Bioreduction of selenite and tellurite by Phanerochaete chrysosporium

Selenium (Se) and tellurium (Te) are metalloids of commercial interest due to their physicochemical properties. The water soluble oxyanions of these elements (selenite, selenate, tellurite and tellurate) exhibit high toxicities; hence, their release in the environment is of great concern. This study demonstrates the potential use of fungi as Se- and Te-reducing organisms. The response of Phanerochaete chrysosporium to the presence of selenite and tellurite was evaluated, as well as its potential application in wastewater treatment and production of nanoparticles. Growth stress and morphological changes were induced in P. chrysosoporium when exposed to selenite and tellurite. Synthesis of Se 0 and Te 0 nanoparticles entrapped in the fungal biomass was observed, as well as the formation of unique Se 0 -Te 0 nanocomposites when the fungus was cultivated concurrently with Se and Te. The response of P. chrysosporium to selenite exposure was investigated in different modes of fungal growth (pellets and biofilm). A bioprocess for selenite removal and Se 0 nanoparticles recovery using an up-flow fungal pelleted reactor was developed. 70% selenite removal (10 mg Se L -1 d -1 ) was achieved under continuous mode. The use of Se 0 nanoparticles immobilized in P. chrysosporium pellets as a new sorbent material for the removal of heavy metals from wastewater was demonstrated. Contents 8 Acknowledgments 14 Summary 16 Résumé 17 Sommario 18 Samenvatting 19 CHAPTER 1 GENERAL INTRODUCTION 20 1.1 Background 21 1.2 Problem statement 21 1.3 Research objectives 22 1.4 Structure of the thesis 23 1.5 References 24 CHAPTER 2 LITERATURE REVIEW 26 Abstract 27 2.1 Introduction 28 2.2 Fungal pellets 28 2.2.1 Fungal pellets: formation and growth 28 2.2.2 Factors influencing the characteristics and formation of pellets 30 2.2.3 Fungal pellets in bioreactors 31 2.3 Fungal pelleted bioreactors for wastewater treatment 33 2.3.1 Potential applications and challenges 33 2.3.2 Reactor configurations 34 2.3.2.1 Stirred tank reactor 34 2.3.2.2 Airlift reactor 36 2.3.2.3 Bubble column reactor 37 2.3.2.4 Fluidized bed reactor 38 2.3.2.5 Hybrid reactors 38 2.3.3 Reactor design for fungal pelleted reactors 39 2.3.3.1 Mixing 39 2.3.3.2 Oxygen transfer 40 2.3.3.3 Shear force 40 2.3.4 Sterile versus non‐sterile conditions 40 2.3.5 Biomass recycle in fungal pelleted reactors 42 2.4 Removal of organic and inorganic pollutants 43 2.4.1 Removal of organic pollutants 43 2.4.1.1 Removal of dyes 44 2.4.1.2 Removal of phenolic compounds 45 2.4.1.3 Removal of pharmaceutical compounds 52 2.4.2 Removal of inorganic pollutants 53 2.5 Scope for further research 54 2.6 Conclusions 55 2.7 References 55 CHAPTER 3 Effects of selenium oxyanions on the white‐rot fungus 64 Abstract 65 3.1 Introduction 66 3.2 Materials and methods 67 3.2.1 Fungal culture and medium composition 67 3.2.2 Batch experiments 67 3.2.2.1 Fungal interaction with selenate and selenite 67 3.2.2.2 Effect of operational parameters on fungal growth, pelletization and Seremoval 68 3.2.3 Transmission electron microscopy (TEM) and electron‐energy lossspectroscopy (EELS) analysis 68 3.2.4 Analytical methods 68 3.3 Results 69 3.3.1 Fungal interaction with Se oxyanions 69 3.3.2 Effect of glucose concentration 73 3.3.3 Effect of pH 74 3.3.4 Effects of Se concentration 75 3.4 Discussion 76 3.4.1 Inhibition of fungal growth induced by Se oxyanions 76 3.4.2 Morphological effects induced by Se oxyanions 77 3.4.3 Removal of Se oxyanions by P. chrysosporium 77 3.4.4 Production of Se0 by P. chrysosporium 79 3.4.5 Potential applications 79 3.5 References 80 CHAPTER 4 Removal