Coagulating precipitation method

Abstract

The invention discloses a coagulating sedimentation method, and belongs to the technical field of water treatment. According to the technical scheme, the method comprises a coagulating sedimentation step, a PAM residue trapping step carried out after the coagulating sedimentation step, and a manganese sand filtering step carried out after the PAM residue trapping step. The PAM residue trapping step comprises the following steps: finishing the trapping of PAM residues by taking polyferric sulfate as a reactant, and controlling the iron ion concentration of produced water after the trapping reaction to be 0.05-0.15 mg / L; the manganese sand filtering step comprises the following steps: inputting the produced water after the trapping reaction into a filtering unit containing a manganese sand filtering material for filtering, and removing iron ions in the produced water after the trapping reaction. The method is applied to the aspect of coagulating sedimentation, solves the problems that an existing coagulating sedimentation method cannot balance the coagulation effect and membrane pollution is caused by PAM residues, can effectively remove low-residue PAM in the coagulating sedimentation process, guarantees the coagulation effect and effectively prevents membrane pollution caused by accumulation of the low-residue PAM.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and in particular relates to a coagulation and sedimentation method. Background Art

[0002] Coagulation and sedimentation technology is widely used in water treatment systems. Pollutants in raw water are polymerized and precipitated by adding coagulants and coagulants (polyacrylamide, etc., also called PAM). The combination of the two agents will greatly improve the efficiency of water treatment. However, PAM is a linear high molecular polymer with a molecular weight of up to 20 million. The residual viscous colloid seriously affects the life of the reverse osmosis membrane and cannot be restored after clogging. Therefore, PAM is not used as much as possible in the reverse osmosis system, or is controlled at an extremely low level. However, PAM can make the reaction faster and more effective. The lack of PAM will greatly reduce the coagulation effect. Therefore, the traditional coagulation and sedimentation process often adopts a three-stage process of "coagulant → PAM → precipitation". However, this process has the following technical problems:

[0003] PAM residue is uncontrollable: In conventional processes, PAM cannot be effectively monitored. To reduce the risk of pollution, the dosage must be strictly limited (≤0.2ppm). However, due to fluctuations in water quality, the actual residual amount is 0.1-0.2ppm, which can easily lead to reverse osmosis membrane pollution. At the same time, because the dosage is strictly controlled, insufficient PAM dosage will lead to incomplete flocculation and sedimentation in heavily polluted water.

[0004] Pollution chain transfer: Traditional process pollution control has the pollution transfer of PAM → colloid pollution → membrane damage;

[0005] Detection blind spot: There is no commercial PAM online detection instrument;

[0006] Low level of intelligence: the dosage depends on manual experience adjustment, the response delay is >4 hours, and it cannot adapt to the dynamic changes of influent water quality. Summary of the invention

[0007] In view of the shortcomings of the prior art, 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 pollution caused by PAM residue. A coagulation and sedimentation method is proposed which can effectively remove low-residual PAM in the coagulation and sedimentation process, thereby ensuring the coagulation effect and effectively preventing the accumulation of low-residual PAM from causing membrane pollution.

[0008] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0009] The present invention provides a coagulation and sedimentation method, comprising a coagulation and sedimentation step, a PAM residue capturing step performed after the coagulation and sedimentation step, and a manganese sand filtering step performed after the PAM residue capturing step;

[0010] The PAM residue capture step includes: using polyferric sulfate as a reactant, and the Fe 3+ produced by the hydrolysis of polyferric sulfate combines with the amide groups of PAM through electrostatic adsorption to complete the capture of PAM residues, and controlling the concentration of iron ions in the produced water after the capture reaction to be 0.05 - 0.15 mg / L;

[0011] The manganese sand filtration step includes: inputting the produced water after the capture reaction into a filtration unit containing manganese sand filter media for filtration to remove iron ions in the produced water after the capture reaction.

[0012] Preferably, the produced water after the capture reaction is input into a filtration unit containing manganese sand filter media for filtration at a filtration rate of 8 - 12 m / h to remove iron ions in the produced water after the capture reaction.

[0013] Preferably, the determination of the dosage of polyferric sulfate in the PAM residue capture step includes: based on the dosage n of PAM in the coagulation sedimentation step, determining the dosage range of polyferric sulfate as m min -m max through beaker experiments, and the initial dosage m of polyferric sulfate approaches m min but is greater than m min .

