An indigenous mixed culture of bacteria collected from a Wastewater Treatment Plant (Brits, North West Province, South Africa), biocatalytically reduced Cr(VI) in the presence of As(III). Both the reduced chromium (Cr(III)) and the oxidised arsenic (As(V)) readily form amorphous hydroxides that can be easily separated or precipitated from the aqueous phase as part of the treatment process. Treatment of Cr(VI) and As(III) before disposal of wastewater is critical since both compounds are known to be carcinogenic and mutagenic at very low concentrations, and acutely toxic at high concentrations. Batch experiments were conducted to evaluate the rate of Cr(VI) reduction under anaerobic condition in the presence of its co-contaminant As(III) typically found in the groundwater and mining effluent. Results showed near complete Cr(VI) reduction under initial Cr(VI) concentrations up to 70 mg/L in a batch amended with 20 mg/L As(III). However, increasing Cr(VI) concentrations up to 100 mg/L resulted in the inhibition of Cr(VI) reduction activity. Further investigation was conducted in a batch reactor amended with 70 mg/L Cr(VI) concentration at different As(III) concentrations ranging from 5-70 mg/L to evaluate the effect of varying As(III) concentration on Cr(VI) reduction efficiency. Results showed that Cr(VI) reduction efficiency increased as As(III) concentrations increased from 5-40 mg/L. However, further increase in As(III) concentration up to 50 mg/L resulted in incomplete Cr(VI) reduction and decrease in Cr(VI) reduction efficiency. These results suggest that the rate of Cr(VI) reduction depends on the redox reaction of As(III) and As(V) with Cr(VI). Moreover, the inhibitory effect observed at high Cr(VI) and As(III) concentration may also be attributed to the dual toxicity effect of Cr(VI) and As(III) on microbial cell. From the above batch kinetic studies lethal concentration of Cr(VI) and As(III) for these strains was evaluated and established. Initial evaluation of the bacteria using 16S rRNA partial sequence method showed that cells in the mixed culture comprised predominantly of the Gram-positive species: Staphylococcus sp., Enterobacter sp., and Bacillus sp. The biokinetic parameters of these strains were estimated using a non-competitive inhibition model with a computer programme for simulation of the Aquatic System “AQUASIM 2.0”. Microbial reduction of Cr(VI) in the presence of As(III) was further investigated in continuous-flow bioreactors (biofilm reactor) under varying Cr(VI) loading rates. The reactor achieved Cr(VI) removal efficiency of more than 96 % in the first three phases of continuous operation at lower Cr(VI) concentration ranging from 20-50 mg/L. However, 20 % decrease in Cr(VI) removal efficiency was observed as Cr(VI) concentration increase up to 100 mg/L. The reactor was able to recover from Cr(VI) and As(III) overloading phase after establishing the resilient nature of the microorganism. Similarly to the batch reactor studies the overall performance of the reactor also demonstrated that the presence of As(III) greatly enhance Cr(VI) reduction in a bioreactor. This was evident by near complete removal of Cr(VI) concentration up to 50 mg/L. The basic mass balance expressions on Cr(VI) along with the non-competitive inhibition model were used to estimate the biokinetic parameters in the continuous flow bioreactor system. Cr(VI) reduction efficiency along the longitudinal column was also evaluated in this study. Results showed that Cr(VI) efficiency increased as Cr(VI) concentration travels along the longitudinal column. Other important factors such as oxygen and pH during biological Cr(VI) reduction in the presence of As(III) oxidation were also evaluated. / Dissertation (MEng)--University of Pretoria, 2014. / tm2015 / Chemical Engineering / MEng / Unrestricted

Arbetet strävar efter att klargöra vem som formulerar frågan – varför har vi slöjd i svensk grundskola? och undersöka vilka empiriska evidens som finns till slöjdämnets försvar och ifrågasättande. Är frågan allmänt levande i samhället eller är den ett hjärnspöke skapat av slöjdlärarna själva. Om slöjdlärare felaktigt upplever ämnet motarbetat och ifrågasatt av samhället kan lärarna själva komma att motarbeta ämnets existens, med destruktiva följder för ämnet som möjlig konsekvens. Om samhället och lärarna däremot ställer sig frågan konstruktivt kan den vitalisera slöjdämnets utövande och innebörd. Studien bygger på två undersökningar med kvantitativ ansatts som strävat efter statistiskt jämförbara resultat. Första undersökningen var en webbstudie med