Tidal flow constructed wetland for treating rural domestic sewage and control method

Abstract

This invention provides a tidal flow constructed wetland for treating rural domestic sewage and a control method thereof. The tidal flow constructed wetland includes a concrete impermeable layer, which is located at the bottom and around the perimeter of the pool. Within the concrete impermeable layer, from bottom to top, are a uniformly distributed water pipe layer, a first packing layer, a second packing layer, a third packing layer, and a covering layer. One end of the uniformly distributed water pipe layer has an inlet pipe, and the bottom of the third packing layer has an outlet pipe. An aeration pipe is located within the third packing layer. Wetland plants, preferably local dominant wetland plant species, are planted on the covering layer. The first packing layer is a mixture of slow-release carbon source and alkali source, the second packing layer is a mixture of sulfur and iron, the third packing layer is a filter adsorption packing, and the covering layer is gravel packing. This invention has the advantages of good purification effect, simultaneous nitrogen and phosphorus removal, siphon self-control, low infrastructure and operating costs, and convenient maintenance when treating rural domestic sewage.

Description

Technical Field

[0001] This invention relates to the field of constructed wetlands, specifically to a tidal flow constructed wetland for treating rural domestic sewage and a control method thereof. Background Technology

[0002] Untreated and indiscriminate discharge of rural domestic sewage can harm the health of rural residents. Rural areas in my country are widely distributed and residents are scattered. Rural domestic sewage is characterized by small discharge volumes, significant fluctuations in water quality and quantity over time, and intermittent discharge, making centralized treatment unsuitable. Furthermore, rural domestic sewage is characterized by low toxicity, high biodegradability, but a low carbon-to-nitrogen ratio.

[0003] Constructed wetland wastewater treatment technology is a wastewater treatment process suitable for the characteristics of rural domestic sewage discharge. It boasts advantages such as low energy consumption and minimal maintenance, and is currently widely used. Common constructed wetlands include surface flow, subsurface flow, and vertical flow constructed wetlands, each with its own significant drawbacks. While these three types of constructed wetlands can effectively remove COD and SS from wastewater, the long-term submerged state of the substrate hinders reoxygenation, resulting in an anaerobic environment that is detrimental to nitrification and consequently, poor TN removal. Furthermore, adding artificial aeration and reoxygenation methods increases investment and operating costs.

[0004] Tidal flow constructed wetlands are based on traditional vertical flow constructed wetlands. By artificially controlling the rise and fall of the operating water level, the water level inside the constructed wetland changes periodically, allowing the substrate to be repeatedly exposed to the atmosphere. The pore suction generated by the tide draws oxygen from the atmosphere into the bed, significantly improving the oxygen transport and utilization efficiency of the wetland bed, thereby enhancing the nitrification process of total nitrogen (TN).

[0005] However, existing patented tidal flow constructed wetland devices have certain shortcomings when applied to rural domestic sewage treatment, requiring further innovation and improvement. Chinese patent CN110668575A discloses a fully automatic, high-efficiency denitrification and phosphorus removal tidal flow constructed wetland and its usage method. It achieves efficient pollutant removal through electromagnetic automatic valves and automatic water controllers, utilizing the principle of rapid inflow and outflow via the "tidal" flow. However, when treating rural domestic sewage with a low carbon-to-nitrogen ratio, the lack of carbon sources affects the denitrification process, leading to excessive TN concentration in the effluent. Chinese patent CN110330109A discloses a self-operating A / O type tidal flow constructed wetland. It achieves self-control of the device through the siphon principle and places the anoxic denitrification zone upstream, fully utilizing the remaining carbon source in the upstream process to facilitate denitrification. However, the deep pool of this device results in less air (oxygen) being absorbed by the deep packing material during the tidal reoxygenation stage, leading to incomplete nitrification. Chinese patent CN113321369A discloses a tidal flow constructed wetland that simultaneously removes nitrogen and phosphorus. By adding pyrite, it promotes sulfur-oxidizing bacteria to carry out sulfur autotrophic denitrification and nitrogen removal under low carbon-to-nitrogen ratio wastewater. The iron ions released in the process have the effect of precipitation and enhanced phosphorus removal. However, during the tidal reoxygenation process, pyrite generates a large amount of sulfate ions under oxygen-rich conditions, which in turn causes new pollutants to appear in the effluent. Summary of the Invention