[0014] Preferably, the initial dosage m of polyferric sulfate = 1.2·m min .

[0015] Preferably, the determination of the dosage of polyferric sulfate in the PAM residue capture step further includes: dynamically controlling the dosage of polyferric sulfate according to the concentration of iron ions in the produced water after the capture reaction:

[0016] When the concentration of iron ions in the produced water after the capture reaction < 0.05 mg / L, increase the dosage of polyferric sulfate;

[0017] When the concentration of iron ions in the produced water after the capture reaction > 0.15 mg / L, reduce the dosage of polyferric sulfate.

[0018] Preferably, the Fe 3+ produced by the hydrolysis of polyferric sulfate combines with the amide groups of PAM through electrostatic adsorption to form a precipitable polymer with a particle size ≥ 50 μm, thereby completing the capture of PAM residues.

[0019] Preferably, the coagulation sedimentation step includes: first adding FeCl3 in the coagulation sedimentation step to react to form Fe(OH)3 colloid; then adding the PAM, and forming large - particle flocs after mechanical stirring, and controlling the turbidity of the effluent ≤ 10 NTU after sedimentation.

[0020] Preferably, the concentration of FeCl3 is 10-20%; the concentration of PAM is 0.1-0.5 mg / L; the rotation speed of the mechanical stirring is 50-100 rpm.

[0021] Preferably, the molar ratio of the dosage of the polymeric ferric sulfate to the dosage of PAM is 3:1-5:1.

[0022] Preferably, the manganese sand filtration step is carried out in a manganese sand filter, and the surface filter material of the manganese sand filter is light anthracite, and the bottom filter material is manganese sand filter material.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] The present invention provides a coagulation sedimentation method, which adds a PAM capture reaction step after the traditional coagulation sedimentation step, captures the residual PAM by adding polymeric ferric sulfate (PFS), and at the same time, by controlling the concentration of iron ions in the produced water after the capture reaction to be 0.05-0.15 mg / L, the removal rate of PAM is ensured, and the PAM residue is changed from "uncontrollable" in the traditional process to "close to zero". An indirect monitoring mechanism based on the feedback of iron ion concentration is established, breaking through the technical bottleneck that PAM cannot be detected online, and realizing that the residual amount is reduced from being uncontrollable in the traditional process to ≤0.01 mg / L. In addition, the manganese sand filtration step is adopted to ensure the synchronous removal of the residue of the newly added reagent (PFS) and eliminate the risk of secondary pollution. Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of a coagulation sedimentation device for the coagulation sedimentation method provided by an embodiment of the present invention;

[0026] In the above figures: 1. Coagulation sedimentation tank; 2. Residual reaction tank; 3. Manganese sand filter. Detailed Embodiments

[0027] The technical solutions in the specific embodiments of the present invention will be described in detail and completely below with reference to the drawings. Obviously, the described embodiments are only some specific embodiments of the general technical solution of the present invention, rather than all embodiments. Based on the general concept of the present invention, all other embodiments obtained by those of ordinary skill in the art fall within the protection scope of the present invention.

[0028] The present invention provides a coagulation sedimentation method, including a coagulation sedimentation step, a PAM residue capture step carried out after the coagulation sedimentation step, and a manganese sand filtration step carried out after the PAM residue capture step. This coagulation sedimentation method adds a PAM capture reaction step after the traditional coagulation sedimentation step, captures the residual PAM by adding polymeric ferric sulfate (PFS), wherein, polymeric ferric sulfate, Fe2(OH) n(SO4) 3-n / 2 , abbreviated as PFS, the Fe 3+ hydrolyzed from it quickly combines with the amide groups of PAM through electrostatic adsorption to form a precipitable polymer with a particle size ≥ 50 μm. The reaction efficiency is more than 3 times higher than that of the traditional method. After PFS and PAM react to form a polymeric precipitate, it is intercepted by the inclined plate sedimentation effect, thereby realizing the removal of PAM. The water flow after treating the PAM residue enters the manganese sand filter. After the produced water enters the manganese sand filter, the manganese sand filter removes trace residual suspended solids and adsorbs residual iron ions through the filtration unit, thereby realizing the adsorption of residual iron ions.

