A device and method for desalination and resource utilization of fluorochemical washing wastewater

Abstract

A device and method for desalination and resource utilization of fluorochemical washing wastewater belongs to the field of wastewater treatment technology. It includes the following steps: a pretreatment stage, a biochemical pretreatment stage, a membrane pretreatment stage, and a reverse osmosis (RO-EDI-EDR) deep treatment stage. The pretreatment required by this invention is simple, typically sufficient for multi-media filtration. It does not increase COD in the concentrate, does not affect the discharge and use of the concentrate, has a higher water recovery rate, lower concentrate discharge volume, high resource utilization, higher resistance to organic fouling, is less prone to scaling and organic contamination, requires no scale inhibitors, has lower operating costs, and is tolerant to free chlorine.

Description

Technical Field

[0001] This invention relates to a device and method for desalination and resource utilization of fluorochemical washing wastewater, belonging to the field of wastewater treatment technology. Background Technology

[0002] Fluorine pollution is a significant form of pollution in the chemical industry. With the expansion of industrial production, the amount of fluorochemical wastewater generated is increasing daily. In recent years, my country's fluorochemical industry has developed rapidly, with the overall market maintaining a growth rate of around 20%. It is expected that the fluorochemical industry will continue to experience rapid growth in the future. Domestic fluoropolymer chemical products mainly consist of polytetrafluoroethylene (PTFE), while the production of vinylidene fluoride (DEF), hexafluoropropylene (HCF), and perfluoroethylene (PFEF) is small, and most are still in the trial production stage. Against the backdrop of increasing demand, the import rate of fluorochemical products remains high.

[0003] From the perspective of fluorochemical production, a large amount of fluoride-containing wastewater is generated during the product manufacturing process. This wastewater can easily pollute soil, water bodies, and vegetation. As a new chemical materials industry, fluorochemicals have broad development prospects. In today's context of balancing economic development and environmental protection, fluorochemical wastewater treatment technology is constantly improving, promoting the development of the entire wastewater treatment industry.

[0004] Fluorochemical wastewater is characterized by high salinity, strong biotoxicity, and poor biodegradability. The focus of fluorochemical wastewater treatment is on inorganic fluoride ions and organic fluorides. Among these, organic fluoride pollutants are highly stable and have poor biodegradability, mainly due to the strong CF bond and high bond energy (approximately 460 kJ / mol) in organic fluorides. Traditional biological wastewater treatment processes are inefficient for organic fluoride wastewater, while some advanced oxidation processes developed in recent years are too costly.

[0005] Traditional processes typically employ pretreatment softening and hardening removal followed by reverse osmosis concentration and desalination, or reverse osmosis followed by chemical softening and resin softening. These processes generally only consider a portion of the treatment functions, leading to issues such as substandard water quality in the later stages of chemical wastewater treatment, low treatment efficiency with resin or chemical softening before and after the membrane system, and high resin replacement costs. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a device and method for the desalination and resource utilization of fluorochemical washing wastewater.

[0007] A method for desalination and resource utilization of fluorochemical washing wastewater includes the following steps: a pretreatment stage, a biochemical pretreatment stage, a membrane pretreatment stage, and a reverse osmosis (RO-EDI-EDR) deep treatment stage.

[0008] A method for desalination and resource utilization of fluorochemical washing wastewater further includes the following steps:

[0009] Pretreatment steps: Inorganic fluoride ions and suspended solids are settled in a high-density sedimentation tank; preliminary filtration and biochemical degradation are performed in an aerated biological filter; dissolved substances and surfactants are further removed in an air flotation tank; effluent is treated with ozone catalytic oxidation to degrade organic fluoride and reduce biotoxicity; effluent then enters an aerobic MBR to remove organic matter and suspended solids; before entering the membrane system, trace removal of suspended solids and organic matter is performed using multi-media filtration and activated carbon filtration to ensure the quality of the wastewater entering the membrane system; concentration is achieved using a UF+RO dual membrane method, and the concentrate is desalinated using EDR to increase permeate production.

[0010] The biochemical pretreatment stage involves the following steps: A high-density tank is used to remove large-particle suspended solids from the fluorochemical washing wastewater. The precipitation of inorganic fluoride ions is enhanced by adding CaCO3 and Ca(OH)2 as a double alkali. A sludge return pump from the high-density tank is used to return some sludge, further enhancing the settling effect of suspended solids and reducing the amount of flocculant used. The effluent from the high-density tank enters an aerated biological filter, where the biochemical flocculation effect of microorganisms in the filter traps small-particle suspended solids and treats easily degradable organic matter in the washing wastewater. The pre-filtered effluent then enters a dissolved air treatment system. The dissolved air flotation (DAF) tank utilizes a high-efficiency dissolved air flotation device to remove fine suspended solids and dissolved organic matter such as surfactants from wastewater. The effluent from the DAF enters an ozone catalytic oxidation filter to degrade organic fluorides using an appropriate OC ratio, converting organic fluorides into easily degradable organic matter. The effluent then enters an aerobic MBR tank where aerobic bacteria further degrade the fluoride, and the MBR membrane's filtration effect ensures a significant reduction in fluoride ion content, suspended solids, and dissolved organic matter, thus achieving the desired biochemical pretreatment effect.

[0011] Membrane pretreatment steps: After pretreatment, the wastewater undergoes secondary filtration through a multi-media filter and an activated carbon filter to ensure that the wastewater does not contain small-diameter suspended solids before entering the membrane. After ultrafiltration, the effluent meets the requirements of reverse osmosis turbidity <1 NTU and SDI <5, which is low and does not cause scaling risk to subsequent concentration.

[0012] The deep treatment steps of the reverse osmosis (RO)-EDI-EDR section are as follows: The reverse osmosis (RO) uses a two-stage desalination system for preliminary desalination. The RO permeate enters the EDI system for deep desalination. The RO concentrate enters the EDR system for further concentration. The permeate is then returned to the ozone catalytic oxidation section for treatment. The concentrate is discharged, achieving the maximum permeate recovery effect.

