Method for pre-oxidation enhanced coagulation and algae removal

Abstract

The present application relates to a kind of pre-oxidation enhanced coagulation algae-removal method, belong to water body algae-removal technical field, the present application proposes a kind of pre-oxidation to algal water using combined ferrate and oxychloride iron material, and then the method of enhanced subsequent coagulation algae-removal is used.The method can guarantee that algal cell is low broken, does not release intracellular algal toxin under the premise, reduces the stability of algal group, to reach the goal of algal cell enhanced coagulation.Free radicals generated by the reaction of ferrate and FeOCl reduce the electronegativity of algal cell extracellular organic matter by oxidation reaction, so that it is easy to occur adsorption, bridging and other reactions with coagulant, the presence of trivalent iron oxide particles generated by the decomposition of potassium ferrate and FeOCl material accelerates the formation and settlement of floc, and strengthens the coagulation process, the present application can accelerate the precipitation of algal cell, and reduce the use amount of pre-mixing agent, avoid the release of intracellular organic matter of algal cell due to excessive pre-oxidation, improve the coagulation algae-removal efficiency of algal pollution.

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] Water from lakes and reservoirs is a crucial source of drinking water in my country, accounting for 52.8% of the nation's centralized drinking water sources in urban areas. With the rapid development of industry and agriculture and the expansion of urbanization, increasing amounts of nitrogen and phosphorus (N) nutrients are being discharged into receiving water bodies along with domestic sewage, causing varying degrees of eutrophication in lakes and reservoirs. According to the "2023 China Ecological Environment Bulletin," most of the major lakes and reservoirs currently undergoing nutrient status monitoring in my country exhibit varying degrees of eutrophication. Algal blooms caused by eutrophication increase water management and maintenance costs, creating significant obstacles for advanced water treatment and the routine maintenance of landscape water. They also disrupt the aquatic ecosystem, seriously threatening the water safety of residents and other organisms, and becoming a major challenge facing the water resources and environment. In particular, for urban agglomerations relying on lakes and reservoirs as water sources, algae blooms can cause problems such as difficulty coagulating wastewater treatment plants, clogging filter tanks, and excessive algae in effluent. These issues impact the normal operation of wastewater treatment plants, straining water supplies, and disrupting residents' daily lives. 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] Currently, the primary, most effective, and most economical method for responding to sudden algal blooms is coagulation and algae removal. This method utilizes the principles of coagulation and sedimentation to remove algal cells. Coagulants destabilize algal cells through electrical neutralization, adsorption bridging, and netting and sweeping. These cells then aggregate with the coagulant to form flocs, which are then removed during the subsequent sedimentation process. However, the inherent properties of algal cells can interfere with coagulation. For example, the anionic nature of extracellular organic matter (EOM) makes it easy for it to form complexes with cationic coagulants or form hydrated ions during coagulation, interfering with coagulation and algae removal.

[0004] When algae blooms and algae concentrations are too high, large amounts of coagulants are consumed and the coagulation effect deteriorates. Chemical pre-oxidation can significantly improve coagulation efficiency without requiring major changes to existing water plant processes. However, the choice and dosage of the oxidant, as well as the duration of the pre-oxidation process, are directly related to the integrity of the algal cell structure. Excessive pre-oxidation may release organic matter within the algal cells, especially algal toxins, further aggravating water pollution. Therefore, developing 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 response to the problems existing in the background technology, the present invention provides a method for pre-oxidation enhanced coagulation algae removal. By adding FeOCl and ferrate during pre-oxidation, the functional group composition of algae extracellular organic matter can be changed, the potential value of algae-containing water can be significantly reduced, the precipitation of algae cells can be accelerated, and the amount of premix used can be reduced, 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:

[0007] The method for pre-oxidation-enhanced coagulation and algae removal uses FeOCl and ferrate for pre-oxidation simultaneously.

[0008] Furthermore, the ratio of ferrate as hexavalent iron to the number of algae cells is 0.18-20 mg:10 6 The molar ratio of potassium ferrate to FeOCl is 1:200-320.

[0009] 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.

[0010] Furthermore, pre-oxidation is performed first, and then an aluminum salt flocculant is added after pre-oxidation.

[0011] Furthermore, the molar ratio of the aluminum salt flocculant to ferrate is 3.5-12:1.

[0012] Furthermore, the method for pre-oxidation enhanced coagulation and algae removal comprises the following steps:

[0013] (1) Add FeOCl powder particles and ferrate aqueous solution into high algae water and stir for pre-oxidation;

[0014] (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;

[0015] (3) Sedimentation: remove algae cells and organic matter released from the algae cells in the water to obtain algae- and organic-free water.

[0016] Furthermore, the pre-oxidation time of step (1) is 10 min-30 min.

