Ultrahigh-cell-density heterotrophic cultivation of the unicellular green microalga Scenedesmus acuminatus and application of the cells to photoautotrophic culture enhance biomass and lipid production.

Hu Jin,Quan Xu,Qiang Hu,Chengwu Zhang,Guoli Hou,Danxiang Han,Kunpeng Li,Wenhua Chuai,Hu Zhang,Zhiwei Zhou

doi:10.1002/bit.27190

Abstract

Although production of biodiesels from microalgae is proved to be technically feasible, a commercially viable system has yet to emerge. High‐cell‐density fermentation of microalgae can be coupled with photoautotrophic cultivation to produce oils. In this study, by optimizing culturing conditions and employing a sophisticated substrate feed control strategy, ultrahigh‐cell‐density of 286 and 283.5 g/L was achieved for the unicellular alga Scenedesmus acuminatus grown in 7.5‐L bench‐scale and 1,000‐L pilot‐scale fermenters, respectively. The outdoor scale‐up experiments indicated that heterotrophically grown S. acuminatus cells are more productive in terms of both biomass and lipid accumulation when they are inoculated in photobioreactors for lipid production as compared to the cells originally grown under photoautotrophic conditions. Technoeconomic analysis based on the pilot‐scale data indicated that the cost of heterotrophic cultivation of microalgae for biomass production is comparable with that of the open‐pond system and much lower than that of tubular PBR, if the biomass yield was higher than 200 g/L. This study demonstrated the economic viability of heterotrophic cultivation on large‐scale microalgal inocula production, but ultrahigh‐productivity fermentation is a prerequisite. Moreover, the advantages of the combined heterotrophic and photoautotrophic cultivation of microalgae for biofuels production were also verified in the pilot‐scale.

Highlights

Microalgae is a promising biomass feedstock for renewable energy production (Hu et al, 2008)
The coupled heterotrophic and photoautotrophic cultivation mode has been studied for many microalgae on different scales, its economic viability remains to be assessed, especially when utilized for biofuel production
The inherent longer doubling time of microalgae, and the lack of effective growth condition optimization as well, have limited their full growth potential. It remains elusive regarding whether heterotrophically grown algal cells could adapt to the stress environmental conditions used for inducing lipid production, such as high‐light and nitrogen depletion conditions, after shifting from heterotrophic to photoautotrophic cultivation mode

Summary

| INTRODUCTION

Microalgae is a promising biomass feedstock for renewable energy production (Hu et al, 2008). The coupled heterotrophic and photoautotrophic cultivation mode has been studied for many microalgae on different scales, its economic viability remains to be assessed, especially when utilized for biofuel production. The inherent longer doubling time of microalgae, and the lack of effective growth condition optimization as well, have limited their full growth potential It remains elusive regarding whether heterotrophically grown algal cells could adapt to the stress environmental conditions used for inducing lipid production, such as high‐light and nitrogen depletion conditions, after shifting from heterotrophic to photoautotrophic cultivation mode. A Scenedesmus acuminatus strain that shows potential in heterotrophic growth and lipid production was obtained in a previous study (Wang, Sun, Li, & Zhang, 2014) Though this S. acuminatus strain accumulated little lipid under heterotrophic conditions, the heterotrophically grown cells can be used as inoculum for lipid production under photoautotrophic conditions. Based upon the results of TE analysis, this study demonstrated the economic viability of the ultrahigh‐cell‐ density fermentation in the entire chain of algal biofuel production

| MATERIALS AND METHODS

| Analytical procedures

| RESULTS

| DISCUSSION

Findings

CONFLICT OF INTERESTS