Search

We have developed a template-free, easily controllable, and simple method for the mass production of hydrogenated iron oxide nanoparticles (NPs). These NPs were formed with a regular spherical shape by underwater plasma discharge treatment at room temperature and atmospheric pressure. The various phases of well-crystallized iron oxide NPs were carefully monitored by controlling the amount of hydrazine. Further, the obtained Brunauer–Emmett–Teller surface area of 67.86 m2/g was much larger than that of a commercial sample (32.40 m2/g), which was further increased to 85.07 m2/g by adjusting the amount of hydrazine. The removal efficiency for heavy metal and organic dyes was obtained to be ~100%, which was 10 times faster than that of the commercial sample. Furthermore, ~100% flocculation efficiency was obtained by using only 6 g/g microalgal cell of the prepared iron oxide, whereas no significant change was observed for commercial iron oxide irrespective of the amount of flocculant. These excellent efficiencies for the removal of pollutant from waste water can be originated in the high specific surface area, relatively positively charged surface, and good crystallinity of the synthesized samples. These indicate that the hydrogenated iron oxide NPs in this study are potentially useful for water purification by serving as an adsorbent, photocatalytic material, and flocculant.

Chlorella is a promising microalga for CO

In the past decade, researchers in the fields of energy production have concentrated on the improvement of new energy storage devices. Lithium-ion batteries (LIBs) and faradaic supercapacitors (FSs) have attracted special attention as a result of the rapid development of new electrode nanomaterials, especially hybrid nanomaterials, which can meet the increasingly higher requirements for future energy, such as the capability to deliver high-power performance and an extremely long life cycle. In these hybrid nanostructures, a series of synergistic effects and unique properties arising from the combination of individual components are a major factor leading to improved charge/discharge capability, energy density, and system lifetime. This paper describes the most recent progress in the growth of hybrid electrode materials for LIBs and FSs systems, focusing on the combination of zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) nanomaterials, respectively.

In this paper, it is first reported that gray hydrogenated TiO2 sphere photocatalysts (H-TiO2) with high reactivity to solar light are mass produced within a few minutes using an underwater discharge plasma modified sol-gel method at room temperature and atmospheric pressure. This plasma modified system is an easy one-step in-situ synthetic process and the crystallinity, hydrogenation, and spherical structure of H-TiO2 are achieved by the synergy effect between the continuous reaction of highly energetic atomic and molecular species generated from the underwater plasma and surface tension of water. The resultant H-TiO2 demonstrated high anatase/rutile bicrystallinity and extended optical absorption spectrum from the ultraviolet (UV) to visible range. Furthermore, various defects including oxygen vacancies and hydroxyl species on the TiO2 surface permitted the enhancement of the photocatalytic performance. It was demonstrated that H-TiO2 photocatalysts showed significant degradation efficiencies for reactive black 5 (RB 5), rhodamine B (Rho B), and phenol (Ph) under solar light irradiation, up to approximately 5 times higher than that of commercial anatase TiO2 (C-TiO2), which resulted in good water purification. Notably, it was also possible to cultivate HepG2 cells using such well-purified water (to degrees up to 76%), with minimal cytotoxicity. Considering all these results, we believe that this novel plasma technology is promising for important environmental applications.

Microalgae can offer several benefits for wastewater treatment with their ability to produce large amounts of lipids for biofuel production and the high economic value of harvested biomass for biogas and fertilizer. This study found that salt concentration (∼45gL-1) had more of an effect than salt type on metabolisms of Chlorella vulgaris for wastewater treatment and biofuel production. Salinity stress decreased the algal growth rate in wastewater by 0.003day-1permScm-1 and slightly reduced nutrient removal rates. However, salinity stress was shown to increase total lipid content from 11.5% to 16.1% while also increasing the saturated portions of fatty acids in C. vulgaris. In addition, salinity increased the algal settling rate from 0.06 to 0.11mday-1 which could potentially reduce the cost of harvesting for algal biofuel production. Overall, C. vulgaris makes a suitable candidate for high salinity wastewater cultivation and biofuel production.

We introduce a novel approach for the high-value production of nano/micro hierarchical structured Sn anodes for lithium-ion batteries (LIBs) by utilizing microalgal biomass residues that collaterally form during oil extraction for biofuel production. The Sn/C composites made from the oil-extracted microalgal biomass residues (the extracted Sn/C) exhibit the following advantages as high-energy-density anodes: 1) a homogeneous distribution of Sn nanoparticles in the carbon matrix (Sn/C), which efficiently relieves the strain caused by volume changes of the active materials; 2) a high porosity of Sn/C composites; and 3) a homogeneous distribution of the hetero elements N and P in the carbon matrix. Overall, the extracted Sn/C exhibit improved electrochemical performance in LIBs compared with the Sn/C composites made from the microalgal biomass residues without oil extraction (non-extracted Sn/C). The extracted Sn/C have improved rate capabilities (160.0 and 72.9 mAh g −1 for the extracted Sn/C and the non-extracted Sn/C, respectively, at the 80th cycle, 3.5 A g −1 ) and improved cycle performances (511.7 and 493.2 mAh g −1 for the extracted Sn/C and the non-extracted Sn/C, respectively, at the 300th cycle, 200 mA g −1 ).

