A method for pH adjustment enhanced coagulation based on wastewater treatment

Abstract

This invention discloses an industrial wastewater treatment method, specifically a pH-adjusted enhanced coagulation method for wastewater treatment, comprising the following steps: taking a certain volume of industrial wastewater into a coagulation tank and stirring it evenly, and measuring the initial pH value; using a dosing system to add acidic or alkaline agents to adjust the industrial wastewater multiple times to obtain multiple first pH thresholds; using a dosing system to sequentially add coagulants and flocculants for coagulation and filtration, obtaining filtrates corresponding to multiple first pH thresholds; after static filtration, measuring the Zeta potential and COD of multiple filtrates; performing linear fitting based on multiple first pH values ​​and the corresponding Zeta potential values ​​of the filtrates to calculate the optimal pH value of the filtrate when the Zeta potential is zero; monitoring the Zeta potential value of the industrial wastewater in real time and dynamically adjusting the optimal pH value based on the Zeta potential value; this invention improves coagulation efficiency by performing linear fitting based on different pH values ​​and the corresponding filtrate Zeta potential values ​​to calculate the optimal pH value of the solution when the Zeta potential is zero.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment, and particularly to a pH-adjusted enhanced coagulation method for wastewater treatment. Background Technology

[0002] In recent years, with the rapid development of industrialization, industries such as petrochemicals, coal, printing and dyeing, and textiles have generated large amounts of industrial wastewater with complex composition, high concentration, and high color during production processes, causing great harm to the ecological environment. Especially as the country has increasingly emphasized the issue of industrial water pollution, national and local wastewater discharge standards have become increasingly stringent, posing a severe challenge to wastewater treatment for enterprises. Developing an efficient and low-cost industrial wastewater treatment method has become a top priority in the field of industrial wastewater treatment.

[0003] Coagulation and sedimentation is a method that uses chemical agents to destabilize colloidal particles in water, causing them to flocculate and aggregate, thereby removing suspended solids and some organic matter. It has advantages such as low cost, simplicity, high efficiency, and stability, and is widely used in industrial wastewater treatment. The zeta potential is closely related to the stability of colloidal particles; generally, the higher the absolute value of the zeta potential, the more stable the particle dispersion system. Typically, the coagulation effect is optimal when the zeta potential is in the range of -5 to 0 mV.

[0004] Currently, most studies on factors affecting coagulation efficiency focus on the type and dosage of coagulants. For example, CN103276113 A discloses a method for adjusting the addition of flocculants to sulfur fumigation neutralization juice based on zeta potential value. CN109748363 A discloses a method for adjusting the dosage of coagulants in wastewater treatment from papermaking reconstituted tobacco production. CN111077186 A discloses a method for determining the flocculation mechanism based on the flocculant dosage and changes in zeta potential value. However, in-depth research on pH is lacking. During coagulation, the pH value of the solution not only directly changes the surface charge of colloidal particles, affecting the form of pollutants in the water, but also affects the form of coagulant hydrolysis products, making it one of the most important factors affecting zeta potential.

[0005] In actual industrial production processes, changes in raw materials and related procedures lead to unstable industrial wastewater quality. The pH of the solution used in coagulation treatment must also be adjusted accordingly to ensure optimal coagulation results. Therefore, it is essential to develop a pH-adjusted enhanced coagulation method based on wastewater treatment principles in industrial wastewater coagulation treatment. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to solve the following technical problems:

[0007] In actual industrial production, changes in raw materials and related processes lead to unstable industrial wastewater quality and significant fluctuations in coagulation efficiency. Zeta potential is the most significant factor affecting coagulation efficiency, and pH value influences zeta potential. Current technologies do not adjust pH during industrial wastewater coagulation, resulting in higher zeta potential values, better colloid stability, and poorer coagulation performance.

[0008] This invention provides a pH-adjusted enhanced coagulation method for wastewater treatment. This method is simple to operate, has a wide range of applications, and can be used to quickly adjust the pH value of industrial wastewater when the wastewater quality is unstable during actual industrial production, ensuring optimal coagulation results.

[0009] This invention is achieved through the following technical solution:

[0010] In industrial wastewater coagulation treatment, a pH-adjusted enhanced coagulation method based on wastewater treatment includes the following steps:

[0011] Take a certain volume of industrial wastewater into a coagulation tank and stir it evenly, then measure the initial pH value.

