No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Biodiesel production with microalgae as feedstock: From strains to biodiesel
Abstract
Due to negative environmental influence and limited availability, petroleum-derived fuels need to be replaced by renewable biofuels. Biodiesel has attracted intensive attention as an important biofuel. Microalgae have numerous advantages for biodiesel production over many terrestrial plants. There are a series of consecutive processes for biodiesel production with microalgae as feedstock, including selection of adequate microalgal strains, mass culture, cell harvesting, oil extraction and transesterification. To reduce the overall production cost, technology development and process optimization are necessary. Genetic engineering also plays an important role in manipulating lipid biosynthesis in microalgae. Many approaches, such as sequestering carbon dioxide from industrial plants for the carbon source, using wastewater for the nutrient supply, and maximizing the values of by-products, have shown a potential for cost reduction. This review provides a brief overview of the process of biodiesel production with microalgae as feedstock. The methods associated with this process (e.g. lipid determination, mass culture, oil extraction) are also compared and discussed.
... Polar lipids, which frequently contain phospholipids and glycolipids, serve as membrane structural components in most circumstances. Under a variety of stress conditions, TAGs are typically observed to accumulate as a form of energy storage [146]. Only TAGs are readily transesterified into biodiesel using traditional techniques, despite the fact that practically all forms of microalgal lipids may be extracted. ...
... Only TAGs are readily transesterified into biodiesel using traditional techniques, despite the fact that practically all forms of microalgal lipids may be extracted. Due to the wide variety of lipids, algae, and microalgal strains, choosing the oleaginous microalgal strains best suited for biodiesel production will require screening a large number of microalgal strains [146][147][148]. A strategically chosen strain can aid not only in the production of higher-quality products but also in the reduction of the number of processing steps required for recovery. ...
Algae are a desirable biodiesel feedstock because they take up little space, have a high algal-cell biomass per unit area, and can sustainably meet a large portion of the world’s future energy needs. Using several bibliometric indicators, this study assesses the research productivity of algae for biodiesel production. The dataset was retrieved from the Scopus database using an appropriate keyword search. The VOSviewer v1.6.18 and Biblioshiny in R -studio were then utilised for bibliometric analysis and network visualisation. The study found that, with the first article being published in 1990 and an annual scientific growth rate of 14.76%, research on algae for the generation of biodiesel is still in its early phases. Although the possibility of utilising algae to produce biodiesel was originally mentioned in 1990, it was only until 2006 that several researchers started to show an interest in the subject. 101 articles were published in 2015, which is the most ever. The most prolific countries in terms of publications, ongoing collaborations and cooperation, best publishing institutions, and prestigious journals, as well as the most productive researchers and the most highly referenced works in the field, have all been recognised and presented. Finally, a keyword co-occurrence analysis of the subject was presented and discussed to provide research insights into the field. The bibliometric indicators of the study are intended to aid researchers in finding potential research topics, high-quality scientific literature, and suitable journals for publishing research on algae for biodiesel production.
... By enhancing the expression of thioesterase, an endogenous enzyme, the total fatty acid content was increased by 72% without changing the relative chain length in the diatom P. tricornutum. Triacylglycerols (TAGs) are considered promising precursors for biofuel synthesis because they have a high energy storage capacity and are made up of energy-dense acyl molecules [69,70]. Glycerol-3-Phosphate Acyltransferase (GPAT), Lysophosphatidate Acyltransferase (LPAAT/AGPAT), and Diacyl Glycerol Acyl Transferase (DGAT) are found in regions of the endoplasmic reticulum. ...
... According to a TEA comparing the entire production costs needed to produce ethanol, butanol, and isobutanol, feedstock contributed the majority (around 32%) of the whole cost [9]. Lignocellulosic biomass is a plentiful and affordable renewable resource that can produce biofuel in various industrial facilities [70]. ...
Microalgae exhibit remarkable potential as a feedstock for biofuel production compared
with other sources, owing to their high areal productivity, low environmental effect, and negligible influence on food security. However, the primary obstacle to the commercialization of algae-based biofuels is the high economic cost due to the low-yield lipid content in the microalgae biomass. Maximizing biomass and lipid production is crucial to improve the economic viability of microalgae for biofuels. Identifying appropriate algal strains, particularly from indigenous environments, and developing those ‘platform strains’ using mutagenesis and genetic-engineering techniques is preferable. The provided discussion of conventional methods to increase microalgae’s biomass and lipid productivity mostly entailed adjusting environmental (such as temperature, light, and salinity) and nutritional (such as nitrogen and phosphorus) parameters. This review illustrated a comprehensive overview of biotechnological approaches and the recent strategies to enhance the lipid productivity of microalgae. The research also emphasized the need to streamline engineering strategies with the
aid of recent advancements in DNA-manipulation techniques to hinder the existing biological intricacies in lipogenesis. This review also discussed the current economic and commercialization of this algal biorefinery along with the drawbacks.
... It provides a closed environment for avoiding contamination from the environment. It also provides highly controlled growth conditions which helps in the generation of single-strain, contaminant-free microalgae [26]. In conjunction, high biomass production per substrate is a result of the translation of a controlled culture system into greater metabolic & nutrient efficiency. ...
Chlorella vulgaris has considerable promise as a raw material for biofuel production since it has a high productivity per unit area, has a minimum influence on the environment, and does not significantly affect food security. Nevertheless, the low fatty content of their biomass poses a considerable economic obstacle for commercialization. Increasing the amount of biomass and lipids produced by these algae is essential for improving the economic feasibility of using them as biofuel sources. This review highlights the significance of identifying appropriate algal strains, namely those found in local environments, and utilising mutagenesis and genetic engineering techniques to create 'platform strains'. Prior endeavours have primarily concentrated on altering environmental and dietary parameters to enhance the production of biomass and lipids. Here, we review a scientific literature that examines biotechnological approaches and develops methodologies designed to increase lipid production, emphasising the importance of aligning engineering efforts with breakthroughs in DNA manipulation tools. In addition, the review research evaluates the present economic and commercial situation of algal biorefineries, including any related disadvantages. In summary, this thorough research highlights the importance of using creative methods to tackle the intricacies of lipogenesis and enhance the economic viability of producing biofuels from algae.
... As a strategy to increase the cost-effectiveness of microalgal production, optimisation of culture medium has been suggested [32]. Microalgal production can be made more cost-effective by employing low-cost resources, such as nutrient-rich wastewater, agricultural by-products, and inexpensive fertilisers [25,33]. In hydroponics, microalgae usually grow spontaneously, but they are considered a critical point because they can cause nutritional competence and pipeline clogs. ...
In order to ensure food security worldwide in the face of current climatic changes, a higher quality and quantity of crops is necessary to sustain the growing human population. By developing a sustainable circular economy and biorefinery approaches, we can move from a petroleum-based to a bio-based economy. Plant biostimulants have long been considered an important source of plant growth stimulants in agronomy and agro-industries with both macroalgae (seaweeds) and microalgae (microalgae). There has been extensive exploration of macroalgae biostimulants. A lack of research and high production costs have constrained the commercial implementation of microalgal biostimulants, despite their positive impact on crop growth, development and yields. The current knowledge on potential biostimulatory compounds, key sources and their quantitative information from algae is summarized in the present review. Our goal is to provide a brief overview of the potential for microalgal biostimulants to improve crop production and quality. A number of key aspects are discussed, including the biostimulant effects caused by microalgae extracts, as well as the feasibility and potential for cocultures and coapplication with other biostimulants and biofertilizers. This article also discusses the current knowledge, recent developments and achievements in extraction techniques, types of applications, timings of applications. Ultimately, this review highlights the potential for microalgal biostimulants for sustainable agricultural practices, the algal biochemical components contributing to these traits, and finally bottlenecks and involved prospects in commercializing microalgal biostimulants.
... As a strategy to increase the cost-effectiveness of microalgal production, the optimisation of culture media has been suggested [46]. Microalgal production can be made more cost-effective by employing low-cost resources such as nutrient-rich wastewater, agricultural by-products, and inexpensive fertilisers [39,47]. In hydroponics, microalgae usually grow spontaneously, but they are considered a critical point because they can cause nutritional competence and pipeline clogs. ...
In order to ensure food security worldwide in the face of current climate changes, a higher quality and quantity of crops are necessary to sustain the growing human population. By developing a sustainable circular economy and biorefinery approaches, we can move from a petroleum-based to a bio-based economy. Plant biostimulants have long been considered an important source of plant growth stimulants in agronomy and agro-industries with both macroalgae (seaweeds) and microalgae (microalgae). There has been extensive exploration of macroalgae biostimulants. A lack of research and high production costs have constrained the commercial implementation of microalgal biostimulants, despite their positive impacts on crop growth, development, and yield. The current knowledge on potential biostimulatory compounds from algae, key sources, and their quantitative information has been summarised in the present review. Our goal is to provide a brief overview of the potential for microalgal biostimulants to improve crop production and quality. A number of key aspects will be discussed, including the biostimulant effects caused by microalgae extracts as well as the feasibility and potential for co-cultures and co-application with other biostimulants and biofertilisers. This article will also discuss the current knowledge, recent developments, and achievements in extraction techniques, types of applications, and timings of applications. Ultimately, this review will highlight the potential of microalgal biostimulants for sustainable agricultural practices, the algal biochemical components that contribute to these traits, and, finally, bottlenecks and involved prospects in commercialising microalgal biostimulants.
... For biomaterials, there are still issues with production due to lower biomass yield, biomass contamination, high maintenance and repair costs of biomass production infrastructure, and the cost of harvesting and extracting materials from biomass [172]. For biogas and biofuel synthesis, there are also issues with the production process and using CO 2 for algae production [175,176]. The production of biomass requires a significant land footprint, significant capital expenses, and significant timely research and development resources for selecting preferable microalgae utilization pathways [175]. ...
... Microalgae are attracting attention as a resource to solve these problems (Stephens et al. 2010). Microalgae are a promising resource for addressing these issues due to their ability to multiply quickly, and independent from arable land's soil fertility (Stephens et al. 2010;Gong and Jiang 2011). ...
Euglena gracilis (E. gracilis) is a unicellular microalga with various applications in medicine, agriculture, aquaculture, health supplement, and jet fuel production. Euglena possibly solves population growth and exhaustion of fossil resources. Efficient cell harvesting is needed for the industry, and the gravity sedimentation method is low cost and does not require any equipment, although it has low efficiency. This study showed that the gravity sedimentation of E. gracilis cells is improved by cultivation in the presence of ethanol (EtOH). The gravity sedimentation of E. gracilis cells cultivated under 0.5% or 1.0% EtOH conditions was faster than that cultivated without EtOH. The mean calculated cell diameter was also found to be largest in cells cultivated under 0.5% or 1.0% EtOH conditions compared to that in cells cultivated without EtOH. Intracellular paramylon content, cell shapes, and motility differed between cells cultivated under 0.5% or 1.0% EtOH conditions and in the absence of EtOH. The results suggest that E. gracilis cultivation with EtOH leads to increased cell productivity, paramylon production, and efficient cell harvesting. KEY POINTS: • Euglena gracilis is an edible microalga producing value-added metabolites. • Ethanol addition upregulates E. gracilis growth and paramylon accumulation. • Gravity sedimentation is accelerated by ethanol-grown E. gracilis cells.
... Species and strain selection are the first and most important steps in the bioprospecting activities of organisms for commercial applications (Indrayani 2017). The selection and screening processes involve stages such as sample collection, isolation, purification, identification, maintenance, and characterization (Gong and Jiang 2011). Microbial selection and screening activities can be done in two ways: selecting and screening microbes from the collection center and the natural environment. ...
Indrayani, Putra RP, Hambali A, Ardiansyah. 2022. Isolation and characterization of extremophile bacteria for hydrolytic enzyme production from Waepella Hot Spring, Sinjai, Indonesia. Biodiversitas 23: 6345-6351. Extremophiles are organisms that have adapted to live in extreme environments. Therefore, they have huge potential for various industrial applications, specifically enzyme production. The aim of this study was to isolate and screen the potential of extremophile bacteria for hydrolytic enzyme production from the Waepella hot spring in Sinjai District, South Sulawesi, Indonesia. The water samples were collected from the hot spring at three different locations. The method of bacterial isolation was the agar plating technique using Tryptic Soy Agar media. The obtained isolates were characterized by examination of colony colors, cell shapes, gram staining, endospore, catalase, and enzymatic activity (amylase, cellulose, protease, lipase, and pectinase). The result showed that a total of eighteen isolates were successfully isolated from Waepella hot springs. Eight isolates showed amylolytic activity, and the highest (22.6± 0.44 mm) activity was observed in isolate BHSS10. Nine isolates had a cellulolytic activity with the highest clear zone of 11.6±0.4 mm (isolate BHSS7). Sixteen isolates had a pectinolytic activity with the highest clear zone of 12±0.24 (isolate BHSS16). Only 3 isolates showed proteolytic activity, and the highest (9.83±0.40 mm) was observed in isolate BHSS15, while none showed lipolytic activity. That is the first report on extremophile bacterial isolation and screening for enzyme production from the hot spring in South Sulawesi, Indonesia.
