Method and system for treating evaporation mother liquor of petrochemical wastewater

Abstract

The invention provides a petrochemical wastewater evaporation mother liquor treatment method, which comprises: adjusting the water quality of a mother liquor generated after petrochemical wastewater evaporation to obtain adjusted wastewater, and carrying out primary treatment on the adjusted wastewater to obtain excess sludge and primary wastewater; carrying out separation treatment on the residual sludge to obtain filtered wastewater, and carrying out oxidation treatment on the filtered wastewater and the preliminary wastewater to degrade organic matters in water to obtain oxidized wastewater; and finally, recycling the treated water body generated by the active treatment of the oxidized wastewater. According to the method, through a step-by-step strategy of firstly precipitating and separating inorganic matters and then deeply oxidizing and degrading the organic matters, deep mineralization of the organic matters in the mother liquor and resource recovery of inorganic salts are realized with lower comprehensive energy consumption and operation cost, and substantial reduction of hazardous wastes is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a method and system for treating petrochemical wastewater evaporation mother liquor. Background Art

[0002] With the continuous development of economy and population growth, water shortage and water pollution problems are becoming increasingly serious and have become a key factor restricting the sustainable development of society. Among them, the wastewater generated by the petrochemical industry, especially the MVR (mechanical vapor recompression) evaporation mother liquor generated during its treatment process, has become a difficult breakthrough point in the field of industrial wastewater treatment. The composition of petrochemical wastewater itself is extremely complex, usually containing oils, phenols, sulfides, heavy metals and high concentrations of salts, such as Cl⁻, SO4 2- 、Na + Currently, the mainstream process for treating petrochemical wastewater utilizes a "pretreatment + biochemical treatment + advanced treatment + MVR evaporation and crystallization" approach. However, after MVR evaporation and crystallization, the mother liquor is highly enriched with recalcitrant organic matter and high salt concentrations, resulting in a total dissolved solids (TDS) content exceeding 200,000 mg / L, making it an extremely difficult-to-treat hazardous waste.

[0003] Existing treatment methods for this type of high-salt, high-organic hazardous waste mother liquor suffer from numerous technical drawbacks. Landfill disposal is extremely expensive, costing at least 3,000 yuan per ton. It not only occupies significant land resources but also poses potential pollution risks. While incineration can treat the mother liquor, it consumes significant energy and requires temperatures exceeding 850°C. It also produces dioxins during the incineration process, creating new environmental problems. Advanced oxidation processes (AOPs) have low reaction efficiency when treating high-salt matrix mother liquors, while also maintaining high reagent costs. In practical applications, membrane concentration technology is susceptible to organic contamination and scaling, significantly shortening the membrane's service life.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The first purpose of the present invention is to provide a method for treating the evaporation mother liquor of petrochemical waste liquid, which can deeply mineralize and decompose organic matter, convert complex organic pollutants in the mother liquor into harmless small molecular substances, and at the same time promote the separation and crystallization of inorganic salts, which is convenient for subsequent recycling and utilization, realizes efficient separation and harmless treatment of the mother liquor, realizes resource utilization and reduces pollution to the environment.

[0006] A second object of the present invention is to provide a system for treating petrochemical waste liquid evaporation mother liquor. This system can be closely coordinated with the above-mentioned treatment method, organically integrating various treatment links to achieve automated and continuous operation, thereby significantly improving treatment efficiency and ensuring the stability and reliability of the treatment effect, thereby achieving the goal of significantly reducing hazardous waste and significantly reducing system energy consumption.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A method for treating petrochemical wastewater evaporation mother liquor comprises the following steps: First, the mother liquor generated after evaporation of petrochemical wastewater is regulated to obtain regulated wastewater, and then the regulated wastewater is preliminarily treated to obtain residual sludge and preliminary wastewater; the residual sludge is separated to obtain filtered wastewater, and the filtered wastewater and the preliminary wastewater are oxidized to degrade organic matter in the water to obtain oxidized wastewater; finally, the oxidized wastewater is activated to produce treated water for recycling.

