A method for anaerobic detoxification of coal chemical wastewater

Abstract

The present invention relates to a method for anaerobic detoxification of coal chemical wastewater, and belongs to the technical field of anaerobic detoxification of coal chemical wastewater. The method comprises pre-treatment to regulate the redox potential of the wastewater to a range of 80mV to 50mV; inoculating a mixed bacterial community of thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria on a polyurethane foam carrier to form a layered biofilm; controlling the redox potential in stages, adding sodium formate under microaerobic conditions to preferentially degrade thiocyanate to produce bicarbonate; adding nano-zero-valent iron to reduce catechol and adsorb cyanide; and adding ethanol and humic acid under strictly anaerobic conditions to degrade phenols. Through the decoupling of bacterial metabolic pathways, the synergistic detoxification of metabolites and the targeted detoxification of nanomaterials, the problems of redundancy of traditional multi-stage reactor equipment, bacterial competitive inhibition and toxic accumulation of intermediate products are solved, and efficient step-by-step degradation of thiocyanate and phenols is achieved in a single reactor, the biodegradability of the wastewater is significantly improved, and a low-toxic environment is provided for subsequent treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of anaerobic detoxification of coal chemical wastewater, and particularly relates to an anaerobic detoxification method for coal chemical wastewater. Background Art

[0002] The coal chemical industry is a core sector that uses coal as a raw material to produce high-value-added products such as synthesis gas, methanol, and olefins. However, the highly toxic wastewater generated during this production process has become a key bottleneck hindering the industry's green development. This wastewater, primarily derived from processes such as coal gasification and coking, is characterized by high pollutant concentrations, complex composition, and strong bioinhibition properties. Typical pollutants include phenols (800-1500 mg / L), thiocyanates (1000-2000 mg / L), and cyanides (50-100 mg / L). Phenols and thiocyanates can easily form a toxic synergistic effect, severely inhibiting microbial activity and rendering traditional biological treatment processes inefficient or even ineffective. With increasingly stringent environmental regulations, the development of efficient and low-cost coal chemical wastewater detoxification technologies to achieve targeted conversion of toxic substances and enhance biodegradability has become a common challenge that the industry urgently needs to address.

[0003] The complete treatment process of coal chemical wastewater is usually divided into three stages:

[0004] 1. In the pretreatment stage, physical and chemical methods (such as coagulation and sedimentation, redox) are used to remove suspended solids and some toxic substances and adjust water quality to create conditions for subsequent biochemical treatment.

[0005] 2. In the biological treatment stage, an anaerobic-aerobic combined process (such as UASB-A / O) is used to degrade organic matter, but it relies on pre-treated low-toxic wastewater to ensure microbial activity.

[0006] 3. In the advanced treatment stage, advanced oxidation (such as ozone, Fenton), adsorption or membrane technology are used to further remove refractory organic matter to ensure that the effluent meets the standards.

[0007] In the above process, anaerobic detoxification in the pretreatment stage is a key step in determining the effectiveness of subsequent treatment. Anaerobic detoxification converts highly toxic pollutants (such as thiocyanate and phenols) into low-toxic or easily degradable forms through biological or chemical means. Currently, conventional anaerobic detoxification methods used in pretreatment mainly include the following three categories:

[0008] (1) Thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria are placed in separate reactors, and microaerobic and strictly anaerobic conditions are controlled respectively to degrade thiocyanate and phenols in a step-by-step manner. However, this method occupies a large area and has high investment costs; the transfer of bacterial colonies across reactors can lead to loss; and intermediate products accumulate between stages, forming a toxic inhibition chain.

[0009] (2) Adding exogenous carbon sources stimulates microbial co-metabolism to degrade toxic substances. However, the imbalance in the distribution of electron donors triggers competition among bacterial communities. The competition for carbon sources between thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria leads to a decrease in degradation efficiency. Excessive carbon source addition increases sludge production and treatment costs.

[0010] (3) Chemical reduction of thiocyanate using zero-valent iron or sodium sulfide, combined with Fenton oxidation to degrade phenols. However, this involves high chemical consumption and a high risk of secondary contamination from iron sludge / sulfur slag. Strong oxidative conditions destroy microbial activity, making it impossible to directly connect with subsequent biological treatment.

[0011] Therefore, there is an urgent need for an innovative method that can achieve efficient step-by-step degradation of thiocyanate and phenols in the same reactor while precisely blocking the regeneration of toxic intermediates, so as to simplify the process, improve efficiency and reduce operating costs. Summary of the Invention

[0012] The present invention overcomes the deficiencies of the prior art and provides a method for anaerobic detoxification of coal chemical wastewater.

[0013] To achieve the above object, the technical solution adopted by the present invention is: a method for anaerobic detoxification of coal chemical wastewater, comprising the following steps:

[0014] S1. Pre-treat wastewater;

[0015] S2, inoculating the wastewater in S1 with a mixed bacterial community including thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria;

[0016] S3, adding sodium formate to the wastewater in S2, controlling the redox potential of the wastewater to -150mV to -100mV and the dissolved oxygen concentration to 0.08-0.3mg / L, for 8-12h;

[0017] S4, adding nano zero-valent iron to the wastewater in S3, stirring and reacting for 20-40 minutes and then standing and separating;

[0018] S5. Adjust the S4 wastewater to weak alkalinity, add ethanol and humic acid to the wastewater, control the redox potential to -300mV to -200mV, and the dissolved oxygen concentration to be lower than 0.05mg / L, and continue for 12-24h.

