Salt-tolerant plant constructed wetland system for treating eutrophic mariculture wastewater

Abstract

The invention provides a salt-tolerant plant constructed wetland system for treating eutrophicated mariculture wastewater, which specifically comprises a lower filler formed by mineral materials, and a middle filler formed by modified zeolite, sodium alginate coated vermiculite, rice husk charcoal, oyster shell, coral sand and diatomite, the surface filler is composed of intertidal zone bottom mud, intertidal zone raw water, coastal saline-alkali soil and composite algae powder, and the three fillers are combined with salt-tolerant plant breeding, bow-shaped water flow optimization and layered collaborative design; the core problems of poor salt tolerance, low adsorption efficiency, easiness in blockage, high maintenance cost and the like of the traditional constructed wetland during treatment of the mariculture wastewater are systematically solved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly to a salt-tolerant plant constructed wetland system for treating eutrophic seawater aquaculture wastewater. Background Art

[0002] A constructed wetland is a ground similar to a marshland that is artificially built and controlled. Sewage and sludge are controllably distributed onto the artificially built wetland. During the process of flowing in a certain direction, the sewage and sludge are mainly treated by the triple synergistic effects of soil, artificial media, plants, and microorganisms. Traditional constructed wetland systems have the following defects:

[0003] (1) Most existing constructed wetland systems use freshwater wetland plants, which have insufficient salt tolerance and poor adaptability to high-salt environments. When the salinity > 15 ppt, their growth is significantly restricted, resulting in plant withering or a decline in metabolic capacity, affecting the nitrogen and phosphorus absorption efficiency. (2) Traditional fillers (such as ordinary sand and gravel) have limited adsorption capacity for dissolved nitrogen and phosphorus in eutrophic wastewater, and are prone to clogging due to organic matter accumulation after long-term operation, requiring frequent replacement. (3) Most existing constructed wetland systems use a linear water flow, with a short wastewater residence time, resulting in insufficient contact between pollutants and fillers and plants, and low total nitrogen and total phosphorus removal rates. (4) Existing constructed wetland systems require frequent maintenance due to filler clogging and plant death, with frequent replacement of fillers every year, and the cost of replanting salt-tolerant plants is high. (5) The filler layer structure of existing constructed wetland systems is single, and no stratified treatment is carried out for different pollutants (such as particulate matter and dissolved nutrient salts), resulting in insufficient synergistic effects of the system.

[0004] Therefore, it has become an urgent problem to provide a constructed wetland system that can treat high-salt aquaculture wastewater, has high pollutant treatment efficiency, and is not easily clogged. Summary of the Invention

[0005] In order to solve the above problems, the present invention provides a salt-tolerant plant constructed wetland system for treating eutrophic seawater aquaculture wastewater, and its construction method and wastewater treatment method are as follows:

[0006] Step 1: Mix and crush mineral materials, sieve them through a 50-60 mesh sieve, then soak them in an organic acid solution for 22-26 h with a solid-liquid mass ratio of 1:3. Filter, discard the filtrate, and calcine the filter residue at 200-300 °C for 1-1.5 h to obtain the lower-layer filler.

[0007] Preferably, the mineral materials include, but are not limited to, one or more of bentonite, kaolin, attapulgite, diatomite, zeolite, sepiolite, calcite, dolomite, apatite, gravel, vermiculite, quartz sand, sea sand, fine sand, and perlite. Most preferably, the mineral materials are sea sand, fine sand, quartz sand, gravel, and perlite, and the mass ratio is 10:7:8:5:4.

[0008] Preferably, the organic acid solution is one of a citric acid solution with a mass fraction of 8-10%, a lactic acid solution with a mass fraction of 10-12%, and an acetic acid solution with a volume fraction of 12-15%.

[0009] Step 2: Mix and soak zeolite and seawater at a mass ratio of 1:3, adjust the pH to 9.3-9.8 with an alkali solution, oscillate at 80-100 °C and 150-200 rpm for 5-6 h, take out the zeolite and calcine it at 500-600 °C for 2-3 h to obtain modified zeolite.

[0010] Mix vermiculite and sodium alginate solution at a mass ratio of 1:4, and introduce carbon dioxide with a flow rate of 0.5-0.6 L / min for 30-40 min to obtain sodium alginate-coated vermiculite.

[0011] Mix, crush, and sieve through a 70-80 mesh the modified zeolite, sodium alginate-coated vermiculite, rice husk charcoal, oyster shell, coral sand, and diatomite to obtain the middle layer filler.

