JP2000262811A - Compound flocculant and sludge treatment method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compound flocculant produced from biomass raw materials, which is safe for animals and plants and does not cause environmental pollution, and to provide a sludge treatment method using the flocculant without using an aluminum salt which is a substance causing Alzheimer's disease nor an acrylamide polymer from which a carcinogenic substance is derived as a flocculant in the treatment of sludge from municipal wastewater and industrial wastewater. SOLUTION: Two types of substances derived from natural biomass raw materials; an alginic acid salt derived from Cryptophyceae and chitin-chitosan derived from shells of crab and shrimp; are used as a flocculant to be added to object water to be treated. A first combination of ammonium alginate with chitin-chitosan, which may be a fertilizer for soil, and a second combination of sodium alginate with chitin- chitosan are suggested as the compound flocculant. In order to heighten the flocculation efficiency, the deacetylation ratio of chitin-chitosan is controlled to be 80% or higher and the pH of alginic acid is controlled to be within 5-7 and then both flocculants are added as an aqueous weakly acidic solution to object water containing sludge. As a result, the flocculants are evenly dispersed in the object water and accelerate flocculation of the sludge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coagulant for coagulating and sedimenting sludge generated from municipal sewage, agricultural settlement drainage, livestock drainage, factory drainage, etc., civil engineering and construction sludge, and more particularly to natural biomass resources. By using an aqueous solution of alkali metal alginate or ammonium alginate, which is a derivative from the above, together with a weakly acidic aqueous solution of chitin / chitosan, which is also a derivative from natural biomass resources, it is safe for animals and plants. The present invention relates to a composite flocculant which does not cause environmental pollution and has a high flocculation / sedimentation efficiency, and a sludge treatment method using the same.

[0002]

2. Description of the Related Art In general, an activated sludge method is generally used as a method for treating various kinds of wastewater containing organic matter. This activated sludge method is a highly efficient wastewater treatment method,
It is the most widely used because of the economical characteristics of high quality treated water.

[0003] Excess sludge and civil engineering / building sludge after treatment by this activated sludge method must be coagulated, settled, filtered and dewatered. In this case, a flocculant described later is added to the suspended sludge to stir the coagulation. This is separated by filtration by a conventional method to separate clear treated water and a hydrated sludge cake.
Clear treated water is discharged after sterilization, but it is customary to return the hydrous sludge cake to the natural environment by landfilling.

In this coagulation process, an inorganic coagulant and a synthetic polymer coagulant have been used in large quantities. Inorganic coagulants include aluminum salts such as sulfuric acid bands and polyaluminum chloride, and water-soluble polysulfates such as iron salts such as ferric chloride, ferric sulfate, and ferric polysulfate (commonly referred to as polyiron). Valent metal salts are often used. Synthetic polymer-based flocculants include cationic synthetic polymers such as polydimethylaminoethyl acrylate, anionic synthetic polymers such as polyacrylamide, hydrolysates thereof, and polyacrylic acid, and other nonionic synthetic polymers. It has been used favorably.

[0005] The sludge separated by these flocculants is
Reclaimed land is used as land for construction or farmland. However, especially when used as agricultural land, it may cause serious safety impairment and environmental pollution. First, the inorganic coagulant not only increases the weight of the hydrated sludge cake because it is a polyvalent metal salt, but also introduces polyvalent metal ions into the soil to modify it into soil that is unsuitable for plant growth. Would. Among them, aluminum ion is also said to be a causative substance of Alzheimer's disease, and has a risk of accumulating in humans through agricultural products. Also, SO
₄ ^2- and Cl ^- which has been found that anionic also undesirable, such as. Second, the synthetic polymer flocculant is accumulated in soil due to its poor biodegradability, and becomes a factor inhibiting plant growth. In particular, since acrylamide, which is a monomer of polyacrylamide, has carcinogenicity and neurotoxicity, there is great concern that acrylamide monomer remains from the viewpoint of safety and environmental pollution.

