Scum formation and consolidation in covered anaerobic lagoons

Abstract

Scum builds up in covered anerobic lagoons that reduces hydraulic retention time, inhibits biogas capture, and damages lagoon covers. We demonstrate that the majority of this biomass sinks when degassed, indicating it mostly consists of undigested sludge floated by biogas. Thus, scum accumulation is inevitable and is not prevented by source control of fats, oils and floating debris; scum must be periodically and mechanically removed. We develop a theory of scum consolidation and desaturation driven by buoyancy and evaporation, and measure scum permeability and compressibility, to predict scum behaviour. Continued scum accumulation leads to densification and eventually crusting. The recommend..