Characterization of fatty acids and hydrocarbons of chlorophycean microalgae towards their use as biofuel source

Microalgae accumulate important biofuel precursors such as fatty acids and hydrocarbons. Identification of microalgal strains with ideal fuel quality precursor profile is important during bioprospection studies. In this direction, thirty two freshwater green microalgae were characterized for their biomass productivity, fatty acid and hydrocarbon composition under autotrophic growth conditions. Scenedesmus dimorphus CFR 1-05/FW, Oocystis pusilla CFR 6-01/FW and Quadrigula lacustris CFR 7-01/FW were high biomass producing strains with shorter doubling time. Lipid accumulation was monitored by nile red staining with mild acetic acid pretreatment (at 7 m mol L⁻¹) to microalgal cells. Six strains viz., S. dimorphus CFR 1-05/FW, Scenedesmus obtusus CFR 1-09/FW, Chlorococum sp. CFR 2-01/FW, C. humicola CFR 2-03/FW, Chlorella sorokiniana CFR 3-01/FW, Dictyosphaerium CFR 5-01/FW showed lipid accumulation of >20% mass fraction at stationary phase. Palmitic, oleic and alpha linolenic acids were major fatty acids in all the chlorophycean species. Fuel grade hydrocarbons which can be directly blended with petroleum fuels were identified. Fourteen strains showed hydrocarbon content of >10% mass fraction of dry biomass. n-Paraffins of chain length between C15 to C20 were predominant hydrocarbons in all the strains. Branched isoprenoid hydrocarbons were detected in Scenedesmus sp. CFR 1- 13/FW constituting 49% mass fraction of total hydrocarbons. High quantities of n-tetradecane (40%) was detected in Kirchneriella cornuta CFR 8-01/FW. The similarity of microalgal hydrocarbon profiles with paraffinic and isoparaffinic fraction of petroleum diesel and compliance of FAME based biodiesel to international standards indicate the suitability of algae derived biofuels for blending with conventional petroleum fuels.     

Microalgal biomass production and carbon dioxide sequestration from an integrated ethanol biorefinery in Iowa: A technical appraisal and economic feasibility evaluation

Microalgae present some advantageous qualities for reducing carbon dioxide (CO₂) emissions from ethanol biorefineries. As photosynthetic organisms, microalgae utilize sunlight and CO₂ to generate biomass. By integrating large-scale microalgal cultivation with ethanol biorefineries, CO₂ sequestration can be coupled with the growth of algae, which can then be used as feedstock for biodiesel production. In this case study, a 50-mgy ethanol biorefinery in Iowa was evaluated as a candidate for this process. Theoretical projections for the amount of land needed to grow algae in raceway ponds and the oil yields of this operation were based on the amount of CO₂ from the ethanol plant. A practical algal productivity of 20 g m⁻² d⁻¹ would require over 2,000 acres of ponds for complete CO₂ abatement, but with an aggressive productivity of 40–60 g m⁻² d⁻¹, a significant portion of the CO₂ could be consumed using less than 1,000 acres. Due to the cold temperatures in Iowa, a greenhouse covering and a method to recover waste heat from the biorefinery were devised. While an algal strain, such as Chlorella vulgaris, would be able to withstand some temperature fluctuations, it was concluded that this process is limited by the amount of available heat, which could maintain only 41 acres at 73 °F. Additional heating requirements result in a cost of 10–40 USD per gallon of algal oil, which is prohibitively expensive for biodiesel production, but could be profitable with the incorporation of high-value algal coproducts.     

Net energy analysis of the production of biodiesel and biogas from the microalgae: Haematococcus pluvialis and Nannochloropsis

Microalgae have been proposed as possible alternative feedstocks for the production of biodiesel because of their high photosynthetic efficiency. The high energy input required for microalgal culture and oil extraction may negate this advantage, however. There is a need to determine whether microalgal biodiesel can deliver more energy than is required to produce it. In this work, net energy analysis was done on systems to produce biodiesel and biogas from two microalgae: Haematococcus pluvialis and Nannochloropsis. Even with very optimistic assumptions regarding the performance of processing units, the results show a large energy deficit for both systems, due mainly to the energy required to culture and dry the microalgae or to disrupt the cell. Some energy savings may be realized from eliminating the fertilizer by the use of wastewater or, in the case of H. pluvialis, recycling some of the algal biomass to eliminate the need for a photobioreactor, but these are insufficient to completely eliminate the deficit. Recommendations are made to develop wet extraction and transesterification technology to make microalgal biodiesel systems viable from an energy standpoint.     

