Method for removing toxic blue-green algae in water by using nano-biochar reinforced coagulant and application of method

Abstract

The invention discloses a method for removing toxic blue-green algae in water by using a nano-biochar reinforced coagulant and application of the method, polyaluminum chloride (PAC) or ferric trichloride (FeCl3) is used as the coagulant for removing toxic blue-green algae in water, and a certain amount of nano-biochar is added as a coagulant aid, so that the coagulation algae removal effect of the traditional coagulant PAC or FeCl3 can be remarkably improved, the dosage of the PAC or FeCl3 is reduced, and the cost is reduced. And the coagulation algae removal cost is saved. In addition, by adding the nano biochar, residues of heavy metal ions (Fe < 3 + > and Al < 3 + >) can be reduced, and potential ecological hazards of traditional coagulation algae removal to the water body are reduced. The method disclosed by the invention is simple to operate, low in manufacturing cost and easy to produce, and has economic and environmental double benefits.

Description

Technical Field

[0001] The invention relates to the technical field of algae removal, and in particular to an application of a nano-biochar enhanced coagulant to remove microalgae in water. Background Art

[0002] Common methods for removing algae in water mainly include physical methods (mechanical collection, sunshade killing, flotation, ultrasonic method, micro-mesh filtration, ultraviolet irradiation, physical adsorption); biological methods (microorganisms, aquatic plants, aquatic animals); chemical methods (coagulation and sedimentation, pre-oxidation, advanced oxidation). Physical methods are not thorough in removing algae, the removal rate is relatively low, and the workload is large, the investment cost is high, and it is not suitable for large-scale use. Although the biological method is low in cost, it has low removal efficiency and slow effect. It is mostly used for in-situ inhibition and regulation of algae in water bodies and is not suitable for sudden water bloom treatment. Chemical methods can be used for in-situ algae bloom emergency control and are also the main methods for ex-situ treatment of algae in water. Common chemical methods include algaecides, coagulation, oxidants, etc. Among them, the addition of algaecides and oxidants is a common in-situ chemical algae removal method. Algaecides can quickly kill algae, but they are prone to cause potential secondary pollution hazards; coagulation is not only used for in-situ chemical algae removal in water bodies, but also widely used for algae removal in water, such as drinking water algae removal.

[0003] In the process of algae resource and energy utilization, coagulation is the main means of algae collection in farms. However, commonly used coagulants contain iron, aluminum and other metal salt compounds. After coagulation and algae removal, the iron, aluminum and other metal compounds in the flocculent sediment will have an adverse effect on the aquatic ecological environment; in the process of algae cultivation, the iron, aluminum and other metal salt compounds contained in the algae collected by coagulation and sedimentation will have an adverse effect on the subsequent resource and energy utilization.

[0004] Biochar is a porous carbon material. Some biochars are widely used in water pollution control due to their large specific surface area and rich functional groups. The main components of biochar are aromatic carbon compounds with stable chemical properties. In the subsequent resource utilization of algae, whether it is fermentation or refining, the impact is small and it does not need to be separated. Studies have shown that biochar can play a certain role in algae coagulation, but the effect is not very obvious. At the same time, the raw materials and preparation methods of biochar have a great influence on the properties of biochar, and the effects of biochar with different raw materials and preparation methods on enhanced coagulation are also very different.

[0005] Therefore, it is very necessary to develop a nano-biochar to enhance the application of coagulants in removing microalgae from water, so as to enhance the effect of traditional coagulation and algae removal while reducing the potential adverse effects of coagulation and sedimentation flocs on water ecology and subsequent resource utilization. Summary of the invention

[0006] The purpose of the present invention is to provide a method and application of removing toxic blue algae in water by using nano-biochar enhanced coagulant to solve the above defects.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method and application of using a nano-biochar enhanced coagulant to remove toxic blue algae in water, the specific steps are as follows: in a water body containing Microcystis aeruginosa, first, in a rapid mixing stage, a traditional coagulant is added as a primary coagulant for coagulation; then in a slow mixing stage, nano-biochar is added as a secondary coagulant to remove Microcystis aeruginosa in the water body and reduce the residual metal ions in the water body.

[0009] Preferably, the nano biochar is nano bamboo chips biochar.

[0010] Preferably, the traditional coagulant is PAC or FeCl3.

[0011] Preferably, the order of adding the traditional coagulant and nano-biochar is: first add the coagulant PAC or FeCl3 and mix for 1 minute, and then add the coagulant aid nano-biochar.

