A denitrification artificial wetland purification method suitable for sewage plant tail water

Abstract

The invention is applicable to the denitrification artificial wetland purification method of tail water of sewage treatment plant, and effectively solves the problems of low nitrogen and phosphorus removal capacity of wetland system and poor pollution purification effect in winter. The tail water of sewage treatment plant enters the biological enhanced clarification tank, and the cellulose carbon source slowly releases the biodegradable carbon source after soaking to improve the biodegradability, and the aquatic plants reduce the suspended matter; the tail water flows into the upward vertical subsurface flow artificial wetland, and the microorganisms attached to the inner surface of the mixed matrix deeply denitrify the tail water through denitrification, and the upper surface of the wetland is planted with emergent plants, and photosynthesis reoxygenation prevents the dissolved oxygen concentration in the tail water from being too low and stinking; the effluent of the vertical subsurface flow artificial wetland enters the surface flow artificial wetland, and the surface flow wetland is provided with a water level regulating water distribution pipeline, and the dissolved oxygen concentration of the water body is further guaranteed by waterfall reoxygenation, and the reducing matrix in the wetland degrades organic matter through internal electrolysis, and the effluent can be better than the surface water Class IV requirement, and the treatment effect is good, the operation cost is low, waste is turned into treasure, and the ecological landscape effect is good.

Description

Technical Field

[0001] The invention relates to an ecological purification technology for polluted water bodies, in particular to a denitrification artificial wetland purification method suitable for tail water of a sewage plant. Background Art

[0002] At present, the removal of nitrogen and phosphorus pollutants in water bodies is a difficult problem in sewage treatment. Most rivers lack natural runoff, and the main source of river water is sewage treatment plant tailwater. Most sewage treatment plant tailwater implements the Class A discharge standard (TN≤15mg / L, TP≤0.5mg / L), which is different from the surface water environmental quality standard. Low C / N, high TN and nitrate nitrogen concentrations are typical characteristics of sewage plant tailwater.

[0003] As a new ecological sewage purification technology, artificial wetland engineering of tailwater of sewage treatment plant is an effective means to eliminate the water quality gap between sewage treatment plant effluent and surface water. However, artificial wetlands have also exposed many problems in the actual application process, such as being easily affected by climatic conditions, limited denitrification and phosphorus removal capacity, easy saturation and clogging of the matrix, easy to be affected by plant species, large area, unreasonable management, irregular design, single ecological service function, etc. These problems have affected the sewage treatment effect of artificial wetlands to a certain extent, shortened the service life of artificial wetlands, and limited the promotion and application of artificial wetlands.

[0004] At present, the key technologies in the design of artificial wetland sewage treatment systems include wetland hydraulic retention time, water conductivity, surface load rate, substrate depth, length and width of treatment units and their ratio, layout of inlet and outlet water systems, and anti-seepage materials. However, there are still many technical problems to be solved, such as wetland system process improvement and treatment system optimization combination, improving nitrogen and phosphorus removal capabilities, ensuring treatment effects in low temperature seasons, and reducing land occupation. Summary of the invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a denitrification artificial wetland purification method suitable for sewage plant tail water, which can effectively solve the problems of low nitrogen and phosphorus removal capacity of the wetland system, poor landscape effect, and poor pollution purification effect in winter.

[0006] The technical solution provided by the present invention is a denitrification artificial wetland purification method applicable to tail water of a sewage plant, comprising the following steps:

[0007] (1) Bio-enhanced clarification:

[0008] A bio-enhanced clarification pool is constructed. The bio-enhanced clarification pool is divided into a filling area and an ecological pond. A net cage is placed on the wall of the filling area. The net cage is filled with suspended balls of φ6-12 mm. The suspended balls are filled with a cellulose carbon source - corn cobs. Dermatophytes, water chestnuts or their composite aquatic plants are planted in the ecological pond.

[0009] The tailwater from the sewage treatment plant first enters the filler area of ​​the bio-enhanced clarification tank, where the corn cobs are soaked to release biodegradable cellulose carbon sources, improving the bioavailability of the tailwater. The tailwater is diverted through the filler area and flows into the ecological pond, where the concentration of suspended solids in the water is reduced by aquatic plants.

