JPH0729120B2 - Method for dehydration concentration of hardly dehydratable sediment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is generated, for example, from waste mud or sewage treatment plants generated during foundation piles for construction and civil engineering, sewer excavation shield construction, retaining wall foundation construction, etc. The present invention relates to a method for dehydrating and concentrating hard-to-dewater sediments that rapidly separates water from hard-to-dewater sediments such as excess sludge.

A large amount of fine clay is mixed in the waste mud used in construction and civil engineering work, and even after the sand stone is separated, it does not easily settle as a sludge-like liquid, which makes it difficult to process. If it is discharged as it is, not only will it pollute the river, but it will also socially damage the environment, such as blocking sewers on the way. In recent years, construction / civil engineering work is rapidly changing from manual excavation to rig construction using water injection, and most of this method is used. Therefore, the waste soil discharged from excavating foundation piles and sewers is not ordinary soil, but is discharged as muddy water diluted with water.

The work of separating soil from this muddy water has become a new issue and various methods have been tried, but there is still no satisfactory method. This is because the clay content contained in this muddy water is minute, so even if treatment with chemicals is performed, the filterability with a dehydrator etc. is poor, dehydration cannot be performed easily, and it is discharged at a high water division ratio. Is forced. Therefore, special vehicles and container vehicles are dumping the landfills with a large amount of water.

INDUSTRIAL APPLICABILITY The present invention is a difficult-to-dehydrated sediment having remarkably improved filterability so that the difficult-to-dewater sediment such as waste mud discharged from these difficult-to-treat construction and civil engineering works can be treated quickly and in an energy-saving manner. It is a dehydration concentration method.

(Prior arts and problems to be solved by the invention) The simplest treatment method of mud water that has been conventionally performed is to set up a sedimentation tank to allow natural sedimentation, remove the supernatant liquid, and dehydrate and dry the sediment by sunlight. However, it is not suitable for recent construction / civil engineering sites because it takes a long time to secure a place for ponds and to return to the original soil quality. Furthermore, as a method of mechanical treatment, after separating the coarse particles contained in the waste mud water using a mud screen or a wet cyclone, once it is stored in the mud tank, a coagulant or coagulant is added to the mud water. After promoting the agglutination reaction and coarsening the particles, fine particles are flocculated and stored in a filtration dehydration tank for sedimentation separation (generally called primary dehydration) to separate into fresh water and sludge. The treated soil obtained at this stage is still highly creamy and highly viscous soil with high water content, and it is inappropriate to dispose of it as it is, but in general, it may have been disposed of at this stage. Is causing.

In order to perform appropriate treatment, after this primary dehydration, secondary dehydration is performed using a filter cloth such as a vacuum dehydrator, mesh press, belt filter, etc. to reduce the water content and solidify. It is difficult to quickly and efficiently dehydrate the aggregated clay that blocks the eyes of the filter cloth. A large amount of filtration area is required, high pressure is applied, and the clogged filter cloth has to be washed while being constantly washed. Not in the present situation.

The muddy water discharged from construction and civil engineering works is mainly bentonite muddy water, shield muddy water, and reverse muddy water, and the amount of discharged water is large. Is created with the maximum value of load fluctuation. As a result, the device becomes bulky. In addition, since the concentration of discharged mud water varies, the coagulant liquid is injected in accordance with the maximum load value so that it can be operated on the safe side, which is an extremely uneconomical treatment method.