[0013] A method for desalination and resource utilization of fluorochemical washing wastewater includes the following steps:

[0014] The biochemical pretreatment stage consists of the following steps: a high-density tank to remove large-particle suspended solids and inorganic fluoride ions; an aerated biological filter to remove small-particle suspended solids and easily degradable organic matter; a dissolved air flotation tank to remove tiny-particle suspended solids and surfactants; an ozone catalytic oxidation filter to degrade organic fluorides and eliminate biotoxicity; and an aerobic MBR tank to degrade organic matter, achieving a good removal effect of suspended solids, biotoxic substances, and surfactants in fluorochemical wastewater.

[0015] Membrane pretreatment steps: SDI and turbidity are reduced through multi-stage filtration and ultrafiltration to mitigate membrane fouling. Finally, RO reverse osmosis-EDI concentration and desalination are carried out, and EDR further concentration is used to improve the utilization rate of permeate.

[0016] The pretreatment stage involves sequentially removing large-particle suspended solids, soluble surfactants, biotoxic substances, and dissolved organic matter. SDI ensures the concentration efficiency of the subsequent desalination stage. The concentration stage utilizes RO-EDI to improve the desalination rate and EDR to treat the concentrate, thereby increasing the water production rate and achieving the desalination and resource utilization effect of fluorochemical washing wastewater.

[0017] The deep treatment steps of the reverse osmosis (RO)-EDI-EDR section are as follows: The reverse osmosis (RO) uses a two-stage desalination system for preliminary desalination. The RO permeate enters the EDI system for deep desalination. The RO concentrate enters the EDR system for further concentration. The permeate is then returned to the ozone catalytic oxidation section for treatment. The concentrate is discharged, achieving the maximum permeate recovery effect.

[0018] Compared to RO, EDR has the following advantages:

[0019] (1) The required pretreatment is simple, usually multi-media filtration can meet the requirements.

[0020] (2) The COD in the concentrate does not increase and does not affect the discharge and use of the concentrate.

[0021] (3) It has a higher water recycling rate, less concentrated water discharge, and a high degree of resource utilization.

[0022] (4) The equipment frequently reverses polarity, which results in higher resistance to organic pollution, making it less prone to scaling and contamination by organic matter.

[0023] (5) No scale inhibitors are required, resulting in lower operating costs.

[0024] (6) Tolerance to free chlorine.

[0025] According to the water quality characteristics of this invention, if the system does not use an ED device but instead uses a single-stage RO-3 and a single-stage RO-4, then to achieve the same 80% recovery rate as ED, the recovery rates of the single-stage RO-3 and single-stage RO-4 are 66.02% and 67.97%, respectively. The recovery rates of both reverse osmosis stages are not high. Furthermore, if a two-stage reverse osmosis system is used, the concentrate discharged from the single-stage RO-4 stage is 4.04 m³. 3 / h, compared to the external drainage volume of 2.94m³ using ED. 3 The volume of water discharged is larger than that of water discharged per hour. The requirement for external discharge in the tender document is ≤5%. The conductivity of the external discharge of the two RO sections is 6901.07, which is not high. The conductivity of the external discharge of the ED section is 9152.36.

[0026] If two-stage reverse osmosis is used instead of ED, the COD after concentration will be around 200 when entering the first-stage RO-4, which does not meet the feed water conditions.

[0027] In summary, compared to reverse osmosis, electrodialysis achieves a higher degree of concentration of inorganic salts, has simpler equipment, and does not require the addition of scale inhibitors. Considering the actual situation of this invention, electrodialysis equipment is the better choice.

[0028] Based on the water quality and treatment requirements of this invention, the design coefficient is 1.15; the biological pretreatment process adopts a high-density sedimentation tank to remove suspended solids and turbidity; the biological filtration treatment stage adopts an aerated biological filter, an air flotation tank, an ozone catalytic oxidation tank, an aerobic tank, and an MBR membrane tank. The overall biological stage can effectively remove COD, ensuring that the influent water quality of the downstream membrane process and the overall effluent water quality meet the standards.

[0029] The membrane pretreatment process employs multi-stage filtration. MBR permeate undergoes multi-stage filtration, including multi-media filters, activated carbon filters, and ultrafiltration, to remove suspended solids, turbidity, and SDI from the treated water, ensuring the stability of the RO membrane process and reducing membrane fouling. The advanced treatment system utilizes a mature reverse osmosis system. The first-stage RO permeate undergoes further desalination before entering the second-stage RO system for a second round of desalination. The dual-stage RO desalination system achieves a desalination rate of 99.75%.

[0030] An EDI system is used after the RO system. The RO permeate undergoes deep desalination treatment. The resistivity of the permeate is greater than 16MΩ, and the overall permeate recovery rate is 95.92%.

[0031] To improve the system recovery rate, the RO concentrate is further concentrated using an EDR system. The primary and secondary RO concentrates are then passed through the EDR system to recover the permeate to the ozone catalytic oxidation system, thereby improving the overall permeate recovery rate. The final waste brine discharge is 2.95 m3 / h, and the waste brine discharge rate is 3.28%. Attached Figure Description

[0032] When considered in conjunction with the accompanying drawings, the invention will be more fully and better understood, and its many accompanying advantages will become readily apparent, by referring to the following detailed description. However, the accompanying drawings, which are provided to further illustrate the invention and form part of this invention, are used to explain the invention and do not constitute an undue limitation thereof, as shown in the figures:

[0033] Figure 1 This is a schematic diagram of the structure of the present invention.

[0034] Figure 2 This is a schematic diagram of the planar structure of the device of the present invention.

[0035] Figure 3 This is a schematic diagram of the process structure of the present invention.

[0036] Figure 4 This is a schematic diagram of the table in this invention.

[0037] Figure 5 Diagram of spiral wound reverse osmosis membrane structure.

[0038] Figure 6 STRO structural diagram.

[0039] Figure 7 DTRO structural diagram. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] Obviously, many modifications and variations made by those skilled in the art based on the spirit of this invention fall within the scope of protection of this invention.

