High-hardness wastewater softening method and application

Abstract

The invention relates to a high-hardness wastewater softening method and application, and the high-hardness wastewater softening method comprises the following steps: adding sodium hydroxide into high-hardness wastewater to obtain a high-hardness wastewater reaction system, introducing carbon dioxide into the high-hardness wastewater reaction system, and controlling the pH value of the reaction system to be reduced to 11.0-12.0, after the reaction is completed, a precipitation reaction is initiated and completed, softened water is obtained after solid-liquid separation, and the initial pH value of a high-hardness wastewater reaction system is larger than 12.0. According to the invention, through a synergistic softening process of strong base prefabrication-instantaneous carbonation triggering, the main body process of the softening reaction is compressed from the traditional hour level to the second level, so that the rapid reaction is realized; in addition, the cost can be obviously reduced, and the shape of settled sludge can be improved.

Description

Technical Field

[0001] This invention relates to the field of hard water softening technology, specifically to a method and application for softening high-hardness wastewater. This invention is particularly applicable to the softening treatment of circulating cooling water discharge, reverse osmosis concentrate, and high-hardness groundwater in industries such as power, chemical, and steel. Background Technology

[0002] High concentrations of calcium and magnesium ions in hard water are the root cause of a series of problems, including scaling in heat exchange equipment, membrane system fouling, and decreased washing efficiency. Softening is an indispensable part of modern industrial water treatment. The mainstream methods currently available are ion exchange and traditional chemical precipitation (double alkali method). While ion exchange is mature and reliable, it suffers from drawbacks such as the need for large amounts of acid-base brine for resin regeneration, the generation of high-salt wastewater, rapidly increasing operating costs with increasing hardness, and high equipment investment, making it unsuitable for treating ultra-high hardness or large-scale wastewater. Traditional chemical precipitation (double alkali method) generates CaCO3 and Mg(OH)2 precipitates by adding NaOH and Na2CO3, but it also has many problems, such as poor economic efficiency, high reagent costs, and the introduction of new impurities, including large amounts of Na+. + When sludge enters water bodies, it puts pressure on subsequent processes that require low sodium ion levels (such as special boilers and the electronics industry) or reverse osmosis systems; the sludge has poor properties, and the resulting precipitates often have imperfect crystal forms, small particle sizes, and poor settling and dewatering performance, resulting in a heavy burden of sludge disposal. Summary of the Invention

[0003] This invention provides a method and application for softening high-hardness wastewater, aiming to achieve deep softening, rapid reaction, cost reduction, and improved sludge properties.

[0004] In a first aspect, the present invention provides a method for softening high-hardness wastewater, comprising: Sodium hydroxide is added to high-hardness wastewater to obtain a high-hardness wastewater reaction system. Carbon dioxide is introduced into the high-hardness wastewater reaction system and the pH value of the reaction system is controlled to drop to between 11.0 and 12.0 to initiate and complete the precipitation reaction. After solid-liquid separation, softened water is obtained. The initial pH value of the high-hardness wastewater reaction system is greater than 12.0.

[0005] In one alternative implementation, the initial pH value is 12.0-13.0; And / or, the total hardness of the high-hardness wastewater is ≥500 mg / L.

[0006] In one optional embodiment, the aeration rate of carbon dioxide introduced into the high-hardness wastewater reaction system is 0.5-2.0 L / (min·L).

[0007] In one alternative implementation, the carbon dioxide is ventilated for 10-60 seconds.

[0008] In one optional embodiment, the carbon dioxide ventilation rate is 0.8-1.2 L / (min·L).

[0009] In one optional implementation, based on a total hardness of 1 g / L for high-hardness wastewater, 1.2-1.8 kg of sodium hydroxide is added per cubic meter of high-hardness wastewater.

[0010] The total hardness of the high-hardness wastewater is expressed as CaCO3. The formula for calculating the total hardness is: Total hardness (as CaCO3) = (Calcium content × 100.09 ÷ 40.08) + (Magnesium content × 100.09 ÷ 24.31) The units for calcium and magnesium content are mol / L.

[0011] In one optional embodiment, when the total hardness of the high-hardness wastewater is 500-1000 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.3-1.5 kg / m³. 3 The carbon dioxide was introduced for 10-20 seconds. When the total hardness of the high-hardness wastewater is >1000 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.5-1.7 kg / m³. 3 The carbon dioxide is introduced for 10-50 seconds.

[0012] In one optional embodiment, when the total hardness of the high-hardness wastewater is 1000-1200 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.5 kg / m³. 3 The carbon dioxide is introduced for 10-50 seconds.