The aggregating agent used here is added in order to be adsorbed on the surface of fine suspended particles and to have a role as a crosslinking agent for binding particles to each other. Therefore, as a conventional coagulant, a polymer compound having a polar group in the molecule for having an adsorbing ability is used. In addition to this adsorption function, the fine particles suspended in the muddy water form an electric double layer that repels each other electrically. By adding the polyelectrolyte with, it is partially neutralized with the electric charge on the surface of the fine particles at the electrolytic group and is fixed to the electrolyte chain of the adsorbed polymer. At that time, if the polymer has a spread much larger than the length of the interparticle distance repelled by the electric double layer, each repelled particle is separated by another electrolyte on the electrolyte polymer chain. The charge of another particle is neutralized, resulting in cross-linking aggregation due to reticulated adsorption, resulting in particle coarsening. As a result, a flocculant has been added and used with the idea that the sedimentation rate increases and separation becomes easier. If a flocculant is actually used in accordance with this idea, the sedimentation speed will certainly be faster than that without addition. The larger the flocs produced, the faster the sedimentation rate.However, those with large flocs are easily broken by mechanical agitation and also contain a large amount of interparticle bound water and surface-adhered water, resulting in a large precipitate volume. After removing the supernatant, the sludge becomes a fluffy, slimy, and poorly filterable precipitate. On the contrary, when flocculating agent and muddy water are reacted with each other, initial flocculation and initial agitation are strongly performed to generate small flocs, and the floc strength is increased, but particles are reduced to obtain a dehydrated soil with a low water content. The filtration resistance in a dehydrator etc. increases and the filter cloth is clogged, which prevents rapid dehydration.

In order to solve these drawbacks, the present invention provides a treatment method for catching the process of flocculation and sedimentation from a completely different viewpoint and eliminating the above disadvantages.

Compared with the conventional method, the processing time is shortened, the volume of processing is greatly reduced by securing a high dehydration product, and the remarkably improved dewatering / filtering property makes it possible to downsize the device and reduce the energy required for it. The purpose is to provide a method of waste mud treatment such as simple construction and civil engineering. The method according to the present invention can exert the same effect not only on the waste mud of civil engineering works but also on the dehydration of general water treatment.

(Means for Solving the Problems) The present invention has been proposed in order to solve the above problems, and the method for dehydrating and concentrating the hardly dehydratable precipitate of the present invention is to add and mix latex to the hardly dehydratable precipitate. Then, add sodium alginate as a hydrophilic protective colloid-forming substance to it, mix it, and add a polyvalent metal ion while making the pH of the mixed solution weakly acidic to insolubilize the latex and the hydrophilic protective colloid-forming substance. It is characterized by performing processing.

Generally, difficult-to-dehydrated sediments such as waste mud have a weak alkaline pH of around 8, but if the difficult-to-dehydrated sediments have a pH of 8 or less, adjust the pH to around 8 beforehand using caustic soda or aqueous ammonia solution. It is preferred to add the latex after this. The latex used is NBR latex, SBR latex, SB latex, Hist latex,
Any acrylate latex, PVC latex, etc. may be used, and the amount used is about 0.1 to 0.5 wt% in terms of latex solid content per 1 m ³ of hardly dehydratable sediment. The latex is preferably used as an aqueous solution of about 3 to 10%.

In the solution thus produced, the fine particles of the latex form an electric double layer and repel each other, and the fine particles of the latex are dispersed in the colloidal liquid and dispersed in water. The latex is sewn between the fine mud particles to come close to each other, and becomes in a state of surrounding the fine mud particles.

After being dispersed and adsorbed and immobilized in this way, when sodium alginate is added to the sludge-adsorbed sludge as a substance forming a hydrophilic protective colloid, these hydrophilic protective colloids are adsorbed on the surface of the sludge. The quality is further absorbed. As a result, the tackiness peculiar to the low molecular weight polymer is lost. If the pH is made weakly acidic in this state,
The latex is decomposed and the low-molecular weight polymer becomes a lump, shrinks and solidifies, and is insolubilized. At this time, when sodium alginate is used as the hydrophilic protective colloid-forming substance, a synergistic effect is produced by the insolubilizing shrinkage of sodium alginate, which is the hydrophilic protective colloid-forming substance adsorbed on the surface of the latex, together with shrinkage and coagulation of the latex.
More specifically, water-swollen sodium alginate molecules are adsorbed on the latex particles adhering to the surfaces of the fine particles, and the fine soil particles are wrapped with a mucous membrane of sodium alginate so as to cover the latex surface. Next, adding a polyvalent metal ion (for example, calcium ion, aluminum ion, magnesium ion, iron ion, etc.) while making the pH of this mixed solution weakly acidic gives a thin layer of latex and sodium alginate which has been swollen until now. Condensation of latex occurs in parallel with the insolubilization of alginic acid so that it surrounds the surface of the sludge, and it strongly contracts while wrapping the sludge. Generally, when only latex is coagulated and dispersed with an acid or the like, the low-molecular weight polymer which is ejected exhibits tackiness. If the slurry is coagulated and dehydrated in the same way using only latex, the dehydrated product will remain sticky, and if it is forcibly squeezed using a filter cloth, etc., the dehydrated slurry will adhere to the filter cloth and be processed well. Can not. However, when the surface of the adsorbed latex is treated with a polyelectrolyte, not only the tackiness of the low molecular weight polymer is lost, but also the condensation-sedimentation separability is remarkably improved, resulting in quick separation into an aqueous layer and a precipitation layer.

