TWI398310B - Degradable and slow-releasing material for enhancing chemical oxidation of contaminated soil and groundwater - Google Patents

Description

Decomposable slow-release substances used to enhance chemical oxidation and treatment of contaminated soil and groundwater

The invention relates to a decomposable sustained-release substance for strengthening chemical oxidation treatment of contaminated soil and groundwater, in particular to a chemical oxidation of contaminated soil and groundwater by using polycaprolactone as a coating material. Remediation of decomposable slow release materials.

According to the regulations on soil and groundwater pollution, the environmental problems related to soil and groundwater pollution have gradually been valued by the government, enterprises and the public. In many pollution cases, chlorine compounds and petroleum are also used. Hydrocarbons account for the largest number of pollution incidents, and the aforementioned organic solvents are extremely harmful to the environment and human health. Therefore, the remediation of soil and groundwater is a necessary task. However, the aforementioned organic solvents are extremely difficult to be decomposed by microorganisms, and therefore artificial intervention is often required for active remediation, which is usually carried out by chemical oxidation to remediate soil and groundwater. In the case of chemical oxidation, it is required to provide a chemical oxidant for a long time under the surface of the earth to chemically promote the oxidative decomposition of pollutants. Common engineering injection methods for injecting chemical oxidants into the surface include: direct injection system for injection wells, extraction and recirculation system, and osmotic wall system. Among them, the permeable wall system is a common development in recent years at home and abroad. Groundwater remediation technology.

The so-called permeable remediation wall refers to the installation of a filling system in an underground environment and the substance that reacts with the pollutants is placed therein. When the contaminated groundwater flows through the permeable remediation wall, it will be degraded by reaction with the reaction substance. (degradation). The permeable wall system has the following advantages: (1) does not require any mechanical equipment and electricity; (2) can treat contaminated groundwater in situ, does not need to extract and recharge groundwater; (3) does not need to redeem organic pollutants Transfer to gas phase products, thus avoiding secondary environmental pollution; (4) For sites that require long-term remediation, local site remediation can be achieved to save manpower and material resources, so the cost of remediation can be effectively reduced. It can be seen from the foregoing advantages that the effectiveness of the wall-removing system depends entirely on the effective release time and concentration of the reactants.

In the conventional permeable wall system, it is usually used as a coating material/condensation material such as cement or gypsum to enable a long-term release effect of a reaction substance such as a chemical oxidant or a biological growth substrate. For example, the Republic of China Announcement No. 583145 discloses an artificial oxygen-releasing composition having a sustained release of oxygen, the composition of which comprises calcium peroxide (CaO ₂ ), sand, peat, cement and water, wherein CaO _{2 is} used for For the release of oxidizing substances. Furthermore, the Chinese Patent Publication No. 200811052 discloses a solid composition containing potassium permanganate component, which comprises potassium permanganate (KMnO ₄ ), cement and sand, wherein potassium permanganate, cement and sand are used. The solid composition is formed by mixing with the formulated water. In addition, the invention patent of the Republic of China Publication No. I273095 discloses a composition and method for treating pollutants in water, the composition comprising dehydrated biological sludge, pore enhancer and cured product for treating pollutants in groundwater The pore enhancer comprises sand, wood chips, rice or straw, and the solidified material comprises cement and water. The composition may further comprise a microbial culture agent selected from the group consisting of ammonium chloride and potassium phosphate.

However, in the above-mentioned conventional permeable wall system, most of the sustained-release substances used are cement or gypsum as a coating material/coagulation material, which can make the reaction substance (such as chemical oxidant or biological growth substrate) long-term. The release effect, but the coating material remaining after the reaction substance is released cannot be decomposed or biodegraded by itself, and the solid waste is left to remain under the surface of the local site, and thus will cause after the pollution is rectified. Secondary environmental pollution of waste at the site.

Therefore, it is necessary to provide a decomposable sustained-release substance for strengthening chemical oxidation treatment of contaminated soil and groundwater to solve the problems of the prior art.

