Pathogen removal in aerobic granular sludge treatment systems

Description

This book describes pathogen removal processes in aerobic granular sludge (AGS) wastewater treatment systems. Faecal indicators (E. coli, Enterococci, coliforms and bacteriophages) were tracked in full-scale AGS facilities and compared to parallel activated sludge (CAS) systems. AGS showed similar removals as the more complex CAS configurations. Removal mechanisms investigated in laboratory-scale reactors showed that the AGS morphology contributes to the removal processes. By tracking E. coli and MS2, it was observed that organisms not attached to the granules are predated by protozoa during aeration. 18S RNA gene analyses confirmed the occurrence of bacterivorous organisms (e.g., Epistylis, Vorticella, Rhogostoma) in the system. Particulate material in the feeding stimulated their development, and a protozoa bloom arose when co-treating with (synthetic) faecal sludge (4 % v/v). An overview of the diverse eukaryotic community in laboratory reactors and real-life applications is also provided. The microbial diversity of the influent was different compared to AGS and CAS sludge samples. However, no clear differences were found between them on species level. This study contributes to a better understanding of the mechanisms behind pathogen removals in AGS systems. Cover Title Page Copyright Page Contents Acknowledgements Summary Samenvatting 1. Introduction 1.1 Theoretical background 1.1.1 AGS technology development 1.2 Pathogens and public health – motivation for this study 1.2.1 Faecal indicator of pathogenic organisms used to analyse water quality 1.3 Research gaps 1.4 Research aim 1.5 Research questions 1.6 Thesis outline 2. Faecal indicators removals in full-scale AGS and CAS systems 2.1 Introduction 2.2 Materials and Methods 2.2.1 Treatment facilities 2.2.2 Sample collection 2.2.3 Sample analysis 2.2.4 Bacteriophages enumeration 2.2.5 Bacteria enumeration 2.2.6 Data analysis 2.3 Results 2.3.1 FIOs concentrations in raw and treated wastewater 2.3.2 Log10 removal 2.3.3 Correlation between microbial organisms and water quality related parameters 2.4 Discussion 2.4.1 FIOs concentrations in raw and treated wastewater 2.4.2 Log10 removal 2.4.3 Correlation between microbial organisms and water quality related parameters 2.5 Conclusions 2.6 Annex 1 2.6.1 Statistical analyses products 3. Unravelling the removal mechanisms of faecal indicators in AGS systems 3.1 Introduction 3.2 Materials and methods 3.2.1 Research design 3.2.2 Laboratory-scale SBR 3.2.3 Synthetic wastewater 3.2.4 Bacterial and viral surrogates 3.2.5 Sample collection and processing 3.2.6 Microbiological sampling process 3.2.7 Optical microscope observation of protozoa 3.2.8 DNA extraction and 18S rRNA gene sequencing 3.2.9 E. coli fluorescence microscopy observations 3.2.10 Attachment of E. coli and MS2 bacteriophages 3.2.11 Contribution of the settling in the AGS reactor 3.3 Results 3.3.1 AGS reactors performance 3.3.2 Fate of the faecal surrogates in the long- term AGS laboratory- scale SBRs 3.3.3 Surrogates concentrations in the sludge and liquid fractions per operational phase 3.3.4 Relationship of attached protozoa and surrogates' removal 3.3.5 Eukaryotic community analysis 3.3.6 Predation recorded using fluorescent staining 3.3.7 Attachment kinetics 3.3.8 Contribution of settling in the AGS reactors to the removal of the faecal surrogates 3.4 Discussion 3.4.1 Reactor performance 3.4.2 Fate of the target surrogates during the operational conditions of the long-term reactors 3.4.3 Faecal surrogates' removals during the anaerobic plug flow feeding 3.4.4 Faecal surrogate removal during the aeration phase 3.4.5 Contribution of the settling in the removal of the faecal surrogates 3.4.6 Overall analysis 3.5 Conclusions 4. Co-treatment of synthetic faecal sludge and wastewater in an AGS system 4.1 Introduction 4.2 Materials and methods 4.2.1 Research design 4.2.2 Development of the synthetic FS recipe 4.2.3 Reactors set- up 4.2.4 Experimental procedures 4.2.5 Media composition 4.2.6 Analytical determinations 4.2.7 Data analysis 4.3 Results 4.3.1 Characterisation of the medium- strength synthetic FS 4.3.2 Evaluating the continuous performance of the AGS reactors 4.3.3 Effects of FS on the granular settle-ability and size distribution 4.3.4 Effects of the synthetic FS on the occurrence of protozoa 4.4 Discussion 4.4.1 Consideration for the development of a medium- strength synthetic FS .. 4.4.2 Effects of the FS on the continuous performance of the AGS reactor 4.4.3 Effects of FS on granular formation and stability 4.4.4 Effects of the synthetic FS on the occurrence of protozoa 4.4.5 The relevance of the findings for future applications 4.5 Conclusions 4.6 Annex 2 5. Eukaryotic community characterisation by 18s rRNA gene analysis in full- scale systems 5.1 Introduction 5.2 Materials and methods 5.2.1 Treatment facilities and sample collection 5.2.2 Sample collection and processing 5.2.3 Microscopy and scanning electron observation 5.2.4 DNA extraction and 18S rRNA gene sequencing 5.2.5 Data analyses 5.3 Results 5.3.1 Diversity and composition per sample 5.3.2 Core microbiota 5.3.3 Dominant eukaryotic structure community 5.3.4 Variation among treatments 5.4 Discussion 5.5 Conclusions 5.6 Annex 6. Outlook and conclusions 6.1 Insights into the pathogen degradation process 6.1.1 The fate of the pathogens and faecal indicators after treatment 6.1.2 Stable granulation with an overgrowth of protozoa in the surfaces 6.1.3 Pathogens and faecal indicators removal mechanisms 6.1.4 Protozoa predators, who are they? References List of acronyms List of Tables List of Figures About the author