Although chlorination remains the main means of disinfection, new sewage treatment facilities are moving towards ultraviolet radiation to treat effluent. But a government consultant said Hong Kong should not introduce UV now as it might become redundant if it goes ahead with biological treatment. Of the 132 sewage works in 24 coastal cities surveyed by Maunsell Consultants, which is conducting the environmental impact assessment on the Harbour Area Treatment Scheme, only a few have adopted UV. About 50 per cent of facilities planned in the next five years will adopt UV radiation, while only 25 per cent of facilities completed within the last 10 years used it. Conservationists worry that chemical residues, even after de-chlorination, could affect marine life. Chlorine is added to the effluent to remove bacteria since the treatment process does not. Bacteria-laden effluent has caused the closure of four Tsuen Wan beaches close to the Stonecutters treatment works. Howard Huang Ju-chang, a disinfection specialist at the University of Science and Technology, said the chlorine is about 0.01 per cent of the average laundry bleach.