A secondary countercurrent adsorption process for phosphorus-containing wastewater and its separation device

Abstract

The present invention relates to the technical field of wastewater treatment and resource recovery, and in particular to a secondary countercurrent adsorption process and a separation device thereof for removing or recovering phosphorus in wastewater using magnetic biochar. The secondary countercurrent adsorption process comprises applying the magnetic biochar to phosphorus-containing wastewater twice in succession in each treatment cycle, and recovering the magnetic biochar applied in the second adsorption process and applying it to the first adsorption process of the next cycle. The secondary countercurrent adsorption process provided by the present invention can make full use of the magnetic biochar, and can realize the recovery and reuse of phosphorus in phosphorus-containing wastewater, effectively alleviating the dilemma of the shortage of phosphorus resources.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment and resource recovery, and in particular to a secondary countercurrent adsorption process and a separation device thereof for removing or recovering phosphorus in wastewater by using magnetic biochar. Background Art

[0002] Phosphorus is one of the essential elements for plant growth, and phosphate fertilizer is an important guarantee for the normal supply of global food. As the raw material for the production of phosphate fertilizer, phosphate rock is a non-renewable resource. It is estimated that by the middle of this century, global phosphate rock will be exhausted, and global food production will be seriously threatened. On the other hand, only a part of the phosphate fertilizer used in large quantities in agricultural production is absorbed by plants, and the remaining large amount of phosphorus elements flow into the water body with surface runoff, resulting in an increase in the phosphorus concentration in the water. When the phosphorus concentration in the water body is greater than 0.02 mg P / L, eutrophication of the water body may occur. Eutrophication of water bodies can cause algal blooms, red tides, etc., posing a serious threat to the balance of the ecosystem, the aquaculture industry, etc. Therefore, the shortage of phosphorus resources and phosphorus pollution in water bodies are currently urgent problems that need to be solved.

[0003] In recent years, the rise of biochar has provided an option for solving the above-mentioned resource and environmental problems. Biochar is a carbonized product of waste biomass. Waste biomass, such as straw, branches, fungus residue, municipal sludge, etc., can be applied to the soil after carbonization, which can not only improve the soil, but also fix the carbon in the waste biomass in the soil, which has the environmental benefits of carbon fixation and emission reduction. At the same time, biochar can also be used in the field of sewage treatment, especially for adsorbing phosphorus in wastewater. For example, invention patents with application numbers CN201610279556.8, CN201910410211.5 and CN202010703363.7 all disclose methods for preparing biochar or modified biochar that can adsorb phosphorus in water. If biochar is first used to adsorb phosphorus in wastewater, and then biochar enriched with phosphorus in wastewater (called phosphorus-rich biochar) is applied to the soil, it can not only improve the soil, but also provide phosphorus for plants, so that the dual purposes of controlling phosphorus pollution in water and recovering phosphorus resources in wastewater can be achieved at the same time. However, the current use of biochar to remove / recover phosphorus from wastewater has problems such as low biochar adsorption capacity utilization, poor phosphorus adsorption capacity, and difficulty in separating and recovering it from wastewater after adsorption. These problems have seriously restricted the further application of biochar in controlling water phosphorus pollution and recovering wastewater phosphorus resources. Summary of the invention

[0004] In order to overcome the defects of the prior art mentioned above, the technical problem to be solved by the present invention is to provide a secondary countercurrent adsorption process which can effectively remove / collect phosphorus in phosphorus-containing wastewater, and a separation device applied to the process.

[0005] In order to solve the above technical problems, the present invention provides a secondary countercurrent adsorption process for phosphorus-containing wastewater, comprising applying magnetic biochar to the phosphorus-containing wastewater twice in succession in each treatment cycle, and recovering the magnetic biochar applied in the second adsorption process and applying it to the first adsorption process of the next cycle.

[0006] Further provided is a separation device for use in the aforementioned two-stage countercurrent adsorption process, comprising:

[0007] Raw water tanks, used to store wastewater containing phosphorus;

[0008] A storage tank for storing a suspension of magnetic biochar;

[0009] A reactor, connected to the raw water tank and the storage tank through pipelines respectively;

[0010] The magnetic structure is arranged at the bottom of the reactor and is used for separating the magnetic biochar and the sludge.

