Application of cerium salt coagulant in water treatment

Abstract

The invention relates to the technical field of water pollution treatment, in particular to application of a cerium salt coagulant in water treatment. The specific application method comprises the following steps: adding the cerium salt coagulant into a to-be-treated water body under stirring, carrying out a coagulation reaction, and settling floc generated by the coagulation reaction to obtain the treated water body, the cerium salt coagulant is cerium-containing nitrate, ammonium nitrate, chlorine salt, sulfate or oxalate; the water body to be treated is a water body containing organic matter-turbidity or algae. The invention solves the problem that the conventional treatment process has low removal effect on algae and organic pollutants in water and the problems of narrow applicable pH range, poor coagulation effect at low temperature and high concentration of residual metal ions in the application process of the traditional coagulant.

Description

Technical Field

[0001] The invention relates to the technical field of water pollution treatment, and in particular to application of a cerium salt coagulant in water treatment. Background Art

[0002] Natural organic matter, also known as Natural Organic Matter, or NOM for short, is a complex mixture existing in natural water bodies. Due to the interaction between the hydrosphere, biosphere, and lithosphere, the composition and properties of NOM vary greatly with seasons and regions. The presence of natural organic matter will also bring a series of problems and hazards to the treatment and use of drinking water. At the same time, in freshwater systems, the massive reproduction of algae will seriously threaten the safety of drinking water. At present, the commonly used coagulation-sedimentation-filtration-disinfection process shows good removal effects in treating suspended matter, colloids, bacteria, and E. coli in water. However, conventional treatment processes have limited removal effects on algae and organic pollutants in water, especially soluble organic pollutants.

[0003] Coagulation is the most important physicochemical treatment technology in water treatment, which can effectively remove suspended particles and macromolecular organic matter in water. In the whole coagulation process, coagulant is the core factor that determines the removal efficiency of pollutants. Common coagulants include aluminum salt coagulants and iron salt coagulants, such as polyaluminum chloride PAC and polyferric sulfate PFS, which are widely used in drinking water treatment and sewage / wastewater treatment. However, aluminum salt coagulants and iron salt coagulants have many disadvantages in the application process. Aluminum salt coagulants have a narrow pH range, poor coagulation effect at low temperatures, and high residual aluminum concentrations bring toxicity problems. Iron salt coagulants are highly corrosive and acidic. Residual iron will make the coagulated effluent have a certain color and odor, and will have an adverse effect on subsequent treatment units. In order to overcome the problems of traditional aluminum salt coagulants and iron salt coagulants, the development of new alternative coagulants has become a hot topic in current research. Summary of the invention

[0004] In order to solve the problem that conventional treatment processes are not very effective in removing algae and organic pollutants in water, and the problems that traditional coagulants have a narrow applicable pH range, poor coagulation effect at low temperatures and high residual metal ion concentration during application, the purpose of the present invention is to provide a cerium salt coagulant for use in water treatment.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] The present invention provides an application of a cerium salt coagulant in water treatment, and a specific application method comprises the following steps:

[0007] A cerium salt coagulant is added to a water body to be treated under stirring to carry out a coagulation reaction. After the flocs produced by the coagulation reaction are settled, the supernatant is separated to obtain a treated water body; the cerium salt coagulant is at least one of a trivalent cerium salt coagulant and a tetravalent cerium salt coagulant; the water body to be treated is a water body containing organic matter and / or algae; for the treatment of water bodies containing organic matter and turbidity, the dosage of the cerium salt coagulant in the water body to be treated is 0.14mmol Ce / / L to 0.49mmol Ce / / L; for the treatment of water bodies containing algae, the dosage of the cerium salt coagulant in the water body to be treated is 0.01mmol / L to 0.06mmol / L.

[0008] The present invention adopts a cerium salt coagulant to remove organic pollutants and / or algae in water, and the generated flocs are larger and have a faster sedimentation rate, which is beneficial to improving the removal effect of algae and organic pollutants in water; and has a better pH application range, wherein the cerium salt coagulant can maintain a turbidity removal rate of more than 90% in the range of pH=3-10, and has a better algae removal performance in the range of pH=5-8, and can better remove chlorophyll a in water, thereby solving the problem that conventional treatment processes have a low removal effect on algae and organic pollutants in water, and the problems of narrow applicable pH range, poor coagulation effect at low temperature and high residual metal ion concentration of traditional coagulants in the application process.

