Method and system for synchronously treating high-salt, high-ammonia-nitrogen and high-COD (Chemical Oxygen Demand) wastewater based on acidic fractionation

Abstract

The invention discloses a method and a system for synchronously treating high-salt, high-ammonia-nitrogen and high-COD (Chemical Oxygen Demand) wastewater based on acidic fractionation. The method comprises the following steps: adding an acid regulator to regulate the pH value to 1.0-6.5 aiming at wastewater with COD (Chemical Oxygen Demand) of more than or equal to 3500 mg / L, TDS (Total Dissolved Solids) of more than or equal to 5000 mg / L and ammonia nitrogen of more than or equal to 150 mg / L Carrying out fractional distillation to keep the ammonium salt and the salt in the base solution; and finally condensing the gas-phase fraction and separating out a primary fraction to obtain main fraction clear water. The COD (Chemical Oxygen Demand) value of the main fraction clear water is lower than 30% of the COD value of the raw water, the ammonia nitrogen value is lower than 15% of the ammonia nitrogen value of the raw water, and the TDS (Total Dissolved Solids) removal rate exceeds 50%. Three pollutants are synchronously reduced through one-time distillation, the method can be matched with industrial waste acid such as waste sulfuric acid and waste hydrochloric acid, waste treatment with waste is achieved, the process is simplified, cost is low, and the method is suitable for three-high wastewater treatment in the industries such as landfill leachate, chemical engineering, pharmacy, printing and dyeing, food processing and coal chemical engineering.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, specifically relating to a method and system for the simultaneous treatment of high-salt, high-ammonia-nitrogen, and high-COD wastewater based on acid fractionation. It is particularly suitable for the integrated treatment of recalcitrant wastewater with high COD ≥ 3500 mg / L, TDS ≥ 5000 mg / L, and ammonia nitrogen ≥ 150 mg / L, and can be widely applied to wastewater treatment scenarios in various industries such as landfill leachate, chemical, pharmaceutical, printing and dyeing, food processing, and coal chemical industries. Background Technology

[0002] This invention targets high-salinity, high-ammonia-nitrogen, and high-COD wastewater. Due to the strong inhibitory effect of high salinity on microorganisms, the biotoxicity of high ammonia nitrogen, and the recalcitrant nature of high COD, this wastewater is widely recognized in the environmental protection industry as difficult to treat, and is extensively generated in various industries such as landfill, chemical, and pharmaceutical. Existing treatment technologies suffer from four core defects that have long remained unresolved: 1. Neutral / alkaline distillation has a long-standing and unresolved technical problem of "excessive ammonia nitrogen-TDS coupling".

[0003] The mainstream neutral / alkaline distillation process stems from a long-standing technical bias in the field: the belief that acidic distillation severely corrodes equipment and easily releases volatile organic compounds, causing secondary pollution; therefore, distillation operations should be carried out in a neutral / alkaline environment. However, under neutral / alkaline conditions, ammonium ions readily hydrolyze to generate free ammonia, which evaporates with water vapor, leading to severe exceedances of ammonia nitrogen in the distillate. Simultaneously, free ammonia has a "carry-over effect" on salts, causing simultaneous exceedances of total dissolved solids (TDS) in the distillate, creating a vicious cycle of "ammonia nitrogen-TDS coupled exceedances." This problem has long plagued the industry, and a fundamental solution has yet to be found.

[0004] 2. Acidic full-fraction distillation cannot solve the problem of excessive COD.

[0005] In recent years, acid distillation technology has emerged, which fixes ammonia nitrogen into ammonium salts under acidic conditions, solving the problem of excessive ammonia nitrogen volatilization. However, in acidic environments, the degree of dissociation of volatile organic acids (acetic acid, propionic acid, etc.) in wastewater is reduced, making them prone to large-scale volatilization with water vapor, resulting in severely excessive COD in the distillate and making it impossible to achieve emission standards. The industry has consistently failed to reveal the core mechanism of COD exceeding standards in acid distillation, nor has it proposed an effective solution, creating a technical obstacle of "ammonia nitrogen meeting standards but COD not meeting standards in acid distillation, and COD meeting standards in alkaline distillation but ammonia nitrogen / TDS not meeting standards."

[0006] 3. It is impossible to achieve a significant reduction in all three indicators simultaneously, resulting in high costs due to process redundancy.

[0007] Existing technologies generally adopt a "step-by-step treatment" approach, with a typical process being "evaporation desalination + alkaline stripping / biological ammonia removal + Fenton / advanced oxidation COD removal". This process is lengthy, requires a lot of equipment, occupies a large area, and is difficult to operate and manage. The costs of reagents and energy consumption are combined, resulting in high costs per ton of water treated. Furthermore, step-by-step treatment cannot achieve coordinated control of the three indicators, and it is very easy for the reduction of one indicator to be insufficient. The industry has not yet provided an integrated technical solution that can achieve a simultaneous and significant reduction of the three indicators.

[0008] 4. Insufficient utilization of waste acid resources and lack of a collaborative plan for hazardous waste reduction.

[0009] The current industrial waste acid is generally disposed of by neutralization, which not only wastes resources but also generates a large amount of sludge and hazardous waste. For the case where distillation residue is hazardous waste, the existing technology has not formed a synergistic solution for the resource utilization of waste acid and the reduction of hazardous waste, and cannot achieve waste-to-waste treatment, which further increases the environmental disposal costs and compliance pressure of enterprises.

[0010] 5. There is a structural contradiction in the disposal of waste acid, namely "more acid than alkali" and insufficient utilization of low-concentration waste acid resources.

[0011] my country generates a large amount of industrial waste acid, while the amount of waste alkali is relatively insufficient, creating a market structure of "more acid than alkali." Traditional waste acid disposal mainly relies on neutralization, but due to the limited source of waste alkali, a large amount of waste acid needs to be concentrated before it can be sold as a resource. The higher the acidity, the more applicable scenarios there are and the lower the disposal cost; the lower the acidity, the greater the treatment difficulty and the higher the disposal cost. Existing wastewater treatment technologies require high concentrations of acid conditioners (usually concentrated sulfuric acid or high-concentration waste acid). Low-concentration waste acid cannot be used directly and still requires high-energy-consuming evaporation and concentration, further increasing the disposal costs and environmental pressure on enterprises. This invention can directly dispose of low-concentration waste acid while treating wastewater, saving customers concentration steam consumption and meeting the dual needs of "treating waste with waste" and energy conservation and consumption reduction.

