INFLUÊNCIA DO AMBIENTE TROPICAL EM LODOS GERADOS NA ESTAÇÃO DE TRATAMENTO DE ESGOTOS DE BARUERI-SP: COMPORTAMENTO DOS METAIS PESADOS

This study aims to characterize the geochemical behavior of Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn incorporated into the sludges produced at Wastewater Treatment Plant (WTP) of Barueri, SP, contrasting the average metal content of the fresh sludges with metal content measured in the same sludges after their exposition to natural tropical climate conditions for about 15 months. The effects of sludges on the soil were also observed. The WTP of Barueri processes sewages from the Sao Paulo Metropolitan Region applying an activated sludge method followed by anaerobic digestion and chemical coagulation with precipitation by Fel3 and Ca(OH)2. Metal content and pH of the produced sludge ("fresh waste") are ordinarily measured by periodical monitoring at WTP. The fresh waste was cumulatively disposed directly over the soil in open air for about 15 months until forming a 2,20m thick layer. During this study, this air-exposed waste ("disposed waste") and the undrlying soil were sampled for determination of pH and heavy metal (Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) content. Results of the analyses showed significant removal of the metais originarily incorporated into the sludge. A superficial l,30m thick layer soil retained small amount of dissolved metais. Anomalous values at deeper zones of the soil profile were obtained only for Ag and Cu. The removal of heavy metais from sludges with no significant retention by the soil below suggests that heavy metais must have remained in solution. Therefore, heavy metais may reach both surface and groundwater, as well as the biota.