Periodic Reporting for period 1 - GRAPHEC (Scalable Graphene-enabled ElectroChemical Treatment for Complete Destruction of “Forever Chemicals” in Contaminated Water)
Reporting period: 2023-06-01 to 2024-11-30
Per- and polyfluoroalkyl substances (PFAS) have been used for decades for a wide range of industrial, commercial, and domestic applications due to their unique temperature and chemical resistance, oil and water repellence, and surfactant properties. Known as “forever chemicals” due to their extreme persistence in the environment. There are now over 9,000 PFAS, known as “forever chemicals”, which have demonstrated toxicity to the immune system and cause cancer, liver damage, and hormone disruption. To date, the water industry must rely on non-destructive technologies like reverse osmosis (RO) and even outdated granular activated carbon (GAC) treatment, however these not only generate waste but are inefficient in removing polar, short-chain PFAS. Electrochemical systems are one of the very few technologies capable of fully degrading PFAS, and they do so just by applying current. However, existing anode materials suffer from major limitations – high price, high energy consumption, and formation of toxic chlorinated byproducts in the presence of chloride, a naturally occurring anion.
Low-cost graphene sponge developed within the ERC StG ELECTRON4WATER overcome these limitations as they do not oxidize chloride, have high surface area, and are electrocatalytically active for PFAS degradation, as well as degradation of other persistent organic and microbial contaminants. In the ERC PoC GRAPHEC, graphene-enabled electrochemical systems were successfully upscaled in terms of the reactor design to fully exploit the graphene sponge electrode surface due to the hydrodynamically optimized inlets and outlets. Moreover, the new reactor design resolved issues with the non-uniform current feeding and facilitated further stacking up of the reactor modules for scale-up. In the next steps, large-capacity prototype units (up to 10 m3/day) will be built and tested on-site within the recently awarded EIC Transition Grant FOREVER-WATER.
Low-cost graphene sponge developed within the ERC StG ELECTRON4WATER overcome these limitations as they do not oxidize chloride, have high surface area, and are electrocatalytically active for PFAS degradation, as well as degradation of other persistent organic and microbial contaminants. In the ERC PoC GRAPHEC, graphene-enabled electrochemical systems were successfully upscaled in terms of the reactor design to fully exploit the graphene sponge electrode surface due to the hydrodynamically optimized inlets and outlets. Moreover, the new reactor design resolved issues with the non-uniform current feeding and facilitated further stacking up of the reactor modules for scale-up. In the next steps, large-capacity prototype units (up to 10 m3/day) will be built and tested on-site within the recently awarded EIC Transition Grant FOREVER-WATER.
The main objectives of the GRAPHEC project were: i) to determine the fate of fluoride released from PFAS molecules and its impact on the graphene sponge electrode lifetime, ii) to verify the occurrence of fouling/scaling when dealing with real waste streams, iii) to optimize the reactor design and determine the range of PFAS influent concentrations it can deal with, and iv) to evaluate key performance indicators (KPI) such as electric energy per order of the developed reactor.
The results achieved so far demonstrated that electrochemical cleavage of the C-F bond at the anode surface leads to the release of highly reactive hydrofluoric acid (HF), which reacts rapidly with the reduced graphene oxide (RGO) coating of the anode, resulting in the fluorination of RGO. Nevertheless, no impact of RGO fluorination could be observed during several months of operation of the graphene-enabled electrochemical system treating highly concentrated PFAS solution. Even though the experiments are still ongoing and will be further continued in the FOREVER-WATER project, data obtained so far indicate that PFAS degradation does not shorten the electrode lifetime.
Long-term continuous operation of graphene-enabled electrochemical system showed a decrease in PFAS removal over time due to the accumulation of PFAS and other anions at the positively charged anode surface, which over time start blocking the access of PFAS molecules and prevent their anodic oxidation. This was resolved by periodic polarity reversals, where switching the anode to negative potentials (e.g. -1.2 V vs Standard Hydrogen Electrode, SHE) sheds off the accumulated anions and restored the anode performance in terms of PFAS removal and degradation.
No fouling of the graphene sponge anode could be observed during >1 year, including storage of the material. This can be explained by the antimicrobial properties of RGO that prevent the development of a biofilm. Cathode scaling due to the formation of calcium and magnesium carbonates is only observed when employing stainless steel cathode and can be avoided by using graphene sponge as a cathode, too.
Lab-scale work performed within the ERC StG ELECTRON4WATER allowed the use of stainless steel anodic current feeder, yet this material undergoes rapid corrosion when employed with real waste streams. This was resolved by using an iridium oxide-based metallic current feeder, which not only eliminates the corrosion but also suppresses chloride oxidation reaction. The performance of graphene-enabled electrochemical system with the new current feeder has been extensively studied and will be published in a scientific paper, currently in preparation.
