Growth and Nitrate Uptake in Nannochloropsis gaditana and Tetraselmis chuii Cultures Grown in Sequential Batch Reactors

Ramis Rafay,Hector H Hernandez,Joao M Uratani,Jorge Rodríguez

doi:10.3389/fmars.2020.00077

Ramis Rafay, Hector H Hernandez + Show 2 more

Open Access

https://doi.org/10.3389/fmars.2020.00077

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Abstract

This study aims to determine the maximum specific biomass growth rates of Nannochloropsis gaditana and Tetraselmis chuii grown in sequential batch reactors. The maximum specific growth rates of N. gaditana and T. chuii were found to be 0.23 ± 0.04 gVSS/gVSS∙d and 0.22 ± 0.05 gVSS/gVSS∙d respectively. Optical density measured at 550 nm (OD550) accurately predict volatile suspended solids (VSS) concentration in N. gaditana growth media but not in T. chuii growth media. We observed decoupling of nitrate uptake from cell growth for both microalgae as growth continued well beyond the point where concentrations of nitrate in the growth media fell below the detection limit. This nitrate decoupling highlights the challenges in current microalgae growth models as growth was independent of the extracellular dissolved nitrogen in the system.

Highlights

Biomass derived from marine microalgae are a potential substitute for feed filler in animal feed and for human consumption
Nannochloropsis gaditana was subjected to consecutive growth cycles in f/2 medium in a Sequential Batch Reactor (SBR) with periodic volatile suspended solids (VSS) analysis and measurements of Optical density measured at 550 nm (OD550)
We used both spectroscopic and mass based measurement methods to gain a better understanding of the observable growth rates of microalgae, as the direct and indirect measurement methods do not completely agree with one another at all times

Summary

Introduction

Biomass derived from marine microalgae are a potential substitute for feed filler in animal feed and for human consumption. Microalgae-based biomass may be a suitable replacement for commodities such as soybeans, meats, rice, and eggs (Borowitzka, 1997; Brown et al, 1997) due to their comparable nutritional values (Table 1). Microalgae represent an opportunity to replace conventional water intensive protein sources. Some microalgae are used as feed to supplement the diets of ruminants such as sheep and cattle in place of conventional protein sources such as soybean meal (Becker, 2007).

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