[0006] The first objective of this invention is to provide a tidal flow artificial wetland for treating rural domestic sewage, addressing the aforementioned problems.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An artificial wetland for treating rural domestic sewage includes a concrete impermeable layer, which is disposed at the bottom and around the perimeter of the pool. Within the concrete impermeable layer, from bottom to top, are a uniformly distributed water distribution pipe layer, a first filler layer, a second filler layer, a third filler layer, and a covering layer.

[0009] The uniformly distributed water pipe layer is provided with an inlet pipe at one end, the third filler layer is provided with an outlet pipe at the bottom, the third filler layer is provided with an air pipe, and wetland plants are planted on the covering layer.

[0010] The first packing layer is a mixture of slow-release carbon source and alkali source, the second packing layer is a mixture of sulfur and iron, the third packing layer is a filter adsorption packing, and the covering layer is a gravel packing.

[0011] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0012] As a preferred technical solution of the present invention: the slow-release carbon source and alkali source mixed filler is selected from rural waste (such as straw and corn cob) with a particle size of 20-50mm, which is pre-treated by crushing and then mixed with limestone with a particle size of 50-100mm in a 1:1 ratio.

[0013] As a preferred technical solution of the present invention: the sulfur-iron mixed filler is made of 10-20mm sulfurite, pyrite and zero-valent iron mixed in a ratio of 1:8:1.

[0014] As a preferred technical solution of the present invention: the filter adsorption packing is a packing with rapid adsorption and filtration function, and the particle size is 5-10mm.

[0015] As a preferred embodiment of the present invention, the gravel filler has a particle size of 20-50 mm and a covering layer thickness of 5-10 cm.

[0016] As a preferred embodiment of the present invention, the volume ratio of the first filler layer to the second filler layer is 1:2-3, and the volume ratio of the first filler layer to the third filler layer is 1:8-10.

[0017] As a preferred embodiment of the present invention, the water outlet pipe is a siphon water outlet pipe.

[0018] As a preferred technical solution of the present invention: the vent pipes are distributed in a grid pattern, with the top being higher than the covering layer and communicating with the atmosphere, and the bottom being slightly higher than the second packing layer and not communicating with the second packing layer, and the pipe wall is provided with small vent holes.

[0019] The second objective of this invention is to provide a method for controlling tidal flow constructed wetlands for rural domestic sewage.

[0020] Therefore, the above-mentioned objective of the present invention is achieved through the following technical solution:

[0021] A method for controlling tidal flow constructed wetlands for treating rural domestic sewage, the method being based on the aforementioned tidal flow constructed wetlands for rural domestic sewage, and comprising the following steps:

[0022] S1: During the flooding stage, rural domestic sewage is collected and sent to the uniform water distribution pipe layer through the inlet pipe for uniform water distribution. The sewage flows from bottom to top. When passing through the first packing layer, the carbon source and limestone release organic matter and a certain alkalinity to improve the sewage quality. During the flooding process, the filter adsorption packing in the third packing layer quickly adsorbs pollutants in the sewage.

[0023] S2: Drainage stage. When the water level in the wetland is higher than the highest point of the siphon pipe, the siphon effect is formed, and the wetland drains quickly. When the water level is lower than the bottom of the siphon pipe, air enters the siphon pipe, the siphon effect is destroyed, and water discharge stops. Oxygen in the air is quickly drawn into the pores of the bed matrix due to the negative pressure of drainage and the gap force. The function of the air pipe is to facilitate the entry of air into the deep filter media and reduce the mass transfer resistance. Under oxygen-rich conditions, microorganisms consume oxygen to decompose organic matter and carry out nitrification. At the same time, the first and second packing layers are still submerged. The zero-valent iron in the second packing layer reacts quickly with the excess oxygen to prevent the sulfur in pyrite and sulfur from being oxidized into sulfate ions and released into the water, thus polluting the water quality.

