Evaluation of the chemical aspects of sludge in sewage treatment stations of Maringá, state of Paraná, Brazil

Abstract

The aim of this research was to evaluate the amount of some metals and nutrients in the sludge of the sewage treatment stations (STS) of Maringá. During the year samples of sludge were collected at STS-2 and STS-3. Previously dried and ground the sludge samples at constant weights were digested by aqua regia. The reading of metal concentrations was made by atomic absorption spectrometry. Nitrogen and carbon were determined by the respective classical methods. Concentration results in total averages were the following, in %: N, 3.04; C, 29.3; Al, 2.93; in mg.g^-1: Ca, 9.31; Mg, 1.93; K, 0.900; Cu, 0.851; Zn, 1.66; Mn, 1.13; Fe, 83.5; in µg.g^-1: Pb, 96.6; Cr, 88.9; Cd, 1.42; in ng.g^-1: Hg, 6.7 respectively. The STS-2 presented the highest levels of macronutrients and a C:N ratio close to 10:1. With regard to heavy metals, copper was the only one that exceeded the average total level found in literature. For total sludge analyzed, copper is the most restricting element for sludge application to agricultural soils.