Biological desalting method for high-concentration wastewater

Abstract

The invention discloses a biological desalting method for high-concentration wastewater, and relates to the technical field of wastewater treatment.According to the biological desalting method for the high-concentration wastewater, efficient removal and resource utilization of salt are achieved through a salt resource oriented conversion technology and a staged biological treatment process, and in the anaerobic stage, the anaerobic stage and the anaerobic stage are separated; sulfate ions in the wastewater are reduced into sulfur ions by using sulfate reducing bacteria, organic matters are decomposed at the same time, the chemical oxygen demand of the wastewater is reduced, in the aerobic stage, sulfur oxidizing bacteria oxidize the sulfur ions into elemental sulfur, resource recovery of sulfur is realized, and in the electrochemical auxiliary stage, the sulfur oxidizing bacteria oxidize sulfur ions into elemental sulfur. According to the method, the salt-tolerant thiobacillus oxidizes chloride ions into chlorine in the microbial electrolytic tank, resource recycling of chlorine is achieved, through the method, the salt content in the wastewater is effectively reduced, valuable elemental sulfur and chlorine are recycled, and remarkable economic and environmental benefits are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, in particular to a biological desalination method for high-concentration wastewater. Background Art

[0002] With the rapid development of industrialization, various industrial production activities have generated a large amount of high-concentration wastewater. These wastewaters come from a wide range of sources, covering many industries such as chemical, pharmaceutical, printing and dyeing, and food processing. The notable feature of high-concentration wastewater is that it contains a large amount of salt, such as chloride ions Cl - , sulfate ion Etc., accompanied by high concentrations of organic pollutants. If these wastewaters are discharged directly without effective treatment, they will cause serious pollution to the soil, water and atmospheric environment and destroy the ecological balance. Therefore, how to efficiently treat high-concentration wastewater and realize resource recycling has become an important issue that needs to be urgently solved in the environmental field.

[0003] At present, the existing technologies for treating salt and organic matter in high-concentration wastewater have many deficiencies, including:

[0004] In terms of salt treatment, traditional physical and chemical methods, such as ion exchange, can remove some salt, but ion exchange resins are easily contaminated and saturated, and need to be frequently regenerated or replaced, which is costly;

[0005] When biological treatment methods are faced with high salt concentrations, the activity of microorganisms will be strongly inhibited, especially when treating complex wastewater containing multiple salts. The interaction between different salt ions will further interfere with the metabolic process of microorganisms, resulting in unstable treatment effects.

[0006] In terms of organic matter treatment, the conventional biological treatment process has a significantly reduced ability to degrade organic matter in a high-salt environment, making it difficult to achieve ideal removal effects. In addition, existing technologies often separate salt removal and organic matter degradation, lacking a coordinated processing approach and making it impossible to achieve efficient recycling of resources.

[0007] In summary, it is difficult for existing high-concentration wastewater treatment technologies to achieve the goal of reducing Cl - , It is of great practical significance to develop a new method that can simultaneously and efficiently remove salt and organic matter in high-concentration wastewater, realize salt resource utilization, reduce treatment costs, and improve treatment stability. Summary of the invention

[0008] The purpose of the present invention is to make up for the shortcomings of the prior art and provide a method for biological desalination of high-concentration wastewater, which can achieve Cl -, Cooperative and efficient removal. In the anaerobic stage, under the gradient salinity domestication, sulfate-reducing bacteria use organic matter as the electron donor to reduce to S 2- . Meanwhile, the organic matter is degraded. In the aerobic stage, sulfur-oxidizing bacteria convert S 2- into elemental sulfur, solving the problem of secondary pollution of sulfide. In the electrochemical stage, halotolerant sulfur bacteria oxidize Cl - to Cl2 with the assistance of voltage, and H2 is co-produced at the cathode for energy recycling, thus realizing the resource utilization of salts and the effective removal of organic matter.

[0009] To solve the above technical problems, the present invention provides the following technical solution: A biological desalination method for high-concentration wastewater. The specific steps of the method are as follows:

[0010] S100. Pass the high-salt wastewater containing Cl - , through a nanofiltration membrane with a molecular weight cut-off of 200 Da to separate the Cl - concentrate and concentrate, and adjust the Cl - concentration to ≤ 80 g / L and concentration to ≤ 50 g / L;

[0011] S200. In the anaerobic stage, introduce the concentrate into an anaerobic reactor. Under an anaerobic environment at 30 - 35 °C and a pH value of 6.5 - 7.5, use composite sulfate-reducing bacteria, taking in the wastewater as the electron acceptor, organic matter as the electron donor and carbon source, and reduce to S 2- through the dissimilatory sulfate reduction pathway;

[0012] S300. In the aerobic stage, flow the anaerobically treated wastewater into an aerobic reactor. Under an aerobic environment, use sulfur-oxidizing bacteria to oxidize S 2- in the wastewater into elemental sulfur S o ;