[0024] S3: Second round of flooding. When the second round of water intake arrives, the packing material is submerged again. The oxygen in the water is rapidly consumed by microorganisms, forming an anaerobic environment. While adsorbing and retaining pollutants, the oxygen-rich nitrification products in the drainage stage are denitrified, and TN is removed from the device in the form of nitrogen.

[0025] Throughout the process, calcium ions released from the first packing layer and metal ions released from the second packing layer combine with phosphates to form precipitates, thus simultaneously removing nitrogen and phosphorus from the wastewater.

[0026] This invention provides a tidal flow constructed wetland and its control method for treating rural domestic sewage, which has the following beneficial effects: The pyrite (mainly FeS2) in the first packing layer provides a growth substrate for sulfur-autotrophic denitrifying bacteria; iron ions can react with phosphate to precipitate and remove phosphorus; agricultural waste slowly releases carbon sources to improve the nutrient ratio, which is conducive to the denitrification process; limestone can provide the required alkalinity for nitrification, which is also conducive to the nitrification process; calcium ions help solidify phosphate, achieving nitrogen and phosphorus removal; the second packing layer contains zero-valent iron, which slows down the oxidation rate of pyrite, reduces the generation of sulfate ions, ensures the quality of effluent, and contains a mixture of... A fixed proportion of zero-valent iron can react with excess oxygen in the air during the drainage and reoxygenation stage, slowing down the oxidation of pyrite and ensuring water quality. Sulfurite promotes the growth of sulfur-autotrophic denitrifying bacteria. The siphon outlet design adapts to water volume fluctuations, quickly intercepting pollutants and achieving anaerobic denitrification during the wet season, and realizing reoxygenation and nitrification during the dry season, reducing investment and saving costs. At the same time, the siphon inlet is located above the second packing layer, ensuring that the first and second packing layers are always submerged, which is conducive to the cultivation and activity of sulfur-autotrophic denitrifying bacteria. The grid-shaped aeration pipe setting improves the reoxygenation efficiency of the deep packing zone and enhances nitrification capacity. Attached Figure Description

[0027] Figure 1 This is an overall structural diagram of the tidal flow constructed wetland for treating rural domestic sewage provided by the present invention.

[0028] In the diagram: 1-First filler layer; 2-Second filler layer; 3-Third filler layer; 4-Covering layer; 5-Wetland plants; 6-Uniformly distributed water pipe layer; 7-Inlet pipe; 8-Outlet pipe; 9-Ventilation pipe; 10-Concrete impermeable layer. Detailed Implementation

[0029] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0030] like Figure 1 As shown, an artificial wetland for treating rural domestic sewage includes a concrete impermeable layer 10, which is disposed at the bottom and around the perimeter of the pool. Within the concrete impermeable layer 10, from bottom to top, are a uniformly distributed water distribution pipe layer 6, a first filler layer 1, a second filler layer 2, a third filler layer 3, and a covering layer 4.

[0031] A water inlet pipe 7 is provided at one end of the uniformly distributed water pipe layer 6, a water outlet pipe 8 is provided at the bottom of the third filler layer 3, and an air vent pipe 9 is provided inside the third filler layer 3. Wetland plants 5 are planted on the covering layer 4, and the wetland plants 5 are preferably local dominant wetland plant species.

[0032] The first packing layer 1 is a mixed packing material of slow-release carbon source and alkali source, the second packing layer 2 is a mixed packing material of sulfur and iron, the third packing layer 3 is a filter adsorption packing material, and the covering layer 4 is a gravel packing material.

[0033] The slow-release carbon source and alkali source mixed filler uses rural waste such as straw and corn cobs with a particle size of 20-50mm. After crushing and pretreatment, it is mixed with limestone with a particle size of 50-100mm in a 1:1 ratio.

[0034] The sulfur-iron mixed filler is made of 10-20mm sulfurite, pyrite and zero-valent iron mixed in a ratio of 1:8:1.

[0035] The filter adsorption packing is a packing material with rapid adsorption and filtration function, such as zeolite, sepiolite, activated carbon, and a certain proportion of their mixture, with a particle size of 5-10mm.

