Method for treating ethylene alkali residue wastewater by homogeneous catalytic wet oxidation

Abstract

The present invention discloses a method for treating ethylene alkali residue wastewater by using homogeneous catalytic wet oxidation, which includes a wet oxidation section, a deep treatment section and a salt treatment section; a homogeneous catalyst is used to treat the ethylene alkali residue wastewater by wet oxidation, the effluent part is treated by primary nanofiltration, the primary nanofiltration concentrated water is returned to the wet oxidation, part of the wet oxidation effluent and the primary nanofiltration produced water are subjected to biochemical treatment and ozone catalytic oxidation to remove COD, and then secondary nanofiltration is performed, the secondary nanofiltration concentrated water sequentially enters the MVR reactor and the segmented crystallization and salt separation, and finally obtains the product sulfate and miscellaneous salt, the secondary nanofiltration produced water is subjected to reverse osmosis, the concentrated water is returned to the biochemical unit, and the produced water meets the reuse standard. In view of the characteristics of high COD, high salt content, high toxicity and difficult degradation of ethylene alkali residue wastewater, the present invention adopts a treatment process with homogeneous catalytic wet oxidation as the core, gives full play to the characteristics of high catalytic activity and high treatment efficiency of homogeneous catalytic wet oxidation, and greatly improves the treatment capacity of wet oxidation.

Description

Technical Field

[0001] The invention relates to a method for treating ethylene alkali residue waste water, in particular to a method for treating ethylene alkali residue waste water by utilizing homogeneous catalytic wet oxidation, and belongs to the technical field of waste water treatment. Background Art

[0002] Ethylene waste alkali liquid is the wastewater produced by alkali washing of cracking gas in the ethylene production process. The pollutant composition is relatively complex, with high content of organic matter, sulfide and salt. It also contains odorous gases such as mercaptans and sulfides, which makes it difficult to treat. With the expansion of the scale of ethylene plants, the discharge of waste alkali liquid continues to increase, and its harmless treatment and comprehensive utilization have become the focus of attention.

[0003] Ethylene alkali residue wastewater must be pretreated before entering the biochemical system, and advanced oxidation is a commonly used pretreatment method, which can turn difficult-to-degrade, highly toxic macromolecular organic matter into degradable, low-toxic small-molecule organic matter or even inorganic matter. Commonly used advanced oxidation methods include ozone catalytic oxidation, electrocatalytic oxidation, photocatalysis, Fenton oxidation, wet oxidation, etc. Among them, electrocatalytic oxidation and photocatalysis are still limited by high treatment costs and are difficult to apply industrially. Fenton oxidation has problems such as complex operation, unstable hydrogen peroxide, and loss of iron ions. With the country's control of ozone pollutants, the application of ozone catalytic oxidation is also limited, and its treatment cost is also high, which is limited to terminal deep treatment.

[0004] At present, the most mainstream method for treating ethylene alkali residue wastewater is wet oxidation, which operates under high temperature (120-320℃) and high pressure (0.5-20MPa) conditions, using gaseous oxygen as an oxidant to oxidize and decompose organic matter in water into small molecular organic or inorganic matter, and has the characteristics of no secondary pollution and low treatment cost. However, traditional wet oxidation requires high temperature and pressure and relatively long residence time, high requirements on equipment materials, high one-time investment, and wet oxidation can only be used as pretreatment, and its effluent also has high COD.

[0005] In order to reduce the temperature and pressure required for the reaction and improve the treatment effect, catalytic wet air oxidation (CWAO) has become a research hotspot in recent years. CN201510274988.5 discloses a catalyst for catalytic wet oxidation of refractory organic wastewater, which is a "precious metal-transition metal-rare earth" composite catalyst, and the main component of the carrier FSC is alumina; CN201410340574.3 discloses a catalyst for catalytic wet oxidation treatment and a preparation method thereof, which uses a precious metal-non-precious metal nanoalloy as an active ingredient and activated carbon as a carrier; CN201510661575.2 discloses a multiphase wet oxidation catalyst, the components of which include a composite oxide carrier and a small amount of precious metal; CN201310621017.4 discloses a method for preparing a catalytic wet oxidation catalyst carrier, which uses activated carbon as a core and amorphous silicon aluminum as a shell.

[0006] The above patents all use heterogeneous catalytic wet oxidation, which has advantages in catalyst separation and recovery and metal loss, but is not necessarily applicable to existing wet oxidation processes. The paper "Industrial Application of Alkali Slag Moderated Wet Oxidation + SBR Treatment Technology" (2011) discloses the alkali slag moderated wet oxidation process of Fushun Petrochemical Research Institute. This process has been promoted and applied in 28 refining and chemical companies and is highly representative. The wet oxidation reactor used is a bubbling flow internal circulation reactor with an inner cylinder. If a heterogeneous catalyst is used in this reactor, its gas-liquid circulation will be seriously affected, and even the reactor and pipeline will be blocked. If a fixed bed method is used, it will bring greater gas resistance, which is more unfavorable for gas-liquid circulation, and the reaction rate will also be greatly reduced.

