Polyformaldehyde wastewater treatment method and application

Abstract

This invention discloses a method and application for treating polyoxymethylene (POM) wastewater, belonging to the field of wastewater treatment technology. The method first involves adding hexadecyltrimethylammonium bromide and ethanol to the wastewater in an anaerobic environment to form micelles that encapsulate POM, and then utilizing anaerobic bacteria to degrade formaldehyde and macromolecular organic matter. Next, the anaerobic effluent is introduced into a facultative anaerobic environment, where a continuous linear decrease in pH triggers the staged disintegration of the micelles, releasing POM. Simultaneously, acclimation bacteria are added in stages according to pH changes to dynamically degrade the released formaldehyde. Finally, complete mineralization is achieved through two-stage biological oxidation in an aerobic environment. This invention blocks the random depolymerization of POM through spatial encapsulation and controls the release rate through sequential acidification, achieving a dynamic balance between formaldehyde formation and biodegradation. This effectively avoids the inhibition of microorganisms by toxicity peaks, significantly improving the removal efficiency of formaldehyde and organic pollutants and the stability of system operation.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method and application for treating polyoxymethylene wastewater. Background Technology

[0002] Polyoxymethylene (POM) is an important chemical raw material. The wastewater generated during its production process contains high concentrations of toxic pollutants such as formaldehyde and trioxymethylene. If it is discharged directly without effective treatment, it will pose a serious threat to the ecological environment and human health. Therefore, the efficient treatment of POM wastewater is an important issue in the field of chemical environmental protection.

[0003] Current fully biological treatment of polyoxymethylene (POM) wastewater mainly adopts a combination of anaerobic, facultative anaerobic, and aerobic processes, which degrade pollutants through microbial metabolism. However, this technology faces significant challenges: the toxicity of formaldehyde in POM wastewater easily inhibits microbial activity, and trioxymethylene readily depolymerizes rapidly to formaldehyde in traditional treatment processes, leading to peak formaldehyde concentrations in the reaction system. This not only inhibits microbial activity but also disrupts the balance between formaldehyde formation and degradation, resulting in low chemical oxygen demand (COD) removal rates and unstable effluent quality, making it difficult to meet stringent discharge standards.

[0004] To address the aforementioned technical bottlenecks, this invention proposes a novel method for the all-biological treatment of polyoxymethylene wastewater. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a method and application for treating polyoxymethylene wastewater. By using a coating system of hexadecyltrimethylammonium bromide and ethanol to delay the polymerization process, and combining it with a method for treating polyoxymethylene wastewater by controlling the release rate through pH gradient acidification, a dynamic balance between formaldehyde generation and microbial degradation is achieved, effectively improving treatment efficiency and effluent quality.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for treating polyoxymethylene wastewater, comprising the following steps:

[0007] Step 1: In an anaerobic environment, anaerobic bacteria are used to degrade formaldehyde and macromolecular organic matter in polyoxymethylene wastewater. At the same time, cationic surfactants and alcohol additives are added to form micelles that encapsulate trioxymethylene.

[0008] Step 2: Continuously linearly acidify the effluent from Step 1, control the pH to decrease at a uniform rate, trigger the phased decomposition and release of trioxymethylene, and simultaneously add acclimatized bacteria to degrade trioxymethylene under facultative anaerobic conditions.

[0009] Step 3: The effluent from Step 2 is subjected to two-stage biological treatment under aerobic conditions.

[0010] Furthermore, the cationic surfactant mentioned in step one is hexadecyltrimethylammonium bromide, and the alcohol auxiliary is ethanol.

[0011] Further, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde is 1.0:1 to 1.4:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.3:1 to 0.5:1.

[0012] Furthermore, the anaerobic bacteria mentioned in step one include Methanobacterium formate and Clostridium butyricum.

[0013] Furthermore, in step two, the acidification rate is 0.10-0.20 pH units / hour, and the endpoint pH is 4.1-4.3.

[0014] Furthermore, the domesticated microbial community mentioned in step two includes Acetobacter pasteurellii, Pseudomonas putida, and Achromobacter maseri.

[0015] Furthermore, the domesticated bacterial population was domesticated in a gradient of formaldehyde-containing culture medium and prepared into a slow-release bacterial agent using a microencapsulation method.

[0016] Furthermore, after step two, anionic surfactants are added to form a complex precipitate, and solid-liquid separation is performed.

[0017] Furthermore, the two-stage biological treatment described in step three includes:

[0018] Primary treatment controls dissolved oxygen at 2.8-3.2 mg / L, and adds soil acid-oxidizing Pseudomonas aeruginosa;

[0019] The secondary treatment controls dissolved oxygen at 1.4-1.6 mg / L, and performs nitrification and denitrification for nitrogen removal.

[0020] Another technical solution provided by the present invention is 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 trioxymethylene concentration is 200 mg / L, and the COD concentration is 3500 mg / L.

