Process and method for removing DOM in initial rainwater

Abstract

The invention belongs to the technical field of water treatment, discloses a process and a method for removing DOM in initial rainwater, and aims to solve the problems that DOM components in runoff rainwater are complex, the removal rate of a traditional process is low, membrane pollution is easily caused, a powder catalyst is difficult to recover and the like. The method comprises the following steps: introducing rainwater into a reactor with a ceramic membrane, and directly adding free-state GAC, CuO and PS; static circulation is firstly carried out at a high shear rotating speed, and GAC and CuO are used for synergistically activating PS to generate a large number of free radicals for in-situ degradation of DOM; and then solid-liquid separation is carried out through suction of a ceramic membrane. Efficient removal of DOM in initial rainwater and membrane pollution control are realized. Under the optimal working condition operation, the total organic carbon (TOC) removal rate can reach 83% or above. The process is simple, operation is stable, the catalyst can be recycled, and the method is suitable for efficient resource utilization of rainwater and has good engineering practical application potential.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, specifically to a method and application for the efficient removal of dissolved organic matter (DOM) from rainwater based on CuO synergistic GAC activation of PS advanced oxidation and coupling with a ceramic membrane. Background Technology

[0002] Due to rapid socio-economic development, industrial and agricultural progress, and the excessive use of waste gas, wastewater, pesticides, and fertilizers, rainwater contains more pollutants. Furthermore, rainwater runoff carries heavy metals, organic matter, nitrogen, phosphorus, and other pollutants, resulting in a complex composition of pollutants in rainwater. This runoff carrying large amounts of unknown pollutants can enter receiving water bodies through stormwater pipes, continuously increasing the types and concentrations of dissolved organic matter (DOM) in natural water bodies, posing a serious threat to the ecological and public health safety of urban communities. However, traditional treatment methods, such as coagulation, flocculation, and microbial degradation, are difficult to effectively remove DOM and easily generate disinfection byproducts (DBPs) with carcinogenic, mutagenic, and teratogenic effects, potentially causing reclaimed water safety issues during rainwater reuse. The GAC / CuO / PS advanced oxidation coupled ceramic membrane technology proposed in this invention can not only remove DOM from rainwater simply and efficiently but also features stable operation, recyclable catalyst, and effective control of membrane fouling.

[0003] Activated carbon, with its large specific surface area and abundant polar functional groups, is a superior adsorbent material widely used for adsorbing pollutants in water, such as heavy metals, ammonia nitrogen, and DOM (determining organic matter). However, previous studies have focused primarily on the application of activated carbon in removing pollutants from wastewater and sludge, with limited research on its use in removing DOM from rainwater. Yet, one of the main reasons for the black and odorous condition of rivers in my country during rainy weather is that rainwater carries large amounts of DOM into water bodies through runoff, causing water environment damage.

[0004] Advanced oxidation processes based on persulfate radicals (SR-AOPs) have become a research hotspot in the field of water treatment due to their high adaptability and effectiveness in disinfection and removal of water pollutants. Current research mainly focuses on enhancing the oxidizing capacity of persulfate to remove pollutants by preparing synthetic and supported metal materials. However, the preparation of these materials is complex and difficult to apply on a large scale for large-volume rainwater treatment. Furthermore, there is limited research on the combined use of activated carbon and metal oxides to activate persulfate for rainwater treatment. Therefore, this invention proposes directly adding GAC and CuO to activate PS, achieving a simple and efficient removal of DOM from rainwater.

[0005] To address the aforementioned problems, this invention combines activated carbon adsorption and advanced persulfate oxidation processes to remove naturally dissolved organic matter (DOM) from actual rainwater. This system utilizes CuO to synergistically activate persulfate with activated carbon, followed by coupled ceramic membrane filtration. This achieves efficient DOM removal from rainwater while simultaneously recovering the CuO catalyst through membrane filtration for repeated use, thereby reducing economic costs. This provides a theoretical basis and practical guidance for the practical application of this technology. Summary of the Invention

[0006] To address the problems in the background technology, this invention provides a combined process technology for efficiently removing DOM from rainwater. This invention uses CuO synergistically with granular activated carbon (GAC) to activate persulfate (PS) and couples it with ceramic membrane filtration (CM). Unlike the static solidification loading of conventional composite catalysts, this invention directly adds free GAC and CuO, forming a dynamic advanced oxidation system coupled with a ceramic membrane under a high shear force flow field, resulting in significant DOM removal efficiency in initial rainwater runoff. Simultaneously, this invention explores the optimal dosage of GAC, CuO, and PS and optimizes the operating system of the GAC / CuO / PS coupled ceramic membrane. The effects of different operating times on UV radiation in rainwater were measured. 254 and TOC removal rate.

