WO2025090826A1

WO2025090826A1 - Processes to remove carbon nanotubes and n-methyl-2-pyrrolidone (nmp) from water

Info

Publication number: WO2025090826A1
Application number: PCT/US2024/052900
Authority: WO
Inventors: William Taylor; Dan Bergamini; Samuel A. Mason; Kylie Marie HENLINE; Justin Wayne HIGGS
Original assignee: Evoqua Water Technologies LLC
Current assignee: Evoqua Water Technologies LLC
Priority date: 2023-10-27
Filing date: 2024-10-25
Publication date: 2025-05-01
Anticipated expiration: 2026-04-27

Abstract

A method of treating wastewater containing carbon nanotubes and N-Methyl-2-pyrrolidone (NMP) comprises introducing one or more settling agents into the wastewater to promote settling of solids from the wastewater and form a dosed wastewater, separating the dosed wastewater into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater, separating the supernatant into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate, and separating the filtrate into a product water having a lower concentration of NMP than the filtrate and a reject having a higher concentration of NMP than the filtrate.

Description

PROCESSES TO REMOVE CARBON NANOTUBES AND N-METHYL-2- PYRROLIDONE (NMP) FROM WATER

CROSS-REFERENCE TO RELATED APPLICATIONS

The present 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

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 a waste stream and, in particular, to a system and apparatus for removing one or more contaminants from battery manufacturing plant waste streams.

SUMMARY

In accordance with one aspect, there is provided a method of treating wastewater containing carbon nanotubes and N-Methyl-2-pyrrolidone (NMP). The method comprises introducing one or more settling agents into the wastewater to promote settling of solids from the wastewater and form a dosed wastewater, separating the dosed wastewater into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater, separating the supernatant into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate, and separating the filtrate into a product water having a lower concentration of NMP than the filtrate and a reject having a higher concentration of NMP than the filtrate.

In some embodiments, the method further comprises adjusting a pH of the dosed wastewater.

In some embodiments, the pH of the dosed wastewater is adjusted to about 8.

In some embodiments, separating the dosed wastewater includes performing a clarification operation on the dosed wastewater.

In some embodiments, the one or more settling agents includes FeCh.

In some embodiments, the one or more settling agents includes a polymeric flocculant. In some embodiments, the method further comprises thickening the sludge to form a thickened sludge and a first recovered water.

In some embodiments, the method further comprises mixing the first recovered water with the wastewater prior to the introduction of the one or more settling agents into the wastewater.

In some embodiments, the method further comprises dewatering the thickened sludge in a filter press to form waste solids and a second recovered water.

In some embodiments, the method further comprises mixing the second recovered water with the wastewater prior to the introduction of the one or more coagulants or flocculants into the wastewater.

In some embodiments, separating the supernatant into the filtrate and the retentate includes passing the supernatant through one of a microfilter or an ultrafilter.

In some embodiments, the method further comprises adjusting a pH of the supernatant prior to passing the supernatant through the one of the microfilter or the ultrafilter.

In some embodiments, the pH of the supernatant is adjusted to about 6.5 prior to passing the supernatant through the one of the microfilter or the ultrafilter.

In some embodiments, separating the filtrate into the product water and the reject includes passing the filtrate through a reverse osmosis unit.

In some embodiments, the method further comprises adjusting a pH of the filtrate prior to passing the filtrate through the reverse osmosis unit.

In some embodiments, the pH of the filtrate is adjusted to about 7 prior to passing the filtrate through the reverse osmosis unit.

In some embodiments, the method further comprises adding an antiscalant to the filtrate prior to passing the filtrate through the reverse osmosis unit.

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

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

In some embodiments, the method further comprises polishing the product water in an ion exchange column. In some embodiments, the ion exchange column includes a mixed bed of cation exchange resin and anion exchange resin.

In some embodiments, the method comprises forming the product water with less than 0.5% of the concentration of NMP in the wastewater.

In some embodiments, the method further comprises mixing at least a portion of the reject from the reverse osmosis unit with the filtrate prior to passing the filtrate through the reverse osmosis unit.

In some embodiments, the method further comprises polishing the product water with activated carbon.

In accordance with another aspect, there is provided a method of treating wastewater containing carbon nanotubes. The method comprises introducing one or more settling agents into the wastewater to promote settling of solids from the wastewater and form a dosed wastewater, separating the dosed wastewater into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater, and separating the supernatant into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises adjusting a pH of the dosed wastewater.

In some embodiments, the pH of the dosed wastewater is adjusted to about 8.

In some embodiments, the one or more settling agents includes FeCh.

In some embodiments, the one or more settling agents includes a polymeric flocculant.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises thickening the sludge to form a thickened sludge and a first recovered water.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises mixing the first recovered water with the wastewater prior to the introduction of the one or more settling agents into the wastewater.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises dewatering the thickened sludge in a filter press to form waste solids and a second recovered water. In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises mixing the second recovered water with the wastewater prior to the introduction of the one or more coagulants or flocculants into the wastewater.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises adjusting a pH of the supernatant prior to passing the supernatant through the one of the microfilter or the ultrafilter.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises adjusting a pH of the filtrate prior to passing the filtrate through the reverse osmosis unit.