[0012] In summary, the industry urgently needs a solution that simplifies processes, can simultaneously and significantly reduce COD, ammonia nitrogen, and TDS, is adaptable to waste acid resource utilization, and has strong industrial applicability. Summary of the Invention

[0013] This invention aims to solve the technical problems existing in the prior art and provide a method and system for simultaneous treatment of high-salt, high-ammonia-nitrogen, and high-COD wastewater based on acid fractionation.

[0014] (a) Technical problems to be solved 1. Reveal the core mechanism of COD exceeding the standard in acidic distillation, break the industry technical contradiction that "acidic distillation meets the ammonia nitrogen standard but COD does not meet the standard, and alkaline distillation meets the COD standard but ammonia nitrogen / TDS does not meet the standard", and solve the long-standing pain point that the three indicators cannot be reduced significantly at the same time; 2. Reveal and sever the intrinsic chain of "ammonia nitrogen-TDS coupling excess" in neutral / alkaline distillation, break through the technical bottleneck of traditional stepwise process, achieve simultaneous and efficient removal of three indicators in one distillation, greatly simplify the process flow and reduce the processing cost; 3. Clarify the synergistic effect of ammonia nitrogen fixation, TDS retention, and COD separation within the pH range of 1.0 to 6.5, optimize the pH adaptation range for high ammonia nitrogen conditions, and provide accurate and practical reference for parameter selection in actual industrial conditions. 4. To realize the resource utilization of industrial waste sulfuric acid, waste hydrochloric acid, and waste acid containing phosphate, and to give priority to the use of waste acid for distillation residues that are hazardous waste, so as to treat waste with waste and achieve the synergistic effect of reducing hazardous waste and reducing treatment costs. 5. Design a dedicated treatment system adapted to this process to lower the threshold for industrialization, reserve flexible adjustment interfaces, and adapt process parameters according to different wastewater qualities to meet the wastewater treatment needs of enterprises in all scenarios.

[0015] (II) Core Technology Principles 1. Ammonia nitrogen fixation core mechanism An acid regulator is added to the wastewater before distillation to precisely adjust it to an acidic environment with a pH of 1.0–6.5. The ammonia nitrogen in the wastewater combines with sulfate, chloride, and phosphate ions provided by the acid regulator to form stable ammonium sulfate, ammonium chloride, and ammonium phosphate salts. These ammonium salts exist in an ionic state in the acidic environment, have high boiling points, and do not volatilize with water vapor, completely solving the problem of excessive ammonia nitrogen caused by the volatilization of free ammonia in neutral / alkaline distillation. For wastewater with extremely high ammonia nitrogen levels (>1000 mg / L), the pH range is optimized to 1.0–5.5 to ensure that high-concentration ammonia nitrogen is completely converted into stable ammonium salts, avoiding excessive ammonia nitrogen levels caused by the volatilization of trace amounts of free ammonia, thus balancing treatment effectiveness with equipment corrosion control.

[0016] 2. TDS Retention and Enhancement Mechanism Those skilled in the art could only anticipate that acidic conditions could fix ammonia nitrogen, but could not anticipate that an acidic environment could simultaneously and significantly improve TDS removal rate. This invention, through extensive experimentation, reveals for the first time that an acidic environment eliminates the interference of free ammonia on the gas-liquid balance and prevents salts from being entrained by water vapor. For high ammonia nitrogen wastewater (≥1000 mg / L), acidic distillation improves TDS removal rate by more than 20% compared to neutral distillation, achieving a chain-like synergistic reaction of "ammonia nitrogen fixation → enhanced TDS removal rate," which constitutes the core of this invention's inventiveness.

[0017] 3. Core Mechanism of COD Compliance This invention, through in-depth research, is the first to systematically reveal the dual mechanism of COD exceeding the standard in distillate under acidic conditions: • (a) Inhibition of dissociation of volatile organic acids: Under acidic conditions, the degree of dissociation of volatile organic acids (such as acetic acid, propionic acid, etc.) in wastewater is significantly reduced, and they exist in molecular form. Their volatility is greatly enhanced, and they are easily evaporated out with water vapor.

[0018] (ii) Promotion of interphase migration of polar organic compounds: More importantly, this invention is the first to discover that during distillation under conventional neutral or alkaline conditions, some oxygen- and nitrogen-containing polar organic compounds (such as alcohols, phenols, amines, heterocyclic compounds, etc.) are effectively "locked" in the distillation residue or slag due to hydrogen bonding with water molecules or their ionic state, making them difficult to volatilize. However, when the system becomes acidic (pH≤6.5), the protonated state or intermolecular forces of these organic compounds change, their hydrophilicity decreases, and their volatility increases, causing them to migrate in large quantities from the residue / slag phase to the gas phase fraction. This "acidity-promoted migration effect" is the fundamental reason why COD exceeds the standard under traditional acid distillation, yet it has long been unrecognized by the industry.

[0019] The synergistic solution of this invention: Based on the above dual mechanism, this invention does not simply avoid acidic environments, but creatively proposes a "fractional distillation + COD-oriented separation" strategy: • Fractional distillation: By utilizing the difference in boiling points between different organic compounds and water, and by controlling the reflux ratio and the number of trays, high-boiling-point COD components are retained in the bottom distillate, while COD components with increased volatility are enriched in the initial fraction.

[0020] • COD-directed separation: By accurately separating the first 1% to 25% of the initial distillate, the COD components that are "driven" into the gas phase by the acidic environment are actively "intercepted", thereby ensuring that the COD of the main distillate water meets the standards.

[0021] 4. pH gradient effect pattern Multiple parallel experiments verified that the ammonia nitrogen removal efficiency exhibits a stable gradient distribution with pH value: under suitable conditions, the ammonia nitrogen removal rate is ≥97% below pH 4.0, ≥90% at pH 5.0, and stably ≥85% at pH 6.5. For ultra-high ammonia nitrogen wastewater with ammonia nitrogen >1000mg / L, the ammonia nitrogen removal rate can be stably ≥98% in the pH range of 1.0 to 5.5. The pH parameters can be precisely matched according to the effluent requirements and wastewater quality of industrial enterprises, taking into account the treatment effect, equipment corrosion, and operating costs.

