Nocardia

Nocardia 400x Gram Stain. Note that Nocardia stains Gram +.

Nocardia is a very distinctive organisms in wastewater. Nocardia has true branching and stains gram positive. The photo above is a gram stained Nocardia filament from recent sample. While a filament, Nocardia forms do not cause bulking. The problem with Nocardia is the foaming caused by their production of hydrophobic extracellular polymeric substances (EPS). The foam is thick, resistant to anti-foams, and is very stable.

What causes Nocardia overgrowth?

• Grease (insoluble fatty acids) - this is why Nocardia is a huge problem in food processing and in high FOG municipal wastewater treatment systems
• Long sludge age - a slow grower, Nocardia requires longer sludge ages to develop. Once in a foam layer on the aeration basin, sludge age is less of a factor as the Nocardia are in the foam.

Control measures:

• Keep grease from entering the aeration basin. We have used collection system treatment to reduce long chain fatty acids (what we call grease) entering the WWTP. By depriving Nocardia of their ecological nice, you can reduce their advantages over "good" bacteria.
• If you have Nocardia foam, increase wasting. You may also need to consider adding bleach or other disinfectant to the RAS line. Although it will miss Nocardia suspended in the foam.
• Spray hypochlorite solution directly on the foam layer. This hits the nocardia directly.