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The feasibility of a carbon recycling system that transforms algal residue to volatile fatty acids (VFAs) for re-cultivating microalgae was evaluated based on a carbon balance analysis of major VFAs consisting of acetate (HAc), propionate (HPr), and butyrate (HBu). This system largely involves two processes: (i) bioconversion of algal residue to VFAs by anaerobic fermentation, and (ii) cultivation of microalgae using the produced VFAs. The carbon balance for each unit process was examined to assess how much carbon in algal residue can be converted to these major VFAs and then assimilated to microalgae biomass. First, the yield and the profile of VFAs from raw algae (RA) and lipid-extracted algae (LEA) at psychrophilic (15 °C), mesophilic (35 °C), and thermophilic conditions (55 °C) were compared. When digesting the LEA under the thermophilic condition, the highest conversion yield, 0.36 (g carbon in VFAs/g carbon in biomass), with a compositional ratio of 6:1:3 (HAc: HPr: HBu) was obtained. Consumption of VFAs for microalgal growth reached a maximum value of 0.66 (g VFAs assimilated to biomass/g VFAs provided) at the compositional ratio of 6:1:3. Consequently, the maximum total carbon recycling ratio was 23.8% when fermenting LEA at the thermophilic condition. Our findings comprehensively revealed that establishing conditions that convert LEA to higher content of acetate is a decisive factor. It was estimated that around 40% of the total carbon from the LEA can be recovered for the production of algal biomass, when increasing the VFA conversion yield beyond 60% by adopting pretreatment methods., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

This study examined the feasibility of using an algal-bacterial process for removal of phenol and NH 4 + -N from differently diluted coke wastewater with simultaneous production of biomass. Under illumination, microalgal-bacterial (MSB) cultures performed complete phenol degradation at all dilutions of coke wastewater while sole microalgal culture (MSA) degraded a maximum of 27.3% of phenol (initial concentration: 24.0mgL -1 ) from 5-fold diluted wastewater. Furthermore, the MSB culture had the highest rate of NH 4 + -N removal (8.3mgL -1 d -1 ) and fatty acid production (20mgL -1 d -1 ) which were 2.3- and 1.5-fold higher than those observed in the MSA cultures, probably due to decreases in toxic organic pollutants. Multivariate analyses indicated that co-cultivation of activated sludge was directly correlated with the elevated removals of phenol and NH 4 + -N. In the presence of sludge, adequate dilution of the coke wastewater can maximize the effect of bacteria on NH 4 + -N removal and biomass production., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

For the efficient separation of lipid extracted from microalgae cells, a novel membrane was devised by introducing a functional polymer coating onto a membrane surface by means of an initiated chemical vapor deposition (iCVD) process. To this end, a steel-use-stainless (SUS) membrane was modified in a way that its surface energy was systemically modified. The surface modification by conformal coating of functional polymer film allowed for selective separation of oil-water mixture, by harnessing the tuned interfacial energy between each liquid phase and the membrane surface. The surface-modified membrane, when used with chloroform-based solvent, exhibited superb permeate flux, breakthrough pressure, and also separation yield: it allowed separation of 95.5 ± 1.2% of converted lipid (FAME) in the chloroform phase from the water/MeOH phase with microalgal debris. This result clearly supported that the membrane-based lipid separation is indeed facilitated by way of membrane being functionalized, enabling us to simplify the whole downstream process of microalgae-derived biodiesel production.

