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Scenedesmus obliquus ABC-009 is a microalgal strain that accumulates large amounts of lutein, particularly when subjected to growth-limiting conditions. Here, the performance of this strain was evaluated for the simultaneous production of lutein and biofuels under three different modes of cultivation - photoautotrophic mode using BG-11 with air or 2% CO2 and heterotrophic mode using YM medium. While it was found that the highest fatty acid methyl ester (FAME) level and lutein content per biomass (%) were achieved in BG-11 medium with CO2 and air, respectively, heterotrophic cultivation resulted in much higher biomass productivity. While the cell concentrations of the cultures grown under BG-11 and CO2 were largely similar to those grown in YM medium, the disparity in the biomass yield was largely attributed to the larger cell volume in heterotrophically cultivated cells. Post-cultivation light treatment was found to further enhance the biomass productivity in all three cases and lutein content in heterotrophic conditions. Consequently, the maximum biomass (757.14 ± 20.20 mg/L/d), FAME (92.78 ± 0.08 mg/L/d), and lutein (1.006 ± 0.23 mg/L/d) productivities were obtained under heterotrophic cultivation. Next, large-scale lutein production using microalgae was demonstrated using a 1-ton open raceway pond cultivation system and a low-cost fertilizer (Eco-Sol). The overall biomass yields were similar in both media, while slightly higher lutein content was obtained using the fertilizer owing to the higher nitrogen content of the medium.

Transcription factor engineering to regulate multiple genes has shown promise in the field of microalgae genetic engineering. Here, we report the first use of transcription factor engineering in Chlorella sp. HS2, thought to have potential for producing biofuels and bioproducts. We identified seven endogenous bZIP transcription factors in Chlorella sp. HS2 and named them HSbZIP1 through HSbZIP7. We overexpressed HSbZIP1, a C-type bZIP transcription factor, in Chlorella sp. HS2 with the goal of enhancing lipid production. Phenotype screening under heterotrophic conditions showed that all transformants exhibited increased fatty acid production. In particular, HSbZIP1 37 and 58 showed fatty acid methyl ester (FAME) yields of 859 and 1,052 mg/l, respectively, at day 10 of growth under heterotrophic conditions, and these yields were 74% and 113% higher, respectively, than that of WT. To elucidate the mechanism underlying the improved phenotypes, we identified candidate HSbZIP1-regulated genes via transcription factor binding site analysis. We then selected three genes involved in fatty acid synthesis and investigated mRNA expression levels of the genes by qRTPCR. The result revealed that the possible HSbZIP1-regulated genes involved in fatty acid synthesis were upregulated in the HSbZIP1 transformants. Taken together, our results demonstrate that HSbZIP1 can be utilized to improve lipid production in Chlorella sp. HS2 under heterotrophic conditions.

Microalgae accumulate abundant lipids and are a promising source for biodiesel. However, carbohydrates account for 40% of microalgal biomass, an important consideration when using them for the economically feasible production of biodiesel. In this study, different acid hydrolysis and post-treatment processing of Chlorella sp. ABC-001 was performed, and the effect of these different hydrolysates on bioethanol yield by Saccharomyces cerevisiae KL17 was evaluated. For hydrolysis using H2SO4, the neutralization using Ca(OH)2 led to a higher yield (0.43 g ethanol/g sugars) than NaOH (0.27 g ethanol/g sugars). Application of electrodialysis to the H2SO4 + NaOH hydrolysate increased the yield to 0.35 g ethanol/g sugars, and K+ supplementation further enhanced the yield to 0.41 g ethanol/g sugars. Hydrolysis using HNO3 led to the generation of reactive species. Neutralization using only NaOH yielded 0.02 g ethanol/g sugars, and electrodialysis provided only a slight enhancement (0.06 g ethanol/g sugars). However, lowering the levels of reactive species further increased the yield to 0.25 g ethanol/g sugars, and K+ supplementation increased the yield to 0.35 g ethanol/g sugars. Overall, hydrolysis using H2SO4 + Ca(OH)2 provided the highest ethanol yield, and the yield was almost same as from conventional medium. This research emphasizes the importance of post-treatment processing that is modified for the species or strains used for bioethanol fermentation.

