Method for treating high-COD (Chemical Oxygen Demand) and high-ammonia-nitrogen wastewater

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a method for treating high-COD (chemical oxygen demand) and high-ammonia-nitrogen wastewater, which comprises the following steps: S1, introducing wastewater into a double-electrode chamber-mixing chamber three-section electrochemical reactor, and adopting a titanium-based PbO2 anode and an IrO2 anode to form an oxidation potential gradient for selective oxidation; s2, effluent passes through a short-cut nitrification reactor and then passes through an anaerobic ammonia oxidation-denitrification coupling reactor for denitrification; s3, removing residual organic matters through a bio-membrane reactor, and controlling CODlt of effluent; 100 mg / L; s4, pre-concentrating by adopting a membrane distillation device and utilizing a low-grade heat source; and S5, treating the concentrated solution through an MVR evaporative crystallization system to produce solid salt and treated water. According to the process, through combination of electrochemical oxidation, short-cut nitrification, anaerobic ammonia oxidation, biological membrane, membrane distillation and MVR, organic unification of efficient conversion of refractory organic matters, autotrophic nitrogen removal, zero discharge of wastewater and resource recovery is realized, and the process has the advantages of high treatment efficiency, low operation cost, low energy consumption and high system stability.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, and more specifically, to a method for treating wastewater with high COD and high ammonia nitrogen. Background Technology

[0002] With the acceleration of industrialization, the discharge of high-concentration organic wastewater from industries such as chemical, pharmaceutical, printing and dyeing, and landfill leachate treatment is increasing year by year. This type of wastewater typically features high chemical oxygen demand (COD), high ammonia nitrogen concentration, and the presence of recalcitrant organic matter and salt accumulation, causing serious pollution to environmental water bodies. Therefore, developing efficient, economical, and stable technologies for treating high-COD and high-ammonia nitrogen wastewater has become an important research direction in the field of water treatment.

[0003] Currently, the treatment of this type of wastewater mainly employs a combination of biological and physicochemical methods. In biological treatment, activated sludge and biofilm processes are widely used due to their mature technology and relatively low operating costs. However, traditional activated sludge processes, when treating high-concentration organic wastewater, suffer from problems such as sludge bulking and deterioration of settling performance due to excessive organic loads. For recalcitrant organic matter, its poor biodegradability makes it difficult for microorganisms to utilize it directly, resulting in a removal efficiency typically below 30%. While biofilm processes offer some resistance to shock loads, they also face bottlenecks such as low removal rates of recalcitrant organic matter and inhibition of nitrifying bacteria under high ammonia nitrogen conditions.

[0004] In terms of physicochemical treatment, coagulation sedimentation and filtration processes can effectively remove suspended solids, colloidal substances, and some large-molecule organic matter from wastewater, but they have almost no ability to remove dissolved small-molecule organic matter and ammonia nitrogen. Advanced oxidation technologies such as Fenton oxidation and ozone oxidation can degrade some recalcitrant organic matter, but they have problems such as high reagent consumption, high operating costs, and potential secondary pollution.

[0005] In recent years, with increasingly stringent industrial wastewater discharge standards and growing demand for wastewater reuse, evaporation concentration technology has been widely used in zero-discharge wastewater treatment. However, traditional evaporation concentration processes face the challenge of significantly increased energy consumption, especially when treating saline wastewater, where steam consumption can reach 0.3-0.4 tons per ton of water evaporated, resulting in high operating costs. Simultaneously, salt accumulation leads to increasingly serious membrane fouling problems in membrane treatment processes, manifested as rapid flux decline, frequent cleaning, and shortened membrane life, severely impacting the stability and economy of the treatment system.

[0006] Existing technologies for treating high-COD and high-ammonia-nitrogen wastewater generally suffer from high carbon source addition costs. Traditional denitrification processes require the addition of external carbon sources such as methanol and sodium acetate to meet the electron donor requirements of denitrifying bacteria. For high-ammonia-nitrogen wastewater with an imbalanced C / N ratio, carbon source addition costs can account for 40%-60% of the total operating costs, and excessive addition can easily lead to excessive effluent COD and nutrient imbalance within the system. Furthermore, pretreatment steps for recalcitrant organic matter (such as iron-carbon microelectrolysis and hydrolysis acidification) often increase the complexity of the process and the floor space required, further increasing overall energy consumption and investment costs.

[0007] In summary, existing technologies for treating high-COD and high-ammonia-nitrogen wastewater still have significant shortcomings in terms of treatment efficiency, operating costs, and system stability. There is an urgent need to develop a new treatment process that can synergistically remove recalcitrant organic matter and achieve efficient denitrification with low energy consumption and low operating costs, so as to achieve economical and efficient treatment of such wastewater. Summary of the Invention

[0008] To address the significant shortcomings of existing high-COD and high-ammonia-nitrogen wastewater treatment technologies in terms of treatment efficiency, operating costs, and system stability, this application provides a method for treating high-COD and high-ammonia-nitrogen wastewater.

