Process for removing carbon nanotubes and N-methyl-2-pyrrolidone (NMP) from water

Abstract

A method of treating wastewater comprising carbon nanotubes and N-methyl-2-pyrrolidone (NMP) includes introducing one or more settling agents into the wastewater to promote settling of solids from the wastewater and form a medicament-treated wastewater; separating the medically treated wastewater into a sludge having an increased carbon nanotube concentration compared to the medically treated wastewater and a supernatant having a reduced carbon nanotube concentration compared to the medically treated wastewater; separating the supernatant into a filtrate and a retentate, the retentate having a solids concentration higher than the solids concentration of the filtrate; and separating the filtrate into product water having a lower NMP concentration than the NMP concentration of the filtrate and a retentate having a higher NMP concentration than the NMP concentration of the filtrate.

Description

Cross-reference to related applications concerning processes for removing carbon nanotubes and N-methyl-2-pyrrolidone (NMP) from water

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 095,417, filed October 27, 2023, and U.S. Provisional Patent Application No. 63 / 697,228, filed September 20, 2024, the contents of which are incorporated herein by reference in their entirety. Background Technology Background

[0002] The aspects and embodiments disclosed herein relate to systems and methods for reducing the concentration of one or more contaminants, such as carbon nanotubes and NMP, from waste streams, and particularly to systems and apparatus for removing one or more contaminants from battery manufacturing plant waste streams. Summary of the Invention

[0003] According to one aspect, a method is provided for treating wastewater containing carbon nanotubes and N-methyl-2-pyrrolidone (NMP). The method includes introducing one or more flocculants into the wastewater to promote the sedimentation of solids and form dosed wastewater; separating the dosed wastewater into sludge and a supernatant, the sludge having an increased carbon nanotube concentration compared to the dosed wastewater, and the supernatant having a decreased carbon nanotube concentration compared to the dosed wastewater; separating the supernatant into a filtrate and a leachate, the leachate having a higher solids concentration than the filtrate; and separating the filtrate into product water and a reject, the product water having a lower NMP concentration than the filtrate, and the reject having a higher NMP concentration than the filtrate.

[0004] In some implementations, the method also includes adjusting the pH of the chemically treated wastewater.

[0005] In some implementations, the pH of the chemically treated wastewater is adjusted to approximately 8.

[0006] In some implementations, separating chemically treated wastewater includes clarification of the chemically treated wastewater.

[0007] In some implementations, one or more settling agents include FeCl3.

[0008] In some implementations, one or more settling agents include polymeric flocculants.

[0009] In some implementations, the method also includes thickening the sludge to form thickened sludge and first recovered water.

[0010] In some implementations, the method further includes mixing the first recovered water with the wastewater before introducing one or more flocculants into the wastewater.

[0011] In some implementations, the method further includes dewatering the thickened sludge in a filter press to form waste solids and second-recovered water.

[0012] In some embodiments, the method further includes mixing the second recovered water with the wastewater before introducing one or more coagulants or flocculants into the wastewater.

[0013] In some implementations, separating the supernatant into filtrate and osmosis includes passing the supernatant through a microfilter or an ultrafilter.

[0014] In some implementations, the method further includes adjusting the pH of the supernatant before passing it through a microfilter or an ultrafilter.

[0015] In some implementations, the pH of the supernatant is adjusted to approximately 6.5 before passing the supernatant through one of a microfilter or an ultrafilter.

[0016] In some implementations, separating the filtrate into product water and retentate includes passing the filtrate through a reverse osmosis unit.

[0017] In some implementations, the method also includes adjusting the pH of the filtrate before passing it through the reverse osmosis unit.

[0018] In some implementations, the pH of the filtrate is adjusted to approximately 7 before the filtrate is passed through the reverse osmosis unit.

[0019] In some implementations, the method further includes adding a scale inhibitor to the filtrate before passing it through the reverse osmosis unit.

[0020] In some embodiments, the method further includes monitoring the NMP concentration in at least one of the filtrate or product water.

[0021] In some embodiments, monitoring the NMP concentration in at least one of the filtrate or product water includes measuring at least one of total Kjeldahl nitrogen (TKN) or total organic carbon (TOC) in at least one of the filtrate or product water, and using the measurement results of at least one of TKN or TOC to determine the NMP concentration.

[0022] In some implementations, the method further includes purifying the product water in an ion exchange column.

[0023] In some embodiments, the ion exchange column comprises a mixed bed of cation exchange resin and anion exchange resin.

[0024] In some embodiments, the method includes forming product water having an NMP concentration of less than 0.5% of the NMP concentration in the wastewater.

[0025] In some embodiments, the method further includes mixing at least a portion of the retentate from the reverse osmosis unit with the filtrate before passing the filtrate through the reverse osmosis unit.

[0026] In some implementations, the method also includes purifying the product water with activated carbon.

[0027] According to another aspect, a method for treating wastewater containing carbon nanotubes is provided. The method includes introducing one or more flocculants into the wastewater to promote the sedimentation of solids from the wastewater and form chemically treated wastewater; separating the chemically treated wastewater into sludge and a supernatant, the sludge having an increased carbon nanotube concentration compared to the chemically treated wastewater, and the supernatant having a decreased carbon nanotube concentration compared to the chemically treated wastewater; and separating the supernatant into a filtrate and a leachate, the leachate having a higher solids concentration than the filtrate.

[0028] In some implementations, the method for treating wastewater containing carbon nanotubes also includes adjusting the pH of the chemically treated wastewater.

[0029] In some implementations, the pH of the chemically treated wastewater is adjusted to approximately 8.

[0030] In some implementations, separating chemically treated wastewater includes clarification of the chemically treated wastewater.

[0031] In some implementations, one or more settling agents include FeCl3.

[0032] In some implementations, one or more settling agents include polymeric flocculants.

[0033] In some implementations, the method of treating wastewater containing carbon nanotubes also includes thickening the sludge to form thickened sludge and first-recovered water.

