JPH10272306A - Method for dewatering waste slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively coagulate solid contents in the form of fine particles in slurry containing cement to effect dewatering efficiently, by adding an inorganic flocculant and a high molecular flocculant, as flocculants, to waste slurry to coagulate solid contents and dewatering the waste slurry. SOLUTION: An inorganic flocculant and high molecular flocculant are added to a waste slurry. The high molecular flocculant is an anionic high molecular flocculant or anionic high molecular flocculant in combination with a cationic high molecular flocculant. The amounts of flocculants to be added are such that 0.1-10 pts.wt. inorganic flocculant and 0.005-3 pts.wt. high molecular flocculants per 100 pts.wt. solid contents in waste slurry, and when an anionic and a cationic flocculant are used as a high molecular flocculant at the same time, the ratio of weight between the anionic flocculant and cationic flocculant is preferably 1:0.5-5. This coagulating and dewatering can be effected easily and efficiently at an area where waste slurry is generated, and dehydrated cakes can be easily transported at a low cost, so that the need for landfilling area can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dewatering wastewater, and more particularly to a method for dewatering wastewater generated in civil engineering and construction works.

[0002]

2. Description of the Related Art In recent years, a large amount of muddy water has been generated in civil engineering and construction works such as underground excavation, ground improvement, and dredging, but the amount of this muddy water tends to further increase. This muddy water usually contains a large amount of water and has high fluidity, which makes it difficult to handle.Conventionally, the muddy water is carried out from the muddy water generation site using a special vehicle such as a vacuum truck and coagulated at the intermediate treatment plant.・ After dewatering, etc., they were landfilled in final disposal sites or dumped in the ocean. However, unloading by special vehicles such as vacuum vehicles requires a large amount of money, it has become difficult to secure final disposal sites, and ocean dumping has been banned in principle from the viewpoint of environmental protection. There are many problems,
It is desired to eliminate or minimize waste.

[0003] For this reason, various methods for carrying out the wastewater after performing some volume reduction treatment at the generation site thereof have been studied. As the volume reduction treatment, for example, after separating solids of relatively large sedimentation with good sedimentation, such as sand and gravel,
Aggregation precipitation and dehydration of solid fine particles are performed. According to this method, the waste material has lost much of its fluidity and has a small volume, so it can be carried out using a cheap dump truck and the number of waste materials can be reduced. Costs can be reduced. or,
Since the amount of waste that needs to be landfilled is reduced, it is also advantageous in terms of disposal costs and securing landfill sites.

[0004]

However, in the conventional wastewater treatment method for performing such a volume reduction treatment, depending on the properties of the wastewater, it is difficult to coagulate and dewater, so that the filtrate becomes turbid and the dewatered cake is dehydrated. There is a problem in that the water content is high, the rate of volume reduction is small, and there is a case where fluidization occurs due to vibration during transportation and handling is poor. In particular, a large amount of muddy water generated by the injection mixing method of injecting a hardening material liquid containing cement into the ground and mixing it with the soil to form a hardened body and strengthen the ground usually contains a large amount of cement, There was a problem that the pH, the solid content, and the viscosity were high, and effective coagulation and dehydration were difficult.

[0005] For this reason, when such wastewater is treated, the treatment capacity is reduced, and it becomes impossible to treat the wastewater on site, or if the treatment capacity is to be ensured, the apparatus becomes large, and the cost increases. However, there are problems such as the need for large equipment costs and large processing sites. In addition, the water content of the dewatered cake is high, fluidized as it is, and its handling is poor.
Further dehydration is difficult, and there is also a problem that it has to be transported and disposed of as industrial waste while paying attention to prevent environmental pollution due to dripping.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in coagulating and dewatering wastewater, which can be carried out easily and efficiently at the site where wastewater is generated, and the resulting dewatered cake can be easily transported. Accordingly, an object of the present invention is to provide an excellent method for dewatering wastewater, which reduces the cost of carrying out the wastewater and reduces the need for securing a landfill site.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, added an inorganic flocculant and a polymer flocculant as a flocculant to wastewater to form a solid content. After the dewatering method, the polymer flocculant is used in combination with an anionic polymer flocculant or a combination of the cationic polymer flocculant and the polymer flocculant, so that even if the waste fluid contains cement, The present inventors have found that the solid content of fine particles in muddy water can be effectively coagulated and can be efficiently dewatered, and have reached the present invention.

That is, the gist of the present invention is a method of dewatering wastewater in which an inorganic flocculant and a polymer flocculant are added to the wastewater as a coagulant to coagulate solids and then dewater. The method for dewatering wastewater is characterized in that the molecular flocculant is an anionic polymer flocculant or a combination of the anionic polymer flocculant and a cationic polymer flocculant.

