Grantee Research Project Results
Final Report: Ultrasonic PVDF In Commercial Membrane Systems Reduces Fouling for Efficient Water Reuse
EPA Contract Number: 68HERC22C0035Title: Ultrasonic PVDF In Commercial Membrane Systems Reduces Fouling for Efficient Water Reuse
Investigators: Frank, Jeff
Small Business: Pure Blue Tech Inc.
EPA Contact: Richards, April
Phase: II
Project Period: January 1, 2022 through December 31, 2023 (Extended to December 31, 2024)
RFA: Small Business Innovation Research (SBIR) Phase II (2022) Recipients Lists
Research Category: Endocrine Disruptors , SBIR - Water , Small Business Innovation Research (SBIR)
Description:
The prime purpose and objective of the two-year project was to design thin, flexible ultrasonic (US) polyvinyl difluoride (PVDF) transducers to be included in membrane elements and test for the US anti-fouling effectiveness in a spiral wound system that could improve operations and maintenance of reverse osmosis membrane systems for water reuse. Pure Blue Tech Inc. successfully achieved this prime technical objective plus other technical and commercial objectives including characterizing acoustic performance in a hollow fiber filtration module, developed, validated, scaled, and advanced commercialization of ultrasonic reverse osmosis membrane elements spirally wound with a thin, flexible, and efficient (PVDF) transducer array.
Summary/Accomplishments (Outputs/Outcomes):
In the course of this Phase II project, we conducted the following research/development:
- Designed, constructed, and tested a flat, flexible, thin ultrasonic transducer suitable for insertion into a 4040 spiral wound element.
- Designed and built suitable electronics for driving and interfacing the ultrasonic transducer.
- Constructed 4040 scale spiral wound elements incorporating said transducer.
- Demonstrated the anti-fouling advantage of this element configuration through side-by-side organic fouling studies.
- Developed methods and procedures for reliably constructing ultrasonically active RO elements.
- Investigated and verified the feasibility of applying ultrasound to mitigate fouling in hollow fiber elements.
Conclusions:
Sprial Wound
We successfully constructed flat, flexible, reliable, food-safe ultrasonic power transducers. We incorporated such transducers into 4”x40” (industrial scale) spiral wound membrane elements constructed in-house. We definitively demonstrated 50-100% reductions in both the rate and degree of membrane fouling in the ultrasonically active elements through side-by-side fouling studies as measured through prevention and reduction of differential pressure rise, feed pressure rise, and flux loss. We established construction methods and protocols for in-house production of ultrasonically active spiral wound RO elements. We determined the feasibility of ultrasonic transmission in the hollow fiber environment and developed an approach for rapidly building on this discovery.
We performed controlled fouling studies which paired an active ultrasonic with an element incorporating no active element. Our first test was done using a very high concentration of Humic Acid, 3500 ppm, to ascertain the effect of ultrasound in an extreme environment. The second test reduced the Humic Acid concentration to 100 ppm. The salt concentration in the tests was 1000 ppm in both cases. In both studies, the active ultrasonic element demonstrated significantly slower development of fouling as observed through reduction of permeate flow, increase in differential pressure, and/or percent rise in feed pressure required for constant permeation rate. In each case a particular frequency, continuous wave ultrasonic waveform was used, at a stable loaded peak to peak voltage. The results of both studies are graphically represented below showing 100% reduction of differential pressure rise and 50% reduction of flux loss (50% improved flux sustainment). These are tremendous results in extremely high 3500 ppm concentration of humic acid (organic foulant). The third graph below shows that compared to the standard control RO element, the USRO element effectively prevented/mitigated both reversible and irreversible fouling from the previous run, as measured by about 10%+ less feed pressure required to maintain equal flux (permeate production).The third graph below shows that, compared to the standard control RO element, the USRO element effectively prevented/mitigated both reversible and irreversible fouling from the previous run, as measured by about 10%+ less feed pressure required to maintain equal flux (permeate production).
Figure 3 – Differential pressure rise comparison between elements, 8/14/2023.
Figure 4 – Normalized permeate flux comparison, USRO vs. Control between elements, 8/14/2023
Figure 5 – Comparison of feed pressure rise for constant permeate flow, 9/25/2023
Hollow Fiber
Based on our earlier work, we expected to find a high attenuation environment inside of the hollow fiber ultrafiltration (HF UF) module that we acquired for this portion of our project. We decided that corroborating our sectional results in a full scale 7”x60” HF UF module would best match industrial and municipal HF facilities. Accordingly, we designed our initial experiments to measure the straight-line intensity gradients arising from radial ensonfication through the module housing. In order to do so, we installed a single HF module vertically in sufficient volume of water to completely submerge the intended propagation paths, utilized a single sheet of our standard PVDF projector material, and placed receiving hydrophones in the module’s permeate channels.
Based on the acoustic characterization results, the application of ultrasound to combat fouling in HF modules seems feasible. The unknowns around the actual process of fouling in HF, effects of flow in the module, and larger scale propagation need to be further investigated, but at this point there is definite promise. This further research and technical feasibility would be understood through the proposed extended commercialization option period in 2024.
Pilots
We spent about 9 months planning and starting work on two industrial-scale field pilots with U.S. Bureau of Reclamation’s Water Quality Improvement Center in Yuma, AZ. The plan has been agreed and work aligned with the plan is well underway. The brackish water reverse osmosis (BWRO) system has been designed and built. It includes four parallel 4”x80” pressure vessels, each containing two 4”x40” spiral wound BWRO elements. Ultrasonic elements will be tested in parallel with control elements and nanopatterned elements. Two pilots will be conducted. The first is estimated to start in Q1 2024 with Welton Mohawk brackish groundwater with irrigation runoff. The second is estimated to start in Q3 2024 with raw Colorado River water. Fouling rates, flows, rejections, pressures and pressure differentials, and operating costs will be monitored, graphed, and compared. The ultrasonic BWRO elements are being built at the time of this report, and the first elements passed 200 psi, 2000 ppm NaCl salt baseline flux and rejection QA/QC tests.
SBIR Phase I:
Ultrasonic PVDF Reduces Membrane Fouling for Efficient Water Reuse | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.