Constructed wetland for aquaculture tail water treatment and method for realizing industrial aquaculture seawater recycling by utilizing constructed wetland

Abstract

The invention relates to the technical field of aquaculture tail water treatment. The invention provides a constructed wetland for aquaculture tail water treatment and a method for realizing industrial aquaculture seawater recycling by utilizing the constructed wetland. The constructed wetland comprises a filler, salt-tolerant plants and a slow-release carbon source, the filler sequentially comprises a cobblestone layer, a volcanic rock layer and a quartz sand layer from bottom to top; the salt-tolerant plants are sea bamboo shoots and sea horse teeth; the slow-release carbon source is bamboo reed, corncob and biochar. According to the invention, by constructing the ecological high-efficiency constructed wetland, cyclic utilization of industrial aquaculture seawater is realized. The constructed wetland constructed by the invention can improve the utilization efficiency of seawater, reduce the discharge of tail water and protect the marine ecological environment.

Description

Technical Field

[0001] The present invention relates to the technical field of aquaculture tail water treatment, and in particular to an artificial wetland for aquaculture tail water treatment and a method for realizing the recycling of factory aquaculture seawater by utilizing the artificial wetland. Background Art

[0002] Currently, most marine aquaculture operations still rely on extensive, direct discharge of tailwater. This indiscriminate discharge poses a serious threat to the ecological environment of receiving waters and may exacerbate the shortage of high-quality aquaculture water. This also reflects the current lack of cost-effective, effective tailwater treatment systems and methods. Therefore, it is imperative to develop a low-cost, high-quality treatment system and method to purify aquaculture tailwater, achieve standard discharge, and minimize its impact on the coastal environment.

[0003] As a bioremediation technology that is currently being studied more, artificial wetlands have the advantages of low investment, low operating costs and low energy consumption, and have been successfully used in the treatment of aquaculture tailwater. Artificial wetlands are composed of three parts: matrix fillers, plants and microorganisms ( Figure 1 ), which can effectively treat aquaculture tailwater, is currently widely used in the treatment of tailwater from freshwater and brackish water aquaculture systems, but has limited application in marine aquaculture systems. The lack of salt-tolerant plants is one of the main limitations on the application of constructed wetlands in marine aquaculture systems. Therefore, selecting suitable salt-tolerant plants has become a key factor in the ability of constructed wetlands to purify marine aquaculture tailwater. Furthermore, existing constructed wetlands focus primarily on fillers and plants, with limited research on microorganisms, limiting their effectiveness in water treatment.

[0004] Furthermore, when currently used in artificial wetlands to treat aquaculture tailwater, the introduced tailwater often lacks a sufficient carbon source, leading to an imbalance in the carbon to nitrogen ratio and limiting treatment efficiency. The addition of slow-release carbon sources can, to a certain extent, address this issue. Furthermore, the current determination of wetland substrate types and ratios is somewhat confusing, further hindering the development of artificial wetland technology. Therefore, developing a novel artificial wetland for aquaculture tailwater treatment and utilizing it to achieve industrial aquaculture seawater recycling has become an urgent issue. Summary of the Invention

[0005] The present invention aims to provide an artificial wetland for aquaculture tailwater treatment and a method for recycling seawater in industrial aquaculture using the artificial wetland. The method involves selecting suitable salt-tolerant plant soil and planting density for the artificial wetland, regularly incorporating a slow-release carbon source, optimizing the artificial wetland tailwater treatment process, and exploring the inherent connection between water quality treatment and the microbial structure of the artificial wetland. This approach aims to ensure that aquaculture tailwater meets discharge standards, reduce pollution to the coastal environment, and restore the coastal ecosystem.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions: The present invention provides an artificial wetland for aquaculture tail water treatment, the artificial wetland comprising filler, salt-tolerant plants and a slow-release carbon source; The fillers are, from bottom to top, a pebble layer, a volcanic rock layer and a quartz sand layer; The salt-tolerant plants are sea asparagus and seahorse teeth; The slow-release carbon sources are reed bamboo, corn cob and biochar.

[0007] Preferably, the thickness of the pebble layer is 10-20% of the total thickness of the filler; the thickness of the volcanic rock layer is 60-80% of the total thickness of the filler; and the thickness of the quartz sand layer is 10-20% of the total thickness of the filler.

[0008] Preferably, the density of the salt-tolerant plants is 20 to 30 plants / m 2 .

[0009] Preferably, the ratio of sea bamboo shoots to sea horse teeth is 1:1~2.

[0010] Preferably, a columnar filling area is provided in the filler, and the columnar filling area consists of a filling tube with holes at the bottom and sides and a slow-release carbon source; the mass ratio of reed bamboo, corn cob and biochar in the slow-release carbon source is 4:(2~3):(1~2), the addition ratio of the slow-release carbon source in the filler is 20~30 g / L, and the replacement cycle of the slow-release carbon source is 60~90d.

[0011] The present invention also provides application of the artificial wetland in recycling utilization of seawater in industrial aquaculture.

[0012] The present invention also provides a method for realizing the recycling of seawater in factory aquaculture by utilizing the artificial wetland, comprising the following steps: adjusting the water quality of the influent, injecting the water into the artificial wetland, testing the water quality after it stays for 20 to 30 hours, and discharging the water after it meets the standards.

