Constructed wetland purification system and method of use

Abstract

The application discloses a kind of artificial wetland purification system and use method, including limestone interception zone, biochar interception zone, confluence ditch, primary sedimentation tank, primary adsorption filter dam, neutralization dam, secondary sedimentation tank, secondary adsorption filter dam, anaerobic fermentation tank, primary subsurface flow pool, secondary subsurface flow pool, submerged plant pool in turn communication;The treatment method based on the system includes the following steps, source interception of surface and shallow soil, preliminary sedimentation, adsorption and filtration after wastewater collection, secondary neutralization and sedimentation treatment of wastewater, followed by anaerobic fermentation, finally through wetland purification treatment, the planted plant is incinerated and recycled heavy metal.The purification system of the application has low investment cost, simple operation, easy maintenance, low energy consumption, significantly improved effluent quality, and is suitable for ecological management of acidic abandoned mine drainage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sewage treatment, in particular to a constructed wetland purification system and a use method thereof. BACKGROUND

[0002] Acid mine drainage is an acid liquid containing a large amount of sulfate and various heavy metal ions, which is formed by the oxidation reaction of sulfide minerals exposed to the surface, water, and atmosphere, and gradually dissolved. The liquid is mainly derived from direct wastewater generated by mining, surface runoff wastewater generated by natural rainfall, and underground wastewater generated by the seepage of pit and cave water. The wastewater has the characteristics of low organic matter content, high concentration of sulfate, and low pH value, and the pH value is usually less than 3, and even less than 2.0. In addition, the wastewater contains a large amount of heavy metal ions such as iron, aluminum, copper, lead, zinc, nickel, and sulfate anions. Untreated acid mine drainage has a great risk to the environment and organisms, especially the harmful heavy metals, which can be enriched through the food chain and cause serious harm to human health.

[0003] The traditional process for treating acid mine drainage mainly includes adsorption method and neutralization precipitation method. The adsorption method uses adsorption materials to adsorb soluble metal ions, and the operation cost of this method is high. The neutralization precipitation method adds alkaline substances to acid mine wastewater to increase the pH value of the wastewater, so that the metal ions are removed in the form of hydroxide precipitation, and a large amount of sludge containing heavy metals is generated, forming secondary pollution.

[0004] The prior art CN102701545A discloses a system and process for auxiliary treatment of acid mine drainage by using a cascade interception dam, which includes three interception zones. The interception zones are distributed in a natural stepped trapezoidal shape, and limestone layers are arranged in the first two interception zones to adjust the pH value of the wastewater and reduce the solubility of heavy metals in the wastewater. A biological layer is arranged in the second interception zone to reduce sulfate ions to sulfur ions, and the sulfur ions form sulfide precipitates with heavy metal ions dissolved in water to settle in the bottom mud. Aquatic plants are planted in the last interception zone to filter and adsorb particulate matters in the wastewater by the root system of the aquatic plants, and to reduce the concentration of heavy metal pollutants in the water. Although this method simplifies the complexity and difficulty of the existing method, it still needs to perform primary treatment on the acid mine wastewater, and the treatment period is not short in essence. In addition, a large amount of sulfide precipitates are easily accumulated in the last two purification processes, and are difficult to remove. SUMMARY

[0005] The present application aims to overcome the problems of high treatment cost and secondary pollution in the prior art, and provides a constructed wetland purification system and treatment method for acid mine drainage, which has the advantages of low treatment cost, high cost performance, recyclable heavy metals, and deep purification of effluent.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a constructed wetland purification system, comprising a limestone interception zone, a biochar interception zone, a confluence ditch, a first-stage sedimentation tank, a first-stage adsorption filter dam, a neutralization dam, a second-stage sedimentation tank, a second-stage adsorption filter dam, an anaerobic fermentation tank, a first-stage subsurface flow tank, a second-stage subsurface flow tank, and a submerged plant tank.

[0007] The limestone interception zone is arranged at the lower part of the hillside runoff area, extends into the ground by 0.15-0.3 meters, the upper part is 0.05-0.1 meters below the ground, the width is 0.2-0.4 meters, and the bottom of the tank is distributed with limestone. The slope runoff and shallow soil runoff in the mine area can enter the limestone interception zone, and all wastewater can be preliminarily neutralized.

[0008] The biochar interception zone is arranged at the lower part of the hillside runoff area, behind the limestone interception zone, extends into the ground by 0.15-0.3 meters, the upper part is 0.05-0.1 meters below the ground, and the width is 0.2-0.4 meters.