[0021] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0022] This invention provides a method for treating polyoxymethylene wastewater. By constructing micelles with cationic surfactants and alcohol additives to encapsulate trioxymethylene and block its spontaneous depolymerization, and by using continuous linear acidification to regulate the micelle disintegration rate to trigger the phased release of trioxymethylene, the method simultaneously matches the sequential degradation capacity of the domesticated microbial community, thereby achieving a dynamic balance between formaldehyde generation and biodegradation. This controls the trioxymethylene conversion process at the source, avoids the inhibition of microorganisms by formaldehyde toxicity peaks, and significantly improves pollutant degradation efficiency and system stability.

[0023] Firstly, by adding the cationic surfactant hexadecyltrimethylammonium bromide and the alcohol auxiliary ethanol to the wastewater, the hydrophobic alkyl chain of hexadecyltrimethylammonium bromide binds to the hydrophobic core of paraformaldehyde through van der Waals forces. Under the effect of ethanol reducing interfacial tension, dense spherical micelles are formed through directional self-assembly, encapsulating paraformaldehyde within the hydrophobic cavity to form a physical barrier. This steric hindrance blocks the contact between paraformaldehyde and water molecules, directly inhibiting the acid-catalyzed ring-opening reaction and preventing the random release of free formaldehyde during the anaerobic stage, thus avoiding instantaneous concentration spikes. Compared to existing technologies where unencapsulated paraformaldehyde directly depolymerizes to produce high concentrations of formaldehyde, this invention isolates toxic substances at the source, further establishing a stable material basis for subsequent acidification and controlled release.

[0024] Secondly, continuous linear acidification is achieved by uniformly adding acid at a rate of 0.10-0.20 pH units / hour. Utilizing the characteristic of hydrogen ions gradually protonating the hexadecyltrimethylammonium bromide quaternary ammonium groups, the surface charge density and hydrophobicity of the micelles are dynamically altered, triggering the staged diffusion and release of encapsulated paraformaldehyde according to the pH gradient. By controlling the protonation process to regulate micelle disintegration, the time-matching of the paraformaldehyde release rate with the metabolic activity of the acclimated bacterial community is directly achieved. Compared to the instantaneous high-concentration formaldehyde release caused by direct acidification in existing technologies, this invention ensures that the amount of free formaldehyde generated remains within the bacterial degradation threshold, further guaranteeing the efficient and continuous progress of the facultative anaerobic biochemical reaction.

[0025] In particular, spatial encapsulation control blocks the initial depolymerization of paraformaldehyde through micellar physical encapsulation, providing a stable precursor for acidification-controlled release. Temporal linear acidification, on the other hand, regulates the phased disintegration of micelles through protonation gradients, transforming encapsulated paraformaldehyde into a time-controlled source of free formaldehyde release. The encapsulation feature ensures that paraformaldehyde is released only during the acidification phase along a predetermined path, while the acidification rate feature matches the release flux to the activity windows of *Acetobacter pastoris* and *Pseudomonas putida*, ultimately achieving a dynamic balance between formaldehyde generation rate and bacterial degradation rate, thus realizing fully controllable mineralization of toxic substances. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a flowchart of a polyoxymethylene wastewater treatment method. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention may be practiced in other ways different from those described herein, and therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below. Unless otherwise specified in the following embodiments, all raw materials were commercially available or prepared using conventional methods in the art. Specifically, *Methanobacterium formate* (DSM 3637), *Clostridium butyricum* (DSMZ 10702), *Achromobacterium martensii* (CGMCC 1.1843), *Pseudomonas putida* (ATCC 49128), *Acetobacter pastoris* (CGMCC 1.41), *Pseudomonas aeruginosa* (ATCC 11228), and *Paracococcus denitrificans* (ATCC 17741) were purchased from *Gnaphalium affine*; cetyltrimethylammonium bromide (analytical grade), ethanol (analytical grade), and betaine (98% purity) were purchased from Sinopharm Reagent.

[0030] Exemplary method:

[0031] like Figure 1 As shown, a fully biochemical method for treating polyoxymethylene wastewater includes the following steps:

[0032] Step 1: In an anaerobic environment, anaerobic bacteria are used to degrade formaldehyde and macromolecular organic matter in polyoxymethylene wastewater. At the same time, cationic surfactants and alcohol additives are added to form micelles that encapsulate trioxymethylene.

[0033] Step 2: Continuously linearly acidify the effluent from Step 1, control the pH to decrease at a uniform rate, trigger the phased decomposition and release of trioxymethylene, and simultaneously add acclimatized bacteria to degrade trioxymethylene under facultative anaerobic conditions.

[0034] Step 3: The effluent from Step 2 is subjected to two-stage biological treatment under aerobic conditions.

[0035] Below, each step will be explained in detail.

