Energy-Density Improvement in Li-Ion Rechargeable Batteries Based on LiCoO2 + LiV3O8 and Graphite + Li-Metal Hybrid Electrodes.

We developed a novel battery system consisting of a hybrid (LiCoO2 + LiV3O8) cathode in a cell with a hybrid (graphite + Li-metal) anode and compared it with currently used systems. The hybrid cathode was synthesized using various ratios of LiCoO2:LiV3O8, where the 80:20 wt% ratio yielded the best electrochemical performance. The graphite and Li-metal hybrid anode, the composition of which was calculated based on the amount of non-lithiated cathode material (LiV3O8), was used to synthesize a full cell. With the addition of LiV3O8, the discharge capacity of the LiCoO2 + LiV3O8 hybrid cathode increased from 142.03 to 182.88 mA h g-1 (a 28.76% improvement). The energy density of this cathode also increased significantly, from 545.96 to 629.24 W h kg-1 (a 15.21% improvement). The LiCoO2 + LiV3O8 hybrid cathode was characterized through X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Its electrochemical performance was analyzed using a battery-testing system and electrochemical impedance spectroscopy. We expect that optimized synthesis conditions will enable the development of a novel battery system with an increase in energy density and discharge capacity.

Electrochemical Behaviors of a Vapor-Phase Polymerized Conductive Polymer Coated on LiV3O8 in Li-Metal Rechargeable Batteries.

A new coating method called vapor-phase polymerization (VPP) is used to coat a conductive polymer on LiV3O8 (LVO) surfaces for the first time in lithium-metal secondary batteries to protect the interface layer and enhance the electrochemical properties of the cathode. The VPP method can be used to coat an appropriate amount of the polymer and homogeneously coat the LVO active material surfaces because of the use of vapor-phase monomers. The presence of the coating layer was confirmed by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. Polymer coating of LVO by VPP results in enhanced cyclic stability and rate capability at various C-rates. At 0.2 C-rate, it has high specific capacities of 254.7 and 272.2 mA h g-1 in the first and second cycles, respectively. Further, the capacity retention is 94.6% from the 2nd cycle to the 100th cycle. The improved electrochemical performance is attributed to the homogeneously conductive polymer formed by VPP, which can improve the electrical conductivity of the active material and inhibit dissolution by preventing direct contact with the electrolyte.

The Ancient Phosphatidylinositol 3-Kinase Signaling System Is a Master Regulator of Energy and Carbon Metabolism in Algae.

Algae undergo a complete metabolic transformation under stress by arresting cell growth, inducing autophagy and hyper-accumulating biofuel precursors such as triacylglycerols and starch. However, the regulatory mechanisms behind this stress-induced transformation are still unclear. Here, we use biochemical, mutational, and "omics" approaches to demonstrate that PI3K signaling mediates the homeostasis of energy molecules and influences carbon metabolism in algae. In Chlamydomonas reinhardtii, the inhibition and knockdown (KD) of algal class III PI3K led to significantly decreased cell growth, altered cell morphology, and higher lipid and starch contents. Lipid profiling of wild-type and PI3K KD lines showed significantly reduced membrane lipid breakdown under nitrogen starvation (-N) in the KD. RNA-seq and network analyses showed that under -N conditions, the KD line carried out lipogenesis rather than lipid hydrolysis by initiating de novo fatty acid biosynthesis, which was supported by tricarboxylic acid cycle down-regulation and via acetyl-CoA synthesis from glycolysis. Remarkably, autophagic responses did not have primacy over inositide signaling in algae, unlike in mammals and vascular plants. The mutant displayed a fundamental shift in intracellular energy flux, analogous to that in tumor cells. The high free fatty acid levels and reduced mitochondrial ATP generation led to decreased cell viability. These results indicate that the PI3K signal transduction pathway is the metabolic gatekeeper restraining biofuel yields, thus maintaining fitness and viability under stress in algae. This study demonstrates the existence of homeostasis between starch and lipid synthesis controlled by lipid signaling in algae and expands our understanding of such processes, with biotechnological and evolutionary implications.

