A treatment process for condensate wastewater

Abstract

The application discloses a kind of treatment processes of condensate wastewater, belong to wastewater treatment technical field.Process includes: S1 after adjusting wastewater pH, Fenton oxidation is carried out, and filtrate is obtained after neutralization, flocculation, filtration;S2 filtrate is distilled under reduced pressure and recovers heat, condensate is sequentially subjected to ozone oxidation, biochemical treatment, modified granular activated carbon treatment, adjusts pH after security filtration and reverse osmosis treatment, effluent discharge reaches standard.The application efficiently degrades recalcitrant organic matter by Fenton oxidation, reduces COD and color, reduces salt load by distillation under reduced pressure, removes COD and ammonia nitrogen by ozone and biochemical synergy, realizes adsorption-catalytic deep purification by modified activated carbon, and finally guarantees that effluent is stable and reaches standard by reverse osmosis, which can realize water resource reuse, and has high treatment efficiency and stable operation.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a process for treating condensate wastewater. Background Technology

[0002] Municipal sludge is a major byproduct of wastewater treatment in urban wastewater treatment plants. Its large volume and complex composition have made it a key target for urban environmental management. Incineration, due to its advantages of significant volume reduction, thorough detoxification, and recoverable heat energy, has become one of the mainstream technologies for municipal sludge disposal. However, during high-temperature incineration, the flue gas contains a large amount of pollutants, which, after condensation and recovery, form municipal sludge incineration condensate wastewater. This wastewater is characterized by high CODcr concentration, high ammonia nitrogen content, high salt content, deep color, and poor biodegradability. It also contains a large amount of recalcitrant aromatic organic matter, humic substances, and trace amounts of heavy metal ions. Direct discharge of this wastewater will cause serious pollution to aquatic environments, endangering ecological security and human health.

[0003] Currently, traditional condensate wastewater treatment processes mostly employ single methods such as Fenton oxidation, flocculation sedimentation, biological treatment, or membrane separation. However, their effectiveness in treating municipal sludge incineration condensate wastewater is limited: single oxidation processes do not completely remove recalcitrant organic matter; flocculation sedimentation struggles to simultaneously reduce ammonia nitrogen and color; conventional biological systems are easily inhibited by high concentrations of pollutants and cannot operate stably; and membrane separation processes are prone to increased operating costs due to membrane fouling. Furthermore, existing processes generally suffer from long treatment processes, large reagent dosages, difficulty in consistently achieving effluent standards, and low resource utilization rates.

[0004] Therefore, developing a high-efficiency, stable treatment process that can simultaneously reduce COD, ammonia nitrogen, and color, and is suitable for treating municipal sludge incineration condensate wastewater, is of great practical significance for improving the environmental protection level of the entire municipal sludge disposal process and reducing water treatment costs. Summary of the Invention

[0005] This invention provides a treatment process for condensate wastewater, which can solve the problems of poor treatment effect, incomplete removal of COD and ammonia nitrogen, and high color in the existing technology for municipal sludge incineration condensate wastewater.

[0006] The objective of this invention can be achieved through the following technical solutions: A process for treating condensate wastewater includes the following steps: S1. Add acid to the condensate wastewater to adjust the pH to 1-6, add FeSO4 and hydrogen peroxide for Fenton oxidation treatment; then filter, add alkali to adjust the pH to 7-10, flocculate, and filter again to obtain the filtrate. S2. The filtrate is distilled under reduced pressure, and then the heat is recovered through a heat exchanger to obtain condensate until no more condensate is generated. The obtained condensate is treated with ozone, biochemical treatment, and modified granular activated carbon, and then the pH is adjusted to 6-9. Finally, it is filtered through a security filter and treated with reverse osmosis before being discharged in compliance with standards.

[0007] Further, in step S1, the acid is an aqueous solution of sulfuric acid or an aqueous solution of hydrochloric acid, and the concentration of the aqueous solution of sulfuric acid or hydrochloric acid is 1 to 4 mol / L.

[0008] Further, in step S1, the ratio of FeSO4 to hydrogen peroxide is 0.2-1 g: 1 mL, and the mass concentration of hydrogen peroxide is 25-30%.

[0009] Furthermore, in step S1, the volume of hydrogen peroxide is 0.4 to 1% of the volume of the condensate wastewater.

[0010] Furthermore, in step S1, the temperature of the Fenton oxidation treatment is 20–30°C, and the time is 20–40 min.

[0011] Further, in step S1, the alkali is sodium hydroxide or potassium hydroxide.

[0012] Further, in step S1, a flocculant may be added for flocculation, wherein the flocculant is polyferric sulfate; the ratio of the flocculant to the condensate wastewater is 0.001-0.003 g: 1 mL.

[0013] Furthermore, in step S2, the temperature of the vacuum distillation is 50-60°C, and the pressure is -0.05 to -0.01 MPa.

[0014] Furthermore, in step S2, the ozone treatment involves subjecting the condensate to deep ozone oxidation treatment, with an ozone injection rate of 5–20 g / L and a deep ozone oxidation treatment time of 5–10 h.

[0015] Further, in step S2, the biochemical treatment is an anaerobic-aerobic treatment; the anaerobic treatment involves passing the condensate into an anaerobic tank for treatment, with a condensate retention time of 72 hours and a CODcr reduction of 100 mg / L; the aerobic treatment involves passing the condensate into an aerobic tank for treatment, with a condensate retention time of 140–170 hours.