fenomenografisk ansats och andra undersökningen var en enkätstudie riktad till slöjdlärare och allmänhet med spridning av randomiserad karaktär. Google-enkätformulär och Google-kalkylark användes för enkät och grafisk presentation. Uppsatsen presenterar sammanfattat teoretiskt bakgrundsmaterial ur rapporter utförda på uppdrag av UNESCO och OECD, vilka visar på estetiska ämnens upplevda förmåga att utveckla studenters lärande i andra ämne genom bl.a. transfereffekter. Rapporterna visar även att dessa upplevda effekter till största del saknar empirisk evidens. För nationellt och direkt slöjdanknutet perspektiv behandlas i uppsatsen fakta ur ämnesutvärderingarna NÄU-13 och NU-03, vilka till del, likt de internationella rapporterna, visar på samma avsaknad av empirisk evidens för estetiska ämnens positiva påverkan på elevernas kunskap och lärande.

Clays are considered as potential host rocks and backfill material for deep geological repositories for radioactive waste. Therefore, profound understanding of radionuclide retention processes at clay mineral surfaces is essential for a long-term safety assessment. This understanding has already been generated in the past for simple chemical systems, in which experiments are easy to conduct and interpretation is straightforward. However, there is still a lack of molecular process understanding when considering complex natural systems (low radionuclide concentrations, high ionic strength, high pH values, multi-mineral solid phases, complex solution composition). This thesis aims to close some of these knowledge gaps, focusing on U(VI) and Np(VI) sorption on clays at (hyper)alkaline conditions. pH values between 10 and 13 can prevail in the near-field of a radioactive waste repository as a result of the degradation of concrete, which is part of the geo-engineered barrier. Existing studies on radionuclide sorption on clays do not exceed pH 10. Therefore, within this work, a comprehensive investigation in the pH range 8-13 was conducted. This included the quantification of radionuclide retention in batch sorption experiments as well as spectroscopic investigations to generate understanding about the underlying retention mechanisms on a molecular level. Beside the pH, additional focus was on the influence of dissolved carbonate and calcium on radionuclide sorption at (hyper)alkaline conditions. Next to two small chapters dealing with the stability and surface charge of Ca-bentonite at (hyper)alkaline conditions (chapter 4.1) and the influence of ISA on U(VI) sorption at high pH values (chapter 4.3), the thesis can be subdivided in two major parts. The first part (chapter 4.2) is a detailed investigation of U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions in mixed electrolyte solutions. Batch sorption experiments were conducted, varying a number of experimental parameters (sorption time, S/L ratio, U(VI) concentration, pH value, carbonate concentration) and assessing their effect on U(VI) sorption. In order to be able to explain the observed sorption behavior, next to U(VI) solubility tests, spectroscopic techniques were applied. The aqueous speciation of U(VI) was investigated with TRLFS, while its surface speciation was probed with ATR FT-IR, site-selective TRLFS, EXAFS and CTR/RAXR. Since the results of this chapter indicated a great importance of the presence of calcium (see below), the second major part of the thesis (chapter 4.4) was dedicated to a careful evaluation of the influence of calcium on An(VI) sorption on clay minerals at (hyper)alkaline conditions. This encompasses the sorption of Ca(II) on Ca-bentonite and its effect on the bentonite surface charge. Furthermore, U(VI) batch sorption experiments with Na-montmorillonite, synthetic kaolinite and muscovite were conducted in 0.1 M NaCl as well as in 0.1 M NaCl + 0.02 M CaCl2 at pH 8-13, in order to quantify the influence of calcium on U(VI) sorption on supposedly Ca-free mineral phases. Site-selective TRLFS was applied with the aim to observe U(VI) sorption species involving calcium. Finally, complementary sorption experiments Np(VI) on muscovite were performed in order to check whether its sorption behavior is analogous to U(VI) under the given conditions. Batch sorption experiments demonstrate that U(VI) retention on Ca-bentonite can be very effective at pH > 10, even in the presence of carbonate and despite the prevalence of anionic aqueous species. Above a certain pH, depending on the concentration of carbonate in solution, carbonate does not play a role in the aqueous U(VI) speciation anymore due to the predominance of