Method for removing algae through pre-oxidation enhanced coagulation

Abstract

The invention relates to a pre-oxidation enhanced coagulation algae removal method, belongs to the technical field of water algae removal, and provides a method for pre-oxidation of algae-containing water by combined use of ferrate and ferric oxychloride materials so as to enhance subsequent coagulation algae removal. According to the method, on the premise of ensuring low damage of algae cells and not releasing intracellular algal toxin, the stability of algae groups is reduced, so that the aim of enhancing coagulation of the algae cells is fulfilled. Free radicals generated by the reaction of ferrate and FeOCl reduce the electronegativity of extracellular organic matters of algae cells through an oxidation reaction, so that the algae cells are easily subjected to adsorption, bridging and other reactions with a coagulant, formation and sedimentation of flocs are accelerated in the presence of ferric oxide particles generated by decomposition of potassium ferrate and a FeOCl material, the coagulation process is enhanced, and the coagulation efficiency is improved. According to the invention, the precipitation of algae cells can be accelerated, the usage amount of the premixing agent is reduced, the release of organic matters in algae cells caused by transition pre-oxidation is avoided, and the coagulation algae removal efficiency of algae pollution is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of water algae removal, and in particular relates to a method for pre-oxidation enhanced coagulation algae removal. Background Art

[0002] Lake and reservoir water is an important source of drinking water in my country, accounting for 52.8% of the country's urban centralized drinking water sources. With the rapid development of industry and agriculture and the expansion of urbanization, more and more N and P nutrients are discharged into receiving water bodies with domestic sewage, causing lakes and reservoirs to show varying degrees of eutrophication. According to the survey results of the "2023 China Ecological Environment Bulletin", most of the important lakes (reservoirs) currently conducting nutrient status monitoring in my country have varying degrees of eutrophication. The algae bloom caused by eutrophication of water bodies increases the cost of water treatment and maintenance, brings many obstacles to the deep treatment of water and the daily maintenance of landscape water, and makes the water ecological environment unbalanced, seriously threatening the water safety of residents and other organisms, and becoming one of the important challenges facing the field of water resources and environment. Especially for urban agglomerations with lakes and reservoirs as water sources, the problems caused by algae, such as difficulty in coagulation of sewage treatment plants, blockage of filter pools, and excessive algae in effluent, have affected the normal operation of sewage treatment plants, caused water supply pressure, and also brought troubles to the normal life of residents. Therefore, pre-treating algae-containing water before it enters the conventional drinking water treatment process is an important entry point for simultaneously improving the quality of drinking water and reducing the operating risks of water plants.

[0003] At present, the most important, effective and economical method to deal with sudden algal blooms is coagulation and algae removal. The coagulation and algae removal method uses the principle of coagulation and sedimentation to remove algae cells. Coagulants destabilize algae cells through electrical neutralization, adsorption bridging and net capture and sweeping, and form flocs with coagulants, which can be removed in the subsequent sedimentation process. However, the properties of algae cells themselves will interfere with the coagulation effect. For example, the anionic characteristics of extracellular organic matter (EOM) are easy to form complexes with cationic coagulants or form hydrated ions during coagulation, which interferes with coagulation and algae removal.

[0004] When algae bloom and the algae concentration is too high, a large amount of coagulant is consumed and the coagulation effect becomes poor. Chemical pre-oxidation can significantly improve the coagulation efficiency without major changes to the existing process of the water plant. However, the selection and dosage of the oxidant and the time of the pre-oxidation process are directly related to the integrity of the algae cell structure. Excessive pre-oxidation may cause the release of organic matter in algae cells, especially algal toxins, further aggravating water pollution. Therefore, the development of a high-efficiency, low-damage, moderate pre-oxidation enhanced coagulation method is a difficult problem that needs to be solved in current engineering applications. Summary of the invention

[0005] In view of the problems existing in the background technology, the present invention provides a method for pre-oxidation enhanced coagulation algae removal, which can change the functional group composition of extracellular organic matter of algae by adding FeOCl and ferrate during pre-oxidation, significantly reduce the potential value of algae-containing water, accelerate the precipitation of algae cells, and reduce the amount of premix used, thereby avoiding the release of intracellular organic matter in algae cells due to excessive pre-oxidation, and improving the coagulation algae removal efficiency of algae pollution.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: The method for pre-oxidation enhanced coagulation and algae removal uses FeOCl and ferrate for pre-oxidation at the same time.