中国微藻生物质能源专利技术分析

大力发展微藻生物质能源是解决能源危机和环境问题的有效途径。文章从微藻资源、微藻培养系统、培养物采收技术、微藻生物柴油炼制、含油微藻综合利用等方面出发,综述了中国微藻生物质能源专利的发展现状,旨在使科研工作者更加全面地了解这一领域发展趋势,并且促进科研工作者对自主知识产权的保护意识。     

Prospects of biodiesel production from microalgae in India

Energy is essential and vital for development, and the global economy literally runs on energy. The use of fossil fuels as energy is now widely accepted as unsustainable due to depleting resources and also due to the accumulation of greenhouse gases in the environment. Renewable and carbon neutral biodiesel are necessary for environmental and economic sustainability. Biodiesel demand is constantly increasing as the reservoir of fossil fuel are depleting. Unfortunately biodiesel produced from oil crop, waste cooking oil and animal fats are not able to replace fossil fuel. The viability of the first generation biofuels production is however questionable because of the conflict with food supply. Production of biodiesel using microalgae biomass appears to be a viable alternative. The oil productivity of many microalgae exceeds the best producing oil crops. Microalgae are photosynthetic microorganisms which convert sunlight, water and CO₂ to sugars, from which macromolecules, such as lipids and triacylglycerols (TAGs) can be obtained. These TAGs are the promising and sustainable feedstock for biodiesel production. Microalgal biorefinery approach can be used to reduce the cost of making microalgal biodiesel. Microalgal-based carbon sequestration technologies cover the cost of carbon capture and sequestration. The present paper is an attempt to review the potential of microalgal biodiesel in comparison to the agricultural crops and its prospects in India.     

Chlorella sorokiniana HS1, a novel freshwater green algal strain,grows and hyperaccumulates lipid droplets in seawater salinity

Salinity is a major abiotic stress for terrestrial plants and freshwater microalgae alike. The most notable physiological response of microalgae like Dunaliella to salinity stress is reduced photosynthesis and production of carotenoids. Here, we report isolation and characterization of a novel freshwater microalgal strain, Chlorella sorokiniana HS1, which grows and hyperaccumulates lipid droplets (LD) in hypersaline conditions greater than seawater salinity. Other freshwater Chlorella strains tested neither grew nor possessed high LD levels in high salt concentration. C. sorokiniana HS1 displayed increase in cell size (200%) and LD, resulting in increased biomass and lipid productivity, respectively, with altered but favourable fatty acid methyl ester composition under salinity stress. Experimental analyses reveal definitive shift from proteins and starch to LD synthesis as well as chlorophyll degradation, response analogous to nitrogen starvation. Acute salt stress (<6 h) in seawater salinity or above resulted in instant accumulation of LD. C. sorokiniana HS1 allows for two phase cultivation, growth phase in freshwater and stress induction phase in seawater for biodiesel production. This strain would therefore significantly reduce costs and production constraints associated with stress induction.     

Oxidative stress-tolerant microalgae strains are highly efficient for biofuel feedstock production on wastewater