[0010] (2) Construct an upstream vertical subsurface artificial wetland to flexibly adjust the water level and prevent the tail water from stinking:

[0011] a) Construction of the upward vertical subsurface flow artificial wetland. The length-width ratio of the substrate bed is 2:1, the substrate bed is 1.2~2.0m deep, the bottom of the bed is paved with plain soil and compacted, then the geotextile anti-seepage cloth is laid, and finally the top is tamped with clay; the end of the water distribution pipe is sealed, the front end of the water collection pipe is sealed, and a 360° rotatable elbow made of PVC is installed at the end. When the outside temperature is low, the rotatable elbow can be adjusted to keep the water level of the substrate bed at different heights to adapt to seasonal changes;

[0012] A mixed matrix of gravel, zeolite, ceramsite and rice stone is laid from bottom to top in the wetland, with a matrix porosity of 35-45%;

[0013] The surface layer of the wetland is planted with emergent plants such as calamus, reed, and Siberian iris;

[0014] The tail water after biological enhancement clarification enters the upstream vertical subsurface artificial wetland. Under the photosynthesis of emergent plants, photosynthetic reoxygenation prevents the tail water from stinking due to low dissolved oxygen concentration, and then flows into the surface flow artificial wetland.

[0015] (3) Construct surface flow artificial wetlands to ensure the water quality of the effluent:

[0016] a) Construct a surface flow artificial wetland. The length-width ratio of the surface flow artificial wetland monomer is 4:1. The substrate bed is 0.4~1.0m deep. The bottom of the bed is paved with plain soil and compacted, and then geotextile anti-seepage cloth is laid. Finally, clay is tamped on top. The bottom of the wetland is paved with a mixed substrate of reduced matrix iron filings and active calcium;

[0017] b) 360° rotatable elbows are installed on both sides of the outer wall of the surface flow wetland distribution channel;

[0018] c) Planting water lilies, Hydrilla verticillata or a mixture of these aquatic plants in the free water areas of wetlands;

[0019] The tail water treated by the upstream vertical subsurface artificial wetland flows into the surface flow artificial wetland, where the organic matter is degraded by electrolysis in the mixed matrix. The outlet is reoxygenated by waterfalls to further ensure the dissolved oxygen concentration in the water body. The synergistic effects of physical, chemical and microbial factors jointly ensure the water quality of the wetland outlet.

[0020] The equipment of the present invention is easy to install and produce, and the method is simple to operate. The tail water of the sewage treatment plant first enters the biological enhanced clarification tank (a net cage is placed on the pool wall of the front-stage filling area, and the net cage is filled with suspended balls of φ6-12 mm, and the suspended balls are filled with cellulose carbon sources, and aquatic plants are planted in the terminal ecological pond). The cellulose carbon source is slowly released after soaking, and the biodegradable carbon source is improved. The aquatic plants can reduce the suspended matter in the tail water; then the tail water flows by gravity into the upward vertical subsurface flow artificial wetland, and the microorganisms attached to the inner surface of the mixed matrix in the wetland deeply denitrify the tail water through denitrification, and the surface layer of the wetland is planted with emergent plants, and the photosynthetic reoxygenation of the plants prevents the dissolved oxygen concentration in the tail water from being too low and stinking; the effluent of the vertical subsurface flow artificial wetland enters the surface flow artificial wetland, and the surface flow wetland is provided with a water level regulating water distribution pipeline, and the dissolved oxygen concentration of the water body is further guaranteed by waterfall reoxygenation, and the reducing matrix in the wetland degrades organic matter through internal electrolysis, so as to ensure the effluent water quality of the wetland. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart of the process equipment of the present invention. DETAILED DESCRIPTION

[0022] The specific implementation modes of the present invention are described in detail below in combination with specific situations. Example

[0023] In a specific implementation of the present invention, a denitrification artificial wetland purification method suitable for tail water of a sewage plant is implemented by the following steps:

[0024] (1) Bio-enhanced clarification:

[0025] A bio-enhanced clarification pool is constructed. The bio-enhanced clarification pool is divided into a filling area 1 and an ecological pond 3. A net cage 2 is placed on the wall of the filling area. The net cage is filled with suspended balls 4 of φ6-12 mm. The density of the suspended balls is lower than the density of the water body. The filling volume is 60-75%. The suspended balls are filled with a cellulose carbon source - corn cobs, with a particle size of 3 cm-4 cm. Dermatophytes, water chestnuts or their composite aquatic plants 5 are planted in the ecological pond.