[0009] The confluence ditch is one or more ditches, which can collect the water flow in the project area to the first-stage sedimentation tank, and the wetland plants are planted on the banks of the ditch.

[0010] The first-stage sedimentation tank has a volume that meets the water collection of the project area, can regulate the water outflow speed, and can preliminarily settle the water pollutants. The wetland plants are planted on the banks of the first-stage sedimentation tank.

[0011] The wetland plants include one or more of Alternanthera philoxeroides, Alternanthera sessilis, Vetiveria zizanioides, Miscanthus sinensis, Phragmites australis, and the like. The wetland plants have strong water and soil conservation ability, strong heavy metal stress resistance, and can grow in the mining area. The wetland plants grow on the banks and can maintain the water and soil.

[0012] The first-stage adsorption filter dam is composed of a frame of a front interception wall and a rear interception wall in the transverse direction and one or more connecting walls in the longitudinal direction, and the frame is filled with biomass carbon. A water retaining wall is arranged at the front of the front interception wall. A cavity is formed between the water retaining wall and the adsorption filter dam. The water flows into the cavity from the top of the water retaining wall, and then flows into the adsorption filter dam from the bottom of the front interception wall. After being filtered by the biomass carbon, the water flows out from the upper part of the rear interception wall.

[0013] The neutralization dam is composed of a frame of a front interception wall and a rear interception wall in the transverse direction and one or more connecting walls in the longitudinal direction, and the frame is filled with blocky alkaline materials such as limestone and calcite. The water flows into the front interception wall of the neutralization dam, and the water flows out from the lower part of the rear interception wall.

[0014] The second-stage sedimentation tank is provided with an inclined plate at the water inlet end, and the tank depth is preferably 3-5 meters.

[0015] The secondary adsorption filter dam is composed of a frame of two transverse front and rear intercepting walls and one or more longitudinal connecting walls, and the frame is filled with biomass carbon; a water retaining wall is arranged at the water inlet end and in front of the front intercepting wall, and a cavity is formed between the water retaining wall and the adsorption filter dam, water flows into the cavity from the top of the water retaining wall, and then flows into the adsorption filter dam from the bottom of the front intercepting wall of the adsorption filter dam, and then flows out from the upper part of the rear intercepting wall of the adsorption filter dam after being filtered by the biomass carbon.

[0016] The anaerobic fermentation tank is provided with fermentation material plant residues selected from plants planted on the bank of the confluence ditch and the bank of the primary sedimentation tank;

[0017] The substrate at the bottom of the primary subsurface pool is biomass carbon, and one or more of calamus, cattail and black rhubarb is planted on the bank of the subsurface pool, and sulfate-reducing bacteria are inoculated simultaneously; the substrate at the bottom of the secondary subsurface pool is biomass carbon, and one or more of reed, water onion and canna is planted on the bank of the subsurface pool, and sulfate-reducing bacteria are inoculated simultaneously;

[0018] The submerged plant tank is planted with one or more of potamogeton crispus, hydrilla verticillata, vallisneria, elodea and stonewort at the bottom, and the plants at the bottom grow fast, have large biomass and strong purification capacity; one or more of alligator weed, water hyacinth, bamboo grass, vetiver, southern di and reed is planted on the bank of the submerged plant tank, the plants on the bank of the submerged plant tank have strong stress tolerance, strong water and soil conservation capacity, reduce water and soil loss of the bank slope, and prevent pollution of the water body.

[0019] The second aspect of the present application provides a use method of the artificial wetland purification system, comprising the following steps:

[0020] Step (1) source interception of surface and shallow soil: the limestone interception belt preliminarily neutralizes the runoff on the slope surface and the shallow soil flow, and neutralizes the pH to 4-5; the subsequent wastewater enters the biomass carbon interception belt, and the iron hydroxide in the wastewater adsorbs other metal ions and co-precipitates part of copper hydroxide;

[0021] Step (2) collection and primary sedimentation: the water flow in the surface and shallow soil enters the confluence ditch, and then is collected and stored in the primary sedimentation tank for preliminary sedimentation;

[0022] Step (3) primary adsorption filtration: the mine acid drainage flows into the primary adsorption filter dam after the preliminary sedimentation in step (2), and is subjected to primary adsorption filtration with the biomass carbon filled in the dam to remove the suspended solids generated in the primary neutralization;

[0023] Step (4) neutralization and precipitation: after the mine acid drainage is filtered by adsorption in step (3), it flows into a neutralization dam, and in the neutralization dam, the wastewater is in contact with alkaline materials such as limestone and calcite to react, and the pH value of the mine wastewater in the neutralization dam is controlled to be 5-6, and then the wastewater reaches a secondary sedimentation tank for sedimentation reaction treatment;