[0012] By using a dosing system to add acidic or alkaline agents to adjust industrial wastewater multiple times, several first pH thresholds can be obtained.

[0013] Coagulant and flocculant were added sequentially using a dosing system for coagulation and filtration to obtain multiple filtrates corresponding to the first pH threshold.

[0014] After standing and filtration, the zeta potential and COD values ​​of multiple filtrates were measured.

[0015] Based on multiple first pH thresholds and the corresponding Zeta potential values ​​of the filtrate, a linear fit was performed to calculate the optimal pH value of the filtrate when the Zeta potential value is zero.

[0016] The zeta potential value of industrial wastewater is monitored in real time, and the optimal pH value is dynamically adjusted based on the zeta potential value.

[0017] To optimize the above technical solution, the specific measures also include:

[0018] Furthermore, the range of the first pH threshold is consistent with the applicable range of the coagulant.

[0019] Furthermore, coagulants and flocculants are added sequentially using a dosing system for coagulation and filtration to obtain multiple filtrates corresponding to the first pH threshold, specifically:

[0020] Add coagulant using a dosing system, and stir according to rate one and time one to obtain intermediate one;

[0021] Flocculant was added to intermediate one using a dosing system, and the mixture was stirred at rate one and time two to ensure that the flocculant and industrial wastewater were mixed evenly to obtain intermediate two.

[0022] Intermediate 2 is stirred at rate 2 and time 3 to generate flocculants, resulting in a mixed solution. After static filtration, the filtrate after coagulation treatment is obtained.

[0023] Furthermore, the coagulant includes one of polyferric sulfate, polyaluminum ferric sulfate, polyferric chloride, and polyaluminum chloride.

[0024] Furthermore, the first rate is greater than the second rate.

[0025] Furthermore, the flocculant includes cationic flocculants or anionic flocculants.

[0026] Furthermore, the time period is 5 minutes.

[0027] Furthermore, the second time is 2 minutes.

[0028] Furthermore, the third time is 10 minutes.

[0029] Furthermore, based on multiple first pH thresholds and the corresponding Zeta potential values ​​of the filtrate, a linear fit was performed to calculate the optimal pH value of the filtrate when the Zeta potential value is zero, specifically:

[0030] ζi = a Xi + b

[0031] Where: ζi represents the Zeta potential value of the filtrate after coagulation at the i-th first pH threshold, a represents the slope, Xi represents the i-th first pH threshold, and b represents the intercept.

[0032] The beneficial effects of this invention are:

[0033] The present invention discloses a pH-adjusted enhanced coagulation method for wastewater treatment. By adjusting the pH of industrial wastewater in the coagulation tank to a set first pH threshold, a coagulation and sedimentation experiment is conducted. Based on different first pH thresholds and the corresponding zeta potential values ​​of the filtrate, linear fitting is performed to calculate the optimal pH value of the solution when the zeta potential value is zero. This method can achieve higher coagulation efficiency, reduce the dosage of coagulants, and lower costs.

[0034] This method is simple to operate and has a wide range of applications. In actual industrial production processes, when changes in raw materials and related processes lead to unstable industrial wastewater quality, this method can be used to quickly adjust the pH value of the solution, ensuring optimal coagulation results.

[0035] This method adjusts the pH of wastewater by real-time monitoring of the Zeta potential value of the solution in the mixing tank, ensuring the coagulation treatment effect of wastewater, providing technical support for the coagulation treatment of industrial wastewater, and providing a reference for the coagulation process design of sewage treatment plants / stations. Attached Figure Description

[0036] Figure 1 This is a flowchart of a pH-adjusted enhanced coagulation method for wastewater treatment according to the present invention.

[0037] Figure 2 This is a linear fitting graph of the pH value and the corresponding zeta potential value of the filtrate in this invention.

[0038] Figure 3 This is a graph showing the relationship between the COD removal rate of this invention and pH value and Zeta potential value.

