CN102718351A - Device and method for sewage desalting - Google Patents

Abstract

A device for desalination of sewage, which mainly includes: a water collection tank is connected to a sedimentation tank through a vortex pipeline mixer, and the vortex pipeline mixer is connected to a coagulant dosing box; the water outlet of the sedimentation tank is connected to a microfiltration system, and the microfiltration system The water outlet of the filter system is connected to the stirring water tank, and the stirring water tank is connected to the antiscalant dosing tank; the water outlet of the stirring water tank is connected to the electric adsorption device, and the water outlet of the electric adsorption device is connected to the water storage container. The invention also discloses a method for desalting sewage. The water production rate of the deep desalted sewage of the invention can reach more than 75%, the desalination rate is greater than 80%, and the desalted sewage can be directly used for industrial circulating cooling water.

Description

A device and method for desalination of sewage

technical field

The invention belongs to the field of advanced sewage treatment, and in particular relates to a desalination device which can be used for secondary effluent of urban sewage treatment plants.

The invention also relates to a method for desalting sewage.

Background technique

In recent years, with the rapid development of science and technology and the country's great investment in the field of environmental protection, my country's industrial water technology has made great progress. As of 2011, water consumption per 10,000 yuan of GDP was 139m ³ , 40.0% lower than in 2008; water consumption per 10,000 yuan of industrial added value was 82m ³ , 37.1% lower than in 2008. However, with economic development, the contradiction between urban water use and industrial water use has become more prominent. The total water use in 2011 was 608 billion m ³ , an increase of 1.0% over the previous year. Among them, industrial water use increased by 0.8%. The increasing scarcity of water resources and the aggravation of pollution have become the key factors restricting the development of some enterprises to a certain extent. In order to protect the environment and save water resources, we must continue to explore ways to improve water resource utilization and reduce sewage discharge. With the continuous improvement of my country's sewage treatment rate, the amount of reclaimed water reuse is also increasing, but the proportion of sewage reuse in waste water discharge is still very low. In this case, the improvement of sewage reuse technology will become the focus of water saving and emission reduction for enterprises.

In industrial production, the amount of industrial circulating cooling water accounts for 80% of the total industrial water consumption on average, and the cooling water intake accounts for 30% to 40% of the total industrial water intake. Therefore, the main way to achieve industrial water saving and emission reduction is to reuse sewage for circulating cooling water make-up water and boiler water. For the secondary effluent of urban sewage treatment plants, conventional sewage recycling technologies including clarification, filtration, and activated carbon adsorption can only remove part of the chroma, suspended solids, turbidity, and organic matter. To meet the requirements of industrial circulating cooling water, it is necessary to further remove the hardness and salinity in the water. In particular, the desalination of sewage has become a bottleneck restricting the development of sewage reuse technology. The current desalination technologies commonly used in sewage reuse mainly include: ion exchange, electrodialysis, nanofiltration, reverse osmosis, electrodeionization, etc.

The ion exchange method is a kind of chemical desalination method, which uses ion exchange technology for desalination. The ion exchange desalination process mainly uses H-type or Na-type cation exchangers and OH-type anion exchangers to remove anions and cations from water through ion exchange reactions, thereby obtaining desalinated water. The essence of ion exchange is to make the electrolyte on the resin react with another electrolyte in the solution. This reaction can be a neutralization reaction or a metathesis reaction. The ion exchange method is widely used in the field of desalination, especially in the removal of Ca, Mg and other ions in water, but it has high requirements for the selection, management and regeneration of resin. In addition, from an economic point of view, when ion exchange technology is used to desalinate, the salt content of influent water should not exceed 500mg/L, and the operating cost of ion exchange resin is high, and the discharge of acid and alkali will cause secondary pollution.

Electrodialysis desalination is under the action of an external DC electric field, using the selective permeability of the anion and cation cross-membrane to anion and cation in the solution to make the ions migrate in a directional manner, that is, anions are only allowed to pass through the anion membrane, and cations are only allowed to pass through the cation membrane. To achieve the separation of solute and solution, so as to achieve the purpose of raw water desalination. In order to ensure the long-term stable and reliable operation of the electrodialysis unit, strict pre-treatment must be carried out before the raw water enters the electrodialyzer to control the turbidity of the raw water below 3NTU and ensure that Fe, Mn, Cl, etc. meet the specified requirements. The desalination rate of the electrodialysis method can reach 80% to 90%, but the working voltage is high, water decomposition is easy to occur, the fouling of the membrane stack is relatively serious, and the surfactant, protein, microorganisms, etc. in the sewage may cause membrane damage. pollute.

