High-hardness wastewater chemical membrane coupling softening method and treatment device

Abstract

The invention provides a high-hardness wastewater chemical membrane coupling softening method which comprises the following steps: firstly, carrying out chemical pretreatment on high-hardness wastewater to obtain softened wastewater, and carrying out flocculent precipitation on the softened wastewater to remove suspended solids and residual hardness ions in the softened wastewater to obtain flocculent precipitation wastewater; the method comprises the following steps: flocculating and precipitating wastewater, filtering the flocculated and precipitated wastewater to obtain filtered wastewater, carrying out membrane separation on the filtered wastewater to obtain separated wastewater, and carrying out evaporative crystallization on the separated wastewater to crystallize salt in the separated wastewater so as to soften the high-hardness wastewater. According to the method, through coupled use of chemical pretreatment and a membrane technology, the softening efficiency is improved, the use of chemical agents is reduced, and the treatment cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular to a chemical membrane coupling softening method and a treatment device for high-hardness wastewater. Background Art

[0002] With the continuous advancement of science and technology and the growing demand for industrial water treatment, the softening treatment of high-hardness wastewater has become a technical problem in the field of industrial water treatment. Hardness ions, mainly calcium ions and magnesium ions, dissolve in water and form insoluble salts, which bring many challenges to industrial production and environmental protection. Traditional chemical softening methods, such as the use of agents such as slaked lime or sodium carbonate, form insoluble precipitates such as magnesium hydroxide and calcium carbonate through chemical reactions, thereby reducing the hardness of wastewater. However, this traditional method has a series of problems.

[0003] The consumption of reagents is huge. In order to effectively remove the hardness ions in wastewater, traditional methods often need to add a large amount of chemical reagents, such as slaked lime or sodium carbonate; this not only increases the treatment cost, but may also cause environmental pollution and waste of resources due to excessive use of reagents. Since chemical reactions require a certain amount of time and conditions, and are affected by multiple factors such as wastewater composition, temperature, pH value, etc., traditional chemical softening methods are often difficult to achieve ideal treatment efficiency when treating high-hardness wastewater, resulting in high effluent hardness. In addition, the generation of a large amount of sludge is also a significant disadvantage of traditional chemical softening methods. A large amount of sludge is generated during the chemical precipitation process. This sludge is not only difficult to handle, but may also cause secondary pollution to the environment. At the same time, the disposal of sludge also increases additional treatment costs. The discharge of chemical reagents and the disposal of sludge may have a negative impact on the ecological environment, such as water pollution and soil pollution.

[0004] As a means of industrial water treatment, membrane technology utilizes the differences in permeability of different components in a mixture through membranes and achieves separation through screening or differences in chemical properties. In terms of removing hardness ions, membrane technology has the advantages of high efficiency, stability, and easy automation control. However, membrane technology also faces some difficult-to-overcome challenges when used alone.

[0005] Among them, membrane fouling is one of the key factors affecting the efficiency and cost of membrane technology treatment. Since impurities such as suspended solids, organic matter, and colloids in wastewater are easily deposited and adsorbed on the membrane surface, the membrane flux decreases, the treatment efficiency decreases, and even frequent cleaning or replacement of membrane components is required. This not only increases the treatment cost, but may also affect the stability and reliability of membrane technology.

[0006] In summary, both traditional chemical softening methods and membrane technology have a series of problems when used alone, which limit their application effects in the field of industrial water treatment.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] The first purpose of the present invention is to provide a method for chemical membrane coupled softening of high-hardness wastewater. This method combines chemical pretreatment with membrane technology to improve the softening efficiency of wastewater, while reducing the use of chemical agents and effectively reducing the overall wastewater treatment cost.

[0009] The second object of the present invention is to provide a high-hardness wastewater chemical membrane coupled softening treatment device used in the above-mentioned high-hardness wastewater chemical membrane coupled softening method, which has a high degree of integration and occupies a small area.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted: A method for chemical membrane coupling softening of high-hardness wastewater comprises the following steps: First, the high-hardness wastewater is chemically pretreated to obtain softened wastewater, and the softened wastewater is flocculated and precipitated to remove suspended solids and remaining hardness ions in the softened wastewater to obtain flocculated and precipitated wastewater. The flocculated and precipitated wastewater is then filtered to obtain filtered wastewater, and the filtered wastewater is then subjected to membrane separation technology to obtain separated wastewater. The separated wastewater is evaporated and crystallized to crystallize the salt in the separated wastewater to achieve softening of the high-hardness wastewater.

