Soil replacement medium as well as preparation method and application thereof

Abstract

The invention discloses a soil replacement medium and a preparation method and application thereof, and belongs to the technical field of municipal engineering, the soil replacement medium provided by the invention comprises an upper planting layer, a middle replacement medium layer, a lower replacement medium layer and a bottom gravel layer from top to bottom; wherein the upper planting layer comprises vermiculite and soil; the middle replacement medium layer comprises sawdust and iron ore from top to bottom; the lower replacement medium layer is river sand; the upper planting layer guarantees the growth environment of plants; the sawdust in the middle-layer filling medium is used for providing a carbon source, the iron ore and phosphate are subjected to complex reaction and generate chemical bonds, the lower-layer filling medium is used for improving the infiltration capacity, and the bottom gravel layer is used for regulating and storing and avoiding blockage, so that pollutant interception and rainwater infiltration are realized. According to the invention, vermiculite is matched with other modifying agents for use, so that the interception effect on pollutants is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of municipal engineering, and more specifically to a soil replacement medium and a preparation method and application thereof. Background Art

[0002] With the rapid development of urbanization, large-scale construction facilities and impermeable pavements have seriously affected the infiltration of surface water, leading to urban waterlogging. Bioretention facilities are relatively mature and widely used stormwater treatment systems. As the main structure of bioretention facilities, soil replacement media plays a vital role in promoting rainwater infiltration and pollutant interception. The organic matter and clay contained in them provide nutrients for the reproduction of microorganisms in the soil, thereby enhancing the removal effect of organic matter, nitrogen, phosphorus and other pollutants in runoff rainwater. If only urban green space soil is used as soil replacement medium, it will cause the soil compaction to increase and the structure to be severely damaged after being rolled by mechanical equipment during urban construction, resulting in poor soil permeability, poor soil aeration, and low soil organic matter content. Therefore, in order to improve the infiltration capacity, specific surface area and adsorption capacity of soil replacement medium, soil conditioners are mixed into the replacement medium. The key composition and structural optimization design of soil replacement medium are key factors in achieving pollutant interception and rainwater infiltration.

[0003] At present, the soil replacement medium of mainstream bioretention facilities is mainly a mixture of soil and improvers such as fly ash, volcanic rock, expanded clay, and coconut coir in different proportions. When selecting media improvers, in addition to physical properties, it is also necessary to consider the availability, cost-effectiveness, environmental friendliness, and removal efficiency of specific pollutants of the material. This requires a comprehensive evaluation of different media improvers. Wang Lijin et al. studied the adsorption performance of nitrogen and phosphorus of 9 groups of media improvers in the "Study on Optimization of Bioretention Facility Fillers Based on Runoff Pollution Control" published in "China Water and Drainage". It was found that the smaller the particle size of vermiculite and the larger the specific surface area, the higher the adsorption of NH4 + The removal rate of -N is close to 100.0%, and the removal rate of phosphate is also the highest. However, due to the large porosity of vermiculite, the interception effect of pollutants is reduced. Summary of the invention

[0004] In view of the above problems, the present invention provides a soil replacement medium and a preparation method and application thereof, wherein vermiculite is used in combination with other improvers to effectively improve the interception effect of pollutants.

[0005] The first object of the present invention is to provide a soil replacement medium, which includes from top to bottom: an upper planting layer, a middle replacement medium layer, a lower replacement medium layer and a bottom gravel layer.

[0006] Among them, the upper planting layer includes vermiculite and soil.

[0007] The middle replacement medium layer includes wood chips and iron ore from top to bottom.

[0008] The lower replacement medium layer is river sand.

[0009] The upper planting layer ensures the growth environment of plants; the wood chips in the middle filling medium are used to provide a carbon source, iron ore and phosphate undergo complexation reactions and generate chemical bonds, the lower filling medium improves infiltration capacity, and the bottom gravel layer is used to regulate and avoid blockage, thereby achieving pollutant interception and rainwater infiltration.

[0010] In a preferred embodiment of the present invention, the volume ratio of vermiculite to soil is 1:4-6, for example, the volume ratio of vermiculite to soil is 1:4, 1:4.5, 1:5, 1:5.5, 1:6, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0011] In a preferred embodiment of the present invention, the thickness of the upper planting layer is 15 cm to 25 cm. For example, the thickness of the upper planting layer is 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, 21 cm, 22 cm, 23 cm, 24 cm, 25 cm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0012] In a preferred embodiment of the present invention, in the middle replacement medium layer, the thickness of the wood chips is 1 cm to 5 cm, for example, the thickness of the wood chips is 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, etc.; the thickness of the iron ore is 14 cm to 23 cm, and the thickness of the iron ore is 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, 21 cm, 22 cm, 23 cm, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are equally applicable.

