Kalpesh K. Sharma

Critical analysis of current microalgae dewatering techniques.

Oil-accumulating Microalgae have the potential to enable large-scale biodiesel production without competing for arable land or biodiverse natural landscapes. However, Microalgae harvesting/dewatering is a major obstruction to industrial-scale processing for biofuel production. The dilute nature of Microalgae in cultivation creates high operational costs for harvesting, thus making microalgal fuel less economical. Within the last decade, significant advances have been made to develop new technologies for dewatering or harvesting of Microalgae. The choice of which harvesting technique to apply depends on the Microalgae cell size and the desired product. Microalgae dewatering processes can broadly be classified as primary and secondary dewatering. This article provides an overview of current dewatering techniques along with a critical analysis of costs and efficiencies, and provides recommendations towards cost-effective dewatering.

Comparison of Microalgae Cultivation in Photobioreactor, Open Raceway Pond, and a Two-Stage Hybrid System

In the wake of intensive fossil fuel usage and CO2 accumulation in the environment, research is targeted towards sustainable alternate bioenergy that can suffice the growing need for fuel and also that leaves a minimal carbon footprint. Oil production from microalgae can potentially be carried out more efficiently, leaving a smaller footprint and without competing for arable land or biodiverse landscapes. However, current algae cultivation systems and lipid induction processes must be significantly improved and are threatened by contamination with other algae or algal grazers. To address this issue, we have developed an efficient two-stage cultivation system using the marine microalga Tetraselmis sp. M8. This hybrid system combines exponential biomass production in positive pressure air lift-driven bioreactors with a separate synchronized high-lipid induction phase in nutrient deplete open raceway ponds. A comparison to either bioreactor or open raceway pond cultivation system suggests that this process potentially leads to significantly higher productivity of algal lipids. Nutrients are only added to the closed bioreactors while open raceway ponds have turnovers of only a few days, thus reducing the issue of microalgal grazers.

Rapid induction of omega-3 fatty acids (EPA) in Nannochloropsis sp. by UV-C radiation

Omega‐3 fatty acids, such as eicosapentaenoic acid (EPA), provide substantial health benefits. As global fish stocks are declining and in some cases are contaminated with heavy metals, there is a need to find more sustainable land‐based sources of these essential fatty acids. The oleaginous microalga Nannochloropsis sp. has been identified as a highly efficient producer of omega‐3 fatty acids. In this study, we present a new process to rapidly induce biosynthesis of essential fatty acids, including EPA in Nannochloropsis sp. BR2. Short exposure to UV‐C at a dose of 100 or 250 mJ/cm2 led to a significant increase in total cellular lipid contents when compared to mock‐treated controls. A low dosage of 100 mJ/cm2 also led to a twofold increase in total EPA content within 24 h that constituted 30% of total fatty acids and up to 12% of total dry weight at higher dosages. UV‐C radiation may find uses as an easily applicable external inducer for large‐scale production of omega‐3 production from microalgae. Biotechnol. Bioeng. 2015;112: 1243–1249.

UV‐C mediated rapidcarotenoid induction and settling performance of Dunaliellasalina and Haematococcus pluvialis

Microalgae are primary producers of organic pigments carotenoids in aquatic environments. However, commercial‐scale microalgae application for high value carotenoids production is rarely economical due to the cost‐effectiveness of carotenoid induction and microalgal harvesting process. Here, we present a novel approach, using a small dose of externally applied UV‐C radiation, to rapidly induce unsaturated fatty acids and carotenoid biosynthesis in Dunaliella salina and Haematococcus pluvialis, and also to significantly promote their swimming cells settling for primary dewatering. The amount of total carotenoids and β‐carotenoid were doubled in 24 h on D. salina upon 50 mJ/cm2 of UV‐C radiation, whereas the astaxanthin yield of H. pluvialis was increased five times in 48 h at 30 mJ/cm2. Meanwhile, 95% of algal cells of D. salina and H. pluvialis settled in 15 h and 2 h, respectively. This novel technique represents a convenient, time‐saving and cost‐effective method for commercial microalgal carotenoids production. Biotechnol. Bioeng. 2015;112: 2106–2114.