Microalgae are a promising alternative source of lipid for biodiesel production. One of the most important decisions is the choice of species to use. High lipid productivity is a key desirable characteristic of a species for biodiesel production. This paper reviews information available in the literature on microalgal growth rates, lipid content and lipid productivities for 55 species of microalgae, including 17 Chlorophyta, 11 Bacillariophyta and five Cyanobacteria as well as other taxa. The data available in the literature are far from complete and rigorous comparison across experiments carried out under different conditions is not possible. However, the collated information provides a framework for decision-making and a starting point for further investigation of species selection. Shortcomings in the current dataset are highlighted. The importance of lipid productivity as a selection parameter over lipid content and growth rate individually is demonstrated.

Lipid productivity as a key characteristic for choosing algal species for biodiesel production

Importance of algae oil as a source of biodiesel

Microalgae feedstocks are gaining interest in the present day energy scenario due to their fast growth potential coupled with relatively high lipid, carbohydrate and nutrients contents. All of these properties render them an excellent source for biofuels such as biodiesel, bioethanol and biomethane; as well as a number of other valuable pharmaceutical and nutraceutical products. The present review is a critical appraisal of the commercialization potential of microalgae biofuels. The available literature on various aspects of microalgae, e.g. its cultivation, life cycle assessment, and conceptualization of an algal biorefinery, has been scanned and a critical analysis has been presented. A critical evaluation of the available information suggests that the economic viability of the process in terms of minimizing the operational and maintenance cost along with maximization of oil-rich microalgae production is the key factor, for successful commercialization of microalgae-based fuels.

Commercialization potential of microalgae for biofuels production

Microalgae biotechnology has recently emerged into the lime light owing to numerous consumer products that can be harnessed from microalgae. Product portfolio stretches from straightforward biomass production for food and animal feed to valuable products extracted from microalgal biomass, including triglycerides which can be converted into biodiesel. For most of these applications, the production process is moderately economically viable and the market is developing. Considering the enormous biodiversity of microalgae and recent developments in genetic and metabolic engineering, this group of organisms represents one of the most promising sources for new products and applications. With the development of detailed culture and screening techniques, microalgal biotechnology can meet the high demands of food, energy and pharmaceutical industries. This review article discusses the technology and production platforms for development and creation of different valuable consumer products from microalgal biomass.

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Bioprocess engineering of microalgae to produce a variety of consumer products

One major challenge to industrial microalgal culturing is to devise and develop technical apparata, cultivation procedures and algal strains susceptible of undergoing substantial increases in efficiency of use of solar energy and carbon dioxide. Despite several research efforts developed to date, there is no such thing as "the best reactor system"- defined, in an absolute fashion, as the one able to achieve maximum productivity with minimum operation costs, irrespective of the biological and chemical system at stake. In fact, choice of the most suitable system is situation-dependent, as both the species of alga available and the final purpose intended will play a role. The need of accurate control impairs use of open-system configurations, so current investigation has focused mostly on closed systems. In this review, several types of closed bioreactors described in the technical literature as able to support production of microalgae are comprehensively presented and duly discussed, using transport phenomenon and process engineering methodological approaches. The text is subdivided into subsections on: reactor design, which includes tubular reactors, flat plate reactors and fermenter-type reactors; and processing parameters, which include gaseous transfer, medium mixing and light requirements.