[0013] In a preferred embodiment of the present invention, the middle layer replacement medium also includes lake bottom mud, which is arranged between wood chips and iron ore, and the thickness of the lake bottom mud is 1 cm to 5 cm. For example, the thickness of the lake bottom mud is 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0014] In a preferred embodiment of the present invention, the thickness of the lower replacement medium layer is 32 cm to 53 cm, for example, 32 cm, 35 cm, 38 cm, 41 cm, 44 cm, 47 cm, 50 cm, 53 cm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0015] In a preferred embodiment of the present invention, the thickness of the bottom gravel layer is 10 cm to 20 cm, and the thickness of the bottom gravel layer is 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, 19 cm, 20 cm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0016] The second object of the present invention is to provide a method for preparing the soil replacement medium, which comprises the following steps: digging the soil and turning the soil.

[0017] From bottom to top, the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer are laid in sequence.

[0018] The upper planting layer is sown with plants.

[0019] The third object of the present invention is to provide the use of the above-mentioned soil replacement medium in pollutant removal.

[0020] In a preferred embodiment of the present invention, the pollutants are organic matter, phosphate, ammonia nitrogen and nitrate nitrogen.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The soil replacement medium in the present invention includes an upper planting layer, a middle replacement medium layer, a lower replacement medium layer and a bottom gravel layer from top to bottom; the upper planting layer ensures the growth environment of plants; the wood chips in the middle replacement medium are used to provide a carbon source, the iron ore and phosphate undergo a complex reaction and generate chemical bonds, the lower replacement medium improves the infiltration capacity, and the bottom gravel layer is used for storage and avoids blockage, thereby achieving pollutant interception and rainwater infiltration.

[0023] The present invention combines the advantages and disadvantages of different medium modifiers and selects different filling methods in different medium layers in order to achieve the best effect in rainwater infiltration and pollutant removal, which is conducive to the efficient reuse of waste resources, fully reducing their occupation of urban space, and increasing the utilization space and use value of river sand resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the structure of a bioretention facility.

[0025] Figure 2 The figure is a comparison of COD removal effects of three application examples under different pollution loads.

[0026] Figure 3 The figure shows a comparison of total phosphorus removal effects of three application examples under different pollution loads.

[0027] Figure 4The figure shows a comparison of the ammonia nitrogen removal effects of three application examples under different pollution loads.

[0028] Figure 5 The figure shows a comparison of the nitrate nitrogen removal effects of three application examples under different pollution loads.

[0029] Figure numerals: 1 - upper planting layer, 2 - middle replacement medium layer, 3 - lower replacement medium layer, 4 - bottom gravel layer, 5 - sediment, 6 - pollutant. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The present invention provides a soil replacement medium as a bioretention facility, such as Figure 1 As shown, the media improver is placed in layers (90-110 cm in height). In the upper planting layer 1, a mixture of vermiculite and soil is placed; the middle replacement medium layer 2 is filled with sawdust, lake mud, and iron ore from top to bottom; the lower replacement medium layer 3 is filled with river sand, and the bottom gravel layer 4 is filled with gravel. The runoff rainwater flows in from top to bottom along the direction of the arrow. The addition of iron ore causes the phosphate in the simulated rainwater to precipitate and react with the iron ions to form a complex as shown in FIG. Figure 1 At the same time, the amorphous iron hydroxide formed on the surface of the iron ore provides a large number of active sites, which are easy to form stable chemical bonds with phosphates, thereby reducing the effluent concentration of total phosphorus (TP).

[0032] The upper planting layer is filled with soil and vermiculite in a ratio of 5:1, with a thickness of 15-25cm. Since vermiculite has a low hardness and swells and softens in rainwater, it is easy to harden if placed alone or if the proportion of vermiculite is too large. Therefore, the present invention chooses to mix soil and vermiculite in a certain proportion, which not only ensures the normal growth environment of plants, but also improves the problems of poor permeability and air permeability of green land soil; increases water holding and water-saving capacity; and improves the removal effect of phosphorus in rainwater. The soil used in the present invention can be obtained by conventional means, and the present invention is not particularly limited here. The soil used in the present invention is garden soil.