[0009] This application provides a method for treating wastewater with high COD and high ammonia nitrogen, employing the following technical solution: A method for treating wastewater with high COD and high ammonia nitrogen includes the following preparation steps: S1. High COD and high ammonia nitrogen wastewater is introduced into a three-stage electrochemical reactor consisting of a dual-electrode chamber and a mixing chamber. The first electrode chamber is controlled to use a titanium-based PbO2 anode and the second electrode chamber is controlled to use a titanium-based IrO2 anode. Selective oxidation is carried out under oxidation potential gradient conditions to convert recalcitrant organic matter into biodegradable substances, thereby increasing the B / C ratio of the effluent to above 0.3. S2. The effluent from step S1 is sequentially fed into a short-cut nitrification reactor and an anaerobic ammonia oxidation-denitrification coupled reactor. Short-cut nitrification is achieved by controlling dissolved oxygen and pH, which partially oxidizes ammonia nitrogen into nitrite nitrogen. Then, under anaerobic conditions, total nitrogen is removed through the synergistic effect of anaerobic ammonia oxidizing bacteria and denitrifying bacteria. Short-cut nitrification stage: Under conditions of dissolved oxygen 0.8-1.0 mg / L, pH 7.8-8.0, and temperature 25-35℃, free ammonia and free nitrite synergistically inhibit nitrite-oxidizing bacteria, allowing ammonia-oxidizing bacteria to oxidize 50% of NH4+. + -N is oxidized to NO2 - -N, nitrite accumulation rate >90%; Anaerobic ammonia oxidation-denitrification stage: Short-cut nitrification effluent, after deoxygenation treatment, enters the anaerobic ammonia oxidation-denitrification reactor. The reactor operates at a temperature of 28-30℃, pH 7.0-8.0, hydraulic retention time of 24 hours, and COD / NO2 ratio... - Under the condition of -N= 2.0, through the synergistic action of anaerobic ammonia oxidizing bacteria and denitrifying bacteria in granular sludge, ammonia nitrogen and nitrite nitrogen are converted into nitrogen gas, while the remaining COD is used for denitrification. S3. Pass the effluent from step S2 into a biofilm reactor to remove residual organic matter and suspended solids, and control the effluent COD to <100 mg / L; S4. Pass the effluent from step S3 into a membrane distillation unit and use a low-grade heat source to pre-concentrate the wastewater to obtain concentrated liquid and distilled water. S5. The concentrate from step S4 is fed into a mechanical vapor recompression evaporation crystallization system. Evaporation crystallization is carried out at an evaporation temperature of 75-85℃ and a compressor pressure ratio of 1.5-2.5 to produce solid salt and treated water.

[0010] By adopting the above technical solution, through a combined process of electrochemical oxidation-short-path nitrification-anaerobic ammonia oxidation-biofilm-membrane distillation-MVR evaporation and crystallization, the organic unity of efficient removal of recalcitrant organic matter, autotrophic denitrification, zero emissions and resource recovery is achieved. It has the advantages of high treatment efficiency, low operating cost, strong system stability and environmental and economic benefits. First, the dual-electrode chamber-mixing chamber three-stage electrochemical reactor uses titanium-based PbO2 and IrO2 anodes to form an oxidation potential gradient, which can efficiently and selectively oxidize recalcitrant organic matter, increasing the B / C ratio to above 0.3, creating conditions for subsequent biological treatment. Second, the coupled short-cut nitrification and anaerobic ammonia oxidation-denitrification process achieves a nitrite accumulation rate of >90% by controlling dissolved oxygen and pH, and can synergistically remove total nitrogen without the need for an external carbon source, significantly reducing operating costs. The S3 biofilm reactor further removes residual organic matter and suspended solids, ensuring that the effluent COD is consistently below 100 mg / L. S4-S5, through membrane distillation pre-concentration combined with MVR evaporation crystallization, converts high-salinity wastewater into solid salt and treated water. Utilizing a low-grade heat source and steam recompression technology, the evaporation energy consumption is reduced by 30%-50% compared to traditional processes, solving the problems of high energy consumption and severe membrane fouling in traditional evaporation. This process as a whole achieves a comprehensive improvement in the efficient removal of recalcitrant organic matter, synergistic removal of ammonia nitrogen, reduced operating costs, and system stability, providing an economical and efficient solution for the treatment of high-concentration organic wastewater.

[0011] Preferably, the three-stage electrochemical reactor with dual electrode chamber and mixing chamber described in step S1 consists of a first electrode chamber, a mixing chamber, and a second electrode chamber connected in series. The first electrode chamber is equipped with a titanium-based PbO2 anode and a first cathode. The second electrode chamber is equipped with a titanium-based IrO2 anode and a second cathode. The mixing chamber is equipped with a mechanical stirring device. Wastewater flows through the first electrode chamber, the mixing chamber, and the second electrode chamber in sequence, forming an oxidation potential gradient. The potential of the first electrode chamber is higher than that of the second electrode chamber.

[0012] By adopting the above technical solution, the first electrode chamber, mixing chamber, and second electrode chamber are connected in series, with an anode and cathode respectively configured in each electrode chamber. A mechanical stirring device is installed in the mixing chamber, allowing wastewater to flow sequentially through the three functional zones, forming a continuous oxidation potential gradient. The potential of the first electrode chamber is higher than that of the second electrode chamber, achieving gradient selective oxidation treatment of recalcitrant organic matter in high-COD and high-ammonia-nitrogen wastewater. The high-potential environment of the first electrode chamber preferentially attacks the inert chemical bonds of recalcitrant organic matter, initially breaking them down into intermediate products. The mechanical stirring in the mixing chamber promotes the uniform mixing and transfer of intermediate products with the electrolyte. The high efficiency of the second electrode chamber creates conditions for deep oxidation. The relatively low potential of the second electrode chamber further converts intermediate products into biodegradable small molecules, thereby avoiding excessive oxidation and energy waste. At the same time, it precisely controls the degree of oxidation to stabilize the B / C ratio of the effluent to above 0.3. This effectively solves the defects of single electrochemical reactors, such as uncontrollable oxidation potential, low conversion efficiency of recalcitrant organic matter, and unstable improvement of biodegradability. It improves the selectivity and energy efficiency of electrochemical pretreatment and provides water quality conditions for the subsequent short-cut nitrification-anaerobic ammonia oxidation biological denitrification process.

[0013] Preferably, in step S1, the current density is 15-25 mA / cm². 2 Gradient oxidation reaction was carried out under the conditions of pH 3.5-5.0 and electrode spacing of 15-20 mm, with a reaction time of 2-4 hours.

