A new concept in constructed wetlands: assessment of aerobic electroconductive biofilters

The METland (R) concept constitutes a hybrid concept for treating wastewater where microbial electrochemical technologies (MET) are integrated with constructed wetlands (CW) to enhance pollutant removal. Although electroactive bacteria (EAB) were thought to be restricted to anaerobic environments, we decided to explore alternative aerobic conditions like those found in down flow vertical CW. Two electroconductive (EC) biofilters fed with real urban wastewater were operated under downflow (aerobic) and upflow (anaerobic) conditions. The objective was to evaluate the impact of the operational mode on both the removal of pollutants and the microbial community profile. Surprisingly, despite the aerobic nature of the downflow EC biofilter, our results revealed an abundance of EAB from the Geobacter genus, opening a new scenario for treating wastewater based on stimulating extracellular electron transfer. Furthermore, the co-presence of Geobacter and Thiobacillus suggests the existence of interspecies electron transfer leading to nitrate respiration in our system. Moreover, the downflow EC biofilter outperformed the anaerobic upflow one in terms of COD, BOD5 and nitrogen removal.