[0007] Homogeneous catalysis has no internal and external diffusion effect and high dispersion, so its catalytic efficiency is higher than heterogeneous catalysis, and the catalyst preparation is much simpler than heterogeneous catalyst. However, the biggest problem of homogeneous catalysis in wet oxidation is the loss of metal catalyst. At present, there are few studies in this direction. CN201210225873.3 provides a method for treating industrial wastewater by homogeneous catalytic wet oxidation, in which a ring gear filler is placed in a fixed bed reactor, and the homogeneous catalyst uses an iron-based catalyst, but the patent does not mention the loss of catalyst and the corresponding solution; CN201210350157.8 provides a method for catalytic wet oxidation pretreatment of glyphosate production wastewater, in which a multi-component homogeneous catalyst is added, and the catalyst is a soluble transition metal mixed salt. The patent also does not mention the problem of catalyst loss. Summary of the invention

[0008] In view of the above shortcomings, the present invention provides a method for treating ethylene alkali residue wastewater, which utilizes a combination of processes such as homogeneous catalytic wet oxidation, membrane technology, special salt-tolerant bacteria, ozone catalytic oxidation, and MVR salt separation to achieve efficient treatment and zero emission of ethylene alkali residue wastewater. At the same time, it also solves the problem of catalyst loss in the homogeneous catalytic process, and can realize the recycling of catalysts.

[0009] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for treating ethylene alkali slag wastewater by homogeneous catalytic wet oxidation, comprising a wet oxidation section, a deep treatment section and a salt treatment section;

[0011] The wet oxidation section includes a regulating tank, a heat exchange unit, a wet oxidation reactor, a cooler and a first-stage nanofiltration; the ethylene alkali residue wastewater first enters the regulating tank, is mixed with the first-stage nanofiltration concentrated water and a homogeneous catalyst, and is acidified for pH adjustment, enters the heat exchange unit, and enters the wet oxidation reactor after heat exchange and temperature increase; the effluent from the wet oxidation reactor is heat exchanged by the heat exchange unit and then cooled by the cooler, part of which enters the first-stage nanofiltration for treatment, and part of which enters the deep treatment section; the first-stage nanofiltration concentrated water is refluxed to the regulating tank, and the first-stage nanofiltration produced water enters the deep treatment section;

[0012] The deep treatment section includes a regulating tank, a biochemical unit and ozone catalytic oxidation in sequence; the partially cooled wet oxidation reactor effluent and the primary nanofiltration product water enter the regulating tank, and after pH adjustment, enter the biochemical unit for treatment. The biochemical unit uses salt-tolerant bacteria GXNYJ-DL-1 to remove COD, and the treated wastewater is subjected to ozone catalytic oxidation to further decompose difficult-to-treat organic matter; wherein the salt-tolerant bacteria GXNYJ-DL-1 ( Halomonas nigrificans ) was deposited in the General Microbiology Center of China Microorganism Culture Collection Administration on July 13, 2020, with the deposit number CGMCC No. 20350;

[0013] The salt treatment section includes secondary nanofiltration, reverse osmosis, MVR reactor and segmented crystallization salt separation unit; the ozone catalytic oxidation effluent enters the secondary nanofiltration for further concentration, the secondary nanofiltration concentrated water enters the MVR reactor and the segmented crystallization salt separation unit in turn, and finally obtains the product sulfate and miscellaneous salts, the secondary nanofiltration produced water is treated by reverse osmosis, the reverse osmosis concentrated water is returned to the biochemical unit, and the reverse osmosis produced water meets the reuse standard and is recycled.

[0014] Furthermore, an acid is added to the adjustment tank to adjust the pH to 2-6; the acid is hydrochloric acid or sulfuric acid, preferably hydrochloric acid.

[0015] Furthermore, the heat exchange unit is composed of multiple heat exchangers, which perform heat exchange on the outlet water of the wet oxidation reactor and the outlet water of the regulating tank. The outlet water of the wet oxidation reactor goes through the tube side, and the outlet water of the regulating tank goes through the shell side. After multiple heat exchanges, the outlet water temperature of the regulating tank rises to 130-160°C, and the outlet water temperature of the wet oxidation reactor decreases to 50-75°C.

[0016] Furthermore, the homogeneous catalyst is a transition metal catalyst selected from one or more of copper, iron, manganese, zinc and nickel, preferably a copper-zinc composite catalyst; the transition metal in the homogeneous catalyst exists in the form of a metal salt compound or complex and is dissolved in the liquid phase.

[0017] Furthermore, the homogeneous catalyst is added according to the COD mass concentration and metal ion mass concentration ratio of 5000:1 to 10:1, and is appropriately supplemented according to the catalyst loss rate and the change in reaction liquid concentration during normal operation.

[0018] Furthermore, the wet oxidation reactor is a bubbling flow inner circulation reactor in an inner cylinder, which uses gaseous oxygen (air) as an oxidant under high temperature and high pressure conditions to oxidize general organic matter in water into small molecular organic matter or inorganic matter; those skilled in the art should understand that ethylene alkali residue wastewater is a typical difficult-to-treat wastewater, and wet oxidation alone has a strong ability to remove sulfides in wastewater, but a weak ability to remove organic matter, but under the condition of a catalyst, oxygen under high temperature and high pressure is more likely to undergo free radical reactions, and the decomposition and conversion ability and reaction rate of organic matter are greatly improved under the action of the strong oxidizing property of free radicals. On the other hand, homogeneous catalysts themselves have high activity and high selectivity, and their treatment of special pollutants is faster and more effective, and their easy loss problem is also solved by membrane technology.

