Showing papers in "Algal Research-Biomass Biofuels and Bioproducts in 2013"

Process development for hydrothermal liquefaction of algae feedstocks in a continuous-flow reactor

Abstract: Wet algae slurries can be converted into an upgradeable biocrude by hydrothermal liquefaction (HTL). High levels of carbon conversion to gravity separable biocrude product were accomplished at relatively low temperature (350 °C) in a continuous-flow, pressurized (sub-critical liquid water) environment (20 MPa). As opposed to earlier work in batch reactors reported by others, direct oil recovery was achieved without the use of a solvent and biomass trace components were removed by processing steps so that they did not cause process difficulties. High conversions were obtained even with high slurry concentrations of up to 35 wt.% of dry solids. Catalytic hydrotreating was effectively applied for hydrodeoxygenation, hydrodenitrogenation, and hydrodesulfurization of the biocrude to form liquid hydrocarbon fuel. Catalytic hydrothermal gasification was effectively applied for HTL byproduct water cleanup and fuel gas production from water soluble organics, allowing the water to be considered for recycle of nutrients to the algae growth ponds. As a result, high conversion of algae to liquid hydrocarbon and gas products was found with low levels of organic contamination in the byproduct water. All three process steps were accomplished in bench-scale, continuous-flow reactor systems such that design data for process scale-up was generated.

Fatty acids profiling: A selective criterion for screening microalgae strains for biodiesel production

Abstract: The type and amount of lipids produced by an algal species directly influence the quality of the achieved biodiesel. This study is the first to report on the isolation process and lipid profile analysis of algal strains obtained from the Persian Gulf as well as 9 previously introduced strains. Biomass productivity and lipid productivity seemed to be adequate criteria for estimating the potential of different microalgae species for producing biodiesel. A principal component analysis (PCA) was applied to the estimated properties of biodiesel and the results obtained were plotted against lipid productivity. This led to the distinction of five different microalgae groups in regard to their potential for biodiesel production. This analysis also highlighted the dependence of the fuel properties on oil saturation level. On that basis, Amphora sp. and the two locally isolated strains ( Dunaliella sp.) formed the extreme groups. The other three groups generated biodiesel of intermediate quality. The highest volumetric lipid productivity (79.08 mg l − 1 day − 1 ) was found in Chlorella vulgaris . Based on the results of bioprospection by FAME profiling, the best approach for obtaining quality algal biodiesel is to mix the oils of distinct cell cultures or to specifically select proper microalgal strains for different climate conditions.

Comparison of microalgal biomass profiles as novel functional ingredient for food products

Abstract: Microalgae are one of the most promising sources for new food and functional food products, and can be used to enhance the nutritional value of foods, due to their well-balanced chemical composition. Knowing their physicochemical characteristics is fundamental for the selection of the most suitable microalgae to specific food technology applications and consequently successful novel foods development. The aim of this study is to screen the chemical composition (e.g., proteins, pigments, fatty acids) and thermogravimetry properties of five microalgae species with potential application in the food industry: Chlorella vulgaris (green and carotenogenic), Haematococcus pluvialis (carotenogenic), Spirulina maxima, Diacronema vlkianum and Isochrysis galbana. C. green and S. maxima presented high protein (38% and 44%, respectively), low fat content (5% and 4%, respectively). The carotenogenic C. vulgaris and H. pluvialis showed a higher carotenoid content, higher fat, low protein and better resistance to thermal treatment. D. vlkianum and I. galbana presented high protein (38–40%) and fat (18–24%) contents with PUFA's ω3, mainly EPA and DHA. Finally, the results from microalgae chemical and thermal analysis were grouped and correlated through Principal Components Analysis (PCA) in order to determine which variables better define and differentiate them.

Pilot plant testing of continuous hydrothermal liquefaction of microalgae

Abstract: We describe a pilot plant for continuous hydrothermal processing of biomass. Results were obtained for two microalgae strains, Chlorella and Spirulina , across a range of biomass loadings (1–10 wt.%), temperatures (250–350 °C), residence times (3–5 min) and pressures (150–200 bar). Overall, the bio-crude yields were found to increase with higher biomass loading, higher temperature and longer residence time. More severe reaction conditions also reduced the oxygen content of the bio-crude, while the nitrogen content was found to increase with higher temperatures, indicating an increase in the bio-crude production from the protein fraction of the algae. The maximum bio-crude yield obtained was 41.7 wt.% for processing Chlorella with a solid loading of 10 wt.% at 350 °C and 3 min residence time. The present results suggest that maximal yields may be obtained in much shorter residence times under continuous flow hydrothermal processing than batch studies have suggested. The maximal yield, however, may not be optimal in terms of properties. A substantial fraction of the feedstock carbon reported to the aqueous phase — this was up to 60% but decreased to 30% at the highest biomass loadings. Gas production (> 90 mol% CO 2 ) increased with severity of processing, reaching up to 5% of the feedstock carbon. Finally, the solid yields consistently decreased with increasing temperatures and residence times.

