Floc Structure and Its Impact on Conditioning, Dewatering and Digestion

Recent experiments in our laboratories have focused on evaluation the structure of floc and the role this structure plays in conditioning requirements, dewatering behavior and the changes in sludge properties that occur with digestion. It has been found that colloidal protein in solution, which originates from the biopolymer matrix of floc plays a critical role in conditioning and dewatering. Protein is released from the floc structure as a result of excessive mixing or when monovalent cations increase in proportion to divalent cations. These proteins are directly related to the optimal polymer conditioning dose and to the dewatering rate. For digestion processes, anaerobic and aerobic digestion processes differ markedly in term of their impact on conditioning and dewatering. The deterioration in sludges resulting from anaerobic digestion appears to be due to protein released from iron that undergoes reduction in the anaerobic environment. Aerobic digestion results in protein degradation and release of colloidal polysaccharides. These contribute to conditioner requirements and account for differences between anaerobic and aerobic sludge conditioner selection and results.