Effect of macrophytes and their microbiota on wastewater treatment efficiency of constructed bioelectrochemical wetlands

PEDETTA, ANDREA ; BOOMAN, GISEL ; CERETTA, MARÍA BELÉN; GIUNTA, SANDRA VALERIA ; BONANNI, SEBASTIÁN; BUSALMEN, JUAN PABLO

Chapadmalal, Buenos Aires, Argentina

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

Sociedad Argentina de Microbiología General

Constructed wetlands are widely used systems for wastewater treatment because of their low cost and simplicity. They consist of a bed filled with particulate material in which macrophytes and microorganisms reduce the concentration of organic matter, nitrogen compounds and phosphorus in the wastewater circulating through it. One of the strategies to optimize this technology is to promote the growth of electroactive microorganisms, giving rise to the so-called bioelectrochemical wetlands. These microorganisms are naturally present in wastewater and are capable of using electrodes as a source or sink of electrons, generating an electric current. In this study, we proposed to evaluate the role of macrophytes and their accompanying microbiota in the wastewater treatment capacity of bioelectrochemical wetlands. Two layers of particulate conductive material were placed in the treatment bed to form electrodes (anode and cathode). The cathodic (upper) region of the treatment bed was seeded with two species of macrophytes, Schoenoplectus californicus and Cyperus papyrus. The systems were fed from the top continuously with a high-load urban wastewater previously subjected to septic tank treatment. A wetland without plants was included as a control. During several months, data on electrode potential, electric current, chemical oxygen demand (COD), nitrogen and phosphorus at the inlet and outlet of the system were recorded. At the end time, the composition of the microorganism community present in the cathodic region was determined by massive sequencing of the 16S gene. While the effect of plants on COD removal was minimal, nitrogen and phosphorus removal increased in the planted systems, which is only partially explained by direct plant uptake. Analysis of the microbial community showed the presence of free-living and rootassociated bacteria with metabolic capabilities that would explain nutrient removal. Although the production of electric current and energy improved considerably in the planted systems, no differences were found in the community of potentially electroactive bacteria between planted and unplanted systems.