Industrial wastewater hardness removal method and system based on cooperative control of pH and medicament

Abstract

The invention is suitable for the technical field of industrial wastewater treatment, and provides an industrial wastewater hardness removal method and system based on pH and agent cooperative control, and the hardness removal method comprises the steps of water quality analysis and parameter setting, accurate pH value regulation and control, carbonate precipitation stage, flocculation stage and solid-liquid separation. The hardness removal system comprises an on-line water quality monitoring unit, a parallel reaction tank unit, a precise medicament adding unit and an intelligent control unit, according to the hardness removal method and system, a set of quantifiable and automatically executable process control logic is provided, and traditional empirical operation is converted into accurate engineering control based on a clear chemical reaction mechanism.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and more specifically, to a method and system for hardening industrial wastewater based on the synergistic control of pH and reagents. Background Technology

[0002] The treatment of high-hardness industrial wastewater (such as wastewater from photovoltaic, chemical, and power industries) is a global challenge. High concentrations of calcium and magnesium ions in the wastewater can easily lead to scaling in subsequent membrane treatment systems, reduced efficiency of heat exchange equipment, and pipe blockage. Therefore, effective softening pretreatment is essential.

[0003] Currently, the mainstream technologies for treating high-hardness wastewater are mainly divided into chemical precipitation and its improved methods, as well as alternative technologies such as ion exchange and membrane separation. However, each of them has its own limitations.

[0004] Traditional chemical precipitation methods (such as lime-soda ash method): calcium carbonate and magnesium hydroxide precipitates are formed by adding lime and soda ash. This method is widely used, but it has the following inherent defects: (1) The treatment efficiency is unstable. Organic matter and scale inhibitors in wastewater will complex with calcium and magnesium ions, which will seriously inhibit the precipitation reaction; (2) A large amount of chemical sludge with high water content is generated, and the disposal cost is high; (3) Magnesium hydroxide is a colloidal precipitate with poor settling performance, which can easily lead to "turbidity" in the effluent; (4) The pH control is rough. Usually, only "alkaline conditions" are required. There is a lack of precise control over the optimal reaction pH range, which affects the thoroughness of precipitation.

[0005] Improved approaches to chemical precipitation (such as "oxidation to break up complexes + optimized reagents") address complexation interference by adding advanced oxidation pretreatment or developing compound reagents. However, this approach increases process complexity and operating costs, and may introduce new sludge or secondary pollution problems, failing to fundamentally solve the synergy and interference issues between reagents within the chemical precipitation process.

[0006] Alternative softening technologies (such as ion exchange, nanofiltration, and electrochemical methods): These technologies produce better effluent quality, but generally suffer from high costs and limited applicability. For example, ion exchange resin regeneration consumes large amounts of salt and generates high-salinity wastewater; membrane methods are prone to fouling and have high investment and maintenance costs; electrochemical methods are energy-intensive. They are difficult to use alone to economically and efficiently treat complex industrial wastewater with high hardness, high suspended solids, and high organic matter content.

[0007] In practice, it has been found that when polyaluminum chloride is used as a flocculant to improve traditional chemical precipitation processes, two key issues can easily lead to system failure:

[0008] (1) Interference between reagents: Sodium carbonate is often added to improve the hardening effect. If the order or timing of PAC and sodium carbonate addition is inappropriate, carbonate ions will preferentially react with aluminum ions in PAC to form aluminum carbonate complexes that have no flocculation effect, resulting in complete deactivation of PAC and loss of flocculation ability of the system.

[0009] (2) Secondary pollution introduced by chemical dosing: Commercial PAC itself contains a certain amount of calcium and magnesium impurities. When the hardness of the influent is not extremely high, excessive addition of PAC based on experience will cause the hardness ions introduced by the PAC itself to offset the treatment effect, and may even lead to the hardness of the effluent being higher than that of the influent.

[0010] Therefore, existing technologies lack a systematic solution for deep hardening that can fundamentally prevent the aforementioned interfering factors and achieve efficient synergistic and precise quantitative control of reagents under strongly alkaline conditions. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the present invention aims to provide a high-hardness industrial wastewater deep hardening system and method that is stable in operation, consumes less reagents, has good sludge settling performance, and can completely avoid reagent interference and secondary pollution. The core of the present invention is to provide a set of quantifiable and automated process control logic, which transforms traditional experience-based operation into precise engineering control based on a clear chemical reaction mechanism.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] A method for hardening industrial wastewater based on the synergistic control of pH and reagents includes the following steps:

[0014] S1. Water quality analysis and parameter setting: Obtain the water quality parameters of the wastewater to be treated, including magnesium ion concentration, and set the target pH value, the upper limit of polyaluminum chloride (PAC) dosage, and the order of addition of each reagent and the minimum time interval between adjacent steps in the control system accordingly.

