CN116081837A - Method for treating ethylene alkali slag wastewater by using homogeneous catalytic wet oxidation - Google Patents

Abstract

The invention discloses a method for treating ethylene alkali slag wastewater by using homogeneous catalytic wet oxidation, which includes a wet oxidation section, an advanced treatment section and a salt treatment section; a homogeneous catalyst is used to carry out wet oxidation treatment on ethylene alkali slag wastewater, and the effluent part is subjected to primary nano Filtration treatment, the primary nanofiltration concentrated water is refluxed to the wet oxidation, part of the wet oxidation effluent and the primary nanofiltration product water are subjected to biochemical treatment and ozone catalytic oxidation to remove COD, and then the secondary nanofiltration is carried out, and the secondary nanofiltration concentrated water enters in sequence The MVR reactor and segmental crystallization separate the salt, and finally obtain the product sulfate and miscellaneous salts. The water produced by the second-stage nanofiltration is reverse osmosis, and the concentrated water is returned to the biochemical unit, and the produced water meets the reuse standard. In view of the high COD, high salt content, high toxicity and refractory characteristics of ethylene alkali slag wastewater, the present invention adopts a treatment process centered on homogeneous catalytic wet oxidation to give full play to the high catalytic activity and high treatment efficiency of homogeneous catalytic wet oxidation characteristics, greatly improving the processing capacity of wet oxidation.

Description

Method for treating ethylene alkali slag wastewater by using homogeneous catalytic wet oxidation

technical field

The invention relates to a treatment method for ethylene alkali slag wastewater, in particular to a method for treating ethylene alkali slag wastewater by using homogeneous catalytic wet oxidation, and belongs to the technical field of wastewater treatment.

Background technique

Ethylene waste lye is the waste water produced by alkali washing of cracked gas in the process of ethylene production. The pollutant composition is relatively complex, with high content of organic matter, sulfide and salt, and also contains malodorous gases such as mercaptan and sulfide. Governance is difficult. With the expansion of the scale of ethylene plants, the discharge of waste caustic soda continues to increase, and its harmless treatment and comprehensive utilization have become the focus of attention.

Ethylene alkali slag wastewater must be pretreated before it can enter the biochemical system, and advanced oxidation is a commonly used pretreatment method, which can convert refractory and highly toxic macromolecular organics into degradable, low-toxic small molecular organics and even inorganic substances. 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 processing costs, and it is difficult for industrial application. Fenton oxidation exists Complicated operation, unstable hydrogen peroxide, loss of iron ions and other problems, the application of ozone catalytic oxidation is also limited with the national control of ozone pollutants, and its treatment cost is also high, which is limited to terminal advanced treatment.

At present, the most mainstream method of ethylene alkali slag wastewater is wet oxidation method, which operates at high temperature (120-320°C) and high pressure (0.5-20MPa), uses gaseous oxygen as an oxidant, and oxidizes and decomposes organic matter in water into small molecules Organic matter or inorganic matter, it 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, which requires high equipment materials and high one-time investment, and wet oxidation can only be used as pretreatment, and its effluent also has high COD.

In order to reduce the temperature and pressure required for the reaction and improve the treatment effect, Catalytic wet air oxidation (CWAO for short) has become a research hotspot in recent years. CN201510274988.5 discloses a catalyst for catalytic wet oxidation of refractory organic wastewater. The catalyst is a "noble metal-transition metal-rare earth" composite catalyst, and the main component of the carrier FSC is alumina; CN201410340574.3 discloses a catalytic wet oxidation treatment Catalysts and preparation methods thereof, which use noble metal-non-noble metal nano-alloys as active components and activated carbon as a carrier; CN201510661575.2 discloses a heterogeneous wet oxidation catalyst, and its components include a composite oxide carrier and a small amount of noble metal; CN201310621017.4 discloses The preparation method of catalyst carrier for catalytic wet oxidation is presented. The carrier uses activated carbon as the core and amorphous silica-alumina as the shell.

