JP2018118191A - Water treatment system - Google Patents

Abstract

A water treatment system using polylactic acid porous particles is provided. [Means for Solving Problems] [1] A raw water tank 1 into which raw water containing anions of inorganic compounds is introduced, a chemical tank 2 holding a chemical solution containing polylactic acid porous particles, and the chemical solution being transferred from the chemical tank 2 to the raw water tank. A water treatment system 10 comprising: [2] A turbid water treatment apparatus in which a mixed liquid of the raw water introduced into the raw water tank 1 and the chemical liquid mixed therein is introduced, and the polylactic acid porous particles contained in the mixed liquid are separated from the supernatant liquid. 5, and a mixed solution sending unit 1a for sending the mixed solution from the raw water tank 1 to the turbid water treatment device 5. The water treatment system 10 according to [1] or [2]. [3] A third storage tank 6 holding a flocculant for aggregating the polylactic acid porous particles; The water treatment system according to [1] or [2], characterized by: [Selection drawing] Fig. 1

Description

  The present invention relates to a water treatment system using polylactic acid porous particles as an adsorbent.

Oxide ions such as selenium, arsenic, and chromium may be contained in wastewater from chemical establishments and construction sites. These anions are highly soluble, depending on inorganic flocculants such as sulfuric acid bands (aluminum sulfate) and PAC (polyaluminum chloride) used in conventional general wastewater treatment, and organic flocculants containing polymer polymers. It is difficult to precipitate and remove. Therefore, in Patent Document 1, selenium, arsenic, and chromium are added to an iron oxide mineral called _{Schwertmannite} [composition formula: Fe ₈ O ₈ (OH) _8-2x (SO ₄ ) _x ; 1 ≦ x ≦ 1.75]. Adsorption methods have been proposed.

JP 2005-95732 A

  However, there is a problem that it is difficult to obtain the high-quality iron oxide mineral described in Patent Document 1 to such an extent that a large amount of waste water can be treated. For this reason, as an anion adsorbent used in a water treatment system, an adsorbent that can adsorb a target anion and can be procured more easily is demanded.

  The present invention provides a water treatment system using polylactic acid porous particles as an adsorbent.

[1] A raw water tank into which raw water containing an anion of an inorganic compound is introduced, a chemical tank for holding a chemical liquid containing polylactic acid porous particles, and a chemical liquid supply for supplying the chemical liquid from the chemical tank to the raw water tank A water treatment system comprising: a unit.
[2] A muddy water treatment apparatus for introducing a mixed liquid of the raw water introduced into the raw water tank and the chemical liquid mixed therewith to separate the polylactic acid porous particles and the supernatant liquid contained in the mixed liquid And a liquid mixture feeding section for feeding the liquid mixture from the raw water tank to the turbid water treatment device. The water treatment system according to [1].
[3] A third storage tank that holds a flocculant that aggregates the polylactic acid porous particles, and a flocculant supply unit that supplies the flocculant from the third storage tank to the turbid water treatment apparatus. The water treatment system according to [2], which is characterized.
[4] A discharge tank that receives and temporarily stores the supernatant liquid, and a supernatant liquid supply section that supplies the supernatant liquid from the turbid water treatment apparatus to the discharge tank. ] The water treatment system as described in.
[5] A mud storage tank that receives the sediment containing the polylactic acid porous particles from the turbid water treatment apparatus, and a sediment first transfer unit that transports the sediment from the turbid water treatment apparatus to the mud storage tank. The water treatment system according to any one of [2] to [4], wherein the water treatment system is provided.
[6] The water according to [5], further comprising: a dehydrator that dehydrates the precipitate; and a precipitate second transfer unit that transfers the precipitate from the mud tank to the dehydrator. Processing system.

  According to the water treatment system of the present invention, an anion of an inorganic compound contained in raw water (treated water) can be adsorbed on the polylactic acid porous particles to obtain water with a reduced concentration of the anion. . Moreover, since the polylactic acid porous particles can be easily chemically synthesized, the procurement thereof is also easy.

It is a mimetic diagram of water treatment system 10 of an example of the present invention. 2 is an adsorption isotherm of selenate ions in polylactic acid porous particles.

