Process for removing naproxen from water using nitrified sludge

Abstract

A process for removing naproxen in water by using nitrification sludge, comprising the following steps: 1) nitrification sludge enrichment culture: wastewater with ammonia nitrogen concentration of 100-200 mg / L is mixed with activated sludge in an aerobic tank, and then sequentially subjected to aerobic reaction, sedimentation treatment, drainage treatment and idle treatment to form a treatment cycle; the hydraulic retention time in each cycle is 24-48 h; after multiple cycle circulations, the enriched nitrification sludge is obtained; 2) the nitrification sludge obtained in step 1) is mixed with the wastewater containing naproxen to be treated, and an ammonia nitrogen compound is added to adjust the initial concentration ratio of ammonia nitrogen to naproxen in the reaction system to 20-200:1; the reaction is carried out at a temperature of 15-30 DEG C and a pH of 7.0-8.5 for 24-48 h. The process has universality for removing naproxen in the environmental concentration range, does not need to add additional chemicals or set up complex treatment units, significantly reduces the material cost and operation cost, and has a better popularization and application prospect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a process for removing naproxen from water using nitrified sludge. Background Technology

[0002] Naproxen (NPX) is a propionic acid-based nonsteroidal anti-inflammatory drug (NSAID) and one of the most widely used antipyretic and analgesic drugs. It is frequently detected in wastewater treatment plant influent and effluent, surface water, and groundwater. Although detected at trace concentrations, it can still produce adverse effects on aquatic organisms, such as oxidative stress, endocrine disruption, and reproductive and developmental toxicity. For example, long-term exposure to environmental concentrations of naproxen can lead to slowed growth, decreased reproductive capacity, and pathological changes in gonadal tissue in zebrafish. Given the widespread distribution of naproxen in the aquatic environment and its potential ecological risks to aquatic organisms and human health, effective and low-cost removal of naproxen from wastewater is a hot research topic.

[0003] In existing technologies, the removal of micropollutants by nitrifying sludge mainly involves two pathways: biosorption and cometabolism. Biosorption relies on the abundant carboxyl, hydroxyl, and amino groups on the surface of the extracellular polymeric substances in nitrifying sludge to bind with organic micropollutants through electrostatic interactions, hydrophobic partitioning, and surface complexation. Cometabolism, on the other hand, is primarily mediated by ammonia monooxygenase secreted by ammonia-oxidizing bacteria. Previous studies have shown that activated sludge systems have a certain removal capacity for naproxen, mainly through cometabolism. However, in practice, the removal efficiency of activated sludge systems for naproxen fluctuates significantly under different operating conditions, and requires the addition of large amounts of auxiliary chemical reagents to achieve the desired effect, limiting practical application and necessitating improvement.

[0004] Therefore, the present invention aims to propose a process for removing naproxen from water using nitrified sludge, which can achieve efficient and deep removal of naproxen from wastewater without the need for additional chemical agents, thereby better meeting practical needs. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a process for removing naproxen from water using nitrified sludge, so as to achieve efficient and deep removal of naproxen from wastewater without the need for additional chemical agents.

[0006] The technical problem solved by this invention is achieved by the following technical solution: A process for removing naproxen from water using nitrified sludge includes the following steps: 1) Nitrified sludge enrichment and cultivation: Wastewater with an ammonia nitrogen concentration of 100~200 mg / L is mixed with activated sludge in an aerobic tank via influent, and then aerobic reaction, sedimentation treatment, drainage treatment and idle treatment are carried out in sequence to form a treatment cycle; the hydraulic retention time in each cycle is 24~48h; after multiple cycles, enriched nitrified sludge is obtained. 2) Mix the nitrified sludge obtained in step 1) with the naproxen-containing wastewater to be treated, add ammonia nitrogen compounds to adjust the initial concentration ratio of ammonia nitrogen to naproxen in the reaction system to be maintained at 20~200:1; then react for 24~48 hours at a temperature of 15~30 ℃ and a pH of 7.0~8.5.