[0033] The thickness of the middle replacement medium layer is 25-30cm, and from top to bottom, it is wood chips with a thickness of 1-5cm, lake mud with a thickness of 1-5cm, and iron ore with a thickness of 14-23cm. The addition of wood chips and lake mud increases the carbon source for the replacement medium and improves the denitrification ability of microorganisms in the replacement medium. The wood chips swell when they come into contact with water, which increases their permeability. The addition of lake mud increases the content of organic matter and promotes the growth and reproduction of microorganisms in the replacement medium. Waste iron ore has the advantages of stable pH, less sulfate by-products, and simultaneous denitrification and phosphorus removal as a water treatment material. It is placed under wood chips and lake mud to support and prevent the upper medium from being washed away, which can not only realize waste recycling, but also adjust the permeability difference of lake mud.

[0034] The lower filling medium is filled with river sand with a thickness of 32-53 cm, which increases the permeability of the soil replacement medium and improves the infiltration capacity.

[0035] The bottom layer is filled with gravel with a thickness of 10-20cm, which not only plays a role in regulating and storing water, but also prevents the upper layer of replacement medium from being washed away and blocking the drainage outlet.

[0036] The following is further described in conjunction with specific examples. In the following specific examples, unless otherwise specified, all raw materials can be sourced from commercial sources.

[0037] Example 1

[0038] This embodiment provides a soil replacement medium, comprising the following steps:

[0039] Dig the soil and turn the soil over; lay the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer from bottom to top.

[0040] Among them, the upper planting layer is made of a mixture of soil and vermiculite in a ratio of 5:1; the thickness is 23cm.

[0041] The middle replacement medium layer is composed of 5 cm thick sawdust, 3 cm thick lake bottom mud and 14 cm thick iron ore from top to bottom.

[0042] The lower layer replacement medium is river sand with a thickness of 45 cm.

[0043] The thickness of gravel in the bottom gravel layer is 20 cm.

[0044] The soil replacement medium in this embodiment is denoted as BVD.

[0045] Example 2

[0046] This embodiment provides a soil replacement medium, comprising the following steps:

[0047] Dig the soil and turn the soil over; lay the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer from bottom to top.

[0048] Among them, the upper planting layer is made of a mixture of soil and vermiculite in a ratio of 5:1; the thickness is 23cm.

[0049] The middle replacement medium layer is 5 cm thick sawdust and 14 cm thick iron ore from top to bottom.

[0050] The lower layer replacement medium is river sand with a thickness of 45 cm.

[0051] The thickness of gravel in the bottom gravel layer is 20 cm.

[0052] The soil replacement medium in this embodiment is denoted as BVF.

[0053] Example 3

[0054] This embodiment provides a soil replacement medium, comprising the following steps:

[0055] Dig the soil and turn the soil over; lay the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer from bottom to top.

[0056] Among them, the upper planting layer is made of a mixture of soil and vermiculite in a ratio of 4:1; the thickness is 15cm.

[0057] The middle replacement medium layer is composed of 1 cm thick wood chips, 5 cm thick lake bottom mud, and 20 cm thick iron ore from top to bottom.

[0058] The lower layer replacement medium is river sand with a thickness of 32 cm.

[0059] The thickness of gravel in the bottom gravel layer is 10 cm.

[0060] Example 4

[0061] This embodiment provides a soil replacement medium, comprising the following steps:

[0062] Dig the soil and turn the soil over; lay the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer from bottom to top.

[0063] Among them, the upper planting layer is made of a mixture of soil and vermiculite in a ratio of 6:1; the thickness is 25cm.

[0064] The middle replacement medium layer is composed of 3 cm thick sawdust, 1 cm thick lake bottom mud and 25 cm thick iron ore from top to bottom.

[0065] The lower layer replacement medium is river sand with a thickness of 53 cm.

[0066] The thickness of gravel in the bottom gravel layer is 20 cm.

[0067] Comparative Example 1

[0068] This comparative example provides a soil replacement medium, comprising the following steps:

[0069] Dig the soil and turn the soil over; lay the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer from bottom to top.

[0070] Among them, the upper planting layer is made of a mixture of soil and vermiculite in a ratio of 5:1; the thickness is 23cm.

[0071] The middle replacement medium layer is 5 cm thick sawdust from top to bottom.

[0072] The lower layer replacement medium is river sand with a thickness of 45 cm.

[0073] The thickness of gravel in the bottom gravel layer is 20 cm.

[0074] The soil replacement medium of this comparative example is recorded as BV.