[0029] The step of capturing PAM residue includes: using polymeric ferric sulfate as a reactant, and the Fe 3+ hydrolyzed from polymeric ferric sulfate combines with the amide groups of PAM through electrostatic adsorption to complete the capture of PAM residue, and controls the concentration of iron ions in the produced water after the capture reaction to be 0.05 - 0.15 mg / L. By controlling the concentration of iron ions in the produced water after the capture reaction to be 0.05 - 0.15 mg / L, the removal rate of PAM is ensured, realizing the change of PAM residue from "uncontrollable" in the traditional process to "close to zero", establishing an indirect monitoring mechanism based on the feedback of iron ion concentration, breaking through the technical bottleneck that PAM cannot be detected online, and realizing the reduction of the residual amount from being uncontrollable in the traditional process to ≤ 0.01 mg / L. In a preferred embodiment, the Fe 3+ hydrolyzed from polymeric ferric sulfate combines with the amide groups of PAM through electrostatic adsorption to form a precipitable polymer with a particle size ≥ 50 μm, thereby completing the capture of PAM residue.

[0030] The concentration of iron ions in the produced water after the above capture reaction is detected by an on-line iron ion detector, the residual amount of iron ions is monitored in real time, and the dosing amount of the PFS dosing pump is controlled to ensure that the residual amount of iron ions is within a certain range, which not only ensures the complete reaction and removal of PAM, but also does not result in excessive residual iron ions.

[0031] The manganese sand filtration step includes: inputting the produced water after the capture reaction into a filtration unit containing manganese sand filter media for filtration to remove iron ions in the produced water after the capture reaction. In a preferred embodiment, the produced water after the capture reaction is input into a filtration unit containing manganese sand filter media for filtration at a filtration rate of 8 - 12 m / h to remove iron ions in the produced water after the capture reaction. The produced water of the manganese sand filter will no longer contain PAM and PFS, perfectly solving the potential secondary pollution risk that may be brought by PAM residue and the introduction of new chemicals, and forming a pollution self-blocking mechanism. Natural manganese sand filter media is selected, and for Fe 3+The adsorption capacity ≥ 15 mg / g. At the same time, by controlling the filtration rate at 8 - 12 m / h, it is ensured that the removal rate of residual PFS ≥ 95%. An online iron ion detector is set at the outlet of the filter tank to monitor the iron ion content in the final product water in real time and ensure that the newly added chemicals added during the PAM residual capture process do not cause secondary pollution to the system.

[0032] In a preferred embodiment, the determination of the dosage of polymeric ferric sulfate in the PAM residual capture step includes: taking the dosage n of PAM in the coagulation sedimentation step as a reference, and determining the dosage range of polymeric ferric sulfate as m min -m max , the initial dosage m of polymeric ferric sulfate approaches m min but is greater than m min . In a preferred embodiment, the initial dosage m of polymeric ferric sulfate = 1.2·m min .

[0033] Regarding the determination of the dosage of polymeric ferric sulfate in the above-mentioned PAM residual capture step, it should be noted that in order to ensure the removal effect of PAM, PFS is overdosed slightly. Through the online iron ion detector set at the outlet of the PAM residual reaction tank 2, the dosage of PFS is intelligently controlled. The product water carrying slightly excessive PFS enters the filter tank, and the filter tank will filter the polymer of PAM and PFS, and the excessive PFS (containing iron ions) in the water will also be removed by the adsorption characteristics of the manganese sand filter material for iron ions, and then qualified product water is produced.

[0034] In addition, since PFS and PAM do not react directly, but form a precipitate through polymerization, there is no fixed ratio for the reaction of these two substances, which is also the difficulty in controlling PAM residues. At the same time, because in the same project, the types of suspended substances in the water quality before and after will not change greatly, the consumption ratio of PAM will not vary greatly. Therefore, based on the total amount n value of PAM added at the coagulation sedimentation tank 1, an approximate calculation of the dosage of PFS in the PAM residual reaction tank 2 is carried out. Specifically:

[0035] Set mFe + nPAM = S (precipitate), and the values of m and n need to be confirmed through beaker experiments according to the current water quality of the project. Through beaker experiments, with a fixed n value, the maximum and minimum values of m are determined as m max and m min , according to the detection data of the iron ion detector, control the dosage C value to be adjusted between m max and m min and take the principle of being as close as possible to m min . If the C value of the dosing system exceeds m maxAfterwards, if the concentration of iron ions still does not meet the above - defined range, it indicates that there has been a major change in the influent of the coagulation sedimentation tank 1 beyond the system settings. At this time, the system needs to alarm the operator, and the operator conducts a new experiment to confirm the new m max and m min value.