[0011] The beneficial effect of the present invention is that by using magnetic biochar to enrich phosphorus in phosphorus-containing wastewater, the phosphorus content in the phosphorus-containing wastewater can be effectively reduced, and the phosphorus-enriched magnetic biochar can be easily recovered. In addition, since the magnetic biochar used in the present invention has an adsorption capacity of at least twice adsorbing phosphorus, the magnetic biochar that has only undergone one adsorption process is reapplied to the adsorption process of the next cycle, that is, secondary countercurrent adsorption is achieved, so that the magnetic biochar is fully utilized, thereby improving the removal / recovery rate of phosphorus in phosphorus-containing wastewater by the magnetic biochar. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Shown is a flow chart of cycle 0 in a specific implementation manner of the present invention;

[0013] Figure 2 Shown is a flow chart of the 1st to nth cycles in a specific implementation manner of the present invention;

[0014] Figure 3 Shown is a schematic structural diagram of a separation device in a specific embodiment of the present invention;

[0015] Figure 4 Shown are comparative photos of seed germination and growth in the control group and the treatment group in the experimental example of the present invention.

[0016] Explanation of reference numerals: 1. Raw water tank; 2. Water inlet valve; 3. Water inlet pump; 4. Reactor; 5. First stirring structure; 6. Electromagnetic coil; 7. Magnetic structure; 8. Liquid level meter; 9. Dosing pump; 10. Storage tank; 11. Drain valve; 12. Water outlet pump; 13. Flow meter; 14. Mud discharge valve; 15. Mud discharge pump; 16. PLC system. DETAILED DESCRIPTION

[0017] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in conjunction with the implementation modes and the accompanying drawings.

[0018] A secondary countercurrent adsorption process for phosphorus-containing wastewater comprises applying magnetic biochar to the phosphorus-containing wastewater twice in succession in each treatment cycle, and recovering the magnetic biochar applied in the second adsorption process and applying it to the first adsorption process of the next cycle.

[0019] Among them, the magnetic biochar is a carbonized antibiotic slag containing calcium and / or iron. Specifically, the preparation method of the magnetic biochar is to first heat the dried calcium / iron-rich antibiotic slag to 600°C at a heating rate of 10°C / min under oxygen-limited conditions for pyrolysis and carbonization for 2h, then grind it into powder, wash it with deionized water and disperse it in deionized water. Preferably, the concentration of the magnetic biochar suspension is 30-50g / L. The oxygen-limited condition is carried out under the condition of isolating air or oxygen, or in a nitrogen or carbon dioxide atmosphere. The calcium / iron-rich antibiotic slag is vancomycin fermentation slag, in which the content of calcium and iron is 7-20wt% and the moisture content is 20-50wt%. The magnetic biochar can be aggregated under the action of an external magnetic field to achieve the recovery of the magnetic biochar, and the external magnetic field is preferably generated by an electromagnet and / or a permanent magnet. In this article, the magnetic biochar is prepared as follows: Vancomycin residue (calcium and iron content are 7-20wt%, moisture content is 20-50wt%) is preheated and dried at 105°C for 6h, heated to 600°C at a heating rate of 10°C / min in a nitrogen atmosphere for 2h, and then ground into powder to obtain magnetic biochar with a particle size of less than 0.15mm. The magnetic properties, phosphorus adsorption capacity, antibiotic residue and other data of the magnetic biochar are all proved by the inventor's prior patent application CN11513833A, and are therefore incorporated herein by reference.

[0020] The existing phosphorus removal adsorption process using magnetic biochar usually adopts a primary adsorption, such as the inventor's previous patent application CN11513833A, that is, the magnetic biochar is directly added to the phosphorus-containing wastewater, and solid-liquid separation is performed after the adsorption is completed to complete the adsorption of phosphorus in the wastewater. However, the inventor found in practice that the magnetic biochar still has phosphorus adsorption capacity after a single use, that is, it is difficult to fully utilize the excellent phosphorus adsorption capacity of the magnetic biochar in a single adsorption process. Therefore, the inventor designed a secondary countercurrent adsorption, that is, the addition time of phosphorus-containing wastewater and fresh magnetic biochar is staggered, so that the phosphorus-containing wastewater is added with fresh magnetic biochar at a lower phosphorus concentration level after one adsorption, and the remaining phosphorus is adsorbed and recovered. Among them, the fresh magnetic biochar is unused, and the magnetic biochar used in the first adsorption process is used, that is, the magnetic biochar adsorbed with phosphorus comes from the fresh magnetic biochar used in the second adsorption process in the previous cycle, and they are collected and reused in the first adsorption process of the next cycle. The magnetic biochar used in the first adsorption process can be directly applied to the soil after two adsorption treatments and the remaining substances in the phosphorus-containing wastewater are deposited at the bottom to form sludge to increase the phosphorus content in the soil, thereby realizing the collection and reuse of phosphorus in the phosphorus-containing wastewater.