[0009] Preferably, the cerium salt coagulant is at least one of cerium nitrate, ammonium cerium nitrate, cerium chloride, cerium sulfate and cerium oxalate. Among them, cerium nitrate, cerium chloride, cerium sulfate and cerium oxalate are all trivalent cerium salt coagulants; ammonium cerium nitrate is a tetravalent cerium salt coagulant. In the present invention, compared with the trivalent cerium salt coagulant, the tetravalent cerium salt coagulant has a better removal effect on algae and organic pollutants in water.

[0010] Preferably, the organic matter in the water to be treated is organic matter having light absorption characteristics under ultraviolet light of 254 nm wavelength.

[0011] Preferably, the algae is at least one of Chromococcus, Microcystis, Spirulina, Oscillatoria, Chlorella and diatom.

[0012] Preferably, the treatment of water containing organic matter and turbidity further comprises: adjusting the initial pH of the water to be treated to 3-10 before the coagulation reaction.

[0013] Preferably, the treatment of water containing algae further comprises: adjusting the initial pH of the water to be treated to 5-10 before the coagulation reaction.

[0014] Preferably, the treatment method for water containing organic matter-turbidity is:

[0015] The cerium salt coagulant is hydrolyzed in the water to be treated to form flocs of metal polynuclear hydroxyl compounds; the flocs produced by the hydrolysis of the cerium salt coagulant coagulate and precipitate organic matter and turbidity in the water to be treated through charge neutralization and adsorption, and the supernatant is separated to obtain the treated water.

[0016] Preferably, the method for treating water containing algae is:

[0017] The cerium salt coagulant is hydrolyzed in the water to be treated to form flocs of metal multi-nuclear hydroxyl compounds; the flocs produced by the hydrolysis of the cerium salt coagulant form adsorption bridges between different individual algae cells through charge neutralization, adsorption and sweep flocculation, and entangle the algae cells that are bridged together and are wrapped in the produced flocs to form a clustered structure that aggregates each other.

[0018] Preferably, the residual metal ion concentration in the treated water is ≤0.2 mg / L.

[0019] Preferably, the coagulation reaction time is 15 min to 30 min.

[0020] Preferably, the cerium in the cerium salt coagulant is Ce 4+ or Ce 3+ .

[0021] Beneficial effects of the present invention:

[0022] 1. Compared with traditional coagulants, the present invention adopts cerium salt coagulants to remove organic pollutants and / or algae in water, and the generated flocs are larger, the sedimentation rate is faster, and the decontamination performance is better, which solves the problem that the conventional treatment process is not effective in removing algae and organic pollutants in water, and the problems that traditional coagulants have a narrow applicable pH range, poor coagulation effect at low temperatures, and high residual metal ion concentration during application.

[0023] 2. The method of the present invention has an effect on UV 254 It has good removal effect on DOC and organic matter.

[0024] 3. Compared with traditional coagulants, the present invention has a better pH application range. The CAN coagulant can maintain a turbidity removal rate of more than 90% within the range of pH = 3 to 10.

[0025] 4. Compared with traditional coagulants, the flocs of the present invention are larger in size, generated faster, and show stronger regeneration ability after flocs are broken, and have better sedimentation performance.

[0026] 5. Compared with traditional coagulants, the present invention has better algae removal performance in the range of pH = 5 to 8 and can better remove chlorophyll a in water. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The treatment effects of different dosages of cerium salt coagulant and PAC on simulated organic matter and turbidity water samples in Example 1 of the present invention are shown in Figure 1. Among them, (a) is the effect of PAC dosage on turbidity removal rate; (b) is the effect of PAC dosage on UV 254 removal rate; (c) the effect of CAN dosage on turbidity removal rate; (d) the effect of CAN dosage on UV 254 removal rate; (e) is the effect of CCl dosage on turbidity removal rate; (f) is the effect of CCl dosage on UV 254 The effect of removal rate.

[0028] Figure 2 The pH value and zeta potential of the effluent of the cerium salt coagulant and PAC in Example 1 of the present invention for the treatment of organic matter in simulated organic matter and turbidity water samples. Among them, (a) is the zeta potential and pH of the effluent of PAC; (b) is the zeta potential and pH of the effluent of CAN; (c) is the zeta potential and pH of the effluent of CCl.

[0029] Figure 3 The effects of different pH values ​​on the effects of cerium salt coagulants and PAC on simulated organic matter and turbidity water samples in Example 1 of the present invention are shown in Figure 1. (a) is the effect of initial pH value on the coagulation effect of PAC; (b) is the effect of initial pH value on the coagulation effect of CAN; (c) is the effect of initial pH value on the coagulation effect of CCl.

[0030] Figure 4 The particle size changes of the cerium salt coagulant and PAC in Example 1 of the present invention during the floc growth, breakage and regrowth of simulated organic matter and turbidity water samples.

