A method for recovering and recycling ammonia nitrogen from terramycin pharmaceutical wastewater

Abstract

This application discloses a method for ammonia nitrogen recovery and resource utilization of oxytetracycline pharmaceutical wastewater, belonging to the field of pharmaceutical wastewater treatment. The method is used for wastewater treatment, and the wastewater in the equalization tank meets the following conditions: COD≤800mg / L, TDS≤5g / L, oxytetracycline residue≤10mg / L, and initial ammonia nitrogen concentration of 800mg / L-1200mg / L. The method includes staged pH pretreatment, membrane contact deammoniation, dynamic pH control, ultrasonic antifouling, and resource recovery. It can achieve resource utilization of wastewater by targeting and inhibiting membrane fouling and increasing the added value of the products, thus solving the technical problems of insufficient membrane fouling control and limited product functionality in existing technologies.

Description

Technical Field

[0001] This application belongs to the field of pharmaceutical wastewater treatment, and more specifically, it relates to a method for the recovery and resource utilization of ammonia nitrogen from oxytetracycline pharmaceutical wastewater. Background Technology

[0002] In the process of oxytetracycline production, in addition to the wastewater stock solution containing high concentrations of organic matter and residual oxytetracycline molecules formed after preliminary separation, precipitation and crystallization treatment, wastewater from the oxytetracycline pharmaceutical conditioning tank will also be generated.

[0003] The wastewater from the oxytetracycline pharmaceutical equalization tank has the following characteristics: (1) The ammonia nitrogen concentration in the wastewater from the oxytetracycline equalization tank is high (800~1200 mg / L), but COD≤800 mg / L and TDS≤5 g / L. The organic matter in the wastewater from the oxytetracycline equalization tank is mainly composed of small molecule metabolites. (2) When using traditional membrane contact deammoniation technology, there are problems such as membrane fouling, membrane flux decay rate≥30% / h, and the purity of the obtained ammonium sulfate≤85%.

[0004] Meanwhile, the prior art also provides a process for treating ammonia nitrogen wastewater using membrane technology. See Chinese Patent Publication No. CN108033597A, which discloses the following technical solution: The process includes the following steps: adjusting the pH of the ammonia nitrogen wastewater to 10-12.5, then passing it through sand filtration, a security filter, and ultrafiltration, before entering a membrane absorption module. Free ammonia in the wastewater is absorbed by the absorbent, and the wastewater after ammonia nitrogen removal is neutralized and discharged. Sand filtration uses quartz sand with a particle size of 2-4 mm; the security filter has a filtration accuracy of 4-5 μm; ultrafiltration is performed using an ultrafiltration membrane module, where the ultrafiltration membrane is made of polypropylene with a pore size of 0.008-0.01 μm; the membrane in the membrane absorption module is a hydrophobic membrane made of polypropylene; the membrane absorption module includes at least three membrane absorption modules connected in series.

[0005] The aforementioned existing technologies employ a single pH condition, such as fixing the pH at 10.5, without considering the interference of oxytetracycline molecules on ammonia nitrogen mass transfer. This results in a lack of optimized pH control strategies for wastewater with low organic matter content. Furthermore, these existing technologies do not design antifouling measures for the low turbidity and high stability characteristics of the oxytetracycline pharmaceutical equalization tank wastewater, and membrane flux decline rates are generally ≥30% / h.

[0006] Furthermore, existing technologies for ammonia nitrogen treatment in oxytetracycline wastewater primarily employ stripping, biological denitrification, or chemical precipitation. However, each of these traditional ammonia nitrogen treatment methods has its limitations. For instance, biological denitrification requires the addition of a large amount of carbon source and has a long start-up period; it is also susceptible to the influence of toxic substances in the oxytetracycline pharmaceutical equalization tank wastewater, making stable operation difficult. Stripping requires maintaining high pH conditions and consumes a lot of energy, resulting in high costs. Moreover, the high COD, high salinity, and antibiotic inhibition of the oxytetracycline equalization tank wastewater directly lead to low efficiency in stripping, and it is prone to foaming and secondary pollution. In actual operation, the generated ammonium salts contain calcium... 2+ Mg 2+ Impurities result in low purity, making them difficult to utilize as resources; the chemical precipitation method requires strict control of reaction conditions, and the resulting byproducts are difficult to directly utilize as resources.

