Iron matrix improved artificial wetland system for purifying river water

Abstract

The invention discloses an iron matrix improved artificial wetland system for purifying river water, which is characterized in that on the basis of purifying pollutants in a water body by utilizing the synergistic effect of microorganisms, plants and fillers, sponge iron is introduced to be combined with common wetland fillers, so that the treatment effect of an artificial wetland is improved, and the efficient purification of polluted river water is realized. The artificial wetland system improved by the sponge iron not only has a good removal effect on conventional pollutants such as ammonia nitrogen and COD (Chemical Oxygen Demand), but also has good impact resistance and removal effect on a new pollutant such as antibiotics. The sponge iron and the common wetland filler used in the invention have the advantages of low cost, stable chemical properties, easy transportation and treatment and the like, and are suitable for large-scale water purification treatment of polluted river water.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and particularly relates to an iron matrix improved constructed wetland system for river water purification. Background Art

[0002] Matrix filler clogging is a complex phenomenon in the operation of constructed wetland systems, which is mainly caused by the combined action of multiple factors such as the deposition of influent suspended solids, the formation of chemical precipitates, the excessive proliferation of biofilms, and the expansion of plant roots. The dynamic changes of internal environmental parameters (such as pH value, redox potential, etc.) in the system will accelerate the physical wear of the matrix structure, resulting in a significant decrease in porosity.

[0003] Dissolved oxygen (DO) is a key environmental factor that regulates the pollutant removal efficiency of constructed wetland (CWs) systems. Its concentration change determines the pollutant removal effect by affecting the microbial metabolic pathway. For organic matter removal, the DO concentration is positively correlated with the aerobic degradation efficiency. However, the system often suffers from insufficient DO due to the preferential consumption of oxygen by organic matter, which not only limits nitrification but also triggers oxygen competition between the organic matter degradation and nitrification processes, ultimately restricting the total nitrogen (TN) removal efficiency. In terms of phosphorus removal, aerobic environment provides ideal metabolic conditions for polyphosphate-accumulating bacteria, enabling them to efficiently absorb phosphorus using oxygen as an electron acceptor, which is significantly better than the phosphorus removal effect under anoxic conditions. The influent carbon-nitrogen ratio (C / N ratio) is a key factor that regulates the microbial nitrogen transformation process, and its change regulates the nitrogen removal pathway by affecting the microbial community structure and metabolic activity. Research shows that the change of C / N ratio will significantly affect the competition relationship between heterotrophic denitrifying bacteria and anaerobic ammonium oxidation (AMX) bacteria: a higher C / N ratio promotes heterotrophic denitrification but inhibits AMX activity. Temperature is a key environmental factor that regulates the functions of macrophytes and microorganisms in constructed wetland (CWs) systems, and its seasonal fluctuation significantly changes the pollutant removal efficiency of the system by affecting the microbial metabolic activity.

[0004] In actual engineering applications, constructed wetland systems face problems such as permeability attenuation caused by matrix filler clogging, inhibition of biochemical reactions under low-temperature environments, nitrification / denitrification coupling disorders caused by difficult DO regulation, and insufficient denitrification carbon sources caused by C / N ratio imbalance. These technical barriers seriously restrict the stability of the treatment efficiency and the large-scale popularization and application of constructed wetlands. Therefore, it is urgent to develop a new type of constructed wetland system. Summary of the Invention

[0005] The object of the present invention is to provide an iron matrix modified artificial wetland system for river water purification. On the basis of purifying pollutants in water by the synergistic action of microorganisms, plants and fillers, a low-cost and chemically stable iron-based material, sponge iron, is introduced into the fillers, so as to improve the treatment effect of the artificial wetland and achieve the efficient purification of polluted river water. The artificial wetland system modified by the iron matrix not only has good removal effects on conventional pollutants such as ammonia nitrogen and COD, but also has good impact resistance and removal effects on new pollutants such as antibiotics. The sponge iron and ordinary wetland fillers used in the present invention have the advantages of low cost, stable chemical properties, easy transportation and treatment, etc., and are suitable for large-scale water quality purification treatment of polluted river water.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: An iron matrix modified artificial wetland system for river water purification, the iron matrix modified artificial wetland system includes a water distribution area, a main body area and a water collection area. An inlet is arranged on one side of the water distribution area, and three outlets are evenly arranged on one side of the water collection area; the main body area includes a gravel layer at the bottom layer, a main reaction layer composed of ordinary wetland fillers and sponge iron, and a soil layer at the top layer; a quartz sand layer is laid between the main reaction layer and the soil layer, and reeds are planted in the soil layer; three PVC pipes are inserted into the main body area for in-situ determination of DO, ORP, temperature and pH value and sampling of fillers.

