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Optimization of a wet microalgal lipid extraction procedure for improved lipid recovery for biofuel and bioproduct production
... Reducing the solvent volume relative to the amount of biomass being extracted is essential for any large-scale extraction operation. The efficacy of solvent extraction of intracellular lipids is known to be improved by pretreating the biomass in various ways [10,11,15,19,20,24, 28]. Pretreatment methods include mechanical disruption of cells, thermal treatments, the use of lytic chemicals and irradiation with microwaves and ultrasound. ...
... A previous supposedly optimal method for extraction of lipids from Chlorella sp. and Scenedesmus sp. required a pretreatment of the biomass paste with acids and alkalis and a subsequent extraction with hexane at 75 °C [28]. Only about 77% of the transesterifiable lipids could be recovered [28]. ...
... required a pretreatment of the biomass paste with acids and alkalis and a subsequent extraction with hexane at 75 °C [28]. Only about 77% of the transesterifiable lipids could be recovered [28]. The solvent demand was enormous at 60 mL per g (dry basis) of the biomass [28]. ...
A 1-step extraction process is reported for near quantitative (N 96%) extraction of the total lipids from the biomass paste (~72% moisture by weight) of the marine microalga Nannochloropsis salina. The composition of the solvent mixture of chloroform, methanol and water is first optimized for a near quantitative extraction of the lipids. The optimal solvent mixture is found to be chloroform, methanol and water in the volume ratio of 5.7:3:1. This solvent composition is then used in a 1-step extraction process to optimize the extraction time, temperature and the volume of the solvent mixture required for extraction from 1 g dry equivalent of the biomass paste. The optimal extraction conditions are found to be 25 °C in a 2-h extraction process using 33 mL of the solvent mixture. Compared to the commonly used Bligh and Dyer extraction protocol, the proposed 1-step extraction reduced the mixed solvent use by ~48% and the extraction time by ~78%.
... During WLEP [92], biomass dewatered by centrifugation (with moisture content as much as 85%) is first subject to acid hydrolysis with 1 M sulfuric acid at 90°C, base hydrolysis with 5 M sodium hydroxide at 90°C, and followed by a second centrifugation. Several subsequent precipitation/centrifugation stages follow, requiring a second acid treatment and a final extraction step using hexane [92,93]. WLEP is ideally applied with pre-treatment techniques to microalgal slurries, e.g. ...
... Drying biomass requires significant energy; utilizing WLEP to negate this results in overall energy gain rather than a negative energy balance [94]. The optimized WLEP defined by Sathish & Sims [93] and improved by Sathish et al. [94] allows biomass to be fractionated into three streams apart from the targeted lipid phase; residual hydrolyzed biomass, aqueous phase, and solid precipitate phase. By separating each fraction, this process allows them to be recycled, creating a zero-waste system, providing an economic advantage. ...
... Also known as in-situ transesterification, it involves simultaneous extraction of lipids from dewatered (not dried) biomass and reaction with excess methanol. Due to water content in wet biomass, an acid pre-treatment may be required, followed by base-catalyzed transesterification [93]. A comparative study showed that a reaction temperature of 90°C was ineffective for biodiesel production with water content > 20%, but could yield 100% conversion at a temperature of 150°C [114]. ...
The current COVID-19 pandemic is forcing radical change in the global energy economy. All energy sectors have experienced profound economic contraction in 2020, with the notable exception of renewable energy, which has grown by nearly 3%. These unprecedented circumstances offer a pristine opportunity to create new jobs, technologies, and infrastructure, aimed at engineering a climate-friendly and sustainable energy future. This review explores several pathways to renewable bioenergy by developing microalgal biorefinery systems which capitalize upon the unique abilities of microalgae to sequester carbon and produce biomass for bioenergy feedstock, without compromising food security or land use. This review further highlights the necessity of synergistically coupled upstream and downstream techniques to realize the economic viability of microalgal biorefinery systems, and details possible product pathways using either whole or fractionated biomass. The zero-waste circular biorefinery approach, when specifically tailored to local conditions, in terms of regional climate, economics, infrastructure, and available resources, is the answer to economically competitive microalgal bioenergy. The most promising emergent methods for microalgal biomass valorization to fungible bioenergy are reviewed herein.
... The Extraction of protein and lipid led to a 29-37% enhanced yield of methane. Sathish et al. [78] modified a lipid extraction procedure described by Ref. [53] from wet algal biomass mixture of Chlorella and Scenedesmus species and were able to extract 77% of transesterifible lipids. The procedure generated processed residual biomass having a high C/N ratio, an aqueous phase rich in nitrogen, phosphorus and carbon and a solid precipitated fraction highly rich in protein (70% by weight). ...
... The procedure generated processed residual biomass having a high C/N ratio, an aqueous phase rich in nitrogen, phosphorus and carbon and a solid precipitated fraction highly rich in protein (70% by weight). Besides, the procedure described by Sathish et al. [78] also generated nutrient-rich aqueous phase that can be used a growth supplement for microalgae, a highly proteinaceous solid precipitate and processed residual biomass from which other value-added products and biofuels can be obtained. EROI of 0.33 and global warming potential (GWP) of À 43.6g CO 2 -e MJ À 1 was reported, which reflects an energetically and environmentally appropriate biorefinery. ...
Numerous studies on the techno-economic and life cycle assessment of microalgal biodiesel production are available in the literature, and an overwhelming majority of such studies suggest that the standalone production of biodiesel is currently unviable. The production of microalgal biomass using the currently available technologies costs approximately $4.92 kg−1, which is unacceptably high for biodiesel production. The challenges lie in high biomass production cost and unfavorable energetic balance and significant process, and engineering advancements are desirable before mass-scale production of algal oil and biodiesel at a cost-competitive price is realized. On the other hand, various high-value products sourced from microalgae are already commercialized. The biomass production cost of $4.92 kg−1is more than acceptable if such products are also derived which, according to some estimates, may command a price as high as $123 kg−1 biomass. It is expected that with process modifications and engineering advancements, the biomass production cost can be brought down to as low as $0.50 kg−1. Moreover, coupling phycoremediation of pollution loads in waste streams to microalgal biomass production offers economic (up to $170 t−1 biomass produced) and environmental gains (90% reduction in water footprint, improved GHG balance, and a substantial reduction in external input of fertilizers). Such approaches are more likely to translate into an economically appealing and environmentally desirable business model. The current study is an attempt to analyze some of the recent research investigations addressing the concept of a microalgal biorefinery for the production of biodiesel.
... We have previously shown that lipid recovery from wet Tetraselmis sp. biomass lead to 68% of recoverable lipids (58% of transesterifiable lipids) from lyophilized biomass [10] and a recently optimized method obtained 77% of transesterifiable lipids from wet biomass [26]. In the present study, lipid extraction from different wet algal slurries was improved through applying pretreatments and a solvent mixture which was compared to extraction from wet biomass without pretreatment and using hexane only.) ...
... Although these values do not seem very high, improved lipid yields can be expected if lipid biosynthesis can be further induced during algae cultivation; e.g. by applying other stresses exogenously [27,28]. Pretreatment by UV-C and using a hexane:ethanol solvent mixture has led to 73% of transesterifiable lipids in the extracted lipids (Supplementary Figure 2) which is comparable to the 72% obtained by Sathish et al. [26]. Amongst the dominant fatty acids, palmitoleic acid (C16:1) allocated the highest amount with N40% of the total fatty acids. ...
Microalgae-based lipids are considered a good feedstock for various applications, including biodiesel and omega-3-rich oil production. However, developing new lipid extraction and recovery techniques are required to make microalgal oil a more economically competitive feedstock. To avoid the costly process of complete drying of algal biomass, extraction from wet slurry was improved. Potentially cost-effective and scalable processes were investigated and developed that enable total rupture of nutrient-starved microalgal cells to facilitate lipid recovery directly from wet algal slurry, including pretreatments (thermal treatment, UV-C light radiation and osmotic shock) and the use of a solvent mixture. Using hexane and ethanol on UV-C and thermally pre-treated algal slurries led to more than doubling of the total extractable lipids and total transesterifiable lipids, compared to biomass that was not pretreated and when hexane only was used as the solvent. Lipids (25% w/dry weight), triacylglycerol (13%) and fatty acid methyl esters (17%) were recovered from UV-C pre-treated algal slurry (1000 mJ/cm² UV-C). The residual defatted biomass was analysed for further applications and contained carbohydrates (≈ 15% w/dry weight) that may be suitable for bioethanol production through fermentation.
