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To effectively improve biomass growth and flue-gas CO 2 fixation of microalgae, acid-tolerant Euglena gracilis was modified with cobalt-60 γ-ray irradiation and polyethylene glycol (PEG) adaptive screening to obtain the mutant strain M800. The biomass dry weight and maximum CO 2 fixation rate of M800 were both 1.47 times higher than that of wild strain, which was attributed to a substantial increase in key carbon fixation enzyme RuBisCO activity and photosynthetic pigment content. The high charge separation quantum efficiency in PSII reaction center, efficient light utilization and energy regulation that favors light conversion, were the underlying drivers of efficient photosynthetic carbon fixation in M800. M800 had stronger antioxidant capacity in sufficient high-carbon environment, alleviating lipid peroxidation damage. After adding 1 mM PEG, biomass dry weight of M800 reached 2.31 g/L, which was 79.1 % higher than that of wild strain. Cell proliferation of M800 was promoted, the apoptosis and necrosis rates decreased., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Catalysts with hierarchical porous structures and increased active defects play a crucial role in catalyzing the conversion of microalgae lipids. However, the template methods used for pore expansion and the acidification process employed to enhance activity are cumbersome and prone to deactivation. It is necessary to propose a simple and versatile synthetic approach to overcome these challenges. By modulating N,N-dimethylformamide basicity with formic acid, MOF-808 exhibited enhanced coordination of benzene-1,3,5-tricarboxylic acid to Zr-clusters, creating three types of functional defects. These defects increased pore size from 1.63 nm to 5.34 nm and enhanced catalyst acidity by 22.8%, while maintaining high porosity. The active catalytic sites were confirmed to be defect sites (exposed Zr 4+ ) through density functional theory. Compared to regular MOF-808, catalyst MOF-808-3/1 shows enhanced hierarchical porosity and increased acidity, enabling efficient conversions at reduced reaction temperature (100 °C) and pressure (352 kPa) compared to 200 °C and 4036 kPa, respectively., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

In order to explain reasons why flue-gas CO 2 (normally containing high CO 2 ) enhanced carbon fixation and lipids synthesis with increased photochemical electron production in microalgae cells. Focused ion beam scanning electron microscopy (FIB-SEM) was combined with proteomics and phosphorylation modification mics to clarify mechanisms of lipids synthesis at protein and organelle levels in Chlorella pyrenoidosa cells cultivated with high CO 2 concentration (15 % v/v). The volumes of chloroplast and endoplasmic reticulum in subcellular organelles increased by 47 % and 306 %, respectively, compared with the control, which improved conversion efficiency of starch grains to lipids (lipid content increased by 57 %). Proteomics and modifications omics revealed that protein translation and ribosome structure and biogenesis-related enzymes were significantly modified by phosphorylation, which regulated protein biological functions. Glycolysis, pentose phosphate pathway and other carbohydrate metabolic pathways were markedly enriched and promoted the expression of lipid synthase, which was consistent with enhanced carbon fixation in photosynthesis, expansion of subcellular organelles and improved lipids synthesis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

To determine the optimal CO 2 concentration for microalgal biomass cultivated with industrial flue gas and improve carbon fixation capacity and biomass production. Functional metabolism pathways of significantly regulated genes in Nannochloropsis oceanica (N. oceanica) with various nitrogen/phosphorus (N/P) nutrients for CO 2 fixation were comprehensively clarified. At 100 % N/P nutrients, the optimum CO 2 concentration was 70 % and the maximum biomass production of microalgae was 1.57 g/L. The optimum CO 2 concentration was 50 % for N or P deficiency and 30 % for both N and P deficiency. The optimal combination of CO 2 concentration and N/P nutrients caused significant up regulation of proteins related to photosynthesis and cellular respiration in the microalgae, enhancing photosynthetic electron transfer efficiency and carbon metabolism. Microalgal cells with P deficiency and optimal CO 2 concentration expressed many phosphate transporter proteins to enhance P metabolism and N metabolism to maintain a high carbon fixation capacity. However, inappropriate combination of N/P nutrients and CO 2 concentrations caused more errors in DNA replication and protein synthesis, generating more lysosomes and phagosomes. This inhibited carbon fixation and biomass production in the microalgae with increased cell apoptosis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