[0042] It will be apparent to those skilled in the art that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when an element or component is referred to as “connected” to another element or component, it may be directly connected to the other element or component, or there may be intermediate elements or components. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description, "multiple" means two or more, unless otherwise explicitly specified.

[0044] Unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection (welding, riveting, and bolting) or an electrical connection; they can refer to a direct connection or an indirect connection through intermediate devices; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0045] Those skilled in the art will understand that, unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art.

[0046] To facilitate understanding of the embodiments, further explanations and descriptions will be provided below, and the various embodiments do not constitute a limitation on the embodiments of the invention.

[0047] Example 1: As Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, a method for desalination and resource utilization of fluorochemical washing wastewater has limited pretreatment of suspended solids, hardness, and biotoxic substances. General processes only consider a portion of the treatment functions, resulting in substandard water quality in the later stages of chemical wastewater treatment. The use of resin or chemical softening treatment before and after the membrane system has low treatment efficiency, and the replacement cost of the resin is high.

[0048] A method for desalination and resource utilization of fluorochemical washing wastewater includes the following steps: In the pretreatment stage, a high-density sedimentation tank is used to precipitate inorganic fluoride ions and suspended solids; an aerated biological filter is used for preliminary filtration and biochemical degradation; an air flotation tank is used for further removal of dissolved and surfactant substances; the effluent is treated with ozone catalytic oxidation to degrade organic fluoride and reduce biotoxicity; the effluent then enters an aerobic MBR to remove organic matter and suspended solids; before entering the membrane system, multi-media filtration and activated carbon filtration are used for final trace removal of suspended solids and organic matter to ensure the quality of the wastewater entering the membrane system; a UF+RO dual-membrane process is used for concentration; EDR is used to desalinate the concentrate to increase permeate flow; and EDI is used to treat the permeate to ensure a high permeate concentration. Compared with resin and chemical softening, this method offers better treatment performance and economic benefits.

[0049] A desalination and resource utilization device for fluorochemical washing wastewater mainly includes a biochemical pretreatment section consisting of a high-density tank, an aerated biological filter, a dissolved air flotation tank, an ozone catalytic oxidation filter, and an aerobic MBR tank; a membrane pretreatment section consisting of a multi-media filter, an activated carbon filter, an ultrafiltration filter, and a deep treatment process including reverse osmosis (RO), EDI, and EDR.

[0050] A device for desalination and resource utilization of fluorochemical washing wastewater includes a biochemical pretreatment structure: Fluorochemical washing wastewater is fed into an equalization tank 1.0; the effluent from equalization tank 1.0 is connected to the inlet of a high-density sedimentation tank 1.1; the effluent from high-density sedimentation tank 1.1 is connected to an aerated biological filter 1.2; the sludge outlet of high-density sedimentation tank 1.1 is discharged into a sludge storage tank; the effluent from aerated biological filter 1.2 is connected to a dissolved air flotation tank 1.3; the backwash water outlet of aerated biological filter 1.2 is discharged back to equalization tank 1.0; and the effluent from dissolved air flotation tank 1.3 is connected to... The scum outlet of ozone catalytic oxidation unit 1.4 and flotation tank 1.3 is discharged to the sludge storage tank. The outlet of ozone catalytic oxidation unit 1.4 is connected to aerobic MBR membrane tank 1.5. The backwash water outlet of ozone catalytic oxidation unit 1.4 is discharged to equalization tank 1.0. The outlet of aerobic MBR membrane tank 1.5 is connected to intermediate water tank 2.0. The sludge outlet of aerobic MBR membrane tank 1.5 is discharged to the sludge storage tank. The outlet of the sludge storage tank is connected to plate and frame dewatering machine. The sludge from the plate and frame dewatering machine is transported off-site. The filtrate outlet of the plate and frame dewatering machine is discharged to equalization tank 1.0.

[0051] A device for desalination and resource utilization of fluorochemical washing wastewater, comprising a membrane pretreatment structure: the outlet of intermediate water tank 2.0 is connected to multi-media filter 2.1, the outlet of multi-media filter 2.1 is connected to activated carbon filter 2.2, the backwash water outlet of multi-media filter 2.1 is discharged to equalization tank 1.0, the outlet of activated carbon filter 2.2 is connected to ultrafiltration 2.3, the backwash water outlet of activated carbon filter 2.2 is discharged to equalization tank 1.0, the outlet of ultrafiltration 2.3 is connected to ultrafiltration product water tank 3.0, the backwash water outlet of ultrafiltration 2.3 is discharged to equalization tank 1.0, and the outlet of ultrafiltration product water tank 3.0 is connected to primary RO-13.1.

[0052] A desalination and resource utilization device for fluorochemical washing wastewater, comprising a first-stage RO-1, a first-stage RO-2, and a second-stage RO. The structure of the reverse osmosis (RO)-EDI-EDR deep treatment section is as follows: The RO-1 permeate outlet is connected to the RO-1 permeate tank 3.5; the RO-1 concentrate outlet is connected to the concentrate tank; the concentrate tank outlet is connected to the RO-1 stage; the RO-2 permeate outlet is connected to the RO-1 permeate tank 3.5; the RO-2 concentrate outlet is connected to the concentrate tank 2; the concentrate tank 2 outlet is connected to the EDR system 3.3; the EDR system 3.3 permeate outlet is connected to the ozone catalytic oxidation unit 1.4; the EDR system 3.3 concentrate is discharged externally; the RO-1 permeate tank 3.5 outlet is connected to the RO stage; the RO-2 permeate outlet is connected to the RO-2 stage 3.6; the RO-2 permeate outlet is connected to the concentrate tank; the RO-2 permeate tank 3.6 outlet is connected to the EDI system 3.4; the EDI system 3.4 outlet is connected to the nitrogen-sealed water tank 3.7; the EDI system 3.4 concentrate outlet is connected to the RO-1 stage 3.5; the nitrogen-sealed water tank 3.7 outlet is connected to the reuse pipeline.