[0019] Furthermore, in step S1, the pretreatment includes detecting the initial redox potential of the wastewater, controlling the redox potential of the wastewater to -80mV to -50mV, adding ferrous sulfate and polyacrylamide to the wastewater, adjusting the pH of the wastewater to neutral, stirring for 20-50min, and standing for 30-50min; wherein the addition amount of ferrous sulfate is 0.3-0.8g / L, and the addition amount of polyacrylamide is 5-15mg / L.

[0020] Furthermore, in step S1, the method for controlling the redox potential of wastewater includes:

[0021] If the initial redox potential is greater than -50mV, add 0.8-1.2g / L ferrous sulfate, stir for 15-30min, let it settle for 30-40min, filter and adjust the pH to 6.6-7.0;

[0022] If the initial redox potential is less than -80mV, add 3%-5% concentration hydrogen peroxide solution, control the dissolved oxygen to 0.3-0.5mg / L for aeration, and simultaneously introduce nitrogen purge at a rate of 0.3-0.5L / min for 15-30min until the redox potential stabilizes to above -80mV.

[0023] Furthermore, in step S2, the thiocyanate-degrading bacteria include at least one of Thiobacillus denitrificans, Thiobacillus thiooxidans, and Thiobacillus thioexcreta; and the phenol-hydrolyzing bacteria include at least one of Clostridium butyricum and Clostridium perfringens;

[0024] In the mixed bacterial community, thiocyanate-degrading bacteria account for 50%-70% by volume, and phenol-hydrolyzing bacteria account for 30%-50%.

[0025] Furthermore, in step S2, the method of inoculating the mixed bacterial flora includes:

[0026] S21, activating the thiocyanate-degrading bacteria and the phenol-hydrolyzing bacteria in culture medium respectively, and mixing the activated thiocyanate-degrading bacteria and the phenol-hydrolyzing bacteria to obtain a mixed bacterial solution;

[0027] S22, soaking the polyurethane foam carrier in a sodium hydroxide solution and rinsing until it becomes neutral;

[0028] S23, mixing the mixed bacterial solution with the polyurethane foam carrier, and placing the mixture in a shaking table for adsorption;

[0029] S24, mixing the polyurethane foam carrier with the attached bacterial strain with the wastewater, stirring at a low speed to ensure that the bacterial colony and the wastewater are fully in contact; and allowing the carrier to settle to form a stratified biofilm;

[0030] Among them, the polyurethane foam carrier is 50-200μm and the specific surface area is ≥800m² / m³.

[0031] Furthermore, in step S3, the total amount of sodium formate added is 0.3-0.8 g / L, which is added in two times, with the first addition amount being 60%-80% of the total amount added, and the remaining amount is added at an interval of 4-6 hours.

[0032] Furthermore, in step S4, the particle size of the nano-zero-valent iron is 30-80 nm, and the dosage is 0.05-0.2 g / L; after stirring the reaction, the nano-zero-valent iron is separated by centrifugation or filtration.

[0033] Furthermore, the separated nano-zero-valent iron is regenerated by acid washing, specifically by immersing the nano-zero-valent iron in a 0.5-1.0 mol / L hydrochloric acid solution, shaking for 20-40 minutes, and rinsing with clean water until neutral.

[0034] Furthermore, in step S5, the dosage of ethanol is 0.2-0.5 g / L, which is added to the wastewater in three equal amounts, with an interval of 2-3 hours each time; the dosage of humic acid is 40-60 mg / L, which is added to the wastewater in the form of dry powder.

[0035] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0036] The present invention provides an anaerobic detoxification method for coal chemical wastewater. By regulating the redox potential, optimizing the ratio of mixed bacteria and the directional detoxification of nano-zero-valent iron, the step-by-step and efficient degradation of thiocyanate and phenols is achieved in a single reactor, while blocking the sulfur cycle regeneration and the accumulation of toxic intermediates, solving the problem of bacterial metabolic conflicts in traditional processes, and significantly improving the biodegradability of wastewater, providing a low-toxic environment for subsequent treatment.

[0037] The present invention adopts a mixed bacterial community of denitrifying Thiobacillus and Clostridium butyricum. Based on the differences in the metabolic characteristics of denitrifying Thiobacillus and Clostridium butyricum, the redox potential is controlled in stages, from -150mV to -100mV in the microaerobic stage and from -300mV to -200mV in the strict anaerobic stage. Denitrifying Thiobacillus preferentially degrades thiocyanate in a microaerobic environment to generate bicarbonate as a carbon source; Clostridium butyricum utilizes ethanol and a preceding carbon source to degrade phenols under strictly anaerobic conditions. The metabolic pathways of the two bacterial communities are decoupled, avoiding degradation inhibition caused by conflicts in environmental conditions in traditional processes. Traditional processes require the installation of multiple stages of reactors, and competition among bacterial communities leads to a decrease in degradation efficiency. The present invention achieves functional separation of bacterial communities through segmented redox potential, simplifies the process and improves synergistic efficiency.

[0038] The nano-zero-valent iron in this invention selectively reduces catechol and adsorbs cyanide, while chelating with humic acid to stabilize free toxic substances. The nano-zero-valent iron reduces catechol to low-toxic cyclohexanol while simultaneously forming a Prussian blue precipitate with cyanide. Humic acid adsorbs toxic substances through its functional groups, reducing their free concentration and effectively inhibiting the oxidation of catechol to quinones and the regeneration of thiocyanate, significantly reducing the concentration of toxic intermediates. Traditional processes rely on physical adsorption or chemical precipitation, which makes it difficult to effectively block the regeneration of intermediates. However, this invention achieves targeted removal of toxic substances through the synergistic effect of nanomaterials and humic acid. Furthermore, the nano-zero-valent iron can be recycled after acid washing and regeneration, reducing material consumption.