In some embodiments, the method of treating wastewater containing carbon nanotubes further comprises adding an antiscalant to the filtrate prior to passing the filtrate through the reverse osmosis unit.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawing:

FIG. l is a simplified process flow for treatment of wastewater in accordance with aspects and embodiments disclosed herein;

FIG. 2 illustrates a process flow for treatment of wastewater in accordance with aspects and embodiments disclosed herein;

FIG. 3 illustrates a portion of a process flow for treatment of wastewater in accordance with aspects and embodiments disclosed herein;

FIG. 4 illustrates an alternative process flow for treatment of wastewater in accordance with aspects and embodiments disclosed herein; FIG. 5 illustrates a portion of a process flow used in a test of methods as disclosed herein;

FIG. 6 illustrates a portion of a process flow used in another test of methods as disclosed herein; and

FIG. 7 illustrates a portion of a process flow used in another test of methods as disclosed herein.

DETAILED DESCRIPTION

Carbon nanotubes (CNTs) have gained significant attention in the field of battery technology due to their unique properties and potential to improve battery performance. Carbon nanotubes are very small in size, have high strength, and are excellent conductors of electricity. When incorporated into electrodes, they can enhance the electrical conductivity of the electrode materials, which results in lower internal resistance. Additionally, carbon nanotubes have a high surface area, which means they can accommodate more electrochemically active materials.

While carbon nanotubes (CNTs) are promising for various applications, their potential release into the environment, and particularly into water, raises concerns about possible environmental and health impacts such as, e.g., environmental toxicity, bioaccumulation in animals and humans, etc. Current municipal wastewater treatment plants are not equipped to remove or treat for CNTs. Accordingly, there is a need for systems and/or processes configured to remove and/or treat CNTs in wastewater.

Additionally, battery manufacturing processes often use N-Methyl-2-pyrrolidone (NMP) (chemical formula C5H9NO) as a solvent in the production of lithium-ion batteries. For example, NMP may be used to dissolve polyvinylidene fluoride (PVDF), which is a common binder material for the electrodes in lithium-ion batteries. However, NMP is considered to be environmentally hazardous and thus, like CNTs, there is a need for systems and/or processes configured to remove and/or treat NMP in wastewater.

Aspects and embodiments disclosed herein pertain to systems and processes to remove or at least reduce the amount carbon nanotubes in water. Additionally and/or alternatively, aspects and embodiments disclosed herein pertain to systems and processes to remove or at least reduce the amount of NMP in water.

The proposed solution involves removal and concentration of the carbon nanotubes into a smaller- volume sludge and to prevent the accidental discharge of carbon nanotubes to the industrial wastewater sewer. The presence of carbon nanotubes would typically occur with other high amounts of solids and organics in the wastewater. Thus, sending the wastewater directly to tight membrane technology would lead to membrane fouling and lack of performance. As such, alternative processes may be utilized to remove carbon nanotubes from wastewater.

Referring to FIGS. 1 and 2, process flow diagrams in accordance with embodiments of the present disclosure are illustrated. In some embodiments, the process to remove carbon nanotubes from water may include the following acts:

1 . One or more settling agents is introduced into wastewater including CNT s from a manufacturing process to promote settling of solids from the wastewater and form a dosed wastewater. In some embodiments the wastewater is sent through a sweeping coagulation process using pH adjustment by sodium hydroxide (NaOH) addition and addition of ferric chloride (FeCh) and/or other coagulants or settling agents. (FIG. 1 Act 10.)

2. The dosed wastewater is separated into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater. In some embodiments, the pH-adjusted dosed wastewater is sent through a clarification process utilizing a polymeric flocculant to promote settling the newly formed solids into a sludge. (Also FIG. 1 Act 10.)

3. Sludge-bearing solids are sent for further thickening and then to a filter press. (FIG. 1 Act 20)

4. The supernatant is separated into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate. In some embodiments supernatant from the clarifier is sent to an ultrafilter or microfilter membrane treatment unit to perform this separation operation. (FIG. 1 Act 30)

5. Ultrafilter/microfilter backwash, filter press filtrate, and any overflow/decant water is sent back to an equalization tank in front of the treatment system.

The filtrate may be separated into a product water having a lower concentration of NMP than the filtrate and a reject having a higher concentration of NMP than the filtrate. In some embodiments, filtrate from the ultrafilter/microfilter may be sent to a reverse osmosis (RO) system (FIG. 1 Act 40) such that the product water may be returned for use as water for the manufacturing process. In some embodiments, the water from the ultrafilter/microfilter is pH adjusted and/or subject to anti-scalant addition prior to sending to the RO system. In other embodiments, for example, those which are more concerned with the removal of carbon nanotubes than NMP from the wastewater, the RO system may be omitted from the process, as shown in FIG. 4 and the filtrate from the ultrafilter or microfilter membrane treatment unit may be considered the product water.