[0008] Preferably, the preliminary treatment is to perform flocculation and sedimentation treatment on the regulated wastewater using chemical agents, and the chemical agent is at least one of a flocculant, a coagulant aid, lime, and ferric chloride.

[0009] Preferably, in the separation treatment, filter press dehydration is used to separate mud and water to obtain filtered wastewater and mud residue.

[0010] Preferably, the flocculation and sedimentation treatment is carried out in a step-by-step manner, and the step-by-step treatment is a two-stage treatment to ensure the clean elimination of easily precipitated matter.

[0011] Preferably, the oxidation treatment uses oxidation technology to reduce the content of organic matter in the filtered wastewater and the preliminary wastewater.

[0012] Preferably, the activation treatment is to use activated carbon to completely eliminate the residual organic matter in the oxidation wastewater.

[0013] First, the treatment method of the present invention addresses the complex characteristics of the mother liquor produced after evaporation of petrochemical wastewater, which is high in salt, organic matter, and toxic substances, achieving harmless and resourceful treatment. This method primarily leverages the intertwined state of organic matter and inorganic salts, and removes organic matter in a graded manner. Water quality is first regulated to stabilize the physicochemical conditions, creating suitable conditions for subsequent treatment. A two-stage flocculation and sedimentation treatment process uses chemical agents to gradually remove substances such as fluorine and phosphorus. Separation is then followed by a subsequent step in the flocculation and sedimentation process, where the water in the residual sludge is removed and converted into sludge. The filtered wastewater, rich in soluble salts, and the initially treated wastewater enter an oxidation treatment unit, where, under a low-temperature environment, it efficiently degrades recalcitrant organic matter, converting it into small-molecule acids or CO2, significantly improving the biodegradability of the wastewater. Finally, activated carbon adsorption is used as a final step to completely remove residual trace organic matter and color, ensuring that the mother liquor meets harmless standards for reuse or discharge.

[0014] The present invention also provides a treatment system for the above-mentioned petrochemical wastewater evaporation mother liquor treatment method, comprising: Along the direction of the mother liquor generated after the evaporation of petrochemical wastewater, a regulating unit, a preliminary treatment unit, a filtration unit, an oxidation unit, and an active adsorption unit are sequentially arranged; The regulating unit is provided with a collecting tank for collecting the mother liquor and performing homogenization treatment on the mother liquor to stabilize the water quality and water quantity of the mother liquor; The preliminary treatment unit is provided with a flocculation sedimentation tank assisted by chemical agents to separate and regulate suspended organic matter in the wastewater; The filtration unit presses out and separates the liquid in the residual sludge through a filter press; The oxidation unit utilizes oxidation technology to decompose the molecular structure of organic matter in the filtered wastewater and the preliminary wastewater to reduce the organic matter content; The active adsorption unit is used to remove residual organic matter and trace impurities in the oxidation wastewater.

[0015] Preferably, it also includes a reuse water pool, which is used to collect the treated water generated by the active treatment and is connected to the regulating unit.

[0016] Preferably, it further comprises a sludge storage tank, which is used to temporarily store the sludge generated in the preliminary treatment unit and the filtration unit.

[0017] The collection tank in the regulating unit of the present invention can not only collect the mother liquor but also realize homogenization treatment in it. The homogenization operation buffers the salt concentration fluctuation and organic load impact of the mother liquor, avoids the failure of subsequent chemical agents due to acid-base imbalance, and creates the best conditions for flocculation reaction, laying the foundation for subsequent treatment steps. The flocculation sedimentation tank of the preliminary treatment unit uses the bridging adsorption effect of chemical agents to efficiently separate suspended organic matter and colloidal particles in the water. The two-stage treatment mode ensures the thorough removal of pollutants and significantly reduces the treatment pressure of subsequent units. The filter press of the filtration unit realizes deep separation of mud and water by mechanical pressing, reduces the volume of sludge and recovers mud residue with low water content at the same time, prevents pollutants from entering the downstream link with the mud-water mixture, and improves the recycling rate of water resources. The oxidation unit serves as the deep treatment center, using strong oxidizing free radicals to crack the organic molecular chain, converting large molecular organic matter into harmless small molecules, and essentially reducing the toxicity of wastewater. The activated adsorption unit serves as the last barrier to water safety. The microporous adsorption characteristics of activated carbon capture residual organic matter and trace impurities to ensure that the treated water meets the reuse standard. A gradient treatment chain is formed between the various units. The conditioning unit provides homogenized influent for primary treatment, flocculation and sedimentation reduce the pollutant load in the oxidation unit, filter press dehydration avoids ineffective oxidant consumption, and activated adsorption compensates for the limitations of the oxidation process. The closed-loop design of the reuse water tank achieves cascaded utilization of water resources. The accompanying sludge storage tank centrally stores and temporarily processes sludge, preventing secondary contamination. Ultimately, a complete closed loop from source control to end-of-pipe treatment is established, significantly improving the energy efficiency and economic efficiency of system operation while reducing hazardous waste.

