Method and system for treating high-salinity organic wastewater

Abstract

The invention provides a method and a system for treating high-salinity organic wastewater. The method comprises the following steps: pretreating the high-salinity organic wastewater; inputting the pretreated high-salt organic wastewater into a nanofiltration unit, and treating the high-salt organic wastewater by the nanofiltration unit to obtain concentrated water containing organic matters, produced water containing monovalent salt and produced water containing multivalent salt; concentrating and recovering the produced water containing the monovalent salt so as to recover the monovalent salt in the produced water; and carrying out crystallization recovery on the produced water containing the multivalent salt so as to recover the multivalent salt in the produced water. The method can realize high-efficiency recovery of resources in the high-salt organic wastewater, and promotes up-to-standard discharge of the wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment, and in particular to a method and system for treating high-salt organic wastewater. Background Art

[0002] With the rapid development of industry, the generation of high-salinity organic wastewater is increasing. This wastewater has a complex composition, containing high concentrations of salt and organic matter. If discharged directly without effective treatment, it not only causes serious environmental pollution but also wastes water resources. Traditional wastewater treatment methods have difficulty effectively separating and recovering salt and organic matter from high-salinity organic wastewater, and are unable to meet increasingly stringent environmental protection requirements.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The first object of the present invention is to provide a method for treating high-salt organic wastewater, which can effectively recover monovalent salts and multivalent salts in the wastewater, which not only helps to meet the discharge standards of the wastewater, but also helps to improve resource utilization.

[0005] The second object of the present invention is to provide a treatment system used in the above method. When the system is applied to the treatment of high-salt organic wastewater, it can separate and recover the salt in the wastewater, improve the utilization rate of water resources, and reduce environmental pollution.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A method for treating high-salt organic wastewater comprises the following steps: Pre-treatment of high-salt organic wastewater; The pretreated high-salt organic wastewater is input into a nanofiltration unit to obtain concentrated water containing organic matter, produced water containing monovalent salts, and produced water containing polyvalent salts through the nanofiltration unit; Concentrating and recovering the produced water containing the monovalent salt to recover the monovalent salt therein; The produced water containing the multivalent salts is crystallized and recovered to recover the multivalent salts therein.

[0007] For the treatment of high-salinity organic wastewater, this solution utilizes a process flow that combines pretreatment with nanofiltration membrane separation technology. Through the selective separation of the nanofiltration unit, organic matter, monovalent salts, and polyvalent salts in the wastewater are effectively separated and recovered. This process not only improves the purity and recovery rate of salt recovery, but also reduces the burden and cost of subsequent treatment by intercepting organic matter. Ultimately, this achieves resourceful utilization of both water and salt in the wastewater, in line with the requirements of a circular economy and sustainable development.

[0008] Preferably, the pretreatment of the high-salt organic wastewater includes sequentially feeding the high-salt organic wastewater into a regulating tank, a flocculation sedimentation tank, and a sand filter for treatment. This pretreatment solution can effectively remove suspended matter and colloids from the high-salt organic wastewater, improve wastewater quality, reduce the load on subsequent treatment, increase overall treatment efficiency, create favorable conditions for subsequent nanofiltration salt separation, and ultimately achieve resource utilization of water resources and salt in the wastewater.

[0009] Preferably, when the high-salt organic wastewater is treated in the flocculation sedimentation tank, the flocculant dosage in the flocculation sedimentation tank is 50-80 mg / L, and the coagulant dosage in the flocculation sedimentation tank is 1-3 mg / L. In the process of treating high-salt organic wastewater in the flocculation sedimentation tank, the flocculant dosage is controlled at 50-80 mg / L, and the coagulant dosage is controlled at 1-3 mg / L. This specific dosage ratio can efficiently flocculate suspended matter and colloids in the wastewater, forming dense flocs and promoting their precipitation, thereby reducing the sludge volume and reducing the difficulty and cost of subsequent treatment. At the same time, this also helps to reduce the risk of subsequent nanofiltration membrane contamination, extend the service life of the membrane, and improve the overall treatment efficiency. In addition, this dosage range takes into account economy while ensuring the treatment effect, avoids waste of reagents, and can be flexibly adjusted according to changes in wastewater quality to ensure the stability of the treatment effect.

[0010] Preferably, the flocculant is at least one of polyaluminum chloride, aluminum sulfate, ferric chloride, and ferrous sulfate. Preferably, the flocculant is a mixture of polyaluminum chloride and ferrous sulfate, and the mass ratio of polyaluminum chloride to ferrous sulfate in the flocculant is (1.2-2.5):1. Preferably, the mass ratio of polyaluminum chloride to ferrous sulfate in the flocculant is 2:1. Preferably, when adding the flocculant, ferrous sulfate is added first, followed by polyaluminum chloride.

