A rapid-start-up, biodegradable permeable reactive wall system and its applications

Abstract

This invention discloses a rapidly start-up and biodegradable permeable reactive barrier system and its application. The system includes an inlet zone, a reaction zone, and an outlet zone arranged sequentially along the water flow direction. The reaction zone is filled with a composite reaction medium comprising filler, sulfide nano-zero-valent iron, anaerobic functional bacteria, and slow-release nutrients. This permeable reactive barrier system, through the combined action of the components in the composite reaction medium, can construct a synergistic remediation mechanism of rapid chemical start-up and long-term biological maintenance within the reaction zone. It is used to treat organic pollutant wastewater, significantly improving treatment efficiency and degradation effect while reducing treatment costs. It has advantages such as short start-up cycle, low intermediate product accumulation, low clogging risk, and good compatibility. Furthermore, it features simple process, stable operation, and convenient maintenance. It demonstrates broad engineering applications in the field of in-situ long-term groundwater remediation, showing high potential value and promising application prospects.

Description

Technical Field

[0001] This invention belongs to the field of in-situ remediation technology for water pollution, and relates to a permeable reactive barrier system that can be quickly started up and biodegraded and its application. Background Technology

[0002] Permeable reactive barrier (PRB) technology has attracted widespread attention due to its ability to continuously treat contaminated groundwater in situ. Existing technology provides a permeable reactive barrier system in which the reactive barrier components are positioned between a first and a second impermeable wall and consist of multiple independent reaction units, sequentially arranged along the groundwater flow direction as a pre-oxidation-reduction zone, a core adsorption-biodegradation zone, and a deep purification and regulation zone. This permeable reactive barrier system employs a multi-stage series structure of "pre-oxidation-reduction zone - core adsorption - biodegradation zone - deep purification and regulation zone," essentially configuring spatial partitions according to different pollutant removal functions. Specifically, the pre-stage focuses on oxidation-reduction, the middle stage on adsorption and biological denitrification, and the post-stage on deep purification of heavy metals and pH regulation. Although this approach emphasizes differentiated functions, it is not a continuous reaction chain triggered by a single core reactive factor, making it difficult to achieve the technical effect of "rapid detoxification - continuous transformation of intermediate products - deep degradation" within the same area. Furthermore, in the aforementioned permeable reactive barrier system, the filling materials in each zone are configured with different functional fillers for different removal tasks. Specifically, the pre-treatment zone uses nano-zero-valent iron-biochar gel composite spheres, the intermediate zone uses zeolite-nitrogen-fixing bacteria composite fillers and sulfur autotrophic denitrification fillers, with built-in CaO2 slow-release oxygen agent and PCL slow-release carbon source modules, and the downstream section uses hematite-limestone composite fillers. Clearly, the core logic remains that different materials correspond to different pollutants or different functional sections. Although this material system can achieve segmented removal, it is difficult to achieve an intrinsic connection between the rapid initial start-up and the subsequent biomineralization of intermediate products. Therefore, this material system is only suitable for treating COD and NH4. + NO3 -While this technology addresses complex pollution such as nitrogen and heavy metals, it struggles to effectively remediate groundwater contaminated with nitroaromatic compounds. Furthermore, the aforementioned permeable reactive barrier (PRB) system utilizes nano-zero-valent iron as the reaction medium, achieving pollutant transformation through reduction reactions. However, this technology still faces several challenges in practical engineering applications: 1) Nano-zero-valent iron is prone to aggregation and surface passivation, leading to rapid degradation of reactivity and poor long-term operational stability; 2) Relying solely on chemical reduction is insufficient for complete mineralization of pollutants, easily resulting in the accumulation of toxic intermediates; 3) During long-term operation, the reaction medium is prone to clogging and decreased activity, limiting the PRB's lifespan. Simultaneously, although this permeable PRB system mitigates clogging and reduces maintenance costs through biomimetic microchannels, reverse pulse flushing, and modular replacement, its technical design still necessitates specialized backflushing devices for easily clogged areas and local replacement mechanisms for failed packing materials. This indicates that its solutions for iron-based material reaction product deposition, packing deactivation, and long-term hydraulic degradation primarily rely on remedial measures at the operational and maintenance levels, rather than fundamentally mitigating these risks through changes in the amount of reaction materials used and the reaction mechanism design.

[0003] It is evident that existing PRB systems, which use zero-valent iron or nano-zero-valent iron as the core, generally suffer from problems such as material agglomeration and surface passivation, difficulty in complete mineralization due to simple chemical reduction, easy accumulation of intermediate products, media blockage, and long start-up cycles of simple biological PRB. As a result, existing permeable reactive wall systems have shortcomings such as long start-up cycles, easy accumulation of intermediate products, high risk of blockage, and poor adaptability.

[0004] For the reasons stated above, this invention is proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a permeable reactive wall system that can be quickly started-up and biodegraded and its application.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A permeable reactive wall system that can be quickly started up and biodegraded is provided, wherein the permeable reactive wall system is provided with an inlet zone, a reaction zone and an outlet zone in sequence along the water flow direction; the reaction zone is filled with a composite reaction medium, which includes filler, sulfide nano-zero valent iron, anaerobic functional bacteria and slow-release nutrient components.

[0007] In a further improvement to the aforementioned permeable reactive wall system, the dosage of sulfide nano-zero valent iron in the reaction zone is 0.01 g / L to 0.10 g / L based on the volume of the reaction zone; the S / Fe molar ratio in the sulfide nano-zero valent iron is 0.01 to 0.10; and the particle size of the sulfide nano-zero valent iron is 20 nm to 200 nm.

