The potential of mixed-species biofilms to address remaining challenges for economically-feasible microalgal biorefineries: a review

Several key challenges are hindering large-scale cultivation of microalgae for industrial purposes, including wastewater treatment, carbon capture, biomass production, and renewable energy production. These challenges are closely related to efficacy of 1) resource utilization, 2) biomass production, and 3) harvesting. This review describes how attached or biofilm cultivation of microalgae and/or cyanobacteria with heterotrophic bacteria in consortia could simultaneously resolve these technical obstacles, thereby reducing monetary and energetic costs of producing microalgal bioenergy. Symbiotic relationships between these organisms reduces the need for aeration or exogenous supplementation of nutrients. Additionally, this review details how increasing biodiversity correlates with diversity of functionality (carbon capture and nitrification) and how attached/biofilm cultivation can improve photosynthetic efficiency and water footprint. Mixed-species biofilms have persisted for billions of years across earth’s natural history because they are some of nature’s most highly efficient biosystems, and they deserve more dedicated study and broader application in bioenergy production. This review details the practical connections between microalgal-bacterial consortia, attached/biofilm cultivation, waste-to-value biorefining, and relevance to bioenergy production and value-added products (VAPs); four topics previously unconnected in a single review. As such this review aims to bridge current knowledge gaps across multiple research fields and industrial sectors, towards the goal of efficient, economical, and climate-forward microalgal bio-services and bioenergy production.