JP2019141778A - Anaerobic digestion tank startup method and anaerobic digestion system - Google Patents

Abstract

To provide an anaerobic digestion tank startup method and an anaerobic digestion system that provide an easy start-up method for digestive tanks, as well as ensure ease of work related to startup and smooth startup.SOLUTION: An anaerobic digestion tank startup method includes: charging water and/or seed sludge into a digestion tank 2 where a concentrating mechanism 1 is arranged in the previous stage of a treatment flow; concentrating the seed sludge and raw sludge, to obtain concentrated sludge; charging the concentrated sludge into a digestion tank; and increasing the amount of the concentrated sludge charged into the digestion tank 2.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for starting an anaerobic digester and an anaerobic digestion system.

  Anaerobic digestion treatment decomposes sewage sludge and organic wastewater generated at water treatment facilities at sewage treatment plants by metabolic action of anaerobic microorganisms, reduces sludge and wastewater, and collects methane gas generated in the decomposition process. This process can be used as a reusable resource and has been widely used.

  The decomposition process of anaerobic digestion is performed by gasifying organic components in sludge by the action of acid-producing bacteria and methanogenic bacteria, which are anaerobic microorganisms, and decomposes during the acidic fermentation period, acidic decline period, and alkaline fermentation period. It goes through the process. For this reason, it is important to maintain anaerobic microorganisms in the digestion tank that are commensurate with the amount of sewage sludge and organic wastewater that is introduced into the digestion tank, and the pH, organic acid concentration and temperature compared to acid-producing bacteria. It is important to maintain the optimal conditions suitable for the growth of methanogenic bacteria that are sensitive to fluctuations and slow in growth rate, and to keep the balance of the organic degradation process.

  To start up a digester that performs anaerobic digestion, first fill the tank with water and conduct an airtight test on the piping system. Thereafter, if possible, sludge containing anaerobic microorganisms (seed sludge) is introduced into the digestion tank, and raw sludge to be digested is introduced. Gradually increase the input amount of raw sludge and allow the anaerobic microorganisms to grow sufficiently in the digestion tank. Normally, it is known that steady operation is possible in 50 to 60 days after the seed sludge is introduced (see, for example, Non-Patent Document 1).

  Inputting seed sludge into the digestion tank before starting the input of raw sludge introduces activated anaerobic microorganisms necessary for digestion into the digestion tank from the start, so the amount of seed sludge input The more it is, the shorter the time it takes to adapt. However, it is often difficult to fill the digestion tank only with seed sludge in advance from the viewpoint of securing the necessary amount, and in many cases it is generally less than 1/2 of the digestion tank capacity.

  The digestibility is proportional to the amount of anaerobic microorganisms retained in the digester, that is, the sludge concentration in the digester. At the beginning of raw sludge input, the sludge concentration in the digestion tank is lower than in normal operation and the digestion capacity is low, so it is necessary to suppress the amount of raw sludge input. Generally, it is 5% or less of the solid content in the digested sludge. . By continuing the input of raw sludge, the sludge concentration in the digestion tank gradually increases, and the input amount of raw sludge can be increased.

  In the anaerobic digestion, the retained amount of the anaerobic microorganisms in the digested sludge and the retained amount of the alkali are important factors. Alkaline content in digested sludge is generally based on total alkalinity, and is suitable for the growth of methanogenic bacteria due to its buffer action that suppresses excessive pH drop caused by organic acids generated during the decomposition of organic matter in anaerobic digestion. The optimum pH can be maintained.

  At the beginning of charging, the total alkalinity in the digested sludge is lower than that in steady operation and the pH buffering capacity is low, so the pH is likely to decrease due to organic acid accumulation due to an increase in the input amount of raw sludge. It is possible to increase the input amount of raw sludge by increasing the concentration of alkali as well as the concentration.

  In recent years, attempts have been made to shorten the digestion tank startup period. In Japanese Patent No. 4819757, after introducing seed sludge into an anaerobic digester, a part of the sludge in the digester is extracted, and the extracted sludge is dehydrated to obtain dehydrated sludge. To be returned to. According to this, it is described that anaerobic digestion system can be started up in a short time even with a small amount of seed sludge.

Japanese Patent No. 4819757

Japan Sewerage Association, “Guidelines for Sewerage Maintenance and Management-2014 edition”, issued on September 12, 2014, p. 832-834

  However, in the method of Non-Patent Document 1, an acclimatization period of about 50 to 60 days is required after the start-up process of the digestion tank, and the entire start-up period of the digestion tank is half a year to one year. It takes a long time. In general, the heating required for digestion tank operation is performed using methane gas generated from the digestion tank as energy, but during the start-up period when it is difficult to recover and use methane gas, additional fuel is required. It also takes. Moreover, in the acclimatization period at the initial stage of start-up, wastewater having a sludge concentration that is difficult to dewater, in which a small amount of raw sludge is mixed with the water filled in the digestion tank, flows out or is drawn out of the tank. During that time, the drained wastewater is treated in the water treatment facility, and the sludge obtained by the treatment in the water treatment facility is returned. However, the load on the water treatment facility is significantly increased during the start-up period of the digester. There is also the problem of rising. Therefore, it is desirable that the start-up period be as short as possible.

  The invention described in Patent Document 1 has a moisture content of 85% by mass from sludge dewatering that is one of sludge treatment methods such as centrifugal dehydrator, screw press dehydrator, rotary press dehydrator and the like. The following dewatered sludge is used, and this dewatered sludge is re-introduced into the digestion tank to achieve early start-up.

  The dehydrated sludge is generally sludge dehydrated to such an extent that it can be handled as a solid, and is also called a dehydrated cake. Usually, the water content is 85% or less.