[0008] In a further improvement to the aforementioned permeable reactive wall system, the dosage of sulfide nano-zero valent iron in the reaction zone is 0.02 g / L to 0.08 g / L based on the volume of the reaction zone; the S / Fe molar ratio in the sulfide nano-zero valent iron is 0.02 to 0.06; and the particle size of the sulfide nano-zero valent iron is 50 nm to 150 nm.

[0009] In a further improvement to the aforementioned permeable reactive barrier system, the anaerobic functional bacteria are a microbial community containing sulfate-reducing bacteria, or a complex microbial community containing sulfate-reducing bacteria, iron-reducing bacteria, and facultative anaerobic degrading bacteria; the anaerobic functional bacteria attach to the surface and internal pores of the packing material through circulating biofilm formation or negative pressure inoculation; the inoculation amount of the anaerobic functional bacteria is 1% to 10% of the reaction zone volume. In a further improvement to the aforementioned permeable reactive wall system, the inoculation amount of the anaerobic functional bacteria is 3% to 8% of the volume of the reaction zone.

[0010] In a further improvement to the aforementioned permeable reactive wall system, the filler material is biochar.

[0011] In a further improvement to the aforementioned permeable reactive wall system, the slow-release nutrient components include slow-release carbon sources and nutrient salt components.

[0012] In a further improvement to the aforementioned permeable reactive wall system, the slow-release carbon source is at least one of polylactic acid, starch, cellulose, sodium acetate, and sodium lactate.

[0013] In a further improvement to the aforementioned permeable reactive wall system, the nutrient components include a nitrogen source, a phosphorus source, and trace elements.

[0014] In a further improvement of the aforementioned permeable reactive wall system, the mass percentage of the slow-release nutrient components in the composite reactive medium is 1% to 20%.

[0015] In a further improvement of the aforementioned permeable reactive wall system, the mass percentage of the slow-release nutrient components in the composite reactive medium is 3% to 10%.

[0016] As a general technical concept, the present invention also provides an application of the above-mentioned permeable reactive wall system in the treatment of organic pollutant wastewater.

[0017] The above-mentioned application is further improved by using a permeable reactive wall system to continuously treat organic pollutant wastewater, including the following steps: passing the organic pollutant wastewater into the permeable reactive wall system, allowing the organic pollutant wastewater to flow through the reaction zone, controlling the hydraulic retention time of the organic pollutant wastewater in the reaction zone to be 6 h to 72 h, and completing the treatment of the organic pollutant wastewater.

[0018] In a further improvement to the above application, the hydraulic retention time of the organic pollutant wastewater in the reaction zone is 24 h to 72 h.

[0019] In a further improvement to the above application, the organic pollutants contained in the organic pollutant wastewater are nitro aromatic compounds.

[0020] Compared with the prior art, the advantages of the present invention are as follows: (1) In view of the shortcomings of existing permeable reactive wall systems, such as long start-up period, easy accumulation of intermediate products, high risk of blockage and poor adaptability, this invention creatively proposes a permeable reactive wall system that can be quickly started-up and biodegraded. The system is provided with an inlet zone, a reaction zone and an outlet zone in sequence along the water flow direction. The reaction zone is filled with a composite reaction medium, which includes filler, sulfide nano zero-valent iron, anaerobic functional bacteria and slow-release nutrient components. The permeable reactive barrier system of this invention aims to construct a synergistic repair mechanism of "rapid chemical initiation and long-term biological maintenance" within the reaction zone through the combined action of various components in the composite reaction medium. Specifically, it uses sulfide nano-zero valent iron (S-nZVI) as the core initiation factor of the system, realizing three major initiation functions: ① Chemical reduction initiation - rapidly transforming pollutants and shortening the system initiation cycle from 7-30 days in traditional biological PRB to less than 72 hours; ② Microenvironment construction initiation - consuming dissolved oxygen in situ and actively creating an anaerobic microenvironment, providing decisive conditions for the long-term colonization of functional bacteria; ③ Bioactivity activation initiation - enriching functional bacterial communities and activating metabolic activity through micro-interface reactions. This "one dose, three initiations" micro-initiation mechanism is the core innovation of this invention, leveraging the staged synergy and long-term operation of the entire system with extremely low material consumption. The chemical-biological tiered synergistic system constructed using S-nZVI and anaerobic functional bacteria conforms to the tiered synergistic enhancement mechanism, fully leveraging the dual advantages of S-nZVI's "ignition and start-up" and anaerobic functional bacteria's "long-term degradation." The intervention of S-nZVI can enrich a variety of functional bacterial groups, including sulfate-reducing bacteria, and enhance extracellular polymer secretion and key enzyme activity. Meanwhile, the long-term metabolic activities of microorganisms can also alleviate media passivation. The two form a positive feedback loop, which significantly improves the overall removal efficiency and system stability of nitro aromatic compounds. Experiments show that the tiered synergistic system can achieve a removal rate of over 95% for nitro aromatic compounds, and the concentration of major intermediate products (such as corresponding amino compounds) is significantly lower than that of single chemical methods, effectively reducing the risk of secondary pollution. By synergistically designing S-nZVI with slow-release nutrient components, this invention effectively avoids the drawbacks of traditional high-dose zero-valent iron PRB, such as easy clogging and rapid activity decay. It also solves the engineering problem of slow start-up of purely biological PRB. Its engineering value lies in: ① Cost advantage – material usage is reduced by more than 90%; ② Anti-clogging advantage – extremely low solid loading ensures long-term hydraulic conductivity performance of the system. Compared with traditional nZVI-PRB, the S-nZVI dosage of this invention is reduced by 90%–99%, significantly reducing the risk of pore blockage in the reaction zone. After 12 months of simulated operation, the hydraulic conductivity coefficient decay rate is less than 15% (traditional nZVI-PRB is typically >40%); ③ Long-lasting advantage – after the start-up function is completed, it can transform into an electron shuttle to continuously participate in the reaction, achieving long-term synergy between chemistry and biology.