The use of microalgal biomass as feedstock for biofuels has been discussed for decades as it provides a sustainable approach to producing fuels for the future. Nonetheless, its feasibility has not been established yet and various aspects of biomass applications such as CO2 biofixation should also be explored. Therefore, in this study, the CO2 biofixation and lipid/carbohydrate production potential of Chlorella sp. ABC-001 were examined under various nitrogen concentrations. The highest biomass productivity and CO2 biofixation rate of 0.422 g/l/d and 0.683 g/l/d, respectively, were achieved under a nitrogen-rich condition (15 mM nitrate). Carbohydrate content was generally proportional to initial nitrate concentration and showed the highest value of 41.5% with 15 mM. However, lipid content showed an inverse relationship with nitrogen supplementation and showed the highest value of 47.4% with 2.5 mM. In consideration as feedstock for biofuels (bioethanol, biodiesel, and biogas), the sum of carbohydrate and lipid contents were examined and the highest value of 79.6% was achieved under low nitrogen condition (2.5 mM). For lipid-based biofuel production, low nitrogen supplementation should be pursued. However, considering the lower feasibility of biodiesel, pursuing CO2 biofixation and the production of carbohydrate-based fuels under nitrogenrich condition might be more rational. Thus, nitrogen status as a cultivation strategy must be optimized according to the objective, and this was confirmed with the promising alga Chlorella sp. ABC-001.

Microalgae-derived docosahexaenoic acid (DHA) production has been considered an alternative technology to overcome several disadvantages of fish oil-based DHA production. Despite its potential, efficient production methods for DHA have been rarely reported. Accordingly, in this study we investigated the potential application of Jerusalem artichoke and lipid-extracted algae (LEA) hydrolysates as inexpensive sources of carbon and other nutrients for DHA production using Aurantiochytrium sp. KRS101. Response surface methodology (RSM) with central composite design (CCD) was used to determine the maximum point of DHA productivity in the presence of 51.9 g L−1 fructose and 4.9 g L−1 yeast extract. Hydrolysis of 76.6 g L−1 Jerusalem artichoke powder with 0.25 N sulfuric acid at 70 °C yielded the desired concentration of fructose for use as the medium. Cultivation of the microalgae using the Jerusalem artichoke hydrolysate (JAH) and JAH + LEA (JLH-1) resulted in 27.8% and 31.3% improvements in biomass productivity, respectively, compared with the basal medium control. In addition, simultaneous one-step hydrolysis of Jerusalem artichoke and LEA (JLH-2) resulted in 7.2% higher biomass and 47% higher DHA yields than that obtained from hydrolyzing the two components separately (JLH-1). These results suggested that a strategy using JAH combined with LEA could replace expensive nutrient sources and produce efficient and eco-friendly DHA from Aurantiochytrium sp. KRS101.

2,3‐Butanediol (2,3‐BDO) is a promising bulk chemical owing to its high potential in industrial applications. Here, we engineered Klebsiella oxytoca for the economic production of 2,3‐BDO using mixed sugars from renewable biomass. First, to improve xylose consumption, the xylose transporter gene (xylE) was integrated into the methylglyoxal synthase A (mgsA)‐coding gene loci, and the engineered CHA004 strain showed much faster consumption of xylose than wild‐type (WT) strain with 1.4‐fold increase of overall sugar consumption rate. To further improve sugar utilization, we performed adaptive laboratory evolution for 90 days. The evolved strain (CHA006) was evaluated by cultivating it in the media containing single‐ or mixed‐sugars, and it was clearly observed that CHA006 has improved sugar consumption and 2,3‐BDO production than those of the parental strain. Finally, we demonstrated the superiority of CHA006 by culturing in two lignocellulosic hydrolysates derived from sunflower or pine tree. Particularly, in the pine tree hydrolysate containing xylose, glucose, galactose, and mannose, the CHA006 strain showed much improved consumption rates for all sugars, and 2,3‐BDO productivity (0.73 g L−1 hr−1) increased by 3.2‐fold compared to WT strain. We believe that the engineered CHA006 strain can be a potential host in the development of economic bioprocess for 2,3‐BDO through efficient utilization of mixed sugars derived from lignocellulosic biomass.

