Sometimes a normal vital MLSS organism can exhibit behaviors that we don't want. From forming "Zoogleal" EPS to building sheathed filaments, these organisms respond to environmental factors and do things that we don't want in a treatment system. From a science standpoint, this is a discussion of phenotype (what you see) vs genotype (what DNA is present). However, we are increasingly able to predict what causes this bad behavior and can take corrective actions.
Example 1 - Zoogleal (Non-filamentous) bulking
In typical activated sludge and decline phase growth systems, often Zooglea type organisms are the most common genera found when looking at DNA. In addition to degrading many organic components of BOD5, these organisms are also great for denitrification and making EPS needed for floc/biofilm formation. Problems come when high Zooglea (or Thauera) populations meet conditions that cause excess EPS production. Example triggers include:
Example 2 - Sphaerotilus natans
A common sheathed filament, S. natans can often be seen in filamentous bulking sludges. Under normal conditions with sufficient D.O., S. natans grows as a typical floc forming organisms. In response to stress of low D.O., we see the formation of the sheath and filamentous growth.
Example 1 - Zoogleal (Non-filamentous) bulking
In typical activated sludge and decline phase growth systems, often Zooglea type organisms are the most common genera found when looking at DNA. In addition to degrading many organic components of BOD5, these organisms are also great for denitrification and making EPS needed for floc/biofilm formation. Problems come when high Zooglea (or Thauera) populations meet conditions that cause excess EPS production. Example triggers include:
- high soluble BOD5 (they store soluble BOD as EPS)
- Low N or P which slows cell metabolism - resulting in organics being stored in EPS
Example 2 - Sphaerotilus natans
A common sheathed filament, S. natans can often be seen in filamentous bulking sludges. Under normal conditions with sufficient D.O., S. natans grows as a typical floc forming organisms. In response to stress of low D.O., we see the formation of the sheath and filamentous growth.
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