A water treatment method based on coagulation coupled spontaneous flotation process

Abstract

A water treatment method based on coagulation-coupled spontaneous flotation process, the steps are as follows: adding a cross-linking agent to the water body to be treated with a dissolved oxygen content of more than 4 mg / L, stirring at a speed of 100-200 rpm for 30-120 seconds for uniform mixing, then adding a coagulant, stirring at a speed of 400-600 rpm for 15-60 seconds for uniform mixing, and finally standing for 10-20 minutes to complete flotation. The water treatment process based on coagulation-coupled spontaneous flotation of the present invention effectively utilizes the dissolved gas in the water, and by controlling the addition ratio, addition method and hydraulic conditions of the cross-linking agent and the coagulant, a cloud-like gel floccules is obtained, which can effectively encapsulate the dissolved gas oxygen and realize spontaneous, stable and efficient flotation. Compared with traditional processes, the water treatment method based on coagulation-coupled spontaneous flotation process of the present invention shortens the operation time, does not require additional gas dissolving devices and pressure equipment, effectively reduces the infrastructure and operation costs of the wastewater treatment plant, and reduces carbon emissions.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a water treatment method based on a coagulation-coupled spontaneous flotation process. Background Art

[0002] Coagulation is an indispensable pre-unit operation technology in many sewage treatment processes. Its treatment efficiency largely determines the operating conditions, treatment costs and final effluent quality of subsequent processes; and flotation, as an efficient solid-liquid separation technology, can effectively remove pollutants in water bodies when coupled with coagulation process. Due to its simple operation, the coagulation-pressurized dissolved air flotation process has been widely used in algae removal, mineral separation, drug degradation, brewing wastewater treatment and seawater desalination. This process mainly relies on a large number of fine bubbles generated by pressure equipment, which adhere to the surface of flocs produced by coagulation during the floating process, and then float to the liquid surface area together to form a large amount of foam or scum, so as to effectively remove pollutants. However, this process requires the cooperation of pressure and dissolved air equipment, which greatly increases the construction, operation and maintenance costs of sewage treatment plants. In addition, for the traditional coagulation-pressurized dissolved air flotation technology, bubbles are adsorbed on the surface of flocs produced by coagulation, and the collision of flocs with each other during the rising process usually leads to partial gas desorption, resulting in reduced or fluctuating flotation efficiency.

[0003] With the increasing shortage of water resources and water pollution in recent years, how to improve the efficiency of the existing coagulation-pressurized dissolved air flotation process and reduce the operating cost has become a hot topic in the field of water treatment. Although subsequent improvement processes, including mixed ozone coagulation, colloidal gas adsorption, etc., can improve the gas flotation efficiency to a certain extent, the more expensive gas source and complex operating procedures have greatly increased the cost and power consumption of industrialization. Jin Pengkang et al. reported a microbubble ozone-coagulation-flotation process (CN201310654568), which achieved a change in the order of ozone addition by switching the two branches on the reflux pipe, that is, the mutual conversion of ozone addition before and after coagulation, achieving good pollutant removal efficiency. However, under the action of ozone, the molecular weight of pollutants is significantly reduced, and the oxidation process of this unsaturated organic matter accelerates the consumption of ozone. In addition, the stability and oxidation capacity of ozone are significantly affected by factors such as temperature and pH, and further debugging and monitoring are required.

[0004] Therefore, in order to reduce the expensive gas source and the operation and maintenance costs of the equipment, it is necessary to improve the traditional coagulation-pressure dissolved air flotation process for water treatment. Summary of the invention

[0005] Based on this, the present invention provides a water treatment method based on coagulation-coupled spontaneous flotation process to solve the technical problem that the traditional coagulation-pressurized dissolved air flotation process ignores the original dissolved gas in the wastewater, and the additional air source and aeration equipment increase the energy consumption, construction and operation costs, thereby increasing the carbon emissions of the sewage treatment plant.

[0006] To achieve the above object, the present invention provides a water treatment method based on coagulation coupled spontaneous flotation process, which comprises the following steps:

[0007] A cross-linking agent is added to the water body to be treated with a dissolved oxygen content of more than 4 mg / L, and the mixture is stirred at a speed of 100-200 rpm for 30-120 seconds for uniform mixing, and then a coagulant is added, and the mixture is stirred at a speed of 400-600 rpm for 15-60 seconds for uniform mixing, and finally the mixture is allowed to stand for 10-20 minutes to complete flotation; wherein the cross-linking agent is at least one of sodium alginate, laminarin, and enteromorpha polysaccharide, and the coagulant is at least one of aluminum sulfate, polyaluminum chloride, ferric chloride, and polyferric sulfate. In terms of mass concentration, the dosage ratio of the cross-linking agent to the coagulant is 3:2-3:1, preferably 2:1.

