Ethyl hexanoate production wastewater treatment method

Abstract

The invention discloses an ethyl hexanoate production wastewater treatment method, which comprises: S1, sequentially carrying out an oxidation-reduction reaction, pH value adjustment and flocculation precipitation treatment on caproic acid production process wastewater through a first treatment system to obtain pretreated effluent; s2, mixing the pretreated effluent in the S1 and the ethyl hexanoate production wastewater, feeding the mixture into a second treatment system, and sequentially carrying out pH value adjustment, anaerobic bacteria treatment, denitrifying bacteria treatment, aerobic bacteria treatment and anoxic denitrification treatment to obtain standard water and reflux water; s3, the reflux water in the S2 flows back to a second treatment system through a pipeline, so that the reflux water, the pretreated effluent and the ethyl hexanoate production wastewater are mixed, and the reflux water is subjected to secondary treatment. According to the method, a chemical precipitation method, an iron-carbon micro-electrolysis method and a biological treatment method are combined, so that the operation management cost is reduced, the effluent quality is ensured to be stable and reach the standard, and the pollution to the water ecological environment is reduced.

Description

Technical Field

[0001] The present invention relates to the field of production wastewater treatment in the chemical industry, and particularly to a method for treating wastewater from ethyl hexanoate production. Background Art

[0002] Ethyl hexanoate has a fruity aroma like pineapple and banana as well as a wine aroma, and is commonly used in the preparation of fruity edible flavors such as apple, pineapple, banana, etc. and wine flavors such as brandy and liquor. The production of ethyl hexanoate generally adopts acid-alcohol esterification reaction and rectification technology. First, sec-octanol and concentrated nitric acid react under the catalysis of V2O5 to generate the main product hexanoic acid, and then an esterification synthesis reaction is carried out with ethanol, and the ethyl hexanoate product is obtained by vacuum rectification.

[0003] The wastewater from ethyl hexanoate production mainly comes from the wastewater from hexanoic acid production process, the wastewater from ethyl hexanoate synthesis process, and the wastewater from equipment and floor cleaning. Among them, the wastewater from hexanoic acid production process contains residual nitric acid and reaction by-products (such as acetic acid, butyric acid, valeric acid, heptanoic acid, etc.), and has the characteristics of high COD, high nitrate nitrogen, high total nitrogen, and low pH value. Among them, the highest COD can reach hundreds of thousands of milligrams per liter, the pH value can be as low as 0.5, and the highest nitrate nitrogen can reach thousands of milligrams per liter. The various water quality indicators of the wastewater from ethyl hexanoate synthesis process are relatively low, but also have the characteristics of high COD and low pH value. In summary, according to the nature of such wastewater, the wastewater from ethyl hexanoate production is one of the relatively difficult organic wastewaters to treat.

[0004] In view of the characteristics of high COD and low pH value of the wastewater from hexanoic acid production process, at present, the treatment of wastewater from hexanoic acid production mainly involves adding a large amount of alkaline agents such as NaOH and Ca(OH)2 to the wastewater. After the too low pH value is neutralized, conventional processes such as biochemical treatment are used to degrade COD, denitrify, etc. Adding a large amount of alkaline agents will significantly increase the daily operating cost of the sewage treatment station of ethyl hexanoate production enterprises, and thus bring a heavy cost pressure to the enterprises. In addition, too much Na + , Ca 2+And other salts can affect the stable operation of the subsequent biochemical system. For example, Chinese Patent No. CN106745979A discloses a method for treating acidic wastewater from strontium ferrite pre-sintered material. Aiming at the problems of the existing acidic wastewater treatment process, such as many process steps, complex operation, high equipment requirements and high cost, the present invention provides a method for treating acidic wastewater from strontium ferrite pre-sintered material. a. Discharge the acidic wastewater from strontium ferrite pre-sintered material into a grit chamber. After standing for 10-12 hours, the supernatant is discharged into a neutralization aeration tank; b. Add sodium hydroxide to the neutralization aeration tank to adjust the pH value of the solution to 6-9; c. Transfer the water in the neutralization aeration tank to a secondary sedimentation tank, add a sedimentation agent, stand for sedimentation, and the supernatant is recycled or discharged for treatment. The treatment of the acidic wastewater in this patent mainly involves adding a large amount of alkaline agents such as NaOH and Ca(OH)₂ to the wastewater. After the too low pH is neutralized, conventional processes such as biochemical treatment are used to degrade COD, denitrify, etc. The large amount of alkaline agents added will significantly increase the daily operation cost of the enterprise's sewage treatment station, thus bringing a heavy cost pressure to the enterprise.

[0005] Therefore, it has become a problem worthy of research to provide a method for treating ethyl hexanoate production wastewater that can improve the wastewater treatment efficiency, reduce the wastewater treatment cost, and ensure that the effluent of the wastewater meets the standards stably. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for treating ethyl hexanoate production wastewater. The pretreatment process of the wastewater from the present invention's hexanoic acid production adopts the iron-carbon micro-electrolysis + neutralization-flocculation sedimentation tank process. After the pretreatment effluent is mixed with the wastewater from ethyl hexanoate synthesis, the neutralization + UASB + A / O process is adopted. It can not only effectively degrade COD, but also reduce the amount of alkali added for neutralization, improve the wastewater treatment efficiency, reduce the wastewater treatment cost, and ensure that the effluent of the wastewater meets the standards stably. The present invention has the characteristics of high treatment efficiency, stable operation, saving operation cost, and convenient management.

