JP2021159828A - Method and apparatus for treating organic waste liquid - Google Patents

Abstract

To provide a technique for reducing a cost increase due to addition of chemicals and preventing scale generation in an anaerobic fermentation treatment facility for organic waste liquid that easily forms MAP.SOLUTION: An apparatus for treating organic waste liquid includes: an aeration device 11; a MAP crystallizer 10 that accepts an entire amount of organic waste liquid containing at least magnesium ions before anaerobic treatment and crystallizes MAP particles; an anaerobic treatment device 20 that receives the MAP removal treatment product from the MAP crystallizer 10 and performs anaerobic treatment; MAP removal treatment product introduction lines 13f and 23 that send the MAP removal treatment product from the MAP crystallizer 10 to the anaerobic treatment device 20; a digestive fluid return line 21 for returning at least a part of a digestive juice from the anaerobic treatment device 20 to the MAP crystallizer 10; and a digestive fluid discharge line 22 that extracts the rest of the digestive juice from the anaerobic treatment device 20 to outside of a system.SELECTED DRAWING: Figure 1

Description

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

The method of methane fermentation treatment of organic waste liquid is that the operating cost is low, the digested sludge after methane fermentation treatment is biologically stable, and the digestion gas (methane gas) obtained by methane fermentation treatment is used as energy. There are many benefits, such as what you can do. Therefore, in recent years, there has been an increasing demand for methane fermentation equipment for organic waste liquids such as kitchen waste, leftover food, food and beverage production residues, sewage sludge, organic wastewater treatment sludge, and livestock manure.

In the methane fermentation facility, methane fermentation tank is a reducing atmosphere, ammonium ion (NH 4 ^_+), phosphate ions (PO 4 ^_3-) is in the eluted friendly environment in 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”) are precipitated by 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, in addition to the methane fermentation tank, there are often cases where MAP-derived scale is generated in the system in which the digestive juice in the methane fermentation tank stays or circulates. The scale had to be removed by periodically shutting down the equipment because it could block the digestion pump and cause the methane fermenter stirrer to malfunction. If the scale is significant, it may be necessary to drain the entire amount of digestive juice in the methane fermentation tank and clean the inside of the tank. In that case, a huge amount of digestive juice disposal cost is required. Furthermore, it will be necessary to suspend the operation of the equipment for a long period of time until the digestive juice is discharged, cleaned, and restarted. Furthermore, since it is necessary to outsource the treatment of waste while the operation of the methane fermentation facility is stopped, the cost burden is large.

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

Republished WO2006 / 078012 states that a magnesium compound is added to the digested sludge in a method for preventing scale in the pipe when the digested sludge generated by anaerobic digestion of the organic waste liquid is transported by pipe. The digested sludge containing MAP was treated with a crystallization step of crystallization of MAP and a step of removing the residue from the digested sludge, and the fine particles containing MAP were removed from the digested sludge which had undergone the crystallization step and the step of removing the residue. A method for preventing scale in a pipe is described, which comprises transporting the digested sludge from which the fine particles have been removed by pipe. Further, at this time, it is described that when aeration treatment, decompression treatment or the like is used in combination, decarboxylation is performed to raise the pH, and MAP can be precipitated more efficiently.

According to JP-A-2017-217640, the digested liquor after the methane fermentation treatment is introduced into a MAP crystallization apparatus to crystallize the MAP, and the digested liquor after removing the MAP particles is returned to the methane fermenter. It is described that the risk of scale generation derived from MAP is reduced by not adding Mg to the digestive juice and by adding an organic acid to the digestive juice being returned from the MAP crystallizer to the methane fermenter to lower the pH. ing.

In Japanese Patent Application Laid-Open No. 2019-181388, the digestive juice from the methane fermentation apparatus is supplied to the MAP crystallization apparatus, the MAP is crystallized, and then the MAP particles are supplied to the cyclone to separate the MAP particles in the digestive juice. By adding a pH lowering agent or phosphorus remover to the separation liquid and supplying it to the membrane separation device, and returning the membrane filtration concentrated digestion solution to the methane fermentation device, the formation of MAP is suppressed regardless of changes in the water quality of the water to be treated. It is described that it can suppress the damage or occlusion of the membrane.

Japanese Unexamined Patent Publication No. 2003-117306 Republished WO 2006/078012 JP-A-2017-217640 Japanese Unexamined Patent Publication No. 2019-181388

In the conventionally proposed method, when an organic waste liquid containing magnesium ions is anaerobic digested in a methane fermenter having a pH of 7 to 8, it is contained in the organic waste liquid or anaerobic microorganisms. It is possible to prevent phosphate ions derived from organic phosphorus supplied as a nutrient source and ammonium ions derived from organic nitrogen from reacting with magnesium ions and crystallizing as magnesium ammonium phosphate (MAP). However, the prevention of scale generation in the entire methane fermentation facility is not sufficient, and there is room for improvement such as an increase in cost due to the addition of chemicals.

