Preparation method and application of sewage desalting agent

Abstract

The invention discloses a preparation method and application of a sewage desalting agent, and the sewage desalting agent is obtained by mixing calcium hydroxide and magnesium oxide in proportion. The sewage desalting agent prepared by the invention realizes efficient synergistic removal of silicate and phosphate, reduces subsequent membrane pollution, and can solve the problem of low overall removal rate of silicate and phosphate in a pretreatment system on the premise of controlling the overall agent adding cost of a sewage treatment device.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of a sewage desalination agent and application of the prepared sewage desalination agent, and in particular to a preparation method of a sewage desalination agent and application thereof. Background Art

[0002] In the petrochemical, fine chemical and other industries, industrial wastewater usually contains high concentrations of silicates, phosphates and other soluble salts, which require sewage treatment. Traditional pretreatment processes mostly use a single agent for chemical precipitation, which has problems such as incomplete silicate removal, high phosphate treatment costs, and serious fouling of the membrane system. The existing technology uses a high-density clarification tank combined with a double membrane process to solve the above problems, but its pretreatment system has limited efficiency in the synergistic removal of salts such as silicon and phosphorus, and relies on multi-stage dosing, which makes the process complicated. Summary of the invention

[0003] In order to solve the above problems, the first object of the present invention is to provide a method for preparing a sewage desalination agent to solve the problems raised in the above background technology.

[0004] The second object of the present invention is to provide a sewage desalination agent synthesized by the above method.

[0005] The third object of the present invention is to provide a sewage desalination agent synthesized by the above method for use in sewage desalination.

[0006] To achieve the first object of the present invention, the present invention provides the following technical solutions:

[0007] A method for preparing a sewage desalting agent comprises the following steps: mixing calcium hydroxide and magnesium oxide in a mass ratio of (1.3-1.5:1) to obtain the sewage desalting agent.

[0008] Preferably, the mass ratio of the calcium hydroxide to the magnesium oxide is 1.4:1.

[0009] To achieve the second purpose of the present invention, the technical solution provided by the present invention is: a sewage desalination agent synthesized by any of the above methods.

[0010] To achieve the third object of the present invention, the technical solution provided by the present invention is: comprising the following steps:

[0011] Step (1): adding a sewage desalting agent to the reaction zone of a high-density clarification tank, and mixing the agent and the sewage thoroughly by stirring to obtain a mixture;

[0012] Step (2): adjusting the pH of the mixture to 9-11 for reaction to generate calcium silicate and magnesium phosphate, and flocculating to obtain floccules;

[0013] Step (3): The flocs are subjected to solid-liquid separation in the inclined tube sedimentation area, the effluent enters the ultrafiltration-reverse osmosis system for further desalination, and the sludge is concentrated, dehydrated and then discharged.

[0014] Among them, the sewage desalting agent is the sewage desalting agent synthesized by the above method.

[0015] The reaction mechanism is as follows:

[0016] Removal of silicate: Calcium hydroxide reacts with silicate (SiO3 2- ) to form insoluble calcium silicate precipitate:

[0017] Ca(OH)2 + SiO3 2- →CaSiO3↓ + 2OH-

[0018] Removal of phosphate: Magnesium oxide reacts with phosphate (PO4 3- ) to form insoluble magnesium phosphate precipitate:

[0019] 3MgO + 2PO4 3- + 3H2O → Mg3(PO4) 2 ↓ + 3H2O

[0020] Preferably, the dosage of the sewage desalting agent is 2.0 - 3.5 g / L.

[0021] Preferably, in step (1), the sewage is put into the high-density clarifier, and then sewage desalting agent, polyaluminum chloride, sodium carbonate, polyacrylamide and other agents are put in. The agents and the sewage are fully mixed by stirring to obtain a mixture.

[0022] Preferably, in step (2), the pH of the mixture is adjusted to 9 - 11, the reaction time is 30 - 60 minutes, calcium silicate and magnesium phosphate are generated, and coagulation and flocculation reactions are carried out to obtain flocs.

[0023] Preferably, in step (3), the flocs are subjected to solid-liquid separation in the inclined tube sedimentation area, the effluent enters the ultrafiltration security filter for ultrafiltration; the water permeating through the ultrafiltration membrane enters the reverse osmosis security filter, the effluent of the reverse osmosis security filter enters the reverse osmosis membrane, the produced desalted water enters the RO product water tank, the produced reverse osmosis concentrated water is discharged to the RO concentrated water tank for mud-water separation, the produced wastewater flows into the dual-membrane wastewater tank, and the sludge is concentrated, dehydrated and then discharged.

