The Effect of Bound Water on Filtration and Consolidation Characteristics of Excess Activated Sludge Treated by Freezing and Thawing Treatment

Activated sludge has bound water which adheres tightly to the surface and in the inside of suspended solid (microorganisms). To study the effect of the bound water on the filtration and consolidation characteristics, the wet basis average specific filtration resistance αav.w (base solid contains the bound water) and the wet basis modified consolidation coefficient Ce.w are rationally derived and compared with the dry basis ones αav.d, Ce.d (base solid does not contain the bound water) which have been used conventionally. The wet and dry basis filtration and consolidation characteristics are measured using both the sewage excess activated sludge and that treated by the freezing and thawing treatment. αav, w is determined from the constant pressure filtering test by the analytical method proposed in this paper. The value of αav.w is smaller than that of the dry basis one. The measured values of αav.w for the excess activated sludge decrease to about one-fifty fifth by the freezing and thawing process and the improvement of the filtration characteristics is very large. Ce.w is also determined from the constant pressure consolidation test by the analytical method proposed in this paper. The values of Ce. w are larger than those of the dry basis one, and nearly constant in the applied pressure range (p= 206 2950 kPa) of this experiment.