JP2019217475A - Sludge treatment method and sludge treatment system - Google Patents

Abstract

To provide a sludge treatment method and a sludge treatment system capable of reducing an amount of a phosphorus component evaporated during combustion and suppressing an adverse effect on a combustion furnace.SOLUTION: A sludge treatment method of the present invention includes: a precipitation step of adding a precipitant to a digestion liquid of sludge to precipitate at least a part of a phosphorus component contained in the digestion liquid; and a combustion step of burning digested sludge obtained from the digestion liquid treated in the precipitation step. In the precipitation step, it is preferable to use a precipitation agent containing a calcium-based substance. In particular, the calcium-based substance is preferably at least one selected from the group consisting of calcium chloride, calcium hydroxide, and calcium carbonate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sludge treatment method and a sludge treatment system.

  BACKGROUND ART As a method of treating hydrated sludge such as sewage sludge discharged from a sewage treatment plant, combustion treatment in a combustion furnace is often used due to restrictions on environmental pollution prevention and the problem of depletion of landfill disposal sites.

  Dewatered sludge obtained by digesting sewage sludge (hereinafter also simply referred to as “sludge”) contains phosphorus at a high concentration (about 30% in terms of ash). For this reason, when the sludge is burned, the phosphorus component contained in the sludge evaporates and adheres to the walls of the combustion furnace as a phosphate compound, damaging the furnace wall of the combustion furnace, clogging the exhaust pipe, There are problems such as corrosion of the heat exchange tube.

  Therefore, in the treatment of sludge, studies have been made to reduce the amount of phosphorus contained in the sludge.

  As a technique for removing phosphorus, a method using magnesium ammonium phosphate (MAP) is known. However, such a method requires an ammonia component and has a problem of a long reaction time. Could not be solved sufficiently.

  Also, polyaluminum chloride (PAC) and ferric polysulfate are known as a flocculant or a phosphorus recovery agent for flocculating fine particles and suspended matter in sludge (for example, Non-Patent Document 1).

  However, when polyaluminum chloride or ferric polysulfate is used, the above-mentioned problem of adverse effects on a combustion furnace or the like cannot be sufficiently solved. In particular, when the digested sludge contains a relatively high content of phosphorus (for example, the content in incinerated ash is 10% by mass or more), the above-described problems are more likely to occur. It was noticeable. Further, these are expensive, and there are also problems in cost and increase in the amount of ash generated.

Efficient phosphorus recovery and recycling of flocculants in sewers, Yasuhiro Takahashi, Yasuhiro Hori, Journal of the Society of Inorganic Materials, Japan 12, 200-206 (2005)

  An object of the present invention is to provide a sludge treatment method and a sludge treatment system capable of reducing the amount of phosphorus component evaporated during combustion and suppressing the adverse effect on a combustion furnace.

Such an object is achieved by the present invention described below.
Sludge treatment method of the present invention, a precipitation step of adding a precipitant to the digestion liquid of the sludge, to precipitate at least a part of the phosphorus component contained in the digestion liquid,
A combustion step of burning digested sludge obtained from the digested liquid treated in the precipitation step.

  In the sludge treatment method of the present invention, it is preferable that the method further includes a precipitate removal step of removing at least a part of the phosphorus component precipitated in the precipitation step outside the system before the combustion step.

  In the sludge treatment method of the present invention, it is preferable to use a precipitant containing a calcium-based substance in the precipitation step.

  In the method for treating sludge of the present invention, the calcium-based material is preferably at least one selected from the group consisting of calcium chloride, calcium hydroxide, and calcium carbonate.

  In the sludge treatment method of the present invention, it is preferable that the calcium-based substance and the aluminum-based substance are used in combination in the precipitation step as the precipitant.

In the method for treating sludge of the present invention, when the amount of calcium contained in the precipitant is X _Ca [mol] and the amount of aluminum is X _Al [mol], 0.1 ≦ X _Ca / X _Al It is preferable to satisfy the relationship of ≦ 10.

  In the method for treating sludge of the present invention, the aluminum-based material is preferably at least one selected from the group consisting of polyaluminum chloride, aluminum sulfate, aluminum nitrate, and aluminum acetate.

  In the sludge treatment method of the present invention, it is preferable that the combustion temperature in the combustion step be 500 ° C or more and 1500 ° C or less.

The sludge treatment system of the present invention, a precipitation treatment unit that adds a precipitant to the sludge digestion liquid, and precipitates at least a part of the phosphorus component contained in the digestion liquid,
And a combustion furnace for burning digested sludge obtained from the digested liquid treated in the precipitation treatment section.

In the sludge treatment system of the present invention, the sludge treatment system includes an anaerobic tank for methane fermentation, an anoxic tank for nitrification and denitrification, and an aerobic tank for aerobic bacteria digestion. Department,
It is preferable that the precipitation treatment section is provided downstream of the oxygen-free tank and upstream of the aerobic tank.

In the sludge treatment system of the present invention, the sludge treatment system includes a anaerobic tank for methane fermentation, an anoxic tank for nitrification and denitrification, and an aerobic tank for aerobic bacteria digestion. With
It is preferable that at least one of the anaerobic tank and the anoxic tank also functions as the precipitation processing unit.

  ADVANTAGE OF THE INVENTION According to this invention, the sludge processing method and sludge processing system which can reduce the amount of the phosphorus component evaporated at the time of combustion and can suppress the bad influence which gives to a combustion furnace can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows 1st Embodiment of the sludge processing system of this invention typically. It is a flowchart showing a 1st embodiment of a sludge processing method of the present invention. It is a figure which shows 2nd Embodiment of the sludge processing system of this invention typically. It is a figure which shows the 3rd Embodiment of the sludge processing system of this invention typically. FIG. 5 is a diagram schematically illustrating an example of an adsorption processing unit included in the processing system illustrated in FIG. 4. It is a flowchart showing a 3rd embodiment of the sludge processing method of the present invention. It is a figure which shows 4th Embodiment of the sludge processing system of this invention typically. FIG. 8 is a diagram schematically illustrating a relationship between an adsorption processing unit and an anaerobic tank included in the processing system illustrated in FIG. 7. It is a graph which shows the relationship between the addition amount of a precipitating agent and the precipitation rate of phosphorus when using calcium chloride as a precipitating agent. It is a graph which shows the relationship between the addition amount of a precipitating agent when using calcium hydroxide as a precipitating agent, and the precipitation rate of phosphorus. It is a graph which shows the relationship between the addition amount of a precipitating agent and the precipitation rate of phosphorus when magnesium chloride is used as a precipitating agent. It is a graph which shows the relationship between the addition amount of a precipitating agent and the precipitation rate of phosphorus when polyaluminum chloride is used as a precipitating agent. It is a graph which shows the relationship between the combustion temperature of digested sludge, and the phosphorus content in the sludge ash obtained by combustion. 4 is a graph showing the relationship between the amount of adsorbent added and the adsorption rate of phosphorus when dolomite is used as an adsorbent in the step of adsorbing a phosphorus component on the surface of the adsorbent, reacting with and adsorbing one component of the adsorbent. It is a graph which shows the relationship between the addition amount of an adsorbent and the adsorption rate of phosphorus at the time of using dolomite hydroxide as an adsorbent. It is a graph which shows the relationship between the amount of addition of an adsorbent, and the adsorption rate of phosphorus when light burning dolomite (average particle diameter: 1 mm) is used as an adsorbent. It is a graph which shows the relationship between the amount of addition of an adsorbent, and the adsorption rate of phosphorus when light burning dolomite (average particle diameter: 3 mm) is used as an adsorbent. It is a graph which shows the relationship between pH and the adsorption rate of phosphorus when dolomite is used as an adsorbent. It is a graph which shows the relationship between pH and the adsorption rate of phosphorus when hydroxide dolomite is used as an adsorbent. It is a graph which shows the relationship between pH and the adsorption rate of phosphorus when light burning dolomite (average particle diameter: 1 mm) is used as an adsorbent. It is a graph which shows the relationship between pH and the adsorption rate of phosphorus when light burning dolomite (average particle diameter: 3 mm) is used as an adsorbent. It is a graph which shows the relationship between the contact time of the to-be-processed object with the adsorbent, and the adsorption rate of phosphorus.

Hereinafter, preferred embodiments of the present invention will be described in detail.
<< 1st Embodiment >>
Hereinafter, a first embodiment of a sludge treatment method and a sludge treatment system will be described.

