JP4501432B2 - Anaerobic treatment method and apparatus - Google Patents

Description

  The present invention is a method for anaerobic treatment with a high load by bringing the liquid to be treated into contact with granular sludge, in particular, an anaerobic treatment method suitable for anaerobic treatment of the liquid to be treated in which crystals such as alkaline earth metals are likely to precipitate, and It relates to the device.

  As a method of treating organic wastewater such as beet wastewater and starch wastewater, sludge blanket is formed by forming granulated sludge with high density and high sedimentation, and upwardly circulating organic wastewater containing soluble BOD. UASB (Upflow Anaerobic Sludge Blanket: Upflow anaerobic sludge blanket) that performs anaerobic treatment at high load and high speed by contacting in the state of forming a slab is employed. In this method, solid organic substances with a low digestion rate are separated and treated separately, and only soluble organic substances with a high digestion rate are processed at high speed with high load by anaerobic treatment using granular sludge with high anaerobic microorganism density. It is.

As a further development of this UASB, EGSB (Expanded) is used that allows high-velocity reaction tanks to flow at a higher flow rate, expands the sludge blanket at a high expansion rate, and performs anaerobic treatment at a higher load. (Granule Slide Blanket) is also performed. These anaerobic treatments using granular sludge such as UASB and EGSB are methods for maintaining and growing sludge containing anaerobic microorganisms in a granular state and performing anaerobic treatment with high load, high speed and high efficiency. Since these methods can maintain anaerobic microorganisms at a high concentration as granules, they can be processed at a high load of 10 to 25 kg / m ³ / d as a CODcr volume load, and in recent years, they have been widely used in Japan. ing.

  However, when alkaline earth metals such as calcium and magnesium are present in the wastewater, it tends to react with the coexisting bicarbonate, phosphoric acid, or ammonium salt to precipitate crystals, especially under high pH conditions. In this case, the crystal growth rate is high, and problems such as blockage of the pipe, breakage of the shaft due to precipitation on the stirring blades, or reduction of the reaction volume due to adhesion or blockage in the reaction vessel, etc. are caused. In particular, if these inorganic components accumulate excessively in the granule, the fluidity of the granule sludge decreases and accumulates at the bottom, or the amount of active cells retained in the granule decreases. For this reason, the processing efficiency is deteriorated, which leads to a very large problem in the long term.

  In order to prevent these problems, it is conceivable to inject acid into the reaction tank to keep the pH low. However, in the reaction tank, organic acid is consumed by the methane formation reaction, and carbonic acid is generated, so the pH rises. Because of the tendency, a large amount of acid is required, and the operating cost is high. In addition, since methanogens are sensitive to changes in pH, if the acid is added too much to reach pH <6, the rate of the methanogenesis reaction will be greatly reduced, resulting in a great risk in terms of operation management. Not right.

  Non-Patent Document 1 proposes a method for anaerobic treatment at a high load and high speed by removing calcium in the previous stage of the reaction vessel. This method is a method of precipitating calcium in the liquid to be treated on the surface of a carrier such as sand using carbonic acid contained in the treated water. FIG. 3A is a flowchart showing the anaerobic processing method of Non-Patent Document 1. In FIG. 3A, reference numeral 1 denotes an anaerobic treatment tank, which comprises a high-load anaerobic treatment tank that performs high-load and high-speed treatment using granular sludge such as UASB method. Reference numeral 2 denotes a crystallization tank, which is configured so that a reaction solution is brought into contact with a fluidized bed filled with a carrier such as sand to precipitate a crystal precipitation component such as calcium.

  The anaerobic treatment method of FIG. 3 (a) supplies the liquid to be treated from the line L1 and mixes it with the return treatment liquid returned from the line L2, and crystal treatment components such as calcium in the liquid to be treated and the treatment liquid. The inside bicarbonate is reacted to produce a crystal-precipitating substance such as calcium bicarbonate, and the crystals are precipitated in the crystallization tank 2 and removed. The liquid to be treated from which the crystals have been removed is introduced into the anaerobic treatment tank 1 from the line L3 and subjected to an anaerobic treatment at a high load and a high speed. A part of the processing liquid in the anaerobic processing tank 1 is returned from the line L2 to the crystallization tank 2, and the remaining part is discharged out of the system from the line L4.

