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What should I do if a large grease or oil spill hits my biological treatment unit?

9/21/2015

 
Picture
Grease and Nocardia foam on oxidation ditch. (http://web.deu.edu.tr)
No matter how careful you operate the collection and pretreatment systems, the biological unit sometimes receives spills or shock-loads. Today, I am going into one of the most common spills - grease or oil (let's use FOG from now on for grease). What makes FOG so difficult is:
  • Insoluble nature makes it difficult for bacteria compared to soluble organics.
  • Takes time to degrade!
  • Causes foaming on aeration basins
  • Contributes to floating sludge on secondary clarifiers
  • MLSS has oil droplets and excess water which makes for messy dewatering
  • Fixed Film or mobilized beds can become coated with FOG - which can foul the media by "smothering" the biofilm
  • Long term high FOG can encourage problem microbes such as Nocardia (causes thick greasy foam)
In this case, we will discuss response actions to a one time high FOG release into the system. In most cases we do the following:
  1. Get ready to add anti-foam & secondary clarifier polymers.
  2. Increase wasting rates to get rid of FOG saturated MLSS.
  3. Try to maintain a Dissolved Oxygen (DO) above 2.0 mg/L to maximize biological activity.
  4. Check upstream to find cause of FOG and try to make prevent further introduction of FOG.
  5. With high wasting rates, it is a good idea to add bioaugmentation cultures to increase the number of active degrading microbes in the mixed liquor.
  6. In fixed film systems adding bioaugmentation cultures can help re-establish the biofilm that was damaged by the FOG. It may be necessary to actually clean some of the media with surfactants if there is heavy grease buildup.

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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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