Biodegradation experiments of the non-ionic surfactants Igepal C-620 (an alkyl-phenol ethoxylate) and Neodol 25-7 (an alcohol ethoxylate) were performed, and biodegradation assessed by concentration, foam potential and surface tension measurements. Igepal C-62 0 biodegraded much slower than Neodol 25-7. The foaming of activated sludge was significantly enhanced by the presence of surfactants, but surfactants alone could not generate a stable foam if the sludge did not contain Nocardia cells. It was also found that products of surfactant biodegradation which were not detected by standard non-ionic surfactant analysis method (CTAS) might still possess some foam-enhancing ability. The results indicate that slowly biodegradable surfactants can enhance the foaming of Nocardia-containing sludge and increase the trapping of Nocardia foam in activated sludge plants.

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