[0031] Figure 5 The treatment effects of cerium salt coagulant and PAC on turbidity and chlorophyll a of simulated algae-containing water samples in Example 2 of the present invention, as well as the residual metal concentration of the effluent. (a) The effect of PAC dosage on coagulation effect; (b) The effect of CAN dosage on coagulation effect; (c) The effect of CCl dosage on coagulation effect. Initial pH = 7; Algae cell concentration 3×10 6 cells / mL.

[0032] Figure 6 The zeta potential of the effluent of the cerium salt coagulant and PAC on the simulated algae-containing water sample at different pH values ​​in Example 2 of the present invention. (a) is the zeta potential of the PAC floc; (b) is the zeta potential of the CAN and CCl flocs.

[0033] Figure 7The effects of different pH values ​​on the coagulation effect of cerium salt coagulant and PAC and the residual metal concentration in the effluent in Example 2 of the present invention. (a) is the effect of initial pH value on PAC coagulation; (b) is the effect of initial pH value on CAN coagulation; (c) is the effect of initial pH value on CCl coagulation; (d) is the change of floc zeta potential under different pH. The PAC dosage is 0.21mmol Al / L; the CAN and CCl dosages are 0.04mmol Ce / L.

[0034] Figure 8 is the floc size in the cerium salt coagulant and PAC coagulation process in Example 2 of the present invention. Solution pH = 7.0; algae cell concentration is 3×10 6 cells / mL.

[0035] Fig. 9 This is a SEM picture of the cerium salt coagulant and PAC in Example 2 of the present invention on the accumulation of coagulated flocs in a simulated algae-containing water sample. Among them, (a1) is the SEM picture of PAC on the first day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (a2) is the SEM picture of PAC on the fourth day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (a3) ​​is the SEM picture of PAC on the eighth day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (b1) is the SEM picture of CAN on the first day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (b2) is the SEM picture of CAN on the fourth day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (b3) is the SEM picture of CAN on the eighth day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (c1) is the SEM picture of CCl on the first day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (c2) is the SEM picture of CCl on the fourth day when the coagulated flocs of the simulated algae-containing water sample were accumulated; (c3) is the SEM picture of CCl on the eighth day when the coagulated flocs of the simulated algae-containing water sample were accumulated. Initial pH = 7.0; PAC dosage is 0.21 mmol Al / L; CAN and CCl dosage is 0.04 mmol Ce / L. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0037] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0038] At present, some companies have begun to produce lanthanum coagulants specifically for water treatment applications, and some scholars have begun to explore the application of cerium-based materials in coagulation treatment. However, the cerium coagulant used is Ce(III) instead of Ce(IV), and the effect of Ce(III) coagulant is not good, so it is necessary to study Ce(IV) agents. In previous studies, coagulants were used to treat water bodies such as river water containing organic matter such as natural humic acid. However, in freshwater systems, the proliferation of algae will seriously threaten the safety of drinking water. At present, water treatment systems contain a large number of algae, such as Chromococcus, Microcystis, Spirulina, Oscillatoria, Chlorella and diatoms. Therefore, it is of great significance to develop efficient coagulants for organic matter-turbidity and algae in water bodies.

[0039] The present invention mainly investigates the differences between cerium salt coagulants of different valence states and traditional coagulant PAC in coagulation effect, coagulation mechanism and floc characteristics. The advantages of cerium salt over traditional coagulants are clarified. Compared with traditional coagulants, cerium salt coagulants have better decontamination performance and can better remove organic pollutants in water, with larger flocs and faster sedimentation. The present invention can provide theoretical support for the further application of cerium salt coagulants in actual water treatment processes.

[0040] The present invention can solve the disadvantages of the traditional coagulant PAC, such as small flocs, poor sedimentation, and poor treatment effect on organic pollutants, and can be widely used in the removal of turbidity, phosphate, organic matter, and algae. The preparation is simple and fast, the repeatability is good, and the quantitative production is easy. The coagulation performance is excellent, the metal residue is low, and the sedimentation performance is good.

[0041] The present invention provides an application of a cerium salt coagulant in removing organic matter and turbidity in water. The specific application method comprises the following steps:

[0042] Add a cerium salt coagulant to a water body containing turbidity and organic matter; stir for a certain period of time, and then let it stand for a certain period of time to allow the water body to condense flocculent sediments; when the flocculent sediments settle to the bottom of the water, separate the clear liquid above the flocculent sediments in the water body, and the separated clear liquid is the water body after removing turbidity and organic matter.