[0007] Furthermore, in step 1), the reaction is carried out in a sequencing batch reactor. During the aerobic reaction stage, the dissolved oxygen concentration is controlled at 2.0~2.5 mg / L by intermittent aeration. Stirring is maintained during the reaction, and the stirring rate is 180~240 r / min.

[0008] Furthermore, in step 1), the pH is maintained at 7.5~7.7 and the temperature is maintained at 20~25 ℃ during the cycle.

[0009] Furthermore, in step 1), each treatment cycle consists of 4-6 minutes of water inlet, 100-150 minutes of sedimentation treatment, 4-6 minutes of drainage, 40-60 minutes of idle treatment, and the remainder is the aerobic reaction time.

[0010] Furthermore, in step 1), each treatment cycle consists of 5 minutes of water inlet, 120 minutes of sedimentation treatment, 5 minutes of drainage, 50 minutes of idle treatment, and the remainder is the aerobic reaction time.

[0011] Furthermore, in step 1), the total time of the cycle is not less than 60 days.

[0012] Furthermore, in step 1), the concentration of volatile suspended solids in the mixed liquor of the obtained nitrified sludge is 1000~1500 mg / L.

[0013] Further, in step 2), the inoculation amount of the nitrifying sludge corresponds to a sludge load of naproxen in the wastewater of 0.01~1.5 mg COD / (g VSS·d).

[0014] Furthermore, in step 2), an ammonia nitrogen compound is added to adjust the initial concentration ratio of ammonia nitrogen to naproxen in the reaction system to be maintained at 60~100:1.

[0015] Furthermore, in step 2), the initial concentration of naproxen in the wastewater to be treated is 0.05~0.5 mg / L, and the dissolved oxygen during the treatment process is 2.0~2.5 mg / L.

[0016] Beneficial Effects: The process for removing naproxen from water using nitrified sludge described in this invention involves inoculating activated sludge with wastewater and then subjecting it to a unique acclimation treatment to prepare highly active nitrified sludge. This nitrified sludge is then mixed with naproxen-containing wastewater, and under specific conditions, the reaction is controlled to adjust the concentration ratio of ammonia nitrogen to naproxen to enhance co-metabolism efficiency, thereby achieving highly efficient removal of naproxen from wastewater. The process described in this invention is universally applicable to the removal of naproxen within a wide range of environmental concentrations. It requires no additional chemical additives or complex treatment units, significantly reducing material and operating costs, and possesses excellent prospects for widespread application. Attached Figure Description

[0017] Figure 1 This is a comparison chart of the removal effect of nitrified sludge on naproxen under different hydraulic retention times in Example 1 of the present invention.

[0018] Figure 2 This is a comparison chart of the ammonia nitrogen removal effect of nitrifying sludge under different hydraulic retention times in Example 1 of the present invention.

[0019] Figure 3 This is a comparison chart of naproxen removal effects under different ammonia nitrogen / naproxen ratios in Example 2 of the present invention.

[0020] Figure 4 This is a comparison chart of naproxen removal effects between the experimental group and the inhibitor control group in Example 3 of the present invention.

[0021] Figure 5 The image shows the removal effect of naproxen at different initial concentrations in Example 3 of this invention. Detailed Implementation

[0022] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments. Example 1

[0023] In this embodiment, the process for removing naproxen from water using nitrified sludge includes the following steps: 1) Enrichment and cultivation of nitrified sludge: Five sequencing batch reactors with a total volume of 4 L and an effective volume of 3 L were set up and numbered R1 to R5 respectively. Aerobic activated sludge was inoculated into wastewater with an ammonia nitrogen concentration of 150 mg / L by means of influent. Then, aerobic reaction, sedimentation treatment, drainage treatment and idle treatment were carried out in sequence to form a treatment cycle. After multiple cycles, enriched nitrified sludge was obtained.

