Chroococcus minor cathode and polyphenolic mediated anode for enhancing bioenergy and bioremediation in a novel...

The algal biocathode offers a sustainable, cost-effective alternative to chemical cathodes in microbial desalination cells (MDCs). This study evaluated Chroococcus minor as a biocathode with Shewanella putrefaciens MTCC 8104 (Sh-MDC) and mixed culture (Mx-MDC) exoelectrogens in a novel concentrically arranged MDC using sago effluent as anolyte and 30 g/L NaCl in the central desalination chamber. The influence of microalgal growth on MDC performance was monitored over 30 days. Sh-MDC achieved a peak power density of 31.7 ± 0.6 mW/m², while Mx-MDC reached 20.8 ± 0.4 mW/m² between days 10-15, comparable to abiotic MDCs. Mx-MDC recorded the highest COD removal (92.9 ± 2 %) between days 25-30, along with significant removal of metals (Al, Ag, Pb) from sago effluent. Microbial community analysis of Mx-MDC revealed a high abundance of electrogenic populations. The system's application for brackish water treatment in the desalination chamber was assessed. To improve performance, plant-derived mediators, Chrysopogon zizanioides (vetiver) and Allium cepa (onion) peel extracts were added to the anode chamber. The C. zizanioides-mediated Mx-MDC exhibited a 1.98-fold increase in power density compared to non-mediated systems. COD removal and desalination efficiencies improved to 94.3 ± 1.9 % and 21.5 ± 0.43 %, respectively. Thus, C. zizanioides extract is a sustainable mediator enhancing the performance of Mx-MDC over Sh-MDC. Optimizing electrogenic populations and adapting Chroococcus minor to brackish conditions can further improve MDC efficiency, while the harvested algal biomass offers potential reuse, supporting a circular economy.