[0013] Preferably, the water quality of the influent is: pH 7.2~8.7, total ammonia nitrogen 2.32~2.88 mg / L, nitrite nitrogen 0.36~0.50 mg / L, nitrate nitrogen 1.02~1.25 mg / L, total nitrogen 7.22~7.86 mg / L, and total phosphorus 1.12~1.31 mg / L.

[0014] Preferably, the water quality standards before discharge are: pH 7.5~8.3, total ammonia nitrogen 0.19~0.35 mg / L, nitrite nitrogen 0.05~0.10 mg / L, nitrate nitrogen 0.20~0.31 mg / L, total nitrogen 2.05~2.59 mg / L, and total phosphorus 0.31~0.40 mg / L.

[0015] The present invention provides an artificial wetland for treating aquaculture tail water and a method for realizing the recycling of factory-scale aquaculture seawater by using the artificial wetland. The artificial wetland comprises a filler, salt-tolerant plants and a slow-release carbon source; the filler comprises, from top to bottom, a pebble layer, a volcanic rock layer and a quartz sand layer; the salt-tolerant plants are sea asparagus and seahorse teeth; and the slow-release carbon source comprises reed bamboo, corn cobs and biochar.

[0016] Beneficial effects: 1. The present invention selects suitable salt-tolerant plants for the construction of artificial wetlands. The resulting ecologically efficient artificial wetlands can achieve the recycling of seawater in factory aquaculture.

[0017] 2. The present invention explores the relationship between the water purification capacity of artificial wetlands and the microbial flora from the perspective of microbial structure. Nitrifying bacteria play a vital role in water treatment, especially in the field of tail water treatment. They convert ammonia nitrogen compounds in water into nitrites and nitrates through catalysis, completing the nitrification process, thereby reducing the degree of water pollution. Denitrifying bacteria also play a very important role in the sewage treatment process, especially in the removal of ammonia nitrogen. Through the three processes of ammonification, nitrification and denitrification, denitrifying bacteria can reduce nitrates and nitrites to nitrogen gas, thereby completely removing nitrogen elements from the water body and achieving the purpose of purifying water quality. This process not only helps to reduce the nitrogen content in the water, but also helps to maintain the pH stability of the water environment.

[0018] 3. Slow-release carbon sources balance the C / N ratio and effectively improve treatment efficiency. The use of exogenous carbon sources is an important step in the water treatment process, especially in sewage treatment. The addition of exogenous carbon sources is mainly to solve the problem of insufficient carbon sources, improve the efficiency of biological treatment, and thus improve the effluent water quality.

[0019] 4. The constructed artificial wetland can improve the utilization efficiency of seawater, reduce the discharge of tail water and protect the marine ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the artificial wetland system; Figure 2 This is a diagram of the artificial wetland experimental device; Figure 3The removal rates of total ammonia nitrogen, total nitrogen and total phosphorus in aquaculture tail water at different hydraulic retention times; Figure 4 is the removal efficiency of total ammonia nitrogen in marine aquaculture tail water by different salt-tolerant plants; Figure 5 is the removal efficiency of nitrite nitrogen from marine aquaculture tail water by different salt-tolerant plants; Figure 6 is the removal efficiency of nitrate nitrogen from marine aquaculture tail water by different salt-tolerant plants; Figure 7 is the removal efficiency of total nitrogen in marine aquaculture tail water by different salt-tolerant plants; Figure 8 is the removal efficiency of total phosphorus in marine aquaculture tail water by different salt-tolerant plants; Figure 9 The distribution diagram of bacterial colony structure on the quartz sand surface of different devices (phylum level); Figure 10 The distribution map of bacterial colony structure on the volcanic rock surface of different devices (phylum level); Figure 11 It is the treatment efficiency of the artificial wetland model on various water quality indicators of aquaculture tail water during the pilot period. DETAILED DESCRIPTION

[0021] The present invention provides an artificial wetland for aquaculture tail water treatment, the artificial wetland comprising filler, salt-tolerant plants and a slow-release carbon source; The fillers are, from bottom to top, a pebble layer, a volcanic rock layer and a quartz sand layer; The salt-tolerant plants are sea asparagus and seahorse teeth; The slow-release carbon sources are reed bamboo, corn cob and biochar.

[0022] In the present invention, the thickness of the pebble layer is preferably 10-20% of the total thickness of the filler, more preferably 15%; the thickness of the volcanic rock layer is preferably 60-80% of the total thickness of the filler, more preferably 70%; the thickness of the quartz sand layer is preferably 10-20% of the total thickness of the filler, more preferably 15%.

[0023] In the present invention, the density of the salt-tolerant plants is preferably 20 to 30 plants / m 2 , more preferably 25 plants / m 2 .

[0024] In the present invention, the ratio of sea bamboo shoots to sea horse teeth is preferably 1:1~2, and more preferably 1:1.5.

[0025] In the present invention, the filler is preferably provided with a columnar filling area, and the columnar filling area is preferably composed of a plastic filling tube with holes at the bottom and sides and a slow-release carbon source; the volume ratio of reed bamboo, corn cob and biochar in the slow-release carbon source is preferably 4: (2~3): (1~2), and more preferably 4:2.5:1.5. The addition ratio of the slow-release carbon source in the filler is preferably 20~30 g / L, and more preferably 25 g / L. The replacement cycle of the slow-release carbon source is 60~90d, and further optimized to 75d.