In order to improve CO 2 biofixation efficiency of microalgae cultivated with coal-chemical flue gas, CO 2 gradient domestication was employed to improve high-concentration CO 2 tolerance and photoautotrophic growth of acid-tolerant Euglena gracilis. The dried biomass yield of photoautotrophic growth of E.gracilis increased from 1.09 g/L (wild-type strain) by 21 % to 1.32 g/L with CO 2 gradient domestication to 15 % CO 2 . The RuBisCO activity and biomass production of E.gracilis strain domesticated to 99 % CO 2 were 2.63 and 3.4 times higher, respectively, than those of wild-type strain. The chlorophyll a and b contents were 2.52 and 1.79 times higher, respectively, than those of wild-type strain. Superoxide dismutase and catalase activities of 99 % CO 2 -domesticated strain increased to 1.24 and 6 times, which reduced peroxide damage under high carbon stress and resulted in lower apoptotic and necrotic rates of domesticated strain. Thus, this work provides valuable guidance for CO 2 fixation and adaptive evolution of E. gracilis in industrial flue gas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

In order to investigate light penetration and flashing light frequency for microalgal cell-CO 2 bubble culture system in a raceway pond, user-defined function for CO 2 mass transfer and bubble scattering models coupled with discrete ordinates radiation model were adopted to clarify simultaneous effects of microalgal cell absorption and CO 2 bubble scattering. Light intensity along the microalgal suspension depth attenuated more rapidly with increased biomass concentration, decreased bubble generation diameter, increased CO 2 gas content and incident light intensity. Ratio of light zone decreased from 81.13 % to 20.00 % when biomass concentration increased from 0 to 0.4 g/L because of light absorption and shading effects of microalgae. When bubble generation diameter increased from 0.1 to 1.6 mm, ratio of light zone increased from 37.95 % to 42.64 %, while microalgal flashing light cycle first decreased to a valley of 1.81 s at 0.8 mm and then increased. Local light intensity in the upper layers was more enhanced due to lots of CO 2 bubbles gathering and reflecting more light with decreased bubble diameter and increased gas content. Light attenuated more rapidly in microalgal suspension with decreased bubble generation diameter and increased CO 2 gas content because of increased bubble diffraction coefficient and contact area. When initial CO 2 volume fraction increased from 0.02 to 0.2, flashing light frequency of microalgal cells decreased from 0.55 to 0.29 Hz and light zone time ratio φ decreased from 36.90 % to 18.40 %. At a biomass concentration of 0.1 g/L and a bubble flow rate of 0.1 m/s, the maximum light penetration and microalgal growth rate was achieved when bubble diameter, incident light intensity and gas content were optimally at 0.8 mm, 200 W/m 2 and 0.02, respectively. This work provides data support and theoretical guidance for photobioreactor design and optimization of light energy utilization., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

An acid-base bifunctional catacknalyst with coordinatively unsaturated cobalt-nitrogen active sites Co-N x (x < 4) was synthesized to convert microalgal lipids with high acid value into biodiesel. Pyrolysis destroyed Co-N 4 coordination structure in ZIF-67 and released coordinatively unsaturated Co-N x and uncoordinated N sites, which resulted in the Lewis/Brønsted acid ratio increasing from 0.1 to 11.45 and the basicity increasing from 0.96 to 6.05 mmol/g. According to DFT calculations, the adsorption energy of free fatty acid (FFA) on Co-N 2 site (-1.003 eV) exceeded that on Co-N 4 site (-0.271 eV). The strong interaction between Co-N 2 site and FFA increased electropositivity of carbonyl carbon atom in FFA from 1.379 to 1.529 eV and promoted esterification. The pyrolysis-induced defects generated more mesopores to promote the transportation of lipid molecules inside the catalyst. Therefore, the conversion efficiency of microalgal lipids into biodiesel over the ZC-450 catalyst (96.7%) was higher than that over the ZIF-67 catalyst (69.5%)., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In order to optimize light distribution for promoting biomass growth rate of Chlorella pyrenoidosa, concave walls were installed in plate photobioreactors (PBR) to generate rotational flow field of microalgal solution circulated from top inlets to bottom outlets. Flow vortices in four corners of concave-wall PBR resulted in decreased mixing time and increased mass transfer coefficient. The CO 2 bio-fixation by C. pyrenoidosa increased by 27% and chlorophyll-a concentration enhanced by 18.5% in concave-wall PBR compared to those in control (flat-wall) PBR. The concave walls diverge light rays to enhance frontal light exposure and supply more light photons into interior regions of PBRs. The promotion in light distribution and vortex flow field with concave walls enhanced light and nutrients utilization by microalgal cells, leading to an increased biomass growth rate by 21%., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

