Optimizing Fucoxanthin production in Chaetoceros sp. Using conditioned wastewater and tailored culture conditions

Abstract

Fucoxanthin is a naturally occurring carotenoid with various biological activities. Compared to macroalgae, microalgae (such as diatoms) not only have a faster growth rate but also can accumulate higher levels of fucoxanthin. However, the cost of the culture medium is a crucial limiting factor in the large-scale production of microalgal fucoxanthin. In this study, it was first screened for microalgal strains with optimal fucoxanthin production based on aquaculture wastewater. System factors such as initial inoculation density, nitrogen‑phosphorus (N/P) ratio, and light intensity were then optimized. Further, pilot-scale cultivation of Chaetoceros sp. was conducted based on the optimized conditions, using response surface methodology. These results showed that the fucoxanthin production for Chaetoceros sp. ZJ was best when the ratio of aquaculture wastewater to culture medium was 1:3. Optimal inoculation density was 2.6 × 10⁵ cells/mL; the nitrogen‑phosphorus ratio was 25.61 to 1.0; the light intensity was 1597.74 lx.; the resulting yield of fucoxanthin reached 40.13 mg/L under these conditions. In a 100-Liter tubular photobioreactor, the yield of fucoxanthin for Chaetoceros sp. ZJ reached 33 mg/L. This study provides a theoretical basis for the utilization of wastewater to cultivate Chaetoceros sp., and to create fucoxanthin as a commercial resource. Using nutrient-rich wastewater for microalgae cultivation enables both environmental pollution mitigation and valuable bioproduct generation.