The main object of the present invention is to provide a decomposable sustained-release substance for strengthening chemical oxidation treatment of contaminated soil and groundwater, which uses polycaprolactone (PCL) as a coating material for coating pollution remediation. The reaction material, which not only can slowly release the pollution-remediation reaction substance for a long time to degrade the organic pollutants in the soil and/or groundwater, and the coating material itself can be biodegraded or recyclable, thereby being advantageous In order to improve the effect of slow release of pollution remediation, solve the problem of waste generation after remediation, increase the convenience of pollution remediation and reduce the cost of pollution remediation.

A secondary object of the present invention is to provide a decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater, which uses starch as a pore-promoting material to cause pollution remediation in the coating material. The reaction substance can be slowly released outward through the micropores formed by the starch, and the starch is accompanied by the passage of the water body, which does not cause pore blockage of the aquifer soil, thereby facilitating the promotion of the sustained release, reaction and transmission effects of the permanganate.

To achieve the above object, the present invention provides a decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater, comprising: polycaprolactone (PCL), starch and at least one pollution remediation reaction The substance, wherein the weight ratio of the polycaprolactone, the starch and the reaction remediation reaction substance is 0.5 to 1.25:0.6 to 1.0:0.2 to 0.3.

In one embodiment of the present invention, the weight ratio of the composition of the polycaprolactone, the starch, and the reactive substance for pollution remediation is 1.25:1.0:0.25.

In an embodiment of the invention, the reaction remediation reaction material is a chemical oxidant.

In an embodiment of the invention, the chemical oxidizing agent is selected from the group consisting of permanganates (eg, potassium permanganate KMnO ₄ ), persulfates (eg, persulfate), or peroxides (eg, magnesium peroxide, MgO). ₂ , calcium peroxide CaO ₂ ) or zero-valent iron (Fe ⁰ ).

In one embodiment of the invention, the sustained release material is applied to a permeable wall system.

In one embodiment of the invention, the permeable wall system is buried in a field soil having chlorinated organic contaminants or petroleum hydrocarbons.

In an embodiment of the invention, the sustained release material is formed into a cubic block, a sphere, a cylinder, a ring, a strip, a sheet or an irregular shape.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

The invention provides a decomposable sustained-release substance for strengthening chemical oxidation treatment of contaminated soil and groundwater, which is mainly applied to a permeable wall system for being placed in the existing soil with chlorine-containing pollutants. To remediate the local soil and/or groundwater contaminated by organic pollutants, preferably organic pollutants containing chlorine (or bromine) or petroleum hydrocarbons such as trichloroethylene (trichloroethylene, TCE), tetrachloroethylene (PCE), dioxin-like compounds, gasoline, diesel, marine fuel, various industrial lubricants or the like.

In a preferred embodiment of the present invention, the decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater mainly comprises: polycaprolactone (PCL), starch (starch) and at least one kind The reaction material for pollution remediation has a composition ratio of 0.5 to 1.25:0.6 to 1.0:0.2 to 0.3.

In a preferred embodiment of the present invention, the polycaprolactone (PCL) is a synthetic high molecular polymer, which usually uses ε-caprolactone to form a polycaprolactone polymer through ring-opening polymerization. polymer. Polycaprolactone is a thermoplastic crystalline polyester having a melting point of about 80 ° C and decomposing at a high temperature of 250 ° C. If it is placed in a humid environment at normal temperature, it is easily degraded by microorganisms. In the present invention, since polycaprolactone has a very low melting point and is biodegradable, the present invention uses polycaprolactone as a coating material for a sustained-release substance.