[0016] Further, in step S2, the modified granular activated carbon treatment involves adding the modified granular activated carbon to the condensate and treating it at a temperature of 20-30°C for 10-30 minutes; the amount of modified granular activated carbon added is 5-9 kg per ton of condensate after biochemical treatment.

[0017] Further, in step S2, the method for preparing the modified granular activated carbon is as follows: S21. Dissolve dopamine in Tris buffer, add granular activated carbon, stir at room temperature for 6-8 hours, wash, and dry to obtain PDA@activated carbon; S22. Sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate was added to deionized water, PDA@activated carbon was added, and the mixture was reacted at 50-60℃ for 1-2 hours. After washing and drying, modified PDA@activated carbon was obtained. S23. Add FeCl3·6H2O and terephthalic acid to DMF, mix ultrasonically, then add modified PDA@activated carbon, disperse ultrasonically for 10-20 min, react at 140-160℃ for 10-12 h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

[0018] Further, in step S21, the ratio of dopamine, Tris buffer, and granular activated carbon is 0.5-1g: 20mL: 0.5g.

[0019] Furthermore, in step S21, the granular activated carbon is produced from fruit shells or coconut shells as raw materials, with a particle size of 15-20 mesh.

[0020] Further, in step S22, the ratio of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate, deionized water, and PDA@activated carbon is 0.1-0.2g: 20mL: 0.2g.

[0021] Further, in step S23, the ratio of FeCl3·6H2O, terephthalic acid, DMF, and modified PDA@activated carbon is 4g:2.5-3g:40mL:0.5g.

[0022] Furthermore, in step S2, the reagent used to adjust the pH is any one of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, or sodium bicarbonate.

[0023] Furthermore, in step S2, the security filter removes solid particles with a diameter greater than or equal to 0.05 micrometers.

[0024] Furthermore, in step S2, the pressure of the reverse osmosis treatment is 4-6 MPa.

[0025] The beneficial effects of this invention are: 1. In the treatment process of this invention, S1 generates strong oxidizing hydroxyl radicals under acidic conditions through Fenton oxidation to efficiently degrade recalcitrant organic matter in the condensate wastewater and reduce toxicity. Combined with neutralization, flocculation, and filtration, it further removes suspended solids and heavy metal ions, significantly reducing COD and color. In S2, vacuum distillation recovers volatiles and heat, reducing salt and low-boiling-point loads. Ozone oxidation further breaks down and mineralizes residual organic matter and improves biodegradability. Biochemical treatment utilizes microbial metabolism to economically and efficiently remove residual COD and ammonia nitrogen. Modified granular activated carbon deeply purifies trace pollutants and color through adsorption-catalysis synergy. Finally, after pH adjustment, security filtration, and reverse osmosis treatment, dissolved salts and trace organic matter are effectively retained, ensuring stable discharge of effluent that meets standards and enabling water resource reuse.

[0026] 2. In the modified activated carbon of this invention, polydopamine acts as a multifunctional adhesive layer, firmly coating the surface of the activated carbon. Its abundant phenolic hydroxyl groups can directly adsorb impurities such as organic matter and heavy metal ions in wastewater through hydrogen bonding and π-π interactions. Subsequently, sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate is covalently grafted onto the polydopamine layer via a Michael addition reaction. The sulfur atoms in the thioether bond have a strong coordination complexing ability for heavy metal ions such as mercury and lead, which can selectively remove trace amounts of toxic heavy metals from wastewater. Heavy metal ions and their complexes themselves easily contribute to color, so the simultaneous removal of heavy metals can synergistically reduce the color of wastewater. The grafted imidazolium groups form coordination bonds with the metal ions of the iron-based MOF, providing high-density nucleation sites for the in-situ growth of the MOF, making the MOF uniformly and firmly anchored on the activated carbon surface, thereby significantly improving the removal efficiency of COD, ammonia nitrogen, color, and dissolved salts. Sodium sulfonate groups significantly enhance the hydrophilicity of the material surface, improve the interfacial wettability between the aqueous phase and the active sites, and increase the mass transfer efficiency of dissolved oxygen and polar organic pollutants to the active sites of MOF. This provides favorable conditions for the catalytic activation of dissolved oxygen to generate reactive oxygen species by iron-based MOF under light-free conditions. The supported iron-based MOF utilizes the adsorption enrichment effect and the redox activity of the iron centers to promote the catalytic oxidation and deep degradation of organic matter in an oxygenated water environment. Degradation products detach from the activated carbon surface, regenerating the adsorption sites of the activated carbon in situ and extending the material's service life. This achieves synergistic adsorption and catalytic degradation, significantly improving the removal efficiency of COD, ammonia nitrogen, color, etc. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0028] A process for treating condensate wastewater includes the following steps: S1. Add acid to the condensate wastewater to adjust the pH to 1-6, add FeSO4 and hydrogen peroxide for Fenton oxidation treatment; then filter, add alkali to adjust the pH to 7-10, flocculate, and filter again to obtain the filtrate. In step S1 of this invention, acid is first added to the condensate wastewater to adjust the pH to 1-6, providing a suitable strongly acidic environment for Fenton oxidation. This ensures that ferrous ions react with hydrogen peroxide to generate highly active hydroxyl radicals. These radicals non-selectively attack aromatic organic matter, humic substances, and heterocyclic compounds in the wastewater, decomposing them into small-molecule organic acids or carbon dioxide, thereby significantly reducing COD and eliminating biotoxicity. After the reaction, the iron sludge precipitate produced by Fenton oxidation is removed by filtration. Then, alkali is added to adjust the pH to 7-10, causing residual iron ions to form ferric hydroxide flocs and adsorb some organic matter, while creating neutral to weakly alkaline conditions for subsequent flocculation. After adding a flocculant (such as polyferric sulfate), suspended particles, colloids, and large-molecule organic matter are further coagulated through charge neutralization and net-sweeping action to form dense flocs. Finally, a clear filtrate is obtained through secondary filtration. This series of operations can simultaneously achieve chemical oxidation and chain breaking of recalcitrant organic matter, separation of iron sludge, pH adjustment, and deep removal of suspended solids, significantly reducing wastewater color, COD, and turbidity, and creating low-load, low-toxicity influent conditions for subsequent vacuum distillation and biochemical treatment.