Five technologies, coagulation, electro-flotation (EF), electro-coagulation-flotation (ECF), centrifugation, and membrane filtration, were systematically assessed for their adequacy of harvesting Aurantiochytrium sp. KRS101, a heterotrophic microalgal species that has much higher biomass concentration than photoautotrophic species. Coagulation, EF, and ECF were found to have limited efficiency. Centrifugation was overly powerful to susceptible cells like Aurantiochytrium sp. KRS101, inducing cell rupture and consequently biomass loss of over 13%. Membrane filtration, in particular equipped with an anti-fouling turbulence generator, turned out to be best suited: nearly 100% of harvesting efficiency and low water content in harvested biomass were achieved. With rotation rate increased, high permeate fluxes could be attained even with extremely concentrated biomass: e.g., 219.0 and 135.0 L/m(2)/h at 150.0 and 203.0 g/L, respectively. Dynamic filtration appears to be indeed a suitable means especially to obtain highly concentrated biomass that have no need of dewatering and can be directly processed., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Triiodide resin (TR) was used to generate axenic cultures of microalgae by employing the antibacterial capability of triiodide. A Nannochloropsis gaditana culture contaminated with bacteria was passed through a column filled with TR using the gravity flow. Based on analyses of flow cytometry and vital staining using a fluorescent dye SYTOX Green, three cycles of TR treatments remarkably reduced the number of viable bacteria but had little effects on the microalgae. This novel approach is a simple, rapid, and cost-effective method that can be used to isolate axenic cultures of microalgae., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This work describes the development of a microalga-mediated process for simultaneous removal of residual ammonium nitrogen (NH4(+)-N) and production of lipids from biologically treated coke effluent. Four species of green algae were tested using a sequential mixotrophic process. In the first phase-CO2-supplied mixotrophic condition-all microalgae assimilated NH4(+)-N with no evident inhibition. In second phase-volatile fatty acids (VFAs)-supplied mixotrophic condition-removal rates of NH4(+)-N and biomass significantly increased. Among the microalgae used, Arctic Chlorella sp. ArM0029B had the highest rate of NH4(+)-N removal (0.97 mg/L/h) and fatty acid production (24.9 mg/L/d) which were 3.6- and 2.1-fold higher than those observed under the CO2-supplied mixotrophic condition. Redundancy analysis (RDA) indicated that acetate and butyrate were decisive factors for increasing NH4(+)-N removal and fatty acid production. These results demonstrate that microalgae can be used in a sequential process for treatment of residual nitrogen after initial treatment of activated sludge., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Changes in algal and bacterial communities during thiocyanate (SCN(-)) decomposition in a microalga-mediated process were studied. Pyrosequencing indicated that Thiobacillus bacteria and Micractinium algae predominated during SCN(-) hydrolysis, even after its complete degradation. Principal components analysis and evenness profiles (based on the Pareto-Lorenz curve) suggested that the changes in the bacterial communities were driven by nitrogen and sulfur oxidation, pH changes, and photoautotrophic conditions. The populations of predominant microalgae remained relatively stable during SCN(-) hydrolysis, but the proportion of bacteria - especially nitrifying bacteria - fluctuated. Thus, the initial microalgal population may be crucial in determining which microorganisms dominate when the preferred nitrogen source becomes limited. The results also demonstrated that microalgae and SCN(-)-hydrolyzing bacteria can coexist, that microalgae can be effectively used with these bacteria to completely treat SCN(-), and that the structure of the algal-bacterial community is more stable than the community of nitrifying bacteria alone during SCN(-) degradation., (Copyright © 2015. Published by Elsevier Ltd.)

In this work, the effects of several factors, such as temperature, reaction time, and solvent and acid quantity on in situ transesterification yield of wet Nannochloropsis salina were investigated. Under equivalent total solvent volume to biomass ratio, pure alcohol showed higher yield compared to alcohol-chloroform solvent. For esterifying 200 mg of wet cells, 2 ml of methanol and 1 ml of ethanol was sufficient to complete in situ transesterification. Under temperatures of 105 °C or higher, 2.5% and 5% concentrations of sulfuric acid was able to successfully convert more than 90% of lipid within 30 min when methanol and ethanol was used as solvents respectively. Also, it was verified that the optimal condition found in small-scale experiments is applicable to larger scale using 2 L scale reactor as well., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

An interest in biodiesel as an alternative fuel for diesel engines has been increasing because of the issue of petroleum depletion and environmental concerns related to massive carbon dioxide emissions. Researchers are strongly driven to pursue the next generation of vegetable oil-based biodiesel. Oleaginous microalgae are considered to be a promising alternative oil source. To commercialize microalgal biodiesel, cost reductions in oil extraction and downstream biodiesel conversion are stressed. Herein, starting from an investigation of oil extraction from wet microalgae, a review is conducted of transesterification using enzymes, homogeneous and heterogeneous catalysts, and yield enhancement by ultrasound, microwave, and supercritical process. In particular, there is a focus on direct transesterification as a simple and energy efficient process that omits a separate oil extraction step and utilizes wet microalgal biomass; however, it is still necessary to consider issues such as the purification of microalgal oils and upgrading of biodiesel properties., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Ionic liquids have many applications, one of which entails their utilization as powerful solvents. In the present study, various experimental conditions of ionic liquid-mediated direct transesterification were investigated in terms of lipid-extracting ionic liquids, catalyst, reaction time, reaction temperature and volume of methanol to achieve effective FAME conversion with wet microalgal feedstock, Nannochloropsis oceanica. With ionic liquid, [Bmim][CF3SO3], highest fatty acid methyl ester (FAME) yield was shown. Among many experimental parameters, the two most critical factors to enhance FAME conversion were characteristic of ionic liquids and volume of methanol. Optimized ionic liquid-mediated direct transesterification of wet N. oceanica, compared with a control experiment using chloroform and methanol, increased the FAME conversion yield by 11-fold.

