RELATIONSHIP BETWEEN TEMPERATURE AND GROWTH OF ORGANISMS CAUSING NOCARDIA FOAMS IN ACTIVATED-SLUDGE PLANTS

Foaming, an operational problem in activated sludge plants, is commonl y caused by actinomycetes of the genera Nocardia, Rhodococcus, Gordona , Tsukamurella and Mycobacterium, and such foams are often referred to as Nocardia foams. This paper addresses conflicting reports about the temperature at which foaming occurs by determining the temperatures a t which various nocardioforms will grow in pure culture. Strains teste d included foam isolates, type strains of organisms reported in the li terature to be involved In foaming, and type strains of related actino mycetes. The data showed that all three categories contained organisms that grew at 5 degrees C, and these were principally Rhodococcus spp. Thus the so-called Nocardia foams at low temperatures are more likely to be caused by Rhodococcus species. Although some foam isolates, esp ecially Nocardia pinensis, grew over a relatively narrow range of temp eratures, this growth range is still sufficient for them to cause prob lems in many plants. A few isolates grew at 40 degrees C or higher, su ggesting these were more likely to occur in plants treating warm waste water or possibly could grow in foam where ambient air temperature is high.