Nanofiltration, also known as "low pressure reverse osmosis", can remove solute ions with a diameter of about 1nm, and the molecular weight cut-off is about 200-1000. It has a high interception of some high-priced salts in sewage, and can remove 2/ 3 salinity, 4/5 hardness, more than 90% dissolved carbon and THM precursor, the effluent is close to the safe drinking water standard. However, for industrial circulating water, there is no significant advantage because it has basically no removal effect on monovalent ions, ammonia nitrogen, etc., and is easy to scale.

Reverse osmosis is currently a widely used sewage desalination process. It uses a pressure greater than the osmotic pressure of the solute as the driving force and uses a semi-permeable membrane to filter the solvent and solute in the solution. The process of reverse osmosis includes pretreatment, membrane separation and posttreatment. The reverse osmosis membrane is a semi-permeable film made of special materials (such as aromatic polyamide, etc.) and processing methods. Under the action of external pressure, it can selectively permeate some components of the aqueous solution, so as to achieve the purpose of desalination, purification or concentration separation. The reverse osmosis process has a wide range of applications, such as: large boiler make-up water, various industrial pure water, drinking water, etc. However, the water yield of the reverse osmosis membrane is low, generally around 60%, and it has high requirements for the influent water. In addition, it is necessary to add a large amount of acid and alkali when cleaning the membrane module, which will cause adverse effects on the environment.

Electrodeionization is a desalination process that combines "electrodialysis + ion exchange". The ion transport channel" migrates to the surface of the membrane and enters the concentrated chamber through the ion exchange membrane. The polarization existing in the diffusion layer where the resin and membrane are in contact with the water phase causes the water to dissociate into H+ and OH-, except for some of which participate in the load current. Most of them regenerate the resin, so that the three processes of ion exchange, migration, and electrical regeneration occur together and promote each other, realizing the process of continuous ion removal. This method can remove most of the salt in sewage without adding acid-base regeneration, but this technology is limited to the production of pure water and is not suitable for desalination with high salt water content.

Electro-adsorption technology (EST) is a technology that combines electrochemical theory with adsorption separation technology. It achieves water purification and purification by enriching and concentrating soluble salts and other charged substances in water on the electrode surface by applying an external voltage. A new water treatment technology for salt removal. When the raw water flows in the space formed by the cathode and anode, the charged particles (ions, colloidal particles, organic matter and bacteria, etc.) in the water will migrate to the oppositely charged electrodes respectively, be adsorbed by the electrodes and stored in the electric double layer under the action of the electric field force. , to achieve the separation of charged particles (impurities) from water, and desalinated water flows out from the other end. When the electrode is de-energized or momentarily reversed, the charged particles accumulated on the electrode will fall off from the electrode and be washed away under the action of water flow or electric field force, and the electrode will be regenerated. Compared with the traditional method, the regeneration of the system does not need to use any acid, alkali and salt solution, it is only completed through the discharge of the electrodes, and will not cause secondary pollution; this method has low energy consumption, simple operation, and the water yield is in the More than 70%, it has better anti-fouling ability and longer service life than reverse osmosis.

In general, the electro-adsorption device has no special restrictions on residual chlorine, organic matter, and high-priced ions in the influent. It is usually required that the turbidity is less than 5NTU, the content of suspended solids is less than 5mg/L, the oil is less than 3ml/L, and the pH value is about 6-9. . Therefore, sand filter, fiber filter, security filter, etc. are generally used for pretreatment. However, as the treatment process progresses, the load gradually increases, the regeneration times are frequent, and even the electrodes need to be replaced frequently. In addition, the conventional method of removing bicarbonate in raw water by adding acid to prevent scaling of the electro-adsorption device is less safe and difficult to operate.

Contents of the invention

The object of the present invention is to provide a device for desalination of sewage.