  In this method, a crystal-precipitating component such as calcium is reacted with bicarbonate to generate a crystal-precipitating substance, and then crystals are precipitated in the crystallization tank 2, so that the reaction and the crystal precipitation are separated. It is a process. For this reason, the precipitation of crystals proceeds depending on the degree of supersaturation of a crystal-precipitating substance such as calcium bicarbonate. If the degree of supersaturation is not reached, the rate of crystal precipitation is slow and the crystal removal efficiency is not high. Moreover, in order to reach the supersaturation level, it is necessary to return a large amount of treated water, and the treated water is circulated several tens of times as much as the raw water so that the carbonic acid concentration in the anaerobic treatment tank 1 and the carbonic acid concentration in the crystallization tank 2 are as much as possible. Must be equal. Then, the concentration of crystallizable substances such as calcium bicarbonate introduced into the anaerobic treatment tank 1 without reaching the supersaturation and the precipitation of crystals is high, and these are the tank wall, piping, granule sludge, etc. It precipitates in. In addition, operating conditions such as providing a surface that can be crystallized by intermittently withdrawing the carrier and supplying a new carrier are necessary, and it is difficult and practical in terms of controllability and maintenance, and is low in cost. It is also expensive.

  FIG. 3 (b) is a flowchart showing the anaerobic treatment method for beet sugar drainage disclosed in Patent Document 1. In the anaerobic treatment method of FIG. 3B, the liquid to be treated is supplied from the line L1, introduced into the reaction tank 3 together with the acid fermentation liquid returned from the line L2, and stirred and mixed by the stirrer 4 to react. Crystals are precipitated, introduced into the solid-liquid separation tank 5 from the line L6, and the crystals are removed by sedimentation. The liquid to be treated from which the crystals have been removed is introduced into the acid fermentation tank 6 from the line L6 and subjected to acid fermentation. A part of the acid fermentation liquid is returned from the line L2 to the reaction tank 3, and the remainder is anaerobic treatment tank from the line L3. Introduced into No. 1, high-load and high-speed anaerobic treatment (methane fermentation) is performed, and the treatment liquid is discharged out of the system from L4. Crystals settled and separated in the solid-liquid separation tank 5 are discharged from the line L7 to the outside of the system.

In this method, acid fermentation broth is added to the beet sugar production wastewater as the liquid to be treated, and the calcium in the liquid to be treated reacts with the organic acid in the acid fermentation liquid to precipitate crystals as an insoluble organic acid calcium compound. And anaerobic treatment consisting of two stages of acid fermentation and methane fermentation by high-load anaerobic treatment after the crystals are separated. However, in this method, the reaction rate of organic acid and calcium is slow, the solubility of lower fatty acid calcium is relatively high, and it is easily ionized especially in the neutral to high pH range, so that calcium easily flows out into the liquid again. In addition, there is a problem that it is combined with carbonic acid again in the methane fermenter to produce a scale such as calcium carbonate.
van Lagerak, A. Hamelers, B. and Lettinga, G: Influent Calcium Removal By Crystalization Reusing Anaerobic Effluent Alkalinity `roc. 8th International Conf. On Anaerobic Digestion Vol.2 Japanese Patent Laid-Open No. 5-38499

An object of the present invention, the anaerobic treatment that utilizes granular sludge, is removed by precipitation with efficiently crystallized alkaline earth metal or other deposition components contained in the liquid to be treated, the grayed Ranyuru sludge It is intended to provide an anaerobic treatment method and apparatus that can prevent the precipitation of inorganic crystals, efficiently perform high-load anaerobic treatment, and easily dispose of separated sludge.

