Biosolids as Gels: A New Way of Looking at Conditioning and Dewatering

Fundamental improvements in conditioning and dewatering can be accomplished with an accurate understanding of the biosolids being processed. Historically, the structures of sludges and biosolids have often been likened to systems of rigid pArticles suspended in water. A new insight has been developed recently in which biosolids are characterized as a “gel.” In this work, physical characterizations of activated sludge, digested biosolids, and synthetic gel suspensions are compared and explained using this conceptual model. Physical appearance of the sludges at the micron level, using Scanning Electron Microscopy (SEM), verify this gel-like matrix structure. Characterizations by swelling and deswelling ability, shear resistance, and rheometric behavior were shown to be consistent with this model as well. Even if the matrix structure has embedded pArticles, the gel structure is still the major factor that affects conditioning and dewaterability. Thus, breaking the gel structure that retains water may lead to an improvement in dewaterability.