Fitorremediação de metais pesados e clorobenzenos em lodo de esgoto cultivado com Pennisetum purpureum

Abstract

A major limitation of sewage sludge agricultural use is the presence of pollutants, which can affect the environment and the health of living beings. Therefore, efforts should be made in order to develop efficient techniques to reduce these contaminants in waste, especially those related to phytoremediation processes, which are inexpensive and easy to apply. The objective of this study was to evaluate the effect of cultivation in sewage sludge on heavy metal and chlorobenzenes 1,4-CB and 1,3,5-CB concentrations, seeking the safe use of this waste in agriculture. The experiment was conducted at the ICA/UFMG greenhouse, during 150 days, using a randomized block design. The treatments, 5 replicates, corresponded to 5 periods of Pennisetum purpureum Schum. cultivation in sewage sludge portions (30, 60, 90, 120 and 150 days from planting cuttings) and two controls (sludge uncultivated plots and planting of grass on the ground). After 150 days the grasses grown in soil showed the total dry mass of 1.5 times that of plants grown in the residue. In the sewage sludge and grassy organic tissues were only detected As, Cu and Zn, but only the last two components were present in the composition of phytolith. The kidnapping of Zn and Cu in phytoliths is highly relevant because it may be related to failure to detect phytotoxic effects of these metals on the grass. In addition, the chemical stability presented by these siliceous structures guarantees the permanent removal of these elements of the food chain. Although, the grass under study have not framed in hyperaccumulator plant criteria, the high biomass production and phytoliths the leverages for use in cultivation in sewage sludge systems. During the monitoring of chlorobenzenes was observed that after 30 days of cultivation the sewage sludge plots showed increases in levels of 1,4-CB and 1,3,5-CB on the order of 15.5 and 8.36 times, respectively, the contents found in the sewage sludge before the start of cultivation. After 150 days there were no significant differences between the concentrations of 1,4-CB control (not cultivated) and treatment with the plant grown in sewage sludge. On the other hand, the control, at 0-10 and 10-20 cm, showed higher concentrations of 1,3,5-CB, compared to the same depths grown sewage sludge. The permanence of chlorobenzenes over time may be related to contaminant chemical structure, which has characteristics recalcitrant to decomposition. However, the sludge grown in 10-20 cm depth, there was a decrease in the concentrations of 1,4-CB, while at a depth of 20-30 cm, both concentrations of 1,4-CB and 1,3,5-CB decreased. The observed reductions may be the result of interactions between mutualistic decomposing microorganisms and the roots of P. purpureum, which promotes decomposition.