Coagulation sedimentation method

Abstract

This invention discloses a coagulation and sedimentation method, belonging to the field of water treatment technology. The technical solution includes a coagulation and sedimentation step, a PAM residue capture step following the coagulation and sedimentation step, and a manganese sand filtration step following the PAM residue capture step. The PAM residue capture step includes: using polyferric sulfate as a reactant to capture PAM residue, and controlling the iron ion concentration in the permeate after the capture reaction to be 0.05-0.15 mg / L. The manganese sand filtration step includes: inputting the permeate after the capture reaction into a filtration unit containing manganese sand filter media for filtration to remove iron ions from the permeate after the capture reaction. This invention, applied to coagulation and sedimentation, solves the problem that existing coagulation and sedimentation methods cannot balance coagulation effect and membrane fouling caused by PAM residue. It can effectively remove low-residual PAM in the coagulation and sedimentation process, thus ensuring coagulation effect while effectively preventing membrane fouling caused by the accumulation of low-residual PAM.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, and particularly relates to a coagulation and sedimentation method. Background Technology

[0002] Coagulation and sedimentation technology is widely used in water treatment systems. By adding coagulants and flocculants (such as polyacrylamide, also known as PAM), pollutants in the raw water are polymerized and precipitated. The combination of these two agents greatly improves water treatment efficiency. However, PAM is a linear high-molecular-weight polymer with a molecular weight of up to 20 million. Its residual viscous gel-like substance severely affects the lifespan of reverse osmosis membranes, and once clogged, it cannot be restored. Therefore, PAM is avoided as much as possible in reverse osmosis systems, or its level is controlled at extremely low levels. However, PAM can make the reaction faster and more effective; a lack of PAM will significantly reduce the coagulation effect. Therefore, traditional coagulation and sedimentation processes often adopt a three-stage process of "coagulant → PAM → sedimentation." However, this process has the following technical problems: Uncontrollable PAM residue: In conventional processes, PAM cannot be effectively monitored, and the dosage must be strictly limited (≤0.2 ppm) to reduce the risk of contamination. However, due to fluctuations in water quality, the actual residue can reach 0.1-0.2 ppm, which can easily lead to reverse osmosis membrane fouling. At the same time, because the dosage is strictly controlled, insufficient PAM dosage in heavily polluted water can lead to incomplete flocculation and sedimentation. Contamination chain transmission: Traditional process contamination control involves the transmission of contamination from PAM to colloidal contamination to membrane damage; Detection blind spot: There are currently no commercially available online PAM detection instruments; Low level of intelligence: the dosage of chemicals depends on manual experience for adjustment, the response delay is >4 hours, and it cannot adapt to dynamic changes in the influent water quality. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is that the existing coagulation and sedimentation methods cannot balance the coagulation effect and the membrane fouling caused by PAM residue. The present invention proposes a coagulation and sedimentation method that can effectively remove low residual PAM in the coagulation and sedimentation process, thus ensuring the coagulation effect and effectively preventing membrane fouling caused by the accumulation of low residual PAM.

[0004] To solve the aforementioned technical problem, the technical solution adopted by the present invention is as follows: The present invention provides a coagulation sedimentation method, including a coagulation sedimentation step, a PAM residue collection step performed after the coagulation sedimentation step, and a manganese sand filtration step performed after the PAM residue collection step. The PAM residue collection step includes: using polyferric sulfate as a reactant, the Fe³⁺ produced by the hydrolysis of the polyferric sulfate +It binds to the amide groups of PAM through electro-adsorption, thereby capturing PAM residues, and controls the iron ion concentration in the product water after the capture reaction to be 0.05-0.15 mg / L. The manganese sand filtration step includes: inputting the permeate after the capture reaction into a filtration unit containing manganese sand filter media for filtration to remove iron ions from the permeate after the capture reaction.

[0005] Preferably, the permeate after the capture reaction is fed into a filter unit containing manganese sand filter media at a filtration rate of 8-12 m / h to remove iron ions from the permeate after the capture reaction.