[0014] By adopting the above technical solution, the operating parameters of electrochemical oxidation were optimized, ensuring the efficient conversion of recalcitrant organic matter into biodegradable substances. At the same time, it avoided increased energy consumption and electrode wear due to excessive current density, as well as decreased oxidation efficiency due to improper pH, thus greatly improving oxidation efficiency.

[0015] Preferably, the current density in step S1 is adjusted based on the influent COD concentration: when the influent COD is 5000-10000 mg / L, the current density is controlled at 15-20 mA / cm². 2 When the influent COD is 10000-20000 mg / L, the control current density is 20-25 mA / cm². 2 .

[0016] By adopting the above technical solution, intelligent control of the electrochemical oxidation process is realized. Different oxidation intensities are used for wastewater with different pollution loads, which not only ensures the full oxidation of high-concentration COD wastewater, but also avoids energy waste in the treatment of low-concentration COD wastewater and reduces operating power consumption.

[0017] Preferably, the anaerobic ammonia oxidation-denitrification section in step S2 adopts an upflow anaerobic sludge bed reactor. The particle size of the anaerobic ammonia oxidation granular sludge in the reactor is 2-4 mm, the sludge concentration is 8000-12000 mg / L, and the upflow velocity is controlled at 0.5-1.0 m / h to maintain the stability of the granular sludge bed.

[0018] By adopting the above technical solution, a high-biomass, high-activity granular sludge bed was formed. Anaerobic ammonia oxidizing bacteria and denitrifying bacteria formed a stable micro-ecological environment inside the granules. The granular structure is conducive to maintaining the oxygen-sensitive characteristics of anaerobic ammonia oxidizing bacteria. At the same time, the denitrifying bacteria created strict anaerobic conditions by consuming residual dissolved oxygen. The control of the upflow velocity achieved a balance between hydraulic conditions and sludge retention, effectively preventing sludge loss and ensuring stable denitrification efficiency under high ammonia nitrogen conditions. This overcame the problems of easy damage to nitrifying bacteria and poor system stability in high ammonia nitrogen wastewater.

[0019] Preferably, step S2 controls the short-cut nitrification process by real-time monitoring of pH and dissolved oxygen, and stops aeration when pH > 8.0.

[0020] By adopting the above technical solution, the short-cut nitrification process is controlled by real-time monitoring of pH and dissolved oxygen. Aeration is stopped when pH > 8.0. At this point, the synergistic inhibitory effect of free ammonia and free nitrite selectively inhibits the activity of nitrite-oxidizing bacteria while maintaining the activity of ammonia-oxidizing bacteria. This achieves stable accumulation of nitrite nitrogen and avoids NOB from converting NO2 into NO2. - -N is further oxidized to NO3. - -N reduces substrate competition for subsequent anaerobic ammonium oxidation reactions, ensuring the smooth operation of the short-cut nitration-anaerobic ammonium oxidation process and reducing operating costs.

[0021] Preferably, the biofilm reactor in step S3 is a moving bed biofilm reactor or an aerated biofilter, using polyurethane sponge packing or ceramsite, controlling dissolved oxygen at 3-4 mg / L, hydraulic retention time at 4-6 hours, and volumetric loading at 1.5-2.5 kg COD / (m³). 3 .d).

[0022] Biofilm formation is achieved using polyurethane sponge filler or ceramsite carriers at dissolved oxygen levels of 3-4 mg / L, hydraulic retention time of 4-6 hours, and volumetric loading of 1.5-2.5 kg COD / (m³). 3Under the conditions described in .d), the strong retention capacity and high biomass characteristics of the biofilm effectively remove residual organic matter and suspended solids after pretreatment, ensuring that the COD of the effluent is consistently below 100 mg / L, meeting the water quality requirements for membrane distillation feedwater, avoiding the membrane fouling problem caused by organic matter and suspended solids in the membrane treatment in the background technology, extending the service life of the membrane, and improving the stability of system operation.

[0023] Preferably, the membrane distillation apparatus in step S4 employs vacuum membrane distillation or air-gap membrane distillation, the membrane material is a hydrophobic PTFE hollow fiber membrane, the hot-side temperature is 60-80℃, the cold-side temperature is 20-30℃, and the membrane flux is 5-15 L / (m²). 2 (.h), retention rate ≥ 99.9%.

[0024] Vacuum membrane distillation or air-gap membrane distillation technology is employed, using hydrophobic PTFE hollow fiber membranes. Operation is carried out at a hot-side temperature of 60-80℃ and a cold-side temperature of 20-30℃. The vapor pressure difference across the membrane drives water vapor to permeate through the membrane pores, achieving the separation of water and dissolved solids. Membrane flux reaches 5-15 L / (m²). 2 With a rejection rate of >99.9%, it can effectively remove impurities such as salt and organic matter from wastewater, pre-concentrate the wastewater, significantly reduce the amount of water treated by subsequent MVR evaporation and crystallization, and reduce evaporation energy consumption; membrane distillation can be operated under normal or reduced pressure, with relatively relaxed requirements on the quality of influent water, and can utilize low-grade heat sources, solving the problems of high energy consumption and serious membrane fouling in traditional evaporation concentration and membrane treatment.

[0025] Preferably, before step S5, a nanofiltration salt separation step is included: the concentrate obtained in step S4 is separated by a nanofiltration membrane with a sulfate ion rejection rate of ≥98% and a chloride ion rejection rate of ≤20%, to obtain a sodium sulfate-rich side and a sodium chloride-rich side, which are then fed into different MVR evaporators for salt separation and crystallization.