[0007] Further, the thickness of the gravel layer is 2 cm, and the particle size of the gravel is 10-20 mm.

[0008] Further, the mass ratio of the ordinary wetland filler to the sponge iron is 5:1, and the particle sizes are both 5-10 mm.

[0009] Further, the thickness of the main reaction layer is 15 cm.

[0010] Further, the thickness of the soil layer is 9 cm.

[0011] Further, the thickness of the quartz sand layer is 1 cm.

[0012] Further, 6 reeds are planted in each soil layer with a size of 45 cm×33 cm.

[0013] The present invention also provides the application of the above iron matrix modified artificial wetland system in the purification of polluted river water.

[0014] The beneficial effects of the present invention are as follows: (1) By changing the single filler component in the traditional artificial wetland and combining sponge iron with ordinary wetland fillers, the present invention can improve the resistance of the artificial wetland to antibiotics and achieve the efficient purification of polluted river water.

[0015] (2) By introducing suitable wetland plants such as reeds in the constructed wetland, the present invention improves the removal efficiency of nitrogen, further enhances the permeability and stability of the filler, promotes the rapid precipitation of suspended solids and the acceleration of water circulation, thereby effectively preventing the clogging of the wetland system.

[0016] (3) The sponge iron used in the present invention has a rich pore structure inside, which is beneficial to intercept pollutants. Its surface is a rough structure similar to coral, with a huge specific surface area, greatly improving the capture ability of pollutants and the attachment efficiency of the microbial film. During the water washing process, a large amount of highly active iron oxides will be generated on the sponge iron. The sponge iron contains a large amount of Fe, Si, and O elements. The main components are iron oxides and silicon oxides, which can enhance the adsorption effect of the filler on nitrogen and phosphorus and strengthen the removal effect of nitrogen and phosphorus.

[0017] (4) The common wetland filler used in the present invention is widely used in constructed wetlands. Its main components are silicon compounds and calcium compounds, which can improve the removal effect of nitrogen and phosphorus by the adsorption of nitrogen and phosphorus by the filler. A large number of holes are distributed on its surface, with a rich pore structure, which can provide sufficient active sites. The surface and pore walls of the common wetland filler are rough, with a large specific surface area, which is beneficial to the attachment of the biofilm, can effectively improve the interception efficiency of pollutants and the growth efficiency of the biofilm. There are also cluster structures on the surface of the common wetland filler, which can provide rich attachment sites for the biofilm. Brief Description of the Drawings

[0018] Figure 1 is a side view of the iron matrix improved constructed wetland system for river water purification of the present invention, where 1 - inlet water tank; 2 - inlet pipe; 3 - pump; 4 - PVC pipe; 5 - reeds; 6 - soil layer; 7 - outlet; 8 - gravel layer; 9 - quartz sand layer; 10 - filler layer, from left to right are 11 - water distribution area, 12 - main area and 13 - water collection area.

[0019] Figure 2 is a top view of the iron matrix improved constructed wetland system for river water purification of the present invention, where 1 - inlet water tank; 2 - inlet pipe; 3 - pump; 4 - PVC pipe; 5 - reeds; 6 - soil layer; 7 - outlet; 8 - gravel layer. Detailed Embodiments

[0020] In order to make the content described in the present invention easier to understand, the following further describes the technical solutions of the present invention in combination with specific embodiments, but the present invention is not limited thereto.