  FIG. 1 is a diagram schematically showing a first embodiment of a sludge treatment system of the present invention. FIG. 2 is a process chart showing a first embodiment of the sludge treatment method of the present invention. In the following description, the lower side in FIG. 1 is referred to as “lower” or “lower”, and the upper side in FIG. 1 is referred to as “upper” or “upper”. The same applies to FIGS. 3, 4, 5, and 7, which will be described later.

  The method for treating sludge of the present invention includes a precipitation step of adding a precipitant 41 to a digestion liquid S of sludge to precipitate at least a part of a phosphorus component contained in the digestion liquid S, and a digestion sludge SS treated in the precipitation step. And a combustion step of burning.

  Further, the sludge treatment system 1 of the present invention includes a precipitation treatment section (sedimentation tank) 40 for adding a precipitation agent 41 to the digestion liquid S of the sludge to precipitate at least a part of the phosphorus component contained in the digestion liquid S, A combustion furnace 60 is provided for burning the digested liquid S processed in the precipitation processing section 40 and the digested sludge SS obtained from the residual sludge.

  According to the present invention, it is possible to provide a sludge treatment method and a sludge treatment system capable of reducing the amount of phosphorus component evaporated during combustion and suppressing an adverse effect on a combustion furnace.

  In particular, in the present invention, prior to the sludge (digested sludge SS) combustion step (combustion treatment in the combustion furnace 60), the phosphorus component contained in the sludge digestion liquid S is separated from the sludge (digestion sludge section 40). ) To reduce the concentration of the phosphorus component contained in the digestive juice S in a dissolved state.

  When the concentration of the phosphorus component contained in the digested juice S in a dissolved state is high, the phosphorus component evaporates due to combustion, and easily affects the furnace wall, the exhaust pipe, the heat exchange pipe, and the like of the combustion furnace 60. By precipitating the phosphorus component contained in the digestive juice S, the above-mentioned adverse effects can be suppressed. More specifically, by depositing the phosphorus component contained in the digestive juice S as a precipitate, the precipitate can be removed (recovered) out of the system by a method such as solid-liquid separation. Further, by making the phosphorus component a precipitate having a higher decomposition temperature and higher stability, the above-mentioned adverse effects can be suppressed even when the precipitate is not removed outside the system.

  The sludge that is the source of the material to be treated may be of any type as long as it contains a phosphorus component, and is discharged in large quantities with the treatment of sewage and night soil from households or the purification of factory wastewater. This is a concept that includes solid matter formed by agglomeration of organic final products, and includes mud-like waste that shows intermediate properties between solid and liquid.

Phosphorus is usually contained in the digestive fluid S, which is the object to be treated, in the form of phosphate ions, phosphates, oxides, and the like, which are the main forms. In this specification, a compound containing phosphorus (including an ionic substance) including these forms and a phosphorus atom contained in the compound may be simply referred to as phosphorus. Further, in the present specification, the phosphate, the phosphate ions (PO 4 ^_3-) and pyrophosphate ion (P 2 _O 7 ^_4-) of phosphoric acid such as polyphosphoric acid, such as anionic, cationic And a salt containing

  In the sludge treatment method of the present embodiment, in the digestion step of digesting the sludge S1, each of the methane fermentation treatment, the nitrification denitrification treatment, and the aerobic bacteria digestion treatment is performed.

  In the sludge treatment system according to the present embodiment, the digestion treatment unit 20 that digests the sludge S1 includes an anaerobic tank (a methane fermentation treatment unit) 21 that performs a methane fermentation treatment, and an oxygen-free tank (a nitrification denitrification treatment) that performs a nitrification denitrification treatment. A nitrification denitrification processing unit) 22 and an aerobic tank (aerobic bacteria digestion processing unit) 23 for performing aerobic bacteria digestion processing are provided.

  In the methane fermentation treatment (anaerobic tank 21), methane fermentation that mainly decomposes sludge S1 by anaerobic microorganisms is performed.

  In the nitrification denitrification treatment (anoxic tank 22), the ammoniacal nitrogen generated in the methane fermentation treatment (anaerobic tank 21) is converted into nitrate nitrogen and nitrite nitrogen by nitrification, and then changed to nitrogen gas by a reduction reaction. .

  In the aerobic bacterium digestion treatment (aerobic tank 23), the aerobic bacteria digest or dissolve the organic matter contained in the material to be treated (digestion liquor S in which digestion of sludge S1 has partially progressed). Phosphorus components contained in the state are taken into dephosphorus bacteria (aerobic bacteria).

  Further, the sludge treatment method of the present embodiment has a dehydration step of dehydrating the digested sludge SS and a drying step of drying at a timing after the digestion step and the precipitation step and before the combustion step. I have.

  And the sludge treatment system of this embodiment is a dehydration device 50 for dehydrating digested sludge SS, which is downstream of the digestion treatment section 20 and the precipitation treatment section 40 and upstream of the combustion furnace 60, and A drying device 70 for drying digested sludge SS dehydrated by the device 50 is provided.

  With such a configuration, the sludge treatment can be performed more efficiently, and the effects of the present invention can be more remarkably exhibited.

  Further, the sludge treatment system of the present invention is provided with a transfer means (not shown) for transferring sludge (sludge as a solid content and a liquid component such as digestion liquid) between the respective devices. You may.

  The sludge treatment method of the present invention can be suitably implemented using the sludge treatment system of the present invention.

<Digestion process (digestion processing section)>
[Methane fermentation treatment (anaerobic tank)]
First, in the methane fermentation treatment (anaerobic digestion treatment), in the anaerobic tank 21, the sludge S1, which is an organic waste, is decomposed by anaerobic microorganisms to reduce the volume while producing methane gas.

  It is preferable that the anaerobic tank 21 is provided with a fixed bed of microorganisms for holding the anaerobic microorganisms at a high concentration. For example, the fermenter can be filled with a microbial carrier (for example, a glass fibrous or carbon fiber microbial carrier) to form a fixed bed (not shown).

  The sludge S1 introduced into the anaerobic tank 21 is digested by anaerobic microorganisms and decomposed to methane gas.

  Further, the anaerobic tank 21 is preferably provided with a heat retaining device (not shown) for maintaining the sludge S1 at the activation temperature of the anaerobic microorganisms.

Thereby, the sludge S1 in the anaerobic tank 21 can be maintained at a fermentation temperature suitable for methane-producing microorganisms, for example, from a medium temperature range to a high temperature range (about 37 ° C. or more and about 55 ° C. or less), and methane production is performed more efficiently Can be.
The anaerobic tank 21 may be of a floating floor type instead of a fixed floor, for example.

  Organic substances such as organic acids contained in the sludge S1 are decomposed by the methane-producing anaerobic microorganisms to generate methane gas and carbon dioxide gas. The methane generated by the methane fermentation treatment can be collected and reused as an energy resource.

  And the sludge S1 (also the digestion liquid S) subjected to the methane fermentation treatment (anaerobic digestion treatment) contains an organic residue. Since the digestive juice S obtained through the methane fermentation treatment (anaerobic digestion treatment) contains a large amount of ammonia nitrogen and phosphorus, discharging the digestive juice as it is is regulated because it affects the environment. I have. Therefore, in the present embodiment, the phosphorus component is precipitated from the digestion liquid S by providing the precipitation treatment unit 40, and the content of the phosphorus component contained in the digested sludge SS to be incinerated in a form that easily affects the furnace In the case of incineration, it is possible to effectively prevent problems such as corrosion in the incinerator due to excessive evaporation of phosphorus components.

  The sludge S1 and digestion liquid S subjected to methane fermentation treatment in the anaerobic tank 21 are supplied to an oxygen-free tank 22, which is a nitrification and denitrification processing unit. In other words, the sludge (digestion liquid S) subjected to the methane fermentation treatment is thereafter subjected to the nitrification denitrification treatment.

[Nitrification denitrification treatment (oxygen-free tank)]
In the nitrification denitrification process, in the anoxic tank 22, ammonia nitrogen generated in the methane fermentation process is changed to nitrogen gas.

  In the illustrated configuration, the anoxic tank (nitrification and denitrification processing unit) 22 includes nitrate nitrogen and nitrite nitrogen contained in the digested liquid S (the liquid phase treated in the anaerobic tank 21), which is an object to be treated. 221 to reduce nitrogen to nitrogen by microbial (denitrifying bacteria) treatment, and nitrate nitrogen and nitrite nitrogen by microbial (nitrate, nitrite) treatment of ammoniacal nitrogen under aerobic conditions An aerobic part 222 is provided.