[0006]

In order to solve such disadvantages of the inorganic flocculant and the synthetic polymer flocculant, natural polymer flocculants have been studied. This is because a natural polymer is considered to satisfy safety and environmental preservation.

Among them, alginic acid obtained from brown algae (JP-A-6-182349) and chitosan obtained by treating crab and shrimp shells (JP-A-59-1).
No. 60509) has come to attract attention. However, as research on alginic acid and chitosan has progressed, it has been found that these substances alone do not have sufficient coagulation and sedimentation action on organic and inorganic sludge.

[0008] In recent years, studies have been made to increase the coagulation action synergistically by using alginic acid and chitosan together with other substances.

For example, JP-A-10-152683 proposes a composite flocculant using sodium alginate and an acrylamide / acrylic acid copolymer in combination. However, as described above, the acrylamide monomer has carcinogenicity and neurotoxicity, and even if its aggregating action is large, it cannot be used in combination with acrylamide from the viewpoint of safety and environmental conservation.

Japanese Patent Application Laid-Open No. Sho 57-130599 discloses an example in which sodium alginate and chitosan are used in combination as a flocculant. In particular, JP-A-10-57
No. 968 discloses a sequential addition method in which sodium alginate is first added to and mixed with wastewater, and then chitosan is added and mixed.

Since sodium ions generated from sodium alginate are monovalent cations, they have an effect of inhibiting the growth of plants even when they enter the soil, as compared with polyvalent metal ions found in conventional inorganic coagulants. Is small. However, even in the case of high concentrations of sodium ions, salt-damaging effects are exhibited, so that care must be taken when handling them.

However, even when caution is given to the quantitative handling of sodium alginate, the above-mentioned conventional example only describes that an aqueous sodium alginate solution and an aqueous chitosan or neutral solution are sequentially added to muddy water. Therefore, the pH conditions of the aqueous sodium alginate solution, the deacetylation rate of chitosan, and the like are completely unknown, and it is difficult to say that the optimum conditions for the aggregation action have been clarified. Conversely, the chitosan can be considered as a chitosan having a deacetylation rate of 100%.

Accordingly, a first object of the present invention is to find an alginate having an aggregating effect that does not generate metal cations, and to provide a composite aggregating agent having higher safety and environmental protection. . A second object of the present invention is to provide an effective coagulation method by clarifying the optimum conditions such as the pH condition of sodium alginate and the deacetylation rate of chitosan when using sodium alginate. is there.

[0014]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages, and the invention of claim 1 is a composite flocculant characterized by using an ammonium alginate salt and chitin / chitosan in combination. It is.

According to a second aspect of the present invention, an aqueous dispersion of alginic acid is neutralized with aqueous ammonium to prepare an aqueous ammonium alginate solution having a pH of 5 to 7 and a weakly acidic aqueous solution of chitin / chitosan is prepared. A sludge treatment method characterized by adding both aqueous solutions to the water to be treated.

In the invention of claim 3, the combined weight ratio of ammonium alginate and chitin / chitosan is set to 8: 2 to 3: 7, and both agents are added simultaneously or sequentially, and the order of addition is not limited in the sequential addition. A sludge treatment method according to claim 2.

The invention according to claim 4 is the method for treating sludge according to claim 2 or 3, wherein chitin / chitosan obtained by deacetylating chitin to 80% or more is used as the chitin / chitosan.

According to a fifth aspect of the present invention, alginic acid is neutralized with an alkali metal hydroxide to prepare an alkali metal alginate aqueous solution having a pH of 5 to 7 and a weakly acidic aqueous solution of chitin / chitosan. And a sludge treatment method characterized by adding both aqueous solutions to the water to be treated.

The invention according to claim 6 is that the combined weight ratio of the alkali metal alginate and chitin / chitosan is 8: 2 to 3: 7.
The sludge treatment method according to claim 5, wherein both agents are added simultaneously or sequentially, and the order of addition is not limited in the sequential addition.

