50 mg of the NS was suspended in 45 mL sterilized saline solution. Then the solution was homogenized by sonication at 35 kHz for 1 min with a sonicator. After that, 5 mL of saline-washed bacterial cell was added into 45 mL sterilized saline solution containing 1.0 g L-1 photocatalyst. The photocatalytic disinfection was initiated by turning on light. At different time intervals, aliquots of the sample were extracted and serially diluted with saline solution. 0.1 mL of the diluted sample was then immediately spread onto nutrient agar plates and incubated at 37 C for 24 h to deter mine the number of viable cells. In parallel with the photocatalytic disinfection, three control experiments: a light control, a dark control and a blank control, were carried out to prove the occurrence of photocatalytic disinfection required the coexistence of light irradiation and photocatalyst.