To facilitate the lipid extraction from Nannochloropsis oceanica with thick cell wall using switchable hydrophilicity solvent, ultrasound-assisted N, N, N', N'-tetraethyl-1,3-propanediamine (TEPDA) was used to effectively destruct the cell wall. TEPDA cations were adsorbed on the cells via electrostatic force and formed the electron-donor-acceptor (EDA) complex with the hydroxyl groups in cellulose. This broke the hydrogen-bonding interactions between cellulose chains and stripped them from cell wall, thus reducing the cell wall thickness from 141 nm to 68.6 nm. Moreover, TEPDA cations neutralized the negatively charged phospholipid bilayers, decreasing the cell surface zeta potential from -27.5 eV to -14.1 eV. The local electrostatic equilibrium led to cell membrane leakage. The ultrasound promoted the stripping of the cellulose chains at a power intensity of 0.5 W/mL and frequency of 20 kHz, achieving the lipid extraction efficiency of 98.2% within 2 h at a volume ratio of 1:4 of wet microalgae to TEPDA., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

To protect microalgae that are used for photosynthetic CO 2 fixation against high NO concentrations from coal-fired flue gas, 500 μM exogenous spermidine was added into Chlorella sp. solution resulting in an elevation of biomass yield by 30.5% under 327 ppm NO. Metabolomics, proteomics and enzyme activities were analyzed, revealing three effects of spermidine on Chlorella sp. resistance to NO stress. First, spermidine induced NO fixation in amino acids and their metabolites, mainly in form of 5-oxoproline (1.51-fold), which occurred through intracellular conversion reactions between citrulline and arginine. Accordingly, cellular respiration was strengthened along with a weakened NO inhibition, which enhanced active transport with ATP consumption. Second, spermidine guarded Chlorella sp. against peroxidation damage by improving activity of antioxidant enzymes. Finally, it protected the photosynthetic system of Chlorella sp. by increasing abundance of related enzymes to enhance carbon fixation. Thus exogenous spermidine improved biomass production against NO environment., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