  However, when trying to pump dewatered sludge as described in Patent Document 1 to a digester using a pump, piping, or the like, high power is required and piping or pumps are frequently clogged. In other words, it is actually difficult to pump the dewatered sludge described in Patent Document 1 to the digestion tank using a pump. In order to return the dewatered sludge to the digestion tank, a conveyor such as a belt conveyor is required separately, which increases the size of the apparatus. In addition, a conveyor installed separately for transferring dewatered sludge to the digestion tank can be used only when the digestion tank is started up, and is not versatile.

  In general water treatment facilities currently in operation, digestion facilities and sludge dewatering facilities are often deployed at remote locations. The dewatering equipment includes a dehydrator for performing sludge dewatering, a transporter for transporting the dewatered sludge discharged from the dewaterer, a hopper for storing the transported sludge, and the like. In addition, the dehydration equipment is often configured indoors, and from the viewpoint of sludge transfer by the transporter, the dehydrator is often installed on the first floor high place or the middle floor or higher. Further, from the viewpoint of consideration of the work environment, there is a case where the conveying path from the dehydrator to the hopper is closed with a cover or the like as a deodorizing measure.

  Therefore, when the technology described in Patent Document 1 is applied to an existing water treatment facility, a transport vehicle is installed or a large transport facility is temporarily installed for transporting sludge to a digestion facility far from the dehydration facility. It also has to be transported. Moreover, since it is necessary to transfer from the high place in a building to the said digesting tank of the outdoors, and it is necessary to take out dehydrated sludge from the obstructed conveyance path, it is difficult in reality.

  Furthermore, in the invention described in Patent Document 1, the sludge extracted from the digester is dehydrated to discharge a large amount of water in the sludge, so that the alkali content in the sludge is lost along with the water. By returning sludge from which alkali content has been lost by dehydration to the digestion tank, the solid content concentration (TS concentration) increases, but the alkali content does not increase. Anaerobic digestion treatment keeps the alkali content suitable for the TS concentration of the digested sludge, and even if the organic acid concentration rises, it can keep the pH near neutral optimum for digestion reaction by the buffering action of the alkali content. Although it is possible, when the alkali content corresponding to the TS concentration is insufficient, it is difficult to maintain a pH near neutral optimum for the digestion reaction.

  Furthermore, organic acids tend to accumulate during the start-up period during which the digestion reaction is likely to be unstable. When the alkali content corresponding to the TS concentration is not maintained, the pH is maintained near neutrality, which is more optimal for the digestion reaction. Becomes difficult. In order to proceed a stable digestion reaction after mixing dewatered sludge, it may be necessary to add an alkaline agent to the digester.

The amount of alkali is represented by the corresponding concentration of calcium carbonate (CaCo ₃ ) and is generally measured by the total alkalinity, which is the oxygen consumption up to pH 4.8. The total alkalinity in the sludge varies depending on the sludge concentration. When the TS concentration is about 2%, it is about 2500 to 2700 mg-CaCO ₃ / L, and about 3% is about 3900 to 4100 mg-CaCO ₃ / L.

  Further, as in the invention described in Patent Document 1, an organic polymer flocculant is generally used to make anaerobic digested sludge into a dehydrated sludge having a water content of 85% or less. It depends on the properties of the sludge that is subject to For example, the Japan Sewage Works Association, a local joint corporation, machine equipment standard specifications issued in 2016, June 1, 2016, p. According to 12-15, 12-16, 12-23, 12-44 (reference document 1), the addition amount is approximately 1.1 to 2.1% with respect to the solid amount contained in the target sludge. Generally, the target value is used, but in order to achieve the target moisture content of the dewatered sludge, there are many cases where the injection rate is 2.0% or more. In addition, the Environmental Technology Society, monthly magazine “Environmental Technology” August 2004 issue, research paper “Effect of polymer flocculant on anaerobic digestion of surplus sludge from sewage treatment”, p. In the report of 631-638 (reference document 2), there is no influence when the amount of the organic polymer flocculant added is 1% or less with respect to the amount of solids contained in the sludge. Yes, it is described that digestion inhibition occurs at 2 to 3% or more, and the technique described in Patent Document 1 may cause similar digestion inhibition.

  Furthermore, when returning dehydrated sludge to a digestion tank, it is necessary to disperse dehydrated sludge in digested sludge. Since dehydrated sludge has properties close to solids as described above, there is a concern that even if it is put into the digestion tank as it is, it will not be sufficiently re-dissolved in the tank.

  Further, according to Reference 2, it is described that the inhibition by the organic polymer flocculant is an activity inhibition of anaerobic digestive bacteria, and the amount of the organic polymer flocculant locally increases unless re-dissolved. There is a concern that it will not function.

  In recent years, for the purpose of reducing sludge treatment capacity, organic polymer flocculants are added in advance to anaerobic digestion raw sludge and concentrated to digest. The risk of digestion inhibition by the polymer flocculant increases.

  Furthermore, in the digestion tanks used in recent digestion treatments, it is difficult to crush and disperse the cake on the cake, such as gas stirring that causes the sludge in the tank to flow by gas jets and low speed stirring using large stirring blades. Since there is a growing concern that even if dehydrated sludge is returned to the digestion tank, it will not be sufficiently re-dissolved in the tank, a separate facility for dissolving or crushing dehydrated sludge may be required.

  In view of the above-described problems, the present invention provides an anaerobic digestion system that provides a method for quickly and stably starting up a digester, and also has the convenience of work related to startup and smooth startup.

  In order to achieve the above-mentioned purpose, the present inventors diligently studied, and, as a result, a concentrating mechanism was disposed in the previous stage of the digestion tank, and the concentrated sludge was concentrated to a higher concentration than the sludge charged into the normal digestion tank in the concentrating mechanism. It has been found that the introduction of the water into the digester is one of the effective means.

