The basis for successful innovation of bioelectrochemical remediation technologies are potent microbial strains and a set of methods to understand and assess the degradation performance. A considerable number of enrichment cultures of pollutant degrading microorganisms capable to oxidise arsenite, to reduce nitrate, to dehalogenate PCB-, TCE-, TCA-, TBBPA or to metabolise antibiotics have been obtained from environmental samples and are utilised in various technologies.
ELECTRA has established a catalogue of (chemical)analytical methods to assess the bioavailability and fate of pollutants in environmental matrices and treatment systems. This also includes methods to characterize microbial communities and to monitor the expression of degradative genes. Lastly, ecotoxicological tests were selected to provide an effect-based assessment of remediation technologies.
Within the individual treatment concepts the following progress can be highlighted.
Low energy and no chemicals technologies: with this approach we targeted contaminated groundwater and soils/sediments. Two types of BES - tubular and fluidized bed- were designed and operated to successfully remove nitrate (>1kgNO3-·m-3·d-1), and to oxidise arsenite present in GW to compliance with standards.
Partners also tackled the bioelectrochemical treatment for hydrocarbons and lower chlorinated solvents pollution in GW. An effective sequential reductive/oxidative bioelectrochemical process was designed that permitted the complete mineralization of perchloroethylene into nonharmful compounds, driving microbial dechlorinating metabolism through the use of electric currents. The combined removal of oxidizable and reducible contaminants was also realized in a bio-electrical well, for in-situ treatment of e.g toluene or petroleum hydrocarbons.
Four different soil treatment concepts using the ‘Snorkel’ approach and the amendment of biochar in the soil are being tested for the removal of aromatic hydrocarbons and pesticides. Direct interspecies electron transfer (DIET) via electrically conductive materials seems to play a role here in the anaerobic oxidation of petroleum hydrocarbons in contaminated sites.
Controlled mobilisation of heavy metals can help to decontaminate soils. With a so-called Redox-Stat we selectively mobilized 12% of antimony in shooting range soils, which can then be recovered safely.
No energy and low chemicals technologies: these approaches work by e.g. enlarging the area of influence of electrodes in a reactive barrier for groundwater remediation. The electrochemical characterization of sediments revealed their capacitive properties which induce a detrimental high resistance. Adding conductive activated carbon particles and applying alternating current eventually turned the sediments into a Faraday conductor.
Further, bio-palladium nanoparticles were successfully produced and applied to reduce halogenated compounds (e.g. fluorinated pharmaceuticals) in secondary effluent. 80-95% removal was observed in a continuously operated lab-scale reactor.
Various other ELECTRA solutions were relying on electrochemically enhanced constructed wetlands for wastewater treatment. An electron-sink method for controlling the electron flow through adequate bed materials improved the removal of pharmaceuticals residues and the reduction of chemical bulk parameters from raw or secondary treated (municipal) wastewater.
Another technology tested alternative operational modes of constructed wetlands with electrochemical production of oxygen nanobubbles or direct oxygenation by oxygen/air nanobubbles to degrade toluene and phenols.
Of the 14 technologies, six achieved TRL between 4 and 8 with clear identification of both potential and bottlenecks for commercial/industrial exploitation. Adapted control strategies are needed to fully tap the potential of some of the technologies. This also extends to the compatibility of bioelectrochemical systems for remediation with existing benchmark technologies. ELECTRA used life cycle assessment and cost-effectiveness analysis to pinpoint environmental and economic advantages of the tested approaches. Our analysis showed that the field-tested technologies seem to be competitive with their respective benchmarks (such as ion exchange, adsorption or advanced oxidation), regarding both the environmental and economic performance. They might also become competitive for application cases in off grid situations where installation of infrastructure to operate more intensive technologies based on high use of materials, chemicals or energy would unnecessarily drive costs.
Market uptake and implementation of ELECTRA technologies will also be governed by legal frames and market structures. For the field-tested technologies, we found their performance already complying with environmental legislation (discharge limit or threshold values). From our stakeholder workshop and attendance to environmental fairs we experienced positive feedback on the approaches from utilities and companies.
