Expression dewatering of mixed sludges

Filtration followed by expression characteristics of mixtures of clay and activated sludge are first reported in this study. Experimental results indicate that the average specific resistance of the mixed sludge exhibits an ideal-solution like behavior, that is, a linear combination of pure clay and activated sludges with the weight percentage as a parameter. In expression stage, nevertheless, the influence is highly nonlinear. The presence of a little amount of activated sludge can significantly increase both the expression creep effect and the portion of secondary consolidation. The consolidation stage data are interpreted by the Terzaghi-Voigt combined model, from which the model parameters are evaluated accordingly. As the activated sludge is added, both the difficulty of creeping of constituting particles within the sludge cake and the fraction of moisture attributed to the secondary consolidation increases rapidly, revealing a highly nonlinear characteristics. The dewatering efficiency of mixed sludge is discussed.