The present invention is the following anaerobic treatment method and apparatus.
(1) An alkaline earth metal concentration of 200 to 3000 mg / L is brought into contact with granule sludge to prevent inorganic crystals from precipitating on the granule sludge and to perform anaerobic treatment with high load. And
Mix the liquid to be treated with the return treatment liquid and the return sludge , maintain the reaction liquid at a pH of 7.5 or higher , and react the precipitation components in the liquid to be treated and the bicarbonate in the return treatment liquid in the presence of the return sludge. A reaction step of precipitating crystals,
A solid-liquid separation step of separating the reaction liquid into solid and liquid, and returning separated sludge of 0.5 to 10 times the volume of the liquid to be treated to the reaction process as return sludge;
An anaerobic treatment process in which the separation liquid of the solid-liquid separation process is brought into contact with the granular sludge and subjected to anaerobic treatment, and a treatment liquid having a capacity of 0.5 to 5 times the amount of the liquid to be treated is returned to the reaction process as a return treatment liquid. An anaerobic treatment method including and.
(2) The method according to ( 1 ) above, wherein the return sludge feed amount is changed continuously or intermittently, and the pH of the reaction solution is maintained at 7.5 or more by adding an alkali as necessary.
(3) The method according to (1) or (2) above, comprising an acid fermentation step in which the separation liquid in the solid-liquid separation step is subjected to acid fermentation and the acid fermentation solution is sent to the anaerobic treatment step.
(4) The method according to (3) above, wherein the second treatment liquid having a low concentration of the precipitation component is supplied to the acid fermentation step.
(5) A processing apparatus that anaerobically treats with a high load by bringing a liquid to be treated having an alkaline earth metal concentration of 200 to 3000 mg / L into contact with granule sludge and preventing inorganic crystals from precipitating on the granule sludge. There,
Mix the liquid to be treated with the return treatment liquid and the return sludge , maintain the reaction liquid at a pH of 7.5 or higher , and react the precipitation components in the liquid to be treated and the bicarbonate in the return treatment liquid in the presence of the return sludge. A reaction vessel for precipitating crystals,
A solid-liquid separation tank that separates the reaction liquid into solid and liquid, and returns 0.5 to 10 times the volume of the liquid to be treated as return sludge to the reaction tank;
An anaerobic treatment tank in which the separation liquid in the solid-liquid separation tank is brought into contact with the granular sludge and an anaerobic treatment is performed, and a treatment liquid of 0.5 to 5 times the volume of the liquid to be treated is returned to the reaction tank as a return treatment liquid. An anaerobic treatment device including and.
(6) The apparatus according to the above (5), which comprises an acid fermentation tank that causes an acid fermentation of a separated liquid in a solid-liquid separation tank and sends the acid fermentation liquid to an anaerobic treatment tank.
(7) The apparatus according to (6) above, wherein the second liquid to be treated having a low concentration of the precipitation component is supplied to the acid fermentation tank.

The liquid to be treated in the present invention may be any liquid containing an organic substance that can be treated by anaerobic treatment by contacting with granular sludge, but the present invention is particularly alkaline earth such as calcium and magnesium. It is suitable for the treatment of liquids containing other metals and other precipitation components. The alkaline earth metal concentration of the liquid to be treated is suitable for treatment at 200 to 3000 mg / L. Examples of such liquids to be treated include beet wastewater and starch wastewater, which contain calcium, magnesium, phosphoric acid, ammonia and the like at a relatively high concentration.

  The anaerobic treatment in the present invention is a high-load anaerobic treatment in which the liquid to be treated is brought into contact with the granular sludge, and the liquid to be treated such as UASB and EGSB is in an upward flow with a high flow rate. A high-load anaerobic treatment in which an anaerobic treatment is performed by passing the material through is preferable. The granular sludge in the present invention is sludge in which sludge containing anaerobic microorganisms is granulated by the self-granulating action of microorganisms to form sedimentary granules. Such granular sludge may be formed on a carrier or may be formed without a carrier.