[0026] By adopting the above technical solution, nanofiltration membranes are used to filter divalent ions (SO42-). 2- The high rejection rate of ) and the high rejection rate of monovalent ions (Cl) - The selective separation characteristics of sodium sulfate and sodium chloride with low rejection rate separate the concentrate into a sodium sulfate-rich side and a sodium chloride-rich side, which are then fed into different MVR evaporators for salt separation and crystallization. This achieves effective separation and separate recovery of sodium sulfate and sodium chloride, producing high-purity solid salt products. It avoids the problem that mixed salts are difficult to utilize as resources and can only be disposed of as hazardous waste, improves the resource value and economic benefits of wastewater treatment, and solves the problems of high disposal costs and resource waste caused by mixed salts generated by evaporation and crystallization.

[0027] Preferably, the heat source of the membrane distillation system in step S4 comes from the residual heat of the condensate generated by the MVR evaporation and crystallization system in step S5, realizing the cascade utilization of energy within the system; the produced distilled water is used as supplementary water for the MVR evaporation and crystallization system, forming a recycling of water resources.

[0028] By adopting the above technical solution, the waste heat of the condensate generated by the MVR evaporation and crystallization system in step S5 is used as the heat source of the membrane distillation system in step S4, realizing the cascade utilization of energy within the system. Membrane distillation can meet the operating temperature requirements by utilizing low-grade waste heat, without the need for additional energy consumption. At the same time, the membrane distillation product water is reused as supplementary water for the MVR evaporation and crystallization system, forming a water resource recycling system. The entire system has high thermal energy utilization and low water consumption.

[0029] In summary, this application has the following beneficial effects: This invention achieves a unified approach to efficient removal of recalcitrant organic matter, autotrophic denitrification, zero discharge, and resource recovery through a combined process of electrochemical oxidation, short-cut nitrification, anaerobic ammonia oxidation, biofilm, membrane distillation, and MVR evaporation and crystallization. First, the three-stage electrochemical reactor (dual-electrode chamber-mixing chamber) uses titanium-based PbO2 and IrO2 anodes to form an oxidation potential gradient, enabling efficient and selective oxidation of recalcitrant organic matter and increasing the B / C ratio to over 0.3, thus improving the biodegradability of wastewater and creating conditions for subsequent biological treatment. Second, the coupled process of short-cut nitrification and anaerobic ammonia oxidation-denitrification achieves a nitrite accumulation rate >90% through precise control of dissolved oxygen and pH. The synergistic effect of anaerobic ammonia oxidizing bacteria and denitrifying bacteria efficiently removes total nitrogen without the need for external carbon sources, significantly reducing operating costs and solving the problem of high carbon source addition costs in traditional denitrification. The biofilm reactor further removes residual organic matter and suspended solids, ensuring that the effluent COD remains consistently below 100 mg / L. Membrane distillation pre-concentration combined with MVR evaporation crystallization utilizes a low-grade heat source and vapor recompression technology to reduce evaporation energy consumption compared to traditional processes, achieving zero wastewater discharge and salt resource recovery. This process offers advantages such as high treatment efficiency, low operating costs, low energy consumption, and strong system stability. Detailed Implementation Example

[0030] Example 1

[0031] Wastewater: COD concentration is 5000 mg / L, ammonia nitrogen concentration is 500 mg / L, and salt content is 5%.

[0032] A method for treating wastewater with high COD and high ammonia nitrogen includes the following preparation steps: S1. High COD and high ammonia nitrogen wastewater is introduced into a three-stage electrochemical reactor consisting of a dual-electrode chamber and a mixing chamber. The first electrode chamber is controlled to use a titanium-based PbO2 anode and the second electrode chamber is controlled to use a titanium-based IrO2 anode. Selective oxidation is carried out under oxidation potential gradient conditions to convert recalcitrant organic matter into biodegradable substances, thereby increasing the B / C ratio of the effluent to 0.3. This dual-electrode chamber-mixing chamber three-stage electrochemical reactor consists of a first electrode chamber, a mixing chamber, and a second electrode chamber connected in series. The first electrode chamber is equipped with a titanium-based PbO2 anode and a first cathode (316L stainless steel). The second electrode chamber is equipped with a titanium-based IrO2 anode and a second cathode (316L stainless steel). The mixing chamber is equipped with a mechanical stirring device. Wastewater flows sequentially through the first electrode chamber for 1 hour, the mixing chamber for 0.25 hours, and the second electrode chamber for 0.75 hours, with a total reaction time of 2 hours, forming an oxidation potential gradient. The potential of the first electrode chamber is higher than that of the second electrode chamber. In step S1, the conditions for both the first and second electrode chambers are: current density 15 mA / cm². 2 Gradient oxidation reaction was carried out under the conditions of pH 3.5 and electrode spacing of 15 mm; When the influent COD is 5000 mg / L, the control current density is 15 mA / cm². 2 ; S2. The effluent from step S1 is sequentially fed into a short-cut nitrification reactor and an anaerobic ammonia oxidation-denitrification coupled reactor. Short-cut nitrification is achieved by controlling dissolved oxygen and pH, which partially oxidizes ammonia nitrogen into nitrite nitrogen. Then, under anaerobic conditions, total nitrogen is removed through the synergistic effect of anaerobic ammonia oxidizing bacteria and denitrifying bacteria. Short-cut nitrification stage: Under conditions of dissolved oxygen 0.8 mg / L, pH 7.8, and temperature 25℃, free ammonia and free nitrite synergistically inhibit nitrite-oxidizing bacteria, allowing ammonia-oxidizing bacteria to oxidize 50% of NH4+. + -N is oxidized to NO2 - -N, nitrite accumulation rate 90%; Anaerobic ammonia oxidation-denitrification stage: The effluent from short-cut nitrification is deoxygenated and then enters the anaerobic ammonia oxidation-denitrification reactor. The reactor operates at a temperature of 28℃, pH 7.0, hydraulic retention time of 24 hours, and COD / NO2... - Under the condition of -N= 2.0, through the synergistic action of anaerobic ammonia oxidizing bacteria and denitrifying bacteria in granular sludge, ammonia nitrogen and nitrite nitrogen are converted into nitrogen gas, while the remaining COD is used for denitrification. The anaerobic ammonia oxidation-denitrification section adopts an upflow anaerobic sludge bed reactor. The average particle size of the anaerobic ammonia oxidation granular sludge in the reactor is 2 mm, the sludge concentration is 8000 mg / L, and the upflow velocity is controlled at 0.5 m / h to maintain the stability of the granular sludge bed. Step S2 controls the short-cut nitrification process by real-time monitoring of pH and dissolved oxygen, and stops aeration when pH > 8.0; S3. Pass the effluent from step S2 into a biofilm reactor to remove residual organic matter and suspended solids, and control the COD of the effluent to 100 mg / L. In step S3, the biofilm reactor is a moving bed biofilm reactor or an aerated biofilter, using polyurethane sponge packing material, with dissolved oxygen controlled at 3 mg / L, hydraulic retention time at 4 hours, and volumetric loading at 1.5 kg COD / (m³). 3 .d); S4. Pass the effluent from step S3 into a membrane distillation unit and use a low-grade heat source to pre-concentrate the wastewater to obtain concentrated liquid and distilled water. Step S4 uses a membrane distillation apparatus employing vacuum membrane distillation or air-gap membrane distillation. The membrane material is a hydrophobic PTFE hollow fiber membrane. The hot-side temperature is 60℃, the cold-side temperature is 20℃, and the membrane flux is 5 L / (m²). 2 .h), retention rate 99.9%; Before step S5, there is also a nanofiltration salt separation step: the concentrate obtained in step S4 is separated by a nanofiltration membrane with a sulfate ion rejection rate of 99% and a chloride ion rejection rate of 20%, resulting in a sodium sulfate-rich side and a sodium chloride-rich side, which are then fed into different MVR evaporators for salt separation and crystallization. After separation, the solutions obtained from the different MVR evaporators are combined to obtain a concentrate.