Another object of the present invention is to provide a method for desalting sewage by using the above-mentioned device.

In order to achieve the above object, the device for sewage desalination provided by the present invention mainly includes:

The sump is connected to the sedimentation tank through a vortex pipeline mixer, and the vortex pipeline mixer is connected to the coagulant dosing box;

The water outlet of the sedimentation tank is connected to the microfiltration system, and the water outlet of the microfiltration system is connected to the stirring water tank, which is connected to the antiscalant dosing tank;

The water outlet of the stirring water tank is connected with the electric adsorption device, and the water outlet of the electric adsorption device is connected with the water storage container.

Said device, wherein, between the sump and the vortex pipeline mixer, between the water outlet of the sedimentation tank and the microfiltration system, between the water outlet of the stirring water tank and the electro-adsorption device, and between the water outlet of the electro-adsorption device and the water storage container Flow meters and centrifugal pumps are installed in each room; flow pumps and metering pumps are installed between the vortex pipeline mixer and the coagulant dosing tank, between the stirring water tank and the antiscalant dosing tank; the bottom of the sedimentation tank is installed with centrifugal pump.

Said device, wherein, the material of the microfiltration system is polyvinylidene fluoride, the structure is a hollow fiber type, and the membrane pore diameter is 0.2 μm.

The device described above, wherein the electro-adsorption device uses carbon aerogel as the electrode material.

The method for desalting sewage by using the above-mentioned device provided by the present invention, the main process is as follows:

1) Sewage and coagulant enter the vortex pipeline mixer together, and use coagulation to remove suspended solids, colloids, a small amount of bacteria and phosphate, and reduce turbidity;

2) The effluent of the vortex pipeline mixer enters the sedimentation tank, and the effluent after precipitation is filtered by a microfiltration system to remove macromolecular dissolved organic matter and coliform bacteria, and further reduce turbidity;

3) The effluent filtered by the microfiltration system enters the stirring water tank and is added with antiscalant, and the treated sewage enters the electric adsorption device for desalination;

4) The effluent after desalination enters the water storage container.

The method, wherein the sewage is the secondary effluent of urban sewage treatment plants, the COD _Cr content in the sewage is below 100 mg/L, the NH ₃ -N content is below 15 mg/L, the suspended matter content is below 20 mg/L, and the conductivity At about 1500μs/cm, the total dissolved solids are 800-1200mg/L.

The method, wherein the coagulant is polyferric chloride and polydimethyldiallylammonium chloride, and the mass ratio is 5:1.

The method, wherein the pressure of the microfiltration system is 0.05-0.2MPa.

The method, wherein the scale inhibitor is MDC-200 type scale inhibitor.

The method described above, wherein the electro-adsorption device uses carbon aerogel as the electrode material, adopts the mode of alternate operation of two-stage modules, the operation process is automatically controlled by PLC, and the work and regeneration of each module can be automatically switched.

The invention provides a treatment process capable of deep desalination and reuse of sewage. The sewage and coagulant enter the vortex pipeline mixer together, and use coagulation to remove impurities such as suspended solids, colloids, and a small amount of bacteria, as well as phosphate and reduce turbidity. , the effluent enters the sedimentation tank, and after precipitation, the effluent is filtered by the hollow fiber microfiltration membrane to remove macromolecular dissolved organic matter, coliform bacteria, etc., and further reduce the turbidity. The effluent enters the dosing water tank, and the scale inhibitor is added by the metering pump , to prevent the long-term operation of the electro-adsorption device from causing the insoluble salts such as calcium carbonate, magnesium carbonate and calcium sulfate to concentrate and precipitate out of scale. The pretreated sewage enters the electric adsorption device for desalination. The water production rate of this method can reach more than 75%, and the desalination rate is greater than 80%. The desalted sewage can be directly used for industrial circulating cooling water.

Description of drawings

Figure 1 is a schematic diagram of the device of the present invention.

Explanation of main component symbols in the attached drawings:

1 water collection tank; 2 sedimentation tank; 3 microfiltration system; 4 stirring water tank; 5 electric adsorption device; 6 water storage container; , 12, 13, 14, 15 centrifugal pumps; 16, 17, 18, 19, 20, 21 flow meters; 22 vortex pipeline mixers; 23 mechanical stirring devices.

