CN113979546A

CN113979546A - Tidal flow regulated and controlled magnetite constructed wetland

Info

Publication number: CN113979546A
Application number: CN202111438953.2A
Authority: CN
Inventors: 陈一; 秦豪; 严俊; 易多; 郭富成
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2021-11-25
Filing date: 2021-11-25
Publication date: 2022-01-28

Abstract

The invention discloses a tidal flow regulated and controlled magnetite constructed wetland which is characterized by comprising a wetland main body, wherein a bearing layer, a reaction layer and a surface layer are sequentially paved in the wetland main body from bottom to top; wetland plants are planted on the surface layer, and the reaction layer is formed by filling natural magnetite; the top of the wetland main body is provided with a water inlet pipe, the bottom of the wetland main body is provided with a water outlet, the water outlet is connected with a siphon pipe, and the other end of the siphon pipe is connected with a water tank; the highest point of the siphon is lower than the water inlet pipe, and the liquid level of the water tank is lower than the water outlet. The invention has the advantages of delaying wetland blockage, being beneficial to improving the removal capability of organic matters, ammonia nitrogen, nitrate and phosphorus, and the like.

Description

Tidal flow regulated and controlled magnetite constructed wetland

Technical Field

The invention relates to the technical field of artificial wetland technology and sewage treatment, in particular to a tidal flow regulated magnetite artificial wetland.

Background

The artificial wetland is a sewage treatment technology for strengthening the purification capacity of the natural wetland through artificial construction and management control on the basis of purifying sewage by the natural wetland, and is a composite system consisting of a water-permeable substrate, plants, animals, a water body and microorganisms. The traditional artificial wetland mainly removes ammonia nitrogen through the processes of matrix adsorption, surface oxidation, plant absorption and the like. Because the substrate adsorption capacity, the surface dissolved oxygen content and the plant absorption capacity are limited, the removal capacity of the artificial wetland to ammonia nitrogen is limited and the effect is poor. In addition, for phosphorus compounds, the traditional artificial wetland is mainly removed through processes of substrate adsorption, precipitation, plant absorption and the like. However, the removal rate of phosphorus in the artificial wetland is gradually reduced after the artificial wetland is operated for a long time due to the limitation of substrate adsorption capacity and plant biomass. Along with the long-time operation of the wetland, organic matters such as a biological film and the like on the substrate are continuously accumulated, and finally the wetland is blocked.

At present, the artificial wetland technology plays an important role in sewage treatment of small towns, and the sewage is not treated by a main sewage treatment structure, so that the sewage has higher organic load, ammonia nitrogen and phosphorus concentration. For the sewage, the removal capacity of the artificial wetland for organic matters and ammonia nitrogen is greatly limited by the diffusion rate of dissolved oxygen, and the removal of phosphorus is only limited by filler adsorption, plant absorption and precipitation, so that the phosphorus can not be removed while the organic matters and ammonia nitrogen are efficiently removed, and the blockage of the wetland caused by the accumulation of organic matters can not be relieved.

The automatic regulation of the water level of the wetland by using the siphon is one of the main methods for solving the problem of oxygen deficiency at the bottom of the artificial wetland, for example, the technical proposal of different tidal flow artificial wetlands is respectively disclosed in the patents with the publication number of CN214060071U, the name of the system is "tidal flow artificial wetland sewage purification system", the publication number of CN211770576U, the name of the system is "artificial wetland system integrating horizontal subsurface flow and tidal flow", the publication number of CN206457320U, the name of the system for treating rural domestic sewage by intermittent aeration tidal flow artificial wetland and the like, but the artificial wetland technology utilizing tidal flow regulation still can not remove the phosphorus in the sewage with high efficiency, the mechanism of the tidal flow phosphorus removal is approximately the same as that of the activated sludge method, namely aerobic phosphorus absorption and anaerobic phosphorus release and phosphorus removal by sludge discharge, but the common artificial wetland can not achieve better phosphorus removal effect without sludge discharge and can not relieve the wetland blockage problem caused by the accumulation of organic matters without sludge discharge.

Therefore, the construction of a novel artificial wetland technology with high-efficiency pollutant removal capacity and anti-blocking capacity has important significance for sewage treatment and sustainable resource development.

