The dechlorination effectiveness of ultraviolet (UV) irradiation and its effects on marine biofilm community were investigated in a pilot-scale seawater reverse osmosis (SWRO) process. Lab-scale feasibility tests were conducted for three sources of low-pressure UV (LPUV), vacuum UV (VUV) and medium-pressure UV (MPUV) lamps. As a result, a VUV lamp was chosen for the pilot process because this lamp ensured efficient dechlorination in raw seawater at UV dose < 700 mJ/cm(2). In a pilot plant test, the VUV irradiation successfully dechlorinated the seawater without damaging the reverse osmosis membrane. The VUV irradiation decreased the bacterial diversity of biofilm community. The results indicate that simultaneous dechlorination and disinfection were successfully achieved using VUV irradiation for SWRO. Therefore, the VUV irradiation can be used as an alternative dechlorination strategy in SWRO. This paper also provides the niche information of the UV-resistant microbial community; this information may be useful to guide the disinfection strategy further. (C) 2016 Published by Elsevier B.V.