Ultraviolet and Chlorine Disinfection of Mycobacterium in Wastewater: Effect of Aggregation

Mycobacteria naturally aggregate in water, a characteristic that may serve to protect them against disinfection in wastewater. Secondary effluent was spiked with Mycobacterium terrae (M. terrae), sequentially filtered through 100‐, 41‐, and 20‐μm nylon filters to partition aggregate sizes, confirmed using particle‐size analysis and microscopy. Each sample was exposed to doses of UV light (10 to 60 mJ/cm 2 at 254 nm) and free chlorine (27 to 150 mg‐min/L at 4°C). Inactivation of M. terrae in wastewater was initially rapid, with 2.5 log reduction at 14 mJ/cm 2 and 56 mg‐min/L for UV and free chlorine, respectively. However, in effluent and 100‐μm filtered wastewater, spiked M. terrae was present to the highest doses evaluated. Interestingly, M. terrae passed through 41‐ and 20‐μm filters were inactivated rapidly, with no survivors after moderate disinfection doses. Inactivation of Mycobacteria in wastewater may be compromised by aggregates larger than 41 microns.