[0024] Step (5) secondary adsorption filtration: after the mine acid drainage is neutralized and precipitated in step (4), it flows into a secondary adsorption filtration dam, and is subjected to secondary adsorption filtration with biomass carbon filled in the dam to remove suspended solids generated by secondary neutralization;

[0025] Step (6) anaerobic fermentation: after the mine acid wastewater is neutralized and precipitated for multiple times, it further flows into an anaerobic fermentation tank, and anaerobic microorganisms in the anaerobic fermentation tank ferment plant residues as carbon sources to decompose the plant residues into low-carbon small molecule COD, and the COD and SO4 2- The ratio of the two is between 1.9 and 2.1.

[0026] Step (7) wetland purification: after neutralization, precipitation, adsorption filtration in the previous six steps, the wastewater further enters a primary subsurface pool, a secondary subsurface pool and a submerged plant pool, and is subjected to substrate adsorption with biomass carbon in the two subsurface pools and biological reaction with sulfate-reducing bacteria to reduce sulfate ions in the wastewater to sulfur ions, and then the submerged plants adsorb sulfur-containing pollutants in the wastewater and increase the dissolved oxygen in the water body, and the submerged plants can absorb nitrogen, phosphorus and other nutrients in the water body.

[0027] Step (8) heavy metal recovery: the plants on the bank of the collection ditch in the harvesting system and the bank of the primary sedimentation tank are subjected to high-temperature pyrolysis to recover biochar, and the sediment is collected to recover heavy metals therein.

[0028] Further, the wastewater in step (2) stays in the primary sedimentation tank for 12-48 hours, and the water quantity of the primary sedimentation tank is adjusted to control the water quantity in the subsequent steps; the pH of the primary sedimentation tank is 4-5.

[0029] Further, the wastewater in step (4) stays in the secondary sedimentation tank for 12-48 hours.

[0030] Further, the sludge formed by the sedimentation reaction of the secondary sedimentation tank is collected and discharged, and the discharged sludge is dewatered and dried to form a mud cake which is naturally stacked.

[0031] Compared with the prior art, the beneficial effects of the present application are:

[0032] 1. By setting limestone interception zone and biochar interception zone in turn before the mountain produces runoff, the surface flow and shallow soil flow are neutralized, adsorbed and filtered, the pH value of the collected sewage is improved, the iron ions in the wastewater are preliminarily precipitated, the pollutant concentration is reduced, which is beneficial to further treatment, reduces the difficulty of subsequent treatment, reduces the operation and maintenance cost as a whole, and is beneficial to improve the water quality of effluent. On the other hand, compared with limestone and biochar in the subsequent wetland, the limestone interception zone and the biochar interception zone are more easy to set, add and replace.

[0033] 2. After the preliminary precipitation and adsorption treatment, the neutralization dam is set again, the pH value of the wastewater is controlled between 5-6, the concentration of copper ions which are toxic to microorganisms in the subsequent steps is precisely controlled, so that a large amount of copper ions are precipitated, on the one hand, the poisoning of microorganisms in the fermentation tank can be avoided, so that the microorganisms can decompose plant residues to provide carbon source and electron donor for sulfate reducing bacteria in the subsequent subsurface flow tank, on the other hand, the sulfate reducing bacteria in the subsurface flow tank which are resistant to copper are avoided, and the cost is reduced; secondly, by one-step neutralization and adsorption, iron and copper are precipitated, and the accumulated sludge at the bottom of the sedimentation tank contains a large amount of heavy metal ions, so as to avoid secondary pollution and treatment cost. At the same time, a primary sedimentation tank and a primary adsorption and filtration dam are arranged at the front end of the neutralization dam, so as to reduce the particle content and pollutant concentration of the water body, reduce the blockage of the neutralization dam, and prolong the service life of the filler in the neutralization dam.

[0034] 3. Two adsorption and filtration dams are set, so that the heavy metals in the wastewater are adsorbed by contacting with a large amount of biomass carbon, and the heavy metals can be recovered by treating the biochar adsorbed with heavy metals, so that the heavy metals are recovered by treating the neutralization and precipitation.

[0035] 4. By setting an anaerobic fermentation tank in advance, the wastewater is treated by anaerobic fermentation, and a variety of small molecules of carbon are produced in the fermentation process, which is beneficial to the survival of sulfate reducing bacteria in the subsurface flow wetland, and improves the activity of sulfate reducing bacteria in the subsequent steps.