[0013] S400. Introduce the Cl - concentrate into a two-chamber microbial electrolytic cell MEC for electrochemical assistance. Apply a voltage through the electrode system in the MEC, and use halotolerant sulfur bacteria and electrochemical assistance to oxidize Cl - in the wastewater to Cl2 gas at the anode, and produce H2 at the cathode;

[0014] S500. Introduce the effluent from S400 into a vacuum evaporation crystallizer to concentrate and precipitate NaCl crystals. Obtain industrial salt with a purity ≥ 99% through centrifugal separation. The final effluent salinity is ≤ 500 mg / L, and the concentrated mother liquor is returned to S400 for cyclic treatment.

[0015] Furthermore, the S200 performs gradient salinity domestication on the composite sulfate-reducing bacteria in an anaerobic environment with a temperature of 30 - 35 °C and a pH value of 6.5 - 7.5.

[0016] Even further, the domestication process of the S200 on the composite sulfate-reducing bacteria is as follows:

[0017] The initial salinity is 3%, 0.2 g / L of cysteine and 0.5 g / L of sodium lactate are added, and the domestication lasts for 48 h;

[0018] The salinity is increased to 5%, 0.1 g / L of ferrous sulfate and 0.3 g / L of yeast extract are added, and the domestication lasts for 36 h;

[0019] The salinity is increased to 8%, 0.05 g / L of sodium selenite is added, and the domestication lasts for 24 h.

[0020] Even further, during the process where the S200 is reduced to S reduced to S 2- In the process, an FeCl2 solution is synchronously added. The molar ratio of Fe 2+ :S 2- in the FeCl2 solution is 1:1, generating FeS precipitate and recovering it through magnetic separation. When magnetic separation of FeS is carried out, the magnetic field intensity is 0.5 - 1.0 T, the recovery rate of FeS is ≥ 90%, and the purity of the obtained FeS is ≥ 85%.

[0021] Even further, the temperature in the aerobic reactor of the S300 is 25 - 30 °C, the pH value is 7.0 - 8.0, the dissolved oxygen concentration is 2 - 4 mg / L, and the hydraulic retention time is controlled to be 5 - 8 h to create a growth and metabolism environment for sulfur-oxidizing bacteria.

[0022] Even further, during the electrochemical assistance process of the S400, the temperature is 30 - 35 °C and the pH value is 6.0 - 7.0.

[0023] Even further, the S100 nanofiltration membrane is a polyamide composite membrane, with sulfonic acid groups grafted on the surface, the cut-off molecular weight is 200 ± 10 Da, the operating pressure is 1.8 - 2.5 MPa, and the separation factor is ≥ 15.

[0024] Even further, in the S500, the pressure of vacuum evaporation crystallization is -0.08 to -0.09 MPa, the temperature is 45 - 50 °C, the rotation speed of centrifugally separating NaCl crystals is 2500 - 3500 rpm, and the residual amount of Cl - is ≤ 100 mg / L, and the crystallization mother liquor is refluxed to step S400 for cyclic treatment.

[0025] Compared with the prior art, this high-concentration wastewater biological desalination method has the following beneficial effects:

[0026] 1. The high-concentration wastewater biological desalination method of the present invention realizes the efficient removal and resource utilization of salts through the salt resource-oriented conversion technology and the staged biological treatment process. In the anaerobic stage, sulfate-reducing bacteria are used to reduce sulfate ions in the wastewater to sulfide ions, while decomposing organic matter and reducing the chemical oxygen demand of the wastewater. In the aerobic stage, sulfur-oxidizing bacteria oxidize sulfide ions to elemental sulfur, achieving the resource recovery of sulfur. In the electrochemically assisted stage, halotolerant sulfur bacteria oxidize chloride ions to chlorine gas in a microbial electrolytic cell, achieving the resource recovery of chlorine. Through this method, not only the salt content in the wastewater is effectively reduced, but also valuable elemental sulfur and chlorine gas are recovered, with significant economic and environmental benefits.

[0027] 2. The treatment method of the present invention has stability and wide adaptability. In the microbial treatment stage, the composite sulfate-reducing bacteria are acclimated to different salinity gradients, enabling them to adapt to high-salt environments and maintain high activity under different salinity conditions. When facing high-concentration wastewater from different sources and with different compositions, this method can effectively separate and adjust the concentration of salts in the wastewater by adjusting the separation parameters of the nanofiltration membrane, thereby realizing the treatment of various complex wastewaters.

[0028] Other advantages, objectives, and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings without creative efforts based on these drawings.

[0030] Figure 1 It is a flowchart of a high-concentration wastewater biological desalination method. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] In order to further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention objective, the following will, in conjunction with the drawings and preferred embodiments, describe in detail the specific embodiments, structures, features, and effects of the present invention as follows.

