Treatment and resource utilization method of rural breeding sewage

Abstract

The invention discloses a treatment and resource utilization method of rural cultivation sewage. According to the method, nitrogen and phosphorus nutrient substances can be obtained through resource recovery on the basis of remarkably reducing the chemical oxygen demand value, the total nitrogen value and the phosphorus phosphate value of the sewage. According to the invention, pollutant components and relative content of actual rural cultivation sewage are fully considered, and organic substances in the sewage are degraded in the anode region through the microbial electrochemical action; phosphate radicals and part of ammonium ions in sewage are deposited on a cellulose membrane in a struvite crystal form in a supersaturated state by utilizing a magnesium ion modified nano cellulose membrane, redundant NH4 < + > is directionally migrated to a cathode region under the action of an electric field and is converted into NH3, and the NH3 is absorbed by an acid solution to form a nitrogen fertilizer. The method realizes resource utilization of nitrogen and phosphorus nutrient elements while efficiently removing pollutants in the rural cultivation sewage, and provides a scientific, economic and efficient method for actual treatment of the rural cultivation sewage.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rural sewage treatment, and particularly relates to a method for treating and recycling rural breeding sewage. BACKGROUND

[0002] The progress of modern breeding technology has led to the intensive development of rural breeding farms, which has resulted in the high concentration of water resource utilization and breeding sewage discharge. The sewage generated by pig farms, chicken farms and other breeding farms contains a large amount of nutrients represented by nitrogen and phosphorus. If such sewage is directly discharged into the environment, it will cause serious eutrophication pollution of water bodies, and even may pose a threat to human health. Therefore, it is of great necessity, foresight and strategic value to research and develop scientific and efficient rural breeding sewage treatment technology.

[0003] At present, the common treatment methods for nitrogen and phosphorus pollutants in sewage include biological method and chemical method, but these conventional methods have certain defects. For example, biological nitrogen removal generally adopts a two-stage process of nitrification-denitrification, and the cost required for nitrification aeration process alone accounts for more than half of the wastewater treatment cost; when the nitrogen and phosphorus concentrations in the sewage are high, substances represented by ammonia may have toxic effects on microorganisms, thereby causing the biological treatment system to fail. The chemical method requires the addition of specific chemical reagents, and the high cost of reagents limits the large-scale promotion of this method in actual treatment; in addition, due to the complexity of rural breeding sewage, it is difficult to accurately dose the chemical reagents in actual treatment, and if the reagent dosage is not properly controlled in the chemical treatment process, it may cause secondary water pollution.

[0004] It should be particularly noted that nitrogen, phosphorus and other elements are the main pollution components in rural breeding sewage, and they are also essential nutrients for biological growth, playing a crucial role in the biological growth process. As we all know, there is a large amount of nitrogen in the air, and a small part of it can be reduced to ammonia by nitrogen-fixing bacteria in nature, which can then be absorbed by organisms. However, the ammonia generated by the biological nitrogen fixation process is far from enough to meet the needs of biological growth. In industry, Haber-Bosch process can be used to reduce molecular nitrogen to ammonia with hydrogen. However, this process needs to be carried out under harsh conditions of high temperature and high pressure, and the energy consumption in this process accounts for 1% of the global energy consumption, and the carbon dioxide emissions account for 1.4% of the global carbon dioxide emissions. On the other hand, phosphorus is a typical sedimentary element, which originates from rock weathering and ends in water deposition. In the biosphere, most of the phosphorus can only flow in one direction and cannot be recycled. Therefore, phosphate is a non-renewable resource, and at the current rate of exploitation, China's phosphorus resources will be exhausted in seventy years. SUMMARY

[0005] The present application aims at the problem of difficulty in treating rural breeding wastewater and high cost of treatment and the current situation of a large amount of nitrogen and phosphorus in the wastewater, and provides a novel method for treating rural breeding wastewater, which can significantly reduce the chemical oxygen demand (COD) value, total nitrogen (TN) value and phosphorus (PO4 3- -P) value and recycle nitrogen and phosphorus nutrients.

[0006] In the first aspect, the present application provides a method for treating and recycling rural breeding wastewater, which uses a treatment device including a reaction tank, an anode, a magnesium ion modified nanocellulose membrane and a cathode. The anode, the cathode and the magnesium ion modified nanocellulose membrane are all arranged in the reaction tank. The distance between the anode and the magnesium ion modified nanocellulose membrane is 1-6 cm. The anode uses polypyrrole-nanocellulose loaded with active bacteria. An ammonia gas outlet is arranged on the reaction tank.

