Method for treating wastewater containing oxalic acid cod and applications thereof

Abstract

The application relates to the field of environmental protection, and discloses a treatment method of oxalic acid-containing COD wastewater and application thereof. The method comprises the following steps: adding a calcium-containing neutralizing agent into the oxalic acid-containing COD wastewater to perform a contact reaction, then performing membrane separation to obtain slurry solid and first filtrate, then performing sedimentation on the slurry solid, and performing solid-liquid separation to obtain calcium oxalate precipitation and second filtrate; the pH of the oxalic acid-containing COD wastewater is below 1.5, and the COD content is above 2000 mg / L. The treatment method can effectively reduce the COD content of the oxalic acid-containing wastewater, ensure that the COD content of supernatant after treatment is stable and meets the standard, and can recover oxalic acid in the wastewater, so that the recycling of resources is realized.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, and discloses a method for treating oxalic acid-containing COD wastewater and its application. Background Technology

[0002] Currently, the main treatment processes and methods for COD wastewater include electrolysis, incineration, multi-effect evaporation concentration and crystallization, and biological methods. Electrolysis can treat both metal-containing and COD-containing wastewater, but it is affected by water quality and has certain concentration requirements for pollutants, making it unsuitable for wastewater with low and fluctuating concentrations. Incineration treats wastewater using incineration technology, suitable for treating non-volatile and non-degradable wastewater, but it has high operating costs, is unsuitable for low-COD wastewater, and produces harmful gases. Multi-effect evaporation concentration and crystallization is a chemical unit operation method that uses heating to evaporate part of the solvent, separating water and organic matter. Because multi-effect evaporation concentration and crystallization has different treatment effects on wastewater of different qualities and has high energy consumption, it is unsuitable for treating low-concentration wastewater and is therefore mostly used in the pretreatment stage of wastewater. The biological process, also known as the sequencing batch activated sludge process, is an activated sludge wastewater treatment technology that operates in an intermittent aeration mode. During operation, it operates in an orderly and intermittent manner, alternating between processes. The COD removal rate is between 32.2% and 76.2%. However, for industrial wastewater with low COD concentrations, the process route is long and the operating cost is high.

[0003] It is evident that the above methods are not applicable to the treatment of industrial wastewater with different COD contents, especially acidic COD wastewater. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of the lack of effective methods for treating oxalic acid-containing COD wastewater in the prior art, and to provide a method for treating oxalic acid-containing COD wastewater. The treatment method provided by this invention can effectively reduce the COD content of oxalic acid-containing wastewater, ensure that the COD content of the supernatant after treatment is stably within the standard, and simultaneously recover oxalic acid from the wastewater, achieving resource recycling.

[0005] To achieve the above objectives, the present invention provides a method for treating oxalic acid-containing COD wastewater. The method includes: adding a calcium-containing neutralizing agent to the oxalic acid-containing COD wastewater for a contact reaction, followed by membrane separation to obtain a slurry solid and a first filtrate, then settling the slurry solid, and after solid-liquid separation, obtaining calcium oxalate precipitate and a second filtrate; wherein the pH of the oxalic acid-containing COD wastewater is below 1.5 and the COD content is above 2000 mg / L.

[0006] A second aspect of the present invention provides the application of the treatment method described herein in waste liquid treatment.

[0007] The treatment method provided by this invention utilizes a combined process of neutralization, sedimentation, and membrane separation. This effectively reduces the COD content of oxalic acid-containing wastewater, ensures the COD content of the supernatant meets standards after treatment, and simultaneously recovers oxalic acid from the wastewater, achieving resource recycling. Furthermore, the treatment method requires fewer pieces of equipment, has lower raw material costs, simpler procedures, and is easier to operate. It significantly shortens treatment time, improves treatment efficiency, and ultimately achieves a stable and controllable treatment process for acidic COD wastewater. Attached Figure Description

[0008] Figure 1 This is a flow chart for the treatment of COD-containing wastewater containing oxalic acid. Detailed Implementation

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0010] This invention provides a method for treating oxalic acid-containing COD wastewater. The method includes: adding a calcium-containing neutralizing agent to the oxalic acid-containing COD wastewater for a contact reaction, followed by membrane separation to obtain a slurry solid and a first filtrate, then settling the slurry solid, and finally separating the solid and liquid to obtain calcium oxalate precipitate and a second filtrate; wherein the pH of the oxalic acid-containing COD wastewater is below 1.5 and the COD content is above 2000 mg / L.