  First, in the anoxic part 221, nitric nitrogen and nitrite contained in the digestive juice S are changed to nitrogen gas by nitrifying bacteria (denitrifying bacteria) that prefer an anoxic state (denitrification treatment). Next, the digestive juice S is sent to the aerobic part 222. In the aerobic part 222, the ammoniacal nitrogen contained in the digestive juice S is changed into nitrate nitrogen and nitrite nitrogen by microorganisms (nitrite and nitrite). Next, the digestive juice S is sent to the oxygen-free part 221. Thus, the digestive juice S circulates internally between the anoxic part 221 and the aerobic part 222.

  This makes it possible to reduce the amounts of ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen contained in the digestive juice.

  In the illustrated configuration, one oxygen-free tank 22 and one aerobic tank 23 are provided, but a plurality of combinations of the oxygen-free tank 22 and the aerobic tank 23 may be provided. Further, the digestive fluid S may be configured to be repeatedly circulated in the same anoxic tank 22 and aerobic tank 23.

  In the anaerobic tank 21 and the anoxic tank 22, the phosphorus concentration in the digestive juice S increases because the phosphorus is removed.

[Aerobic bacteria digestion treatment (aerobic tank)]
In the aerobic bacterium digestion process, in the aerobic tank 23, the aerobic bacteria digest or remove the organic matter contained in the material to be treated (the digestion liquor S in which digestion of the sludge S1 has partially progressed). Phosphorus bacteria (a kind of aerobic bacteria) take in phosphorus components contained in a dissolved state.

  Thereby, for example, the content of the phosphorus component contained in the digested juice S in a dissolved state can be sufficiently reduced, so that the digested juice S after the main treatment can be treated as wastewater.

<Precipitation process (precipitation processing unit)>
The sludge S1 digested in the anaerobic tank 21 and the anoxic tank 22 is subjected to a dehydration treatment (solid-liquid separation) to separate it into digested sludge SS and digested liquid S.

  The digested sludge SS is subjected to a dehydration step and a combustion step, and the digested liquid S is subjected to a precipitation step in the precipitation processing unit 40.

  In the precipitation step, the digestion fluid S is brought into contact with the precipitant 41 in the precipitation processing unit 40 to precipitate at least a part of the phosphorus component contained in the digestion fluid S as a phosphate.

  In particular, in the present embodiment, the precipitation processing unit 40 is provided downstream of the anoxic tank 22 and upstream of the aerobic tank 23, and the deposition step includes nitrification denitrification processing and aerobic bacteria digestion processing. Perform at the timing between. That is, in the present embodiment, the precipitation step is performed during the digestion step.

  Thereby, the content of phosphorus contained in a dissolved state in the digestion liquid S supplied to the aerobic tank 23 (aerobic bacteria digestion treatment) can be sufficiently reduced, and finally supplied to the combustion furnace 60. The content of the phosphorus component contained in the digested sludge SS in a form that easily affects the furnace can be further reduced. As a result, at the time of incineration, it is possible to more effectively prevent problems such as corrosion in the combustion furnace 60 due to evaporation of excessive phosphorus components.

  In addition, by disposing the precipitation processing unit 40 upstream of the aerobic tank 23, the digested sludge SS (new bacteria) generated during the digestion treatment in the aerobic tank 23 contains a phosphorus component having a low decomposition temperature. Can be effectively prevented. That is, the concentration of phosphorus contained in newly generated digested sludge SS can be reduced.

  The precipitation processing unit 40 includes a precipitant adding means 42 for adding a precipitant 41 to the digestive juice S, and deposits a phosphorus component contained in the digestive juice S in a dissolved state as a phosphate.

As the precipitant adding means 42, for example, a hopper or the like can be used.
The precipitant adding means 42 may add the precipitant 41 as a solid or as a liquid (for example, an aqueous solution of the precipitant 41).

Further, as shown in the figure, the precipitation processing section 40 preferably includes a stirring means 43 for mixing the digestive juice S and the added precipitant 41.
Thereby, the digestive juice S and the precipitant 41 can be more efficiently contacted.

  A precipitation removing step of removing (recovering) at least a part of the phosphorus component (precipitate) precipitated by the addition of the precipitant 41 to the outside of the system at a timing before a combustion step described later in detail. Is also good.

  The precipitate removed (separated) in the precipitate removal step usually contains phosphate as a main component, has relatively high purity, and has a low impurity content. Therefore, the removed (separated) precipitate is in a form that can be easily used as a resource.

  In this way, by reusing the deposited phosphorus component (phosphate), the final amount of industrial waste can be reduced.

Precipitates can be suitably removed by solid-liquid separation.
Specific methods for removing precipitates include, for example, filtration, centrifugation, decantation, screw press, roller press, rotary drum screen, belt screen, vibrating screen, multi-plate vibration filter, vacuum dehydration, pressure dehydration, belt Examples of the method include press, centrifugal concentration dehydration, and multiple disk dehydration, and one or more selected from these methods can be used.

The precipitant 41 may have a function of accelerating the precipitation of phosphate or the like, and for example, calcium chloride (CaCl ₂ ), calcium hydroxide (Ca (OH) ₂ ), calcium carbonate (CaCO ₃ ), and the like. calcium-based material, magnesium chloride (MgCl _2), magnesium hydroxide (Mg _(OH) 2), magnesium-based material such as magnesium carbonate (MgCO _3), polyaluminum chloride _{([Al 2 (OH) n Cl 6} -n ] _{m (where} a 1 ≦ n ≦ 5, preferably satisfy the relation of m ≦ 10.)), aluminum sulfate, aluminum nitrate, aluminum-based material, ferric polysulfate such aluminum acetate, iron salts Can be used, but are selected from the group consisting of calcium-based, magnesium-based, and aluminum-based materials. At least one is preferably used that, it is more preferable to use calcium-based material.

  By using at least one selected from the group consisting of a calcium-based material, a magnesium-based material, and an aluminum-based material, a phosphate having a particularly high melting point can be formed. Even when a relatively large amount of precipitate is contained in the digested sludge SS after the precipitate removal step by simplifying the precipitate removal step, it is possible to effectively prevent the above-described problem from occurring. .

Above all, the above-mentioned calcium-based material is an ionic material, and can suitably function as the precipitant 41, and while efficiently supplying the calcium component that becomes a part of the phosphate to the system, the pH of the mixture is increased. Can be suitably adjusted. As a result, in this step, the usage of the precipitant 41 mixed with the digestive juice S can be suppressed, and this step can be efficiently advanced. Further, by using such a calcium-based precipitant (calcium-based substance), a relatively large precipitate can be easily formed. Therefore, the removal of the precipitate in the precipitate removal step is easy. In addition, by using such a calcium-based precipitant (calcium-based substance), a phosphate having a relatively high melting point (for example, Ca ₃ (PO ₄ ) ₂ (melting point 1670 ° C.), Ca ₂ P ₂ O ₇ (melting point: 1353 ° C.) can be suitably precipitated.

An example of a reaction formula when a calcium-based substance is used as the precipitant 41 will be described below.
CaCl ₂ + 2H ₃ PO ₄ → Ca (H ₂ PO ₄ ) ₂ + 2HCl
Ca (H ₂ PO ₄ ) ₂ → Ca (HPO ₄ ) + H ₃ PO ₄
2Ca (HPO ₄ ) → Ca ₂ P ₂ O ₇ + H2O
CaCl ₂ + H ₄ P ₂ O ₇ → Ca ₂ P ₂ O ₇ + 4HCl
Ca (OH) ₂ + 2H ₃ PO ₄ → Ca (H ₂ PO ₄ ) ₂ + 2H ₂ O
Ca (H ₂ PO ₄ ) → Ca (HPO ₄ ) + H ₃ PO ₄
2Ca (HPO ₄ ) → Ca ₂ P ₂ O ₇ + H ₂ O
CaCO ₃ + H ₂ O → Ca (OH) ₂ + CO ₂
Ca (OH) ₂ + 2H ₃ PO ₄ → Ca (H ₂ PO ₄ ) ₂ + 2H ₂ O
Ca (H ₂ PO ₄ ) → Ca (HPO ₄ ) + H ₃ PO ₄
2Ca (HPO ₄ ) → Ca ₂ P ₂ O ₇ + H ₂ O

  In particular, the precipitant 41 is preferably at least one selected from the group consisting of calcium chloride, calcium hydroxide, and calcium carbonate, and calcium chloride is preferable.

  Thereby, the above-described effects are more remarkably exhibited. In particular, calcium chloride has high solubility in water, and the precipitation reaction proceeds more quickly, so that this step can be performed more efficiently. Further, calcium chloride can be easily and stably obtained, and is relatively inexpensive as compared with other precipitants. This is advantageous from the viewpoint of reduction of sludge treatment cost and stable treatment.

