V. Lund et D. Hongve, ULTRAVIOLET-IRRADIATED WATER CONTAINING HUMIC SUBSTANCES INHIBITS BACTERIAL METABOLISM, Water research, 28(5), 1994, pp. 1111-1116
Disinfection of drinking water by u.v. irradiation has been observed t
o reduce the biofilm formation in the pipes in a pilot plant. An appar
ently inhibitory effect that persists in the water after the u.v. trea
tment has been studied in the laboratory. Reduced numbers of viable ba
cteria and reduced bacterial metabolism were observed when irradiated
waters were inoculated with fresh bacteria. Approximately 60% of the h
eterotrophic bacteria in the water samples were inactivated within a I
h contact time with freshly u.v. disinfected water. The uptake rates o
f labelled tracer substances were significantly reduced when the bacte
ria were exposed to irradiated water. The inhibitory effect seems to l
ast for at least 1 week. High concentrations of organic matter seem to
counteract the inhibitory effect. No relationship was found between u
.v. dose and effect within the dose range tested. The observed effects
may be explained by the action of oxidizing reagents such as hydroxyl
radicals, produced in photochemical reactions between u.v. irradiatio
n and humic substances in the water.