[0006] Preferably, the determination of the dosage of polyferric sulfate in the PAM residue collection step includes: using the dosage n of PAM in the coagulation and precipitation step as a benchmark, determining the dosage range of polyferric sulfate as m through a beaker experiment. min -m max The initial dosage m of the polyferric sulfate is close to m min But greater than m min .

[0007] Preferably, the initial dosage of the polyferric sulfate is m = 1.2·m min .

[0008] Preferably, determining the dosage of polyferric sulfate in the PAM residue capture step further includes: dynamically controlling the dosage of polyferric sulfate based on the iron ion concentration in the product water after the capture reaction. When the concentration of iron ions in the product water after the trapping reaction is <0.05 mg / L, the dosage of polyferric sulfate should be increased. When the concentration of iron ions in the product water after the trapping reaction is >0.15 mg / L, reduce the dosage of the polyferric sulfate.

[0009] Preferably, the Fe³⁺ produced by the hydrolysis of the polyferric sulfate + It binds to the amide groups of PAM through electro-adsorption to form a precipitable polymer with a particle size ≥50 μm, thereby completing the capture of PAM residues.

[0010] Preferably, the coagulation and sedimentation step includes: first adding FeCl3 to react and generate Fe(OH)3 colloid; then adding PAM, and forming large-particle flocs after mechanical stirring, and controlling the turbidity of the effluent to ≤10 NTU after sedimentation.

[0011] Preferably, the concentration of FeCl3 is 10-20%; the concentration of PAM is 0.1-0.5 mg / L; and the mechanical stirring speed is 50-100 rpm.

[0012] Preferably, the molar ratio of the amount of polyferric sulfate added to the amount of PAM added is 3:1-5:1.

[0013] Preferably, the manganese sand filtration step is carried out in a manganese sand filter, wherein the surface filter media of the manganese sand filter is light anthracite, and the bottom filter media is manganese sand.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a coagulation and sedimentation method that adds a PAM capture reaction step after the traditional coagulation and sedimentation step. Residual PAM is captured by adding polyferric sulfate (PFS). Simultaneously, by controlling the iron ion concentration in the treated water after the capture reaction to 0.05-0.15 mg / L, the PAM removal rate is guaranteed, transforming the "uncontrollable" PAM residue of traditional processes into "near-zero." An indirect monitoring mechanism based on iron ion concentration feedback is established, overcoming the technical bottleneck of PAM's inability to be detected online. The residual amount is reduced from being unmonitorable in traditional processes to ≤0.01 mg / L. Furthermore, a manganese sand filtration step ensures the simultaneous removal of the newly added PFS residue, eliminating the risk of secondary pollution. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a coagulation and sedimentation device for a coagulation and sedimentation method provided in an embodiment of the present invention; In the above diagrams: 1. Coagulation sedimentation tank; 2. Residual reaction tank; 3. Manganese sand filter. Detailed Implementation

[0016] The technical solutions in specific embodiments of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are merely some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0017] This invention provides a coagulation and sedimentation method, including a coagulation and sedimentation step, a PAM residue collection step following the coagulation and sedimentation step, and a manganese sand filtration step following the PAM residue collection step. This coagulation and sedimentation method adds a PAM collection reaction step after the conventional coagulation and sedimentation step, collecting residual PAM by adding polyferric sulfate (PFS), wherein the polyferric sulfate contains Fe2(OH) n (SO4)3 n / 2 PFS, abbreviated as PFS, refers to Fe produced by hydrolysis. 3+The PFS rapidly combines with the amide groups of PAM through electro-adsorption to form a precipitable polymer with a particle size ≥50μm. The reaction efficiency is more than 3 times higher than that of traditional methods. After the PFS and PAM react to form a polymeric precipitate, it is intercepted by inclined plate sedimentation, thereby removing PAM. The water with residual PAM after treatment enters the manganese sand filter. After entering the manganese sand filter, the filter unit removes trace residual suspended solids and adsorbs residual iron ions, thus achieving the adsorption of residual iron ions.