[0007] In summary, the applicant believes that there is currently no wastewater treatment process with differentiated design for the wastewater from the oxytetracycline pharmaceutical equalization tank, which means that the potential for efficient ammonia recovery from the wastewater has not been fully explored. Therefore, there is an urgent need to develop a low-energy-consumption, high-purity ammonia recovery process tailored to the characteristics of the wastewater from the oxytetracycline pharmaceutical equalization tank in order to solve the problems existing in the current technology. Summary of the Invention

[0008] The purpose of this application is to provide a method for ammonia nitrogen recovery and resource utilization of oxytetracycline pharmaceutical wastewater, which can achieve the resource utilization of wastewater by targeting and inhibiting membrane fouling and increasing the added value of products, thereby solving the technical problems of insufficient membrane fouling control and single product function in the prior art.

[0009] To achieve the above objectives, this application employs the following technical solution:

[0010] The method for ammonia nitrogen recovery and resource utilization from oxytetracycline pharmaceutical wastewater described in this application includes the following steps:

[0011] (1) Staged pH pretreatment: The pH of the wastewater in the equalization tank was adjusted to 9.5 and left to stand for 30 minutes, so that oxytetracycline molecules preferentially released free ammonia through competitive adsorption of hydroxyl groups; then the pH of the wastewater in the equalization tank was adjusted to 10.5, so that the ammonia nitrogen release efficiency was maximized through the protonation reaction of hydroxide ions and amino groups.

[0012] (2) Membrane contact deammoniation: The wastewater after staged pH pretreatment is passed into the hydrophobic hollow fiber membrane module. An ammonia nitrogen concentration gradient is formed between the wastewater side of the hydrophobic hollow fiber membrane module and the 1.5M sulfuric acid absorbent on the absorption side of the hydrophobic hollow fiber membrane module. The wastewater flow rate is controlled at 132 mL / min and the reaction temperature is controlled at 30℃, so that free ammonia can be converted into ammonium ions after passing through the hydrophobic hollow fiber membrane module.

[0013] (3) Dynamic pH control: The initial pH of the absorbent on the absorbent side of the hydrophobic hollow fiber membrane module is set to 1.0, and the final pH of the absorbent is maintained at 6.0 to form ammonium sulfate crystallization conditions;

[0014] (4) Ultrasonic antifouling: An ultrasonic cleaning device is installed downstream of the hydrophobic hollow fiber membrane module. The working frequency is set to 35KHz, and backwashing is performed for 30 seconds every 60 minutes to inhibit membrane fouling.

[0015] (5) Resource recycling: Collect ammonium sulfate crystals from the ultrasonic antifouling process, and after centrifugation, add 0.5wt% oxytetracycline degradation intermediate as raw material for antibacterial slow-release fertilizer.

[0016] As one of the preferred technical solutions, in this application, the wastewater in the equalization tank meets the following conditions: COD≤800mg / L, TDS≤5g / L, oxytetracycline residue≤10mg / L, and initial ammonia nitrogen concentration of 800mg / L-1200mg / L.

[0017] As one of the preferred technical solutions, in this application, the hydrophobic hollow fiber membrane material used in the hydrophobic hollow fiber membrane module is composite polypropylene, the pore size of the hydrophobic hollow fiber membrane is 0.1μm~0.2μm, the inner diameter of the membrane fiber is 0.8mm~1.0mm, and the outer diameter is 1.2mm~1.5mm.

[0018] As one of the preferred technical solutions, in this application, the ammonium sulfate crystals obtained from the resource recovery have a purity of ≥92%, the ammonia nitrogen recovery rate in membrane contact deammoniation is ≥90%, and the ultrasonic antifouling measures can make the membrane flux attenuation rate ≤5% / h.