[0036] In a preferred embodiment, the determination of the dosage of polymeric ferric sulfate in the PAM residual capture step further includes: dynamically controlling the dosage of polymeric ferric sulfate according to the concentration of iron ions in the effluent after the capture reaction:

[0037] When the concentration of iron ions in the effluent after the capture reaction is < 0.05 mg / L, increase the dosage of polymeric ferric sulfate; when the concentration of iron ions in the effluent after the capture reaction is > 0.15 mg / L, reduce the dosage of polymeric ferric sulfate.

[0038] The determination of the dosage of polymeric ferric sulfate is carried out by a hierarchical determination method. Specifically:

[0039] Primary control: Based on the dosage n of PAM in the coagulation sedimentation tank 1, determine the dosage range of PFS (m min -m max ) through beaker experiments. The initial dosage preferably approaches m min (saving chemicals);

[0040] Real - time correction: According to the feedback of the iron ion detector (increase the dosage when the outlet concentration is < 0.05 mg / L, and reduce the dosage when it is > 0.15 mg / L), dynamically adjust the dosage C of PFS to ensure that the PAM removal rate ≥ 99.9%.

[0041] In a preferred embodiment, the coagulation and sedimentation step includes: first adding FeCl3 in the coagulation and sedimentation step to react to form Fe(OH)3 colloid; then adding PAM, and after mechanical stirring, large - particle - size flocs are formed, and the turbidity of the effluent is controlled ≤ 10 NTU after sedimentation.

[0042] It should be noted that in coagulation and sedimentation, usually, a coagulant is first added to the water to make the suspended solids in the water polymerize to form larger flocs. Generally, these flocs are not large enough and will float on the water surface and cannot be removed by sedimentation. At this time, PAM (polyacrylamide), a linear high - molecular - weight polymer, is added to the water. Polyacrylamide is a polymer with a molecular weight of 10 million - 20 million, which is easily soluble in water and has a very large number of network nodes. Under the action of PAM, the flocs will quickly aggregate to form larger flocs, which can be well removed by the sedimentation tank, achieving the purpose of water purification. PAM is a very important and widely used chemical in water treatment.

[0043] However, PAM also has significant drawbacks, mainly manifested in three aspects: 1. A small amount of PAM is almost harmless, but a large dose of PAM is neurotoxic, and excessive intake can cause nerve damage to humans; 2. Since PAM is a linear polymer, the unreacted residual PAM will accumulate on the surfaces of subsequent containers, reverse osmosis membranes and other equipment to form a viscous colloid. This type of colloid is very difficult to remove and becomes one of the largest pollution sources for the damage of ultrafiltration membranes and reverse osmosis membranes; 3. PAM cannot be effectively measured and monitored, and there is no relevant instrument to detect the residual PAM in water. Therefore, the usual dosing amount is based on experience, and the final residual amount in water is not within the controlled range of the system. Based on these three characteristics, although PAM is an essential chemical in water treatment, its use has always been very cautious. It requires a large amount of manpower to regularly and periodically disassemble the subsequent equipment, and judge whether the PAM dosing amount is appropriate and whether the dosing amount needs to be adjusted by the amount of colloid attached to the inner surface of the equipment. This method has a very large workload and is particularly subject to the responsibility, skills and judgment ability of the operators. Once misjudgment occurs, it will cause damage to the subsequent equipment. Therefore, how to effectively remove the residual PAM has become extremely urgent.