[0036] 5. The microorganisms in the subsurface flow wetland and the biomass carbon are attached to each other, the attached area is increased, the wastewater is fully contacted, and the sulfate reducing bacteria are more beneficial to play a role; at the same time, a large amount of plants for adsorbing COD are planted on the bank of the subsurface flow tank, when the amount of plant residues added in the anaerobic fermentation tank is too much, the growth of sulfate reducing bacteria in the subsurface flow tank can be inhibited, so as to affect the removal of sulfate ions in the wastewater.

[0037] 6. The terminal submerged plant tank further reduces the nitrogen, phosphorus, COD and heavy metals in the water body, and deeply improves the water quality of effluent.

[0038] Therefore, the purification system has the advantages of low investment cost, simple operation, convenient maintenance, low energy consumption, good effluent water quality, and is suitable for ecological management of acid mine drainage. Attached Figure Description

[0039] Figure 1 This is a process flow diagram of the processing system of the present invention. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but the scope of protection is not limited to the description.

[0041] like Figure 1 As shown, an artificial wetland purification system includes a limestone interception zone, a biochar interception zone, a drainage ditch, a primary sedimentation tank, a primary adsorption filtration dam, a neutralization dam, a secondary sedimentation tank, a secondary adsorption filtration dam, an anaerobic fermentation tank, a primary subsurface flow tank, a secondary subsurface flow tank, and a submerged plant pond, all connected in sequence.

[0042] A limestone interception zone is deployed at the lower part of the hillside runoff area, extending 0.15-0.3 meters underground, with its upper part 0.05-0.1 meters below ground level and a width of 0.2-0.4 meters. Limestone is distributed at the bottom of the zone. This limestone interception zone collects and initially neutralizes surface runoff and shallow soil runoff from the mining area. A biochar interception zone is then installed after the limestone interception zone, extending 0.15-0.3 meters underground, with its upper part 0.05-0.1 meters below ground level and a width of 0.2-0.4 meters. The limestone and biochar interception zones neutralize, adsorb, and filter surface runoff and shallow soil runoff from the hillside, increasing the pH value of the collected wastewater and initially reducing pollutant concentration, which is beneficial for further treatment and reduces the difficulty of subsequent treatment.

[0043] The confluence ditch is one or more ditches. Water overflowing after being treated by limestone interception zone and biomass carbon interception zone enters the confluence ditch, and then the water flow in the project area is collected into the primary sedimentation tank. Wetland plants are planted on the banks of the ditch.

[0044] The primary sedimentation tank has a volume sufficient to meet the water collection volume of the project area, allows for regulation of the effluent flow rate, and enables the initial settling of pollutants in the water. Wetland plants are planted along the banks of the primary sedimentation tank. These wetland plants include one or more of the following: Alternanthera philoxeroides, Alternanthera philoxeroides, Vetiver, Miscanthus sinensis, Reed, and Phragmites communis. These wetland plants have strong soil and water conservation capabilities, are relatively resistant to heavy metal stress, and can grow in mining areas. Growing along the banks helps conserve soil and water.

[0045] The primary adsorption filter dam is a frame composed of two transverse front and back intercepting walls and one or more longitudinal connecting walls, and the frame is filled with biomass carbon; a water retaining wall is arranged at the water inlet end and in front of the front intercepting wall, and a cavity is formed between the water retaining wall and the adsorption filter dam, water flows into the cavity from the top of the water retaining wall, and then flows into the adsorption filter dam from the bottom of the front intercepting wall of the adsorption filter dam, and then flows out from the upper part of the rear intercepting wall of the adsorption filter dam after passing through the filtering substrate of the biomass carbon. The neutralization dam is a frame composed of two transverse front and back intercepting walls and one or more longitudinal connecting walls, and the frame is filled with limestone, calcite and other blocky alkaline materials; water flows into the upper part of the front intercepting wall of the neutralization dam, and water flows out from the lower part of the rear intercepting wall.

[0046] The inclined plate is arranged at the water inlet end of the secondary sedimentation tank, and the depth of the tank is 3-5 meters. The secondary adsorption filter dam has the same structure as the primary adsorption filter dam. After purification in the previous steps, the water quality is improved to a certain extent.

[0047] The plant residues in the anaerobic fermentation tank are used as fermentation materials, and under the metabolic activities of anaerobic bacteria such as yeast and lactic acid bacteria, the plant residues are degraded and decomposed into low-carbon small molecules, which provide carbon source, trace elements and electron donor for the growth of sulfate-reducing bacteria in the subsequent process, thereby improving the activity of sulfate-reducing bacteria.

