WO2023181430A1

WO2023181430A1 - Metal salt aggregating agent

Info

Publication number: WO2023181430A1
Application number: PCT/JP2022/023668
Authority: WO
Inventors: 禎治糠谷; 伸哉近藤; 達郎戸嶋; 美穂駒井
Original assignee: 日鉄鉱業株式会社
Priority date: 2022-03-22
Filing date: 2022-06-13
Publication date: 2023-09-28
Also published as: KR20230138876A; TW202337831A; KR102592806B1; JP2023139777A

Abstract

The total content of aluminum ions and iron ions in 1 liter of this metal salt aggregating agent is 5.7 mol or less, wherein the mole ratio (Cl/Fe) between chlorine ions and iron ions is 28 or more, the mole ratio (SO4/Al2O3) between sulfate ions and aluminum ions in terms of aluminum oxide is 0.15 or less, and the coliform removal ratio is 83% or more. By virtue of mixing polyferric sulfate and polyaluminum chloride and using same in combination, this metal salt aggregating agent exhibits higher storage stability and aggregating performance compared with the case where polyferric sulfate and polyaluminum chloride are individually used, and this metal salt aggregating agent can also be applied to a wide range of treatment waste liquids having various characteristics. This metal salt aggregating agent also has a coliform removal action.

Description

metal salt flocculant

The present invention relates to metal salt flocculants and various chemicals containing iron ions and aluminum ions used in wastewater treatment. The present invention also relates to a metal salt flocculant and various drugs that also have the effect of removing E. coli.

At sewage treatment plants and human waste treatment plants, iron-based and aluminum-based metal salt flocculants are applied to the water being treated to improve the quality of effluent water, reduce the amount of waste, ensure smooth operation, and extend the life of the facility. It is used by inserting it into the Typical iron-based flocculants include ferric chloride, polyferric sulfate, and ferrous sulfate solutions, and aluminum-based flocculants include aluminum sulfate, aluminum chloride, and polyaluminum chloride. .

Ferric polysulfate is one of the representative examples of iron-based inorganic flocculants, and is widely used in sewage treatment plants and human waste treatment because it has deodorizing and dephosphorizing effects. Polyferric sulfate is represented by the general formula ([Fe ₂ (OH)n(SO ₄ ) _3-n/2 ]m, where 0<n≦2, m is a natural number), and is composed of ferric sulfate, which is an iron-based raw material. It can be obtained by a method such as adding sodium nitrite and an oxidizing agent as a catalyst to a monoferric (FeSO ₄ ) solution to allow an oxidation reaction to proceed (Patent Document 1).
Polyaluminum chloride (commonly known as PAC) is one of the representative examples of aluminum-based inorganic flocculants.It has a high ability to treat suspended solids and soluble organic matter, has a wide optimum pH range, and is not affected by water temperature. It is widely used in water treatment plants because it is possible to reduce the concentration of coagulant added and the water after treatment is not colored. PAC is a flocculant having a certain basicity (=m/3n×100) (Patent Document 2), has the general formula Aln(OH)mCl _{3n-m (3n>m), and is a flocculant that has a certain basicity (=m/3n×100) and is expressed by the general formula Aln(OH)mCl 3n-m} (3n>m), and is a flocculant that has a certain basicity (=m/3n×100). It can be obtained by adding aluminum hydroxide to a solution and heating and pressurizing it in a pressure-resistant reactor (Patent Documents 3 and 4).

In general, inorganic flocculants with a high concentration of the main inorganic component have a higher flocculating effect, which makes it possible to reduce the amount of chemicals used and is also advantageous in terms of transportation. For example, by making polyferric sulfate a higher concentration (total iron concentration of 12.5% or more) compared to regular products (total iron concentration of 11.0 to 12.5%) and reducing the water content, , has high flocculation ability and dewatering ability, and can reduce product transportation costs.

Polyaluminum chloride manufactured and sold in Japan for use as a water treatment flocculant has an Al ₂ O ₃ concentration of approximately 10% (weight percent) or more (hereinafter referred to as a regular product). High-concentration products with an Al ₂ O ₃ concentration exceeding 15% are not sold in Japan due to problems with solution stability, but high-concentration products with an Al ₂ O ₃ concentration exceeding 10% are not sold in Japan. Inventions related to products have already been reported (Patent Documents 5 and 6). Patent Document 5 discloses a method for producing a highly basic aluminum chloride solution with an Al ₂ O ₃ concentration of 5 to 25 wt%, and Patent Document 6 discloses a method for producing a highly basic aluminum chloride solution with an Al ₂ O ₃ concentration of 16 to 25%. A highly concentrated flocculant containing aluminum as a main ingredient is disclosed.

In recent years, attempts have been made to mix iron-based flocculants and aluminum-based flocculants and use them as a metal salt flocculant containing iron ions and aluminum ions, in order to bring out their respective characteristics. (Patent Documents 7 and 8).
Patent Document 7 discloses an inorganic flocculant having an Al/Fe weight ratio of 1/30 to 1/2, and Patent Document 8 discloses an iron-containing flocculant having an Al/Fe molar ratio of 0.06 to 1.0. Discloses a flocculant using waste hydrochloric acid.