[0012] Preferably, the ratios of the initial algae density of the traditional coagulant, nano-biochar and toxic blue algae in water are:

[0013] PAC: NBC: Initial algae density = 10 mg / L: 0.5 g / L: (1×10 6 cells / mL), the removal rate of toxic blue algae in water can reach more than 90%.

[0014] Preferably, the preparation method of the nano biochar comprises the following steps:

[0015] S1, crushing and grinding bamboo sawdust into powder by a crusher, placing it in a muffle furnace, pyrolyzing and carbonizing it at 700° C. for 1 hour, and finally cooling it and sieving it with a 100-mesh sieve to obtain 100-mesh bamboo biochar;

[0016] Preferably, S2, the prepared 100-mesh bamboo biochar is ground using a planetary ball mill at 350 r / min for 4 days, with grinding balls having diameters of 8 mm, 10 mm and 15 mm, and a ball-to-powder ratio of 10:1, thereby obtaining nano biochar.

[0017] Preferably, in step S1, the heating rate of pyrolysis carbonization in the muffle furnace is 10°C / min.

[0018] Preferably, in step S2, during the grinding process of the planetary ball mill, the material is cooled for 5 minutes after every 5 minutes of grinding until the grinding is completed.

[0019] The beneficial effects of the present invention are:

[0020] The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water, using a traditional coagulant as a primary coagulant and nano-biochar as a secondary coagulant, is used to remove Microcystis aeruginosa and reduce metal ion residues in water. The method is simple to operate, low in manufacturing cost, easy to produce, and can significantly improve the removal efficiency of traditional coagulants on Microcystis aeruginosa, reduce metal ions (Fe 3+ 、Al 3+ ) residues, which has dual benefits of economy and environment. At the same time, nano-biochar can reduce the dosage of traditional coagulants such as PAC or FeCl3 while strengthening the traditional coagulants to remove Microcystis aeruginosa, thereby reducing the metal ions (Fe 3+ 、Al 3+ ) content and reduce the treatment cost of algae-containing water bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : Comparison of the effects of FeCl3 dosage and enhanced coagulation method on flocculation effect; (a) FeCl3×NBC, (b) NBC+FeCl3, (c) FeCl3+NBC, (d) FeCl3+NBC (small dosage).

[0022] Figure 2 : Comparison of the effects of different nano-biochar dosages on enhancing PAC coagulation;

[0023] Figure 3 :(a) Comparison of residual Al ion content in water with different addition amounts of PAC and PAC: nano-biochar added step by step; (b) Comparison of residual Fe ion content in water with different addition amounts of FeCl3 and FeCl3 and nano-biochar added step by step. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with the embodiments. It should be noted that these are merely examples and illustrations of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should be deemed to fall within the protection scope of the present invention.

[0025] Embodiment 1:

[0026] The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water, the specific steps are as follows:

[0027] (1) In water bodies containing Microcystis aeruginosa, the OD680 value of Microcystis aeruginosa is around 0.2, and the algae density is around 1×10 6cells / mL (reaching the level of severe algal bloom);

[0028] (2) The water containing Microcystis aeruginosa was collected and mixed rapidly at 150 RPM for 1 minute (rapid mixing stage), slowly mixed at 75 RPM for 15 minutes (slow mixing stage) in a constant temperature shaking incubator at 25°C and pH 8.2, and finally settled for 30 minutes. A coagulation experiment was performed under these conditions.

[0029] Enhanced coagulation is added in three situations:

[0030] a.FeCl3×NBC: Add ferric chloride and nano-carbon simultaneously and mix quickly.

[0031] b.FeCl3+NBC: Ferric chloride is used as coagulant and nano-biochar is used as coagulant aid. The primary coagulant ferric chloride is added in the rapid mixing stage, and the secondary coagulant nano-biochar is added in the slow flocculation stage.

[0032] c.NBC+FeCl3: Nano-biochar is used as coagulant and ferric chloride is used as flocculant. The primary coagulant nano-biochar is added in the rapid mixing stage, and the secondary coagulant ferric chloride is added in the slow flocculation stage.

[0033] After coagulation is completed, the density of Microcystis aeruginosa and Fe ions in the water are tested.

[0034] The preparation process of the nano biochar in step (2) comprises the following steps:

[0035] S1. The bamboo sawdust was crushed and ground into powder by a crusher, and then placed in a muffle furnace. The temperature of the muffle furnace was increased by 10° C. / min, and pyrolysis carbonization was performed at 700° C. for 1 hour. Finally, the mixture was cooled and sieved with a 100-mesh (0.15 mm) sieve to obtain 100-mesh bamboo biochar;

[0036] S2. The prepared 100-mesh bamboo biochar was ground using a planetary ball mill (model: MITR-YXQM-0.4L) at 350 r / min for 4 days. The grinding ball diameters were 8 mm, 10 mm and 15 mm, and the ball-to-powder ratio was 10:1. During the grinding process of the planetary ball mill, the grinding was continued for 5 min and then cooled for 5 min to prevent biochar accumulation caused by temperature increase until the grinding was completed, thereby obtaining nano-biochar.

