JP7246339B2 - Method and apparatus for treating organic waste liquid - Google Patents

Description

The present invention relates to a method and apparatus for treating organic waste liquid, and more particularly to a method and apparatus for treating organic waste liquid containing at least magnesium ions.

The method of methane fermentation treatment of organic waste liquid has low operating costs, the biological stability of digested sludge after methane fermentation treatment, and the use of digestion gas (methane gas) obtained from methane fermentation treatment as energy. There are many advantages such as being able to Therefore, in recent years, the demand for methane fermentation equipment for organic waste liquids such as kitchen waste, leftover food, food and beverage manufacturing residue, sewage sludge, organic wastewater treatment sludge, and livestock manure is increasing.

In the methane fermentation facility, the inside of the methane fermentation tank is in a reducing atmosphere, which is an environment in which ammonium ions (NH ₄ ⁺ ) and phosphate ions (PO ₄ ³⁻ ) are easily eluted into the solution. Therefore, when the concentration of magnesium ions (Mg ²⁺ ) in the methane fermentation tank is high, crystals of magnesium ammonium phosphate (hereinafter referred to as “MAP”) precipitate due to the following chemical equilibrium reaction.
Mg ²⁺ +NH ₄ ⁺ +HPO ₄ ²⁻ +5H ₂ O+OH ⁻ ⇔Mg(NH ₄ )(PO ₄ ).6H ₂ O
In methane fermentation equipment, cases of MAP-derived scale are often seen in the methane fermentation tank as well as in the system in which the digestive fluid in the methane fermentation tank stays or circulates. Since scale leads to clogging of the digestive juice extraction pump and failure of the methane fermentation tank agitator, it was necessary to periodically stop the operation of the equipment and remove it. If the scale is significant, it may be necessary to discharge all the digestive fluid in the methane fermentation tank and clean the inside of the tank. In that case, disposal costs for a huge amount of digestive fluid are required. Furthermore, it becomes necessary to stop the operation of the facility for a long period of time until the digestive juice is discharged, cleaned, and restarted. Furthermore, since it is necessary to outsource waste treatment while the methane fermentation equipment is out of operation, the cost burden is also large.

Several techniques have been proposed in the past for MAP-derived scale countermeasures. For example, Japanese Unexamined Patent Application Publication No. 2003-117306 describes that a crystallization method has been used as one method for removing specific ions from liquid. In addition, it is described that magnesium is added to precipitate MAP crystals in wastewater containing phosphate ions and ammonium ions, such as the dehydrated filtrate of anaerobic digestion sludge. In the example of the publication, it is described that the treated water of methane fermentation contains phosphorus and ammonia, and magnesium ammonium phosphate (MAP) is crystallized by supplying magnesium and alkali, and dephosphorization treatment is performed. It is

Republished WO 2006/078012 describes a method for preventing scale in piping when transporting digested sludge generated by anaerobic digestion of an organic waste liquid by adding a magnesium compound to the digested sludge. and a screen residue removal step of removing screen residue from the digested sludge, and fine particles containing MAP are removed from the digested sludge that has undergone the crystallization step and the residue removal step. A method for preventing scale in pipes is described, which is characterized in that the digested sludge from which the fine particles have been removed is transported by pipes. In addition, it is described that if aeration treatment, depressurization treatment, or the like is used in combination at this time, decarboxylation is performed to raise the pH, and MAP can be precipitated more efficiently.

In JP-A-2017-217640, the digestive liquid after methane fermentation treatment is introduced into a MAP crystallizer to crystallize MAP, and the digestive liquid after removing MAP particles is returned to the methane fermentation tank. , reducing the risk of MAP-derived scale formation by not adding Mg to the digestive juice and adding an organic acid to the digestive juice on the way back from the MAP crystallizer to the methane fermentation tank to lower the pH. ing.

In JP-A-2019-181388, a digestive juice from a methane fermentation apparatus is supplied to a MAP crystallizer to crystallize MAP, and then supplied to a cyclone to separate MAP particles in the digestive juice. By adding a pH-lowering agent or a phosphorus-removing agent to the separated liquid and supplying it to the membrane separator, and returning the membrane-filtered concentrated digestive liquid to the methane fermentation apparatus, the generation of MAP is suppressed regardless of changes in the quality of the water to be treated. It is described that it can prevent damage or obstruction of the membrane.

JP-A-2003-117306 Republished WO2006/078012 Japanese Patent Application Laid-Open No. 2017-217640 Japanese Patent Application Laid-Open No. 2019-181388

In the conventionally proposed method, when an organic waste liquid containing magnesium ions is anaerobicly digested in a methane fermentation tank having a pH of 7 to 8, the amount of anaerobic microorganisms contained in the organic waste liquid or Phosphate ions derived from organic phosphorus and ammonium ions derived from organic nitrogen, which are supplied as nutrients, react with magnesium ions to avoid crystallization as magnesium ammonium phosphate (MAP). However, the prevention of scale formation in the entire methane fermentation facility is not sufficient, and there is room for improvement such as the increase in cost due to the addition of chemicals.

Moreover, when performing methane fermentation treatment under high load conditions, it is necessary to stabilize the methane fermentation treatment by subjecting the organic waste liquid before the methane fermentation treatment to acid fermentation treatment or solubilization treatment. Since the pH of the organic waste liquid after the acid fermentation treatment is lowered to 3 to 5, it is necessary to add alkali to the organic waste liquid in order to obtain the pH of 7 to 8 required for the methane fermentation treatment, which increases the cost.

An object of the present invention is to provide a technique for reducing the cost increase due to the addition of chemicals and preventing the formation of scale in anaerobic fermentation treatment facilities for organic waste liquids that tend to form MAP.