[0011] Preferably, the method for chemically pretreating high-hardness wastewater is to add at least one of limestone and sodium carbonate to the high-hardness wastewater.

[0012] Preferably, a flocculant is used in the flocculation and precipitation step, and the flocculant is at least one of polyaluminium chloride and ferrous sulfate.

[0013] Preferably, in the flocculation sedimentation step, sludge is produced by precipitation, and the sludge is subjected to plate and frame filter pressing to obtain a mud cake.

[0014] Preferably, in the step of filtering the flocculated wastewater, multi-media filtration is first performed to remove suspended matter and unprecipitated hardness ions in the flocculated wastewater.

[0015] Preferably, the membrane separation technology uses a nanofiltration membrane to effectively intercept divalent and higher ions and remove organic pollutants.

[0016] Preferably, in the evaporation and crystallization step, the filtered wastewater is evaporated at high temperature to crystallize the salt in the filtered wastewater.

[0017] Preferably, the salt crystals produced in the evaporation crystallization step are mixed salt crystals, and the mixed salt crystals are classified to separate pure elemental salts.

[0018] Through the combined use of chemical pretreatment, flocculation precipitation, filtration and membrane separation technology, the method can efficiently remove hardness ions (such as calcium, magnesium, etc.) in wastewater and soften the wastewater. This helps to reduce the corrosion of wastewater to pipelines and equipment, and at the same time improve the reuse value of wastewater. In the flocculation precipitation step, by adding flocculants, suspended solids and remaining hardness ions in wastewater can be effectively removed, further improving the water quality. The filtration step can remove finer suspended matter and unprecipitated hardness ions, ensuring the smooth progress of subsequent membrane separation and evaporation crystallization steps. Through the evaporation crystallization step, the salt in the wastewater can be crystallized and precipitated, avoiding the pollution of the environment by salt. At the same time, the mixed salt crystals are classified to separate pure elemental salts, which is also helpful for the recovery and reuse of resources. The method of the present invention combines a variety of treatment technologies, reduces the treatment cost by optimizing the treatment process, and reduces the treatment and disposal costs of sludge by plate and frame filter pressing. The use of nanofiltration membranes for membrane separation can effectively intercept divalent and higher ions and remove organic pollutants, reducing the load of subsequent treatment steps. Through evaporation, crystallization and salt classification treatment, resource recovery and reuse can be achieved, which reduces treatment costs and contributes to environmental protection and sustainable development. Compared with single chemical softening or membrane treatment, this composite method has higher treatment efficiency and lower energy consumption, reduces the use of chemicals and reduces treatment costs, and achieves softening and resource utilization of high-hardness wastewater. Chemical pretreatment, flocculation sedimentation, filtration and membrane separation technologies each have unique treatment effects. Their combined use can exert their synergistic effects and improve overall treatment efficiency. According to the specific water quality and treatment requirements of the wastewater, the parameters and operating conditions of each treatment step can be flexibly adjusted to meet different treatment needs.

[0019] The present invention also provides a treatment device for high-hardness wastewater chemical membrane coupling softening method, comprising: A softening tank, a flocculation sedimentation tank, a multi-media filter, a nanofiltration component and an evaporation crystallization component are sequentially arranged along the direction of high-hardness wastewater inflow; The softening tank is a place for chemical pretreatment of high-hardness wastewater, which can significantly reduce the total hardness of high-hardness wastewater; The flocculation sedimentation tank is connected to the softening tank to perform flocculation sedimentation on the softened wastewater to remove suspended solids and hardness ions in the softened wastewater; The multi-media filter is connected to the flocculation sedimentation tank to remove suspended matter and unprecipitated hardness ions in the water; The nanofiltration component is connected to the multi-media filter to achieve deep softening of the filtered wastewater and remove organic pollutants; The nanofiltration component is connected to the evaporation crystallization component and is used for concentrating the separated wastewater to achieve crystallization of salt and recovery of valuable minerals.

