Enhanced wastewater treatment using constructed wetlands with electrical energy application

CERETTA, MARIA BELEN; MASSAZZA DA; MELLONI, TOMAS; BUSALMEN, JUAN P.; BONANNI, SEBASTIAN

Buenos Aires, Mar del Plata

Congreso; XVIII Congreso Argentino de Microbiología General (SAMIGE); 2023

SAMIGE

Recently, the application of electro-active bacteria in constructed wetlands for wastewater (WW) treatment has gained attention (Bioelectrochemical Wetlands-BW). These systems consist of a shallow vessel filled with porous material and two layers of conductive material forming electrodes. Electro-active bacteria interact with these electrodes using them as electron acceptors (anode) and donors (cathode) for their metabolism, overcoming the limitations imposed by the lack of appropriate chemical sources in some WW. Although positive results have been achieved in the removal of organic matter (OM), the same was not found for other compounds such as ammonium or nitrate, probably because the equilibrium potentials of the electrodes are not favorable for bacterial activity. The aim of this study was to enhance the removal efficiency of nitrogenous species and OM from WW treated with BW with external application of electrical energy. This new approach attempts to optimize the electrode potential to stimulate bacteria growth, increasing their activity and improving the efficacy in the treatment process. Scaled BW consists of columns measuring 110 mm in diameter and 60 cm in height, filled with gravel and coke (conductive material). These systems were fed downflow with sewage WW (SW). Four treatments were carried out in duplicated: two with external electrical energy application to set different voltage differences (ΔE) between the electrodes of 800 mV and 1400 mV, targeting potential values favorable for bacterial activity, a set of control systems with unconnected electrodes (open circuit-OC) and the remaining set with connected electrodes but without electrical energy application (closed circuit-CC). Samples were collected at the inlet and outlet of all columns to measure chemical oxygen demand (COD), nitrate and ammonium concentrations, pH and turbidity. While pH remained constant in all systems, considerable reduction of COD was achieved for ΔE800 mV, ΔE1400 mV, CC, and CA treatments, decreasing from 159.67 to 14.68, 28.00, 19.67, and 44.67 mgO2.L-1, respectively. Total N concentration also decreased, from 45.75 to 20.51, 12.91, 20.31, and 20.51 mg.L-1 in ΔE800 mV, ΔE1400 mV, CC, and OC, respectively. A similar trend was observed in turbidity. Although the differences between treatments with current application compared to CC or OC were not statistically significant, greater removals of OM and nitrogenous compounds were observed in the first ones. Current values (1.37 mA for ΔE800 mV and 3.71 mA for ΔE1400 mV) were much lower than the theoretical maximum that the systems could provide considering full bioelectrochemical treatment of the contaminants in the inflow (10.72 mA), suggesting the existence of deficiencies in electrode configuration and conductivity. Current efforts are directed towards improving the design and conductivity of the electrodes to further explore the potential of this promising strategy.