The wastewater targeted in the present invention is, for example, wastewater generated in civil engineering and construction works such as underground excavation, ground improvement, and dredging. In many cases, sand and gravel having a particle size of 74 μm or more are used. A solid material with a relatively large particle size and good sedimentation,
It contains solids having a relatively small particle size and a low sedimentation property, such as silt and clay having a particle size of less than 74 μm.
It often contains solids having a relatively large particle size and a good sedimentation property, such as sand and gravel having a size of μm or more.

In the injection mixing method in which a hardening material liquid containing cement is injected into the ground and mixed with the soil to form a hardened body and the ground is strengthened, a strong alkali containing cement and having a high solid content and high viscosity is used. Muddy water is generated in large quantities, and this wastewater is difficult to coagulate and dewater efficiently by the conventional coagulation and dehydration methods, whereas the method of the present invention facilitates coagulation and dehydration. Suitable for treating wastewater.

In the method of the present invention, the target wastewater may be coagulated and dewatered as it is. However, from the viewpoints of increasing the processing capacity, improving the reusability of the dewatered cake, and maintaining the dewatering machine, etc. It is preferable to separate sand and gravels in a sieve or the like. As a device for separating sand and gravel, a device that is compact and has a large processing capacity is preferable in practical use. For example, a vibrating sieve, an in-plane motion sieve, a rotating sieve, a liquid cyclone, or the like can be suitably used. The nature of the wastewater, sand,
What is necessary is just to select suitably according to the separation size, quantity, etc. of gravel.

As the coagulant used in the present invention, it is necessary to use a combination of an inorganic coagulant and an anionic polymer coagulant, and a combination of an inorganic coagulant, an anionic polymer coagulant and a cationic polymer coagulant. It is preferable to use them. By using such a combination of flocculants, a large and strong floc can be obtained, the water content of the dehydrated cake is low, and the filtrate can be efficiently and favorably dewatered without turbidity due to suspension. On the other hand, the use of an inorganic flocculant or a polymer flocculant alone or a combination of an inorganic flocculant and a cationic polymer flocculant is not preferable because the floc is small and weak, so that the dehydration efficiency is poor and the filtrate becomes cloudy.

The inorganic coagulant used here includes ferric chloride, ferrous sulfate, ferric sulfate, ferric polysulfate,
Iron salts such as polyferric chloride, aluminum salts such as aluminum sulfate, aluminum chloride, potassium aluminum sulfate, ammonium ammonium sulfate, sodium aluminate, polyaluminum chloride, and polyaluminum sulfate;
Examples thereof include iron-aluminum salts such as iron-containing aluminum sulfate and aluminum-containing polyiron sulfate, and zinc salts such as zinc chloride and zinc sulfate. Preferred are ferric chloride, ferric sulfate, ferric polysulfate, and polychlorinated salts. Ferric, polyaluminum chloride, polyaluminum sulfate, aluminum-containing aluminum sulfate, aluminum-containing polyiron sulfate, more preferably ferric polysulfate, polyferric chloride, depending on the properties of the target wastewater One or more of these can be used.

The anionic polymer flocculants used herein include acrylamide, (meth) acrylic acid,
Acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid, or a copolymer with a salt thereof, or any of polyacrylamide partial hydrolysates, preferably having a molecular weight of 5,000,000 or more, more preferably having a molecular weight of 5,000,000 or more More than 10 million. Examples of the cationic polymer coagulant include a copolymer of acrylamide with dialkylaminoalkyl (meth) acrylate, dialkylaminoalkyl (meth) acrylamide or a salt or quaternary compound thereof, or a copolymer of these cationic monomers. Homopolymer or copolymer having a molecular weight of 200
It is preferably 10,000 or more, more preferably 30 or more.
More than 100,000. These polymer flocculants, if necessary, may be used in combination of two or more, and were copolymerized by adding a small amount of other water-soluble monomers copolymerizable with the above-mentioned monomers. Those can also be used.

When the muddy water contains cement,
The pH of the mud is 10 or more, and when the cement concentration is high as in the mud of the injection mixing method, the pH is often 12 or more. However, since neutralization of this mud requires a large amount of acid and is not practical, a coagulant is added to the mud as it is to perform coagulation and dehydration. In such a case, the inorganic coagulant can be used even in a strongly alkaline region, and an iron-based inorganic coagulant having a high floc density is preferable, and among them, ferric polysulfate and polyferric chloride are more preferable. As the anionic polymer flocculant, the degree of anion (ion equivalent, pH 1
(0, colloid titration) of 0.5 to 1.5 meq / g is preferably used, and an anionic degree of 0.5 to 1.0 meq / g is more preferable. The cationic polymer flocculant has a degree of cation (ion equivalent, pH 4, colloid titration) of 0.2 to 2.0 me.
A weak cationic polymer flocculant of q / g is preferred, and a cationic degree of 1.0 to 2.0 meq / g is more preferred.

