WO2016103985A1

WO2016103985A1 - Method for recycling used absorbent article

Info

Publication number: WO2016103985A1
Application number: PCT/JP2015/082281
Authority: WO
Inventors: 孝義小西; 利夫平岡
Original assignee: ユニ・チャーム株式会社
Priority date: 2014-12-26
Filing date: 2015-11-17
Publication date: 2016-06-30

Abstract

The purpose of the invention is to effectively recycle even treated wastewater including waste in a method for recycling absorbent articles (paper diapers etc.) including excrement. Disclosed is a method for recycling used absorbent articles in which at least one type of material constituting the absorbent articles is collected and recycled from the used absorbent articles, the method comprising: an ozone treatment step of treating used absorbent articles with ozone water; an ozone concentration adjustment step of adjusting the ozone concentration of the wastewater from the ozone treatment step to 0.1 ppm by mass or less; and a microbial fuel cell step of introducing the ozone-concentration-adjusted wastewater into a microbial fuel cell, to reduce the TOC concentration in the wastewater and also collect electric power produced by power generation.

Description

Recycling method of used absorbent articles

The present invention relates to a method for recycling a used absorbent article in which at least one material constituting the absorbent article is recovered from the used absorbent article and regenerated.

Patent Document 1 is capable of effectively reusing used paper diapers as recycled materials, and flexibly contributing to the reduction of CO ₂ emissions compared to the case where used paper diapers are disposed without being recycled. A recycling method for used paper diapers that can be used is disclosed. The recycling method consists of (1) mixing fermented bacteria while crushing paper diapers containing a lot of water such as excrement, and (2) fermenting and drying fertilizer and pulp, etc. (3) After the completion of fermentation, perform the second heating, heat sterilize and dry the residual moisture, produce a regenerated product, (4) use the regenerated material as a fuel (solid fuel), as thermal energy They are collected and reused.

International Publication No. 2006/134941

However, in the method described in Patent Document 1, (1) it is necessary to mix fermenting bacteria, and equipment and operations such as storage, storage, and addition amount adjustment of the fermenting bacteria are required, and (2) fermentation and drying are performed. In order to promote, large heating energy is required. (3) Heat sterilization and residual moisture drying require drying up to around 100 ° C., and the moisture content is dried from 65% to 5%. Requires a large amount of heating energy, requires high temperature safety measures (insulation and heat resistance), and equipment such as steam treatment that contains a large amount of odor generated during heating. (4) The product is a solid fuel, it is difficult to reuse it in ordinary households and facilities without facilities, and CO ₂ is generated due to reuse by combustion, Thermal recycling By and use applications is limited, there is a problem in that.

The present invention has been made paying attention to such conventional problems, and can be used as a treated wastewater containing pulp fibers, plastic / nonwoven fabric components, and filth that can recycle absorbent articles (such as paper diapers) containing excreta. By separating and treating wastewater containing waste, which was previously valuable, using a microbial fuel cell, recovering power from microorganisms while performing wastewater treatment by microbial decomposition, and reusing it as electrical energy, the above problems can be solved. It is a solution.

That is, the present invention is a method for recycling a used absorbent article that recovers and regenerates at least one material constituting the absorbent article from the used absorbent article, the method comprising the used absorbent article. Treatment with ozone water, ozone concentration adjustment step to adjust the ozone concentration of the wastewater from the ozone treatment step to 0.1 ppm or less, and wastewater adjusted with ozone concentration is put into the microbial fuel cell and drained And a microbial fuel cell process for recovering the electric power generated by power generation.

Preferably, the method further includes a step of adjusting the pH of the waste water from the ozone treatment step to 2.0 or more and 7.0 or less.
Preferably, the pH of the waste water from the microbial fuel cell process is less than 8.0.
Preferably, the method further includes a step of adjusting the TOC concentration of the waste water from the ozone treatment step to 10,000 mg / L or less.
Preferably, the TOC concentration of the waste water from the microbial fuel cell process is 2000 mg / L or less.

According to the present invention, it is possible to recover power by power generation simultaneously with purification of water from wastewater containing recycling that has not been recycled and that has increased the burden of purification treatment, and complete recycling of used absorbent articles. System becomes possible. It is possible to increase the activity of microorganisms by giving organic matter (soil, chemicals, decomposed SAP, micropulp fiber, etc.) in the treated wastewater as food in an environment where microorganisms can efficiently act. By recovering power from the power, residual organic matter that has been disposed of as a recycling residue until now can be recycled as power. In the conventional microbial treatment, air supply by aeration is essential at the aerobic treatment center. However, since the microbial fuel cell is anaerobic treatment, aeration is not necessary and the running energy cost is low.

FIG. 1 shows a recycling system flow including the method of the present invention. FIG. 2 shows a schematic diagram of a microbial fuel cell. FIG. 3 shows the results of current generation and water purification (TOC reduction) in treatment with the microbial fuel cell of the example.

The absorbent article is not particularly limited, and examples thereof include disposable diapers, incontinence pads, urine removing pads, sanitary napkins, panty liners, and the like. Of these, incontinence pads and disposable diapers that are collected together in a facility or the like are preferable because they do not require separation and have a relatively large amount of pulp.

Absorbent articles are usually composed of materials such as pulp fibers, superabsorbent polymers, non-woven fabrics, plastic films and rubber. That is, the material constituting the absorbent article (hereinafter also simply referred to as “constituent material”) refers to pulp fiber, superabsorbent polymer, nonwoven fabric, plastic film, rubber and the like. The at least one material constituting the absorbent article refers to at least one of pulp fiber, superabsorbent polymer, nonwoven fabric, plastic film, rubber, etc., preferably from the group consisting of pulp fiber, nonwoven fabric and plastic film. At least one selected, and more preferably pulp fiber. Hereinafter, the case where pulp fibers are recovered will be mainly described as an example, but the present invention is not limited thereto.