[0033] S5. The concentrate from step S4 is fed into a mechanical vapor recompression evaporation crystallization system, where it is evaporated and crystallized at an evaporation temperature of 75°C and a compressor pressure ratio of 1.5 to produce solid salt and treated water. The heat source of the membrane distillation system in step S4 comes from the residual heat of the condensate generated by the MVR evaporation and crystallization system in step S5, realizing the cascade utilization of energy within the system; the produced distilled water is used as supplementary water for the MVR evaporation and crystallization system, forming a water resource recycling system.

[0034] Example 2 Wastewater: COD concentration is 10000 mg / L, ammonia nitrogen concentration is 600 mg / L, and salt content is 3%.

[0035] A method for treating wastewater with high COD and high ammonia nitrogen includes the following preparation steps: S1. High COD and high ammonia nitrogen wastewater is introduced into a three-stage electrochemical reactor consisting of a dual-electrode chamber and a mixing chamber. The first electrode chamber is controlled to use a titanium-based PbO2 anode and the second electrode chamber is controlled to use a titanium-based IrO2 anode. Selective oxidation is carried out under oxidation potential gradient conditions to convert recalcitrant organic matter into biodegradable substances, thereby increasing the B / C ratio of the effluent to 0.4. The three-stage electrochemical reactor with dual electrode chamber and mixing chamber described in step S1 consists of a first electrode chamber, a mixing chamber, and a second electrode chamber connected in series. The first electrode chamber is equipped with a titanium-based PbO2 anode and a first cathode (316L stainless steel). The second electrode chamber is equipped with a titanium-based IrO2 anode and a second cathode (316L stainless steel). The mixing chamber is equipped with a mechanical stirring device. Wastewater flows sequentially through the first electrode chamber for 1.5 hours, the mixing chamber for 0.5 hours, and the second electrode chamber for 1 hour. The reaction time is 3 hours, forming an oxidation potential gradient. The potential of the first electrode chamber is higher than that of the second electrode chamber. In step S1, the conditions for both the first and second electrode chambers are: current density 20 mA / cm². 2 Gradient oxidation reaction was carried out under the conditions of pH 4 and electrode spacing of 18 mm; When the influent COD is 10000 mg / L, the control current density is 20 mA / cm³. 2 ; S2. The effluent from step S1 is sequentially fed into a short-cut nitrification reactor and an anaerobic ammonia oxidation-denitrification coupled reactor. Short-cut nitrification is achieved by controlling dissolved oxygen and pH, which partially oxidizes ammonia nitrogen into nitrite nitrogen. Then, under anaerobic conditions, total nitrogen is removed through the synergistic effect of anaerobic ammonia oxidizing bacteria and denitrifying bacteria. Short-cut nitrification stage: Under conditions of dissolved oxygen 0.9 mg / L, pH 7.9, and temperature 30℃, free ammonia and free nitrite synergistically inhibit nitrite-oxidizing bacteria, allowing ammonia-oxidizing bacteria to oxidize 50% of NH4+. + -N is oxidized to NO2 - -N, nitrite accumulation rate 93%; Anaerobic ammonia oxidation-denitrification stage: The effluent from short-cut nitrification is deoxygenated and then enters the anaerobic ammonia oxidation-denitrification reactor. The reactor operates at a temperature of 29℃, pH 7.5, hydraulic retention time of 24 hours, and COD / NO2 ratio... - Under the condition of -N= 2.0, through the synergistic action of anaerobic ammonia oxidizing bacteria and denitrifying bacteria in granular sludge, ammonia nitrogen and nitrite nitrogen are converted into nitrogen gas, while the remaining COD is used for denitrification. The anaerobic ammonia oxidation-denitrification section adopts an upflow anaerobic sludge bed reactor. The average particle size of the anaerobic ammonia oxidation granular sludge in the reactor is 3 mm, the sludge concentration is 10000 mg / L, and the upflow velocity is controlled at 0.8 m / h to maintain the stability of the granular sludge bed. Step S2 controls the short-cut nitrification process by real-time monitoring of pH and dissolved oxygen, and stops aeration when pH > 8.0; S3. Pass the effluent from step S2 into a biofilm reactor to remove residual organic matter and suspended solids, and control the effluent COD to 90 mg / L. Step S3 involves a moving bed biofilm reactor or an aerated biological filter, using polyurethane sponge packing material, with dissolved oxygen controlled at 3.5 mg / L, hydraulic retention time at 5 hours, and volumetric loading at 2.0 kg COD / (m³). 3 .d); S4. Pass the effluent from step S3 into a membrane distillation unit and use a low-grade heat source to pre-concentrate the wastewater to obtain concentrated liquid and distilled water. The membrane distillation apparatus described in step S4 employs vacuum membrane distillation or air-gap membrane distillation. The membrane material is a hydrophobic PTFE hollow fiber membrane. The hot-side temperature is 70°C, the cold-side temperature is 25°C, and the membrane flux is 10 L / (m²). 2 .h), retention rate >99.9%; Before step S5, there is also a nanofiltration salt separation step: the concentrate obtained in step S4 is separated by a nanofiltration membrane with a sulfate ion rejection rate of 99% and a chloride ion rejection rate of 15%, resulting in a sodium sulfate-rich side and a sodium chloride-rich side, which are then fed into different MVR evaporators for salt separation and crystallization. After separation, the solutions obtained from the different MVR evaporators are combined to obtain a concentrate.

