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Trends and Bottlenecks in the Sustainable Mitigation of Environmental Issues Using Microalgae
Published in Kalyan Gayen, Tridib Kumar Bhowmick, Sunil K. Maity, Sustainable Downstream Processing of Microalgae for Industrial Application, 2019
Debasish Das, Tridib Kumar Bhowmick, Muthusivaramapandian Muthuraj
Microalgae utilize natural resources, such as freely available sunlight, as the major energy source and adequately available atmospheric CO2 as the carbon source for growth under photoautotrophic nutrition conditions (Muthuraj et al. 2014). These organisms possess photosynthetic activity that accounts for more than 50% of global photosynthesis, which effectively converts the energy of photosynthetically active radiation (PAR) at a wavelength band of 400 to 700 into a biomass via oxidation and reduction reactions. This accompanies the sequestration of atmospheric CO2 in the form of a carbon source with a higher efficiency—up 10% to 50% compared to higher plants (Cheng et al. 2013). They also have the ability to grow under heterotrophic conditions by utilizing organic carbon compounds as the carbon and energy source. Photoheterotrophic cultivation requires light as the chief energy source and organic carbon compounds as the source of carbon (i.e., it requires both carbohydrate sugars and light at the same time for maximal productivity) (Chen et al. 2011). On the contrary, few microalgal strains follow mixotrophic growth conditions in which they perform both heterotrophic and light-dependent functions of growth in a simultaneous and independent manner (Muthuraj et al. 2014). With these wide nutritional types and capability to utilize different trophic modes, the organism has evolved well to organize metabolic pathways and transport machinery for efficient functioning under different cultivation conditions and in wastewaters.
An Overview of Fermentative Hydrogen Production Technologies
Published in Sonil Nanda, Prakash K. Sarangi, Biohydrogen, 2022
Prakash K. Sarangi, Sonil Nanda, Ajay K. Dalai, Janusz A. Kozinski
A special group of photoheterotrophic microorganisms such as purple non-sulfur bacteria mediates photo-fermentation (Wakerley et al., 2017). These organisms have great potential for the production of hydrogen using a wide array of organic and inorganic substances, which are an excellent source of electrons (Kuehnel and Reisner, 2018). These microorganisms can potentially convert organic wastes to hydrogen in the presence of light under nitrogen-deficit conditions. Because such bacteria lack Photosystem II, they help in the elimination of some difficulties associated with oxygen inhibition of hydrogen production. These microorganisms as compared to that of biophotolysis of water produce a substantial amount of hydrogen (Hao et al., 2018). In this process, biohydrogen production using photosynthetic bacteria is accomplished through a nitrogenase enzyme system in which light energy is necessary. The production of biohydrogen is detected through the conversion of reduced organic acids as the carbon source in the presence of light by purple non-sulfur bacteria with the help of the nitrogenase enzyme system (Sarangi and Nanda, 2020). In this process, purple non-sulfur photosynthetic bacteria perform photosynthesis in the absence of oxygen using light as an energy source for synthesizing hydrogen (Adessi and De Philippis, 2014; Eroglu and Melis, 2011). Bacterial photosystem produces two electrons with four adenosine triphosphate (ATP) molecules that help in the production of hydrogen from organic acids with a nitrogenase system. The purple non-sulfur bacteria, thereby increasing the biohydrogen recovery by integrating dark and photo-fermentation have detected the better use of organic acids as effluents from the dark fermentation (Liu et al., 2006).
Sustainable Wastewater Treatment Using Microalgae Technology
Published in Akinola Rasheed Popoola, Emeka Godfrey Nwoba, James Chukwuma Ogbonna, Charles Oluwaseun Adetunji, Nwadiuto (Diuto) Esiobu, Abdulrazak B. Ibrahim, Benjamin Ewa Ubi, Bioenergy and Environmental Biotechnology for Sustainable Development, 2022
Emeka G. Nwoba, John N. Idenyi, Christiana N. Ogbonna, James C. Ogbonna, Mathias A. Chia
Since most of the microalgae culture systems for treatment of organic carbon-containing wastewaters are illuminated, the mode of nutrition is mixotrophic or photoheterotrophic rather than photoautotrophic (Ogbonna and McHenry 2015; Ogbonna and Moheimani 2015). In mixotrophic mode of nutrition, microalgae use light and organic carbon as the sources of energy and both organic and inorganic carbons as the sources of carbon. On the other hand, photoheterotrophic mode of nutrition involves the use of light as the energy source while organic carbon is used as the carbon source. In practical term, mixotrophic and photoheterotrophic cultures can be used interchangeably since both involve the presence of light and organic and inorganic carbon sources. Nevertheless, in mixotrophic cultures, photoautotrophic and heterotrophic metabolic activities proceed independently, depending on the species (Ogbonna et al. 2002a, b), while in photoheterotrophic cultures, light is required for metabolism of the organic carbon. Depending on microalgae species and culture conditions, light can inhibit organic carbon uptake, while under other conditions, the presence of organic carbon depresses photosynthetic O2 evolution and inhibits respiration and enzymes of Calvin cycle (Liu et al. 2009). However, in most cases, cell growth in mixotrophic cultures is much higher than in photoautotrophic and heterotrophic cultures (Ogbonna et al. 2002a, b). Higher cell growth in mixotrophic cultures can be attributed to the fact that organic carbon assimilation is not limited by lack of oxygen since it is continuously generated by photosynthesis, while oxygen concentration does not rise to inhibitory level since it is continuously being used for organic carbon assimilation. Furthermore, organic carbon assimilation (respiration) results in carbon dioxide evolution which stimulates photosynthesis. Better pH stability has also been reported for mixotrophic cultures (Kong et al. 2011).
Hydrogen derived from algae and cyanobacteria as a decentralized fueling option for hydrogen powered cars: Size, space, and cost characteristics of potential bioreactors
Published in International Journal of Sustainable Transportation, 2020
Karin Kolbe, Stefan Lechtenböhmer, Manfred Fischedick
Hydrogen can also be produced photoautotrophically or photoheterotrophically from algae or cyanobacteria. Such production routes could be feasible carbon neutral alternatives to current production methods. Algae and cyanobacteria are particularly interesting for both biohydrogen and biogas production because they grow faster and produce more biomass per hectare than conventional energy crops (Rodolfi et al., 2009). Apart from nutrients, photoautotrophic organisms only need sunlight and CO2 to grow. Photoheterotrophic organisms can produce hydrogen with the help of nutrients, sunlight and organic carbon sources such as acids or sugars (Hallenbeck & Benemann, 2002; McKinlay & Harwood, 2010; Meher Kotay & Das, 2008). These processes lead to the sequestration of carbon dioxide and could therefore be a sustainable production process for hydrogen in the future. However, if photoheterotrophic processes are used, the production of carbon sources such as acids and sugars leads to emissions prior to the actual hydrogen production process.