Non-destructive monitoring of biomass and astaxanthin in Haematococcus pluvialis biofilms: a reflectance spectroscopy approach

International audience

English. Biofilm-based systems have gained increasing attention for microalgae cultivation due to their potential to improve productivity, decrease water and energy demands and eventually lower operating costs. The effective operation of these systems is based on process control, which requires on-line monitoring of process variables such as biomass concentration and pigments content. Although several methods and technologies to monitor parameters in microalgae-suspended cultures are available, tools to monitor non-destructively biofilm-based systems are still missing. To address this limitation, we propose the use of reflectance spectroscopy as a potential solution. This technique, which measures the light reflected at specific wavelengths, is widely used to remotely analyze the composition and physiology of plants and microphytobenthos communities.In this study, a biofilm-based rotating system was developed for cultivating Haematococcus pluvialis for astaxanthin production. The biomass and astaxanthin dynamics were followed under several light and nutrient conditions. Reflectance spectra data (Vis-NIR; 380-1000 nm) were collected at the biofilm surface, and analyzed to identify the spectral bands that correlated the most with biomass concentration and astaxanthin content. Reflectance indexes were afterwards calculated, and linear models were established between biomass concentration and an index based on near-infrared (NIR λ750-900 nm) and λ525 nm, as well as between astaxanthin content and an index using λ563 and λ637 nm.For the first time, a non-destructive monitoring tool based on reflectance spectroscopy was developed for microalgae biofilm characterization. Our findings address one of the limitations in process control, and have the potential to improve the operation of biofilm-based systems, making them a promising technology for microalgal cultivation and the production of high-value compounds.