[0007] The purpose of the present invention is achieved as follows: A method for treating ethyl hexanoate production wastewater, comprising the following steps: S1. Pass the wastewater from the hexanoic acid production process through a first treatment system to carry out oxidation-reduction reaction, pH adjustment, and flocculation sedimentation treatment in sequence to degrade the COD in the wastewater from the hexanoic acid production process and obtain the pretreatment effluent; S2. Mix the pretreatment effluent in S1 with the ethyl hexanoate production wastewater and send it to a second treatment system to carry out pH adjustment, anaerobic bacteria treatment, denitrifying bacteria treatment, aerobic bacteria treatment, and anoxic denitrification treatment in sequence to degrade the organic matter in the pretreatment effluent, the ethyl hexanoate production wastewater, and the reflux effluent, and obtain the qualified water and the reflux water; S3. Recycle the reflux water in S2 to the second treatment system through a pipeline, so that the reflux water, the pretreated effluent, and the ethyl hexanoate production wastewater are mixed, and the reflux water is treated for the second time.

[0008] The first treatment system includes a 1# regulating tank 1, a 1# lift pump 2 located in the 1# regulating tank 1, a 1# neutralization tank 4 connected to the 1# lift pump 2 through a pipeline, a 2# lift pump 5 located in the 1# neutralization tank 4, an iron-carbon microelectrolysis tower 7 connected to the 2# lift pump 5 through a pipeline, and a neutralization-flocculation sedimentation tank connected to the outlet end of the iron-carbon microelectrolysis tower 7 through a pipeline. The outlet end of the neutralization-flocculation sedimentation tank is connected to the second treatment system through a pipeline.

[0009] The neutralization-flocculation sedimentation tank includes a neutralization zone 12 connected to the top outlet end of the iron-carbon microelectrolysis tower 7 through a pipeline, a flocculation zone 13 located on the right side of the neutralization zone 12, and a sedimentation zone 16 located on the right side of the flocculation zone 13. The neutralization reaction zone 12 is provided with a 1# pH adjustment device 6 and an on-line pH meter; the flocculation zone 13 is provided with a stirrer 14, a 1# PAM dosing device 15, and an on-line pH meter; the sedimentation zone 16 adopts an upflow countercurrent inclined tube sedimentation tank, and inclined tube fillers 17 are provided in the sedimentation zone 16.

[0010] The iron-carbon microelectrolysis tower 7 is provided with a 1# aeration system 11, an iron-carbon microelectrolysis tower water distribution system 10, a TCMF composite filler 8, and an on-line pH meter. The wastewater uniformly enters the iron-carbon microelectrolysis tower 7 through the iron-carbon microelectrolysis tower water distribution system 10 and then overflows the TCMF composite filler 8. The TCMF composite filler 8 includes iron powder, carbon powder, a small amount of natural MnO2 powder, and zeolite powder, and does not add any inert components such as clay, ensuring high activity and no sludge generation of the filler. The oxide adheres to the surface of extremely fine iron particles with very little adhesion and can be shed by aeration. The TCMF composite filler 8 has no caking effect, a long service life, and high use efficiency. The wastewater undergoes an electrochemical reaction in the TCMF composite filler 8 to degrade COD and part of ammonia nitrogen. The iron-carbon microelectrolysis tower 7 is provided with an iron-carbon microelectrolysis sampling port 9 to analyze the removal effect, and the process parameters are adjusted according to the analysis results of the iron-carbon microelectrolysis sampling port 9.

[0011] The second treatment system includes an adjustment pond 18, a No. 3 lift pump 19 located in the adjustment pond 18, a No. 2 neutralization pond 20 connected to the No. 3 lift pump 19 through a pipeline, a No. 4 lift pump 21 located in the No. 2 neutralization pond 20, a UASB reactor 23 connected to the No. 4 lift pump 21 through a pipeline, an anoxic pond 26 connected to the top of the UASB reactor 23 through a pipeline, an aerobic pond 28 located on the right side of the anoxic pond 26, a secondary sedimentation tank 31 located on the right side of the aerobic pond 28, and a clear water tank 32 located in the secondary sedimentation tank 31. A No. 5 lift pump 33 is provided in the clear water tank 32; the supernatant after sedimentation in the secondary sedimentation tank 31 enters the clear water tank 32, and the water discharged from the clear water tank 32 meets the standards for discharge. By using the No. 5 lift pump 33, part of the clear water is lifted and recycled to the adjustment pond 18.

[0012] The specific operation of S1 is as follows: The wastewater from the caproic acid production process is transported to the No. 1 adjustment pond 1 by a workshop pump, lifted to the No. 1 neutralization pond 4 by the No. 1 lift pump 2, and after the pH value is adjusted to 2.5 - 3.0 by the No. 1 pH adjustment device 6, it is then lifted to the iron-carbon microelectrolysis tower 7 by the No. 2 lift pump 5. Through the TCMF composite packing 8 in the tower, an oxidation-reduction reaction occurs between the packing and the organic matter in the wastewater, reducing the COD and increasing the pH value of the wastewater at the same time; the effluent from the iron-carbon microelectrolysis tower 7 flows by gravity into the neutralization zone 12 of the neutralization-flocculation sedimentation tank. The NaOH solution is added by the No. 1 pH adjustment device 6 to react with Fe 2+ 、Fe 3+ in the wastewater to form insoluble ferric hydroxide. Then the wastewater enters the flocculation zone 13, and after the PAM solution is added by the No. 1 PAM dosing device 15 for flocculation, the wastewater enters the sedimentation zone 16. After sedimentation, the supernatant enters the No. 2 pH adjustment pond 18 and is mixed with the wastewater from the ethyl caproate production and the recycled water.