[0018] The PAM residue collection step includes: using polyferric sulfate as a reactant, and hydrolyzing the polyferric sulfate to produce Fe... 3+ The amide groups of PAM bind to the PAM residue via electro-adsorption, thus capturing the residue and controlling the iron ion concentration in the post-capture water to be 0.05-0.15 mg / L. By controlling the iron ion concentration in the post-capture water to 0.05-0.15 mg / L, the removal rate of PAM is guaranteed, transforming the PAM residue from "uncontrollable" in traditional processes to "near zero." An indirect monitoring mechanism based on iron ion concentration feedback is established, overcoming the technical bottleneck of PAM's inability to be detected online, and reducing the residue level from unmonitorable in traditional processes to ≤0.01 mg / L. In a preferred embodiment, Fe³⁺ produced by the hydrolysis of polyferric sulfate... + It binds to the amide groups of PAM through electro-adsorption to form a precipitable polymer with a particle size ≥50 μm, thereby completing the capture of PAM residues.

[0019] The iron ion concentration in the product water after the above-mentioned capture reaction is detected by an online iron ion detector to monitor the residual iron ion level in real time and control the dosage of the PFS dosing pump to ensure that the residual iron ion level is within a certain range, thus ensuring complete removal by PAM without leaving excessively high levels of iron ions.

[0020] The manganese sand filtration process includes: inputting the permeate after the trapping reaction into a filtration unit containing manganese sand media for filtration to remove iron ions from the permeate. In a preferred embodiment, the permeate after the trapping reaction is input into the filtration unit containing manganese sand media at a filtration rate of 8-12 m / h to remove iron ions from the permeate. The permeate from the manganese sand filter will no longer contain PAM and PFS, perfectly solving the potential secondary pollution risks brought about by PAM residue and the introduction of new agents, forming a self-blocking pollution mechanism. Natural manganese sand media is selected for its effectiveness against Fe³⁺. + The adsorption capacity is ≥15 mg / g. Simultaneously, by controlling the filtration speed at 8-12 m / h, the residual PFS removal rate is ensured to be ≥95%. An online iron ion detector is installed at the filter outlet to monitor the final product water iron ion content in real time, ensuring it remains below the set value and that newly added reagents during the PAM residue collection process do not cause secondary pollution to the system.

[0021] In a preferred embodiment, determining the dosage of polyferric sulfate in the PAM residue collection step includes: using the dosage n of PAM in the coagulation and precipitation step as a baseline, determining the dosage range of polyferric sulfate as m through beaker experiments. min -m max The initial dosage m of polyferric sulfate approaches m min But greater than m min In a preferred embodiment, the initial dosage of polyferric sulfate is m = 1.2·m min .

[0022] Regarding the determination of the dosage of polyferric sulfate (PFS) in the above-mentioned PAM residue collection step, it should be noted that, to ensure the removal effect of PAM, a slight excess of PFS will be added. This PFS dosage is intelligently controlled by an online iron ion detector installed at the outlet of PAM residue reaction tank 2. The permeate carrying the slight excess of PFS enters the filter bed, where it filters out the polymers of PAM and PFS. Excess PFS (containing iron ions) in the water will also be removed by the iron ion adsorption properties of the manganese sand filter media, thus producing qualified permeate.