[0011] According to a preferred embodiment of the present invention, the pH of the oxalic acid-containing COD wastewater is 0.1-0.6, and the COD content is 3500-5000 mg / L.

[0012] In this invention, there are no special requirements for the type of calcium neutralizing agent. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the calcium neutralizing agent is one or more of calcium hydroxide and calcium oxide.

[0013] In this invention, the dosage of the calcium-containing neutralizing agent can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the dosage of the calcium-containing neutralizing agent is such that the pH of the solution after the contact reaction is 7-8. Controlling the pH of the solution within the aforementioned range is beneficial for oxalic acid in COD wastewater to precipitate with the calcium-containing neutralizing agent and precipitate out in solid form in the solution, facilitating subsequent separation and recovery.

[0014] In this invention, the contact reaction is carried out under dynamic conditions. There are no special requirements for the dynamic conditions. For example, the contact reaction can be carried out under stirring conditions. There are no special requirements for the stirring speed, which can be selected according to actual needs. This will not be elaborated here.

[0015] In this invention, there are no special requirements for the instruments and equipment used in the contact reaction. Commonly used reaction instruments are applicable to this invention. For example, the contact reaction can be carried out in a neutralization reaction tank.

[0016] In this invention, there are no special requirements for the contact reaction time, which can be selected according to actual needs. For example, the reaction time can be 25-300 min, preferably 30-180 min.

[0017] In this invention, there are no special requirements for the type of membrane separation equipment. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the membrane separation is performed using an expanded membrane filtration device.

[0018] In this invention, there are no special requirements for the instruments and equipment used in the membrane separation process. Commonly used membrane separation equipment can be applied to this invention. According to a preferred embodiment of this invention, a swirling membrane filtration device can be used for the membrane separation. Preferably, the swirling membrane filtration device is capable of automatic backwashing and continuous feeding.

[0019] In this invention, after the contact reaction is completed in the neutralization reaction tank, the suspension in the neutralization reaction tank can be sent to the membrane separation equipment for membrane separation using a slurry pump. There are no special requirements for the type of slurry pump; any commonly used pump can be used in this invention, and it can be selected according to actual needs. Further details are omitted here.

[0020] In this invention, there are no special requirements for the sedimentation method. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the sedimentation is natural sedimentation. By using natural sedimentation, the solids in the slurry first settle to the bottom under the action of gravity, and then further solid-liquid separation is carried out. This facilitates faster completion of the subsequent solid-liquid separation and reduces energy consumption during the subsequent solid-liquid separation, avoiding unnecessary energy waste.

[0021] In this invention, there are no special requirements for the instruments and equipment used in the sedimentation process, and they can be selected according to actual needs. According to a preferred embodiment of this invention, the sedimentation is carried out in a sedimentation tank.

[0022] In this invention, there are no special requirements for the solid-liquid separation method. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the solid-liquid separation is centrifugation.

[0023] In this invention, there are no special requirements for the instruments and equipment used for solid-liquid separation; commonly used solid-liquid separation equipment is suitable for this invention. According to a preferred embodiment of this invention, a centrifuge can be used for the solid-liquid separation. There are no special requirements for the type of centrifuge; commonly used centrifuges are suitable for this invention, and can be selected according to actual needs, which will not be elaborated here.

[0024] In this invention, after the slurry solid settles in the settling tank, it can be pumped to a centrifuge for solid-liquid separation. There are no special requirements for the type of slurry pump; any commonly used pump can be used in this invention and can be selected according to actual needs. Further details are omitted here.

[0025] In this invention, after the solid-liquid separation is completed, the solid-phase calcium oxalate precipitate is recovered, and the second filtrate can be reused in the contact reaction.

