A zero-valent iron / slow-release carbon-zeolite combined groundwater denitrification partition type permeable reactive wall and operation process

Abstract

This invention discloses a zoned permeable reactive barrier (PRB) for groundwater denitrification using a combination of zero-valent iron / slow-release carbon and zeolite, and its operating process. The PRB's structure comprises: (1) a quartz sand water distribution zone; (2) Fe... 0 / C-Denitrifying bacteria reaction zone; (3) Zeolite adsorption zone. This invention uses a mixture of biomass slow-release carbon and artificial slow-release carbon as a slow-release carbon source, and adds zero-valent iron to construct Fe 0 The / C system, using a mixed denitrifying bacteria agent for rapid start-up, and a zoned permeable reactive barrier (PRB) operation process for groundwater denitrification have been developed. This includes: filling processes based on different media permeability coefficients, reaction zone packing material compatibility based on different slow-release rates, and operating parameters based on different groundwater nitrogen pollutant concentrations. This invention improves the adaptability of the PRB process to hydrogeological conditions, accelerates the start-up of the denitrification process, ensures denitrification effectiveness during the start-up phase, improves denitrification efficiency during operation, and extends remediation time.

Description

[0001]

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[0002] This invention relates to a zoned permeable reactive barrier for groundwater denitrification using a combination of zero-valent iron / slow-release carbon and zeolite, and its operating process, belonging to the field of groundwater remediation technology. [Background Technology]

[0003] With the rapid development of industry and agriculture, the problem of "three nitrogen" pollution in groundwater has intensified year by year, threatening the safety of groundwater drinking water. Nitrates and nitrite These substances can induce methemoglobinemia, impair the oxygen-carrying capacity of hemoglobin, and generate carcinogenic factors under the action of secondary amines, thus posing a threat to human and animal health. Therefore, it is urgent to remediate the "three nitrogens" pollution in landfill groundwater.

[0004] In existing groundwater remediation projects involving nitrogen oxides, phosphorus, and hydrogen monoxide (PNO3) pollution, PRB remediation technology is widely used and has achieved good purification results. In groundwater primarily contaminated with pollutants, biological denitrification reaction walls are mainly used for remediation. However, a major drawback of denitrification reaction walls is their slow start-up process. To accelerate biological start-up, domestic and international scholars have conducted relevant research on microbial inoculation methods. Although this can shorten the acclimatization period of microorganisms, it still cannot avoid the problem of low denitrification efficiency during the start-up period. In addition, the presence of carbon sources can easily lead to excessive organic matter content in the effluent. Chinese patent application No. 202110563302.X, published on August 27, 2021, discloses a method for denitrification and nitrogen removal in groundwater using a co-culture denitrification method with a zero-valent iron-modified biochar composite packing column and a permeable reaction wall. This method uses iron shavings as the source of zero-valent iron and sodium acetate as the carbon source, and denitrifies by inoculating denitrifying bacteria, thereby significantly improving denitrification efficiency and reducing costs. Chinese patent application No. 202210048918.8, published on January 17, 2022, discloses a method based on Fe... 0 - A composite permeable reactive wall system using bentonite-modified biochar filler and its application. This method involves pumping nutrient solution into a composite filler inoculated with denitrifying bacteria (quartz sand, Fe). 0 Bentonite-modified biochar and resin were used to remove chlorinated organic matter and nitrates from groundwater. The above scheme demonstrates the application of zero-valent iron and microorganisms in improving the denitrification efficiency of permeable reactive barriers in groundwater. However, it suffers from problems such as the inability to continuously release carbon sources and unstable release rates, as well as high long-term maintenance costs. Therefore, accelerating the start-up of denitrification and selecting suitable slow-release carbon sources to extend treatment time and reduce the concentration of organic matter in the effluent are particularly important.

