What causes classic sludge bulking?

Classic sludge bulking is primarily caused by younger sludge, which refers to immature biomass that has not yet developed the characteristics necessary to settle properly. Younger microorganisms are often still in the exponential growth phase, leading to a higher production of floating and filaments that do not compact well during sedimentation.

This immature biomass lacks the means to effectively settle in the aerobic digestion process, as it does not have the cellular density needed to overcome buoyancy. The presence of excessive flocculation as a result of young, active microorganisms leads to a fluffy and less cohesive blanket of sludge, exacerbating issues with separation in secondary treatment processes.

In contrast, older sludge or more mature biomass tends to have developed better settling characteristics. The presence of adequate oxygen levels generally supports healthy microbial activity without causing bulking, while excessive nutrients might contribute to population growth but do not directly define the bulking phenomenon in the presence of younger sludge. Overall, it's the predominance of younger sludge that is crucial in causing classic sludge bulking.