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

Since homogeneous catalysis has no internal and external diffusion effects and high dispersion, its catalytic efficiency is higher than that of heterogeneous catalysis, and the catalyst preparation is much simpler than that of heterogeneous catalysts, but the biggest problem with homogeneous catalysis in wet oxidation is Loss of metal catalyst. At present, there are few studies in this direction. CN201210225873.3 provides a method for homogeneous catalytic wet oxidation treatment of industrial wastewater. A ring gear packing is placed in the fixed bed reactor. The homogeneous catalyst uses an iron-based catalyst, but the patent does not mention Catalyst loss and corresponding solutions; CN201210350157.8 provides a catalytic wet oxidation pretreatment method for glyphosate production wastewater, adding a multi-component homogeneous catalyst, the catalyst is a soluble transition metal mixed salt, the patent also does not mention the catalyst Churn problem.

Contents of the invention

In view of the above deficiencies, the present invention provides a treatment method for ethylene alkali slag wastewater, which can realize the treatment of ethylene alkali slag wastewater by using a combination of processes such as homogeneous catalytic wet oxidation, membrane technology, special salt-tolerant bacteria, ozone catalytic oxidation, and MVR salt separation. High-efficiency treatment and zero emissions, and also solve the problem of catalyst loss in the homogeneous catalytic process, which can realize the recycling of catalysts.

In order to realize above technical purpose, the technical scheme that the present invention adopts is as follows:

A method for treating ethylene alkali slag wastewater by using homogeneous catalytic wet oxidation, including a wet oxidation section, an advanced 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 primary nanofiltration; the ethylene alkali slag wastewater first enters the regulating tank, is mixed with the concentrated water of the primary nanofiltration, and a homogeneous catalyst. Add acid to adjust the pH, enter the heat exchange unit, and then enter the wet oxidation reactor after heat exchange; the effluent from the wet oxidation reactor is cooled by the cooler after heat exchange by the heat exchange unit, part of it enters the first-level nanofiltration for treatment, and part of it enters the Advanced treatment section; the first-stage nanofiltration concentrated water returns to the regulating tank, and the first-stage nanofiltration product water enters the advanced treatment section;

The advanced treatment section includes a regulating tank, a biochemical unit and ozone catalytic oxidation in sequence; the partially cooled wet oxidation reactor effluent and first-stage nanofiltration water enter the regulating tank, and enter the biochemical unit for treatment after pH adjustment. The biochemical unit adopts The salt-tolerant bacteria GXNYJ-DL-1 removes COD, and the treated wastewater is subjected to ozone catalytic oxidation to further decompose refractory organic matter; among them, the salt-tolerant bacteria GXNYJ-DL-1 ( Halomonas nigrificans ) has been preserved on July 13, 2020 In the General Microbiology Center of China Microbiological Culture Collection Management Committee, the preservation number is CGMCC No. 20350;

The salt treatment section includes secondary nanofiltration, reverse osmosis, MVR reactor and segmented crystallization and salt separation unit; the effluent from ozone catalytic oxidation enters the secondary nanofiltration for further concentration, and the concentrated water of the secondary nanofiltration enters the MVR reactor and separation unit in turn. The stage crystallization and salt separation unit finally obtains the product sulfate and miscellaneous salts. The secondary nanofiltration product water is treated by reverse osmosis, and the reverse osmosis concentrated water is sent back to the biochemical unit. The reverse osmosis product water reaches the reuse standard and is recycled.

Further, 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.

Further, the heat exchange unit is composed of a plurality of heat exchangers to exchange heat between 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 heat exchange, 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.

Further, 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 is a metal salt compound Or in the form of complexes, and dissolved in the liquid phase.

Further, the homogeneous catalyst is added according to the ratio of COD mass concentration to metal ion mass concentration of 5000:1-10:1, and is properly supplemented according to the loss rate of the catalyst and the change of the concentration of the reaction solution during normal operation.