[0021] Specifically, the secondary countercurrent adsorption process for phosphorus-containing wastewater comprises the following steps:

[0022] S1, Cycle 0:

[0023] S11, adding the magnetic biochar into the phosphorus-containing wastewater twice in succession and stirring;

[0024] S12, collecting the magnetic biochar and discharging the supernatant of the phosphorus-containing wastewater, and separating to obtain phosphorus-containing magnetic biochar, sludge and phosphorus-removed wastewater;

[0025] S2, Cycle 1:

[0026] S21, adding the phosphorus-containing magnetic biochar obtained in S12 to the new phosphorus-containing wastewater, stirring and recovering, to obtain old magnetic biochar;

[0027] S22, adding fresh magnetic biochar into phosphorus-containing wastewater, stirring and recovering, to obtain phosphorus-containing magnetic biochar;

[0028] S23, removing the supernatant of the phosphorus-containing wastewater, and separating to obtain sludge and phosphorus-removed wastewater;

[0029] S3, second cycle:

[0030] S31, adding the phosphorus-containing magnetic biochar obtained in S22 to the new phosphorus-containing wastewater, stirring and recovering, to obtain old magnetic biochar;

[0031] S32, adding fresh magnetic biochar into phosphorus-containing wastewater, stirring and recovering, to obtain phosphorus-containing magnetic biochar;

[0032] S33, removing the supernatant of the phosphorus-containing wastewater, and separating to obtain sludge and phosphorus-removed wastewater.

[0033] Among them, see Figure 1 and Figure 2 As shown, the 0th cycle is the startup phase, which is only run once in the entire phosphorus removal process. Its purpose is to adsorb phosphorus in phosphorus-containing wastewater while providing phosphorus-containing magnetic biochar for the next cycle. In one embodiment, the sludge and phosphorus-containing magnetic biochar are not separated in S12, but are directly mixed with the phosphorus-containing wastewater put into the 1st cycle. The 1st cycle applies the phosphorus-containing magnetic biochar collected in the 0th cycle to its first adsorption process, i.e., S21, so that the remaining phosphorus adsorption capacity of the phosphorus-containing magnetic biochar is fully utilized, and when its complete or nearly complete phosphorus adsorption capacity is utilized, it is the old magnetic biochar (phosphorus-rich biochar), which is mixed with part of the sludge before S22 and collected, and directly applied to the soil as a phosphate fertilizer. The magnetic biochar used in its second adsorption process is collected after use and continues to be used in the first adsorption process (i.e., S31) in the second cycle to end the life cycle of the magnetic biochar in the secondary countercurrent adsorption process. Of course, the present invention is not limited to only two cycles, and the subsequent cycle repeats the second cycle until all phosphorus-containing wastewater is completely treated. Of course, the second cycle is optional, and is only used here to show the subsequent countercurrent mode of magnetic biochar, which can be removed or added according to actual needs.

[0034] Preferably, the concentration of the magnetic biochar in the phosphorus-containing wastewater is 1 to 3 g / L. The specific amount of the magnetic biochar added is mainly determined by the content of phosphorus in the phosphorus-containing wastewater. In an exemplary embodiment, when the phosphorus concentration in the phosphorus-containing wastewater is 2.15 mg / L, the concentration of the magnetic biochar in the phosphorus-containing wastewater is 3 g / L. The concentration of the magnetic biochar in the phosphorus-containing wastewater is applicable to each step in the specific method, such as S11, S21, S22, S31, and S32. Among them, since the magnetic biochar in the present invention is mainly added to the phosphorus-containing wastewater in the form of a suspension, and the sludge needs to be discharged during the first adsorption process of each cycle, that is, the volume of the phosphorus-containing wastewater is constantly changing, the concentration is used to limit the amount of magnetic biochar added to ensure that the phosphorus element and the magnetic biochar in the phosphorus-containing wastewater are always in a suitable ratio, thereby ensuring the efficient adsorption process.

[0035] Wherein, the stirring time is 1 to 3 hours, and the stirring rate is 120 to 300 rpm.