[0026] The tailwater of the sewage treatment plant first enters the packing area 1 of the biological enhanced clarification tank, where the corn cobs are soaked to release biodegradable cellulose carbon sources, thereby improving the life of the tailwater; the tailwater is diverted through the packing area 1 and enters the ecological pond 3, where duckweed, water chestnut or their composite aquatic plants 5 are planted to reduce the concentration of suspended matter in the water body and slow down the frequency of matrix blockage in the subsequent upward vertical subsurface artificial wetland, with the hydraulic retention time being no more than 4 hours;

[0027] (2) Construct an upstream vertical subsurface artificial wetland to prevent the tail water from stinking:

[0028] a) Construction of the vertical subsurface artificial wetland with upward flow: the length-width ratio of the 6-unit matrix bed is 2:1, the matrix bed depth is 1.2~2.0m, the bed bottom is paved with 20cm of plain soil and then 450g / m 2 Geotextile anti-seepage cloth, and finally 10cm clay is added to compact it; PVC is used for water distribution pipes and water collection pipes, with a pipe diameter of 15cm, and 0.7cm water distribution holes / water collection holes are opened every 50cm. The end of the water distribution pipe is sealed, the front end of the water collection pipe is sealed, and a 360° rotatable elbow made of PVC is installed at the end. When the outside temperature is low, the rotatable elbow can be adjusted to make the water level of the matrix bed at different heights to adapt to seasonal changes;

[0029] A mixed matrix 8 of gravel with a particle size of 3cm-5cm, zeolite with a particle size of 2cm-3cm, ceramsite with a particle size of 1cm-2cm, and rice stone with a particle size of 0.5cm-1cm is laid from bottom to top in the wetland, and the matrix porosity is 35-40%;

[0030] The surface of the wetland is planted with calamus, reed, cattail, Siberian iris, etc. The planting density is 35-45cm between plants and 35-45cm between rows;

[0031] The tail water after biological enhancement clarification enters the upstream vertical subsurface artificial wetland. Under the photosynthesis of emergent plants, photosynthetic reoxygenation prevents the tail water from stinking due to low dissolved oxygen concentration. The surface hydraulic load of the upstream vertical subsurface artificial wetland is not higher than 0.55m 3 / m 2 d, hydraulic retention time 0.8d~1.5d, then flows into surface flow artificial wetland;

[0032] (3) Construct surface flow artificial wetlands to ensure the water quality of the effluent:

[0033] a) Construct a surface flow artificial wetland. The length-width ratio of the surface flow artificial wetland is 4:1. The substrate bed is 0.4-1.0m deep. The bottom of the bed is paved with 20cm of plain soil and then 450g / m 2 Geotextile anti-seepage cloth, and finally 10cm clay tamping on it, the bottom of the wetland is laid with a reduction matrix iron filings and active calcium mixed matrix 10, the laying thickness is 20cm, and the matrix volume ratio is 2:8;

[0034] b) 360° rotatable elbows made of PVC are installed on both sides of the outer wall of the surface flow wetland drainage channel;

[0035] c) Planting water lilies, Hydrilla verticillata or a mixture of these aquatic plants in free water areas of wetlands11;

[0036] The tailwater treated by the upstream vertical subsurface artificial wetland flows into the surface flow artificial wetland, where the organic matter is degraded by electrolysis in the mixed matrix. The outlet is reoxygenated by waterfall to further ensure the dissolved oxygen concentration of the water body. The synergistic effects of physical, chemical and microbial factors jointly ensure the water quality of the wetland outlet. The surface hydraulic load is ≤0.06m 3 / m 2 ·d. The effluent COD, NH3-N, TP and other water qualities are better than Class IV water standards, and TN ≤ 4.0 mg / L. Example

