A method for treating electroplating wastewater by using bioreduction of biogas slurry combined with iron bio-oxidation

Abstract

The present application belongs to the technical field of wastewater treatment, and discloses a method for treating electroplating wastewater by using bioreduction of biogas slurry and combined iron bio-oxidation, which is a secondary combined use technology for removing various heavy metals in electroplating wastewater by iron bio-oxidation, comprising the following steps: (1) collecting fermentation biogas slurry, and performing ultraviolet irradiation sterilization after aeration; (2) adding potassium dichromate solution and fresh nutrient solution to the sludge system, and culturing anaerobic sludge; (3) adding treated biogas slurry to the anaerobic sludge, and repeatedly domesticating chromium-reducing microorganisms; (4) configuring a mixed solution of comprehensive electroplating wastewater and biogas slurry according to a certain proportion; (5) building a primary treatment biological reactor, and reducing Cr(VI) in wastewater by anaerobic biological reduction under the promotion of pyrite; and (6) building a secondary biological reactor filled with straw biomass charcoal, and generating iron oxides under the action of functional bacteria to continue adsorbing Cd, Cu and Ni ions in wastewater.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, specifically relating to a method for treating electroplating wastewater using a combination of biogas slurry microbial reduction and iron biological oxidation. Background Technology

[0002] Chemical reduction, adsorption, and ion exchange methods are frequently used to remove heavy metals from water bodies; however, these methods are expensive, consume large amounts of chemicals, and are prone to causing secondary pollution. In contrast, biological reduction methods offer milder reaction conditions, lower chromium sludge production, and are more efficient and environmentally friendly. Chromium-reducing bacteria can convert Cr(VI) into low-toxicity and low-migration Cr(III), and then achieve chromium pollution control in water bodies through solid-liquid separation. However, chromium-containing wastewater from industries such as electroplating and metal processing is generally lacking in nutrients and has poor biodegradability, which seriously affects the application effect of Cr(VI) biological reduction in treating actual chromium-containing wastewater. External nutrient sources are needed as carbon and electron donors for chromium-reducing bacteria. Typically, adding organic substances such as ethanol, lactic acid, and glucose is generally costly and impractical for treating high-concentration chromium-containing wastewater. Furthermore, actual wastewater often contains multiple heavy metal ions such as copper, cadmium, and nickel, which need to be removed simultaneously. Currently, developing low-energy-consumption, high-efficiency green biological processes for treating electroplating wastewater has become an inevitable choice.

[0003] In recent years, there has been a strong push to develop an ecological circular agriculture model centered on biogas projects. While biogas projects can generate clean energy (CH4) while treating organic waste, the resulting biogas slurry and residue are difficult to dispose of, especially the slurry. Biogas slurry is generally weakly alkaline and contains a large amount of organic matter, as well as nitrogen and phosphorus. Typically, biogas slurry can be absorbed by plants as organic fertilizer, but in practice, its application in farmland is significantly affected by seasonality, and there is insufficient land for timely utilization. Other studies have shown that, with proper formulation, biogas slurry can be used to cultivate microalgae to obtain biofuels and for recovering nitrogen fertilizer. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for treating electroplating wastewater using a combination of biogas slurry microbial reduction and iron bio-oxidation. The method utilizes pretreatment to obtain a weakly alkaline biogas slurry containing abundant organic matter, serving as a nutrient source and electron donor for chromium bioreduction. Simultaneously, natural pyrite is added to cultured, specially formulated anaerobic sludge to accelerate the bioreduction of Cr(VI) in the wastewater. Then, under the action of functional bacteria, biogenic iron oxides are produced, which adsorb and chemically bond with heavy metals, thereby removing Cd, Cu, and Ni from the wastewater. This invention improves the efficiency of biological treatment of chromium-containing industrial wastewater and, more importantly, expands the reuse methods of biogas slurry.

[0005] The specific steps are as follows:

[0006] (1) Pretreatment of biogas slurry: Collect fermented biogas slurry, let it stand for 4-6 hours, and discard the bottom sediment;

[0007] (2) Anaerobic sludge culture: Collect sludge from the anaerobic tank, wash it, and remove it with nitrogen gas. Add it to a sealed container, add tryptone medium, and add potassium dichromate solution for culture.

