CN114455749A

CN114455749A - Method for optimally controlling concentration of organic matters and residual aluminum in coagulation-ultrafiltration effluent

Info

Publication number: CN114455749A
Application number: CN202210218967.1A
Authority: CN
Inventors: 黄鑫; 何溢恬; 石宝友
Original assignee: Research Center for Eco Environmental Sciences of CAS
Current assignee: Research Center for Eco Environmental Sciences of CAS
Priority date: 2022-03-08
Filing date: 2022-03-08
Publication date: 2022-05-10

Abstract

The present disclosure provides a method for optimally controlling the concentration of organic matters and residual aluminum in coagulation-ultrafiltration effluent, which comprises: introducing carbon dioxide gas into raw water to be treated to obtain a solution to be treated with a preset pH value; adding a first adding amount of aluminum-based coagulant into the solution to be treated, and stirring at a first stirring speed to obtain a pre-mixed condensate; adding a second dosage of aluminum-based coagulant into the pre-coagulation liquid, stirring at a second stirring speed, and stirring at a third stirring speed to obtain a coagulation liquid; and filtering the coagulating liquid through a hollow fiber ultrafiltration membrane at a preset flow rate to obtain a treated solution.

Description

Method for optimally controlling concentration of organic matters and residual aluminum in coagulation-ultrafiltration effluent

Technical Field

The disclosure relates to the technical field of water treatment, in particular to a method for optimally controlling the concentration of organic matters and residual aluminum in coagulation-ultrafiltration effluent.

Background

The coagulation-ultrafiltration short-flow treatment process can effectively remove colloidal particles and macromolecular organic matters in water, has the advantages of small occupied area, simple operation and the like, and is a water treatment process with great development prospect.

The aluminum-based coagulant is the most widely used inorganic flocculant, the suitable adding range is wide, and the formed floc has good settling property. However, the removal effect of the aluminum-based coagulant on organic matters depends on the properties of the organic matters, for example, the removal effect of the aluminum-based coagulant on small-molecular organic matters is inferior to that of large-molecular organic matters, which causes the problems of subsequent ultrafiltration membrane pollution, high organic matter content in ultrafiltration effluent and the like, and increases the risk of forming disinfection byproducts. In addition, the use of an aluminum-based coagulant increases the content of dissolved aluminum in water, and ultrafiltration has poor interception effect on the dissolved aluminum. If the residual dissolved aluminum in the effluent enters the pipe network, a series of conversions can be carried out to form aluminum hydrate precipitates, which causes adverse effects such as the rising of water turbidity of the pipe network and the reduction of disinfection effect. When the total aluminum in the factory water exceeds 100 mug/L, the risk that the content of the aluminum in the pipe network water exceeds the standard is increased.

Increasing the dosage of the aluminum salt coagulant can effectively improve the removal rate of organic matters, but high dosage can cause the content of residual aluminum in effluent to increase and increase the cost of medicament. The inorganic and organic composite coagulant can improve the removal effect of coagulation on organic matters and reduce the content of residual aluminum, but the manufacturing process is more complicated and the cost is higher.

Disclosure of Invention

In view of the above, the main object of the present disclosure is to provide a method for optimizing and controlling the concentration of organic matter and residual aluminum in coagulation-ultrafiltration effluent, so as to at least partially solve at least one of the above mentioned technical problems.

In order to achieve the above objects, there is provided, as an embodiment of an aspect of the present disclosure, a method for optimally controlling organic matter and residual aluminum concentration in coagulation-ultrafiltration effluent, including: introducing carbon dioxide gas into raw water to be treated to obtain a solution to be treated with a preset pH value; adding a first adding amount of aluminum-based coagulant into the solution to be treated, and stirring at a first stirring speed to obtain a pre-mixed condensate; adding a second dosage of aluminum-based coagulant into the pre-mixed condensate, stirring at a second stirring speed, and stirring at a third stirring speed to obtain a pre-mixed condensate; and filtering the coagulation liquid through a hollow fiber ultrafiltration membrane at a preset flow rate to obtain a treated solution.

According to the embodiment of the disclosure, the purity of the carbon dioxide gas is more than or equal to 99.5%; the flow rate of the carbon dioxide gas is 0.35L/min to 0.45L/min.