Pulsed electric field assisted extraction of intracellular valuables from microalgae

Abstract: This paper discusses the application of pulse electric field (PEF) treatment for the cell disintegration of the fresh water microalgae Auxenochlorella protothecoides. The algae were cultivated under controlled conditions in a closed photo-bioreactor. After algae harvest the algae suspensions were concentrated and PEF treated with square pulses with a duration of 1 μs. We investigated the influence of specific treatment energy (52–211 kJ/kg suspension), electric field strength (23–43 kV/cm) and biomass concentration (36–167 g dry weight per kg suspension) on cell disintegration. For all pulse parameters applied, the PEF induced cell disintegration resulted in the release of soluble intracellular matter into the suspension. The disintegration efficiency increased with increasing specific treatment energy, whereas the field strength hardly had any influence. For suspensions with a biomass content of 100 g dry weight per kg suspension the electrical energy input necessary for considerable cell rupture was in the range of 1 MJ/kg dried algae. This is equivalent to 4.8% of the upper heating value of the algae. Although the treated algae contained lipids, PEF treatment only led to the spontaneous release of soluble components. The selectiveness of the process might offer the opportunity to use PEF treatment in a biorefinery concept, where soluble algae ingredients are extracted before solvent extraction of lipids is performed.

Cultivation of microalgae on artificial light comes at a cost

Abstract: Microalgae are potential producers of bulk food and feed compounds, chemicals, and biofuels. To produce these bulk products competitively, it is important to keep costs of raw material low. Light energy can be provided by sun or lamps. Sunlight is free and abundant. Disadvantages of sunlight, however, include day/night cycles, changes in weather conditions, and seasonal changes. These fluctuations in irradiance can be prevented by applying artificial lighting. Artificial lighting will not only increase productivity but will also increase costs associated with microalgae cultivation. This cost increase is recognized, but a detailed quantitative evaluation was still missing. The costs and energy balance related to microalgae cultivation employing artificial light was evaluated with a literature study. We calculated that current application of artificial light will increase production costs by 25.3 $ per kilogram of dry-weight biomass. From these calculations, it was determined that 4% to 6% of energy from electric input is fixed as chemical energy in microalgae biomass. Energy loss and increased production cost may be acceptable in the production of high value products, but in general they should be avoided. Microalgae cultivation programs should therefore focus on employing sunlight.

New insights into the biodiversity and applications of cyanobacteria (blue-green algae)—Prospects and challenges

Abstract: Cyanobacteria (blue-green algae) are Gram-negative oxygenic photosynthetic prokaryotes with a long evolutionary history. They have potential applications in diverse areas, especially in agriculture, as nutrient supplements in agriculture and industry (as biofertilizer, plant growth promoting rhizobacteria and as biocontrol agents). Their role as food supplements/nutraceuticals and in bioremediation and wastewater treatment is an emerging area of interest. In addition, they are known to produce wide array of bioactive compounds (secondary metabolites) with diverse biological activities — including antiviral, antibacterial, antifungal, antimalarial, antitumoral and anti-inflammatory properties, having therapeutic, industrial and agricultural significance. One of the major problems has been regarding their classification being incongruent with the phylogeny, because the phenotype of cyanobacterial strains is known to be altered under different environmental/nutritional conditions. However, because of their simple growth needs, they are the favourite model organisms for deeper understanding of several metabolic processes and for the production of recombinant compounds of medicinal and commercial value. In recent years, cyanobacteria have gained interest for producing third generation biofuels (both biomass and H2 production). With the recent advances in metabolic engineering techniques and availability of genome sequences, novel approaches are being explored for realising the potential of cyanobacteria. Our review provides an overview of the polyphasic approaches used in the analyses of cyanobacterial biodiversity and the potential of these organisms in providing viable solutions to global problems of food, energy and environmental degradation, which need further impetus through adoption of multidisciplinary collaborative programs.