[0075] After the soil replacement medium is loaded in the above manner, in order to enable the microbial system to form quickly and exert a stable removal effect, the soil replacement medium is domesticated with microorganisms. On April 11, 2023, the water intake points were selected from Meihu Lake on the campus of Zhengzhou University and the rainwater outlet of the drainage pipe of Henan Institute of Geology and Mining, and mixed rainwater was used to irrigate the test column for one month. During the inoculation period, the water distribution: dry cycle ratio was 1:3, and a certain dry-wet cycle ratio was maintained so that the permeability and oxygen content of the entire system can be restored in each cycle. A preliminary test simulating rainfall was carried out to allow the microorganisms in the rainwater biofilter device to begin to grow, cultivate a microbial community as soon as possible, and initially establish the microbial diversity inside the rainwater biofilter device.

[0076] During the rainfall process, the pollutant concentration of runoff rainwater is affected by the rain type, duration and intensity of rainfall. The initial rainwater will bring a higher pollutant concentration due to flushing the ground. As the rainfall time increases, the pollutant concentration will gradually decrease. In order to verify the pollutant removal effect of the present invention, artificial simulated rainwater is configured for verification. The artificial rainwater is configured with tap water. Referring to the average pollutant concentration in the road runoff rainwater in Changzhi City, the pollutant concentration is configured at three different concentration levels: low concentration, medium concentration and high concentration. The low concentration is close to the average pollution concentration of road rainwater runoff in Changzhi City. As shown in Table 1. In order to explore the effects of soil replacement media on COD and NO under different pollution loads. 3- -N、NH4 +-N, TP purification effect, specially set three pollution load concentrations of low, medium and high. This test selected the water distribution flow rate of 126.42mL / min under medium rainfall intensity as the water distribution flow rate of this test.

[0077] Table 1 Concentration of pollutants

[0078] Pollutants COD(mg / L) <![CDATA[NO3 - -N(mg / L)]]> <![CDATA[NH4 + -N(mg / L)]]> TP(mg / L) Low concentration 100 5 3 1 Medium concentration 150 10 6 3 High concentration 200 15 9 5

[0079] According to the design rainfall corresponding to 87% of the annual runoff control rate of Changzhi City, rainfall was carried out with a total water volume of 14L, water intake for 120min, sampling every 30min, and no sampling during the first 40min if no water flowed out. The removal of pollutants under different pollution loads was studied.

[0080] The bioretention facility BV prepared in comparative example 1, the bioretention facility BVF prepared in example 2, and the bioretention facility BVD prepared in example 1 were watered by a water tank in combination with a peristaltic pump under low, medium, and high pollution loads. The rainfall lasted for 120.0 min. After each water distribution, water was replenished one day after the end of each water distribution. Each operation was performed three times under each pollution load.

[0081] Before each operation, samples were taken at the outlet to measure COD and NO 3- -N、NH4 + -N, TP and other conventional indicators, through the data to analyze the impact of various soil replacement media on the purification effect of bioretention facilities under different pollution loads. The facility flooding height is 200mm-300mm.

[0082] Depend on Figure 2 As shown in the figure, the COD removal rate of BVD is higher than that of BVF under low pollution load. As the pollutant concentration increases, BVF has the highest COD removal rate, which can reach 93.65%. This is because the addition of lake sediment in BVD provides more carbon sources in the medium, and the incomplete utilization of microorganisms leads to the release of organic matter or the death of microorganisms, which increases the effluent concentration of COD. The improvement of COD removal rate of BVF facility indicates that the utilization of COD by microorganisms in bioretention facilities is promoted under medium pollution load conditions. When the pollutant load continues to increase, the utilization of COD by microorganisms gradually approaches saturation, so the COD removal rates of the three facilities are reduced under high pollution load.

[0083] Depend on Figure 3 As shown in the figure, when the influent concentration is low, the TP effluent quality is relatively good, and the removal efficiency of the three devices is more than 85%. The low, medium and high concentration effluents can meet the Class III-V water quality standards in the "Surface Water Environmental Quality Standards", indicating that the bioretention facility has a strong resistance to the impact of pollutant concentration fluctuations. The iron ore added to the replacement medium participates in autotrophic denitrification. As shown in Table 2, the iron ore contains a large amount of Al and Fe, of which Fe3+ and Al 3+ Easy to phosphate (PO4 3- ) undergoes precipitation reaction and is fixed in the bioretention facility. Therefore, the removal effect of TP in the two devices with iron ore added is better than that in the device without iron ore.

