Dear paolo, Nocardia is a ...
Published by Prem Baboo, Researcher at www.researchGate.net
Dear paolo,
Nocardia is a genus of weakly staining Gram-positive, catalase-positive, rod-shaped bacteria . It forms partially acid-fast beaded branching filaments (acting as fungi, but being truly bacteria ). It contains a total of 85 species. Some species are nonpathogenic, while others are responsible for nocardiosis . Severe Nocardial foams cause a number of operational problems. These include aesthetics, odors, and safety hazards if they overflow basins to cover walkways and handrails. In cold weather these foams can freeze, necessitating "pick and shovel" removal.
Higher aeration basin temperature provides favorable conditions for the growth of Nocardia while M. parvicella grows at lower temperatures. Due to the physical interlocking of the filaments in the foam provides stability to the foam and this type of foam is difficult to remove by antifoam chemicals. Nocardia and M.parvicella bacteria are tolerant to chlorine and are found within the flocs so, high chlorine dosages required for this type of foam control.
Foaming and bulking problems in ASPs are associated with the presence of a variety of filamentous bacteria along with that parameters have been identified as the causative agents of filamentous bulking and foaming. In situ, filamentous bacteria, Sphaerotilus spp. and Leptothrix spp. Microthrix parvicella, Corynebacterium, Dietzia, Gordonia, Skermania, Mycobacterium, Nocardia, Rhodococcus, and Tsukamurella are the key organic degraders and offer the skeletal matrix for the formation of compact flocs.
Conditions that Contribute to Nocardia Growth / Foam
- Low F:M (0.08-0.35 lbs BOD) and long MCRT (10-40 days)
- High levels of surfactants and fat, oil, and grease (F.O.G.)
- Internal recycling of floating material
- Warm temperatures generally above 60°F (15.55°C)
- Very low effluent BOD (observation)
How to control
To overcome the Nocardia problem high dose of chlorine is required which may destroy the activated sludge floc and negatively effect the settling characterstics of the sludge .It was observed to exert a total destruction of the filamentous texture between the flocs, leaving only a lot of loose and chopped filament fragments with resulting turbidity in the bulk solution. All of these filaments grow on grease and oil, and these can become a problem when grease and oil are high in amount in the influent wastewater. Systems that lack primary clarification (the main grease and oil removal mechanism) appear to suffer more foaming problems. Communities with enforced grease and fat ordinances appear to suffer less from foaming problems. Also, disposal of septage, which contains substantial grease and oil content, to small activated sludge systems has been associated with foaming problems. Note that Nocardia here is used as a group name rather than a specific species. Recent work has shown that a number of actinomycetes can cause foaming and include Nocardia amarae, N. pinensis, N. rhodochrus and other Nocardia-like species. These are often collectively referred to as the Nocardioforms, or the foam-causing actinomycetes. Nocardia and M. parvicella also occur at a longer sludge age. The sludge age at which these filaments can be controlled is a function of the wastewater temperature, being lower at higher temperature. Nocardia appears to be favored at higher aeration basin temperatures and M. parvicella at lower aeration basin temperatures. Nocardia can usually be controlled by a sludge age below 6-8 days and M. parvicella at a sludge age below 8-10 days at moderate wastewater temperatures. However, many plants have had to reduce the sludge age to less than 2 days for Nocardia control, and this may be inconsistent with other process goals, such as nitrification or sludge handling capability. A third factor in the growth of Nocardia and M. parvicella is septicity or low oxygen conditions.