Seawater disinfection by chlorine dioxide and sodium hypochlorite. A comparison of biofilm formation

摘要

Continuous seawater disinfection by chlorine dioxide (ClO_2) was studied at residual concentrations of 0.2 and 0.4 mg ClO_2 L~(-1) and compared with sodium hypochlorite (NaClO) disinfection at 1 mg L~(-1) of free chlorine. The results revealed that both disinfectants decrease the biological activity and cell counts in seawater. When NaClO was used, both the cell counts and the adenosine triphosphate (ATP) level were diminished (1.8 log and 76 %, respectively); however, when ClO_2 was used, the ATP level decreased to the same level as with NaClO (78-84 %), but the cell counts were reduced only weakly (～0.1 log). The biofilm concentration in seawater without disinfectants reached 700 pg ATP cm~(-2) after 40 days, whereas in the treated lines, the biofilms remained below 1 pg ATP cm~(-2) irrespective of the disinfectant and dose used. ClO_2 generated much less trihalomethanes than NaClO (＜1 vs. 154 μg L~(-1)). Bromoform (77-96 %) was the predominant chemical species found in disinfected seawater.