Scalable reactor developed for housing the graphene sponge electrodes was demonstrated to be able to deal with PFAS influent concentrations up to 500 ng/L of short chain PFBS. The obtained electric energy per order (Eeo) of the new reactor design is in the range of 20-50 kWh/m3 and degrades 90-99% of C4-C8 PFAS in one-pass, flow-through mode in synthetic electrolytes and real wastewater. This compares favorably to the destruction methods based on supercritical water oxidation (SCWO), hydrothermal alkaline treatment (HALT) and plasma, where their energy consumption is ~1,000 kWh/m3 and ~100 kWh/m3, respectively. Moreover, these processes cannot be operated in continuous mode (SCWO, HALT) or treat larger volumes of waste (plasma). SCWO and HALT operate at high temperatures (≥370°C) and pressures (>20 MPa), whereas plasma-based water treatment is difficult to upscale, e.g. due to the limited depth of plasma penetration.
The results achieved so far demonstrated that electrochemical cleavage of the C-F bond at the anode surface leads to the release of highly reactive hydrofluoric acid (HF), which reacts rapidly with the reduced graphene oxide (RGO) coating of the anode, resulting in the fluorination of RGO. Nevertheless, no impact of RGO fluorination could be observed during several months of operation of the graphene-enabled electrochemical system treating highly concentrated PFAS solution. Even though the experiments are still ongoing and will be further continued in the FOREVER-WATER project, data obtained so far indicate that PFAS degradation does not shorten the electrode lifetime.
Long-term continuous operation of graphene-enabled electrochemical system showed a decrease in PFAS removal over time due to the accumulation of PFAS and other anions at the positively charged anode surface, which over time start blocking the access of PFAS molecules and prevent their anodic oxidation. This was resolved by periodic polarity reversals, where switching the anode to negative potentials (e.g. -1.2 V vs Standard Hydrogen Electrode, SHE) sheds off the accumulated anions and restored the anode performance in terms of PFAS removal and degradation.
No fouling of the graphene sponge anode could be observed during >1 year, including storage of the material. This can be explained by the antimicrobial properties of RGO that prevent the development of a biofilm. Cathode scaling due to the formation of calcium and magnesium carbonates is only observed when employing stainless steel cathode and can be avoided by using graphene sponge as a cathode, too.
Lab-scale work performed within the ERC StG ELECTRON4WATER allowed the use of stainless steel anodic current feeder, yet this material undergoes rapid corrosion when employed with real waste streams. This was resolved by using an iridium oxide-based metallic current feeder, which not only eliminates the corrosion but also suppresses chloride oxidation reaction. The performance of graphene-enabled electrochemical system with the new current feeder has been extensively studied and will be published in a scientific paper, currently in preparation.
Scalable reactor developed for housing the graphene sponge electrodes was demonstrated to be able to deal with PFAS influent concentrations up to 500 ng/L of short chain PFBS. The obtained electric energy per order (Eeo) of the new reactor design is in the range of 20-50 kWh/m3 and degrades 90-99% of C4-C8 PFAS in one-pass, flow-through mode in synthetic electrolytes and real wastewater. This compares favorably to the destruction methods based on supercritical water oxidation (SCWO), hydrothermal alkaline treatment (HALT) and plasma, where their energy consumption is ~1,000 kWh/m3 and ~100 kWh/m3, respectively. Moreover, these processes cannot be operated in continuous mode (SCWO, HALT) or treat larger volumes of waste (plasma). SCWO and HALT operate at high temperatures (≥370°C) and pressures (>20 MPa), whereas plasma-based water treatment is difficult to upscale, e.g. due to the limited depth of plasma penetration.
The recently awarded EIC Transition Grant FOREVER-WATER involves ICRA as the coordinating institution, whereas the creation of a spin-off company GRAPHEC is foreseen for 2025, with Dr Nick Duinslaeger as Chief Executing Officer (CEO). For running the large-scale prototypes on-site in three selected testbeds (semiconductor industry, PFAS-contaminated groundwater and landfill leachate), the project involves an environmental consultancy/tech provider Amphos 21 (Spain), and CEA Leti (France), a microelectronics tech developer. To further improve the scalability of the graphene sponge electrode synthesis, FOREVER-WATER counts with the participation of Fraunhofer IKTS (Germany). The EIC Transition Grant will enable us to reach a technology readiness level (TRL) 6, demonstrating the technology on-site. Furthermore, it will provide access to EIC training and dissemination activities. In addition, ICRA team (Dr Nick Duinslaeger and Prof Jelena Radjenovic) is currently participating in a training program of Creative Destruction lab (www.creativedestructionlab.com) which offers entrepreneurial mentorship, funding opportunities, IPR and business development support to science and technology-based pre-seed and seed stage companies. This, together with the EIC support, will propel the soon-to-be created spin-off company growth and hiring of the first key personnel with business profile. The results obtained within the ERC PoC GRAPHEC unequivocally demonstrate the suitability of graphene-enabled electrochemical system for PFAS destruction in different types of contaminated water (e.g. landfill leachate, tap water, fluoropolymer-laden semiconductor wastewater) with a highly competitive Eeo values (≤50 kWh/m3). It demonstrated the full scalability of the technology, with so far achieved ~6 months lifetime of the graphene sponge electrodes.