[0036] Step 1 involves using anaerobic bacteria in an anaerobic environment to bioconvert formaldehyde into low-toxicity formic acid, while simultaneously degrading macromolecular organic matter to improve biodegradability. At the same time, micelles are constructed using hexadecyltrimethylammonium bromide and ethanol to encapsulate paraformaldehyde, forming both encapsulated and free paraformaldehyde, thus blocking its depolymerization pathway, as detailed below.

[0037] Firstly, polyoxymethylene wastewater is injected into the anaerobic reactor, and the pH is adjusted to the range of 6.8-7.2 using a 10% sodium hydroxide solution. The temperature is maintained at 35±0.5℃ through a steam coil, and nitrogen is continuously introduced to stabilize the oxidation-reduction potential in the range of -320 to -280mV. The hydraulic retention time is set to 48-60 hours.

[0038] Anaerobic bacteria include *Methanobacterium formate* and *Clostridium butyricum*. *Methanobacterium formate* expresses formaldehyde superoxide dismutase, which captures four molecules of formaldehyde and one molecule of water. Through aldehyde transfer and proton exchange, it generates one molecule of acetic acid and two molecules of formic acid. This process consumes reduced coenzyme F420 and achieves electronic equilibrium at a redox potential of -300 mV. *Clostridium butyricum* secretes dextranase to hydrolyze the β-1,4 glycosidic bonds of polysaccharides, generating glucose monomers and dimers. Its secreted metalloproteinases cleave protein peptide bonds, producing oligopeptides with a molecular weight less than 500 Da. This macromolecular carbon chain cleavage reduces the proportion of recalcitrant COD and increases the B / C ratio.

[0039] Specifically, *Methanobacter formic acid* was cultured on 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 (sole carbon source), pH 7.0; *Clostridium butyricum* was cultured on 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 *Methanobacter formic acid* and *Clostridium butyricum* were cultured at 37°C in an anaerobic workstation (nitrogen:hydrogen:carbon dioxide = 85:10:5) for 72 hours to the late logarithmic phase.

[0040] Specifically, the culture media of Methanobacter formic acid and Clostridium butyricum were centrifuged at 8000 rpm for 10 minutes under nitrogen protection, the supernatant was discarded, and the culture was resuspended in anaerobic physiological saline to 1 / 10 of the original volume. The Methanobacter formic acid dry weight of 12 mg / mL and the Clostridium butyricum dry weight of 4 mg / mL were mixed to form a bacterial suspension. The suspension was injected into the bottom of the anaerobic reactor through a closed pipeline using a positive pressure delivery method, and the inoculum amount was 12% of the effective volume of the anaerobic reactor.

[0041] Secondly, hexadecyltrimethylammonium bromide was dissolved in an aqueous ethanol solution and injected into polyoxymethylene wastewater under a stirring rate of 200 rpm. The molar ratio of hexadecyltrimethylammonium bromide to trioxymethylene was 1.0:1 to 1.4:1; the molar ratio of ethanol to hexadecyltrimethylammonium bromide was 0.3:1 to 0.5:1.

[0042] Hexadecyltrimethylammonium bromide hydrophobic alkyl chains align under the influence of ethanol, forming spherical micelles. Paraformaldehyde, due to its hydrophobicity, is encapsulated within the micelle core, and its cyclic structure is spatially blocked by the hexadecyl chains, preventing it from contacting water molecules for acid-catalyzed ring-opening reactions. Ethanol enhances the stability of the micelle structure by reducing the interfacial tension.

[0043] Step 2 involves continuously linearly acidifying the wastewater to lower its pH. This pH change triggers the phased disintegration and release of encapsulated paraformaldehyde, controlling the release rate. Simultaneously, acclimatized bacteria are added to dynamically degrade the generated formaldehyde as the pH decreases, achieving a dynamic balance between formaldehyde generation and biodegradation and avoiding toxicity peaks.

[0044] After adjusting the anaerobic effluent to neutral, it is introduced into the anoxic reactor. A 0.5M sulfuric acid solution is added to the anoxic reactor at a rate of 0.10-0.20 pH units per hour, causing the system pH to drop uniformly to a final value of 4.2±0.1, which is maintained for 24-36 hours. The temperature is maintained at 30±1℃, the oxidation-reduction potential is -100 to +50 mV, and the dissolved oxygen is maintained at 0.5-0.8 mg / L. Optionally, an online pH meter is used to collect data every 2 minutes, and the peristaltic pump speed is adjusted using a PID algorithm to control pH fluctuations to ≤±0.05.

[0045] The protonation degree of the quaternary ammonium group in the cetyltrimethylammonium bromide molecule increases with decreasing pH. Specifically, at pH > 6.0, the high positive charge on the micelle surface forms an electrostatic barrier, inhibiting the release of paraformaldehyde; in the pH range of 5.0-6.0, protonation leads to the exposure of the hydrophobic core of the micelles, and paraformaldehyde is released through diffusion; at pH < 5.0, cetyltrimethylammonium bromide is completely converted into cationic monomers, and the micelle structure disintegrates, releasing residual paraformaldehyde.