[0048] The substrate at the bottom of the primary subsurface flow tank is biomass carbon, and one or more of acorus calamus, cattail, black three-angle is planted on the bank, and sulfate-reducing bacteria are inoculated. The secondary subsurface flow tank is the same as the primary subsurface flow tank.

[0049] The submerged plant tank is planted with one or more of carex rostrata, hydrilla verticillata, vallisneria, potamogeton, fox tail, and the like on the bottom, and the plants on the bottom grow fast, have large biomass and strong purification capacity; the submerged plant tank is planted with one or more of eichhornia crassipes, lotus, miscanthus, vetiver, south di, reed, and the like on the bank, and the plants on the bank have strong stress tolerance and strong water and soil conservation capacity, which reduces water and soil loss on the bank slope and prevents pollution of the water body.

[0050] The plant residues in the anaerobic fermentation tank come from the plants planted on the bank of the confluence ditch, the primary sedimentation tank, the primary subsurface flow tank and the secondary subsurface flow tank.

[0051] According to the above purification process, the water quality of the acid mine drainage treated is monitored as shown in Tables 1 and 2.

[0052] Table 1

[0053]

[0054] Table 2

[0055]

[0056] Based on the above purification system, a use method of the constructed wetland purification system comprises the following steps:

[0057] Step (1) source interception of surface and shallow soil: the limestone interception belt preliminarily neutralizes the slope runoff and the shallow soil runoff, and the pH is neutralized to 4-5; the wastewater after pH neutralization enters the biomass charcoal interception belt, and the iron and part of the copper hydroxide in the slope runoff and the shallow soil runoff are intercepted through adsorption, and various metal ions are co-precipitated with the iron hydroxide through adsorption.

[0058] Step (2) collection and primary precipitation: the water flow in the surface and shallow soil enters the collecting ditch, and then is collected and stored in the primary precipitation tank, the water force stays in the primary precipitation tank for 12-48 hours for preliminary precipitation, and the water quantity after the primary precipitation tank can be adjusted to adjust the water quantity in the subsequent steps; the primary precipitate is mainly the silt brought by the runoff and the chemical precipitate caused by the preliminary neutralization (pH is 4-5).

[0059] Step (3) primary adsorption filtration: the mine acid drainage after the preliminary precipitation in step (2) flows into the primary adsorption filtration dam through the water retaining wall, and is subjected to primary adsorption filtration with the biomass carbon filled in the dam; the primary filtration is used for removing the suspended matter generated in the preliminary neutralization.

[0060] Step (4) neutralization and precipitation: the mine acid drainage after the adsorption filtration in step (3) flows into the neutralization dam, the wastewater in the neutralization dam is contacted and reacted with the alkaline materials such as limestone and calcite, and then reaches the secondary precipitation tank, and the water force stays in the secondary precipitation tank for 12-48 hours. In the neutralization dam, the pH value of the mine wastewater is adjusted to 5-6, at the same time, the dissolution and hydrolysis of the carbonate in the limestone provide a large amount of hydroxyl ions, which further precipitate the copper ions in the wastewater. In the secondary precipitation tank, the secondary precipitate is the copper hydroxide precipitate formed in the neutralization dam, at this time, a part of the sulfate ions will form calcium sulfate with small solubility, which will be collected at the bottom of the secondary precipitation tank to form sludge to be discharged, and the sludge will be dewatered and dried in the drying plant, and the dried mud cake is naturally stacked.

[0061] Step (5) secondary adsorption filtration: the mine acid drainage after the neutralization and precipitation in step (4) flows into the secondary adsorption filtration dam through the water retaining wall, and is subjected to secondary adsorption filtration with the biomass carbon filled in the dam; the secondary filtration is used for removing the suspended matter generated in the secondary neutralization.

[0062] Step (6) anaerobic fermentation: after the mine acid wastewater is neutralized and precipitated for several times, the water quality is improved, and the wastewater further flows into the anaerobic fermentation tank. At the same time, the plant residues are put into the anaerobic fermentation tank for fermentation, so as to provide a carbon source for the anaerobic microorganisms and reduce the oxidation-reduction potential of the water body. At the same time, the plant residues are decomposed into low-carbon small molecules, which provide substrates for the subsequent sulfate-reducing bacteria. In this step, the addition amount of the plant residues is controlled, and the mass ratio of the COD small molecules after the decomposition of the plant residues to the sulfate ions in the wastewater is greater than 1.8. In this way, when the wastewater enters the subsurface flow tank, a part of the COD small molecules is adsorbed, and the ratio can be reduced to 1.4-1.8.