Disclosure of Invention

Aiming at the defects of the prior art, the technical problems to be solved by the invention are as follows: how to provide a magnetite artificial wetland for tidal flow regulation and control, which can delay wetland blockage and is beneficial to improving the removal capacity of organic matters, ammonia nitrogen, nitrate and phosphorus.

In order to solve the technical problems, the invention adopts the following technical scheme:

the magnetite constructed wetland for tidal flow regulation and control is characterized by comprising a wetland main body, wherein a bearing layer, a reaction layer and a surface layer are sequentially paved in the wetland main body from bottom to top; wetland plants are planted on the surface layer, and the reaction layer is formed by filling natural magnetite; the top of the wetland main body is provided with a water inlet pipe, the bottom of the wetland main body is provided with a water outlet, the water outlet is connected with a siphon pipe, and the other end of the siphon pipe is connected with a water tank; the highest point of the siphon is lower than the water inlet pipe, and the liquid level of the water tank is lower than the water outlet.

Before sewage flows in from the water inlet pipe at the top of the wetland main body, the water level is low, magnetite is in contact with water and air to perform oxidation reaction in a microenvironment and separate out Fe2+ and Fe3+, Fe2+ is further oxidized into Fe3+, and part of Fe3+ reacts with phosphate to generate precipitates to be deposited on the surface of the magnetite. Along with the inflow of sewage, the water level rises and submerges natural magnetite, so that the magnetite is isolated from air to form an anoxic environment, and the anaerobic Fe3+ on the surface of the magnetite is used as an electron acceptor to oxidize ammonia nitrogen and organic matters under the action of microorganisms and is reduced into Fe2 +. Meanwhile, phosphate in a precipitation state is unavailable for plants, and the plants can obtain phosphorus from the surface of magnetite by secreting organic acid, so that the release of Fe3+ and part of Fe2+ can be promoted, and the oxidation of ammonia nitrogen and the decomposition of organic matters are further promoted. In addition, the organic matters can be thoroughly oxidized into carbon dioxide by dissimilatory iron reduction (namely, microorganisms oxidize the organic matters by using high-valence metal ions as electron acceptors under anaerobic conditions), so that the carbon dioxide is discharged out of a wetland system, and Fe3+ is reduced into Fe2 +. The system can not accumulate nitrate nitrogen under anaerobic condition, the microorganisms can remove the nitrate nitrogen through heterotrophic denitrification when organic matters exist, and the microorganisms can also utilize Fe2+ as an electron acceptor to perform autotrophic denitrification after the organic matters are consumed. And (3) with the continuous inflow of the sewage, the water level gradually returns to the highest point of the siphon, the siphon is filled with the sewage to generate a siphon phenomenon, the sewage in the wet land body is gradually discharged, the filler above the water outlet is exposed in the air again, and the reduced Fe2+ is oxidized into Fe3+ again after contacting with the water and the air, and enters the next circulation. Therefore, the constructed wetland has good capability of removing organic matters, ammonia nitrogen, nitrate and phosphorus, and is not easy to block.

Furthermore, the surface layer is formed by filling gravels, and the particle size of the gravels is 0.8-1.2 cm.

The gravel is used as surface packing to filter most suspended matters in the inlet water, so that the inside of the wetland is prevented from being blocked.

Furthermore, the bearing layer is formed by filling gravels, quartz or cobblestones with the grain diameter of 1.5-3 cm.

Gravel, quartz or cobblestone with larger grain diameter and stable structure is used as the filler of the supporting layer to prevent the accumulation of sediment and block the packed bed.

Further, the particle size of the natural magnetite is 1-2 cm.

Further, the highest point of the siphon is higher than the top of the reaction layer.

Therefore, before siphonage is generated on the siphon, the sewage can completely submerge the natural magnetite in the reaction layer, so that all the natural magnetite is isolated from air and is in an anoxic environment, and the reduction of Fe3+ into Fe2+ is facilitated.

Furthermore, the water outlet is positioned at the junction of the bearing layer and the reaction layer.

Therefore, after sewage in the wetland main body is pumped by the siphon, all natural magnetite can be in contact with air, and Fe2+ is oxidized into Fe3+ so as to be beneficial to subsequent circulating water treatment.

Further, the water outlet is provided with a filter grid, and the pores of the filter grid are smaller than the particle size of the natural magnetite.

Thus, the natural magnetite can be prevented from flowing out with the water flow.

