Periodic Reporting for period 4 - ELECTRON4WATER (Three-dimensional nanoelectrochemical systems based on low-cost reduced graphene oxide: the next generation of water treatment systems)
Periodo di rendicontazione: 2021-11-01 al 2023-06-30
To minimize the effects of water pollution and alleviate water scarcity, urban water infrastructure will have to be re-invented through implementation of innovative low-cost, energy-efficient decentralized water and wastewater treatment systems, and use of alternative water resources. Electrochemical systems offer several advantages as they do not use chemical reagents, do not form a residual waste stream, operate at ambient temperature and pressure, are robust, versatile and have a small footprint. However, despite all the above-mentioned benefits, they have two major limitations: i) high energy consumption, in particular for the degradation of persistent contaminants such as , poly- and per-fluoroalkyl substances (PFAS), and ii) formation of toxic organic and inorganic chlorinated byproducts in the presence of chloride, a naturally occurring anion.
ELECTRON4WATER project developed a new electrode material, graphene sponge electrode, produced using a low-cost, bottom-up synthesis method with an estimated cost of the synthesis at lab scale being below 50€ per m2 of the material, which is orders of magnitude lower compared to the price of commercial electrode materials (3-6,000€ per m2). The bulk synthesis method developed allows easy functionalization of the graphene-based coating, thus making it possible to tailor the electrode properties and performance. Given its three-dimensionality and porous structure, graphene sponge electrode offers high surface area and can be operated in flow-through mode, thus reducing the mass transfer limitations. The main advantage of the developed material is that it demonstrates electrochemical inertness to chloride, and does not form any chlorine, chlorate, and perchlorate due to chloride oxidation, even at high anodic current densities. This characteristic, coupled with the capacity of graphene sponge anode to effectively oxidize and degrade even the most persistent contaminants such as PFAS, represents a major breakthrough in electrochemical water treatment, and is a step towards practical applications of electrochemical systems in water and wastewater treatment. The invention enables electrochemical treatment of even brackish, highly polluted wastewater (e.g. reverse osmosis brines, landfill leachate), often rich in PFAS and other contaminants, but without compromising the process performance due to the formation of toxic and persistent byproducts. The synthesis and application of graphene sponge electrodes for water treatment has been patented and is the focus of an ERC Proof of Concept Grant GRAPHEC.
Furthermore, ELECTRON4WATER project developed an electrode material based on nanostructured coating of manganese oxide, capable of selectively oxidizing sulfide to elemental sulfur, which could be easily separated and recovered from the solution. Given that manganese is an earth-abundant element, and that the electrode is produced using a controllable and low-cost electrochemical deposition process, the developed synthesis method is both low cost and easily scalable. This material enabled a selective and rapid removal of sulfide in the form of elemental sulfur particles. Given that the formed sulfur particles are not retained at the electrode surface but accumulated in the solution in the conditions of wastewater treatment, sulfur can be easily separated, which effectively excludes any possibility of sulfide reformation, as well as avoids the passivation of the anode surface. The anode developed in the ELECTRON4WATER project is the first reported anode material capable of such performance and represents a significant step towards in situ electrochemical sulfide control in sewage and other parts of wastewater treatment systems where sulfide formation is an issue (e.g. anaerobic digestion).
ELECTRON4WATER project developed a new electrode material, graphene sponge electrode, produced using a low-cost, bottom-up synthesis method with an estimated cost of the synthesis at lab scale being below 50€ per m2 of the material, which is orders of magnitude lower compared to the price of commercial electrode materials (3-6,000€ per m2). The bulk synthesis method developed allows easy functionalization of the graphene-based coating, thus making it possible to tailor the electrode properties and performance. Given its three-dimensionality and porous structure, graphene sponge electrode offers high surface area and can be operated in flow-through mode, thus reducing the mass transfer limitations. The main advantage of the developed material is that it demonstrates electrochemical inertness to chloride, and does not form any chlorine, chlorate, and perchlorate due to chloride oxidation, even at high anodic current densities. This characteristic, coupled with the capacity of graphene sponge anode to effectively oxidize and degrade even the most persistent contaminants such as PFAS, represents a major breakthrough in electrochemical water treatment, and is a step towards practical applications of electrochemical systems in water and wastewater treatment. The invention enables electrochemical treatment of even brackish, highly polluted wastewater (e.g. reverse osmosis brines, landfill leachate), often rich in PFAS and other contaminants, but without compromising the process performance due to the formation of toxic and persistent byproducts. The synthesis and application of graphene sponge electrodes for water treatment has been patented and is the focus of an ERC Proof of Concept Grant GRAPHEC.
Furthermore, ELECTRON4WATER project developed an electrode material based on nanostructured coating of manganese oxide, capable of selectively oxidizing sulfide to elemental sulfur, which could be easily separated and recovered from the solution. Given that manganese is an earth-abundant element, and that the electrode is produced using a controllable and low-cost electrochemical deposition process, the developed synthesis method is both low cost and easily scalable. This material enabled a selective and rapid removal of sulfide in the form of elemental sulfur particles. Given that the formed sulfur particles are not retained at the electrode surface but accumulated in the solution in the conditions of wastewater treatment, sulfur can be easily separated, which effectively excludes any possibility of sulfide reformation, as well as avoids the passivation of the anode surface. The anode developed in the ELECTRON4WATER project is the first reported anode material capable of such performance and represents a significant step towards in situ electrochemical sulfide control in sewage and other parts of wastewater treatment systems where sulfide formation is an issue (e.g. anaerobic digestion).
