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Heterotrophic cultures of microalgae: metabolism and potential products
Water research, 2011
This review analyzes the current state of a specific niche of microalgae cultivation; heterotrophic growth in the dark supported by a carbon source replacing the traditional support of light energy. This unique ability of essentially photosynthetic microorganisms is shared by several species of microalgae. Where possible, heterotrophic growth overcomes major limitations of producing useful products from microalgae: dependency on light which significantly complicates the process, increase costs, and reduced production of potentially useful products. As a general role, and in most cases, heterotrophic cultivation is far cheaper, simpler to construct facilities, and easier than autotrophic cultivation to maintain on a large scale. This capacity allows expansion of useful applications from diverse species that is now very limited as a result of elevated costs of autotrophy; consequently, exploitation of microalgae is restricted to small volume of high-value products. Heterotrophic culti...
Heterotrophic growth of microalgae: metabolic aspects
World Journal of Microbiology and Biotechnology, 2014
Microalgae are considered photoautotrophic organisms, however several species have been found living in environments where autotrophic metabolism is not viable. Heterotrophic cultivation, i.e. cell growth and propagation with the use of an external carbon source under dark conditions, can be used to study the metabolic aspects of microalgae that are not strictly related to photoautotrophic growth and to obtain high value products. This manuscript reviews studies related to the metabolic aspects of heterotrophic grow of microalga. From the physiological and metabolic perspective, the screening of microalgal strains in different environments and the development of molecular and metabolic engineering tools, will lead to an increase in the number of known microalgae species that growth under strict heterotrophic conditions and the variety of carbon sources used by these microorganisms.
Microalgae: The Multifaceted Biomass of the 21st Century
Biomass [Working Title], 2020
Microalgae are unicellular, eukaryotic organisms which possess unique qualities of replication, producing biomass as a precursor for biofuels, nutraceuticals, biofertilizer, and fine chemicals including hydrocarbons. Microalgae access nitrates and phosphates in wastewater from municipalities, industries, and agricultural processes to grow. Wastewater is, therefore, culture media for microalgae, and provides the needed nutrients, micronutrients, inorganic and organic pollutants to produce microalgae biomass. Suitable strains of microalgae cultivated under mesophilic conditions in wastewater with optimized hydrodynamics, hydraulic retention time (HRT), luminous intensity, and other co-factors produce biomass of high specific growth rate, high productivity, and with high density. The hydrodynamics are determined using a range of bioreactors from raceway ponds, photobioreactors to hybrid reactors. Carbon dioxide is used in the photosynthetic process, which offers different growth stimul...
The Role of Heterotrophic Microalgae in Waste Conversion to Biofuels and Bioproducts
Processes, 2021
In the last few decades, microalgae have attracted attention from the scientific community worldwide, being considered a promising feedstock for renewable energy production, as well as for a wide range of high value-added products such as pigments and poly-unsaturated fatty acids for pharmaceutical, nutraceutical, food, and cosmetic markets. Despite the investments in microalgae biotechnology to date, the major obstacle to its wide commercialization is the high cost of microalgal biomass production and expensive product extraction steps. One way to reduce the microalgae production costs is the use of low-cost feedstock for microalgae production. Some wastes contain organic and inorganic components that may serve as nutrients for algal growth, decreasing the culture media cost and, thus, the overall process costs. Most of the research studies on microalgae waste treatment use autotrophic and mixotrophic microalgae growth. Research on heterotrophic microalgae to treat wastes is still ...
Recent Advances in Improving Ecophysiology of Microalgae for Biofuels
Book Chapter, 2017
Ability of microalgae for biofuel production has been intensively investigated. Microalgae are capable of acting as sunlight driven fuel factories, which can help to convert excess carbon dioxide (CO2) into lipid and starch-based biofuels. The merits of using algae as biofuel feedstock are that multiple biofuels can be produced from single biomass source. Studies have suggested that algae alone can produce more than 50,000 kg/acre/year of biomass, which could be utilized for biofuel production (Gimpel et al. 2013). In spite of many published reports on competitive strains and algal culture conditions, a wide scope still remains for understanding algal biodiversity and ecophysiological properties. Earlier studies have suggested that accumulation of energy reserves, their localization, and regulation inside the microalgal cell is governed by various external abiotic factors such as light intensity, temperature, pH, and supply of nitrogen and phosphorus. This chapter is aimed to give overall view of major environment stresses and approaches used to engineer microalgae for biofuel production. In depth engineering strategies and effect of abiotic factors on production of high energy yielding compounds (lipid and starch) have been discussed.
