Produced wastewater from Barnett Shale formation that was collected from a well after 100 days of production was used as the only source of bacteria and electron donors in the MFC. Fig. 1 shows the power density and polarization curves of the MFC only fed with produced water (TDS = 86,000 mg/L). Bacteria from the Barnett Shale colonized the MFC anode and transferred electrons to its surface to produce a maximum power density of 47 mW/m2(0.14 V and 0.42 mA), comparable to the power density of 71 mW/m2 obtained using a mixed culture from Galveston Bay under 100,000 mg/L NaCL [10]. The COD removal efficiency was of68% (CODout= 3350 ± 70 mg/L), yielding a Coulombic efficiency of 10% over 58 days.