Note that in this specification, a calcium salt of phosphoric acid means calcium ion (Ca ²⁺ ) and a phosphate-based anion (phosphate ion (PO ₄ ³⁻ ) or pyrophosphate ion (P ₂ O ₇ ⁴ )). ^- ) And the like.

Examples of such calcium salts of phosphoric acid include Ca ₂ P ₂ O ₇ , Ca ₃ (PO ₄ ) ₂ , tricalcium phosphate (Ca (H ₂ PO ₄ ) ₂ ), and anhydrous calcium hydrogen phosphate (CaHPO). ₄ ), hydroxyapatite (HAP) (Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ ), and hydrates thereof.

  In this step, two or more substances may be used in combination as the precipitant 41.

  Thereby, for example, it is possible to further increase the precipitation rate of the phosphate contained in the digestive juice S while suppressing the amount of the precipitation agent 41 used. Further, for example, the precipitate deposited in the precipitation step can be grown larger, and the removal of the precipitate in the precipitate removal step becomes easier. Further, by adjusting the composition of the precipitated phosphate as a whole, it is possible to more effectively prevent the adverse effect on the combustion furnace 60 and the like.

  When two or more substances are used in combination as the precipitant 41, these plural substances may be added, for example, as a mixture, or substances having different compositions may be applied at different timings.

  For example, a calcium-based material and an aluminum-based material may be used in combination as the precipitant 41.

  Thereby, the precipitation rate of the phosphate contained in the digestive juice S can be further increased while the amount of the precipitation agent 41 used is suppressed. Further, the precipitates deposited in the precipitation step can be grown larger, and the removal of the precipitates in the precipitate removal step can be further facilitated. Further, the thermal stability of the precipitates can be further improved, and even if the precipitate removal step is omitted, adverse effects on the combustion furnace 60 and the like can be more effectively prevented. Further, by omitting the deposit removal step, the sludge treatment efficiency can be further improved.

When a calcium-based material and an aluminum-based material are used in combination, the aluminum-based material is preferably at least one selected from the group consisting of polyaluminum chloride and an aluminum salt.
Thereby, the above-mentioned effects are more remarkably exhibited.

In this step, when a calcium-based material and an aluminum-based material are used in combination as the precipitant 41, it is preferable that the following conditions be satisfied. That is, when the amount of calcium contained in the precipitant 41 used in this step is X _Ca [mol] and the amount of aluminum is X _Al [mol], 1.0 ≦ X _Ca / X _Al ≦ 4. 0, more preferably 1.3 ≦ X _Ca / X _P ≦ 3.0, more preferably 1.5 ≦ X _Ca / X _Al ≦ 2.5. More preferably,
Thereby, the above-mentioned effects are more remarkably exhibited.

The composition of the precipitate depends on the composition of the precipitant 41.
For example, when a calcium-based substance is used as the precipitant 41, the precipitate contains calcium-based salts such as Ca ₃ (PO ₄ ) ₂ , Ca (H ₂ PO ₄ ) ₂ , and CaHPO ₄ .

When an aluminum-based material is used as the precipitant 41, the precipitate contains an aluminum-based salt such as AlPO ₄ .

When an iron-based substance is used as the precipitant 41, the precipitate contains an iron-based salt such as FePO ₄ or Fe ₃ (PO ₄ ) ₂ .

  The pH of the mixture containing the digestive juice S and the precipitant 41 in this step (the pH at the end of this step) is preferably 3 or more and 13 or less, more preferably 5 or more and 10 or less.

  This makes it possible to more efficiently precipitate the solid phosphate, and more effectively prevent the deposited salt from being redissolved.

  The treatment temperature in this step is not particularly limited, but is preferably 0 ° C or more and 90 ° C or less, more preferably 10 ° C or more and 80 ° C or less, and even more preferably 15 ° C or more and 60 ° C or less.

  Thereby, the phosphate can be efficiently precipitated by the precipitant 41, and the present step can be efficiently performed in a short time.

  At the end of the present step (precipitation step), the removal rate of phosphorus as a dissolved component contained in the digestive juice S (the removal rate of phosphorus from the digestive juice S, which is an object to be treated without any treatment, The value converted to P. The precipitation rate is not particularly limited, and varies depending on the situation in the combustion furnace 60, but is preferably 10% by mass or more and 98% by mass or less, and is preferably 50% by mass or more and 90% by mass or less. More preferably, there is.

  Thereby, the effect of the present invention is more remarkably exhibited, and the adverse effect on the combustion furnace 60 and the like can be more effectively suppressed.

  On the other hand, if the removal rate of phosphorus as a dissolved component is too low, the effects of the present invention as described above may not be sufficiently exhibited.

  On the other hand, even if the removal rate of phosphorus as a dissolved component is unnecessarily increased, the degree of adverse effects on incinerators and the like hardly changes, causing problems such as an increase in the amount of the precipitant 41 used, and sludge treatment. It is not preferable from the viewpoint of efficiency, cost, and the like.

  The digestion liquid S subjected to the precipitation treatment in the precipitation treatment unit 40 is supplied to the aerobic tank (aerobic bacteria digestion treatment unit) 23 of the digestion treatment unit 20, where the aerobic bacteria digestion treatment by the aerobic bacteria as described above is performed. A dephosphorization treatment by a dephosphorus bacterium is performed.

<Dehydration process (dehydrator)>
After the digestion treatment and the precipitation treatment, the digested sludge SS containing the digested liquid S that has been treated is supplied to the dehydration device 50.

  In the dehydration step, the dewatering device 50 performs a dehydration treatment on the digested sludge SS to lower the water content of the digested sludge SS.

  Thereby, the combustion process can be performed more efficiently without lowering the combustion temperature in the combustion furnace 60.

  As the dewatering device 50, for example, a dewatering device such as a belt press dewatering device, a centrifugal dewatering device, and a filter press can be used.

  Here, most of the phosphorus contained in the original digestive juice S has been converted to a phosphate having a higher decomposition temperature and a higher stability through the precipitation step (precipitation treatment section 40). The amount of phosphorus taken into the dephosphorus bacteria (a kind of aerobic bacteria) in the aerobic tank (aerobic bacteria digestion treatment) is relatively small, and is generated in the aerobic tank 23. Digested sludge SS (excess sludge) also has a low content of phosphorus components evaporated during combustion.

  The dewatered digested sludge SS may be further subjected to a drying treatment using a heating dryer or the like.

  As the heating dryer, for example, a dryer such as a hot air dryer, a belt dryer, or a kiln dryer can be employed.

  Thereby, the water content of the digested sludge SS can be further reduced, and the combustion step can be performed more efficiently.

  The digested sludge SS dehydrated by the dehydrator 50 is supplied to the combustion furnace 60. In other words, the digested sludge SS that has been subjected to the dehydration step is thereafter subjected to the combustion step.

<Combustion process (combustion furnace)>
In the combustion step, the digested sludge SS subjected to the above-described treatment is burned in the combustion furnace 60.

  At this time, if the digested sludge SS has a low moisture content due to the dehydration treatment, the present process can be performed more efficiently while preventing the undesired decrease in the combustion temperature more effectively. Also, the control of the combustion temperature becomes easy.

  As the combustion furnace 60, for example, a fluidized bed combustion furnace, a rotary combustion furnace, a fixed bed combustion furnace, a stalker type combustion furnace, a gasification and melting furnace, and the like can be used.

  The combustion furnace 60 is preferably a fluidized bed combustion furnace having a fluidized medium layer made of a high-temperature fluidized medium (sand) 61. By injecting the digested sludge SS into the high-temperature fluidized medium (sand) 61, the digested sludge SS can be uniformly burned in a shorter time by utilizing the calorie of the flowing sand.

  In the example shown in FIG. 1, a combustion furnace 60 as a fluidized bed combustion furnace has a cylindrical shape extending in a vertical direction, and the inside thereof is partitioned by a dispersion plate 62 that allows upward movement of gas. The lower side of the dispersion plate 62 is a gas supply unit 63. Above the dispersion plate 62, there is a fluidized medium layer made of sand, which is the fluidized medium 61. The gas supply unit 63 can send a high-temperature gas supplied from the outside to the upper fluidized medium layer via the dispersion plate 62. The fluidized medium layer is caused to flow by the gas supplied from the gas supply unit 63.

  Then, by injecting the digested sludge SS into the high-temperature fluidized medium 61, the digested sludge SS can be burned evenly in a shorter time by using the calorific value of the fluidized sand.

