MFC-cascade stacks maximise COD reduction and avoid voltage reversal under adverse conditions.

Six continuous-flow Microbial Fuel Cells (MFCs) configured as a vertical cascade and tested under different electrical connections are presented. When in parallel, stable operation and higher power and current densities than individual MFCs were observed, despite substrate imbalances. The cascading dynamic allowed for a cumulative COD reduction of >95% in approximately 5.7h, equivalent to 7.97 kg COD m(-3) d(-1). Under a series configuration, the stack exhibited considerable losses until correct fluidic/electrical insulation of the units was applied, upon which the stack also exhibited superior performance. In both electrical configurations, the 6 MFC system was systematically starved for up to 15 d, with no significant performance degradation. The results from the 14-month trials, demonstrate that cascade-stacking of small units can result in enhanced electricity production (vs single large units) and treatment rates without using expensive catalysts. It is also demonstrated that substrate imbalances and starvation do not necessarily result in cell-voltage reversal.