[0024] The inoculated material in each reactor was activated sludge from the aerobic tank of a municipal wastewater treatment plant, which originated from the same source. The wastewater was synthetic wastewater, containing 846 mg / L NH4HCO3, 900 mg / L NaHCO3, 20 mg / L KH2PO4, 20 mg / L MgSO4·7H2O, 10 mg / L CaCl2·2H2O, and 0.5 mL / L of trace element solution.

[0025] Each reactor receives 1.5 L of water per cycle and discharges 1.5 L of water, with a volume exchange ratio of 0.5.

[0026] During the aerobic reaction phase in each reactor, dissolved oxygen was controlled at 2.4 mg / L through intermittent aeration, with a stirring rate of 230 r / min, pH maintained at 7.6, and temperature at 23 ℃. The concentration of volatile suspended solids in the mixed liquor was monitored every 3 days during the acclimation process.

[0027] After acclimatization for 60 days, 500 mL of sludge from each reactor was centrifuged at 4000 rpm for 5 min, and the supernatant was discarded. The mixture was washed three times with deionized water to completely remove ammonia, nitrate, and nitrite from the sludge-water mixture, and then concentrated to obtain nitrified sludge for later use.

[0028] In R1 to R5, the treatment time for each cycle is 6 h, 8 h, 12 h, 18 h, and 24 h, respectively, and the hydraulic retention time is 12 h, 16 h, 24 h, 36 h, and 48 h, respectively; the influent time is 5 min, the sedimentation treatment time is 120 min, the drainage time is 5 min, the idle time is 50 min, and the aerobic reaction time is 3 h, 5 h, 9 h, 15 h, and 21 h, respectively.

[0029] During the aerobic reaction stage, the dissolved oxygen concentration was controlled at 2.0~2.5 mg / L using intermittent aeration. Stirring was maintained during the reaction at a rate of 200 r / min. During the cycle, the pH was maintained at 7.6 and the temperature at 24 ℃. Each cycle consists of 5 minutes of influent, 120 minutes of sedimentation, 5 minutes of effluent, and 50 minutes of idle time; the remainder is for aerobic reaction.

[0030] The enrichment and cultivation time for nitrified sludge was 60 days. After 60 days of acclimatization, the VSS in each reactor was found to be stable within the range of 1000~1500 mg / L.

[0031] 2) The nitrified sludge obtained in step 1) was mixed with the naproxen-containing wastewater to be treated. The initial concentration of naproxen in the wastewater was 0.5 mg / L, and the initial concentration of ammonia nitrogen was 30 mg / L. The inoculum amount of the nitrified sludge corresponded to a naproxen sludge load of 0.38~0.58 mg COD / (g VSS·d) in the wastewater. Specifically, for R1 to R5, the inoculum amount of nitrified sludge corresponded to an initial naproxen sludge load of 0.54, 0.47, 0.41, 0.39, and 0.43 COD / (g VSS·d) in the wastewater, respectively. Before the reaction, ammonia nitrogen compounds were added to adjust the initial concentration ratio of ammonia nitrogen to naproxen in the reaction system to 60:1. The reaction was carried out at a temperature of 25 ℃ and a pH of 8.0, with stirring maintained during the reaction at a stirring rate of 150 r / min, and dissolved oxygen maintained at 2.5 mg / L.

[0032] Samples were taken at 0, 6, 12, 24, 36 and 48 hours, filtered through a 0.22 μm aqueous PES membrane, and the concentration of naproxen was determined by high performance liquid chromatography.

[0033] The results are as follows Figure 1 and Figure 2 As shown, the results indicate that the cycle treatment time during the acclimation stage in the preparation of nitrifying sludge has a significant impact on the naproxen removal capacity of the nitrifying sludge. Extending the hydraulic retention time from 12 h to 36 h gradually increased the naproxen removal rate from 45.2% to 89.0% at 48 h, and the ammonia nitrogen removal rate also increased from 68.5% to 96.5%, indicating that appropriately extending the hydraulic retention time is beneficial for the enrichment of ammonia-oxidizing bacteria and the enhancement of their cometabolism activity. When the hydraulic retention time was further extended to 48 h, the removal rate decreased slightly (88.2%), possibly related to sludge aging. Considering both removal effect and operational efficiency, the optimal hydraulic retention time range during the acclimation stage is 24–48 hours, with 36 hours being the preferred value. Example 2

[0034] This embodiment mainly tests the effect of different ammonia nitrogen / naproxen concentration ratios on the removal effect.