Special Publication No. 51-17516 Special Publication No. 47-21401 Special Publication No. 49-21239 Japanese Patent Publication No. 09-142837 Japanese Patent Application Laid-Open No. 52-111496 Japanese Patent Application Publication No. 2000-70609 Japanese Unexamined Patent Publication No. 63-7808 Japanese Unexamined Patent Publication No. 1-180210

An example of the use of a metal salt flocculant containing iron ions and aluminum ions is that adding iron-based polyferric sulfate to reducing wastewater may cause some coloring, so to prevent this, aluminum chloride or It is known to use a flocculant containing sulfuric acid. Additionally, in paper factories and the like, iron-based flocculants are sometimes mixed with the aluminum-based chemicals that are mainly used in order to impart a deodorizing effect.
However, it is known that problems may occur depending on the combination.
For example, a combination of aluminum chloride and ferric polysulfate provides a high aggregation effect, but is highly corrosive and has storage stability problems such as alum precipitation due to temperature drop. Although the combination of sulfuric acid band and ferric polysulfate has low corrosivity and excellent stability, it requires a large amount of chemicals to be added compared to other flocculants, making it uneconomical.
In addition, metal salt flocculants containing iron and aluminum ions have been prepared by mixing iron-based ferric chloride and polyferric sulfate with polyaluminum chloride, which has the highest cohesive force among aluminum-based materials. However, storage stability was extremely poor, including gelation in a short period of time, and it has not been commercially available.
Furthermore, in metal salt flocculants containing iron ions and aluminum ions, in Patent Documents 7 and 8, the main cation is iron ions, but metal salt flocculants with a composition in which aluminum ions are present in a large amount relative to iron ions are used. The preparation of the iron-containing polyaluminum chloride has not been previously reported.

The first objective of the present invention is to mix and combine polyferric sulfate and polyaluminum chloride, both of which are known to have high flocculation ability, compared to when each is used alone. To provide a metal salt flocculant containing iron ions and aluminum ions, which has higher flocculation ability, has excellent storage stability, and can be applied to a wide range of treated wastewater having various characteristics. It is.
A second object of the present invention is to provide a metal salt flocculant that also has the effect of removing E. coli.

In order to solve these problems, the metal salt flocculant of the present invention is composed of the following technical means.
[1] A metal salt flocculant, in which the total content of aluminum ions and iron ions is 5.7 moles or less in 1 liter of the metal salt flocculant, and the molar ratio of chloride ions to iron ions (Cl/ Fe) is 28 or more, the molar ratio of aluminum ions (SO ₄ /Al ₂ O ₃ ) in terms of sulfate ions and aluminum oxide is 0.15 or less, and the removal rate of E. coli is higher than 83%. Flocculant.
[2] The metal salt flocculant according to [1], wherein the molar ratio of chloride ions to iron ions (Cl/Fe) is 50 or more and 104 or less.
[3] The metal salt flocculant according to [1] or [2], which has an E. coli removal rate of higher than 90%.
[4] The metal salt flocculant according to [1] or [2], which has a pH of 3.7 to 4.2 (100 times diluted solution) and a specific gravity of 1.35 to 1.45.
[5] A flocculant containing the metal salt flocculant according to [1] or [2].
[6] A water quality improving agent containing the metal salt flocculant according to [1] or [2].
[7] A deodorant containing the metal salt flocculant according to [1] or [2].
[8] A dehydrating agent containing the metal salt flocculant according to [1] or [2].
[9] A wastewater color reducing agent containing the metal salt flocculant according to [1] or [2].
[10] A method for treating sludge wastewater, the method comprising the step of adding the metal salt flocculant according to [1] or [2] to sludge wastewater.
[11] A method for purifying and deodorizing water, the method comprising the step of adding the metal salt flocculant described in [1] or [2] to water in which pathogenic microorganisms are thought to be present.
[12] A new method for using the metal salt flocculant according to [1] or [2] for removing pathogenic microorganisms in wastewater.
[13] A new method for using the metal salt flocculant according to [1] or [2] for removing E. coli from wastewater.

According to the first aspect of the metal salt flocculant of the present invention, by mixing and combining polyferric sulfate and polyaluminum chloride, which are known to have a high flocculating ability, the metal salt flocculant has a high flocculating ability. However, it has become possible to provide a metal salt flocculant containing iron ions and aluminum ions, which has excellent storage stability and can be applied to a wide range of treated wastewater having various characteristics.
According to a second aspect of the present invention, there is provided a metal salt flocculant which, in addition to the above-mentioned effects, further has an E. coli removing effect.