[0005] for Natural clinoptilolite has advantages such as high adsorption capacity, low price, and good stability, making it suitable for adsorption. Dissolved oxygen (DO) in water and As electron acceptors compete with each other, the addition of zero-valent iron (ZVI) reduces dissolved oxygen (DO) in the water. Therefore, adding ZVI to biological systems can accelerate the initiation of denitrification and enhance its performance. On the other hand, the presence of microorganisms can significantly enhance denitrification by biodegrading and consuming the hydrogen bubbles generated by ZVI corrosion. Therefore, constructing an Fe / C coupling system can not only accelerate the initiation of biological denitrification, but also improve the removal efficiency during the biological initiation period. Removal rate. However, ZVI has many problems in engineering applications, such as easy agglomeration due to its small particle size, easy oxidation leading to a reduction in the iron content that actually plays a reducing role, easy migration with groundwater, and small specific area, which makes it prone to caking and seriously affects the removal rate. The removal effect; while sponge iron contains high Fe 0 Its composition and loose, porous internal structure give it a specific surface area approximately 10 times that of ordinary ZVI, compared to that in water. It allows for more thorough contact and more complete redox reactions, and is also cheaper. Furthermore, sponge iron can rapidly dissolve iron ions, exhibits strong electrochemical enrichment, and has high surface energy. It removes impurities from wastewater through physical adsorption, redox reactions, and flocculation sedimentation. Therefore, sponge iron is an excellent... Chemicals also produce raw materials.

[0006] The slow-release carbon sources used for denitrification mainly fall into two categories: (1) natural solid slow-release carbon sources, such as straw, cotton, rice husks, corn cobs, reeds, sawdust, and other natural plants; (2) biodegradable polymers, including polylactic acid (PLA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), polybutylene succinate (PBS), etc. Compared with inexpensive natural solid organic matter, biodegradable polymers produce better effluent quality, lower color and TOC, and are more stable and easier to control during denitrification. However, their higher price limits their application in the water treatment field. Sawdust produces fewer byproducts (N2O, DOC) during denitrification and has a longer carbon release cycle. PBS has good biodegradability, a lower price, good water resistance, and good mechanical properties, making it a leader among biodegradable plastic materials.

[0007] Based on the above analysis, optimizing and developing a PRB process that is efficient, durable, rapidly bio-activated, low in operating costs, and can simultaneously remove "three nitrogens" from landfill groundwater is urgently needed in the industry to improve groundwater environmental quality and ensure the safety of groundwater drinking water. [Summary of the Invention]

[0008] In view of the above-mentioned shortcomings and industry needs, the present invention provides a zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination and its operation process.

[0009] This invention is achieved through the following technical solution: using natural biomass slow-release carbon sources and artificial slow-release carbon sources as slow-release carbon sources, adding denitrifying bacteria agents for initiation inoculation, and selecting zero-valent iron as... Chemical reducing agent, constructing Fe 0 The / C system addresses potential issues during the chemical reduction of zero-valent iron. Zeolite, which has good adsorption performance and is economically available, is used for adsorption. This invention provides a zoned permeable reactive barrier (PRB) for groundwater denitrification using a combination of zero-valent iron / slow-release carbon and zeolite, and its operating process. Its structural features are as follows (see...). Figure 1 ), along the groundwater flow direction from top to bottom are: (1) quartz sand water distribution area; (2) Fe 0 / C-Denitrifying bacteria reaction zone; (3) Zeolite adsorption zone. The zero-valent iron / slow-release carbon-zeolite combined groundwater denitrification zoned permeable reactive barrier (PRB) and its operation process provided by the present invention can realize the rapid start-up of denitrification, improve the efficiency of PRB in the simultaneous removal of "three nitrogens" in groundwater, and ensure its operation efficiency.