  In one aspect of the present invention completed on the basis of the above knowledge, water and / or seed sludge is introduced into a digestion tank in which a concentration mechanism is arranged in the previous stage of the treatment flow, and seed sludge and raw sludge are concentrated. There is provided a method for starting an anaerobic digester that includes obtaining concentrated sludge, introducing the concentrated sludge into the digester, and increasing the amount of the concentrated sludge charged into the digester.

  In the present invention, the process of “injecting water and / or seed sludge into a digestion tank in which a concentration mechanism is arranged in the previous stage of the treatment flow” is a generally performed initial procedure, and details thereof are particularly limited. It is not something. That is, in the process of “injecting water and / or seed sludge into a digestion tank in which a concentration mechanism is arranged in the previous stage of the processing flow”, after the water or seed sludge is introduced into the digestion tank alone or both, It includes a process that can be appropriately performed by those skilled in the art at the initial stage of start-up, in which an anaerobic state is established and heating is performed as necessary.

  The “concentration mechanism” in the present invention refers to one of sludge treatment techniques, by increasing the TS concentration to about several to tens of wt% by solid-liquid separation of sludge, and effectively allowing digestion and dehydration processes to function. It refers to an apparatus or facility that concentrates sludge and discharges concentrated sludge.

  According to this method, since the alkalinity of digested sludge is generated in the process of decomposing organic matter, the alkalinity retained by the sludge in the digestion tank is not lost by concentrating the raw sludge before the organic component is decomposed. It is possible to provide a start-up method that is both stable and shortened.

  According to another aspect of the present invention, water and / or seed sludge is introduced into a digestion tank in which a concentration mechanism is disposed in the front stage of the treatment flow, the raw sludge is concentrated to obtain the concentrated sludge, and the concentration Introducing sludge into the digestion tank, extracting a part of the sludge in the digestion tank to obtain a drawn sludge, concentrating at least a part of the drawn sludge together with the raw sludge, and returning to the digester An anaerobic digester start-up method is provided.

  According to this method, the problem of digestion inhibition derived from the flocculant added in large quantities to produce sludge having a low water content such as dewatered sludge by returning the extracted sludge from the digester to the digester. In addition, it is possible to reduce problems such as alkali content lost in a large amount in the process of generating dewatered sludge and piping clogging. In addition, there is no need for a dissolving device for dissolving special dewatered sludge in the digestion tank, and it is possible to provide a start-up method that achieves both easy work and smooth start-up.

  In another aspect of the present invention, water and / or seed sludge is introduced into a digestion tank in which a concentration mechanism is disposed in the front stage of the treatment flow, and seed sludge and raw sludge are concentrated to obtain concentrated sludge. Adding the concentrated sludge to the digestion tank, extracting a part of the sludge from the digestion tank to obtain a extracted sludge, and at least a part of the extracted sludge together with the seed sludge and the raw sludge. A method for starting an anaerobic digester is provided that includes concentrating and returning to the digester, and increasing the amount of concentrated sludge that is input to the digester.

  In yet another embodiment of the method for starting up the anaerobic digester according to the present invention, when water and / or seed sludge is introduced into the digester, the seed sludge is added when the seed sludge is introduced. Injecting the digestion tank after the concentration process in the concentration mechanism.

  In yet another embodiment, the method for starting an anaerobic digester according to the present invention includes using sludge generated from an existing digester as seed sludge.

  In yet another embodiment of the method for starting up the anaerobic digester according to the present invention, the flocculant is added in an amount of 0.2 to 1.5% by mass with respect to the solid amount of sludge supplied to the concentration mechanism and concentrated. Including processing.

  In yet another embodiment, the method for starting up the anaerobic digester according to the present invention includes supplying concentrated sludge having a sludge concentration of 4 to 12% by mass to the digester.

  In yet another aspect, the present invention is arranged between a concentration mechanism for concentrating raw sludge to obtain concentrated sludge, a digestion tank for anaerobically digesting the concentrated sludge, a digestion tank and a concentration mechanism, An anaerobic digestion system is provided that includes a pipe that circulates a portion of the extracted sludge extracted from the system to a concentration mechanism.

  In one embodiment, the anaerobic digestion system according to the present invention may further include sludge supply means for supplying seed sludge to the concentration mechanism. When seed sludge can be supplied from a digester that is in operation, is abolished, and is scheduled to be stopped for a long time, or is operating for a long time, disposed in the same treatment plant as the digester, sludge supply means because it already has a function that can be supplied continuously Is no longer necessary.

  In another embodiment of the anaerobic digestion system according to the present invention, there is provided an anaerobic digestion system in which the concentration mechanism includes a concentration mechanism attached to the digestion tank for the purpose of increasing the concentration of sludge to be introduced into the digestion tank. .

  In yet another embodiment of the anaerobic digestion system according to the present invention, the digester performs anaerobic digestion of sludge having a sludge concentration of 1 to 12% by mass to discharge 0.5 to 9% by mass of digested sludge. It is a digester. In the case of a digester with a concentrating mechanism attached to the digester, it is desirable to perform digestion treatment by introducing a concentrated sludge having a high sludge concentration of 4 to 12% by mass, preferably 6 to 10% by mass. In the present embodiment, such a form is defined as a high-concentration digester and will be described hereinafter.

  ADVANTAGE OF THE INVENTION According to this invention, while providing the digestive tank early startup method, the anaerobic digestion system which also has the simplicity of the operation | work regarding startup, and smooth startup property can be provided.

