Strategies for enhancing bioelectrochemical remediation of petroleum hydrocarbons

Globally, Petroleum Hydrocarbons (PH) contamination in the environment is widespread due to accidental spillages, leakages and indiscriminate disposal. PH pollutants are continuously a concern because of their high toxicity to humans and the environment. While there have been efforts to remediate these pollutants from the environment, the conventional approaches are very slow, expensive and energy-intensive among other challenges. These necessitate the quest for remediation approaches that are cost effective, environmentally friendly and sustainable. Recently, there have been efforts to develop new or enhance existing biological approaches that are considered largely as better alternatives to other remediation methods. Bioelectrochemical System (BES), an emerging biotechnology approach with a wide range of applications, has been adjudged as one of the cost-effective and environmentally friendly methods that has the potential to enhance faster degradation of petroleum hydrocarbon pollutants. Despite its potential, MFC is faced with several limitations. To this end, BES research aimed at enhancing the degradation of petroleum hydrocarbon pollutants was carried out in this study.

Samples from PH polluted matrices (groundwater, sediment and soil) in the Niger-Delta region of Nigeria were collected. A metagenomic analysis of these samples showed that the phylum Proteobacteria was dominant in soil and groundwater while Campilobacterota was dominant in the sediment. Using two culture-based approaches and screening pressures, PH degraders that are facultative anaerobes with good electrochemical activity and but not mandatory that could produce biosurfactant were isolated. Each isolate was identified using 16s rRNA region to exclude any potential pathogen. 5 isolates across the matrices produced biosurfactant with emulsification Index ranging from 30%-99%. When compared to a negative control and positive control (Shewanella oneidensis), several isolates had good electrochemical activity (peak currents) that were greater than that of S. oneidensis by about 24.2-194.5%. After the screening, 14, 11 and 6 isolates were selected from soil, sediment and groundwater respectively Microbial Fuel Cell (MFC) experiments.

MFC experiments augmented with microcosms were compared with MFC augmented with single pure strain from each matrix. The result of the MFC variables (i.e. voltage over time and power density) for microcosm experiments showed a better performance compared to that of the pure strains. Hence, the microcosm integration was selected for MFC experiments.
Subsequently, bioreactors containing waterlogged soil polluted with 200000 µg of benzene and 100000 µg of phenanthrene in three different experimental design were set ups. The first that contained an MFC, microcosm and 5% biochar and the second that contained MFC and microcosm had the best performance that degraded 200000 µg and 100000 µg of benzene phenanthrene completely within six days while the negative control degraded about 6300 µg and 34.8 µg of benzene and phenanthrene respectively. The overall results from the experiments suggest that augmentation of the right microcosm with BES could be the game changer in the remediation of petroleum hydrocarbon.