[0053] The biochemical pretreatment section utilizes a high-density tank to remove large-particle suspended solids from fluorochemical washing wastewater. It also enhances the precipitation of inorganic fluoride ions by adding CaCO3 and Ca(OH)2 as a double alkali. Furthermore, it uses a sludge return pump in the high-density tank to return some of the sludge, thereby enhancing the settling effect of suspended solids and reducing the amount of flocculant used. The effluent from the high-density tank enters the aerated biological filter, where the biochemical flocculation effect of microorganisms in the filter traps small-diameter suspended solids and treats easily degradable organic matter in the washing wastewater. The pre-filtered effluent then enters the dissolved air flotation tank, where a high-efficiency dissolved air flotation device removes small-diameter suspended solids and dissolved organic matter such as surfactants from the wastewater. The flotation effluent then enters the ozone catalytic oxidation filter, where an appropriate OC ratio degrades organic fluorides, converting them into easily degradable organic matter. The effluent then enters the aerobic MBR tank, where aerobic bacteria further degrade the effluent, and the MBR membrane filters effectively, ensuring a significant reduction in fluoride ion content, suspended solids, and dissolved organic matter, thus completing the biochemical pretreatment process.

[0054] The membrane pretreatment section structure produces effluent with good quality after pretreatment. It then undergoes secondary filtration through the multi-media filter and activated carbon filter to ensure that the wastewater does not contain small-diameter suspended solids before entering the membrane. After ultrafiltration, the effluent meets the requirements of reverse osmosis turbidity <1 NTU and SDI <5, thus avoiding the risk of scaling in subsequent concentration.

[0055] The reverse osmosis (RO)-EDI-EDR deep treatment section structure uses a two-stage desalination system for preliminary desalination. The RO permeate enters the EDI system for deep desalination, and the RO concentrate enters the EDR system for further concentration. The permeate is then returned to the ozone catalytic oxidation section for further treatment, and the concentrate is discharged, achieving the maximum permeate recovery effect.

[0056] A desalination and resource utilization device for fluorochemical washing wastewater comprises a biochemical pretreatment section that uses a high-density tank to remove large-particle suspended solids and inorganic fluoride ions, an aerated biological filter to remove small-particle suspended solids and easily degradable organic matter, a dissolved air flotation tank to remove tiny-particle suspended solids and surfactants, an ozone catalytic oxidation filter to degrade organic fluorides and eliminate biotoxicity, and an aerobic MBR tank to degrade organic matter, achieving good removal effects of suspended solids, biotoxic substances, and surfactants in fluorochemical wastewater. The membrane pretreatment section utilizes multi-stage filtration and ultrafiltration to reduce SDI and turbidity, mitigating membrane fouling. Finally, RO reverse osmosis-EDI concentration and desalination are achieved, and EDR further concentration improves the permeate utilization rate. This invention utilizes pretreatment to sequentially remove large-particle suspended solids, dissolved surfactants, biotoxic substances, dissolved organic matter, and SDI, ensuring the concentration efficiency of the subsequent desalination stage. The concentration stage uses RO-EDI to improve the desalination rate, and EDR treatment of the concentrate improves the permeate utilization rate, achieving a good desalination and resource utilization effect for fluorochemical washing wastewater.

[0057] Example 2: Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, a desalination and resource utilization device for fluorochemical washing wastewater mainly includes a biochemical pretreatment section, namely a high-density tank 1.1, an aerated biological filter 1.2, a dissolved air flotation tank 1.3, an ozone catalytic oxidation filter 1.4, and an aerobic MBR tank 1.5; a membrane pretreatment section, namely a multi-media filter 2.1, an activated carbon filter 2.2, and an ultrafiltration system 2.3; and a reverse osmosis RO-EDI-EDR deep treatment section, namely a reverse osmosis RO 3.1-EDR system 3.3-EDI system 3.4.

[0058] A method for desalination and resource utilization of fluorochemical washing wastewater is proposed. The method utilizes a high-density tank 1.1 to remove large-particle suspended solids from the fluorochemical washing wastewater, and enhances the precipitation of inorganic fluoride ions by adding CaCO3 and Ca(OH)2 as a double alkali. The method also utilizes the sludge return pump of the high-density tank 1.1 to return part of the sludge, thereby enhancing the sedimentation effect of suspended solids and reducing the amount of flocculant used. The effluent from the high-density tank enters the aerated biological filter 1.2. Utilizing the biochemical flocculation effect of microorganisms in the filter and the characteristics of the volcanic rock composite biological filter media—namely, well-developed micropores, strong interception capacity, low resistance, high strength, and good stability—small-diameter suspended solids are intercepted, and easily degradable organic matter in the washing wastewater is treated. The pre-filtered effluent then enters the dissolved air flotation tank 1.3. A high-efficiency dissolved air flotation device removes small-diameter suspended solids and dissolved organic matter such as surfactants from the wastewater. The flotation effluent then enters the ozone catalytic oxidation filter 1.4. Using a suitable OC ratio determined through small-scale experiments and a carbon-based ozone catalytic oxidation process, organic fluorides are degraded, converting them into easily degradable organic matter. The effluent then enters the aerobic MBR tank 1.5. Through the degradation by aerobic bacteria in the aerobic tank and the filtration effect of the MBR membrane, the fluoride ion content, suspended solids, and dissolved organic matter content in the effluent are significantly reduced, completing the biochemical pretreatment process.

[0059] The effluent quality after pretreatment is good. It undergoes secondary filtration through a multi-media filter 2.1 and an activated carbon filter 2.2 to ensure that the wastewater does not contain small-diameter suspended solids before entering the membrane. After treatment by ultrafiltration 2.3, the effluent meets the requirements of reverse osmosis turbidity <1NTU and SDI <5, which is low and does not cause scaling risk in subsequent concentration.

[0060] The reverse osmosis (RO) system 3.1 uses a two-stage desalination system for initial desalination. The RO permeate then enters the EDI system 3.4 for deep desalination. The RO concentrate then enters the EDR system 3.3 for further concentration. The permeate is then returned to the ozone catalytic oxidation section for further treatment, and the concentrate is discharged, achieving the maximum permeate recovery effect.