... WLEP allows for direct (or in situ) transesterification by simultaneous extraction of lipids from dewatered (up to 20% water content) biomass and reaction with excess methanol [102]. Apart from high-purity microalgal lipids, side streams of WLEP include lipid-extracted residual biomass with a favorable C/N ratio (54.6:1) for further biological upgrading, an aqueous phase containing valuable nitrogen, phosphorus, and carbon species, and a solid precipitate containing 70% proteins [103]. Each of these side streams can be utilized as products such as biofertilizer, or valorized as rich feedstocks for other upgrading pathways, such as anaerobic digestion. ...
Several key challenges are hindering large-scale cultivation of microalgae for industrial purposes, including wastewater treatment, carbon capture, biomass production, and renewable energy production. These challenges are closely related to efficacy of 1) resource utilization, 2) biomass production, and 3) harvesting. This review describes how attached or biofilm cultivation of microalgae and/or cyanobacteria with heterotrophic bacteria in consortia could simultaneously resolve these technical obstacles, thereby reducing monetary and energetic costs of producing microalgal bioenergy. Symbiotic relationships between these organisms reduces the need for aeration or exogenous supplementation of nutrients. Additionally, this review details how increasing biodiversity correlates with diversity of functionality (carbon capture and nitrification) and how attached/biofilm cultivation can improve photosynthetic efficiency and water footprint. Mixed-species biofilms have persisted for billions of years across earth’s natural history because they are some of nature’s most highly efficient biosystems, and they deserve more dedicated study and broader application in bioenergy production. This review details the practical connections between microalgal-bacterial consortia, attached/biofilm cultivation, waste-to-value biorefining, and relevance to bioenergy production and VAPs; four topics previously unconnected in a single review. As such this review aims to bridge current knowledge gaps across multiple research fields and industrial sectors, towards the goal of efficient, economical, and climate-forward microalgal bio-services and bioenergy production.
... Among various microalgae, attempts have been made to test the treatability of livestock wastewater using Chlorella sp.[9], Botoryococcus sp.[10], Scenedesmus sp.[11], Ankistrodesmus sp.[11], etc. The extracted oil contents from those microalgae are from a low of 14% up to 63%[12], and the lipids can be transesterified into fatty acid methyl ester (FAME), the main components of biodiesel[13]. Moreover, the non-lipid biomass fraction consisting of protein, which constitutes approximately 60% of microalgal dry weight (DW), can also be processed to methane via anaerobic digestion and is applicable to aquaculture or agriculture as feedstock. ...
... The fractionation of the algal biomass by step-wised acid and base hydrolysis, followed by solvent extraction and centrifugation. This process has the advantage of utilising more of the biomass but the complexity of the process may not be commercially viable [22]. ...
... Comparison of lipids extraction efficiency with different extraction methods. extraction following ultrasonication (Lee and Han, 2015) or double steps of acid-base hydrolysis (Sathish et al., 2015). The yield of major lipid fraction of the tested microalgae with different extraction methods were shown in Fig. 5. ...
High moisture content in wet algal biomass hinders effective performance of current lipid extraction methods. An improved aqueous extraction method combing thermal and enzymatic lysis was proposed and performed in algal slurry of Nannochloropsis oceanica (96.0% moisture) in this study. In general, cell-wall of N. oceanica was disrupted via thermal lysis and enzymatic lysis and lipid extraction was performed using aqueous surfactant solution. At the optimal conditions, high extraction efficiencies for both lipid (88.3%) and protein (62.4%) were obtained, which were significantly higher than those of traditional hexane extraction and other methods for wet algal biomass. Furthermore, an excessive extraction of polar lipid was found for wet biomass compared with dry biomass. The advantage of this method is to efficiently extract lipids from high moisture content algal biomass and avoid using organic solvent, indicating immense potential for commercial microalgae-based biofuel production.
... Most of the previous studies focused on the infl uence of C:N ratio on the total lipid content and fatty acid composition (Jiang et al., 2012;Sathish et al., 2015). ...
Mass microalgal culture plays an irreplaceable role in aquaculture, but microalgal productivity is restricted by traditional autotrophic culture conditions. In the present study, a Tetraselmis chuii strain belonging to the phylum Chlorophyta was isolated from south Yellow Sea. The growth rate and biomass productivity of this strain was higher under mixotrophic conditions with different carbon:nitrogen (C:N) ratios than those under autotrophic conditions. When the C:N ratio was 16, the optical density and biomass productivity were 3.7- and 5-fold higher than their corresponding values under autotrophic culture conditions, respectively. Moreover, T. chuii synthesized more polysaccharides and total lipids under mixotrophic conditions. In addition, T. chuii cultured under mixotrophic conditions synthesized more types of fatty acids than autotrophic culture conditions. At a C:N ratio of 16, the percentage of C16:0 and C18:1 reached 30.08% and 24.65% of the total fatty acid (TFA) content, respectively. These findings may provide a basis for largescale mixotrophic culture of T. chuii, as a potential bait-microalga.
... One possibility is to use switchable solvents which can be cycled between a polar and a nonpolar character simply by using CO 2 , eliminating the need for solvent recovery through distillation [87]. Equally promising is the recent demonstration of a wet lipid extraction procedure allowing relatively high (80%) recovery of lipids from wet algal biomass (84% moisture content) [88][89][90][91][92]. ...
With impending climate change and ever decreasing supplies of easily extractable fossil fuel, means to produce renewable and sustainable replacement fuels are being sought. Plants or algae appear ideal since they can use sunlight to fix CO2 into usable fuel or fuel feedstocks. However, as the world population approaches the 1010 (10 billion) mark, the use of agricultural land to produce fuel instead of food cannot be justified. Microalgal biofuel production is under intense investigation due to its promise as a sustainable, renewable biofuel that can be produced using non-arable land and brackish or non-potable water. Some species accumulate high levels of TAGs (triacylglycerols) that can be converted to fatty acid esters suitable as replacement diesel fuels. However, there are many technical barriers to the practical application of microalgae for biofuel production and thus a number of significant challenges need to be met before microalgal biodiesel production becomes a practical reality. These include developing cost-effective cultivation strategies, low energy requiring harvesting technologies, and energy efficient and sustainable lipid conversion technologies. The large culture volumes that will be necessary dictate that the necessary nutrients come from wastewaters, such as the effluents from secondary treatment of sewage. Economical and energy sparing harvesting will require the development of novel flocculation or floatation strategies and new methods of oil extraction/catalysis that avoid the extensive use of solvents. Recent advances in these critical areas are reviewed and some of the possible strategies for moving forward are outlined.
... To achieve sustainable production of bio-oil from microalgae, methods for recycling nutrients in microalgae need to be developed (Borowitzka and Moheimani, 2013;Clarens et al., 2010;Greenwell et al., 2010;Liew et al., 2014;Rosch et al., 2012). Extraction from microalgae to obtain lipids and valuable by-products have been reported (Chaudry et al., 2015;Sathish et al., 2015), in which chemicals have been isolated and fractionated. The defatted microalgae has been converted into (1) gas by anaerobic digestion (Borowitzka and Moheimani, 2013;Chisti, 2007;Davis et al., 2011) and catalytic hydrothermal gasification (Frank et al., 2012), and into (2) biocrude by hydrothermal liquefaction (Delrue et al., 2013;Zhu et al., 2013) and pyrolysis (Wang et al., 2015), however less attention has been paid to the recycle of nutrients. ...
Defatted heterotrophic microalgae (Aurantiochytrium limacinum SR21) was treated with high temperature water (175 to 350 °C, 10 to 90 min) to obtain nitrogen and phosphorous nutrients as a water soluble fraction (WS). Yields of nitrogen and phosphorous recovered in WS varied from 38 to 100% and from 57 to 99%, respectively. Maximum yields of nitrogen containing compounds in WS were proteins (43%), amino acids (12%) and ammonia (60%) at treatment temperatures of 175, 250 and 350 °C, respectively. Maximum yield of phosphorous in WS was 99% at a treatment temperature of 250 °C. Cultivation experiments of microalgae (A. limacinum SR21) using WS obtained at 200 and 250 °C showed positive growth. Water soluble fractions from hydrothermal treatment of defatted microalgae are effective nitrogen and phosphorous nutrient sources for microalgae cultivation.