[0029] S2. The filtrate is distilled under reduced pressure, and then the heat is recovered through a heat exchanger to obtain condensate until no more condensate is generated. The obtained condensate is treated with ozone, biochemical treatment, and modified granular activated carbon, and then the pH is adjusted to 6-9. Finally, it is filtered through a security filter and treated with reverse osmosis before being discharged in compliance with standards.

[0030] In step S2 of this invention, the filtrate obtained in S1 is first subjected to vacuum distillation. Utilizing the principle of lower boiling point under low pressure, water is evaporated, effectively preventing organic matter from charring or salt from scaling due to high temperatures. Simultaneously, the distillation process leaves most inorganic salts and non-volatile organic compounds in the concentrate, thus achieving preliminary separation of salts and water. The distilled water vapor is condensed and its heat recovered via a heat exchanger. This heat can be used to preheat raw water or for process insulation, significantly reducing overall process energy consumption. The resulting condensate is then passed through ozone for deep oxidation. Ozone directly or indirectly generates hydroxyl radicals at room temperature, further breaking down and mineralizing residual recalcitrant organic matter, and converting large molecules into smaller molecules, significantly improving the biodegradability of the wastewater. The ozone effluent then enters the... The wastewater enters the biological treatment system, first passing through an anaerobic tank where anaerobic microorganisms hydrolyze and acidify complex organic matter, producing methane and simultaneously achieving denitrification. It then passes through an aerobic tank where aerobic microorganisms thoroughly degrade remaining organic matter and convert ammonia nitrogen into nitrate. The effluent from the biological treatment is further treated with modified granular activated carbon to deeply remove trace pollutants and reduce color. Afterward, alkali or acid is added to adjust the pH to 6-9 to meet discharge standards. The effluent then passes through a security filter to remove suspended particles and protect the reverse osmosis membrane. Finally, reverse osmosis treatment is performed, where the membrane removes dissolved salts, small-molecule organic matter, and trace heavy metals. The produced water meets industrial reuse or direct discharge standards, while the concentrate is treated by spray drying or incineration for zero-discharge disposal. Through this multi-stage synergistic process, this invention achieves simultaneous and efficient removal of COD, ammonia nitrogen, color, salinity, and heavy metals from condensate wastewater, while recovering heat energy and water resources, resulting in significant environmental and economic benefits.

[0031] In some embodiments, in step S1, the acid is an aqueous solution of sulfuric acid or hydrochloric acid, and the concentration of the aqueous solution of sulfuric acid or hydrochloric acid is 1–4 mol / L. This concentration range can effectively adjust the pH of the wastewater to the optimal acidity range required for the Fenton reaction, ensuring that ferrous ions and hydrogen peroxide efficiently generate hydroxyl radicals; if the acid concentration is too low, the pH will be too high, the Fenton oxidation efficiency will decrease, and the degradation of organic matter will be incomplete; if the acid concentration is too high, it will waste reagents and increase the consumption of alkali for subsequent neutralization.

[0032] In some embodiments, in step S1, the ratio of FeSO4 to hydrogen peroxide is 0.2–1 g:1 mL, and the mass concentration of hydrogen peroxide is 25–30%. This ratio ensures a good match between ferrous ions and hydrogen peroxide, generating sufficient hydroxyl radicals and avoiding insufficient catalytic activity and incomplete oxidation of organic matter due to insufficient FeSO4. Excessive FeSO4, on the other hand, greatly increases the production of iron sludge, increasing the filtration burden and sludge disposal costs.

[0033] In some embodiments, in step S1, the volume of hydrogen peroxide is 0.4 to 1% of the volume of the condensate wastewater. This dosage provides sufficient oxidant to effectively degrade recalcitrant organic matter; too little hydrogen peroxide results in incomplete oxidation and low COD removal rate; too much hydrogen peroxide may cause residual oxidant to interfere with subsequent biochemical treatment and increase reagent costs.

[0034] In some embodiments, in step S1, the Fenton oxidation treatment is carried out at a temperature of 20–30°C for 20–40 min. These conditions ensure a moderate reaction rate, sufficient generation of hydroxyl radicals, and avoid ineffective decomposition of hydrogen peroxide due to high temperatures; if the temperature is too low or the time is too short, the reaction will be incomplete; if the temperature is too high or the time is too long, energy consumption will increase and side reactions may occur.

