Method for efficiently removing perchlorate in wastewater based on quaternary ammonium salt assisted ultrafiltration

Abstract

The invention discloses a method for efficiently removing perchlorate in wastewater based on quaternary ammonium salt assisted ultrafiltration, which comprises the following steps: adding quaternary ammonium salt with the carbon chain length of C12-C16 into perchlorate wastewater, enabling quaternary ammonium cations and perchlorate to form nanoscale floc through hydrophobic interaction, electrostatic attraction and Van der Waals force, and filtering through an ultrafiltration membrane to obtain the perchlorate. The high-selectivity and high-efficiency removal of the perchlorate in the wastewater is realized. The method is simple and convenient to operate, can be completed only by adding trace quaternary ammonium salt and combining the trace quaternary ammonium salt with a conventional ultrafiltration process, does not need complex equipment or a regeneration process, avoids the problem of secondary pollution caused by an adsorption material, and is remarkably improved in environmental friendliness. Meanwhile, the composite material also has good anti-anion interference capability and low flux attenuation. The method is wide in material source, low in cost, easy and convenient to operate, free of regeneration, low in operation cost and free of secondary waste, has good engineering popularization potential and is particularly suitable for on-site rapid treatment and large-scale application of perchlorate wastewater.

Description

Technical Field

[0001] The invention belongs to the field of wastewater treatment, and in particular relates to a method for efficiently removing perchlorate in wastewater based on quaternary ammonium salt-assisted ultrafiltration. Background Art

[0002] Perchlorate is a water-soluble anion with high solubility, strong stability, and strong migration and diffusion capabilities. It is widely present in industrial wastewater such as rocket propellants, fireworks, and explosives. In recent years, due to the influence of fireworks manufacturing and perchlorate-containing industrial activities, it has been frequently detected in industrial wastewater and surrounding water bodies in many places, and has become a typical persistent inorganic pollutant that has attracted much attention. Perchlorate has strong environmental persistence and is difficult to degrade in the natural environment. It can enter the groundwater system through surface runoff or leakage, causing persistent pollution. Therefore, it is of great environmental significance and practical urgency to treat perchlorate wastewater to meet standards and control emissions, and to build an efficient and feasible removal technology system. Currently, many methods for treating perchlorate wastewater have been reported, including ion exchange, membrane separation, chemical reduction, and biodegradation. Although these methods have demonstrated certain treatment effects under laboratory or pilot test conditions, most suffer from complex operating conditions, high material costs, weak anti-interference capabilities, and difficulties in engineering scale-up. This makes it difficult to achieve large-scale, low-cost, and sustainable and stable operation in industrial wastewater treatment, limiting their widespread application in practical engineering. Therefore, there is an urgent need to develop a simple, cost-effective, highly adaptable, and easily scalable method for the efficient removal of perchlorate wastewater, in order to meet the actual needs of industrial wastewater discharge standards and environmental risk control. Summary of the Invention

[0003] In view of the problems existing in the above-mentioned prior art, the object of the present invention is to provide a method for efficiently removing perchlorate in wastewater based on quaternary ammonium salt-assisted ultrafiltration. The method has simple process, low cost, and can efficiently remove perchlorate in wastewater. In order to achieve the above object, the present invention adopts the following technical solutions: A highly efficient method for removing perchlorate from wastewater based on quaternary ammonium salt-assisted ultrafiltration comprises: adding a quaternary ammonium salt with a carbon chain length of C12–C16 into the perchlorate wastewater; the quaternary ammonium cations and the perchlorate form nanoscale flocs through hydrophobic interaction, electrostatic attraction and van der Waals forces; and then filtering through an ultrafiltration membrane to achieve highly efficient removal of perchlorate from the wastewater.

[0004] Preferably, the concentration of the quaternary ammonium salt with a carbon chain length of C12-C16 is 0.1-8.0 mM.

[0005] Preferably, the concentration of perchlorate in the perchlorate wastewater is as low as 0.02 mM.

[0006] Preferably, the quaternary ammonium salt with a carbon chain length of C12-C16 is DTAB, TTAB or CTAB. The present invention has the following beneficial effects: (1) The present invention provides a highly efficient removal method for perchlorate in wastewater based on ultrafiltration assisted by quaternary ammonium salts. The method utilizes the synergistic effect (including hydrophobic effect, electrostatic attraction and van der Waals force) between quaternary ammonium salts and perchlorate to form flocs that can be retained by ultrafiltration membranes. The flocs are then filtered through ultrafiltration membranes for solid-liquid separation, thereby achieving highly selective and efficient removal (>99%) of perchlorate in wastewater, which is significantly superior to traditional ion exchange or adsorption technologies.