[0019] As one of the preferred technical solutions, in this application, the solution used to adjust the pH of the wastewater in the equalization tank during the staged pH pretreatment is a potassium hydroxide solution or a sodium hydroxide solution, and the pH adjustment process is carried out by stirring with a flow mixer.

[0020] As one of the preferred technical solutions, in this application, the oxytetracycline degradation intermediate added during resource recovery includes one of dehydrated tetracycline, dihydrotetracycline, isotetracycline, and desdimethylaminooxytetracycline.

[0021] Compared with the prior art, the beneficial effects of this application are:

[0022] 1. This application enables efficient nitrogen removal and ammonia nitrogen resource utilization. By dynamically adjusting the pH to 9.5 to 10.5 and using a hydrophobic hollow fiber membrane module composed of a spirally woven membrane curtain, this application can achieve an ammonia nitrogen removal rate of 84% in the oxytetracycline equalization tank wastewater within 2 hours, and can recover high-purity ammonium sulfate for direct use in the production of slow-release fertilizer.

[0023] 2. This application achieves its goal through structural innovation of anti-pollution membrane curtains by coating the surface of the membrane curtains with a hydrophobic coating, which can reduce the adsorption of hydroxyl groups in oxytetracycline molecules, reduce the rate of membrane flux decay, and extend the service life of hydrophobic hollow fiber membrane modules.

[0024] 3. This application features low cost and easy maintenance. Through modular membrane modules, this application reduces floor space, improves the efficiency of membrane curtain replacement and maintenance, and its process offers advantages such as simple operation, low membrane fouling, high resource recovery rate, and environmental friendliness, making it suitable for widespread use in the treatment of wastewater from oxytetracycline pharmaceutical equalization tanks. Attached Figure Description

[0025] Figure 1 This is a graph showing the relationship between the ammonia nitrogen content in the wastewater from the oxytetracycline pharmaceutical equalization tank and time.

[0026] Figure 2 This is a schematic diagram of the structure of a hydrophobic hollow fiber membrane module.

[0027] In the diagram: 1. Water outlet; 2. Hydrophobic hollow fiber membrane module; 3. Wastewater tank; 4. Acid inlet; 5. Water inlet; 6. Peristaltic pump; 7. Acid tank outlet; 8. Acid tank; 9. Ultrasonic transducer; 10. Acid outlet. Detailed Implementation

[0028] The technical solutions described in this application will be further described below with reference to the accompanying drawings and embodiments.

[0029] The technical solution and principle of the ammonia nitrogen recovery and resource utilization method for oxytetracycline pharmaceutical wastewater described in this application are as follows:

[0030] (1) Staged pH pretreatment:

[0031] It includes primary regulation and secondary regulation. Primary regulation involves adjusting the pH of the wastewater in the regulating tank to 9.5 and letting it stand for 30 minutes to encourage oxytetracycline molecules to preferentially release free ammonia (NH3) through competitive adsorption by hydroxyl groups, while also partially degrading to generate intermediates such as dehydrated tetracycline (ATC).

[0032] The wastewater from the oxytetracycline pharmaceutical equalization tank is a mixture of raw wastewater, resin regeneration water, workshop flushing water, equipment cooling water, and low-concentration wastewater. The raw wastewater and resin regeneration water are the core pollution sources. Mixing them in the pH equalization tank neutralizes extreme pH levels; for example, acidic resin regeneration water complements alkaline raw wastewater, reducing reagent consumption during individual treatment. Simultaneously, the dilution effect mitigates the risk of high salinity and antibiotic inhibition of subsequent biological units. After multiple equalization and pretreatment processes, its organic load is relatively low, but it still exhibits high ammonia nitrogen and relatively high total dissolved solids (TDS). Furthermore, the equalization tank wastewater is primarily used to adjust process parameters, has fewer interfering substances, and exhibits relatively stable water quality and good biodegradability. Therefore, it allows for higher selectivity and lower chemical dosage during nitrogen removal and recovery.