Further, when the methane fermentation treatment is carried out under a high load condition, it is necessary to stabilize the methane fermentation treatment by subjecting the organic waste solution before the methane fermentation treatment to an acid fermentation treatment or a solubilization treatment. Since the pH of the organic waste liquid after the acid fermentation treatment drops to 3 to 5, it is necessary to add an 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 a cost increase due to the addition of a chemical and preventing scale generation in an anaerobic fermentation treatment facility for an organic waste liquid that easily forms a MAP.

The present inventors reduce the amount of magnesium ions introduced into an anaerobic treatment apparatus by removing MAP particles by MAP crystallization treatment of at least the entire amount of the organic waste liquid containing at least magnesium ions before the anaerobic treatment. It is possible to suppress MAP crystallization in the anaerobic treatment apparatus, and acid fermentation or methane in the MAP crystallization apparatus by aerating the organic waste liquid during the MAP crystallization treatment performed before the anaerobic treatment. It has been found that fermentation can be suppressed and MAP crystallization and growth can be promoted, and the present invention has been completed.

The present invention provides the following organic waste liquid treatment method and treatment apparatus.
[1] Before the anaerobic treatment, the entire amount of the organic waste liquid containing at least magnesium ions is introduced into a MAP crystallization device containing MAP seed crystals, and acid fermentation or methane fermentation is suppressed while aeration to produce MAP particles. MAP crystallization step to crystallize and
A MAP particle removing step of separating the MAP particles crystallized in the MAP crystallization step to obtain a MAP removing treated product, and a MAP particle removing step.
An anaerobic treatment step of introducing the MAP removal treatment product obtained in the MAP particle removal step into an anaerobic treatment apparatus and performing an anaerobic treatment, and at least a part of the digestive juice after the anaerobic treatment is used as an alkali source. A method for treating an organic waste liquid, which is returned to the MAP crystallizer.
[2] In the MAP crystallization step, the organic waste liquid containing at least magnesium is exposed to air so that the redox potential (oxidation-reduction potential based on the silver / silver chloride electrode) is −400 mV or more. The method for treating an organic waste liquid according to the above [1].
[3] In the MAP crystallization step, the aeration amount 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 [1]. The method for treating an organic waste liquid.
[4] The organic waste liquid according to any one of the above [1] to [1], which is aerated by introducing air into the MAP crystallization apparatus by an air lift method in the MAP crystallization step. Processing method.
[5] A MAP crystallization device provided with an aeration device, which receives the entire amount of the organic waste liquid containing at least magnesium ions before the anaerobic treatment and crystallizes the MAP particles.
An anaerobic treatment device that receives the MAP removal treatment product from the MAP crystallization device and performs anaerobic treatment.
A MAP removal treatment product introduction line that sends a MAP removal treatment product from the MAP crystallization device to the anaerobic treatment device, and
A digestive juice return line that returns at least a part of the digestive juice from the anaerobic treatment apparatus to the MAP crystallization apparatus, and
A digestive juice discharge line that extracts the rest of the digestive juice from the anaerobic treatment device to the outside of the system,
A device for treating organic waste liquid.
[6] The organic waste liquid treatment device according to the above [5], wherein the aeration device is an air lift including a control unit for setting an introduced air amount.

[Definition]
In the present application, the term "organic waste liquid" refers to slurry-like organic waste containing a large amount of solid content of production residues such as human waste, residual rice, food and beverages, and organic sludge such as sewage sludge and organic wastewater treatment sludge. , Livestock manure, human waste, sewage, and organic wastewater such as production wastewater of foods and beverages. In the "organic waste liquid" used for the MAP crystallization treatment in the present invention, if the solid content concentration is too high, MAP crystallization in the MAP crystallization tank does not proceed easily, and the piping of the MAP crystallization tank may be clogged. , The solid matter concentration is preferably 20 v / v% or less. In the present application, an organic wastewater having a solid substance concentration such as SS (suspended solids) of 0 v / v% or more and 4 v / v% or less may be particularly referred to as “organic wastewater”.

In the present application, "digestive juice" is used as a general term including slurry-like organic waste containing a large amount of solid content, digested sludge obtained by anaerobic digestion of sludge, and anaerobic treated water obtained by anaerobicly treating organic wastewater.

Further, in the present application, "fine MAP" or "fine MAP" means MAP particles that do not grow on the surface of the MAP seed crystal and remain in the form of fine particles of less than 0.05 mm.

According to the present invention, it is possible to reduce the cost increase due to the addition of the chemicals required in the conventional method, and to prevent the generation of scale in the anaerobic fermentation treatment facility of the organic waste liquid which easily forms MAP.

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

Since the MAP crystallization treatment of the organic waste liquid before the anaerobic treatment is performed while aeration, acid fermentation and methane fermentation in the MAP crystallization device are suppressed, and the amount of methane generated during the anaerobic treatment after the anaerobic treatment. Can be prevented from decreasing. Further, by suppressing the methane fermentation in the MAP crystallization apparatus, it is possible to prevent the generation and leakage of dangerous flammable gas during the MAP crystallization treatment.