[0007] Furthermore, the ratio of ferrate in terms of hexavalent iron to the number of algae cells is 0.18-20 mg:10 6 per algal cell, the molar ratio of potassium ferrate to FeOCl is 1:200-320.

[0008] Furthermore, FeOCl powder particles are first added to the algae-containing water and stirred evenly, and then the ferrate aqueous solution is added to the algae-containing water for pre-oxidation.

[0009] Furthermore, pre-oxidation is performed first, and then an aluminum salt flocculant is added after pre-oxidation.

[0010] Furthermore, the molar ratio of the aluminum salt flocculant to ferrate is 3.5-12:1.

[0011] Furthermore, the method for pre-oxidation enhanced coagulation algae removal comprises the following steps: (1) Add FeOCl powder particles and ferrate aqueous solution into high algae water and stir for pre-oxidation; (2) adding an aqueous solution of an aluminum salt flocculant to the algae-containing water that has been pre-oxidized in step (1), and stirring and mixing the mixture thoroughly; (3) Sedimentation: removing algae cells and organic matter released from the algae cells in the water to obtain algae- and organic-free water.

[0012] Furthermore, the pre-oxidation time of step (1) is 10 min-30 min.

[0013] Furthermore, the bottom residue settled in step (3) is filtered.

[0014] Beneficial effects of the present invention: The present invention significantly reduces the demand for soluble potassium ferrate oxidant by additionally adding FeOCl powder. The combination of FeOCl and ferrate can achieve pre-oxidation of algae cells while ensuring that the algae cell wall is intact and not damaged, and algae toxins do not leak out. At the same time, it also avoids the problem of excessive residual iron ions caused by excessive addition of iron salts. The method of the present invention has the advantages of non-toxicity, low residue, no secondary pollution, high efficiency, etc., can achieve an algae cell removal rate of more than 90%, reduce the demand for coagulants by strengthening coagulation, avoid transitional sludge from clogging the filter membrane, and the final remaining iron salt content is lower than the national standard for drinking water.

[0015] The reagents and materials used in the present invention are all commonly used agents or catalyst materials in the field of water treatment, and the preparation method is simple and the cost is low. When applied on site, it is only necessary to set a pre-oxidation device between the outlet pipe of the primary pump station of the existing water treatment plant and the mixing unit of the water plant or in the mixing unit of the water plant, and then enter the coagulation sedimentation, filtration and other units to remove the settled algae cells. The whole process is simple to operate and does not require additional complex processing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a comparison diagram of water bodies treated by Example 1, Comparative Example 1 and Comparative Example 2 of the present invention; Figure 2 It is a comparison diagram of water bodies using different treatment methods in Example 3 of the present invention. DETAILED DESCRIPTION

[0017] In order to make the objectives, technical solutions and beneficial effects of the present invention clearer, the preferred embodiments of the present invention will be described in detail below to facilitate understanding by technicians.

[0018] The method for pre-oxidation enhanced coagulation algae removal uses FeOCl and ferrate in combination for pre-oxidation, and specifically includes the following steps: (1) Pre-oxidation: Add FeOCl powder particles into high algae water, stir evenly, then add ferrate aqueous solution and stir for 10-30 minutes for pre-oxidation. The ratio of ferrate (in terms of hexavalent iron) to algae cell number is 0.18-20 mg:10 6 The molar ratio of ferrate to FeOCl is 1:200-320 per algal cell.

[0019] (2) Flocculation: After the pre-oxidation is completed, add aluminum salt flocculant to the pre-oxidized water.

[0020] The molar ratio of aluminum salt flocculant to ferrate is 3.5-12:1. After adding the flocculant, stir to fully mix the flocculant and the water.

[0021] (3) Sedimentation: The algae cell removal rate in the clear liquid after sedimentation can reach over 90%, and the iron content in the resulting water is lower than the national standard for drinking water.

[0022] (4) Filtration: The precipitated residue is filtered to obtain algal residue and filtrate. The algal cell removal rate of the filtrate is greater than 90%.

[0023] The trivalent iron and FeOCl particles generated by the decomposition of aluminum salts and hexavalent iron constitute a combined coagulant system, which promotes the formation and growth of flocs, removes algae cells and organic matter released from the algae cells in the water through sedimentation and filtration, and obtains water with low algae cell and organic matter content.

