Chromium(III) biosorption onto spent grains residual from brewing industry : equilibrium, kinetics and column studies

The use of industrial wastes for wastewater treatment as a strategy to their re-use and valorisation may provide important advances toward sustainability. The present work gives new insights into heavy metal biosorption onto low-cost biosorbents, studying chromium(III) biosorption onto spent grains residual from a Portuguese brewing industry both in batch and expanded bed column systems. Experimental studies involved unmodified spent grains and spent grains treated with NaOH. Metal uptake followed a rapid initial step, well described by the pseudo-second-order kinetic model up to 27 h, indicating chemisorption to be the rate-limiting step. Beyond this period intraparticle diffusion assumed an important role in the uptake global kinetics. The best fit for equilibrium data was obtained using the Langmuir model, with unmodified spent grains having the higher maximum uptake capacity (q max = 16.7 mg g1). In open system studies, using expanded bed columns, the best performance was also achieved with unmodified spent grains: Breakthrough time (C/C i = 0.25) and total saturation time (C/C i = 0.99) occurred after 58 and 199 h of operation, corresponding to the accumulation of 390 mg of chromium(III), 43.3 % of the total amount entering the column. These results suggest that alkali treatment does not improve spent grains uptake performance. Changes in biomass composition determined by Fourier transform infrared spectroscopy suggested hydroxyl groups and proteins to have an important role in chromium(III) biosorption. This study points out that unmodified spent grains can be successfully used as low-cost biosorbent for trivalent chromium.The authors would like to thank the Portuguese brewing industry UNICER for all the support and FCT (Fundacao para a Ciencia e a Tecnologia) financial support through the Grant PRAXIS XXI/BD/15945/98

Optical study of the effect of gamma radiation and heavy metals on microorganisms (Bacteria)

Radionuclide and heavy metal pollution are the main concerns for the environment nowadays as thousands of waste sites around the world pose a serious threat to all living organisms and humans, in particular. Therefore, the focus of this study is on the development of novel-sensing technologies for the detection of radionuclides and heavy metals in water utilizing microorganisms. Several optical methods, i.e., fluorescence microscopy, fluorescence spectroscopy, and UV-vis spectrophotometer were exploited here for studying the effect of γ-radiation (from Co-57 source) and one of the heavy metal ions (Cd+2) on two types of bacteria, namely Escherichia coli (E. coli) and Deinococcus radiodurans (D. radiodurans). All three optical methods gave consistent and correlated results in regards to the gamma radiation. An exponential decay in bacterial counts with the increase in γ-radiation dose was observed in E. coli bacteria samples, while D. radiodurans bacteria appeared to be much less affected by γ-radiation and showed even a small increase in the bacteria counts at low-radiation doses followed by a rather moderate decay at intermediate and high doses. The effect of Cd2+ on bacteria is more complex, however, and the method of fluorescence microscopy gave the most reliable account in live bacteria concentration. Both E. coli and D. radiodurans bacteria showed similar effects of a moderate decay of bacteria counts with the increase in CdCl2 concentration. Comparative analysis of the results obtained shows a clear possibility of pattern recognition of the presence of γ-radiation and heavy metals using the above two bacteria