[0013] The specific operations of S2 are as follows: The effluent from the sedimentation area 16 is discharged into the 2# regulation tank 18, where it is mixed with the low-concentration wastewater discharged from the ethyl hexanoate workshop and the system return effluent. Then, it is lifted to the 2# neutralization tank 20 by the 3# lift pump 19. The NaOH solution is added through the 2# pH adjustment device 22 to finely adjust the pH value to 6.5 - 7.2. Then, it is lifted to the UASB reactor 23 by the 4# lift pump 21. Most of the organic pollutants such as COD are degraded under the decomposition of anaerobic bacteria in the reactor. After that, the wastewater flows by gravity into the A / O reaction tank. The wastewater first enters the anoxic tank 26 (A tank), where the nitrate nitrogen in the wastewater is converted into nitrogen gas under the action of denitrifying bacteria. Then, the aerobic bacteria in the aerobic tank 28 (O tank) degrade and remove most of the organic pollutants under the action of aeration and oxygenation, and convert ammonia nitrogen into nitrate nitrogen. The internal reflux system in the tank is used to reflux the mixed liquid in the aerobic tank 28 to the anoxic tank 26, and denitrification occurs in the anoxic environment in the tank to achieve the purpose of removing TN in the wastewater. Then, solid-liquid separation is carried out in the secondary sedimentation tank 31. The supernatant is discharged into the clear water tank 32, and part of the clear water is refluxed to the 2# regulation tank 18 by the 5# lift pump, and the other part is discharged up to the standard.

[0014] The UASB reactor 23 is equipped with a UASB water distribution system 24 and a water seal tank 25. Most of the organic pollutants such as COD are degraded under the decomposition of anaerobic bacteria in the UASB reactor 23. A liquid-gas-solid three-phase separator is arranged at the top of the UASB reactor 23. The biogas generated by the anaerobic reaction is collected through the water seal tank 25 and sent to the waste gas treatment system for treatment. The anoxic tank 26 is equipped with a submersible agitator 27. The nitrate nitrogen in the wastewater is converted into nitrogen gas under the action of denitrifying bacteria in the anoxic tank 26. The nitrified liquid refluxed from the aerobic tank is denitrified in the anoxic environment to achieve the purpose of removing TN in the wastewater.

[0015] The aerobic tank 28 is equipped with a 2# aeration system 29 and a nitrified liquid reflux pump 30. The aerobic bacteria in the aerobic tank 28 degrade and remove most of the organic pollutants under the condition of aeration and oxygenation, and convert ammonia nitrogen into nitrate nitrogen. Then, part of the mixed liquid in the aerobic tank 28 is refluxed to the anoxic tank 26 by the nitrified liquid reflux pump 30.

[0016] The beneficial effects of the present invention are as follows: 1. According to the characteristics of the ethyl hexanoate production wastewater with high COD, low pH value, high ammonia nitrogen and high total nitrogen and the existing wastewater treatment process, the present invention combines the chemical precipitation method, the iron-carbon microelectrolysis method and the biological treatment method, which not only reduces the operation and management cost, but also ensures that the effluent quality reaches the standard stably, and reduces the pollution to the water ecological environment.

[0017] 2. The TCMF composite filler of the present invention comprises iron powder, carbon powder, a small amount of natural MnO2 powder and zeolite powder, without adding any inert components such as clay, ensuring high efficiency of the filler activity and no sludge generated by itself. The oxide adheres to the surface of extremely fine iron particles with very little adhesion force, and it falls off by aeration. The TCMF composite filler 8 has no caking effect, long service life and high use efficiency. Electrochemical reaction occurs in the TCMF composite filler 8 for the wastewater to degrade COD and partial ammonia nitrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the flow chart of the present invention; In the figure: 1# regulating tank 1, 1# lift pump 2, flowmeter 3, 1# neutralization tank 4, 2# lift pump 5, 1# pH regulating device 6, iron-carbon micro-electrolysis tower 7, TCMF composite filler 8, iron-carbon micro-electrolysis sampling port 9, iron-carbon micro-electrolysis tower water distribution system 10, 1# aeration device 11, neutralization-flocculation sedimentation tank neutralization area 12, neutralization-flocculation sedimentation tank flocculation area 13, agitator 14, 1# PAM dosing device 15, neutralization-flocculation sedimentation tank sedimentation area 16, inclined tube filler 17, 2# regulating tank 18, 3# lift pump 19, 2# neutralization tank 20, 4# lift pump 21, 2# pH regulating device 22, UASB reactor 23, UASB water distribution system 24, water seal tank 25, anoxic tank 26, propeller 27, aerobic tank 28, 2# aeration device 29, nitrification liquid reflux pump 30, secondary sedimentation tank 31, clear water tank 32, 5# lift pump 33, blower 34. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The present invention will be further described below in conjunction with the drawings and embodiments.