This precipitate is of course insoluble in water, has coarse particles, is non-adhesive, has good filterability, can be filtered with a coarse filter cloth, requires only a small pressure during dehydration, and has a low water content. It can be treated exactly like ordinary soil and can be used not only as landfill or land preparation soil, but also reduces the tackiness and water retention characteristic of clay and forms a hard ground that does not become mud again when water is added. can do.

(Example) Next, the Example of this invention is described.

Bentonite waste mud discharged from foundation work and civil engineering works is settled in a mud tank after passing through a mud screen, and then the lower layer is pulled out, and, for example, a rubber latex aqueous solution is added to the sludge as it is. , Mix thoroughly with a stirrer. Next, an aqueous solution of sodium alginate is added and the mixture is further stirred to adsorb it on the solid matter in the mud water. After that, when the pH was gradually made acidic while stirring the aqueous solution of polyvalent metal salt such as polyaluminum chloride (PAC), the slurry in the form of slurry began to rapidly solidify and the soda salt equivalent of sodium alginate When the injection of the polyvalent metal salt aqueous solution is completed, it is completely solidified and solidified in the same manner and separated into a water layer and a soil layer.
The solidified soil does not solubilize even when dispersed in water again, solidifies into small particles, has high strength, and forms a stable solid matter.

In addition, in order to remove water as efficiently as possible when treating mud water, the conventional method is applied as it is, and an anionic or inorganic flocculant based on a polyacrylic acid amide type or maleic acid copolymer is used. If added to mud water in advance to promote flocculation and sedimentation, separate the supernatant into the primary dehydration layer, increase the soil concentration, and add rubber latex to save the amount of sodium alginate added. You can

Sodium alginate is easily adsorbed on the surface of soil dispersed in muddy water, and in low-concentration muddy water with high water content, it is preferentially adsorbed on the upper soil and does not reach the soil particles in the lower layer of the mud storage tank. Unless the sodium alginate is added more than necessary, the entire surface in the mud cannot be coated in the same manner.

In order to make up for this, there is a method of adding in the fluidized bed as a continuous proportional addition method, but it is difficult to secure a place in a narrow construction site, and the batch method is often more convenient.

In this way, using a polymer flocculant, add a latex latex solution to a slurry that has been concentrated to a certain degree and stir it until it becomes uniform. The latex latex will cover the surface of the aggregated fine particles in every corner. It's just like the bean jam wrapped in thin skin. A film formed by further adsorbing sodium alginate in the form of a thin film on the rubber latex layer and then insolubilizing it becomes a porous water-permeable film. This film serves as a filter cloth that wraps the water-containing flocs, and when it becomes insoluble, the porous film undergoes a strong shrinkage. The shrinkage at this time shrinks while the rubber latex that has been atomized until now and the alginic acid molecule that has been linearly stretched bends and entangles, so that it shrinks by itself while acting as a filter cloth. Therefore, it exerts the effect of squeezing out the water in the enclosed floc mass without applying mechanical pressure from the outside.
This is the most important feature of the present invention, which is fundamentally different from the coagulation and coarsening of fine particles by the coagulant.

Next, more specific examples of the present invention will be described.

Example 1 Moisture 92-95 in shielded mud discharged from a civil engineering site
Since the waste liquid containing the wt% primary貯泥tank, carboxyl against 1 m ³ which contained 60～65Wt% moisture in the underlying mud漿物of sediment Shizu沈, rubber latex (Nipol 2570X5 styrene-butadiene latex 50% aqueous solution was made into 5% aqueous solution and 50 liters was added.