[0032] As Figure 1 shown, the present invention proposes a specific process for a high-concentration wastewater biological desalination method. The specific steps of this method are as follows:

[0033] S100. Use a polyamide composite membrane with a molecular weight cut-off of 200 ± 10 Da, which has sulfonic acid groups grafted on its surface. Under the condition of an operating pressure of 1.8 - 2.5 MPa, filter and treat the high-salt wastewater containing Cl - . to separate and obtain Cl - concentrate and concentrate. In this process, the nanofiltration membrane has a separation factor of ≥ 15 for . After ensuring effective separation, adjust the Cl - concentration to ≤ 80 g / L, and concentration to ≤ 50 g / L;

[0034] S200. Under an anaerobic environment at 30 - 35 °C and a pH value of 6.5 - 7.5, conduct gradient salinity domestication on the composite sulfate-reducing bacteria. The domestication process is as follows: Set the initial salinity to 3%, add 0.2 g / L cysteine and 0.5 g / L sodium lactate to the culture medium, domesticate for 48 h, then raise the salinity to 5%, add 0.1 g / L ferrous sulfate and 0.3 g / L yeast extract, and continue to domesticate for 36 h; Finally, raise the salinity to 8%, add 0.05 g / L sodium selenite, and domesticate for 24 h. After completion of domestication, introduce the concentrate into the anaerobic reactor. Inside the reactor, the composite sulfate-reducing bacteria use in the wastewater as an electron acceptor, use organic matter COD as an electron donor and carbon source, and reduce to S 2- through the dissimilatory sulfate reduction pathway. During this reduction process, synchronously add an FeCl2 solution to ensure that the molar ratio of Fe 2+ :S 2- = 1:1, generate FeS precipitate, and use a magnetic separation device with a magnetic field strength of 0.5 - 1.0 T to separate and recover the FeS precipitate. The FeS recovery rate is ≥ 90%, and the obtained FeS purity is ≥ 85%;

[0035] S300. Introduce the anaerobically treated wastewater into the aerobic reactor, control the temperature in the aerobic reactor at 25 - 30 °C, adjust the pH value to 7.0 - 8.0, maintain the dissolved oxygen concentration at 2 - 4 mg / L, and set the hydraulic retention time to 5 - 8 h to create a suitable growth and metabolic environment for sulfur-oxidizing bacteria. Under such an environment, the sulfur-oxidizing bacteria oxidize S 2- in the wastewater to elemental sulfur S o ;

[0036] S400. Introduce Cl -The concentrated solution is introduced into a two-chamber microbial electrolysis cell (MEC). Under the conditions of 30 - 35 °C and a pH value of 6.0 - 7.0, a voltage is applied through the electrode system in the MEC. With the aid of halotolerant Thiobacillus and electrochemistry, Cl in the wastewater - is anodized to Cl2 gas at the anode, and H2 is generated at the cathode;

[0037] S500. The effluent from step S400 is introduced into a vacuum evaporation crystallizer and concentrated under the conditions of a pressure of -0.08 to -0.09 MPa and a temperature of 45 - 50 °C to precipitate NaCl crystals. Then, a centrifuge is used to separate the precipitated crystals at a rotational speed of 2500 - 3500 rpm to obtain industrial salt with a purity ≥ 99%, and the resulting Cl - residual amount ≤ 100 mg / L. The remaining concentrated mother liquor after separation is returned to step S400 for cyclic treatment, and the final effluent salinity ≤ 500 mg / L.

[0038] Example 1

[0039] This example aims to verify the basic process feasibility of the biological desalination method for high-concentration wastewater, as well as whether the expected treatment effect and resource recovery goal can be achieved.

[0040] Select high-concentration wastewater discharged from a chemical industrial park, where the Cl - concentration is 100 g / L, concentration is 60 g / L, and the COD concentration is 1500 mg / L, and treat it:

[0041] Nanofiltration membrane separation and concentration adjustment: A polyamide composite nanofiltration membrane with a molecular weight cut-off of 200 Da is used. The membrane surface is grafted with sulfonic acid groups. Under the operating pressure of 1.8 MPa, the wastewater is filtered and separated to obtain Cl - concentrated solution and concentrated solution. After adjustment, the Cl - concentrated solution concentration reaches 80 g / L, concentrated solution concentration reaches 50 g / L. During this process, ensure the effective separation of the two ions;

[0042] Anaerobic treatment: The concentrated solution with adjusted concentration is introduced into an anaerobic reactor with an anaerobic environment at a temperature of 30 °C and a pH value of 6.5, and inoculated with domesticated composite sulfate-reducing bacteria. During the reaction, the composite sulfate-reducing bacteria use in the wastewater as the electron acceptor, use organic matter COD as the electron donor and carbon source, and reduce to S 2- through the dissimilatory sulfate reduction pathway. At the same time, according to Fe 2+ :S 2-Add FeCl2 solution in a molar ratio of 1:1 synchronously to generate FeS precipitate subsequently;