... Among various microalgae, attempts have been made to test the treatability of livestock wastewater using Chlorella sp.[9], Botoryococcus sp.[10], Scenedesmus sp.[11], Ankistrodesmus sp.[11], etc. The extracted oil contents from those microalgae are from a low of 14% up to 63%[12], and the lipids can be transesterified into fatty acid methyl ester (FAME), the main components of biodiesel[13]. Moreover, the non-lipid biomass fraction consisting of protein, which constitutes approximately 60% of microalgal dry weight (DW), can also be processed to methane via anaerobic digestion and is applicable to aquaculture or agriculture as feedstock. ...
Photoautotrophic microalgae offer high promise for a tertiary treatment of livestock wastewater owing to their rapid growth and nutrient uptake. To screen better microalga for the tertiary treatment, batch photobioreactor tests were conducted using Chlorella emersonii, Chlorella sorokiniana, and Botryococcus braunii. This study evaluated their specific growth rates, CO2 utilization rates, and nutrient removal rates to provide appropriate selection guidelines. Based on statistical comparisons, results indicate that selecting the right microalgae was the key to success in the tertiary treatment since each microalga responded differently, even under the same light, temperature, and nutrient conditions. Among the tested species, Chlorella emersonii was found to present the fastest photoautotrophic growth, total inorganic carbon (TIC) utilization, and nutrient removal for livestock wastewater treatment. Regression results identified that its specific growth and total nitrogen removal rates were as high as 0.51 day⁻¹ and 0.18 day⁻¹, respectively. Estimated TIC utilization over the supplied TIC was much higher (~34%) than those of others (11%-18%). This systemic evaluation of rate-limiting factors provides a quantitative understanding of the kinetic-based selection strategy of microalgae to polish livestock wastewater with better effluent quality.
... To facilitate quantitative genetic and applied breeding efforts that target crop improvement via enhanced tolerance to environmental stressors mediated by the cuticle (e.g., water status regulation, frost resistance, plant-pest and -pathogen interactions, and protection from UV irradiation [1]), we require methods that simultaneously extract both hydrophobic and amphipathic extracellular surface lipids, and that can be efficiently applied to large-scale experiments. Recent optimization of lipid extraction methods for large numbers of samples has been a particular focus with microalgae [7][8][9][10][11], as related to the biological engineering of molecules that have biofuel applications. These methods are primarily directed at the medium-to highthroughput extraction of total cellular lipids, and are improvements on the lower-throughput, classical methods for extraction of homogenized animal tissues published by Folch [12] and Bligh and Dyer [13], which differed in the amounts of solvent and the relative ratios of the chloroform-methanol extraction solution. ...
Aerial plant organs possess a diverse array of extracellular surface lipids, including both non-polar and amphipathic constituents that collectively provide a primary line of defense against environmental stressors. Extracellular surface lipids on the stigmatic silks of maize are composed primarily of saturated and unsaturated linear hydrocarbons, as well as fatty acids, and aldehydes. To efficiently extract lipids of differing polarities from maize silks, five solvent systems (hexanes; hexanes:diethyl ether (95:5); hexanes:diethyl ether (90:10); chloroform:hexanes (1:1) and chloroform) were tested by immersing fresh silks in solvent for different extraction times. Surface lipid recovery and the relative composition of individual constituents were impacted to varying degrees depending on solvent choice and duration of extraction. Analyses were performed using both silks and leaves to demonstrate the utility of the solvent- and time-optimized protocol in comparison to extraction with the commonly used chloroform solvent. Overall, the preferred solvent system was identified as hexanes:diethyl ether (90:10), based on its effectiveness in extracting surface hydrocarbons and fatty acids as well as its reduced propensity to extract presumed internal fatty acids. Metabolite profiling of wildtype and glossy1 seedlings, which are impaired in surface lipid biosynthesis, demonstrated the ability of the preferred solvent to extract extracellular surface lipids rich in amphipathic compounds (aldehydes and alcohols). In addition to the expected deficiencies in dotriacontanal and dotriacontan-1-ol for gl1 seedlings, an unexpected increase in fatty acid recovery was observed in gl1 seedlings extracted in chloroform, suggesting that chloroform extracts lipids from internal tissues of gl1 seedlings. This highlights the importance of extraction method when evaluating mutants that have altered cuticular lipid compositions. Finally, metabolite profiling of silks from maize inbreds B73 and Mo17, exposed to different environments and harvested at different ages, revealed differences in hydrocarbon and fatty acid composition, demonstrating the dynamic nature of surface lipid accumulation on silks.
... Although using wet algal biomass as the substrate for lipid extraction can reduce energy, this method needs to be further verified since water content of microalgal biomass might significantly affect the efficiency of lipid extraction [104]. Using organic solvents, Sathish et al. [105] optimized a wet microalgal lipid extraction process, and achieved the transesterifiable lipids of 77%. Reddy et al. [106] applied subcritical water to extract lipids from wet algae, obtained the reduction of energy required for the extraction by 2-8 folds. ...
In response to the energy crisis, global warming and climate changes, microalgae have received increasingly global attention as a renewable, alternative and sustainable source for the production of biodiesel. Much original research regarding microalgal biodiesel production has been reported. However, microalgal biodiesel faces plenty of challenges that current cultivation and biodiesel conversion is economically unfeasible for industrial applications on a large scale. This perspective paper first briefly discusses the latest advances in liquid transportation biodiesel production from microalgal biomass, including microalgal growth, biomass harvesting and drying, lipid extraction and biodiesel conversion. Subsequently, strategies for the future development of microalgal biodiesel have been proposed and discussed, in an attempt to reduce the cost gap. From the microalgal biodiesel production chain perspective, genetic and metabolic engineering, isolation of suitable species, high-efficiency bioreactor development, efficient culturing system development, optimal harvest process design, high-efficiency lipid extraction and transesterification method development will have critical roles to play. It is worthy of note that the increase of the outcome credits can also realize the reduction of the economic gap, and the main measures include appropriate glycerol recovery and reutilization, integration with wastewater treatment and CO2 mitigation together with microalgal biorefinery for the production of multiple co-products with high values. Finally, concluding remarks are put forward.
... Direct transesterification (i.e., in situ transesterification) without lipid extraction pretreatment step has an advantage of simultaneous lipid extraction and conversion of lipid into BD. The simpler unit operations have economically feasibility when the same reaction efficiency can be achieved [224]. In this regard, in situ transesterification of lipid in Chlorella vulgaris without lipid extraction was also performed [223]. ...
High lipid content and excellent CO 2 fixation capability of microalgae by photosynthesis have made microalgal biodiesel (BD) a promising carbon-neutral fuel. Nonetheless, the commercialization of BD has not yet been realized because of expensive and energy-intensive cultivation, pretreatment, and BD conversion processes in reference to 1 st generation BD production. To resolve the issues, this study comprehensively reviewed the current technical developments of microalgal BD production process and suggested promising future studies. Current microalgal BD production processes highly rely on the processes developed from 1 st generation BD process, namely base-catalyzed transesterifications. However, the base-catalyzed suffers from saponification reaction and low production yield due to high water and free fatty acid contents in microalgae. Vigorous pretreatments such as dewatering, drying, esterification of free fatty acid, and purification are required for high yield of microalgal BD production, making this process economically not attractive. As efforts to construct new transesterification platform, novel approaches tolerant to impurities such as thermally induced non-catalytic transesterifications were suggested. The thermally induced reactions allowed in situ conversion of microalgal lipid into BD (≥ 95 wt. % yield) within 1 min of reaction at ≥ 350 C. This process resists to presence of water and free fatty acids and does not require lipid extraction process. To make this process more promising, it was suggested lowering reaction temperature for thermally induced transesterifications. In addition, pilot study, in-depth life cycle assessment, and economic analysis were suggested to assess economic viability and environmental impacts.
... Recently, Chatsungnoen and Chisti [182] have analyzed the effectiveness of solvent mediated oil extraction from dry and wet biomass of six different microalgae from fresh-and marine water, and found that the oils could be extracted equally effectively from both freezedried and the paste samples. The Bligh and Dyer [183] method is one of the most common methods of solvent extraction of total lipids from algal biomass [184][185][186], where a mixture of different solvents of different polarities is used during the extraction process. In order to improve the basic Bligh and Dyer method, many modifications have been adopted [184]. ...