[0061] The biochemical pretreatment section utilizes a high-density tank (1.1) to remove large-particle suspended solids and inorganic fluoride ions, an aerated biological filter (1.2) to remove small-particle suspended solids and easily degradable organic matter, a dissolved air flotation tank (1.3) to remove tiny-particle suspended solids and surfactants, an ozone catalytic oxidation filter (1.4) to degrade organic fluorides and eliminate biotoxicity, and an aerobic MBR tank (1.5) to degrade organic matter, achieving a good removal effect of suspended solids, biotoxic substances, and surfactants in fluorochemical wastewater. The membrane pretreatment section utilizes multi-stage filtration and ultrafiltration (2.3) to reduce SDI and turbidity, thereby mitigating membrane fouling. Finally, RO reverse osmosis-EDI concentration and desalination, and EDR re-concentration to improve the utilization rate of permeate.

[0062] This invention utilizes pretreatment to sequentially remove large-particle suspended solids, soluble surfactants, biotoxic substances, soluble organic matter, and SDI, ensuring the concentration efficiency of the subsequent desalination stage. The concentration stage uses RO-EDI to improve the desalination rate, and uses EDR to treat the concentrate to improve the water production rate, achieving a good desalination and resource utilization effect for fluorochemical washing wastewater.

[0063] A desalination and resource utilization device for fluorochemical washing wastewater mainly includes a high-density biochemical pretreatment section, an aerated biological filter, a dissolved air flotation tank, an ozone catalytic oxidation filter, and an aerobic MBR tank; a membrane pretreatment section with a multi-media filter, an activated carbon filter, and an ultrafiltration / reverse osmosis (RO)-EDI-EDR deep treatment section. This invention removes suspended solids, turbidity, and COD in the biochemical pretreatment section, removes suspended solids, turbidity, and SDI in the membrane pretreatment section, and achieves a deep desalination and permeate recovery rate of 95.92% in the reverse osmosis (RO)-EDI-EDR deep treatment section. The desalinated fluorochemical washing wastewater is then used to produce pure water, achieving resource utilization as recycled water for production, thus realizing the resource reuse of fluorochemical washing wastewater.

[0064] Example 3: As Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown, a method for desalination and resource utilization of fluorochemical washing wastewater is described, based on... Figure 3 This is a system flow diagram for the desalination and resource utilization of fluorochemical washing wastewater. The device is divided into a high-density biochemical pretreatment section, followed by an aerated biological filter, a dissolved air flotation tank, an ozone catalytic oxidation filter, and an aerobic MBR tank. The membrane pretreatment section includes a multi-media filter, an activated carbon filter, and an ultrafiltration / reverse osmosis (RO)-EDI-EDR deep treatment section. In actual implementation cases, detailed process comparisons were conducted based on specific water quality and operating conditions, as detailed below:

[0065] 1. Influent and effluent water quality and quantity

[0066] 1.1 Influent water quality

[0067] The wastewater from this invention originates from the washing wastewater during the production of fluorinated resins, and its water quality is shown in Table 1-1.

[0068] Table 1-1 Influent Water Quality

[0069]

[0070]

[0071] 1.2 The effluent parameters are shown in Table 1-2.

[0072] 1. System wastewater discharge rate: ≤5%

[0073] 2. Production water flow rate: ≥90t / h

[0074] Table 1-2 Effluent Indicators

[0075]

[0076] Based on existing water quality and quantity requirements, the key considerations during implementation are:

[0077] The system design fully considers design margins, with an overall system margin coefficient of 1.15. Water pumps and corresponding spare parts are added as needed for each individual unit to ensure continuous and stable system operation.

[0078] 2. Given the scarcity of land resources, the treatment technologies adopted should prioritize small footprint and high operational efficiency. While ensuring convenient construction, installation, and maintenance, the treatment structures should be concentrated as much as possible to save land and maximize green space.

[0079] 3. The water intake of the project often varies with time and season. The project should consider a modular design concept, which can combine the system operation according to the current water volume and the future increase in water volume, so as to reduce operating costs.

[0080] 2. Process Comparison

[0081] Biochemical pretreatment steps:

[0082] The biochemical pretreatment section includes a high-density tank, an aerated biological filter, a dissolved air flotation tank, an ozone catalytic oxidation filter, and an aerobic MBR tank. The comparison mainly focuses on the processes before the aerobic MBR membrane tank in this process, as detailed below:

[0083] Wastewater has high levels of suspended solids and turbidity. Sedimentation is the main process for removing suspended solids from water. Conventional sedimentation processes for removing suspended solids include inclined plate tube sedimentation tanks, horizontal flow sedimentation tanks, and high-density sedimentation tanks, as shown in Table 1-3, which compares commonly used processes.

[0084] Table 1-3 Comparison of Precipitation Processes

[0085]

[0086] Based on the above comparison, and taking into account the investment cost, operational stability, and ease of operation, a high-density sedimentation tank is selected to remove suspended solids and turbidity from the water. The combination of high-density sedimentation tank and air flotation tank to remove suspended solids and turbidity from wastewater has the advantages of mature and stable technology and high removal efficiency.

[0087] After surface-active substances and large-particle suspended solids are removed in high-density sedimentation tanks and dissolved air flotation tanks, COD is removed using an aerated biological filter, ozone catalytic oxidation, and aerobic tanks, ensuring the stable operation of the subsequent membrane system. The aerated biological filter simultaneously performs biodegradation and filtration, representing a fully mature technology. Furthermore, the selected volcanic rock composite biological filter media features well-developed micropores, strong interception capacity, low resistance, high strength, and good stability, ensuring stable COD removal.

[0088] The ozone catalytic oxidation process parameters were determined through experimental comparison. The main process flow is as follows:

[0089] a) According to the owner's experiments, the main sources of COD and membrane clogging pollutants in this wastewater are dispersants, and ozone oxidation can effectively remove COD and alleviate membrane clogging.

