Adsorbent

Abstract

Provided is an adsorbent with high finished product value, using dehydrated sludge obtained by dehydrating sludge generated in a water purification plant, sludge deposited in rivers, lakes, and the like as a raw material. 【Solution means】An adsorbent developed for effective reuse of sludge. It is obtained by pulverizing a dried product obtained by drying cake-like dehydrated sludge, which is made from sludge as a raw material, at a relatively low temperature of 150 to 400 °C for a short time to the required size. It is also an adsorbent obtained by adding other raw materials to the above adsorbent. Furthermore, it is an adsorbent characterized by granulating the above adsorbent.

Description

Technical Field

[0001] The present invention relates to an adsorbent made from dehydrated sludge obtained by dehydrating sludge and the like generated in a water purification plant.

Background Art

[0002] Generally, in the industrial field of adsorbents, natural organic substances are steamed and widely used as deodorants for activated carbon. Or refined from natural resources such as petroleum, and widely used as a filter in the manufacturing process of Japanese sake and the like as petroleum activated carbon. Or substances obtained by collecting and incinerating natural resources such as soil and diatomaceous earth are mixed with plaster, gypsum, etc. and used as wall materials.

[0003] Although natural organic substances, petroleum, and soil used as raw materials for these adsorbents are abundant, they are finite, regionally biased, and their quality varies, and the processing costs are also huge. In particular, the natural resource diatomaceous earth is gradually depleting, and for this reason, the price of the product as an adsorbent is gradually showing an upward trend.

[0004] On the other hand, the sludge that has settled in the sedimentation tank at the water purification plant, after being dehydrated, most of it has been landfilled or disposed of as industrial waste. Also, the sludge (mud) deposited in rivers, lakes, etc. is collected by mechanical means such as suction by a pump or excavation by a shovel, and after mixing cement or a coagulant to solidify it, it has been landfilled. Also, as another method of disposing of sludge, there was a method of mixing dehydrated sludge with fertilizer and using it for farmland.

[0005] In recent years, the amount of sludge generated at water purification plants has been increasing, and more than 70% of it has been landfilled as industrial waste, but it has become increasingly difficult to secure landfill sites every year. Also, when using dehydrated sludge mixed with fertilizer for farmland, if it contains harmful substances such as soluble aluminum and arsenic during pollution, there is a risk of becoming a pollution source, so there are restrictions on its use for farmland, and in fact, only a very small amount has been used.

[0006] For example, Japanese Patent Application Laid-Open Nos. 6-090617 and 7-059459 describe a method for producing sintered soil using dehydrated sludge as a raw material. However, firing at a high temperature of 800°C to 1100°C is an essential requirement, which is technically quite different from the present invention that does not require a firing process.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the above circumstances, this invention aims to provide an adsorbent with high finished product value using dehydrated sludge obtained by dehydrating sludge generated at a water purification plant, sludge deposited in rivers, lakes, etc. as a raw material, and to achieve effective reuse of sludge.

Means for Solving the Problems

[0009] This invention is devised to achieve the above object, and is an adsorbent obtained by pulverizing a dried product obtained by drying cake-like dehydrated sludge after dehydration using sludge as a raw material at a relatively low temperature of 150 to 400°C and for a short time to a required size.

[0010] Also, it is an adsorbent obtained by adding other raw materials to the above adsorbent. Furthermore, it is an adsorbent characterized in that the above adsorbent is granulated.

[0011] Since this adsorbent is completed through the steps of drying and then pulverizing the raw material, the above steps are necessarily included in the constitution as an object.

Effects of the Invention

[0012] Water purification plants exist in various locations, enabling the securement of quantitatively stable raw materials. By manufacturing them locally, the transportation costs of the adsorbent can be kept low, and since materials that were previously discarded as industrial waste are reused, significant environmental protection effects can be obtained from an environmental conservation perspective.

