Student Research: Eileen Wong
There is growing concern over human exposure to Mycobacterium avium complex (MAC) due to their ubiquitous presence in natural waters and extreme resistance to both chemical and physical disinfectants in drinking water treatment processes. However, little is know about the effectiveness of physico-chemical processes to remove MAC in drinking water treatment processes. Therefore, we determined the removal of MAC by coagulation/flocculation/sedimentation process in typical drinking water treatment conditions. The removal of a clinical strain of MAC (M. avium HMCO2) was determined using standard jar test equipment (Phipps & Bird, Inc., Richmond, VA). Coagulation was performed at 100 rpm for 30 seconds with alum concentrations of 25 and 50 mg/L at pH 4â5 at room temperature. Flocculation was performed at a reduced speed (30 rpm) for 20 minutes, which was followed by 60 minutes of sedimentation. MAC was assayed in Middlebrook 7H10 agar containing OADC enrichment and 0.5% glycerol, and E. coli was assayed in nutrient agar. The removal of MAC by 25 mg/L of alum was ~0.5 log10, which is much less than that for E. coli (~2 log10). Even with an elevated alum concentration of 50 mg/L, the removal rates of both MAC and E. coli did not change significantly. Overall, the results of this study suggests that coagulation/ flocculation/ sedimentation process in drinking water treatment may not be effective in removing MAC in typical treatment conditions.