Microalgal biofuels are not yet economically viable due to high material and energy costs associated with production process. Microalgae cultivation is a water-intensive process compared to other downstream processes for biodiesel production. Various studies found that the production of 1 L of microalgal biodiesel requires approximately 3000 L of water. Water recycling in microalgae cultivation is desirable not only to reduce the water demand, but it also improves the economic feasibility of algal biofuels as due to nutrients and energy savings. This review highlights recently published studies on microalgae water demand and water recycling in microalgae cultivation. Strategies to reduce water footprint for microalgal cultivation, advantages and disadvantages of water recycling, and approaches to mitigate the negative effects of water reuse within the context of water and energy saving are also discussed., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A cost-efficient process devoid of several washing steps was developed, which is related to direct cultivation following the decomposition of the sterilizer. Peracetic acid (PAA) is known to be an efficient antimicrobial agent due to its high oxidizing potential. Sterilization by 2 mM PAA demands at least 1 h incubation time for an effective disinfection. Direct degradation of PAA was demonstrated by utilizing components in conventional algal medium. Consequently, ferric ion and pH buffer (HEPES) showed a synergetic effect for the decomposition of PAA within 6 h. On the contrary, NaNO3, one of the main components in algal media, inhibits the decomposition of PAA. The improved growth of Chlorella vulgaris and Synechocystis PCC6803 was observed in the prepared BG11 by decomposition of PAA. This process involving sterilization and decomposition of PAA should help cost-efficient management of photobioreactors in a large scale for the production of value-added products and biofuels from microalgal biomass.

Open raceway ponds are cost-efficient for mass cultivation of microalgae compared with photobioreactors. Although low-cost options like wastewater as nutrient source is studied to overcome the commercialization threshold for biodiesel production from microalgae, a cost analysis on the use of wastewater and other incremental increases in productivity has not been elucidated. We determined the effect of using wastewater and wavelength filters on microalgal productivity. Experimental results were then fitted into a model, and cost analysis was performed in comparison with control raceways. Three different microalgal strains, Chlorella vulgaris AG10032, Chlorella sp. JK2, and Scenedesmus sp. JK10, were tested for nutrient removal under different light wavelengths (blue, green, red, and white) using filters in batch cultivation. Blue wavelength showed an average of 27% higher nutrient removal and at least 42% higher chemical oxygen demand removal compared with white light. Naturally, the specific growth rate of microalgae cultivated under blue wavelength was on average 10.8% higher than white wavelength. Similarly, lipid productivity was highest in blue wavelength, at least 46.8% higher than white wavelength, whereas FAME composition revealed a mild increase in oleic and palmitic acid levels. Cost analysis reveals that raceways treating wastewater and using monochromatic wavelength would decrease costs from 2.71 to 0.73 $/kg biomass. We prove that increasing both biomass and lipid productivity is possible through cost-effective approaches, thereby accelerating the commercialization of low-value products from microalgae, like biodiesel.

Calcium ion and trace metals play important roles in various metabolisms of photosynthetic organisms. In this study, simple methods were developed to extract calcium ion and micronutrients from oyster shell and common soil, and the prepared extracts were tested as a replacement of the corresponding chemicals that are essential for growth of microalgae. The oyster shell and soil were treated with 0.1 M sodium hydroxide or with 10 % hydrogen peroxide, respectively. The potential application of these natural sources to cultivation was investigated with Spirulina maxima. When compared to standard Zarrouk medium, the Spirulina maxima cultivated in a modified Zarrouk media with elements from oyster shell and soil extract exhibited increases in biomass, chlorophyll, and phycocyanin by 17, 16, and 64 %, respectively. These results indicate that the extracts of oyster shell and soil provide sufficient amounts of calcium and trace metals for successful cultivation of Spirulina maxima.

The present study assessed the use of hydrolysate of lipid extracted algal biomass (LEA) combined with the sugar factory wastewater (SFW) as a low cost nutrient and a carbon source, respectively for microalgal cultivation. Microalgal strain Ettlia sp. was both mixotrophically and heterotrophically cultivated using various amounts of hydrolysate and SFW. The culture which was grown in medium containing 50% LEA hydrolysate showed highest growth, achieving 5.26 ± 0.14 gL(-1) after 12 days of cultivation. The addition of SFW increased the lipid productivity substantially from 5.8 to 95.5 mg L(-1)d(-1) when the culture medium was fortified with 20% SFW. Gas chromatography analysis indicated a noticeable increase of 20% in C16 and C18 fraction in FAME distribution under above condition. Therefore, it can be concluded that the combination of LEA hydrolysate and sugar factory waste water can be a powerful growth medium for economical algal cultivation., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Advances in harvesting of microalgae are needed for the efficient and economical production of microalgal biodiesel. In addition to improvements in recovery efficiency, developments in harvest technology should focus on reducing the adverse impact of subsequent processes, and should also allow water recycling. We investigated a continuous electrochemical approach for microalgal biodiesel production. Instead of conventional DC, pulsed DC was applied as a method of polarity exchange and its performance was analyzed in terms of recovery efficiency, electricity consumption, and residual Al concentration. Under optimized pulsed-DC conditions, 32 % less electricity was required and 7 % less Al was remained after continuous harvesting and there was no decrease in recovery efficiency compared to the continuous harvesting by conventional DC. We also examined the effect of this new protocol on biodiesel quality and water reusability. There were no differences in the microalgal oil composition before and after electrolytic harvesting. In addition, the harvested oil quality, based on four key parameters, was superior to that produced by other terrestrial crops. Lastly, there was no retardation of growth in recycled medium relative to that in fresh medium.