Energy is the utmost requirement for driving the organization and maintenance of entire ecosystem. Our continued dependency on fossil fuels such as coal, petroleum and natural gas as the prime source of energy has led to serious concerns about the future energy supply and security. Furthermore, over-consumption of carbon-based fossil energy sources raises serious environmental issues of global warming and climate change. To overcome the global energy demand and to enable economic as well as ecological development in a sustainable manner, technological progress for the utilization of renewable natural energy are essential to protect the environment and save energy in today's increasingly competitive world. To this end, algal biofuels are being claimed as an apt alternative energy source and in recent past, several taxonomic groups of algae have been studied and reported as an alternative to fossil fuels. It is envisaged that algal biomass could be readily processed into the raw material to make cost-effective biofuels and is being explored as an emergent and renewable green energy crops for the production of biofuels, especially biodiesel. Development of astonishing technological innovations in the field of algal genetic engineering has triggered remarkable output across the global energy sector for better biofuels. Several new techniques are being adopted for large-scale farming of microalgae intended for biofuel production. However, there are certain constraints for commercial-scale energy production from algae. The present review discusses the technological development and current information on the cultivation and process of biodiesel production form algae. Also, discussed are the technological development and genomic insights into the algal biomass and triacylglycerol accumulation for enhanced biodiesel production.
... The second route is wet lipid extraction. In the wet lipid extraction, transesterifiable lipids are first extracted from wet microalgae (moisture content: [ 80 wt.%) through acid-or base-catalyzed hydrolysis with the removal of chlorophyll (Sathish et al. 2015;Sathish and Sims 2012). The lipids are further transformed into fatty acid methyl esters (i.e., biodiesel) via transesterification (Jung et al. 2018). ...
Plastic waste generation has been increasing considerably, which bring about several environmental problems such as microplastics. In addition to the plastic pollution, the reduction in the use of petrochemical plastics is a key aspect to enhance sustainability. To alleviate the problems, the development of an innovative solution is rightly expected. Bioplastics are an alternative for conventional petrochemical plastics, recently gaining in a lot of attention. Microalgae can be an attractive source for the production of bioplastics given that they have a very distinctive growth yield in comparison to typical lignocellulosic biomass. Therefore, the employment of microalgae to produce bioplastics affords a golden opportunity to enhance sustainability of plastic usage. Given recent scientific research achievements in bioplastic production from microalgae, a review of the achievements is required. In this regard, this study was aimed at providing a review on the production of bioplastics using microalgae, which laid great emphasis on determining the current state of microalgal bioplastic production technologies and offering potential processes and applications. The prospect of bioplastic production based on microalgae is also discussed, and important points and challenges facing further research into the microalgal bioplastics are highlighted.
... India has 434 species of red algae, 194 species of brown algae and 216 species of green algae. More than 60 species were commercially used in India for agar, carrageenan, algin production and pharmaceutical use, particularly in agricultural applications for crop development [15,16]. One of the greatest contemporary sustainable biological plant growth promoters is seaweed extract biostimulants. ...
Seaweeds are an important component of the marine ecosystem and that can operate as an organic biostimulant for terrestrial plants. The biochemical ingredients of seaweed liquid organic biostimulant (SLB) produced plant have been improved, and their demand has recently increased due to multiple by-products. The present study deals with the effect of seaweed liquid organic biostimulant derived from Turbinaria ornata, Sargassum wightii and Halimeda opuntia at different doses like 10, 20, 30, 40, 50 and 100% on the growth and biochemical profile changes of common edible grain Vigna radiata. According to the findings, 20% of SLB from H. opuntia show the highest growth, proximate compositions, mineral contents, fatty and amino acid contents in V. radiata. The seed germination was obtained maximum in 20% SLB soaked seeds of V. radiata. The fatty acid contents were observed high in H. opuntia fertiliser fed V. radiata; palmitic acid (281.2 ± 0.04 mg/100 g) was found to be maximum in all treatment grown V. radiata. Saponins and terpenoids were highly present in T. ornata and S. wightii grown VR plant. The highest plant length (31.3 cm) was observed in T. ornata and lowest (17.1 cm) in S. wightii grown plants. Chlorophyll-a and b concentration was increased significantly (p < 0.01; p < 0.03) in T. ornata extract. The carotenoid content was increased significantly in S. wightii extract and decreased (p < 0.04) in chemical fertiliser grown plant V. radiata. The highest antioxidant activity (6.80 ± 0.01 mg/l) was observed in HO fed VR and the lowest (4.317 ± 0.03 mg/l) was recorded in TO fed VR. This technique can be used in organic farming for sustainable agriculture, which is a better alternative as an environmentally friendly approach. The current study revealed that SLB had certain environmental advantages over chemical fertilisers. Seaweed liquid organic biostimulant, if used on a wider scale, might have a substantial positive environmental influence on agricultural production. Seaweed extract with superior benefits at lower concentrations should be used at very high dilution rates in the agricultural field to increase seed germination rates while without impacting the native beneficial microorganisms present in the soil.
Algal Green Chemistry: Recent Progress in Biotechnology presents emerging information on green algal technology for the production of diverse chemicals, metabolites, and other products of commercial value. This book describes and emphasizes the emerging information on green algal technology, with a special emphasis on the production of diverse chemicals, metabolites, and products from algae and cyanobacteria.
Topics featured in the book are exceedingly valuable for researchers and scientists in the field of algal green chemistry, with many not covered in current academic studies. It is a unique source of information for scientists, researchers, and biotechnologists who are looking for the development of new technologies in bioremediation, eco-friendly and alternative biofuels, biofertilizers, biogenic biocides, bioplastics, cosmeceuticals, sunscreens, antibiotics, anti-aging, and an array of other biotechnologically important chemicals for human life and their contiguous environment. This book is a great asset for students, researchers, and biotechnologists.
Microalgas apresentam alta variedade biológica e podem ser aplicados em vários setores. A separação destes microrganismos é um desafio, uma vez que apresentam baixas densidades e são encontradas em suspensão no meio de cultura. Para otimizar o processo de secagem da biomassa das microalgas, o objetivo deste trabalho foi otimizar o uso do spray dryer em relação a secagem por estufa e por liofilização, bem como reconhecer o rendimento de biomassa, o teor lipídico, a composição dos ácidos graxos e a composição elementar (CHNS) para cada método testado. A secagem de biomassa de Chlorella vulgaris por spray dryer provou ser uma técnica alternativa mais rápida e eficiente para ser empregada em escala laboratorial.
This study evaluated osmotic shock pre-treatment, a solvent-free wet lipid extraction method, on two lipid-rich microalgal species, Dunaliella salina and Chaetoceros muelleri. The biogas potential of the lipid-spent microalgae was evaluated to assess the suitability of an integrated biorefinery of biodiesel and biogas production. The obtained results revealed the high potential of the diatom C. muelleri for biofuels production when silica starvation is applied at the final stages of the cultures. The osmotic shock had a higher impact on C. muelleri than on D. salina, with a lipid recovery efficiency of 72% and 21% respectively. Besides the high percentage of lipids recovered with this method for C. muelleri, the lipid-spent biomass showed ones of the highest methane yields reported for microalgae, 484 mL CH4 g VS⁻¹. Overall, these results indicate that C. muelleri could be a target species for combined biodiesel and biogas biorefinery.
The amount of water removed from harvested algae and the required quantity of solvent for efficient oil recovery impact the overall economic viability of transforming algae to bioenergy. Thus, in this study, the effect of total solids (TS) content and solvent-to-biomass ratio on oil recovery from Nannochloropsis oculata and Nannochloropsis salina (both referred to in this work as Nannocloropsis spp. and representative of marine species of algae) and Scenedesmus obliquus (a freshwater specie) was studied using modified Bligh & Dyer (B-D) method and Soxhlet extraction (with either hexane or ethanol as solvent). Adopting the modified B-D method, a maximum oil content exists between 10 and 20wt% TS. Oil recovered with ethanol (with no pretreatment) and hexane (on acid-hydrolyzed algae) with thimble increases with both TS (varied from 10 to 20wt%) and solvent-to-biomass ratio (varied from 10 to 25). Conversely, oil yield increases with solvent-to-biomass ratio but reduces with TS due to enhanced mixing and mass transfer, increase in partition coefficient of lipids during downstream separation at lower TS, and implementation of hexane extraction without thimble. Hexane extraction was subsequently performed on acid hydrolyzed algae in a scale-up model and a 98% performance was achieved while about 60% of algal oil at the optimum data point was transformed to biodiesel with no significant impact by the solvent-to-biomass ratio or scale-up. Ethanol recovers mostly polar lipids and potentially forms an azeotrope with water which makes green diesel production less favorable and solvent recoverability challenging, respectively while the use of a large quantity of chloroform is unsafe. Thus, ethanol extraction and modified Bligh-Dyer methods were not performed in the scale-up model. Results from the application of our techno-economic analysis (TEA) model indicate that predicted sale price of Hydrotreated Algal Oil (HTAO) at each of the oil extraction data points decreases with increase in the oil content of algae, using a base case of 10000 barrel per day of HTAO with credits from animal feed and nutraceutical production. At the optimum data point, the predicted sale price of HTAO is $8.59 per gallon.