... Glucose and xylose are the most typically sugars incepted from lignocellulosic biomass. As a result, oleaginous yeast strains that consume both sugars (glucose and xylose) are preferable, as are those that can ingest minor sugars such as mannose, galactose, or arabinose [8][9][10]. Dilute acid hydrolysis has been confirmed to be a rapid and affordable method for generating sugars from lignocellulosic biomass [7]. ...
Microbial lipid produced using yeast fermentation with in-expensive carbon sources such as hydrolysate from lignocellulosic may be an opportunity feedstock for biodiesel manufacturing. Furfural and 5-hydroxymethylfurfural (5-HMF) that can be engendered during acid hydrolysis of lignocellulose had been brought merely or concurrently into a culture medium comprising a mixture of two sugars (glucose and xylose) as carbon sources to investigate the sole inhibitory actions and their synergic enforcement on the growth and lipid production of Lipomyces starkeyi InaCC Y604. The used strain exhibited a particular resistance level against each of the archetypal inhibitor compounds. When fermented using medium-contained furfural as a sole inhibitor compound, L. starkeyi InaCC Y604 accumulated the highest microbial lipid (67.06%). While, when a mixture of furfural and 5-HMF was used as the inhibitor compounds in the fermentation medium, the microbial lipid production was achieved at 66.9%. Meanwhile, microbial lipid production was achieved at 63.68% when 5-HMF was used as the sole inhibitor in the fermentation medium. L. starkeyi InaCC Y604 showed the dexterity to tolerate inhibitors (furfural and 5-HMF) and the combination of fatty acid methyl esters (FAMEs) was unchanged by the existence of inhibitor compounds. The considerable FAMEs comply with oleic, palmitic, stearic, palmitoleic, and linoleic acids.
... To date several attempts have been made to reduce the production cost of biodiesel, some of them are as follows: (Gong and Jiang, 2011): ...
Globally, the demand for energy is increasing with an emphasis on green fuels for a sustainable future. As the urge for alternative fuels is accelerating, microalgae have emerged as a promising source that can not only produce high lipid but many other platform chemicals. Moreover, it is a better alternative in comparison to conventional feedstock due to yearlong easy and mass cultivation, carbon fixation, and value-added products extraction. To date, numerous studies have been done to elucidate these organisms for large-scale fuel production. However, enhancing the lipid synthesis rate and reducing the production cost still remain a major bottleneck for its economic viability. Therefore, this study compiles information on algae-based biodiesel production with an emphasis on its unit operations from strain selection to biofuel production. Additionally, strategies to enhance lipid accumulation by incorporating genetic, and metabolic engineering and the use of leftover biomass for harnessing bio-products have been discussed. Besides, implementing a biorefinery for extracting oil followed by utilizing leftover biomass to generate value-added products such as nanoparticles, biofertilizers, biochar, and biopharmaceuticals has also been discussed.
... The synthesis of TAG inside the microalgal system requires different genetic and molecular approaches, to modify the metabolic pathways. Lipid (TAG) biosynthesis is directly or indirectly linked to acetyl CoA, thus, several genetic and molecular strategies have been proposed to increase the accumulations of TAG such as (a) overexpression of thioesterase gene can promote fatty acid profile through reducing feedback inhibition with an resultant increase in acyl-ACP concentration [136], (biodiesel production with microalgae as feedstock: from strains), (b) elimination of enzyme leading to beta-oxidation of fatty acids, (c) knockdown of gene or enzyme which down-regulates the synthesis of lipid accumulation [134], (d) upregulate the expression of acetyl CoA carboxylase (ACC) gene promotes the conversion of acetyl-CoA to malonyl-CoA [25], (e) up-regulation of the lipid synthesis gene such as pyruvate dehydrogenase E1 (PDH2), acetyl-CoA carboxylase (ACCase), beta-ketoacyl-ACP synthetase (KAS) and malonyl-CoA ACP transacylase (MAT) [96], (f) blocking of starch synthesis genes [23] and (g) overexpression of glutathione activity and transformation of the calmodulin and MAPK expression [137]. A few reports have been published regarding genetic modification for lipid biosynthesis in microalgae e.g., C. reinhardtii [138], Phaeodactylum tricornutum [139], Chlorella ellipsoidea [140]. ...
Microalgae (MA) biorefinery is a vital platform for the conversion of biomass into biofuels, biomaterials, and bioactive substances and it can remediate the pollutant from the environment. Moreover, its commercialization can enable a jump start towards resolving energy and economic crisis. However, the major bottleneck in biorefinery includes (i) low biomass and biomolecules production, (ii) high cost, (iii) less economic viability, (iv) high energy requirement, and (v) environmental impacts of the process. Furthermore, the lack of advanced models or algorithms for process designing and limited genetic and molecular knowledge is a key bottleneck. Thus, there is an urgent need for novel integrated microalgal bioenergy conversion methods that provide economic and environmental balance. Moreover, advanced molecular knowledge in the microalgal research pipeline can be developed that improves the biosynthesis of biomolecules. Furthermore, novel technological development is required that automatically controls and monitors the microalgal biorefinery. Thus, the current review describes a comparative analysis of the gaps from previous studies. Subsequently, it highlights advanced cutting-edge cultivation and molecular and genetic approaches for enhancing biomass and biomolecules. It critically evaluates the potential of artificial intelligence (AI) algorithms and IoTs-based sensors used in microalgal cultivation, system optimization pipeline, and other aspects. Finally, it aims to provide a conceptual scenario and integrated mechanisms of multiple biofuel production with co-products formation concerning zero-carbon and waste footprint to maintain a circular-bioeconomy. Additionally, it also offers elaboration on recent life-cycle-assessment (LCA), techno-economic analysis (TEA) of recent microalgal biofuels biorefinery, and algal biofuels' current and future market trends towards sustainability key challenges and opportunities. This review will contribute critically to the novelty and significance in the field of microalgae biorefinery to develop smarter, safer, cleaner, greener, and economically efficient techniques for exhaustive energy recovery tactics and pathway to a digitalized the future of MA biorefinery.
... Microalgae-based products are still niche commodities, the production of which could be encouraged by environmental sustainability policies. Microalgae are suitable alternatives to fossil fuels for the production of biofuels and as agricultural crops for human and animal food applications [13][14][15][16][17]. However, in contrast to research or review articles regarding the microalgal potential for biotechnological purposes, which are easily accessible through scientific search engines, it is difficult to get a precise idea of the true microalgal market and some of its sectors. ...
Microalgae are currently considered an attractive source of highly valuable compounds for human and animal consumption, including polyunsaturated fatty acids (PUFAs). Several microalgaederived compounds, such as omega-3 fatty acids, pigments, and whole dried biomasses are available on the market and are mainly produced by culturing microalgae in open ponds, which can be achieved with low setup and maintenance costs with respect to enclosed systems. However, open tanks are more susceptible to bacterial and other environmental contamination, do not guarantee a high reproducibility of algal biochemical profiles and productivities, and constrain massive cultivation to a limited number of species. Genetic engineering techniques have substantially improved over the last decade, and several model microalgae have been successfully modified to promote the accumulation of specific value-added compounds. However, transgenic strains should be cultured in closed photobioreactors (PBRs) to minimize risks of contamination of aquatic environments with allochthonous species; in addition, faster growth rates and higher yields of compounds of interest can be achieved in PBRs compared to open ponds. In this review, we present information collected about the major microalgae-derived commodities (with a special focus on PUFAs) produced at industrial
scale, as well genetically-engineered microalgae to increase PUFA production. We also critically analyzed the main bottlenecks that make large-scale production of algal commodities difficult, as well as possible solutions to overcome the main problems and render the processes economically and environmentally safe.
... Several processes that can be employed to minimize the cost involved in the production of algal biomass, including the utilization of low-cost resources such as agricultural by-products and nutrient-rich wastewaters (Gong and Jiang, 2011). Furthermore, recycling wastewaters for the microalgae production may be able to reduce reliance on other inorganic fertilizers, while also generating additional revenue from hydroponic co-productions and providing sustainable and innovative bio-fertilizers with commercial potential in crop production (Coppens et al., 2016;Zhang et al., 2017). ...
... However, the quality and quantity of natural sunlight is affected by daily and seasonal variations. [13] They have disadvantages such as water loss by evaporation, limited transfer of CO 2 to the crop due to its low concentration in the air and its diffusion into the atmosphere, limited control of growing conditions, high susceptibility to contamination, extensive surface requirements, long production periods, reduced biomass production and limited light penetration. [14] The depths that are usually utilized are from 0.2 to 0.3 m to provide sufficient light. ...
This study evaluates the removal of COD and nitrogen from poultry wastewater in photobioreactors. Cell growth, the effect of light intensity (3200, 9800, and 12000 lux) and air flow (1.6, 3.2, and 4.8 L min-1) as a source of CO2 in bold basal medium and wastewater with different concentrations of COD were evaluated. The growth kinetics were modeled by using the Gompertz model and logistic model for both culture media. COD removals of up to 95% were achieved, and poultry wastewater was found to be a viable growing medium for Chlorella vulgaris. Finally, the wastewater met Mexican standards, and biomass was obtained with products valued as lipids (3.2 g lipid/100 g biomass) and proteins (342.94 mg L-1). The culture was found to have a dilatory behavior, and the rheological models of Ostwald de Waele, Ostwald de Waele linealized and Herschel Bulkley were utilized, showing a laminar behavior.
... Chlorella sp., Scenedesmus sp., Chlorococcum sp., Neochloris sp.) and Eustigmatophyceae (e.g. Nannochloropsis sp. and Pavlova sp.) are widely used for biodiesel production due to their high lipid content (up to 65%) (Gong and Jiang, 2011). ...
The use of indigenous microalgae strains for locally generated domestic (DWW) and livestock wastewater (LWW) treatment is essential for effective and economical applications. Phototrophic microalgae-based biofuel production also contributes to carbon sequestration via CO2 fixation. However, simultaneous consideration of both isolation and screening procedures for locally collected indigenous microalgae strains is not common in the literature. We aimed to isolate indigenous microalgae strains from locally collected samples on coastlines and islands in South Korea. Among five isolated strains, Chlorella sorokiniana JD1-1 was selected for DWW and LWW treatment due to its ability to grow in waste resources. This strain showed a higher specific growth rate in DWW than artificial growth medium (BG-11) with a range of 0.137–0.154 d−1. During cultivation, 96.5%–97.1% of total nitrogen in DWW and 89.2% in LWW was removed. Over 99% of total phosphorus in DWW and 96.4% in LWW was also removed. Finally, isolated C. sorokiniana JD1-1 was able to fix CO2 within a range of 0.0646–0.1043 g CO2 L−1 d−1. These results support the domestic applications of carbon sequestration–efficient microalgae in the waste-to-energy nexus.
... ). This result is higher than Maynardo et al. (2015), which reports that their lipid weights were 0.005 g and 0.01 g, respectively. In addition, Chavoshi and Shariati. (2019) was also noted, when microalgae are stressed, the lipids contained in the microalgae can also accumulate more under high salinity pressure and high light intensity. Moreover, Gong and Jiang. (2011), also reported that high lipid content in microalga shows that this organism shows an auspicious potential in the biotechnology industry, for example, biodiesel production. ...
Nannochloropsis sp is marine microalga and widely cultured for its benefits. Pigments, lipid, and fatty acid compounds of Nannochloropsis sp are essential elements in the industry. This research aimed to determine the best light intensity on the growth rate, cell density and size, biomass, pigments (chlorophyll a, b, carotenoids), total lipid and fatty acid profile. Nannochloropsis sp. culture was carried out with three light intensity treatments (100, 155, and 180 μmol), with two replications. Periodicity was set up (16:8) with the ratio of dark (8h) to light (16h). The highest cell density and total pigment content of 180 μmol were significantly different (p<0.05) with 155 and 100 μmol. The highest weight of chlorophyll a, b, and carotenoids were found from the intensity of 180 treatment (p < 0.05), followed by 155 and 100 μmol as the smallest one. The bigger cell size was reached from 180 and 155 treatments compared to 100 μmol treatment. The higher wet weight was gained from 155 (564 grams) and followed by 180 μmol (549 grams). The 100 μmol light intensity produced the lowest wet weight (490 gr) (p<0.05). The highest total lipid content was obtained from 155 μmol treatment (0.14 g ww). The microalgae contain SFA/Saturated Fatty Acids (Palmitic, Stearic Acid) and UFA/Unsaturated Fatty Acid (Oleic Acid). The microalgae from 180 μmol produced Eicosanoic acid (Omega-6). The production of certain compounds has differed in light intensity. In the future, the light intensity can be adapted as the alternative solution for producing microalgae for industrial approach, whether for pigments or biodiesel production.