[0034] In some implementations, the method of treating wastewater containing carbon nanotubes further includes mixing the first recovered water with the wastewater before introducing one or more flocculants into the wastewater.

[0035] In some embodiments, the method of treating wastewater containing carbon nanotubes also includes dewatering thickened sludge in a filter press to form waste solids and second-recovered water.

[0036] In some embodiments, the method of treating wastewater containing carbon nanotubes further includes mixing second-recovered water with the wastewater before introducing one or more coagulants or flocculants into the wastewater.

[0037] In some implementations, separating the supernatant into filtrate and osmosis includes passing the supernatant through a microfilter or an ultrafilter.

[0038] In some implementations, the method for treating wastewater containing carbon nanotubes further includes adjusting the pH of the supernatant before passing it through one of a microfilter or an ultrafilter.

[0039] In some implementations, the pH of the supernatant is adjusted to approximately 6.5 before passing the supernatant through one of a microfilter or an ultrafilter.

[0040] In some implementations, separating the filtrate into product water and retentate includes passing the filtrate through a reverse osmosis unit.

[0041] In some implementations, the method for treating wastewater containing carbon nanotubes also includes adjusting the pH of the filtrate before passing it through a reverse osmosis unit.

[0042] In some implementations, the pH of the filtrate is adjusted to approximately 7 before the filtrate is passed through the reverse osmosis unit.

[0043] In some implementations, the method for treating wastewater containing carbon nanotubes also includes adding an antiscalant to the filtrate before passing it through a reverse osmosis unit. Attached Figure Description

[0044] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures is represented by the same numbers. For clarity, not every component may be labeled in every drawing. In the drawings: Figure 1 is a simplified process flow diagram for treating wastewater according to the aspects and embodiments disclosed herein; Figure 2 illustrates a process flow diagram for treating wastewater according to the aspects and embodiments disclosed herein; Figure 3 illustrates a portion of a process flow diagram for treating wastewater according to the aspects and embodiments disclosed herein; Figure 4 illustrates an alternative process flow diagram for treating wastewater according to the aspects and embodiments disclosed herein; Figure 5 illustrates a portion of a process flow diagram used in testing the method as disclosed herein; Figure 6 illustrates a portion of a process flow diagram used in another test of the method as disclosed herein; and Figure 7 illustrates a portion of a process flow diagram used in another test of the method as disclosed herein. Detailed Description

[0045] Carbon nanotubes (CNTs) have garnered significant attention in the field of battery technology due to their unique properties and potential to improve battery performance. Carbon nanotubes are extremely small in size, possess high strength, and are excellent electrical conductors. When incorporated into electrodes, they can enhance the conductivity of electrode materials, resulting in lower internal resistance. Furthermore, carbon nanotubes have a high surface area, meaning they can accommodate more electrochemically active materials.

[0046] While carbon nanotubes (CNTs) hold promise for a variety of applications, their potential release into the environment, particularly into water, raises concerns about possible environmental and health impacts such as environmental toxicity and bioaccumulation in animals and humans. Current municipal wastewater treatment plants are not equipped to remove or treat CNTs. Therefore, systems and / or processes configured to remove and / or treat CNTs in wastewater are needed.

[0047] In addition, N-methyl-2-pyrrolidone (NMP) (chemical formula C5H9NO) is commonly used as a solvent in lithium-ion battery production processes. For example, NMP can be used to dissolve polyvinylidene fluoride (PVDF), a common binder material used in electrodes in lithium-ion batteries. However, NMP is considered environmentally harmful, and therefore, as with CNTs, systems and / or processes are required to remove and / or treat NMP in wastewater.

[0048] The aspects and embodiments disclosed herein relate to systems and processes for removing or at least reducing the amount of carbon nanotubes in water. Additionally and / or alternatively, the aspects and embodiments disclosed herein relate to systems and processes for removing or at least reducing the amount of NMP in water.

[0049] The proposed solution involves removing and concentrating carbon nanotubes into a smaller volume of sludge, and preventing the accidental discharge of carbon nanotubes into industrial wastewater sewers.

[0050] The presence of carbon nanotubes is typically associated with other significant amounts of solids and organic matter in wastewater. Therefore, directly feeding wastewater into compact membrane technologies will lead to membrane fouling and inadequate performance. Alternative processes can therefore be utilized to remove carbon nanotubes from wastewater.

[0051] Referring to Figures 1 and 2, a process flow diagram of an embodiment according to this disclosure is illustrated. In some embodiments, the process for removing carbon nanotubes from water may include the following action: 1. Introducing one or more flocculants into wastewater containing CNTs from the manufacturing process to promote the sedimentation of solids from the wastewater and form chemically treated wastewater. In some embodiments, the wastewater is sent through a purge coagulation process using pH adjustment by adding sodium hydroxide (NaOH) and ferric chloride (FeCl3) and / or other coagulants or flocculants. (Figure 1, Action 10).

[0052] 2. The chemically treated wastewater is separated into sludge and a supernatant, wherein the sludge has an increased carbon nanotube concentration compared to the chemically treated wastewater, and the supernatant has a decreased carbon nanotube concentration compared to the chemically treated wastewater. In some embodiments, the pH-adjusted chemically treated wastewater is sent through a clarification process that utilizes a polymeric flocculant to promote the settling of newly formed solids into sludge (see also Figure 1, Action 10).

[0053] 3. The solids carrying the sludge are sent for further thickening and then to a filter press. (Figure 1, Action 20).

[0054] 4. The supernatant is separated into filtrate and osmotic residue, the osmotic residue having a higher solids concentration than the filtrate. In some embodiments, the supernatant from the clarifier is sent to an ultrafiltration membrane treatment unit or a microfiltration membrane treatment unit for this separation operation (Figure 1, Action 30).

[0055] 5. The backwash flow from the ultrafiltration / microfiltration unit, the filtrate from the filter press, and any overflow / decantation water are returned to the equalization tank upstream of the treatment system.