With reference to FIG. 2, in one embodiment of the disclosed system and process influent wastewater 105, for example, wastewater including CNTs and NMP is introduced into an equalization tank 110 in which it is mixed with water returned from one or more downstream process steps. The wastewater is pumped via a transfer pump P into a reaction tank 115 in which one or more settling agents may be introduced into the wastewater to promote settling of solids from the wastewater and form a dosed wastewater. The one or more settling agents may include FeCh. Additionally, the pH of the dosed wastewater may be adjusted, for example, to about 8 by the addition of a pH adjustment agent such as NaOH into the reaction tank 115.

The dosed wastewater is transferred from the reaction tank 115 into a polymer addition tank/clarifier 120 in which the dosed wastewater is separated into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater. A polymeric flocculant may be added to the dosed wastewater in the polymer addition tank/clarifier 120 to facilitate the solid/liquid separation. Supernatant 125 from the polymer addition tank/clarifier 120 may be transferred to a break tank 130 while separated solids/sludge 135 is transferred via a pump P to a sludge thickening tank 140 to form a thickened sludge and a first recovered water 250.

The supernatant from the break tank 130 is sent to a microfiltration or ultrafiltration unit 145 in which the supernatant is separated into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate. In some embodiments, the pH of the supernatant is adjusted prior to passing the supernatant through the microfilter or the ultrafilter, for example, to a pH of 6.5 by the addition of a pH adjustment agent such as H2SO4 or NaOH into the break tank 130 or into a conduit between the break tank 130 and the microfiltration or ultrafiltration unit 145.

Filtrate from the microfiltration or ultrafiltration unit 145 is transferred into a mixing tank 150 in which the pH of the filtrate is adjusted, for example, to about 7 by the addition of a pH adjustment agent such as H2SO4 or NaOH. An antiscalant may also be added to the filtrate in the mixing tank 150.

In the alternate embodiment shown in FIG. 4 tank 150 may be omitted and tank 155 may be used as a holding tank for filtrate from the microfiltration or ultrafiltration unit 145 with no chemical addition. Tank 155 may be used to provide filtrate for return to the microfiltration or ultrafiltration unit 145 as backflush water 160.

Returning to FIG. 2, the filtrate is transferred from the mixing tank 150 into a reverse osmosis feed tank 155. At least a portion of the filtrate may be returned to the microfiltration or ultrafiltration unit 145 from the reverse osmosis feed tank 155 for use as backflush water 160.

The filtrate from the reverse osmosis feed tank is 155 is treated in a primary reverse osmosis unit 165 to separate the filtrate into a product water having a lower concentration of NMP than the filtrate and a reject having a higher concentration of NMP than the filtrate. Reject 170 from the primary reverse osmosis unit 165 may be further treated in a brine recovery reverse osmosis unit 175. Reject 180 from the brine recovery reverse osmosis unit 175 may be further treated in an evaporator 185 for further water recovery. At least a portion of the reject 170 from the primary reverse osmosis unit 165 may be mixed with the filtrate prior to passing the filtrate through the primary reverse osmosis unit 165.

Permeate from the primary reverse osmosis unit 165 and brine recovery reverse osmosis unit 175 may be combined with water recovered in the evaporator 185 as product water 205 which may be reused in the factory from which the wastewater 105 was obtained or discharged to the environment. In some examples, the product water 205 may include less than 0.5% or less than 0.3% of the concentration of NMP in the wastewater 105. In some embodiments, the product water may be further treated or polished in polishing unit 210 (See FIG. 3), for example, an ion exchange column including a mixed bed of cation exchange resin and anion exchange resin or with activated carbon.

Concentrate 190 from the evaporator 185 may be combined with chemically enhanced backflush water 195 from the microfiltration or ultrafiltration unit 145 in a storage tank 200 for eventual disposal or further treatment.

Thickened sludge from the sludge thickening tank 140 may be pumped via a pump P to a filter press 220 in which additional water is recovered from the sludge to form waste solids (filter cake 230) and a second recovered water 240.

The first recovered water 250 may be combined with the second recovered water 240 as well as with backflush water 255 from the microfiltration or ultrafiltration unit 145 in a break tank 260 and may be pumped via a pump P back to the beginning of the process for mixing with the influent wastewater 105 in equalization tank 110 prior to the introduction of the one or more settling agents into the wastewater 105. In various embodiments, the concentration of NMP in at least one of the filtrate from the microfiltration or ultrafiltration unit 145 or the product water 205 may be monitored to confirm that the system and process is operating properly. Monitoring the concentration of NMP in the at least one of the filtrate or the product water may include measuring at least one of total Kjeldahl nitrogen (TKN) or total organic carbon (TOC) in the at least one of the filtrate or the product water 205 and utilizing results of the measurement of the at least one of the TKN or TOC to determine the concentration of NMP.

Example

A treatability study was conducted to determine the effectiveness of the proposed process to remove carbon nanotubes from water as shown and described with respect to FIGS. 1-2. The goal of this study was to explore methods to de-water the CNTs removed by coagulation, flocculation, sedimentation (CFS) and to develop a treatment scheme to reduce the CNT concentration in the supernatant from the CFS process to the minimum detection limit. Two samples (“Sample A” and “Sample B’7”Sample C”) totalling about 200 gallons of water that were used for the remainder of the study.