[0022] 5. The universal principle of acid regulators The core function of the acid regulator described in this invention is to provide H+ ions to precisely adjust the pH of wastewater to 1.0–6.5, thereby converting ammonia nitrogen into stable, non-volatile ammonium salts. Those skilled in the art will understand that any acidic substance capable of releasing H+ ions (including but not limited to inorganic or organic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, and citric acid, as well as corresponding industrial waste acids) can achieve the stabilization and fixation of ammonia nitrogen, provided that its addition is sufficient to lower the wastewater pH to the target range. The effect depends solely on the final pH value and is independent of the type of acid.

[0023] Meanwhile, the concentration of the acid regulator only affects the dosage volume and ease of operation, without changing the technical principle of this invention. Although a large dosage is required for extremely low concentrations (e.g., 0.05 mol / L) of dilute acid, it can still adjust the wastewater to the target pH and achieve ammonia nitrogen fixation, and low-value waste acid can be utilized for resource recovery. Concentrated acids with extremely high concentrations (e.g., 20 mol / L) require very small dosages and require careful operation, but pH adjustment can still be achieved. Therefore, any acid regulator with a concentration in the range of 0.05 mol / L to 20 mol / L can be applied to this invention, and all can achieve the core technical effect of simultaneously and significantly reducing the three indicators.

[0024] It should be noted that, to avoid safety and environmental risks, this invention does not use acids with strong oxidizing properties or high toxicity, including nitric acid (HNO3), perchloric acid (HClO4), hydrofluoric acid (HF), and waste acids containing the above components. All operations must comply with the "Regulations on the Safety Management of Hazardous Chemicals" and relevant safety standards.

[0025] (III) Technical Solution First aspect: A method for simultaneous treatment of high-salt, high-ammonia-nitrogen, and high-COD wastewater based on acid fractionation. This method is applicable to high-salinity, high-ammonia-nitrogen, and high-COD wastewater with COD ≥ 3500 mg / L, TDS ≥ 5000 mg / L, and ammonia nitrogen ≥ 150 mg / L. The core steps are as follows: 1. Acidity regulation Add one or more acid regulators selected from sulfuric acid, hydrochloric acid, phosphate-containing acidic compounds, waste sulfuric acid, waste hydrochloric acid, and phosphate-containing waste acidic compounds to the wastewater. After stirring and mixing, adjust the wastewater to an acidic environment with a pH of 1.0 to 6.5. This converts the ammonia nitrogen in the wastewater into stable ammonium salts, eliminates the competitive inhibition of free ammonia on the volatilization of organic matter, and ensures that the distillation process is kept stable in this acidic environment.

[0026] • Acid regulator concentration range: The total acid concentration of sulfuric acid / waste sulfuric acid, calculated as H2SO4, is 0.5-105% (fuming sulfuric acid containing free SO3), with an optimized range of 15-80%, preferably 30-70%; the total acid concentration of hydrochloric acid / waste hydrochloric acid, calculated as HCl, is 0.5-38%, with an optimized range of 5-31%, preferably 10-20%; the mass concentration of phosphate-containing acid compounds / corresponding waste acid, calculated as H3PO4 equivalent, is 0.5-99.5%, with an optimized range of 5-85%.

[0027] • Precise pH matching rule: Adjust the pH to the range of 1.0 to 6.5 according to the ammonia nitrogen concentration in the wastewater, taking into account both the control of acid corrosion of the distillation equipment and the stabilization effect of ammonium salt; when ammonia nitrogen > 1000 mg / L, the pH is adjusted to 1.0 to 5.5; when ammonia nitrogen ≤ 1000 mg / L, the pH is adjusted to 5.5 to 6.5.

[0028] • Resource-based adaptation rules: In cases where distillation residues are identified as hazardous waste, waste sulfuric acid, waste hydrochloric acid, and waste acid compounds containing phosphate ions should be given priority as acid regulators to achieve waste treatment with waste and reduce the cost of hazardous waste disposal.

[0029] 2. Fractional distillation The acidified wastewater is introduced into a fractional distillation equipment that is resistant to acid corrosion with pH ≤ 6.5 for fractional distillation to separate the gaseous fraction and the distillate bottom liquid, so that the ammonium salt and the salts in the wastewater are simultaneously retained in the distillate bottom liquid.

[0030] • Process parameters: The absolute pressure of distillation is 0.005~0.1 MPa, and the distillation temperature is 33~100℃.

[0031] • Equipment Material Matching: The materials of the distillation equipment should be precisely matched according to the pH range of the wastewater: 316L stainless steel, duplex stainless steel 2205, carbon steel kettle with acid-resistant coating, or acid-resistant fiberglass should be selected when pH is 2.5 to 6.5; titanium alloy or Hastelloy should be selected when pH is ≤1 or when the added concentration is >98% sulfuric acid; impermeable graphite, polytetrafluoroethylene lining material, or silicon carbide ceramic should be selected; when hydrochloric acid is added as an acid regulator, the equipment materials should be strictly matched according to the corresponding pH range.

[0032] • Separation Accuracy Explanation: To achieve higher effluent quality requirements (e.g., COD reduced to below 20% of raw water value, ammonia nitrogen reduced to below 10% of raw water value), a fractionation column with a higher theoretical plate number or an increased number of internal layers can be selected based on the target separation effect. Simultaneously, the reflux ratio (the ratio of reflux liquid to produced liquid, typically 0.5:1 to 5:1) can be adjusted. A higher reflux ratio results in higher gas-liquid mass transfer efficiency and more thorough COD separation, but also increases energy consumption. Coordinated adjustment of the theoretical plate number and reflux ratio can achieve an optimal balance between separation effect and operating cost.

[0033] 3. COD-directed separation The gaseous fraction is condensed and separated to directionally separate the high-COD organic phase, yielding the main distillate water. The COD value of the main distillate water is less than 30% of that of the raw water, the ammonia nitrogen value is less than 15% of that of the raw water, and the TDS removal rate exceeds 50%.