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

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

The schematic diagram of an example of the apparatus configuration for carrying out the method for treating an organic waste liquid of this invention. The enlarged explanatory view of the air lift tube 11a portion of the MAP crystallization apparatus 10 of FIG. The schematic diagram of another example of the apparatus configuration for carrying out the method for treating an organic waste liquid of this invention.

Embodiment

Hereinafter, the present invention will be specifically described 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 organic waste liquid treatment device of the present invention includes an aeration device 11, a MAP crystallizing device 10 that receives the entire amount of the organic waste liquid containing at least magnesium ions before the anaerobic treatment and crystallizes MAP particles.
An anaerobic treatment device 20 that receives a MAP removal treatment product from the MAP crystallization device 10 and performs an anaerobic treatment.
MAP removal treatment product introduction lines 13f and 23 for sending the MAP removal treatment product from the MAP crystallization device 10 to the anaerobic treatment device 20 and
A digestive juice return line 21 that returns at least a part of the digestive juice from the anaerobic treatment apparatus 20 to the MAP crystallization apparatus 10 and
A digestive juice discharge line 22 for extracting the rest of the digestive juice from the anaerobic treatment apparatus 20 to the outside of the system, and a digestive juice discharge line 22.
To be equipped.

In the processing apparatus shown in FIG. 1, the MAP crystallization apparatus 10 includes a crystallization reactor 12 that crystallizes MAP from organic waste liquid, and a liquid cyclone 13a that recovers coarse MAP particles formed in the crystallization reactor 12. , A liquid cyclone 13b that returns fine MAP particles formed in the crystallization reactor to the crystallization reactor 12.

The crystallization reactor 12 has a cylindrical shape having an inverted conical portion at the lower portion, and a cylindrical drawing portion 12a is formed at the bottom portion which is the apex of the inverted conical portion at the lower portion. The drawing portion 12a is connected to a MAP liquid feeding line 15 that sends a slurry containing the pulled out MAP particles to the liquid cyclone 13, and an air lift pipe 11a that functions as an aeration device. The extraction unit 12a draws out the organic waste liquid containing the MAP particles that settle in the crystallization reactor 12, and also functions as an air introduction unit from the aeration device 11. The MAP particles formed in the crystallization reactor 12 descend while causing a swirling flow on the wall surface of the inverted conical portion at the lower part of the crystallization reactor 12, and the MAP particles having a heavy specific gravity act on the lower wall surface side by the action of centrifugal force. It is concentrated in the bottom and settles in the pull-out portion 12a at the bottom. The organic waste liquid containing the concentrated MAP particles is introduced into the liquid cyclones 13a and 13b via the MAP liquid feeding 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 extraction portion 12a by the buoyancy of the air, separates the gas and liquid in the upper air chamber 11b, and separates the air lift pipe 11a. The organic waste liquid is returned to the crystallization reactor 12 via the return line 11c. The air lift pipe 11a is connected to an air supply source 11e, and is connected to an air supply pipe 11d having a blower 11f, an air volume adjusting 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 with a pH meter and an ORP meter (Ag / AgCl electrode), the air volume adjusting valve 11 g is operated so that the ORP becomes -400 mV or more. The amount of aeration can be adjusted.

An organic waste liquid introduction line 14, a digestive juice 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 part of the crystallization reactor 12, respectively. The digestive juice return line 21 is separate from the organic waste liquid introduction line 14 because MAP particles may be generated if the organic waste liquid and the digestive liquid are mixed before being introduced into the crystallization reactor 12. Must be connected to the MAP crystallization reactor 12. The organic waste liquid is introduced into the crystallization reactor 12 via the organic waste liquid introduction line 14. The digestive juice from the anaerobic treatment apparatus 20, which will be described later, is returned to the crystallization reactor 12 via the digestive juice return line 21. Fine MAP particles from the liquid cyclone 13b are returned to the crystallization reactor 12 via the discharge pipe 13d. The overflow containing the fine MAP particles separated by the liquid cyclone 13a is returned to the crystallization reactor 12 via the overflow pipe 13e.