[0033] During this stage, oxytetracycline molecules (C 22 H 24 The hydroxyl groups (-OH) of N2O9 compete with free ammonia (NH3) for adsorption on the surface of the hydrophobic hollow fiber membrane module via hydrogen bonding, as shown in the following reaction:

[0034] Hydroxyl dissociation of oxytetracycline: oxytetracycline -OH + OH − →Oxytetracycline-O − +H2O.

[0035] Deprotonated hydroxyl groups ( - O - The NH3 molecules bind to the hydrophobic coating on the membrane surface through van der Waals forces, releasing adsorption sites and promoting the diffusion of NH3.

[0036] Oxytetracycline side chain cleavage: Under alkaline conditions, the C6 hydroxyl group of oxytetracycline undergoes an elimination reaction with the C5a hydrogen to generate anhydrous tetracycline (ATC): oxytetracycline ATC+H2O, the degradation product has a lower molecular weight and enhanced hydrophobicity, which reduces the clogging of subsequent membrane pores.

[0037] Secondary adjustment: After standing for 30 minutes, adjust the pH of the wastewater in the equalization tank to 10.5. Utilize the protonation reaction of hydroxide ions (OH-) with amino groups to achieve an ammonia nitrogen release efficiency of over 95%, while simultaneously accelerating the breakage of oxytetracycline side chains to generate tetracycline (ETC).

[0038] During pH adjustment, i.e., alkali adjustment, a vortex mixer is used to enhance reaction uniformity and prevent local pH fluctuations from causing oxytetracycline molecules to repolymerize.

[0039] When the pH increases to 10.5, the amino group (-NH2) in the oxytetracycline molecule is further deprotonated and forms a competitive mass transfer with free ammonia: -NH2 + OH- - →-NH - +H₂O. Deprotonated amino group (-NH₃)- It binds to cation sites on the membrane surface, weakening its interference with NH3 adsorption and increasing the ammonia nitrogen release efficiency to over 95%.

[0040] (2) Membrane contact deamination:

[0041] The pretreated wastewater is fed into a hydrophobic hollow fiber membrane module, which includes a primary membrane filter with a pore size of 0.45 μm and a secondary gas separation membrane curtain. The primary membrane filter retains oxytetracycline degradation intermediates and colloidal substances. The secondary gas separation membrane curtain is a composite polypropylene membrane with a pore size of 0.05 μm to 0.2 μm, preferably 0.1 μm to 0.15 μm, and a porosity >55%. The hydrophobic hollow fiber membrane module can construct an ammonia nitrogen mass transfer channel, utilizing the concentration gradient between the wastewater side and the absorbent side to drive the diffusion of free ammonia. The absorbent side of the hydrophobic hollow fiber membrane module uses a 1.5M sulfuric acid absorbent, with the wastewater flow rate in the equalization tank controlled at 132 mL / min and the reaction temperature controlled at 30℃. The hydrophobic hollow fiber membrane module allows free ammonia to react internally with the absorbent on the absorbent side to form ammonium ions.

[0042] In this process, ① concentration gradient-driven transmembrane diffusion occurs.

[0043] According to Fick's law, the mass transfer flux (J) of free ammonia is determined by the concentration gradient (ΔC) and diffusion coefficient (D) across the membrane:

[0044]

[0045] Wastewater side (high concentration): At pH=10.5, NH4 + The NH3 balance is biased towards NH3 (accounting for >90%), and the concentration of free ammonia is significantly increased.

[0046] Absorbing side (low concentration): H+ in sulfuric acid solution (pH=1.0) + At extremely high concentrations, NH3 rapidly protonates into NH4. + (NH3 + H) + → NH4 + ), to maintain the concentration gradient on the absorption side.

[0047] ② The impact of membrane structure optimization on mass transfer.

[0048] Pore ​​size selection for composite polypropylene membranes: This pore size range can retain oxytetracycline degradation intermediates while allowing NH3 to pass freely, achieving a molecular sieving effect.