[0039] Phased redox potential control and decoupling of bacterial metabolic pathways provide a window for toxicity blocking by nano-zero-valent iron and humic acid. During the microaerobic phase, sulfide ions produced by thiocyanate-degrading bacteria react with ferrous ions to form ferrous sulfide precipitates, blocking the sulfur cycle and regenerating cyanide. Simultaneously, nano-zero-valent iron initially adsorbs thiocyanate degradation intermediates. During the strictly anaerobic phase, toxic intermediates produced by phenol-hydrolyzing bacteria during phenol degradation are reduced by nano-zero-valent iron, and humic acid further complexes cyanide, forming a closed-loop metabolic chain. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0041] Figure 1 This is a flow chart of an anaerobic detoxification method for coal chemical wastewater;

[0042] Figure 2 It is a flow chart of the method for inoculating a mixed bacterial flora. DETAILED DESCRIPTION

[0043] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0044] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below. The materials not specifically described below are all purchased from commercial sources or prepared by conventional methods in the field. Among them, some of the materials are from the following sources: Denitrifying Thiobacillus DSM 12475, gray algae; Clostridium butyricum CICC 10390, China Industrial Microorganism Culture Collection Administration Center; Sodium formate, AR (Shanghai test); Nano zero-valent iron DK-Fe-50, Beike Nano; Ethanol, 75% (Shanghai test); Humic acid, BR (source leaf); Polyurethane foam carrier, (Covestro China); polyacrylamide, anion adsorbent (Shanghai trial); ferrous sulfate (ferrous sulfate heptahydrate), AR (Shanghai trial).

[0045] Exemplary methods:

[0046] like Figure 1 As shown, a method for anaerobic detoxification of coal chemical wastewater comprises the following steps:

[0047] S1. Pre-treat wastewater;

[0048] S2, inoculating the wastewater in S1 with a mixed bacterial community including thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria;

[0049] S3, adding sodium formate to the wastewater in S2, controlling the redox potential of the wastewater to -150mV to -100mV and the dissolved oxygen concentration to 0.08-0.3mg / L, for 8-12h;

[0050] S4, adding nano zero-valent iron to the wastewater in S3, stirring and reacting for 20-40 minutes and then standing and separating;

[0051] S5. Adjust the S4 wastewater to weak alkalinity, add ethanol and humic acid to the wastewater, control the redox potential to -300mV to -200mV, and the dissolved oxygen concentration to be lower than 0.05mg / L, and continue for 12-24h.

[0052] This method achieves the stepwise degradation of thiocyanate and phenols within the same reactor by controlling the redox potential and dissolved oxygen in stages, and by adding electron donors and functional materials. This method leverages the interaction of the metabolites of thiocyanate-degrading and phenol-hydrolyzing bacteria to create a synergistic effect. Specifically, under microaerobic conditions (redox potential of -150mV to -100mV), thiocyanate-degrading bacteria preferentially degrade thiocyanate, generating bicarbonate as a carbon source. After switching to strictly anaerobic conditions (redox potential of -250mV to -200mV), phenol-hydrolyzing bacteria efficiently degrade phenols using ethanol and bicarbonate, while nano-zero-valent iron blocks toxic intermediates.

[0053] Below, each step will be described in detail.

[0054] The pretreatment in step S1 involves testing the wastewater's initial redox potential, controlling it between -80mV and -50mV, adding ferrous sulfate and polyacrylamide, adjusting the pH to neutral, stirring the wastewater for 20-50 minutes, and allowing it to stand for 30-50 minutes. This pretreatment provides a stable environment for subsequent bacterial colonization. Ferrous sulfate not only precipitates sulfide, but its residual ferrous ions also contribute to the subsequent sulfur cycle blocking process.

[0055] The dosage of ferrous sulfate is 0.3-0.8 g / L, and the dosage of polyacrylamide is 5-15 mg / L. Ferrous sulfate is added by dissolving solid ferrous sulfate heptahydrate in water at a mass ratio of 1:5, evenly sprinkling the solution into the wastewater and stirring to ensure complete dissolution. Adding 0.3-0.8 g / L of ferrous sulfate provides ferrous ions for sulfide precipitation, reducing sulfide toxicity. Polyacrylamide, as a polymer flocculant, adsorbs colloidal particles and suspended matter, forming easily settling flocs. Polyacrylamide itself does not participate in redox reactions, but by removing suspended organic matter (phenolic polymers), it indirectly reduces subsequent bacterial inhibition.

[0056] Methods for controlling the redox potential of wastewater include:

[0057] If the initial redox potential is greater than -50mV, add 0.8-1.2g / L ferrous sulfate, stir for 15-30 minutes, let it settle for 30-40 minutes, filter, and adjust the pH to 6.6-7.0. The redox potential can be significantly reduced by the reducing properties of high-concentration ferrous sulfate.

[0058] If the initial redox potential is less than -80mV, add a 3%-5% hydrogen peroxide solution, control the dissolved oxygen level to 0.3-0.5mg / L for aeration, and simultaneously introduce nitrogen purge at a rate of 0.3-0.5L / min for 15-30 minutes until the redox potential stabilizes above -80mV. Hydrogen peroxide, as a strong oxidant, directly oxidizes reducing substances (ferrous ions, organic matter, sulfides) in the wastewater, releasing electrons and raising the redox potential.