[0063] Step (7) wetland purification: after the neutralization, precipitation, adsorption and filtration in the previous six steps, the wastewater further flows into the first-stage subsurface flow tank, the second-stage subsurface flow tank and the submerged plant tank in sequence, and is subjected to substrate adsorption with the biomass carbon in the two subsurface flow tanks and biological reaction with the sulfate-reducing bacteria, so as to reduce the sulfate ions to sulfur ions. Then, the wastewater is contacted with the submerged plants again, the submerged plants adsorb the sulfur-containing pollutants, increase the dissolved oxygen of the water body, slow down the water flow, and are beneficial to control the resuspension of the sulfur-containing sediment and fix the sediment. At the same time, the submerged plants can absorb the nitrogen, phosphorus and other nutrient elements in the water body.

[0064] Step (8) heavy metal recovery: the plants on the bank of the collecting ditch in the harvesting system and the bank of the first-stage precipitation tank are subjected to high-temperature pyrolysis to recover the biochar, and the sediment is collected to recover the heavy metals therein.

[0065] Since the concentration of the metal ions and the pH of the solution and the hydroxide solubility product exist the following relationship:

[0066] lg[M n+ ]=lgKsp+14n-npH

[0067] In the formula, [M n+ ] is the concentration of the metal ions, Ksp is the solubility product constant of the metal hydroxide, and n is the valence state of the metal ions.

[0068] According to the above formula and Table 1, the pH at which the hydroxide of each metal ion is completely formed into a precipitate can be calculated. According to formula 1, in the use method of the artificial wetland purification system, most of the heavy metal ions are not directly formed into a precipitate and transferred to the sludge in the two neutralization treatments in steps (1) and (4), so that secondary environmental pollution is avoided, and most of the heavy metal ions are enriched in steps (6)-(8) of the subsequent process.

[0069] The pH of the neutralized acid mine drainage in step (4) is 5-6, which is suitable for anaerobic microorganism fermentation of plant residues and reduces the oxidation-reduction potential of the water body. As shown in Table 2, most of the copper ions are removed in step (4), which avoids the inhibition of copper ions on the activity of lactate dehydrogenase, reduces the generation of lactic acid, and also avoids the possible inhibition of copper ions on the growth of lactic acid bacteria and yeast, resulting in a decrease in the fermentation rate.

[0070] In step (6), the plant residues are anaerobically fermented by lactic acid bacteria and yeast, which provides a large amount of low-carbon small molecules (such as lactic acid and acetic acid) for sulfate-reducing bacteria to decompose and utilize as substrates. At the same time, since most of the copper ions are removed in step (4), the toxicity of copper ions to sulfate-reducing bacteria is also avoided, so it is not necessary to specially screen sulfate-reducing bacteria that are resistant to copper ions. In step (6), since the Acorus calamus, Typha angustifolia, and Sparganium stoloniferum with strong adsorption capacity of COD are planted around the undercurrent pool, when the amount of plant residues added is excessive, the plants in the undercurrent pool can further adsorb the excess small molecule COD, which can stabilize the COD / SO4 2- concentration ratio in the pool water, so that the sulfate-reducing bacteria are superior to other bacteria in competitive growth, which is beneficial to improve the ability of sulfate-reducing bacteria to reduce SO4 2- .

[0071] According to the above purification process, the water quality of the acid mine drainage treated is shown in Table 3. After 7 steps of treatment, the water quality is obviously improved.

[0072] Table 3

[0073]

[0074] Example 2

[0075] The present embodiment provides an artificial wetland purification system, which comprises a limestone interception zone, a biochar interception zone, a confluence ditch, a primary sedimentation tank, a primary adsorption and filtration dam, a secondary sedimentation tank, a secondary adsorption and filtration dam, an anaerobic fermentation tank, a primary undercurrent pool, a secondary undercurrent pool, and a submerged plant pool, which are sequentially connected. Compared with Example 1, the present embodiment lacks a neutralization dam treatment link (i.e., the limestone in the neutralization dam is completely consumed without being refilled). The specific treatment steps refer to the content of Example 1.

[0076] According to the above purification process, the water quality of the acid mine drainage treated is shown in Table 4.