  In the present invention, in such anaerobic treatment, anaerobic treatment is performed while preventing the deposition of scale components such as calcium and magnesium on the vessel wall, piping, etc., and avoiding the accumulation of inorganic components in the granular sludge. I do. Therefore, in the present invention, in the reaction step, the liquid to be treated is mixed with the return treatment liquid and the return sludge, and the precipitation component in the liquid to be treated and the bicarbonate in the return treatment liquid are reacted in the presence of the return sludge. Crystals are precipitated. In the solid-liquid separation step, the reaction solution is subjected to solid-liquid separation, and the separated sludge is returned to the reaction step as return sludge. In the anaerobic treatment process, the separation liquid in the solid-liquid separation process is brought into contact with the granular sludge to perform high-load anaerobic treatment, and the treatment liquid is returned to the reaction process as a return treatment liquid. The above treatment is effective for organic effluents containing a high concentration of nitrogen, or effluents that have already undergone acid generation. It is preferable to provide an acid fermentation process in which the separated liquid in the liquid separation process is subjected to acid fermentation and the acid fermentation liquid is sent to the anaerobic treatment process. It can also be made to supply.

The anaerobic treatment apparatus used for such treatment brings a liquid to be treated having an alkaline earth metal concentration of 200 to 3000 mg / L into contact with granule sludge, and prevents inorganic crystals from precipitating in the granule sludge. A processing device that performs anaerobic treatment with a load, wherein the liquid to be treated is mixed with the return treatment liquid and the return sludge, and the reaction liquid is maintained at a pH of 7.5 or higher, so that the precipitate components in the liquid to be treated and the return treatment liquid are mixed. The reaction tank in which bicarbonate is reacted in the presence of return sludge and crystals are precipitated, and the reaction solution is solid-liquid separated, and the separated sludge having a capacity of 0.5 to 10 times the amount of liquid to be treated is used as return sludge. The solid-liquid separation tank to be returned to the reaction tank and the separation liquid in the solid-liquid separation tank are brought into contact with the granular sludge and subjected to anaerobic treatment, and the treatment liquid of 0.5 to 5 times the volume of the liquid to be treated is returned. Consists of an anaerobic treatment tank that is returned to the reaction tank as a liquid In the case of wastewater in which the acid generation reaction still proceeds, it is preferable to include an acid fermentation tank in which the separated liquid in the solid-liquid separation tank is acid-fermented and the acid fermentation liquid is sent to the anaerobic treatment tank. The flow path can also be configured to supply the second liquid to be treated with a low concentration of the precipitating component to the tank.

  A normal reaction tank is used as the reaction tank, and the reaction is preferably performed in a stirred state. In this case, the reaction tank is preferably stirred with air or a stirrer such as a mixer. Although the reaction vessel can be omitted depending on circumstances, it is desirable to secure it as a reaction vessel in consideration of stability. In addition to the inflow path of the liquid to be treated, the reaction tank is connected with the inflow path of the return processing liquid and the returned sludge, but these may be communicated separately or may be joined together. As the solid-liquid separation tank, a sedimentation separation tank is generally used, but filtration, centrifugation, and other separation means may be used.

In the above process, in the reaction process, the liquid to be processed is caused to flow into the reaction tank, and at the same time, the process liquid in the subsequent anaerobic process is also returned. The amount of the return processing liquid to be returned to the reaction process is determined by the scale component concentration of the liquid to be processed, the alkalinity of the water to be treated , the pH of the reaction tank, etc., but 0.5 to 5 times the volume of the liquid to be processed. that be in the range of amount. The amount of returned sludge (separated solids in the solid-liquid separation tank) returned to the reaction process is also determined by the scale component concentration of the liquid to be treated, the alkalinity of the water to be treated, the pH of the reaction tank, etc. you 0.5 times the range of 10 volumes.

In the reaction step, the reaction solution pH7.5 or higher, Ru preferably reacted maintained 8-8.5. For this purpose, an alkali such as sodium hydroxide can be added to the reaction solution. When alkali is added, alkali may be injected into the reaction tank, but in order to reduce the amount of sludge generated by generating denser crystals, sludge (separated solids) in the solid-liquid separation tank is used in the reaction tank. The alkali may be injected into the line before the reaction tank, and it is more preferable to adjust the pH by providing another pH adjustment tank. While changing the amount of returned sludge continuously or intermittently, the pH of the reaction solution can be maintained at 7.5 or more by adding alkali as necessary.