Chemical flocculation is considered to be an overall low-cost and up-scalable process for harvesting of microalgae. In this study a new flocculation approach utilizing metal coagulant (Fe2(SO4)3) and sulfuric acid (H2SO4) was introduced for harvesting of Chlorella sp. KR-1, which overcome two main issues of contamination and reuse of coagulant. Reduction of pH successfully released precipitates attached to the microalgae, and the remaining acidic solution containing recovered ferric ions could be reused for harvesting up to three times with high, better-than 98% efficiencies. Moreover, the acid-treated microalgal biomass could be directly used for lipid extraction without additional catalyst. High extraction yields of around 32% were achieved with FAME conversion efficiencies of around 90%. The integrated approach devised in the present study is expected to make the best use of the age-old yet effective harvesting means of flocculation, which can be a practical and economical option in microalgal biorefinery.

In situ transesterification (direct conversion) of microalgal cells is a promising method to produce biodiesel from microalgae because it integrates the oil extraction and conversion process in one step. Not only biodiesel but also a few biochemicals can be produced through this process because both lipids and carbohydrates are converted under acidic conditions. Levulinic acid ester (levulinate) is one of the byproducts of in situ transesterification, which can be used as an additive in fuels or fragrances. This study investigated the effect of cell composition and reactive variables on the productivity of levulinic acid ester. The cell compositions of microalgal strains were compared between Nannochloropsis and Chlorella , and more levulinate was produced from carbohydrate-rich Chlorella cells. Both reaction temperature and acid concentration highly affected the levulinate yield, whereas the type of alcohols did not have much influence on the yield. Consequently, more than 40 mol% glucose inside the cell was converted to levulinate with a 15 v% sulfuric acid concentration at 130 °C.

The electrochemical conversion of CO2 can include renewable surplus electricity storage and CO2 utilisation. This review focuses on the microbial CO2 electrobiorefinery based on microbial electrosynthesis (MES) which merges electrochemical and microbial conversion to produce biofuels and higher-value chemicals. In this review, recent developments are discussed about bioelectrochemical conversion of CO2 into biofuels and chemicals in MES via microbial CO2-fixation and electricity utilisation reactions. In addition, this review examines technical approaches to overcome the current limitations of MES including the following: engineering of the biocathode, application of electron mediators, and reactor optimisation, among others. An in-depth discussion of strategies for the CO2 electrobiorefinery is presented, including the integration of the biocathode with inorganic catalysts, screening of novel electroactive microorganisms, and metabolic engineering to improve target productivity from CO2.

Anaerobic ammonium oxidation (anammox), a low-energy-consuming technology, can be used to remove nitrogen from industrial saline wastewater. However, high salinity inhibits anammox microbial activity. This study investigated the effect of salinity on nitrogen removal performance and microbial community structure. The experiment used an up-flow anammox reactor fed with synthetic wastewater with salinity increased from 0.5 to 2.5%. Results indicated that 80% nitrogen removal efficiency can be achieved at 2% salinity with a nitrogen loading rate of 2.0 kg-N/m3/d. Anammox performance significantly deteriorated at 2.5% salinity. High-throughput sequencing revealed that Planctomycetes (representative anammox bacteria) increased with salinity, replacing Proteobacteria (representative heterotrophic denitrifying bacteria) in the microbial community. qPCR analysis indicated that relative abundance of “Candidatus Kuenenia” within anammox bacteria increased from 3.96 to 83.41%, corresponding to salinity of 0.5–2.0%, and subsequently decreased to 63.27% at 2.5% salinity, correlating with nitrogen-removal performance. Thus, anammox has potential in nitrogen removal from wastewater with salinity up to 2%.

Blue-green microalgal blooms have been caused concerns about environmental problems and human-health dangers. For removal of such cyanobacteria, many mechanical and chemical treatments have been trialled. Among various technologies, the flocculation-based harvesting (precipitation) method can be an alternative if the problem of the low yield of recovered biomass at low concentrations of cyanobacteria is solved. In the present study, it was utilized mixtures of magnesium aminoclay [MgAC] and cerium aminoclay [CeAC] with different particle sizes to harvest cyanobacteria feedstocks with ∼100% efficiency within 1h by ten-fold lower loading of ACs compared with single treatments of [MgAC] or [CeAC]. This success was owed to the compact networks of the different-sized-ACs mixture for efficient bridging between microalgal cells. In order to determine the usage potential of biomass harvested with AC, the mass was heat treated under the reduction condition. This system is expected to be profitably utilizable in adsorbents and catalysts.

Recently, biofuels and nutraceuticals produced from microalgae have emerged as major interests, resulting in intensive research of the microalgal biorefinery process. In this paper, recent developments in cell-wall disruption and extraction methods are reviewed, focusing on lipid and astaxanthin production from the biotechnologically important microalgae Chlorella and Haematococcus, respectively. As a common, critical bottleneck for recovery of intracellular components such as lipid and astaxanthin from these microalgae, the composition and structure of rigid, thick cell-walls were analyzed. Various chemical, physical, physico-chemical, and biological methods applied for cell-wall breakage and lipid/astaxanthin extraction from Chlorella and Haematococcus are discussed in detail and compared based on efficiency, energy consumption, type and dosage of solvent, biomass concentration and status (wet/dried), toxicity, scalability, and synergistic combinations. This report could serve as a useful guide to the implementation of practical downstream processes for recovery of valuable products from microalgae including Chlorella and Haematococcus.

