Zn, Ni, Cu, Fe and S in sewage sludge: chemical behaviour, adsorption and treatment proposal / Zn, Ni, Cr, Cu, Fe e S em Iodo de esgoto: comportamento químico, adsorção e proposta de tratamento

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The increase of the wastewater treated volume in Brazil has demanded alternatives to the sewage sludge final disposal. At first, agricultural use is one of the viable recommendations since sludge is rich in organic matter, macro and micronutrients necessary to the fertility of the soil. However, it is necessary to consider the environmental impact of some of these elements such as Hg, As, Cd, Pb, Ag, Cu, Zn among others, on the soil, biota and surface and subterranean water. ETE Barueri is the biggest treatment plant in the state of São Paulo and receives domestic and industrial effluents and for this reason heavy metals are found in the sludge in contents highly above those allowed by federal Brazilian legislation (CONAMA, 2006). Based on these aspects this study mainly investigated the fluctuation in the concentration of the elements Zn, Ni, Cr, Cu and Fe in 30 samples of sludge, collected in the rainy and dry periods, over a year, in order to check: the influence of seasonality on its quality for agricultural purposes; their possible associations with other elements and its distribution in the solid phase in the sludge matrix (exchangeable ions fraction, organic matter fraction, humic and fulvic acids fraction, carbonates fraction, iron and manganese oxihydroxides fraction) as well as the adsorption capability of these metals by the peat, as a recommendation for treatment. The methods used for this research included the chemical analysis by ICP-OES and X-ray fluorescence (FRX), their statistical analysis, the chemical fractionation, the infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive scan (EDS), the X-ray diffraction (XRD), the thermal analysis and the isotopic ratios analysis ?34S. The last four techniques were used, specially, to investigate the origin of the sulphur present in the sludge. The adsorption experiments with the peat were conducted in bulk. The obtained results showed that the concentrations of several of the chemical elements present in the sewage sludge, among them nickel, zinc and sulphur, varied in relation to the pluvial precipitations, often being above values allowed by legislation. It was also found that the greater percentages of the metals in the sewage sludge were associated with the fraction of the poorly crystallised iron oxihydroxides and not with the organic matter, a rather relevant component of its matrix. In the organic matter fraction, the amount of copper was the highest amongst the other elements. The FTIR spectrums indicated the low decomposition degree of that organic matter. Human feces, surfactants and fossil fuels appeared as probable origin of the sulphur in the sludge. The "rainwater solution" extracted nickel and copper from the sewage sludge in the experiments in bulk, and the peat adsorbed the nickel preferably to the copper. The percentages of Zn and Ni, associated with the humic and fulvic acids, retained by the peat, were higher in pH 6,5 than in pH 8,5. The copper had the opposite behaviour. The results obtained allow us to state that any utilization of this type of sludge requires previous treatment.

ASSUNTO(S)

metais pesados sewage sludge adsorption lodo de esgoto fractionation heavy metals comportamento químico sulphur adsorção

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