“…[16], thus the specific surface area of the particulates can be calculated using the following equation: [18] where S ϭ the specific surface area (m 2 /g); ⌫ m ϭ the monolayer dye adsorption density (mol/g-SS); N ϭ the Avogadro's number (6.023 ϫ 10 23 molecules/mole); A ϭ the area occupied by a single dye molecule (m 2 /molecule). Comparing with other methods used for specific surface area determination, such as BET method (20,21) and permeametry (22), the dye adsorption method can be performed under in situ conditions. The primary, secondary, and tertiary sludge samples collected at different wastewater treatment plants in Wil- mington, DE, Philadelphia, PA, Baltimore, MD, and Washington, DC, at different times were used.…”