[0026] In the present invention, the holes at the bottom and side of the plastic filling tube facilitate the release of the carbon source, and the carbon source can be regularly implanted into the tube and the carbon source residue can be removed through the cylinder.

[0027] The present invention also provides application of the artificial wetland in recycling utilization of seawater in industrial aquaculture.

[0028] The present invention also provides a method for realizing the recycling of seawater in factory aquaculture by utilizing the artificial wetland, comprising the following steps: after the artificial wetland to be constructed is in stable operation, the water quality of the influent is adjusted, the water is injected into the artificial wetland, the water quality is tested after it stays for 20 to 30 hours, and the water is discharged after meeting the standards.

[0029] In the present invention, the water quality of the influent is preferably: pH 7.2-8.7, total ammonia nitrogen 2.32-2.88 mg / L, nitrite nitrogen 0.36-0.50 mg / L, nitrate nitrogen 1.02-1.25 mg / L, total nitrogen 7.22-7.86 mg / L, total phosphorus 1.12-1.31 mg / L, more preferably: pH 7.5-8.5, total ammonia nitrogen 2.60 mg / L, nitrite nitrogen 0.43 mg / L, nitrate nitrogen 1.13-1.14 mg / L, total nitrogen 7.54-7.55 mg / L, total phosphorus 1.21-1.22 mg / L.

[0030] In the present invention, the water quality standard before discharge is preferably: pH 7.5-8.3, total ammonia nitrogen 0.19-0.35 mg / L, nitrite nitrogen 0.05-0.10 mg / L, nitrate nitrogen 0.20-0.31 mg / L, total nitrogen 2.05-2.59 mg / L, total phosphorus 0.31-0.40 mg / L, more preferably: pH 7.8-8.2, total ammonia nitrogen 0.27 mg / L, nitrite nitrogen 0.07-0.08 mg / L, nitrate nitrogen 0.25-0.26 mg / L, total nitrogen 2.32-2.35 mg / L, total phosphorus 0.35-0.36 mg / L.

[0031] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] Example 1

[0033] A method for recycling seawater in factory aquaculture using artificial wetlands comprises the following steps: (1) Lay a pebble layer at the lowest part of the artificial wetland, and control the thickness of the pebble layer to 10% of the total thickness; (2) Lay a volcanic rock layer on top of the pebble layer, and control the thickness of the volcanic rock layer to 80% of the total thickness; (3) Laying a quartz sand layer on top of the volcanic rock layer, with the thickness of the quartz sand layer controlled to be 10% of the total thickness. After laying the quartz sand layer, the filler material of the artificial wetland is obtained; (4) On the filling material, 25 plants / m 2 The standard planting of sea asparagus and sea horse teeth is maintained at a ratio of 1:1.5; (5) The treated and dried Phragmites australis, corn cobs, and biochar were mixed in a volume ratio of 4:2:1 to obtain a slow-release carbon source. The slow-release carbon source was added at a rate of 20 g / L and implanted into the filler through a cylindrical tube to construct an artificial wetland. The carbon source replacement cycle was 90 days. (6) After the artificial wetland is running stably, adjust the water quality of the inlet water and inject the water into the artificial wetland. After the water stays for 25 hours, test the water quality and discharge it after it meets the standards.

[0034] Note: The influent water quality is as follows: pH 7.2-8.4, total ammonia nitrogen 2.32-2.55 mg / L, nitrite nitrogen 0.36-0.42 mg / L, nitrate nitrogen 1.02-1.10 mg / L, total nitrogen 7.22-7.46 mg / L, total phosphorus 1.12-1.20 mg / L; The water quality standards before discharge are: pH 7.4~8.2, total ammonia nitrogen 0.19~0.26 mg / L, nitrite nitrogen 0.05~0.08 mg / L, nitrate nitrogen 0.20~0.25 mg / L, total nitrogen 2.05~2.27 mg / L, and total phosphorus 0.31~0.34 mg / L.

[0035] Example 2

[0036] A method for recycling seawater in factory aquaculture using artificial wetlands comprises the following steps: (1) Lay a pebble layer at the lowest part of the artificial wetland, and control the thickness of the pebble layer to 20% of the total thickness; (2) Lay a volcanic rock layer on top of the pebble layer, and control the thickness of the volcanic rock layer to 60% of the total thickness; (3) Laying a quartz sand layer on top of the volcanic rock layer, with the thickness of the quartz sand layer controlled to be 20% of the total thickness. After laying the quartz sand layer, the filler material of the artificial wetland is obtained; (4) On the filling material, 20 plants / m 2 The standard planting of sea asparagus and sea horse teeth, the ratio of sea asparagus and sea horse teeth is kept at 1:1; (5) The treated and dried Phragmites australis, corn cobs and biochar were mixed in a volume ratio of 4:3:1.5 to obtain a slow-release carbon source. The slow-release carbon source was added at a rate of 30 g / L and implanted into the filler through a cylindrical tube to construct an artificial wetland. The carbon source replacement cycle was 60 days. (6) After the artificial wetland is running stably, adjust the water quality of the inlet water and inject the water into the artificial wetland. After the water stays for 30 hours, test the water quality and discharge it after it meets the standards.