[0056] The filtrate can be separated into product water and retentate, wherein the product water has a lower NMP concentration than the filtrate, and the retentate has a higher NMP concentration than the filtrate. In some embodiments, the filtrate from the ultrafiltration / microfiltration unit can be fed to a reverse osmosis (RO) system (Figure 1, Action 40), allowing the product water to be returned for use in the manufacturing process. In some embodiments, the water from the ultrafiltration / microfiltration unit is pH-adjusted and / or subjected to antiscalant addition before being fed to the RO system. In other embodiments, such as those where the focus is more on removing carbon nanotubes from wastewater than NMP, as shown in Figure 4, the RO system can be omitted from the process, and the filtrate from the ultrafiltration or microfiltration unit can be considered product water.

[0057] Referring to Figure 2, in one embodiment of the disclosed system and process, influent wastewater 105, such as wastewater containing CNTs and NMPs, is introduced into an equalization tank 110, where it is mixed with water returned from one or more downstream process steps. The wastewater is pumped via transfer pump P to a reaction tank 115, where one or more flocculants can be introduced into the wastewater to promote the settling of solids and form chemically treated wastewater. One or more flocculants may include FeCl3. Additionally, the pH of the chemically treated wastewater can be adjusted to, for example, about 8 by adding a pH adjuster such as NaOH to the reaction tank 115.

[0058] The chemically treated wastewater is transferred from reaction tank 115 to polymer addition tank / clarifier 120, where it is separated into sludge and supernatant. The sludge has an increased carbon nanotube concentration compared to the chemically treated wastewater, while the supernatant has a decreased carbon nanotube concentration. A polymer flocculant can be added to the chemically treated wastewater in polymer addition tank / clarifier 120 to promote solid / liquid separation. The supernatant 125 from polymer addition tank / clarifier 120 can be transferred to break tank 130, while the separated solids / sludge 135 is transferred via pump P to sludge thickening tank 140 to form thickened sludge and first recovered water 250.

[0059] The supernatant from the interrupted flow tank 130 is sent to a microfiltration or ultrafiltration unit 145, where it is separated into a filtrate and a residue, the residue having a higher solids concentration than the filtrate. In some embodiments, before passing the supernatant through the microfiltration or ultrafiltration unit, the pH of the supernatant is adjusted to, for example, 6.5 by adding a pH adjuster such as H₂SO₄ or NaOH to the interrupted flow tank 130 or to the conduit between the interrupted flow tank 130 and the microfiltration or ultrafiltration unit 145.

[0060] The filtrate from the microfiltration or ultrafiltration unit 145 is transferred to a mixing tank 150, where the pH of the filtrate is adjusted to, for example, about 7 by adding a pH adjuster such as H2SO4 or NaOH. A scale inhibitor may also be added to the filtrate in the mixing tank 150.

[0061] In an alternative embodiment shown in Figure 4, tank 150 can be omitted, and tank 155 can be used as a retention tank for the filtrate from the microfiltration unit or ultrafiltration unit 145 without the addition of chemicals. Tank 155 can be used to provide the filtrate for return to the microfiltration unit or ultrafiltration unit 145 as backwash water 160.

[0062] Referring back to Figure 2, the filtrate is transferred from the mixing tank 150 to the reverse osmosis feed tank 155. At least a portion of the filtrate can be returned from the reverse osmosis feed tank 155 to the microfiltration or ultrafiltration unit 145 for use as backwash water 160.

[0063] The filtrate from the reverse osmosis feed tank 155 is treated in the primary reverse osmosis unit 165 to separate the filtrate into product water and retentate, wherein the product water has a lower NMP concentration than the filtrate, and the retentate has a higher NMP concentration than the filtrate. The retentate 170 from the primary reverse osmosis unit 165 can be further treated in the brine recovery reverse osmosis unit 175. The retentate 180 from the brine recovery reverse osmosis unit 175 can be further treated in the evaporator 185 for further water recovery. At least a portion of the retentate 170 from the primary reverse osmosis unit 165 can be mixed with the filtrate before passing it through the primary reverse osmosis unit 165.

[0064] The permeate from the primary reverse osmosis unit 165 and the brine recovery reverse osmosis unit 175 can be combined with the water recovered in the evaporator 185 as product water 205, which can be reused in the plant from which wastewater 105 is obtained or discharged into the environment. In some instances, product water 205 may contain an NMP concentration of less than 0.5% or less than 0.3% of the NMP concentration in wastewater 105. In some embodiments, the product water may be further treated or purified in a purification unit 210 (see Figure 3) or with activated carbon, for example, an ion exchange column comprising a mixed bed of cation exchange resin and anion exchange resin.

[0065] The concentrate 190 from the evaporator 185 can be combined with chemically enhanced backwash water 195 from the microfiltration unit or ultrafiltration unit 145 in the storage tank 200 for final disposal or further treatment.

[0066] Thickened sludge from sludge thickening tank 140 can be pumped to filter press 220 via pump P. In filter press 220, additional water is recovered from the sludge to form waste solids (filter cake 230) and second recovered water 240.

[0067] The first recovered water 250 can be combined with the second recovered water 240 and the backwash water 255 from the microfiltration unit or ultrafiltration unit 145 in the cut-off tank 260, and can be pumped back to the beginning of the process via pump P for mixing with the wastewater 105 flowing into the equalization tank 110 before introducing one or more flocculants into the wastewater 105.

[0068] In various embodiments, the NMP concentration in at least one of the product water 205 or the filtrate from the microfiltration unit or ultrafiltration unit 145 can be monitored to confirm proper system and process operation. Monitoring the NMP concentration in at least one of the filtrate or product water may include measuring at least one of total Kjeldahl nitrogen (TKN) or total organic carbon (TOC) in at least one of the filtrate or product water 205, and determining the NMP concentration using the measurement results of at least one of TKN or TOC. Detailed Implementation

[0069] Example A treatability study was conducted to determine the effectiveness of the proposed process for removing carbon nanotubes from water, as shown and described with respect to Figures 1-2. The aim of this study was to explore methods for dewatering CNTs removed by coagulation, flocculation, and sedimentation (CFS) and to develop a treatment scheme to reduce the CNT concentration in the supernatant from the CFS process to the lowest detection limit. Two samples totaling approximately 200 gallons of water (“Sample A” and “Sample B” / “Sample C”) were used for the remainder of the study.