Further, the wet oxidation reactor is a bubbling flow internal circulation reactor in the 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 substances; those skilled in the art should understand that ethylene alkali slag wastewater is a typical difficult-to-treat wastewater, and wet oxidation alone has a strong ability to remove sulfides in wastewater, and a weak ability to remove organic matter, but under the condition of catalyst , Oxygen under high temperature and pressure is more likely to undergo free radical reactions, and under the action of strong oxidizing properties of free radicals, the decomposition and transformation ability and reaction rate of organic matter are greatly improved. On the other hand, the homogeneous catalyst itself has high activity and high selectivity, and its treatment of special pollutants is more rapid and effective, and the problem of its easy loss is also solved by membrane technology.

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

Further, the cooling medium of the cooler is circulating water, which further lowers the temperature of the effluent from the wet oxidation reactor to 30-50°C, meeting the temperature requirements of the subsequent nanofiltration membrane.

Further, the outlet water of the cooler is divided into two streams, one stream flows to the first-stage nanofiltration unit, and the other stream flows to the regulating pool, and the water flowing to the regulating pool accounts for 1% to 40%.

Further, the first-stage nanofiltration water production rate is 50%-75%, and the membrane pore size is between 1-5nm, which can intercept metals, high-valent salts (such as sulfates, carbonates), Macromolecular organic matter (relative molecular mass greater than 200), etc., is intercepted and enters the concentrated water side, in which the metal of the homogeneous catalyst flows back to the regulating tank, and returns to the wet oxidation reactor for recycling after heat exchange and heating; the first-stage nanofiltration product water includes Unreacted small molecule organic matter, monovalent salts and ammonia nitrogen.

Further, an alkali is added in the adjustment tank to adjust the pH to 6-9, and the alkali is sodium hydroxide or potassium hydroxide.

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

Further, the biochemical unit is selected from BAF or MBR process, which can not only remove COD but also has a filtering function, the dissolved oxygen is controlled above 2mg/L, and the residence time of wastewater is 12-96h.

Further, the ozone catalytic oxidation unit utilizes the hydroxyl radicals generated under the catalytic action of ozone, which can further degrade the residual naphthenic acid and phenolic substances in the wastewater, and improve the biodegradability of the wastewater; the dosage of ozone is 50- 500mg (O ₃ )/L (water).

Those skilled in the art should understand that the salt-tolerant bacteria GXNYJ-DL-1 used in the biochemical unit solves the problem that common bacteria cannot survive under the condition of high salt content, and its resistance to sulfide toxicity also solves the problem that common bacteria cannot survive under the presence of a large amount of sulfate. Salt-tolerant bacteria have problems with high sulfide concentration or even inability to survive due to uneven aeration or local anaerobic bacteria. It is especially suitable for high-salt wastewater with sulfate as the main body, such as oil refining alkali slag wastewater; those skilled in the art It should also be understood that ozone catalytic oxidation is an advanced oxidation method with high processing costs, and its optimal processing link is terminal advanced treatment. The homogeneous catalytic wet oxidation at the front end of the present invention removes most of the Organic matter, the biochemical unit uses special salt-tolerant bacteria to further remove organic matter, so that the processing load and processing cost of the ozone catalytic oxidation unit are within a controllable range. The main function of ozone catalytic oxidation is to further remove organic matter, which can reduce miscellaneous salts (solid Hazardous waste) production, improve the purity of sodium sulfate products.

Further, the water production rate of the secondary nanofiltration is between 55% and 80%, and the membrane pore size is between 1 and 5nm, which mainly serves to further concentrate the high-salt wastewater.

Further, 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 and making the effluent meet the reuse standard;

Further, the steam generated by the MVR reactor is condensed and recycled, and the liquid phase enters the crystallizer for segmental crystallization and salt separation. The salt separation technology is based on the fact that the solubility of most salts varies with temperature increases with increasing temperature, while the solubility of Na ₂ SO ₄ decreases with the increase of temperature. Under high temperature conditions, with the concentration of salt, Na ₂ SO ₄ is first precipitated due to supersaturation, and high-purity Na ₂ SO ₄ is obtained. When the temperature drops, continuing to concentrate will cause other salts to precipitate due to supersaturation, resulting in miscellaneous salts, including sodium chloride, sodium carbonate, catalytic metal salts, etc., and may also contain a small amount of organic matter.

