JPWO2019189549A1 - Sludge treatment method, sludge treatment system and adsorbent manufacturing method - Google Patents

Abstract

The sludge treatment method of the present invention includes an adsorption step of bringing the digestive juice of sludge into contact with an adsorbent and adsorbing at least a part of the phosphorus component contained in the digestive juice to the adsorbent to remove it, It is characterized by having a combustion step of burning the digested sludge obtained by removing at least a part of the phosphorus component from the digestive juice. According to the present invention, it is possible to provide a sludge treatment method and treatment system capable of reducing the amount of phosphorus components that evaporate during combustion and suppressing adverse effects on the combustion furnace.

Description

The present invention relates to a sludge treatment method, a sludge treatment system, and a method for producing an adsorbent.

As a method for treating sewage sludge discharged from a sewage treatment plant, combustion treatment in a combustion furnace is often adopted due to restrictions on prevention of environmental pollution and problems 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 (for example, about 30% in terms of ash). Therefore, when the sludge is burned, the phosphorus component contained in the sludge evaporates and adheres to the wall of the combustion furnace as a phosphoric acid compound, damaging the furnace wall of the combustion furnace or clogging the exhaust pipe. Problems such as corroding the heat exchange tube have occurred.

Therefore, in the treatment of sludge, research is being conducted to reduce the amount of phosphorus contained in the sludge.

As a phosphorus removal technique, a method using magnesium ammonium phosphate (MAP) is known, but such a method also has a problem of an ammonia component and a long reaction time, and is described above. Could not solve the problem sufficiently.

Further, polyaluminum chloride (PAC) and ferric sulfate are known as a flocculant or a phosphorus recovering agent that agglomerates fine particles and suspended matter in sludge (for example, Non-Patent Document 1).

However, when polyaluminum chloride and ferric sulfate are used, the above-mentioned problem of adverse effects on the combustion furnace and the like cannot be sufficiently solved. In particular, when the digested sludge contains phosphorus at a relatively high content (for example, a content such that the content in the incinerated ash is 10% by mass or more), the above-mentioned problems become more serious. It occurred prominently. In addition, these are expensive, and there are problems in terms of cost and an increase in the amount of ash generated.

On the other hand, water used in factories and mines may contain many pollutants such as heavy metals. When draining such contaminated water, it is necessary to sufficiently remove the pollutants.

In addition, well water and the like in contaminated soil may also contain pollutants such as heavy metals, and when used as domestic water such as drinking water, it is necessary to sufficiently remove the pollutants.

Conventionally, a large amount of adsorbent has been used for removing pollutants (see, for example, Patent Document 1). However, when the treatment with an adsorbent is performed in an alkaline liquid (for example, in a liquid having a hydrogen ion index (pH) of 10 or more), the heavy metal cannot be sufficiently adsorbed or the adsorbed heavy metal is redissolved. It was difficult to remove the pollutants sufficiently.

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)

Japanese Unexamined Patent Publication No. 2013-696

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 components that evaporate during combustion and suppressing adverse effects on a combustion furnace, and hydrogen using sludge as a raw material. It is an object of the present invention to provide a method for producing an adsorbent capable of producing an adsorbent capable of efficiently removing heavy metals even when the ion index (pH) is large.

Such an object is achieved by the following invention.
The sludge treatment method of the present invention includes an adsorption step in which the digestive juice of sludge is brought into contact with an adsorbent, and at least a part of the phosphorus component contained in the digestive juice is adsorbed on the adsorbent to be removed.
It is characterized by having a combustion step of burning digestive sludge obtained by removing at least a part of a phosphorus component from the digestive juice in the adsorption step.

In the sludge treatment method of the present invention, it is preferable to use dolomites as the adsorbent in the adsorption step.

In the sludge treatment method of the present invention, the dolomites are preferably hydroxylated dolomite.

In the sludge treatment method of the present invention, the dolomites are preferably dolomite.

In the sludge treatment method of the present invention, it is preferable to carry out the adsorption step under the conditions of pH 3 or more and 13 or less.

In the sludge treatment method of the present invention, the combustion temperature in the combustion step is preferably 500 ° C. or higher and 1500 ° C. or lower.

The sludge treatment system of the present invention includes an adsorption treatment unit that brings the digestive juice of sludge into contact with an adsorbent and adsorbs at least a part of the phosphorus component contained in the digestive juice to the adsorbent to remove it.
It is characterized by including a combustion furnace for burning digestive sludge obtained by removing at least a part of a phosphorus component from the digestive juice in the adsorption treatment unit.

The method for producing an adsorbent of the present invention includes an adsorption step of bringing sludge digestive juice into contact with dolomites and adsorbing at least a part of phosphorus components contained in the digestive juice to the dolomites.
It is characterized by having a calcining step of calcining the dolomites in contact with the digestive juice.

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 components that evaporate during combustion and suppressing adverse effects on a combustion furnace, and also to provide a sludge treatment system, and a hydrogen ion index (pH). It is possible to provide a method for producing an adsorbent capable of producing an adsorbent capable of efficiently removing heavy metals even in a large state using sludge as a raw material.

FIG. 1 is a diagram schematically showing a first embodiment of the sludge treatment system of the present invention. FIG. 2 is a diagram schematically showing an example of an adsorption processing unit included in the processing system shown in FIG. FIG. 3 is a process diagram showing a first embodiment of the sludge treatment method of the present invention. FIG. 4 is a diagram schematically showing a second embodiment of the sludge treatment system of the present invention. FIG. 5 is a diagram schematically showing the relationship between the adsorption processing unit and the anaerobic tank included in the processing system shown in FIG. FIG. 6 is a graph showing the relationship between the amount of the adsorbent added and the phosphorus removal rate when dolomite is used as the adsorbent. FIG. 7 is a graph showing the relationship between the amount of the adsorbent added and the phosphorus removal rate when hydrodromite is used as the adsorbent. FIG. 8 is a graph showing the relationship between the amount of the adsorbent added and the phosphorus removal rate when light-baked dolomite having an average particle size of 1 mm is used as the adsorbent. FIG. 9 is a graph showing the relationship between the amount of the adsorbent added and the phosphorus removal rate when light-baked dolomite having an average particle size of 3 mm is used as the adsorbent. FIG. 10 is a graph showing the relationship between pH and phosphorus removal rate when dolomite is used as an adsorbent. FIG. 11 is a graph showing the relationship between pH and the removal rate of phosphorus when hydrolymite is used as an adsorbent. FIG. 12 is a graph showing the relationship between pH and phosphorus removal rate when light-baked dolomite having an average particle size of 1 mm is used as an adsorbent. FIG. 13 is a graph showing the relationship between pH and phosphorus removal rate when light-baked dolomite having an average particle size of 3 mm is used as an adsorbent. FIG. 14 is a graph showing the relationship between the contact time of the object to be treated with the adsorbent and the phosphorus removal rate. FIG. 15 is a graph showing the relationship between the amount of phosphorus adsorbed by the adsorbent when calcined dolomite and activated carbon are used as the adsorbent. FIG. 16 is a graph showing the relationship between the combustion temperature of digested sludge and the phosphorus content in sludge ash obtained by combustion. FIG. 17 shows the calcined dolomite used as a raw material, the adsorbent obtained by adsorbing the phosphorus component on the calcined dolomite and then calcining, and the state in which Pb is adsorbed on the adsorbent. , X-ray diffraction (XRD) analysis results. FIG. 18 shows each heavy metal per unit mass of the adsorbent when a standard solution containing chromium, nickel, arsenic, cadmium and lead at a content of 2 ppm was treated with the adsorbent of Example 1. It is a graph which shows the adsorption amount. FIG. 19 shows each heavy metal per unit mass of the adsorbent when a standard solution containing chromium, nickel, arsenic, cadmium and lead at a content of 2 ppm was treated with the adsorbent of Example 2. It is a graph which shows the adsorption amount.

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

FIG. 1 is a diagram schematically showing a first embodiment of the sludge treatment system of the present invention. FIG. 2 is a diagram schematically showing an example of an adsorption processing unit included in the processing system shown in FIG. FIG. 3 is a process diagram showing a first embodiment of the sludge treatment method of the present invention. In the following description, the lower side in FIGS. 1 and 2 is referred to as "lower side" or "lower side", and the upper side in FIGS. 1 and 2 is referred to as "upper side" or "upper side". The same applies to FIG. 4, which will be described later.

In the sludge treatment method of the present invention, the digestive juice S of the sludge is brought into contact with the adsorbent 36, and at least a part of the phosphorus component contained in the digestive juice S is adsorbed on the adsorbent (phosphorus component adsorbent) 36 to remove it. It has an adsorption step of performing the adsorption step and a combustion step of burning the digested sludge SS obtained by removing at least a part of the phosphorus component from the digestive juice S in the adsorption step.