According to an embodiment of the present disclosure, the range of the preset pH value includes: 6.2 to 6.8.

According to the embodiment of the disclosure, the mass ratio range of the first addition amount of the aluminum-based coagulant to the second addition amount of the aluminum-based coagulant comprises 2: 10-10: 2; the mass of the first and second amounts of the aluminum-based coagulant is calculated by aluminum.

According to the embodiment of the disclosure, the first stirring speed comprises 280-320 rpm.

According to the embodiment of the present disclosure, the second stirring speed includes 75-85 rpm.

According to an embodiment of the present disclosure, the third stirring speed includes 35 to 45 rpm.

According to the embodiment of the disclosure, the membrane aperture range of the hollow fiber ultrafiltration membrane is 0.01-0.03 mu m, and the flow rate is 50-80L/min.

According to an embodiment of the present disclosure, further comprising: measuring the content of residual total aluminum, the content of residual dissolved aluminum and the content of organic matters in the treated solution; determining the content of the particle aluminum according to the content of the residual total aluminum and the content of the residual dissolved aluminum.

According to an embodiment of the present disclosure, the determining the content of the particulate aluminum according to the residual total aluminum content and the residual dissolved aluminum content includes: determining the content of the particulate aluminum based on the difference between the residual total aluminum content and the residual dissolved aluminum content.

According to the embodiment of the disclosure, the pH value of raw water to be treated is adjusted to 6.2-6.8 by using carbon dioxide, so that aluminum in a coagulant exists mainly in the form of aluminum hydroxide and is easier to remove by ultrafiltration, and partially negatively charged organic matters can be neutralized with hydrogen ions under weak acidic conditions to generate self-aggregation. When the first dosage of the aluminum-based coagulant is added, aluminum is neutralized with dissolved organic matters with negative electricity in the rapid hydrolysis process, and simultaneously the pH value of a water sample is further reduced, so that the second dosage of the aluminum-based coagulant forms more aluminum hydroxide under the condition of more proper pH value, and flocs formed in the first dosage of the aluminum-based coagulant in the rapid stirring stage are bridged, so that the particle size of the flocs is increased, and the content of the organic matters and residual aluminum in ultrafiltration effluent is effectively reduced.

Drawings

FIG. 1 is a flow chart of a method for optimizing control of organic matter and residual aluminum concentration in coagulation-ultrafiltration effluent according to an embodiment of the present disclosure;

FIG. 2 shows the contents of organic substances in raw water and effluent to be treated in example 1 of the present disclosure;

FIG. 3 is a graph showing the residual aluminum concentration in the raw water and effluent to be treated in example 1 of the present disclosure;

FIG. 4 is a schematic diagram of a pH change process in example 1 of the present disclosure;

FIG. 5 is a graph of the theoretical aluminum concentration change at various pH values in example 1 of the present disclosure;

FIG. 6 shows the contents of organic substances in raw water and effluent to be treated in example 2 of the present disclosure;

FIG. 7 shows the residual aluminum concentration in the raw water and effluent to be treated in example 2 of the present disclosure;

fig. 8 is a schematic diagram of a process of pH change in example 2 of the present disclosure.

Detailed Description

For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

The pH value has a certain influence on the form of the organic matter. The polymerization degree of the soluble organic matters is increased under the acidic condition, and the particle size is rapidly increased, so that the removal effect of the organic matters in the coagulation and ultrafiltration processes can be improved. In addition, the proportion of dissolved aluminum and particulate aluminum can be controlled by adjusting the pH value, thereby indirectly influencing the coagulation effect and improving the concentration of residual aluminum.

Based on the inventive concept, the embodiment of the disclosure provides a method for optimally controlling the concentration of organic matters and residual aluminum in coagulation-ultrafiltration effluent.

Fig. 1 is a flow chart of a method for optimally controlling the concentration of organic matter and residual aluminum in coagulation-ultrafiltration effluent according to an embodiment of the present disclosure.

As shown in fig. 1, the method for optimally controlling the concentration of organic matters and residual aluminum in the coagulation-ultrafiltration effluent according to the embodiment of the present disclosure includes steps S001 to S004.

