Bug of the Month: Dead Filamentous Bacteria and Their Significance

Based on experience viewing a high amount of mixed liquor samples under fluorescent microscopy, it appears common to have a high percentage of dead bacteria within the floc (there is a previous article about how these dead bacteria aid in flocculation), and for most filamentous bacteria in activated sludge samples (greater than 90%) to usually appear to be alive and viable. Generally, it appears common for most systems to have an estimated 40-80% of their bacteria viable. Systems with extended aeration and higher sludge retention times tend to have lower bacterial viability, whereas younger sludges (those with shorter retention times) tend