Polyformaldehyde wastewater treatment method and application

Abstract

The invention discloses a polyformaldehyde wastewater treatment method and application, and belongs to the technical field of wastewater treatment. The method comprises the following steps: firstly, in an anaerobic environment, adding hexadecyl trimethyl ammonium bromide and ethanol into wastewater to form micelles to wrap trioxymethylene, and degrading formaldehyde and macromolecular organic matters by using anaerobic flora; secondly, introducing anaerobic effluent into a facultative environment, triggering micelles to disintegrate and release trioxymethylene in stages by continuously and linearly reducing pH, and meanwhile, adding domestication flora in stages according to pH change so as to dynamically degrade released formaldehyde; and finally, thorough mineralization is realized through two-stage biological oxidation in an aerobic environment. According to the invention, random depolymerization of trioxymethylene is blocked by space wrapping, and the release rate is controlled by time sequence acidification, so that formaldehyde generation and biodegradation are dynamically balanced, inhibition of toxicity peak on microorganisms is effectively avoided, and the removal efficiency of formaldehyde and organic pollutants and the operation stability of the system are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for treating polyoxymethylene wastewater and its application. Background Art

[0002] As an important chemical raw material, the wastewater generated in the production process of polyoxymethylene contains highly toxic pollutants such as formaldehyde and trioxymethylene. If directly discharged without effective treatment, it will pose a serious threat to the ecological environment and human health. Therefore, the efficient treatment of polyoxymethylene wastewater is an important topic in the field of chemical environmental protection.

[0003] Currently, the full biochemical treatment of polyoxymethylene wastewater mainly adopts a combined process route of anaerobic, facultative anaerobic, and aerobic, and degrades pollutants through microbial metabolism. However, this technology faces significant challenges: due to the toxicity of formaldehyde in polyoxymethylene wastewater, it is easy to inhibit the microbial activity, and trioxymethylene is easily depolymerized rapidly to generate formaldehyde in the traditional treatment process, resulting in a peak value of formaldehyde concentration in the reaction system, which not only inhibits the microbial activity but also breaks the balance between formaldehyde generation and degradation, causing problems such as low chemical oxygen demand removal rate and unstable effluent quality, and it is difficult to meet the strict discharge standards.

[0004] In view of the above technical bottlenecks, the present invention proposes a new method for the full biochemical treatment of polyoxymethylene wastewater. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a method for treating polyoxymethylene wastewater and its application. A method for treating polyoxymethylene wastewater is provided, which delays the depolymerization process through a wrapping system of cetyltrimethylammonium bromide and ethanol, and combines pH gradient acidification to control the release rate, so as to achieve the dynamic balance between formaldehyde generation and microbial degradation, and effectively improve the treatment efficiency and effluent quality.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for treating polyoxymethylene wastewater, comprising the following steps: Step 1: In an anaerobic environment, use anaerobic flora to degrade formaldehyde and macromolecular organic matter in polyoxymethylene wastewater, and simultaneously add a cationic surfactant and an alcohol auxiliary agent to form micelles to wrap trioxymethylene; Step 2: Continuously linearly acidify the effluent from Step 1, control the pH to decrease uniformly, trigger the staged disintegration of trioxymethylene to release trioxymethylene, and simultaneously add domesticated flora to degrade trioxymethylene under facultative anaerobic conditions; Step 3: Perform two-stage biological treatment on the effluent from Step 2 under aerobic conditions.

[0007] Furthermore, in Step 1, the cationic surfactant is cetyltrimethylammonium bromide, and the alcohol auxiliary agent is ethanol.

[0008] Further, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.0:1 to 1.4:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.3:1 to 0.5:1.

[0009] Further, the anaerobic flora in Step 1 includes Methanobacterium formicicum and Clostridium butyricum.

[0010] Further, in Step 2, the acidification rate is 0.10 - 0.20 pH units / hour, and the end-point pH is 4.1 - 4.3.

[0011] Further, the domesticated flora in Step 2 includes Acetobacter pasteurianus, Pseudomonas putida, and Achromobacter marplatensis.

[0012] Further, the domesticated flora is domesticated by a formaldehyde-containing medium gradient and prepared into a slow-release microbial agent by the microencapsulation method.

[0013] Further, after Step 2, an anionic surfactant is added to form a complex precipitate and solid-liquid separation is carried out.

[0014] Further, the two-stage biological treatment in Step 3 includes: In the primary treatment, the dissolved oxygen is controlled at 2.8 - 3.2 mg / L, and Pseudomonas oxydans is added. In the secondary treatment, the dissolved oxygen is controlled at 1.4 - 1.6 mg / L, and nitrification and denitrification are carried out for nitrogen removal.

[0015] Another technical solution provided by the present invention: an application of the above method in the treatment of polyoxymethylene wastewater, wherein the formaldehyde concentration in the polyoxymethylene wastewater is 250 mg / L, the paraformaldehyde concentration is 200 mg / L, and the COD concentration is 3500 mg / L.