[0035] In this embodiment, the process for removing naproxen from water using nitrified sludge includes the following steps: 1) Enrichment and cultivation of nitrified sludge: In this example, the nitrified sludge is the nitrified sludge prepared by R4 in Example 1.

[0036] 2) The experiment was conducted in six 500 mL beakers. The nitrified sludge obtained in step 1) was centrifuged and washed according to the method in Example 1, and then resuspended in 500 mL of synthetic wastewater containing different ammonia nitrogen / naproxen concentration ratios. The initial concentration of naproxen in each group was fixed at 0.5 mg / L, and the initial concentrations of ammonia nitrogen were set to 5, 10, 30, 50, 100, and 150 mg / L, respectively, corresponding to initial ammonia nitrogen to naproxen concentration ratios of 10:1, 20:1, 60:1, 100:1, 200:1, and 300:1. The reaction was carried out at room temperature (25 ℃), stirring rate (150 r / min), and dissolved oxygen (2.5 mg / L). Samples were taken at 0, 6, 12, 24, 36, and 48 hours to determine the concentrations of naproxen and ammonia nitrogen.

[0037] The results are as follows Figure 3 As shown, the concentration ratio of ammonia nitrogen to naproxen has a significant impact on the removal efficiency. The naproxen removal rate initially increases and then decreases with increasing ratio. When the ratio is 10:1, the ammonia nitrogen concentration is too low, failing to fully activate the ammonia monooxygenase secreted by ammonia-oxidizing bacteria, resulting in insufficient initiation of the co-metabolism reaction and a low removal rate. Increasing the ratio to 20:1 significantly enhances the co-metabolism effect and significantly improves the removal rate. Within the range of 60:1 to 100:1, ammonia monooxygenase activity is fully activated, and the naproxen removal rate reaches its peak. Further increasing the ratio to 200:1 and above leads to substrate competition between excess ammonia nitrogen and naproxen, causing a gradual decrease in the removal rate. The ammonia nitrogen removal rate remains above 93% under all conditions, indicating that the system's nitrification function is basically stable. Based on comprehensive analysis, the optimal initial concentration ratio of ammonia nitrogen to naproxen for efficient naproxen removal is determined to be 20–200:1, preferably 60–100:1. Example 3

[0038] This embodiment uses the nitrified sludge prepared by group R4 in Example 1, and conducts two experiments under the optimal concentration ratio of 60:1 determined in Example 2.

[0039] Contribution Quantification Experiment: 500 mL of nitrified sludge prepared from group R4 was centrifuged and washed according to the method in Example 1, and then suspended in synthetic wastewater containing naproxen and ammonia nitrogen. An experimental group and an inhibitor control group were set up. The initial concentration of naproxen was 0.5 mg / L, and the initial concentration of ammonia nitrogen was 30 mg / L (ratio 60:1). The inhibitor control group was additionally treated with 12 mg / L allyl thiourea to inhibit AMO enzyme activity. The reaction was carried out at room temperature (25 ℃), a stirring rate of 150 r / min, and dissolved oxygen of 2.0–2.5 mg / L. Naproxen concentration was measured at 0, 6, 12, 24, 36, and 48 hours.

[0040] The results are as follows Figure 4As shown, the removal rate of naproxen in the experimental group reached 89.0% after 48 h, while that in the inhibitor control group was only 8.5%. This demonstrates that under optimal acclimatization HRT and optimal ratio conditions, AMO enzyme-mediated co-metabolism is the dominant pathway for naproxen removal, while biosorption contributes relatively little.