[0019] Furthermore, the reaction temperature of the wet oxidation reactor is 150-300°C, the reaction pressure is 2MPa-10MPa, and the liquid space velocity is 0.25-4h -1 , the gas-liquid volume ratio is 20:1~500:1.

[0020] Furthermore, the cooling medium of the cooler is circulating water, which further cools the outlet water of the wet oxidation reactor to 30-50°C, meeting the temperature requirements of the subsequent nanofiltration membrane.

[0021] Furthermore, the effluent from the cooler is divided into two streams, one flowing to the primary nanofiltration unit, and the other flowing to the regulating tank. The water volume flowing to the regulating tank accounts for 1% to 40%.

[0022] Furthermore, the primary nanofiltration water production rate is 50% to 75%, and the membrane pore size is between 1 and 5 nm. The metals of the homogeneous catalyst, high-valent salts (such as sulfates, carbonates), macromolecular organic matter (relative molecular mass greater than 200), etc. can be intercepted and enter the concentrated water side after interception, wherein the metals of the homogeneous catalyst are refluxed to the regulating tank and returned to the wet oxidation reactor for recycling after heat exchange and temperature rise; the primary nanofiltration water production includes unreacted small molecular organic matter, monovalent salts and ammonia nitrogen.

[0023] Furthermore, alkali is added into the regulating tank to adjust the pH to 6-9, and the alkali is sodium hydroxide or potassium hydroxide.

[0024] Furthermore, the salt concentration of the biochemical unit influent is controlled to be below 250 g / L, preferably 50 to 130 g / L. The salt-tolerant bacteria GXNYJ-DL-1 used in the present invention can still maintain vitality and a high organic matter removal efficiency at a salt concentration of 250 g / L. Considering the growth of the salt-tolerant bacteria and the organic matter removal efficiency, the salt concentration is preferably 50 to 130 g / L; the salt-tolerant bacteria GXNYJ-DL-1 also has a high tolerance to sulfide toxicity.

[0025] Furthermore, the biochemical unit is selected from BAF or MBR process, which can not only remove COD but also has filtering function, the dissolved oxygen is controlled above 2 mg / L, and the wastewater retention time is 12 to 96 hours.

[0026] Furthermore, the ozone catalytic oxidation unit utilizes the hydroxyl radicals generated by ozone under the catalytic action to further degrade the residual cyclohexane acids and phenolic substances in the wastewater, thereby improving the biodegradability of the wastewater; the ozone dosage is 50-500 mg (0 3 ) / L(water).

[0027] Those skilled in the art should understand that the salt-tolerant bacteria GXNYJ-DL-1 used in the biochemical unit solves the problem that ordinary bacteria cannot survive under high salt conditions. Its sulfide resistance toxicity also solves the problem that ordinary salt-tolerant bacteria cannot survive due to high sulfide concentrations or even due to uneven aeration or local anaerobic oxidation of the bacterial community in the presence of a large amount of sulfate. It is particularly suitable for high-salt wastewater such as refinery alkali residue wastewater with sulfate as the main component; those skilled in the art should also understand that ozone catalytic oxidation is an advanced oxidation method with very high treatment cost, and its optimal treatment link is the terminal deep treatment. The homogeneous catalytic wet oxidation at the front end of the present invention removes most of the organic matter at a lower cost. The biochemical unit uses special salt-tolerant bacteria to further remove the organic matter, so that the treatment load and treatment cost of the ozone catalytic oxidation unit are within a controllable range. The most important function of ozone catalytic oxidation is to further remove organic matter, which can reduce the generation of miscellaneous salts (solid hazardous waste) and improve the purity of the sodium sulfate product.

[0028] Furthermore, the secondary nanofiltration water production rate is between 55% and 80%, and the membrane pore size is between 1 and 5 nm, which mainly plays a role in further concentrating high-salt wastewater.

[0029] Furthermore, the reverse osmosis water production rate is between 50% and 80%, and the membrane pore size is less than 1nm, which mainly plays the role of purifying water quality so that the effluent meets the reuse standard;

[0030] Furthermore, the steam generated by the MVR reactor is condensed and recycled, and the liquid phase enters the crystallizer for segmented crystallization and salt separation. The salt separation technology is based on the following: in the range of 50-120°C, the solubility of most salts increases with increasing temperature, while Na 2 SO 4 The solubility of Na decreases with increasing temperature. Under high temperature conditions, as the salt concentrates, 2 SO 4 Firstly, it is precipitated due to supersaturation to obtain high-purity Na 2 SO 4 When the temperature drops, continued concentration will cause other salts to precipitate due to supersaturation to obtain mixed salts, including sodium chloride, sodium carbonate, catalytic metal salts, etc., and may also contain a small amount of organic matter.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] (1) In view of the characteristics of high COD, high salt content, high toxicity and difficulty in degradation of ethylene alkali residue wastewater, the present invention adopts a treatment process with homogeneous catalytic wet oxidation as the core, giving full play to the characteristics of high catalytic activity and high treatment efficiency of homogeneous catalytic wet oxidation, greatly improving the treatment capacity of wet oxidation.

