Graded coupling advanced treatment system and method for high-concentration formaldehyde wastewater

Abstract

The invention relates to the technical field of industrial wastewater treatment and recycling, in particular to a graded coupling advanced treatment system and method for high-concentration formaldehyde wastewater. A data acquisition module acquires the formaldehyde concentration of inlet water in real time and transmits the formaldehyde concentration to a detoxification conversion module; the detoxification conversion module controls alkali addition and heating reaction according to the concentration data, so that formaldehyde is converted into an intermediate product; the buffer conditioning module balances water quality through cooling and homogenization; the oxidation promoting module enables the intermediate product to react with ozone to generate small-molecular organic acid under the action of a catalyst; the biochemical mineralization module metabolizes organic matters by using microorganisms; the water outlet verification module detects water quality and triggers a discharge signal. According to the invention, toxicity is reduced step by step through a graded coupling process, biodegradability is improved, the technical problem that direct biochemical treatment of high-concentration formaldehyde wastewater is not feasible is solved, and efficient deep treatment and stable up-to-standard discharge are realized.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and resource utilization technology, and in particular to a graded coupled deep treatment system and method for high-concentration formaldehyde wastewater. Background Technology

[0002] Formaldehyde, a pollutant widely used in various industrial sectors such as chemical engineering, resin synthesis, and pharmaceuticals, is characterized by its recalcitrant nature and high biotoxicity, making it a key focus in industrial wastewater treatment. In particular, formaldehyde wastewater with concentrations exceeding 2000 mg / L exhibits a strong inhibitory and even bactericidal effect on microorganisms, rendering direct biochemical treatment virtually impossible. This characteristic presents a fundamental challenge to wastewater treatment.

[0003] Wastewater treatment is a particularly prominent challenge in the production and use of polyoxymethylene (POM). As one of the five major engineering plastics, POM's production process generates industrial wastewater containing high concentrations of toxic pollutants such as formaldehyde and trioxymethylene. Direct discharge of this wastewater without effective treatment will cause irreversible damage to the soil, water bodies, and other ecological environments, and seriously threaten human health. Therefore, the efficient treatment of POM wastewater has become a crucial issue that urgently needs to be addressed in the chemical environmental protection field. The production process of its core monomers (such as trioxymethylene) inevitably generates formaldehyde-containing process wastewater. Based on its generation method and characteristics, wastewater is mainly divided into two categories: continuous discharge wastewater (continuous discharge) and intermittent discharge wastewater (intermittent discharge). Continuous discharge wastewater mainly originates from stable drainage points in the process, such as process condensate, solvent recovery water, and vacuum drainage, and its flow rate and pollutant concentration are relatively stable. Intermittent discharge wastewater mainly occurs during non-continuous operations, such as reactor cleaning, equipment maintenance flushing, floor washing, and accidental discharge. Its characteristics include irregular discharge, large instantaneous flow, and usually extremely high and drastic fluctuations in formaldehyde concentration.

[0004] Existing technologies for treating high-concentration formaldehyde and polyoxymethylene (POM) wastewater suffer from the following technical challenges: Formaldehyde's strong bioinhibitory properties cause irreversible suppression of microbial metabolic activity at concentrations exceeding 2000 mg / L, leading to the loss of degradation capacity in activated sludge or biofilm systems and rendering direct biochemical treatment processes ineffective. In POM production scenarios, the trioxymethylene component in the wastewater is prone to depolymerization in existing treatment processes, continuously releasing free formaldehyde and causing sudden spikes in formaldehyde concentration within the reaction system, creating toxic shock loads. This fluctuation not only exacerbates the inhibitory effect on microorganisms but also disrupts the dynamic stability of biological treatment, ultimately resulting in low organic matter removal rates and effluent quality exceeding standards, failing to meet environmental protection requirements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a graded coupled deep treatment system and method for high-concentration formaldehyde wastewater, solving the technical problem that direct biochemical treatment of high-concentration formaldehyde wastewater is not feasible due to the strong biological inhibitory properties of formaldehyde.

[0006] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows: In a first aspect, the present invention provides a graded coupled deep treatment system for high-concentration formaldehyde wastewater, including a data acquisition module, a detoxification and conversion module, a buffer conditioning module, an oxidation enhancement module, a biochemical mineralization module, and an effluent verification module; The data acquisition module collects formaldehyde concentration data of the influent in real time and transmits the formaldehyde concentration data to the detoxification conversion module; The detoxification conversion module receives formaldehyde concentration data transmitted by the data acquisition module, calculates the amount of alkali added based on the formaldehyde concentration data, controls the alkali addition unit to adjust the pH value, and controls the heating unit to maintain the reaction temperature, so that formaldehyde reacts to generate intermediate products, and the wastewater after the intermediate products are generated is transported to the buffer conditioning module. The buffer conditioning module receives wastewater from the detoxification and conversion module, reduces the wastewater temperature through a heat exchange device, balances water quality fluctuations through a homogenization tank, and then transports the temperature-reduced and homogenized wastewater to the oxidation enhancement module. The oxidation enhancement module receives wastewater and ozone oxidant from the buffer conditioning module, and reacts the intermediate products with ozone in a solid catalyst bed to generate small molecule organic acids. The wastewater after generating small molecule organic acids is then transported to the biochemical mineralization module. The biochemical mineralization module receives wastewater from the oxidation enhancement module, and in the membrane bioreactor, the microbial community metabolizes organic matter, and then the metabolized wastewater is transported to the effluent verification module. The effluent verification module receives wastewater from the biochemical mineralization module, uses an online formaldehyde analyzer to detect formaldehyde concentration, and uses an online COD monitor to detect COD value. When the formaldehyde concentration and COD value are consistently lower than preset limits, an emission signal is triggered.

[0007] Furthermore, in the high-concentration formaldehyde wastewater graded coupling deep treatment system of the present invention, the data acquisition module includes an online formaldehyde concentration analyzer and a pH sensor. The online formaldehyde concentration analyzer collects the formaldehyde concentration value of the influent, and the pH sensor collects the acidity and alkalinity value of the wastewater. The formaldehyde concentration value and acidity / alkalinity value are transmitted to the central controller. The central controller compares the formaldehyde concentration value with a preset threshold range of 2000 mg / L to 4000 mg / L. When the formaldehyde concentration value is within the preset threshold range, a start signal is generated and transmitted to the detoxification conversion module.

[0008] Furthermore, in the high-concentration formaldehyde wastewater staged coupled deep treatment system of the present invention, the detoxification conversion module includes an alkali addition unit and a heating and stirring unit. The alkali addition unit receives the formaldehyde concentration value transmitted by the data acquisition module. The central controller calculates the amount of sodium hydroxide to be added based on the formaldehyde concentration value and controls the molar ratio of formaldehyde to sodium hydroxide within the range of 0.2:1 to 4:1. The heating and stirring unit maintains the reaction temperature at 85°C to 100°C through a temperature control system. Under stirring conditions, formaldehyde molecules undergo a polymerization reaction to generate hydroxy aldehydes and low-carbon alcohol intermediates, reducing the residual formaldehyde concentration in the effluent to below 1000 mg / L.

[0009] Furthermore, in the high-concentration formaldehyde wastewater graded coupling deep treatment system of the present invention, the buffer conditioning module includes a heat exchange device and a homogenization tank. The heat exchange device exchanges heat with cooling water through a heat exchange surface to reduce the temperature of the wastewater transported by the detoxification conversion module from 85°C to 100°C to 40°C to 50°C. The homogenization tank mixes the effluent from different time periods to balance water quality fluctuations, and the cooled wastewater is then transported to the oxidation enhancement module.

