HEAVY-METALS AND DISPOSAL ALTERNATIVES FOR AN ANAEROBIC SEWAGE-SLUDGE

Treatment of wastewater unavoidably results in the generation of huge quantities of sludge in which pollutants concentrate and which must be disposed of. There may be significant levels not only of salts and or ganic pollutants, but also of heavy metals, which are of particular co ncern. The presence of these substances causes environmental damage in soil, plants, groundwater and air. The classical disposal alternative s at hand include thermal treatment (incineration), land application a nd ocean dumping, all of these being objectionable to some extent beca use of major problems created by the pollutants in the sludge. Knowled ge of the heavy metal content of the sludge is a key step in selecting or in ruling out the various disposal alternatives. An anaerobically stabilized sewage sludge from an urban-residential wastewater treatmen t facility has been collected and studied in order to identify the mos t suitable disposal alternative. The sludge has been analyzed for its calorific value and heavy metal content. Sequential chemical extractio n of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Ph, Zn) has been carried ou t using selective extractants in order to determine changes which occu r in the chemical partitioning of heavy metals in the present use as f ertilizer. Significant concentrations of lead, copper and zinc have be en found, but metals levels in the sludge are within the limits establ ished for its use in agriculture. Lixiviation of the metals into seawa ter has also been explored. Lead, cadmium and chromium are noticeably lixiviated.