... There are a number of processes that can be employed to minimize the cost of algae production, including the exploitation of low-cost resources such as nutrient-rich wastewaters and agricultural by-products (Gong and Jiang 2011). Furthermore, recycling greenhouse wastewaters for the production of microalgae may be able to reduce reliance on other fertilizers, such as inorganic fertilizers, while also generating additional income from hydroponic co-productions (Zhang et al. 2017;Barone et al. 2019). ...
Bio-fertilization is a sustainable agricultural practice that includes using bio-fertilizers to increase soil nutrient content resulting in higher productivity. Soil micro-flora has been exposed to improve soil fertility and increase biomass productivity and identified as a correct environmentally friendly bio-based fertilizer for pollution-free agricultural applies. The majority of cyanobacteria can fix nitrogen from the atmosphere and several species including Anabaena sp., Nostoc sp., and Oscillatoria angustissima is known to be effective cyanobacterial based bio fertilizers. Acutodesmus dimorphus, Spirulina platensis Chlorella vulgaris, Scenedesmus dimorphus, Anabaena azolla, and Nostoc sp. are some of the green microalgae and cyanobacteria species that have been successfully used as bio fertilizers to boost crop growth. Also, Chlorella vulgaris is one of the most commonly used microalgae in bio fertilizer studies. The addition of seaweed species that are Sargassum sp. and Gracilaria verrucosa leads to chemical changes as a soil fertility indicator on clay and sandy soils, and the addition of seaweed conditioner to soil can improve its organic content, return pH to normal, and reduce C/N ratio in both sandy and clay soil. This review provides an effective approach to increase soil fertility via environmentally friendly bio-based fertilizer using micro and macro algae. Instead of the usage of inorganic and organic fertilizers that have polluted impacts to soil as aggregation of heavy metals, in addition to there their human carcinogenic effects.
... Microalgae, in contrast to all of the above, are essentially utilized for lipid synthesis and accumulation so that they can be used as a feedstock for biodiesel production (Gong and Jiang, 2011;Behera et al., 2015;Goh et al., 2019). This is an indirect route to valorise the industrial waste and put it to use for sustainable fuel production Idris et al., 2018;Cheah et al., 2018;Wu et al., 2017). ...
The consumption of primary energy gets enhanced on a daily basis with the increase of population and modern industries. In 2015, it was reported that the energy consumption was over 150,000,000 Gigawatt hour (GWh) and it is predicted that by the year 2050 the consumption will increase by 57%. Fortunately, the emergence of biofuels has proved a potential substitute to the current growing demand in energy market and reduces the threat to the environment. Among the wide array of biofuels, biodiesel has received a great amount of focus due to being an environmentally friendly biofuel as it is bio-degradable and renewable having less emissions as compared to petro-diesel. From another point of view, regarding the catalysis of biodiesel production, there is great interest recently to use heterogeneous catalysts, specially those derived from wastes, instead of homogeneous ones. This chapter provides an overview on the attempts which were done over the last years to utilize inorganic wastes to produce catalysts active for biodiesel synthesis. It covers the catalyst preparation conditions besides the optimum conditions of biodiesel synthesis using various catalysts and feedstocks.
... Microalgae, in contrast to all of the above, are essentially utilized for lipid synthesis and accumulation so that they can be used as a feedstock for biodiesel production (Gong and Jiang, 2011;Behera et al., 2015;Goh et al., 2019). This is an indirect route to valorise the industrial waste and put it to use for sustainable fuel production Idris et al., 2018;Cheah et al., 2018;Wu et al., 2017). ...
Biodiesel is produced commonly by alcoholysis of lipid feedstock using homogeneous catalysts (e.g. KOH) soluble in an alcohol phase. Unfortunately, this process involves multiple purification steps of biodiesel and glycerol due to catalyst existence in both phases that hinder process viability. Besides, contents of free fatty acids FFAs > 2 wt%, and the presence of moisture limit the application of homogeneously catalyzed transesterification. Accordingly, heterogeneous catalysis is preferred owing to the ease of catalyst separation as well as its reusability. Within the field of heterogeneous catalysis, there is an ongoing trend to produce highly active solid catalysts based on chicken, animal and fish wastes as a way of waste management. This chapter introduces a review on the use of different fish and animal wastes, including their bones and fish scales, to produce active catalysts for biodiesel synthesis from various feedstocks, e.g. edible and non-edible oils. Besides, kinetic studies will be summarized as an essential aspect for the scale-up of the production process. Moreover, it will mention some of the techno-economic aspects related to the utilization of these wastes in the catalysis of biodiesel production and their impact on process feasibility.
... The algal system's TAG synthesis pathway can be acetyl CoA-dependent or -independent (Banerjee et al. 2020). According to (Gong and Jiang 2011) overexpression of thioesterase may enhance the FA profile by reducing feedback inhibition caused by increasing the acyl-ACP concentration, but blocking FA oxidation enzymes can raise lipid levels. The increase in TAG accumulation in algae is mainly due to the overexpression of important enzymes or the inhibition of enzymes that regulate lipid accumulation. ...
Microalgae have been studied for their ability to photosynthesize natural chemicals with industrial and biomedical implications. Bioproducts from microalgae are gaining more and more attention due to their promising future, special properties, current demand and increasing energy costs. Bioproducts from microalgae are considered sustainable, cost-effective, and efficient food sources. However, low yields and high production costs limit the commercial potential of microalgae. To address these challenges, genetically engineered microalgal strains can produce algal biomass with high lipid and/or carotenoid synthesis for efficient biomedical use and other applications. Genetic modification and metabolic engineering of microalgal species can help produce extremely stress-tolerant strains with enhanced bioproduct properties. Several studies have shown that these approaches significantly affect lipid and carotenoid production by microalgae. This review article addresses recent breakthroughs in the genetic and metabolic evolution of microalgae and focuses on lipid and carotenoid synthesis for biomedical applications. Metabolic and genomic design of microalgae will help promote and commercialize their products. The need to integrate such systems to support microalgal research is also highlighted.
... However, until now, the use of microalgae for applications in agriculture is an undergoing initiation, and the production of microalgae is only an emerging activity, due to its potential economic and commercial opportunities, but shows high costs of cultivation [44,45]. An interesting solution to increase the cost-effectiveness of this process may be represented by the application of low-cost resources, such as nutrient-rich wastewaters and agricultural byproducts [31,45,46]. ...
The pollution of water caused by the excessive presence of organic and inorganic compounds, such as nitrates, phosphates, heavy metals, antibiotics, agrochemicals, etc., is one of the major environmental problems in many countries. Various approaches to remediate wastewater are available, and this review mainly provides the state of the art about the possible adoption of microalgae-based treatments (phycoremediation), which may represent a good alternative to conventional purification methods. Because of its composition, wastewater can provide several nutritional compounds (e.g., carbon, nitrogen, and phosphorus), which represent the essential nutrients for microalgae growth. Microalgae are also attracting the interest of worldwide researchers due to their multipurpose applications; in particular, microalgae cells can represent a useful feedstock for various sectors, among these, the agricultural sector. This review proposes a detailed description of the possible application of microalgae in the process of remediation of wastewaters of different sources, highlighting their possible advantages. Moreover, the review aims to report the application of the microalgae biomasses and their extracts in agriculture, as microalgae-based products can represent a valid alternative to traditional agrochemicals, offering sustainable solutions to improve agricultural technologies. Therefore, since the recently developed wastewater depuration technology based on phycoremediation may directly provide valuable microalgae biomasses, it can be used as a powerful starting means to produce agricultural products able to improve yield and quality of crops (biostimulants, biofertilizers), as well as induce pest and disease resistance (biopesticides).
... Marine algae are eukaryotic and prokaryotic photosynthetic organisms, and have more than 40,000 species, which play an important role in marine ecosystem (Khan et al., 2018). Their biomass has attracted significant attention due to their capability to grow on non-arable land, and they possess promising capacity for carbon sequestration (Gong and Jiang, 2011;Grima et al., 2003). Moreover, their valuable chemicals are regarded as a promising feedstock for biorefineries. ...
Marine microalgae offer a promising feedstock for biofuels and other valuable compounds for biorefining and carry immense potential to contribute to a clean energy and environment future.
However, it is currently not economically feasible to use marine algae to produce biofuels, and the potential bioactive chemicals account for only a small market share. The production of algal biomass with multiple valuable chemicals is closely related to the algal species, cultivation conditions, culture systems, and production modes. Thus, higher requirements for screening of dominant algal strains, developing integrated technologies with the optimum culture conditions, efficient cultivation systems, and production modes to exploit algal biomass for biorefinery applications, are all needed. This review summarizes the screening of dominant microalgae, discusses the environmental conditions that may affect the growth, as well as the culture systems and production modes, and further emphasizes the valorization options of the algal biomass, which should help to offer a sustainable approach to run a profitable marine algae production system.
... Transesterification is the most ordinary procedure in the biodiesel yield from microalgae lipids (Zhou et al., 2012a). Transesterification is a multi-step continuous reaction in which triglyceride is generally reacted with methanol (methanolysis) and transformed into monoglycerides, diglycerides, eventually producing the fatty acid methyl ester (FAME, called biodiesel) and corresponding glycerol (by-products) (Gong and Jiang, 2011). Fig. S1 showed the overall reactions to transesterification. ...
The boost of the greenhouse gases (GHGs, largely carbon dioxide – CO2) emissions owing to anthropogenic activity is one of the biggest global threats. Bio-CO2 emission reduction has received more and more attention as an environmentally sustainable approach. Microalgae are very popular in this regard because of excellent speed of growth, low costs of production, and resistance to extreme environments. Besides, most microalgae can undergo photosynthesis, where the CO2 and solar energy can be converted into sugar, and subsequently become biomass, providing a renewable and promising biofuel strategy with a few outstanding benefits. This review focuses on presenting CO2 sequestration by microalgae towards wastewater treatment and biodiesel production. First, the CO2 fixation mechanism by microalgae viz., sequestration and assimilation of CO2 in green microalgae as well as cyanobacteria were introduced. Besides, factors affecting CO2 sequestration in microalgae, containing microalgae species and cultivation conditions, such as light condition, photobioreactor, configuration, pH, CO2 concentration, temperature, and medium composition, were then comprehensively discussed. Special attention was given to the production of biodiesel as third-generation biofuel from various wastewater (CO2 biofixation), including processing steps of biodiesel production by microalgae, biodiesel production from wastewater, and improved methods. Furthermore, current life cycle assessment (LCA) and techno-economic analysis (TEA) used in biodiesel production were discussed. Finally, the research challenges and specific prospects were considered. Taken together, this review provides useful and updated information to facilitate the development of microalgal “green chemistry” and “environmental sustainability”.
... The consequences can be seen in the form of climate change due to the greenhouse effect. Hence, scientists, legislators, and governments are all seeking a superior alternative source of energy (Gong and Jiang, 2011). ...
The world is substantially reliant on fossil fuels and the rapid depletion of these fuels raise the concern to find out alternative efficient energy resources. Microalgae biofuels emerged as one of the promising alternate renewable sources of energy that have the capability to substitute fossil fuels. This paper presents a new approach to explore the assessment of the oil content in microalgae using microscopic images. A novel method for the automatic estimation of oil content in the microalgae from the microscopic images has been developed in the present study using different imaging techniques. An automated computer vision based method is employed for the segmentation of the cells and oil content particles from the microscopic images of microalgae. The segmented cells were then analysed to compute the present oil particles as the main region of interest for the analysis of the lipid content. The proposed algorithm uses resolution invariant features such as the ratio of the area of the region of interests for the estimation of the oil content and that discriminatory information regarding the oil content remains unchanged under any resolution. Finally, the findings of the conventional approach were compared to the predicted values of the extracted oil content obtained from the proposed methodology where a low average error of 6.071% is obtained in all test microscopic image samples. The developed framework is computationally efficient and has a low time complexity, making it suitable for usage in real-world applications.
... Ma et al (2014) also suggest the N. oceanica IMET1 as an excellent strain for lipid production due to its high lipid productivity of 158 mg L -1 d -1 . The ideal microalgae as an alternative biodiesel source must have high growth rate, lipid content and lipid productivity (Griffiths & Harrison 2009;Gong & Jiang 2011). In addition, microalgal species with a wide salinity tolerance is preferred for outdoors cultivation to obtain reliable cultures for long period (Indrayani 2017;Indrayani et al 2019Indrayani et al , 2020. ...
