A method for closed lagoon solidification treatment of sewage

Abstract

The present application relates to the technical field of building construction, in particular to a sewage pond sealing and solidification treatment method. The sewage pond sealing and solidification treatment method comprises: backfilling spoil in a sewage pond; injecting a rock-soil solidifying agent slurry into the spoil in a surface layer area of the sewage pond and stirring and solidifying to form a solidified soil layer; the rock-soil solidifying agent slurry comprises a solidifying agent powder and water, and the solidifying agent powder comprises the following components in mass fractions: cement: 10-40 parts, slag powder: 30-60 parts, fly ash: 10-30 parts, waste gypsum: 5-25 parts, water glass: 5-15 parts, stone powder slag: 5-20 parts, and slag: 5-15 parts. The present application aims to improve the problem of high sewage treatment cost for sewage ponds.

Description

Technical Field

[0001] This invention relates to the technical field of building construction, and more specifically, to a method for sealing and solidifying sewage ponds. Background Technology

[0002] In some areas, due to inadequate sewage treatment facilities, large amounts of wastewater are discharged into low-lying ponds, gradually forming large-scale sewage ponds over the years. The wastewater in these ponds contains various harmful substances, which not only directly harm groundwater and soil but also affect the entire ecological environment.

[0003] Currently, the treatment of sewage ponds mostly involves directly adding inorganic or organic cementitious materials, such as cement and lime, to the pond for solidification. These cementitious materials undergo physical and chemical reactions with water, generating a large amount of hydrated gels (such as hydrated calcium silicate, hydrated calcium ferrite, hydrated calcium aluminoferrite, ettringite, etc.) and minerals (such as calcium carbonate, calcium hydroxide, etc.), thereby solidifying the sewage within these stone-like structures. However, since the sewage in the pond relies entirely on these cementitious materials for solidification, the required material costs are high. Sufficient amounts of cement and lime need to be added to the water, relying on the sewage and cement / lime to form a viscous cement slurry for further solidification and hardening to form stone-like structures. Summary of the Invention

[0004] The present invention aims to improve the problem of high sewage treatment costs in current sewage ponds.

[0005] To address the above problems, the present invention provides a method for sealing and solidifying wastewater ponds, comprising:

[0006] Backfill the sewage pond with slag and soil;

[0007] A soil and rock solidification agent slurry is injected into the slag in the surface area of ​​the sewage pond and stirred and solidified to form a solidified soil layer.

[0008] The soil and rock solidification agent slurry includes solidification agent powder and water. The solidification agent powder includes the following components in parts by weight: cement: 10 to 40 parts, slag powder: 30 to 60 parts, fly ash: 10 to 30 parts, waste gypsum: 5 to 25 parts, water glass: 5 to 15 parts, stone powder slag: 5 to 20 parts, and furnace slag: 5 to 15 parts.

[0009] Optionally, the height of the solidified soil layer is 3m to 6m.

[0010] Optionally, before backfilling the wastewater pond with slag, the following steps are also included:

[0011] A closed curtain is constructed along the circumference of the sewage pond, the bottom of which is below the bottom of the sewage pond and extends to the clay layer.

[0012] Optionally, the height of the enclosed curtain extending into the clay layer shall not be less than 3m.

[0013] Optionally, the enclosed curtain is formed by mixing the soil and rock-solidifying agent slurry with soil and then stirring and solidifying it.

[0014] Optionally, the distance between the enclosed curtain and the edge of the sewage pond is 1m to 2m.

[0015] Optionally, the enclosed curtain includes multiple curing agent piles, which are connected by a single-hole drilling method or a partial overlapping method.

[0016] Optionally, the backfilling of the sewage pond with slag soil includes: the moisture content of the slag soil not exceeding 25%.

[0017] Optionally, in the soil and rock solidification agent slurry, the mass ratio of the solidification agent powder to water is 1:(1.5 to 3).