[0059] In step S2, the thiocyanate-degrading bacteria include at least one of denitrifying Thiobacillus, thiooxidans, and expelling Thiobacillus, which degrade thiocyanate ions into sulfide ions, ammonia, and bicarbonate ions via thiosulfate reductase. Phenol-hydrolyzing bacteria include at least one of Clostridium butyricum and Clostridium perfringens, which are strictly anaerobic and secrete phenol hydroxylase to catalyze the ring opening of phenol to produce acetic acid and propionic acid. Among them, the degradation rate of thiocyanate by denitrifying Thiobacillus is significantly higher than that of other strains, and it tolerates microaerobic conditions; Clostridium butyricum has a strong tolerance to phenols, uses ethanol as an electron donor, and secretes phenol hydroxylase to catalyze the ring opening of phenol.

[0060] In the mixed bacterial community, thiocyanate-degrading bacteria account for 50%-70% by volume, and phenol-hydrolyzing bacteria account for 30%-50%, ensuring that thiocyanate-degrading bacteria dominate in the early stage and avoiding premature consumption of electron donors by phenol-hydrolyzing bacteria.

[0061] like Figure 2 As shown, the method of inoculating a mixed flora includes:

[0062] S21, activating the thiocyanate-degrading bacteria and the phenol-hydrolyzing bacteria in culture medium respectively, and mixing the activated thiocyanate-degrading bacteria and the phenol-hydrolyzing bacteria to obtain a mixed bacterial solution;

[0063] S22, soaking the polyurethane foam carrier in a NaOH solution and rinsing until it becomes neutral;

[0064] S23, mixing the mixed bacterial solution with the polyurethane foam carrier, and placing the mixture in a shaking table for adsorption;

[0065] S24. Mix the polyurethane foam carrier with attached bacteria with wastewater, stir at low speed to ensure full contact between bacteria and wastewater; let it stand and settle to form a layered biofilm.

[0066] In step S21, thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria are placed in Postgate C medium (containing 500 mg / L thiocyanate ion, pH 6.8) and RCM medium (containing 200 mg / L phenol, pH 7.0), respectively, and activated at 30° C. in a nitrogen atmosphere for 3 hours. The activated thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria are mixed to obtain a mixed bacterial solution.

[0067] In step S22, a polyurethane foam carrier having a pore size of 50-200 μm and a specific surface area of ​​≥800 m² / m³ is soaked in a 0.1 M sodium hydroxide solution for 1 hour and rinsed until neutral;

[0068] In step S23, the mixed bacterial solution and the polyurethane foam carrier are mixed at a mass ratio of 1:20, placed on a shaker, and adsorbed at 50 rpm and 30°C for 2 hours;

[0069] In step S24, the polyurethane foam carrier with attached bacteria is mixed with wastewater in a mass-to-volume ratio of 1:10 to 1:50, evenly poured into the reactor, and stirred at a low speed of 30 rpm for 30 minutes to ensure that the bacteria and wastewater are in full contact; the carrier is allowed to settle for 1 hour to form a layered biofilm.

[0070] In traditional processes, bacterial communities must be separated into multiple reactors due to competition. This method uses a polyurethane foam carrier to solidify the mixed bacterial community, achieving functional separation within a single reactor. The high-surface-area carrier shortens biofilm formation time and significantly reduces bacterial loss, thereby improving process stability.

[0071] In step S3, the total amount of sodium formate added is 0.3-0.8 g / L, which is added in two times, with the first addition amount being 60%-80% of the total amount added, and the remaining amount is added at an interval of 4-6 hours; the redox potential is controlled to be -150 mV to -100 mV, the dissolved oxygen is 0.1-0.3 mg / L, and the pH is 6.5-7.0 until the thiocyanate concentration drops below 100 mg / L.

[0072] Sodium formate is added via a peristaltic pump at a rate of 0.1-0.5g / (L·h). The initial addition quickly establishes a reducing environment and activates the bacterial flora. Supplementary additions maintain metabolic stability and prevent excessive Thiobacillus proliferation. Microaeration is simultaneously achieved with a nitrogen and oxygen mixture, with an oxygen content of 1%-3%, maintaining a microaerobic environment of 0.1-0.3mg / L dissolved oxygen.

[0073] Thiobacillus denitrificans uses thiocyanate as an electron acceptor and sodium formate as a carbon source to catalyze the reaction, producing bicarbonate and hydrogen sulfide. Hydrogen sulfide reacts with ferrous ions to form iron sulfide precipitates, blocking the sulfur cycle. Simultaneously, the bicarbonate produced by thiocyanate degradation provides a carbon source for the subsequent degradation of phenols.

[0074] In step S4, the particle size of the nano-zero-valent iron is 30-80 nm, and the dosage is 0.05-0.2 g / L; after stirring the reaction, the nano-zero-valent iron is separated by centrifugation or filtration.

[0075] The separated nano-zero-valent iron is regenerated by acid washing. The specific steps are: immersing the nano-zero-valent iron in a 0.5-1.0 mol / L hydrochloric acid solution, shaking for 20-40 minutes, and rinsing with clean water until neutral.

[0076] The active sites on the nano-zero-valent iron surface directly reduce the catechol intermediate to low-toxic cyclohexanol. Simultaneously, they adsorb cyanide to form a Prussian blue precipitate, rapidly blocking the toxicity of the intermediate. The nano-zero-valent iron is recovered through centrifugation, and then soaked in hydrochloric acid to remove the surface passivation layer and restore its activity, enabling the recycling of the nano-zero-valent iron.