[0007] (2) The method of the present invention is simple to operate and can be completed by combining a trace amount of quaternary ammonium salt with a conventional ultrafiltration process. It does not require complex equipment or regeneration processes, avoids secondary pollution caused by adsorption materials, and significantly improves environmental friendliness. At the same time, the present invention also has good resistance to anion interference, low flux attenuation (<10%), and a wide range of material sources and low cost. It is suitable for rapid integration and promotion in existing water treatment systems, and is particularly suitable for the efficient and low-cost treatment of perchlorate wastewater, showing excellent engineering application potential and environmental benefits.

[0008] (3) Compared with traditional ion exchange or adsorption processes, the present invention is easy to operate, does not require regeneration, has low operating costs, and produces no secondary waste. It has good engineering promotion potential and is particularly suitable for on-site rapid treatment and large-scale application of perchlorate wastewater. BRIEF DESCRIPTION OF THE DRAWINGS In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0009] Figure 1 The flocs formed by quaternary ammonium salts with different carbon chain lengths and perchlorate; Figure 2 The particle size results of flocs formed by quaternary ammonium salts with different carbon chain lengths and perchlorate; Figure 3 The results show the effect of the concentration of quaternary ammonium salt with a carbon chain length of C12, specifically CTAB, on the removal of perchlorate by quaternary ammonium salt-assisted ultrafiltration; Figure 4 The results show the effects of quaternary ammonium salts with different carbon chain lengths on the removal of perchlorate by quaternary ammonium salt-assisted ultrafiltration. Figure 5 The flux changes during the ultrafiltration process of perchlorate removal assisted by quaternary ammonium salts with different carbon chain lengths; Figure 6 The effect of different added substances on the removal rate of perchlorate; Figure 7 The results of membrane flux and perchlorate removal rate changes during multiple cycles are shown; Figure 8 This is the elemental characterization result of CTAB-perchlorate floccules; Figure 9 This is the infrared characterization result of CTAB-perchlorate flocs; Figure 10 The results are for the durability of the ultrafiltration membrane and the cyclic stability of the removal process; Figure 11 These are the structural formulas of several typical quaternary ammonium salts with different carbon chain lengths. DETAILED DESCRIPTION

[0010] In the following description, specific details such as particular system structures and techniques are provided for purposes of illustration, not limitation, to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0011] This invention provides a highly efficient method for removing perchlorate from wastewater using quaternary ammonium salt-assisted ultrafiltration. Its core working principle is to utilize quaternary ammonium salts (QACs) of specific carbon chain lengths (C12–C16) to synergize with perchlorate ions to form tiny (nanoscale) flocs that can be retained by ultrafiltration membranes. These flocs are then efficiently retained by the ultrafiltration membranes, achieving highly efficient removal of perchlorate from wastewater. The specific working mechanism is as follows: 1) Synergistic effect induces floc formation: When a small amount of quaternary ammonium salts with a chain length of C12–C16 are added to perchlorate wastewater, the perchlorate and quaternary ammonium cations form a stable complex through hydrophobic interactions, electrostatic attraction, and van der Waals forces. This complex exhibits a tendency to transition from repulsive to attractive interactions, inducing the spontaneous aggregation of flocs. 2) Formation of flocs that can be retained by ultrafiltration membrane: The particle size of the formed quaternary ammonium salt-perchlorate flocs is larger than the pore size of the ultrafiltration membrane and can be efficiently retained by the ultrafiltration membrane.

[0012] 3) Ultrafiltration membrane separation process: Wastewater is filtered through an ultrafiltration membrane under low pressure, trapping quaternary ammonium salt-perchlorate flocs and achieving physical removal of perchlorate. Over 99% of the perchlorate concentration in the purified wastewater is removed. This process exhibits minimal flux loss (approximately 10%) and effectively resists interference from coexisting anions. Example 1 Commercial polyvinylidene fluoride flat ultrafiltration membranes were used for the experiments. Before each use, the membranes were soaked in deionized water for 24 hours to fully pre-wet them. Subsequently, they were hydraulically compacted in the ultrafiltration apparatus for 2 hours at a pressure of 2 bar to ensure structural stability and consistent performance. During the experiments, the feed liquid was continuously stirred at a controlled speed of 500 rpm to ensure uniform mixing of the solution.

