The aim of this Ph.D. was to develop a technology for the remediation of seleniferous soils/sediments and to explore microbial reduction of selenium oxyanions under different respiration conditions and bioreactor configurations. Seleniferous soil collected from the wheat-grown agricultural land in Punjab (India) was characterized and its soil washing was optimized by varying parameters, where addition of oxidizing agents showed a maximum selenium removal efficiency. Aquatic plants, Lemna minor and Egeria densa were used to study phytoremediation of the selenium-rich soil leachate containing oxidizing agents. Additionally, migration of the soluble selenium fraction from the upper to the lower layers and its subsequent reduction and accumulation in the lower layers of the soil column was observed during soil flushing. Furthermore, the soil leachate containing selenium oxyanions obtained from soil washing was treated in a UASB reactor by varying the organic feed. Ex situ bioremediation of selenium oxyanions was studied under variable conditions. An aerobic bacterium (Delftia lacustris) capable of transforming selenate and selenite to elemental selenium was isolated and characterized. Anaerobic bioreduction of selenate coupled to methane oxidation was investigated in serum bottles and a biotrickling filter using marine sediment as inoculum. Finally, the effect of contamination of other chalcogen oxyanions (tellurium) on selenium bioreduction was studied in a continuous system (UASB reactor).
1 General Introduction
1.2. Problem Statement
1.3. Research objectives
1.4. Structure of thesis
2 Literature review - Environmental impact and bioremediation of seleniferous soils and sediments
2.2. Selenium in the soil environment
2.3. The biogeochemical selenium cycle
2.4. Selenium essentiality
2.5. Plant - selenium interactions
2.6. Microbe - selenium interactions
2.7. Bioremediation of seleniferous soils
3 Optimisation of soil washing for seleniferous soil from Northern India
3.2. Materials and methods
4 In situ and ex situ bioremediation approaches for removal and recovery of selenium from seleniferous soils of Northern India
4.2. Materials and methods
5 Phytoremediation of seleniferous soil leachate using the aquatic plants Lemna minor and Egeria densa
5.2. Materials and methods
6 Selenate reduction by Delftia lacustris under aerobic conditions
6.2. Materials and methods
7 Selenate bioreduction using methane as electron donor inoculated with marine sediment in a biotrickling filter
7.2. Materials & methods
8 Formation of Se(0), Te(0) and Se(0)-Te(0) nanostructures during simultaneous bioreduction of selenite and tellurite in upflow anaerobic sludge blanket reactor
8.2. Materials and methods
9 Discussion, Conclusion and Perspectives
9.1. General discussion
9.2. Selenium removal and biotreatment of seleniferous soil
9.3. Biological treatment by microbial reduction
9.4. 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.