Microbiological modulation of suspended particulate matter dynamics: A study of biological flocculation in nutrient-enriched waters

Abstract

The study of suspended particulate matter (SPM) dynamics has conventionally focused on physical and hydrodynamical interactions, with little attention paid on exploring the role of SPM as a micro-ecosystem that sustains a wide diversity of microbial colonies. This thesis puts forth a new paradigm of SPM dynamics that integrates mineral, chemical, and biological components into one framework to emphasize the role of microorganisms in altering the chemistry and structure of SPM, which further affect its transport and deposition. Microbiological modulation of SPM dynamics was investigated in this thesis by coupling experiments with numerical models. Experimental results revealed that the size of biomass-affected SPM was approximately 60% larger and the capacity dimension was 2% lower as compared to biomass-free SPM. In contrast, the average settling velocity was observed to be nearly invariant for all SPM types. It was also found that the probability for SPM to aggregate was highly dependent on SPM shape and surface asperity, suggesting that microorganisms can alter SPM collision and aggregation kinematics through their role in modifying SPM structure and shape. Analyses coupling experimental results and a biogeochemical model further reveal the feedback interactions between minerals, chemicals, and microorganisms. It shows how changes in sediment and water qualities can have impacts on microorganisms that in turn modify SPM characteristics and result in further alteration of sediment and water qualities. This thesis provides an insight into the role played by microorganisms in engineering the architecture and altering the chemistry of SPM, with experimental evidence and simulation results put forth to emphasize that the contributions of nutrients and microorganisms cannot be neglected in modelling and predicting SPM dynamics.