SEOUL, Oct 15 (Reuters) - South Korea's CJ Group participated in a round of preliminary bidding for a controlling stake in water purifier firm Coway Co Ltd, the group's holding company CJ Corp said in a regulatory filing on Thursday.

Private equity firms Affinity Equity Partners, Carlyle Group and two Chinese companies are also among those expressing interest in the 30.9 percent stake in Coway, the Korea Economic Daily reported earlier on Thursday.

(Reporting by Joyce Lee; Editing by Edmund Klamann)