[0036] The supernatant accounts for 70-90% of the total volume of the phosphorus-containing wastewater. The proportion of the supernatant to the total volume of the phosphorus-containing wastewater is mainly related to the impurities (forming sludge) in the phosphorus-containing wastewater and the amount of magnetic biochar added.

[0037] See also Figure 3 As shown, a separation device applied to the aforementioned two-stage countercurrent adsorption process comprises:

[0038] Raw water tank 1, used to store phosphorus-containing wastewater;

[0039] A storage tank 10, used for storing a suspension of magnetic biochar;

[0040] The reactor 4 is connected to the raw water tank 1 and the storage tank 10 through pipelines respectively;

[0041] The magnetic structure 7 is arranged at the bottom of the reactor 4 and is used to separate the magnetic biochar and the sludge.

[0042] The reactor 4 is provided with a first stirring structure 5, and the storage tank 10 is provided with a second stirring structure. That is, the first stirring structure 5 and the second stirring structure are provided to stir the raw materials (phosphorus-containing wastewater and magnetic biochar) and the magnetic biochar suspension in the reactor 4. The first stirring structure 5 promotes the uniform dispersion of the magnetic biochar in the phosphorus-containing wastewater and its full contact with the phosphorus-containing wastewater by stirring. The second stirring structure promotes the uniform dispersion of the magnetic biochar in its continuous phase (deionized water) by stirring, thereby ensuring its addition amount.

[0043] The magnetic structure 7 is preferably an electromagnet and / or a permanent magnet.

[0044] The reactor 4 is provided with a low-level liquid gauge 8 and a high-level liquid gauge 8 for controlling the volume of the raw material in the reactor 4 .

[0045] In one embodiment, the raw water tank 1 is pumped into the reactor 4 through the water inlet pump 3, and the pipeline connecting the two is provided with a water inlet valve 2. Optionally, at least one group of electromagnetic coils 6 is provided on the container of the reactor 4 to promote the rapid sedimentation of the magnetic biochar. The container of the reactor 4 is provided with at least one drain port for removing the supernatant and at least one sewage outlet for removing the sludge, and the sewage outlet is provided at the bottom of the magnetic structure 7, and the space enclosed by the magnetic structure 7 is connected to the inner cavity of the reactor 4. Therefore, the magnetic structure 7 can be turned on or off to select whether to separate the magnetic biochar from the sludge during the sludge discharge process. The sewage outlet is connected to a sludge discharge valve 14 and a sludge discharge pump 15. Preferably, the magnetic structure 7 can generate an induced magnetic field strength of 3000 to 5000Gs. Among them, the drain port is connected to the outlet pump 12 through a pipeline, and a drain valve 11 is provided on the pipeline connected to the two, and a flow meter 13 is provided downstream of the outlet pump 12. The sewage outlet is connected to the sludge pump through a pipeline, and a sludge valve 14 is provided on the pipeline connected thereto. The storage tank 10 is connected to the reactor 4 through a dosing pump 9. Of course, in order to realize the automation of the separation device, it is preferred that the water inlet pump 3, the first stirring structure 5, the second stirring structure, the electromagnetic coil 6, the magnetic structure 7, the high level gauge 8, the low level gauge 8, the dosing pump 9, the sludge pump and the water outlet are all connected to the PLC system 16.

[0046] Example 1

[0047] A secondary countercurrent adsorption process for phosphorus-containing wastewater comprises the following steps:

[0048] S1. The aquaculture tail water (phosphorus-containing wastewater, from eel farms, with a phosphorus concentration of 2.15 mg / L) is pumped into the reactor through the water inlet pump, and the fresh magnetic biochar suspension is pumped into the reactor through the dosing pump. At this time, the concentration of magnetic biochar in the aquaculture tail water (including the original volume of aquaculture tail water and the volume of magnetic biochar suspension) is 3 g / L, and stirred at 300 rpm for 1.5 h;

[0049] S2. Continue to add fresh magnetic biochar to the aquaculture tail water at a ratio of 3 g / L and stir at 300 rpm for 1.5 h;

[0050] S3, turning on the magnetic structure to enrich the magnetic biochar at the bottom of the reactor, and separating the supernatant (accounting for 80% of the total volume of the wastewater), the remaining sludge and the magnetic biochar;

[0051] S4, pump new aquaculture tail water into the reactor, add the magnetic biochar separated in S3 into the reactor, and stir at 300 rpm for 1.5 h;

[0052] S5, turning on the magnetic structure to allow the magnetic biochar to accumulate at the bottom of the reactor, and discharging the sludge mixed with the magnetic biochar;

[0053] S6, add fresh magnetic biochar suspension at a ratio of 3 g / L and stir at 300 rpm for 1.5 h;

[0054] S7. Turn on the magnetic structure to enrich the magnetic biochar at the bottom of the reactor, and separate the supernatant (accounting for 80% of the total volume of the wastewater), the remaining sludge and the magnetic biochar (retained for continued use in the next cycle).