Although it does not specifically limit as a pulp fiber, A fluffy pulp fiber, a chemical pulp fiber, etc. can be illustrated.

Superabsorbent polymer, also called SAP (Superabsorbent Polymer), has a three-dimensional network structure in which water-soluble polymers are appropriately cross-linked and absorbs water several tens to several hundreds of times. It is insoluble in water, and once absorbed water does not release even when a certain pressure is applied, for example, starch-based, acrylic acid-based, amino acid-based particulate or fibrous polymers can be exemplified. it can.

Examples of the nonwoven fabric include spunlace nonwoven fabric and air-through nonwoven fabric formed from cellulose fibers such as rayon, thermoplastic resin fibers, and the like.

Examples of the plastic film include polyolefin forms (for example, polypropylene film), polyester films (for example, polyethylene terephthalate film), and the like.

Examples of rubber include natural rubber, synthetic rubber, and elastic fibers such as spandex.

The method of the present invention includes an ozone treatment step of treating a used absorbent article with ozone water.
In this step, the superabsorbent polymer contained in the used absorbent article is decomposed, reduced in molecular weight, and solubilized. Here, the state in which the highly water-absorbing polymer is decomposed, reduced in molecular weight, and solubilized refers to a state of passing through a 2 mm screen mesh. That is, in this step, the superabsorbent polymer is decomposed to such an extent that it passes through a 2 mm screen mesh.
The ozone water used in this step refers to water in which ozone is dissolved. The ozone water can be prepared using, for example, an ozone water generator (ozone generator OS-25V manufactured by Mitsubishi Electric Corporation, ozone water exposure tester ED-OWX-2 manufactured by Ecodesign Co., Ltd.).

The ozone concentration of the ozone water is not particularly limited as long as it is a concentration capable of decomposing the superabsorbent polymer, but is preferably 1 to 50 ppm by mass, more preferably 2 to 40 ppm by mass, and further preferably Is 3 to 30 ppm by mass. If the concentration is too low, the superabsorbent polymer cannot be completely solubilized, and the superabsorbent polymer may remain in the collected and regenerated constituent material (for example, pulp fiber). On the other hand, if the concentration is too high, the oxidizing power also increases, which may damage the recovered and reconstructed constituent material (for example, pulp fiber) and may cause a problem in safety.

The time for immersing in ozone water is not particularly limited as long as it is a time during which the superabsorbent polymer can be decomposed. The time of immersion in ozone water may be short if the ozone concentration of ozone water is high, and a long time is required if the ozone concentration of ozone water is low.
The product of the ozone concentration (ppm) of ozone water and the time (minute) of immersion in ozone water (hereinafter also referred to as “CT value”) is preferably 100 to 6000 ppm · min, more preferably 200 to 4800 ppm · min. More preferably, it is 300 to 3600 ppm · min. If the CT value is too small, the superabsorbent polymer cannot be completely solubilized, and the superabsorbent polymer may remain in the collected and regenerated constituent material (for example, pulp fiber). On the other hand, if the CT value is too large, there is a risk of damage to the collected and recycled constituent materials (for example, pulp fibers), a reduction in safety, and an increase in manufacturing costs.
As described above, the time of immersion in ozone water depends on the ozone concentration of ozone water, but is preferably 5 to 120 minutes, more preferably 10 to 100 minutes, and still more preferably 20 to 80 minutes.

The amount of ozone water is not particularly limited as long as it is an amount capable of decomposing the superabsorbent polymer, but is preferably 300 to 5000 parts by mass with respect to 100 parts by mass (dry basis) of the used absorbent article. More preferably, it is 500 to 4000 parts by mass, and still more preferably 800 to 3000 parts by mass. If the amount of ozone water is too small, the superabsorbent polymer cannot be completely solubilized, and the superabsorbent polymer may remain in the collected and regenerated constituent material (for example, pulp fiber). On the other hand, if the amount of the ozone-containing aqueous solution is too large, the production cost may increase.

In the ozone treatment step, the method of immersing the used absorbent article in ozone water is not particularly limited. For example, ozone water may be put in a container and the used absorbent article may be put in the ozone water. While being immersed, the contents of the container may be stirred, but may not be stirred. Alternatively, ozone gas may be blown into the ozone water contained in the container, and a weak flow may be generated in the ozone water by raising the bubbles of the ozone gas. The temperature of the ozone water is not particularly limited as long as it is a temperature that can decompose the superabsorbent polymer. Although ozone water may be heated, it may remain at room temperature.

In the ozone treatment process, the superabsorbent polymer is subjected to the oxidative decomposition action by ozone, the three-dimensional network structure of the superabsorbent polymer is destroyed, and the superabsorbent polymer loses its water retention, has a low molecular weight and is solubilized. The superabsorbent polymer with high fluidity dissolves in ozone water. Further, hot melt adhesives used for bonding absorbent articles and the like are also oxidized and deteriorated with ozone water, and the bonding strength between the constituent materials of the absorbent articles is weakened. Further, in this process, the used absorbent article is primarily disinfected by the disinfection action of ozone, or the constituent material (for example, pulp fiber) to be recovered and regenerated is disinfected, bleached, and deodorized.

