Process for treating maleic anhydride wastewater at low cost

Abstract

The invention relates to the field of industrial wastewater treatment, in particular to a process for low-cost treatment of maleic anhydride wastewater, which realizes low-cost treatment of refractory COD (Chemical Oxygen Demand) by utilizing the combination of calcium chloride, ferric trichloride and PAM (Polyacrylamide); the treatment steps roughly comprise charge adjustment, coagulation and flocculation and ozone oxidation; compared with an existing treatment mode adopting a traditional demulsifier, a large amount of COD (Chemical Oxygen Demand) is removed before ozone is treated by adopting the scheme, the ozone consumption is reduced, effective ozone adding is ensured, and the normal operation of a depth line function is realized; the problem that the maleic anhydride wastewater contains refractory COD (Chemical Oxygen Demand) is solved at low cost; according to the process, data confirms that the maleic anhydride wastewater is treated at relatively low cost; reuse of reclaimed water is realized; and qualified discharge is ensured.

Description

Technical Field

[0001] The invention relates to the field of industrial wastewater treatment, and in particular to a process for treating maleic anhydride wastewater containing refractory COD at low cost by combining calcium chloride, ferric chloride and PAM. Background Art

[0002] n-Butane is partially oxidized by air under the action of vanadium-phosphorus-oxygen catalyst to form maleic anhydride. In the reaction process, there are problems with the control of various conditions, including carbon four separation, n-butane oxidation, solvent absorption and analysis, product refining and other processes. Due to the operation of the maleic anhydride unit, the wastewater will contain organic components such as maleic acid, phthalic anhydride, and dibutyl phthalate DBP. The emulsification and dispersion properties of some of the above components lead to an increase in the COD of the effluent, and the reuse of reclaimed water and the compliance of the system with emission standards are also great challenges. According to current market research, the treatment of maleic anhydride wastewater is a common problem, and the cost of adding demulsifiers is high.

[0003] In the current treatment process, anaerobic, biochemical and deep processes are used to treat the wastewater. However, lipids and phthalic anhydride substances in maleic anhydride wastewater penetrate in the biochemical stage and interfere with coagulation and flocculation in the deep treatment stage, so that the COD of anaerobic effluent is in the range of 1500-1700 mg / L, the COD of biochemical effluent is still raised to 800 mg / L, the high-density effluent T-Fe is raised to 30 mg / L, and the COD of ozone contact tank effluent is raised to 620 mg / L. All the external discharge pressure is given to the ozone generator. Under the condition of large water volume operation and treatment, the deep ozone addition far exceeds the design capacity, and the external discharge faces great difficulties.

[0004] The treatment cost of using traditional demulsifiers in high-density sedimentation tanks in existing processes is: Daily processing cost: 200g / m3*40m3*24*15000=2880 (yuan); Cost per ton of water: 2880 (Yuan) / (40m 3 *24h) = 3 (yuan) / ton; Using general demulsification technology, according to the maleic anhydride raw water 40m 3 / h, the unit price of demulsifier is 15,000 yuan / ton, not counting the acid and alkali costs for pH adjustment, the daily demulsification cost is 2,880 yuan, and the cost per ton of water is 3 / ton.

[0005] At present, one of the common methods of high-density wastewater treatment is coagulation and flocculation through iron salts. It can treat a large amount of COD at the front end of the ozone contact tank. However, during use, the colloid precipitation of iron hydroxide and the colloid adsorption of COD affect the biochemical treatment effect, reduce the colloid and iron pollution of the regenerated water membrane, and achieve standard discharge and reuse of reclaimed water at low cost. The problem needs to be solved. Summary of the invention