[0077] In step S5, the dosage of ethanol is 0.2-0.5 g / L, which is added to the wastewater in three equal amounts, with an interval of 2-3 hours each time; the dosage of humic acid is 40-60 mg / L, which is added to the wastewater in the form of dry powder; the redox potential is controlled to be -300 mV to -200 mV and the pH is controlled to be 7.0-7.5.

[0078] The initial addition of ethanol activates Clostridium butyricum, followed by two additional additions at 2-3 hour intervals to maintain its metabolic activity. Clostridium butyricum secretes phenol hydroxylase, catalyzing the degradation of phenol to acetic acid. Residual bicarbonate from Thiobacillus serves as a supplemental carbon source, promoting acetic acid production. Humic acid, with its high molecular weight structure, contains numerous functional groups (carboxyl and hydroxyl groups), which form complexes or physically adsorb with phenol degradation intermediates (catechol and hydroquinone) and cyanide (cyanide ion), reducing their free concentration and minimizing their toxicity to microorganisms.

[0079] Example 1:

[0080] In this example, the wastewater sample was a coal gasification process wastewater from a coal chemical plant. The pollutant concentrations included 1400 mg / L thiocyanate, 1000 mg / L phenols, and 80 mg / L cyanide. The pH of the wastewater sample was 10.5, and the initial redox potential of the wastewater was -60 mV. The wastewater sample was treated as follows.

[0081] S1: Add 0.5 g / L ferrous sulfate and 10 mg / L polyacrylamide to the wastewater, adjust the pH to 6.8, stir at 200 rpm for 30 min, let it stand for 40 min, remove the precipitated flocs, and detect that the redox potential is stable at -65 mV.

[0082] S2: Thiobacillus denitrificans and Clostridium butyricum were mixed in a 60%:40% volume ratio. Thiobacillus denitrificans was pre-activated in Postgate C medium containing 500 mg / L thiocyanate for 3 hours, and Clostridium butyricum was pre-activated in RCM medium containing 200 mg / L phenol for 3 hours. A polyurethane foam carrier with a pore size of 150 μm and a specific surface area of ​​1000 m² / m³ was soaked in 0.1 mol / L sodium hydroxide solution for 1 hour, rinsed to neutrality, and then mixed with the mixed bacterial solution at a mass ratio of 1:20. The mixture was placed in a 50 rpm shaker at 30°C for 2 hours of adsorption. The carrier loaded with the bacterial community was added to the S1 wastewater at a mass-to-volume ratio of 1:20, stirred at a low speed of 30 rpm for 30 minutes, and allowed to stand for 1 hour to form a stratified biofilm.

[0083] S3: Sodium formate was added to the wastewater in S2 twice, with the first addition of 0.35 g / L (70% of the total amount of 0.5 g / L), and an additional 0.15 g / L was added after an interval of 4 hours. The redox potential was controlled at -120 mV, the dissolved oxygen concentration at 0.2 mg / L, and the pH at 7.0 through micro-aeration with nitrogen and oxygen mixture (oxygen content 2%). The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0084] S4: Add 0.1 g / L of 50 nm nano-zero-valent iron to the wastewater in S3. Stir at 300 rpm for 30 minutes, then centrifuge at 3000 rpm for 10 minutes to separate the solids. Regenerate the separated nano-zero-valent iron by shaking with 0.8 mol / L hydrochloric acid for 30 minutes, rinse with clean water until neutral, and then recycle.

[0085] S5: Adjust the pH of the wastewater to 7.2, add ethanol three times (0.1 g / L each time, with an interval of 2 hours) and 50 mg / L of humic acid, introduce nitrogen to control the redox potential to -250 mV and the dissolved oxygen concentration to <0.05 mg / L, and continue the reaction for 18 hours.

[0086] Example 2:

[0087] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0088] S3: Sodium formate was added to the wastewater in S2 twice, with an initial addition of 0.48 g / L and an additional addition of 0.12 g / L after 4 hours. The redox potential was controlled at -150 mV, the dissolved oxygen concentration at 0.1 mg / L, and the pH at 7.0 through micro-aeration with a nitrogen-oxygen mixture (oxygen content 1%). The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0089] Example 3:

[0090] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0091] S3: Sodium formate was added to the wastewater in S2 twice, with an initial addition of 0.28 g / L and an additional addition of 0.12 g / L after an interval of 4 hours. The solution was aerated with a nitrogen-oxygen mixture (oxygen content 3%) to control the redox potential to -100 mV, the dissolved oxygen concentration to 0.3 mg / L, and the pH to 7.0. The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0092] Example 4:

[0093] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0094] S5: Adjust the pH of the wastewater to 7.2, add ethanol (0.13 g / L each time, with an interval of 2 hours) and 50 mg / L of humic acid three times, introduce nitrogen to control the redox potential to -300 mV and the dissolved oxygen concentration to <0.03 mg / L, and continue the reaction for 18 hours.

[0095] Example 5:

[0096] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0097] S5: Adjust the pH of the wastewater to 7.2, add ethanol (0.067 g / L each time, with an interval of 2 hours) and humic acid 50 mg / L three times, introduce nitrogen to control the redox potential to -200 mV and the dissolved oxygen concentration to <0.05 mg / L, and continue the reaction for 18 hours.