[0044] The present invention adds a PAM capture reaction step after the traditional coagulation and sedimentation step. By adding polyferric sulfate (PFS) to capture the residual PAM, at the same time, by controlling the iron ion concentration in the produced water after the capture reaction to be 0.05 - 0.15 mg / L, the removal rate of PAM is ensured, and the residual PAM is changed from "uncontrollable" in the traditional process to "close to zero". An indirect monitoring mechanism based on the feedback of iron ion concentration is established, breaking through the technical bottleneck that PAM cannot be detected online, and realizing that the residual amount is reduced from being uncontrollable in the traditional process to ≤0.01 mg / L. In addition, a manganese sand filtration step is adopted to ensure the synchronous removal of the residual of the newly added chemical (PFS) and eliminate the risk of secondary pollution. The above-mentioned coagulation and sedimentation method can reduce the residual amount of PAM from 0.1 mg / L, which is strictly controlled in the traditional process, to below 0.01 mg / L, and greatly extend the service life of ultrafiltration and reverse osmosis membranes. It is applicable to scenarios sensitive to colloid pollutants such as reverse osmosis pretreatment for municipal and seawater desalination, and industrial circulating water treatment.

[0045] At the same time, the above-mentioned coagulation and sedimentation method realizes the threshold-free optimization of all original processes by adding a new integrated filter module for PAM polymerization reaction precipitation and manganese sand filtration without modifying the existing sedimentation tank.

[0046] In a preferred embodiment, the concentration of FeCl3 is 10-20%; the concentration of PAM is 0.1-0.5 mg / L; the rotation speed of mechanical stirring is 50-100 rpm. It can be understood that the concentration of FeCl3 can also be 12%, 14%, 16%, 18% and any point value within this range, the concentration of PAM can also be 0.2 mg / L, 0.3 mg / L, 0.4 mg / L and any point value within this range, and the rotation speed of mechanical stirring can also be 60 rpm, 70 rpm, 80 rpm, 90 rpm and any point value within this range.

[0047] In a preferred embodiment, the molar ratio of the dosage of polymeric ferric sulfate to the dosage of PAM is 3:1-5:1. This technical solution specifically defines the molar ratio of the dosage of polymeric ferric sulfate to the dosage of PAM. Within this range, it can not only ensure the complete removal of PAM, but also avoid the difficulty of subsequent iron ion removal caused by excessive dosage of polymeric ferric sulfate.

[0048] In a preferred embodiment, the manganese sand filtration step is carried out in the manganese sand filter 3. The surface filter material of the manganese sand filter 3 is light anthracite, and the bottom filter material is manganese sand filter material. The filtration unit is provided with a double-layer medium. The surface filter material is light anthracite, which intercepts the suspended solids that have not been completely precipitated in the polymerization reaction; the bottom filter material is manganese sand filter material, and the manganese sand filter material has a very good adsorption effect on iron ions, and the residual iron ions are adsorbed through the manganese sand filter material. A layer of light anthracite filter material is arranged above the manganese sand filter material, and the anthracite filter material first intercepts and removes the trace suspended solids that have not been completely precipitated.

[0049] The above coagulation and precipitation method realizes the breakthrough of residual control: the PAM residue changes from "uncontrollable" in the traditional process to "approaching zero", the iron ion concentration in the produced water after the capture reaction is stable at 0.05-0.15 mg / L, and the iron ion concentration passing through the manganese sand filter tank is stable below 0.0075 mg / L, meeting the requirements of the reverse osmosis membrane for inlet water (Fe≤0.1 mg / L).

[0050] Improvement in efficiency and adaptability: The dosage of PAM can be increased to more than 0.5 mg / L, the coagulation and precipitation efficiency is increased by 20%, and the system response time is shortened from 4 hours of manual operation to 5 minutes of automatic control.

[0051] Cost advantage: The frequency of membrane replacement is reduced, the chemicals are added without blindness, and the labor maintenance cost is reduced by 50%.

[0052] In addition, if you want to further improve the control accuracy and automation level of the above coagulation and sedimentation, you can also develop a machine learning model for water quality parameters and chemical dosage, replacing the manual beaker test, so as to improve the chemical dosing accuracy to ±5%, and adapt to the water quality fluctuation scenario. Based on the traditional coagulation and sedimentation (three-stage) unit chemical dosing method, configure the FeCl3 and PAM adaptive chemical dosing devices, and the two chemicals are intelligently adjusted according to the actual water quality. The adopted solution can be: the water flow, water quality and chemical dosage data of the entire treatment unit are summarized into the intelligent control center (PLC and DCS systems) in real time, and the trigger conditions are identified through the preset program of the intelligent control center, and the chemical dosage of each chemical dosing pump is adjusted in real time. The machine automatically enters relevant data and learns independently. If the chemical dosage ratio preset by the program is inaccurate, the machine will automatically adjust according to the actual operation value and automatically correct the default value that allows modification in the original logic program. One way is:

[0053] Establish the correlation model between influent turbidity (NTU), pH, temperature (°C) and chemical dosage:

[0054] C = f(n, T, turbidity, pH) + ΔC(Fe 2+ )

[0055] Among them, ΔC is the correction amount of iron ion concentration deviation, and a preset working condition library (including more than 20 typical water quality working conditions) is formed through training with historical data.

