a processing environment, sufficiently ensure bacteria that contribute to the linkage, and maintain activity. Environmental factors that affect acid production include temperature, time, pH, and the like. If the temperature is not within the proper range, it takes time to generate the acid, the decomposition of the organic matter stops in the middle, or the relay is not performed properly. In addition, since the pH is lowered by the generated organic acid, when the amount of the organic substance flows in a large amount and the decomposition reaction proceeds at once, the pH is excessively lowered and the reaction may be stopped.

  The anaerobic digester in the sewage treatment plant has strong elements of sludge treatment, not water treatment. In the case of water treatment, the decomposition of organic substances dissolved in water is the main, whereas in the case of sludge treatment, organic substances suspended in water are decomposed, and time factors are important. . In the case of water treatment, the acid generation and methane fermentation processes are often separated and a separate reaction tank is provided. In many cases, the treatment is performed transiently. In the case of the treatment, not only the chain reaction is often performed in one reaction tank, but also in the case where the sludge is intermittently supplied, the acid generation and the methane fermentation should be performed simultaneously. Many. For this reason, the state of the sludge supplied to the digester often affects the anaerobic process.

  For example, the digester is often controlled at a temperature around 35 ° C or around 55 ° C. On the other hand, the temperature of the sludge to be supplied may be close to 30 ° C. in summer, but may fall below 15 ° C. in winter. At 15 ° C., the activity of anaerobic bacteria related to sludge digestion is significantly reduced. In particular, in a high-temperature digestion tank that manages the inside of the tank at 55 ° C., the residence time of the sludge in the tank is shorter by taking advantage of its activity, and it is often managed in 10 days at the longest from 5 days. The amount of 1/5 to 1/10 is supplied to the amount of sludge in the tank. Actually, since sludge is reduced in the digestion tank, even if 1/5 amount is supplied, it is actually the same as supplying 1/3 amount. If it does so, since 1 weight part of 15 degreeC sludge will be supplied with respect to 2 weight part of 55 degreeC sludge, the temperature fall will occur immediately after supplying the periphery of the supplied sludge.

  For this reason, if the bacteria present in the digestion tank do not have sufficient activity, the resolution of the organic matter may become unstable or deteriorate, and the anaerobic process may be broken. Therefore, when the temperature of the supplied sludge is low, it is necessary to further increase the activity of the bacteria present in the digestion tank.

  Moreover, the sludge supplied to the anaerobic digestion tank flows in through the route of the sewer pipe → first sedimentation basin → sludge concentration tank (device). During this time, it may be exposed to an environment with low oxygen for a long time and may have been degraded by anaerobic bacteria that have been in contact with the inflow or that have entered the sewage. In such a case, the organic substance decomposition reaction and the methane generation reaction in the digestion tank proceed smoothly. However, since this decomposition has happened in a so-called manner and is not controlled by human involvement, it varies depending on various factors. As described above, the sludge residence time in the anaerobic digester is only a few days to a few dozen days at the longest. For this reason, if sludge that has not been subjected to organic acid decomposition is suddenly supplied to the microbiota formed when sludge that has been subjected to organic acid decomposition is supplied in advance, anaerobic processes will be hindered, and methane formation will occur. The performance drops. Therefore, when the organic acid decomposition of the sludge to be supplied has not progressed, it is necessary to further increase the activity of the bacteria present in the digester.

  As described above, the treatment process in the anaerobic digester at the sewage treatment plant has unique properties. Therefore, in order to stably carry out the process up to the generation of methane, (1) measure the temperature change of the sludge slurry supplied to the anaerobic digester, and take measures to maintain the activity of the bacteria when it is low (2) Grasping progress of sludge slurry supplied to anaerobic digestion tank, and when it is low, taking measures to maintain the activity of bacteria increases methane gas production and concentration (partial pressure) However, there have been no examples of management focusing on these points so far. Furthermore, it is required to shift the species of methanogenic bacteria to a more efficient species = Methanosarcina.

