Iron-carbon synergetic aeration reinforced artificial wetland system

Abstract

The invention provides an iron-carbon synergistic aeration reinforced artificial wetland system which sequentially comprises a supporting layer, an iron-carbon composite functional layer, a gravel layer and a plant layer from bottom to top, aeration pipes are arranged in the vertical direction of each layer in a penetrating mode, and the iron-carbon composite functional layer is composed of pyrite and biochar and is inoculated with activated sludge. According to the invention, the charcoal and the pyrite are jointly applied to the constructed wetland, and aeration is carried out, so that nutrients and heavy metals in the low C / N wastewater can be efficiently removed at the same time. The iron ore and the high-porosity matrix (such as charcoal) are uniformly mixed, so that the effective adhesive force and the contact area of microorganisms and the iron ore are improved, and the denitrification capacity of the vertical flow constructed wetland is finally improved. In addition, compared with complete heterotrophic denitrification, the mixed nutrition denitrification based on the iron ore can effectively reduce the requirements of the vertical flow constructed wetland on organic carbon and alkalinity, and reduces the risk of secondary pollution and blockage at the same time.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control and ecological restoration engineering technology, and in particular relates to an iron-carbon synergistic aeration enhanced constructed wetland system. Background Technology

[0002] Inter-basin water transfer and large-scale canal projects alter the hydrodynamic characteristics of existing river ecosystems. Limited water transfer volumes and reduced flow rates lead to decreased self-purification capacity of water bodies. Combined with agricultural non-point source pollution and discharges along the canal routes, this makes canal water bodies susceptible to eutrophication, threatening aquatic ecological security. Therefore, there is an urgent need to develop efficient, economical, and eco-friendly water purification technologies to ensure the aquatic ecological security of inter-basin projects.

[0003] Constructed wetlands, as an ecological restoration technology, are widely used in water quality improvement projects for polluted rivers and water diversion projects due to their simple structure, low operating costs, and high landscape value. However, traditional constructed wetlands have the following shortcomings: poor denitrification efficiency in wastewater with low C / N ratios—the lack of external carbon sources limits denitrification; insufficient dissolved oxygen (DO)—nitrification is inhibited, resulting in low ammonia nitrogen removal efficiency; limited phosphorus removal capacity—conventional packing materials (sand, gravel) become saturated quickly; and the system is prone to clogging and has poor long-term stability.

[0004] In recent years, researchers have been trying to introduce a variety of functional materials into constructed wetlands to improve water treatment performance.

[0005] Biochar possesses a high specific surface area, abundant pores, and functional groups, enabling it to serve as a microbial carrier and adsorb organic matter and nutrients, demonstrating outstanding performance in pollutant removal. Iron ore, widely found in nature (especially pyrite), can act as an electron donor in autotrophic denitrification reactions, reducing nitrates to nitrogen gas while releasing Fe²⁺. + / Fe³ + It forms precipitates with phosphate ions, improving phosphorus removal efficiency; the enhanced aeration technology promotes nitrification and aerobic degradation processes by increasing dissolved oxygen levels, forming aerobic-anoxic zones and enhancing the coupling effect of nitrification and denitrification.

[0006] However, the synergistic effect of using biochar or iron ore alone is insufficient, and improper aeration system design may lead to increased energy consumption or microbial imbalance. Therefore, it is necessary to scientifically couple iron ore and biochar with the aeration system to construct an iron-carbon synergistic aeration enhanced constructed wetland system to achieve efficient removal of nitrogen, phosphorus, and organic matter from wastewater with a low C / N ratio. Summary of the Invention

[0007] To achieve the above objectives, the present invention provides an iron-carbon synergistic aeration enhanced constructed wetland system, which includes, from bottom to top, a support layer, an iron-carbon composite functional layer, a gravel layer and a plant layer. Aeration pipes are provided vertically through each layer. The iron-carbon composite functional layer is composed of pyrite and biochar and is inoculated with activated sludge.