[0018] Optionally, in the solidified soil layer, the mass ratio of the slag soil to the soil and rock solidification agent powder is 1:(0.2 to 0.25).

[0019] The beneficial effects of the fluidized solidified soil layer of the present invention are:

[0020] This invention employs a construction method that involves first backfilling the sewage pond with excavated soil, and then injecting a soil-stabilizing agent slurry into the surface area of ​​the excavated soil. The excavated soil, water, and soil-stabilizing agent are thoroughly mixed into a fluid mixture. After solidification, this fluid mixture forms a solidified soil layer with certain strength, impermeability, water stability, and corrosion resistance. Compared to related technologies that use a single cementing material to solidify all areas of sewage, this invention only solidifies the sewage within a certain depth range at the top of the sewage pond. The solidification area is small, and it consumes a large amount of construction waste such as excavated soil. The proportion of soil-stabilizing agent does not exceed 30%, significantly reducing construction and material costs. The unsolidified excavated soil at the bottom of the sewage pond can both seal the sewage between the solidified soil layer and the clay layer and serve as a transitional soil layer, reducing the mutual influence between the solidified soil layer and the clay layer and preventing harmful substances in the solidified soil layer from contaminating the clay layer. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the sewage pond before backfilling in an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the structure during the backfilling of the sewage pond in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the structure for filling and solidifying a sewage pond in an embodiment of the present invention;

[0024] Figure 4 This is a top view of the enclosed curtain in an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached diagram: 1. Sewage pond; 2. Enclosed curtain; 3. Solidified soil layer; 4. Unsolidified soil layer; 5. Clay layer; 6. Grouting pump; 7. Slag. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0027] This invention provides a method for sealing and solidifying a sewage pond, comprising: backfilling the sewage pond with slag; injecting a soil-stabilizing agent slurry into the slag in the surface area of ​​the sewage pond, and stirring and solidifying it to form a solidified soil layer. The soil-stabilizing agent slurry comprises a solidifying agent powder and water. The solidifying agent powder comprises the following components in parts by weight: cement: 10 to 40 parts, slag powder: 30 to 60 parts, fly ash: 10 to 30 parts, waste gypsum: 5 to 25 parts, water glass: 5 to 15 parts, stone powder slag: 5 to 20 parts, and furnace slag: 5 to 15 parts.

[0028] Figure 1 This is a schematic diagram of the structure of the sewage pond 1 before backfilling in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the sewage pond 1 during backfilling in an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the sewage pond 1 after backfilling and solidification in an embodiment of the present invention. (Refer to...) Figures 1 to 3 Below the bottom of the sewage pond 1 is a clay layer 5, which is a soil layer composed of clay. It has poor water permeability and air permeability and excellent seepage prevention performance. The slag 7 in the sewage pond 1 includes the upper solidified soil layer 3 and the lower unsolidified soil layer 4.

[0029] This invention employs a construction method that involves first backfilling the sewage pond 1 with excavated soil 7, and then injecting a soil-stabilizing agent slurry into the surface area of ​​the excavated soil 7. The excavated soil 7, water, and soil-stabilizing agent are thoroughly mixed into a fluid mixture. After solidification, this fluid mixture forms a solidified soil layer 3 with certain strength, impermeability, water stability, and corrosion resistance. In the solidified area of ​​the surface of the sewage pond 1, some sewage participates in the chemical reaction and is consumed, while another portion of the sewage is fixed and encapsulated within the solidified soil layer 3 by the solidified gel, preventing the leakage of harmful substances from the sewage into the surrounding environment. In the lower, unsolidified soil layer 4, the sewage is gradually solidified by the clay layer 5 or fill soil to adsorb harmful substances from the sewage. Ultimately, all harmful substances in the sewage pond 1 are sealed within the enclosed space formed by the solidified soil layer 3 and the impermeable clay layer 5, preventing them from seeping or leaking into the surrounding area.