《Water treatment system》
The water treatment system according to the first aspect of the present invention includes a raw water tank into which raw water containing an anion of an inorganic compound is introduced, and a chemical tank holding a chemical solution containing polylactic acid porous particles, which is used by mixing with the raw water. And a chemical solution supply unit for supplying the chemical solution from the chemical tank to the raw water tank. An example of this water treatment system is shown in FIG.

A water treatment system 10 in FIG. 1 includes a raw water tank 1, a chemical tank 2, and a chemical solution supply unit 2a.
The chemical solution supply unit 2 a is configured by a pipe, a pump, and a valve that connect the chemical tank 2 and the raw water tank 1.

  The water treatment system 10 introduces a mixed solution of the raw water introduced into the raw water tank 1 and the chemical solution mixed therewith, and separates the polylactic acid porous particles and the supernatant contained in the mixed solution. The muddy water treatment apparatus 5 is provided as an arbitrary configuration.

  The water treatment system 10 is supplied to the muddy water treatment device 5 and holds a flocculant for aggregating the polylactic acid porous particles; and a third storage tank 6; until the supernatant is received and discharged to the outside. A discharge tank 7 for temporarily storing a supernatant; a mud tank 8 for receiving a precipitate containing the polylactic acid porous particles from the muddy water treatment apparatus 5; and a dehydrating apparatus 9 for dehydrating the precipitate. It is provided as a configuration.

The muddy water treatment device 5 is connected to a mixed solution feeding portion 1 a that sends the mixed solution from the raw water tank 1 to the muddy water treatment device 5.
The muddy water treatment device 5 is connected to a coagulant supply unit 6 a that supplies the flocculant from the third storage tank 6 to the muddy water treatment device 5.
Connected to the discharge tank 7 is a supernatant liquid supply section 5 a for supplying the supernatant liquid from the muddy water treatment device 5 to the discharge tank 7.
The sediment storage tank 8 is connected to a sediment first transfer section 5b for transferring the sediment from the muddy water treatment device 5 to the mud storage tank 8.
The dewatering device 9 is connected to a second precipitate transfer section 8 a that transfers the precipitate from the mud storage tank 8 to the dewatering device 9.
Each part which performs said connection is comprised by well-known connection members, such as piping, a valve, and a pump.

《Water treatment method》
The water treatment method described below is a method for reducing anions of inorganic compounds contained in raw water (treated water) using the water treatment system of the first aspect described above. By this water treatment method, clean treated water is obtained. Below, the method using the water treatment system 10 is demonstrated.

First, raw water containing an anion of an inorganic compound is introduced into the raw water tank 1 from outside such as a raw water storage tank (not shown) via an appropriate means (for example, a pipe, a water truck, etc.) (introduction process).
Next, a chemical liquid containing polylactic acid porous particles is introduced from the chemical tank 2 to the raw water tank 1 through the chemical liquid supply unit 2a, and the raw water and the chemical liquid are mixed (mixing step). In this mixed liquid, the anion of the inorganic compound comes into contact with and adsorbs on the polylactic acid porous particles. Then, the liquid mixture containing polylactic acid porous particles is transferred from the raw water tank 1 to the turbid water treatment device 5 through the liquid mixture feeding part 1a.
As a dispersion medium of polylactic acid porous particles in the chemical solution, for example, water is preferable.

  Next, the liquid mixture introduced into the water tank of the muddy water treatment device 5 is allowed to stand, and a precipitate containing polylactic acid porous particles is allowed to settle. When a flocculant (for example, polyaluminum chloride, polymer flocculant, etc.) is supplied from the third storage tank 6 to the muddy water treatment device 5 via the flocculant supply unit 6a, sedimentation of the precipitate can be promoted. After the precipitate containing the polylactic acid porous particles settles, the supernatant liquid in which the anion concentration of the inorganic compound is reduced is transferred to the discharge tank 7 via the supernatant liquid sending part 5a, and temporarily stored. , Discharge it to the outside of the river at an appropriate timing. Moreover, you may return a supernatant liquid to the raw | natural water tank 1 as needed. On the other hand, the sediment containing the precipitated polylactic acid porous particles is treated as sludge and transferred from the turbid water treatment device 5 to the mud storage tank 8 via the sediment first transfer section 5b and temporarily stored. Thereafter, the sludge is transferred from the mud storage tank 8 to the dewatering device 9 such as a filter press through the precipitate second transfer section 8a, and the sludge is dehydrated to obtain a dehydrated cake containing polylactic acid porous particles. The dehydrated cake is properly disposed of by known methods. Since the dehydrated water is considered to be less clean than the supernatant, it is preferably returned to the raw water tank 1.