Further, in the sludge treatment system 1 of the present invention, the sludge digestive liquid S is brought into contact with the adsorbent 36, and at least a part of the phosphorus component contained in the digestive liquid S is adsorbed on the adsorbent 36 to be removed. A unit (adsorption tank) 30 and a combustion furnace 60 for burning the digested sludge SS obtained by removing at least a part of the phosphorus component from the digestive liquid S in the adsorption treatment unit 30 are provided.

According to the present invention as described above, it is possible to provide a sludge treatment method and a sludge treatment system capable of reducing the amount of phosphorus components that evaporate during combustion and suppressing adverse effects on the combustion furnace.

In particular, in the present invention, prior to the sludge (digestion sludge SS) combustion step (combustion treatment in the combustion furnace 60), the phosphorus component contained in the sludge digestion liquid S is adsorbed in the sludge adsorption step (adsorption treatment unit 30). ) To reduce the concentration of phosphorus components contained in sludge (digested sludge SS) and digestive juices.

If the phosphorus concentration contained in the digested sludge SS is high, the phosphorus component evaporates due to combustion and tends to adversely affect the furnace wall, exhaust pipe, heat exchange pipe, etc. of the combustion furnace 60. However, in the present invention, the phosphorus component is removed. By doing so, the above-mentioned adverse effects can be suppressed. In addition, the phosphorus concentration contained in the final digestive juice can be sufficiently lowered.

The sludge, which is the source of the object to be treated, may be any sludge as long as it contains a phosphorus component, and a large amount of sludge is discharged along with the treatment of sewage and urine from households or the purification of factory wastewater. , The concept includes solids formed by agglomeration of organic final products and mud-like wastes showing intermediate properties between solids and liquids.

Further, in the digestive juice S which is the object to be treated, phosphorus is usually contained in the main forms such as phosphate ion, phosphate and oxide. In the present 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 sludge treatment method of the present embodiment, in the digestion step of digesting the sludge S1, each treatment of methane fermentation treatment, nitrification denitrification treatment, and aerobic bacterium digestion treatment is performed.

In the sludge treatment system of the present embodiment, the digestion treatment unit 20 that digests the sludge S1 has an anaerobic tank (methane fermentation treatment unit) 21 that performs methane fermentation treatment and an anoxic tank (oxygenation treatment unit) that performs nitrification denitrification treatment. It is provided with a nitrification denitrification treatment unit) 22 and an aerobic tank (aerobic bacterium digestion treatment unit) 23 for performing an aerobic bacterium digestion treatment.

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

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 converted into nitrogen gas by a reduction reaction. ..

In the aerobic bacterium digestion treatment (aerobic tank 23), the aerobic bacterium digests or dissolves the organic matter contained in the object to be treated (digestive juice S in which the digestion treatment for sludge S1 has partially progressed). The phosphorus component contained in the state is taken up by the aerobic bacterium Dephosphorus.

Further, the sludge treatment method of the present embodiment includes a dehydration step of dehydrating the digested sludge SS and a drying step of drying after the digestion step and the adsorption step and before the combustion step. There is.

The sludge treatment system of the present embodiment is on the downstream side of the digestion treatment unit 20 and the adsorption treatment unit 30, and is on the upstream side of the combustion furnace 60, a dehydration device 50 for dehydrating the digestion sludge SS, and dehydration. A drying device 70 for drying the digested sludge SS dehydrated by the device 50 is provided.

With such a configuration, sludge can be treated more efficiently, and the effect of the present invention can be exhibited more remarkably.

Further, even if the sludge treatment system of the present invention includes a transfer means (not shown) for transferring sludge (sludge as solid content and liquid content such as digestive juice) as an object to be treated between each device. Good.

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

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

The anaerobic tank 21 is preferably provided with a fixed bed of microorganisms that retains a high concentration of anaerobic microorganisms. For example, a microbial carrier (for example, a microbial carrier made of glass fiber, carbon fiber, etc.) can be filled in the fermenter to form a fixed bed (not shown).

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

Further, it is preferable that the anaerobic tank 21 is provided with a device (not shown) that keeps the sludge S1 at the active temperature of the anaerobic microorganism group.

As a result, the sludge S1 in the anaerobic tank 21 can be maintained at a fermentation temperature suitable for methanogenic microorganisms, for example, from a medium temperature range to a high temperature range (for example, about 37 ° C. or higher and 55 ° C. or lower), and methane production can be more efficiently performed. It can be carried out.
The anaerobic tank 21 may have a floating floor system instead of the fixed floor, for example.

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

The sludge S1 (also in the digestive juice S) subjected to the methane fermentation treatment, which is an anaerobic digestion treatment, contains an organic residue. Since the digestive juice S obtained through the methane fermentation treatment, which is an anaerobic digestive treatment, contains a large amount of ammoniacal nitrogen and phosphorus, it is regulated to release the digestive juice as it is because it affects the environment. There is. Therefore, in the present embodiment, phosphorus is removed from the digestive juice S by providing the adsorption treatment unit 30, and the load due to phosphorus thereafter is reduced to finally reduce the content of the phosphorus component contained in the digestive sludge SS. During incineration, it is possible to effectively prevent the occurrence of problems such as corrosion in the incinerator due to the evaporation of excess phosphorus components.

The sludge S1 and the digestive juice S that have been methane-fermented in the anaerobic tank 21 are supplied to the oxygen-free tank 22 that is the nitrification and denitrification treatment section. In other words, the sludge (digestive liquid S) subjected to the methane fermentation treatment is then subjected to the nitrification denitrification treatment.

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

In the illustrated configuration, the anoxic tank (nitrification denitrification treatment unit) 22 contains nitrate nitrogen and nitrite contained in the digestive juice S (that is, the liquid phase treated in the anaerobic tank 21) which is the object to be treated. Anoxic part 221 that reduces sex nitrogen to nitrogen by microbial (denitrification) treatment, and nitrate by treating ammoniacal nitrogen with microorganisms (at least one of nitrifying bacteria and nitrite bacteria) under aerobic conditions. It is provided with an aerobic portion 222 that produces nitrogen and nitrite nitrogen.

First, in the anoxic section 221, nitrifying bacteria (denitrifying bacteria) that prefer an anoxic state change nitrate nitrogen and nitrite nitrogen contained in the digestive juice S into nitrogen gas (denitrification treatment). Next, the digestive juice S is sent to the aerobic unit 222. In the aerobic portion 222, the ammoniacal nitrogen contained in the digestive juice S is changed to nitrate nitrogen and nitrite nitrogen by a microorganism (at least one of nitrifying bacteria and nitrite bacteria). The digestive juice S is then sent to the anoxic section 221. In this way, the digestive juice S circulates internally between the anoxic portion 221 and the aerobic portion 222.

As a result, the amount of ammoniacal nitrogen, nitrate nitrogen, and nitrite nitrogen contained in the digestive juice can be reduced.

In the illustrated configuration, the oxygen-free tank 22 and the aerobic tank 23 are provided one by one, but a combination of the oxygen-free tank 22 and the aerobic tank 23 may be provided in a plurality of stages. Further, the digestive juice S may be configured to repeatedly circulate the same oxygen-free tank 22 and the aerobic tank 23.

In the anaerobic tank 21 and the anoxic tank 22, phosphorus is exhaled from the dephosphorizing bacteria, so that the phosphorus concentration in the digestive juice S becomes high.

[Aerobic bacteria digestion treatment (aerobic tank)]
In the aerobic bacterium digestion treatment, in the aerobic tank 23, the aerobic bacterium digests the organic matter contained in the object to be treated (that is, the digestive juice S in which the digestion treatment for the sludge S1 has partially progressed). , Dephosphorizing bacteria, which are aerobic bacteria, take in the phosphorus component contained in the dissolved state.

As a result, for example, the content of the phosphorus component contained in the digestive juice S in a dissolved state can be sufficiently lowered, so that the digestive juice S after this treatment can be treated as wastewater.

<Adsorption process (adsorption processing unit)>
In the adsorption step, in the adsorption treatment unit 30, the digestive juice S is brought into contact with the adsorbent 36, and at least a part of the phosphorus component contained in the digestive juice S is adsorbed on the adsorbent 36 to be removed.

In particular, in the present embodiment, the adsorption treatment unit 30 is provided on the downstream side of the oxygen-free tank 22 and on the upstream side of the aerobic tank 23, and the adsorption steps include nitrification denitrification treatment and aerobic bacteria digestion treatment. Do it at the timing between. That is, in the present embodiment, the adsorption step is performed during the digestion step.

As a result, the phosphorus content in the digestive juice S provided in the aerobic tank 23 (aerobic bacterium digestion treatment) can be sufficiently lowered, and in the digestive sludge SS finally supplied to the combustion furnace 60. The content of phosphorus contained in the above can be sufficiently lowered. As a result, it is possible to more effectively prevent the occurrence of problems such as corrosion in the incinerator 60 due to the evaporation of the excess phosphorus component at the time of incineration.