[0010] Furthermore, in the staged coupled deep treatment system for high-concentration formaldehyde wastewater described in this invention, the oxidation enhancement module includes a solid catalyst bed and an ozone dosing unit. The solid catalyst bed is filled with a supported transition metal oxide catalyst, and the ozone dosing unit adjusts the ozone dosage according to the influent chemical oxygen demand (COD) value. The ozone dosage is... Wastewater and ozone react in the catalyst bed. Ozone decomposes to produce hydroxyl radicals. The hydroxyl radicals react with intermediate products to produce formic acid and acetic acid, small molecule organic acids. The BOD to COD ratio of the effluent reaches more than 0.5.

[0011] Furthermore, in the high-concentration formaldehyde wastewater staged coupled deep treatment system of the present invention, the biochemical mineralization module adopts a membrane bioreactor. The membrane bioreactor receives wastewater containing small molecule organic acids such as formic acid and acetic acid from the oxidation enhancement module. The microbial community uses formic acid and acetic acid as substrates for metabolism, and the metabolic products are carbon dioxide and water. The microfiltration membrane module or ultrafiltration membrane module separates the microbial community from the wastewater. The microbial community is retained in the membrane bioreactor, and the separated wastewater is transported to the effluent verification module.

[0012] Furthermore, in the graded coupled deep treatment system for high-concentration formaldehyde wastewater described in this invention, the effluent verification module includes an online formaldehyde analyzer and an online chemical oxygen demand (COD) monitor. The online formaldehyde analyzer detects the formaldehyde concentration in the wastewater transported by the biochemical mineralization module, and the online COD monitor detects the COD value in the wastewater. The formaldehyde concentration value and the COD value are transmitted to the central controller. The central controller compares the formaldehyde concentration value with the 1 mg / L limit and the COD value with the 50 mg / L limit. When the formaldehyde concentration value is lower than 1 mg / L and the COD value is lower than 50 mg / L, the central controller generates a discharge signal. When either value exceeds the limit, the central controller generates a return signal to send the wastewater back to the biochemical mineralization module.

[0013] Furthermore, in the graded coupled deep treatment system for high-concentration formaldehyde wastewater described in this invention, the formaldehyde concentration value of the data acquisition module is also transmitted to the central controller of the detoxification conversion module. The central controller adjusts the reaction time according to the formaldehyde concentration value. When the formaldehyde concentration value is between 2000 mg / L and 3000 mg / L, the reaction time is set to 180 minutes to 300 minutes. When the formaldehyde concentration value is between 3000 mg / L and 4000 mg / L, the reaction time is set to 30 minutes to 180 minutes.

[0014] Furthermore, in the staged coupled deep treatment system for high-concentration formaldehyde wastewater described in this invention, the concentration data of hydroxy aldehydes and low-carbon alcohols intermediate products in the effluent of the detoxification and conversion module are transmitted to the ozone dosing unit of the oxidation enhancement module. The ozone dosing unit adjusts the ozone dosage according to the intermediate product concentration value. When the intermediate product concentration value is between 500 mg / L and 1000 mg / L, the ozone dosage is set to... When the concentration of intermediate products is between 1000 mg / L and 2000 mg / L, the ozone dosage is set as follows: .

[0015] Secondly, the present invention provides a graded coupled deep treatment method for high-concentration formaldehyde wastewater, applied to the graded coupled deep treatment system for the high-concentration formaldehyde wastewater, comprising: Step 1: Collect formaldehyde concentration data in the influent in real time and transmit the formaldehyde concentration data to the detoxification and conversion treatment unit. Step 2: Receive formaldehyde concentration data, calculate the amount of alkali to be added based on the formaldehyde concentration data, control the addition of alkali solution to adjust the pH value, control the heating to maintain the reaction temperature, so that formaldehyde reacts to generate hydroxy aldehydes and low carbon alcohol intermediates, and transport the wastewater after the intermediates are generated to the buffer conditioning treatment unit. Step 3: Receive wastewater from the detoxification and conversion treatment unit, reduce the wastewater temperature through heat exchange, balance water quality fluctuations through homogenization, and then send the cooled and homogenized wastewater to the oxidation enhancement treatment unit. Step 4: Receive wastewater and ozone oxidant from the buffer conditioning unit, and react the intermediate products with ozone in a solid catalyst bed to generate formic acid and acetic acid, which are small molecule organic acids. Then, transport the wastewater after generating the small molecule organic acids to the biochemical mineralization unit. Step 5: Receive wastewater from the oxidation enhancement treatment unit, metabolize organic matter in the membrane bioreactor using microbial flora, and then transport the metabolized wastewater to the effluent verification treatment unit. Step 6: Receive wastewater from the biochemical mineralization treatment unit, detect formaldehyde concentration and chemical oxygen demand (COD) value. When the formaldehyde concentration is below 1 mg / L and the COD value is below 50 mg / L, trigger the discharge signal.

[0016] The beneficial effects of this invention are: The beneficial effects of this invention are as follows: This invention, through the hierarchical coupling of a data acquisition module, a detoxification and conversion module, a buffer conditioning module, an oxidation enhancement module, a biochemical mineralization module, and an effluent verification module, systematically solves the problem of biological inhibition in high-concentration formaldehyde wastewater. The data acquisition module identifies the influent formaldehyde concentration in real time, providing initial parameters for subsequent treatment. The detoxification and conversion module converts formaldehyde into low-toxicity intermediates under alkaline heating conditions, significantly reducing biological toxicity. The buffer conditioning module balances water quality fluctuations through cooling and homogenization, providing stable influent conditions for the oxidation enhancement module. The oxidation enhancement module utilizes ozone catalytic oxidation to break down large molecular intermediates into small-molecule organic acids, greatly improving the biodegradability of the wastewater. The biochemical mineralization module relies on microbial metabolism to achieve complete mineralization of organic matter. The effluent verification module forms a closed-loop quality control, ensuring that the final effluent meets standards. This modular collaborative strategy guides the material flow through data flow, achieving efficient treatment throughout the entire process from toxicity identification to compliant discharge, effectively overcoming the direct inhibition of microorganisms by formaldehyde, and improving the system's resilience and operational economy. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on the accompanying drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of a graded coupled deep treatment method for high-concentration formaldehyde wastewater according to the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The technical solutions provided by various embodiments of this invention will be described in detail below with reference to the accompanying drawings.

[0020] To better understand the purpose of this invention, the invention will now be described in further detail.

[0021] In a first aspect, the present invention provides a graded coupled deep treatment system for high-concentration formaldehyde wastewater, comprising a data acquisition module, a detoxification and conversion module, a buffer conditioning module, an oxidation enhancement module, a biochemical mineralization module, and an effluent verification module connected sequentially along the wastewater flow direction; The data acquisition module collects formaldehyde concentration data of the influent in real time and transmits the formaldehyde concentration data to the detoxification conversion module; The detoxification conversion module receives formaldehyde concentration data transmitted by the data acquisition module, calculates the amount of alkali added based on the formaldehyde concentration data, controls the alkali addition unit to adjust the pH value, and controls the heating unit to maintain the reaction temperature, so that formaldehyde reacts to generate intermediate products, and the wastewater after the intermediate products are generated is transported to the buffer conditioning module. The buffer conditioning module receives wastewater from the detoxification and conversion module, reduces the wastewater temperature through a heat exchange device, balances water quality fluctuations through a homogenization tank, and then transports the temperature-reduced and homogenized wastewater to the oxidation enhancement module. The oxidation enhancement module receives wastewater and ozone oxidant from the buffer conditioning module, and reacts the intermediate products with ozone in a solid catalyst bed to generate small molecule organic acids. The wastewater after generating small molecule organic acids is then transported to the biochemical mineralization module. The biochemical mineralization module receives wastewater from the oxidation enhancement module, and in the membrane bioreactor, the microbial community metabolizes organic matter, and then the metabolized wastewater is transported to the effluent verification module. The effluent verification module receives wastewater from the biochemical mineralization module, uses an online formaldehyde analyzer to detect formaldehyde concentration, and uses an online COD monitor to detect COD value. When the formaldehyde concentration and COD value are consistently lower than preset limits, an emission signal is triggered.