[0020] As Figure 1 shown, a method for treating wastewater from ethyl hexanoate production comprises the following steps: S1. The wastewater from the ethyl hexanoate production process is subjected to oxidation-reduction reaction, pH value adjustment and flocculation sedimentation treatment in sequence through the first treatment system to degrade the COD in the wastewater from the ethyl hexanoate production process, and the pretreated effluent is obtained.

[0021] The first treatment system comprises 1# regulating tank 1, 1# lift pump 2 located in 1# regulating tank 1, 1# neutralization tank 4 connected to 1# lift pump 2 through a pipeline, 2# lift pump 5 located in 1# neutralization tank 4, iron-carbon micro-electrolysis tower 7 connected to 2# lift pump 5 through a pipeline, and a neutralization-flocculation sedimentation tank connected to the water outlet end of the iron-carbon micro-electrolysis tower 7 through a pipeline. The water outlet end of the neutralization-flocculation sedimentation tank is connected to the second treatment system through a pipeline. The 2# lift pump 5 is equipped with a float level gauge and a flowmeter.

[0022] The neutralization - flocculation sedimentation tank includes a neutralization zone 12 connected to the top water outlet end of the iron - carbon micro - electrolysis tower 7 through a pipeline, a flocculation zone 13 on the right side of the neutralization zone 12, and a sedimentation zone 16 on the right side of the flocculation zone 13. The neutralization reaction zone 12 is equipped with a 1# pH adjustment device 6 and an on - line pH meter; the flocculation zone 13 is equipped with a stirrer 14, a 1# PAM dosing device 15 and an on - line pH meter; the sedimentation zone 16 adopts an up - flow counter - current inclined tube sedimentation tank, and inclined tube fillers 17 are arranged in the sedimentation zone 16.

[0023] The iron - carbon micro - electrolysis tower 7 is equipped with a 1# aeration system 11, an iron - carbon micro - electrolysis tower water distribution system 10, TCMF composite fillers 8 and an on - line pH meter. Wastewater uniformly enters the iron - carbon micro - electrolysis tower 7 through the iron - carbon micro - electrolysis tower water distribution system 10 and then overflows the TCMF composite fillers 8. The TCMF composite fillers 8 include iron powder, carbon powder, a small amount of natural MnO2 powder and zeolite powder, without adding any inert components such as clay, ensuring high - efficiency filler activity and no self - generated sludge. Oxides adhere to the surface of extremely fine iron particles with very little adhesion and can be shed by aeration. The TCMF composite fillers 8 have no caking effect, long service life and high use efficiency. Wastewater undergoes an electrochemical reaction in the TCMF composite fillers 8 to degrade COD and part of ammonia nitrogen. The iron - carbon micro - electrolysis tower 7 is provided with an iron - carbon micro - electrolysis sampling port 9 to analyze the removal effect, and process parameters are adjusted according to the analysis results of the iron - carbon micro - electrolysis sampling port 9. The iron - carbon micro - electrolysis tower 7 is equipped with a 1# aeration device 11, which is supplied with oxygen by a blower 34. An on - line pH meter is equipped to real - time monitor the reaction pH value in the tower. The specific operation of S1 is as follows: The wastewater from the caproic acid production process is transported to the 1# regulating tank 1 by a workshop pump, lifted to the 1# neutralization tank 4 by a 1# lift pump 2, and after the pH value is adjusted to 2.5 - 3.0 by the 1# pH adjustment device 6, it is then lifted to the iron - carbon micro - electrolysis tower 7 by a 2# lift pump 5. Through the TCMF composite fillers 8 in the tower, an oxidation - reduction reaction occurs between the organic matter in the wastewater, reducing COD while increasing the pH value of the wastewater; that is, there is an electrode potential difference of 1.2V between the positive and negative electrodes between iron and carbon in the TCMF composite fillers 8. Under acidic conditions, an electrochemical reaction occurs. The anode (Fe) iron is corroded and changes into divalent iron ions entering the solution, and the cathode (C) generates hydroxide ions (OH−), which lose an electron to become hydroxyl radicals (·OH) or active oxygen [O], degrading the refractory organic matter in the wastewater, reducing COD while removing part of the ammonia nitrogen and also increasing the pH value of the wastewater. The effluent of the iron - carbon micro - electrolysis tower 7 flows into the neutralization zone 12 of the neutralization - flocculation sedimentation tank by gravity, and the NaOH solution is added by the 1# pH adjustment device 6 to react with Fe 2+ 、Fe 3+After the reaction to generate the insoluble ferric hydroxide, the pH value is adjusted to be between 6.0 and 6.5, and an online pH meter is equipped to monitor the pH value in the neutralization zone in real time. The wastewater enters the flocculation zone 13, and after adding PAM solution for flocculation by the 1# PAM dosing device 15, it is stirred and mixed by the stirrer 14; the wastewater enters the sedimentation zone 16, and after sedimentation, Fe(OH)3 and other suspended matters are precipitated, and are discharged to the sludge tank through the sludge discharge system, and the supernatant enters the 2# pH adjustment tank 18, and is mixed with the ethyl hexanoate production wastewater and the reflux water.

[0024] S2. Mix the pretreated effluent in S1 and the ethyl hexanoate production wastewater and send them into the second treatment system to sequentially adjust the pH value, anaerobic treatment, denitrifying bacteria treatment, aerobic bacteria treatment and anoxic denitrification treatment, so as to degrade the organic matters in the pretreated effluent, the ethyl hexanoate production wastewater and the reflux effluent, and obtain the qualified water and the reflux water.