[0023] Furthermore, since PFS and PAM do not react directly but form precipitates through polymerization, the reaction ratio between these two substances is not constant, which is a challenge in controlling PAM residue. At the same time, because the types of suspended solids in the water do not change significantly before and after the process in the same project, the consumption ratio of PAM will not differ significantly. Therefore, we use the total amount of PAM (n) added at coagulation sedimentation tank 1 as a basis to approximate the amount of PFS added in PAM residue reaction tank 2. Specifically: The formula is set as mFe + nPAM = S (precipitate). The values ​​of m and n need to be confirmed through beaker experiments based on the current water quality of the project. Through beaker experiments, the maximum and minimum values ​​of m are determined using a fixed n value. max and m min Based on the detection data from the iron ion detector, the dosage C value is controlled within m. max and m min Adjust between, and get as close as possible to m min As a principle. If the C-value of the dosing system exceeds m max If the iron ion concentration still does not meet the above-mentioned limit range, it indicates that a significant change has occurred in the influent to coagulation sedimentation tank 1 that is outside the system settings. In this case, the system needs to alarm the operator, who will then conduct a re-experiment to confirm the new m. max and m min value.

[0024] In a preferred embodiment, determining the dosage of polyferric sulfate in the PAM residue collection step further includes: dynamically controlling the dosage of polyferric sulfate based on the iron ion concentration in the product water after the collection reaction. Increase the dosage of polyferric sulfate when the iron ion concentration in the product water after the trapping reaction is <0.05 mg / L; decrease the dosage of polyferric sulfate when the iron ion concentration in the product water after the trapping reaction is >0.15 mg / L.

[0025] The dosage of polyferric sulfate is determined through a grading method, specifically: Primary control: Based on the PAM dosage n in the coagulation sedimentation tank, the PFS dosage range (m) was determined through beaker experiments. min -m max The initial dosage should preferentially approach m. min (Saving medicine); Real-time correction: Based on feedback from the iron ion detector (increase the dosage when the outlet concentration is <0.05 mg / L, and decrease the dosage when it is >0.15 mg / L), dynamically adjust the PFS dosage C to ensure that the PAM removal rate is ≥99.9%.

[0026] In a preferred embodiment, the coagulation and sedimentation step includes: first adding FeCl3 to react and generate Fe(OH)3 colloid; then adding PAM, and forming large-particle flocs after mechanical stirring; and controlling the turbidity of the effluent to ≤10 NTU after sedimentation.

[0027] It's important to note that coagulation and sedimentation typically involve first adding a coagulant to the water to cause suspended solids to aggregate and form larger flocs. These flocs are usually not large enough and will float on the surface, failing to settle and be removed. At this point, PAM (polyacrylamide), a linear polymer with a molecular weight of 10-20 million, is added to the water. PAM is readily soluble in water and has numerous network nodes. Under the action of PAM, the flocs rapidly aggregate, forming larger flocs that are then effectively removed by the sedimentation tank, achieving water purification. PAM is a very important and widely used agent in water treatment.

[0028] However, PAM also has significant drawbacks, mainly in three aspects: 1. Small amounts of PAM are almost harmless, but large doses are neurotoxic, and excessive intake can lead to nerve damage; 2. Because PAM is a linear polymer, unreacted residual PAM will accumulate on the surface of downstream containers, reverse osmosis membranes, and other equipment, forming a sticky colloid. This type of colloid is very difficult to remove, becoming one of the biggest sources of contamination for ultrafiltration and reverse osmosis membranes; 3. PAM cannot be effectively measured and monitored. There are no instruments to detect residual PAM in water, so the dosage is usually based on experience, and the final residual amount in the water is not within the system's controllable range. Based on these three characteristics, although PAM is an indispensable and important agent in water treatment, its use has always been very cautious. It requires a large amount of manpower to frequently and periodically disassemble downstream equipment and manually judge whether the PAM dosage is appropriate and whether adjustments are needed by observing the amount of colloid adhering to the inner surface of the equipment. This method is extremely labor-intensive and highly dependent on the operator's sense of responsibility, skill level, and judgment. Misjudgment can lead to damage to subsequent equipment. Therefore, effectively removing PAM residues has become an urgent issue.