[0090] b) Design an experiment to compare the treatment effects of ozone catalytic oxidation and ozone contact oxidation processes, and determine that the process is ozone catalytic oxidation.

[0091] c) Experiments were conducted to determine the core process parameters, including ozone dosage and contact time, to ensure the COD removal effect and avoid membrane clogging. This invention utilizes a carbon-based ozone catalytic oxidation process, which does not generate secondary pollution, has strong oxidation capacity, fast reaction speed, high ozone utilization rate, and low investment and operating costs. As shown in Tables 1-4, this invention is a recognized advanced technology for organic wastewater treatment.

[0092] Table 1-4 Comparison of ozone contact oxidation and catalytic ozone oxidation

[0093]

[0094] The raw water COD is ≤800mg / L. The process design calculation shows that the COD entering the ozone catalytic oxidation system is 378mg / L, with a removal rate of 52.75%. The removal rate of the target pollutants, surfactants 1350mg / L and 275mg / L, is also 52.75%. At this time, the corresponding concentrations of surfactant 1 and surfactant 2 are 166mg / L and 36mg / L, respectively. Using the concentrations of surfactant 1 and surfactant 2 at this time as the experimental pilot concentrations, based on the previous experimental results, the target value is to achieve a removal rate of 91% for surfactant 1 without fouling the membrane. At this time, the amount of COD removed is 195mg / L.

[0095] Compare the effects of ozone contact oxidation alone and carbon-based catalyst-catalyzed ozone oxidation on the oxidative degradation of surfactants;

[0096] The experimental conditions were set based on empirical values, selecting an O3 / ΔCOD ratio of 1.5 to achieve the target removal rate, with an ozone dosage of approximately 290-300 mg / L. Experimental data showed that catalytic oxidation was significantly more efficient than contact oxidation; for the same contact reaction time, catalytic oxidation could increase COD removal by approximately 60 mg / L.

[0097] In summary, carbon-based material-catalyzed ozone oxidation is significantly superior to conventional ozone contact oxidation. Therefore, carbon-based material-catalyzed ozone oxidation is recommended for advanced oxidative degradation of COD.

[0098] Membrane pretreatment stage steps: The membrane pretreatment stage includes a multi-media filter, an activated carbon filter, and an ultrafiltration unit. The multi-media filter and activated carbon filter ensure the stability of the feed water to the ultrafiltration and reverse osmosis membranes, reduce mechanical damage and contamination to downstream processes, lower the risk of membrane clogging, and ensure system recovery rate and stability. This process primarily involves comparing and selecting the appropriate ultrafiltration unit.

[0099] To meet the requirements of reverse osmosis turbidity <1 NTU and SDI <5, it is necessary to further remove suspended solids, organic matter and some COD from the water. This requires the installation of higher precision filters. Currently, ultrafiltration is widely used as a pretreatment before reverse osmosis.

[0100] As shown in Table 1-4, ultrafiltration is divided into tubular ultrafiltration and hollow fiber ultrafiltration. Hollow fiber ultrafiltration membranes can be further categorized into pressure ultrafiltration and submerged ultrafiltration based on the reactor type. Pressure ultrafiltration is further divided into internal pressure ultrafiltration and external pressure ultrafiltration based on the membrane. External pressure ultrafiltration is mostly made of PVDF and is suitable for most wastewater treatment. Internal pressure membranes are mostly made of PES, which is more brittle and has smaller inlet channels, making it prone to fouling. Tubular ultrafiltration, with its larger internal channels, is suitable for water with higher turbidity, but its high flushing velocity results in high operating costs.

[0101] This invention removes metal salts from the influent through a multi-stage mixing reaction, followed by sedimentation and multi-media filtration, resulting in water with low turbidity and lower operating energy consumption. The hollow fiber ultrafiltration membrane can fully meet the usage requirements. However, the influent water is high-salt wastewater, which is prone to crystallization during operation. Therefore, aeration purging is not suitable for membrane fouling cleaning. For internal pressure membranes, high-flow-rate flushing can be selected to minimize crystallization clogging.

[0102] Table 1-5 Comparison of Ultrafiltration Membranes

[0103]

[0104]

[0105] In this invention, the influent undergoes a multi-stage treatment reaction to remove COD, and then passes through a multi-stage filtration medium, resulting in low turbidity in the water. The hollow fiber ultrafiltration membrane can fully meet the usage requirements. Furthermore, this process requires low investment, therefore, an external pressure ultrafiltration membrane is selected for this stage of the process.

[0106] The deep treatment section of the reverse osmosis (RO-EDI-EDR) process involves comparing and selecting between reverse osmosis and electrodialysis.

[0107] Reverse osmosis membrane elements feature wide flow channels, high permeate flow rate, and high fouling resistance. Their special element and membrane design can withstand ultra-high feed water pressure, improving salt recovery during the process. Furthermore, the RO pressure vessel used in each concentration stage is a 6-core container, ensuring more uniform permeate flow and guaranteeing a more stable reverse osmosis system and higher final permeate quality. Based on reverse osmosis simulation software, the rationality of performance parameters such as flux, recovery rate, feed water flow rate, concentrate flow rate, feed water pressure, and inter-stage pressure drop for each section and each reverse osmosis membrane element is analyzed to design the optimal configuration of the reverse osmosis system. The automatic valve configuration of this invention enables automatic start-up and permeate production, automatic shutdown and flushing, automatic cleaning, automatic shutdown alarm in case of an accident, and automatic cleaning reminders.

[0108] Different reverse osmosis membranes and technologies are selected to achieve the best cost-effectiveness for different feed water qualities.

[0109] like Figure 5 , Figure 6 and Figure 7 As shown, the spiral-wound reverse osmosis (RO) membrane has a spiral structure, also known as a spiral structure. It consists of multi-leaf membrane bags. Each leaf membrane bag comprises two membrane sheets with their front and back facing each other, a product water channel placed between the two membrane sheets, and a turbulent mesh-like feed water channel placed on the membrane surface. Three sides of the membrane bag are sealed with adhesive, and the fourth side is open onto a perforated product water collection pipe. It has advantages such as uniform water flow distribution, high resistance to fouling, low replacement costs, simple external piping, and easy cleaning and maintenance.

