In the light of the pursuit of circular economies, wastewater treatment facilities are nowadays considered as multi-functional facilities, in which their main goals extend beyond traditional removal of contaminates to include recovery of value-added products and energy management. In this context, microbial fuel cells (MFCs) represent a new approach that can simultaneously enhance the treatment of waste streams and generate electricity. Although MFCs represent a promising technology for renewable energy production, they have not been successfully scaled up mainly due to the relatively-low electric current generation and high cost associated with MFCs operation, especially when complex organic wastes (e.g., sewage sludge) are used as the sole substrate. For this proof-of-concept effort, we investigated the co-treatment approach to mitigate the low bioavailability of organic matter in sewage sludge by mixing it with animal manure wastewater. We documented the efficiency of thermophilic MFCs (55 °C), in terms of solids and pathogen reduction, and electricity generation, and compared its efficiency with a control MFC fed with sewage sludge only. Compared to control MFC, MFCs fed with mixed influent exhibited much higher electricity generation (i.e., 200 ± 24 mW/m2 versus 35 ± 3.1 mW/m2) with ~ 72 ± 5 % and 66 ± 3 % reduction in chemical oxygen demand (COD) and volatile solids (VS) concentration, respectively. Electrochemical impedance spectroscopy of bioanodes, which evaluate the electroactive biofilm – anode interaction, followed the same trend with the MFC fed with the mixed substrate (sewage sludge and animal manure wastewater) had the lowest charge transfer resistance (Rct) (i.e., 51 Ω) compared to 650 Ω for control MFC. In addition, we estimated the efficiency of MFCs for inactivating the pathogens based on the MPN counting of T. coliform, F. Coliform, and E. coli in the final effluent of each MFC compared to the bioreactors influents. The MPN counting demonstrates almost a complete pathogen inactivation for each MFCs. High-throughput sequencing revealed that increasing the organic matter bioavailability was associated with increasing relative abundances of phylotypes that are most closely related to anode respiration (Geobacteraceae). Our results demonstrate that MFCs could be a potential alternative to other inefficient environmental biotechnologies to recover energy from sewage sludge by controlling the availability of organic matter.

Co-substrate approach for enhanced electricity production and solids reduction of sewage sludge in a thermophilic microbial fuel cell

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ACS Fall 2022

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