The adsorbent 36 may be capable of adsorbing the phosphorus component in the digestive juice S, and for example, dolomites, calcium hydroxide (Ca (OH) ₂ ), calcium carbonate (CaCO ₃ ), magnesium hydroxide (Mg (Mg). OH) ₂ ), magnesium carbonate (MgCO ₃ ) and the like can be mentioned, and one or a combination of two or more selected from these can be used.
Above all, in the adsorption step, it is preferable to use dolomites as the adsorbent 36.

As a result, the phosphorus component contained in the digestive juice S can be efficiently adsorbed by the dolomites. In addition, heavy metals contained in the digestive juice S can be efficiently removed together with the phosphorus component.

Examples of the dolomites used in this step include dolomite, hydroxylated dolomite (digested dolomite, including dolomite plaster), light-baked dolomite, dolomite clinker, and the like, and one or more selected from these are used in combination. be able to.

Above all, by using the hydroxylated dolomite, the phosphorus component contained in the digestive juice S can be more efficiently adsorbed on the dolomites. In addition, heavy metals contained in the digestive juice S can be removed more efficiently.

Further, by using dolomite, the range of selection of dolomites as the adsorbent 36 is widened, and the conditions such as the particle size and the pore diameter of the dolomites can be adjusted to the optimum conditions. Further, since the adsorbent 36 is cheaper, it is advantageous from the viewpoint of further reducing the sludge treatment cost.
In the present specification, the light-baked dolomite refers to calcined dolomite that has been calcined at a calcining temperature of 600 ° C. or lower.

The adsorbent 36 used in this step is usually porous.
As a result, the unit mass of the adsorbent 36 and the surface area per unit volume can be increased, and the efficiency of removing the phosphorus component can be further improved.

The average pore diameter of the adsorbent 36 (particularly dolomites) 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 adsorption efficiency of the phosphorus component by the adsorbent 36 while ensuring the durability of the adsorbent 36. In addition, heavy metals contained in the digestive juice S can be removed more efficiently.

The BET specific surface area of the adsorbent 36 (particularly dolomites) 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.

As a result, the adsorption efficiency of the phosphorus component by the adsorbent 36 can be further improved. In addition, heavy metals contained in the digestive juice S can 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 thereof is preferably 3 μm or more and 300 mm or less, preferably 100 μm or more. It is more preferably 250 mm or less, further preferably 1 mm or more and 200 mm or less, and most preferably 10 mm or more and 150 mm or less.

As a result, the unit mass of the adsorbent 36 and the surface area of the particles per unit volume can be increased, the phosphorus component can be uniformly adsorbed on the adsorbent 36, and the particulate adsorbent 36 is unintentionally aggregated. It is effectively prevented from being stowed, and the fluidity and ease of handling of the adsorbent 36 are improved. Further, the filling property (easiness of filling, followability to the shape of the container) into the container (for example, the column 35) can be improved.

At least a part of the phosphorus component to be adsorbed on the adsorbent 36 in the adsorption step may be 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.), phosphite and its salts, peroxomonophosphoric acid and its salts, phosphones Acids and their salts, phosphinic acid and its salts, phosphorus oxides such as diphosphorus pentoxide, phosphorus halides such as phosphorus pentoxide, phosphoryl halides such as phosphoryl chloride, calcium monophosphate, calcium diphosphate Phosphate calcium and the like can be mentioned.

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

As a result, the phosphorus component can be efficiently adsorbed 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. 2, the adsorption treatment unit 30 connects the treatment tank 31 containing the digestive juice S, the column (container) 35 filled with the adsorbent 36, and the treatment tank 31 and the lower portion of the column 35. The first pipe 32 that supplies the digestive juice S from the treatment tank 31 to the column 35, and the digestive liquid S that is arranged by connecting the upper part of the column 35 and the treatment tank 31 and has passed through the column 35. It has a second pipe 33 that returns to the processing tank 31.

In the illustrated configuration, the digestive juice S is supplied from the lower part of the treatment tank 31 to the column 35 through the first pipe 32. The digestive juice S may be supplied to the column 35 from the upper part of the treatment tank 31.

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

As a result, the digestive juice S can be distributed inside the column 35, and the adsorbent 36 filled in the column 35 and the digestive juice S can be brought into contact with each other more efficiently to remove the phosphorus component contained in the digestive juice S. , The adsorbent 36 can be efficiently adsorbed. In particular, when dolomites are used as the adsorbent 36, the phosphorus component can be efficiently adsorbed by the dolomites even in the pores of the dolomites.

The digestive juice 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 action of the adsorbent 36, the concentration of phosphorus in the digestive juice S after passing through the column 35 is lower than that in the digestive juice S before passing through the column 35.

Further, by circulating the digestive juice S between the treatment tank 31 and the column 35, the adsorption treatment can be repeated and the phosphorus component can be more efficiently adsorbed on the adsorbent 36.

By passing the digestive juice S through the column 35 filled with the adsorbent 36, the digestive liquid S can be easily separated from the adsorbent 36 after being brought into contact with the adsorbent 36.

Further, by making the column 35 a removable cartridge, the adsorbent 36 can be easily replaced. In addition, the adsorbent 36 that has adsorbed the phosphorus component can be easily recovered.

The digestive juice S may contain a large amount of solids (contaminants), and if the digestive juice S is passed through the column 35 as it is, the column 35 may be clogged due to the solids.

Therefore, it is preferable to remove a relatively large solid content (contaminants) from the digestive juice S supplied to the column 35 so that the column 35 is not clogged. For example, as shown in FIG. 2, the contaminant removing means 34 such as a filter, a screen, a trommel, and a vortex diversion tank (swirl diversion tank) is arranged at the entrance or the middle of the first pipe 32. preferable.

As a result, the digestive juice S and the adsorbent 36 can be brought into contact with each other more stably for a long period of time while effectively preventing clogging of the column 35. In addition, the frequency of maintenance of the processing system 1 (including replacement of the adsorbent 36) can be reduced, and the efficiency of processing the digestive juice S can be further improved.

The treatment time of this step (the contact time of the digestive juice S entering the column 35 and the contact time with the adsorbent 36, that is, 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. More preferably, it is 3 hours or less.

As a result, it is possible to further improve the adsorption efficiency of the phosphorus component by the adsorbent 36 while effectively preventing the treatment efficiency of the digestive juice S from decreasing.

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

As a result, the phosphorus component can be efficiently adsorbed by the adsorbent 36, and this step can be efficiently performed in a short time.

At the end of this step (adsorption step), the removal rate of phosphorus as a dissolving component contained in the digestive juice S (the removal rate of phosphorus from the digestive juice S, which is the object to be treated without any treatment, is an element. The value converted to 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, and more preferably 50% by mass or more and 90% by mass or less. preferable.

As a result, the effect of the present invention is more prominently exhibited, and the adverse effect on the combustion furnace 60 and the like can be suppressed more effectively.

On the other hand, if the removal rate of phosphorus as a dissolving 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 dissolving component is increased more than necessary, the degree of adverse effect on the incinerator or the like hardly changes, the amount of the adsorbent 36 used increases, and the time required for the adsorption process is longer than necessary. It causes a problem that the digestive juice S becomes long, which is not preferable from the viewpoint of processing efficiency and cost of the digestive juice S.

The digestive juice S used in the adsorption step is supplied to the aerobic tank (aerobic bacterium digestion treatment section) 23 of the digestion treatment section 20, and is subjected to the aerobic bacterium digestion treatment by the aerobic bacterium as described above and the dephosphorization bacterium. Is dephosphorized by.

<Dehydration process (dehydration device)>
After the digestion treatment and the adsorption treatment, the digestive sludge SS containing the treated digestive juice S is supplied to the dehydrator 50.

In the dehydration step, the digestion sludge SS is dehydrated using the dehydration apparatus 50 to reduce the water content of the digestion sludge SS.

As a result, the combustion step can be performed more efficiently without lowering the combustion temperature in the combustion furnace 60.

As the dehydrating device 50, for example, a dehydrating device such as a belt press type dehydrating device, a centrifuge type dehydrating device, or a filter press can be adopted.

Here, most of the phosphorus originally contained in the digestive juice S is removed from the system by adsorption by the adsorbent 36 in the adsorption step, and the aerobic tank (aerobic bacterium digestion treatment). The amount of phosphorus taken up by the dephosphorized bacteria (a type of aerobic bacteria) in the aerobic tank 23 is reduced, and the content of phosphorus contained in the digestive sludge SS (surplus sludge) generated in the aerobic tank 23 is It has dropped significantly.

The dehydrated digested sludge SS may be further dried using a heat dryer or the like.

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

As a result, the water content of the digested sludge SS can be made lower, and the combustion step can be performed more efficiently.

The digested sludge SS dehydrated by the dehydrating device 50 is supplied to the combustion furnace 60. In other words, the digested sludge SS subjected to the dehydration step is then subjected to the combustion step.

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

At this time, if the water content of the digested sludge SS is lowered by the dehydration treatment, the present step can be performed more efficiently while more effectively preventing an unintentional decrease in the combustion temperature. In addition, the combustion temperature can be easily controlled.