[0025] The second treatment system includes a 2# adjustment tank 18, a 3# lift pump 19 located in the 2# adjustment tank 18, a 2# neutralization tank 20 connected to the 3# lift pump 19 through a pipeline, a 4# lift pump 21 located in the 2# neutralization tank 20, a UASB reactor 23 connected to the 4# lift pump 21 through a pipeline, an anoxic tank 26 connected to the top of the UASB reactor 23 through a pipeline, an aerobic tank 28 located on the right side of the anoxic tank 26, a secondary sedimentation tank 31 located on the right side of the aerobic tank 28, and a clear water tank 32 located in the secondary sedimentation tank 31. A 5# lift pump 33 is provided in the clear water tank 32; the supernatant after sedimentation in the secondary sedimentation tank 31 enters the clear water tank 32, and the water discharged from the clear water tank 32 meets the standards and is discharged. Using the 5# lift pump 33, part of the clear water is lifted and refluxed to the 2# adjustment tank 18.

[0026] The UASB reactor 23 is provided with a UASB water distribution system 24 and a water seal tank 25; most of the organic pollutants such as COD are degraded in the UASB reactor 23 under the decomposition of anaerobic bacteria. A liquid-gas-solid three-phase separator is arranged at the top of the UASB reactor 23, and the biogas generated by the anaerobic reaction is collected through the water seal tank 25 and sent to the waste gas treatment system for treatment; The anoxic tank 26 is provided with a submersible propeller 27; in the anoxic tank 26, the nitrate nitrogen in the wastewater is converted into nitrogen under the action of denitrifying bacteria; the nitrification liquid refluxed to the aerobic tank is denitrified in an anoxic environment to achieve the purpose of removing TN in the wastewater.

[0027] The aerobic tank 28 is provided with a 2# aeration system 29 and a nitrification liquid reflux pump 30; the aerobic bacteria in the aerobic tank 28 degrade and remove most of the organic pollutants under the condition of aeration and oxygen supply, and convert ammonia nitrogen into nitrate nitrogen; then, part of the mixed liquid in the aerobic tank 28 is refluxed to the anoxic tank 26 by using the nitrification liquid reflux pump 30.

[0028] The wastewater treated in the aerobic tank 28 enters the secondary sedimentation tank 31 for sedimentation and separation of mud and water, and the supernatant is discharged into the clear water tank 32. The supernatant after sedimentation in the secondary sedimentation tank 31 enters the clear water tank 32, and the water discharged from the clear water tank 32 meets the discharge standards. By using the 5# lift pump 33, part of the clear water is lifted and recycled to the 2# regulating tank 18 to balance the influent water quality.

[0029] The specific operation of S2 is as follows: The water discharged from the sedimentation area 16 is discharged into the 2# regulating tank 18 and mixed with the low-concentration wastewater discharged from the ethyl hexanoate workshop and the effluent recycled from the system, so that the three kinds of wastewater are fully mixed and evenly distributed. After the water quality is stabilized, it is lifted to the 2# neutralization tank 20 by the 3# lift pump 19. The 3# lift pump 19 is equipped with a float level gauge and an electromagnetic flowmeter. In the 2# neutralization tank 20, NaOH solution is added by the 2# pH adjustment device 22 to finely adjust the pH value of the wastewater to 6.5 - 7.2 to meet the influent conditions of the UASB reactor 23. Then it is lifted to the UASB reactor 23 by the 4# lift pump 21. The 4# lift pump 21 is equipped with a float level gauge and a flowmeter. The wastewater enters the UASB reactor 23 through the water distribution system 24 of the UASB reactor 23. Most of the organic pollutants such as COD are degraded under the decomposition of anaerobic bacteria in the UASB reactor 23. Then the wastewater flows into the A / O reaction tank by gravity. The wastewater first enters the anoxic tank 26 (A tank), and the nitrate nitrogen in the wastewater is converted into nitrogen gas under the action of denitrifying bacteria. The biogas generated by the anaerobic reaction is collected by the water seal tank 25 and sent to the waste gas treatment system for treatment. The wastewater enters the anoxic tank 26, which is equipped with a submersible agitator 27. The wastewater enters the aerobic tank 28, and is aerated and oxygenated by the 2# aeration system 29. Aerobic bacteria degrade and remove most of the organic pollutants and convert ammonia nitrogen into nitrate nitrogen. Then part of the mixed liquid in the aerobic tank is recycled to the anoxic tank 26 by the nitrification liquid recycle pump 30. Under the anoxic environment in the anoxic tank 26, denitrification is carried out to achieve the purpose of removing TN in the wastewater. Then, solid-liquid separation is carried out in the secondary sedimentation tank 31, and the supernatant is discharged into the clear water tank 32. The water discharged from the clear water tank 32 meets the discharge standards. Part of the clear water is recycled to the 2# regulating tank 18 by the 5# lift pump to balance the influent water quality.

[0030] S3: The recycled water in S2 is recycled to the second treatment system through a pipeline, so that the recycled water, the pretreated effluent and the ethyl hexanoate production wastewater are mixed, and the recycled water is treated for the second time.