[0029] This invention adds a PAM capture reaction step after the traditional coagulation and sedimentation step. Residual PAM is captured by adding polyferric sulfate (PFS). Simultaneously, by controlling the iron ion concentration in the product water after the capture reaction to 0.05-0.15 mg / L, the PAM removal rate is guaranteed, transforming the "uncontrollable" PAM residue in traditional processes into "near-zero." An indirect monitoring mechanism based on iron ion concentration feedback is established, overcoming the technical bottleneck of PAM's inability to be detected online. The residual amount is reduced from being unmonitorable in traditional processes to ≤0.01 mg / L. Furthermore, a manganese sand filtration step ensures the simultaneous removal of the newly added reagent (PFS) residue, eliminating the risk of secondary pollution. This coagulation and sedimentation method can reduce PAM residue from the strictly controlled 0.1 mg / L of traditional processes to below 0.01 mg / L, significantly extending the lifespan of ultrafiltration and reverse osmosis membranes. It is suitable for scenarios sensitive to colloidal pollutants, such as reverse osmosis pretreatment in municipal and seawater desalination plants, and industrial circulating water treatment.

[0030] Meanwhile, the above-mentioned coagulation and sedimentation method can achieve seamless optimization of all existing processes without modifying the existing sedimentation tank by adding a new PAM polymerization reaction sedimentation and manganese sand filtration integrated filter module.

[0031] In a preferred embodiment, the concentration of FeCl3 is 10-20%; the concentration of PAM is 0.1-0.5 mg / L; and the mechanical stirring speed is 50-100 rpm. It is understood that the concentration of FeCl3 can also be any value within the range of 12%, 14%, 16%, 18%, and so on; the concentration of PAM can also be any value within the range of 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, and so on; and the mechanical stirring speed can also be any value within the range of 60 rpm, 70 rpm, 80 rpm, 90 rpm.

[0032] In a preferred embodiment, the molar ratio of polyferric sulfate to PAM dosage is 3:1-5:1. This technical solution specifically limits the molar ratio of polyferric sulfate to PAM dosage, which not only ensures complete removal of PAM within this range, but also avoids the difficulty of subsequent iron ion removal caused by excessive addition of polyferric sulfate.

[0033] In a preferred embodiment, the manganese sand filtration step is carried out in a manganese sand filter 3. The surface filter media of the manganese sand filter 3 is light anthracite, and the bottom filter media is manganese sand. The filtration unit is equipped with a double-layer medium. The surface filter media is light anthracite, which intercepts suspended solids that have not been completely precipitated during the polymerization reaction. The bottom filter media is manganese sand, which has a very good adsorption effect on iron ions, and the adsorption of residual iron ions is completed through the manganese sand filter media. Light anthracite filter media is placed on top of the manganese sand filter media, and the anthracite filter media first intercepts and removes trace suspended solids that have not been completely precipitated.

[0034] The above coagulation and sedimentation method has achieved a breakthrough in residue control: PAM residue has changed from "uncontrollable" in traditional processes to "approaching zero". The iron ion concentration in the product water after the capture reaction is stable at 0.05-0.15 mg / L, and the iron ion concentration after passing through the manganese sand filter is stable at below 0.0075 mg / L, which meets the requirements of reverse osmosis membrane feed water (Fe≤0.1mg / L).

[0035] Improved efficiency and adaptability: PAM dosage can be increased to over 0.5 mg / L, coagulation and sedimentation efficiency is increased by 20%, and system response time is shortened from 4 hours for manual operation to 5 minutes for automatic control.

[0036] Cost advantages: Reduced membrane replacement frequency, avoids blind addition of chemicals, and reduces manual maintenance costs by 50%.