Detailed ways

The invention combines the pretreatment method with the electric adsorption technology, provides a treatment process for deep desalination and reuse of sewage, and further improves the desalination effect.

Please refer to FIG. 1 , which is a schematic diagram of the device of the present invention: the sump 1 is connected to the sedimentation tank 2 through a vortex pipeline mixer 22 , and the vortex pipeline mixer 22 is also connected to the coagulant dosing box 8 .

The water outlet of the sedimentation tank 2 is connected to the microfiltration system 3 , and the water outlet of the microfiltration system 3 is connected to the stirring water tank 4 equipped with a mechanical stirring device 23 , and the stirring water tank 4 is connected to the scale inhibitor dosing tank 7 .

The water outlet of the stirring water tank 4 is connected to the electrosorption device 5 , and the water outlet of the electrosorption device 5 is connected to the water storage container 6 . Wherein, between the sump 1 and the vortex pipeline mixer 22, between the water outlet of the sedimentation tank 2 and the microfiltration system 3, between the water outlet of the stirring water tank 4 and the electrosorption device 5, between the water outlet of the electrosorption device 5 and the Flow meters 16 , 18 , 20 , 21 and centrifugal pumps 11 , 12 , 13 , 14 are respectively installed between the water storage containers 6 .

Flowmeters 17, 19 and metering pumps 9, 10 are respectively installed between the vortex pipeline mixer 22 and the coagulant dosing box 8, and between the stirring water tank 4 and the antiscalant dosing box 7.

A centrifugal pump 15 is installed at the bottom of the sedimentation tank.

The sewage depth desalination method of the present invention is as follows:

The secondary effluent of the urban sewage treatment plant enters the sump 1, and directly enters the vortex pipeline mixer 22 through the suction of the centrifugal pump 11. The flow rate is controlled by the flow meter 16, and the coagulant dosing tank 8 is added by the metering pump 9. The coagulant acts on the vortex pipeline mixer 22 for coagulation and sedimentation, and the dosage of the coagulant is controlled by the flow meter 17 . The flocs produced by sedimentation are discharged through the centrifugal pump 15 at the bottom of the sedimentation tank 2 after sedimentation. The effluent enters the microfiltration system 3 through the suction of the centrifugal pump 12, and the flow rate is controlled by the flow meter 18. The effluent of the microfiltration system 3 enters the stirring water tank 4, and the scale inhibitor is extracted from the scale inhibitor dosing tank 7 by the metering pump 10. Finally, put into the stirring water tank 4, and the stirring water tank 4 is provided with a mechanical stirring device 23 to ensure that the incoming water and the scale inhibitor are evenly mixed. The dosage of the scale inhibitor is controlled by the flow meter 19. The purpose of adding the scale inhibitor is to prevent electric adsorption Fouling occurs during long-term operation of the device. The treated effluent is pumped into the electro-adsorption device 5 through the centrifugal pump 13 for desalination, and the flow rate is controlled by the flow meter 20 . The generated desalted water is pumped into the water storage container 6 through the centrifugal pump 14 , and the flow rate is controlled by the flow meter 21 . The water production rate of the method can reach more than 75 percent, the desalination rate is more than 80 percent, and the desalted sewage can be directly used for industrial circulating cooling water.

The sewage referred to in the present invention is from the secondary effluent of urban sewage treatment plants, the content of COD _Cr is below 100mg/L, the content of NH ₃ -N is below 25mg/L, the content of suspended solids is below 30mg/L, and the conductivity is below 1500μs/L cm, and the total dissolved solids are around 1000mg/L.

The sedimentation tank of the present invention is a known device. The coagulant and antiscalant dosing device of the present invention is composed of a metering pump and a dosing box with a stirring pump inside. The dosing pump is provided with a filter screen, and the outlet is equipped with a pulse buffer and a safety valve. Corrosion-resistant dissolution baskets should be installed in the medicine box.

The material of the microfiltration membrane of the present invention is polyvinylidene fluoride (PVDF), the structure is a hollow fiber type, the membrane aperture is 0.2 μm, and the operating pressure is 0.05-0.2 MPa.