In this study, acid-catalyzed hot-water extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. was performed, and its yield-enhancing effects were investigated. The total fatty acid content of the Aurantiochytrium sp. was 482.5mg/g cell, of which 141.7mg/g cell (29.4% of total fatty acids) was DHA. The lipid-extraction yield by acid-catalyzed hot-water treatment was compared with those by organic solvents. Among the various acid-catalyzed hot-water treatment conditions, the most optimal were 1.00% H2SO4 concentration, 100°C, 30min, under which the lipid-extraction yield was 472.4mg/g cell, and most of the DHA was extracted (29.2% of total fatty acids). Acid-catalyzed hot-water extraction treatment markedly improved the lipid-extraction yield of Aurantiochytrium sp., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In this work, a method for simultaneously degrading the toxic pollutant, thiocyanate, and producing microalgal lipids using mixed microbial communities was developed. Aerobic activated sludge was used as the seed culture and thiocyanate was used as the sole nitrogen source. Two cultivation methods were sequentially employed: a lithoautotrophic mode and a photoautotrophic mode. Thiocyanate hydrolysis and a nitrification was found to occur under the first (lithoautotrophic) condition, while the oxidized forms of nitrogen were assimilated by the photoautotrophic consortium and lipids were produced under the second condition. The final culture exhibited good settling efficiency (∼ 70% settling over 10 min), which can benefit downstream processing. The highest CO2 fixation rate and lipid productivity were observed with 2.5% and 5% CO2, respectively. The proposed integrated algal-bacterial system appears to be a feasible and even beneficial option for thiocyanate treatment and production of microbial lipids., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Identification of novel microalgal strains with high lipid productivity is one of the most important research topics in renewable biofuel research. However, the major bottleneck in the strain screening process is that currently known methods for the estimation of microalgal lipid are laborious and time-consuming. The present study successfully employed sulpho-phospho-vanillin (SPV) colorimetric method for direct quantitative measurement of lipids within liquid microalgal culture. The SPV reacts with lipids to produce a distinct pink color, and its intensity can be quantified using spectrophotometric methods by measuring absorbance at 530nm. This method was employed for a rapid quantification of intracellular lipid contents within Chlorella sp., Monoraphidium sp., Ettlia sp. and Nannochloropsis sp., all of which were found to have lipid contents ranging in between 10% and 30%. Subsequent analysis of the biomass using gas chromatography confirmed that our protocol is highly accurate (R(2)=0.99)., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

This work addresses a reliable in situ transesterification process which integrates lipid extraction from wet microalgae, and its conversion to biodiesel, with a yield higher than 90 wt.%. This process enables single-step production of biodiesel from microalgae by mixing wet microalgal cells with solvent, methanol, and acid catalyst; and then heating them in one pot. The effects of reaction parameters such as reaction temperature, wet cell weight, reaction time, and catalyst volume on the conversion yield are investigated. This simultaneous extraction and transesterification of wet microalgae may enable a significant reduction in energy consumption by eliminating the drying process of algal cells and realize the economic production of biodiesel using wet microalgae., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Despite receiving increasing attention during the last few decades, the production of microalgal biofuels is not yet sufficiently cost-effective to compete with that of petroleum-based conventional fuels. Among the steps required for the production of microalgal biofuels, the harvest of the microalgal biomass and the extraction of lipids from microalgae are two of the most expensive. In this review article, we surveyed a substantial amount of previous work in microalgal harvesting and lipid extraction to highlight recent progress in these areas. We also discuss new developments in the biodiesel conversion technology due to the importance of the connectivity of this step with the lipid extraction process. Furthermore, we propose possible future directions for technological or process improvements that will directly affect the final production costs of microalgal biomass-based biofuels., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Cultivation is the most expensive step in the production of biodiesel from microalgae, and substantial research has been devoted to developing more cost-effective cultivation methods. Plant hormones (phytohormones) are chemical messengers that regulate various aspects of growth and development and are typically active at very low concentrations. In this study, we investigated the effect of different phytohormones on microalgal growth and biodiesel production in Chlamydomonas reinhardtii and their potential to lower the overall cost of commercial biofuel production. The results indicated that all five of the tested phytohormones (indole-3-acetic acid, gibberellic acid, kinetin, 1-triacontanol, and abscisic acid) promoted microalgal growth. In particular, hormone treatment increased biomass production by 54 to 69 % relative to the control growth medium (Tris-acetate-phosphate, TAP). Phytohormone treatments also affected microalgal cell morphology but had no effect on the yields of fatty acid methyl esters (FAMEs) as a percent of biomass. We also tested the effect of these phytohormones on microalgal growth in nitrogen-limited media by supplementation in the early stationary phase. Maximum cell densities after addition of phytohormones were higher than in TAP medium, even when the nitrogen source was reduced to 40 % of that in TAP medium. Taken together, our results indicate that phytohormones significantly increased microalgal growth, particularly in nitrogen-limited media, and have potential for use in the development of efficient microalgal cultivation for biofuel production.

