Bioremediation of petroleum hydrocarbons using microbial fuel cells

Environmental pollution by petroleum hydrocarbons has serious environmental consequences on critical natural resources upon which all living things (including mankind) largely depend. Microbial fuel cells (MFCs) could be employed in the treatment of these environmental pollutants with concomitant bioelectricity generation. Therefore, the overarching objective of this study was to develop an MFC system for the effective and efficient treatment of petroleum hydrocarbons in both liquid and particulate systems. Biodegradation of target hydrocarbons, phenanthrene and benzene, was investigated in dual-chambered microbial fuel cells (MFCs) using different inoculum types - Shewanella oneidensis MR1 14063, Pseudomonas aeruginosa NCTC 10662, mixed cultures and their combinations thereof. All the inocula showed high potentials for phenanthrene and benzene degradation in liquid systems with a minimum degradation efficiency of 97 % and 86 % respectively with concomitant power production (up to 1.25 mWm-2). The performance of MFCs fed with a mixture of phenanthrene and benzene under various operating conditions - temperature, substrate concentration, addition of surfactants and cathodic electron acceptor type – was investigated. The interaction effects of three selected operating parameters - external resistance, salinity and redox mediator were also investigated using response surface methodology. The outcomes of this study demonstrated the robustness of MFCs with good degradation performance (range 80 - 98 %) and maximum power production up to 10 mWm-2 obtained at different treatment conditions. Interactive effects existed among the chosen independent factors with external resistance having a significant impact on MFC performance, with maximum power output of 24 mWm-2 obtained at optimised conditions - external resistance (69.80 kΩ) , redox mediator (29.30μM, Riboflavin) and salinity (1.3 % w/v NaCl). The treatment of a mixture of phenanthrene and benzene using two different tubular MFCs designed for both in situ and ex situ applications in aqueous systems was investigated over long operational periods (up to 155 days). The outcomes of this work demonstrated stable MFC performance at harsh nutrient conditions and ambient temperatures. Simultaneous removal of petroleum hydrocarbons (> 90 %) and bromate, used as catholyte, (up to 79 %) with concomitant biogenic electricity generation (i.e. peak power density up to 6.75 mWm-2) were observed. The performance of a tubular MFC system in phenanthrene-contaminated soil was investigated in the last study. The outcomes of this work has demonstrated the simultaneous removal of phenanthrene (86%) and bromate (95%) coupled with concomitant bioelectricity generation (about 4.69 mWm-2) using MFC systems within a radius of influence (ROI) up to 8 cm. The overall outcomes of this study suggest the possible application of MFC technology in the effective treatment of petroleum hydrocarbons contaminated groundwater or industrial effluents and soil systems (mostly in subsurface environments), with concomitant energy recovery. MFC technology could potentially be utilised as an independent system in lieu of other bioremediation technologies (e.g. pump and treat, electrobioremediation or permeable reactive barriers) or integrated with existing infrastructure such as monitoring wells or piezometers.