1. Sample Description

The historical data on the wastewater (WW) and the as-received analysis of sample A and B are shown in Table 1. Sample B biofouled before it could be treated. A fresh sample made up with the same CNT paste as used in sample B was received and given the sample number C. See Table 1 for as-received analysis.

Table 1. Historical and As-Received Sample Analysis

2. Coagulation, Flocculation, and Sedimentation (CFS)

CFS jar tests were previously done on sample A. For this example, the preferred FeCh dose was 450 mg/L based on the low turbidity in the supernatant. These conditions were used for batch testing. Similar jar tests were performed on samples B and C to determine the preferred iron dose for that batch test.

2.1. Jar Test on Sample B

Screening jar tests were conducted on sample B to determine the preferred iron dose. Jar Test Procedure:

• Added NaOH to pH 8.0.

• Added FeCh while maintaining pH 8.0 with NaOH.

• Stirred for 15 minutes.

• Added 1 mg/L ChemTreat® P817E (HMW anionic emulsion flocculant).

• Stirred quickly for 20s and slowly for 2 minutes.

• Settled for 1 hour.

• Analyzed supernatant for turbidity.

Greater than 400 mg/L FeCh was needed to produce a clear and colorless supernatant with low turbidity (Table 2).

Table 2. Chemical Doses and Results from Sample B Screening Tests

2.2. Jar Test on Sample C

Screening jar tests were conducted on sample C to determine the preferred iron dose.

The 350 mg/L dose of FeCL produced a clear and colorless supernatant with a < 0.2 NTU turbidity (Table 3).

Table 3. Jar Test Results for Sample C

2.3. Batch Test on Sample A

The least turbid supernatant with the least amount of FeCh for sample A was 450 mg/L FeCh. The batch treated was 125 gallons in a 200 gallon tank. The same mixing time and settling time as used in the jar testing was used for the batch treatment. The chemicals added and supernatant quality are shown in Table 4. The turbidity was slightly higher than observed in the jar testing but still good enough quality to run through the ultrafilter.

Table 4. Batch Test for 75 Treatment Chemicals and Results

2.4. Batch Test on Sample C

A dose of 350 mg/L FeCL for sample C produced the least turbid supernatant. A 100 gallon batch was treated in a 200 gallon tank. The same mixing time and settling time as used in the jar testing was used for the batch treatment. The chemicals added and supernatant quality are shown in Table 5. The turbidity was slightly higher than observed in the jar testing but still of sufficient quality to run through the ultrafilter.

Table 5. Batch Test for C Treatment Chemicals and Results

3. Ultrafiltration (UF)

UF Equipment Details

The influent processed through the UF was supernatant from the batch treatment. The conditions used to run the UF are shown in Table 6.

Table 6. UF Information and Operating Conditions

*Changed to 62 minutes for sample C run because of the low pressure for the duration of the run with sample A.

UF Results (Sample A)

The supernatant from the batch treatment of sample A was pH adjusted to 6.5 to desaturate the water with respect to ferric hydroxide using 27 mg/L H2SO4 before processing through the UF. The influent was well stirred for the duration of the run to keep solids suspended and homogenized. The sample volume allowed for a 76 hour run through the UF. The pressure remained under 2 psi for the duration of the run. No cleanings were needed. There were issues with the pressure measurement for the first five hours which resulted in the omission of initial pressure data.

The turbidity of the UF filtrate was monitored throughout the run and was well below the method detection limit of 0.3 NTU. Results of the UF filtrate analysis are shown in Table 7. Table 7. UF Filtrate Quality (Sample A)

UF Results (Sample C) The UF was not cleaned after running for 72 hours with treated sample A (see previous section). While waiting for the fresh sample, the UF was rinsed and backwashed with DI water to prevent biogrowth from accumulating. The backwash frequency was also changed to a backwash every 60 minutes (90% recovery) instead of 30 minutes (95% recovery). The supernatant from the batch treatment of sample C was pH adjusted to 6.5 to de-saturate with respect to ferric hydroxide using 6 mg/L H2SO4 before being processed through the UF. The influent was well stirred for the duration of the run to keep solids suspended and homogenized. The sample volume allowed for a 53 hour run through the UF. The pressure remained under 2 psi for the duration of the run. No cleanings were needed. The turbidity of the UF filtrate was monitored throughout the run and was below the method detection limit of 0.3 NTU. Results from UF filtrate analysis are shown in Table 8. UF feed and filtrate were also sent to a third party lab for CNT analysis.

Table 8. UF Filtrate Quality (Sample C)

4. Reverse Osmosis (RO)

RO Equipment Details

The feed to the reverse osmosis (RO) system was filtrate from the UF test.

