Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: V. Leite x
  • Refine by Access: All Content x
Clear All Modify Search

In recent decades, nitrogenous compounds, arising from various anthropogenic sources, have become significant components of precipitation and have been shown to have some profound effects on both species richness and dominance of some plant communities. To examine how nitrogen addition can affect the species composition of Central Great Plains prairie plant communities, we applied N fertilizer at five levels for each of five consecutive years at two sites in south-central Kansas with similar rainfall and temperature regimes. One site was a tallgrass prairie and the other was a sand prairie community. The treatments consisted of N additions at the rate of 0, 5, 10, 20, and 40 g N/m2 in the form of solid urea. Within permanent plots, we monitored annually species richness and evenness, and percentage cover by cool-season graminoids, N-fixing species, and annual/biennial species. All these measures varied considerably among years at both sites, but N treatment effects were evident at the sand prairie site only. At the sand prairie, in general species richness and percentage cover by legumes declined with N addition. Moreover, species were excluded non-randomly from N addition plots, with several species apparently particularly intolerant of N addition. The results reinforce a relationship, observed in Europe and the northern Great Plains, between N addition and plant biodiversity decline in grassland communities, and may point to a serious conservation concern for rare species under a chronic regime  of N-enhanced precipitation.

Restricted access

Abstract  

The present study describes the aerobic biodegradation process of a mixture of sanitary sewage sludge and lubricating oil. TG/DTG curves confirmed that the applied aerobic biological treatment decreased the organic material content and caused significant modifications in the thermal behavior of the studied substrates after the functioning period.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
A. Barros
,
S. Prasad
,
V. Leite
,
A. Souza
,
G. Marino
,
Crislene Morais
, and
Marta Conceição

Abstract  

The present study was carried out for evaluating the retention behavior of sanitary sewage in relation to cadmium and cobalt ions in an ascendant continuous-flow reactor. It was found that the studied sludge presented a high assimilation of the metals, probably due to the presence of anionic groups, which favors adsorption and complexation processes. Thermal analyses of the samples showed a shift in the thermal decomposition of the ‘in natura’ sludge, when compared with those of the samples spiked with the metals, confirming the possibility of interactions between the heavy metals and the anionic groups present in the sludge.

Restricted access

Abstract  

Isothermal decomposition kinetic of three lanthanide mixed complexes with the general formula of Ln(thd)3phen (where Ln=Nd3+, Sm3+ or Er3+, thd=2,2,6,6-tetramethyl-3,5-heptanodione and phen=1,10-phenanthroline) has been studied in this work. The powders were characterized by their melting point, elemental analysis, FTIR spectroscopy and thermogravimetry. The isothermal TG curves have been recorded under the same conditions at 265–285, 265–285 and 250–270°C for Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen, respectively. The kinetic parameters, i.e. activation energy, reaction order and frequency factor were obtained through the technique of lineal regression using the relation g(α)=kt+g 0. The analysis was done at decomposed fractions between 0.10–0.90. The values of activation energy were: 114.10, 114.24 and 115.04 kJ mol–1 for the Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen complexes, respectively. The kinetic models that best described the isothermal decomposition reaction the complexes were R1 and R2. The values of activation energy suggests the following decreasing order of stability: Nd(thd)3phen<Sm(thd)3phen<Er(thd)3phen.

Restricted access

Abstract

In the present study, TiO2 nanopowder was partially coated with Al2O3 precursors generated by a polymeric precursor method in aqueous solution. The system of nanocoated particles formed an ultra thin structure on the TiO2 nanoparticle surfaces, where the particle is the core and the nanocoating (additive) is the shell. The nanocoating process led to the obtainment of nanoparticles with important surface characteristics and catalytic behavior in the bioethanol dehydration reaction, with improved activity and particular selectivity in comparison to their non-coated analogs. Ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased with increasing Al2O3 content in the catalysts. It is important to highlight that the TiO2–Al2O3 catalysts presented satisfactory values of selectivity toward hydrogen, in spite of the deactivation observed during the period of the test.

Restricted access

Abstract  

The conventional treatments of effluents containing heavy metals produce significant quantities of byproducts with recalcitrant characteristics, making necessary looking after alternative techniques in order to avoid the production of new contaminated residues. Sorption process of chromium and zinc in vertical columns loaded with sewage sludge and organic solid waste has been studied in this work. The data from the TG curves of the two sorbents presented significant differences when they were submitted to the metal uptake, being noticed the displacement of the thermal events towards lower temperatures for both types of sorbents studied. As it was expected, for both sorbents, an increase in the mass of samples has been observed at the completion of the thermal tests upon metal uptake. Therefore, these facts demonstrate that during the biosorption process a physico-chemical interaction took place between sorbents and metals, as it was evidenced by the more than 100 K increase in the decomposition temperatures as well as the variation of the ΔH values of the samples.

Restricted access