Today, all mentions of Zooglea tend to be in a negative light. Under the microscope mature Zoogleal type colonies appear as fingers. The key visual clue is the gelatinous matrix that contains the cells. The extracellular materials move from promoting floc formation to entrapping water and creating viscous bulking.
Now what conditions favor Zooglea or other microbes responsible for viscous bulking:
- High levels of soluble organics - (you can address this through step-feed of influent)
- Macronutrient (C:N:P) imbalance that favors organisms that an uptake scarce nutrients (often I see viscous bulking with low soluble phosphorus but nitrogen is also critical)
- Changes in influent makeup, temperature, pH, or any stress that causes microbes to encapsulate in a EPS matrix.