[0007] The method for treating rural breeding wastewater comprises the following steps:

[0008] Step 1: introducing the treated rural breeding wastewater into the reaction tank.

[0009] Step 2: applying a voltage between the anode and the cathode. The organic matter in the treated rural breeding wastewater is oxidized and degraded at the anode. The phosphate and ammonium ions in the treated rural breeding wastewater react to form crystals at the magnesium ion modified nanocellulose membrane; the remaining ammonium ions are directionally diffused to the cathode and react to form ammonia gas.

[0010] Preferably, the treatment device further comprises an acid absorption module. The acid absorption module is connected to the ammonia gas outlet on the reaction tank through a pipeline. The acid absorption module stores an acidic solution for absorbing ammonia gas to form ammonium salt. The acidic solution is nitric acid or sulfuric acid solution, and the concentration is 3 mol / L.

[0011] Preferably, the struvite crystals attached to the magnesium ion modified nanocellulose membrane are collected after a preset time.

[0012] Preferably, when the speed of generating struvite crystals on the magnesium ion modified nanocellulose membrane is lower than a preset value, the magnesium ion modified nanocellulose membrane is immersed in sodium hydroxide solution and magnesium chloride solution in sequence for regeneration. The regenerated magnesium ion modified nanocellulose membrane is reinstalled in the reaction tank for use.

[0013] Preferably, the cathode uses a platinum metal sheet.

[0014] Preferably, the magnesium ion modified nanocellulose membrane is located between the anode and the cathode.

[0015] As preferred, the polypyrrole-nanocellulose is prepared by the following process: mixing pyrrole into nanocellulose culture medium, obtaining pyrrole-containing nanocellulose film after biological culture; adding potassium persulfate to make pyrrole on the nanocellulose polymerize into polypyrrole to obtain polypyrrole-nanocellulose. The mass fraction of polypyrrole in the polypyrrole-nanocellulose is 15wt%.

[0016] As preferred, the process of loading active bacteria on the polypyrrole-nanocellulose is as follows: taking rural aquaculture wastewater, adding anaerobic sludge, immersing the polypyrrole-nanocellulose into the rural aquaculture wastewater to load the active bacteria on the polypyrrole-nanocellulose. The rural aquaculture wastewater is additionally added every 1d. After 7d-14d, the polypyrrole-nanocellulose loaded with active bacteria is obtained.

[0017] As preferred, in step two, the voltage is 0-0.5V, the reaction temperature is 10℃-40℃, and the reaction time is 1d-10d.

[0018] As preferred, the preparation method of the magnesium ion modified nanocellulose film is as follows:

[0019] (1) The nanocellulose film is immersed into a high iodate solution, a hydroxyapatite catalyst is added, and the reaction is carried out at 20℃-80℃ for 1h-8h.

[0020] (2) The solid product obtained in step (1) is immersed into a glycine solution, sodium thiosulfate is added, and the reaction is carried out at 20℃-80℃ for 1h-6h.

[0021] (3) The solid product obtained in step (2) is sequentially immersed into a sodium hydroxide solution and a magnesium chloride solution to obtain the magnesium ion modified nanocellulose film.

[0022] As preferred, in step (1), the high iodate solution is a potassium iodate or sodium iodate solution with a concentration of 0.05mol / L-0.5mol / L; the addition amount of the nanocellulose film is 0.1g / L-1g / L; and the addition amount of the hydroxyapatite catalyst is 0.02g / L-0.2g / L.

[0023] As preferred, in step (2), the concentration of the glycine solution is 0.1mol / L-1mol / L; and the addition amount of the sodium thiosulfate is 0.2g / L-2g / L.

[0024] As preferred, in step (3), the concentration of the sodium hydroxide solution is 0.1-0.5 mol / L, the reaction temperature is 25°C, and the reaction time is 0.5-4 h; the concentration of the magnesium chloride solution is 0.2-2 mol / L, the reaction temperature is 25°C, and the reaction time is 1-6 h.

[0025] As preferred, the size of the anode and the cathode is both 2 cm x 2 cm.

[0026] As preferred, the initial water quality indexes of the rural aquaculture wastewater are as follows: COD value 800-3500 mg / L, total nitrogen value (TN) 1100-4600 mg / L, ammonia nitrogen value (NH4 + -N) 920-3950 mg / L, and phosphoric acid phosphorus value (PO4 3- -P) 60-300 mg / L.