[0036] The gravel filler has a particle size of 20-50mm, and the cover layer thickness is 5-10cm.

[0037] The volume ratio of the first packing layer 1 to the second packing layer 2 is 1:2-3, and the volume ratio of the first packing layer 1 to the third packing layer 3 is 1:8-10.

[0038] The water outlet pipe 8 is a siphon water outlet pipe, with the water inlet located 5cm above the second packing layer 2, and the highest point of the siphon water outlet pipe being 5-10cm above the top of the cover layer 4.

[0039] The ventilation pipes 9 are arranged in a grid pattern. The top is higher than the cover layer 4 and is connected to the atmosphere. The bottom is slightly higher than the second packing layer 2 and is not connected to the second packing layer 2. The pipe wall is provided with small ventilation holes.

[0040] The capacity of tidal flow constructed wetlands is approximately 60-65% of the daily discharge of rural domestic sewage.

[0041] This invention also provides a method for controlling tidal flow constructed wetlands for treating rural domestic sewage as described above, comprising the following steps:

[0042] S1: During the flooding stage, rural domestic sewage is collected and sent to the uniform water distribution pipe layer through the inlet pipe for uniform water distribution. The sewage flows from bottom to top. When passing through the first packing layer, the carbon source and limestone release organic matter and a certain alkalinity to improve the sewage quality. During the flooding process, the filter adsorption packing in the third packing layer quickly adsorbs pollutants in the sewage.

[0043] S2: Drainage stage. When the water level in the wetland is higher than the highest point of the siphon pipe, the siphon effect is formed, and the wetland drains quickly. When the water level is lower than the bottom of the siphon pipe, air enters the siphon pipe, the siphon effect is destroyed, and water discharge stops. Oxygen in the air is quickly drawn into the pores of the bed matrix due to the negative pressure of drainage and the gap force. The function of the air pipe is to facilitate the entry of air into the deep filter media and reduce the mass transfer resistance. Under oxygen-rich conditions, microorganisms consume oxygen to decompose organic matter and carry out nitrification. At the same time, the first and second packing layers are still submerged. The zero-valent iron in the second packing layer reacts quickly with the excess oxygen to prevent the sulfur in pyrite and sulfur from being oxidized into sulfate ions and released into the water, thus polluting the water quality.

[0044] S3: Second round of flooding. When the second round of water intake arrives, the packing material is submerged again. The oxygen in the water is rapidly consumed by microorganisms, forming an anaerobic environment. While adsorbing and retaining pollutants, the oxygen-rich nitrification products in the drainage stage are denitrified, and TN is removed from the device in the form of nitrogen.

[0045] Throughout the process, calcium ions released from the first packing layer and metal ions released from the second packing layer combine with phosphates to form precipitates, thus simultaneously removing nitrogen and phosphorus from the wastewater.

[0046] Specifically, the aforementioned tidal flow constructed wetland for treating rural domestic sewage is implemented through the following device:

[0047] The pilot-scale apparatus consists of an acrylic column with a diameter of 30 cm and a height of 90 cm. The column is equipped with water distribution pipes from bottom to top, a 5 cm thick layer of mixed corn cob and limestone filler, a 15 cm thick layer of mixed sulfur stone, pyrite and zero-valent iron filler, a 50 cm thick layer of zeolite and a 5 cm thick layer of gravel. Reeds are planted on top of the gravel.

[0048] The main ventilation pipe has a diameter of 3cm, the branch pipe has a diameter of 2cm, the branch pipe spacing is 10cm, the branch pipe opening diameter is 0.5cm, the main pipe height is 60cm, it is buried in the zeolite layer and gravel layer, and the top is 5cm above the gravel layer.

[0049] The siphon tube has a diameter of 2cm, the highest point of the siphon tube is 5cm above the top of the gravel layer, and the bottom of the siphon tube is 2cm above the sulfur-iron mixed filler layer.