[0033] (2) The present invention solves the problem of catalyst loss in homogeneous catalytic wet oxidation by combining wet oxidation with membrane technologies such as nanofiltration membranes and electrodialysis single anion membranes, thereby achieving catalyst recycling. The catalyst of the present invention uses a price-controllable non-precious metal catalyst, which ensures cost control while ensuring the effect.

[0034] (3) In order to solve the problem of continuous salt concentration caused by nanofiltration, the present invention uses a non-precious metal catalyst as the catalyst and adopts a treatment method in which part of the wet oxidation effluent bypasses the nanofiltration and directly enters the next unit. This is similar to the "circulating water sewage discharge" method, which maintains the salt balance and saves the desalination unit. The lost catalyst is small in amount and cheap in price, and can be supplemented through the front end. The overall treatment cost is lower than that of full catalyst recovery.

[0035] (4) The salt-tolerant strain GXNYJ-DL-1 used in the present invention not only has excellent salt tolerance, but also has a strong ability to tolerate sulfide toxicity, strong vitality, high stability, and a large salt tolerance range. It plays an irreplaceable role in the treatment of ethylene alkali slag wastewater in the present invention, and lays a foundation for the use of subsequent catalytic oxidation processes and overall cost control.

[0036] (5) Existing ethylene alkali residue wastewater is mostly pre-treated by dilution, with the dilution multiple being as high as dozens of times. The scale of wastewater treatment is greatly increased, and the treatment equipment requires a large floor space. The process scheme provided by the present invention does not require wastewater dilution, has a small treatment scale, and occupies a small area, and ultimately achieves zero discharge of wastewater.

[0037] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 . Growth curve of the strain in Example 1 under different salt contents;

[0039] Figure 2 . COD removal rate of the strain in Example 1 at different salt contents;

[0040] Figure 3 In Example 2, the strain was in S 2- Growth curves under concentrations;

[0041] Figure 4 . Flow chart of treatment of ethylene alkali slag wastewater in Example 3.

[0042] Description of biological material deposit

[0043] The high salt-tolerant strain provided by the present invention ( Halomonas nigrificans )GXNYJ-DL-1, deposited in the General Microbiology Center of China Microbiological Culture Collection Administration; Address: Institute of Microbiology, Chinese Academy of Sciences, No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing; Deposit number: CGMCC No. 20350; Deposit date: July 13, 2020. DETAILED DESCRIPTION

[0044] The present invention is further described in detail below in conjunction with specific examples. The examples are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples.

[0045] Example 1

[0046] Determination of salt tolerance of highly salt-tolerant bacteria GXNYJ-DL-1:

[0047] The growth curves of the strains under different salt concentrations are shown in Figure 1 As shown in Figure 2, the COD removal rate of the strain at different salt concentrations after 72 hours is as follows: Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the strain grows better at a salt concentration of 10-130 g / L. The increase in salt content is accompanied by an increase in the adaptation period, but the COD removal rate (initial phenol COD is about 1247 mg / L) is maintained at a high level. At a salt concentration of 250 g / L, the strain adaptation period is as long as 50 h. After the adaptation period, the strain begins to enter the growth period, and the OD 600 The value increased significantly, indicating that the strain was not completely dead, and the corresponding COD removal rate exceeded 50%.

[0048] This example shows that the strain GXNYJ-DL-1 has strong salt tolerance and can still achieve a COD removal rate of 53% at a salt concentration of 250 g / L, but the optimal salt concentration is between 50 and 130 g / L.

[0049] Example 2

[0050] The resistance of highly salt-tolerant bacteria GXNYJ-DL-1 to S 2- Toxicity assay:

[0051] In different S 2- The growth curve at the concentration Figure 3 As shown, the first 24 hours is the static period, and the last 48 hours is the shaking reaction period. Figure 3 It can be seen that the growth of the strains was very slow during the static period, which was restricted by dissolved oxygen on the one hand and S 2- Toxicity inhibition, after 24h static period, shaking reaction began, at which time the strain concentration began to increase significantly, but compared with Example 1, the strain growth was relatively slow; after two days of growth, the overall OD 600 The value increased from 0.25 to 0.45, indicating that the strain did not 2- After a relatively long adaptation period, it gradually recovered its vitality, especially when the concentration of 300 mg / L S 2- The strain concentration of samples continued to increase steadily.

[0052] This example shows that strain GXNYJ-DL-1 has strong resistance to S 2- Toxicity capability, especially suitable for treating wastewater containing high sulfate content.