[0035] In some embodiments, in step S1, the alkali is sodium hydroxide or potassium hydroxide. This type of alkali has good solubility and reacts rapidly, quickly restoring the pH to 7-10 and promoting the formation of iron ions into flocs.

[0036] In some embodiments, in step S1, a flocculant, specifically polyferric sulfate, may be added during flocculation. The ratio of the flocculant to the condensate wastewater is 0.001–0.003 g: 1 mL. This dosage effectively neutralizes the colloidal charge and generates flocs, simultaneously removing suspended solids and some organic matter. Insufficient flocculant results in small flocs and slow sedimentation; excessive flocculant increases sludge volume and may leave residual iron ions in the effluent.

[0037] In some embodiments, in step S2, the temperature of the vacuum distillation is 50–60°C, and the pressure is -0.05–-0.01 MPa. These conditions allow for the evaporation of moisture at low temperatures, preventing the charring of organic matter and recovering heat energy. Evaporation efficiency is low when the temperature is too low or the vacuum level is insufficient; excessively high temperatures or excessively high vacuum levels result in high energy consumption and may cause low-boiling-point substances to enter the condensate.

[0038] In some embodiments, in step S2, the ozone treatment involves subjecting the condensate to deep ozone oxidation, with an ozone injection rate of 5–20 g / L and a deep ozone oxidation treatment time of 5–10 h. These parameters ensure sufficient contact between ozone and wastewater, breaking down and mineralizing recalcitrant organic matter and improving biodegradability. Insufficient ozone or too short a treatment time results in incomplete oxidation; excessive ozone or too long a treatment time increases energy consumption and the burden on exhaust gas treatment.

[0039] In some embodiments, in step S2, the biochemical treatment is an anaerobic-aerobic treatment; the anaerobic treatment involves passing the condensate into an anaerobic tank for treatment, with a condensate retention time of 72 hours and a CODcr reduction of 100 mg / L; the aerobic treatment involves passing the condensate into an aerobic tank for treatment, with a condensate retention time of 140–170 hours. These biochemical conditions ensure sufficient hydrolysis, acidification, and denitrification in the anaerobic stage, while the aerobic stage thoroughly degrades organic matter and ammonia nitrogen. Too short a retention time results in insufficient microbial degradation; too long a retention time increases tank volume and raises investment and operating costs.

[0040] In some embodiments, in step S2, the modified granular activated carbon treatment involves adding the modified granular activated carbon to the condensate and treating it at a temperature of 20–30°C for 10–30 minutes. The amount of modified granular activated carbon added is 5–9 kg per ton of condensate after biochemical treatment. This dosage and time ensure that the activated carbon fully adsorbs and catalyzes pollutants; too little dosage or too short a time results in poor treatment effect; too much dosage wastes materials and increases solid waste; and too long a time does not significantly improve efficiency.

[0041] In some embodiments, the method for preparing the modified granular activated carbon in step S2 is as follows: S21. Dissolve dopamine in Tris buffer, add granular activated carbon, stir at room temperature for 6-8 hours, wash, and dry to obtain PDA@activated carbon; Granular activated carbon possesses advantages such as large specific surface area, well-developed pore structure, strong adsorption capacity, and relatively low cost, making it widely used in wastewater pretreatment. However, it has few surface functional groups and insufficient hydrophilicity, resulting in poor adsorption selectivity for polar organic pollutants and heavy metal ions. Furthermore, it lacks catalytically active sites, hindering the deep degradation of pollutants. To address these shortcomings, this invention dissolves dopamine in Tris buffer solution, adds it to granular activated carbon, and stirs at room temperature for 6–8 hours. Utilizing the oxidative self-polymerization reaction of dopamine under weakly alkaline and aerobic conditions, a thin and robust polydopamine (PDA) coating is formed on the activated carbon surface. This coating is rich in catechol and amino groups, which, on the one hand, directly adsorb organic matter and heavy metal ions in wastewater through hydrogen bonding and π-π interactions; on the other hand, it provides abundant chemical anchors for subsequent grafting of functional molecules, thereby significantly enhancing the surface reactivity and multifunctionality of the activated carbon.

[0042] S22. Sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate was added to deionized water, PDA@activated carbon was added, and the mixture was reacted at 50-60℃ for 1-2 hours. After washing and drying, modified PDA@activated carbon was obtained. In the above steps, the thiol group (-SH) in the sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate molecule undergoes a Michael addition reaction with the quinone group in the PDA coating at 50-60℃, covalently grafted onto the PDA@activated carbon surface via thioether bonds (CS), resulting in modified PDA@activated carbon. The grafted imidazolium group can form strong coordination bonds with the metal ions of the iron-based MOF, providing high-density nucleation sites for the in-situ growth of the MOF and ensuring uniform and firm loading of the MOF. At the same time, the sodium sulfonate group significantly enhances the hydrophilicity of the material surface, promoting the enrichment of water molecules and dissolved oxygen around the active sites, providing a favorable microenvironment for subsequent photocatalytic oxidation without light. In addition, the sulfur atom in the thioether bond (CS) has a strong coordination complexing ability for heavy metal ions such as mercury and lead, which can selectively remove trace amounts of toxic heavy metals from wastewater. Heavy metal ions and their complexes themselves easily contribute to color, so the simultaneous removal of heavy metals can synergistically reduce the color of wastewater.

