Biological Treatment of Chlorhexidine Digluconate-Containing Waste Water. IV. Tublar Contact Aeration Treatment

The effective removal of CHG (Chlorhexidine digluconate) from CHG-containing wastewater was investigated by use of a tublar wastewater treatment contactor with a honeycomb tube made of PVC (Poly vinyl chloride) as a supporter of biofilm. To the contactor, 30 ppm of activated sludge acclimated to the wastewater at the concentration of 0.5 ppm CHG was added and the wastewater containing about 20 ppm CHG was fed continuosly at the hydraulic retention time of 12 or 24 h. The removal rate of CHG in this experiment was 23% at the 1st day and 40-50% after the 4th day at the 12 h-hydraulic retention time and was 60-80% in the following 24 h-hydraulic retention time. The effects of temperature on the removal rate of CHG were then investigated at 10°C, 15°C and 20°C under the hydraulic retention time of 12 h. The results showed that CHG was removed less as temperature descended, contrary to expectation of the physical adsorption theory. However, at 10°C under the hydraulic retention time of 24 h, the removal rate of CHG was more than that at 20°C under the hydraulic retention time of 12 h. Furthermore, 70-80% of CHG in the wastewater containing 60-70 ppm CHG was removed at 10°C under the hydraulic retention time of 24 h. As wastewater treatment time went by, biofilm on the surface of the supporter increased. Biofilm increased on the supporter was slipped easily off by giving a soft shock in order to prevent the honeycomb tube from clogging. The removal rate of CHG recovered completely in a few days after biofilm was slipped off.