Permeable reaction wall and reaction system suitable for remediation of groundwater pollution in ionic rare earth mining areas

Abstract

The invention discloses a permeable reaction wall and a reaction system suitable for the remediation of groundwater pollution in ionic rare earth mining areas. The permeable reaction wall is provided with a nitrification zone, a denitrification zone and an adsorption zone in sequence along the water flow direction, and a transition zone is sandwiched between the nitrification zone, the denitrification zone and the adsorption zone; the filler in the nitrification zone includes a nitrifying bacteria agent, a first zero-valent iron, an alkaline agent, a slow-release oxidant and gravel; the filler in the denitrification zone includes a denitrifying bacteria agent, a second zero-valent iron, a solid carbon source, an alkaline agent and gravel. Through scientific and reasonable research and development and design of active fillers, green economy, high-activity microorganisms and zero-valent iron-based composite materials are adopted, and microbial remediation, chemical reduction, physical adsorption and other technologies are coupled to regulate the pH value of groundwater, redox conditions and other parameters, so as to effectively treat the acidification and NH4 + ‑N, NO3 ‑ ‑N, heavy metal pollution problem, easy to maintain, and can operate stably for a long time.

Description

Technical Field

[0001] The invention belongs to the technical field of groundwater remediation, and in particular relates to a permeable reaction wall and a reaction system thereof suitable for remediation of groundwater pollution in ionic rare earth mining areas. Background Art

[0002] Ionic rare earth ores are important strategic mineral resources and are widely distributed in southern provinces such as Jiangxi, Guangdong, Hunan, Guangxi, and Fujian. Ionic rare earth ores are mainly formed in granite weathered for many years under the humid and hot climate conditions in the south. The thickness of the deposit is usually 5 to 30 meters, and the ore body generally has weak permeability. The mining process of rare earth ores mainly uses ammonium sulfate and other electrolyte leaching agents to inject them into the ore body in situ to exchange and recover the rare earth ions. This mining method leaves a large amount of ammonium salts in the ore body. At the same time, the associated heavy metals such as Pb, Cd, and As in the ore body are also dissolved under the action of acidic leaching agents, and are continuously migrated and transformed through rainwater leaching and infiltration, causing groundwater acidification and NH 4 + -N, NO 3 The excessive levels of ⁻-N, heavy metals and other indicators have brought about a series of ecological and environmental problems.

[0003] For groundwater pollution in ionic rare earth mining areas, the extraction-treatment ex situ remediation method is usually adopted. This technology has simple equipment, convenient construction, and quick initial results, but it also has the disadvantages of large interference and high energy consumption, and the remediation effect for low permeability groundwater is poor.

[0004] Permeable reactive barrier (PRB) refers to a passive in-situ groundwater treatment technology filled with a medium. It is installed in the cross-section of the contaminated groundwater flow path. Through the contact between the reactive material filled in the wall and the groundwater, the polluted components in the water are degraded and retained, thereby achieving the purpose of repairing the contaminated groundwater.

[0005] Compared with "ex situ remediation", the use of unpowered, low-energy permeable reaction wall (PRB) for in situ remediation of groundwater pollution is more long-lasting and more suitable as a means of remediation of groundwater in ionic rare earth mining areas.

[0006] The patent document with the publication number CN 215209010 U discloses a groundwater ammonia nitrogen pollution remediation system based on a permeable reaction wall, which includes a reaction section, an adsorption section and a low permeability section arranged in sequence along the groundwater seepage direction. The reaction section is sequentially provided with a nitrification permeable reaction wall and a denitrification permeable reaction wall along the hydraulic seepage direction; the interior of the nitrification permeable reaction wall is filled with a solution containing nitrite bacteria, nitrate bacteria and nutrients and quartz sand; the denitrification permeable reaction wall is divided into a heterotrophic aerobic denitrification zone and an anaerobic autotrophic denitrification zone, which are separated by a partially penetrated partition. The heterotrophic aerobic denitrification zone is filled with aerobic denitrifying bacteria and a solution containing methanol, ethanol or acetic acid and quartz sand, and an oxygen injection pipe is arranged on the wall; the anaerobic autotrophic denitrification zone is filled with hydrogen autotrophic denitrifying bacteria and quartz sand, and a hydrogen injection pipe is arranged on the wall; the adsorption section is filled with zeolite and inert filler quartz sand; the low permeability section is filled with fine sand and inert filler quartz sand.

