Zoogloeal mass is most typically observed in which unit process?

• A. Trickling Filters
• B. Aeration Basin
• C. Primary Clarifier
• D. Disinfection Basin

Answer: (A)

Zoogloeal mass is the thick, gelatinous biofilm that bacteria produce when growing on surfaces in an attached-growth system. This mucilaginous layer forms on the media of a trickling filter as microorganisms degrade organics and trap solids, creating a visible slime layer that coats the bed. In a trickling filter, wastewater is sprayed over a bed of media, fostering this biofilm, so the zoogloea mass is a characteristic sign of that unit process. In contrast, an aeration basin relies on suspended growth with flocs, the primary clarifier is mainly settlement of solids without a thick surface biofilm, and a disinfection basin is downstream of treatment and doesn’t feature this kind of mass.