The aeration basins at West Point Treatment Plant in Seattle experienced periodic foaming caused by nocardiaform filamentous bacteria.
Although the foaming problem did not significantly affect significantly secondary effluent quality, it made process control more difficult by acting as a barrier for oxygen transfer to the bulk liquid. It was also linked to digester foaming, which proved harder to control. Digester foam can overflow the cover, cause pumps to become gas-bound and reduce digestion capacity.
Plant staff found it prudent to solve the problem at the source instead of downstream. Accordingly, they tested control of secondary process foaming through the addition of a cationic