The present inventors reduced the amount of magnesium ions introduced into the anaerobic treatment apparatus by removing MAP particles by subjecting the entire amount of organic waste liquid containing at least magnesium ions to MAP crystallization before anaerobic treatment. It is possible to suppress MAP crystallization in the anaerobic treatment device, and to aerate the organic waste liquid during the MAP crystallization treatment performed before the anaerobic treatment, so that acid fermentation or methane in the MAP crystallizer The inventors have found that fermentation can be suppressed to promote MAP crystallization and growth, and have completed the present invention.

The present invention provides the following organic waste liquid treatment method and treatment apparatus.
[1] Before anaerobic treatment, the entire amount of organic waste liquid containing at least magnesium ions is introduced into a MAP crystallizer containing MAP seed crystals, and acid fermentation or methane fermentation is suppressed while aeration is performed to remove MAP particles. A MAP crystallization step for crystallization;
a MAP particle removal step for obtaining a MAP-removed product by separating the MAP particles crystallized in the MAP crystallization step;
an anaerobic treatment step of introducing the MAP-removed product obtained in the MAP particle removal step into an anaerobic treatment apparatus and subjecting it to anaerobic treatment; A method for treating an organic waste liquid to be returned to the MAP crystallizer.
[2] In the MAP crystallization step, the organic waste liquid containing at least magnesium is aerated so that the oxidation-reduction potential (the oxidation-reduction potential based on the silver/silver chloride electrode) becomes -400 mV or higher. The method for treating an organic waste liquid according to the above [1].
[3] The above [1], wherein in the MAP crystallization step, the amount of aeration and/or the return amount of the digestive juice is adjusted so that the pH of the organic waste liquid containing at least magnesium is 7 or more and 9 or less. ] or the method for treating an organic waste liquid according to [1].
[4] The organic waste liquid according to any one of [1] to [1] above, wherein in the MAP crystallization step, aeration is performed by introducing air into the MAP crystallizer by an air lift method. Processing method.
[5] A MAP crystallizer equipped with an aerator for receiving the entire amount of organic waste liquid containing at least magnesium ions before anaerobic treatment and crystallizing MAP particles;
an anaerobic treatment device that receives the MAP-removed product from the MAP crystallizer and performs anaerobic treatment;
a MAP-removed material introduction line for sending the MAP-removed material from the MAP crystallizer to the anaerobic treatment apparatus;
a digestive liquid return line for returning at least part of the digestive liquid from the anaerobic treatment device to the MAP crystallizer;
a digestive fluid discharge line for extracting the rest of the digestive fluid from the anaerobic treatment apparatus to the outside of the system;
An organic waste liquid treatment apparatus comprising:
[6] The organic waste liquid treatment apparatus according to [5], wherein the aeration device is an air lift having a controller for setting the amount of introduced air.

[definition]
In the present application, "organic liquid waste" refers to slurry-like organic waste containing a large amount of solid content from manufacturing residues such as kitchen waste, leftover food, food and beverages, and organic sludge such as sewage sludge and organic wastewater treatment sludge. , livestock manure, manure, sewage, and organic wastewater such as food and beverage manufacturing wastewater. If the "organic waste liquid" to be subjected to the MAP crystallization treatment in the present invention has an excessively high concentration of solid matter, MAP crystallization in the MAP crystallization tank will be difficult to proceed, and there is a risk of clogging the piping of the MAP crystallization tank. , the solid concentration is preferably 20 v/v% or less. In the present application, an organic waste liquid having a solid matter concentration of 0 v/v % or more and 4 v/v % or less such as SS (suspended solids) may be particularly referred to as "organic waste water".

In the present application, the term “digestive juice” is used as a general term including digested sludge obtained by anaerobic digestion of slurry-like organic waste and sludge containing a large amount of solids, and anaerobic treated water obtained by anaerobic treatment of organic wastewater.

In the present application, "fine MAP" or "fine MAP" means MAP particles that remain in the form of fine particles of less than 0.05 mm without growing on the surface of the MAP seed crystal.

According to the present invention, it is possible to reduce the increase in cost due to the addition of chemicals required in the conventional method, and to prevent scale formation in anaerobic fermentation treatment facilities for organic waste liquids that tend to form MAP.

Since the organic waste liquid before anaerobic treatment is subjected to MAP crystallization treatment to remove magnesium ions from the organic waste liquid and then introduced into the anaerobic treatment apparatus, ammonium ions derived from organic nitrogen and organic Even if phosphate ions derived from polyphosphorus are generated, magnesium ions are deficient, and MAP crystallization, which causes scale, can be prevented.

Since the MAP crystallization treatment of organic waste liquid before anaerobic treatment is performed while aerating, acid fermentation and methane fermentation in the MAP crystallizer are suppressed, and the amount of methane generated during anaerobic treatment after MAP crystallization treatment is suppressed. can be prevented from decreasing. In addition, by suppressing methane fermentation in the MAP crystallizer, it is possible to prevent the generation and leakage of dangerous combustible gas during the MAP crystallization process.

By introducing the digestive fluid after the anaerobic treatment as an alkali source into the MAP crystallization apparatus, it is possible to cover the large amount of alkali source required for the MAP crystallization treatment and reduce the cost associated with the addition of chemicals. .

