Novel bioelectrochemical strategies for domesticating the electron flow in constructed wetlands

Amanda Prado; Carlos A Ramírez-Vargas; Carlos A Arias; Abraham Esteve-Núñez

doi:10.1016/j.scitotenv.2020.139522

Novel bioelectrochemical strategies for domesticating the electron flow in constructed wetlands

Sci Total Environ. 2020 Sep 15:735:139522. doi: 10.1016/j.scitotenv.2020.139522. Epub 2020 May 21.

Authors

Amanda Prado¹, Carlos A Ramírez-Vargas², Carlos A Arias², Abraham Esteve-Núñez³

Affiliations

¹ Chemical Engineering Department, Universidad de Alcalá, Alcalá de Henares, Spain; IMDEA Agua, Parque Tecnológico de la Universidad de Alcalá, 28805, Alcalá de Henares, Spain. Electronic address: amanda.prado@edu.uah.es.
² Department of Biology, Aarhus University, Ole Worms Allé 1, 8000 Aarhus C, Denmark; WATEC, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark.
³ Chemical Engineering Department, Universidad de Alcalá, Alcalá de Henares, Spain; IMDEA Agua, Parque Tecnológico de la Universidad de Alcalá, 28805, Alcalá de Henares, Spain; METfiler, Carrión de los Céspedes, Sevilla, Spain. Electronic address: abraham.esteve@uah.es.

PMID: 32492567
DOI: 10.1016/j.scitotenv.2020.139522

Abstract

Constructed wetlands are an effective biofilter-based technology for treating wastewater in a sustainable way; however, their main disadvantage is a large area footprint. To cope with this limitation a new generation of constructed wetlands, the METlands®, have been recently reported. METlands® replace gravel with a granular electrically conductive material to enhance the oxidative metabolisms of electroactive bacteria by facilitating the flux of electron through the material and, consequently, increase bioremediation rates. In this work we evaluated the performance of a new electron sink (e-sink) device with the purpose of controlling and enhancing the electrochemical consumption of electrons from microbial metabolism without energy consumption. The e-sink device was integrated inside the biofilter bed and was tested using different electron acceptors with high redox potentials, like oxygen and hypochlorite. Interestingly, the presence of the e-sink allowed novel redox gradients to form inside the METland® and, consequently, a new electron flow was demonstrated by measuring both the electric potential and current density profiles of the bed. Three independent biofilters were constructed and operated under flooded conditions. Ec-coke and electroconductive biochar (ec-biochar) were used as electrically conductive bed materials, while gravel was used as an inert control. Furthermore, e-sink integration inside the electrically conductive bed outperformed METlands® for removing pollutants, already much more efficient than standard gravel biofilters. COD removal was increased from 90% in METland® to 95% in the e-sink METland® as compared to 75% for the control, while total nitrogen removal was enhanced from 64% in METland® to 71% in e-sink METland® as compared to 55% for the control. Our results indicate that increasing the electrochemical availability of electron acceptors by using the e-sink will be a suitable method for controlling the electron flow inside the filter bed and can be integrated in full scale METlands® for achieving high removal rates.

Keywords: Constructed wetland; Ec-biochar; Electroactive bacteria; METland®; Microbial electrochemical technologies.