[0056] Variable frequency control technology: Adopt a digital variable frequency chemical dosing pump (accuracy ±1%), and adjust the output flow in real time according to the control signal, and the dosing fluctuation range ≤ ±5%.

[0057] Next, in combination with Figure 1 , another possible implementation manner of the present invention is given.

[0058] 1) Process flow

[0059] Coagulation and sedimentation stage:

[0060] The raw water enters the coagulation sedimentation tank 1, and FeCl3 (concentration 10-20%) is added through the chemical dosing device to react to generate Fe(OH)3 colloid;

[0061] PAM (concentration 0.1-0.5 mg / L) is added, and large-particle-size flocs are formed through mechanical stirring (rotation speed 50-100 rpm), and the effluent turbidity after sedimentation ≤ 10 NTU.

[0062] Residual reaction stage:

[0063] The produced water enters the residual reaction tank 2, and polymeric ferric sulfate (concentration 5-10%) is added through the PFS chemical dosing device, and the initial value of the dosing amount C is m min (determined through beaker experiments, such as mmin = 1.2n);

[0064] Mechanically accelerate stirring (rotation speed 200 - 300 rpm) to promote the reaction of PFS and PAM. After precipitation is formed, it is discharged from the bottom of the tank, and the reaction time is 10 - 15 minutes.

[0065] Manganese sand filtration stage:

[0066] The water after reaction enters the manganese sand filter 3, and the filtration rate is controlled at 10 m / h. The manganese sand filter media adsorbs and removes the residual Fe 3+ , and the produced water meets the reverse osmosis feed water standard.

[0067] Intelligent control stage:

[0068] The iron ion detector monitors the Fe concentration at the outlet of the reaction tank in real time, and the signal is transmitted to the control center; 2+ Concentration, and the signal is transmitted to the control center;

[0069] The control center calculates the correction value of the PFS dosing amount according to the preset model, and adjusts the dosing amount through the variable frequency pump to form a closed loop of "detection - feedback - adjustment".

[0070] 2) Parameter calibration method

[0071] Beaker experiment steps:

[0072] Take 1 L of raw water, fix the PAM dosing amount n (such as 0.5 mg / L), and sequentially add different doses of PFS (0.5n, 1.0n, 1.5n, 2.0n);

[0073] After stirring for 5 minutes, let it stand for 30 minutes, and detect the iron ion concentration in the supernatant to determine m min (Minimum effective dosing amount, Fe 2+ = 0.05 mg / L) and m max (Critical excessive dosing amount, Fe 2+ = 0.15 mg / L).

[0074] Machine learning training:

[0075] Collect operation data for more than 30 days, input water quality parameters (turbidity, pH, temperature), dosing amount, and iron ion concentration, and train to form a dosing strategy model with an error rate ≤ 5%.

[0076] Through the deep integration of process innovation, control innovation, and equipment innovation, the above method has achieved three core breakthroughs: technological breakthrough: solving the industry problems of undetectable PAM residues and easy contamination of newly added chemicals, and constructing a closed-loop control system of "reaction - detection - adsorption"; performance breakthrough: PAM removal rate > 99.9%, iron ions in the produced water ≤ 0.1 mg / L, system response time < 5 minutes; value breakthrough: reducing membrane maintenance costs, saving 15%+ in chemical and energy consumption costs, and providing a "zero-risk, high-adaptability" solution for reverse osmosis pretreatment.

[0077] To introduce the coagulation and sedimentation method provided by the embodiments of the present invention more clearly and in detail, the following will be described in combination with specific embodiments.