[0008] As a further preferred technical solution of the present invention, the dissolved oxygen content of the water to be treated needs to be higher than 8 mg / L, and the flotation temperature needs to be higher than 5°C.

[0009] As a further preferred technical solution of the present invention, the water body to be treated is natural surface water, algae-containing surface water, printing and dyeing wastewater, papermaking wastewater, mining wastewater, brewing wastewater, antibiotic wastewater or microplastic-contaminated water.

[0010] Abundant dissolved gases (such as dissolved oxygen) exist in a variety of polluted water bodies, such as surface water with algae outbreaks, domestic sewage, industrial wastewater, etc. Dissolved oxygen can be used as a flotation carrier to achieve its effective utilization in the coagulation-coupled spontaneous flotation process (referred to as the coagulation-flotation process). Inspired by clouds, it is envisaged to form lighter gel-like flocs to effectively encapsulate the dissolved gases contained in the sewage itself during the coagulation process, and finally complete spontaneous floating under the action of buoyancy. Therefore, the coagulation-flotation process proposed in the present invention can produce the effect of spontaneous flocculent flotation when the dissolved oxygen content is higher than 4 mg / L without the introduction of an additional gas source, which will greatly reduce the operating cost of the coagulation and flotation process.

[0011] In addition, in the traditional coagulation-pressure dissolved air flotation technology, coagulation and flotation are two independent process units. In contrast, the integration of coagulation and flotation devices can be achieved through the spontaneous adsorption and encapsulation of bubbles by flocs, which can effectively reduce the infrastructure investment of sewage treatment plants. The technical core of this process lies in how to generate low-density gel flocs through the selection of coagulants and cross-linking agents, the control of dosage and the optimization of hydraulic conditions, so as to effectively encapsulate dissolved gas to achieve spontaneous flotation process, thereby achieving stable process efficiency and lower water treatment costs.

[0012] The cross-linking agent of the present invention is used to provide a large amount of -COOH and -OH, and the coagulant is used to provide Al 3+ or Fe 3+ , crosslinking agent and coagulant can produce -AlO6 or -FeO6. The characteristics of the water purifier system of the present invention are as follows: first, -COOH produces chelation (crosslinking) effect with metal ions, secondly, -OH produces the strongest adsorption binding energy for O2, and thirdly, the -AlO6 (-FeO6) structural site (the steric hindrance of the adsorption process is relatively large); Al 3+ Has a higher Fe 3+ Lighter atomic mass and higher charge density (same charge carrying capacity and smaller ionic radius); Fe 3+ Can produce more than Al 3+ Stronger floc characteristics (larger structural size and anti-crushing strength). Therefore, different water purification agent combinations can target different pollutant water systems and design water resource recovery strategies tailored to local conditions.

[0013] Preferably, the combination of sodium alginate (or Enteromorpha polysaccharide) and polyaluminium chloride (or aluminium sulfate) can produce a stronger cross-linking effect (-AlO6), and can form a three-dimensional network cross-linking structure with a lower classification dimension, which is suitable for cross-linking flotation of wastewater with low organic matter and high-density suspended particles; the combination of laminarin and polyaluminium chloride (or aluminium sulfate) can produce a stronger gas adsorption capacity (more -OH), which is suitable for purification flotation of wastewater with high turbidity or high pollutant concentration; the combination of sodium alginate (or Enteromorpha polysaccharide) and polyferric chloride (or ferric chloride) can produce a stronger floc crushing resistance (-FeO6), which is suitable for capture and flotation of high-turbidity wastewater with high organic matter content.