[0098] Example 6:

[0099] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0100] S2: Thiobacillus denitrificans and Clostridium butyricum were mixed in a 50%:50% volume ratio. Thiobacillus denitrificans was pre-activated in Postgate C medium containing 500 mg / L thiocyanate for 3 hours, and Clostridium butyricum was pre-activated in RCM medium containing 200 mg / L phenol for 3 hours. A polyurethane foam carrier with a pore size of 150 μm and a specific surface area of ​​1000 m² / m³ was soaked in 0.1 mol / L sodium hydroxide solution for 1 hour, rinsed to neutrality, and then mixed with the mixed bacterial solution at a mass ratio of 1:20. The mixture was placed in a shaker at 50 rpm and adsorbed at 30°C for 2 hours. The carrier loaded with the bacterial community was added to the S1 wastewater at a mass-to-volume ratio of 1:20, stirred at a low speed of 30 rpm for 30 minutes, and allowed to stand for 1 hour to form a stratified biofilm.

[0101] S3: Sodium formate was added to the wastewater in S2 twice, with an initial addition of 0.3 g / L and an additional addition of 0.2 g / L after 4 hours. The redox potential was controlled at -120 mV, the dissolved oxygen concentration at 0.2 mg / L, and the pH at 7.0 through micro-aeration with a nitrogen-oxygen mixture (oxygen content 2%). The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0102] Example 7:

[0103] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0104] S2: Thiobacillus denitrificans and Clostridium butyricum were mixed in a 70%:30% volume ratio. Thiobacillus denitrificans was pre-activated in Postgate C medium containing 500 mg / L thiocyanate for 3 hours, and Clostridium butyricum was pre-activated in RCM medium containing 200 mg / L phenol for 3 hours. A polyurethane foam carrier with a pore size of 150 μm and a specific surface area of ​​1000 m² / m³ was soaked in 0.1 mol / L sodium hydroxide solution for 1 hour, rinsed to neutrality, and then mixed with the mixed bacterial solution at a mass ratio of 1:20. The mixture was placed in a 50 rpm shaker at 30°C for 2 hours of adsorption. The carrier loaded with the bacterial community was added to the S1 wastewater at a mass-to-volume ratio of 1:20, stirred at a low speed of 30 rpm for 30 minutes, and allowed to stand for 1 hour to form a stratified biofilm.

[0105] S3: Sodium formate was added to the wastewater in S2 twice, with an initial addition of 0.44 g / L and an additional addition of 0.11 g / L after an interval of 4 hours. The redox potential was controlled at -120 mV, the dissolved oxygen concentration at 0.15 mg / L, and the pH at 7.0 through micro-aeration with a nitrogen-oxygen mixture (oxygen content 1.5%). The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0106] Example 8:

[0107] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0108] S2: Thiobacillus denitrificans and Clostridium butyricum were mixed in a 50%:50% volume ratio. Thiobacillus denitrificans was pre-activated in Postgate C medium containing 500 mg / L thiocyanate for 3 hours, and Clostridium butyricum was pre-activated in RCM medium containing 200 mg / L phenol for 3 hours. A polyurethane foam carrier with a pore size of 150 μm and a specific surface area of ​​1000 m² / m³ was soaked in 0.1 mol / L sodium hydroxide solution for 1 hour, rinsed to neutrality, and then mixed with the mixed bacterial solution at a mass ratio of 1:20. The mixture was placed in a 50 rpm shaker at 30°C for 2.5 hours of adsorption. The carrier loaded with the bacterial community was added to the S1 wastewater at a mass-to-volume ratio of 1:20, stirred at a low speed of 30 rpm for 30 minutes, and allowed to stand for 1 hour to form a stratified biofilm.

[0109] S3: Sodium formate was added to the wastewater in S2 twice, with an initial addition of 0.52 g / L and an additional addition of 0.13 g / L after an interval of 4 hours. The redox potential was controlled at -150 mV, the dissolved oxygen concentration at 0.08 mg / L, and the pH at 7.0 through micro-aeration with a nitrogen-oxygen mixture (oxygen content 0.8%). The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0110] S5: Adjust the pH of the wastewater to 7.2, add ethanol (0.13 g / L each time, 2 hours apart) and humic acid 50 mg / L three times, introduce nitrogen to control the redox potential to -300 mV and the dissolved oxygen concentration to <0.02 mg / L, and continue the reaction for 18 hours.

[0111] Example 9:

[0112] This embodiment is similar to embodiment 1, but is different from embodiment 1 in that:

[0113] S2: Thiobacillus denitrificans and Clostridium butyricum were mixed in a 70%:30% volume ratio. Thiobacillus denitrificans was pre-activated in Postgate C medium containing 500 mg / L thiocyanate for 3 hours, and Clostridium butyricum was pre-activated in RCM medium containing 200 mg / L phenol for 3 hours. A polyurethane foam carrier with a pore size of 150 μm and a specific surface area of ​​1000 m² / m³ was soaked in 0.1 mol / L sodium hydroxide solution for 1 hour, rinsed to neutrality, and then mixed with the mixed bacterial solution at a mass ratio of 1:20. The mixture was placed in a 50 rpm shaker at 30°C for 2 hours of adsorption. The carrier loaded with the bacterial community was added to the S1 wastewater at a mass-to-volume ratio of 1:20, stirred at a low speed of 30 rpm for 30 minutes, and allowed to stand for 1 hour to form a stratified biofilm.

[0114] S3: Sodium formate was added to the wastewater in S2 twice, with an initial addition of 0.28 g / L and an additional addition of 0.12 g / L after an interval of 4 hours. The solution was aerated with a nitrogen-oxygen mixture (oxygen content: 3.2%) to control the redox potential at -100 mV, the dissolved oxygen concentration at 0.3 mg / L, and the pH at 7.0. The reaction was continued for 10 hours until the thiocyanate concentration dropped below 95 mg / L.

