When bulking organisms do not cause bulking - how environmental conditions trigger conversion into bulking forms
We have a list of "good" and "bad" microbes in wastewater plants. Filamentous bulking occurs when microbes grow into high surface area filaments preventing proper settling and solids compaction. In addition to filaments, we also have non-filamentous or Zoogleal bulking where excessive biological polymers create a gel that traps water in the floc - this creates compaction problems, floating scum, and sometimes billowing clarifier beds. As we see more MBR systems, non-filamentous bulking interferes with normal membrane operations due to pore blinding by biological polymers.
Aster Bio's Environmental Genomics (genetic testing of MLSS) has found multiple examples of "bulking" organism DNA being present when the system is not yet bulking. In these cases, the organisms are not yet at a bulking threshold or conditions such as sufficient D.O. keep the microbes in their non-filamentous form. An example of sufficient D.O. preventing filament growth happens with S. natans. While often a severe filament, S. natans also effectively removes organics from wastewater. When it grows under aerobic conditions with supporting microbes, S. natans works within the floc as single cells.
As for non-filamentous bulking, conditions that promote excessive EPS production include high soluble BOD (organic acids), low nutrients, and low F/M or food scarcity.
Unlike microscopic or settling tests, genetic testing monitors these organisms before they exhibit problem behaviors. This is due to genetic testing being for specific genotypes vs microscopic exam where we look for phenotypes (appearance or form).
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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