Strategies for enhancing lipid production from indigenous microalgae isolates

Basic oxygen furnace slag as a support material for the cultivation of indigenous marine microalgae

Attached cultivation of microalgae is a suitable strategy for attaining high biomass productivity with effortless harvesting. This study evaluates the feasibility of using Basic Oxygen Furnace Slag (BOFS) as a carrier for microalgae cultivation. Among the three indigenous microalgae (namely, Chlorella sorokiniana PTC13, Tetraselmis suecica SC5, and Nannochloropsis oceanica DG), which were examined for their capability of attached growth on BOFS, T. suecica SC5 showed the best attached-growth performance (2.52 mg/g slag). Optimizing the cultivation parameters (agitation rate, 200 rpm; added sodium acetate, 1 g/L; light intensity, 300 µmol/m²/s) further enhanced the attached biomass yield to 6.38 mg/g slag. The microalgae-attached slag can be used as the seed for re-growth for three additional cycles and the biomass yield and productivity both enhanced from 6.00 to 11.58 mg/g slag and 497 to 760 mg/L/d, respectively. This study demonstrated the potential of using T. suecica SC5-attached BOFS to construct artificial reefs.

Enhancing biomass, lipid production, and nutrient utilization of the microalga Monoraphidium sp. QLZ-3 in walnut shell extracts supplemented with carbon dioxide

Microalgae are a promising biofuel resource, but their high cost and low productivity hinder their commercial applications. In the present study, Monoraphidium sp. QLZ-3 was cultivated in walnut shell extracts (WSE) supplemented with carbon dioxide (CO₂). Biomass was enhanced from 0.40 g L^-1 to 1.18 g L^-1, and lipid content reached 49.54% in WSE-12% CO₂ media. Biomass and lipid productivity reached 196.88 and 97.52 mg L^-1 d^-1, which were 1.33- and 1.57-fold higher than those of the control, respectively. The amount of carbohydrates increased, but the protein contents decreased. Furthermore, the application of CO₂ promoted nutrient and polyphenol absorption and upregulated the expression levels of lipid biosynthetic genes of this WSE-cultivated alga. These results indicated that coupling WSE and CO₂ could be an efficient strategy to enhance biofuel production by microalgae.

Exploring the potency of integrating semi-batch operation into lipid yield performance of Chlamydomonas sp. Tai-03

Third generation biofuels, also known as microalgal biofuels, are promising alternatives to fossil fuels. One attractive option is microalgal biodiesel as a replacement for diesel fuel. Chlamydomonas sp. Tai-03 was previously optimized for maximal lipid production for biodiesel generation, achieving biomass growth and productivity of 3.48 ± 0.04 g/L and 0.43 ± 0.01 g/L/d, with lipid content and productivity of 28.6 ± 1.41% and 124.1 ± 7.57 mg/L/d. In this study, further optimization using 5% CO₂ concentration and semi-batch operation with 25% medium replacement ratio, enhanced the biomass growth and productivity to 4.15 ± 0.12 g/L and 1.23 ± 0.02 g/L/d, with lipid content and productivity of 19.4 ± 2.0% and 239.6 ± 24.8 mg/L/d. The major fatty acid methyl esters (FAMEs) were palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2). These short-chain FAMEs combined with high growth make Chlamydomonas sp. Tai-03 a suitable candidate for biodiesel synthesis.

Development of Aurantiochytrium limacinum SR21 cultivation using salt-rich waste feedstock for docosahexaenoic acid production and application of natural colourant in food product

Microalgae biorefinery is presently receiving a lot of attention as driven by its production of high value-added products. In this study, an oleaginous microalga Aurantiochytrium limacinum SR21 was cultured for docosahexaenoic acid (DHA) production using 20% (w/v) of K₂HPO₄-waste feedstock to replace 0.005% (w/v) of KH₂PO₄ in the flask culture. DHA is an essential nutrient for human's brain functionalities. Collectively, the K₂HPO₄-waste feedstock with working concentration of 0.005% (w/v) in the cultivation prompted a higher lipid content (8.29%) and DHA production (128.81 mg.L^-1). Moreover, natural plant pigment products containing stabilised betacyanins were utilised as natural red colourants for hard candy production. This study develops microalgal cultivation using salt-rich waste feedstock for a higher lipid and DHA content as well as application of natural colouring agents in food products.