[0043] Aerobic treatment: The wastewater after anaerobic treatment flows into the aerobic reactor. In the aerobic reactor, control the temperature at 25 °C, adjust the pH value to 7.0, maintain the dissolved oxygen concentration at 2 mg / L, and set the hydraulic retention time to 5 h. Under such an environment, sulfur-oxidizing bacteria utilize S in the wastewater 2- to carry out metabolic activities and oxidize it to elemental sulfur S o ;

[0044] Electrochemical assisted treatment: Introduce the Cl - concentrate into a two-chamber microbial electrolysis cell MEC. In the MEC, keep the temperature at 30 °C and the pH value at 6.0. Apply a voltage through the electrode system. Under the combined action of halophilic sulfur bacteria and electrochemical assistance, Cl in the wastewater - is oxidized to Cl2 gas at the anode, and H2 is generated at the cathode;

[0045] Evaporation crystallization and product recovery: Introduce the effluent of MEC into a vacuum evaporation crystallizer, set the pressure to -0.08 MPa and the temperature to 45 °C to gradually precipitate NaCl crystals. Use a centrifuge to centrifuge the crystals at a rotational speed of 2500 rpm. After the separated crystals are subjected to purity detection, the purity of NaCl crystals reaches 99.2%. At the same time, conduct salinity detection on the separated effluent, and the final effluent salinity is 450 mg / L;

[0046] Treatment effect: After 30 consecutive days of operation, the COD removal rate in the anaerobic stage reaches 80%, the FeS recovery rate is 90%, and the purity is 85%; S in the aerobic stage 2- is completely converted into elemental sulfur; the conversion rate of Cl - to Cl2 in the electrochemical stage is 85%; the purity of the finally obtained NaCl crystals is 99.2%, and the effluent salinity is 450 mg / L, which proves the feasibility of the basic process

[0047] Example 2

[0048] This example focuses on studying the influence of this treatment method on the treatment effect of high-concentration wastewater and the resource recovery efficiency under different temperature conditions, so as to provide a basis for optimizing the process temperature parameters.

[0049] Use the same high-concentration wastewater sample discharged from a chemical industrial park as in Example 1, with its Cl - concentration of 100 g / L, concentration of 60 g / L, and COD concentration of 1500 mg / L;

[0050] Nanofiltration membrane separation and concentration adjustment: A polyamide composite nanofiltration membrane with a molecular weight cut-off of 200 Da is used. The surface of the membrane is grafted with sulfonic acid groups. Under the condition of an operating pressure of 1.8 MPa, the wastewater is filtered and separated to obtain Cl - concentrate and concentrate. After adjustment, the Cl - concentrate concentration reaches 80 g / L, the concentrate concentration reaches 50 g / L. In this process, ensure the effective separation of the two ions;

[0051] Anaerobic stage temperature adjustment: Introduce the S concentrate into the anaerobic reactor, set the temperature to 32 °C, keep the pH value at 7.0, and inoculate the domesticated composite sulfate-reducing bacteria. During the reaction process, the composite sulfate-reducing bacteria use the in the wastewater as the electron acceptor, the organic matter COD as the electron donor and carbon source, and reduce to S 2- through the dissimilatory sulfate reduction pathway. At the same time, add FeCl2 solution synchronously according to the molar ratio of Fe 2+ :S 2- of 1:1 to generate FeS precipitate for subsequent use;

[0052] Aerobic stage temperature adjustment: The wastewater after anaerobic treatment flows into the aerobic reactor. Raise the temperature of the aerobic reactor to 28 °C, keep the pH value at 7.0, maintain the dissolved oxygen concentration at 2 mg / L, and the hydraulic retention time is still 5 h. Use sulfur-oxidizing bacteria to oxidize S 2- to elemental sulfur;

[0053] Electrochemical-assisted stage temperature adjustment: Introduce the Cl - concentrate into the two-chamber microbial electrolytic cell MEC. In the MEC, set the temperature to 33 °C, adjust the pH value to 6.5, apply the same voltage as in Example 1, and use salt-tolerant sulfur bacteria and electrochemical assistance to oxidize Cl - to Cl2 gas, and H2 is produced at the cathode;

[0054] Evaporation crystallization and product recovery: Introduce the MEC effluent into a vacuum evaporation crystallizer, set the pressure to -0.08 MPa and the temperature to 45 °C to gradually precipitate NaCl crystals. Use a centrifuge to centrifuge the crystals at a speed of 2500 rpm. After the separated crystals are subjected to purity detection, the purity of the NaCl crystals reaches 99.2%. At the same time, perform salinity detection on the separated effluent, and the final effluent salinity is 450 mg / L;

[0055] Treatment effect: After 30 days of operation, it was found that the COD removal rate in the anaerobic stage increased to 83%, and the FeS-related indicators remained stable; the production of elemental sulfur in the aerobic stage increased slightly; the Cl2 production in the electrochemical stage increased, and the Cl - conversion rate reached 88%; the final purity of NaCl crystals was 99.3%, and the effluent salinity was 420 mg / L, indicating that appropriately increasing the temperature at each stage can improve the treatment effect to a certain extent.