  JP-A-4-300758 and JP-A-3-154692 (Patent Documents 1 and 2) provide nutrition to wastewater introduced into an anaerobic reactor in a method for anaerobically treating organic wastewater such as sewage, industrial wastewater, and sludge. It is described that a solution of a nitrogen compound, a phosphoric acid compound, a nickel compound or a cobalt compound is added as a salt solution according to the organic substance concentration in the wastewater and the organic substance concentration in the treated water.

  Japanese Patent Laid-Open No. 3-165895 (Patent Document 3) describes that nickel, iron, and cobalt are added to an organic waste liquid to perform a methane fermentation treatment.

  In JP-A-11-28445 (Patent Document 4), after pulverizing business wastes such as garbage, straw and agricultural and fishery waste, iron compounds such as ferrous chloride, nickel compounds such as nickel chloride, It is described that a nutrient salt composed of at least one of cobalt compounds such as cobalt chloride is added and stirred at 55 to 60 ° C. for methane fermentation treatment.

  In addition, the method of adding a calcium compound or an iron salt with respect to an anaerobic processing apparatus is described in the patent 3387241 (patent document 5) and the patent 3814851 (patent document 6).

However, Patent Documents 5 and 6 all relate to a method of upwardly circulating organic wastewater into a sludge blanket formed of granular sludge, and the addition target of calcium compound or iron salt is different from the present invention. . Patent Documents 3 and 4 are intended to improve the sedimentation of granules by generating CaCO ₃ or FeS and filling the voids inside the granules and prevent the granules from rising and flowing out. Therefore, the action of the calcium compound or iron salt is different from the method of the present invention.

  As mentioned above, methane gas generated in an anaerobic digester will be used effectively, and in addition to increasing the amount of methane gas generated efficiently, increasing the methane concentration and stabilizing the methane concentration Has come to be required.

  However, the conventional method of adjusting the temperature of the anaerobic digester to the temperature range of the methanogen (around 35 ° C or around 55 ° C) is mainly to promote digestion and increase the sludge volume reduction rate. Since it was aimed, it was not possible to increase the concentration of methane gas (partial pressure) even though the total amount of methane gas generated could be increased.

There are two reasons for this.
(1) A methanogen is a fungus that is active at the end of the aforementioned linkage system. Methanogens are biologically inferior bacteria, as seen in the limited aptitude temperature range, and the growth rate is small compared to other bacteria. By raising the temperature of the anaerobic digester, the activity of anaerobic bacteria becomes active and the digestion rate is increased. However, if the amount of sludge supplied to the digestion tank (anaerobic digestion tank) is increased, the residence time of sludge in the anaerobic digestion tank will be shortened, so the growth of methanogens will not be in time, and as a result However, methane gas may not be generated. For example, when the amount of sludge input to the digestion tank increases, if the intake of acetic acid of the methanogen decreases, the delivery of organic acids in the chain system will be delayed, and organic acids will remain in the system and will be involved in organic acid generation Fungus activity may be reduced. In addition, the activity of the bacterium may be reduced due to a decrease in pH associated with organic acid production, and as a result, the methane concentration and the amount of methane production may be reduced. In this way, the amount of generated methane gas is not stabilized when the amount of sludge charged changes and the load of the digestion tank varies due to temperature control alone.
(2) There are mainly the following two types of methanogens in the sewage sludge treatment system.
(I) Methanosaeta (filamentous fungi)
(Ii) Methanosarcina (dispersed bacteria)
Not only are these shapes (forms) different, but the following properties have been reported.

Filamentous fungi: Acetic acid utilization rate 8kg / m ³ -day, digestion required days around 20 days Dispersed bacteria: Acetic acid utilization rate 30kg / m ³ -day, digestion required days around 5 days Therefore, disperse bacteria should be propagated as dominant species If it is possible, it can cope with the environmental changes and fluctuations as described in (1) above. However, in the treatment environment using sewage sludge as “bait”, there are a lot of filamentous fungi. I understand.

