Caravelli Alejandro H, Zaritzky Noemí E
Centro de Investigación y Desarrollo en Criotecnología de Alimentos (CIDCA), CCT - CONICET - La Plata Fac, Ciencias Exactas, Universidad Nacional de La Plata, 47 y 116 La Plata, Argentina.
J Hazard Mater. 2009 Sep 15;168(2-3):1346-58. doi: 10.1016/j.jhazmat.2009.03.018. Epub 2009 Mar 18.
The hexavalent chromium biological reduction constitutes a safe and economical detoxification procedure of wastewaters containing Cr(VI). However, little research has been done to evaluate Cr(VI) tolerance and reduction capacity of microbial cultures under different growth conditions. The aims of this work were (a) to evaluate the capacity of Sphaerotilus natans to reduce Cr(VI) to Cr(III) in a continuous system limited in carbon and energy source or in nitrogen source, (b) to evaluate the toxic effect of Cr(VI) on this microorganism, (c) to carry out a complete analysis of Cr(VI) reduction by S. natans not only in continuous regime but also in batch system, and (d) to model the obtained results mathematically. S. natans exhibited great resistance to Cr(VI) (19-78 mg l(-1)) and optimal growth in continuous and batch systems using a mineral medium supplemented only with citric acid as organic substrate. In carbon- and energy-limited continuous systems, a maximum percentual decrease in Cr(VI) by 13% was reached for low influent Cr(VI) concentration (4.3-5.32 mg Cr(VI)l(-1)); the efficiency of the process did not notoriously increase as the length of cellular residence time was increased from 4.16 to 50h. A nitrogen-limited continuous operation with a cellular residence time of 28.5h resulted in a Cr(VI) decrease of approximately 26-32%. In batch system, a mathematical model allowed to predict the Cr(VI) concentration as a function of time and the ratio between the initial Cr(VI) concentration and that of the biomass. High concentrations of initial Cr(VI) and biomass produced the highest performance of the process of Cr(VI) reduction reached in batch system, aspects which should be considered in detoxification strategies of wastewaters.
六价铬生物还原构成了一种安全且经济的含Cr(VI)废水解毒程序。然而，关于在不同生长条件下微生物培养物对Cr(VI)的耐受性和还原能力的研究甚少。本研究的目的是：(a)评估浮游球衣菌在碳源和能源或氮源受限的连续系统中将Cr(VI)还原为Cr(III)的能力；(b)评估Cr(VI)对该微生物的毒性作用；(c)不仅在连续模式下，而且在间歇系统中对浮游球衣菌还原Cr(VI)进行全面分析；(d)对所得结果进行数学建模。浮游球衣菌对Cr(VI)（19 - 78 mg l(-1)）表现出很强的抗性，并且在仅添加柠檬酸作为有机底物的矿物培养基的连续和间歇系统中生长最佳。在碳源和能源受限的连续系统中，对于低进水Cr(VI)浓度（4.3 - 5.32 mg Cr(VI)l(-1)），Cr(VI)的最大百分比降低达到13%；随着细胞停留时间从4.16小时增加到50小时，该过程的效率并未显著提高。细胞停留时间为28.5小时的氮受限连续操作导致Cr(VI)降低约26 - 32%。在间歇系统中，一个数学模型能够预测Cr(VI)浓度随时间以及初始Cr(VI)浓度与生物量浓度之比的变化。高浓度的初始Cr(VI)和生物量产生了间歇系统中Cr(VI)还原过程的最高性能，这些方面在废水解毒策略中应予以考虑。