[0020] The invention of claim 7 is the method for treating sludge according to claim 5 or 6, wherein chitin / chitosan obtained by deacetylating chitin to 80% or more is used as the chitin / chitosan.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies on alginate having an aggregating ability that does not generate metal ions. As a result, ammonium alginate is most preferable, and by using this in combination with chitin / chitosan. It has been conceived that a composite flocculant having high safety and environmental preservation can be provided.

In the first aspect of the present invention, since ammonium alginate does not contain a metal atom, it does not leave metal ions in the soil, and at the same time has sludge flocculation performance. Further, the ammonium salt is a nitrogen fertilizer, and is extremely safe because it is a nitrogen fertilizer using biomass as a raw material. It is considered that the safety is higher than that of a conventional nitrogen fertilizer represented by inorganic ammonium sulfate. Therefore, even if the ammonium alginate remains in the soil, it acts as a nitrogen fertilizer and gives suitable conditions for the growth of the plant. Therefore, ammonium alginate was selected from this point.

Alginic acid is a natural mucous polysaccharide contained in brown algae as a biomass resource, is an important constituent of the cell wall, and is a filling material between cells. Industrially, it is extracted, precipitated and separated as alginic acid from giant kelp, makombu, kajime and the like. Structurally, alginic acid is a linear acidic polysaccharide in which D-mannuronic acid and L-guluronic acid are linked in various ratios by 1 → 4.

The alginic acid is converted to a pH value with aqueous ammonia.
= 5-7 to produce an aqueous solution of ammonium alginate. When the aqueous solution of ammonium alginate is prepared in the acidic region of PH = 5 to 7 in this way, it is found that the coagulation and sedimentation performance of the sludge increases when added to the water to be treated, for unknown reasons.

In the present invention, a biomass composite flocculant is constituted by using chitin / chitosan, which is a biomass resource, and the above-mentioned ammonium alginate. Even when both components are simultaneously added to the water to be treated, or when they are sequentially added, a strong coagulation effect on sludge is exhibited. The sequential addition includes both the case where chitin / chitosan is added after the addition of ammonium alginate, or the case where chitin / chitosan is added first and ammonium alginate is added later.

Chitin is a major component of shells and cell walls of crustaceans such as crabs and shrimps and insects, and forms a complex with calcium and proteins. As a biomass resource that is bio-generated on earth, it accounts for the second amount after cellulose. A substance obtained by removing calcium and protein from the chitin is called chitin, and a substance obtained by deacetylating the chitin is called chitosan. Both chitin and chitosan are natural polymers. However, it is difficult to deacetylate chitin by 100%, and even with a substance called chitosan, chitin and chitosan are complexed at a predetermined ratio. In the present invention, such a composite substance is called chitin / chitosan.

In the scientific name, chitin is β- (1 → 4) -2-
Acetamide-2-deoxy-β-D-glucose and chitosan is β- (1 → 4) -2-amino-2-deoxy-β-D-glucose. Chitin / chitosan has a molecular structure in which these two types coexist.

As the chitin / chitosan used in the present invention, Koyo Chitosan (trade name, sold by Koyo Chemical Co., Ltd.) or Flownac R (trade name, sold by Kyowa Technos Co., Ltd.) is used. Since chitin / chitosan is a substance produced from natural biomass resources, its safety for humans and animals is extremely high. In addition, it is reported that, of course, it has not only mutagenicity against microorganisms but also strong antimutagenicity.

As described above, JP-A-59-16050
No. 9 describes that chitin / chitosan functions as a flocculant for sludge dewatering. However, tests by the present inventors have revealed that the cohesion performance is small when used alone. Chitin with such small coagulation performance
Empirical elucidation has not yet been made on why strong aggregation performance is exhibited when chitosan is used in combination with ammonium alginate of a similar character. But,
The present inventors now believe that, since chitin / chitosan has a cationic functional group, this cationic functional group may exert the same coagulation promoting effect on the water to be treated as a polyvalent metal cation. In any case, the synergistic effect of chitin / chitosan and ammonium alginate discovered by the present inventors has led to the completion of a safe and powerful flocculant.