[0034] • Specific process: After the vapor fraction is condensed, the initial fraction of 1% to 25% by volume is separated as the high COD organic phase, and the remaining 75% to 99% of the fraction is separated as the main fraction, water. The initial fraction separation ratio can be automatically adjusted according to online COD monitoring data to ensure that the COD of the main fraction meets the requirement of being 30% lower than the COD value of the raw water.

[0035] Explanation of the technical meaning of "COD is less than 30% of the raw water" in this invention The statement in this invention that "the COD value of the main distillate water is less than 30% of the COD value of the raw water" is not the upper limit of the technical effect (the examples have shown that it can be reduced to 2% to 5%), but rather the lower limit guarantee that this invention can stably achieve under different operating conditions and different types of distillation equipment.

[0036] The COD removal rate is closely related to the core process parameter of this invention, "initial fraction separation ratio," and the type of distillation equipment used. • When the COD of the raw water is 3500-10000 mg / L, only 1%-5% of the initial fraction needs to be separated, and the COD of the main fraction can be reduced to less than 5% of that of the raw water. • When the COD of the raw water is 10,000 to 100,000 mg / L, it is necessary to separate 5% to 15% of the initial fraction, and the COD of the main fraction can be reduced to less than 10% of that of the raw water. • When the COD of the raw water is ≥100000mg / L, 15% to 25% of the initial fraction needs to be separated: if ordinary distillation equipment is used, the COD of the main fraction can be reduced to 15% to 25% of the raw water; if a high-efficiency distillation column with ≥30 theoretical plates is used, it can be controlled to within 10% of the raw water.

[0037] In summary, regardless of the distillation equipment used or the concentration range of wastewater being treated, this invention can guarantee that the COD of the main fraction is reduced to at least 30% of the COD value of the raw water. The superior removal effect (2%–5%) in the embodiments is a further manifestation of this invention under preferred parameters and does not constitute a limitation on the scope of protection.

[0038] Explanation of the technical meaning of "TDS removal rate exceeding 50%" in this invention Similarly, the "TDS removal rate exceeding 50%" mentioned in this invention is a lower limit guarantee, not an upper limit of the technical effect. The TDS removal rates in all embodiments exceed 92%, far higher than 50%. The core mechanism of this invention (acidic fixation of ammonia nitrogen → elimination of free ammonia → avoidance of salt entrainment) dictates that TDS retention is an inevitable result. Those skilled in the art can reasonably predict that, as long as the acidic adjustment and fractional distillation steps of this invention are implemented, the TDS removal rate cannot be lower than 50%. The 50% lower limit reflects the robustness and industrial applicability of this invention; the superior removal effect (above 92%) in the embodiments does not constitute a limitation on the scope of protection.

[0039] 4. Optional post-processing steps (a) Pretreatment: When the turbidity of the wastewater is ≥100 NTU, a coagulation and filtration pretreatment step is added before acidification. 50-100 mg / L polyaluminum chloride (PAC) or 1-5 mg / L polyacrylamide (PAM) is added to the wastewater. After coagulation and stirring, the wastewater is filtered until the turbidity of the effluent is ≤50 NTU to avoid suspended solids from affecting the distillation efficiency. (b) Waste gas treatment: The trace amounts of ammonia-containing waste gas generated by distillation are absorbed by spraying with 10% to 15% sodium hydroxide solution and then discharged in compliance with standards; (c) Distillate water treatment: If the main distillate water meets the requirements, it is directly discharged or reused; if it does not meet the requirements, it is returned to the fractionation distillation equipment for secondary treatment. (d) Residue disposal: Mix the high COD organic phase with the distillation bottom liquid and reflux it to the front end of the process for further treatment, or add sodium hydroxide / calcium hydroxide alkaline neutralizing agent to adjust the pH to 6.0-9.0. After identification by the "Hazardous Waste Identification Standard" (GB5085) series of standards, dispose of it in compliance with the classification of hazardous waste and non-hazardous waste. (e) Enhanced Biodegradability Pretreatment (Optional): After treatment with this invention, the COD, ammonia nitrogen, and TDS of the main distillate are significantly reduced, and it can usually be directly introduced into the subsequent biological treatment system. However, for some special wastewaters containing a large amount of recalcitrant organic matter (such as some chemical and pharmaceutical wastewaters), even if the COD has been reduced to below 30% of the original water, its biodegradability (BOD / COD ratio) may still be low. In this case, conventional biodegradability enhancement pretreatment units (such as advanced oxidation, hydrolysis acidification, iron-carbon micro-electrolysis, etc.) can be selectively added before the main distillate enters the biological treatment system to further improve the overall treatment effect. This addition step is not necessary to achieve the basic objective of this invention, and those skilled in the art can flexibly choose it according to the actual wastewater quality and treatment requirements.

[0040] The second aspect: A system for the simultaneous treatment of high-salt, high-ammonia-nitrogen, and high-COD wastewater based on acid fractionation. This system is a dedicated industrial system designed to adapt to the above-mentioned acid fractionation method. It can flexibly adjust process parameters according to different wastewater qualities, is compatible with all types of acid-resistant distillation equipment, and has a low threshold for industrialization.

[0041] The core of this system includes a feed unit, an acidity adjustment unit, a fractionation distillation unit, a COD directional separation unit, and a control unit connected in sequence to all units: 1. Feeding Unit: Used to supply the system with wastewater having a chemical oxygen demand (COD) ≥3500 mg / L, total dissolved solids (TDS) ≥5000 mg / L, and ammonia nitrogen (NH3-N) ≥150 mg / L. 2. Acidity Adjustment Unit: Used for precise addition of acid regulators to wastewater, adjusting the wastewater to the target acidic environment of pH 1.0–6.5, converting ammonia nitrogen into stable ammonium salts, and eliminating the competitive inhibition of free ammonia on the volatilization of organic matter; includes an acid-resistant stirring tank, acid storage tank, metering dosing pump, and online pH monitor. The metering dosing pump and online pH monitor are linked for control, and can automatically adjust the dosage of acid regulators according to the real-time pH value of the wastewater, ensuring that the wastewater remains stably in the target acidic environment throughout the distillation process.

