Norbert Jordan

Extracellular Polymeric Substances Govern the Surface Charge of Biogenic Elemental Selenium Nanoparticles

The origin of the organic layer covering colloidal biogenic elemental selenium nanoparticles (BioSeNPs) is not known, particularly in the case when they are synthesized by complex microbial communities. This study investigated the presence of extracellular polymeric substances (EPS) on BioSeNPs. The role of EPS in capping the extracellularly available BioSeNPs was also examined. Fourier transform infrared (FT-IR) spectroscopy and colorimetric measurements confirmed the presence of functional groups characteristic of proteins and carbohydrates on the BioSeNPs, suggesting the presence of EPS. Chemical synthesis of elemental selenium nanoparticles in the presence of EPS, extracted from selenite fed anaerobic granular sludge, yielded stable colloidal spherical selenium nanoparticles. Furthermore, extracted EPS, BioSeNPs, and chemically synthesized EPS-capped selenium nanoparticles had similar surface properties, as shown by ζ-potential versus pH profiles and isoelectric point measurements. This study shows that the EPS of anaerobic granular sludge form the organic layer present on the BioSeNPs synthesized by these granules. The EPS also govern the surface charge of these BioSeNPs, thereby contributing to their colloidal properties, hence affecting their fate in the environment and the efficiency of bioremediation technologies.

Selenium(IV) uptake by maghemite (γ-Fe2O3).

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11). Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing ((2)C) and bidentate mononuclear edge-sharing ((1)E) inner-sphere surface complexes was observed, with a trend toward solely (1)E complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the Se(IV)O3 unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters.

Entrapped elemental selenium nanoparticles affect physicochemical properties of selenium fed activated sludge.

Selenite containing wastewaters can be treated in activated sludge systems, where the total selenium is removed from the wastewater by the formation of elemental selenium nanoparticles, which are trapped in the biomass. No studies have been carried out so far on the characterization of selenium fed activated sludge flocs, which is important for the development of this novel selenium removal process. This study showed that more than 94% of the trapped selenium in activated sludge flocs is in the form of elemental selenium, both as amorphous/monoclinic selenium nanospheres and trigonal selenium nanorods. The entrapment of the elemental selenium nanoparticles in the selenium fed activated sludge flocs leads to faster settling rates, higher hydrophilicity and poorer dewaterability compared to the control activated sludge (i.e., not fed with selenite). The selenium fed activated sludge showed a less negative surface charge density as compared to the control activated sludge. The presence of trapped elemental selenium nanoparticles further affected the spatial distribution of Al and Mg in the activated sludge flocs. This study demonstrated that the formation and subsequent trapping of elemental selenium nanoparticles in the activated sludge flocs affects their physicochemical properties.

Probing the surface speciation of uranium (VI) on iron (hydr)oxides by in situ ATR FT-IR spectroscopy.

The surface speciation of uranium(VI) on maghemite (γ-Fe2O3) was elucidated at the spectroscopic level for the first time. By means of in situ ATR FT-IR measurements, the formation of uranium(VI) outer-sphere complexes was revealed under anoxic conditions and in ambient atmosphere at mildly acid conditions. This type of complexation was verified by the frequency of the ν3(UO2) mode observed for the surface species, the impact of the ionic strength of the background electrolyte on U(VI) sorption and by the high reversibility of the sorption process monitored by on line spectroscopy. The impact of carbonate ions from atmospherically derived CO2 on U(VI) sorption on maghemite was investigated. Although the surface speciation of the carbonate ions presumably change from a monodentate coordination on maghemite to a bidentate coordination in the ternary sorption system, the U(VI) speciation is not changed. A contrasting juxtaposition of comparable results obtained from maghemite and ferrihydrite reveals a basically different type of U(VI) complexation, namely outer and inner spheric coordination.

Sediment-bound trace metals in Golfe-Juan Bay, northwestern Mediterranean: Distribution, availability and toxicity

The concentration, potential mobility, cation exchange capacity and toxicity of eight sediment-bound metals in Golfe-Juan Bay, France were examined. Results revealed significant spatial gradient of metal contamination along Golfe-Juan coast. The distribution and concentration of the metals appear to be influenced by the geochemical properties of the sediment, proximity to anthropogenic sources and general water circulation in the bay. The portion of trace metals found in the exchangeable, carbonate, oxidizable and reducible fractions of the sediment constitute 31%-58% of the total sediment-bound trace metal content, suggesting significant potential for remobilization of metals into the water column. Pb and Ni content of the sediment exceed the limits of the French marine sediment quality. Whole sediment extracts showed acute toxicity to marine rotifers. This study concludes that monitoring and management of sediment-bound trace metals in Golfe-Juan Bay are important so as not to underestimate their availability and risk to the marine ecosystems.