It is the schematic which shows the example of the water treatment system suitable for application of the anaerobic digestion system which concerns on embodiment of this invention. It is the schematic which shows the example of another water treatment system suitable for application of the anaerobic digestion system which concerns on embodiment of this invention. It is the schematic which shows an example of the anaerobic digestion system which concerns on the 1st Embodiment of this invention. It is the schematic which shows an example of the anaerobic digestion system which concerns on the 2nd Embodiment of this invention. It is the schematic which shows an example of the anaerobic digestion system which concerns on the modification of the 2nd Embodiment of this invention. It is a graph showing the simulation result of the change of the digested sludge solid substance density | concentration in a digester with respect to a starting period. It is a graph showing the simulation result which evaluated the change of the amount of digested sludge alkalis in a digestion tank with respect to a start-up period by total alkalinity. It is a graph showing the simulation result of the change of the organic polymer flocculent density | concentration in a digester with respect to a starting period.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The following embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is to describe the structure, arrangement, etc. of components as follows. It is not something specific.

<Water treatment system>
Before explaining the anaerobic digestion system according to the embodiment of the present invention, an example of a water treatment system suitable for application of the present anaerobic digestion system is shown in FIG. 1 and FIG. 2, but not limited to the following examples. Of course.

  As shown in FIG. 1, a water treatment system according to an embodiment of the present invention uses a sewage supplied to a sewage treatment facility of a water treatment plant as a raw water, a first settling basin 20 for solid-liquid separation of the raw water, A reaction tank 30 that decomposes and stabilizes organic suspended solids and dissolved organic substances that have not been removed in the sedimentation basin 20 by the action of microorganisms, and a final sedimentation basin 40 that solid-liquid separates the activated sludge treated in the reaction tank, A mechanical concentration mechanism 50 for mechanically concentrating excess sludge generated in the reaction tank 30 and the final sedimentation basin 40, a gravity concentration mechanism 60 for gravity concentrating sludge generated by solid-liquid separation in the initial sedimentation basin 20, a mechanical concentration mechanism 50, and The mixing tank 70 for mixing the sludge concentrated by the gravity concentration mechanism 60 or the unconcentrated sludge and the sludge supplied from the mixing tank 70 are digested under anaerobic conditions by the action of methane fermentation bacteria and the like to reduce the volume. And a digester 90.

  Alternatively, as shown in FIG. 2, a mechanical concentration mechanism 80 may be further provided between the digestion tank 90 and the mixing tank 70.

  The anaerobic processing system according to the embodiment of the present invention can be suitably implemented when starting up the digester tank 90 in which the concentration mechanism is arranged in the previous stage of the processing flow. For example, as shown in FIG. 1, a water treatment system having a mechanical concentration mechanism 50 and a gravity concentration mechanism 60 in the front stage of the digestion tank 90, a mechanical concentration mechanism 50, a gravity concentration mechanism 60, as shown in FIG. It is suitable for a water treatment system or the like having a mechanical concentrating mechanism 80 in the front stage of the digestion tank 90. When the water treatment system shown in FIG. 1 is applied to the anaerobic digestion system according to the embodiment of the present invention described below, the mechanical concentration mechanism 50 and / or the gravity concentration mechanism 60 is replaced with the concentration mechanism 1 according to the present embodiment. Can be used as When the water treatment system as shown in FIG. 2 is applied to the anaerobic digestion system according to the embodiment of the present invention, the mechanical concentrating mechanism 50 and / or the gravity concentrating mechanism 60 and / or the mechanical concentrating mechanism 80 are installed in the present embodiment. It can utilize as the concentration mechanism 1 which concerns on embodiment. Details of the anaerobic digestion system according to the first and second embodiments of the present invention will be described below.

(First embodiment)
As shown in FIG. 3, the anaerobic treatment system according to the first embodiment of the present invention concentrates seed sludge and raw sludge to obtain concentrated sludge, and anaerobic digestion treatment of the concentrated sludge. And a seed sludge supply means 5 for supplying the seed sludge to the concentration mechanism 1. There is no particular limitation on the supply source of the seed sludge, but it is preferable to use the digester 4 or the like that is currently in operation or is in operation but is scheduled to be shut down in the future. The seed sludge supply means 5 is not particularly limited as long as it is a means capable of transporting existing digested sludge, such as a pipe and a transporter.

  The raw sludge used in the present invention is not particularly limited as long as it contains organic components that can be digested by anaerobic microorganisms such as methane-fermenting bacteria and hydrogen-fermenting bacteria. For example, sewage sludge generated in a water treatment facility of a sewage treatment plant, or organic waste water including waste water generated in a food factory, a paper mill, a livestock farm, or the like can be used.

  Biological organic resources such as biomass may be mixed with the raw sludge. Specifically, raw garbage, okara, shochu, etc. can be mixed with raw sludge.

  The concentration mechanism 1 is not particularly limited as long as it is a device that increases the concentration of low-concentration sludge to a TS concentration of about several tens of wt% or more by solid-liquid separation and effectively functions the digestion and dehydration processes. For example, the concentration mechanism 1 performs gravity concentration, centrifugal concentration, levitation concentration, belt filtration concentration, screen concentration, and the like to concentrate sludge. The concentration mechanism 1 can include a concentration device, a granulation tank, and a chemical supply device.

  When concentrating sludge, chemicals such as a special flocculant are not necessary for sludge with good dewaterability, but for sludge with poor condensability, inorganic substances such as polyferric sulfate, PAC, and sulfuric acid bands are used. A system flocculant or an organic polymer flocculant may be added alone or in combination.

  Although not limited to the following, the concentration mechanism 1 is configured so that the solid matter concentration of the sludge input to the concentration mechanism 1 is not less than the TS concentration of the raw sludge and not more than 12 wt%, preferably 4 to 12 wt%, more preferably 6 It is preferable to concentrate to -10 wt%.