[0053] Example 3

[0054] Using the process of the present invention to treat ethylene alkali residue wastewater

[0055] The process flow chart for treating ethylene alkali slag wastewater is as follows: Figure 4 As shown: the ethylene alkali residue wastewater first enters the regulating tank, is mixed with the primary nanofiltration concentrated water and the homogeneous catalyst, and is acidified for pH adjustment, and then enters the heat exchange unit. The heat exchange unit uses a heat exchanger to exchange heat between the effluent from the wet oxidation reactor and the effluent from the regulating tank. The effluent from the wet oxidation reactor goes through the tube side, and the effluent from the regulating tank goes through the shell side. After heat exchange and temperature increase, it enters the wet oxidation reactor; the effluent from the wet oxidation reactor enters the heat exchange unit for heat exchange and cooling, and then is cooled in the cooler and divided into two streams, one directly enters the regulating tank, and the other enters the primary nanofiltration. The primary nanofiltration concentrated water is returned to the regulating tank. The water produced by the first-stage nanofiltration flows to the regulating tank; the pH value of the regulating tank is adjusted by adding alkali to meet the pH requirements of sludge microorganisms, and the effluent from the regulating tank enters the biochemical unit; the biochemical unit uses salt-tolerant bacteria GXNYJ-DL-1 to treat wastewater, and the effluent from the biochemical enters the ozone catalytic oxidation, and the effluent from the ozone catalytic oxidation enters the second-stage nanofiltration; the concentrated water from the second-stage nanofiltration enters the MVR and crystallization unit, and finally obtains impurities and product sulfate. The water produced by the second-stage nanofiltration is further treated by reverse osmosis, and the concentrated water produced is returned to the biochemical unit. The water produced by reverse osmosis meets the reuse standards and can be recycled.

[0056] The water quality of a certain ethylene alkali slag wastewater is as follows: COD 24950mg / L, chloride ion 1705mg / L, sulfate ion 10400mg / L, total salt content 53000mg / L, sulfide 3100mg / L, ammonia nitrogen 43mg / L, organic nitrogen 290mg / L, total nitrogen 400mg / L, pH 12.1, and the inlet flow rate is 20t / h.

[0057] The above-mentioned ethylene alkali residue wastewater 20t / h first enters the regulating tank, where it is mixed with the primary nanofiltration concentrated water and the homogeneous catalyst, and hydrochloric acid is added to adjust the pH to 5. The flow rate after mixing is 27.5t / h; the homogeneous catalyst adopts a copper-zinc composite catalyst. After mixing, the copper metal ion concentration in the liquid is about 80mg / L, and the zinc metal ion concentration is about 80mg / L. After heat exchange, the wastewater temperature of the regulating tank outlet water rises to 150°C and enters the wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 200°C, the pressure is 4MPa, and the liquid space velocity is 1h -1, the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 65°C by the heat exchange unit, then cooled to 45°C by the cooler, and then divided into two streams, one of which enters the primary nanofiltration for catalyst recovery, with a flow rate of 21.5 t / h, the catalyst recovery rate is 78.2%, one stream directly enters the lower regulating tank, with a flow rate of 6t / h; the pore size of the first-stage nanofiltration membrane is 1.5nm, the water production rate is 65.1%, the metal catalyst, sulfate, macromolecular organic matter, etc. are intercepted and enter the concentrated water side, and most of the sodium, potassium, chloride ions, ammonia nitrogen, small molecular organic matter, etc. pass through the nanofiltration membrane into the water production side, the first-stage nanofiltration concentrated water is refluxed to the regulating tank, and the first-stage nanofiltration produced water enters the regulating tank; the regulating tank is adjusted to pH 6.5 by adding sodium hydroxide, and then enters the biochemical unit; the biochemical unit adopts BAF process, the strain is salt-tolerant bacteria GXNYJ-DL-1, the dissolved oxygen is controlled at more than 2mg / L, the wastewater retention time is 48h, and the effluent enters the secondary nanofiltration after ozone catalytic oxidation treatment, and the ozone dosage is 150mg(O 3 ) / L (water); the pore size of the secondary nanofiltration membrane is also 1.5nm, the water production rate is 64.3%, the concentrated water enters the MVR and crystallization unit, and finally obtains sodium sulfate with a purity of 96.1%. The produced water is further treated by reverse osmosis, and the reverse osmosis water production rate is 55.5%. The reverse osmosis concentrated water is returned to the biochemical unit, and its produced water COD is 33mg / L, the salt content is less than 1500mg / L, and the total nitrogen is less than 5mg / L, which meets the reuse standard and can be recycled. The pollution factor removal effect of each unit is shown in Table 1, and the wet oxidation treatment efficiency is shown in Table 2.

[0058] Table 1

[0059]

[0060] Table 2

[0061]

[0062] It can be seen from this embodiment that the process method of the present invention realizes the efficient operation of homogeneous catalytic wet oxidation. In view of the problems of high COD, high toxicity, and difficulty in degradation of ethylene alkali residue wastewater, the COD removal rate of the wet oxidation unit of this embodiment is as high as 96.4%, the total nitrogen removal rate is 88.2%, and the sulfide removal rate is greater than 99%, ultimately achieving zero discharge of ethylene alkali residue wastewater. At the same time, through the combination with membrane technology, the loss problem of homogeneous catalyst is solved, and the catalyst recovery rate of this embodiment can reach 78.2%.

[0063] Example 4

[0064] use Figure 4 The process shown in the figure treats a certain ethylene alkali residue wastewater

[0065] The water quality of a certain ethylene alkali slag wastewater is as follows: COD 40150mg / L, chloride ion 2610mg / L, sulfate ion 18500mg / L, total salt content 83000mg / L, sulfide 5100mg / L, ammonia nitrogen 66mg / L, organic nitrogen 500mg / L, total nitrogen 750mg / L, pH 12.3, and the inlet flow rate is 20t / h.