Nutrient-rich wastewater may provide a sustainable means to cultivate microalgal biomass for biofuel use, yet many microalgal strains are very sensitive to wastewater due to toxicity caused by abiotic and biotic stresses. Naturally adapted strains that can efficiently grow in wastewater effluent are therefore of interest, however, the mechanisms by which such strains tolerate wastewater conditions are unknown. This study isolated indigenous chlorophyte microalgae strains from a municipal secondary wastewater effluent tank. The strains were identified by molecular phylogenetics and characterised by their ability to utilise exogenous organic carbon sources for mixotrophic growth and on the basis of oxidative stress tolerance, in order to elucidate the mechanisms of wastewater adaptation. Two of the strains, identified as Chlorella luteoviridis and Parachlorella hussii, could grow very well in raw wastewater due to their substantial tolerance to oxidative stress, which is highly induced by the wastewater environment. These strains exhibited high ascorbate peroxidase activity allowing increased scavenging of reactive oxygen species compared to strains that are not well adapted to the wastewater conditions. Both strains displayed high biomass and lipid productivity values in wastewater effluent. The accumulated lipids were suitable for biodiesel usage with characteristics equivalent to palm oil- and sunflower oil-derived biodiesel. The strains were also efficient in nutrient remediation from the wastewater. These results demonstrate the potential of these two strains for future biofuel applications coupled to wastewater remediation and highlight the importance of oxidative stress tolerance as a key indicator of efficient wastewater growth.     

Falling film evaporation characteristics of microalgae suspension for biofuel production

Microalgae, one of the important biofuel producers, have received considerable attention recently. Dewatering is one of the bottlenecks for its industrialization due to the dilute nature of the suspensions and the small cell size. Traditional liquid–solid separation processes are not efficient for dewatering of microalgae suspensions. In this study, falling film evaporation was employed for dewatering of microalgae suspension, which is a popular process for concentrating heat sensitive materials. The heat transfer coefficient was as high as 9414.20 W/m² K with mass flow rate of 0.233 kg/s, ΔT of 1.21 °C, and microalgae concentration of 60 g/L. The falling film evaporation process can be made highly energy efficient if it is coupled with Mechanical Vapor Recompression (MVR) or Thermal Vapor Recompression (TVR) system. Heat and mass transfer characteristics of falling film evaporation of microalgae suspension have been investigated here. This will provide the fundamentals for future feasibility study of utilizing the falling film evaporation in the microalgal industry.     

Exploring alkaline pre-treatment of microalgal biomass for bioethanol production

We have investigated, for the first time, the alkaline pre-treatment of microalgal biomass, from the species Chlorococcum infusionum, using NaOH for bioethanol production. This pre-treatment step aims to release and breakdown entrapped polysaccharides in the microalgae cell walls into fermentable subunits. Three parameters were examined here; the concentration of NaOH, temperature and the pre-treatment time. The bioethanol concentration, glucose concentration and the cell size were studied in order to determine the effectiveness of the pre-treatment process. Microscopic analysis was performed to confirm cell rupturing, the highest glucose yield was determined to be 350 mg/g, and the maximum bioethanol yield obtained was 0.26 g ethanol/g algae using 0.75% (w/v) of NaOH and 120 °C for 30 min. Overall, the alkaline pre-treatment method proved to be promising option to pre-treat microalgal biomass for bioethanol production.     

Two Mychonastes isolated from freshwater bodies are novel potential feedstocks for biodiesel production

Microalgae have been considered as ideal feedstocks for biodiesel production but the potential application is still under investigations. Here, eight kinds of microalgae were identified from water samples based on the morphologic and phylogenetic analyses. Among these eight microalgae, two Mychonastes S4 and S15 exhibited relative faster growth rate in the early culture stage and the highest contents of lipids. The two Mychonastes also showed higher C18:1 contents than the two Chlorella which were traditionally considered to be potential species for biodiesel production. As one kind of less researched microalgae, this study suggests Mychonastes should be a potential feedstock for biodiesel production. The application of the microalgal biodiesel still have some limiting factors, however, it is promising based on better lipid extraction technology and more relevant studies.     