[0030] Compared to related technologies that use a single cementing material to solidify sewage in all areas, this invention only solidifies sewage within a certain depth range in the upper part of the sewage pond 1. The solidification area is small, and it consumes a large amount of construction waste such as engineering excavated soil 7. The proportion of the soil-stabilizing agent does not exceed 30%, significantly reducing construction and material costs. The unsolidified excavated soil 7 in the lower part of the sewage pond 1 can both seal the sewage between the solidified soil layer 3 and the clay layer 5, and also serve as a transitional soil layer, reducing the mutual influence between the solidified soil layer 3 and the clay layer 5, and preventing harmful substances in the solidified soil layer 3 from contaminating the clay layer 5.

[0031] The soil and rock solidification agent of this invention is composed of various industrial solid wastes (slag powder, fly ash, waste gypsum, water glass, stone powder slag, furnace slag, etc.). These solid wastes all contain varying degrees of active silicon, aluminum, calcium, and other minerals. Under the activation of the additive, the activity of these minerals in the various industrial solid wastes can be maximized, enabling them to participate in chemical reactions. When the proportions of the various industrial solid wastes reach the optimal level, the active silicon, aluminum, calcium, and other minerals in these solid wastes undergo hydration reactions with water to generate hydrated cementitious minerals and other crystalline minerals; on the other hand, they can chemically react with the active minerals in clay minerals to generate hydrated gel minerals and other crystalline minerals.

[0032] Therefore, compared to traditional cement materials, the active minerals in these industrial solid wastes, as well as the minerals that have been activated, not only react chemically with water to generate hydrated gel minerals (hydrated calcium silicate, hydrated calcium aluminate, hydrated calcium ferrite, ettringite, etc.) and other crystalline minerals (calcium carbonate, magnesium carbonate, calcium hydroxide, etc.), but also react further with clay minerals in the soil to generate similar hydrated gel minerals and other crystalline minerals. Therefore, compared to cement materials, mixing the soil-stabilizing agent of this invention with soil can generate more hydrated gel minerals and other crystalline minerals. These hydrated gel minerals and crystalline minerals grow within the soil, connecting unreacted soil aggregates and encapsulating them. This dual action results in soil reinforced by the solidifying agent exhibiting higher strength, impermeability, water stability, and corrosion resistance, more effectively fixing and encapsulating harmful substances within the solidified soil layer 3.

[0033] In some optional embodiments, the cement in the curing agent powder is specifically PO 42.5 cement with a specific surface area ≥380m². 2 / kg, loss on ignition ≤4.0%; the blast furnace slag powder uses S95 grade blast furnace slag powder with a specific surface area ≥400m². 2 / kg, loss on ignition ≤3.0%; the fly ash is specifically grade II fly ash, with a specific surface area ≥300m². 2 / kg, fineness (residue on 45μm square-hole sieve) ≤20%, activity index ≥75%; waste gypsum specifically desulfurized gypsum or phosphogypsum, with CaSO4·2H2O content ≥85%; water glass modulus between 2.0 and 3.5; stone powder slag specific surface area ≥350m² 2 / kg; Slag is the waste residue discharged during the blast furnace smelting of pig iron, and the moisture content of the slag is controlled within 5%.

[0034] In some alternative embodiments, refer to Figure 3 As shown, the height of the solidified soil layer 3 is 3m to 6m. The wastewater treated by the solidified soil layer 3 includes wastewater that participates in chemical reactions and the remaining wastewater that is fixed in the solidified soil layer 3. This invention only solidifies the slag soil 7 in the surface area, achieving the effect of sealing and solidifying the wastewater while effectively isolating the solidified soil layer 3 and the clay layer 5 through the slag soil 7 in the lower area, thus preventing the relevant components in the solidified soil layer 3 from affecting the clay layer 5.

[0035] In some alternative embodiments, refer to Figure 1 As shown, before backfilling the slag 7 into the sewage pond 1, the process also includes: constructing a closed curtain 2 along the circumference of the sewage pond 1, with the bottom of the closed curtain 2 located below the bottom of the sewage pond 1 and extending to the clay layer 5.

