Establishment of the Permeability Model for Soft Solid Sludge Conditioned with Flocculants

Permeability plays a decisive role in the dewatering process and reflects the difficulty of filtration, especially for soft solid material such as sludge. In this paper, the physicochemical properties and dewatering performance of sludge conditioned with different kinds of flocculants were investigated. Results showed that the flocculant could change the sludge microstructure such as floc morphology, specific surface area, and fractal dimension. Compared with filtration pressure, flocculants had a greater influence on sludge permeability which was a significant negative correlation with filtration pressure and was a positive correlation with flocculant dosage. In order to describe the fact that fluid flows through the porous voids for soft solid sludge, the improved Kozeny constant was corrected. Research showed that permeability was more significant in the dewatering process for the sludge conditioned with inorganic flocculants than that with organic flocculants. The Kozeny constant was not only relevant with suspension nature but also with filtration pressure. The range of the improved Kozeny constant was reasonably determined based on flocculant type, concentration, and filtration pressure, which was of great help to project applications. For raw sludge, the improved Kozeny constant was 958 times than that of the original value, and it decreased significantly for conditioned sludge.