Ultraviolet irradiation for controlling biofouling in OTEC heat exchangers: A preliminary report

Experiments have been on-going at the Seacoast Test Facility of the Natural Energy Laboratory of Hawaii on the Big Island of Hawaii examining various means for controlling biofouling in OTEC heat exchangers. These methods include using amertap balls, nylon brushes, and chlorination. One method in particular under investigation is the use of ultraviolet irradiation, which is well documented in the medical and microbiological fields for killing bacteria and other microorganisms. In OTEC heat exchangers, the mechanism for biofouling is usually initiated by the presence of seawater bacteria which eventually attract higher order organisms leading to the growth of a fouling film which is resistant to heat transfer. Thus, the ultraviolet experiments are being directed towards killing or stunning the seawater bacteria before they reach the heat exchanger surface. Preliminary results have shown that seawater bacteria are significantly different from the well documented human bacteria and that the kill rates associated are not as high as anticipated.