[0018] Compared with the prior art, the present invention has the following beneficial effects: By placing flocculation and sedimentation in the early stages, the process effectively separates and concentrates specific inorganic substances such as fluorine and phosphorus, forming a precipitate. After filtration, it can be transported as low-moisture sludge, significantly reducing the total amount of final hazardous waste (target reduction rate >90%). More importantly, this step preemptively removes some interfering substances, paving the way for efficient subsequent treatment. By gradually removing inorganic precipitates and deeply degrading organic matter, the goals of inorganic salt fractionation recovery and organic matter mineralization are ultimately achieved, transforming traditionally "hazardous waste" into a recyclable resource and significantly reducing the need for and cost of landfill or incineration disposal.

[0019] This "desalination first, then oxidation" strategy effectively reduces the inhibition of high-salt substrates on oxidation reactions and significantly improves the decomposition efficiency of difficult-to-degrade organic matter. The subsequent activated carbon adsorption unit serves as a guarantee to further capture residual organic matter. The synergistic effect of the two-stage treatment ensures that the organic matter is deeply mineralized and decomposed rather than simply transferred, reducing toxicity at the source; thus overcoming high-salt inhibition and achieving deep mineralization of organic matter. The entire system's treatment chain is compact and highly targeted. The front-end flocculation, sedimentation, and filter press units remove a large amount of inorganic solids with relatively low energy consumption, reducing the load on the subsequent advanced oxidation unit, thereby indirectly reducing the reagent and energy consumption of the advanced oxidation process. The activated carbon adsorption effluent is directly recycled or discharged, systematically reducing the overall energy consumption target by ≥30%. Furthermore, resource recovery (salt and some sediment) also brings potential economic benefits, further reducing treatment costs.

[0020] By adopting a step-by-step strategy of first separating inorganics through precipitation and then deeply oxidizing and degrading organics, we have successfully overcome the pain point of high-salt and high-organic matter intertwining, making it difficult to economically and efficiently separate and decontaminate them. This fundamentally avoids the high cost and land occupation risks of solidification and landfill, the high energy consumption and dioxin / fly ash pollution risks of incineration, and the fouling and scaling issues of membrane concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other purposes, features, and advantages of the present application will become more apparent through a more detailed description of the embodiments of the present application in conjunction with the accompanying drawings. The accompanying drawings are intended to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the present application and do not constitute a limitation of the present application. In the drawings, the same reference numerals generally represent the same components or steps. Figure 1 A schematic flow chart of a method for treating petrochemical wastewater evaporation mother liquor provided in this application; Figure 2 This is a schematic diagram of the overall process of a petrochemical wastewater evaporation mother liquor treatment system provided in this application. DETAILED DESCRIPTION

[0022] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0023] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with the embodiments.