[0043] Specifically, a simulated water sample containing 5 mg / L to 50 mg / L humic acid and 1 mg / L to 10 mg / L kaolin is used, and a cerium salt coagulant is added to the simulated water sample, and the amount of the cerium salt coagulant added to the simulated water sample is 0.14 mmol Ce / L to 0.49 mmol Ce / L; the stirring procedure is: rapid stirring at 300 rpm to 250 rpm for 20 s to 30 s to mix the water sample, and immediately adding the agent after the stirring, stirring at 250 rpm to 200 rpm for 1 min to 2 min, and then slowly stirring at 40 rpm to 50 rpm for 10 to 20 min.

[0044] The present invention provides an application of a cerium salt coagulant in removing algae from water, and the specific application method comprises the following steps:

[0045] A cerium salt coagulant is added to a water body containing algae, stirred for a certain period of time, and then left to stand for a certain period of time, so that the algae coagulate into flocculent sediments; when the flocculent sediments settle to the bottom of the water, the clear liquid above the flocculent sediments in the water body is separated, and the separated clear liquid is the water body after the floating algae are removed.

[0046] Specifically, when the cerium salt coagulant is added to the water body containing algae, the dosage of the cerium salt coagulant in the water body containing phytoplankton is 0.01mmol Ce / L~0.06mmol Ce / L; the stirring procedure is: rapid stirring at 300rpm~250rpm for 20s~30s to mix the water sample, and then immediately adding the agent after the end, stirring at 250rpm~200rpm for 1min~2min, and then slowly stirring at 40rpm~50rpm for 10~20min.

[0047] The algae is at least one of Chrococcus, Microcystis, Spirulina, Oscillatoria, Chlorella and diatom.

[0048] The technical solution of the present invention is further described below through specific embodiments.

[0049] In the following examples, the methods are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified. Chemical oxygen demand is referred to as COD.

[0050] In the following embodiments, UV 254 It indicates the absorbance of water sample at 254nm wavelength, which reflects the absorption capacity of certain organic matter in water sample to ultraviolet light. 254 The value is closely related to the concentration of organic matter in the water and can indirectly reflect the content of organic matter such as humic acid in the water.

[0051] UV in water 254 The removal rate indicates the removal rate of organic matter with absorption characteristics under ultraviolet light of 254nm wavelength in water, which can reflect the removal of humic acid and other organic matter containing C=C double bonds and C=O double bonds in water samples.

[0052] Example 1

[0053] An application of a cerium salt coagulant in removing organic matter and turbidity in water, the specific application method is as follows:

[0054] Humic acid-kaolin was used as a simulated water sample with turbidity-organic matter coexistence: 10 mL of humic acid stock solution with a concentration of 1 g / L and 3 mL of kaolin stock solution with a concentration of 5 g / L were taken, and tap water was added to make the volume 1 L to obtain a simulated water sample with a turbidity of 18.0 ± 0.5 NTU and a humic acid concentration of 10 mg / L. Before coagulation, the simulated water sample was adjusted to the required pH value with 0.1 M NaOH and 0.1 M HCl. Kaolin was purchased from Sinopharm Chemical Reagent Co., Ltd., and humic acid was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0055] Chemicals: Cerium ammonium nitrate and cerium chloride were selected as cerium salt coagulants, and the traditional coagulant polyaluminium chloride was used as a comparison to explore the effects of different coagulants on the treatment of organic matter and turbidity in simulated water samples. Among them, cerium ammonium nitrate is abbreviated as CAN, cerium chloride is abbreviated as CCl, and the traditional coagulant polyaluminium chloride is abbreviated as PAC.

[0056] The coagulation experiment of humic acid-kaolin simulated water sample was carried out in a 1L system. The stirring program was set as follows: rapid stirring at 250rpm for 30s to mix the water sample, and then the reagent was added immediately after the end. After stirring at 200rpm for 1min, it was slowly stirred at 40rpm for 15min. After standing for 20min, a certain amount of supernatant was drawn with a syringe for further analysis.

[0057] Example 1 mainly explores the performance of different cerium salt coagulants and PAC in removing turbidity and organic matter in water at different dosages and pH values. The main detection indicators include effluent pH value, residual turbidity, UV 254 Removal efficiency and residual metal ion concentration.

[0058] Test 1: The effect of coagulants on turbidity and UV in water was investigated when the PAC dosage was 0.07mmol Al / L to 0.42mmol Al / L, the CAN dosage was 0.14mmolCe / L to 0.49mmol Ce / L, and the CCl dosage was 0.14mmol Ce / L to 0.49mmol Ce / L, and the initial pH of the water sample was 8.0. 254 The removal rate of Figure 1 shown.

