A composite type manganese-based constructed wetland denitrification and greenhouse gas emission reduction system and method

Abstract

The present application relates to the technical field of water treatment, and particularly relates to a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system and method, which comprises: a water inlet bucket for containing wastewater to be treated; a first wetland unit, the bottom of which is provided with a first water inlet connected to the water inlet bucket, the top of which is provided with a first water outlet and opposite sides of which are provided with a backwater inlet; the first wetland unit is filled with volcanic rocks in the lower layer and manganese ore in the upper layer, and wetland plants are planted on the top of the manganese ore; a second wetland unit, the top of which is provided with a second water inlet connected to the first water outlet, the bottom of which is provided with a second water outlet and a backwater outlet, and the backwater outlet is connected to the backwater inlet; the second wetland unit is filled with volcanic rocks in the whole and wetland plants are planted on the top of the second wetland unit; the present application solves the problems of insufficient total nitrogen removal efficiency and intensified greenhouse gas emission when the constructed wetland treats wastewater with high ammonia nitrogen load.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system and method. Background Technology

[0002] Carbon emissions from traditional wastewater treatment account for a large proportion of total social carbon emissions, while constructed wetlands have significant low-carbon advantages compared to traditional activated sludge processes, with carbon emissions only 1 / 10 to 1 / 7 of those from traditional wastewater treatment plants.

[0003] However, conventional constructed wetlands operate in anoxic / anaerobic environments for extended periods, leading to an imbalance in the redox environment. In particular, when treating wastewater with low organic and high ammonia nitrogen loads, the insufficient dissolved oxygen and carbon sources limit the nitrification / denitrification processes, thereby exacerbating greenhouse gas emissions and significantly restricting the promotion and application of low-carbon operation of constructed wetlands. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system and method, which solves the problems of insufficient total nitrogen (TN) removal efficiency and increased greenhouse gas emissions when constructed wetlands treat wastewater with high ammonia nitrogen load.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] In a first aspect, the present invention provides a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system, comprising:

[0007] The inlet tank is used to hold the wastewater to be treated.

[0008] The first wetland unit has a first water inlet at the bottom connected to the water inlet tank, a first water outlet at the top and a return water inlet on the opposite side; the lower layer of the first wetland unit is filled with volcanic rock and the upper layer is filled with manganese ore, and wetland plants are planted on top of the manganese ore.

[0009] The second wetland unit has a second water inlet at the top that is connected to the first water outlet, a second water outlet at the bottom, and a return water outlet that is connected to the return water inlet; the second wetland unit is entirely filled with volcanic rock and wetland plants are planted on its top.

[0010] As a further implementation, a pump is provided between the first water inlet and the water inlet tank, between the first water outlet and the second water inlet, and between the return water inlet and the return water outlet.

[0011] As a further implementation, the manganese ore has a particle size of 2-4 mm, and the volcanic rock has a particle size of 2-4 mm.

[0012] As a further implementation, the wetland plant is sweet flag (Acorus calamus).

[0013] As a further implementation, the first inlet and the first outlet are arranged diagonally, and the second inlet and the second outlet are arranged diagonally.

[0014] Secondly, the present invention provides a method for denitrification and greenhouse gas emission reduction using a composite manganese-based constructed wetland, employing the composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system as described in the first aspect, comprising the following steps:

[0015] The wastewater to be treated is drawn from the inlet tank, enters from the bottom of the first wetland unit, and exits from the top; then, it enters from the top of the second wetland unit and exits from the bottom. The hydraulic residence time is the same for each wetland unit. The first wetland unit operates with continuous inflow and outflow, while the second wetland unit operates intermittently and is divided into two stages: drainage and filling within one hydraulic residence time. During drainage, the wastewater in the second wetland unit is discharged at a certain rate, and the water level decreases. During the filling stage, the system stops drainage, and the wastewater in the second wetland unit is pumped into the first wetland unit with a 100% recirculation ratio until the initial water level is reached.

[0016] As a further implementation method, the hydraulic retention time is the same, which is 1 day, and the ratio of drainage time to water filling time of the second wetland unit is 6h:18h.

[0017] As a further implementation method, the hydraulic retention time is the same, which is 1 day, and the ratio of drainage time to water filling time of the second wetland unit is 12h:12h.

[0018] As a further implementation method, the hydraulic retention time is the same, which is 1 day, and the ratio of drainage time to water filling time of the second wetland unit is 18h:6h.

[0019] As a further implementation method, to ensure that the total nitrogen influent load of the system remains constant, the drainage and return wastewater volume of the second wetland unit changes accordingly under different drainage-filling time conditions. When the system is running, this is reflected in the change of the remaining wastewater level after the drainage of the second wetland unit.