[0036] This invention involves mixing a soil-stabilizing agent into a slurry and then mixing and solidifying it with the soil to form a closed curtain 2 with good impermeability. The closed curtain 2 penetrates to a certain depth into the impermeable clay layer 5, thereby completely isolating sewage within the closed area formed by the closed curtain 2, the solidified soil layer 3, and the clay layer 5, preventing harmful substances in the sewage pond 1 from seeping and migrating into the surrounding environment.

[0037] Specifically, refer to Figure 1 and Figure 4 As shown, in this invention, the distance between the closed curtain 2 and the edge of the sewage pond 1 is 1m to 2m. In the figure, h is the height of the closed curtain 2 entering the clay layer 5, and h is not less than 3m, that is, the bottom of the closed curtain 2 is below the clay layer 5 and at least 3m below the surface of the clay layer 5. This is beneficial to fully improve the isolation performance of the closed area and prevent harmful substances in the sewage pond 1 from seeping and migrating into the surrounding environment.

[0038] In some optional embodiments, the enclosed curtain 2 is formed by mixing and solidifying a soil-stabilizing agent slurry with soil. Specifically, refer to... Figure 4As shown, the closed curtain 2 includes multiple solidification agent piles, specifically formed by connecting multiple solidification agent piles through a single-hole drilling method or a partial overlapping method. Each solidification agent pile can be manufactured by a biaxial or triaxial mixing pile machine, including: after determining the position of the closed curtain 2, the soil-rock solidification agent slurry is delivered to the drill rod of the triaxial mixing pile machine through the grouting pump 6. A high-pressure rubber air duct and a high-pressure rubber grouting pipe are connected to the top of the drill rod of the mixing pile machine. The grouting pipe is connected to the grouting pump 6 at the slurry preparation stage to deliver the soil-rock solidification agent slurry. The air duct is connected to an air compressor to deliver compressed air. During drilling, the drill bit sprays out the soil-rock solidification agent slurry and compressed air, while multiple mixing blades are welded to the drill rod. The rotation of the drill rod drives the mixing blades to rotate, thoroughly mixing the slurry and soil. The compressed air ejected from the drill bit also acts as a turbulent and agitating agent, further mixing the soil and rock-solidifying agent slurry into a fluid mixture. After the solidified slurry, which is uniformly mixed with the soil, solidifies, it forms a solidified pile. A series of solidified piles connected in one hole form a continuous, closed curtain for seepage prevention.

[0039] Optionally, backfilling the sewage pond 1 with excavated soil 7 includes ensuring that the moisture content of the excavated soil 7 does not exceed 25%. Specifically, the excavated soil 7 can be sourced from soil near the sewage pond 1, or it can be construction waste soil from surrounding construction sites. The excavated soil 7 is crushed using a crushing bucket equipped with an excavator or loader to fully break down clumps and large particles in the soil into smaller particles. After crushing, the soil is piled up, screened to remove particles larger than 50mm, and then dried to ensure that its moisture content does not exceed 25%, so as to absorb as much sewage as possible in the later stage.

[0040] In some optional embodiments, the soil and rock solidification agent slurry is composed of a mixture of solidification agent powder and water, and the mass ratio of solidification agent powder to water in the soil and rock solidification agent slurry is 1:(1.5 to 3). In the solidified soil layer 3, the mass ratio of slag soil 7 to solidification agent powder is 1:(0.2 to 0.25).

