Effects of tannery sludge incineration slag pretreatment on sludge dewaterability

Chemical conditioning pretreatment does not always improve sludge dewaterability sufficiently for flocculated sludges with high compressibilities. In this study, tannery sludge incineration slag (TSIS) was used as a skeleton builder, in combination with cationic polyacrylamide (CPAM), to condition tannery sludge. The results showed that pretreating the sludge with a combination of TSIS and CPAM considerably improved sludge dewaterability over CPAM conditioning alone. The optimum TSIS and CPAM dosages were 150% dry solid (DS) and 10 kg/t DS, respectively, which generated a maximal net sludge solids yield (10.3 kg/m2 h) and a minimal time to filter (7 s). The negative charge of the sludge particles was neutralized by the positive charge of the dissolved metal ions of the TSIS, resulting in larger floc sizes. Compressibility and porosity measurements and scanning electron microscope (SEM) images indicated that the TSIS formed a porous and incompressible structure during mechanical dewatering.

The high compressibility of flocculated sludge results in sludge cake particles being deformed during the compression stage. The reduction of sludge filterability is due to the cake voids closed and, as a result, the formation of a layer of low permeability on the filter medium. However, in the case of flocculated TSIS-sludge, the sludge cake can form a permeable and more rigid lattice structures which prevent the formation of an impermeable layer of sludge.Figure optionsDownload as PowerPoint slideHighlights
► First scientific attempt to apply sludge incineration slag to sludge dewatering.
► Combine TSIS with CPAM present great advantages over CPAM conditioning alone.
► TSIS conditioned can destroy the surface electric double layers structure of sludge.
► TSIS aided to build incompressible and porous structure during mechanical dewatering.