[0037] In a specific implementation of the present invention, a denitrification artificial wetland purification method suitable for tail water of a sewage plant is provided, wherein the surface of the wetland is planted with calamus, reed, cattail, Siberian iris emergent plants, with a planting density of 40 cm plant spacing and 40 cm row spacing;

[0038] The surface hydraulic load of the vertical subsurface artificial wetland is 0.55m 3 / m 2 ·d, hydraulic retention time 0.8d~1.0d, then it flows into the surface flow artificial wetland.

[0039] The integrated purification system of the present invention is scientifically and rationally designed, easy to produce and construct, has good treatment effect, low operating cost, good ecological landscape effect, and turns waste into treasure. The effluent water quality can be better than the surface water Class IV requirement, and the field test shows that the effect is very good. The relevant experimental data are as follows:

[0040] A wetland project in Henan Province uses the technology described in this invention to treat the tailwater of a sewage treatment plant. The wetland is designed to have a scale of 60,000 m 3 / d, the wetland system adopts the combined process of "biologically enhanced clarifier + upstream vertical subsurface artificial wetland + horizontal subsurface artificial wetland + surface flow artificial wetland + stabilization pond". The tail water of the sewage treatment plant in the industrial agglomeration area (implementing the first-level A emission standard) flows into the biologically enhanced clarifier by gravity through the culvert. Denitrification fillers are placed in the biologically enhanced clarifier. After biological retention and clarification, the tail water flows into the upstream vertical subsurface distribution channel by gravity. Reeds, calamus, cattails, Siberian iris and other emergent plants are planted on the surface of the wetland to prevent the wetland from denitrification and oxygen consumption causing the tail water to stink. The effluent from the vertical subsurface wetland enters the horizontal subsurface wetland distribution channel, and the oxygen-enriched tail water passes through the horizontal subsurface wetland to further remove oxygen-consuming pollutants. A rotating elbow is set in the effluent channel to achieve water level regulation while waterfall reoxygenation further ensures the dissolved oxygen concentration of the tail water. The effluent from the horizontal subsurface wetland enters the surface flow wetland. Mixed matrix is ​​laid and aquatic plants are planted in the surface flow wetland to ensure the effluent water quality of the wetland. Long-term monitoring data from local monitoring stations and third-party monitoring data show that wetland effluent COD, ammonia nitrogen, TP and other water quality indicators are better than the surface water Class IV water standard of the "Surface Water Environmental Quality Standard" (GB3838-2002), and the effluent TN is ≤4.0mg / L.

[0041] The present invention compared the carbon release effects of reed straw, sycamore bark, corn cobs, etc. through batch soaking experiments. The results showed that the B / C of sewage treatment plant tail water can be increased from 0.18 to ≥0.3 by soaking corn cobs, which creates conditions for denitrification by submerged flow wetlands. The average removal rate of total nitrogen by submerged flow wetlands can reach 71%, and the effluent TN is ≤4.0 mg / L.

[0042] Aiming at the typical characteristics of sewage plant tail water, such as low C / N, high TN and nitrate nitrogen concentrations, innovatively integrated wetland processes with different functions are used. First, the tail water of the sewage plant enters the biological enhanced clarification tank, which adjusts the water quality such as B / C and DO while minimizing the suspended solids, delaying the subsequent blockage cycle of the subsurface wetland; the reason why the subsurface wetland is selected as an upward vertical subsurface wetland is that while strengthening the denitrification, the surface emergent plant roots on the substrate bed are used for reoxygenation, and the effluent DO (dissolved oxygen) concentration is ≥3.5mg / L, which prevents excessive oxygen consumption during the denitrification process and the water body from stinking, and also provides sufficient DO for the subsequent surface flow wetland carbon removal and phosphorus removal; corn cobs release carbon sources irregularly, which is To ensure the effluent effect of the wetland purification system and enhance the carbon removal and phosphorus removal capacity of the surface flow wetland, a mixed matrix such as iron filings and active calcium is laid in the surface flow wetland, and iron-carbon micro-electrolysis and chemical precipitation are used to remove carbon and phosphorus. The setting of a 360° rotatable elbow, combined with the operation mode of tidal flow, can further delay the blockage of the wetland matrix bed, and adjust the water level of the matrix bed in time to ensure the effect of the wetland system, especially in winter. The main control indicators of the wetland effluent COD, ammonia nitrogen, TP, etc. are better than those of surface water Class IV, and the effluent TN is ≤4.0mg / L.