[0037] Furthermore, to further improve the control precision and automation of the aforementioned coagulation and sedimentation process, a machine learning model for water quality parameters and dosage can be developed to replace manual beaker tests, improving dosing precision to ±5% and adapting to water quality fluctuations. Based on the traditional three-stage coagulation and sedimentation unit dosing method, FeCl3 and PAM adaptive dosing devices can be configured, with both chemicals intelligently adjusted according to actual water quality conditions. The proposed solution involves real-time aggregation of water flow, water quality, and chemical dosing data from the entire treatment unit into an intelligent control center (PLC and DCS system). The intelligent control center uses a preset program to identify triggering conditions and adjust the dosing amount of each dosing pump in real time. The machine automatically inputs relevant data and learns autonomously. If the preset chemical dosing ratio is inaccurate, the machine will automatically adjust based on actual operating values ​​and automatically correct any default values ​​allowed for modification in the original logic program. One approach is as follows: Establish a correlation model between influent turbidity (NTU), pH, temperature (°C) and chemical dosage: C = f(n, T, turbidity, pH) + ΔC(Fe) 2+ ) ΔC is the correction amount for iron ion concentration deviation, which is trained using historical data to form a preset operating condition library (containing more than 20 typical water quality operating conditions).

[0038] Variable frequency control technology: A digital variable frequency dosing pump (accuracy ±1%) is adopted, which adjusts the output flow rate in real time according to the control signal, and the dosage fluctuation range is ≤ ±5%.

[0039] The following is combined Figure 1 Furthermore, another possible implementation of the present invention is given.

[0040] 1) Process Flow Coagulation and sedimentation stage: Raw water enters coagulation sedimentation tank 1, and FeCl3 (concentration 10-20%) is added through a dosing device to react and generate Fe(OH)3 colloid. Add PAM (concentration 0.1-0.5 mg / L), and mechanically stir (speed 50-100 rpm) to form large-particle flocs. After sedimentation, the turbidity of the effluent is ≤10 NTU.

[0041] Residual reaction stage: Permeate enters residual reaction tank 2, where polyferric sulfate (concentration 5-10%) is added via a PFS dosing device. The initial dosage C is m. min (Determined through beaker experiments, such as m) min =1.2n); Mechanically accelerated stirring (200-300 rpm) promotes the reaction between PFS and PAM. After precipitation, the precipitate is discharged from the bottom of the tank. The reaction time is 10-15 minutes.

[0042] Manganese sand filtration stage: After the reaction, the water enters manganese sand filter 3, with the filtration rate controlled at 10 m / h. The manganese sand filter media adsorbs and removes residual Fe³⁺. + The produced water meets the reverse osmosis feed water standards.

[0043] Intelligent control stage: The iron ion detector monitors the Fe²⁺ at the outlet of the reaction tank in real time. + Concentration, the signal is transmitted to the control center; The control center calculates the PFS dosage correction value based on the preset model and adjusts the dosage through the variable frequency pump, forming a closed loop of "detection-feedback-adjustment".

[0044] 2) Parameter calibration method Beaker Experiment Procedure: Take 1 L of raw water, fix the PAM dosage n (e.g., 0.5 mg / L), and add different doses of PFS (0.5n, 1.0n, 1.5n, 2.0n) sequentially. After stirring for 5 minutes, let stand for 30 minutes, and then measure the iron ion concentration in the supernatant to determine m. min (Minimum effective dosage, Fe²) + =0.05 mg / L) and m max (Critical excess dosage, Fe²) + =0.15 mg / L).

[0045] Machine learning training: Collect more than 30 days of operational data, input water quality parameters (turbidity, pH, temperature), dosage, and iron ion concentration, and train to form a dosing strategy model with an error rate of ≤5%.

[0046] The above method achieves three core breakthroughs through the deep integration of process innovation, control innovation, and equipment innovation: Technological breakthrough: solving the industry problems of undetectable PAM residues and easy contamination from new reagents, and constructing a closed-loop control system of "reaction-detection-adsorption"; Performance breakthrough: PAM removal rate > 99.9%, iron ion concentration in permeate ≤ 0.1 mg / L, and system response time < 5 minutes; Value breakthrough: reducing membrane maintenance costs, saving 15%+ in reagent and energy costs, and providing a "zero-risk, highly adaptable" solution for reverse osmosis pretreatment.

[0047] To provide a clearer and more detailed description of the coagulation and sedimentation method provided in the embodiments of the present invention, specific embodiments will be described below.