In order to reutilize Fe 2 O 3 particles in flue gas from coal-fired power plant as a ferrum nutrient for improving microalgae growth, Na-Citrate was proposed to chelate FeCl 3 derived from Fe 2 O 3 and HCl reactions to promote biomass and lipid productivities of Chlorella PY-ZU1. Fe-Citrate gave much higher biomass and lipid productivities than FeCl 3 , Fe-EDTA, Fe-DTPA and Fe-HEDTA, because organic chelator prevented Fe 3+ from depositing, lower stability constant resulted in easier dissociation of ferric chelate, smaller chelate facilitated Fe 2+ (reduced from Fe 3+ ) transportation through cell membranes. The biomass growth and photosynthetic capacity of Chlorella PY-ZU1 cultivated with Fe-Citrate (converted from Fe 2 O 3 particles) medium were similar to those with commercial ferric ammonium citrate medium. The biomass and lipid productivities of Chlorella PY-ZU1 cultivated with 5 mg L -1 Fe-Citrate medium were 1.30 and 1.72 times, respectively, higher than those with FeCl 3 growth medium., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A staggered woven mesh (SWM) aerator equipped with three variable-micropore layers was developed to enhance the CO 2 conversion into HCO 3 - in a recycling water pipeline for promoting CO 2 utilization efficiency and Arthrospira growth in large-scale raceway ponds. The input CO 2 gas was broken into smaller bubbles (0.78- 2.43 mm) through the first-stage shear with axial rectangles, second-stage shear with radial rectangles (equivalent pore diameter = 150 μm), and third-stage shear with uniform micropores. A high-speed camera (MotionXtra HG-100K CMOS) and an Image J image processing software were employed to capture the bubble pictures. Compared to the traditional steel pipe (TSP) aerator, the bubble generation diameter and time in the SWM aerator reduced by 72.3% and 48.6%, respectively. The optimized structure (ε = 14, pore = 23 μm) of the SWM aerator promoted the carbonization efficiency and HCO 3 - conversion efficiency into biomass by 78.6% and 64.6% than the TSP aerator. Further, the chlorophyll fluorescence and biomass measurements showed an increase in the actual photochemical efficiency (analyzed by Hansatech FMS1 chlorophyll fluorescence instrument) and biomass yield by 1.8 times and 80.1%., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Microalgae are significantly affected by the spectra composition with various wavelengths. The development of light harvesting pigments can be controlled with specific wavelength of filtered light received by microalgae. Coverage of open raceway pond using transparent colored polyvinyl chloride sheets (PVCS) to filter light spectra, was assessed for the capacity to enhance biomass growth rate. Results showed that orange PVCS filtered light spectra at wavelengths from 480 to 665 nm, increased biomass dry weight (3.3 g/L) by 61% compared with control condition (white PVCS = 350-750 nm). Light spectra filtered through orange PVCS were more easily absorbed by the light harvesting pigment protein complex (phycobilisome) of Arthrospira platensis cells and subsequently transferred to intracellular photosynthesis reaction centers. Therefore, A. platensis cells cultivated with light spectra filtered through orange PVCS contained 62.7 mg/L chlorophyll-a and 23.5 mg/L carotenoid, which were 40% and 29% higher than control condition (with white PVCS)., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, the Tesla-valve (TV) baffles were used to optimize the flow field in a column photobioreactor (PBR) in order to promote mass transfer of CO 2 gas in the solution. The TV baffles were composed of many tilted plates with central holes and curved arcs facing downwards, installed along inner rising section of the column PBR. Many clockwise and anti-clockwise vortices were generated during the rising flow while passing through proposed TV baffles. An optimum TV baffle structure (30° plate angle, 8 cm arc width) decreased mixing time by 36.4% and increased the mass transfer coefficient by 50%. The TV baffles supported the movement of the A.platensis cells between light and dark regions to enhance their photochemical efficiency ϕPSII by 24.6% and Fv/Fm by 12.7%. Therefore, the biomass yield increased by 28.1% and exhibited an increased helix pitch and trichome length in comparison with traditional column PBR without baffles., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Poor light utilization efficiency and large occupied area of traditional raceway pond photobioreactors result in low areal microalgal biomass yield in industrial applications. In this study, a pond-tubular hybrid photobioreactor (PTH-PBR) comprising raceway ponds and horizontal tubes was developed to strengthen flash light effect and improve areal microalgal biomass yield. The highest flash cycle frequency (0.63 Hz) of microalgae cells along flow pathway was obtained in the raceway pond of PTH-PBR when shaded area percentage was 20% and ratio of adjacent tube interval to tube diameter was 1, which enhanced microalgal biomass yield by 31.2% than traditional raceway pond. Meanwhile, intracellular chlorophyll content increased by 33.6% and PSII maximum quantum yield (F v /F m ) increased by 8.1% due to decreased photoinhibition stress. The areal microalgal biomass yield of PTH-PBR was 54.7% higher than that of traditional raceway pond without horizontal tubes., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Computational fluid dynamics were used to analyze the flash light effect and CO 2 bubble behavior in an optimized flow field generated by double paddlewheels in a flat plate photoreactor to enhance microalgal biomass productivity. The increased D/w ratio significantly enhanced the average turbulent kinetic energy and flash cycle frequency. However, the effects became weak when the D/w ratio was over 0.67. Appliance of double paddlewheels increased flash cycle frequency from 0.035 to 0.121 Hz and increased light time ratio from 8.3% to 31.5%. Meanwhile, the bubble dynamic behavior was characterized using population balance model. The average bubble size reduced by 24.4% and the bubble rising velocity reduced by 10.6%, which facilitated CO 2 mixing and mass transfer in microalgal solution. Therefore, biomass accumulation of microalgae Chlorella in the photoreactor with double paddlewheels increased by 62.3% under 15% CO 2 ., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The heavy metal sources of large-scale raceway pond microalgae cultivation with flue gas were investigated to reduce heavy metal contents in microalgae during cultivation. The microalgae were cultivated with power plant flue gas (as C source) and circulating cooling seawater (added with N and P nutrients) for 6 days. The Pb, Cd, Hg, and As contents in microalgae were 0.91, 0.22, 0.08, and 0.28 ppm, respectively, which are nearly within the available national standard for food-grade microalgae. The heavy metal contents in microalgae with two membrane materials, namely, elastic polyethylene and random copolymer polypropylene, barely increased. The Hg, As, and Pb contents in microalgae cells cultivated with pure CO 2 were 16.67%, 69.23%, and 70.33% that of cells cultivated with CO 2 from flue gas. The Pb, As, and Hg contents in cells cultivated with fresh water were reduced by 38.46%, 15.38%, and 37.50%, respectively, compared with those cultivated with seawater. The heavy metal contents in microalgae were further reduced and controlled.

