Microalgae are gaining interest as sustainable biofactories for the industrial-scale production of Phycocyanin (PC), a phycobiliprotein (PBP) with significant antioxidant, anti-inflammatory, and nutraceutical properties. Among them, red extremophilic species such as Galdieria spp. have emerged as particularly promising sources due to their ability to thrive in harsh conditions, enabling the production of high-purity C-Phycocyanin (C-PC) with reduced contamination risks. The growing demand for natural pigments, supported by a global market forecasted to expand at a compound average growth rate (CAGR) of 7% through 2030, calls for scalable, cost-efficient, and environmentally sustainable strategies.This review critically examines upstream and downstream approaches for C-PC production from Rhodophyta, including cultivation regimes (autotrophic, heterotrophic, and mixotrophic), extraction and purification techniques, with a focus on operational performance, purity index, and process sustainability. Finally, we highlight persistent methodological gaps, such as protocol heterogeneity and the lack of standardization, and propose integrated strategies to support future biotechnological applications and large-scale deployment. The development of unified quality benchmarks, robust production protocols, and biorefinery models is essential to unlock the full commercial potential of red algal-derived C-PC. Graphical abstract

Drug removal from urban wastewater (UW) is a topic of growing interest. The new European Directive addresses this problem by introducing quaternary treatment by 2045, as part of the “Zero Pollution” plan from a One Health perspective. In this context, the role of microalgae remains very promising in achieving clean and safe effluents, although its cost–benefit ratio needs to be carefully evaluated. The purpose of this review is to disclose the latest approaches to drug removal and energy recovery from UWs adopting different algae (Chlorella spp., Galdieria spp., and Scenedesmus spp.), to provide a detailed background for further research towards the development of new effective strategies on UW remediation while producing clean energy. We examined the most recent studies, considering most drugs found in wastewater, their management, as well as strategies used to recover energy while being mindful of a circular economy. There is growing interest in algae-based systems. The latest findings on algae–bacteria consortia show that it could be a better alternative to suspended biomass and represent a way to manage drug waste. This finding suggests that large-scale experiments should be conducted to confirm the potential benefits of such waste treatments.

The growing demand for rare earth elements (REEs), heavy metals (HMs) and precious metals (PMs) has intensified interest in sustainable recovery strategies from secondary resources, including mining residues, industrial effluents and waste electrical and electronic equipment (WEEE). These streams represent exposure interfaces, because soluble and bioavailable metal species may persist, bioaccumulate and contribute to oxidative stress, genotoxicity, carcinogenic outcomes and chronic systemic effects. This systematic review, conducted following PRISMA guidelines, evaluates the thermoacidophilic red microalga Galdieria spp. as an extremophilic platform for metal bioremediation, recovery and upstream risk reduction. Galdieria spp. combines tolerance to low pH, elevated temperature and high metal loads with rapid surface biosorption and, in living biomass, slower intracellular sequestration and detoxification. Its interaction with REEs, PMs and toxic HMs is mediated by cell-wall functional groups, extracellular polymeric substances, redox-active processes and metabolic flexibility shaped partly by horizontal gene transfer (HGT). The review discusses matrix complexity and adsorption–desorption cycles, highlighting their implications for real industrial streams. Overall, Galdieria spp. emerges as a robust extremophilic bio-interface for selective metal recovery, hazardous waste mitigation, circular-economy biorefinery models and prevention of metal-associated risks to environmental and human health, while current scale-up limitations and process-oriented research priorities are identified.