Novel bioremediation processes for treatment of seleniferous soils and sediment

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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).  Read more... Abstract: 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) Content: Cover Title Page Copyright Page Table of Contents Acknowledgement Summary Abstract Résumé Sommario CHAPTER 1: General Introduction 1.1. Background 1.2. Problem Statement 1.3. Research objectives 1.4. Structure of thesis References CHAPTER 2: Literature review -- Environmental impact and bioremediation of seleniferous soils and sediments Abstract 2.1. Introduction 2.2. Selenium in the soil environment 2.2.1. Selenium content and species present in soils and sediments 2.2.2. Sources of selenium in soil 2.2.3. Sources of selenium in sediments. 2.3. The biogeochemical selenium cycle2.3.1. Selenium speciation 2.3.2. Isotopic speciation of selenium 2.3.3. Factors affecting selenium speciation in soil 2.3.4. Role of the soil compartment in the biogeochemical selenium cycle 2.4. Selenium essentiality 2.4.1. Metabolic role of selenium in animals and humans 2.4.2. Selenium toxicity 2.4.3. Selenium deficiency 2.5. Plant -- selenium interactions 2.5.1. Selenium metabolism in plants 2.5.2. Role of rhizospheric microorganisms 2.6. Microbe -- selenium interactions 2.6.1. Selenium metabolism in microorganisms 2.6.2. Aerobic reduction. 2.6.3. Anaerobic reduction2.7. Bioremediation of seleniferous soils 2.7.1. Phytoremediation by use of selenium hyperaccumulators 2.7.2. Phytoremediation by genetic engineering of plants 2.7.3. Microbial remediation by bioaugmentation 2.7.4. Microbial remediation by volatilization 2.7.5. Microbial remediation by in situ bioreduction of selenium 2.7.6. Ex situ bioremediation by soil washing 2.8. Conclusions References CHAPTER 3: Optimisation of soil washing for seleniferous soil from Northern India Abstract 3.1. Introduction 3.2. Materials and methods. 3.2.1. Sample collection and characterisation3.2.2. Soil flushing 3.2.3. Soil washing 3.3. Results 3.3.1. Soil characterisation 3.3.2. Se leaching in column by soil flushing Figure 3.1. (a) Se extracted (%) from the soil with respect to the total leachate and 3.3.3. Optimisation of soil washing 3.4. Discussion 3.4.1. Se migration in the soil column 3.4.2. Optimization of seleniferous soil washing 3.4.3. Practical implications 3.5. Conclusion References. CHAPTER 4: In situ and ex situ bioremediation approaches for removal and recovery of selenium from seleniferous soils of Northern IndiaAbstract 4.1. Introduction 4.2. Materials and methods 4.2.1. Sample collection and chemicals 4.2.2. In situ treatment using microcosms 4.2.3. Seleniferous soil leachate preparation and UASB reactor operation 4.2.4. Characterisation of anaerobic granular sludge 4.2.5. Analysis 4.3. Results 4.3.1. In situ microcosm for anaerobic reduction of selenium 4.3.2. Treatment of soil leachate in a UASB reactor.