Innovative Cultivation-Transformation-Accumulation Strategy for <i>Haematococcus pluvialis</i> : Integrated Research from Small-Scale Optimization to Pilot-Scale Validation and Environmental-Economic Sustainability Assessment

To address the challenges of high cell mortality, low astaxanthin yield, and elevated costs in traditional one- and two-stage Haematococcus pluvialis cultivation, this study developed a novel Cultivation-Transformation-Accumulation (CTA) strategy. The CTA framework sequentially optimized biomass growth (stage I), induced stress-resistant nonmotile cells via 1 g/L NaCl (stage II), and maximized astaxanthin accumulation (stage III), achieving a 61.1% yield enhancement over 0 g/L NaCl. Small-scale experiments demonstrated the superiority of the CTA strategy, yielding 3.0% astaxanthin content (1.4 and 1.2 times higher than that of one- and two-stage methods, respectively) without costly centrifugation. Pilot-scale trials identified tubular photobioreactors (T-PBRs) as optimal, achieving a biomass of 3.6 g/L, an astaxanthin concentration of 116.9 mg/L, and a CO2 fixation rate of 299.3 mg/L/d. Integrated life cycle and economic analyses revealed the dual advantages of T-PBRs over column photobioreactors and plate photobioreactors: minimal environmental impact and drastic cost reductions (67.4–74.1% for astaxanthin production). The study also discusses strategies for industrial system optimization and the feasibility of full outdoor cultivation. This centrifugation-free CTA strategy establishes a sustainable pathway for high-efficiency industrial astaxanthin production, contributing to alleviating the survival-productivity paradox in algal biotechnology.