  In the combustion step, the furnace temperature during combustion (maximum furnace temperature) is preferably 500 ° C or more and 1500 ° C or less, more preferably 550 ° C or more and 900 ° C or less.

  Thus, the present process can be efficiently performed in a short time while reducing the amount of energy required for the combustion process. Further, adverse effects on the combustion furnace 60 and the like can be more effectively prevented.

  The processing time (combustion time at 500 ° C. or higher) of this step is preferably 1 minute to 120 minutes, more preferably 5 minutes to 30 minutes.

Thus, the present process can be performed efficiently while reducing the cost required for the combustion treatment.
The digested sludge SS burned in this step becomes combustion ash, which is a processing product.

<< 2nd Embodiment >>
FIG. 3 is a diagram schematically showing a second embodiment of the sludge treatment system of the present invention.

  Hereinafter, a second embodiment of the sludge treatment method and the sludge treatment system of the present invention will be described with reference to this drawing, but the description will be focused on the differences from the above-described embodiment, and the same items will be described. Is omitted.

  This embodiment is the same as the first embodiment except that the relationship between the digestion step (digestion processing unit 20) and the precipitation step (precipitation processing unit 40) is different.

  More specifically, in the embodiment described above, the precipitation processing unit 40 is provided downstream of the anaerobic tank 21 and the anoxic tank 22 that constitute the digestion processing unit 20, and the anaerobic digestion processing and the nitrification denitrification processing are performed. After that, the precipitation treatment is performed. However, in the present embodiment, the anaerobic tank 21 and the oxygen-free tank 22 are provided with the precipitating agent adding means 42 and the stirring means 43, respectively. It is configured to perform a precipitation treatment during methane fermentation treatment and during anoxic treatment (nitrification denitrification treatment). In other words, the anaerobic tank 21 and the oxygen-free tank 22 are configured to also function as a precipitation processing unit.

  With such a configuration, the digestion treatment and the precipitation treatment can be performed more efficiently, and the efficiency of the entire sludge treatment method can be further improved.

  In the illustrated configuration, the precipitation treatment is performed in both the anaerobic tank 21 and the oxygen-free tank 22, but the precipitation treatment may be performed in only one of them.

<< 3rd Embodiment >>
FIG. 4 is a diagram schematically showing a third embodiment of the sludge treatment system of the present invention. FIG. 5 is a diagram schematically illustrating an example of an adsorption processing unit included in the processing system illustrated in FIG. FIG. 6 is a process chart showing a third embodiment of the sludge treatment method of the present invention.

  Hereinafter, a sludge treatment method and a sludge treatment system according to a third embodiment of the present invention will be described with reference to these drawings. However, differences from the above-described embodiment will be mainly described, and similar items will be described. Description is omitted.

  This embodiment is the same as the first embodiment, except that the present embodiment further includes an adsorption step (adsorption processing unit 30) in addition to the above-described steps (configuration).

  More specifically, in the present embodiment, the adsorption processing unit 30 is provided downstream of the anaerobic tank 21 and the anoxic tank 22 constituting the digestion processing unit 20 and upstream of the precipitation processing unit 40. And an adsorption step is performed prior to the deposition step.

  With such a configuration, the content of the phosphorus component in the digested sludge SS supplied to the combustion step (combustion furnace 60) can be further reduced. As a result, the amount of the phosphorus component evaporated during combustion can be further reduced, and the adverse effect on the combustion furnace can be more effectively suppressed.

<Adsorption process (adsorption processing unit)>
In the adsorption step, the digestion liquid S is brought into contact with the adsorbent 36 in the adsorption processing section 30, and at least a part of the phosphorus component contained in the digestion liquid S is adsorbed on the adsorbent 36 and reacted with the adsorbent component. Precipitated and removed as calcium phosphate or magnesium phosphate.

  In particular, in the present embodiment, the adsorption processing unit 30 is provided on the downstream side of the anoxic tank 22 and on the upstream side of the aerobic tank 23, and the adsorption step includes nitrification denitrification processing and aerobic bacteria digestion processing. Perform at the timing between. That is, in the present embodiment, the adsorption step is performed during the digestion step.

  This makes it possible to lower the phosphorus content in the digestion liquid S supplied to the aerobic tank 23 (aerobic bacteria digestion treatment). The content of phosphorus contained can be made lower. As a result, at the time of incineration, it is possible to more effectively prevent problems such as corrosion in the combustion furnace 60 due to evaporation of excessive phosphorus components.

The adsorbent 36 may be any as long as it can adsorb the phosphorus component in the digestive juice S. Examples of the adsorbent 36 include dolomite, calcium hydroxide (Ca (OH) ₂ ), and calcium carbonate (CaCO ₃ ). One or more selected ones can be used in combination.
Among them, in the adsorption step, it is preferable to use dolomite as the adsorbent 36.

  Thereby, the phosphorus component contained in the digestive juice S can be efficiently adsorbed to dolomite. In addition, heavy metals contained in the digestive juice S can be efficiently removed together with the phosphorus component.

  The dolomites used in this step include dolomite, hydroxylated dolomite (digested dolomite, including dolomite plaster), lightly burned dolomite, dolomite clinker, and the like, and one or more selected from these are used in combination. be able to.

  Above all, by using hydroxide dolomite, the phosphorus component contained in the digestive juice S can be more efficiently adsorbed to dolomite. Further, heavy metals contained in the digestive juice S can be removed more efficiently.

  Further, by using dolomite, the range of choice of dolomite as the adsorbent 36 is expanded, and conditions such as the particle size and pore diameter of the dolomite can be adjusted to optimal conditions. Further, since the adsorbent 36 is cheaper, it is advantageous from the viewpoint of further reducing the sludge treatment cost.

The adsorbent 36 used in this step is usually porous.
Accordingly, the surface area per unit mass (unit volume) of the adsorbent 36 can be increased, and the phosphorus component removal efficiency can be further improved.

  The average pore diameter of the adsorbent 36 (particularly, dolomite) is not particularly limited, but is preferably 1 nm or more and 100 μm or less, more preferably 2 nm or more and 100 μm or less, and further preferably 50 nm or more and 30 μm or less. preferable.

  This makes it possible to further improve the efficiency of adsorbing the phosphorus component by the adsorbent 36 while ensuring the durability of the adsorbent 36. Further, heavy metals contained in the digestive juice S can be removed more efficiently.

The BET specific surface area of the adsorbent 36 (particularly, dolomite) is not particularly limited, but is preferably 10 m ² / g or more, and more preferably 40 m ² / g or more and 1000 m ² / g or less.

  Thereby, the adsorption efficiency of the phosphorus component by the adsorbent 36 can be further improved. Further, heavy metals contained in the digestive juice S can also be removed more efficiently.

  The shape and size of the adsorbent 36 (particularly, dolomites) are not particularly limited, but when the adsorbent 36 is in the form of particles, the average particle size is preferably 3 μm or more and 200 mm or less, and 100 μm or more. It is more preferably 100 mm or less, and still more preferably 1 mm or more and 50 mm or less.

  Thus, the particle surface area per unit mass (unit volume) of the adsorbent 36 can be increased, the phosphorus component can be uniformly adsorbed on the adsorbent 36, and the particulate adsorbent 36 undesirably aggregates. Is effectively prevented, and the fluidity of the adsorbent 36 and the ease of handling are improved. Further, the filling property (ease of filling, followability to the shape of the vessel) of the vessel (for example, the column 35) can be improved.

  It is sufficient that at least a part of the phosphorus component adsorbed by the adsorbent 36 in the adsorption step is contained in the digestive juice S in a dissolved state.

  Examples of the phosphorus component adsorbed by the adsorbent 36 in this step include phosphate ions and salts thereof (for example, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, trisodium phosphate, hydrogen phosphate). Disodium, sodium dihydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, calcium dihydrogen phosphate, etc.), phosphorous acid and its salts, peroxomonophosphate and its salts, phosphon Acids and salts thereof, phosphinic acids and salts thereof, phosphorus oxides such as diphosphorus pentoxide, phosphorus halides such as phosphorus pentachloride, phosphoryl halides such as phosphoryl chloride, calcium monophosphate, calcium diphosphate And the like.

  The pH of the mixture containing the digestive juice S and the adsorbent 36 in this step (the pH at the end of this step) is preferably 3 or more and 13 or less, more preferably 5 or more and 10 or less.

  Thereby, the phosphorus component can be adsorbed efficiently by the adsorbent 36, and this step can be performed more efficiently.