[0011] In the above technical solution, by selecting at least one of polyaluminium chloride, aluminium sulfate, ferric chloride and ferrous sulfate as the flocculant added to the flocculation sedimentation tank, a good flocculation effect can be ensured during the pretreatment process. In a further solution, polyaluminium chloride and ferrous sulfate are considered as flocculants added to the flocculation sedimentation tank. The reason why these two are specifically used among many flocculants is that the inventors have found through research that the combination of these two flocculants can achieve charge neutralization and adsorption bridging complementarity, thereby improving the flocculation effect. Specifically, polyaluminium chloride, as an inorganic polymer flocculant, is hydrolyzed to generate [Al6(OH) 12 ] 6+Polynuclear hydroxyl complexes, such as Fe₂⁺, rapidly compress the double layer of colloidal particles through charge neutralization and form large, loose flocs through adsorption bridging. They achieve high removal rates for organic colloids and suspended solids (SS). The Fe₂⁺ in ferrous sulfate hydrolyzes to Fe(OH)₂ (which subsequently oxidizes to Fe(OH)₃), which can form dense flocs through netting and sweeping. These flocs have a strong binding capacity for sulfides and heavy metal ions (such as Cr₃⁺ and Pb₂⁺), and the strong positive charge of Fe₃⁺ can neutralize negatively charged colloidal particles. Combined, polyaluminium chloride (PAC) can compensate for the inefficiency of ferrous sulfate under alkaline conditions, while ferrous sulfate enhances the PAC's ability to remove heavy metals and sulfides. Furthermore, after the PAC rapidly neutralizes the charge, the ferric hydroxide flocs formed by the ferrous sulfate quickly fill the voids within the PAC flocs, forming dense, faster-settling composite flocs. In addition, polyaluminium chloride can play an auxiliary role in the redox of ferrous sulfate, and it can encapsulate the reduction product in the flocs through adsorption and bridging. In short, the combination of the two can significantly improve the flocculation effect.

[0012] The above scheme also limits the mass ratio of polyaluminium chloride and ferrous sulfate. This mass ratio combination can take into account both cost and flocculation effect. Specifically, on the one hand, the unit price of polyaluminium chloride is usually high. Mixing the two in the above ratio can reduce the total reagent cost while ensuring that polyaluminium chloride can dominate the charge neutralization effect. On the other hand, too much polyaluminium chloride will cause the flocs to be too loose, and too much ferrous sulfate may introduce too much Fe³⁺, resulting in an increase in the chromaticity of the treated wastewater. Combining the two in a specific mass ratio can take into account the floc density (SV 30 =15-20%) and turbidity removal rate (>90%). On the other hand, the hydroxyl complex formed by polyaluminium chloride can adsorb free iron ions, avoiding the increase of separation costs in subsequent processes, and can accelerate the sedimentation of ferric hydroxide colloid, effectively preventing the increase of effluent chromaticity.

[0013] Preferably, the coagulant aid is at least one of polyacrylamide, activated silicic acid, and sodium carbonate; preferably, the coagulant aid is a mixture of polyacrylamide and activated silicic acid, and the mass ratio of polyacrylamide to activated silicic acid in the coagulant aid is (3-5):1; preferably, the mass ratio of polyacrylamide to activated silicic acid in the coagulant aid is 4:1.

[0014] In the above technical solution, by selecting at least one of polyacrylamide, activated silicic acid, and sodium carbonate as the coagulant added to the flocculation sedimentation tank, the flocculation effect during the pretreatment process can be effectively improved. In a further solution, a solution of mixing polyacrylamide with activated silicic acid is considered. The colloid surface formed by the activated silicic acid has a negative charge and can preferentially adsorb the positively charged aluminum / iron salt flocculant hydrolysis products (such as Al(OH) 3+), forming "patches" of local charge neutralization, promoting the destabilization of colloidal particles. The silicate colloid provides a porous structure, serving as the "skeleton" of the aluminum / iron salt flocs and enhancing their density. The long-chain polymers of polyacrylamide connect micro-flocs through hydrogen bonds and van der Waals forces, forming large-scale flocs, which increase sedimentation rate and enhance flocculation and sedimentation efficiency. The flexible chain structure of polyacrylamide resists ionic interference and mechanical shear damage, achieving excellent flocculation and sedimentation effects in high-salt environments. Furthermore, activated silica can adsorb hydrophobic organic matter (such as humic acid), reducing its toxicity to the active sites of polyacrylamide. Polyacrylamide, through hydrophobic interactions, encapsulates hydrophilic small-molecule organic matter (such as alcohols), preventing them from penetrating the flocs. In summary, the combined application of these two agents helps improve flocculation and sedimentation efficiency and resistance to salt and interference (such as organic matter).