[0043] The matrix is ​​the basis for the survival of wetland plants and microorganisms. On the one hand, these matrices provide a stable attachment surface for the growth of microorganisms, and on the other hand, they provide carriers and nutrients for aquatic plants. Different matrices have different removal capabilities for different pollutants in sewage. Combined with the water quality characteristics of sewage plant effluent, a variety of matrices such as zeolite, expanded clay, gravel, etc. with strong carbon removal, nitrogen removal and phosphorus removal are selected. If different matrices are mixed and laid, the porosity of the filler will be reduced, the water flow distribution will be affected, the hydraulic state will be changed, the permeability of the matrix will be affected, and the removal effect will be affected. Different matrices are laid in layers, and the layered laying should be as uniform as possible. The average removal rates of COD, ammonia nitrogen, TP and TN in the upward vertical submerged flow wetland were 38.52%, 74.16%, 42.78% and 70.55% respectively. The effect is very good and was unexpected.

[0044] The above clearly shows that compared with the prior art, the present invention has obvious technical advantages. On the basis of learning from the CASS sewage treatment process, a new type of biological enhanced clarification tank process is proposed, and a new type of denitrification artificial wetland integrated purification system suitable for sewage plant tail water is integrated and innovated. The water quality of the effluent COD, NH3-N, TP, etc. of the integrated purification system is better than the surface water Class IV water standard of the "Surface Water Environmental Quality Standard" (GB3838-2002), and the effluent TN is ≤4.0mg / L.

[0045] A rotatable elbow is installed in the upstream vertical subsurface flow and surface flow wetland water collection system, which can conveniently adjust the water level of the system according to the characteristics of the climate environment. Combined with insulation measures such as plant residues or film covering, it can ensure the treatment effect of the new denitrification artificial wetland integrated purification system in winter, and the water temperature of the vertical subsurface flow wetland is not lower than 7°C;

[0046] The application of industrial waste, agricultural waste and other materials in wetland construction is not only conducive to the resource utilization of waste, but also improves the biodegradability of wastewater. The B / C can be increased to ≥0.3. While ensuring the denitrification effect of the wetland, the COD removal effect is enhanced through iron-carbon micro-electrolysis to ensure the water quality of the effluent. The integrated purification system of the present invention has the advantages of good treatment effect, low operating cost, turning waste into treasure, and good ecological landscape effect. The operating cost can be reduced by more than 30%. At the same time, the effluent can be better than the Class IV requirement of surface water. It is a major innovation in the treatment of tailwater from sewage treatment plants and has significant economic and social benefits.

