Célia Regina Granhen Tavares

BACTERIAL POPULATION OF A TWO-PHASE ANAEROBIC DIGESTION PROCESS TREATING EFFLUENT OF CASSAVA STARCH FACTORY

Different groups of microorganisms in a two-phase anaerobic system were enumerated to evaluate the prevalence of specific groups and species. Total and fecal coliforms showed similar values both in acidogenic and methanogenic reactors. The fecal streptococci were 4-fold higher in the acidogenic reactor, when compared with those of the methanogenic reactor. As expected, no methane forming or sulfate reducing bacteria were found in the acidogenic reactor. The populations of methanogenic bacteria were dominated by a mixed population of straight to curved rods and multicellular filaments which strongly resembled members of the genus Methanosaeta. Seven prevalent species of facultative anaerobic gram-negative bacteria were identified as Previdencia alcalifacienciens, Providencia rettgeri, Enterobacter cloaceae, Citrobacter freundii, Klebsiella oxytoca, Proteus pennri and Yersinia enterocolitica. The species Pseudomonas aeruginosa, Stenotrophomonas maltophila and Acinotobacter iwoffi, were the most frequently isolated glucose non-fermenting gram-negative bacilli. Among these species, only P. aeruginosa was present in high number in each sample.

Stabilization of Swine Wastes by Anaerobic Digestion

The purpose of this study was to evaluate the efficiency of the anaerobic digestion to reduce the organic load of swine waste. Anaerobic digestion is a biological means of decomposition of manure in an oxygen-free environment, and has the advantage of producing a fuel gas (methane) and an odor-free residue rich in nutrients, which can be used as fertilizer. The experiments were carried out in laboratory scale batch digester, at temperature controlled at 35 ± 2°C, without agitation. The digester was fed with 5% and 15% manure slurry. Results showed an average reduction of TCOD of 58% and DCOD of 85%. The methane content of biogas varied from 55 to 65% and stabilized sludge presented characteristics for use in agriculture.

Biosorption study of Ni2+ and Cr3+ by Sargassum filipendula: kinetics and equilibrium

In this work, the biosorption of Cr3+ and Ni2+ by Sargassum filipendula pre-treated with CaCl2 was studied. Kinetic and equilibrium experiments were carried out for mono- and multi-component solutions in a batch reactor at pH 3.0 and 30 oC. The results from the kinetic experiments showed that Cr3+ adsorbs slower than Ni2+. This behavior was explained by means of a mechanistic analysis, which showed that Cr3+ uptake presented three adsorption stages, whereas Ni2+ adsorption presents only two. The mono-component equilibrium data, along with binary kinetic data obtained from mono-component experiments, showed that, although the kinetics for Cr3+ removal are slower, the biomass had a stronger affinity for this ion. Almost all Ni2+ is desorbed from the biomass as Cr3+ adsorbs. The binary equilibrium data also presented this behavior. The binary data was also modeled by using modified forms of the Langmuir, Jain and Snoeyink, and Langmuir-Freundlich isotherms. However, the prediction obtained presented low accuracy. An alternative modeling with artificial neural networks was presented and the results showed that this technique could be a promising tool to represent binary equilibrium data. The main contribution of this work was to obtain experimental data for Cr3+/Ni2+ adsorption, which is a system rarely found in the literature and that provides information that could be used in process modeling and simulation.