  It should be noted that organic wastewater is treated by flowing upward water into an anaerobic reaction tank, and the UASB method (Upflow Anaerobic Sludge Blanket) and the EGSB method (Expanded Granular Sludge Bed) are used. In the expanded bed, anaerobic bacteria form granules, increase the packing density of the bacteria, and prevent the filamentous fungi from flowing out with a sedimentation rate greater than the upward flow rate. Although attempts have been made to breed, it is preferable that the dispersal bacteria are the dominant species in the anaerobic digester which is the subject of the present invention.

  Even in the UASB method and the EGSB method, the center of the generated granule actually forms “particles” with predominantly filamentous fungi, but there are many dispersal bacteria in the layer near the surface. It is known in many actual machine surveys, academic studies and experiments.

JP-A-4-300758 JP-A-3-154692 JP-A-3-165895 JP-A-11-28445 Japanese Patent No. 3387241 Japanese Patent No. 3814851

  As described above, there are two main methanogens present in an anaerobic digester at a sewage treatment plant: Methanosaeta (filamentous fungus) and Methanosarcina (dispersing fungus). By setting the dispersal bacteria that have higher acetic acid utilization rate than the filamentous fungus as the preferred species, the anaerobic digestion reaction will be faster and the methane gas concentration in the generated digestion gas will be higher. It tends to be a preferred species. One reason for this is that the generational life of dispersed bacteria is short. Once the balance of reproduction / growth of dispersed bacteria is lost, the dispersed bacteria become inferior species. In particular, when the amount of sludge input to the anaerobic digestion tank is large, the dispersal bacteria are pushed out of the tank and the number of bacteria is decreasing, and as described above, methane production is rate limiting and the relay of organic matter is delayed. End up.

  Another reason why filamentous fungi tend to become dominant species is that the activity of the dispersal bacteria decreases due to lack of additives such as Fe, Ni and Co. By adding additives such as Fe, Ni, Co, etc. to the environment where the organic acid relay process is stagnant due to the lack of such additives, or the acetic acid consumption rate is reduced, the dispersal bacteria are Shift to dominant species and increase methane production and methane production rate. As described above, since the dispersive bacteria have a short generation life, the required amount of Fe, Ni, Co, etc. is larger than that of the filamentous fungi.

  Anaerobic bacteria, unlike aerobic bacteria, do not require a large amount of nitrogen components, as required by aerobic bacteria, because the cell growth rate is not so fast. On the other hand, as described above, anaerobic bacteria relay the decomposition of organic substances, but this paradoxically limits the types of organic substances that can be decomposed, that is, the bacteria themselves have few types of degrading enzymes. It will be. Further, as is well known, trace metals such as Fe, Co, and Ni are required to make the enzyme work efficiently.

  Actual sewerage facilities often lack such trace metals. As described above, the sludge residence time in the sewage anaerobic digestion tank is clearly shorter than the residence time in the water treatment system, so that the replacement of the cells is severe. Even anaerobic bacteria that do not grow quickly cannot be expected to accumulate trace metals unless they are maintained in the system, so the necessary amount must be appropriately supplemented.

  In the method and apparatus for anaerobic digestion treatment of sewage treatment sludge, the present invention is not an upward circulating water type reaction tank, but an aerobic digestion tank with a stirring / mixing type in the tank or a sludge supplied to the Fe, By adding an additive containing at least one of Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co so that the dispersal bacteria become the dominant species An object of the present invention is to provide an anaerobic digestion method and apparatus for sewage treatment sludge that can improve the environment, increase the amount of methane gas produced, and increase the methane gas concentration (partial pressure).

  The method of anaerobic digestion of sewage treatment sludge according to the present invention comprises anaerobic digestion of sewage treatment sludge composed of primary sludge settled in a first sedimentation basin and / or surplus sludge extracted from a biological treatment reaction tank in a sewage treatment plant. In the method of anaerobic digestion of sewage treatment sludge to be subjected to anaerobic digestion in a tank, Fe, Cu, Zn, Mg, Mn, K, Ca, Ni are added to the sludge introduced into the anaerobic digestion tank or the anaerobic digestion tank. , Mo, Se, S, V, Cr, I, and a method for adding an additive containing at least one of Co.

