AimsTo investigate the medium-pressure (MP) and low-pressure (LP) Ultraviolet (UV) susceptibility and the repair potential of Enterococcus faecalis (DSM 20478) after UV treatment. Methods and ResultsA range of UV doses from 4 to 19mJcm(-2) was selected in this study. Photoreactivation and dark repair performance were investigated under fluorescent light or in the dark respectively. The inactivation and repair performance of UV disinfection under a range of salinities (0, 1%, 3%) and temperature (4 and 25 degrees C) were compared. Results indicated that MP UV exposure resulted in higher inactivation efficiency against Ent.faecalis than LP UV exposure. For repair potential, LP UV resulted in a greater level of light repair than MP UV. Effect of salinity on the inactivation and repair of Ent.faecalis was correlated with UV sources, whereas low temperature generally adversely affected the inactivation efficiency and final repair levels after both MP and LP UV exposure. ConclusionsBoth salinity and temperature demonstrated to play an important role in the inactivation and repair capability when UV light was used to treat ballast water. Significance and Impact of the StudyConsidering that UV-treated ballast water is exposed or discharged to marine water environment in many countries with various temperature and salinity conditions, results of this study provide significant implications for the management of public health associated with ballast water treatment and discharge.