[0037] Through the above-mentioned preparation process of nano-biochar, after repeated tests, the performance parameters of the 100-mesh bamboo biochar prepared in step S1 and the nano-biochar prepared in step S2 were obtained, as shown in Table 1 for details.

[0038] Table 1. Performance parameters of 100-mesh bamboo biochar and nano-biochar.

[0039]

[0040] As can be seen from Table 1, the nano biochar prepared by the method of the present invention has excellent performance, smaller particle size and pore size, and larger specific surface area and pore volume.

[0041] Before the enhanced coagulation experiment, FeCl3 alone was used as a coagulant without using nano-biochar as a comparative experiment to obtain the coagulation effect data of different FeCl3 dosages. The specific data are shown in Table 2.

[0042] Table 2. Coagulation effect data of different dosages of FeCl3

[0043]

[0044]

[0045] As can be seen from Table 2, excessive FeCl3 will reduce the removal efficiency of Microcystis aeruginosa and increase the residual amount of iron ions in the water. FeCl3 needs to be used in a smaller dosage to ensure less residual iron ions, and has a significant removal effect on Microcystis aeruginosa. The FeCl3 dosage in Table 2 is 50mg / L to 60mg / L, and the removal rate increases from 74.65% to 98.65%, which is a significant improvement, and the residual iron ions are relatively small. Therefore, 50mg / L is selected as the dosage for the enhanced experiment to ensure that the residual Fe ion content is low under the premise of significant algae removal effect.

[0046] On the basis of the above experiments, different ratios of the main coagulant (FeCl3) to nano-biochar were set in the process of applying nano-biochar in steps (2) a, b, and c (50 mg / L: 0 g / L, 50 mg / L: 0.5 g / L, 50 mg / L: 1 g / L, 50 mg / L: 1.5 g / L, 50 mg / L: 2 g / L), where the control group was a group without adding nano-biochar; each group of experiments was repeated three times. The coagulation results of FeCl3 coagulation and the three enhanced coagulation methods are shown in Table 3.

[0047] Table 3. Coagulation results of FeCl3 coagulation and three enhanced coagulation methods

[0048]

[0049]

[0050] As shown in Table 3 and Figure 1As shown in (a), (b) and (c), there are three dosing methods: FeCl3×NBC, NBC+FeCl3 and FeCl3+NBC. The treatment effects of the two dosing methods of FeCl3×NBC and NBC+FeCl3 are far lower than that of FeCl3+NBC. When the NBC dosage reaches 2g / L, the algae removal rates of FeCl3×NBC and NBC+FeCl3 can only reach 87.01% and 86.52%, respectively, while the FeCl3+NBC method has reached 95.24% when the dosage is 0.5g / L. The possible reason is that when flocs are not generated in the early stage, ferric chloride uses NBC as particles to coagulate with Microcystis aeruginosa cells at the same time, which disperses the coagulation effect of ferric chloride. In the dosing method of FeCl3+NBC, NBC is used as a coagulant added in the flocculation stage. After the ferric chloride is initially coagulated to form basic flocs, it wraps the flocs to make them interconnected and settle quickly, so as to achieve a higher coagulation efficiency.

[0051] Based on the above experiments, the FeCl3+NBC addition method was refined. After testing the water body, the data on the enhanced FeCl3 coagulation effect of different nano-biochar addition amounts are shown in Table 4. Figure 1 (d) as shown.

[0052] Table 4. Data on the effect of different nano-biochar dosages on FeCl3 coagulation

[0053]

[0054] From Table 4, Figure 1 (d) Figure 3 (b) It can be seen that the algae removal rate of the experimental group increased from 73.47% to 76.06%, 86.37%, 95.24%, and 97.78% compared with the control group; the algae density also increased from 0.23×10 6 cells / L decreased to 0.22×10 6 cells / L, 0.12×10 6 cells / L, 0.06×10 6 cells / L, 0.02×10 6 cells / L. At the same time, the residual amount of Fe ions was reduced from 0.31ppm to 0.26ppm, 0.22ppm, 0.15ppm and 0.11ppm respectively.

[0055] It can be seen that in the rapid mixing stage, adding the traditional coagulant FeCl3 as a primary coagulant for coagulation; and then in the slow mixing stage, adding the nano bamboo chip biochar prepared in Example 1 as a coagulant aid can significantly improve the removal efficiency of Microcystis aeruginosa in the water body and reduce the residual Fe ions in the water body.