[0013] Since the drying temperature of this adsorbent is relatively low at 150 - 400 °C, energy can be conserved and fuel costs can be suppressed, contributing to the reduction of production costs and environmental protection.

[0014] This adsorbent is relatively stable physically and is a crystal of bound microelements such as aluminum and silicon, for example, and thus acts effectively on the adsorption of inorganic compounds. Furthermore, since this adsorbent has been dried, it is harmless and odorless, and being porous with high water permeability, water retention, and air permeability, it is optimal for the adsorption of inorganic compounds, phosphorus, arsenic, oil, etc.

[0015] This adsorbent can be used to produce an optimal adsorbent for the target adsorbate by formulating a mixture with other raw materials as required.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0017] The details of the present invention will be described below.

Examples

[0018] The manufacturing method according to the present invention uses purified water sludge generated in the process of purifying water from rivers, lakes, etc. as raw materials, and the basic flow of the manufacturing process is a dehydration process, a drying process, and a pulverization process. Furthermore, it includes a mixing / blending process and a granulation process, which will be described after Example 2. FIG. 1 is a manufacturing process flow chart of the present invention.

[0019] The components of the purified water sludge are those that are combined and precipitated with silicon, etc. by aluminum ions introduced as a flocculant into natural sand particles, mainly composed of inorganic components, and constitute relatively homogeneous clay. Depending on the source water used by the water purification plant, the purified water sludge may contain about 10-20% of organic matter.

[0020] As the dehydration method in the dehydration process, there are mechanical dehydrations such as gravity dehydration, pressure dehydration, and vacuum dehydration, and methods such as solar drying, resulting in dehydrated sludge cakes. At this stage, about 60-65% of moisture is contained.

[0021] By drying the dehydrated sludge cake within the temperature range of 150-400°C for approximately 30 minutes, a homogeneous and porous inorganic adsorbent can be obtained. For drying, heat sources such as heat conversion by electricity, heat obtained by burning gas or oil are utilized.

[0022] The sludge that has undergone the drying process is pulverized in the pulverization process. The pulverization preferably has an average particle size of about 1-7 mm, but can be appropriately changed depending on the intended use. The completed adsorbent obtained in this way is porous, has water permeability, water retention, and air permeability, and further has surface hydroxyl groups, so it has excellent adsorption properties for inorganic compounds.

[0023] For the aluminum ions when aggregating and precipitating turbidity in the water purification plant, flocculants of aluminum salts such as polyaluminum chloride and aluminum sulfate are used. Such sludge can be easily obtained at the water purification plant. As long as the sludge contains aluminum salts, the aluminum contained in these sludges contributes to the adsorption of inorganic compounds such as phosphorus and arsenic, so it can be used as an adsorbent.

Examples

[0024] The completed adsorbent can also be used by adding it to other raw materials as needed.

[0025] For example, it is also possible to mix this adsorbent with plaster, add water and knead it, and use it as a wall material for buildings such as houses. Instead of plaster, gypsum, cement, etc. may be used.

Examples

[0026] It is also possible to add a binder to the adsorbent for granulation, add other raw materials for granulation, and use it as a granulated product.

[0027] For example, it is also possible to mix this adsorbent with fertilizer, add a binder and knead it, and then granulate it into granules for use as a plant-growing material or a fertilizer for vegetables, etc.

Examples

[0028] This adsorbent can be mixed with a fragrance, add a liquid such as water to make a liquid-type fragrance, or add a binder and granulate it into granules for use as, for example, a jelly-like fragrance.

Examples

[0029] The process of setting the optimal drying temperature conditions and the test results of the adsorption effect of the adsorbent are described below.

[0030] To set the optimal drying temperature conditions, thermoanalytical measurements were carried out. The sample was placed in an analyzer, and the temperature was maintained at that temperature for 30 minutes in 100 °C steps up to 1000 °C. The sludge sample shows a decrease in weight as the temperature rises. Since the weight change is an endothermic change, it is considered to be the evaporation of water. The evaporation of water continues up to 150 °C, and a gradual decrease in weight continues from 200 °C to 500 °C. However, since the sample shows exotherm, it is considered that the combustion of organic substances is occurring. It was found that the weight loss was 1% and the organic matter content was very low. No change was observed above 500 °C. Figure 2 is a graph of the weight change of the sample by temperature in the drying test.