By subjecting the organic waste liquid to MAP crystallization treatment before anaerobic treatment, magnesium ions derived from the organic waste liquid are removed, scale generation is suppressed in the anaerobic treatment apparatus, and MAP is recovered as a useful phosphorus source. can do.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an example of an apparatus configuration for carrying out the organic waste liquid treatment method of the present invention. FIG. 2 is an enlarged explanatory view of the air lift tube 11a portion of the MAP crystallizer 10 of FIG. 1; FIG. 2 is a schematic diagram of another example of an apparatus configuration for carrying out the method for treating an organic waste liquid of the present invention.

embodiment

The present invention will be specifically described below with reference to the accompanying drawings, but the present invention is not limited thereto.
FIG. 1 shows an outline of an example of an apparatus configuration for carrying out the method for treating an organic waste liquid of the present invention.

The apparatus for treating an organic waste liquid of the present invention comprises an aerator 11, a MAP crystallizer 10 for receiving the entire amount of an organic waste liquid containing at least magnesium ions before anaerobic treatment and crystallizing MAP particles;
an anaerobic treatment device 20 that receives the MAP-removed product from the MAP crystallizer 10 and performs anaerobic treatment;
MAP-removed material introduction lines 13f and 23 for sending the MAP-removed material from the MAP crystallizer 10 to the anaerobic treatment apparatus 20;
a digestive liquid return line 21 for returning at least part of the digestive liquid from the anaerobic treatment device 20 to the MAP crystallizer 10;
a digestive fluid discharge line 22 for extracting the rest of the digestive fluid from the anaerobic treatment device 20 to the outside of the system;
Equipped with

In the processing apparatus shown in FIG. 1, the MAP crystallizer 10 includes a crystallization reactor 12 that crystallizes MAP from an organic waste liquid, and a hydrocyclone 13a that collects coarse MAP particles formed in the crystallization reactor 12. , a hydrocyclone 13 b for returning fine MAP particles formed in the crystallization reactor to the crystallization reactor 12 .

The crystallization reactor 12 has a cylindrical shape with an inverted conical portion at the bottom, and a cylindrical draw-out portion 12a is formed at the bottom, which is the apex of the inverted conical shape at the bottom. Connected to the drawing part 12a are a MAP liquid feed line 15 for sending the slurry containing the drawn MAP particles to the liquid cyclone 13 and an air lift pipe 11a functioning as an aerator. The withdrawal part 12 a withdraws the organic waste liquid containing MAP particles that settles in the crystallization reactor 12 and also functions as an introduction part for air from the aeration device 11 . The MAP particles formed in the crystallization reactor 12 descend on the wall surface of the inverted conical portion at the bottom of the crystallization reactor 12 while causing a swirling flow, and the MAP particles with high specific gravity move downward toward the wall surface due to the action of centrifugal force. and settles in the bottom withdrawal 12a. An organic waste liquid containing concentrated MAP particles is introduced into hydrocyclones 13a and 13b via MAP liquid feed line 15 by pumping. As shown in an enlarged view in FIG. 2, the air lift pipe 11a blows air from the lower part, raises the organic waste liquid from the withdrawal part 12a by the buoyancy of the air, and separates the gas and liquid in the upper air chamber 11b. The organic effluent is returned to crystallization reactor 12 via return line 11c. The air lift pipe 11a is connected to an air supply pipe 11d which is connected to an air supply source 11e and has a blower 11f, an air volume control valve 11g and a check valve 11h. Based on the results of measuring the pH and ORP of the organic waste liquid in the crystallization reactor 12 using a pH meter and an ORP meter (Ag/AgCl electrodes), the air volume control valve 11g was operated so that the ORP was −400 mV or higher. can be used to adjust the amount of aeration.

An organic waste liquid introduction line 14, a digestive liquid return line 21, a discharge pipe 13d, an overflow riser pipe 13e, and an air lift pipe return line 11c are connected to the upper portion of the crystallization reactor 12, respectively. The digestive liquid return line 21 is separate from the organic waste liquid introduction line 14 because MAP particles may be generated if the organic liquid waste and the digestive liquid are mixed before being introduced into the crystallization reactor 12. must be connected to the MAP crystallization reactor 12 at . An organic waste liquid is introduced into the crystallization reactor 12 via an organic waste liquid introduction line 14 . The digestive liquid from the anaerobic treatment device 20 (to be described later) is returned to the crystallization reactor 12 via the digestive liquid return line 21 . Fine MAP particles from the hydrocyclone 13b are returned to the crystallization reactor 12 via the discharge pipe 13d. Via the overflow riser 13e, the overflow containing fine MAP particles separated in the hydrocyclone 13a is returned to the crystallization reactor 12.

The hydrocyclones 13a and 13b are of inverted cone shape, with MAP particle discharge pipes 13c and 13d at the bottom, which is the apex of the inverted cone, overflow risers 13e and 13f at the top, and discharge from the crystallization reactor 12 at the sides. Inflow pipes 13g and 13h for inflowing organic waste liquid containing MAP particles are connected respectively. The organic waste liquid containing MAP from the crystallization reactor 12 is introduced into the hydrocyclones 13a and 13b, descends on the inverted conical walls inside the hydrocyclones 13a and 13b while causing a swirling flow, and MAP particles with a heavy specific gravity are produced. is concentrated on the lower wall surface side by the action of centrifugal force, and is continuously or intermittently extracted from the discharge pipes 13c and 13b. Organic effluent from which MAP particles have been removed is removed via overflow risers 13e and 13f. In the hydrocyclone 13a, coarse MAP particles are withdrawn through a discharge pipe 13c, and organic waste liquid containing fine MAP particles is returned to the crystallization reactor 12 via an overflow riser pipe 13e. In the hydrocyclone 13b, the fine MAP particles are returned to the crystallization reactor 12 through the discharge pipe 13d, and the MAP-removed material from which the fine MAP particles have also been removed passes through the overflow riser pipe 13f to the acid fermentation tank or It is sent to the storage tank 30 or the anaerobic treatment device 20 . In order to recover MAP particles of different sizes in the hydrocyclones 13a and 13b, in the initial stage of the MAP crystallization process, the entire amount of the organic waste liquid from the withdrawal section 12a of the crystallization reactor 12 is introduced into the hydrocyclone 13b, At the stage when the MAP particles grow in the crystallization reactor 12 and coarse MAP particles are formed, part or all of the slurry from the withdrawal section 12a of the crystallization reactor 12 is introduced into the hydrocyclone 13a. switch roads. The switching of the flow path can be performed using a normal flow path switching means such as a switching valve (not shown).