[0020] Preferably, a salt separation component is connected behind the evaporation crystallization component, and the salt separation component separates pure elemental salt according to the difference in melting point and solubility of different salt crystals.

[0021] The treatment device forms a continuous and efficient treatment process by sequentially arranging softening tanks, flocculation sedimentation tanks, multi-media filters, nanofiltration components and evaporation crystallization components along the inflow direction of high-hardness wastewater. Each treatment unit treats specific pollutants, ensuring the improvement of overall treatment efficiency. The design of the treatment device is simple and clear, and the connections between the various treatment units are tight and smooth. This makes the operation process simple and easy, and also reduces maintenance costs. In addition, due to the use of advanced membrane technology and evaporation crystallization technology, the energy consumption and waste emissions generated by the device during the treatment process are also relatively low.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) By adding limestone and / or sodium carbonate through chemical pretreatment, the present invention can significantly reduce the total hardness of high-hardness wastewater, laying a good foundation for subsequent treatment. The flocculation and precipitation step uses polyaluminum chloride and / or ferrous sulfate high-efficiency flocculants to effectively remove suspended solids and residual hardness ions and improve water transparency. The continuous use of multi-media filters and nanofiltration components further removes suspended matter, unprecipitated hardness ions and organic pollutants to achieve deep purification of wastewater. The evaporation and crystallization component evaporates the treated wastewater at high temperature to crystallize the salt, which not only achieves the concentration treatment of wastewater, but also promotes the recovery of valuable minerals. The introduction of the salt separation component utilizes the differences in melting points and solubility of different salt crystals to successfully separate pure elemental salts, thereby improving the efficiency and purity of resource recovery. The entire process reduces wastewater discharge and reduces pollution to the environment.

[0023] (2) The treatment devices provided by the present invention are arranged in sequence along the inflow direction of high-hardness wastewater, with a compact process and simple operation, which reduces energy consumption and labor costs in the treatment process. By optimizing the parameters and process conditions of each treatment step, the overall treatment efficiency is improved, and the treatment time and cost are reduced. In particular, the plate and frame filter press treatment step of sludge effectively reduces the volume and water content of the sludge, and reduces the cost of sludge treatment and disposal. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] By describing the embodiments of the present application in more detail in conjunction with the accompanying drawings, the above and other purposes, features and advantages of the present application will become more apparent. The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the accompanying drawings, the same reference numerals generally represent the same components or steps. Figure 1 A schematic diagram of the overall process of a chemical membrane coupled softening method for high-hardness wastewater provided in this application. DETAILED DESCRIPTION

[0025] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be appreciated by those skilled in the art that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work, all belong to the scope of protection of the present invention. If specific conditions are not indicated in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0026] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with the implementation methods.

[0027] The present application provides a chemical membrane coupled softening method for high-hardness wastewater. Specifically, a receiving tank for high-hardness wastewater is connected in front of the softening tank of the present invention. The receiving tank is a facility with a large-capacity storage function and corrosion resistance, which is used to receive and temporarily store high-hardness wastewater. The receiving tank is equipped with an automatic water inlet valve, a flow control component and a homogenization component. The receiving tank is used to receive high-hardness wastewater from industrial emissions or other sources, and achieves preliminary homogenization of the wastewater through stirring. It can provide uniform, stable and reliable high-hardness wastewater for subsequent treatment steps, ensuring the continuity and reliability of the entire high-hardness wastewater treatment process.

[0028] The softening tank receives high-hardness wastewater sent from the receiving tank. The softening tank is equipped with a dosing component. By adding chemical agents, chemical reactions occur with the hardness ions in the water, namely calcium and magnesium ions, to generate insoluble calcium carbonate and magnesium hydroxide precipitates, thereby greatly reducing the total hardness of the high-hardness wastewater and alleviating the burden on subsequent treatment steps. At the same time, it can also reduce the use of chemical agents, reduce the treatment cost of high-hardness wastewater, and protect the environment.