[0008] (3) Sludge acclimatization: Add the biogas slurry obtained after pretreatment to the anaerobic sludge cultivated in step (2). As the Cr(VI) content in the solution decreases, potassium dichromate solution is added on time for repeated acclimatization. When the Cr(VI) concentration can be reduced to below 3.0 mg / L within 1 to 3 days, the acclimatization is completed.

[0009] (4) Prepare a mixed solution of biogas slurry and comprehensive wastewater: Collect comprehensive electroplating wastewater, mix it with biogas slurry obtained from biogas slurry pretreatment to form a mixed solution, stir and adjust the pH to 5.0-6.5;

[0010] (5) Primary reaction process: Pyrite is added to the reactor of the primary reaction process, and then acclimated anaerobic sludge is added to the reactor; then, the mixed solution is added, and the hydraulic retention time is 10-16 hours.

[0011] (6) Secondary reaction process: Carbon particles are filled into the reactor of the secondary reaction process with a porosity of 80-90%; then, functional bacteria suspension is inoculated to fix the functional bacteria on the surface of the carbon particles to form a biofilm. The effluent from the primary reaction process is then introduced into the reactor of the secondary reaction process, with a hydraulic retention time of 18-24 hours.

[0012] Furthermore, the biogas slurry pretreatment also includes aeration to reduce ammonia nitrogen content;

[0013] Furthermore, the biogas slurry after aeration is sterilized by ultraviolet irradiation.

[0014] Furthermore, in the anaerobic sludge cultivation, fresh liquid culture medium and potassium dichromate solution are added every one cycle, and the cultivation is carried out for 4 cycles, with each cycle lasting 3-10 days;

[0015] Furthermore, the reactor used in the primary reaction process is an upflow reactor, which is equipped with a screen at the bottom and an exhaust port and a gas absorption device at the top of the reactor.

[0016] Furthermore, the reactor used in the secondary reaction process is an upflow reactor;

[0017] Furthermore, the charcoal particles are straw biochar;

[0018] Furthermore, the fermented biogas slurry is the filtrate produced after the pig farm's manure, urine, and flushing wastewater have been fully fermented in a biogas digester and the biogas residue has been removed;

[0019] Furthermore, after the aforementioned pretreatment of the biogas slurry, the ammonia nitrogen concentration of the fermented biogas slurry is 100–145 mg / L, and the COD concentration is 3600–4500 mg / L.

[0020] Furthermore, after adding potassium dichromate solution in step (2), the initial Cr(VI) concentration of the sludge system is 40-60 mg / L;

[0021] Furthermore, in step (3), the volume ratio of anaerobic sludge to added biogas slurry is 8-10:1;

[0022] Furthermore, in step (4), the volume ratio of the combined electroplating wastewater to the biogas slurry is 15-20:1;

[0023] Furthermore, the dosage of pyrite added is 0.8–1.2 g / L;

[0024] Furthermore, the carbon particles have a particle size of 1.5–2.5 cm;

[0025] Furthermore, the functional bacterium is Klebsiella sp. Strain M3, with accession number CCTCC M2021261; it was deposited at the China Center for Type Culture Collection on March 24, 2021.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) The treated biogas slurry can be used as a carbon source and electron donor for the biological reduction of Cr(VI), so that a large amount of biogas slurry can be effectively utilized and environmental pollution can be reduced. At the same time, the application of biogas slurry reduces the amount of nutrients used in the biological reduction of Cr(VI) and reduces the cost of wastewater treatment.

[0028] (2) The use of a small amount of pyrite in the primary bioreactor can promote the bioreduction process of Cr(VI) and accelerate the reaction progress, while the generated Fe 2+ Ions can serve as an iron source for functional bacteria during the secondary reaction process, which is beneficial for producing iron oxides with high adsorption capacity.