[0016] The present invention solves the defects existing in the background technology, and the present invention has the following beneficial effects: A method for treating polyoxymethylene wastewater provided by the present invention constructs a micelle to wrap paraformaldehyde by a cationic surfactant and an alcohol assistant to block its spontaneous depolymerization, and adopts continuous linear acidification to control the micelle disintegration rate to trigger the staged release of paraformaldehyde, and synchronously matches the sequential degradation ability of the domesticated flora, realizing the dynamic balance between formaldehyde generation and biodegradation, thereby controlling the paraformaldehyde conversion process at the source, avoiding the inhibition of the toxicity peak of formaldehyde on microorganisms, and significantly improving the pollutant degradation efficiency and system stability.

[0017] In the first aspect, by adding cationic surfactant hexadecyltrimethylammonium bromide and alcohol auxiliary ethanol to the wastewater, the hydrophobic alkyl chain of hexadecyltrimethylammonium bromide is combined with the van der Waals force of the hydrophobic core of trioxymethylene, and the trioxymethylene is self-assembled to form dense spherical micelles under the action of ethanol to reduce the interfacial tension, and the trioxymethylene is wrapped in the hydrophobic cavity to form a physical barrier. The contact between trioxymethylene and water molecules is blocked by steric hindrance, and the acid-catalyzed ring-opening reaction is directly inhibited, avoiding the random release of free formaldehyde in the anaerobic stage to cause instantaneous concentration shock; compared with the prior art where the unencapsulated trioxymethylene directly depolymerizes to produce high-concentration formaldehyde, the present invention isolates toxic substances from the source, and further establishes a stable material basis for subsequent acidification and controlled release.

[0018] Secondly, continuous linear acidification is achieved by uniformly adding acid at a rate of 0.10-0.20 pH units / hour, and the characteristics of hydrogen ions gradually protonating the quaternary ammonium groups of hexadecyltrimethylammonium bromide are used to dynamically change the surface charge density and hydrophobicity of the micelles, triggering the diffusion and release of the encapsulated triformaldehyde in stages according to the pH gradient. By controlling the protonation process to regulate the disintegration of the micelles, the time matching of the triformaldehyde release rate and the metabolic activity of the domesticated bacterial community is directly achieved; compared with the instantaneous high-concentration formaldehyde release caused by direct acidification in the prior art, the present invention keeps the free formaldehyde generation within the degradation threshold of the bacterial community, further ensuring the efficient and continuous biochemical reaction in the anaerobic stage.

[0019] In particular, the spatial dimension of encapsulation control blocks the initial depolymerization of triformaldehyde through micelle physical encapsulation, providing a stable precursor for acidification controlled release; the linear acidification in the time dimension regulates the phased disintegration of micelles through the protonation gradient, converting the encapsulated triformaldehyde into a time-controlled free formaldehyde release source. The encapsulation characteristics ensure that triformaldehyde can only be released according to the set path during the acidification stage, while the acidification rate characteristics match the release flux to the activity window of Acetobacter pasteurianus and Pseudomonas putida, ultimately achieving a dynamic balance between the formaldehyde generation rate and the bacterial degradation rate, and realizing the fully controllable mineralization of toxic substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. Figure 1 The present invention is a flow chart of a method for treating polyoxymethylene wastewater. DETAILED DESCRIPTION

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0022] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below. Unless otherwise specified in the following embodiments, all raw materials are obtained through commercial purchase or prepared by conventional methods in the art. Among them, Methanobacterium formicicum (DSM 3637), Clostridium butyricum (DSMZ 10702), Achromobacter madrynensis (CGMCC 1.1843), Pseudomonas putida (ATCC 49128), Acetobacter pasteurianus (CGMCC 1.41), Acidovorax facilis (ATCC 11228), and Paracoccus denitrificans (ATCC 17741) were all purchased from Huizao Biology; cetyltrimethylammonium bromide (analytical pure), ethanol (analytical pure), and betaine (purity 98%) were all purchased from Sinopharm Reagents.

[0023] Exemplary method: As Figure 1 shown, a full biochemical polyformaldehyde wastewater treatment method includes the following steps: Step 1: In an anaerobic environment, use anaerobic bacteria to degrade formaldehyde and macromolecular organic matter in polyformaldehyde wastewater, and at the same time add a cationic surfactant and an alcohol auxiliary to form micelles to wrap trimethylolpropane formal; Step 2: Continuously linearly acidify the effluent from Step 1, control the pH to decrease uniformly, trigger the staged disintegration of trimethylolpropane formal to release trimethylolpropane formal, and simultaneously add domesticated bacteria to degrade trimethylolpropane formal under anoxic conditions; Step 3: Perform two-stage biological treatment on the effluent from Step 2 under aerobic conditions.

[0024] Next, each step will be introduced in detail.

[0025] In Step 1, in an anaerobic environment, anaerobic bacteria are used to biologically convert formaldehyde into low-toxic formic acid, and at the same time, macromolecular organic matter is degraded to improve biodegradability; at the same time, micelles are formed by cetyltrimethylammonium bromide and ethanol to wrap trimethylolpropane formal, forming encapsulated trimethylolpropane formal and free trimethylolpropane formal, blocking its depolymerization path, as follows.

[0026] In the first aspect, polyoxymethylene wastewater is injected into an anaerobic reactor, and the pH is adjusted to the range of 6.8 - 7.2 using a sodium hydroxide solution with a mass concentration of 10%. The temperature is maintained at 35 ± 0.5 °C through a steam coil, nitrogen is continuously introduced to stabilize the redox potential in the range of -320 to -280 mV, and the hydraulic retention time is set to 48 - 60 hours.