[0017] Furthermore, the bottom residue settled in step (3) is filtered.

[0018] Beneficial effects of the present invention:

[0019] By adding additional FeOCl powder, the present invention significantly reduces the requirement for soluble potassium ferrate oxidant. The combined use of FeOCl and ferrate achieves pre-oxidation of algal cells while ensuring the integrity of the algal cell walls and preventing the leakage of algal toxins. This also avoids the problem of excessive residual iron ions that can result from excessive iron salt addition. The method of the present invention offers advantages such as non-toxicity, low residue, no secondary pollution, and high efficiency. It can achieve an algal cell removal rate of over 90%, reduces the need for coagulant through enhanced coagulation, prevents clogging of filter membranes by excessive sludge, and ultimately ensures that the remaining iron salt content is below the national drinking water standard.

[0020] The reagents and materials used in the present invention are all commonly used pharmaceuticals or catalysts in the water treatment field. The preparation method is simple and low-cost. For field application, a pre-oxidation device is simply installed between the outlet pipe of the primary pump station and the mixing unit of the water treatment plant, or within the mixing unit of the water treatment plant. The water then enters the coagulation, sedimentation, and filtration units to remove settled algal cells. The entire process is simple to operate and does not require additional complex processing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is a comparison diagram of water bodies treated with Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;

[0022] Figure 2 3 is a comparison diagram of water bodies treated by different methods in Example 3 of the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, 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.

[0024] The method for pre-oxidation enhanced coagulation algae removal uses FeOCl and ferrate in combination for pre-oxidation, specifically comprising the following steps:

[0025] (1) Pre-oxidation: Add FeOCl powder particles to high algae water, stir evenly, then add ferrate aqueous solution and stir for 10-30 minutes for pre-oxidation. The ratio of ferrate (calculated as hexavalent iron) to algae cell number is 0.18-20 mg:10 6 The molar ratio of ferrate to FeOCl is 1:200-320.

[0026] (2) Flocculation: After the pre-oxidation is completed, aluminum salt flocculant is added to the pre-oxidized water.

[0027] The molar ratio of the aluminum salt flocculant to the ferrate is 3.5-12:1. After the flocculant is added, stirring is performed to fully mix the flocculant and the water.

[0028] (3) precipitation, more than 90% of the algae cell removal rate can be achieved in the supernatant after precipitation, and the iron content of the obtained water body is lower than the national standard for drinking water.

[0029] (4) filtration, the bottom slag of the precipitation is filtered to obtain algae slag and filtrate, and the algae cell removal rate of the filtrate is greater than 90%.

[0030] The aluminum salt, the trivalent iron and FeOCl particles generated by the decomposition of the hexavalent iron, etc. constitute a combined coagulant system, promote the formation and increase of the flocs, remove the algae cells and the organic matters released from the algae cells in the water through sedimentation and filtration, and obtain water with low content of algae cells and organic matters.

[0031] The main principle of the present application is that the FeOCl powder has a large number of positive charges on the surface, which can preliminarily neutralize the negative charges on the surface of the algae cells. The ferrate reacts with the FeOCl to generate active oxygen species including hydroxyl radicals, which pre-oxidize the algae cells, change the functional group composition of the extracellular organic matters, significantly reduce the zeta potential value of the algae liquid, and make the algae cells easy to settle. Then, the coagulant is added, and after stirring and coagulation, the trivalent iron oxide generated by the decomposition of the high-valence iron and the adsorption, bridging and entrainment of the FeOCl powder strengthen the formation, settlement and volume increase of the algae-containing flocs, so that the algae cells can be directly removed from the water by precipitation. Example 1

[0032] The laboratory self-sustaining blue-green algae (Microcystis aeruginosa) is diluted with a solution containing 1.0 mmol / L NaHCO3 and 15.0 mmol / L sodium perchlorate to form 10 6 × 106cells / mL of high algae water to be treated.

[0033] The above simulated high algae water is treated by the method of the present application to strengthen the algae removal:

[0034] (1) 200 mL of simulated algae water is poured into a beaker, FeOCl powder particles (25 mg / L) are added to the high algae water, stirred uniformly, and then a potassium ferrate (0.001 mmol / L) aqueous solution is added. The mixture is stirred on a magnetic stirrer at a speed of 250 r / min for 30 min.

[0035] (2) polyaluminum chloride (PAC, 2 mg / L) is added, and the mixture is stirred on a magnetic stirrer at a speed of 180 r / min for 2 min, 80 r / min for 6 min, and 50 r / min for 9 min, and then settled for 30 min.

[0036] The upper clear liquid is taken for analysis, and the algae cell removal rate is 98%, and the turbidity is reduced to 2 NTU.

[0037] Comparative Example 1

[0038] 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, and then allowed to settle for 30 min. Flocs were generated, but no precipitation was observed. A comparison of the water treated in Example 1 and Comparative Example 1 is shown in the attached figure. Figure 1 .