[0007] The above-mentioned existing technologies can achieve autotrophic and heterotrophic synergistic denitrification, and can also increase the overall nitrification and denitrification reaction time, thereby improving the efficiency of ammonia nitrogen pollution remediation in many aspects, but have the following shortcomings: ① The methanol, ethanol, etc. filled in the heterotrophic aerobic denitrification zone are liquids that are easily diluted and diffused in groundwater, and cannot provide a continuous carbon source, shortening the service life of the reaction zone and increasing the operation and maintenance cost; ② The anaerobic autotrophic denitrification zone needs to be regularly injected with hydrogen, which increases the operation and maintenance cost and safety risks; ③ The low permeability section is intended to increase the groundwater residence time, but if it is not combined with an effective water-proof and diversion structure, it is easy to cause groundwater bypass, affecting the remediation effect.

[0008] Publication number CN 114804346 A discloses a permeable reaction wall system for repairing groundwater contaminated by heavy metals, ammonia nitrogen and nitrates. The system comprises a ferrous ore permeable reaction wall, an anaerobic ammonium oxidation permeable reaction wall and a deep treatment permeable reaction wall which are sequentially arranged along the seepage direction of the groundwater pollution plume; the filler of the ferrous ore permeable reaction wall adopts one or two of siderite particles and pyrite particles; the structure of the anaerobic ammonium oxidation permeable reaction wall adopts an anaerobic ammonium oxidation permeable reaction wall body or multiple groups of anaerobic ammonium oxidation permeable reaction wall monomers coupled with a ferrous ore layer, and the permeable reaction wall body or the monomer is filled with polypropylene ring filler; the deep treatment permeable reaction wall contains a modified zeolite and volcanic rock composite filter material; the permeable reaction wall has a built-in steel support, and the steel support is coated with a permeable geotextile on the outside, and the wall permeability coefficient is controlled to be more than twice the permeability coefficient of the aquifer, and is kept equal or gradually increased along the seepage direction of the groundwater pollution plume.

[0009] The above existing technologies can repair heavy metal, ammonia nitrogen and nitrate pollution, but they are not applicable to the groundwater environment of ionic rare earth mines. The specific analysis is as follows: ① The fine control of anaerobic ammonia oxidation reaction requires high requirements and is difficult to achieve in the groundwater environment; ② The pyrite and siderite filled in the reaction wall often contain metal impurities such as Mg, Mn, Ni, and Cu, which are easily dissolved in the acidic groundwater of ionic rare earth mining areas, causing SO 4 2- and other metal pollution, and may also generate precipitated passivation fillers, block the reaction wall, and reduce the permeability and repair efficiency of the reaction wall; ③ The regulation of groundwater levels by the pumping wells and injection wells at the front end of the reaction wall increases the cost of project operation and maintenance, and is difficult to apply in ionic rare earth mining areas that lack water and electricity supply on a large scale.

[0010] In summary, it is necessary to develop a permeable reaction wall suitable for the remediation of groundwater pollution in ionic rare earth mining areas. Summary of the invention

[0011] In view of the problems in the related art, the present invention proposes a permeable reaction wall and a reaction system suitable for the remediation of groundwater pollution in ionic rare earth mining areas, so as to overcome the above-mentioned technical problems existing in the existing related art.

[0012] The technical solution of the present invention is achieved in this way:

[0013] A permeable reaction wall suitable for remediation of groundwater pollution in ionic rare earth mining areas, wherein a nitrification zone, a denitrification zone and an adsorption zone are sequentially arranged along the water flow direction, and a transition zone is sandwiched between the nitrification zone, the denitrification zone and the adsorption zone, and the filling material of the transition zone includes gravel;

[0014] The filler of the nitrification zone includes nitrifying bacteria agent, first zero-valent iron, alkaline agent, slow-release oxidant and gravel;

[0015] The filler of the denitrification zone includes a denitrifying bacteria agent, a second zero-valent iron, a solid carbon source, an alkali agent and gravel.

[0016] First, in the nitrification zone, the ammonia nitrogen in the pollution plume is converted into nitrate nitrogen by utilizing the aerobic nitrification of nitrifying bacteria;

[0017] The first zero-valent iron is used to reduce, adsorb and passivate heavy metal ions associated with rare earth minerals such as Pb, Cd, and As in groundwater, and on the other hand, the low-concentration iron ions released promote the above-mentioned nitrification reaction and improve the conversion rate of ammonia nitrogen;

[0018] The alkaline agent is used to adjust the pH of groundwater so that the pH of groundwater is maintained at 7-8, and to neutralize the hydrogen ions generated by the above-mentioned nitrification reaction;

[0019] The slow-release oxidant keeps the dissolved oxygen concentration in the groundwater above 2 mg / L, providing sufficient oxygen for aerobic nitrification;

[0020] The gravel is used to disperse the above-mentioned active filler and increase the permeability coefficient of the nitrification zone.

