Mechanisms for Overdosing in Sludge Conditioning

The mechanisms responsible for overdosing are studied using organic polymers as well as inorganic chemicals as sludge conditioners. Anaerobically stored sludges were used to minimize changes of sludge characteristics due to microbial activity within the period of experimentation. Conditioned sludge is considered as a two-phase system consisting of a liquid phase and a solid phase. Sludge dewaterability is characterized by capillary suction time (CST) and specific resistance to filtration (SRF), and the sludge liquid phase is characterized by its viscosity. Based on the experimental results, it is concluded that: overdosing is only associated with polymer conditioning; the traditional use of CST and SRF does not explicitly account for the mechanisms causing overdosing behavior; increasing viscosity of the liquid phase, not reduced flocculation performance, is primarily responsible for overdosing as measured by CST and SRF: and CST is incapable of detecting measurable changes in sludge dewaterability within a fairly wide range around the optimal polymer dosage.