Ozone water is preferably acidic. More preferably, the pH of the ozone water is 2.5 or less, more preferably 0.5 to 2.5, and still more preferably 1.0 to 2.4. By using acidic ozone water, the water absorption expansion of the initial superabsorbent polymer can be suppressed, and the decomposition and removal effect of the superabsorbent polymer by ozone is dramatically improved, that is, the superabsorbent polymer in a short time. Can be disassembled. Moreover, the disinfection effect by an acid can also be provided by processing with acidic ozone water. By the way, the principle of suppressing the water absorption expansion of the superabsorbent polymer is that the negatively charged carboxyl group is neutralized by the positively charged hydrogen ion in the acidic aqueous solution, so that the ion repulsive force of the carboxyl group is reduced. It is considered that the water absorbing power will be weakened. If the pH of the ozone water is too low, the water absorption capacity of the pulp fiber may be reduced when the constituent material to be recovered and recycled is pulp fiber. If the pH is too low, it is not clear why the water absorption capacity of the pulp fiber is lowered, but it is considered that the pulp fiber itself is denatured.

Acidic ozone water can be prepared by adding an acid to ozone water.
The acid is not particularly limited, and an inorganic acid and an organic acid can be used, but an organic acid is preferable. Since organic acids function in a weak acid range and are environmentally friendly, organic acids are preferred from the viewpoint of safety and environmental burden. Although it does not specifically limit as an organic acid, Tartaric acid, glycolic acid, malic acid, a citric acid, a succinic acid, an acetic acid, ascorbic acid etc. can be mentioned, Especially, a citric acid is preferable.
The pH of the acidic ozone water can be adjusted depending on the type of acid and the amount of acid added. The concentration of the organic acid in the acidic ozone water is not limited as long as the pH is within a predetermined range, but is preferably 0.1 to 5.0% by mass, more preferably 0.2 to 3.0% by mass. %, And more preferably 0.5 to 2.0% by mass.
Further, by adjusting the pH to 2.5 or less with an organic acid, it is difficult to directly touch ozone gas, and the disinfecting effect inside the disposable diaper can be enhanced.

When used absorbent articles are added to ozone water, the pH of the ozone water may change. When the pH of the ozone water differs before and after the used absorbent article is added, the pH of the ozone water here refers to the pH of the ozone water after the used absorbent article is added.
The pH can be adjusted, for example, by putting the used absorbent article and ozone water in the treatment tank, adding the acid to the stirring tank while stirring, and adding the acid when the pH of the solution in the treatment tank reaches a predetermined pH. Stop adding.

When the ozone treatment is completed, the product is separated into used absorbent articles from which the superabsorbent polymer has been removed and waste water. The wastewater contains decomposition products of the superabsorbent polymer, dirt, fine pulp, and the like. This wastewater is hereinafter referred to as “drainage from the ozone treatment process”. The method for separating the used absorbent article and the waste water is not particularly limited. For example, a stopper may be provided at the bottom of the container, the ozone water may be discharged by removing the stopper, or the used absorbent article may be removed from the container, and then the ozone water may be discharged from the container. . When discharging ozone water, for example, it passes through a 2 mm screen mesh and is discharged.

The method of this invention includes the ozone concentration adjustment process of adjusting the ozone concentration of the waste_water | drain from an ozone treatment process to 0.1 mass ppm or less. The ozone concentration of the wastewater charged into the microbial fuel cell is 0.1 mass ppm or less, preferably 0 to 0.05 mass ppm, more preferably 0 to 0.01 mass ppm. If the ozone concentration is high, microorganisms in the next microbial fuel cell process are killed, so the ozone concentration is adjusted to 0.1 ppm or less in order to protect the microorganisms.
The method for reducing the ozone concentration is not particularly limited. For example, a method of diluting with water, a method of adding a reducing agent (for example, silica, alumina, manganese dioxide, ferrous oxide, nickel oxide), activated carbon adsorption There are decomposition methods, thermal decomposition methods, alkali cleaning methods, chemical solution reduction methods such as sodium sulfite.
If the ozone concentration of the waste water from the ozone treatment step is already 0.1 ppm by mass or less at the end of the ozone treatment, this step need not be provided separately. Regardless of whether or not the ozone concentration is actually adjusted, the embodiment is within the scope of the present invention as long as the ozone concentration of the wastewater put into the microbial fuel cell is 0.1 mass ppm or less.

The pH of waste water from the ozone treatment step is preferably 2.0 or more and 7.0 or less. If the pH is too low, microorganisms in the microbial fuel cell process of the next process may be killed. If the pH is too high, the power generation efficiency of the next microbial fuel cell process may be reduced. That is, the method of this invention can include the process of adjusting pH of the waste_water | drain from an ozone treatment process to 2.0 or more and 7.0 or less. Adjustment of pH can be performed by adding an alkali or an acid to waste water. The step of adjusting the pH can be performed simultaneously with the ozone concentration adjusting step, that is, both the ozone concentration and the pH may be adjusted in the ozone concentration adjusting step.

The TOC concentration of the waste water from the ozone treatment step is preferably 10,000 mg / L or less, more preferably 100 to 5000 mg / L, still more preferably 300 to 3000 mg / L. If the TOC concentration is too high, the processing time efficiency of the microbial fuel cell process of the next process may be reduced. When the TOC concentration is too low, nutrients for microorganisms in the microbial fuel cell process of the next process are insufficient, and the activity of the microorganisms may be reduced. That is, the method of this invention can include the process of adjusting the TOC density | concentration of the waste_water | drain from an ozone treatment process to 10,000 mg / L or less. The TOC concentration can be adjusted by diluting the waste water from the ozone treatment process with water. The step of adjusting the TOC concentration can be performed simultaneously with the ozone concentration adjusting step. That is, in the ozone concentration adjusting step, both the ozone concentration and the TOC concentration may be adjusted, or the ozone concentration, the pH, and the TOC. Three of the densities may be adjusted.