[0007] This invention is achieved through the following technical solution, specifically including the following steps:

[0008] (1) Pump the rainwater to be treated into the reactor equipped with a flat ceramic membrane, and add granular activated carbon (GAC) and copper oxide (CuO) powder; turn on the electric stirrer in the reactor to a high shear speed (e.g., 800~1000 rpm) to fully mix GAC and CuO in the rainwater. After mixing for 2~5 minutes, add persulfate (PS) to the reactor while maintaining the above high shear stirring state, keep the outlet valve closed, and the system is in static circulation mode (the water produced by the suction pump is completely returned to the reactor) for 10~30 minutes. During this period, under the dynamic synergy of GAC and CuO, DOM in the rainwater is degraded in situ; where GAC is 10~100 mg / L, CuO is 10~100 mg / L, and PS is 100~1000 mg / L.

[0009] (2) After completing the static cycle, switch to dynamic operation. Turn on the peristaltic pump connected to the flat ceramic membrane to perform solid-liquid separation; the effluent is discharged into the product water tank, while GAC, CuO and macromolecular pollutants are completely retained in the reactor, realizing the recovery, enrichment and recycling of the catalyst. The peristaltic pump (suction pump) adopts an intermittent operation mode, with an operation cycle of 8 minutes of suction and 2 minutes of rest, and a flow rate of 10-100 LMH.

[0010] Furthermore, the flat ceramic membrane is made of Al2O3 with an average pore size of 0.1 μm and a filtration flux of 10~100 LMH.

[0011] Furthermore, the system has two operating modes that can be switched: Static circulation mode: the system outlet valve is closed, and the water produced by the suction pump is fully returned to the reactor for the purpose of thorough mixing of materials and establishment of an environment for catalyst activation in the early stage;

[0012] Dynamic operating conditions: The inlet pump continuously replenishes raw water, and the suction pump extracts clean water to the product water tank to achieve continuous flow filtration treatment.

[0013] Furthermore, the treatment target is initial roof or road runoff rainwater with an initial total organic carbon (TOC) content of 5-30 mg / L.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] 1. In this invention, under high-speed stirring, free GAC particles form a microfluidic bed. The high-speed movement of the particles produces a mechanical scrubbing effect on the ceramic membrane surface. At the same time, the strong oxidizing free radicals generated by CuO / PS effectively degrade the attached sticky DOM macromolecules, destroy the basis for the formation of the gel layer, and slow down the rise rate of transmembrane pressure difference (TMP).

[0016] 2. This invention directly adds GAC, CuO and PS, which not only greatly reduces costs compared to synthetic and supported materials, but also facilitates large-scale practical rainwater treatment. Furthermore, through the synergistic effect of adsorption and advanced oxidation, it improves the removal rate of DOM. CuO and GAC form a synergistic activation system, which enhances the utilization efficiency of PS. Finally, ceramic membrane filtration is used to achieve catalyst recovery and pollutant retention. Attached Figure Description

[0017] The invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 This is a schematic diagram of the apparatus for the GAC / CuO / PS pre-oxidation enhanced ceramic membrane filtration process of the present invention.

[0019] Figure 2 To compare the effects of different combined processes on UV radiation in rainwater at the dosage levels described in Example 4. 254 ( Figure 2 a) and TOC ( Figure 2 b) shows the removal effect.

[0020] Figure 3 The images show the XRD patterns of GAC and CuO before and after the reaction in the GAC / CuO / PS system in Example 4.

[0021] Figure 4The image shows XPS plots of Cu 2p before and after the reaction in the GAC / CuO / PS system in Example 4.

[0022] Figure 5 The images show EPR radical detection diagrams in different systems in Example 4; where (a) is a full spectrum comparison diagram and (b) is a diagram showing local characteristic peaks and radical attribution. Detailed Implementation

[0023] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention and provide detailed implementation methods, but the scope of protection of the present invention is not limited to the following embodiments.