In addition, it has been found that a deacetylation ratio of chitin / chitosan is preferably 80% or more in order to efficiently exert the aggregation effect when used in combination with ammonium alginate. This point is disclosed in JP-A-59-16050.
It does not overlap with 67 to 75% described in Japanese Patent Publication No. 9 and is found for the first time by the present inventors. Therefore, for example, in Koyo Chitosan, S
K-10 (85% or more), SK-50 (80% or more),
Among SK-200 (80% or more) and SK-400 (80% or more), N (90%)
% Or more), $ 250 (90% or more) and the like can be applied to the present invention. The figures in parentheses indicate the deacetylation rate.

To add chitin / chitosan to the water to be treated, first, an acidic aqueous solution of chitin / chitosan is prepared, and this aqueous solution of chitin / chitosan is added to the water to be treated.
Chitin / chitosan dissolves uniformly in the water to be treated and exerts a sludge aggregation action.

As the acid for dissolving chitin / chitosan, either an organic acid or an inorganic acid can be used. For example, acetic acid, hydrochloric acid,
Formic acid, lactic acid, malic acid, adipic acid and the like.

The combined weight ratio of ammonium alginate and chitin / chitosan is preferably from 8: 2 to 3: 7. Within this range, the coagulation effect is good, and a combination ratio suitable for the properties of the water to be treated can be selected.

A second aspect of the present invention is to clarify the conditions for using alkali metal alginate and chitin / chitosan as coagulants. As previously mentioned,
Japanese Patent Application Laid-Open No. 57-130599 discloses a method of sequentially adding sodium alginate and chitosan. However, the present invention is not limited to a sodium salt, and an alkali metal alginate can be used. The alkali metal salt generates a monovalent cation similarly to the sodium salt, so that the aggregation action is exerted similarly to the sodium salt.

In addition, it has been found that, when chitin / chitosan, which is a complex of chitin and chitosan, is used instead of mere chitosan and the deacetylation rate is 80% or more, the aggregation effect is enhanced. In particular, if the alkali metal alginate aqueous solution adjusted to PH = 5 to 7 and the weakly acidic aqueous solution of chitin / chitosan are added to the water to be treated, the effect of coagulating the sludge is increased.

The combined weight ratio of alkali metal alginate and chitin / chitosan is also preferably 8: 2 to 3: 7. Within this range, the coagulation effect is good, and a combination ratio suitable for the properties of the water to be treated and the sludge to be treated can be selected.

Further, in the practice of the first and second aspects of the present invention, inorganic muddy water generated from civil engineering and construction sites can be targeted, but wastewater such as municipal sewage, agricultural settlement drainage, livestock drainage, and factory drainage can be used. The characteristics are also exhibited when sludge generated by treating activated sludge, that is, organic sludge. When targeting this organic sludge, it is preferable to adjust the pH of the sludge to a range of 5 to 7 before adding the flocculant of the present invention.

In the above two inventions, ammonium alginate, alkali metal alginate and chitin.
Since chitosan is a polymer, the aqueous solution tends to have a high viscosity. When the viscosity becomes high, when added to the sludge, diffusion is not performed quickly, and uneven distribution may occur in the sludge. Therefore, the concentration of the aqueous solution is 1 wt. % Or less is preferable.