[0015] The above technical solution strictly limits the mass ratio of polyacrylamide to activated silicic acid. This is because the inventors discovered during their research that too little activated silicic acid can lead to insufficient skeleton support, loose and fragile flocs, and reduced sedimentation rate. Too much activated silicic acid causes the silica colloid to occupy too many adsorption sites, inhibiting the bridging effect of polyacrylamide and potentially introducing excess silicon residue. Combining the two in a specific mass ratio can enhance their synergistic coagulant effect and minimize any adverse effects between them.

[0016] Preferably, the filter media in the sand filter is quartz sand, and the filtration rate of the sand filter is 8-10 m / h. This solution uses quartz sand filter media and controls the filtration rate appropriately, which not only helps improve the efficiency of high-salinity organic wastewater treatment, but also optimizes the economic and environmental friendliness of the overall process, creating favorable conditions for subsequent nanofiltration separation and resource recovery.

[0017] Preferably, the method further comprises: feeding the concentrated water into an organic matter treatment unit to treat organic matter in the concentrated water; preferably, the organic matter treatment unit comprises an oxidation device and a biological treatment device. By sequentially treating the organic matter in the concentrated water using the oxidation device and the biological treatment device, the organic matter in the concentrated water can be effectively degraded, so that the treated wastewater meets discharge standards, thereby effectively reducing pollution to the environment.

[0018] Preferably, the concentrating and recovering the produced water containing monovalent salts comprises: evaporating and concentrating the produced water containing monovalent salts; wherein the evaporation temperature is 80-90° C. By concentrating and recovering the produced water containing monovalent salts at a specific temperature, efficient separation and recovery of the monovalent salts can be achieved, thereby improving resource utilization.

[0019] Preferably, the crystallization recovery of the produced water containing polyvalent salts includes: cooling crystallization or evaporative cooling combined crystallization of the produced water containing polyvalent salts; wherein the cooling temperature is 10-15°C. By adopting a specific cooling temperature to recover the produced water containing polyvalent salts, efficient separation and recovery of polyvalent salts can be achieved, thereby improving resource utilization.

[0020] The present invention also provides a system for treating high-salt organic wastewater, which is used to implement the method of any of the above embodiments; the system includes: a pretreatment unit, a nanofiltration unit and a recovery unit arranged in sequence along the flow direction of the high-salt organic wastewater, and the recovery unit includes a monovalent salt recovery subunit and a polyvalent salt recovery subunit.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes a process flow that combines pretreatment with nanofiltration membrane separation technology. Through selective separation in the nanofiltration unit, it effectively separates and recovers organic matter, monovalent salts, and polyvalent salts from wastewater. This process not only improves the purity and recovery rate of salt recovery, but also reduces the burden and cost of subsequent treatment by intercepting organic matter. Ultimately, it achieves resourceful utilization of both water and salt in wastewater, meeting the requirements of a circular economy and sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings: Figure 1 Schematic diagram of a system for treating high-salt organic wastewater provided by an embodiment of the present invention.

[0023] In the figure: 1. Equalization tank; 2. Flocculation sedimentation tank; 3. Sand filter; 4. Nanofiltration unit; 5. Evaporation concentration device; 6. Cooling device; 7. Oxidation device; 8. Biological treatment device. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments and the accompanying drawings, 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 are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0025] Example 1 See Figure 1 As shown, this embodiment provides a high-salt organic wastewater treatment system, which includes: a pretreatment unit, a nanofiltration unit 4 and a recovery unit arranged in sequence along the flow direction of the high-salt organic wastewater, and the recovery unit includes a monovalent salt recovery subunit and a polyvalent salt recovery subunit.

[0026] like Figure 1 As shown, the pretreatment unit includes a regulating tank 1, a flocculation sedimentation tank 2 and a sand filter 3. The monovalent salt recovery subunit can be an evaporation concentration device 5, such as a triple-effect evaporation concentration crystallization device. The multivalent salt recovery subunit can be a cooling device 6.

[0027] Continue reading Figure 1 The system may also include an organic matter treatment unit, which includes an oxidation unit 7 and a biological treatment unit 8. In the oxidation unit 7, a Fenton oxidation process can be used, with the addition of ferrous sulfate and hydrogen peroxide, to effectively degrade organic matter. In the biological treatment unit 8, an activated sludge process can be used, with a sludge concentration controlled at 3-5 g / L and a residence time of 12-24 hours, to further reduce the organic matter content and ensure that the treated wastewater meets discharge standards.