Hereinafter, the adsorption processing unit 30 will be described in detail.
As shown in FIG. 5, the adsorption processing unit 30 connects the processing tank 31 containing the digestive juice S, a column (container) 35 filled with the adsorbent 36, and the processing tank 31 and the lower part of the column 35. The first pipe 32 for supplying the digestion liquid S from the processing tank 31 to the column 35 and the upper part of the column 35 and the processing tank 31 are connected to each other. And a second pipe 33 returning to the processing tank 31.

  In the illustrated configuration, the digestion liquid S is supplied to the column 35 from the lower part of the processing tank 31 through the first pipe 32. In addition, the digestion liquid S may be configured to be supplied to the column 35 from above the processing tank 31.

  When the digestive fluid S is passed through the column 35, it is preferable to pass the digestive fluid S from the lower side of the column 35 to the upper side as shown.

  Thereby, the digestive juice S can be spread throughout the column 35, and the adsorbent 36 filled in the column 35 and the digestive juice S are brought into more efficient contact with each other to reduce the phosphorus component contained in the digestive juice S. The adsorbent 36 can be efficiently adsorbed. In particular, when dolomite is used as the adsorbent 36, the phosphorus component can be efficiently adsorbed to the dolomite even in the pores of the dolomite.

  The digested liquid S that has passed through the column 35 is returned from the upper part of the column 35 to the processing tank 31 through the second pipe 33.

  Due to the adsorption effect of the adsorbent 36, the digestive juice S after passing through the column 35 has a lower phosphorus concentration than the digestive juice S before passing through the column 35.

  Further, by circulating the digestive liquid S between the treatment tank 31 and the column 35, the adsorption process is repeatedly performed, and the phosphorus component can be adsorbed on the adsorbent 36 more efficiently.

  Passing the digestive juice S through the column 35 filled with the adsorbent 36 facilitates separation of the digestive juice S from the adsorbent 36 after contact with the adsorbent 36.

  Further, by making the column 35 a detachable cartridge, the replacement of the adsorbent 36 can be easily performed. Further, the adsorbent 36 that has adsorbed the phosphorus component can be easily collected.

  Note that the digestive juice S may contain a large amount of solids (impurities), and if the digestive juice S is passed through the column 35 as it is, the solids may cause the column 35 to be clogged.

  Therefore, it is preferable to remove relatively large solids (contaminants) from the digested liquid S supplied to the column 35 to such an extent that the column 35 is not clogged. For example, as shown in FIG. 5, it is preferable to arrange a foreign matter removing means 34 such as a filter, a screen, a trommel, and a vortex type water separation tank (swirl water separation tank) at the entrance of the first pipe 32 or in the middle thereof. preferable.

  Thereby, the digestive juice S and the adsorbent 36 can be more stably contacted for a long period of time while effectively preventing the column 35 from being clogged. Further, the frequency of maintenance of the processing system 1 (including the replacement of the adsorbent 36) can be reduced, and the efficiency of the processing of the digestive juice S can be further improved.

  The processing time of this step (the time for which the digestive liquid S enters the column 35 and contacts the adsorbent 36, ie, the residence time) is not particularly limited, but is preferably 1 minute or more and 1 day or less, and is preferably 10 minutes or more and 3 minutes or less. More preferably, the time is not more than the time.

  Thus, the efficiency of adsorbing the phosphorus component by the adsorbent 36 can be further improved while effectively preventing the processing efficiency of the digestive juice S from decreasing.

  The treatment temperature in this step is not particularly limited, but is preferably 0 ° C or more and 90 ° C or less, more preferably 10 ° C or more and 80 ° C or less, and even more preferably 15 ° C or more and 60 ° C or less.

  Thus, the phosphorus component can be efficiently adsorbed by the adsorbent 36, and the present step can be efficiently performed in a short time.

  At the end of this step (adsorption step), the removal rate of phosphorus as a dissolved component contained in digestive juice S (the removal rate of phosphorus from digestive juice S, which is an object to be treated without any treatment, The value converted into P) is not particularly limited, and varies depending on the situation in the combustion furnace 60, but is preferably 10% by mass or more and 98% by mass or less, more preferably 50% by mass or more and 90% by mass or less. preferable.

  Thereby, the effect of performing the adsorption step is more remarkably exhibited, and the adverse effect on the combustion furnace 60 and the like can be more effectively suppressed.

  On the other hand, if the removal rate of phosphorus as a dissolved component is too low, the effect of performing the above-described adsorption step may not be sufficiently exerted.

  On the other hand, even if the removal rate of phosphorus as a dissolved component is increased more than necessary, the degree of adverse effects on incinerators and the like hardly changes, the amount of the adsorbent 36 used increases, and the time required for the adsorption step is longer than necessary. This causes problems such as an increase in the length of the digestive juice S, which is not preferable from the viewpoints of the processing efficiency and cost of the digestive juice S.

  In the present embodiment, the digestion liquid S subjected to the adsorption step is supplied to the precipitation processing unit 40, and is subjected to the above-described precipitation processing.

<< 4th Embodiment >>
FIG. 7 is a diagram schematically showing a fourth embodiment of the sludge treatment system of the present invention. FIG. 8 is a diagram schematically illustrating a relationship between an adsorption processing unit and an anaerobic tank included in the processing system illustrated in FIG. 7.

  Hereinafter, a sludge treatment method and a sludge treatment system according to a fourth embodiment of the present invention will be described with reference to these drawings. However, differences from the above-described embodiment will be mainly described, and similar items will be described. Description is omitted.

  This embodiment is the same as the third embodiment except that the relationship between the digestion step (digestion processing unit 20) and the adsorption step (adsorption processing unit 30) is different.

  More specifically, in the third embodiment described above, the adsorption processing unit 30 is provided downstream of the anaerobic tank 21 and the anaerobic tank 22 constituting the digestion processing unit 20, and the anaerobic digestion processing and nitrification Although the adsorption treatment is performed after the nitrogen treatment, in the present embodiment, the adsorption treatment part 30 ′ is provided in each of the anaerobic tank 21 and the anoxic tank 22, and the anaerobic treatment (the methane fermentation treatment) is performed. ) And during the oxygen-free treatment (nitrification denitrification treatment).

  The adsorption processing section 30 'includes a column (container) 35, an adsorbent 36, a first pipe 32, a second pipe 33, and impurity removing means 34 similar to those described in the first embodiment. .

  With such a configuration, the digestion treatment and the adsorption treatment can be performed more efficiently, and the efficiency of the entire sludge treatment method can be further improved.

  Although the adsorption processing unit 30 'is provided in both the anaerobic tank 21 and the anoxic tank 22 in the configuration shown in the figure, it may be provided in only one of them.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited thereto.

  For example, the sludge treatment method of the present invention may include steps other than the above-described steps (for example, a pretreatment step, an intermediate treatment step, a post-treatment step, and the like).

  Further, for example, the sludge treatment system of the present invention may have a configuration other than the above-described configuration (for example, a pretreatment device, an intermediate treatment device, a post-treatment device, and the like).

  Further, in the above-described embodiment, the configuration in which the precipitation processing unit is provided on the downstream side of the oxygen-free tank and on the upstream side of the aerobic tank, and at least one of the anaerobic tank and the oxygen-free tank is also a precipitation processing unit. Although the functioning configuration (the configuration in which the precipitant is added to at least one of the anaerobic tank and the oxygen-free tank) has been described, for example, at least one of the anaerobic tank and the oxygen-free tank (if only one is used, The tank is more effective), a precipitation treatment section is provided, a digestion solution separated by a solid-liquid separation membrane is introduced into the precipitation treatment section, and a precipitation agent is added in the precipitation treatment section. Good. In this case, the digestion liquid processed in the precipitation processing unit may be configured to be returned to the anaerobic tank and the anoxic tank. In particular, in this case, it is preferable to separate and collect the precipitate deposited from the digested solution that has been treated, and return the digested solution from which the precipitate has been removed to the anaerobic tank and the oxygen-free tank. Further, the digestion solution may be circulated between the anaerobic tank, the oxygen-free tank and the precipitation treatment section to repeatedly perform the precipitation treatment.

  Further, in the above-described embodiment, the case where the treatment with the aerobic bacterium is performed after the precipitation treatment is representatively described, but the treatment with the aerobic bacterium may be omitted. More specifically, for example, when phosphorus can be sufficiently precipitated by the precipitation treatment, the treatment with aerobic bacteria may be omitted.

  In addition, in the case where the adsorption step is performed in addition to the precipitation step, in the above-described embodiments (the third and fourth embodiments), the case where the adsorption step is performed before the deposition step has been described. A step may be performed.