The use of chemical fertilizers in agriculture poses problems for the health of the soil and the environment. Biofertilizers and microalgal biostimulants emerge as an alternative to reduce these damages. This study aimed to understand how microalgae are inserted in the process of developing biofertilizers/biostimulants. A search for research articles was carried out in the Scopus and Web of Science databases and resulted in 87 relevant studies. By analyzing these articles, it was possible to structure this review to understand how microalgal biofertilizers and biostimulants act on plants. The purpose of microalgal biofertilizer is to add nutrients to the soil. The use of wastewater for microalgal growth makes the process less costly and is a treatment alternative. Culture media with higher levels of nitrogen, and microalgae that remove higher levels of nitrate result in biomass with higher levels of protein. Microalgal biostimulants are associated with compounds that can encourage plant growth. These compounds can promote enzymatic and antifungal activity, act similarly to phytohormones, and participate in the synthesis of proteins and amino acids in plants. Microalgal biofertilizers/biostimulants can be part of integrated biorefinery concepts. The integration of the production of these products with the development of biofuels increases the economic viability of these bioproducts. Even though there is a lot of talk about the use of biorefineries, there are few studies on the effective application of this concept with the use of microalgal biomass. An in-depth analysis of the mechanism of action of microalgae in the development of bioproducts for agriculture can make the process more economically advantageous and sustainable.
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Renewable ethanol and isopropanol were employed for lipid transesterification in wet microalgae cells to produce biodiesel with low crystallization temperature and reduce the alcohol volume needed for biodiesel production. Decreased droplet size and lipid polarity were observed after transesterification with alcohol in microalgae cells. Such decrease was beneficial in extracting lipid from microalgae with apolar hexane. The effects of reaction temperature, reaction time, and alcohol volume on microwave-assisted transesterification with ethanol and isopropanol were investigated, and results were compared with those with methanol. Microwave-assisted transesterification with ethanol and isopropanol, which were more miscible with lipid in cells, resulted in higher fatty acid alkyl ester (FAAE) yields than that with methanol when the reaction temperature was lower than 90 °C. The ethanol and isopropanol volumes in the transesterification with 95% FAAE yield were only 75% of the methanol volume. The crystallization temperatures (0.19 °C and -3.15 °C) of biodiesels produced from wet microalgae through lipid transesterification in cells with ethanol and isopropanol were lower than that with methanol (2.08 °C), which was favorable for biodiesel flow in cold districts and winter.
In addition to biodiesel production from algae, the production of other valuable bioproducts facilitates the development of an algae-based biorefinery platform. The goal of this study was to utilize the aqueous fraction from a novel algal wet lipid extraction procedure as the medium for the production of a bio product, poly(3-hydroxybutyrate) (PHB), via the growth of recombinant Escherichia coli. PHB yield was measured at 34 % of the E. coli dry cell mass, and was increased to 51 % when the algae aqueous medium was supplemented with glucose. While the addition of inorganic nutrients to the aqueous phase did not increase PHB production or growth of E. coli, growth of E. coli was observed to increase with the supplementation of carbon substrate (glucose). The addition of carbon rich waste to the aqueous fraction of wastewater-derived algae may in the future provide a sustainable alternative. Future research will be directed at evaluating this concept to develop a sustainable process for the production of bioplastics through an algae-based biorefinery platform.
The rise in global population has led to explorations of alternative sources of energy and food. Because corn and soybean are staple food crops for humans, their common use as the main source of dietary energy and protein for food-producing animals directly competes with their allocation for human consumption. Alternatively, de-fatted marine microalgal biomass generated from the potential biofuel production may be a viable replacement of corn and soybean meal due to their high levels of protein, relatively well-balanced amino acid profiles, and rich contents of minerals and vitamins, along with unique bioactive compounds. Although the full-fatted (intact) microalgae represent the main source of omega-3 (n-3) polyunsaturated fatty acids including docohexaenoic acid (DHA) and eicosapentaenoic acid (EPA), the de-fatted microalgal biomass may still contain good amounts of these components for enriching DHA/EPA in eggs, meats, and milk. This review is written to highlight the necessity and potential of using the de-fatted microalgal biomass as a new generation of animal feed in helping address the global energy, food, and environmental issues. Nutritional feasibility and limitation of the biomass as the new feed ingredient for simple-stomached species are elaborated. Potential applications of the biomass for generating value-added animal products are also explored.
Two major considerations of the emerging algae biofuel industry are the energy intensive dewatering of the algae slurry and nutrient management. The proposed closed loop process which involves nutrient recycling of the aqueous phase from the hydrothermal liquefaction of microalgae offers a solution to both aspects. Hydrothermal liquefaction has been shown to be a low energy process for bio-crude production from microalgae. For the purpose of this research, microalgae strains of Chlorella vulgaris, Scenedesmus dimorphus and the cyanobacteria Spirulina platensis and Chlorogloeopsis fritschii were processed in batch reactors at 300 °C and 350 °C. Following liquefaction the product phases were separated and the water phase recovered. The bio-crude yields ranged from 27 to 47 wt.%. The bio-crudes were of low O and N content and high heating value making them suitable for further processing. The water phase was analysed for all major nutrients, TOC and TN to determine the suitability of the recycled aqueous phase for algae cultivation. Growth trials were performed for each algae strain in a standard growth medium and compared to the growth rates in a series of dilutions of the recycled process water phase. Growth was determined by cell count and chlorophyll a absorbance. Growth occurred in heavy dilutions where the amount of growth inhibitors was not too high. The results show that the closed loop system using the recovered aqueous phase offers a promising route for sustainable oil production and nutrient management for microalgae.
The rapid increase of CO(2) concentration in the atmosphere combined with depleted supplies of fossil fuels has led to an increased commercial interest in renewable fuels. Due to their high biomass productivity, rapid lipid accumulation, and ability to survive in saline water, microalgae have been identified as promising feedstocks for industrial-scale production of carbon-neutral biodiesel. This study examines the principles involved in lipid extraction from microalgal cells, a crucial downstream processing step in the production of microalgal biodiesel. We analyze the different technological options currently available for laboratory-scale microalgal lipid extraction, with a primary focus on the prospect of organic solvent and supercritical fluid extraction. The study also provides an assessment of recent breakthroughs in this rapidly developing field and reports on the suitability of microalgal lipid compositions for biodiesel conversion.
The Logan City Environmental Department operates a facility that consists of 460 acres of fairly shallow lagoons (~ 5'deep) for biological wastewater treatment that meets targets for primary and secondary treatments (solids, biological oxygen demand (BOD), and pathogen removal). Significant natural algal growth occurs in these lagoons, which improves BOD removal through oxygenation and also facilitates N removal through volatilization as ammonia under high pH conditions created by algal growth. Phosphorus, however, is non-volatile and stays in the water and likely cycles in and out of algal cells as they grow and die in the lagoons. In the near future, the regulatory limits on phosphorus released from the Logan wastewater treatment facility are likely to become significantly lower to counter potential downstream eutrophication. One way to potentially lower phosphorus levels in the wastewater effluent is through management of algal growth in the lagoons. As mentioned above, algae growth naturally occurs in the treatment lagoons and if the algal biomass is harvested when growth yields are highest, the phosphorus contained in the cells could be removed to obtain phosphorus-free water. The algal biomass could then be used for production of biofuels. This research focuses on laboratory and pilot assessments to show the ability of algae indigenous to the Logan lagoons to uptake phosphorus and produce biomass that can be used for biofuel production.
