Enhancement of the Settling and Dewatering Properties of Activated Sludge by Humus Soil

This study has investigated in a comparative fashion the effect of cations and humus soil on the settling and dewatering of activated sludge. The results from experiments indicate that humus soil could enhance the settling and dewatering properties of activated sludge. Cations leaching from the humus soil played an important role in improving settling and dewatering of activated sludge. Divalent cations, Ca²⁺ and Mg²⁺, had positive effects on the sludge characteristics, while the settling and dewatering was not affected or slightly deteriorated by the monovalent cations, K⁺ and Na⁺. Reduction of sludge volume index (SVI) with an increase of humus soil or equivalent addition was remarkable, while the zone setting velocity (ZSV) increased. The capillary suction time (CST) decreased with increasing dosage of the humus soil power or equivalent cations; however, cake solids content was calibrated against the humus soil or equivalent cations. Improvement in dewaterability of the sludge by addition of humus soil was higher than that of equivalent cations mixture. With the contract time, the humus soil also could enhance the settling and dewatering of the sludge.