Benzalkonium chloride (Osvan) and chlorhexidine (Hibitane), recently developed disinfectants, have been used widely hospitals and medical schools. In the present paper, the author describes the degradability of Osvan and Hibitane in a laboratory-scale submerged fixed-film reactor. The degradation rates of these disinfectants were increased by acclimating the activated sludge to daily increasing concentration of disinfectants in the apparatus. After acclimation, 150ppm (mg/l) of Osvan and 75ppm

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... f Hibitane were decomposed in this manner. It was also found that Hibitane, cresol and phenol were decomposed by the activated sludge after acclimation to Osvan. Similarly, Osvan, cresol and phenol were decomposed by the activated sludge after acclimation to Hibitane.