In the treatment apparatus shown in FIG. 1, the anaerobic treatment apparatus 20 is a methane fermentation tank. As the methane fermenter, a methane fermenter commonly used in the technical field, such as a complete mixing methane fermenter, a carrier-filled methane fermenter, and a high-load methane fermenter can be used. However, the methane fermentation tank in the treatment apparatus of the present invention includes a MAP-removed product introduction line 23 for introducing the MAP-removed product from which MAP particles have been removed by the MAP crystallizer 10 and subjecting it to methane fermentation treatment, and a methane fermentation It comprises a digestive juice discharge line 21 for returning at least part of the digestive juice to the MAP crystallizer and a digestive juice discharge line 22 for extracting the rest of the digestive juice.

The processing apparatus shown in FIG. 1 further includes an acid fermentation tank or storage tank 30 between the MAP crystallizer 10 and the anaerobic treatment apparatus (methane fermenter) 20 . Acid fermenters or reservoirs commonly used in the art can be used without limitation. By providing an acid fermentation tank, the amount of anaerobic digestion sludge can be reduced. By providing the storage tank, the MAP-removed material can be diluted before being subjected to the anaerobic treatment, and the concentration of magnesium ions in the MAP-removed material introduced into the anaerobic treatment apparatus can be further reduced.

FIG. 3 shows an outline of another example of the configuration of an apparatus for carrying out the method for treating an organic waste liquid of the present invention.
The organic waste liquid treatment apparatus of the present invention comprises an aerator 111, a MAP crystallizer 110 for receiving the total amount of organic waste liquid containing at least magnesium ions before anaerobic treatment and crystallizing MAP particles;
an anaerobic treatment device 120 that receives the MAP-removed product from the MAP crystallizer 110 and performs anaerobic treatment;
a digestive fluid return line 121 for returning at least part of the digestive fluid from the anaerobic treatment device 120 to the MAP crystallizer 110;
a digestive juice discharge line 122 for extracting the rest of the digestive juice from the anaerobic treatment device 120;
Equipped with

In the processing apparatus shown in FIG. 3, the MAP crystallizer 110 comprises a first crystallization reactor 112 and a second crystallization reactor 113 . An organic waste liquid introduction line 114a for introducing an organic waste liquid and an aeration line 111a for introducing air are connected to the lower portion of the first crystallization reactor 112, respectively. An organic waste liquid introduction line 114b for introducing an organic waste liquid and an aeration line 111b for introducing air are connected to the lower portion of the second crystallization reactor 113, respectively.

The first crystallization reactor 112 has a lower crystallization reaction section 112a and an upper solid-liquid separation section 112b. An inner cylinder 117 is provided in the solid-liquid separation section 112b. A MAP-removed material discharge line 118 for overflowing the MAP-removed material is connected to the solid-liquid separation section 112b. A reduced-diameter portion having an inverted conical shape is formed in the lower portion of the solid-liquid separation portion 112b. The crystallization reaction part 112a has a cylindrical shape with a diameter equal to the minimum diameter of the diameter-reduced part of the solid-liquid separation part 112b. A discharge pipe 112c for discharging MAP particles is connected. The organic waste liquid introduced into the crystallization reaction section 112a of the first crystallization reactor 112 through the organic waste liquid introduction line 114a is aerated by the air introduced from the aeration line 111a to form MAP particles. The slurry-like organic waste liquid containing MAP particles rises toward the inner cylinder 117 of the solid-liquid separation section 112b as the bubbles rise. MAP particles with a high specific gravity descend while causing a swirling flow on the wall surface of the inverted cone, are concentrated on the lower wall surface side by the action of centrifugal force, and are continuously or intermittently extracted from the discharge pipe 112c. Fine MAP particles with a low specific gravity rise with air bubbles. When entering the solid-liquid separation section 112b, which has a larger diameter than the crystallization reaction section 112a, the rising speed decreases, so the fine MAP particles enter the inner cylinder 117 along with the air bubbles and stay inside the inner cylinder 117. Coarse MAP particles are recovered from the discharge pipe 112c at the bottom of the first crystallization reactor 112, and fine MAP particles flow inside the inner cylinder 117 at the top of the first crystallization reactor 112, and the first crystallization MAP particles formed in reactor 112 are separated from the organic effluent. The MAP particles and the separated organic waste liquid are withdrawn from the MAP-removed material discharge line 118 and sent to the anaerobic treatment apparatus 120 .

