Landfill is a prevalent method for wastewater sludge disposal. Laboratory tests were conducted to study engineering property of sludge solidified by fly ash
lime and silty clay of varied ratios. The experiment results revealed that the strength of solidified sludge was as high as it is required for landfill; and permeability was improved significantly. Using freeze-drying technology and scanning electron microscope (SEM)
the microstructure of solidified sludge is studied. It is found that the compactness of sludge was improved after solidification
which is an important reason for strength improvement. Applying theory of fractal geometry
quantitative analysis is carried out on the SEM images. The analysis reveals a considerable positive correlation between fractal dimension and strength.