Linking Complex Nutrient Kinetics and Ecological Processes within a Photosynthetic Mixed Microbial Community

Anthropogenic point and non-point nutrient sources have long been implicated in the eutrophication and disruption of surface waters. The application of algal biotechnologies provides opportunities to remediate municipal, agricultural, and industrial waste streams while enhancing nutrient cycling and producing an economically valuable product in the form of algal biomass. Despite interest in the development of these technologies there exist limitations in understanding the complex behavior of mixed algal-bacterial microbial communities, which may in turn constrain the performance of such systems in an engineered setting. The goal of this dissertation is to identify how nutrient loading in photobioreactors affects the microbial community and its ability to carry out nutrient uptake and produce algal biomass. One of the major barriers in the way of algal-based biotechnology's adoption is the high energy costs associated with dewatering biomass prior to processing. To address this challenge, a novel bioreactor called a high density bioreactor (HDBR) was adapted to a photobioreactor configuration. Over the course of experimentation we demonstrate that HDBRs are able to consistently produce highly dense biomass, while removing the bulk of nutrients and producing high quality effluent with low suspended solids content. Metagenomic analysis was employed to characterize the functional capabilities and taxonomic composition of the microbial communities within the reactors. We found Chlamydomonas reinhardtii and Parachlorella kessleri to be the two dominant algal strains and a member of the Leptolyngbya genus to be the dominant Cyanobacteria species. Nitrifying and denitrifying bacteria composed a small but significant amount of the microbial community; their abundances were quantified using real-time quantitative PCR (qPCR). This information was used to interpret and explain the patterns in nitrification and nitrogen removal carried out by the community as a whole. Further reactor studies were carried out to characterize the impact that N species availability (NH4+ vs NO3-) had on total nitrogen removal, and how organic carbon availability impacted those dynamics. It was determined that, in these systems, NO3- loading was more dominant in determining microbial community structure, that NH4+ had little effect (at least within these experiments), and that having NPOC available significantly increased nitrogen and phosphate removal. It was also demonstrated that observed removal rates can be modeled as a function of the nutrient loading parameters using the constrained variance of the microbial community obtained from redundancy analysis.Ph.D., Environmental Engineering -- Drexel University, 201