Heavy metal solids association in sewage sludges

• Published in: Water research (Oxford) 1989, Vol.23 (3), p.285-291
• Main Authors: Lake, D.L., Kirk, P.W.W., Lester, J.N.
• Format: Article
• Language: English
• Subjects: Applied sciences; complexation capacity; conditional stability constants; Exact sciences and technology; heavy metal complexation; heavy metal speciation; heavy metals; ion selective electrodes; Pollution; sewage sludge; Urban and domestic wastes; Wastes
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/0043-1354(89)90093-6

In order to study the metal binding characteristics of raw, activated and anaerobically digested sewage sludges, each sludge was passed through a range of filter pore sizes. Each filtrate was then subjected to complexation titration with cadmium, copper and lead using ion selective electrodes to follow the free metal ion concentration. Calibration of the electrodes was extended using metal-ion buffer standards. Conditional stability constants and complexation capacities were determined for each metal in each sludge fraction. The stability of complexes formed in each sludge type followed the general order copper > lead > cadmium. Both copper and lead formed more stable complexes in the treated sludges than in the raw sludge. In general, the capacities of raw and digested sludges to complex all three metals (in terms of unit mass of solids) decreased with increasing particle size. However, the converse was true for activated sludge, particularly for copper, suggesting a lesser contribution from surface area related phenomena. It is concluded that the digestion of sludge plays an important role in controlling the mobility and environmental dispersion of these metals.