METland® Microbial Electrochemical Technologies (METs)
- Nymphe
- 12 hours ago
- 6 min read
At the heart of the NYMPHE project are innovative technologies designed to restore contaminated environments. To bring these solutions closer to a wider audience, we are launching a dedicated article series showcasing each technology. This is the second interview in the series, focusing on advanced wastewater treatment solutions. Today’s spotlight is on METland® Microbial Electrochemical Technologies (METs), developed by the Metfilter team under the leadership of Dr Abraham Esteve Núñez, Professor at the University of Alcalá and Scientific Director at METfilter S.L., Madrid. The technology is being developed within the EU-funded NYMPHE project.
WASTEWATER TECHNOLOGY: METland® Microbial Electrochemical Technologies (METs)
Objective: METland® aims to electrobioremediate pollutants from water.
Technology description:
The METland approach is an innovative combination of microbial electrochemical technologies (METs) and constructed wetlands (CWs) that can significantly enhance wastewater treatment and pollutant removal. Rather than using gravel, METland employs a biocompatible electroconductive material to encourage the growth and metabolism of electroactive bacteria. By utilizing an electroconductive bed designed in a short-circuit mode, this system can effectively remove pollutants through the microbial metabolism process without requiring an external circuit. Additionally, the METland’s remarkably low land footprint (0.1m2/pe) sets it apart from traditional CWs, due to the high pollutant removal rate achieved by these microorganisms.
From the very beginning, METland was not designed to harvest energy but to outperform conventional CW for removing pol- lutants from wastewater. Thus, classical electrochemical terms such as anode and cathode were replaced by the use of a single electroconductive material operated as microbial electrochemical snorkel. Indeed, METland technology arose in a simple and robust way, replacing inert material such as gravel in constructed wetlands (CWs) by conductive materials that boost electroactive bacteria and, eventually, allow interconnection between microbial communities, obtaining optimal synergies leading to efficient removal from wastewater .
In METland, just a sole electroconductive bed is operative; thus, classical bioelectro- chemical configuration using two electrodes (anode and cathode) or three electrodes (working, counter, and reference) are absent, so no current circulating between different electrodes could be monitored. However, researchers from Aarhus University came with an elegant solution inspired by an electrochemical methodology developed to measure electrical current in cable bacteria from sediments. Precisely, the method aims to measure electric potentials (EPs) due to charge differences that eventually generate ionic/electron fluxes that can be detected in electrolyte conduc- tors through tailor-made EP sensors A similar concept was applied to identify parameters such as EP, ionic current, Coulombic efficiency, and profiles along with the depth of the METland .
EP profiles together with an adapted version of Ohm’s Law allow us to calculate a key parameter such as the ionic current density J (A/m2) J =- σ dΨdz, where σ is the electrical conductivity of wastewater in the sampling points (S/m), and dΨ/dz is the EP gradient (V/m).
METland® solution has reached different TRL depending on the configuration and nature of wastewater to be treated. Indeed, TRL 9 was reached for conventional urban wastewater or winery but eg. polluted groundwater is still in TRL 7 .
Why METland is a novel solution?
In contrast to conventional gravel-based CW, the presence of electrically conductive carbonaceous material clearly led to a marked difference between the microbial communities colonizing the constructed wetlands and the METlands.. The current understanding of how electroactive microbial communities operate in METland suggests that microbial extracellular electron transfer, either in the form of DIET (direct interspecies electron transfer) or CIET (conductiveparti-cle-mediated interspecies electron transfer) are clearly involved. In such syntrophic inter- actions, electroactive microorganism like those from genus Geobacter must play a key role according to their high presence, c. 12% in some carbonaceous-based material such as electroconductive biochar. Actually, Geobacter was reported elsewere to interchange electrons with quinone groups from humic acids in sediments, so it is reasonable to expect their high abundance in quinone-rich materials such as biochar. Although bacteria from Geobacter genus are typically studied as acetate oxidizer, some species such as Geobacter bemidjiensis also predominate in METlands and biodegrade end-products (butanol, ethanol, formate, lactate) from fermenters.