As the combustion furnace 60, for example, a fluidized layer combustion furnace, a rotary combustion furnace, a fixed layer combustion furnace, a stalker type combustion furnace, a gasification melting furnace, or the like can be adopted.

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

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

Then, by charging the digested sludge SS into the high-temperature fluid medium 61, the digested sludge SS can be burned evenly in a shorter time by utilizing the heat amount of the fluidized sand.

In the combustion step, the combustion temperature (particularly, the maximum combustion temperature) is preferably 500 ° C. or higher and 1500 ° C. or lower, and more preferably 550 ° C. or higher and 900 ° C. or lower.

As a result, this process can be efficiently performed in a short time while reducing the amount of energy required for the combustion process. In addition, it is possible to more effectively prevent adverse effects on the combustion furnace 60 and the like.

The processing time of this step (particularly, the burning time at 500 ° C. or higher) is preferably 1 second or more and 120 minutes or less, and more preferably 5 seconds or more and 10 minutes or less.

As a result, this process can be efficiently performed while reducing the amount of energy required for the combustion process.

The digested sludge SS burned in this process becomes combustion ash which is a treatment product.
Further, in the adsorption step, the adsorbent 36 (particularly dolomites) adsorbing the phosphorus component is adsorbed containing phosphorus by, for example, firing (particularly firing at a firing temperature of 300 ° C. or higher and 1000 ° C. or lower). It can be reused as an agent. This adsorbent can be used, for example, as an adsorbent that adsorbs heavy metals with excellent efficiency.

By reusing the adsorbent 36 after the treatment in this way, the final amount of industrial waste can be reduced.

<< Second Embodiment >>
FIG. 4 is a diagram schematically showing a second embodiment of the sludge treatment system of the present invention. FIG. 5 is a diagram schematically showing the relationship between the adsorption processing unit and the anaerobic tank included in the processing system shown in FIG.

Hereinafter, the sludge treatment method and the second embodiment of the sludge treatment system of the present invention will be described with reference to these figures, but the differences from the above-described embodiments will be mainly described, and the same matters will be described. The explanation is omitted.

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

More specifically, in the above-described embodiment, the adsorption treatment unit 30 is provided on the downstream side of the anaerobic tank 21 and the anoxic tank 22 constituting the digestion treatment unit 20, and the anaerobic digestion treatment and the nitrification denitrification treatment. However, in the present embodiment, the adsorption treatment unit 30'is attached to the anaerobic tank 21 and the anoxic tank 22, respectively, and is undergoing the methane fermentation treatment, which is the anaerobic treatment. And it is configured to perform an adsorption treatment during the nitrification denitrification treatment, which is an oxygen-free treatment.

The adsorption processing unit 30'includes a column (container) 35, an adsorbent 36, a first pipe 32, a second pipe 33, and a contaminant removing means 34, which are the same as 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 sludge treatment method as a whole can be further improved.

Although the adsorption treatment unit 30'is attached to both the anaerobic tank 21 and the oxygen-free tank 22 in the illustrated configuration, it may be attached to only one of them.

[Manufacturing method of adsorbent]
Next, the method for producing the adsorbent of the present invention will be described.

The method for producing an adsorbent of the present invention includes an adsorption step of bringing sludge digestive juice into contact with dolomites and adsorbing at least a part of phosphorus components contained in the digestive juice to the dolomites, and the digestive juice. It has a firing step of firing the dolomites that have been brought into contact with each other.

As a result, even when the hydrogen ion index (pH) is large, an adsorbent capable of efficiently removing heavy metals (that is, a heavy metal adsorbent) can be produced using sludge as a raw material. A method can be provided. In particular, an adsorbent capable of efficiently removing heavy metals can be produced inexpensively and with high productivity. In addition, the result product (adsorbent that adsorbs phosphorus component (that is, phosphorus component adsorbent)) generated by sludge treatment can be effectively used, and new waste is generated in the sludge treatment process. Can be effectively prevented.

Further, by sharing the adsorption step in the sludge treatment method according to the present invention described above with the adsorption step in the adsorbent production method of the present invention, the sludge including the sludge treatment method and the adsorbent production method can be used. As a whole treatment process, it is possible to produce an adsorbent (that is, a heavy metal adsorbent) capable of removing heavy metals that may adversely affect the environment while suppressing adverse effects on equipment and new generation of waste. Therefore, the entire sludge treatment process can be made environmentally and equipment friendly.

Further, in the production method of the present invention, it is possible to produce an adsorbent capable of removing arsenic, which has been particularly difficult to remove at a high removal rate in the past, at a high removal rate.

<Adsorption process>
In the adsorption step, the dolomites are brought into contact with the digestive juice of sludge. As a result, the phosphorus component contained in the digestive juice is adsorbed on the dolomites.

As the dolomites used in this step, the adsorbent 36 used in the sludge treatment method and treatment system according to the present invention described above can be preferably used.

In particular, by using dolomite hydroxide, the formation of a chemical bond between the phosphate ion and Ca constituting the dolomites can be more preferably promoted in the subsequent firing step.

Further, by using dolomite, the range of selection of dolomites as a raw material is widened, and conditions such as particle size and pore diameter of dolomite can be suitably adjusted. In addition, since the raw material is cheaper, it is advantageous from the viewpoint of further reducing the production cost of the adsorbent (heavy metal adsorbent).

The dolomites used in this step (that is, dolomites as a raw material) are usually porous.
As a result, the unit mass of the adsorbent (heavy metal adsorbent) and the surface area per unit volume can be increased, and the efficiency of removing heavy metals can be further improved. Furthermore, the specific surface area can be increased by the firing step.

The average pore diameter of the dolomites as a raw material 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.

This makes it possible to further improve the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent) while ensuring the durability of the adsorbent (heavy metal adsorbent). The average pore diameter can be adjusted, for example, according to the firing conditions in the firing step.

Examples of the phosphorus compound to be brought into contact with dolomites in this step (that is, the phosphorus compound contained in the digestive juice of sludge) include phosphoric acid and salts thereof (for example, ammonium phosphate, diammonium hydrogen phosphate, dihydrogen phosphate). Ammonium, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, calcium dihydrogen phosphate, etc.), phosphite and its salts , Peroxomonophosphate and its salts, Phosphonic acid and its salts, Phosphonic acid and its salts, Phosphorus oxides such as diphosphorus pentoxide, Phosphorus halides such as phosphorus pentachloride, Phosphoryl halides such as phosphoryl chloride, Examples thereof include calcium phosphate such as calcium monophosphate and calcium diphosphate.

The ratio of dolomites to phosphorus compounds (that is, phosphorus compounds contained in the digestive juice of sludge) is not particularly limited, but the amount of phosphorus compounds adsorbed on dolomites is 100 parts by mass of dolomites in terms of the amount of phosphate ions. With respect to (%), it is preferably 0.1 part by mass or more and 20 parts by mass or less, and more preferably 1 part by mass or more and 2 parts by mass or less.

As a result, the amount of phosphorus compounds adsorbed on dolomites can be increased while suppressing the amount of phosphorus compounds remaining without being adsorbed on dolomites, and phosphorus, which is more expensive than dolomite, can be saved. Further, the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent) can be further improved.

In this step, the pH of the mixture containing dolomites and the digestive juice of sludge is preferably 3 or more and 13 or less, and more preferably 5 or more and 10 or less.

As a result, the phosphorus compound contained in the digestive juice of sludge can be efficiently adsorbed by dolomites, and the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent) can be further improved.

The treatment time of this step (that is, the contact time between the dolomites and the digestive juice of sludge) is preferably 1 minute or more and 1 day or less, and more preferably 10 minutes or more and 3 hours or less.

This makes it possible to effectively prevent a decrease in the productivity of the adsorbent (heavy metal adsorbent) and further improve the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent).

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

As a result, the phosphorus compound can be efficiently adsorbed by dolomites while reducing the amount of energy required for producing the adsorbent (heavy metal adsorbent), and this step can be efficiently performed in a short time.

In the adsorption step, the phosphorus component contained in the digestive juice is adsorbed on the dolomites, and then solid-liquid separation is performed (solid-liquid separation step).

In addition, the phosphorus-adsorbed dolomites, which are solids obtained in the solid-liquid separation step, are subjected to a drying treatment (drying step).

The treatment temperature in the drying step is not particularly limited, but is preferably 300 ° C. or lower, and more preferably 70 ° C. or higher and 300 ° C. or lower.

Then, using the dried phosphorus-adsorbed dolomites, the firing step described in detail below is performed.

<Baking process>
In the firing step, dolomites (that is, dolomites adsorbed with a phosphorus component) that have been brought into contact with the digestive juice of sludge are calcined.

As a result, the phosphoric acid component is immobilized on the adsorbent (dolomites), and the adsorption capacity of heavy metals is improved as compared with the dolomites as a raw material. In particular, the adsorption capacity of heavy metals under alkaline conditions is significantly improved.