[0037] Note: The water quality of the influent is: pH 7.3-8.7, total ammonia nitrogen 2.51-2.88 mg / L, nitrite nitrogen 0.43-0.50 mg / L, nitrate nitrogen 1.16-1.25 mg / L, total nitrogen 7.61-7.86 mg / L, total phosphorus 1.24-1.31 mg / L; The water quality standards before discharge are: pH 7.5~8.3, total ammonia nitrogen 0.24~0.35 mg / L, nitrite nitrogen 0.07~0.10 mg / L, nitrate nitrogen 0.23~0.31 mg / L, total nitrogen 2.31~2.59 mg / L, and total phosphorus 0.36~0.40 mg / L.

[0038] Example 3

[0039] A method for recycling seawater in factory aquaculture using artificial wetlands comprises the following steps: (1) Lay a pebble layer at the lowest part of the artificial wetland, and control the thickness of the pebble layer to 15% of the total thickness; (2) Lay a volcanic rock layer on top of the pebble layer, and control the thickness of the volcanic rock layer to 70% of the total thickness; (3) Laying a quartz sand layer on top of the volcanic rock layer. The thickness of the quartz sand layer is controlled to be 15% of the total thickness. After laying the quartz sand layer, the filler material of the artificial wetland is obtained. (4) On the filling material, 30 plants / m 2 The standard planting of sea asparagus and sea horse teeth, the ratio of sea asparagus to sea horse teeth is maintained at 1:2; (5) The treated and dried reed bamboo, corn cob and biochar were mixed in a volume ratio of 4:2.5:1.3 to obtain a slow-release carbon source. The slow-release carbon source was added at a rate of 25 g / L and implanted into the filler through a cylindrical tube to construct an artificial wetland. The carbon source replacement cycle was 75 days. (6) After the artificial wetland is running stably, adjust the water quality of the inlet water and inject the water into the artificial wetland. After the water stays for 20 hours, test the water quality and discharge it after it meets the standards.

[0040] Note: The water quality of the influent is: pH 7.5-8.6, total ammonia nitrogen 2.40-2.63 mg / L, nitrite nitrogen 0.39-0.45 mg / L, nitrate nitrogen 1.08-1.20 mg / L, total nitrogen 7.41-7.66 mg / L, total phosphorus 1.18-1.25 mg / L; The water quality standards before discharge are: pH 7.7~8.5, total ammonia nitrogen 0.22~0.27 mg / L, nitrite nitrogen 0.06~0.08 mg / L, nitrate nitrogen 0.23~0.28 mg / L, total nitrogen 2.22~2.41 mg / L, and total phosphorus 0.33~0.40 mg / L.

[0041] Test example

[0042] 1. Construction of artificial wetland device

[0043] This experiment was conducted at the Dongying Experimental Base of Shandong Institute of Marine Resources and Environment. The artificial wetland experimental device can be found at Figure 2 The device uses an acrylic round barrel with a diameter of 60cm, a height of 70cm, and a thickness of 0.8cm. A water outlet is set at 2cm from the bottom, and quartz sand, volcanic rock, and pebbles are used as fillers. From bottom to top, 10cm of pebbles (particle size 1~2cm), 50cm of volcanic rock (3~6mm), and 10cm of quartz sand (particle size 2~4mm) are filled in layers. Three plants with strong salt tolerance and good water purification effect are selected: Suaeda salsa, seahorse teeth, and sea asparagus, and the seedlings are planted 10 cm from the top, with a planting density of 30 plants / m 2 At the same time, a plant-free device was designed to explore the hydraulic retention time. Both the experimental and control groups were implanted with a carbon source of 30 g / L using a ratio of Phragmites australis, corncobs, and biochar (4:2:1.5), with a replacement cycle of 60 days.

[0044] At the beginning of the experiment, the aquaculture water from the experimental base was inoculated into the device for a 40-day microbial acclimation stabilization period. After preliminary experiments, the measured water quality indicators were stable, ensuring the stable operation of the experimental device.

[0045] 2. Experimental design and operation

[0046] The experiment was conducted at the Dongying Experimental Base of the Shandong Institute of Marine Resources and Environment from April to October 2021, with temperatures ranging from 20°C to 32°C and relative humidity ranging from 50% to 85%. The influent during the experiment consisted of industrial discharge from the experimental base's grouper aquaculture system, filtered through a curved screen. Basic water quality indicators during the experiment included: temperature 22.5–25.5°C, salinity 25–26, pH 7.3–8.6, and dissolved oxygen >7 mg / L. In addition, the influent contained total ammonia nitrogen of 2.20–2.45 mg / L, nitrite nitrogen of 0.30–0.42 mg / L, nitrate nitrogen of 1.06–1.17 mg / L, total nitrogen of 7.28–7.53 mg / L, and total phosphorus of 1.04–1.49 mg / L.

[0047] (1) Determination of the optimal hydraulic retention time

[0048] The optimal hydraulic retention time (HRT) was determined using a plant-free device. The constructed wetland operated with periodic intermittent water inflow, with HRTs set at 10, 20, 30, and 40 hours. Aquaculture tailwater flowed slowly and evenly into the device through the inlet. The experiment began after the effluent stabilized. Water samples were collected from the device's water intake at a fixed time of 8:00 AM daily, with each sample volume approximately 250 mL. Two parallel experiments were performed, with each cycle repeated three times.