Salinity affects growth and biochemical composition of microalgae and the ability of microalgae to tolerate wide range of salinity is one of the important criteria for successful mass cultivation in outdoor open pond systems for any commercial application. The aim of this study was to determine the growth and lipid production of the newly isolated marine microalga Nannochloropsis sp. UHO3 at increasing salinity. The strain was isolated from a coastal area in Kendari, Southeast Sulawesi, Indonesia in June 2017. The strain was cultured in 500 mL Schott bottles containing 300 mL f/2 medium at increasing salinities from 2 to 7% NaCl, light intensity of about 100 μmol photon m-2 s-1 , 12:12 hours light and dark cycles at ambient room temperatures. The highest specific growth rate (0.779±0.02 d-1) was achieved at 3% salinity and the lowest (0.455±0.02d-1) was obtained at 7% salinity. The cultures grown at 3% salinity had the highest lipid content and lipid productivity (22.06±2.92% Ash-Free Dry Weight (AFDW) and 0.161±0.009g L-1 d-1 , respectively). This study suggests that the alga has a wide salinity tolerance (2-7% NaCl) and produce high lipid at 3-4% salinity. Hence, the species is potential for outdoor mass cultivation in saline-hypersaline media for biodiesel feedstock due to its high growth rate and lipid productivity.
In spite of the increased energy requirement in the mechanical globe and the contamination issues induced by extensive utilization of renewable energies, the necessity for developing sustainable and eco-friendly energy sources is rising. Biodiesels are a significant alternative for petroleum-derived fuel with the advantages like renewability, eco-friendliness, lubricity, and flexibility. Microbes are highly efficient feed stocks for production of biodiesel owing to their least process requirements, rapid production rates, and ease of ramp up for technical development. The production of sustainable biodiesel using microbes has gained appreciable advances in commercialization. Recently, biodiesels derived using Rhodosporidium species, fungus, lignocellulose, and microalgae are commercialized. Sustainable biodiesel has been commercialized in different countries mainly Brazil, South Africa, the USA, the European Union, Indonesia, Malaysia, and Germany. The recent advances in microbial biodiesel commercialization and global biodiesel commercialization are described in this chapter. Different microbial sources and techniques for biofuel production are also summarized.
In today’s linear economy, waste streams, environmental pollution, and social economic problems are increasing with population growth. Biorefinery is the sustainable processing of renewable biomass into a spectrum of marketable bio-based products and energy chemicals. To overcome the growing gap between environmental sustainability and economic growth and to achieve the goal of a circular economy, the development of a circular bio-based industry, where biomass and its by-products can be processed into biofuels, biochemicals, biomaterials, feed, and food, is mandatory. Since the biorefineries combine the necessary technologies for the conversion of biomass to cost-competitive bio-based energy chemicals become a commercial reality. In this chapter, a succinct overview of the classification of biorefineries, natural feedstocks, current challenges on the biorefineries, and important aspects of future perspectives has been provided.
Microalgae such as Chlorella pyrenoidosa, Scenedesmus obliquus and Chlorella sorokiniana were cultivated in domestic wastewater for biohydrogen production. The comparison between the microalgae was executed based on biomass productions, biochemical yields and nutrient removal efficiencies. S. obliquus showed the possibility of growing in domestic wastewater reaching maximum biomass production, lipid, protein, carbohydrate yield and nutrient removal efficiency. All the three microalgae reached high biomass production of 0.90, 0.76 and, 0.71 g/L, respectively for S. obliquus, C. sorokiniana and C. pyrenoidosa. A higher protein content (35.76%) was obtained in S. obliquus. A similar pattern of lipid yield (25.34-26.23%) and carbohydrate yield (30.32-33.21%) was recorded in all selected microalgae. Chlorophyll-a content was higher in synthetic media-grown algae compared algae grown in wastewater. The maximum nutrient removal efficiencies achieved were 85.54% of nitrate by C. sorokiniana, 95.43% of nitrite by C. pyrenoidosa, ∼100% of ammonia and 89.34% of phosphorus by C. sorokiniana. An acid pre-treatment was applied to disintegrate the biomass of microalgae, followed by dark fermentation in batch mode to produce hydrogen. During fermentation process, polysaccharides, protein and lipids were consumed. Maximum hydrogen production of 45.50 ± 0.32 mLH2/gVS, 38.43 ± 0.42 mLH2/gVS and 34.83 ± 1.82 mL/H2/gVS was achieved by C. pyrenoidosa, S. obliquus and C. sorokiniana respectively. Overall, the results revealed the potential of microalgal cultivation in wastewater coupled with maximum biomass production lead to biohydrogen generation for environmental sustainability.
O setor agrícola e agroindustrial surge como impulsionadores da economia do Brasil e de muitos países em desenvolvimento. Porém suas atividades causam preocupações acerca dos impactos ambientais que têm gerado ao ambiente. Dessa forma, várias pesquisas surgem em busca de alternativas para diminuir os efeitos adversos. As microalgas têm sido utilizadas para minimizar o impacto ambiental causado por algumas atividades do setor agroindustrial, em função de seus vários fatores benéficos. Podem ser aplicadas em diversas vertentes do ramo agrícola e tecnológico. No entanto, apesar dos atributos serem favoráveis ao solo, plantas e ambiente, ainda não é amplamente difundido em território brasileiro. O objetivo do trabalho foi discorrer sobre os benefícios das microalgas em várias atribuições do setor agrícola e agroindustrial. A metodologia utilizada neste trabalho foi a revisão bibliográfica. Foram abordados aspectos sobre os efeitos das microalgas como biofertilizantes na agricultura, o uso na limpeza de efluentes oriundos na suinocultura, como fonte de cultivo em vinhaça e, por fim, os impactos socioeconômicos e ambientais na produção de biocombustíveis. Concluiu-se que a utilização desse micro-organismo nos setores agrícola e agroindustrial é promissor. Seu principal papel se desempenha na busca pela atenuação dos impactos ambientais para agricultura e pecuária, além de auxiliar na redução de custos com produção de biocombustíveis, já que as microalgas não interferem negativamente na produção dos produtos agrícolas e energéticos. Palavras-chave: Biofertilizantes. Efluentes da Suinocultura. Biocombustíveis. Impacto Ambiental. Abstract The agricultural and agro-industrial sectors are the economy driving forces in Brazil and in many developing countries, but their activities cause concerns about the environmental impacts it has generated on the environment, so several studies have emerged in search of alternatives to decrease these adverse effects. Microalgae have been used to minimize the environmental impact caused by some activities in the agro-industrial sector due to its many beneficial factors and can be applied in different aspects of the agricultural and technological fields. However, although the attributes are favorable to the soil, plants and the environment, it is still not widespread in Brazilian territory. The objective of this study was to discuss the benefits of microalgae in various attributions of the agricultural and agro-industrial sector. The methodology used in this work was the literature review. It addressed their effects as biofertilizers in agriculture, their use in cleaning effluents from pig farming and as a source of cultivation in vinasse, and finally, the socioeconomic and environmental impacts on the biofuels production. It is concluded that the use of this microorganism in the agricultural and agro-industrial sectors is promising, with its main performance being the search for the environmental impacts mitigation for agriculture and livestock, as well as helping to reduce costs with the biofuels production, since microalgae do not interfere negatively in the production of agricultural and energy products. Keywords: Biofertilizers. Swine Effluents. Biofuels. Environmental Impact.
The current world energy crisis and increasing greenhouse gas emissions demand a shift from fossil-based fuels to alternative and sustainable biofuels. The innate potential of microalgae over traditional terrestrial feedstocks to provide a high-quality and sustainable fuel portfolio has been recognized. Microalgae are known to mitigate atmospheric CO2 and convert it to valuable metabolites and bioactive compounds. The high growth rate of microalgal biomass with no additional requirements of feed and arable land makes microalgae as realistic alternative to existing biofuels sources. Micro-algae can store more primary metabolites under abiotic stress, which can be used as a possible source of energy. These metabolite storing abilities of microalgae have become a point of interest for the scientific community as the accumulated lipids serve as potential feedstock for biodiesel production by transesterification, whereas the carbohydrates can be used as the feedstock for bioethanol production by fermentation. Although microalgae-based biofuels are viable sources of energy, their commercialization and deployment in the fuel market remain a challenge. As a result, efforts are being undertaken to make it more cost-effective. This review describes the microalgae biorefinery method for producing biofuel along with its commercial potential, latest research updates in biofuel research, strategies to improve the algal metabolite content along with the limitations of using algal biomass for biofuels with possible solutions to overcome those limitations.
The purpose of this present study is to demonstrate the potentialities of the alga Chlorella pyrenoidosa as a source of energy of third generation, based on the increase of biomass yield, by the use of systems of culture developed, these latter are doped by are doped with optically active molecules, allowing for shifting the light to the area of photosynthesis adapted to the alga, what increasing the maximum biomass concentration compared to the neutral system (non-doped) chosen as a reference by a factor of 2 from 3 th days of culture. We have also, realized a simple extraction of the oil of cultivated alga, the yield acquired is interesting, it is of the order of 40.17%, this oil undergoes a conversion to a biodiesel by the reaction of transesterification, which gives us a yield of 92.56%. In effect, based on the results above, this work leads to the conclusion that, the alga Chlorella pyrenoidosa rich in lipids ,constitutes a choice dilicate for the operate as raw material for the production of energy that is sustainable and renouvlabe.
Microalgae are one of the impressive life forms. Since microalgae are a photosynthetic organism, they are produced in conditions which include light, water, CO 2 , nutrients and with proper temperature and pH. Hence, the cultivation circumstances of microalgae are of great importance for maximum production. Lately, microalgae are in the spotlight for biofuel generations, microalgal compounds and industrial uses. Furthermore, biofuels created from microalgae are recognized as the most important renewable sources of industrial manufacturing. This chapter explicates general information about algae, and systems used to cultivate microalgae for these applications and future research.
In this review article, recent contributions of potential uses of microalgae (green and cyanobacteria) in the agricultural and livestock sector, such as in the production of biofertilizers, biostimulants, and soil conditioning, are presented and discussed. Recent research was compiled to provide information on the productivity in microalgae biomass, dry biomass, and percentages of proteins from microalgae biomass, in addition to the definition of the best models of photobioreactors available for the cultivation of over thirty microalgae species. Ideal cultivation conditions, including the use of seven types of wastewaters as a substrate, are presented to show readers the best production routes for this specific type of biomass. Information on improvements in environmental services provided by microalgae cultivation are also included, such as bioremediation of wastewater and recovery of resources, in addition to the biofixation of CO2, which serves to mitigate air pollution. The bioremediation potential of mixotrophic, heterotrophic, and photoautotrophic microalgae cultures is demonstrated in the average removals of COD (71.1%), BOD5 (78.2%), NH4⁺ (93.4%), and P (88.5%) found according to the cited articles. Comparisons between the performance of biomass versus conventional fertilizers are discussed critically and objectively, based on the results of experiments with more than ten crop plants. Furthermore, to fulfill the purpose of this mini review, the research needs for future advancements of modern agriculture using microalgae are highlighted, including assessments on different soil types, plants, and microalgae biomass application methods. Finally, the challenges faced by microalgae biotechnology in expanding its contribution to the bioeconomy are also evaluated, namely, reducing pressure on natural resources, providing innovative agriculture, less dependent on energy inputs, and contributing to the sustainability of the planet.
As a substitute for conventional plastics in the market, bioplastics are winning their reputation. Pursuant to the researches carried out, in spite of being notably biodegradable in nature bioplastics have the similar qualities as conventional polymers. On the seeking for substitute for conventional plastics we found profusely existing, readily extractable algae as a superior source considering it does not rival with food roots for the bioplastic synthesis. This review covers the capacity of both microalgae and macroalgae in producing bioplastic considering polycarbohydrates present in the algae, such as cellulose, alginate, and carrageenan, have the ability to generate bioplastic. Consequently, the species employed as sources for bioplastic synthesis and various applications of algae-derived bioplastic were abbreviated.
Increasing pollution, exhausting fossil fuels and increasing demand for energy without harming human food lead researchers to microalgae as a useful source of biofuels. Microalgae behave like tiny reactors producing a variety of useful fuels. Microalgae have high biomass and oil content, which can easily be converted to fuels in one or two steps. Microalgae require minimal input for the growth – sunlight, CO 2 , water and a few nutrients that are already available in wastewater. It helps in reducing greenhouse gases as well as conserving our natural resources. It does not require separate land or water reservoir for the growth. When coupled with a wastewater treatment plant, the fuel production can be a cheaper and more sustainable technique. Cultivation of microalgae, production of biofuels and use of catalysis in biofuel applications are discussed in detail in this chapter. This third‐generation fuel needs researchers' attention to make it a wide, economic and environmentally friendly technique. The synergy approach towards biofuel production should be the next step for meeting the future energy demand.