[0056] Example 3

[0057] This example is used to test the adaptability of the method to different high-concentration wastewaters and evaluate its universality.

[0058] Select high-concentration wastewater with a Cl - concentration of 90 g / L, a concentration of 40 g / L, a COD concentration of 2000 mg / L, and containing a small amount of heavy metal ions (such as copper ions, zinc ions, etc.).

[0059] Nanofiltration membrane separation and concentration adjustment: Use a polyamide composite nanofiltration membrane with a molecular weight cut-off of 200 Da. The surface of the membrane is grafted with sulfonic acid groups. Under the condition of an operating pressure of 1.8 MPa, the wastewater is filtered and separated to obtain Cl - concentrate and concentrate. After adjustment, the concentration of Cl - concentrate reaches 80 g / L, and the concentration of concentrate reaches 50 g / L to ensure the effective separation of the two ions;

[0060] Anaerobic treatment: Introduce the concentrate with adjusted concentration into the anaerobic reactor to create an anaerobic environment at 30 °C and a pH value of 6.5. Inoculate the domesticated composite sulfate-reducing bacteria. During the reaction process, the composite sulfate-reducing bacteria use as the electron acceptor, the organic matter COD in the wastewater as the electron donor and carbon source, and reduce to S 2- , and simultaneously add FeCl2 solution to maintain the Fe 2+ :S 2- molar ratio of 1:1;

[0061] Aerobic treatment: The wastewater after anaerobic treatment flows into the aerobic reactor. In the aerobic reactor, the temperature is controlled at 25 °C, the pH value is adjusted to 7.0, the dissolved oxygen concentration is maintained at 2 mg / L, and the hydraulic retention time is set to 5 h. Use sulfur-oxidizing bacteria to oxidize S 2- to elemental sulfur;

[0062] Electrochemical assisted treatment: Add Cl -The concentrated solution is introduced into a two-chamber microbial electrolysis cell (MEC). Inside the MEC, the temperature is maintained at 30 °C and the pH value is 6.0. A voltage is applied through the electrode system, and halophilic thiobacilli and electrochemical assistance are utilized to oxidize Cl - to Cl2 gas, and H2 is generated at the cathode;

[0063] Evaporation crystallization and product recovery: The effluent from the MEC is introduced into a vacuum evaporation crystallizer. The pressure is set at -0.08 MPa and the temperature is 45 °C to gradually precipitate NaCl crystals. A centrifuge is used to centrifuge the crystals at a rotational speed of 2500 rpm;

[0064] Treatment effect: After 30 days of continuous treatment, the COD removal rate in the anaerobic stage reaches 78%. The mass of FeS recovered by magnetic separation is not significantly affected by heavy metal ions. Elemental sulfur is normally generated in the aerobic stage. The conversion of Cl - is smooth in the electrochemical stage, and the conversion rate is 82%. The purity of the finally obtained NaCl crystals is 99.1%, and the effluent salinity is 480 mg / L, proving that this method also has a good treatment effect on high-concentration wastewater containing special components and has a certain universality.

[0065] Example 4

[0066] In this example, by adjusting the gradient salinity acclimation process of the composite sulfate-reducing bacteria, the influence of the optimized acclimation method on microbial activity and overall treatment effect is explored.

[0067] The same high-concentration wastewater sample discharged from a chemical industrial park as in Example 1 is used, with a Cl - concentration of 100 g / L, a concentration of 60 g / L, and a COD concentration of 1500 mg / L;

[0068] Optimized acclimation of the composite sulfate-reducing bacteria: The initial salinity is set at 3%. 0.3 g / L of cysteine and 0.6 g / L of sodium lactate are added to the culture medium, and the acclimation time is extended to 50 h;

[0069] The salinity is increased to 5%, 0.15 g / L of ferrous sulfate and 0.4 g / L of yeast extract are added, and the acclimation time is adjusted to 40 h;

[0070] The salinity is increased to 8%, 0.08 g / L of sodium selenite is added, and the acclimation time is set at 28 h;