/pdf/microalgal-reactors-a-review-of-enclosed-system-designs-and-4satxmahtc.pdf

Microalgal Reactors: A Review of Enclosed System Designs and Performances

Twelve algal strains representing the classes Cyanophyceae, Prymnesiophyceae, Bacillariophyceae, Rhodophyceae, Cryptophyceae, Chlorophyceae, Xantophyceae and Eustigmatophyceae were selected mainly from the culture collection of the Norwegian Institute for Water Research (NIVA). The algae were grown as continuous cultures in a 1.8 l. reactor, internally illuminated with an 11 W fluorescent tube. The retention time was adjusted in the range 2–4 days to fit the growth rate of the algae. The growth responses and fatty acid composition were analysed. The maximum production rate was obtained with Pseudokirchneriella subcapitata (0.63 g 1−1 day−1) and the lowest with Porphyridium cruentum 0.13 g 1−1 day−1. Arachidonic acid (AA) and eicosapentaenoic acid (EPA) were the dominating polyunsaturated fatty acids (PUFAs) in P. cruentum, while only EPA accumulated in Phaeodactylum tricornutum. Docosahexaenoic acid (DHA) was the major PUFA in Isochrysis galbana, while Pavlova sp. had both EPA and DHA. This is the first report on the fatty acid profiles of Nannochloropsis oceanica, Chroococcus sp., Synechococcus sp. and Tribonema sp.

https://moritz.botany.ut.ee/~olli/b/Patil07.pdf

Fatty acid composition of 12 microalgae for possible use in aquaculture feed

Growing Chlorella sp. on meat processing wastewater for nutrient removal and biomass production.

The interaction effects between irradiance and temperature on growth rates ofNannochloropsis oceanicawere determined in both laboratory cultures and large-scale tubular photobioreactors. Growth responses were investigated in 48 batch cultures subjected to crossing light/temperature gradients ranging from 34–80μmol photons m−2s−1and 14.5–35.7∘C respectively. Comparisons were made to growth responses observed in production systems (200L biofences) operated in climate-regulated greenhouses with controlled temperature and artificial light gradients. Cellular responses showed increasing specific growth rates as a function of temperature, with a peak at 25–29∘C, after which the growth became increasingly unstable. The optimum temperature for growth increased with higher light intensities up to approximately 28∘C at 80μmol photons m−2s−1. At low light intensities the specific growth rate was less affected by temperature. The maximum daily production measured in the biofence systems increased proportionally with irradiation and reached approximately 0.7gL−1d−1at 1030μmol photons m−2s−1average daily radiation for a culture temperature of 24∘C. This corresponds to a daily yield of 140g per day in a 200L biofence system. When specific growth rates for the biofence cultures were measured at different densities and plotted against temperature, results showed a peak with the 24∘C temperature treatment. This peak became less pronounced as the density increased in the cultures. This is consistent with the laboratory results; increasing cell density in the biofence cultures resulted in less average light cell−1, which produced the same temperature dependent response as seen by reducing the external irradiance exposure for the dilute laboratory cultures.

https://moritz.botany.ut.ee/%7Eolli/b/Sandnes05.pdf

Combined influence of light and temperature on growth rates of Nannochloropsis oceanica: linking cellular responses to large-scale biomass production

Plants developed under high (90%) relative air humidity (RH) have previously been shown to have large, malfunctioning stomata, which results in high water loss during desiccation and reduced dark induced closure. Stomatal movement is to a large extent regulated by abscisic acid (ABA). It has therefore been proposed that low ABA levels contribute to the development of malfunctioning stomata. In this study, we investigated the regulation of ABA content in rose leaves, through hormone analysis and β-glucosidase quantification. Compared with high RH, rose plants developed in moderate RH (60%) and 20 h photoperiod contained higher levels of ABA and β-glucosidase activity. Also, the amount of ABA increased during darkness simultaneously as the ABA-glucose ester (GE) levels decreased. In contrast, plants developed under high RH with 20 h photoperiod showed no increase in ABA levels during darkness, and had low β-glucosidase activity converting ABA-GE to ABA. Continuous lighting (24 h) resulted in low levels of β-glucosidase activity irrespective of RH, indicating that a dark period is essential to activate β-glucosidase. Our results provide new insight into the regulation of ABA under different humidities and photoperiods, and clearly show that β-glucosidase is a key enzyme regulating the ABA pool in rose plants.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2012.02580.x

High relative air humidity and continuous light reduce stomata functionality by affecting the ABA regulation in rose leaves