In the electro-adsorption device of the present invention, carbon aerogel is selected as the electrode material, the operating voltage is 1.5V, the flow rate is 2.0m ³ /h, and the entire system operation period is automatically controlled by PLC.

Example

This process is used to desalinate the effluent from the secondary sedimentation tank of a city sewage treatment plant as raw water. The pH value of the raw water is 7.75, the turbidity is 7NTU, the SS is 7.5mg/L, the conductivity is 1175μs/cm, and the COD _Cr value is 90mg/ L, TN is 22.13mg/L, TP is 0.83mg/L, and the total salt content is 1150mg/L. After the raw water enters the clarification tank for coagulation and sedimentation, the suspended solids and colloidal substances are removed by adding polyferric chloride, and the effluent is treated with a 0.2μm microfiltration membrane. After the suspended solids are lower than 5mg/L, the turbidity is lower than 2NTU, and the COD _Cr value is lower than 50mg/L, the conductivity of the effluent drops below 500μs/cm. After adding the scale inhibitor, the content of suspended solids and turbidity increase, but it does not affect the quality of the influent water of the electro-adsorption device. The effluent enters the electro-adsorption device for desalination, the conductivity is reduced by about 80%, the water production rate can reach more than 75%, and the desalination rate is greater than 80%. The desalinated sewage can be directly used for industrial circulating cooling water.

Claims (10)

1. device that is used for the sewage desalination mainly comprises:

Water collecting basin connects settling tank through the eddy current type line mixer, and this eddy current type line mixer connects the coagulating agent dosing tank;

The water outlet of settling tank connects microfiltration systems, and the water outlet of this microfiltration systems connects the stirring water tank, and this stirring water tank is connected with the Scale inhibitors dosing tank;

The water outlet that stirs water tank connects the electro-adsorption device, and the water outlet of this electro-adsorption device connects tank.

2. device according to claim 1; Wherein, between water collecting basin and the eddy current type line mixer, between settling tank water outlet and the microfiltration systems, stir between water outlet of water tank and the electro-adsorption device, under meter and impeller pump respectively be installed between electro-adsorption device water outlet and the tank;

Between eddy current type line mixer and the coagulating agent dosing tank, stir between water tank and the Scale inhibitors dosing tank flow pump and volume pump respectively be installed;

The settling tank bottom is equipped with impeller pump.

3. device according to claim 1 and 2, wherein, the material of microfiltration systems is a pvdf, and structure is the tubular fibre formula, and membrane pore size is 0.2 μ m.

4. device according to claim 1 and 2, wherein, the electro-adsorption device adopts charcoal-aero gel to do electrode materials.

5. the method for a sewage desalination, main flow process is:

1) sewage and coagulating agent together get into the eddy current type line mixer, utilize coagulation to remove suspended substance, colloid, a small amount of bacterium and phosphoric acid salt, and reduce turbidity;

2) water outlet of eddy current type line mixer gets into settling tank, and the water outlet of post precipitation is filtered through microfiltration systems and removed macromole dissolved organic matter, coliform, and further reduces turbidity;

3) water outlet after microfiltration systems filters gets into and stirs water tank and add Scale inhibitors, and the sewage after the processing gets into the electro-adsorption device and carries out desalination;

4) water outlet after the desalination gets in the tank.

6. method according to claim 5, wherein, sewage is the urban wastewater treatment firm secondary effluent, COD in the sewage _CrContent below 100mg/L, NH ₃-N content is below 15mg/L, and suspension content is below 20mg/L, and specific conductivity is about 1500 μ s/cm, and total dissolved solid is at 800-1200mg/L.

7. method according to claim 5, wherein, coagulating agent is poly-ferric chloride and Poly Dimethyl Diallyl Ammonium Chloride, mass ratio is 5: 1.

8. method according to claim 5, wherein, the pressure of microfiltration systems is 0.05-0.2MPa.

9. method according to claim 5, wherein, Scale inhibitors is a MDC-200 type Scale inhibitors.

10. method according to claim 5, wherein, the electro-adsorption device adopts charcoal-aero gel to do electrode materials, adopts the mode of two-rank module alternate run, and operational process is controlled through PLC automatically, and each module work realizes automaticallying switch with regeneration.

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