System and method for settling soluble silicate to reduce COD (Chemical Oxygen Demand)

Abstract

The invention discloses a system for settling soluble silicate and reducing COD (Chemical Oxygen Demand), which comprises a secondary sedimentation tank, a PAC (Poly Aluminum Chloride) reaction tank and a PAM (Polyacrylamide) reaction tank which are connected in sequence, and also comprises a pH regulation and control unit arranged in the secondary sedimentation tank and used for controlling the pH value of wastewater to be 6.5-7.0, and a temperature regulation and control unit arranged in the secondary sedimentation tank and used for controlling the pH value of the wastewater to be 6.5-7.0. The temperature regulation and control unit is used for controlling the temperature of the wastewater to be 35-40 DEG C, and the flocculation reaction unit is arranged in a PAC reaction tank and a PAM reaction tank and used for accelerating precipitation of suspended solids and colloidal substances. By accurately regulating and controlling the pH value and the temperature and cooperating with medicament adding and sludge discharging operation, COD can be effectively reduced, the problem of exceeding the standard is solved, the output of unqualified wastewater is reduced, the temporary storage requirement of a buffer pool is reduced, the purposes of reducing cost and improving efficiency are achieved, complex equipment and process transformation are not needed, the method can be achieved through existing facility adjustment, and application and popularization are facilitated.

Description

Technical Field

[0002] This invention relates to the field of wastewater treatment technology, and in particular to a system and method for reducing COD by settling soluble silicates. Background Technology

[0004] COD, or Chemical Oxygen Demand, measures the total amount of organic matter and other reducing substances in water that can be oxidized by strong oxidants (such as potassium dichromate). COD is a core indicator in environmental monitoring and wastewater treatment because it can quickly and relatively accurately reflect the degree of organic pollution in water bodies. Reducing COD means reducing oxygen-consuming substances, allowing water bodies to maintain sufficient dissolved oxygen, thereby restoring water health and preventing black and odorous water.

[0005] In the process of treating silicate-containing wastewater in denitrification units, due to the presence of difficult-to-remove silicate components in the wastewater, COD data often rises abnormally in the coagulation section after the biochemical reaction, leading to frequent exceedances of process parameters and the generation of large amounts of substandard wastewater. This substandard wastewater cannot be discharged in a timely manner and must be temporarily stored in a buffer tank. However, buffer tanks have the problems of large footprint and shallow depth, resulting in waste of land resources and increased treatment costs.

[0006] A wastewater treatment denitrification filter device is disclosed in Chinese patent document CN217479144U. The wastewater treatment denitrification filter device includes a mixing tank, a filter body, a clear water tank and a wastewater tank. The mixing tank is equipped with an inlet pipe and a carbon source dispensing pipe. A filter brick layer is provided at the bottom of the filter body, and a filter layer is provided above the filter brick layer. An aeration device and a water washing device are provided at the bottom of the filter body. The outlets of the aeration device and the water washing device are both connected to the filter brick layer. The inlet of the water washing device is connected to the clear water tank. A wastewater pipe is provided at the top of the filter body and is connected to the wastewater tank. By incorporating a mixing tank, the carbon source and wastewater can be thoroughly mixed, thereby ensuring the effectiveness of the nitrification and denitrification reaction. As nitrates in the wastewater undergo denitrification under the action of microorganisms, nitrogen gas is produced and accumulates in the filter layer. By incorporating an aeration device and a water washing device, the filter layer can be air-washed and water-washed to ensure that the nitrogen gas in the filter layer can be fully released. However, this wastewater treatment denitrification filter device does not completely treat silicate components.