[0046] Furthermore, the acclimated bacterial flora included *Achromobacterium martensii*, *Pseudomonas putida*, and *Acetobacter pasteurellii*, obtained through acclimation culture: A basic inorganic salt medium containing 200 mg / L formaldehyde (0.7 g / L potassium dihydrogen phosphate, 0.85 g / L dipotassium hydrogen phosphate, and 1.2 g / L ammonium sulfate) was used. Under conditions of 30 ± 1℃ and dissolved oxygen of 0.5–1.0 mg / L, the pH was gradually decreased (initially from 6.0 to 4.2) over 24 hours, while the formaldehyde concentration was simultaneously increased (from 50 to 200 mg / L). 1 mM betaine was added to enhance the acid tolerance of the bacteria. After acclimation, the bacterial solution was concentrated to 10 μL by centrifugation under nitrogen protection. 9 Sustained-release microcapsules with a particle size of 150±20μm were prepared using the calcium alginate-chitosan double encapsulation method, with poly(β-hydroxybutyrate) carbon source loaded inside.

[0047] When the pH dropped to 6.0, 3 g / L of *Acetobacter pastoris* microcapsules were added; when the pH dropped to 5.0, 4 g / L of *Pseudomonas putida* microcapsules were added; *Achromobacter valerate* remained as a resident flora at 5 g / L dry weight throughout the process. In the pH range of 6.0-5.0, *Acetobacter pastoris* oxidized formaldehyde to formic acid via quinone-dependent formaldehyde dehydrogenase; in the pH range of 5.0-4.0, the acid-stable formaldehyde dehydrogenase of *Pseudomonas putida* mineralized formaldehyde to carbon monoxide; *Achromobacter valerate* assimilated residual pollutants through the serine cycle, and its high-affinity formaldehyde transporter was activated at formaldehyde concentrations greater than 80 mg / L, improving substrate capture efficiency. Furthermore, the flora maintained the conformational stability of intracellular enzymes under betaine osmotic protection, preserving its survival rate under acidic conditions.

[0048] Further, sodium dodecyl sulfate, an anionic surfactant, is added to form a complex precipitate with the residual hexadecyltrimethylammonium bromide, which is then separated by an inclined plate sedimentation tank.

[0049] Step 3: Under aerobic conditions, formic acid and residual organic matter are thoroughly mineralized through two-stage biological treatment, while ammonia nitrogen nitrification and deep removal of total nitrogen are completed simultaneously, as detailed below.

[0050] The effluent from the anoxic reactor is introduced into the high-load aeration tank of the first stage of the two-stage aerobic reactor, where dissolved oxygen is controlled at 3.0±0.2 mg / L, temperature is maintained at 30±1℃, oxidation-reduction potential is +250 to +350 mV, and hydraulic retention time is 8-10 h. Suspended biological carriers (specific surface area > 500 m² / m³) are added, and soil acid-oxidizing Pseudomonas aeruginosa is added at 3-5 g / L. The effluent from the first-stage high-load aeration tank is introduced into the second-stage low-load nitrification tank, where dissolved oxygen is controlled at 1.5±0.1 mg / L, temperature is maintained at 30±1℃, oxidation-reduction potential is +100 to +150 mV, and hydraulic retention time is 10-16 h. An immobilized nitrifying bacteria membrane module is installed, with a filling rate of not less than 40%.

[0051] Under aseptic conditions, *Pseudomonas aeruginosa* strains were inoculated into a selective medium containing sodium formate (the sole carbon source) (the formulation included 0.8 g / L dipotassium hydrogen phosphate, 0.6 g / L potassium dihydrogen phosphate, 1.0 g / L ammonium sulfate, 0.2 g / L magnesium sulfate, 0.05 g / L calcium chloride, and 3.0 g / L sodium formate, pH 7.0) and cultured at 30°C and 180 rpm for 48 hours until the late logarithmic phase. After culture, the culture was centrifuged at 8000 rpm for 10 min, the supernatant was discarded, and the medium was resuspended in sterile physiological saline and concentrated to 1 / 10 of its original volume. This concentrate was then directly added to a primary high-load aeration tank, with a final concentration of 3-5 g / L (based on dry bacterial weight).

[0052] The nitrifying bacteria were sourced from nitrified sludge from municipal wastewater treatment plants. In the SBR reactor, an inorganic autotrophic culture medium (formulation including ammonium chloride 0.5 g / L, sodium bicarbonate 1.0 g / L, potassium dihydrogen phosphate 0.3 g / L, magnesium sulfate 0.1 g / L, calcium chloride 0.02 g / L, pH 7.8) was used to gradually increase the ammonia nitrogen load (initially 0.2 kgN / m³ to an endpoint of 0.8 kgN / m³). 3 (d) Control the dissolved oxygen concentration to 2.0-3.0 mg / L, 30℃, and pH 7.5-8.0, and acclimatize for 21 days until the ammonia nitrogen oxidation rate exceeds 10 mgN / gVSS·h. In an anoxic environment, inoculate the denitrifying bacteria into the denitrification medium (formulation 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), purge with nitrogen for 30 minutes to remove oxygen, seal, and incubate at 30℃ for 72 hours until the nitrate removal rate is greater than 90%. After incubation, centrifuge and concentrate the bacterial solution, mix it with nitrifying bacteria at a dry weight ratio of 6:4, and fill it into the secondary low-load nitrification tank through an immobilized bacterial membrane module.