[0015] S2. Precise pH control: Wastewater is introduced into the reaction tank, alkaline agents are added to the reaction tank, and the pH value of the reaction system is rapidly increased and stably maintained in the range of 11.3 to 11.7 through stirring and real-time monitoring.

[0016] S3, Carbonate precipitation stage: After the pH value reaches and stabilizes within the target range, sodium carbonate solution is added to the reaction tank after a first preset delay, so that it reacts with calcium ions in the wastewater to generate calcium carbonate precipitate, which coexists with magnesium hydroxide precipitate that has already formed under alkaline conditions.

[0017] S4, Flocculation Stage: After confirming that the sodium carbonate solution has been added sufficiently, after a second preset delay, polyaluminum chloride (PAC) solution is added to the reaction tank. The concentration of PAC added shall not exceed 1.25 g / L of wastewater based on commercial solids.

[0018] S5. Solid-liquid separation: Add coagulant to the reaction tank to cause the formed flocs to coagulate into dense flocs. Then, the mixture is separated by sedimentation to obtain softened effluent.

[0019] The present invention is further configured such that, in step S2, the target pH value is preferably 11.5.

[0020] The present invention is further configured such that the first preset delay is 1 to 2 minutes to ensure that hydroxide ions and magnesium ions react fully to generate magnesium hydroxide crystal nuclei.

[0021] The present invention is further configured such that the second preset delay is at least 1 minute, so as to ensure that the residual carbonate ions in the water react fully with the calcium and magnesium ions, and avoid interference with the aluminum ions in the subsequently added PAC.

[0022] The present invention is further configured such that: in step S4, the dosage of PAC is dynamically adjusted according to the influent magnesium ion concentration of the wastewater to be treated, and the calculation formula is: PAC dosage (g / L) = min(k × [Mg²) + ], 1.25), where k is a coefficient, ranging from 0.01 to 0.015 L / mg, [Mg² + [This represents the magnesium ion concentration in the influent, in mg / L.]

[0023] The present invention is further configured such that: in step S3, when the concentration of calcium ions in the wastewater to be treated is lower than a set threshold, carbon dioxide gas is introduced into the reaction system, and calcium carbonate precipitate is generated by the bicarbonate ions formed in the water under the condition of pH 9-10, which replaces or partially replaces the addition of sodium carbonate solution.

[0024] The present invention is further configured such that steps S1 to S5 are carried out intermittently or continuously in one or more parallel reaction tanks, and the influent flow rate is dynamically allocated in real time by an intelligent control unit according to the effluent water quality of each reaction tank.

[0025] To achieve the above objectives, this invention provides a method for deep hardness removal of high-hardness industrial wastewater based on the synergistic control of pH and reagents, the core of which lies in the following three synergistic control elements:

[0026] 1. Narrow pH window control: The pH of the reaction system is precisely stabilized within a narrow range of 11.3 to 11.7, with an optimal value of 11.5. This pH range is the optimal range for both the formation of optimal crystal nuclei for magnesium hydroxide precipitation and the optimal flocculation efficiency of PAC.

[0027] 2. Forced Sequential Addition: The irreversible addition sequence of "alkali (e.g., NaOH) → sodium carbonate (Na2CO3) → polyaluminum chloride (PAC) → polyacrylamide (PAM)" must be strictly followed. A minimum time interval is set between adjacent steps to ensure sufficient reaction, ensuring that the next reagent is introduced only after the previous stage reaction is basically completed.

[0028] 3. Hard upper limit and dynamic control of PAC dosage: The PAC dosage is dynamically calculated and controlled based on the influent hardness (especially magnesium ion concentration), and its absolute upper limit based on the solid content of commercial PAC must not exceed 1.25 g / L. This fundamentally eliminates the risk of secondary pollution caused by the introduction of external hardness impurities due to excessive PAC dosage.

[0029] Specifically, the method includes the following steps:

[0030] S1. Water Quality Analysis and Parameter Setting: Analyze the hardness of the influent, especially the magnesium ion concentration. Set the target pH value (e.g., 11.5), the maximum PAC dosage (≤1.25 g / L), and the delay parameters between the dosing sequences of each reagent in the control system.

