Removal of Pb(II) from wastewaters by fontinalis antipyretica biomass: experimental study and modelling

Aquatic bryophytes are frequently used as biomonitors for trace metals in aquatic ecosystems. Nevertheless, their special characteristics also allow using them as biosorbents to clean industrial wastewaters. As biosorption is a low cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In this study, the ability of the aquatic bryophyte Fontinalis antipyretica to remove lead from simulated wastewaters was evaluated. Previously, the effect on biosorption of parameters such as the initial solution pH, contact time and initial metal ion concentration was investigated. The biosorption process is highly pH-dependent, and the favorable pH for maximum Pb2+ adsorption on the aquatic moss was found to have an optimum value in the range 4.0-6.0. The equilibrium sorption capacity of lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L-1, the uptake capacity at equilibrium was 4.8 mg g-1. Nevertheless, when the initial concentration increased up to 100 mg L-1, the uptake of lead was 10 times higher. Maximum adsorption rates were achieved almost in the first 10-20 min of contact, and a further increase in the contact time had a negligible effect on the Pb2+ sorption. Three kinetic models (pseudo-first order, pseudo-second order and Elovich) were fitted to the experimental data and compared by the F-test. The pseudo-second order biosorption kinetic model provided the better correlation with the experimental data . Probably the chemisorption is the rate-limiting step and the biosorption mechanism follows a pseudo-second order reaction model. The applicability of the Langmuir and Freundlich adsorption isotherms to the present system was also assessed. The equilibrium experimental data of lead sorption was very well described by the Langmuir model with R^2 values exceeding 0.993. The maximum lead sorption capacity by Fontinalis antipyretica attained a value of 68 mg of lead ions per gram of aquatic moss

Remoção de metais por biossorção em resíduos de algas granulados

A biossorção é uma propriedade de determinados tipos de biomassa morta que permite a ligação e concentração de iões metálicos, a partir de soluções aquosas, que podem ser muito diluídas. O processo pode ser usado na purificação de efluentes industriais que contêm metais. O estudo do processo de biossorção por um subproduto da indústria de extracção do agar, que contém restos de alga Gelidium, imobilizado num polímero orgânico seguiu os seguintes passos: 1) caracterização do biossorvente; 2) determinação das relações de equilíbrio, 3) determinação da cinética do processo, 4) determinação dos tempos de breakthrough em adsorvedor de cestos e numa coluna de biossorção com escoamento contínuo. O biossorvente foi caracterizado em termos da área superficial específica, densidade aparente, densidade real, porosidade, tamanho das partículas e distribuição de tamanho de poros, utilizando diferentes técnicas: adsorção de N2 e de azul de metileno, porosimetria de mercúrio, picnometria de hélio e microscopia electrónica de varrimento. A caracterização química do biossorvente baseou-se na determinação dos principais constituintes químicos presentes na estrutura da biomassa e na identificação e quantificação dos sítios activos da superfície, usando as técnicas de análise por espectroscopia do infravermelho (FTIR), microanálise por raios X e titulação potenciométrica ácido-base. Concluiu-se que a superfície do biossorvente é caracterizada por uma distribuição heterogénea de dois principais grupos químicos: ácido carboxílico e hidroxilo. Foram realizadas experiências cinéticas em adsorvedor fechado, a partir das quais se determinou o tempo de equilíbrio e o valor da difusividade homogénea do metal no biossorvente. Determinaram-se as capacidades de biossorção dos diferentes adsorventes para cada ião metálico, a partir das isotérmicas de adsorção a diferentes valores de pH, temperatura e força iónica da solução. Foram desenvolvidos modelos de transferência de massa, baseados na difusão externa e intraparticular, para descrever o processo de biossorção e dessorção em adsorvedor de cestos e numa coluna de leito fixo de escoamento descendente, sendo o equilíbrio descrito pela isotérmica de Langmuir e pela lei de acção de massa, respectivamente para a etapa de adsorção e dessorção