Potential of Bioenergy Production from Microalgae
Review Article, 2014
There is increasing interest for sustainable bioenergy production to mitigate greenhouse gas emissions and reduce reliance on fossil fuels. Biofuel can be generated from a wide variety of feedstock types including algae. Algae are an attractive feedstock for the production of liquid and gaseous biofuels that do not need to directly compete with food production. However, both the sustainability and the economic viability of algal biofuels have been questioned, particularly with regard to high carbon and fertiliser input requirements, and high cultivation and production costs. Improved understanding and modifications at a biological level, of algal genetics, carbon storage metabolism, photosyn-thesis and algal physiology, have the potential for significant advances in algal biofuel feasibility. This is being driven by advances in genomic technologies to provide the potential for genetic and metabolic engineering, plus the development of high-throughput techniques for the screening of natural strains for suitable biofuel characteristics.
Microalgae As A Sustainable Source Of Bioenergy: Present Status And Future Prospects
Nova Science Publishers, New York, 2018
An enormous amount of interest has been raised on the use of microalgae-based technologies for the production of a sustainable source of bioenergy and high-value coproducts. Biotechnological exploitation of microalgae for human welfare is a recent phenomenon although these wonderful organisms exist on this planet since archeological era. Microalgae are eukaryotic photosynthetic microorganism known for their rapid growth. The main microalgae are Scenedesmus, Chlorella, Spirulina, Dunaliella and Haematococcus are currently cultivated photo-synthetically for the production of verity of bioenergy and valuable products. Micro-algal biomass have high biotechnological potential and it is being use as a source of drugs in pharmaceutical industries, biochemicals, biofuels (bio-diesel, bio-gas, bio-ethanol and bio-butanol), bio-fertilizer, biopigments and dye, renewable food, Polyunsaturated fatty acid (DHA, EPA, GLA), feed, cosmetic, sink for greenhouse gases, soil amelioration, bioremediation and other applications such as treatment of wastewater. A major bottleneck in the application of microalgae to such processes is low productivity of the culture, both in terms of biomass and product. Comparison of productivity between economically important microalgae
3 Biotech
Microalgae are microscopic algae in sizes ranging from a few micrometers to several hundred micrometers. On average, half of the oxygen in the atmosphere is produced by the photosynthetic process of microalgae, so the role of these microorganisms in the life cycle of the planet is very significant. Pharmaceutical products derived from microalgae and commercial developments of a variety of supplements extracted from them originate from a variety of their specific secondary metabolites. Many of these microalgae are a reservoir of unique biological compounds including carotenoids, antioxidants, fatty acids, polysaccharides, enzymes, polymers, peptides, pigments, toxins and sterols with antimicrobial, antiviral, antifungal, antiparasitic, anticoagulant, and anticancer properties. The present work begins with an introduction of the importance of microalgae in renewable fuels and biodiesel production, the development of healthy food industry, and the creation of optimal conditions for efficient biomass yield. This paper provides the latest research related to microalgae-derived substances in the field of improving drug delivery, immunomodulatory, and anticancer attributes. Also, the latest advances in algal biocompounds to combat the COVID-19 pandemic are presented. In the subject of cultivation and growth of microalgae, the characteristics of different types of photobioreactors, especially their latest forms, are fully discussed along with their advantages and obstacles. Finally, the potential of microalgae biomass in biotechnological applications, biofuel production, as well as various biomass harvesting methods are described.
Cultivation of Microalgae at Extreme Alkaline pH Conditions: A Novel Approach for Biofuel Production
ACS Sustainable Chemistry & Engineering, 2017
A major challenge to the economic viability of outdoor cultivation of microalgae is the high cost of CO 2 supply, even when microalgae farms are co-located with point sources of CO 2 emissions. In addition, the global capacity for algae biofuel generation is severely restricted when microalgae farm locations are constrained by proximity to CO 2 sources along with the additional limitations of low slope lands and favorable climate. One potential solution to the impediments of CO 2 supply cost and availability is through cultivation of microalgae in highly alkaline pH solutions (pH>10) that are effective at scavenging CO 2 from the atmosphere at high rates. The extreme alkaline pH media would also mitigate culture crashes due to microbial contamination and predators. In this study, we report the indoor and outdoor phototrophic cultivation of a microalgae isolate (Chlorella sorokiniana str. SLA-04) adapted to grow in unusually high pH environments. The isolate was cultivated in a growth medium at pH>10 without any inputs of concentrated CO 2. Both indoor and outdoor studies showed biomass and lipid productivities that were comparable to those reported for other microalgae cultures cultivated in near-neutral pH media (pH 7-8.5) under similar conditions. SLA-04 cultures also showed high lipid productivity and high glucose-to-lipid conversion efficiency when cultivated mixotrophically in the presence of glucose as an organic carbon source. From the energy content (calorific value) of the lipids produced and glucose consumed, a relatively high 0.62 lipid calories were produced per glucose calorie consumed. In conclusion, our results demonstrate the feasibility of microalgae cultivation in extremely high pH media (pH>10) as a novel strategy for biofuel production without dependence on concentrated CO 2 inputs.