Claims

1. A denitrification artificial wetland purification method suitable for sewage plant tail water, characterized in that: This is accomplished by the following steps: 1) Bio-enhanced clarification: A bio-enhanced clarification tank is constructed. The bio-enhanced clarification tank is divided into a filling area (1) and an ecological pond (3). A net cage (2) is placed on the wall of the filling area. The net cage is filled with suspended balls (4) of φ6-12 mm. The density of the suspended balls is lower than the density of the water body. The filling volume is 60-75%. The suspended balls are filled with a cellulose carbon source - corn cobs, with a particle size of 3 cm-4 cm. Dermatophytes, water chestnuts or their composite aquatic plants (5) are planted in the ecological pond. The tailwater from the sewage treatment plant first enters the packing area (1) of the bio-enhanced clarification tank, where the corn cobs are soaked to release biodegradable cellulose carbon sources, thereby improving the bioavailability of the tailwater. The tailwater is diverted through the packing area (1) and enters the ecological pond (3), where duckweed, water chestnuts, or a composite aquatic plant (5) thereof are planted to reduce the concentration of suspended solids in the water body and slow down the frequency of matrix blockage in the subsequent upstream vertical subsurface flow artificial wetland. The hydraulic retention time is no more than 4 hours. 2) Construct an upward vertical subsurface artificial wetland to prevent the tail water from stinking: a) Construction of an upward vertical subsurface artificial wetland: the length-to-width ratio of the substrate bed (6) is 2:1, the substrate bed depth is 1.2-2.0 m, 20 cm of plain soil is laid on the bottom of the bed and compacted, and then 450 g / m 2 Geotextile anti-seepage cloth, and finally 10cm clay is added to compact it; PVC is used for water distribution pipes and water collection pipes, with a pipe diameter of 15cm, and 0.7cm water distribution holes / water collection holes are opened every 50cm. The end of the water distribution pipe is sealed, the front end of the water collection pipe is sealed, and a 360° rotatable elbow made of PVC is installed at the end. When the outside temperature is low, the rotatable elbow can be adjusted to make the water level of the matrix bed at different heights to adapt to seasonal changes; A mixed matrix (8) of gravel with a particle size of 3 cm to 5 cm, zeolite with a particle size of 2 cm to 3 cm, ceramsite with a particle size of 1 cm to 2 cm, and rice stone with a particle size of 0.5 cm to 1 cm is laid from bottom to top in the wetland, with a matrix porosity of 35 to 40%; The surface layer of the wetland is planted with calamus, reed, cattail, Siberian iris (7), with a planting density of 35-45 cm between plants and 35-45 cm between rows; The tail water after biological enhancement clarification enters the upstream vertical subsurface artificial wetland. Under the photosynthesis of emergent plants, photosynthetic reoxygenation prevents the tail water from stinking due to low dissolved oxygen concentration. The surface hydraulic load of the upstream vertical subsurface artificial wetland is not higher than 0.55m 3 / m 2 d, hydraulic retention time 0.8d~1.5d, then flows into surface flow artificial wetland; 3) Construct surface flow artificial wetlands to ensure the water quality of the effluent: a) Constructing a surface flow artificial wetland. The length-width ratio of the surface flow artificial wetland (9) is 4:

1. The substrate bed is 0.4-1.0 m deep. The bottom of the bed is paved with 20 cm of plain soil and then 450 g / m 2 Geotextile anti-seepage cloth, and finally 10cm of clay is added to compact it. The bottom of the wetland is paved with a mixed matrix of iron filings and active calcium (10), with a thickness of 20cm and a matrix volume ratio of 2:8; b) 360° rotatable elbows made of PVC are installed on both sides of the outer wall of the surface flow wetland drainage channel; c) Planting water lilies, Hydrilla verticillata or a mixture of these aquatic plants in free water areas of wetlands (5); The tailwater treated by the upstream vertical subsurface artificial wetland flows into the surface flow artificial wetland, where the organic matter is degraded by electrolysis in the mixed matrix. The outlet is reoxygenated by waterfall to further ensure the dissolved oxygen concentration of the water body. The synergistic effects of physical, chemical and microbial factors jointly ensure the water quality of the wetland outlet. The surface hydraulic load is ≤0.06m 3 / m 2 ·d. The effluent COD, NH3-N and TP water quality indicators are better than Class IV water standards, and TN ≤ 4.0 mg / L.

2. The denitrification artificial wetland purification method suitable for sewage plant tail water according to claim 1, characterized in that: The surface layer of the wetland is planted with calamus, reed, cattail and Siberian iris emergent plants (7) with a planting density of 40 cm between plants and 40 cm between rows.

3. The denitrification artificial wetland purification method suitable for sewage plant tail water according to claim 1, characterized in that: The surface hydraulic load of the vertical subsurface artificial wetland is 0.55m 3 / m 2 ·d, hydraulic retention time 0.8d~1.0d, then it flows into the surface flow artificial wetland.

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