[0041] Environmental suitability experiment: This experiment was conducted in six 500 mL beakers. 500 mL of nitrified sludge prepared from group R4 was centrifuged and washed according to the method in Example 1, and then suspended in synthetic wastewater containing naproxen and ammonia nitrogen. The initial concentrations of naproxen in each beaker were 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5 mg / L, respectively, and the ammonia nitrogen concentration was 30 mg / L for all groups. The reaction was carried out at room temperature (25 ℃), a stirring rate of 150 r / min, and dissolved oxygen of 2.0–2.5 mg / L. Naproxen concentrations were measured at 0, 6, 12, 24, 36, and 48 hours.

[0042] The results are as follows Figure 5 As shown, within the environmental concentration range of 0.05–0.5 mg / L, the removal rate of naproxen after 48 hours can reach 87.5%–93.5%, with the removal rate decreasing slightly as the initial concentration increases. This verifies the high efficiency and universality of the method of the present invention at real environmental concentration levels of naproxen.

[0043] In summary, this invention identifies two key process parameters for achieving efficient naproxen removal: a hydraulic retention time of 24–48 h (preferably 36 h) during the acclimation stage, and an ammonia nitrogen to naproxen initial concentration ratio of 20:1–200:1 (preferably 60–100:1) during the removal stage. Under the optimal parameter combination, co-metabolic transformation contributes approximately 90%, and the removal rate reaches 87.5%–93.5% within the environmental concentration range. This invention has significant practical application value.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A process for removing naproxen from water using nitrified sludge, characterized in that, Includes the following steps: 1) Nitrified sludge enrichment and cultivation: Wastewater with an ammonia nitrogen concentration of 100~200 mg / L is mixed with activated sludge in an aerobic tank via influent, and then aerobic reaction, sedimentation treatment, drainage treatment and idle treatment are carried out in sequence to form a treatment cycle; the hydraulic retention time in each cycle is 24~48h; after multiple cycles, enriched nitrified sludge is obtained. 2) Mix the nitrified sludge obtained in step 1) with the naproxen-containing wastewater to be treated, add ammonia nitrogen compounds to adjust the initial concentration ratio of ammonia nitrogen to naproxen in the reaction system to be maintained at 20~200:1; then react for 24~48 hours at a temperature of 15~30 ℃ and a pH of 7.0~8.

5.

2. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 1), the reaction is carried out in a sequencing batch reactor. During the aerobic reaction stage, the dissolved oxygen concentration is controlled at 2.0~2.5 mg / L by intermittent aeration. Stirring is maintained during the reaction, and the stirring rate is 180~240 r / min.

3. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 1), the pH is maintained at 7.5~7.7 and the temperature is maintained at 20~25 ℃ during the cycle.

4. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 1), each treatment cycle consists of 4-6 minutes of water inlet, 100-150 minutes of sedimentation, 4-6 minutes of drainage, 40-60 minutes of idle time, and the remainder is for aerobic reaction.

5. The process for removing naproxen from water using nitrified sludge according to claim 4, characterized in that, In step 1), each cycle consists of 5 minutes of water intake, 120 minutes of sedimentation treatment, 5 minutes of drainage, 50 minutes of idle treatment, and the remainder is for aerobic reaction time.

6. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 1), the total time of the cycle is not less than 60 days.

7. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 1), the concentration of volatile suspended solids in the mixed liquor of the nitrified sludge is 1000~1500 mg / L.

8. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 2), the inoculation amount of the nitrifying sludge corresponds to a sludge load of naproxen in the wastewater of 0.01~1.5 mg COD / (g VSS·d).

9. The process for removing naproxen from water using nitrified sludge according to claim 8, characterized in that, In step 2), an ammonia nitrogen compound is added to adjust the initial concentration ratio of ammonia nitrogen to naproxen in the reaction system to be maintained at 60~100:

1.

10. The process for removing naproxen from water using nitrified sludge according to claim 1, characterized in that, In step 2), the initial concentration of naproxen in the wastewater to be treated is 0.05~0.5 mg / L, and the dissolved oxygen concentration during the treatment process is 2.0~2.5 mg / L.

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