Method for treating sludge water, method for reusing sludge water, and method for producing cement molded body

Abstract

To provide a method for treating sludge water capable of storing sludge water for a relatively long period while reducing solidification of sludge solids, a method for reusing sludge water, and a method for producing a cement molded body.SOLUTION: A method for treating sludge water includes an injecting step of injecting a gas containing carbon dioxide into the sludge water, wherein, in the injecting step, a molar concentration ratio of the carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for treating sludge water, a method for reusing sludge water, and a method for manufacturing a cement molded body.

Background Art

[0002] The water obtained by removing aggregates from the washing wastewater used for washing transport vehicles, mixers, etc. in a ready-mixed concrete factory is called recovered water. The recovered water is divided into supernatant water containing hydrated products such as calcium hydroxide and calcium silicate hydrate eluted from cement, and sludge water containing sludge solids mostly composed of the hydrated products.

[0003] In order to reuse the sludge water as mixing water for concrete, it is stored in a sludge water tank in the factory and then distributed from the sludge water tank to manufacturing facilities in the factory through pipes.

[0004] However, when the sludge water is stored for a long time, a hydration reaction occurs between the sludge solids and water contained in the sludge water, causing the sludge solids to solidify in the sludge water tank or pipes. Therefore, various methods have been proposed to reduce the solidification of the sludge solids.

[0005] For example, Patent Document 1 discloses a method for using fresh sludge water containing a setting retarder containing a setting retardation component as a stabilizer and used as mixing water.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, the method of adding a stabilizer to the sludge water, as described in Patent Document 1, is not sufficient in terms of long-term storage of the sludge water, and there is room for improvement.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide a method for treating sludge water, a method for reusing sludge water, and a method for manufacturing a cement molded body that can reduce the consolidation of sludge solids and can be stored for a relatively long period of time.

Means for Solving the Problems

[0009] The method for treating sludge water according to the present invention is a method for treating sludge water, including a blowing step of blowing a gas containing carbon dioxide into the sludge water, and in the blowing step, the ratio of the molar concentration of the carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more.

[0010] The method for treating sludge water according to the present invention can, with such a configuration, reduce the consolidation of sludge solids and can be stored for a relatively long period of time.

[0011] In the method for treating sludge water according to the present invention, in the blowing step, the ratio of the molar concentration of the carbon dioxide to calcium oxide contained in the sludge water may be 1.0 or more and 20.0 or less.

[0012] The method for treating sludge water according to the present invention can, with such a configuration, further reduce the consolidation of sludge solids and can be stored for a relatively long period of time.

[0013] In the method for treating sludge water according to the present invention, the content of the sludge solids contained in the sludge water may be 20% by mass or less with respect to the entire sludge water.

[0014] The method for treating sludge water according to the present invention can, with such a configuration, further reduce the consolidation of sludge solids and can be stored for a relatively long period of time.

[0015] The sludge water treatment method according to the present invention may be such that the sludge water is recovered from the washing wastewater of ready-mixed concrete having a water-cement ratio of 35% by mass or more and 65% by mass or less.

[0016] With such a configuration, the sludge water treatment method according to the present invention can further reduce the consolidation of sludge solids while being able to store for a relatively long period of time.

[0017] In a wastewater treatment facility that performs a recovery process of removing aggregates from the washing wastewater of ready-mixed concrete to recover sludge water, a stirring process of stirring the sludge water, and a dehydration process of dehydrating and separating sludge solids from the sludge water, the blowing step may be performed in at least one process selected from the group consisting of the recovery process, the stirring process, and the dehydration process.

[0018] With such a configuration, the sludge water treatment method according to the present invention can suppress the consolidation of sludge solids in the sludge water tank or piping in the wastewater treatment facility.

[0019] The sludge water reuse method according to the present invention is a method of reusing sludge water, and the sludge water treated by the above-described sludge water treatment method is reused as a material for a cement molded body.

[0020] The sludge water reuse method according to the present invention can obtain a cement molded body with relatively suppressed reduction in compressive strength by reusing sludge water that can reduce the consolidation of sludge solids even when stored for a relatively long period of time as a material for a cement molded body.