In this study, we aimed to demonstrate the feasibility of the application of biocompatible liquid type fluorescent carbon nanodots (C-paints) to microalgae by improving microalgae productivity. C-paints were prepared by a simple process of ultrasound irradiation using polyethylene glycol (PEG) as a passivation agent. The resulting C-paints exhibited a carbonyl-rich surface with good uniformity of particle size, excellent water solubility, photo-stability, fluorescence efficiency, and good biocompatibility ( 20% higher than the control cell content). A C-paints concentration of 1–10.0 mg mL−1 induced an approximately >1.8 times higher astaxanthin content than the control cells. The high light delivery effect of non-cytotoxic C-paints was applied as a stress condition for H. pluvialis growth and was found to play a major role in enhancing productivity. Notably, the results from this study are an essential approach to improve astaxanthin production, which can be used in various applications because of its therapeutic effects such as cancer prevention, anti-inflammation, immune stimulation, and treatment of muscle-soreness.

The residual biomass of Chlorella sp. KR-1 obtained after lipid extraction was used for saccharification and bioethanol production. The carbohydrate was saccharified using simple enzymatic and chemical methods using Pectinex at pH 5.5 and 45°C and 0.3N HCl at 121°C for 15min with 76.9% and 98.2% yield, respectively, without any pretreatment. The residual biomass contained 49.7% carbohydrate consisting of 82.4% fermentable sugar and 17.6% non-fermentable sugar, which is valuable for bioethanol fermentation. Approximately 98.2% of the total carbohydrate was converted into monosaccharide (fermentable+non-fermentable sugar) using dilute acid saccharification. The fermentable sugar was subsequently fermented to bioethanol through separate hydrolysis and fermentation with a fermentation yield of 79.3%. Overall, 0.4g ethanol/g fermentable sugar and 0.16g ethanol/g residual biomass were produced.

Microalgae have received significant attention as promising resources for biodiesel. However, the downstream processes for the production of biodiesel, which range from cultivation, harvesting, dewatering, and lipid extraction to oil upgrading, are economically impracticable and can be improved. Therefore, efficient microalgal harvesting and integrated technologies are required to realize microalgae-based biodiesel. Herein, tri-functional (cationic, magnetic, and lipophilic) carbon microparticles filled with magnetite (Fe 3 O 4 ) are synthesized through one-step aerosol spray pyrolysis and applied in microalgal harvesting and serial microalgal lipid entrapment. Carbon microparticles are tri-functional in the following respects: (i) the cationic carbon microparticles facilitate flocculation with anionic microalgae due to electrostatic attractions; (ii) the magnetic properties of the carbon microparticles, owing to embedded magnetites, enable the separation of microalgal flocs from low concentration cultures (∼2 g L −1 ) with a separation efficiency of 99%; and (iii) the lipophilicity enables the recovery of lipid droplets extracted from oleaginous microalgae. Microalgal lipids are directly separated through adsorption onto magnetic carbon microparticles from concentrated microalgal slurries after harvesting. The tri-functionality may facilitate the integrated use of magnetic carbon microparticles in microalgal biorefineries and the tri-functional microparticles could potentially be applied in various areas such as biomedicine, catalysis, magnetism, energy materials, and environmental remediation.

In this study, a simultaneous process of harvesting biomass and extracting crude bio-oil was attempted from wet microalgae biomass using FeCl 3 and Fe 2 (SO 4 ) 3 as both coagulant and cell-disrupting agent. A culture solution of Chlorella sp. KR-1 was firstly concentrated to 20 g/L and then proceeded for cell disruption with the addition of H 2 O 2 . Optimal dosage were 560 and 1060 mg/L for FeCl 3 and Fe 2 (SO 4 ) 3 , showing harvesting efficiencies of more than 99%. Optimal extraction conditions were identified via the response surface method (RSM), and the extraction yield was almost the same at 120 °C for both iron salts but FAME compositions after transesterification was found to be quite different. Given iron salts were a reference coagulant in water treatment in general and microalgae harvesting in particular, the present approach of using it for harvesting and oil-extraction in a simultaneous manner can serve as a practical route for the microalgae-derived biodiesel production.

Rapid pyrolysis of two Chlorella sp. KR-1 samples, with triglyceride content of 23.8 and 44.9wt%, was conducted using pyrolysis gas chromatograph-mass spectrometry over a temperature range (400–600 °C). The effects of triglyceride content of the microalgal cells and pyrolysis temperature on the structure and distribution of products were analyzed and the pyrolysis products were classified according to number of carbons and chemical species. The triglyceride content of microalgal cells was found to affect the concentration of free fatty acids, hydrocarbons, and derivatives of carbohydrates. In the case of the lipid-rich sample, free fatty acids originating from triglyceride decomposition were found to be the predominant compounds whereas sugar-dehydrated products such as anhydroglucose were the predominant compounds in the case of the lipid-poor sample.

In this study, oxidized dye wastewaters were tested for their potential to be used as a cheap coagulant for microalgae harvesting. Two dyes (methylene blue (MB) and methyl orange (MO)) were selected as model dyes, and the Fenton-like reaction under high temperature (90 °C, 1 min) employed as an oxidative treatment option. A maximum harvesting efficiency over 90% was obtained with both MB and MO at a dilution ratio of 5:1 (dye wastewater: cell culture), when the optimal oxidation condition was 20 mg/L of dye, 1 mM of FeCl3, and 0.5% of H2O2 concentration. This phenomenon could be explained by the possibility that amine groups are formed and exposed in oxidized dyes, which act as a kind of amine-based coagulant just like chitosan. This study clearly showed that dye wastewater, when properly oxidized, could serve as a potent coagulant for microalgae harvesting, potentially rendering the harvesting cost reduced to a substantial degree.

