Investigating a cascade of seven hydraulically connected microbial fuel cells

Seven miniature microbial fuel cells (MFCs) were hydraulically linked in sequence and operated in continuous-flow (cascade). Power output and treatment efficiency were investigated using varying organic loads, flow-rates and electrical configurations. When fed synthetic wastewater low in organic load (1mM acetate) only the first MFC operated stably over a 72-h period. Acetate feedstock at 5mM was enough to sustain the first four MFCs, and 10mM acetate was sufficient to maintain all MFCs at stable power densities. COD was reduced from 69 to 25mg/L (64%, 1mM acetate), 319-34mg/L (90%, 5mM acetate) and 545-264mg/L (52%, 10mM acetate). Fluctuating flow-rates improved performance in downstream MFCs. When connected electrically in parallel, power output was two-fold and current production 10-fold higher than when connected in series. The results suggest cascades of MFCs could be employed to complement or improve biological trickling filters.