[0056] Embodiment 2:

[0057] The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water, the specific steps are as follows:

[0058] (1) In water bodies containing Microcystis aeruginosa, the OD680 value of Microcystis aeruginosa is around 0.2, and the algae density is around 1×10 6 cells / mL (reaching the level of severe algal bloom);

[0059] (2) Collect the above-mentioned water containing Microcystis aeruginosa, add PAC as the main coagulant in a constant temperature shaking incubator at a temperature of 25°C and a pH of 8.2, and rapidly mix at 150RPM for 1 minute (rapid mixing stage); then add nano-biochar as a coagulant, slowly mix at 75RPM for 15 minutes (slow mixing stage), and finally settle for 30 minutes. After the coagulation is completed, the density of Microcystis aeruginosa and Al ions in the water are detected.

[0060] The preparation process of the nano biochar in step (2) is the same as the preparation process of the nano biochar in Example 1.

[0061] Before the enhanced coagulation experiment, PAC alone was used as a coagulant without using nano-biochar as a comparative experiment to obtain the coagulation effect data of different PAC dosages. The specific data are shown in Table 5.

[0062] Table 5. PAC coagulation effect data at different dosages

[0063]

[0064] As shown in Table 5, with the increase of PAC dosage, the algae removal rate continued to increase. 20 mg / L PAC can achieve an algae removal rate of 95.51%, but the residual Al ion also reached 675.75 ppb. In the table, 10 mg / L is significantly higher than 5 mg / L, and the residual Al ion is low, so 10 mg / L is selected for nano-biochar enhanced coagulation experiment.

[0065] In the process of applying nano-biochar in step (2) above, the order of addition obtained in Example 1 is used, and PAC is set as the primary coagulant to be added in the rapid stirring stage, and nano-biochar is set as the secondary coagulant to be added in the slow flocculation stage (ie, PAC+NBC). Different ratios of coagulant (PAC) to nano-biochar (10 mg / L: 0 g / L, 10 mg / L: 0.1 g / L, 10 mg / L: 0.3 g / L, 10 mg / L: 0.5 g / L, 10 mg / L: 0.7 g / L), wherein the control group is a group without adding nano-biochar; each group of experiments is repeated three times.

[0066] After the coagulation, the water body was tested and the data of different nano-biochar dosages to enhance the PAC coagulation effect were shown in Table 6. Figure 2 shown.

[0067] Table 6. Data on the effect of different nano-biochar dosages on enhancing PAC coagulation

[0068]

[0069] From Table 6, Figure 2 , Figure 3 (a) It can be seen that the algae removal rate of the experimental group increased from 58.02% to 74.08%, 84.64%, 90.62%, and 94.84% compared with the control group; the algae density also increased from 0.36×10 6 cells / L decreased to 0.22×10 6 cells / L, 0.13×10 6 cells / L, 0.08×10 6 cells / L, 0.04×10 6 cells / L; at the same time, the residual amount of Al ions decreased from 448.39ppb to 465.81ppb, 326.06ppb, 284.64ppb, and 255.90ppb, respectively. Comparison with Table 5 shows that, while maintaining a similar algae removal rate, the addition of NBC reduces the use of PAC and reduces the residual Al ions in the water from 675.75ppb to 255.90ppb.

[0070] It can be seen that in the fast mixing stage, adding the traditional coagulant PAC as the primary coagulant for coagulation; and then in the slow mixing stage, adding the nano-biochar prepared in Example 1 as the secondary coagulant can significantly improve the removal efficiency of Microcystis aeruginosa in the water body and reduce the residual Al ions in the water body. The effect is basically consistent with the strengthening effect in Example 1.

[0071] Embodiment 3:

[0072] The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water, the specific steps are as follows:

[0073] (1) In water bodies containing Microcystis aeruginosa, the density of Microcystis aeruginosa is the experimental variable;

[0074] (2) Collect the above-mentioned water containing Microcystis aeruginosa, add PAC as the main coagulant in a constant temperature shaking incubator at a temperature of 25°C and a pH of 8.2, and rapidly mix at 150RPM for 1 minute (rapid mixing stage); then add nano-biochar as a coagulant, slowly mix at 75RPM for 15 minutes (slow mixing stage), and finally settle for 30 minutes. After the coagulation is completed, the density of Microcystis aeruginosa and Al ions in the water are detected.

[0075] The preparation process of the nano biochar in step (2) is the same as the preparation process of the nano biochar in Example 1.