[0084] Table 2 Physical and chemical properties of medium improvers

[0085]

[0086] Depend on Figure 4 As shown in the figure, when the influent water is of different concentrations, the rainwater has a good removal effect after passing through the bioretention facility. After the influent water is of medium, high and low concentrations, the ammonia nitrogen concentration of the BVF effluent is the lowest, all less than 0.50 mg / L, and the removal rate is about 98.00%, reaching the Class II water quality standard in the "Surface Water Environmental Quality Standard". + -N purification effect is inferior to BVF. As the pollutant concentration increases, the three facilities have a higher purification effect on NH4 + -N purification effect is still maintained at a high level, indicating that the bioretention facility has not yet reached saturation for the adsorption of ammonia nitrogen. When the influent concentration is high, the removal efficiency of BVF and BVD is still above 80.00%. Since vermiculite is a layered silicate mineral, it has good adsorption properties. NH4 + -N is effectively adsorbed by vermiculite. Physical adsorption is mainly due to the porous structure of vermiculite providing a large number of adsorption sites, while chemical adsorption is due to the negatively charged silicate layer on the surface of vermiculite and NH4 + -N charges are attractive.

[0087] Depend on Figure 5 As shown, the three facilities are 3- The removal rates of -N from high to low are BVF>BVD>BV. 3- The removal rates of -N decreased with the increase of influent pollutant concentration, while the removal rates of NO 3- -N removal rate has been on an upward trend, and the removal rate can reach 92.35% under high pollution load. Due to the addition of dual carbon sources of lake sediment and wood chips, the high-carbon environment in the bioretention facility is conducive to the growth of denitrifying bacteria, alleviating the impact of pollution load. The removal rates of BVF and BV from the pollution load were 95.46% and 72.23%, respectively, which dropped to 92.68% and 64.23% after the high pollution load was increased. Compared with BVD added to lake sediment, the organic matter content of BVF and BV soil replacement media is relatively small. As the pollutant concentration increases, due to insufficient electron donors, the carbon source becomes the most important factor in removing NO 3- -N limiting factor, leading to the bioretention facility's NO 3--N's purification effect is reduced.

[0088] According to the characteristics of different media conditioners, river sand, vermiculite, lake sediment, wood chips and iron ore are selected as soil replacement media. By mixing / layering the media conditioners, better water penetration, pollutant removal effect and adaptation to different environmental conditions can be achieved. The present invention is not only conducive to the efficient reuse of waste resources and fully reduces their occupation of urban space, but also increases the utilization space and use value of lake sediment. Through scientific methods and technological innovation, the present invention develops a soil replacement medium with high cost-effectiveness and superior performance, so that bioretention facilities can play a greater role in urban rainwater management.

[0089] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0090] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A soil replacement medium, characterized in that: The soil replacement medium includes from top to bottom: an upper planting layer, a middle replacement medium layer, a lower replacement medium layer and a bottom gravel layer; Among them, the upper planting layer includes vermiculite and soil; The middle replacement medium layer includes wood chips and iron ore from top to bottom; The lower replacement medium layer is river sand; The upper planting layer ensures the growth environment of plants; the wood chips in the middle filling medium are used to provide a carbon source, iron ore and phosphate undergo complexation reactions and generate chemical bonds, the lower filling medium improves infiltration capacity, and the bottom gravel layer is used to regulate and avoid blockage, thereby achieving pollutant interception and rainwater infiltration.

2. A soil replacement medium according to claim 1, characterized in that: In the upper planting layer, the volume ratio of vermiculite to soil is 1:4-6.

3. A soil replacement medium according to claim 1, characterized in that: The thickness of the upper planting layer is 15cm to 25cm.

4. A soil replacement medium according to claim 1, characterized in that: In the middle replacement medium layer, the thickness of the wood chips is 1 cm to 5 cm, and the thickness of the iron ore is 14 cm to 23 cm.

5. A soil replacement medium according to claim 1, characterized in that: The middle layer replacement medium also includes lake bottom mud, which is arranged between the wood chips and the iron ore, and the thickness of the lake bottom mud is 1 cm to 5 cm.

6. A soil replacement medium according to claim 1, characterized in that: The thickness of the lower replacement medium layer is 32cm to 53cm.

7. A soil replacement medium according to claim 1, characterized in that: The thickness of the bottom gravel layer is 10cm to 20cm.

8. A method for preparing the soil replacement medium according to any one of claims 1 to 7, characterized in that: The following steps are involved: digging and turning the soil; From bottom to top, lay the bottom gravel layer, the lower replacement medium layer, the middle replacement medium layer and the upper planting layer in sequence; The upper planting layer is sown with plants.

9. Use of the soil replacement medium according to any one of claims 1 to 7 in pollutant removal.

10. Use of the soil replacement medium according to claim 9 in pollutant removal, characterized in that: The pollutants are organic matter, phosphate, ammonia nitrogen and nitrate nitrogen.

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