  In the water treatment method described above, the following anion adsorption method and polylactic acid porous particle synthesis method can be applied.

<Anion adsorption method>
In the raw water tank 1, the anion can be adsorbed to the polylactic acid porous particles by bringing the raw water containing anions of inorganic compounds into contact with the polylactic acid porous particles.

  Examples of the inorganic compound include inorganic compounds containing inorganic elements such as selenium, arsenic, chromium, fluorine, sulfur, and phosphorus. Specific examples include selenium, arsenic, chromium oxo acid, hydrofluoric acid (hydrofluoric acid), sulfuric acid, phosphoric acid, and the like.

  The inorganic compound is preferably an oxo acid from the viewpoint of exhibiting a high adsorptive power to polylactic acid porous particles, and more preferably a monovalent or divalent anion of an inorganic oxo acid containing the inorganic element. Here, the oxo acid is an inorganic compound in which a hydroxyl group (—OH) and an oxo group (═O) are bonded to one inorganic atom, and a proton of the hydroxyl group can be eliminated. Oxo acid can be an oxo acid ion from which the proton is eliminated in water.

As the oxo acid, selenium oxo acid is preferable from the viewpoint of exhibiting high adsorbing power on polylactic acid porous particles, and selenium oxo acid ions include selenate ions (SeO ₄ ²⁻ ), selenate hydrogen ions ( HSeO ₄ ⁻ ), selenite ion (SeO ₃ ²⁻ ), and hydrogen selenite ion (HSeO ₃ ⁻ ).

  One type of anion of the inorganic compound contained in the raw water may be used, or two or more types may be used.

  In the present invention, the polylactic acid porous particles used as an adsorbent for the anions of the inorganic compound are not particularly limited as long as they have fine pores small enough to adsorb the anions of the inorganic compound. The average pore diameter of the fine pores of the polylactic acid porous particles is preferably 0.001 μm to 5 μm, more preferably 0.001 μm to 1 μm, and more preferably 0.001 μm to 0.5 μm. When the porous structure of the polylactic acid porous particles has the above-described preferable micropores, the anion of the inorganic compound is easily trapped physically or chemically in the microspace. Moreover, the porous structure of the polylactic acid porous particles having the above-mentioned preferable micropores is preferable because it provides a large surface area capable of adsorbing anions of inorganic compounds as in the case of activated carbon.

  In the mixed liquid of the present invention, when the polylactic acid porous particles come into contact with the anion of the inorganic compound, it is considered that the anion of the inorganic compound is trapped and adsorbed by the porous structure of the polylactic acid porous particle.

  In the mixed solution, the pH of the mixed solution (polylactic acid porous particle dispersion) during the treatment for adsorbing the anion of the inorganic compound to the polylactic acid porous particles is preferably 4 or more and 9 or less, and preferably 4 or more and 7 The following is more preferable, and the acidity of 4 or more and 6 or less is more preferable. The method for adjusting the pH of the mixed solution is not particularly limited, and examples thereof include a method of adding hydrochloric acid and sodium hydroxide.

When the pH of the mixed solution is 4 or more and 7 or less, hydrolysis of the polylactic acid porous particles can be suppressed, and the anion adsorption force of the inorganic compound by the polylactic acid porous particles can be further increased.
When the mixed solution is on the weakly acidic side, the mechanism by which the anion adsorption force of the inorganic compound is further increased is unknown, but the following may be considered as a factor. That is, (1) pH affects the porous structure, (2) A part of the ester bond constituting the main chain of polylactic acid is cleaved during the formation of the porous structure, and the carboxyl produced by the cleavage It is conceivable that the elimination of the proton of the group and the hydroxyl group (formation of a negative charge) is suppressed.