[0070] 1. Sample Description Historical data on the wastewater (WW) and the on-sample analyses of Sample A and Sample B are shown in Table 1. Sample B was biocontaminated before it could be treated. Fresh samples prepared using the same CNT paste as Sample B were received and assigned sample number C. On-sample analyses are shown in Table 1.

[0071] Table 1. Historical and Sample Analysis (as is)

[0072] 2. Coagulation, flocculation, and sedimentation (CFS) were previously performed on sample A using a jar test. For this embodiment, based on the low turbidity in the supernatant, a preferred FeCl3 dosage of 450 mg / L was used. These conditions were applied to the batch test. Similar jar tests were performed on samples B and C to determine the preferred iron dosage for this batch test.

[0073] 2.1. Canning test of sample B: Canning test of sample B was performed to determine the preferred iron dosage.

[0074] Tank test procedure: • Add NaOH to pH 8.0.

[0075] • Add FeCl3 while maintaining pH 8.0 with NaOH.

[0076] • Stir for 15 minutes.

[0077] • Add 1 mg / L ChemTreat ®P817E (HMW anionic emulsion flocculant).

[0078] • Stir quickly for 20 seconds and then stir slowly for 2 minutes.

[0079] • Settlement lasts for 1 hour.

[0080] • Analyze the turbidity of the supernatant.

[0081] A concentration of FeCl3 greater than 400 mg / L is required to produce a clear and colorless supernatant with low turbidity (Table 2).

[0082] Table 2. Chemical dosages and results from the screening test of Sample B

[0083] 2.2. Canister Test for Sample C A canister test was performed on sample C to determine the preferred iron dosage. A dosage of 350 mg / L FeCl3 produced a clear and colorless supernatant with turbidity <0.2 NTU (Table 3).

[0084] Table 3. Can test results for sample C

[0085] 2.3. Batch Testing of Sample A For sample A, the least turbid supernatant with the minimum FeCl3 concentration was 450 mg / L FeCl3. The batches processed were 125 gallons in a 200-gallon tank. The same mixing and settling times as used in the tank test were applied to the batch processing. The added chemicals and supernatant mass are shown in Table 4. The turbidity was slightly higher than that observed in the tank test, but still of good enough quality to run through the ultrafiltration.

[0086] Table 4. Batch testing and results of 75 treatment chemicals

[0087] 2.4. Batch Testing of Sample C A 350 mg / L dose of FeCl3 in Sample C produced the least turbid supernatant. 100-gallon batches were processed in 200-gallon tanks. The same mixing and settling times as used in the tank tests were applied to the batch processing. The added chemicals and supernatant mass are shown in Table 5. Turbidity was slightly higher than observed in the tank tests, but still sufficient for operation through the ultrafiltration system.

[0088] Table 5. Batch testing and results of C-processed chemicals

[0089] 3. Ultrafiltration (UF) UF equipment detailsThe influent processed by UF is the supernatant from the batch processing. The conditions for operating UF are shown in Table 6.

[0090] Table 6. UF Information and Operating Conditions

[0091] *Because of the low pressure during the running time of sample A, the running time of sample C was changed to 62 minutes.

[0092] UF results (sample A) Prior to UF treatment, the pH of the supernatant from batch processing of sample A was adjusted to 6.5 using 27 mg / L H2SO4 to desaturate water relative to ferric hydroxide. The influent was thoroughly agitated for the duration of the run to maintain solid suspension and homogenization. The sample volume allowed for a 76-hour run through the UF. The pressure was maintained at 2 psi for the duration of the run. No cleaning was required. Problems with pressure measurements during the first five hours resulted in the omission of initial pressure data.

[0093] The turbidity of the UF filtrate was monitored throughout the operation, and the turbidity of the UF filtrate was well below the method detection limit of 0.3 NTU. The results of the UF filtrate analysis are shown in Table 7.

[0094] Table 7. UF filtrate mass (sample A)

[0095] UF results (sample C) After a 72-hour run with treated sample A, the UF was not cleaned (see previous section). While awaiting fresh sample, the UF was flushed and backwashed with DI water to prevent bio-growth buildup. The backwashing frequency was also changed to once every 60 minutes (90% recovery) instead of once every 30 minutes (95% recovery). Before passing through the UF, the supernatant from the batch processing of sample C was pH adjusted to 6.5 with 6 mg / L H2SO4 to desaturate relative to ferric hydroxide. The influent was thoroughly agitated for the continuous run duration to maintain solid suspension and homogenization. The sample volume allowed for a 53-hour run through the UF. The pressure was maintained at 2 psi for the continuous run duration. No cleaning was required.

[0096] The turbidity of the UF filtrate was monitored throughout the operation, and the turbidity of the UF filtrate was below the method detection limit of 0.3 NTU. The results from the analysis of the UF filtrate are shown in Table 8. The UF feed and filtrate were also sent to a third-party laboratory for CNT analysis.

