Selective recovery of coagulants from water clarifier sludge by the use offibrous ion exchangers

A new technology for removal and recovery of coagulants from water clarifie r sludge has been optimized at laboratory scale pilot plant level. The proc ess is based on the use fibrous exchangers showing good kinetic and thermod ynamic performance toward coagulant species (Al, Fe) present in the acidic leachate (pH 3.5) from water clarifier sludge. The innovation allows for th e solution of the environmental problem related to clarifier sludge disposa l (residual solids after metals leaching are safely applied to land), and q uantitative recovery of coagulants to the water potabilisation operations. Process optimisation, by using real clarifier sludge from the Sinni River W ater Works (Apulian Water Authority, S.E. Italy), was carried-out and resul ts are illustrated in the paper. A commercial weak cation fibrous exchanger (Fiban K4) with carboxylate functionality, selectively removed aluminium a nd ferric species in "moving bed" unit operations with the resin re-circula ting through the stationary exhaustion and regeneration baths. Resin regene ration was efficiently carried-out by the use of 0.4M NaOH solution for qua ntitative recovery of almost pure coagulants, ready for reuse. Together wit h process optimisation, the paper also reports some mechanistic indications on the fibrous resin performance toward polyvalent metal species retention at the resin functional groups.