Systematic investigation of biomass and lipid productivity by microalgae in photobioreactors for biodiesel application

Abstract

We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterizing their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the "light-limited" regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25-37% of DW), while the highest TAG content was found in C. vulgaris (11-14% of DW). These two species showed similar TAG productivities.

Influence of varying nitrogen levels on lipid accumulation in Chlorella sp.

“…Maximum concentrations are found at N 1.5 as 9.4 and 13.8 lg/mL on 7th and 10th day of inoculation, respectively. Similar results had been reported in literature showing decreased chlorophyll synthesis in the absence of a nitrogen source (Pruvost et al 2011;Da Silva et al 2009). Protein productivity has also been found to be dependent on nitrate concentration (Table 1).…”

Composition of Algal Oil and Its Potential as Biofuel

“…The latter are accumulated under stress conditions, like nitrogen limitation, and exhibit most desirable properties for conversion to biodiesel [28,50]. As described above, high specific lipid contents are attained on the expense of low biomass productivities [51]. These technical challenges must be approached by sophisticated cultivation strategies, such as phased or spatial separation of high biomass productivity and lipid accumulation in two different process phases or bioreactor compartments.…”

Exploitation of Microalgae Species for Nutraceutical Purposes: Cultivation Aspects

“…This is because microalgae are photoautotrophic similar to higher plants; they have a much higher growth rate compared to other land plants; can sustainably be cultivated in non-arable land; and they only need meagre amounts of growth nutrients, freshwater, brackish or marine water, and available sunlight or alternatively low energy consuming LED lights. Under specific growth conditions, certain microalgae biomass may contain macromolecule carbohydrates (up to 60%, [3,4]); lipids (up to 70%, [5,6]); proteins (up to 60%, [7]); and other high-value-added biomolecules (HVABs) such as astaxanthin in Haematococcus pluvialis (up to 7%, [8]); β-carotene in Dunaliella salina (up to 12%, [9]), EPA in Phaeodactylum tricornutum (39% of total fatty acids, [10]), DHA in heterotrophic microalga Crypthecodinium cohnii (45% of oil, [11]) and in photoautotrophic microalga Diacronema lutheri (19.2% of total fatty acids, [12]), phycocyanin in Arthrospira (Spirulina) platensis (17.5%, [13]), etc. During the last decade, microalgae have been researched for commercially viable production of biofuels, for which, the cultivation, harvesting and biomass extraction technologies remained cost challenging.…”