[0024] The present invention provides a method for treating petrochemical wastewater evaporation mother liquor, Figure 1Specifically, petrochemical wastewater undergoes "pretreatment + biochemical treatment + advanced treatment + MVR evaporation and crystallization" to produce the mother liquor to be treated by this invention. The mother liquor is first stabilized and homogenized in a conditioning unit. The conditioned wastewater then undergoes a two-stage flocculation and sedimentation treatment: First, flocculants and coagulants are added under rapid stirring to remove most suspended oils and colloidal particles. Subsequently, lime and ferric chloride are added to the stirring zone to precipitate and remove calcium, magnesium ions, and residual heavy metal impurities. The residual sludge produced after flocculation is separated and dewatered, resulting in a sludge residue that is transported for disposal. The separated filtered wastewater is then mixed with the initial wastewater after initial treatment (flocculation and sedimentation) and transported to the oxidation reaction zone. This mixed wastewater is treated under ozone catalysis. A continuous reaction under the action of a titanium dioxide catalyst breaks down recalcitrant macromolecular organic compounds, such as polycyclic aromatic hydrocarbons, into low-toxic, small-molecule compounds. Finally, the oxidation wastewater undergoes activation treatment, utilizing the adsorption properties of activated carbon to thoroughly remove residual organic matter and trace impurities, ensuring that the treated water meets reuse standards and is then recycled. This forms a closed-loop treatment process of "impurity removal - detoxification - purification - reuse." The entire process reduces hazardous waste by over 90%.

[0025] Example The practical application of the petrochemical wastewater evaporation mother liquor treatment process of the present invention is shown in Figure 2 As shown, the practical application of the petrochemical wastewater evaporation mother liquor treatment system of the present invention includes the following processes: First, the high-salt, high-organic mother liquor (TDS > 200,000 mg / L) generated by the MVR evaporation process is transported via a closed pipeline to a regulating tank. A level sensor and a stirring device are installed within the tank, dynamically adjusting the residence time (approximately 4-6 hours) based on real-time data. The inlet flow rate is automatically adjusted to achieve water homogenization and buffer water volume, ensuring a stable treatment load for subsequent units. The conditioned wastewater is then pumped via a lift pump to the first-stage flocculation and sedimentation tank, where PAC (polyaluminum chloride), PAM (polyacrylamide), lime, and ferric chloride are added in sequence. The lime reacts with fluoride ions in the water to form calcium fluoride precipitates, while the ferric chloride reacts with phosphorus to form phosphate precipitates. The PAC and PAM promote the coagulation and sedimentation of these precipitates, effectively removing fluoride, phosphorus, and other substances from the wastewater. After passing through the first-stage flocculation sedimentation tank, residual sludge and preliminary wastewater are generated, which are divided into two lines; the residual sludge enters the first filtration unit and passes through the filter press to form a gray-white mud cake with low moisture content (tests show that the fluorine and phosphorus retention rates are greater than 95%), which is temporarily stored in the sludge storage tank as general solid waste for external transportation and disposal; the preliminary wastewater and the filtered wastewater generated by the first filtration unit are pumped into the second-stage flocculation sedimentation tank, and PAC (polyaluminum chloride), PAM (polyacrylamide), lime and ferric chloride are added in sequence, followed by filtration in the second filtration unit for mud and water separation. The total amount of hazardous waste is reduced from the source through multi-stage sedimentation and separation, laying a solid foundation for the final system hazardous waste reduction of more than 90%; some colloidal organic matter and large molecular organic matter complexed with inorganic salts are removed in advance to reduce the load of the oxidation unit.

[0026] The supernatant from the second-stage flocculation sedimentation tank, along with the filtrate separated from the second filtration unit, enters the oxidation unit. The ozone advanced oxidation technology utilizes free radicals generated by strong oxidizing substances to destroy the molecular structure of refractory organic matter in the water, converting it into relatively easily degradable small molecules. This effectively reduces the concentration of refractory organic matter in the wastewater, reducing the burden on subsequent treatment. The treated oxidized wastewater enters the active treatment phase.

[0027] During the activation treatment phase, the oxidized wastewater is treated through an activated carbon filter. Activated carbon, with its large specific surface area and rich pore structure, can further remove residual, recalcitrant organic matter from the water through physical and chemical adsorption. The effluent quality after activated carbon adsorption treatment is significantly improved, meeting reuse and discharge standards. The effluent is then returned to the reuse water pool for use in the Tianjie treatment unit, achieving water recycling. This reduces the company's fresh water usage and mitigates the environmental impact of direct wastewater discharge.

