Enhanced Oil Production by the Tropical Marine Diatom Thalassiosira Sp. Cultivated in Outdoor Photobioreactors

Abstract

Microalgae-derived oils have potential as a biofuel feedstock. To produce microalgal oils at a large scale, large amounts of nutrients and energy are needed to grow the algae. In this study, we evaluated three types of agricultural fertilizer (AF)-based culture media (AF1, AF2, and AF3) based on a previously published enriched seawater (ES) medium to produce biomass and oils from Thalassiosira sp. Under laboratory conditions, the highest cell productivity of Thalassiosira sp. was obtained with the AF3 medium. Thalassiosira sp. cultured in the AF3 medium produced 10.4 ± 0.9 mg L dayoils, which is significantly higher than the 5.8 ± 0.7 mg L dayproduced in the ES medium. The higher production was due to the presence of nitrate and trace elements, both of which played roles in enhancing biomass and oil content, respectively. During cell growth, resting spores appeared inside the cells and were a marker to harvest the cells. Because of the abundant availability of sunlight in the tropics during the year, the oil production of Thalassiosira sp. in the AF3 medium was scaled up using outdoor photobioreactors under different weather conditions (rainy and dry seasons). Thalassiosira sp. produced more unsaturated fatty acids during the rainy season and produced more saturated fatty acids during the dry season. This study also demonstrated that it was possible to culture Thalassiosira sp. under outdoor conditions using a low-cost agricultural fertilizer-based culture medium (AF3 medium) to produce biodiesel feedstock with an annual production of 8.1 ± 0.4 t ha during the dry season and of 23.9 ± 6.8 t ha during the rainy season.

Long-term monitoring of the biomass and production of lipids by Nitzschia palea for biodiesel production

“…The dry weight biomass of outdoor culture of N. palea (x′ = 0.16, n = 24) was significantly (P ≤ 0.05) lower than that under laboratory conditions (x′ = 0.27, n = 8). Moreover, the percentage dry weight biomass (% dw) of the n-hexane eluate of intracellular lipids of this diatom was higher under laboratory (26.2% dw) than under outdoor growth (8.54% dw) conditions, These results are in a perfect agreement with previous findings ( Hu et al, 2008 , Hu et al, 2006 , Starr, 1978 , Sharma and Singh, 2009 , Pintaka et al, 2017 , Almutairi, 2020 ).…”

“…The outdoor production of lipids and biomass were monitored for a full annual cycle, involving distinct seasonal variations in ambient temperature and radiant energy, parameters shown to control algal biomass development ( Reynolds, 1984 ) and lipid production ( Haas et al, 2009 , Hu et al, 2008 , Sharma and Singh, 2009 , Matsumoto et al, 2017 , Pintaka et al, 2017 ). The dry weight biomass of N. palea varied considerably between 0.11 g l −1 and 0.25 g l −1 with a mean annual value of 0.16 g l −1 .…”

A Critical Review on the Status and Progress of Microalgae Cultivation in Outdoor Photobioreactors Conducted over 35 Years (1986–2021)

“…was 50% higher during the rainy season than in the dry season. However, the biomass had a higher content of saturated fatty acids during the dry season and more unsaturated fatty acids during the rainy season [121]. In the dry season, the culture received twice the solar irradiance compared with the rainy season.…”

“…A study conducted in Indonesia showed that Thalassiosira sp. grown during rainy and dry seasons had different biochemical compositions [121]. Carlozzi and Sacchi (2001) observed a mean Lowry protein content of Rhodopseudomonas palustris that decreased by around 2% in July compared with January, and crude protein always remained 10% higher than Lowry protein content [104].…”

“…The adaptation period can vary depending on outdoor conditions, as demonstrated in a study that found Thalassiosira sp. took two days longer to adapt during the dry season than in the rainy season, after which it began to grow rapidly [121]. A study showed that the productivity of Nannochloropsis sp.…”