[0031] Application example: A wastewater treatment station of a chemical enterprise in Henan. The wastewater discharge of the caproic acid production process of this chemical enterprise is 20 m 3 / d, and the wastewater discharge of the ethyl hexanoate synthesis process is 125 m 3 / d. According to the water quality characteristics of each section, the wastewater from the caproic acid production process is pretreated separately as high-concentration wastewater, and the designed treatment capacity is 25 m 3 / d, and after pretreatment, it is mixed with the synthetic process wastewater of ethyl hexanoate with low concentration for further treatment. The total designed water volume is 160 m 3 / d. The designed influent water quality of the above two sections is as follows: 1. High-concentration influent water quality COD ≤ 200000 mg / L, NH3-N ≤ 600 mg / L, TN ≤ 5000 mg / L, SS ≤ 150 mg / L, pH value 0.5 - 1.0.

[0032] 2. Low-concentration influent water quality COD ≤ 5000 mg / L, NH3-N ≤ 10 mg / L, TN ≤ 200 mg / L, SS ≤ 100 mg / L, pH value 3.5 - 5.0.

[0033] Aiming at the characteristics of high COD and low pH value of the wastewater from the ethyl hexanoate production process, the iron-carbon micro-electrolysis process is first adopted. It can not only degrade a large amount of COD, but also make full use of the characteristic that the influent pH value required for the iron-carbon micro-electrolysis reaction is 2.5 - 3.0, greatly reducing the amount of alkali added for neutralization and avoiding the introduction of excessive Na + , Ca 2+ and other salts, ensuring the stable operation of the subsequent biochemical system. It is found through small-scale test research that the effluent pH after the iron-carbon micro-electrolysis reaction is 4.0 - 5.0, and it can further reduce the dosage of the subsequent operating alkali solution. Due to the formation of iron salts, the effluent contains some colloids and suspended solids, and then the flocculation precipitation process is adopted for removal. Therefore, the iron-carbon micro-electrolysis + flocculation precipitation process is adopted for the pretreatment of high-concentration wastewater.

[0034] After the high-concentration pre-treated effluent is mixed with the low-concentration wastewater, the COD is still as high as 20,000 mg / L, the total nitrogen is close to 1,000 mg / L, and the pH value is 4.0 - 5.0. To further reduce the influent load and increase the influent pH value, it is considered to return 100% of the system effluent. On this basis, the anaerobic unit of the biochemical unit adopts the UASB process. To ensure the pH value requirement of the UASB influent, a neutralization tank is added at the front end. The residence time of the UASB reactor is 2 days, so that the small molecule acids in the wastewater are fully degraded, and the macromolecule acids or lipid substances are decomposed into small molecule substances. Since the total phosphorus content in the wastewater is low and the total nitrogen is high, mainly in the form of nitrate nitrogen, the aerobic unit of the biochemical unit adopts the A / O process. The A pool accounts for 55% of the total volume of the A / O. The nitrate nitrogen in the wastewater is first denitrified in the A pool, and part of the carbon source in the wastewater can be consumed to reduce the COD. The O pool adopts a rotary cutting aerator made of ABS material, which reduces the risk of corrosion of the aerator caused by incorrect regulation of the influent pH. At the same time, to increase the biomass in the aerobic pool, combined packing is added in the first half of the aerobic pool. To improve the removal rate of total nitrogen, the mixed liquor reflux ratio is controlled at 400% - 600%, and the sludge reflux ratio is controlled at 50% - 100%. Combining the results of the small-scale test and the discharge standard, the high-concentration pre-treatment process for this project is determined to be the iron-carbon micro-electrolysis + neutralization-flocculation sedimentation tank process, and the neutralization + UASB + A / O process is adopted after mixing.

[0035] The specific design content is as follows: One 1# regulating tank 1 is set, with dimensions of 5.0 m × 5.0 m × 4.0 m, and two 1# lift pumps 2 are configured, each equipped with a floating ball liquid level gauge and an electromagnetic flowmeter 3.

[0036] One 1# neutralization tank 4 is set, with dimensions of 1.2 m × 1.0 m × 3.0 m, and two 2# lift pumps 5 are set, each equipped with a floating ball liquid level gauge and a flowmeter. Another set of on-line pH meter is provided and linked with the 1# pH adjustment device 6.

[0037] One iron-carbon micro-electrolysis tower 7 is set, with dimensions of φ1.6 m × 6.0 m, and a set of on-line pH meter is provided to monitor the reaction pH value in the tower in real time. The built-in TCMF composite filler 8 is composed of iron powder, carbon powder, and trace catalytic elements natural MnO2 powder and zeolite powder, among which the ratio of iron powder to carbon powder is 1:1. The iron-carbon micro-electrolysis tower 7 is equipped with a set of iron-carbon micro-electrolysis tower water distribution system 10 and a set of 1# aeration device 11, and an iron-carbon micro-electrolysis sampling port 9 is set for analyzing the catalytic effect.

[0038] One neutralization - flocculation sedimentation tank is provided, with dimensions of 1.4 m × 1.2 m × 3.0 m. The neutralization area 12 has dimensions of 1.2 m × 0.6 m × 1.5 m. One set of on - line pH meter is installed in the tank, and perforated pipes are set at the bottom of the tank for air agitation; the flocculation area 13 has dimensions of 1.2 m × 0.6 m × 1.5 m. One set of mixer 14 is installed in the tank, and it is equipped with one set of 1# PAM dosing device 15; the sedimentation area 16 has dimensions of 1.2 m × 0.8 m × 2.7 m. Inclined tube packing 17 is installed in the tank, and sludge discharge pipes are set at the bottom of the tank, and two sludge discharge pumps are equipped. 3 Two sludge discharge pumps are provided.