Microalgae are regarded as a promising feedstock for biofuels and value-added products but still suffer from an inefficient lipid extraction process. In the present study, a simple and energy-efficient extraction method is demonstrated to extract oil directly from the wet cake (260 g/L) of Nannochloropsis sp. with an assist from the high shear mixer (HSM). After the initial solvent screening, the composition of co-solvent and operating conditions were optimized according to lipid composition and extraction yield. The high shear-assisted extraction process was found to achieve 83% lipid extraction yield (94% for EPA) in 5 min and 95% yield (100% for EPA) in 30 min with minimal amounts of solvents (0.9 ml hexane, 0.39 ml ethanol, and 0.057 ml sulfuric acid for 1 g of wet cell) at 8000 rpm, 55 °C. In comparison with various two-step wet extraction methods, the HSM offers the most economical extraction in terms of specific energy consumption of 1.38 MJ/kg dry cell. Therefore, the HSM can be considered as an attractive alternative to conventional extraction methods, providing a new paradigm of wet extraction for microalgae.

Microalgal lipid-derived biofuels have been regarded as promising candidate materials to replace fossil fuels, but their production cost, especially for lipid extraction, still must be lowered substantially for field application. Although lipid extraction from concentrated wet microalgae using a nonpolar solvent is considered as a feasible method, an effective recovery method to regain the nonpolar solvent with microalgal lipid from the emulsified extraction mixture has not yet been addressed significantly. In this study, microalgal lipid is cost-efficiently recovered in continuous manner directly from the emulsified, highly concentrated extraction mixture by utilizing a surface-modified filter. The surface of a highly porous sponge filter is modified conformally by an oil-absorbing but water-repellent polymer coating via an initiated chemical vapor deposition (iCVD) process. Concentrated wet

Heterotrophic cultivation can be a preferred option for commercial microalgal biorefinery owing to its significantly higher productivity and lipid content leading to high value products. However, l...

Sugar refinery washing water (SRWW) contains abundant levels of carbon sources and lower levels of contaminants than other types of wastewater, which makes it ideal for heterotrophic cultivation of microalgae. Here, carbon sources in SRWW were utilized for conversion into the form of value-added docosahexaenoic acid (DHA) using Aurantiochytrium sp. KRS101. Since SRWW is not a defined medium, serial optimizations were performed to maximize the biomass, lipid, and DHA yields by adjusting the nutrient (carbon, nitrogen, and phosphorus) concentrations as well as the application of salt stress. Optimum growth performance was achieved with 30% dilution of SRWW containing a total organic carbon of 95,488 mg L−1. Increasing the nutrient level in the medium by supplementation of 9 g L−1 KH2PO4 and 20 g L−1 yeast extract further improved the biomass yield by an additional 14%, albeit at the expense of a decrease in the lipid content. Maximum biomass, lipid, and DHA yields (22.9, 6.33, and 2.03 g L−1, respectively) were achieved when 35 g L−1 sea salt was applied on a stationary phase for osmotic stress. These results demonstrate the potential of carbon-rich sugar refinery washing water for DHA production using Aurantiochytrium sp. KRS101 and proper cultivation strategy.

In the hydrolysis of microalgae with a solid catalyst, a novel rotating packed bed reactor (RPBR) was developed to improve the recyclability of the Amberlyst 36, a solid-acid catalyst. In a previous study, the hydrolysis of Golenkinia sp. using Amberlyst 36 with nitric acid in a conventional batch reactor was carried out, but the solid catalyst could only be recycled for four consecutive runs due to damage to the catalyst structure. As a solution to this catalyst degradation/destruction problem, Amberlyst 36 was charged in the packed bed column and was rotated instead of using impellers in an autoclave reactor. The packed bed column prevented the solid-acid catalyst from physical attrition caused by stirring with impellers, resultantly the recyclability of the solid catalyst increased dramatically. In addition to this, our approach of using the rotating packed bed column facilitated the particle-particle interactions between the catalyst and biomass, as a result of which high sugar yields of more than 70% (g/g) was achieved within four runs. Moreover, the reusability of Amberlyst 36 could be raised to 11 runs by simply employing a combination of two additional processes, sonication and reactivation processes with sulfuric acid solution. With our novel approach of using RPBR, a solid catalyst can be used perpetually for hydrolysis of algal biomass, which makes the process of hydrolysis efficient and economical compare to the conventional batch reactor.

