The electrochemical microbial tree: A new concept for wastewater treatment

Most wastewater treatment plants involve activated sludge units, in which the organic matter to be removed is oxidised by aerobic microorganisms. These units are highly energy intensive because of the power consumed to force oxygen transfer to the wastewater by aeration. An innovative device is presented here; it is called the electrochemical microbial tree (EMT) and is based on the opposite strategy: the organic matter is drawn up from the wastewater towards the air phase by capillary action along a porous structure, which hosts the mi-croorganisms that oxidise the organic matter. The EMTs were made of carbon felt, with the bottom immersed in wastewater (14 cm), while the top emerged into the air at different heights (4, 8 or 12 cm). COD removal increased linearly with the height of the aerial section. The greatest height led to COD removal rates of 807 +/- 62 mg O2/L/h, i.e. 2.6 times those of the control experiments. During COD removal, the pH decreased from 7.6 to 7.4 +/- 0.2 with EMTs, while it increased to 7.9 +/- 0.1 in the controls. The biofilm on the immersed section developed as the height of the aerial section increased. Many electroactive species were identified in the microbial populations, belonging to the Bacteroidia, Gam-maproteobacteria and Clostridia classes. These observations revealed that electron transfer along the conductive felt contributed to organic matter oxidation, in parallel with mass transfer by capillarity. These pioneering results present the EMT as a promising new wastewater treatment disposal system that does not require any energy input.

Automated summary

Most wastewater treatment plants rely on energy-intensive activated sludge units, but this study introduces a promising alternative called the electrochemical microbial tree (EMT). The EMT uses capillary action to draw organic matter from the wastewater up to an aerial section where microorganisms oxidize it, resulting in high COD removal rates. The EMT also lowers pH and promotes the formation of biofilm, demonstrating its potential as an energy-free wastewater treatment system.