The second crystallization reactor 113 is a cylinder with an inverted cone-shaped reduced diameter section at the bottom. A digestive liquid return line 121 for returning at least a part of the digestive liquid from the anaerobic treatment device 120 described later is connected to the top of the reverse conical reduced diameter portion of the second crystallization reactor 113 . An air lift pipe 119 is provided above the reduced-diameter portion of the second crystallization reactor 113 having an inverted conical shape. The airlift pipe 119 is connected to the inner cylinder 117 of the first crystallization reactor 112, and sends the fine MAP particles flowing inside the inner cylinder 117 to the second crystallization reactor 113, and also to the second crystallization reactor. Coarse MAP particles grown in 113 are sent to a first crystallization reactor 112 . Under the condition that the amount of rising air in the second crystallization reactor 113 is small and bubbles do not enter the air lift tube 119, fine MAP particles are ejected from the inner cylinder 117 of the first crystallization reactor 112 into the second crystallization reactor due to the density difference. Free flow to 113. On the other hand, when coarse MAP particles are formed in the second crystallization reactor 113, the amount of rising air is increased to send the coarse MAP particles to the first crystallization reactor 112 by airlift through the airlift pipe 119. . An overflow pipe 118 a is connected to the upper portion of the second crystallization reactor 113 to send the overflow from the second crystallization reactor 113 to the first crystallization reactor 112 .

In the MAP crystallizer 110 shown in FIG. Adjust the amount of aeration. The amount of aeration can be adjusted by adjusting the amount of air introduced from the aerator 111 and switching the introduction of air to the first crystallization reactor 112 or the second crystallization reactor 113 .

In the treatment apparatus shown in FIG. 3, the anaerobic treatment apparatus 120 is a methane fermentation tank. As the methane fermentation tank, a methane fermentation tank commonly used in the technical field, such as a UASB-type methane fermentation tank, a carrier-filled methane fermentation tank, or a high-load methane fermentation apparatus, can be used. However, the methane fermentation tank in the treatment apparatus of the present invention is equipped with a MAP-removed product introduction line 123 for introducing the MAP-removed product from which MAP particles have been removed by the MAP crystallizer 110 and subjecting it to methane fermentation treatment. After the digestive juice after methane fermentation is stored in the storage tank 140, at least part of it is returned to the lower part of the second crystallization reactor 113 of the MAP crystallizer 120 through the digestive juice discharge line 121, and the digestive juice is discharged. Withdraw the remainder of the digestive fluid via line 122 .

The treatment apparatus shown in FIG. 3 further includes an acid fermentation tank 130 between the MAP crystallizer 110 and the anaerobic treatment apparatus (methane fermentation tank) 120 . As the acid fermenter, any acid fermenter commonly used in the art can be used without limitation. By providing an acid fermentation tank, the amount of anaerobic digestion sludge can be reduced.

The MAP crystallizer and the anaerobic treatment apparatus used in the treatment apparatus of the present invention are not limited to the above examples, and any apparatus commonly used in the technical field can be used in combination.

The organic waste liquid treatment method of the present invention includes: (1) The entire amount of an organic waste liquid containing at least magnesium ions is introduced into a MAP crystallizer containing MAP seed crystals before anaerobic treatment, and acidified with aeration. (2) a MAP particle removal step of separating the MAP particles crystallized in the MAP crystallization step to obtain a MAP-removed product; and (3) an anaerobic treatment step of introducing the MAP-removed product obtained in the MAP particle removal step into an anaerobic treatment apparatus and subjecting it to anaerobic treatment. The alkalinity source required in the MAP crystallization step is supplied by returning at least part of the digested liquid after the anaerobic treatment to the MAP crystallizer.

In the anaerobic treatment of organic waste liquids, organic nitrogen and organic phosphorus are usually added as nutrients for anaerobic microorganisms, so ammonium ions derived from organic nitrogen and phosphate ions derived from organic phosphorus are generated. It reacts with magnesium ions in the organic waste liquid to crystallize magnesium ammonium phosphate (MAP), and MAP accumulates as scale in the anaerobic treatment apparatus. In the treatment method of the present invention, before the anaerobic treatment, the organic waste liquid is introduced into the MAP crystallizer to crystallize MAP, and the magnesium ions in the organic waste liquid are removed. A large amount of magnesium ions are not introduced into the granules, and crystallization of MAP can be prevented even when nitrogen or phosphorus is added as a nutrient source for anaerobic microorganisms.

The treatment method of the present invention treats an organic waste liquid containing at least magnesium ions. For example, slurry-like organic waste liquid containing a large amount of solids such as kitchen waste, leftover food, manufacturing residue such as food and beverages, organic sludge such as sewage sludge and organic wastewater treatment sludge, livestock manure, night soil, sewage, And organic wastewater such as manufacturing wastewater of foods and beverages can be treated. Organic waste such as manufacturing residue containing a large amount of solids can be made to flow by removing large solids using a sedimentation separator or separation screen, or by diluting or solubilizing before MAP crystallization. It can be made into a slurry-like organic waste liquid having properties.

In the present invention, the organic waste liquid introduced into the MAP crystallizer before the anaerobic treatment and subjected to the MAP crystallization treatment contains at least magnesium ions. The presence of phosphate ions and ammonium ions is required for the formation of MAP, and these are contained in organic effluents or in digested sludge returned from anaerobic treatment processes. there is In order to minimize the amount of magnesium ions contained in the MAP-removed material introduced into the anaerobic treatment apparatus, almost all of the magnesium ions contained in the organic waste liquid are crystallized as MAP in the MAP crystallization step. It is preferably removed by analysis. Therefore, if the amount of phosphate ions or ammonium ions is less than the stoichiometric ratio with magnesium ions and there is a risk that magnesium ions will remain, phosphate ions or ammonium ions are added to the MAP crystallizer. is preferred. The digestive fluid after anaerobic treatment contains phosphate ions and ammonium ions derived from organic phosphorus and organic nitrogen added as nutrients for anaerobic microorganisms. In the present invention, the phosphate ions and ammonium ions required for MAP crystallization can also be supplied by returning the digestive fluid after the anaerobic treatment to the MAP crystallization step.