[0014] The water treatment method based on the coagulation-coupled spontaneous flotation process of the present invention can achieve the following beneficial effects by adopting the above technical scheme:

[0015] 1) In the present invention, the amount of cross-linking agent is higher than that of coagulant, and the cross-linking agent is added before the coagulant to ensure that the pollutants can be encapsulated in the floccules together with the cross-linking agent during subsequent adsorption and net capture. A high dose of cross-linking agent can ensure a lower Al content than the national water purification standard (0.2 mg / L).3+ Residue (0.0485~0.0837mg / L);

[0016] 2) The total time of hydraulic stirring required after the addition of the coagulant in the present invention (within 2 minutes) and the total time required for coagulation purification to be completed (within 20 minutes) are shorter, which effectively shortens the service life of the flocculation tank in industrial water purification. During the flotation process, the bubbles are mainly distributed inside the flocs and can be stably present for a long time within 8 hours, thereby satisfying the requirements of gas desorption from water and stable floating flocs, making the flotation process more efficient and stable;

[0017] 3) The floc size formed by the coagulation-coupled spontaneous flotation of the present invention has an obvious normalization trend, and its macroscopic structure is more like a "cloud". The larger floc size can effectively increase the collision probability among pollutants, coagulants and bubbles, thereby improving the purification disadvantage of low collision and adhesion efficiency caused by the small floc size of the traditional external gas flotation method.

[0018] 4) Compared with the traditional coagulation-pressurized dissolved air flotation technology, the present invention has two obvious advantages: (1) The present invention eliminates the need for external air source and pressure equipment, and the coagulation tank and air flotation tank can be integrated, which significantly reduces the construction and operation costs of the water treatment plant; (2) The dissolved gas of the present invention can be effectively encapsulated in the gel flocs instead of being adsorbed on the surface, resulting in a faster flotation process and more stable flotation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0020] Figure 1 Schematic diagram of desorption of microbubbles in gel flocs of the present invention.

[0021] Figure 2 This is a diagram showing the treatment efficiency of algae-containing surface water by the coagulation-coupled spontaneous flotation process in Example 1.

[0022] Figure 3-1 It is a curve diagram of the organic matter removal rate in the treatment efficiency of heavy metal wastewater by the coagulation-coupled spontaneous flotation process in Example 2;

[0023] Figure 3-2 The heavy metal removal rate curve of the treatment efficiency of heavy metal wastewater by the coagulation-coupled spontaneous flotation process in Example 2;

[0024] Figure 3-3 The turbidity removal rate curve of the treatment efficiency of heavy metal wastewater by the coagulation-coupled spontaneous flotation process in Example 2;

[0025] Figure 4This is a time relationship diagram of the gel floccules floating in the water sample in Example 2;

[0026] Figure 5 The treatment efficiency of dye wastewater by coagulation-coupled spontaneous flotation process in Example 3 is shown. The horizontal axis corresponds to the stirring time of adding cross-linking agent and coagulant under different hydraulic conditions. For example, 5-15 is the stirring time of adding cross-linking agent for 5s and the stirring time of adding coagulant for 15s.

[0027] Figure 6 These are pictures of water samples before, during and after flotation of acid red dye in Example 3.

[0028] Figure 7 These are water sample pictures corresponding to the effects of various process conditions that deviate from the optimal range on the flotation effect.

[0029] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0031] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0032] Natural polysaccharides (sodium alginate, kelp polysaccharide, enteromorpha polysaccharide) can quickly form gels under a wide range of water conditions. - The -OH group exhibits polyanionic behavior, and the -OH group can adsorb and aggregate negatively charged dissolved gases in water or electronegative microbubbles on the interface. 3+ Can be effectively used with three-COO - Cross-linking occurs, and some free Al 3+ The negatively charged organic matter is complexed in an electrically neutral way. At the same time, the residual crosslinking agent in the water is captured by adsorption bridging and net sweeping, and it is captured and encapsulated in floccules. At this time, due to the floccules in the crosslinking process, the system will be divided into two regions - liquid phase region (Ⅰ) and floc region (Ⅱ). Figure 1As shown in the figure, in zone II, due to the encapsulation of the flocs and the ability of the polymer gel to absorb and hold a large amount of water, a high concentration of organic polymer solution appeared, which undoubtedly affected the saturated solubility of the dissolved gas in the water sample inside the flocs, turning the saturated solution or nearly saturated solution (initial water sample) of the dissolved gas into a supersaturated solution. The metastable water environment in the flocs is composed of microbubbles, aluminum and -COO attached in the initial stage. - The conjugated structure (-AlO6) produced by cross-linking and the hydroxyl groups in the molecular structure of the cross-linking agent are used as sites to precipitate supersaturated gas, thereby generating bubbles visible to the naked eye. The small flocs dispersed in zone II will gradually collide, adhere and gather during the hydrolysis of the coagulant to form large flocs with higher aggregation. As the gas precipitation process proceeds, the buoyancy of the flocs as a whole slowly increases until the flocs float on the liquid surface, and the coagulation-spontaneous flotation phenomenon occurs. On the other hand, most of the cross-linking agents in zone I are encapsulated into zone II along with the pollutants, and their own body concentration is significantly reduced, ensuring a lower organic matter residual concentration in zone I. The mechanism of action of ferric chloride, polyferric sulfate and cross-linking agent in the water purifier system is the same as that of aluminum sulfate and polyaluminum chloride, which will not be repeated here. Therefore, the combination of natural polysaccharides and aluminum / iron salt coagulants shows great potential in realizing gel floc formation and spontaneous flotation processes.