Furthermore, an overflow port is arranged on the water tank, and the height of the overflow port is lower than that of the water outlet.

Therefore, the water level of the water tank can be ensured to be lower than the water outlet all the time.

In summary, the invention has the following advantages:

1. the tidal flow magnetite constructed wetland utilizes tidal change to enable the packed bed to be always in aerobic and anaerobic cyclic change, and organic matters and ammonia nitrogen are efficiently removed in the aerobic and anaerobic cyclic change.

2. Magnetite is used as a reaction layer filler, the magnetite is in contact with water and air when the water level is low, oxidation reaction is carried out on the magnetite in a microenvironment and Fe2+ and Fe3+ are separated out, Fe2+ is further oxidized into Fe3+, part of Fe3+ reacts with phosphate to generate precipitates deposited on the surface of the magnetite, Fe3+ on the surface of the magnetite in an anaerobic state along with the rise of the water level is used as an electron acceptor to oxidize ammonia nitrogen and organic matters under the action of microorganisms, and the iron is reduced into Fe2 +.

3. The system can not accumulate nitrate nitrogen under anaerobic conditions, microorganisms can remove the nitrate nitrogen through heterotrophic denitrification when organic matters exist, the microorganisms can also utilize Fe2+ as an electron acceptor to perform autotrophic denitrification after the organic matters are consumed, the siphon tube discharges water in the wetland after the water level reaches a certain height, the filler is exposed in the air again, and the Fe2+ is oxidized into Fe3+ again when being contacted with the water and the air.

Drawings

Fig. 1 is a schematic structural diagram of an embodiment of the present invention.

Fig. 2 to 4 are comparison graphs of total phosphorus, ammonia nitrogen and COD concentration of effluent treated by the artificial wetland and the conventional artificial wetland in anaerobic conditions, respectively.

Fig. 5 is a graph showing a comparison of the porosity after the constructed wetland treatment according to the present embodiment and the conventional constructed wetland treatment.

Detailed Description

The present invention will be described in further detail with reference to examples.

In the specific implementation: as shown in fig. 1 and fig. 2, the magnetite artificial wetland for tidal flow regulation comprises a wetland main body 1, wherein a supporting layer 5, a reaction layer 4 and a surface layer 3 are sequentially paved in the wetland main body 1 from bottom to top; wetland plants 2 are planted on the surface layer 3, and the reaction layer 4 is formed by filling natural magnetite; a water inlet pipe 6 is arranged at the top of the wetland main body 1, a water outlet 7 is arranged at the bottom of the wetland main body, a siphon pipe 8 is connected to the water outlet 7, and a water tank 9 is connected to the other end of the siphon pipe 8; the highest point of the siphon 8 is lower than the water inlet pipe 6, and the liquid level of the water tank 9 is lower than the water outlet 7. Specifically, the water tank 9 is provided with an overflow port, and the height of the overflow port is lower than that of the water outlet 7. The water outlet 7 is positioned at the junction of the supporting layer 5 and the reaction layer 4. In order to prevent the natural magnetite from flowing out of the water outlet with the water, the water outlet 7 has a filter grid, the pores of which are smaller than the particle size of the natural magnetite.

In the embodiment, gravels, quartz or cobblestones with larger particle size and stable structure are used as the filler of the supporting layer, the reference range of the particle size is 1.5-3cm, the height of the filler of the supporting layer is 10cm (the filler of the supporting layer with large particle size prevents the bottom of the wetland from being blocked), natural magnetite is used as the filler of the reaction layer, the reference range of the particle size is 1-2cm, the height of the filler of the reaction layer is 50cm (the height of the reaction layer is used for realizing good aerobic and anaerobic alternation), the gravels are used as the surface filler, the reference range of the particle size is 0.8-1.2cm, and the height of the surface filler is 10cm (the surface filler with small particle size is used for filtering most suspended substances and preventing the inside of the wetland from being blocked).

The wetland plants 2 are emergent aquatic plants such as windmill grass planted in the wetland main body 1 (the windmill grass is evergreen plants and can secrete organic acid in four seasons), the wetland continuously feeds water through the water inlet pipe, in the embodiment, the water retention time of the wetland system is 3 days by adjusting the water inlet flow and designing the size of the wetland, namely the continuous water inlet level of the wetland rises from a water level line II 11 (the lowest water level, namely the height of a water outlet 7) to a water level line I10 (the highest water level, namely the height of the highest point of a siphon pipe 8) for 3 days, and the flow of the siphon pipe is far greater than that of the water inlet pipe so as to ensure that the water level of the system can be lowered from the water level line I10 (the highest water level) to the water level line II 11 (the lowest water level) in a short time (about 1 hour).