The method of the present invention includes a microbial fuel cell process in which wastewater whose ozone concentration is adjusted is introduced into a microbial fuel cell to reduce the TOC concentration in the wastewater and to collect power generated by power generation.
Here, the microbial fuel cell refers to a device that uses microorganisms to convert organic substances as fuel into electric energy. A microbial fuel cell immerses the negative electrode and the positive electrode in a solution of an organic substance as a fuel, and collects electrons generated when the organic substance is oxidatively decomposed by microorganisms in the negative electrode, and the electrons move to the positive electrode via an external circuit. In the positive electrode, electrons are consumed by the reduction reaction of the oxidizing agent. Electrons flow due to the difference in redox potential between the chemical reaction occurring at the negative electrode and the chemical reaction occurring at the positive electrode, and energy corresponding to the product of the potential difference between the two electrodes and the current flowing through the external circuit is obtained in the external circuit.
In the microbial fuel cell process, wastewater whose ozone concentration has been adjusted is introduced into the microbial fuel cell to reduce the TOC concentration in the wastewater and to recover power generated by power generation. In the microbial fuel cell, the TOC concentration in the wastewater is reduced by oxidizing and decomposing organic matter such as decomposition products of the superabsorbent polymer, filth, and fine pulp contained in the wastewater whose ozone concentration is adjusted, And power generation is performed.
The microorganism used in the microbial fuel cell is not particularly limited as long as it can contribute to oxidative decomposition of organic substances and generation of electric energy, but mainly hydrogen-producing microorganisms are used. A facultative anaerobic bacterium is preferably used.

An example of the configuration of the microbial fuel cell used in the present invention is shown in FIG. In the figure, 1 is an ozone treatment drainage tank, 2 is a pump, 3 is a negative electrode reaction tank, 4 is a negative electrode, 5 is a proton exchange membrane, 6 is a positive electrode tank, 7 is a positive electrode, 8 is a tester, 9 is a personal computer, 10 is sludge A sedimentation tank, 11 is a pump, and 12 is a purified water tank.

The pH of the wastewater from the microbial fuel cell process is preferably less than 8.0. If the pH of the wastewater from the microbial fuel cell process is too high, the power generation efficiency of the microbial fuel cell process is reduced.

It is preferable that the TOC concentration of the waste water from the microbial fuel cell process is 2000 mg / L or less. If the TOC concentration of the wastewater from the microbial fuel cell process is 2000 mg / L or less, the purification process can be easily performed in a general septic tank in the next process. Moreover, when draining directly from a microbial fuel cell process, it is preferable that the TOC density | concentration of waste water is 30 mg / L or less.

In the method of the present invention, prior to the ozone treatment step, the used absorbent article is physically applied to the used absorbent article in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less. May be included to decompose the used absorbent article into pulp fibers and other materials (hereinafter also simply referred to as “decomposition step”).
In this step, the used absorbent article is decomposed into pulp fibers and other materials by applying a physical force to the used absorbent article.
Absorbent articles are usually composed of materials such as pulp fibers, superabsorbent polymers, non-woven fabrics, plastic films and rubber. In this decomposition step, the used absorbent article is decomposed into the above materials. The degree of decomposition is not limited as long as at least a part of the pulp fiber can be recovered, and may not be complete or may be partial.
Here, the method of applying a physical force to the used absorbent article is not limited, and examples thereof include stirring, tapping, thrusting, vibration, tearing, cutting, crushing, and the like. Of these, stirring is preferred. Stirring can be performed in a treatment tank equipped with a stirrer such as a washing machine.
When the method of the present invention includes a decomposition step, the object to be treated in the next ozone treatment step is not the used absorbent article itself, but a collection of constituent materials of the absorbent article generated by the decomposition of the used absorbent article. Although it becomes a body or a part thereof (for example, pulp fiber), the case of treating them with ozone water is also regarded as corresponding to the “ozone treatment step” in the present invention.

This decomposition step is performed in an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less. By using an aqueous solution containing polyvalent metal ions or an acidic aqueous solution having a pH of 2.5 or less, the superabsorbent polymer swollen by absorbing water in the used absorbent article is dehydrated.
A superabsorbent polymer has a hydrophilic group (for example, —COO ⁻ ), and a water molecule is bonded to the hydrophilic group through a hydrogen bond, so that a large amount of water can be absorbed. When a superabsorbent polymer that absorbs water is placed in an aqueous solution containing a polyvalent metal ion such as calcium ion, the polyvalent metal ion is bonded to a hydrophilic group (for example, —COO ⁻ ) (for example, —COO—Ca—OCO). -), The hydrogen bond between the hydrophilic group and the water molecule is broken, the water molecule is released, the superabsorbent polymer is dehydrated, and the superabsorbent polymer that has absorbed water is dissolved in an acidic aqueous solution of pH 2.5 or less. , The negatively charged hydrophilic group (for example, —COO ⁻ ) is neutralized by the positively charged hydrogen ion (H ⁺ ) (for example, —COOH), so that the ion repulsive force of the hydrophilic group is weakened. Suck Force is reduced, the superabsorbent polymer is believed to be dehydrated.
By dehydrating the superabsorbent polymer, separation of the pulp fiber and superabsorbent polymer is facilitated. When attempting to decompose used absorbent articles in normal water, the superabsorbent polymer absorbs water and swells, increasing the solid content concentration in the tank and reducing the processing efficiency of mechanical decomposition operations. It can be avoided by carrying out in an aqueous solution containing a valent metal ion or an acidic aqueous solution having a pH of 2.5 or lower.