[0008] In some embodiments, the activated sludge is taken from a wastewater treatment plant in Chongqing (mixed liquor suspended solids concentration MLSS = 3000 mg / L). Organic matter and nutrients such as nitrogen and phosphorus are periodically added to the activated sludge, and intermittent aeration is performed. After acclimatization, microorganisms are inoculated into the substrate within the wetland. The substrate consists of biochar and pyrite, which are completely soaked in the activated sludge for 24 hours and thoroughly mixed before being loaded into the constructed wetland system. The microorganisms include aerobic ammonia-oxidizing and nitrifying bacteria, such as Nitrosomonas (ammonia-oxidizing bacteria) and Nitrospira (nitrifying bacteria), and anaerobic denitrifying bacteria, such as Denitrosoma and Azospira.

[0009] In some embodiments, the iron-carbon composite functional layer accounts for 50% of the total height of the support layer, the iron-carbon composite functional layer and the gravel layer. Preferably, the height ratio of the support layer, the iron-carbon composite functional layer and the gravel layer is 10:30:20.

[0010] In some embodiments, the biochar particle size is 2-5 mm.

[0011] In some embodiments, the iron-carbon composite functional layer is composed of pyrite and biochar in a volume ratio of 2:1, forming an enhanced phosphorus removal type iron-carbon composite functional layer.

[0012] In some embodiments, the iron-carbon composite functional layer is composed of pyrite and biochar in a 1:1 volume ratio to form a nitrogen-phosphorus balanced iron-carbon composite functional layer.

[0013] In some embodiments, the iron-carbon composite functional layer is composed of pyrite and biochar in a volume ratio of 1:2, forming an enhanced denitrification type iron-carbon composite functional layer.

[0014] In some embodiments, the support layer is filled with gravel with a particle size of 5 to 10 mm.

[0015] In some embodiments, the gravel layer is filled with gravel with a particle size of 5 to 10 mm.

[0016] In some embodiments, the system is provided with an inlet valve for allowing water to enter the support layer.

[0017] In some embodiments, a middle valve and an end valve are respectively provided at the middle and top ends of the iron-carbon composite functional layer for water intake and substrate intake.

[0018] In some embodiments, a drainage valve is provided in the gravel layer for water discharge.

[0019] In some embodiments, the plant layer is planted with wetland plants, including one or more of canna lilies and sedges.

[0020] In some embodiments, the aeration pipe is provided with aeration holes in sequence along the vertical direction and is connected to an aeration stone and an air pump for supplying gas to the system.

[0021] In a second aspect, the present invention provides the application of the iron-carbon synergistic aeration enhanced constructed wetland system in wastewater treatment.

[0022] In some implementations, the application includes: S1 allows wastewater to flow through the inlet valve into the support layer and enter the system; S2, the wastewater then enters the iron-carbon composite functional layer from bottom to top, where it undergoes purification, nitrification, denitrification and phosphorus removal under the action of ammonia-oxidizing bacteria, nitrifying bacteria and denitrifying bacteria to obtain clean water; S3, clean water enters the gravel layer, part of which is discharged through the drain valve, and the other part is used for plant growth in the plant layer.

[0023] In some implementations, the air pump supplies air at a rate of 0.5~1.0 L / min, using an intermittent aeration mode (aeration for 2 hours, then 1 hour off). The aeration air source is compressed air, used to supply oxygen externally and control the internal DO concentration and aeration time to improve pollutant removal efficiency.

[0024] In some implementations, the water retention time is set to 2 hours, controlled by a peristaltic pump at the inlet valve.

[0025] Technical effect

[0026] In the iron-carbon synergistic aeration enhanced constructed wetland system of the present invention, the iron-carbon composite functional layer is composed of pyrite and biochar. Pyrite provides electrons to drive autotrophic denitrifying bacteria to remove nitrates (NO3) from wastewater. -The nitrogen gas (N2) is reduced to nitrogen. The high specific surface area and porous structure of the biochar (purchased from Henan, wood-based biochar) provide an excellent attachment carrier for these microorganisms (ammonia-oxidizing bacteria, nitrifying bacteria, and denitrifying bacteria), while simultaneously adsorbing pollutants in wastewater. The combined effect of biochar and pyrite improves the total nitrogen (TN) removal efficiency. The iron ions produced by the oxidation of iron ore can form precipitates with phosphate ions in wastewater, and the adsorption effect of biochar can also assist in phosphorus removal. The coupling of the two can synergistically enhance the phosphorus removal effect. It is suitable for wastewater with low C / N ratios, municipal sewage, and canal ecological conservation areas; the synergistic effect of iron ore and biochar achieves efficient coupling of autotrophic-heterotrophic denitrification and chemical precipitation phosphorus removal; it improves the total nitrogen (TN) removal rate and total phosphorus (TP) removal rate, effectively reducing the concentration of pollutants, and has good effects under both high and low pollution loads.

