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 agriculture increases heavy metal contamination in soils. This demands controlled use to avoid hazardous situations. This work measures the heavy metals content in sludge and its potential as a fertilizer in agriculture. Samples were collected from the Penha urban sewage plant, the largest in Rio de Janeiro. Heavy metals (Cd, Zn, Cu, Pb and Ni), were measured by atomic absorption spectrometry after sludge digestion with 4N nitric acid, and showed slightly higher concentrations of Pb compared to 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 following parameters: N, P, K, Ca, Mg, Na, Al, CEC and organic matter. A slight fertility enhancement could be observed. Salination risk with higher amount of sludge input in podzol soils, frequent in these coastal regions, needs monitoring.