In this embodiment, the second water level line is an initial water inlet level, and the height of the second water level line is the joint of the supporting layer and the reaction layer, and the first water level line is a water outlet level, and the height of the first water level line is about 55-60cm higher than that of the second water level line, and the height of the first water level line is to ensure that the reaction layer can completely treat the anaerobic state. The inoculated microorganisms are important when the wetland system starts to operate, sludge (such as mixed sludge of digested methanogenic sludge and activated sludge) containing anaerobic bacteria such as iron ammonia oxidizing bacteria and dissimilatory metal reducing bacteria and aerobic bacteria such as nitrobacteria is inoculated, generally, the system is more suitable for treating small-scale domestic sewage (the specific scale is determined according to the population of a user) in rural areas, the domestic sewage of a plurality of households flows into the wetland system through a water inlet pipeline, pollutants (including ammonia nitrogen, COD (chemical oxygen demand), phosphate, nitrate nitrogen and the like) are removed mainly through physical, biological and chemical actions of a reaction layer filler after entering the wetland system, when the water level rises to a water level line I, a siphon pipe starts to automatically discharge the treated clean water out of the wetland system, the water level drops to a water level II again, and the system continuously treats the inlet water.

Control experiment:

the magnetite constructed wetland and the constructed wetland filled with gravels in the embodiment are respectively adopted to treat domestic sewage with the same water quality, and after the system runs to the stable water outlet, the water quality is detected once every 3 days, and the monitoring is continuously carried out for 24 times.

The experimental data are shown in fig. 2 to 4, in which "gravel" is the experimental data of the water outlet of the control group in which the reaction layer filler is gravel, and "magnetite" is the experimental data of the water outlet of the experimental group in which the reaction layer filler is magnetite. The first-order A marked water concentration lines (dotted lines) in FIGS. 2 to 4 are the first-order A marked water concentrations (0.5mg/L, 5mg/L and 50mg/L) of total phosphorus, ammonia nitrogen and COD, respectively.

It can be seen from the figure that the concentrations of ammonia nitrogen, total phosphorus and COD in the effluent water treated by the magnetite artificial wetland of the embodiment under the anaerobic condition are all obviously lower than those of a control group, and are all kept below the concentration of the first-level A standard effluent water in the long-time treatment process of 72 days, the operation life is long, and the sewage treatment effect is obvious.

As shown in fig. 5, in order to show the change of the porosity before and after the treatment of the sewage by using the magnetite artificial wetland and the artificial wetland filled with the gravels in the present embodiment, 90 days is the time span from the start of the operation of the artificial wetland to the stabilization of the effluent, and 72 days between 90 days and 162 days is the time span for the continuous operation of the artificial wetland. And detecting the porosity of the two groups of artificial wetlands before, after and after the operation of the artificial wetlands. As can be seen directly from the graph, the rate of decrease in the porosity of the gravel-packed artificial wetland was faster before the effluent stabilized, and the porosity continued to decrease after 72 days of continuous operation. However, the artificial wetland of the embodiment has stable porosity reduction rate, and still has good porosity after continuous operation for 72 days, so that the tidal flow circulates Fe2+ and Fe3+ in the magnetite filler, thereby obviously prolonging the operation life of the wetland and delaying the blockage of the wetland.