[0048] Example 1 (1) Implementation background and application scenarios Treatment target: A reverse osmosis pretreatment system at a coastal power plant. The raw water is seawater (turbidity 50-80 NTU, suspended solids 150-200 mg / L, pH 8.0-8.5). The designed treatment capacity is 500 m³ / d. The target permeate should meet the reverse osmosis feed water requirements (PAM residue <0.01 mg / L, Fe²⁺). + ≤0.1mg / L, turbidity ≤5NTU).

[0049] The core equipment configuration is shown in Table 1.

[0050] Table 1 Core Equipment Configuration

[0051] (2) Specific implementation steps 2.1 Coagulation and sedimentation stage (upgrading of traditional process) Coagulant addition: Raw water enters coagulation sedimentation tank 1, and 15% FeCl3 solution is added through a dosing device. The dosage is automatically adjusted according to the turbidity of the raw water (baseline value: 10 mg / L, increase by 2 mg / L for every 10 NTU increase in turbidity).

[0052] Stirring conditions: mechanical stirring speed 50 rpm, reaction time 10 minutes, forming Fe(OH)3 colloidal flocs.

[0053] PAM aids in coagulation: Add 0.5 mg / L of anionic PAM (molecular weight 15 million), mix it thoroughly with water through a pipeline mixer, and use its adsorption bridging effect to polymerize the colloid into large-particle flocs (particle size ≥ 50 μm).

[0054] Sedimentation time: 30 minutes, effluent turbidity reduced to 10-15 NTU, suspended solids removal rate ≥85%.

[0055] 2.2 Residual PAM Removal Stage PFS Smart Dosing: The dosage range of PFS was calibrated using beaker experiments: with a PAM dosage of n = 0.5 mg / L as the baseline, the m... min =1.0n, m max =1.5n.

[0056] The initial dosage C=1.0n=0.5mg / L is injected into the residual reaction tank 2 by a variable frequency dosing pump (accuracy ±1%), and the reagent concentration is 5%.

[0057] Reaction principle: PFS hydrolysis produces Fe³⁺ +It forms a polymer precipitate with the amide groups of PAM through electro-adsorption.

[0058] Mechanically accelerated mixing: Stirring speed 250 rpm, reaction time 15 minutes, to ensure that PFS and residual PAM are in full contact to form settleable flocs with a particle size ≥80μm, which are discharged from the bottom of the reaction tank.

[0059] Real-time monitoring of iron ions: An iron ion detector is installed at the outlet of the reaction tank to provide real-time concentration data to the control center. If Fe² + <0.05mg / L (insufficient PFS dosage), increase C value by 5%; If Fe² + >0.15mg / L (PFS excess), reduce C value by 5%; The concentration was eventually stabilized at 0.08-0.12 mg / L, ensuring a PAM removal rate of ≥99.9%.

[0060] 2.3 Manganese sand filtration stage (residual reagent removal) Filtering parameters: The filtration rate is controlled at 10 m / h, the thickness of the anthracite filter layer is 0.4 m, the thickness of the manganese sand filter layer is 0.8 m, and backwashing is started after 24 hours of filtration.

[0061] Backwashing conditions: When the pressure difference is ≥0.1MPa, automatic air-water combined backwashing is performed to restore the adsorption capacity of the filter media.

[0062] Removal effect: Residual PFS and iron ions were adsorbed by manganese sand, reducing the Fe concentration in the permeate to 0.08 mg / L, which meets the reverse osmosis feed water requirements (≤0.1 mg / L), with no new pollutant residues.

[0063] 2.4 Intelligent control of the entire process Data collection: The system collects eight parameters in real time: influent flow rate (electromagnetic flow meter), turbidity, pH, temperature, FeCl3 dosage, PAM dosage, PFS dosage, and iron ion concentration, and records them every 5 minutes.