[0021] Compared with conventional permeable reactive barrier systems, the permeable reactive barrier system of this invention, under the combined action of the components in the composite reactive medium, can construct a synergistic repair mechanism of "rapid chemical initiation and long-term biological maintenance" within the reaction zone, thereby enhancing the overall degradation effect and achieving the following unexpected technical effects: (1.1) Significantly improved start-up speed. Unlike traditional biological PRBs which require a long period of microbial adaptation, this invention utilizes sulfide nano-zero valent iron (S-nZVI) to rapidly complete the initial reduction of pollutants during the start-up phase and simultaneously construct an anaerobic microenvironment, shortening the system start-up cycle to less than 72 hours, thereby significantly improving the problem of slow start-up of purely biological systems.

[0022] (1.2) The removal pathway is more complete, and the risk of intermediate product accumulation is lower. Although a standalone chemical reduction system can achieve rapid start-up, it is prone to insufficient continuous repair capacity due to material passivation, and intermediate products accumulate. In this invention, by introducing anaerobic functional bacteria and slow-release nutrients, the intermediate products generated by chemical reduction can be further transformed and deeply degraded. The system can achieve a removal rate of more than 95% for nitro aromatic compounds, while significantly reducing the risk of intermediate products and secondary pollution.

[0023] (1.3) Lower risk of clogging, better long-term hydraulic stability, and superior engineering economy and ease of operation and maintenance. In this invention, sulfide nano-zero valent iron (S-nZVI) no longer undertakes the long-term task of separate decontamination, but instead transfers the responsibility of long-term repair to the activated anaerobic functional bacteria and slow-release nutrient system. This reduces the dependence on the continuous consumption of highly active iron materials and reduces the system instability caused by rapid decline in activity. Furthermore, on the one hand, the sulfide nano-zero valent iron (S-nZVI) strategy reduces material consumption by more than 90%; on the other hand, the system can achieve long-term stable operation by replenishing and maintaining the activity of sulfide nano-zero valent iron (S-nZVI), slow-release nutrient components, and bacterial communities in stages, instead of relying mainly on high-frequency large-scale packing replacement to maintain performance. Therefore, the overall maintenance cost and operational complexity are lower.

[0024] (1.4) Stronger adaptability to target pollutants. Existing technologies focus on general treatment of groundwater with complex pollution in landfills, while the present invention is a reaction system specifically constructed for the pollution characteristics of target pollutants (such as nitro aromatic compounds). It takes into account both the characteristics of easy reduction and transformation and the need for anaerobic bacteria to further degrade their intermediate products. Therefore, in specific application scenarios with clear objectives, the technical effects of this application are more focused and targeted.

[0025] Therefore, the permeable reactive wall system of this invention operates in a phased synergistic mode. In the start-up phase, sulfide nano-zero-valent iron serves as the core initiating factor, exerting multiple initiation functions to rapidly chemically reduce organic pollutants (such as nitro aromatic compounds), construct an anaerobic microenvironment in situ, and stimulate the metabolic activity of anaerobic functional bacteria. In the continuous operation phase, the long-term activated anaerobic functional bacteria utilize slow-release nutrients to deeply biodegrade intermediate products, forming a synergistic remediation mechanism of "rapid chemical initiation and long-term biological maintenance." This system can be widely used to treat organic pollutant wastewater, significantly improving treatment efficiency and degradation effect while also reducing treatment costs. It has advantages such as short start-up cycle, low intermediate product accumulation, low clogging risk, and good adaptability. At the same time, the system is characterized by simple process, stable operation, and convenient maintenance. It shows broad engineering applications in the field of in-situ long-term remediation of groundwater, with high potential value and good application prospects.

[0026] (2) The present invention also provides an application of a permeable reactive wall system in the treatment of organic pollutant wastewater. Specifically, the permeable reactive wall system is used to continuously treat organic pollutant wastewater, including the following steps: the organic pollutant wastewater is introduced into the permeable reactive wall system, so that the organic pollutant wastewater flows through the reaction zone, and the composite reaction medium in the reaction zone is used to trigger a step-by-step synergistic degradation effect, thereby completing the efficient degradation of organic matter in the wastewater. For example, when used to treat boiling water containing nitro aromatic compounds, the specific steps are as follows: Start-up Phase I – Rapid Chemical Reduction Start-up: In the initial stage of system operation (0–72 hours, adjustable depending on hydrological conditions), S-nZVI first contacts nitro aromatic compounds, utilizing their high reactivity for rapid chemical reduction. The Fe on the surface of S-nZVI… 0 The active sites provided by the FeS layer rapidly reduce nitro (-NO2) to amino (-NH2), generating intermediate products such as corresponding amino compounds. This process not only reduces the biotoxicity of pollutants, but also significantly shortens the start-up period required by traditional biological PRB (usually 7 to 30 days).

[0027] Phase II – In-situ Construction of Microenvironment: During the chemical reduction process, the reaction of S-nZVI with water and the reduction of pollutants simultaneously consume dissolved oxygen in the groundwater, forming a local anaerobic microenvironment (DO<0.2 mg / L) in the reaction zone. This microenvironment actively constructed by S-nZVI creates decisive conditions for the long-term colonization and metabolism of subsequent anaerobic functional bacteria, without the need for additional chemical deoxygenation or physical isolation measures.