[0024] Preferably, after the sewage is subjected to electro-de-salting treatment, the removal rate of silicate in the sewage is ≥95%, and the removal rate of phosphate is ≥98%.

[0025] Compared with the prior art, the beneficial effects of the present invention:

[0026] (1) The desalting agent for sewage prepared in the present invention is an optimized ratio of calcium hydroxide and magnesium oxide, which realizes the efficient synergistic removal of silicate and phosphate, reduces subsequent membrane fouling, and can solve the problem of low overall removal rate of silicate and phosphate in the pretreatment system on the premise of controlling the overall dosing cost of the sewage treatment device; among them, the silicate removal rate is ≥95%, and the phosphate removal rate is ≥98%, which is significantly better than the treatment with a single agent; the chemical cleaning cycle of the ultrafiltration membrane is extended by more than 50%, and the desalination rate of the reverse osmosis membrane is stable above 99.6%, which can ensure the long-term stable operation of the dual-membrane system of ultrafiltration (UF) and reverse osmosis (RO).

[0027] (2) The desalting agent for sewage prepared in the present invention can simplify the process flow, perform desalting pretreatment before the dual-membrane system of ultrafiltration and reverse osmosis, only requires single dosing, without traditional multi-stage dosing, reduces the operation complexity and the dosing cost, and is applicable to chemical wastewater with high salt, high silicon and phosphorus.

[0028] (3) The precipitate generated during the application of the desalting agent for sewage in the present invention is non-toxic and has high stability, avoiding secondary pollution. Detailed implementation mode

[0029] The following further analyzes the present invention in combination with specific embodiments. Obviously, the described ones are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope protected by the present invention.

[0030] Calcium hydroxide and magnesium oxide used in the following examples or comparative examples of the present invention are all commercially available.

[0031] Example 1

[0032] In a wastewater treatment device of a certain PetroChina Company Limited, the raw water contains SiO3 2- at 150 mg / L and PO4 3- at 80 mg / L.

[0033] (1) Mix calcium hydroxide and magnesium oxide in a mass ratio of 1.4:1 to obtain a desalting agent for sewage.

[0034] (2) The sewage flows by gravity to the sewage treatment plant. After being homogenized in a new peak regulation tank, it is pumped into a high-density clarifier. The desalting agent for sewage is added to the reaction zone of the high-density clarifier at a dosing amount of 2.5 g / L, and then other agents such as polyaluminum chloride, sodium carbonate, and polyacrylamide are added. The agents are fully mixed with the sewage by stirring to obtain a mixture.

[0035] (3) Adjust the pH of the mixture to 10.5 for reaction. The reaction time is 45 minutes to generate calcium silicate and magnesium phosphate, and coagulation and flocculation reactions are carried out to obtain flocs.

[0036] (4) The flocs are subjected to solid-liquid separation in the inclined tube sedimentation area. The effluent first enters a multi-media filter to remove suspended solids and turbidity, and then the normal effluent enters an ultrafiltration security filter to intercept fine particles and prevent large particle substances from damaging the subsequent ultrafiltration membrane. The effluent of the ultrafiltration security filter enters ultrafiltration. A circulation pump is provided on the concentrated water side. Colloidal particles and macromolecular organic matters in the water are retained on the concentrated water side, while water and low molecular weight solutes are allowed to pass through the ultrafiltration membrane to form product water and enter the ultrafiltration water tank for ultrafiltration; the ultrafiltration product water can be lifted by an ultrafiltration backwash pump as ultrafiltration backwash water, or lifted by an ultrafiltration product water pump and enter a reverse osmosis security filter, and a non-oxidizing bactericide, a reducing agent and a scale inhibitor are added. The effluent of the reverse osmosis security filter is pressurized by a high-pressure pump and then enters the reverse osmosis membrane. The produced desalted water enters the RO product water tank and is sent out as fresh water make-up water. The produced reverse osmosis concentrated water is discharged to the RO concentrated water tank for mud-water separation. The produced wastewater flows into the dual-membrane wastewater tank, and the sludge is concentrated, dehydrated and then discharged.

[0037] The final treatment results are as follows:

[0038] The silicate is reduced to 5 mg / L, and the removal rate reaches 96.7%; the phosphate is reduced to 1.2 mg / L, and the removal rate reaches 98.5%; the operation cycle of the ultrafiltration membrane is extended from 7 days to 12 days, and the conductivity of the reverse osmosis product water ≤ 400 μS / cm.