In this study, pyrite (FeS2) was used for lipid extraction as well as esterification processes for microalgae-based biodiesel production. An iron-mediated oxidation reaction, Fenton-like reaction, produced an expected degree of lipid extraction, but pyrite was less effective than FeCl3 commercial powder. That low efficiency was improved by using oxidized pyrite, which showed an equivalent lipid extraction efficiency to FeCl3, about 90%, when 20 mM of catalyst was used. Oxidized pyrite was also employed in the esterification step, and converted free fatty acids to fatty acid methyl esters under acidic conditions; thus, the fatal problem of saponification during esterification with alkaline catalysts was avoided, and esterification efficiency over 90% was obtained. This study clearly showed that pyrite could be utilized as a cheap catalyst in the lipid extraction and esterification steps for microalgae-based biodiesel production.

Microalgae, as biodiesel feedstock, are promising renewable energy sources that can be continuously developed into the future. Because recovery of microalgal lipid from dry microalgae incurs high costs, particularly in the dewatering process, wet extraction has been suggested as an attractive alternative approach. In the present study, the feasibility of a sonication-assisted homogenization system for lipid extraction from Chlorella vulgaris was evaluated. To that end, lipid-extraction performance, according to reaction time, cell concentration, and solvent type, was investigated. The initial fatty acid content of the C. vulgaris was 360.2 mg/g cell. The combination of sonication and homogenization broke up the microalgal cell walls, thereby facilitating lipid recovery. By this method, the lipid-recovery yields were increased compared with that by solo use of either homogenization or sonication. Further, chloroform-methanol, as a recovery solvent, significantly enhanced lipid recovery (237.5 mg lipid/g cell at 60 min reaction time) relative to hexane (152.0 mg lipid/g cell at 60 min reaction time).

Hydrodeoxygenation (HDO) processes have been developed to remove the oxygenated compounds in lipids. However, the HDO process consumes excess hydrogen. As opposed to the HDO process, decarboxylation does not require hydrogen. In this study, decarboxylation of oleic acid without hydrogen was carried out over unsupported CoMo catalysts. Unsupported CoMo catalysts were prepared by a co-precipitation method. The Co/Mo ratio was systematically varied to optimize unsupported CoMo catalyst. The catalyst properties were studied using various characterization techniques and related to the activity results in decarboxylation.

The endocrine-disrupting chemical, bisphenol A (BPA) has attracted much attention due to its estrogenic activity and widespread environmental distribution. The toxicity and cellular stresses of BPA to Chlamydomonas mexicana and Chlorella vulgaris and its biodegradation/bioaccumulation by both microalgae were investigated. The 120-h EC 50 of BPA for C. mexicana and C. vulgaris were 44.8 and 39.8 mg L −1 , respectively. The dry cell weight and chlorophyll a content of both microalgae decreased with increasing BPA concentration higher than 10 mg L −1 . Growth of C. vulgaris was significantly inhibited at 50 mg L −1 BPA compared to C . mexicana . Total nitrogen (TN) and total phosphorous (TP) removal was higher in C . mexicana than in C. vulgaris . Microalgae performed the bioaccumulation and biodegradation of BPA to varying extents at different initial BPA concentrations. The highest rates of BPA biodegradation, 24 and 23% by C. mexicana and C. vulgaris , respectively, were achieved at 1 mg L −1 BPA. Both the total fatty acid and carbohydrate contents increased with increasing BPA concentration. This study demonstrated that C. mexicana was more tolerant to BPA and could be used for treatment of BPA contaminated aqueous systems.

The tendency towards agglomeration and oxidation of nanoscale zero-valent iron (nZVI) particles limits its application for in situ groundwater and soil remediation. Although the effect of surface coatings on nanoparticle stabilization has been commonly practiced, the effect of preparation procedures on aging of stabilized nZVI needs to be investigated. The effect of washing and storage, up to seven days, on aging of Mg-aminoclay (MgAC) coated nZVI is evaluated, following three procedures: pre- and post-storage washing with a 1 mM NaHCO3 solution, and pre-storage washing with a stabilizer (MgAC) solution. Even though the initial particle size is identical, the observed size of pre-washed nZVI increases up to six times. This high aggregation tendency appears to be due to the desorption of MgAC during washing and storage, as verified by a decrease in the zeta potential, indicating a decrease of repulsion between nZVI particles. On the other hand, pre-storage washing is essential, in order to retain nZVI reactivity, by removal of residual reactants in the synthesis mixture. The reactivity of nZVI is examined with three parameters: optical density at 508 nm as a measure of particle concentration, reactive iron content measured by H2 generation with acid digestion, and nitrate reduction capacity. All three parameters decrease significantly for post-storage washed nZVI, which corresponds to XRD results that exhibit transformation of Fe(0) to iron oxides. The reactivity tests display high linear correlations (r2>0.95, p

The purpose of the present study was to develop enhanced membrane technologies that can avoid fatal fouling problems, thus making it possible to concentrate microalgae solutions efficiently. A conductive filter called ‘electro-membrane’ was manufactured and then tested in a CFEF (cross-flow electro-filtration) system. In continuous mode, the applied electric field enhanced the harvesting performance by 150%, demonstrating the anti-fouling property of the synthesized electro-membrane. In discrete mode, the membrane surface, in which microalgae cells were clogged, was almost completely cleansed by the use of a periodic powerful repulsive force, resulting in flux recovery to the initial high level.