Development of hydrothermal liquefaction and upgrading technologies for lipid-extracted algae conversion to liquid fuels

Abstract: Bench-scale tests were performed for lipid-extracted microalgae (LEA) conversion to liquid fuels via hydrothermal liquefaction (HTL) and upgrading processes. Process simulation and economic analysis for a large-scale LEA HTL and upgrading system were developed based on the best available experimental results. The system assumed an LEA feed rate of 608 dry metric tons/day and that the feedstock was converted to a crude HTL bio-oil and further upgraded via hydrotreating and hydrocracking to produce liquid fuels, mainly alkanes. Performance and cost results demonstrated that HTL and upgrading is effective for converting LEA to liquid fuels. The liquid fuels annual yield was estimated to be 26.9 million gallon gasoline-equivalent (GGE) and the overall energy efficiency on a higher heating value (HHV) basis was estimated to be 69.5%. The variation range of the minimum fuel selling price (MFSP) was estimated to be $2.07 to $7.11/GGE by combining the effects of selected process factors. Key factors affecting the production cost were identified to be the LEA feedstock cost, final products yields, and the upgrading equipment cost. The impact of plant scale on MFSP was also investigated.

A review on production of poly β hydroxybutyrates from cyanobacteria for the production of bio plastics

Abstract: The increasing effect of non-degradable plastic wastes is a growing concern. As an alternative, researches are being attempted from living resource to produce bio plastics on the basis of their biodegradability. Due to their cost effect nature, now the scientists are searching an alternative resource like photoautotrophic cyanobacteria. In this review the promising importance and growing awareness of using cyanobacteria as PHB resource are being reported. Many publications evidenced that various cyanobacterial species accumulate intracellular poly-β-hydroxybutyrate granules as energy and carbon reserves inside their cells when they are in stress conditions. PHB is biodegradable, environmental friendly and biocompatible thermoplastics. Varying in toughness and flexibility, depending on their formulation, they can be used in various ways similar to many non-biodegradable petrochemical plastics currently in use. Promising strategies involve genetic engineering of microorganisms to introduce production pathways are being investigated for the past two decades. Such kind of researches focusing on the use of alternative substrates, novel extraction methods, genetically enhanced species and mixed cultures with a view to make PHB from cyanobacteria (blue green algae) more commercially attractive are presented and discussed.

Mixotrophic growth with acetate or volatile fatty acids maximizes growth and lipid production in Chlamydomonas reinhardtii

Abstract: We measured the growth of and lipid production by the model microalga Chlamydomonas reinhardtii under different phototrophic, heterotrophic, and mixotrophic conditions to determine the optimal conditions for growth and biodiesel production. In particular, we examined cell growth and yield of fatty acid methyl esters (FAMEs) when C. reinhardtii was cultured in the presence of different organic carbon sources (acetate, glucose, glycerol, and sucrose). C. reinhardtii grew under various conditions, but mixotrophic cultivation was best. The greatest biomass production (2.15 g L − 1 in 5 days) and FAME yield (16.41% of biomass) were observed under mixotrophic cultivation with acetate (10 g L − 1 ). As an alternative to acetate, we additionally tested the use of volatile fatty acids (VFAs; acetic, propionic, and butyric acids), which can be inexpensively produced through fermentation of food waste. The highest FAME yield (19.02% of biomass) and biomass production (2.05 g L − 1 in 5 days) were obtained with 5 g L − 1 of VFAs. This result indicates that VFAs can serve as an inexpensive alternative carbon source for maximizing lipid production in mixotrophic cultivation of C. reinhardtii .

Efficient coagulation of microalgae in cultures with filamentous fungi

Abstract: To overcome the daunting technical barriers of algae biofuels and photosynthetic biorefineries, a novel cultivation technology has been developed to concentrate, harvest, and enhance microalgae-based biofuels and bioproducts through pelletization. The technology involves the co-cultivation of microalgae with fungi to achieve optimized pelletization with a 2-to-10-mm diameter. This pelletization enables the complete removal of single algal cells from the liquid medium to allow their extraction and harvest by simple filtration. In addition, the pelletization process results in significantly increased biomass, lipid, and bioproduct yields. If successfully scaled up, this technology has the potential to improve the sustainability and economic viability of the production of algal biofuels.

Initial risk assessment of genetically modified (GM) microalgae for commodity-scale biofuel cultivation

Abstract: Genetic modification (GM) of microalgae to improve commercial production of biofuels is underway. Inevitable governmental regulations will likely address environmental, economic and human health impacts. Proactive addressing of such regulatory protection goals should begin now, during early development of this new, potentially large and transformative industry. We present strategies for ecological risk assessment of GM algae for commercial mass cultivation assuming that escape of GM algae into the environment is unavoidable. We consider the potential ecological, economic and health impacts of GM algae that persist in and alter natural ecosystems. Horizontal gene transfer with native organisms is of particular concern for certain traits, especially when cultivating GM cyanobacteria. In general, we predict that most target GM algal traits are unlikely to confer a selective advantage in nature, and thus would rapidly diminish, resulting in low but nonzero ecological risk. Genetic and mechanical containment, plus conditional matching of GM algal traits to unnatural cultivation conditions, would further reduce risk. These hypothetical predictions must be verified through rigorous ongoing monitoring and mesocosm experiments to minimize risk and foster public and regulatory acceptance.