[0042] 3. Fractional distillation unit: Connected to the discharge end of the acidity adjustment unit, this fractional distillation equipment is resistant to acid corrosion with pH ≤ 6.5. It is used for fractional distillation of acidic wastewater to achieve efficient gas-liquid separation, allowing ammonium salts and salts in the wastewater to be simultaneously retained in the distillation bottom liquid. The equipment type is selected from single-effect / multi-effect fractional distillation equipment, continuous packed / plate fractionation tower, batch enamel-lined distillation kettle, and forced circulation / falling film / rising film fractional distillation equipment.

[0043] 4. COD Directional Separation Unit: Connected to the vapor phase outlet of the fractionation distillation unit, it is used for condensation, phase separation, and precise separation of COD from the vapor phase fraction to obtain the main distillate (pure water); it includes a phase separation tank, a primary fraction collection tank, a main fraction collection tank, a COD monitor, and a proportional control valve, which can automatically adjust the primary fraction separation ratio based on online COD monitoring data.

[0044] 5. Control Unit: Connected to the acidity adjustment unit, fractionation distillation unit, and COD directional separation unit respectively, it is used to control process parameters such as acid regulator dosage, wastewater pH value, distillation temperature, absolute pressure, and fraction separation ratio to achieve fully automated operation.

[0045] Optional supporting units: This system can also be equipped with a pretreatment unit, a waste gas treatment unit, a distillate water treatment unit, and a residue disposal unit. Each supporting unit is connected to the control unit to achieve full-process linkage control.

[0046] (iv) Beneficial effects The present invention, through the above-described technical solution, achieves outstanding substantive features and significant technological progress compared to the prior art, with the following specific beneficial effects: 1. Achieve simultaneous and significant reductions in three pollutants, breaking through industry technological bottlenecks. This invention overcomes the long-standing industry bias that "acidic distillation achieves ammonia nitrogen standards but not COD standards, and alkaline distillation achieves COD standards but not ammonia nitrogen / TDS standards." A single distillation process simultaneously achieves: COD reduction to below 30% of the raw water COD (i.e., removal rate exceeding 70%), ammonia nitrogen reduction to below 15% of the raw water ammonia nitrogen (i.e., removal rate exceeding 85%), and TDS removal rate exceeding 50% (actually exceeding 92% in the example). All three indicators are significantly reduced, substantially lowering the load and cost of subsequent treatment.

[0047] 2. Optimized adaptability to high ammonia nitrogen operating conditions, resulting in significantly higher treatment efficiency than existing technologies. This invention targets wastewater with extremely high ammonia nitrogen levels (>1000 mg / L). The optimized pH range is 1.0–5.5, ensuring complete fixation of high-concentration ammonia nitrogen and reducing the ammonia nitrogen value to below 10% of the original water level. Simultaneously, in an acidic environment with pH ≤ 6.5, a significant improvement in TDS removal rate is achieved. Compared to neutral distillation, the ammonia nitrogen removal rate increases from 60.7% to over 97.2%.

[0048] 3. Achieve resource utilization of waste acid, significantly reducing treatment costs and hazardous waste production. This invention can directly utilize industrial waste sulfuric acid, waste hydrochloric acid, and waste acid containing phosphate as acid regulators to achieve waste treatment. For distillation residues that are hazardous waste, waste acid is given priority. This invention can simultaneously reduce the volume of waste acid and the scale of hazardous waste disposal. The cost per ton of water treated is reduced by 15% to 30% compared to existing technologies, and the amount of hazardous waste generated is reduced by more than 90% compared to step-by-step processes.

[0049] Furthermore, this invention fully leverages the resource utilization opportunities presented by the "acid-heavy, alkali-sparse" market structure for waste acid: in traditional waste acid disposal, low-concentration waste acid becomes a burden for enterprises due to high concentration and disposal costs. This invention has broad requirements for the concentration of the acid regulator (as low as 0.05 mol / L H+ equivalent, approximately equivalent to 0.25% sulfuric acid), achieving synergy between wastewater treatment and waste acid disposal without pre-concentration. Taking 13% dilute sulfuric acid as an example, traditional methods require evaporation and concentration to over 50% before sale, consuming approximately 0.3–0.5 tons of steam to evaporate 1 ton of dilute sulfuric acid; however, this invention directly uses it as an acid regulator, saving over 0.3 tons of steam per ton of dilute sulfuric acid disposed of, while eliminating the costs of waste acid neutralization and the generation of hazardous sludge. Calculations show that the overall treatment cost per ton of water can be reduced by 10%–15% compared to existing technologies.

[0050] 4. The system is highly adaptable to specialized applications and has a low barrier to industrialization. This invention designs a dedicated system adapted to acidic fractionation processes, compatible with all types of acid-resistant distillation equipment. It does not require large-scale modifications to existing distillation equipment, only acid-resistant and corrosion-resistant adaptations are needed. It is suitable for new and renovation projects of enterprises of different sizes. The system can flexibly adjust pH, distillation parameters, and fraction separation ratios according to the wastewater quality, adapting to the wastewater treatment needs of multiple industries and operating conditions. Attached Figure Description

[0051] Figure 1 The diagram shows the process flow of the method of the present invention (dashed boxes / line segments represent optional units / process routes). The diagram marks 1-pretreatment process (optional), 2-acidity adjustment process, 3-fractional distillation process, 4-COD directional separation process, 5-main fraction treatment process, 6-residue treatment process, and 7-waste gas treatment process, clearly defining the core technical indicators for simultaneous and significant reduction of three indicators. Optional units are marked with dashed boxes.

[0052] Figure 2 The attached diagram is a structural schematic of the system of the present invention (dashed boxes indicate optional units). The reference numerals are: 1-feeding unit, 2-pretreatment unit, 3-acidity adjustment unit, 4-fractional distillation unit, 5-COD directional separation unit, 6-control unit, 7-waste gas treatment unit, 8-distillate water treatment unit, 9-residue disposal unit. Each unit is connected in sequence according to the material flow direction and signal flow direction. The control unit is connected to all units by signal. Optional supporting units are marked with dashed boxes.