[0027] In a second aspect, the application provides a use of the magnesium ion modified nanocellulose membrane in treating wastewater containing both ammonium ions and phosphate ions.

[0028] Compared with the prior art, the application has the following beneficial effects:

[0029] 1. The application fully considers the pollutant components and relative contents of the actual rural aquaculture wastewater, degrades the organic matter in the wastewater by the anodic oxidation through the microbial electrochemical action, and makes the phosphate and part of the ammonium ions in the wastewater deposit on the membrane in the form of struvite (Mg(NH4)PO4·6H2O) crystallization under the supersaturation state through the magnesium ion modified nanocellulose membrane, so that the excess NH4 + is migrated to the cathode under the action of the electric field and converted into NH3, and then the nitrogen fertilizer is formed through the absorption of the acid solution. The application realizes the resource utilization of the nitrogen and phosphorus nutrients while efficiently removing the pollutants in the rural aquaculture wastewater, and provides a scientific, economical and efficient method for treating the actual rural aquaculture wastewater.

[0030] 2. The application sets the magnesium ion modified nanocellulose membrane between the anode and the cathode of the electrochemical reaction; the phosphate (PO4 3- ) and part of the ammonium (NH4 + ) ions generated in the anode of the electrochemical reaction pass through the magnesium ion modified nanocellulose membrane; a large amount of magnesium ions loaded on the modified nanocellulose membrane make the magnesium ions, PO4 3- and NH4 + around the magnesium ion modified nanocellulose membrane be in a local supersaturation state, so that PO4 3- and NH4 + are combined with Mg2+ The reaction forms struvite crystals and deposits on the membrane; only the magnesium ion modified nanocellulose membrane needs to be replaced after the reaction, so that rapid recovery of phosphorus and part of nitrogen can be realized. Compared with the method of adding magnesium salt to produce precipitation in sewage, the struvite crystals can be collected without centrifugation, filtration and other treatments, and the obtained struvite has higher purity; at the same time, the problem of secondary water pollution caused by the difficulty in controlling the amount of magnesium salt is fundamentally solved.

[0031] 3、The magnesium ion modified nanocellulose membrane used in the application can be regenerated by being immersed in sodium hydroxide solution and magnesium chloride solution in sequence for reaction after long-term use and consumption of magnesium ions.

[0032] 4、The polypyrrole-nanocellulose is selected as the carrier of active bacteria in the application; and the polypyrrole-nanocellulose loaded with active bacteria is used as the anode of electrochemical reaction, compared with commercialized carbon materials such as carbon felt, nanocellulose can effectively increase the loading amount of active bacteria and the contact probability of organic matter and active bacteria, thereby improving the treatment efficiency of sewage. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a structure schematic view of the treatment device used in embodiment 1 of the application.

[0034] Figure 2 It is a comparison chart of COD value, TN, NH4 + -N value and PO4 3- -P value of the treated rural breeding wastewater in embodiment 1 of the application before and after treatment.

[0035] Figure 3 It is a comparison chart of COD value, TN, NH4 + -N and PO4 3- -P removal rate of embodiment 1 and comparative example 1 of the application.

[0036] Figure 4 It is a comparison chart of effluent COD value and time required for reaching discharge standard of embodiment 1 and comparative example 2 of the application.

[0037] Figure 5 It is a comparison chart of effluent PO4 3- -P value of embodiment 1 and comparative example 3 and comparative example 4 of the application.

[0038] Figure 6 It is a comparison chart of COD value, TN, NH4 + -N and PO4 3- -P removal rate of embodiment 1 and comparative example 5 of the application.

[0039] Figure 7A comparison chart of the crystallization quality and purity of the crystalline obtained in Example 1 and Comparative Example 5 of the present application.

[0040] Figure 8 A chart of the cyclic removal effect of PO4 3- -P in sewage by the magnesium ion modified nanocellulose membrane used in Example 2 of the present application.

[0041] The reference numerals: 1, anode; 2, power supply; 3, magnesium ion modified nanocellulose membrane; 4, cathode; 5, acid absorption module. DETAILED DESCRIPTION

[0042] The technical solutions in the present application will be described clearly and completely in combination with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0043] Example 1

[0044] A method for treating rural aquaculture wastewater, which removes organic matter in rural aquaculture wastewater through microbial electrochemical action, removes phosphate and part of ammonium salt through a magnesium ion modified nanocellulose membrane, and converts excess nitrogen into nitrogen fertilizer through acid solution absorption, so as to achieve the purpose of deep treatment of wastewater and resource utilization of nitrogen and phosphorus.