[0013] In one optional embodiment, when the total hardness of the high-hardness wastewater is 800-900 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.3 kg / m³. 3 The carbon dioxide was introduced for 10-20 seconds.

[0014] Secondly, the present invention also provides an application of the above-described method in the softening of high-hardness wastewater, wherein the high-hardness wastewater includes industrial circulating cooling water, boiler feedwater, or municipal water.

[0015] The technical solution of this invention has the following advantages: 1. The present invention provides a method for softening high-hardness wastewater, comprising: adding sodium hydroxide to high-hardness wastewater to obtain a high-hardness wastewater reaction system; introducing carbon dioxide into the high-hardness wastewater reaction system and controlling the pH value of the reaction system to drop to between 11.0 and 12.0 to initiate and complete a precipitation reaction; and after solid-liquid separation, obtaining softened water, wherein the initial pH value of the high-hardness wastewater reaction system is greater than 12.0.

[0016] This invention utilizes a synergistic softening process of "strong alkali pretreatment - instantaneous carbonation triggering" to compress the main softening reaction process from the traditional "hours" to "seconds", achieving rapid reaction; it also has outstanding softening ability, and can significantly reduce costs and improve the shape of settled sludge. Attached Figure Description

[0017] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the process flow of an embodiment of the present invention; Figure 2 This is the curve showing the relationship between the residual hardness of the effluent and pH under different carbon dioxide aeration times in Embodiment 1 of the present invention. Figure 3 This is the curve showing the relationship between the residual hardness of the effluent and pH under different carbon dioxide aeration times in Embodiment 2 of the present invention. Figure 4 This is a curve showing the relationship between the residual hardness and pH of the effluent under different carbon dioxide aeration times in Comparative Example 1 of this invention. Detailed Implementation

[0019] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0020] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0021] This invention employs a synergistic softening process of "strong alkali pretreatment - instantaneous carbonation triggering". The characteristic of this method is that it is not a simple step-by-step dosing, but rather it "triggers" the high-energy reaction environment created by the first step (alkalization) by precisely controlling the time and intensity of the second step (carbonation).

[0022] This invention provides a method for softening high-hardness wastewater, comprising the following sequential and closely connected steps: S1: Alkalization A high-hardness wastewater reaction system is obtained by adding solid sodium hydroxide or a high-concentration solution to the hard water to be treated, under vigorous stirring (stirring intensity G > 300 s). -1 This process involves completely dissolving and thoroughly mixing the wastewater. The endpoint control indicator for this step is to rapidly and stably raise the pH value of the high-hardness wastewater reaction system to 12.0-13.0.

[0023] Chemical effects: Mg 2+ + 2OH - → Mg(OH)2(s) (Initial formation of microcrystalline nuclei) S2: Carbonation Within 1 minute of alkalization, high-purity carbon dioxide gas should be immediately introduced into the water. The control parameters for this step are particularly important. Ventilation rate (V): 0.5-2.0L CO2 / (minutes per liter), the optimal range is 0.5-1.2L. CO2 / (minutes per liter). This rate ensures that a unit volume of water can acquire enough carbon dioxide molecules per unit time to form a dense cluster of bubbles, providing a huge gas-liquid mass transfer area.

[0024] Aeration time (t): 10-60s, with 20-40s being optimal for water with a total hardness of 800-1200mg / L.

[0025] Chemical effects: HCO3 - + OH - → CO3 2- + H2O CO3 2- +Ca 2+ →CaCO3(s) HCO3 - With large amounts of OH in the water - and remaining CO3 2- A new carbonic acid equilibrium system is rapidly established. This process is not a gradual decrease in pH, but rather triggers drastic fluctuations in pH and dramatic changes in ion concentration in local micro-regions. This "disturbance" completely disrupts the metastable state of CaCO3.

[0026] Synergistic precipitation triggering: The aforementioned perturbation provides a large number of nucleation sites for CaCO3 crystallization, and the Mg(OH)2 microcrystal nuclei pre-formed in step S1 become the optimal heterogeneous nucleation substrate. CaCO3 preferentially grows rapidly on these substrates, forming a dense flocculent interwoven with Mg(OH)2. This process is completed within seconds, accompanied by a rapid and stable drop in pH from above 12 to the ideal range of 11.0-12.0.

[0027] S3: Solid-liquid separation After the reaction is complete, a large number of coarse and dense precipitates are formed in the water body. Solid-liquid separation is then carried out to obtain softened water.

