Analyzing Microalgae-Bacteria Population Changes in Response to Environmental Parameters for Improved Wastewater Treatment

Microalgae are incredible organisms that have a variety of uses such as wastewater treatment, fertilizer, livestock feed, and bio-compound production. Microalgae require a light source and minimal nutrients space to proliferate, making them an environmentally friendly and sustainable option for such processes. The Sustainable Wastes-to-Bioproducts Engineering Center at Utah State University is developing and implementing a Rotating Algae Biofilm Reactor (RABR) to remove total nitrogen and phosphorous from the Central Valley Wastewater Reclamation Facility wastewater effluent. Harmful compounds such as nitrates and phosphates are metabolized by the microalgae and converted into useful bioproducts, resulting in a circular economy. These RABRs are being optimized to treat the expected increase in human waste from the Salt Lake valley and meet the new Environmental Protection Agency's wastewater effluent guidelines. This study used a biological-based optimization approach by investigating the complex microbial-bacteria communities within the RABR biofilms. The purpose of this study was to characterize biofilm communities in the RABR inoculum, throughout system scale-up, identify key algal constituents, and identify environmental parameters for optimal RABR operating parameters. Metagenomic amplicon sequencing of the 16S, 18S, ITS, and 23S rRNA genes was used to characterize the prokaryotic, eukaryotic, fungal, and phototrophic communities, respectively, for a well-rounded understanding of the biofilm microecosystem. Microscopy was used as a complimentary and secondary method of microalgal classification. This study found that the CVWRF trickling filter can be used as an inoculum from May to November. At the lab-scale, the data suggested temperature can be used to modify prokaryotic and eukaryotic communities, while harvesting frequency can be used to alter phototrophic communities. At the bench-scale, polyester substratum tended to allow for higher species richness while cotton hosted a high abundance of Chlorella. A significant find was discovering that none of the communities significantly changed with scale-up suggesting long-term stability of the microalgae-bacteria populations. This study resulted in a pipeline that can be used in future research to characterize microalgae-bacteria biofilms. The workflow was successfully implemented to discover significant relationships between genera and RABR operating parameters, providing valuable data to the scientific community and a step forward to optimizing the RABR for simultaneous wastewater treatment and valuable compound production.