[0045] As Figure 1 shown, a method for treating rural aquaculture wastewater, which uses a treatment device including a reaction tank, an anode 1, a power supply 2, a magnesium ion modified nanocellulose membrane 3, a cathode 4 and an acid absorption module 5. The anode 1, the cathode 4 and the magnesium ion modified nanocellulose membrane 3 are all arranged in the reaction tank. The magnesium ion modified nanocellulose membrane 3 is located between the anode 1 and the cathode 4. The distance between the anode 1 and the magnesium ion modified nanocellulose membrane is 3 cm.

[0046] The cathode 4 uses a 2cm×2cm metal platinum sheet. The anode 1 uses a 2cm×2cm polypyrrole-nanocellulose loaded with active bacteria. The powered cathode 4 and anode 1 are used to promote the degradation of organic matter in the treated rural aquaculture wastewater by the active bacteria. The magnesium ion modified nanocellulose membrane 3 is used to react with phosphate and ammonium ions in the rural aquaculture wastewater to generate struvite crystals, thereby reducing the total nitrogen and total phosphorus in the treated rural aquaculture wastewater and realizing the resource recovery of phosphorus and nitrogen.

[0047] The power supply 2 adopts a direct-current stabilized power supply. The anode 1 and the cathode 4 are respectively connected with the positive and negative poles of the power supply 2. A stripping device is arranged at the bottom of the area close to the cathode in the reaction tank, which is used to strip out the ammonium ions to form ammonia gas near the cathode. The part above the liquid surface in the cavity of the reaction tank is communicated with the acid absorption module 5 through a pipeline. The acid absorption module 5 stores an acidic absorption liquid. The acidic absorption liquid is specifically a nitric acid solution with a concentration of 3 mol / L. The ammonia gas generated in the reaction tank is output to the acid absorption module 5 and absorbed.

[0048] The specific steps of the rural breeding wastewater treatment method are as follows:

[0049] Step one, the treated rural breeding wastewater is introduced into the side close to the anode of the reaction tank. The treated rural breeding wastewater is the wastewater output from the primary sedimentation tank in the breeding farm, which contains organic pollutants, phosphate ions and ammonium ions. The phosphate ions and ammonium ions are mainly generated in the primary sedimentation tank.

[0050] Step two, the power supply 2 supplies power to the anode 1 and the cathode 4, the control voltage is 0.4V, and the reaction temperature is 25℃. During the reaction process, the organic matter in the treated rural breeding wastewater is degraded at the anode, the phosphate and part of the ammonium ions are deposited on the magnesium ion modified nanocellulose membrane in the form of struvite crystals, and the remaining ammonium ions are converted into ammonia at the cathode and then absorbed by the acidic absorption liquid to form ammonium salt which can be used as nitrogen fertilizer. In this process, not only the pollutants in the treated rural breeding wastewater can be removed, but also the nitrogen and phosphorus resources can be recycled.

[0051] Step three, after the reaction reaches the preset time, the magnesium ion modified nanocellulose membrane is replaced, and the struvite crystals are collected from the replaced magnesium ion modified nanocellulose membrane. The struvite crystals can be used as raw materials for the production of phosphorus fertilizer.

[0052] The preparation process of the active bacteria loaded polypyrrole-nanocellulose is as follows:

[0053] (1) Preparation of polypyrrole-nanocellulose: pyrrole is mixed into the nanocellulose culture medium, and after biological culture, nanocellulose film containing pyrrole is obtained; then potassium persulfate is added to polymerize the pyrrole on the nanocellulose into polypyrrole, and polypyrrole-nanocellulose is obtained. The mass fraction of polypyrrole in polypyrrole-nanocellulose is 15wt%.

[0054] (2) Preparation of polypyrrole-nanocellulose loaded with active bacteria: 200 mL of pig farm breeding wastewater from supernatant of primary sedimentation tank of a rural pig farm was taken, anaerobic sludge from a sewage treatment plant was added, and polypyrrole-nanocellulose was immersed in the pig farm breeding wastewater, so that active bacteria were loaded on the polypyrrole-nanocellulose. Fresh pig farm breeding wastewater was added every 1 day, and after 10 days, the polypyrrole-nanocellulose loaded with active bacteria was taken out. The active bacteria were formed by enrichment of bacterial flora in the anaerobic sludge in the pig farm breeding wastewater environment; the active bacteria can biologically decompose organic pollutants in the pig farm breeding wastewater, and an electric field environment helps to promote the reaction.