[0027] The anaerobic flora includes Methanobacterium formicicum and Clostridium butyricum. Methanobacterium formicicum expresses formaldehyde dismutase to capture four molecules of formaldehyde and one molecule of water, and through aldehyde group transfer and proton exchange reactions, one molecule of acetic acid and two molecules of formic acid are generated; this process consumes reduced coenzyme F420 and achieves electron balance at a redox potential of -300 mV. Clostridium butyricum secretes dextranase to hydrolyze the β-1,4 glycosidic bond of polysaccharides, generating glucose monomers and dimers; the metalloprotease it secretes cleaves protein peptide bonds, and the product is oligopeptides with a molecular weight less than 500 Da. The breakage of large molecular carbon chains reduces the proportion of refractory COD and increases the B / C ratio.

[0028] Specifically, Methanobacterium formicicum uses a modified BCM medium: potassium dihydrogen phosphate 0.35 g / L, ammonium chloride 0.5 g / L, magnesium sulfate 0.1 g / L, calcium chloride 0.02 g / L, sodium bicarbonate 4 g / L, cysteine hydrochloride 0.5 g / L, yeast extract 2 g / L, sodium acetate 1 g / L, formaldehyde 100 mg / L (the only carbon source), pH 7.0; Clostridium butyricum uses an RCM medium: beef extract 3 g / L, peptone 10 g / L, glucose 5 g / L, soluble starch 1 g / L, sodium chloride 5 g / L, sodium acetate 3 g / L, cysteine hydrochloride 0.5 g / L. Both Methanobacterium formicicum and Clostridium butyricum are cultured in a 37 °C anaerobic workstation (nitrogen: hydrogen: carbon dioxide = 85:10:5) for 72 hours until the late logarithmic phase.

[0029] Specifically, the culture solutions of Methanobacterium formicicum and Clostridium butyricum are centrifuged at 8000 rpm for 10 minutes under nitrogen protection. After discarding the supernatant, they are resuspended with anaerobic saline to 1 / 10 of the original volume; they are mixed in a ratio of 12 mg / mL of the dry weight of Methanobacterium formicicum to 4 mg / mL of the dry weight of Clostridium butyricum to form a bacterial suspension; and it is injected into the bottom of the anaerobic reactor by positive pressure through a closed pipeline, and the inoculation amount is 12% of the effective volume of the anaerobic reactor.

[0030] In the second aspect, cetyltrimethylammonium bromide is dissolved in an ethanol aqueous solution and injected into the polyoxymethylene wastewater under the condition of a stirring rate of 200 rpm. The molar ratio of cetyltrimethylammonium bromide to trioxymethylene is 1.0:1 to 1.4:1; the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.3:1 to 0.5:1.

[0031] The hydrophobic alkyl chains of cetyltrimethylammonium bromide are oriented to form spherical micelles under the action of ethanol. Trioxymethylene is encapsulated in the micelle core due to its hydrophobicity, and its cyclic structure is spatially blocked by the cetyl chains, preventing it from contacting water molecules and undergoing acid-catalyzed ring-opening reaction. Ethanol enhances the structural stability of the micelles by reducing the interfacial tension of the micelles.

[0032] In Step 2, the pH of the wastewater is decreased by continuous linear acidification. The change in pH triggers the staged disintegration of the encapsulated trioxymethylene to release trioxymethylene, controlling the release rate of trioxymethylene. At the same time, a domesticated microbial community is added. During the pH decrease, the generated formaldehyde is dynamically degraded, achieving a dynamic balance between formaldehyde generation and biodegradation and avoiding the toxicity peak.

[0033] After adjusting the anaerobic effluent to neutral, it is introduced into an anoxic reactor. A 0.5 M sulfuric acid solution is added to the anoxic reactor at a rate of 0.10 - 0.20 pH units per hour, causing the pH of the system to decrease uniformly to the end point of 4.2 ± 0.1 and lasting for 24 - 36 h. The temperature is maintained at 30 ± 1 °C, the redox potential is -100 to +50 mV, and the dissolved oxygen is 0.5 - 0.8 mg / L. Optionally, an online pH meter is used to collect data every 2 minutes, and the rotation speed of the peristaltic pump is adjusted through a PID algorithm to control the pH fluctuation ≤ ±0.05.

[0034] The degree of protonation of the quaternary ammonium group in the cetyltrimethylammonium bromide molecule increases with the decrease of pH. When pH > 6.0, a high positive charge on the micelle surface forms an electrostatic barrier, inhibiting the release of trioxymethylene. When the pH is in the range of 5.0 - 6.0, protonation causes the exposure of the hydrophobic core of the micelle, and trioxymethylene is released by diffusion. When pH < 5.0, cetyltrimethylammonium bromide is completely converted into cationic monomers, and the micelle structure disintegrates to release the residual trioxymethylene.