Screening and selection of growth-promoting bacteria for Dunaliella cultures

Abstract: Previous studies have demonstrated that bacteria influence microalgal metabolism, suggesting that the selection and characterization of growth-promoting bacteria should offer a new strategy for improving industrial algal cultivation. In the present study, 48 cultivable bacteria were isolated from marine microalgae species and identified using 16S rRNA phylogenetic analysis. The recovered bacteria were found to be members of the α- and γ-Proteobacteria, Cytophaga–Flavobacterium–Bacteroides (CFB) and gram-positive monophyletic clusters. To address the effect of these bacteria on the growth of Dunaliella sp. individually, an experimental high-throughput tool was developed to simultaneously compare replicated associations. A two-step approach was used to monitor growth rate and biomass accumulation of Dunaliella sp. in mixed culture with bacteria, which proved the high-throughput device to be an efficient tool for the selection of growth-promoting bacteria. Depending on the bacterial strain involved, inhibitory effects were recorded for maximal microalgal growth rate, whereas inhibitory and stimulating effects were registered on microalgal biomass accumulation and nitrogen incorporation. Organic nitrogen remineralization by Alteromonas sp. SY007 and Muricauda sp. SY244 is discussed to explain the higher biomass and ammonium incorporation of Dunaliella sp. obtained under nitrogen-limited conditions. These bacteria could be considered as helpers for N accumulation in Dunaliella sp. cells.

Optimizing protein isolation from defatted and non-defatted Nannochloropsis microalgae biomass

Abstract: Microalgae are a promising source of lipids for biofuel production. To improve the economic feasibility and sustainability of this biofuel feedstock, one should create value for co-products after lipid extraction. Thus, protein isolation from the defatted biomass presents an opportunity. To extract algae protein, temperature and pH were evaluated to maximize the extraction from Nannochloropsis biomass. Maximum quantity of protein was solubilized at 60 °C and pH 11 and recovered at pH 3.2. The isolated protein fractions contained 56.9% and 40.5% protein when using isopropanol (IPA) defatted and non-defatted biomass as the starting materials, with protein yields being 16 and 30%, respectively. The IPA-defatting treatment significantly decreased the protein extraction yield. These values are low compared with soybean protein isolates (> 90% protein and ~ 60% yield). The relatively high protein content (> 34%) in the pH 11 insoluble fraction indicates needs for further extraction optimization. The nitrogen and amino acid content of the initial materials and all the fractions were determined and the calculated nitrogen to protein conversion factor was in the range of 4.06–4.70. The possibility of the presence of conjugated protein, i.e., N-containing glycoproteins, is also discussed.

Feedstocks for fuels and chemicals from algae: Treatment of crude bio-oil over HZSM-5

Abstract: Crude bio-oil produced from hydrothermal liquefaction of Nannochloropsis sp was reacted over HZSM-5 catalyst with high pressure H2. The effects of reaction temperature (400–500 °C), reaction time (0.5–4 h), and catalyst loading (5–50 wt.%) on the composition and yields of the oil and gas products were determined. Treatment greatly reduced the heteroatom (N, O, and S) content in the oil. S was reduced to below detection limits (< 0.1 wt.%) at all reaction conditions investigated. The lowest N/C ratio achieved is about 25% of the original N/C ratio in the crude bio-oil. The O/C ratio of the oil treated at 450 and 500 °C was an order of magnitude lower than that in the crude bio-oil. The carbon content of the oil increased at all reaction conditions investigated, but the H/C ratios of the oils treated at 450 and 500 °C fell below that of the crude bio-oil due to their high aromatic content and the migration of H atoms into the gaseous products. This study demonstrates the opportunities to engineer the composition of the products that emerge from this catalytic treatment of the crude bio-oil. Catalytic processing at 400 °C produced a paraffinic oil that was 95 wt.% C and H and retained 87% of the energy content of the crude bio-oil. This product would be useful as a feedstock for liquid transportation fuels. Catalytic processing at 500 °C, on the other hand, produced a freely flowing liquid mixture composed of aromatic hydrocarbons in 44 wt.% yield along with a hydrocarbon gas stream in 19 wt.% yield. These products, which could be useful as feedstocks for industrial chemicals, contained 70% of the carbon originally present in the crude bio-oil.