  In the reaction step, when the liquid to be treated is mixed and reacted with the return treatment liquid and the return sludge, precipitation components such as calcium ions in the liquid to be treated and carbonic acid or bicarbonate ions (pH 7.5 or more in the return treatment liquid). In this case, carbonate ions) react with each other to form insoluble or hardly soluble precipitated products such as calcium carbonate. When magnesium, phosphorus, and nitrogen are contained in the liquid to be treated, the magnesium ions in the liquid to be treated react with the phosphate ions and ammonium ions returned from the methane fermentation tank to react with the magnesium phosphate ammonium ( MAP) etc.

  These precipitateable products precipitate as fine crystal particles at the start of the reaction, but as the crystal particles stay in the reaction tank or circulate between the solid-liquid separation tank and the return sludge, New crystals are deposited with the particles as nuclei and grow into large particles that are easy to precipitate and separate. In this case, the precipitation component in the liquid to be treated, such as calcium ions, and the carbonate or bicarbonate ions in the return treatment liquid are contact-reacted in the presence of crystals of the return sludge composed of the same components, Reaction occurs on the surface of the returned sludge crystal, and the precipitated product such as calcium carbonate produced by the reaction is directly deposited on the surface of the returned sludge crystal simultaneously with the reaction, and the crystal grows. When starting up the apparatus, the crystal can be taken out from another apparatus and used as a seed crystal.

  As described above, the above reaction is a catalytic reaction, and the reaction product is directly deposited on the surface of the crystal. Therefore, the precipitation of the product occurs even if the supersaturation degree of the precipitating product is not high. Therefore, even if the reaction solution enters the anaerobic treatment tank, the deposition of scale components such as calcium and magnesium on the vessel walls and piping is prevented, and the accumulation of inorganic components in the granular sludge is prevented. Avoided. And since a crystal grows by precipitation of a crystal | crystallization, the sedimentation property of a crystal | crystallization becomes high and solid-liquid separation property becomes high.

  The reaction solution in the reaction step is subjected to solid-liquid separation in the solid-liquid separation step, a part of the separated sludge is returned to the reaction step as return sludge, and a part is discharged out of the system as surplus crystals. The separation liquid in the solid-liquid separation process is subjected to anaerobic treatment in contact with granule sludge in the anaerobic treatment process, the treatment liquid is returned to the reaction process as a return treatment liquid, and a part is discharged out of the system as a treatment liquid. . The method of anaerobically treating the separated liquid in the solid-liquid separation process as it is in the anaerobic treatment process is a liquid to be treated whose pH is not lowered by acid fermentation, for example, organic waste water containing nitrogen at a high concentration, or acid generation has already been completed. In the case of a liquid to be treated in which the acid production reaction still proceeds, the pH is lowered again in the acid production reaction. The scale component cannot be removed.

  When processing these liquids to be treated, a reaction step and a solid-liquid separation step are provided before the acid fermentation step in which the pH is lowered to sufficiently remove scale components, and the solid-liquid separation step separation solution is subjected to acid fermentation. After acid fermentation in the process, high-load anaerobic treatment (methane fermentation) is performed in the anaerobic treatment process. In this case, all of the acid fermentation liquor is sent to the anaerobic treatment step, and a part of the treatment solution of the anaerobic treatment step is returned to the reaction step, where an insoluble compound is precipitated. It is possible to separate the liquid to be treated into two or more systems, and when one of them is at high temperature and the calcium concentration (or magnesium or phosphorus concentration) is high, the liquid to be treated in that system is separated and introduced into the reaction process. It is preferable to perform reaction, crystallization, solid-liquid separation, and then mix with low-concentration wastewater to perform acid fermentation and high-load anaerobic treatment (methane fermentation). Thereby, the injection amount of alkali can be reduced, and the removal rate of calcium and other scale-generating components can be increased. As the treatment operation and apparatus for acid fermentation and high-load anaerobic treatment, those generally employed can be adopted.

  The above-mentioned treatment eliminates blockage of pipes and the like, and scale components are less likely to precipitate in the granule, so that the sludge activity can be kept high and stable treatment can be performed at high load. Can do. The separated sludge (precipitate) separated from the solid-liquid separation tank is in a very high density state, and is very easy to dehydrate and dispose of. In the case of decanter wastewater from a starch factory where phosphoric acid and magnesium should be removed, the precipitate is MAP and has a high fertilizing effect, so it can be used as a good fertilizer.