[0039] Comparative Example 2 (same as Example 1 except that FeOCl is not added)

[0040] The algae removal was carried out using the same simulated high algae water as in Example 1, omitting the addition of FeOCl and adding only potassium ferrate aqueous solution. The solution was stirred for 10-30 minutes for pre-oxidation. The ratio of potassium ferrate (calculated as hexavalent iron) to algae cell number was 0.198 mg:10 6 Then, polyaluminium chloride (PAC, 2 mg / L) was added and 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. The mixture was then allowed to settle for 30 min. Some flocs settled, but most remained suspended.

[0041] The comparison of the water bodies after treatment of 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 picture is the high-algae water to be treated, the second picture is the treatment result of Comparative Example 1, the third picture is the treatment result of Comparative Example 2, and the fourth picture is the treatment result of Example 1.

[0042] 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. Excessive pre-oxidation will not cause the release of intracellular organic matter in the algal cells, especially the release of algal toxins. Example 2

[0043] In the summer, the water in an inland lake in a certain city has an algal bloom, the water turns green, fish and shrimps and other aquatic organisms die, and there is a strange smell, which affects the lives of nearby residents. 5 / L, and the turbidity reached 32 NTU.

[0044] The above-mentioned landscape water polluted by algae bloom is used for algae removal as follows:

[0045] (1) Collect lake water where algal blooms have occurred along the shore of the lake, collect 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.

[0046] (2) Pour 250 mL of high-algae water to be treated into 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.

[0047] (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.

[0048] The supernatant was analyzed and the algal cell removal rate was 98%. The turbidity was reduced to 10 NTU, and the lake water was significantly clarified. Example 3

[0049] According to the monitoring station, a water supply plant reservoir was found to be eutrophic, with the concentration of algae cells reaching 10 4 The water plant originally used polyaluminium chloride (PAC) as a flocculant at a dosage of 15 mg / L. After the algal bloom occurred, the flocculant dosage was increased to 22 mg / L, but the results were still unsatisfactory, with only 72% algal cell removal and 5% turbidity removal. The plant's original process flow involved mixing raw water in a mixing tank, flocculation in a flocculation tank, sedimentation in a sedimentation tank, filtration in a filter, and finally, clear water entering the pipe network.

[0050] Take the above-mentioned eutrophication-polluted water source for enhanced algae removal, as follows:

[0051] 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 algal cells was 0.198 mg:33.3 mg:10 4 Algal cells.

[0052] 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.

[0053] 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.

[0054] The comparison of the water body treated by the original treatment method of the water plant and the water body treated by the method of the present invention is shown in Figure 2 (Sampling location: outlet of inclined plate sedimentation tank), Figure 2In the figure, the left picture shows the treatment result of the method of the present invention, and the right picture shows the treatment result of the original treatment method of the water supply plant.

[0055] The reagents used in the above examples can be replaced by sodium ferrate instead of potassium ferrate to achieve the same technical effect.

[0056] The method of the present invention only requires adding a pre-oxidation tank with a stirring device to the existing water treatment process. The changes to the existing water treatment process are relatively small, and the additional equipment cost is low. It has strong adaptability to currently commonly used water treatment devices.

[0057] In each embodiment, the method for detecting the algal cell removal rate is:

[0058] The cell number was determined using a JSY-FL-055 plant cell counter, and the algae cell removal rate was calculated as: the number of algae cells after treatment / the number of algae cells in the original water*100%.

[0059] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. 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 by: FeOCl and ferrate were used for pre-oxidation; the ratio of ferrate to algal cell number was 0.18-20 mg as hexavalent iron:10 6 The molar ratio of ferrate to FeOCl is 1:200-320 per algal cell.

2. The method for pre-oxidation enhanced coagulation and algae removal according to claim 1, characterized in that: First, 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.

3. The method for pre-oxidation enhanced coagulation and algae removal according to claim 1, characterized in that: Pre-oxidation is carried out first, and then aluminum salt flocculant is added after pre-oxidation.

4. The method for pre-oxidation enhanced coagulation and algae removal according to claim 3, characterized in that: The molar ratio of the aluminum salt flocculant to ferrate is 3.5-12:

1.

5. The method for pre-oxidation enhanced coagulation and algae removal according to any one of claims 1 to 4, 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: remove algae cells and organic matter released from the algae cells in the water to obtain algae- and organic-free water.

6. The method for pre-oxidation enhanced coagulation and algae removal according to claim 5, characterized in that: The pre-oxidation time of step (1) is 10 min to 30 min.

7. The method for pre-oxidation enhanced coagulation and algae removal according to claim 5, characterized in that: The settled bottom residue in step (3) is filtered.

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