The main outcomes of the ELECTRON4WATER project are:
1) Demonstrated capability of anodically and cathodically polarized graphene sponge electrodes to degrade a range of persistent organic contaminants such as pesticides, antibiotics, iodinated contrast agents and others and even PFAS, categorized as “forever chemicals” due to their extreme persistency in advanced water/wastewater treatment. This, coupled with the fact that the system does not lead to the formation of toxic chlorinated byproducts, opens up the possibility of treating highly complex and brackish PFAS-laden streams such as landfill leachate, reverse osmosis concentrates and others. This outcome represents a major breakthrough in the field.
2) Demonstrated electrochemical disinfection of persistent microbial contaminants using graphene sponge electrodes. Flow-through system equipped with graphene sponge anode and cathode could effectively inactivate Escherichia coli via mechanisms of electroporation, thus enabling complete disinfection (5 log E. coli removal) of real tap water. Moreover, the study demonstrated the possibility of exploiting the capacitance of graphene to lower the energy consumption by applying current in an intermittent mode.
3) New mechanism for a highly selective and efficient removal of sulfide from complex waste streams was proposed, based on using anodes with active manganese coating. The project proposed a new concept of manganese oxide-mediated, purely chemical oxidation of sulfide, whereas the application of current was needed only to ensure the in situ regeneration of the spent manganese oxide. Moreover, the final product being the colloidal sulfur particles could be easily separated from the treated stream, thus enabling resource recovery, and avoiding the downstream reformation of sulfide (existing limitation of all other sulfide control strategies).
1) Demonstrated capability of anodically and cathodically polarized graphene sponge electrodes to degrade a range of persistent organic contaminants such as pesticides, antibiotics, iodinated contrast agents and others and even PFAS, categorized as “forever chemicals” due to their extreme persistency in advanced water/wastewater treatment. This, coupled with the fact that the system does not lead to the formation of toxic chlorinated byproducts, opens up the possibility of treating highly complex and brackish PFAS-laden streams such as landfill leachate, reverse osmosis concentrates and others. This outcome represents a major breakthrough in the field.
2) Demonstrated electrochemical disinfection of persistent microbial contaminants using graphene sponge electrodes. Flow-through system equipped with graphene sponge anode and cathode could effectively inactivate Escherichia coli via mechanisms of electroporation, thus enabling complete disinfection (5 log E. coli removal) of real tap water. Moreover, the study demonstrated the possibility of exploiting the capacitance of graphene to lower the energy consumption by applying current in an intermittent mode.
3) New mechanism for a highly selective and efficient removal of sulfide from complex waste streams was proposed, based on using anodes with active manganese coating. The project proposed a new concept of manganese oxide-mediated, purely chemical oxidation of sulfide, whereas the application of current was needed only to ensure the in situ regeneration of the spent manganese oxide. Moreover, the final product being the colloidal sulfur particles could be easily separated from the treated stream, thus enabling resource recovery, and avoiding the downstream reformation of sulfide (existing limitation of all other sulfide control strategies).
ELECTRON4WATER departs from the mainstream research on electrochemical performance of graphene-based materials and other, metal-based nanostructured materials, which has been focused on supercapacitors, solar cells, sensors and hydrogen energy generation/storage devices. The project developed for the first time a graphene sponge electrode material that is electrochemically inert towards chloride, thus circumventing a major limitation of electrochemical water treatment systems. This electrochemical behavior of anodically polarized graphene-based materials had not been reported previously in the scientific community. The project also documented the impact of inorganic ions on the performance and energy consumption of graphene sponge electrodes, crucial role of atomic dopants and other functionalities added to the active graphene coating in tailoring of its electrochemical activity. Graphene sponge electrodes were also shown to be able to degrade persistent microbial contaminants even at low applied currents through mechanism such as electroporation, thus evidencing again unique properties of this material.
Furthermore, ELECTRON4WATER project developed new, manganese oxide-based materials and demonstrated their unique capability to oxidize sulfide to elemental sulfur with high selectivity and efficiency, even in complex waste streams. Although the affinity of manganese towards sulfide was well known in nature (e.g. sediments), it had not been exploited for sulfide management in wastewater treatment. Furthermore, the process proposed is based on an entirely new approach of using low applied currents only to ensure the regeneration of the manganese oxide active coating after reacting with sulfide, resulting in a very low overall energy consumption.
Furthermore, ELECTRON4WATER project developed new, manganese oxide-based materials and demonstrated their unique capability to oxidize sulfide to elemental sulfur with high selectivity and efficiency, even in complex waste streams. Although the affinity of manganese towards sulfide was well known in nature (e.g. sediments), it had not been exploited for sulfide management in wastewater treatment. Furthermore, the process proposed is based on an entirely new approach of using low applied currents only to ensure the regeneration of the manganese oxide active coating after reacting with sulfide, resulting in a very low overall energy consumption.