[0010] A zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite and its operating process are characterized by employing a mixture of biomass-released carbon and artificially released carbon as the slow-release carbon source, and adding zero-valent iron to construct Fe... 0 The / C system, using a mixed denitrifying bacteria agent, enables rapid start-up. A zoned permeable reactive barrier operation process for groundwater denitrification was developed, including: filling processes based on different media permeability coefficients, reaction zone packing material compatibility based on different slow-release rates, and operating parameters based on different groundwater nitrogen pollutant concentrations. The specific process steps are as follows:

[0011] S1: A zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination and its operation process, characterized by the following filling process steps based on different media permeability coefficients:

[0012] S101: The structural features of the PRB reaction chamber include: the chamber body and partitions are made of rigid perforated plates; the chamber body is divided into three compartments: a quartz sand water distribution area, an Fe... 0 / C-Denitrifying bacteria reaction zone, zeolite adsorption zone; the packing box frame adopts an interlocking assembly design, and the top frame has a prefabricated hoisting point.

[0013] S102: Filling of the quartz sand water distribution zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill the groundwater distribution zone with quartz sand of different gradations (0.063mm-0.2mm, 0.2mm-0.4mm, 0.4mm-2.0mm and greater than 2.0mm) along the direction of groundwater flow. The filling thickness is 50-500mm. The permeability coefficient of the quartz sand water distribution zone is not less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit. When filling quartz sand of different gradations, use baffles to assist in the filling.

[0014] S103:Fe 0 / C- Filling of the denitrifying bacteria reaction zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill with a mixed packing material of 100-2000 mm thick containing zero-valent iron, slow-release carbon source, and denitrifying bacteria agent. 0 The permeability coefficient of the C-denitrifying bacteria reaction zone is no less than twice the permeability coefficient of the aquatic medium in the hydrogeological unit.

[0015] S104: Filling the zeolite adsorption zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill the zeolite with different gradations (greater than 6.0mm, 6.0-4.0mm, 4.0-2.0mm and 2.0-0.5mm) along the direction of groundwater flow. The filling thickness is 50-500mm. The permeability coefficient of the zeolite adsorption zone is not less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit. When filling zeolite with different gradations, use baffles to assist in the filling.

[0016] S105: After the PRB reaction box is filled, it is assembled and then hoisted through the prefabricated hoisting points of the reaction box.

[0017] S2: A zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination and its operation process, characterized in that the reaction zone packing material compatibility process steps based on different slow-release rates are as follows:

[0018] S201: The types, particle sizes, and compatibility of slow-release carbon sources are as follows: (1) Slow-release carbon sources include biomass slow-release carbon and artificial slow-release carbon. Biomass slow-release carbon mainly includes: pine bark, olive pomace, sawdust, cork, corn stalks, poplar leaves, sawdust, rice straw, coconut shell flakes, rice husks, corn cobs, cotton, sawdust, canna lilies, reeds, lemongrass, cattails, etc. Artificial slow-release carbon mainly includes: polyvinyl chloride (PCL), polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), polylactic acid (PLA), β-hydroxybutyrate-co-β-hydroxyvalerate (PHBV), polyvinyl alcohol (PVA), polybutylene succinate (PBS), etc. (2) Biomass slow-release carbon is usually in a rough and irregular shape with an average size of 1.0 to 10.0 mm; artificial slow-release carbon is usually in a regular shape with an average size of 1.0 to 10.0 mm. (3) Based on the carbon release rate of the slow-release carbon source with different denitrification carbon source requirements, adjust the ratio of biomass slow-release carbon and artificial slow-release carbon, with a mass ratio of 1:10 to 9:10.

[0019] S202: The types, particle sizes, and compatibility of zero-valent iron are as follows: (1) The main types of zero-valent iron include: nano-zero-valent iron, blast furnace slag, hematite, siderite, iron shavings, sponge iron, etc. (2) Except for nano-zero-valent iron, the other zero-valent iron fillers are usually granular, with a size of 2.0 to 4.0 mm. (3) The mass ratio of zero-valent iron to slow-release carbon source is 1:3 to 1:8. (4) Except for nano-zero-valent iron, the other zero-valent iron fillers are acid-washed with 0.2 to 1.0 mol / L for 10 to 60 min to improve their reactivity.

[0020] S203: The composition, form, and compatibility of denitrifying bacteria agents are as follows: (1) The main components of denitrifying bacteria agents are: denitrifying bacteria, Bacillus, Pseudomonas, activating enzymes, and polysaccharides, etc. (2) The main forms of denitrifying bacteria agents include: powder, granules, and fluid. (3) The mixing amount of denitrifying bacteria agents is 2-10% of the mass of the slow-release carbon source.