[0027] Enhanced aeration system: In the iron-carbon synergistic aeration enhanced constructed wetland system of this invention, a PVC perforated pipe is inserted, connecting aeration stones and an oxygenation pump. The dissolved oxygen concentration is controlled by adjusting the aeration rate and aeration time. Aeration increases the DO concentration, promoting nitrification and organic matter oxidation. The DO concentration can be controlled to maintain the microenvironmental balance of the system; the removal rates of ammonia nitrogen and COD are significantly improved.

[0028] Optimized iron ore-biochar ratio; stratified structure and hydraulics; the combination of industrially produced biochar and iron ore effectively reduces costs. Biochar neutralizes acid produced by iron ore and provides a suitable environment for microbial attachment; stratified flow and controlled hydraulic retention time; industrially produced biochar is characterized by low price and high yield; iron ore is the most abundant and widely distributed sulfide mineral on Earth and is widely used in wastewater treatment. The system maintains a stable pH (6.5~7.5), enhancing operational stability; improves the uniformity of water flow distribution and reduces the risk of clogging; the use of industrial by-product biochar and natural iron ore makes the materials economical and readily available. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the iron-carbon synergistic aeration enhanced constructed wetland system according to Embodiment 1 of the present invention; Figure 2 This is a cross-sectional view of the PVC perforated aeration pipe of Embodiment 1 of the present invention; Figure 3 The process concept of the iron-carbon synergistic aeration enhanced constructed wetland system of the present invention is shown.

[0030] Explanation of markings in the diagram: 1-Base plate, 2-Inlet valve, 3-Acrylic pipe body, 4-Middle valve of functional layer, 5-End valve of functional layer, 6-PVC perforated pipe, 7-Outlet valve, 8-Gravel layer, 9-Iron-carbon functional layer, 10-Supporting layer. Detailed Implementation

[0031] Biochar, as an emerging functional material, has been applied in constructed wetlands to enhance the removal of traditional pollutants due to its large surface area, excellent structure, and reactive functional groups. However, research on the treatment effects and mechanisms of biochar on pollutants such as heavy metals and complex organic matter, as well as the application of novel iron-biochar matrices in constructed wetlands, is limited.

[0032] Pyrite-based constructed wetlands are a promising technology, particularly for treating nitrate-contaminated water. Over long-term operation, pyrite-based constructed wetlands are more effective at controlling ammonia nitrogen production, exhibiting long-term, highly efficient biological denitrification performance. Under low C / N ratio conditions, the addition of 100% pyrite significantly promotes TN removal. It can act as an electron donor in the autotrophic denitrification process, promoting denitrification, and the iron-containing metabolites produced can remove phosphate ions, promoting phosphorus removal. Pyrite oxidation releases Fe. 2+ / Fe 3+ It reacts with phosphate to form stable precipitates (such as lapis lazuli and iron phosphate), significantly improving phosphorus removal efficiency (up to 90% or more).

[0033] Traditional constructed wetland treatment methods suffer from limitations such as insufficient dissolved oxygen, which restricts microbial activity and results in poor nitrogen and phosphorus removal. Adding aeration to the wetland system provides sufficient dissolved oxygen, improving the efficiency of organic matter removal. Sufficient oxygen stimulates microbial activity, increasing their numbers and metabolic capacity. Aeration increases dissolved oxygen in the wetland, significantly improving the nitrification rate and effectively reducing ammonia nitrogen content in wastewater. By rationally controlling the aeration intensity and duration, denitrification can be promoted, converting nitrate nitrogen into nitrogen gas released into the air, achieving effective nitrogen removal. Aeration improves the growth environment for microorganisms and enhances their metabolic activity. Some polyphosphate-accumulating bacteria can excessively absorb phosphorus from wastewater under aerobic conditions and convert it into polyphosphate stored intracellularly; phosphorus can be removed from the wetland system through regular sludge removal.