[0021] The method for manufacturing a cement molded body according to the present invention is a method for manufacturing a cement molded body containing cement, aggregates, and water, wherein the water contains the sludge water treated by the above-described sludge water treatment method.

[0022] The manufacturing method of the cement molded body according to the present invention can produce a cement molded body in which the reduction of the compressive strength is relatively suppressed because the water contains sludge water that can reduce the consolidation of the sludge solid content even when stored for a relatively long period of time.

Effect of the Invention

[0023] According to the present invention, it is possible to provide a method for treating sludge water that can be stored for a relatively long period while reducing the consolidation of sludge solid content, a method for reusing sludge water, and a method for manufacturing a cement molded body.

Modes for Carrying Out the Invention

[0024] Hereinafter, the method for treating sludge water, the method for reusing sludge water, and the method for manufacturing a cement molded body according to the present embodiment will be described.

[0025] <Method for Treating Sludge Water> The method for treating sludge water according to the present embodiment is a method for treating sludge water, and includes a blowing step of blowing a gas containing carbon dioxide into the sludge water.

[0026] In this specification, sludge water is water containing sludge solid content among the water obtained by removing aggregates from the washing wastewater used for washing transport vehicles, mixers, etc. in a ready-mixed concrete factory. Most of the sludge solid content is composed of hydration products, and further includes aggregate fine particles and the like. The hydration products contain calcium-based compounds. Examples of the calcium-based compounds include calcium oxide, calcium hydroxide, calcium silicate hydrate, calcium aluminate hydrate, and the like.

[0027] As the cement which is a raw material of ready-mixed concrete, there is no particular limitation. For example, Portland cement such as ordinary Portland cement, early-strength Portland cement, super-early-strength Portland cement, low-heat Portland cement, moderate-heat Portland cement, sulfate-resistant Portland cement, white Portland cement, etc. defined in JIS R 5210:2019; Mixed cements such as blast furnace cement, fly ash cement, silica cement, etc.; Known cements such as super rapid hardening cement, alumina cement, etc. can be used. Note that the cement may be used alone or in combination of two or more kinds.

[0028] From the viewpoint of reducing the consolidation of the sludge solids and storing for a relatively long period, the content of the sludge solids contained in the sludge water is preferably 20% by mass or less, more preferably 15% by mass or less, with respect to the whole sludge water. Further, the content of the sludge solids is preferably 1.0% by mass or more, more preferably 5.7% by mass or more.

[0029] From the viewpoint of reducing the consolidation of the sludge solids and storing for a relatively long period, the sludge water is preferably recovered from the washing drainage of ready-mixed concrete having a water-cement ratio of 35% by mass or more and 65% by mass or less, more preferably recovered from the washing drainage of ready-mixed concrete having a water-cement ratio of 40% by mass or more and 60% by mass or less. Here, the water-cement ratio is the mass ratio of water and cement in ready-mixed concrete.

[0030] Examples of the gas containing carbon dioxide used in the blowing step include industrial carbon dioxide, air, carbon dioxide generated during the firing of cement clinker, exhaust gas containing nitrogen oxides, etc.

[0031] The concentration of carbon dioxide contained in the gas containing carbon dioxide is not particularly limited, but can be, for example, 10% by volume or more and 100% by volume or less.

[0032] In the blowing process, the flow rate of the gas containing carbon dioxide is not particularly limited, but for example, it can be 1 NL / min or more and 100 NL / min or less. Here, NL / min is the unit of the gas flow rate at 1 atmosphere, a temperature of 0 °C, and a humidity of 0 RH%.

[0033] In the blowing process, the time for blowing the gas containing carbon dioxide is not particularly limited, but for example, when the concentration of carbon dioxide is 100% by volume, it can be 6 minutes or more and 120 minutes or less.

[0034] In the blowing process, the molar concentration ratio of carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more, preferably 1.0 or more and 20.0 or less, and more preferably 5.0 or more and 10.0 or less, from the viewpoint of reducing the consolidation of the sludge solids while storing for a relatively long period.