[0115] S5: Adjust the pH of the wastewater to 7.2, add ethanol (0.067 g / L each time, with an interval of 2 hours) and humic acid 50 mg / L three times, introduce nitrogen to control the redox potential to -200 mV and the dissolved oxygen concentration to <0.05 mg / L, and continue the reaction for 18 hours.

[0116] Experimental Example 1:

[0117] The anaerobic detoxification comparison table corresponding to Examples 1-9 is shown in the following table:

[0118] Table 1 Comparison table of wastewater samples and anaerobic detoxification

[0119]

[0120] The wastewater treated in Examples 1-9 was measured for thiocyanate degradation rate with reference to GB / T 23852-2009 (Analysis of Industrial Thiocyanate); phenol degradation rate with reference to HJ503-2009 (Determination of Volatile Phenols - 4-Aminoantipyrine Spectrophotometric Method); cyanide residual rate with reference to HJ 484-2009 (Determination of Cyanide - Volumetric and Spectrophotometric Method); and catechol concentration with reference to GB / T 23960-2009 (Catechol for Industrial Use). The results are shown in the following table:

[0121] Table 2 Experimental results

[0122]

[0123] Experimental data show that the thiocyanate removal rate, phenol degradation rate, cyanide residual rate and catechol concentration are all significantly correlated with the staged redox potential control and bacterial community ratio. When the redox potential of step S3 is controlled in the microaerobic range of -120mV to -150mV, the redox potential of step S5 is controlled in the strictly anaerobic range of -250mV to -300mV, and the bacterial community ratio is 60% denitrifying thiobacillus and 40% butyric acid clostridium, the pollutant degradation effect is optimal. Example 1 uses S3 redox potential of -120mV, S5 redox potential of -250mV and a bacterial community ratio of 60:40, the thiocyanate removal rate reaches 92.1%, the phenol degradation rate is 89.3%, the cyanide residual rate is 18.7%, and the catechol concentration is only 0.12mg / L. In contrast, in Example 9, when S3 had an ORP of -100 mV, S5 had an ORP of -200 mV, and a bacterial composition ratio of 70:30, the thiocyanate removal rate was 81.2%, the phenol degradation rate was 75.4%, the cyanide residual rate was 28.7%, and the catechol concentration reached a high of 1.89 mg / L. This data demonstrates that the ORP must be strictly below -100 mV during the microaerobic phase to activate thiocyanate-degrading bacteria, while it must be below -250 mV during the strictly anaerobic phase to activate phenol-hydrolyzing bacteria. Furthermore, the bacterial composition ratio must balance the metabolic rates of the two bacterial compositions.

[0124] In Example 1, the S3 redox potential was -120 mV, the S5 redox potential was -250 mV, the bacterial community consisted of 60% denitrifying Thiobacillus and 40% butyric Clostridium, and a thiocyanate removal rate of 92.1%, a phenol degradation rate of 89.3%, a cyanide residual rate of 18.7%, and a catechol concentration of 0.12 mg / L was achieved, with the best overall performance.

[0125] During the microaerobic stage (S3), a redox potential of -120 mV activates the thiosulfate reductase of Thiobacillus denitrificans, degrading thiocyanate into sulfide and bicarbonate. Simultaneously, Clostridium butyricum remains dormant due to its microaerobic sensitivity, preventing competition between the two bacterial communities for the electron donor, sodium formate. Sulfide ions combine with residual ferrous ions from pretreatment to form ferrous sulfide, blocking the cyanide residues caused by sulfur regeneration and reducing the cyanide residue rate to 18.7%. During the strictly anaerobic stage (S5), a redox potential of -250 mV completely inhibits the activity of sulfur-reducing bacteria and activates the phenol hydroxylase of Clostridium butyricum, which uses ethanol and bicarbonate generated in the previous stage to degrade phenols into acetic acid, achieving a phenol degradation rate of 89.3%.

[0126] Bicarbonate produced by Thiobacillus denitrificans provides a supplementary carbon source for Clostridium butyricum, reducing ethanol consumption. Simultaneously, nano-zero-valent iron selectively adsorbs catechol during the S4 stage and reduces it to low-toxic cyclohexanol, resulting in a catechol concentration of only 0.12 mg / L. The active sites on the nano-zero-valent iron surface further bind to cyanide to form a Prussian blue precipitate, blocking cyanide toxicity. Strict anaerobic conditions inhibit the oxidation of catechol to quinones, forming a closed-loop metabolic chain.

[0127] In addition, although the use of S5 with an oxidation-reduction potential of -300 mV in Example 4 further reduced the cyanide residual rate to 15.8%, the phenol degradation rate of 86.7% was still lower than that of Example 1 due to the unadjusted bacterial composition. In Example 6, the use of 50% denitrifying Thiobacillus bacteria resulted in premature consumption of sodium formate, and the phenol degradation rate was only 88.1%.

[0128] In Example 9, the S3 redox potential was -100 mV, the S5 redox potential was -200 mV, the bacterial community consisted of 70% denitrifying Thiobacillus and 30% butyric Clostridium, and a thiocyanate removal rate of 81.2%, a phenol degradation rate of 75.4%, a cyanide residual rate of 28.7%, and a catechol concentration of 1.89 mg / L was achieved, which had the worst overall performance.

[0129] In the S3 stage, the redox potential (REDX) of -100 mV approaches the aerobic threshold, inhibiting the activity of denitrifying Thiobacillus enzymes. This results in incomplete thiocyanate degradation, and the residual thiocyanate condenses with phenolic intermediates to form thiophenols, which are 3-5 times more toxic than the original pollutants. In the S5 stage, the redox potential (REDX) of -200 mV fails to completely inhibit the activity of sulfur-reducing bacteria. Regenerated sulfur ions combine with cyanide to form iron sulfide and ferrocyanide precipitates, consuming the active sites of the nano-zero-valent iron and resulting in a cyanide residual rate as high as 28.7%.

