Is the production of microalgae and the derived bioproducts sustainable? A meta-review outlining the challenges and opportunities of circular bioeconomy and zero-waste approaches

Microalgae are a renewable and versatile feedstock for a multitude of bioproducts (protein feeds and foods, high-added value compounds for nutraceuticals and pharmaceuticals, biofuels, biofertilizers, and bioplastics), offering the potential for CO2 bio-sequestration. While microalgae-based production systems have garnered significant scientific interest, their techno-economic-environmental viability is still challenged by many limitations. Key research questions emerge: What are the prospects for scaling up microalgae-based production systems? Can microalgal bioproducts achieve true sustainability? This study aims to respond with a systematic meta-review of recent literature containing economic and environmental scientific information. A narrative synthesis is combined with data collection, homogenisation, and appraisal to provide a synoptic framework that captures the latest trends from techno-economic analysis and life cycle assessment, identifying enablers and barriers within a future perspective. The analysis of production costs and GHG emissions reveals a general tendency of poor performance and competitiveness of microalgal bioproducts. However, several optimistic estimates are found within a broad variability of results. Promising strategies are the valorisation of waste streams and the implementation of multi-product biorefinery models, in line with circular bioeconomy and zero-waste principles. The adoption of low-carbon energy technologies and the direct exploitation of sunlight present a additional opportunities to abate GHG emissions. Further potential lies in incentivising pilot projects, which are essential in accelerating process maturity. From a holistic perspective, advancing sustainability will require addressing the social dimension and multi-criteria optimisation. On the other hand, legislative barriers and customer acceptability must be managed through the interaction of academia, industry, and policymakers. Such efforts are crucial to unlock microalgae’s full potential and support the microalgal industry's real-world applicability, striving to achieve enhanced market penetration through green and cost-effective production processes.