[0021] Example 1 Construction of the iron matrix improved constructed wetland system for river water purification The side view and top view of the iron matrix improved constructed wetland system for river water purification of the present invention are as Figure 1 - Figure 2As shown in the figure, where 1 - inlet water tank; 2 - inlet pipe; 3 - pump; 4 - PVC pipe; 5 - reed; 6 - soil layer; 7 - outlet; 8 - gravel layer; 9 - quartz sand layer; 10 - packing layer. This system uses a plastic water tank with a length of 45 cm, a width of 33 cm, and a height of 30 cm as the artificial wetland pool body. From left to right, there are 11 - water distribution area, 12 - main body area, and 13 - water collection area. An inlet is set on one side of the water distribution area, and three outlets are evenly set on one side of the water collection area. The main body area is laid in four layers. The bottom layer is laid with a 2-cm-thick gravel layer (particle size 10 - 20 mm) to play a supporting role; the middle is a 15-cm main reaction layer, composed of a filler of ordinary wetland filler / sponge iron = 5:1 (particle sizes are all between 5 - 10 mm); the top layer is laid with a 9-cm-thick soil layer to facilitate plant growth; a 1-cm-thick quartz sand layer is laid between the main reaction layer and the soil layer for separating the soil and the filler. Three PVC pipes (diameter 5 cm, height 35 cm) are inserted into the main body area for in-situ determination of DO, ORP, temperature, and pH value, as well as sampling of the filler. To avoid the photodegradation of antibiotics and the growth of algae, the outer layer of the device is wrapped with light-shielding cloth. Reed, which is commonly used in wetlands and has strong reproductive ability, is selected as the wetland plant for this experiment, and 6 plants are planted in the soil layer.

[0022] The above-mentioned sponge iron was purchased from Huixin Filler and Filter Media Manufacturer in Zhengzhou, Henan Province; The above-mentioned ordinary wetland filler was purchased from Hangzhou Qinlin Ecological Technology Co., Ltd.

[0023] This filler (ordinary wetland filler / sponge iron = 5:1) needs to be biofilm - attached before use. During the biofilm - attachment period, artificial simulated wastewater prepared with tap water is used, and appropriate trace elements required for the growth of microorganisms are added to ensure the normal growth of microorganisms. The composition of the simulated wastewater during the biofilm - attachment period is shown in Table 1. In this experiment, the activated sludge inoculation method is used for biofilm - attachment. The inoculated sludge comes from the CASS tank of Fuzhou University Town Wastewater Treatment Plant. Before use, this filler is washed with ultrapure water to remove surface dust and impurities, then dried in an oven and poured into the constructed wetland device. Then, the simulated wastewater is poured in. The volume ratio of the simulated wastewater to the sludge is 10:1 for reactor biofilm - attachment and microorganism domestication. During the biofilm - attachment period, the hydraulic retention time (HRT) is set to 48 h, continuous influent is adopted, and the biofilm - attachment lasts for two weeks. During this period, the concentration values of COD, ammonia nitrogen, nitrate nitrogen, TP, TN, and nitrite nitrogen are measured every two days to observe the concentration changes of pollutants in the influent and effluent. When it is observed that a yellow - brown biofilm is formed on the filler and the pollutant removal rate of the effluent is high and stable, it proves that the biofilm - attachment is successful. After the biofilm - attachment is successful, it enters the microorganism domestication stage. In the domestication stage, actual simulated wastewater starts to be influent. The composition of the simulated wastewater is shown in Table 2. Continuous - flow influent is adopted, and the domestication lasts for two weeks. The hydraulic retention time (HRT) is 48 h, and the effluent COD, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, TN, TP, DO, PH, and ORP values are measured every two days. When the removal rate of COD by the constructed wetland system reaches more than 70%, it proves that the iron - matrix modified constructed wetland system starts successfully, and the subsequent experiments will use this iron - matrix modified constructed wetland. The concentration of trace elements added to the simulated wastewater during the biofilm - attachment period and the domestication stage is 1 mL / L, and the component of the trace element solution is shown in Table 3.

[0024] Table 1 Main components of the simulated wastewater during the biofilm - attachment period Table 2 Main components of the simulated wastewater during the domestication stage Table 3 Main components of the trace element solution Example 2 First, explore the water quality purification effect of the iron - matrix modified constructed wetland system under different hydraulic retention times. The water sample is taken from the downstream river channel water of a certain river, and the simulated wastewater used for influent is prepared with reference to the collected water sample. Its relevant indicators are shown in Table 4. Set 3 groups of experiments, and continuously operate for 20 days at hydraulic retention times of 16 h, 24 h, and 32 h respectively. The indicators such as COD, TP, TN, ammonia nitrogen, nitrate nitrogen, and antibiotics in the effluent are detected every two days. The effluent water quality indicators and removal rates are shown in Table 5.