FIG. 1 is a processing flow diagram of a sewage treatment plant (actual test field 1). FIG. 2 is a processing flow diagram of a sewage treatment plant (actual test field 2). FIG. 3 is a diagram showing the sludge capacity index (SVI) of the reaction tank. FIG. 4 is a diagram showing the change in TP concentration in the final sedimentation tank overflow water.

[Metal salt flocculant 1]
The present inventors have discovered that by adding and mixing a predetermined amount of polyferric sulfate to polyaluminum chloride, a metal containing iron ions and aluminum ions has high storage stability and excellent water treatment performance. It was discovered that a salt flocculant can be obtained.
That is, the present invention provides a metal salt flocculant in which the total content of aluminum ions and iron ions is 5.7 moles or less in 1 liter of the metal salt flocculant, and the molar ratio of chloride ions to iron ions is (Cl/Fe) is 28 or more, and the molar ratio of aluminum ions (SO ₄ /Al ₂ O ₃ ) in terms of sulfate ions and aluminum oxide is 0.15 or less.
Generally, when polyferric sulfate having a low basicity is blended with polyaluminum chloride having a high basicity, the gelation reaction of the polyaluminum chloride proceeds as the pH decreases. Further, iron ions in the ferric polysulfate generate iron hydroxide and become insolubilized as the pH increases. However, by adjusting the quantitative relationship of the ions constituting the metal salt flocculant of the present invention within a predetermined range, sulfate ions necessary for stabilizing polyaluminum chloride are replenished and gelation is suppressed. In addition, stability can be maintained for iron ions in ferric polysulfate by reducing the supply of alkali.
Generally, whether a water treatment agent can exist stably in a solution state (storage stability) is often determined by the cation concentration and the molar ratio of anions to cations. Therefore, a stable region was determined based on Al+Fe [mol/L], Cl/Fe (molar ratio), and SO ₄ /Al ₂ O ₃ (molar ratio). Note that Cl/Al ₂ O ₃ and SO ₄ /Fe have specific values depending on the chemicals used (polyaluminum chloride and polyferric sulfate), and these molar ratios do not change even if the mixing ratio of both chemicals is changed. Therefore, there is no need to consider it here.
As a result, it was possible to obtain a metal salt flocculant containing iron ions and aluminum ions, which was mainly composed of polyaluminum chloride and mixed with polyferric sulfate. This is a new finding found by the present inventors that is not found in the prior art.

As mentioned above, attempts have been made to produce a high-performance flocculant by mixing polyaluminum chloride with ferric chloride or polyferric sulfate, but the storage stability of the mixed solution It was not successful due to bad nature. In the present invention, such a long-standing problem was solved by adjusting the anion/cation (molar ratio), and the present inventors speculate that this is due to the following mechanism.

That is, polyaluminum chloride as a flocculant often contains sulfate ions, and it is thought that these sulfate ions contribute to the flocculating properties and chemical stability of polyaluminum chloride.
In the present invention, by adjusting the content of sulfate ions and adding sulfate ions in the form of polyferric sulfate, the chemical stability of the mixed solution is not only improved, but although it has not been confirmed, Among the polynuclear complexes (multimers) formed by aluminum ions and iron ions, the proportion of a certain polynuclear complex may be high, and this may contribute to the improvement of the water treatment properties of the metal salt flocculant of the present invention. We estimate that it may be contributing.
In fact, as specifically described below, the metal salt flocculant of the present invention is a flocculant that has significant effects over a wide range of areas.

The polyaluminum chloride used in the present invention preferably has an Al concentration in the range of 2 to 6 mol/L. In addition, the Fe concentration of the ferric polysulfate is preferably in the range of 2 to 4 mol/L.
If the amount of ferric polysulfate added is small, the stability of the iron-containing polyaluminum chloride will be poor and it will not be possible to exhibit good flocculation ability. Moreover, if the amount added is large, the hydrolysis of the ferric polysulfate will progress and iron-based precipitates will precipitate as a by-product, which is not preferable.
The metal salt flocculant obtained in the present invention preferably has a pH of 3.7 to 4.2 (100 times diluted solution) and a specific gravity of 1.35 to 1.45.

The metal salt flocculant obtained by mixing is not only effective as a flocculant, but also has excellent performance in removing phosphorus, nitrogen, COD, or SS, and is effective in deodorization, dehydration, color reduction, bacteria and virus removal, and fluorine. It also has excellent performance in removing TOC. Therefore, by taking advantage of these properties, it can be used not only as a flocculant but also as a wide variety of wastewater treatment agents.

(others)
The metal salt flocculant according to the first embodiment can be injected with the same equipment as ordinary polyaluminum chloride, as is clear from the actual machine test in the chromaticity reduction test described below. Additionally, since the amount of medicine used can be reduced, the frequency of transportation and reception by lorries will be reduced. This leads to reductions in required labor and personnel costs.

[Metal salt flocculant 2]
Although the present invention has been mainly described with respect to the metal salt flocculant according to the first embodiment, the present invention is not limited to the above content. The differences from the metal salt flocculant according to the first embodiment will be mainly explained.