[0043] S23. Add FeCl3·6H2O and terephthalic acid to DMF, mix ultrasonically, then add modified PDA@activated carbon, disperse ultrasonically for 10-20 min, react at 140-160℃ for 10-12 h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

[0044] The above steps involve dissolving FeCl3·6H2O and terephthalic acid in DMF, ultrasonically mixing, adding modified PDA@activated carbon, ultrasonically dispersing for 10–20 min, and then solvothermal reacting at 140–160℃ for 10–12 h. Iron ions coordinate with terephthalic acid to form an iron-based MOF, which preferentially nucleates and grows on the activated carbon surface under the anchoring effect of imidazole groups. After cooling, washing, and drying, modified granular activated carbon is obtained. The supported iron-based MOF can catalytically activate dissolved oxygen in water under light-free conditions, continuously generating various reactive oxygen species such as superoxide radicals, hydroxyl radicals, and singlet oxygen. This deeply mineralizes adsorbed organic matter, while the degradation products regenerate the adsorption sites of activated carbon in situ, thus achieving a synergistic cycle of adsorption-catalysis-regeneration, significantly improving the removal efficiency of COD, ammonia nitrogen, color, etc.

[0045] In some embodiments, in step S21, the ratio of dopamine, Tris buffer, and granular activated carbon is 0.5–1 g: 20 mL: 0.5 g. This ratio allows dopamine to form a uniform and complete polydopamine coating on the activated carbon surface, providing sufficient active sites; if there is too little dopamine, the coating will be incomplete and there will be insufficient grafting sites; if there is too much dopamine, the coating will be too thick, clogging the pores of the activated carbon and reducing the adsorption capacity.

[0046] In some embodiments, in step S21, the granular activated carbon is produced from fruit shells or coconut shells, with a particle size of 15-20 mesh. This raw material and particle size range give the activated carbon a rich microporous and mesoporous structure, high mechanical strength, and suitability as a composite carrier; when the particle size is too large, the specific surface area decreases, and the adsorption performance declines; when the particle size is too small, it is easily broken during stirring, increasing the loss of fine powder.

[0047] In some embodiments, in step S22, the ratio of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate, deionized water, and PDA@activated carbon is 0.1–0.2 g: 20 mL: 0.2 g. This ratio ensures sufficient grafting of functional molecules at a moderate grafting density, providing enough imidazolium anchoring sites and sulfonic acid hydrophilic groups without over-covering the PDA layer; too few functional molecules result in insufficient grafting and unstable MOF loading; too many waste raw materials and may form multilayer physical adsorption, affecting mass transfer.

[0048] In some embodiments, in step S23, the ratio of FeCl3·6H2O, terephthalic acid, DMF, and modified PDA@activated carbon is 4g:2.5-3g:40mL:0.5g. This ratio allows the iron-based MOF to grow uniformly in situ on the activated carbon surface, with a moderate loading and high catalytic activity. If there is too little iron salt or ligand, the MOF crystallization will be incomplete and the loading will be low; if there is too much, free MOF particles will be generated, clogging the pores of the activated carbon.

[0049] In some embodiments, in step S2, the reagent used for pH adjustment is any one of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, or sodium bicarbonate. These alkaline reagents can precisely adjust the pH of the effluent to 6-9 to meet discharge standards while avoiding the introduction of harmful ions; if the dosage is too small, the pH will be too low, affecting subsequent reverse osmosis; if the dosage is too large, the pH will be too high, which may cause metal hydroxide precipitation or membrane scaling.

[0050] In some embodiments, in step S2, the security filtration removes solid particles with a diameter greater than or equal to 0.05 micrometers. This precision effectively traps residual flocs, microorganisms, and fine activated carbon powder, protecting the reverse osmosis membrane from particulate contamination. If the filtration precision is too coarse, particles will enter the reverse osmosis system, causing membrane blockage; if the precision is too fine, it will increase filtration resistance and require frequent filter replacements.

[0051] In some embodiments, in step S2, the pressure of the reverse osmosis treatment is 4–6 MPa. This pressure range provides sufficient driving force for water to pass through the reverse osmosis membrane, effectively desalinating and retaining trace amounts of organic matter; if the pressure is too low, the water production is small and the desalination rate is low; if the pressure is too high, energy consumption increases and the membrane module may be compressed, shortening the membrane life.

[0052] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0053] The composition of the condensate wastewater of this invention is as follows: CODcr is 102000 mg / L, BOD5 is 8000 mg / L, NH3-N (ammonia nitrogen) is 16000 mg / L, conductivity is 89000 μs / cm, color is 1100, and pH is 9.

[0054] Preparation Example 1 The method for preparing the modified granular activated carbon in this preparation example is as follows: S21. Dissolve 0.5g of dopamine in 20mL of Tris buffer, add 0.5g of granular activated carbon (produced from coconut shell, particle size 20 mesh), stir at room temperature for 6h, wash, dry, and obtain PDA@activated carbon. S22. Add 0.1g of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate to 20mL of deionized water, add 0.2g of PDA@activated carbon, react at 50℃ for 1h, wash, dry, and obtain modified PDA@activated carbon; S23. Add 4g FeCl3·6H2O and 2.5g terephthalic acid to 40mL DMF, mix by sonication, then add 0.5g modified PDA@activated carbon, sonicate for 10min, react at 140℃ for 10h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