Hydrothermal liquefaction (HTL) has recently received increasing attention due to its advantages in rapid reaction, using wet feedstocks with no lipid-content restriction. These characteristics make HTL especially suitable for conversion of algae into biocrude oil. This paper aims to provide a state-of-the-art review of HTL technologies from a perspective of algal biorefinery. In this review, we first summarize the updated researches and technologies of algae HTL. Specially, an "Environmental-Enhancing Energy" (E2E) paradigm based on algal biorefinery has been proposed and discussed. Second, the principles and crucial factors for algae HTL are discussed with focus on (1) algae species and characteristics including lipids, proteins and carbohydrates; (2) the operational parameters including total solids, holding temperature, retention time and catalysts; and (3) the critical principles of HTL reaction and the role of deoxygenation and denitrogenation. In addition, potential applications of HTL are discussed. Prospective and challenges of HTL for algal biorefinery are finally addressed including feedstock preparation, scale-up of algae HTL, and process integration.
The feasibility of microalgae production for biodiesel was discussed. Although algae are not yet produced at large scale for bulk applications, there are opportunities to develop this process in a sustainable way. It remains unlikely, however, that the process will be developed for biodiesel as the only end product from microalgae. In order to develop a more sustainable and economically feasible process, all biomass components (e.g. proteins, lipids, carbohydrates) should be used and therefore biorefining of microalgae is very important for the selective separation and use of the functional biomass components. If biorefining of microalgae is applied, lipids should be fractionated into lipids for biodiesel, lipids as a feedstock for the chemical industry and ω-3 fatty acids, proteins and carbohydrates for food, feed and bulk chemicals, and the oxygen produced should be recovered also. If, in addition, production of algae is done on residual nutrient feedstocks and CO2, and production of microalgae is done on a large scale against low production costs, production of bulk chemicals and fuels from microalgae will become economically feasible.In order to obtain that, a number of bottlenecks need to be removed and a multidisciplinary approach in which systems biology, metabolic modeling, strain development, photobioreactor design and operation, scale-up, biorefining, integrated production chain, and the whole system design (including logistics) should be addressed. Copyright © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd
The pyrolysis of Scenedesmus sp. and Jatropha seedshell cake (JSC) was investigated under similar operating condition in a fluidized bed reactor for comparison of pyrolytic behaviors from different species of lipids-containing biomass. Microalgae showed a narrower main peak in differential thermogravimetric curve compared to JSC due to different constituents. Pyrolysis liquid yields were similar; liquid's oil proportion of microalgae is higher than JSC. Microalgae bio-oil was characterized by similar carbon and hydrogen contents and higher H/C and O/C molar ratios compared to JSC due to compositional difference. The pyrolytic oils from microalgae and JSC contained more oxygen and nitrogen and less sulfur than petroleum and palm oils. The pyrolytic oils showed high yields of fatty oxygenates and nitrogenous compounds. The microalgae bio-oil features in high concentrations of aliphatic compounds, fatty acid alkyl ester, alcohols and nitriles. Microalgae showed potentials for alternative feedstock for green diesel, and commodity and valuable chemicals.
The pyrolysis of Scenedesmus sp. and Jatropha seedshell cake (JSC) was investigated under similar operating condition in a fluidized bed reactor for comparison of pyrolytic behaviors from different species of lipids-containing biomass. Microalgae showed a narrower main peak in differential thermogravimetric curve compared to JSC due to different constituents. Pyrolysis liquid yields were similar; liquid’s oil proportion of microalgae is higher than JSC. Microalgae bio-oil was characterized by similar carbon and hydrogen contents and higher H/C and O/C molar ratios compared to JSC due to compositional difference. The pyrolytic oils from microalgae and JSC contained more oxygen and nitrogen and less sulfur than petroleum and palm oils. The pyrolytic oils showed high yields of fatty oxygenates and nitrogenous compounds. The microalgae bio-oil features in high concentrations of aliphatic compounds, fatty acid alkyl ester, alcohols and nitriles. Microalgae showed potentials for alternative feedstock for green diesel, and commodity and valuable chemicals.
This study assessed the intake, total and partial apparent digestibility of nutrients, pH, ruminal ammonia concentration, nitrogen efficiency usage, and productive performance of beef cattle fed with different soybean meal replacement levels with inactive dry yeast (IDY 0, 250, 500, 750, and 1000 g/kg). The forage:concentrate ratio was 60:40 and the forage source was corn silage. Concentrates were formulated to comprise 220.0 g/kg CP independent of treatments. In the first experiment (EXP 1), 35 Nelore bulls with an initial average weight of 370 ± 42 kg were distributed across a completely randomized design, with five treatments and seven replicates to assess nutrient intake and performance. EXP 1 lasted 98 days and was divided into a 14-day adaptation period and three experimental periods of 28 days each. In the second experiment (EXP 2), five castrated Nelore steers with an initial average weight of 320 ± 39 kg were fistulated in the rumen and abomasum and distributed in a 5 × 5 Latin square design, balanced for residual effect. The purpose of this experiment was to assess the total and partial digestibility of nutrients, pH, ruminal ammonia nitrogen, and nitrogen efficiency of usage. EXP 2 lasted 90 days, divided into five experimental periods. Each period lasted 18 days and was divided into 10 days for adaptation to the diets and 8 days to collect samples. The intake of dry matter (DMI) decreased linearly (P = 0.03) with increased dietary IDY levels. Conversely, the intake of neutral detergent fiber assayed with a heat-stable amylase and corrected for ash and nitrogenous compounds [aNDFom(n)] in g/day (P = 0.043), and the g/kg body weight (P = 0.011) increased linearly as IDY was added to the concentrate. The experimental diets showed no effect (P > 0.05) on the total and partial apparent nutrient digestibility. IDY had no effect (P > 0.05) on ruminal pH, ruminal ammonia nitrogen, or dietary nitrogen efficiency. Additionally, IDY had no effect on productive performance variables, with the exception of average daily gain (ADG), which decreased linearly (P = 0.028) as IDY was added to the concentrate. IDY addition resulted in decreases in DMI and ADG for beef cattle in feedlots (EXP 2). However, the apparent digestibility of nutrients and microbial efficiency were not affected. In addition, IDY did not reduce feed conversion or carcass gain. The high market price of soybean meal might make feasible its total replacement by IDY, even considering the possibility of a small reduction in ADG.
Two experiments were conducted to determine the influence of lipid extracted algae (LEA) on OM digestibility, N flow, and rumen fermentation. Six samples of LEA were evaluated representing two species of microalgae (Nannochloropsis sp. (n = 3) or Chlorella sp. (n =3). Four dual-flow continuous flow fermenters (2,700 mL) were used in a Latin square design to evaluate LEA in forage or concentrate diets compared with soybean meal (SBM). Temperature (39°C), pH, solid (5%/h) and liquid (10%/h) dilution rates, and feed schedule were maintained constant. Each experimental period consisted of 6-d adaptation and 4-d sampling periods. There were 7 treatments consisting of 6 different samples of LEA and a soybean meal control (SOY). Diets for Exp.1 were formulated to be 13.0% CP (DM basis) using either SBM or LEA and met or exceeded the requirements of a nonpregnant and nonlactating beef cow (450 kg). The forage portion consisted of sorghum-sudan hay (6.4% CP and 46.2% TD; DM basis) and alfalfa (26.1% CP and 82.3% TDN; DM basis). Concentrate diets used in Exp. 2 met or exceeded the nutrient requirements of a (400 kg) growing steer and contained 85% fine ground corn and included 7% (DM basis) SBM or LEA. Data were analyzed as mixed effects model considering the effect of each LEA compared with SBM. Orthogonal contrasts were used to determine the overall effect of LEA genus vs. SOY. True OM digestibility were not influenced by LEA addition to forage diets (P > 0.08) but increased with Chlorella LEA addition to concentrate diets (P < 0.01) but not Nannochloropsis LEA. Degradation of N was greater for SOY with forage diets and LEA for concentrate diets (P < 0.0001). Total VFA production was greatest for SOY in forage diets and increased when LEA was added to concentrate diets (P < 0.0001). Microbial efficiency (MOEFF) did not differ between SOY and LEA in forage diets (P ≤ 0.08). In concentrate diets Nannochloropsis decreased MOEFF (P < 0.01). Microbial efficiency results for Chlorella were more variable for Nannochloropsis with one Chlorella sp. increasing MOEFF by 36% over SOY (P < 0.05) and the other Chlorella sp. decreasing MOEEF by approximately 42% compared with SOY (P < 0.01). Overall the results from both experiments are promising for LEA as a protein feedstuff in ruminant diets. Further research is necessary to fully understand the interactions and consequences of upstream processes and what role algal strain plays in LEA quality.