[0028] Initiation Phase III -- Bioactivity-Driven: The intervention of S-nZVI not only provides the initial electron donor, but its corrosion products (Fe) 2+ Fe 3+The surface properties of S-nZVI can significantly enrich functional microbial communities, including sulfate-reducing bacteria, and enhance the secretion of extracellular polymers and the activity of key enzymes. Shake-flask experiments showed that the presence of trace amounts of S-nZVI can increase the metabolic activity of functional microbial communities by 30% to 50%, acting as a "catalyst" or "igniter" for biological reactions, laying the foundation for subsequent long-term biodegradation.

[0029] Continuous Operation Phase – Deep Biodegradation: After S-nZVI completes its startup function, the long-term activated anaerobic functional bacteria (especially sulfate-reducing bacteria) utilize the electron donors and nutrients continuously released by the slow-release nutrient components to carry out deep biotransformation of intermediate products generated by chemical reduction, maintain the system's reducing properties and promote the final mineralization of pollutants. During this process, S-nZVI and its corrosion products can also act as electron shuttles or conductive media to promote direct interspecies electron transfer (DIET), further enhancing bioreduction efficiency and achieving tiered synergy and long-term stable operation of the system. Attached Figure Description

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0031] Figure 1 This is a schematic diagram of the structure of the rapidly start-up-biodegradable permeable reactive wall system in Embodiment 1 of the present invention.

[0032] Figure 2 The graphs show the degradation curves of nitrobenzene by different permeable reactive wall systems in Examples 1 and 1-2 of the present invention.

[0033] Figure 3 This is a comparison chart of the two-stage degradation rate constants of p-nitrobenzene in different permeable reactive wall systems in Example 1 and Comparative Examples 1-2 of the present invention.

[0034] Figure 4 This is a comparison chart showing the degradation effects of a standalone S-nZVI permeable reactive wall system and an S-nZVI / SRB coupled permeable reactive wall system on nitrobenzene under different S-nZVI dosage conditions in Example 2 of the present invention.

[0035] Figure 5 This is a comparison chart showing the degradation effect of the S-nZVI / SRB coupled permeable reactive wall system on nitrobenzene constructed under different SRB inoculation conditions in Example 3 of the present invention.

[0036] Legend: 1. Inlet zone; 1-1. First permeable packing material; 2. Reaction zone; 2-1. Packing material; 2-2. Sulfide nano-zero valent iron; 2-3. Anaerobic functional bacteria; 3. Outlet zone; 3-1. Second permeable packing material; 4. Injection port; 5. First injection port; 6. Second injection port. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0038] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the average values ​​of more than three repeated experiments.

[0039] Example 1 like Figure 1 As shown, a permeable reactive wall system includes an inlet zone 1, a reaction zone 2, and an outlet zone 3 in sequence along the water flow direction, with each zone interconnected to form a continuous seepage structure.

[0040] In this embodiment, the inlet zone 1 and the outlet zone 3 are filled with a first permeable filler 1-1 and a second permeable filler 3-1.

[0041] In this embodiment, the top of the reaction zone 2 is provided with an injection port 4 for injecting anaerobic functional bacteria, a first injection port 5 for injecting slow-release nutrient components, and a second injection port 6 for adding sulfide nano-zero valent iron. The interior is filled with a composite reaction medium, which includes filler 2-1, sulfide nano-zero valent iron 2-2, and anaerobic functional bacteria 2-3.

[0042] In this embodiment, both the inlet and outlet zones are constructed using highly permeable fillers. A mixture of quartz sand and gravel with a particle size of 2–5 mm is selected to ensure the stable introduction and uniform discharge of groundwater, while also buffering hydraulic impacts and intercepting suspended particles.

[0043] In this embodiment, the thickness of the influent zone is 0.25 m, the thickness of the effluent zone is 0.25 m, and the thickness of the reaction zone is 1.00 m. Based on the hydrogeological conditions of the contaminated site, the system influent flow rate is set to control the hydraulic residence time of groundwater in the reaction zone to 72 h and the linear flow velocity to 0.10 m / d to 0.20 m / d.

[0044] In this embodiment, the filler material in the reaction zone is a mixture of quartz sand and biochar. Quartz sand serves as the filler material to ensure the system's permeability; biochar acts as a high specific surface area carrier to enhance the dispersibility and adhesion stability of sulfide nano-zero valent iron (S-nZVI) and anaerobic functional bacteria. The mass ratio of quartz sand to biochar is 4:1, and the total mass of the filler material accounts for 80% of the total mass of the composite reaction medium.

[0045] In this embodiment, S-nZVI was prepared as follows: FeCl3·6H2O was dissolved in deoxygenated and deionized water to prepare a 0.05 mol / L ferric chloride solution; under continuous high-purity nitrogen protection, a mixed solution of sodium borohydride and sodium thiosulfate was added dropwise to the ferric chloride solution for liquid-phase reduction, with the addition rate controlled at 5.0 mL / min and the stirring speed at 300 r / min, and the reaction was carried out for 90 min to obtain an S-nZVI suspension; after washing three times with anhydrous ethanol and magnetic separation, the suspension was dried under vacuum at 50℃ for 12 h to obtain solid S-nZVI. The S / Fe molar ratio in the prepared S-nZVI was controlled at 0.033, and the particle size was 50 nm to 90 nm.