Energy plays a crucial role in development and industrialization and is fulfilled by using non-renewable fossil fuels. The drawbacks of fossil fuels are non-renewable as well as the generation of toxic pollutants to the atmosphere. Thus, it will be very difficult to fulfil the energy demands in the future. Looking to the current energy needs, researchers are focussing on an alternative to fossil fuels. Biofuels are the sustainable option for the fulfilment of energy demands made up by biomass of different substrates. However, their conversion process is high cost, and low production rate makes them non-compatible to fossil fuels. Microalgae biomass is considered a good substrate for the production of biofuel. It accumulates lipids and carbohydrate in their cell which is generally biorefined for the production of biofuels. The microalgal is a substantial candidate for biofuel production and fulfilment of energy demand to resolving the upcoming energy crisis. Thus, this chapter discussed the role of microalgae and biorefinery steps for the production of biofuels.
Sustainability is an important part of natural resource management since it implies increased production efficiency, reduced environmental effects, and enhanced social welfare. Continuous usage of fossil fuels depletes reserves, generates greenhouse effects, and escalates climate-related problems. Therefore, the primary goal is to generate alternative renewable energy sources capable of satisfying energy demand. First-generation biofuels, derived mostly from food crops and oil seeds, and second-generation biofuels, derived primarily from nonfood crops and feedstock, are inefficient and contribute to the escalation of environmental issues. Recent technological advancements enable the production of third-generation biofuels from microalgae, which can be used as a viable alternative to first- and second-generation biofuels while mitigating the problems associated with first- and second-generation biofuels. Microalgae are photosynthetic organisms that grow in the form of sunlight, carbon dioxide, nutrients (nitrogen, phosphorus, and potassium), and carbohydrates. The principal components derived from microalgae are lipids, carbohydrates, and proteins. These valuable products need less time to produce and are an important source of biofuel. The current chapter focuses on methods for improving microalgae-to-biofuel conversion. It also emphasizes biomass growth technology, harvesting techniques, biomass conversion technologies, and value-added microalgae commodities. Furthermore, it discusses the benefits and environmental prospects of using biofuels as an alternative to renewable energy resources, as well as the challenges and recommendations in commercial biofuel applications.
The release of organic and inorganic pollutants generated from domestic, agricultural, and industrial water activities can have a serious impact on the environment. Conventional treatment processes (primary and secondary) have shown excellent efficiencies in removing the easily settled solids and oxidizing the organic matters present in wastewater. However, secondary effluents are loaded with nutrients (nitrogen and phosphorus), cause eutrophication, and more long-term environmental problems due to the presence of refractory organics and heavy metals that are discharged. Microalgae-based wastewater treatment systems are gaining popularity in recent years and offer a simple and cost-effective tertiary biotreatment process combined with the production of valuable biomass that can be utilized for several purposes. Microalgae include eukaryotic microalgae and prokaryotic cyanobacteria, which have high potential to grow in a harsh environment, can utilize inorganic carbon and nutrients, and are capable of photosynthesis. As a result, microalgae can be used to remove carbon, nitrogen, and phosphorus from wastewater and aid disinfection due to the increase in pH during photosynthesis. Oxygen produced by microalgae can support the biological treatment of wastewater by providing oxygen to the heterotrophic bacteria. In addition, microalgae hold amazing potential for the removal of heavy metals, as well as some toxic organic compounds, and can be used for CO2 biofixation from the air, without the production of secondary pollutants. The produced algae biomass can be used for the production of food, biofuels, and different chemicals. Algae can have a good capacity for the production of polymer, fatty acids, pharmaceuticals, and cosmochemical products. In this chapter, we will highlight the role of micro-algae in the treatment of wastewater.
Emergent strategies for biofuel production have revolutionized the field of sustainable and eco-friendly energy generation. With decades of research inputs, scientists have now successfully started employing greener alternatives to traditional chemical syntheses. Green technological intervention in biofuel production largely relied on application of enzymatic biotransformation reactions, which essentially faced challenges of enzymatic availability, stability, reproducibility, cost-effectiveness and limited reusability. Technological advances coupled with handy molecular tools of metabolic and genetic engineering led to the development of robust whole-cell catalysts which removed the bottle-necks of free enzyme catalysis bringing a paradigm shift in biofuel technology. Fatty acid alkyl esters derived from transesterification of natural triglycerides, and commonly known as biodiesel, could largely be obtained by application of stable extra- and/or intracellular expression of lipases and transesterification capabilities attributed to new generation whole cell biocatalysts. Recently, the screening and isolation of such organisms suitable for application as whole cell catalysts in biodiesel production is focussed on sources usually considered to be wastes largely dumped in the environment. Organisms thriving on such waste materials are considered to be robust and are frequently tamed naturally to be tolerant to the conditions which are otherwise contemplated to be toxic for most other life forms. This chapter provides a comprehensive summary of research attempts being made for the development of whole cell catalysts obtained from a variety of wastes for their efficient application in biodiesel production.
The excessive demand for fossil fuels has caused severe environmental impacts, such as GHG-related effects and widespread pollution. Firstly, it is essential to identify the main problems arising from fossil fuel production and consumption, which will enable the search and implementation of technological, sustainable, and economical alternatives to mitigate the current issue. With the modern technological advances in this specific area, the use of biofuels has expanded, given their high potential of production from diverse classes of biomass. Producing biodiesel from microalgae oil specifically, as a way of obtaining clean and renewable energy, can play a significant role in this context, and the process is of high interest to the energy sector. Biodiesels are produced through mixtures of ethyl esters or fatty acid methyl esters, which are generated by the synthesis of oil with alcohol in the presence of the enzyme alcohol lipase. There are clear challenges linked to the new technologies employed to obtain biofuels from microalgae, and there also are strong prospects to these approaches, since they are very energy-efficient and environmentally friendly. Thus being, the present review describes the main aspects associated with biodiesel production from microalgae, highlighting the fundamentals of the technique, the immobilization processes followed, the use of solvents to optimize reaction media, bioreactor systems, as well as the performance optimization of microalgae biodiesel-based engines, while considering important economic and environmental aspects. Future trends in the biofuel scientific research and industry are also included, aiming at fostering discussions on the development of other significant advances in the use of microalgae lipase and oil technology for biodiesel production.
For thousands of years, crop production has almost entirely depended on conventional agriculture. However, the reality is changing. The ever-growing population, global climate change, soil degradation and biotic/abiotic stresses are a growing threat to food production and security. Thus, sustainable alternatives to increase crop production for a population projected to reach 9.8 billion by 2050 are a major priority. In addition to vertical and soilless farming, innovative products based on bioresources, including plant growth stimulants, have been a target for sustainable food production. Such solutions have led to the exploitation of microorganisms, including microalgae and cyanobacteria as potential bioresources for food and plant biostimulant products. Microalgae (eukaryotic) and cyanobacteria (prokaryotic) are photosynthetic microorganisms with the capacity to synthesize a vast array of bioactive metabolites from atmospheric CO2 and inorganic nutrients. The present review outlines the nutritional value of microalgae and cyanobacteria as alternative food resources. The potential aspects of microalgae and cyanobacteria as stabilizers of the net change in soil organic carbon (C) levels for reduced farmland degradation are also highlighted. The applications of microalgae and cyanobacteria as remedies for improved soil structure and fertility, and as enhancers of crop productivity and abiotic stress tolerance in agricultural settings are outlined. This review also discusses the co-cultivation of crops with microalgae or cyanobacteria in hydroponic systems to favor optimum root CO2/O2 levels for optimized crop production.
Biostimulants play an important role in modern agricultural management. It involves exploitation of microorganisms as an eco-friendly tool for sustainable agriculture. This chapter focuses on use of micro and macroalgal biostimulants in crop production, summarizing methods of cultivation, harvest and extraction of bioactive principles. It also provides an overview on biochemical constituents of algal biostimulants which supports the usage of algal biostimulants for managing biotic and abiotic stresses in plants. It also examines the importance of algae in crop production and evaluated the benefits of soil amendments, seed priming, foliar spray and hydroponic systems. This chapter highlights the benefits of algae-based biofertilizers and biostimulants in enhancing plant growth, productivity and development of tolerance to various abiotic stresses. The challenges in commercialization of algal biostimulants are also discussed along with the future prospects.
Fossil fuel a non-renewable and indispensable part of energy source, but its negative effects are enhancing pollution in the environment, and thus its replacement is necessary. Biofuel is a good option that is capable of meeting energy demand. Biofuels are made up by using various kinds of food crops and lignocellulosic biomass. But it competes with food crops, and its conversion process is very tedious and expensive, resulting in many problems. On the other hand, microalgae feedstock contains a lot of lipids and carbohydrates, which is a good choice for making biofuels. A series of process is required for biofuel formation from microalgae. It requires selection and screening of microalgae and biorefinery process. Their biorefinery process increases overall operational cost. Therefore, low-cost integrated approach is required for reducing the operational cost of biofuel production. Integrated approach such as utilization of wastewater and atmospheric carbon dioxide (CO2) can be used for microalgae cultivation. Genetic modification is another alternative integrated technology for enhancement of lipid and carbohydrate production which also reduces the overall cost. So this chapter elucidates the microalgae feedstock for biofuel production, their advantages and constraint that arise during biofuel production. This chapter also addresses the different low-cost integrated method that can reduce the overall cost of biofuel production. So, maybe this chapter delivers a piece of valuable information that will fill the gap in biofuel production.
The lipid production potential of 8 microalgae species was investigated. Among these eight species, the best strain was a dominant bloom-causing dinoflagellate, Prorocentrum donghaiense ; this species had a lipid content of 49.32±1.99% and exhibited a lipid productivity of 95.47±0.99 mg L ⁻¹ d ⁻¹ , which was 2-fold higher than the corresponding values obtained for the oleaginous microalgae Nannochloropsis gaditana and Phaeodactylum tricornutum . P. donghaiense, which is enriched in C16:0 and C22:6, is appropriate for commercial DHA production. Nitrogen or phosphorus stress markedly induced lipid accumulation to levels surpassing 75% of the dry weight, increased the C18:0 and C17:1 contents, and decreased the C18:5 and C22:6 contents, and these effects resulted in decreases in the unsaturated fatty-acid levels and changes in the lipid properties of P. donghaiense such that the species met the biodiesel specification standards. Compared with the results obtained under N-deficient conditions, the enhancement in the activity of alkaline phosphatase of P. donghaiense observed under P-deficient conditions could partly alleviate the adverse effects on the photosynthetic system exerted by P deficiency to induce the production of more carbohydrates for lipogenesis. The supernatant of the algicidal bacterium Paracoccus sp. Y42 culture lysed P. donghaiense without decreasing its lipid content, which resulted in facilitation of the downstream oil extraction process and energy savings through the lysis of algal cells. The Y42 supernatant treatment improved the lipid profiles of algal cells by increasing their C16:0, C18:0 and C18:1 contents and decreasing their C18:5 and C22:6 contents, which is favourable for biodiesel production.
IMPORTANCE
This study demonstrates the high potential of P. donghaiense , a dominant bloom-causing dinoflagellate, for lipid production. Compared with previously studied oleaginous microalgae, P. donghaiense exhibit greater potential for practical application due to its higher biomass and lipid contents. Nutrient deficiency and the algicidal bacterium Paracoccus sp. Y42 could improve the suitability of the lipid profile of P. donghaiense for biodiesel production. Furthermore, Paracoccus sp. Y42 effectively lyse algal cells, which facilitates the downstream oil extraction process for biodiesel production and results in energy savings through the lysing of algal cells. This study provides a more promising candidate for the production of DHA for human nutritional products and of microalgal biofuel, as well as a more cost-effective method for breaking algal cells. The high lipid productivity of P. donghaiense and algal cell lysis by algicidal bacteria contribute to reductions in the production cost of microalgal oil.
Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester
carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers
worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted
to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based
ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases
for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns
about large biofuel mandates and highlights the value of using waste products.
This report has been commissioned by Sustainable Energy Ireland in order to provide an overview of marine
algae as an energy resource, from either macroalgae or microalgae. It is also required to assess the potential
resource in Ireland, determine the level of activity and identify research and development knowledge gaps.
A biofuels obligation scheme is being proposed in Ireland which will see a percentage of fossil-fuels for
transport being displaced by biofuels, ultimately reaching 10% (on an energy basis) by 2020. The
achievement of this ambitious target is contingent on finding and commercialising new resources for
transport fuel, as current feedstocks are not sufficient to meet the target.
Microalgae are being widely researched as a fuel due to their high photosynthetic efficiency and their ability
to produce lipids, a biodiesel feedstock. Macroalgae (or seaweeds) do not generally contain lipids and are
being considered for the natural sugars and other carbohydrates they contain, which can be fermented to
produce either biogas or alcohol-based fuels.
A supply-chain analysis was carried out for both macroalgae and microalgae, technologies identified and
research topics proposed to evaluate commercialisation potential of these resources for energy. For the
purposes of this report tentative roadmaps based on high, medium and low scenarios are hypothesised for
development of these resources by 2020.