[0039] Example 2

[0040] In a wastewater treatment device of a certain Petrochemical Corporation, the raw water contains SiO3 2- 1 of 50 mg / L and PO4 3- of 80 mg / L.

[0041] (1) Mix calcium hydroxide and magnesium oxide in a mass ratio of 1.3:1 to obtain a sewage desalting agent.

[0042] (2) The sewage flows by gravity to the sewage treatment plant. After being homogenized in the new peak regulation tank, it is pumped and lifted into the high-density clarifier. The sewage desalting agent is added to the reaction area of the high-density clarifier at a dosage of 2.0 g / L, and then agents such as polyaluminum chloride, sodium carbonate, and polyacrylamide are added. The agents are fully mixed with the sewage by stirring to obtain a mixture.

[0043] (3) Adjust the pH of the mixture to 9 for reaction. The reaction time is 30 minutes to generate calcium silicate and magnesium phosphate, and coagulation and flocculation reactions are carried out to obtain flocs.

[0044] (4) The flocs are subjected to solid-liquid separation in the inclined tube sedimentation area. The effluent first enters the multi-media filter to filter out suspended solids and turbidity, and then the normal effluent enters the ultrafiltration security filter to intercept fine particles and prevent large particle substances from damaging the subsequent ultrafiltration membrane. The effluent of the ultrafiltration security filter enters the ultrafiltration. A circulation pump is provided on the concentrated water side. Colloidal particles and macromolecular organic substances in the water are retained on the concentrated water side, while water and low molecular weight solutes are allowed to pass through the ultrafiltration membrane to form product water and enter the ultrafiltration water tank for ultrafiltration; the ultrafiltration product water can be lifted by the ultrafiltration backwash pump to be used as ultrafiltration backwash water, or lifted by the ultrafiltration product water pump and enter the reverse osmosis security filter, and non-oxidizing biocide, reducing agent and scale inhibitor are added. The effluent of the reverse osmosis security filter is pressurized by a high-pressure pump and then enters the reverse osmosis membrane. The produced desalted water enters the RO product water tank and is sent out as fresh water make-up water. The produced reverse osmosis concentrated water is discharged to the RO concentrated water tank for sludge-water separation. The produced wastewater flows into the dual-membrane wastewater tank, and the sludge is concentrated, dehydrated and then discharged.

[0045] The final treatment results are as follows:

[0046] The silicate is reduced to 6 mg / L, and the removal rate reaches 96.0%; the phosphate is reduced to 1.5 mg / L, and the removal rate reaches 98.1%; the operation cycle of the ultrafiltration membrane is extended from 7 days to 12 days, and the conductivity of the reverse osmosis product water ≤ 400 μS / cm.

[0047] Example 3

[0048] In the wastewater treatment device of a certain Petrochemical Corporation, the raw water contains SiO3 2- 1 of 50 mg / L and PO4 3- of 80 mg / L.

[0049] (1) Mix calcium hydroxide and magnesium oxide in a mass ratio of 1.5:1 to obtain a sewage desalting agent.

[0050] (2) The sewage flows by gravity to the sewage treatment plant. After being homogenized in the new peak regulation tank, it is pumped and lifted into the high-density clarifier. The sewage desalting agent is added to the reaction area of the high-density clarifier at a dosage of 3.5 g / L, and then agents such as polyaluminum chloride, sodium carbonate, and polyacrylamide are added. The agents are fully mixed with the sewage by stirring to obtain a mixture.

[0051] (3) Adjust the pH of the mixture to 11 for reaction. The reaction time is 60 minutes to generate calcium silicate and magnesium phosphate, and coagulation and flocculation reactions are carried out to obtain flocs.

[0052] (4) The flocs achieve solid-liquid separation in the inclined tube sedimentation area. The effluent first enters the multi-media filter to filter out suspended solids and turbidity. Then, the normal effluent enters the ultrafiltration security filter to intercept fine particles and prevent large particle substances from damaging the subsequent ultrafiltration membrane. The effluent of the ultrafiltration security filter enters the ultrafiltration. A circulation pump is provided on the concentrated water side. Colloidal particles and macromolecular organic substances in the water are retained on the concentrated water side, while water and low molecular weight solutes are allowed to pass through the ultrafiltration membrane to form product water, which enters the ultrafiltration water tank for ultrafiltration. The ultrafiltration product water can be lifted by the ultrafiltration backwash pump to be used as ultrafiltration backwash water, or lifted by the ultrafiltration product water pump to enter the reverse osmosis security filter, and non-oxidizing bactericide, reducing agent and scale inhibitor are added. The effluent of the reverse osmosis security filter is pressurized by a high-pressure pump and then enters the reverse osmosis membrane. The produced demineralized water enters the RO product water tank and is sent out as fresh water makeup water. The produced reverse osmosis concentrated water is discharged to the RO concentrated water tank for sludge-water separation. The produced wastewater flows into the dual-membrane wastewater tank, and the sludge is concentrated, dehydrated and then discharged.