[0053] In this step, soil acid-oxidizing Pseudomonas secretes formate dehydrogenase, which oxidizes formate to carbon dioxide, eliminating the potential toxicity of formate accumulation in step one. In the nitrification stage, nitrifying bacteria oxidize ammonia nitrogen to nitrite, and nitrite to nitrate; in the denitrification stage, denitrifying bacteria reduce nitrate to nitrogen gas.

[0054] Example 1:

[0055] Step 1: Inject polyoxymethylene wastewater with a formaldehyde concentration of 250 mg / L, a trioxymethylene concentration of 200 mg / L, and a COD concentration of 3500 mg / L into the anaerobic reactor. Add a 10% sodium hydroxide solution to adjust the pH of the system to 7.0. Maintain a constant temperature of 35.0℃ using a steam coil and continuously purge nitrogen to maintain an oxidation-reduction potential of -300 mV. Keep the hydraulic retention time constant at 48 h. Simultaneously, add pre-cultured anaerobic bacteria, with a dry weight concentration of 12.0 mg / mL formic acid methanobacterium and 4.0 mg / mL butyric acid clostridium, with an inoculation volume of 12% of the effective volume of the anaerobic reactor. At the same time, dissolve hexadecyltrimethylammonium bromide in an ethanol aqueous solution and inject it into the polyoxymethylene wastewater under a stirring speed of 200 rpm. The molar ratio of hexadecyltrimethylammonium bromide to trioxymethylene is 1.0:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.3:1.

[0056] Step 2: The anaerobic effluent is introduced into the facultative anaerobic reactor, and the pH is adjusted to 7.5. 0.5 mol / L sulfuric acid solution is added at a rate of 0.13 pH / h to linearly reduce the pH of the wastewater to the final value of 4.2, with a hydraulic retention time of 36 h. When the pH drops to 6.0, 3.0 g / L calcium alginate microcapsules containing Acetobacter pasteurellii microcapsules are added. When the pH drops to 5.0, 4.0 g / L Pseudomonas putida microcapsules are added, while maintaining 5.0 g / L Achromobacter martensii throughout the process. At the reaction endpoint, sodium dodecyl sulfate with a molar ratio of 1:1.2 to hexadecyltrimethylammonium bromide is added to form a complex precipitate, which is then separated into solid and liquid phases by a slanted plate sedimentation tank with a surface loading of 1.2 m³ / (m²·h).

[0057] Step 3: The facultative effluent is fed into a primary high-load aeration tank, with the dissolved oxygen concentration controlled at 3.0 mg / L and a hydraulic retention time maintained at 8.0 h. 3.0 g / L of soil acid-oxidizing Pseudomonas bacteria is added, and a tank with a specific surface area of ​​550 m² is filled. 2 / m 3 The suspended biological carrier has a carrier filling rate of 45%; it is then introduced into a secondary low-load nitrification tank, where the dissolved oxygen concentration is controlled at 1.5 mg / L and the hydraulic retention time is 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.

[0058] Example 2:

[0059] Unlike Example 1, in step two of this example, 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.

[0060] Example 3:

[0061] Unlike Example 1, in step two of this example, 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.

[0062] Example 4:

[0063] Unlike Example 1, in step one of this example, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde is 1.2:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.4:1. The rest is the same as in Example 1.

[0064] Example 5:

[0065] Unlike Example 1, in this example, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde in step one is 1.2:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.4:1; in step two, 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.

[0066] Example 6:

[0067] Unlike Example 1, in this example, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde in step one is 1.2:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.4:1; in step two, 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.

[0068] Example 7:

[0069] Unlike Example 1, in step one of this example, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde is 1.4:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.5:1. The rest is the same as in Example 1.

[0070] Example 8:

[0071] Unlike Example 1, in this example, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde in step one is 1.4:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.5:1; in step two, 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.

[0072] Example 9:

[0073] Unlike Example 1, in this example, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde in step one is 1.4:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.5:1; in step two, 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.

[0074] Comparative Example 1:

[0075] Step 1: Inject polyoxymethylene wastewater with a formaldehyde concentration of 250 mg / L, a trioxymethylene concentration of 200 mg / L, and a COD concentration of 3500 mg / L into the anaerobic reactor. Add a 10% sodium hydroxide solution to adjust the pH of the system to 7.0. Maintain a constant temperature of 35.0℃ using a steam coil and continuously purge nitrogen to maintain an oxidation-reduction potential of -300 mV. Keep the hydraulic retention time constant at 48 h. Simultaneously add pre-cultured anaerobic bacteria, with a dry weight concentration of 12.0 mg / mL formic acid methanobacterium and 4.0 mg / mL butyric acid clostridium, and the inoculation volume accounts for 12% of the effective volume of the anaerobic reactor.