Influence of Water Depth on Microalgal Production, Biomass Harvest, and Energy Consumption in High Rate Algal Pond Using Municipal Wastewater.

The high rate algal ponds (HRAP) powered and mixed by a paddlewheel have been widely used for over 50 years to culture microalgae for the production of various products. Since light incidence is limited to the surface, water depth can affect microalgal growth in HRAP. To investigate the effect of water depth on microalgal growth, a mixed microalgal culture constituting three major strains of microalgae including Chlorella sp., Scenedesmus sp., and Stigeoclonium sp. (CSS), was grown at different water depths (20, 30, and 40 cm) in the HRAP, respectively. The HRAP with 20cm of water depth had about 38% higher biomass productivity per unit area (6.16 ± 0.33 g·m⁻²·d⁻¹) and required lower nutrients and energy consumption than the other water depths. Specifically, the algal biomass of HRAP under 20c m of water depth had higher settleability through larger floc size (83.6% settleability within 5 min). These results indicate that water depth can affect the harvesting process as well as cultivation of microalgae. Therefore, we conclude that water depth is an important parameter in HRAP design for mass cultivation of microalgae.

Application of high-salinity stress for enhancing the lipid productivity of Chlorella sorokiniana HS1 in a two-phase process.

Increased lipid accumulation of algal cells as a response to environmental stress factors attracted much attention of researchers to incorporate this stress response into industrial algal cultivation process with the aim of enhancing algal lipid productivity. This study applies high-salinity stress condition to a two-phase process in which microalgal cells are initially grown in freshwater medium until late exponential phase and subsequently subjected to high-salinity condition that induces excessive lipid accumulation. Our initial experiment revealed that the concentrated culture of Chlorella sorokiniana HS1 exhibited the intense fluorescence of Nile red at the NaCl concentration of 60 g/L along with 1 g/L of supplemental bicarbonate after 48 h of induction period without significantly compromising cultural integrity. These conditions were further verified with the algal culture grown for 7 days in a 1 L bottle reactor that reached late exponential phase; a 12% increment in the lipid content of harvested biomass was observed upon inducing high lipid accumulation in the concentrated algal culture at the density of 5.0 g DW/L. Although an increase in the sum of carbohydrate and lipid contents of harvested biomass indicated that the external carbon source supplemented during the induction period increased overall carbon assimilation, a decrease in carbohydrate content suggested the potential reallocation of cellular carbon that promoted lipid droplet formation under high-salinity stress. These results thus emphasize that the two-phase process can be successfully implemented to enhance algal lipid productivity by incorporating high-salinity stress conditions into the pre-concentrated sedimentation ponds of industrial algal production system.

Microalgal diversity fosters stable biomass productivity in open ponds treating wastewater.

It is established that biodiversity determines productivity of natural ecosystems globally. We have proved that abiotic factors influenced biomass productivity in engineered ecosystems i.e. high rate algal ponds (HRAPs), previously. This study demonstrates that biotic factors, particularly microalgal diversity, play an essential role in maintaining stable biomass productivity in HRAP treating municipal wastewater by mutualistic adaptation to environmental factors. The current study examined data from the second year of a two-year study on HRAP treating municipal wastewater. Microalgal diversity, wastewater characteristics, treatment efficiency and several environmental and meteorological factors were documented. Multivariate statistical analyses reveal that microalgae in uncontrolled HRAPs adapt to adverse environmental conditions by fostering diversity. Subsequently, five dominant microalgal strains by biovolume were isolated, enriched, and optimum conditions for high biomass productivity were ascertained. These laboratory experiments revealed that different microalgal strains dominate in different conditions and a consortium of these diverse taxa help in sustaining the algae community from environmental and predatory pressures. Diversity, niche or seasonal partitioning and mutualistic growth are pertinent in microalgal cultivation or wastewater treatment. Therefore, enrichment of selective species would deprive the collective adaptive ability of the consortium and encourage system vulnerability especially in wastewater treatment.