The liquid cyclones 13a and 13b are inverted cones, with MAP particle discharge tubes 13c and 13d at the bottom, which are the apex of the inverted cone, overflow risers 13e and 13f at the top, and 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 liquid cyclones 13a and 13b, and descends on the inverted conical wall surface inside the liquid cyclones 13a and 13b while causing a swirling flow, and the MAP particles having a heavy specific gravity. 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. The organic waste liquid from which the MAP particles have been removed is taken out via the overflow pipes 13e and 13f. In the liquid cyclone 13a, the coarse MAP particles are extracted from the discharge pipe 13c, and the organic waste liquid containing the fine MAP particles is returned to the crystallization reactor 12 via the overflow pipe 13e. In the liquid cyclone 13b, fine MAP particles are returned to the crystallization reactor 12 via the discharge pipe 13d, and the MAP removal treated product from which the fine MAP particles are also removed is passed through the overflow rising pipe 13f to the acid fermenter or the acid fermenter. It is sent to the storage tank 30 or the anaerobic treatment device 20. In order to recover MAP particles having different sizes in the liquid cyclones 13a and 13b, in the initial stage of the MAP crystallization treatment, the entire amount of the organic waste liquid from the extraction portion 12a of the crystallization reactor 12 is introduced into the liquid cyclone 13b. When the growth of MAP particles progresses in the crystallization reactor 12 and coarse MAP particles are formed, a part or all of the slurry from the drawn portion 12a of the crystallization reactor 12 is introduced into the liquid cyclone 13a. Switch the road. The flow path can be switched by 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 fermenter. As the methane fermentation tank, a methane fermentation tank usually used in the art such as a completely mixed methane fermentation tank, a carrier-filled methane fermentation tank, and a high-load methane fermentation apparatus can be used. However, in the methane fermentation tank in the processing apparatus of the present invention, the MAP removal processed product introduction line 23 and the methane fermentation are introduced in order to introduce the MAP removal processed product from which the MAP particles have been removed by the MAP crystallization apparatus 10 and to use it for the methane fermentation treatment. It is provided with a digestive juice discharge line 21 for returning at least a part of the subsequent digestive juice to the MAP crystallization apparatus, and a digestive juice discharge line 22 for extracting the rest of the digestive juice.

In the treatment apparatus shown in FIG. 1, an acid fermentation tank or a storage tank 30 is further provided between the MAP crystallization apparatus 10 and the anaerobic treatment apparatus (methane fermentation tank) 20. As the acid fermentation tank or storage tank, an acid fermentation tank or storage tank usually used in the art can be used without limitation. By providing an acid fermenter, the amount of anaerobic digested sludge can be reduced. By providing the storage tank, the MAP-removed product can be diluted before being subjected to the anaerobic treatment to further reduce the concentration of magnesium ions in the MAP-removed product introduced into the anaerobic treatment apparatus.

FIG. 3 outlines another example of an apparatus configuration 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 includes an aeration apparatus 111, a MAP crystallization apparatus 110 that receives the entire amount of the organic waste liquid containing at least magnesium ions before the anaerobic treatment and crystallizes MAP particles.
An anaerobic treatment device 120 that receives a MAP removal treatment product from the MAP crystallization device 110 and performs anaerobic treatment.
A digestive juice return line 121 that returns at least a part of the digestive juice from the anaerobic treatment apparatus 120 to the MAP crystallization apparatus 110, and
A digestive juice discharge line 122 for extracting the rest of the digestive juice from the anaerobic treatment apparatus 120, and a digestive juice discharge line 122.
To be equipped.

In the processing apparatus shown in FIG. 3, the MAP crystallization apparatus 110 includes a first crystallization reactor 112 and a second crystallization reactor 113. An organic waste liquid introduction line 114a for introducing organic waste liquid and an aeration line 111a for introducing air are connected to the lower part of the first crystallization reactor 112, respectively. An organic waste liquid introduction line 114b for introducing organic waste liquid and an aeration line 111b for introducing air are connected to the lower part 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. The solid-liquid separation unit 112b is provided with an inner cylinder 117. A MAP removal processed product discharge line 118 for overflowing the MAP removal processed product is connected to the solid-liquid separation unit 112b. A reduced diameter portion having an inverted conical shape is formed in the lower portion of the solid-liquid separating portion 112b. The crystallization reaction section 112a has a cylindrical shape having the minimum diameter of the reduced diameter portion of the solid-liquid separation section 112b as the diameter, and the lower portion of the crystallization reaction section 112a is formed in an inverted conical shape, and the apex of the inverted conical shape is formed. 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 via the organic waste liquid introduction line 114a forms MAP particles while being aerated by the air introduced from the aeration line 111a. The slurry-like organic waste liquid containing the MAP particles rises toward the inner cylinder 117 of the solid-liquid separation unit 112b as the bubbles rise. The heavy MAP particles descend on the inverted conical wall surface while causing a swirling flow, 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 light specific density rise with bubbles. When entering the solid-liquid separation unit 112b having a diameter larger than that of the crystallization reaction unit 112a, the ascending rate decreases, so that fine MAP particles enter the inner cylinder 117 with bubbles and stay inside the inner cylinder 117. The coarse MAP particles are recovered from the discharge pipe 112c at the lower part of the first crystallization reactor 112, and the fine MAP particles flow in the inner cylinder 117 at the upper part of the first crystallization reactor 112, so that the first crystallization occurs. The MAP particles formed in the reactor 112 are separated from the organic effluent. The organic waste liquid separated from the MAP particles is extracted from the MAP removal processed product discharge line 118 and sent to the anaerobic treatment apparatus 120.