Energy crises, global warming, and climatic changes call for technological and commercial advances in
manufacturing high-quality transportation fuels from unconventional feedstocks. Microalgae is one of the most
promising sources of biofuels due to the high yields attained per unit area and because it does not displace food crops. Neochloris oleabundans (Neo) microalga is an important promising microbial source of single-cell oil (SCO). DiVerent experimental growth and lipid production conditions were evaluated and compared by using optical density (540 nm), dry-weight determination, and flow cytometry (FC). Best Neo average biomass productivity was obtained at 30°C under conditions of nitrogen-sufciency and CO2 supplementation (N+/30°C/CO2), with an average doubling time of 1.4 days. The second and third highest productivities occurred with N-sufcient cultures without CO2 supplementation at 26°C (N+/26°C) and at 30°C (N+/30°C), with doubling times of 1.7 and 2.2 days, respectively. Microbial lipid production was monitored by flow cytometry using Nile red (NR), a lipophilic fuorochrome that possesses several advantageous characteristics for in situ screening near real time (at line). Results showed maximum lipid content (56%) after 6 days of nitrogen depletion under nitrogen starvation without CO2 supplementation (N¡/30°C), followed by N¡/30°C/CO2 and N¡/ 26°C conditions with 52% lipid content, after 5 and 6 days of N starvation, respectively. The adequate fatty acid pro- Wle and iodine value of Neo lipids reinforced this microalga as a good source of SCO, in particular for use as biodiesel.
An inexpensive and simple solar device was constructed and monitored for drying microalgal biomass with 90% moisture content. The drier is capable of producing about 140g dry biomass per sq.m of collector area in 3–5 hours. The dried biomass contains less than 10% moisture and is biologically of good quality. The experiments are done with two microalgae - Spirulina and Scenedesmus.
Biomass and eicosapentaenoic acid (EPA) productivities were investigated in a flat panel airlift loop reactor ideally mixed by static mixers. Growth with ammonium, urea and nitrate as nitrogen source were performed at different aeration rates. Cultures grew on ammonium but the decay of pH strongly inhibited biomass increase. On urea biomass productivity reached 2.35 g L–1d–1at an aeration rate of 0.66 vvm (24 h light per day, 1000 mol photon m–2s–1). Aeration rates between 0.33 vvm and 0.66 vvm and maximal productivities on urea were linearly dependent. Productivity on nitrate never exceeded 1.37 g L–1d–1. In the range of maximum productivity photosynthesis efficiency of 10.6% was reached at low irradiance (250 mol photon m–2s–1). Photosynthesis efficiency decreased to 4.8% at 1000 mol photon m–2s–1. At these high irradiances the flat panel airlift reactor showed a 35% higher volume productivity than the bubble column. At continuous culture conditions the influence of CO2concentration in the supply air was tested. Highest productivities were reached at 1.25% (v/v) CO2where the continuous culture yielded 1.04 g L–1d–1(16 h light per day, 1000 mol photon m–2s–1). The average EPA content amounted to 5.0% of cell dry weight, that resulted in EPA productivities of 52 mg L–1d–1(continuous culture, 16 h light per day) or 118 mg L–1d–1(batch culture, 24 h light per day).
Chlorella kessleri was cultivated in artificial wastewater using diurnal illumination of 12 h light/12 h dark (L/D) cycles. The inoculum density
was 105 cells/mL and the irradiance in light cycle was 45 μmol m2 s−1 at the culture surface. As a control culture, another set of flasks was cultivated under continuous illumination. Regardless
of the illumination scheme, the total organic carbon (TOC) and chemical oxygen demand (COD) was reduced below 20% of the initial
concentration within a day. However, cell concentration under the L/D lighting scheme was lower than that under the continuous
illuminating scheme. Thus the specific removal rate of organic carbon under L/D cycles was higher than that under continuous
illumination.
This result suggested thatC. kessleri grew chemoorganotrophically in the dark periods. After 3 days, nitrate was reduced to 136.5 and 154.1 mg NO3
−-N/L from 168.1 mg NO3
−-N/L under continuous illumination and under diurnal cycles, respectively. These results indicate nitrate removal efficiency
under continuous light was better than that under diurnal cycles. High-density algal cultures using optimized photobioreactors
with diurnal cycles will save energy and improve organic carbon sources removal.
Oxygen evolution from aScenedesmus obliquus dominated outdoor culture was followed in a small volume chamber, irradiated either by continuous white light or under light/dark frequencies between 0.05 to 5000 Hz, using arrays of high intensity red light emitting diodes (LED's). By placing neutral density filters in the path of the white light, light saturation curves of the oxygen evolution (P/I curves) were measured using diluted aliquots of algal cultures. The results clearly showed that photosynthetic rates increased exponentially with increasing light/dark frequencies, that a longer dark period in relation to the light period does not necessarily lead to higher photosynthetic rates (efficiencies), and that algae do not acclimate to a specific light/dark frequency. One of the most important factors that influenced photosynthetic rates, either under continuous illumination or intermittent, was whether the algae were dark or light acclimated. Low light/dark frequencies were perceived by the algae as low light conditions, whilst the opposite was true for high frequencies. The light utilisation efficiency in a fluctuating light/dark environment depended on the acclimated state of the algae, the specific frequency of the fluctuations and the duration of the exposure. Since the frequencies determined the perceived quantities of light, dark reactions played an important role in determining the average photosynthetic efficiencies. These results have important implications for algal biotechnology.
An account is given of the setting up and use of a novel type of closed tubular photobioreactor at the Academic and University Centre in Nove Hrady, Czech Republic. This "penthouse-roof" photobioreactor was based on solar concentrators (linear Fresnel lenses) mounted in a climate-controlled greenhouse on top of the laboratory complex combining features of indoor and outdoor cultivation units. The dual-purpose system was designed for algal biomass production in temperate climate zone under well-controlled cultivation conditions and with surplus solar energy being used for heating service water. The system was used to study the strategy of microalgal acclimation to supra-high solar irradiance, with values as much as 3.5 times the ambient value, making the approach unique. The cultivation system proved to be fully functional with sufficient mixing and cooling, efficient oxygen stripping and light tracking. Experimental results (measurement of the maximum photochemical yield of PSII and non-photochemical quenching) showed that the cyanobacterium Spirulina (= Arthrospira) platensis cultivated under sufficient turbulence and biomass density was able to acclimate to irradiance values as high as 7 mmol photon m–2 s–1. The optimal biomass concentration of Spirulina cultures in September ranged between 1.2 to 2.2 g L–1, which resulted in a net productivity of about 0.5 g L–1 d–1 corresponding to a biomass yield of 32.5 g m–2 d–1 (based on the minimum illuminated surface area of the photobioreactor).
AbstractDescribed are new solid base catalysts for transesterification of seed oil triglycerides to fatty acid methyl esters, a key
step in biodiesel production. These were prepared by substituting Fe3+ ions substitute for a fraction of the Al3+ ions in
the Mg/Al layered double hydroxide lattices of hydrotalcites (HTC) and calcining to give porous metal oxides (PMOs). These
iron-doped PMOs are much stronger bases than those derived from undoped or Ga3+ doped HTCs and are effective catalysts for
the methanol transesterification of triacetin (glycerol triacetate) and of soybean oil.
Graphical AbstractNew solid base catalysts for transesterification of seed oil triglycerides to fatty acid methyl esters, a key step in biodiesel
production, were prepared by substituting Fe3+ for Al3+ cations in hydrotalcite (HTC) structures and calcining to give porous metal oxides.
The use of algae to capture carbon dioxide as a method for greenhouse gas mitigation is discussed. A small fraction of the sunlight energy that bathes Earth is captured by photosynthesis and drives most living systems. Life on Earth is carbon-based and the energy is used to fix atmospheric carbon dioxide into biological material (biomass), indeed fossil fuels that we consume today are a legacy of mostly algal photosynthesis. Algae can be thought of as marine and freshwater plants that have higher photosynthetic efficiencies than terrestrial plants and are more efficient capturing carbon (Box 1). They have other favourable characteristics for this purpose. In the context of New Zealand energy strategy and policy I discuss progress in growing algae and seaweeds with emphasis on their application for exhaust flue carbon recycling for possible generation of useful biomass. I also introduce schemes utilising wild oceanic algae for carbon dioxide sequestration and the merits and possible adverse effects of using this approach. This paper is designed as an approachable review of the science and technology for policy makers and a summary of the New Zealand policy environment for those wishing to deploy biological carbon sequestration.
In this study, 120-l annular columns were used to cultivate Tetraselmis suecica outdoors. The mass transfer at different aeration rates and the influence of the harvest rate on productivity and biochemical composition were investigated. The potential of the system was evaluated by estimating productivity at full-scale. Two different arrangements to simulate a full-scale plant and determine the “overall areal productivity” (OAP) were experimented with. In August 2003, one experimental column (full-scale column) was placed between seven dummy columns. All the reactors were positioned at a distance of 0.8 m wall to wall and centred at the vertices of equilateral triangles. A second experimental column (isolated column) was placed in a separate area under full sunlight. In August 2004, the columns were placed side by side in an east–west oriented row at a distance of 0.24 m wall to wall.In the first experiment, the mean volumetric productivity of the full-scale column was not significantly lower than that achieved by the isolated column (0.46 against 0.49 g l− 1 day− 1) in spite of the shading by the dummy units. The average OAP and efficiency of conversion of visible solar radiation (PE) were 36.3 g m− 2 day− 1 and 9.4%, respectively. In the second experiment, the full-scale column attained a mean volumetric productivity of 0.42 g l− 1 day− 1. The OAP and the PE were 38.2 g m− 2 day− 1 and 9.3%, respectively.
Supplementary feeding was an effective method of enhancing growth of juvenile Pacific oysters (Crassostrea gigas) at a nursery site with low to moderate levels of natural phytoplankton (chlorophyll a, 0.68±0.29 μg l−1). Over five experiments, oysters (500–700 μm) were fed supplementary rations of live microalgae or microalgal pastes. Supplementary diets were added to naturally occurring seston at a ration of 7 mg day−1 ml−1 oysters (initial oyster bed volume). These levels increased the total phytoplankton concentration by 50 to 207%. Variation in the environmental conditions between experiments influenced oyster growth rates. Increases in oyster growth rates were high in animals supplemented with Chaetoceros calcitrans (instantaneous growth rate, k=0.062 day−1), Dunaliella tertiolecta (k=0.059 day−1), Isochrysis sp. (strain T. ISO) (k=0.059 day−1), an Australian isolate of Rhodomonas salina (k=0.074 day−1) and pastes of Skeletonema costatum (k=0.064 day−1) and C. calcitrans (k=0.059 day−1). These rates were significantly greater than in the oysters fed a reference supplementary diet, Pavlova pinguis (range for experiments; k=0.049–0.066 day−1) and in the control (i.e., non-supplementary fed) oysters (range for experiments, k=0.034–0.043 day−1). P. pinguis was a more effective diet when it was grown under 24:0 h L:D (k=0.066 day−1) than when grown under a 12:12 h L:D regime (k=0.061 day−1). C. calcitrans paste (4- to 14-days-old) (k=0.059 day−1) gave similar growth to live C. calcitrans (k=0.062 day−1), which indicated the promise of pastes as an off-the-shelf alternative to live diets. The effectiveness of D. tertiolecta—a diet lacking the polyunsaturated fatty acids 20:5n−3 and 22:6n−3—indicated that the oysters received sufficient quantities in background phytoplankton to sustain a high growth rate. The essential nature of these fatty acids was demonstrated when all oysters retained higher percentages of 20:5n−3 and 22:6n−3 than other fatty acids. Initial cost estimates for supplementary feeding show that it will add 2 to 3% to juvenile oyster production costs during the nursery phase when oysters are 0.5 to ∼3 mm in size.
The feasibility of removing algae from water and wastewater by chemical flocculation techniques was investigated. Mixed cultures of algae were obtained from both continuous- and batch-fed laboratory reactors. Representative cationic, anionic, and nonionic synthetic organic polyelectrolytes were used as flocculants. Under the experimental conditions, chemically induced algal flocculation occurred with the addition of cationic polyelectrolyte, but not with anionic or nonionic polymers, although attachment of all polyelectrolyte species to the algal surface is shown. The mechanism of chemically induced algal flocculation is interpreted in terms of bridging phenomena between the discrete algal cells and the linearly extended polymer chains, forming a three-dimensional matrix that is capable of subsiding under quiescent conditions. The degree of flocculation is shown to be a direct function of the extent of polymer coverage of the active sites on the algal surface, although to induce flocculation by this method requires that the algal surface charge must concurrently be reduced to a level at which the extended polymers can bridge the minimal distance of separation imposed by electrostatic repulsion. The influence of pH, algal concentration, and algal growth phase on the requisite cationic flocculant dose is also reported.