[0012] Preferably, the salinity of the seawater is 25-30 ppt.

[0013] Preferably, the alkali solution is a 0.5-1 mol / L sodium hydroxide solution or a 0.5-1 mol / L potassium hydroxide solution.

[0014] Preferably, the mass fraction of the sodium alginate solution is 3-5%.

[0015] Preferably, the mass ratio of the modified zeolite, sodium alginate-coated vermiculite, rice husk charcoal, oyster shell, coral sand, and diatomite is 7:5:4:2:5:50.

[0016] Step 3: Mix the intertidal zone bottom mud and in-situ coastal saline-alkali soil evenly, spray the original intertidal zone water until the water content reaches 60-65%, sprinkle the composite algal powder on the surface, cover with a light-shielding film, and statically cultivate for 7-8 days to obtain the surface layer filler.

[0017] Preferably, the mass ratio of the intertidal zone bottom mud, in-situ coastal saline-alkali soil, and composite algal powder is 7:3:1.

[0018] Preferably, the composite algal powder includes chlorella, spirulina powder and sargassum powder, and the mass ratio is 2:1:1. Most preferably, the chlorella, spirulina powder and sargassum powder can be directly purchased from the market.

[0019] Step 4: Lay a lower layer of packing material with a thickness of 20 - 30 cm, a middle layer of packing material with a thickness of 40 - 50 cm, and a surface layer of packing material with a thickness of 10 - 15 cm from bottom to top inside the pool body. An outlet unit and an inlet unit are arranged on the pool body. In the water flow direction, they are the inlet unit, the packing material, and the outlet unit in sequence. There are several baffles on the inner wall of the pool body to make the water flow in a bow shape from the inlet unit to the outlet unit.

[0020] Step 5: Transplant suaeda salsa, sesuvium portulacastrum and limonium sinense into the packing material. The transplanting density of suaeda salsa is 9 - 10 plants / m 2 , the transplanting density of sesuvium portulacastrum is 5 - 6 plants / m 2 , and the transplanting density of limonium sinense is 4 - 5 plants / m 2 ;

[0021] Step 6: When treating wastewater, perform wet-dry alternation daily. Taking the packing material height as 100% water level, the water level rises to 95 - 100% within 6 - 7 h during the water inlet period, and the water level drops to 0 - 5% within 5 - 6 h during the drainage period.

[0022] The present invention has the following advantages:

[0023] (1) The present invention selects highly salt-tolerant suaeda salsa, sesuvium portulacastrum and limonium sinense, and combines with the composite algal powder in the surface layer of the packing material to form a "plant - microorganism - algae" three-level treatment system, solving the problems of insufficient salt tolerance of traditional plants and limited removal rates of TN and TP.

[0024] (2) The lower layer of the packing material of the present invention is modified by organic acid, and the specific surface area is significantly increased, significantly improving the adsorption efficiency. The sodium alginate-coated vermiculite in the middle layer of the packing material can improve the adsorption efficiency of ammonia nitrogen through ion exchange, overcoming the problem of low adsorption efficiency of traditional packing materials, and the system is not easily blocked and can operate for a long time.

[0025] (3) Through the baffle design, the present invention makes the water flow in a bow shape, significantly prolonging the wastewater residence time and significantly improving the removal rate of organic pollutants, solving the problem that the straight-line design of the constructed wetland leads to insufficient contact between pollutants and the packing material and plants.

[0026] (4) The lower layer of the packing material of the present invention intercepts particulate matter, the middle layer of the packing material adsorbs dissolved nitrogen and phosphorus, and the surface layer degrades organic matter, forming gradient purification and solving the problem of single function of traditional single-layer packing materials.

[0027] (5) During the treatment of wastewater, the daily wet-dry alternation of the present invention promotes oxygen exchange, reduces the formation of anaerobic areas, significantly reduces the packing blockage rate, and reduces the maintenance cost. Description of the Drawings

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0029] Figure 1 It is the overall view of the pool body.

[0030] Figure 2 It is the sectional view of this wetland system. Specific embodiments

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] Embodiment 1

[0033] Combined with the attached Figure 1-2 , this embodiment constructs a salt-tolerant plant artificial wetland system for treating eutrophic seawater aquaculture wastewater according to the following method;

[0034] Step 1: Mix sea sand, fine sand, quartz sand, gravel and perlite in a mass ratio of 10:7:8:5:4, crush them, pass through a 60-mesh sieve, then soak them in a 10% citric acid solution by mass for 24 h, with a solid-liquid mass ratio of 1:3, filter, remove the filtrate, and calcine the filter residue at 300 °C for 1 h to obtain the lower layer filler.