According to the present invention, the liquid to be treated having an alkaline earth metal concentration of 200 to 3000 mg / L is mixed with the returning treatment liquid and the returning sludge, and the reaction liquid is maintained at a pH of 7.5 or more, thereby precipitating in the liquid to be treated. The components and bicarbonate in the return treatment liquid are reacted in the presence of the return sludge to precipitate crystals, the reaction liquid is solid-liquid separated, and 0.5 to 10 times the volume of the treated liquid is returned. The sludge is returned to the reaction process, and the separation liquid in the solid-liquid separation process is brought into contact with the granular sludge for anaerobic treatment, and the treatment liquid having a volume 0.5 to 5 times the amount of the liquid to be treated is reacted as the return treatment liquid. since so as to return to step, it can be removed by precipitation with efficiently crystallized alkaline earth metal or other depositable substances contained in the treatment liquid, inorganic in by the rig Ranyuru sludge thereto Efficient high-load anaerobic by preventing crystal precipitation Process it is possible to perform, it can be disposed of in separate sludge obtained easily anaerobic processing method and apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A to 1C are flowcharts showing an anaerobic treatment method and apparatus according to another embodiment of the present invention. 1 (a) to 1 (c), reference numeral 1 denotes an anaerobic treatment tank, which comprises a high-load anaerobic treatment tank that performs high-load and high-speed treatment using granular sludge such as UASB. 3 is a reaction tank, and it is comprised so that it may stir and mix with the stirrer 4 and may be made to react. Reference numeral 5 denotes a solid-liquid separation tank, which is configured to perform solid-liquid separation by sedimentation separation. Reference numeral 6 denotes an acid fermenter, which is configured to perform acid fermentation while keeping the liquid to be treated anaerobic.

  The anaerobic treatment method of FIG. 1 (a) supplies the liquid to be treated from the line L1 and introduces it into the reaction tank 3 together with the return treatment liquid returned from the line L2 and the return sludge returned from the line L8. Alkali is injected from the line L10 and stirred and mixed with the stirrer 4 to maintain the pH at 7.5 or higher. Presence of sludge that returns crystal precipitation components such as calcium in the liquid to be treated and carbonic acid or bicarbonate in the liquid. By reacting downwardly, a crystal depositing substance such as calcium bicarbonate to be produced is deposited on the crystal of the return sludge to grow the crystal. The reaction solution in the reaction vessel 3 is introduced into the solid-liquid separation vessel 5 from the line L5, where the crystals are settled and removed. A part of the separated sludge settled and separated in the solid-liquid separation tank 5 is returned from the line L8 to the reaction tank 3, and a part is discharged from the line L7 to the outside of the system. The to-be-processed liquid which removed the crystal | crystallization is introduce | transduced into the anaerobic processing tank 1 from the line L3, and an anaerobic process (methane fermentation) of high load and high speed is performed using granule sludge. A part of the processing liquid in the anaerobic processing tank 1 is returned from the line L2 to the reaction tank 3, and the remaining part is discharged from the system as a final processing liquid from the line L4. The anaerobic treatment method and apparatus of FIG. 1 (a) are applied to the treatment of a liquid to be treated whose pH does not decrease by acid fermentation.

  The anaerobic treatment method and apparatus of FIG. 1B are applied to the treatment of the liquid to be treated so that the acid production reaction still proceeds, and includes an acid fermentation tank 6. The anaerobic treatment method of FIG. 1 (b) is performed in substantially the same manner as the method of FIG. 1 (a), but the liquid to be treated from which crystals have been removed in the solid-liquid separation tank 5 is introduced into the acid fermentation tank 6 from the line L6. The acid fermentation liquid is entirely introduced into the anaerobic treatment tank 1 from the line L3, and an anaerobic treatment (methane fermentation) at high load and high speed is performed. Thereby, the acid fermentation liquid which produced | generated the organic acid by acid fermentation in the acid fermenter 6 decomposes | disassembles by methane fermentation, a fluctuation | variation of pH is lost, and scale components, such as calcium, can be removed efficiently.