Further, starch is also used as a pore-promoting material in the sustained-release substance of the present invention, which can be dissolved or softened by water after being wetted, thereby forming numerous micropores in the coating material (polycaprolactone) ( Pores), so that the pollutants for remediation and remediation coated in the coating material can be slowly released outward through the micropores formed by the starch, thereby facilitating the promotion of permanganate sustained release, reaction and transmission effects, and at the same time Starch can also form micropores along with the passage of water to avoid causing pore blockage in the aquifer. In the present invention, the particle size of the starch is substantially between a millimeter (mm) to a micrometer (um) grade (ie, between 10 ^-3 and 10 ^-6 meters), and the present invention can be based on the sustained-release substance. The preset slow release rate is used to adjust the particle size or amount of starch, and thus is not limited.

In addition, the reaction remediation reaction substance is a chemical oxidant, and the chemical oxidant is selected from a chemical substance having an oxidizing ability, such as a permanganate (such as potassium permanganate KMnO ₄ ), a persulfate or peroxidation. a substance (such as magnesium peroxide MgO ₂ , calcium peroxide CaO ₂ ) or zero-valent iron (Fe ⁰ ), etc., and preferably potassium permanganate, which chemically promotes the oxidative decomposition of organic pollutants .

In a preferred embodiment of the invention, the decomposable sustained release material for enhancing chemical oxidation treatment of contaminated soil and groundwater can be prepared by the following steps of the manufacturing method: First, preparing polycaprolactone (PCL) Plastic, which can be directly purchased commercially or by self-utilization of ε-caprolactone via ring-opening polymerization; then, the polycaprolactone plastic is put into a mixer for stirring, and a temperature of about 75 to 85 ° C is utilized. Heating and melting the polycaprolactone plastic; after heating and melting the polycaprolactone plastic, a predetermined weight ratio of the starch and at least one pollution remediation reaction substance (for example, potassium permanganate crystal KMnO ₄ ) are sequentially or simultaneously put into the same mixer Stirring internally to uniformly mix the polycaprolactone plastic into a mixed molten material; finally, pouring the mixed molten material into a model container to solidify and solidify into a predetermined solid shape, for example, forming a cubic block, a sphere, a cylinder, a ring, a strip, a sheet or an irregular shape, or the like, or the present invention may first form the mixed molten material into a whole piece or a whole piece, and then Using the cutting method to split it up into several pieces or the number of small pieces.

Referring to Fig. 1, in the preferred embodiment of the present invention, the weight ratio of polycaprolactone, starch and the reaction material for pollution remediation (e.g., potassium permanganate KMnO ₄ ) is preferably 1.25: 1.0: 0.25, which can be prepared according to the weight ratio and the steps of the above manufacturing method to form a biodegradable sustained-release substance in a block shape, and is used for soil and groundwater pollution remediation. For example, Figure 1 illustrates the application of the biodegradable slow release material of the present invention to a passive permeable wall system 10 that is excavated at a site 11 to include a trench 12, the trench 12 extends through a surface layer 111 (unsaturated layer) of the site site 11 and into a groundwater layer 112 (saturated water layer) of the site site 11 for a predetermined depth to form a funnel-shaped water collection structure, the trench 12 is filled with at least one sustained release material 21 and optionally further filled with at least one filler 22 (e.g., in situ soil or sand, but without the use of cement) to form a wall 20 .

Therefore, as shown in Fig. 1, when a groundwater 31 contaminated with organic contaminants flows into the remediation wall 20, the sustained release material 21 of the remediation wall 20 can be slowly released through the corresponding micropores produced by the moisture dissolution of the starch. The reaction substance for pollution remediation, for example, the release of potassium permanganate (KMnO ₄ ), which also produces microporosity after continuous release of the reaction substance for remediation. Therefore, the pollutant remediation reaction material can be slowly released to the filler 22 or the inner wall of the trench 12 along the micropores connected to each other to perform redox reaction with organic pollutants (for example, chlorine-containing organic pollutants). To degrade organic pollutants. At the same time, the starch which is dissolved by moisture is also a substance which can be biodegradable or utilized, and promotes the growth of microorganisms near the rectification wall 20 to accelerate the rate of decomposition of organic pollutants by the microorganisms, and at the same time, the micropores which the starch can form with the passage of the water body can Avoid causing clogging of the aquifer soil pores of the groundwater layer 112. Therefore, the sustained-release substance 21 of the present invention can surely greatly reduce the concentration of organic contaminants contained in the groundwater 32 which flows out through the rectification wall 20.