Shape change of biogenic elemental selenium nanomaterials from nanospheres to nanorods decreases their colloidal stability

Microbial reduction of selenium oxyanions under mesophilic (30 °C) and thermophilic (55 °C) conditions produces biogenic elemental selenium nanospheres (BioSe-Nanospheres) and nanorods (BioSe-Nanorods), respectively. While the properties of BioSe-Nanospheres are well studied, the colloidal properties of BioSe-Nanorods have not yet been investigated. Therefore, this study characterized the surface properties of BioSe-Nanorods, compared their colloidal properties with BioSe-Nanospheres and elucidated the formation of BioSe-Nanorods in the presence of a capping agent. This study demonstrated that BioSe-Nanorods, like BioSe-Nanospheres, are capped by extracellular polymeric substances (EPS) as evidenced by infrared spectroscopy. The EPS capped BioSe-Nanorods were less colloidally stable than EPS capped BioSe-Nanospheres as demonstrated by the formers less negative zeta potential values when exposed to 10 mM NaCl. In fresh lake water, BioSe-Nanospheres showed a 91.6 (±0.5)% settling efficiency, while BioSe-Nanorods displayed a settling efficiency of 97.1 (±0.5)%. The lower colloidal stability and higher settling efficiency was due to a 7 times less negative surface charge of BioSe-Nanorods compared to BioSe-Nanospheres at pH 7.2. Further, this study observed that the formation of BioSe-Nanorods might proceed via BioSe-Nanospheres through orientation attachment followed by anisotropic growth as well as a solid-solution-solid mechanism. This study demonstrates the importance of the shape of nanoparticles in determining their bioremediation effectiveness and fate in the environment.

Selenium(IV) Sorption Onto γ-Al2O3: A Consistent Description of the Surface Speciation by Spectroscopy and Thermodynamic Modeling

The sorption processes of Se(IV) onto γ-Al2O3 were studied by in situ Infrared spectroscopy, batch sorption studies, zeta potential measurements and surface complexation modeling (SCM) in the pH range from 5 to 10. In situ attenuated total reflection fourier-transform infrared (ATR FT-IR) spectroscopy revealed the predominant formation of a single inner-sphere surface species at the alumina surface, supporting previously reported EXAFS results, irrespective of the presence or absence of atmospherically derived carbonate. The adsorption of Se(IV) decreased with increasing pH, and no impact of the ionic strength was observed in the range from 0.01 to 0.1 mol L-1 NaCl. Inner-sphere surface complexation was also suggested from the shift of the isoelectric point of γ-Al2O3 observed during zeta potential measurements when Se(IV) concentration was 10-4 mol L-1. Based on these qualitative findings, the acid-base surface properties of γ-Al2O3 and the Se(IV) adsorption edges were successfully described using a 1-pK CD-MUSIC model, considering one bidentate surface complex based on previous EXAFS results. The results of competitive sorption experiments suggested that the surface affinity of Se(IV) toward γ-Al2O3 is higher than that of dissolved inorganic carbon (DIC). Nevertheless, from the in situ experiments, we suggest that the presence of DIC might transiently impact the migration of Se(IV) by reducing the number of available sorption sites on mineral surfaces. Consequently, this should be taken into account in predicting the environmental fate of Se(IV).

Removal and recovery of uranium(VI) by waste digested activated sludge in fed-batch stirred tank reactor

This study demonstrated the removal and recovery of uranium(VI) in a fed-batch stirred tank reactor (STR) using waste digested activated sludge (WDAS). The batch adsorption experiments showed that WDAS can adsorb 200 (±9.0) mg of uranium(VI) per g of WDAS. The maximum adsorption of uranium(VI) was achieved even at an acidic initial pH of 2.7 which increased to a pH of 4.0 in the equilibrium state. Desorption of uranium(VI) from WDAS was successfully demonstrated from the release of more than 95% of uranium(VI) using both acidic (0.5 M HCl) and alkaline (1.0 M Na2CO3) eluents. Due to the fast kinetics of uranium(VI) adsorption onto WDAS, the fed-batch STR was successfully operated at a mixing time of 15 min. Twelve consecutive uranium(VI) adsorption steps with an average adsorption efficiency of 91.5% required only two desorption steps to elute more than 95% of uranium(VI) from WDAS. Uranium(VI) was shown to interact predominantly with the phosphoryl and carboxyl groups of the WDAS, as revealed by in situ infrared spectroscopy and time-resolved laser-induced fluorescence spectroscopy studies. This study provides a proof-of-concept of the use of fed-batch STR process based on WDAS for the removal and recovery of uranium(VI).

Adsorption of selenium(VI) onto nano transition alumina

The adsorption of selenium(VI) onto nano transition alumina (γ/δ-Al2O3) was investigated at both macroscopic and molecular levels. The uptake of selenium(VI) was found to decrease upon increasing pH (5–10) and ionic strength (0.01–0.1 mol L−1 NaCl). At the molecular level, in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy established the predominant formation of a bidentate outer-sphere surface complex throughout the investigated pH range. The acid–base surface properties of transition alumina (surface charge) together with the Se(VI) adsorption edges were successfully described using a 1-pK charge distribution surface complexation model involving one outer-sphere selenium(VI) surface species, namely {(AlOH20.5+)2SeO42−} as suggested by the IR studies. Blind predictions of literature data yielded good agreement in particular in NaCl systems. These new spectroscopy based results can be implemented in reactive transport models to enable more consistent and trustworthy prognostic modeling of the environmental fate of selenium(VI).