[0021] S204: The types, particle sizes, and compatibility of zeolites are as follows: (1) Zeolite types include: sodium zeolite, anticline zeolite, clinoptilolite, chalcogenide, cyclohexane, flaky zeolite, mordenite, zeolite, zeolite, calcium cross-linked zeolite, calcareous zeolite, artificial zeolite, etc. (2) The zeolite particle size is 0.5-10 mm. (3) According to claim 3, the zeolite adsorption zone adopts a gradation from large to small, which is the opposite of the quartz sand water distribution zone.

[0022] S205: The compatibility of reaction zone fillers based on different slow-release rates includes: doping, mixing, layering, coating, etc., and the permeability coefficient of the filling material is not less than the final permeability coefficient of quartz sand.

[0023] S3: A zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination and its operating process, characterized by the following operating process based on different groundwater nitrogen pollutant concentrations: Groundwater At that time, the hydraulic residence time (HRT) was 0.4 days; When the concentration is 30–50 mg / L, the HRT is 0.4–1.6 days; At that time, the HRT was 1.6–16 days.

[0024] The principle of this invention is: during the start-up phase of a zoned PRB (Potentially Specific Removal Booster), nitrogen removal is mainly achieved through physical and chemical processes in the influent. Reduced to zero-valent iron And N2, within this stage of the system The nitrogen is adsorbed by the zeolite adsorption layer at the end of the reactor. As the reactor's biological start-up is complete, biological denitrification gradually becomes dominant. First, under the action of microorganisms, the slow-release carbon source is degraded into small-molecule nutrients, primarily providing carbon for the biological reaction; at the front end of the partitioned PRB, microorganisms denitrify through aerobic denitrification... and NO2 - Converted to N2; through nitration, the system's... Transform into Throughout the entire PRB reactor, not only denitrification removes... Some microorganisms also participate in autotrophic denitrification using zero-valent iron, utilizing zero-valent iron to reduce... The product Fe(II) acts as an electron donor, oxidizing Fe(II) to Fe(III) and simultaneously reducing it.

[0025] Compared with existing processes, the beneficial effects of the present invention are as follows:

[0026] (1) Fe is constructed by adding zero-valent iron. 0 The / C system can quickly complete the start-up of biological denitrification (the start-up period is about 10 days) and ensure that the PRB continuously and stably releases carbon sources during the biological start-up period, maintaining a high nitrogen removal efficiency and significantly improving the nitrogen removal effect.

[0027] (2) The present invention provides a zero-valent iron / slow-release carbon-zeolite combined groundwater denitrification zoned permeable reactive barrier and its operation process for denitrifying groundwater. After the biological denitrification is started, it achieves efficient removal of nitrate, ammonia nitrogen and total nitrogen.

[0028] (3) The apparatus required for the reaction is simple, easy to operate, and has high denitrification efficiency. [Attached Image Description]

[0029] Figure 1A schematic diagram of a zoned permeable reactive barrier structure for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination provided by the present invention (the shape and size can be adjusted according to requirements);

[0030] Wherein, a—zeolite adsorption zone (coarse sand); b—zeolite adsorption zone (fine sand); c—Fe 0 / C - Denitrifying bacteria reaction zone; d - Quartz sand water distribution zone (coarse sand); e - Quartz sand water distribution zone (fine sand).

[0031] Figure 2 A schematic diagram of a zoned permeable reactive barrier filling process for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination provided by the present invention (the shape and size can be adjusted according to requirements);

[0032] The stuffing box body and partitions are made of rigid perforated plates. When filling with quartz sand of different grades, partitions are used to assist in the filling process.