[0046] In this embodiment, sulfate-reducing bacteria were selected as the anaerobic functional bacteria. The acclimatization and cultivation method is as follows: SRB medium was prepared with the following composition: 0.5 g / L K₂HPO₄, 1.0 g / L NH₄Cl, 1.0 g / L Na₂SO₄, 0.1 g / L CaCl₂·2H₂O, 2.0 g / L MgSO₄·7H₂O, 2.0 g / L sodium lactate, and 1.0 g / L yeast extract. The pH was adjusted to 7.2, and high-purity N₂ was introduced for deoxygenation for 30 min. The medium was then sealed and autoclaved at 120℃ for 30 min. Under aseptic conditions, Desulfovibrio vulgaris bacterial culture was inoculated and cultured at 37℃ until OD₂O₃ was reached. 600 The concentration is 0.4–0.6 to obtain an active bacterial solution, which is then used after at least three subcultures.

[0047] The slow-release nutrient component comprises lactate (as a slow-release carbon source) and compound nutrient salts (containing nitrogen, phosphorus, and trace elements), with a total mass accounting for 5% of the total mass of the compound reaction medium. This component is used to continuously and slowly release electron donors and nutrient sources to maintain the long-term metabolic activity of anaerobic functional bacteria and the reducing environment within the reaction zone.

[0048] The quartz sand, biochar, S-nZVI, and slow-release nutrient components were mixed evenly in the specified proportions and then packed into the reaction zone, compacted, and ensured to be packed evenly. Subsequently, active SRB bacterial solution was injected through injection port 4, and a negative pressure inoculation method was used to ensure the bacterial solution was evenly distributed in the pores of the packing material, ultimately achieving an inoculation amount of anaerobic functional bacteria reaching 5% (v / v) of the reaction zone volume. The dosage of S-nZVI in the reaction zone was 0.05 g / L based on the reaction zone volume.

[0049] An application of the above-mentioned permeable reactive wall system in the treatment of organic pollutant wastewater specifically involves the continuous treatment of nitro aromatic compound (nitrobenzene) wastewater using the permeable reactive wall system, including the following steps: Simulated contaminated groundwater containing 100 mg / L nitrobenzene was continuously introduced into the constructed permeable reactive barrier system. The system was operated with a pH controlled at 6.5–7.5 and a dissolved oxygen (DO) concentration controlled below 0.5 mg / L (preferably below 0.2 mg / L). The contaminated groundwater flowed sequentially through the influent zone, reaction zone, and effluent zone. In the reaction zone, it came into full contact with the composite reaction medium and reacted. The hydraulic retention time of the groundwater in the reaction zone was controlled at 72 h, and the operating temperature was 35℃.

[0050] In the initial stage of operation, S-nZVI preferentially performs initial chemical reduction of nitrobenzene, while simultaneously constructing a low-oxygen / anaerobic reduction environment suitable for the growth of anaerobic functional bacteria by consuming dissolved oxygen in situ. In the middle and later stages of operation, the long-term activated anaerobic functional bacteria utilize electron donors continuously supplied by slow-release nutrients to perform deep biodegradation of intermediate products and residual pollutants generated from nitrobenzene reduction, thereby achieving staged synergistic remediation and long-term stable operation of polluted groundwater.

[0051] Comparative Example 1: Construction and operation of standalone S-nZVI permeable reactive wall systems This comparative example constructs a permeable reactive barrier system with only S-nZVI added and no anaerobic functional bacteria, to evaluate the effect of chemical reduction alone on the remediation of groundwater contaminated with nitroaromatic compounds, and compares it with the synergistic system of Example 1.

[0052] The specific construction and operation methods are the same as in Example 1, the only difference being that: no anaerobic functional bacteria are inoculated in the reaction zone, and no bacterial agent injection step is set up. The composite reaction medium only contains filler (quartz sand and biochar, mass ratio 4:1), S-nZVI (addition amount 0.05 g / L) and slow-release nutrient components.

[0053] Simulated groundwater containing 100 mg / L nitrobenzene was introduced into the PRB system under the same conditions, with the hydraulic retention time controlled at 72 h, the operating pH at 6.5–7.5, and the dissolved oxygen controlled below 0.5 mg / L.

[0054] Comparative Example 2: Construction and operation of standalone SRB permeable reactive barrier systems This comparative example constructs a permeable reactive barrier system inoculated only with anaerobic functional bacteria and without S-nZVI, to evaluate the effectiveness of biodegradation alone in remediating groundwater contaminated with nitroaromatic compounds.

[0055] The specific construction and operation methods are the same as in Example 1, the only difference being that S-nZVI is not added in the reaction zone, and the composite reaction medium only contains filler (quartz sand and biochar, mass ratio 4:1), anaerobic functional bacteria (SRB, inoculum amount 5% v / v) and slow-release nutrient components.

[0056] Simulated groundwater containing 100 mg / L nitrobenzene was introduced into the PRB system under the same conditions, with the hydraulic retention time controlled at 72 h, the operating pH at 6.5–7.5, and the dissolved oxygen controlled below 0.5 mg / L.

[0057] In Example 1 and Comparative Examples 1-2, samples were taken at 0, 0.25, 0.5, 1, 2, 12, 24, 48 and 72 h after the system started running, and the concentration of nitrobenzene, pH, redox potential and dissolved oxygen in the water were measured.

[0058] Figure 2 The graphs show the degradation curves of nitrobenzene by different permeable reactive wall systems in Examples 1 and 1-2 of the present invention.