And S001, introducing carbon dioxide gas into the raw water to be treated to obtain a solution to be treated with a preset pH value.

In step S002, after a first amount of aluminum-based coagulant is added to the solution to be treated, the solution is stirred at a first stirring speed to obtain a pre-mixed coagulant.

In some embodiments, the aluminum-based coagulant includes polyaluminum chloride, aluminum sulfate, and the like.

In step S003, after the second amount of aluminum-based coagulant is added to the pre-coagulation liquid, the pre-coagulation liquid is stirred at the second stirring speed and then at the third stirring speed to obtain the pre-coagulation liquid.

In step S004, the coagulation liquid is filtered through a hollow fiber ultrafiltration membrane at a preset flow rate to obtain a treated solution.

According to the embodiment of the disclosure, the purity of the carbon dioxide gas is more than or equal to 99.5%; the flow rate of the carbon dioxide gas is 0.35L/min-0.45L/min. For example, the purity of carbon dioxide gas is 99.7%, 99.8%, 99.97%, 99.99%; the flow rate of carbon dioxide gas was 0.37L/min, 0.38L/min, 0.40L/min, 0.44L/min.

According to an embodiment of the present disclosure, the range of the preset pH value includes: 6.2 to 6.8. For example 6.3, 6.4, 6.5, 6.6, 6.7.

According to the embodiment of the disclosure, the mass ratio range of the first dosage of the aluminum-based coagulant to the second dosage of the aluminum-based coagulant comprises 2: 10-10: 2; the mass of the first and second dosing of the aluminium-based coagulant is calculated as aluminium. For example, the mass ratio of the first and second dosing amounts of aluminium-based coagulant is in the range of 3:10, 5:10, 10:10, 6:2, 8: 2.

In some embodiments, the mass of the first and second dosed amounts of aluminium-based coagulant is in mg/L in aluminium, for example: the aluminum-based coagulant added in each liter of raw water to be treated is converted into 10mg by mass of aluminum.

According to an embodiment of the present disclosure, the first stirring speed includes 280 to 320 rpm. For example, the first stirring speed is 290rpm, 300rpm, 310 rpm; wherein, when the first stirring speed is 290rpm, the maintaining time of the first stirring speed is 1.0-2.0 min.

According to an embodiment of the present disclosure, the second stirring speed comprises 75-85 rpm. For example, the second stirring speed is 76rpm, 78rpm, 81rpm, 83 rpm; wherein, when the second stirring speed is 80rpm, the maintaining time of the second stirring speed is 10-15 min.

According to an embodiment of the present disclosure, the third stirring speed comprises 35 to 45 rpm. For example, the third stirring speed is 36rpm, 38rpm, 41rpm, 43 rpm; wherein, when the third stirring speed is 40rpm, the maintaining time of the third stirring speed is 15-25 min.

According to the embodiment of the disclosure, the membrane aperture range of the hollow fiber ultrafiltration membrane comprises 0.01-0.03 μm. For example, the membrane pore size range of the hollow fiber ultrafiltration membrane includes 0.015 μm, 0.02 μm, 0.025 μm; wherein the membrane aperture of the hollow fiber ultrafiltration membrane is 0.02 mu m, and the preset flow rate of filtration is 50-80L/min.

According to an embodiment of the present disclosure, further comprising: determining the content of residual total aluminum, the content of residual dissolved aluminum and the content of organic matters in the treated solution; and determining the content of the particle aluminum according to the content of the residual total aluminum and the content of the residual dissolved aluminum.

In some embodiments, the residual total aluminum content of the treated solution is determined after 24h of digestion of the treated solution by adding concentrated nitric acid dropwise.

In some embodiments, residual total aluminum content refers to all forms of aluminum in the treated solution; the residual dissolved aluminum content refers to all forms of aluminum that can pass through a 0.45 μm pore size in the treated solution.

In some embodiments, inductively coupled plasma mass spectrometry is used to determine the residual total aluminum content, the residual dissolved aluminum content.

According to an embodiment of the present disclosure, determining a content of particulate aluminum from a residual total aluminum content and a residual dissolved aluminum content comprises: determining the content of the granular aluminum according to the difference between the residual total aluminum content and the residual dissolved aluminum content.