hydrolysis. TRLFS measurements revealed a clear correlation between sorption behavior and aqueous U(VI) speciation, showing that retention reaches a maximum at pH 10-12, where UO2(OH)3− is the predominant aqueous species. This raised the question whether the strong retention can be achieved by adsorption of an anionic species to the negatively charged mineral surface or rather by precipitation of uranates. By in situ ATR FT-IR and CTR/RAXR experiments the formation of U(VI) precipitates on the mineral surface was observed at U(VI) concentrations of 2×10-5 M and 5×10-5 M, respectively. However, solubility tests at sub-micromolar U(VI) concentrations, which were also applied in the batch sorption experiments, showed that the observed complete U(VI) removal at pH 10-12 cannot be attributed to precipitation of (earth) alkali-uranates from the solution. In order to unambiguously distinguish between surface precipitation and surface complexation, direct spectroscopic investigations of the U(VI) complexes on the Ca-bentonite surface were performed with site-selective TRLFS and EXAFS. The occurrence of luminescence line-narrowing and the frequency of the total symmetric stretch vibration obtained from the site-selective TRLFS emission spectra, indicate the presence of two U(VI) surface complexes. Also EXAFS spectroscopy confirmed the presence of two independent U(VI) sorption species on Ca-bentonite at pH 8-13. With increasing pH, the nature of the retained U(VI) complexes shifts from bidentate inner-sphere surface complexes with an overall equatorial coordination of five adsorbed on aluminol or silanol edge sites to surface complexes with a 4-fold equatorial coordination, resembling the aqueous species UO2(OH)42−. For the first time, a 4-fold coordination in the equatorial plane of U(VI) was univocally proven with the help of a multiple-scattering feature originating from the strong symmetry of the complexes, and without the need for error-prone shell fitting. The lack of scattering paths from the substrate and the comparatively high value for the total symmetric stretch vibration indicate that the high-pH-component is an outer-sphere complex. Concerning the character of the second sorption species at very high pH it was hypothesized that the anionic uranyl hydroxide complexes are mediated to the surface by calcium cations. It was found that calcium sorbs strongly on Ca-bentonite between pH 8 and 13. Also zeta potential measurements showed a partial compensation of the strongly negative surface charge of Ca-bentonite due to adsorption of calcium. U(VI) sorption on kaolinite and muscovite was strongly reduced in the absence of calcium at pH > 10. An increased retention upon addition of calcium proved the sorption enhancing effect of calcium at pH 10-12. Site-selective TRLFS allowed the spectroscopic observation and identification of calcium-induced U(VI) sorption complexes on muscovite. The obtained spectra correspond to the outer-sphere species found on Ca-bentonite. Combining the findings from batch sorption, zeta potential, TRLFS and EXAFS suggests that calcium adsorbs to the mineral surface in the first place, displaying locally positively charged sites which enable an electrostatically driven attachment of anionic uranyl hydroxides. The same effect could also be demonstrated for Np(VI) sorption on muscovite, which was also strongly enhanced in the presence of calcium at pH 9-12. ISA leads to a mobilization of U(VI) at (hyper)alkaline conditions only when present in very high excess of U(VI). A reduction of sorption on Ca-bentonite and the formation of aqueous U(VI)-ISA complexes, detected with TRLFS, occurred at an U:ISA ratio of 1:100,000. Such conditions are not likely to be found in deep geological repository environments. Based on these findings it can be concluded that under certain alkaline repository conditions, where precipitation does not occur (due to very low concentrations or kinetic restraints), U(VI) and Np(VI) are still effectively retained in argillaceous minerals and rocks by adsorption despite the anionic character of prevailing aqueous species. Repulsive forces between the actinide species and the mineral surfaces are overcome by mediating Ca2+. This finding is of great relevance, as also the migration of very small amounts of uranium or neptunium out of waste repositories could lead to a hazardous accumulation in the long term. The achieved knowledge gain concerning radionuclide retention at environmental conditions helps to take the next step towards realistic long-term safety assessment of nuclear waste repositories.