The amount of the coagulant to be added cannot be unconditionally determined because the optimum range varies depending on the properties of the target mud water, the solid concentration, and the type of the coagulant. 0.1 to 10 parts by weight of the agent, 0.005 to 3 parts by weight of the polymer flocculant, preferably 0.2 to 5 parts by weight of the inorganic flocculant and 0.01 to 0 parts by weight of the polymer flocculant. .
5 parts by weight. When anionic and cationic are used together as a polymer flocculant, the weight ratio of the respective amounts added is preferably from 1: 0.5 to 5, more preferably from 1 to 1 to 3.

The form of the flocculant to be used may be a powder, an aqueous solution or an emulsion. In the case of an emulsion, it may be a normal phase emulsion or a reverse phase emulsion, but is preferably an aqueous solution or an emulsion.

The dehydrator used in the present invention includes a pressure dehydrator such as a filter press, a screw press, a belt press and a drum press, a vacuum dehydrator such as an Oliver filter and a belt filter, a vacuum pressure dehydrator, a screw decanter and the like. Although centrifugal dewatering machines are mentioned, considering that it is most effective to treat the wastewater at the site of generation of wastewater, it is preferable to use a screw press or A screw decanter is preferable, and a screw decanter is more preferably used. The centrifugal force of this screw decanter is preferably from 200 to 1200 G, more preferably from 300 to 800 G, in consideration of maintainability. Also,
If particular emphasis is placed on reducing the water content of the dewatered cake, a filter press may be used depending on the situation.

The obtained dehydrated cake may be disposed of in a landfill, but can be reused as a material for bricks, tiles, ceramics and the like, or as a raw material for cement. To transport this dehydrated cake,
It is also possible to use a normal dump truck.

The water discharged in the dehydration step can be reused on site as washing water for the apparatus, cutting water, kneading water for cement and the like. If necessary, it may be subjected to a treatment such as pH adjustment and discharged. As the pH adjuster, the above-mentioned acidic substances and alkaline substances can be used.

In order to enhance the reusability of the dewatered cake, a solidifying agent can be added, kneaded and solidified, if necessary, and it can be formed into granules or aggregates as needed. . As a solidifying agent, when the wastewater does not contain cement, a hydrophilic acrylic polymer, sodium silicate and its hardener, and sodium silicate and cement can be used, but when the wastewater contains cement, sodium silicate is used. It is preferable to use a solidifying agent containing the compound or a combination thereof with a hydrophilic acrylic polymer.

[0022] The treatment method of the present invention is preferably carried out at or near the site where wastewater is generated, whereby the effects of the present invention become more remarkable. This wastewater may be stored in an appropriate facility before the treatment method of the present invention is performed.

[0023]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, the following five types of model sludge were prepared and used for civil engineering and construction sludge such as jet grout sludge. The cement used was ordinary Portland cement, and the sand used was Toyoura standard sand. As silt and clay, kaolin (Georgiakaolin, manufactured by ENGELHARD, average particle size: 4.8 μm) is used for muddy water 1 and S is used for muddy water 2 and 3.
AM clay (manufactured by Amanomi Sangyo Co., Ltd., pyrophyllite, particle size 3 to 6 μm), wastewater 4 contains red clay (Hakone, moisture content 24)
%), And black soil (originated from Sagami, water content 51%) was used as the wastewater 5. Table 1 shows the results of the evaluation of the aggregation and dehydration of these wastewaters. Mud water composition (% by weight) Water Cement Silt / Clay Sand Mud water 1 45 15 40 0 Mud water 2 50 20 300 0 Mud water 3 500 0 40 10 Mud water 4 55 10 35 0 Mud water 5 60 10 30 0 Table 1 , Abbreviated wastewater 1 to 5 as S1 to S5, respectively.

Examples 1 to 11 and Comparative Examples 1 to 7 300 ml of the above-mentioned wastewater was put into a 500 ml beaker,
The coagulant shown in Table 1 was added to this, and the mixture was stirred and mixed with a spatula for 20 seconds to coagulate and flocculate the solid content in the muddy water. Next, a total amount of the liquid containing the floc was transferred to a small centrifugal filter (manufactured by Sanyo Rikagaku Kikai Seisakusho, basket diameter 130 mm, filter bag 15).
(0 mesh) with a centrifugal force of 600 G for 1.5 minutes. Floc size, strength, turbidity of the filtrate obtained by dehydration, and moisture content of the dehydrated cake were measured. The following flocculants were used. Table 1 shows the results.