[0033] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments and comparative experiments.

[0034] Embodiment 1:

[0035] The natural surface water of Kuihe River in Xuzhou City, Jiangsu Province during the algae outbreak period was used as the water sample to be treated. It was mixed evenly, and then the cross-linking agent-laminarin was added to the water sample to be treated, and it was quickly stirred at 150 rpm for 40 seconds, and then the coagulant-aluminum sulfate (the dosage ratio of laminarin to aluminum sulfate was 2:1) was added, and it was stirred at 400 rpm for 20 seconds, and then it was left to float for 20 minutes. After the flotation, the clear liquid was taken to determine the removal efficiency of algae. The results are as follows: Figure 2 shown.

[0036] After testing and analyzing the water quality of the treated water samples, the relevant information of the original water samples is as follows: dissolved oxygen (13-20 mg / L), extracellular polysaccharides (15-20 mg / L), pH (7.20-8.20), temperature (25-30°C). Figure 2 It can be seen that during the algae bloom period, the surface water of Xuzhou City mainly contains several common dominant algae species such as Oscillatoria, Nostoc, Chlorella, and Tetrasodium, and the water body can be called algal bloom wastewater.

[0037] A laminarin-aluminum sulfate composite agent was selected and applied to the coagulation-coupled spontaneous flotation process. The abundant dissolved oxygen can respond immediately to the flotation process (completed within 3 to 8 minutes). With the continuous increase of the dosage of aluminum sulfate (measured in aluminum), the dosage ratio of laminarin to aluminum sulfate was maintained at 2:1, and the algae removal rate continued to increase. At a dosage of 14 mg / L, more than 95% of the algae can be removed. The algae removal efficiency is excellent, which shows a strong application potential in the actual algae wastewater treatment.

[0038] Embodiment 2:

[0039] Humic acid-nano-titanium dioxide simulated heavy metal contaminated wastewater was used as the water sample to be treated, and its preparation method was as follows: 1.0 g of humic acid and 0.4 g of sodium hydroxide were accurately weighed and dissolved in 800 mL of deionized water. After fully dissolved, the volume was adjusted to 1 L to obtain a humic acid stock solution, which was then stored in a brown reagent bottle; 14 mg of nano-titanium dioxide particles were accurately weighed and added to 28 mL of the humic acid stock solution. After ultrasonic mixing, the solution was dispersed and adjusted to 14 L of tap water to obtain a humic acid-nano-titanium dioxide simulated water sample, in which the contents of nano-titanium dioxide and HA were 1 mg / L and 2 mg / L, respectively.

[0040] Mix the prepared simulated water sample evenly, then add the crosslinking agent-sodium alginate to the water to be treated, stir rapidly at 200 rpm for 30 seconds, then add the coagulant-polyaluminium chloride (or aluminium sulfate), stir at 500 rpm for 15 seconds, and then let it stand for flotation for 12 minutes. After the flotation is completed, take the clear liquid to determine the removal efficiency of organic matter, nano-titanium dioxide and turbidity. The results are as follows: Figures 3-1 to 3-3 The dissolved oxygen content in the simulated water is 8.0-8.8 mg / L, and the temperature is 20-25°C. After about 10 minutes of flotation, the gel flocs can spontaneously and quickly float to the liquid surface as a whole. The relationship between the floating of the gel flocs and time is shown in the figure. Figure 4 shown.

[0041] from Figures 3-1 to 3-3 It can be seen that the coagulation-coupled spontaneous flotation process has a good treatment efficiency for heavy metal wastewater: low coagulant addition concentration (4-6 mg / L) can still maintain the removal rate of organic matter and metal oxide nanoparticles above 60%, and the removal rate of turbidity reaches more than 90%. At a higher coagulant addition concentration (8-10 mg / L), the removal rates of organic matter, metal oxide nanoparticles and turbidity can reach about 75%, 90% and 95% respectively. In addition, the results of Figure 3 show that the dosage ratio of cross-linking agent to coagulant is an important factor affecting the performance of the coagulation-coupled spontaneous flotation process. For the humic acid-nano-titanium dioxide simulated water sample, the optimal dosage ratio is 2:1, which meets the requirements of a smaller dosage, that is, a higher removal rate.