[0028] In this embodiment, the nanofiltration unit 4 can use a nanofiltration membrane to selectively separate different salts and organic matter according to their molecular size and charge characteristics. During the nanofiltration process, by controlling parameters such as operating pressure, temperature and flow rate, efficient separation of monovalent salts and multivalent salts can be achieved, while most organic matter is intercepted. The nanofiltration unit 4 can use a BW30-400 / 34 nanofiltration membrane assembly, the operating pressure is controlled at 1.5-2.5MPa, the temperature is controlled at 25-35°C, and the wastewater flow rate can be controlled at 0.8-1.2m / s. In this embodiment, the following method is used to treat high-salt organic wastewater: First, the high-salinity organic wastewater undergoes pretreatment: it is introduced into a regulating tank with a retention time of 6-8 hours to achieve uniform and stable water quality and volume. The wastewater is then fed into a flocculation sedimentation tank for sedimentation. Flocculants and coagulants are added to the flocculation tank at a dosage of 50-80 mg / L and 1-3 mg / L, respectively. After a reaction time of 20-30 minutes and sedimentation time of 1-2 hours, the wastewater is fed into a sand filter. This sand filter uses quartz sand as filter media and operates at a filtration rate of 8-10 m / h to further remove suspended matter.

[0029] Then, the pretreated high-salt organic wastewater is input into the nanofiltration unit, the operating pressure is controlled at 1.5-2.5MPa, the temperature is controlled at 25-35°C, and the wastewater flow rate can be controlled at 0.8-1.2m / s.

[0030] The produced water containing monovalent salts filtered through the nanofiltration unit is fed into a triple-effect evaporation, concentration, and crystallization unit. The evaporation temperature is controlled at 80-90°C, and the crystallization time is 3-5 hours to achieve salt crystallization recovery. Produced water containing multivalent salts is crystallized using cooling according to their solubility curves. The cooling temperature is controlled at 10-15°C, and the crystallization time is 4-6 hours to improve the recovery rate and purity of the salts.

[0031] The concentrated water from the nanofiltration unit is then fed into an oxidation unit for 1-2 hours of oxidation treatment, effectively degrading organic matter. It then enters a biological treatment unit using an activated sludge process, controlling the sludge concentration at 3-5g / L and a retention time of 12-24 hours. The treated water is then discharged directly.

[0032] In this embodiment, the flocculant is a mixture of polyaluminium chloride and ferrous sulfate, with a mass ratio of polyaluminium chloride to ferrous sulfate of 2:1. The coagulant aid is a mixture of polyacrylamide and activated silicic acid, with a mass ratio of polyacrylamide to activated silicic acid of 4:1.

[0033] Example 2 The difference between this embodiment and embodiment 1 is that the mass ratio of polyaluminium chloride to ferrous sulfate is 1.2:1.

[0034] Example 3 The difference between this embodiment and embodiment 1 is that the mass ratio of polyaluminium chloride to ferrous sulfate is 2.5:1.

[0035] Example 4 The difference between this embodiment and embodiment 1 is that the mass ratio of polyaluminium chloride to ferrous sulfate is 5:1.

[0036] Example 5 The difference between this embodiment and embodiment 1 is that the mass ratio of polyaluminium chloride to ferrous sulfate is 1:2.

[0037] Example 6 The difference between this embodiment and embodiment 1 is that only polyaluminium chloride is used.

[0038] Example 7 The difference between this embodiment and embodiment 1 is that only ferrous sulfate is used.

[0039] Example 8 The difference between this embodiment and embodiment 1 is that the mass ratio of polyacrylamide to activated silicic acid is 3:1.

[0040] Example 9 The difference between this embodiment and embodiment 1 is that the mass ratio of polyacrylamide to activated silicic acid is 5:1.

[0041] Example 10 The difference between this embodiment and embodiment 1 is that the mass ratio of polyacrylamide to activated silicic acid is 1:1.

[0042] Example 11 The difference between this embodiment and embodiment 1 is that the mass ratio of polyacrylamide to activated silicic acid is 8:1.

[0043] Example 12 The difference between this embodiment and embodiment 1 is that the coagulant aid is polyacrylamide.

[0044] Example 13 The difference between this embodiment and embodiment 1 is that the coagulant aid is activated silicic acid.

