Nocardia amarae, a common cause of disruptive foaming in waste treatment plants, is a slow growing, usually gram-positive, chemoautotrophic, filamentous, strict aerobe that produces the biosurfactant Trehalose. Colonies can be brown, pink, orange, red, purple, gray or white, so color alone is not a key to identifying this species. N. amarae, member of the Actinomycetes family, is not motile, so it relies on movement of the water to carry it through the system. It produces catalase, urease and nitrate reductase enzymes, but not casease.  The foam from Nocardia amarae is usually a viscous brown color, unless algae is entrapped in it, in which case it appears green and brown. See photos of this species in wastewater at the Santa Cruz Productions Database, from link in references. 
The gram-negative, motile, Alcaligenes paemba, strain SI-1 produces two biosurfactants that are ALSO based on Trehalose, a diester and a tetraester, both of which can cause similar foaming problems caused by Nocardia amarae.
Another gram-negative strain of marine origin, Alcanivorax barkamensis, produces a D-glucose-based biosurfacfant that can also induce foaming in wastewater.
|Nostocoida limicola is yet another filamentous species cited as a common cause of disruptive foaming in waste treatment plants, motile in its Hormogonia and sometimes Trichome phases. This oxygenic phototrophic member of the Actinomycetes phyllum, often forms a confluent gel encasing flattened discs or large sheets of cells, forming symbiotic relationships with other species. Staining gram-positive, Nostocoida produces round cells within tight coil formations  Nostocoida can also be identified by their starburst effect formations using phase contrast microscopy at 400 to 1000x magnification. After chlorination, a few dead cells sticking out identify stress to this species. See photos of this species in wastewater at the Santa Cruz Productions Database, from link in references |
Thiothrix spp.,the second most common cause of disruptive foaming in wastewater treatment plants appears as straight to slightly curved cells with rectangular shape form filaments up to 500 microns in length, in multicellular rigid filaments, staining gram-negative, with obligately aerobic respiration. Thiothrix are mixotrophic, using several small organic carbons and reduced inorganic sulfur sources for growth and energy.  Thiothrix I is one of the largest filaments found using phase contrast microscopy at 400 to 1000x magnification. Thiothrix II produces rectangular filaments up to 200 microns in length and are easily identified by their starburst effect formations, using phase contrast microscopy at 400 to 1000x magnification. (8) See photos of this species in wastewater at the Santa Cruz Productions Database, from link in references 
Some bacterial biosurfactants produce effects beyond emulsifying substrates with water for easier digestion, and antibiotic activity is well-known for Surfactin, the major biosurfactant produced by Bacillus subtilis, known to reduce surface tension from 72 to 27.9 from a dosage as low as 0.005%. Surfactin is a 7-amino-acid ring structure coupled with one molecule of 3-hydroxy-13-methyl-etrodecanoic acid. Closely related, Bacillus licheniformis produces an F-P moety, based on a lactone and hydrophilic peptide ring structure.
|Microthrix parvicella, another common cause of disruptive foaming in waste treatment plants, producing filaments up to 400 microns in length, easily visualized by phase contrast microscopy at 400x magnification. This species is usually found outside floc, tangling with structures in the system, but can also be found hanging out of the floc.  See photos of this species in wastewater at the Santa Cruz Productions Database, from link in references  A paper published in Applied & Environmental Microbiology, October 1983, p.832 - 839, by Herman Slijkhuis, suggests that this species requires sources of both reduced nitrogen and sulfur, in addition to fats that include oleic acid, to thrive . This concept could be tested by introducing a strain of SOB (sulfur-oxidizing bacteria) that does NOT simultaneously reduce either nitrate or nitrite. The optimal strain for this test would be Starkeya novella, ATCC 8093, which has been reported to oxidize up to 200 ppm hydrogen sulfide in 2 hours; up to 30 ppm of dimethyl sulfide in 7 hours and up to 50 ppm of mercaptans in 3 hours . Valerie Anne Edwards personally screened Starkeya novella, ATCC 8093 against acetic, butyric, hexanoic, isobutyric, isovaleric, lactic and stearic fatty acids, with the result that all were degraded within 12 hours. In a separate test on Difco's Spirit Blue Agar, which contains 10 g/L Pancreatic Digest of Casein, 5 g/L Yeast extract, 20 g/L agar and 0.15 g/L Spirit Blue dye, which was supplemented with Difco's Lipoidal emulsion that contained tributyrin and polysorbate 80 (aka Tween 80), Starkeya novella ATCC 8093 grew strongly, indicating the possibility that this strain could be encouraged to competitively exclude M. parvicella from embattled wastewater treatment plants.|
|Sphaerotilus natans, is another filamentous species, and yet it is reputed to increase settleability by branching between flocs, increasing surface area. Cells are straight to slightly curved, up to 1000 microns in length and stain gram-negative. These large cells can be easily visualized by phase contrast microscopy at 100x magnification.  See photos of this species in wastewater at the Santa Cruz Productions Database, from link in references |
|Certain conditions favor the proliferation of filamentous species. A low F/M (food to mass) ratio favors filamentous organisms, because their higher ratio of surface area to volume provides them with a selective advantage for securing nutrients in nutrient limited environments. When a plant runs an extremely long sludge age, the slower growing filaments have a better chance to establish a strong colony. As a strict aerobe, high levels of oxygen are necessary to sustain this species. Mesophilic, Nocardia amarae thrives in temperatures from 17 to 37 °C. The presence of high levels of fats, oils and greases or hydrocarbons and phenols, can encourage this species, particularly when insufficient levels of nitrogen and phosphorus are present to balance these carbon sources.|
|Many waste treatment plants become dependent on the use of chemical antifoams to partially control the foaming. Chemical antifoams control the symptoms, WITHOUT addressing the cause of the foaming. If a silicone antifoam, such as Alken Antifoam 880, is used, floc forming, beneficial bacteria will not be harmed, but some other chemical antifoams CAN damage the floc forming strains, giving the the filamentous species an even greater advantage, thereby increasing the problem. A newer option to knock down the foam and destabilize Nocardia is application of Alken Nu-Bind 1, a uniquely formulated product that combines a high-molecular-weight humified soil extract base, delivering settling through its natural cationic charge, with a talented consortium of floc-forming Bacillus, that produce high levels of protease, amylase, esterase, esterase-lipase, lipase, cellulase and xylanase By following initial treatment with Alken Clear-Flo 7015, complete control of the plant bulking and foaming can be restored in less than two weeks.|