[0042] Embodiment 3:

[0043] Acid red simulated printing and dyeing wastewater was used as the water sample to be treated. The preparation method was as follows: accurately weigh 0.1 g of acid red dye and dissolve it in 800 mL of deionized water. After it was fully dissolved, the volume was fixed to 1000 mL. The dissolved oxygen content in the simulated water quality was 9.5-10.8 mg / L.

[0044] The prepared printing and dyeing wastewater simulation water sample was mixed evenly, and then the dosage ratio (mass concentration) of the cross-linking agent to the coagulant was 2:1. The organic flocculant-Enteromorpha polysaccharide was first added to the water to be treated, and stirred rapidly at 200 rpm for 5-150 seconds, and then the inorganic coagulant-ferric chloride (or polyferric sulfate) was added, and stirred at 500 rpm for 15-60 seconds, and then allowed to float for 20 minutes. After the flotation, the clear liquid was taken to determine the removal efficiency of the dye. The results are as follows: Figure 5 The water samples before, during and after flotation are shown in Figure 6 As shown, the red substance in the cup is acid red dye.

[0045] from Figure 5 It can be seen that the coagulation-coupled spontaneous flotation process has a good treatment effect on printing and dyeing wastewater, and the removal rate can reach more than 80% after 20 minutes of flotation. Figure 5 The results show that hydraulic conditions have a great influence on the efficiency of the coagulation-coupled spontaneous flotation process. For the simulated printing and dyeing wastewater sample, the organic flocculant-Enteromorpha polysaccharide is added to the water sample to be treated, and it is rapidly stirred at 200 rpm for 60 seconds, and then the inorganic coagulant-ferric chloride (or polyferric sulfate) is added, and it is stirred at 500 rpm for 30 seconds, and finally it is left to float for 20 minutes to achieve an 85% dye removal rate. In addition, from Figure 5 It can be seen that when the hydraulic conditions are outside the range of "stirring at a speed of 100-200 rpm for 30-120 seconds" or "stirring at a speed of 400-600 rpm for 15-60 seconds", there is basically no spontaneous flotation phenomenon and the resulting dye removal rate is very low.

[0046] Embodiment 4:

[0047] The same experimental objects and water treatment methods as in Example 1 were selected, and only the coagulant was replaced with polyferric sulfate (or ferric chloride, or polyaluminium chloride). With a dosage ratio of 2:1 between the cross-linking agent and the coagulant, the algae removal rate of 80-95% could be achieved at a dosage of about 14 mg / L of the coagulant.

[0048] Embodiment 5:

[0049] The same experimental objects as those in Implementation 2 and the water treatment method with the same process parameters were selected, and only the flocculant was replaced with Enteromorpha polysaccharide and the coagulant was replaced with polyferric sulfate (or ferric chloride). The test results are as follows: Under different dosage ratios of the cross-linking agent and the coagulant, the best effect is achieved when the dosage ratio of the mass concentration is 2:1, and a smaller dosage can achieve a higher removal rate. When the coagulant is added at a concentration of (6-8 mg / L), the removal rates of organic matter, metal oxide nanoparticles and turbidity can reach about 78%, 92% and 95% respectively, which is equivalent to the technical effect of Example 2.

[0050] Embodiment 6:

[0051] The same experimental objects and water treatment methods as those in implementation 3 were selected, and only the flocculant was replaced by laminarin and the coagulant was replaced by polyaluminium chloride (or aluminium sulfate). In the experimental test, laminarin was added to the water sample to be treated, and the mixture was stirred rapidly at 200 rpm for 60 seconds, and then polyaluminium chloride (or aluminium sulfate) was added, and the mixture was stirred at 500 rpm for 30 seconds, and finally the mixture was allowed to stand for flotation for 20 minutes, and a dye removal rate of 76% was achieved. Moreover, when the hydraulic conditions were outside the range of "stirring at a speed of 100-200 rpm for 30-120 seconds" or "stirring at a speed of 400-600 rpm for 15-60 seconds", that is, the stirring time of adding the flocculant was too long or too short, or the stirring time of adding the coagulant was too long or too short, there was basically no spontaneous flotation phenomenon, and the removal rate of the obtained dye was very low, less than 8%.