[0035] Furthermore, the domesticated microbial community includes Achromobacter marplatensis, Pseudomonas putida, and Acetobacter pasteurianus, and is obtained through domestication and cultivation: Using a basic inorganic salt medium containing 200 mg / L of formaldehyde (0.7 g / L of potassium dihydrogen phosphate, 0.85 g / L of dipotassium hydrogen phosphate, 1.2 g / L of ammonium sulfate), at 30 ± 1 °C and a dissolved oxygen of 0.5 - 1.0 mg / L, the pH is gradually decreased (from an initial 6.0 to the end point of 4.2) in a 24-hour cycle, while the formaldehyde concentration is increased (from 50 to 200 mg / L), and 1 mM of betaine is added to enhance the acid tolerance of the bacteria. After domestication, the bacterial solution is centrifugally concentrated to 10 9 CFU / mL under nitrogen protection, and slow-release microcapsules with a particle size of 150 ± 20 μm are prepared by the calcium alginate-chitosan double embedding method, with poly-β-hydroxybutyrate carbon source loaded inside.

[0036] When the pH drops to 6.0, 3 g / L of Acetobacter pasteurianus microcapsules are added; when the pH drops to 5.0, 4 g / L of Pseudomonas putida microcapsules are added; Achromobacter marplatensis exists throughout the process as a resident flora at a dry weight of 5 g / L. In the pH range of 6.0 - 5.0, Acetobacter pasteurianus oxidizes formaldehyde to formic acid through quinone-dependent formaldehyde dehydrogenase; in the pH range of 5.0 - 4.0, the acid-stable formaldehyde dehydrogenase of Pseudomonas putida mineralizes formaldehyde to carbon monoxide; Achromobacter marplatensis assimilates residual pollutants through the serine cycle, and its high-affinity formaldehyde transporter is activated when the formaldehyde concentration is greater than 80 mg / L, improving the substrate capture efficiency. In addition, the flora maintains the conformational stability of intracellular enzymes under the osmotic protection of betaine and maintains the survival rate under acidic conditions.

[0037] Furthermore, the anionic surfactant sodium dodecyl sulfate is added to form a complex precipitate with the residual cetyltrimethylammonium bromide and is separated by an inclined plate sedimentation tank.

[0038] In Step 3, under aerobic conditions, the complete mineralization of formic acid and residual organic matter is achieved through two-stage biological treatment, and ammonia nitrogen nitrification and total nitrogen deep removal are completed synchronously, as follows.

[0039] The facultative anaerobic effluent is introduced into the first high-load aeration tank of the two-stage aerobic reactor, controlling the dissolved oxygen at 3.0 ± 0.2 mg / L, maintaining the temperature at 30 ± 1 °C, the redox potential at +250 to +350 mV, the hydraulic retention time at 8 - 10 h, filling with suspended biological carriers (specific surface area > 500 m² / m³), and adding 3 - 5 g / L of Pseudomonas acidovorans; the effluent from the first high-load aeration tank is introduced into the second low-load nitrification tank, controlling the dissolved oxygen at 1.5 ± 0.1 mg / L, maintaining the temperature at 30 ± 1 °C, the redox potential at +100 to +150 mV, the hydraulic retention time at 10 - 16 h, with an immobilized nitrifying bacteria membrane module inside and a filling rate of not less than 40%.

[0040] Under sterile conditions, the Pseudomonas acidovorans strain is inoculated into a selective medium containing sodium formate (the sole carbon source) (the formula includes 0.8 g / L of dipotassium hydrogen phosphate, 0.6 g / L of potassium dihydrogen phosphate, 1.0 g / L of ammonium sulfate, 0.2 g / L of magnesium sulfate, 0.05 g / L of calcium chloride, 3.0 g / L of sodium formate, pH 7.0), and cultured in a shaker at 30 °C and 180 rpm for 48 hours until the late logarithmic phase. After the culture is completed, the culture solution is centrifuged at 8000 rpm for 10 min, the supernatant is discarded, and the cells are resuspended and concentrated to 1 / 10 of the original volume with sterile physiological saline and directly added to the first high-load aeration tank, controlling the final concentration at 3 - 5 g / L (calculated as dry cell weight).

[0041] The nitrifying bacteria group uses nitrifying sludge from a municipal sewage treatment plant as the bacterial source. In an SBR reactor, an inorganic autotrophic medium (formula includes 0.5 g / L ammonium chloride, 1.0 g / L sodium bicarbonate, 0.3 g / L potassium dihydrogen phosphate, 0.1 g / L magnesium sulfate, 0.02 g / L calcium chloride, pH 7.8) is used to gradually increase the ammonia nitrogen load (from an initial 0.2 to a final 0.8 kgN / m 3 ·d), control the dissolved oxygen concentration at 2.0 - 3.0 mg / L, 30 °C, and pH 7.5 - 8.0, and domesticate for 21 days until the ammonia nitrogen oxidation rate exceeds 10 mgN / gVSS·h. In an anoxic environment, the denitrifying bacteria strain is inoculated into a denitrifying medium (formula includes 0.8 g / L potassium nitrate, 2.0 g / L sodium acetate, 0.7 g / L dipotassium hydrogen phosphate, 0.1 g / L magnesium sulfate, pH 7.2), nitrogen is passed through for 30 minutes to remove oxygen and then sealed, and statically cultured at 30 °C for 72 hours until the nitrate removal rate is greater than 90%. After the cultivation is completed, the bacterial liquid is centrifuged and concentrated, and mixed according to the dry weight ratio of nitrifying bacteria to denitrifying bacteria of 6:4, and filled into a secondary low-load nitrification tank through an immobilized biofilm module.