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

(1) In view of the characteristics of high COD, high salt content, high toxicity and refractory degradation of ethylene alkali slag wastewater, the present invention adopts a treatment process centered on homogeneous catalytic wet oxidation to give full play to the high catalytic activity of homogeneous catalytic wet oxidation, The characteristics of high processing efficiency have greatly improved the processing capacity of wet oxidation.

(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 membrane and electrodialysis single anion membrane, and realizes the recycling of the catalyst; the price of the catalyst used in the present invention is The controllable non-precious metal catalyst achieves controllable cost while ensuring the effect.

(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 nanofiltration and directly enters the next unit, similar to "circulation The method of "water sewage discharge" maintains the salt balance and saves the desalination unit; the loss of catalyst is small, and the price is cheap, which can be added through the front end, and the overall treatment cost is lower than that of catalyst recovery.

(4) The salt-tolerant bacterial 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-tolerant range. It plays an irreplaceable role in the treatment of alkali slag wastewater, laying the foundation for the use of subsequent catalytic oxidation processes and overall cost control.

(5) The existing ethylene alkali slag wastewater is often pretreated by dilution, and the dilution factor is as high as dozens of times. The scale of the final sewage treatment is greatly increased, and the treatment device needs a large area. However, the process scheme provided by the present invention does not require wastewater Dilution, small treatment scale, small footprint, and finally zero discharge of wastewater.

Other features and advantages of the present invention will be described in detail in the detailed description that follows.

Description of drawings

Fig. 1. the growth curve of bacterial strain in embodiment 1 under different salinity;

Fig. 2. bacterial strain in embodiment 1 is to the removal rate of COD under different salinity;

Fig. 3. bacterial strain in embodiment 2 is at the growth curve of S ^2- concentration;

Fig. 4. the processing flowchart of ethylene alkali slag wastewater in embodiment 3.

Instructions for Preservation of Biological Materials

The highly salt-tolerant strain ( Halomonas nigrificans ) GXNYJ-DL-1 provided by the present invention is preserved in the General Microbiology Center of the China Microbiological Culture Collection Management Committee; address: Institute of Microbiology, Chinese Academy of Sciences, No. 3, No. 1, Beichen West Road, Chaoyang District, Beijing; Deposit number: CGMCC No. 20350; Deposit date: July 13, 2020.

Detailed ways

The present invention will be described in further detail below in conjunction with specific embodiments. Embodiments are carried out on the premise of the technical solutions of the present invention, and detailed implementation methods and specific operation processes are provided, but the protection scope of the present invention is not limited to the following embodiments.

Example 1

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

The growth curves of the strains at different salt concentrations are shown in Figure 1, and the COD removal rates of the strains at different salt concentrations after 72 hours are shown in Figure 2. It can be seen from Figure 1 and Figure 2 that the growth of the strain is better under the salt concentration of 10-130g/L, and the increase of salt content will be accompanied by the increase of adaptation period, but the COD removal rate (initial phenol COD is about 1247mg/L) is maintained At a relatively high level; at a salt concentration of 250g/L, the strain adapts to a period of up to 50 hours. After the adaptation period, the strain begins to enter the growth phase, and the OD ₆₀₀ value increases significantly, indicating that the strain is not completely dead, and the corresponding COD removal rate exceeds 50 %.

It can be seen from this example that the strain GXNYJ-DL-1 has strong salt tolerance, and the COD removal rate can still reach 53% at a salt concentration of 250g/L, but the optimal salt concentration is 50-130g/L.

Example 2

Determination of S2 ^- toxicity resistance of highly salt-tolerant bacteria GXNYJ-DL-1:

The growth curves of the strains under different S ² -concentrations are shown in Figure 3. The first 24h is the resting period, and the last 48h is the shaking reaction period. It can be seen from Figure 3 that the growth of bacterial strains during the standing period is very slow. On the one hand, it is restricted by dissolved oxygen, and on the other hand, it is inhibited by the toxicity of ^S2- . growth, but compared with Example 1, the growth of the bacterial strain is relatively slow; after two days of growth, the overall OD ₆₀₀ value rose to 0.45 from 0.25, indicating that the bacterial strain did not lose vigor due to the toxicity of S in the early ^stage. After a relatively long adaptation period, the vigor gradually recovered, especially in the S ^{2 -} sample containing 300mg/L, the concentration of the strain was still increasing steadily.