[0097] Table 8. Mass of UF filtrate (Sample C)

[0098] 4. Reverse osmosis (RO) RO equipment details The feed to the reverse osmosis (RO) system is the filtrate from the UF test. Equipment and operating conditions are as follows: RO element…………………DuPont Filmtec BW30-2540; Element type………………Membrane composite element; Quantity……………… 1; Surface area…………………28 ft 3 Dimensions……………………2.5” diameter × 40” length Flux rate………………12 gfd Flow rate……………………2 gpm Recovery rate…………………47% RO is operated in open loop (as depicted in Figure 5), which requires the concentrate tank to be maintained at a continuous 14-gallon operating time. It takes approximately 50 minutes to reach a 47% recovery rate. At this point, the run is placed in recirculation mode because, due to an error in the calculation, a 90% recovery rate is believed to have been achieved. The run continues in recirculation mode for 4 hours. This is accomplished by placing the permeate line in the concentrate tank and stopping the pump that is injecting more feed water. The failure to achieve a 90% recovery rate due to an error in the calculation of sample volume was determined to be insignificant to the study, as the maximum recovery rate can be accurately predicted using software based on saturation and contamination limits. Furthermore, salt passage can also be predicted at a 90% recovery rate. In the context of a reuse application, the difference in permeate mass between the pilot unit at 47% recovery and the target 90% recovery rate is expected to be negligible.

[0099] RO results (sample A) After achieving a 47% recovery rate, the operation continued in recirculation mode, and very small pressure changes were observed (Table 9). The transmembrane pressure (TMP) remained unchanged during operation. Complex samples of feed, permeate, and retentate were analyzed (Table 10).

[0100] Table 9. Operational data for RO operation (Sample A)

[0101] Table 10. RO feed, permeate, and retentate quality

[0102] RO results (sample C) After achieving a 47% recovery rate, the operation continued in recirculation mode, and no pressure changes were observed (Table 11). Transmembrane pressure (TMP) remained unchanged during the operation. Composite samples of feed, permeate, and retentate were sent for analysis (Table 12).

[0103] Table 11. Operational data for RO operation (sample C)

[0104] Table 12. RO feed, permeate, and retentate quality (Sample C)

[0105] Ion exchange (IX) IX device details The RO permeate (137B) was run through a column containing a mixed-bed resin (TM-9). TM-9 is a premium-grade mixed-bed resin composed of a 1:1 stoichiometric mixture of C-211 SG H and A-464 SG OH. C-211 SG H is a strong acid cation exchange resin made of polystyrene and crosslinked with divinylbenzene. A-464 SG OH is a strong base type I porous gel anion exchange resin composed of styrene. Details about the column are shown below.

[0106] Resin Type: TM-9 (MBV NR-6) Resin Form: Hydrogen / Hydrogen Hydroxide Column Diameter: 1.0 inch Column Height: 16 inches Resin Bed Depth: 12 inches Flow Rate: 1 gpm / ft 3 Process flow: The resin is flushed downflow before the RO permeate is run through it. The resin is flushed with deionized water for 2 hours. At the end of the flushing, the conductivity of the effluent is 1.10 µS / cm.

[0107] The conductivity of the influent (RO permeate) was 30.7 µS / cm. A grab sample of the effluent was collected after a 36-minute run. The conductivity of the grab sample was 0.74 µS / cm. The complex of the sample collected at the end of the 1X run had a conductivity of 1.18 µS / cm. For reference, deionized water has a conductivity of 4.40 µS / cm, and ultrapure water has a conductivity of 0.89 µS / cm. Effluent from the column was collected after processing more than 5 bed volumes (54-minute runs). The effluent was sent for analysis, and the results are shown in Table 13.

[0108] Table 13. IX Results

[0109] 1 There may be contamination that causes the Ca content in the IX effluent to be slightly higher than the Ca content in the IX feed.

[0110] Filter press Filter press equipment details A concave plate filter press was used to test and determine the dewatering performance of CNT solids.

[0111] The solids were thickened by settling for approximately one week. The supernatant was decanted, and the sludge was used as feed to a filter press. It was placed in a sample reservoir and pressurized with compressed air. The feed pressure started at 25 psi and was staged up to a final pressure of 100 psi. An air-drying step was performed at 40 psi for 5 minutes before the filter cake was discharged to simulate a full-scale system.

[0112] Results (Sample A) The filter cake is rigid and will easily pass the paint filter test because there is no free liquid. The filter cake easily releases from the cloth. The filter cake is both rigid and brittle. The dry solids content of the filter cake is 59% by weight. See Table 14 for further details.

[0113] Table 14. Filter Press Test Results (Sample A)

[0114] The filtrate from the first two minutes of the test contained more solids than most of the filtrate; this fraction was separated and not added to the remaining filtrate. A significant amount of solids passed through the cloth, particularly during the first part of the test. As the run continued, the turbidity of the filtrate decreased. The TSS of the combined filter press filtrate was 440 mg / L. The turbidity of the filtrate from this TSS analysis was also measured, and the turbidity of this filtrate was 7.8 NTU, indicating that some solids did indeed pass through the 1.5 µm filter paper used for the TSS.

[0115] The CNTs in the filter press filtrate were also analyzed. The filtrate was analyzed twice: the analysis labeled "supernatant" showed 1.53 µg / L, and the analysis labeled "suspension" showed 45.6 µg / L. Results are labeled accordingly. Note the higher standard deviation of the suspension sample, attributed to its inhomogeneity, even after sonication. The significant difference between the supernatant and suspension results also indicates a large number of CNTs adsorbed on the surface of larger particles that can settle in the suspension.

[0116] Results (Sample C) The filter cake is rigid and will easily pass the paint filter test because there is no free liquid. The filter cake easily detaches from the cloth. The filter cake is both rigid and brittle. The dry solids content of the filter cake is 33% by weight. See Table 15 for further details.

[0117] Table 15. Filter Press Test Results (Sample C)

[0118] The cloth used for this test had previously been used in two trials using the same waste stream. Those trials were discontinued due to various operational problems. The filtrate from the first two minutes of the test contained more solids than the majority of the filtrate; this portion was separated and not added to the remaining filtrate. The remaining filtrate was relatively clear and colorless. The turbidity of the combined filter press filtrate was 2.9 NTU.

[0119] Research Conclusions Using a combination of FeCl3 and anionic flocculants, purge coagulation effectively removed CNTs from both wastewater samples. After treating sample A, the CNT concentration decreased to 60 ng / L. Coagulation, flocculation, and sedimentation prior to the UF also mitigated the fouling tendency observed when attempting direct microfiltration of the raw CNT waste stream. It is assumed that the CNTs are coated with a binder material, which causes fouling when the membrane is subjected to high concentrations of CNTs. Adding a CFS step adds another unit process to the treatment scheme, but it protects the UF membrane from fouling and allows for the use of a more energy-efficient dead-end filtration UF.