[0035] The molar concentration of carbon dioxide with respect to 1 L of sludge water is not particularly limited, but for example, it can be 1.3 mol / L or more and 26.8 mol / L or less.

[0036] The molar concentration of the carbon dioxide can be obtained by using the following formula (1) from the concentration of the carbon dioxide, the flow rate of the gas containing the carbon dioxide, the time for blowing the gas, and the volume of the gas per mole under standard conditions (0 °C, 1 atmosphere). Molar concentration of carbon dioxide (mol / L) = [{(Concentration of carbon dioxide (volume %) / 100) × Gas flow rate (NL / min) × Blowing time of the gas (min)} / 22.4] / Amount of sludge water (L) ···(1)

[0037] The molar concentration of calcium oxide with respect to 1 L of sludge water is not particularly limited, but for example, it can be 0.5 mol / L or more and 1.4 mol / L or less.

[0038] The molar concentration of the calcium oxide can be determined by using the following formula (2) from the content of calcium oxide (mass %), the molecular weight of calcium oxide, and the mass of the sludge solid content. Molar concentration of calcium oxide (mol / L) = [{Amount of sludge water (g) × (Content of sludge solid content (mass %) / 100) × 0.8 × (Content of calcium oxide (mass %) / 100)} / 56] / Amount of sludge water (L) ··· (2)

[0039] The content of the calcium oxide is not particularly limited with respect to the total amount of the sludge solid content, but can be, for example, 40 mass % or more and 70 mass % or less.

[0040] As the content of the calcium oxide, a value obtained by measuring using a fluorescent X-ray analyzer (for example, ZSX Primus IV manufactured by Rigaku Corporation) based on the method specified in JIS R 5204:2019 can be used.

[0041] Examples of the method of blowing a gas containing carbon dioxide include simply bubbling, bubbling while stirring, bubbling while irradiating ultrasonic waves, and the like. Among these, the method of blowing a gas containing carbon dioxide is preferably a method of bubbling while stirring.

[0042] The method for treating sludge water according to the present embodiment may be performed in a wastewater treatment facility that performs a recovery process of removing aggregates from the washing wastewater of ready-mixed concrete to recover sludge water, a stirring process of stirring the sludge water, and a dehydration process of dehydrating and separating sludge solid content from the sludge water.

[0043] In the recovery process, for example, the washing wastewater discharged from a transport vehicle, mixer, etc. in a ready-mixed concrete plant is transported to a sieve machine by a transport device such as a car wash chute. Next, in the sieve machine, aggregates are removed from the washing wastewater, and sludge water is recovered, and the sludge water is distributed to a sludge water tank. Examples of the sieve machine include a vibro screen, a sand cyclone, a fine sand cyclone, a crusher, etc.

[0044] In the stirring process, for example, the sludge water stored in the above-mentioned sludge water tank is stirred.

[0045] In the dehydration process, for example, sludge water is distributed from the above-mentioned sludge water tank to a dehydration device. Next, in the dehydration device, the sludge water is separated into sludge solids and supernatant water. Examples of the dehydration device include an immediate dehydration unit, a filter press, etc.

[0046] The blowing step in the method for treating sludge water according to the present embodiment is preferably performed in at least one treatment selected from the group consisting of the recovery treatment, the stirring treatment, and the dehydration treatment.

[0047] In the recovery treatment, the blowing step is preferably performed in a pipe for distributing sludge water to a sludge water tank.

[0048] In the stirring treatment, the blowing step is preferably performed in the sludge water tank.

[0049] In the dehydration treatment, the blowing step is preferably performed in a pipe for distributing sludge water to a dehydration device.

[0050] The sludge water treated by the method for treating sludge water according to the present embodiment can be reused as mixing water for concrete or mortar which is a cement molded body.

[0051] The sludge water treatment method according to this embodiment is a method for treating sludge water, which includes a blowing step of blowing a gas containing carbon dioxide into the sludge water. In the blowing step, by having the ratio of the molar concentration of the carbon dioxide to calcium oxide contained in the sludge water be 1.0 or more, while reducing the consolidation of sludge solids, it can be stored for a relatively long period.

