Nocardia in Wastewater
Problem: Nocardia forms in activated sludge plants and sequencing batch reactors (SBRs).
Cause: Wastewater plants that receive a lot of fat, oil, grease and surfactants.
Solution: Control Nocardia with these products:
We use Foam Buster and Qwik-Zyme L to degrade the foam. Defoamers will not work when it comes to controlling Nocardia because Nocardia has too much surface tension and it sees the defoamer as food. Call the Bugman to get fast answers. For those who want to understand Nocardia further read on and do not hesitate to call. Our products and technical service to solve this problem are extraordinary.
In small amounts, Nocardia are quite beneficial for the wastewater system as they add stability to the floc structure and keep it from breaking up or shearing. In large amounts, however, these branching bacteria can wreak havoc. Nocardia are opportunists and succeed when the health of naturally-occurring bacteria are vulnerable. Once they gain a foothold, they can take over your system causing poor settling and/or foaming.
Nocardia is a Gram positive, Neisser negative, true branching filamentous bacterium that does not have a sheath and does not contain sulfur granules. It is a common cause of foam and floating sludge (1). This filament has a longer generation time than most floc-forming bacteria and goes through several stages of growth (1). The Early Phase consists of Gram positive cylindrical cells that may not be recognized, as it does not yet cause foam, but as the temperature begins to rise the single cells progress to an intermediate stage where they begin to form small nodes and branches which rapidly elongate once the temperature rises above 320°F (16o°C) (1). This fully branched Advanced Phase then causes an open, lacy floc structure, somewhat similar to tree roots, that causes persistent foam when aerated (1).
Conditions that Contribute to Nocardia Growth / Foam
- Low F:M (0.08-0.35 lbs BOD) and long MCRT (10-40 days) (1, 2)
- High levels of surfactants and fat, oil, and grease (F.O.G.) (2)
- Internal recycling of floating material (2)
- Warm temperatures generally above 320°F (16o°C) (2)
- Very low effluent BOD (observation)
Most floc-forming bacteria will grow rapidly when their preferred substrate is available and die off once it has been used up in a “feast and famine” model. Once Nocardia senses that its preferred substrate is becoming limited in the environment, it can switch to a slower growth mode consuming less energy and eventually reaching higher concentrations than floc-forming bacteria (1). This survival mechanism is also in effect when nutrients are low and/or competition by other organisms is high and enables Nocardia to maintain a stable background population (1). It is also possible for Nocardia to form resting structures and can adapt to UV radiation and dryness which are environmental challenges in foam (1).
- Brown foam is caused by undigested nutrients rising to the surface from the mixed liquor. Brown persistent foam indicates a problem in the system, but does NOT mean the Nocardia is the culprit.
- A distinguishing indication of Nocardia-caused foaming in very low efficient BOD levels.
The hydrophobic cells attach at air-water interfaces (e.g., Bubbles), similar to how oil droplets do (3), by adhering to hydrophobic surfaces (2), and can be transported to the surface concentrating the Nocardia in the foam and out of the mixed liquor (1, 4). There, the branched filaments can form a floating net that can further trap oil droplets and gas bubbles (1) and may also hinder liquid drainage, and subsequent foam collapse, by forming thick layers of interlocking hydrophobic particles that result in stronger lamella than would normally be formed (4, 5). The cells are also thought to secrete a biosurfactant (surface-active substance) that reduces the surface tension of the sludge and can contribute to formation of foam and longer lasting foam (1, 3, 4, 5). This excreted lipid material, along with any nutrients transported up by air bubbles, may give the foam a brown appearance when it collects on the surface of bubbles in the foam (1, 3). The hydrophobicity of the cell walls may be due to the presence of long chain mycolic acids on their surfaces along with other factors (4). Even if the foam drains, it will still contain concentrated amounts of Nocardia compared to the mixed liquor (4).
Nocardia Control Strategies
Caution: As a chemical disinfectant, chlorine needs to remain in contact with a target for a period of time, preferably across a large surface area, to exert an effect upon the target organism(s). Upon addition of chlorine, Nocardia filaments tend to break up into dissipated cell units that reduce surface area enabling cell survival until the chlorine has been diluted to the point that the cells can grow and branch again (1). If you decide to add chlorine, waste heavily so the dissipated cells are removed from the system.
General Guidelines for Nocardia Removal
- Once foam has accumulated Nocardia, it provides a source of “seeds” for future Nocardia growth and foaming incidences. The only way to truly remove the Nocardia from the system is to skim or suction off the foam and land apply it or otherwise destroy it (1, 2). Never attempt recirculation of scum or foam containing Nocardia (2).
- Antifoams could also be used initially to control the foaming, but it is not recommended to continue use as they are traditionally mixtures of hydrophobic liquids and solids that may lose effectiveness if continually applied (6). Adding nonionic surfactants, often present in non-silicone antifoams, will enhance foam volume and transport of Nocardia cells if additional surfactants are present (2, 6).
- It is known that reducing sludge age helps to wash the Early Phase single cell Nocardia out of the system before it can reach its Advanced Phase branched form (1). However, this may result in incomplete nitrification and if the F:M decreases and/or the temperature decrease, an abundance of Microthrix parvicella may develop and cause foam (2, 5).
- Further reduction of the levels of fats, oil, grease, and surfactants in the influent or addition of our Foam Buster or Qwik-Zyme L enzyme to digest these materials will also help to control Nocardia foaming incidences (2).
Aquafix offers biological treatment options depending on the growth phase of Nocardia in the system. At the Early Phase, it is recommended to add Qwik-Zyme L to enzymatically degrade incoming or persistent high levels of fat, oil, and grease. Once the Advanced Phase (branched form) is reached, you must physically remove the foam containing most of the Nocardia organisms and then apply Qwik-Zyme L followed by Foam Buster to digest the incoming surfactants.
At AQUAFIX, we have the expertise to help our customers resolve tough bulking and foaming issues. We consult with you to determine which product or products will solve your problem. For most foaming problems cause by Nocardia, we recommend the following:
In some cases, we recommend clients couple this treatment with Qwik-Zyme L, an enzyme catalyst that breaks up grease and foam caused by Nocardia fast.
Qwik-Zyme L – Enzymatically Break Down Surfactants and F.O.G.
Foam Buster – Digests Surfactants
- Glymph, Tony. Wastewater Microbiology: A Handbook for Operators. Denver, CO: American Water Works Association, 2005. pp.76-78, 95-97
- “Microthrix Parvicella.” asissludge.com. 2000. Activated sludge information systems. October 2009.
- Iwahori, K., Tokutomi, T., Miyata, N., and Fujita, M. Formation of Stable Foam by the Cells and Culture Supernatant of Gordonia (Nocardia) amarae. Journal of Bioscience and Bioengineering. 92(1): 77-79, 2001
- Jenkins, D., Richard, M. G., and Daigger, G. T.. Manual on the Causes and Control of Activated Sludge Bulking, Foaming and other Solids Separation Problems 3rd Edition. London: IWA Publishing. 01 Sep 2003.
- Heard, J., Harvey, E., Johnson, B. B., Wells, J. D., and Angove, M. J. The effect of filamentous bacteria on foam production and stability. Colloids and Surfaces B: Biointerfaces. 63(1): 21-26, 2008
- “Antifoam What Is It?” D-Foam Incorporated. October 2009.