[0049] The role of hydrophobic coating: The membrane surface is coated with fluoropolymer, with a contact angle >120°, which can reduce the adsorption of hydrophilic substances and reduce the membrane flux decay rate to below 5% / h.

[0050] (3) Dynamic pH control:

[0051] The pH of the sulfuric acid solution on the absorber side of the hydrophobic hollow fiber membrane module is set to 1.0. It is then circulated into the secondary gas separation membrane curtain of the hydrophobic hollow fiber membrane module via a peristaltic pump. The sulfuric acid reacts with the free ammonia that permeates into the secondary gas separation membrane curtain to form ammonium sulfate ((NH4)2SO4). The pH of the sulfuric acid solution on the absorber side of the hydrophobic hollow fiber membrane module is eventually maintained at 6.0 to create conditions for the crystallization of ammonium sulfate.

[0052] In this process, the chemical control of acid absorption and crystallization includes the reaction kinetics of ammonium sulfate formation, namely, the acid-base neutralization reaction of NH3 with sulfuric acid is a fast second-order reaction:

[0053] 2NH3 + H2SO4 → (NH4)2SO4

[0054] The initial pH of the absorption solution was 1.0, ensuring H... + An excess of NH3 will push the reaction to the right, preventing unreacted NH3 residue.

[0055] When the pH of the absorbent solution rises to 6.0, the solution reaches the isoelectric point of ammonium sulfate (pI=5.5), and supersaturation triggers crystal nucleation. By controlling the temperature and stirring rate, high-purity crystals with uniform particle size can be obtained.

[0056] (4) Ultrasonic antifouling:

[0057] A 35kHz ultrasonic cleaning device is installed downstream of the hydrophobic hollow fiber membrane module, and backwashing is performed for 30 seconds every 60 minutes. By removing contaminants from the membrane surface through cavitation effect, membrane fouling can be reduced, and the membrane flux decay rate can be reduced to <5%.

[0058] When the cavitation bubbles generated by ultrasound break on the membrane surface, they release microjets and shock waves, which can effectively remove pollutants such as inorganic scale and organic residues.

[0059] (5) Resource recycling:

[0060] After centrifugation, the collected ammonium sulfate crystals were mixed with 0.5 wt% oxytetracycline degradation intermediate as a raw material for an antibacterial slow-release fertilizer. The addition of the oxytetracycline degradation intermediate in this step achieves synergistic effects of slow release and antibacterial activity through the following mechanisms: carrier complexation, antibacterial enhancement, and chelation. Specifically, carrier complexation involves the intermediate adsorbing onto the surface of the ammonium sulfate crystals to form a microporous slow-release structure. Antibacterial enhancement utilizes the intermediate's inhibitory activity against soil pathogens such as Fusarium wilt and Ralstonia solanacearum, thus suppressing rhizosphere diseases. Chelation involves the interaction of intermediates such as isotetracycline with trace metal ions (Fe...). 2+ Zn 2+ Chelation enhances the utilization of trace metal ions by fertilizers.

[0061] In this step, after adding 0.5 wt% of oxytetracycline degradation intermediate (such as ETC), ETC molecules adsorb onto the surface of ammonium sulfate crystals, forming a porous structure with a pore size of 2-5 nm, thus delaying the degradation of NH4+. + Release rate. The ketone group (C=O) in ETC can react with Fe in the soil. 2 + Zn 2+ It forms stable complexes and improves the utilization rate of trace elements.