As polyvalent metal ions, alkaline earth metal ions, transition metal ions, and the like can be used.
Alkaline earth metal ions include beryllium, magnesium, calcium, strontium and barium ions. Preferred aqueous solutions containing alkaline earth metal ions include aqueous solutions of calcium chloride, calcium nitrate, calcium hydroxide, calcium oxide, magnesium chloride, magnesium nitrate, etc. Among them, an aqueous solution of calcium chloride is preferable.

The transition metal ion is not limited as long as it is incorporated into the superabsorbent polymer, and examples thereof include ions of iron, cobalt, nickel, copper and the like. Examples of the aqueous solution containing a transition metal ion include aqueous solutions of transition metal inorganic acid salts, organic acid salts, complexes, and the like. From the viewpoint of cost and availability, an aqueous solution of an inorganic acid salt or an organic acid salt is preferable. Examples of inorganic acid salts include iron salts such as iron chloride, iron sulfate, iron phosphate and iron nitrate, cobalt salts such as cobalt chloride, cobalt sulfate, cobalt phosphate and cobalt nitrate, nickel salts such as nickel chloride and nickel sulfate, Examples thereof include copper salts such as copper chloride and copper sulfate. Examples of the organic acid salts include iron lactate, cobalt acetate, cobalt stearate, nickel acetate, and copper acetate.

In the case of using an aqueous solution containing a polyvalent metal ion, an aqueous solution of a calcium compound is preferable in consideration of safety and price. Among calcium compounds, ozone used in the subsequent process has the property of decomposing on the alkali side, so an aqueous solution of calcium chloride that is weakly alkaline as close to neutral as possible is stronger than calcium hydroxide or calcium oxide, which is a strong alkali. preferable. The pH of the aqueous solution containing polyvalent metal ions is not particularly limited, but is preferably 11 or less. In the case of using an alkaline compound, the pH of the aqueous solution is preferably greater than 7 and 11 or less.

The amount of the polyvalent metal ion is preferably 4 mmol or more, more preferably 4.5 to 10 mmol, further preferably 5 to 8 mmol, per 1 g (dry mass) of the superabsorbent polymer. If the amount of polyvalent metal ions is too small, dehydration of the superabsorbent polymer will be insufficient. If the amount of polyvalent metal ions is too large, excess polyvalent metal ions remain in the treatment liquid without being taken into the superabsorbent polymer, leading to wasted polyvalent metal salts and increasing the treatment cost.

The concentration of the polyvalent metal ion in the aqueous solution containing the polyvalent metal ion is not particularly limited as long as it is a concentration at which the polyvalent metal ion is taken into the superabsorbent polymer, but is preferably 10 to 1000 mmol / L, more preferably. 50 to 700 mmol / liter, more preferably 200 to 400 mmol / liter. If the concentration is too low, dehydration of the superabsorbent polymer will be insufficient. If the concentration is too high, excess polyvalent metal ions remain in the treatment liquid without being taken into the superabsorbent polymer, leading to wasted polyvalent metal ions and increasing the treatment cost.
When a calcium chloride aqueous solution is used as an aqueous solution containing polyvalent metal ions, the concentration of calcium chloride is preferably 1% by mass or more, but even if it is increased to 10% by mass or more, the effect does not change. Is preferably 10 to 10% by mass, more preferably 3 to 6% by mass.

When an acidic aqueous solution is used, the pH of the acidic aqueous solution is 2.5 or less, preferably 0.5 to 2.5, and more preferably 1.0 to 2.4. If the pH is too high, the superabsorbent polymer may be insufficiently dehydrated. If the pH is too low, the pulp fibers recovered due to strong acid may be damaged.

As the acidic aqueous solution having a pH of 2.5 or less, any aqueous solution of an inorganic acid or an organic acid can be used as long as the pH is 2.5 or less. Is preferred. Examples of the organic acid include tartaric acid, glycolic acid, malic acid, citric acid, succinic acid, and acetic acid, and citric acid is preferable.

When an aqueous solution of organic acid is used, the concentration of the organic acid in the aqueous solution is not particularly limited as long as the pH is 2.5 or less, but is preferably 0.1 to 10.0% by mass, more preferably 0.8. It is 5 to 8.0% by mass, and more preferably 1.0 to 5.0% by mass. If the concentration is too low, the superabsorbent polymer may be insufficiently dehydrated. If the concentration is too high, organic acid may be wasted.

The method of the present invention may include, after the decomposition step, a step of separating the pulp fibers from the mixture of pulp fibers and other materials generated in the decomposition step (hereinafter also simply referred to as “separation step”).
In the separation step, the pulp fibers are separated from a mixture of pulp fibers and other materials (superabsorbent polymer, nonwoven fabric, plastic film, rubber, etc.) produced by the decomposition of the used absorbent article. In this step, at least a part of the pulp fiber is separated and recovered. Not all of the pulp fibers need be recovered. Further, other materials may be separated and recovered together with the pulp fibers. Although depending on the separation method, usually, at least a part of the superabsorbent polymer is mixed into the separated pulp fiber. For example, in the method of separating by sieving, when the pulp fiber is recovered as a sieve, most of the superabsorbent polymer is mixed into the separated and recovered pulp fiber. In this step, the decomposed constituent material is preferably separated into a fraction containing pulp fibers and a superabsorbent polymer and a fraction containing non-woven fabric, plastic film and rubber. However, the fraction containing pulp fiber and superabsorbent polymer may contain some nonwoven fabric, plastic film and rubber, and the fraction containing nonwoven fabric, plastic film and rubber will contain some pulp fiber and superabsorbent polymer. May be included.
A method for separating pulp fibers is not limited, but, for example, a method for separating and separating in water using a difference in specific gravity of decomposed constituent materials, and having a predetermined mesh of constituent materials having different sizes. Examples thereof include a method of separating through a screen and a method of separating with a cyclone centrifuge.
The separated pulp fibers are mixed with a high water-absorbing polymer. In the ozone treatment step after the separation step, the superabsorbent polymer remaining in the separated pulp fibers is removed by decomposing, reducing the molecular weight, and solubilizing.

