CHARACTERIZATION AND DEWATERING OF ACTIVATED-SLUDGE FROM THE PULP ANDPAPER-INDUSTRY

Floc properties and dewatering of activated sludge from the pulp and p aper industry were studied prior to and after an oxidative conditionin g using Fenton's reagent. Sludge samples were taken from four treatmen t plants, which differed with respect to organic loadings and wastewat er source. Poor dewaterability was typical of heavily loaded sludges a nd a positive correlation between filtrability and the concentration o f exopolysaccharides was observed. Oxidative conditioning improved the dewaterability of all the sludges tested, but especially that of heav ily loaded sludges. Lab-scale piston press results were also comparabl e with those of controls conditioned with polyelectrolytes. As a resul t of the conditioning, the surface charge density of the flocs decreas ed and the contact angles of filter cakes were increased, which enhanc ed flocculation and settleability. It is possible that hydroxyl groups am oxidized during the oxidative treatment to carboxyl groups, which are more hydrophobic at low pH. This hypothesis was partly supported b y FTIR-analysis, but obviously other mechanisms were also involved.