[0006] In view of the status of the above-mentioned prior art, the present invention provides a low-cost process for treating maleic anhydride wastewater by comprehensively understanding the characteristics of maleic anhydride wastewater and starting from the wastewater treatment mechanism. The process can restore the coagulation and flocculation functions through charge regulation and iron hydroxide colloidal precipitation, thereby reducing the cost of maleic anhydride wastewater treatment, achieving large-scale removal of COD at the front end of the ozone contact tank, reducing ozone consumption, achieving normal function of the depth line, ensuring qualified external discharge, and reusing the reclaimed water.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a process for treating maleic anhydride wastewater at a low cost, which specifically comprises the following steps: The COD of the maleic anhydride wastewater after biochemical treatment is 800 mg / L-820 mg / L, and the pH of the effluent from the secondary sedimentation tank is in the range of 8-8.5; Step 1, adjusting the charge, supplementing the ion concentration by adding calcium chloride, and adding calcium chloride to the biochemical wastewater so that the addition amount is 150~200 ppm; Step 2, coagulation and flocculation, taking the organic wastewater after the charge is adjusted in step 1, adding a flocculant ferric chloride, wherein the concentration of ferric chloride used is 150-200 mg / L, and the stirring speed is 200-220 rpm. After the coagulation is completed, 1-2 mg / L of a flocculant PAM is added, and the stirring speed is 40-50 rpm, so that the high-density sedimentation tank can achieve the coagulation of iron hydroxide colloids, and the coagulation and flocculation are completed at 20-25°C; the COD of the water effluent from the high-density sedimentation tank after flocculation and sedimentation is partially removed, thereby reducing the difficulty of treatment in the ozone contact tank; Step 3: Ozone oxidation: ozone is continuously introduced into the water after the coagulation and flocculation treatment in step 2 to further oxidize the remaining COD.

[0008] Furthermore, based on the above scheme, in step 3, the COD can be reduced from 800 mg / L to 200 mg / L through the high-density sedimentation tank and the ozone contact tank.

[0009] Compared with the existing traditional demulsifier treatment method, the present invention has the following beneficial effects: This solution can remove a large amount of COD before ozone, reduce ozone consumption, ensure effective ozone addition, and achieve normal function of the depth line; it can solve the problem of maleic anhydride wastewater containing difficult-to-degrade COD at a low cost; The daily processing cost of this technology is: 200g / m3*400m3*24*1400=2688 (yuan); Cost of treating one ton of water: 2688 yuan / (400m3*24h)=0.28 yuan / ton; Using this technology, based on the calculation of 400m3 / h of wastewater per day on a single line, the daily cost of calcium chloride is 2,688 yuan, and the cost per ton of water is 0.28 yuan / ton. The process has been proven by data to achieve relatively low-cost treatment of maleic anhydride wastewater, reuse of reclaimed water, and ensure that the discharge is qualified. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a comparison chart of demulsification after adding different concentrations of calcium chloride to the biochemical pool of the present invention.

[0011] Figure 2 This is the COD curve of the effluent after adding different concentrations of calcium chloride to the biochemical pool.

[0012] Figure 3 A comparison chart of the coagulation and flocculation effluent produced by a demulsifier and the coagulation and flocculation effluent produced by the solution of the present invention. DETAILED DESCRIPTION

[0013] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0014] Low-cost process for treating maleic anhydride wastewater. Lipids and phthalic anhydride substances in maleic anhydride wastewater penetrate in the biochemical stage and interfere with coagulation and flocculation in the deep treatment stage, so that the anaerobic effluent COD is in the range of 1500-1700 mg / L, the biochemical effluent COD is still raised to 800 mg / L, and the effluent pH of the secondary sedimentation tank is 8~8.5.

[0015] The specific steps include: Step 1, adjusting the charge, supplementing the ion concentration by adding calcium chloride, and adding calcium chloride to the biochemical wastewater so that the addition amount is 150~200 ppm; Step 2, coagulation and flocculation, taking the organic wastewater after the charge is adjusted in step 1, adding a flocculant ferric chloride, wherein the concentration of ferric chloride used is 150 mg / L, and the stirring speed is set to 200 rpm. After the coagulation is completed, 1-2 mg / L of a flocculant PAM is added, and the stirring speed is 40 rpm, so that the high-density sedimentation tank can achieve the coagulation of the iron hydroxide colloid, and the coagulation and flocculation are completed at 25°C; the COD of the water effluent from the high-density sedimentation tank after flocculation and sedimentation is partially removed; Step 3, ozone oxidation, continuously passing ozone into the water after the coagulation and flocculation treatment in step 2 to further oxidize the remaining COD; Based on the above scheme, in step 3, COD can be reduced from 800 mg / L to 200 mg / L through the high-density sedimentation tank and ozone contact tank.

[0016] The following are several embodiments.

[0017] Example 1 The physicochemical characteristics of the effluent from the secondary sedimentation tank containing the difficult-to-degrade COD in this embodiment are as follows: pH 8.2, COD concentration 800 mg / L.

