Efficient nitrogen and phosphorus removal device and method for mariculture tail water

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to an efficient nitrogen and phosphorus removal device and method for mariculture tail water. The device comprises a microbial electrolysis cell, and the microbial electrolysis cell comprises a cathode region and an anode region which are communicated in sequence; a cathode metal net is arranged in the cathode region, the cathode metal net is embedded in a cathode region filler, the cathode region filler comprises elemental sulfur particles, enriched sulfur reducing bacteria and sulfur oxidizing bacteria, and the addition amount of the sulfur reducing bacteria and the sulfur oxidizing bacteria is 10%-20% of the effective volume of a cavity of the cathode region; an anode metal net is arranged in the anode area, and secondary modified biochar is wrapped in the anode metal net; the cathode metal net and the anode metal net are respectively connected with the cathode and the anode of the solar panel. The device disclosed by the invention has relatively high sulfide and phosphorus adsorption capacity and a good treatment effect. The invention further provides an efficient nitrogen and phosphorus removal method for the mariculture tail water.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and specifically relates to a device and method for efficiently removing nitrogen and phosphorus from seawater aquaculture tail water. Background Art

[0002] By the end of 2023, all coastal provinces in my country have promulgated marine aquaculture effluent discharge standards. Taking Shandong Province as an example, its first-level standard requires a total nitrogen emission concentration limit of 3.0 mg / L and a total phosphorus emission concentration limit of 0.5 mg / L. The second-level standard requires a total nitrogen emission concentration limit of 5.0 mg / L and a total phosphorus emission concentration limit of 1.0 mg / L. Nitrogen and phosphorus concentrations are important factors that limit the discharge of marine aquaculture effluents to meet the standards.

[0003] Marine aquaculture tailwater has the characteristics of high salinity, high ion concentration, low C / N, and the nitrogen concentration in the tailwater fluctuates with the feeding time, which limits the efficiency of biological denitrification and phosphorus removal. Biological denitrification has the characteristics of low cost and high efficiency. It is the main denitrification method for marine aquaculture tailwater, but carbon sources need to be added to improve the denitrification efficiency of tailwater. Traditional carbon sources such as sodium acetate, glucose, methanol, etc. can effectively improve the denitrification efficiency, but the fluctuation of nitrogen concentration in tailwater will lead to insufficient denitrification efficiency or cause secondary pollution. For example, the sulfate concentration in marine aquaculture tailwater is high, which is easy to generate toxic sulfides. Using solid degradable polymers as carbon sources can improve the denitrification efficiency of aquaculture tailwater, but the cost is relatively high. For example, one ton of polycaprolactone can reach tens of thousands of yuan. Using elemental sulfur particles as solid electron donors, the aquaculture tailwater denitrification process is achieved through the sulfur autotrophic denitrification process, which can realize the ready-to-use electrons. It has been widely used for denitrification of low C / N wastewater. However, when used for denitrification of marine aquaculture tailwater, the low solubility of elemental sulfur particles leads to slow growth of elemental sulfur biofilm, and the high dissolved oxygen concentration in the aquaculture tailwater leads to low elemental sulfur utilization rate, which limits the application of sulfur autotrophic denitrification in marine aquaculture tailwater. In addition, the sulfur autotrophic denitrification process has almost no removal effect on total phosphorus, which further limits the application of sulfur autotrophic denitrification technology in marine aquaculture tailwater. Therefore, in the process of treating marine aquaculture tailwater with sulfur autotrophic denitrification technology, there are problems such as low elemental sulfur utilization rate and poor denitrification and phosphorus removal effects caused by the low solubility of elemental sulfur particles and high dissolved oxygen in the tailwater. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a highly efficient denitrification and dephosphorization device for marine aquaculture tail water, which has high sulfide and phosphorus adsorption capacity and good treatment effect. The present invention also provides a highly efficient denitrification and dephosphorization method for marine aquaculture tail water.

[0005] The high-efficiency denitrification and dephosphorization device for marine aquaculture tail water of the present invention comprises a microbial electrolysis cell, wherein the microbial electrolysis cell comprises a cathode region and an anode region connected in sequence;

[0006] A cathode metal mesh is provided in the cathode area, and the cathode metal mesh is embedded in the cathode area filler. The cathode area filler includes sulfur particles, enriched sulfur-reducing bacteria and sulfur-oxidizing bacteria, and the amount of sulfur-reducing bacteria and sulfur-oxidizing bacteria added is 10%-20% of the effective volume of the cathode area cavity; an anode metal mesh is provided in the anode area, and the anode metal mesh is wrapped with secondary modified biochar; the cathode metal mesh and the anode metal mesh are respectively connected to the negative electrode and the positive electrode of the solar panel.

[0007] Preferably, the cathode region and the anode region are arranged side by side, and the tops of the two are connected.

[0008] Preferably, the cathode metal mesh and the anode metal mesh are both titanium metal meshes, and a plurality of cathode metal meshes are arranged in parallel.