The second crystallization reactor 113 is a cylinder having an inverted conical reduced diameter portion at the bottom. A digestive juice return line 121 for returning at least a part of the digestive juice from the anaerobic treatment apparatus 120, which will be described later, is connected on the inverted conical diameter-reduced portion of the second crystallization reactor 113. An air lift tube 119 is provided above the inverted conical diameter-reduced portion of the second crystallization reactor 113. The air lift tube 119 is connected to the inner cylinder 117 of the first crystallization reactor 112, sends fine MAP particles flowing inside the inner cylinder 117 to the second crystallization reactor 113, and also sends the second crystallization reactor 113. The coarse MAP particles grown in 113 are sent to the 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 released from the inner cylinder 117 of the first crystallization reactor 112 due to the density difference in the second crystallization reactor. It naturally flows down 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 and the coarse MAP particles are sent to the first crystallization reactor 112 by air lift via the air lift pipe 119. .. An overflow pipe 118a that sends the overflow from the second crystallization reactor 113 to the first crystallization reactor 112 is connected to the upper part of the second crystallization reactor 113.

In the MAP crystallization apparatus 110 shown in FIG. 3, the aeration apparatus 111 is provided so that the ORP (Ag / AgCl electrode) of the organic waste liquid in the first crystallization reactor 112 and the second crystallization reactor 113 is −400 mV or more. Adjust the amount of aeration. The aeration amount can be adjusted by adjusting the amount of air introduced from the aeration device 111 and switching the introduction of air into 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 fermenter. As the methane fermentation tank, a methane fermentation tank usually used in the technical field such as a UASB type methane fermentation tank, a carrier-filled methane fermentation tank, and a high-load methane fermentation apparatus can be used. However, the methane fermentation tank in the processing apparatus of the present invention is provided with a MAP removal processed product introduction line 123 in order to introduce the MAP removal processed product from which the MAP particles have been removed by the MAP crystallization apparatus 110 and to use it for the methane fermentation treatment. After the digestive juice after methane fermentation is stored in the storage tank 140, at least a part thereof is returned to the lower part of the second crystallization reactor 113 of the MAP crystallization apparatus 120 via the digestive juice discharge line 121, and the digestive juice is discharged. The balance of the digestive juice is extracted through the line 122.

In the treatment apparatus shown in FIG. 3, an acid fermentation tank 130 is further provided between the MAP crystallization apparatus 110 and the anaerobic treatment apparatus (methane fermentation tank) 120. As the acid fermenter, an acid fermenter usually used in the art can be used without limitation. By providing an acid fermenter, the amount of anaerobic digested sludge can be reduced.

The MAP crystallization device and the anaerobic treatment device used in the processing device of the present invention are not limited to the above-mentioned examples, and devices generally used in the technical field can be used in any combination.

The method for treating an organic waste liquid of the present invention is as follows: (1) Before the anaerobic treatment, the entire amount of the organic waste liquid containing at least magnesium ions is introduced into a MAP crystallizer containing a MAP seed crystal, and the acid is exposed while being aerated. A MAP crystallization step of suppressing fermentation or methane fermentation to crystallize MAP particles, and (2) a MAP particle removal step of separating the MAP particles crystallized in the MAP crystallization step to obtain a MAP removal treated product. , (3) An anaerobic treatment step of introducing the MAP removal treated product obtained in the MAP particle removing step into an anaerobic treatment apparatus and performing anaerobic treatment. The alkali source required in the MAP crystallization step is supplied by returning at least a part of the digestive juice after the anaerobic treatment to the MAP crystallization apparatus.

Normally, since organic nitrogen and organic phosphorus are added as a nutrient source for anaerobic microorganisms in the anaerobic treatment of organic waste liquid, ammonium ions derived from organic nitrogen and phosphate ions derived from organic phosphorus are generated. Reacting with magnesium ions in the organic waste liquid, magnesium ammonium phosphate (MAP) crystallizes, 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 the MAP, and magnesium ions in the organic waste liquid are removed. Even if nitrogen or phosphorus is added as a nutrient source for anaerobic microorganisms without introducing a large amount of magnesium ions, MAP crystallization can be prevented.

The treatment method of the present invention targets an organic waste liquid containing at least magnesium ions. For example, slurry-like organic waste liquid containing a large amount of solids such as production residues of kitchen waste, residual rice, foods and beverages, organic sludge such as sewage sludge and organic wastewater treatment sludge, livestock manure, urine, sewage, etc. In addition, organic wastewater such as production wastewater of foods and beverages can be treated. Organic wastes such as production residues containing a large amount of solids flow by removing large solids using a sedimentation separation device or a separation screen, or by dilution treatment or solubilization treatment before MAP crystallization treatment. It can be a slurry-like organic waste liquid having a property.