[0110] The spiral-wound high-pressure reverse osmosis (STRO) membrane module is a novel structural membrane module specifically developed for the treatment of high-concentration wastewater. Utilizing the structure of this invention, the membrane sheet is an industrial anti-fouling RO membrane. The grid channel employs a parallel grid structure, distinct from conventional spiral-wound membranes, enabling long-term stable operation in areas where conventional spiral-wound membranes cannot be used. The grid of the spiral-wound high-pressure reverse osmosis membrane module adopts a trapezoidal structure, allowing wastewater / feed solution to flow within the channels formed by the grid, similar to flow within a tubular membrane. The resistance of the diamond-shaped grid is significantly lower. Simultaneously, the internal transverse reinforcing ribs increase turbulence during feed solution flow, reducing concentration polarization and thus greatly improving the fouling resistance of the ST membrane module.

[0111] Disc tube reverse osmosis (DTRO) is a type of reverse osmosis membrane module specifically designed to treat wastewater with high concentrations of organic matter and high salinity. Its core technology is the disc tube membrane column. Reverse osmosis membranes and hydraulic guide plates are stacked together, secured with a central tie rod and end plates, and then placed inside a pressure-resistant sleeve to form a membrane column. DTRO overcomes the clogging issues common in reverse osmosis systems when handling high-organic-matter and high-salt wastewater.

[0112] The working principle of spiral-wound reverse osmosis (RO) membranes: Pressurized feed liquid enters through the inlet at one end of the membrane housing and flows parallel to the central tube through the feed channel formed by the feed separator, passing over the membrane surface. During this process, some liquid flows out from the outlet at the other end of the membrane housing, forming a concentrate; while the remaining liquid permeates through the membrane flows in a spiral direction through the permeate separator channel inside the membrane bag, eventually flowing into the central tube and being discharged. This flow pattern not only ensures effective filtration of the feed liquid but also allows the permeate to be smoothly discharged, completing the entire filtration process.

[0113] The working principle of the spiral-wound high-pressure reverse osmosis membrane (STRO): The feed flow process of the STRO membrane element is the same as that of the spiral-wound RO; its structure is further optimized based on the spiral-wound RO technology. The element integrates the design advantages of open channels and spiral-wound elements, innovatively adopting a unique 45° diamond-shaped double-layer open channel structure. This design significantly optimizes the feed channel and the effective area of ​​the membrane, while making the pressure more stable. This design further improves the unobstructed flow of the feed channel and the effective area of ​​the membrane. To improve the efficiency of the freshwater channel and reduce pressure loss, the STRO membrane element shortens the blade length and increases the number of blades. This design shortens the freshwater channel length, thereby reducing the pressure loss in the freshwater channel. Simultaneously, it makes the net driving pressure along the membrane tend to be uniform, thus maintaining the consistency of water flux at different points on the membrane surface. This design reduces the degree of concentration polarization, allowing the membrane's permeation performance to be better utilized.

[0114] The working principle of Disc Tube Reverse Osmosis (DTRO): The disc tube membrane module uses an open flow channel, allowing the feed solution to smoothly enter the pressure vessel and flow to the other end of the module through the channel between the guide plate and the outer shell. At the other end flange, the feed solution enters the guide plate through eight channels, forming a short path for rapid flow across the filter membrane. After passing through the filter membrane, the liquid reverses at a 180° angle to the other membrane surface, and then flows into the next guide plate from the groove in the center of the guide plate. In this way, a double "S" shaped path is formed on the membrane surface from the circumference of the guide plate to the center, then back to the circumference, and then back to the center. The concentrate finally flows out from the feed end flange. The DT membrane module adopts a high-strength and pressure-resistant design, capable of withstanding higher osmotic pressures; its raised guide plate forms a unique open flow channel, thereby improving the membrane's antifouling ability, reducing pretreatment requirements, making cleaning more thorough, and extending the membrane's service life. This design makes the module more advantageous in dealing with various operating conditions.

[0115] Table 1-6 Comparison of Spiral Wrap-up Reverse Osmosis, Spiral Wrap-up High Pressure Reverse Osmosis, and DTRO Technologies

[0116]

[0117]

[0118] As shown in Tables 1-6 and in summary, considering the overall technological maturity, floor space, operating costs, service life, and concentrate recovery rate, spiral wound reverse osmosis technology has advantages such as high effective salt recovery rate, low investment cost, low operating cost, and small floor space. Furthermore, considering the influent water quality of this invention, spiral wound reverse osmosis technology has even more significant advantages.

[0119] Therefore, the present invention adopts spiral wound reverse osmosis technology for both the first-stage and second-stage reverse osmosis, and the effluent meets the owner's requirements for reclaimed water reuse, achieving the best overall process effect.

[0120] The pressures for the first and second stages of concentration are 9.0 bar and 8.9 bar, respectively, while the pressure for the second stage of reverse osmosis is 8.6 bar. Therefore, the R-BW8040-FR400 8-inch brackish water reverse osmosis membrane element is selected for seawater desalination in the first and second stages of concentration to ensure the quality of the effluent and lower operating costs while meeting the pressure requirements.

[0121] The process comparison for EDR and EDI systems following the reverse osmosis system is as follows:

[0122] EDR System: RO concentrate is further desalinated via EDR treatment, increasing reclaimed water volume and reducing wastewater discharge. The EDR system used in this invention allows for adjustments to operating parameters such as voltage, current, flow rate, and pressure to maintain permeate flow and effluent quality even when the raw water's ion concentration and conductivity fluctuate within a certain range. The EDR system can arbitrarily adjust voltage and current to achieve different desalination rates for wastewater, making desalination very convenient. Furthermore, the EDR system has a reversal function, automatically controlling the reversal to effectively prevent scaling and precipitation, providing a self-cleaning effect. In this invention, the permeate from the first-stage RO concentrate still contains some COD after EDR treatment. Therefore, this reclaimed permeate is recycled to the ozone catalytic oxidation stage to remove COD, ensuring reclaimed water quality and reducing the risk of membrane clogging.