[0055] According to the test, the average phosphorus concentration in all the supernatants separated in this example is 0.427 mg / L, which meets the first-level standard limit (0.5 mg / L) of the "Freshwater Pond Aquaculture Water Discharge Requirements" (SC / T 9101-2007).

[0056] Example 2

[0057] A secondary countercurrent adsorption process for phosphorus-containing wastewater comprises the following steps:

[0058] S1. The aquaculture tail water (phosphorus-containing wastewater from eel farms, with a phosphorus concentration of 1.02 mg / L) is pumped into the reactor through the water inlet pump, and the fresh magnetic biochar suspension is pumped into the reactor through the dosing pump. At this time, the concentration of magnetic biochar in the aquaculture tail water (including the original volume of aquaculture tail water and the volume of magnetic biochar suspension) is 2 g / L, and stirred at 120 rpm for 2 hours;

[0059] S2. Continue to add fresh magnetic biochar to the aquaculture tail water at a ratio of 2 g / L and stir at 120 rpm for 2 h;

[0060] S3, turning on the magnetic structure to enrich the magnetic biochar at the bottom of the reactor, and separating the supernatant (accounting for 90% of the total volume of the wastewater), the remaining sludge and the magnetic biochar;

[0061] S4, pump new aquaculture tail water into the reactor, add the magnetic biochar separated in S3 into the reactor, and stir at 120 rpm for 2 h;

[0062] S5, turning on the magnetic structure to allow the magnetic biochar to accumulate at the bottom of the reactor, and discharging the sludge mixed with the magnetic biochar;

[0063] S6, add fresh magnetic biochar suspension at a ratio of 2 g / L and stir at 120 rpm for 2 h;

[0064] S7. Turn on the magnetic structure to enrich the magnetic biochar at the bottom of the reactor, and separate the supernatant (accounting for 90% of the total volume of the wastewater), the remaining sludge and the magnetic biochar (retained for use in the next cycle).

[0065] After testing, the average phosphorus concentration in all the supernatants separated in this example was 0.351 mg / L, which met the first-level standard limit (0.5 mg / L) of the "Freshwater Pond Aquaculture Water Discharge Requirements" (SC / T 9101-2007).

[0066] Comparative Example 1

[0067] An existing treatment process for phosphorus-containing wastewater, the specific steps are as follows:

[0068] S1. Add magnetic biochar to the aquaculture tail water (same as in Example 2) to a concentration of 2 g / L and stir at 120 rpm for 4 h;

[0069] S2. Turn on the magnetic structure to allow the magnetic biochar to accumulate at the bottom of the reactor and discharge the supernatant. The magnetic biochar is discharged together with the sludge.

[0070] After testing, the phosphorus concentration in the supernatant separated in this comparative example was 0.608 mg / L, which did not meet the primary standard limit (0.5 mg / L) of the "Freshwater Pond Aquaculture Water Discharge Requirements" (SC / T 9101-2007).

[0071] Example 3

[0072] The phosphorus-rich biochar discharged in step S5 of Example 1 was collected and dried for seed germination experiments. The specific experimental method is: put a layer of filter paper in the culture dish, and then evenly spread 0.3g of phosphorus-rich biochar on the filter paper (diameter 10cm), moisten it with ultrapure water, and sprinkle 10 quinoa seeds. The group added with phosphorus-rich biochar was recorded as the treatment group, and the group without phosphorus-rich biochar added (quinoa seeds were directly sprinkled on the filter paper moistened with ultrapure water) was recorded as the control group, where three parallel groups were set for the treatment group and the control group. Add an equal volume of ultrapure water daily and culture at room temperature (about 28°C). After 7 days, the growth condition of quinoa is as follows. Figure 4 As shown in Table 1, the germination rate, growth rate and stem length of quinoa were calculated, and the results were averaged and summarized in Table 1. Figure 3 It can be seen that the germination rate, growth rate and stem length of the treatment group were higher than those of the control group, indicating that the addition of phosphorus-rich biochar has a promoting effect on the growth of quinoa, and this promoting effect comes from the phosphorus element enriched in the phosphorus-rich biochar.

