HEAVY-METALS IN SLUDGE FROM THE SEWAGE-TREATMENT PLANT OF RIO-DE-JANEIRO

The final disposal of sewage sludge on soils as a compost for agricult ure increases heavy metal contamination in soils. This demands control led use to avoid hazardous situations. This work measures the heavy me tals content in sludge and its potential as a fertilizer in agricultur e. Samples were collected from the Penha urban sewage plant, the large st in Rio de Janeiro. Heavy metals (Cd, Zn, Cu, Pb and Ni), were measu red by atomic absorption spectrometry after sludge digestion with 4N n itric acid, and showed slightly higher concentrations of Pb compared t o other sludge from other origins. Soil treated with 2, 5 and 10 tons of sewage sludge/ha and control after 60 days was analysed for the fol lowing parameters: N, P, K, Ca, Mg, Na, Al, CEC and organic matter. A slight fertility enhancement could be observed. Salination risk with h igher amount of sludge input in podzol soils, frequent in these coasta l regions, needs monitoring.