[0022] The staged coupled deep treatment system for high-concentration formaldehyde wastewater achieves step-by-step purification of wastewater through modular design. The system integrates a data acquisition module, a detoxification and transformation module, a buffer conditioning module, an oxidation enhancement module, a biochemical mineralization module, and an effluent verification module sequentially along the wastewater flow direction. Each module is arranged according to the logical order of pollutant speciation and toxicity reduction, with preceding modules providing suitable influent conditions for subsequent modules, forming a synergistic treatment chain.

[0023] The data acquisition module, serving as the system's entry point, is equipped with online monitoring devices such as a formaldehyde concentration analyzer and a pH sensor to collect real-time data on influent formaldehyde concentration and pH levels. The collected data is transmitted to the central controller, which compares it to a preset concentration range to determine whether the wastewater falls into the category of high-concentration formaldehyde wastewater, providing a decision-making basis for subsequent process startup. This module's function is to perform initial water quality identification, ensuring that the system only activates treatment processes for the target wastewater, avoiding resource waste.

[0024] After receiving formaldehyde concentration data from the data acquisition module, the detoxification and conversion module activates the alkali dosing unit and the heating and stirring unit. The central controller calculates the sodium hydroxide dosage based on the formaldehyde concentration, controlling the molar ratio of formaldehyde to alkali within the optimized range, and maintains the reaction temperature through a temperature control system. Under alkaline heating conditions, formaldehyde molecules undergo a polymerization reaction to generate hydroxy aldehydes and lower alcohol intermediates, significantly reducing the biological toxicity of the wastewater. The core of this stage is to convert highly toxic formaldehyde into low-toxicity organic compounds, creating feasibility for biological treatment.

[0025] The buffer conditioning module physically conditions the effluent from the detoxification and conversion module. It lowers the wastewater temperature through heat exchange with a cooling medium via a heat exchanger, and the homogenization tank mixes effluent from different time periods to balance water quality fluctuations. After cooling, the wastewater temperature adapts to the downstream oxidation reaction requirements, and water quality homogenization reduces shock loads. This module plays a crucial role in connecting the upstream and downstream processes, mitigating the impact of the high-temperature effluent from the preceding process on the catalyst, and ensuring the stable operation of the oxidation enhancement module.

[0026] The oxidation enhancement module introduces ozone oxidant and a solid catalyst bed, catalyzing the decomposition of ozone to generate hydroxyl radicals. These radicals attack large molecular intermediates in the buffered and conditioned wastewater, breaking down their chains to form small-molecule organic acids such as formic acid and acetic acid. The reaction significantly improves the biodegradability of the wastewater, bringing the BOD to COD ratio to a level that is bioavailable to microorganisms. This step reconstructs the molecular structure of organic matter through advanced oxidation technology, opening up a biological treatment pathway.

[0027] The biochemical mineralization module employs a membrane bioreactor, where a microbial community metabolizes small-molecule organic acids in the effluent from the oxidation enhancement module, mineralizing organic matter into carbon dioxide and water. Microfiltration or ultrafiltration membrane modules achieve sludge-water separation, retaining microorganisms to maintain a high biomass. This module achieves deep purification through biological methods, economically and efficiently removing all organic matter.

[0028] The effluent verification module is equipped with an online formaldehyde analyzer and an online COD monitor to continuously monitor the effluent quality after biochemical mineralization. The test data is automatically compared with emission standard limits. If the formaldehyde concentration and COD value remain below preset thresholds, an emission signal is triggered; otherwise, a backflow mechanism is activated. This module forms a closed-loop control of the treatment process, ensuring that the final effluent meets emission standards.

[0029] The system's modules are interconnected via data and material flows. The initial judgment from the data acquisition module drives the setting of detoxification and transformation parameters. The characteristics of the effluent after detoxification guide the buffer conditioning operation. The data from the oxidation enhancement module supporting biodegradability improvement supports biochemical mineralization efficiency. The effluent verification results provide feedback on system performance. This hierarchical coupling strategy progressively overcomes the biological inhibition of formaldehyde, achieving fully controllable treatment from toxicity identification to achieving compliant emissions.

[0030] The data acquisition module is equipped with an online formaldehyde concentration analyzer and a pH sensor. The online formaldehyde concentration analyzer uses spectrophotometry to monitor the formaldehyde concentration in the influent in real time, while the pH sensor uses a glass electrode method to detect the acidity or alkalinity of the wastewater. Monitoring data is transmitted to the central controller via analog or digital signals. The central controller runs a comparison algorithm to dynamically compare the formaldehyde concentration value with a preset threshold range. When the formaldehyde concentration falls within the threshold range, the central controller generates a start signal and transmits it to the detoxification conversion module via an industrial communication protocol. This design enables the system to automatically identify high-concentration formaldehyde wastewater, providing accurate initial data support for subsequent treatment processes and avoiding resource waste.

[0031] The detoxification and conversion module integrates an alkali solution dosing unit and a heating and stirring unit. After receiving formaldehyde concentration data from the data acquisition module, the alkali solution dosing unit uses a central controller to calculate the sodium hydroxide dosage based on a preset model, controlling the metering pump to precisely add the alkali solution. The heating and stirring unit is linked to a temperature control system via a jacketed reactor to maintain the reaction temperature within a high-temperature range, and the stirrer employs a turbine design to promote mixing. Under alkaline heating conditions, formaldehyde molecules undergo an aldol condensation reaction to generate hydroxy aldehydes and lower alcohol intermediates, significantly reducing the residual formaldehyde concentration. This process achieves chemical detoxification of formaldehyde, converting highly toxic pollutants into low-toxicity organic compounds, creating feasibility for biological treatment.

[0032] The buffer conditioning module includes a heat exchanger and a homogenization tank. The heat exchanger uses a plate heat exchanger connected to the cooling water circulation system, exchanging heat through metal heat exchange surfaces to cool the high-temperature wastewater to a suitable range. The homogenization tank is designed with a plug-flow structure, utilizing the tank's volumetric effect to mix effluent from different time periods and balance water quality fluctuations. The cooled wastewater has a stable temperature, and water homogenization reduces shock loads, providing stable influent conditions for the oxidation enhancement module. This module plays a crucial role in connecting the preceding and following processes, mitigating the impact of high temperatures on the catalyst and ensuring continuous system operation.

[0033] The oxidation enhancement module includes a solid catalyst bed and an ozone dosing unit. The solid catalyst bed is filled with supported transition metal oxide catalysts, such as manganese oxide supported on an alumina carrier, forming a porous structure to increase the reaction surface area. The ozone dosing unit adjusts the output of the ozone generator according to the estimated chemical oxygen demand (COD) of the influent. Ozone is injected into the catalyst bed through a microporous diffuser, coming into countercurrent contact with the wastewater. On the catalyst surface, ozone decomposes to generate hydroxyl radicals. These radicals attack the molecular chains of intermediate products, generating small-molecule organic acids such as formic acid and acetic acid. After the reaction, the ratio of biological oxygen demand (BOD) to chemical oxygen demand (COD) in the wastewater increases, enhancing its biodegradability.

[0034] The biochemical mineralization module employs a membrane bioreactor (MBR), within which specialized microbial communities, such as aerobic nitrifying bacteria, are cultivated. These microorganisms metabolize by oxidizing and enhancing the small-molecule organic acids in the effluent. The MBR integrates a microfiltration membrane module made of polyvinylidene fluoride (PVDF) with a pore size in the micrometer range, achieving mud-water separation. The microbial metabolic products are carbon dioxide and water; membrane retention maintains high biomass, enhancing treatment efficiency. This module achieves deep mineralization of organic matter through biological methods, offering economic and high efficiency.

[0035] The effluent verification module is equipped with an online formaldehyde analyzer and an online chemical oxygen demand (COD) monitor. The formaldehyde analyzer uses an electrochemical sensor to detect residual formaldehyde concentration, while the COD monitor uses ultraviolet digestion colorimetry to measure COD values. Monitoring data is transmitted to the central controller in real time. The controller executes its judgment logic, automatically comparing the detected values ​​with emission standard limits. When both formaldehyde concentration and COD values ​​remain below the limits, the controller triggers a discharge signal; otherwise, it generates a reflux command, returning the wastewater to the biochemical mineralization module. This design forms a closed-loop control system, ensuring that the effluent meets standards.