In the MAP crystallization step, when acid fermentation or methane fermentation progresses, the pH of the organic waste liquid drops to an acidic range, inhibiting MAP crystallization and growth. Therefore, in the MAP crystallization step, it is necessary to maintain the pH of the organic waste liquid in a neutral range to a weakly alkaline range (7.0 or more and 9.0 or less, preferably 7.5 or more and 8.5 or less). be. In the present invention, since the digestive fluid after the anaerobic treatment contains a large amount of alkaline components, by returning it to the MAP crystallization process, the alkaline chemicals that had to be added separately in the conventional method can be eliminated. can be made unnecessary.

Acid fermentation or methane fermentation proceeds in an anaerobic atmosphere. In the present invention, since the organic waste water before the anaerobic treatment is subjected to the MAP crystallization treatment, it contains a large amount of organic components that facilitate acid fermentation or methane fermentation. However, progress of acid fermentation inhibits MAP crystallization, progress of methane fermentation generates combustible gas, and there is a danger that combustible gas may leak from the MAP crystallizer. In the present invention, in order to suppress the progress of acid fermentation or methane fermentation in the MAP crystallization process, the inside of the MAP crystallizer is aerated to prevent the anaerobic atmosphere in which acid fermentation or methane fermentation proceeds. It is necessary. Preferably, the organic waste liquid in the MAP crystallization step is aerated so that the oxidation-reduction potential (the oxidation-reduction potential based on the silver/silver chloride electrode) becomes -400 mV or higher. However, it is not necessary to carry out the MAP crystallization step in a general aerobic atmosphere, and the oxidation-reduction potential (oxidation-reduction potential based on silver/silver chloride electrode) is preferably −400 mV or more and +100 mV or less, more preferably. is -200 mV or more and +50 mV or less, particularly preferably -100 mV or more and 0 mV or less. Excessive aeration decarboxylates the organic waste liquid, excessively raises the pH, generates fine MAP particles, and volatilizes odorous components such as ammonia and hydrogen sulfide. This is not preferable because the nitrification reaction progresses and the pH is lowered. It is desirable to measure the oxidation-reduction potential and control the amount of aeration so as to keep it within the above range. The amount of aeration required for one-hour treatment with a MAP crystallizer having a capacity of 1 m ³ is, for example, 0.5 m ³ /(m ³ hr) or more and 2 m ³ /(m ³ hr) or less, more preferably 0.8 m. ³ /(m ³ ·hr) or more and 1.2 m ³ /(m ³ ·hr) or less. Aeration is preferably carried out by an air lift method in which air is introduced from the lower part of the MAP crystallizer to raise air bubbles inside the MAP crystallizer. Also, in order to control the amount of aeration, air can be introduced using an air lift preferably equipped with a control section (for example, a flow control valve, blower control by an inverter, etc.) for setting the amount of introduced air. It is more preferable to use an air lift having a controller that automatically controls the amount of introduced air based on the measured value of the oxidation-reduction potential.

The MAP crystallization process is performed in a MAP crystallizer containing MAP seeds. A "MAP seed" is a coarse MAP particle on which the MAP particle grows. As the MAP seed crystals, MAP particles formed during the preceding treatment may be used, MAP particles precipitated in a separate crystallization reactor as shown in FIG. 3 may be used, phosphate rock, dolomite, Powders or granules such as bone charcoal, activated carbon, silica sand, and calcium silicate may also be used. In order to crystallize and grow MAP on the surface of the MAP seed crystal, the MAP seed crystal preferably has a grain size of 0.05 mm or more and 5.0 mm or less. For example, when a slurry-like organic waste liquid containing solids is introduced into a MAP crystallizer, the particle size of the MAP seed crystal is preferably 0.1 mm or more and 0.5 mm or less. When a liquid organic waste liquid such as waste water is introduced into the MAP crystallizer, the grain size of the MAP seed crystal is preferably 1 mm or more and 5 mm or less.

The amount of MAP seed crystals packed in the MAP crystallizer is 3 w/v% or more and 6 w/v% or more in the case of a slurry-like organic waste liquid containing solids in order to grow large MAP particles on the surface of the MAP seed crystals. v % or less is preferable, and in the case of liquid organic waste liquid such as organic waste water, 40 w/v % or more and 50 w/v % or less is preferable.

Next, the crystallized MAP particles are separated, and the MAP-removed product from which the MAP particles are removed is introduced into the anaerobic treatment apparatus. Here, the MAP-removed product is a liquid after removing coarse MAP particles or a slurry containing a very small amount of fine MAP particles. Since fine MAP particles are difficult to separate and may remain in the treated material and be introduced into the anaerobic treatment apparatus, the MAP particles should be 0.05 mm or more and 3 mm or less, preferably 0 mm or less, on the surface of the MAP seed crystal. It is desirable to grow the thickness from 1 mm to 0.5 mm.

The MAP-removed material from which the MAP particles have been removed is anaerobicly treated in an anaerobic treatment apparatus to produce anaerobic digestion sludge and digestive juice. Normally, the digestive juice is withdrawn from the anaerobic treatment apparatus, and the anaerobic digestion sludge is dehydrated. In the present invention, a portion of the digestive fluid containing a large amount of alkaline components is returned to the MAP crystallizer as an alkali source, thereby reducing the organic waste liquid in the MAP crystallizer to pH 7.0, which is necessary for MAP crystallization. As described above, the pH can be adjusted to preferably 7.0 or more and 9.0 or less, more preferably 7.5 or more and 8.5 or less. If the pH is less than 7.0, not only does crystallization become difficult to progress, hydrogen sulfide present in the liquid volatilizes, deteriorating the surrounding environment, and organic components such as organic acids also present in the liquid volatilize. loss is likely to occur. On the other hand, if the pH exceeds 9.0, not only is fine MAP likely to be generated, but ammonia present in the liquid volatilizes, resulting in a deterioration of the surrounding environment. The state of the alkalinity of the organic waste liquid can be determined more accurately by looking at the increase or decrease in alkalinity. The alkalinity is preferably adjusted to 1000 to 10000 mg/L as M-alkalinity.