[0120] UF removed CNTs to below the detection limit, which ranged from 5 ng / L to 25 ng / L, depending on the sample size. Runs were conducted for 129 hours without requiring cleaning, and no pressure exceeding 2 psi was established. After the initial 76 hours, the backwash frequency was increased by 30 to 60 minutes, consistent with 90% and 95% recoveries, respectively. The absence of TMP increase during the 76-hour test supports the hypothesis that the removal of contaminating material during the CFS step, as observed in previous studies, leads to more stable and sustainable UF performance.

[0121] For any sample, there was no increase in TMP during the RO run on the UF filtrate. The achieved recovery was only 47% due to errors in the calculations. However, achievable recoveries can be predicted using software modeling with the analytical data included herein. Recovery rates of approximately 90% should be expected. Although the RO run time was relatively short due to the limited sample volume, no contamination was observed. Mixed-bed ion exchange resins were used to further improve the quality of the RO permeate. IX resin reduced the conductivity from 31 µS / cm to 1 µS / cm, which is lower than that of deionized water.

[0122] There were differences in dehydration performance between the two samples. The solids from the treatment of sample A were dehydrated within 55 minutes, producing a filter cake with a dry solids content of 59%. The solids from the treatment of sample C took 345 minutes (approximately 5.75 hours) to press and produce a filter cake with a dry solids content of 33%. Both filter cakes did detach easily from the cloth and were stiff. The filtrate was better during the press filtration of the solids from sample C, but this is likely because the cloth was reused. Once the cloth is used once, the filtrate quality generally improves.

[0123] As discussed above, lithium-ion battery manufacturing processes typically use N-methyl-2-pyrrolidone (NMP) (chemical formula C5H9NO) as a solvent, resulting in the presence of NMP in cathode wastewater. NMP (C5H9NO) is considered a major source of organic carbon in wastewater streams. To meet specific water reuse specifications (e.g., < 1.5 mg / L total organic carbon (TOC)), ~99.7% of the present NMP should be retained or removed during the treatment process.

[0124] NMP is highly soluble in water and should not pose a risk of contaminating or rendering the RO system insoluble when it is retained and concentrated. However, limited data are available regarding the use of commercially available membrane composite membranes for NMP retention.

[0125] According to embodiments of this disclosure, an NMP rejection rate was established using a synthetic wastewater solution incorporating a known concentration of NMP. Currently, there is no known quantitative method for NMP determination; therefore, TOC and total Kjeldahl nitrogen (TKN) are combined with synthetic water containing no other sources of TKN and TOC as surrogates. This method was used to determine the NMP rejection rate using a high-rejection-rate seawater RO element under both first-stage and second-stage RO operating conditions.

[0126] Table 16 provides the design basis and processing objectives for an example of blended anodic and cathodic flow.

[0127] Table 16. Design Basis and Processing Objectives

[0128] BDL = Below detection limit (not provided) (1) In previous studies, the cathode TOC concentration and the blended cathode / anode TOC concentration were 505 mg / L and 238 mg / L, respectively.

[0129] Synthetic sample (108A) was prepared using deionized (DI) water and laboratory-grade chemicals. The DI water (125 gallons) was doped with 250 mg / L NMP. Sodium hydroxide (NaOH) was added to a pH of approximately 1 mg / L to 6.8. The sample was filtered using a 0.2-micron filter. The sample was clear, colorless, odorless, and free of settleable solids. Initial analyses of synthetic sample 108A are shown in Table 17.

[0130] Table 17. Initial analysis of sample 108A

[0131] (1) It is calculated by averaging the TOC equivalent and the TKN equivalent.

[0132] A concentration of 160 mg / L is stoichiometrically equivalent to 264 mg / L NMP, and 35 mg / L TKN is stoichiometrically equivalent to 245 mg / L NMP, with an average of 255 + / - 13 mg / L NMP in the synthetic samples.

[0133] A reverse osmosis synthetic sample (108A) was used in RO tests to characterize the product water quality. The tests were conducted using a single 2.5-inch RO membrane. The retentate was recycled to a concentration tank to bring the dissolved solids back to an appropriate concentration for recovery in the target system. The permeate from the first-stage test was then used in a similar manner to simulate the second-stage RO system.

[0134] Reverse Osmosis Test - First Stage RO RO operating conditions are as follows: Membrane: FilmTec Fortilife XC70 2540; Effective area: 28 ft. 2 Feed temperature: 70°F; Permeate flux: 16 gfd; Target recovery: 44%, 88%; Flow rate per 2.5-inch vessel: 1.5 gpm. Figure 6 shows the equipment configuration for concentrating dissolved solids to the appropriate concentration for the target system recovery. A recirculation cooler is used to maintain a constant temperature in the concentration tank supplying the feed solution to the RO module. A metering pump operating at a flow rate equal to the permeate flow rate maintains the volume in the concentration tank at 12 gallons while concentrating the dissolved salts.

[0135] Table 18 below shows the RO pressure, feed temperature, and conductivity of permeate grab and retentate grab samples collected during operation.

[0136] Once a 44% recovery rate is achieved, permeate and retentate grab samples are collected for analysis. Concentration continues until an 88% recovery rate is achieved, at which point both the retentate and permeate streams are diverted to separate collection tanks. The metering pump flow rate is set to equal the sum of the permeate and retentate flow rates, thus maintaining the concentration tank volume at 12 gallons. The equipment configuration used for this part of the experiment is shown in Figure 7. One hour later, a complex sample is collected from the well-mixed permeate tank. The analytical results for the retentate and permeate grab samples are shown in Table 18. The analytical results for the permeate complex sample are shown in Table 19.