This study examines how one of the most influential Swedish newspapers, Aftonbladet,reports about the suburb Rosengård. Rosengård is located in Malmö and have become asymbol of Sweden’s suburbs and immigration policy. Both national and internationalmedia have reported about organized crime, shootings and different social problems inRosengård. The area is considered to be a particularly vulnerable area. At the sametime, many researchers believe that the media reporting regarding suburbs does notnecessarily correspond to the reality. The methods used in this study are a quantitativeand qualitative content analysis. The material studied are news articles concerningRosengård that were published in Aftonbladet in the last five years. The purpose was to,based on Goffman’s framing theory, investigate how Aftonbladet frames Rosengård andthe people who lives there. The purpose was also to investigate whether Aftonbladet,based on Hall’s and Said’s theories of representation and orientalism, creates an “us andthem”-perspective. The results show that Rosengård is portrayed as a criminal andproblematic area. As in previous research about media and suburbs, the results of thisstudy show that Rosengård is presented as a different and deviant area in comparison tothe “ordinary society”. It is rarely people living in the area who are quoted, referencedor described in the articles. Instead, it is often the police or government officials whogets to describe the situation in Rosengård. In cases where the residents in the area areallowed to speak, or are described, it is often based on their role as immigrants. The factthat these articles emphasize that the residents are immigrants but have made a careerand are against crime, we believe that Aftonbladet creates an us-and-them-perspective.This is based on that Aftonbladet portrays the residents as exceptional cases to “theordinary immigrant”. The consequences of Aftonbladet frames could be that the societygets an idea of the area that does not have to agree with the reality and that Rosengårdbecomes even more segregated.

Teil A: Es wurde gezeigt, dass das Transportverhalten von Uran in der Umwelt und an den ehemaligen Uranabbaustätten stark von der Anwesenheit und Aktivität natürlich vorkommender Mikroorganismen abhängt. Die Untersuchungen zeigten, dass die Isolate eine hohe Toleranz gegenüber Uran aufweisen und in der Lage sind, relativ hohe Mengen an Uran zu immobilisieren und aus der umgebenden Lösung zu entfernen. Durch anaerobe Versuche konnte gezeigt werden, dass die mikrobielle Reduktion von Uran(VI) allein durch die Zugabe von 10 mM Glycerin bei zukünftigen Anwendungen als in situ Biosanierungsapplikationen genutzt werden könnte. Die Ergebnisse dieser Arbeit konnten die Wechselwirkungsmechanismen zwischen natürlich vorkommenden Mikroorganismen und Uran im Detail beschreiben und neue Zusammenhänge zwischen aktivem und inaktivem Stoffwechsel der Mikroorganismen zeigen. Zusammenfassend können diese einen wertvollen Beitrag zur Entwicklung von Biosanierungsansätzen für die Behandlung von Radionuklid-kontaminierten Standorten aus der ehemaligen Bergbauindustrie leisten. Teil B: Im Speichel dominiert neben einem kleinen Bindungsanteil an dem Enzym alpha-Amylase die Komplexierung mit anorganischen Liganden, im Magen dominiert aufgrund des sauren pH-Wertes das Eu- bzw. Cm-Aquo-Ion, und im Darm dominiert neben anorganischen Komplexen die Bindung der Metallionen an das Glycoprotein Mucin. Die starke Komplexfähigkeit von Mucin gegenüber dreiwertigen f-Elementen könnte die Absorption dieser im menschlichen Körper unterdrücken und deren Exkretion fördern. Die Ergebnisse dieser Arbeit geben neue Einblicke in das biochemische Verhalten dreiwertiger f-Elemente und können zudem zur Einschätzung von Gesundheitsrisiken nach der Inkorporation von Radionukliden und der Entwicklung von Dekontaminationstherapien beitragen.