[0053] The process valves, pumps, and other conventional auxiliary equipment not shown in the attached diagrams are all conventional technical means in this field. Detailed Implementation

[0054] In this invention, "absolute pressure" refers to pressure measured with absolute vacuum as the zero point. At standard atmospheric pressure (approximately 0.1 MPa), an absolute pressure of 0.1 MPa corresponds to atmospheric pressure (gauge pressure of 0 MPa), and an absolute pressure of 0.005 MPa corresponds to a gauge pressure of -0.095 MPa. Those skilled in the art will understand that absolute pressure and gauge pressure can be converted by adding or subtracting atmospheric pressure; they are essentially the same.

[0055] It should be noted that the separation ratio of the initial fraction in this invention can be adjusted according to the content of volatile organic compounds (VOCs) in the wastewater. For wastewater with extremely low VOC content, the initial fraction ratio can be as low as 1% while still ensuring that the COD of the main fraction meets the standards; for wastewater with high VOC content, the initial fraction ratio may need to be increased to 15%–25%. The following examples fully cover the range of 1%–25%, but the scope of protection of this invention is not limited thereto.

[0056] The "fractional distillation" described in this invention refers to the process of collecting the generated gaseous fractions sequentially in segments (i.e., dividing them into a primary fraction and a main fraction) during distillation. Any distillation apparatus capable of achieving gas-liquid separation and allowing for segmented collection of fractions can be used to implement the fractional distillation steps of this invention.

[0057] All test items in the following examples comply with current national standards: COD testing is based on "Determination of Chemical Oxygen Demand in Water - Dichromate Method" (HJ828-2017); ammonia nitrogen testing is based on "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method" (HJ535-2009); TDS testing is based on "Determination of Total Dissolved Solids in Water - Gravimetric Method" (HJ / T51-1999); and turbidity testing is based on "Determination of Turbidity in Water - Portable Turbidity Meter Method" (HJ1075-2019). All experimental data are the average of three parallel experiments, and the relative deviation of parallel experiments is ≤5%.

[0058] Example 1: Validation of full-gradient pH for landfill leachate treatment (including pH 1.0) Experimental objective: To verify the treatment effect of the method of the present invention in the whole range of pH 1.0 to 6.5 in the landfill leachate scenario, and to verify the effectiveness of the pH gradient adaptation rule; Experimental wastewater: leachate from an old landfill, COD 8500 mg / L, TDS 12000 mg / L, ammonia nitrogen 320 mg / L, pH 7.2, turbidity 180 NTU; Pretreatment: Add 50 mg / L PAC, stir at 250 r / min for 20 min, and filter through a plate and frame filter until the turbidity is ≤50 NTU; Experimental groups: using the same wastewater and the same distillation parameters, with only the pH adjustment value differing to ensure uniqueness of the variables; Process parameters: 40% industrial sulfuric acid is added as an acid regulator to adjust the pH to 1.0, 2.0, 3.0, 4.5, 6.0 and 6.5 respectively; negative pressure distillation absolute pressure is 0.02MPa, distillation temperature is 60℃, and the mass ratio of gas phase fraction to bottom liquid is 0.8:1. The first 15% of the initial fraction is used as the high COD organic phase. Processing result: pH value, main fraction COD (mg / L), COD reduction to raw water ratio, main fraction ammonia nitrogen (mg / L), ammonia nitrogen reduction to raw water ratio, main fraction TDS (mg / L), TDS removal rate. Do these three indicators meet the standards? 1.0 152 1.79% Not detected 0% 405 96.6% Yes 2.0 132 1.55% Not detected 0% 415 96.5% Yes 3.0 142 1.67% Not detected 0% 435 96.4% Yes 4.5 150 1.76% Not detected 0% 445 96.3% Yes 6.0 165 1.94% 8.6 2.7% 460 96.2% Yes 6.5 180 2.12% 14.4 4.5% 480 96.0% Yes Conclusion: Within the entire pH range of 1.0 to 6.5, the method of this invention can reduce COD to below 30% of the raw water, ammonia nitrogen to below 15% of the raw water, and TDS removal rate to over 50% (actually >96%), verifying the effectiveness of the full protection range of pH 1.0 to 6.5.

[0059] Example 2: Specific verification of ultra-high ammonia nitrogen wastewater in the pH range of 1.0–5.5 Experimental objective: To verify the treatment effect of the present invention on wastewater with ultra-high ammonia nitrogen concentration (>1000 mg / L) in the pH range of 1.0–5.5; Experimental wastewater: Production wastewater from a fine chemical enterprise, COD 7200 mg / L, TDS 22000 mg / L, ammonia nitrogen 1200 mg / L, pH 8.2, turbidity 75 NTU; Process parameters: Add 31% industrial waste hydrochloric acid, adjust pH to 1.0, 2.0, 3.2, 4.0, 5.0 and 5.5 respectively, negative pressure distillation absolute pressure 0.01MPa, distillation temperature 46℃, gas phase fraction to bottom liquid mass ratio 0.75:1, separate the first 20% of the initial fraction; Processing result: pH value, main fraction COD (mg / L), COD reduction to raw water ratio, main fraction ammonia nitrogen (mg / L), ammonia nitrogen reduction to raw water ratio, main fraction TDS (mg / L), TDS removal rate, whether the three items meet the standards. 1.0 200 2.80% 10.7 0.89% 850 96.1% Yes 2.0 202 2.81% 10.8 0.90% 855 96.1% Yes 3.2 210 2.92% 12.6 1.05% 880 96.0% Yes 4.0 215 2.99% 14.4 1.20% 895 95.9% Yes 5.0 220 3.06% 16.8 1.40% 910 95.9% Yes 5.5 228 3.17% 19.2 1.60% 925 95.8% Yes Conclusion: For wastewater with ultra-high ammonia nitrogen (>1000 mg / L), the removal rates of COD, ammonia nitrogen, and TDS all remained stable and met the standards within the pH range of 1.0–5.5.

[0060] Example 3: Validation of ultra-high COD wastewater treatment Experimental wastewater: Fermentation wastewater from a pharmaceutical company, COD 18000 mg / L, TDS 15000 mg / L, ammonia nitrogen 280 mg / L, pH 6.8; Processing technology: Add 85% industrial orthophosphoric acid to adjust the pH to 5.8, perform negative pressure distillation at an absolute pressure of 0.03 MPa and a distillation temperature of 69℃, and separate the first 25% fraction; Treatment results: COD of the main fraction was 380 mg / L (reduced to 2.11% of the original water), ammonia nitrogen was undetectable, and TDS was 750 mg / L (removal rate 95.0%). All three indicators met the requirements.