At water treatment sites, in addition to processes such as sludge settling and phosphorus/nitrogen removal as described above, E. coli removal was also performed. Conventionally, sludge sedimentation and E. coli removal have been performed in separate steps using different chemicals.
In recent years, awareness of reducing environmental impact has been increasing, as exemplified by the term Sustainable Development Goals (SDGs). In the field of water treatment, by reducing the amount of chemicals used in water treatment, it is possible to reduce the power consumption of equipment such as pumps that add chemicals, and to reduce the amount of carbon dioxide released when transporting chemicals by tank truck. There was a need to suppress the release of
As a result of a sincere study on further improving the functions of metal salt flocculants, the present inventors discovered that metal salt flocculants, in addition to the above-mentioned basic performance, also have the function of an E. coli remover. .

That is, the metal salt flocculant according to the second embodiment is a metal salt flocculant in which the total content of aluminum ions and iron ions is 5.7 mol or less in 1 liter of the metal salt flocculant. , the molar ratio of chloride ions to iron ions (Cl/Fe) is 28 or more, the molar ratio of aluminum ions (SO ₄ /Al ₂ O ₃ ) in terms of sulfate ions and aluminum oxide is 0.15 or less, and E. coli The present invention relates to a metal salt flocculant having a removal rate of higher than 83%.

According to the metal salt flocculant according to the second embodiment, sludge settling, etc. and E. coli removal can be performed in one step using one type of chemical, thereby simplifying the entire water treatment process. can. Furthermore, by making the chemicals used for water treatment multi-functional, the amount of chemicals used in the overall water treatment can be suppressed, and as a result, the energy required for transporting the chemicals can be reduced.

The mechanism by which the metal salt flocculant according to the second embodiment removes E. coli is not clear, but due to the coagulation-sedimentation effect, E. coli is captured in flocs together with sludge, and then discharged as surplus sludge in the final settling tank. It is thought that this is because of this. It is also believed that the bactericidal effect is exerted by the influence of residual chlorine derived from the drug.

In order to improve the effect of removing E. coli, it is preferable that the area has a high concentration of chlorine ions. Specifically, the molar ratio of chloride ions to iron ions (Cl/Fe) is preferably 28 or more, more preferably 50 or more and 104 or less.
This is because if it is less than 28, the chemical stability of the drug is low and iron hydroxide is precipitated. This is because if it exceeds 104, side effects due to the coexistence of iron ions will be reduced, and there is a risk that residual chlorine contained in the treated water will be in an excessive amount. If there is a large amount of residual chlorine in the treated water, the disinfection effect will be more sustainable, but there are concerns that it may have a negative impact on aquatic organisms living in the water area to which it is discharged.
Moreover, the removal rate of E. coli is more preferably higher than 90%. There is no upper limit to the removal rate of E. coli, and it is 100% or less or about 98%.

The present invention is not limited to metal salt flocculants, but also relates to various methods that take advantage of the characteristics of the metal salt flocculants 1 and 2 described above.

[Sludge wastewater treatment method]
The present invention relates to sludge treatment and wastewater treatment in sewage treatment.
That is, the present invention relates to a method for treating sludge wastewater, which includes a step of adding the metal salt flocculant 1 or 2 described above to the sludge wastewater.
According to Metal Salt Flocculant 1 or 2, as described later in the Examples section, the following items are achieved: phosphorus/nitrogen removal performance, deodorizing property (hydrogen sulfide suppression effect), color reduction, and sludge settling property (SV value). It has good effects. Furthermore, compared to the case where polyaluminum chloride is used as a chemical, the sedimentation properties of sludge are improved at an addition rate of about 50% of the added mass of polyaluminum chloride, and the phosphorus removal performance is equivalent to that of polyaluminum chloride.

When the metal salt flocculant 2 is added, in addition to the above-mentioned performance, it also has the effect of removing pathogenic microorganisms, such as Escherichia coli. By adding the metal salt flocculant 2 to the sludge, the removal rate of E. coli becomes higher than 83%, preferably higher than 90%.
Considering that the removal rate of E. coli when polyaluminum chloride is added as a drug is about 75%, according to Metal Salt Flocculant 2, although the amount added is less than 50% of the added mass of polyaluminum chloride, , the removal rate of E. coli can be greatly improved.
According to this method, sludge sedimentation, etc. and E. coli removal can be performed in one step using one type of chemical, so that it is possible to simultaneously simplify the work process and reduce the amount of chemicals used in the overall water treatment.

[Water purification and deodorization method]
In addition to sewage treatment, the present invention also relates to a method for purifying and deodorizing waste water such as tap water and gray water.
That is, the present invention also relates to a method for purifying and deodorizing water, which includes the step of adding the metal salt flocculant 1 or 2 described above to water in which pathogenic microorganisms are thought to be present. Despite the small amount of chemicals added, it is possible to purify and deodorize water due to its phosphorus and nitrogen removal performance, deodorizing properties (hydrogen sulfide suppression effect), color reduction, and pathogenic microorganism removal properties.