The plasma treatment method was employed to characterize nitrogen (N)-doped nanoporous TiO 2 photocatalysts (N-nTiO 2 ) of ∼18 nm diameter. With respect to the organic dye degradation efficiencies and antibacterial properties after exposure to visible-light irradiation, N-nTiO 2 showed better performance than the alternative commercial 5 nm anatase TiO 2 (TiO 2 ), as-grown nanoporous TiO 2 (as-grown nTiO 2 ), and Ar-plasma-treated nanoporous TiO 2 (nTiO 2 ) photocatalysts. This was attributed mainly to N-nTiO 2 ’s higher anatase/brookite phase crystallinity and large surface area (375.9 m 2 g − 1 ). The N doping of N-nTiO 2 was confirmed by a shift of ∼0.25° toward the higher angles in the XRD patterns and high-resolution X-ray photoelectron spectroscopy (HR-XPS) surface analysis results. Additionally, N-nTiO 2 ’s total surface energy was significantly increased. Its photoluminescence (PL) response and apparent quantum yield inhibited the recombination of holes and electrons and decreased the band-gap energy (Eg − 1 for N-nTiO 2 , respectively. In contrast, under exposure to visible light, the value for nTiO 2 was 0.395 h − 1 . Moreover, the antibacterial activity indicated that ∼100% of both Escherichia coli ( E. coli ) and Staphylococcus aureus ( S. aureus ) were destroyed after 30 min visible-light irradiation while photostability was maintained. Considering all of these results, it was concluded that N-nTiO 2 is an excellent solar-light-activated photocatalyst candidate for water/waste treatment and medical applications.

In this study, crude oil was extracted from Nannochloropsis salina for biodiesel production using FeCl3 as a catalyst. Scanning electron microscopy (SEM) analysis revealed that microalgae cells became wrinkled or burst after reaction. An optimal extraction condition, via the response surface methodology (RSM), was evaluated with respect to FeCl3 concentration (1–3 mM), reaction time (30–90 min) and temperature (60–100 °C). At a condition of FeCl3 of 2 mM, 90 min, and 87 °C, a maximum extraction yield of 213 mg/g biomass and a FAME conversion rate of more than 80% were achieved. In light of FeCl3 being a reference coagulant, even for microalgae harvesting, its use for lipid extraction is expected to conceivably reduce the overall cost of microalgae-derived biodiesel production.

In the present study, a simple magnetic-particle recycling strategy was developed for harvest of the oleaginous microalga Chlorella sp. KR-1. The method entails the flocculation of microalgal cells and bare-Fe3O4 magnetic particles (bMP) by electrostatic attraction and the subsequent recovery of the bMP from the harvested flocs by electrostatic repulsion below and above the isoelectric points (IEP), respectively. For 10 recycles, the bMP showed 94-99% and 90-97% harvest and recovery efficiencies, respectively. Furthermore, neither the use of bMP nor pH adjustment showed any adverse effect on the microalgal cell growth or the co-existing bacterial species, as confirmed from the subsequent medium-recycling test and denaturing gradient gel electrophoresis (DGGE) analysis.

In microalgae-based biorefinement, the integration of harvesting and lipid extraction steps could reduce the costs of downstream processes. One potential of integrated methods, microalgae harvesting by aminoclay-conjugated TiO2 has been considered. Therein, aminoclay plays an efficient role in microalgae flocculation and direct cell disruption by TiO2 photocatalytic performance under UV-light irradiation. In the present study, two TiO2 photocatalysts, a commercial anatase/rutile bicrystalline (of ∼5 nm diameter) and anatase/brookite bicrystalline (of ∼3.5 nm diameter) by sol–gel reaction at room temperature, were distributed uniformly onto an aminoclay matrix by ultrasound-irradiated TiO2 particles, resulting in aminoclay-conjugated TiO2 composites. Within 10 min, the injection of aminoclay-conjugated TiO2 into the prepared 1.5 g/L-concentration microalgal feedstocks produced an ∼85% harvesting efficiency for oleaginous Chlorella sp. KR-1. Subsequently, the harvested wet-microalgae biomass was UV-irradiated at 365 nm for 3 h, thereby effecting the disruption of ∼95% of cells.

In this study, a novel enzymatic pretreatment of Chlorella vulgaris for dark fermentative hydrogen production (DFHP) was performed using crude hydrolytic extracellular enzyme solution (CHEES) extracted from the H2 fermented effluent of food waste. It was found that the enzyme extracted at 52 h had the highest hydrolysis efficiency of microalgal biomass, resulting in the highest H2 yield of 43.1 mL H2/g dry cell weight along with shorter lag periods. Even though a high amount of VFAs was accumulated in CHEES, especially butyrate, the fermentative bacteria on the DFHP was not affected from product inhibition. It also appears that the presence of organic acids, especially lactate and acetate, contained in the CHEES facilitated enhancement of H2 production acted as a co-substrate. Therefore, all of the experimental results suggest that the enhancement of DFHP performance caused by CHEES has a dual role as the hydrolysis enhancer and the co-substrate supplier.