[0059] like Figure 2 As shown, in the standalone S-nZVI system, nitrobenzene is mainly removed by chemical reduction. In the initial stage (0–2 h), the removal rate is rapid, and the nitrobenzene concentration decreases significantly. However, as the reaction continues, the S-nZVI surface gradually passivates, and the reactivity decreases. In the middle and later stages (2–72 h), the removal rate slows down significantly, and a certain concentration of unconverted nitrobenzene and its reduction intermediates (such as nitrosamines and aniline) remains in the effluent. These results indicate that while the standalone chemical system has the advantage of rapid start-up, its sustained remediation capacity is limited, and there is a risk of intermediate product accumulation.

[0060] like Figure 2 As shown, the degradation of nitrobenzene by the standalone SRB system mainly relies on the metabolic transformation of microorganisms. In the initial stage of operation (0–12 h), the pollutant concentration decrease is not significant due to the microbial community still being in the adaptation period, and the start-up is relatively slow. As the microbial community gradually adapts to the environment and proliferates (12–72 h), the system's removal capacity for nitrobenzene gradually increases, but the overall treatment cycle is long, and the remediation efficiency is insufficient in the initial stage. These results indicate that while standalone biological systems possess the potential for continuous degradation, they have an inherent limitation of slow start-up.

[0061] like Figure 2 As shown, compared with Comparative Examples 1 and 2, the coupling system of Example 1 of the present invention achieved faster start-up degradation in 0-2 h (removal rate exceeding 50% in 2 h) and maintained continuous degradation capability in 2-72 h. After 72 h, the C / CO ratio of nitrobenzene in the effluent was less than 0.1, and the total degradation rate reached more than 95%.

[0062] Therefore, compared with Comparative Examples 1 and 2, the permeable reactive wall system coupled system constructed in this invention has the dual advantages of rapid start-up and continuous degradation. In the initial stage of operation, the pollutant concentration decreased significantly; in the middle and later stages of operation, the nitrobenzene and its intermediate products in the effluent continued to decrease, indicating that the coupled system can effectively achieve synergistic remediation of initial chemical reduction and subsequent biodegradation.

[0063] Figure 3 This is a comparison chart of the two-stage degradation rate constants of p-nitrobenzene in different permeable reactive wall systems in Example 1 and Comparative Examples 1-2 of the present invention.

[0064] Figure 3 The results show that the apparent rate constant (k) of the permeable reactive wall system coupled system constructed in Example 1 of this invention in the 0-2 h stage is... obs The efficacy was 1.6 times that of the S-nZVI treatment group alone and 12.1 times that of the SRB treatment group alone; k in the 2–72 h phase obs This is 2.9 times that of the SRB-only treatment group, while the S-nZVI-only treatment group showed almost no degradation of nitrobenzene at this stage. Therefore, in the permeable reactive wall system of this invention, the presence of S-nZVI reduces the difficulty of subsequent biotransformation of nitrobenzene and promotes the rapid establishment of dominance by anaerobic functional bacteria by creating a low-oxygen environment; the anaerobic functional bacteria further transform the intermediate products generated from the initial reduction of S-nZVI, while maintaining the system's reducibility, thus achieving a complementary advantage between chemical reduction and biodegradation.

[0065] During the operation of the permeable reactive wall system of this invention, the repair process within the reaction zone can be divided into two stages: (1) The first stage is the rapid start-up stage (0-2 h). In this stage, trace amounts of S-nZVI first rapidly chemically reduce nitrobenzene, gradually converting it into nitroso, hydroxylamine and aniline intermediates. At the same time, it consumes dissolved oxygen in the groundwater, rapidly establishing a local hypoxic / anaerobic reduction environment, thus creating conditions for the subsequent functioning of anaerobic functional bacteria.

[0066] (2) The second stage is the continuous degradation stage (2-72 h). During this stage, anaerobic functional bacteria maintain high activity under the continuous supply of electron donors and nutritional support from the slow-release nutrient components, and continuously biotransform and degrade the aforementioned reduction intermediates and residual nitrobenzene, thereby achieving deep purification of polluted groundwater.

[0067] Example 2: Investigating the effects of different S-nZVI dosages on the degradation performance of permeable reactive wall systems In Example 2, the permeable reactive wall system used was basically the same as that in Example 1, except that in Example 2, the S-nZVI dosage in the permeable reactive wall system was set at four levels: 0.01 g / L, 0.02 g / L, 0.05 g / L and 0.10 g / L, and a total of 8 parallel experiments were set up, with other conditions being the same.

[0068] Following the treatment method in Example 1, nitrobenzene wastewater was treated using a standalone S-nZVI permeable reactive wall system and an S-nZVI / SRB coupled permeable reactive wall system constructed under different S-nZVI dosage conditions. The dynamic changes in nitrobenzene concentration were monitored over 72 hours, and the removal rate was calculated and compared.

[0069] Figure 4 This is a comparison chart showing the degradation effects of a standalone S-nZVI permeable reactive wall system and an S-nZVI / SRB coupled permeable reactive wall system on nitrobenzene under different S-nZVI dosage conditions in Example 2 of the present invention.

[0070] Figure 4 The results showed that in the S-nZVI system alone, the removal efficiency of nitrobenzene monotonically increased with increasing S-nZVI dosage. Specifically, at a dosage of 0.01 g / L, the system had few active reduction sites, resulting in weak initial reduction and a removal rate of less than 20% after 72 h. Increasing the dosage to 0.02 g / L improved the removal capacity, achieving a removal rate of approximately 25% after 72 h. Further increases to 0.05 g / L and 0.10 g / L increased the number of electron donors in the system, with removal rates reaching over 40% and 70% after 72 h, respectively. These results indicate that under chemical reduction conditions alone, a higher S-nZVI dosage provides more active sites, resulting in stronger electron donation and better reduction and degradation of pollutants. However, higher dosages also imply higher material consumption and engineering costs, and the accumulation of intermediate products remains a concern.