[0055] The preparation process of the magnesium ion modified nanocellulose film is as follows:

[0056] (1) A sodium periodate solution with a concentration of 0.4 mol / L was prepared, and the nanocellulose film was immersed therein, and a hydroxyapatite catalyst was added. The addition amount of nanocellulose to the sodium periodate solution was 0.5 g / L, and the reaction was carried out at 50°C for 4 h. After the reaction was completed, deionized water was used for cleaning. The addition amount of the hydroxyapatite catalyst was 0.1 g / L.

[0057] (2) The product obtained in step (1) was immersed in a glycine solution with a concentration of 0.6 mol / L, and 0.4 g / L of sodium thiosulfate was added. The reaction was carried out at 40°C for 4 h. After the reaction was completed, deionized water was used for cleaning.

[0058] (3) The product obtained in step (2) was first immersed in a sodium hydroxide solution with a concentration of 0.2 mol / L, and the reaction was carried out at 25°C for 1 h. Then it was immersed in a magnesium chloride solution with a concentration of 0.5 mol / L, and the reaction was carried out at 25°C for 2 h. After the reaction was completed, deionized water was used for cleaning, and the magnesium ion modified nanocellulose film was obtained. The relative content of magnesium ions in the obtained magnesium ion modified nanocellulose film was 1.3 mmol / g.

[0059] The typical structural formula of the obtained magnesium ion modified nanocellulose film is shown in the following formula 1.

[0060]

[0061] Wherein: is nanocellulose

[0062] Typical structural formula of the magnesium ion modified nanocellulose film of formula 1

[0063] In this embodiment, the treated rural breeding wastewater was pig farm wastewater from supernatant of primary sedimentation tank of a rural pig farm, and the volume of the treated rural breeding wastewater was 1000 mL. The initial water quality indexes of the treated rural breeding wastewater were as follows: COD value 1300 mg / L, total nitrogen value (TN) 1450 mg / L, ammonia nitrogen value (NH4 +-N) 1320 mg / L, phosphorus value (PO4 3- -P) value 120 mg / L.

[0064] As shown in Figure 2 Table 1, after 4d reaction, the COD value, TN, NH4 + -N value and PO4 3- -P value of the effluent of the treated rural aquaculture wastewater decreased to 18 mg / L (removal rate 98.6%), 7 mg / L (removal rate 99.5%), 4 mg / L (removal rate 99.7%) and 0.2 mg / L (removal rate 99.8%) respectively, all of which were lower than the first level A effluent discharge standard specified in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002). At the same time, 0.91 g of Mg(NH4)PO4·6H2O crystal was collected on the magnesium ion modified nanocellulose membrane, and 6.12 g of NH4NO3 fertilizer was obtained in the acid solution. The purity of Mg(NH4)PO4·6H2O was calculated by testing the nitrogen content in the crystal, combined with the following formula (1):

[0065]

[0066] wherein, is the purity of Mg(NH4)PO4·6H2O crystal; n N , M MAP and m CRY are the number of moles of nitrogen element in the crystal, the molecular weight of Mg(NH4)PO4·6H2O and the mass of the obtained crystal respectively.

[0067] Finally, it was calculated that the purity of the recovered Mg(NH4)PO4·6H2O crystal was 95.36%.

[0068] Comparative Example 1

[0069] A method for treating rural aquaculture wastewater, the specific process is: the treated rural aquaculture wastewater consistent with Example 1 is directly treated by a conventional anaerobic-aerobic two-stage biological process.

[0070] After 4d biological treatment, the COD value, TN, NH4 + -N value and PO4 3- -P value of the effluent were 78 mg / L, 288 mg / L, 195 mg / L and 56 mg / L respectively, and the removal rates were 94%, 80%, 85% and 53% respectively, which were significantly lower than the results obtained in Example 1, and far from reaching the standard for allowing direct discharge of effluent (see Figure 3 ).

[0071] The treatment time was extended to 7d, the COD value, TN, NH4+ -N and PO4 3- The P values were 26 mg / L, 262 mg / L, 160 mg / L and 49 mg / L, respectively. As can be seen from Comparative Example 1, the conventional anaerobic-aerobic two-stage biological process has a good effect on the removal of organic matter in the pig farm wastewater, but the removal of TN and PO4 3- The removal of P is not ideal, and even if the treatment time is prolonged, the treated pig farm wastewater cannot be directly discharged, and the high concentration of nitrogen in the rural breeding wastewater has a certain biological toxicity to microorganisms. In addition, the conventional anaerobic-aerobic two-stage biological process used in this comparative example fails to collect any nitrogen and phosphorus nutrients, and cannot realize the resource utilization of pig farm wastewater.