[0036] The formaldehyde concentration data from the data acquisition module is also transmitted to the central controller of the detoxification and conversion module. The controller adjusts the reaction time according to the concentration range. For lower concentration ranges, a longer reaction time is set to fully convert formaldehyde; for higher concentration ranges, the reaction time is shortened to avoid excessive energy consumption. Time adjustment is achieved through a programmable logic controller, which works in conjunction with temperature control to optimize reaction efficiency. This data flow enhances the system's adaptability and helps cope with fluctuations in influent water.

[0037] The concentration data of intermediate products in the effluent from the detoxification and conversion module is transmitted to the ozone dosing unit of the oxidation enhancement module. The ozone dosing unit dynamically adjusts the ozone dosage based on the concentration value. When the intermediate product concentration is low, a lower ozone dosage ratio is used to save oxidant costs; when the concentration is high, the ozone dosage is increased to ensure chain breaking effect. The adjustment mechanism is based on a feedback control algorithm, combined with catalyst activity monitoring, to improve oxidation efficiency. This coordinated design optimizes resource utilization and strengthens inter-module synergy.

[0038] Secondly, the present invention provides a graded coupled deep treatment method for high-concentration formaldehyde wastewater, applied to the graded coupled deep treatment system for the high-concentration formaldehyde wastewater, comprising: Step 1: Collect formaldehyde concentration data in the influent in real time and transmit the formaldehyde concentration data to the detoxification and conversion treatment unit. Step 2: Receive formaldehyde concentration data, calculate the amount of alkali to be added based on the formaldehyde concentration data, control the addition of alkali solution to adjust the pH value, control the heating to maintain the reaction temperature, so that formaldehyde reacts to generate hydroxy aldehydes and low carbon alcohol intermediates, and transport the wastewater after the intermediates are generated to the buffer conditioning treatment unit. Step 3: Receive wastewater from the detoxification and conversion treatment unit, reduce the wastewater temperature through heat exchange, balance water quality fluctuations through homogenization, and then send the cooled and homogenized wastewater to the oxidation enhancement treatment unit. Step 4: Receive wastewater and ozone oxidant from the buffer conditioning unit, and react the intermediate products with ozone in a solid catalyst bed to generate formic acid and acetic acid, which are small molecule organic acids. Then, transport the wastewater after generating the small molecule organic acids to the biochemical mineralization unit. Step 5: Receive wastewater from the oxidation enhancement treatment unit, metabolize organic matter in the membrane bioreactor using microbial flora, and then transport the metabolized wastewater to the effluent verification treatment unit. Step 6: Receive wastewater from the biochemical mineralization treatment unit, detect formaldehyde concentration and chemical oxygen demand (COD) value. When the formaldehyde concentration is below 1 mg / L and the COD value is below 50 mg / L, trigger the discharge signal.

[0039] The staged coupled deep treatment method for high-concentration formaldehyde wastewater begins with the real-time identification of influent characteristics by the water quality monitoring and treatment unit. This unit is equipped with an online formaldehyde concentration analyzer and a pH sensor, continuously measuring the formaldehyde concentration in the influent based on spectrophotometry or electrochemical methods, while simultaneously monitoring the wastewater's pH and temperature. The collected data is transmitted to a central controller via signal transmission lines. The controller compares the measured formaldehyde concentration values ​​with preset threshold ranges to determine whether the wastewater belongs to the high-concentration formaldehyde wastewater category, providing initial parameter settings for subsequent detoxification and conversion treatment units.

[0040] After receiving formaldehyde concentration data from the water quality monitoring and treatment unit, the central controller initiates the alkali dosing and heating control program of the detoxification and conversion treatment unit. Based on the formaldehyde concentration value, the controller calculates the sodium hydroxide dosage using a built-in algorithm, driving the metering pump to control the alkali dosing and ensuring the molar ratio of formaldehyde to sodium hydroxide is within the optimized range. The heating and stirring unit maintains the reaction temperature through a jacketed reactor, promoting mixing of wastewater and alkali under stirring conditions. In the alkaline heating environment, formaldehyde molecules undergo aldol condensation, transforming into low-toxicity intermediates such as hydroxy aldehydes and lower alcohols, significantly reducing the residual formaldehyde concentration and completing chemical detoxification and pollutant transformation.

[0041] The effluent from the detoxification and conversion treatment unit flows into the buffer conditioning treatment unit, where it undergoes physical conditioning through a heat exchanger and a homogenization tank. The heat exchanger, employing a plate or tubular structure, is connected to the circulating cooling water system and exchanges heat through metal heat exchange surfaces, reducing the high-temperature wastewater to a suitable temperature range. The homogenization tank utilizes volumetric effects to mix effluent from different time periods, balancing water quality fluctuations and providing stable temperature and uniform water quality influent conditions for the subsequent oxidation and enhancement treatment unit, thus preventing shock loads from affecting the catalytic reaction efficiency.

[0042] After buffering and conditioning, the wastewater enters the oxidation and enhancement treatment unit, where it works synergistically with ozone oxidants. The ozone generator adjusts the ozone dosage based on the estimated chemical oxygen demand (COD) of the influent. Ozone gas is injected into a reaction bed packed with a solid catalyst through a microporous diffuser. The catalyst is a supported transition metal oxide, providing a porous surface to promote ozone decomposition and the generation of hydroxyl radicals. These free radicals attack the large molecular intermediates in the wastewater, breaking them down into smaller organic acids such as formic acid and acetic acid. This increases the biodegradability of the wastewater to a level that is usable by microorganisms, achieving a fundamental improvement in its biodegradability.

[0043] The effluent from the oxidation enhancement treatment unit is introduced into the biochemical mineralization treatment unit, where it undergoes deep purification using a membrane bioreactor. A specialized microbial community is trained within the reactor to metabolize organic matter into carbon dioxide and water using small-molecule organic acids from the influent as a carbon source. Microfiltration or ultrafiltration membrane modules achieve sludge-water separation; the purified water permeates through the membrane as effluent, while activated sludge is completely retained, maintaining high biomass within the reactor and improving treatment stability and efficiency.

[0044] The final effluent enters the effluent verification and treatment unit, where an online formaldehyde analyzer and an online chemical oxygen demand (COD) monitor continuously detect water quality indicators. The analyzer uses an electrochemical sensor to detect formaldehyde concentration, while the monitor uses ultraviolet digestion colorimetry to measure COD values. The detection data is transmitted to the control system in real time and automatically compared with emission standard limits. When both formaldehyde concentration and COD values ​​remain below the limits, the system generates a discharge signal allowing effluent discharge; if either indicator exceeds the limit, a backflow command is triggered, sending the wastewater back to the biochemical mineralization treatment unit for reprocessing, forming a closed-loop quality control system. This invention guides the material flow through data flow, progressively overcoming the biological inhibition of formaldehyde, and achieving a complete path from toxicity identification to compliant discharge.