[0071] Wastewater treatment process: The composite sulfate-reducing bacteria after optimized acclimation are inoculated into the anaerobic reactor. The subsequent treatment steps are the same as in Example 1, that is, the adjusted concentrated solution enters the anaerobic reactor and reacts in an anaerobic environment at 30 °C and a pH value of 6.5. An FeCl2 solution is added synchronously to maintain Fe2+ :S 2- The wastewater after anaerobic treatment with a molar ratio of 1:1 flows into the aerobic reactor and undergoes aerobic treatment under the conditions of 25 °C, pH value of 7.0, dissolved oxygen concentration of 2 mg / L, and hydraulic retention time of 5 h. Cl - The concentrated liquid is introduced into the dual-chamber microbial electrolysis cell MEC, and electrochemical assisted treatment is carried out by applying voltage under the conditions of 30 °C and pH value of 6.0; finally, the effluent of MEC is introduced into a vacuum evaporation crystallizer, and NaCl crystals are concentrated and precipitated under the conditions of a pressure of -0.08 MPa and a temperature of 45 °C, with a centrifugal speed of 2500 rpm.

[0072] Treatment effect: After 30 days of operation, it is found that the COD removal rate in the anaerobic stage is increased to 85%, the FeS recovery rate reaches 92%, and the purity is increased to 88%; the treatment effects in the subsequent aerobic and electrochemical stages are also slightly improved. The final purity of NaCl crystals is 99.4%, and the effluent salinity is 400 mg / L, indicating that the optimized gradient salinity domestication method can enhance the microbial activity and improve the treatment effect.

[0073] Example 5

[0074] This example mainly studies the effect of different hydraulic retention times in the aerobic stage on the oxidation of S by sulfur-oxidizing bacteria 2- and the impact on the overall treatment process.

[0075] Using the same high-concentration wastewater sample discharged from a chemical industrial park as in Example 1, with a Cl - concentration of 100 g / L, concentration of 60 g / L, and COD concentration of 1500 mg / L;

[0076] Nanofiltration membrane separation and concentration adjustment: Using a polyamide composite nanofiltration membrane with a molecular weight cut-off of 200 Da, with sulfonic acid groups grafted on the membrane surface, the wastewater is filtered and separated under the operating pressure of 1.8 MPa to obtain Cl - concentrated liquid and concentrated liquid. After adjustment, the concentration of Cl - concentrated liquid reaches 80 g / L, the concentration of concentrated liquid reaches 50 g / L. During this process, ensure the effective separation of the two ions;

[0077] Anaerobic treatment: Introduce the concentrated liquid with adjusted concentration into the anaerobic reactor, which has an anaerobic environment with a temperature of 30 °C and a pH value of 6.5, and inoculate the domesticated composite sulfate-reducing bacteria. During the reaction, the composite sulfate-reducing bacteria use in the wastewater as the electron acceptor, use the organic matter COD as the electron donor and carbon source, and reduce to S through the dissimilatory sulfate reduction pathway2- , meanwhile, add FeCl2 solution synchronously according to the molar ratio of Fe 2+ :S 2- of 1:1 to generate FeS precipitate subsequently;

[0078] Adjustment of hydraulic retention time in the aerobic stage: Conduct comparative experiments by setting the hydraulic retention time at 6 h, 7 h, and 8 h respectively in the aerobic stage. When the hydraulic retention time is 6 h, the wastewater after anaerobic treatment flows into the aerobic reactor. Under the conditions of 25 °C, pH value of 7.0, and dissolved oxygen concentration of 2 mg / L, sulfur-oxidizing bacteria are used to oxidize S 2- to elemental sulfur; when the hydraulic retention time is 7 h, with other conditions unchanged, only extend the hydraulic retention time, and observe the oxidation effect of sulfur-oxidizing bacteria and its impact on the subsequent treatment process; when the hydraulic retention time is 8 h, also keep other conditions unchanged and further extend the hydraulic retention time for the experiment;

[0079] Electrochemical assisted treatment: Introduce the Cl - concentrate into a two-chamber microbial electrolytic cell MEC. In the MEC, keep the temperature at 30 °C and the pH value at 6.0. Apply a voltage through the electrode system. Under the combined action of halophilic sulfur-oxidizing bacteria and electrochemical assistance, Cl in the wastewater - is oxidized to Cl2 gas at the anode, and H2 is generated at the cathode;

[0080] Evaporation crystallization and product recovery: Introduce the effluent of MEC into a vacuum evaporation crystallizer, set the pressure at -0.08 MPa and the temperature at 45 °C to gradually precipitate NaCl crystals. Use a centrifuge to centrifuge the crystals at a rotational speed of 2500 rpm. After the separated crystals are subjected to purity detection, the purity of NaCl crystals reaches 99.2%. Meanwhile, conduct salinity detection on the separated effluent, and the final effluent salinity is 450 mg / L;

[0081] Treatment effect: After 30 days of operation monitoring, when the hydraulic retention time is 6 h, S in the aerobic stage 2- is oxidized relatively completely, and the output of elemental sulfur is stable; when the hydraulic retention time is extended to 7 h and 8 h, the output of elemental sulfur increases slightly, but the overall treatment efficiency does not increase significantly, and the load of the subsequent treatment process increases slightly. It can be comprehensively known that 6 h is the preferred hydraulic retention time in the aerobic stage. At this time, the final purity of NaCl crystals is 99.2%, and the effluent salinity is 430 mg / L.