This study describes the development of a microfluidic device for the high-throughput screening of culture conditions, such as the optimum sodium acetate concentration for promoting rapid growth and high lipid accumulation of Chlamydomonas reinhardtii. An analysis of the microalgal growth on the microfluidic device revealed an optimum sodium acetate concentration of 5.72 g L(-1). The lipid content, determined by the 4,4-Difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene (BODIPY® 505/515) staining method, increased with the sodium acetate concentration. The results were found to be statistically reproducible with respect to cell growth and lipid production. Other nutrient conditions, including the nitrogen and phosphorus concentrations, can also be optimized on the same microfluidic platform. The microfluidic device performance results agreed well with the results obtained from the flask-scale experiments, validating that the culture conditions were scalable. Finally, we, for the first time, established a method for the absolute quantification of the microalgal lipid content in the picoliter culture volumes by comparing the on-chip and off-chip data. In conclusion, we successfully demonstrated the high-throughput screening of sodium acetate concentrations that induced high growth rates and high lipid contents in C. reinhardtii cells on the microfluidic device.

In the present study, spent yeast from a brewery was used as the growth substrate for the docosahexaenoic acid (DHA)-rich microalga, Aurantiochytrium sp. KRS101. A significant biomass yield (6.69 g/l/d) was obtained using only spent yeast as the growth substrate, with simple stirring as pretreatment. Maximization of nutrient utilization through the use of stepwise cultivation increased the yield to 31.8 g/l of biomass. DHA constituted 38.2% (w/w) of the total fatty acids, and the highest DHA productivity was observed when the C/N ratio was 20:1 (w/w). Spent yeast thus served as a good growth substrate for the production of DHA. Economic assessment revealed that stepwise cultivation using spent yeast as either the sole growth substrate or as a nutrient source could substantially reduce the production cost of microalgal DHA., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Microalgae have great potential as a feedstock for biofuel production. Continuous operation is an important benefit of the continuous electrolytic microalgae (CEM) harvest system, but it is necessary to optimize cultivability and recovery efficiency in order to improve overall performance. Two pairs of best-candidate electrodes for polarity exchange (PE) were examined to improve these two key factors: (i) aluminum and dimensionally stable anode (Al-DSA), and (ii) Al-platinum (Al-Pt). Al-DSA was better than Al-Pt because it led to less cell damage and was less expensive. Moreover, cell viability and recovery were improved by optimizing the timing of PE. A P1:P2 ratio of 1:1.5 at 5min and 1:1.2 at 10min yielded the best results, with greatly reduced electricity consumption and enhanced cell viability and recovery. The CEM harvest system appears to be a well-suited option for the harvest of microalgae for biofuel production., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

There is increasing interest in the use of microalgae as a renewable source for the production of fuels and chemicals, but improvements are needed in all steps of this process, including harvesting. A continuous microalgae harvest system was developed based on electrolysis, referred to here as a continuous electrolytic microalgae (CEM) harvest system. This innovative system combines cultivation and harvesting and enables continuous and efficient concentration of microalgae. The electrodes were subject to a polarity exchange (PE) in the middle of the operation to further improve the harvest efficiency. Use of PE, rather than conventional electro-coagulation-flotation (ECF), led to more efficient cell recovery and more uniform recovery over the entire harvest chamber. In addition, PE increased the cell growth rate and the circulated cells remained intact after harvesting., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

As energy and environment have become urgent issues, there has been increasing needs to develop alternative energy source, such as microalgal bio-fuel. In this study, we investigated the growth and lipid contents of microalgae Nannochloris oculata under various environmental conditions for biodiesel production. Our results indicated that biomass productivities of N. oculata were correlated with increasing nitrogen concentrations up to 37.5 ppm. High irradiance using 230-250 μmol/m(2) led to higher biomass yields than low irradiance of 160-180 μmol/m(2). Biomass productivities increased further by manipulating surface to volume ratio (S/V), which in turn enhanced light penetration. Finally, optimal biomass productivities (1.04 g/l day) could be achieved by the supplementation of yeast extract. Lipid contents and fatty acid profiles of N. oculata were affected by the different growth conditions. Lipid contents of N. oculata decreased as nitrogen concentration increased. Lower temperature (15 °C) resulted in higher lipid content than higher temperature (25 °C). Fatty acid profiles of N. oculata indicated that palmitic acid (C16:0) and linoleic acid (C18:2) were the two most abundant fatty acids, but the supplementation of yeast extract increased linolenic acid (C18:3) content. Our results suggested the feasibility of N. oculata for the biodiesel production.