[0059] like Figure 1 (a) and (b) of PAC on turbidity and UV in water 254 The removal rate was greatly improved with the increase of PAC dosage. When the PAC dosage was 0.14mmol Al / / L, the turbidity removal rate reached more than 90%, UV 254 The removal rate reaches more than 65%. Under the condition of higher dosage of PAC, UV 254 The removal rate growth trend tends to be stable.

[0060] like Figure 1 (c) and (d) show the effects of CAN on turbidity and UV in water. 254 The removal rate was greatly improved with the increase of CAN dosage. When the CAN dosage was 0.28mmol Ce / / L, the turbidity removal rate reached more than 90%, UV 254 The removal rate is over 70%. Under the condition of high dosage, UV 254 The removal rate growth trend tends to be stable.

[0061] like Figure 1 (e) and (f) show the effect of CCl on turbidity and UV in water. 254 The removal rate increases first and then decreases with the increase of CCl dosage. When the CCl dosage is 0.28mmol Ce / / L, the turbidity removal rate reaches more than 85%, UV 254 The removal rate reached more than 75%. When the CCl dosage was greater than 0.35mmol Ce / / L, CCl had no significant effect on turbidity and UV in water. 254 The removal rate gradually decreases.

[0062] Test 2: Examine the variation curves of floc zeta potential and effluent pH value with the amount of coagulant added. Figure 2 shown.

[0063] Depend on Figure 2 It can be seen that the effluent pH decreases with the increase of coagulant dosage. When the dosage of coagulant PAC is 0.42mmol / L, the effluent pH value remains at around 7.5. When the dosage of cerium salt coagulant CAN is 0.49mmol / L, the coagulation ends, and the effluent pH value decreases to 6.21. When the dosage of cerium salt coagulant CCl is 0.49mmol / L, the effluent pH decreases to 6.47. It can be seen that CAN shows a lower effluent pH, which is attributed to Ce 4+ The ion valence is higher and the ion radius is smaller, which leads to a higher degree of hydrolysis than Ce. 3+ , can combine more OH - .

[0064] For PAC, the zeta potential of the flocs increases sharply with the increase of the dosage. For CCl and CAN, the zeta potential of the flocs increases gradually with the increase of the dosage. The turbidity removal capacity has a good correlation with the zeta potential, which shows that adsorption charge neutralization plays an important role in the coagulation process of PAC, CCl and CAN. The charge neutralization capacity of PAC is slightly larger than that of cerium salt coagulants CCl and CAN, but due to Figure 1 It can be seen that PAC has a strong effect on the UV 254The removal rate is relatively low, which is mainly related to the stronger organic matter adsorption capacity of cerium salt coagulants CCl and CAN.

[0065] Test 3: Investigate the residual metal ion concentration after coagulation with different coagulants.

[0066] The supernatant of the coagulated water at the optimal dosage was taken to determine the residual metal ion concentration after coagulation with different coagulants. The results are shown in Table 1.

[0067] Table 1 Residual metal ion concentrations of different coagulants after coagulation

[0068]

[0069] From the results in Table 1, we can see that the order of residual metal ion concentration of different coagulants is as follows: C CCl >C PAC >C CAN ; C residual metal ion concentration. Therefore, for the treatment process with high residual metal concentration requirements for coagulation effluent and acidic raw water quality, the use of coagulant CAN is more effective.

[0070] Test 4: Investigate the effect of coagulants on turbidity and UV at different initial pH values 254 And the removal effect of DOC.

[0071] The performance of the coagulant varies significantly with the pH value of the water sample. The initial turbidity of the water sample was 18±0.5NTU, the humic acid concentration was 10mg / L, the PAC, CAN and CCl dosages were all 0.35mmol / L, and the coagulation experiment method was as described above. The initial pH values ​​were 3, 4, 5, 6, 7, 8, 9, and 10, respectively. The effects of the coagulant on turbidity and UV under different initial pH conditions were investigated. 254 And the removal effect of DOC. The experimental results are as follows Figure 3 shown.

[0072] Depend on Figure 3 It can be seen that compared with PAC and CCl, the coagulant CAN exhibits better turbidity removal performance under acidic conditions; and compared with PAC, CAN has a better coagulation effect in the pH range of 3 to 9 and has stronger pH adaptability.

[0073] Test 5: To explore the flocs’ resistance to breakage and their ability to regenerate after breakage.

[0074] After the slow stirring was completed, a shear force of 200 rpm was applied to the generated flocs for 3 min, and then the slow stirring speed was restored to 40 rpm to further explore the flocs' resistance to breakage and their ability to regenerate after breakage. Figure 4 shown.