The potential of microalgae as a source of sustainable energy, nutritional supplements and specialized chemicals necessitates a thorough evaluation of the methods of harvesting microalgae with regards to the bioproduct(s) desired. This research assessed the effect of coagulation, flocculation, and centrifugation on the wet lipid extraction procedure, which fractionated microalgae into hydrolyzed biomass for fermentation into acetone, butanol, and ethanol, an aqueous phase as growth media for genetically engineered Escherichia coli, and a lipid fraction for the production of biodiesel. Biomass harvested by cationic starches, alum, and centrifugation produced 30, 19, and 22.5mg/g of dry wt. algae of total combined acetone, butanol, and ethanol, respectively. Higher biodiesel production was also observed for the cationic starches (9.6mg/g of dry wt. algae) than alum (0.6mg/g of dry wt. algae) harvested biomass. The results suggested significant effect of the harvesting methods on the yields of bioproducts.
Biogas produced from anaerobic digestion is a versatile and environment friendly fuel which traditionally utilizes cattle dung as the substrate. In the recent years, owing to its high content of biodegradable compounds, algal biomass has emerged as a potential feedstock for biogas production. Moreover, the ability of algae to treat wastewater and fix CO2 from waste gas streams makes it an environmental friendly and economically feasible feedstock. The present review focuses on the possibility of utilizing wastewater as the nutrient and waste gases as the CO2 source for algal biomass production and subsequent biogas generation. Studies describing the various harvesting methods of algal biomass as well as its anaerobic digestion have been compiled and discussed. Studies targeting the most recent advancements on biogas enrichment by algae have been discussed. Apart from highlighting the various advantages of utilizing algal biomass for biogas production, limitations of the process such as cell wall resistivity towards digestion and inhibitions caused due to ammonia toxicity and the possible strategies for overcoming the same have been reviewed. The studies compiled in the present review indicate that if the challenges posed in translating the lab scale studies on phycoremediation and biogas production to pilot scale are overcome, algal biogas could become the sustainable and economically feasible source of renewable energy.
Hydrothermal liquefaction of algae biomass is a promising technology for the production of sustainable biofuels, but the non-oil, aqueous co-product of the process has only been examined to a limited extent. The aqueous phase from liquefaction of the alga Nannochloropsis oculata (AqAl) was used to make growth media for model heterotrophic microorganisms Escherichia coli, Pseudomonas putida, and Saccharomyces cerevisiae. Growth rates, yields, and carbon/nitrogen/phosphorus uptake were measured. E. coli and P. putida could grow using AqAl as the sole C, N, and P source in media containing 10vol.%-40vol.% AqAl with the best growth occurring at 20vol.%. S. cerevisiae could grow under these conditions only if the media were supplemented with glucose. The results indicate that in a biorefinery utilizing algae liquefaction, the aqueous co-product may be recycled via microbial cultures with significantly less dilution than previously published methods.
To better understand the pyrolysis of microalgae, the different roles of three major components (carbohydrates, proteins, and lipids) were investigated on a pyroprobe. Cellulose, egg whites, and canola oil were employed as the model compounds of the three components, respectively. Non-catalytic pyrolysis was used to identify and quantify some major products and several reaction pathways were proposed for the pyrolysis of each model compound. Catalytic pyrolysis was then carried out with HZSM-5 for the production of aromatic hydrocarbons at different temperatures and catalyst to feed ratios. The aromatic yields of all feedstocks were significantly improved when the catalyst to biomass ratio increased from 1:1 to 5:1. Egg whites had the lowest aromatic yield among the model compounds under all reaction conditions, which suggests that proteins can hardly be converted to aromatics with HZSM-5. Lipids, although only accounted for 12.33% of Chlorella, contributed about 40% of aromatic production from algal biomass.
Life-cycle assessment has been used to investigate the global warming potential (GWP) and fossil-energy requirement of a hypothetical operation in which biodiesel is produced from the freshwater alga Chlorella vulgaris, grown using flue gas from a gas-fired power station as the carbon source. Cultivation using a two-stage method was considered, whereby the cells were initially grown to a high concentration of biomass under nitrogen-sufficient conditions, before the supply of nitrogen was discontinued, whereupon the cells accumulated triacylglycerides. Cultivation in typical raceways and air-lift tubular bioreactors was investigated, as well as different methods of downstream processing. Results from this analysis showed that, if the future target for the productivity of lipids from microalgae, such as C. vulgaris, of 40 tons ha−1 year−1 could be achieved, cultivation in typical raceways would be significantly more environmentally sustainable than in closed air-lift tubular bioreactors. While biodiesel produced from microalgae cultivated in raceway ponds would have a GWP 80% lower than fossil-derived diesel (on the basis of the net energy content), if air-lift tubular bioreactors were used, the GWP of the biodiesel would be significantly greater than the energetically equivalent amount of fossil-derived diesel. The GWP and fossil-energy requirement in this operation were found to be particularly sensitive to (i) the yield of oil achieved during cultivation, (ii) the velocity of circulation of the algae in the cultivation facility, (iii) whether the culture media could be recycled or not, and (iv) the concentration of carbon dioxide in the flue gas. These results highlight the crucial importance of using life-cycle assessment to guide the future development of biodiesel from microalgae.
Continued growth and intensification of aquaculture production depends upon the development of sustainable protein sources to replace fish meal in aquafeeds. This document reviews various plant feedstuffs, which currently are or potentially may be incorporated into aquafeeds to support the sustainable production of various fish species in aquaculture. The plant feedstuffs considered include oilseeds, legumes and cereal grains, which traditionally have been used as protein or energy concentrates as well as novel products developed through various processing technologies. The nutritional composition of these various feedstuffs are considered along with the presence of any bioactive compounds that may positively or negatively affect the target organism. Lipid composition of these feedstuffs is not specifically considered although it is recognized that incorporating lipid supplements in aquafeeds to achieve proper fatty acid profiles to meet the metabolic requirements of fish and maximize human health benefits are important aspects. Specific strategies and techniques to optimize the nutritional composition of plant feedstuffs and limit potentially adverse effects of bioactive compounds are also described. Such information will provide a foundation for developing strategic research plans for increasing the use of plant feedstuffs in aquaculture to reduce dependence of animal feedstuffs and thereby enhance the sustainability of aquaculture.
Ammonia concentrations of 4 g N/l or more inhibited thermophilic digestion of cattle manure. A stable digestion of cattle manure could be maintained with ammonia concentrations up to 6 g N/l after 6 months of operation. However, the methane yield was reduced and the concentration of volatile fatty acids increased from 1 to 3 g/l as acetate, compared to controls with an ammonia concentration of 2.5 g N/l. The temporary strong inhibition following an one-step increase in ammonia concentration was reduced by applying a gradual increase. The specific methanogenic activity of ammonia-inhibited reactors (6 g N/l) with acetate or hydrogen as substrate was reduced by 73 and 52%, respectively. Tests of ammonia toxicity on the acetate- and hydrogen-utilizing populations showed a higher sensitivity of the aceticlastic compared to the hydrogenotrophic methanogens; the specific growth rate for the aceticlastic methanogens was halved at ammonia concentrations of 3.5 g N/l, compared to 7 g N/l for the hydrogenotrophic methanogens.
Algae are the fastest-growing plants in the world. Industrial reactors for algal culture are open ponds, photobioreactors and closed systems. Algae are very important as a biomass source. Algae will some day be competitive as a source for biofuel. Different species of algae may be better suited for different types of fuel. Algae can be grown almost anywhere, even on sewage or salt water, and does not require fertile land or food crops, and processing requires less energy than the algae provides. Algae can be a replacement for oil based fuels, one that is more effective and has no disadvantages. Algae are among the fastest-growing plants in the world, and about 50% of their weight is oil. This lipid oil can be used to make biodiesel for cars, trucks, and airplanes. Microalgae have much faster growth-rates than terrestrial crops. the per unit area yield of oil from algae is estimated to be from 20,000 to 80,000 l per acre, per year; this is 7–31 times greater than the next best crop, palm oil. The lipid and fatty acid contents of microalgae vary in accordance with culture conditions. Most current research on oil extraction is focused on microalgae to produce biodiesel from algal oil. Algal-oil processes into biodiesel as easily as oil derived from land-based crops.