[0039] Figure 4 This is a comparison chart of COD removal rates after coagulation without pH adjustment and after enhanced coagulation with adjusted wastewater pH. Detailed Implementation

[0040] To clarify the technical solution and working principle of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0041] like Figure 1-2 As shown, this invention provides a pH-adjusted enhanced coagulation method for wastewater treatment. This method is for the treatment of industrial wastewater and includes the following steps:

[0042] Step S1: Take a certain volume of industrial wastewater into the coagulation tank and stir it evenly, and measure the initial pH value;

[0043] Step S2: Use a dosing system to add acidic or alkaline reagents multiple times to adjust the industrial wastewater and obtain multiple initial pH values;

[0044] Specifically: First, pH affects the hydrolysis reaction of coagulants and the formation of metal complexes, thus impacting the efficiency of coagulants in removing colloidal particles from water through charge neutralization adsorption or entrapment. Second, adding acidic or alkaline agents to wastewater—that is, adding positively or negatively charged electrolytes—affects the charge characteristics of colloidal particles, compresses the electric double layer, and neutralizes the charge on the particles, leading to a gradual decrease in the absolute value of the zeta potential. This weakens the stability of the colloidal particle dispersion system, making it easier to remove through coagulation and sedimentation. Therefore, the pH threshold should be set appropriately to match the pH range of the selected coagulant.

[0045] Step S3: Use the dosing system to add coagulant and flocculant sequentially to obtain multiple filtrates corresponding to the first pH threshold.

[0046] Specifically, coagulation includes two processes: coagulation and flocculation. After adding coagulant to the water sample, the colloidal particles lose stability and aggregate into tiny flocs through compression of the double electric layer and charge neutralization. Then, flocculant is added, and through adsorption bridging and trapping, the tiny flocs form larger flocs, which are then removed by sedimentation.

[0047] S31: Add coagulant using a dosing system, and stir according to rate one and time one to obtain intermediate one;

[0048] In this embodiment, the coagulant used is one of polyferric sulfate (PFS), polyaluminum ferric sulfate (PAFS), polyferric chloride (PFC), polyaluminum chloride (PAC), etc., and the time is 5 minutes.

[0049] S32: A certain volume of flocculant is added to intermediate one using a dosing system, and the mixture is stirred according to rate one and time two to make the flocculant and industrial wastewater evenly mixed to obtain intermediate two; in this embodiment, rate one is not specifically limited.

[0050] In this embodiment, PAM is used as the flocculant, and the time is 2 minutes.

[0051] S33: Stir intermediate 2 at rate 2 and time 3 to generate flocculants and obtain a mixed solution. After static filtration, obtain the filtrate after coagulation treatment; time 3 is 10 min.

[0052] Specifically: In order to avoid the flocs being broken up due to excessive speed during the stirring process, the second speed is less than the first speed. This implementation scheme does not specifically limit the second speed.

[0053] Step S4: After standing and filtering, measure the Zeta potential and COD values ​​of multiple filtrates.

[0054] Step S5: Based on multiple first pH thresholds and the corresponding zeta potential values ​​of the filtrate, perform linear fitting to calculate the optimal pH value of the filtrate when the zeta potential value is zero.

[0055] Specifically: When the amount of electrolyte in the solution reaches a certain level, all the charge carried by the colloid is neutralized. At this point, the repulsive force between the colloidal particles is minimal, the stability is worst, and it is most easily removed by coagulation. Therefore, based on different pH values ​​and the corresponding Zeta potential values ​​of the filtrate, a linear fit is performed, with the horizontal axis representing the solution pH value and the vertical axis representing the Zeta potential value, to find the pH value of the solution corresponding to a Zeta potential value of zero.

[0056] The fitted equation is: ζi = aXi + b; where: ζi represents the Zeta potential value of the filtrate after coagulation following the first pH threshold obtained after the i-th adjustment, in mV; a represents the slope; Xi represents the first pH threshold of the solution after the i-th adjustment; b represents the intercept.

[0057] like Figure 3 As shown, R² is the correlation coefficient, which represents the degree of agreement between the experimental data and the fitted equation. The closer the R² value is to 1, the higher the degree of agreement and the more reliable the data.

[0058] Step S6: Monitor the Zeta potential value of industrial wastewater in real time and dynamically adjust the optimal pH value based on the Zeta potential value.

[0059] The steps described above are for clarity only. In practice, they can be combined into one step or some steps can be broken down into multiple steps. As long as they include the same logical relationship, they are all within the scope of protection of this patent. Adding insignificant modifications or introducing insignificant designs to the algorithm or process, but without changing the core design of the algorithm and process, are also within the scope of protection of this patent.

[0060] The following is the coagulation treatment process for industrial wastewater at different pH values.