[0036] S5. The concentrated liquid from step S4 is fed into a mechanical vapor recompression evaporation crystallization system, where it is evaporated and crystallized at an evaporation temperature of 80°C and a compressor pressure ratio of 2 to produce solid salt and treated water. The heat source of the membrane distillation system in step S4 comes from the residual heat of the condensate generated by the MVR evaporation and crystallization system in step S5, realizing the cascade utilization of energy within the system; the produced distilled water is used as supplementary water for the MVR evaporation and crystallization system, forming a water resource recycling system.

[0037] Example 3 Wastewater: COD concentration is 20,000 mg / L, ammonia nitrogen concentration is 700 mg / L, and salt content is 4%.

[0038] A method for treating wastewater with high COD and high ammonia nitrogen includes the following preparation steps: S1. High COD and high ammonia nitrogen wastewater is introduced into a three-stage electrochemical reactor consisting of a dual-electrode chamber and a mixing chamber. The first electrode chamber is controlled to use a titanium-based PbO2 anode and the second electrode chamber is controlled to use a titanium-based IrO2 anode. Selective oxidation is carried out under oxidation potential gradient conditions to convert recalcitrant organic matter into biodegradable substances, thereby increasing the B / C ratio of the effluent to 0.5. The three-stage electrochemical reactor with dual electrode chamber and mixing chamber described in step S1 consists of a first electrode chamber, a mixing chamber, and a second electrode chamber connected in series. The first electrode chamber is equipped with a titanium-based PbO2 anode and a first cathode (316L stainless steel). The second electrode chamber is equipped with a titanium-based IrO2 anode and a second cathode (316L stainless steel). The mixing chamber is equipped with a mechanical stirring device. Wastewater flows sequentially through the first electrode chamber for 2 hours, the mixing chamber for 0.5 hours, and the second electrode chamber for 1.5 hours. The reaction time is 4 hours, forming an oxidation potential gradient. The potential of the first electrode chamber is higher than that of the second electrode chamber. In step S1, the conditions for both the first and second electrode chambers are a current density of 25 mA / cm². 2 Gradient oxidation reaction was carried out under the conditions of pH 5.0 and electrode spacing of 20 mm; When the influent COD is 20000 mg / L, the control current density is 25 mA / cm². 2 ; S2. The effluent from step S1 is sequentially fed into a short-cut nitrification reactor and an anaerobic ammonia oxidation-denitrification coupled reactor. Short-cut nitrification is achieved by controlling dissolved oxygen and pH, which partially oxidizes ammonia nitrogen into nitrite nitrogen. Then, under anaerobic conditions, total nitrogen is removed through the synergistic effect of anaerobic ammonia oxidizing bacteria and denitrifying bacteria. Short-cut nitrification stage: Under conditions of dissolved oxygen 1.0 mg / L, pH 8.0, and temperature 35℃, free ammonia and free nitrite synergistically inhibit nitrite-oxidizing bacteria, allowing ammonia-oxidizing bacteria to oxidize 50% of NH4+. + -N is oxidized to NO2 - -N, nitrite accumulation rate 95%; Anaerobic ammonia oxidation-denitrification stage: The effluent from short-cut nitrification is deoxygenated and then enters the anaerobic ammonia oxidation-denitrification reactor. The reactor operates at a temperature of 30℃, pH 8.0, hydraulic retention time of 24 hours, and COD / NO2 ratio... - Under the condition of -N= 2.0, through the synergistic action of anaerobic ammonia oxidizing bacteria and denitrifying bacteria in granular sludge, ammonia nitrogen and nitrite nitrogen are converted into nitrogen gas, while the remaining COD is used for denitrification. The anaerobic ammonia oxidation-denitrification section adopts an upflow anaerobic sludge bed reactor. The average particle size of the anaerobic ammonia oxidation granular sludge in the reactor is 4 mm, the sludge concentration is 12000 mg / L, and the upflow velocity is controlled at 1.0 m / h to maintain the stability of the granular sludge bed. Step S2 controls the short-cut nitrification process by real-time monitoring of pH and dissolved oxygen, and stops aeration when pH > 8.0; S3. Pass the effluent from step S2 into a biofilm reactor to remove residual organic matter and suspended solids, and control the effluent COD to 80 mg / L. Step S3 involves a moving bed biofilm reactor or an aerated biological filter, using expanded clay aggregate, with dissolved oxygen controlled at 4 mg / L, hydraulic retention time at 6 hours, and volumetric loading at 2.5 kg COD / (m³). 3 .d); S4. Pass the effluent from step S3 into a membrane distillation unit and use a low-grade heat source to pre-concentrate the wastewater to obtain concentrated liquid and distilled water. Step S4 uses a membrane distillation apparatus employing vacuum membrane distillation or air-gap membrane distillation. The membrane material is a hydrophobic PTFE hollow fiber membrane. The hot-side temperature is 80℃, the cold-side temperature is 30℃, and the membrane flux is 15 L / (m²). 2 .h), retention rate >99.9%; Before step S5, there is also a nanofiltration salt separation step: the concentrate obtained in step S4 is separated by a nanofiltration membrane with a sulfate ion rejection rate of 98% and a chloride ion rejection rate of 10%, respectively obtaining a sodium sulfate-rich side and a sodium chloride-rich side, which are then fed into different MVR evaporators for salt separation and crystallization. After separation, the solutions obtained from the different MVR evaporators are combined to obtain a concentrate.