Conversion of microalgae to biofuel

This paper primarily presents an overall review of the use of microalgae as a biofuel feedstock. Among the microalgae that have potential as biofuel feedstock, Chlorella, specifically, was thoroughly discussed because of its ability to adapt both to heterotrophic and phototrophic culture conditions. The lipid content and biomass productivity of microalgae can be up to 80% and 7.3 g/l/d based on the dried weight of biomass, respectively, making microalgae an ideal candidate as a biofuel feedstock. The set-up of the system and the biomass productivity of microalgae cultivated in an open pond and a photobioreactor were also compared in this work. The effect of the culture condition is discussed based on the two-stage culture period. The issues that were discussed include the light condition and the CO₂, DO and N supply. The microalgal productivities under heterotrophic and phototrophic culture conditions were also compared and highlighted in this work. The harvesting process and type of flocculants used to aid the harvesting were highlighted by considering the final yield of biomass. A new idea regarding how to harvest microalgae based on positive and negative charges was also proposed in this work. The extraction methods and solvents discussed were primarily for the conventional and newly invented techniques. Conversion processes such as transesterification and thermochemical processes were discussed, sketched in figures and summarized in tables. The cost–benefit analysis of heterotrophic culture and the cultivation system was highlighted at the end of this work. Other benefits of microalgae are also mentioned in this work to give further support for the use of microalgae as a feedstock for biofuel production.     

Emission analysis of Botryococcus braunii algal biofuel using Ni-Doped ZnO nano additives for IC engines

Microalgae biodiesel has been considered ?as a clean renewable fuel for diesel marine engines. This is due to its optimistic characterizations such as ?rapid growth rate, high productivity, and its ability to convert CO₂ into fuel. In this study, the use of microalgae biodiesel, obtained from Botryococcus braunii, as an alternative fuel for diesel marine engines has been investigated. The diesel engine is verified experimentally using Ni-Doped ZnO nano additive blends with algae biodiesel and neat diesel fuel. The results showed that doped nano additive blends? produce less emission compared to B20.     

Flue gas waste heat affects algal liquid temperature for microalgal production in column photobioreactors

To explore the effects of waste heat (50–170°C) from steel plant flue gas on the column photobioreactor algal liquid temperature for microalgal production, a flue gas-microalgal liquid heat transfer model was developed that simulated the microalgal growth environment for flue-gas carbon dioxide (CO₂) fixation. The simulation results showed that the influence of high-temperature flue gas weakened with the increasing microalgal liquid temperature due to enhanced evaporation and heat dissipation. Increasing the flue gas temperature and aeration rate resulted in a higher microalgal liquid temperature up to a maximum increase of 4.16°C at an ambient temperature of 25°C, an aeration rate of 2 L/min, and a flue gas temperature of 170°C. In an experiment on the effect of incubation temperature on the growth rate of microalgae, at an optimal temperature of 35°C, the Chlorella sp. PY-ZU1 growth rate exhibited a remarkable increase of 104.7% compared to that at 42.5°C. Therefore, modulating the flue gas conditions can significantly increase the microalgal growth rate for CO₂ fixation, making it a promising approach to increase biomass production for efficient carbon utilization.     

Biomass and lipid productivities of marine microalgae isolated from the Persian Gulf and the Qeshm Island

In this work, the screening of 147 microalgal strains from the Persian Gulf and the Qeshm Island (Iran) were done in order to choose the best ones, in terms of growth (biomass) rate and lipid content for biodiesel production. A methodology, combining experiments in lab-scale and pilot plant (open pond) used to produce and evaluate biomass and lipid productivity is presented for the systematic investigation of the potential of different microalgae species. The culture conditions, including photo flux (180 ??E m⁻² s⁻¹), photoperiod (12 h light/dark), temperature (25 °C), pH (≈8), air (carbon dioxide) and growth medium, were kept constant for all experiments. Microalgae were screened in two stages using optical density (for evaluation of biomass concentration) and Nile red and gas chromatography (for determination of lipid content and fatty acid fractions). In general, maximum specific growth rate and the maximum biomass productivity were obtained after 8-12-day culture. Nannochloropsis sp. and Neochloris sp. were selected from the marine microalgal culture collection, due to their high biomass (50 and 21.7 g L⁻¹, respectively) and oil content (52% and 46%, respectively). If the purpose is to produce biodiesel only from one species, Nannochloropsis sp. presented the most adequate fatty acid profile, namely linolenic and other polyunsaturated fatty acids. However, the microalgae Chlorella sp. can also be used if associated with other microalgal oils. In addition, selected strains could be potent candidates for commercial production in the open pond culture.     