Algae-bacteria interactions: Evolution, ecology and emerging applications.

Algae and bacteria have coexisted ever since the early stages of evolution. This coevolution has revolutionized life on earth in many aspects. Algae and bacteria together influence ecosystems as varied as deep seas to lichens and represent all conceivable modes of interactions - from mutualism to parasitism. Several studies have shown that algae and bacteria synergistically affect each other's physiology and metabolism, a classic case being algae-roseobacter interaction. These interactions are ubiquitous and define the primary productivity in most ecosystems. In recent years, algae have received much attention for industrial exploitation but their interaction with bacteria is often considered a contamination during commercialization. A few recent studies have shown that bacteria not only enhance algal growth but also help in flocculation, both essential processes in algal biotechnology. Hence, there is a need to understand these interactions from an evolutionary and ecological standpoint, and integrate this understanding for industrial use. Here we reflect on the diversity of such relationships and their associated mechanisms, as well as the habitats that they mutually influence. This review also outlines the role of these interactions in key evolutionary events such as endosymbiosis, besides their ecological role in biogeochemical cycles. Finally, we focus on extending such studies on algal-bacterial interactions to various environmental and bio-technological applications.

Ni/MgO-MgAl2O4 Catalysts with Bimodal Pore Structure for Steam-CO2-Reforming of Methane.

The bead type MgO-MgAl2O4 catalyst supports with bimodal pore structures were fabricated via an extrusion molding of gels derived from the precursor mixture of mesoporous MgO particles and aluminum magnesium hydroxide, followed by heat treatment. To investigate the effect of macro pore structures on the catalytic activity of the Ni/MgO-MgAl2O4 catalysts in the steam and carbon dioxide reforming of methane (SCR), two kinds of the catalysts with largely different macro pore volumes and sizes but nearly the same meso pore volume and size were compared. The bimodal catalyst with a large macro pore size and volume exhibited a highly enhanced CO2 conversion from 22.3 to 37.1% but a slightly reduced CH4 conversion from 95.3 to 92.1% at the same feed ratio. The SCR results show that the large macro pores can lead to a highly enhanced mass transfer rate of CO2 absorption into the pore channels of the magnesium alumina spinel.

Polypropylene Bundle Attached Multilayered Stigeoclonium Biofilms Cultivated in Untreated Sewage Generate High Biomass and Lipid Productivity.

The potential of microalgae biofuel has not been realized because of the low productivity and high costs associated with the current cultivation systems. In this study, a new low-cost and transparent attachment material was tested for cultivation of a filamentous algal strain, Stigeoclonium sp., isolated from wastewater. Initially, the different materials tested for Stigeoclonium cultivation in untreated wastewater were nylon mesh, polyethylene mesh, polypropylene bundle (PB), polycarbonate plate, and viscose rayon. Among the materials tested, PB led to a firm attachment, high biomass (53.22 g/m(2), dry cell weight), and total lipid yield (5.8 g/m(2)) with no perceivable change in FAME profile. The Stigeoclonium-dominated biofilm consisted of bacteria and extracellular polysaccharide, which helped in biofilm formation and for effective wastewater treatment (viz., removal efficiency of total nitrogen and total phosphorus corresponded to ~38% and ~90%, respectively). PB also demonstrated high yields under multilayered cultivation in a single reactor treating wastewater. Hence, this system has several advantages over traditional suspended and attached systems, with possibility of increasing areal productivity three times using Stigeoclonium sp. Therefore, multilayered attached growth algal cultivation systems seem to be the future cultivation model for large-scale biodiesel production and wastewater treatment.

Organic carbon, influent microbial diversity and temperature strongly influence algal diversity and biomass in raceway ponds treating raw municipal wastewater.

