Effect of cell rupturing methods on the drying characteristics and lipid compositions of microalgae

Experimental and modelling studies of convective and microwave drying kinetics for microalgae

Conventional microalgal drying consumes huge time and contributes to 60-80% of downstream process costs. With the aim to develop an effective and rapid drying process, the present study evaluated the performance of microwave based drying (MWD) with a power range of 360-900 W and compared with the conventional oven drying (OD) at 40-100 °C. MWD was found to be efficient due to uniform and volumetric heating because of dipolar interaction, with an effective diffusivity of 0.47 × 10^-9-1.63 × 10^-9 m² s^-1, comparatively higher than OD. Activation and specific energy of 32.43 W g^-1 and 42.9-56.07 kWh kg^-1 was projected respectively, and a falling rate period with best fit for Newton and Henderson-Pabis model was observed for MWD. Uniform heating from internal sub-surface avoided cell distress, resulting in 14.4% higher lipid yield and significant preservation of biochemical components that can be processed into bioenergy and valuable products in microalgal biorefinery.

Effect of Drying Methods on Lutein Content and Recovery by Supercritical Extraction from the Microalga Muriellopsis sp. (MCH35) Cultivated in the Arid North of Chile

In this study, we determined the effect of drying on extraction kinetics, yield, and lutein content and recovery of the microalga Muriellopsis sp. (MCH35) using the supercritical fluid extraction (SFE) process. The strain was cultivated in an open-raceways reactor in the presence of seawater culture media and arid outdoor conditions in the north of Chile. Spray-drying (SD) and freeze-drying (FD) techniques were used for dehydrating the microalgal biomass. Extraction experiments were performed by using Box-Behnken designs, and the parameters were studied: pressure (30–50 MPa), temperature (40–70 °C), and co-solvent (0–30% ethanol), with a CO₂ flow rate of 3.62 g/min for 60 min. Spline linear model was applied in the central point of the experimental design to obtain an overall extraction curve and to reveal extraction kinetics involved in the SFE process. A significant increase in all variables was observed when the level of ethanol (15–30% v/v) was increased. However, temperature and pressure were non-significant parameters in the SFE process. The FD method showed an increase in lutein content and recovery by 0.3–2.5-fold more than the SD method. Overall, Muriellopsis sp. (MCH35) is a potential candidate for cost-effective lutein production, especially in desert areas and for different biotechnological applications.

Biofuel from Microalgae: Sustainable Pathways

As the demand for biofuels increases globally, microalgae offer a viable biomass feedstock to produce biofuel. With abundant sources of biomass in rural communities, these materials could be converted to biodiesel. Efforts are being done in order to pursue commercialization. However, its main usage is for other applications such as pharmaceutical, nutraceutical, and aquaculture, which has a high return of investment. In the last 5 decades of algal research, cultivation to genetically engineered algae have been pursued in order to push algal biofuel commercialization. This will be beneficial to society, especially if coupled with a good government policy of algal biofuels and other by-products. Algal technology is a disruptive but complementary technology that will provide sustainability with regard to the world’s current issues. Commercialization of algal fuel is still a bottleneck and a challenge. Having a large production is technical feasible, but it is not economical as of now. Efforts for the cultivation and production of bio-oil are still ongoing and will continue to develop over time. The life cycle assessment methodology allows for a sustainable evaluation of the production of microalgae biomass to biodiesel.

Drying Characteristics of Chlorella pyrenoidosa Using Oven and its Evaluation for Bio-Ethanol Production

The objective of this research is to study the influence of temperature on drying and changes in carbohydrate composition during the drying. Chlorella pyrenoidosa was dried in oven at various temperatures and initial weight 2 g. The initial moisture content of Chlorella pyrenoidosa was 487.2% dry weight and the composition was hemicellulose (62.76), cellulose (2.39), and lignin (0.46% dry weight). Every 5 min, the moisture content was recorded. The critical moisture contents of Chlorella pyrenoidosa at 50, 60, and 70 °C are 7.2, 3.9, and 3.1% dry weight, respectively. Meanwhile, the equilibrium water contents are 0.53, 0.32, and 0.12% dry weight, respectively. The carbohydrate content in Chlorella pyrenoidosa cell as a result FTIR analysis indicates that the higher temperature of drying the carbohydrate content increases. Drying of Chlorella pyrenoidosa at temperatures of 50, 60, and 70 °C will decrease moisture content without disturb carbohydrate molecule, so the carbohydrate content increases. Therefore, drying of Chlorella pyrenoidosa before converting become bio-ethanol will give benefit to increase the carbohydrate content and initial rupturing of it’s cell.

