Hydrocarbonoclastic Biofilm-Based Microbial Fuel Cells: Exploiting Biofilms at Water-Oil Interface for Renewable Energy and Wastewater Remediation

Abstract

Microbial fuel cells (MFCs) represent a promising technology for sustainable energy generation, which leverages the metabolic activities of microorganisms to convert organic substrates into electrical energy. In oil spill scenarios, hydrocarbonoclastic biofilms naturally form at the water-oil interface, creating a distinct environment for microbial activity. In this work, we engineered a novel MFC that harnesses these biofilms by strategically positioning the positive electrode at this critical junction, integrating the biofilm's natural properties into the MFC design. These biofilms, composed of specialized hydrocarbon-degrading bacteria, are vital in supporting electron transfer, significantly enhancing the system's power generation. Next-generation sequencing and scanning electron microscopy were used to characterize the microbial community, revealing a significant enrichment of hydrocarbonoclastic Gammaproteobacteria within the biofilm. Notably, key genera such as Paenalcaligenes, Providencia, and Pseudomonas were identified as dominant members, each contributing to the degradation of complex hydrocarbons and supporting the electrogenic activity of the MFCs. An electrochemical analysis demonstrated that the MFC achieved a stable power output of 51.5 μW under static conditions, with an internal resistance of about 1.05 kΩ. The system showed remarkable long-term stability, which maintained consistent performance over a 5-day testing period, with an average daily energy storage of approximately 216 mJ. Additionally, the MFC effectively recovered after deep discharge cycles, sustaining power output for up to 7.5 h before requiring a recovery period. Overall, the study indicates that MFCs based on hydrocarbonoclastic biofilms provide a dual-functionality system, combining renewable energy generation with environmental remediation, particularly in wastewater treatment. Despite lower power output compared to other hydrocarbon-degrading MFCs, the results highlight the potential of this technology for autonomous sensor networks and other low-power applications, which required sustainable energy sources. Moreover, the hydrocarbonoclastic biofilm-based MFC presented here offer significant potential as a biosensor for real-time monitoring of hydrocarbons and other contaminants in water. The biofilm's electrogenic properties enable the detection of organic compound degradation, positioning this system as ideal for environmental biosensing applications.

Keywords: MFC; bioelectrochemical systems; oil spill bioremediation; sustainable energy generation; wastewater remediation; water–oil interface.

Figure 1

(a) Schematic representation of the 100-L MFC showing the placement of electrodes, Nafion panels, and diesel layer. (b) Photograph of the MFC during its construction, illustrating the assembly of the plexiglass panels and the Nafion panels. The positions where the positive and negative electrodes will subsequently be mounted are indicated.

Figure 2

Experimental setup for long-term performance evaluations, including the MFC, EH4295 board, electrolytic capacitor, resistor, and acquisition board.

Figure 3

SEM micrographs of the membranous layer that develops at the oil–water interface of the MFC (3BF1; one out of nine samples): (a) The membranous layer above a lipid phase (*) where rod-shaped bacteria are clearly visible, embedded within the layer and aggregated on its surface (arrows), on the water side. (b) Lipid side of the layer with rod-shaped structures visible under the membranous layer (inset).

Figure 4

Diagram showing the percentage of microbial Classes (a) and Genera (b) found in the initial inoculum and in the MFC at the end of the experiment. For the MFC data, the values reported in the pie charts were obtained by averaging the analyses performed on the 9 samples collected.

Figure 5

Phylogenetic tree illustrating the evolutionary relationships among the predominant microbial families, genera, and species identified in the MFC. The tree structure combines family-level (**), genus-level (*), and species-level insights, providing a comprehensive overview of the microbial community composition.

Figure 6

(a) Voltage (left y-axis) and current (right y-axis) measurements of the MFC. The resistances used for each discharging step are reported in the figure. The data are obtained by averaging 5 measurements performed at 1-h intervals on the same day. (b) Peak power output as a function of current. Experimental data are shown as symbols, while the fitting curve is represented by the dashed line. Error bars, both for current and power values, indicate 5 different measurements performed at 1-h intervals on the same day.

Figure 7

(a) Voltage (left axis) and current (right axis) evolution of the MFC during the static output power characterization. (b) Static power output as a function of current. Experimental data are shown as symbols, with the fitting curve represented by the dashed line. Error bars, both for current and power values, indicate 5 different measurements performed at 1-h intervals on the same day.

Figure 8

(a) Voltage (left y-axis) and corresponding current (right y-axis) across the 100 kΩ resistor over a 5-day period, showing 8-h discharges between 16-h recovery cycles. The EH4295 board switches off after approximately 7.5 h, indicating the deep discharge status. The inset shows the integrated electric charge value for each day. (b) Power output of the MFC immediately after the 8-h measurement cycles (purple symbols with blue fitting curve) and one hour later (green symbols with red fitting curve and corresponding equation). (c) Zoomed view of the power output immediately after the 8-h measurement cycles and related fitting equation. Error bars, both for current and power values and for both curves, indicate the 5 different acquisitions performed in the considered days of measurements.