[0071] Further analysis suggests that pollutant removal in a standalone S-nZVI system primarily relies on electron transfer and chemical reduction on the S-nZVI surface. As the S-nZVI dosage increases, the number of active reaction sites per unit volume of the system increases, enhancing electron supply capacity and thus promoting the gradual reduction of nitro groups in nitrobenzene molecules, thereby improving the overall degradation efficiency of the system. Therefore, under single chemical remediation conditions, a higher dosage of S-nZVI is more conducive to the rapid removal of nitrobenzene. However, a single chemical system requires a large amount of S-nZVI, increasing material consumption and reducing the system's engineering economics.

[0072] In the S-nZVI coupled with SRB permeable reactive wall system, the remediation effect corresponding to different S-nZVI dosages exhibits a different variation pattern than that of the S-nZVI system alone.

[0073] Figure 4 The results also showed that when the S-nZVI dosage was 0.01 g / L and 0.02 g / L, although the system could produce a certain initial reduction effect on nitrobenzene, the rapid conversion effect on pollutants was limited due to the low dosage. Furthermore, the system's ability to construct a low dissolved oxygen reduction environment was relatively insufficient, making it difficult to fully exert the initiation and promotion effect on SRB. Therefore, the overall synergistic degradation effect was not ideal.

[0074] When the S-nZVI dosage was increased to 0.05 g / L, the coupled system exhibited the best remediation effect. At this dosage, on the one hand, S-nZVI could rapidly convert nitrobenzene into intermediate products that are more easily bioavailable and further degraded, reducing the difficulty of subsequent microbial degradation; on the other hand, S-nZVI continuously consumed dissolved oxygen in the system during the reaction, which was conducive to the rapid formation of a hypoxic / anaerobic environment suitable for SRB growth and metabolism in the reaction zone, thereby promoting the establishment of SRB activity and the exertion of sustained biodegradation. At this point, the initial rapid reduction effect of S-nZVI and the subsequent sustained degradation effect of SRB were well matched, and the system as a whole exhibited a superior synergistic remediation effect.

[0075] When the S-nZVI dosage was further increased to 0.10 g / L, although the initial chemical reduction capacity of the system was further enhanced, the overall synergistic advantage of the coupled system did not increase significantly. This may be because excessively high concentrations of S-nZVI could lead to an overly strong chemical reduction process dominating the reaction system, thus affecting the adaptation, growth, and stable metabolism of SRB, weakening the synergistic relationship between S-nZVI and SRB. Simultaneously, excessive dosage would increase material consumption, which is detrimental to the system's engineering economy. Therefore, in coupled systems, a higher S-nZVI dosage is not necessarily more beneficial; rather, there exists a suitable range to achieve efficient synergy between chemical reduction and biodegradation.

[0076] Comparing the above experimental results, it can be seen that when S-nZVI acts alone to degrade nitrobenzene, its degradation effect increases with increasing dosage; that is, the higher the dosage of S-nZVI, the better the degradation effect. In the S-nZVI-SRB coupled system, a dosage of 0.05 g / L effectively exerts its initial rapid reduction effect on nitrobenzene and significantly promotes the initiation and subsequent continuous metabolism of SRB, thus achieving the best synergistic degradation effect. Therefore, 0.05 g / L can be considered the preferred dosage concentration of S-nZVI in the coupled remediation system of this invention. At this concentration, S-nZVI can fully utilize its rapid initiation and microenvironment construction functions while forming an optimal synergistic match with SRB, achieving efficient removal of pollutants and long-term stable operation of the system.

[0077] Example 3: Investigating the effect of different SRB inoculum amounts on the degradation performance of a permeable reactive wall system In Example 3, the permeable reactive wall system used was basically the same as that in Example 1, except that the inoculation amount of anaerobic functional bacteria (SRB) in the permeable reactive wall system was set to 0%, 1%, 2%, 5%, and 10% (v / v) respectively, and 5 parallel PRB reaction media were constructed, with other conditions being the same.

[0078] Following the treatment method in Example 1, a permeable reactive wall system constructed under different SRB inoculation conditions was used to treat nitrobenzene wastewater. The dynamic changes in nitrobenzene concentration were monitored over 72 hours, and the removal rate was calculated and compared.

[0079] By monitoring the degradation of nitrobenzene in each group of PRB over 72 h, the effects of different SRB inoculum amounts on the synergistic system, particularly on the system's sustained degradation capacity, were evaluated.

[0080] Figure 5 This is a comparison chart showing the degradation effect of the S-nZVI / SRB coupled permeable reactive wall system on nitrobenzene constructed under different SRB inoculation conditions in Example 3 of the present invention.

[0081] like Figure 5 As shown, the results indicate that when the inoculum size of anaerobic functional bacteria is 1% (v / v), the system's sustained degradation capacity in the later stages is insufficient; when the inoculum size is increased to 2% (v / v), the concentration of nitrobenzene in the effluent decreases significantly; when the inoculum size is 5% (v / v), the synergistic effect of chemical reduction and biodegradation in the system is most obvious, and the pollutant removal effect and operational stability are both superior; when the inoculum size is further increased to 10% (v / v), the nitrobenzene removal efficiency in the system decreases instead.