[0053] The final treatment results are as follows:

[0054] The silicate is reduced to 5 mg / L, and the removal rate reaches 96.7%; the phosphate is reduced to 1.3 mg / L, and the removal rate reaches 98.4%; the operation cycle of the ultrafiltration membrane is extended from 7 days to 12 days, and the conductivity of the reverse osmosis product water ≤ 400 μS / cm.

[0055] Comparative Example 1

[0056] In the wastewater treatment device of a certain Petrochemical Corporation, the raw water contains SiO3 2- at 150 mg / L and PO4 3- at 80 mg / L.

[0057] (1) The sewage flows by gravity to the sewage treatment plant. After being homogenized in the new peak regulation tank, it is pumped and lifted into the high-density clarifier. Calcium hydroxide is added to the reaction area of the high-density clarifier at a dosage of 2.5 g / L, and then agents such as polyaluminum chloride, sodium carbonate, and polyacrylamide are added. The agents are fully mixed with the sewage by stirring to obtain a mixture.

[0058] (2) The pH of the mixture is adjusted to 10.5 for reaction. The reaction time is 45 minutes to generate calcium silicate and magnesium phosphate, and coagulation and flocculation reactions are carried out to obtain flocs.

[0059] (3) The flocs achieve solid-liquid separation in the inclined tube sedimentation area. The effluent first enters the multi-media filter to filter out suspended solids and turbidity. Then, the normal effluent enters the ultrafiltration safety filter to intercept fine particles and prevent large particle substances from damaging the subsequent ultrafiltration membrane. The effluent of the ultrafiltration safety filter enters the ultrafiltration. A circulation pump is provided on the concentrated water side. Colloidal particles and macromolecular organic substances in the water are retained on the concentrated water side, while water and low molecular weight solutes are allowed to pass through the ultrafiltration membrane to form product water, which enters the ultrafiltration water tank for ultrafiltration. The ultrafiltration product water can be lifted by the ultrafiltration backwash pump to be used as ultrafiltration backwash water, or lifted by the ultrafiltration product water pump to enter the reverse osmosis safety filter, and non-oxidizing biocide, reducing agent and scale inhibitor are added. The effluent of the reverse osmosis safety filter is pressurized by a high-pressure pump and then enters the reverse osmosis membrane. The produced desalted water enters the RO product water tank and is sent out as fresh water make-up water. The produced reverse osmosis concentrated water is discharged to the RO concentrated water tank for sludge-water separation. The produced wastewater flows into the dual-membrane wastewater tank, and the sludge is concentrated, dehydrated and then discharged.

[0060] The final treatment results are as follows:

[0061] The silicate is reduced to 30 mg / L, and the removal rate reaches 80.0%; the phosphate is reduced to 75 mg / L, and the removal rate reaches 6.25%.

[0062] Comparative Example 2

[0063] In the wastewater treatment device of a certain Petrochemical Corporation, the raw water contains SiO3 2- at 150 mg / L and PO4 3- at 80 mg / L.

[0064] (1) The sewage flows by gravity to the sewage treatment plant. After being homogenized in the new peak regulation tank, it is pumped and lifted into the high-density clarifier. Magnesium oxide is added to the reaction area of the high-density clarifier at a dosage of 2.5 g / L, and then flocculants such as polyaluminum chloride, sodium carbonate, and polyacrylamide are added. The agents are fully mixed with the sewage by stirring to obtain a mixture.

[0065] (2) The pH of the mixture is adjusted to 10.5 for reaction. The reaction time is 45 minutes to generate calcium silicate and magnesium phosphate, and coagulation and flocculation reactions are carried out to obtain flocs.

