Investigating Steam Application for Reducing Foaming in Activated Sludge Systems

Filamentous foam, the dispersion of gas bubbles that creates a dense brown scum layer on the surface of activated sludge basins and secondary clarifiers, is caused by the predominance of mycolic acid-containing actinomycetes, such as Gordonia amarae (formerly Nocardia amarae) and the filament Microthrix parvicella. The accumulation of foam causes a variety of operational, safety, and aesthetic problems in wastewater treatment plants. Current approaches for controlling foam include: operational adjustments, (e.g. decreasing mean cell residence times); additional structures (e.g. classifying selectors); and non-specific measures, such as water sprays, polymer addition, and chlorination. In particular, operational adjustment and nonspecific measures are hit-or-miss solutions. In this study, the use of steam to destroy filamentous foam-forming bacteria was explored as an alternative foam control measure. The effects of steam pressure (and thus temperature) and exposure time on decreasing filaments, foam potential, and foam stability, were evaluated. It was observed that nocardioforms became less abundant with increased levels of pressure and exposure time combinations, with the lowest abundance levels occurring at a treatment combination of 70 psi and 60 min. The data shows that the M. parvicella filaments do not respond to steam treatments as well as the nocardioforms. The results for foam potential and foam stability show that the foam potential is unaffected by steam treatments but the foam stability is greatly affected by the treatments. The approach shows promise in reducing foaming in activated sludge and subsequent downstream solids handling facilities, such as anaerobic digestion, especially for facilities that already have the equipment for steam production.