[0039] One 2# regulating tank 18 is provided, with dimensions of 10.0 m × 9.0 m × 4.0 m. Two 3# lift pumps 19 are configured, and each is equipped with a float level gauge and an electromagnetic flowmeter.

[0040] One 2# neutralization tank 20 is provided, with dimensions of 3.0 m × 3.0 m × 4.0 m. Two 4# lift pumps 21 are provided, one in use and one in reserve, and are equipped with float level gauges and electromagnetic flowmeters. Additionally, one set of on - line pH meter is provided and is linked with the 2# pH adjustment device 22.

[0041] Two UASB reactors 23 are provided, with each single - unit dimension of 6.4 m × 6.4 m × 8.1 m. Two layers of liquid - gas - solid three - phase separators are installed at the top inside the reactor, and a uniform water distribution system 24, a sludge discharge system and a three - phase separator flushing system are provided at the bottom. The biogas generated from the anaerobic reaction is sent to the waste gas treatment system for treatment after passing through two water seal tanks 25 provided.

[0042] One A / O reaction tank is provided, with a total dimension of 17.6 m × 16.2 m × 6.0 m. Among them, the anoxic tank 26 has dimensions of 17.6 m × 8.4 m × 6.0 m, and low - speed submersible propellers 27 are installed inside the tank. The aerobic tank 28 has dimensions of 17.6 m × 6.8 m × 6.0 m, and the 2# aeration device 29 made of ABS is installed at the bottom of the tank. A nitrification liquid reflux pump 30 (centrifugal pump) is installed at the end of the aerobic tank 28, which is used to reflux the nitrification liquid to the anoxic section, and an electromagnetic flowmeter is installed on the reflux pipeline to accurately control the mixed liquid reflux ratio.

[0043] One secondary sedimentation tank 31 is provided, which adopts a vertical - flow sedimentation tank with dimensions of 4.4 m × 4.4 m × 5.5 m. One set of central cylinder is provided, and the sludge discharge pipes at the bottom of the tank also serve as sludge reflux pipes. Centrifugal pumps are provided to reflux the sludge to the anoxic tank or transport the excess sludge to the sludge storage tank.

[0044] One clear water tank 32 is provided, with dimensions of 4.4 m × 4.0 m × 5.0 m. A 5# lift pump 33 is provided to reflux part of the effluent to the front - end 2# regulating tank 18.

[0045] The effluent quality after passing through the above wastewater treatment system meets the requirements of Table 1 of the Local Standard of Henan Province, "Indirect Discharge Standard for Water Pollutants in the Chemical Industry" (DB41 / 1135 - 2016), specifically: COD ≤ 300 mg / L, NH₃-N ≤ 30 mg / L, TN ≤ 50 mg / L, SS ≤ 150 mg / L, and pH value is 6 - 9.

[0046] The above wastewater treatment system is not only applicable to the wastewater from ethyl hexanoate production, but also applicable to other similar wastewater with high COD, low pH value, high ammonia nitrogen and high total nitrogen, and can provide reference for the treatment of wastewater with similar characteristics.

Claims

1. A method for treating ethyl caproate production wastewater, characterized in that: The following steps are involved: S1, subjecting the caproic acid production process wastewater to oxidation-reduction reaction, pH adjustment, and flocculation and precipitation treatment in sequence through a first treatment system to degrade COD in the caproic acid production process wastewater to obtain pretreated effluent; S2, mixing the pretreated effluent in S1 and the ethyl caproate production wastewater and sending them to the second treatment system for adjusting the pH value, anaerobic bacteria treatment, denitrifying bacteria treatment, aerobic bacteria treatment and anoxic denitrification treatment in sequence, so as to degrade organic matter in the pretreated effluent, the ethyl caproate production wastewater and the reflux effluent to obtain qualified water and reflux water; S3, returning the reflux water in S2 to the second treatment system through the pipeline, so that the reflux water, the pre-treated water and the ethyl caproate production wastewater are mixed, and the reflux water is subjected to secondary treatment.

2. The method for treating ethyl caproate production wastewater according to claim 1, wherein: The first treatment system includes a 1# regulating tank, a 1# lifting pump located in the 1# regulating tank, a 1# neutralization tank connected to the 1# lifting pump through a pipeline, a 2# lifting pump located in the 1# neutralization tank, an iron-carbon micro-electrolysis tower connected to the 2# lifting pump through a pipeline, and a neutralization-flocculation sedimentation tank connected to the water outlet of the iron-carbon micro-electrolysis tower through a pipeline, and the water outlet of the neutralization-flocculation sedimentation tank is connected to the second treatment system through a pipeline.

3. The method for treating ethyl caproate production wastewater according to claim 2, wherein: The neutralization-flocculation sedimentation tank comprises a neutralization zone connected to the top water outlet of the iron-carbon micro-electrolysis tower through a pipeline, a flocculation zone located on the right side of the neutralization zone, and a sedimentation zone located on the right side of the flocculation zone. The neutralization reaction zone is provided with a 1# pH adjustment device and an online pH meter; the flocculation zone is provided with an agitator, a 1# PAM dosing device and an online pH meter; the sedimentation zone adopts an upflow type counter-current inclined tube sedimentation tank, and an inclined tube filler is provided in the sedimentation zone.

