Selective Alum Recovery From Clarifier Sludge

Hoping to save money and to reduce solid waste, water utilities are evaluating various alternatives for the disposal of clarifier sludge containing 30 to 50 percent hydrated aluminum hydroxide. In this work, the authors studied a selective, simple‐to‐operate alum recovery process using composite membranes made of fine particles of chelating polymers entrapped in thin sheets of porous polytetrafluoroethylene. Laboratory studies using the sludge from the Allentown (Pa.) Water Treatment Plant showed that alum can be recovered selectively without any significant carryover of organic matter (trihalomethane precursors), manganese, or other heavy metals into the recovered alum. The composite membrane was quite robust and durable and exhibited a high affinity toward dissolved aluminum.