[0049] (2) Experiment on the purification effect of tailwater using different plant artificial wetland devices

[0050] Devices were designed based on the different plant species, named CW-P1 (P1 represents Suaeda salsa), CW-P2 (P2 represents Hippocampus hornbeam), and CW-P3 (P3 represents Asparagus sphaerocarpus). Once the experimental devices were running stably, water samples were collected before and after treatment based on the established hydraulic retention time. Two parallel constructed wetlands were designed for each group, and seven samples were collected before and after each experiment.

[0051] 3. Detection method

[0052] The detection methods of water quality related indicators refer to the "Marine Monitoring Specification" (GB 17378-2007), among which total ammonia nitrogen (TAN) uses Nessler's reagent colorimetry, nitrite nitrogen (NO2 - -N) using the naphthalene ethylenediamine hydrochloride spectrophotometric method, nitrate nitrogen (NO3 - The zinc-cadmium reduction method was used for total nitrogen (TN) and total phosphorus (TP) were oxidized by potassium persulfate.

[0053] Microbial community composition and diversity testing: Microbial samples were collected by skimming off the surface fillers of different devices. Fillers (quartz sand, volcanic rock materials) were collected from 10-30 cm inside each device and placed in sterile fresh-keeping bags. The samples were refrigerated and brought back to the laboratory and stored at 4°C. Microbial community testing was then performed at Shanghai Meiji Biotechnology Co., Ltd. High-throughput sequencing was then used to detect microorganisms on the surface of the fillers at different levels using operational taxonomic units (OTUs). The specific steps are as follows: (1) Extraction of genomic DNA The genomes of the filler microorganisms were extracted using the QIAGEN DNeasy PowerSoil Pro Kit (47014) according to the manufacturer's instructions. Following extraction, 16S rDNA V4-V5 region sequencing was performed by Shanghai Meiji Biotechnology Co., Ltd. to analyze the distribution of microbial communities in the filler at different levels across the different treatment groups.

[0054] (2) High-throughput sequencing

[0055] Based on the Illumina Miseq 2×300 bp sequencing platform, paired-end sequencing was used to construct a small fragment library for paired-end sequencing. First, PCR amplification was performed using primers corresponding to the 16S V4-V5 region. The PCR amplification reaction system used was 30 μl: 2×Taq master mix 15 μl, primers 341F / 805R 1.0 μl each, genomic DNA 10 ng, dd 0 to 30 μl. PCR conditions: denaturation at 95°C for 30 s, 30 cycles of (94°C for 15 s, 55°C for 25 s, 72°C for 30 s), and a final extension at 72°C for 5 min.

[0056] PCR products were electrophoresed on a 2% agarose gel. The target band (400-450 bp) was selected and recovered using the GeneJET Gel Extraction Kit from Thermo Scientific. Finally, libraries were constructed using the NEB Next® Ultra™ DNA Library Prep Kit for Illumina from New England Biolabs. After quantification and library detection using Qubit, paired-end sequencing of the community DNA fragments was performed on the Illumina MiSeq platform. Valid sequences were obtained by checking and removing questionable sequences using the QIIME software called USEARCH. Operational Taxonomic Units (OTUs) and principal component analysis (PCA) were then used for analysis. OTU delineation simplifies data structure and facilitates comparison of microbial community samples from different sources at a defined taxonomic level. All effective tag sequences of all samples were clustered using Uparse software, and sequences with a similarity of 97% were clustered into one OTU (operational taxonomic unit), and clustering and species classification analysis were performed based on OTUs.

[0057] 4. Data statistical analysis

[0058] The single-factor method was used to analyze the significance of the differences in laboratory test data, and SPSS 19.0 and Excel 2010 were used to plot and analyze the obtained data.

[0059] Experimental results

[0060] 1. Removal rates of total ammonia nitrogen, total nitrogen and total phosphorus in aquaculture tail water at different hydraulic retention times

[0061] The treatment efficiency of total ammonia nitrogen, total nitrogen and total phosphorus in aquaculture tail water with different hydraulic retention time is shown in Figure 2. Figure 3. The results showed that with the increase of hydraulic retention time, the removal rates of TAN, TN and TP in the tail water showed a trend of first increasing and then decreasing, reaching a high level at the 20th and 30th hours, which were 68.17%, 78.04%, 78.57% and 74.15%, 80.54%, 83.39%, respectively. All indicators were significantly improved compared with the 10th hour (P<0.05). However, at the 40th hour, the removal rates of various indicators showed a certain downward trend. This may be because the long closure time affected the growth of the bacterial community and the respiration of the plant roots, resulting in a decrease in the wetland's ability to purify water quality. The specific reasons need further analysis. Based on the above results, under the conditions of this experiment, a hydraulic retention time of 20~30h for the artificial wetland can meet the purification requirements of the aquaculture tail water quality.

[0062] 2. Removal efficiency of total ammonia nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands

[0063] The removal efficiency of total ammonia nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands is shown in Figure 2. Figure 4 . As can be seen from the figure, as the experimental time goes by, the removal rates of TAN by the three different devices first increase and then tend to be stable, but there are also small fluctuations. The removal effects of different devices on TAN are quite significant and different. The removal rate of total ammonia nitrogen in the CW-P1 treatment group was maintained between 59.61% and 71.58%, the removal rate of total ammonia nitrogen in the CW-P2 treatment group was maintained between 65.79% and 80.73%, and the removal rate of total ammonia nitrogen in the CW-P3 treatment group was maintained between 72.70% and 82.61%. It can be seen that the removal efficiency of total ammonia nitrogen by artificial wet Mediterranean horse teeth and sea asparagus is at a higher level, while the removal efficiency of alkali sedge is lower than that of sea horse teeth and sea asparagus.