[0007] A wastewater mixing flocculation sedimentation tank and wastewater treatment process with a dosing system are disclosed in Chinese patent document CN119735328A. The wastewater mixing flocculation sedimentation tank and wastewater treatment process with a dosing system include the following steps: (1) wastewater enters the pretreatment unit to remove large particulate suspended solids; (2) wastewater flows into the pH adjustment tank, and pH adjuster is added through the dosing system to adjust the pH value to 9-11; (3) ferrous sulfate is added to the coagulation reaction tank to reduce hexavalent chromium to trivalent chromium and promote the flocculation reaction; (4) polyaluminum chloride is further added through the flocculation reaction tank to form flocs. This invention gradually removes suspended solids and various heavy metals in wastewater through a multi-unit combined treatment process to ensure that the effluent quality meets the standards. It adopts a compact and reasonable process layout, reduces the floor space, and is suitable for small and medium-sized wastewater treatment plants. It introduces an automated dosing control system for precise dosing and reduces operating costs, but the treatment of silicate components in the wastewater mixing flocculation sedimentation tank and wastewater treatment process with a dosing system is incomplete.

[0008] A flocculant dosing process and apparatus are disclosed in Chinese patent document CN118598307A. This process and apparatus includes two dosing systems: a flocculant dosing system and a coagulant dosing system. The flocculant dosing system includes a flocculant dosing tank, a flocculant dosing pump, and a flocculant dosing point connected in sequence. The coagulant dosing system also includes a coagulant dosing tank, a coagulant dosing pump, and a coagulant dosing point connected in sequence. The outlet pipes of the two dosing systems can be connected in parallel, and connecting pipes and valves are installed simultaneously. Baffles are installed in the reaction tank, separating the upper and lower sections. Adjacent baffles connect to the top and bottom of the reaction tank, respectively, and the baffles are staggered and evenly arranged. PAC and PAM are added after the second baffle in the reaction tank for flocculation and sedimentation, causing tiny colloidal substances to precipitate, achieving a pretreatment effect to remove suspended solids. This invention improves the processing efficiency of subsequent processes and can extend the service life of reverse osmosis membrane elements, saving the purchase cost of membrane elements. However, the dosing process of this flocculant and the coagulation section of the device often result in abnormally high COD data, causing frequent exceedances of process indicators.

[0009] To address the shortcomings of the existing technologies, providing a system and method for reducing COD by precipitating soluble silicates is a worthwhile research topic. Summary of the Invention

[0011] The purpose of this invention is to overcome the shortcomings of wastewater containing difficult-to-remove silicate components, which easily leads to abnormally high COD data in the coagulation stage after biochemical reaction. This invention provides a system and method for reducing COD by settling soluble silicates, achieving the technical effect of effectively reducing COD and solving the problem of exceeding standards.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A system and method for reducing COD by settling soluble silicates, comprising a secondary settling tank, a PAC reaction tank, and a PAM reaction tank connected in sequence, and further comprising:

[0014] A pH control unit is installed in the secondary sedimentation tank and is used to control the pH value of the wastewater between 6.5 and 7.0.

[0015] A temperature control unit is installed in the secondary sedimentation tank and is used to control the wastewater temperature at 35℃-40℃.

[0016] The flocculation reaction unit is set in the PAC reaction tank and the PAM reaction tank. The flocculation reaction unit is used to accelerate the sedimentation of suspended solids and colloidal substances. This method does not require complex equipment and process modification. It can be achieved by adjusting existing facilities, which is convenient for promotion and application. It can also reduce the amount of unqualified wastewater generated, reduce the need for buffer tank temporary storage, and achieve the purpose of cost reduction and efficiency improvement.

[0017] Optionally, the pH control unit includes a pH meter installed in the secondary sedimentation tank, a sulfuric acid tank and a sulfuric acid dosing pump installed outside the secondary sedimentation tank, and a first automatic control system electrically connected to the pH meter and the sulfuric acid dosing pump, providing a reliable technical guarantee for improving COD removal efficiency.

[0018] Optionally, the temperature control unit includes a temperature sensor installed in the secondary sedimentation tank, a cooling water pump connected to the secondary sedimentation tank, and a second automatic control system electrically connected to the temperature sensor and the cooling water pump, which avoids the negative impact of temperature fluctuations on microbial activity and chemical reaction efficiency, and improves the stability of system operation.

[0019] Optionally, the flocculation reaction unit includes a PAC tank and a PAC dosing pump connected to the PAC reaction tank, and a PAM tank and a PAM dosing pump connected to the PAM reaction tank, which improves the removal efficiency of suspended solids and colloidal substances and creates favorable conditions for subsequent solid-liquid separation.