[0123] EDI System: EDI is a revolutionary water treatment technology that cleverly combines electrodialysis and ion exchange technologies, producing high-quality pure water continuously without the need for acids or alkalis. It boasts advanced technology, ease of operation, and excellent environmental characteristics. This invention employs an EDI system as the final step in this process, ensuring stable and high-quality produced water.

[0124] Both reverse osmosis and electrodialysis have high-efficiency concentration functions. The comparison of the performance of the two technologies is shown in Table 1-7.

[0125] Table 1-7 Comparison of Reverse Osmosis and Electrodialysis Technologies

[0126]

[0127]

[0128] As described above, the embodiments of the present invention have been explained in detail. However, many modifications are possible as long as they do not substantially depart from the inventive point and effects of the present invention, which will be obvious to those skilled in the art. Therefore, all such modifications are also included within the protection scope of the present invention.

Claims

1. A method for desalination and resource utilization of fluorinated industrial washing wastewater, characterized in that, The method comprises the following steps: biochemical pretreatment step, membrane pretreatment step, reverse osmosis RO-EDI-EDR deep treatment step, biochemical pretreatment step: high-density sedimentation tank is used to remove large-size suspended solids in fluorine chemical washing wastewater, CaCO3 and Ca(OH)2 double-alkali method is added to enhance the precipitation of inorganic fluorine ions, and part of sludge is returned by using a sludge return pump of the high-density sedimentation tank to enhance the sedimentation effect of suspended solids and reduce the use amount of flocculants, the effluent of the high-density sedimentation tank is introduced into an aerobic biological filter to intercept small-size suspended solids by using the biochemical flocculation effect of microorganisms in the filter and to treat easily-degradable organic matters in the washing wastewater, the primary filtered effluent is introduced into a dissolved air flotation tank to remove small-size suspended solids in the wastewater and surfactants in the washing wastewater by using a high-efficiency dissolved air flotation device, the air-flotation effluent is introduced into an ozone catalytic oxidation filter to degrade organic fluorine compounds by using a proper OC ratio, the organic fluorine compounds are degraded into easily-degradable organic matters, the effluent is introduced into an aerobic MBR tank to degrade the organic matters by using the degradation of aerobic bacteria in the aerobic tank and the filtration effect of the MBR membrane, the fluorine ion content, the solid suspended matter content and the soluble organic matter content in the effluent are greatly reduced, and the biochemical pretreatment effect is achieved, membrane pretreatment step: after pretreatment, secondary filtration is performed by using a multi-medium filter and an activated carbon filter to ensure that the wastewater does not contain small-size suspended solids before entering the membrane, after ultrafiltration treatment, the effluent meets the requirements of reverse osmosis turbidity < 1 NTU and SDI < 5, reverse osmosis RO-EDI-EDR deep treatment step: two-stage desalination system is used in reverse osmosis RO to perform primary desalination treatment, the reverse osmosis water is introduced into an EDI system to perform deep desalination, the reverse osmosis concentrated water is introduced into an EDR system to perform secondary concentration, the produced water is returned to the ozone catalytic oxidation section for treatment, the concentrated water is discharged, and the maximum water recovery effect is achieved.

2. The fluorine chemical washing wastewater desalination resource utilization device according to claim 1, characterized in that, The fluorinated chemical washing wastewater is connected to a regulating tank, the water outlet of the regulating tank is connected to the water inlet of a high-density sedimentation tank, the water outlet of the high-density sedimentation tank is connected to a biological aerated filter, the sludge outlet of the high-density sedimentation tank is connected to a sludge storage tank, the water outlet of the biological aerated filter is connected to a gas floatation tank, the backwash water outlet of the biological aerated filter is connected to the regulating tank, the water outlet of the gas floatation tank is connected to an ozone catalytic oxidation unit, the sludge outlet of the gas floatation tank is connected to the sludge storage tank, the water outlet of the ozone catalytic oxidation unit is connected to an aerobic MBR membrane tank, the backwash water outlet of the ozone catalytic oxidation unit is connected to the regulating tank, the water outlet of the aerobic MBR membrane tank is connected to an intermediate water tank, the sludge outlet of the aerobic MBR membrane tank is connected to the sludge storage tank, the outlet of the sludge storage tank is connected to a plate-frame dewatering machine, the sludge of the plate-frame dewatering machine is transported out, the filtrate outlet of the plate-frame dewatering machine is connected to the regulating tank, the water outlet of the intermediate water tank is connected to a multi-medium filter, the water outlet of the multi-medium filter is connected to an activated carbon filter, the backwash water outlet of the multi-medium filter is connected to the regulating tank, the water outlet of the activated carbon filter is connected to an ultrafiltration device, the backwash water outlet of the activated carbon filter is connected to the regulating tank, the water outlet of the ultrafiltration device is connected to an ultrafiltration water tank, the backwash water outlet of the ultrafiltration device is connected to the regulating tank, the water outlet of the ultrafiltration water tank is connected to a first RO-1, the water outlet of the first RO-1 is connected to a first water production tank, the concentrated water outlet of the first RO-1 is connected to a concentrated water tank 1, the water outlet of the concentrated water tank 1 is connected to a first RO-2, the water outlet of the first RO-2 is connected to the first water production tank, the concentrated water outlet of the first RO-2 is connected to a concentrated water tank 2, the water outlet of the concentrated water tank 2 is connected to an EDR system, the water outlet of the EDR system is connected to the ozone catalytic oxidation unit, the concentrated water of the EDR system is discharged, the water outlet of the first water production tank is connected to a second RO, the water outlet of the second RO is connected to a second water production tank, the concentrated water outlet of the second RO is connected to the concentrated water tank 1, the water outlet of the second water production tank is connected to an EDI system, the water outlet of the EDI system is connected to a nitrogen sealing water tank, the concentrated water outlet of the EDI system is connected to the first water production tank, and the water outlet of the nitrogen sealing water tank is connected to a reuse pipeline.

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