[0042] In this step, Pseudomonas acidovorans secretes formate dehydrogenase to oxidize formic acid to carbon dioxide, eliminating the potential toxicity of formic acid accumulation in Step 1. In the nitrification stage, nitrifying bacteria are used to oxidize ammonia nitrogen to nitrite and then oxidize nitrite to nitrate; in the denitrification stage, denitrifying bacteria are used to reduce nitrate to nitrogen.

[0043] Example 1:

[0044] Step 1: Inject polyoxymethylene wastewater with a formaldehyde concentration of 250 mg / L, a paraformaldehyde concentration of 200 mg / L, and a COD concentration of 3500 mg / L into an anaerobic reactor. Add a 10% sodium hydroxide solution by mass concentration to adjust the system pH to 7.0, keep the temperature constantly controlled at 35.0 °C through a steam coil, and continuously pass nitrogen to maintain the oxidation-reduction potential at -300 mV. The hydraulic retention time is fixed at 48 h; simultaneously add a pre-cultured anaerobic bacteria group, where the dry weight concentration of Methanobacterium formicicum is 12.0 mg / mL and the dry weight concentration of Clostridium butyricum is 4.0 mg / mL, and the inoculation volume accounts for 12% of the effective volume of the anaerobic reactor; at the same time, dissolve cetyltrimethylammonium bromide in an ethanol aqueous solution and inject it into the polyoxymethylene wastewater under the condition of a stirring rate of 200 rpm, where the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.0:1 and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.3:1.

[0045] Step 2: Introduce the anaerobic effluent into the facultative reactor, adjust the pH to 7.5, and uniformly add a 0.5 mol / L sulfuric acid solution at a rate of 0.13 pH / hour to linearly reduce the pH of the wastewater to the end point value of 4.2, with a hydraulic retention time of 36 h; when the pH drops to 6.0, add microcapsules of Acetobacter pasteurianus encapsulated with 3.0 g / L calcium alginate, and when the pH drops to 5.0, add microcapsules of Pseudomonas putida at 4.0 g / L, while maintaining Achromobacter marplatensis at 5.0 g / L throughout the process; add sodium dodecyl sulfate with a molar ratio of 1:1.2 to cetyltrimethylammonium bromide at the reaction end point to form a complex precipitate, and perform solid-liquid separation through a lamella sedimentation tank with a surface loading of 1.2 m³ / (m²·h).

[0046] Step 3: Pass the facultative effluent into the first-stage high-load aeration tank, control the dissolved oxygen concentration at 3.0 mg / L and maintain a hydraulic retention time of 8.0 h, add 3.0 g / L Pseudomonas acidovorans and fill the suspended biological carrier with a specific surface area of 550 m 2 / m 3 ; the carrier filling rate is 45%; then pass it into the second-stage low-load nitrification tank, control the dissolved oxygen concentration at 1.5 mg / L and the hydraulic retention time at 12.0 h. In the immobilized nitrifying bacteria membrane module with a filling rate of 50%, nitrifying bacteria and denitrifying bacteria are combined at a dry weight ratio of 6:4 to complete nitrification and denitrification treatment.

[0047] Example 2:

[0048] Differing from Example 1, in Step 2 of this example, a 0.5 mol / L sulfuric acid solution is uniformly added at a rate of 0.15 pH / hour. The rest is the same as Example 1.

[0049] Example 3:

[0050] Differing from Example 1, in Step 2 of this example, a 0.5 mol / L sulfuric acid solution is uniformly added at a rate of 0.20 pH / hour. The rest is the same as Example 1.

[0051] Example 4:

[0052] Differing from Example 1, in Step 1 of this example, the molar ratio of cetyltrimethylammonium bromide to trioxane is 1.2:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.4:1. The rest is the same as Example 1.

[0053] Example 5:

[0054] Different from Example 1, in Step 1 of this example, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.2:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.4:1; in Step 2, a 0.5 mol / L sulfuric acid solution is added at a uniform rate of 0.15 pH / hour. The rest is the same as in Example 1.

[0055] Example 6:

[0056] Different from Example 1, in Step 1 of this example, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.2:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.4:1; in Step 2, a 0.5 mol / L sulfuric acid solution is added at a uniform rate of 0.20 pH / hour. The rest is the same as in Example 1.

[0057] Example 7:

[0058] Different from Example 1, in Step 1 of this example, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.4:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.5:1. The rest is the same as in Example 1.

[0059] Example 8:

[0060] Different from Example 1, in Step 1 of this example, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.4:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.5:1; in Step 2, a 0.5 mol / L sulfuric acid solution is added at a uniform rate of 0.15 pH / hour. The rest is the same as in Example 1.

[0061] Example 9:

[0062] Different from Example 1, in Step 1 of this example, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.4:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.5:1; in Step 2, a 0.5 mol / L sulfuric acid solution is added at a uniform rate of 0.20 pH / hour. The rest is the same as in Example 1.

[0063] Comparative Example 1: Step 1: Inject polyoxymethylene wastewater with a formaldehyde concentration of 250 mg / L, a paraformaldehyde concentration of 200 mg / L, and a COD concentration of 3500 mg / L into the anaerobic reactor. Add a sodium hydroxide solution with a mass concentration of 10% to adjust the pH of the system to 7.0. Constantly control the temperature at 35.0 °C through a steam coil, and continuously introduce nitrogen to maintain the redox potential at -300 mV. The hydraulic retention time is fixed at 48 h. Synchronously add a pre-cultured anaerobic flora, with the dry weight concentration of Methanobacterium formicicum being 12.0 mg / mL and the dry weight concentration of Clostridium butyricum being 4.0 mg / mL. The inoculation volume accounts for 12% of the effective volume of the anaerobic reactor.