[0009] Preferably, the preparation method of the secondary modified biochar is: soaking agricultural waste in an alkaline solution for alkaline modification, then thermally cracking to obtain biochar, soaking the biochar in a metal ion solution, and drying to obtain the secondary modified biochar.

[0010] Preferably, the agricultural waste is one or both of corn cobs and corn stalks.

[0011] Preferably, the alkaline solution is a 0.1-0.2 mol / L NaOH solution, and the immersion time in the alkaline solution is 1-2 h.

[0012] Preferably, the thermal cracking temperature is 600-700°C.

[0013] Preferably, the metal ion solution is a FeCl3 solution or an AlCl3 solution with a concentration of 0.1-0.2 mol / L.

[0014] Preferably, the bottom of the cathode region is connected to the water inlet distribution area, and the bottom of the anode region is connected to the water outlet aeration area.

[0015] Preferably, the water inlet distribution area is arranged at the lower part of the cathode area, and is an inverted cone structure, which is filled with large-particle fillers, and the water inlet distribution area and the cathode area are separated by a porous partition. The large-particle fillers are preferably pebbles, which are used to evenly disperse the seawater aquaculture tail water in the device and improve the treatment efficiency; the outlet aeration area is provided with a microporous aeration device at the water inlet, which is used to further remove the by-products such as sulfide and ammonia nitrogen that may appear in the tail water after passing through the denitrification and phosphorus removal functional area, and minimize the by-products of seawater aquaculture tail water treatment. The microporous aeration device is preferably an aeration disk.

[0016] The method for efficiently removing nitrogen and phosphorus from seawater aquaculture tail water of the present invention is to process the seawater aquaculture tail water through the above-mentioned device, and sequentially through the cathode area and the anode area.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The solar panel is equipped with a storage battery, which acts as a DC power source and saves electricity costs;

[0019] 2. The solar panel stably transports electrons to the cathode area through an external circuit. A portion of the electrons are used by the enriched sulfur-reducing bacteria to convert sulfur into sulfides / polysulfides with strong biological affinity, which are then used by sulfur-oxidizing bacteria to promote nitrogen removal and shorten the startup time of the device.

[0020] 3. The anode area is filled with secondary modified biochar. Alkali modification will destroy the smooth structure of the surface of agricultural waste and increase its pore structure and specific surface area. The specific surface area and the content of metal oxide functional groups of metal ion modified biochar are improved, which improves the adsorption capacity of biochar for phosphorus and sulfide. The secondary modification increases the surface micropores, mesopore ratio and functional group content of biochar, effectively adsorbing phosphate in wastewater and sulfide / polysulfide produced in the cathode area, reducing secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of a highly efficient denitrification and dephosphorization device for marine aquaculture tail water according to the present invention;

[0022] Figure 2 It is a schematic diagram of the side view structure of the highly efficient denitrification and dephosphorization device for seawater aquaculture tail water of the present invention;

[0023] Figure 3 It is a schematic diagram of the top view of the structure of the highly efficient denitrification and dephosphorization device for seawater aquaculture tail water of the present invention;

[0024] In the figure, 1. cathode area; 2. anode area; 3. titanium metal mesh; 4. water outlet; 5. solar panel; 6. water inlet and water distribution area; 7. water outlet aeration area; 8. sulfur particles; 9. secondary modified biochar; 10. aeration plate; 11. air pump. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments.

[0026] Unless otherwise specified, all raw materials used in the examples are commercially available.

[0027] Example 1

[0028] The high-efficiency denitrification and dephosphorization device for marine aquaculture tail water of the present invention comprises, in order of flow direction, an inlet water distribution area 6, a microbial electrolysis cell and an outlet aeration area 7, wherein the microbial electrolysis cell comprises a cathode area 1 and an anode area 2;

[0029] The water inlet distribution area 6 is arranged at the bottom of the cathode area 1, and the water inlet distribution area 6 and the cathode area 1 are separated by a porous partition. The water inlet distribution area 6 is an inverted cone structure, and is filled with pebbles. A water inlet pipe is arranged at the bottom of the water inlet distribution area 6. The cathode area 1 and the anode area 2 are arranged side by side, and the tops of the two are connected. The bottom of the anode area 2 is connected to the water outlet aeration area 7, and the top of the water outlet aeration area 7 is provided with a water outlet 4. The water outlet aeration area 7 is provided with a microporous aeration disk 10 at the water inlet, and the microporous aeration disk 10 is connected to an air pump 11;

[0030] Three titanium metal meshes 3 arranged in parallel are provided in the cathode area 1, and the titanium metal meshes 3 are embedded in the cathode area filler, and the cathode area filler includes sulfur elemental particles 8, enriched sulfur-reducing bacteria and sulfur-oxidizing bacteria; a titanium metal mesh 3 is provided in the anode area 2, and secondary modified biochar 9 is wrapped in the titanium metal mesh 3; the titanium metal meshes 3 in the cathode area 1 and the anode area 2 are respectively connected to the negative electrode and the positive electrode of the solar panel 5.