[0045] The staged coupled deep treatment system for high-concentration formaldehyde wastewater includes a regulating tank, a primary biodegradability-optimized saccharification reactor, a first intermediate water tank, a secondary hydroxyl radical directional oxidation reactor, a second intermediate water tank, a tertiary high-efficiency biochemical reactor, and an effluent tank, connected sequentially along the wastewater flow direction. The regulating tank is used for homogenization, flow rate equalization, and temperature regulation of the wastewater, achieving stable influent flow and concentration to provide balanced conditions for subsequent treatment. The primary biodegradability-optimized saccharification reactor is equipped with an alkali dosing system, a heating and temperature control device, and a stirring device. The alkali dosing system automatically calculates and adds sodium hydroxide based on the influent formaldehyde concentration, controlling the molar ratio of formaldehyde to sodium hydroxide within the range of 0.2:1 to 4:1. The heating and temperature control device maintains the reaction temperature within a precise range of 85℃, 95℃, or 100℃ using steam or heat transfer oil. The stirring device promotes mixing. The process involves polymerizing formaldehyde under alkaline conditions to produce low-toxicity intermediates such as hydroxy aldehydes and lower alcohols. The first intermediate water tank acts as a buffer unit, using a heat exchanger (such as a plate heat exchanger) to lower the temperature of the saccharification effluent from high temperatures to 40-50°C. The tank's volumetric effect balances water quality fluctuations, providing stable influent for the oxidation stage. The second-stage hydroxyl radical directional oxidation reactor is filled with a transition metal oxide composite catalyst (such as supported manganese oxide) and connected to an ozone generation system. The ozone dosage is adjusted according to the influent COD value. Within the specified range, wastewater and ozone come into countercurrent or cocurrent contact within the catalyst bed, with a residence time of 40-60 minutes. Catalytic ozone decomposition generates hydroxyl radicals, which break down large molecular intermediates into smaller organic acids such as formic acid and acetic acid, significantly increasing the B / C ratio to above 0.5. A second intermediate tank further buffers the oxidized effluent, ensuring uniform water quality. The tertiary high-efficiency bioreactor is preferably a membrane bioreactor (MBR), where microbial communities metabolize using small organic acids as substrates. The hydraulic retention time is controlled at 12-20 hours, and microfiltration or ultrafiltration membrane modules achieve sludge-water separation, retaining microorganisms to maintain high biomass and thoroughly mineralizing organic matter. The effluent tank is used for final water collection and is equipped with online monitoring equipment. Through modular integration, the system achieves synergy between data flow and material flow. For example, water quality monitoring data drives the setting of saccharification parameters, and data on the biodegradability of the oxidized effluent supports biochemical efficiency, forming a closed-loop control.

[0046] In practical application, the staged coupled deep treatment method for high-concentration formaldehyde wastewater involves a primary biodegradability-optimized saccharification pretreatment. Wastewater with formaldehyde concentrations of 2000 mg / L to 4000 mg / L is pumped into the saccharification reactor. In the presence of an alkaline catalyst (such as NaOH), the alkali dosage is calculated based on real-time monitoring of the formaldehyde concentration, controlling the molar ratio of formaldehyde to NaOH within the range of 0.2:1 to 4:1. The reaction temperature is precisely maintained at 85℃, 95℃, or 100℃, and the saccharification time is set to 30-300 minutes based on concentration fluctuations (e.g., for concentrations of 2000-3000 mg / L). (Setting the time to 180-300 minutes for concentrations of g / L, and 30-180 minutes for concentrations of 3000-4000 mg / L). Under stirring conditions, formaldehyde molecules are directionally converted into hydroxy aldehydes and lower alcohols through the Cannizaro reaction and aldol condensation reaction, reducing the residual formaldehyde concentration to below 1000 mg / L and initially reducing biotoxicity. S2 secondary hydroxyl radical catalytic oxidation breaks down the chain, introducing the saccharification effluent into the catalytic oxidation reactor. The ozone dosage is adjusted according to the concentration of intermediate products in the saccharification effluent (e.g., 500-2000 mg / L). (Setting the time to 30-180 minutes for intermediate product concentrations of 500-1000 mg / L). At a concentration of 1000-2000 mg / L, ozone decomposes under the action of a solid catalyst to generate hydroxyl radicals, which attack large molecular chains and generate small molecule organic acids. The residence time is 40-60 minutes, the pH is controlled at 7.2-8.0, and the temperature is 40-50℃, increasing the B / C ratio to above 0.5, thus fundamentally improving biodegradability. The S3 three-stage biological deep mineralization involves introducing the oxidized wastewater into a membrane bioreactor with a hydraulic retention time of 12-20 hours. Microbial communities (such as aerobic nitrifying bacteria) metabolize small molecule organic matter, and the metabolic products are [unspecified]. Membrane separation ensures sludge retention, resulting in effluent formaldehyde concentrations below 0.5 mg / L and COD consistently below 50 mg / L. The final effluent is monitored online by an effluent verification module. If the indicators consistently meet the standards, a discharge signal is triggered; otherwise, the wastewater is returned for reprocessing. This method, through graded coupling, progressively reduces toxicity and improves biodegradability, solving the technical problem that direct biological treatment of high-concentration formaldehyde wastewater is infeasible. For example, in wastewater with an initial formaldehyde concentration of 2505 mg / L, by controlling the HCHO:NaOH molar ratio at 0.2:1, the temperature at 85℃, and the saccharification time at 180 minutes, the residual formaldehyde concentration was reduced to 1050 mg / L, and the B / C ratio was increased to 0.22. In the subsequent oxidation stage, ozone was added, and after 40 minutes of reaction, the formaldehyde concentration was reduced to 192 mg / L, and the B / C ratio reached 0.62. In the biological stage, the HRT was 12 hours, and the effluent COD was below 50 mg / L.

[0047] This embodiment investigates the impact of key parameters in the saccharification process on the treatment efficiency of high-concentration formaldehyde wastewater through systematic laboratory experiments. The experiment uses response surface methodology as its design basis, with formaldehyde removal rate and the B / C ratio (the ratio of biochemical oxygen demand to chemical oxygen demand) as the core evaluation indicators, examining three key parameters: Independent variable A: molar ratio of formaldehyde to sodium hydroxide (HCHO:NaOH), with 7 levels: 0.2:1, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, and 4:1.

[0048] Independent variable B: reaction temperature, with 3 levels: 85℃, 95℃, and 100℃.

[0049] Independent variable C: saccharification time, set at 15 levels: 30 min, 35 min, 40 min, 50 min, 55 min, 60 min, 70 min, 85 min, 90 min, 100 min, 130 min, 150 min, 180 min, 240 min, 300 min.

[0050] The experiment used prepared high-concentration formaldehyde wastewater (initial formaldehyde concentration range 2000-4000 mg / L), and representative experiments were conducted in the saccharification reactor as follows: Example 1-1: Simulated wastewater with an initial formaldehyde concentration of 2505 mg / L was used. NaOH was added to the reactor, controlling the HCHO:NaOH molar ratio at 0.2:1. The reaction system was heated to 85°C and maintained at a constant temperature for saccharification reactions at 60 minutes, 180 minutes, and 300 minutes, respectively. The effluent parameters were measured: after 60 minutes of saccharification, the residual formaldehyde concentration was 2200 mg / L, BOD was 0.42 g / L, and the B / C ratio was 0.19; after 180 minutes of saccharification, the residual formaldehyde concentration decreased to 1050 mg / L, BOD increased to 0.55 g / L, and the B / C ratio improved to 0.22; after 300 minutes of saccharification, the residual formaldehyde concentration decreased to 850 mg / L, BOD was 0.48 g / L, and the B / C ratio was 0.15.

[0051] Examples 1-2: Simulated wastewater with an initial formaldehyde concentration of 2995 mg / L was used. The HCHO:NaOH molar ratio was controlled at 0.5:1, and the saccharification reaction was carried out at 85℃. Results: After 60 minutes of saccharification, the residual formaldehyde concentration was 1850 mg / L, BOD was 0.52 g / L, and the B / C ratio was 0.18; after 150 minutes of saccharification, the residual formaldehyde concentration decreased to 950 mg / L, BOD was 0.68 g / L, and the B / C ratio was 0.24; after 240 minutes of saccharification, the residual formaldehyde concentration decreased to 835 mg / L, BOD was 0.60 g / L, and the B / C ratio was 0.16.