[0021] In the denitrification zone, the nitrate nitrogen generated in the nitrification zone is further converted into nitrogen gas by utilizing the anaerobic denitrification action of denitrifying bacteria;

[0022] The cathode hydrogen generated by the second zero-valent iron reacting with water accelerates the hydrogen autotrophic denitrification process of the denitrifying bacteria and improves the treatment efficiency of nitrate nitrogen;

[0023] Compared with liquid carbon sources (such as methanol, ethanol, etc.), the solid carbon source of the present invention can continuously and slowly release organic carbon, promote denitrification reaction, and is not easily washed away with water flow, which effectively prolongs the service life of the present invention and reduces operation and maintenance costs.

[0024] The alkali agent is the same as the nitrification zone, and is used to adjust the pH of groundwater so that the pH of groundwater is maintained at 7 to 8, thereby ensuring the pH adjustment function of the present invention;

[0025] The gravel is used to disperse the above-mentioned active filler and increase the permeability coefficient of the denitrification zone.

[0026] The adsorption zone is used to further adsorb ammonia nitrogen, nitrate nitrogen, and heavy metals in the groundwater, and at the same time adsorb a small amount of organic matter that may remain during the denitrification reaction.

[0027] The transition zone is mainly used to filter mineral particles such as clay in groundwater to prevent blockage of each reaction zone, and at the same time separate each reaction zone to maintain independent internal reaction conditions to avoid mutual interference.

[0028] From the above description, it can be seen that the present invention sets up multifunctional zones such as transition zone, nitrification zone, denitrification zone and adsorption zone according to the groundwater pollution characteristics of ionic rare earth mining areas, and also carries out scientific and reasonable research and development design of active fillers of permeable reaction walls, adopts green, economical, highly active microorganisms and zero-valent iron-based composite materials, couples microbial remediation, chemical reduction, physical adsorption and other technologies, regulates groundwater pH value, redox conditions and other parameters, and effectively treats groundwater acidification and NH in ionic rare earth mining areas. 4 + -N, NO 3 ⁻-N, heavy metal pollution problem, the repair effect is good, and the effluent water quality is stable.

[0029] In addition, the scientific design of the active fillers and the layer structure enables the active fillers to work synergistically with each other, and the treatment of pollutants in each functional area is progressive, so that the permeable reaction wall of the present invention can operate stably and unpowered for a long time, without the need to set up surface treatment facilities, is easy to maintain, can operate stably for a long time, and has good practicality and economy.

[0030] Preferably, the permeable reaction wall is stacked with a first transition zone, a nitrification zone, a second transition zone, a denitrification zone, a third transition zone, an adsorption zone and a fourth transition zone in sequence along the water flow direction.

[0031] The first transition zone, nitrification zone, second transition zone, denitrification zone, third transition zone, adsorption zone and fourth transition zone are respectively arranged along the direction of the water flow cross section.

[0032] Preferably, the weight ratio of the nitrifying bacteria agent, the first zero-valent iron, the alkaline agent, the slow-release oxidant, and the gravel in the nitrification zone is 1:0.4-0.5:0.5-0.6:2-3:10;

[0033] Preferably, the nitrifying bacteria agent is obtained by culturing activated sludge, with ammonia oxidizing bacteria and nitrite oxidizing bacteria as the dominant bacteria, and the effective bacterial species content is ≥10 7 CFU / g, which can convert ammonia nitrogen in the pollution plume into nitrate nitrogen through nitrification.

[0034] Specifically, the nitrifying bacteria agent of the present invention is a nitrifying bacteria agent produced by Bio-Feng Biotechnology (Guangdong) Co., Ltd.

[0035] Preferably, the first zero-valent iron is prepared by mixing and compounding zero-valent iron of different particle sizes of 0.1 to 5 mm in any proportion. On the one hand, it is used to reduce, adsorb and passivate heavy metal ions associated with rare earth minerals such as Pb, Cd, and As in groundwater. On the other hand, the released low-concentration iron ions promote the above-mentioned nitrification reaction and improve the ammonia nitrogen removal rate.

