The objective of the present study was to investigate the effectiveness of spark plasma discharges on the inactivation of acid-producing bacteria (APB) and sulfate-reducing bacteria (SRB) in produced water. Tests were conducted in both static batch mode and once-through flow mode. The residual effect of plasma treatment was assessed by two different protocols: immediate incubation after plasma treatment and incubation after 24-h storage in a tank post-treatment. In the batch test, 10-min plasma treatment of water showed a total 3-log reduction of APB and 2-log reduction of SRB based on cfu/mL data in the case of clear produced water. In the once-through flow test, 2-log reduction of APB was observed in the case of clear produced water, whereas 1-log to 1.5-log reductions were observed in the case of darkly opaque produced water. The energy efficiency for the once-through flow test with APB for the opaque produced water was 1.7 kJ/L per 1-log reduction. UV radiation together with active plasma species produced by the spark discharge was instrumental in the inactivation of APB and SRB in both clear and dark produced water. (C) 2015 Elsevier B.V. All rights reserved.