[0029] (3) Functional bacteria oxidize Fe in the secondary reaction 2+ The iron oxides generated by the ions can continue to adsorb heavy metals such as Cr(VI), Cd, Cu, and Ni in the primary effluent, greatly reducing the concentration of heavy metals in the final effluent and improving wastewater treatment efficiency.

[0030] (4) The organic matter in the biogas slurry can serve as a nutrient source for the primary biological reduction of Cr(VI) and as a nutrient source for the functional bacteria in the secondary reaction. Moreover, the excess organic matter can be adsorbed and retained by the straw biochar filling the secondary reaction, thereby ensuring that the COD and ammonia nitrogen in the effluent meet the discharge standards.

[0031] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings.

[0032] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments in conjunction with the accompanying drawings. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0034] Figure 1 This is a flowchart of a method for treating electroplating wastewater using biogas slurry microbial reduction combined with iron biological oxidation. Specific Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. In the following description, specific details such as specific configurations and components are provided merely to help fully understand the embodiments of this application. Therefore, those skilled in the art should understand that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. In addition, for clarity and brevity, descriptions of known functions and structures are omitted in the embodiments.

[0036] It should be understood that the phrase "an embodiment" or "this embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "an embodiment" or "this embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0037] Furthermore, reference numerals and / or letters may be repeated in different examples within this application. Such repetition is for the purpose of simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or settings discussed.

[0038] In this article, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. The term " / and" in this article describes another type of relationship between related objects, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the related objects before and after it are in an "or" relationship.

[0039] In this article, the term "at least one" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, "at least one of A and B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0040] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion.

[0041] Example 1

[0042] This invention provides a method for enhancing the biological treatment efficiency of comprehensive electroplating wastewater, comprising the following steps:

[0043] (1) Pretreatment of biogas slurry: Collect pig manure fermentation biogas slurry, let it stand for 4 hours, and discard the bottom sediment; after aeration, make the ammonia nitrogen concentration of biogas slurry about 100 mg / L and the COD concentration about 3600 mg / L; and sterilize the treated biogas slurry by ultraviolet irradiation.

[0044] (2) Cultivating anaerobic sludge: Collect sludge from the anaerobic pond of the urban sewage treatment plant, wash it 3 times, blow it with nitrogen for 20 minutes, and put it into a sealed container; add tryptone medium and potassium dichromate solution to make the initial Cr(VI) concentration of the sludge system 40 mg / L, and incubate it at 30℃; add fresh liquid medium and potassium dichromate solution every week, and incubate for 4 weeks.

[0045] (3) Sludge acclimatization: Every week, add the biogas slurry obtained after treatment in step (1) to the anaerobic sludge cultivated in step (2) at a volume ratio of 8:1. As the Cr(VI) content in the solution decreases, potassium dichromate solution is added on time. Repeat the acclimatization until the Cr(VI) concentration can be reduced to below 3.0 mg / L within 1 day, and the acclimatization is completed.

[0046] (4) Prepare a mixture of biogas slurry and comprehensive wastewater: Collect comprehensive electroplating wastewater with Cr(VI), Cd, Cu and Ni concentrations of 20-30 mg / L, 1-3 mg / L, 4-6 mg / L and 7-10 mg / L respectively. Mix the comprehensive electroplating wastewater and the treated biogas slurry at a volume ratio of 15:1, stir evenly and adjust the pH to 6.0.

[0047] (5) Cr(VI) bioreduction reaction (first-order reaction): An upflow reactor can be used as the experimental setup. First, a layer of natural pyrite is laid at the bottom of the reactor, with a total content of 0.8 g / L. Then, acclimated anaerobic sludge is added to the reactor. Next, a peristaltic pump is used to pump the mixture of biogas slurry and electroplating wastewater into the reactor at a certain flow rate. The hydraulic retention time is 10 hours, and the effluent is connected to the subsequent second-order reaction.