In order to increase the economic feasibility of biodiesel production from microalgae, the residual biomass after biodiesel production can be utilized as biosorbent for heavy metal removal. In this study, biosorption of chromium by residual Nannochloris oculata after lipid extraction was investigated. Increased surface area of N. oculata was observed after lipid extraction. Cr(III) removal increased as the pH increased from 2 to 6, while Cr(VI) removal was highest at pH 2 and it decreased with the increase in pH. Cr(VI) was reduced to Cr(III) in the presence of biomass under acidic conditions; X-ray photoelectron spectroscopy revealed that the converted Cr(III) was bound to the biomass. Chromium removal was significantly enhanced at high chromium concentrations, which indicates that surface reactions may occur at high chromium/biomass ratios. FTIR study indicated that phosphate and carboxyl functional groups of the biomass were mainly responsible for chromium binding., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

ABSTRACT Gasification of microalgae feedstock generates mineral ash. In this work, raw ash is produced from lipid-extracted algal biomass of the Nannochloropsis salina strain. Prior to using it as filler for composite fabrication with poly(vinyl alcohol), raw ash (RASH) is activated with NaOH and surface modified with (3-aminopropyl)triethoxysilane. Surface modification of activated ash (PASH) significantly improves interfacial interaction between surface-modified ash (GASH) and polymer matrix. Higher ultimate tensile strength of PVA/GASH composites is recorded, compared with PVA/RASH and PVA/PASH. Young's modulus of biocomposites appears to increase proportionally to loading of the fillers. Thermal properties of polymeric materials of PVA with these ashes are stable. This is the first report to demonstrate the utilization of microalgal ash, the leftover after completed gasification of algal biomass, as an efficient filler for production of value-added polymeric materials. It is proposed that microalgal ash is capable of improving the economic feasibility of microalgae-based biorefinery. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43599. [ABSTRACT FROM AUTHOR]

Oil recovery from microalgal cells is a crucial step in microalgal biodiesel production. Cell disruption is an essential step for lipid extraction from algal biomass. Performance of a new un-conventional disruption method for microalgae cell lysis is reported. Triiodide resin was used for cell disruption for oil recovery from microalgae liquid culture. Cell disruption efficiency depended on contact time and resin quantity along with microalgal strain characteristics. Microalgal strains with a rigid cell structure and small cell size required long contact time and more resin. Time required for cell lysis varied from 30 to 180 min. Cell disruption efficiency and oil extraction ranged from 50 to 100% and 50 to 80% respectively. Cell lysis and oil recovery were dependent largely on microalgal strains and its oil content. During cell disruption process with the triiodide resin, oil was distributed into three different phases. Water phase contained about 20% of total oil, 40–50% remained within the ruptured cells and the remaining 20–30% was adsorbed onto the resin. Triiodide resin-assisted microalgae cell lysis is a low energy process as it is operated at ambient conditions. [ABSTRACT FROM AUTHOR]

Most conventional processes for algal biodiesel production involve separate lipid extraction steps or require usage of dry biomass that incurs extra cost and an energy intensive drying step. A novel process that involves dehydration of wet biomass via pretreatment with ethanol followed by direct in situ transesterification into biodiesel was investigated in this study. Under mild esterification at 80 °C for 30 min, pretreating the wet biomass twice with 3 volumes of ethanol resulted in a nearly four-fold increase of fatty acid ethyl ester (FAEE) yield from 3.04 mg to 11.78 mg, while increasing the ethanol from 1 volume to 10 volumes resulted in a six fold increase of yield from 3.18 to 18.29 mg. The FAEE yield further increased when the esterification reaction was run at higher temperature and longer durations of up to 120 °C for 2 h. The overall positive impact of the pretreatment step on the final yield was far greater for milder reaction conditions, which makes the process more attractive in terms of economics and energy savings. In addition, it was found that the yield is unaffected by the choice of alcohol, which means methanol and butanol can also be used for the process. Lastly, it was found that the low concentration of water in the FAEE containing spent ethanol meant that both the solvent and sulfuric acid could be reused to further concentrate the quantity of FAEE in the final product mixture. [ABSTRACT FROM AUTHOR]

