Flocculation-dewatering behavior of waste activated sludge particles under chemical conditioning with inorganic polymer flocculant: Effects of typical sludge properties

The effects of typical sludge properties (solids concentration, soluble extracellular polymeric substances (SEPS) and alkalinity) on waste activated sludge flocculation-dewatering behavior and mechanisms under chemical conditioning with inorganic polymer flocculant-polyaluminum chloride (PACl) were systematically examined in this study. The results indicated that increasing the solids concentration was conductive to sludge dewatering and could greatly decrease the PACl demand in chemical conditioning. Solids concentration had important effects on properties of sludge floc flocculated with PACl, floc structure was more compact and of low EPS concentration at high solids concentrations. High levels of SEPS were adverse to sludge dewaterability after flocculation with PACl, since the SEPS could interact with hydroxy-aluminium through complexation and increase the demand of coagulants. In addition, advantageous speciations of hydroxy-aluminium were rapidly converted into amorphous hydroxides with low flocculation activity at high alkalinity, so the sludge conditioning efficiency was greatly declined. At the same time, the dominant mechanism of chemical conditioning was changed from charge neutralization to sweep coagulation. Finally, this study provides control strategies at complex sludge properties for improving the effectiveness of PACl as a chemical conditioner.