Removal of chromium (VI) and cadmium (II) from aqueous solution by a bacterial biofilm supported on granular activated carbon

A biofilm of Arthrobacter viscosus, supported on granular activated carbon, removed between 100% and 50% of Cr(VI) and between 100% and 20% of Cd(II) from solutions with initial concentrations between 4–11 mgmetal Lˉ¹ and a flow residence time of 1.2 min. For experiments of lower initial concentrations, a steady-state removal of 50% was reached after 71 bed volumes of Cr solution passed through the biosorbent bed and a steady-state removal of 30% was reached after 47 bed volumes of Cd solution passed through a similar bed. Final uptakes of 8.5 mgCr gˉ¹ carbon and 4.2 mgCd gˉ¹ carbon were determined for initial concentrations of 10 mgCr Lˉ¹ and 11 mgCd Lˉ¹, respectively. The influence on the overall process of two different surface treatments of the support was evaluated and compared with the behavior of a support not treated.Fundação para a Ciência e Tecnologia (FCT) - PRAXIS/P/EQU/12017/1998

Fixação simultânea de metais pesados e compostos orgânicos em matriz biológica

Foi utilizado um biofilme de Arthrobacter viscosus suportado em carvão activado granular (GAC) para remover metais pesados e compostos orgânicos presentes em soluções líquidas diluídas. Nos ensaios com metais pesados e na ausência de compostos orgânicos foram utilizados dois diferentes suportes: um tratado com HNO3 e outro com H2O2. Os ensaios realizados com soluções mistas tiveram como suporte do biofilme, o carvão activado sem qualquer tipo de tratamento. A gama de concentrações estudadas, para as soluções de um só metal, variou de 4-77 mg/l para o crómio, 5-95 mg/l para o cádmio, 8-165 mg/l para o chumbo e 2.5-42 mg/l para o ferro. Em relação às soluções mistas, foram utilizadas concentrações iniciais de crómio entre 10-200 mg/l para uma concentração de composto orgânico de 60 mg/l. De uma forma global conseguiram-se melhores resultados com os metais crómio, chumbo e ferro, tendo-se concluído que o cádmio exerce um efeito tóxico sobre as bactérias. Em relação às soluções mistas, fixou-se a atenção na remoção de crómio e verificou-se que esta é ligeiramente afectada pela presença do composto orgânico (ortocresol>fenol>clorofenol). O estudo comparativo entre os três compostos orgânicos indica que a sua remoção não é sensível a concentrações crescentes do metal no caso do fenol e do clorofenol, ao contrário da remoção de ortocresol que é evidentemente afectada pela presença do Cr em concentrações crescentes.Fundação para a Ciência e a Tecnologia (FCT

Equilibrium modelling of a biosorption system consisting of a bacterial biofilm supported on a GAC for removal of chromium (VI) and organics compounds from a aqueous solution

The removal of heavy metals linked to organic compounds like phenol, chlorophenol, and o- cresol, is one of the most important environmental problems yet to be solved. The retention of these contaminants by a biofilm supported on granular activated carbon is a promising technology for the treatment of diluted solutions, as the biofilm is able to retain the metallic ions and the support will help to fix them for further catalytic applications. The addition of three different organic compounds, i.e., phenol, o-cresol, and chlorophenol, to the metallic solution was studied to better describe the real industrial effluent. A modeling approach for an expanded bed biosorption system was presented using the ADR (Advection-Dispersion Reaction) equation as the basis of the mathematical description. Several biosorption studies were made using a bacterial biofilm of Arthrobacter viscous supported on pre-treated granular activated carbon in a mini-column arrangement and the obtained data were compared with the predicted by the model. The initial chromium (VI) and organic compound concentration ranged from 10 to 100 mg/L. This is an abstract of a paper presented at the 7th World Congress of Chemical Engineering (Glasgow, Scotland 7/10-14/2005).(undefined

Dependence of Ga-doped ZnO thin film properties on different sputtering process parameters: Substrate temperature, sputtering pressure and bias voltage

This paper reports on the effects of different sputtering deposition process parameters (substrate temperature, sputtering pressure and bias voltage) on the electrical, optical, structural and morphological properties of gallium-doped ZnO (ZnO:Ga) of ~1 μm thick. These highly transparent and conductive films were deposited on glass surfaces by d.c. pulsed magnetron sputtering from a GZO (ZnO(95.5):Ga2O3(4.5)) ceramic target in an argon atmosphere. X-ray diffraction experiments show that all films have a hexagonal wurtzite structure with the [001] preferred crystallographic direction, and themorphology of the films (obtained fromscanning electron microscope analysis) is sensitive to the process parameters. All ZnO:Ga films have an average transmittance above 80% in the visible region, and the lowest electrical resistivity of 3.03 × 10−4 Ω·cm was achieved for the sample submitted to the lowest bias voltage (−40 V), which corresponds to a carrier concentration and a carrier mobility of 6.99 × 1020 cm−3 and 29.49 cm2 V−1 s−1, respectively. A high substrate temperature, high sputtering pressure and lownegative bias voltage (within the range of studied parameters) proved to be very promising on obtaining optimized ZnO:Ga films, ensuring suitable properties for application as transparent electrodes in photovoltaic cells.The authors acknowledge the funding from the Portuguese Innovation Agency (AdI), project reference WinDSC-21539, co-funded by FEDER/POFC

Novel environmental catalysts prepared with residual metals on bioactive nanomaterials

Volatile organic compounds (VOCs), which are emitted from many industrial processes and transport activities, constitute an important concern for the scientific community due to their role in atmospheric pollution and subsequent impact on human health. Among the various methods that can be applied to efficiently control VOCs emissions, catalytic oxidation over solid catalysts seems to be the most efficient and cost-effective technology. Catalysts used for the treatment of gas streams contaminated with VOCs are mostly based on noble metals. Using low cost transition metals such as chromium to replace the noble metal in the catalysts is quite desirable in terms of economical and practical consideration. The catalytic oxidation of 1,2-dichlorobenzene was investigated over NaY and NaX zeolites, loaded with chromium through the action of a robust biosorption system consisting of a bacterial biofilm supported on the zeolites. The results of biosorption showed that the maximum metal removal efficiency was 20%, in both systems based on NaYor NaX, starting from solutions with chromium(VI) concentrations ranging from 50 to 250 mgCr/L [1]. The bacterial biofilm, Arthrobacter viscosus, supported on the zeolite reduces Cr(VI) to Cr(III). The Cr(III) is retained in the zeolite by ion exchange. The new catalysts were characterized by spectroscopic methods (FTIR and ICP-AES), surface analysis (XRD) and thermal analysis (TGA). These catalysts, Cr/FAU, prepared through this new procedure present good activity and selectivity for 1,2-dichlorobenzene oxidation in wet air at 350oC. The study was extended to the oxidation of ethyl acetate and to the oxidation of ethanol [2]