This study sets out to harvest microalgae through auto-flocculation by manipulating the interactive effect of calcium, phosphate, and polysaccharides (PSAs). The harvesting efficiency (H.E) of 91 ± 2.7% was achieved for Ettlia sp. through auto-flocculation. The H.E was attributed to the chelation of calcium and PSAs present in microalgae medium. In the absence of PSAs, the H.E reduced to 64 ± 05% only. The addition of phosphate (34 ± 0.13 mg L−1) increased the H.E to 73 ± 1.5%. Zeta-potential measurements showed that the harvesting was induced by charge neutralization and inter-particle bridging. The PSAs-based auto-flocculation was tested for Chlorella sp. too but it turned out the H.E of 51 ± 1.3% only. The flocculation did not take place when the co-harvesting of Ettlia sp. and Chlorella sp. was carried out. It is concluded that each microalgae specie shows different auto-flocculation mechanism due to variation in their PSAs characteristics. It triggers up the need for setting up a distinct protocol for different microalgae species to assess their auto-flocculation potential.

Background Current efforts on the optimization of the two-stage cultivation using stress-induced lipid accumulation have mostly focused only on the lipid induction stage. Although recent studies have shown that stress-induced lipid accumulation is affected by the physiological status of the cells harvested at the preceding cultivation stage, this issue has hardly been examined hitherto. Such a study needs to be carried out in a systematic way in order to induce lipid accumulation in a consistent and predictable manner with regard for variances seen at the cultivation stage. Results After a photoautotrophic cultivation of Chlorella sorokiniana HS1 in a modified BG11, harvested cells were re-suspended in the fresh medium, and then NaCl was added as the sole stress inducer with light illumination to induce additional accumulation of lipid. Effects of culture temperature on the lipid accumulation were analyzed by the Kruskal–Wallis test. From the microscopic observation, we had observed a definite increase in lipid body induced by the stress since the cell entered a stationary phase. A multiple linear regression model was developed so as to identify significant parameters to be included for the estimation of lipid induction. As a result, several key parameters at the end of cultivation, such as cell weight, total lipid content, chlorophyll a in a cell, and Fv/Fm, were identified as the important proxy variables for the cell’s physiological status, and the modeling accuracy was achieved by 87.6%. In particular, the variables related to Fv/Fm were shown to have the largest influence, accounting for 65.7% of the total variance, and the Fv/Fm had an optimal point of maximum induction at below its average. Clustering analysis using the K-means algorithm indicated that the algae which are 0.15 pg cell−1 or less in chlorophyll concentration, regardless of other conditions, had achieved high induction results. Conclusion Experimental results showed that it usually achieves high lipid induction after the cells naturally end their division and begin to synthesize lipid. The amount of lipid induction could be estimated by the selected proxy variables, and the estimation method can be adapted according to practical situations such as those with limited measurements.

This study aimed to investigate the symbiotic relationship of two freshwater microalgae species, Ettlia sp. and Chlorella sp. HS-2 to improve biomass productivity. The species were co-cultivated autotrophically under the inoculation ratios (Chlorella/Ettlia) of 1:01, 1:04, 1:08, and 1:16. The performance of co-cultivation was compared with monoculture. It found that the co-cultivation returned higher biomass productivity (P

This study investigated the growth-dependent role of algal organic matters (AOMs) to achieve high removal efficiency (R.E) of microalgae. The results showed that the microalgae cells produced 96 ± 2% of total AOMs as loose bound AOMSS (LB-AOMs) and 4 ± 1% as cell-bound (CB-AOMs) in exponential phase. In stationary phase, LB-AOMs and CB-AOMs were 46 ± 0.7percentage and 54 ± 0.2 percentage, respectively. The R.Es in exponential and stationary phase were 83 ± 2.6% and 66 ± 1.2%, respectively. It is found that the difference of biomass concentration (between exponential and stationary phase) had no significant impact on the R.E (P > 0.01). Further investigations revealed that LB-AOMs inhibit flocculation in exponential and CB-AOMs in stationary phase; however, CB-AOMs showed stronger inhibition than the LB-AOMs (P < 0.01). The provision of calcium (17 ± 0.9 mg/L) to the culture reduced the AOMs inhibition and improved the R.E from 66 ± 1.2% (in control) to 90 ± 4.2%. An increase in R.E was attributed to the interaction of calcium with AOMs and subsequently acting as a flocculant. The findings of this study can be valuable to improve the performance of auto-flocculation technology, which is mainly limited by the presence of AOMs.