[0020] The beneficial effects of the present invention are as follows:

[0021] 1. This invention fills a first wetland unit with manganese ore and optimizes the redox environment of the constructed wetland by intermittently operating a second wetland unit and coupling backflow to the first wetland unit. This enhances the manganese cycling process between Mn(II) and bio-based MnOx, thereby improving the efficiency of the manganese cycling between Mn(II) and bio-based MnOx. The enhanced manganese cycling process promotes the synergistic effect of chemical oxidation and biological autotrophic denitrification in nitrogen conversion, achieving efficient nitrogen removal and N2O emission reduction in wastewater.

[0022] 2. In this invention, the first wetland unit operates continuously, while the second wetland unit operates intermittently and refluxes. The combination of the two enables the periodic alternation of aerobic and anoxic conditions within the second wetland unit, thereby allowing the nitrification-denitrification reaction to proceed fully and achieving efficient conversion and removal of ammonia nitrogen.

[0023] 3. The composite manganese-based constructed wetland of this invention does not require aeration at an ammonia nitrogen load of 9 g / (m³). 2 Under condition d), a total nitrogen removal rate of >72.8% and an N2O conversion rate of <0.74% can be achieved. ， Furthermore, when the ratio of drainage time to water filling time in the second wetland unit was 12h:12h, the total nitrogen removal rate was 92.5% and the N2O conversion rate was 0.09%. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a schematic diagram of the composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system in an embodiment of the present invention;

[0026] Figure 2 This is a diagram showing the specific operation mode and water level change of the intermittently operating second wetland unit under different drainage-filling time ratios in an embodiment of the present invention; wherein, 2(a) is a drainage time-filling time ratio of 6h:18h, 2(b) is a drainage time-filling time ratio of 12h:12h, and 2(c) is a drainage time-filling time ratio of 18h:6h.

[0027] The diagram exaggerates the spacing or dimensions between parts to show their positions; the diagram is for illustrative purposes only.

[0028] The components are: 1. Water inlet tank; 2. Peristaltic pump; 3. Wetland plants; 4. First wetland unit; 4-1. First water inlet; 4-2. First water outlet; 4-3. Return water inlet; 5. Second wetland unit; 5-1. Second water inlet; 5-2. Second water outlet; 5-3. Return water outlet. Detailed Implementation

[0029] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] Example 1

[0031] In a typical embodiment of the present invention, reference is made to Figure 1 As shown, a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system includes: a water inlet tank 1, a first wetland unit 4, and a second wetland unit 5. In this embodiment, the length, width, and height of the first wetland unit 4 and the second wetland unit 5 are 20cm, 20cm, and 50cm, respectively.

[0032] Water inlet tank 1 is used to hold the wastewater to be treated.

[0033] The first wetland unit 4 has a first water inlet 4-1 at its bottom, connecting to the water inlet tank 1, and a first water outlet 4-2 on one side of its top, with a return water inlet 4-3 on its opposite side. The first wetland unit 4 contains two layers of filling material, such as... Figure 1 As shown, the lower layer of the first wetland unit 4 is filled with volcanic rock, the upper layer is filled with manganese ore, and wetland plants 3 are planted on top of the manganese ore.

[0034] In this embodiment, the upper layer of manganese ore is 20cm thick, the lower layer of volcanic rock is 25cm thick, the particle size of the manganese ore is 2-4mm, and the particle size of the volcanic rock is 2-4mm.

[0035] This embodiment also includes a second wetland unit 5, which has a second inlet 5-1 at its top, connected to a first outlet 4-2. The bottom of the second wetland unit 5 has a second outlet 5-2 and a return water outlet 5-3, connected to a return water inlet 4-3. The second outlet 5-2 is lower than the return water outlet 5-3. The second wetland unit 5 is entirely filled with volcanic rock, and wetland plants 3 are planted on its top. In this embodiment, the volcanic rock has a particle size of 2-4 mm, and the thickness of the filled volcanic rock is 45 cm.

[0036] In this embodiment, the first inlet 4-1 and the first outlet 4-2 are arranged diagonally, and the second inlet 5-1 and the second outlet 5-2 are arranged diagonally.

[0037] In this embodiment, wetland plant 3 is sweet flag (Acorus calamus), and the planting density of sweet flag is 200 plants / m². 2 .

[0038] Pumps are installed between the first inlet 4-1 and the inlet tank 1, between the first outlet 4-2 and the second inlet 5-1, and between the return water inlet 4-3 and the return water outlet 5-3. Among them, the pump between the first inlet 4-1 and the inlet tank 1 is a peristaltic pump 2.

