Distribución química de plomo, cromo y cadmio en lodos cloacales y sus cenizas

A five-step sequential extraction method was applied to determine the distribution of Pb, Cr and Cd in sewage sludge, and ashes produced by incineration, collected at the wastewater treatment plant. Sewage sludge can contain high concentrations of heavy metals and most heavy metals are present in the ashes and dust produced by incineration. The different ways of sewage sludge disposition are: as fertilizer, landfilling, ocean dumping– theoretically forbidden since 1998, and the incineration. At the moment, most of the municipalities in Argentina are trying to adopt landfilling and biocomposting as main alternatives for the final disposition of sewage sludge. The use of sludge as soil conditioner and their incineration were studied. In the sequential extraction of sewage sludge and its ash, the rates of Cr and Cd associated with the fraction soluble in water, soluble in acidic substances and easily reducible is considerably high. This aspect must be considered when the sewage sludge is used as a source of nutrients for plants and soil conditioner because this proportion of heavy metals can be easily removed. Other aspect to consider is the release of heavy metals during sludge combustion. The same fraction of heavy metals is easily released during this phenomenon and requires a scrubber to be retained. In the case of the ashes, this type of solid waste should be categorized as hazardous waste and therefore care should be taken in its final disposition.