The disclosure is further illustrated by the following comparative examples and examples. In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. Moreover, the details of the following embodiments may be combined arbitrarily, without conflict, into other possible embodiments.

Example 1

S1: taking Suzhou Changjiang river water as experimental raw water, wherein the pH value is 7.3-7.4;

s2: introducing carbon dioxide gas with the purity higher than 99.5% into the experimental raw water to obtain a treatment solution with the preset pH value of 6.5, wherein the flow rate of the carbon dioxide gas is 0.4L/min, and the utilization rate of the carbon dioxide is 90.2%;

s3: adding 5.1 mu L (0.3mg/L calculated by aluminum) of polyaluminium chloride in a first adding amount into the solution to be treated obtained in the step S2, and stirring at a stirring speed of 300rpm for 1.5min to obtain a pre-mixed condensate, wherein the content of Al in the polyaluminium chloride is 5.8%;

s4: adding a second amount of polyaluminium chloride (11.9 mu g/L (0.7mg/L in terms of aluminum) into the pre-mixed condensate obtained in the step S3, stirring at a stirring speed of 80rpm for 11min, and then stirring at a stirring speed of 40rpm for 20min to obtain a mixed condensate;

s5: filtering the mixed condensate obtained in the step S4 through a hollow fiber ultrafiltration membrane at a preset flow rate of 50L/min to obtain a treated solution, wherein the membrane material for filtering the hollow fiber membrane is polyvinylidene fluoride, and the membrane aperture is 0.02 mu m;

s6: and collecting a certain amount of the treated solution obtained in the step S5, performing a series of pretreatment such as corresponding acid addition and membrane filtration, and measuring the contents of organic matters, residual total aluminum (all forms of aluminum in the filtered water) and residual dissolved aluminum (all forms of aluminum which can pass through the pore diameter of 0.45 mu m in the filtered water).

Comparative example 1

The procedure of example 1 was repeated, except that "the first treatment solution having a predetermined pH of 5.5 was obtained in step S2".

Comparative example 2

The steps are the same as those of embodiment 1 except for "no step S2".

Comparative example 3

The procedure of example 1 was followed, except that "after adding 17. mu.L (1mg/L in terms of aluminum) of polyaluminum chloride in the first amount to the test stock water directly in S3 without steps S2 and S4".

The content of organic matters in the experimental raw water and the effluent in the measurement results is shown in fig. 2; the concentrations of residual aluminum in the raw experimental water and the effluent are shown in FIG. 3.

FIG. 2 is a schematic diagram showing the contents of organic substances in experimental raw water and effluent water in the measurement results of example 1, comparative example 2 and comparative example 3.

As shown in FIG. 2, examples 1, comparative examples 1, 2 and 3 are UV sensitive₂₅₄The removal rates of (a) were 75.9%, 72.9%, 74.0% and 71.0%, respectively; the removal rates for soluble organic compounds (DOC) were 35.4%, 23.4%, 32.1% and 28.6%, respectively. Therefore, under the condition of the pH of experimental raw water, the mode of adding the polyaluminium chloride by two stages in the comparative example 2The removal capacity of the organic matters is superior to that of the mode of adding all the polyaluminium chloride at one time in the comparative example 3; the removal capacity of the method for adjusting the pH of the raw water to 6.5 and coupling the two-stage coagulant adding is better than that of the method for adjusting the pH of the raw water to 5.5 and coupling the two-stage coagulant adding in the comparative example 1.

FIG. 3 is a schematic diagram showing the residual aluminum concentrations in the experimental raw water and the effluent in the measurement results of example 1, comparative example 2 and comparative example 3.