[0075] Depend on Figure 4 It can be seen that the three coagulant flocs all show a certain degree of regeneration ability after being broken, but the flocs of CAN have the largest particle size and the fastest growth rate; and larger flocs usually have a faster sedimentation rate, which can shorten the hydraulic retention time in practical applications. This shows that compared with PAC and CCl, the flocs of coagulant CAN have the largest particle size and the fastest growth rate, have a faster sedimentation rate, and can effectively shorten the hydraulic retention time.

[0076] Example 2

[0077] An application of a cerium salt coagulant in removing algae from water, the specific application method is as follows:

[0078] The algae solution was collected after 12 to 14 days of growth. The algae solution contained Microcystis aeruginosa. Microcystis aeruginosa was purchased from the Institute of Aquatic Biology and cultured in BG-11 medium. The algae solution was mixed with 0.9% NaCl solution and the initial concentration of the mixed algae solution was adjusted to 3×10 6 cells / mL, OD 680 =0.2±0.05, as the simulated water sample; and the initial pH value of the simulated water sample solution was adjusted with 0.1 M NaOH and 0.1 M HCl.

[0079] The coagulation experiment of simulated water samples containing algae was carried out in a 500mL system. The stirring program was set as follows: rapid stirring at 250rpm for 30s to mix the water sample, and then the reagent was added immediately after the end. After stirring at 200rpm for 2min, it was slowly stirred at 40rpm for 15min. After standing for 20min, a certain amount of supernatant was drawn with a syringe for further analysis.

[0080] Agents: Cerium ammonium nitrate and cerium chloride were selected as cerium salt coagulants, and the traditional coagulant polyaluminium chloride was used as a comparison to explore the removal effect of different coagulants on algae in simulated water samples containing algae. Among them, cerium ammonium nitrate is abbreviated as CAN, cerium chloride is abbreviated as CCl, and the traditional coagulant polyaluminium chloride is abbreviated as PAC.

[0081] Example 2 mainly explores the removal effect of tetravalent cerium salt CAN, trivalent cerium salt CCl and traditional commercial coagulant polyaluminium chloride PAC on drinking water source algae. The effects of coagulant dosage and solution pH on the coagulation and algae removal effect are studied to find the optimal coagulation conditions for removing intact algae cells, and to compare and analyze the removal effects and action mechanism differences of coagulants of different valence states of cerium salts. The main detection indicators include effluent pH value, residual turbidity, residual chlorophyll a and residual metal ion concentration.

[0082] Test 6: Investigate the effect of coagulant dosage on coagulation effect.

[0083] For the initial pH = 7 and the algae cell density of 3×10 6 cells / mL of simulated water samples containing algae, the removal rate changes of chlorophyll a and turbidity by different coagulants were investigated under the conditions of PAC dosage of 0.07mmol Al / L~0.42mmol Al / L, CAN and CCl dosage of 0.01mmol Ce / L~0.06mmolCe / L. The results are shown in Figure 5 .

[0084] Depend on Figure 5 It can be seen that the dosage of coagulant required for the coagulation of the simulated water sample containing algae in Example 2 is much lower than the optimal dosage of coagulant in the humic acid-kaolin simulated water sample in Example 1. Because algae-derived organic matter AOM can be used as a polymer additive to reduce the required dosage of coagulant. When the dosage of coagulants CAN and CCl is 0.01mmol / L~0.04mmol / L, the removal rates of turbidity and chlorophyll a increase with the increase of the dosage of coagulant. When the dosage is 0.04mmol / L, the removal rates of turbidity and chlorophyll a are the highest. The removal rates of turbidity and chlorophyll a in the CAN group reached 95.79% and 95.02%, respectively, and the removal rates of turbidity and chlorophyll a in the CCl group reached 97.25% and 98.62%, respectively; and when the dosage of PAC is 0.07mmol / L~0.21mmol / L, the removal rates of chlorophyll a and turbidity can be maintained above 90%.

[0085] From the above analysis, it can be seen that the cerium salt coagulants CAN and CCl have stronger removal performance on algae, and the optimal dosage of CAN and CCl is lower than that of PAC, and the effluent metal ion concentration of CAN and CCl groups is also much lower than that of PAC group, avoiding the adverse effects of residual metal ions on subsequent treatment units.

[0086] Test 7: Investigate the effect of coagulant dosage on floc zeta potential.