[0024] Example 1

[0025] Take 15 L of initial runoff rainwater with an initial TOC concentration of approximately 10 mg / L and enter Figure 1 In the reactor shown, 60 mg / L GAC and 30 mg / L CuO were added, and the mixture was stirred at a high shear speed (1000 rpm) until homogeneous. After mixing for 3 minutes, 300 mg / L PS was added, and static circulation (effluent recirculation) was performed for 30 minutes at a high shear speed (1000 rpm). Subsequently, a peristaltic pump was started (vacuuming for 8 minutes, pausing for 2 minutes). After the operation was completed, a 15 ml sample was taken, and the TOC removal rate was measured to be 57.54%.

[0026] Example 2

[0027] Take 15 L of initial runoff from the same source, add 90 mg / L GAC, 50 mg / L CuO and 700 mg / L PS, turn on the high shear stirring speed (1000 rpm), and operate according to the same integrated system operation steps as in Example 1. Take 15 ml of sample and the TOC removal rate is 66.27%.

[0028] Example 3

[0029] Take 15 L of initial runoff from the same source, add 30 mg / L GAC, 70 mg / L CuO and 500 mg / L PS, turn on the high shear stirring speed (1000 rpm), and operate the integrated system according to the same operating steps as in Example 1. Take 15 ml of sample and the TOC removal rate is 45.04%.

[0030] Example 4

[0031] Take 15 L of initial runoff from the same source, add 60 mg / L GAC, 50 mg / L CuO and 500 mg / L PS, turn on the high shear stirring speed (1000 rpm), and operate according to the same integrated system operation steps as in Example 1. Take 15 ml of sample and the TOC removal rate is 83.87%.

[0032] Under the operating conditions of Example 4, the transmembrane pressure difference (TMP) was recorded in real time using a pressure sensor. The records showed that the initial TMP of the system was 5.2 kPa, and after 10 hours of continuous operation, the TMP only slowly increased to 11.5 kPa, indicating a low membrane fouling rate and excellent permeability stability and antifouling ability.

[0033] Comparative Example 1

[0034] 15 L of initial runoff from the same source was collected, and only 60 mg / L of GAC was added (without CuO and PS). The system was operated at a high shear stirring speed (1000 rpm) following the same integrated system operation procedure as in Example 1. A 15 ml sample was taken, and the TOC removal rate was measured to be only 34.3%. After continuous operation for 8 hours, the TMP rose to 26.8 kPa.

[0035] Comparative Example 2

[0036] Take 15 L of initial runoff from the same source, add 60 mg / L of GAC and 500 mg / L of PS, turn on the high shear stirring speed (1000 rpm), and operate according to the same integrated system operation steps as in Example 1. Take 15 ml of sample and the TOC removal rate is only 49.95%.

[0037] Comparative Example 3

[0038] Take 15 L of initial runoff from the same source, add 50 mg / L of CuO powder and 500 mg / L of PS (without GAC), and operate according to the same integrated system operation procedure as in Example 1. After the operation, take 15 mL of sample, and the TOC removal rate is only 41.25%.

[0039] Comparative Example 4

[0040] Take 15 L of initial runoff from the same source, add 60 mg / L GAC and 50 mg / L CuO (without PS), and operate according to the same integrated system operation procedure as in Example 1. After the dynamic operation is completed, take 15 mL of sample, and the TOC removal rate is only 38.60%.

[0041] Comparative Example 5

[0042] 15 L of initial runoff from the same source was collected, and the dosage of the reagents was exactly the same as in Example 4 (60 mg / L GAC, 50 mg / L CuO, 500 mg / L PS), but the speed of the electric stirrer was reduced from high shear speed (800 rpm) to low speed (200 rpm). At this speed, the operation record showed that after 10 hours of continuous operation, due to the lack of mechanical scrubbing by GAC, a partially oxidized DOM gel layer rapidly accumulated on the membrane surface, and the TMP increased from the initial 5.2 kPa to 28.6 kPa. At the same time, the TOC removal rate was measured to be 64.15%.