In order to supply the alkalinity source necessary for the MAP crystallization process, the return amount of the digestive liquid is 3 parts by volume or more and 10 parts by volume or less with respect to 1 part by volume of the organic waste liquid in the MAP crystallizer. Addition of an alkaline chemical from the outside can be made unnecessary. For example, when an organic waste liquid containing a large amount of solids is introduced into the MAP treatment apparatus, the amount of the organic waste liquid is 4.0 to 10.0 parts by volume, preferably 4.5 to 10.0 parts by volume. It is desirable to return 0 parts by volume or less of the digestive juice, and when introducing organic wastewater with a low solid content into the MAP treatment apparatus, 3.0 parts by volume or more and 7.0 parts by volume per 1 part by volume of organic wastewater Thereafter, it is desirable to return preferably 4.0 to 5.0 volume parts of the digestive juice. If the amount of digestive liquid returned is excessive, ammonia volatilizes in the MAP crystallizer, or crystallization progresses too much, and fine MAP particles are precipitated instead of being precipitated on the surface of the MAP seed crystals, resulting in poor recovery. I don't like it because it makes it difficult.

[Comparative Example 1]
Organic waste (COD: 100,000 g/m ³ , phosphate ions ^: 650 g/m ³ , magnesium ions: 400 g/ m ³ , Kjeldahl nitrogen: 8,400 g/m ³ , pH: about 3.7) is added after removing foreign matter to prepare an organic waste liquid, which is then passed through an acid fermentation tank with a capacity of 20 m ³ to a capacity of 200 m ³ . anaerobic treatment equipment (methane fermentation tank) and not the MAP crystallizer.

The organic waste liquid is adjusted to a solid content of 5% in an acid fermentation tank. At this time, the average nitrogen content in the acid fermentation tank is 4.5 kg/m ³ , the phosphorus content is 600 g/m ³ , and the magnesium content is about 200 g/m ³ . In the acid fermenter, hydrolysis of the organic wastewater proceeded to produce organic acids, and the pH dropped to about 4 or less.

The organic waste liquid that has passed through the acid fermentation tank is introduced into the methane fermentation tank and decomposed into methane and carbon dioxide by the action of methane fermentation bacteria. At this time, the organic acid was converted to gas and removed, and the decomposition of the protein contained in the organic matter produced ammonia, so that the pH in the methane fermentation tank increased to about 7-8.

The organic liquid waste from this food processing plant contains nitrogen, phosphorus, and magnesium. scale has occurred. Problems such as failure of the agitator in the methane fermentation tank, clogging of pipes, and deposition of sandy MAP crystals in the methane fermentation tank occurred due to scale generation. If scale generation progresses, after emptying the anaerobic treatment equipment (methane fermentation tank) with a capacity of ^200m3 , dredging and cleaning with chemicals, it will be necessary to acclimate the methane fermentation bacteria for more than 2 months and restart. As a result, the operation of the organic waste liquid must be stopped for several months.

[Example 1]
An example of treating an organic waste liquid from a food processing plant in Comparative Example 1 by the treatment method of the present invention will be described.

The processing apparatus used in this embodiment has the configuration shown in FIG. As a MAP crystallizer, a MAP crystallizer equipped with an air lift tube shown in FIG. 2 was used.
First, an organic waste liquid (COD: about 50,000 g/m ³ , phosphate ions: about 375 g/m ³ , magnesium ions: about 200 g/m ³ , Kjeldahl nitrogen: about 4,200 g/m ³ , pH: about 3.7) was introduced into a 25 m ³ MAP crystallizer. A digestive liquid was introduced into the MAP crystallizer 10 from an anaerobic treatment apparatus (methane fermentation tank) 20 via a digestive liquid return line 21 . The amount of the digestive liquid introduced was adjusted according to the pH of the organic waste liquid in the MAP crystallizer. Specifically, air is introduced into the organic waste liquid in the MAP crystallizer from the air lift tube 11a, and aeration is performed so that the oxidation-reduction potential (AgCl/Ag electrode) of the organic waste liquid becomes -400 mV or higher. , the digestive juice was introduced so that the pH of the organic wastewater rose to about 7.5, and the progress of acid fermentation and methane fermentation was suppressed. Gases containing carbon dioxide, hydrogen sulfide, ammonia, etc. were generated from the MAP crystallizer. This gas was treated with deodorizing equipment in the food processing factory to prevent volatilization.

The MAP particles to be crystallized in the MAP crystallizer are extracted from the MAP crystallizer, the MAP-removed product is put into a raw material tank with a capacity of about 20 ^m3 , and water is added to suppress the inhibition of methane fermentation by ammonia. diluted with The MAP-removed product after dilution was introduced into an anaerobic treatment apparatus (methane fermentation tank) with a capacity of 200 m ³ and subjected to anaerobic treatment.

As described above, the facility could be operated stably without stopping treatment due to scale generation, and about 360 m ³ of biogas was generated per day. In addition, by introducing air into the MAP crystallizer, the MAP crystallizer could be operated safely without generating combustible gas.

After crystallization and removal of MAP in the MAP crystallizer, phosphate ions and magnesium ions in the MAP-removed product were 50 mg/L and 40 mg/L, respectively. It is believed that no further MAP crystallization occurred in the anaerobic treatment unit because the phosphate ion and magnesium ion concentrations were low and the MAP crystallization reaction reached equilibrium.