  As shown in FIG. 3, the concentration mechanism 1 is preferably in the form of the mechanical concentration mechanism 80 shown in FIG. 2 that is attached to and adjacent to the digestion tank 2 or integrated with the digestion tank 2. As a result, it is possible to concentrate the sludge suitable for start-up and to easily transfer the concentrated sludge concentrated by the concentration mechanism 1 to the digestion tank 2. For example, if the concentration mechanism 1 is installed in the upper part of the digestion tank 2 and configured to convey the concentrated sludge by gravity, a means for conveying the concentrated sludge becomes substantially unnecessary.

  The concentration mechanism 1 is preferably a mechanical concentration mechanism for performing a mechanical concentration process from the viewpoint of early start-up. As the mechanical concentrating mechanism, for example, it is preferable to use screen concentrating by an apparatus equipped with a wedge wire screen, a bar screen, or the like.

  Although it does not specifically limit as the digester 2, For example, a complete mixing type digester can be used. The digestion tank 2 is provided with an agitation facility in order to homogenize the liquid in the tank and uniform the temperature distribution, and to prevent the occurrence of scum. In digester 2, organic substances in sludge are hydrolyzed to volatile organic acids and lower alcohols by the action of anaerobic bacteria, and then intermediate products such as organic acids are converted to methane, dioxide by the action of methane fermentation bacteria. Decomposed into carbon, ammonia, etc.

  As the digestion tank 2, for example, a general sewage sludge anaerobic digestion apparatus having a TS concentration of 1 to 6 wt%, typically 2 to 4 wt% is used.

  Furthermore, as the digester 2, the sludge concentration to be added to the digester is concentrated to a high concentration, so that the sludge can be introduced in a small volume, and a large amount of digestion gas is generated from a small amount of sludge in the small-capacity digester 2. Includes a concentration digester. For example, an apparatus capable of anaerobic digestion of sludge having a TS concentration of 4 to 12 wt%, desirably 6 to 10 wt% is used.

  For example, according to the experiments by the present inventors, a digestion tank 2 capable of treating sludge having a TS concentration of 6 to 10 wt% is a high-concentration digester, so that conventional sludge having a TS concentration of about 2 to 4 wt% is treated. Since the volume of the digestion tank 2 can be reduced to about 1/2 to 1/8 of the digestion tank for digestion of sludge, the installation space can be reduced and the entire system can be downsized.

  Next, a method for starting up the anaerobic digester 2 according to the first embodiment will be described with reference to FIG.

  First, water or seed sludge alone or both are put on the digestion tank 2 and heated under anaerobic conditions. Specifically, for example, water or seed sludge alone or both in the digestion tank 2 is stretched to a stirrable water level with a stirrer installed in the digestion tank, and then the air in the digestion tank 2 is infused with nitrogen or the like. By substituting with the active gas, the inside of the digestion tank 2 can be brought into an anaerobic state.

  In the process of applying water or seed sludge alone or both to the digester 2, the digester 2 is generally equipped with a stirrer and a heating device not shown, and the stirrer and the warmer are operated. It is desirable to fill the digester 2 with water or seed sludge alone or both to a possible water level.

  Furthermore, in the process of stretching water or seed sludge alone or both in the digestion tank 2, it is desirable to fill the digestion tank 2 with the seed sludge as much as possible. If possible, the volume is 100% or less based on the volume of the tank capacity, 50% or less if the required amount cannot be secured, 30% or less if it cannot be secured, 10% or less if it cannot be secured further. Is preferably used together with water up to a water level at which the stirrer and heating device can operate. If seed sludge cannot be secured, it can be started up even if the digester 2 is filled with water alone.

  Next, seed sludge and raw sludge are supplied to the concentration mechanism 1 and concentrated to obtain concentrated sludge. The raw sludge and seed sludge are concentrated in the concentration mechanism 1 to a level equal to or higher than the raw sludge TS concentration during steady operation.

  Next, the concentrated concentrated sludge is charged into the digestion tank 2. The amount of concentrated sludge to be input is set to an amount that can be input depending on the processing capacity of the concentration mechanism 1 or the amount of seed sludge that can be supplied to the concentration mechanism 1. The amount of raw sludge contained in the concentrated sludge is not limited to the following, but starts with the amount of raw sludge in which the amount of solids in the raw sludge during steady operation is 1/3 or less. Except for the case where 100% of the seed sludge is filled with respect to the digestion tank volume before the sludge is charged, the digestion capacity of the digestion tank is lower than that during steady operation. In some cases, organic acid accumulates in the digested sludge and the treatment is not stable.

  Next, the input amount of concentrated sludge is increased by gradually increasing the amount of raw sludge supplied to the concentration mechanism 1. In consideration of the growth of anaerobic microorganisms present in the digestion tank 2, the amount of raw sludge is preferably gradually increased by 10% or less, preferably 4 to 6% of the solid content in the digestion tank. In digestion tank 2, paying attention to the amount of digestion gas generated in digestion tank 2, the concentration of carbon dioxide in digestion gas, the concentration of sludge in digestion tank 2, the organic acid and pH, etc. are measured regularly. Observe the progress of.

  The temperature and pH in the digestion tank 2 can be appropriately set according to conditions such as the type of anaerobic microorganisms (methane fermentation bacteria) contained in the sludge, the sludge load of the sludge to be input, and the sludge concentration. The temperature is generally 25 to 65 ° C, preferably 30 to 40 ° C. In the case of thermophilic bacteria, the temperature is 50 to 60 ° C. The pH is generally 6.5 to 8, preferably 6.8 to 7.6.

