Water environment

Abstract: We report a novel procedure to synthesize a new type of water separation membrane using graphene oxide (GO) nanosheets such that water can flow through the nanochannels between GO layers while unwanted solutes are rejected by size exclusion and charge effects. The GO membrane was made via layer-by-layer deposition of GO nanosheets, which were cross-linked by 1,3,5-benzenetricarbonyl trichloride, on a polydopamine-coated polysulfone support. The cross-linking not only provided the stacked GO nanosheets with the necessary stability to overcome their inherent dispensability in water environment but also fine-tuned the charges, functionality, and spacing of the GO nanosheets. We then tested the membranes synthesized with different numbers of GO layers to demonstrate their interesting water separation performance. It was found that the GO membrane flux ranged between 80 and 276 LMH/MPa, roughly 4–10 times higher than that of most commercial nanofiltration membranes. Although the GO membrane in the present deve...

Abstract: In soils, dissolved organic matter (DOM) is probably the most bioavailable fraction of soil organic matter, since all microbial uptake mechanisms require a water environment. Bioavailability describes the potential of microorganisms to interact with DOM. It is a prerequisite for biodegradation and can be restricted, if DOM is present in small pores or within soil aggregates and therefore not accessible for microorganisms. DOM biodegradation is defined as the utilisation of organic compounds by soil microorganisms quantified by the disappearance of DOM or O2 or by the evolution of CO2. The controlling factors for DOM biodegradability can be divided into three groups, namely, intrinsic DOM quality parameters, soil and solution parameters and external factors. DOM characteristics that generally enhance its biodegradability are high contents of carbohydrates, organic acids and proteins for which the hydrophilic neutral fraction seems to be a good estimate. In contrast, aromatic and hydrophobic structures that can also be assessed by UV absorbance decrease DOM biodegradability, either due to their recalcitrance or due to inhibiting effects on enzyme activity. Effects of solution parameters such as Al, Fe, Ca and heavy metal concentrations on DOM biodegradability have been documented in various studies, however with different, sometimes conflicting results. Inhibitory effects of metals are generally attributed to toxicity of the organic complexes or the free metal ions. In contrast, the enhanced degradability observed in the presence of metal ions may be due to flocculation, as larger structures will provide better attachment for microbial colonies. As degradation is dependent on microbial activity, the composition and density of the microbial population used in the degradation studies also influence biodegradation. Site-specific factors, such as vegetation, land use and seasonality of meteorological parameters control DOM composition and soil and soil solution properties and therefore also affect its biodegradability. The major obstacle for a better understanding of the controls of DOM biodegradability is the lack of a standardised methodology or at least systematic comparisons between the large number of methods used to assess DOM biodegradability.

Abstract: Using a 32-echo imaging pulse sequence, T2 relaxation decay curves were acquired from five white- and six gray-matter brain structures outlined in 12 normal volunteers. The water contents of white and gray matter were 0.71 (0.01) and 0.83 (0.03) g/ml, respectively. All white-matter structures had significantly higher myelin water percentages (signal percentage with T2 between 10 and 50 ms) than all gray-matter structures. The range in geometric mean T2 of the main peak for both white and gray matter was from 70 to 86 ms. T2 distributions from the posterior internal capsules and splenium of the corpus callosum were significantly wider (width is related to water environment inhomogeneity) than those from any other white- or gray-matter structures. Thus, quantitative measurement and analysis of T2 relaxation reveals differences in brain tissue water environments not discernible on conventional MR images. These differences may make short T2 components reliable markers for normal myelin.

Abstract: The use of antibiotics may accelerate the development of antibiotic resistance genes (ARGs) and bacteria which shade health risks to humans and animals. The emerging of ARGs in the water environment is becoming an increasing worldwide concern. Hundreds of various ARGs encoding resistance to a broad range of antibiotics have been found in microorganisms distributed not only in hospital wastewaters and animal production wastewaters, but also in sewage, wastewater treatment plants, surface water, groundwater, and even in drinking water. This review summarizes recently published information on the types, distributions, and horizontal transfer of ARGs in various aquatic environments, as well as the molecular methods used to detect environmental ARGs, including specific and multiplex PCR (polymerase chain reaction), real-time PCR, DNA sequencing, and hybridization based techniques.

Abstract: Foreword R.F. Rubio. Preface. 1. Mining and the Water Environment. 2. Mine Water Chemistry. 3. Mine Water Hydrology. 4. Active Treatment of Polluted Mine Waters. 5. Passive Treatment of Polluted Mine Waters. Appendix. References. Index.