[0055] Preparation Example 2 The method for preparing the modified granular activated carbon in this preparation example is as follows: S21. Dissolve 0.8g of dopamine in 20mL of Tris buffer, add 0.5g of granular activated carbon (produced from coconut shell, particle size 20 mesh), stir at room temperature for 7h, wash, dry, and obtain PDA@activated carbon; S22. Add 0.15g of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate to 20mL of deionized water, add 0.2g of PDA@activated carbon, react at 55℃ for 1.5h, wash, and dry to obtain modified PDA@activated carbon; S23. Add 4g FeCl3·6H2O and 2.7g terephthalic acid to 40mL DMF, mix by sonication, then add 0.5g modified PDA@activated carbon, sonicate for 15min, react at 150℃ for 11h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

[0056] Preparation Example 3 The method for preparing the modified granular activated carbon in this preparation example is as follows: S21. Dissolve 1g of dopamine in 20mL of Tris buffer, add 0.5g of granular activated carbon (produced from coconut shell, particle size 20 mesh), stir at room temperature for 8h, wash, dry, and obtain PDA@activated carbon. S22. Add 0.2g of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate to 20mL of deionized water, add 0.2g of PDA@activated carbon, react at 60℃ for 2h, wash, dry, and obtain modified PDA@activated carbon; S23. Add 4g FeCl3·6H2O and 3g terephthalic acid to 40mL DMF, mix by ultrasonication, then add 0.5g modified PDA@activated carbon, disperse by ultrasonication for 20min, react at 160℃ for 12h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

[0057] Compare with Example 1 The only difference between this comparative example and preparation example 1 is that "2-mercapto-1H-benzimidazole-5-sulfonate sodium" was replaced with an equal amount of "2-mercaptobenzimidazole".

[0058] Compare with Example 2 The only difference between this comparative example and preparation example 1 is that an equal amount of sodium 2-mercaptoethanesulfonate was used to replace sodium 2-mercapto-1H-benzo[d]imidazole-5-sulfonate.

[0059] Compare with Example 3 The only difference between this comparative example and preparation example 1 is that sodium 2-mercapto-1H-benzo[d]imidazole-5-sulfonate is omitted. Specifically: S21. Dissolve 0.5g of dopamine in 20mL of Tris buffer, add 0.5g of granular activated carbon (produced from coconut shell, particle size 20 mesh), stir at room temperature for 6h, wash, dry, and obtain PDA@activated carbon. S22. Add 4g FeCl3·6H2O and 2.5g terephthalic acid to 40mL DMF, mix by sonication, then add 0.5g PDA@activated carbon, sonicate for 10min, react at 140℃ for 10h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

[0060] Compare with Example 4 The only difference between this comparative example and preparation example 1 is that step S23 is omitted. Specifically: S21. Dissolve 0.5g of dopamine in 20mL of Tris buffer, add 0.5g of granular activated carbon (produced from coconut shell, particle size 20 mesh), stir at room temperature for 6h, wash, dry, and obtain PDA@activated carbon. S22. Add 0.1g of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate to 20mL of deionized water, add 0.2g of PDA@activated carbon, react at 50℃ for 1h, wash, and dry to obtain modified granular activated carbon.

[0061] Compare with Example 5 The only difference between this comparative example and preparation example 1 is that steps S22 and S23 are omitted. Specifically: Dissolve 0.5g of dopamine in 20mL of Tris buffer, add 0.5g of granular activated carbon (produced from coconut shells, with a particle size of 20 mesh), stir at room temperature for 6h, wash, and dry to obtain modified granular activated carbon.

[0062] Example 1 This embodiment provides a process for treating condensate wastewater, including the following steps: S1. Add 1 mol / L hydrochloric acid aqueous solution to 1000 mL of condensate wastewater to adjust the pH to 3.5-4, add 0.8 g FeSO4 and 4 mL of 25% hydrogen peroxide for Fenton oxidation treatment at 20℃ for 20 min; then filter, add sodium hydroxide to adjust the pH to 8-9, add 1 g of flocculant polyferric sulfate for flocculation, and filter to obtain filtrate; S2. The filtrate is subjected to vacuum distillation at 50℃ and -0.05 MPa. Heat is then recovered via a heat exchanger to obtain condensate, continuing until no more condensate is generated. Ozone is injected into the condensate via a Venturi jet for vigorous mixing for 5 hours (ozone flow rate 5 g / L). The mixture is then subjected to anaerobic-aerobic treatment (anaerobic treatment is conducted in an anaerobic tank with a condensate residence time of 72 hours, reducing CODcr by 100 mg / L; aerobic treatment is conducted in an aerobic tank with a condensate residence time of 1 hour). After 40 hours, the condensate after biochemical treatment is obtained; then, the modified granular activated carbon obtained in Preparation Example 1 is added (the amount of modified granular activated carbon added is 5 kg / ton of biochemically treated condensate), and the mixture is treated at 20°C for 10 minutes; then, sodium hydroxide is added to adjust the pH value to 7-8, and solid particles with a particle size greater than or equal to 0.05 micrometers are filtered out by security filtration; then, reverse osmosis treatment is carried out at 4 MPa, and the effluent is qualified discharge water. The concentrate obtained from the reverse osmosis treatment is spray-dried or sent to a combustion furnace for combustion treatment.