[0028] Through the coordinated operation of the above units, this method and system successfully achieved the effective treatment and reuse of wastewater evaporation mother liquor, which not only solved the wastewater pollution problem, achieved deep mineralization decomposition of organic matter and fractionation and crystallization recovery of inorganic salts, but also realized the recycling of water resources and achieved good environmental and economic benefits.

[0029] In summary, the method of the present invention abandons previous mother liquor treatment technologies and adopts a stepped collaborative treatment mechanism to effectively address the disposal challenges of high-salt, high-organic content evaporation mother liquor. This integrated system, while retaining the existing MVR evaporation process framework, uses graded treatment to overcome the salt-organic content bottleneck. This reduces the cost per ton of water treatment, improves industrial salt recovery, and reduces energy consumption by ≥30%. This provides a reliable technology for near-zero discharge of high-salt hazardous waste in the petrochemical industry and is worthy of widespread promotion and application.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating petrochemical wastewater evaporation mother liquor, characterized in that: The steps include: First, the mother liquor generated after evaporation of petrochemical wastewater is regulated to obtain regulated wastewater, and then the regulated wastewater is preliminarily treated to obtain residual sludge and preliminary wastewater; the residual sludge is separated to obtain filtered wastewater, and the filtered wastewater and the preliminary wastewater are oxidized to degrade organic matter in the water to obtain oxidized wastewater; finally, the oxidized wastewater is activated to produce treated water for recycling.

2. The method for treating petrochemical wastewater evaporation mother liquor according to claim 1, characterized in that: The preliminary treatment is to use chemical agents to perform flocculation and sedimentation treatment on the regulated wastewater, and the chemical agent is at least one of a flocculant, a coagulant aid, lime, and ferric chloride.

3. The method for treating petrochemical wastewater evaporation mother liquor according to claim 1, characterized in that: In the separation process, filter press dehydration is used to separate mud and water to obtain filtered wastewater and mud residue.

4. The method for treating petrochemical wastewater evaporation mother liquor according to claim 2, characterized in that: The flocculation and sedimentation treatment is carried out in a step-by-step manner, and the step-by-step treatment is a two-stage treatment to ensure the clean elimination of easily precipitated matter.

5. The method for treating petrochemical wastewater evaporation mother liquor according to claim 1, characterized in that: The oxidation treatment adopts oxidation technology to reduce the content of organic matter in the filtered wastewater and the preliminary wastewater.

6. The method for treating petrochemical wastewater evaporation mother liquor according to claim 1, characterized in that: The activation treatment is to use activated carbon to completely eliminate the organic matter remaining in the oxidation wastewater.

7. A system for treating petrochemical wastewater evaporation mother liquor according to any one of claims 1 to 6, characterized in that: include: Along the direction of the mother liquor generated after the evaporation of petrochemical wastewater, a regulating unit, a preliminary treatment unit, a filtration unit, an oxidation unit, and an active adsorption unit are sequentially arranged; The regulating unit is provided with a collecting tank for collecting the mother liquor and performing homogenization treatment on the mother liquor to stabilize the water quality and water quantity of the mother liquor; The preliminary treatment unit is provided with a flocculation sedimentation tank assisted by chemical agents to separate and regulate suspended organic matter in the wastewater; The filtration unit presses out and separates the liquid in the residual sludge through a filter press; The oxidation unit utilizes oxidation technology to decompose the molecular structure of organic matter in the filtered wastewater and the preliminary wastewater to reduce the organic matter content; The active adsorption unit is used to remove residual organic matter and trace impurities in the oxidation wastewater.

8. The petrochemical wastewater evaporation mother liquor treatment system according to claim 7, characterized in that: It also includes a reuse water pool, which is used to collect the treated water generated by the active treatment and is connected to the regulating unit.

9. The petrochemical wastewater evaporation mother liquor treatment system according to claim 7, characterized in that: It also includes a sludge storage tank, which is used to temporarily store the sludge produced in the preliminary treatment unit and the filtration unit.

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