The temperature at which the anions of the inorganic compound are adsorbed on the polylactic acid porous particles in the mixed liquid is not particularly limited, and is preferably 4 to 40 ° C, more preferably 4 to 30 ° C, and further preferably 4 to 20 ° C. preferable.
When the temperature is within the above range, the anion adsorption force of the inorganic compound by the polylactic acid porous particles can be increased. When it is at least the lower limit of the above temperature range, the diffusion rate of the anion of the inorganic compound in the mixed solution is increased, and the efficiency of adsorbing in contact with the polylactic acid porous particles is further increased. When the temperature is not more than the upper limit of the above temperature range, hydrolysis of the polylactic acid porous particles can be suppressed, and the anion adsorption force of the inorganic compound by the polylactic acid porous particles can be increased.

The amount of polylactic acid porous particles in contact with the raw water is not particularly limited with respect to the content of the target anion contained in the raw water, and the target anion can be sufficiently adsorbed empirically through preliminary experiments. Can be set to the confirmed amount.
Usually, if the amount of polylactic acid porous particles to be contacted is increased, the amount of anions that can be adsorbed also increases. For example, the adsorption amount of inorganic oxoacid ions by polylactic acid porous particles is 0.45 to 1.5 mol. / Kg.

  Examples of a method for recovering the polylactic acid porous particles having adsorbed anions from the mixed solution include a precipitation method and a filtration method. Examples of the precipitation method include a method in which the mixed solution is allowed to stand to precipitate, a method in which a sulfuric acid band, PAC, a polymer polymer flocculant, and the like are added to the mixed solution to cause aggregation to precipitate. Thereafter, the treatment liquid is obtained as a supernatant liquid of the precipitated polylactic acid porous particles or a filtrate obtained by filtering the precipitated polylactic acid porous particles.

  When an adsorption method is adopted in which a polylactic acid porous particle powder is packed into a column and raw water is allowed to flow into this column, the polylactic acid porous particle adsorbs the anion of the inorganic compound and removes the anion. The treated liquid can be obtained by flowing out of the column.

  In the water treatment method described above, an anion adsorbent having polylactic acid porous particles can be used as the main component of the adsorbent. Here, “main component” means a component having the largest adsorption amount when the adsorption amount of the target anion between the components of the adsorbent is compared. This anion adsorbent may further have a holding member for holding an adsorbent (polylactic acid porous particles).

  The shape of the polylactic acid porous particles as the adsorbent is not particularly limited, and may be a spherical shape, a spheroid shape, or any other indefinite shape. A polylactic acid porous particle dispersion (suspension) in which polylactic acid porous particles of these shapes are dispersed in a solvent such as water can also be used as an adsorbent.

  Examples of the holding member include containers, columns (cylinders), baskets, nets, and the like that hold polylactic acid porous particles inside. In addition, a holding member capable of fixing the polylactic acid porous particles on the surface can also be employed, and examples thereof include a form in which the polylactic acid porous particles are fixed on the surface of the plate material.

《Synthesis of polylactic acid porous particles》
The polylactic acid porous particles used in the present invention are those chemically synthesized by a known method, and those obtained by the method for producing polylactic acid porous particles disclosed in JP-A-2009-242728 are preferable.

  In the method for producing polylactic acid porous particles described in the above publication, (i) polylactic acid and a first solvent which is a good solvent for polylactic acid are mixed, and the mixture is heated to melt polylactic acid. And (ii) a cooling step of cooling the melt obtained by the melting step at a temperature at which polylactic acid crystallizes or solidifies. This production method further includes (iii) a separation step of separating polylactic acid crystals from the melt after the cooling step, and (iv) polylactic acid crystals obtained by the separation step, and the solubility of polylactic acid. It is preferable to have a washing step of contacting a second solvent having a high solubility of the first solvent to wash the polylactic acid crystals, and (v) a drying step of drying the polylactic acid crystals after the washing step.

  According to the above production method, for example, the average particle size is 99 to 700 μm, the average pore size of the pores constituting the porous structure is about 0.27 μm to 1.4 μm, and the variation coefficient of the pore size is 25% or less. Thus, polylactic acid porous particles having a crystallinity of 50% or more can be easily obtained.

