Microalgal biomass quantification from the non-invasive technique of image processing through red\u2013green\u2013blue (RGB) analysis

J L Salgueiro,L Pérez,Ángeles Cancela,Clara Míguez,Ángel Sanchez

doi:10.1007/s10811-021-02634-6

Abstract

Continuous monitoring of biomass concentration in microalgae cultures is essential and one of the most important parameters to measure in this field. This study aims at digital image processing in RGB and greyscale models, being a simple and low-cost method for cell estimation. Images obtained from different photobioreactors with wastewater and at different conditions for the cultivation of Chlorella vulgaris were analyzed. The results suggested that this technique is very effective under controlled lighting conditions, in contrast to photobioreactors placed outdoors and of different design, presenting a lower linearity. The accuracy of the method could be improved with a high-quality charge-coupled device (CCD) camera. The development of efficient methods to assess biomass concentration is an important and necessary step towards large-scale microalgae cultivation. The colour analysis technique has a great potential to meet the needs of monitoring cultures in a cost-effective and automated way using simple and cheap instruments.

Highlights

Microalgae are considered an important raw material in a number of promising biotechnological applications, as well as offering advantages in reducing the environmental impact of industrial pollution
Within online biomass estimation or with the possibility of becoming online, we mainly find the measurement of optical density (OD) by a spectrophotometer, in situ microscopy (Bluma et al, 2010), flow cytometry (FC) (Hyka et al, 2013), fluorometry (2D) and infrared spectroscopy (NIR)
Digital image processing using the RGB and greyscale models is proposed for the cell measurement of the microalga C. vulgaris in different culture media

Summary

Introduction

Microalgae are considered an important raw material in a number of promising biotechnological applications, as well as offering advantages in reducing the environmental impact of industrial pollution. OD measurement can introduce inaccuracies in the estimation of biomass concentration when cells change their morphology and composition, that is, their optical properties (Griffiths et al, 2011; Chioccioli et al, 2014). For this reason, experts recommend OD in cases where the microalgal biomass to be measured is at low cell concentrations (Lu et al, 2017), limiting its use outside the laboratory scale. The problems related to the other online measurement techniques mentioned above are the time involved in the analysis; the cost, due to the amount of material needed or its maintenance (Benavides et al, 2015); and the fact that they can be invasive and destructive of the culture medium

Objectives

Methods

Results

Discussion

Conclusion