[0031] The preparation method of the secondary modified biochar 9 is as follows: the agricultural waste is soaked in an alkaline solution for alkaline modification, and then thermally cracked to obtain biochar, and the biochar is soaked in a metal ion solution and dried to obtain the secondary modified biochar 9.

[0032] Agricultural waste is corn cobs and corn stover.

[0033] The alkaline solution is 0.1 mol / L NaOH solution, and the immersion time of the alkaline solution is 1 hour.

[0034] The thermal cracking temperature is 650℃.

[0035] The metal ion solution is FeCl3 solution with a concentration of 0.1 mol / L.

[0036] The above device is used to treat the tail water of aquaculture in a certain aquaculture farm. The tail water enters the water distribution area 6 through the water inlet pump. The hydraulic retention time is 6-48h, the water temperature is 18℃, the dissolved oxygen concentration in the cathode area 1 is 0.01mg / L, the dissolved oxygen concentration in the anode area 2 is 0.03mg / L, the dissolved oxygen concentration in the aeration area is 3.0mg / L, and the pH value of the whole equipment is 7.2. The nitrate content of the influent is 30mg / L, the ammonia nitrogen content is 3mg / L, the phosphate content is 6.0mg / L, and the COD content is 15mg / L. The denitrification and phosphorus removal of the denitrification and phosphorus removal device with continuous water inflow is shown in Table 1.

[0037] Table 1 Continuous water inflow nitrogen and phosphorus removal test table

[0038]

[0039] A titanium metal mesh is provided in the cathode region 1, which is embedded in the sulfur particles 8. The sulfur-reducing bacteria use the electrons provided by the cathode to reduce the sulfur to S which is more easily used by the sulfur-oxidizing bacteria.2- or S n 2- , achieving sulfur conversion. Sulfur oxidizing bacteria use S 2- or S n 2- , converting nitrate into nitrogen gas to achieve denitrification. In the anode area 2, the secondary modified biochar 9 has high sulfide and phosphate adsorption characteristics. When the influent nitrate concentration is 30 mg / L and the phosphate concentration is 6 mg / L, the hydraulic retention time is 6-48h, the effluent concentration of nitrate drops to 0.3-5.2 mg / L, and the effluent concentration of phosphate drops to 0 mg / L.

Claims

1. A highly efficient denitrification and dephosphorization device for marine aquaculture tail water, characterized in that: The microbial electrolysis cell comprises a cathode region (1) and an anode region (2) which are connected in sequence; A cathode metal mesh is provided in the cathode region (1), and the cathode metal mesh is embedded in a cathode region filler, and the cathode region filler includes sulfur elemental particles (8), enriched sulfur-reducing bacteria and sulfur-oxidizing bacteria, and the amount of sulfur-reducing bacteria and sulfur-oxidizing bacteria added is 10%-20% of the effective volume of the cathode region cavity; an anode metal mesh is provided in the anode region (2), and secondary modified biochar (9) is wrapped in the anode metal mesh; the cathode metal mesh and the anode metal mesh are connected to the negative electrode and the positive electrode of the solar panel (5) respectively.

2. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 1, characterized in that: The cathode metal mesh and the anode metal mesh are both titanium metal meshes (3), and a plurality of cathode metal meshes are arranged in parallel.

3. The high-efficiency denitrification and dephosphorization device for seawater aquaculture tail water according to claim 1, characterized in that: The preparation method of the secondary modified biochar (9) is as follows: agricultural waste is soaked in an alkaline solution for alkaline modification, then thermally cracked to obtain biochar, and the biochar is soaked in a metal ion solution and dried to obtain the secondary modified biochar (9).

4. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 3, characterized in that: The agricultural waste is one or both of corn cobs and corn stover.

5. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 3, characterized in that: The alkaline solution is a 0.1-0.2 mol / L NaOH solution, and the soaking time of the alkaline solution is 1-2 hours.

6. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 3, characterized in that: The thermal cracking temperature is 600-700℃.

7. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 3, characterized in that: The metal ion solution is FeCl3 solution or AlCl3 solution with a concentration of 0.1-0.2 mol / L.

8. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 1, characterized in that: The bottom of the cathode region (1) is connected to the water inlet distribution region (6), and the bottom of the anode region (2) is connected to the water outlet aeration region (7).

9. The highly efficient denitrification and dephosphorization device for seawater aquaculture tail water according to claim 8, characterized in that: The water inlet distribution area (6) is arranged at the lower part of the cathode area (1) and is an inverted cone structure filled with large-diameter fillers. A microporous aeration device is arranged at the water inlet of the water outlet aeration area (7).

10. A method for efficient nitrogen and phosphorus removal from marine aquaculture tail water, characterized in that: The seawater aquaculture tail water is processed by the device according to any one of claims 1 to 9, passing through the cathode area and the anode area in sequence.

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