Equipment and operating conditions were as follows:

RO Element . DuPont Filmtec BW30-2540

Element Type . Thin-Film Composite

Elements, quantity . 1

Surface area . 28 fit³

Dimensions . 2.5” diameter x 40” long

Flux Rate . 12 gfd

Flow Rate . 2 gpm

Recovery . 47%

The RO was run in open loop (depicted in FIG. 5), which required the concentrate tank to remain at 14 gallons for the duration of the run. It took about 50 minutes to reach a recovery of 47%. The run was put in recirculation at this time because, due to an error in calculation, it was believed that the 90% recovery had been achieved. The run was continued in recirculation mode for 4 hours. This was done by placing the permeate line in the concentrate tank and stopping the pump that was injecting more feed water. Failure to achieve 90% recovery due to a miscalculation in sample volume was determined to be non- critical to the study because maximum recovery based on saturation and scaling limitations can be accurately predicted using software. In addition, salt passage can also be predicted at 90% recovery. The difference in permeate quality of the pilot unit at 47% recovery and the targeted 90% recovery is expected to be negligible in the context of re-use implications.

RO Results (Sample A)

After reaching 47% recovery, the run was continued in recirculation mode and very little pressure change was observed (Table 9). The transmembrane pressure (TMP) did not change during the run. Composite samples of the feed, permeate, and reject were analyzed (Table 10). Table 9. Operating Data for RO Run (Sample A)

Table 10. RO Feed, Permeate, and Reject Quality

RO Results (Sample C)

After reaching 47% recovery, the run was continued in recirculation mode and no pressure change was observed (Table 11). The transmembrane pressure (TMP) did not change during the run. Composite samples of the feed, permeate, and reject were sent out for analysis (Table 12).

Table 11. Operating Data for RO Run (Sample C)

Table 12. RO Feed, Permeate, and Reject Quality (Sample C)

Ion Exchange (IX) IX Equipment Details

The RO permeate (137B) was run through a column with a mixed bed resin (TM-9). TM-9 is a premium grade mixed bed resin consisting of a 1 : 1 chemical equivalent mix of C- 211 SG H and A-464 SG OH. C-211 SG H is a strong acid cation exchange resin that is manufactured from polystyrene and is crosslinked with divinylbenzene. A-464 SG OH is a strong base Type I porous gel anion resin consisting of a styrene. The details on the column are shown below.

Resin Type: TM-9 (MBV NR-6)

Resin Form: Hydrogen/Hydroxide

Column Diameter: 1.0 inches

Column Height: 16 inches

Resin Bed Depth: 12 inches

Flow Rate: 1 gpm/ft³

Process Flow: Downflow

The resin was rinsed before running RO permeate through. The resin was rinsed with deionized water for 2 hours. The conductivity in the effluent at the end of the rinse was 1.10 pS/cm.

The conductivity in the influent (RO permeate) was 30.7 pS/cm. A grab sample of the effluent was taken after 36 minutes of runtime. The conductivity of the grab sample was 0.74 pS/cm. A composite of the sample taken at the end of the IX run had a conductivity of 1.18 pS/cm. For reference, deionized water has a conductivity of 4.40 pS/cm, and ultrapure water has a conductivity of 0.89 pS/cm. The effluent from the column was collected after more than 5 bed volumes (54 minutes into run) were processed. The effluent was sent for analysis and results are shown in Table 13.

Table 13. IX Results

than in the IX feed.

Filter Press Filter Press Equipment Details

Testing was performed to determine dewaterability of CNT solids using a recessed plate filter press.

The solids were thickened by settling for about a week. Supernatant was decanted, and the sludge was used as feed for the filter press. It was placed in the sample reservoir and pressurized with compressed air. The feed pressure was started at 25 psi and staged to the final pressure of 100 psi. Prior to discharging the filter cake, an air-dry step was done for five minutes at 40 psi to simulate the full-scale system.

Results (Sample A) The filter cake was firm and would easily pass a paint filter test as there was no free liquid. The cake released well from the cloth. It was firm and crumbly. The dry solids content of the filter cake was 59% by weight. See Table 14 for additional details.

Table 14. Filter Press Test Results (Sample A)

The filtrate from the first two minutes of the test contained more solids than the bulk of the filtrate; this portion was isolated and not added to the rest of the filtrate. There were a lot of solids that passed through the cloth, especially during the first part of the test. The turbidity of the filtrate decreased as the run continued. The TSS of the composite filter press filtrate was 440 mg/L. The turbidity of the filtrate from that TSS analysis was also measured and was 7.8 NTU indicating that some solids did pass through the 1.5 pm filter paper used for TSS.

The filter press filtrate was also analyzed for CNTs. There were two analyses given for the filtrate. The analysis labeled “supernatant” was 1.53 pg/L and the one labeled “suspension” was 45.6 pg/L. The results were flagged noting that the standard deviation of the suspension sample was high which was attributed to the inhomogeneity of the suspension, even after sonication. It was also noted that the significant difference in the results of the supernatant and suspension suggests that a high amount of CNT was adsorbed on the surface of larger particles which can settle in the suspension.

Results (Sample C) The filter cake was firm and would easily pass a paint filter test as there was no free liquid. The cake released well from the cloth. It was firm and crumbly. The dry solids content of the filter cake was 33% by weight. See Table 15 for additional details. Table 15. Filter Press Test Results (Sample C)

The cloth used for this test was previously used for two trials with the same waste stream. These trials were aborted due to various issues with the runs. The filtrate from the first two minutes of testing contained more solids than the bulk of the filtrate; this portion was isolated and not added to the rest of the filtrate. The rest of the filtrate was relatively clear and colorless. The turbidity of the composite filter press filtrate was 2.9 NTU.

