Adsorption characteristics of dye onto sludge particulates

The dye adsorption characteristics of sludge particulates, both primary and secondary, were studied. Major factors such as pH, SS (suspended solid), a nd ionic strength on dye adsorption were evaluated. An anionic dye, new coc cine acid red #18 was used as the adsorbate. Results show that dye adsorpti on is a fast process and can reach equilibrium in 30 min. Results also show that pH is the most important factor determining the dye adsorption. Decre asing pH can significantly increase the adsorption of the dye. Greater adso rption density can be achieved at SS less than 1 g/L. However, at SS concen tration greater than 1 g/L, the dye adsorption density remains relatively u nchanged. It is found that the increase in the ionic strength decreases the dye adsorption density. Dye adsorption can be described by a multilayer ad sorption isotherm. The multilayer adsorption model allows the calculation o f both the monolayer adsorption density (i.e., the maximum first layer adso rption density) and the equilibrium constants for the first layer and subse quent adsorption. Based on the monolayer adsorption capacity, it is possibl e to determine the specific surface area of various sludge particles. (C) 1 998 Academic Press.