[0052] In order to further study the influence of various process parameters on water treatment in the coagulation-coupled spontaneous flotation process, the following comparative tests were carried out:

[0053] (1) As a comparative experiment of Example 2, when other process parameters and conditions remain unchanged, only the dosage of coagulant is insufficient. After flotation, the macroscopic results of the water sample are as follows: Figure 7 As shown in a, it can be seen that the pollutant removal efficiency is limited and the degree of floc aggregation is not high; similarly, the same comparative experiment is conducted on Example 1, and the comparative experimental results are the same as those of Example 2.

[0054] (2) As a comparative experiment of Example 1, when other process parameters and conditions remain unchanged, only the dosage of the cross-linking agent is insufficient. The macroscopic results of the water sample after flotation are as follows: Figure 7 As shown in b, it can be seen that the floccules are stratified to produce a "sandwich" structure, which cannot produce an ideal flotation effect; similarly, the same comparative experiment is conducted on Example 2, and its comparative experimental results are the same as those of Example 1.

[0055] (3) As a comparative experiment of Example 2, when other process parameters and conditions remain unchanged, only the dissolved oxygen content in the water sample to be treated is insufficient (less than 4 ml / L). Due to the lack of dissolved oxygen as a flotation carrier, the macroscopic results of the water sample after flotation are as follows: Figure 7 As shown in Figure c, it can be seen that the floccules are deposited in the lower layer of the water and cannot complete the flotation phenomenon. Moreover, when the dissolved oxygen content is lower than 4 ml / L, the removal rate of organic matter and metal oxide nanoparticles is less than 10% when the optimal dosage ratio of cross-linking agent and coagulant and the maximum dosage are adopted, which cannot meet the needs of industrial wastewater treatment.

[0056] (4) As a comparative experiment of Example 2, when other process parameters and conditions remain unchanged and only the order of adding coagulant and cross-linking agent is reversed, a typical cross-linking structure cannot be generated, a large amount of organic cross-linking agent remains in the liquid phase, the coagulant cannot effectively fix the cross-linking agent, and only a small amount of microbubbles are generated outside the flocs. The macroscopic results of the water sample after flotation are as follows: Figure 7 As shown in middle d.

[0057] (5) As a comparative experiment of Example 1, when other process parameters and conditions remain unchanged and only the hydraulic conditions deviate from the preferred range, the stirring time of adding the cross-linking agent is greater than 120 s and / or the stirring time of adding the coagulant is greater than 60 s. Because the action time is too long, the flocculent encapsulation of microbubbles will fail (e.g. Figure 7 Insufficient shear force will lead to reduced cross-linking efficiency and delayed flotation time.

[0058] Although specific embodiments of the present invention are described above, those skilled in the art should understand that these are merely examples and that various changes or modifications may be made to the embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is limited only by the appended claims.

Claims

1. A water treatment method based on coagulation coupled spontaneous flotation process, characterized in that: The following steps are involved: Add a cross-linking agent to the water to be treated with a dissolved oxygen content of more than 4 mg / L, and stir at a speed of 100-200 rpm for 30-120 seconds to mix evenly, then add a coagulant, and stir at a speed of 400-600 rpm for 15-60 seconds to mix evenly, and finally stand for 10-20 minutes to complete spontaneous flotation; wherein the cross-linking agent is at least one of sodium alginate, laminarin, and enteromorpha polysaccharide, and the coagulant is at least one of aluminum sulfate, polyaluminum chloride, ferric chloride, and polyferric sulfate; Calculated by mass concentration, the dosage ratio of cross-linking agent to coagulant is 3:2-3:

1.

2. The water treatment method based on coagulation coupled spontaneous flotation process according to claim 1 is characterized in that: Calculated by mass concentration, the dosage ratio of cross-linking agent to coagulant is 2:

1.

3. The water treatment method based on coagulation coupled spontaneous flotation process according to claim 1, characterized in that: The dissolved oxygen content of the water body to be treated is higher than 8 mg / L.

4. The water treatment method based on coagulation coupled spontaneous flotation process according to any one of claims 1 to 3, characterized in that: The water body to be treated is natural surface water, algae-containing surface water, printing and dyeing wastewater, papermaking wastewater, mining wastewater, brewing wastewater, antibiotic wastewater or microplastic-contaminated water.

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