[0026] According to a preferred embodiment of the present invention, the method for treating oxalic acid-containing COD wastewater further includes: detecting the COD content of the first filtrate; if the COD content is unqualified, returning the first filtrate to carry out the contact reaction; if the COD content is qualified, directly discharging the first filtrate.

[0027] In this invention, after membrane separation, the COD content of the first filtrate is detected, and different treatments are applied based on the COD content analysis. If the COD content of the filtrate is within acceptable limits, it can be discharged or used in the next operation step; if the COD content is outside acceptable limits, it is reused in the neutralization reaction tank. In this invention, a COD content ≤ 100 mg / L is considered acceptable.

[0028] The treatment method provided by this invention utilizes a combined process of neutralization, sedimentation, and membrane separation. This effectively reduces the COD content of wastewater, ensures the COD content of the supernatant meets standards after treatment, and simultaneously recovers oxalic acid from the wastewater, achieving resource recycling. Furthermore, the treatment method requires fewer pieces of equipment, has lower raw material costs, simpler procedures, and is easier to operate. It significantly shortens treatment time, improves efficiency, and ultimately achieves a stable and controllable treatment process for acidic COD wastewater.

[0029] Example 1 Wastewater containing oxalic acid and COD was collected from a catalyst production process. The treatment process is as follows: Figure 1 As shown, the specific steps include: 1) Take 500 ml of COD-containing wastewater samples twice, and label them A1 and A2 respectively. Keep the original sample A1 as a control sample.

[0030] 2) Transfer sample A2 to a neutralization reaction vessel, add 24.5 g of calcium oxide, stir thoroughly to bring the pH of the solution to 7.5, and react for 30 minutes.

[0031] 3) After the reaction, the suspension in the neutralization reaction tank is sent to an expansion membrane filter that can automatically backwash and continuously feed for filtration using a slurry pump.

[0032] 4) The clarified liquid separated by the membrane filtration equipment enters the clarified liquid storage tank and its COD content is analyzed. If the COD content is qualified, it is discharged or used for the next operation process. If the COD content is not qualified, it is reused in the neutralization reaction. A sample of the clarified liquid is taken and numbered A3. Water sample A3 is sent to a testing agency to test its pH and COD content. The results are shown in Table 1.

[0033] 5) The concentrated slurry separated by the diaphragm filter is transferred to the settling tank, left to stand for 2 hours, and then separated into layers. It is then pumped to a centrifuge for centrifugation. The solid precipitate (calcium oxalate, etc.) is recovered and reused, and the filtrate is returned to the neutralization reaction tank for further reaction.

[0034] Example 2 Another type of wastewater containing oxalic acid and COD is taken from the production process of a certain catalyst. The treatment process is as follows: Figure 1 As shown, the specific steps include: 1) Take 500 ml of COD-containing wastewater samples twice, and label them B1 and B2 respectively. Keep the original sample B1 as a control sample.

[0035] 2) Transfer sample B2 to a neutralization reaction vessel, add 24.5 g of calcium oxide, stir thoroughly to bring the pH of the solution to 7.7, and react for 30 minutes.

[0036] 3) After the reaction, the suspension in the neutralization reaction tank is sent to an expansion membrane filter that can automatically backwash and continuously feed for filtration using a slurry pump.

[0037] 4) The clarified liquid separated by the membrane filtration equipment enters the clarified liquid storage tank and its COD content is analyzed. If the COD content is qualified, it is discharged or used for the next operation process. If the COD content is not qualified, it is reused in the neutralization reaction. A sample of the clarified liquid is taken and labeled B3. Water sample B3 is sent to a testing agency to test its pH and COD content. The results are shown in Table 1.

[0038] 5) The concentrated slurry separated by the diaphragm filter is transferred to the settling tank, left to stand for 2 hours, and then separated into layers. It is then pumped to a centrifuge for centrifugation. The solid precipitate (calcium oxalate, etc.) is recovered and reused, and the filtrate is returned to the neutralization reaction tank for further reaction.

[0039] Example 3 The difference compared to Example 1 is that 19.6 grams of calcium oxide were added.