Femtosecond laser ablation of dentin

The surface morphology, structure and composition of human dentin treated with a femtosecond infrared laser (pulse duration 500 fs, wavelength 1030 nm, fluences ranging from 1 to 3 J cm(-2)) was studied by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The average dentin ablation threshold under these conditions was 0.6 +/- 0.2 J cm(-2) and the ablation rate achieved in the range 1 to 2 mu m/pulse for an average fluence of 3 J cm(-2). The ablation surfaces present an irregular and rugged appearance, with no significant traces of melting, deformation, cracking or carbonization. The smear layer was entirely removed by the laser treatment. For fluences only slightly higher than the ablation threshold the morphology of the laser-treated surfaces was very similar to the dentin fracture surfaces and the dentinal tubules remained open. For higher fluences, the surface was more porous and the dentin structure was partially concealed by ablation debris and a few resolidified droplets. Independently on the laser processing parameters and laser processing method used no sub-superficial cracking was observed. The dentin constitution and chemical composition was not significantly modified by the laser treatment in the processing parameter range used. In particular, the organic matter is not preferentially removed from the surface and no traces of high temperature phosphates, such as the beta-tricalcium phosphate, were observed. The achieved results are compatible with an electrostatic ablation mechanism. In conclusion, the high beam quality and short pulse duration of the ultrafast laser used should allow the accurate preparation of cavities, with negligible damage of the underlying material

Aplicabilidade do musgo aquático fontinalis antipyretica na bioacumulaçãode iões metálicos (Cd2+)

Com este estudo pretende-se compreender quantitativa e qualitativamente a acumulação e a libertação de iões cádmio em solução aquosa, por uma briófita aquática - Fontinalis antipyretica – na perspectiva duma aplicação, quer na biomonitorização de cursos de água, quer na descontaminação de efluentes industriais. A acumulação de cádmio e posterior eliminação pelo musgo foi estudada em laboratório expondo as plantas a concentrações de cádmio na gama 0,5 – 2,5 mg l-1, durante um período de contaminação de 144 h, e depois a água isenta de metal durante um período de descontaminação de 192 h. Foi ajustado um modelo cinético de transferência de massa de primeira ordem aos dados experimentais

Wetting response of KrF laser ablated polyimide surfaces

The wettability of polyimide surfaces microstructured using KrF laser radiation at fluences above the material ablation threshold was studied by static contact angle measurements. The laser-treated surfaces present a morphology consisting of conical features whose dimensions and areal density depend on the fluence. The effect of these parameters on the surface apparent contact angle depends on the wetting regime. When wetting occurs in the homogeneous regime, the apparent contact angle of the treated surfaces increases with the radiation fluence because the cone dimensions increase. In contrast, when wetting occurs in the heterogeneous regime, the apparent contact angle increases with the radiation fluence because the average distance between cones increases. The apparent water contact angle of the laser-treated surfaces can reach values as high as 162 degrees, as compared to 75 degrees for virgin polyimide

Multi-scaled femtosecond laser structuring of stationary titanium surfaces

The evolution of the topography of titanium surfaces treated with femtosecond laser radiation in stationary conditions as a function of radiation fluence and number of laser pulses is investigated. Depending on the processing parameters, ripples, microcolumns, wavy or smooth surfaces can be obtained. The ripples predominate for fluences near the damage threshold of titanium (0.2+/-0.1) J/cm(2), while microcolumns form during the first 200 pulses for fluences between (0.6+/-0.2) and (1.7+/-0.2) J/cm(2). A wavy topography develops for fluences and number of pulses higher than (1.7+/-0.2) J/cm(2) and 300, respectively. A bimodal surface topography consisting of surface ripples overlapping a microcolumnar topography can be obtained if the surfaces are firstly treated to create microcolumns followed by laser treatment with a lower fluence near the ablation threshold of the material, in order to generate periodic rippl

