D. Petruzzelli et al., Selective recovery of coagulants from water clarifier sludge by the use offibrous ion exchangers, SOLVENT EXT, 17(6), 1999, pp. 1587-1602
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.