Single node cuttings with one mature leaf were taken from Rosa ×hybrida ‘Baroness  ̓and rooted in water culture. The plants were subjected to either 90% (high) or 70% (moderate) relative humidity (RH) in climate chambers. Single stem roses with intact roots were transferred to 40% (low) RH to investigate the stomatal response to water stress. Moderate RH plants showed decreasing leaf conductance from day 1 to day 3 during both light and dark phases, in contrast to high RH roses, which showed almost similar leaf conductances during the 3 days. Leaf samples were studied with a light microscope (LM) and a scanning electron microscope (SEM) to quantify morphological and structural changes. Epidermal imprints showed a signifi cantly higher number of stomata and longer stomata, as well as a wider stomatal apertures on roses grown at high RH. The high RH leaves showed a reduced density of vascular tissue and thinner leaves when compared to moderate RH leaves. Enlarged intercellular air-space (ICA) was found due to a reduced number of spongy and palisade mesophyll cells. No obvious difference in shape, size, undulation or the structure of the epicuticular wax was observed in SEM between high and moderate RH grown leaves. In conclusion, roses subjected to high RH showed differences in leaf anatomy, stomatal morphology and stomatal function, which may explain the loss of water control of these plants. Stomatal ontogenesis should occur at RH conditions below 85% to secure roses with a high postharvest quality potential. morphological changes as described for plants regenerated in vitro. In addition, the study was undertaken to evaluate if differences in leaf morphology between high and moderate RH could explain the distinct postharvest behavior of these roses. Materials and Methods PLANT MATERIAL AND GROWING CONDITIONS. Rooted stems of Rosa ×hybrida ‘Baroness  ̓were grown in growth chambers from single-node segments with a mature leaf in water culture (Torre and Fjeld, 2001). During the rooting period, RH was kept above 90%. After rooting, RH was adjusted to either high: 90% ± 5% (–14.2 MPa) or moderate: 70% ± 5% (–48.2 MPa) RH. Temperature was kept at 20 ± 1 °C and the CO2 at 700 ± 50 μL–1·L–1 during the entire experimental period. All experiments were carried out during the darkest period of the year (January to April and September to December) with a minimal infl uence of natural sunlight. Artifi cial light provided by high-pressure-sodium-lamps (SON-T) was supplied 20 h every 24 h period with a 4 h dark period given in between. The average light intensity was 75 ± 10 μmol·m–2·s–1 (measured with a L1-185; LI-COR). Plants were harvested at commercial stage, A (Itzhaki et al., 1990). POROMETER MEASUREMENTS. Leaf conductance (mmol·m–2·s–1) was measured on the same plant for three days to study the stomatal response to water stress. Roses with intact roots were transferred from the chambers directly to a test room, placed in 0.5-L vases with double destilled water and acclimated for 8 h before the fi rst measurement with an AP4 porometer (Delta-T Devices LTD, Cambridge, U.K). The temperature in the test room was 20 °C, RH was 40% (–127.4 MPa) and an irradiation level of 14 μmol·m–2·s–1 was provided by fl uorescent tubes for 12 h per day. Measurements were taken on the abaxial side of the leaves, twice daily, once in the light period and once in the dark period (3 h after light off), corresponding to a time when plants had light or Received for publication 16 Oct. 2002. Accepted for publication 28 Jan. 2003. The authors thank Vigdis Revhaug for technical assistance. Thanks also to Elisabeth Eng and Trygve Krekling (Department of Chemistry and Biotechnology) and Nina Nagy (Norwegian Forest Research Institute) for assistance during the microscopy work. The work was fi nancially supported by the Norwegian Research Council, project number 107008/111.

/pdf/leaf-anatomy-and-stomatal-morphology-of-greenhouse-roses-5dfkxav94a.pdf

Hans Ragnar Gislerød

Papers

Fatty acid composition of 12 microalgae for possible use in aquaculture feed

Growing Chlorella sp. on meat processing wastewater for nutrient removal and biomass production.

Combined influence of light and temperature on growth rates of Nannochloropsis oceanica: linking cellular responses to large-scale biomass production

High relative air humidity and continuous light reduce stomata functionality by affecting the ABA regulation in rose leaves

Leaf Anatomy and Stomatal Morphology of Greenhouse Roses Grown at Moderate or High Air Humidity