A reaction network for the hydrothermal liquefaction of Nannochloropsis sp.

Abstract: We isolated the solid, aqueous-phase, and biocrude product fractions from the hydrothermal liquefaction of Nannochloropsis sp. and then further reacted each individually. These results permitted construction of a detailed reaction network for hydrothermal liquefaction that comprises the pathways for consumption and formation of each product fraction. We used the reaction network to develop a quantitative kinetic model and estimated its parameters using experimental results for the hydrothermal liquefaction of Nannochloropsis sp. at different temperatures and times. The model accurately predicted previously published biocrude and gas yields for the hydrothermal treatment of Nannochloropsis sp., though predictions became poorer further outside the experimental parameter space used to determine the model parameters. The reaction path between aqueous-phase products and heavy biocrude switches direction during the course of liquefaction. It initially produces aqueous-phase products, but after several minutes it consumes aqueous-phase products and produces heavy biocrude. The activation energies for the gas formation pathways (66 and 80 kJ/mol) are in good accord with the value (71 kJ/mol) estimated from literature for algae gasification in supercritical water [2]. The model predicts that the yields of light and heavy biocrudes are highest at temperatures > 300 °C and reaction times

Development of a foam flotation system for harvesting microalgae biomass

Abstract: The lack of efficient and cost-effective technologies for harvesting bulk quantities of microalgae biomass is a major obstacle to commercialisation of algae-derived biofuels. This article demonstrates the efficacy of a foam harvester that combines dispersed air flotation with foam fractionation to allow harvesting, concentration, and physical separation of particles in suspension. Fractional factorial experiments using polystyrene latex beads were combined with trials using microalgae to determine the relative importance of key design and operational variables (air flow rate, batch run time, foam column height, surfactant concentration, and surfactant type) on the particle concentration factor. The model revealed that highest concentration factors were gained using the following variables and variable interactions: cationic cetyl trimethylammonium bromide (CTAB), lower surfactant concentrations, and CTAB combined with high column heights. Variables that increased foam residence time produced the greatest concentration factors. Analyses of the harvest economics revealed that foam flotation consumes only 0.015 kWh/m 3 providing an advantageous cost–benefit relationship, and outcompeting many commonly used bulk harvesting technologies.

Microwave assisted lipid extraction from microalgae using biodiesel as co-solvent

Abstract: This study reports the solvent potential of biodiesel (methyl soyate) for microalgal lipid extraction while employing microwave-assisted extraction (MAE). Two co-solvent systems, BD20 and BD40 containing 20% and 40% of biodiesel in ethanol respectively, were experimented at 80 °C, 100 °C, and 120 °C in MAE. Results were compared to those of the MAE using chloroform and ethanol (1:2) as well as conventional 8 h Soxhlet extraction. Results indicated that approximately 66% and 78% of the oil within the cells were extracted with BD40 at 80 °C and 100 °C, respectively. Increase in temperature to 120 °C increased the efficiency of BD40 extraction to 115.5%, relative to conventional Soxhlet extraction. The BD20 co-solvent on the other hand extracted 27%, 34%, and 24% of oil at 80 °C, 100 °C, and 120 °C temperatures respectively. MAE using chloroform and ethanol showed 32%, 93%, and 108% of oil compared to Soxhlet. Data indicated that increase in biodiesel proportion in the co-solvent and increased temperature lead to more efficient extraction. Scanning electron microscope (SEM) images were used to discern the cell structures before and after the extraction. This study was aimed at identifying benign alternatives for the traditional toxic solvents like n -hexane for extracting microalgal lipids.

Life cycle assessment of a microalgae biomass cultivation, bio-oil extraction and pyrolysis processing regime

Abstract: Life cycle assessment (LCA) of a microalgae biomass cultivation, bio-oil extraction and pyrolysis processing regime is a useful means to gauge the likely environmental impact of this prospective new development on an industrial scale. Coupled to thermal conversion via slow pyrolysis, the prospect of biologically ‘sequestering’ carbon derived from microalgae biomass as biochar, added to soil, is considered. However, an intensive closed culturing photobioreactor system coupled to a pyrolysis process incurs a net increase in global warming and overall life cycle impact, notwithstanding biochar application to soil. Results indicate that up to 50% of environmental impact in certain categories stems from the upstream influence of fertiliser production. Energy used in flue gas delivery and pumping during cultivation is also considerable, suggesting that current practice in closed cultivation systems does not yet adequately trade-off biomass productivity against operating intensity. Drying of the harvested microalgae biomass for pyrolysis processing is potentially a major hurdle in terms of process viability also. Overall, utilisation of nutrients derived from waste streams, integrating renewable energy and capture of process heat for more efficient drying are essential levers for reducing the environmental impact of this proposition.