The large water footprint is one of the major bottlenecks for the sustainable microalgae-based biorefinery. In order to reduce the amount of water that is needed for mass cultivation of microalgae, the reusability of culture medium for further algal growth was tested. Chlorella vulgaris was cultivated in recycled medium that was obtained from harvesting microalgal cells by using either centrifugation or flocculation with FeCl 3 or alum. The present study shows that centrifugation and flocculation with FeCl 3 are equally effective (> 90%) for harvesting C. vulgaris without any deleterious effects on algal growth when recycled media was used. However, even low concentration (< 5 ppm) of residual alum was shown to inhibit microalgal growth. More interestingly, the recycled media obtained after centrifugation or flocculation with FeCl 3 had a positive effect on biomass and lipid productivity of C. vulgaris . Extracellular substances such as carbohydrate, proteins, or ferric ions in the recycled media appear to cause these positive effects. Furthermore, change of pH to 2–3 and washing with water were found to effectively remove the residual ferric ions that are present in either harvested biomass or biodiesel, respectively. These results suggest that the use of recycled medium for microalgal cultivation is possible, and the choice of harvest methods must be carefully made when the recycling of culture medium is considered for microalgal cultivation. [ABSTRACT FROM AUTHOR]

A cost-efficient process devoid of several washing steps was developed, which is related to direct cultivation following the decomposition of the sterilizer. Peracetic acid (PAA) is known to be an efficient antimicrobial agent due to its high oxidizing potential. Sterilization by 2 mM PAA demands at least 1 h incubation time for an effective disinfection. Direct degradation of PAA was demonstrated by utilizing components in conventional algal medium. Consequently, ferric ion and pH buffer (HEPES) showed a synergetic effect for the decomposition of PAA within 6 h. On the contrary, NaNO, one of the main components in algal media, inhibits the decomposition of PAA. The improved growth of Chlorella vulgaris and Synechocystis PCC6803 was observed in the prepared BG11 by decomposition of PAA. This process involving sterilization and decomposition of PAA should help cost-efficient management of photobioreactors in a large scale for the production of value-added products and biofuels from microalgal biomass. [ABSTRACT FROM AUTHOR]

The use of wastewater has been investigated to overcome the economic challenge involved with a production of microalgae-based biodiesel. In this study, to achieve economical biodiesel production along with effective wastewater treatment at the same time, anaerobically treated brewery wastewater (ABWW) was utilized as a low-cost nutrient source, in the cultivation of Chlorella protothecoides. About 96 and 90 % of total nitrogen and phosphorus in ABWW were removed, respectively, while C. protothecoides was accumulating 1.88 g L of biomass. The C. protothecoides grown in ABWW showed increases in cell size and cell aggregation, resulting in a near 80 % enhanced harvesting efficiency within 20 min, as compared with only 4 % in BG-11. In addition, the total fatty acid content of the C. protothecoides grown in ABWW increased by 1.84-fold (35.94 ± 1.54 % of its dry cell weight), relative to that of BG-11. [ABSTRACT FROM AUTHOR]

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 (2.15gL−1 in 5days) and FAME yield (16.41% of biomass) were observed under mixotrophic cultivation with acetate (10gL−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 (2.05gL−1 in 5days) were obtained with 5gL−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. [Copyright &y& Elsevier]

The synthesis of aminoclays with Mg2+ or Fe3+, placed in metal centers by sol–gel reaction with 3-aminopropyltriethoxysilane (APTES) as a precursor, is demonstrated, producing –(CH2)3NH2 organo-functional pendants which are covalent-bonding onto cationic metals. The protonated amine groups in aqueous solution lead the efficient sedimentation (harvesting) of microalgae biomass within approximately 5 min and 120 min for fresh and marine species, respectively. To our surprise, the aminoclays did not depend on microalgae species or media for microalgae harvesting. In particular, the harvesting efficiency (%) of microalgae was not decreased in a wide pH region. The harvesting mechanism can be explained by the sweep flocculation of microalgae, which is confirmed by measurement of zeta potential of aminoclay in aqueous solution where aminoclay shows a positively charged surface in a wide pH region. In order to reduce the cost of aminoclays and to make the harvesting procedures simple, the membrane process using aminoclay-coated cotton filter is introduced for the treatment of 1 L-scale microalgae stocks. It is successfully performed with three recycles using the same aminoclay-coated cotton filter after removing the harvested microalgae biomass. Conclusively, the aminoclay-based microalgae harvesting systems are a promising means of reducing the cost of downstream processes in microalgae-based biorefinery. [ABSTRACT FROM AUTHOR]

