Correlating sludge constituents with digester foaming risk using sludge foam potential and rheology

Foam potential and viscometer ramp tests (VRTs) were conducted for three municipal wastewater treatment plants to determine if these methods can relate to mechanisms of foaming to physical and biological constituents in sludge. At all plants, digester volatile solids (VS) concentration correlated (R² > 0.41) with increases in plastic viscosity, a VRT parameter corresponding to foaming risk. Plastic viscosity also correlated with foam-causing bacteria Gordonia (R² = 0.38). Foam potential test values increased with Microthrix parvicella (R²> 0.28). For one plant, suspected foam-causing bacteria Mycobacterium negatively correlated with parameters representing foam risk. Microscopic filament counting correlated (R² = 0.97) with quantitative polymerase chain reaction (qPCR) for Gordonia, suggesting that the more accessible counting method can reliably quantify foam-causing bacteria. Foam potential tests and VRTs resulted in plant-specific correlations with foam-related constituents. Therefore, these tests may provide useful evidence when investigating causes of digester foam events.