A compressional rheological approach to characterize biosludge with implications to dewatering

Biosludge is a complex material, and it often presents challenges in industries such as the pulp and paper sector, particularly during dewatering processes. This study investigates the mechanical behavior of the biosludge using compressional rheology to understand the factors governing cake formation, permeability, and compressibility. Our findings reveal that increasing the solids concentration from ∼5 to ∼10 wt. % results in a substantial reduction in permeability, decreasing it by over an order of magnitude and thereby limiting dewatering efficiency. This increase in solids concentration also leads to a marked rise in compressive yield stress. Additionally, as compression progresses, the shear yield stress intensifies, and the storage and loss moduli become more pronounced. Consequently, as water is progressively removed, the material exhibits greater resistance to flow under applied stress. However, the addition of a positively charged polymer (cationic polyacrylamide) enhances dewaterability by increasing permeability, reducing compressive yield stress, and increasing the shear yield stress. Furthermore, the study identifies an optimal compression velocity crucial for effective water removal, balancing interconnected network formation and water migration. This study provides a fundamental understanding of the limitations inherent to the dewatering process and offers a quantitative framework to evaluate the role of polymer addition in enhancing dewaterability.