[0045] Experimental Example 1 The systems and methods of Examples 1-13 were used to treat high-salinity organic wastewater (initial COD of 1000 mg / L, salt concentration of 12%) using the same flocculant and coagulant dosages (100 mg / L flocculant, 2 mg / L coagulant). The COD and salinity of the treated water were measured after treatment in the biological treatment unit. The final salinity of the treated water in each group did not exceed 5%, and the COD value was less than 150 mg / L, meeting discharge standards. The COD test results are shown in Table 1 below.

[0046] Table 1 Test results

[0047] Comparing Examples 1-7, it can be found that when polyaluminum chloride and ferrous sulfate are mixed and the mass ratio is 1.2-2.5:1, the organic matter removal rate is higher, among which the organic matter removal rate is highest when the mass ratio of polyaluminum chloride to ferrous sulfate is 2:1, indicating that the best flocculation and precipitation effect can be obtained when the two are mixed and a specific mass ratio is adopted.

[0048] Comparing Example 1 with Examples 8-13, it was found that the organic matter removal rate was higher when polyacrylamide and activated silicic acid were mixed at a mass ratio of 3-5:1, with the best being achieved at a mass ratio of 4:1. This indicates that the optimal coagulant effect can be achieved when the two are mixed at a specific mass ratio.

[0049] In summary, the solution of the present invention can efficiently separate organic matter and salt in high-salt organic wastewater and achieve efficient recovery of monovalent salt and polyvalent salt, which not only helps to meet the discharge standards of wastewater, but also helps to improve resource utilization.

[0050] 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 high-salt organic wastewater, characterized in that: The following steps are involved: Pre-treatment of high-salt organic wastewater; The pretreated high-salt organic wastewater is input into a nanofiltration unit to obtain concentrated water containing organic matter, produced water containing monovalent salts, and produced water containing polyvalent salts through the nanofiltration unit; Concentrating and recovering the produced water containing the monovalent salt to recover the monovalent salt therein; The produced water containing the multivalent salts is crystallized and recovered to recover the multivalent salts therein.

2. The method according to claim 1, characterized in that The pretreatment of high-salt organic wastewater comprises: The high-salt organic wastewater is sequentially input into a regulating tank, a flocculation sedimentation tank and a sand filter tank for treatment.

3. The method according to claim 2, characterized in that When the high-salt organic wastewater is treated by using the flocculation sedimentation tank, the dosage of the flocculant in the flocculation sedimentation tank is 50-80 mg / L, and the dosage of the coagulant aid in the flocculation sedimentation tank is 1-3 mg / L.

4. The method according to claim 3, characterized in that The flocculant is at least one of polyaluminium chloride, aluminium sulfate, ferric chloride and ferrous sulfate; Preferably, the flocculant is a mixture of polyaluminium chloride and ferrous sulfate, and the mass ratio of polyaluminium chloride to ferrous sulfate in the flocculant is (1.2-2.5):1; Preferably, the mass ratio of polyaluminium chloride to ferrous sulfate in the flocculant is 2:

1.

5. The method according to claim 4, characterized in that The coagulant aid is at least one of polyacrylamide, activated silicic acid, and sodium carbonate; Preferably, the coagulant aid is a mixture of polyacrylamide and activated silicic acid, and the mass ratio of polyacrylamide to activated silicic acid in the coagulant aid is (3-5):1; Preferably, the mass ratio of polyacrylamide to activated silicic acid in the coagulant aid is 4:

1.

6. The method according to claim 2, characterized in that The filter material in the sand filter is quartz sand filter material, and the filtration speed of the sand filter is 8-10m / h.

7. The method according to any one of claims 1 to 6, characterized in that The method further comprises: Inputting the concentrated water into an organic matter treatment unit to treat the organic matter in the concentrated water; Preferably, the organic matter treatment unit includes an oxidation device and a biological treatment device.

8. The method according to any one of claims 1 to 6, characterized in that The concentrated recovery of the produced water containing monovalent salt comprises: The produced water containing monovalent salt is evaporated and concentrated; wherein the evaporation temperature is 80-90°C.

9. The method according to any one of claims 1 to 6, characterized in that The crystallization recovery of the produced water containing the multivalent salt comprises: The produced water containing the multivalent salt is subjected to cooling crystallization or evaporative cooling combined crystallization; wherein the cooling temperature is 10-15°C.

10. A system for treating high-salt organic wastewater, characterized in that: Used to implement the method described in any one of claims 1-9; the system includes: a pretreatment unit, a nanofiltration unit and a recovery unit arranged in sequence along the flow direction of high-salt organic wastewater, and the recovery unit includes a monovalent salt recovery subunit and a polyvalent salt recovery subunit.

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