In this study, pre-biodiesel-production lipid extraction from microalgae (Chlorella vulgaris) was performed. The yield-enhancing effects of ionic liquid blends on the lipid extraction were investigated. The initial fatty acids content of the C. vulgaris was 292.2 mg/g cell. The lipid extraction yield using single ionic liquids was compared with the yield obtained with organic solvents and ionic liquid mixtures, respectively. The yield by hexane–methanol solvent was 185.4 mg/g cell. Among the 12 ionic liquids, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-methyl imidazolium diethylphosphate, 1-ethyl-3-methyl imidazolium tetrafluoroborate, and 1-ethyl-3-methyl imidazolium chloride showed high (>200.0 mg/g cell) lipid extraction yields. Although the yields of 1-ethyl-3-methyl imidazolium ethyl sulfate and 1-ethyl-3-methyl imidazolium thiocyanate were only 60.5 and 42.7 mg/g cell, respectively, the yield for their mixture (weight ratio of 1:1) was improved to 158.2 mg/g cell. Similarly, whereas the lipid extraction yield of 1-ethyl-3-methyl imidazolium hydrogen sulfate was just 35.2 mg/g cell, that for its mixture with 1-ethyl-3-methyl imidazolium thiocyanate (weight ratio of 1:1) was boosted to 200.6 mg/g cell. Overall, the synergistic effects of the ionic liquid mixtures with different anions improved the lipid extraction yield of C. vulgaris.

In the present study the short term aquatic ecotoxicity of water-solubilized aminoclay nanoparticles (ANPs) of ~51±31 nm average hydrodynamic diameter was characterized. An ecotoxicological evaluation was carried out utilizing standard test organisms of different phyla and trophic levels namely the eukaryotic microalga Pseudokirchneriella subcapitata, the crustacean Daphnia magna and the bioluminescent marine bacteria Vibrio fisheri. The effective inhibitory concentration (EC50) with 95% confidence limits for the microalga was 1.29 mg/L (0.72-1.82) for the average growth rate and 0.26 mg/L (0.23-0.31) for the cell yield. The entrapping of algal cells in aggregates of ANP may play a major role in the growth inhibition of algae P. subcapitata. No inhibition was observed for V. fisheri up to 25,000 mg/L (no observed effect concentration; NOEC). For D. magna no immobilization was observed in a limit test with 100 mg/L in 24 h while in 48 h a single animal was immobilized (5% inhibition). Correspondingly, the NOEC of ANP in 24 h was 100 mg/L and the lowest observed effect concentration (LOEC) for 48 h was 100 mg/L. Therefore it can be considered to use ANP as an algal-inhibition agent at concentrations100 mg/L without affecting or only mildly affecting other organisms including zooplanktons, but further studies on the environmental fate and chronic toxicity of ANP is needed to confirm this.

Microalgal biofuel is garnering many positive and promising reviews as a fuel for the next generation while research effort continues to improve the efficiency of its harvesting for commercial success. In this report, magnetophoretic harvesting of microalgae is conducted through a three-step process, which includes functionalization of magnetic particles by (3-aminopropyl)triethoxysilane (APTES), magnetic separation, and detachment of magnetic particles by increasing pH to higher than the isoelectric point. Detachment process is specifically focused and found that the use of larger magnetic particles is more efficient for detachment of magnetic particles from algae-particle conglomerates. The detaching efficiency improves from 12.5% to 85% when the particle size is increased from 108 nm to 1.17 μm. Smaller magnetic particles provide larger contact area to microalgae and form strong electrostatic binding to negatively-charged microalgae when pH is lower than the isoelectric point.

In this study, lipid extraction from Chlorella vulgaris was performed by using mixtures of molten salt and ionic liquid. The yield-enhancing effects of blending of molten salt with ionic liquid were investigated. Among the three molten salts (Zn(NO 3 ) 2 ·6H 2 O, Mg(ClO 4 ) 2 ·6H 2 O, and FeCl 3 ·6H 2 O), FeCl 3 ·6H 2 O showed a high lipid extraction yield (113.0 mg/g cell) and good reaction performance. When FeCl 3 ·6H 2 O was mixed with [Emim]OAc (5:1, w/w), the lipid extraction yield increased to 227.6 mg/g cell, a performance similar to that of single [Emim]OAc (218.7 mg/g cell). When lipid was extracted by the FeCl 3 ·6H 2 O/[Emim]OAc mixture at a 5:1 (w/w) blending ratio, 90 °C temperature, and 1 h duration, the fatty acid content of the extracted lipid was 981.7 mg/g lipid, indicating less than 2% impurity. The lipid extraction from C . vulgaris was improved by the synergistic effects of molten salt and ionic liquid with different ions.

Currently, although microalgae biorefinery is gaining attention in proportion to its demonstrated benefits, certain technical requirements need to be met, and cost issues need to be resolved before effective commercialization can be achieved. In both respects, multi-functional nanoparticles have been proposed as a promising potential solution. This review discusses the extensive studies that have been completed in the field of nanoparticles-aided microalgae biorefinery studies. Nanoparticle-support applications include cell/biomass growth enhancement and intracellular active compound production by induction of stress environments, application of backscattering light, and nutritional alteration. In the microalgae harvesting process, diverse nanoparticles can improve harvesting efficiency in a short time. In addition, the ability to re-use nanomaterials, as well as the integration of cell harvesting, disruption, and extraction also contributes to cost reduction. Moreover, many different nanocatalysts offer the ability to enhance biodiesel conversion efficiency. We hope that this review, in sketching out the current state of nano-aided technology in microalgae biorefinery, will contribute illuminating context and useful information for ongoing and future research.