Furthermore, since the micropores corresponding to the dissolution of the starch after being dissolved by the moisture (the micropores generated after the release of the reaction remediation reaction substance) need to take a long time to form a microchannel to make the pollution remediation reaction The substance can be released to the outside, so that the present invention can achieve the sustained release effect by this principle, so that the sustained-release substance 21 can continuously and slowly release the reaction substance for the pollution remediation for a long period of time. In the preferred embodiment of the present invention, the weight ratio of the starch and the particle size thereof can be controlled to adjust the pore size of the microvoid which may be formed by the slow release material 21 due to the moisture of the starch, thereby controlling the reaction substance for the pollution remediation. Release rate. If the micropores formed by the starch are too large, the release rate of the reaction remediation reaction substance to the groundwater 31 is too high, so that the effect of long-term release cannot be achieved; conversely, if the micropores formed by the starch are too small, The release rate of the reaction substance for causing the pollution remediation to be released into the groundwater 31 is too slow, so that the concentration thereof is too low to effectively oxidize the organic contaminants in the groundwater 31. Therefore, in a preferred embodiment of the present invention, the weight ratio of the composition of the polycaprolactone, the starch, and the reaction remediation reaction substance (for example, potassium permanganate KMnO ₄ ) must be maintained at 0.5 to 1.25:0.6 to 1.0:0.2 to Within the composition range of 0.3, for example, preferably 1.25:1.0:0.25, but it may also be 0.75:0.7:0.225 or 1.0:0.8:0.25 or 1.1:0.9:0.275, etc., in order to form an appropriate pore diameter. Size (ie between 10 ^-3 and 10 ^-6 meters).

On the other hand, the coating material of the sustained-release substance 21 of the present invention, that is, polycaprolactone (PCL) itself is biodegradable, so that the sustained-release substance 21 is used to constitute the curing wall 20 After the reaction material for the pollution remediation is completely released, it is not necessary to remove the sustained release material 21 from the trench 12 of the remediation wall system 10, and the polycaprolactone remaining in the sustained release material 21 will be self-retained in the soil. Since microorganisms are decomposed, waste is not generated, so that the problem of secondary environmental pollution caused by waste can be prevented.

Referring to FIG. 2, it is disclosed that the sustained-release substance 21 of the preferred embodiment of the present invention comprises polycaprolactone, starch and a reaction substance for pollution remediation (for example, potassium permanganate KMnO ₄ ) in a weight ratio of 1.25. : 1.0: 0.25, and the sustained release substance 21 was immersed in deionized water to carry out an experiment of release concentration (mg/L, mg/liter) and release time (days). As shown in Fig. 2, the sustained-release substance 21 can maintain a sustained release effect of a release concentration of 32 mg/L (mg/L) or more for about 66 days, wherein on the sixth day, the reaction remediation reaction substance ( The release concentration of potassium permanganate) suddenly rose sharply to above 100 mg/L. Then, between the 6th and 22nd days, the concentration of the reaction remediation reaction substance (potassium permanganate) can be as high as 800 to 900 mg/L, which is the peak period of release. Subsequently, after about the 34th day, the release concentration of the pollutant remediation reaction substance (potassium permanganate) fell again below 100 mg/L, and gradually decreased, but remained above 32 mg/L. After the 66th day, the release concentration drops below 32 mg/L, at which time it has fallen below an effective concentration value, but it can continue to oxidatively degrade a small amount of organic pollutants until the sustained release substance 21 is completely released for the pollution remediation. The reaction material (potassium permanganate).

