Bioprospecting for Nordic photosynthetic consortia for wastewater treatment, carbon capture, and value creation

Abstract

Microalgal biotechnology has been proposed as a potential solution to multiple global challenges, especially carbon capture, wastewater treatment, and bioproduction of valuable fuels and materials. Conventional microalgal monoculture is, however, too costly for production of any but the most high-value biocompounds. To fully exploit the capabilities of microalgae as a solution to these global crises, this dissertation reports a different approach, using constructed photosynthetic consortia and a hybrid liquidbiofilm cultivation technique. Emulating natural environments in artificial systems allows for the cultivation of robust and resilient cultures which can adapt as a community to changing conditions. During each study, photosynthetic consortia were constructed from Nordic species sampled from local ecosystems, which reduced the light and temperature requirements of cultivation; this approach is applicable in every environment where photosynthetic consortia are indigenous. Samples were taken from various natural aquatic environments (e.g., tree bark, lakes, stormwater reservoirs) and human-made environments (e.g., a home aquarium and wastewater treatment plant). These cultures were combined prior to each experiment with the aim of improving carbon capture, wastewater treatment, and bioproduction, while simultaneously reducing operational costs. All studies demonstrated that, when cultivating consortia, the biological functions of the system can be tailored to different industrial applications, but that there are tradeoffs to consider as well.

A hybrid cultivation technique was developed, combining conventional liquid suspension with different surfaces to encourage biofilm formation, thereby facilitating simultaneous attached and pelagic growth of consortia species. Over the course of this dissertation, hybrid cultivation was scaled up and fine-tuned, exploring different wastewaters and light regimes, to optimise carbon capture, wastewater treatment, and production of biomass and polyhydroxybutyrate (PHB, a bioplastic precursor) by photosynthetic consortia. Finally, different approaches were applied to elucidate the most viable bioenergy upgrading pathways for protein- and carbohydrate-rich consortia biomass within a biorefinery scheme. This dissertation determined that wastewater blending and cultivation of mixed-species consortia can solve some challenges associated with cultivation; primarily the need for pH adjustment and micronutrient supplementation. Further work on manipulating environmental conditions, such as light regime, should be explored as a process control for targeting different industrial applications.

Hybrid cultivation of Nordic mixed-species consortia improved carbon capture, pollutant removal, and bioproduction, but the studies reported herein also demonstrate that, despite improved results, photosynthetic consortia cannot do all of these things simultaneously. Importantly, the biological functions of an artificial photosynthetic ecosystem can be artificially adapted and steered towards specific industrial aims; e.g., high PHB yield or effective biomass production, but not both at the same time. This adaptability and resilience to different environmental conditions gives consortia cultivation a marked advantage over conventional liquid-suspension monocultures, which can significantly improve the economic viability of microalgal bioproducts and bioservices.