Design optimization of hydrodynamic cavitation (HC) was performed for the sake of maximally extracting internal lipids directly from wet microalgae. Different types of orifice plates (α = 2.5–10%; β = 1–10%) were designed for a HC system and examined in terms of cavity formation; and cavitation effect was demonstrated by way of lipid extraction from microalgae. Basic operating parameters of HC, such as flux, flow rate, and the number of rotation, were examined and based on them, the upper and lower limits of cavitation number identified to be 3.37 ± 0.01 (α = 2.5% and β = 1%) and 1.01 ± 0.00 (α = 7.5% and β = 1%), respectively. The maximum lipid extraction (46.0 ± 3.7%) was obtained at 5% of both α and β. A low β value resulted in high vapor pressure, which has a crucial effect on the cell disruption caused by the creation and extinction of cavities. Also, the number of treatment per minute through the orifice proved to be a crucial factor for cell disruption. On the other hand, a high α value caused a surge pressure driven by violent fluctuation of flow. The cavitation effects of HC were able to be well visualized in terms of pressure variation using CFD. This study showed that the HC is indeed a very promising cell disruptor and its effectiveness can be further enhanced by way of design optimization.

The consumption of energy and resources such as water in the cultivation and harvesting steps should be minimized to reduce the overall cost of biodiesel production from microalgae. Here we present a biocompatible and rapid magnetophoretic harvesting process of oleaginous microalgae by using chitosan–Fe 3 O 4 nanoparticle composites. Over 99% of microalgae was harvested by using the composites and the external magnetic field without changing the pH of culture medium so that it may be reused for microalgal culture without adverse effect on the cell growth. Depending on the working volume (20–500 mL) and the strength of surface magnetic-field (3400–9200 G), the process of harvesting microalgae took only 2–5 min. The method presented here not only utilizes permanent magnets without additional energy for fast harvesting but also recycles the medium effectively for further cultivation of microalgae, looking ahead to a large scale economic microalgae-based biorefinement.

In this study, individual pretreatments (acid and ultrasonic) and a combination of these pretreatments were optimized to enhance the efficiency of dark fermentative hydrogen production (DFHP) from microalgal biomass. The experimental results show that the maximum H 2 production performance of 42.1 mL H 2 /g dry cell weight (dcw) was predicted at 0.79% (v/w) HCl and at a specific energy input (SEI) of 49,600 kJ/kg dcw in the combined pretreatment, while it was limited in both individual pretreatments. Repeated batch testing of the predicted optimal conditions revealed that the combined pretreatment conditions for DFHP from microalgal biomass were successfully optimized by increasing the solubilization of the feedstock and by reducing the formation of the toxic 5-hydroxymethylfurfural (HMF).

The purpose of the present study is to reduce fouling formation, a fatal problem of membrane technology by means of surface-coating with a functional coating material, i.e., hydrophilic polyvinyl alcohol (PVA) polymer. The PVA coating caused the membrane surface to become more hydrophilic and it was confirmed by decreased contact angles up to 64% compared to the un-modified membranes. The surface-coated membrane found to exhibit substantially enhanced performance: a maximum flux increase of 36% and almost 100% recovery rate. Maximum concentration factor of 77 also was modeled in the present study. These results show that the membrane performance can be improved simply by applying a surface-active coating, even to the level of economic feasibility.

In this study, the effects of enzymatic hydrolysis on lipid extraction from microalga (Chlorella vulgaris) were investigated prior to biodiesel production. The initial fatty acids content of C. vulgaris was 87.6 mg/g cell. The microalgal cell walls were hydrolyzed by cellulases and then their lipid fractions were extracted using various organic solvents such as hexane, methanol, and chloroform. Optimal pH and temperature for the enzymatic hydrolysis were pH 4.8 and 50 °C, respectively, and the maximal hydrolysis yield was 85.3%, which was achieved after 72 h. After the enzymatic hydrolysis, the lipid extraction yield by the organic solvents was improved compared to when there was no enzymatic hydrolysis process, by 1.29–1.73-fold depending on the solvents used. The total fatty acid methyl ester (FAME) productivity through the enzymatic hydrolysis was higher than when there was no enzymatic hydrolysis, by 1.10–1.69-fold depending on the solvents used. When lipid was extracted from the C. vulgaris after the enzymatic hydrolysis in chloroform-methanol solution, FAME productivity was 59.4 mg FAME/g cell.

Microalgae biorefinement has attracted in intensive academic and industrial interest worldwide for its potential to replace petrol biofuels as economically and environmentally advantageous alternatives. However, harvesting and lipid extraction remain as critical and difficult issues to be resolved. In the present study, four amino-groups functionalized organic-nano clays were prepared. Specifically, Mg or Al or Ca backboned and covalently linked with 3-aminopropyltriethoxysilane or 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane by sol-gel reaction under ambient conditions, resulted in Mg-APTES clay, Al-APTES clay, Ca-APTES clay, and Mg-N3 clay, respectively. Each organic-nanoclay was utilized for lipid extraction from wet microalgae biomass. As a result, the lipid-extraction efficiency of paste docosahexaenoic acid (DHA)-rich Chlorella sp. with low lipid content was high, while one of paste oleaginous Chlorella sp. with high lipid content was relatively low. Despite the low lipid-extraction efficiencies in all of the wet microalgae biomass, the conversion of the extracted lipids' fatty acids to biodiesel was nearly 100%.

Deoxygenation of microalgal oil obtained by pyrolysis of microalgae was carried out for the production of hydrocarbon fuel from biomass by metal supported catalyst. Oleic acid was used as a model reactant to select an optimized catalyst. Effects of support, metal species, and metal loading on catalytic performance were investigated. Activated carbon showed better performance than silica as a support. Considering various factors in model reaction, such as metal loading, reaction temperature, activity for deoxygenation, and selectivity for decarboxylation, 5 wt% platinum supported on activated carbon (5 wt% Pt/C) was selected as an optimized catalyst. Based on these results, deoxygenation of the pyrolysis oil from Chlorella sp. KR-1 was conducted at 623 and 673 K over this selected catalyst. The product after catalytic deoxygenation was mainly composed of pure hydrocarbons, and its oxygen content was below 2.0%. The fraction in the product of which the boiling point was less than 623 K was about 90%. These properties could allow this upgraded oil to be used for transportation fuel. However, the degree of oxygen removal with microalgal pyrolysis oil was lower than that with oleic acid, implying that impurities in the pyrolysis oil may inhibit the deoxygenation reaction.