[0052] Examples 1-3: Simulated wastewater with an initial formaldehyde concentration of 3355 mg / L was used. The HCHO:NaOH molar ratio was controlled at 1:1, and the saccharification reaction was carried out at 95℃. Results: After 40 minutes of saccharification, the residual formaldehyde concentration was 1750 mg / L, BOD was 0.58 g / L, and the B / C ratio was 0.20; after 90 minutes of saccharification, the residual formaldehyde concentration decreased to 980 mg / L, BOD increased to 0.72 g / L, and the B / C ratio increased to 0.25; after 130 minutes of saccharification, the residual formaldehyde concentration decreased to 850 mg / L, BOD was 0.65 g / L, and the B / C ratio decreased to 0.13.

[0053] Examples 1-4: Simulated wastewater with an initial formaldehyde concentration of 3816 mg / L was used. The HCHO:NaOH molar ratio was controlled at 1.5:1, and saccharification experiments were conducted at 95℃. Results: After 40 minutes of saccharification, the residual formaldehyde concentration was 1650 mg / L, BOD was 0.65 g / L, and the B / C ratio was 0.19; after 70 minutes of saccharification, the residual formaldehyde concentration decreased to 920 mg / L, BOD was 0.82 g / L, and the B / C ratio increased to 0.23; after 100 minutes of saccharification, the residual formaldehyde concentration decreased to 830 mg / L, BOD was 0.75 g / L, and the B / C ratio decreased to 0.11.

[0054] Examples 1-5: Simulated wastewater with an initial formaldehyde concentration of 4002 mg / L was used. The HCHO:NaOH molar ratio was controlled at 2:1, and the saccharification reaction was carried out at 100℃. Results: After 35 minutes of saccharification, the residual formaldehyde concentration was 1580 mg / L, BOD was 0.68 g / L, and the B / C ratio was 0.17; after 60 minutes of saccharification, the residual formaldehyde concentration significantly decreased to 900 mg / L, BOD was 0.82 g / L, and the B / C ratio reached 0.22; after 85 minutes of saccharification, the residual formaldehyde concentration decreased to 820 mg / L, BOD was 0.78 g / L, and the B / C ratio decreased to 0.08.

[0055] Examples 1-6: Simulated wastewater with an initial formaldehyde concentration of 3754 mg / L was used. The HCHO:NaOH molar ratio was controlled at 3:1, and the saccharification reaction was carried out at 100℃. Results: After 30 minutes of saccharification, the residual formaldehyde concentration was 1250 mg / L, BOD was 0.78 g / L, and the B / C ratio was 0.21; after 55 minutes of saccharification, the residual formaldehyde concentration decreased to 900 mg / L, BOD was 0.95 g / L, and the B / C ratio reached 0.25; after 90 minutes of saccharification, the residual formaldehyde concentration decreased to 810 mg / L, BOD was 0.83 g / L, and the B / C ratio decreased to 0.10.

[0056] Examples 1-7: Simulated wastewater with an initial formaldehyde concentration of 3611 mg / L was used. The HCHO:NaOH molar ratio was controlled at 4:1, and the saccharification reaction was carried out at 100℃. Results: After 50 minutes of saccharification, the residual formaldehyde concentration was 1148 mg / L, BOD was 0.82 g / L, and the B / C ratio was 0.20; after 85 minutes of saccharification, the residual formaldehyde concentration decreased to 872 mg / L, BOD decreased to 0.73 g / L, and the B / C ratio decreased to 0.09.

[0057] The above experiments show that by optimizing the molar ratio, temperature, and saccharification time, saccharification treatment can effectively reduce the formaldehyde concentration to below 1000 mg / L and initially improve the B / C ratio, laying the foundation for subsequent oxidation treatment. Optimal parameter range: molar ratio 0.2:1-4:1, temperature 85-100℃, saccharification time 30-300 minutes.

[0058] Example 2: Ozone catalytic oxidation deep treatment experiment; This embodiment aims to verify the advanced treatment effect of ozone catalytic oxidation on saccharification effluent, clarify its role in improving biodegradability (B / C ratio), and optimize ozone dosing parameters. The experiment was conducted in a catalytic oxidation reactor using a solid catalyst (supported transition metal oxide). The ozone dosage was adjusted (range) according to the influent COD value. The reaction temperature was controlled at 40-50℃, the pH at 7.2-8.0, and the contact time at 40-60 minutes. Representative experiments are as follows: Example 2-1: Ozone was added to saccharification effluent with a formaldehyde concentration of 823 mg / L at a dosage ratio of 1:1, and the reaction was carried out at 40°C and pH=7.5 for 40 minutes. Results: The formaldehyde concentration decreased to 192 mg / L, COD was 362 mg / L, BOD was 224 mg / L, and the B / C ratio increased to 0.62.

[0059] Example 2-2: Ozone was added to saccharification effluent with a formaldehyde concentration of 725 mg / L at a dosage ratio of 0.38 g O3 / g COD, and the reaction was carried out at 40°C and pH=7.2 for 40 minutes. Results: The formaldehyde concentration decreased to 158 mg / L, COD was 320 mg / L, BOD was 195 mg / L, and the B / C ratio was 0.61.

[0060] Examples 2-3: Adding formaldehyde to saccharified water with a formaldehyde concentration of 780 mg / L, Ozone was added at a specific dosage ratio, and the reaction was carried out at 38℃ and pH=7.2 for 40 minutes. Results: The formaldehyde concentration decreased to 192 mg / L, COD was 362 mg / L, BOD was 224 mg / L, and the B / C ratio was 0.62.

[0061] Examples 2-4: Adding formaldehyde to saccharified water with a formaldehyde concentration of 1685 mg / L, Ozone was added at a specific dosage, and the reaction was carried out at 40℃ and pH=7.5 for 40 minutes. Results: Formaldehyde concentration decreased to 598 mg / L, COD was 765 mg / L, BOD was 382 mg / L, and B / C ratio was 0.50.

[0062] Examples 2-5: Adding formaldehyde to saccharified water with a formaldehyde concentration of 2150 mg / L, Ozone was added at a specific dosage, and the reaction was carried out at 40℃ and pH=7.2 for 40 minutes. Results: The formaldehyde concentration decreased to 615 mg / L, COD was 780 mg / L, BOD was 390 mg / L, and the B / C ratio was 0.50.

[0063] Examples 2-6: Adding formaldehyde to saccharified water with a formaldehyde concentration of 837 mg / L, Ozone was added at a specific dosage ratio, and the reaction was carried out at 45℃ and pH=8.0 for 50 minutes. Results: Formaldehyde concentration decreased to 121 mg / L, COD was 332 mg / L, BOD was 221 mg / L, and the B / C ratio increased to 0.67.

[0064] Examples 2-7: Ozone was added to saccharification effluent with a formaldehyde concentration of 910 mg / L at a dosage ratio of 0.46 g O3 / g COD, and the reaction was carried out at 45°C and pH=7.3 for 50 minutes. Results: The formaldehyde concentration decreased to 245 mg / L, COD was 430 mg / L, BOD was 279 mg / L, and the B / C ratio was 0.65.

[0065] Examples 2-8: Adding formaldehyde to saccharified water with a formaldehyde concentration of 1562 mg / L, Ozone was added at a specific dosage ratio, and the reaction was carried out at 45℃ and pH=7.6 for 50 minutes. Results: The formaldehyde concentration decreased to 372 mg / L, COD was 592 mg / L, BOD was 332 mg / L, and the B / C ratio was 0.56.

[0066] Examples 2-9: Adding formaldehyde to saccharified water with a formaldehyde concentration of 1823 mg / L, Ozone was added at a specific dosage, and the reaction was carried out at 45℃ and pH=7.5 for 50 minutes. Results: Formaldehyde concentration decreased to 538 mg / L, COD was 712 mg / L, BOD was 378 mg / L, and B / C ratio was 0.53.

[0067] Examples 2-10: Adding formaldehyde to saccharified water with a formaldehyde concentration of 875 mg / L, Ozone was added at a specific dosage ratio, and the reaction was carried out at 50℃ and pH=7.2 for 60 minutes. Results: Formaldehyde concentration decreased to 95 mg / L, COD was 325 mg / L, BOD was 195 mg / L, and B / C ratio was 0.60.

