Key issues to consider in microalgae based biodiesel production

Energy Education Science and Technology Part A: Energy Science and Research 05/2012; 29(1):563-576.


All nations have been confronted with the energy crisis due to depletion of finite fossil fuels reserves, which results an increasing global demand of biofuels for energy security, economic stability and reduction in climate change effects, and generate the opportunity to explore new biomass sources. The production of sustainable bioenergy is a challenging task in the promotion of biofuels for replacing the fossil based fuels to mitigate challenges of fossil based energy consumption. Algae might be a very promising source of biomass in this context as it sequesters a significant quantity of carbon from atmosphere and industrial gases and is also very efficient in utilizing the nutrients from industrial effluents and municipal wastewater. If developed sustainably, the algae biofuel industry may be able to provide large quantities of biofuels with potentially minimal environmental impacts. However, in order to realize this, a complete analysis of full life cycle impact of algal biofuel production in the context of issues such as water resource management, land use impact, energy balance and air emissions are very necessary. The commercial-scale production of algae requires careful consideration of many issues that can be broadly categorized into four main areas: selecting algae species that produce high oil levels and grow well in specified environments, algae growth methods, water sources and related issues, and nutrient and growth inputs.

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    • "The mass transfer coefficient (kL) (m/s) for a slightly soluble gaseous substrate can be determined using eq. (1) 28 1/V L dNG S /dt = KL S /H(PG S – PL S ),(1)where NG S is the molar substrate transferred from the gas phase, V L (L) the reactor volume, PG S and PL S (atm) are the partial pressures of the gas in gas and liquid phase, H (L atm/mol) is the Henry's law constant and (m 2 /L) is the gas–liquid interface surface area for unit volume. The difference in the partial pressures of the gases is the driving force for mass transfer and thus controls the solubility of the gaseous substrate. "

    Preview · Article · Feb 2016 · Current science
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    • "Likewise, autotrophic microorganisms also play a vital role in the fixation and utilization of CO 2 in nature. Photoautotrophic microorganisms such as algae and cyanobacteria [1] [2] have great potential to assimilate CO 2 into cellular carbon; however, the photosynthesis process cannot take place without light and the algae cannot withstand high concentration of CO 2, [3] [4] [5] [6] resulting in a low efficiency of CO 2 fixation in a high-density cultivation reactor. Alternatively, CO 2 fixation by chemoautotrophic microorganisms represents another important biosynthetic process. "
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    ABSTRACT: Abstract As non-photosynthetic microbial community (NPMC) isolated from seawaters utilized inorganic carbon sources for carbon fixation, the concentrations and ratios of Na2CO3, NaHCO3, and CO2 were optimized by response surface methodology design. With H2 as the electron donor, the optimal carbon sources were 270 mg/L Na2CO3, 580 mg/L NaHCO3, and 120 mg/L CO2. The carbon fixation efficiency as respond to total organic carbon (TOC) was up to 30.59 mg/L with optimal carbon sources, which was about 50% higher than that obtained with CO2 as the sole carbon source. The mixture of inorganic carbon sources developed a buffer system to prevent acidification or alkalization of the medium caused by CO2 or Na2CO3, respectively. Furthermore, CO2 and HCO3(-), the starting points of carbon fixation in the pathways of Calvin-Benson-Bassham and 3-hydroxypropionate cycles, were provided by the carbon source structure to facilitate carbon fixation by NPMC. However, in the presence of mixed electron donors composed of 1.25% Na2S, 0.50% Na2S2O3, and 0.457% NaNO2, the carbon source structure did not exhibit significant improvement in the carbon fixation efficiency, when compared that achieved with CO2 as the sole carbon source. The positive effect of mixed electron donors on inorganic carbon fixation was much higher than that of the carbon source structure. Nevertheless, the carbon source structure could be used as an alternative to CO2 when using NPMC to fix carbon in industrial processes.
    Full-text · Article · Nov 2014 · Environmental Technology
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    • "Although microalgae are able to survive at a variety of tempera - tures , optimal temperature for growth is limited to a narrow range ( 20 – 30°C ) ( Singh et al . , 2012 ) . Generally , in optimal temperature range , rise in temperature leads to improved microalgal biomass production . Temperatures above the optimal range cause growth declines , in severe conditions , even kill microalgae cells . How - ever , low temperatures seem to reduce the biomass loss caused by respiration during dark periods ( We"
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    ABSTRACT: Microalgal biofuels are currently considered to be the most promising alternative to future renewable energy source. Microalgae have great potential to produce various biofuels, including biodiesel, bioethanol, biomethane, and biohydrogen. Cultivation of biofuel-producing microalgae demands favorable environmental conditions, such as suitable light, temperature, nutrients, salinity, and pH. However, these conditions are not always compatible with the conditions beneficial to biofuel production, because biofuel-related compounds (such as lipids and carbohydrates) tend to accumulate under environmental-stress conditions of light, temperature, nutrient, and salt. This paper presents a brief overview of the effects of environmental conditions on production of microalgal biomass and biofuel, with specific emphasis on how to utilize environmental stresses to improve biofuel productivity. The potential avenues of reaping the benefits of enhanced biofuel production by environmental stresses while maintaining high yields of biomass production have been discussed.
    Full-text · Article · Jul 2014 · Frontiers in Energy Research
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