[0013] First, a predetermined concentration of quaternary ammonium salts (QACs) was added to a solution containing perchlorate (ClO4 ⁻ ) in the water sample, mix well and let it stand for 5 minutes to promote the reaction between quaternary ammonium salt and ClO4 ⁻ The filtration process was complete, allowing the flocs to form stable flocs. Subsequently, the filtrate entered the ultrafiltration module using continuous cross-flow ultrafiltration mode. The transmembrane pressure was maintained at 0.2 MPa, and the system temperature was strictly controlled at 25.0 ± 0.1°C to ensure constant experimental conditions. During the filtration process, filtrate samples were collected in batches, and the perchlorate concentration was determined using ion chromatography or other appropriate methods. The perchlorate removal efficiency was calculated based on the inlet and outlet concentrations. When studying the impact of environmental parameters on removal performance, different coexisting anions were added to the feed solution or the pH was adjusted, while other conditions remained unchanged.

[0014] 1. Study the quaternary ammonium salts with carbon chain lengths from C6 to C18 (see Figure 11 ) interacts with perchlorate to form flocs, the results are shown in Figure 1 and Figure 2 .

[0015] Depend on Figure 1 The results show that only quaternary ammonium salts with medium carbon chain lengths, specifically C12-C16 (DTAB, TTAB, CTAB), can induce significant macroscopic flocculation, producing dense white precipitates, while quaternary ammonium salt systems with shorter chain lengths (C6-C10) and ultra-long chain lengths (C18) remain transparent, with no obvious floc formation. This phenomenon reflects the balance mechanism between hydrophobic interaction and ion migration: longer carbon chains enhance hydrophobic interaction and promote aggregation, while shorter carbon chains increase ion migration rate but lack hydrophobicity. For common anions (NO3 - BrO3 - Br - 、SO4 2- 、ClO3 - 、HCO3 - 、Cl - PO4 2- The selectivity test of the above common anions showed that they neither induced floc formation nor inhibited the formation of quaternary ammonium salt-perchlorate flocs, but showed a strong affinity for ClO4 ⁻ High affinity and aggregation selectivity.

[0016] like Figure 2As shown, dynamic light scattering (DLS) analysis further verified that the quaternary ammonium salt solution with a carbon chain length of C6 to C18 did not form aggregates, but when ClO4 was added to the quaternary ammonium salt solution, ⁻ Afterwards, DTAB, TTAB, and CTAB quickly generated size-stable flocs within 1 minute, with average hydrodynamic diameters of 262 nm, 274 nm, and 298 nm, respectively, and a concentrated size distribution. This indicates that the floc particle size is uniform and the ultrafiltration membrane pore size (about 80 nm) is much smaller than the floc size, indicating good retention potential.

[0017] 2. Study the effect of different concentrations of quaternary ammonium salts with carbon chain lengths of C6-C18 on the removal of perchlorate by ultrafiltration (1) Using quaternary ammonium salts of different carbon chain lengths at different concentrations (0.1-8.0 mM) to assist ultrafiltration treatment of perchlorate wastewater (concentration of 0.1 mM), the results are shown in Figure 3 . Depend on Figure 3 As shown in the results of A, only quaternary ammonium salts with carbon chain lengths of C12-C16 can achieve significant ClO4 removal with the assistance of ultrafiltration. ⁻ Removal effect. Specifically, the ClO4 corresponding to 0.1 mM quaternary ammonium salts of different carbon chain lengths ⁻ The removal rates were 11% for DTAB, 25% for TTAB, and 37% for CTAB. The removal rate of perchlorate increased significantly with the increase of quaternary ammonium salt concentration. When the CTAB concentration exceeded 4.0 mM, the removal rate was close to 100%. This removal effect was achieved when the quaternary ammonium salt concentration was lower than its critical micelle concentration (CMC) (see Figure 3 This can also be achieved when B) in the figure is used, breaking the limitation of traditional membrane electrocoagulation (MEUF) that requires exceeding CMC.

[0018] (2) 1 mM was selected as the operating concentration of quaternary ammonium salts with different carbon chain lengths to test the removal effect of perchlorate at different concentrations (0.02-0.3 mM). The results are shown in Figure 4 .