  In one aspect of the method of the present invention, the temperature of sludge introduced into the anaerobic digester or the temperature in the anaerobic digester is measured, and the additive is added when the temperature is lower than a predetermined temperature.

  In one aspect of the method of the present invention, the pH of the sludge introduced into the anaerobic digester or the pH in the anaerobic digester is measured, and the additive is added when the pH is higher than a predetermined value.

  In one aspect of the method of the present invention, the ORP of the sludge introduced into the anaerobic digester or the ORP in the anaerobic digester is measured, and the additive is added when the ORP is higher than a predetermined value.

  In one aspect of the method of the present invention, M alkalinity (acid consumption) of sludge introduced into the anaerobic digestion tank or M alkalinity in the anaerobic digestion tank is measured, and this M alkalinity is determined from a predetermined value. When the content is too low, the additive is added.

  In one aspect of the method of the present invention, the volatile fatty acid concentration of sludge introduced into the anaerobic digester or the volatile fatty acid concentration in the anaerobic digester is measured, and the volatile fatty acid concentration is lower than a predetermined value. Sometimes the additive is added.

  In the method of the present invention, the sewage treatment sludge may be concentrated and then introduced into the anaerobic digester.

  The apparatus for anaerobic digestion of sewage treatment sludge according to the present invention anaerobically digests sewage treatment sludge composed of primary sludge settled in a first sedimentation basin of a sewage treatment plant and / or excess sludge extracted from a biological treatment reaction tank. In the anaerobic digester of sewage treatment sludge having an anaerobic digester, the sludge introduced into the anaerobic digester or the anaerobic digester, Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo , Se, S, V, Cr, I and Co, an anaerobic digester of sewage treatment sludge provided with an adding means for adding an additive consisting of at least one kind, and sludge introduced into the anaerobic digester Or measuring means for measuring at least one water quality index value of temperature, pH, ORP, M alkalinity and volatile fatty acid concentration of the liquid in the anaerobic digester, and at least one water quality index value measured by the measuring means Predetermined range Is characterized in that a control means for operating said adding means when departing.

  In the present invention, when at least one water quality index value of temperature, pH, ORP, M alkalinity and volatile fatty acid concentration of sludge or anaerobic digester liquid introduced into the anaerobic digester deviates from a predetermined range. Since the additive is added, the additive can be appropriately added.

  Various research reports have been made that Fe, Ni and Co are effective in maintaining and improving the activity of methanogens. When Mn is further added to these three kinds of metals, among the two main methanogens existing in the anaerobic digester installed in the sewage treatment plant, Methanosaeta, Methanosarcina, the methane production rate is higher, And the latter with low total amount of methane generated per microbial cell can be shifted to dominant species, and the methane production ability of the digester can be enhanced.

  An element selected from Cu, Zn, Mg, K, Ca, Mo, Se, S, V, Cr, I, or one or more of its metal salts, an anaerobic digester By adding / mixing in advance to the sludge supplied to or directly adding to the anaerobic digester, the enzyme of the bacteria involved in acid generation can be activated and the acid generating ability can be enhanced. For example, Se serves as a catalyst necessary for normal action of lipid hydrolase, and Cu and Zn are indispensable elements for ATP production and storage.

It is a flowchart which shows embodiment of this invention. It is explanatory drawing of an experiment method. It is explanatory drawing of an experiment method. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

  As shown in FIG. 1, in a preferred embodiment of the present invention, sewage treatment sludge composed of primary sludge and / or surplus sludge at the sewage treatment site is introduced into the mixing tank 1, and the additive is added by the additive addition means 2. To do. This additive is at least one element or compound of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co. The additive may be added to the anaerobic digestion tank 3, but Fe or the like may be taken into the anaerobic digestion sludge and settle down, so it is added to the sludge upstream of the anaerobic digestion tank 3. It is preferred that The mixing tank 2 preferably includes a stirrer 2a.

  Before introducing the initial sludge and / or excess sludge into the mixing tank 1, the sludge may be concentrated by a concentrator. The concentration device may be a gravity concentration tank or a mechanical concentration device such as a centrifuge.