[0082] Comparative example 1

[0083] By comparing with the single biological treatment method, highlight the performance in treating high-concentration wastewater.

[0084] Adopt the high-concentration wastewater sample discharged from the same chemical industrial park as in Example 1, and its Cl- with a concentration of 100 g / L, with a concentration of 60 g / L and a COD concentration of 1500 mg / L;

[0085] Treatment steps: A single biological treatment method is adopted, that is, the wastewater is directly introduced into the bioreactor of the conventional activated sludge process without special treatment such as salt separation and gradient acclimation. In the bioreactor, the temperature is maintained at 25 °C, the pH value is 7.0, the dissolved oxygen concentration is maintained at 2 - 3 mg / L by aeration, and the hydraulic retention time is set at 12 h.

[0086] Treatment effect: After 30 days of operation, the microbial activity is severely inhibited by the high - concentration salt. The COD removal rate is only 30%, no sulfur ions are reduced and oxidized, and the effective removal and resource utilization of Cl - cannot be achieved during the treatment process. Since no special separation and crystallization treatment is carried out, no NaCl crystals are produced. When the final effluent is detected, the salinity is still as high as over 900 mg / L.

[0087] Comparative Example 2

[0088] Verify the importance of gradient salinity acclimation for the activity of composite sulfate - reducing bacteria and the overall treatment effect.

[0089] Use the same high - concentration wastewater sample discharged from a chemical industrial park as in Example 1, with its Cl - concentration of 100 g / L, concentration of 60 g / L, and COD concentration of 1500 mg / L;

[0090] Treatment steps: Adopt the same wastewater treatment process as in Example 1, but do not perform gradient salinity acclimation on the composite sulfate - reducing bacteria in the anaerobic stage. Directly use the unacclimated strain for treatment. In the anaerobic reactor, control the temperature at 30 °C, adjust the pH value to 6.5, inoculate the unacclimated composite sulfate - reducing bacteria, and simultaneously add FeCl2 solution to keep the Fe 2+ :S 2- molar ratio of 1:1. The subsequent aerobic treatment, electrochemically assisted treatment, and evaporation crystallization steps are the same as in Example 1.

[0091] Treatment effect: After 30 days of operation, the COD removal rate in the anaerobic stage is only 60%. By magnetic separation and recovery of the generated FeS precipitate, the recovery rate and purity of FeS are significantly reduced, being 70% and 75% respectively; the treatment effects in the aerobic stage and the electrochemical stage are also affected. The amount of elemental sulfur generated in the aerobic stage decreases, and the conversion rate of Cl - converted to Cl2 in the electrochemical stage drops to 70%; the purity of the finally obtained NaCl crystals is 97%, and the effluent salinity is 700 mg / L.

[0092] In summary, according to the treatment effect indexes of a biological desalination method for high-concentration wastewater provided by Embodiment 1 to Embodiment 5 and Comparative Example 1 and 2, the specific data are shown in the following table:

[0093]

[0094]

[0095] As shown in the above table, by analyzing the monitoring results of Embodiment 1 to 5 and the comparative examples, it can be seen that each embodiment shows good treatment effects and resource recovery capabilities when treating high-concentration wastewater. In the anaerobic stage, by optimizing the gradient salinity domestication process of composite sulfate-reducing bacteria (such as Embodiment 4), adjusting the temperature (such as Embodiment 2), etc., the microbial activity can be significantly improved, thereby increasing the COD removal rate, which can reach up to 85%. At the same time, the stable microbial metabolism also ensures the high recovery rate and purity of FeS. In the aerobic stage, sulfur-oxidizing bacteria can efficiently convert S 2- into elemental sulfur, and wastewater with different contents (such as Embodiment 3) does not cause obvious interference to it. In the electrochemical stage, appropriate conditions such as temperature (such as Embodiment 2) can promote halophilic sulfur bacteria to oxidize Cl- to Cl2, with the highest conversion rate reaching 88%. Finally, through vacuum evaporation crystallization and centrifugal separation, NaCl crystals with a purity of 99.1% - 99.4% can be obtained, and the effluent salinity can also be controlled at 400 - 480 mg / L. In contrast, Comparative Example 1 uses the traditional single biological treatment method, which is inhibited by high-concentration salts, with extremely low microbial activity, and all treatment indexes are far lower than those of the embodiments, making it impossible to achieve effective treatment and resource recovery. In Comparative Example 2, the gradient salinity domestication was not carried out, resulting in limited microbial activity, leading to a COD removal rate of only 60% in the anaerobic stage and a Cl - conversion rate dropping to 70% in the electrochemical stage, and the purity of NaCl crystals is also relatively low.

