Soil-derived humics for enhanced power generation, wastewater treatment, and desalination using microbial desalination cell

Microbial Desalination Cell (MDC) is an emerging technology that enhances wastewater treatment, desalinates the saline water, and produces bioelectricity. However, inefficient electron transfer between bacteria and electrode limits bioelectricity production in the MDC. Hence, in this study, soil-derived phenolic-rich humic substances, namely humic acid (HA) and fulvic acid (FA), were utilized as natural external mediators to enhance electricity generation in the MDC. Cyclic voltammetry (CV) analysis revealed that HA showed a distinct redox peak, whereas FA exhibited the highest current response, confirming their electron-shuttling properties. Electrochemical impedance spectroscopy (EIS) revealed that the addition of FA highly reduced the charge transfer resistance from 151.61 to 10.43 Ω (at 100 mg/L) as compared to HA. The TPC and DPPH analyses reported that the presence of functional groups in HA and FA imparted antioxidant properties that may be responsible for the enhanced bioelectrochemical performance. The redox properties of HA and FA were tested in MDCs, and the presence of HA improved the electricity production and showed maximum higher power density (79.52 ± 0.6 mW/m 2 ) as compared to FA (59.55 ± 0.9 mW/m 2 ) and control (34.66 ± 0.5 mW/m 2 ), respectively. In contrast, FA showed higher COD removal (95.8 ± 0.3%) and desalination efficiency (40.6 ± 0.5%) than HA and control MDC. Further, this study provided supporting evidence for considering HA/FA as potential alternatives to synthetic mediators based on their resource availability, extraction yield, and potential for low-cost, large-scale production in the future due to their extraction from naturally available resources.