[0130] A 70% prevalence of Thiobacillus denitrificans resulted in excessive consumption of sodium formate during the S3 stage. In the S5 stage, Clostridium butyricum was unable to effectively degrade phenols due to insufficient electron donors, leading to catechol accumulation to 1.89 mg / L. Microaerobic infiltration into the S5 stage partially oxidized catechol to quinones, which, along with thiophenols, inhibited the ATP synthase activity of Clostridium butyricum, further weakening its metabolic capacity. Simultaneously, iron sulfide precipitation coated the surface of the zero-valent iron nanoparticles, depriving them of their cyanide adsorption capacity, creating a vicious cycle of toxicity accumulation and bacterial suppression.

[0131] In summary, redox potential control and bacterial composition achieved full-chain degradation of thiocyanate, phenols, cyanide, and catechol through metabolic pathway decoupling and product interaction. A redox potential threshold of -120 mV in the microaerobic phase activated denitrifying Thiobacillus and blocked sulfur cycle side reactions. A redox potential threshold of -250 mV in the strictly anaerobic phase activated Clostridium butyricum and inhibited the formation of toxic intermediates. A 60% denitrifying Thiobacillus and 40% butyric Clostridium balance balanced metabolic resource allocation.

[0132] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A method for anaerobic detoxification of coal chemical wastewater, characterized in that: The following steps are involved: S1. Pre-treat wastewater; S2, inoculating the wastewater in S1 with a mixed bacterial community including thiocyanate-degrading bacteria and phenol-hydrolyzing bacteria; S3, adding sodium formate to the wastewater in S2, controlling the redox potential of the wastewater to -150mV to -100mV and the dissolved oxygen concentration to 0.08-0.3mg / L, for 8-12h; S4, adding nano zero-valent iron to the wastewater in S3, stirring and reacting for 20-40 minutes and then standing and separating; S5. Adjust the S4 wastewater to a weak alkaline state, add ethanol and humic acid to the wastewater, control the redox potential to -300mV to -200mV, and the dissolved oxygen concentration to below 0.05mg / L, for 12-24h; In step S2, the thiocyanate-degrading bacteria include at least one of denitrifying Thiobacillus, thiooxidans, and excreting Thiobacillus; the phenol-hydrolyzing bacteria include at least one of Clostridium butyricum and Clostridium perfringens; and in the mixed bacterial community, the thiocyanate-degrading bacteria account for 50%-70% by volume, and the phenol-hydrolyzing bacteria account for 30%-50% by volume. In step S2, the method of inoculating the mixed bacterial flora includes: S21, activating the thiocyanate-degrading bacteria and the phenol-hydrolyzing bacteria in culture medium respectively, and mixing the activated thiocyanate-degrading bacteria and the phenol-hydrolyzing bacteria to obtain a mixed bacterial solution; S22, soaking the polyurethane foam carrier in a sodium hydroxide solution and rinsing until it becomes neutral; S23, mixing the mixed bacterial solution with the polyurethane foam carrier, and placing the mixture in a shaking table for adsorption; S24. Mix the polyurethane foam carrier with attached bacteria with wastewater, stir at low speed to ensure full contact between bacteria and wastewater; let it stand and settle to form a layered biofilm.

2. The method according to claim 1, characterized in that In step S1, the pretreatment includes detecting the initial redox potential of the wastewater, controlling the redox potential of the wastewater to -80mV to -50mV, adding ferrous sulfate and polyacrylamide to the wastewater, adjusting the pH of the wastewater to neutral, stirring for 20-50min, and standing for 30-50min; wherein the addition amount of ferrous sulfate is 0.3-0.8g / L, and the addition amount of polyacrylamide is 5-15mg / L.

3. The method according to claim 2, characterized in that In step S1, the method for controlling the redox potential of wastewater includes: If the initial redox potential is greater than -50mV, add 0.8-1.2g / L ferrous sulfate, stir for 15-30min, let it settle for 30-40min, filter and adjust the pH to 6.6-7.0; If the initial redox potential is less than -80mV, add 3%-5% concentration hydrogen peroxide solution, control the dissolved oxygen to 0.3-0.5mg / L for aeration, and simultaneously introduce nitrogen purge at a rate of 0.3-0.5L / min for 15-30min until the redox potential stabilizes to above -80mV.

4. The method according to claim 1, wherein In step S3, the total amount of sodium formate added is 0.3-0.8 g / L, which is added in two times, with the first addition amount being 60%-80% of the total amount added, and the remaining amount is added at an interval of 4-6 hours.

5. The method according to claim 1, wherein In step S4, the particle size of the nano-zero-valent iron is 30-80 nm, and the dosage is 0.05-0.2 g / L; after stirring the reaction, the nano-zero-valent iron is separated by centrifugation or filtration.

6. The method according to claim 5, characterized in that The separated nano-zero-valent iron is regenerated by acid washing. The specific steps are: immersing the nano-zero-valent iron in a 0.5-1.0 mol / L hydrochloric acid solution, shaking for 20-40 minutes, and rinsing with clean water until neutral.

7. The method according to claim 1, characterized in that In step S5, the dosage of ethanol is 0.2-0.5 g / L, which is added to the wastewater in three equal amounts, with an interval of 2-3 hours each time; the dosage of humic acid is 40-60 mg / L, which is added to the wastewater in the form of dry powder.

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