To make alginate as flocculant A,
Alginic acid as a chemical experimental reagent or grade G of Kimitsu ALGIN manufactured by Kimitsu Chemical Industry Co., Ltd. is dispersed in water at a concentration of 0.25 to 1.0%, and an aqueous solution of caustic soda or aqueous ammonia is added dropwise to PH =
A solution which was neutralized to a desired position within the range of 5 to 7 and dissolved transparently was used. In the case of Kimitsu ALGING G, since the viscosity of the aqueous solution after dissolution tends to increase, it is desirable to make the concentration as low as possible in order to diffuse well when added to the raw sludge water. For example, 0.25%
A concentrated aqueous solution is prepared. 0.5 was prepared by neutralizing alginic acid, a chemical experimental reagent, to pH = 5 with aqueous ammonia.
% Aqueous solution is hereinafter referred to as A1 (0045).
Kimitsu ALGIN manufactured by u Chemical Industry Co., Ltd.
A 0.25% aqueous solution prepared by neutralizing G with an aqueous solution of sodium hydroxide to PH = 5 is hereinafter referred to as A2 (004
9) A 0.25% aqueous solution prepared by neutralizing Kimitsu ALGING G with ammonia water to PH = 5
3 (0053).

In order to prepare chitin / chitosan as the flocculant B, SK-400, a general-purpose grade of KOYO chitosan having a deacetylation ratio of 80% or more manufactured by Koyo Chemical Co., Ltd., may be used depending on the case. A 0.5% acetic acid aqueous solution of N grade in Flownac R manufactured by Technos and having an acetylation ratio of 90% or more was used. The use ratio of the flocculants A and B depends on the properties of the sludge to be treated, but generally, it may be selected from the range of A / B = 8/2 to 3/7 (weight ratio).

As described above, the order of adding the coagulants A and B is not particularly limited. When both are added simultaneously, when A is added first and B is added later, B is added first and A is added later, and a method that maximizes the aggregation effect can be adopted. Suffice to say, in many cases, inorganic sludge generated from civil engineering and construction sites is suitable, but organic sludge such as surplus sludge after activated sludge treatment is suitable. Often appropriate.

The agitation after the addition of the flocculant is such that it is evenly distributed throughout to improve mixing with the sludge.
Slow mixing is preferred. In particular, when organic sludge is targeted, the strength of the floc after coagulation is not sufficiently strong, so that too strong stirring or too long stirring results in undesirable results.

The floc formation state should be at least 20 min. While standing still, visual observation was continued, 5A filter paper was spread on a water pump and Nutsche, and the mixture was filtered under reduced pressure. The filtration speed, the clarity of the filtrate, and the water content of the wet sludge cake were measured using an infrared moisture meter F manufactured by Kett.
105 ° C. × 75 min. It was determined by heating, and a comprehensive judgment was made from them.

[0044]

EXAMPLES Hereinafter, the composite flocculant according to the present invention and the sludge treatment method using the same will be described in detail with reference to examples.

[Example 1: Ammonium alginate and chitin / chitosan ... inorganic sludge] In this example, inorganic muddy water was used in order to check whether or not it was possible to coagulate and sediment inorganic wastewater generated from civil engineering and construction sites. The coagulant of the present invention was applied to a dispersion in which baked kaolin was dispersed in water at a concentration of 5,000 ppm as an artificial substitute for.
Among the coagulants of the present invention, as A, a reagent, alginic acid, is dispersed in water so as to have a concentration of 0.5%, and ammonia water is added dropwise with stirring, and the pH is adjusted to 5.0. Then, the solution was transparently dissolved. Therefore, the solution was stopped there and the solution A1 was used. As B, a 0.5% aqueous acetic acid solution of Koyo Chitosan SK-400 was used. The results are shown in Table 1. In the table, the amount of kaolin recovered was determined by subjecting the aggregated kaolin to natural filtration using a No. 2 filter paper and leaving the remaining on the filter paper at 105 ° C.
In an air bath until the weight became constant, and the ratio of the amount recovered was shown.

[0046]

[Table 1]

As is clear from Table 1, the calcined kaolin dispersion did not aggregate at all even with ammonium alginate alone (Comparative Example 1-1) or chitin / chitosan alone (Comparative Example 1-2). When used together in the range of 1 to 1/2, aggregation is apparently caused visually and precipitates (Examples 1-1 to 1-3), and the kaolin recovery rate also exceeds 90%. Further, A1 and B were sequentially added (Examples 1-1, 1-
Both in the case of 2) and in the case of simultaneous addition (Example 1-3), good coagulated sedimentation was obtained.

