Effective astaxanthin production from flocculated Haematococcus pluvialis via biofilm cultivation in a tri-layer tray bioreactor.

Haematococcus pluvialis, renowned for its high astaxanthin content, is a prime candidate for commercial-scale production of natural astaxanthin. While biofilm cultivation shows potential for enhancing astaxanthin accumulation in H. pluvialis, it faces challenges in effectively harvesting green-vegetative H. pluvialis and mitigating the "dark zone" issue within the biofilm. Our study demonstrated that flocculation using a combination of chitosan and NaOH was an effective method for harvesting green-vegetative H. pluvialis, which surpasses centrifugation in both biomass and astaxanthin production. A tri-layer tray bioreactor was developed to enhance astaxanthin production via biofilm redistribution by using a rinsing method, and its effectiveness was further supported by a tray photobioreactor with an integrated automatic rinsing system. The biofilm method achieved an optimal specific light energy consumption for astaxanthin production of 9.42 kWh g at the light intensity of 150 μmol m s, presenting its potential for commercial-scale cultivation of H. pluvialis for astaxanthin production.