[0043] Comparative Example 6

[0044] 15 L of initial runoff from the same source was collected, and only 50 mg / L CuO powder and 500 mg / L PS (without GAC) were added. The membrane was run at the same high-shear stirring speed (800 rpm) as in Example 4. The operation record showed that the TMP rose to 30.5 kPa in less than 6 hours, causing severe membrane fouling. The TOC removal rate was measured to be only 42.80%.

[0045] Figure 1 The diagram shows the operating device of this technology, which mainly includes: an inlet tank, a reactor (with a built-in electric stirrer and a flat ceramic membrane), a peristaltic pump (used for inlet and outlet water suction respectively), a pressure sensor (monitoring TMP), and a paperless recorder.

[0046] Figure 2 Using GAC-CM and GAC / PS-CM as control systems, the TOC and UV values ​​were measured within 5 hours of operation for this technology. 254 Comparison of removal results. (By...) Figure 2 (a) and (b) show that under the three pretreatment systems, the UV in rainwater... 254 Both the TOC value and the TOC value showed a significant decrease in the first 30 minutes of the static cycle, and maintained a slow, fluctuating downward trend in subsequent runs.

[0047] Specifically, UV 254 The removal effects were as follows: UV removal efficiency within 1 hour under GAC / CuO / PS-CM treatment. 254 The value is from 0.939 cm. -1 Decreased to 0.326 cm -1 It maintained a slow downward trend, with a value of 0.204 cm at the end of the 5-hour run. -1 The removal rate was 78.27%; UV radiation within 1 hour under GAC / PS-CM treatment. 254 Values ​​from 0.998 cm -1 Decreased to 0.528 cm -1After 2 hours, a fluctuating downward trend emerged, and the value was 0.51 cm at the end of the 5th hour. -1 The removal rate was 48.9%; UV radiation within 1 hour under GAC-CM treatment. 254 Value from 1.135 cm -1 It decreased to 0.772 cm. -1 After 1.5 hours, a fluctuating downward trend emerged, and the value reached 0.736 cm at the end of the 5th hour. -1 The removal rate was 32%. TOC removal rate and UV... 254 Maintaining a similar trend, the difference lies in the larger fluctuations in TOC values ​​during the later stages of static cycling in both the GAC / CuO / PS-CM and GAC / PS-CM systems. This may be because the addition of PS generates intermediate products during DOM degradation, which accumulate in the water under static cycling, leading to greater TOC fluctuations. Among the three systems, the GAC / CuO / PS-CM treatment showed the highest TOC removal rate (83.35%), decreasing from 9.79 mg / L to 1.63 mg / L after 30 minutes, compared to the optimal removal rate of 56.7% in the GAC / PS-CM system. This represents a significant improvement of 26.65%, indicating that the addition of CuO, under the combined activation of GAC and CuO, can more effectively promote the generation of more active species by PS to degrade organic matter. Overall, the three pretreatment coupled ceramic membranes showed significant improvement in the removal of UV radiation from rainwater. 254 In terms of TOC removal effectiveness, GAC / CuO / PS-CM > GAC / PS-CM > GAC-CM.

[0048] Figure 3 The images show the XRD patterns of GAC and CuO before and after the reaction in the GAC / CuO / PS system in Example 4. Figure 3 It can be seen that the broad peak of GAC is weak near 2θ=26°, and the broad peak of GAC becomes weaker after the reaction. This may be because the functional groups on the surface of GAC participate in the reaction and the signal is masked by the adsorption of organic matter by GAC itself. Sharp peaks are visible at 2θ=35.5° and 38.7°, which are the strongest characteristic peaks of CuO. This indicates that the CuO crystal structure is intact before the reaction, while the peak intensity decreases significantly after the reaction, indicating that CuO is consumed during the reaction. PS is activated through the valence state transformation from Cu(II) to Cu(I). This suggests that during the reaction, GAC acts as an adsorbent to adsorb organic matter, enhances the dispersibility of CuO, and provides an electron transfer pathway. Meanwhile, Cu in CuO... 2+ Reduced to Cu + The two work synergistically to efficiently activate PS and generate more ·OH and SO4. ·- This significantly improves the removal of DOM from rainwater.