Beyond state of the art:
Micropollutants such as drugs and pharmaceutical compounds are typically recalcitrant during conventional biological wastewater treatment systems. In this context, electrobiore mediation is a new discipline where electroactive material couple respiration of insoluble electron acceptor (e.g., electrodes) with metabolism of pollutants. Thus, flooded METland was reported to successfully remove micropollutants both under HSSF. Another relevant finding of METland is the preferential estereoselective biodegradation of herbicides and pharmaceuticals such as propanolol (A true indicator of proper bioelectroremediation of pharma pollutants by METland was the complete detoxifi citation of effluent using microinvertebrates (Daphnia magna) and algae (Raphidoelis subcapitata) as bioreporters.
The successful biodegradation of such complex pollutants could be due to the special synergies among microbial communities colonizing the electroconductive bed. An optimal redox interconnected community would allow a better use of the metabolic resources of the community as a whole, and eventually, sharing electrons may promote to oxidize or reduce functional groups of different nature. Nymphe objetive regardin micropollutants aims to forze evolution of microbial communities by synthetic biology tolos to enhance the synergic relationship among electroactive bacteria.
Results of technology development and implementation:
In the past decade, full-scale METlands have been constructed following two main con- figurations: constructed and modular. Constructed METlands follow similar design methods to traditional CWs. Indeed, they have been applied under different environmental and operating conditions in diverse geographic regions (while achiev- ing COD removal efficiencies of c. 90% . A life cycle assessment (LCA) study suggested that they are an environmentally sustainable wastewater treatment technology Their optimal locations for implementation have been investigated using geospatial tools such as multicriteria evaluation and sensitivity .In contrast, modular METlands are systems that can be implemented with no civil engineering but as a “plug- and-play” solution . Modular METlands can host conductive beds of higher height (23 m) than the one applied in conventional CWs (B0.8 m), upgrading in such a way the wastewater load treatment capacity of the system. Interestingly, its modular nature allows to follow a 3D lego-like engineering (http://www.mobimet.es) to replicate and satisfy the needs from final user. The first treatment plant completely based on modular METland tech- nology was built by METfilter in Otos municipality (Murcia, Spain). Specifically, two modu- lar systems covering a total surface of 16 m2 treat approximately 25 m3 of wastewater per day in 2016. The wastewater treatment in this wwtp design in two phases operating in line, including recirculation to guarantee nitrogen removal. First, the raw wastewater flows into a septic tank divided in three chambers hydraulically connected (primary treatment). This phase contributes to homogenize the raw wastewater by buffering the peaks and allowing solids to settle and scum to float. The solids were anaerobically digested in the presence of electrocoductive material, reducing the volume of sludge. The effluent liquid was homogeneously distributed by pulses over the top of the downflow modular METland and percolated through the conductive media to remove COD and nitrify. Finally, the treated water is collected from METland and is discharged into the environment or recirculated into the primary system for denitrification. Plants from genus Phragmites are distributed in the entire surface area to uptake nutrients and supply oxygen into the cathodic area of the electrocon- ductive bed. Furthermore, the WWT is optimized for peaks of wastewater and assuring the fulfillment of the discharge limits. This configuration was capable of reducing the areal foot- print by 30-fold, operating in the range of 0.08 m2/p.e. with no clogging. Similar METland designs are also operative in other locations such as a camping site for 1000 inhabitants (Los escullos, Spain) in just 50 m2.
Modular METland can also treat wastewater from industrial wastewater with high organic load (3k 2 15k COD) with organics removal rates ranging from 2 kg-COD/m2/d in the oil and gas sector to 10 kg-COD/m2/d in winery wastewater. However, the use of vegetation is sometimes not possible due to the toxic nature of some industrial wastewater. In such cases, the devices should probably be named just electroactive biofilter since the absence of plants does not fit the original wetland concept.
Speaker: Dr. Abraham Esteve Núñez, Professor at the University of Alcalá, Scientific Director, MEtfilter S.L., Madrid, Spain.
Interviewer: Agnieszka Sznyk, PhD, President of the Board, The Institute of Innovation and Responsible Development, INNOWO. I
In our Technology Booklet, we showcase 10 solutions currently under development:
4 wastewater treatment technologies
3 soil remediation technologies
3 microbiome modelling approaches
Read the full technology overview: https://www.nympheproject.eu/media
This interview is a part of Nymphe project (New system-driven bioremediation of polluted habitats and environment) More about project: https://www.nympheproject.eu/ Project funded by the European Union Grant Agreement ID: 101060625
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