Further, by firing, Ca constituting the dolomites is chemically bonded (ionic bonded) with Pa to form a calcium phosphate compound, so that the adsorbent can be used in a wide pH range (particularly, the pH is 5 or more). Desorption of the phosphorus component when the (heavy metal adsorbent) comes into contact with the object to be treated is effectively prevented, and a stable and excellent adsorption capacity is exhibited.
Moreover, not only heavy metals but also F (fluorine) can be suitably removed.

Further, in a low pH region (for example, a region where the pH is 3 or less), the phosphorus component can be suitably dissolved, and the heavy metal adsorbed on the adsorbent (heavy metal adsorbent) can be suitably eluted. Thereby, the adsorbent (heavy metal adsorbent) and the heavy metal can be suitably separated, and for example, the heavy metal can be preferably reused. In particular, it is particularly advantageous when noble metals (Au, Ag, Pt, Pd, Rh, Ir, Ru, Os) and rare metals (for example, Cr, Mn, Co, Ni, Mo, W, Bi, etc.) are adsorbed. Is.

The above-mentioned excellent effect is obtained by adsorbing the phosphorus component to an adsorbent (particularly dolomites) in the firing step and immobilizing it, and simply mixing the dolomites and the phosphorus compound. It cannot be obtained by contacting solids. More specifically, for example, in a phosphorus-containing aqueous solution or the like, even if the dolomites and the phosphorus compound are simply brought into contact with each other, the reactivity is poor, and if the firing treatment is not performed, the solution is subjected to a high concentration of alkaline conditions. When the treated product is treated, the phosphoric acid component is easily eluted, and the effect of improving the removal efficiency of heavy metals cannot be stably obtained.

Examples of calcium phosphate-based compounds include calcium phosphate (Ca (H ₂ PO ₄ ) ₂ and its hydrate), anhydrous calcium hydrogen phosphate (CaHPO ₄ ), and hydroxyapatite (HAP) (Ca ₁₀ (PO _{4 ) 6} (OH). ) Examples of compounds containing phosphate ions and calcium ions such as _{2) and the like.}

The processing temperature in the firing step (particularly, the maximum firing temperature) is preferably 300 ° C. or higher and 1000 ° C. or lower, and more preferably 400 ° C. or higher and 900 ° C. or lower.

As a result, while reducing the amount of energy required for producing the adsorbent (heavy metal adsorbent), it is possible to more efficiently form a chemical bond between the phosphate ion and Ca constituting the dolomites, and it is possible to form a chemical bond in a short time. This process can be performed efficiently.

The treatment time in the firing step (particularly, the heating time at a temperature of 300 ° C. or higher) is not particularly limited, but is preferably 0.3 hours or more and 10 hours or less, and is preferably 1 hour or more and 5 hours or less. More preferably, it is 2 hours or more and 3 hours or less.

This makes it possible to effectively prevent a decrease in the productivity of the adsorbent (heavy metal adsorbent) and further improve the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent).

Further, the heating in the firing step may be carried out so as to be held at a substantially constant temperature, or may be carried out so as to be held at a plurality of different holding temperatures. Further, the heating in the firing step may be performed so that the temperature rise rate is substantially constant and the temperature decrease rate is substantially constant, and at least one of the temperature rise rate at the time of temperature rise and the temperature decrease rate at the time of temperature reduction may be set to a substantially constant rate. It may be carried out so as to change with time.

More specifically, for example, in the firing step, the temperature is raised at a predetermined heating rate (first heating rate), and when the temperature reaches a predetermined temperature (first temperature), a predetermined time (first) is reached. (Holding time) is held at the first temperature (the temperature rise rate is set to zero), and then the temperature is raised at a predetermined temperature rise rate (second temperature rise rate) different from the first temperature rise rate. When the predetermined temperature (second temperature) is reached, the temperature is held at the second temperature for a predetermined time (second holding time) (the heating rate is set to zero), and then the predetermined temperature lowering rate (first). The temperature is lowered at the temperature lowering rate), and when the predetermined temperature (third temperature) is reached, the temperature is held at the third temperature for a predetermined time (third holding time) (that is, the temperature lowering rate is set to zero). After that, the temperature may be lowered at a predetermined temperature lowering rate (second temperature lowering rate) different from the first temperature lowering rate.

The first temperature can be, for example, a temperature of 100 ° C. or higher and 300 ° C. or lower.
The second temperature can be the above-mentioned maximum firing temperature.
The third temperature can be, for example, a temperature of 100 ° C. or higher and 300 ° C. or lower.

The first holding time can be, for example, 10 minutes or more and 4 hours or less.
The second holding time can be, for example, 30 minutes or more and 5 hours or less.
The third holding time can be, for example, 10 minutes or more and 4 hours or less.

The first heating rate can be 5 ° C. or higher and 20 ° C. or lower.
The second heating rate can be 10 ° C. or higher and 40 ° C. or lower.
The first temperature lowering rate can be 2 ° C. or higher and 15 ° C. or lower.
The second temperature lowering rate can be 5 ° C. or higher and 20 ° C. or lower.

The firing step may be performed in any atmosphere, but is preferably performed in air.
As a result, an apparatus having a relatively simple structure can be used in the firing step, and it is not necessary to adjust the composition of the atmosphere or the like, and the productivity of the adsorbent (heavy metal adsorbent) can be improved. Further, even when the digestive juice of sludge contains a phosphorus compound other than phosphoric acid (including a salt of phosphoric acid), the oxidation number of phosphorus is adjusted in this step to efficiently form a calcium phosphate-based compound. Can be done.

<Watering process>
The calcined product obtained in the calcining step as described above may be used as it is as an adsorbent (heavy metal adsorbent), but a liquefaction step of hydration may be further provided after the calcining step.

This improves the chemical stability of the adsorbent (heavy metal adsorbent). Further, the hydrophilicity of the adsorbent (heavy metal adsorbent) is improved. For example, when the object to be treated by the adsorbent (heavy metal adsorbent) contains water, the adsorbent (heavy metal adsorbent) and the object to be treated Affinity with (wetting property of the object to be treated with the adsorbent (heavy metal adsorbent)) can be further improved. As a result, for example, the object to be treated can be suitably penetrated into the pores of the adsorbent (heavy metal adsorbent), and the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent) is further improved.

The liquefaction step can be performed by bringing the fired product into contact with water, for example, immersing the fired product in a liquid containing water or spraying the fired product with a liquid containing water. It can be done by things such as.

According to the method for producing an adsorbent (heavy metal adsorbent) of the present invention as described above, a simple method for producing an adsorbent capable of efficiently removing heavy metals even when the hydrogen ion index (pH) is large. Can be manufactured efficiently.

Further, in the method for producing an adsorbent (heavy metal adsorbent) of the present invention, by adjusting the production conditions, more specifically, for example, the ratio of the phosphorus compound to the dolomites, the heat treatment conditions in the firing step, and the like. The ease of adsorption of heavy metals can be adjusted. Thereby, for example, the selectivity of a specific type of heavy metal can be enhanced, and it can be suitably applied to the recovery, purification, etc. of the specific heavy metal.

[Adsorbent (heavy metal adsorbent)]
Next, the adsorbent (heavy metal adsorbent) produced by the above-mentioned method for producing an adsorbent will be described.

The adsorbent (heavy metal adsorbent) according to the present invention contains dolomites and phosphate ions, and at least a part of the phosphate ions chemically bonds (ionic bonds) with Ca constituting the dolomites, and is a calcium phosphate-based compound. Is characterized by forming.

This makes it possible to provide an adsorbent capable of efficiently removing heavy metals even when the hydrogen ion index (pH) is large.

In particular, the adsorbent (heavy metal adsorbent) according to the present invention can remove arsenic, which has been particularly difficult to remove with a high removal rate in the past, with a high removal rate.

In the adsorbent (heavy metal adsorbent) according to the present invention, it is preferable that most of the phosphate ions are chemically bonded to Ca constituting dolomites.

More specifically, when 1 g of the adsorbent is mixed with 10 mL of water at 25 ° C., the elution amount of phosphate ions is preferably 100 ppm or less, more preferably 50 ppm or less, and more preferably 30 ppm or less. It is even more preferable to have it.

When such conditions are satisfied, phosphorus is more stably fixed in the adsorbent (heavy metal adsorbent), and the adsorbent (heavy metal adsorbent) is used for a long period of time, or a large amount of object to be treated. (When a large amount of the object to be treated is brought into contact with the adsorbent (heavy metal adsorbent)), the heavy metal can be stably removed with excellent efficiency.

The elution amount of phosphate ions when the adsorbent (heavy metal adsorbent) is mixed with water is measured, for example, by mixing the adsorbent (heavy metal adsorbent) and water and stirring for 1 hour. Can be sought.

The fact that the phosphate ion is chemically bonded to Ca constituting dolomites means that, for example, the adsorbent (heavy metal adsorbent) was brought into contact with water as described above and then brought into contact with a low pH liquid. In some cases, it can be confirmed by the fact that the elution amount of phosphate ions increases significantly.