Biodiesel has received much attention in recent years. Although numerous reports are available on the production of biodiesel from vegetable oils of terraneous oil-plants, such as soybean, sunflower and palm oils, the production of biodiesel from microalgae is a newly emerging field. Microalgal biotechnology appears to possess high potential for biodiesel production because a significant increase in lipid content of microalgae is now possible through heterotrophic cultivation and genetic engineering approaches. This paper provides an overview of the technologies in the production of biodiesel from microalgae, including the various modes of cultivation for the production of oil-rich microalgal biomass, as well as the subsequent downstream processing for biodiesel production. The advances and prospects of using microalgal biotechnology for biodiesel production are discussed.
Sustainable production of renewable energy is being hotly debated globally since it is increasingly understood that first generation biofuels, primarily produced from food crops and mostly oil seeds are limited in their ability to achieve targets for biofuel production, climate change mitigation and economic growth. These concerns have increased the interest in developing second generation biofuels produced from non-food feedstocks such as microalgae, which potentially offer greatest opportunities in the longer term. This paper reviews the current status of microalgae use for biodiesel production, including their cultivation, harvesting, and processing. The microalgae species most used for biodiesel production are presented and their main advantages described in comparison with other available biodiesel feedstocks. The various aspects associated with the design of microalgae production units are described, giving an overview of the current state of development of algae cultivation systems (photo-bioreactors and open ponds). Other potential applications and products from microalgae are also presented such as for biological sequestration of CO2, wastewater treatment, in human health, as food additive, and for aquaculture.
Acetone, butanol, and ethanol (ABE) fermentation by Clostridium saccharoperbutylacetonicum N1-4 using wastewater algae biomass as a carbon source was demonstrated. Algae from the Logan City Wastewater Lagoon system grow naturally at high rates providing an abundant source of renewable algal biomass. Batch fermentations were performed with 10% algae as feedstock. Fermentation of acid/base pretreated algae produced 2.74 g/L of total ABE, as compared with 7.27 g/L from pretreated algae supplemented with 1% glucose. Additionally, 9.74 g/L of total ABE was produced when xylanase and cellulase enzymes were supplemented to the pretreated algae media. The 1% glucose supplement increased total ABE production approximately 160%, while supplementing with enzymes resulted in a 250% increase in total ABE production when compared to production from pretreated algae with no supplementation of extraneous sugar and enzymes. Additionally, supplementation of enzymes produced the highest total ABE production yield of 0.311 g/g and volumetric productivity of 0.102 g/Lh. The use of non-pretreated algae produced 0.73 g/L of total ABE. The ability to engineer novel methods to produce these high value products from an abundant and renewable feedstock such as algae could have significant implications in stimulating domestic energy economies.
Ultrasound at 20Hz was applied at different energy levels (Es) to treat Scenedesmus biomass, and organic matter solubilization, particle size distribution, cell disruption and biochemical methane potential were evaluated. An Es of 35.5 and 47.2MJ/kg resulted in floc deagglomeration but no improvement in methane production compared to untreated biomass. At an Es of 128.9, cell wall disruption was observed together with a 3.1-fold organic matter solubilization and an approximately 2-fold methane production in comparison with untreated biomass. Thermal pretreatment at 80°C caused cell wall disruption and improved anaerobic biodegradability 1.6-fold compared to untreated biomass. Since sonication caused a temperature increase in samples to as high as 85°C, it is likely that thermal effects accounted for much of the observed changes in the biomass. Given that ultrasound treatment at the highest Es studied only increased methane production by 1.2-fold over thermal treatment at 80°C, the higher energy requirement of sonication might not justify the use of this approach over thermal treatment.
Microalgae biotechnology has recently emerged into the lime light owing to numerous consumer products that can be harnessed from microalgae. Product portfolio stretches from straightforward biomass production for food and animal feed to valuable products extracted from microalgal biomass, including triglycerides which can be converted into biodiesel. For most of these applications, the production process is moderately economically viable and the market is developing. Considering the enormous biodiversity of microalgae and recent developments in genetic and metabolic engineering, this group of organisms represents one of the most promising sources for new products and applications. With the development of detailed culture and screening techniques, microalgal biotechnology can meet the high demands of food, energy and pharmaceutical industries. This review article discusses the technology and production platforms for development and creation of different valuable consumer products from microalgal biomass.
Anaerobic digestion is an attractive waste treatment practice in which both pollution control and energy recovery can be achieved. Many agricultural and industrial wastes are ideal candidates for anaerobic digestion because they contain high levels of easily biodegradable materials. Problems such as low methane yield and process instability are often encountered in anaerobic digestion, preventing this technique from being widely applied. A wide variety of inhibitory substances are the primary cause of anaerobic digester upset or failure since they are present in substantial concentrations in wastes. Considerable research efforts have been made to identify the mechanism and the controlling factors of inhibition. This review provides a detailed summary of the research conducted on the inhibition of anaerobic processes. The inhibitors commonly present in anaerobic digesters include ammonia, sulfide, light metal ions, heavy metals, and organics. Due to the difference in anaerobic inocula, waste composition, and experimental methods and conditions, literature results on inhibition caused by specific toxicants vary widely. Co-digestion with other waste, adaptation of microorganisms to inhibitory substances, and incorporation of methods to remove or counteract toxicants before anaerobic digestion can significantly improve the waste treatment efficiency.
Due to resource depletion and climate change, lipid-based algal biofuel has been pointed out as an interesting alternative because of the high productivity of algae per hectare and per year and its ability to recycle CO(2) from flue gas. Another option for taking advantage of the energy content of the microalgae is to directly carry out anaerobic digestion of raw algae in order to produce methane and recycle nutrients (N, P and K). In this study, a life-cycle assessment (LCA) of biogas production from the microalgae Chlorella vulgaris is performed and the results are compared to algal biodiesel and to first generation biodiesels. These results suggest that the impacts generated by the production of methane from microalgae are strongly correlated with the electric consumption. Progresses can be achieved by decreasing the mixing costs and circulation between different production steps, or by improving the efficiency of the anaerobic process under controlled conditions. This new bioenergy generating process strongly competes with others biofuel productions.
Microalgal lipids are the oils of future for sustainable biodiesel production. However, relatively high production costs due to low lipid productivity have been one of the major obstacles impeding their commercial production. We studied the effects of nitrogen sources and their concentrations on cell growth and lipid accumulation of Neochloris oleoabundans, one of the most promising oil-rich microalgal species. While the highest lipid cell content of 0.40 g/g was obtained at the lowest sodium nitrate concentration (3 mM), a remarkable lipid productivity of 0.133 g l(-1) day(-1) was achieved at 5 mM with a lipid cell content of 0.34 g/g and a biomass productivity of 0.40 g l(-1) day(-1). The highest biomass productivity was obtained at 10 mM sodium nitrate, with a biomass concentration of 3.2 g/l and a biomass productivity of 0.63 g l(-1) day(-1). It was observed that cell growth continued after the exhaustion of external nitrogen pool, hypothetically supported by the consumption of intracellular nitrogen pools such as chlorophyll molecules. The relationship among nitrate depletion, cell growth, lipid cell content, and cell chlorophyll content are discussed.
About five decades ago, the mass production of certain protein-rich micro-algae was considered as a possibility to close the predicted so called "protein gap". Comprehensive analyses and nutritional studies have demonstrated that these algal proteins are of high quality and comparable to conventional vegetable proteins. However, due to high production costs as well as technical difficulties to incorporate the algal material into palatable food preparations, the propagation of algal protein is still in its infancy. To date, the majority of micro-algal preparations are marketed as health food, as cosmetics or as animal feed.
Continued use of petroleum sourced fuels is now widely recognized as unsustainable because of depleting supplies and the contribution of these fuels to the accumulation of carbon dioxide in the environment. Renewable, carbon neutral, transport fuels are necessary for environmental and economic sustainability. Biodiesel derived from oil crops is a potential renewable and carbon neutral alternative to petroleum fuels. Unfortunately, biodiesel from oil crops, waste cooking oil and animal fat cannot realistically satisfy even a small fraction of the existing demand for transport fuels. As demonstrated here, microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels. Like plants, microalgae use sunlight to produce oils but they do so more efficiently than crop plants. Oil productivity of many microalgae greatly exceeds the oil productivity of the best producing oil crops. Approaches for making microalgal biodiesel economically competitive with petrodiesel are discussed.
Inhibition of anaerobic digestion process: a review
- Y Chen
- J J Cheng
- K S Creamer
Chen, Y., Cheng, J.J., Creamer, K.S., 2008. Inhibition of anaerobic digestion process: a
review. Bioresour. Technol. 99, 4044-4064.