[0041] It should be noted that the calculation of the fill volume in sewage pond 1 includes two parts: one part is the fill volume required for the upper solidified soil layer 3, and the other part is the fill volume required for the lower unsolidified soil layer 4. The fill volumes required for the solidified soil layer 3 and the unsolidified soil layer 4 can be calculated respectively using the following formula (Ⅰ):

[0042]

[0043] In formula (I), ρ is the density of the water-soil mixture formed after adding slag to the sewage pond. The upper solidified soil layer is greatly affected by the disturbance caused by the movement of excavators, dump trucks, and other mechanical equipment. Therefore, in a specific embodiment, the density of the water-soil mixture in the solidified soil layer can be taken as 1.4 t / m³. 3Because the lower unconsolidated soil layer is buried at a greater depth, it is less affected by the movement of machinery such as excavators and dump trucks. Therefore, the density of the soil-water mixture in the unconsolidated soil layer can be taken as 1.35 t / m³. 3 G1 represents the density of the wastewater, which in a specific embodiment can be 1 t / m³. 3 G2 represents the density of the slag, which in a specific embodiment can be 2.60 t / m³. 3 ω is the moisture content of the slag, m1 is the total mass of the required slag, and m2 is the mass of the sewage in the sewage pond.

[0044] Furthermore, the mass of the curing agent powder required for the construction of the enclosed curtain can be estimated using the following method: First, calculate the mass of soil that reacts with the soil-rock solidifying agent slurry during the construction of the enclosed curtain. This can be calculated by multiplying the total volume of the area where the enclosed curtain will be opened by the soil density. After calculating the mass of soil that reacts with the soil-rock solidifying agent slurry, further calculate the required mass ratio of the curing agent powder using the mass ratio calculation.

[0045] The present invention will be described in detail below through specific embodiments:

[0046] (I) Determination of the formulation and dosage of soil and rock solidification agent slurry

[0047] Experiment to determine the formulation of soil and rock solidification agent grout:

[0048] The curing agent powder was prepared according to Table 1. Then, the curing agent powder and water were mixed evenly at a ratio of 1:1.5 to obtain a soil and rock curing agent slurry. Finally, the soil and rock curing agent slurry was mixed into the slag at a mass ratio of 1:0.2 (slag and curing agent powder). The interfacial shear strength of the slag and soil was tested at different times, namely 3d, 7d, 14d, and 28d. The interfacial shear strength data are shown in Table 2.

[0049] Table 1. Formulation of curing agent powder

[0050]

[0051] Table 2. Interfacial shear strength data for each formulation.

[0052]

[0053]

[0054] According to Tables 1 and 2, the best interfacial shear strength of formula No. 5 is obtained. The best curing agent powder formula is 10 parts cement, 30 parts slag powder, 15 parts fly ash, 25 parts waste gypsum, 10 parts water glass, 5 parts stone powder slag, and 5 parts furnace slag.

[0055] Test to determine the dosage of soil and rock solidification agent grout:

[0056] The soil and rock solidifier slurry was prepared according to the optimal solidifier powder formula (Formula 5). The soil and rock solidifier slurry formed by Formula 5 was mixed into the slag and rock at a mass ratio of 1:(0.15-0.3). The interfacial shear strength of the slag and rock was tested at 3d, 7d, 14d, and 28d. The interfacial shear strength data are shown in Table 3.

[0057] Table 3. Interfacial shear strength data under different soil and rock solidification agent slurry dosages.

[0058]

[0059] When the 28-day strength requirement is 4.0 MPa, based on cost control and strength margin requirements, the minimum admixture with an interfacial shear strength of 4.0*(1+20%)=4.8 MPa or higher should be selected. As shown in Table 3, in the embodiments of the present invention, the admixture range that meets the design strength requirements and has the lowest cost is: the mass ratio of slag and solidifying agent powder is 1:0.25.

[0060] (II) Construction of the Enclosed Curtain

[0061] First, mark a point 1m from the edge of the sewage pond to form a closed curtain construction area. Using a three-axis mixing pile machine, drill downwards within the marked area while simultaneously injecting the prepared soil-rock slurry (prepared in step (I)) at the optimal dosage. After the soil-rock slurry and soil are evenly mixed, solidification forms a solidified pile. Continuously connecting these solidified piles in one hole forms a closed curtain. The bottom of the closed curtain penetrates 4m into the clay layer.

[0062] (III) Filling and solidifying the sewage pond with soil.