Algae based wastewater treatment coupled to biofuel production has financial benefits and practical difficulties. This study evaluated the factors influencing diversity and growth of indigenous algal consortium cultivated on untreated municipal wastewater in a high rate algal pond (HRAP) for a period of 1 year using multivariate statistics. Diversity analyses revealed the presence of Chlorophyta, Cyanophyta and Bacillariophyta. Dominant microalgal genera by biovolume in various seasons were Scenedesmus sp., Microcystis sp., and Chlorella sp. Scenedesmus sp., persisted throughout the year but none of three strains co-dominated with the other. The most significant factors affecting genus dominance were temperature, inflow cyanophyta and organic carbon concentration. Cyanophyta concentration affected microalgal biomass and diversity, whereas temperature impacted biomass. Preferred diversity of microalgae is not sustained in wastewater systems but is obligatory for biofuel production. This study serves as a guideline to sustain desired microalgal consortium in wastewater treatment plants for biofuel production.

Enhancing microalgal biomass productivity by engineering a microalgal-bacterial community.

This study demonstrates that ecologically engineered bacterial consortium could enhance microalgal biomass and lipid productivities through carbon exchange. Phycosphere bacterial diversity analysis in xenic Chlorella vulgaris (XCV) confirmed the presence of growth enhancing and inhibiting microorganisms. Co-cultivation of axenic C. vulgaris (ACV) with four different growth enhancing bacteria revealed a symbiotic relationship with each bacterium. An artificial microalgal-bacterial consortium (AMBC) constituting these four bacteria and ACV showed that the bacterial consortium exerted a statistically significant (P<0.05) growth enhancement on ACV. Moreover, AMBC had superior flocculation efficiency, lipid content and quality. Studies on carbon exchange revealed that bacteria in AMBC might utilize fixed organic carbon released by microalgae, and in return, supply inorganic and low molecular weight (LMW) organic carbon influencing algal growth and metabolism. Such exchanges, although species specific, have enormous significance in carbon cycle and can be exploitated by microalgal biotechnology industry.

A cost analysis of microalgal biomass and biodiesel production in open raceways treating municipal wastewater and under optimum light wavelength.

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.

Chelatococcus caeni sp. nov., isolated from a biofilm reactor sludge sample.

A polyphasic taxonomic study was carried out on strain EBR-4-1(T), which was isolated from a biofilm reactor in the Republic of Korea. The cells of the strain were Gram-stain-negative, non-spore-forming, motile and rod-shaped. Comparative 16S rRNA gene sequence studies showed a clear affiliation of this strain to the Alphaproteobacteria, and it was most closely related to Chelatococcus daeguensis CCUG 54519(T), Chelatococcus sambhunathii HT4(T), and Chelatococcus asaccharovorans DSM 6462(T) with 16S rRNA gene sequence similarities to the type strains of these species of 98.8 %, 98.7 %, and 96.3 %, respectively. The G+C content of the genomic DNA of strain EBR-4-1(T) was 68.7 mol%. Phenotypic and chemotaxonomic data [Q-10 as the major ubiquinone; C19 : 0cycloω8c, C18 : 1 2-OH, and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) as the major fatty acids] supported the affiliation of strain EBR-4-1(T) to the genus Chelatococcus. On the basis of the polyphasic evidence, it is proposed that strain EBR-4-1(T) should be assigned to a new species, Chelatococcus caeni sp. nov. The type strain is EBR-4-1(T) ( = KCTC 32487(T) = JCM 30181(T)).

Flaviflexus salsibiostraticola sp. nov., an actinobacterium isolated from a biofilm reactor.

