The HPC in raw water and filtration effluent from a WTP were inactivated by DBD plasma ( Fig. 2 B); however, the extent of inactivation depended on the duration of treatment. The initial concentration of HPC bacteria in raw water and filtration water was 3.0 × 10 4 CFU/ml and 4.0 × 10 3 CFU/ml, respectively. After treatment for 30 s, the inactivation ratios of HPC in raw water and filtration effluent were only 1.0 log and 1.2 log, respectively. However, when the treatment was extended to 120 s, no viable HPC were detected in filtration effluent (the inactivation ratio was 3.6 log), and the HPC in raw water decreased to 3 CFU/ml (the inactivation ratio was 4.0 log). When the treatment was further increased to 240 s, no HPC were detected in raw water. Compared to Staphylococcus aureus and Escherichia coli ( Fig. 2 A), the HPC exhibited obvious resistance ( P < 0.05) to plasma treatment because the complicated HPC contained some bacteria with a stronger resistance to plasma treatment than did either Staphylococcus aureus or Escherichia coli individually.