The method of the present invention cleans the used absorbent article and constitutes the used absorbent article by stirring the used absorbent article in an aqueous solution or water containing a disinfectant after the ozone treatment step. A step of decomposing into materials (hereinafter also simply referred to as “cleaning / decomposing step”) may be included.

The water used in the cleaning / decomposition process does not necessarily include a disinfectant, but an aqueous solution containing the disinfectant may be used. The disinfectant is not particularly limited, and examples thereof include chlorine dioxide, acidic electrolyzed water, and ozone water.
In the case of using an aqueous solution containing a disinfectant, the concentration of the disinfectant in the aqueous solution containing the disinfectant is not particularly limited as long as the disinfecting effect is exhibited, but is preferably 10 to 300 ppm by mass, more preferably 30 to 280 ppm by mass, more preferably 50 to 250 ppm by mass. If the concentration is too low, a sufficient disinfection effect cannot be obtained, and bacteria or the like may remain in the recovered pulp fiber. On the other hand, if the concentration is too high, not only will the disinfectant be wasted, but the pulp fibers may be damaged and safety problems may occur.

Stirring in the washing / decomposition step is not particularly limited as long as the residue of the absorbent article is washed and decomposed into constituent materials, but can be performed using, for example, a washing machine. The stirring conditions are not particularly limited as long as the residue of the absorbent article is washed and decomposed into constituent materials. For example, the stirring time is preferably 5 to 60 minutes, more preferably 10 to 50 minutes. More preferably, it is 20 to 40 minutes.

In the cleaning / decomposition process, the residue of the absorbent article from which the polymer absorbent material has been removed is washed, and the absorbent article is broken down into constituent materials. In the ozone water immersion step, the hot melt adhesive used for bonding of absorbent articles is oxidized and deteriorated with ozone water, and the bonding strength between the constituent materials of the absorbent articles is weakened. -In a decomposition process, an absorbent article can be easily decomposed | disassembled into a constituent material by stirring. When an aqueous solution containing a disinfectant is used, disinfection with a disinfectant is also performed.

When antibacterial agent treatment is performed after the ozone treatment step, the antibacterial agent treatment is simultaneously performed in the cleaning / decomposition step by adding a cationic antibacterial agent to an aqueous solution or water containing a disinfectant used in the cleaning / decomposition step. Can do. That is, when the antibacterial agent treatment is performed after the ozone treatment step, the aqueous solution or water containing a disinfectant used in the cleaning / decomposition step preferably contains a cationic antibacterial agent. Since the cationic antibacterial agent adsorbs to the pulp fiber and the pulp fiber is anionic, the cationic antibacterial agent adsorbed to the pulp fiber is not easily desorbed, so that the cationic antibacterial agent remains in the final recycled pulp. To do. However, when many steps are performed before the final step, the cationic antibacterial agent is desorbed little by little in each step, and the content of the cationic antibacterial agent in the finally obtained recycled pulp decreases. Therefore, from the viewpoint of the content of the cationic antibacterial agent in the recycled pulp, the antibacterial agent treatment is preferably carried out at a stage as close to the final process as possible.

The method of the present invention may include a step of separating the pulp fibers from the decomposed material of the used absorbent article (hereinafter simply referred to as “pulp fiber separation step”) after the cleaning / decomposition step.
A method for separating pulp fibers is not limited, but, for example, a method for separating and separating in water using a difference in specific gravity of decomposed constituent materials, and having a predetermined mesh of constituent materials having different sizes. Examples thereof include a method of separating through a screen and a method of separating with a cyclone centrifuge.

The method of the present invention may include a step of washing the separated pulp fibers (hereinafter referred to as “pulp fiber washing step”) after the pulp fiber separation step.
The method for washing the separated pulp fibers is not limited, but for example, the separated pulp fibers can be put in a mesh bag and rinsed with water.

The method of the present invention may include a step of dehydrating the washed pulp fiber (hereinafter referred to as “pulp fiber dehydration step”) after the pulp fiber washing step.
The method for dewatering the washed pulp fibers is not limited. For example, the washed pulp fibers contained in the mesh bag can be dehydrated with a dehydrator.
The pulp fiber washing step and the pulp fiber dehydration step may be performed once, but may be alternately repeated a plurality of times.

The method of the present invention may include a step of drying the dehydrated pulp fiber (hereinafter referred to as “pulp fiber drying step”) after the pulp fiber dehydration step. Since the pulp fiber obtained by the method of the present invention is less prone to mold even in a wet state, it can be stored in a wet state without being dried, and therefore a drying step is not necessarily provided.

The method of the present invention may further include a step of separating and collecting the plastic material (hereinafter referred to as “plastic material separating and collecting step”). Here, the plastic material refers to a nonwoven material, a film material, an elastomer material, and the like. The plastic material separation and recovery step can be performed in parallel with the pulp fiber separation step after the washing and decomposition step. In the plastic material separation and recovery step, the same washing step, dehydration step and drying step as the pulp fiber washing step, pulp fiber dehydration step and pulp fiber drying step can be included. The recovered plastic material can be used as a solid fuel by, for example, RPF processing.