[0062] In this application, a peristaltic pump 6 is connected to an acid tank 8 via an acid tank outlet 7. The outlet of the peristaltic pump 6 is connected to an acid inlet 4 in the hydrophobic hollow fiber membrane module 2. The acid outlet 10 of the hydrophobic hollow fiber membrane module 2 is connected to the acid tank 8 via a pipeline, thus realizing a complete acid operation loop to meet the reaction of the acid with free ammonia in the hydrophobic hollow fiber membrane module 2. The hydrophobic hollow fiber membrane module 2 includes a primary membrane filter and a secondary gas separation membrane curtain. The secondary gas separation membrane curtain is a spiral woven membrane curtain with a hydrophobic coating on its surface to reduce the adsorption of hydroxyl groups in oxytetracycline molecules. The primary membrane filter is used to retain oxytetracycline degradation intermediates and colloidal substances, and the secondary gas separation membrane curtain is a composite polypropylene membrane. On both sides of the hydrophobic hollow fiber membrane module 2 are a wastewater tank 3 and an acid tank 8, respectively, and are equipped with an outlet 1, an acid outlet 10, an acid inlet 4, and a water inlet 5. The hydrophobic hollow fiber membrane module 2 described in this application is a selection made by those skilled in the art based on existing technology to meet the above requirements, thereby forming ammonia-nitrogen mass transfer channels on both sides of the hydrophobic hollow fiber membrane module 2 and using the concentration gradient between the wastewater side and the absorbent side to drive the diffusion of free ammonia. An ultrasonic transducer 9 is provided downstream of the hydrophobic hollow fiber membrane module 2.

[0063] Based on the above technical solutions and principles, this application provides the following embodiments:

[0064] Example 1: The wastewater used in this example was taken from a oxytetracycline pharmaceutical factory in Jiuquan City. 5L of wastewater (NH4+) from the oxytetracycline pharmaceutical equalization tank was taken. + (The ammonia nitrogen concentration was approximately 1130 mg / L). After adjusting the pH to 10.5, the solution was introduced into a hydrophobic hollow fiber membrane module, creating an ammonia nitrogen concentration gradient between the wastewater and absorber sides. This promoted the transmembrane absorption of free ammonia from the wastewater into the absorbent. The absorbent consisted of 500 mL of 1.5 M sulfuric acid solution, which reacted to form ammonium sulfate. Ammonia nitrogen concentrations were measured at different treatment times (0 min, 30 min, 60 min, and 120 min).

[0065] Pour 250 mL of acid absorption solution into a beaker and place it in a constant temperature water bath to stabilize at 25 °C. The stable temperature can be monitored in real time with a thermometer.

[0066] While continuously stirring, the ammonium sulfate solid generated and collected during the above reaction process was added in batches, and stirred for 15 minutes after each addition until completely dissolved.

[0067] When the added ammonium sulfate solid no longer dissolves (i.e., persistent undissolved crystals appear at the bottom of the beaker, and there is no decrease after stirring for 1 hour), it is considered to have reached saturation.

[0068] The undissolved ammonium sulfate solid was collected by filtering with pre-weighed quantitative filter paper. The filter paper and solid were dried in an oven at 105°C to constant weight. After cooling, the mass of the undissolved solid (m1) was weighed. The mass of the undissolved solid (m1) was subtracted from the total amount added (m0) to obtain a mass of 180g of dissolved ammonium sulfate. The solubility was calculated to be 72g / mL.

[0069] The simulation results show that in actual wastewater treatment, the recovered ammonium sulfate crystals can be used as industrial raw materials (such as in fertilizer production), reducing wastewater treatment costs. Based on the experimental data, it is estimated that approximately 720 kg of ammonium sulfate (72 g / 100 mL × 1000) can be recovered per cubic meter of sulfuric acid-containing wastewater (1.5 M). At a market price of 0.9 yuan / kg, this would generate approximately 648 yuan / m³. 3 The direct benefits are significant. However, in practical applications, it is necessary to combine online monitoring and dynamic control to balance recovery efficiency and energy consumption costs, ultimately achieving the goal of resource recovery from wastewater treatment.

[0070] The results are shown in the table below.