[0031] S2, Precise pH Enhancement: When wastewater enters the reaction tank, the intelligent control unit automatically adds alkaline solution (such as NaOH) through PID regulation based on real-time feedback from a high-precision pH sensor, and with strong stirring, the pH value in the reaction tank is rapidly increased and stabilized within the target range (such as 11.5±0.2).

[0032] S3, Carbonate Precipitation Stage: After the pH stabilizes, delay for 1-2 minutes (first preset delay) before starting the sodium carbonate dosing system. This delay ensures that the OH- - With Mg 2+ The reaction proceeds completely to form Mg(OH)₂ crystal nuclei. Subsequently, sodium carbonate is added, reacting with the remaining Ca... 2+ The reaction produces CaCO3 precipitate. This stage continues until the online hardness meter shows a flattening hardness decrease curve. In a preferred embodiment, when the influent calcium ion concentration is low, carbon dioxide gas can be introduced into the water, utilizing the generated bicarbonate ions to form calcium carbonate under pH 9-10 conditions, thereby replacing or reducing the addition of sodium carbonate.

[0033] S4, PAC flocculation stage: After confirming sufficient sodium carbonate addition (which can be judged by setting a fixed time or the rate of hardness decrease), delay for at least 1 minute (second preset delay) before starting the PAC dosing system. The control system calculates the PAC dosage (g / L) based on the influent magnesium ion concentration using the formula: PAC dosage (g / L) = min(k * [Mg 2+ The dosage is calculated and controlled in real time using a coefficient (1.25 L / mg, preferably 0.01-0.015 L / mg). This strict timing control absolutely avoids Al in PAC. 3+ With residual CO3 in the water 2- It becomes inactive upon contact.

[0034] S5. PAM Coagulation and Sedimentation: After the PAC is thoroughly mixed (approximately 30 seconds), anionic PAM is added, causing the fine hydroxide and carbonate precipitates to coagulate with the flocs formed by the PAC into large, dense flocs. The mixture then enters a high-efficiency solid-liquid separation unit (such as a high-density sedimentation tank) for rapid sedimentation and separation.

[0035] A hard removal system for implementing a hard removal method includes:

[0036] The online water quality monitoring unit is used to monitor the hardness, pH value, and flow rate of the influent and effluent in real time.

[0037] The parallel reaction tank unit includes at least two independent reaction tanks, each equipped with a stirring device and a high-precision pH sensor; this enables continuous or alternating operation of the process and enhances the system's resistance to shock loads.

[0038] The precise dosing unit includes independent storage tanks for storing alkaline reagents, sodium carbonate solution, PAC solution, and coagulant, as well as metering pumps connected to the corresponding reaction tanks via pipelines. It consists of four independent storage tanks, metering pumps, and dosing points, corresponding to alkaline solution, sodium carbonate, PAC, and PAM, respectively. Each dosing pipeline is independently programmed and controlled by the control system to ensure precise quantitative and sequential dosing.

[0039] The intelligent control unit is connected to the sensors in the online water quality monitoring unit, the parallel reaction tank unit, and the metering pump in the precise dosing unit. The intelligent control unit is configured as follows:

[0040] (a) The dosage of the alkaline agent is controlled according to the set target pH value and the feedback signal from the high-precision pH sensor;

[0041] (b) The metering pumps of the corresponding reagents are started and stopped sequentially according to the preset irreversible addition sequence of "alkaline reagent → sodium carbonate solution → PAC solution → coagulant" and the minimum time interval between adjacent steps.

[0042] (c) Based on the magnesium ion concentration in the influent measured by the online water quality monitoring unit, calculate and control the dosage of PAC solution according to the formula in claim 5 to ensure that it does not exceed the upper limit value;

[0043] The intelligent control unit is used to receive real-time signals from online water quality instruments (hardness, pH, flow rate), and has a built-in control algorithm. Based on the set pH value and real-time feedback, it adjusts the amount of alkaline solution added using PID; (2) it forces the start and stop of each reagent metering pump according to the preset sequence and time interval; (3) it calculates and controls the amount of PAC added in real time according to the above formula based on the online reading of magnesium ion concentration in the influent, ensuring that it does not exceed the upper limit; (4) optionally, it dynamically optimizes the allocation of influent flow rate based on the effluent quality of the parallel reaction tank.

[0044] A high-efficiency solid-liquid separation unit is used to receive and process the mixed liquid from the parallel reaction tank unit to achieve rapid sedimentation of flocs and sludge thickening; a high-density sedimentation tank or similar device with inclined tube / inclined plate packing is used to achieve rapid sedimentation of flocs and sludge thickening to ensure clear effluent.

