Heavy metal uptake by natural zeolite and metals partitioning in sewage sludge compost

A major limitation of land application of sewage sludge compost is the potential high heavy metal content due to the metal content of the original sludge. Zeolites may be useful as metal scavengers in metal-rich sludges. The natural zeolite, clinoptilolite has the ability to take up heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn). The aim of the reported work was to determine the metal forms most readily taken up by a natural zeolite when used as a bulking material during the composting process. Using a sequential extraction procedure in the raw sludge and in the final products after 150 days of maturity, the heavy metal content was associated with five fractions; the exchangeable, the carbonate, the reducible, the organic and the residual. It was found that a significant percentage of the metals not taken up by the zeolite was associated with the residual fraction, which is considered an inert form.