Investigation of biomass concentration, lipid production, and cellulose content inChlorella vulgariscultures using response surface methodology

Abstract

The microalgae Chlorella vulgaris produce lipids that after extraction from cells can be converted into biodiesel. However, these lipids cannot be efficiently extracted from cells due to the presence of the microalgae cell wall, which acts as a barrier for lipid removal when traditional extraction methods are employed. Therefore, a microalgae system with high lipid productivity and thinner cell walls could be more suitable for lipid production from microalgae. This study addresses the effect of culture conditions, specifically carbon dioxide and sodium nitrate concentrations, on biomass concentration and the ratio of lipid productivity/cellulose content. Optimization of culture conditions was done by response surface methodology. The empirical model for biomass concentration (R(2) = 96.0%) led to a predicted maximum of 1123.2 mg dw L(-1) when carbon dioxide and sodium nitrate concentrations were 2.33% (v/v) and 5.77 mM, respectively. For lipid productivity/cellulose content ratio (R(2) = 95.2%) the maximum predicted value was 0.46 (mg lipid L(-1) day(-1) )(mg cellulose mg biomass(-1) )(-1) when carbon dioxide concentration was 4.02% (v/v) and sodium nitrate concentration was 3.21 mM. A common optimum point for both variables (biomass concentration and lipid productivity/cellulose content ratio) was also found, predicting a biomass concentration of 1119.7 mg dw L(-1) and lipid productivity/cellulose content ratio of 0.44 (mg lipid L(-1) day(-1) )(mg cellulose mg biomass(-1) )(-1) for culture conditions of 3.77% (v/v) carbon dioxide and 4.01 mM sodium nitrate. The models were experimentally validated and results supported their accuracy. This study shows that it is possible to improve lipid productivity/cellulose content by manipulation of culture conditions, which may be applicable to any scale of bioreactors.

Superior triacylglycerol (TAG) accumulation in starchless mutants of Scenedesmus obliquus: (II) evaluation of TAG yield and productivity in controlled photobioreactors

“…It is likely that the cell wall will account for a substantial part of this residual biomass. Although little is known about the cell wall composition of S. obliquus and other microalgae, it is hypothesized that this residual biomass consists largely of carbohydrates (other than starch) such as cellulose, which is known to be a major constituent of the cell wall of S. obliquus and other microalgae [32,33]. …”

Investigation of an integrated approach for bio‐crude recovery and enzymatic hydrolysis of microalgae cellulose for glucose production

“…For LC cultures the CO 2 concentration in the air was adjusted to 0.015 L/L (1.5 vol %) and NaNO 3 concentration to 3.77 mmol/L; for HC content cultures the CO 2 concentration was adjusted to 0.0233 L/L (2.33 vol %) and NaNO 3 concentration to 1.77 mmol/L. These values were obtained from previous studies on the effect of culture conditions on cellulose content and algae growth . For all the cultures the media was adjusted to pH 6.6 and sterilized in an autoclave at 121 °C and 144.79 kPa for 15 min.…”

“…Each microalgae culture (LC and HC) consisted of 3 replicate flasks containing 3 L of culture media and 0.5 L of inoculum with a biomass concentration of 380 mg dry mass of biomass per litre of media. The experimental setup for algae cultivation is described in detail by Aguirre and Bassi . Biomass was harvested after 16 days of culturing by centrifugation, and then freeze‐dried for 24 h. To quantify the cellulose content after cultivation, the Updegraff method was used .…”

“…These values were obtained from previous studies on the effect of culture conditions on cellulose content and algae growth. [13] For all the cultures the media was adjusted to pH 6.6 and sterilized in an autoclave at 121 8C and 144.79 kPa for 15 min. Cultures were incubated at room temperature (23-25 8C) with continuous air-CO 2 bubbling (7 L/min) for 15 days.…”

“…In the first stage, microalgae were cultivated under different carbon dioxide (CO 2 ) and sodium nitrate (NaNO 3 ) concentrations to produce biomass with different cellulose contents, following the approach in Aguirre and Bassi. [13] The microalgae with the lowest and highest cellulose contents were denoted as LC and HC, respectively. These biomasses were used to analyze the effects of cellulose and lipid content on HPS bio-crude recovery efficiency.…”