[Other embodiments]
As described above, the present invention has been described by way of embodiments, but the statements and drawings that form part of this disclosure should not be understood as limiting the present invention. Various alternative embodiments, implementations, and operational techniques will be apparent to those skilled in the art from this disclosure.
For example, the metal salt flocculant described in the embodiments can be used in a new usage method. That is, the present invention provides a new method for using a metal salt flocculant in which the metal salt flocculant 1 or 2 described above is used to remove pathogenic microorganisms in waste water, and a new method for using the metal salt flocculant 1 or 2 in the removal of pathogenic microorganisms in waste water. It also relates to a new method of using metal salt flocculants for the removal of.
Thus, it goes without saying that the present invention includes various embodiments not described here. Therefore, the technical scope of the present invention is determined only by the matters specifying the invention in the claims that are reasonable from the above description.

[Metal salt flocculant 1]
The following experiment was conducted on the metal salt flocculant according to the first embodiment.
(Characteristics evaluation)
The properties of the prepared metal salt flocculant were evaluated from the following viewpoints.
(1) Sludge settling property (SV value)
Activated sludge was filled in a 1-liter graduated cylinder, each drug to be evaluated was added thereto, and the sludge settling ability of each drug was evaluated based on the height of the sludge separated from solid and liquid after being allowed to stand for a predetermined period of time. Here, SV in SVn represents the sludge volume, and n represents the elapsed time (minutes) after standing.
(2) Removal characteristics of TP, TN, COD, and SS components Each of the chemicals to be evaluated was added to the activated sludge, and the supernatant water after being allowed to stand for 1 hour was examined for water quality. TP represents total phosphorus, TN represents total nitrogen, COD represents chemical oxygen demand, and SS represents suspended solids. The removal characteristics of each drug for these components were evaluated from the residual amount [mg/L] of these components.
(3) Deodorizing properties (hydrogen sulfide suppression effect)
Each chemical to be evaluated was added to the raw sludge and left to stand for 4 hours, and the concentration of hydrogen sulfide (H ₂ S [ppm]) contained in the supernatant water was measured using a gas detector. It can be evaluated that the lower the concentration of hydrogen sulfide remaining in the supernatant water, the better the deodorizing properties.
(4) Dehydration Each chemical to be evaluated was added to the digested sludge, and the moisture content [%] of the cake after pressurization and dehydration was measured.
(5) Decrease in chromaticity Each chemical to be evaluated was added to the biological reaction tank of the sewage treatment plant, and the chromaticity of the overflow water in the final settling tank was measured.
[Example 1]

(Drug preparation and stability evaluation)
For polyaluminum chloride with different Al concentrations from 5.08 to 5.87 mol/L, polyferric sulfate with an Fe concentration of 2.93 mol/L and a specific gravity of 1.484 was added to SO ₄ of each component. /Al ₂ O ₃ molar ratio in the range of 0.07 to 0.17 was mixed and added in a 250 mL plastic bottle to obtain 200 g of a mixed solution. 1 g of the obtained sample was collected, diluted with 100 mL of pure water, and the pH of the solution was measured. After measuring the specific gravity of the remaining samples, they were stored at room temperature for one month to evaluate their storage stability.
Table 1 shows the mixing conditions of polyaluminum chloride and polyferric sulfate in molar amounts of each component (Al and Fe), and the stability of the metal salt flocculant of the present invention after mixing.

From the experimental results summarized in Table 1, the total amount of aluminum ions and iron ions in 1L is 5.7 moles or less, the molar ratio of chloride ions to iron ions (Cl/Fe) is 28 or more, and the sulfate ions and It can be seen that the metal salt flocculant of the present invention exists stably when the molar ratio of aluminum ions (SO ₄ /Al ₂ O ₃ ) in terms of aluminum oxide is 0.15 or less.
[Example 2]

(Sludge settling properties and removal characteristics of each component)
1,000 mL of activated sludge (TS: 0.2%) sampled from a sewage treatment plant was collected in a 1 L graduated cylinder, and polyaluminum chloride (M ³⁺ 2.5 mol/L), polyferric sulfate (M ³⁺ 2. 9 mol/L), metal salt flocculant of the present invention (M ³⁺ 5.3 mol/L (Al ³⁺ 5.1 mol/L, Fe ³⁺ 0.2 mol/L), Cl/Fe: 65, SO ₄ /Al ₂ O ₃ :0.04) were added and mixed under the conditions shown in Table 2. The sedimentation properties (SV ₁₀ , SV ₃₀ ) of the sludge were measured after standing for 10 minutes and after standing for 30 minutes. Here, M ³⁺ represents the total concentration of trivalent metal ions (ie, Al ³⁺ and Fe ³⁺ ) contained in the drug.
Further, the supernatant water after being left standing for 1 hour was analyzed for the amount of remaining components of TP, TN, COD, and SS. As shown in Table 2, the amount of each drug added was set so that M ³⁺ was the same for each drug.
The test results are shown in Table 2. Here, TS is an abbreviation for total evaporation residue (total solids), and here indicates the amount of sludge as solids.

