Nannochloropsis oceanica Cultivation in Pilot-Scale Raceway Ponds—From Design to Cultivation

Abstract

Raceways ponds are the microalgal production systems most commonly used at industrial scale. In this work, two different raceway configurations were tested under the same processing conditions to compare their performance on the production of Nannochloropsis oceanica. Biomass productivity, biochemical composition of the produced biomass, and power requirements to operate those reactors were evaluated. Water depths of 0.20 and 0.13 m, and culture circulation velocities of 0.30 and 0.15 m s−1 were tested. A standard configuration, which had a full channel width paddlewheel, proved to be the most energy efficient, consuming less than half of the energy required by a modified configuration (had a half channel width paddlewheel). The later showed to have slightly higher productivity, not enough to offset the large difference in energetic consumption. Higher flow velocity (0.30 m s−1) led to a 1.7 g m−2 d−1 improvement of biomass productivity of the system, but it increased the energy consumption twice as compared to the 0.15 m s−1 flow velocity. The latter velocity showed to be the most productive in lipids. A water depth of 0.20 m was the most suitable option tested to cultivate microalgae, since it allowed a 54% energy saving. Therefore, a standard raceway pond using a flow velocity of 0.3 m s−1 with a 0.20 m water depth was the most efficient system for microalgal cultivation. Conversely, a flow velocity of 0.15 m s−1 was the most suitable to produce lipids.

Operation Regimes: A Comparison Based on Nannochloropsis oceanica Biomass and Lipid Productivity

“…San Pedro et al (2014) reported lipid productivity values between 50-60 mg L −1 day −1 in a 340 L vertical tubular PBR operated in continuous mode using a 0.1 day −1 dilution rate under similar weather conditions. The higher values are due to higher biomass productivity achieved by the authors, since the attained lipid content was similar (20-30%) [15] The lipid content values reached in the present study in a tubular PBR for N. oceanica (19.1-24.0%) were higher than the ones obtained by Cunha et al (2020) (13.2-19.0%), in a raceway reactor using the same strain, in the same location and time of the year [40]. This result highlights that the tubular horizontal PBR produces biomass with higher quality for biofuel than that cultivated in open systems.…”

Assessment of Eicosapentaenoic Acid (EPA) Production from Filamentous Microalga Tribonema aequale: From Laboratory to Pilot-Scale Study

“…Therefore, culture depth is an important parameter in open raceway ponds that may affect not only microalgal growth but also biochemical composition of the cells. It was reported that a culture depth of 12-15 cm was optimal for production of algal storage lipids [46,47] and secondary carotenoids [48]. In this study, however, the optimal culture depth was 20-25 cm for a maximum cellular EPA content of 3.4% (w/w) and a higher EPA productivity of 344.5 mg m −2 d −1 than that obtained from the cultures maintained at 10-15 cm depth (i.e., 3.1% EPA and EPA productivity of 290 mg L −1 d −1 ) (Table 4).…”

Overview and Challenges of Large-Scale Cultivation of Photosynthetic Microalgae and Cyanobacteria

“…Suitable mixing is, therefore, critical for productive algae cultivation. On a large scale, mixing is generated by paddlewheels in ponds [ 94 ] and pumps in closed systems. As pumps are becoming more energy-efficient, their application increases even in ponds.…”