  The sludge to which the additive has been added is introduced into the anaerobic digester 3 and heated as necessary. For example, the sludge is appropriately stirred at 55 to 60 ° C. and is organic with anaerobic microorganisms such as acid-producing bacteria and methanogens. Treat organic substances in waste with methane fermentation. The generated digestion gas is taken out through the digestion gas extraction pipe 4. An anaerobic digestion liquid produced by digestion in the anaerobic digestion tank 3 is introduced into the solid-liquid separation means 5, and the dehydrated cake and the separated liquid are separated by filtration separation using a screen, membrane, etc., sedimentation separation treatment, or centrifugal separation treatment. Solid-liquid separation.

  The liquid component separated by solid-liquid separation is returned to the mixing tank 1. The solid content is taken out of the system and processed separately, or effectively used for the production of fuel, fertilizer, building materials and the like. A part of the solid content may be returned to the mixing tank 1 or the anaerobic digestion tank 3.

  Of the above-mentioned additives, the metal is preferably added as a soluble salt granule, pulverized product, powder or aqueous solution.

  S and Se may be added as a single powder or granule, or may be added in the form of sulfide, selenide, sulfate, selenate granule, powder or aqueous solution.

  I is preferably added in the form of iodide granules, powder or aqueous solution.

  In addition, it is easy to add any of the additives as an aqueous solution. In addition, if the additive is dissolved in water in advance and is in an ionic form, it is not only easily mixed and diffused into the sludge slurry present in the digestion tank, but also easily taken into the target anaerobic bacteria, preferable.

  Fe, Zn, and Mg are highly reactive and may be precipitated by binding to sulfides or may react with phosphorus to precipitate scales such as MAP. is necessary. In such a case, it is preferable not to add Fe, Zn, or Mg directly to the digestion tank, but to supply it to the digestion tank after previously mixing it with sludge supplied to the digestion tank. The metals may be added all at once, the order of addition may be determined or added in order, or the place of addition may be changed in consideration of the above effects.

  Which additive is effective is determined by adding the additive to a sample in which the sludge slurry in the digestion tank and the sludge introduced into the digestion tank are mixed in advance and leaving it at an appropriate temperature for several days (this In some cases, it is more preferable to stir continuously or intermittently with a stirrer more preferably), and a test for measuring the amount of gas generated and the methane gas concentration (partial pressure) can be performed. Which additive is deficient depends on the history until the input sludge flows in, and also varies depending on the season, so it is preferable to determine in advance by conducting the above test.

  The appropriate addition amount can also be examined by variously changing the conditions in this test. In addition, if it is the range which does not exceed 1% per weight of the total solid substance of input sludge, even if an additive is excessively added rather than an appropriate quantity, there will be no influence on microbe activity.

  Thus, only 1 type may be added and 2 or more types may be added. You may make it add a several additive within the said addition rate range. When adding 2 or more types, each additive may be mixed and added, may be added separately simultaneously, and may be added separately at different times of addition.

  As described above, when the temperature of the sludge slurry supplied to the anaerobic digester decreases, a local temperature decrease occurs when the sludge slurry flows into the digester, and the activity of the anaerobic bacteria decreases. At this time, if the necessary elements are supplied, the decrease in activity can be minimized. In addition, if the temperature of the sludge supplied to the anaerobic digestion tank is lowered, it is expected that it has not undergone decomposition when it passes through the route of the sewage pipe → first sedimentation basin → sludge concentration tank (device). . In general, below 25 ° C., the activity of anaerobic bacteria is significantly reduced.

Therefore, in the present invention, the temperature of the sludge introduced into the anaerobic digester 3 (for example, the temperature of the sludge in the mixing tank 1) or the temperature of the liquid in the anaerobic digester 3 is measured, and this temperature is a predetermined value. You may make it add an additive when it is lower than (temperature). In this case, it is preferable to increase the additive amount as the difference between the detected temperature and the predetermined value increases. There is no limit on the threshold temperature, the treatment plant at the value that matches the processing equipment, can be set freely, in the case of typical sewage treatment plant anaerobic digestion tank supplying sludge, generally 17 ℃ is a standard.