A Gram-stain-positive, aerobic, non-motile, non-spore-forming, cocci-shaped actinobacterium, designated strain EBR4-1-2(T), was isolated from a biofilm reactor in Korea. Comparative 16S rRNA gene sequence studies showed the isolate was clearly affiliated with the class Actinobacteria, and was related most closely to Flaviflexus huanghaiensis H5(T), showing 98.9 % similarity. Cells of strain EBR4-1-2(T) formed yellow colonies on R2A agar, contained MK-9(H4) as the predominant menaquinone, and included C18 : 1ω9c, C16 : 0, C16 : 1ω9c and C14 : 0 as the major fatty acids. The cell-wall peptidoglycan type was A5α (l-Lys-l-Ala-l-Lys-d-Glu). The G+C content of the genomic DNA of strain EBR4-1-2(T) was 65.6 mol%. Thus, the combined genotypic and phenotypic data supported the conclusion that strain EBR4-1-2(T) represents a novel species of the genus Flaviflexus, for which the name Flaviflexus salsibiostraticola sp. nov. is proposed. The type strain is EBR4-1-2(T) ( = KCTC 33148(T) = JCM 19016(T)).

Nutrient removal and biofuel production in high rate algal pond using real municipal wastewater.

This study evaluated the growth and nutrient removal ability of an indigenous algal consortium on real untreated municipal wastewater in a high rate algal pond (HRAP). The HRAP was operated semicontinuously under different hydraulic retention times (HRT: 2, 4, 6, and 8 days). The average removal efficiencies of chemical oxygen demand, and total nitrogen and phosphate of real municipal wastewater were maintained at 85.44 ± 5.10%, 92.74 ± 5.82%, and 82.85 ± 8.63%, respectively, in 2 day HRT. Algae dominated the consortium and showed high settling efficiency (99%), and biomass and lipid productivity of 0.500 ± 0.03 g/l/day and 0.103 ± 0.0083 g/l/day (2 day HRT), respectively. Fatty acid methyl ester analysis revealed a predominance of palmitate (C16:0), palmitoleate (C16:1), linoleate (C18:2), and linolenate (C18:3). Microalgal diversity analyses determined the presence of Chlorella, Scenedesmus, and Stigeoclonium as the dominant microalgae. The algal consortium provides significant value not only in terms of energy savings and nutrient removal but also because of its bioenergy potential as indicated by the lipid content (20-23%) and FAME profiling.

Variibacter gotjawalensis gen. nov., sp. nov., isolated from soil of a lava forest.

A novel bacterial strain designated GJW-30(T) was isolated from soil of the lava forest, Gotjawal, located in Aewol, Jeju, Korea. Strain GJW-30(T) was found to be strictly aerobic, Gram-negative and to form pleomorphic, non-motile rods and white colonies on R2A agar. The major fatty acids were identified as C18:1ω7c, C16:0 and C17:0, the predominant isoprenoid quinone as Q-10, the polar lipids as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, an unidentified aminolipid and an unidentified lipid. The cell-wall sugar pattern of strain GJW-30(T) was found to be composed of glucose, ribose and rhamnose and meso-DAP as the diagnostic diamino acid in the cell-wall peptidoglycan. The DNA G+C content of strain GJW-30(T) is 62.2 mol%. Phylogenetic analysis, based on 16S rRNA gene sequence similarities, showed that strain GJW-30(T) forms a deep branch within the order Rhizobiales, sharing the highest level of sequence homology with Bradyrhizobium oligotrophicum LMG 10732(T) (93.6 %). On the basis of the phenotypic, chemotaxonomic and phylogenetic characteristics, strain GJW-30(T) is considered to represent a novel genus and species, for which the name Variibacter gotjawalensis gen. nov., sp. nov. (the type strain is GJW-30(T) = KCTC 32391(T) = CECT 8514(T) = LMG 28093(T)) is proposed.

Two-stage cultivation of two Chlorella sp. strains by simultaneous treatment of brewery wastewater and maximizing lipid productivity.