In the present invention, the organic waste liquid introduced into the MAP crystallization apparatus before the anaerobic treatment and subjected to the MAP crystallization treatment contains at least magnesium ions. The presence of phosphate and ammonium ions is required to form the MAP, which is either contained in the organic effluent or in the digestive sludge returned from the anaerobic treatment step. There is. In order to reduce the amount of magnesium ions contained in the MAP removal treatment product introduced into the anaerobic treatment apparatus as much as possible, almost all of the magnesium ions contained in the organic waste liquid in the MAP crystallization step are crystallized as MAP. It is preferable to analyze and remove it. Therefore, when the amount of phosphate ion or ammonium ion is smaller than the chemical quantity ratio with magnesium ion and there is a possibility that magnesium ion remains, the phosphate ion or ammonium ion is added to the MAP crystallizer. Is preferable. The digestive juice after the anaerobic treatment contains phosphate ions and ammonium ions derived from organic phosphorus and organic nitrogen added as a nutrient source for anaerobic microorganisms. In the present invention, by returning the digested juice after the anaerobic treatment to the MAP crystallization step, phosphate ions and ammonium ions necessary for MAP crystallization can also be supplied.

In the MAP crystallization step, when acid fermentation or methane fermentation proceeds, the pH of the organic waste liquid drops to an acidic range, and MAP crystallization and growth are inhibited. Therefore, in the MAP crystallization step, it is necessary to maintain the pH of the organic waste liquid in the neutral range to the weak 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 juice after the anaerobic treatment contains a large amount of alkaline components, by returning it to the MAP crystallization step, an alkaline drug that had to be added separately in the conventional method can be added. It can be unnecessary.

Acid fermentation or methane fermentation proceeds in an anaerobic atmosphere. In the present invention, since the organic wastewater before the anaerobic treatment is subjected to the MAP crystallization treatment, it contains a large amount of organic components in which acid fermentation or methane fermentation is likely to proceed. However, the progress of acid fermentation inhibits MAP crystallization, the progress of methane fermentation generates flammable gas, and there is a risk that the flammable gas leaks from the MAP crystallization tank. In the present invention, in order to suppress the progress of acid fermentation or methane fermentation in the MAP crystallization step, the inside of the MAP crystallization apparatus is aerated to prevent an anaerobic atmosphere in which acid fermentation or methane fermentation proceeds. It is necessary. Preferably, the organic waste liquid in the MAP crystallization step is exposed to air so that the redox potential (oxidation-reduction potential based on the silver / silver chloride electrode) is −400 mV or more. However, it is not necessary to perform the MAP crystallization step in a general aerobic atmosphere, and the redox potential (oxidation-reduction potential based on the silver / silver chloride electrode) is preferably −400 mV or more and + 100 mV or less, more preferably. The air may be exposed so as to be −200 mV or more and + 50 mV or less, particularly preferably −100 mV or more and 0 mV or less. Excessive aeration causes decarboxylation of the organic waste liquid, causing the pH to rise excessively to generate fine MAP particles, and volatilizing odorous components such as ammonia and hydrogen sulfide, and further, in an aerobic atmosphere. It is not preferable because it causes a problem that the nitrification reaction proceeds and the pH is lowered. It is desirable to measure the redox potential and control the aeration amount so as to regulate within the above range. The amount of aeration required for 1 hour treatment with a capacity of 1 m ^{3 of the MAP crystallizer 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. ^{It is 3} / (m ³ · hr) or more and 1.2 m ³ / (m ³ · hr) or less. The aeration is preferably performed by an air lift method in which air is introduced from the lower part of the MAP crystallizer and bubbles are raised in the MAP crystallizer. Further, in order to control the aeration amount, air can be introduced by using an air lift provided with a control unit (for example, a flow rate adjusting valve, a blower control by an inverter, etc.) for setting the amount of introduced air. It is more preferable to use an air lift having a control unit that automatically controls the amount of introduced air based on the measured value of the redox potential.

The MAP crystallization step is performed in a MAP crystallization apparatus containing MAP seed crystals. A "MAP seed crystal" is a coarse MAP particle that grows MAP particles on its surface. As the MAP seed crystal, MAP particles formed during the preceding treatment may be used, MAP particles precipitated in another crystallization reactor may be used as shown in FIG. 3, and phosphate ore, dolomite, and the like. It may be a powder or particles such as bone charcoal, activated carbon, silica sand, and calcium silicate. Since MAP is crystallized and grown on the surface of the MAP seed crystal, the MAP seed crystal preferably has a particle size of 0.05 mm or more and 5.0 mm or less. For example, when a slurry-like organic waste liquid containing a solid content 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, and is organic. When a liquid organic waste liquid such as wastewater is introduced into a MAP crystallizer, the particle size of the MAP seed crystal is preferably 1 mm or more and 5 mm or less.

The filling amount of the MAP seed crystal in the MAP crystallizer is 3 w / v% or more 6 w / in the case of a slurry-like organic waste liquid containing a solid content in order to grow into large MAP particles on the surface of the MAP seed crystal. V% or less is preferable, and in the case of a liquid organic waste liquid such as organic waste liquid, 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 have been removed is introduced into an anaerobic treatment apparatus. Here, the MAP removal treated product is a slurry containing a very small amount of liquid or fine MAP particles after removing coarse MAP particles. Since fine MAP particles are difficult to separate and may remain in the processed material and be introduced into an anaerobic treatment apparatus, the MAP particles are 0.05 mm or more and 3 mm or less, preferably 0, on the surface of the MAP seed crystal. It is desirable to grow to 1 mm or more and 0.5 mm or less.