[0061] Example 1

[0062] A certain volume of industrial wastewater sample was placed in a beaker with an initial pH of 8.1. The pH of the sample was adjusted to 8 using concentrated sulfuric acid. The beaker was placed on a magnetic stirrer at room temperature, and PFS was added at a volume ratio of 0.2% to the water sample. The mixture was stirred rapidly at 400 r / min for 5 min. Then, PAM was added at a volume ratio of 0.3% to the water sample (1‰), and the mixture was stirred rapidly for 2 min. The stirring speed was then adjusted to 150 r / min and stirred slowly for 10 min. After the reaction was complete, the mixture was allowed to stand and filtered. The Zeta potential and COD of the filtrate were measured. The results showed that when the pH of the water sample was 8, the COD removal rate was 33.9%, and the Zeta potential of the filtrate was ζ1 = -20.36 mV.

[0063] Example 2

[0064] Take an industrial wastewater sample of the same volume as described above in a beaker, adjust the pH of the sample to 7 with concentrated sulfuric acid, and carry out coagulation and sedimentation reaction according to the same experimental procedure as above. The results show that when the pH of the sample is 7, the COD removal rate is 48.2%, and the Zeta potential value of the filtrate is ζ2 = -14.85 mV.

[0065] Example 3

[0066] Take an industrial wastewater sample of the same volume as described above in a beaker, adjust the pH of the sample to 6 with concentrated sulfuric acid, and carry out coagulation and sedimentation reaction according to the same experimental procedure as above. The results show that when the pH of the sample is 6, the COD removal rate is 75.6%, and the Zeta potential value of the filtrate is ζ3 = -3.38 mV.

[0067] Example 4

[0068] Take an industrial wastewater sample of the same volume as described above in a beaker, adjust the pH of the sample to 5 with concentrated sulfuric acid, and carry out coagulation and sedimentation reaction according to the same experimental procedure as above. The results show that when the pH of the sample is 5, the COD removal rate is 68.8%, and the Zeta potential value of the filtrate is ζ4 = 5.85 mV.

[0069] Example 5

[0070] Take an industrial wastewater sample of the same volume as described above in a beaker, adjust the pH of the sample to 4 with concentrated sulfuric acid, and carry out coagulation and sedimentation reaction according to the same experimental procedure as above. The results show that when the pH of the sample is 5, the COD removal rate is 51.3%, and the Zeta potential value of the filtrate is ζ5 = 8.78 mV.

[0071] Linear fitting was performed based on the Zeta potential values ​​ζ1-ζ5 of the filtrates corresponding to different pH values ​​of 8-4, such as... Figure 2 As shown, the fitting equation is: ζi = -7.898 Xi + 42.596; where: ζi represents the Zeta potential value of the filtrate after coagulation in the i-th pH adjustment, in mV; the slope is -7.898; Xi represents the pH value of the solution in the i-th adjustment; the intercept is 42.596; the correlation coefficient R² = 0.960, and the experimental data and the fitting equation are in good agreement.

[0072] When ζi = 0, the isoelectric point is reached, the repulsive force between particles is minimized, and the coagulation effect is optimal. The pH value Xi is calculated to be 5.4 based on the fitted equation. This indicates that the best coagulation effect can be achieved when the pH of the solution is adjusted to 5.4.

[0073] Take an industrial wastewater sample of the same volume as described above in a beaker, adjust the pH of the sample to the optimal value with concentrated sulfuric acid, and carry out coagulation and sedimentation reaction according to the same experimental procedure as above. The results show that when the pH of the sample is 5.4, the COD removal rate is as high as 79.3%, and the coagulation effect is the best.

[0074] Figure 3The graph shows the relationship between COD removal rate, pH value, and Zeta potential. When the pH is below 6, the COD removal rate gradually increases with increasing pH, while the absolute value of the Zeta potential gradually decreases. At pH 6, the COD removal efficiency is highest, and the absolute value of the Zeta potential is lowest at 3.38 mV. Further increasing the pH at this point leads to a decrease in COD removal rate and a gradual increase in the absolute value of the Zeta potential. This is because under weakly acidic conditions, the hydrolysis products of the coagulant PFS are mainly polynuclear hydroxyl complexes with high valence positive charges, which adsorb negatively charged colloidal particles in the water through charge neutralization. When the pH exceeds 6, further increasing the pH hinders the hydrolysis reaction of PFS, leading to the formation of low-charge positive polynuclear complex ions and metal hydroxide colloidal precipitates. This reduces the ability to neutralize colloidal particles in the water, increases the absolute value of the Zeta potential, and worsens the coagulation effect.

