1,721,286 research outputs found
Adsorptive removal of heavy metals from groundwater by iron oxide based adsorbents
No full textIn general groundwater is preferred as a source of drinking water because of its convenient availability and its constant and good quality. However this source is vulnerable to contamination by several substances. Substances that can pollute groundwater are divided into substances that occur naturally and substances produced or introduced by human activities. Naturally-occurring substances causing pollution of groundwater include for example, iron, manganese, ammonium, fluoride, methane arsenic, and radionuclides. Substances resulting from human activities include, for example, nitrates, pesticides, synthetic organic chemicals and hydrocarbons, heavy metals etc.Water ManagementCivil Engineering and Geoscience
Biotechnological applications for electronic waste water processing
Get PDFMany elements as copper, selenium, tellurium and rare earth elements are strategic elements in hightech electronics. Many of them are essential trace elements in living organisms, but also a potential toxin with very low threshold concentrations. Environmental biotechnological applications using bacterial biomineralization have the potential not only to remove these metals from contaminated waters, but also to sequester them in a reusable form. Biomineralization of many metals has been observed in phylogenetically diverse microorganisms isolated from pristine and contaminated environments, yet it is one of the poorly understood biogeochemical processes. Microbial respiration of metals and metalloids is unique as the microbial cells are presented with both soluble and insoluble (Me0) forms as terminal electron acceptor. This presentation will highlight biomineralization of metals, metalloids and rare earth elements and its potential biotechnologies in bioremediation and wastewater treatment.Many elements as copper, selenium, tellurium and rare earth elements are strategic elements in hightech electronics. Many of them are essential trace elements in living organisms, but also a potential toxin with very low threshold concentrations. Environmental biotechnological applications using bacterial biomineralization have the potential not only to remove these metals from contaminated waters, but also to sequester them in a reusable form. Biomineralization of many metals has been observed in phylogenetically diverse microorganisms isolated from pristine and contaminated environments, yet it is one of the poorly understood biogeochemical processes. Microbial respiration of metals and metalloids is unique as the microbial cells are presented with both soluble and insoluble (Me0) forms as terminal electron acceptor. This presentation will highlight biomineralization of metals, metalloids and rare earth elements and its potential biotechnologies in bioremediation and wastewater treatment
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Removal of H2S and volatile organic sulfur compounds by silicone membrane extraction
No full textBACKGROUND: This study explores an alternative process for the abatement and/or desulfurization of H2S and volatile organic sulfur compounds (VOSC) containing waste streams, which employs a silicone-based membrane to simultaneously remove H2S and VOSC. An extractive membrane reactor allows the selective withdrawal of VOSC and H2S simultaneously from the waste stream, while preventing direct contact between the waste stream and the absorbing solution and/or the biological treatment system. The influence of the sulfur compounds, membrane characteristics, extractant and pH was studied. RESULTS: Sulfide and the VOCS studied, i.e. methanethiol (MT), ethanethiol (ET) and dimethylsulfide (DMS) were removed from the synthetic wastewater using a silicone rubber membrane. Methanethiol showed the highest (8.72 x 10(-6) m s(-1)) overall mass transfer coefficient (k(ov)) and sulfide the lowest k(ov) value (1.23 x 10(-6) m s(-1)). Adsorption of the VOCS into the silicone membrane reduced the overall mass transfer coefficient. The k(ov) when using Fe(III)EDTA(-) as extractant (5.81 x 10(-7) m s(-1)) for sulfide extraction was one order of magnitude lower than with anaerobic water (2.54 x 10(-6) m s(-1)). On the other hand, the sulfide removal efficiency with Fe(III)EDTA(-) was higher (84%) compared with anaerobic water (60%) as extractant. An additional mass transfer resistance was formed by elemental sulfur which remained attached to the membrane surface. CONCLUSIONS: Extraction of sulfide and VOCS from a synthetic wastewater solution through a silicone rubber membrane is a feasible process as alternative to the techniques developed to treat VOSC emissions. Optimizing the aqueous absorption liquid can increase the efficiency of extraction based processes. (C) 2008 Society of Chemical Industr
The essential toxin: The changing perception of selenium in environmental sciences
No full textDuring the last decades, the perception of selenium has undergone substantial changes. While its toxic effects were recognized causing hair and hoof loss in animals during the 1930s, its essential role in microbial, animal and human metabolism has been recognized later, i.e. with the discovery of selenium deficiency causing ¿white muscle disease¿ in feedstock in the 1950s. Nowadays, the positive effect of systematic selenium supplementation is discussed in manifold topics such as cancer or diabetes prevention and avian influenza susceptibility. Treatment of selenium containing waste streams poses a notable challenge to environmental engineers, and to date no ultimate solution has been found for e.g. the selenium contamination in agricultural areas of the western USA. For the future, selenium contamination carries an imminent danger, if the increasing energy demand is covered by fossil fuel combustion, which will lead to major selenium emission and toxicity. This review presents current knowledge of selenium¿s role in environmental sciences and outlines potentially feasible treatment options targeting a variety of selenium contaminated waste stream
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