[0061] Example 4: Comparison and verification of the effects of acidic fractionation with existing technologies Experimental wastewater: Same as in Example 1; Grouping: • Experimental group: This invention (pH 3.0, separation of the initial 15% fraction); • Control group 1: Neutral distillation (pH 7.2, COD-free directional separation); • Control group 2: Acidic full-fraction distillation (pH 6.0, COD-free directional separation); result: Group COD reduced to raw water ratio Ammonia nitrogen reduced to raw water ratio TDS (mg / L) Whether TDS removal rate meets standard The experimental group had 1.94% and 2.7% of the samples, with 460 samples and 96.2% respectively. Control group 1: 34.0% 40.0% 2860 76.2% No Control group 2: 49.0% 0% 455 96.2% No (COD exceeded the standard) Conclusion: This invention alone can achieve simultaneous compliance with all three indicators, and the TDS removal rate far exceeds 50%.

[0062] Example 5: Waste Acid Resource Utilization and Hazardous Waste Validation Experimental wastewater: COD 6800mg / L, TDS 9500mg / L, ammonia nitrogen 350mg / L; distillation residue is hazardous waste. Treatment process: The pH is adjusted to 5.9 using waste citric acid solution (pH 1.5), and the first 15% of the initial fraction is separated. Results: The main fraction COD was 220 mg / L (3.24%), ammonia nitrogen was undetectable, and TDS was 380 mg / L (removal rate 96.0%), meeting the standards.

[0063] Example 6: Validation of extremely low concentration acid regulator (0.1 mol / L H⁺) The experimental wastewater was treated the same as in Example 1. 0.1 mol / L dilute sulfuric acid (20% by volume) was added to adjust the pH to 6.0. Fractional distillation was then performed according to the distillation parameters of Example 1 (absolute pressure 0.02 MPa, reboiler temperature 60℃), separating the first 15% fraction. Results: The main fraction showed COD of 175 mg / L (2.06% of raw water), ammonia nitrogen of 10.2 mg / L (3.2% of raw water), and TDS of 490 mg / L (removal rate 95.9%), all meeting the standards.

[0064] Example 7: Validation of a medium-concentration acid regulator (5 mol / L H⁺, industrial hydrochloric acid) The experimental wastewater was the same as in Example 1. 5 mol / L industrial hydrochloric acid was added to adjust the pH to 6.0. Distillation parameters were the same as in Example 6, and the first 15% fraction was separated. Results: The main fraction had COD of 160 mg / L (1.88% of the original water), ammonia nitrogen of 8.9 mg / L (2.8% of the original water), and TDS of 455 mg / L (removal rate 96.2%), all three indicators meeting the standards.

[0065] Example 8: Validation of high-concentration acid regulator (18 mol / L H⁺, concentrated sulfuric acid) The experimental wastewater was the same as in Example 1. 18 mol / L concentrated sulfuric acid was pre-diluted, cooled, and added. The pH was adjusted to 6.0, and the distillation parameters were the same as in Example 6. The first 15% fraction was separated. Results: The main fraction had COD of 155 mg / L (1.82% of the original water), ammonia nitrogen of 8.2 mg / L (2.6% of the original water), and TDS of 448 mg / L (removal rate 96.3%), all three indicators meeting the standards.

[0066] Example 9: Validation of wastewater treatment containing high volatile organic compounds (methanol) The experimental wastewater was methanol-containing chemical wastewater with a COD of 3800 mg / L, TDS of 6800 mg / L, and ammonia nitrogen of 220 mg / L. 30% waste sulfuric acid was added to adjust the pH to 6.5. The absolute pressure was 0.02 MPa, the distillation temperature was 55℃, and the first 1% fraction was separated. Results: The main fraction had a COD of 180 mg / L (4.74% of the original water), an ammonia nitrogen of 10 mg / L (4.55% of the original water), and a TDS of 520 mg / L (removal rate 92.4%), all three indicators meeting the standards.

[0067] Example 10: Validation of ultra-high concentration organic wastewater (COD ≥ 100,000 mg / L) The experimental wastewater was concentrated leachate from a landfill RO reactor, with COD 125,000 mg / L, TDS 68,000 mg / L, and ammonia nitrogen 12,500 mg / L. Industrial waste sulfuric acid was added to adjust the pH to 3.0. A high-efficiency distillation column with 30 theoretical plates was used for distillation at 75℃ and 0.02 MPa absolute pressure, separating the first 25% fraction. Results: The main fraction had COD of 2338 mg / L (1.87% of the original water), ammonia nitrogen <5 mg / L (0.04% of the original water), and TDS of 980 mg / L (removal rate 98.6%), all three indicators meeting the standards.

[0068] Example 11: Verification of treatment under atmospheric distillation conditions Experimental wastewater: Same as in Example 1 (landfill leachate, COD 8500 mg / L, TDS 12000 mg / L, ammonia nitrogen 320 mg / L, pH 7.2) Preprocessing: Same as in Example 1 Process parameters: Acid adjuster: 40% industrial sulfuric acid, adjusting pH to 4.0; Distillation method: Atmospheric distillation (absolute pressure approximately 0.1 MPa); Distillation temperature: 98~102℃ (bottom of column); Reflux ratio: 1.5:1; Initial fraction separation ratio: 15% (volume ratio) Reference settings: • Control group 1: Same pH 4.0, atmospheric distillation, no separation of the initial fraction (collect the whole fraction); • Control group 2: pH not adjusted (raw water pH 7.2), atmospheric distillation, no separation of initial fraction. Processing result: Group COD (mg / L) COD reduction to raw water ratio Ammonia nitrogen (mg / L) Ammonia nitrogen reduction to raw water ratio TDS (mg / L) TDS removal rate All three parameters simultaneously meet the standards In this invention, the experimental group 195 showed a 2.29% success rate, 8.5% a success rate, and 2.66% a success rate; the experimental group 460 showed a 96.2% success rate. Control group 1: 3120 36.7% 8.2 2.56% 465 96.1% No (COD exceeded the standard) Control group 2: 1150 13.5% 192 60.0% 860 92.8% No (ammonia nitrogen exceeded the standard) Conclusion: Under atmospheric pressure distillation conditions, the method of this invention can still achieve the core technical effects of reducing COD to below 30% of the raw water, reducing ammonia nitrogen to below 15% of the raw water, and achieving a TDS removal rate of over 50%. Compared with negative pressure distillation, the effects are slightly different, but both are far superior to the lower limit of compliance, proving that this invention is also applicable to atmospheric pressure industrial scenarios and is not limited to negative pressure conditions.