(Evaluation of sludge settling properties)
As a result of adding each agent to activated sludge, the metal salt flocculant of the present invention had the best sludge settling property (SV value) at a smaller amount than polyaluminum chloride or polyferric sulfate. . Particularly when paying attention to the SV ₁₀ value, there was a significant difference in the initial sedimentation rate, which indicates that the drug has excellent immediate efficacy.
Since the use of the metal salt flocculant of the present invention greatly improves the solid-liquid separability of treated water, it can be used in all types of water treatment equipment for the purpose of flocculation (e.g. flocculation tanks, biological reaction tanks, gravity concentration tanks, etc.). Available.

(Evaluation of removal characteristics of TP, TN, COD, and SS components)
The metal salt flocculant of the present invention was able to remove more TP, TN, COD, and SS from supernatant water with a smaller amount added than polyaluminum chloride or polyferric sulfate. .
Therefore, by using the metal salt flocculant of the present invention, it is possible to efficiently remove and recover the above-mentioned components, and therefore, it is expected to be effective in countering eutrophication and improving water quality.
[Example 3]

(Deodorization/Hydrogen sulfide suppression)
1,000 mL of raw sludge (TS 1.1%) sampled from a sewage treatment plant was collected in a 1 L measuring cylinder, and each of the polyaluminum chloride, polyferric sulfate, and metal salt flocculant of the present invention used in Example 2 was collected. The drugs were added and mixed under the conditions shown in Table 3. After standing still for 4 hours, 100 mL of the supernatant water was collected in a 300 mL Erlenmeyer flask, sealed, and shaken, and the hydrogen sulfide concentration in the gas phase was measured using a gas detection tube. The amount of the drug added was set so that the trivalent metal ion concentrations were equal, as described above. The test results are shown in Table 3.

(Evaluation of deodorizing properties)
The removal rate of hydrogen sulfide was in the order of polyaluminum chloride<metal salt flocculant of the present invention<polyferric sulfate. Generally, the immobilization of sulfur by iron ions greatly contributes to suppressing hydrogen sulfide, so the metal salt flocculant of the present invention exhibited a higher hydrogen sulfide suppressing effect than ordinary polyaluminum chloride.
Therefore, the metal salt flocculant of the present invention can also be used as a deodorizer in water treatment. Possible usage examples include sewage treatment plants, wastewater treatment facilities, pumping stations, and mud pumping facilities.
[Example 4]

(Dehydration properties)
300 mL of digested sludge (TS 1.3%) sampled from a sewage treatment plant was collected in a 500 mL beaker, and each inorganic flocculant used in Example 2 (polyaluminum chloride, polyferric sulfate, metal salt flocculant of the present invention) ) and a polymer flocculant (0.3 wt%, 170 ppm) were added and mixed under the conditions shown in Table 4. After filtration for 60 seconds, the cake was dehydrated under pressure and the moisture content of the cake was measured. The amount of the drug added was set so that the trivalent metal ion concentrations were equal, as described above.
The test results are shown in Table 4.

(Evaluation of dehydration characteristics)
The dehydration properties were good in the order of polyaluminum chloride < polyferric sulfate < the metal salt flocculant of the present invention. With the metal salt flocculant of the present invention, the moisture content of the cake was reduced by 1.5 points compared to when no chemical was added.
As described above, the metal salt flocculant of the present invention can also be used in a dehydrator for the purpose of reducing the water content of sludge, which ultimately leads to a reduction in sludge transportation and treatment costs.
[Example 5]

(Chromaticity reduction characteristic)
The polyaluminum chloride (25 mg/L) used in Example 2 was placed at the end of the biological reaction tank of the sewage treatment plant with the flow shown in Figure 1 (daily average inflow water amount: approximately 33,000 m ³ /day, standard activated sludge method). Alternatively, the metal salt flocculant (14 mg/L) of the present invention was continuously injected for one week. The drug was added into the liquid in a biological reaction tank using a diaphragm metering pump. The amount of the drug added was set so that the trivalent metal ion concentrations were equal, as described above. Overflow water was periodically sampled from the final settling tank located after the biological reaction tank, and its chromaticity was measured.
The test results are shown in Table 5. Here, the average value and minimum value of chromaticity are weekly average values.

(Evaluation of chromaticity reduction characteristics)
With the metal salt flocculant of the present invention, a significant decrease in chromaticity was observed when the amount added was smaller than that of polyaluminum chloride.
Therefore, the agent of the present invention is expected to be used not only for sewage but also for wastewater such as clean water and gray water.

(Other benefits)
According to the actual machine test in the color reduction test, the metal salt flocculant of the present invention could be injected using the same equipment as ordinary polyaluminum chloride. Additionally, since the amount of medicine used can be reduced, the frequency of transportation and reception by lorries will be reduced, which will lead to a reduction in required labor and personnel costs.