[0020] A method for reducing COD by precipitating soluble silicates includes the following steps:

[0021] Step 1: pH and temperature control. The pH and temperature of the biochemically treated silicate wastewater are controlled between 6.5 and 7.0, and between 35℃ and 40℃, so that the silicate is converted into soluble silicate.

[0022] Step 2: Chemical Dosing and Flocculation. Polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the wastewater treated in Step 1 to carry out coagulation and flocculation reactions; the dosage of PAC is 80 mg / L and the dosage of PAM is 2 mg / L.

[0023] Step 3: Sedimentation and sludge removal. The wastewater after flocculation in Step 2 is sent to a sedimentation tank for solid-liquid separation, and the sludge removal frequency of the sedimentation tank is increased to at least 4 times a day, so as to obtain effluent with COD meeting the standards.

[0024] Optionally, the pH value adjustment in step one is achieved through a first automatic control system. The first automatic control system monitors the pH value of the wastewater in real time through a pH meter and interlocks the start and stop of the sulfuric acid dosing pump to stabilize the pH value within the set range.

[0025] The first automatic control system is integrated into the DCS and is used to manually set the pH control parameter range and switch to automatic mode on the DCS interface.

[0026] Optionally, the temperature regulation in step one is achieved through a second automatic control system. The second automatic control system monitors the wastewater temperature in real time through a temperature sensor and interlocks the start and stop of the cooling water pump to stabilize the temperature within the set range.

[0027] The second automatic control system is integrated into the DCS and is used to manually set the temperature control parameter range and switch to automatic mode on the DCS interface, which improves the reliability and repeatability of the processing effect and reduces the risk of unstable processing effect due to temperature fluctuations.

[0028] Optionally, the wastewater in step one originates from the post-coagulation section after treatment by the denitrification unit. By clearly identifying the wastewater source as the post-coagulation section after treatment by the denitrification unit, process parameters and equipment configuration are optimized based on the wastewater characteristics of this specific section.

[0029] Positive and beneficial effects: 1. This system and method for reducing COD by settling soluble silicates can effectively reduce COD and solve the problem of exceeding standards by precisely controlling pH and temperature, and combining the addition of reagents with sludge discharge operations.

[0030] 2. This system and method for reducing COD by settling soluble silicates reduces the amount of substandard wastewater generated, reduces the need for buffer tank storage, and achieves the goal of cost reduction and efficiency improvement.

[0031] 3. The system and method for reducing COD by precipitating soluble silicates. This method does not require complex equipment and process modifications, and can be achieved by adjusting existing facilities, making it easy to promote and apply. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the system of the present invention;

[0034] Figure 2 This is a schematic diagram of the method of the present invention. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0037] Example 1

[0038] like Figure 1 and Figure 2 As shown, a system and method for reducing COD by settling soluble silicates includes a secondary settling tank, a PAC reaction tank, and a PAM reaction tank connected in sequence, and further includes:

[0039] The pH control unit is located in the secondary sedimentation tank and is used to control the pH value of the wastewater between 6.5 and 7.0.

[0040] Temperature control unit, which is installed in the secondary sedimentation tank, is used to control the wastewater temperature at 35℃-40℃.

[0041] The flocculation reaction unit is set in the PAC reaction tank and the PAM reaction tank. The flocculation reaction unit is used to accelerate the sedimentation of suspended solids and colloidal substances. This method does not require complex equipment and process modification. It can be achieved by adjusting the existing facilities, which is convenient for promotion and application. It can also reduce the amount of unqualified wastewater generated, reduce the need for buffer tank temporary storage, and achieve the purpose of cost reduction and efficiency improvement.