[0137] Table 18. Pressure, Temperature, and Conductivity of the First Stage RO Test

[0138] Table 19. Analysis Results of Samples Taken from the First Stage of RO Process

[0139] (1) It is calculated by averaging the TOC equivalent and the TKN equivalent.

[0140] Reverse Osmosis Test – Second Stage RO The first-stage RO permeate is used as feed for the second-stage RO test and is treated with the same RO membrane used in the first-stage RO test. The retentate is recycled to a concentration tank to bring the dissolved solids back to an appropriate concentration for recovery in the target system.

[0141] RO operating conditions are as follows: Membrane: FilmTec Fortilife XC70 2540; Effective area: 28 ft. 2 Feed temperature: 70°F; Permeate flux: 18 gfd; Target recovery: 45%, 90%; Flow rate per 2.5-inch vessel: 1.5 gpm. Figure 6 shows the equipment configuration for concentrating dissolved solids. A recirculation cooler is used to maintain a constant temperature in the concentration tank supplying the feed solution to the RO module. A metering pump, operating at a flow rate equal to the permeate flow rate, keeps the volume in the retentate tank constant at 12 gallons while concentrating the dissolved salts.

[0142] Table 20 shows the RO pressure, feed temperature, and conductivity of permeate grab samples and retentate grab samples collected during operation.

[0143] Once a 45% recovery rate is achieved, permeate and retentate grab samples are collected for analysis. Concentration continues until a 90% recovery rate is achieved, at which point both the retentate and permeate streams are directed to separate collection tanks. The metering pump flow rate is set to equal the sum of the permeate and retentate flow rates, thus maintaining the concentration tank volume at 12 gallons. The equipment configuration used for this part of the experiment is shown in Figure 7. Two hours later, complex samples are collected from the well-mixed permeate tank. The analytical results for the retentate and permeate grab samples are shown in Table 21. The analytical results for the permeate complex samples are shown in Table 22.

[0144] Table 20. Pressure, Temperature, and Conductivity of the Second Stage RO Process

[0145] Table 21. Analysis results of samples captured during the second stage of RO.

[0146] (1) It is calculated by averaging the TOC equivalent and the TKN equivalent.

[0147] Table 22. Analytical results of RO permeate complex samples

[0148] (1) It is calculated by averaging the TOC equivalent and the TKN equivalent.

[0149] Ion exchange purification Equipment and operating parameters Ion exchange (IX) column experiments are required to further purify anions and cations in the RO permeate to prevent them from rising during water reuse. The RO permeate is run through a column containing a mixed-bed resin (TM-9). TM-9 is a premium-grade mixed-bed resin composed of a 1:1 stoichiometric mixture of C-211 SG H and A-464 SG OH. C-211 SG H is a strong acid cation exchange resin made of polystyrene and crosslinked with divinylbenzene. A-464 SG OH is a strong base type I porous gel anion exchange resin composed of styrene. Details about the column are shown below.

[0150] Resin Type: TM-9 (MBV NR-6) Resin Form: Hydroxide / Hydrogen Hydrogen Column Diameter: 1.0” Column Height: 16.0” Resin Bed Depth: 12” Flow Rate: 1 gpm / ft 3 (21 mL / min) Process flow: The resin was rinsed with deionized water in a downflow manner for four hours, after which the RO permeate was run through the resin. The conductivity of the effluent at the end of rinsing was 0.83 µS / cm.

[0151] result The conductivity of the influent (second-pass RO permeate) was 1.25 µS / cm. A grab sample of the effluent was collected after a 36-minute run. The conductivity of the grab sample was 0.68 µS / cm. The complex of the sample collected at the end of the 1X run had a conductivity of 0.99 µS / cm. For reference, deionized water has a conductivity of 1.72 µS / cm, and ultrapure water has a conductivity of 0.30 µS / cm. Effluent from the column was collected after processing more than 5 bed volumes (54-minute runs). The effluent was sent for analysis, and the results are shown in Table 23 below.

[0152] Table 23. Ion exchange results

[0153] (1) It is calculated by averaging the TOC equivalent and the TKN equivalent.

[0154] In conclusion, the synthetic wastewater contained approximately 254 mg / L of NMP, and the concentration was confirmed based on the stoichiometric ratio of nitrogen to carbon in NMP, compared with TKN and TOC analyses.

[0155] FilmTec Fortilife XC70 was used at pH 6.8 standard units, 70 oThe first-stage RO operation with F and 16 gfd exhibited NMP rejection rates of 97% and 96% at 44% and 88% recoveries, respectively. The permeate mass in the grab sample collected from a single element at the 44% recovery point represents the average water mass expected from a system operating at 88% recovery under these design conditions. The grab sample collected from a single element at 88% recovery represents the water mass from the tail element of a system operating at 88%.

[0156] FilmTec Fortilife XC70 was used at pH 6.8 standard units, 70 o The second-stage RO operation with F and 18 gfd exhibited NMP rejection rates of 83% and 84% at 45% and 90% recoveries, respectively. The permeate mass in the grab sample collected from a single element at the 45% recovery point represents the average water mass expected from a system operating at 90% recovery under these design conditions. The grab sample collected from a single element at 90% recovery represents the water mass from the tail element of a system operating at 90%.

[0157] When using FilmTec Fortilife XC70 film at 70°C between 16 GFD and 18 GFD. o During F operation, the NMP rejection rate is expected to be in the range of 83%-97%.

[0158] Ion exchange did not remove NMP, which is a nonionic compound.

[0159] The wording and terminology used herein are for descriptive purposes and should not be considered restrictive. As used herein, the term "plurality" refers to two or more items or components. The terms "comprising," "including," "carrying," "having," "containing," and "involving," whether in the written description, claims, or similar texts, are open-ended terms, meaning "including but not limited to." Therefore, the use of such terms implies coverage of the items listed thereafter and their equivalents, as well as additional items. Regarding claims, only the transitional phrases "consisting of..." and "consisting substantially of..." are closed or semi-closed transitional phrases, respectively. The use of ordinal terms such as "first," "second," "third," and similar terms modifying claim elements in claims does not, in itself, imply any priority, precedence, or order of one claim element relative to another claim element, or the chronological order in which the actions of the methods are performed, but is merely used as markers to distinguish one claim element having a certain name from another element having the same name (but for the purpose of using ordinal terms).