[0049] Figure 4 The image shows XPS plots of Cu 2p before and after the reaction in the GAC / CuO / PS system in Example 4. Figure 4 The high-resolution XPS images of Cu 2p from the unreacted mixture show a clear Cu 2p peak at 934.5–935.5 eV. 3 / 2 The main peak, with typical satellite peaks appearing in the 940–945 eV range, indicates that copper on the sample surface is mainly in the form of Cu. 2+ The presence of this morphology is a characteristic signal of CuO, indicating that high-valence copper predominates in the system before the reaction. However, after the PS activation reaction, Figure 4 (a) The Cu 2p spectrum underwent significant changes: Cu 2+ The main peak intensity decreased significantly, and the satellite peaks in the 940–945 eV region weakened considerably, while the Cu in the low binding energy region (~932.5 eV) showed a more pronounced decrease. + The peak intensity increased significantly. These changes indicate that some Cu... 2+ Reduced to Cu + Cu undergoes a reversible Cu transition during the activation of PS. 2+ / Cu + Redox cycle, in which Cu + It can act as an active site to promote the activation of PS to generate SO4. ·- The generated Cu²⁺ can be converted back into Cu under the action of the activated carbon conductive network, and contains reactive oxygen species such as ·OH. + This process maintains the continuous catalytic activity of the system. This valence state cycle is an important mechanistic basis for the efficient activation of PS and the removal of DOM in the GAC / CuO / PS system.

[0050] Figure 5 To detect EPR radicals in different systems in Example 4, the types of active free radicals in the GAC / PS and GAC / CuO / PS systems were identified using electron paramagnetic resonance (EPR) with DMPO as a trapping agent. Figure 5 It can be seen that O2 exists in both systems. - ·OH and SO4 ·- The figure shows that the peak intensities of the three free radicals in the GAC / CuO / PS system are significantly higher than those in the GAC / PS system. This indicates that compared to adding GAC alone, the addition of CuO can more efficiently activate PS to generate more free radicals, thereby enhancing oxidation activity and achieving the best DOM removal effect.

[0051] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A process for removing DOM from rainwater using a GAC / CuO / PS coupled ceramic membrane, characterized in that, Includes the following steps: (1) The rainwater to be treated is introduced into the reactor containing the ceramic membrane, and granular activated carbon (GAC) and copper oxide (CuO) powder are added into the reactor. High shear stirring is turned on to make the GAC and CuO fully mixed in the rainwater. (2) Under the condition of continuous high shear stirring, persulfate (PS) is added to the reactor. Under the action of GAC and CuO, the PS is activated to generate free radicals, which are used to oxidize and degrade the dissolved organic matter in the rainwater in situ. (3) Turn on the suction pump connected to the ceramic membrane to perform solid-liquid separation, and discharge the effluent into the product water tank. The GAC, CuO and incompletely degraded macromolecular pollutants are retained in the reactor by the ceramic membrane, realizing the in-situ enrichment and recycling of the catalyst.

2. The process for removing DOM from rainwater using a GAC / CuO / PS coupled ceramic membrane according to claim 1, characterized in that, The dosage of GAC is 10~100 mg / L, the dosage of CuO is 10~100 mg / L, and the dosage of PS is 100~1000 mg / L.

3. The process for removing DOM from rainwater using a GAC / CuO / PS coupled ceramic membrane according to claim 1, characterized in that, In step (1), the speed of the high shear speed stirring is set to 800~1000 rpm.

4. The process for removing DOM from rainwater using a GAC / CuO / PS coupled ceramic membrane according to claim 1, characterized in that, The operation process of steps (1) to (3) is divided into two stages: static loop and dynamic operation. Premixing and static circulation stage: After adding the reagent, close the system outlet valve and return all the water produced by the suction pump to the reactor for 10-30 minutes; Dynamic operation and membrane filtration stage: After the static circulation is completed, the inlet pump continuously replenishes the raw water, and the suction pump extracts the purified water and discharges it to the product water tank for continuous flow filtration treatment.

5. The process for removing DOM from rainwater using a GAC / CuO / PS coupled ceramic membrane according to claim 1, characterized in that: In step (3), the suction pump adopts an intermittent operation mode with an operation cycle of 8 minutes of suction and 2 minutes of rest, and the membrane flux operation range is 10~100 LMH.

6. The process for removing DOM from rainwater using a GAC / CuO / PS coupled ceramic membrane according to claim 1, characterized in that: The ceramic membrane is made of Al2O3 material with an average pore size of 0.1 μm.

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