As shown in FIG. 3, the raw water of Yangtze river is mainly granular aluminum, and the content of dissolved aluminum is lower than 40 mug/L, while the content of dissolved aluminum in the super-filtered water of comparative example 3, comparative example 2 and comparative example 1 is significantly higher than that of the raw water, and the residual total aluminum content is close to or even exceeds 100 mug/L, which may increase the risk of exceeding the aluminum content of the pipe network water. The residual total aluminum content of the comparative example 3 and the comparative example 2 is similar, which shows that the control effect of the mode of adding all polyaluminium chloride at one time under the condition of the pH of the experimental raw water is equivalent to the control effect of the mode of adding polyaluminium chloride by two sections separately. In contrast, example 1 can control the residual total aluminum at an extremely low level below 5 μ g/L, which illustrates that the residual aluminum content in the ultrafiltrated water can be effectively controlled by adjusting the pH of the raw water to 6.5 and coupling the two-stage addition manner in example 1, whereas the dissolved aluminum content is high and difficult to be removed by filtration under the conditions of adjusting the pH of the raw water to pH 5.5 and coupling the two-stage addition manner in comparative example 1.

As shown in FIG. 4, the pH varied to decrease and then increase during each agitation.

As shown in fig. 5, the theoretical concentration of aluminum at each pH value tended to decrease as the pH of the solution increased. When the pH of the solution is 6.5, the first dosage of polyaluminum chloride is added to quickly generate electric neutralization, and the pH of the water sample is further reduced to 6.3-6.4 in the hydrolysis process. As shown in FIG. 5, under the condition of pH value of 6.3-6.4, more aluminum hydroxide is generated by the second adding amount of polyaluminum chloride than at pH value of 6.5, so that the generated aluminum hydroxide can be bridged with formed flocs to enhance the net trapping and sweeping effect, and can be combined with more negatively charged organic matters to achieve the effect of simultaneously controlling the content of the organic matters and residual aluminum in the ultrafiltration effluent.

Example 2

S1: additionally adding 10mg/L of humic acid to tap water to simulate organic matters rich in humic acid to serve as experimental raw water, wherein the pH value is 7.5-7.8;

s2: introducing carbon dioxide gas with the purity higher than 99.5% into the experimental raw water to obtain a first treatment solution with the preset pH value of 6.5, wherein the flow rate of the carbon dioxide gas is 0.4L/min, and the utilization rate of the carbon dioxide is 88.5%;

Comparative example 4

The procedure of example 2 was repeated, except that "the first treatment solution having a predetermined pH of 5.5 was obtained in step S2".

Comparative example 5

The steps are the same as those of embodiment 2 except for "no step S2".

Comparative example 6

FIG. 6 is a schematic representation showing the contents of organic substances in the experimental raw water and the effluent in the results of the measurements of example 2, comparative example 4, comparative example 5 and comparative example 6.

As shown in FIG. 6, examples 2, comparative examples 4, comparative examples 5, and comparative examples 6 are UV-sensitive₂₅₄The removal rates of (a) were 70.0%, 68.5%, 56.2% and 60.0%, respectively; the removal rates for soluble organic compounds (DOC) were 24.5%, 28.1%, 18.7% and 17.1%, respectively. Therefore, under the condition of the pH of the experimental raw water, the removal capacity of the mode of adding the polyaluminium chloride by two sections in the comparative example 5 to the organic matters is superior to that of the mode of adding all the polyaluminium chloride by one time in the comparative example 6; the removal capacity of the humic acid organic matter by the mode of adjusting the pH of the raw water to 6.5 and coupling the two-stage coagulant adding is better than that by the mode of adjusting the pH of the raw water to 5.5 and coupling the two-stage coagulant adding in the comparative example 4.

FIG. 7 is a graph schematically showing the residual aluminum concentrations in the experimental raw water and the effluent in the results of the measurements of example 2, comparative example 4, comparative example 5 and comparative example 6.

As shown in FIG. 7, the total aluminum content in the raw water is 40 μ g/L, while the residual total aluminum content in the ultrafiltration effluent of comparative example 6, comparative example 5 and comparative example 4 is significantly higher than that of the raw water, even exceeds 100 μ g/L, so that the risk of the aluminum content exceeding the standard of the water in the pipe network is greatly increased. Comparative example 5 the residual total aluminium content is lower than comparative example 6, which shows that the effect of controlling the residual aluminium content by separately adding polyaluminium chloride in two stages under the condition of the pH of the experimental raw water is better than that of adding all polyaluminium chloride in one step. Example 2 can control the residual total aluminum at about 5 μ g/L, which illustrates that example 2 can effectively control the residual aluminum content of the ultrafiltrated effluent by adjusting the raw water pH to 6.5 and coupling the two-stage feeding mode, and that the dissolved residual aluminum content is high and difficult to be removed by filtration under the conditions of the experimental raw water pH and pH 5.5.