[0036] Preferably, the weight ratio of the denitrifying bacteria agent, the second zero-valent iron, the solid carbon source, the alkaline agent and the gravel in the denitrification zone is 1:0.2-0.3:1-1.2:0.2-0.3:10;

[0037] The denitrifying bacteria agent is obtained by culturing activated sludge, with denitrifying bacteria as the dominant bacteria, such as Pseudomonas, red sulfur bacteria, Alcaligenes, etc., and the effective bacteria content is ≥10 7 CFU / g, which can convert nitrate nitrogen in the pollution plume into nitrogen gas through denitrification.

[0038] Specifically, the denitrifying bacterial agent of the present invention is a denitrifying bacterial agent produced by Bio-Feng Biotechnology (Guangdong) Co., Ltd.

[0039] Specifically, the second zero-valent iron is prepared by mixing zero-valent iron of different particle sizes of 0.1 to 5 mm in any proportion, and the cathode hydrogen generated by the reaction with water accelerates the hydrogen autotrophic denitrification process of the above-mentioned denitrifying bacteria.

[0040] Preferably, the alkali agent comprises limestone and sodium bicarbonate in a weight ratio of 1:0.1-0.2, and is used to adjust the pH of groundwater so that the pH of groundwater is maintained at 7-8, and neutralize the hydrogen ions generated by the nitrification reaction in the nitrification zone.

[0041] Preferably, the slow-release oxidant comprises an active oxygen-releasing agent and a binder coating the active oxygen-releasing agent, and the slow-release oxidant is used to provide sufficient oxygen for the nitrification reaction to maintain the dissolved oxygen concentration of the groundwater above 2 mg / L.

[0042] Specifically, the active oxygen-releasing agent may be calcium peroxide, magnesium peroxide, persulfate, etc., and the binder may be attapulgite, alginate, paraffin, silicon oxide, etc.

[0043] The weight ratio of the active oxygen-releasing agent to the binder is 1:0.2-0.5. The active oxygen-releasing agent is calcium peroxide, and the binder is attapulgite. The active oxygen-releasing agent is prepared by a conventional process of granulation followed by packaging.

[0044] Preferably, the solid carbon source comprises a biomass raw material and biochar in a weight ratio of 1:9-11, the biomass raw material is plant particles (such as corn cobs, sawdust, etc.) with a particle size of 10-30 mm, and the biochar has a particle size of 1-3 mm. Compared with liquid carbon sources (such as methanol, ethanol, etc.), the two solid carbon sources designed in the present invention can continuously and slowly release organic carbon, promote denitrification, and the solid carbon source is not easy to flow away with the water flow, effectively extending the service life of the present invention and reducing operation and maintenance costs.

[0045] Preferably, the gravel can be quartz, feldspar, rock chips, etc. More preferably, the gravel is quartz sand with a particle size of 10 to 30 mm, which is used to disperse the active filler in each functional area and increase the permeability coefficient of each reaction area.

[0046] Preferably, the filler of the adsorption zone includes zeolite and biochar in a weight ratio of 5:1, which is used to further adsorb ammonia nitrogen, nitrate nitrogen, and heavy metals in groundwater, and at the same time adsorb a small amount of organic matter that may remain during the denitrification reaction.

[0047] Specifically, the particle size of the zeolite is 5 to 10 mm, and the particle size of the biochar is 1 to 3 mm.

[0048] The biochar is produced by Shida (Qingyuan) Environmental Restoration Technology Co., Ltd.

[0049] Preferably, the transition zone is filled with quartz, feldspar, rock chips, etc. More preferably, the gravel is quartz sand with a particle size of 10 to 30 mm.

[0050] Preferably, the thickness of the transition zone is 0.5 to 1.5 m; the thickness of the nitrification zone is 2 to 3 m; the thickness of the denitrification zone is 2 to 3 m; the thickness of the adsorption zone is 2 to 3 m;

[0051] The present invention also discloses a reaction system suitable for the remediation of groundwater pollution in ionic rare earth mining areas, comprising a water-isolating structure and the above-mentioned permeable reaction wall, wherein the permeable reaction wall is higher than the highest water level in the deployment area to ensure complete treatment of the groundwater pollution plume.

[0052] The transition zone is provided with a plurality of monitoring wells, which are hollow structures. The monitoring wells are vertically inserted in the transition zone with the tops exposed. The monitoring wells have a sieve hole area for water flow to enter, and the sieve hole area has a plurality of sieve holes. The top of the sieve hole area is higher than the highest water level in the layout area, and the bottom of the sieve hole area reaches the bottom of the monitoring well. The monitoring wells are designed to separately track and evaluate the water quality of groundwater inlet and outlet water in each reaction zone of the permeable reaction wall, and comprehensively evaluate the repair effect of the permeable reaction wall.