[0064] Step 2: Introduce the anaerobic effluent into the facultative anaerobic reactor, adjust the pH to 4.2, and the hydraulic retention time is 36 h. Throughout the process, maintain 3.0 g / L of microcapsules of Acetobacter pasteurianus, Pseudomonas putida, and 5.0 g / L of Achromobacter marplatensis encapsulated in calcium alginate microcapsules.

[0065] Step 3: Pass the facultative anaerobic effluent into the first-stage high-load aeration tank, control the dissolved oxygen concentration at 3.0 mg / L and maintain a hydraulic retention time of 8.0 h. Add 3.0 g / L of Pseudomonas acidovorans and fill the suspended biological carrier with a specific surface area of 550 m 2 / m 3 The carrier filling rate is 45%. Subsequently, pass it into the second-stage low-load nitrification tank, control the dissolved oxygen concentration at 1.5 mg / L and the hydraulic retention time at 12.0 h. In the immobilized nitrifying bacteria membrane module with a filling rate of 50%, nitrifying bacteria and denitrifying bacteria are combined at a dry weight ratio of 6:4 to complete nitrification and denitrification treatment.

[0066] Experimental Example 1: The parameter comparison tables of Examples 1-9 and Comparative Example 1 are shown in the following table: Table 1 Parameter Comparison Table of Examples and Comparative Examples

[0067] Based on Examples 1-9 and Comparative Example 1, the following detections were carried out: 1. Refer to HJ 601-2011 "Water Quality - Determination of Formaldehyde - Acetylacetone Spectrophotometric Method" to determine the instantaneous maximum concentration of formaldehyde dynamically released in the anoxic reactor, denoted as the formaldehyde peak value (unit: mg / L). Specifically, in Step 2, collect 50 mL of water samples at the outlet of the anoxic reactor every 30 minutes, filter through a 0.45 μm filter membrane to remove suspended microbial microcapsules and precipitates; take 10 mL of the filtrate, 10 mL of acetylacetone reagent (150 g of ammonium acetate, 3 mL of glacial acetic acid, and 2 mL of acetylacetone made up to 1 L), heat in a water bath at 60 °C for 15 minutes, and cool to room temperature; measure the absorbance at a wavelength of 412 nm, calculate the concentration through the standard curve (formaldehyde standard solution 0 - 5 mg / L), and record the highest concentration value throughout the acidification process, that is, the formaldehyde peak value (unit: mg / L).

[0068] 2. Detect the formaldehyde concentration of the influent water in Step 1 and the formaldehyde concentration of the effluent water in Step 3, and calculate the formaldehyde removal rate (unit: %) based on the formaldehyde concentration of the influent water in Step 1 and the formaldehyde concentration of the effluent water in Step 3.

[0069] 3. Refer to HJ 828-2017 "Water Quality - Determination of Chemical Oxygen Demand - Dichromate Method" to determine the chemical oxygen demand (COD) concentrations of the influent water in Step 1 and the effluent water in Step 3, and calculate the COD removal rate. Specifically, sample the influent water in Step 1 and the effluent water in Step 3; take 20 mL of water sample, 10 mL of 0.25 mol / L potassium dichromate solution, and 30 mL of concentrated sulfuric acid - silver sulfate reagent, reflux and digest at 165 °C for 2 hours; after cooling, add an indicator (ferroin), and titrate with ammonium ferrous sulfate until the end point of reddish-brown. Calculate the COD removal rate (unit: %) based on the chemical oxygen demand concentrations of the influent water in Step 1 and the effluent water in Step 3.

[0070] 4. Use headspace injection gas chromatography to determine the concentrations of trioxymethylene (TOX) in the influent water in Step 1 and the effluent water in Step 3, and calculate the TOX removal rate (unit: %). In this experimental example, take 10 mL of the influent water sample and the effluent water sample in Step 3, add 0.5 g of sodium chloride to destroy the residual cetyltrimethylammonium bromide micelle structure and 0.2 g of anhydrous sodium sulfate for dehydration, vortex and oscillate for 2 minutes and then let it stand for stratification, take 1.0 mL of the supernatant and place it in a 20 mL headspace vial and seal; equilibrate at 90 °C for 30 minutes to fully volatilize trioxymethylene, separate through an FFAP capillary column (30 m × 0.32 mm × 0.5 μm), the column temperature program is to hold at 60 °C for 2 minutes, increase to 200 °C at a rate of 15 °C / min and hold for 5 minutes, the carrier gas flow rate is 1.2 mL / min, and quantify with an FID detector; establish a standard curve of 1 - 50 mg / L by the external standard method, qualitatively analyze according to the retention time of 8.2 minutes, and quantitatively calculate the concentration by peak area to calculate the TOX removal rate.

