Multidisciplinary assessment of microbial fuel cells with river sediments historically contaminated by hydrocarbons amended with compost

A multi-disciplinary approach was adopted for the investigation of microbial fuel cells (MFCs), encompassing electrical, chemical, microbiological, biomolecular and spectroscopic analyses. This study involved a 4-month experiment utilising river sediment as the electrolyte, with a history of contamination by hydrocarbons (TPHs and PAHs). The MFCs were set up under various conditions, including the addition of compost (3 %) and in both open and closed circuit configurations. Batch conditions (no MFCs) were utilised as the control. Electricity production in MFCs started after approximately 2 weeks in the presence of compost. These MFCs exhibited the most optimal electrical outputs over the experimental period. The outputs ranged from 173 to 8.2 mW/m2 at the beginning and end of the testing period, respectively. Accordingly, the highest microbial activity was observed in MFCs with compost, particularly at the anode, where the highest percentage of electrogenic genera (e.g. Pseudomonas) were also detected. Interestingly, Pseudomonas encompasses species capable to degrade hydrocarbons, emphasising the metabolic versatility of these bacterial genera. As indicated by the Vis-NIR spectroscopy, a reduction in organic pollutants was observed at the end of the experiment. This finding was confirmed through chemical analyses, which detected varying removal percentages based on the condition and hydrocarbon type. The PAH removal rate was found to be up to 95 %, which suggests the presence of adapted microorganisms in the sediment. Ecotoxicological tests (with the bacterium Aliivibrio fischeri and the crustacean Heterocypris incongruens) found the absence of acute effects on both organisms. However, a significant inhibition growth was recorded for the crustacean at the end of the experiment, likely due to incomplete PAH degradation, leading to the formation of potentially toxic transformation products or their increased bioavailability.