[0053] The water-proof structure surrounds the left and right sides and the bottom of the permeable reaction wall to form a U-shaped impermeable wall.

[0054] Compared with the prior art, the present invention designs a water-isolating structure and the above-mentioned permeable reaction wall according to the hydrogeological conditions and groundwater pollution characteristics of the ionic rare earth mining area to ensure the complete treatment of the pollution plume. At the same time, there is no need for pumping wells, injection wells, hydrogen injection and other control equipment, making the present invention particularly suitable for application in ionic rare earth mining areas with a large lack of water and electricity supply, and the cost of engineering operation and maintenance is relatively low.

[0055] Preferably, the nitrification zone and the denitrification zone are provided with a plurality of injection wells, the main body of the injection well is a hollow structure, the injection well is vertically inserted with the top exposed, the injection well has a through-hole area, the through-hole area has a plurality of through holes, and the bottom of the through-hole area is lower than the lowest water level of the layout area.

[0056] The injection well is used to appropriately supplement the repair agent for water quality problems, such as injecting liquid repair agents, filling replaceable solid repair agents, aeration and oxygenation, etc., so as to adjust the groundwater quality parameters, so that the microorganisms maintain a high degradation activity, and improve the repair effect and service life of the reaction wall. In addition, the injection well also has a gas conduction function, which can discharge the nitrogen generated by the denitrification reaction and has a gas conduction function.

[0057] Preferably, the plurality of monitoring wells and injection wells are arranged along the cross-sectional direction of the water flow.

[0058] Preferably, the diameter of the injection well is Φ50-110 mm.

[0059] Preferably, the permeability coefficient of the water-proof structure is less than 10 -6 cm / s.

[0060] Preferably, the bottom edge of one side of the anti-seepage enclosure in the water inlet direction extends deep into the relatively impermeable layer to form a water diversion bottom wall for guiding deep groundwater. The water diversion bottom wall penetrates into the relatively impermeable layer by at least 0.5m to prevent contaminated deep groundwater from flowing around the bottom of the anti-seepage enclosure. The design of the water diversion bottom wall enables the present invention to not only improve and repair shallow diving above the relatively impermeable layer, but also to control and improve deep diving above the relatively impermeable layer.

[0061] It should be noted that the “relatively impermeable layer” is usually a granite bedrock with a low degree of weathering and no cracks, and a permeability coefficient of less than 10 -6 cm / s.

[0062] Preferably, the left and right sides of the anti-seepage wall in the water inlet direction are extended and expanded to the left and right respectively to form a water diversion expansion wall to ensure that the pollution plume can be fully accommodated and guided. The water diversion expansion wall extends to connect with the left and right sides of the water diversion bottom wall, completely collecting and diverting shallow groundwater and deep groundwater to the permeable reaction wall.

[0063] The design of the water diversion bottom wall and the water diversion expansion wall enables the present invention to collect shallow groundwater and deep groundwater at the same time, and divert them to the permeable reaction wall to avoid groundwater bypass, which is beneficial to the comprehensive restoration of polluted groundwater. At the same time, it reduces the engineering difficulty of excavating the deep foundation pit of the reaction wall and saves the amount of active filler.

[0064] Specifically, in actual construction, the U-shaped anti-seepage enclosure can be realized by laying and fixing a HDPE anti-seepage membrane, and the water diversion bottom wall and water diversion expansion wall can be constructed using cement rotary jet pile technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention;

[0066] Figure 2 It is a schematic diagram of the relative position of the present invention and the groundwater environment;

[0067] Figure 3 for Figure 2 A magnified image of point A;

[0068] Figure 4 A top view of the present invention;

[0069] Figure 5 is a side view of the present invention;

[0070] Figure 6 It is a data line graph of ammonia nitrogen and nitrate after the implementation of the present invention.