[0071] The results are shown in the following table: Table 2 Comparison Table of Treatment Results

[0072] In Comparative Example 1, since trioxymethylene encapsulation for controlled release and gradient acidification were not adopted, a formaldehyde concentration peak of 305 mg / L appeared in Step 2, resulting in significant limitations in the formaldehyde removal rate (72.1%), COD removal rate (83.5%), and TOX removal rate (76.3%). In contrast, in Examples 1-9, cetyltrimethylammonium bromide and ethanol were used to construct micelles to encapsulate trioxymethylene, and continuous linear acidification was adopted to control the release rate. The formaldehyde peak values were all reduced to below 148 mg / L (the lowest was 68 mg / L). The formaldehyde removal rate was increased to 84.5%-97.6%, the COD removal rate reached 89.6%-97.3%, and the TOX removal rate was increased to 87.3%-99.1%. On the one hand, increasing the molar ratio of cetyltrimethylammonium bromide to trioxymethylene and the molar ratio of ethanol to cetyltrimethylammonium bromide can enhance the micelle stability and reduce the formaldehyde peak value. For example, the peak value in Example 1 was 135 mg / L, while the peak value in Example 4 was 92 mg / L. On the other hand, if the acidification rate is too fast, the instantaneous release amount of formaldehyde will exceed the degradation capacity of the microbial community. For example, the peak value in Example 3 was 148 mg / L; if it is too slow, the reaction cycle will be prolonged and the metabolic activity of the microbial community will decline. For example, the formaldehyde removal rate in Example 1 was 86.7%, while Example 5 with an acidification rate of 0.15 pH / h achieved the optimal degradation efficiency.

[0073] In Examples 1-9, cetyltrimethylammonium bromide, ethanol, and trioxymethylene formed micelles to encapsulate and block spontaneous depolymerization. Linear acidification was used to trigger the staged release of trioxymethylene, and the microbial community degraded it according to the time sequence; the formaldehyde generated dynamically during the pH drop was degraded, achieving the dynamic balance between formaldehyde generation and biodegradation and avoiding the toxicity peak. In the anaerobic stage, the hydrophobic alkyl chain of cetyltrimethylammonium bromide formed spherical micelles with the assistance of ethanol, encapsulating the hydrophobic trioxymethylene in the core, and blocking its contact with water molecules through steric hindrance to inhibit the acid-catalyzed ring-opening reaction. In the facultative anaerobic stage, the pH was continuously linearly decreased, and the protonation degree of cetyltrimethylammonium bromide increased with the decrease of pH to slowly release trioxymethylene; the domesticated microbial community added synchronously was used for facultative anaerobic biochemical treatment, making the formaldehyde generation rate and biodegradation rate dynamically match and avoiding the inhibition of the microbial community by the toxicity peak.

[0074] Specifically, cetyltrimethylammonium bromide embeds into the non-polar hydrophobic core (the methyl region in the cyclic structure of paraformaldehyde) of paraformaldehyde molecules through its hydrophobic cetyl long chain, and realizes intermolecular binding through van der Waals forces and hydrophobic interactions. At the same time, the hydrophilic quaternary ammonium salt head group of cetyltrimethylammonium bromide faces the aqueous phase, and self-assembles in the solution to form a micelle skeleton, which wraps paraformaldehyde in the hydrophobic cavity of the micelle, forming a physical barrier to block the contact between paraformaldehyde and water molecules and inhibiting the acid-catalyzed ring-opening reaction. Ethanol, as an amphoteric co-solvent, forms hydrogen bonds between its short-chain hydroxyl groups and the quaternary ammonium salt head groups of cetyltrimethylammonium bromide, reducing the interfacial energy of the micelles and enhancing the dispersion stability of the micelles. At the same time, the ethyl chain of ethanol inserts into the molecular gap of cetyltrimethylammonium bromide, and by adjusting the curvature radius and packing parameter of the micelles, promotes the formation of spherical micelles with uniform size and dense structure, optimizing the encapsulation efficiency of paraformaldehyde molecules. In addition, ethanol weakens the hydrogen bond interaction between paraformaldehyde molecules, assisting the hydrophobic chain of cetyltrimethylammonium bromide to embed more efficiently into the hydrophobic region of paraformaldehyde, forming a cetyltrimethylammonium bromide and ethanol encapsulation system, and enhancing the anti-dissociation ability of the micelles in an anaerobic environment.

[0075] When the pH of the wastewater continuously decreases linearly, hydrogen ions combine with the quaternary ammonium salt head groups to protonate them, and the surface charge density and hydrophobicity of the micelles change dynamically, resulting in the dominance of van der Waals gravitational force between the micelles and instability and rupture. The hydrophobic core of the micelles is gradually exposed, and the encapsulated paraformaldehyde molecules are released. By controlling the injection rate of hydrogen ions to regulate the disassembly rate of the micelles, the slow release conversion of paraformaldehyde from the encapsulated state to the free state is realized, catalyzing the depolymerization of free paraformaldehyde, synchronizing with the metabolism of the matching microbial community, and then realizing the dynamic matching of the formaldehyde generation rate and the biodegradation rate.