[0066] The above-mentioned ethylene alkali residue wastewater 20t / h first enters the regulating tank, where it is mixed with the primary nanofiltration concentrated water and homogeneous catalyst, and hydrochloric acid is added to adjust the pH to 4.9. The flow rate after mixing is 29 t / h; the homogeneous catalyst adopts a copper-zinc composite catalyst. After mixing, the copper metal ion concentration in the liquid is about 100mg / L, and the zinc metal ion concentration is about 100mg / L. After heat exchange, the wastewater temperature of the regulating tank outlet water rises to 150°C and enters the wet oxidation reactor; the reaction temperature of the wet oxidation reactor is 200°C, the pressure is 4MPa, and the liquid space velocity is 1h -1 , the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 65°C by the heat exchange unit, then cooled to 45°C by the cooler, and then divided into two streams, one of which enters the primary nanofiltration for catalyst recovery, with a flow rate of 20 t / h, the catalyst recovery rate is 68.9%, one stream directly enters the lower regulating tank, with a flow rate of 9t / h; the pore size of the first-stage nanofiltration membrane is 1.5nm, the water production rate is 55%, the metal catalyst, sulfate, macromolecular organic matter, etc. are intercepted and enter the concentrated water side, and most of the sodium, potassium, chloride ions, ammonia nitrogen, small molecular organic matter, etc. pass through the nanofiltration membrane into the water production side, the first-stage nanofiltration concentrated water is refluxed to the regulating tank, and the first-stage nanofiltration produced water enters the regulating tank; the regulating tank adds sodium hydroxide to adjust the pH to 6.4, and then enters the biochemical unit; the biochemical unit adopts the BAF process, the strain is the salt-tolerant bacteria GXNYJ-DL-1, the dissolved oxygen is controlled at more than 2mg / L, the wastewater retention time is 60h, and the effluent enters the secondary nanofiltration after ozone catalytic oxidation treatment, and the ozone dosage is 160mg(O 3 ) / L (water); the pore size of the secondary nanofiltration membrane is also 1.5nm, the water production rate is 51.8%, and the concentrated water enters the MVR and crystallization unit, and finally obtains sodium sulfate with a purity of 96.5%. The produced water is further treated by reverse osmosis, and the reverse osmosis water production rate is 50%. The reverse osmosis concentrated water is returned to the biochemical unit, and its produced water COD is 35mg / L, the salt content is less than 1500mg / L, and the total nitrogen is less than 5mg / L, which meets the reuse standard and can be recycled. The removal effect of pollution factors of each unit is shown in Table 3, and the wet oxidation treatment efficiency is shown in Table 4.

[0067] Table 3

[0068]

[0069] Table 4

[0070]

[0071] It can be seen from this embodiment that the process method of the present invention can treat ethylene alkali residue wastewater of different concentrations, and ultimately achieves efficient treatment of ethylene alkali residue wastewater by adjusting the amount of catalyst added, two-stage nanofiltration water production rate, biochemical residence time, ozone dosage, reverse osmosis water production rate and other methods.

[0072] Example 5

[0073] use Figure 4 The process shown in the figure treats a certain ethylene alkali residue wastewater

[0074] The water quality of ethylene alkali slag wastewater is as follows: COD 61000mg / L, chloride ion 4510mg / L, sulfate ion 30500mg / L, total salt content 155000mg / L, sulfide 10100mg / L, ammonia nitrogen 120mg / L, organic nitrogen 700mg / L, total nitrogen 980mg / L, pH 12.5, and inlet flow rate 20t / h.

[0075] The total salt content of ethylene alkali residue wastewater is 155000 mg / L, which has exceeded the optimal salt tolerance range (10-130 g / L) of the salt-tolerant bacteria GXNYJ-DL-1. In order to obtain a better treatment effect, the ethylene alkali residue wastewater is diluted with a small amount of fresh water at this time. The volume ratio of ethylene alkali residue wastewater to fresh water is 1:1. After dilution, the total salt content of the mixed water is below 80000 mg / L. The specific operating conditions for the treatment of alkali residue wastewater are similar to those in Example 4, and zero discharge of ethylene alkali residue wastewater is finally achieved.

[0076] This embodiment shows that the present invention can effectively treat ultra-high concentration ethylene alkali residue wastewater with only a small amount of dilution water.

[0077] Example 6

[0078] The water quality of the treated ethylene alkali residue wastewater is the same as that in Example 3, and the process route, implementation steps, and reaction parameters are also the same as those in Example 3. Only the type of catalyst is different. The treatment results of the wet oxidation unit are shown in Table 5, and the concentration of the pollution factors of each unit is shown in Table 6.

[0079] Table 5

[0080]

[0081] Table 6

[0082]

[0083] As can be seen from Tables 5 and 6, when a single copper catalyst is used, the catalyst dosage is 160 mg / L, and the COD removal rate and total nitrogen removal rate of the final wet oxidation unit are slightly increased, but the COD of the biochemical unit effluent increases to 351 mg / L. When the ozone dosage remains unchanged, the ozone catalytic effluent COD increases to 200 mg / L. The reason is that excessive copper ions will passivate biological enzymes, thereby inhibiting sludge microorganisms to a certain extent. Although the copper-zinc composite catalyst used in Example 3 has a slightly reduced treatment efficiency, the inhibitory effect on microorganisms is within an acceptable range. In this embodiment, the water quality of the terminal effluent can be ensured by adjusting the dosage of ozone in the ozone catalytic unit, and the corresponding treatment cost will increase slightly.

