Resource utilization method and device for high-salinity wastewater

Abstract

The invention discloses a high-salinity wastewater resource utilization method and device, belongs to the technical field of chemical engineering, and relates to wastewater treatment. The invention relates to a high-salinity wastewater resource utilization method which comprises the following steps: (1) deep removal of organic matters in a high-salinity system: realizing selective separation and removal of the organic matters in wastewater by using a synergistic effect of a flocculating agent and a catalyst; (2) mixed salt separation and recycling: realizing stable separation of sodium chloride and sodium sulfate through the design of MCR-nanofiltration-reverse osmosis multi-membrane coupling synergistic gradient coupling and reflux nesting; and (3) stable control of evaporative crystallization of a complex system: a scale inhibitor, humic acid and a defoaming agent are used, and fractional crystallization and purification are realized through high-temperature firing. According to the method, recycling circulating water can be saved, a large amount of sodium chloride and sodium sulfate are recycled as byproducts, COD and ammonia nitrogen are reduced, the recycling rate of sodium sulfate and sodium chloride is larger than 85%, and the water recycling rate is larger than 95%.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology and relates to wastewater treatment, specifically to a method and apparatus for the resource utilization of high-salinity wastewater. Background Technology

[0002] Coking wastewater mainly originates from the primary cooling of coke oven gas, production water used in the coking process, and steam condensate wastewater. Valuable resources within this wastewater primarily include sodium chloride, sodium sulfate, and reusable water. Sodium chloride is one of the most basic raw materials in the chemical industry, with a wide range of industrial applications, often referred to as the "mother of the chemical industry." Sodium sulfate is mainly used in the pulp, detergent, glass, dye, and textile industries, and is also used as a raw material for water glass, ultramarine, and other chemical products. This saline wastewater was once utilized as quenching water, but current processes, limited by membrane recovery rates such as reverse osmosis, generate approximately 30% membrane-concentrated high-salt wastewater. This wastewater is characterized by high levels of recalcitrant organic matter and impurities such as silicon, leading to unstable crystallization and salt separation processes, making zero discharge and resource utilization difficult.

[0003] The main approach to zero discharge of high-salinity wastewater currently involves separating and crystallizing the impurities in the wastewater to obtain high-value-added industrial salt products while simultaneously reusing the water. Existing salt separation and crystallization processes primarily include thermal separation and nanofiltration separation. Thermal separation relies on the principle that sodium chloride and sodium sulfate have different solubilities at different temperatures. However, this method has a narrow separation range, and the quality of the crystallized salt is difficult to stabilize when water quality fluctuates. Nanofiltration separation utilizes the Donnan effect of nanofiltration membranes to concentrate divalent salts to a higher concentration on the concentrate side, while monovalent salts pass through the nanofiltration membrane on the product water side, thus achieving separation. This method has a wider adaptability range for ion ratios, is more stable, and easier to control, making it more advantageous in the desalination and crystallization process of high-salinity coking wastewater. After nanofiltration separation, high-salinity wastewater yields a solution of inorganic salts with high concentrations of sodium chloride and sodium sulfate, which are then evaporated and crystallized to obtain the product salt. However, due to the high content of refractory organic matter, calcium, silicon and other impurities in high-salt wastewater, it will have a significant impact on processes such as nanofiltration desalination and evaporation crystallization, resulting in unstable operation of nanofiltration desalination and evaporation crystallization processes, making it difficult to achieve zero discharge and resource utilization.

[0004] Due to the high organic content of high-salinity wastewater, the raw COD is generally in the range of 5000-20000 mg / L, typically containing various recalcitrant organic compounds such as phenols, nitrogen-containing heterocyclic compounds, and polycyclic aromatic hydrocarbons (PAHs). Furthermore, processes such as gas washing, condensation, and purification introduce certain concentrations of inorganic ions such as Na+, Ca2+, Cl-, and SO42- into the wastewater. These factors contribute to the generally complex composition, poor biodegradability, and high treatment difficulty of coking wastewater. Therefore, achieving low-cost removal of organic matter and efficient concentration and crystallization of inorganic salts from high-salinity wastewater has become a key technological bottleneck restricting the zero discharge of coking wastewater.

[0005] To address the aforementioned problems in existing technologies, a method and apparatus for the resource utilization of high-salinity wastewater have been developed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the resource utilization of high-salinity wastewater.

[0007] Another object of the present invention is to provide an apparatus for the resource utilization of high-salinity wastewater.