[0071] Reference numerals

[0072] 1. Waterproof structure;

[0073] 101. Anti-seepage wall;

[0074] 102. Water diversion bottom wall;

[0075] 103. Divert water to expand the wall;

[0076] 2. Permeable reactive wall;

[0077] 201a, first transition zone;

[0078] 202, nitrification zone;

[0079] 201b, second transition zone;

[0080] 203, denitrification zone;

[0081] 201c, third transition zone;

[0082] 204, adsorption zone;

[0083] 201d, Fourth Transition Zone;

[0084] 3. Monitoring well; 301. Screen hole;

[0085] 4. Injection well; 401. Through hole;

[0086] 5. Ground;

[0087] 6. Maximum water level;

[0088] 7. Relatively impermeable layer. DETAILED DESCRIPTION

[0089] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0090] In the description of the present invention, it should be understood that the terms center, longitudinal, lateral, length, width, thickness, up, down, front, back, left, right, vertical, horizontal, top, bottom, inside, outside, clockwise, counterclockwise, etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0091] Reference Figures 1 to 5 The arrows in the attached drawings indicate the direction of groundwater flow. This embodiment is a reaction system suitable for the remediation of groundwater pollution in ionic rare earth mining areas. The engineering application of the present invention is carried out in a certain ionic rare earth mining area in Guangdong Province.

[0092] The reaction system comprises a water-proof structure 1 and a permeable reaction wall 2. The permeable reaction wall 2 is higher than the highest water level 6 of the deployment area to ensure complete treatment of the pollution plume.

[0093] The permeable reaction wall 2 is 20 m long, 10.5 m wide and 4.9 m deep.

[0094] The permeable reaction wall 2 is provided with a nitrification zone 202 , a denitrification zone 203 and an adsorption zone 204 in sequence along the water flow direction, and a transition zone is sandwiched between the nitrification zone 202 , the denitrification zone 203 and the adsorption zone 204 .

[0095] Specifically, the permeable reaction wall 2 is stacked with a first transition zone 201a, a nitrification zone 202, a second transition zone 201b, a denitrification zone 203, a third transition zone 201c, an adsorption zone 204 and a fourth transition zone 201d in sequence along the water flow direction;

[0096] The first transition zone 201a, the nitrification zone 202, the second transition zone 201b, the denitrification zone 203, the third transition zone 201c, the adsorption zone 204 and the fourth transition zone 201d are respectively arranged along the direction of the water flow cross section.

[0097] The filler of the nitrification zone 202 includes a nitrifying bacteria agent, a first zero-valent iron, an alkali agent, a slow-release oxidant and gravel in a weight ratio of 1:0.45:0.55:2.5:10;

[0098] The nitrifying bacteria agent is obtained by culturing activated sludge, with ammonia oxidizing bacteria and nitrite oxidizing bacteria as the dominant bacteria, and the effective bacteria content is ≥10 7 CFU / g, which can convert ammonia nitrogen in the pollution plume into nitrate nitrogen through nitrification.

[0099] Specifically, the nitrifying bacteria agent of the present invention is a nitrifying bacteria agent produced by Bio-Feng Biotech (Guangdong) Co., Ltd.

[0100] The first zero-valent iron is prepared by mixing and compounding zero-valent iron with different particle sizes of 0.1-5 mm in any proportion.

[0101] The filler of the denitrification zone 203 includes a denitrifying bacteria agent, a second zero-valent iron, a solid carbon source, an alkali agent and gravel in a weight ratio of 1:0.25:1.1:0.25:10.

[0102] The denitrifying bacteria agent is obtained by culturing activated sludge, with denitrifying bacteria as the dominant bacteria, such as Pseudomonas, red sulfur bacteria, Alcaligenes, etc., and the effective bacteria content is ≥10 7 CFU / g, which can convert nitrate nitrogen in the pollution plume into nitrogen gas through denitrification.

[0103] Specifically, the denitrifying bacterial agent of the present invention is a denitrifying bacterial agent produced by Bio-Feng Biotechnology (Guangdong) Co., Ltd.

[0104] The second zero-valent iron is prepared by mixing zero-valent iron with different particle sizes of 0.1 to 5 mm in any proportion.

[0105] The alkali agent comprises limestone and sodium bicarbonate in a weight ratio of 1:0.15.

[0106] The slow-release oxidant comprises an active oxygen-releasing agent and a binder coating the active oxygen-releasing agent, so that the dissolved oxygen concentration of groundwater is maintained above 2 mg / L.

[0107] Specifically, the active oxygen-releasing agent may be calcium peroxide, magnesium peroxide, persulfate, etc., and the binder may be attapulgite, alginate, paraffin, silicon oxide, etc.

[0108] The weight ratio of the active oxygen-releasing agent to the binder is 1:0.2-0.5. The active oxygen-releasing agent is calcium peroxide, and the binder is attapulgite. The active oxygen-releasing agent is prepared by a conventional process of granulation followed by packaging.