[0063] Before the formal backfilling, soil is first evenly spread around the sewage pond. After the spread soil has slightly solidified, it is used as a construction platform for backfilling the next day. During the formal backfilling, soil is taken from near the sewage pond or construction waste from a distance is transported to the vicinity. The soil or construction waste is screened to remove large particles and then piled up near the sewage pond to dry appropriately, ensuring that its moisture content does not exceed 25%, so as to absorb as much sewage as possible later. Then, an excavator or loader is used to evenly push the screened soil into the sewage pond until the pond is completely filled. Specifically, a boat-type excavator can be used for backfilling and the surface of the backfill is leveled.

[0064] Then, the excavator, equipped with a dual-wheel mixing head, was used to mix and solidify an area 5m below the surface of the sewage pond. Two mixing heads were symmetrically distributed on either side of the connecting rod and nozzle. The soil-stabilizing agent slurry was supplied from the back-end system through the spray pipe into the nozzle. The mixing heads, with their spirally distributed cutters, cut the soil three-dimensionally and rotated, employing a vertical up-and-down mixing and solidification method. The mixing equipment moved forward, gradually deepening the mixing and spraying of the solidifying agent until it reached the bottom of the designated area. Then, the mixing equipment reversed direction, slowly raising and spraying the solidifying agent. The rate of raising or lowering the mixing head was controlled at 0.1-0.2 m / s, and the spraying rate of the solidifying agent was controlled at 100-200 kg / min. Simultaneously, the area to be solidified was laid out and divided into blocks, with an overlap width of at least 5cm between adjacent blocks to avoid incomplete mixing, ultimately forming a uniform solidified soil layer.

[0065] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method for sealing and solidifying wastewater ponds, characterized in that, include: Backfill the sewage pond with slag and soil; A soil and rock solidification agent slurry is injected into the slag in the surface area of ​​the sewage pond and stirred and solidified to form a solidified soil layer. The soil and rock solidification agent slurry includes solidification agent powder and water. The solidification agent powder includes the following components in parts by weight: cement: 10 to 40 parts, slag powder: 30 to 60 parts, fly ash: 10 to 30 parts, waste gypsum: 5 to 25 parts, water glass: 5 to 15 parts, stone powder slag: 5 to 20 parts, and furnace slag: 5 to 15 parts.

2. The method for sealing and solidifying sewage ponds according to claim 1, characterized in that, The height of the solidified soil layer is 3m to 6m.

3. The method for sealing and solidifying sewage ponds according to claim 1, characterized in that, Before backfilling the sewage pond with slag, the following steps are also included: A closed curtain is constructed along the circumference of the sewage pond, the bottom of which is below the bottom of the sewage pond and extends to the clay layer.

4. The method for sealing and solidifying sewage ponds according to claim 3, characterized in that, The height of the enclosed curtain extending into the clay layer shall not be less than 3m.

5. The method for sealing and solidifying sewage ponds according to claim 3, characterized in that, The enclosed curtain is formed by mixing the soil and rock solidification agent slurry with soil and then solidifying it.

6. The method for sealing and solidifying sewage ponds according to claim 5, characterized in that, The distance between the enclosed curtain and the edge of the sewage pond is 1m to 2m.

7. The method for sealing and solidifying sewage ponds according to claim 3, characterized in that, The enclosed curtain includes multiple curing agent piles, which are connected by a single-hole drilling method or a partial overlapping method.

8. The method for sealing and solidifying sewage ponds according to claim 1, characterized in that, The backfilling of the sewage pond with slag soil includes: the moisture content of the slag soil not exceeding 25%.

9. The method for sealing and solidifying sewage ponds according to claim 1, characterized in that, In the soil and rock solidification agent slurry, the mass ratio of the solidification agent powder to water is 1:(1.5 to 3).

10. The method for sealing and solidifying sewage ponds according to claim 9, characterized in that, In the solidified soil layer, the mass ratio of the slag to the soil and rock solidification agent powder is 1:(0.2 to 0.25).

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