  The anaerobic treatment method and apparatus of FIG. 1 (c) can separate the liquid to be treated into two or more systems, one of which is a high temperature and high concentration of calcium (or magnesium or phosphorus concentration). It is applied to processing, and is configured to introduce a low concentration liquid to be processed into the acid fermenter 6 for processing. The anaerobic treatment method of FIG. 1 (c) is performed in substantially the same manner as the method of FIG. 1 (b), but the high temperature and calcium concentration (or magnesium or phosphorus concentration) of the liquids to be treated separated into two systems are high. The liquid to be treated is introduced into the reaction tank 3 from the line L1, and the reaction is performed in substantially the same manner as in FIG. 1B. The low concentration liquid to be treated separated from the liquid to be treated is fed from the line L9 to the acid fermentation tank 6. The acid fermentation treatment is performed together with the liquid to be treated from which the crystals have been removed in the solid-liquid separation tank 5, and the entire acid fermentation liquid is introduced into the anaerobic treatment tank 1 from the line L3, and an anaerobic treatment with high load and high speed ( Perform methane fermentation. Thereby, the injection amount of alkali can be reduced, and the removal rate of calcium and other scale-generating components can be increased.

  According to the anaerobic treatment method and apparatus of FIGS. 1A to 1C, the liquid to be treated is mixed with the return treatment liquid and the return sludge, and in the reaction tank 3, the precipitate components and the return treatment liquid in the treatment liquid are mixed. The bicarbonate in the reaction is reacted in the presence of the return sludge to precipitate crystals, the reaction liquid in the reaction tank 3 is solid-liquid separated in the solid-liquid separation tank 5, and the separated sludge is returned to the reaction tank 3 as return sludge. The separation liquid in the solid-liquid separation tank 5 is brought into contact with the granular sludge in the anaerobic treatment tank 1 and subjected to high-load anaerobic treatment, and the treatment liquid is returned to the reaction tank 3 as a return treatment liquid. It is possible to efficiently crystallize and remove the alkaline earth metal and other precipitating components contained therein, thereby preventing inorganic crystals from precipitating in the reaction tank 3, piping or granule sludge, Highly efficient anaerobic treatment can be performed Disposal of separated sludge is also easy.

Comparative Example 1:
Using the apparatus shown in FIG. 3 (a), as a liquid to be treated, synthetic wastewater having an average water quality shown in Table 1 (glucose + acetic acid is mixed 1: 1 with CODcr, yeast extract is added at about 100 mg / L, and calcium source is used. High load anaerobic treatment was performed under the treatment conditions shown in Table 2. As a result, the CODcr removal rate of the treated water is 50-60% as shown in Fig. 2, and the granular sludge has a gradually reduced VSS / SS ratio as shown in Table 3. The sludge retention amount (VSS) was about ½ of that at the start. In order for the scale components to accumulate in the lower part of the anaerobic treatment tank 1 and the piping to be closed and to operate continuously, it was necessary to periodically clean the piping and remove the scale in the tank.

Example 1:
Using the apparatus of FIG. 1 (a), high-load anaerobic treatment was performed under the treatment conditions shown in Table 4 using the same waste water having the average water quality shown in Table 1 as Comparative Example 1 as the liquid to be treated. As seed sludge for the reaction tank 3, the waste water from the actual apparatus was added and a continuous water flow test was started. Table 5 shows the water quality of the treatment results during stable operation for about 2 months. The drawn sludge in the solid-liquid separation tank 5 was an inorganic sludge with a T-Ca concentration of 5450 mg / L and a VSS / SS ratio of 34%. On the other hand, the T-Ca of the separation liquid in the solid-liquid separation tank 5 is 185 mg / L, whereas the anaerobic treatment water is T-Ca 220 mg / L, and accumulation (removal) of Ca in the anaerobic treatment tank 1 is observed. I couldn't. That is, the precipitated Ca was removed in the solid-liquid separation tank 5. Table 6 shows the properties of the granular sludge in the anaerobic treatment tank 1. In this test, there was almost no accumulation of scale components in the granular sludge in the reaction tank within about 5 months of operation, and the VSS / SS ratio was 83.2% after 5 months compared to 86.8% of the seed sludge.