[0028] Example 1 This embodiment provides a method for softening groundwater with high hardness and high calcium ion ratio, the process flow of which is as follows: Figure 1 As shown, it includes: Take the total hardness as 1100 mg / L (Ca 2+ 400 mg / L, Mg 2+ 1L of raw water sample (40 mg / L, pH=7.8).

[0029] Add 1.5g of sodium hydroxide (NaOH) and stir until completely dissolved. At this point, the pH of the water is >12.

[0030] Introduce 99.9% CO2 gas into the water at a flow rate of 1 L / min and continue aeration for 20 seconds.

[0031] After the reaction is complete, the water sample is filtered to achieve solid-liquid separation.

[0032] The total hardness and calcium ion concentration of the filtrate were determined by EDTA titration.

[0033] Results: After treatment, the total hardness of the water sample decreased to 24 mg / L, the calcium ion concentration decreased to 9.6 mg / L, the magnesium ion concentration was undetectable, and the hardness removal rate reached 97.82%.

[0034] Figure 2 This is a curve showing the relationship between the residual hardness of the effluent and pH under different carbon dioxide aeration times in this embodiment.

[0035] Example 2 This embodiment provides a method for softening concentrated water from reverse osmosis treatment with medium hardness, including: The total hardness is taken as 830 mg / L (Ca 2+ 160.32 mg / L, Mg 2+1 L of reverse osmosis concentrate sample (167.68 mg / L, pH=7.8).

[0036] Add 1.0g of sodium hydroxide (NaOH) and stir until completely dissolved. At this point, the pH of the water is >12.

[0037] Introduce 99.9% CO2 gas into the water at a flow rate of 1 L / min and continue aeration for 10 seconds.

[0038] After the reaction is complete, the water sample is filtered to achieve solid-liquid separation.

[0039] The total hardness and calcium ion concentration of the filtrate were determined by EDTA titration.

[0040] Results: After treatment, the total hardness of the water sample decreased to 130 mg / L, the calcium ion concentration decreased to 40 mg / L, the magnesium ion concentration decreased to 12 mg / L, and the hardness removal rate reached 84.15%.

[0041] Figure 3 This is a curve showing the relationship between the residual hardness of the effluent and pH under different carbon dioxide aeration times in this embodiment.

[0042] Example 3 This embodiment provides a method for softening groundwater with high hardness and high magnesium ion content, including: Take the total hardness as 1250 mg / L (Ca 2+ 200 mg / L, Mg 2+ 1L of raw water sample (255 mg / L, pH=7.5).

[0043] Add 2.0g of sodium hydroxide (NaOH) and stir until completely dissolved. At this point, the pH of the water is 12.7.

[0044] Introduce 99.9% CO2 gas into the water at a flow rate of 1 L / min and continue aeration for 30 seconds.

[0045] After the reaction is complete, the water sample is filtered to achieve solid-liquid separation.

[0046] The total hardness and calcium ion concentration of the filtrate were determined by EDTA titration.

[0047] Results: After treatment, the total hardness of the water sample decreased to 45 mg / L, the calcium ion concentration decreased to 15 mg / L, and the magnesium ion concentration decreased to 4.8 mg / L. The hardness removal rate reached 96.4%, and the magnesium hardness removal rate reached 98.1%.

[0048] Example 4 This embodiment provides a method for softening circulating water and wastewater in a steel plant, including: Take 1L of raw water sample with a total hardness of 950 mg / L (pH=8.8) and a trace amount of scale inhibitor (HEDP, approximately 3mg / L).

[0049] Add 1.7g of sodium hydroxide (NaOH) and stir until completely dissolved. At this point, the pH of the water is 12.6.

[0050] 99.9% CO2 gas was introduced into the water at a flow rate of 1 L / min and aerated continuously for 25 seconds.

[0051] After the reaction is complete, the water sample is filtered to achieve solid-liquid separation.

[0052] The total hardness and calcium ion concentration of the filtrate were determined by EDTA titration.

[0053] Results: The total hardness of the treated water sample decreased to 110 mg / L, and the hardness removal rate reached 88.4%, indicating that the present invention has a certain tolerance to common low-concentration organophosphorus scale inhibitors and has wider applicability.

[0054] Comparative Example 1 This comparative example provides a method for softening concentrated water from reverse osmosis treatment with medium hardness, including: The total hardness is taken as 830 mg / L (Ca 2+ 160.32 mg / L, Mg 2+ 1 L of reverse osmosis concentrate sample (167.68 mg / L, pH=7.8).

[0055] Add 1.0g of calcium hydroxide and stir.