[0096] In summary, the biological desalination method for high-concentration wastewater of the present invention, through a unique three-stage biological treatment process of "anaerobic reduction - aerobic oxidation - electrochemical dechlorination" and optimization measures for the gradient salinity domestication of microorganisms, can achieve efficient salt removal and resource utilization, while effectively reducing the effluent salinity, with stable and good treatment effects when treating high-concentration wastewater, compared with traditional methods and unoptimized treatment methods.

[0097] The above are only the preferred embodiments of the present invention and do not impose any formal restrictions on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments with equivalent changes within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A biological desalination method for high-concentration wastewater, characterized in that, The specific steps of this method are as follows: S100. Pass the high-salt wastewater containing Cl - and through a nanofiltration membrane with a molecular weight cut-off of 200 Da to separate the Cl - concentrate and concentrate, and adjust the Cl - concentration to ≤ 80 g / L and concentration to ≤ 50 g / L; S200. In the anaerobic stage, the concentrate is introduced into the anaerobic reactor, and under the anaerobic environment of 30 - 35 °C and a pH value of 6.5 - 7.5, using the composite sulfate-reducing bacteria, with in the wastewater as the electron acceptor, organic matter COD as the electron donor and carbon source, through the dissimilatory sulfate reduction pathway, is reduced to S 2- ; S300. In the aerobic stage, the wastewater after anaerobic treatment is introduced into an aerobic reactor. Under aerobic conditions, sulfur-oxidizing bacteria are utilized to oxidize S in the wastewater 2- to elemental sulfur S 0 ; S400. Introduce the Cl - concentrate into a two-chamber microbial electrolysis cell (MEC) for electrochemical assistance. Apply a voltage through the electrode system in the MEC, and use halophilic thiobacilli and electrochemical assistance to oxidize Cl - in the anode into Cl2 gas, and generate H2 at the cathode; S500: Introduce the effluent from S400 into a vacuum evaporation crystallizer to concentrate and precipitate NaCl crystals. Obtain industrial salt with a purity ≥ 99% through centrifugal separation. The final effluent salinity ≤ 500 mg / L, and return the remaining concentrated mother liquor to S400 for cyclic treatment.

2. The biological desalination method for high-concentration wastewater according to claim 1, characterized in that, In S200, under an anaerobic environment with a temperature of 30 - 35 °C and a pH value of 6.5 - 7.5, gradient salinity domestication is carried out on the composite sulfate-reducing bacteria.

3. The biological desalination method for high-concentration wastewater according to claim 2, wherein, The domestication process of the composite sulfate-reducing bacteria in S200 is as follows: The initial salinity is 3%, add 0.2 g / L cysteine and 0.5 g / L sodium lactate, and domesticate for 48 h; The salinity is increased to 5%, add 0.1 g / L ferrous sulfate and 0.3 g / L yeast extract, and domesticate for 36 h; The salinity is increased to 8%, add 0.05 g / L sodium selenite, and domesticate for 24 h.

4. A biological desalination method for high-concentration wastewater according to claim 1, characterized in that, The S200 Restore to S 2- During the process, FeCl2 solution is added simultaneously. 2+ :S 2- The molar ratio is 1:1, and FeS precipitation is generated and recovered by magnetic separation. The magnetic field intensity during magnetic separation of FeS is 0.5-1.0T, the FeS recovery rate is ≥90%, and the purity of the obtained FeS is ≥85%.

5. A biological desalination method for high-concentration wastewater according to claim 1, characterized in that, In the aerobic reactor of S300, the temperature is 25 - 30 °C, the pH value is 7.0 - 8.0, the dissolved oxygen concentration is 2 - 4 mg / L, and the hydraulic retention time is controlled to be 5 - 8 h to create a growth and metabolic environment for sulfur-oxidizing bacteria.

6. The biological desalination method for high-concentration wastewater according to claim 1, wherein, During the electrochemically assisted process of S400, the temperature is 30 - 35 °C and the pH value is 6.0 - 7.

0.

7. A biological desalination method for high-concentration wastewater according to claim 1, characterized in that, The S100 nanofiltration membrane is a polyamide composite membrane with sulfonic acid groups grafted on its surface, having a molecular weight cut-off of 200 ± 10 Da, an operating pressure of 1.8 - 2.5 MPa, and for a separation factor ≥ 15.

8. A biological desalination method for high-concentration wastewater according to claim 1, characterized in that, The pressure of vacuum evaporation crystallization in the S500 is -0.08 to -0.09 MPa, the temperature is 45 - 50 °C, the rotation speed for centrifugally separating NaCl crystals is 2500 - 3500 rpm, and the resulting Cl - residual amount ≤ 100 mg / L, and the crystallization mother liquor is refluxed to step S400 for cyclic treatment.

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