  If the sludge supplied to the anaerobic digester is not decomposed, the pH of the sludge is often in a high state (because the amount of organic acid produced is small). Therefore, in the present invention, the pH of the sludge introduced into the anaerobic digestion tank 3 (for example, the pH of the sludge in the mixing tank 1) or the pH of the liquid in the anaerobic digestion tank 3 is measured, and this pH is a predetermined value. The additive may be added at a higher temperature. In this case, it is preferable to increase the additive amount as the difference between the detected pH and the predetermined value increases. This predetermined value is preferably set in the range of 6-7.

  Moreover, if the sludge supplied to the anaerobic digester has not been decomposed, the sludge oxidation reduction potential (ORP) value is often high. Therefore, in the present invention, the ORP of the sludge introduced into the anaerobic digester 3 (for example, the ORP of the sludge in the mixing tank 1) or the ORP of the liquid in the anaerobic digester 3 is measured, and this ORP is a predetermined value. The additive may be added at a higher temperature. In this case, it is preferable to increase the additive amount as the difference between the detected ORP and the predetermined value increases. This predetermined value is preferably set in the range of −100 to 0 mV.

If the sludge supplied to the anaerobic digester has not been decomposed, the acid consumption (M-alkalinity) in the sludge is often low. Therefore, in the present invention, the M alkalinity of the sludge introduced into the anaerobic digester 3 (for example, the M alkalinity of the sludge in the mixing tank 1) or the M alkalinity of the liquid in the anaerobic digester 3 is measured. An additive may be added when the M alkalinity is lower than a predetermined value. In this case, it is preferable to increase the additive amount as the difference between the detected M alkalinity and the predetermined value increases. This predetermined value is preferably set in the range of 50 to 200 mg / L-asCaCO _3, particularly 50 to 150 mg / L-asCaCO ₃ .

  If the sludge supplied to the anaerobic digester is not decomposed, the volatile fatty acid concentration (VFA: Volatile Fatty Acid) in the sludge is often low. VFA is usually the total amount of acetic acid, propionic acid and butyric acid. Therefore, the VFA concentration in the sludge slurry supplied to the anaerobic digestion tank (for example, the VFA concentration of sludge in the mixing tank 1) or the VFA concentration of the liquid in the anaerobic digestion tank 3 is measured, and this VFA concentration is a predetermined value. The additive may be added at a lower temperature. In this case, it is preferable to increase the amount of additive as the difference between the detected VFA concentration and the predetermined value increases. The predetermined value varies depending on the treatment site, and also varies depending on the mixing ratio of the initial settling sludge and excess sludge, but is preferably set in the range of about 0 to 1000 mg / L, particularly 10 to 500 mg / L.

  In the present invention, two or more items (water quality index values) of the temperature, pH, ORP, M alkalinity, and VFA concentration are measured, and any one of the items deviates from the predetermined value range. May be added.

  The addition control of the additive may be performed by automatic control or manual control.

  In the following Examples and Comparative Examples, the first settling sludge of an actual municipal sewage treatment plant is used as the treated sludge (hereinafter referred to as raw sludge), and the anaerobic digester sludge of this sewage treatment plant is used as the digester sewage sludge. Using. The temperature of the raw sludge is 17 ° C, and the temperature of the digester tank sludge is 33 ° C.

[Comparative Example 1]
As shown in FIG. 2, 100 mL of raw sludge and 400 mL of digestion tank sludge were added as they were to an Erlenmeyer flask (capacity: 500 mL).

  As shown in FIG. 3, a rubber stopper equipped with a stainless steel tube capable of discharging the generated gas was inserted into the mouth of the Erlenmeyer flask. The stainless steel tube is connected to the stainless steel tube, and after the inside is filled with water and the air inside is replaced, the stainless steel tube is led into a graduated cylinder in a separate water tank, and the gas generated in the Erlenmeyer flask is stored in this graduated cylinder. The upper part is collected at

  This Erlenmeyer flask was bathed in a water bath adjusted to a temperature of 35 to 40 ° C. after the start of the test, and the inside was kept at approximately 37 ° C. Further, the inside of the flask can be stirred with a stir bar and a magnetic stirrer.