[0052] The sludge water treatment method according to this embodiment is such that, in the blowing step, by having the ratio of the molar concentration of the carbon dioxide to calcium oxide contained in the sludge water be 1.0 or more and 20.0 or less, it can further reduce the consolidation of sludge solids while being able to be stored for a relatively long period.

[0053] The sludge water treatment method according to this embodiment is such that, by having the content of sludge solids contained in the sludge water be 20 mass% or less with respect to the entire sludge water, it can further reduce the consolidation of sludge solids while being able to be stored for a relatively long period.

[0054] The sludge water treatment method according to the present invention is such that, by having the sludge water be recovered from the washing wastewater of ready-mixed concrete having a water-cement ratio of 35 mass% or more and 65 mass% or less, it can further reduce the consolidation of sludge solids while being able to be stored for a relatively long period.

[0055] The sludge water treatment method according to the present invention is such that, in a wastewater treatment facility that performs a recovery process of removing aggregates from the washing wastewater of ready-mixed concrete to recover sludge water, a stirring process of stirring the sludge water, and a dehydration process of dehydrating and separating sludge solids from the sludge water, the blowing step is performed in at least one process selected from the group consisting of the recovery process, the stirring process, and the dehydration process. Thus, in the wastewater treatment facility, it is possible to suppress the consolidation of sludge solids in the sludge water tank and piping.

[0056] <Method for Reusing Sludge Water> The sludge water reuse method according to this embodiment is a method for reusing sludge water, which reuses the sludge water treated by the above-described sludge water treatment method as a material for a cement molded body.

[0057] The sludge water treated by the above-described sludge water treatment method is preferably used as a material for concrete or mortar, which is a cement molded body, and more preferably as mixing water.

[0058] The sludge water reuse method according to this embodiment is a method for reusing sludge water, which reuses sludge water capable of reducing the consolidation of sludge solids even when stored for a relatively long period as a material for a cement molded body, thereby obtaining a cement molded body with relatively suppressed reduction in compressive strength.

[0059] <Manufacturing method of cement molded body> The manufacturing method of the cement molded body according to this embodiment is a manufacturing method of a cement molded body containing cement, aggregate, and water, wherein the water contains the sludge water treated by the above-described sludge water treatment method.

[0060] The water includes the sludge water treated by the above-described sludge water treatment method. The water may be, for example, water obtained by mixing the sludge water with tap water, industrial water, recycled water, groundwater, river water, rainwater, etc.

[0061] The blending amount of the water can be, for example, 150 kg / m 3 : per unit amount (kg / m 3 per 1 m 3 of the cement composition) and 210 kg / m 3 or less. When two or more types of water are included, the blending amount is the total blending amount of the water.

[0062] The cement is not particularly limited and may be the above-described cement.

[0063] The blending amount of the cement can be, for example, per unit amount (kg / m3 : per cubic meter of the cement composition 3 in terms of mass), 230 kg / m 3 or more and 750 kg / m 3 or less. When two or more types of cement are included, the blending amount is the total blending amount of the cement.

[0064] As the aggregate, fine aggregate and / or coarse aggregate can be used. Note that the fine aggregate refers to an aggregate that completely passes through a 10 mm sieve and 85% or more by mass through a 5 mm sieve, and the coarse aggregate refers to an aggregate that remains 85% or more by mass on a 5 mm sieve (JIS A 0203:2019).

[0065] Examples of the fine aggregate include natural sand such as river sand, land sand, mountain sand, sea sand, crushed sand, limestone crushed sand, etc. specified in JIS A 5308:2019 Appendix A Ready-mixed concrete aggregate, blast furnace slag, etc. Also, silica sand produced by crushing and classifying silica stone may be used. Note that the fine aggregate may be used alone or in combination of two or more types.

[0066] The blending amount of the fine aggregate is, for example, per unit amount (kg / m 3 : per cubic meter of the cement composition 3 in terms of mass), 500 kg / m 3 or more and 1200 kg / m 3 or less. When two or more types of fine aggregate are included, the blending amount is the total blending amount of the fine aggregate.