[0035] Step 2: Mix zeolite and seawater with a salinity of 30 ppt in a mass ratio of 1:3 and soak them, and adjust the pH to 9.5 with a 0.5 mol / L sodium hydroxide solution, oscillate at 90 °C and 180 rpm for 5 h, take out the zeolite and calcine it at 550 °C for 2.5 h to obtain modified zeolite; mix vermiculite and a 5% sodium alginate solution by mass in a ratio of 1:4, and introduce carbon dioxide with a flow rate of 0.5 L / min for 30 min to obtain sodium alginate-coated vermiculite; mix the modified zeolite, sodium alginate-coated vermiculite, rice husk charcoal, oyster shell, coral sand and diatomite in a mass ratio of 7:5:4:2:5:50, crush them, and pass through a 70-80 mesh sieve to obtain the middle layer filler.

[0036] Step 3: Mix the intertidal zone sediment and in-situ coastal saline-alkali soil evenly, spray the original water from the intertidal zone until the water content reaches 60%, sprinkle the composite algal powder on the surface, cover it with a light-shielding film and let it stand for cultivation for 7 days to obtain the surface filler. The mass ratio of the intertidal zone sediment, in-situ coastal saline-alkali soil and composite algal powder is 7:3:1. The composite algal powder includes Chlorella, Spirulina powder and Sargassum powder, and the mass ratio is 2:1:1.

[0037] Step 4: Lay a lower filler 4 with a thickness of 25 cm, a middle filler 3 with a thickness of 50 cm, and a surface filler 2 with a thickness of 12 cm in the pool body 1 from bottom to top in sequence. An outlet pipe 103 and an inlet pipe 102 are arranged on the pool body 1. In the water flow direction, they are the inlet pipe 102, the filler and the outlet pipe 103 in sequence. A number of baffles 101 are arranged on the inner wall of the pool body 1 to make the water flow in a bow shape from the inlet pipe 102 to the outlet pipe 103.

[0038] Step 5: Transplant Suaeda glauca, Sesuvium portulacastrum and Limonium sinense into the filler. The transplanting density of Suaeda glauca is 10 plants / m 2 , the transplanting density of Sesuvium portulacastrum is 5 plants / m 2 , and the transplanting density of Limonium sinense is 5 plants / m 2 .

[0039] Step 6: When treating wastewater, perform wet-dry alternation daily. Taking the filler height as 100% water level, the water level rises to 95 - 100% within 6 - 7 h during the water inlet period, and the water level drops to 0 - 5% within 5 - 6 h during the water drainage period.

[0040] Test Example 1

[0041] Use the constructed artificial wetland system in Example 1 to treat seawater aquaculture wastewater: salinity 25 - 30 ppt, total nitrogen (TN) 45 - 50 mg / L, total phosphorus (TP) 8 - 10 mg / L, and COD 120 - 150 mg / L.

[0042] Collect water samples after the end of the daily drainage period. Detect total nitrogen (TN) by potassium persulfate digestion-ultraviolet spectrophotometry (GB 11894-89), detect total phosphorus (TP) by ammonium molybdate spectrophotometry (GB 11893-89), detect COD by potassium dichromate method (HJ 828-2017). Record the daily influent and effluent concentrations continuously for 30 days and calculate the removal rate.

[0043] Removal rate = (1 - effluent concentration / influent concentration) × 100%.

[0044] Run continuously for 12 months, measure the hydraulic conductivity (K value) of the middle packing once a month. If the decrease is >10%, it is regarded as a clogging risk. Take samples quarterly to analyze the change in the porosity of the packing, count the plant coverage rate and root development once a month, record the number of dead plants, and detect the removal rates of TN, TP, and COD once a quarter, and compare with the initial data.