[0076] Step 2: Introduce the anaerobic effluent into the facultative anaerobic reactor, adjust the pH to 4.2, and maintain a hydraulic retention time of 36 hours. Throughout the process, maintain microcapsules of Acetobacter pasteurellii, Pseudomonas putida, and Achromobacter martensii encapsulated with 3.0 g / L calcium alginate.

[0077] Step 3: The facultative effluent is fed into a primary high-load aeration tank, with the dissolved oxygen concentration controlled at 3.0 mg / L and a hydraulic retention time maintained at 8.0 h. 3.0 g / L of soil acid-oxidizing Pseudomonas bacteria is added, and a tank with a specific surface area of ​​550 m² is filled. 2 / m 3 The suspended biological carrier has a carrier filling rate of 45%; it is then introduced into a secondary low-load nitrification tank, where the dissolved oxygen concentration is controlled at 1.5 mg / L and the hydraulic retention time is 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.

[0078] Experimental Example 1:

[0079] The parameter comparison table for Examples 1-9 and Comparative Example 1 is shown in the table below:

[0080] Table 1 Comparison of Parameters between Examples and Comparative Examples

[0081]

[0082] Based on Examples 1-9 and Comparative Example 1, the following tests were performed:

[0083] 1. Refer to HJ 601-2011 "Determination of Formaldehyde in Water - Acetylacetone Spectrophotometric Method" to determine the instantaneous highest concentration of formaldehyde dynamically released in the anoxic reactor, recorded as the formaldehyde peak value (unit: mg / L). Specifically, in step two, collect 50 mL of water sample every 30 minutes at the outlet of the anoxic reactor, filter it through a 0.45 μm filter membrane to remove suspended microbial microcapsules and precipitates; take 10 mL of filtrate, add 10 mL of acetylacetone reagent (150 g ammonium acetate, 3 mL glacial acetic acid, and 2 mL acetylacetone, and dilute to 1 L), heat in a 60℃ water bath for 15 minutes, and cool to room temperature; measure the absorbance at a wavelength of 412 nm, calculate the concentration using a standard curve (formaldehyde standard solution 0-5 mg / L), and record the highest concentration value throughout the acidification process, i.e., the formaldehyde peak value (unit: mg / L).

[0084] 2. Detect the formaldehyde concentration in the influent of step one and the formaldehyde concentration in the effluent of step three, and calculate the formaldehyde removal rate (unit: %) based on the formaldehyde concentration in the influent of step one and the formaldehyde concentration in the effluent of step three.

[0085] 3. Refer to HJ 828-2017 "Determination of Chemical Oxygen Demand in Water - Dichromate Method" to determine the chemical oxygen demand (COD) concentrations of the influent in step one and the effluent in step three, and calculate the COD removal rate. Specifically, samples are taken from the influent in step one and the effluent in step three; 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 are added and refluxed at 165℃ for 2 hours; after cooling, an indicator (ferroin) is added, and titrated with ferrous ammonium sulfate to a reddish-brown endpoint. Based on the COD concentrations of the influent in step one and the effluent in step three, the COD removal rate (unit: %) is calculated.

[0086] 4. The concentration of paraformaldehyde (TOX) in the influent of step one and the effluent of step three was determined by headspace chromatography, and the TOX removal rate (unit: %) was calculated. In this experimental example, 10 mL of samples from the influent of step one and the effluent of step three were taken, 0.5 g of sodium chloride was added to destroy the residual cetyltrimethylammonium bromide micelle structure, and 0.2 g of anhydrous sodium sulfate was added for dehydration. After vortexing for 2 minutes, the mixture was allowed to stand for separation. 1.0 mL of the supernatant was placed in a 20 mL headspace vial and sealed. The sample was equilibrated at 90 °C for 30 minutes to allow the paraformaldehyde to fully volatilize. Separation was performed using an FFAP capillary column (30 m × 0.32 mm × 0.5 μm). The column temperature program was 60 °C for 2 minutes, then increased to 200 °C at 15 °C / min and held for 5 minutes. The carrier gas flow rate was 1.2 mL / min, and quantification was performed using an FID detector. A standard curve of 1-50 mg / L was established using the external standard method. The concentration was determined qualitatively based on the retention time of 8.2 minutes, and the concentration was calculated quantitatively based on the peak area. The TOX removal rate was then calculated.