[0076] In Example 5, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde is 1.2:1, the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.4:1, and the acidification rate is 0.15 pH / h, and the encapsulation control and the acidification rate achieve efficient coordination. In the spatial dimension, cetyltrimethylammonium bromide and ethanol form micelles to physically isolate paraformaldehyde from water molecules through the hydrophobic core, and cetyltrimethylammonium bromide with a molar ratio of 1.2:1 to paraformaldehyde forms a dense encapsulation layer, blocking the random release of free formaldehyde from the source. In the time dimension, the uniform acidification at 0.15 pH / h regulates the disassembly process of the micelles through the protonation gradient, making the release kinetic curve of paraformaldehyde match the metabolic activity window of the microbial community. Therefore, Example 5 compresses the formaldehyde release flux below the maximum degradation threshold of the microbial community, realizing slow release and degradation simultaneously. Furthermore, the formaldehyde peak value is only 68 mg / L, and the TOX removal rate reaches 99.1%.

[0077] In Example 9, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde was 1.4:1, and the acidification rate was 0.20 pH / h. Compared with Example 5, increasing the dosage of cetyltrimethylammonium bromide in Example 9 improved the encapsulation rate, but the residual surfactant adsorbed on the cell membrane of the bacteria, inhibiting the activity of formaldehyde dehydrogenase. At the same time, accelerating acidification caused the pH to drop rapidly to 4.0 within 24 hours, resulting in the concentrated release of paraformaldehyde before pH 5.0, inhibiting the bacterial community, making the degradation ability of the bacterial community lag behind the release rate, and causing the formaldehyde peak to rise back to 94 mg / L and the TOX removal rate to drop to 97.6%.

[0078] In Example 1, the molar ratio of cetyltrimethylammonium bromide to paraformaldehyde was 1.0:1, and the acidification rate was 0.10 pH / h. Compared with Example 5, reducing the dosage of cetyltrimethylammonium bromide in Example 1 decreased the micelle encapsulation rate, increased the initial free formaldehyde, and had a relatively weak sustained-release barrier. Slowing down the acidification extended the reaction time to 36 hours, and the release of paraformaldehyde was slow in the pH 6.0 - 5.0 range. The bacterial community was partially dormant due to insufficient substrate supply, the activity of quinone-dependent formaldehyde dehydrogenase of Acetobacter pasteurianus decreased, and the formaldehyde degradation efficiency decreased, resulting in a waste of metabolic resources in terms of time.

[0079] In summary, by controlling the encapsulation of cetyltrimethylammonium bromide and ethanol, the concentration distribution of paraformaldehyde is controlled in space, and the acidification rate redistributes the time release flux, converting the originally explosive formaldehyde generation into a controllable sequential release. Combining with the domestication of the bacterial community to dynamically match the formaldehyde generation rate and the biodegradation rate, a dynamic balance is achieved.

[0080] Based on the ideal embodiments of the present invention as inspiration, through the above description, relevant personnel can make various changes and modifications completely within the scope of the technical idea of this invention without deviation. The technical scope of this invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for treating polyoxymethylene wastewater, characterized in that, It includes the following steps: Step 1: In an anaerobic environment, use anaerobic bacteria to degrade formaldehyde and macromolecular organic matter in the polyoxymethylene wastewater. At the same time, add a cationic surfactant and an alcohol assistant to form micelles to wrap trimethylolpropane formal; Step 2: Continuously linearly acidify the effluent from Step 1, control the pH to decrease uniformly, trigger the staged disintegration of trimethylolpropane formal to release trimethylolpropane formal, and simultaneously add domesticated bacteria to degrade trimethylolpropane formal under anoxic conditions; Step 3: Perform two-stage biological treatment on the effluent from Step 2 under aerobic conditions.

2. The method according to claim 1, characterized in that, The cationic surfactant described in Step 1 is cetyltrimethylammonium bromide, and the alcohol assistant is ethanol.

3. The method according to claim 2, wherein The molar ratio of cetyltrimethylammonium bromide to trimethylolpropane formal is 1.0:1 to 1.4:1, and the molar ratio of ethanol to cetyltrimethylammonium bromide is 0.3:1 to 0.5:

1.

4. The method according to claim 1, characterized in that, The anaerobic bacteria described in Step 1 include Methanobacterium formicicum and Clostridium butyricum.

5. The method according to claim 1, characterized in that, In Step 2, the acidification rate is 0.10 - 0.20 pH units / hour, and the final pH is 4.1 - 4.

3.

6. The method according to claim 1, characterized in that, The domesticated bacteria described in Step 2 include Acetobacter pasteurianus, Pseudomonas putida, and Achromobacter marplatensis.

7. The method according to claim 6, characterized in that, The domesticated bacteria are gradient domesticated with a formaldehyde-containing medium and prepared into a slow-release bactericide by the microencapsulation method.

8. The method according to claim 1, wherein After Step 2, add an anionic surfactant to form a complex precipitate and perform solid-liquid separation.

9. The method according to claim 1, characterized in that The two-stage biological treatment described in Step 3 includes: For the first-stage treatment, control the dissolved oxygen at 2.8 - 3.2 mg / L and add Pseudomonas oxydans; For the second-stage treatment, control the dissolved oxygen at 1.4 - 1.6 mg / L and perform nitrification and denitrification for nitrogen removal.

10. Use of the method according to any one of claims 1-9 in the treatment of polyoxymethylene wastewater, characterized in that, The formaldehyde concentration in the polyoxymethylene wastewater is 250 mg / L, the trimethylolpropane formal concentration is 200 mg / L, and the COD concentration is 3500 mg / L.

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