[0029] The flocculation sedimentation tank is connected to the softening tank to receive the softened wastewater sent from the softening tank. The flocculation sedimentation tank is provided with a reagent dosing component having an agitator so that the added coagulant can be evenly mixed with the softened wastewater to form larger flocs that are easy to separate and accelerate the sedimentation process of suspended solids and hardness ions. An inclined plate is provided on the upper part of the flocculation sedimentation tank. The setting of the inclined plate enhances the sedimentation effect, improves the sedimentation efficiency, and provides favorable conditions for subsequent multi-media filtration and nanofiltration treatment.

[0030] Preferably, the flocculation sedimentation tank is also connected to a sludge treatment facility, which is a mechanical dehydration device that uses a plate and frame filter press to separate mud and water, squeeze out water from the sludge, and form a relatively dry solid waste, namely a mud cake.

[0031] The multi-media filter receives wastewater after flocculation and sedimentation. The multi-media filter is filled with filter materials of different particle sizes and densities. These materials can effectively intercept suspended matter and unprecipitated hardness ions in the water. Through multi-stage filtration, the wastewater after flocculation and sedimentation is further purified, the water quality is improved, and the stable operation of the subsequent nanofiltration components is ensured.

[0032] The nanofiltration component is connected to the multi-media filter to receive the filtered wastewater. The nanofiltration component is a nanofiltration membrane separation device, in which the nanofiltration membrane is a semi-permeable membrane with selective permeability that can effectively intercept divalent and higher ions, so that the filtered wastewater can be softened, thereby improving the overall water quality of the filtered wastewater and providing better wastewater for subsequent evaporation and crystallization steps.

[0033] The evaporation crystallization component is connected to the nanofiltration component to receive the separated wastewater. The evaporation crystallization component is a multi-effect evaporator. The separated wastewater is heated at high temperature so that the salt in the separated wastewater is crystallized to obtain mixed salt crystals.

[0034] Preferably, the evaporation crystallization component is also connected to the salt separation component, which has a heat treatment unit and a separation unit. The difference in melting point and solubility of different salts is used to classify the mixed salt crystals to obtain elemental salts, so that further purification and classification achieves maximum recycling of resources.

[0035] The practical application of the high hardness wastewater chemical membrane coupling softening method of the present invention is shown in Figure 1 As shown, a chemical plant produces a large amount of wastewater containing calcium, magnesium ions and organic pollutants. The treatment device of the present invention is used, which specifically includes the following process: First, the high-hardness wastewater produced daily is sent to the receiving pool, and the high-hardness wastewater in the receiving pool is transported to the softening pool through a pipeline. According to the water quality of the high-hardness wastewater, 300 grams of lime and 200 grams of sodium carbonate are added to each cubic meter of high-hardness wastewater. These chemical agents react with the calcium and magnesium ions in the high-hardness wastewater to generate insoluble calcium carbonate and magnesium hydroxide precipitation. Then the softened wastewater enters the flocculation sedimentation tank, and polyaluminum chloride is added as a flocculant in the flocculation sedimentation tank, wherein the addition amount is 50 grams per cubic meter of softened wastewater. Polyaluminum chloride reacts with the tiny particles and colloidal substances in the softened wastewater to form larger flocs and accelerate the sedimentation of the precipitate, which is easy to separate, and removes the suspended solids and the remaining hardness ions in the softened wastewater, making the wastewater clearer; further, the suspended solids are discharged into the sludge treatment facility for mud and water separation, and the water in the sludge is squeezed out to form a mud cake, and the remaining water will be sent back to the flocculation sedimentation tank. The wastewater after flocculation and precipitation is sent to a multi-media filter, which is filled with quartz sand, anthracite and manganese sand. These materials are arranged from large to small according to particle size and density, and can further remove suspended matter and unprecipitated hardness ions in the wastewater after flocculation and precipitation. Then the filtered wastewater is sent to the nanofiltration membrane separation equipment, in which the nanofiltration membrane can effectively intercept divalent and above ions. After being treated by the nanofiltration membrane, the high-hardness wastewater is deeply softened. At the same time, some organic pollutants and chromaticity can be removed to obtain clear water and wastewater after nanofiltration. The water quality of the clear water meets the production water standard and is directly reused in the production process of the chemical plant. The wastewater after nanofiltration is sent to the multi-effect evaporator, which evaporates at high temperature so that the salt in the wastewater after nanofiltration gradually crystallizes and precipitates; the clear liquid is reused in the production process of the chemical plant, and the mixed salt crystals obtained after evaporation and concentration are collected and sent to the salt separation component, which separates the mixed salt crystals into clean elemental salts.