Switchable solvent N, N, N', N'-tetraethyl-1,3-propanediamine (TEPDA) was proposed to extract lipids from wet Nannochloropsis oceanica with a 5% higher extraction efficiency than chloroform-methanol. It was found that TEPDA acted mainly as an organic solvent to soften and dissolve lipids, while a small amount of TEPDA was dissociated into tertiary amine ion, i.e.,(C 2 H 5 ) 2 N-(CH 2 ) 3 -NH + (C 2 H 5 ) 2 . This cation acted as a surfactant to promote cell disruption and lipid separation. With moisture increasing from 0 to 84 wt%, more TEPDA was dissociated into cationic surfactant to induce local rearrangement of phospholipid bilayers in cell membranes through electrostatic interaction, resulting in the fractal dimension of disrupted cells increased from 1.49 to 1.66. Accordingly, the yield of fatty acid methyl ester (FAME) through transesterification of lipids extracted with TEPDA increased by 9%, while FAME yield from lipids extracted with chloroform and n-hexane decreased by 41% and 65%, respectively., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A single helical baffle (SHB), consisting of twisted turns, was developed to convert straight flow into spiral flow in a Chlorella PY-ZU1 open raceway pond (ORWP) bubbled with 15% CO 2 . Microalgal solution flowing through the SHB alternative helical interspaces generated whirling flow both vertically and horizontally, which decreased mixing and increased mass transfer rates. The optimized SHB had a pitch length to total SHB length ratio of 0.13 and SHB diameter to ORWP single channel width ratio of 0.30, which decreased mixing times and increased mass transfer coefficients by 41.1% and 38.4% respectively. SHB moved Chlorella PY-ZU1 from the ORWP bottom to the top, increasing light exposure for photosynthesis. Cellular electron transfer rates and photochemical efficiency (φPSII) increased by 18%, chlorophyll a content increased by 16% and variable to maximum fluorescence ratio increased by 13%. The microalgal biomass of SHB ORWP was 23% higher than that of conventional ORWP., Competing Interests: Declaration of Competing Interest Jun Cheng supervised the whole project, Ameer Ali Kubar designed the experimental setup, analyzed data and wrote manuscript; Ameer Ali Kubar, Wangbiao Guo, Santosh Kumar and Yanmei Song performed experiments on equipment s such as open raceway pond, pH probes (InPro3253i/SG/120 Mettler Toledo), mass flow meter (SevenstarCS200, China), dissolved oxygen probes (InPro6850i/ 12/120 Mettler Toledo), Plant Efficiency Analyzer fluorometer (PEA, Hansatech, UK), photosensitive electrode (GLZ-C, Zhejiang Top Instrument Co., Ltd. China) and magnetic stirrer. Then collected the data using above instruments; all authors discussed the results and contributed to the final manuscript., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The light distribution and light/dark cycle were improved in 900 L tangential spiral-flow column photobioreactors (TSCP) to promote CO 2 fixation with Arthrospira sp. cells. Solar irradiation model was employed in CFD simulation to investigate light distribution and light/dark cycle in flow field composed of culture medium, CO2 bubbles and Arthrospira sp. cells under actual sunlight irradiation considering geolocation and time. An accurate way to divide light/dark zone based on saturate light intensity and light intensity field was adopted for the first time. When Arthrospira sp. cell concentration increased from 0.1 to 0.9 g/L, light/dark cycle frequency of cells firstly increased from 0.650 Hz to 0.868 Hz and then decreased to 0.117 Hz. Intracellular chlorophyll a content and carotenoids content of Arthrospira sp. cells in TSCP were 6% and 41% higher than those in conventional bubble column photobioreactor. This promoted cellular photosynthesis and stress resistance, which contributed to increase CO 2 fixation rate of Arthrospira sp. cells by 59%. When CO 2 aeration rate, CO 2 volume concentration, and circulating pump power were 0.210 L/min, 15%, and 30 W, chlorophyll a content, helix pitch, and CO 2 fixation rate of Arthrospira sp. cells all reached peak values of 8.769 mg/L, 78.26 μm and 0.358 g/L/d, respectively., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review, of the manuscript entitled “Improving light distribution and light/dark cycle of 900 L tangential spiral−flow column photobioreactors to promote CO(2) fixation with Arthrospira sp. cells”., (Copyright © 2020 Elsevier B.V. All rights reserved.)

