Selective recovery of alum from clarifier sludge using composite ion-exchange membranes

Alum recovery from clarifier sludge produced by water treatment plants has received considerable attention because of the following reasons: (1) Recovered alum can be reused in water treatment plants so that the operation cost of water treatment can be greatly reduced. (2) Since aluminum hydroxide constitutes almost 30%--50% of the total solid content in clarifier sludge, alum recovery will greatly reduce the volume of clarifier sludge. (3) The toxicity of free and complexed aluminum toward aquatic life has concerned many researchers. In recent years, alum recovery from clarifier sludge has been studied by many researchers. The most widely used method for alum recovery is acidic extraction using sulfuric acid. Because the acidic extraction process is nonselective, it is imperative to develop a selective process. The objectives of this study are to evaluate the feasibility of the two-step process for alum recovery, to understand the characteristics of the membranes: the strong acid membrane and the chelating membrane, and to evaluate the feasibility of recovered alum as a coagulant.