[0078] Example 1

[0079] (1) Implementation background and application scenarios

[0080] Treatment object: The reverse osmosis pretreatment system of a coastal power plant. The raw water is seawater (turbidity 50 - 80 NTU, suspended solid content 150 - 200 mg / L, pH 8.0 - 8.5), and the designed treatment scale is 500 m 3 / d, and the target produced water meets the requirements of reverse osmosis inlet water (PAM residue < 0.01 mg / L, Fe 2+ ≤ 0.1 mg / L, turbidity ≤ 5 NTU).

[0081] The core equipment configuration is shown in Table 1.

[0082] Table 1 Core equipment configuration

[0083]

[0084] (2) Specific implementation steps

[0085] 2.1 Coagulation and sedimentation stage (upgrading of traditional process)

[0086] Coagulant dosing:

[0087] The raw water enters the coagulation sedimentation tank 1, and a 15% concentration FeCl3 solution is dosed through the dosing device. The dosing amount is automatically adjusted according to the raw water turbidity (reference value: 10 mg / L, and 2 mg / L is increased for every 10 NTU increase in turbidity).

[0088] Stirring conditions: The mechanical stirring speed is 50 rpm, and the reaction time is 10 minutes to form Fe(OH)3 colloidal flocs.

[0089] PAM coagulant aid:

[0090] Add anionic PAM (molecular weight of 15 million) at a concentration of 0.5 mg / L, and mix it thoroughly with water through a pipeline mixer. Utilize its adsorption bridging effect to polymerize the colloid into large-sized flocculants (particle size ≥ 50 μm).

[0091] Sedimentation time: 30 minutes, the effluent turbidity drops to 10 - 15 NTU, and the suspended solid removal rate ≥ 85%.

[0092] 2.2 Residual PAM reaction removal stage

[0093] Intelligent dosing of PFS:

[0094] Calibrate the dosing range of PFS through beaker experiments: Based on the PAM dosing amount n = 0.5 mg / L, determine m min = 1.0n (0.5 mg / L), m max = 1.5n (0.75 mg / L).

[0095] Initial dosing amount C = 1.0n = 0.5 mg / L, and inject it into the residual reaction tank 2 by a variable-frequency dosing pump (accuracy ±1%), with the reagent concentration of 5%.

[0096] Reaction principle: PFS hydrolyzes to produce Fe 3+ , and forms a polymer precipitate through electrostatic adsorption with the amide groups of PAM.

[0097] Mechanically accelerated stirring:

[0098] Stirring speed 250 rpm, reaction time 15 minutes, ensure that PFS and residual PAM are in full contact, form precipitable flocs with a particle size ≥ 80 μm, and discharge them from the bottom of the reaction tank.

[0099] Real-time monitoring of iron ions:

[0100] Install an iron ion detector at the outlet of the reaction tank, and real-time feedback the concentration data to the control center:

[0101] If Fe 2+ <0.05 mg / L (insufficient dosing of PFS), increase the C value by 5%;

[0102] If Fe 2+ >0.15 mg / L (excessive dosing of PFS), reduce the C value by 5%;

[0103] Finally, stabilize at 0.08 - 0.12 mg / L to ensure that the PAM removal rate ≥ 99.9%.

[0104] 2.3 Manganese sand filtration stage (removal of residual reagents)

[0105] Filtration parameters:

[0106] The filtration rate is controlled at 10 m / h, the anthracite filter layer thickness is 0.4 m, the manganese sand filter layer thickness is 0.8 m, and backwashing is started after 24 hours of filtration time.

[0107] Backwashing conditions: When the pressure difference ≥ 0.1 MPa, air-water combined backwashing is automatically carried out to restore the adsorption capacity of the filter media.

[0108] Removal effect:

[0109] Residual PFS and iron ions are adsorbed by manganese sand, the Fe concentration in the produced water drops to 0.08 mg / L, meeting the reverse osmosis feed water requirement (≤ 0.1 mg / L), and there is no new pollutant residue.

[0110] 2.4 Intelligent control of the whole process

[0111] Data acquisition:

[0112] Eight parameters including influent flow rate (electromagnetic flowmeter), turbidity, pH, temperature, FeCl3 dosage, PAM dosage, PFS dosage, and iron ion concentration are collected in real time and recorded every 5 minutes.