It is considered that the sludge should be electrically neutralized in order to coagulate and settle the sludge. In the present embodiment, since the kaolin dispersion liquid is considered to have a positive charge, A1 having a negative charge
The hypothesis that adding either A1 or B at the same time, or adding A1 and B simultaneously, would give better results than adding B with a positive charge first. .

[Example 2: Sodium alginate and chitin / chitosan: organic sludge] In this example, as a representative of the organic sludge, the surplus treated with activated sludge of the wastewater from agricultural settlements generated at Kobe Treatment Plant in Saijo City, Ehime Prefecture. The experiment was performed on sludge. The characteristics of this sludge are MLSS = 20,000 ppm
PH = 3.6. The organic sludge was adjusted to pH = 6.5 using an aqueous solution of caustic soda in advance or used without adjustment (marked with ♯). Examples of the flocculant A include Kimits
u ALGING G in aqueous sodium hydroxide solution at pH = 5.0
0.25% aqueous sodium alginate solution A2 prepared by neutralization
Aggregation experiments were performed using a 0.5% aqueous acetic acid solution of 00. The results are shown in Table 2. In the table, the sludge cake moisture content is
5A filter paper was spread on Nutsche and filtered under reduced pressure using a water jet pump. The cake was taken in a petri dish and measured using a Kett infrared moisture meter FD-600.

[0050]

[Table 2]

In Example 2, which is a representative of organic sludge,
Excess sludge treated with activated sludge (MLSS = 20,000, PH = 3.6) at Kobe Sewage Treatment Plant in Saijo City, Ehime Prefecture was subjected to a coagulation test using sodium alginate and chitosan. PH =
Regarding the sludge adjusted to 6.5, neither sodium alginate (A2) alone (Comparative Example 2-1) nor chitosan (B) alone (Comparative Example 2-2) was hard to coagulate. In particular, PH
Is not adjusted (Comparative Example 2-4), A2 / B ≒ 5
It was found that coagulation was difficult even with the simultaneous addition of / 5. However, in the case of sludge adjusted to PH = 6.5 (Example 2-1)
~ 2-3) proved to coagulate both simultaneously and sequentially when A2 / B is in the range of 7/3 to 5/5. For this reason, it is desirable to adjust the pH of the organic sludge water to 5th to 7th in the same manner as the pH of A2.

With respect to the theory of electrical neutralization of coagulation, since organic sludge is considered to have a negative charge, in the case of sequential addition, coagulant B was added first, and A2 was added later. The hypothesis was once affirmed because Comparative Example 2-3, in which A2 was added first and B was added later, was not sufficiently agglomerated even when the amount of addition was the same.

[Example 3: Ammonium alginate and chitin / chitosan ... organic sludge] In this example, as in Example 2, treated sludge treated with activated sludge of agricultural settlement wastewater at a Kobe treatment plant was subjected to PH treatment in advance. = 6.5 or 0.5% ammonium alginate aqueous solution A1 prepared by neutralizing the reagent alginic acid with aqueous ammonia as a flocculant A or Kimits
u 0.25 prepared in a similar manner from ALGING G
% Aqueous ammonium alginate solution A3 was used. As coagulant B, 0.5% of Koyo Chitosan SK-400
Aggregation experiments were performed using acetic acid aqueous solution. Table 3 shows the results
It was shown to. In the table, the water content of the sludge cake was determined by laying a 5A filter paper on Nutsche and filtering the mixture under reduced pressure using a water flow pump.
It was measured using.

[0054]

[Table 3]

In Example 3, using the same sludge as used in Example 2, an agglomeration test was conducted using ammonium alginate and chitosan in combination. For sludge previously adjusted to PH = 6.5, if (A3 or A1) / B = 8/2 to 8/2 (Examples 3-1 to 3-7), even if added simultaneously,
Even in the case of sequential addition, in the case of sequential addition, regardless of the order of A4 and B, agglomeration occurred to a degree that could be filtered. The minimum required amount of flocculant is also 0.4% vs. SS for A4 and B respectively, thus A +
It was found that even if the amount was reduced to about B = 0.8% vs. SS, the state of aggregation was not significantly changed.