of selenite from wastewater in a Phanerochaete chrysosporium pellet based fungal bioreactor 85 Abstract 86 4.1 Introduction 87 4.2 Materials and methods 88 4.2.1 Strain, medium composition and pre‐cultivation of fungal cultures 88 4.2.2 Bioreactor configuration and operating conditions 88 4.2.3 Analytical methods 92 4.2.4 Statistical analysis 93 4.3 Results 93 4.3.1 Bioreactor operation in batch mode 93 4.3.2 Continuous bioreactor operation at constant Se concentrations 93 4.3.3 Bioreactor response to spikes of Se concentration 94 4.3.4 Evolution and growth of the fungal biomass 96 4.4 Discussion 96 4.4.1 Removal of SeO32‐ in a fungal pelleted bioreactor 96 4.4.2 Response of the system to Se spikes 98 4.4.3 Fungal morphology in the bioreactor 99 4.4.4 Operational advantages of fungal pelleted reactors 99 4.4.5 Longevity of reactor operation 100 4.5 Conclusions 101 4.6 References 101 CHAPTER 5 Sorption of zinc onto elemental selenium nanoparticles 105 5.1 Introduction 107 Abstract 106 5.2 Experimental 108 5.2.1 Biosorbent preparation 108 5.2.2 Biosorbent characterization 108 5.2.2.1 Potentiometric titration 108 5.2.2.2 SEM and FT‐IR 108 5.2.3 Batch adsorption experiments 109 5.2.4 Analytical methods 109 5.3 Results 110 5.3.1 Characterization of biosorbent material 110 5.3.2 Effects of operational parameters on sorption capacity of nSe0‐pellets 112 5.3.2.1 Effect of pH on Zn sorption 112 5.3.2.2 Effect of biosorbent dose on Zn sorption 114 5.3.3 Sorption kinetics 114 5.3.4 Adsorption isotherms 115 5.4 Discussion 117 5.4.1 Sorption mechanisms of Zn onto nSe0 pellets 117 5.4.2 Effects of operational parameters on sorption capacity of nSe0‐pellets 118 5.4.3 Potential applications 120 5.4.4 Conclusions 120 5.5 References 121 CHAPTER 6 Effect of selenite on the morpholoy and respiratory activity of 123 Abstract 124 6.2 Materials and methods 126 6.2.1 Fungal strain and culturing conditions 126 6.2.2 Biofilm growth and exposure experiments 126 6.2.3 Microsensor measurements 128 6.2.3.1 Estimation of diffusion coefficients 128 6.2.3.2 Estimation of biofilm physical properties based on diffusion coefficients andO2 inhibition 129 6.2.4 Biofilm sectioning and imaging 129 6.2.5 Analytical methods 130 6.2.5.1 Performance parameters of the flow‐cell reactor 130 6.2.5.2 Statistical analysis 130 6.3 Results 130 6.3.1 Influence of short‐term SeO32‐ exposure on P. chrysosporium biofilm activity 130 6.3.2 Influence of long‐term SeO32‐ exposure on P. chrysosporium biofilm activityand structure 133 6.3.2.1 Response to low Se influent concentration (10 mg Se L‐1) 133 6.3.2.2 Response to high Se influent concentration (20 mg Se L‐1) 135 6.4 Discussion 136 6.4.1 Inhibition of developed P. chrysosporium biofilms by SeO32‐ 136 6.4.2 Influence of SeO32‐ on the physical and morphological properties of P.chrysosporium biofilms 137 6.5 Conclusions 139 6.6 References 139 CHAPTER 7 Biomineralization of tellurium and selenium‐tellurium 142 Abstract 143 7.1 Introduction 144 7.2 Materials and methods 145 7.2.1 Fungal strain and culturing conditions 145 7.2.2 Batch experiments 145 7.2.2.1 Exposure to Se and Te oxyanions 145 7.2.2.2 Incubation with simultaneous presence of TeO32‐ and SeO32‐ 145 7.2.3 Characterizations of fungal morphology 146 7.2.4 Analytical methods 146 7.3 Results 146 7.3.1 Fungal interaction with chalcogen oxyanions 146 7.3.2 Effect of Se:Te ratio on TeO32‐ reduction 146 7.3.3 Fungal morphology 149 7.3.4 Electron microscopic analysis 150 7.4 Discussion 150 7.4.1 P. chrysosporium as a TeO32‐‐reducing organism 150 7.4.2 Synergetic effect of SeO32‐and TeO32‐on P. chrysosporium 152 7.4.3 Morphological effects induced by TeO32‐ and Se‐Te combinations 153 