The amount of aeration required to raise the oxidation-reduction potential (AgCl/Ag electrode) in the MAP crystallizer to −400 mV or higher was 1.0 m ³ /(m ³ ·h). The amount of digestive juice required to raise the pH to about 7.5 was 66 m ³ /day for 16.5 m ³ /day of organic waste liquid.

About 40 kg of MAP particles per day could be recovered in the MAP crystallizer without adding external agents such as a magnesium source. The recovered MAP particles could be effectively used as fertilizer.

[Comparative Example 2]
Example 1, except that 90 v/v% of the organic effluent was introduced into the MAP crystallizer prior to the anaerobic treatment, and 10 v/v% of the remaining organic effluent was initially introduced into the anaerobic treatment unit. When treated under the same conditions as in 1, the amount of aeration required to raise the oxidation-reduction potential (AgCl/Ag electrode) of the organic waste liquid in the MAP crystallizer to -400 mV or more was 1.0 m ³ /(m ³ · h), the amount of digestive liquid required to raise the pH of the organic waste liquid to about 7.5 was 60 m ³ /day. After crystallization and removal of MAP in the MAP crystallizer, the phosphate ions and magnesium ions in the MAP-removed product were 50 mg/L and 40 mg/L, respectively. Since it was introduced into the anaerobic treatment apparatus, magnesium ions (200 mg/L) in the organic waste liquid were introduced into the anaerobic treatment apparatus in addition to 40 mg/L of magnesium ions in the MAP-removed material. As the crystallization reaction progressed, fine MAP was crystallized in the anaerobic treatment apparatus (methane fermentation tank) and scale was observed.

[Comparative Example 3]
When the treatment was carried out under the same conditions as in Example 1 except that the MAP crystallizer was operated without adjusting the aeration amount, the oxidation-reduction potential (Ag/AgCl electrode) of the organic waste liquid in the MAP crystallizer was about -450 mV. and fell below -400 mV, acid fermentation progressed and the pH dropped to 6.7, and it became impossible to maintain pH 7.0 or higher. As a result, MAP was not crystallized, and the amount of magnesium ions introduced into the anaerobic treatment apparatus was about 150 mg/L, which could not be reduced. Since the magnesium ion concentration was high, the reaction with phosphate ions and ammonium ions proceeded in the anaerobic treatment apparatus, and scale was observed due to MAP crystallization.

10, 110: MAP crystallizer 20, 120: Anaerobic treatment device (methane fermentation tank)
30, 130: acid fermentation tanks 11, 111: aeration equipment (air lift system)
11a, 119: air lift pipes 13f, 23, 118, 123: MAP-removed product introduction lines 21, 121: digestive fluid return lines 22, 122: digestive fluid discharge lines

Claims (9)

Before the anaerobic treatment, the entire amount of organic waste liquid containing at least magnesium ions is introduced into a MAP crystallizer containing MAP seed crystals to suppress acid fermentation or methane fermentation while aerating to crystallize MAP particles. a MAP crystallization step;
a MAP particle removal step for obtaining a MAP-removed product by separating the MAP particles crystallized in the MAP crystallization step;
an anaerobic treatment step of introducing the MAP-removed product obtained in the MAP particle removal step into an anaerobic treatment apparatus and subjecting it to anaerobic treatment; using at least a portion of digested sludge after anaerobic treatment as an alkali source A method for treating an organic waste liquid to be returned to the MAP crystallizer. 2. Aeration is performed in the MAP crystallization step so that the organic waste liquid containing at least magnesium has an oxidation-reduction potential (an oxidation-reduction potential based on a silver/silver chloride electrode) of −400 mV or more. The method for treating the organic waste liquid according to 1. 3. The amount of aeration and/or the return amount of digested sludge is adjusted in the MAP crystallization step so that the organic waste liquid containing at least magnesium has a pH of 7 or more and 9 or less. A method for treating an organic waste liquid as described. 4. The method for treating an organic waste liquid according to claim 1, wherein in the MAP crystallization step, aeration is performed by introducing air into the MAP crystallizer by an air lift method. When at least part of the digested sludge after the anaerobic treatment is returned to the MAP crystallizer as an alkalinity source, the digested sludge is not mixed with the organic waste liquid before being introduced into the MAP crystallizer. The method for treating an organic waste liquid according to any one of claims 1 to 4, characterized by: Claims 1 to 5, characterized in that the digested sludge returned to the MAP crystallizer is 3 parts by volume or more and 10 parts by volume or less with respect to 1 part by volume of the organic waste liquid in the MAP crystallizer. The method for treating an organic waste liquid according to any one of the items. a MAP crystallizer equipped with an aerator, receiving the entire amount of organic waste liquid containing at least magnesium ions before anaerobic treatment, and crystallizing MAP particles;
an anaerobic treatment device that receives the MAP-removed product from the MAP crystallizer and performs anaerobic treatment;
a MAP-removed material introduction line for sending the MAP-removed material from the MAP crystallizer to the anaerobic treatment apparatus;
a digested sludge return line for returning at least part of the digested sludge from the anaerobic treatment device to the MAP crystallizer;
A digested sludge discharge line for extracting the rest of the digested sludge from the anaerobic treatment apparatus to the outside of the system;
An organic waste liquid treatment apparatus comprising: 8. The apparatus for treating organic waste liquid according to claim 7 , wherein the aeration device is an air lift having a controller for setting the amount of introduced air. 9. The organic waste liquid treatment apparatus according to claim 7, wherein said digested sludge return line is provided separately from a line for supplying said organic waste liquid to said MAP crystallizer.

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