[0087] like Figure 6 As shown in the figure, the zeta potential of the flocs generated by the coagulant increases with the increase in the dosage. When the dosage of the coagulant PAC is 0.07mmol / L, the zeta potential of the flocs reaches +1.824mV. When the dosage of CAN and CCl is 0.06mmol / L, the zeta potential of the flocs reaches +5.358mV and +2.796mV respectively. This shows that the three coagulants have the same ability to neutralize the charge and remove algae cells.

[0088] Figure 6It shows that when the dosage of PAC is 0.03mmol / L, and the dosage of CAN and CCl is 0.05mmol / L, the amplitude of the negative zeta potential value is small, and then the charge reversal occurs at a higher dosage, and the zeta potential value of the flocculent becomes positive. These results show that charge neutralization plays a certain dominant role in the coagulation process of the three coagulants. The highest removal efficiency was achieved when the dosage of CAN and CCl was 0.04mmol / L. At this time, the zeta potential value of the floccules after flocculation was negative, proving that charge neutralization is not the only mechanism, and adsorption and sweep flocculation are also involved in the coagulation of algae cells by cerium salt coagulants. Ce 4+ It exists in water as a cationic amorphous hydroxide precipitate, which can cause sweep flocculation and provide adsorption sites for negatively charged pollutants, resulting in Ce 4+ The excellent coagulation effect of CCl on algae cells is related to the phospholipids on the cell surface, indicating that Ce 3+ It has strong adsorption and removal ability for phosphate.

[0089] Test 8: Investigate the effect of pH on coagulation.

[0090] pH is an important factor affecting coagulation effect. In order to investigate the effect of pH on coagulation, the initial pH values ​​of simulated water samples containing algae were adjusted to 5, 6, 7, 8, 9, and 10. The results are as follows: Figure 7 shown.

[0091] Depend on Figure 7 It can be seen that CAN has a high chlorophyll a and turbidity removal rate under the initial pH = 5-8. PAC maintains a removal rate of more than 90% under the condition of pH = 7-9. The suitable pH range of CCl is narrow, and the chlorophyll a and turbidity removal rates of more than 90% can be achieved only under the condition of pH = 6-7. When the pH rises to 10, the coagulation efficiency of the three coagulants on algal cells is low. PAC performs better than cerium salt coagulants under alkaline conditions. However, within the pH range of the solution investigated, the residual aluminum content is more correlated with pH. At pH = 5, 6 and 10, the residual aluminum content exceeds the national drinking water standard, that is, >0.2 mg / L. In addition, when pH = 5, the residual metal ion concentration of CAN's effluent is significantly lower than that of PAC and CCl. This is because the hydrolysis state of metal salts is different. For example Figure 7As shown in Figure (d), when the pH is less than 9, the floc zeta potential of PAC is positive. When the pH increases to 10, the floc zeta potential of PAC drops rapidly to -15.55mV, which shows that electrical neutralization is the main mechanism of PAC coagulation and algae removal. However, whether it is CCl coagulant or CAN coagulant, the floc zeta potential is negative in the range of pH = 5 to 10, indicating that electrical neutralization is not the only mechanism of action. This shows that cerium salt coagulants remove algae from water bodies through multiple mechanisms.

[0092] Test 9: Investigate the effect of floc size on coagulation effect during the coagulation process.

[0093] The particle size, uniformity and density of the flocs formed during the coagulation process determine the coagulation effect. The changes in the particle size of the three coagulants CAN, CCl and PAC at pH = 7 were monitored online using a laser particle size analyzer. The results are as follows: Figure 8 shown.

[0094] Depend on Figure 8 It can be seen that the floc particle size generated by CAN and CCl is significantly larger than that generated by PAC. The floc particle size generated by CAN and CCl reaches 1200μm after stirring for 9 minutes; while the maximum particle size of PAC is only 203μm. Compared with the traditional PAC coagulant, the two cerium salt coagulants CAN and CCl grow faster and have larger floc sizes. They can form larger aggregates in a shorter time and maintain larger floc particle sizes at each stage, namely steady state, after crushing and after regeneration. At the same time, compared with PAC, CAN has better sedimentation performance, shorter retention time and larger and more compact flocs, which can reduce the construction area of ​​flocculation and sedimentation units, which is conducive to reducing capital costs and floor space.

[0095] Test 10: Explore the changes in algal cell morphology after coagulation.

[0096] In order to further explore the changes in algal cell morphology after coagulation, an algal accumulation experiment was conducted on the flocs after coagulation. The flocs were taken on the 1st, 4th and 8th day after coagulation and the morphology was observed by scanning electron microscopy. The results are as follows: Fig. 9 shown.

