Use of alternative disinfectants, individually and in combination, in aquacultural wastewater treatment

Abstract

The inactivation effect of chlorine, iodine, ozone and UV irradiation was compared between phosphate buffered saline and waste water collected from a fish farm, with the fish-pathogenic bacterium Aeromonas salmonicida subsp. salmonicida as the model organism. In addition, the effect of combining chlorine, iodine or ozone with UV was evaluated. A tenfold increase in initial chlorine concentration, from 0.2 to 2.0 mg l−1. had to be applied to maintain the same level of inactivation in waste water as in PBS. Iodine was less efficient than chlorine in PBS. by demanding a concentration of 1.0 mg l−1 to obtain the same rate of inactivation as with 0.2 mg l−1 chlorine. However, no difference between the two halogens was evident in the low-quality water. An initial ozone concentration of 0.1 mg l−1 in PBS caused a rapid drop in bacterial viability for the first 20 s after which the curve levelled off. By continuous ozonation of waste water, a residual oxidant concentration of about 0.3 mg l−1 had to be established before a rapid inactivation was observed. The UV inactivation profiles in PBS and waste water were almost identical, with a 99.9% reduction in viability after 48 and 50 s. respectively. When UV irradiation was combined with chlorine, a less than additive effect, as compared with the sum of individual death rates by the two treatments, was observed. The corresponding UV/iodine combination at least gave an additive effect in both water qualities. No increment in inactivation rate in PBS was observed when ozone was used in combination with UV, as compared with ozone alone.