[0033] Figure 3 A schematic diagram of a partitioned permeable reactive wall box assembly process for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combined application is provided by the present invention (the shape and size can be adjusted according to requirements);

[0034] The stuffing box frame adopts an interlocking assembly design, with prefabricated hoisting points on the top frame. After the stuffing is filled, the interlocking assembly is carried out, and the hoisting operation is carried out through the prefabricated hoisting points of the reaction tank.

[0035] Figure 4 The example diagram shows the optimal process verification diagram of a zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination, provided by the present invention.

[0036] In the examples, after groundwater was treated by the denitrification method of the present invention, the removal rates of nitrate, ammonia nitrogen, and total nitrogen reached 84.56%, 87%, and 76.99%, respectively, and the effluent NO3... - With a concentration of ≤5.0 mg / L, it can stably meet the requirements of the "Groundwater Quality Standard" (GB / T14848 2017) (Class II water).

Detailed Implementation Methods

[0037] This embodiment provides a zoned permeable reactive barrier and its operation process for groundwater denitrification using a combination of zero-valent iron / slow-release carbon and zeolite. The raw water in this embodiment is groundwater containing "three nitrogens". The concentration is approximately 30 mg / L. This invention provides a zoned permeable reactive barrier for groundwater denitrification using a combination of zero-valent iron / slow-release carbon and zeolite, and its operating process, comprising the following steps:

[0038] S1: Groundwater containing "trinitrogen" flows sequentially through the (1) quartz sand water distribution zone of the zoned permeable reactive barrier; (2) Fe 0 / C-Denitrifying bacteria reaction zone; (3)Zeolite adsorption zone.

[0039] S2: A mixture of biomass-released carbon and artificially released carbon is used as the slow-release carbon source, with zero-valent iron added to construct Fe. 0 The / C system, with mixed denitrifying bacteria, enables rapid startup. A zoned permeable reactive barrier operation process for groundwater denitrification has been developed, including: filling processes based on different media permeability coefficients, reaction zone packing compatibility based on different slow-release rates, and operating parameters based on different groundwater nitrogen pollutant concentrations.

[0040] Step S2 specifically includes:

[0041] S201: Filling process steps based on different media permeability coefficients: (1) Structural features of the PRB reaction chamber include (see Figure 2 The enclosure and partitions are made of rigid perforated plate; the enclosure is divided into three compartments: a quartz sand water distribution area, and an Fe... 0 / C-Denitrifying bacteria reaction zone, zeolite adsorption zone; the packing box frame adopts an interlocking assembly design, and the top frame is prefabricated for hoisting. (2) Filling of the quartz sand distribution zone: According to the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, quartz sand of different grades (0.063mm-0.2mm, 0.2mm-0.4mm, 0.4mm-2.0mm and greater than 2.0mm) are filled along the direction of groundwater flow. The filling thickness is 200mm. The permeability coefficient of the quartz sand distribution zone is not less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit. When filling quartz sand of different grades, a partition is used to assist in filling. (3) Fe 0 / C- Filling of the denitrifying bacteria reaction zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill with a 600mm thick mixed packing material containing zero-valent iron, slow-release carbon source, and denitrifying bacteria agent. 0 / C- The permeability coefficient of the denitrifying bacteria reaction zone is not less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit; (4) Filling of the zeolite adsorption zone: According to the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill zeolite with different gradations (greater than 6.0mm, 6.0-4.0mm, 4.0-2.0mm and 2.0-0.5mm) along the direction of groundwater flow, with a filling thickness of 200mm, Fe 0 / C- The volume ratio of the denitrifying bacteria reaction zone to the zeolite adsorption zone is 3:1. The permeability coefficient of the zeolite adsorption zone is not less than twice the permeability coefficient of the aquatic medium in the hydrogeological unit. When filling zeolite of different grades, use baffles to assist in filling. (5) After the PRB reaction box is filled, perform interlocking assembly and hoisting operation through the prefabricated hoisting point of the reaction box (see Figure 3 ).