[0063] Example 2 This embodiment provides a process for treating condensate wastewater, including the following steps: S1. Add 2 mol / L hydrochloric acid aqueous solution to 1000 mL of condensate wastewater to adjust the pH to 3.5-4, add 4.2 g FeSO4 and 7 mL of 28% hydrogen peroxide for Fenton oxidation treatment at 25℃ for 30 min; then filter, add sodium hydroxide to adjust the pH to 8-9, add 2 g of flocculant polyferric sulfate for flocculation, and filter to obtain filtrate; S2. The filtrate is subjected to vacuum distillation at 55℃ and -0.03MPa. Heat is then recovered via a heat exchanger to obtain condensate, continuing until no more condensate is generated. Ozone is injected into the condensate via a Venturi jet for vigorous mixing for 8 hours (ozone flow rate 13g / L). Then, it undergoes anaerobic-aerobic treatment (anaerobic treatment is carried out in an anaerobic tank with a condensate residence time of 72 hours, reducing CODcr by 100mg / L; aerobic treatment is carried out in an aerobic tank with a condensate residence time of 1 hour). After 55 hours, the condensate after biochemical treatment is obtained; then the modified granular activated carbon obtained in Preparation Example 1 is added (the amount of modified granular activated carbon added is 7 kg / ton of biochemically treated condensate), and the mixture is treated at 25°C for 20 minutes; then sodium hydroxide is added to adjust the pH value to 7-8, and solid particles with a particle size greater than or equal to 0.05 micrometers are filtered out by security filtration; then reverse osmosis is performed at 5 MPa, and the effluent is qualified discharge water. The concentrate obtained from the reverse osmosis treatment is spray-dried or sent to a combustion furnace for combustion treatment.

[0064] Example 3 This embodiment provides a process for treating condensate wastewater, including the following steps: S1. Add 4 mol / L hydrochloric acid aqueous solution to 1000 mL of condensate wastewater to adjust the pH to 3.5-4, add 10 g FeSO4 and 10 mL of 30% hydrogen peroxide for Fenton oxidation treatment at 30℃ for 40 min; then filter, add sodium hydroxide to adjust the pH to 8-9, add 3 g of flocculant polyferric sulfate for flocculation, and filter to obtain filtrate; S2. The filtrate is subjected to vacuum distillation at 60℃ and -0.01 MPa. Heat is then recovered via a heat exchanger to obtain condensate, continuing until no more condensate is generated. Ozone is injected into the condensate via a Venturi jet for vigorous mixing for 10 hours (ozone flow rate 20 g / L). Then, it undergoes anaerobic-aerobic treatment (anaerobic treatment is carried out in an anaerobic tank, with a condensate residence time of 72 hours and a CODcr reduction of 100 mg / L; aerobic treatment is carried out in an aerobic tank, with a condensate residence time of...). The condensate obtained after biochemical treatment was obtained after 170 hours; then the modified granular activated carbon obtained in Preparation Example 1 was added (the amount of modified granular activated carbon added was 9 kg / ton of biochemically treated condensate), and the mixture was treated at 30°C for 30 minutes; then sodium hydroxide was added to adjust the pH value to 7-8, and solid particles with a particle size greater than or equal to 0.05 micrometers were filtered out by security filtration; then reverse osmosis treatment was carried out at 6 MPa, and the effluent was qualified discharge water. The concentrate obtained from the reverse osmosis treatment was spray-dried or sent to a combustion furnace for combustion treatment.

[0065] Example 4 The only difference between this embodiment and Example 3 is that the modified granular activated carbon obtained in Example 1 is replaced with an equal amount of the modified granular activated carbon obtained in Example 2.

[0066] Example 5 The only difference between this embodiment and Example 3 is that the modified granular activated carbon obtained in Example 1 is replaced with an equal amount of the modified granular activated carbon obtained in Example 3.

[0067] Comparative Example 1 The only difference between this comparative example and Example 1 is that the "modified granular activated carbon obtained in Preparation Example 1" is replaced with an equal amount of "modified granular activated carbon obtained in Comparative Example 1".

[0068] Comparative Example 2 The only difference between this comparative example and Example 1 is that the "modified granular activated carbon obtained in Preparation Example 1" is replaced with an equal amount of "modified granular activated carbon obtained in Comparative Example 2".

[0069] Comparative Example 3 The only difference between this comparative example and Example 1 is that the "modified granular activated carbon obtained in Preparation Example 1" is replaced with an equal amount of "modified granular activated carbon obtained in Comparative Example 3".

[0070] Comparative Example 4 The only difference between this comparative example and Example 1 is that the modified granular activated carbon obtained in Preparation Example 1 was replaced with an equal amount of the modified granular activated carbon obtained in Comparative Example 4.

[0071] Comparative Example 5 The only difference between this comparative example and Example 1 is that the modified granular activated carbon obtained in Preparation Example 1 was replaced with an equal amount of the modified granular activated carbon obtained in Comparative Example 5.

[0072] Comparative Example 6 The only difference between this comparative example and Example 1 is that an equal amount of "granular activated carbon (produced from coconut shells with a particle size of 20 mesh)" was used to replace "the modified granular activated carbon obtained in Preparation Example 1".