Claims

1. A method for treating wastewater containing carbon nanotubes and N-methyl-2-pyrrolidone (NMP), the method comprising: One or more flocculants are introduced into the wastewater to promote the sedimentation of solids from the wastewater and form chemically treated wastewater; The chemically treated wastewater is separated into sludge and supernatant, the sludge having an increased carbon nanotube concentration compared to the chemically treated wastewater, and the supernatant having a decreased carbon nanotube concentration compared to the chemically treated wastewater; the supernatant is separated into filtrate and leachate, the leachate having a higher solids concentration than the filtrate; and the filtrate is separated into product water and retentate, the product water having a lower NMP concentration than the filtrate, and the retentate having a higher NMP concentration than the filtrate.

2. The method according to claim 1 further includes adjusting the pH of the wastewater treated with the reagent.

3. The method of claim 2, wherein the pH of the chemically treated wastewater is adjusted to approximately 8.

4. The method according to claim 1, wherein the one or more flocculants include FeCl3.

5. The method according to claim 1, wherein the one or more settling agents comprise polymeric flocculants.

6. The method according to claim 1, further comprising: The sludge is thickened to form thickened sludge and first recycled water; And the first recovered water is mixed with the wastewater before introducing the one or more flocculants into the wastewater.

7. The method according to claim 6, further comprising: The thickened sludge is dewatered in a filter press to form waste solids and second-recovered water; And the second recovered water is mixed with the wastewater before introducing one or more coagulants or flocculants into the wastewater.

8. The method of claim 1, wherein separating the supernatant into the filtrate and the osmotic residue comprises passing the supernatant through a microfilter or an ultrafilter.

9. The method of claim 8, further comprising adjusting the pH of the supernatant before passing the supernatant through one of the microfilter or the ultrafilter.

10. The method of claim 9, wherein the pH of the supernatant is adjusted to about 6.5 before passing the supernatant through one of the microfilter or the ultrafilter.

11. The method of claim 1, wherein separating the filtrate into the product water and the retentate comprises passing the filtrate through a reverse osmosis unit.

12. The method of claim 11, further comprising adjusting the pH of the filtrate before passing the filtrate through the reverse osmosis unit.

13. The method of claim 12, wherein the pH of the filtrate is adjusted to about 7 before the filtrate is passed through the reverse osmosis unit.

14. The method of claim 11, further comprising adding a scale inhibitor to the filtrate before passing the filtrate through the reverse osmosis unit.

15. The method of claim 1, further comprising monitoring the NMP concentration in at least one of the filtrate or the product water.

16. The method of claim 15, wherein monitoring the NMP concentration in at least one of the filtrate or the product water comprises measuring at least one of total Kjeldahl nitrogen (TKN) or total organic carbon (TOC) in at least one of the filtrate or the product water, and determining the NMP concentration using the measurement result of at least one of the TKN or TOC.

17. The method of claim 1, further comprising purifying the product water in an ion exchange column.

18. The method of claim 17, wherein the ion exchange column comprises a mixed bed of cation exchange resin and anion exchange resin.

19. The method of claim 1, comprising forming the product water having an NMP concentration of less than 0.5% of the NMP concentration in the wastewater.

20. The method of claim 1, further comprising mixing at least a portion of the retentate from the reverse osmosis unit with the filtrate before passing the filtrate through the reverse osmosis unit.

21. The method according to claim 1, further comprising purifying the product water with activated carbon.

22. A method for treating wastewater containing carbon nanotubes, the method comprising: One or more flocculants are introduced into the wastewater to promote the sedimentation of solids from the wastewater and form chemically treated wastewater; The chemically treated wastewater is separated into sludge and supernatant, the sludge having an increased carbon nanotube concentration compared to the chemically treated wastewater, and the supernatant having a decreased carbon nanotube concentration compared to the chemically treated wastewater; and the supernatant is separated into filtrate and leachate, the leachate having a higher solids concentration than the filtrate.

23. The method of claim 22, further comprising adjusting the pH of the chemically treated wastewater.

24. The method of claim 23, wherein the pH of the chemically treated wastewater is adjusted to approximately 8.

25. The method of claim 22, wherein the one or more settling agents comprise FeCl3.

26. The method of claim 22, wherein the one or more settling agents comprise polymeric flocculants.

27. The method of claim 22, further comprising: The sludge is thickened to form thickened sludge and first recycled water; And the first recovered water is mixed with the wastewater before introducing the one or more flocculants into the wastewater.

28. The method of claim 27, further comprising: The thickened sludge is dewatered in a filter press to form waste solids and second-recovered water; And the second recovered water is mixed with the wastewater before introducing one or more coagulants or flocculants into the wastewater.

29. The method of claim 22, wherein separating the supernatant into the filtrate and the osmotic residue comprises passing the supernatant through a microfilter or an ultrafilter.

30. The method of claim 29, further comprising adjusting the pH of the supernatant before passing the supernatant through one of the microfilter or the ultrafilter.

31. The method of claim 30, wherein the pH of the supernatant is adjusted to about 6.5 before passing the supernatant through one of the microfilter or the ultrafilter.

32. The method of claim 22, wherein separating the filtrate into the product water and the retentate comprises passing the filtrate through a reverse osmosis unit.

33. The method of claim 32, further comprising adjusting the pH of the filtrate before passing the filtrate through the reverse osmosis unit.

34. The method of claim 33, wherein the pH of the filtrate is adjusted to approximately 7 before the filtrate is passed through the reverse osmosis unit.

35. The method of claim 32, further comprising adding a scale inhibitor to the filtrate before passing the filtrate through the reverse osmosis unit.

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