[0048] (6) Adsorption reaction of biogenic iron oxide (secondary reaction): The experimental setup can be an upflow reactor. First, fill the reactor with straw biochar particles with a particle size of 1.5 cm and a porosity of about 90%; then, inoculate with Klebsiella sp. Strain M3 suspension and culture at 30°C for 7 days; finally, pass the effluent from experimental step (5) through the reactor from bottom to top at a certain flow rate, with a hydraulic retention time of 18 hours. The entire reactor can operate stably for 70 days. The effluent Cr(VI), Cu, and Ni are all below 0.5 mg / L, Cd concentration is below 0.1 mg / L, COD concentration is below 30 mg / L, and ammonia nitrogen is below 15 mg / L, meeting the requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0049] Example 2

[0050] (1) Pretreatment of biogas slurry: Collect biogas slurry from pig manure fermentation, let it stand for 5 hours, and discard the bottom sediment; after aeration, the ammonia nitrogen concentration of the biogas slurry is about 120 mg / L and the COD concentration is about 4000 mg / L; the treated biogas slurry is sterilized by ultraviolet irradiation.

[0051] (2) Cultivating anaerobic sludge: Collect sludge from the anaerobic pond of the urban sewage treatment plant, wash it 3 times, blow it with nitrogen for 20 minutes, and put it into a sealed container; add tryptone medium and potassium dichromate solution to make the initial Cr(VI) concentration of the sludge system 50 mg / L, and incubate it at 30℃; add fresh liquid medium and potassium dichromate solution every week, and incubate for 4 weeks.

[0052] (3) Sludge acclimatization: Every week, add the biogas slurry obtained after treatment in step (1) to the anaerobic sludge cultivated in step (2) at a volume ratio of 9:1. As the Cr(VI) content in the solution decreases, potassium dichromate solution is added on time. Repeat the acclimatization until the Cr(VI) concentration can be reduced to below 3.0 mg / L within 1.5 days, and the acclimatization is completed.

[0053] (4) Prepare a mixture of biogas slurry and comprehensive wastewater: Collect comprehensive electroplating wastewater with Cr(VI), Cd, Cu and Ni concentrations of 20-30 mg / L, 1-3 mg / L, 4-6 mg / L and 7-10 mg / L respectively. Mix the comprehensive electroplating wastewater and the treated biogas slurry at a volume ratio of 18:1, stir evenly and adjust the pH to 6.0.

[0054] (5) Cr(VI) bioreduction reaction (first-order reaction): The experimental setup can be an upflow reactor. First, a layer of natural pyrite is laid at the bottom of the reactor, with a total content of 1.0 g / L. Then, acclimated anaerobic sludge is added to the reactor. Next, a peristaltic pump is used to pump the mixture of biogas slurry and electroplating wastewater into the reactor at a certain flow rate. The hydraulic retention time is 12 hours, and the effluent is connected to the subsequent second-order reaction.

[0055] (6) Adsorption reaction of biogenic iron oxide (secondary reaction): The experimental setup can be an upflow reactor. First, fill the reactor with straw biochar particles with a particle size of 2.0 cm and a porosity of about 90%; then, inoculate with Klebsiella sp. Strain M3 suspension and culture at 30°C for 7 days; finally, pass the effluent from experimental step (5) through the reactor from bottom to top at a certain flow rate, with a hydraulic retention time of 20 hours. The entire reactor can operate stably for 68 days. The effluent Cr(VI), Cu, and Ni are all below 0.5 mg / L, Cd concentration is below 0.1 mg / L, COD concentration is below 30 mg / L, and ammonia nitrogen is below 15 mg / L, meeting the requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0056] Example 3

[0057] (1) Pretreatment of biogas slurry: Collect biogas slurry from pig manure fermentation, let it stand for 6 hours, and discard the bottom sediment; after aeration, the ammonia nitrogen concentration of the biogas slurry is about 140 mg / L and the COD concentration is about 4500 mg / L; the treated biogas slurry is sterilized by ultraviolet irradiation and then kept for use.

[0058] (2) Cultivating anaerobic sludge: Collect sludge from the anaerobic pond of the urban sewage treatment plant, wash it 3 times, blow it with nitrogen for 20 minutes, and put it into a sealed container; add tryptone medium and potassium dichromate solution to make the initial Cr(VI) concentration of the sludge system 60 mg / L, and incubate it at 30℃; add fresh liquid medium and potassium dichromate solution every week, and incubate for 4 weeks.