  The digestion tank 2 generally discharges the same amount of sludge as the amount of the introduced sludge to the outside of the digestion tank by overflow or extraction by a pump or the like. Usually, it is transferred to the latter stage equipment, but the low concentration sludge at the start-up stage is first returned to the settling basin 20 and may be treated together with the raw water.

  It is desirable to supply seed sludge to the concentration mechanism 1 as much as possible. However, when the total amount of raw sludge and seed sludge exceeds the processing capacity of the concentration mechanism 1, the supply amount of seed sludge is reduced and concentrated within the processing capacity range of the concentration mechanism 1 and put into the digester 2. When the supply amount of the raw sludge reaches the amount during steady operation and the sludge concentration in the digestion tank 2 is stabilized, the start-up operation is completed.

  According to the anaerobic digestion system and the start-up method using the same according to the first embodiment, seed sludge and raw sludge having a stable digestion reaction are input to the digestion tank 2, so that the amount of raw sludge is input. The sludge having a high concentration close to the amount of sludge input during steady operation can be input to the digestion tank 2 from the start-up when it is necessary to reduce the amount. Thereby, high concentration of the sludge density | concentration in the tank in the digestion tank 2 can be achieved at an early stage. Moreover, since the digested sludge of the existing digester 4 can be used as seed sludge, there is little inhibition of the digestion reaction.

  Furthermore, according to the start-up method of the anaerobic digester according to the first embodiment, since the mixed sludge of seed sludge and raw sludge is put into the digester 2 while being concentrated, the start-up is performed. It is particularly preferably used when the seed sludge is continuously obtained. That is, according to the start-up method of the anaerobic digester according to the first embodiment, by using a mode in which a small amount of seed sludge is mixed with the raw sludge and concentrated and then supplied to the digester 2, the digester When seed sludge is charged to 2, it is not necessary to transfer and sludge the seed sludge in a large amount in the initial stage, and a sludge having a stable concentration can be always supplied into the digestion tank 2. For example, when seed sludge is put into a new digester, seed sludge in an amount of about 1/35 to 1/12 of the capacity of the digester 2 cannot be obtained, but a small amount of seed sludge is continuously obtained. The effect can be further demonstrated by carrying out in some cases.

  Furthermore, according to the method according to the first embodiment, the addition rate when the flocculant is used in the concentration mechanism 1 is 0.2 to 1.5% on a weight basis with respect to the amount of solids contained in the sludge. It is preferable to set the degree. If too much flocculant is added to the sludge, the contact efficiency between the organic components in the sludge and the anaerobic microorganisms will be reduced and the activity of the anaerobic microorganisms will be inhibited, and the decomposition of the sludge will be inhibited. May occur. Conversely, if the amount of the flocculant added is too small, the effect due to the addition of the flocculant may not be sufficiently obtained. Although depending on the components of the sludge, the addition rate of the flocculant used in the concentration mechanism 1 can be 0.3 to 1.0% on a weight basis in one embodiment, and another embodiment In the range of 0.4 to 0.7%.

(Second Embodiment)
As shown in FIG. 4, the anaerobic treatment system according to the second embodiment of the present invention includes a concentration mechanism 1 that concentrates raw sludge to obtain concentrated sludge, and a digester 2 that performs anaerobic digestion of the concentrated sludge. And a pipe 3 that is disposed between the digestion tank 2 and the concentration mechanism 1 and circulates a part of the extracted sludge extracted from the digestion tank 2 to the concentration mechanism 1. Since the structure of the concentration mechanism 1 and the digester 2 is substantially the same as the structure shown in FIG.

  After the sludge in the digestion tank 2 is extracted, the extracted sludge (referred to as “extracted sludge”) is sent to the subsequent equipment installed in the subsequent stage of the digestion tank 2 for water treatment, while the extracted sludge is extracted. A part or all of the above is returned to the concentrating mechanism 1 or the pipe 3 connected to the preceding stage of the concentrating mechanism 1 via the pipe 3.

  The drawn sludge has a digested sludge TS concentration of 9 wt% or less (that is, a moisture content of 91 wt% or more) in a steady state, although it depends on the sludge concentration of the sludge treated in the digestion tank 2. The digested sludge TS concentration of a general anaerobic digestion treatment is typically 0.5 to 9 wt% (water content 91 to 99.5 wt%), and more typically 2 to 9 wt% (water content 91). ~ 98 wt%). The concentration of digested sludge TS in the high concentration anaerobic digestion treatment is typically 3 to 7 wt% (water content 93 to 97 wt%) more typically.

  A pump mechanism (not shown) is disposed in the pipe 3. As described above, since the TS concentration of the drawn sludge according to the present embodiment is 9 wt% or less, the sludge concentration is lower than that of the dehydrated sludge as described in Patent Document 1, and transportation is easy. In addition, the piping can be fed while suppressing clogging of the pump.

  Furthermore, even in the concentrated sludge treated by the concentration mechanism 1, the TS concentration is 12% or less, and is easy to transport. As a result, compared with the case where dehydrated sludge having a low water content is transported to the digestion tank using a transporter or the like, it is possible to simplify the equipment for returning the extracted sludge.

  According to the start-up method according to the present embodiment, a part of the sludge in the digestion tank 2 is extracted and returned to the concentration mechanism 1, concentrated together with the raw sludge to a predetermined concentration by the concentration mechanism 1, and then returned to the digestion tank 2. By putting it in, the extracted sludge from the digestion tank can be used as high-concentration seed sludge. As a result, early start-up of the digester 2 can be realized without greatly changing the environment in the digester 2.

  Next, a method for starting an anaerobic digester according to the second embodiment of the present invention will be described with reference to FIG.