[0025] Table 4 Average influent water quality indicators Table 5 Average Effluent Water Quality Indexes and Removal Rates As can be seen from the data in the above table, under different hydraulic retention times, the iron matrix improved constructed wetland system has excellent removal effects on different pollutants. For example, in the removal of NO3 - -N, due to the occurrence of iron autotrophic denitrification, sponge iron can use its own zero-valent iron and divalent iron ions as electron donors and nitrate nitrogen as an electron acceptor in the case of insufficient carbon source, and finally convert NO3 - -N into nitrogen gas. In addition, sponge iron can also undergo chemical denitrification, directly reducing NO3 - -N to other N forms, promoting the transformation of NO3 - -N, and its average removal rate can reach up to 96.8%. For phosphorus pollutants in water, after adding sponge iron to the system, iron can react with air and water to generate Fe(OH)2 and Fe(OH)3 colloids, which further enhances the removal effect of phosphorus pollutants through the adsorption of the colloids. Therefore, under different hydraulic retention times, its average removal rate can also be stably maintained above 90%.

[0026] For different pollutant indexes, the hydraulic retention times for each system to obtain the best removal effect are different. In terms of the overall removal effect, 24 h is the best hydraulic retention time.

[0027] Example 3 Next, the water quality purification effect of the iron matrix improved constructed wetland system under different concentrations of antibiotics was explored. The simulated wastewater used for the influent was also prepared with reference to the water samples collected from the downstream river channel of a certain river, and its relevant indexes are shown in Table 6. The SMX concentrations of antibiotics in the influent of the 3 groups of experiments were 0 mg / L, 1 mg / L, and 10 mg / L respectively, and they were operated for 20 days at a hydraulic retention time of 24 h. The indexes such as COD, TP, TN, ammonia nitrogen, nitrate nitrogen, and antibiotics in the effluent were detected every two days. The effluent water quality indexes and removal rates are shown in Table 7.

[0028] Table 6 Average Influent Water Quality Indexes Table 7 Average Effluent Water Quality Indexes and Removal Rates It can be seen from the data in the above table that in the constructed wetland systems with different concentrations of antibiotics added, although the removal effects of various pollutants have decreased to varying degrees, they all maintain a relatively high removal efficiency, and the water quality indicators of the effluent also meet the quality standards of the corresponding functional zones of the waters where the reference water quality is located. In the face of the increasing SMX pollution load, sponge iron exhibits good buffering performance and can effectively alleviate the stress of SMX on the removal rates of indicators such as ammonia nitrogen, COD, and TP.

[0029] It should be noted that under the stress of 1 and 10 mg / L SMX, the average removal rate of NO3 - -N hardly changed compared with that without the addition of SMX. During the entire experimental operation stage, the average effluent concentration was 0.31 mg / L to 0.52 mg / L, and the average removal rate only decreased from 94.7% to 91.1%. Moreover, as an iron mineral, sponge iron is more favorable for the adsorption of SMX, which mainly exists in the form of negative ions in water. There will also be hydrogen bond interactions between SMX and the mineral, which also promotes the removal of SMX to a certain extent. In addition, the surface complexation between SMX and the oxides or hydroxides on the iron surface also helps to enhance the adsorption of SMX. Therefore, the addition of sponge iron can enhance the adsorption effect of SMX.

[0030] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. An iron matrix improved artificial wetland system for river water purification, characterized by: The iron-matrix improved artificial wetland system comprises a water distribution area, a main area and a water collection area. A water inlet is arranged on one side of the water distribution area, and three water outlets are evenly arranged on one side of the water collection area. The main area comprises a bottom gravel layer, a main reaction layer composed of ordinary wetland fillers and sponge iron, and an uppermost soil layer. A quartz sand layer is laid between the main reaction layer and the soil layer, and reeds are planted in the soil layer. Three PVC pipes are inserted into the main area for in-situ determination of DO, ORP, temperature, pH value and filler sampling.

2. The iron matrix improved artificial wetland system according to claim 1, characterized in that: The thickness of the gravel layer is 2 cm, and the particle size of the gravel is 10-20 mm.

3. The iron matrix improved artificial wetland system according to claim 1, characterized in that: The mass ratio of ordinary wetland filler to sponge iron is 5:1, and the particle size is 5-10mm.

4. The iron matrix improved artificial wetland system according to claim 1, characterized in that: The thickness of the main reaction layer is 15 cm.

5. The iron matrix improved artificial wetland system according to claim 1, characterized in that: The thickness of the soil layer is 9 cm.

6. The iron matrix improved artificial wetland system according to claim 1, characterized in that: The thickness of the quartz sand layer is 1 cm.

7. The iron matrix improved artificial wetland system according to claim 1, characterized in that: Six reeds were planted in each 45 cm × 33 cm soil layer.

8. Use of the iron-based modified artificial wetland system according to any one of claims 1 to 7 in the purification of polluted river water.

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