[Metal salt flocculant 2]
[Example 6], [Comparative example 1]
The following experiment was conducted on the metal salt flocculant according to the second embodiment.
(actual machine test)
(Equipment outline)
An actual machine test was conducted using a treatment plant equipped with a treatment facility (system A) and a treatment facility (system B) as shown in the flow diagram of FIG. 2. The average daily inflow volume of the treatment plant is 34,000 m ³ /day, and the treatment method is the standard activated sludge method, and for the purpose of nitrogen removal, operation is performed using a pseudo-step inflow type two-stage nitrification-denitrification method (6 trains). . In addition, in order to perform advanced treatment of phosphorus, polyaluminum chloride (PAC) is added as a flocculant before the final reaction tank in another series (step flow type two-stage nitrification-denitrification method with coagulant). . A portion of the treated water undergoes sand filtration, ozone treatment, and chlorine disinfection, and is then reused as water for nearby parks.

(Test method)
As the flocculant to be injected, commercially available polyaluminum chloride (PAC) (specific gravity: 1.214, Cl/Al ₂ O ₃ : 2.7) was used in Comparative Example 1, and highly concentrated iron aluminum (specific gravity: 1.214) was used in Example 6. 445, Cl/Fe: 63, SO ₄ /Al ₂ O ₃ : 0.08, Cl/Al ₂ O ₃ : 3.3, SO ₄ /Fe: 1.4). The concentration of trivalent metal ions (Al ³⁺ , Fe ³⁺ ) contained in the drug was 2.38 mol/L in Comparative Example 1 (PAC) and 5.35 mol/L in Example 6 (high concentration iron aluminum). Ta.
PAC and high-concentration iron-aluminum were added to a treatment facility (A system) using a step flow type two-stage nitrification-denitrification method using a flocculant. The drug was injected at the front stage of the final tank of the reaction tank, and PAC and high-concentration iron-aluminum were injected for two weeks each using a metering pump (addition rate Comparative Example 1 (PAC): 34 mg/L, Example 6 (high-concentration iron-aluminum) ): 17 mg/L). In addition, a treatment facility (B system) using a standard activated sludge method (simulated step inflow type two-stage nitrification and denitrification method) was selected as a blank. Activated sludge from the final reaction tanks of systems A and B and overflow water from the final settling tank were periodically sampled to evaluate sludge settling properties and water quality. The test was conducted from November 26, 2020 to December 17, 2020.

(Test results)
(Evaluation of sludge settling properties)
The sludge capacity index (SVI) of the reaction tank is shown in Figure 3. In contrast to the SVI of the blank B system of 300 to 400 mL/g, the SVI of the A system was 150 to 300 mL/g during PAC injection and 100 to 200 mL/g during high concentration iron-aluminum injection. The settling properties of sludge were improved by the injection of flocculant, and it was thought that especially high-concentration iron-aluminum had a higher flocculation effect.

(Evaluation of phosphorus/nitrogen removal performance)
Figure 4 shows the change in TP concentration in the final sedimentation tank overflow water. The TP concentration of system A was constant between 0.05 and 0.50 mg/L during the injection period of PAC and high concentration iron-aluminum. Although the addition rate of high-concentration iron-aluminum was approximately 50% of PAC, it was shown that the same phosphorus removal could be performed because the metal ion concentration was the same as that of PAC. There was no significant difference in the TN concentration when PAC and high-concentration iron-aluminum were injected, and it is thought that the nitrogen removal performance due to biological reaction was constant.

(Ecoli bacteria, odor substance removal evaluation)
Table 6 shows the analysis results of the number of E. coli bacteria, residual chlorine concentration, and odor substance concentration (geosmin, 2-methylisoborneol) in the final sedimentation tank overflow water.

The number of E. coli in system A was lower than that of the blank system B, and the removal rate was about 75 to 83% during PAC injection and about 90% during high concentration iron aluminum injection. The residual chlorine (free residual chlorine/combined residual chlorine) concentration is the same for both A and B systems, and the values are low, and it is considered that the concentration does not have disinfecting power.
It is generally thought that some of the pathogenic microorganisms in sewage (E. coli, norovirus, cryptosporidium, etc.) are adsorbed to sludge, become entangled in flocs, and are removed from the treated water as they coagulate and settle. The number of E. coli is also correlated with the SVI values of A and B systems, and since there is no chlorine component with disinfecting power in the treated water, it is thought that E. coli was removed from the treated water through coagulation and precipitation in this test. Furthermore, no E. coli was detected in the recycled water that had undergone sand filtration, ozone treatment, and chlorine disinfection.
Since the concentration of odorants was low in both Type A and Type B, and there was no significant difference in the analytical values, no superior deodorizing effect was confirmed by the injection of the flocculant in this test.