The MAP-removed product from which the MAP particles have been removed is anaerobic-treated in an anaerobic treatment device to produce anaerobic digestive sludge and digestive juice. Normally, the digestive juice is extracted from the anaerobic treatment device to the outside of the system, and the anaerobic digestive sludge is dehydrated. In the present invention, by returning a part of the digestive juice containing a large amount of alkaline components to the MAP crystallization treatment apparatus as an alkaline source, the organic waste liquid in the MAP crystallization apparatus is pH 7.0 required for MAP crystallization. As described above, the pH can be adjusted preferably 7.0 or more and 9.0 or less, and more preferably 7.5 or more and 8.5 or less. When the pH is lower than 7.0, not only the crystallization becomes difficult to proceed, but also the hydrogen sulfide present in the liquid volatilizes and the surrounding environment deteriorates, and the organic components also present in the liquid due to the volatilization of organic acids and the like. There is a problem that the loss is likely to occur. On the other hand, when the pH exceeds 9.0, not only is it easy to generate fine MAPs, but there is also a problem that ammonia present in the liquid volatilizes and the surrounding environment deteriorates. The state of the alkaline content 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 alkali source required for the MAP crystallization treatment, the amount of digestive juice returned 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 crystallization device. It is possible to eliminate the need for addition of an alkaline chemical from the outside. For example, when an organic waste liquid having a high solid content is introduced into a MAP treatment apparatus, 4.0 parts by volume or more and 10.0 parts by volume or less, preferably 4.5 parts by volume or more per volume part of the organic waste liquid. It is desirable to return digestive juice of 0 parts by volume or less, and when organic wastewater with a low solid content is introduced into the MAP treatment device, 3.0 parts by volume or more and 7.0 parts by volume of organic wastewater is introduced. Hereinafter, it is preferable to return the digestive juice of 4.0 parts by volume or more and 5.0 parts by volume or less. If the amount of digestive juice returned is excessive, ammonia may volatilize in the MAP crystallizer, or crystallization may proceed too much and fine MAP particles may precipitate and recover without precipitating on the surface of the MAP seed crystal. It is not preferable because it becomes difficult.

[Comparative Example 1]
Approximately 3,000 m ³ / year of waste Organic waste generated at food processing plants (COD: 100,000 g / m ³ , phosphate ion: 650 g / m ³ , magnesium ion: 400 g / year m ³ , Kjeldahl nitrogen: 8,400 g / m ³ , pH: about 3.7) is added after removing foreign substances to prepare an organic waste liquid, and then via an acid fermenter with ^{a capacity of 20 m 3 and a capacity of 200 m 3} The treatment performed by the conventional method of introducing into the anaerobic treatment apparatus (methane fermenter) and not introducing into the MAP crystallization apparatus will be described.

The organic waste liquid is adjusted to a liquid having a solid content of 5% in an acid fermenter. At this time, the nitrogen content in the acid fermenter is about 4.5 kg / m ^{3 on} average, phosphorus is 600 g / m ³ , and magnesium is about ^{200 g / m 3.} In the acid fermenter, the organic waste liquid was hydrolyzed to produce an organic acid, and the pH was lowered 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 fermenting bacteria. At this time, the organic acid was converted into gas and removed, and ammonia was generated by the decomposition of the protein contained in the organic matter, so that the pH in the methane fermentation tank rose to about 7 to 8.

The organic waste liquid from this food processing factory contains nitrogen, phosphorus and magnesium, and MAP is generated in the methane fermentation tank, near the liquid level in the methane fermentation tank and around the extraction pipe of digestive juice. Scale has occurred. The generation of scale caused problems such as failure of the methane fermenter stirrer, blockage of piping, and accumulation of sandy MAP crystals in the methane fermenter. If scale generation progresses, it will be necessary ^{to empty the anaerobic treatment device (methane fermenter) with a capacity of 200 m 3} , dredging it, cleaning it with chemicals, and then acclimatizing and restarting the methane fermenting bacteria for another two months or more. Therefore, the operation of organic waste liquid will have to be stopped for several months.

[Example 1]
An example of treating the organic waste liquid from the food processing factory of 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 the MAP crystallization device, a MAP crystallization device provided with the air lift tube shown in FIG. 2 was used.
First, the food after removing the foreign matter organic waste from processing plants and hydro to prepare the organic waste (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.} The digestive juice was introduced into the MAP crystallization apparatus 10 from the anaerobic treatment apparatus (methane fermentation tank) 20 via the digestive juice return line 21. The amount of digestive juice 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 redox potential (AgCl / Ag electrode) of the organic waste liquid becomes -400 mV or more. , The digestive juice was introduced so that the pH of the organic waste liquid rose to about 7.5, and the progress of acid fermentation and methane fermentation was suppressed. Gas containing carbon dioxide, hydrogen sulfide, ammonia and the like was generated from the MAP crystallizer. This gas was treated in a deodorizing facility in a food processing factory to prevent volatilization.