[0008] This invention is achieved through the following technical solution: A method for the resource utilization of high-salinity wastewater includes: (1) Deep removal of organic matter in high-salt systems: The synergistic effect of flocculants and catalysts is used to achieve selective separation and removal of organic matter in wastewater; (2) Mixed salt separation and resource utilization: Through the design of MCR-nanofiltration-reverse osmosis multi-membrane coupling synergistic gradient coupling and reflux nesting, the stable separation of sodium chloride and sodium sulfate is achieved; (3) Stabilization control of evaporation crystallization in complex systems: using scale inhibitors, humic acid and defoamers, stepwise crystallization purification is achieved through high-temperature calcination.

[0009] Furthermore, the flocculant is an epioxypropyl dodecyl dimethyl ammonium chloride flocculant, wherein the quaternary ammonium group, epoxy group and long-chain dodecyl group, while neutralizing ions in wastewater, improve the flocculation effect through adsorption and cross-linking.

[0010] The catalyst is an ozone catalyst, preferably a porous stainless steel electrode ozone catalyst. The porous structure can enhance the catalytic ability of the stainless steel electrode ozone catalyst and, together with the flocculant, enhance the separation and removal of organic matter in wastewater.

[0011] In the mixed salt separation process, ion exchange resin is used to remove hardness, chemical precipitation is used to remove fluoride and silicon, and nanofiltration is used to separate salts, so as to achieve stable and efficient separation of sodium chloride and sodium sulfate.

[0012] The scale inhibitor is fulvic acid.

[0013] The mass ratio of the scale inhibitor to the defoamer is 4:1~1.5.

[0014] Furthermore, the present invention also provides an apparatus for performing the above method, comprising a pretreatment apparatus, an organic matter treatment apparatus, a nanofiltration desalination apparatus, and an evaporation crystallization apparatus connected in sequence by pipelines; The pretreatment device is used to treat high-salinity wastewater by sedimentation and filtration; The aforementioned organic matter treatment device is used for the selective separation and efficient removal of organic matter from high-salt wastewater; The nanofiltration desalination device achieves stable and efficient separation of sodium chloride and sodium sulfate in high-salt wastewater through multi-membrane system coupling. The evaporation crystallization device achieves effective purification of crystalline salt products through high-temperature calcination and stepwise crystallization.

[0015] The organic matter treatment device is a catalytic-biochemical treatment device; The nanofiltration salt separation device is a multi-membrane system coupling device, preferably an MCR-nanofiltration-reverse osmosis device.

[0016] The bottoms of the organic matter treatment device and the nanofiltration desalination device are connected to the pretreatment device through pipelines to form a cycle.

[0017] This invention designs and develops a novel covalently bonded flocculant with long-chain quaternary ammonium groups and a porous stainless steel electrode ozone catalyst for the targeted removal of organic matter from high-salinity wastewater. It constructs a deep flocculation process based on the novel flocculant and catalyst, and an improved ozone catalytic oxidation technology. Through optimization of process operating conditions, it achieves selective separation and efficient removal of organic matter from wastewater, enabling simple, efficient, and inexpensive deep regeneration and resource recovery of high-salinity wastewater. Simultaneously, it explores the interaction mechanisms between water molecules, ions, and organic matter with the surface and multiple interfaces of nanofiltration membrane pores in complex systems. Based on this, it systematically regulates the removal of hardened substances by ion exchange resin. The study investigated the interactions and constraints among the chemical precipitation defluorination and silica removal and nanofiltration salt separation units. Through the synergistic effect of each membrane unit in the MCR-nanofiltration-reverse osmosis multi-membrane coupling technology, and the design of gradient coupling and reflux nesting, stable and efficient separation of sodium chloride and sodium sulfate was achieved. Flocculated acid, humic acid, and defoamers were screened for treating high-salt wastewater from the coking industry, along with compound formulations that can simultaneously inhibit scale and defoam. The scale inhibition and defoaming mechanisms of the scale inhibitors and defoamers were elucidated, and the mechanism of induced crystallization was explored in depth, improving the application of scale inhibition, defoaming, and induced crystallization. Effective purification of crystalline salt products was achieved through high-temperature calcination and stepwise crystallization methods.

[0018] This invention can effectively solve the technical difficulties in the process of zero discharge of high-salt wastewater and resource utilization of inorganic salts in the coking industry, provide technical support for zero discharge of high-salt wastewater, save recycled water, recover a large amount of sodium chloride and sodium sulfate as by-products, and reduce COD and ammonia nitrogen emissions. The recovery rate of sodium sulfate and sodium chloride is greater than 85%, and the water reuse rate is greater than 95%. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the device of the present invention; In the diagram: 1-Pretreatment device, 2-Organic matter treatment device, 3-Nanofiltration salt separation device, 4-Evaporation crystallization device. Detailed Implementation

[0020] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0021] An apparatus for the resource utilization of high-salinity wastewater includes a pretreatment device 1, an organic matter treatment device 2, a nanofiltration desalination device 3, and an evaporation crystallization device 4, which are connected in sequence via pipelines. The pretreatment device 1 is used to treat high-salinity wastewater by sedimentation and filtration. The organic matter treatment device 2 is used to selectively separate and efficiently remove organic matter from the high-salinity wastewater. The nanofiltration desalination device 3 achieves stable and efficient separation of sodium chloride and sodium sulfate from the high-salinity wastewater through multi-membrane system coupling. The evaporation crystallization device 4 effectively purifies the crystallized salt products through high-temperature calcination and stepwise crystallization. The bottoms of the organic matter treatment device 2 and the nanofiltration desalination device 3 are respectively connected to the pretreatment device 1 through pipelines to form a circulation.

