An Investigation for the Key Role of Surfactants in Activated Sludge Dewatering

Abstract

In this research, compared with common chemical extractants, the efficacies of extracting extracellular polymeric substances (EPS) from activated sludge using cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were studied. The results indicated that both CTAB and SDS had good extraction ability, and at the dosage of 0.2 g/g DS (dry solid), the amounts of the extracted EPS were 154.7 mg/g VSS and 77.6 mg/g VSS, respectively. SDS extracted EPS by its solubilization property, while CTAB extracted EPS by the synergistic effect of solubilization property, replacement of metal cation from activated sludge and release of intracellular materials. The dewatering performances of activated sludge conditioned with CTAB and SDS were also investigated. Capillary suction time (CST), water content in sludge cake and bound water were used to evaluate the sludge dewatering behaviours. The results showed that, compared with commercial cationic polyelectrolyte, CPAM, CTAB and SDS could significantly reduce the water content in sludge cake and bound water. However, SDS did not help in improving the filtration performance in the whole dosage range. For CTAB, only when the dosage was above 0.1 g/g DS, the filtration rate increased due to the reaggregation of dispersed sludge flocs. The dewatering performances of activated sludge conditioned with CTAB and SDS were dependent on detaching and dissolving of EPS from activated sludge, which resulted in the changes in sludge floc structure.