[0042] S202: Process steps for compatibility of reaction zone packing based on different slow-release rates: (1) Slow-release carbon sources include biomass slow-release carbon and artificial slow-release carbon, of which biomass slow-release carbon is sawdust and artificial slow-release carbon is polybutylene succinate (PBS). The sawdust is rough and irregular, with an average size of 1.0 to 5.0 mm; PBS is white crystalline elliptical cylindrical particles with an average size of 2 mm × 3 mm × 3 mm. Based on the carbon release rate of the slow-release carbon source according to the different denitrification carbon source requirements, the ratio of biomass slow-release carbon and artificial slow-release carbon is adjusted to a mass ratio of 1:2. (2) Zero-valent iron is selected from sponge iron, which is brownish-brown granular with a size of 2.0 to 4.0 mm. It is acid-washed with 0.5 mol / L for 40 min to improve the reaction activity. The mass ratio of zero-valent iron to slow-release carbon source is 1:4. (3) The denitrifying bacteria agent is in powder form, and the main components are denitrifying bacteria, Bacillus, Pseudomonas, activating enzymes and polysaccharides, etc. The amount of denitrifying bacteria mixed is 5% of the mass of the slow-release carbon source. (4) Natural clinoptilolite is selected as the zeolite, with a particle size of 0.5-10 mm. (5) Based on the requirements of different slow-release rates, the reaction zone packing adopts mixed packing, and the permeability coefficient of the packing material is not less than the final permeability coefficient of the quartz sand.

[0043] S203: Operating procedures based on different groundwater nitrogen pollutant concentrations: groundwater The concentration was approximately 30 mg / L, the HRT was 1.6 days, and the ambient temperature was 18–20 °C.

[0044] After treatment with the above-mentioned denitrification methods, the removal rates of nitrate, ammonia nitrogen, and total nitrogen in the groundwater reached 84.56%, 87%, and 76.99%, respectively. It can stably meet the requirements of the "Groundwater Quality Standard" (GB / T14848 2017) (Class II water) (see...) Figure 4 ).

[0045] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make several improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A zoned permeable reactive barrier operation process for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite, characterized in that, from top to bottom along the groundwater flow direction, it consists of: (1-1) a quartz sand water distribution zone; (1-2) an Fe... 0 / C-Denitrifying bacteria reaction zone; (1-3) Zeolite adsorption zone; A mixture of biomass-released carbon and artificially released carbon was used as the slow-release carbon source, and zero-valent iron was added to construct Fe. 0 The / C system, with its rapid start-up of mixed denitrifying bacteria, is a zoned permeable reactive barrier (PRB) operation process for groundwater denitrification, including: The filling process is based on different media permeability coefficients, the compatibility of reaction zone packing materials based on different slow release rates, and the operating parameters are based on different groundwater nitrogen pollutant concentrations.

2. The operating process of a zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination as described in claim 1, characterized in that, The filling process steps based on different media permeability coefficients are as follows: (2-1) The structural features of the PRB reaction chamber include: the chamber body and partitions are made of rigid perforated plates; the chamber body is divided into three compartments: a quartz sand water distribution area, an Fe... 0 / C-Denitrifying bacteria reaction zone, zeolite adsorption zone; the packing box frame adopts an interlocking assembly design, and the top frame has prefabricated hoisting points; (2-2) Filling of the quartz sand distribution zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, quartz sand with different gradations from small to large is filled along the direction of groundwater flow. The different gradations are 0.063 mm-0.2 mm, 0.2 mm-0.4 mm, 0.4 mm-2.0 mm and greater than 2.0 mm, respectively. The filling thickness is 50~500 mm. The permeability coefficient of the quartz sand distribution zone is not less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit. When filling quartz sand with different gradations, baffles are used to assist in the filling. (2-3)Fe 0 / C- Filling of the denitrifying bacteria reaction zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill with a mixed packing material of 100~2000 mm containing zero-valent iron, slow-release carbon source, and denitrifying bacteria agent. 0 / C- The permeability coefficient of the denitrifying bacteria reaction zone is no less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit. (2-4) Filling the zeolite adsorption zone: Based on the permeability coefficient of the aquifer medium in the hydrogeological unit where the PRB is located, fill the zeolite with different gradations from large to small along the direction of groundwater flow. The different gradations are greater than 6.0 mm, 6.0-4.0 mm, 4.0-2.0 mm and 2.0-0.5 mm, respectively. The filling thickness is 50~500 mm. The permeability coefficient of the zeolite adsorption zone is not less than twice the permeability coefficient of the aquifer medium in the hydrogeological unit. When filling zeolite with different gradations, use baffles to assist in filling. (2-5) After the PRB reaction box is filled, it is assembled and hoisted through the prefabricated hoisting point of the reaction box.