The pH of the sludge at this time should be around 8. If the pH is low, adjust the pH to around 8 using caustic soda. next,
This mixture is rotated at low speed (100 to 150 rpm) with a stirrer to uniformly adsorb the rubber latex on the surface of the mud particles.

Next, an aqueous solution of sodium alginate adjusted to about 3% is added as sodium alginate so as to be equivalent to 0.2% by weight, and the mixture is further stirred to be adsorbed on the rubber latex adsorbed on the surface of the mud particles. After adjusting the pH to around 6.5,
10.5% as polyaluminum chloride (PAC), basicity 45
% Solution of 1.3% is slowly added with stirring. The agitation at this time is performed at a low speed, and the soil particles to be granulated become larger if the strong shearing force is not applied. When the polyaluminum chloride to be added approaches the sodium salt equivalent of sodium alginate, solidification occurs rapidly, and the water contained in the mud soil begins to separate, and separates into a coagulum and water. In this state, the muddy water is no longer water-soluble and has become an agglomerate of soil with significantly improved dehydration.

The mixture of this agglomerate and water could be quickly dehydrated without squeezing it with a normal dehydrator such as a filter press, and the dehydration product having a low water content was obtained.

Example 2 In order to continuously dehydrate and separate the reverse mud water discharged from foundation works, etc., coarse particles such as pebbles are removed through a mud screen, and after passing through a mud water tank, it is led to a reactor for reaction with a flocculant, where 10 to 50 gr for 1 m ^{3 of} muddy water
The floc is formed while adjusting the pH to around 8 by adding the flocculant of.

Next, the muddy water that has been flocculated is introduced into a primary filtration dehydration tank and separated into fresh water and mud. The mud remaining after filtration here is creamy and has a water content of about 50%, but the particles are fine and have a high water-retaining power, and are clay-like and sticky. To 1 m ^{3 of} this clay-like primary dehydrated product, 50 liters of a rubber latex aqueous solution diluted with water to an amount of 5% is added, and well mixed with stirring. An aqueous solution of sodium alginate adjusted to about 3% is added to a paste-like uniform sludge.
Add 0.1% by weight of an aqueous solution of chito acid, which has been added so as to have an amount of 2% by weight and then acidified with acetic acid, and then gradually add 2.3 liters of a 20% calcium chloride solution while stirring. If the stirring at this time is also performed at a low speed, the generated clod particles become larger. When the amount of calcium chloride to be added approaches the sodium salt equivalent of sodium alginate, solidification occurs rapidly, and the state is the same as that shown in Example 1,
A dehydrated product with a water content of 25 to 28% was easily obtained.

Example 3 Excess sludge discharged from sewage treatment plants is one that is extremely difficult to dehydrate. This is a sludge having a large compaction property, which causes clogging of the filter cloth, sludge that is attached to the filter cloth does not easily fall off, is time-consuming to wash the filter cloth, and is difficult to obtain uniform dehydration.

50ppm of acrylic amide type coagulant was added to the sludge stock solution of sewage activated sludge (concentration of solids 2%), and the mixture was stirred and mixed to generate flocs. Moisture 90
A dehydrated cake of about% is obtained. To this, 50 liters of a 5% rubber latex solution is added and well mixed and dispersed with a kneader stirrer or the like.

Add sodium alginate 10 to the paste that has become uniform.
% To add 0.2% by weight of the aqueous solution to adjust the pH.
After adjusting to 6-7, polyaluminum chloride (PAC)
When 1.6 kg was added slowly with stirring, it solidified rapidly near the soda salt equivalent of sodium alginate, condensed and dehydrated, water and sludge were separated, and sludge became a dry, granular, non-adhesive solid substance. The dehydration filterability was remarkably improved, high pressure was not required, and dehydration up to about 50% was possible with the conventional dehydrator.

Claims (1)

[Claims] 1. A latex is added to and mixed with a hardly dehydratable precipitate, and then sodium alginate as a hydrophilic protective colloid-forming substance is added and mixed therewith, while the pH of the mixed solution is made weakly acidic, and a polyvalent metal is added. A method for dehydrating and concentrating a hardly dehydratable precipitate, which comprises insolubilizing a latex and a hydrophilic protective colloid-forming substance by adding ions.