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Why you don't want "old" sludge - how operating in endogenous respiration can hurt activated sludge effluent quality

11/6/2017

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Extended Aeration Activated Sludge System
Extended aeration biological treatment systems operate at a lower F/M than the original activated sludge designs. Why did we move to extended aeration over other aerobic treatment systems?
  • More resistance to hydraulic and shock/toxic loading events
  • Lower solids yield (although you can argue that you are just moving the aerobic digester into the treatment basin)
  • Enables nutrient removal - both N & P
  • Better removal of xenobiotics - pharmaceuticals, pesticides, and other recalcitrant or insoluble organics

​While operating in extended aeration mode has a lot of upside, running a system at too low an F/M ratio can be counter productive and effluent quality can decline. As you move further into endogenous respiration (very low F/M) the following things happen:
  • Biological polymers holding floc together begin to degrade
  • The living or active portion of the biomass decreases - meaning inert solids must be handled by clarifiers and pumps.
  • Energy cost increase for maintaining aerobic conditions with high levels of biosolids
  • Low F/M filaments can increase bulking
  • Encapsulation (often called Zoogleal bulking)
  • Turbidity and "fines" begin to carryover into the effluent with the MLSS settling very fast and not removing the small particles

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    Author

    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.

    View my profile on LinkedIn

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