Scenario evaluation of open pond microalgae production

Abstract: To evaluate microalgae production in large scale open ponds under different climatologic conditions, a model-based framework is used to study the effect of light conditions, water temperature and reactor design on trends in algae productivity. Scenario analyses have been done for two algae species using measured weather data of the Netherlands and Algeria. The effects of temperature control, photo-inhibition and using monthly or yearly fixed biomass concentrations are estimated by a sensitivity analysis. The calculation-based results show that climate conditions such as solar irradiation and temperature dynamics play an important role in open raceway ponds. In moderate climate zones low and high temperatures over a season suppress growth. At high latitudes this effect is important as light levels vary much during the day and between seasons. Optimal biomass concentrations in ponds depend on location, pond depth and algae species. Pond design, location and algae species interact and productivity cannot be based solely on general or assumed efficiencies. It is essential to select algae species that have a suitable growth rate, light absorption coefficient and the ability to grow over a broad temperature range. The presented approach gives a framework to validate specific cultivation systems.

Water-soluble polysaccharides from the brown alga Eisenia bicyclis: Structural characteristics and antitumor activity

Abstract: Water-soluble polysaccharides were isolated from the brown alga Eisenia bicyclis , which was collected near the coast of the Republic of Korea. The structures of laminaran and fucoidan were investigated. Laminaran from E. bicyclis was determined to be a glucan with β-(1 → 6) side chains linked to a β-(1 → 3) backbone with relatively few branch points. Based on nuclear magnetic resonance (NMR) data, the ratio of the β-(1 → 3) and β-(1 → 6) linkages was estimated as 2.6:1. Fucoidan from E. bicyclis was found to contain 1,3-linked fucose residues, some 1,6-, 1,2,6-, 1,4,6-linked galactose residues and traces of mannose and xylose. In addition, the amount of sulfate in fucoidan was 13.2%. Those polysaccharides were non-cytotoxic to human melanoma SK-MEL-28 and colon cancer DLD-1 cells. Laminaran and fucoidan from E. bicyclis inhibited the colony formation of those cells. Therefore, they may have potential as antitumor agents.

Strategic enhancement of algal biomass and lipid in Chlorococcum infusionum as bioenergy feedstock

Abstract: Algal biomass can serve as rich source of bioproducts including lipids for diverse commercial applications. Both biomass production and lipid accumulation are limited by several factors, of which nutrients play a vital role. In the present investigation, the nutritional requirement for the growth by a (an autotrophic) Chlorococcum infusionum was determined using a Plackett–Burman based statistical screening experiment. Five out of the fifteen factors of a reported production medium were found to be significantly affecting the biomass growth. The components NaNO3, K2HPO4, FeSO4.7H2O and KOH had direct proportional correlation with biomass production, while MgSO4 showed inverse proportional relationship in the selected experimental range. Nitrogen was the most influential factor with an effect contribution of 45.77% and a very low p-value of

Production of recombinant enzymes in the marine alga Dunaliella tertiolecta

Abstract: Photosynthetic marine algae are attractive targets for the production of biofuels and bio-products because they have the ability to capture and fix carbon dioxide using solar energy and they grow in seawater, thereby minimizing fresh water usage. Algae are a large and diverse group and transformation of algal chloroplasts has been limited to very few examples, mainly the model freshwater alga, Chlamydomonas reinhardtii. However, the potential for metabolic engineering and recombinant protein production using algal chloroplasts has been well demonstrated in this model species. Here we report the transformation of the chloroplast of the marine green alga Dunaliella tertiolecta. D. tertiolecta is an ideal species for biofuel production because it can maintain relatively high growth rates in a wide range of pH and salt concentrations, and because it contains relatively high lipid content. Here we show that transformation of the chloroplast of D. tertiolecta can occur by homologous recombination and selection for resistance to the antibiotic erythromycin using the erythromycin esterase gene, ereB. We successfully produce measurable quantities of five different classes of recombinant enzymes; xylanase, α-galactosidase, phytase, phosphate anhydrolase, and β-mannanase, in the plastids of D. tertiolecta or C. reinhardtii. This was achieved by transforming the plastid of D. tertiolecta via particle bombardment using a D. tertiolecta psbD promoter with 5′ UTR and psbA terminator with 3′ UTR to drive stable expression of codon optimized transgenes. Similar strategies should allow for recombinant protein production in many species of marine algae.