[0069] Safety and environmental protection operating instructions: The acid regulators used in this invention should avoid using acids with strong oxidizing properties or high toxicity, including but not limited to nitric acid (HNO3), perchloric acid (HClO4), hydrofluoric acid (HF), and waste acids containing the above components. For easily exothermic acids such as concentrated sulfuric acid (≥70%), slow injection and stirring cooling should be used during addition to prevent local overheating and sudden boiling. Although hydrochloric acid does not pose an explosion risk, its high volatility requires the waste gas treatment unit to have alkaline spray absorption capabilities. Fuming sulfuric acid (containing free SO3, concentration ≥100%) has strong oxidizing properties and a risk of violent exothermic reactions; therefore, strict safety protection measures must be implemented when using it.

[0070] Summary of Implementation Examples: The TDS removal rate of all embodiments exceeded 92%, far higher than the lower limit requirement of 50%, fully supporting the claim that "the TDS removal rate exceeds 50%".

[0071] Conventional substitutions and minor adjustments to process parameters and equipment structures made by those skilled in the art based on the core principles of this invention, without any creative effort, do not depart from the protection scope of this invention.

Claims

1. A method for simultaneous treatment of high-salinity, high-ammonia-nitrogen, and high-COD wastewater based on acid fractionation, wherein the high-salinity, high-ammonia-nitrogen, and high-COD wastewater has a chemical oxygen demand (COD) ≥3500 mg / L, total dissolved solids (TDS) ≥5000 mg / L, and ammonia nitrogen (NH3-N) ≥150 mg / L, characterized in that, Includes the following steps: (1) Acidity adjustment: Add acid regulator to wastewater to adjust the wastewater to an acidic environment of pH 1.0 to 6.5, so that the ammonia nitrogen in the wastewater is converted into ammonium salt; (2) Fractional distillation: The wastewater after acidification in step (1) is introduced into an acid-resistant fractional distillation equipment for fractional distillation to obtain gaseous fraction and distillation bottom liquid; (3) COD directional separation: The gas phase fraction obtained in step (2) is condensed and then the initial fraction with a volume ratio of 1% to 25% is separated to obtain the main fraction, water.

2. The method according to claim 1, characterized in that, In step (3), the COD value of the main distillate water is 30% lower than that of the raw water, the ammonia nitrogen value is 15% lower than that of the raw water, and the TDS removal rate is more than 50%.

3. The method according to claim 1, characterized in that, In step (2), the process parameters for fractional distillation are: the absolute pressure of distillation is 0.005 to 0.1 MPa, and the distillation temperature is 33 to 102℃.

4. The method according to claim 1, characterized in that, In step (3), the separation ratio is automatically adjusted within the range of 1% to 25% according to the COD index requirements of the main distillate water.

5. The method according to claim 1, characterized in that, In step (1), the acid regulator is at least one of inorganic acid, organic acid or corresponding waste acid, but does not include nitric acid, perchloric acid, hydrofluoric acid and waste acid containing the above components; the mass concentration of the acid regulator is 0.5% to 100%; the acid regulator is sulfuric acid or waste sulfuric acid, and its mass concentration is 0.5% to 105%.

6. The method according to claim 1, characterized in that, It also includes one or more post-processing steps: (a) Waste gas treatment: The waste gas generated during distillation is absorbed by alkaline spray before being discharged; (b) Distillate water treatment: The main distillate water is tested. If its COD, ammonia nitrogen, and TDS indicators do not meet the predetermined reuse or discharge standards, it is recycled to the fractionation distillation equipment for secondary treatment. (c) Residue disposal: The initial fraction and distillate separated in step (3) are adjusted to pH 6.0 to 9.0, identified according to the hazardous waste identification standard, and disposed of in compliance with the classification based on the identification results.

7. A simultaneous treatment system for high-salt, high-ammonia-nitrogen, and high-COD wastewater for implementing the method of claim 1, wherein the high-salt, high-ammonia-nitrogen, and high-COD wastewater is wastewater with a chemical oxygen demand (COD) ≥3500 mg / L, total dissolved solids (TDS) ≥5000 mg / L, and ammonia nitrogen (NH3-N) ≥150 mg / L, characterized in that, include: • An acid conditioning unit includes an acid-resistant stirring tank, an acid storage tank, a metering dosing pump, and an online pH monitor. The metering dosing pump is linked to the online pH monitor for control and is used to add an acid conditioner to the wastewater to adjust the wastewater to an acidic environment with a pH of 1.0 to 6.

5. • The fractional distillation unit is a fractional distillation device that is resistant to acidic corrosion corresponding to the pH value of the wastewater it treats. It is connected to the discharge end of the acidity adjustment unit and is used to fractional distill the acidic wastewater. • COD directional separation unit, connected to the gas phase outlet of the fractionation distillation unit, includes a phase separation tank, a primary fraction collection tank, a main fraction collection tank, a COD monitor, and a proportional control valve, used to condense the gas phase fraction and separate the primary fraction to obtain the main fraction, purified water; • The control unit is connected to the acidity adjustment unit, fractionation distillation unit, and COD directional separation unit respectively, and is used to control the dosage of acid regulator, wastewater pH value, distillation temperature, absolute pressure, and fraction separation ratio in a coordinated manner.

8. The system according to claim 7, characterized in that, It also includes one or more of the following: pretreatment unit, waste gas treatment unit, distillate water treatment unit, and residue disposal unit. Each supporting unit is connected to the control unit to achieve full-process linkage control. The pretreatment unit is used for coagulation and filtration pretreatment of high-turbidity wastewater.

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