What is Nocardia and how to useful in Activated Sludge Processes?
Nocardia is a genus of Gram-positive, catalase-positive, rod-shaped bacteria that stains faintly. It generates beaded branching filaments that are somewhat acid-fast (acting as fungi, but being truly bacteria). It has 85 different species. Some species are non-pathogenic, whereas others cause nocardiosis. Most Nocardia infections are caused by bacterial inhalation or traumatic introduction.
Nocardia forms are classified into nine genera. Rhodococcus and Nocardia are two of these genera implicated in activated sludge foaming, with the latter being the more well-known problem.
How is Nocardia foam best controlled?
Nocardia are distinguished by branch-like hyphae that extend from the cell wall in a manner similar to fungus hyphae. These branches connect to other filaments and flocs. Their food consists of simple and complex organic materials like as fats, oils, and grease (FOG). These are slow developing organisms that thrive in the aerobic conditions provided by an aeration tank. These actinomycetes typically have a hard time competing with other wastewater bacteria, but once established, they're a pain to get rid of.
Nocardia, when present in low amounts, helps to stabilize floc structure!
The bacteria can rapidly degrade biochemical oxygen demand (BOD), which is advantageous in high-strength wastewater. In greater quantities, Nocardia can rip the floc apart and rapidly destroy BOD- starved floc forming bacteria.
When filaments float to the surface as a result of their low-density fatty acid membrane and the waxy, hydrophobic biosurfactant that covers their bodies, dense, brown foam develops. Bubbles from the aeration system can also aid in the flotation of the filaments but these are not commonly connected with sludge thickening.
Unfortunately, the prerequisites for a Nocardia epidemic remain unknown!
Any change in temperature, pH, dissolved oxygen (DO), solids content, or nutrients, in general, may cause an epidemic. Warm temperatures with a high concentration of FOG, a low food to mass (F/M) ratio, and/or a high mean cell residence period are thought to promote Nocardiaforms.Since nocardia forms develop slowly, they require plenty of time to multiply, and their increased surface area aids in nutrient acquisition under low F/M conditions. Some believe that anaerobic conditions in areas of the aeration tank or surfactants can also promote Nocardia development.
Conclusion
Nocardia foam treatment options are also much contested.Using a high-volume water spray will momentarily break down the foam, but it will reappear. A better method is to skim off extra foam to prevent bacteria from being recycled back into the system.
Chlorination is not a good idea. The branching Nocardia filaments hinder enough disinfectant contact while killing healthy floc bacteria. Although many firms advocate defoaming treatments, the interlocking filaments are frequently too stable for these chemicals as well. Most publications advise lowering your MCRT to less than 8 days while increasing (F/M).
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