Enhanced hydrogen production through co-cultivation of Chlamydomonas reinhardtii CC-503 and a facultative autotrophic sulfide-oxidizing bacterium under sulfurated conditions

Photoproduction of H₂ using microalgae has been considered as a promising approach for developing sustainable hydrogen energy. The algae C. reinhardtii CC-503 was co-cultured with a facultative autotroph sulfur-oxidizing bacterium Thuomonas intermedia BCRC 17547 to improve H₂ production. The maximum H₂ production of co-culture at sulfur deficiency conditions was 122 μmol/mg Chl with algae/bacteria ratio as 60:1, which was 2.8-fold higher than that of the pure algal culture. Na₂S₂O₃ treatment can result in a maximum H₂ photoproduction rate of 255 μmol/mg Chl, which was 5.9 and 2.1 times higher than those of pure algae culture and co-culture without Na₂S₂O₃. Co-cultivation under sulphate condition can also significantly increase the biomass, respiratory rate, starch content and hydrogenase activity of C. reinhardtii. By supplement of Na₂S₂O₃, persistent (52 days) H₂ production of bacteria/algae co-culture can be achieved. Our results demonstrated that co-culture of C. reinhardtii CC-503 and bacteria BCRC17547 is a cost-effective strategy for improving photobiological H₂ production.     

Parameters influencing the design of photobioreactor for the growth of microalgae

Carbon dioxide sequestration using microalgae is the most promising method for combating global warming. Growth of microalgae is influenced by the availability of carbon dioxide, number of photons, initial concentration of microalgae and nutrients. The transfer of carbon dioxide from flue gas and absorption of photons from sunlight are influenced by the surface area/volume ratio of photobioreactor. The growth rate of microalgae follows lag, log, deceleration and stationary phases. The rate of growth increases with concentration of microalgae till an optimum concentration of algae is reached and then decreases for any fixed operating conditions and selected microalgae. At an optimum concentration the rate is the highest always. Operating a photobioreactor at this optimum concentration with highest surface area to volume ratio would require the smallest size of photobioreactor for a given production rate. Based on the review on the performance of various existing photobioreactors and the growth mechanism of microalgae it is observed that the design and operation of an efficient photo bioreactor system should consider (1) providing highest spread area to volume ratio (2) maintaining optimum concentration matching the highest rate (3) harvesting the excess microalgae formed over the optimum concentration to maintain the optimum concentration and (4) adding nutrients to the growth medium to maintain nutrient concentration at a constant level.     

Resource demand implications for US algae biofuels production scale-up

Photosynthetic microalgae with the potential for high biomass and oil productivities have long been viewed as a promising class of feedstock for biofuels to displace petroleum-based transportation fuels. Algae offer the additional benefits of potentially being produced without using high-value arable land and fresh water, thereby reducing the competition for those resources between expanding biofuels production and conventional agriculture. Algae growth can also be enhanced by the use of supplemental CO₂ that could be supplied by redirecting concentrated CO₂ emissions from stationary industrial sources such as fossil-fired power plants, cement plants, fermentation industries, and others. In this way, algae may offer an effective means to capture carbon emissions for reuse in renewable fuels and co-products, while at the same time displacing fossil carbon fuels to help bring about a net reduction in overall carbon emissions. Significant displacement of petroleum fuels will require that algae feedstock production reach large volumes that will put demands on key resources. This scenario-based analysis provides a high-level assessment of land, water, CO₂ and nutrient (nitrogen, phosphorus) demands resulting from algae biofuel feedstock production reaching target levels of 10 billion gallons per year (BGY), 20 BGY, 50 BGY, and 100 BGY for four different geographical regions of the United States. Different algae productivities are assumed for each scenario region, where relative productivities are nominally based on annual average solar insolation. The projected resource demands are compared with data that provide an indication of the resource level potentially available in each of the scenario regions. The results suggest that significant resource supply challenges can be expected to emerge as regional algae biofuel production capacity approaches levels of about 10 BGY. The details depend on the geographic region, the target feedstock production volume, and the level of algae productivity that can be achieved. The implications are that the supply of CO₂, nutrients, and water, in particular, can be expected to severely limit the extent to which US production of algae biofuel can be sustainably expanded unless approaches are developed to mitigate these resource constraints in parallel to emergence of a viable algae technology. Land requirements appear to be the least restrictive, particularly in the Western half of the country where larger quantities of potentially suitable classes of land exist. Within the limited scope and assumptions of this analysis, sustainable photosynthetic microalgae biofuel feedstock production in the US in excess of about 10 BGY will likely be a challenge due to other water, CO₂ and nutrient resource limitations. Developing algae production approaches that can effectively use non-fresh water resources and minimize both water and nutrient requirements will help reduce resource constraints. Providing adequate CO₂ resources for enhanced algae production appears the biggest challenge, and could emerge as a constraint at oil production levels below 10 BGY.     