Conclusions of Study

Sweep coagulation effectively removed CNTs from both wastewater samples using a combination of FeCh and anionic flocculant. The CNT concentration was decreased to 60 ng/L after treatment of sample A. Coagulation, flocculation, and settling prior to the UF also alleviated the fouling tendencies that were observed when attempting direct microfiltration of the raw CNT waste stream. It is hypothesized that the CNTs were coated with a binder material that was causing fouling when the membrane was subjected to high concentrations of CNTs. Adding the CFS step adds an additional unit process to the treatment scheme, but it protects the UF membrane from fouling and enables the use of a more energy efficient deadend filtration UF.

The UF removed CNTs to less than the detection limit which was 5 -25 ng/L depending on how much sample was used. The run did not build pressure over 2 psi for 129 hours with no cleaning required. The backwash frequency was increased for 30 minutes to 60 minutes after the first 76 hours consistent with 90% and 95% recovery, respectively. The lack of TMP increase over the 76 hour trial supports the hypothesis that the material that caused fouling in the prior study was removed during the CFS step resulting in more stable and sustainable UF performance.

There was also no TMP increase during the RO run on the UF filtrate for either sample. The recovery reached was only 47%, due to an error in calculation. However, the recovery that could be reached can be predicted using software modeling with the analytical data included herein. Recovery on the order of 90% should be expected. While the RO runtime was relatively short due to limited sample volume, no fouling was observed. Mixed bed ion exchange resin was used to further improve the quality of the RO permeate. The IX resin reduced the conductivity from 31 pS/cm to 1 pS/cm, which is lower than deionized water.

There were differences between the two samples in terms of dewaterability. The solids generated from the treatment of sample A dewatered in 55 minutes and produced a cake with a dry solids content of 59%. Solids from treatment of sample C took 345 minutes (about 5.75 hours) to press and produced a cake with 33% dry solids. Both cakes did release well from the cloth and were firm. The filtrate was better during the filter press done on solids from sample C, but that may have been because the cloth was reused. Filtrate quality often improves once the cloth is used once.

NMP Removal

As discussed above, lithium-ion battery manufacturing processes often use N-Methyl- 2-Pyrrolidone (NMP) (chemical formula C5H9NO) as a solvent, resulting in NMP being present in the cathode wastewater. NMP (C5H9NO) is believed to be the primary source of organic carbon in the wastewater stream. In order to meet a particular water reuse specification (e.g., < 1.5 mg/L total organic carbon (TOC)), -99.7% of the NMP present should be rejected or removed in the treatment process. NMP is highly soluble in water and should not pose a risk of fouling the RO system or becoming insoluble as it is rejected and concentrated. However, limited data is available on the rejection of NMP using commercially available thin-film composite membranes.

In accordance with an embodiment of the present disclosure, a rate of rejection for NMP using a synthetic wastewater solution spiked to a known concentration of NMP is established. Currently, there is no known quantitative method for NMP determination, therefore TOC and total Kjeldahl nitrogen (TKN) were used as surrogates in conjunction with a synthetic water the does not contain other sources of TKN and TOC. This method was used to determine NMP rejection under both first and second pass RO operating conditions using high-rejection seawater RO elements.

The design basis and treatment targets for the example based on the anode and cathode streams being blended is provided in Table 16.

Table 16. Design Basis & Treatment Targets

BDL = Below Detection Limit (not provided)

(1) The cathode and blended cathode/anode TOC concentrations were 505 and 238 mg/L, respectively in a previous study.

The synthetic sample (108A) was prepared using deionized (DI) water and laboratory grade chemicals. The DI water (125 gallons) was spiked with 250 mg/L of NMP. A dose of approximately 1 mg/L of sodium hydroxide (NaOH) was added to a pH of 6.8. The sample was filtered using a 0.2-micron filter. The sample was clear, colorless, odorless, and contained no settleable solids. The initial analysis of the synthetic sample 108A is shown in Table 17.

Table 17. Initial Analysis of Sample 108A

(1) Calculated by averaging the TOC and TKN equivalents.

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 which averages to 255 +/- 13 mg/L NMP in the synthetic sample.

Reverse Osmosis

Synthetic sample (108 A) was utilized for a RO trial to characterize product water quality. The trial was performed using a single 2.5-in RO membrane. Reject was recycled to the concentration tank to cycle the dissolved solids to the appropriate concentration for the targeted system recovery. Permeate from the first pass trial was then used in similar fashion to simulate a second pass RO system.