[0071] Time / min 0 30 60 120 Ammonia nitrogen content (mg / L) 1130 500 300 180

[0072] After the wastewater from the oxytetracycline pharmaceutical equalization tank entered the membrane contact ammonia removal system, the ammonia nitrogen concentration decreased significantly with increasing time, dropping to 500 mg / L at 30 minutes, 300 mg / L at 60 minutes, and 180 mg / L at 120 minutes. This indicates that the membrane contact ammonia removal technology can rapidly establish a concentration gradient between the wastewater side and the acidic absorption side, allowing free ammonia in the wastewater to diffuse rapidly towards the absorption side. The initial decrease (0-30 minutes) was larger, possibly due to the high concentration gradient promoting a faster ammonia mass transfer rate; however, the rate of decrease slowed down in the later stages (60-120 minutes), indicating that the system gradually approached an equilibrium state.

[0073] Overall, after 120 minutes of treatment, the ammonia nitrogen concentration decreased from 1130 mg / L to 180 mg / L, with a removal efficiency of approximately 84%. This verifies the high efficiency of the process in recovering ammonia nitrogen from the oxytetracycline pharmaceutical conditioning tank wastewater under optimized pH conditions, and provides technical support for subsequent resource utilization (such as generating high-purity ammonium salts).

[0074] Oxytetracycline contains multiple hydroxyl (-OH) and amino (-NH2) groups in its molecular structure, with the chemical formula C22H24N2O9. The behavior of these groups in aqueous solution directly affects ammonia nitrogen (NH3 / NH4). + The mass transfer efficiency of ).

[0075] Under neutral or weakly alkaline conditions, hydroxyl groups (-OH) are adsorbed onto the membrane surface or the absorbent interface through hydrogen bonding or hydrophobic interactions, forming a physical barrier. This steric hindrance forces free ammonia (NH3) to migrate along a more tortuous path, increasing its contact time with the absorbent and thus improving absorption efficiency.

[0076] Under alkaline conditions (pH > 9), the amino group gradually deprotonates to -NH, which carries a negative charge and reacts with cations (such as H+) on the membrane surface or in the absorbent. + Na + To reduce competitive adsorption of free ammonia, current technologies have not effectively addressed the competitive adsorption of oxytetracycline molecules, leading to accelerated membrane fouling, low ammonia-nitrogen mass transfer efficiency, and decreased product purity. For example, in the problem of accelerated membrane fouling, hydroxyl groups adsorb onto the membrane pores or hydrophobic layer surface, forming an organic fouling layer, resulting in a membrane flux decay rate as high as 60% / h. Regarding the low ammonia-nitrogen mass transfer efficiency, amino groups are still partially deprotonated under alkaline conditions, occupying active sites in the absorbent (such as H+), inhibiting the transfer of free ammonia to the absorbent. In the problem of decreased product purity, oxytetracycline molecules compete with sulfate ions for binding, leading to the contamination of ammonium sulfate with antibiotic degradation intermediates (such as dehydrated tetracycline), resulting in a purity ≤85%.

[0077] This application addresses the issue that existing technologies using a single pH condition do not consider the interference of oxytetracycline molecules on ammonia nitrogen mass transfer. It employs staged pH control. For example, in the initial stage (0-30 minutes), the wastewater pH is gradually increased from 7.2 to 9.5, utilizing the competitive adsorption characteristics of hydroxyl and amino groups in oxytetracycline molecules to preferentially release free ammonia. In the dynamic enhancement stage (30-120 minutes), the pH is further increased to 10.5, maximizing ammonia nitrogen release efficiency through the protonation reaction of hydroxide ions and amino groups. That is, within the initial 30 minutes, the ammonia nitrogen removal rate reaches as high as 55% (i.e., decreasing from 1130 mg / L to 500 mg / L), gradually stabilizing in the later stages, while avoiding excessive deprotonation of oxytetracycline molecules (-NH3). + It adsorbs into the membrane pores, reducing the risk of membrane fouling.

[0078] In this application, an ultrasonic transducer is installed downstream of the membrane module, with a frequency of 35kHz. Backwashing is initiated for 30 seconds every 60 minutes. The cavitation effect caused by the ultrasonic waves is used to remove inorganic scale layers such as CaCO3 and Mg(OH)2 and organic residues from the membrane surface. This helps to maintain stable membrane flux and represents a significant improvement over traditional processes. Furthermore, the extended membrane lifespan can effectively reduce operation and maintenance costs.