The light greatly affects the physiological properties of microalgae, but the outcome is species-specific. To improve the traits of microalgae suitable for biofuel production, we investigated the influence of the light on biomass and lipid productivity of Chlorella sp. HS2. Photosynthetic performance in terms of relative electron transport rate (rel. ETR) was maximized at 450 μmol photons m−2 s−1, which allowed cells to reach high biomass productivity of 1.10 g L−1 day−1. Although the stress was induced by excessive irradiance under 750 μmol photons m−2 s−1, Chlorella sp. HS2 was able to maintain a high growth rate and achieved higher biomass productivity (1.34 g L−1 day−1) compared to that of other Chlorella species. In an effort to understand the relationship between photosynthesis and biomass productivity, we found out that effective quantum yield [Y(II)] and rel. ETR of Chlorella sp. HS2 is relatively higher than that of Chlorella vulgaris. The total lipid content decreased as the light intensity increased at the exponential phase. Interestingly, however, this trend was reversed during the stationary phase. This implies that the high light may synergistically induce lipids when the cells undergo nutrient starvation. The lipid content and productivity continued to increase up to 0.25 g L−1 day−1 even after the light saturation point. The fraction of esterifiable lipid suitable for biodiesel production rapidly increased from 50% to 99% during the stationary phase. These results suggest that species-specific high light based cultivation can be an effective strategy to improve the lipid productivity in Chlorella sp. HS2.

Chlorella spp. are green algae that are found across wide-ranging habitats from deserts to arctic regions, with various strains having adapted to survive under diverse environmental conditions. In this study, two novel Chlorella strains (ABC-002, ABC-008) were isolated from a freshwater lake in South Korea during the winter season and examined for possible use in the biofuel production process. The comparison of ABC-002 and ABC-008 strains with Chlorella vulgaris UTEX265 under two different temperatures (10°C, 25°C) revealed their cold-tolerant phenotypes as well as high biomass yields. The maximum quantum yields of UTEX25, ABC- 002, and ABC-008 at 10°C were 0.5594, 0.6747, and 0.7150, respectively, providing evidence of the relatively higher cold-resistance capabilities of these two strains. Furthermore, both the biomass yields and lipid content of the two novel strains were found to be higher than those of UTEX265; the overall lipid productivities of ABC-002 and ABC-008 were 1.7 ~ 2.8 fold and 1.6 ~ 4.2 fold higher compared to that of UTEX265, respectively. Thus, the high biomass and lipid productivity over a wide range of temperatures indicate that C. vulgaris ABC-002 and ABC-008 are promising candidates for applications in biofuel productions via outdoor biomass cultivation.

Flocculation is an effective technique for harvesting microalgae due to low energy input and being scalable up to industrial algaculture. In this study, four different flocculants at various concentration, and pH levels were employed for the harvesting of Chlorella sp. HS2. Among the tested flocculants, chitosan showed the highest flocculation efficiency of 99.6% ± 0.25 at 10 mg L−1 dosage, pH 8.0 and 30 min of sedimentation. It turned out that the choice of flocculants had minimum impact on the fatty acids methyl ester (FAME) yield and composition. When the reusability of the spent medium for each flocculant was investigated, the culture supernatant obtained from chitosan-based harvesting method had lower growth inhibitory effects in comparison to those harvested using the other flocculants. The cost analysis also favored chitosan-based flocculation, because it returned the highest flocculant efficiency while the flocculant dosage was the lowest. Due to its high harvest efficiency and low impact on the water footprint, it was concluded that the chitosan offer promising advantages over other flocculants.

Economical production of fucose from fucoidan requires an efficient process for the separation of high-purity fucose from fucoidan hydrolysate. To address this issue, we aimed to develop a simulated-moving-bed (SMB) process that could be well tailored to the final-stage purification of fucoidan hydrolysate while ensuring the attainment of high purity and high recovery. For this task, we first determined the intrinsic parameters of all the components in the fucoidan hydrolysate. The resulting intrinsic parameters were then applied to the optimal design of the considered SMB process, in which the optimal column configuration and operation parameters leading to the highest removal rates for the side-products (or impurities) of the fucoidan hydrolysate were determined using a genetic-algorithm and a column-model in combination. On the basis of such optimal configurations and operation parameters, the SMB experiments were carried out while loading a real fucoidan-hydrolysate solution into the SMB feed port. It was confirmed from the experimental results that the developed process in this study was quite effective in the continuous-mode recovery of fucose from the fucoidan hydrolysate with high purity (nearly 100%) and little loss (