[0087] The results are shown in the table below:

[0088] Table 2 Comparison of Processing Results

[0089]

[0090] Comparative Example 1, lacking the use of paraformaldehyde encapsulation for controlled release and gradient acidification, exhibited a formaldehyde concentration peak of 305 mg / L in step two, significantly limiting the formaldehyde removal rate (72.1%), COD removal rate (83.5%), and TOX removal rate (76.3%). In contrast, Examples 1-9, using hexadecyltrimethylammonium bromide and ethanol to construct micelles encapsulating paraformaldehyde and employing continuous linear acidification to control the release rate, reduced the formaldehyde peak to below 148 mg / L (minimum 68 mg / L), increasing the formaldehyde removal rate to 84.5%-97.6%, the COD removal rate to 89.6%-97.3%, and the TOX removal rate to 87.3%-99.1%. Furthermore, increasing the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde and the molar ratio of ethanol to hexadecyltrimethylammonium bromide enhances micelle stability and reduces the formaldehyde peak, as seen in Example 1 (peak 135 mg / L) and Example 4 (peak 92 mg / L). On the other hand, if the acidification rate is too fast, the instantaneous release of formaldehyde will exceed the degradation capacity of the microbial community, such as the peak value of 148 mg / L in Example 3; if it is too slow, the reaction cycle will be prolonged and the metabolic activity of the microbial community will decrease, such as the formaldehyde removal rate of 86.7% in Example 1, while Example 5, with an acidification rate of 0.15 pH / h, achieves the optimal degradation efficiency.

[0091] Examples 1-9 utilize cetyltrimethylammonium bromide, ethanol, and paraformaldehyde to form micelles that block spontaneous depolymerization. Linear acidification triggers the phased release of paraformaldehyde, which is then degraded sequentially by the bacterial community. The formaldehyde is dynamically degraded as the pH decreases, achieving a dynamic balance between formaldehyde formation and biodegradation, thus avoiding toxicity peaks. In the anaerobic stage, the hydrophobic alkyl chains of cetyltrimethylammonium bromide, assisted by ethanol, form spherical micelles that encapsulate the hydrophobic paraformaldehyde within their core. Steric hindrance prevents contact between paraformaldehyde and water molecules, inhibiting acid-catalyzed ring-opening reactions. In the facultative anaerobic stage, the pH is continuously and linearly decreased, utilizing the increased protonation degree of cetyltrimethylammonium bromide with decreasing pH to slowly release paraformaldehyde. Simultaneously added acclimatized bacterial communities provide facultative anaerobic biochemical treatment, dynamically matching the formaldehyde formation rate with the biodegradation rate, thus avoiding the inhibition of bacterial communities by toxicity peaks.

[0092] Specifically, hexadecyltrimethylammonium bromide (HMBB) embeds its hydrophobic hexadecyl chain into the nonpolar hydrophobic core of the paraformaldehyde molecule (the methyl region in the paraformaldehyde ring structure), achieving intermolecular bonding through van der Waals forces and hydrophobic interactions. Simultaneously, the hydrophilic quaternary ammonium salt head group of HMBB faces the aqueous phase, self-assembling in solution to form a micelle framework that encapsulates paraformaldehyde within the hydrophobic cavities of the micelles, forming a physical barrier that blocks contact between paraformaldehyde and water molecules and inhibits acid-catalyzed ring-opening reactions. Ethanol, as an amphoteric co-solvent, forms hydrogen bonds between its short-chain hydroxyl groups and the quaternary ammonium salt head group of HMBB, reducing the interfacial energy of the micelles and enhancing their dispersion stability. Furthermore, the ethyl chain of ethanol inserts into the intermolecular spaces of HMBB, adjusting the radius of curvature and packing parameters of the micelles to promote the formation of uniformly sized, densely structured spherical micelles, optimizing the encapsulation efficiency of paraformaldehyde molecules. In addition, ethanol weakens the hydrogen bonding between paraformaldehyde molecules, which helps the hydrophobic chains of hexadecyltrimethylammonium bromide to embed more efficiently into the hydrophobic regions of paraformaldehyde, forming a hexadecyltrimethylammonium bromide and ethanol encapsulation system, thereby enhancing the micelles' resistance to dissociation in anaerobic environments.

[0093] As the pH of wastewater decreases linearly and continuously, hydrogen ions combine with the quaternary ammonium salt head groups, protonating them. This leads to dynamic changes in the surface charge density and hydrophobicity of the micelles, causing van der Waals forces to dominate and resulting in instability and breakage. The hydrophobic core of the micelles is gradually exposed, releasing the encapsulated paraformaldehyde molecules. By controlling the rate of hydrogen ion addition to regulate the micelle disintegration rate, a slow-release conversion of paraformaldehyde from its encapsulated state to its free state is achieved. This catalyzes the depolymerization of free paraformaldehyde, synchronizing with the metabolism of matching bacterial communities, thereby achieving a dynamic match between the formaldehyde generation rate and the biodegradation rate.