[0073] The results of wastewater treatment in Examples 1 to 5 and Comparative Examples 1 to 6 were statistically analyzed, and the results are shown in Table 1: Table 1

[0074] As shown in Table 1, the effluent water quality indicators of Examples 1-5 were significantly better than those of Comparative Examples 1-6. Specifically, the CODcr, BOD5, ammonia nitrogen, conductivity, and color of Examples 1-5 were all at low levels, and with the optimization of process parameters (such as increasing ozone dosage and activated carbon dosage), the effluent water quality improved step by step, and the pH value stabilized in the near-neutral range. In contrast, the effluent indicators of Comparative Examples 1-6 were significantly worse than those of the Examples. Among them, the treatment effects of Comparative Example 1 (lacking sulfonic acid groups) and Comparative Example 2 (lacking imidazole groups) decreased, the effect of Comparative Example 3 (without functional molecule grafting) was even worse, the effects of Comparative Example 4 (without MOF) and Comparative Example 5 (PDA modification only) were further reduced, and the treatment effect of Comparative Example 6 (pure activated carbon) was the worst, with high levels of CODcr, ammonia nitrogen, and color, and the pH value deviating from neutral. The above results show that the modified granular activated carbon (polydopamine-sulfonic acid-imidazolium-anchored iron-based MOF) used in this invention has a synergistic effect of various functional groups, and has excellent removal capabilities for COD, ammonia nitrogen, color and dissolved salts in condensate wastewater. At the same time, it can accurately control the pH of the effluent. The overall treatment effect is significantly better than the control scheme with unmodified activated carbon or lacking any functional group.

[0075] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A process for treating condensate wastewater, characterized in that, Includes the following steps: S1. Add acid to the condensate wastewater to adjust the pH to 1-6, add FeSO4 and hydrogen peroxide for Fenton oxidation treatment; then filter, add alkali to adjust the pH to 7-10, flocculate, and filter again to obtain the filtrate. S2. The filtrate is distilled under reduced pressure, and then the heat is recovered through a heat exchanger to obtain condensate until no more condensate is generated. The obtained condensate is treated with ozone, biochemical treatment, and modified granular activated carbon, and then the pH is adjusted to 6-9. Finally, it is filtered through a security filter and treated with reverse osmosis before being discharged in compliance with standards.

2. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S1, the acid is an aqueous solution of sulfuric acid or an aqueous solution of hydrochloric acid, and the concentration of the aqueous solution of sulfuric acid or hydrochloric acid is 1-4 mol / L; The ratio of FeSO4 to hydrogen peroxide is 0.2–1 g: 1 mL, and the mass concentration of hydrogen peroxide is 25–30%. The volume of the hydrogen peroxide is 0.4% to 1% of the volume of the condensate wastewater; The alkali is sodium hydroxide or potassium hydroxide; The flocculation process may involve adding a flocculant, which is polyferric sulfate; the ratio of the flocculant to the condensate wastewater is 0.001–0.003 g: 1 mL.

3. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S1, the temperature of the Fenton oxidation treatment is 20-30°C and the time is 20-40 min.

4. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S2, the temperature of the vacuum distillation is 50-60℃ and the pressure is -0.05 to -0.01 MPa; The ozone treatment involves subjecting the condensate to deep ozone oxidation, with an ozone injection rate of 5–20 g / L and a deep ozone oxidation treatment time of 5–10 h.

5. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S2, the biochemical treatment is an anaerobic-aerobic treatment; the anaerobic treatment involves passing the condensate into an anaerobic tank for treatment, with a residence time of 72 hours and a CODcr reduction of 100 mg / L; the aerobic treatment involves passing the condensate into an aerobic tank for treatment, with a residence time of 140–170 hours.

6. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S2, the modified granular activated carbon treatment involves adding the modified granular activated carbon to the condensate and treating it at a temperature of 20–30°C for 10–30 minutes. The amount of modified granular activated carbon added is 5–9 kg per ton of condensate after biochemical treatment.

7. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S2, the method for preparing the modified granular activated carbon is as follows: S21. Dissolve dopamine in Tris buffer, add granular activated carbon, stir at room temperature for 6-8 hours, wash, and dry to obtain PDA@activated carbon; S22. Sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate was added to deionized water, PDA@activated carbon was added, and the mixture was reacted at 50-60℃ for 1-2 hours. After washing and drying, modified PDA@activated carbon was obtained. S23. Add FeCl3·6H2O and terephthalic acid to DMF, mix ultrasonically, then add modified PDA@activated carbon, disperse ultrasonically for 10-20 min, react at 140-160℃ for 10-12 h, cool to room temperature, wash, and dry to obtain modified granular activated carbon.

8. The condensate wastewater treatment process as described in claim 7, characterized in that, In step S21, the ratio of dopamine, Tris buffer, and granular activated carbon is 0.5-1g: 20mL: 0.5g; In step S21, the granular activated carbon is produced from fruit shells or coconut shells as raw materials, with a particle size of 15-20 mesh. In step S22, the ratio of sodium 2-mercapto-1H-benzo[d]imidazolium-5-sulfonate, deionized water, and PDA@activated carbon is 0.1-0.2 g: 20 mL: 0.2 g; In step S23, the ratio of FeCl3·6H2O, terephthalic acid, DMF, and modified PDA@activated carbon is 4g:2.5-3g:40mL:0.5g.

9. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S2, the reagent used to adjust the pH is any one of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, or sodium bicarbonate.

10. The condensate wastewater treatment process as described in claim 1, characterized in that, In step S2, the security filter removes solid particles with a diameter greater than or equal to 0.05 micrometers. The pressure for the reverse osmosis treatment is 4–6 MPa.

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