[0042] The pH control unit includes a pH meter installed inside the secondary sedimentation tank, a sulfuric acid tank and a sulfuric acid dosing pump installed outside the secondary sedimentation tank, and a first automatic control system electrically connected to the pH meter and the sulfuric acid dosing pump. It adopts a closed-loop control system consisting of the pH meter, sulfuric acid tank, sulfuric acid dosing pump and the first automatic control system. Through real-time monitoring-feedback-adjustment automatic control logic, it ensures that the pH value is stable within the set range, realizes the precision and automation of pH control, overcomes the lag and instability problems of manual dosing, ensures the conditional stability of the silicate conversion reaction, and provides a reliable technical guarantee for improving COD removal efficiency.

[0043] The temperature control unit includes a temperature sensor installed in the secondary sedimentation tank, a cooling water pump connected to the secondary sedimentation tank, and a second automatic control system electrically connected to the temperature sensor and the cooling water pump. This constructs an intelligent temperature control network composed of the temperature sensor, the cooling water pump, and the second automatic control system. Through real-time temperature monitoring and linkage control of the cooling equipment, the optimal temperature environment for the biochemical reaction is maintained, ensuring that the silicate conversion reaction takes place under optimal temperature conditions. This improves the reaction rate and conversion efficiency, while avoiding the negative impact of temperature fluctuations on microbial activity and chemical reaction efficiency, thus enhancing the stability of system operation.

[0044] The flocculation reaction unit includes a PAC tank and a PAC dosing pump connected to the PAC reaction tank, and a PAM tank and a PAM dosing pump connected to the PAM reaction tank, establishing a complete reagent dosing system. This system enables precise dosing and thorough mixing of coagulants and flocculants, optimizes floc formation conditions, improves the removal efficiency of suspended solids and colloidal substances, and creates favorable conditions for subsequent solid-liquid separation.

[0045] Example 2

[0046] A method for reducing COD by precipitating soluble silicates includes the following steps:

[0047] Step 1: pH and temperature control. The pH and temperature of the biochemically treated silicate wastewater are controlled between 6.5 and 7.0, and between 35℃ and 40℃, so that the silicate is converted into soluble silicate.

[0048] Step 2: Chemical Dosing and Flocculation. Polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the wastewater treated in Step 1 to carry out coagulation and flocculation reactions; the dosage of PAC is 80 mg / L and the dosage of PAM is 2 mg / L.

[0049] Step 3: Sedimentation and sludge removal. The wastewater after flocculation in Step 2 is sent to a sedimentation tank for solid-liquid separation, and the sludge removal frequency of the sedimentation tank is increased to at least 4 times a day, so as to obtain effluent with COD meeting the standards.

[0050] In step one, the pH value is adjusted by the first automatic control system. The first automatic control system monitors the pH value of the wastewater in real time through a pH meter and interlocks the start and stop of the sulfuric acid dosing pump to stabilize the pH value within the set range.

[0051] The first automatic control system is integrated into the DCS, which is used to manually set the pH control parameter range and switch to automatic mode on the DCS interface.

[0052] The temperature control in step one is achieved through the second automatic control system. The second automatic control system monitors the wastewater temperature in real time through a temperature sensor and interlocks the start and stop of the cooling water pump to stabilize the temperature within the set range.

[0053] The second automatic control system is integrated into the DCS. It is used to manually set the temperature control parameter range and switch to automatic mode on the DCS interface. By precisely controlling pH and temperature, and coordinating with reagent addition and sludge discharge operations, it can effectively reduce COD and solve the problem of exceeding the standard. It ensures the accuracy and stability of temperature and pH control, provides a constant temperature environment for silicate conversion reaction, significantly improves the reliability and repeatability of treatment effect, and reduces the risk of unstable treatment effect caused by temperature fluctuation.

[0054] The wastewater in step one comes from the post-coagulation section after the denitrification unit. Since the source of the wastewater is clearly the post-coagulation section after the denitrification unit, the process parameters and equipment configuration are optimized based on the characteristics of the wastewater in this specific section.