[0059] (3) Sludge acclimatization: Every week, add the biogas slurry obtained after treatment in step (1) to the anaerobic sludge cultivated in step (2) at a volume ratio of 10:1. As the Cr(VI) content in the solution decreases, potassium dichromate solution is added on time. Repeat the acclimatization until the Cr(VI) concentration can be reduced to below 3.0 mg / L within 2 days, and the acclimatization is completed.

[0060] (4) Prepare a mixture of biogas slurry and comprehensive wastewater: Collect comprehensive electroplating wastewater with Cr(VI), Cd, Cu and Ni concentrations of 20-30 mg / L, 1-3 mg / L, 4-6 mg / L and 7-10 mg / L respectively. Mix the comprehensive electroplating wastewater and the treated biogas slurry at a volume ratio of 15:1, stir evenly and adjust the pH to 6.0.

[0061] (5) Cr(VI) bioreduction reaction (first-order reaction): An upflow reactor can be used as the experimental setup. First, a layer of natural pyrite is laid at the bottom of the reactor, with a total content of 1.2 g / L. Then, acclimated anaerobic sludge is added to the reactor. Next, a peristaltic pump is used to pump the mixture of biogas slurry and electroplating wastewater into the reactor at a certain flow rate. The hydraulic retention time is 14 hours, and the effluent is connected to the subsequent second-order reaction.

[0062] (6) Adsorption reaction of biogenic iron oxide (secondary reaction): The experimental setup can be an upflow reactor. First, fill the reactor with straw biochar particles with a particle size of 2.5 cm and a porosity of about 90%; then, inoculate with Klebsiella sp. Strain M3 suspension and culture at 30°C for 7 days; finally, pass the effluent from experimental step (5) through the reactor from bottom to top at a certain flow rate, with a hydraulic retention time of 24 hours. The entire reactor can operate stably for 65 days. The effluent Cr(VI), Cu, and Ni are all below 0.5 mg / L, Cd concentration is below 0.1 mg / L, COD concentration is below 30 mg / L, and ammonia nitrogen is below 15 mg / L, meeting the requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0063] Comparative Example 1

[0064] No biogas slurry was applied

[0065] (1) Pretreatment of biogas slurry: Collect biogas slurry from pig manure fermentation, let it stand for 6 hours, and discard the bottom sediment; after aeration, the ammonia nitrogen concentration of the biogas slurry is about 140 mg / L and the COD concentration is about 4500 mg / L; the treated biogas slurry is sterilized by ultraviolet irradiation and then kept for use.

[0066] (2) Cultivating anaerobic sludge: Collect sludge from the anaerobic pond of the urban sewage treatment plant, wash it 3 times, blow it with nitrogen for 20 minutes, and put it into a sealed container; add tryptone medium and potassium dichromate solution to make the initial Cr(VI) concentration of the sludge system 60 mg / L, and incubate it at 30℃; add fresh liquid medium and potassium dichromate solution every week, and incubate for 4 weeks.

[0067] (3) Sludge acclimatization: Every week, add the biogas slurry obtained after treatment in step (1) to the anaerobic sludge cultivated in step (2) at a volume ratio of 10:1. As the Cr(VI) content in the solution decreases, potassium dichromate solution is added on time. Repeat the acclimatization until the Cr(VI) concentration can be reduced to below 3.0 mg / L within 2 days, and the acclimatization is completed.

[0068] (4) Mixed solution of comprehensive wastewater: Collect comprehensive electroplating wastewater with Cr(VI), Cd, Cu and Ni concentrations of 20-30 mg / L, 1-3 mg / L, 4-6 mg / L and 7-10 mg / L respectively, and adjust the pH to 6.0.

