Electrocatalytic Removal of Low-Concentration Uranium Using TiO2 Nanotube Arrays/Ti Mesh Electrodes.

Groundwater containing naturally occurring uranium is a conventional drinking water source in many countries. Removal of low concentrations of uranium complexes in groundwater is a challenging task. Here, we demonstrated that the TiO2 nanotube arrays/Ti (TNTAs/Ti) mesh electrode could break through the concentration limit and efficiently remove low concentrations of uranium complexes from both simulated and real groundwater. U(VI) complexes in groundwater were electro-reduced to UO2 and deposited on the TNTAs/Ti mesh electrode surface. The adsorption rate and electron transfer rate of the anatase TNTAs/Ti mesh electrode were twice that of the rutile TNTAs/Ti mesh electrode. Therefore, the anatase TNTAs/Ti mesh electrode exhibited excellent electrocatalytic activity toward the electrochemical removal of U(VI), which could work at a higher potential and significantly reduce the energy consumption of U(VI) removal. The U(VI) adsorption capacity on the anatase TNTAs/Ti mesh electrode was limited due to the low U(VI) concentration. However, the anatase TNTAs/Ti mesh electrode displayed a huge U(VI) removal capacity using the electroreduction method, where adsorption and reduction of U(VI) were mutually promoted and induced continuous accumulation of UO2 on the electrode. The accumulated UO2 can be easily recovered in dilute HNO3, and the electrode can be used repeatedly.

Capacity, stability and energy requirement of divalent mercury uptake by non-methylating/non-demethylating bacteria.

Methylmercury (MeHg) uptake by demethylating bacteria and inorganic divalent mercury [Hg(II)] uptake by methylating bacteria have been extensively investigated because uptake is the initial step of the intracellular Hg transformation. However, MeHg and Hg(II) uptake by non-methylating/non-demethylating bacteria is overlooked, which may play an important role in the biogeochemical cycling of mercury concerning their ubiquitous presence in the environment. Here we report that Shewanella oneidensis MR-1, a model strain of non-methylating/non-demethylating bacteria, can take up and immobilize MeHg and Hg(II) rapidly without intracellular transformation. In addition, when taken up into MR-1 cells, the intracellular MeHg and Hg(II) were proved to be hardly exported over time. In contrast, adsorbed mercury on cell surface was observed to be easily desorbed or remobilized. Moreover, inactivated MR-1 cells (starved and CCCP-treated) were still capable of taking up nonnegligible amounts of MeHg and Hg(II) over an extended period in the absence and presence of cysteine, suggesting that active metabolism may be not required for both MeHg and Hg(II) uptake. Our results provide an improved understanding of divalent mercury uptake by non-methylating/non-demethylating bacteria and highlight the possible broader involvement of these bacteria in mercury cycling in natural environments.

Spatial distribution, pollution assessment, and source identification of heavy metals in the Yellow River.

The discharge of pollutants into the Yellow River has been strictly controlled since 2013 due to the severe pollution. Thus, the overall water quality of the Yellow River has been becoming better year by year. However, the contamination status and source identification of heavy metals from the entire Yellow River remains unclear. Our results demonstrated that heavy metal contents in sediments showed little changes over time, whereas significant alleviation was observed in surface water compared to the reported metal concentrations before 2013. No heavy metal contamination was observed in surface water, and the distribution of all heavy metals in surface water fluctuated along the mainstream without a significant spatial difference. Heavy metals in sediments were assessed as low to moderate contamination degree. The majority of heavy metal concentrations were higher in the upstream and midstream than that in the downstream. Besides anthropogenic activities, the natural contribution from soil erosion of the Loess Plateau was also an important source of heavy metals in the Yellow River sediments. Our results highlight that control of anthropogenic activities and soil erosion of the Loess Plateau are necessary measures to reduce heavy metals in the Yellow River.