[0039] S5. The concentrate from step S4 is fed into a mechanical vapor recompression evaporation crystallization system, where it is evaporated and crystallized at an evaporation temperature of 85°C and a compressor pressure ratio of 2.5 to produce solid salt and treated water. The heat source of the membrane distillation system in step S4 comes from the residual heat of the condensate generated by the MVR evaporation and crystallization system in step S5, realizing the cascade utilization of energy within the system; the produced distilled water is used as supplementary water for the MVR evaporation and crystallization system, forming a water resource recycling system.

[0040] Example 4 A method for treating wastewater with high COD and high ammonia nitrogen. This embodiment differs from Embodiment 1 in that, in step S1, the current density is 15 mA / cm². 2 Gradient oxidation reaction was carried out under the conditions of pH 3 and electrode spacing of 15 mm for 2 hours.

[0041] Example 5 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this embodiment and Embodiment 1 is that the upflow velocity in step S2 is controlled at 1.2 m / h.

[0042] Example 6 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this embodiment and Embodiment 1 is that the nanofiltration desalination step is omitted.

[0043] Comparative Example Comparative Example 1 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this comparative example and Example 1 is that S1 uses a single titanium-based PbO2 anode reactor, with a current density of 15 mA / cm², pH 3.5, and a reaction time of 2 hours.

[0044] Comparative Example 2 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this comparative example and Example 1 is that the first electrode chamber uses a titanium-based IrO2 anode and the second electrode chamber uses a titanium-based PbO2 anode.

[0045] Comparative Example 3 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this comparative example and Example 1 is that the first step of wastewater treatment is omitted and the wastewater is directly treated in steps S2-S5.

[0046] Comparative Example 4 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this comparative example and Example 1 is that step S2 does not include short-cut nitrification, but directly performs anaerobic ammonia oxidation.

[0047] Comparative Example 5 A method for treating wastewater with high COD and high ammonia nitrogen. The difference between this comparative example and Example 1 is that step S4 is omitted, and the concentrate directly enters step S5.

[0048] Detection methods / test methods The water obtained from Examples 1-6 and Comparative Examples 1-5 was subjected to the following tests: COD detection: Refer to HJ 828-2017; Ammonia nitrogen detection: Refer to HJ 535-2009 Nessler's reagent spectrophotometric method; Total nitrogen: Refer to HJ 636-2012 Alkaline potassium persulfate digestion ultraviolet spectrophotometric method; TDS: The TDS of the water treated in step S5 was tested according to GB / T 5750.4-2023; the experimental data are shown in Table 1. Table 1. Experimental data of Examples 1-6 and Comparative Examples 1-5

[0049] The experimental data above show that the process described in this application not only has a better removal effect on COD and ammonia nitrogen, but also has a high TDS removal efficiency, realizing the resource recovery of salt and the recycling of water resources.

[0050] A comparison of Example 1 with Comparative Examples 1-5 reveals the following: Compared to Comparative Example 1, the dual-electrode chamber-mixing chamber three-stage electrochemical reactor increased the COD removal rate from 96.1% to 99.8%, indicating that the oxidation potential gradient design can more efficiently improve the biodegradability of wastewater; Compared to Comparative Example 2, the configuration of PbO2 pre-treatment and IrO2 post-treatment improved the removal rate and showed that the anodic sequence is crucial for selective oxidation; Compared to Comparative Example 3 (electrochemical steps omitted), the COD and ammonia nitrogen removal rates increased, indicating that electrochemical pretreatment is a prerequisite for subsequent biochemical treatment; Compared to Comparative Example 4, the total nitrogen removal rate increased from 42.2% to 99.4%, indicating that short-cut nitrification-anaerobic ammonia oxidation coupling is the core of achieving efficient autotrophic nitrogen removal; Compared to Comparative Example 5, the total nitrogen removal rate increased, indicating that membrane distillation pre-concentration plays a key role in ensuring effluent quality and reducing evaporation energy consumption.

[0051] A comparison of Examples 1 and 4-5 shows that in Example 4, lowering the pH from 3.5 to 3.0 reduced the total nitrogen removal rate from 99.4% to 94.6%, while increasing the conductivity of the MVR condensate on the Na2SO4-rich side from 28 μS / cm to 35 μS / cm. This indicates that excessively low pH inhibits electrochemical oxidation efficiency and subsequent biochemical reaction activity. In Example 5, increasing the upflow velocity from 0.5 m / h to 1.2 m / h reduced the COD and ammonia nitrogen removal rates to 97.8% and 97.1%, respectively. This indicates that excessively high hydraulic shear leads to the loss of anaerobic ammonia oxidation granular sludge, disrupting the stable micro-ecological environment within the reactor. In conclusion, key parameters such as the pH of electrochemical oxidation and reactor hydraulic conditions must be strictly controlled within the optimal range to ensure efficient and stable system operation.