[0064] 3. Removal efficiency of nitrite nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands

[0065] The removal efficiency of nitrite nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands is shown in Figure 2. Figure 5 As shown in the figure, as the experiment progressed, the CW-P2 and CW-P3 treatment groups showed a significant decrease in the NO2 - The removal efficiency of -N showed a trend of increasing first and then decreasing, with the highest treatment efficiency appearing at around 7.15, which were 76.56% and 77.37% respectively. - -N removal efficiency dropped to 66.00% and 69.25% respectively. - The overall removal efficiency of -N showed an upward trend and then a stable trend. After the plateau period, the removal rate remained between 64% and 70%.

[0066] 4. Removal efficiency of nitrate nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands

[0067] The removal efficiency of nitrate nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands is shown in Figure 2. Figure 6 As can be seen from the figure, before July 15, the three different devices had a significant impact on NO3 - The removal efficiency of NO3 showed a significant upward trend, rising from 31.95% to 52.05%, 34.38% to 58.40%, and 33.28% to 60.45%, respectively. After that, it showed a downward and then upward trend over time, which may be related to changes in environmental factors such as temperature, salinity, and pH. - -N treatment efficiency of the seahorse tooth device was higher than that of the other two treatment groups, and the treatment efficiency of the seahorse tooth device was slightly lower than that of the sea asparagus group, but the difference between the two was not significant. - The treatment efficiency of -N was at a low level, and the treatment efficiency after 7.5 was significantly lower than that of the other two treatment groups.

[0068] 5. Removal efficiency of total nitrogen from marine aquaculture tailwater by different salt-tolerant plants in constructed wetlands

[0069] The removal efficiency of total nitrogen from marine aquaculture tail water by different salt-tolerant plants in artificial wetlands is shown in Figure 2. Figure 7 As can be seen from the figure, the processing trends of total nitrogen by different plant devices are similar, with a significant upward trend before 7.5, and then a relatively stable period to 9.24. This is consistent with the treatment of inorganic nitrogen (TAN, NO2 - -N and NO3 - The treatment trends for TN (N) were somewhat different. The inorganic nitrogen plateau appeared after July 15, suggesting that the constructed wetland may have a stronger ability to remove organic nitrogen. Furthermore, there was no significant difference in TN removal rates among the three different devices before July 15. Afterward, the TN removal efficiency of the CW-P1 group decreased, reaching 48.82% at 9.4°C. However, the TN removal efficiencies of CW-P2 and CW-P3 both remained above 50%, reaching 56.44% and 52.93%, respectively, at 9.4°C, significantly higher than those of the CW-P1 treatment group.

[0070] 6. Removal efficiency of total phosphorus in marine aquaculture tail water by different salt-tolerant plants in artificial wetlands

[0071] The removal efficiency of total phosphorus in marine aquaculture tail water by different salt-tolerant plants in artificial wetlands is shown in Figure 2. Figure 8. As can be seen from the figure, after 7.15, the TP removal efficiency of different treatment groups gradually stabilized. The TP removal rate of CW-P1 was maintained between 63% and 67%, the TP removal rate of CW-P2 was maintained between 66% and 75%, and the TP removal rate of CW-P3 was maintained between 70% and 77%. The results show that the removal rate of TP by the sea asparagus device is at a relatively high level, followed by the seahorse tooth treatment group, while the salsa device has a lower TP treatment efficiency than the other two groups. The experimental results also show that at 9.4, the TP removal rate of different treatment groups showed a certain downward trend, which may be due to the slowdown of plant growth in the later period and the limited absorption capacity.

[0072] 7. Analysis of microbial community diversity in artificial wetlands with different salt-tolerant plants

[0073] Constructed wetlands are composed of substrates, plants, and microorganisms. The substrate can provide a carrier for the growth of microorganisms, and the roots of artificial wetland plants can produce secretions to promote the enrichment of root microorganisms. Microorganisms are extremely active components in artificial wetland purification. The biomass and activity of microorganisms directly affect the treatment effect of microorganisms on organic pollutants. Generally speaking, nitrification-denitrification is the main way to achieve denitrification. The nitrification process is mainly completed by nitrifying bacteria to convert ammonia nitrogen into nitrate nitrogen. The denitrification process uses denitrifying bacteria with the participation of electron donors to achieve denitrification.

[0074] (1) Richness and diversity of microbial populations

[0075] Table 1 shows the diversity indicators of the microbial communities on the experimental quartz sand and volcanic rock surfaces. As can be seen from the table, the sequencing coverage was above 99%, indicating that the sequencing depth was reasonable and generally representative of the sample. The Shannon index primarily reflects the number of species and individuals in the community, as well as their uniformity. A higher Shannon value indicates greater community diversity. The Chao1 index and ACE index primarily reflect community richness; higher values ​​indicate greater community richness.

[0076] Table 1 Alpha Indices statistics

[0077] As shown in Table 1, under the same experimental conditions, the Shannon Index, ACE Index, and Chao1 Index of microorganisms on the quartz sand and volcanic rock surfaces in the Hippocampus and Asparagus salsa devices were significantly higher than those in the Suaeda salsa device. This may be because Hippocampus and Asparagus salsa have more developed root systems, which increase plant enzyme activity and enhance nutrient absorption and utilization, thereby increasing the richness and diversity of the community in the device. This further confirms that the CW-P2 and CW-P3 devices are the most effective in purifying water.

