The present study investigated the biological treatment of produced water in a microbial electrochemical cell (MXC). The main objectives were to develop a novel spiral microbial electrochemical cell (SMXC) and test its performance for produced water treatment under highly saline conditions (salinity > 200000 ppm). The bioelectrochemical performance of the system was also evaluated in terms of power and hydrogen production over time. The comparatively inexpensive material and ease of application increased the feasibility of the SMXC configuration for produced water treatment. Optimal SMXC performance as a microbial fuel cell was achieved at a maximum open circuit potential of 330 mV, maximum power density of 0.65 mW m(-3), and internal resistance of 110 k Omega. Hydrogen gas was generated in a SMXC as a microbial electrolysis cell at a rate of 400 ml-H-2 m(-3) day(-1) and showed a total hydrogen recovery of 0.18%. A consequential reduction in the organic content of produced water (about 90%) indicates efficient biological treatment without costly saline acclimation. (C) 2015 Elsevier Ltd. All rights reserved.