Cinética de degradação microbiológica de torta de filtro no solo na presença de cádmio e níquel. / Filter cake microbiologycal degradation kinetics in soil on the presence of cadmium and nickel.




It was evaluated the effect of doses of nickel and cadmium on the degradation of the organic matter applied to soil by means of filter cake in a respirometry trial. Soil employed was Latossolo Vermelho Amarelo, sampled in the field at depth of 0-20 cm. It were applied doses of 0; 28; 56; 112 and 200 mg kg-1 Cd and 0; 62,5; 125; 250 and 500 mg kg-1 Ni as CdCl2.2,5H2O and NiCl2.6H2O, respectively. The filter cake doses were 0, 40, 80 e 120 Mg ha-1, defined in a sugarcane crop basis. In the start of the experiment, a require metals mass was added to 800g soil mass, after filter cake incorporation. It were applied 2 liter glass flask with a closed stopple. Soil moisture was adjusted to 80% of the water holding capacity value and the incubation carried out at 28 degrees Celsius during 72 days. The two trials, one for nickel and the other for cadmium, were established in a 5 x 4 factorial and fully randomized design with 3 replications. The CO2 gas evolved from soil due to microbial respiration was absorbed in a fixed volume of NaOH solution and its amount was then estimated by a condutometric method. After the incubation period the soil pH and the metal content extracted by the DTPA-TEA pH 7,3 solution were determined. Respiratory curves were established through the accumulated amount of CO2 evolved from soil using a double phase first order kinetics model and the metal effect was analyzed with basis on the first order rate constants. The metals effect was evaluated in constant velocity role obtained by adjusts. Considering the soil pH, measured at the end of the incubation period, it was observed a trend of pH increasing as doses of cadmium increase, applied on the greater filter cake doses. Concerning nickel, in filter cake absence or in the 40 Mg ha-1 dose of there was no response and the most expressive effect of pH rising occurred in dose of 120 Mg ha-1 of filter cake in the presence of 500 mg kg-1 nickel. In general the extraction of cadmium in the soil, at the end of the experiment, by solution DTPA-TEA pH 7,3 was greater than nickel. The filter cake affected more the efficiency extraction of nickel than cadmium. The accumulated total CO2 production was affected negatively as cadmium as for nickel in direct ratio to the doses of the metals. It was still observed a positive effect of metals on the degradation speed of filter cake organic matter. The kinetic parameters indicated that, under effect of studied metals, the filter cake is degraded in a lesser ratio, but in a faster manner. Considering the percentage of organic material degradation, it was concluded that the negative effect of cadmium and nickel was similar, with a reduction of 46 and 48 %, respectively. The cadmium effect on the degradation was more pronounced with 50 mg kg-1, while the nickel effect rose linearly with metal doses increase.


agricultural wastes cádmio metal pesado no solo soil microbiology cinética química microbiologia do solo cadmium nickel heavy metal in soil resíduos agrícolas níquel chemical kinetics

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