Electrochemical removal of microalgae with an integrated electrolysis-microbial fuel cell closed-loop system

Abstract

Uncontrolled algal growth in water systems causes a number of serious issues that range from unpleasant odours and tastes to eutrophication. In this work, we propose for the first time to integrate an electrolysis process with the microbial fuel cell (MFC) technology as a sustainable way to treat algal contamination in water systems. Removal of chlorophyll-a by electrolysis was investigated in a fixed bed electrochemical reactor. The effect that operative parameters, such as current density and hydrodynamics, have on the process was analysed by using Chlorella vulgaris as a model of microalgae. Based on these results, a combined closed-loop system was developed in which the electrolysis unit was coupled with a cascade of miniature single chambered air-cathode MFCs. The electrolysis of C. vulgaris was performed under an applied current density of 25 A m−2 and for Reynolds equal to 13. The treated water was fed into a cascade of MFCs for further treatment and energy generation. The effect of the electrode surface area and of the number of MFCs in the cascade on both algae removal efficiency and power output was investigated. It resulted that the greater the active area of the electrodes in the MFCs, and the larger the number of fuel cells, the better the performance of the stack. The integrated system led to a 20% of reduction on the electrical energy requirement of the electrochemical reactor, giving the best results when the electrode surface area of the MFCs in the cascade was 0.32 cm2. Our approach provides a sustainable alternative to current algal removal systems that not only is chemical-free but also aims to be energy-neutral, thus reducing the large amount of energy that current water treatments require.