[0067] Examples of the coarse aggregate include natural aggregates such as river gravel, mountain gravel, sea gravel, etc. specified in JIS A 5308:2019 Appendix A Ready-mixed concrete aggregate, artificial aggregates such as crushed stone of sandstone, hard limestone, basalt, andesite, etc., recycled aggregates, etc. Note that the coarse aggregate may be used alone or in combination of two or more types.

[0068] The blending amount of the coarse aggregate is, for example, per unit amount (kg / m 3 : per cubic meter of the cement composition 3(per unit mass) and can be 700 kg / m 3 or more and 1300 kg / m 3 or less. When two or more types of coarse aggregates are included, the blending amount is the total blending amount of the coarse aggregates.

[0069] The method for manufacturing a cement molded body according to the present embodiment can obtain a cement molded body by mixing cement, aggregate, and water.

[0070] The method for manufacturing a cement molded body according to the present embodiment is a method for manufacturing a cement molded body containing cement, aggregate, and water, wherein the water contains sludge water capable of reducing the consolidation of sludge solids even when stored for a relatively long period, thereby manufacturing a cement molded body in which the reduction of compressive strength is relatively suppressed.

[0071] The present invention includes the following aspects. [1] A method for treating sludge water, including an injection step of injecting a gas containing carbon dioxide into the sludge water, wherein in the injection step, the ratio of the molar concentration of carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more, the method for treating sludge water. [2] The method for treating sludge water according to [1], wherein in the injection step, the ratio of the molar concentration of carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more and 20.0 or less. [3] The method for treating sludge water according to [1] or [2], wherein the content of sludge solids contained in the sludge water is 20% by mass or less based on the total sludge water. [4] The method for treating sludge water according to any one of [1] to [3], wherein the sludge water is recovered from the washing wastewater of ready-mixed concrete having a water-cement ratio of 35% by mass or more and 65% by mass or less. [5] A recovery process of removing aggregate from the washing wastewater of ready-mixed concrete and recovering sludge water, and a stirring process of stirring the sludge water, A dehydration treatment for dehydrating and separating sludge solids from the sludge water, In a wastewater treatment facility that performs The sludge water treatment method according to any one of [1] to [4], wherein the blowing step is performed in at least one treatment selected from the group consisting of the recovery treatment, the stirring treatment, and the dehydration treatment. [6] A method for reusing sludge water, A method for reusing sludge water, wherein the sludge water treated by the sludge water treatment method according to any one of [1] to [5] is reused as a material for a cement molded body. [7] A method for manufacturing a cement molded body containing cement, aggregate, and water, The method for manufacturing a cement molded body, wherein the water contains the sludge water treated by the sludge water treatment method according to any one of [1] to [5].

Examples

[0072] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0073] [Preparation of Sludge Water] According to the following examples and comparative examples, the following sludge water was prepared. As the cement, ordinary Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd.) was used.

[0074] (Comparative Example 1: Preparation of Sludge Water 1) Simulating the agitator truck washing wastewater collected from a ready-mixed concrete plant, 240 g of ordinary Portland cement and 60 g of sand with a particle size of 150 μm or less as fine aggregate particles were added to 1700 g of tap water so that the content of sludge solids was 15% by mass, and sludge water 1 was prepared.

[0075] (Comparative Example 2: Preparation of Sludge Water 2) Sludge water 1 was stirred for about 120 minutes to prepare sludge water 2.

[0076] (Comparative Example 3: Preparation of Sludge Water 3) While stirring Sludge Water 1, carbon dioxide gas was blown in at 10 NL / min for 1.2 minutes to prepare Sludge Water 3.

[0077] (Comparative Example 4: Preparation of Sludge Water 4) Aggregates were removed from the agitator truck washing wastewater collected from a ready-mixed concrete plant, and tap water was added so that the concentration of sludge solids became 5.7 mass%, thereby preparing Sludge Water 4.

[0078] (Reference Example 1: Preparation of Sludge Water 5) Aggregates were removed from the washing wastewater collected from a transporter at a ready-mixed concrete plant, and tap water was added so that the concentration of sludge solids became 5.7 mass%, thereby preparing the mixture. After storing the obtained preparation for one day, sodium gluconate was added as a retarder at 0.05 mass% based on the total amount of the preparation to prepare Sludge Water 5.

