Degradation of digested sewage sludge in marine sediment-water model systems, and fate of metals

Cores of marine sediment were used in model systems to examine degradation of digested sewage sludge in the marine environment at the sediment-water interface. Models of both accumulative and dispersive sites were used, at sludge loadings greater than those applied at sea disposal sites. Mineralization to carbon dioxide was measured using an infra-red gas analyser, and the proportionate mineralization of the added organics increased as loading rate decreased. About 60% of the added organic carbon was mineralized at the lowest rate applied (0.01 kg solids m −2 · d −1) over the 133 days of the experiment. Metals added to the model systems in the sludge (Zn, Pb) were immobilized by the sediment and not exported from the model.