The aim of this study was to investigate the feasibility and optimization of formic acid production in the microbial electrolysis desalination and chemical-production cell ( MEDCC). The maximum current density in the MEDCC with 72 cm of the anode fiber length (72-MEDCC) reached 24.0 +/- 2.0 A/m(2), which was much higher than previously reported. The maximum average formic acid production rate in the 72-MEDCC was 5.28 times higher than that in the MEDCC with 24 cm of the anode fiber length (37.00 +/- 1.15 vs. 7.00 +/- 0.25 mg/h). High performance in the 72-MEDCC was attributed to small membrane spacing (1 mm), high flow rate (1500 lL/min) on the membrane surface and high anode biomass. The minimum electricity consumption of 0.34 +/- 0.04 kWh/kg in the 72-MEDCC was only 3.1-18.8% of those in the EDBMs. The MEDCC should be a promising technology for the formic acid production. (C) 2017 Elsevier Ltd. All rights reserved.