[0055] The working principle of this invention is as follows:

[0056] By precisely controlling the reaction conditions, soluble silicates that are difficult to remove from wastewater are transformed into a form that can be removed by conventional flocculation and sedimentation, thereby effectively reducing the chemical oxygen demand caused by silicates. The traditional secondary sedimentation tank stage incorporates synergistic regulation of pH and temperature. By precisely controlling the wastewater in a slightly acidic environment of pH 6.5-7.0 and a specific temperature range of 35°C-40°C, optimal thermodynamic and kinetic conditions are provided for the transformation of silicates, allowing them to change from a stable soluble state to an easily settling form. The silicate particles, after undergoing optimized conditions, form dense flocs through charge neutralization and adsorption bridging under the action of chemicals. Finally, high-frequency sludge discharge enhances the solid-liquid separation efficiency of the sedimentation tank, promptly removing the flocs containing silicates and organic matter as sludge from the sludge system, ultimately achieving effluent with COD compliance.

[0057] The above is only used to illustrate the technical solution of the present invention and not to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the spirit and scope of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A system for reducing COD by settling soluble silicates, comprising a secondary settling tank, a PAC reaction tank, and a PAM reaction tank connected in sequence, characterized in that, Also includes: A pH control unit is installed in the secondary sedimentation tank and is used to control the pH value of the wastewater between 6.5 and 7.

0. A temperature control unit is installed in the secondary sedimentation tank and is used to control the wastewater temperature at 35℃-40℃. A flocculation reaction unit is provided in the PAC reaction tank and the PAM reaction tank. The flocculation reaction unit is used to accelerate the precipitation of suspended solids and colloidal substances.

2. The system for reducing COD by precipitating soluble silicates according to claim 1, characterized in that: The pH control unit includes a pH meter installed inside the secondary sedimentation tank, a sulfuric acid tank and a sulfuric acid dosing pump installed outside the secondary sedimentation tank, and a first automatic control system electrically connected to the pH meter and the sulfuric acid dosing pump.

3. The system for reducing COD by precipitating soluble silicates according to claim 1, characterized in that: The temperature control unit includes a temperature sensor installed in the secondary sedimentation tank, a cooling water pump connected to the secondary sedimentation tank, and a second automatic control system electrically connected to the temperature sensor and the cooling water pump.

4. The system for reducing COD by precipitating soluble silicates according to claim 1, characterized in that: The flocculation reaction unit includes a PAC tank and a PAC dosing pump connected to the PAC reaction tank, and a PAM tank and a PAM dosing pump connected to the PAM reaction tank.

5. A method for reducing COD by precipitating soluble silicates according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1: pH and temperature control. The pH and temperature of the biochemically treated silicate wastewater are controlled between 6.5 and 7.0, and between 35℃ and 40℃, so that the silicate is converted into soluble silicate. Step 2: Chemical Dosing and Flocculation. Polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the wastewater treated in Step 1 to carry out coagulation and flocculation reactions; the dosage of PAC is 80 mg / L and the dosage of PAM is 2 mg / L. Step 3: Sedimentation and sludge removal. The wastewater after flocculation in Step 2 is sent to a sedimentation tank for solid-liquid separation, and the sludge removal frequency of the sedimentation tank is increased to at least 4 times a day, so as to obtain effluent with COD meeting the standards.

6. The method for reducing COD by precipitating soluble silicates according to claim 5, characterized in that: The pH value regulation in step one is achieved through the first automatic control system. The first automatic control system monitors the pH value of the wastewater in real time through a pH meter and interlocks the start and stop of the sulfuric acid dosing pump to stabilize the pH value within the set range. The first automatic control system is integrated into the DCS and is used to manually set the pH control parameter range and switch to automatic mode on the DCS interface.

7. The method for reducing COD by precipitating soluble silicates according to claim 5, characterized in that: The temperature regulation in step one is achieved through a second automatic control system. The second automatic control system monitors the wastewater temperature in real time through a temperature sensor and interlocks the start and stop of the cooling water pump to stabilize the temperature within the set range. The second automatic control system is integrated into the DCS and is used to manually set the temperature control parameter range and switch to automatic mode on the DCS interface.

8. The method for reducing COD by precipitating soluble silicates according to claim 5, characterized in that: The wastewater in step one comes from the post-coagulation section after treatment by the denitrification device.

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