Reverse Osmosis Trial - First Pass RO

The RO operating conditions were as follows:

Membrane: FihnTec Fortilife XC70 2540

Active Area: 28 ft2

Feed Temperature: 70°F

Permeate Flux: 16 gfd

Targeted Recoveries: 44%, 88%

Flow per 2.5-in Vessel: 1.5 gpm

FIG. 6 shows the equipment configuration used to concentrate the dissolved solids to the appropriate concentration for the targeted system recovery. A recirculating chiller was used to maintain constant temperature in the concentration tank that supplied the RO module with feed solution. The volume in the concentration tank was maintained at 12 gallons with a metering pump operating at a flow rate equal to the permeate flow rate while concentrating the dissolved salts.

Table 18 below shows RO pressures, feed temperatures, and conductivities of permeate and reject grab samples taken during the run.

Once 44% recovery was reached, permeate and reject grab samples were collected for analysis. Concentration continued until 88% recovery had been reached, at which time both the reject and permeate streams were directed to separate collection tanks. The metering pump flow was set to equal the sum of the permeate and reject flows, so the concentration tank volume remained at 12 gallons. See FIG. 7 for the equipment configuration used for this portion of the trial. After an hour, a composite sample was taken from the well-mixed permeate storage tank. Analytical results for reject and permeate grab samples are shown in Table 18. Analytical results for the permeate composite sample are shown in Table 19.

Table 18. First Pass RO Pressures, Temperature, and Conductivities

Table 19. First Pass RO Grab Sample Analytical Results

(1) Calculated by averaging the TOC and TKN equivalents.

Reverse Osmosis Trial - Second Pass RO

First pass RO permeate was used as feed for the second pass RO trial and was processed with the same RO membrane used in the first pass RO trial. Reject was recycled to the concentration tank to cycle the dissolved solids to the appropriate concentration for the targeted system recovery.

The RO operating conditions were as follows:

Membrane: FilmTec Fortilife XC70 2540

Active Area: 28 ft²

Feed Temperature: 70 °F

Permeate Flux: 18 gfd

Targeted Recoveries: 45, 90%

Flow per 2.5-in Vessel: 1.5 gpm

FIG. 6 shows the equipment configuration used to concentrate the dissolved solids. A recirculating chiller was used to maintain constant temperature in the concentration tank that supplied the RO module with feed solution. The volume in the reject tank was kept constant at 12 gallons with a metering pump operating at a flow rate equal to the permeate flow rate while concentrating the dissolved salts.

Table 20 shows RO pressures, feed temperature, and conductivities of permeate and reject grab samples taken during the run.

Once 45% recovery was reached, permeate and reject grab samples were collected for analysis. Concentration continued until 90% recovery had been reached, at which time both the reject and permeate streams were directed to separate collection tanks. The metering pump flow was set to equal the sum of the permeate and reject flows, so the concentration tank volume remained at 12 gallons. See FIG. 7 for the equipment configuration used for this portion of the trial. After two hours, a composite sample was taken from the well-mixed permeate storage tank. Analytical results for reject and permeate grab samples are shown in Table 21. Analytical results for the permeate composite sample are shown in Table 22.

Table 20. Second Pass RO Pressures, Temperature, and Conductivities

Table 21. Second Pass RO Grab Sample Analytical Results

(1) Calculated by averaging the TOC and TKN equivalents.

Table 22. RO Permeate Composite Sample Analytical Results

(1) Calculated by averaging the TOC and TKN equivalents.

Ion Exchange Polishing

Equipment and Operating Parameters

An ion exchange (IX) column experiment was requested to further polish the anions and cations in the RO permeate to avoid cycling up when the water is reused. The RO permeate was run through a column with a mixed bed resin (TM-9). TM-9 is a premium grade mixed bed resin consisting of a 1 : 1 chemical equivalent mix of C-211 SG H and A-464 SG OH. C-211 SG H is a strong acid cation exchange resin that is manufactured from polystyrene and is crosslinked with divinylbenzene. A-464 SG OH is a strong base Type I porous gel anion resin consisting of a styrene. The details on the column are shown below.

Resin Type: TM-9 (MBV NR-6)

Resin Form: Hydrogen/Hydroxide

Column Diameter: 1.0”

Column Height: 16.0”

Resin Bed Depth : 12”

Flow Rate: 1 gpm/ft3 (21 mL/min)

Process Flow: Downflow

The resin was rinsed with deionized water for four hours before running RO permeate through it. The conductivity in the effluent at the end of the rinse was 0.83 pS/cm.

Results

The conductivity in the influent (second pass RO permeate) was 1.25 pS/cm. A grab sample of the effluent was taken after 36 minutes of runtime. The conductivity of the grab sample was 0.68 pS/cm. A composite of the sample taken at the end of the IX run had a conductivity of 0.99 pS/cm. For reference, deionized water has a conductivity of 1.72 pS/cm, and ultrapure water has a conductivity of 0.30 pS/cm. The effluent from the column was collected after more than 5 bed volumes (54 minutes into run) were processed. The effluent was sent for analysis and results are shown in Table 23 below. Table 23. Ion Exchange Results

(i) Calculated by averaging the TOC and TKN equivalents

Conclusions

The synthetic wastewater was spiked with approximately 254 mg/L of NMP, and the concentration was confirmed based on the stoichiometric ratio of nitrogen to carbon in NMP as compared to TKN and TOC analyses.