7.4.4 Production of nTe0 and nSe‐Te 153 7.5 Conclusions 155 7.6 References 155 CHAPTER 8 Mycotechnology for the treatment of Se and Te 159 Abstract 160 8.1 Mycotechnology 161 8.2 Fungal technology in the removal of Se and Te from wastewater 161 8.3 Fungi as Se0 and Te0 nanofactories 164 8.4 Novel hybrid fungal sorbents containing nanoparticles for wastewatertreatment 166 8.5 Fungal technology for the removal of Se and potential applications of theSe0 nanoparticles immobilized in fungal pellets 167 8.6 Conclusions and future perspectives 168 8.7 References 169 Appendix 1 172 Biography 177 Publications 178 Conferences 178 Sense 180 Content: 1 General introduction 1.1 Background 1.2 Problem statement 1.3 Research objectives 1.4 Structure of the thesis 1.5 References 2 Literature review 2.1 Introduction 2.2 Fungal pellets 2.2.1 Fungal pellets: formation and growth 2.2.2 Factors influencing the characteristics and formation of pellets 2.2.3 Fungal pellets in bioreactors 2.3 Fungal pelleted bioreactors for wastewater treatment 2.3.1 Potential applications and challenges 2.3.2 Reactor configurations 2.3.3 Reactor design for fungal pelleted reactors 2.3.4 Sterile versus non-sterile conditions 2.3.5 Biomass recycle in fungal pelleted reactors 2.4 Removal of organic and inorganic pollutants 2.4.1 Removal of organic pollutants 2.4.2 Removal of inorganic pollutants 2.5 Scope for further research 2.6 Conclusions 2.7 References 3 Effects of selenium oxyanions on the fungus Phanerochaete chrysosporium 3.1 Introduction 3.2 Materials and methods 3.2.1 Fungal culture and medium composition 3.2.2 Batch experiments 3.2.3 Transmission electron microscopy (TEM) and electron-energy loss spectroscopy (EELS) analysis 3.2.4 Analytical methods 3.3 Results 3.3.1 Fungal interaction with selenium oxyanions 3.3.2 Effect of glucose concentration 3.3.3 Effect of pH 3.3.4 Effects of selenium concentration 3.4 Discussion 3.4.1 Inhibition of fungal growth induced by selenium oxyanions 3.4.2 Morphological effects induced by selenium oxyanions 3.4.3 Removal of selenium oxyanions by P. chrysosporium 3.4.4 Production of Se0 by P. chrysosporium 3.4.5 Potential applications 3.5 References 4 Removal of selenite from wastewater in a Phanerochaete chrysosporium pellet based fungal bioreactor 4.1 Introduction 4.2 Materials and methods 4.2.1 Strain, medium composition and pre-cultivation of fungal cultures 4.2.2 Bioreactor configuration and operating conditions 4.2.3 Analytical methods 4.2.4 Statistical analysis 4.3 Results 4.3.1 Bioreactor operation in batch mode 4.3.2 Continuous bioreactor operation at constant selenium concentrations 4.3.3 Bioreactor response to spikes of selenium concentration 4.3.4 Evolution and growth of the fungal biomass 4.4 Discussion 4.4.1 Removal of selenite in a fungal pelleted bioreactor 4.4.2 Response of the system to selenium spikes 4.4.3 Fungal morphology in the bioreactor 4.4.4 Operational advantages of fungal pelleted reactors 4.4.5 Longevity of reactor operation 4.5 Conclusions 4.6 References 5 Sorption of zinc onto elemental selenium nanoparticles immobilized in Phanerochaete chrysosporium pellets 5.1 Introduction 5.2 Experimental 5.2.1 Biosorbent preparation 5.2.2 Biosorbent characterization 5.2.3 Batch adsorption experiments 5.2.4 Analytical methods 5.3 Results 5.3.1 Characterization of biosorbent material 5.3.2 Effects of operational parameters on sorption capacity of nSe0-pellets 5.3.3 Sorption kinetics 5.3.4 Adsorption isotherms 5.4 Discussion 5.4.1 Sorption mechanisms of Zn onto nSe0 pellets 5.4.2 Effects of operational parameters on sorption capacity of nSe0-pellets 5.4.3 Potential applications 5.4.4 Conclusions 5.5 References 6 Effect of