Growth characteristics,biohydrogen production and photochemical activity of photosystems in green microalgae Parachlorella kessleri exposed to nitrogen deprivation

The biohydrogen (H₂) generation in green microalgae is associated with electron transfer during photosynthesis. In this study, the ability of Parachlorella kessleri RA-002 isolated in Armenia to generate biohydrogen (H₂) in TAP and Tamiya media with and without nitrogen deprivation have been determined. Nitrogen deprivation led to a suppression of the growth rate and a decrease in the content of photosynthetic pigments in algae, as well as to increase of H₂ yield. The highest H₂ yield was found during the growth of algae in TAP and Tamiya media under nitrogen-deprived conditions, which was 4–5 times more compared to control cells grown without nitrogen deprivation. Diuron inhibited this process, indicating that H₂ generation was due to PS II activities. The analysis of the effect of nitrogen-deprived conditions on the activity of photosystem I and II has been carried out. Nitrogen deprivation suppressed of photosynthetic activity of PS II (up to 20% compared to control) that facilitated the formation of anaerobic conditions increasing the total yield of H₂.     

A power-law sensitivity analysis of the hydrogen-producing metabolic pathway in Chlamydomonas reinhardtii

Melis et al. have demonstrated that the green alga Chlamydomonas reinhardtii, when deprived of sulfur, can produce hydrogen gas for 70 h, then can resume hydrogen gas production after a brief period of “recharging” in the presence of sulfur. Here we describe an S-system model of H₂ production by C. reinhardtii. Through that model we investigate the sensitivity of H₂ production to photosynthetic efficiency, and to contention for the protons produced by the photolysis of water, between hydrogen production on the one hand, and ATP consumption by cellular functions outside the H₂ production path on the other. The model identifies for experimental investigation several potential systemic constraints on any genetic re-engineering effort aimed at increasing the H₂ production efficiency of the alga.     

On the calculation of solar radiation in hazy atmospheres and on turbidity in Ibadan

A previous model is examined in greater detail for the harmattan haze periods (November to January) of 1975–1980 at Ibadan, when the atmosphere is often heavily overcast with dust. It is shown that for air mass (m) and turbidity (β) product values of mβ > 4.05 the scattering transmittance τ_scat, for the instantaneous direct solar radiation becomes negative, while for mβ < 0.22 τ_scat changes too rapidly, thus failing to give acceptable values of irradiation for such periods. This problem is overcome by employing the limits 0.22 mβ 3.07 in the calculations, which corresponds to β of 0.40 and 0.22 for “very hazy” and “hazy-hot clear” atmospheres, respectively. The resulting daily and monthly average total insolation are mainly within ± 15% and ± 10%, respectively, of the experimental data provided by the International Institute of Tropical Agriculture (I.I.T.A.), Ibadan.The variation of the turbidity in the city is also studied for all days of the six years. Daily average values 0.10 β 0.175 occur on about 60% of the days, while “clear” (β < 0.125) and “very hazy” (β 0.40) weather days have about 16% and 12.37%, respectively. Some 74.4% of the very hazy days fall within the harmattan period during which the monthly average turbidity is often higher than 0.35.