[0064] Dynamic adjustment algorithm: The control center trains a dosing model using historical data. When the raw water turbidity suddenly rises to 100 NTU, it automatically matches the "high turbidity condition" and increases the PAM dosage to 0.6 mg / L. The initial PFS dosage is adjusted to 1.1n = 0.66 mg / L to ensure that the product water turbidity is ≤5 NTU.

[0065] Threshold alarm: If the iron ion concentration still exceeds the standard (>0.15mg / L) after the PFS dosage reaches mmax=0.75mg / L, the system will trigger an audible and visual alarm, prompting the operator to recalibrate the m value using a beaker test to avoid sudden changes in water quality that could lead to treatment failure.

[0066] The test results are shown in Tables 2 and 3.

[0067] Table 2 Comparison of Water Quality Indicators

[0068] Table 3 Comparison of Performance Parameters

Claims

1. A coagulation and sedimentation method, comprising a coagulation and sedimentation step, characterized in that, It also includes a PAM residue capture step performed after the coagulation and sedimentation step, and a manganese sand filtration step performed after the PAM residue capture step. The PAM residue collection step includes: Polyferric sulfate is used as a reactant, and the Fe³⁺ produced by the hydrolysis of the polyferric sulfate + It binds to the amide groups of PAM through electro-adsorption, thereby capturing PAM residues, and controls the iron ion concentration in the product water after the capture reaction to be 0.05-0.15 mg / L; The manganese sand filtration step includes: The permeate after the capture reaction is fed into a filtration unit containing manganese sand filter media for filtration to remove iron ions from the permeate after the capture reaction. The determination of the dosage of polyferric sulfate in the PAM residue collection step includes: Based on the dosage n of PAM in the coagulation and sedimentation step, the dosage range of polyferric sulfate was determined to be m using beaker experiments. min -m max The initial dosage m of the polyferric sulfate is close to m min But greater than m min Ensure PAM removal rate ≥ 99.9%; The raw water being treated is seawater with a turbidity of 50. 80 NTU, suspended solids content 150 200 mg / L, pH 8.0 8.

5.

2. The coagulation and sedimentation method according to claim 1, characterized in that, The permeate after the capture reaction is fed into a filtration unit containing manganese sand at a filtration rate of 8-12 m / h to remove iron ions from the permeate.

3. The coagulation and sedimentation method according to claim 1, characterized in that, The initial dosage of the polyferric sulfate is m = 1.2·m. min .

4. The coagulation and sedimentation method according to claim 1, characterized in that, The determination of the dosage of polyferric sulfate in the PAM residue collection step also includes: The dosage of polyferric sulfate is dynamically controlled based on the iron ion concentration in the product water after the capture reaction. When the concentration of iron ions in the product water after the trapping reaction is <0.05 mg / L, the dosage of polyferric sulfate should be increased. When the concentration of iron ions in the product water after the trapping reaction is >0.15 mg / L, reduce the dosage of the polyferric sulfate.

5. The coagulation and sedimentation method according to claim 1, characterized in that, The Fe³ produced by the hydrolysis of polyferric sulfate + It binds to the amide groups of PAM through electro-adsorption to form a precipitable polymer with a particle size ≥50 μm, thereby completing the capture of PAM residues.

6. The coagulation and sedimentation method according to claim 1, characterized in that, The coagulation and sedimentation step includes: first adding FeCl3 to react and generate Fe(OH)3 colloid; then adding PAM, and forming large-particle flocs after mechanical stirring, and controlling the turbidity of the effluent to ≤10 NTU after sedimentation.

7. The coagulation and sedimentation method according to claim 6, characterized in that, The concentration of FeCl3 is 10-20%; the concentration of PAM is 0.1-0.5 mg / L; and the mechanical stirring speed is 50-100 rpm.

8. The coagulation and sedimentation method according to claim 1, characterized in that, The manganese sand filtration step is carried out in a manganese sand filter, wherein the surface filter media of the manganese sand filter is light anthracite, and the bottom filter media is manganese sand.

Images