[0097] Depend on Fig. 9 It can be seen that after CAN coagulation treatment, a large amount of metal hydrolyzates completely wrapped the algae cells. In addition, the algae cells were tightly aggregated and wrapped in flocs, and gathered together to form a cluster of mass structures. However, the algae surface treated with CCl and PAC was not completely covered with metal hydrolyzates, and most of the algae cells were still aggregated and partially exposed. The morphology of the algae cells was clearly visible and intact without obvious rupture.

[0098] As the accumulation progressed, on the fourth day, many algal cells in the CAN flocs began to shrink and break, the cells gradually lysed, and the structure began to collapse. Fig. 9 However, some algal cells treated with CCl and PAC showed signs of fragmentation on the 4th day, and a large number of them were fragmented on the 8th day, and the fragmentation of the CCl group was less than that of the PAC group.

[0099] The experimental results show that CAN coagulant has a certain damaging effect on algal cells in flocs, while CCl has less damaging effect on algal cells and is not easy to cause algal cells to rupture.

[0100] In summary, the cerium salt coagulant CAN has better coagulation effect in terms of turbidity removal and organic matter than traditional coagulants, and the flocs are larger and have better sedimentation performance. In addition, when the initial pH value of the water sample changes, the coagulation effect of CAN is relatively stable, and the organic matter removal rate and algae removal rate in the range of pH = 3 to 9 are significantly higher than those of PAC.

[0101] In the simulated water sample experiment containing algae, compared with the traditional coagulant PAC, CAN and CCl have faster growth rate and larger floc size, and show stronger regeneration ability after floc breaking. And the metal ion concentration of effluent is much lower than that of the traditional coagulant PAC. The study of algae aging shows that for cerium salt coagulants, it is best to treat sludge in a faster cycle, among which CCl is relatively less destructive to algal cells, which can better guide the application in actual engineering.

[0102] In the case where both organic matter and algae appear in the water, more coagulants need to be added for treatment because the above substances are negatively charged. However, since algae have extracellular polymers that can better promote coagulation, the amount of coagulant used in the mixed treatment of the two should be less than the amount used for separate treatments.

[0103] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Application of a cerium salt coagulant in water treatment, characterized in that: The specific application method includes the following steps: The cerium salt coagulant is added to the water body to be treated under stirring to carry out a coagulation reaction, and after the flocs produced by the coagulation reaction are settled, the supernatant is separated to obtain the treated water body; The cerium salt coagulant is at least one of a trivalent cerium salt coagulant and a tetravalent cerium salt coagulant; The water body to be treated is a water body containing organic matter and / or algae; For the treatment of water containing organic matter and turbidity, the dosage of the cerium salt coagulant in the water to be treated is 0.14mmolCe / / L to 0.49mmolCe / / L; For the treatment of water bodies containing algae, the dosage of the cerium salt coagulant in the water body to be treated is 0.01 mmol / L to 0.06 mmol / L.

2. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The cerium salt coagulant is at least one of cerium nitrate, ammonium cerium nitrate, cerium chloride, cerium sulfate and cerium oxalate.

3. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The organic matter in the water to be treated is organic matter having light absorption characteristics under ultraviolet light of 254nm wavelength.

4. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The algae in the water body to be treated is at least one of Chrococcus, Microcystis, Spirulina, Oscillatoria, Chlorella and diatoms.

5. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: Regarding the treatment of water bodies containing organic matter and turbidity, before the coagulation reaction, it also includes: adjusting the initial pH of the water body to be treated to 3-10.

6. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The treatment of water bodies containing algae, before the coagulation reaction, also includes: adjusting the initial pH of the water body to be treated to 5-10.

7. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The treatment method for water containing organic matter-turbidity is: The cerium salt coagulant is hydrolyzed in the water to be treated to form flocs of metal polynuclear hydroxyl compounds; The flocs produced by the hydrolysis of the cerium salt coagulant coagulate and precipitate the organic matter and turbidity in the water body to be treated through charge neutralization and adsorption, and the supernatant is separated to obtain the treated water body.

8. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The treatment methods for water bodies containing algae are: The cerium salt coagulant is hydrolyzed in the water to be treated to form flocs of metal polynuclear hydroxyl compounds; The flocs produced by the hydrolysis of the cerium salt coagulant form adsorption bridges between different individual algae cells through charge neutralization, adsorption and sweep flocculation, and entangle the algae cells that are bridged together and wrap them in the produced flocs to form a clustered structure.

9. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The residual metal ion concentration in the treated water is ≤0.2mg / L.

10. The use of the cerium salt coagulant in water treatment according to claim 1, characterized in that: The coagulation reaction time is 15min to 30min.

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