Nutrient remediation rates in municipal wastewater and their effect on biochemical composition of the microalga Scenedesmus sp. AMDD

Abstract: article i nfo Keywords: Microalgae Chemostat Bioenergy Biofuels Wastewater Microalgae are very efficient at removing nutrients from municipal wastewater and may be a viable tertiary wastewater treatment while additionally improving the economics of microalgal cultivation for biofuel production.Therelativequantitiesandproductivitiesoffattyacids,carbohydratesandproteinsweredetermined inthemicroalgaScenedesmussp.AMDDgrownintreatedmunicipalwastewaterincontinuouschemostatsunder different dilution rates or hydraulic retention times. The dilution rate of the chemostat exerted a strong control overthebiochemical composition of the cultivated biomassand clear differences inthe patterns of accumulation of cellular constituents were detected. Maximum carbohydrate and protein productivities were estimated to be 130 and 120 mg L −1 d −1 , respectively, at dilution rates of 0.5 d −1 and 1.05 d −1 , respectively. Fatty acid productivity was fairly constant at about 20 mg L −1 d −1 across all tested dilution rates. Total fatty acid only accumulated when growth rates were very low or when a prolonged nutrient starvation regime was imposed by interrupting the supply of wastewater to the chemostat. Monounsaturated fatty acids increased by 250%, whereas polyunsaturated fatty acids decreased by 60% and saturated fatty acids remained fairly constant, from the highest dilution rate of 1.05 d −1 to nutrient starved cells. The rate of wastewater nutrient remediation therefore strongly controls the composition of the biomass, thereby controlling its commercial applicability.

The synchronized cell cycle of Neochloris oleoabundans and its influence on biomass composition under constant light conditions

Abstract: article i nfo The effect of cell cycle stage on biomass composition of the green microalgae Neochloris oleoabundanswas inves- tigated. N. oleoabundans was grown under constant light conditions in a flat panel photobioreactor operated as a turbidostat. Even though light conditions were constant, a synchronized cell division was observed with the cells dividing by multiple fission during the natural night. Presumably, the circadian clock was responsible for 'gating' cell division to this specific time frame. Oscillations in starch, protein and pigment content were observed during the cell cycle. These oscillations could be solely contributed to the cell cycle stage of the synchronized culture, since all experimental conditions were kept constant. A maximum in starch, protein and fatty acid content was obtained just before cell division. Biomass yield was also greatly influenced by the cell cycle and declined to a minimum during cell division. These findings highlight that knowledge of the cell cycle is of importance in microalgae process optimization.

Characterization of dissolved organic matters responsible for ultrafiltration membrane fouling in algal harvesting

Abstract: A major challenge of membrane ultrafiltration technology for large-scale microalgal harvesting and recycling of used culture media is membrane fouling, and the chemical nature and molecular properties of fouling are not well understood. To determine possible membrane fouling mechanism, a bench-scale hollow fiber polyvinylchloride (PVC) ultrafiltration membrane unit was employed to harvest the unicellular green alga Chlorella zofingiensis grown in a flat plate photobioreactor. It revealed that Chlorella, bacteria, and dissolved organic matter (DOM) each clogged the membrane, and yet the most severe membrane fouling was caused by DOM, which was also found to be most difficult to remove from the membrane by periodical backwashing. DOM was further fractionated by high performance size exclusion chromatography (HPSEC) into three fractions, i.e., hydrophilic acid fraction (HPI-A), hydrophilic non-acid fraction (HPI-NA) and hydrophobic acid fraction (HPO-A), of which HPI-NA, particularly in a molecular weight range of 7–11 kDa, was the major foulants. The results also showed that a carbohydrate fraction of DOM caused greater membrane fouling than a protein fraction did.