[0024] The main principle of the present invention is that the surface of FeOCl powder carries a large amount of positive charge, which can preliminarily neutralize the negative charge on the surface of algae cells. Ferrate reacts with FeOCl to generate active oxygen species including hydroxyl radicals, pre-oxidizes algae cells, and significantly reduces the potential value of algae liquid and makes algae cells easy to settle by changing the functional group composition of extracellular organic matter. Then, a coagulant is added, and after stirring and coagulation, under the adsorption, bridging and entrainment of trivalent iron oxides produced by the decomposition of high-valent iron and FeOCl powder, the formation and sedimentation of algae flocs are enhanced, the floc volume is increased, and the algae cells can be directly precipitated and removed from the water. Example 1

[0025] Laboratory autotrophic cyanobacteria (Microcystis aeruginosa) were used to dilute it with a solution containing 1.0 mmol / L NaHCO3 and 15.0 mmol / L sodium perchlorate to form a 10 6 High algae water to be treated with an algae cell concentration of cells / L.

[0026] The method of the present invention is used to enhance algae removal in the above-mentioned simulated high algae water: (1) Place 200 mL of simulated algae water in a beaker, add FeOCl powder particles (25 mg / L) into the high algae water, stir evenly, add potassium ferrate (0.001 mmol / L) aqueous solution, and stir on a magnetic stirrer at 250 r / min for pre-oxidation for 30 min.

[0027] (2) Add polyaluminium chloride (PAC, 2 mg / L) and stir on a magnetic stirrer at 180 r / min for 2 min, 80 r / min for 6 min, and 50 r / min for 9 min, then allow to settle for 30 min.

[0028] The supernatant was analyzed and the algae cell removal rate was 98% and the turbidity was reduced to 2 NTU.

[0029] Comparative Example 1 The same simulated high algae water as in Example 1 was used for algae removal. Compared with Example 1, step (1) was omitted and polyaluminium chloride (PAC, 2 mg / L) was directly added to the simulated high algae water. The mixture was stirred on a magnetic stirrer at 180 r / min for 2 min, 80 r / min for 6 min, and 50 r / min for 9 min before settling for 30 min. Flocs were generated but no aggregate precipitation was observed. A comparison of the water bodies treated in Example 1 and Comparative Example 1 is shown in the attached figure. Figure 1 .

[0030] Comparative Example 2 (same as Example 1 except that FeOCl is not added) The algae removal was carried out using the same simulated high algae water as in Example 1, omitting the addition of FeOCl and only adding potassium ferrate aqueous solution, stirring for 10 min-30 min for pre-oxidation, wherein the ratio of potassium ferrate (in terms of hexavalent iron) to the number of algae cells was 0.198 mg:10 6 Then polyaluminium chloride (PAC, 2mg / L) was added and stirred on a magnetic stirrer at 180r / min for 2min, 80r / min for 6min, and 50r / min for 9min before settling for 30min. Some flocs were produced, but most of them were still suspended.

[0031] The comparison of the water bodies after treatment in Example 1, Comparative Example 1 and Comparative Example 2 is shown in the attached figure. Figure 1 , attached Figure 1 In the figure, from left to right, the first figure is the high algae water to be treated, the second figure is the treatment result of comparative example 1, the third figure is the treatment result of comparative example 2, and the fourth figure is the treatment result of embodiment 1.

[0032] The method of the present invention can also achieve rapid precipitation of algal cells during algal bloom events, and the amount of coagulant used is greatly reduced, and the release of intracellular organic matter in algal cells, especially algal toxins, will not be caused by excessive pre-oxidation. Example 2

[0033] In the summer, an inland lake in a city has an algal bloom, the water turns green, fish and shrimp die, and there is a peculiar smell, which affects the lives of nearby residents. 5 / L, and the turbidity reached 32 NTU.

[0034] The landscape water polluted by algae bloom is used for algae removal as follows: (1) Collect lake water where algal blooms have occurred along the shore of the lake, bring it back to the laboratory, remove floating impurities on the surface, and perform short-term aeration to prepare the high-algae water to be treated.

[0035] (2) Place 250 mL of high-algae water to be treated in a beaker, add FeOCl powder particles (40 mg / L) into the high-algae water, stir evenly, add potassium ferrate (0.101 mmol / L) aqueous solution, and stir on a magnetic stirrer at 200 r / min for pre-oxidation for 10 min.

[0036] (3) Add polyaluminium chloride (PAC, 5 mg / L) and stir on a magnetic stirrer at 180 r / min for 2 min, 80 r / min for 6 min, and 50 r / min for 9 min, then allow to settle for 30 min.

