COMPARISON OF SELECTED METHODS FOR RELATIVE ASSESSMENT OF SURFACE-CHARGE ON WASTE SLUDGE BIOMASS

Industrial pollution has directed much concern about contamination of fresh-water systems by metal-laden effluents. Research has shown that activated sludge has potential for the removal of heavy metals from co ntaminated effluents. Much of the biosorptive capacity of the sludge m ay be attributable to the net negative charge present on the sludge su rface, thus facilitating binding to positive metal cations. Detection of surface charge may serve as an excellent indicator of the adsorptio n potential of sludges and other potential biosorbents. Ten waste acti vated sludges were screened for surface charge using 3 different metho ds, viz., streaming current method, millivolt quantification method an d the colloid titration technique. All 3 methods were capable of detec ting surface charge and facilitated ranking of 10 sludges on the basis of electronegativity. Although charge determination using the titrati on method has most frequently been used, the millivolt quantification technique proved to be a more feasible and applicable method to detect surface charge of suspended sludge solids. The results from 3 methods employed showed that the sample from Southern Works, S9, was most ele ctronegative.