Extraction of proteins from microalgae using integrated method of sugaring-out assisted liquid biphasic flotation (LBF) and ultrasound

In this study, a simple sugaring-out supported by liquid biphasic flotation technique combined with ultrasonication was introduced for the extraction of proteins from microalgae. Sugaring-out as a phase separation method is novel and has been used in the extraction of metal ions, biomolecules and drugs. But, its functioning in protein separation from microalgae is still unknown. In this work, the feasibility of sugaring-out coupled with ultrasound for the extraction of protein was investigated. Primary studies were carried out to examine the effect of sonication on the microalgae cell as well as the separation efficiency of the integrated method. Effect of various operating parameters such as the concentration of microalgae biomass, the location of sonication probe, sonication time, ultrasonic pulse mode (includes varying ON and OFF duration of sonication), concentration of glucose, types of sugar, concentration of acetonitrile and the flow rate in the flotation system for achieving a higher separation efficiency and yield of protein were assessed. Besides, a large-scale study of the integration method was conducted to verify the consistency of the followed technique. A maximum efficiency (86.38%) and yield (93.33%) were attained at the following optimized conditions: 0.6% biomass concentration, 200 g/L of glucose concentration, 100% acetonitrile concentration with 5 min of 5 s ON/10 s OFF pulse mode and at a flow rate of 100 cc/min. The results obtained for large scale were 85.25% and 92.24% for efficiency and yield respectively. The proposed liquid biphasic flotation assisted with ultrasound for protein separation employing sugaring-out demonstrates a high production and separation efficiency and is a cost-effective solution. More importantly, this method provides the possibility of extending its application for the extraction of other important biomolecules.

Response surface optimization of lipid and protein extractions from Spirulina platensis using ultrasound assisted osmotic shock method

In this study, we optimized the process for extracting lipids and proteins from wet biomasses of Spirulina sp. using a 4-kHz ultrasonic osmotic shock method with ultrasound enhancement at a constant frequency of 40 kHz. Optimization was conducted using a response surface methodology (RSM) at an osmotic NaCl concentration of 10-30%, solvent:biomass ratio of 5-15 v/w, and extraction times of 20-50 min. The present osmotic shock method with ultrasound irradiation increased lipid yields to 6.65% in the presence of 11.9% NaCl, a solvent:biomass ratio of 12:1 v/w, and a 22-min extraction time, and protein yields to 43.96% with 15.12% NaCl, a solvent:biomass ratio of 10:1 v/w, and a 30-min extraction time.

Proteins recovery from wet microalgae using liquid biphasic flotation (LBF)

In this work, the extraction of microalgal protein from wet Chlorella sorokiniana species using alcohol/salt liquid biphasic flotation (LBF) with the aid of ultrasonication for cell rupturing was proposed. The effect of varying crude feedstock concentration, flotation time, salt type, salt concentration, alcohol type, alcohol concentration, initial volumes of salt and alcohol were investigated. After the optimization process, the highest proportion of protein recovered in the top phase was achieved with 250g/L ammonium sulphate, 60% (v/v) 2-propanol, 1.0V_R,initial, 20g/L crude biomass load, 4mm³/min air flowrate and 10min of flotation time. The recycling of phase components was introduced to minimize the use of alcohol and salt in the corresponding LBF. It was demonstrated that top phase (alcohol) recycling can achieve increasing performance for three consecutive recycling runs. Under optimized process conditions, the proportion of protein recovered in the top phase was 88.86% for the third recycle run.