While the potential of hydrothermal liquefaction (HTL) of microalgae to produce biocrude regardless of the types of microalgae (biomass-agnostic) has been noted, the quality of biocrude and the Energy Return On Investment (EROI) of HTL of various microalgal species have not been compared in detail. Here we report that the quality of biocrude and the EROI of microalgal HTL are directly dependent on the lipid contents of microalgae. When Nannochloropsis oceanica (30.2% lipid content) and Golenkinia sp. (17.3% lipid content) were compared for the quality of HTL in terms of the total yield, asphaltene/non-asphaltene contents, heteroatom (O, N, and S) concentrations, and the effective hydrogen-to-carbon ratios (H/C eff ) of the biocrudes, N. oceanica with high lipid content produced biocrude that can be more suitable for catalytic upgrading to transportation fuels than the biocrude from Golenkinia sp. with low lipid content. HTL of N. oceanica at low temperature (200 °C) in particular produced the biocrude with EROI that was better than that of Golenkinia sp. These results strongly support that the choice of microalgae with high lipid content is still a key factor that must be considered for biocrude production as much as it is regarded important for biodiesel production using microalgal biomass. [ABSTRACT FROM AUTHOR]

The oleaginous microalga Nannochloropsis sp. has been spotlighted as a promising candidate in genetic engineering research for biodiesel production. However, one of the major bottlenecks in the genetic manipulation against Nannochloropsis sp. is low transformation efficiency. Based on the idea that they grow rapidly in broth culture, the effect of conditioned medium on colonization and transformation efficiency of Nannochloropsis salina was investigated. Cells grown on agar plates with 20–40% conditioned medium produced colonies that were approximately 2.3-fold larger than cells grown without conditioned medium. More importantly, the transformation efficiency was about 2-fold greater on plates with 30% conditioned medium relative to those without conditioned medium. In addition, FAME productivity in liquid cultures with 100% conditioned medium increased up to 20% compared with cultures of control medium. These results suggest that conditioned medium can be applied for efficient transformation and cost-effective cultivation of N. salina for biodiesel production. [ABSTRACT FROM AUTHOR]

A dynamic microfiltration system has been receiving increasing attention as a means of preventing membrane fouling phenomena that reduce microalgae harvesting efficiency. This study describes the addition of a perforated disk to a dynamic microfiltration system for effective membrane-based microalgae harvesting. Fluid velocity near the membrane surface and shear stress on the membrane surface, as generated by different disks and rotation speeds, were simulated by computational fluid dynamics software, SolidWorks. A high correlation of shear stress on the membrane with microalgae harvesting efficiency was validated by a simulation-based empirical approach. Notably, fluid velocity near the membrane surface and average shear stress on the membrane surface with the perforated disk were approximately 2- and 7-fold, respectively, higher than observed with an unperforated disk. In empirical-experimental microfiltration of Chlorella vulgaris , the perforated disk (800 rpm) showed a 2-fold-higher plateau permeate flux of 381 L/m 2 /h compared with the unperforated disk (800 rpm), enabling a 2-fold-greater alleviation of microalgal fouling at the same rotation speed. The perforated disk was found to be an effective generator of high shear stress in dynamic microfiltration, resulting in improved filtration during harvesting of microalgae. [ABSTRACT FROM AUTHOR]

Highlights: [•] Structural correlation between cellular development and lipid body accumulation. [•] HTP screening of thraustochytrid using FACS with different fluorescent dyes. [•] Found that BODIPY 505/515 with less concentration of DMSO effective for FACS. [•] Established a quantitative baseline for lipids accumulation and/or microalgal growth. [Copyright &y& Elsevier]

Highlights: [•] Optimized FACS condition for single-cell sorting of C. reinhardtii and its mutants. [•] Comparison of BODIPY 505/515 and NileRed for FACS screening of microalgae. [•] Found that BODIPY 505/515 with less concentration of DMSO effective for FACS. [•] Distinguished C. reinhardtii and its mutants by chlorophyll level with FACS. [•] Established a quantitative baseline for lipids accumulation and/or microalgal growth. [ABSTRACT FROM AUTHOR]

Abstract: High-cost downstream process is a major bottleneck for producing microalgal biodiesel at reasonable price. Conventional lipid extraction process necessitates biomass drying process, which requires substantial amount of energy. In this regard, lipid extraction from wet biomass must be an attractive solution. However, it is almost impossible to recover lipid directly from wet microalgae with current technology. In this study, we conceived osmotic shock treatment as a novel method to extract lipid efficiently. Osmotic shock treatment was applied directly to wet Chlamydomonas reinhardtii biomass with water content >99%, along with both polar and non-polar organic solvents. Our results demonstrated that osmotic shock could increase lipid recovery approximately 2 times. We also investigated whether the presence of cell wall or different cell stages could have any impact on lipid recovery. Cell wall-less mutant stains and senescent cell phase could display significantly increased lipid recovery. Taken together, our results suggested that osmotic shock is a promising technique for wet lipid extraction from microalgal biomass and successfully determined that specific manipulation of biomass in certain cell phase could enhance lipid recovery further. [Copyright &y& Elsevier]