[0022] During operation, the steps are as follows: (1) The coking high-salt wastewater is precipitated and filtered through the pretreatment device 1 and input into the organic matter treatment device 2. The organic matter treatment device 2 is a catalytic-biochemical treatment device. During operation, epoxypropyl dodecyl dimethyl ammonium chloride flocculant and ozone catalyst are added to separate and remove organic matter in the wastewater. The quaternary ammonium group, epoxy group and long chain dodecyl group in the wastewater undergo charge neutralization with the ions in the wastewater and flocculate the organic matter through adsorption and cross-linking. (2) The wastewater after organic matter removal is input into the nanofiltration desalination device 3 for nanofiltration desalination. Device 3 is a membrane system. Through the design of MCR-nanofiltration-reverse osmosis multi-membrane coupling, synergistic gradient coupling and reflux nesting, the stable separation of sodium chloride and sodium sulfate is achieved, and the wastewater is de-hardened, defluorinated and desilted; (3) The wastewater after being treated by the membrane system is input into the evaporation crystallization device 4. The scale inhibitor, fulvic acid, humic acid and defoamer are used to achieve step-by-step crystallization purification by high temperature calcination; the scale inhibitor is continuously added at 20~40ppm and the defoamer is intermittently added at 5~15ppm to ensure that the mass ratio of scale inhibitor to defoamer is 4:1~1.5.

[0023] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A method for the resource utilization of high-salinity wastewater, characterized in that, include: (1) Deep removal of organic matter in high-salt systems: The synergistic effect of flocculants and catalysts is used to achieve selective separation and removal of organic matter in wastewater; (2) Mixed salt separation and resource utilization: Through the design of MCR-nanofiltration-reverse osmosis multi-membrane coupling synergistic gradient coupling and reflux nesting, the stable separation of sodium chloride and sodium sulfate is achieved; (3) Stabilization control of evaporation crystallization in complex systems: using scale inhibitors, humic acid and defoamers, stepwise crystallization purification is achieved through high-temperature calcination.

2. The method for resource utilization of high-salinity wastewater according to claim 1, characterized in that, The flocculant is glycidyl dodecyl dimethyl ammonium chloride flocculant.

3. The method for resource utilization of high-salinity wastewater according to claim 1, characterized in that, The catalyst mentioned is an ozone catalyst.

4. The method for resource utilization of high-salinity wastewater according to claim 3, characterized in that, The ozone catalyst is a porous stainless steel electrode ozone catalyst.

5. The method for resource utilization of high-salinity wastewater according to claim 1, characterized in that, In the mixed salt separation process, ion exchange resin is used to remove hardness, chemical precipitation is used to remove fluoride and silicon, and nanofiltration is used to separate salts, so as to achieve stable and efficient separation of sodium chloride and sodium sulfate.

6. The method for resource utilization of high-salinity wastewater according to claim 1, characterized in that, The scale inhibitor is fulvic acid.

7. The method for resource utilization of high-salinity wastewater according to claim 1, characterized in that, The mass ratio of the scale inhibitor to the defoamer is 4:1~1.

5.

8. An apparatus for performing the method of any one of claims 1-7, characterized in that, It includes a pretreatment unit, an organic matter treatment unit, a nanofiltration desalination unit, and an evaporation crystallization unit, which are connected in sequence by pipelines. The pretreatment device is used to treat high-salinity wastewater by sedimentation and filtration; The aforementioned organic matter treatment device is used for the selective separation and efficient removal of organic matter from high-salt wastewater; The nanofiltration desalination device achieves stable and efficient separation of sodium chloride and sodium sulfate in high-salt wastewater through multi-membrane system coupling. The evaporation crystallization device achieves effective purification of crystalline salt products through high-temperature calcination and stepwise crystallization.

9. The apparatus according to claim 8, characterized in that, The organic matter treatment device is a catalytic-biochemical treatment device; the nanofiltration desalination device is an MCR-nanofiltration-reverse osmosis device.

10. The apparatus according to claim 8, characterized in that, The bottoms of the organic matter treatment device and the nanofiltration desalination device are connected to the pretreatment device through pipelines to form a cycle.

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