From this example, it can be seen that the strain GXNYJ-DL-1 has strong resistance to S ² -toxicity, and is especially suitable for treating wastewater containing high sulfate.

Example 3

Process method of the present invention for treating ethylene alkali slag waste water

The process flow chart for the treatment of ethylene alkali residue wastewater is shown in Figure 4: the ethylene alkali residue wastewater first enters the adjustment tank, mixes with the first-level nanofiltration concentrated water and a homogeneous catalyst, and adds acid to adjust the pH, and then enters the heat exchange unit. The heat exchange unit uses a heat exchanger to exchange heat between 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 to the tube side, and the outlet water of the regulating tank goes to the shell side. The outlet water enters the heat exchange unit for heat exchange and cooling, and then is divided into two streams after being cooled by the cooler, one directly enters the regulating tank, the other enters the first-stage nanofiltration, the first-stage nanofiltration concentrated water returns to the regulating tank, and the first-stage The nanofiltration produced water flows to the regulating tank; the pH of the regulating tank is adjusted by adding alkali to meet the pH requirements of the 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 the wastewater, and the biochemical effluent enters the Ozone catalytic oxidation, ozone catalytic oxidation effluent enters the secondary nanofiltration; secondary nanofiltration concentrated water enters the MVR and crystallization unit, and finally obtains miscellaneous salts and product sulfates, and the secondary nanofiltration product water is further treated by reverse osmosis to produce concentrated The water is returned to the biochemical unit, and the reverse osmosis produced water meets the reuse standard and can be recycled.

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 The nitrogen is 290mg/L, the total nitrogen is 400mg/L, the pH is 12.1, and the influent flow rate is 20t/h.

The 20t//h ethylene alkali residue wastewater first enters the regulating tank, where it is mixed with the first-stage nanofiltration concentrated water and a homogeneous catalyst, and hydrochloric acid is added to adjust the pH to 5, and the flow rate after mixing is 27.5t/h; the homogeneous catalyst Using a copper-zinc composite catalyst, the concentration of copper metal ions in the mixed liquid is about 80mg/L, and the concentration of zinc metal ions is about 80mg/L. After heat exchange, the temperature of the effluent from the regulating tank rises to 150°C and enters the wet oxidation reactor; wet oxidation The reaction temperature of the reactor is 200°C, the pressure is 4MPa, the liquid space velocity is 1h ^-1 , and the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 65°C by the heat exchange unit, and then cooled to 45°C by the cooler. Then it is divided into two streams, one stream enters the first-stage nanofiltration for catalyst recovery, the flow rate is 21.5 t/h, the catalyst recovery rate is 78.2%, and the other stream directly enters the lower regulating tank, the flow rate is 6t/h; the first-stage nanofiltration membrane The pore size is 1.5nm, and the water production rate is 65.1%. Metal catalysts, sulfates, macromolecular organic substances, etc. are trapped into the concentrated water side, and most of sodium, potassium, chloride ions, ammonia nitrogen, and small molecular organic substances enter through the nanofiltration membrane. On the product water side, the primary nanofiltration concentrated water returns to the regulating tank, and the primary nanofiltration product 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 the BAF process, and the bacteria It is a salt-tolerant bacteria GXNYJ-DL-1, the dissolved oxygen is controlled above 2mg/L, the residence time of wastewater is 48h, the effluent is subjected to ozone catalytic oxidation treatment and then enters the secondary nanofiltration, and the dosage of ozone is 150mg(O ₃ )/L (water); the pore size of the secondary nanofiltration membrane is also 1.5nm, and 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 water rate is 55.5%, and the concentrated reverse osmosis water is returned to the biochemical unit. The COD of the produced water 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 removal effect of each unit pollution factor is shown in Table 1, and the wet oxidation treatment efficiency is shown in Table 2.