[0072] Comparative Example 2

[0073] A method for treating rural breeding wastewater, the difference between this comparative example and Example 1 is that the polypyrrole-nanocellulose loaded with active bacteria is replaced by commercialized carbon felt. The carbon felt loaded with active bacteria is used as the anode for treating pig farm wastewater, and other treatment processes and conditions are the same as those in Example 1.

[0074] After 4 days of reaction, the final effluent COD value was 104 mg / L.

[0075] The treatment time was extended to 8 days, and the effluent COD value decreased to 49 mg / L. Comparing the results of Comparative Example 2 with Example 1 (see Figure 4 ), it can be seen that when the polypyrrole-nanocellulose loaded with active bacteria is used as the anode, its treatment efficiency for organic matter in the wastewater is much higher than that of the commercialized carbon felt, and the time required for reaching the discharge standard (referring to the first level A effluent discharge standard specified in the "Urban Sewage Treatment Plant Pollutant Discharge Standard" (GB 18918-2002)) is much lower than that of the commercialized carbon felt under the same experimental conditions. This is because the nanocellulose has an ultra-high specific surface area and a specific three-dimensional network structure, which is more conducive to the loading of active bacteria and the contact between organic matter in the wastewater and active bacteria, thereby improving the treatment efficiency of the wastewater.

[0076] Comparative Example 3

[0077] A method for treating rural breeding wastewater, the difference between this comparative example and Example 1 is that the magnesium ion modified nanocellulose membrane is not set in the reaction tank, and other treatment processes and conditions are the same as those in Example 1. The final effluent PO4 3- The P value was 119 mg / L, and no crystals were collected during the process.

[0078] Comparative Example 4

[0079] A method for treating rural aquaculture wastewater, the difference between the present comparative example and example 1 is that the magnesium ion modified nanocellulose membrane is replaced by a nanocellulose membrane which is not modified by magnesium ions, and other treatment processes and conditions are the same as those in example 1. The final effluent PO4 3- The P value is 111 mg / L, and no crystals are collected during the process.

[0080] Comparing the results of comparative example 3 and comparative example 4 with example 1 (see Figure 5 ), it can be seen that the removal of phosphate in wastewater and the formation of Mg(NH4)PO4·6H2O crystals are achieved through magnesium ions on the modified nanocellulose membrane, and nanocellulose plays a role as a carrier.

[0081] Comparative example 5

[0082] A method for treating rural aquaculture wastewater, the difference between the present comparative example and example 1 is that no anode, cathode, and magnesium ion modified nanocellulose membrane are provided, and only magnesium salt is directly added in the reaction tank to remove PO4 3- and part of NH4 + in the wastewater.

[0083] In the present comparative example, 0.4 g of magnesium chloride is added (this amount is the amount of magnesium ions required to completely precipitate PO4 3- in the wastewater theoretically), and the stirring reaction is carried out for 12 h. The final effluent COD value, TN, NH4 + -N value, and PO4 3- -P value are 1258 mg / L, 1275 mg / L, 1140 mg / L, and 16 mg / L, respectively; 0.78 g of precipitate is collected by centrifugal separation, and it can be calculated from formula (1) that the purity of Mg(NH4)PO4·6H2O crystals in the obtained precipitate is 77.39%.

[0084] Comparing the results of comparative example 5 with example 1 (see Figure 6 and Figure 7 ), it can be seen that directly adding magnesium salt in the wastewater can achieve the purpose of removing most of PO4 3- and part of NH4 + , but the quality and purity of the precipitate obtained by this method are significantly lower than those obtained by collecting crystals with magnesium ion modified nanocellulose membrane in example 1. In addition, this method cannot effectively remove COD in the wastewater, and it is difficult to collect most of the nitrogen elements in the wastewater.

[0085] Example 2

[0086] A method for treating rural aquaculture wastewater, the difference between the present comparative example and example 1 is that the magnesium ion modified nanocellulose membrane is replaced by a nanocellulose membrane which is not modified by magnesium ions, and other treatment processes and conditions are the same as those in example 1. The final effluent PO4

[0087] The preparation process of the magnesium ion modified nanocellulose membrane used in this embodiment is as follows:

[0088] (1) A sodium periodate solution with a concentration of 0.4 mol / L is prepared, and the nanocellulose membrane is immersed therein, and a hydroxyapatite catalyst is added, the addition amount of nanocellulose is 0.5 g / L, and the reaction is carried out at 50°C for 4 h, and after the reaction is completed, it is washed with deionized water. The amount of hydroxyapatite catalyst used is 0.1 g / L.