[0113] Dynamic adjustment algorithm:

[0114] The control center forms a dosing model through training with historical data. When the raw water turbidity suddenly rises to 100 NTU, the "high turbidity condition" is automatically matched, the PAM dosage is increased to 0.6 mg / L, and the initial PFS dosage is adjusted to 1.1n = 0.66 mg / L to ensure that the produced water turbidity ≤ 5 NTU.

[0115] Threshold alarm:

[0116] If the iron ions are still exceeded the standard (> 0.15 mg / L) after the PFS dosage reaches mmax = 0.75 mg / L, the system triggers an audible and visual alarm, prompting the operator to re-perform the beaker experiment to calibrate the m value to avoid treatment failure caused by sudden water quality changes.

[0117] The test results are shown in Tables 2 and 3.

[0118] Table 2 Comparison of water quality indicators

[0119] Test Items Raw Water Water Produced by Traditional Process Water Produced by the Invention Standard Limit Turbidity (NTU) 60 8-10 ≤5 ≤10 (Reverse Osmosis Feed Water) Residual PAM (mg / L) - 0.1-0.3 ＜0.01 ＜0.05 <![CDATA[Fe 2+ (mg / L)]]> 0.02 0.2-0.3 0.08 ≤0.1 Suspended Solids (SS, mg / L) 180 20-30 ≤10 ≤50

[0120] Table 3 Comparison of performance parameters

[0121] Index Traditional Process The Invention Improvement Range PAM Dosage (mg / L) ≤0.2 0.5-0.6 +150％ System Response Time 4 - 8 hours (Manual) 5 minutes (Automatic) +90％ Membrane Fouling Cycle 3 - 6 months Over 12 months +100％ Reagent Cost (Yuan / ton of Water) 0.8 0.65 -18.75％

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 filtering step performed after the PAM residue capture step; The PAM residue capture step comprises: Polyferric sulfate is used as a reactant, and the Fe 3+ Combined with the amide group of PAM through electrical adsorption, the PAM residue is captured, and the iron ion concentration of the produced water after the capture reaction is controlled to be 0.05-0.15 mg / L; The manganese sand filtering step comprises: The produced water after the capture reaction is input into a filter unit containing manganese sand filter material for filtration to remove iron ions in the produced water after the capture reaction.

2. The coagulation sedimentation method according to claim 1, characterized in that: The produced water after the capture reaction is input into a filter unit containing manganese sand filter material at a filtration rate of 8-12m / h for filtration to remove iron ions in the produced water after the capture reaction.

3. The coagulation sedimentation method according to claim 1, characterized in that: The determination of the dosage of the polyferric sulfate in the PAM residue capture step includes: Based on the dosage n of PAM in the coagulation and sedimentation step, the dosage range of the polyferric sulfate is determined to be m by the beaker experiment. min -m max The initial dosage of the polyferric sulfate m approaches m min But greater than m min .

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

5. The coagulation sedimentation method according to claim 3, characterized in that: The determination of the dosage of the polyferric sulfate in the PAM residue capture step also includes: According to the concentration of iron ions in the produced water after the capture reaction, the dosage of the polyferric sulfate is dynamically controlled: When the iron ion concentration of the produced water after the capture reaction is less than 0.05 mg / L, the dosage of the polyferric sulfate is increased; When the iron ion concentration of the produced water after the capture reaction is greater than 0.15 mg / L, the dosage of the polyferric sulfate is reduced.

6. The coagulation sedimentation method according to claim 1, characterized in that: The Fe produced by the hydrolysis of the polyferric sulfate 3+ It combines with the amide group of PAM through electrical adsorption to form a precipitable polymer with a particle size of ≥50μm, thereby completing the capture of PAM residues.

7. The coagulation sedimentation method according to claim 1, characterized in that: The coagulation and sedimentation step comprises: firstly adding FeCl3 in the coagulation and sedimentation step to react and generate Fe(OH)3 colloid; then adding the PAM to form large-size floccules after mechanical stirring, and controlling the turbidity of the effluent to be ≤10NTU after sedimentation.

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

9. The coagulation sedimentation method according to claim 1, characterized in that: The molar ratio of the dosage of the polyferric sulfate to the dosage of the PAM is 3:1-5:

1.

10. The coagulation sedimentation method according to claim 1, characterized in that: The manganese sand filtering step is carried out in a manganese sand filter, the surface filter material of the manganese sand filter is light anthracite, and the bottom filter material is manganese sand filter material.

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