[0052] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for treating wastewater with high COD and high ammonia nitrogen, characterized in that, The preparation steps include the following: S1. High COD and high ammonia nitrogen wastewater is introduced into a three-stage electrochemical reactor consisting of a dual-electrode chamber and a mixing chamber. The first electrode chamber is controlled to use a titanium-based PbO2 anode and the second electrode chamber is controlled to use a titanium-based IrO2 anode. Selective oxidation is carried out under oxidation potential gradient conditions to convert recalcitrant organic matter into biodegradable substances, thereby increasing the B / C ratio of the effluent to above 0.

3. S2. The effluent from step S1 is sequentially fed into a short-cut nitrification reactor and an anaerobic ammonia oxidation-denitrification coupled reactor. Short-cut nitrification is achieved by controlling dissolved oxygen and pH, which partially oxidizes ammonia nitrogen into nitrite nitrogen. Then, under anaerobic conditions, total nitrogen is removed through the synergistic effect of anaerobic ammonia oxidizing bacteria and denitrifying bacteria. Short-cut nitrification stage: Under conditions of dissolved oxygen 0.8-1.0 mg / L, pH 7.8-8.0, and temperature 25-35℃, free ammonia and free nitrite synergistically inhibit nitrite-oxidizing bacteria, allowing ammonia-oxidizing bacteria to oxidize 50% of NH4+. + -N is oxidized to NO2 - -N, nitrite accumulation rate >90%; Anaerobic ammonia oxidation-denitrification stage: Short-cut nitrification effluent, after deoxygenation treatment, enters the anaerobic ammonia oxidation-denitrification reactor. The reactor operates at a temperature of 28-30℃, pH 7.0-8.0, hydraulic retention time of 24 hours, and COD / NO2 ratio... - Under the condition of -N= 2.0, through the synergistic action of anaerobic ammonia oxidizing bacteria and denitrifying bacteria in granular sludge, ammonia nitrogen and nitrite nitrogen are converted into nitrogen gas, while the remaining COD is used for denitrification. S3. Pass the effluent from step S2 into a biofilm reactor to remove residual organic matter and suspended solids, and control the effluent COD to <100mg / L; S4. Pass the effluent from step S3 into a membrane distillation unit and use a low-grade heat source to pre-concentrate the wastewater to obtain concentrated liquid and distilled water. S5. The concentrate from step S4 is fed into a mechanical vapor recompression evaporation crystallization system. Evaporation crystallization is carried out at an evaporation temperature of 75-85℃ and a compressor pressure ratio of 1.5-2.5 to produce solid salt and treated water.

2. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: The dual-electrode chamber-mixing chamber three-stage electrochemical reactor described in step S1 consists of a first electrode chamber, a mixing chamber, and a second electrode chamber connected in series. The first electrode chamber is equipped with a titanium-based PbO2 anode and a first cathode. The second electrode chamber is equipped with a titanium-based IrO2 anode and a second cathode. The mixing chamber is equipped with a mechanical stirring device. Wastewater flows through the first electrode chamber, the mixing chamber, and the second electrode chamber in sequence, forming an oxidation potential gradient. The potential of the first electrode chamber is higher than that of the second electrode chamber.

3. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: In step S1, the current density is 15-25 mA / cm². 2 Gradient oxidation reaction was carried out under the conditions of pH 3.5-5.0 and electrode spacing of 15-20 mm, with a reaction time of 2-4 hours.

4. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: The current density in step S1 is adjusted based on the influent COD concentration: when the influent COD is 5000-10000 mg / L, the current density is controlled at 15-20 mA / cm². 2 When the influent COD is 10000-20000 mg / L, the control current density is 20-25 mA / cm². 2 .

5. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: The anaerobic ammonia oxidation-denitrification section in step S2 adopts an upflow anaerobic sludge bed reactor. The particle size of the anaerobic ammonia oxidation granular sludge in the reactor is 2-4 mm, the sludge concentration is 8000-12000 mg / L, and the upflow velocity is controlled at 0.5-1.0 m / h to maintain the stability of the granular sludge bed.

6. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: Step S2 controls the short-cut nitrification process by real-time monitoring of pH and dissolved oxygen, and stops aeration when pH > 8.

0.

7. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: The biofilm reactor described in step S3 is a moving bed biofilm reactor or an aerated biofilter, using polyurethane sponge packing or ceramsite, with dissolved oxygen controlled at 3-4 mg / L, hydraulic retention time at 4-6 hours, and volumetric loading at 1.5-2.5 kg COD / (m³). 3 .d).

8. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: The membrane distillation apparatus described in step S4 employs vacuum membrane distillation or air-gap membrane distillation. The membrane material is a hydrophobic PTFE hollow fiber membrane. The hot-side temperature is 60-80℃, the cold-side temperature is 20-30℃, and the membrane flux is 5-15 L / (m²). 2 (.h), retention rate ≥ 99.9%.

9. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: Before step S5, there is also a nanofiltration salt separation step: the concentrate obtained in step S4 is separated by a nanofiltration membrane with a sulfate ion rejection rate of ≥98% and a chloride ion rejection rate of ≤20%, to obtain a sodium sulfate-rich side and a sodium chloride-rich side, which are then fed into different MVR evaporators for salt separation and crystallization.

10. The method for treating high COD and high ammonia nitrogen wastewater according to claim 1, characterized in that: The heat source of the membrane distillation system in step S4 comes from the residual heat of the condensate generated by the MVR evaporation and crystallization system in step S5, realizing the cascade utilization of energy within the system; the produced distilled water is used as supplementary water for the MVR evaporation and crystallization system, forming a water resource recycling system.

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