• Energy Research

Abstract Major challenges in cultivation, harvesting, CO2 capture and downstream processing of microalgae biomass have to be confronted for successful commercial deployment. This study explored a sustainable process train to mass-produce a native marine algal strain, Nannochloropsis salina, for biocrude production and CO2 capture. The microalga was cultivated in a 3-m2 raceway pond with manual agitation, 10-m2 raceway ponds with and without CO2 supplementation and a 120-m2 pond with CO2 supplementation using carbonation column reactor (CCR). During the above experiments, the areal productivities obtained ranged from 7.5 to 34.4 g m−2 d−1 and the lipid content was between 29 and 80%. This study also demonstrated a novel 10 KLPD (kilolitres per day) capacity electropreciflocculation (ePF) reactor (∼0.56–0.78 KWh/KL) and filter press for biomass harvesting with 98.24% efficiency. The CO2 capture of N. Salina estimated was in the range of 45.38–208.12 tons ha−1 y−1, and the average was 95.39 tons ha−1 y−1. The cost estimated based on the 120-m2 pond trials was $3.46/kg of dry algal biomass. Thus the findings provide immense scope for future research on large-scale cultivation of Nannochloropsis salina for biofuel production and carbon capture applications.

AbstractThe potential of microalgal biomasses for the production of biochemicals such as pigments, vitamins, antibiotics, polysaccharides, proteins, essential fatty acids, bio-flocculants, enzymes, etc. is well known. The purpose of this study was to cultivate two cyanobacterial species namely Chroococcus turgidus and Oscillatoria sp., isolated from industrial effluents, using a suitable growth medium in a large-scale High Rate Algal (HRA) pond. The biomolecules such as total protein, total carbohydrate and total lipid, and the pigments chlorophyll, phycobilins, β-carotene, were analysed at regular intervals during cultivation. In addition, the total bacterial cell numbers were enumerated during the study and their influence on algal growth was studied. The algal biomass was harvested by low-cost methods such as auto-flocculation and auto-floatation.

Energy security has become a serious global issue and a lot of research is being carried out to look for economocially viable and environment-friendly alternatives. The only solution that appears to to meet the futuristic needs is the use of renewable energy. Although various forms of renewable energy are being currently used, the prospects of producing carbon-neutral biofuels from microalgae appears bright because of its unique features such as suitability of growing in open ponds required for production of a commodity product, high CO2-sequestering capability, ability to grow in wastewater/seawater/brackishwater and high lipid productivity. The major process constraint in the microalgal biofuel technology is the cost-effective and efficient extraction of lipids. The objective of this article is to provide a comprehensive review on various methods of lipid extraction from microalgae available till date, as well as to discuss their advantages and disadvantages. The article covers all areas of lipid extraction procedures including solvent extraction procedures, mechanical approaches and solvent-free procedures apart from some of the latest extraction technologies. A lot more research efforts are required in this area for successful implementation of this technology at a production scale.