[0034] This invention combines biochar and pyrite in constructed wetlands with aeration, enabling the simultaneous and efficient removal of nutrients and heavy metals from low C / N wastewater. The uniform mixing of pyrite with a high-porosity matrix, such as biochar, enhances the effective adhesion and contact area between microorganisms and the pyrite, ultimately improving the nitrogen removal capacity of vertical flow constructed wetlands. Furthermore, compared to fully heterotrophic denitrification, pyrite-based mixed-nutrient denitrification effectively reduces the demand for organic carbon and alkalinity in vertical flow constructed wetlands, while also reducing the risk of secondary pollution and clogging.

[0035] The embodiments of the present invention are described below with reference to the accompanying drawings to make the technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0036] Example 1: An iron-carbon synergistic aeration enhanced constructed wetland system

[0037] This embodiment is based on the construction of the Pinglu Canal ecological conservation area.

[0038] The main body of the experimental device consists of an acrylic tube 3 and a base plate 1. A water inlet valve 2 is installed at the bottom, and a water outlet valve 7 is installed at the top; a PVC perforated pipe 6 is inserted in the center of the system, and an aeration stone is connected to the bottom and an air pump is connected.

[0039] The system, from bottom to top, is as follows: Support layer 10: 10cm thick, filled with gravel with a particle size of 5~10mm; Iron-carbon composite functional layer 9: 30cm thick, filled with a mixture of pyrite and biochar (particle size 2-5mm) in a certain proportion, and inoculated with activated sludge. The inoculated sludge was taken from the Chongqing Wastewater Treatment Plant (MLSS=3000 mg / L). Organic matter and nutrients such as nitrogen and phosphorus were added to the activated sludge regularly, and it was intermittently aerated. After acclimatization, microorganisms were inoculated into the substrate in the wetland, including ammonia-oxidizing bacteria and nitrifying bacteria enriched in the aerobic zone, such as Nitrosomonas (ammonia-oxidizing bacteria) and Nitrospira (nitrifying bacteria); and anoxic denitrifying bacteria enriched in the anoxic zone, such as Denitrosoma and Azospira. Gravel layer 8: 20cm thick, serving as the outflow distribution layer; Vegetation layer: Plant wetland plants such as canna lilies and sedges.

[0040] Operating mode: Wastewater enters from the bottom and flows through the system in a bottom-in, top-out manner. The air pump supplies air at a rate of 0.5~1.0L / min, using intermittent aeration mode (aeration for 2 hours, then 1 hour off). The hydraulic retention time is set to 2 hours.

[0041] The filler material of this constructed wetland system needs to be cleaned with tap water before use. Wastewater flows into the device through a peristaltic pump and flows upward evenly in a bottom-in, top-out manner, avoiding the formation of dead zones.

[0042] Wastewater first enters the support layer 10 through inlet valve 2. The support layer is filled with gravel and then flows into the iron-carbon composite functional layer 9. The wastewater composition includes COD 100 mg / L, total nitrogen 20 mg / L, and total phosphorus 3 mg / L. The hydraulic retention time is set to 2 hours, and the aeration pump is started with an air supply of 0.5~1.0 L / min. An intermittent aeration mode is adopted (aeration for 2 hours, then stop for 1 hour). Under the action of inoculated microorganisms, the wastewater undergoes purification, nitrification, and denitrification in the iron-carbon composite functional layer. The COD removal rate can reach more than 92%, and the effluent concentration is below 8 mg / L; the total nitrogen removal rate can reach 80%, and the effluent concentration is below 5 mg / L.

[0043] A middle valve 4 and an end valve 5 are respectively installed in the iron-carbon composite functional layer 9 for water intake and monitoring of biochar iron ore. Finally, the gravel layer flowing into the top layer is discharged by the drainage valve 7. Healthy canna lilies with a height of 20cm are planted on the top of the wetland device.

[0044] In this embodiment, the hydraulic retention time is controlled by a peristaltic pump at the inlet, allowing for the setting of different hydraulic retention times. The wastewater is configured in the laboratory based on on-site monitoring data. After treatment by the system, the COD removal rate can reach over 92%, with a concentration below 8 mg / L; the total nitrogen removal rate can reach 80%, with a concentration of around 5 mg / L; and the total phosphorus removal rate can reach over 75%.

