During Phase 4, no foaming incidents occurred in any of the three digesters. Digesters 1 and 4 were unmixed except for heated recirculation and no grit transfers or foam abatement were conducted in Digester 1. Grit transfers were conducted almost daily in Digester 4. Digester 2 was mixed 25% of the time, and only three grit transfers and foam abatement events were conducted over the entire Phase 4 duration. No foam was recorded during this period, despite a significant RG7227 in foam abatement procedures. G. amarae counts were estimated twice and were below the threshold levels.
During Phase 5, when all of the digesters were unmixed except for heated recirculation, no foaming events were recorded. However, of the nine filament counts conducted during this period, only the last one was above the threshold filament level. In the absence of high G. amarae counts as well as being unmixed, the digesters did not record any foaming incidents under both scenarios of operating with and without foam abatement. These results suggest that mixing is only a contributor to foaming if a primary cause is present. Therefore, there is no apparent effect of mixing on AD foaming during this phase due to lack of a primary cause of foaming, such as filaments in the feed sludge.