Enhanced Cr(VI) removal from groundwater by Fe0-H2O system with bio-amended iron corrosion

A one-pot bio-iron system was established to investigate synergetic abiotic and biotic effects between iron and microorganisms on Cr(VI) removal. More diverse iron corrosion and reactive solids, such as green rusts, lepidocrocite and magnetite were found in the bio-iron system than in the Fe⁰-H₂O system, leading to 4.3 times higher Cr(VI) removal efficiency in the bio-iron system than in the Fe⁰-H₂O system. The cycling experiment also showed that the Cr(VI) removal capacity of Fe⁰ in the bio-iron system was 12.4 times higher than that in the Fe⁰-H₂O system. A 62days of life-span could be achieved in the bio-iron system, while the Fe⁰-H₂O system lost its efficacy after 30days. Enhanced effects of extra Fe²⁺ on Cr(VI) removal was observed, largely contributed to the adsorbed Fe²⁺ on iron surface, which could function as an extra reductant for Cr(VI) and promote the electron transfer on the solid phase. The results also showed that the reduction of Cr(VI) by microorganisms was insignificant, indicating the adsorption/co-precipitation of Cr by iron oxides on iron surface was responsible for the overall Cr(VI) removal. Our study demonstrated that the bio-amended iron corrosion could improve the performance of Fe⁰ for Cr(VI) removal from groundwater.

Oceanic oxygenation events in the anoxic Ediacaran ocean

The ocean-atmosphere system is typically envisioned to have gone through a unidirectional oxygenation with significant oxygen increases in the earliest (ca. 635 Ma), middle (ca. 580 Ma), or late (ca. 560 Ma) Ediacaran Period. However, temporally discontinuous geochemical data and the patchy metazoan fossil record have been inadequate to chart the details of Ediacaran ocean oxygenation, raising fundamental debates about the timing of ocean oxygenation, its purported unidirectional rise, and its causal relationship, if any, with the evolution of early animal life. To better understand the Ediacaran ocean redox evolution, we have conducted a multi-proxy paleoredox study of a relatively continuous, deep-water section in South China that was paleogeographically connected with the open ocean. Iron speciation and pyrite morphology indicate locally euxinic (anoxic and sulfidic) environments throughout the Ediacaran in this section. In the same rocks, redox sensitive element enrichments and sulfur isotope data provide evidence for multiple oceanic oxygenation events (OOEs) in a predominantly anoxic global Ediacaran-early Cambrian ocean. This dynamic redox landscape contrasts with a recent view of a redox-static Ediacaran ocean without significant change in oxygen content. The duration of the Ediacaran OOEs may be comparable to those of the oceanic anoxic events (OAEs) in otherwise well-oxygenated Phanerozoic oceans. Anoxic events caused mass extinctions followed by fast recovery in biologically diversified Phanerozoic oceans. In contrast, oxygenation events in otherwise ecologically monotonous anoxic Ediacaran-early Cambrian oceans may have stimulated biotic innovations followed by prolonged evolutionary stasis.

The effects of flow rate and concentration on nitrobenzene removal in abiotic and biotic zero-valent iron columns

This study investigated the effects of varying nitrobenzene (NB) loadings via increasing flow rate or influent NB concentration mode on the removal efficiency in zero-valent iron (ZVI) columns sterilized (abiotic) or preloaded with acclimated microorganisms (biotic). It was shown that physical sequestration via adsorption/co-precipitation and reductive transformation of NB to aniline (AN) were the two major mechanisms for the NB removal in both abiotic and biotic ZVI columns. The NB removal efficiency decreased in both columns as the flow rate increased from 0.25 to 1.0mLmin(-1) whereas the AN recovery increased accordingly, with relatively high AN recovery observed at the flow rate of 1.0mLmin(-1). At the constant flow rate of 0.5mLmin(-1), increasing influent NB concentration from 80 to 400μmolL(-1) resulted in decreasing of the overall NB removal efficiency from 79.5 to 48.6% in the abiotic column and from 85.6 to 62.5% in the biotic column. The results also showed that the sequestration capacity and chemical reduction capacity were respectively 72% and 157.6% higher in the biotic column than in the abiotic column at the same tested hydraulic conditions and NB loadings. The optimal flow rates and influent NB concentrations were at 0.5mLmin(-1) and 80μmolL(-1) for the abiotic column and 2.0mLmin-1 and 240μmolL(-1) for the biotic column, respectively. This study indicated that microorganisms not only enhanced overall reduction of NB, but also facilitated NB sequestration within the porous media and that the optimal loading conditions for overall removal, sequestration, and reduction of NB may be different. Optimal operation conditions should be found for preferred sequestration or transformation (or both) of the target contaminants to meet different goals of groundwater remediation with the ZVI-PRB systems.

Epidemiological transition and distribution of stroke incidence in Tianjin, China, 1988-2010

OBJECTIVES

To examine the trends in epidemiological transition of stroke over the last two decades in Tianjin, and investigate the subtypes of stroke.

STUDY DESIGN

A population-based epidemiological study using data from the Stroke Incidence Surveillance System of the Tianjin Centres for Disease Control and Prevention from 1988 to 2010.

METHODS

Almost 500,000 cases were analysed to examine changes in the incidence of stroke between 1988 and 2010 by age, sex, subtype, year and urban/rural status.

RESULTS

The incidence of stroke amongst males increased from 136.8/100,000 in 1988 to 387.0/100,000 in 2010, and the incidence amongst females increased from 65.9/100,000 in 1988 to 249.7/100,000 in 2010. Over the study period, the proportion of haemorrhagic strokes decreased and the proportion of ischaemic strokes increased sharply in both men and woman; the differences were significant.

CONCLUSION

The distribution of stroke subtypes changed dramatically over the study period. Changes in trend and subtypes of stroke have raised new challenges and there is a need for adjustment for stroke prevention in Tianjin.