[0045] Table 1 Pollutant removal effect in 30 days (average value)

[0046] Inlet concentration (mg / L) Outlet concentration (mg / L) Removal rate (%) TN 48.2 5.6 88.4 TP 9.1 0.8 91.2 COD 135.5 22.3 83.5

[0047] Table 2 Long-term operation stability (12 months)

[0048] Number of times of packing blockage 0 times Plant survival rate 95％ TN removal rate attenuation 3.2％ TP removal rate attenuation 3.0％ COD removal rate attenuation 2.9％

[0049] As can be seen from Tables 1-2, the average removal rates of TN, TP, and COD by the constructed constructed wetland system of the present invention are as high as 88.4%, 91.2%, and 83.5% respectively within 30 days. The wet-dry alternating operation and the layered packing structure enable the system to run continuously for 12 months without clogging. The attenuation of the removal rates of TN, TP, and COD only decreases by 2.9-3.2% and the system performance is stable. The plant survival rate is >90%, verifying the synergistic effect of salt-tolerant plants and the packing.

[0050] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater, characterized in that, It includes a pond body, a lower layer of filler, a middle layer of filler, a surface layer of filler and salt-tolerant plants; The lower layer of filler, the middle layer of filler and the surface layer of filler are sequentially laid from bottom to top inside the pond body. An outlet unit and an inlet unit are arranged on the pond body. In the water flow direction, they are the inlet unit, the filler and the outlet unit in sequence. A number of baffles are provided on the inner wall of the pond body to make the water flow in a bow shape from the inlet unit to the outlet unit. Suaeda glauca, Sesuvium portulacastrum and Limonium sinense are transplanted into the filler; The lower layer of filler is a modified mineral material. The middle layer of filler includes modified zeolite, sodium alginate-coated vermiculite, rice husk charcoal, oyster shell, coral sand and diatomite. The surface layer of filler includes intertidal zone bottom mud, intertidal zone raw water, coastal saline-alkali soil and composite algal powder.

2. The salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater according to claim 1, characterized in that, The preparation method of the said modified mineral material is to mix and crush the mineral material, sieve it, then soak it in an organic acid solution for 22 - 26 h, filter it, remove the filtrate, and calcine the filter residue at 200 - 300 °C for 1 - 1.5 h to obtain the modified mineral material.

3. A salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater according to claim 2, characterized in that, The said mineral materials are sea sand, fine sand, quartz sand, gravel and perlite, and the mass ratio is 10:7:8:5:

4.

4. A salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater according to claim 2, characterized in that, The said organic acid solution is one of a citric acid solution with a mass fraction of 8 - 10%, a lactic acid solution with a mass fraction of 10 - 12% and an acetic acid solution with a volume fraction of 12 - 15%.

5. A salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater according to claim 1, wherein, The preparation method of the said middle layer of filler is to mix and soak zeolite with seawater, adjust the pH with an alkali solution, shake it, take out the zeolite and calcine it to obtain modified zeolite; mix vermiculite with a sodium alginate solution and introduce carbon dioxide to obtain sodium alginate-coated vermiculite; Mix and crush the modified zeolite, sodium alginate-coated vermiculite, rice husk charcoal, oyster shell, coral sand and diatomite to obtain the middle layer of filler.

6. The salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater according to claim 5, wherein The mass ratio of the said modified zeolite, sodium alginate-coated vermiculite, rice husk charcoal, oyster shell, coral sand and diatomite is 7:5:4:2:5:

50.

7. The salt-tolerant plant constructed wetland system for treating eutrophicated seawater aquaculture wastewater according to claim 1, wherein The preparation method of the said surface layer of filler is to mix the intertidal zone bottom mud and the coastal saline-alkali soil evenly, spray the intertidal zone raw water until the water content reaches 60 - 65%, sprinkle the composite algal powder on the surface, cover it with a light-shielding film and let it stand for cultivation to obtain the surface layer of filler.

8. A salt-tolerant plant constructed wetland system for treating eutrophic seawater aquaculture wastewater according to claim 7, characterized in that, The mass ratio of the said intertidal zone bottom mud, in-situ coastal saline-alkali soil and composite algal powder is 7:3:

1.

9. A salt-tolerant plant constructed wetland system for treating eutrophic seawater aquaculture wastewater according to claim 7, characterized in that, The said composite algal powder includes chlorella, spirulina powder and sargassum powder, and the mass ratio is 2:1:

1.

10. The method for treating eutrophicated seawater aquaculture wastewater by the constructed wetland system according to any one of claims 1-9, characterized in that, When treating wastewater, dry-wet alternation is carried out daily. Taking the filler height as 100% water level, the water level rises to 95 - 100% within 6 - 7 h during the water inlet period, and the water level drops to 0 - 5% within 5 - 6 h during the water drainage period.

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