Assessing an Algae-Based Biorefinery for Wastewater Treatment and Pigment Extraction

Rising populations are placing significant strain on traditional waste management, prompting the need for circular systems in urban projects to recycle valuable nutrients from wastewater. Introducing a biorefinery framework, microalgae cultivation on digestate effluents produces pigments for natural dyes, reducing nutrient release and offering eco-friendly alternatives to synthetic products. Successful extraction of phycocyanin (the blue pigment) was achieved with an optimal 75% wastewater (WW) and 20% media composition, yielding the highest phycobiliprotein content (132.93 mg/g DW (dry weight)) coupled with impressive nutrient removal rates of 7.41, 1.31, and 11.73 (mg.L − 1.d − 1) for NH, PO4, and TN (total nitrogen) respectively. The framework’s scalability was evaluated in a Swedish urban development context, showcasing the potential of biorefinery concepts to convert waste into resources and supply natural pigments for textiles. Comparison with other studies showed that nutrient removal rates and PC yields are comparable to other wastewater-based systems with moderate biomass production, despite using a food-waste digestate stream. Our innovation also emphasized the high purity of phycocyanin (food-grade level), which many earlier studies don’t report. Our study also provides insights into future development and discusses the limitations of practical applications.