[0076] In the experiment, in order to determine the influence of initial algae density, PAC dosage and NBC dosage, the three main influencing factors, namely initial algae density, PAC dosage and NBC dosage, were selected, and the removal rate of Microcystis aeruginosa was used as the investigation index. 4 )Orthogonal experiment (Table 7), the results analysis is shown in Table 8.

[0077] Table 7. Orthogonal experiment table

[0078]

[0079] Table 8. Orthogonal experiment results and analysis

[0080]

[0081]

[0082] From the range analysis in Table 8, it can be seen that RB>RA>RC, and the three influencing factors are ranked in order of significance: PAC dosage, initial algae density, and NBC dosage, that is, PAC dosage has the greatest impact on the removal rate of Microcystis aeruginosa, followed by initial algae density, and NBC dosage has the least impact. According to the analysis results, the optimal solution is B3A2C2, but considering that excessive PAC dosage will greatly increase the residual Al ions, at the same time, the algae removal effect of B2A2C2 is not much different from that of B3A2C2, and the residual aluminum ion content is relatively low. In summary, the optimal solution is determined to be B2A2C2, that is, PAC dosage of 10 mg / L, initial algae density of 1×10 6 cells / mL, NBC dosage 0.5g / L.

[0083] Finally, according to the orthogonal experimental results, the determined optimal process conditions were verified. From Table 2 in Example 1, it can be seen that the removal rate of Microcystis aeruginosa under the optimal process conditions is greater than 90%, indicating that the process is feasible.

[0084] It can be seen from Example 1 and Example 2 that the method and application of the present invention to remove toxic blue algae in water by using nano-biochar enhanced coagulant, using traditional coagulants such as PAC or FeCl3 as primary coagulants and nano-biochar as secondary coagulant aids, is used to remove Microcystis aeruginosa and reduce metal ion residues in water. Example 3 also lists the optimal process conditions for initial algae density, PAC, and nano-biochar dosage. The method is simple to operate, has low manufacturing cost, is easy to produce, can significantly improve the removal efficiency of traditional coagulants for Microcystis aeruginosa, and reduce metal ions (Fe 3+ 、Al 3+ ) residues, which has dual benefits of economy and environment. At the same time, nano-biochar can reduce the dosage of traditional coagulants such as PAC or FeCl3 while strengthening the traditional coagulants to remove Microcystis aeruginosa, thereby reducing the metal ions (Fe 3+ 、Al 3+ ) content and reduce the treatment cost of algae-containing water bodies.

[0085] The above is an exemplary description of the invention. Obviously, the specific implementation of the present invention is not limited to the above-mentioned method. As long as such non-substantial improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method and application of using nano-biochar to enhance coagulant to remove toxic blue algae in water, characterized in that: The specific steps are as follows: In water containing Microcystis aeruginosa, first, in the rapid mixing stage, traditional coagulants are added as primary coagulants for coagulation; then in the slow mixing stage, nano-biochar is added as a secondary coagulant to remove Microcystis aeruginosa in the water and reduce the residual metal ions in the water.

2. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 1, characterized in that: The nano biochar is nano bamboo cuttings biochar.

3. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 1, characterized in that: The traditional coagulant is PAC or FeCl3.

4. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 1, characterized in that: The order of adding the traditional coagulant and the nano-biochar is: first add the coagulant PAC or FeCl3 and mix for 1 minute, then add the coagulant aid nano-biochar.

5. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 1, characterized in that: The initial algae density ratios of the traditional coagulant, nano-biochar and toxic blue algae in water are: PAC: NBC: Initial algae density = 10 mg / L: 0.5 g / L: (1×10 6 cells / mL), the removal rate of toxic blue algae in water can reach more than 90%.

6. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 1, characterized in that: The nano biochar and its preparation method include the following steps: S1, crushing and grinding bamboo sawdust into powder by a crusher, placing it in a muffle furnace, pyrolyzing and carbonizing it at 700° C. for 1 hour, and finally cooling it and sieving it with a 100-mesh sieve to obtain 100-mesh bamboo biochar; S2. The prepared 100-mesh bamboo biochar was ground using a planetary ball mill at 350 r / min for 4 days, with grinding balls of 8 mm, 10 mm and 15 mm in diameter and a ball-to-powder ratio of 10:1, thereby obtaining nano-biochar.

7. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 4, characterized in that: In step S1, the heating rate of pyrolysis carbonization in the muffle furnace is 10°C / min.

8. The method and application of nano-biochar enhanced coagulant to remove toxic blue algae in water according to claim 4, characterized in that: In step S2, during the grinding process of the planetary ball mill, the mill is cooled for 5 minutes after every 5 minutes of grinding until the grinding is completed.

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