The present invention is not limited to the above embodiments, but includes various modifications and design changes within the technical scope of the present invention without departing from the technical concept of the present invention.

[0057]

Industrial Applicability As described in detail above, the present invention is intended to improve the safety and environmental protection of treated water such as urban sewage, agricultural settlement drainage, livestock drainage, factory drainage, civil engineering sludge, etc., which have increased rapidly in recent years. Cleaning can be performed efficiently while ensuring the property.

According to the first aspect, since the composite flocculant is a combination of ammonium alginate obtained from biomass resources and chitin / chitosan, it is safe for animals and plants including humans and without polluting the natural environment. This has the effect of efficiently coagulating and settling sludge from the water to be treated. Accordingly, a coagulant that has been used in large quantities in the past, that is, a coagulant that replaces an acrylamide polymer in which an aluminum salt or monomer that is a causative substance of Alzheimer's disease is called a carcinogen or neurotoxin, has been provided. In the near future, the effect of the present invention to protect soil from environmental pollution is extremely large.

According to the second aspect, since both coagulants are added as an aqueous solution, the coagulant can be uniformly dispersed and dissolved in the water to be treated, and the coagulation effect can be remarkably improved by setting the pH to an optimum value. .

According to the third aspect, by adding both coagulants within a specific weight ratio range, the coagulation effect can be made more efficient.

According to claim 4, the deacetylation rate is 80%.
By using the above-mentioned chitin / chitosan, it is possible to optimize the synergistic effect of aggregation with ammonium alginate.

According to the fifth aspect, the alkali metal alginate and chitin / chitosan are added to the water to be treated as a weakly acidic aqueous solution. The aggregation effect can be remarkably improved.

According to the sixth aspect, since the alkali metal alginate and chitin / chitosan are prepared and added in a specific weight ratio, the aggregation effect can be enhanced.

According to claim 7, the deacetylation rate is 80%.
By using the above-mentioned chitin / chitosan, it is possible to optimize the synergistic effect of aggregation with the alkali metal alginate.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D015 BA10 BA11 BB09 BB17 CA10 CA12 DB32 DB33 EA04 EA06 EA14 EA16 EA32 4D059 AA05 AA09 BE31 BE56 BE60 BE61 DA01 DB18 DB26 EB05 EB20

Claims (7)

[Claims] 1. A composite flocculant comprising a combination of ammonium alginate and chitin / chitosan. 2. Alginate is neutralized with aqueous ammonia to form P
Preparing an aqueous solution of ammonium alginate in the range of H = 5-7, and preparing a weakly acidic aqueous solution of chitin / chitosan;
A method for treating sludge, comprising adding both aqueous solutions to the water to be treated. 3. The method according to claim 2, wherein the combined weight ratio of ammonium alginate and chitin / chitosan is 8: 2 to 3: 7, and both agents are added simultaneously or sequentially, and the order of addition is not limited in the sequential addition. Sludge treatment method. 4. The sludge treatment method according to claim 2, wherein chitin / chitosan obtained by deacetylating chitin to 80% or more is used as the chitin / chitosan. 5. An alginic acid is neutralized with an alkali metal hydroxide to prepare an aqueous solution of an alkali metal alginate having a pH of 5 to 7, and a weakly acidic aqueous solution of chitin / chitosan is prepared. A method for treating sludge, which is added to treated water. 6. The combination weight ratio of the alkali metal alginate and chitin / chitosan is set to 8: 2 to 3: 7, and both agents are added simultaneously or sequentially, and the order of addition is not limited in the sequential addition. The sludge treatment method described in the above. 7. The method for treating sludge according to claim 5, wherein chitin / chitosan obtained by deacetylating chitin to 80% or more is used as the chitin / chitosan.