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

► Cascade-type MFC stack achieves cumulative COD reduction >95% in <6 h. ► COD removal is equivalent to a competitive reduction rate of 7.97 kg COD m−3 d−1. ► Electrical insulation of feeds is needed in series configuration to avoid losses. ► Substrate imbalance/starvation/series connections do not cause reversal in stacks.