[0078] Table 1 also shows that the Chao1 Index, ACE Index, and Shannon Index of microorganisms on the surfaces of different fillers exhibit different trends. Among the microorganisms on the quartz sand surface, the Shannon Index, ACE Index, and Chao1 Index of the seahorse tooth device were all higher than those on the sea bamboo shoot device, while the opposite trend was observed for the microorganisms on the volcanic rock surface. Furthermore, the results show that the Chao1 Index, ACE Index, and Shannon Index of microorganisms on the volcanic rock surface were significantly higher than those on the quartz sand surface within the same device. Therefore, volcanic rock exhibits a stronger microbial biofilm formation capacity under the same conditions. This may be due to the high porosity and permeability of volcanic rock, which provides a living space for microbial attachment and is more conducive to plant rooting. This enhances the synergistic effect between the filler, plants, and microorganisms, promoting the enrichment of microorganisms on the filler surface and enriching biodiversity.

[0079] (2) Microbial community analysis

[0080] The diversity and community composition of filler microorganisms are closely related to the water purification effect. The colony structure distribution diagram of different filler samples in each device is as follows: Figure 9 、 Figure 10 The top ten OTU sequences with the highest relative abundance in each sample were classified at the phylum level. The results showed that the total number of sequences from the Proteobacteria, Bacteroidota, Actinobacteriota, and Chloroflexi phyla accounted for more than 80% of the total sequences in the surface microorganisms of different devices and different fillers. These microorganisms are dominant bacteria and provide good biodegradation conditions for the effective operation of artificial wetland devices.

[0081] Results revealed significant differences in the community composition of microorganisms attached to filler surfaces, with some genera representing the same phyla but varying proportions. In the microbial composition of both the quartz sand and volcanic rock surfaces, Proteobacteria were significantly higher in the CW-P3 sea asparagus treatment (57.41%) and the other two treatments, respectively, followed by the CW-P2 seahorse tooth treatment (44.68%) and the CW-P1 Suaeda salsa treatment (40.87%). Bacteroidetes, on the other hand, showed an opposite trend, with the CW-P3 sea asparagus treatment having the lowest proportions (20.18%) and 21.08%, respectively. Among the microbial communities on the quartz sand surface, Actinobacteria and Chloroflexi were significantly higher in the Suaeda salsa treatment than in the other two treatments. Among the microbial communities on the volcanic rock surface, Chloroflexi were still the highest in the Suaeda salsa treatment (2.87%), while Actinobacteria were the highest in the sea asparagus treatment (5.25%).

[0082] in conclusion

[0083] This experiment used a small-scale artificial wetland device for outdoor experiments to study the treatment effects of different plants on seawater aquaculture tailwater after the implantation of carbon sources. Analysis of effluent quality and microbial sequencing results showed that the device operated well and had significant treatment effects. The following conclusions were drawn: (1) Under the inlet conditions of this experiment, when the hydraulic retention time is 20~30h, the purification requirements of aquaculture tail water quality can be met, and the removal rates of TAN, TN and TP are 68.17%, 78.04% and 78.57% respectively.

[0084] (2) Under the influent conditions of this experiment, the artificial wetlands with different plants showed different effects on the removal of various water quality indicators. Among them, the removal effects of the sea asparagus and seahorse teeth devices were better than those of the salsa suaeda device group. The removal rates of TAN, TN and TP in the sea asparagus artificial wetland were the highest at 82.61%, 58.80% and 77.02%, respectively, while the removal rates of TAN, TN and TP in the seahorse teeth artificial wetland were the highest at 80.73%, 56.61% and 74.56%, respectively.

[0085] (3) Under the inlet conditions of this experiment, through the analysis of the number, activity and functional diversity of microorganisms in the device, it can be seen that when using sea asparagus and seahorse teeth to treat seawater aquaculture tail water, the treatment effect of artificial wetlands can be enhanced, the synergistic decontamination ability of plants and microorganisms can be improved, and technical support can be provided for the remediation of factory-scale seawater aquaculture tail water.

[0086] Test Example 2: Pilot test of a module for artificial wetland purification of seawater and industrial aquaculture tailwater

[0087] 1. Pilot plant layout and results

[0088] The pilot test of the artificial wetland to purify seawater factory aquaculture tailwater module was carried out from April 2022 to October 2022 at the Yellow River Delta Marine Fisheries Research and Extension Center, with a pilot area of ​​36 m 3 The artificial wetland was constructed by filling pebbles (particle size 1-2 cm) 10 cm, volcanic rocks (3-6 mm) 50 cm, and quartz sand (particle size 2-4 mm) 10 cm in layers from bottom to top. The plants selected were sea asparagus and seahorse teeth, with a density of 30 plants / m 2The carbon source was a 1:1 ratio of Phragmites australis, corncob, and biochar at a ratio of 4:2:1, at a rate of 20 g / L. The carbon source replacement cycle was 75 days, and the hydraulic retention time was 25 hours. During the pilot test, the influent was industrial aquaculture effluent treated by curved sieve filtration. Basic water quality indicators during the experiment included: temperature 22.5-25.5°C, salinity 25-26, pH 7.5-8.5, and dissolved oxygen >7 mg / L. In addition, influent total ammonia nitrogen was 2.30-2.75 mg / L, influent nitrite nitrogen was 0.33-0.43 mg / L, influent nitrate nitrogen was 1.10-1.19 mg / L, influent total nitrogen was 7.32-7.63 mg / L, and influent total phosphorus was 1.08-1.29 mg / L. After the device stabilized, samples were collected in May, June, July, August, and September to analyze water quality changes before and after inflow. Details are shown in Table 2.