  Here, the “particle diameter” of the polylactic acid porous particles is the diameter of the maximum inscribed circle with respect to the two-dimensional shape of the polylactic acid porous particles observed with an electron microscope. For example, when the two-dimensional shape of polylactic acid porous particles is a shape that is reasonable to approximate a circle (when it is closer to a circle than other shapes), the diameter of the circle is the particle diameter and approximates an ellipse When it is appropriate to do so, the minor axis of the ellipse is the particle diameter, and when it is reasonable to approximate a square, the length of the side of the square is the particle diameter, and when it is reasonable to approximate the rectangle The length of the short side of the rectangle is the particle diameter. The “average particle size” is obtained by observing and measuring the particle size of a plurality of randomly selected particles with an electron microscope and calculating the average value. The number of particles to be measured is not particularly limited, but is preferably 20 or more, for example.

The coefficient of variation of the particle diameter of the group of polylactic acid porous particles is calculated by the equation of standard deviation of observed particle diameter ÷ average value × 100 (%), and the smaller the value, the more uniform the particle diameter is shown. .
The coefficient of variation of the group of polylactic acid porous particles used in the present invention is preferably 25% or less, preferably 20% or less, and more preferably 15% or less. By using polylactic acid porous particles having a uniform particle diameter, stable and homogeneous adsorption performance can be obtained.

  The “pore diameter” of the polylactic acid porous particle is the diameter of the maximum inscribed circle with respect to the opening shape of the hole. For example, when the opening shape of the hole is a shape that is reasonable to approximate a circle (from other shapes) Is the diameter of the circle), if it is reasonable to approximate an ellipse, the minor axis of the ellipse, and if it is reasonable to approximate a square, the length of the side of the square If it is reasonable to approximate a rectangle, it is the length of the short side of the rectangle. The “average pore diameter” is obtained by observing and measuring the pore diameters of a plurality of randomly selected holes with a microscope and calculating the average value. The number of holes to be measured is not particularly limited, but is preferably 20 or more, for example.

The variation coefficient of the pore diameter of the pores constituting the porous structure of the polylactic acid porous particle is calculated by the equation of standard deviation of observed pore diameter ÷ average value × 100 (%), and the smaller the value, the more uniform the pore diameter. It is a porous particle.
The coefficient of variation of the polylactic acid porous particles used in the present invention is preferably 45% or less, preferably 35% or less, and more preferably 25% or less. By using polylactic acid porous particles having a uniform pore size, stable and homogeneous adsorption performance can be obtained.

The crystallinity of the polylactic acid porous particles can be measured by a differential scanning calorimetry method (DSC method). The DSC method can be performed, for example, by packing a sample of 5 to 10 mg in an aluminum pan and raising the temperature from room temperature to 150 ° C. at 5 ° C./min at 5 ° C./min while flowing a small amount of nitrogen in the DSC apparatus. . The crystallinity χc is obtained by the following equation.
(Expression) χc (%) = ΔHm ÷ ΔHf × 100
In the above formula, ΔHm represents the heat of fusion of the sample measured by the DSC apparatus, and ΔHf represents the equilibrium heat of fusion of 100% crystalline polylactic acid.
The crystallinity of the polylactic acid porous particles used in the present invention is preferably 50% or more, more preferably 60% or more. The higher the degree of crystallinity, the higher the mechanical strength such as toughness of the polylactic acid porous particles, and the easier the handling and operation when carrying out the anion adsorption method of the present invention.

[Synthesis of porous polylactic acid particles]
High purity poly L-lactic acid (molecular weight: 100,000 to 300,000) was added to diethyl phthalate in the ampule tube so as to have a concentration of 10% by mass. The air in the ampoule tube was replaced with nitrogen, and the ampoule tube was sealed with a gas burner. The ampoule tube was immersed in an oil bath at 160 ° C. for 10 minutes to melt the poly L-lactic acid, and water at 0 ° C. It was immersed in the bath for 20 minutes. This cooling produced polylactic acid particles in the ampoule tube.
The above particles were taken out from the ampule tube and collected by a filtration method. After washing by adding 1000 ml of methanol to about 10 g of the obtained particles, the particles were collected by a filtration method. The particles were dried by vacuum drying to obtain the desired polylactic acid porous particles.
A part of the produced polylactic acid porous particles was subjected to gold sputtering, observed with a scanning electron microscope (SEM), and the particle diameter thereof was measured.
As a result of the measurement, the produced polylactic acid porous particles had an average particle size of about 40 μm, a coefficient of variation of about 25%, an average pore size of about 0.4 μm, and a coefficient of variation of about 40%. It was.

