Recent years have seen a growing interest in the application of chalcogenide nanoparticles (NPs), e.g. Se, Te, CdSe and CdTe NPs, in various industrial sectors including energy, petroleum refining and in the field of biology and medicine. Moreover, due to the high toxicity of chalcogen oxyanions, their release into the environment is of great concern. Thus, emphasis was given in this study on the development of a novel microbial synthesis process of chalcogenide NPs by combining biological treatment of Se/Te containing wastewaters with biorecovery in the form of Se NPs, Te NPs and CdSe NPs. Enrichment of Se-oxyanion reducing microorganisms was carried out to simultaneously remove selenite (Se(IV)) and cadmium (Cd(II)) from wastewaters by combining bioremediation of toxic Se-rich wastewater with the biorecovery of Se as CdSe NPs. The results showed compositional changes in the extracellular polymeric substances (EPS) matrix of the anaerobic granular sludge upon exposure to Cd(II) and Se(IV) and identified the roles of EPS fractions in the biogenesis of CdSe NPs. Besides, it was found that the EPS on the surface of the biogenic Se NPs play a major role in lowering the bioavailability and toxicity of biogenic Se(0) compared to chemogenic Se(0) NPs. An upflow anaerobic sludge blanket (UASB) reactor was used for the first time to continuously remove tellurite from wastewater and recover biogenic Te(0).
1 General introduction
1.2. Problem description
1.3. Research objectives
1.4. Structure of the thesis
2 Literature review
2.2. Quantum dots and their properties
2.3. Metal Chalcogenide QDs
2.4. Biological metal chalcogenides
2.5. Sulfur based chalcogenides
2.6. Selenium based chalcogenides
2.7. Tellurium based chalcogenides
2.8. Mechanisms of biological synthesis of metal chalcogenides
2.9. Applications of chalcogenide QDs
3 Biological removal of selenate and ammonium by activated sludge in a sequencing batch reactor
3.2. Materials and Methods
4 Effect of heavy metal co-contaminants on selenite bioreduction by anaerobic granular sludge
4.2. Materials and methods
5 Biosynthesis of CdSe nanoparticles by anaerobic granular sludge
5.2. Materials and Methods
6 Modification of extracellular polymeric substances (EPS) of anaerobic granular sludge used for synthesis of cadmium selenide nanoparticles
6.2. Materials and methods
7 Continuous removal and recovery of tellurium in an upflow anaerobic granular sludge bed (UASB) reactor
7.2. Materials and methods
8 A comparison of fate and toxicity of selenite, biogenically and chemically synthesized selenium nanoparticles to the Zebrafish (Danio rerio) embryogenesis
8.2. Materials and methods
9 Discussion, conclusions and perspectives
9.1. General discussion
9.2. Synthesis of biogenic chalcogen alloys (e.g. Se/Te)
9.3. Future perspectives
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.