[0069] (5) Cr(VI) bioreduction reaction (first-order reaction): An upflow reactor can be used as the experimental setup. First, a layer of natural pyrite is laid at the bottom of the reactor, with a total content of 1.2 g / L. Then, acclimated anaerobic sludge is added to the reactor. Next, a peristaltic pump is used to pump the mixture of biogas slurry and electroplating wastewater into the reactor at a certain flow rate. The hydraulic retention time is 14 hours, and the effluent is connected to the subsequent second-order reaction.

[0070] (6) Adsorption reaction of biogenic iron oxides (secondary reaction): An upflow reactor can be used as the experimental setup. First, straw biochar particles with a particle size of 2.5 cm are filled into the reactor, with a porosity of about 90%. Then, Klebsiella sp. Strain M3 suspension is inoculated and cultured at 30°C for 7 days. Finally, the effluent from step (5) is passed through the reactor from bottom to top at a certain flow rate, with a hydraulic retention time of 24 hours. Within 8 days of reactor operation, the effluent Cr(VI), Cu, and Ni concentrations are all below 0.5 mg / L, Cd concentration is below 0.1 mg / L, COD concentration is below 30 mg / L, and ammonia nitrogen is below 15 mg / L, meeting the requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996). However, after 8 days, the concentration of heavy metals in the effluent gradually increases. After 14 days, the concentrations of Cr(VI), Cu, and Ni in the effluent all exceed 10 mg / L. After 18 days, the concentration of heavy metals in the effluent is almost close to the concentration in the influent.

[0071] Comparative Example 2

[0072] No pyrite deposit

[0073] (1) Pretreatment of biogas slurry: Collect biogas slurry from pig manure fermentation, let it stand for 6 hours, and discard the bottom sediment; after aeration, the ammonia nitrogen concentration of the biogas slurry is about 140 mg / L and the COD concentration is about 4500 mg / L; the treated biogas slurry is sterilized by ultraviolet irradiation and then kept for use.

[0074] (2) Cultivating anaerobic sludge: Collect sludge from the anaerobic pond of the urban sewage treatment plant, wash it 3 times, blow it with nitrogen for 20 minutes, and put it into a sealed container; add tryptone medium and potassium dichromate solution to make the initial Cr(VI) concentration of the sludge system 60 mg / L, and incubate it at 30℃; add fresh liquid medium and potassium dichromate solution every week, and incubate for 4 weeks.

[0075] (3) Sludge acclimatization: Every week, add the biogas slurry obtained after treatment in step (1) to the anaerobic sludge cultivated in step (2) at a volume ratio of 10:1. As the Cr(VI) content in the solution decreases, potassium dichromate solution is added on time. Repeat the acclimatization until the Cr(VI) concentration can be reduced to below 3.0 mg / L within 2 days, and the acclimatization is completed.

[0076] (4) Prepare a mixture of biogas slurry and comprehensive wastewater: Collect comprehensive electroplating wastewater with Cr(VI), Cd, Cu and Ni concentrations of 20-30 mg / L, 1-3 mg / L, 4-6 mg / L and 7-10 mg / L respectively. Mix the comprehensive electroplating wastewater and the treated biogas slurry at a volume ratio of 15:1, stir evenly and adjust the pH to 6.0.

[0077] (5) Cr(VI) bioreduction reaction (first-order reaction): The experimental setup can be an upflow reactor. First, add acclimated anaerobic sludge to the reactor; then, use a peristaltic pump to pump in the mixed reaction solution of biogas slurry and electroplating wastewater at a certain flow rate. The hydraulic retention time is 14 hours, and the effluent is connected to the subsequent second-order reaction.

[0078] (6) Adsorption reaction of biogenic iron oxides (secondary reaction): An upflow reactor can be used as the experimental setup. First, straw biochar particles with a particle size of 2.5 cm are filled into the reactor, with a porosity of about 90%. Then, Klebsiella sp. Strain M3 suspension is inoculated and cultured at 30°C for 7 days. Finally, the effluent from step (5) is passed through the reactor from bottom to top at a certain flow rate, with a hydraulic retention time of 24 hours. The entire reactor can operate stably for 30 days, with Cr(VI), Cu, and Ni in the effluent all below 0.5 mg / L, Cd concentration below 0.1 mg / L, COD concentration below 30 mg / L, and ammonia nitrogen below 15 mg / L, meeting the requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996). However, after 30 days, Cd, Cu, and Ni in the effluent gradually increase, exceeding the control requirements of the Integrated Wastewater Discharge Standard (GB 8978-1996).