The first pass RO operated with a FilmTec Fortilife XC70 at pH 6.8 s.u., 70°F, 16 gfd demonstrated 97% and 96% rejection of NMP at 44% and 88% recovery, respectively. The permeate quality in the grab sample collected from the single element at the 44% recovery point is representative of the average water quality expected from a system operating at 88% recovery under this design condition. The grab sample collected from the single element at 88% recovery is representative of the water quality from the tail element of a system operating at 88%.

The second pass RO operated with a FilmTec Fortilife XC70 at pH 6.8 s.u., 70°F, 18 gfd demonstrated 83% and 84% rejection of NMP at 45% and 90% recovery, respectively. The permeate quality in the grab sample collected from the single element at the 45% recovery point is representative of the average water quality expected from a system operating at 90% recovery under this design condition. The grab sample collected from the single element at 90% recovery is representative of the water quality from the tail element of a system operating at 90%. NMP rejection is expected to be in the 83-97% range when operated between 16-18 gfd with FihnTec Fortilife XC70 membranes at 70°F.

Ion exchange did not remove NMP, which is a non-ionic compound. The phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 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 or the claims and the like, are open-ended terms, i.e., to mean “including but not limited to.” Thus, the use of such terms is meant to encompass the items listed thereafter, and equivalents thereof, as well as additional items. Only the transitional phrases “consisting of’ and “consisting essentially of,” are closed or semi-closed transitional phrases, respectively, with respect to the claims. Use of ordinal terms such as “first,” “second,” “third,” and the like in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Claims

What is claimed is: CLAIMS

1. A method of treating wastewater containing carbon nanotubes and N-Methyl-2- pyrrolidone (NMP), the method comprising: introducing one or more settling agents into the wastewater to promote settling of solids from the wastewater and form a dosed wastewater; separating the dosed wastewater into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater; separating the supernatant into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate; and separating the filtrate into a product water having a lower concentration of NMP than the filtrate and a reject having a higher concentration of NMP than the filtrate.

2. The method of claim 1 , further comprising adjusting a pH of the dosed wastewater.

3. The method of claim 2, wherein the pH of the dosed wastewater is adjusted to about

8.

4. The method of claim 1 , wherein the one or more settling agents includes FeCh.

5. The method of claim 1 , wherein the one or more settling agents includes a polymeric flocculant.

6. The method of claim 1, further comprising: thickening the sludge to form a thickened sludge and a first recovered water; and mixing the first recovered water with the wastewater prior to the introduction of the one or more settling agents into the wastewater.

7. The method of claim 6, further comprising: dewatering the thickened sludge in a filter press to form waste solids and a second recovered water; and mixing the second recovered water with the wastewater prior to the introduction of the one or more coagulants or flocculants into the wastewater.

8. The method of claim 1 , wherein separating the supernatant into the filtrate and the retentate includes passing the supernatant through one of a microfilter or an ultrafilter.

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

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

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

14. The method of claim 11 , further comprising adding an antiscalant to the filtrate prior to passing the filtrate through the reverse osmosis unit.

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

16. The method of claim 15, wherein monitoring the concentration of NMP in the at least one of the filtrate or the product water includes measuring at least one of total Kjeldahl nitrogen (TKN) or total organic carbon (TOC) in the at least one of the filtrate or the product water and utilizing results of the measurement of the at least one of the TKN or TOC to determine the concentration of NMP.

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

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

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

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

21. The method of claim 1 , further comprising polishing the product water with activated carbon.

22. A method of treating wastewater containing carbon nanotubes, the method comprising: introducing one or more settling agents into the wastewater to promote settling of solids from the wastewater and form a dosed wastewater; separating the dosed wastewater into a sludge having an increased concentration of carbon nanotubes as compared to the dosed wastewater and a supernatant having a reduced concentration of carbon nanotubes as compared to the dosed wastewater; and separating the supernatant into a filtrate and a retentate, the retentate having a higher concentration of solids than the filtrate.

23. The method of claim 22, further comprising adjusting a pH of the dosed wastewater.

24. The method of claim 23, wherein the pH of the dosed wastewater is adjusted to about 8.

25. The method of claim 22, wherein the one or more settling agents includes FeCh.

26. The method of claim 22, wherein the one or more settling agents includes a polymeric flocculant.

27. The method of claim 22, further comprising: thickening the sludge to form a thickened sludge and a first recovered water; and mixing the first recovered water with the wastewater prior to the introduction of the one or more settling agents into the wastewater.

28. The method of claim 27, further comprising: dewatering the thickened sludge in a filter press to form waste solids and a second recovered water; and mixing the second recovered water with the wastewater prior to the introduction of the one or more coagulants or flocculants into the wastewater.

29. The method of claim 22, wherein separating the supernatant into the filtrate and the retentate includes passing the supernatant through one of a microfilter or an ultrafilter.

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

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

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

34. The method of claim 33, wherein the pH of the filtrate is adjusted to about 7 prior to passing the filtrate through the reverse osmosis unit.

35. The method of claim 32, further comprising adding an antiscalant to the filtrate prior to passing the filtrate through the reverse osmosis unit.