In den 80-iger Jahren war die DDR hinter den USA und Kanada der drittgrößte Uranproduzent mit einer Jahresproduktion von ca. 200.000 Tonnen. Die Gewinnung erfolgte durch konventio­nellen Bergbau, durch in- situ- oder offene Haufenlagerung. Die Urangewinnung auf dem Ter­ritorium der ehemaligen DDR wurde nach der Wiedervereinigung eingestellt und mit der Sa­nierung der Altstandorte begonnen. Nach Einstellung des Uranabbaus muss die Wasserhaltung solange betrieben werden, bis eine kontrollierte Flutung der Bergbauschächte erfolgen kann. Die dabei anfallen­den Grubenwässer werden je nach Schadstoffkonzentration direkt in den Vorfluter abgeleitet oder in geeigneten Aufbereitungsanlagen meist durch Flockung und Adsorption behandelt. Dieses praktisch oft angewandte Grubenwasserreinigungsverfahren bezüglich Uran und den auftretenden Begleitelementen Chrom und Arsen hat den entscheidenden Nachteil, dass die anfallenden schwermetallhaltigen Fällschlämme auf Deponien verbracht werden müssen. Durch Niederschlags­ereignisse oder ansteigendes Grundwasser besteht die Gefahr, dass die Deponien wieder ausgelaugt werden und somit eine erneute Mobilisierung von Schwermetallen in die Umwelt erfolgt. Die Sanierung kontaminierter Gebiete, insbesondere Sedimente, Sondermüll-deponien, Standorte ehemaliger Galvanikbetriebe, Betriebsflächen chemischer Industriestandorte, Rieselfelder oder Orte der Klärschlammaufbereitung erfordern neue Herangehensweisen an das gegenwärtig hochaktuelle Problem der Rehabilitation. Es wurde deshalb u.a. im Rahmen dieser Arbeit ein Konzept auf Grundlage der elektrochemischen Umset­zung im "verdünnten" elektrochemischen Festbettreaktor entwickelt, das es gestattet, die mo­bilen Schwermetallspezies im Boden bzw. Deponiekörper in immobile Schwermetallverbindungen um­zuwandeln. Damit kann die Nachsorge und Sicherung solcher Deponiekörper bezüglich einer Remobilisierung wesentlich kostengünstiger gestaltet werden. Ausgehend von diesem Konzept sollen Möglichkeiten, Einsatzbedingungen und -grenzen der Immobilisierung von Schwermetallen am Beispiel von Uran(VI), Chrom(VI), Arsen(III) und chlorierten Kohlenwasserstoffe aufgezeigt werden. Elektrochemische Verfahren zur Sanierung kontaminierter Böden, Schlämme und Sedimente befinden sich international in einer dynamischen Forschungs- und Entwicklungsphase. Sie sind einzeln und in Verfahrenskombinationen einsetzbar und werden, bei verantwortungsvoller Handhabung, in absehbarer Zeit auch als zertifizierte Verfahren in Deutschland in bestimmten Sanierungsvorhaben ihre Leistungsfähigkeit beweisen. Gegenwärtig befinden sie sich in Deutschland noch im Stadium der Forschung und Entwicklung, während international (z.B. USA, Niederlande) schon kommerzielle Anwendungen angeboten werden. Zur objektiven Beurteilung ihrer Leistungsfähigkeit und Einsatzgrenzen bedarf es spezieller Grundkenntnisse. Elektrochemische Remediationsverfahren können als ergänzende, in Einzelfällen auch als alternative Verfahren zur Sediment- und Bodensanierung angesehen werden. Sie haben dann eine Chance auf Einsatz, wenn vor Ort (in- situ) saniert werden soll. Von ihrem Prinzip her, sind sie preiswerter als Bodenaushub und Verbrennung. Das Sanierungsziel besteht in einer möglichst vollständigen Konzentrierung oder Umsetzung der Wasserschadstoffe an der Feststoffmatrix.

Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors. Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 lm show a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical spectra, with two cavity modes being observed at different energies for orthogonal polarizations.

We conclusively explain the different lasing mode energies in ZnO nano- and microcavities observed by us and reported in literature. The limited penetration depth of usually used excitation lasers results in an inhomogeneous spatial gain region depending on the structure size and geometry. Hence, weakly or even nonexcited areas remain present after excitation, where modes are instantaneously suppressed by excitonic absorption. We compare the effects for ZnO microwires, nanowires, and tetrapod-like structures at room temperature and demonstrate that the corresponding mode selective effect is most pronounced for whispering-gallery modes in microwires with a hexagonal cross section. Furthermore, the absorptive lasing mode suppression will be demonstrated by correlating the spot size of the excitation laser and the lasing mode characteristic of a single ZnO nanowire.

The village-based microfinance approach Village Savings and Loan Associations (VSLAs) has been implemented in developing countries for three decades, and is found to be an effective tool in alleviating poverty and facilitating access to financial services in rural areas.  This study, done in collaboration with Vi Agroforestry, aimed to investigate the impact of VSLA activities on female empowerment in Rwanda, and more specifically, how women's access to and control over assets have been affected by VSLA participation. The term 'female empowerment' refers to the process by which women gain control and power over their own life situations and their ability to make strategic choices, that is, the capacity to turn choices into desired actions and outcomes.  A qualitative methodology has been used, where the main data collection consisted of six individual interviews with VSLA staff responsible for implementing, monitoring and evaluating VSLA groups in six different districts, and two focus group interviews with female VSLA participants in two different districts, carried out during April and May 2021.  The findings show that VSLA participation significantly accelerates the process of female empowerment in both household and community domains for women in Rwanda and that VSLA is an efficient first step in moving from a marginalised position in the society. However, women are still in many cases restricted from claiming all potential benefits from VSLA participation by structures that dictate normative gender roles and power structures. The findings highlight the importance of continued gender-related and financial training in order to further increase female access to and control over resources through VSLAs.

Studiens syfte är att beskriva och kritiskt analysera historielärares tal om sin undervisning i relation till läroplanens mål om historiemedvetenhet, kulturmöten och mångfald för historia i årkurs 6. Genom att fördjupa oss i lärarnas utsagor har det varit möjligt att definiera ett antal diskurser i historielärares tal om sin undervisning i årskurs 4–6. Studien baseras på intervjuer med fem lärare som arbetar i tre olika kommuner och deras berättelser är fundamentet för analysen. För att genomföra analysen har kritisk diskursanalys använts som verktyg.  Studiens centrala resultat är att lärarnas tal utgår från att det vill elevernas bästa, samtidigt som det blir uppenbart att den interkulturella pedagogiken inte sätter sin prägel på undervisningen. Utöver detta framträder postkoloniala föreställningar genom uttryck som ”vi” och ”de andra” i lärarnas tal. Därav går det att identifiera två diskurser gällande interkulturell pedagogik, diskursen om ”vi” och ”de andra” samt den homogena kontra heterogena diskursen och dess påverkan för praktiken. Detta kan potentiellt leda till en historieundervisning som reproducerar etnocentriska normer och andrafierar icke-svenska elever.  Studiens kunskapsbidrag är därmed för det första av betydelse för att medvetandegöra lärare om olika förgivettagande och normer som artikuleras och vilka konsekvenser detta kan få för eleverna. För det andra bidrar studien till att belysa komplexiteten i historielärarnas uppdrag och hur politiska beslut så som läroplanens utformning utgör betydande utmaningar för den yrkesaktiva läraren, vilket igen innebär implikationer för möjligheten för interkulturell historieundervisning.