[0079] In this application, suspended solids and Fe are removed by chemical precipitation. 3+ Cu 2+ The removal of heavy metal ions helps prevent physical blockage of membrane pores, controls COD in wastewater to ≤800 mg / L, and reduces interference from organic matter on the diffusion of free ammonia, thus enabling efficient separation of ammonia nitrogen and oxytetracycline under low organic matter conditions.

Claims

1. A method for recovering and recycling ammonia nitrogen from terramycin pharmaceutical wastewater, characterized in that, The method includes the following steps: (1) Staged pH pretreatment: The pH of the wastewater in the equalization tank was adjusted to 9.5 and left to stand for 30 minutes, so that the oxytetracycline molecules preferentially released free ammonia through competitive adsorption of hydroxyl groups; then the pH of the wastewater in the equalization tank was adjusted to 10.5, so that the amino groups in the oxytetracycline molecules underwent deprotonation reaction through hydroxide ions, thereby maximizing the ammonia nitrogen release efficiency. (2) Membrane contact deammoniation: The wastewater after staged pH pretreatment is passed into the hydrophobic hollow fiber membrane module. An ammonia nitrogen concentration gradient is formed between the wastewater side of the hydrophobic hollow fiber membrane module and the 1.5M sulfuric acid absorbent on the absorption side of the hydrophobic hollow fiber membrane module. The wastewater flow rate is controlled at 132 mL / min and the reaction temperature is controlled at 30℃, so that free ammonia can be converted into ammonium ions after passing through the hydrophobic hollow fiber membrane module. (3) Dynamic pH control: The initial pH of the absorbent on the absorbent side of the hydrophobic hollow fiber membrane module is set to 1.0, and the final pH of the absorbent is maintained at 6.0 to form ammonium sulfate crystallization conditions; (4) Ultrasonic antifouling: An ultrasonic cleaning device is installed downstream of the hydrophobic hollow fiber membrane module. The working frequency is set to 35kHz, and backwashing is performed for 30 seconds every 60 minutes to inhibit membrane fouling. (5) Resource recycling: Ammonium sulfate crystals collected during the ultrasonic antifouling process are centrifuged and then 0.5wt% of oxytetracycline degradation intermediate is added as a raw material for antibacterial slow-release fertilizer.

2. The method according to claim 1, wherein the method is characterized in that: The wastewater in the equalization tank meets the following conditions: COD≤800mg / L, TDS≤5g / L, oxytetracycline residue≤10mg / L, and initial ammonia nitrogen concentration of 800mg / L-1200mg / L.

3. The method according to claim 1, wherein the method is characterized in that: The hydrophobic hollow fiber membrane module uses a composite polypropylene membrane material. The pore size of the hydrophobic hollow fiber membrane is 0.1μm~0.2μm, the inner diameter of the membrane fiber is 0.8mm~1.0mm, and the outer diameter is 1.2mm~1.5mm.

4. The method according to claim 1, wherein the method is characterized in that: The ammonium sulfate crystals obtained from the resource recovery have a purity of ≥92%, the ammonia nitrogen recovery rate in membrane contact deammoniation is ≥90%, and the ultrasonic antifouling measures can reduce the membrane flux attenuation rate to ≤5% / h.

5. The method for ammonia nitrogen recovery and resource utilization of oxytetracycline pharmaceutical wastewater according to claim 1, characterized in that: In the staged pH pretreatment, the solution used to adjust the pH of the wastewater in the equalization tank is a potassium hydroxide solution or a sodium hydroxide solution, and the pH adjustment process is carried out by stirring with a flow mixer.

6. The method for ammonia nitrogen recovery and resource utilization of oxytetracycline pharmaceutical wastewater according to claim 1, characterized in that: The oxytetracycline degradation intermediates added during the resource recovery include one of dehydrated tetracycline, dihydrotetracycline, isotetracycline, and desdimethylaminooxytetracycline.

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