[0019] Depend on Figure 4 The results show that low concentration ClO4 ⁻ Can be completely removed by treating 0.1 mM ClO4 with 1 mM quaternary ammonium salt ⁻ The removal rates were 51% for DTAB, 62% for TTAB, and 79% for CTAB. In the blank control experiment, the quaternary ammonium salt was first filtered through the membrane without reacting with ClO4 ⁻ When mixed, no removal effect was observed, further confirming that floc pre-formation is the key to efficient separation. 3. Study the flux changes in the ultrafiltration process of perchlorate removal assisted by quaternary ammonium salts with different carbon chain lengths Depend on Figure 5The results showed that the ultrafiltration process showed excellent water flux stability, the flux attenuation was less than 15% after 200 minutes of continuous ultrafiltration operation, and the addition of quaternary ammonium salt effectively slowed down the decline in membrane fouling flux.

[0020] 4. Competition experiment: Study the effect of different added substances (NO3 - BrO3 - Br - 、SO4 2- 、ClO3 - 、HCO3 - 、Cl - PO4 2- ) on the removal rate of perchlorate Depend on Figure 6 The results show that even if the concentration of other anions is ClO4 ⁻ 10 times of that, it will not affect ClO4 ⁻ The removal efficiency reflects the high selectivity and anti-interference ability of the method of the present invention.

[0021] 5. Actual wastewater treatment The results of using CTAB-assisted ultrafiltration to treat fireworks manufacturing wastewater are shown in Figure 7 .

[0022] Depend on Figure 7 The results show that within 60 minutes, ClO4 ⁻ The removal rate reached 99%, and the flux only dropped by about 10%; the multi-cycle test showed that after 6 consecutive filtrations of ClO4 ⁻ The removal rate is maintained above 85%, 6. Analysis of ultrafiltration membrane surface morphology and AFM CTAB-perchlorate flocs (CTAB–ClO4 ⁻ flocs) were characterized by Figure 8 The EDS element mapping diagram shows that nitrogen (N), oxygen (O) and chlorine (Cl) elements are evenly distributed in the flocs, confirming the interaction between CTAB and perchlorate (ClO4 ⁻ ) uniformity in the formed flocs.

[0023] Depend on Figure 9 Mid-infrared spectroscopy (FT-IR) showed that CTAB–ClO4 ⁻ The flocs retain CTAB and ClO4 ⁻ The characteristic absorption peak of the original material was not found, and no new absorption peak appeared, indicating that the floc formation was mainly due to physical action rather than the formation of new chemical bonds.

[0024] 7. Reusability of ultrafiltration membrane and cyclic stability of removal process The reusability of the membrane was verified by multiple filtration cycles. After each filtration cycle, the membrane surface was rinsed with deionized water for 2 minutes to remove residual flocs and restore membrane flux and performance.

[0025] Depend on Figure 10 The results showed that the surface roughness of the ultrafiltration membrane could be restored to its original state by cleaning, which verified the excellent reusability of the ultrafiltration membrane and the cyclic stability of the removal process. In summary, this study reveals the mechanism by which quaternary ammonium salt alkyl chain length influences perchlorate floc formation, demonstrating that medium-chain quaternary ammonium salts rapidly form stable flocs far exceeding the membrane pore size through hydrophobic and ionic interactions, significantly improving ultrafiltration retention efficiency. This collaborative process is simple to operate, highly selective, and significantly inhibits membrane fouling, demonstrating potential for industrial application.

[0026] The present invention is not limited to the above-mentioned specific implementation methods. Various changes made by ordinary technicians in this field based on the above-mentioned concept without creative work are all within the scope of protection of the present invention.

Claims

1. A method for efficiently removing perchlorate from wastewater by ultrafiltration assisted by quaternary ammonium salts, characterized in that: include: Quaternary ammonium salts with a carbon chain length of C12–C16 are added to perchlorate wastewater. The quaternary ammonium cations and perchlorate form nanoscale flocs through hydrophobic interaction, electrostatic attraction and van der Waals forces, and then filtered through an ultrafiltration membrane to achieve efficient removal of perchlorate in the wastewater.

2. A method for efficiently removing perchlorate in wastewater assisted by quaternary ammonium salt ultrafiltration according to claim 1, characterized in that: The concentration of the quaternary ammonium salt solution with a carbon chain length of C12-C16 is 0.1-8.0 mM.

3. A method for efficiently removing perchlorate in wastewater assisted by quaternary ammonium salts according to claim 1, characterized in that: The perchlorate concentration in the wastewater was as low as 0.02 mM.

4. A method for efficiently removing perchlorate in wastewater based on quaternary ammonium salt-assisted ultrafiltration according to claim 1, characterized in that: The quaternary ammonium salt with a carbon chain length of C12-C16 is DTAB, TTAB or CTAB.

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