[Example 1]
A sodium selenate aqueous solution (pH 6) containing 10 mg / L of selenium was prepared. The following experiment was conducted using the polylactic acid porous particles obtained by the above synthesis.
0.015, 0.025, 0.05, 0.1, 0.2, 0.5, 1.0 (unit: 0.015, 0.025, 0.05, 0.1, 0.2) are added to the aqueous solution containing selenate ions. (w / w%) at each concentration. After this aqueous solution was stirred at 20 ° C. for 1 hour, the polylactic acid porous particles were collected by filtration, and the selenate ion concentration of the filtrate from which the polylactic acid porous particles were removed was determined according to JIS K0102: 2013 “67. The hydride generation ICP emission spectroscopic analysis method.
By the above test, adsorption isotherms for the selenate ions of the polylactic acid porous particles were obtained (FIG. 2). From the results shown in FIG. 2, it was confirmed that the equilibrium concentration of dissolved selenate ions was reduced to an environmental standard (0.01 mg / L) or less by adding polylactic acid porous particles. Considering that the selenium concentration contained in the waste water at the construction site is about 0.03 to 0.1 mg / L, it is understood that the waste water containing selenium can be sufficiently treated by the present invention.

[Comparative Example 1]
Experiments were conducted in the same manner as in Example 1 except that commercially available crosslinked acrylic resin particles (average particle size of about 20 μm, non-porous) were used instead of the polylactic acid porous particles.
As a result, the selenate ion concentration of the aqueous solution was 10 mg / L, the same as before the test.

  From the above results, it is clear that the water treatment system according to the present invention makes it possible to obtain treated water from which the target anions are removed from the raw water by bringing the raw water and the polylactic acid porous particles into contact with each other in the raw water tank.

  The configurations and combinations thereof in the embodiments described above are examples, and additions, omissions, substitutions, and other modifications of known configurations are possible without departing from the spirit of the present invention.

  The present invention can be widely applied to uses for purifying contaminated water containing heavy metals such as selenium, arsenic, and chromium.

DESCRIPTION OF SYMBOLS 1 ... Raw water tank, 1a ... Mixed liquid feeding part, 2 ... Chemical tank, 2a ... Chemical liquid supply part, 5 ... Turbid water processing apparatus, 5a ... Supernatant liquid feeding part, 5b ... Precipitate first transfer part, 6 ... First Three storage tanks, 6a ... flocculant supply part, 7 ... discharge tank, 8 ... mud tank, 8a ... second sediment transfer part, 9 ... dehydrator, 10 ... water treatment system

Claims (6)

A raw water tank into which raw water containing anions of inorganic compounds is introduced;
A chemical tank for holding a chemical solution containing polylactic acid porous particles;
A chemical solution supply unit for supplying the chemical solution from the chemical tank to the raw water tank;
A water treatment system comprising: A turbid water treatment device for introducing a mixed liquid of the raw water introduced into the raw water tank and the chemical liquid mixed therewith, and separating the polylactic acid porous particles and the supernatant liquid contained in the mixed liquid;
A liquid mixture feeding section for feeding the liquid mixture from the raw water tank to the muddy water treatment device;
The water treatment system according to claim 1, comprising: A third storage tank holding a flocculant for aggregating the polylactic acid porous particles;
A flocculant supply unit for supplying the flocculant from the third storage tank to the muddy water treatment device;
The water treatment system according to claim 2, comprising: A discharge tank for receiving and temporarily storing the supernatant liquid;
A supernatant liquid feeding section for feeding the supernatant liquid from the muddy water treatment apparatus to the discharge tank;
The water treatment system according to claim 2, comprising: A mud storage tank for receiving a precipitate containing the polylactic acid porous particles from the muddy water treatment device;
A precipitate first transfer section for transferring the precipitate from the muddy water treatment device to the mud tank;
The water treatment system according to any one of claims 2 to 4, wherein the water treatment system is provided. A dehydrator for dehydrating the precipitate;
A precipitate second transfer section for transferring the precipitate from the mud tank to the dehydrator;
The water treatment system according to claim 5, comprising:

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