The extraction of cedarwood oil (CWO) using supercritical carbon dioxide (SC-CO2) has been investigated with respect to the effects of extraction temperature and pressure, length of extraction, and age of cedarwood chips. Steam distilled and SC-CO2 derived CWOs were compared by gas chromatography and sensory evaluation, The extraction of CWO increased with extraction temperature, except at the lowest pressure utilised. The highest percentage contribution of thujopsene to the SC-CO2 derived CWO occurred with the combination of 1500 psi and 70 degrees C or 100 degrees C. Essentially all of the CWO was extracted from the wood matrix in the first 10 min, however, complete extraction of water required ca, 25 min. The amount of CWO extracted decreased with increasing age of the cedarwood chips. This decrease was greatest for the more volatile hydrocarbon components, thujopsene and cedrene, The mean weight percentage yields of CWO for steam distillation and SC-CO2 extraction were 1.3 and 4.4%, respectively. An experienced analytical sensory panel selected the SC-CO2 derived CWO as being more similar to the original cedarwood chips than the steam distilled CWO, Volatile collections performed on SC-CO2 extracted, steam distilled and unextracted cedarwood chips indicated that the SC-CO2 extracted chips released almost no volatiles, whereas the unextracted chips released a higher amount of volatiles. The steam distilled cedarwood chips released an intermediate level of volatiles. Copyright (C) 2000 John Wiley & Sons, Ltd.
This paper is concerned with the performance of a relatively new form of metal-iron coagulant, Polyferric Sulphate (PFS), which has received very little research attention to date. Laboratory experiments have been undertaken in which the coagulation performance of PFS, Ferric sulphate, Aluminium sulphate and Poly aluminium chloride have been studied using 'model' waters containing single cultures of algae ( Anabaena flosaquae and Astenonella formosa) and other 'model' waters prepared by mixing aquatic humic substances with Asterionella formosa at different concentration ratios. Physico-chemical variables such as colloid charge, floc number concentration and size distribution, DOC concentration and turbidity, have been determined to quantify treatment performance. The performance of PFS was found to be superior to the other coagulants and this was believed to be due to the presence of more highly charged cation species. For all coagulants there was an approximate stoichiometry between coagulant dose and the dissolved organic carbon concentration.
Lipid decomposition studies in frozen fish have led to the development of a simple and rapid method for the extraction and purification of lipids from biological materials. The entire procedure can be carried out in approximately 10 minutes; it is efficient, reproducible, and free from deleterious manipulations. The wet tissue is homogenized with a mixture of chloroform and methanol in such proportions that a miscible system is formed with the water in the tissue. Dilution with chloroform and water separates the homogenate into two layers, the chloroform layer containing all the lipids and the methanolic layer containing all the non-lipids. A purified lipid extract is obtained merely by isolating the chloroform layer. The method has been applied to fish muscle and may easily be adapted to use with other tissues.
The effectiveness of the use of seawater and of magnesium in the removal of microalgae from oxidation pond effluents was investigated using the jar test procedure. The results indicated that the major flocculation reaction is the magnesium hydroxide precipitation at pH 11.5. The next step was to intensify the liquid-solids separation by use of a fluidized bed flocculator packed with 800 μm inert resin particles provided with an inclined multitubular settler. The total suspended solids abatement could reach 95% with a superficial upflow velocity of 30 m/h corresponding to a residence time through the whole unit of 5 minutes only. The energy requirement quantified by the pressure drop through the bed is very low. Besides, the waste sludge extracted from the settler is easily thickened.
The extraction of cedarwood oil (CWO) using supercritical carbon dioxide (SC-CO2) has been investigated with respect to the effects of extraction temperature and pressure, length of extraction, and age of cedarwood chips. Steam distilled and SC-CO2 derived CWOs were compared by gas chromatography and sensory evaluation. The extraction of CWO increased with extraction temperature, except at the lowest pressure utilised. The highest percentage contribution of thujopsene to the SC-CO2 derived CWO occurred with the combination of 1500 psi and 70°C or 100°C. Essentially all of the CWO was extracted from the wood matrix in the first 10 min, however, complete extraction of water required ca. 25 min. The amount of CWO extracted decreased with increasing age of the cedarwood chips. This decrease was greatest for the more volatile hydrocarbon components, thujopsene and cedrene. The mean weight percentage yields of CWO for steam distillation and SC-CO2 extraction were 1.3 and 4.4%, respectively. An experienced analytical sensory panel selected the SC-CO2 derived CWO as being more similar to the original cedarwood chips than the steam distilled CWO. Volatile collections performed on SC-CO2 extracted, steam distilled and unextracted cedarwood chips indicated that the SC-CO2 extracted chips released almost no volatiles, whereas the unextracted chips released a higher amount of volatiles. The steam distilled cedarwood chips released an intermediate level of volatiles. Copyright © 2000 John Wiley & Sons, Ltd.
A green alga, Chlorococcum littorale, has a tolerance to extremely high-CO2 conditions (Kodama et al., J. Marine Biotech. 1 (1993) 21–25). In order to elucidate the mechanism underlying the resistance to such high CO2 levels, we compared the changes in excitation energy ditribution between photosystem I (PS 1) and photosystem II (PS II) by 77 K fluorescence in cells of the high CO2-resistant C. littorale and the non-resistant Stichococcus bacillaris. Immediately after the cell are transferred from air to 40% CO2, the F714/F687 ratio derived from 77 K fluorescence increases in C. littorale cells, suggesting an increase of transition from state 1 to state 2. During this period, more than 80% of plastoquinone A is in the reduced form and the activity of PS I increass. Eventually the F714/F687 ratio, the concentration of reduced plastoquinone A and PS I activity decrease. However, no significant increase of F714/F687 ratio is observed after the transfer of S. bacillaris cells from air to 40% CO2. The level of reduced plastoquinone A in S. bacillaris gradually increases and the activity of PS I does not show a large change. During the transient period, the level of the D1 protein is approximately constant in C. littorale cells, but is lowered in S. bacillaris. These results suggest that, under extremely high-CO2 conditions, PS II is protected from photoinhibition by control of the state transition in C. littorale cells, whereas such a protection mechanism does not function in the alga S. bacillaris, non-resistant to CO2.
Of various methods for lipid recovery in Botryococcus braunii UTEX 572, the most effective method was disruption of the cells with a bead-beater followed by extraction with chloroform/methanol (2:1, v/v). This gave a lipid content of 28.6% of dry wt. There was a significant relationship between in vivo fluorescence of cells stained with Nile Red and lipid content in B. braunii determined gravimetrically (r2 = 0.997). This suggested that the Nile Red staining as a rapid method was as good as the gravimetric method commonly used for lipid determination which requires toxic solvents and considerable time-consuming manipulations. © Rapid Science Ltd. 1998
Cross-flow microfiltration and ultrafiltration techniques have become a suitable process for the separation of micro-organisms in a variety of biotechnical applications. In this paper, eight commercial membranes (IRIS, Orelis, Miribel, France) were evaluated for the harvest-ing of two marine microalgae: Haslea ostrearia and Skeletonema costatum, both widely cultivated in western France (Région des Pays de Loire). The effects of cross-flow velocity, transmembrane pressure, concentration and the characteristics of suspensions are discussed. The ultrafiltration membrane (polyacrylonitrile, 40 kDa) proves to be the most efficient in the peculiar conditions of low pressure and low tangential velocity for a long-term operation. © 1999 Elsevier Science B.V. All rights reserved.
The commercial culture of microalgae is now over 30 years old with the main microalgal species grown being Chlorella and Spirulina for health food, Dunaliella salina for β-carotene, Haematococcus pluvialis for astaxanthin and several species for aquaculture. The culture systems currently used to grow these algae are generally fairly unsophisticated. For example, Dunaliella salina is cultured in large (up to approx. 250 ha) shallow open-air ponds with no artificial mixing. Similarly, Chlorella and Spirulina also are grown outdoors in either paddle-wheel mixed ponds or circular ponds with a rotating mixing arm of up to about 1 ha in area per pond. The production of microalgae for aquaculture is generally on a much smaller scale, and in many cases is carried out indoors in 20–40 1 carboys or in large plastic bags of up to approximately 1000 1 in volume. More recently, a helical tubular photobioreactor system, the BIOCOIL™, has been developed which allows these algae to be grown reliably outdoors at high cell densities in semi-continuous culture. Other closed photobioreactors such as fiat panels are also being developed. The main problem facing the commercialisation of new microalgae and microalgal products is the need for closed culture systems and the fact that these are very capital intensive. The high cost of microalgal culture systems relates to the need for light and the relatively slow growth rate of the algae. Although this problem has been avoided in some instances by growing the algae heterotrophically, not all algae or algal products can be produced this way.
Phaeodactylum tricornutum and Chaetoceros sp. (Badllariophyceae), Isochrysis galbana (clone T-Iso) and Pavlova lutheri (Prymnesiophyceae), Nannochloris atomus (Chlorophyceae), Tetraselmis sp. (Prasinophyceae), and Gymnodinum sp. (Dinophyceae) were cultured at different extents of nutrient-limited growth: 50 and 5% of μmax. The lipid content of the algae was in the range 8.3–29.5% of dry matter and was generally higher in the Prymnesiophyceae than in the Prasinophyceae and the Chlorophyceae. Increasing extent of phosphorus limitation resulted in increased lipid content in the Bacillariophyceae and Prymnesiophyceae and decreased lipid content in the green flagellates N. atomus and Tetraselmis sp.
The fatty acid composition of the algae showed taxonomic conformity, especially for the Bacillariophyceae, where the major fatty adds were 14:0, 16:0, 16:1, and 20:5n-3. These fatty acids were dominant also in the Prymnesiophyceae together with 22:6n-3. An exception was I. galbana, in which 18:1 was the major monounsaturated fatty add and 20:5n-3 was absent. The fatty acids of N. atomus and Tetraselmis sp. varied somewhat, but 16:0, 16:1, 18:1, 18:3n-3, and 20:5n-3 were most abundant. Gymnodinum sp. contained mainly 16:0, 18:4n-3, 20: 5n-3, and 22:6n-3. An increased level of nutrient limitation (probably phosphorus) resulted in a higher relative content of 16:0 and 18:1 and a lower relative content of 18:4n-3, 20:5n-3, and 22:6n-3. The nutrient limitation probably reduced the synthesis of n-3 polyunsaturated fatty acids.
Ethanol was used for the extraction and purification of lipids from the biomass of the microalga Phaeodactylum tricornutum. This microalga is an oil-rich substrate with a high proportion of eicosapentaenoic acid (EPA). The process consisted of two steps. First, ethanol (96% vol/vol) was used to extract the lipids from the lyophilized biomass. Second, a biphasic system was formed by adding water and hexane to the extracted crude oil. In this way, most of the lipids were transferred to the hexanic phase while most impurities remained in the hydroalcoholic phase. The first step was carried out by two consecutive extractions at room temperature, each with 5 mL ethanol per gram of biomass, for 10 and 1.25 h, respectively. Under these conditions, over 90% of the saponifiable lipids in the biomass were extracted. In the second step, the percentage of water in the hydroalcoholic phase, the hexane/hydroalcoholic phase ratio and the number of extraction steps were optimized. A water content of 40% vol/vol in the hydroalcoholic phase provided the highest lipid recovery. A recovery yield of 80% was obtained by four consecutive extractions with a hexane/hydroalcoholic phase ratio of 0.2 (vol/vol). Equilibrium distribution data of the lipids between the hydroethanolic and the hexanic phases were also obtained in order to predict the lipid recovery yield of the extraction. This process is an alternative to the traditional methods of lipid extraction, which uses less toxic solvents and reduces the total amount of solvents used.
A series of [Mg(1−x)Alx(OH)2]x+(CO3)x/n2− hydrotalcite materials with compositions over the range x = 0.25–0.55 have been synthesised using an alkali-free coprecipitation route. All materials exhibit XRD patterns characteristic of the hydrotalcite phase with a steady lattice expansion observed with increasing Mg content. XPS measurements reveal a decrease in both the Al and Mg photoelectron binding energies with Mg incorporation which correlates with the increased intra-layer electron density. All materials are effective catalysts for the liquid phase transesterification of glyceryl tributyrate with methanol for biodiesel production. The rate increases steadily with Mg content, with the Mg rich Mg2.93Al catalyst an order of magnitude more active than MgO, with pure Al2O3 being completely inert. The rate of reaction also correlates with intralayer electron density which can be associated with increased basicity.