[0084] Example 7

[0085] The water quality of the ethylene alkali slag wastewater is the same as that in Example 3, and the process route, implementation steps, and reaction parameters are also the same as those in Example 3. The difference is that the catalyst is replaced by a monoferric catalyst, and the pH of the regulating tank in the wet oxidation section is adjusted to 3, and the pH of the deep treatment section is adjusted back to 6.5. The treatment results of the wet oxidation unit are shown in Table 7.

[0086] Table 7

[0087]

[0088] It can be seen from this example that when a single iron catalyst is used with the same dosage, the COD removal rate of the homogeneous catalytic wet oxidation is slightly increased compared with Example 3, but the total nitrogen removal rate is reduced to 77.6%.

[0089] Example 8

[0090] The water quality of the ethylene alkali slag wastewater is the same as that in Example 3, and the process route, implementation steps, and reaction parameters are also the same as those in Example 3. The difference is that the catalyst is replaced with a single nickel catalyst. The treatment results of the wet oxidation unit are shown in Table 8.

[0091] Table 8

[0092]

[0093] It can be seen from this example that, when a nickel catalyst is used, the COD removal rate and total nitrogen removal rate of homogeneous catalytic wet oxidation are decreased to varying degrees compared with Example 3, so it is necessary to increase the residence time and ozone dosage of the subsequent biochemical unit. The nickel dosage of this example is 160 mg / L. When the catalyst recovery rate is 78.2%, the nickel content that finally enters the biochemical unit is 10.5 mg / L. The "Petroleum Refining Industry Pollutant Emission Standard" GB31570-2015 requires that the total nickel ion concentration of wastewater shall not be greater than 1 mg / L. However, due to the zero-emission process route adopted by the present invention, there is almost no nickel in the reverse osmosis water, and the nickel is finally present in the miscellaneous salts of the MVR unit.

[0094] Comparative Example 1

[0095] The water quality of ethylene alkaline slag wastewater treated in Comparative Example 1 is the same as that in Example 3, and the process route, implementation steps, and reaction parameters are also the same as those in Example 3, but no metal catalyst is added. The results of the wet oxidation unit treatment are shown in Table 9.

[0096] Table 9

[0097]

[0098] It can be seen from this comparative example that without adding a catalyst, conventional wet oxidation is used, and the reaction conditions are the same as those in Example 3. The final COD removal rate is only 43.5%, the total nitrogen removal rate is only 16.2%, and the sulfide removal rate is within an acceptable range. Therefore, the conventional wet oxidation process has limited removal capabilities for organic matter and total nitrogen, and COD removal is more of a pseudo-COD removal caused by sulfides.

[0099] Comparative Example 2

[0100] The water quality of the ethylene alkali slag wastewater treated in Comparative Example 2 is the same as that in Example 3, and the process route, implementation steps, and reaction parameters are also the same as those in Example 3. Only common bacteria are added to the biochemical unit. The results of the pollution factor concentrations of the key units are shown in Table 10.

[0101] Table 10

[0102]

[0103] It can be seen from Table 10 that when ordinary bacteria are added to the biochemical unit, the COD of the effluent from the biochemical unit is 521 mg / L when the total salt content is as high as 63950 mg / L. The COD removal rate is only 14.3%, which is much lower than that in Example 3. This is because ordinary bacteria basically do not have salt tolerance and cannot adapt to high-salt environments.

[0104] It can be seen from this comparative example that the salt-tolerant bacteria GXNYJ-DL-1 used in the biochemical unit has more advantages than ordinary bacteria in the deep treatment section of the ethylene alkali slag wastewater. It has the advantages of a wide salt tolerance range, strong impact resistance and high treatment efficiency.

[0105] Comparative Example 3

[0106] The water quality of the ethylene alkaline slag wastewater treated in Comparative Example 3 is the same as that in Example 4. The process route, implementation steps, and reaction parameters are also the same as those in Example 4. The biochemical unit (including salt-tolerant bacteria) is eliminated, and the effluent from the regulating tank is directly fed into the ozone catalytic oxidation. The concentrations of pollution factors in key units are shown in Table 11.

[0107] Table 11

[0108]

[0109] It can be seen from Table 11 that when the ozone concentration is constant, that is, the ozone dosage is 160 mg (O 3 ) / L (water), the COD of the regulating pool effluent was reduced from 1126 mg / L to 958 mg / L, and to 112 mg / L in Example 4 (the effluent from ozone catalytic oxidation in Example 4), it was necessary to continue to add about 800 mg (O 3 ) / L(water) ozone, the treatment cost will increase by about 24 yuan / t(water), which will greatly increase the overall operating cost.