A cultivation system in the two-stage photoautotrophic-photoheterotrophic/mixotrophic mode was adapted to maximize lipid productivity of two freshwater strains of Chlorella sp. grown in brewery wastewater (BWW). The endogenous Chlorella sp. isolated from BWW had a higher growth rate than wild-type Chlorella vulgaris (UTEX-265) while C. vulgaris (UTEX-265) had a higher maximal biomass and lipid contents than that of endogenous Chlorella sp., resulting in more than 90% of the inorganic nutrients in both total nitrogen (TN) and phosphorus (TP) was removed during the first stage in the two-stage photoautotrophic-photoheterotrophic mode in each Chlorella sp. The maximal biomass and lipid contents of C. vulgaris (UTEX-265) for single stage photoautotrophic cultivation were 1.5 g/L and 18%, respectively. Importantly, during two-stage photoautotrophic-photoheterotrophic cultivation for C. vulgaris (UTEX-265), the biomass was increased to 3.5 g/L, and the lipid productivity was increased from 31.1 to 108.0mg/L day.

Microalgae-associated bacteria play a key role in the flocculation of Chlorella vulgaris.

Flocculation is most preferred method for harvesting microalgae, however, the role of bacteria in microalgal flocculation process is still unknown. This study proves that bacteria play a profound role in flocculating by increasing the floc size resulting in sedimentation of microalgae. A flocculating activity of 94% was achieved with xenic Chlorella vulgaris culture as compared to 2% achieved with axenic culture. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA gene of xenic C. vulgaris culture revealed the presence of Flavobacterium sp., Terrimonas sp., Sphingobacterium sp., Rhizobium sp. and Hyphomonas sp. as microalgae-associated bacteria. However when Flavobacterium, Terrimonas, Sphingobacterium were eliminated by fluorescence activated cell sorter (FACS), flocculating activity reduced to 3%. Further studies with cell free extracts also suggest that bacterial extracellular substances might also have a role in enhancing flocculation. We conclude that the collective presence of certain bacteria is the determining factor in flocculation of C. vulgaris.

Lipid droplet synthesis is limited by acetate availability in starchless mutant of Chlamydomonas reinhardtii.

Phenotypic and genotypic changes in Chlamydomonas reinhardtii BafJ5, a starchless mutant, with respect to lipid metabolism was studied in different trophic states under nitrogen (N) sufficient and limited conditions. Interestingly, cellular lipid content increased linearly with input acetate concentration with highest lipid content (∼42%) under nitrogen limitation and mixotrophic state. RT-qPCR studies indicate that key fatty acid biosynthesis genes are down-regulated under N limitation but not under mixotrophic state, whereas, ACS2, encoding Acetyl-CoA synthetase, and DGTT4, encoding Diacylglycerol O-acyltransferase, are up-regulated under all conditions. These results collectively indicate that acetate is the limiting factor and central molecule in lipid droplet synthesis. The study also provides further evidence of the presence of a chloroplast pathway for triacylglycerol synthesis in microalgae.

Novel approach for the development of axenic microalgal cultures from environmental samples.

We demonstrated a comprehensive approach for development of axenic cultures of microalgae from environmental samples. A combination of ultrasonication, fluorescence-activated cell sorting (FACS), and micropicking was used to isolate axenic cultures of Chlorella vulgaris Beyerinck (Beijerinck) and Chlorella sorokiniana Shihira & R.W. Krauss from swine wastewater, and Scenedesmus sp. YC001 from an open pond. Ultrasonication dispersed microorganisms attached to microalgae and reduced the bacterial population by 70%, and when followed by cell sorting yielded 99.5% pure microalgal strains. The strains were rendered axenic by the novel method of micropicking and were tested for purity in both solid and liquid media under different trophic states. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene confirmed the absence of unculturable bacteria, whereas fluorescence microscopy and scanning electron microscopy (SEM) further confirmed the axenicity. This is the most comprehensive approach developed to date for obtaining axenic microalgal strains without the use of antibiotics and repetitive subculturing.