[0039] Example 2

[0040] This embodiment provides a method for denitrification and greenhouse gas emission reduction using a composite manganese-based constructed wetland, employing the composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system as described in Embodiment 1, and includes the following steps:

[0041] Peristaltic pump 2 draws the wastewater to be treated from inlet tank 1, allowing water to enter from the bottom of the first wetland unit 4 and exit from the top; then, water enters from the top of the second wetland unit 5 and exits from the bottom. The hydraulic residence time is the same for each wetland unit. The first wetland unit 4 operates with continuous inflow and outflow, while the second wetland unit 5 operates intermittently and is divided into two stages: drainage and filling within one hydraulic residence time. During drainage, wastewater in the second wetland unit 5 is discharged at a certain speed, and the water level decreases. During the filling stage, the system stops drainage, and wastewater in the second wetland unit 5 is pumped back into the first wetland unit 4 with a 100% recirculation ratio until the initial water level is reached.

[0042] Ensure the total nitrogen influent load of the system remains constant (9g / (m³)). 2 ·d)) remains unchanged, that is, the pump speed of the inlet peristaltic pump remains unchanged. Under different drainage-filling time conditions, the drainage and return wastewater volume of the second wetland unit 5 changes accordingly. When the system is running, it is reflected in the change of the remaining wastewater level after the drainage of the second wetland unit 5.

[0043] In this embodiment, the hydraulic retention time of each wetland unit is the same, which is 1 day. The ratio of drainage time to water filling time in the second wetland unit 5 is 6h:18h, 12h:12h, and 18h:6h, as follows: Figure 2 As shown.

[0044] This embodiment demonstrates a significantly enhanced denitrification effect in treating wastewater with low organic matter and high ammonia nitrogen compared to using any single method. This is not only due to the aerobic-anoxic environment created by intermittent operation, but also because the subsequent wetland recirculation and aeration improves the redox conditions of the MnOx substrate, resulting in higher recycling efficiency between Mn(II) and biological MnOx(IV). In short, MnOx can reduce ammonia nitrogen (NH4+) under anoxic conditions. + -N) is oxidized to nitrate nitrogen (NO3) - -N), Mn 2+ The NO3 is generated and accumulated through the above process. Then, it is removed through denitrification combined with Mn(II) oxidation. --N, due to the presence of refluxed DO, Mn(II) is re-oxidized to biogenic MnOx by manganese-oxidizing bacteria under aerobic conditions, participating in NH4+. + -N oxidation enables the cyclic transformation of Mn(IV) and Mn(II), ultimately achieving efficient removal of nitrogen from wastewater and reduction of N2O emissions.

[0045] Experimental Example 1

[0046] The composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system described in Example 1, with a daily water treatment capacity of 10L, was constructed to remove COD and NH4+. + Wastewater with N, TN, and TP concentrations of 100 mg / L, 35 mg / L, 40 mg / L, and 3 mg / L, respectively, was drawn from the inlet tank using an inlet peristaltic pump, following the method described in Example 2. Figure 2 As shown in (a), the ratio of drainage time to water filling time for the second wetland unit 5 is 6h:18h. During the 6h drainage period, the discharge volume of the second wetland unit 5 is 4 times the inflow volume, and the water level drops to 1 / 4 of the original level. During the 18h water filling period, the system stops discharging water, and the wastewater in the second wetland unit 5 is pumped into the first wetland unit 4 with a 100% reflux ratio until the initial water level is reached.

[0047] The experimental results show that when the drainage-filling time ratio is 6h:18h, and the TN (total nitrogen) influent load is 9g / (m³), 2 At time d), the nitrogen removal rate was 72.8%, and the N2O conversion rate was 0.74%.

[0048] Experimental Example 2

[0049] To construct a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system as described in Example 1, with a daily water treatment capacity of 10L, wastewater with COD, TN, and TP concentrations of 100mg / L, 40mg / L, and 3mg / L, respectively, is drawn from the inlet tank using an inlet peristaltic pump, following the method described in Example 2. Figure 2 As shown in (b), the ratio of drainage time to water filling time for the second wetland unit 5 is 12h:12h. During the 12h drainage period, the discharge volume of the second wetland unit 5 is twice the inflow volume, and the water level drops to half of its original level. During the 12h water filling period, the system stops discharging water, and the wastewater in the second wetland unit 5 is pumped into the first wetland unit 4 with a 100% reflux ratio until the initial water level is reached.

[0050] The test results show that when the drainage-filling time ratio is 12h:12h, and the TN influent load is 9g / (m³), 2 At time d), the nitrogen removal rate was 92.5%, and the N2O conversion rate was 0.09%.

[0051] Experimental Example 3

[0052] To construct a composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system as described in Example 1, with a daily treatment capacity of 10L, wastewater with COD, TN, and TP concentrations of 100mg / L, 40mg / L, and 3mg / L, respectively, is drawn from the inlet tank using an inlet peristaltic pump, following the method described in Example 2. Figure 2 As shown in (c), the ratio of drainage time to water filling time for the second wetland unit 5 is 18h:6h. During the 18h drainage period, the discharge volume of the second wetland unit 5 is 4 / 3 times the inflow volume, and the water level drops to 3 / 4 of the original level. During the 6h water filling period, the system stops discharging water, and the wastewater in the second wetland unit 5 is pumped into the first wetland unit 4 with a 100% reflux ratio until the initial water level is reached.