[0045] In this embodiment, the iron-carbon synergistic aeration enhanced constructed wetland system has a PVC perforated pipe 6 inserted in the center, with an aeration stone connected to the bottom and a pipeline connected to an air pump. The aeration air source is compressed air, which is used to supply oxygen externally and control the DO concentration and aeration time in the system to enhance the pollutant removal efficiency. When aeration is turned on, the total nitrogen removal rate is increased by more than 20% compared with no aeration, and the COD removal rate is increased by 20-30%.

[0046] Example 2: System Construction with Different Iron-Carbon Dosage Ratios

[0047] Three sets of iron-carbon synergistic aeration enhanced constructed wetland systems were set up. In the iron-carbon composite functional layer 9, the volume ratio of pyrite to biochar was as follows: Dosage ratio A: Pyrite; Biochar = 2:1 (enhanced phosphorus removal type); Dosage ratio B: Pyrite; Biochar = 1:1 (Nitrogen-phosphorus balanced type); Dosage ratio C: Pyrite; Biochar = 1:2 (enhanced denitrification type); 1. Dosage ratio A (iron ore: biochar = 2:1) Working principle: A high proportion of pyrite can release a large amount of Fe²⁺. + / Fe³ + It rapidly forms precipitates with phosphates (such as ferric phosphate), resulting in high phosphorus removal efficiency. The sulfides (S²⁺) produced by the oxidation of pyrite... - Denitrifying bacteria can drive nitrate reduction, but insufficient biochar support limits the accumulation of denitrifying bacteria, and the oxidation of large amounts of pyrite produces acid (H+). + Biochar, on the other hand, contains less, and when this exceeds its buffering capacity, it can easily lead to a drop in pH, thereby inhibiting microbial activity.

[0048] Performance characteristics: It is only suitable for wastewater with high phosphorus content (above 3 mg / L), but due to the low proportion of biochar and insufficient denitrification carrier, the nitrogen removal efficiency is limited, for example, the removal rate of nitrate nitrogen is only 43%. Since the oxidation of pyrite will cause system acidification and large pH fluctuations, an additional alkalinity adjuster needs to be added.

[0049] 2. Dosage ratio B (iron ore: biochar = 1:1)

[0050] Working principle: Nitrogen and phosphorus are removed synergistically, and iron ore provides Fe²⁺. + Phosphorus removal and sulfide-driven autotrophic denitrification. Biochar adsorbs phosphorus, slowly releases carbon sources to support heterotrophic denitrification, and enriches microorganisms. Biochar neutralizes acid produced by pyrite, maintaining a near-neutral pH (6.5~7.5) and preserving acid-base balance. Microenvironment improvement: The porous structure of biochar promotes aerobic / anaerobic partitioning, facilitating nitrification-denitrification coupling.

[0051] Performance characteristics: It can achieve simultaneous and efficient removal of nitrogen and phosphorus. It has good pH buffering capacity and high microbial activity, improving system stability. It is suitable for medium- to high-concentration nitrogen and phosphorus wastewater (such as aquaculture and municipal sewage, with nitrogen and phosphorus concentrations of approximately 10 mg / L and 1-3 mg / L, respectively).

[0052] 3. Dosage ratio C (iron ore: biochar = 1:2)

[0053] Working principle: Enhanced denitrification and buffering: Biochar primarily adsorbs organic matter and provides a slow-release carbon source, significantly promoting heterotrophic denitrification. Its porous structure is suitable for microbial habitation, facilitating the enrichment of nitrifying / denitrifying bacteria. With low iron ore content, chemical precipitation is weak; phosphorus is mainly adsorbed by biochar and bound by the iron coating. It minimizes acidification risk, and its strong buffering capacity helps maintain system pH stability (7.0–8.0).

[0054] Performance characteristics: It boasts the highest nitrogen removal efficiency, achieving a total nitrogen removal rate of 80-95% (especially for wastewater with a low C / N ratio). However, its phosphorus removal capacity is relatively weak (60-75%), relying on the regeneration capacity of biochar after adsorption saturation. The system offers good sustainability: low iron leaching and no risk of sulfide toxicity.