3. The operating process of a zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination as described in claim 1, characterized in that, The reaction zone packing formulation process based on different sustained-release rates is as follows: (3-1) The types, particle sizes, and compatibility of the slow-release carbon sources are as follows: (1) Slow-release carbon sources include biomass slow-release carbon and artificial slow-release carbon. Biomass slow-release carbon mainly includes: pine bark, olive pomace, sawdust, cork, corn stalks, poplar leaves, sawdust, rice straw, coconut shell chips, rice husks, corn cobs, cotton, sawdust, canna lilies, reeds, lemongrass, and cattails. Artificial slow-release carbon mainly includes: polyvinyl chloride (PCL), polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), polylactic acid (PLA), β-hydroxybutyrate-co-β-hydroxyvalerate (PHBV), polyvinyl alcohol (PVA), and polybutylene succinate (PBS). (2) Biomass-released carbon is coarse and irregular in shape, with an average size of 1.0~10.0 mm; artificially released carbon is regular granules with an average size of 1.0~10.0 mm. (3) Based on the carbon release rate of the slow-release carbon source with different carbon source requirements for denitrification, adjust the ratio of biomass slow-release carbon and artificial slow-release carbon, with a mass ratio of 1:10 to 9:10; (3-2) The types, particle sizes, and compatibility of zero-valent iron are as follows: (1) The main types of zero-valent iron include: nano zero-valent iron, blast furnace slag, hematite, siderite, iron shavings, and sponge iron; (2) Except for nano-zero valent iron, the other zero valent iron fillers are in granular form with a size of 2.0~4.0 mm; (3) The mass ratio of zero-valent iron to slow-release carbon source is 1:3~1:8; (4) Except for nano-zero-valent iron, the other zero-valent iron fillers are acid-washed with 0.2~1.0 mol / L for 10~60 min to improve their reactivity; (3-3) The components, forms, and compatibility of denitrifying bacteria agents are as follows: (1) The main components of the denitrifying bacteria agent are: denitrifying bacteria, Bacillus, Pseudomonas, activating enzymes and polysaccharides; (2) The main forms of denitrifying bacteria agents include: powder, granules and fluid; (3) The mixing amount of denitrifying bacteria is 2-10% of the mass of the slow-release carbon source; (3-4) The types, particle sizes, and compatibility of zeolites are as follows: (1) The types of zeolites include: sodium zeolite, anticline zeolite, clinoptilolite, chalcogenide, cyclohexene, scabra zeolite, mordenite, zeolite, zeolite, calcium cross zeolite, calcareous zeolite, and artificial zeolite. (2) The particle size of the zeolite is 0.5~10 mm; (3) As described in claim 2, the zeolite adsorption zone adopts a gradient from large to small, which is the opposite of the quartz sand water distribution zone; (3-5) The compatibility of reaction zone fillers based on different slow release rates includes: doping, mixing, layering, and coating. The permeability coefficient of the filling material shall not be less than the final permeability coefficient of the quartz sand.

4. The operating process of a zoned permeable reactive barrier for groundwater denitrification using zero-valent iron / slow-release carbon-zeolite combination as described in claim 1, characterized in that, The operating processes based on different groundwater nitrogen pollutant concentrations are as follows: groundwater When the concentration is <30 mg / L, the hydraulic retention time (HRT) is 0.4 d; When the concentration is 30-50 mg / L, the HRT is 0.4-1.6 days; When the concentration is >50 mg / L, the HRT is 1.6~16 days.

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