[0056] 99.9% CO2 gas was introduced into the water at a flow rate of 1 L / min and aerated for 60 seconds (because Ca(OH)2 dissolves slowly and has low reaction efficiency, the aeration time was extended to ensure a full reaction).

[0057] After the reaction is complete, the water sample is filtered to achieve solid-liquid separation.

[0058] The total hardness and calcium ion concentration of the filtrate were determined by EDTA titration.

[0059] Results: The total hardness of the water sample decreased to 680 mg / L after treatment, and the hardness removal rate reached 17.07%.

[0060] Figure 4 This is a curve showing the relationship between the residual hardness and pH of the effluent under different carbon dioxide aeration times in this comparative example.

[0061] This comparative example significantly highlights the unexpectedly high efficiency of the NaOH technology solution employed in this invention.

[0062] Comparative Example 2 This comparative example provides a method for softening groundwater with high hardness and high calcium ion content, including: Take the total hardness as 1100 mg / L (Ca 2+ 400 mg / L, Mg 2+ 1L of raw water sample (40 mg / L, pH=7.8).

[0063] Add 1.5g of sodium hydroxide (NaOH) and stir until completely dissolved. At this point, the pH of the water is >12.

[0064] 99.9% CO2 gas was introduced into the water at a flow rate of 1 L / min and aerated continuously for 120 seconds.

[0065] After the reaction is complete, the water sample is filtered to achieve solid-liquid separation.

[0066] The total hardness and calcium ion concentration of the filtrate were determined by EDTA titration.

[0067] Results: The total hardness of the water sample decreased to 224 mg / L after treatment, and the hardness removal rate reached 79.64%.

[0068] Experimental Example 1 Long-term operational stability test: Simulate the conditions of Example 1 and run continuously for 50 batches.

[0069] Operation: Using automated equipment, 50 batches of water with the same quality as in Example 1 were continuously prepared, each batch being 1L, and processed strictly according to the parameters of this invention (1.5g NaOH, 1.0 L / min CO2, 20 seconds).

[0070] Results: The average total hardness of the effluent from 50 batches was 26.5 mg / L, with a standard deviation of ±3.2 mg / L; the average pH of the effluent was 8.3, with a standard deviation of ±0.2. This demonstrates that the process of this invention has excellent repeatability and operational stability, meeting the requirements for continuous industrial operation.

[0071] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for softening high-hardness wastewater, characterized in that, include: Sodium hydroxide is added to high-hardness wastewater to obtain a high-hardness wastewater reaction system. Carbon dioxide is introduced into the high-hardness wastewater reaction system and the pH value of the reaction system is controlled to drop to between 11.0 and 12.0 to initiate and complete the precipitation reaction. After solid-liquid separation, softened water is obtained. The initial pH value of the high-hardness wastewater reaction system is greater than 12.

0.

2. The method according to claim 1, characterized in that, The initial pH value is 12.0-13.0; And / or, the total hardness of the high-hardness wastewater is ≥500 mg / L.

3. The method according to claim 1 or 2, characterized in that, The aeration rate of carbon dioxide introduced into the high-hardness wastewater reaction system is 0.5-2.0 L / (min·L).

4. The method according to claim 3, characterized in that, The carbon dioxide is ventilated for 10-60 seconds.

5. The method according to claim 3, characterized in that, The carbon dioxide ventilation rate is 0.8-1.2 L / (min·L).

6. The method according to claim 1, characterized in that, For high-hardness wastewater with a total hardness of 1 g / L, add 1.2-1.8 kg of sodium hydroxide per cubic meter of high-hardness wastewater.

7. The method according to claim 6, characterized in that, When the total hardness of the high-hardness wastewater is 500-1000 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.3-1.5 kg / m³. 3 The carbon dioxide was introduced for 10-20 seconds. When the total hardness of the high-hardness wastewater is >1000 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.5-1.7 kg / m³. 3 The carbon dioxide is introduced for 10-50 seconds.

8. The method according to claim 7, characterized in that, When the total hardness of the high-hardness wastewater is 1000-1200 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.5 kg / m³. 3 The carbon dioxide is introduced for 10-50 seconds.

9. The method according to claim 7, characterized in that, When the total hardness of the high-hardness wastewater is 800-900 mg / L, the dosage of sodium hydroxide in the high-hardness wastewater is 1.3 kg / m³. 3 The carbon dioxide was introduced for 10-20 seconds.

10. The application of the method according to any one of claims 1-9 in the softening of high-hardness wastewater, wherein the high-hardness wastewater includes industrial circulating cooling water, boiler feedwater or municipal water.

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