(chromaticity, turbidity)
Table 7 shows the measurement results of the color and turbidity of the final settling tank overflow water.

The chromaticity of system A was lower than that of system B, and it could be said that the clarity of the treated water was improved by the injection of the flocculant. The chromaticity at the time of high-concentration iron-aluminum injection was 10 degrees, and the chromaticity decreased to the standard value level (10 degrees or less) for hydrophilic water. The turbidity was approximately 2.0 regardless of the type of flocculant, and no major difference was observed in the analytical values of the A and B systems.

(Possibility of using water treated with coagulant as recycled sewage water)
Reclaimed sewage water can be used as (1) water for flushing, (2) water for sprinkling, (3) water for landscaping, and (4) water for hydrophilic purposes.The water quality standards include E. coli count, turbidity, pH, appearance, and chromaticity. , there is an odor. Based on these items, the degree of water quality improvement due to the use of flocculants was evaluated. In this test, the blank treated water was excluded from the evaluation because the turbidity and odor concentration were low.
As mentioned above, injection of a flocculant is effective in reducing chromaticity, and this test showed that it improved to the standard value level. Regarding the number of E. coli bacteria, 75 to 90% of E. coli bacteria could be removed from the treated water by injection of the flocculant. However, it fell short of the standards (1), (2), and (4) of "not being detected" and the standard value of (3) of 10 CFU/mL. Therefore, it is currently difficult to achieve the standard value for the number of coliform bacteria by simply injecting a coagulant, and we believe that it is necessary to combine it with more advanced treatment (chlorine disinfection and ozone treatment) in order to use treated water as recycled water. It will be done.
When using a flocculant, the removal rate of E. coli largely depends on the flocculating ability of the flocculant used. Therefore, a higher removal effect can be expected by increasing the number of cations to be implanted, but it is necessary to consider other factors such as pH to determine the appropriate implantation rate.
In this flocculant injection test, the quality of the treated water was not improved to the standard value for reclaimed sewage water in terms of the number of coliform bacteria, but it was found that the use of a flocculant can reduce the concentration of pathogenic microorganisms by a certain percentage. . In sewage treatment, reducing the concentration of pathogenic microorganisms in treated water is synonymous with reducing the risk of pathogen exposure for workers. Therefore, the use of coagulants was considered to be significant not only in improving sewage treatment capacity but also in reducing the risk of infection among workers at treatment plants.

In a chemical injection test into a biological treatment system aimed at removing nitrogen and phosphorous, high-concentration iron-aluminum improved the settling properties of sludge at an addition rate of about 50% of PAC, and showed the same phosphorus removal performance as PAC. It was done.
By injecting the flocculant, the number of E. coli bacteria was reduced by about 75 to 90%. Escherichia coli is thought to be removed as the sludge coagulates and settles, and the use of flocculants was expected to have the effect of improving the removal rate of pathogenic microorganisms adsorbed to the sludge.
Although the removal of E. coli from sewage by coagulant injection did not reach the standard value for recycled sewage water, it was shown that it could be improved by adjusting the amount added. Reducing the concentration of pathogenic microorganisms in treated water leads to a reduction in the risk of pathogen exposure for treatment plant workers, and the use of flocculants is thought to contribute to reducing this risk.

Claims

A metal salt flocculant,
The total content of aluminum ions and iron ions in 1 liter of metal salt flocculant is 5.7 mol or less,
The molar ratio of chloride ions to iron ions (Cl/Fe) is 28 or more,
The molar ratio of aluminum ions (SO 4 /Al 2 O 3 ) in terms of sulfate ions and aluminum oxide is 0.15 or less,
A metal salt flocculant with a removal rate of more than 83% of E. coli.
The metal salt flocculant according to claim 1, wherein the molar ratio of chloride ions to iron ions (Cl/Fe) is 50 or more and 104 or less.
The metal salt flocculant according to claim 1 or 2, wherein the removal rate of E. coli is higher than 90%.
The metal salt flocculant according to claim 1 or 2, which has a pH of 3.7 to 4.2 (100 times diluted solution) and a specific gravity of 1.35 to 1.45.
A flocculant containing the metal salt flocculant according to claim 1 or 2.
A water quality improving agent containing the metal salt flocculant according to claim 1 or 2.
A deodorant containing the metal salt flocculant according to claim 1 or 2.
A dehydrating agent containing the metal salt flocculant according to claim 1 or 2.
A wastewater color reducing agent containing the metal salt flocculant according to claim 1 or 2.
A method for treating sludge wastewater, the method comprising the step of adding the metal salt flocculant according to claim 1 or 2 to the sludge wastewater.
A method for purifying and deodorizing water, the method comprising the step of adding the metal salt flocculant according to claim 1 or 2 to water in which pathogenic microorganisms are thought to exist.
A new method for using the metal salt flocculant according to claim 1 or 2 for removing pathogenic microorganisms in wastewater.
A new method for using a metal salt flocculant according to claim 1 or 2 for removing E. coli from wastewater.