[0025]

[Table 1]

In Table 1, FC in the column of inorganic flocculant indicates ferric chloride, PFS indicates ferric polysulfate, and PAC
Represents polyaluminum chloride, and FS represents ferric sulfate. Further, weak 1 in the column of anionic polymer flocculant is an acrylamide polymer having a molecular weight of about 15 million and a weak anionic polymer flocculant having an anion degree of 0.7 meq / g. About 15 million acrylamide-based polymers with an anion degree of 1.4 meq / g, indicating a weak anionic polymer flocculant. Inside are acrylamide-based polymers with a molecular weight of about 15 million and anion degree of 2.0 meq / g. Is a strong anionic polymer flocculant having a molecular weight of about 15 million and an anionic degree of 3.0 meq / g. Nonionic is an acrylamide polymer. It is a nonionic polymer flocculant having a molecular weight of about 15,000,000.

In the column of cationic polymer flocculant, weak 1 is an acrylamide polymer having a molecular weight of about 6,000,000 and a weak cationic polymer flocculant having a cationicity of 1.2 meq / g. Represents an acrylamide polymer having a molecular weight of about 6 million and a weak cationic polymer flocculant having a cation degree of 1.9 meq / g. Inside is an acrylamide polymer having a molecular weight of about 6 million and a cation degree of about 6 million. 2.5me
A strong cationic polymer flocculant having a molecular weight of about 6 million and having a cation degree of 4.5 meq / g is shown as a medium cationic polymer flocculant having a q / g.

In Table 1, the amount of the coagulant added is shown as parts by weight based on 100 parts by weight of the solid content in the muddy water. However, PF
S and PAC indicate parts by weight of the liquid.

In Table 1, the size of the floc is visually determined as follows.
2.5 mm, x is less than 1 mm. In addition, the flock strength indicates that the touch is 触, which is hard and hard to break, △, which is slightly soft and slightly broken, and ×, which is soft and fragile. ○ in the turbidity of the filtrate in the dehydration status column
を indicates extremely slight, △ indicates slight turbidity, and × indicates large turbidity. The water content of the dewatered cake indicates the percentage (%) of water in the dewatered cake obtained in the dewatering step.

As shown in Table 1, by adding an inorganic flocculant and an anionic polymer flocculant or a cationic polymer flocculant to both of them to the wastewater, the solid content in the wastewater is flocculated and dehydrated. Can be satisfactorily obtained (Examples 1 to 11). On the other hand, when other coagulants are used alone or in combination,
The floc condition is poor and the dewatering condition is not good (Comparative Examples 1 to 4).
7).

[0031]

According to the present invention, a large amount of muddy water generated from civil engineering and construction work can be easily and efficiently coagulated and dehydrated at the site where the muddy water is generated. The obtained dehydrated cake can be reused as a material for bricks, tiles, porcelain, etc., or as a raw material for cement, and the filtrate can be reused on site as washing water or the like. Moreover, it is easy to carry out, the cost can be reduced, and the problem of securing landfill sites can be reduced.

Claims (5)

[Claims] 1. A method of treating wastewater, comprising adding an inorganic flocculant and a polymer flocculant as a flocculant to the wastewater to aggregate solids in the wastewater and then dewatering the wastewater. A method for treating wastewater, wherein the agent is an anionic polymer flocculant or a combination of the anionic polymer flocculant and a cationic polymer flocculant. 2. The method for treating wastewater according to claim 1, wherein the wastewater contains cement. 3. An inorganic coagulant of 0.1 to 10 parts by weight and a polymer coagulant of 0.0
The addition amount is from 0.5 to 3 parts by weight, and the polymer flocculant is an anionic polymer flocculant, or the weight ratio of the addition amount of the anionic polymer flocculant to the cationic polymer flocculant is 1:
3. The method for treating muddy water according to claim 1, wherein the amount is 0.5 to 5. 4. The inorganic coagulant is an iron-based inorganic coagulant, the anionic polymer coagulant is a weak anionic polymer coagulant, and the cationic polymer coagulant is a weak cationic polymer coagulant. 4. The method for treating muddy water according to claim 3, wherein: 5. The method for treating wastewater according to claim 3, wherein the iron-based inorganic coagulant is ferric polysulfate or polyferric chloride.