Table 1

Table 2

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

Example 4

Using the process shown in Figure 4 to treat a certain ethylene alkali slag wastewater

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 The nitrogen is 500mg/L, the total nitrogen is 750mg/L, the pH is 12.3, and the influent flow rate is 20t/h.

The 20t//h ethylene alkali slag wastewater first enters the regulating tank, where it is mixed with the first-stage nanofiltration concentrated water and the homogeneous catalyst, and hydrochloric acid is added to adjust the pH to 4.9, and the flow rate after mixing is 29 t/h; the homogeneous catalyst Copper-zinc composite catalyst is used, the concentration of copper metal ions in the mixed liquid is about 100mg/L, and the concentration of zinc metal ions is about 100mg/L. The temperature of the effluent from the regulating tank rises to 150°C after heat exchange and enters the wet oxidation reactor; wet oxidation The reaction temperature of the reactor is 200°C, the pressure is 4MPa, the liquid space velocity is 1h ^-1 , and the gas-liquid volume ratio is 100:1; the wet oxidation effluent is cooled to 65°C by the heat exchange unit, and then cooled to 45°C by the cooler. Then it is divided into two streams, one stream enters the first-stage nanofiltration for catalyst recovery, the flow rate is 20 t/h, and the catalyst recovery rate is 68.9%, and the other stream directly enters the lower regulating tank with a flow rate of 9 t/h; the first-stage nanofiltration membrane The pore size is 1.5nm, and the water production rate is 55%. Metal catalysts, sulfates, macromolecular organic substances, etc. are trapped into the concentrated water side, and most of sodium, potassium, chloride ions, ammonia nitrogen, and small molecular organic substances enter through the nanofiltration membrane. On the product water side, the primary nanofiltration concentrated water returns to the regulating tank, and the primary nanofiltration product water enters the regulating tank; the regulating tank is adjusted to pH 6.4 by adding sodium hydroxide, and then enters the biochemical unit; the biochemical unit adopts the BAF process, and the bacteria It is a salt-tolerant bacteria GXNYJ-DL-1, the dissolved oxygen is controlled above 2mg/L, the residence time of wastewater is 60h, the effluent is subjected to ozone catalytic oxidation treatment and then enters the secondary nanofiltration, and the dosage of ozone is 160mg(O ₃ )/L (water); the pore size of the secondary nanofiltration membrane is also 1.5nm, and the water production rate is 51.8%. The concentrated water enters the MVR and the crystallization unit, and finally obtains sodium sulfate with a purity of 96.5%. The water rate is 50%, and the reverse osmosis concentrated water is returned to the biochemical unit. The COD of the produced water 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 each unit pollution factor is shown in Table 3, and the wet oxidation treatment efficiency is shown in Table 4.

table 3

Table 4

It can be seen from this example that the process of the present invention can treat ethylene alkali slag wastewater with different concentrations, by adjusting the amount of catalyst added, the water production rate of two-stage nanofiltration, the biochemical residence time, the dosage of ozone, the water production rate of reverse osmosis, etc. A variety of ways to finally realize the efficient treatment of ethylene alkali slag wastewater.

Example 5

Using the process shown in Figure 4 to treat a certain ethylene alkali slag wastewater

The water quality of ethylene alkali residue 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, influent flow 20t/h.

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

It can be seen from this example that the present invention can effectively treat ultra-high concentration ethylene alkali slag wastewater with only a small amount of dilution water.

Example 6

The water quality of the ethylene alkali slag wastewater treatment is the same as that of Example 3, and the process route, implementation steps, and reaction parameters are also the same as that of Example 3. Only the type of catalyst is different. See Table 5 for the treatment results of the wet oxidation unit, and see Table 5 for the concentration of each unit pollution factor. 6.

table 5

Table 6

From Table 5 and Table 6, it can be seen that the COD removal rate and total nitrogen removal rate of the final wet oxidation unit increased slightly when the single copper catalyst was used, and the catalyst dosage was 160 mg/L, but the COD of the effluent of the biochemical unit increased to 351mg/L, when the dosage of ozone remains unchanged, the COD of ozone-catalyzed effluent rises to 200mg/L. Tracing it to its cause is that excessively high copper ions will passivate biological enzymes, thereby produce a certain degree of inhibitory effect to sludge microorganisms, and the copper-zinc composite catalyst that embodiment 3 adopts, although treatment efficiency drops slightly, but the inhibitory effect on microorganisms The effect is within the acceptable range. In this embodiment, the water quality of the terminal effluent can be guaranteed by adjusting the dosage of ozone in the ozone catalytic unit, and the corresponding treatment cost will increase slightly.