  First, water or seed sludge alone or both are put on the digestion tank 2 and heated under anaerobic conditions. Specifically, for example, water or seed sludge alone or both in the digestion tank 2 is stretched to a stirrable water level with a stirrer installed in the digestion tank 2, and then the air in the digestion tank 2 is changed to nitrogen or the like. By substituting with the inert gas, the inside of the digestion tank 2 can be brought into an anaerobic state.

  Next, the raw sludge is supplied to the concentration mechanism 1, and the raw sludge is concentrated to obtain the concentrated sludge. In the concentration mechanism 1, first, the raw sludge is concentrated to a level equal to or higher than the raw sludge TS concentration during steady operation.

  Next, the concentrated sludge is charged into the digestion tank 2. The initial input amount of concentrated sludge is not limited to the following, but as an example of a general method, the amount of solid sludge in the raw sludge during steady operation starts with an amount of raw sludge that is 1/3 or less. .

  Next, the amount of concentrated sludge thrown into the digester 2 is gradually increased. In digestion tank 2, paying attention to the amount of digestion gas generated in digestion tank 2, the concentration of carbon dioxide in digestion gas, the concentration of sludge in digestion tank 2, the organic acid and pH, etc. are measured regularly. Observe the progress of.

  The amount of the extracted sludge discharged from the digestion tank 2 is gradually increased after the amount of the concentrated sludge input to the digestion tank 2 is gradually increased and the concentration of the sludge TS in the digestion tank 2 reaches a concentration that can be concentrated in the concentration mechanism 1. A part or the whole is supplied together with the raw sludge to the concentration mechanism 1, concentrated, and returned to the digester 2. The other extracted sludge is sent to a water treatment facility or a sludge treatment facility (the latter-stage facility in FIG. 4) in the subsequent stage.

  The amount of the extracted sludge supplied to the concentration mechanism 1 with respect to the total amount of the extracted sludge is preferably supplied as much as possible within the processing capacity of the concentration mechanism 1. Although it is different depending on the treatment, it is not limited to the following. In the initial stage of startup when the total amount of sludge is less than the amount of sludge input during steady operation, 100% of the extracted sludge is supplied to the concentrating mechanism 1 to increase the amount of raw sludge and the total amount of raw sludge and extracted sludge is In the latter stage of startup, which is greater than the sludge input amount, it is desirable to gradually reduce the ratio of the extracted sludge and to input the sludge input amount during steady operation to the digester. When the sludge load of the concentrated sludge reaches the planned input sludge load, the start-up is completed.

  According to the start-up method of the anaerobic digester according to the second embodiment, part of the extracted sludge extracted from the digester 2 is concentrated together with the raw sludge and returned to the digester 2. Therefore, even when there is little or no seed sludge that can be introduced into the digestion tank 2, the concentration of sludge in the digestion tank 2 can be increased at an early stage, and the startup period can be shortened.

  Furthermore, according to the method according to the second embodiment, the drawn sludge having a high water content (for example, about 91% or more) is returned to the concentrating mechanism 1, so that piping pumping by a pump is easy and a simple device is used. Early equipment startup is possible. Further, the solid-liquid separation process of the drawn sludge is also performed by the concentration mechanism 1 disposed in the vicinity of the digestion tank 2, whereby the entire apparatus can be reduced in size.

  Furthermore, according to the method according to the second embodiment, the water content of the sludge concentrated by the concentration mechanism 1 is very high compared to the water content of the dewatered sludge disclosed in Patent Document 1, so that it is dissolved in the liquid. The loss of alkali content is small. For example, in the case of concentrated sludge with digested sludge having a moisture content of 97% and moisture content of 92% (TS concentration 8%) and dehydrated sludge having a moisture content of 85% (TS concentration 15%), the concentrated sludge is more dehydrated sludge. The alkali content is about twice as high. For this reason, the amount of the alkaline agent added in the digestion tank 2 is small or unnecessary, and it is easy to maintain the pH in the tank.

  Furthermore, according to the method according to the second embodiment, since the raw sludge containing the organic matter that is decomposed and becomes an alkali component is also concentrated by the concentration mechanism 1, the total alkalinity of the digestion tank 2 also increases at an early stage. It becomes easier to maintain the pH.

(Modification)
As shown in FIG. 5, the anaerobic digestion system according to the modification of the second embodiment is provided with seed sludge supply means 5 for supplying seed sludge to the concentration mechanism 1. Different from the system. Since others are substantially the same as the anaerobic digestion system of FIG. 4, duplicate description is abbreviate | omitted.

  According to the anaerobic digestion system and start-up method according to the modification of the second embodiment, the sludge concentration of the concentrated sludge is increased earlier by concentrating the seed sludge together with the raw sludge with the concentration mechanism 1. The digester 2 can be further started up earlier. Further, in the system shown in FIG. 5, the raw sludge, the extracted sludge, and the seed sludge that are put into the digestion tank 2 can be once concentrated in the concentration mechanism 1 and then supplied to the digestion tank 2. Compared to the case where different sludges are separately charged into the digestion tank 2, the state in the digestion tank 2 can be stably maintained.

(Other variations)
Although the present invention has been described according to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments and operational techniques will be apparent to those skilled in the art.

  In the above-described embodiment, when the digester 2 is started up, first, the process of heating the digester 2 alone or both with water or seed sludge and heating under anaerobic conditions is described, but the seed sludge is used. In this case, it is preferable that the seed sludge is not supplied as it is to the digestion tank 2 but is supplied to the digestion tank 2 after the seed sludge is concentrated by the concentration mechanism 1 in advance. By concentrating the seed sludge to be supplied into the digester 2 in the concentration mechanism 1 in advance, the digester 2 can have a higher sludge concentration compared to the case where unconcentrated seed sludge is supplied. You can complete the launch.

