Analysis of herbicide biosorption by means of a phenomenological mathematical distributed parameter model.

A distributed parameter model and two lumped parameter models were used in order to find the rate-limiting step in the adsorption process of a herbicide (Diuron) by Moringa oleifera husks, a possible low-cost adsorbent. For that, four kinetics assays, differentiated by the initial Diuron concentration, were performed. Langmuir isotherm well represented the equilibrium data and through this evaluation, Moringa husks proved to be a potential adsorbent for Diuron removal from water. The internal mass transfer resistance, analysed as a distributed parameter model, was found to better represent the experimental data. This fact enabled the simulation of the process according to the variation of time and space, which contributed to the better understanding of the adsorption process.

Adsorption of naturals hormones estrone, 17ß-estradiol, and estriol by rice husk: monocomponent and multicomponent kinetics and equilibrium.

In the present study, the use of the rice husk biomass as an alternative biosorbent for treating the estrone, 17 ß-estradiol, and estriol hormones in monocomponent and multicomponent systems was investigated. The high-performance liquid chromatography technique (HPLC-UV) was applied in order to quantify the hormones, validating this method according to ANVISA and INMETRO. The biosorbent presented functional groups typical of cellulose, hemicellulose, lignin, and proteins, with an amorphous, fibrous, and porous surface. The best performance was obtained with a neutral pH and at room temperature (25[Formula: see text]C). The equilibrium times in batch systems were 60 min for the estrone, and 120 min for 17 ßestradiol and estriol. The monocomponent kinetics of adsorption of estrone and estriol were adequately described by the pseudo-first-order model, whereas for the 17 ß estradiol both pseudo-first-order and pseudo-second-order models well described the experimental data. For the multicomponent system, the kinetics of adsorption was appropriately represented by the pseudo-first-order model, demonstrating that the number of active sites was the limiting factor of the process. The monocomponent adsorption isotherms were adequately fitted by the Langmuir model, reaching adsorption capacities of 2.698, 1.649, and 0.979 mg g-1 for the estrone, 17 ßestradiol, and estriol hormones, respectively. The ternary isotherm models did not represent the experimental data, indicating that there was no competition among the hormones. The reactions presented favourable and spontaneous characteristics. The rice husk biomass showed a great potential as an adsorbent when treating effluents contaminated with hormones.

Mathematical modelling applied to the rate-limiting mass transfer step determination of a herbicide biosorption onto fixed-bed columns.

The herbicide removal of Diuron in a fixed-bed column packed with the Moringa oleifera bark biosorbent was investigated experimentally and through phenomenological mathematical modelling. To understand the physical phenomena involved, the steps of external mass transfer resistance, internal mass transfer resistance and the adsorption phenomenon itself were considered as possible limiting steps in the herbicide mass transfer from the liquid to the solid phase. In the developing process of the internal mass transfer resistance model, two hypotheses were considered: constant mass transfer coefficient and mass transfer coefficient as a function of the herbicide concentration in the biosorbent. The experimental breakthrough curves were obtained for different flow rates and feed concentrations, in order to evaluate the model's predictive capacity. The mass transfer parameter values of the mathematical models were estimated using the simplex downhill optimization method. The model that considers the resistance a mass transfer internal with parameter Ks variable represented effectively the dynamic behaviour of the herbicide biosorption process in fixed-bed column, in the various evaluated conditions, indicating that this mechanism controls the biosorption process. Thus, the phenomenological mathematical modelling proved to be an analysis important tool, understanding and the herbicide adsorption systems design in a fixed-bed column.

Potencial de biossorção do zinco pela macrófita egeria densa / Biosorption potential of zinc by egeria densa macrophytes

Neste trabalho, foi estudada a capacidade de biossorção da macrófita aquática Egeria densa seca na remoção do íon zinco. Os testes cinético e de equilíbrio foram realizados em sistema de batelada com temperatura, agitação e pH controlados. Os resultados obtidos na cinética de biossorção demonstram uma rápida remoção do zinco (II), com tempo de equilíbrio em torno de 45 minutos e taxa de remoção superior a 70 por cento. O modelo cinético de pseudo-segunda ordem foi o que melhor representou os dados experimentais. No estudo do equilíbrio, verificou-se que o modelo de Langmuir ajustou-se melhor aos dados experimentais, com capacidade máxima de sorção de 0,92 mequiv g-1 e razão entre as taxas de sorção e dessorção de 0,829 L g-1 em pH 5. Os resultados obtidos demonstram que a macrófita E. densa tem potencial para ser utilizada em sistemas de tratamento de efluentes industriais.

In this paper, the removal potential on Zn ion by macrophyte Egeria densa has been studied. The influence of the metal solution pH, the plant drying and the metal solution temperature, and biosorbent grain size was previously studied in batch systems. Adsorption kinetic and equilibrium experiments of metals onto E. densa were performed under controlled temperature and permanent shaking. In adsorption kinetic tests for Zn (II) the equilibrium time was around 45 min. The biosorption kinetic data were well fitted by a pseudo-second order model. The equilibrium data at pH 5 were described a rather better by the Langmuir isotherm than the Freundlich one, with an adsorption rate and maximum metal content values of 0,829L g-1and 0,92 mequiv g-1, respectively, for Langmuir model. The macrophytes E. densa could be used as biosorbent material in industrial effluent treatment system.