Foam Busters: Investigating the Causes of Foaming in Anaerobic Digesters

The Hill Canyon Treatment Plant (HCTP) implemented primary sludge (PS) and waste activated sludge (WAS) co-thickening to increase the digester capacity and decrease the dewatering costs. This operational change coincided with the appearance of digester foaming in the three conventional mesophilic anaerobic digesters. The objective of this study was to identify site-specific factors that could affect foaming at HCTP. Our digester foaming investigation included foam potential tests, surfactant analyses, and microbiological analyses. Digester 1 showed a high foaming potential and unstable foam while Digester 2 and 3 samples did not foam. Samples from the three digesters showed surfactant levels that could contribute to foam stability. The levels in Digester No. 1 were 12% higher than levels in the other two digesters, potentially making it more susceptible to foaming. Fluorescence in situ hybridization (FISH) results showed that archaea filaments were present in the foam samples, which are known foaming causing organisms. Thus, filamentous organisms and surfactants in the feed may contribute to foaming in the anaerobic digesters.