TABLE 2.

Summary of samples used in membrane hybridizations

Wastewater treatment plant	Type of activated sludge system, wastewater treated	Sample locations	Foaming frequency
San Francisco Southeast Water Pollution Control Plant, San Francisco, Calif.	High-purity oxygen, municipal wastewater	RAS, anaerobic digester sludge	Always
Richmond Wastewater Treatment Plant, Richmond, Calif.	Conventional, municipal wastewater	RAS, anaerobic digester sludge	Intermittent
City of Sacramento Regional Wastewater Treatment Plant, Sacramento, Calif.	High-purity oxygen, municipal wastewater	RAS, anaerobic digester sludge	Intermittent (summer)
Oakland East Bay Municipal Utilities District (EBMUD), Oakland, Calif.	High-purity oxygen, municipal wastewater	RAS, anaerobic digester sludge	Intermittent
Urbana-Champaign Sanitary District Northeast Treatment Plant, Urbana, Ill.	Contact stabilization municipal wastewater	Aeration tank foam, aeration tank mixed liquor, anaerobic digester foam, anaerobic digester sludge	Recurrent
Wisconsin	Completely mixed, milk-processing wastewater	Aeration tank foam, aeration tank mixed liquor	Frequent