Sludge production in microbial bioelectrochemical systems (BES) was assessed in conjunction with anaerobic and aerobic control reactors. Effluent after primary settling tank (EAPS) and depleted EAPS spiked with acetate were treated. The reactors were loaded with total suspended solids (TSS) and chemical oxygen demand (COD) at average loading rates of 22 mg TSS d(-1) L-1 and 86 mg COD d(-1) L-1, respectively. Carbon cloth anode equipped BES reactors delivered the highest performance. They achieved on average a COD removal of 80%, a Coulomb efficiency of 77% for EAPS, a maximum current density of 39 mu A cm(-3)/175 mu A cm(-2) for EAPS and a TSS removal of 59%, yielding a sludge production of only 80 mg TSS per g DCOD. This study provides further evidence that BES can improve the economics of wastewater treatment via lower sludge production as well as providing a framework for understanding sludge production in BES. (C) 2015 Elsevier Ltd. All rights reserved.