More specifically, it can be confirmed by significantly increasing the elution amount of phosphate ions when 1 g of the adsorbent (heavy metal adsorbent) is mixed with 10 mL of 1N hydrochloric acid at 25 ° C.

The elution amount of phosphate ions when 1 g of the adsorbent (heavy metal adsorbent) is mixed with 10 mL of 1N hydrochloric acid at 25 ° C is the total phosphorus (adsorption amount) contained in the adsorbent (heavy metal adsorbent). It is preferably 30% or more, more preferably 60% or more, and even more preferably 80% or more.

When such a condition is satisfied, more phosphorus is fixed in the adsorbent (heavy metal adsorbent), and a particularly excellent ability to remove heavy metals can be obtained. Therefore, when the adsorbent (heavy metal adsorbent) is used for a long period of time, or when a large amount of the object to be treated is treated (that is, when a large amount of the object to be treated is brought into contact with the adsorbent (heavy metal adsorbent)). However, heavy metals can be stably removed with excellent efficiency.

The elution amount of phosphate ions when the adsorbent (heavy metal adsorbent) is mixed with 1N hydrochloric acid is measured after, for example, the adsorbent (heavy metal adsorbent) and 1N hydrochloric acid are mixed and stirred for 1 hour. Can be obtained by performing.

The adsorbent (heavy metal adsorbent) is usually a porous body.
As a result, the unit mass of the adsorbent (heavy metal adsorbent) and the surface area per unit volume can be increased, and the efficiency of removing heavy metals can be further improved.

The average pore diameter of the adsorbent (heavy metal adsorbent) 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.

This makes it possible to further improve the efficiency of removing heavy metals by the adsorbent while ensuring the durability of the adsorbent (heavy metal adsorbent).

The BET specific surface area of the adsorbent (heavy metal adsorbent) 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.
As a result, the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent) is further improved.

The shape and size of the adsorbent (heavy metal adsorbent) are not particularly limited, but when the adsorbent (heavy metal adsorbent) is in the form of particles, the average particle size is preferably 3 μm or more and 300 mm or less. It is more preferably 100 μm or more and 250 mm or less, further preferably 1 mm or more and 200 mm or less, and most preferably 10 mm or more and 150 mm or less.

[How to remove heavy metals]
Next, a method for removing heavy metals using the adsorbent (heavy metal adsorbent) of the present invention will be described.

The heavy metal can be removed by bringing the adsorbent (heavy metal adsorbent) according to the present invention into contact with the object to be treated containing the heavy metal.
As a result, heavy metals can be efficiently removed from the object to be treated.

The form of the object to be treated when removing heavy metals is not particularly limited, but usually has fluidity, and examples thereof include liquid (including paste and slurry) and gaseous.

In particular, the form of the object to be treated is preferably liquid. As a result, the object to be treated can be suitably contacted with the adsorbent (heavy metal adsorbent) (for example, preferably penetrates into the pores of the adsorbent (heavy metal adsorbent)) to remove heavy metals more efficiently. it can.

When the adsorbent (heavy metal adsorbent) is brought into contact with the object to be treated, the pH (hydrogen ion index) of the mixture of the adsorbent (heavy metal adsorbent) and the object to be treated is preferably 5 or more. The above is more preferable, and 11 or more and 14 or less is further preferable.

As a result, the efficiency of removing heavy metals by the adsorbent (heavy metal adsorbent) can be further improved. In particular, with the conventional adsorbent, in the high pH region as described above, the removal efficiency of heavy metals may be remarkably lowered, but with the adsorbent (heavy metal adsorbent) according to the present invention, there is a tendency that the removal efficiency of heavy metals is remarkably lowered. Particularly excellent heavy metal removal efficiency can be obtained in the high pH region as described above. That is, when the adsorbent is used at a high pH as described above, the above effect is more prominently exhibited.

In particular, when the heavy metal to be removed is Pb (lead), the pH at the time of contact between the adsorbent (heavy metal adsorbent) and the object to be treated is preferably 5 or more, and the heavy metal to be removed is Cd (cadmium). ), The pH at the time of contact between the adsorbent (heavy metal adsorbent) and the object to be treated is preferably 8 or more, and when the heavy metal to be removed is a heavy metal other than Pb and Cd, the adsorbent (heavy metal adsorbent). The pH at the time of contact between the heavy metal adsorbent) and the object to be treated is preferably 10 or more.

The object to be treated may be anything that may contain heavy metals to be removed, such as factories, laboratories, power plants, building demolition sites, wastewater from mines, etc. Examples include sewage sludge combustion ash, liquids containing the ash, and well water.

The object to be treated may contain a heavy metal to be removed, regardless of whether or not it actually contains a heavy metal.

However, the content of heavy metals in the object to be treated (when a plurality of types of heavy metals are contained, the total content of these heavy metals) is not particularly limited, but is preferably 0.001 ppm or more and 100,000 ppm or less. It is more preferably 0.01 ppm or more and 10,000 ppm or less.

As a result, the removal rate (adsorption rate) of heavy metals can be made particularly high, and the content of heavy metals in the object to be treated after treatment can be made particularly low.

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

For example, the sludge treatment method and the adsorbent (that is, heavy metal adsorbent) manufacturing method of the present invention have steps other than the above-mentioned steps (for example, pretreatment step, intermediate treatment step, posttreatment step, etc.). You may. For example, the method for producing an adsorbent (heavy metal adsorbent) of the present invention may include a step of crushing or crushing the fired product or a step of classifying the fired product after the firing step. Further, the method for producing an adsorbent (heavy metal adsorbent) of the present invention may include a molding step for obtaining an adsorbent (heavy metal adsorbent) molded into a predetermined shape.

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 apparatus, an intermediate treatment apparatus, a posttreatment apparatus, etc.).

In the above-described embodiment, the case where the treatment with aerobic bacteria is performed after the adsorption treatment has been typically described, but the treatment with aerobic bacteria may be omitted. More specifically, for example, if phosphorus can be sufficiently removed by the adsorption treatment, the treatment with aerobic bacteria may be omitted.

Further, in the above-described embodiment, the method for producing the adsorbent (heavy metal adsorbent) of the present invention has been typically described with respect to the case where the liquefaction step is provided after the firing step, but the method for producing the adsorbent of the present invention is described. , It does not have to have a liquefaction step.

Hereinafter, the present invention will be described in detail based on specific examples, but the present invention is not limited thereto.

<< 1 >> Relationship between the amount of adsorbent and the phosphorus removal rate (Experimental Example 1)
First, 0.5N hydrochloric acid was prepared.

Next, 200 mL of this hydrochloric acid was separated, and 10 g of sludge ash was added thereto to completely dissolve the phosphorus component.

Next, 100 mL of the hydrochloric acid in which the phosphorus component was dissolved was dispensed into each of the three containers, and particulate dolomite ore having an average particle size of 1 mm: 0.3 g, 0.5 g, and 1.0 g was added thereto. In addition, it was stirred for 30 minutes.

After the stirring was completed, the adsorbent (raw dolomite) 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 the adsorption rate of the phosphorus component by the adsorbent (raw dolomite) was determined from the result.

Further, except that the amount of the adsorbent (raw dolomite) used was variously changed, the measurement was carried out in the same manner as described above to determine the adsorption rate of the phosphorus component by the adsorbent (raw dolomite).
The results of this experiment are shown in FIG.

(Experimental Example 2)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 1 except that dilomite hydroxide having an average particle size of 1 mm was used instead of the rough dolomite having an average particle size of 1 mm as the adsorbent. ..
The results of this experiment are shown in FIG.

(Experimental Example 3)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 1 except that lightly baked dolomite having an average particle size of 1 mm was used as the adsorbent instead of the rough dolomite having an average particle size of 1 mm. ..
The results of this experiment are shown in FIG.

(Experimental Example 4)
The adsorption rate of the phosphorus component by the adsorbent was determined in the same manner as in Experimental Example 1 except that lightly baked dolomite having an average particle size of 3 mm was used as the adsorbent instead of the rough dolomite having an average particle size of 1 mm. ..
The results of this experiment are shown in FIG.

As is clear from FIGS. 6 to 9, it can be seen that the phosphorus component in the sludge can be efficiently removed by adsorption by bringing the sludge into contact with an adsorbent (particularly dolomites).

Further, in any of the adsorbents, the removal rate of phosphorus increases as the amount of the adsorbent increases. In particular, in Experimental Examples 2 to 4 using dolomite hydroxide and dolomite lightly as the adsorbent, 1 g of the adsorbent Phosphorus can be removed at a rate of almost 100%.

<< 2 >> Relationship between pH and phosphorus removal rate (Experimental Example 5)
First, sludge was prepared. This sludge contained phosphorus.