[0068] Example 2-11: Adding formaldehyde to saccharification effluent with a formaldehyde concentration of 895 mg / L, Ozone was added at a specific dosage, and the reaction was carried out at 50℃ and pH=7.4 for 60 minutes. Results: Formaldehyde concentration decreased to 78 mg / L, COD was 305 mg / L, BOD was 218 mg / L, and B / C ratio was 0.71.

[0069] Example 2-12: Adding formaldehyde to saccharified water with a formaldehyde concentration of 915 mg / L, Ozone was added at a specific dosage ratio, and the reaction was carried out at 50℃ and pH=8.0 for 60 minutes. Results: Formaldehyde concentration decreased to 245 mg / L, COD was 430 mg / L, BOD was 279 mg / L, and the B / C ratio increased to 0.65.

[0070] Example 2-13: Adding formaldehyde to saccharified water with a formaldehyde concentration of 1638 mg / L, Ozone was added at a specific dosage, and the reaction was carried out at 50℃ and pH=7.6 for 60 minutes. Results: The formaldehyde concentration decreased to 305 mg / L, COD was 562 mg / L, BOD was 315 mg / L, and the B / C ratio was 0.56.

[0071] Example 2-14: Adding formaldehyde to saccharification effluent with a formaldehyde concentration of 2012 mg / L, Ozone was added at a specific dosage, and the reaction was carried out at 50℃ and pH=7.5 for 60 minutes. Results: The formaldehyde concentration decreased to 468 mg / L, COD was 718 mg / L, BOD was 368 mg / L, and the B / C ratio was 0.51.

[0072] Example 2-15: Adding formaldehyde to saccharified water with a formaldehyde concentration of 2400 mg / L, Ozone was added at a specific dosage ratio, and the reaction was carried out at 50℃ and pH=7.5 for 60 minutes. Results: Formaldehyde concentration decreased to 540 mg / L, COD was 890 mg / L, BOD was 445 mg / L, and B / C ratio was 0.50.

[0073] The above experiments demonstrate that ozone catalytic oxidation can significantly improve the biodegradability of wastewater (B / C ratio exceeding 0.5), making small-molecule organic matter more easily degraded by microorganisms. The optimal ozone dosage is... Combined with saccharification pretreatment, efficient and in-depth treatment of formaldehyde wastewater can be achieved.

[0074] The core challenge in treating high-concentration formaldehyde wastewater lies in the irreversible inhibition of microbial metabolic activity when formaldehyde concentrations exceed 2000 mg / L, leading to the failure of existing biochemical treatment processes. Particularly in the production of polyoxymethylene (POM), the formaldehyde concentration in intermittently discharged wastewater fluctuates drastically, and the trioxymethylene component easily depolymerizes, releasing free formaldehyde and creating a toxic shock load. This invention addresses this technical challenge by proposing a staged, coupled deep treatment scheme. Through a modular system, toxicity is reduced step-by-step and biodegradability is improved, achieving stable wastewater discharge that meets standards.

[0075] The system is implemented based on a data acquisition module, a detoxification and conversion module, a buffer conditioning module, an oxidation enhancement module, a biochemical mineralization module, and an effluent verification module connected sequentially along the wastewater flow direction. An online formaldehyde concentration analyzer and a pH sensor are installed at the inlet of the data acquisition module to collect real-time data on influent formaldehyde concentration and pH. The central controller compares the formaldehyde concentration value with a preset threshold range and generates a start signal, which is then transmitted to the detoxification and conversion module. Upon receiving the signal, the detoxification and conversion module's alkali dosing unit calculates the sodium hydroxide dosage based on the formaldehyde concentration, controlling the formaldehyde-to-sodium hydroxide molar ratio within an optimized range. The heating and stirring unit maintains the reaction temperature through a temperature control system, promoting the polymerization reaction of formaldehyde molecules to generate hydroxy aldehydes and lower alcohol intermediates under stirring conditions. The buffer conditioning module is connected to a cooling water circulation system via a heat exchange device to reduce the wastewater temperature, and the equalization tank balances water quality fluctuations, providing stable influent conditions for the oxidation enhancement module. In the oxidation enhancement module, a solid catalyst bed is filled with supported transition metal oxide catalysts. The ozone dosing unit adjusts the ozone dosage according to the influent chemical oxygen demand (COD). Wastewater reacts with ozone on the catalyst surface, and hydroxyl radicals attack the intermediate product molecular chains to generate small-molecule organic acids such as formic acid and acetic acid. The biochemical mineralization module uses a membrane bioreactor, where microbial communities metabolize using small-molecule organic acids as substrates. Microfiltration or ultrafiltration membrane modules achieve sludge-water separation, retaining microorganisms to maintain high biomass. The effluent validation module uses an online formaldehyde analyzer and an online COD monitor to detect the final effluent. The central controller compares the effluent to emission limits and triggers emission or recirculation signals.

[0076] The implementation of the method begins with the real-time identification of influent characteristics by the water quality monitoring and treatment unit. An online formaldehyde concentration analyzer continuously measures the concentration using spectrophotometry, while a pH sensor monitors the acidity and alkalinity. The data is transmitted to a central controller to determine the start and stop of the treatment. The detoxification and conversion treatment unit, based on the concentration data, drives the addition of alkaline solution and controls the reaction temperature and time, allowing formaldehyde to be directionally converted into low-toxicity intermediates under alkaline heating. For example, in a laboratory pilot test, wastewater with an initial formaldehyde concentration of 2505 mg / L was treated by controlling the formaldehyde to sodium hydroxide molar ratio at 0.2:1, the reaction temperature at 85°C, and the saccharification time at 180 minutes, resulting in a residual formaldehyde concentration below 1050 mg / L. The buffer conditioning treatment unit cools the wastewater using a plate heat exchanger and mixes effluent from different time periods in a homogenization tank, reducing the temperature from a high-temperature range to a suitable range for the oxidation reaction. The oxidation enhancement treatment unit introduces ozone oxidant, with the ozone dosage adjusted based on the estimated chemical oxygen demand (COD) of the saccharified effluent. The reaction takes place in a solid catalyst bed for 40 to 60 minutes, increasing the biodegradability ratio of the wastewater. The example shows that saccharified effluent with a formaldehyde concentration of 823 mg / L, reacted with an ozone dosage of 0.43 g / g COD, resulting in a biodegradation ratio of 0.62. The biochemical mineralization treatment unit operates in a membrane bioreactor with a hydraulic retention time controlled between 12 and 20 hours, where microbial metabolism mineralizes organic matter into carbon dioxide and water. The effluent validation treatment unit continuously monitors formaldehyde concentration and COD values; when these values ​​remain consistently below preset limits, the system completes the treatment process.

[0077] The data flow of this invention runs through all modules. The initial judgment of the water quality monitoring module drives the setting of detoxification and conversion parameters; the characteristics of the saccharification effluent guide the buffer conditioning operation; the data from the oxidation enhancement module supporting the biodegradability improvement supports the biochemical mineralization efficiency; and finally, the effluent verification forms a closed-loop control. This hierarchical coupling strategy overcomes the biological inhibition of formaldehyde step by step. Relying on the synergy of chemical detoxification, catalytic oxidation, and biomineralization, it makes high-concentration formaldehyde wastewater biochemically treatable and is applicable to both continuous and intermittent wastewater discharge scenarios in polyoxymethylene production.

