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 (1 mM acetate) only the first MFC operated stably over a 72-h period. Acetate feedstock at 5 mM was enough to sustain the first four MFCs, and 10 mM acetate was sufficient to maintain all MFCs at stable power densities. COD was reduced from 69 to 25 mg/L (64%, 1 mM acetate), 319-34 mg/L (90%, 5 mM acetate) and 545-264 mg/L (52%, 10 mM 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. (C) 2012 Elsevier Ltd. All rights reserved.