[0109] The solid carbon source comprises a biomass raw material and biochar in a weight ratio of 1:10, the biomass raw material is a corn cob with a particle size of 10 to 30 mm, and the biochar has a particle size of 1 to 3 mm.

[0110] The gravel is quartz sand with a particle size of 10 to 30 mm.

[0111] The filler of the adsorption zone 204 includes zeolite and biochar in a weight ratio of 5:1, the particle size of the zeolite is 5-10 mm, and the particle size of the biochar is 1-3 mm.

[0112] The biochar is produced by Shida (Qingyuan) Environmental Restoration Technology Co., Ltd.

[0113] The thickness of the transition zone is 1 m, the thickness of the nitrification zone 202 is 3 m, the thickness of the denitrification zone 203 is 3 m, and the thickness of the adsorption zone 204 is 3 m.

[0114] Each of the transition zones is provided with a plurality of (specifically 2 in this embodiment) monitoring wells 3, the monitoring wells 3 being hollow structures, vertically inserted in the transition zone with the top exposed, the monitoring well 3 having a sieve hole area for water flow to enter, the sieve hole area having a plurality of evenly distributed sieve holes 301, the top of the sieve hole area being higher than the highest water level 6 of the arrangement area, and the bottom of the sieve hole area extending to the bottom of the monitoring well 3, the monitoring well 3 is designed to respectively track and evaluate the water quality of the groundwater inlet and outlet water of each reaction zone of the permeable reaction wall 2, and comprehensively evaluate the repair effect of the permeable reaction wall 2.

[0115] The nitrification zone 202 and the denitrification zone 203 are each provided with a plurality of (specifically 5 in this embodiment) injection wells 4, the main body of the injection well 4 is a hollow structure, the injection well 4 is vertically inserted and the top is exposed, the injection well 4 has a through hole area, the through hole area has a plurality of evenly distributed through holes 401, and the bottom end of the through hole area is lower than the lowest water level of the layout area. The diameter of the injection well 4 is Φ80mm.

[0116] The monitoring wells 3 and injection wells 4 in each functional area are arranged along the cross-sectional direction of the water flow.

[0117] The water-proof structure 1 surrounds the left and right sides and the bottom of the permeable reaction wall 2 to form a U-shaped anti-seepage wall 101. The permeability coefficient of the water-proof structure 1 is less than 10 -6 cm / s.

[0118] The bottom edge of one side of the anti-seepage wall 101 in the water inlet direction extends deep into the relatively impermeable layer 7 to form a water diversion bottom wall 102 for guiding deep groundwater. The water diversion bottom wall 102 extends 70.5 meters into the relatively impermeable layer.

[0119] The “relatively impermeable layer 7” is a granite bedrock with a low degree of weathering and no cracks, and a permeability coefficient of <10 -6 cm / s.

[0120] The left and right sides of the anti-seepage wall 101 in the water inlet direction are extended and expanded to the left and right directions respectively to form a water diversion expansion wall 103 to ensure that the pollution plume can be fully accommodated and guided. The water diversion expansion wall 103 extends to connect with the left and right sides of the water diversion bottom wall 102, completely collecting and diverting shallow groundwater and deep groundwater to the permeable reaction wall 2.

[0121] In actual construction, after the foundation pit is constructed, a fixed HDPE anti-seepage membrane is laid inside the foundation pit to form the U-shaped anti-seepage enclosure 101, and the water diversion bottom wall 102 and the water diversion expansion wall 103 can be constructed using cement rotary jet pile technology.

[0122] Reference Figure 6 After the above-mentioned reaction system was put into operation, the groundwater quality in the area gradually improved, and with the growth of microorganisms and the enhancement of nitrification and denitrification, the remediation effect of the reaction system gradually improved.

[0123]

[0124] The reaction system was operated for 10 months without any additional injection or aeration. The pH of the groundwater downstream of the reaction system increased from 5.4 to 6.9; ammonia nitrogen dropped from the inlet concentration of 27.36 mg / L to 0.3 mg / L, with a removal rate of 98.9%; nitrate nitrogen dropped from the inlet concentration of 14.9 mg / L to 1.4 mg / L, with a removal rate of 90.6%; the excessive heavy metal lead index dropped from the inlet concentration of 0.057 mg / L to below the detection limit, with a removal rate of 100.0%.

[0125] All indicators are lower than Class III standards of the Groundwater Quality Standard (GB / T 14848-2017), achieving the restoration goal, indicating that the present invention can effectively improve and repair the pollution of groundwater in ionic rare earth mining areas, and the effect is long-lasting and stable, and basically requires no maintenance.