[0079] (Example 1: Preparation of Sludge Water 6) While stirring Sludge Water 1, carbon dioxide gas (carbon dioxide concentration: 100% by volume) was blown in at 10 NL / min for 120 minutes to prepare Sludge Water 6.

[0080] (Example 2: Preparation of Sludge Water 7) While stirring Sludge Water 1, the same carbon dioxide gas as in Example 1 was blown in at 10 NL / min for 60 minutes to prepare Sludge Water 7.

[0081] (Example 3: Preparation of Sludge Water 8) While stirring Sludge Water 1, the same carbon dioxide gas as in Example 1 was blown in at 10 NL / min for 40 minutes to prepare Sludge Water 8.

[0082] (Example 4: Preparation of Sludge Water 9) While stirring Sludge Water 1, the same carbon dioxide gas as in Example 1 was blown in at 10 NL / min for 30 minutes to prepare Sludge Water 9.

[0083] (Example 5: Preparation of Sludge Water 10) While stirring Sludge Water 1, the same carbon dioxide gas as in Example 1 was blown in at 10 NL / min for 12 minutes to prepare Sludge Water 10.

[0084] (Example 6: Preparation of Sludge Water 11) While stirring Sludge Water 1, the same carbon dioxide gas as in Example 1 was blown in at 10 NL / min for 6 minutes to prepare Sludge Water 11.

[0085] (Example 7: Preparation of Sludge Water 12) While stirring Sludge Water 4, the same carbon dioxide gas as in Example 1 was blown in at 10 NL / min for 120 minutes to prepare Sludge Water 12.

[0086] Table 1 shows the concentration of sludge solids, the presence or absence of carbon dioxide (CO2) in the sludge water, the stirring time, the CO2 blowing time, the number of moles of calcium oxide (CaO) contained in the sludge water, the number of moles of the blown CO2, and the ratio of the molar concentration of CO2 to CaO in each of the sludge waters prepared above.

[0087]

Table 1

[0088] [Test 1: Evaluation of Consolidation of Sludge Water] The sludge waters corresponding to each example and comparative example were stored in a constant temperature room at 20 ± 2°C for 7 days or 33 days.

[0089] For each of the sludge waters stored for 7 days and those stored for 33 days, the penetration resistance value was determined based on JIS A 1147. Specifically, using a Proctor penetrometer (manufactured by Marui Co., Ltd.), the measurement was carried out so that the time required for penetration was about 10 seconds, and the penetration resistance value was determined.

[0090] Based on the following criteria from the penetration resistance value, the presence or absence of consolidation of each sludge water was evaluated. ◎: No consolidation; 0.4 N / mm 2Less than ○: Slightly consolidated; 0.4 N / mm 2 1.0 N / mm or more 2 Less than ×: Consolidated; 1.0 N / mm 2 1.0 N / mm or more

[0091] Table 2 shows the evaluation results of the penetration resistance values and the presence or absence of consolidation for each example, comparative example, and [example].

[0092] [Table 2]

[0093] [Test 2: Evaluation of the coagulation time of sludge water] In accordance with JIS R 5201, the coagulation time of sludge water was evaluated. As a pretreatment, first, the amount of water in the sludge water corresponding to each example and comparative example was adjusted so that the standard softness became 6 ± 1 mm. Next, each sludge water with the adjusted amount of water was stored in a constant temperature room at 20 ± 2 °C for 1 day or 7 days. The coagulation time was evaluated based on the following criteria with respect to the start time or end time of the sludge water prepared using reference water (tap water) based on Appendix C of JIS A 5308.

[0094] ◎: Start time within ±20 minutes, end time within ±30 minutes ○: Start time exceeding ±20 minutes and within ±30 minutes, end time exceeding ±30 minutes and within ±60 minutes ×: Start time exceeding ±30 minutes, end time exceeding ±60 minutes

[0095] Table 3 shows the evaluation results of the coagulation time. Also, Table 4 shows the formulations of the sludge water for each example, each comparative example, and the reference example used in the evaluation of the coagulation time.