FIG. 1 shows a recycling system flow including the method of the present invention. According to this recycling system, used absorbent articles such as used diapers are first crushed and decomposed (preferably in an SAP inactivated state), then treated with ozone water, and then washed, disinfected, and screen separated. In practice, it is divided into a fraction containing mainly plastic and non-woven fabric and a fraction containing mainly pulp and waste water. In addition, the waste water generated in the crushing / decomposing process and the waste water generated in the cleaning / disinfection / screen separation are also added to the fraction mainly containing pulp and waste water as necessary. Plastics and non-woven fabrics become solid fuel (RPF). The fraction mainly containing pulp and waste water is further separated into pulp and waste water. The pulp is washed, preferably sterilized, deodorized, bleached, dehydrated and dried to recover and reuse the pulp. The waste water is adjusted to water quality such as ozone concentration, pH, and TOC, and then charged into the negative electrode tank of the microbial fuel cell. Wastewater generated by the washing of the pulp is also fed into the negative electrode tank of the microbial fuel cell as necessary. In the microbial fuel cell, the TOC of the wastewater is reduced, and at the same time, the power generated by the power generation is recovered. The wastewater with reduced TOC is further purified as necessary and discharged into sewage or the like.

The method of the present invention has the following advantages.
Since microorganisms grow naturally in the fuel cell, it is not always necessary to add them. It only needs to be replenished when the activity drops.
Microbial (anaerobic) biodegradation enables solids reduction and pathogenic bacteria detoxification (death).
Power generation and storage by battery system (when battery is installed) is possible.
In order to secure an active environment for microorganisms, temperature control may be performed so as to reach room temperature (20 ° C to 40 ° C).
The high-concentration COD wastewater generated by the recycling process can also be harmlessly processed by diluting to a certain concentration or less.
By changing to electric power, which is the most versatile energy resource, it can be reused without special equipment.
Used absorbent articles can be completely recycled (used products ⇒ recycled into pulp fiber, RPF, and electricity).

In the examples, the following ozone water generator was used.
[Ozone water generator]
Manufacturer: Mitsubishi Electric Corporation Name: Ozone generator Model: OS-25V
Ozone water concentration variable range: 1-80mg / m ³
Ozone water exposure tank volume: 30L

[SAP treatment with ozone water]
SAP decomposition was performed by blowing 150 g of SAP in 20 L of 1% citric acid aqueous solution and blowing 80 g / m ³ of ozone gas for 1 hour. The treated water quality after the treatment for 1 hour was TOC 3700 mg / L, pH 2.5, and ozone water concentration 16.8 mass ppm.

[Adjustment of ozone treatment wastewater]
The ozone treated waste water after SAP decomposition is diluted with tap water so that the TOC is about 500 mg / L and about 1000 mg / L, and the TOC is diluted to about 500 mg / L. The pH was adjusted to about 6.5, 6.0, 5.5, 5.0, and 3.0. Table 1 shows the pH, TOC, and ozone concentration of the ozone-treated waste water after preparation.

[Microorganisms]
The microorganism used in the examples is a sludge composed of a mixed microorganism population, has high polymer degrading activity on cellulose, pectin, etc., has high self-aggregation property, and has a sedimentation coefficient indicating sedimentation separation of microorganisms and purified water. ₃₀ is about 20-40%, and is a complex system of aerobic bacteria contained in wild activated yeast such as Hansenula, Kluybaromyces, Candida, Trichosporon, Pichia, Yarrowia, Debaryomyces and other normal activated sludge. It is a mixed microbial sludge that has been acclimatized and cultured for 3 years or more with carboxymethylcellulose as a carbon source and acclimatized with pulverized pulp for 2 years or more.

[TOC degradation by microorganisms]
A 2 L graduated cylinder was filled with 1 L of sludge composed of the microorganisms at a concentration of 1.6 g-MLSS / L, and then the ozone-treated waste water was injected at a flow rate of 0.5 L / d for a total of 1 L over 2 days. The TOC after the treatment (after 2 days) was measured, and the TOC decomposition rate was calculated. The results are shown in Table 1.
It was confirmed that TOC decomposition (water purification) by microbial treatment can be efficiently decomposed at a pH of 2 to 7 and a TOC of 1080 mg / L or less. Moreover, although efficiency became a little worse, it turned out that it can process even if TOC density | concentration is high. Preferably, the processing time efficiency is better when processing at TOC 10,000 mg / L or less. More preferably, the TOC is 5,000 mg / L or less.

[TOC degradation rate and pH fluctuation]
After charging 1 L of sludge composed of the above microorganisms at a concentration of 1.6 g-MLSS / L into a 2 L graduated cylinder, the flow rate of ozone treatment wastewater adjusted to pH 2.95 and TOC 537 mg / L was 0.5 L / d. The change in the TOC decomposition rate over time and the pH fluctuation in the tank were examined. The results are shown in Table 2.
It is known that the pH in the tank changes to the alkali side as the decomposition of the TOC proceeds, and it is known that the power generation efficiency of the fuel cell is lowered on the alkali side, and can be kept below pH 8 after the treatment. It is important to manage by state. The optimal decomposition rate is preferably 80% or more, and the pH in the tank after treatment is preferably less than 8.0.
Based on the above results, in order to perform water purification and power generation treatment of the wastewater from the recycling treatment with the microbial fuel cell, the water quality when it is introduced into the treatment layer is adjusted to pH 2.0 to 7.0 at TOC 10000 mg / L or less. As a result, the TOC decomposition rate is 80% or more and the purification process can be performed efficiently. By controlling the wastewater concentration and flow velocity so that the inside of the treatment tank is not alkalized, it is possible to perform treatment without impairing the power generation efficiency of the microbial fuel cell. Moreover, the microbial fuel cell process is an anaerobic process, and aeration is not required unlike the conventional activated sludge process, and the processing power cost can be reduced. As a result, it is possible to recover power from power generation through recycling at the same time as water purification, from wastewater containing recycling that has not been recycled and that has increased the burden of purification treatment, enabling a complete recycling system for used absorbent articles. It becomes.