[0036] It can be seen that the present invention has a high treatment efficiency by combining double alkali softening and hardness removal, nanofiltration membrane separation and evaporation crystallization, and can effectively realize the resource utilization and harmless treatment of high-hardness wastewater. It integrates the advantages of chemical softening, physical filtration and membrane separation technology, and can efficiently and economically treat high-hardness wastewater, especially suitable for wastewater treatment scenarios with high calcium and magnesium content. In addition, through the design of evaporation crystallization and salt separation, it can also recycle the minerals in high-hardness wastewater, thereby improving the overall value of wastewater treatment.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chemical membrane coupled softening method for high hardness wastewater, characterized in that: The steps include: First, the high-hardness wastewater is chemically pretreated to obtain softened wastewater, and the softened wastewater is flocculated and precipitated to remove suspended solids and remaining hardness ions in the softened wastewater to obtain flocculated and precipitated wastewater. The flocculated and precipitated wastewater is then filtered to obtain filtered wastewater, and the filtered wastewater is then subjected to membrane separation technology to obtain separated wastewater. The separated wastewater is evaporated and crystallized to crystallize the salt in the separated wastewater to achieve softening of the high-hardness wastewater.

2. The chemical film coupling softening method according to claim 1, characterized in that: The method for chemically pretreating high-hardness wastewater is to add at least one of limestone and sodium carbonate to the high-hardness wastewater.

3. The chemical film coupling softening method according to claim 1, characterized in that: A flocculant is used in the flocculation and precipitation step, and the flocculant is at least one of polyaluminium chloride and ferrous sulfate.

4. The chemical film coupling softening method according to claim 3, characterized in that: In the flocculation and sedimentation step, sludge is produced by precipitation, and the sludge is subjected to plate and frame filter pressing to obtain a mud cake.

5. The chemical film coupling softening method according to claim 1, characterized in that: In the step of filtering the flocculated wastewater, multi-media filtration is first performed to remove suspended matter and unprecipitated hardness ions in the flocculated wastewater.

6. The chemical film coupling softening method according to claim 1, characterized in that: The membrane separation technology uses a nanofiltration membrane to effectively intercept divalent and higher ions and remove organic pollutants.

7. The chemical film coupling softening method according to claim 1, characterized in that: In the evaporation and crystallization step, the filtered wastewater is evaporated at high temperature to crystallize the salt in the filtered wastewater.

8. The chemical coupling softening method according to claim 7, characterized in that: The salt crystals produced in the evaporation crystallization step are mixed salt crystals, and the mixed salt crystals are classified to separate pure elemental salts.

9. A chemical membrane coupled softening treatment device for high hardness wastewater according to any one of claims 1 to 8, characterized in that: include: A softening tank, a flocculation sedimentation tank, a multi-media filter, a nanofiltration component and an evaporation crystallization component are sequentially arranged along the direction of high-hardness wastewater inflow; The softening tank is a place for chemical pretreatment of high-hardness wastewater, which can significantly reduce the total hardness of high-hardness wastewater; The flocculation sedimentation tank is connected to the softening tank to perform flocculation sedimentation on the softened wastewater to remove suspended solids and hardness ions in the softened wastewater; The multi-media filter is connected to the flocculation sedimentation tank to remove suspended matter and unprecipitated hardness ions in the water; The nanofiltration component is connected to the multi-media filter to achieve deep softening of the filtered wastewater and remove organic pollutants; The nanofiltration component is connected to the evaporation crystallization component and is used for concentrating the separated wastewater to achieve crystallization of salt and recovery of valuable minerals.

10. The processing device according to claim 9, characterized in that The evaporation crystallization component is connected to a salt separation component, and the salt separation component separates pure elemental salt according to the difference in melting point and solubility of different salt crystals.

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