[0045] When the parallel reaction tank unit has multiple reaction tanks, the wastewater flow rate entering each reaction tank is dynamically optimized and allocated based on the effluent hardness data of each reaction tank.

[0046] The high-efficiency solid-liquid separation unit is a high-density sedimentation tank with inclined tubes or inclined plate packing.

[0047] The advantages of this invention are (beneficial effects). Attached Figure Description

[0048] Figure 1 This is a flowchart of the steps in the industrial wastewater hardening method of the present invention.

[0049] Figure 2 This is a block diagram of the industrial wastewater hardening system of the present invention.

[0050] Figure 3 This is a block diagram illustrating the control principle of the intelligent control unit of the present invention. Detailed Implementation

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0052] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0053] In this invention, unless otherwise stated, the directional terms such as "up" and "down" generally refer to the directions shown in the accompanying drawings, or to the vertical, perpendicular, or gravitational direction; similarly, for ease of understanding and description, "left" and "right" generally refer to the left and right shown in the accompanying drawings; "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0054] Example: Hardness removal project for high-hardness wastewater of a photovoltaic enterprise

[0055] Raw water quality and existing problems:

[0056] Raw water quality: Total hardness 780-820 mg / L (calculated as CaCO3), of which magnesium ions (Mg) 2+ 75-85 mg / L, calcium ions (Ca 2+ Approximately 170 mg / L.

[0057] Existing process: The traditional "three-alkali method" (lime + soda ash + PAC) was used, resulting in large fluctuations in effluent hardness (150-300 mg / L), which often exceeded the standard. In addition, the sludge produced was loose, and there was sludge leakage in the sedimentation tank.

[0058] Modifications based on this invention:

[0059] Equipment upgrade: A high-precision online pH meter and online hardness meter were installed in the existing reaction tank. Independent storage tanks for sodium carbonate, PAC, and PAM, as well as precision metering pumps, were added, and a new PLC control cabinet was installed to integrate all control logic.

[0060] Parameter settings: In the PLC control system, set the core parameters as follows: target reaction pH = 11.5; set the upper limit of PAC addition to 1.20 g / L (with a safety margin of 1.25 g / L); set the addition sequence delay as follows: after alkali addition → delay for 2 minutes → add sodium carbonate → wait for hardness to decrease and stabilize (approximately 5-7 minutes) → delay for 1 minute → add PAC → delay for 30 seconds → add PAM. The coefficient k is set to 0.012 L / mg.

[0061] Execution result:

[0062] The system operated continuously and stably for 30 days, with the total hardness of the effluent remaining stable at 20-40 mg / L, and the calcium ion removal rate reaching 97.6% and the magnesium ion removal rate reaching 92.8%.

[0063] The average PAC consumption decreased significantly from 1.8 g / L before the modification to 1.05 g / L, demonstrating a clear drug-saving effect.

[0064] The resulting flocs are dense, and the sludge settling speed has increased from about 3 m / h to 8 m / h, extending the operating cycle of the subsequent filter press by about 50%.

[0065] Comparative verification experiment:

[0066] To verify the criticality of the dosing sequence, the control mode was manually switched to "simultaneous addition of alkali and sodium carbonate" during operation. Within 2 hours after the switch, the hardness of the effluent rose to over 200 mg / L, and the water quality became significantly turbid.

[0067] After restoring the strict sequence of "alkali first, then sodium carbonate" as specified in this invention, the system quickly returned to normal within 4 hours, and the hardness and clarity of the effluent returned to excellent levels. This experiment strongly demonstrates that the forced sequential addition is the key to the effectiveness and high efficiency of the technical solution of this invention.