A comparative study of microfiltration and ultrafiltration for algae harvesting

Abstract: The present work deals with the filtration and concentration of algae ( Chlorella ) from a diluted culture medium using six commercial microfiltration membranes (MFP2, MFP5 and MFP8 with different pore sizes) and ultrafiltration membranes (FS40PP, FS61PP and ETNA10PP with different Molecular Weight Cut-Off (MWCO)). The effects of the operating conditions, e.g. feed solution temperature, TMP (transmembrane pressure), VCF (volume concentration factor) and cross-flow velocity on the filtration performance were investigated. The results showed that permeate fluxes increased with the increase in feed solution temperature, and the fluxes were probably limited by released extracellular polymeric substances (EPS) at higher temperatures. The permeate fluxes increased slowly with increasing TMP up to a certain limit, and after that the fluxes were stable or even decreased. The higher cross-flow velocity can significantly decrease particles accumulating on the surface of membrane, and thus leading to higher permeate flux. Although ETNA10PP exhibited much less fouling than other membranes, the permeate flux of this membrane was not higher than other membranes most likely due to the fact that this membrane is the ‘tightest’ membrane with MWCO 10,000. The performance of UF and MF membranes was compared for this application. The interesting finding of our work is that microfiltration and ultrafiltration showed very similar performance in terms of permeate flux under the same operation conditions at low TMP.

Analysis of water footprint of a photobioreactor microalgae biofuel production system from blue, green and lifecycle perspectives

Abstract: Microalgae are currently being investigated as a feedstock for the commercial production of transportation fuels, due to their potential scalability and sustainability advantages over conventional feedstocks. The water consumption of microalgae has been postulated to be a resource barrier for large-scale production. This study presents an assessment of the water footprint (WF) of a closed photobioreactor-based biofuel production system, where microalgae cultivation is simulated with geographical and temporal resolution. The assessment focuses on the WF as modeled for four different fuel conversion pathways, and in 10 continental US locations corresponding to high productivity yields. The WF is comprehensively assessed using a hybrid approach which combines process and economic input–output lifecycle analysis method, using three metrics: blue, green and lifecycle WF. Results show that the blue WF of microalgae biofuels varies between 23 and 85 m 3 · GJ − 1 depending on process and geographic location. The green WF shows that microalgae cultivation may reduce the required local water withdrawals. Water credits from the co-products vary with allocation methods and end uses, from credits of less than 4 m 3 · GJ − 1 up to credits of 334 m 3 · GJ − 1 . Results for the net lifecycle WF with coproduct credits vary between 80 and − 291 m 3 · GJ − 1 . Discussion focuses on the sensitivity of microalgae biofuel WF and highlights potential local and national strain of water resources relative to other fuels and biofuels.

Glycogen synthesis is a required component of the nitrogen stress response in Synechococcus elongatus PCC 7942

Abstract: Carbon fixation and production of reductant by cyanobacteria can exceed new biomass synthesis rates when the supply of essential nutrients is limiting. Under these circumstances metabolic balance is achieved by diversion of excess carbon and reductant to synthesis of glycogen, which can accumulate to more than 50% of cellular dry biomass. We discovered that when glycogen synthesis was abolished, by deletion of the gene for glucose-1-phosphate adenylyl transferase (glgC), Synechococcus elongatus PCC 7942 was unable to degrade its phycobilisomes in response to nitrogen stress. Furthermore, nitrogen deprived glgC null cells recalibrated the levels of glycolytic and TCA cycle intermediates. Specifically, succinate, fumarate, and 2-oxoglutarate, a metabolic indicator of cellular nitrogen status and metabolic effector of the global nitrogen regulator NtcA, accumulated within and were excreted by glgC null cells under nitrogen stress. Moreover, intracellular accumulation and excretion of 2-oxoglutarate from nitrogen stressed glgC null cells coincided temporally with suppression of nblA transcription, while internalization of 2-oxoglutarate by nitrogen deprived wild type cells delayed both nblA expression and phycobilisome degradation. Furthermore, glgC null cells exhibited a non-bleaching phenotype in response to sulfur and phosphate stress. These data indicate that glycogen synthesis is a required component of the global response to nutrient stress.

Life-cycle and techno-economic analysis of utility-connected algae systems

Abstract: For many years, it has been suggested that mitigation of atmospheric carbon dioxide (CO 2 ) emissions can be achieved by fixing CO 2 as algal biomass. New EPA regulations limit greenhouse gas emissions from new power plants, and thus power plants have additional impetus to decide if co-location with algal ponds is a feasible strategy for CO 2 mitigation. Herein we provide some illustrative benchmarking calculations based on fundamental relationships to highlight the general concerns for algae-utility co-location. We introduce our own life-cycle and techno-economic analysis software to analyze utility-specific concerns, such as total pond area, the percentage of CO 2 in the flue gas, and the CO 2 utilization efficiency. The results indicate that localized strategies should be pursued to reduce the excessive energy requirements for long-distance CO 2 delivery. Furthermore, research should focus on improving the ability of growth reactors to efficiently utilize CO 2 . Improvements in CO 2 delivery methods, such as absorption of CO 2 into liquid media, could greatly reduce energy inputs and thus improve the process economics and sustainability.