selenite on the morpholoy and respiratory activity of Phanerochaete chrysosporium biofilms 6.1 Introduction 6.2 Materials and methods 6.2.1 Fungal strain and culturing conditions 6.2.2 Biofilm growth and exposure experiments 6.2.3 Microsensor measurements 6.2.4 Biofilm sectioning and imaging 6.2.5 Analytical methods 6.3 Results 6.3.1 Influence of short-term SeO3 2- exposure on P. chrysosporium biofilm activity 6.3.2 Influence of long-term SeO3 2- exposure on P. chrysosporium biofilm activity 6.4 Discussion 6.4.1 Inhibition of developed P. chrysosporium biofilms by SeO3 2- 6.4.2 Influence of SeO3 2- on the physical and morphological properties of P. chrysosporium biofilms 6.5 Conclusions 6.6 References 7 Biomineralization of tellurium and selenium-tellurium nanoparticles by the white-rot fungus Phanerochaete chrysosporium 7.1 Introduction 7.2 Materials and methods 7.2.1 Fungal strain and culturing conditions 7.2.2 Batch experiments 7.2.3 Characterizations of fungal morphology 7.2.4 Analytical methods 7.3 Results 7.3.1 Fungal interaction with chalcogen oxyanions 7.3.2 Effect of Se:Te ratio on tellurite reduction 7.3.3 Fungal morphology 7.3.4 Electron microscopic analysis 7.4 Discussion 7.4.1 P. chrysosporium as a tellurite-reducing organism 7.4.2 Synergetic effect of selenite and tellurite on P. chrysosporium 7.4.3 Morphological effects induced by tellurite and Se-Te combinations 7.4.4 Production of nTe0 and nSe-Te 7.5 Conclusions 7.6 References 8 Mycotechnology for the treatment of Se and Te contaminated effluents and biomineralization of Se0 and Te0 nanoparticles 8.1 Mycotechnology 8.2 Fungal technology in the removal of Se and Te from wastewater 8.3 Fungi as Se0 and Te0 nanofactories 8.4 Novel hybrid fungal sorbents containing nanoparticles for wastewater 8.5 Fungal technology for the removal of selenium and potential applications of the Se0 nanoparticles immobilized in fungal pellets 8.6 Conclusions and future perspectives 8.7 References Appendix 1 Selenium (Se) and tellurium (Te) are metalloids of commercial interest due to their physicochemical properties. The water soluble oxyanions of these elements (selenite, selenate, tellurite and tellurate) exhibit high toxicities; hence, their release in the environment is of great concern. This study demonstrates the potential use of fungi as Se- and Te-reducing organisms. The response of __Phanerochaete chrysosporium__ to the presence of selenite and tellurite was evaluated, as well as its potential application in wastewater treatment and production of nanoparticles. Growth stress and morphological changes were induced in __P. chrysosoporium__ when exposed to selenite and tellurite. Synthesis of Se0 and Te0 nanoparticles entrapped in the fungal biomass was observed, as well as the formation of unique Se0-Te0 nanocomposites when the fungus was cultivated concurrently with Se and Te. The response of __P. chrysosporium__ to selenite exposure was investigated in different modes of fungal growth (pellets and biofilm). A bioprocess for selenite removal and Se0 nanoparticles recovery using an up-flow fungal pelleted reactor was developed. 70% selenite removal (10 mg Se L-1 d-1) was achieved under continuous mode. The use of Se0 nanoparticles immobilized in __P. chrysosporium__ pellets as a new sorbent material for the removal of heavy metals from wastewater was demonstrated. The release of the water soluble oxyanions of selenium (Se) and tellurium (Te) in the environment is of great concern due to their high toxicities. Development of technologies for Se- and Te- removal, as well as their recovery, are imperative. This study demonstrates the potential of fungi as Se- and Te-reducing organisms.