  During the 7-day test period, the amount of gas generated was determined from the volume of gas collected with a graduated cylinder. The results are shown in FIG. After the test is completed, a sample for gas analysis is collected from the gas layer accumulated in the graduated cylinder using a syringe, and the methane gas concentration, carbon dioxide concentration, nitrogen gas concentration, and hydrogen sulfide concentration (vol%) are measured by gas chromatography. did. The results are shown in Table 1.

[Comparative Example 2]
This was carried out in the same manner as in Comparative Example 1 except that the raw sludge was preheated to 28 ° C. with a hot water bath and added to the Erlenmeyer flask together with the digester sludge. The results are shown in FIG.

[Example 1]
In advance for raw sludge
Ferrous chloride: 0.1% by weight
Nickel chloride: 0.001% by weight
Cobalt chloride: 0.001% by weight
Manganese chloride: 0.0003 wt%
Was added in the form of an aqueous solution, and the mixture was stirred and mixed for 1 hour in the same manner as in Comparative Example 1. The results are shown in FIG.

  The metal salt aqueous solution is prepared by dissolving each metal salt in 5 mL of water and adjusting the pH to 6.

[Discussion]
As shown in Table 1, Example 1 in which the metal salt was added to the raw sludge was compared with Comparative Example 1 (without any pretreatment) and Comparative Example 2 (the raw sludge was preheated to 28 ° C.). The amount of gas generated is large and the methane gas concentration is high.

[Comparative Examples 3 to 5, Example 2]
After adjusting the raw sludge by carrying out the following pretreatment in advance, the temperature was raised to 35 ° C. in a hot water bath. Experiments were conducted in the same manner as in Comparative Example 1 except that 100 mL of raw sludge heated to 35 ° C. and 400 mL of digestion tank sludge at 33 ° C. were added to the Erlenmeyer flask.

Comparative Example 3: Standing for 24 hours at 35 ° C. Comparative Example 4: Standing for 24 hours at 25 ° C. Comparative Example 5: Refrigerated storage at 4 ° C. Example 2: Refrigerated storage at 4 ° C. Pre-feed sludge
Ferrous chloride: 0.1% by weight
Nickel chloride: 0.001% by weight
Cobalt chloride: 0.001% by weight
Manganese chloride: 0.0003 wt%
Was added in the form of an aqueous solution and stirred and mixed, and then digester sludge was added.

  The aqueous metal salt solution is prepared by dissolving each metal salt in 5 mL of water and adjusting the pH to 7.

  FIG. 5 and Table 2 show the gas generation amount and gas composition analysis results. Table 3 shows the pH, ORP, M-alkalinity, and VFA concentration in the flask on the seventh day after the start of the experiment.

[Discussion]
As shown in Tables 2 and 3, Comparative Example 5 has a smaller total gas generation amount than Comparative Examples 3 and 4, and the methane gas concentration in the generated gas is lower. This is because the anaerobic process has not progressed, pH and ORP are high, and M-alkalinity and VFA concentration are low.

  In Example 2, Fe, Ni, Co, and Mn salts were added to Comparative Example 5. In Example 2, the initial gas generation amount is smaller than those in Comparative Examples 3 and 4, but the rate of increase from about three days later is far apart, and the final gas generation amount and methane gas concentration can be increased. It was.

  The state of sludge in the flask can be grasped by pH, or by ORP, M-alkalinity, and VFA concentration.

For example, in this sludge treatment system, the threshold value is pH: 7 (-)
ORP: -100 (mV)
M-alkalinity: 90 (mg / L as CaCO ₃ )
VFA: 10 (mg / L)
If the salt of Fe, Ni, Co, Mn is added when it deviates from these (when it exceeds pH, ORP, M-alkalinity, VFA concentration, etc.) The generation effect can be increased, the amount of gas generated can be increased, and the methane concentration can be increased.