As shown in fig. 8, the pH varied to decrease and then increase during each stirring in example 2. When the pH value of the solution is 6.5, the aluminum and the humic acid with negative electricity rapidly generate an electric neutralization effect when the first adding amount of polyaluminum chloride is added, the pH value of the solution is further reduced to 6.3-6.4 in the aluminum hydrolysis process, and after the second adding amount of polyaluminum chloride generates more aluminum hydroxide, the polyaluminum chloride can be combined with formed flocs to generate more flocs and can be continuously neutralized with the humic acid, so that the effect of simultaneously controlling the content of the organic matters and the content of the aluminum in the ultrafiltration effluent is achieved.

According to the method for optimally controlling the concentration of the organic matters and the residual aluminum in the coagulation-ultrafiltration effluent, provided by the embodiment of the disclosure, the pH of raw water is adjusted to 6.2-6.8 by using carbon dioxide, so that aluminum in a coagulant exists mainly in the form of aluminum hydroxide and is easier to be removed by ultrafiltration, and the organic matters with negative electricity under the weak acidic condition can be neutralized with hydrogen ions to generate self-aggregation. When the first adding amount of polyaluminium chloride is added, aluminum is neutralized with dissolved organic matters with negative electricity in the rapid hydrolysis process, simultaneously, the pH value of a water sample is further reduced, so that the second adding amount of polyaluminium chloride forms more aluminum hydroxide under the more proper pH condition, and flocs formed in the first adding amount of polyaluminium chloride in the rapid stirring stage are bridged, so that the particle size of the flocs is increased, the net-catching roll sweeping and electric neutralization effects are enhanced, and the content of the organic matters and residual aluminum in ultrafiltration effluent is effectively reduced.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims

1. A method for optimally controlling the concentration of organic matters and residual aluminum in coagulation-ultrafiltration effluent comprises the following steps:

introducing carbon dioxide gas into raw water to be treated to obtain a solution to be treated with a preset pH value;

adding a first adding amount of aluminum-based coagulant into the solution to be treated, and stirring at a first stirring speed to obtain a pre-mixed condensate;

adding a second dosage of aluminum-based coagulant into the pre-mixed condensate, stirring at a second stirring speed, and stirring at a third stirring speed to obtain a pre-mixed condensate;

and filtering the coagulating liquid through a hollow fiber ultrafiltration membrane at a preset flow rate to obtain a treated solution.

2. The method of claim 1, wherein,

the purity of the carbon dioxide gas is more than or equal to 99.5 percent;

the flow rate of the carbon dioxide gas is 0.35L/min-0.45L/min.

3. The control method according to claim 1,

the preset pH value range comprises: 6.2 to 6.8.

4. The method of claim 1, wherein,

the mass ratio range of the first dosage of the aluminum-based coagulant to the second dosage of the aluminum-based coagulant is 2: 10-10: 2;

the mass of the first and second dosing amounts of the aluminum-based coagulant is calculated as aluminum.

5. The method of claim 1, wherein the first stirring speed comprises 280-320 rpm.

6. The method of claim 1, wherein the second stirring speed comprises 75-85 rpm.

7. The method of claim 1, wherein the third stirring speed comprises 35-45 rpm.

8. The method of claim 1, wherein the hollow fiber ultrafiltration membrane has a membrane pore size ranging from 0.01 to 0.03 μm and a flow rate of 50 to 80L/min.

9. The method of claim 1, further comprising:

determining the content of residual total aluminum, the content of residual dissolved aluminum and the content of organic matters in the treated solution;

and determining the content of the particle aluminum according to the content of the residual total aluminum and the content of the residual dissolved aluminum.

10. The method of claim 9, wherein said determining a content of particulate aluminum from said residual total aluminum content and said residual dissolved aluminum content comprises:

determining the content of the particulate aluminum based on the difference between the residual total aluminum content and the residual dissolved aluminum content.