[0077] Table 4

[0078]

[0079] As can be seen from the above table, when the wastewater does not undergo re-neutralization treatment with alkaline materials such as limestone and calcite before entering the secondary sedimentation tank, the pH value at the outlet of the secondary sedimentation tank is in the range of 4-5, and at this time, the content of other metal ions such as copper ions in the wastewater is still maintained at a high concentration in addition to the iron ions, and they are not completely precipitated into sludge as in Example 1, and at this time, the wastewater directly enters the anaerobic fermentation tank, and most of the heavy metal ions in the wastewater are toxic to the anaerobic microorganisms (such as yeast and lactic acid bacteria) in the anaerobic fermentation tank, especially the copper ions, cadmium ions and lead ions in the wastewater, so the activity of the anaerobic microorganisms in the anaerobic fermentation tank is seriously affected, and the COD content in the wastewater after fermentation is small, which leads to slow reproduction of the sulfate-reducing bacteria in the subsurface flow tank, and the sulfate ions in the wastewater cannot be effectively reduced.

[0080] On the one hand, due to the inactivation of the anaerobic microorganisms in the anaerobic fermentation tank, the plant residues cannot be decomposed into small molecule COD as the carbon source substrate for the sulfate-reducing bacteria in the subsurface flow tank, and in the absence of the carbon source substrate, the sulfate-reducing bacteria cannot reduce a large amount of sulfate ions in the wastewater to hydrogen sulfide. On the other hand, the mine wastewater entering the subsurface flow tank also contains a large amount of metal ions, which also affects the activity of ordinary sulfate-reducing bacteria. Although the activity of the sulfate-reducing bacteria is not high, the plants in the subsurface flow tank and the resting tank can further adsorb the COD and metal ions in the wastewater, so that their concentrations decrease slightly, but the concentrations of the heavy metal ions and the sulfate ions in the final effluent are still very high, which still causes great pollution to the environment.

[0081] In the above examples, the plants such as Acorus calamus, Typha angustifolia and Sparganium stoloniferum are planted on the bank of the subsurface flow tank, which is to absorb the COD of the wastewater at the outlet of the anaerobic fermentation tank, and to control the ratio of COD to SO4 2- If the plants such as Acorus calamus, Typha angustifolia and Sparganium stoloniferum are not planted on the bank of the subsurface flow tank, under the action of the microorganisms in the anaerobic fermentation tank, the plant residues are decomposed into a large amount of small molecule COD, and the ratio of the COD to the sulfate ions in the wastewater exceeds 2.2. When such wastewater enters the subsurface flow tank, since the plants such as Acorus calamus, Typha angustifolia and Sparganium stoloniferum are not planted in the subsurface flow tank, the excess COD in the wastewater cannot be adsorbed and removed, which leads to inhibition of the growth of the inoculated sulfate-reducing bacteria in the subsurface flow tank, and the sulfate ions in the wastewater cannot be timely reduced to sulfur ions, so the sulfate-reducing bacteria cannot form sulfide precipitates with other heavy metal ions, which is not conducive to the removal of heavy metals.

Claims

1. An artificial wetland purification system, characterized in that, The system comprises, in sequence, a limestone interception zone, a biochar interception zone, a confluence channel, a primary sedimentation tank, a primary adsorption filtration dam, a neutralization dam, a secondary sedimentation tank, a secondary adsorption filtration dam, an anaerobic fermentation tank, a primary subsurface flow tank, a secondary subsurface flow tank, and a submerged plant pond. The limestone and biochar interception zones are set along the foot of the slope at the lower part of the runoff generation area. The confluence channel collects wastewater overflowing from the biochar interception zone. The primary and secondary adsorption filtration dams are filled with biochar. The neutralization dam is filled with blocky alkaline materials of limestone and calcite. The anaerobic fermentation tank is inoculated with anaerobic microorganisms and uses plant residues as fermentation material. The banks of the primary and secondary subsurface flow tanks are planted with plants, and the bottom of the tanks is inoculated with sulfate-reducing bacteria using biochar as a substrate. The bottom of the submerged plant pond is planted with aquatic plants.

2. The constructed wetland purification system according to claim 1, characterized in that, The limestone interception zone extends 0.15-0.3 meters underground, with its upper part 0.05-0.1 meters below the ground surface and a width of 0.2-0.4 meters. Limestone is distributed at the bottom of the pool. The limestone interception zone collects and preliminarily neutralizes the surface runoff and shallow soil runoff from the mining area. The biochar interception zone is set after the limestone interception zone, extending 0.15-0.3 meters underground, with its upper part 0.05-0.1 meters below the ground surface and a width of 0.2-0.4 meters.

3. The constructed wetland purification system according to claim 1, characterized in that, The primary adsorption filter dam is a frame composed of two horizontal front and rear intercepting walls and multiple vertical connecting walls, with biomass carbon filling the frame. A water-retaining wall is set in front of the front intercepting wall, forming a cavity between the water-retaining wall and the adsorption filter dam. Water flows into the cavity from the top of the water-retaining wall, then enters from the bottom of the front intercepting wall of the adsorption filter dam, passes through the biomass carbon filter matrix, and flows out from the top of the rear intercepting wall.