Cell Disruption of Chaetoceros calcitrans by Microwave and Ultrasound in Lipid Extraction

Downstream processing, such as cell disruption and extraction, constitutes a key step in microalgal-based industrial bioprocesses, mainly due to high costs and environmental impact. In this context, extraction technologies need to be improved, including the use of nonconventional cell disruption techniques suitable for scale-up, such as microwave and ultrasound. Therefore, this study aimed at investigating the effects of different methods of cell disruption (microwave and ultrasound) on lipid extraction from biomass of the diatom Chaetoceros calcitrans cultured in mixotrophic conditions in a medium with natural sea water and residual glycerol, with different treatment times. Both techniques applied to the biomass were efficient; that is, the results were 24.6 ± 1.3% lipids (ultrasound for 5 min) and 24.2 ± 0.9% lipids (microwave for 40 s), with no significant differences between them (p≥0.05). Likewise, there was no significant difference regarding the chemical disruption with hydrochloric acid 2 M as control (24.2 ± 1.0%). The ultrasound method consumed less energy than the microwave method. Both cell disruption methods applied to the biomass resulted in changes in the fatty acid profiles, that is, percentages of saturated fatty acids increased from 7.7% (control) to 16.6% (microwave) and 15.5% (ultrasound), whereas polyunsaturated ones increased from 12.8% (control) to 22.8% (microwave) and 21.8% (ultrasound). Concerning monounsaturated fatty acids, percentages decreased from 79.5% (control) to 60.6% (microwave) and 62.7% (ultrasound).

Mechanical cell disruption of Parachlorella kessleri microalgae: Impact on lipid fraction composition

Samples of nitrogen-starved Parachlorella kessleri containing intact cells (IC), cells ground by bead milling (BM), and cells subjected to high-pressure cell disruption (HPD), together with their supernatants after centrifugation, were compared for granulometry and lipid profiles. The effects of disruption on the lipid profile and organisation were evaluated. The quantity of lipids available for extraction increased with disruption, and up to 81% could be recovered in supernatants after centrifugation, but a marked reorganization occurred. The proportion of amphiphilic free fatty acids and lysophosphatidylcholine increased during disruption due to their release or owing to lipid degradation by enzymes or physical conditions. This effect was more marked in HPD than in BM. Lipids contained in the aqueous phase, after disruption and centrifugation, were enriched in unsaturated fatty acids, BM leading to larger droplets than HPD. The larger liquid lipid droplet would be easier to recover in the following downstream processing.

Development of an oven drying protocol to improve biodiesel production for an indigenous chlorophycean microalga Scenedesmus sp

Drying of wet algal biomass is a major bottleneck in viable commercial production of the microalgal biodiesel. In the present investigation, an oven drying protocol was standardized for drying of wet Scenedesmus biomass at 60, 80 and 100°C with initial sample thickness of 5.0, 7.5 and 10.0mm. The optimum drying temperature was found to be 80°C with a maximum lipid yield of 425.0±5.9mgg(-1) at 15h drying time for 5.0mm thick samples with 0.033kWh power consumption. Partial drying at 80°C up to 10% residual moisture content was efficient showing 93% lipid recovery with 8h drying and a power consumption of 0.017kWh. Scenedesmus biomass was also found to be rich in saturated and mono-unsaturated fatty acids. Thus, the drying protocol demonstrates its suitability to improve the downstream processing of biodiesel production by significantly lowering the power consumption and the drying time.