Claims

1. A high-concentration formaldehyde wastewater grading coupled deep treatment system, characterized in that, It includes a data acquisition module, a detoxification and conversion module, a buffer conditioning module, an oxidation enhancement module, a biochemical mineralization module, and an effluent verification module; The data acquisition module collects formaldehyde concentration data of the influent in real time and transmits the formaldehyde concentration data to the detoxification conversion module; The detoxification conversion module receives formaldehyde concentration data transmitted by the data acquisition module, calculates the amount of alkali added based on the formaldehyde concentration data, controls the alkali addition unit to adjust the pH value, and controls the heating unit to maintain the reaction temperature, so that formaldehyde reacts to generate intermediate products, and the wastewater after the intermediate products are generated is transported to the buffer conditioning module. The buffer conditioning module receives wastewater from the detoxification and conversion module, reduces the wastewater temperature through a heat exchange device, balances water quality fluctuations through a homogenization tank, and then transports the temperature-reduced and homogenized wastewater to the oxidation enhancement module. The oxidation enhancement module receives wastewater and ozone oxidant from the buffer conditioning module, and reacts the intermediate products with ozone in a solid catalyst bed to generate small molecule organic acids. The wastewater after generating small molecule organic acids is then transported to the biochemical mineralization module. The biochemical mineralization module receives wastewater from the oxidation enhancement module, and in the membrane bioreactor, the microbial community metabolizes organic matter, and then the metabolized wastewater is transported to the effluent verification module. The effluent verification module receives wastewater from the biochemical mineralization module, uses an online formaldehyde analyzer to detect formaldehyde concentration, and uses an online COD monitor to detect COD value. When the formaldehyde concentration and COD value are consistently lower than preset limits, an emission signal is triggered.

2. The hierarchical coupling advanced treatment system for high-concentration formaldehyde wastewater according to claim 1, characterized in that, The data acquisition module includes an online formaldehyde concentration analyzer and a pH sensor. The online formaldehyde concentration analyzer collects the formaldehyde concentration value of the influent, and the pH sensor collects the acidity and alkalinity value of the wastewater. The formaldehyde concentration value and acidity and alkalinity value are transmitted to the central controller. The central controller compares the formaldehyde concentration value with a preset threshold range of 2000 mg / L to 4000 mg / L. When the formaldehyde concentration value is within the preset threshold range, a start signal is generated and transmitted to the detoxification conversion module.

3. The hierarchical coupling advanced treatment system for high-concentration formaldehyde wastewater according to claim 2, characterized in that, The detoxification and conversion module includes an alkali addition unit and a heating and stirring unit. The alkali addition unit receives the formaldehyde concentration value transmitted by the data acquisition module. The central controller calculates the amount of sodium hydroxide to be added based on the formaldehyde concentration value and controls the molar ratio of formaldehyde to sodium hydroxide within the range of 0.2:1 to 4:

1. The heating and stirring unit maintains the reaction temperature at 85°C to 100°C through a temperature control system. Under stirring conditions, formaldehyde molecules undergo a polymerization reaction to generate hydroxy aldehydes and low-carbon alcohol intermediates, reducing the residual formaldehyde concentration in the effluent to below 1000 mg / L.

4. The hierarchical coupling advanced treatment system for high-concentration formaldehyde wastewater according to claim 3, characterized in that, The buffer conditioning module includes a heat exchange device and a homogenization tank. The heat exchange device exchanges heat with cooling water through a heat exchange surface, reducing the temperature of the wastewater transported by the detoxification and conversion module from 85°C to 100°C to 40°C to 50°C. The homogenization tank mixes the effluent from different time periods to balance water quality fluctuations, and then transports the cooled wastewater to the oxidation enhancement module.

5. The staged coupled deep treatment system for high-concentration formaldehyde wastewater according to claim 4, characterized in that, The oxidation promotion module comprises a solid catalyst bed and an ozone dosing unit, the solid catalyst bed is filled with a supported transition metal oxide catalyst, the ozone dosing unit adjusts the ozone dosage according to the chemical oxygen demand value of the influent, and the ozone dosage is The wastewater and the ozone are contacted and reacted in the catalyst bed, the ozone is decomposed to generate hydroxyl radicals, the hydroxyl radicals react with intermediate products to generate formic acid and acetic acid small-molecule organic acids, and the BOD / COD ratio of the effluent reaches 0.5 or more.

6. The hierarchical coupling advanced treatment system for high-concentration formaldehyde wastewater according to claim 5, characterized in that, The biochemical mineralization module uses a membrane bioreactor. The membrane bioreactor receives wastewater containing formic acid and acetic acid, small molecule organic acids, from the oxidation enhancement module. The microbial community uses formic acid and acetic acid as substrates for metabolism, and the metabolic products are carbon dioxide and water. The microfiltration membrane module or ultrafiltration membrane module separates the microbial community from the wastewater. The microbial community is retained in the membrane bioreactor, and the separated wastewater is transported to the effluent verification module.

7. The hierarchical coupling advanced treatment system for high-concentration formaldehyde wastewater according to claim 6, characterized in that, The effluent verification module includes an online formaldehyde analyzer and an online chemical oxygen demand (COD) monitor. The online formaldehyde analyzer detects the formaldehyde concentration in the wastewater transported by the biochemical mineralization module, and the online COD monitor detects the COD value in the wastewater. The formaldehyde concentration and COD values ​​are transmitted to the central controller. The central controller compares the formaldehyde concentration value with the 1 mg / L limit and the COD value with the 50 mg / L limit. When the formaldehyde concentration is below 1 mg / L and the COD value is below 50 mg / L, the central controller generates a discharge signal. When either value exceeds the limit, the central controller generates a return signal to send the wastewater back to the biochemical mineralization module.

8. The hierarchical coupling advanced treatment system for high-concentration formaldehyde wastewater according to claim 7, characterized in that, The formaldehyde concentration value from the data acquisition module is also transmitted to the central controller of the detoxification conversion module. The central controller adjusts the reaction time according to the formaldehyde concentration value. When the formaldehyde concentration value is between 2000 mg / L and 3000 mg / L, the reaction time is set to 180 to 300 minutes. When the formaldehyde concentration value is between 3000 mg / L and 4000 mg / L, the reaction time is set to 30 to 180 minutes.

9. The staged coupled deep treatment system for high-concentration formaldehyde wastewater according to claim 8, characterized in that, The intermediate product concentration data of hydroxy aldehyde and low carbon alcohol in the effluent of the detoxification conversion module is transmitted to the ozone adding unit of the oxidation promotion module, the ozone adding unit adjusts the ozone adding amount according to the intermediate product concentration value, when the intermediate product concentration value is 500mg / L to 1000mg / L, the ozone adding amount is set to , when the intermediate product concentration value is 1000mg / L to 2000mg / L, the ozone adding amount is set to .

10. A staged coupled deep treatment method for high-concentration formaldehyde wastewater, applied to the staged coupled deep treatment system for high-concentration formaldehyde wastewater as described in any one of claims 1 to 9, characterized in that, include: Step 1: Collect formaldehyde concentration data in the influent in real time and transmit the formaldehyde concentration data to the detoxification and conversion treatment unit. Step 2: Receive formaldehyde concentration data, calculate the amount of alkali to be added based on the formaldehyde concentration data, control the addition of alkali solution to adjust the pH value, control the heating to maintain the reaction temperature, so that formaldehyde reacts to generate hydroxy aldehydes and low carbon alcohol intermediates, and transport the wastewater after the intermediates are generated to the buffer conditioning treatment unit. Step 3: Receive wastewater from the detoxification and conversion treatment unit, reduce the wastewater temperature through heat exchange, balance water quality fluctuations through homogenization, and then send the cooled and homogenized wastewater to the oxidation enhancement treatment unit. Step 4: Receive wastewater and ozone oxidant from the buffer conditioning unit, and react the intermediate products with ozone in a solid catalyst bed to generate formic acid and acetic acid, which are small molecule organic acids. Then, transport the wastewater after generating the small molecule organic acids to the biochemical mineralization unit. Step 5: Receive wastewater from the oxidation enhancement treatment unit, metabolize organic matter in the membrane bioreactor using microbial flora, and then transport the metabolized wastewater to the effluent verification treatment unit. Step 6: Receive wastewater from the biochemical mineralization treatment unit, detect formaldehyde concentration and chemical oxygen demand (COD) value. When the formaldehyde concentration is below 1 mg / L and the COD value is below 50 mg / L, trigger the discharge signal.

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