4. The constructed wetland purification system according to claim 1, characterized in that, The neutralization dam is a frame consisting of two horizontal intercepting walls (front and rear) and multiple vertical connecting walls. The frame is filled with blocky alkaline materials of limestone and calcite. Water enters from the upper part of the front intercepting wall and exits from the lower part of the rear intercepting wall.

5. The constructed wetland purification system according to claim 1, characterized in that, The banks of the confluence channels and primary sedimentation ponds are planted with wetland plants, including one or more of the following: Alternanthera philoxeroides, Alternanthera philoxeroides, Vetiver, Miscanthus sinensis, Dioscorea opposita, and Reed. The bottom of the submerged plant ponds is planted with one or more of the following: Potamogeton crispus, Hydrilla verticillata, Vallisneria natans, Elodea nuttallii, and Myriophyllum spicatum. The banks of the primary and secondary subsurface flow ponds are planted with one or more of the following: Acorus calamus, Typha orientalis, and Sparganium stoloniferum.

6. A method of using an artificial wetland purification system based on any one of claims 1-5, characterized in that, Includes the following steps, Step (1) Source interception of surface and shallow soil: The limestone interception zone initially neutralizes the runoff from the slope and the runoff from the shallow soil, neutralizing the pH to 4-5; the subsequent wastewater enters the biochar interception zone, where iron hydroxide in the wastewater adsorbs other metal ions and some copper hydroxide co-precipitates. Step (2) Collection and primary sedimentation: Water from the surface and shallow soil flows into the confluence ditch, and is then collected and stored in the primary sedimentation tank for preliminary sedimentation; Step (3) Primary adsorption filtration: After the initial sedimentation in step (2), the acidic mine wastewater flows into the primary adsorption filtration dam and undergoes primary adsorption filtration with the biomass carbon filled in the dam to remove the suspended solids generated during the initial neutralization. Step (4) Neutralization and sedimentation: After the adsorption and filtration in step (3), the acidic mine wastewater flows into the neutralization dam. In the neutralization dam, the wastewater reacts with alkaline materials such as limestone and calcite. The pH value of the mine wastewater is adjusted to 5-6 in the neutralization dam. Then the wastewater goes to the secondary sedimentation tank for sedimentation reaction treatment. Step (5) Secondary adsorption filtration: After neutralization and sedimentation in step (4), the acidic mine wastewater flows into the secondary adsorption filtration dam and undergoes secondary adsorption filtration with the biomass carbon filled in the dam to remove suspended solids generated during the secondary neutralization. Step (6) Anaerobic fermentation: After multiple neutralizations and sedimentations, the acidic mine wastewater flows into an anaerobic fermentation tank. Anaerobic microorganisms in the tank use plant residues as a carbon source for fermentation, decomposing the residues into low-carbon small-molecule COD. The COD reacts with SO4 in the wastewater. 2- The ratio is between 1.9 and 2.1; Step (7) Wetland purification: After the neutralization, sedimentation, adsorption and filtration of the previous 6 steps, the wastewater enters the first-level submersible pool, the second-level submersible pool and the submerged plant pool in turn. It undergoes matrix adsorption with the biomass carbon in the two submersible pools and biological reaction with sulfate-reducing bacteria to reduce sulfate ions in the wastewater to sulfur ions. Subsequently, the submerged plants adsorb sulfur-containing pollutants in the wastewater and increase the dissolved oxygen in the water. At the same time, the submerged plants can absorb nutrients such as nitrogen and phosphorus in the water. Step (8) Heavy metal recovery: Harvest the plants on the banks of the confluence ditches and the primary sedimentation tank within the system, perform high-temperature pyrolysis to recover biochar, and then collect the sediment to recover the heavy metals.

7. The method of use according to claim 6, characterized in that, In step (2), the wastewater stays in the primary sedimentation tank for 12-48 hours. The outflow from the primary sedimentation tank is adjusted to control the amount of water treated in subsequent steps. The pH of the primary sedimentation tank is 4-5.

8. The method of use according to claim 6, characterized in that, In step (4), the wastewater stays in the secondary sedimentation tank for 12-48 hours.

9. The method of use according to claim 6, characterized in that, In step (4), the sediment from the sedimentation reaction that accumulates at the bottom of the secondary sedimentation tank forms sludge and is then discharged. The discharged sludge is dewatered and dried to form mud cakes that are naturally stored.

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