The formate-hydrogen lyase (FHL) complex of Escherichia coli catalyzes the conversion of formate to hydrogen (H2) and carbon dioxide (CO2) under anaerobic conditions in the absence of exogenous electron acceptors. The FHL complex consists of formate dehydrogenase (FdhH) and hydrogenase 3 (Hyd3) that are involved in a series of reactions, including formate oxidation (by FdhH), electron transport (by putative five small subunits of Hyd3) and proton reduction (by HycE, large subunit of Hyd3). In this study, the FHL gene cluster and iscR, a negative regulator of iron–sulfur cluster, of E. coli SH5 (BW25113 ΔhycA ΔhyaAB ΔhybBC ΔldhA ΔfrdAB) were altered to increase the FHL-dependent H2 production activity. When FhlA, a transcriptional regulator of FHL, was overexpressed, the FHL-dependent H2 production activity was improved significantly to 2.03 μmol H2 mg−1 cdw min−1 from 1.41 μmol H2 mg−1 cdw min−1. When an iscR deletion and/or fdhF overexpression was added, the whole-cell FHL activity was improved further to 2.80 μmol H2 mg−1 cdw min−1 (with ΔiscR) and 2.45 μmol H2 mg−1 cdw min−1 (with ΔiscR plus fdhF overexpression), respectively. The increase in whole-cell FHL activity was accompanied by an increase in the activity of its member enzymes, such as HycE and/or FdhH. In addition, the highly active recombinant strains exhibited stable performance during prolonged H2 production with the repeated addition of formate. Overall, the FHL-dependent H2 production activity of E. coli can be improved more than three-fold by modifying the expression of the relevant genes.

In the present work, H 2 production from microalgal biomass via dark fermentation was optimized by response surface methodology (RSM). Substrate concentration and initial pH were varied from 3 to 117 g dry cell weight (dcw)/L and 4.2–9.8, respectively. During the fermentation, pH was not controlled. The optimal condition was found at 76 g dcw/L and initial pH of 7.4, under which yielded 31.2 mL H 2 /g dcw. The results of ANOVA verify that the relationship between substrate concentration and initial pH was slightly interdependent or significantly interactive. Besides, the monitoring alkalinity and pH during the confirmation test clearly showed that dark fermentative H 2 production (DFHP) from microalgal biomass was feasible without addition of external alkaline owing to the disruption of cell wall, which provided buffer capacity (max. 3800 mg as CaCO 3 /L). Therefore, although it involved a batch test, this approach would promote the practical viability of DFHP from microalgal biomass. The main organic acids were acetic and butyric acids which are general metabolites found in successful DFHP.

A novel marine hyperthermophile, Thermococcus onnurineus NA1, was found to grow on C1 carbon compounds, such as formate and carbon monoxide (CO), and produce hydrogen (H 2 ). In the present study, the growth and H 2 production of NA1 were examined to determine its potential as H 2 producer. NA1 showed relatively high specific growth rates, 0.48 h −1 and 0.40 h −1 with CO (20%, v/v) and formate (100 mM), respectively, when cultivated in batch mode in a minimal salt medium fortified with 1.0 g L −1 yeast extract. On the other hand, cell growth in both cases stopped at approximately 6 h and the final cell densities were extremely low at 18.2 and 12.1 mg protein L −1 with CO and formate, respectively. The maximum final cell density could be improved greatly to 36.0 mg protein L −1 by optimizing CO content (50%, v/v) and yeast extract concentration (4.0 g L −1 ), but it was still very low. During the cell growth, formate and CO were used as energy source rather than carbon source. In the resting cell experiments, NA1 exhibited remarkably high H 2 production activities as 385.0 and 207.5 μmol mg protein −1 h −1 for CO and formate, respectively. When formate (100 mM) or CO (100%, v/v) was added repeatedly at 30–35 h intervals, NA1 showed consistent H 2 production for 3 cycles with a yield of approximately 1.0 mol H 2 mol −1 for both CO and formate. This study suggests that T. onnurineus NA1 has a high H 2 production potential from formate or CO but a method for achieving a high cell density culture is needed.

A catalytic decarboxylation process following pyrolysis was developed for the production of transportation fuels from microalgae. The pyrolysis of Chlorella sp. KR-1, which has a triglyceride content of 36.5%, was carried out at 600 °C to obtain feedstock oil for decarboxylation. The major compounds in the pyrolysis oil were free fatty acids with carbon numbers of 16 and 18. Decarboxylation of the pyrolysis oil was performed using a type of hydrotalcite (MG63) as a catalyst at temperatures of 350 °C and 400 °C. Due to the selective reaction by MG63, hydrocarbons with carbon numbers of 15 and 17 were the most abundant compounds in the liquid product. The product yield at a reaction temperature of 400 °C was 78.6% and the degree of oxygen removal was 78.0%. Inert or less active oxygenates for hydrotalcite, such as phenolic compounds and fatty acid alkyl ester, may prevent the complete removal of oxygen. The diesel fraction in the product obtained under the given reaction condition was 83.8%, whereas that of the pyrolysis oil was 35.5%.