  For example, if the amount of seed sludge that can be used is greater than or equal to the capacity of the digestion tank 2, the volume of sludge in the digestion tank is set to a rating or higher by supplying the digestion tank 2 after reducing the volume with the concentration mechanism 1. May be possible. In this case, startup itself becomes unnecessary, and digestion can be performed even if raw sludge exceeding the rated sludge amount is supplied.

  Furthermore, when the digestion tank 2 is a high concentration digestion tank, it is necessary to make the sludge density | concentration in a digestion tank very high compared with a general seed sludge. Since high-concentration digesters are smaller than general digesters, for example, if digested sludge in a suspended digester installed in the same treatment plant can be used, the volume of seed sludge can be reduced. Even in a high-concentration digester, the start-up can be completed early or no start-up is required.

  Hereinafter, examples of the present invention will be described. However, the following examples are examples for better understanding of the present invention and its advantages, and are not intended to limit the present invention.

  A simulation of a digestion tank startup method using an anaerobic digestion system according to the related art and the present invention was performed. Table 1 shows the simulation conditions. In Example 1, the digestion tank 2 was started up using the anaerobic digestion system shown in FIG. In Example 2, the digestion tank 2 was started up using the anaerobic digestion system shown in FIG. In Example 3, the digestion tank 2 was started up using the anaerobic digestion system shown in FIG. Comparative Example 1 is an example in which raw sludge is directly charged into the digester 2. Comparative Example 2 is an example in which the dewatered sludge obtained in the digestion tank 2 is dehydrated to obtain dehydrated sludge, and then the dehydrated sludge is returned to the digestion tank 2.

  In each of Examples 1 to 3 and Comparative Examples 1 and 2, the case where 50% of the digestion tank capacity of digestion sludge from another digestion tank and seed sludge containing desorbed liquid was added was evaluated. Table 2 shows the results of trial calculation of the period required for start-up (start-up period). Fig. 6 shows the change in the sludge TS concentration in the digestion tank over time, and Fig. 7 shows the change in total alkalinity. The polymer flocculant residual rate is shown in FIG.

In all of Examples 1 to 3 and Comparative Examples 1 and 2, the total alkalinity was a value obtained by converting the alkali content generated during the decomposition of the organic matter, and the total alkalinity in the seed sludge was 2650 mg-CaCO ₃ / L.

  In Examples 1 to 3 and Comparative Examples 1 and 2, the residual rate of the organic polymer flocculant in the raw sludge was 0.2% on a weight basis. The organic polymer flocculant addition rate added by sludge concentration in Examples 1 to 3 was 0.5% on a weight basis, and the addition rate added by sludge dehydration in Comparative Example 2 was set to 2.0%.

1: Concentration mechanism 2: Anaerobic digestion tank 3: Pipe 4: Existing digestion tank 5: Seed sludge supply means 20: First sedimentation tank 30: Reaction tank 40: Final sedimentation tank 50: Mechanical concentration mechanism 60: Gravity concentration mechanism 70: Mixing tank 80: Mechanical concentration mechanism 90: Digestion tank

Claims (10)

Throwing water and / or seed sludge into the digester where the concentrating mechanism is located in the previous stage of the treatment flow;
Concentrating seed sludge and raw sludge to obtain concentrated sludge;
Throwing the concentrated sludge into the digester;
Increasing the input amount of the concentrated sludge to the digester, and starting up the anaerobic digester. Throwing water and / or seed sludge into the digester where the concentrating mechanism is located in the previous stage of the treatment flow;
Concentrating raw sludge to obtain concentrated sludge,
Throwing the concentrated sludge into the digester;
Extracting a portion of the sludge in the digestion tank to obtain a drawn sludge;
Concentrating at least a part of the extracted sludge together with the raw sludge and returning it to the digester, a method for starting an anaerobic digester. Throwing water and / or seed sludge into the digester where the concentrating mechanism is located in the previous stage of the treatment flow;
Concentrating seed sludge and raw sludge to obtain concentrated sludge;
Throwing the concentrated sludge into the digester;
Extracting a portion of the sludge from the digestion tank to obtain a drawn sludge;
Concentrating at least a portion of the extracted sludge together with the seed sludge and the raw sludge and returning it to the digester;
Increasing the input amount of the concentrated sludge to be input to the digester, and starting up the anaerobic digester.   When introducing water and / or seed sludge into the digestion tank, when the seed sludge is charged, the seed sludge is concentrated in the concentration mechanism and then charged into the digestion tank. 4. The method for starting an anaerobic digester according to any one of items 3 to 3.   The start-up method of the anaerobic digestion tank of any one of Claims 1-4 including using the sludge generate | occur | produced from the existing digestion tank as said seed sludge.   The anaerobic property according to any one of claims 1 to 5, comprising adding a flocculant in an amount of 0.2 to 1.5% by mass to the solid amount of sludge supplied to the concentration mechanism. How to start up the digester.   The start-up method of the anaerobic digester according to any one of claims 1 to 6, comprising supplying concentrated sludge having a sludge concentration of 4 to 12% by mass to the digester.   A concentration mechanism for concentrating the raw sludge to obtain a concentrated sludge, a digestion tank for anaerobically digesting the concentrated sludge, a digestion tank disposed between the digestion tank and the concentration mechanism, and a drawn sludge extracted from the digestion tank An anaerobic digestion system comprising: a pipe that circulates a part to the concentration mechanism.   The anaerobic digestion system according to claim 8, further comprising sludge supply means for supplying seed sludge to the concentration mechanism.   The anaerobic digestion according to claim 8 or 9, wherein the digester is a digester that performs anaerobic digestion of sludge having a sludge concentration of 1 to 12% by mass to discharge 0.5 to 9% by mass of digested sludge. system.