[0079] The above description is merely a preferred embodiment of the present invention and does not limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments within the spirit and principles of the present invention, achieved through conventional substitutions or by achieving the same function without departing from the principles and spirit of the present invention, fall within the scope of protection of the present invention.

Claims

1. A method for treating electroplating wastewater by using microbial reduction of biogenic iron oxidation combined with biogenic iron oxidation, characterized in that, The method comprises the following steps: (1) Pretreatment of biogas slurry: collect the fermentation biogas slurry, stand still, and discard the bottom sediment; (2) Anaerobic sludge culture: collect the anaerobic tank sludge, elute, and blow off with nitrogen, and then add into a sealed container; add a tryptone culture medium, and add a potassium dichromate solution for culture; (3) Sludge domestication: add the biogas slurry obtained after the pretreatment of the biogas slurry to the anaerobic sludge cultured in step (2), and supplement the potassium dichromate solution in time, and repeat the domestication, and when the Cr(VI) concentration is reduced to below 3.0 mg / L within 1-3 days, the domestication is completed; (4) Configuration of mixed solution of biogas slurry and comprehensive wastewater: collect the comprehensive electroplating wastewater, mix it with the biogas slurry obtained after the pretreatment of the biogas slurry to form a mixed solution, stir, and adjust the pH to 5.0-6.5; (5) Primary reaction process: add pyrite to the reactor of the primary reaction process, and then add the domesticated anaerobic sludge into the reactor; then, add the mixed solution, and the hydraulic retention time is 10-16 hours; (6) Secondary reaction process: fill the reactor of the secondary reaction process with carbon particles, and the void ratio is 80-90%; then, inoculate a functional bacteria suspension, and make the functional bacteria adhere to the surface of the carbon particles to form a biofilm; and then, pass the effluent of the primary reaction process into the reactor of the secondary reaction process, and the hydraulic retention time is 18-24 hours. The functional bacteria are Klebsiella sp. Strain M3, and the preservation number is CCTCC M2021261; and the bacteria were preserved in the China Center for Type Culture Collection on March 24, 2021. In step (4), the volume ratio of the comprehensive electroplating wastewater to the biogas slurry is 15-20:1; and in step (5), the addition amount of the pyrite is 0.8-1.2 g / L.

2. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, The pretreatment of the biogas slurry further comprises aeration, and the ammonia nitrogen content is reduced.

3. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, The biogas slurry treated by aeration is subjected to ultraviolet irradiation sterilization.

4. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, In the anaerobic sludge culture, fresh liquid culture medium and potassium dichromate solution are added every 1 period, and the culture is carried out for 4 periods, and each period is 3-10 days.

5. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, The reactor used in the primary reaction process is an upflow reactor, and a screen is arranged at the bottom of the reactor, and an exhaust hole and a gas absorption device are arranged at the upper part of the reactor; and the reactor used in the secondary reaction process is also an upflow reactor.

6. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, The carbon particles are straw biomass carbon.

7. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, The fermentation biogas slurry is the filtrate obtained after the complete fermentation of pig farm excrement, urine and flushing wastewater in a biogas tank, and the removal of biogas residues.

8. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, After the pretreatment of the biogas slurry, the ammonia nitrogen concentration of the fermentation biogas slurry is 100-145 mg / L, and the COD concentration is 3600-4500 mg / L.

9. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, After the addition of the potassium dichromate solution in step (2), the initial Cr(VI) concentration of the sludge system is 40-60 mg / L.

10. The method for treating electroplating wastewater by combined iron bio-oxidation and bioreduction of biogas slurry microorganisms according to claim 1, characterized in that, In step (3), the volume ratio of the anaerobic sludge to the added biogas slurry is 8-10:1.

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