While lipid extraction from wet microalgae has attracted attention as an economical method for microalgal biofuel production, few studies have focused the actual separation of extract phase from the emulsified extraction mixture. Here, a novel approach which utilizes hydrophobic/oleophilic filter was developed for the efficient solvent recovery. The filter was surface-modified by coating a functional polymer via initiated vapor deposition for the selective solvent permeability. While acid-treated Chlorella sorokiniana HS1 and n-hexane was stirred for lipid extraction, tubular filter module was immersed into the mixture for separation. The mixture was kept stirred during the separation to inhibit the buildup of cell debris on the filter by inducing crossflow on the filter. Extract phase was separated directly from the raffinate phase with high separation efficiency (> 98.3%) while maintaining permeation flux. The place-, space- and energy-efficient strategy reported here could be a useful tool for the solvent extraction process.

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.

For energy-efficient harvesting of microalgae using a hollow fiber membrane, a turbulent jet was implemented to induce local high crossflow velocity near the membrane surface for fouling reduction during microfiltration. The performance of the turbulent jet-assisted module was evaluated and compared to that of a control group that represented other types of flow conditions including the conventional-type hollow fiber membrane module. When assisted by the turbulent jet, permeate flux at the steady-state increased by 126% and the specific energy for filtrating out a unit volume of permeate was reduced by 38% relative to the conventional type. In the results of a computational fluid dynamics analysis, the wall jet created after impingement of the jet flew along the membrane surface with a reduced boundary layer, and it is expected that this provided a scouring phenomenon. Shear stress on the membrane surface increased 3.7-fold on average, and was highest at the point of impingement. With regard to energy efficiency, concentrating on increasing the local fluid velocity near the membrane via turbulent jets rather than increasing the entire feed recirculation is more practical to improve the filtration performance for microalgae harvesting with low power consumption.

An efficient process suitable for a large-scale production of fucose from the seaweed of Undaria pinnatifida was developed in this study. The developed process consisted of a hydrolysis, a series of pretreatment processing for decolorization and deionization, and a final-stage purification using a well-designed simulated-moving bed (SMB) process. First, the optimal acid concentration and reaction time for the seaweed hydrolysis were investigated. The hydrolysate resulting from such investigation was then used to determine the optimal operating conditions for the pretreatment step consisting of an activated-carbon treatment, an electrodialysis, and an ion-exchange processing, which were performed to accomplish decolorization and deionization. On the basis of the optimal conditions that were obtained from the preceding experiments, a series of hydrolysis and pretreatment operations were carried out to secure a sufficiently large amount of decolorized and deionized hydrolysate. This was then moved on to the final purification step based on the use of the SMB process, which was designed such that the detailed recovery of fucose with a very high purity in a continuous mode could be ensured. The results showed that the purity of fucose, which reached 15.4% after the completion of the pretreatment processing, was markedly increased to nearly 100% through the SMB processing. It was also confirmed that the overall loss of fucose amounted to 22.9%, and most of the fucose loss occurred during the electrodialysis and ion-exchange procedures whereas there was almost no loss during the SMB processing.

In this work, the two-stage cultivation of Chlorella sp. HS2 for enhancing the lipid productivity was optimized by adjusting the duration of nitrogen-replete (N+) and -deplete (N−) stages within a 9 day period using urea as nitrogen source. The highest lipid content of 36.7% and productivity of 216.9 mg L−1 d−1 were obtained under five days of N+ followed by four days of N− conditions. Replenishing phosphorus and other nutrients (N−P+O+) at the beginning of the nutrient-starvation resulted in 1.55 and 1.68-folds improvement in lipid productivities compared to the single stage and zero nutrient controls (N−P−O−), respectively. The estimated biodiesel properties based on the fatty acid profiles met all criteria of international standards. The findings of this study indicate that properly adjusting the period of nitrogen availability as well as the presence of other nutrients is highly important in order to maximize the biofuel productivity in two-stage microalgal cultivation.