[0075] Comparative Example 1

[0076] A certain volume of industrial wastewater sample was placed in a beaker with an initial pH of 8.1, and coagulation and sedimentation reactions were carried out according to the same experimental procedures as described above. The results showed that when the pH of the water sample was 8.1, the COD removal rate was 33.1%, and the Zeta potential value of the filtrate was ζ1 = -20.87 mV.

[0077] like Figure 4 As shown, in industrial wastewater treatment, adjusting the pH to reduce the zeta potential value of the wastewater can enhance the coagulation treatment effect.

[0078] In summary, pH value not only directly alters the surface charge of colloidal particles but also affects the morphology of coagulant hydrolysis products, making it one of the most important factors influencing Zeta potential. The method of adjusting wastewater pH based on Zeta potential involves linear fitting based on different pH values ​​and the corresponding filtrate Zeta potential values ​​to calculate the optimal pH value for the solution when the Zeta potential is zero. This achieves the best coagulation effect, reducing the dosage of coagulants and lowering costs. This method allows for the installation of Zeta potential meters in the coagulation tanks of wastewater treatment plants / stations to monitor the Zeta potential value of the solution in real time. By adjusting the pH value of the wastewater, the coagulation treatment effect can be guaranteed, providing technical support for industrial wastewater coagulation treatment and a reference for the design of coagulation processes in wastewater treatment plants / stations.

[0079] The above descriptions are merely embodiments of the present invention. Common knowledge such as specific structures and characteristics known in the solutions are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the technical field to which the invention pertains before the application date or priority date, are able to obtain all prior art in the field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can improve and implement the solution based on the inspiration given in this application and their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application.

[0080] It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of this invention, and these should also be considered within the scope of protection of this invention. These modifications and improvements will not affect the effectiveness of the invention or the practicality of the patent. The scope of protection claimed in this application shall be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A pH-adjusted enhanced coagulation method for wastewater treatment, used to treat industrial wastewater, comprising the following steps: Take a certain volume of industrial wastewater into a coagulation tank and stir it evenly, then measure the initial pH value. Multiple initial pH values ​​are obtained by repeatedly adjusting the initial pH value using an acidic or alkaline dosing system; Coagulant and flocculant were added sequentially using a dosing system for coagulation and filtration to obtain multiple filtrates corresponding to the first pH threshold. After standing and filtration, the zeta potential and COD values ​​of multiple filtrates were measured. Based on multiple first pH thresholds and the corresponding Zeta potential values ​​of the filtrate, a linear fit was performed to calculate the optimal pH value of the filtrate when the Zeta potential value is zero. A Zeta potential meter is installed in the coagulation tank to monitor the Zeta potential value of the industrial wastewater in real time and dynamically adjust the pH to the optimal value obtained by the above linear fitting calculation. Coagulation and filtration are performed by sequentially adding coagulants and flocculants using a dosing system to obtain multiple filtrates corresponding to a first pH threshold. Specifically, the process involves: adding coagulants using the dosing system and stirring at rate one and time one to obtain intermediate one; adding flocculants to intermediate one using the dosing system and stirring at rate one and time two to ensure uniform mixing of the flocculant and industrial wastewater to obtain intermediate two; stirring intermediate two at rate two and time three to generate flocculants, resulting in a mixed solution. After static filtration, the coagulated filtrate is obtained. The coagulants include polyferric sulfate, polyaluminum ferric sulfate, polyferric chloride, and polyaluminum chloride. One of the following; the rate one is greater than the rate two; the flocculant includes: cationic flocculant or anionic flocculant; the time one is 5 min; the time two is 2 min; the time three is 10 min; based on multiple first pH thresholds and the corresponding zeta potential values ​​of the filtrate, linear fitting is performed to calculate the optimal pH value of the filtrate when the zeta potential value is zero, specifically: ζi=aXi+b, where: ζi represents the zeta potential value of the filtrate after coagulation of the first pH threshold obtained after the i-th adjustment, a represents the slope, Xi represents the first pH threshold of the solution after the i-th adjustment, and b represents the intercept.

2. The pH-adjusted enhanced coagulation method for wastewater treatment according to claim 1, characterized in that: The range of the first pH threshold is consistent with the applicable range of the coagulant.

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