[0089] The monthly changes in water treatment efficiency during the pilot period are shown in Figure 11 The results during the pilot test showed that after the system was stabilized, the removal efficiency of each water quality index maintained a good level, including TAN, NO2 - -N, NO3 - The removal rates of -N, TN, and TP were maintained between 85-92%, 78-86%, 72-80%, 60-66%, and 64-74%, respectively. Results showed that the concentrations of total nitrogen and total phosphorus in the treated tailwater were 2.884 and 0.073 mg / L, 2.593 and 0.069 mg / L, 2.573 and 0.052 mg / L, 2.668 and 0.069 mg / L, and 2.904 and 0.057 mg / L in May, June, July, August, and September, respectively. These concentrations all met the first-level standard for marine aquaculture tailwater discharge (DB374676-2023) and also met the water quality requirements for marine aquaculture.

[0090] Table 2 Changes in water quality indicators during the pilot test (mg / L)

[0091] Pilot test conclusion

[0092] Under the conditions of this pilot test, the constructed wetland construction model is as follows: filling material (distributed by depth: pebbles 15%, volcanic rocks 70%, quartz sand 15%), plants (sea asparagus: seahorse teeth = 1:1, density: 30 plants / m 2 ), slow-release carbon source (Arundo donax, corn cob and biochar 4:2:1, implantation amount 20 g / L, replacement cycle 75d), hydraulic retention time 25h, all indicators of aquaculture tail water achieved better treatment effect, and the treatment efficiency can reach 720 L / (m 3 ·d).

[0093] As can be seen from the above embodiments, the present invention provides an artificial wetland for aquaculture tailwater treatment and a method for realizing the recycling of factory-scale aquaculture seawater using the artificial wetland. The artificial wetland includes fillers, salt-tolerant plants, and a slow-release carbon source; the fillers are, from bottom to top, a pebble layer, a volcanic rock layer, and a quartz sand layer; the salt-tolerant plants are sea asparagus and seahorse teeth; and the slow-release carbon sources are reed bamboo, corn cobs, and biochar. The present invention realizes the recycling of factory-scale aquaculture seawater by constructing an eco-efficient artificial wetland. The artificial wetland constructed by the present invention can improve the utilization efficiency of seawater, reduce the discharge of tailwater, and protect the marine ecological environment.

[0094] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An artificial wetland for aquaculture tail water treatment, characterized in that: The artificial wetland comprises fillers, salt-tolerant plants and a slow-release carbon source; The fillers are, from bottom to top, a pebble layer, a volcanic rock layer and a quartz sand layer; The salt-tolerant plants are sea asparagus and seahorse teeth; The slow-release carbon sources are reed bamboo, corn cob and biochar.

2. The artificial wetland according to claim 1, characterized in that The thickness of the pebble layer is 10-20% of the total thickness of the filler; the thickness of the volcanic rock layer is 60-80% of the total thickness of the filler; and the thickness of the quartz sand layer is 10-20% of the total thickness of the filler.

3. The artificial wetland according to claim 1, characterized in that The density of the salt-tolerant plants is 20 to 30 plants / m 2 .

4. The artificial wetland according to claim 1, characterized in that The ratio of the sea asparagus to the seahorse teeth is 1:1~2.

5. The artificial wetland according to claim 1, characterized in that The filler is provided with a columnar filling area, which is composed of a filling tube with holes at the bottom and sides and a slow-release carbon source; the mass ratio of reed bamboo, corn cob and biochar in the slow-release carbon source is 4:(2-3):(1-2), the addition ratio of the slow-release carbon source in the filler is 20-30 g / L, and the replacement cycle of the slow-release carbon source is 60-90 days.

6. Use of the artificial wetland according to any one of claims 1 to 5 in the recycling of seawater in industrial aquaculture.

7. A method for realizing the recycling of seawater in industrial aquaculture using the artificial wetland according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: adjusting the water quality of the influent, injecting the water into the artificial wetland according to any one of claims 1 to 5, detecting the water quality after the water stays for 20 to 30 hours, and discharging the water after it meets the standards.

8. The method according to claim 7, characterized in that The water quality of the influent is: pH 7.2~8.7, total ammonia nitrogen 2.32~2.88 mg / L, nitrite nitrogen 0.36~0.50 mg / L, nitrate nitrogen 1.02~1.25 mg / L, total nitrogen 7.22~7.86 mg / L, and total phosphorus 1.12~1.31 mg / L.

9. The method according to claim 7, characterized in that The water quality standards before discharge are: pH 7.5~8.3, total ammonia nitrogen 0.19~0.35 mg / L, nitrite nitrogen 0.05~0.10 mg / L, nitrate nitrogen 0.20~0.31 mg / L, total nitrogen 2.05~2.59 mg / L, and total phosphorus 0.31~0.40 mg / L.

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