Example 7

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

Table 7

From this example, it can be seen that the single-iron catalyst is used instead, and the dosage remains unchanged. Compared with Example 3, the COD removal rate of the homogeneous catalytic wet oxidation is slightly increased, but the total nitrogen removal rate is reduced to 77.6%.

Example 8

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

Table 8

It can be known from this example that, compared with Example 3, the COD removal rate and total nitrogen removal rate of homogeneous catalyzed wet oxidation have declined to varying degrees, so it is necessary to increase the residence time of the follow-up biochemical unit and the ozone injection rate. Increase the amount. The dosage of nickel in this example is 160mg/L, and in the case of a catalyst recovery rate of 78.2%, the nickel content that finally enters the biochemical unit is 10.5mg/L, which is required in the "Petroleum Refining Industrial Pollutant Discharge Standard" GB31570-2015 The concentration of nickel ions in the total discharge of wastewater shall not be greater than 1mg/L. However, due to the zero-discharge process route adopted by the present invention, there is almost no nickel in the reverse osmosis water, and the nickel finally exists in the miscellaneous salt of the MVR unit.

Comparative example 1

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

Table 9

It can be seen from this comparative example that without adding catalyst, using conventional wet oxidation, the reaction conditions are the same as 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 acceptable. within range. Therefore, the conventional wet oxidation process has limited ability to remove organic matter and total nitrogen, and the removal of COD is more of a pseudo-COD removal caused by sulfide.

Comparative example 2

The water quality of comparative example 2 processing ethylene alkali slag wastewater is the same as that of Example 3, and the process route, implementation steps, and reaction parameters are also the same as Example 3. Only common bacteria are added to the biochemical unit, and the concentration of key unit pollution factors is shown in Table 10. .

Table 10

It can be seen from Table 10 that when common bacteria are added to the biochemical unit, when the total salt content is as high as 63950mg/L, the COD of the effluent of the biochemical unit is 521mg/L, and the COD removal rate is only 14.3%, which is far lower than that of Example 3. This is Because common strains basically do not have salt-tolerant characteristics, they cannot adapt to high-salt environments.

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

Comparative example 3

The water quality of comparative example 3 treating ethylene alkali slag wastewater is the same as in Example 4, and the process route, implementation steps, and reaction parameters are also the same as in Example 4. The biochemical unit (containing salt-tolerant bacteria) is cancelled, and the effluent of the regulating pool directly enters the ozone catalytic oxidation. See Table 11 for the concentration of pollution factors in key units.

Table 11

It can be seen from Table 11 that under the condition that the concentration of ozone dosing remains unchanged, that is, the dosing amount of ozone is 160 mg (O ₃ )/L (water), the COD of the effluent of the regulating tank is reduced from 1126 mg/L to 958 mg/L, and the decrease To 112mg/L in embodiment 4 (ozone catalyzed oxidation oxidizes water in embodiment 4), need to continue to add about 800mg (O ₃ )/L (water) ozone, its treatment cost can increase about 24 yuan/t (water), Thereby the overall operating cost increases substantially.