[0068] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0069] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0070] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0072] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for hardening industrial wastewater based on the synergistic control of pH and reagents, characterized in that: Includes the following steps: S1. Water quality analysis and parameter setting: Obtain the water quality parameters of the wastewater to be treated, including magnesium ion concentration, and set the target pH value, the upper limit of polyaluminum chloride (PAC) dosage, and the order of addition of each reagent and the minimum time interval between adjacent steps in the control system accordingly. S2. Precise pH control: Wastewater is introduced into the reaction tank, alkaline agents are added to the reaction tank, and the pH value of the reaction system is rapidly increased and stably maintained in the range of 11.3 to 11.7 through stirring and real-time monitoring. S3, Carbonate precipitation stage: After the pH value reaches and stabilizes within the target range, sodium carbonate solution is added to the reaction tank after a first preset delay, so that it reacts with calcium ions in the wastewater to generate calcium carbonate precipitate, which coexists with magnesium hydroxide precipitate that has already formed under alkaline conditions. S4, Flocculation Stage: After confirming that the sodium carbonate solution has been added sufficiently, after a second preset delay, polyaluminum chloride (PAC) solution is added to the reaction tank. The concentration of PAC added shall not exceed 1.25 g / L of wastewater based on commercial solids. S5. Solid-liquid separation: Add coagulant to the reaction tank to cause the formed flocs to coagulate into dense flocs. Then, the mixture is separated by sedimentation to obtain softened effluent.

2. The industrial wastewater hardness removal method based on the synergistic control of pH and reagents according to claim 1, characterized in that: In step S2, the target pH value is preferably 11.

5.

3. The method for hardening industrial wastewater based on the synergistic control of pH and reagents according to claim 1, characterized in that: The first preset delay is 1 to 2 minutes to ensure that hydroxide ions and magnesium ions react fully to generate magnesium hydroxide crystal nuclei.

4. The industrial wastewater hardness removal method based on the synergistic control of pH and reagents according to claim 1, characterized in that: The second preset delay is at least 1 minute to ensure that the residual carbonate ions in the water react fully with the calcium and magnesium ions, and to avoid interference with the aluminum ions in the subsequently added PAC.

5. The industrial wastewater hardness removal method based on the synergistic control of pH and reagents according to claim 1, characterized in that: In step S4, the dosage of PAC is dynamically adjusted according to the influent magnesium ion concentration of the wastewater to be treated. The calculation formula is: PAC dosage (g / L) = min(k × [Mg²⁺], 1.25), where k is a coefficient with a value range of 0.01 to 0.015 L / mg, and [Mg²⁺] is the influent magnesium ion concentration in mg / L.

6. The industrial wastewater hardness removal method based on the synergistic control of pH and reagents according to claim 1, characterized in that: In step S3, when the calcium ion concentration in the wastewater to be treated is lower than a set threshold, carbon dioxide gas is introduced into the reaction system, and calcium carbonate precipitate is generated by the bicarbonate ions formed in the water under the condition of pH 9-10, which replaces or partially replaces the addition of sodium carbonate solution.

7. A method for hardening industrial wastewater based on the synergistic control of pH and reagents according to any one of claims 1 to 6, characterized in that: Steps S1 to S5 are performed intermittently or continuously in one or more parallel reaction tanks, and the influent flow rate is dynamically allocated in real time by an intelligent control unit according to the effluent quality of each reaction tank.

8. A hard removal system for implementing the hard removal method according to any one of claims 1 to 7, characterized in that, include: The online water quality monitoring unit is used to monitor the hardness, pH value, and flow rate of the influent and effluent in real time. The parallel reaction tank unit includes at least two independent reaction tanks, each of which is equipped with a stirring device and a high-precision pH sensor. The precise dosing unit includes separate storage tanks for storing alkaline reagents, sodium carbonate solution, PAC solution and coagulant, as well as metering pumps connected to the corresponding reaction tanks via pipelines. The intelligent control unit is connected to the sensors in the online water quality monitoring unit, the parallel reaction tank unit, and the metering pump in the precise dosing unit. The intelligent control unit is configured as follows: (a) The dosage of the alkaline agent is controlled according to the set target pH value and the feedback signal from the high-precision pH sensor; (b) The metering pumps of the corresponding reagents are started and stopped sequentially according to the preset irreversible addition sequence of "alkaline reagent → sodium carbonate solution → PAC solution → coagulant" and the minimum time interval between adjacent steps. (c) Based on the magnesium ion concentration in the influent measured by the online water quality monitoring unit, calculate and control the dosage of PAC solution according to the formula in claim 5 to ensure that it does not exceed the upper limit value; A high-efficiency solid-liquid separation unit is used to receive and process the mixed liquid from the parallel reaction tank unit, so as to achieve rapid sedimentation of flocs and sludge concentration.

9. The hardening system according to claim 8, characterized in that: When the parallel reaction tank unit has multiple reaction tanks, the wastewater flow rate entering each reaction tank is dynamically optimized and allocated based on the effluent hardness data of each reaction tank.

10. The hardening system according to claim 8, characterized in that: The high-efficiency solid-liquid separation unit is a high-density sedimentation tank with inclined tubes or inclined plate packing.

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