[0073] Table 1

[0074] Control group Treatment Group Germination rate (%) 80.00±0.00 96.67±5.77 Growth rate (%) 66.67±5.77 80.00±10.00 Stem length (cm) 1.78±0.48 2.81±0.54

[0075] It can be seen from Example 3 that the secondary countercurrent adsorption process for phosphorus-containing wastewater provided by the present invention and the separation device used therein can realize the recovery and reuse of phosphorus in wastewater, and can provide a new method and approach for alleviating the global shortage of phosphorus resources.

[0076] In summary, compared with the conventional adsorption process, the secondary countercurrent adsorption process provided by the present invention adjusts the time point of adding phosphorus-containing wastewater and magnetic biochar, so that the phosphorus-containing wastewater is treated twice by magnetic biochar, and the adsorption capacity of magnetic biochar is utilized twice. Therefore, the adsorption process and separation device provided by the present invention can improve the utilization rate of biochar adsorption capacity and improve the removal rate of phosphorus in wastewater. The sludge obtained by the adsorption process and separation device of the present invention is a phosphorus-rich biochar. Applying it to the soil can not only improve the soil, but also provide phosphorus for plant growth. Therefore, it can realize the recycling of phosphorus in wastewater, which is conducive to alleviating the global phosphorus resource tension. The adsorption process and separation device provided by the present invention are simple to operate and have a high degree of automation. They can be applied to the deep treatment of phosphorus-containing wastewater such as aquaculture tail water, anaerobic sludge fermentation liquid, and secondary effluent from sewage treatment plants. The design scale can be flexibly selected, and the application prospect is broad.

[0077] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A secondary countercurrent adsorption process for phosphorus-containing wastewater, characterized in that: A separation device is used, wherein the separation device has: Raw water tanks, used to store phosphorus-containing wastewater; A storage tank for storing a suspension of magnetic biochar; A reactor, connected to the raw water tank and the storage tank through pipelines respectively; A magnetic structure, disposed at the bottom of the reactor, for separating magnetic biochar and sludge; The secondary countercurrent adsorption process comprises the following steps: S1, Cycle 0: S11, adding the magnetic biochar into the phosphorus-containing wastewater twice in succession and stirring; S12, collecting the magnetic biochar and discharging the supernatant of the phosphorus-containing wastewater, and separating to obtain phosphorus-containing magnetic biochar, sludge and phosphorus-removed wastewater; S2, Cycle 1: S21, adding the phosphorus-containing magnetic biochar obtained in S12 to the new phosphorus-containing wastewater, stirring and recovering, to obtain old magnetic biochar; S22, adding fresh magnetic biochar into phosphorus-containing wastewater, stirring and recovering, to obtain phosphorus-containing magnetic biochar; S23, removing the supernatant of the phosphorus-containing wastewater, and separating to obtain sludge and phosphorus-removed wastewater; S3, second cycle: S31, adding the phosphorus-containing magnetic biochar obtained in S22 to the new phosphorus-containing wastewater, stirring and recovering, to obtain old magnetic biochar; S32, adding fresh magnetic biochar into phosphorus-containing wastewater, stirring and recovering, to obtain phosphorus-containing magnetic biochar; S33, removing the supernatant of the phosphorus-containing wastewater, and separating to obtain sludge and phosphorus-removed wastewater; The magnetic biochar is carbonized antibiotic bacterial residue containing calcium and / or iron.

2. The two-stage countercurrent adsorption process according to claim 1, characterized in that: The concentration of the magnetic biochar in phosphorus-containing wastewater is 1-3 g / L.

3. The two-stage countercurrent adsorption process according to claim 1, characterized in that: The stirring time is 1-3 hours, and the stirring speed is 120-300 rpm.

4. The two-stage countercurrent adsorption process according to claim 1, characterized in that: The supernatant accounts for 70-90% of the total volume of the phosphorus-containing wastewater.

5. The two-stage countercurrent adsorption process according to claim 1, characterized in that: A first stirring structure is arranged in the reactor.

6. The two-stage countercurrent adsorption process according to claim 1, characterized in that: A second stirring structure is arranged in the storage tank.

7. The two-stage countercurrent adsorption process according to claim 1, characterized in that: A low-level liquid gauge and a high-level liquid gauge are arranged in the reactor.

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