Effect of Isothiazolone on the Performance and Microbial Community Changes in a laboratory Scale Rotating Biological Contactor

Abstract

The effect of isothaiazolones, a commercial biocide widely used in paper and pulp industry, on the performance of laboratory-scale rotating biological contactors (RBCs) as well as biocide efficacy was studied. Biofilms were established on the RBCs and then exposed to the synthetic wastewater containing 0 (control), 3, 6 and 12 ppm isothiazolones at a flow rate of 2.5 litres h-1 for 14 days. The results showed that COD removals at steady state of the control, 3 and 6 ppm RBC units were 68.35 ± 4.40, 57.47 ± 1.75 and 15.27 ± 2.67 % respectively, while COD removal of the 12 ppm RBC unit was totally inhibited after day 12 of the treatment. Isothiazolones could be removed 77% by the RBC unit receiving 3 ppm isothiazolones. At the higher concentrations, however no significant isothiazolone removal occurred. Isothiazolone concentrations up to 3 ppm had no significant effect on viable populations of biofilms and planktonic cells in the RBCs. However, 6 and 12 ppm isothiazolones caused approximately 104-fold and 105-fold reductions of the numbers of colony-forming units in the biofilms. Moreover, when 12 ppm isothiazolones was applied to the system no viable planktonic cells could be detected.