[0126] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also change and modify the above implementation modes. Therefore, the present invention is not limited to the specific implementation modes disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A permeable reaction wall suitable for remediation of groundwater pollution in ionic rare earth mining areas, characterized in that: A nitrification zone, a denitrification zone and an adsorption zone are arranged in sequence along the water flow direction, and a transition zone is sandwiched between the nitrification zone, the denitrification zone and the adsorption zone. The filler of the nitrification zone includes nitrifying bacteria agent, first zero-valent iron, alkaline agent, slow-release oxidant and gravel, and the weight ratio of the nitrifying bacteria agent, first zero-valent iron, alkaline agent, slow-release oxidant and gravel in the nitrification zone is 1:0.4-0.5:0.5-0.6:2-3:10; The slow-release oxidant comprises an active oxygen-releasing agent and a binder coating the active oxygen-releasing agent, and the weight ratio of the active oxygen-releasing agent to the binder is 1:0.2-0.5; The active oxygen-releasing agent is calcium peroxide, magnesium peroxide or persulfate, and the binder is attapulgite, alginate, paraffin or silicon oxide; The filler of the denitrification zone includes a denitrifying bacteria agent, a second zero-valent iron, a solid carbon source, an alkali agent and gravel, and the weight ratio of the denitrifying bacteria agent, the second zero-valent iron, the solid carbon source, the alkali agent and the gravel in the denitrification zone is 1:0.2-0.3:1-1.2:0.2-0.3:10; The alkali agent comprises limestone and sodium bicarbonate in a weight ratio of 1:0.1-0.2; The solid carbon source includes biomass raw materials and biochar in a weight ratio of 1:9-11; The filler of the adsorption zone includes zeolite and biochar in a weight ratio of 5:1; The filler of the transition zone includes gravel.

2. The permeable reactive wall according to claim 1, characterized in that: The permeable reaction wall is stacked with a first transition zone, a nitrification zone, a second transition zone, a denitrification zone, a third transition zone, an adsorption zone and a fourth transition zone in sequence along the water flow direction. The first transition zone, nitrification zone, second transition zone, denitrification zone, third transition zone, adsorption zone and fourth transition zone are respectively arranged along the direction of the water flow cross section.

3. The permeable reactive wall according to claim 1 or 2, characterized in that: The nitrifying bacteria agent has ammonia oxidizing bacteria and nitrite oxidizing bacteria as the dominant bacteria, and the effective bacteria content is ≥10 7 CFU / g.

4. The permeable reactive wall according to claim 1 or 2, characterized in that: The denitrifying bacteria agent has denitrifying bacteria as the dominant bacteria, and the effective bacteria content is ≥10 7 CFU / g.

5. The permeable reactive wall according to claim 1 or 2, characterized in that: The particle size of the gravel is 10 to 30 mm.

6. A permeable reaction system suitable for remediation of groundwater pollution in ionic rare earth mining areas, characterized in that: It comprises a water-proof structure and a permeable reaction wall as claimed in any one of claims 1 to 5; The permeable reaction wall is higher than the highest water level in the deployment area. The transition zone is provided with a plurality of monitoring wells, which are hollow structures, are vertically inserted in the transition zone with the top exposed, have a sieve hole area for water flow to enter, and have a plurality of sieve holes. The top of the sieve hole area is higher than the highest water level in the arrangement area, and the bottom of the sieve hole area reaches the bottom of the monitoring well. The water-proof structure surrounds the left and right sides and the bottom of the permeable reaction wall to form a U-shaped impermeable wall.

7. The permeable reaction system according to claim 6, characterized in that: The bottom edge of one side of the anti-seepage wall in the water inlet direction extends deep into the relatively impermeable layer to form a water diversion bottom wall for guiding deep groundwater, and the water diversion bottom wall extends at least 0.5m into the relatively impermeable layer.

8. The permeable reaction system according to claim 7, characterized in that: The left and right sides of the anti-seepage wall in the water inlet direction extend and expand to the left and right directions respectively to form a water diversion expansion wall. The water diversion expansion wall extends to connect with the left and right sides of the water diversion bottom wall.

9. The permeable reaction system according to any one of claims 6 to 8, characterized in that: The nitrification zone and the denitrification zone are provided with a plurality of injection wells, the main body of the injection well is a hollow structure, the injection well is vertically inserted with the top exposed, the injection well has a through hole area penetrating therethrough, the through hole area has a plurality of through holes, and the bottom end of the through hole area is lower than the lowest water level of the layout area.

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