Debottlenecking Thermophilic Cyanobacteria Cultivation and Harvesting through the Application of Inner-Light Photobioreactor and Chitosan.

Hairuo Zhang,Peng Jin,Mohammad Russel,Jie Tang,Pengyu Chen,Maurycy Daroch

doi:10.3390/plants10081540

Hairuo Zhang, Peng Jin + Show 4 more

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https://doi.org/10.3390/plants10081540

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Abstract

Thermophilic cyanobacteria are a low-carbon environmental resource with high potential thanks to their innate temperature tolerance and thermostable pigment, phycocyanin, which enhances light utilisation efficiency and generates a high-value product. However, large-scale cultivation and harvesting have always been bottlenecks in unicellular cyanobacteria cultivation due to their micrometric size. In this study, a 40-litre inner-light photobioreactor (PBR) was designed for scaled-up cultivation of Thermosynechococcus elongatus E542. By analysing light transmission and attenuation in the PBR and describing it via mathematical models, the supply of light energy to the reactor was optimised. It was found that the hyperbolic model describes the light attenuation characteristics of the cyanobacterial culture more accurately than the Lambert–Beer model. The internal illumination mode was applied for strain cultivation and showed a two-fold better growth rate and four-fold higher biomass concentration than the same strain grown in an externally illuminated photobioreactor. Finally, the downstream harvesting process was explored. A mixture of chitosan solutions was used as a flocculant to facilitate biomass collection. The effect of the following parameters on biomass harvesting was analysed: solution concentration, flocculation time and flocculant concentration. The analysis revealed that a 4 mg L−1 chitosan solution is optimal for harvesting the strain. The proposed solutions can improve large-scale cyanobacterial biomass cultivation and processing.

Highlights

In recent years, research in cyanobacterial biotechnology achieved a lot of interest, but their application capacity cannot achieve its potential due to the low efficiency of large-scale culture and the downstream harvesting process
Since each of the cyanobacterial cells interacts with light using mechanisms of both absorption and scattering in the presence of interference of the growth medium, this results in incident light attenuation that is a function of the cellular density
Whilst the report lacks exact calculations of doubling times, these could be estimated from the growth curves as 2.3 d−1 [31]. When it comes to another thermophilic strain, Thermosynechococcus CL−1 (TCL-1), which was cultivated in small 1–2 L photobioreactors, productivities exceeding those of the BP-1 strain of 3.5 g L−1d−1 have recently been achieved [32]

Summary

Introduction

Research in cyanobacterial biotechnology achieved a lot of interest, but their application capacity cannot achieve its potential due to the low efficiency of large-scale culture and the downstream harvesting process. Cyanobacteria are natural producers of valuable compounds such as phycobiliproteins [1], biopolymers [2] and speciality chemicals [3] and are useful candidates for the bioremediation of water [4]. It appears, that genetic engineering and carbon dioxide valorisation are the most promising disciplines where cyanobacteria can make a long-lasting difference, especially after the discovery and development of new faster growing and more robust strains [5,6,7]. Two crucial areas where such improvements are needed are light energy transfer and harvesting of the biomass, both significant bottlenecks of cyanobacterial biotechnology

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