  In addition, in the case where the adsorption step is performed in addition to the precipitation step, in the above-described embodiments (the third and fourth embodiments), the case where the configuration of the precipitation processing unit is the same as that of the first embodiment has been described. The configuration of the precipitation processing unit may be the same as in the second embodiment.

  Hereinafter, the present invention will be described in detail with reference to specific examples, but the present invention is not limited thereto.

<< 1 >> Relationship between amount of precipitant and phosphorus deposition rate (Experimental example 1)
Phosphoric acid was dissolved in water to prepare a phosphoric acid solution. For comparison, 10 g of ash was added to 200 mL of a 1N hydrochloric acid solution (aqueous hydrogen chloride solution), the phosphorus component was completely dissolved at 80 ° C., and a phosphoric acid solution separated from the residue was also prepared. Next, a 1N sodium hydroxide solution was added while stirring 200 mL of the solution in which the phosphorus component was dissolved, and the pH conditions in the anaerobic digestion tank and digestion denitrification tank were adjusted to pH8. The deposition rate of calcium phosphate was examined while changing the amount of calcium chloride (precipitating agent) to the ratio of phosphorus to calcium (P / Ca).

  After the addition of calcium chloride (precipitating agent) to the phosphorus solution, the mixture was further stirred for 60 minutes, and then the precipitated calcium phosphate was filtered off.

  With respect to the obtained filtrate (liquid), the concentration of the phosphorus component contained in the liquid was determined by the molybdenum blue method, and from the result, the deposition rate of the phosphorus component by the precipitant was determined.

The measurement was performed in the same manner as described above, except that the amount of the precipitant used was variously changed, and the deposition rate of the phosphorus component by the precipitant was determined.
The result of this experiment is shown in FIG.

(Experimental example 2)
Except that calcium hydroxide was used instead of calcium chloride as the precipitant, the deposition rate of the phosphorus component by the precipitant was determined in the same manner as in Experimental Example 1.
FIG. 10 shows the results of this experiment.

(Experimental example 3)
Except for using magnesium chloride instead of calcium chloride as the precipitant, the deposition rate of the phosphorus component by the precipitant was determined in the same manner as in Experimental Example 1.
FIG. 11 shows the results of this experiment.

(Experimental example 4)
Phosphoric acid was completely dissolved in water to prepare a phosphoric acid aqueous solution. Next, a 1N sodium hydroxide solution was added to this solution, and the pH was adjusted to 8 so as to be the same as the pH conditions in the anaerobic digestion treatment tank and digestion denitrification treatment tank. While changing the amount of polyaluminum chloride (precipitating agent), the deposition rate was examined as aluminum phosphate. At that time, the stirring time was fixed at 60 minutes. Thereafter, the precipitated aluminum phosphate was separated by filtration, and the concentration of the phosphorus component contained in the obtained filtrate (liquid) was determined by the molybdenum blue method. From the result, the precipitation of the phosphorus component by polyaluminum chloride was determined. The rate was determined. FIG. 12 shows the result of this experiment.

  As is clear from FIGS. 9 to 12, by contacting the sludge with the precipitant, the phosphorus component in the digested liquid of the sludge is efficiently precipitated by precipitation, and the phosphorus content as the dissolved component is effectively reduced. It can be seen that it can be reduced. Further, in any of the precipitants, as the amount of the precipitant increased, the phosphorus removal rate (precipitation rate) increased.

  As a precipitant, instead of calcium chloride, except that a mixture of calcium hydroxide, calcium carbonate, calcium chloride and polyaluminum chloride was used, the same treatment as in the above experimental example was performed. , The precipitation of the phosphorus component was confirmed.

  As is clear from the above experiment, by contacting the phosphorus ions contained in the digestion fluid with the precipitant, the phosphorus component in the sludge digestion fluid is efficiently precipitated, and the phosphorus content as the dissolved component is effectively reduced. It can be seen that it can be reduced. It was also confirmed that the deposition rate of the phosphorus component depends on the amounts of the phosphorus component and the additive (P / additive ratio).

<< 2 >> Relationship between combustion temperature and phosphorus evaporation First, phosphorus-free digested sludge was prepared.

  Thereafter, the digested sludge was dewatered and dried, and the concentration of the phosphorus component was determined for a part of the sludge in the same manner as described above. A part of the remaining dewatered and dried digested sludge was completely burned in an air atmosphere. At that time, the furnace temperature was 600 ° C. About the obtained combustion ash, the density | concentration of the phosphorus component was calculated | required similarly to the above. From these results, the amount of phosphorus component contained in the sludge ash was determined. Further, the amount of reduction of the phosphorus component by combustion was determined.

In addition, the digested sludge was burned in the same manner as described above, except that the furnace temperature was variously changed, and the amount of reduction of the phosphorus component due to the burning was determined.
FIG. 13 shows the results of this experiment.

  As is clear from FIG. 13, the phosphorus content in the sludge ash was reduced from 30% to 21% by adding a precipitant to the digested liquid of the sludge. In addition, it can be seen that the increase in the furnace temperature during the combustion of the digested sludge lowers the phosphorus content transferred to the combustion ash, and that the phosphorus component evaporates in the combustion process. In particular, it can be seen that the higher the combustion temperature, the lower the phosphorus content of the combustion ash, and thus the higher the evaporation of the phosphorus component.

  From the above results, by adding the precipitating agent to the digestive fluid of sludge, the phosphorus component contained as a dissolved component in the digestive fluid of sludge can be precipitated by the precipitant, the dissolved component in the digestive fluid It has been found that the content of the phosphorus component contained in the steel can be effectively reduced.

  Further, it is presumed that the adverse effect on the combustion furnace can be reduced by lowering the temperature of the combustion furnace during combustion.

<< 3 >> Relationship between amount of adsorbent and phosphorus removal rate (Experimental example 5)
To conduct an experiment in which a phosphorus component is adsorbed on the surface of the adsorbent, reacts with a component or a part of the adsorbent, and precipitates as a substance having a high thermal decomposition temperature (calcium phosphate, magnesium phosphate), first, 0.5N hydrochloric acid is used. Was prepared.

  Next, 200 mL of the hydrochloric acid was fractionated, and 10 g of sludge ash having a phosphorus content of 30% by mass was added thereto to completely dissolve the phosphorus component.

Next, 100 mL was taken out from hydrochloric acid in which the phosphorus component was dissolved, and 0.3 g of a rough dolomite ore (average particle size: 1 mm) was added thereto, followed by stirring for 30 minutes.
After the completion of the stirring, the adsorbent (raw dolomite) was separated by filtration.

  For the obtained filtrate (liquid), the concentration of the phosphorus component contained in the liquid was determined by the molybdenum blue method, and from the result, the adsorption rate of the phosphorus component by the adsorbent (raw dolomite ore) was determined.

In addition, measurement was performed in the same manner as described above except that the amount of the adsorbent (raw dolomite) used was changed, and the adsorption rate of the phosphorus component by the adsorbent (raw dolomite) was determined.
FIG. 14 shows the results of this experiment.

(Experimental example 6)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 5 except that dolomite hydroxide having an average particle diameter of 1 mm was used instead of the raw dolomite having an average particle diameter of 1 mm as the adsorbent. .
FIG. 15 shows the results of this experiment.

(Experimental example 7)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 5 except that lightly burnt dolomite having an average particle diameter of 1 mm was used instead of the raw dolomite having an average particle diameter of 1 mm as the adsorbent. .
FIG. 16 shows the results of this experiment.

(Experimental example 8)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 5 except that lightly-burned dolomite having an average particle diameter of 3 mm was used instead of the raw dolomite having an average particle diameter of 1 mm as the adsorbent. .
FIG. 17 shows the results of this experiment.

  As is clear from FIGS. 14 to 17, it can be seen that the phosphorous component in the sludge can be efficiently removed by bringing the sludge into contact with the adsorbent (particularly dolomite).

  Further, in any of the adsorbents, as the amount of the adsorbent increases, the removal rate of phosphorus increases. Particularly, in Experimental Examples 6 to 8 using dolomite hydroxide and lightly burned dolomite as the adsorbent, 1 g of the adsorbent is used. As a result, phosphorus was removed at a rate of almost 100%.

<< 4 >> Relationship between pH and phosphorus removal rate (Example 9)
Hydrochloric acid or sodium hydroxide is added dropwise to a solution containing phosphorus (digestion fluid) equivalent to digestion fluid during anaerobic treatment (methane fermentation treatment) and anoxic treatment (nitrification denitrification treatment) using anaerobic microorganisms and prescribed Was adjusted to pH.