[0050] The above specific embodiments are used to explain and illustrate the present invention, and are only preferred embodiments of the present invention, not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A tidal flow constructed wetland for treating rural domestic sewage, comprising a concrete impermeable layer (10), wherein the concrete impermeable layer (10) is disposed at the bottom and around the perimeter of the pool, characterized in that: The concrete anti-seepage layer (10) is provided with a uniform water distribution pipe layer (6), a first filler layer (1), a second filler layer (2), a third filler layer (3), and a covering layer (4) from bottom to top. The uniform water distribution pipe layer (6) is provided with an inlet pipe (7) at one end, the third filler layer (3) is provided with an outlet pipe (8) at the bottom, the third filler layer (3) is provided with an air vent (9), and wetland plants (5) are planted on the covering layer (4). The first packing layer (1) is a mixture of slow-release carbon source and alkali source, the second packing layer (2) is a mixture of sulfur and iron, the third packing layer (3) is a filter adsorption packing, and the cover layer (4) is a gravel packing.

2. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The slow-release carbon source and alkali source mixed filler is made of rural waste (such as straw and corn cobs) with a particle size of 20-50mm. After crushing and pretreatment, it is mixed with limestone with a particle size of 50-100mm in a 1:1 ratio.

3. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The sulfur-iron mixed filler is made of 10-20mm sulfurite, pyrite and zero-valent iron mixed in a ratio of 1:8:

1.

4. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The filter adsorption packing is a packing with rapid adsorption and filtration function, and the particle size is 5-10mm.

5. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The gravel filler has a particle size of 20-50 mm and a covering layer thickness of 5-10 cm.

6. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The volume ratio of the first filler layer (1) to the second filler layer (2) is 1:2-3, and the volume ratio of the first filler layer (1) to the third filler layer (3) is 1:8-10.

7. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The outlet pipe (8) is a siphon outlet pipe.

8. The tidal flow constructed wetland for treating rural domestic sewage according to claim 1, characterized in that: The ventilation pipe (9) is arranged in a grid pattern, with the top being higher than the covering layer (4) and communicating with the atmosphere, and the bottom being slightly higher than the second packing layer (2) and not communicating with the second packing layer (2). The pipe wall is provided with ventilation holes.

9. A method for controlling tidal flow constructed wetlands for treating rural domestic sewage, characterized in that: The control method is based on an artificial wetland for rural domestic sewage as described in any one of claims 1-9, and includes the following steps: S1: During the flooding stage, rural domestic sewage is collected and sent to the uniform water distribution pipe layer through the inlet pipe for uniform water distribution. The sewage flows from bottom to top. When passing through the first packing layer, the carbon source and limestone release organic matter and a certain alkalinity to improve the sewage quality. During the flooding process, the filter adsorption packing in the third packing layer quickly adsorbs pollutants in the sewage. S2: During the drainage stage, when the water level in the wetland is higher than the highest point of the siphon pipe, the siphon effect is formed, and the wetland drains quickly. When the water level is lower than the bottom of the siphon pipe, air enters the siphon pipe, the siphon effect is destroyed, and water discharge stops. Oxygen in the air is rapidly drawn into the pores of the bed matrix due to the negative pressure of drainage and the gap force. The function of the ventilation pipe is to facilitate the entry of air into the deep filter media and reduce the mass transfer resistance. Under oxygen-rich conditions, microorganisms consume oxygen to decompose organic matter and carry out nitrification. At the same time, the first and second packing layers are still submerged. The zero-valent iron in the second packing layer reacts rapidly with the excess oxygen to prevent the sulfur in pyrite and sulfur from being oxidized into sulfate ions and released into the water, thus polluting the water quality. S3: Second round of flooding. When the second round of water intake arrives, the packing material is submerged again. The oxygen in the water is rapidly consumed by microorganisms, forming an anaerobic environment. While adsorbing and retaining pollutants, the oxygen-rich nitrification products in the drainage stage are denitrified, and TN is removed from the device in the form of nitrogen.

10. The method for controlling tidal flow constructed wetlands for treating rural domestic sewage according to claim 9, characterized in that: Throughout the process, calcium ions released from the first packing layer and metal ions released from the second packing layer combine with phosphates to form precipitates, thus simultaneously removing nitrogen and phosphorus from the wastewater.

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