  From the above examination results, the sludge in the solid-liquid separation tank 5 is returned to the reaction tank 3 to crystallize inorganic components (Ca, Mg, etc.) in the liquid to be treated and remove them as particles having good sedimentation properties. It is possible. Further, by drawing out the concentrated sludge from the solid-liquid separation tank 5, scaling in the sludge and piping in the anaerobic treatment tank 1 is prevented, and stable anaerobic treatment operation is possible.

  The present invention is applicable to anaerobic treatment methods and apparatuses for organic effluents, such as beet effluent and starch effluent, in which crystals such as alkaline earth metals are likely to precipitate.

(A)-(c) is a flowchart which shows the anaerobic processing method and apparatus by another embodiment of this invention. It is a graph which shows the CODcr removal rate of the treated water of the comparative example 1. (A) is a flowchart which shows the anaerobic processing method of a nonpatent literature 1, (b) is a flowchart which shows the anaerobic processing method of the beet sugar waste_water | drain shown by patent document 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anaerobic processing tank 2 Crystallization tank 3 Reaction tank 4 Stirrer 5 Solid-liquid separation tank 6 Acid fermentation tank

Claims (7)

A method in which an alkaline earth metal concentration of 200 to 3000 mg / L is brought into contact with granule sludge to prevent inorganic crystals from precipitating in the granule sludge, and an anaerobic treatment is performed under a high load,
Mix the liquid to be treated with the return treatment liquid and the return sludge , maintain the reaction liquid at a pH of 7.5 or higher , and react the precipitation components in the liquid to be treated and the bicarbonate in the return treatment liquid in the presence of the return sludge. A reaction step of precipitating crystals,
A solid-liquid separation step of separating the reaction liquid into solid and liquid, and returning separated sludge of 0.5 to 10 times the volume of the liquid to be treated to the reaction process as return sludge;
An anaerobic treatment process in which the separation liquid of the solid-liquid separation process is brought into contact with the granular sludge and subjected to anaerobic treatment, and a treatment liquid having a capacity of 0.5 to 5 times the amount of the liquid to be treated is returned to the reaction process as a return treatment liquid. An anaerobic treatment method including and. The method according to claim 1 , wherein the return sludge feed amount is continuously or intermittently changed, and the pH of the reaction solution is maintained at 7.5 or more by adding an alkali as necessary. The method according to claim 1 or 2 , further comprising an acid fermentation step in which the separation liquid in the solid-liquid separation step is subjected to acid fermentation, and the acid fermentation broth is sent to the anaerobic treatment step. The method of Claim 3 which supplies the 2nd to-be-processed liquid with a low precipitation component density | concentration to an acid fermentation process. A treatment apparatus that anaerobically treats with a high load by bringing a liquid to be treated having an alkaline earth metal concentration of 200 to 3000 mg / L into contact with granule sludge, preventing inorganic crystals from precipitating on the granule sludge,
Mix the liquid to be treated with the return treatment liquid and the return sludge , maintain the reaction liquid at a pH of 7.5 or higher , and react the precipitation components in the liquid to be treated and the bicarbonate in the return treatment liquid in the presence of the return sludge. A reaction vessel for precipitating crystals,
A solid-liquid separation tank that separates the reaction liquid into solid and liquid, and returns 0.5 to 10 times the volume of the liquid to be treated as return sludge to the reaction tank;
An anaerobic treatment tank in which the separation liquid in the solid-liquid separation tank is brought into contact with the granular sludge and an anaerobic treatment is performed, and a treatment liquid of 0.5 to 5 times the volume of the liquid to be treated is returned to the reaction tank as a return treatment liquid. An anaerobic treatment device including and. 6. The apparatus according to claim 5 , further comprising an acid fermenter for fermenting the separated liquid in the solid-liquid separation tank and sending the acid fermented liquid to the anaerobic treatment tank. The apparatus according to claim 6, wherein the second liquid to be treated having a low concentration of the depositing component is supplied to the acid fermenter.

Images