[0018] Step 1: Adjust the charge by adding calcium chloride to the wastewater after biochemical treatment so that the dosage is 200 ppm; Step 2, coagulation and flocculation, taking the organic wastewater after the charge is adjusted in step 1, adding a flocculant ferric chloride, wherein the concentration of ferric chloride used is 150 mg / L, and the stirring speed is set to 200 rpm. After the coagulation is completed, 1 mg / L of a flocculant PAM is added, and the stirring speed is set to 40 rpm, so that the high-density sedimentation tank can achieve the coagulation of iron hydroxide colloids, and the coagulation and flocculation are completed at 25°C; the COD of the water effluent from the high-density sedimentation tank after flocculation and sedimentation is partially removed; Step 3: Ozone oxidation: ozone is continuously introduced into the water after the coagulation and flocculation treatment in step 2 to further oxidize the remaining COD.

[0019] Example 2 The physicochemical characteristics of the effluent from the secondary sedimentation tank containing the difficult-to-degrade COD in this embodiment are as follows: pH 8, COD concentration 820 mg / L.

[0020] Step 1: Adjust the charge by adding calcium chloride to the wastewater after biochemical treatment so that the dosage is 150 ppm; Step 2, coagulation and flocculation, taking the organic wastewater after the charge is adjusted in step 2, adding a flocculant ferric chloride, wherein the concentration of ferric chloride used is 200 mg / L, and the stirring speed is set to 200 rpm. After the coagulation is completed, 1.5 mg / L of a flocculant PAM is added, and the stirring speed is set to 40 rpm, so that the high-density sedimentation tank can achieve the coagulation of the iron hydroxide colloid, and the coagulation and flocculation are completed at 25°C; the COD of the water effluent from the high-density sedimentation tank after flocculation and sedimentation is partially removed; Step 3: Ozone oxidation: ozone is continuously introduced into the water after the coagulation and flocculation treatment in step 3 to further oxidize the remaining COD.

[0021] Comparative Example 1 Step 1, coagulation and flocculation, take the organic wastewater and add a demulsifier, wherein the concentration of the demulsifier is 200 mg / L, and after coagulation is completed, add 1.5 mg / L of flocculant PAM to complete coagulation and flocculation.

[0022] It has been determined that after coagulation and flocculation, the COD of wastewater can be reduced to 500 mg / L. Figure 2 As shown in the attached figure, the flocculation and sedimentation effect is significantly improved after adjusting the charge, and the flocculation effluent is clearer than that of the demulsifier. Figure 3 As shown, the probability of membrane fouling is reduced.

[0023] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0024] The protection scope of the present invention is not limited to this, and any equivalent transformation and modification based on the technical solution of the present invention belongs to the protection scope of the technical solution of the present invention.

Claims

1. A process for treating maleic anhydride wastewater at low cost, characterized in that: The specific steps include: Step 1, adjusting the charge, supplementing the ion concentration by adding calcium chloride, and adding calcium chloride to the biochemical wastewater so that the addition amount is 150~200 ppm; Step 2, coagulation and flocculation, taking the organic wastewater after the charge is adjusted in step 1, adding a flocculant ferric chloride, wherein the concentration of ferric chloride used is 150-200 mg / L, and the stirring speed is set to 200-220 rpm. After the coagulation is completed, 1-2 mg / L of a flocculant PAM is added, and the stirring speed is set to 40-50 rpm, so that the high-density sedimentation tank can achieve the coagulation of the iron hydroxide colloid, and the coagulation and flocculation are completed at 20-25°C; the COD of the water effluent from the high-density sedimentation tank after flocculation and sedimentation is partially removed; Step 3: Ozone oxidation: ozone is continuously introduced into the water after the coagulation and flocculation treatment in step 2 to further oxidize the remaining COD.

2. A low-cost process for treating maleic anhydride wastewater according to claim 1, characterized in that: In step 3, COD can be reduced from 800 mg / L to 200 mg / L after passing through the high-density sedimentation tank and the ozone contact tank.

3. A low-cost process for treating maleic anhydride wastewater according to claim 1, characterized in that: The COD of the maleic anhydride wastewater after biochemical treatment is 800 mg / L-820 mg / L, and the pH of the effluent from the secondary sedimentation tank is in the range of 8-8.5.

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