[0096] [Table 3]

[0097] [Table 4]

[0098] [Test 3: Evaluation of Compressive Strength of Mortar] For Example 7, Comparative Example 4, and Reference Example 1 (hereinafter referred to as each example, etc.), specimens were prepared in accordance with JIS R 5201, and the compressive strength of the mortar was measured and evaluated.

[0099] (Preparation of Specimen) Mortar was prepared according to the formulation shown in Table 5.

[0100] [Table 5]

[0101] Specifically, first, using a kneading mixer (a mechanical kneader specified in JIS R 5201), cement (ordinary Portland cement; manufactured by Sumitomo Osaka Cement Co., Ltd.) and fine aggregate (mountain sand; produced in Kakegawa City, Shizuoka Prefecture) were dry-kneaded for 15 seconds, and then the sludge water corresponding to each example, etc. was added and kneaded for 180 seconds to obtain mortar.

[0102] The obtained mortar was poured into a cylindrical mold (φ50×100 mm) to cure the mortar. The cured mortar was demolded the next day and cured in water at 20°C until the age of 7 days to obtain specimens.

[0103] (Evaluation of Compressive Strength) The compressive strength was evaluated by conducting a compressive strength test based on JIS R 5201 and measuring the compressive strength at the age of 7 days. The compressive strength was evaluated as the ratio of the compressive strength of the specimens of each example, etc. to the compressive strength of the specimens prepared using standard water (tap water) based on Appendix C of JIS A 5308.

[0104] The evaluation results of the compressive strength are shown in Table 6.

[0105] [Table 6]

[0106] As can be seen from Tables 2 and 3, the method for treating the sludge water in each example can store the sludge water for a relatively long period while reducing the consolidation of the sludge solids, as compared with the method for treating the sludge water in each comparative example.

[0107] Also, as can be seen from Table 6, it was found that the test body using the sludge water of Example 7 could relatively suppress the reduction in compressive strength as compared with Comparative Example 4 and Reference Example 1. From this, the method for reusing the sludge water according to the present invention can reuse the sludge water, which can reduce the consolidation of the sludge solids even when stored for a relatively long period, as a material for the cement molded body, thereby obtaining a cement molded body in which the reduction in compressive strength is relatively suppressed. Further, the method for manufacturing the cement molded body according to the present invention can manufacture a cement molded body in which the reduction in compressive strength is relatively suppressed by including the sludge water, which can reduce the consolidation of the sludge solids even when stored for a relatively long period, as the water that is the material of the cement molded body.

Claims

1. A method for treating sludge water, comprising: a blowing step of blowing a gas containing carbon dioxide into the sludge water, wherein, in the blowing step, the molar concentration ratio of the carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more. A method for treating sludge water.

2. The method for treating sludge water according to Claim 1, wherein, in the blowing step, the molar concentration ratio of the carbon dioxide to calcium oxide contained in the sludge water is 1.0 or more and 20.0 or less.

3. The method for treating sludge water according to Claim 1, wherein the content of sludge solids contained in the sludge water is 20% by mass or less based on the total sludge water.

4. The method for treating sludge water according to Claim 1, wherein the sludge water is recovered from the washing wastewater of ready-mixed concrete having a water-cement ratio of 35% by mass or more and 65% by mass or less.

5. A recovery process of removing aggregates from the washing wastewater of ready-mixed concrete to recover sludge water, a stirring process of stirring the sludge water, a dehydration process of dehydrating and separating sludge solids from the sludge water, In a wastewater treatment facility that performs The method for treating sludge water according to Claim 1, wherein the blowing step is performed in at least one process selected from the group consisting of the recovery process, the stirring process, and the dehydration process.

6. A method for reusing sludge water, comprising: Reusing the sludge water treated by the method for treating sludge water according to any one of Claims 1 to 5 as a material for a cement molded body. A method for reusing sludge water.

7. A method for manufacturing a cement molded body containing cement, aggregates, and water, comprising: The method for manufacturing a cement molded body, wherein the water contains the sludge water treated by the method for treating sludge water according to any one of Claims 1 to 5.

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