Next, this sludge was subjected to methane fermentation treatment, which is an anaerobic treatment using anaerobic microorganisms, and nitrification denitrification treatment, which is an oxygen-free treatment, to obtain a digestive juice.
Hydrochloric acid was added dropwise to this digestive juice to adjust the pH to a predetermined value.

Only 100 mL of the digestive juice whose pH was adjusted in this manner was separated, and a predetermined amount of rough dolomite having an average particle size of 1 mm was added thereto, and the mixture was stirred for 30 minutes.

After the stirring was completed, the rough dolomite, which was an adsorbent, 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 the adsorption rate of the phosphorus component by the adsorbent (raw dolomite) was determined from the result. In addition, 80% by mass or more of the phosphorus component in the liquid was phosphoric acid or a salt thereof.

Further, the measurement was carried out 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 (raw dolomite) was determined.
The results of this experiment are shown in FIG.

(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 dilomite hydroxide having an average particle size of 1 mm was used as the adsorbent instead of the rough dolomite having an average particle size of 1 mm. ..
The results of this experiment are shown in FIG.

(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 baked dolomite having an average particle size of 1 mm was used as the adsorbent instead of the rough dolomite having an average particle size of 1 mm. ..
The results of this experiment are shown in FIG.

(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 baked dolomite having an average particle size of 3 mm was used as the adsorbent instead of the rough dolomite having an average particle size of 1 mm. ..
The results of this experiment are shown in FIG.

As is clear from FIGS. 10 to 13, the phosphorus component contained in the digestive juice can be efficiently adsorbed and removed by adding the adsorbent, and the phosphorus component contained in the digestive liquid (liquid) after the adsorption treatment can be efficiently adsorbed and removed. It was confirmed that the content of It was also confirmed that the adsorption rate of the phosphorus component depends on the adsorbent conditions and the pH conditions.

<< 3 >> Relationship between treatment time (contact time) and phosphorus removal rate (Experimental Example 9)
First, sludge was prepared. This sludge contained phosphorus.

Next, this sludge was subjected to methane fermentation treatment, which is an anaerobic treatment using anaerobic microorganisms, and nitrification denitrification treatment, which is an oxygen-free treatment, to obtain a digestive juice.

Only 100 mL of this digested liquid was separated, and 0.8 g of particulate dolomite hydroxide having an average particle size of 1 mm was added thereto, and the mixture was stirred for 30 minutes.

After the stirring was completed, the adsorbent (dolomite hydroxide) 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 the adsorption rate of the phosphorus component by the adsorbent (dolomite hydroxide) was determined from the result.

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

As is clear from FIG. 14, 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 liquid (liquid) after the adsorption treatment is contained. It was confirmed that the amount could be lowered sufficiently. In particular, phosphorus can be removed at a rate of almost 100% in a contact time of about 5 minutes.

<< 4 >> Relationship between initial phosphorus concentration and phosphorus adsorption amount for dolomites and activated carbon First, a plurality of types of phosphoric acid aqueous solutions having a predetermined phosphorus concentration (P-equivalent concentration) were prepared.

For each of these phosphoric acid aqueous solutions, 0.1 g of calcined dolomite as an adsorbent was added to 100 mL of the phosphoric acid aqueous solution, and the mixture was stirred for 30 minutes.

Then, the calcined dolomite was filtered off, and the amount of phosphorus adsorbed by the calcined dolomite (value in terms of P) was determined.

Further, the same treatment as described above was carried out except that activated carbon was used as the adsorbent instead of calcined dolomite, and the amount of phosphorus adsorbed by the activated carbon (value in terms of P) was determined.
The result is shown in FIG.

As is clear from FIG. 15, it can be seen that calcined dolomite, which is a dolomite, has a larger amount of phosphorus adsorbed per unit weight than activated carbon. From this, it can be seen that by using dolomites among various adsorbents, the phosphorus component in the digestive juice of sludge can be adsorbed particularly efficiently. Further, for example, when activated carbon is adsorbed, the activated carbon after adsorbing phosphorus is usually discarded because there is no effective utilization method, but by using dolomites as an adsorbent for phosphorus components. , The dromite after adsorbing phosphorus can be effectively used as an adsorbent capable of efficiently removing heavy metals.

<< 5 >> Relationship between combustion temperature and phosphorus removal rate First, sludge was prepared. This sludge contained phosphorus.

Next, this sludge was subjected to methane fermentation treatment, which is an anaerobic treatment using anaerobic microorganisms, nitrification denitrification treatment, which is an oxygen-free treatment, and aerobic treatment to obtain digestive sludge.

Then, after the digestive sludge was dehydrated and dried, the concentration of the phosphorus component was determined for a part thereof in the same manner as described above. In addition, a part of the remainder of the dehydrated and dried digested sludge was burned at 600 ° C. for 5 minutes. With respect to the combustion ash obtained by combustion, the concentration of the phosphorus component was determined in the same manner as described above. From these results, the amount of phosphorus contained in the sludge ash was determined. In addition, the amount of decrease in phosphorus component due to combustion was determined.

Further, the digested sludge was burned in the same manner as described above except that the combustion temperature was variously changed, and the amount of decrease in the phosphorus component due to the combustion was determined.
The results of this experiment are shown in FIG.

As is clear from FIG. 16, as the combustion temperature of the digested sludge rises, the content of phosphorus transferred to the combustion ash decreases, and it can be seen that the phosphorus component evaporates in the combustion step. In particular, it can be seen that the higher the combustion temperature, the lower the phosphorus content of the combustion ash, and the higher the evaporation amount of the phosphorus component.

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

The adsorbents used in each of the above experimental examples are all porous, have an average pore diameter in the range of 5 nm or more and 30 nm or less, and have a BET specific surface area of 40 m ² / g or more and 1000 m ² / g or less. It was a value within the range of.

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

Further, in the above experimental example, the digestive juice was brought into contact with the adsorbent by adding an adsorbent to the digestive juice and mixing, but the digestive juice can also be passed through a column filled with the adsorbent. It is presumed that the following results can be obtained.

From the above results, it is presumed that the adverse effect on the combustion furnace and the like during combustion can be reduced.

<< 6 >> Production of Adsorbent (Example 1)
First, by the same treatment as described in Experimental Example 5, 30 rough dolomite composed of porous dolomite having an average particle size of 1 mm and an average pore size of 10 to 20 nm and sludge digested liquid were prepared. Mixing and stirring for 1 minute (adsorption step).

After the stirring was completed, solid-liquid separation was performed, and the rough dolomite on which the phosphorus compound was adsorbed was calcined (calcining step). In the firing treatment, first, the temperature is raised from room temperature to 200 ° C. at a heating rate of 10 ° C./min, held at 200 ° C. for 2 hours, and then the temperature is raised to the maximum firing temperature of 800 ° C./min. The temperature is raised in minutes and held at the maximum firing temperature of 800 ° C. for 2 hours, then lowered to 200 ° C. at a temperature lowering rate of 5 ° C./min, held at 200 ° C. for 2 hours, and then lowered to room temperature. Velocity: The temperature was lowered at 10 ° C./min.

Next, the fired product obtained as described above was hydrated by immersing it in water, and then solid-liquid separated and air-dried. Then, it was ground in a mortar to obtain a powdery adsorbent (heavy metal adsorbent). The obtained adsorbent contained 1 part by mass of phosphorus derived from sludge with respect to 100 parts by mass of dolomites.

(Example 2)
An adsorbent (heavy metal adsorbent) was produced in the same manner as in Example 1 except that the amount of sludge digested liquid used was changed. The adsorbent thus obtained contained 3 parts by mass of phosphorus derived from sludge with respect to 100 parts by mass of dolomites.

(Example 3)
An adsorbent (heavy metal adsorbent) was produced in the same manner as in Example 1 except that the firing treatment conditions were changed to 900 ° C. for the maximum firing temperature.

(Example 4)
An adsorbent (heavy metal adsorbent) was produced in the same manner as in Example 1 except that the firing treatment conditions were changed to 700 ° C. for the maximum firing temperature.

(Example 5)
An adsorbent (heavy metal adsorbent) was produced in the same manner as in Example 1 except that the firing treatment conditions were changed to 600 ° C. for the maximum firing temperature.

(Example 6)
An adsorbent (heavy metal adsorbent) was produced in the same manner as in Example 1 except that the firing treatment conditions were changed to 400 ° C. for the maximum firing temperature.

(Example 7)
An adsorbent (heavy metal adsorbent) was produced in the same manner as in Example 1 except that hydroxylated dolomite was used instead of the dolomite rough stone.

(Comparative Example 1)
In this comparative example, the rough dolomite used as a raw material in Example 1 was used as it was as an adsorbent.

(Comparative Example 2)
In this comparative example, the hydroxylated dolomite used as a raw material in Example 7 was used as it was as an adsorbent.

(Comparative Example 3)
In the same manner as in Example 7, after adsorbing the phosphorus compound on the hydroxylated dolomite, solid-liquid separation was performed. Then, the separated solid phase was naturally dried at room temperature without being calcined to obtain an adsorbent.