4. The method for treating ethyl hexanoate production wastewater according to claim 2, wherein: The iron-carbon micro-electrolysis tower is provided with a 1# aeration system, an iron-carbon micro-electrolysis tower water distribution system, a TCMF composite filler and an online pH meter. Wastewater enters the iron-carbon micro-electrolysis tower evenly through the iron-carbon micro-electrolysis tower water distribution system and then flows over the TCMF composite filler. The TCMF composite filler includes iron powder, carbon powder, natural MnO2 powder and zeolite powder. The iron-carbon micro-electrolysis tower is provided with an iron-carbon micro-electrolysis sampling port.

5. The method for treating ethyl hexanoate production wastewater according to claim 1, wherein: The second treatment system includes a 2# regulating tank, a 3# lifting pump located in the 2# regulating tank, a 2# neutralization tank connected to the 3# lifting pump through a pipeline, a 4# lifting pump located in the 2# neutralization tank, a UASB reactor connected to the 4# lifting pump through a pipeline, an anoxic tank connected to the top of the UASB reactor through a pipeline, an aerobic tank located on the right side of the anoxic tank, a secondary sedimentation tank located on the right side of the aerobic tank, and a clear water tank located in the secondary sedimentation tank, wherein a 5# lifting pump is provided in the clear water tank; The supernatant after sedimentation in the secondary sedimentation tank enters the clear water tank. The effluent from the clear water tank meets the discharge standards, and part of the clear water is lifted and returned to the 2# regulating tank using the 5# lifting pump.

6. The method for treating ethyl hexanoate production wastewater according to claim 2, wherein: The specific operation of S1 is as follows: the hexanoic acid production process wastewater is transported to the 1# regulating tank through the workshop pump, lifted to the 1# neutralization tank through the 1# lifting pump, adjusted to a pH value of 2.5-3.0 by the 1# pH adjusting device, and then lifted to the iron-carbon micro-electrolysis tower through the 2# lifting pump, and the TCMF composite filler in the tower undergoes an oxidation-reduction reaction with organic matter in the wastewater to reduce COD while increasing the pH value of the wastewater; the effluent of the iron-carbon micro-electrolysis tower flows into the neutralization zone of the neutralization-flocculation sedimentation tank by gravity, and NaOH solution is added through the 1# pH adjusting device to react with Fe in the wastewater. 2+ , Fe 3+ After the reaction to generate insoluble iron hydroxide, the wastewater enters the flocculation area. After flocculation by adding PAM solution in the 1# PAM dosing device, the wastewater enters the sedimentation area. After sedimentation, the supernatant enters the 2# pH adjustment tank and mixes with the ethyl hexanoate production wastewater and reflux water.

7. The method for treating ethyl hexanoate production wastewater according to claim 5, characterized in that: The specific operation of S2 is as follows: the effluent from the sedimentation area is discharged into the 2# regulating tank and mixed with the low-concentration wastewater discharged from the ethyl hexanoate workshop and the system reflux effluent, and then lifted to the 2# neutralization tank by the 3# lifting pump, and the NaOH solution is added through the 2# pH adjusting device to adjust the pH value to 6.5-7.2, and then lifted to the UASB reactor by the 4# lifting pump, and the COD organic pollutants are degraded by the decomposition of anaerobic bacteria in the reactor. After that, the wastewater first enters the anoxic tank, and the nitrate nitrogen in the wastewater is converted into nitrogen gas under the action of denitrifying bacteria, and then the aerobic bacteria in the aerobic tank degrade and remove organic pollutants under the action of aeration and oxygenation, and convert ammonia nitrogen into nitrate nitrogen; the internal reflux system in the tank is used to return the mixed liquid of the aerobic tank to the anoxic tank, and denitrification is carried out in the anoxic environment in the tank to achieve the purpose of removing TN in the wastewater; Afterwards, mud and water are separated in the secondary sedimentation tank, and the supernatant is discharged into the clean water tank. Then part of the clean water is returned to the 2# regulating tank through the 5# lifting pump, and the other part is discharged in compliance with the standards.

8. The method for treating ethyl hexanoate production wastewater according to claim 5, characterized in that: The UASB reactor is provided with a UASB water distribution system and a water seal tank; the COD organic pollutants are degraded by the decomposition of anaerobic bacteria in the UASB reactor, a liquid-gas-solid three-phase separator is arranged on the top of the UASB reactor, and the biogas generated by the anaerobic reaction is collected by the water seal tank and then sent to the waste gas treatment system for treatment.

9. The method for treating ethyl hexanoate production wastewater according to claim 5, characterized in that: The anoxic pool is provided with a submersible flow propeller; the anoxic pool converts nitrate nitrogen in the wastewater into nitrogen gas under the action of denitrifying bacteria; the nitrified liquid returned from the aerobic pool is denitrified in an anaerobic environment to achieve the purpose of removing TN in the wastewater.

10. The method for treating ethyl hexanoate production wastewater according to claim 5, characterized in that: The aerobic pool is provided with a 2# aeration system and a nitrification liquid reflux pump; the aerobic bacteria in the aerobic pool degrade and remove organic pollutants under aeration and oxygenation conditions, and convert ammonia nitrogen into nitrate nitrogen; and then the nitrification liquid reflux pump is used to return part of the mixed liquid in the aerobic pool to the anoxic pool.

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