[0053] The test results show that when the drainage-filling time ratio is 18h:6h, and the TN influent load is 9g / (m³), 2 At time d), the nitrogen removal rate was 78.7%, and the N2O conversion rate was 0.29%.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite manganese-based constructed wetland system for nitrogen removal and greenhouse gas emission reduction, characterized in that, include: The inlet tank is used to hold the wastewater to be treated. The first wetland unit has a first water inlet at the bottom connected to the water inlet tank, a first water outlet at the top and a return water inlet on the opposite side; the lower layer of the first wetland unit is filled with volcanic rock and the upper layer is filled with manganese ore, and wetland plants are planted on top of the manganese ore. The second wetland unit has a second inlet at the top connected to the first outlet, a second outlet at the bottom, and a return water outlet connected to the return water inlet. The second wetland unit is entirely filled with volcanic rock and its top is planted with wetland plants. The second wetland unit operates intermittently and is divided into two stages: drainage and filling, within one hydraulic residence time. During drainage, wastewater in the second wetland unit is discharged at a certain rate, and the water level decreases. During the filling stage, the system stops drainage, and wastewater in the second wetland unit is pumped into the first wetland unit with a 100% return ratio until the initial water level is reached. The first wetland unit is filled with manganese ore, and through the intermittent operation of the second wetland unit and coupling backflow to the first wetland unit, the redox environment of the constructed wetland is optimized, enhancing Mn(II) and biogenic MnO. x The manganese cycle process between them enhances the reaction of Mn(II) with bio-based MnO. x The enhanced manganese cycle efficiency promotes the synergistic effect of chemical oxidation and biological autotrophic denitrification in nitrogen conversion, achieving efficient removal of nitrogen from wastewater and reduction of N2O emissions.

2. The composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system according to claim 1, characterized in that, Pumps are provided between the first water inlet and the water inlet tank, between the first water outlet and the second water inlet, and between the return water inlet and the return water outlet.

3. The composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system according to claim 1, characterized in that, The manganese ore has a particle size of 2-4 mm, and the volcanic rock has a particle size of 2-4 mm.

4. The composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system according to claim 1, characterized in that, The wetland plant in question is sweet flag (Acorus calamus).

5. The composite manganese-based constructed wetland denitrification and greenhouse gas emission reduction system according to claim 1, characterized in that, The first inlet and the first outlet are diagonally arranged, and the second inlet and the second outlet are diagonally arranged.

6. A method for denitrification and greenhouse gas emission reduction in a composite manganese-based constructed wetland, characterized in that, The process employs the composite manganese-based constructed wetland nitrogen removal and greenhouse gas emission reduction system as described in any one of claims 1-5, comprising the following steps: The wastewater to be treated is drawn from the inlet tank, enters from the bottom of the first wetland unit and exits from the top; then it enters from the top of the second wetland unit and exits from the bottom. The hydraulic residence time of each wetland unit is the same. The first wetland unit operates with continuous inflow and outflow, while the second wetland unit operates intermittently and is divided into two stages: drainage and filling within one hydraulic residence time. During drainage, the wastewater in the second wetland unit is discharged at a certain rate, and the water level drops. During the filling stage, the system stops drainage, and the wastewater in the second wetland unit is pumped into the first wetland unit with a 100% recirculation ratio until the initial water level is reached.

7. The method for denitrification and greenhouse gas emission reduction in a composite manganese-based constructed wetland according to claim 6, characterized in that, The hydraulic retention time is the same, which is 1 day. The ratio of drainage time to water filling time in the second wetland unit is 6h:18h.

8. The method for denitrification and greenhouse gas emission reduction in a composite manganese-based constructed wetland according to claim 6, characterized in that, The hydraulic retention time is the same, which is 1 day. The ratio of drainage time to water filling time in the second wetland unit is 12h:12h.

9. The method for denitrification and greenhouse gas emission reduction in a composite manganese-based constructed wetland according to claim 6, characterized in that, The hydraulic retention time is the same, which is 1 day. The ratio of drainage time to water filling time in the second wetland unit is 18h:6h.

10. A method for denitrification and greenhouse gas emission reduction in a composite manganese-based constructed wetland according to claim 6, characterized in that, To ensure a constant total nitrogen influent load, the drainage and return wastewater volumes of the second wetland unit vary under different drainage-filling time conditions. When the system is running, this variation is reflected in the change in the level of the remaining wastewater after the drainage of the second wetland unit.

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