Table 1 summarizes the production conditions of the adsorbents of each of the Examples and the Comparative Examples, the composition of the adsorbents, and the like. The BET specific surface area is a numerical value obtained by measurement using a surface area measuring device (TriStarII3020 manufactured by Mircometrics). Moreover, in each of the said Examples, the average particle diameter of the adsorbent was a value within the range of 1 mm or more and 3 mm or less. Further, in each of the above-mentioned examples, the pH of the mixture containing the dolomites and the digestive juice of sludge in the adsorption step was 5 or more and 6 or less. Further, in each of the above-mentioned examples, the value of the elution amount of phosphate ions obtained by mixing 1 g of the adsorbent at 25 ° C. with 10 mL of water, stirring for 1 hour, and then performing the measurement is 10 ppm or less. After that, the solid-liquid separation was performed, 1 g of the adsorbent was mixed with 10 mL of 1N hydrochloric acid at 25 ° C., and the mixture was stirred for 1 hour. It was 80% or more of the total phosphorus (adsorption amount) contained in. From this result, it can be seen that in each example, most of the phosphate ions chemically bond with Ca constituting dolomites to form a calcium phosphate-based compound in the adsorbent.

Further, when the components of the adsorbents of the above Examples were analyzed by X-ray diffraction (XRD), all of them contained calcium phosphate compounds (calcium phosphate, anhydrous calcium hydrogen phosphate, hydroxyapatite). It was confirmed that. FIG. 17 shows a calcined dolomite obtained by sintering dolomite used as a raw material at 900 ° C., and an adsorbent obtained by adsorbing a phosphorus component on the sintered dolomite and then calcining (fixing) the dolomite. , And the analysis result of X-ray diffraction (XRD) in the state where Pb is adsorbed on the adsorbent is shown.

<< 7 >> Evaluation First, a standard solution A having a pH of 12 containing arsenic (As) at a content of 2000 ppb and substantially no other heavy metals, and arsenic (As), nickel (Ni), and cadmium (Cd). ), Lead (Pb), and chromium (Cr) were each contained at a content of 2000 ppb, and a standard solution B having a pH of 12 was prepared.

Next, for the adsorbents of each of the Examples and Comparative Examples, separately, the adsorbent: 0.01 g was added to the standard solution A: 50 mL and the standard solution B: 50 mL in Examples 1 and 2. In Examples 3, 4, 5, 5, 6 and 7, an adsorbent: 0.1 g was added, stirred for 1 hour, solid-liquid separated, and the liquid phase was arsenic by ICP mass spectrometry. The content of (As) and chromium (Cr) was determined, and the removal rate by the adsorbent was determined from the value of the content.
These results are summarized in Table 2.

As is clear from Table 2, in the present invention, arsenic, which is a heavy metal, could be removed (adsorbed) with a high removal rate (adsorption rate). In particular, in the past, it was possible to efficiently remove heavy metals in a high pH state, where it was difficult to increase the removal rate of heavy metals.
On the other hand, satisfactory results were not obtained in each comparative example. Moreover, in each comparative example, the removal rate of heavy metals was low, and the measured values were not stable. In particular, such a tendency was remarkable in the measurement of the removal rate of chromium.

Further, regarding the liquid phase after the standard liquid B is treated with the adsorbent as described above, the removal rate of heavy metals (nickel, cadmium, lead, chromium) other than arsenic by the adsorbent is the same as described above. As described above, in each of the present inventions, each heavy metal could be removed (adsorbed) with a high removal rate (adsorption rate), whereas in each comparative example, each heavy metal was removed. The rates were all low.

Further, for the adsorbents of Examples 1 and 2, 0.01 g of the adsorbent was separately added to 50 mL of the standard solution B, and the mixture was stirred for 1 hour. After that, solid-liquid separation is performed, and the content of arsenic (As), nickel (Ni), cadmium (Cd), lead (Pb), and chromium (Cr) in the liquid phase by ICP mass spectrometry (Inductively Coupled Plasma Mass Spectrometry). Was determined, the amount adsorbed by the adsorbent (removal rate) was determined from the value of the content rate, and the amount of adsorption (removal amount) of each heavy metal per 1 g of the adsorbent was determined. The results are shown in FIGS. 18 and 19, respectively. As is clear from these figures, it can be seen that heavy metals can be adsorbed (removed) at a high rate in each case.

Further, with respect to the adsorbents of each of the Examples and Comparative Examples, except that each liquid prepared in the same manner as the standard solution A was used as the standard solution except that the pH was varied between 10 and 14. As a result of the same evaluation as described above, in each of the examples, arsenic, which is a heavy metal, could be removed (adsorbed) with a high removal rate (adsorption rate), whereas in each comparative example, it was possible to remove (adsorb) arsenic. The removal rate of each heavy metal was low.

Further, with respect to the adsorbents of each of the Examples and Comparative Examples, except that each liquid prepared in the same manner as the standard solution B was used as the standard solution except that the pH was varied between 10 and 14. As a result of the same evaluation as described above, in each of the examples, arsenic, which is a heavy metal, could be removed (adsorbed) with a high removal rate (adsorption rate), whereas in each comparative example, it was possible to remove (adsorb) arsenic. The removal rate of each heavy metal was low. Further, with the adsorbents of each of the above-mentioned examples, heavy metals other than arsenic could be removed with a high removal rate as well as arsenic.

The sludge treatment method of the present invention includes an adsorption step of bringing the digestive juice of sludge into contact with an adsorbent and adsorbing at least a part of the phosphorus component contained in the digestive juice to the adsorbent to remove it, and the adsorption step. It has a combustion step of burning the digested sludge obtained by removing at least a part of the phosphorus component from the digestive juice. Further, the sludge treatment system of the present invention includes an adsorption treatment unit that brings the digestive juice of sludge into contact with an adsorbent and adsorbs at least a part of the phosphorus component contained in the digestive juice to the adsorbent to remove it. The adsorption treatment unit includes a combustion furnace for burning the digested sludge obtained by removing at least a part of the phosphorus component 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 phosphorus components that evaporate during combustion and suppressing adverse effects on the combustion furnace. Therefore, the sludge treatment method and sludge treatment system of the present invention have industrial applicability.

Further, the method for producing an adsorbent of the present invention includes an adsorption step of bringing sludge digestive juice into contact with dolomites and adsorbing at least a part of phosphorus components contained in the digestive juice to the dolomites, and the digestion. It has a firing step of firing the dolomites in contact with the liquid. Therefore, it is possible to provide a method for producing an adsorbent, which can produce an adsorbent capable of efficiently removing heavy metals even when the hydrogen ion index (pH) is large, using sludge as a raw material. Therefore, the method for producing an adsorbent of the present invention has industrial applicability.

1 ... Processing system 20 ... Digestion processing unit 21 ... Anaerobic tank (Methane fermentation processing unit)
22 ... Anoxic tank (nitrification and denitrification treatment section)
221 ... Anoxic part 222 ... Aerobic part 23 ... Aerobic tank (Aerobic bacteria digestion processing part)
30 ... Adsorption processing unit (adsorption tank)
30'... Adsorption processing unit 31 ... Processing tank 32 ... First pipe 33 ... Second pipe 34 ... Contaminant removing means 35 ... Column (container)
36 ... Adsorbent 50 ... Dehydrator 60 ... Combustion furnace 61 ... Flow medium (sand)
62 ... Dispersion plate 63 ... Gas supply unit 70 ... Drying device S1 ... Sludge S ... Digestive juice SS ... Digestive sludge

Claims (8)

An adsorption step in which the digestive juice of sludge is brought into contact with an adsorbent, and at least a part of the phosphorus component contained in the digestive juice is adsorbed on the adsorbent to be removed.
A method for treating sludge, which comprises a combustion step of burning digested sludge obtained by removing at least a part of a phosphorus component from the digestive juice in the adsorption step. The sludge treatment method according to claim 1, wherein dolomites are used as the adsorbent in the adsorption step. The sludge treatment method according to claim 2, wherein the dolomites are hydroxylated dolomite. The sludge treatment method according to claim 2, wherein the dolomites are dolomite. The sludge treatment method according to any one of claims 1 to 4, wherein the adsorption step is performed under the condition that the pH is 3 or more and 13 or less. The sludge treatment method according to any one of claims 1 to 5, wherein the combustion temperature in the combustion step is 500 ° C. or higher and 1500 ° C. or lower. An adsorption treatment unit that brings the digestive juice of sludge into contact with an adsorbent and adsorbs at least a part of the phosphorus component contained in the digestive juice to the adsorbent to remove it.
A sludge treatment system comprising a combustion furnace for burning digestive sludge obtained by removing at least a part of a phosphorus component from the digestive juice in the adsorption treatment unit. An adsorption step in which the digestive juice of sludge is brought into contact with dolomites and at least a part of the phosphorus component contained in the digestive juice is adsorbed on the dolomites.
A method for producing an adsorbent, which comprises a firing step of calcining the dolomites in contact with the digestive juice.

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