The tidal flow magnetite constructed wetland utilizes tidal change to enable the packed bed to be always in aerobic and anaerobic cyclic change, and organic matters and ammonia nitrogen are efficiently removed in the aerobic and anaerobic cyclic change. Meanwhile, magnetite is used as a reaction layer filler, when the water level is low, the magnetite is in contact with water and air and is subjected to oxidation reaction in a microenvironment to separate out Fe2+ and Fe3+, Fe2+ is further oxidized into Fe3+, part of Fe3+ reacts with phosphate to generate precipitate and is deposited on the surface of the magnetite, Fe3+ on the surface of the magnetite in an anaerobic state along with the rise of the water level is used as an electron acceptor to oxidize ammonia nitrogen and organic matters under the action of microorganisms and is reduced into Fe2+, meanwhile, the phosphate in the precipitate state is unavailable to plants, the plants can obtain phosphorus from the surface of the magnetite in a manner of secreting organic acid, the organic acid can dissolve the magnetite under the microenvironment to promote the release of Fe3+ and part of Fe2+, further promote the oxidation of ammonia nitrogen and decomposition of the organic matters, and worth mentioning that dissimilatory iron reduction (namely, microorganisms oxidize the organic matters by using high-valence metal ions as the electron acceptor under the anaerobic condition) can thoroughly oxidize the magnetite) the magnetite The water is discharged from the wetland system by forming carbon dioxide, Fe3+ is reduced to Fe2+, the system does not accumulate nitrate nitrogen under anaerobic conditions, the nitrate nitrogen can be removed by heterotrophic denitrification when organic matters exist, the microorganism can also perform autotrophic denitrification by using Fe2+ as an electron acceptor after the organic matters are consumed, the siphon tube discharges the water in the wetland after the water level reaches a certain height, the filler is exposed in the air again, and the Fe2+ is oxidized to Fe3+ again when the Fe2+ is in contact with the water and the air. In other words, when the wetland water level is low, the system is in an aerobic state, ammonia nitrogen and organic matters are removed to a certain extent in the aerobic state, and meanwhile Fe2+ on the surface of the reaction layer filler magnetite is oxidized into Fe3+, Fe3+ and can precipitate phosphate in sewage; after the water level of the wetland rises, the system is in an anaerobic state, microorganisms utilize Fe3+ on the surface of magnetite to carry out iron ammoxidation and dissimilatory metal reduction (organic acid secreted by plants for obtaining phosphorus deposited on the surface of iron ore promotes the release of Fe3 +) on the surface of iron ore) to further oxidize ammonia nitrogen and organic matters into nitrogen and carbon dioxide, and Fe3+ is reduced into Fe2+, and the blockage of the wetland caused by the accumulation of the organic matters is fundamentally relieved by the thorough oxidation of the organic matters. The wetland realizes the automatic adjustment of the height of the water level through the siphon, the change of the height of the water level enables the filler to be in the continuous alternation of aerobic state and anaerobic state, the continuous alternation of the aerobic state and the anaerobic state causes the interconversion between Fe3+ and Fe2+, the interconversion between Fe3+ and Fe2+ promotes the removal of pollutants, and the blockage of the wetland is delayed.

The above description is only exemplary of the present invention and should not be taken as limiting, and any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. The magnetite artificial wetland for tidal flow regulation and control is characterized by comprising a wetland main body (1), wherein a bearing layer (5), a reaction layer (4) and a surface layer (3) are sequentially paved in the wetland main body (1) from bottom to top; wetland plants (2) are planted on the surface layer (3), and the reaction layer (4) is formed by filling natural magnetite; a water inlet pipe (6) is arranged at the top of the wetland main body (1), a water outlet (7) is arranged at the bottom of the wetland main body, a siphon (8) is connected to the water outlet (7), and a water tank (9) is connected to the other end of the siphon (8); the highest point of the siphon (8) is lower than the water inlet pipe (6), and the liquid level of the water tank (9) is lower than the water outlet (7).

2. The tidal flow regulated magnetite constructed wetland of claim 1, wherein the surface layer is packed with gravel having a particle size of 0.8 to 1.2 cm.

3. A tidal flow regulated magnetite constructed wetland according to claim 1, characterised in that the supporting layer (5) is packed with gravel, quartz or cobblestones with a particle size of 1.5-3 cm.

4. The tidal flow regulated magnetite constructed wetland of claim 1, wherein the natural magnetite has a particle size of 1-2 cm.

5. A tidal flow regulated magnetite constructed wetland according to claim 1, characterized in that the highest point of the siphon (8) is higher than the top of the reaction layer (4).

6. A tidal flow regulated magnetite constructed wetland according to claim 1, characterised in that the water outlet (7) is located at the interface of the bearing layer (5) and the reaction layer (4).

7. The tidal flow regulated magnetite constructed wetland according to claim 6, characterized in that the water outlet (7) has a filtration grid with pores smaller than the particle size of natural magnetite.

8. A tidal flow regulated magnetite constructed wetland according to claim 1, characterized in that the water trough (9) has overflow openings at a lower height than the water outlet (7).