[0031] As a result, since the desorption of adsorbed water is completed at 150°C, drying is incomplete at 100°C, and drying is not sufficient at temperatures below 150°C, it is desirable to dry at a drying temperature of 150°C to 400°C for approximately 30 minutes. Considering the energy cost of the heat source for drying, 200°C is appropriate. Note that the drying time can be appropriately selected in relation to the drying temperature.

Example

[0032] Next, the adsorption capacity was tested using this adsorbent. The drying temperatures were set at five levels: 100°C, 200°C, 250°C, 300°C, and 400°C, and the drying time for each was unified to 30 minutes. 0.2 g of the adsorbent dried at each temperature was used as a sample, and comparisons were made including the undried sample.

[0033] For the adsorption test, formaldehyde gas was used, and the procedure was as follows. 1: Adjust formaldehyde gas (80 ppm) at room temperature in a 20 L Tedlar bag. 2: Seal 0.2 g of the sample dried at each temperature in a 2 L Tedlar bag, add the gas from 1), and allow adsorption for 24 hours. 3: Measure the formaldehyde gas concentration in the 2 L Tedlar bag after 24 hours.

[0034] The experimental results of the formaldehyde gas concentration after 24 hours were as follows: 30 ppm at a drying temperature of 100°C, 18 ppm at 200°C, 16 ppm at 250°C, 14 ppm at 300°C, 12 ppm at 400°C, and 75 ppm for the undried case. Note that for measuring the concentration of the residual gas of formaldehyde in this test, a detector tube was used, and the detection limit was 0.05 ppm.

Table 1

[0035] As a result, this adsorbent can adsorb formaldehyde, and the drying temperature in terms of adsorption efficiency is preferably 150°C or higher.

[0036] Furthermore, the adsorption capacity of this adsorbent when mixed with putty as another raw material was tested. The dewatered sludge was dried at 250°C for 30 minutes and then pulverized to obtain an adsorbent. 50% of the adsorbent and 50% of putty were mixed, kneaded with water and dried, and then the adsorption rate of formaldehyde gas was measured.

[0037] 2 g of the sample was sealed in a 20 L Tedlar bag, filled with 20 L of formaldehyde gas (500 μg / m3), left at room temperature for 24 hours, and then DNPH derivatized solid-phase adsorption / solvent extraction-HPLC analysis was performed from the Tedlar bag. Similarly, only formaldehyde gas (500 μg / m3) was used for comparison.

[0038] The formaldehyde gas concentration after 24 hours was 34 μg / m3 in the 20 L Tedlar bag with the sample sealed, and 488 μg / m3 in the 20 L Tedlar bag without the sample sealed. It was clearly demonstrated that the one using this adsorbent had a high adsorption capacity.

[0039] Similarly, for ammonia, it decreased from an initial value of 100 ppm to 0 ppm after 60 minutes, for hydrogen sulfide, it decreased from an initial value of 3.5 ppm to 2.0 ppm after 60 minutes, and for sulfur dioxide, it decreased from an initial value of 5.0 ppm to 2.7 ppm after 60 minutes. See Figures 2 - 3.

Industrial Applicability

[0040] The adsorbent of the present invention can be industrially produced, and the completed adsorbent can be used in various industrial fields.

Claims

1. An adsorbent characterized in that dewatered sludge is dried at a temperature of 150 to 400°C and then pulverized.

2. An adsorbent comprising the adsorbent according to claim 1 and other raw materials added thereto.

3. An adsorbent, characterized in that the adsorbent according to claim 1 is granulated by adding other raw materials to the adsorbent.

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