[0089] (2) The product obtained in step (1) is immersed in a glycine solution with a concentration of 1 mol / L, 1.2 g / L of sodium thiosulfate is added, and the reaction is carried out at 40°C for 4 h, and after the reaction is completed, it is washed with deionized water.

[0090] (3) The product obtained in step (2) is first immersed in a sodium hydroxide solution with a concentration of 0.2 mol / L, and the reaction is carried out at 25°C for 1 h; then it is immersed in a magnesium chloride solution with a concentration of 1.2 mol / L, and the reaction is carried out at 25°C for 2 h. After the reaction is completed, it is washed with deionized water to obtain a magnesium ion modified nanocellulose membrane. The relative content of magnesium ions in the obtained magnesium ion modified nanocellulose membrane is 2.1 mmol / g.

[0091] In this embodiment, after 4 d of reaction, the COD value, TN, NH4 + , PO4 3- values of the effluent are reduced to 17 mg / L, 5 mg / L, 2 mg / L and 0.1 mg / L, respectively, and all indicators are lower than the first level A effluent discharge standard specified in the "Urban Sewage Treatment Plant Pollutant Discharge Standard" (GB 18918-2002). At the same time, 0.96 g of Mg(NH4)PO4·6H2O crystals is collected on the magnesium ion modified nanocellulose membrane, and the purity is 96.04%, and 6.21 g of NH4NO3 fertilizer is obtained in an acid solution.

[0092] In order to investigate the recycling performance of the obtained magnesium ion modified nanocellulose membrane, the above magnesium ion modified nanocellulose membrane is taken out from the reaction solution, washed with deionized water, and then used again for rural aquaculture wastewater treatment, and the experimental conditions remain unchanged. After 5 times of repeated use, the removal rate of PO4 3- -P in the rural aquaculture wastewater by the magnesium ion modified nanocellulose membrane can still reach more than 98% (see Figure 8 ), indicating that the obtained magnesium ion modified nanocellulose membrane has excellent recycling performance.

[0093] The obtained magnesium ion modified nanocellulose membrane is continuously used for treating rural aquaculture wastewater. After 25 cycles, 0.11 g of Mg(NH4)PO4·6H2O crystals are obtained, indicating that most of the magnesium ions on the magnesium ion modified nanocellulose membrane have been consumed. The magnesium ion modified nanocellulose membrane is first immersed in a 0.2 mol / L sodium hydroxide solution at 25°C for 1 h, and then immersed in a 1.2 mol / L magnesium chloride solution at 25°C for 2 h. The regenerated magnesium ion modified nanocellulose membrane is used again for treating rural aquaculture wastewater, and the obtained crystal quality is 0.96 g, indicating that the magnesium ion modified nanocellulose membrane in the application can be regenerated by soaking in a saturated magnesium chloride solution.

[0094] Example 3

[0095] A method for treating rural aquaculture wastewater, which is different from example 1 in that the initial water quality indicators of the treated rural aquaculture wastewater are different, and the other treatment processes and conditions are the same as those of example 1.

[0096] In this example, the treated rural aquaculture wastewater is taken from 1000 mL of pig farm wastewater from the supernatant of a primary sedimentation tank of a rural chicken farm, and the initial water quality indicators are: COD value 990 mg / L, total nitrogen value (TN) 1180 mg / L, ammonia nitrogen value (NH4 + -N) 1090 mg / L, and phosphoric acid phosphorus value (PO4 3- -P) 102 mg / L.

[0097] In this example, after 4 days of reaction, the effluent COD value, TN, NH4 + -N value and PO4 3- -P value are reduced to 12 mg / L, 3.8 mg / L, 2.6 mg / L and 0.1 mg / L, respectively, and all indicators are lower than the first level A effluent discharge standard specified in the "Urban Wastewater Treatment Plant Pollutant Discharge Standard" (GB18918-2002). At the same time, 0.79 g of Mg(NH4)PO4·6H2O crystals are collected on the magnesium ion modified nanocellulose membrane, with a purity of 96.66%, and 5.09 g of NH4NO3 fertilizer is obtained in an acid solution.

[0098] The above is only a preferred embodiment of the application, and therefore cannot limit the scope of the application. Equivalent changes and modifications made in accordance with the scope and content of the application should still be within the scope of the application.