Claims (16)

1. A method for treating ethylene alkali slag wastewater by homogeneous catalytic wet oxidation, including a wet oxidation section, an advanced 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 primary nanofiltration; the ethylene alkali slag wastewater first enters the regulating tank, is mixed with the primary nanofiltration concentrated water, and a homogeneous catalyst. Add acid to adjust the pH, enter the heat exchange unit, and then enter the wet oxidation reactor after heat exchange; the effluent from the wet oxidation reactor is heat exchanged by the heat exchange unit and then cooled by the cooler, part of it enters the first-level nanofiltration for treatment, and part of it enters the deep Treatment section; the concentrated water of the first-stage nanofiltration is returned to the regulating tank, and the product water of the first-stage nanofiltration enters the advanced treatment section; The advanced treatment section includes a regulating tank, a biochemical unit and ozone catalytic oxidation in sequence; the partially cooled wet oxidation reactor effluent and first-stage nanofiltration water enter the regulating tank, and enter the biochemical unit for treatment after pH adjustment. The biochemical unit adopts The salt-tolerant bacteria GXNYJ-DL-1 removes COD, and the treated wastewater is subjected to ozone catalytic oxidation to further decompose refractory organic matter; among them, the salt-tolerant bacteria GXNYJ-DL-1 ( Halomonas nigrificans ) has been preserved on July 13, 2020 In the General Microbiology Center of China Microbiological Culture Collection Management Committee, the preservation number is CGMCC No. 20350; The salt treatment section includes secondary nanofiltration, reverse osmosis, MVR reactor and segmental crystallization and salt separation unit; the ozone catalytic oxidation water enters the secondary nanofiltration for further concentration, and the concentrated water of the secondary nanofiltration enters the MVR reactor and separation unit in turn. The stage crystallization and salt separation unit finally obtains the product sulfate and miscellaneous salts. The secondary nanofiltration product water is treated by reverse osmosis, and the reverse osmosis concentrated water is sent back to the biochemical unit. The reverse osmosis product water reaches the reuse standard and is recycled. 2. The method according to claim 1, characterized in that, adding acid to the adjustment tank to adjust the pH to 2-6, the acid is hydrochloric acid or sulfuric acid, preferably hydrochloric acid. 3. 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 lowers the outlet water temperature of the wet oxidation reactor to 50-75°C. 4. The method according to claim 1, characterized in that, the homogeneous catalyst is a transition metal catalyst, selected from one or more of copper, iron, manganese, zinc and nickel, preferably 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. 5. The method according to claim 4, characterized in that, the homogeneous catalyst is added according to the ratio of the mass concentration of COD to the mass concentration of metal ions of 5000:1 to 10:1, and the loss rate of the catalyst and the reaction solution are used during operation. Concentration changes are added. 6. 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, the liquid space velocity is 0.25-4h ^-1 , the gas-liquid volume The ratio is 20:1～500:1. 7. 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. 8. The method according to claim 1, characterized in that the outlet water from the cooler is divided into two streams, one stream flows to the first-level nanofiltration unit, and the other stream flows to the regulating pool, and the proportion of water flowing to the regulating pool is 1% to 40% %. 9. The method according to claim 1, characterized in that the water production rate of the first-stage nanofiltration is 50%-75%, and the membrane pore size is between 1-5nm. 10. The method according to claim 1, characterized in that adding an alkali to adjust the pH to 6-9 in the adjustment tank, the alkali being sodium hydroxide or potassium hydroxide. 11. The method according to claim 1, characterized in that the salt concentration of the feed water of the biochemical unit is controlled to be below 250 g/L, preferably 50-130 g/L. 12. The method according to claim 1, wherein the biochemical unit is selected from BAF or MBR process, the dissolved oxygen is controlled above 2 mg/L, and the residence time of wastewater is 12-96 hours. 13. The method according to claim 1, characterized in that the dosage of ozone in the ozone catalytic oxidation is 50-500 mg (O ₃ )/L (water). 14. The method according to claim 1, characterized in that the water production rate of the second-stage nanofiltration is between 55% and 80%, and the membrane pore size is between 1 and 5 nm. 15. The method according to claim 1, characterized in that the reverse osmosis water production rate is between 50% and 80%, and the membrane pore size is less than 1nm. 16. The method according to claim 1, characterized in that, the segmental crystallization and salt separation is performed within the range of 50-120°C, the solubility of Na ₂ SO ₄ decreases with the increase of temperature, and the temperature rises first. Precipitate Na ₂ SO ₄ to obtain high-purity Na ₂ SO ₄ , then lower the temperature, other salts are precipitated due to supersaturation, and obtain miscellaneous salts.

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