The identification and characterization of filamentous bacteria and their association with specific plant operating conditions and influent characteristics has been hampered because of morphological variations and differences between process configurations. A study was conducted to isolate and characterize the predominant filamentous bacteria observed in a foaming activated sludge treatment plant. The predominant foam-forming filament was isolated and characterized using microscopic, biochemical and molecular techniques. The phylogenetic analysis of the 16S rRNA gene confirmed that it was Nocardia farcinica, a typical filamentous foam-foaming pathogenic bacterium which is not widely reported outside of South Africa. The bacterium used a variety of substrates for its growth and showed greater affinity to larger and slowly biodegradable compounds. The N. farcinica grew well at temperatures ranging from 12 to 30 degrees C in R2A medium and with a pH ranging from 5.5 to 8.0 and an NaCl concentration of 1 to 5%. This range of conditions shows that N. farcinica can withstand extreme conditions, which results in its proliferation in foaming samples.