Kinetic modelling of cadmium and lead removal by aquatic mosses

Because biosorption is a low cost and effective method for treating metal-bearing wastewaters, understanding the process kinetics is relevant for design purposes. In the present study, the performance of the aquatic moss Fontinalis antipyretica for removing cadmium and lead from simulated wastewaters has been evaluated. Five kinetic models (first-order, pseudo-first-order, Elovich, modified Ritchie second-order and pseudo-second-order) were fitted to the experimental data and compared. Previously, the effect of parameters such as the initial solution pH, contact time, and initial metal ion concentration on biosorption was investigated. The initial pH of the solution was found to have an optimum value in the range of 4.0-6.0. The equilibrium sorption capacity of cadmium and lead by Fontinalis antipyretica increased with the initial metal concentration. For an initial metal concentration of 10 mg L-1, the uptake capacity of the moss, at equilibrium, is the same for both metals (4.8 mg g-1). Nevertheless, when the initial concentration increases up to 100 mg L-1, the uptake of Pb(II) was higher than 78%. The pseudo-second order biosorption kinetics provided the better correlation with the experimental data (R2 ≥ 0.999)

Remoção de metais tóxicos por brió fitas aquáticas

Tradicionalmente a remoção de metais pesados de efluentes é feita usando diversas técnicas normalmente dispendiosas e/ou pouco eficientes para soluções diluídas. A biossorção, processo em que materiais naturais ou seus derivados são usados na remoção e recuperação de metais pesados, proporciona um tratamento alternativo competitivo, pelo que os respectivos parâmetros cinéticos e de equilíbrio devem ser bem conhecidos, de modo a prevenir fracassos na sua aplicação. Foram estudados os processos de bioacumulação/eliminação e de biossorção de Cd, Cr, Pb e Zn pelo musgo aquático F. antipyretica. Relativamente à análise directa da água os musgos apresentam a vantagem de permitirem uma integração de variações no espaço e no tempo, favorecendo o nível de quantificação do contaminante por concentração dos elementos tóxicos e fornecendo informação acerca das espécies biodisponíveis. Realizaram-se experiências em contínuo para determinar as cinéticas de acumulação e libertação de metal pelo musgo. Um modelo cinético de transferência de massa de primeira ordem foi ajustado aos resultados experimentais, sendo determinados fatores de bioconcentração (BCF) e de eliminação biológica (BEF)

Removal of Cu and Cr from an industrial effluent using a packed-bed column with algae gelidium-derived material

The purpose of this work was to evaluate the potential of algal waste from the agar extraction industry, immobilized in a polymer, and the algae Gelidium itself, the raw material of agar extraction, to remove Cu(II) and Cr(III) from industrial effluents. The study involved a Cu(II) bearing effluent and the mixture of this effluent with an effluent containing Cr(VI), previously reduced to Cr(III). The two effluents were collected from metal plating plants, and then filtered and diluted before the biosorption studies. Biosorption results were compared with those obtained from pure Cu(II) and Cu(II)/Cr(III) solution adsorption experiments. Three consecutive adsorption (≈50 mg Cu(II)/l)-desorption (0.1 M HNO3) cycles were carried out with algae Gelidium and two with the composite material, for the Cu(II) effluent. The biomass uptake capacity remained almost constant and close to the obtained for adsorption from pure Cu(II) solution, suggesting that the biomass lifetime was long enough to be used in a continuous industrial process. In the biosorption from Cu(II)/Cr(III) mixtures it was observed that Cr leave the column after the residence time, suggesting that the reduction of Cr(VI) to Cr(III)was not completely achieved. Cr(VI) speciation in aqueous solution produces negatively charged species, that do not bind to the negatively charged carboxylic groups on the biosorbent surface and a low breakthrough time is obtained. An “overshoot”was observed for the Cu(II) concentration, suggesting that Cr(III) has a higher affinity to the binding sites than Cu(II)