While the screening and development of robust algal crops have mostly focused on determining strains that exhibit the highest possible yields of biomass or desirable biomolecules, these criteria do not necessarily lead to finding algal strains with high tolerance to varying outdoor cultivation conditions. Herein, we report Chlorella sp. HS2 isolated from a tidal rock pool nearby a local coastal waterfall that presumably experienced fluctuations in salinity, pH, and temperature. Compared to two reference strains, Chlorella sp. HS2 exhibited relatively high tolerance to a wide range of salinity (0–5% (w/v) of supplemental NaCl), pH (3.0–10.5), and temperature (14–46 °C) with substantially high biomass accumulation. While the supplementation of either gaseous CO2 or sodium bicarbonate enhanced algal growth, the mixotrophic and heterotrophic cultivations of Chlorella sp. HS2 further indicated its propensity to grow favorably under the presence of organic carbon sources. Subsequent PBR cultivation of Chlorella sp. HS2 under optimal light and/or temperature conditions suggested the highest specific growth rate during mixotrophy, while the analyses of the harvested biomass identified palmitate, oleate, and linoleate as major fatty acid methyl esters, and lutein and s-carotene as predominant carotenoids. Substantially, high growth rates of Chlorella sp. HS2 under a wide range of abiotic conditions and different trophic modes with favorable biochemical composition thus strongly support our algal isolate as a robust and reliable algal crop that can be deployed to achieve high production of commercially important biomolecules and to incorporate simultaneous treatment of wastewater or CO2-replete flue gas into algal cultivation.

In this article, a conceptual process design for the production of lactide is proposed, where an one-step gas phase synthesis route is adopted. Then, the proposed process is evaluated and compared ...

Microalgae are promising feedstocks for sustainable and eco‐friendly production of biomaterials, which can be improved by genetic engineering. It is also necessary to optimize the processes to produce biomaterials from engineered microalgae. We previously reported that genetic improvements of an industrial microalga Nannochloropsis salina by overexpressing a basic helix‐loop‐helix transcription factor (NsbHLH2). These transformants showed an improved growth and lipid production particularly during the early phase of culture under batch culture. However, they had faster uptake of nutrients, resulting in earlier starvation and reduced growth during the later stages. We attempted to optimize the growth and lipid production by growing one of the transformants in continuous culture with variable dilution rate and feed nitrogen concentration. Relative to wild‐type, NsbHLH2 transformant consumed more nitrate at a high dilution rate (0.5 day −1), and had greater biomass production. Subsequently, nitrogen limitation at continuous cultivation led to an increased fatty acid methyl ester production by 83.6 mg l −1 day −1. To elucidate genetic mechanisms, we identified the genes containing E‐boxes, known as binding sites for bHLH transcription factors. Among these, we selected 18 genes involved in the growth and lipid metabolism, and revealed their positive contribution to the phenotypes via quantitative real‐time polymerase chain reaction. These results provide proof‐of‐concept that NsbHLH2 can be used to produce biomass and lipids.

Although microalgae produce value-added products, such as lipids, pigments, and polysaccharides using light and carbon dioxide, these intracellular products require costly downstream processes such as extraction and purification. Thus, extracellular products are desirable for economic production. While reported before, the secretion of glycolic acid by microalgal photorespiration has not received attention for industrial applications. We developed a two-stage continuous cultivation system to increase glycolic acid production using a glycolate dehydrogenase (GYD1) deficient mutant of Chlamydomonas reinhardtii which produces high concentrations of glycolic acid. Specifically, 3% CO2 was supplied in the first-stage culture for the production of biomass and ambient air (0.03% CO2) was supplied to the second stage for the production of glycolic acid. As a result, overall glycolic acid productivity reached 82.0 mg L-1 d-1 at a dilution rate of 0.34 d-1. However, as the pH of the second stage decreased to 4.7 due to the increased glycolic acid production, we controlled the pH of the second stage at pH 6.0, resulting in 122.6 mg L-1 d-1 of glycolic acid productivity. Flux balance analysis revealed that the experimental glycolic acid production rate was 69% of the theoretical glycolic acid production rate. The deviation might be due to the toxicity of glycolic acid. When a techno-economic analysis was conducted based on the experimental results, the minimum glycolic acid production cost was estimated to be $31 kg-1, indicating a potential for industrial production. These findings suggest that microalgae can be utilized for the cost-effective industrial production of glycolic acid.