The MAP particles crystallized from MAP crystallizer extracted from MAP crystallizer was charged with MAP removing treated to raw material tank of about 20 m ³ capacity, to suppress the inhibition of methane fermentation with ammonia, water was added Diluted. The diluted MAP-removed product was introduced into an anaerobic treatment apparatus (methane fermenter) having a capacity of ^{200 m 3 and subjected to anaerobic treatment.}

Or by, can be run stably present equipment without causing process stopped by scale formation, biogas approximately 360 m ³ occurs per day. Further, by introducing air into the MAP crystallizer, it was possible to operate safely without generating flammable gas from the MAP crystallizer.

The phosphate ion in the MAP removal treatment product after MAP crystallization and removal in the MAP crystallizer was 50 mg / L, and the magnesium ion was 40 mg / L. Since the phosphate ion concentration and the magnesium ion concentration were low and the MAP crystallization reaction reached equilibrium, it is considered that further MAP crystallization did not occur in the anaerobic treatment apparatus.

The amount of air exposure required to raise the redox potential (AgCl / Ag electrode) in the MAP crystallizer to -400 mV or higher is 1.0 m ³ / (m ³ · h), and the amount of organic waste liquid in the MAP crystallizer the amount of digestive fluid taken to raise the pH to about 7.5 was in 66m ³ / day with respect to organic waste 16.5 m ³ / day.

In the MAP crystallizer, about 40 kg of MAP particles could be recovered per day without adding a chemical such as a magnesium source from the outside. The recovered MAP particles could be effectively used as fertilizer.

[Comparative Example 2]
Examples 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 first introduced into the anaerobic treatment apparatus. When treated under the same conditions as in 1, the amount of aeration required to raise the redox potential (AgCl / Ag electrode) of the organic waste liquid 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 of the organic waste liquid to about 7.5 was 60 m ³ / day. The phosphate ion in the MAP removal treatment product after MAP crystallization and removal in the MAP crystallizer was 50 mg / L and the magnesium ion was 40 mg / L, but 10 v / v% of the organic waste liquid was directly anaerobic. Since it was introduced into the sex treatment device, magnesium ions (200 mg / L) in the organic waste liquid were introduced into the anaerobic treatment device in addition to 40 mg / L of magnesium ions in the MAP removal treated product, and as a result, MAP was introduced. The crystallization reaction proceeded, and the fine MAP in the anaerobic treatment apparatus (methane fermentation tank) crystallized and scale was observed.

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

10, 110: MAP crystallization device 20, 120: Anaerobic treatment device (methane fermenter)
30, 130: Acid fermenter 11, 111: Aeration device (air lift method)
11a, 119: Air lift pipe 13f, 23, 118, 123: MAP removal processed product introduction line 21, 121: Digestive fluid return line 22, 122: Digestive fluid discharge line

Claims (6)

Before the anaerobic treatment, at least the entire amount of the organic waste liquid containing magnesium ions is introduced into a MAP crystallization device containing MAP seed crystals, and acid fermentation or methane fermentation is suppressed while aeration to crystallize MAP particles. MAP crystallization process and
A MAP particle removing step of separating the MAP particles crystallized in the MAP crystallization step to obtain a MAP removing treated product, and a MAP particle removing step.
An anaerobic treatment step of introducing the MAP removal treatment product obtained in the MAP particle removal step into an anaerobic treatment apparatus and performing an anaerobic treatment, and at least a part of the digestive juice after the anaerobic treatment is used as an alkali source. A method for treating an organic waste liquid, which is returned to the MAP crystallizer. The first aspect of the MAP crystallization step is to expose the organic waste liquid containing at least magnesium so that the redox potential (oxidation-reduction potential based on the silver / silver chloride electrode) is −400 mV or more. The method for treating an organic waste liquid described in 1. 2. The method for treating an organic waste liquid according to the above. The method for treating an organic waste liquid according to any one of claims 1 to 3, wherein in the MAP crystallization step, aeration is performed by introducing air into the MAP crystallization apparatus by an air lift method. A MAP crystallization device equipped with an aeration device, which receives the entire amount of the organic waste liquid containing at least magnesium ions before the anaerobic treatment and crystallizes the MAP particles.
An anaerobic treatment device that receives the MAP removal treatment product from the MAP crystallization device and performs anaerobic treatment.
A MAP removal treatment product introduction line that sends a MAP removal treatment product from the MAP crystallization device to the anaerobic treatment device, and
A digestive juice return line that returns at least a part of the digestive juice from the anaerobic treatment apparatus to the MAP crystallization apparatus, and
A digestive juice discharge line that extracts the rest of the digestive juice from the anaerobic treatment device to the outside of the system,
A device for treating organic waste liquid. The organic waste liquid treatment device according to claim 5, wherein the aeration device is an air lift including a control unit for setting the amount of introduced air.

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