Claims

1. A method for treating ethylene alkali slag wastewater by homogeneous catalytic wet oxidation, comprising a wet oxidation section, a deep treatment section and a salt treatment section; The wet oxidation section includes a regulating tank, a heat exchange unit, a wet oxidation reactor, a cooler and a first-stage nanofiltration; the ethylene alkali residue wastewater first enters the regulating tank, is mixed with the first-stage nanofiltration concentrated water and the homogeneous catalyst, and is acidified for pH adjustment, and then enters the heat exchange unit, and enters the wet oxidation reactor after heat exchange and temperature increase; the effluent from the wet oxidation reactor is heat exchanged by the heat exchange unit and then cooled by the cooler, part of which enters the first-stage nanofiltration for treatment, and part of which enters the deep treatment section; the first-stage nanofiltration concentrated water is refluxed to the regulating tank, and the first-stage nanofiltration produced water enters the deep treatment section; the homogeneous catalyst is a transition metal catalyst, selected from one or more of copper, iron, manganese, zinc and nickel; the transition metal in the homogeneous catalyst exists in the form of a metal salt compound or a complex and is dissolved in the liquid phase; the effluent from the cooler is divided into two streams, one flows to the first-stage nanofiltration unit, and the other flows to the regulating tank, and the water volume flowing to the regulating tank accounts for 1% to 40%; The deep treatment section includes a regulating tank, a biochemical unit and ozone catalytic oxidation in sequence; the partially cooled wet oxidation reactor effluent and the primary nanofiltration product water enter the regulating tank, and after pH adjustment, enter the biochemical unit for treatment. The biochemical unit uses the salt-tolerant bacteria GXNYJ-DL-1 to remove COD, and the treated wastewater is subjected to ozone catalytic oxidation to further decompose the difficult-to-treat organic matter; wherein, The halotolerant bacteria GXNYJ-DL-1 ( Halomonas nigrificans ) was deposited in the General Microbiology Center of China Microorganism Culture Collection Administration on July 13, 2020, with the deposit number CGMCC No. 20350; The salt treatment section includes secondary nanofiltration, reverse osmosis, MVR reactor and segmented crystallization salt separation unit; the ozone catalytic oxidation effluent enters the secondary nanofiltration for further concentration, the secondary nanofiltration concentrated water enters the MVR reactor and the segmented crystallization salt separation unit in turn, and finally obtains the product sulfate and miscellaneous salts, the secondary nanofiltration produced water is treated by reverse osmosis, the reverse osmosis concentrated water is returned to the biochemical unit, and the reverse osmosis produced water meets the reuse standard and is recycled.

2. The method according to claim 1, characterized in that Acid is added into the adjustment tank to adjust the pH to 2-6, and the acid is hydrochloric acid or sulfuric acid.

3. The method according to claim 2, characterized in that The acid is hydrochloric acid.

4. The method according to claim 1, characterized in that: The heat exchange unit raises the outlet water temperature of the regulating tank to 130-160°C and reduces the outlet water temperature of the wet oxidation reactor to 50-75°C.

5. The method according to claim 1, characterized in that The homogeneous catalyst is a copper-zinc composite catalyst.

6. The method according to claim 1, characterized in that The homogeneous catalyst is added according to the COD mass concentration and metal ion mass concentration ratio of 5000:1 to 10:1, and is supplemented during operation according to the catalyst loss rate and the change in reaction liquid concentration.

7. The method according to claim 1, characterized in that The reaction temperature of the wet oxidation reactor is 150-300°C, the reaction pressure is 2MPa-10MPa, and the liquid space velocity is 0.25-4h -1 , the gas-liquid volume ratio is 20:1~500:

1.

8. The method according to claim 1, characterized in that The cooler reduces the outlet water temperature of the wet oxidation reactor to 30-50°C.

9. The method according to claim 1, characterized in that: The water production rate of the first-stage nanofiltration is 50% to 75%, and the membrane pore size is between 1 and 5 nm.

10. The method according to claim 1, characterized in that Alkali is added into the regulating tank to adjust the pH to 6-9, and the alkali is sodium hydroxide or potassium hydroxide.

11. The method according to claim 1, characterized in that: The salt concentration of the biochemical unit influent is controlled to be below 250 g / L.

12. The method according to claim 1 or 11, characterized in that: The salt concentration of the biochemical unit influent is controlled to be 50-130 g / L.

13. The method according to claim 1, characterized in that The biochemical unit is selected from BAF or MBR process, the dissolved oxygen is controlled above 2 mg / L, and the wastewater retention time is 12 to 96 hours.

14. The method according to claim 1, characterized in that The ozone dosage in the ozone catalytic oxidation is 50-500 mg (O3) / L (water).

15. The method according to claim 1, characterized in that The water production rate of the secondary nanofiltration is between 55% and 80%, and the membrane pore size is between 1 and 5 nm.

16. The method according to claim 1, characterized in that The water production rate of the reverse osmosis is between 50% and 80%, and the membrane pore size is less than 1nm.

17. The method according to claim 1, characterized in that The segmented crystallization salt separation utilizes the fact that the solubility of Na2SO4 decreases with increasing temperature within the range of 50-120°C. When the temperature is increased, Na2SO4 is first precipitated to obtain high-purity Na2SO4, and then the temperature is lowered, other salts are precipitated due to supersaturation to obtain mixed salts.

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