Referring to Figures 1 and 2, the sustained-release substance 21 of the preferred embodiment of the present invention has the following advantages: (1) can effectively reduce the amount of the reaction substance for the pollution remediation before the reaction with the organic pollutant; 2) After being placed at the contaminated site, it can be used as the remediation wall 20 for on-site pollution remediation. It is not necessary to remove the soil and/or groundwater to its site for remediation, thus eliminating the need for extraction, mechanical equipment and electricity. Cost; (3) the sustained-release substance 21 can be continuously used for up to 66 days; (4) the sustained-release substance 21 completely releases the coating material (polycaprolactone) remaining after the pollution-remediation reaction substance is bio-available Decomposition and recyclable materials, so there is no doubt about waste and secondary pollutants.

As mentioned above, most of the slow-release substances used in the conventional permeable wall system are made of cement or gypsum, but the coating material remains in the existing soil after the reaction material is released. It is decomposed by itself or decomposed by bacteria, and additionally forms a solid waste that remains under the surface of the earth, and thus causes secondary pollution such as local pollution. The sustained release substances of the present invention according to Figs. 1 and 2 are used by using polycaprolactone. (PCL) as a coating material for coating at least one kind of pollution remediation reaction material, which not only can release the pollution remediation reaction substance for a long time to degrade organic pollutants in soil and/or groundwater, and The coated material itself can also be biodegraded or recyclable, which not only helps to improve the release effect of pollution remediation, but also reduces the generation of remediation waste, increases the convenience of pollution remediation and reduces the cost of pollution remediation. Furthermore, the sustained-release substance of the present invention also uses starch as a pore-promoting material, so that the reaction substance for pollution remediation coated in the coating material can be slowly released outward through the micro-pores formed by the starch, thereby accelerating the profit. The sustained release, reaction and transmission effect of potassium permanganate is enhanced, and at the same time, the micropores of the starch accompanying the passage of the water body can be formed to avoid causing pore blockage of the aquifer soil of the groundwater layer 112.

The present invention has been disclosed in its preferred embodiments, and is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

10. . . Renovation wall system

11. . . Local site

111. . . Surface layer

112. . . Groundwater layer

12. . . ditch

20. . . Renovation wall

twenty one. . . Sustained release material

twenty two. . . filler

31. . . groundwater

32. . . groundwater

Fig. 1 is a schematic view showing the use of a decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater according to a preferred embodiment of the present invention.

Figure 2: Decomposable sustained-release substance for strengthening chemical remediation of contaminated soil and groundwater in a preferred embodiment of the present invention is immersed in deionized water for release concentration (mg/L, mg/L) and release time Statistical graph of the experiment (days, days).

10. . . Renovation wall system

11. . . Local site

111. . . Surface layer

112. . . Groundwater layer

12. . . ditch

20. . . Renovation wall

twenty one. . . Sustained release material

twenty two. . . filler

31. . . groundwater

32. . . groundwater

Claims (6)

A decomposable sustained-release substance for strengthening chemical oxidation treatment of contaminated soil and groundwater, comprising polycaprolactone, starch and at least one reaction substance for pollution remediation, wherein the polycaprolactone, starch and pollution remediation reaction The weight ratio of the substance composition is from 0.5 to 1.25:0.6 to 1.0:0.2 to 0.3. The decomposable sustained-release substance for enhancing the chemical oxidation treatment of contaminated soil and groundwater according to the first aspect of the patent application, wherein the weight ratio of the polycaprolactone, the starch and the reaction substance for pollution remediation is sequentially 1.25:1.0:0.25. The decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater, as described in claim 1, wherein the reaction remediation reaction substance is a chemical oxidant. A decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater, as described in claim 3, wherein the chemical oxidant is selected from the group consisting of permanganates, persulfates, peroxides or Zero price iron. The decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater, as described in claim 1, wherein the sustained-release substance is applied to a permeable wall system. A decomposable sustained-release substance for enhancing chemical oxidation treatment of contaminated soil and groundwater, as described in claim 1, wherein the permeable wall system is buried in a chlorinated organic pollutant or a petroleum hydrocarbon One is in the soil.