Isolation of a euryhaline microalgal strain, Tetraselmis sp CTP4, as a robust feedstock for biodiesel production

Bioprospecting for novel microalgal strains is key to improving the feasibility of microalgae-derived biodiesel production. Tetraselmis sp. CTP4 (Chlorophyta, Chlorodendrophyceae) was isolated using fluorescence activated cell sorting (FACS) in order to screen novel lipid-rich microalgae. CTP4 is a robust, euryhaline strain able to grow in seawater growth medium as well as in non-sterile urban wastewater. Because of its large cell size (9-22 mu m), CTP4 settles down after a six-hour sedimentation step. This leads to a medium removal efficiency of 80%, allowing a significant decrease of biomass dewatering costs. Using a two-stage system, a 3-fold increase in lipid content (up to 33% of DW) and a 2-fold enhancement in lipid productivity (up to 52.1 mg L-1 d(-1)) were observed upon exposure to nutrient depletion for 7 days. The biodiesel synthesized from the lipids of CTP4 contained high levels of oleic acid (25.67% of total fatty acids content) and minor amounts of polyunsaturated fatty acids with >= 4 double bonds (< 1%). As a result, this biofuel complies with most of the European (EN14214) and American (ASTM D6751) specifications, which commonly used microalgal feedstocks are usually unable to meet. In conclusion, Tetraselmis sp. CTP4 displays promising features as feedstock with lower downstream processing costs for biomass dewatering and biodiesel refining

Minimising losses to predation during microalgae cultivation

We explore approaches to minimise impacts of zooplanktonic pests upon commercial microalgal crops using system dynamics models to describe algal growth controlled by light and nutrient availability and zooplankton growth controlled by crop abundance and nutritional quality. Losses of microalgal crops are minimised when their growth is fastest and, in contrast, also when growing slowly under conditions of nutrient exhaustion. In many culture systems, however, dwindling light availability due to self-shading in dense suspensions favours slow growth under nutrient sufficiency. Such a situation improves microalgal quality as prey, enhancing zooplankton growth, and leads to rapid crop collapse. Timing of pest entry is important; crop losses are least likely in established, nutrient-exhausted microalgal communities grown for high C-content (e.g. for biofuels). A potentially useful approach is to promote a low level of P-stress that does not adversely affect microalgal growth but which produces a crop that is suboptimal for zooplankton growth

Isolation and screening of euryhaline Tetraselmis spp. suitable for large-scale outdoor culture in hypersaline media for biofuels

Natural saline lakes in Western Australia were sampled for microalgae species and strains with potential for large-scale outdoor cultivation over a wide range of salinities for biofuels production. Using a rational isolation and screening process, several Tetraselmis strains (Chlorophyta, Chlorodendrales) with a broad range of salinity tolerance were identified and were characterised further for their potential for biofuels production. Specific growth rates increased from 0.8 to 1.2 days−1 when the medium salinity was decreased from 11 to 3 % (w/v) NaCl (1.88 to 0.51 M NaCl) in batch cultivation mode, thereby indicating quick adaptation to large salinity changes. In general, ash-free dry weight (AFDW), total lipid, protein and carbohydrate contents per cell were highest in the early stages of growth. Salinity increases led to an increase in cell AFDW, with the highest mean maximum of 2555 ± 659 pg AFDW.cell−1 at 11 % (w/v) NaCl in the strains Tetraselmis MUR 167 and MUR 219 which had been in culture for many years, as compared to the mean maximum of 981 ± 141 pg AFDW.cell−1 the in newly isolated strains MUR 230, 231, 232 and 233. Similar observations on total lipid, protein and carbohydrate content per cell were made between the two groups of strains. Overall, all strains yielded high biomass and total lipid productivities over a very wide range of salinities without large variation in their gross biochemical composition and growth pattern. Based on AFDW and total lipid productivity data, the order of preference for selecting strains for further investigation for large-scale culture was MUR 231 > MUR 233 > MUR 219 > MUR 230 > MUR 232 > MUR 167. The Tetraselmis spp. were also very competitive as shown by the outdoor cultivation of diatom, Halamphora coffeaeformis MUR 158, in parallel with Tetraselmis sp. MUR 167 which resulted in the diatom being outcompeted by the green alga. Our results demonstrate the high commercial potential of euryhaline Tetraselmis spp. for cultivation over a broad range of salinity in outdoor cultures

Pilot-scale continuous recycling of growth medium for the mass culture of a halotolerant Tetraselmis sp. in raceway ponds under increasing salinity: A novel protocol for commercial microalgal biomass production

The opportunity to recycle microalgal culture medium for further cultivation is often hampered by salinity increases from evaporation and fouling by dissolved and particulate matter. In this study, the impact of culture re-use after electro-flocculation of seawater-based medium on growth and biomass productivity of the halotolerant green algal strain Tetraselmis sp., MUR 233, was investigated in pilot-scale open raceway ponds over 5months. Despite a salinity increase from 5.5% to 12% (w/v) NaCl, Tetraselmis MUR 233 grown on naturally DOC-enriched recycled medium produced 48-160% more ash free dry weight (AFDW) biomass daily per unit pond area than when grown on non-recycled medium. A peak productivity of 37.5±3.1gAFDWm-2d-1 was reached in the recycled medium upon transition from ~14% to ~7% NaCl. The combination of high biomass-yielding mixotrophic growth under high salinity has been proven to be a successful sustainable cultivation strategy

Production of biofuels from microalgae

The production of biofuels from microalgae, especially biodiesel, has become a topic of great interest in recent years. However, many of the published papers do not consider the question of scale up and the feasibility of the various processes to be operated at the very large scale required if algal biofuels are to make a meaningful contribution to renewable fuels. All the steps in the process must also be very low cost. This paper discusses the unit processes required for algal biofuels production (i. e., growing the algae, harvesting, dewatering, extraction and conversion to biofuel) and their scalability. In many cases, especially in the lipid extraction step, little is known as yet as to the scalability and economic feasibility of the various processes proposed. We also highlight the key engineering and biological issues which must be resolved for the production of biofuels from microalgae to become an economic reality

Standard methods for measuring growth of algae and their composition

The purpose of this chapter is to present a summary of techniques for measuring growth and analysing chemical composition of microalgae. There are perhaps as many methods and modifications to these methods as there are active phycologists today. Investigators generally employ their own particular adapted methodology. Here, we have attempted to include in this chapter those methods generally employed by several investigators, as well as having general applicability to different laboratories. Among the major methods discussed here are: cell counting, measuring growth techniques and biochemical compositions (lipid, carbohydrates and protein). The audience for whom this chapter is intended is diverse and includes junior to experienced phycologist and/or non-phycologists