[0037] The supernatant was analyzed and the algae cell removal rate was 98%. The turbidity was reduced to 10 NTU, and the lake water was significantly clarified. Example 3

[0038] According to the monitoring station, a water supply plant reservoir was eutrophicated and the algae cell concentration reached 10 4 / L, the raw water turbidity is 10 NTU. The water plant originally used polyaluminium chloride (PAC) as flocculant, with a dosage of 15 mg / L. After the algal bloom occurred, the flocculant dosage was increased to 22 mg / L, but the effect was still not ideal, with an algae cell removal rate of only 72% and a turbidity removal rate of only 5%. The original process flow of the water plant was: raw water, mixing in the mixing tank, flocculation in the flocculation tank, sedimentation in the sedimentation tank, filtration in the filter tank, passing through the clear water tank, and entering the pipe network system.

[0039] Take the above eutrophication-polluted water source for enhanced algae removal, as follows: Potassium ferrate and FeOCl powder were added to the existing pre-oxidation tank of the water plant. The hydraulic retention time was extended to 60 min. The ratio of potassium ferrate and FeOCl powder to algae cells was 0.198 mg:33.3 mg:10 4 Algal cells.

[0040] In the flocculation tank, polyaluminium chloride (PAC) was added, and then the dosage of the original flocculant aluminium chloride was reduced to 15 mg / L.

[0041] After the algae cells were settled in the sedimentation tank, the removal rate was tested to be 92-97%, the turbidity of the water before filtration dropped to 2 NTU, and after being filtered through the filter tank and meeting the standards, it entered the pipe network system.

[0042] The comparison of the water treated by the original treatment method of the water plant and the water treated by the method of the present invention is shown in Figure 2 (Sampling location: outlet of inclined plate sedimentation tank), Figure 2 In the figure, the left figure shows the treatment result of the method of the present invention, and the right figure shows the treatment result of the original treatment method of the water supply plant.

[0043] The reagents used in the above examples can achieve the same technical effect by replacing potassium ferrate with sodium ferrate.

[0044] The method of the present invention only requires adding a pre-oxidation tank with a stirring device to the existing water treatment process, which makes little change to the existing water treatment process and has low added equipment cost, and has strong adaptability to currently commonly used water treatment devices.

[0045] In each embodiment, the detection method of the algae cell removal rate is: The number of cells was determined by a JSY-FL-055 plant cell counter, and the removal rate of algae cells was calculated as follows: the number of algae cells after treatment / the number of algae cells in the original water*100%.

[0046] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for pre-oxidation enhanced coagulation algae removal, characterized in that: Pre-oxidation was performed using FeOCl and ferrate.

2. The method for pre-oxidation enhanced coagulation algae removal according to claim 1, characterized in that: The ratio of ferrate to algae cell number is 0.18-20 mg:10 6 per algal cell, the molar ratio of ferrate to FeOCl is 1:200-320.

3. A method for pre-oxidation enhanced coagulation algae removal according to claim 1 or 2, characterized in that: Firstly, FeOCl powder particles are added to the algae-containing water and stirred evenly, and then the ferrate aqueous solution is added to the algae-containing water for pre-oxidation.

4. A method for pre-oxidation enhanced coagulation algae removal according to claim 1 or 2, characterized in that: Pre-oxidation is performed first, and then aluminum salt flocculant is added after pre-oxidation.

5. The method for pre-oxidation enhanced coagulation algae removal according to claim 4, characterized in that: The molar ratio of the aluminum salt flocculant to ferrate is 3.5-12:

1.

6. A method for pre-oxidation enhanced coagulation algae removal according to any one of claims 1, 2 or 5, characterized in that: The following steps are involved: (1) Add FeOCl powder particles and ferrate aqueous solution into high algae water and stir for pre-oxidation; (2) adding an aqueous solution of an aluminum salt flocculant to the algae-containing water that has been pre-oxidized in step (1), and stirring and mixing the mixture thoroughly; (3) Sedimentation: removing algae cells and organic matter released from the algae cells in the water to obtain algae- and organic-free water.

7. The method for pre-oxidation enhanced coagulation algae removal according to claim 6, characterized in that: The pre-oxidation time of step (1) is 10 min to 30 min.

8. The method for pre-oxidation enhanced coagulation algae removal according to claim 6, characterized in that: Step (3) filtering the settled bottom residue.

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