[Treatment with microbial fuel cell]
In the microbial fuel cell shown in FIG. 2, a 1.6-liter acrylic cylindrical negative electrode reaction tank 3 (diameter 8 cm, height 32 cm) is used, and the negative electrode 4 has a bio-cord made of carbon fibers bundled in a mall shape. (Registered trademark) (made by TB Corp., diameter: 45 mm) is used as one 29 cm, and for the positive electrode 7, a platinum thin film carbon paper (ElectroChem, EC-20-10-7) is cut into a 79 mmφ circle. Using. For the proton exchange membrane 5, NeoSepta CMS manufactured by Astom Co., Ltd. was cut into a circle of 79 mmφ, attached to the opening cut out on the side of the negative electrode reaction tank 3, the outer periphery was fixed with waterproof tape, and the upper surface of the positive electrode tank At the same time, a positive electrode was attached. The negative electrode 4 and the positive electrode 7 were connected with a titanium wire (0.3 mm diameter), and the generated current was monitored and recorded with a tester 8 connected to a personal computer 9.
The negative electrode reaction tank 3 was filled with the microorganisms, and a decomposition test was started at 1.6 L including the microorganisms. Ozone-treated wastewater (residual ozone 0 ppm) with a TOC of 240 ppm by mass (drainage obtained by ozone-treating used diapers) was continuously injected into the negative electrode reactor 3 for 21 days at a flow rate of 0.8 L / 24 hours. Then, drainage was performed at the same flow rate, and current generation and water purification (TOC reduction) were confirmed.
Also, from the 22nd day of continuous injection, the positive electrode was replaced with a new one, and ozone treatment wastewater (residual ozone 0 ppm) having a TOC of 240 mass ppm was continuously injected into the negative electrode reaction tank 3 at 1.2 L / 24 hours for 8 days. Then, drainage was performed from the negative electrode reaction tank 3 at the same flow rate, and current generation and water purification (TOC reduction) were confirmed. The results are shown in FIG.

The generated current yield was calculated as follows.
First, the theoretical value is calculated.
When converting TOC to COD,
TOC 240 ppm × 2.2 = COD 528 ppm
In terms of the amount of electrons at the time of 0.8L wastewater treatment per 24 hours,
COD528 ppm × 0.8 L / 24 h × 4 e ⁻ = 1.690 mol · e ⁻ / 24 h
When converted to coulomb amount,
1.690 × 96500C / mol = 1.630C / 24h
= 1.89 mC / s (1)
When converted to the amount of electrons at the time of 1.2L wastewater treatment per 24 hours,
COD 528 ppm × 1.2 L / 24 h × 4 e ⁻ = 2.5344 mol · e ⁻ / 24 h
When converted to coulomb amount,
2.5344 × 96500 C / mol = 2.4457 C / 24 h
= 2.83 mC / s (2)
The actual yield is then calculated.
(0.8L wastewater treatment per 24 hours)
The average generated current value for 21 days from the start of the experiment is 1.06 mA (maximum value 1.73 mA, minimum value 0.17 mA).
The average generated current for 9 days (10-18 days) was 1.65 mA (maximum value 1.73 mA, minimum value 1.43 mA).
Since the generated current is A = C / s,
The average generated current for 9 days (10-18 days) is
1.65 mA = 1.65 mC / s (3)
From (1) and (3)
Generated current yield = actual value / theoretical value = 1.65 / 1.89 = 87.3%
(At the time of 1.2L wastewater treatment per 24 hours)
The average generated current value for 8 days from the start of the experiment is 2.48 mA (maximum value 2.83 mA, minimum value 1.63 mA).
The average generated current for 3 days (24th to 27th days) was 2.66 mA (maximum value 2.83 mA, minimum value 2.54 mA).
Since the generated current is A = C / s,
The average generated current for the stable 3 days (24th to 27th days) is
2.66 mA = 2.66 mC / s (4)
From (2) and (4)
Generated current yield = actual value / theoretical value = 2.66 / 2.83 = 94.0%

The method of the present invention can be suitably used in a recycling system for used absorbent articles such as disposable diapers.

DESCRIPTION OF SYMBOLS 1 Ozone treatment drainage tank 2 Pump 3 Negative electrode reaction tank 4 Negative electrode 5 Proton exchange membrane 6 Positive electrode tank 7 Positive electrode 8 Tester 9 Personal computer 10 Sludge sedimentation tank 11 Pump 12 Purified water tank

Claims

A method of recycling a used absorbent article for recovering and recycling at least one material constituting the absorbent article from a used absorbent article, wherein the method treats a used absorbent article with ozone water. Ozone treatment process, ozone concentration adjustment process to adjust the ozone concentration of waste water from ozone treatment process to 0.1 mass ppm or less, and waste water adjusted to ozone concentration to microbial fuel cell to reduce TOC concentration in waste water A method comprising a microbial fuel cell step of reducing and recovering power from power generation.
The method according to claim 1, further comprising a step of adjusting the pH of the waste water from the ozone treatment step to 2.0 or more and 7.0 or less.
The method according to claim 1 or 2, wherein the pH of the waste water from the microbial fuel cell process is less than 8.0.
The method according to any one of claims 1 to 3, further comprising a step of adjusting the TOC concentration of waste water from the ozone treatment step to 10,000 mg / L or less.
The method according to any one of claims 1 to 4, wherein the TOC concentration of waste water from the microbial fuel cell process is 2000 mg / L or less.