[0082] Further analysis showed that an appropriate amount of SRB (1%–5%) could form a good synergistic effect with S-nZVI: S-nZVI rapidly initiates degradation and creates a suitable low-oxygen environment for SRB, while SRB provides continuous biodegradation capacity; however, when the SRB inoculum is too high (10%), excessive microorganisms may compete for nutrients and electron donors in the system, or produce metabolic byproducts that affect the reactivity of S-nZVI, leading to a decrease in overall removal efficiency.

[0083] Therefore, taking into account pollutant removal efficiency, maintenance of bacterial activity, and stable system operation, this embodiment preferably uses an anaerobic functional bacteria inoculation amount of 5% (v / v).

[0084] The results above show that, compared with conventional permeable reactive barrier systems, the permeable reactive barrier system of this invention operates in a phased synergistic mode. In the start-up phase, sulfide nano-zero-valent iron serves as the core initiating factor, exerting multiple initiation functions to rapidly chemically reduce organic pollutants (such as nitro aromatic compounds), construct an anaerobic microenvironment in situ, and stimulate the metabolic activity of anaerobic functional bacteria. In the continuous operation phase, the long-term activated anaerobic functional bacteria utilize slow-release nutrients to deeply biodegrade intermediate products, forming a synergistic remediation mechanism of "rapid chemical initiation and long-term biological maintenance." This system can be widely used to treat organic pollutant wastewater, significantly improving treatment efficiency and degradation effect while also reducing treatment costs. It has advantages such as short start-up cycle, low intermediate product accumulation, low clogging risk, and good compatibility. Furthermore, the system features simple process, stable operation, and convenient maintenance, demonstrating broad engineering applications in the field of in-situ long-term groundwater remediation. It has high potential value and promising application prospects.

[0085] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A rapidly start-up, biodegradable, permeable reactive barrier system, characterized in that, The permeable reactive wall system is provided with an inlet zone, a reaction zone and an outlet zone in sequence along the water flow direction; the reaction zone is filled with a composite reaction medium, which includes filler, sulfide nano-zero valent iron, anaerobic functional bacteria and slow-release nutrient components.

2. The permeable reactive wall system according to claim 1, characterized in that, The amount of sulfide nano-zero valent iron added in the reaction zone is 0.01 g / L to 0.10 g / L based on the volume of the reaction zone; the S / Fe molar ratio in the sulfide nano-zero valent iron is 0.01 to 0.10; and the particle size of the sulfide nano-zero valent iron is 20 nm to 200 nm.

3. The permeable reactive wall system according to claim 2, characterized in that, The amount of sulfide nano-zero valent iron added in the reaction zone is 0.02 g / L to 0.08 g / L based on the volume of the reaction zone; the S / Fe molar ratio in the sulfide nano-zero valent iron is 0.02 to 0.06; and the particle size of the sulfide nano-zero valent iron is 50 nm to 150 nm.

4. The permeable reactive wall system according to any one of claims 1 to 3, characterized in that, The anaerobic functional bacteria are a group of bacteria containing sulfate-reducing bacteria, or a complex group of bacteria containing sulfate-reducing bacteria, iron-reducing bacteria, and facultative anaerobic degrading bacteria; the anaerobic functional bacteria attach to the surface and internal pores of the packing material through circulating biofilm formation or negative pressure inoculation; the inoculation amount of the anaerobic functional bacteria is 1% to 10% of the volume of the reaction zone; The slow-release nutrient component includes a slow-release carbon source and nutrient salt components; the slow-release carbon source is at least one selected from polylactic acid, starch, cellulose, sodium acetate, and sodium lactate; the nutrient salt components include a nitrogen source, a phosphorus source, and trace elements; the mass percentage of the slow-release nutrient component in the composite reaction medium is 1% to 20%. The filler is a mixture of quartz sand and biochar; the mass ratio of quartz sand to biochar is 4:

1.

5. The permeable reactive wall system according to claim 4, characterized in that, The inoculum size of the anaerobic functional bacteria is 3% to 8% of the volume of the reaction zone; The mass percentage of the slow-release nutrient components in the composite reaction medium is 3% to 10%. The mass of the filler is 80% of the total mass of the composite reaction medium.

6. The permeable reactive wall system according to any one of claims 1 to 3, characterized in that, The inlet zone, reaction zone, and outlet zone are interconnected and form a continuous seepage structure; the length of the inlet zone in the direction of water flow is 0.25m; the length of the reaction zone in the direction of water flow is 1m; and the length of the outlet zone in the direction of water flow is 0.25m.

7. The permeable reactive wall system according to claim 6, characterized in that, The inlet and outlet water zones are filled with permeable filler material, which is a mixture of quartz sand and gravel.

8. The application of a permeable reactive wall system as described in any one of claims 1 to 7 in the treatment of organic pollutant wastewater.

9. The application according to claim 8, characterized in that, The continuous treatment of organic pollutant wastewater using a permeable reactive barrier system includes the following steps: introducing organic pollutant wastewater into the permeable reactive barrier system, allowing the organic pollutant wastewater to flow through the reaction zone, controlling the hydraulic retention time of the organic pollutant wastewater in the reaction zone to be 6 h to 72 h, and completing the treatment of the organic pollutant wastewater.

10. The application according to claim 9, characterized in that, The hydraulic retention time of the organic pollutant wastewater in the reaction zone is 24 h to 72 h; the linear flow velocity of the organic pollutant wastewater in the reaction zone is controlled at 0.10 m / d to 0.20 m / d; the organic pollutants contained in the organic pollutant wastewater are nitro aromatic compounds.

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