Extração sequencial de cobre e zinco em lodo de esgoto cultivado com capim elefante (Pennisetum purpureum) em diferentes períodos

Abstract

The use of sewage sludge in the agriculture has shown a good alternative for the final disposal of this waste, although there is environmental contamination risk with heavy metals. To mitigate this effect, the sludge phytoremediation can be done, it is fundamental to know the total amounts and chemical forms of the elements in the residue for analysis of their behavior and potential toxicity. Thus, this work aimed to evaluate, through the sequential extraction, Cu and Zn behavior, sewage sludge in cultivated with Pennisetum purpureum in different periods. The experiment was conducted in the greenhouse of the ICA / UFMG, using a randomized complete block. The treatments on 5 replicates corresponded to 5 times of P. purpureum cultivation in sewage sludge portions (30, 60, 90, 120 and 150 days from planting cuttings) and 1 control (sludge portion not cultivated). The total concentrations of Cu and Zn, observed in sewage sludge were below the critical limits of CONAMA Resolution 375, with a reduction of these values with the cultivation of Pennisetum purpureum. The plant cultivation for 150 days reduced the Zn concentration linked sulfides, compared to the unimproved sewage sludge. Furthermore, the increase of grass cultivation period caused a moderate decrease in sludge pH and intensive reduction in Zn concentration in the organic matter, beyond the initial increase and then decrease in the Zn concentration exchangeable on the carbonates on the sulfides and total. On the other hand, there was an increase of concentration of Zn and residual soluble, albeit with slight reduction of the latter at the end of cultivation. For Cu, the increase of the grass cultivation period, there was marked decrease in concentration of the element connected to sulfides and slight initial increase, with subsequent decrease in metal concentration in the residual medium. The maximum amount of Cu, sewage sludge extracted from the plant, occurred at 117 days of culture, while for the Zn, to 150 days. So for phytoremediation purposes of sewage sludge, especially for Zn, it recommended the planting of grass for a period of 150 days.