Comparison of open-air and semi-enclosed cultivation system for massive microalgae production in sub-tropical and temperate latitudes Fabio Roselet a,b, *, Paula Maica ´ a , Tatiana Martins a , Paulo Cesar Abreu b a Po ´s-Graduac ¸a ˜o em Aquicultura, Universidade Federal do Rio Grande, Avenida Ita ´lia km 08, Rio Grande, RS, Brazil b Instituto de Oceanografia, Laborato ´rio de Fitopla ˆncton e Microorganismos Marinhos, Universidade Federal do Rio Grande, Avenida Ita ´lia km 08, Rio Grande, RS, Brazil article info Article history: Received 26 April 2013 Received in revised form 25 September 2013 Accepted 27 September 2013 Available online 15 October 2013 Keywords: Circular tank Agricultural greenhouse Abiotic control Biodiesel feedstock Massive cultivation abstract This study compared open-air and semi-enclosed production system of the marine microalgae Nannochloropsis oculata in a sub-tropical region (32  S; 52  W) under uncontrolled environmental conditions. The semi-enclosed system was composed of 1.2 m 3 circular tanks installed inside of a greenhouse. Water temperature was 4  C higher in the indoor treatment than in the outdoor, mainly in winter although no difference was observed in warmer seasons. Moreover, variation in salinity was observed in the outdoor treatment due to rainfall (winter) and evaporation (spring), whereas indoor treatment experienced an increase (up to 100 PSU) due to evaporation only in warmer seasons. Light transmission was approximately 20% lower in the indoor treatment although cell densities and biomass yields were higher indoor during winter. As the temperature increased (spring) no differ- ences were observed among treatments. In summary, partial control of temperature and salinity in the semi-enclosed system, especially during the colder and rainy season, allowed higher microalgae biomass production. Further experiments must be conducted with CO 2 addition, larger pH range and salinity control. ª 2013 Elsevier Ltd. All rights reserved. 1. Introduction Due to the rapid increase in the price of petroleum, the pro- jected exhaustion of supplies and awareness of environ- mental damage resulting from the historical use of fossil fuels, there has been increased interest in developing alternative technologies for biofuel production [1,2]. One of the most prominent biofuel is biodiesel, produced after the trans- esterification of lipids from various feedstocks, such as seed oil and animal fat [3]. In recent years, the cultivation of microalgae has been pointed out as a viable alternative for the production of biodiesel on a large scale, as they present some advantages when compared to traditional biodiesel feed- stocks [4,5]. Specifically, microalgae do not occupy fertile lands and can be grown using seawater supplemented with commercial fertilizers, or with domestic or industrial effluents [4e7]. According to several authors [6e9], the only practicable microalgae large-scale cultivation systems used commercially are open (raceways and circular tanks) and enclosed (photo- bioreactors) systems. Nevertheless there is still an intense debate concerning the best culture system since both present * Corresponding author. Instituto de Oceanografia, Laborato ´ rio de Fitopla ˆ ncton e Microorganismos Marinhos, Universidade Federal do Rio Grande, Avenida Ita ´ lia km 08, Rio Grande, RS, Brazil. Tel.: þ55 53 32368042. E-mail addresses: fabio.roselet@furg.br, fabio.roselet@gmail.com (F. Roselet). Available online at www.sciencedirect.com http://www.elsevier.com/locate/biombioe biomass and bioenergy 59 (2013) 418 e424 0961-9534/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biombioe.2013.09.014