The variations over time of reactions in lipid classes of Nannochloropsis salina (Monodopsidaceae) and Pauloua lutheri (Prymnesiophyceae) during batch culture growth were studied using a thin layer chromatography-flame ionization detection (TLC-FID) system. The lag phase was marked by an abundance of hydrocarbons in both N. salina (78% of total lipids) and P. lutheri (48%), primarily polyunsaturated hydrocarbons for the former and saturated and monounsaturated hydrocarbons for the latter. The percentages of these compounds lessened rapidly during the exponential phase to reach 2.3 and 4.8% respectively of total lipids.There was no lipid storage during the exponential growth phase. By contrast, during the stationary phase lipids accounted for as much as 50% of dry weight in N. salina and for 30% in P. latheri. The triglycerides, which are primary reserve lipids, showed more rapid anabolism in N. salina (36.5 μg mm−3 biovolume d−1) than in P. lutheri (7.6 μm−3 d−1).The cellular quota of polar lipids in P. lutheri decreased (29 μg mm−3 biovolume) during the stationary phase. This phenomenon parallels the deterioration of the cells caused by nutritive deficiencies which are normal at this stage of growth. Nannochloropsis salina, however, showed no response to this factor.A significant quantity of wax and sterol esters was also found particularly during the first day in both N. salina (95 μg mm−3 biovolume) and P. lutheri (54 μg mm−3 biovolume).Other minor lipid compounds were also identified: alcohols, free fatty acids, free sterols and a pigment peak.
The growth of the red microalga it Porphyridium sp was studied in three bench-scale bioreactors of 13 dm3 volume: a bubble column, an airlift reactor and a modified airlift reactor with helical flow promoters in the top of the downcomer. Most of the experiments reported were run with a photon flux density of 250 µE m−2 s−1, but other illuminances were studied as well. Superficial gas velocities were in the range of 5.4 × 10−4 to 82 × 10−4 m s−1 (0.033–0.5 vvm). Algal growth in the airlift reactor with helical flow promoters had lower gas requirements than in the other reactor configurations. This implies lower costs in air compression and in air and CO2 requirements. It was concluded that the advantages found are related to the particular fluid dynamic characteristics of the reactor.© 2000 Society of Chemical Industry
On the basis of initial harvesting efficiency trials and screening trials to evaluate apparent cell damage and viability, high-speed centrifugation was selected as the most appropriate microalgae harvesting method for developing extended shelf-life concentrates that would collectively meet the requirements of marine hatcheries and nurseries. Bioassay evaluation of stored microalgae concentrates revealed major discrepancies between closely related species of microalgae with regard to the impact of harvesting method on both short-term nutritional quality and shelf-life of stored concentrates. At one extreme, very good retention of nutritional quality was exhibited by high-speed-centrifuged concentrates of Tetraselmis spp. and Chaetoceros calcitrans beyond 8 weeks storage. In contrast, the naked flagellates Pavlova lutheri and Tahitian Isochrysis and the diatom Chaetoceros muelleri exhibited rapid and profound losses in nutritional quality as a consequence of supercentrifugation. Likewise, the impact of storage conditions and the effects of preservatives and other common food additives on the quality and extended shelf-life of stored concentrates was found to be unpredictable and highly species specific. Accordingly, optimum combinations of harvesting and storage, including optimum cell densities, presence or absence of food additives, temperature and, in some cases, gaseous atmosphere and light, had to be specifically tailored to individual species of microalgae in order to maximize the effective shelf-life of their concentrates. Data are presented demonstrating that the best binary concentrate diets developed during the course of this study could sustain growth and survival of larval and juvenile bivalves at rates similar to fresh microalgae culture even after storage periods of 6–8 weeks.
The algae are a polyphyletic, artificial assemblage of O2-evolving, photosynthetic organisms (and secondarily nonphotosynthetic evolutionary descendants) that includes seaweeds (macroalgae) and a highly diverse group of microorganisms known as microalgae. Phycology, the study of algae, developed historically as a discipline focused on the morphological, physiological and ecological similarities of the subject organisms, including the prokaryotic bluegreen algae (cyanobacteria) and prochlorophytes. Eukaryotic algal groups represent at least five distinct evolutionary lineages, some of which include protists traditionally recognized as fungi and protozoa. Ubiquitous in marine, freshwater and terrestrial habitats and possessing broad biochemical diversity, the number of algal species has been estimated at between one and ten million, most of which are microalgae. The implied biochemical diversity is the basis for many biotechnological and industrial applications.
In mass algal cultures, some form of agitation is usually provided; among other effects, this moves the organisms though an optically dense profile and provides mixing. During this transport, medium frequency fluctuations in the light energy supply are perceived by the algae, which are of the order of 1 Hz and less. It has been suggested that turbulence with the resultant light/dark cycles of medium frequency enhances productivity. However, turbulence has two major influences in a well mixed system: it facilitates fluctuating light regimes and increases the transfer rates between the growth medium and the cultured organism. An estimation of productivity as oxygen liberation was measured under laminar and turbulent flow rates, and varying light/dark ratios. Increased turbulence, which increased exchange rates of nutrients and metabolites between the cells and their growth medium, together with increased light/dark frequencies, increased productivity and photosynthetic efficiency.
The flocculation of a pure algal culture of Chlorella ellipsoidia, was evaluated by means of measurements of filtration rate, light transmission and electrophoretic mobility, at algal concentrations of 50–3000mg l−1, polymer concentrations of 0.01–1000 mg 1−1 at pH 4–7. Non-ionic and anionic polyacrylamides, and anionic polystyrene sulfonate with molecular weights of about 1,000,000 failed to show any flocculation at polymer concentrations from 0.01 to 200 mg 1−1. Cationic polyethyleneimine was effective as a flocculant as shown by the results from the three methods of measurement. There was a significant increase in flocculation efficiency as the polymer molecular weight increased from 800 to about 2000 but little improvement above 2000. An effect of pH from 4 to 7 was absent. A variation in the magnesium ion concentration from 2.45 to 0.005 g 1−1 in the nutrient did not produce any effect. Earlier results with crystalline silica and E. coli and these same polymers had shown a similar effect of molecular weight and an influence of pH. A brief discussion is presented on a comparison of results on algae with those of other colloids, it being especially significant that at the same concentration of biocolloid the algae need about 100 times higher concentration of polymer than do E. coli.
The ammonia and phosphorus removal efficiencies of the microalgae Chlorella vulgaris and Scenedesmus dimorphus, during biotreatment of secondary effluent from an agroindustrial wastewater of a dairy industry and pig farming, were evaluated. The microalgae were isolated from a wastewater stabilization pond near Santafé de Bogotá, Colombia. Batch cultures were made using both species in 4-1 cylindrical glass bioreactors each containing 2l of culture. Chlorella vulgaris was also cultivated on wastewater in a triangular bioreactor. Three 216-h experimental cycles were run for each microalga and in each bioreactor. In the cylindrical bioreactor, S. dimorphus was more efficient in removing ammonia than C. vulgaris. However, the final efficiency of both microalgae at the end of each cycle was similar. Both microalgae removed phosphorus from the wastewater to the same extent in a cylindrical bioreactor. Using C. vulgaris, the triangular bioreactor was superior for removing ammonia and the cylindrical bioreactor was superior for removing phosphorus. This study shows the potential of using these microalgae to reduce the environmental pollution of heavily contaminated agroindustrial waters currently disposed of untreated into the waterways and streams of tropical Colombia.
Transesterification reaction of rapeseed oil in supercritical methanol was investigated without using any catalyst. An experiment has been carried out in the batch-type reaction vessel preheated at 350 and 400°C and at a pressure of 45–65 MPa, and with a molar ratio of 1:42 of the rapeseed oil to methanol. It was consequently demonstrated that, in a preheating temperature of 350°C, 240 s of supercritical treatment of methanol was sufficient to convert the rapeseed oil to methyl esters and that, although the prepared methyl esters were basically the same as those of the common method with a basic catalyst, the yield of methyl esters by the former was found to be higher than that by the latter. In addition, it was found that this new supercritical methanol process requires the shorter reaction time and simpler purification procedure because of the unused catalyst.
Biodiesel (fatty acid methyl esters), which is derived from triglycerides by transesterification with methanol, has attracted considerable attention during the past decade as a renewable, biodegradable, and nontoxic fuel. Several processes for biodiesel fuel production have been developed, among which transesterification using alkali-catalysis gives high levels of conversion of triglycerides to their corresponding methyl esters in short reaction times. This process has therefore been widely utilized for biodiesel fuel production in a number of countries. Recently, enzymatic transesterification using lipase has become more attractive for biodiesel fuel production, since the glycerol produced as a by-product can easily be recovered and the purification of fatty methyl esters is simple to accomplish. The main hurdle to the commercialization of this system is the cost of lipase production. As a means of reducing the cost, the use of whole cell biocatalysts immobilized within biomass support particles is significantly advantageous since immobilization can be achieved spontaneously during batch cultivation, and in addition, no purification is necessary. The lipase production cost can be further lowered using genetic engineering technology, such as by developing lipases with high levels of expression and/or stability towards methanol. Hence, whole cell biocatalysts appear to have great potential for industrial application.
Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO2, N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products.
The gap between the theoretical biological potential of microalgae and the biomass productivity obtained with algal culture in tubular biophotoreactors is due to a reduced growth rate related to hydrodynamic stress of pumping. High levels of mixing are necessary to reach a turbulent flow of the culture, in order to optimize the light regime. The optimal conditions of pumping to produce this significant liquid mixing may produce some cell damage. Factors affecting this hydrodynamic stress (geometry of the bioreactor involved, type of pump utilized, morphology of algal cells, physiological conditions of microalgae, etc.) are discussed.
Comparative studies on transesterification methods were presented in this work. Biodiesel is obtained from a chemical reaction called transesterification (ester exchange). The reaction converts esters from long chain fatty acids into mono alkyl esters. Chemically, biodiesel commonly is a fatty acid methyl ester. Vegetable oils can be transesterified by heating them with a large excess of anhydrous methanol and an acidic or basic reagent as catalyst. A catalyst is usually used to improve the reaction rate and yield. In a transesterification reaction, a larger amount of methanol was used to shift the reaction equilibrium to the right side and produce more methyl esters as the proposed product. Several aspects including the type of catalyst (alkaline, acid or enzyme), alcohol/vegetable oil molar ratio, temperature, purity of the reactants (mainly water content) and free fatty acid content have an influence on the course of the transesterification. A non-catalytic biodiesel production route with supercritical methanol has been developed that allows a simple process and high yield because of the simultaneous transesterification of triglycerides and methyl esterification of fatty acids. In the catalytic supercritical methanol transesterification method, the yield of conversion rises to 60–90% for the first 1 min.
Vegetable oil fuels have not been acceptable because they were more expensive than petroleum fuels. With recent increases in petroleum prices and uncertainties concerning petroleum availability, there is renewed interest in vegetable oil fuels for Diesel engines. Dilution of oils with solvents and microemulsions of vegetable oils lowers the viscosity, but some engine performance problems still exist. The purpose of the transesterification process is to lower the viscosity of the oil. Pyrolysis produces more biogasoline than biodiesel fuel. Soap pyrolysis products of vegetable oils can be used as alternative Diesel engine fuel. Methyl and ethyl esters of vegetable oils have several outstanding advantages among other new renewable and clean engine fuel alternatives. The main factors affecting transesterification are the molar ratio of glycerides to alcohol, catalyst, reaction temperature and pressure, reaction time and the contents of free fatty acids and water in oils. The commonly accepted molar ratios of alcohol to glycerides are 6:1–30:1.
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.
A mathematical model to estimate the solar irradiance profile and average light intensity inside a tubular photobioreactor under outdoor conditions is proposed, requiring only geographic, geometric, and solar position parameters. First, the length of the path into the culture traveled by any direct or disperse ray of light was calculated as the function of three variables: day of year, solar hour, and geographic latitude. Then, the phenomenon of light attenuation by biomass was studied considering Lambert-Beer's law (only considering absorption) and the monodimensional model of Cornet et al. (1900) (considering absorption and scattering phenomena). Due to the existence of differential wavelength absorption, none of the literature models are useful for explaining light attenuation by the biomass. Therefore, an empirical hyperbolic expression is proposed. The equations to calculate light path length were substituted in the proposed hyperbolic expression, reproducing light intensity data obtained in the center of the loop tubes. The proposed model was also likely to estimate the irradiance accurately at any point inside the culture. Calculation of the local intensity was thus extended to the full culture volume in order to obtain the average irradiance, showing how the higher biomass productivities in a Phaeodactylum tricornutum UTEX 640 outdoor chemostat culture could be maintained by delaying light limitation. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 701-714, 1997.
Microalgae are considered one of the most promising feedstocks for biofuels. The productivity of these photosynthetic microorganisms
in converting carbon dioxide into carbon-rich lipids, only a step or two away from biodiesel, greatly exceeds that of agricultural
oleaginous crops, without competing for arable land. Worldwide, research and demonstration programs are being carried out
to develop the technology needed to expand algal lipid production from a craft to a major industrial process. Although microalgae
are not yet produced at large scale for bulk applications, recent advances—particularly in the methods of systems biology,
genetic engineering, and biorefining—present opportunities to develop this process in a sustainable and economical way within
the next 10 to 15 years.