Microbial degradation of disinfectants. IV. Treatment by activated sludge of chlorhexidine.

Abstract

To evaluate the effect of the treatment by activated sludge, the concentration of chlorhexidine (CH) in hospital or domestic waste waters before or after pretreatment was determined, in addition to microbiological and physicochemical investigations. The following were clarified : 1) The numbers of coliform group and total count in hospital waste waters were less than those in domestic one. 2) Antimicrobial activity was not observed in the domestic waste waters, whereas observed in the hospital inflow ones. 3) No change in the values of pH, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of both waste waters was observed in the hourly or daily time-course, and the values of pHs in both waste waters were neutral or weakly basic. 4) The values of BOD and COD of outflow waste waters were less than those of inflow ones. From these findings, waste waters were found to be treated appreciably with activated sludge. 5) The determined value of CH in waste waters without pretreatment gave 0.12-0.60 μg/ml and 0.20-0.70 μg/ml by colorimetric and HPLC methods, respectively. These values were almost similar to those determined by the conventional methods. On the other hands, the determined values of CH in waste waters after pretreatment with hydrochloride and Celite gave 1.62-10.30 μg/ml by both methods. These values showed about 5-20 times those determined by the conventional methods. 6) The determined values of CH in inflow and outflow waste waters after the pretreatment described above gave 1.20-4.50 μg/ml and 1.40-3.60 μg/ml by each method, respectively. These results suggested that CH in waste waters was scarcely treated with activated sludge.