[0066] (3) The flocs achieve solid-liquid separation in the inclined tube sedimentation area. The effluent first enters the multi-media filter to remove suspended solids and turbidity. Then, the normal effluent enters the ultrafiltration safety filter to intercept fine particles and prevent large particle substances from damaging the subsequent ultrafiltration membrane. The effluent of the ultrafiltration safety filter enters the ultrafiltration. A circulation pump is provided on the concentrated water side. Colloidal particles and macromolecular organic substances in the water are retained on the concentrated water side, while water and low molecular weight solutes are allowed to pass through the ultrafiltration membrane to form product water and enter the ultrafiltration water tank for ultrafiltration; the ultrafiltration product water can be lifted by the ultrafiltration backwash pump to be used as ultrafiltration backwash water, or lifted by the ultrafiltration product water pump and enter the reverse osmosis safety filter, and non-oxidizing biocides, reducing agents and scale inhibitors are added. The effluent of the reverse osmosis safety filter is pressurized by a high-pressure pump and then enters the reverse osmosis membrane. The produced desalted water enters the RO product water tank and is sent out as fresh water makeup water. The produced reverse osmosis concentrated water is discharged to the RO concentrated water tank for sludge-water separation. The produced wastewater flows into the dual-membrane wastewater tank, and the sludge is concentrated, dehydrated and then discharged.

[0067] The final treatment results are as follows:

[0068] The silicate is reduced to 120 mg / L, and the removal rate reaches 20.0%; the phosphate is reduced to 15 mg / L, and the removal rate reaches 81.2%.

[0069] From Examples 1-3 and Comparative Examples 1-2, it can be seen that the sewage desalting agent prepared by the present invention synergistically removes silicate and phosphate in sewage through the specific ratio of calcium hydroxide and magnesium oxide. The silicate removal rate is ≥95%, and the phosphate removal rate is ≥98%, so as to solve the problems of serious membrane fouling and high operation cost in the traditional process, and significantly improve the treatment efficiency and stability of the dual-membrane system.

[0070] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for preparing a sewage desalting agent, characterized in that: The following steps are involved: Calcium hydroxide and magnesium oxide are mixed in a mass ratio (1.3-1.5:1) to obtain a sewage desalination agent.

2. The method for preparing a sewage desalting agent according to claim 1, characterized in that: The mass ratio of the calcium hydroxide to the magnesium oxide is 1.4:

1.

3. A sewage desalination agent, characterized in that: The sewage desalination agent is prepared according to any one of claims 1 to 2.

4. A method for treating sewage desalination, characterized in that: The following steps are involved: Step (1): adding a sewage desalting agent to the reaction zone of a high-density clarification tank, and mixing the agent and the sewage thoroughly by stirring to obtain a mixture; Step (2): adjusting the pH of the mixture to 9-11 for reaction to generate calcium silicate and magnesium phosphate, and flocculating to obtain floccules; Step (3): the flocculants are separated into solid and liquid in the inclined tube sedimentation zone, the effluent enters the ultrafiltration-reverse osmosis system for further desalination, and the sludge is concentrated and dehydrated before discharge; wherein the sewage desalination agent is prepared according to any one of claims 1 to 3.

5. The method for treating sewage desalination according to claim 4, characterized in that: The dosage of the sewage desalination agent is 2.0-3.5 g / L.

6. The method for treating sewage desalination according to claim 4, characterized in that: In the step (1), sewage is put into a high-density clarification tank, and then sewage desalting agent, polyaluminium chloride, sodium carbonate, polyacrylamide and other reagents are put into the tank, and the reagents and sewage are fully mixed by stirring to obtain a mixture.

7. The method for treating sewage desalination according to claim 4, characterized in that: In the step (2), the pH of the mixture is adjusted to 9-11, the reaction time is 30-60 minutes, calcium silicate and magnesium phosphate are generated, and coagulation and flocculation reactions are carried out to obtain floccules.

8. The method for treating sewage desalination according to claim 4, characterized in that: In the step (3), the flocculants are separated into solid and liquid in the inclined tube sedimentation zone, and the effluent enters the ultrafiltration security filter for ultrafiltration; the water passing through the ultrafiltration membrane enters the reverse osmosis security filter, and the effluent of the reverse osmosis security filter enters the reverse osmosis membrane. The desalted water produced enters the RO water production pool, and the reverse osmosis concentrated water is discharged to the RO concentrated water pool for mud and water separation. The wastewater produced flows into the double membrane wastewater pool, and the sludge is concentrated and dehydrated before being discharged.

9. The method for treating wastewater desalination according to any one of claims 4 to 8, characterized in that: After the sewage is treated with electrical desalination, the silicate removal rate in the sewage is ≥95%, and the phosphate removal rate is ≥98%.