Claims

1. A method for treating and utilizing rural livestock wastewater, characterized in that: The treatment device comprises a reaction tank, an anode (1), a magnesium ion modified nanocellulose membrane (3) and a cathode (4); the anode (1), the cathode (4) and the magnesium ion modified nanocellulose membrane (3) are all arranged in the reaction tank; the distance between the anode and the magnesium ion modified nanocellulose membrane is 1cm-6cm; the anode (1) is polypyrrole-nanocellulose loaded with active bacteria; an ammonia gas outlet connected with the cathode area is arranged on the reaction tank; The specific steps of the method are as follows: Step one: introducing the treated rural breeding wastewater into the reaction tank; Step two: applying voltage between the anode and the cathode; the organic matters in the treated rural breeding wastewater are oxidized and degraded at the anode; the phosphate and ammonium ions in the treated rural breeding wastewater react to form crystals at the magnesium ion modified nanocellulose membrane; the remaining ammonium ions are diffused to the cathode and react to form ammonia gas.

2. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: The treatment device further comprises an acid absorption module; the acid absorption module is connected with the ammonia gas outlet on the reaction tank through a pipeline; the acid absorption module stores an acidic solution for absorbing ammonia gas to form ammonium salt.

3. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: After the reaction reaches the preset time length, the struvite crystals attached to the magnesium ion modified nanocellulose membrane are collected; when the speed of generating struvite crystals on the magnesium ion modified nanocellulose membrane is lower than the preset value, the magnesium ion modified nanocellulose membrane is immersed in a sodium hydroxide solution and a magnesium chloride solution in sequence for regeneration; The regenerated magnesium ion modified nanocellulose membrane is reinstalled in the reaction tank for use.

4. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: In step two, the power-on voltage is 0-0.5V, the reaction temperature is 10℃-40℃, and the reaction time is 1d-10d.

5. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: The magnesium ion modified nanocellulose membrane is located between the anode (1) and the cathode (4).

6. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: The polypyrrole-nanocellulose is prepared by the following process: mixing pyrrole into a nanocellulose culture medium, obtaining a nanocellulose membrane containing pyrrole after biological culture, adding potassium persulfate to polymerize the pyrrole on the nanocellulose into polypyrrole, and obtaining polypyrrole-nanocellulose; wherein the mass fraction of polypyrrole in the polypyrrole-nanocellulose is 15wt%.

7. The method for treating and resource utilization of rural aquaculture wastewater according to claim 6, characterized in that: The process of loading active bacteria on the polypyrrole-nanocellulose is as follows: taking rural breeding wastewater, adding anaerobic sludge, immersing the polypyrrole-nanocellulose in the rural breeding wastewater, and loading active bacteria on the polypyrrole-nanocellulose; additionally adding rural breeding wastewater every 1d; taking out after 7d-14d to obtain polypyrrole-nanocellulose loaded with active bacteria.

8. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: The preparation method of the magnesium ion modified nanocellulose membrane is as follows: (1) immersing the nanocellulose membrane in a high iodate solution, adding a hydroxyapatite catalyst, and reacting at 20℃-80℃ for 1h-8h; (2) immersing the solid product obtained in step (1) in a glycine solution, adding sodium thiosulfate, and reacting at 20℃-80℃ for 1h-6h; (3) immersing the solid product obtained in step (2) in a sodium hydroxide solution and a magnesium chloride solution in sequence for reaction to obtain a magnesium ion modified nanocellulose membrane.

9. The method for treating and resource utilization of rural aquaculture wastewater according to claim 1, characterized in that: In step (1), the periodate solution is a potassium periodate or sodium periodate solution with a concentration of 0.05 mol / L to 0.5 mol / L; the nanocellulose film is added in an amount of 0.1 g / L to 1 g / L; and the hydroxyapatite catalyst is added in an amount of 0.02 g / L to 0.2 g / L. In step (2), the glycine solution has a concentration of 0.1 mol / L to 1 mol / L; and the sodium thiosulfate is added in an amount of 0.2 g / L to 2 g / L. In step (3), the sodium hydroxide solution has a concentration of 0.1 mol / L to 0.5 mol / L, and the reaction conditions are a reaction temperature of 25°C and a reaction time of 0.5 h to 4 h; the magnesium chloride solution has a concentration of 0.2 mol / L to 2 mol / L, and the reaction conditions are a reaction temperature of 25°C and a reaction time of 1 h to 6 h.

10. Use of a magnesium ion-modified nanocellulose film in treating wastewater containing both ammonium ions and phosphate ions.

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