1 Mixing tank 3 Anaerobic digestion tank 5 Solid-liquid separation means

Claims (6)

In the sewage treatment plant, the first settling sludge that settled in the first sedimentation basin and / or the sewage treatment sludge that consists of excess sludge extracted from the biological treatment reaction tank is maintained at a predetermined temperature in the anaerobic digestion tank and anaerobic digestion treatment. In the anaerobic digestion method of sewage treatment sludge
At least one of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co is added to the sludge or anaerobic digester introduced into the anaerobic digester. An anaerobic digestion method of sewage treatment sludge to which an additive containing
Measure the temperature of the sludge introduced into the anaerobic digester or the temperature in the anaerobic digester,
An anaerobic digestion method of sewage treatment sludge, wherein the additive is added when this temperature is lower than a set temperature. In the sewage treatment plant, anaerobic digestion is performed by maintaining the sewage treatment sludge consisting of the initial sludge settled in the first sedimentation basin and / or excess sludge extracted from the biological treatment reaction tank in a predetermined pH range in the anaerobic digestion tank. In the anaerobic digestion method of sewage treatment sludge to be treated,
At least one of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co is added to the sludge or anaerobic digester introduced into the anaerobic digester. An anaerobic digestion method of sewage treatment sludge to which an additive containing
Measure the pH of the sludge introduced into the anaerobic digester or the pH in the anaerobic digester,
An anaerobic digestion method of sewage treatment sludge, wherein the additive is added when the pH is higher than a set value. In the sewage treatment plant, the sewage treatment sludge composed of the first settling sludge settled in the first settling basin and / or the excess sludge extracted from the biological treatment reaction tank is maintained in a predetermined ORP range in the anaerobic digestion tank, and anaerobic digestion is performed. In the anaerobic digestion method of sewage treatment sludge to be treated,
At least one of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co is added to the sludge or anaerobic digester introduced into the anaerobic digester. An anaerobic digestion method of sewage treatment sludge to which an additive containing
Measure the ORP of sludge introduced into the anaerobic digester or the ORP in the anaerobic digester,
An anaerobic digestion method of sewage treatment sludge, wherein the additive is added when the ORP is higher than a set value. In the sewage treatment plant, maintain the sewage treatment sludge consisting of the first settling sludge settled in the first settling basin and / or the excess sludge extracted from the biological treatment reaction tank in a predetermined M alkalinity range in the anaerobic digestion tank. In the anaerobic digestion method of sewage treatment sludge to be anaerobically digested,
At least one of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co is added to the sludge or anaerobic digester introduced into the anaerobic digester. An anaerobic digestion method of sewage treatment sludge to which an additive containing
Measure the M alkalinity of the sludge introduced into the anaerobic digestion tank or the M alkalinity in the anaerobic digestion tank,
An anaerobic digestion method of sewage treatment sludge, wherein the additive is added when the M alkalinity is lower than a set value. In the sewage treatment plant, the sewage treatment sludge consisting of the first settling sludge settled in the first settling basin and / or the excess sludge extracted from the biological treatment reaction tank is set to a predetermined volatile fatty acid concentration range in the anaerobic digestion tank. In the anaerobic digestion method of sewage treatment sludge to be anaerobically digested,
At least one of Fe, Cu, Zn, Mg, Mn, K, Ca, Ni, Mo, Se, S, V, Cr, I, and Co is added to the sludge or anaerobic digester introduced into the anaerobic digester. An anaerobic digestion method of sewage treatment sludge to which an additive containing
Measure the volatile fatty acid concentration of the sludge introduced into the anaerobic digester or the volatile fatty acid concentration in the anaerobic digester,
An anaerobic digestion method of sewage treatment sludge, wherein the additive is added when the volatile fatty acid concentration is lower than a set value.   The method for anaerobic digestion of sewage treatment sludge according to any one of claims 1 to 5, wherein the sewage treatment sludge is concentrated and then introduced into the anaerobic digestion tank.

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