A 100 mL portion of the digested solution whose pH was adjusted in this way was collected, and a predetermined amount of granular dolomite ore (average particle size: 1 mm) was added thereto, followed by stirring for 30 minutes.
After the completion of the stirring, the adsorbent (raw dolomite) was separated by filtration.

  For the obtained filtrate (liquid), the concentration of the phosphorus component contained in the liquid was determined by the molybdenum blue method, and from the result, the adsorption rate of the phosphorus component by the adsorbent (raw dolomite ore) was determined. Note that 80% by mass or more of the phosphorus component in the liquid was phosphoric acid or a salt thereof.

In addition, the measurement was performed in the same manner as described above except that the pH of the digestive juice used for the measurement was variously changed, and the adsorption rate of the phosphorus component by the adsorbent (2 g of raw dolomite) was determined.
FIG. 18 shows the results of this experiment.

(Experimental example 10)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 9 except that dolomite hydroxide having an average particle diameter of 1 mm was used instead of the raw dolomite having an average particle diameter of 1 mm as the adsorbent. .
FIG. 19 shows the results of this experiment.

(Experimental example 11)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 9 except that lightly burnt dolomite having an average particle diameter of 1 mm was used instead of the raw dolomite having an average particle diameter of 1 mm as the adsorbent. .
FIG. 20 shows the result of this experiment.

(Experimental example 12)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 9 except that lightly-burned dolomite having an average particle diameter of 3 mm was used instead of the raw dolomite having an average particle diameter of 1 mm as the adsorbent. .
FIG. 21 shows the results of this experiment.

  As is clear from FIGS. 18 to 21, the addition of the adsorbent makes it possible to efficiently adsorb and remove the phosphorus component contained in the digestive juice, and the phosphorus component contained in the digestive fluid (liquid) after the adsorption treatment. It has been confirmed that the content of can be sufficiently reduced. It was also confirmed that the adsorption rate of the phosphorus component depends on the condition of the adsorbent and the pH condition.

<< 5 >> Relationship between treatment time (contact time) and phosphorus removal rate (Experimental example 13)
A solution (digestion solution) containing phosphorus equivalent to the digestion solution during anaerobic treatment (methane fermentation treatment) and anoxic treatment (nitrification denitrification treatment) using anaerobic microorganisms was prepared.

This digested solution was collected in an amount of 100 mL, and 0.8 g of particulate hydroxide dolomite (average particle size: 1 mm) was added thereto, followed by stirring for 30 minutes.
After completion of the stirring, the adsorbent (hydroxide dolomite) was filtered off.

  For the obtained filtrate (liquid), the concentration of the phosphorus component contained in the liquid was determined by the molybdenum blue method, and from the result, the adsorption rate of the phosphorus component by the adsorbent (dolomite hydroxide) was determined.

In addition, measurement was carried out in the same manner as described above except that the contact time between the digestive juice and the adsorbent (hydroxide dolomite) was changed, and the adsorption rate of the phosphorus component by the adsorbent (hydroxide dolomite) was determined.
FIG. 22 shows the results of this experiment.

  As is clear from FIG. 22, the phosphorus component contained in the digestive juice can be efficiently adsorbed and removed by contact with the adsorbent, and the phosphorus component contained in the digestive fluid (liquid) after the adsorption treatment is contained. It was confirmed that the amount could be reduced sufficiently. In particular, phosphorus can be removed at a rate of almost 100% in a contact time of about 5 minutes.

  From the above results, it was found that the phosphorus component contained in the digested liquid of sludge can be efficiently removed by adsorbing the adsorbent (dolomite) and reacting with the adsorbent component. Thereby, the amount of phosphorus contained in the digestive juice can be reduced, and the concentration of phosphorus contained in the digested sludge can also be reduced. As a result, the phosphorus component that is easily evaporated during combustion is reduced, and the adverse effect on the combustion furnace can be suppressed.

Incidentally, the adsorbent used in the experimental examples 5-13, Both porous, a value in the range average pore diameter of less 30nm or more 5 nm, BET specific surface area of ^{40 m} 2 / g or more 1000 m ² / g or less.

  Further, when the treatment was carried out in the same manner as in each of the experimental examples except that the treatment temperature in the adsorption step was changed within the range of 15 ° C. or more and 60 ° C. or less, the same result as described above was obtained.

  In addition, in the above-described experimental example, the digestive juice and the adsorbent were brought into contact by adding and mixing the adsorbent to the digestive juice, but the digestive juice was passed through a column filled with the adsorbent. It is inferred that the following results are obtained.

  The method for treating sludge of the present invention comprises: a precipitation step of adding a precipitation agent to a digestion solution of sludge to precipitate at least a part of a phosphorus component contained in the digestion solution; and from the digestion solution treated in the precipitation step. And a combustion step of burning the obtained digested sludge. Further, the sludge treatment system of the present invention, a precipitation treatment unit that adds a precipitant to the digestion fluid of sludge, and precipitates at least a part of the phosphorus component contained in the digestion fluid, and is treated in the precipitation treatment unit. A combustion furnace for burning digested sludge obtained from the digested liquid. Therefore, it is possible to provide a sludge treatment method and a sludge treatment system capable of reducing the amount of the phosphorus component evaporated during combustion and suppressing the adverse effect on the combustion furnace. Therefore, the sludge treatment method and the sludge treatment system of the present invention have industrial applicability.

1: Sludge treatment system 20: Digestion treatment unit 21: Anaerobic tank (methane fermentation treatment unit)
22 ... Oxygen-free tank (nitrification and denitrification section)
221 ... anoxic part 222 ... aerobic part 23 ... aerobic tank (aerobic bacteria digestion processing part)
30 ... Suction unit (adsorption tank)
30 '... adsorption treatment part 31 ... treatment tank 32 ... first pipe 33 ... second pipe 34 ... contaminant removal means 35 ... column (vessel)
36 ... adsorbent 40 ... precipitation treatment part (precipitation tank)
41 ... Precipitating agent 42 ... Precipitating agent adding means 43 ... Stirring means 50 ... Dehydrating device 60 ... Combustion furnace 61 ... Fluid medium (sand)
62: Dispersion plate 63: Gas supply unit 70: Drying device S1: Sludge S: Digested liquid SS: Digested sludge

Claims (11)

A precipitation step of adding a precipitating agent to the digestion fluid of sludge, and precipitating at least a part of the phosphorus component contained in the digestion fluid,
A step of burning digested sludge obtained from the digested liquid treated in the precipitation step.   The sludge treatment method according to claim 1, further comprising a deposit removal step of removing at least a part of the phosphorus component precipitated in the precipitation step outside the system before the combustion step.   The method for treating sludge according to claim 1, wherein a precipitation agent containing a calcium-based substance is used in the precipitation step.   The method for treating sludge according to claim 3, wherein the calcium-based substance is at least one selected from the group consisting of calcium chloride, calcium hydroxide, and calcium carbonate.   The sludge treatment method according to claim 3 or 4, wherein in the precipitation step, the calcium-based substance and the aluminum-based substance are used in combination as the precipitating agent. When the amount of calcium contained in the precipitant is X _Ca [mol] and the amount of aluminum is X _Al [mol], the relationship of 0.1 ≦ X _Ca / X _Al ≦ 10 is satisfied. 6. The method for treating sludge according to 5.   The method for treating sludge according to claim 5 or 6, wherein the aluminum-based substance is at least one selected from the group consisting of polyaluminum chloride, aluminum sulfate, aluminum nitrate, and aluminum acetate.   The method for treating sludge according to claim 1, wherein a combustion temperature in the combustion step is 500 ° C. or more and 1500 ° C. or less. A precipitation treatment unit that adds a precipitant to the digestion fluid of sludge and precipitates at least a part of the phosphorus component contained in the digestion fluid,
A sludge treatment system, comprising: a combustion furnace that burns digested sludge obtained from the digested liquid processed in the precipitation processing unit. The sludge treatment system includes an anaerobic tank for performing methane fermentation, an anoxic tank for performing nitrification denitrification, and an aerobic tank for performing aerobic digestion, and a digestion treatment unit including an aerobic tank.
The sludge treatment system according to claim 9, wherein the precipitation treatment unit is provided downstream of the oxygen-free tank and upstream of the aerobic tank. The sludge treatment system includes an anaerobic tank for performing methane fermentation, an anoxic tank for performing nitrification denitrification, and an aerobic tank for performing aerobic digestion, and a digestion treatment unit including an aerobic tank.
The sludge treatment system according to claim 9 or 10, wherein at least one of the anaerobic tank and the anoxic tank also functions as the precipitation treatment unit.

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