[0040] A sample of the clear liquid separated by the diaphragm filter was taken and labeled A4. Water sample A4 was sent to a testing institution to test its pH and COD content. The results are shown in Table 1.

[0041] Example 4 The difference compared to Example 2 is that 18.4 grams of calcium oxide were added.

[0042] A sample of the clear liquid separated by the diaphragm filter was taken and labeled B4. Water sample B4 was sent to a testing institution to test its pH and COD content. The results are shown in Table 1.

[0043] Example 5 The difference from Example 1 is that the neutralizing agent added is calcium hydroxide.

[0044] A sample of the clear liquid separated by the diaphragm filter was taken and labeled A5. Water sample A5 was sent to a testing institution to test its pH and COD content. The results are shown in Table 1.

[0045] Example 6 The difference from Example 2 is that the neutralizing agent added is calcium hydroxide.

[0046] A sample of the clear liquid separated by the diaphragm filter was taken and labeled B5. Water sample B5 was sent to a testing institution to test its pH and COD content. The results are shown in Table 1.

[0047] Comparative Example 1 The difference from Example 1 is that the neutralizing agent added is sodium hydroxide.

[0048] A sample of the clear liquid separated by the diaphragm filter was taken and labeled A6. Water sample A6 was sent to a testing institution to test its pH and COD content. The results are shown in Table 1.

[0049] Comparative Example 2 The difference from Example 2 is that the neutralizing agent added is sodium hydroxide.

[0050] A sample of the clear liquid separated by the diaphragm filter was taken and labeled B6. Water sample B6 was sent to a testing institution to test its pH and COD content. The results are shown in Table 1.

[0051] Table 1 Sample number Sample properties pH value COD content, mg / L A1 Colorless, clear 0.1 4290 A3 Colorless, clear 7.5 44 A4 Colorless, clear 7.0 97 A5 Colorless, clear 7.5 89 A6 Colorless, clear 7.5 286 B1 Colorless, clear 0.1 4430 B3 Colorless, clear 7.7 47 B4 Colorless, clear 6.5 114 B5 Colorless, clear 7.5 93 B6 Colorless, clear 7.5 295 The preferred embodiments of the present invention have been described above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating oxalic acid-containing COD wastewater, characterized in that, The method includes: A calcium-containing neutralizing agent is added to oxalic acid-containing COD wastewater for a contact reaction, followed by membrane separation to obtain a slurry solid and a first filtrate. The slurry solid is then settled, and after solid-liquid separation, calcium oxalate precipitate and a second filtrate are obtained. The oxalic acid-containing COD wastewater has a pH below 1.5 and a COD content above 2000 mg / L.

2. The method according to claim 1, wherein, The oxalic acid-containing COD wastewater has a pH of 0.1-0.6 and a COD content of 3500-5000 mg / L.

3. The method according to claim 1 or 2, wherein, The calcium-containing neutralizing agent is one or more of calcium hydroxide and calcium oxide.

4. The method according to any one of claims 1-3, wherein, The amount of calcium-containing neutralizing agent used ensures that the pH of the solution is 7-8 after the contact reaction is completed.

5. The method according to any one of claims 1-4, wherein, The contact reaction takes place under dynamic conditions; and / or The contact reaction is carried out in a neutralization reaction tank.

6. The method according to any one of claims 1-5, wherein, The membrane separation is performed using an expanded membrane filtration device. Preferably, the expanded membrane filter is capable of automatic backwashing and continuous feeding.

7. The method according to any one of claims 1-6, wherein, The settlement is natural settlement; and / or The settling takes place in a settling tank.

8. The method according to any one of claims 1-7, wherein, The solid-liquid separation is performed by centrifugation; and / or The solid-liquid separation was performed using a centrifuge.

9. The method according to any one of claims 1-8, characterized in that, The method further includes: detecting the COD content of the first filtrate; if the COD content is unqualified, returning the first filtrate to carry out the contact reaction; if the COD content is qualified, directly discharging the first filtrate.

10. The application of the method according to any one of claims 1-9 in wastewater treatment.

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