[0094] In Example 5, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde was 1.2:1, the molar ratio of ethanol to hexadecyltrimethylammonium bromide was 0.4:1, and the acidification rate was 0.15 pH / h. This achieved efficient synergy between encapsulation control and acidification rate. Spatially, the micelles composed of hexadecyltrimethylammonium bromide and ethanol physically isolated paraformaldehyde from water molecules through a hydrophobic core, forming a dense encapsulation layer with the 1.2:1 molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde, thus blocking the random release of free formaldehyde at its source. Temporally, the uniform acidification rate of 0.15 pH / h controlled the micelle disintegration process through a protonation gradient, matching the paraformaldehyde release kinetics curve with the bacterial community's metabolic activity window. Therefore, Example 5 compressed the formaldehyde release flux to below the maximum degradation threshold of the bacterial community, simultaneously achieving slow release and degradation, resulting in a formaldehyde peak of only 68 mg / L and a TOX removal rate of 99.1%.

[0095] In Example 9, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde was 1.4:1, and the acidification rate was 0.20 pH / h. Compared to Example 5, Example 9 increased the dosage of hexadecyltrimethylammonium bromide to improve the encapsulation rate. However, residual surfactant adsorbed onto the bacterial cell membrane, inhibiting formaldehyde dehydrogenase activity. Simultaneously, accelerated acidification caused the pH to drop sharply to 4.0 within 24 hours, resulting in a concentrated release of paraformaldehyde before pH 5.0. This inhibited the bacterial community, causing the degradation capacity to lag behind the release rate, resulting in a rebound in formaldehyde peak to 94 mg / L and a decrease in TOX removal rate to 97.6%.

[0096] In Example 1, the molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde was 1.0:1, and the acidification rate was 0.10 pH / h. Compared to Example 5, Example 1 reduced the amount of hexadecyltrimethylammonium bromide, decreasing the micelle encapsulation rate, increasing the initial free formaldehyde, and resulting in a relatively weak slow-release barrier. Slower acidification extended the reaction time to 36 hours, and paraformaldehyde was released slowly in the pH range of 6.0-5.0. Due to insufficient substrate supply, the bacterial community partially became dormant, leading to a decrease in the quinone-dependent formaldehyde dehydrogenase activity of *Acetobacter pastoris*, reducing formaldehyde degradation efficiency and resulting in a waste of metabolic resources over time.

[0097] In summary, the spatial distribution of paraformaldehyde concentration can be controlled by encapsulating it with hexadecyltrimethylammonium bromide and ethanol, and the acidification rate can be redistributed over time to release flux. This transforms the originally explosive formaldehyde generation into a controllable, time-sequential release. Combined with the dynamic matching of formaldehyde generation rate and biodegradation rate by the domesticated microbial community, a dynamic equilibrium is achieved.

[0098] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for treating polyoxymethylene wastewater, characterized in that, Includes the following steps: Step 1: In an anaerobic environment, anaerobic bacteria are used to degrade formaldehyde and macromolecular organic matter in polyoxymethylene wastewater, while cationic surfactants and alcohol additives are added to form micelles that encapsulate trioxymethylene. Step 2: Continuously linearly acidify the effluent from Step 1, control the pH to decrease at a uniform rate, trigger the phased decomposition and release of trioxymethylene, and simultaneously add acclimatized bacteria to degrade trioxymethylene under facultative anaerobic conditions. Step 3: The effluent from Step 2 is subjected to two-stage biological treatment under aerobic conditions; In step one, the cationic surfactant is hexadecyltrimethylammonium bromide, and the alcohol auxiliary is ethanol; the anaerobic bacteria include Methanobacterium formic acid and Clostridium butyricum. The domesticated microbial community mentioned in step two includes Acetobacter pasteurellii, Pseudomonas putida, and Achromobacter maseri. The two-stage biological treatment described in step three includes: Primary treatment controls dissolved oxygen at 2.8-3.2 mg / L, and adds soil acid-oxidizing Pseudomonas aeruginosa; The secondary treatment controls dissolved oxygen at 1.4-1.6 mg / L, and performs nitrification and denitrification for nitrogen removal.

2. The method according to claim 1, characterized in that, The molar ratio of hexadecyltrimethylammonium bromide to paraformaldehyde is 1.0:1 to 1.4:1, and the molar ratio of ethanol to hexadecyltrimethylammonium bromide is 0.3:1 to 0.5:

1.

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

3.

4. The method according to claim 1, characterized in that, The domesticated bacterial population was domesticated in a gradient of formaldehyde-containing culture medium and then prepared into a slow-release bacterial agent using a microencapsulation method.

5. The method according to claim 1, characterized in that, After step two is completed, anionic surfactants are added to form complex precipitates, and solid-liquid separation is performed.

6. An application of the method according to any one of claims 1-5 in the treatment of polyoxymethylene wastewater, characterized in that, The polyoxymethylene wastewater contained formaldehyde at a concentration of 250 mg / L, trioxymethylene at a concentration of 200 mg / L, and COD at a concentration of 3500 mg / L.

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