[0055] Example 3: Construction of a system with different fill heights

[0056] Under the same dosage ratio, the arrangement height of the iron-carbon composite functional layer 9 is changed: Select the appropriate filling height based on the influent concentration to maximize the use of the iron-carbon composite functional layer 9, avoiding waste due to excessive filling height and poor treatment effect due to insufficient filling height.

[0057] Low dosing height: The height of the iron-carbon composite functional layer 9 is 20 cm. The wastewater contains COD concentrations of 30 mg / L, total nitrogen of 15 mg / L, and total phosphorus of 0.5 mg / L. Iron provides electrons to promote the reduction reaction, and biochar adsorbs pollutants, which is conducive to the attachment and growth of microorganisms. However, due to the small thickness of the functional layer, the subsequent treatment capacity may be limited, making it suitable for the preliminary treatment of low-concentration pollutants.

[0058] Medium dosing height: The height of the iron-carbon composite functional layer 9 is 30 cm. The wastewater contains COD 60 mg / L, total nitrogen 30 mg / L, and total phosphorus 1.5 mg / L. The moderate thickness of the functional layer avoids premature saturation of the iron and carbon, resulting in more stable treatment performance.

[0059] High dosing height: The thickness of the iron-carbon composite functional layer 9 is 40 cm. The wastewater contains COD 60 mg / L, total nitrogen 30 mg / L, and total phosphorus 1.5 mg / L. The relatively large thickness of the functional layer is suitable for treating higher concentrations of pollutants.

Claims

1. An iron-carbon synergistic aeration enhanced constructed wetland system, comprising, from bottom to top, a support layer, an iron-carbon composite functional layer, a gravel layer and a plant layer, wherein aeration pipes are provided vertically through each layer, and the iron-carbon composite functional layer is composed of pyrite and biochar and is inoculated with activated sludge.

2. The iron-carbon synergistic aeration enhanced constructed wetland system according to claim 1, wherein, The iron-carbon composite functional layer accounts for 50% of the combined height of the support layer, the iron-carbon composite functional layer, and the gravel layer.

3. The iron-carbon synergistic aeration enhanced constructed wetland system according to claim 1, wherein, The height ratio of the support layer, the iron-carbon composite functional layer, and the gravel layer is 10:30:

20.

4. The iron-carbon synergistic aeration enhanced constructed wetland system according to claim 1, wherein, At least one of the following must be met: The iron-carbon composite functional layer is composed of pyrite and biochar in a volume ratio of 2:

1. The iron-carbon composite functional layer is composed of pyrite and biochar in a 1:1 volume ratio. The iron-carbon composite functional layer is composed of pyrite and biochar in a volume ratio of 1:

2.

5. The iron-carbon synergistic aeration enhanced constructed wetland system according to claim 1, wherein, At least one of the following must be met: The system is equipped with a water inlet valve to allow water to enter the support layer; A middle valve and an end valve are respectively provided in the middle and top of the iron-carbon composite functional layer for water intake and substrate intake. A drainage valve is provided in the gravel layer for water discharge; The plant layer is planted with wetland plants, including one or more of canna lilies and sedges.

6. The iron-carbon synergistic aeration enhanced constructed wetland system according to claim 1, wherein, The aeration pipe is provided with aeration holes in sequence along the vertical direction, and is connected to aeration stones and an air pump to supply gas to the system.

7. The application of the iron-carbon synergistic aeration enhanced constructed wetland system according to any one of claims 1-6 in wastewater treatment.

8. The application according to claim 7, wherein, The applications include: S1 allows wastewater to flow through the inlet valve into the support layer and enter the system; S2, the wastewater then enters the iron-carbon composite functional layer from bottom to top, where it undergoes purification, nitrification, denitrification and phosphorus removal under the action of ammonia-oxidizing bacteria, nitrifying bacteria and denitrifying bacteria to obtain clean water; S3, clean water enters the gravel layer, part of which is discharged through the drain valve, and the other part is used for plant growth in the plant layer.

9. The application according to claim 7, wherein, The air pump supplies air at a rate of 0.5~1.0L / min, using an intermittent aeration mode, aerating for 2 hours and then stopping for 1 hour.

10. The application according to claim 7, wherein, The water retention time is set to 2 hours and is controlled by a peristaltic pump at the inlet valve.

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