CO 2 capture with microalgae has been put forward in response to global concern on greenhouse gas emission. However, the short residence time and slow diffusion of CO 2 in water limits the growth of microalgae. In order to improve CO 2 transfer from gas phase to liquid phase and utilization by algal cells, polyethylene glycol 200 (PEG 200) was used as CO 2 absorbent to promote growth of Nannochloropsis oceanica with the bubbling of 15 vol% CO 2 . Total inorganic carbon (TIC) absorbed in culture medium remained constant at 5.6 mM when 15 vol% CO 2 was bubbled continuously. PEG 200 in the medium provided additional CO 2 absorption from 0.6 to 4.8 mM when PEG 200 concentration increased from 0.5 to 4 mM. The specific growth rate of N. oceanica reached the maximum (1.41 d -1 ) with 1 mM PEG 200 in culture medium, which was 21.5% higher than the specific growth rate without PEG 200. About 79% of the increase in biomass was attributed to the increased TIC with more CO 2 dissolution in culture medium because of PEG 200, and about 21% was attributed to PEG 200 itself utilized as an organic carbon source. In conclusion, PEG 200 as a CO 2 absorbent can effectively capture flue-gas CO 2 for algal growth., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In order to solve problems associated with a short residence time and low conversion efficiency when CO 2 gas is aerated directly into raceway ponds, a novel porous nickel-foam filled CO 2 absorptive photobioreactor system was developed to promote CO 2 conversion to NaHCO 3 in a short time to improve photosynthesis of microalgal cells. Numerical simulation showed that the porous nickel-foam promoted the Na 2 CO 3 solution radial velocity and CO 2 volume fraction in the CO 2 absorption reactor, which enhanced the reaction rate of CO 2 gas and soluble Na 2 CO 3 . The conversion efficiency of CO 2 gas to soluble NaHCO 3 gradually increased with an increasing nickel-foam pore diameter and a decreasing CO 2 gas outflow rate, while it first increased and then decreased with an increasing relative nickel-foam height in the CO 2 absorption reactor. The conversion efficiency from soluble NaHCO 3 to microalgal biomass first increased and then decreased with an increasing nickel-foam pore diameter (peaking at 2 mm) and relative height (peaking at 0.24); and CO 2 gas outflow rate (peaking at 2 L/min). The chlorophyll fluorescence measurements showed that a sufficient HCO 3 - supply promoted the quantum ratio used for electron transfer (from 0.19 to 0.23) and the maximum photochemical efficiency (from 0.48 to 0.52), resulting in an increased biomass growth rate (by 1.1 times) when the nickel-foam pore diameter increased from 0.1 to 2 mm., Competing Interests: Declaration of competing interest We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review, of the manuscript entitled “A novel porous nickel-foam filled CO(2) absorptive photobioreactor system improving CO(2) conversion with microalgae biomass”., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The weight ratio of Na 2 CO 3 /NaHCO 3 was investigated in order to improve microalgal productivity in large-scale industrial operations by converting NaHCO 3 to Na 2 CO 3 with a growth of Arthrospira platensis cells in 660 m 2 raceway ponds. Two microalgal cultivation systems with a NaHCO 3 by-product (SPBP) and a CO 2 bicarbonation absorber (CBAP) were firstly thoroughly introduced. There was a 13.3% decrease in the initial weight ratio of Na 2 CO 3 /NaHCO 3 resulting in a 25.3% increase in the biomass growth rate with CBAP, compared to that of SPBP. Increased sunlight intensity, solution temperature and pH all resulted in both a higher HCO 3 - absorbance and CO 3 2 - release, thereby increasing the weight ratio of Na 2 CO 3 /NaHCO 3 during the growth of A. platensis. The biomass growth rate was peaked at 39.9 g m -2  day -1 when the weight ratio of Na 2 CO 3 /NaHCO 3 was 3.7. Correspondingly, the cell pigments (chlorophyll a and carotenoid) and trichome size (helix pitch and trichome length) reached to a maximum state of 8.47 mg l -1 , 762 μg l -1 , 57 and 613 μm under the CBAP system., (© 2019 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

Biological CO 2 capture using microalgae is a promising new method for reducing CO 2 emission of coal-fired flue gas. The strain of microalgae used in this process plays a vital role in determining the rate of CO 2 fixation and characteristics of biomass production. High requirements are put forward for algae strains due to high CO 2 concentration and diverse pollutants in flue gas. CO 2 can directly diffuse into the cytoplasm of cells by extra- and intracellular CO 2 osmotic pressure under high CO 2 concentrations. The flue gas pollutants, such as SO x , NO x and fly ashes, have negative effects on the growth of microalgae. This work reviewed the state-of-the-art advances on microalgae strains used for CO 2 fixation, focusing on the modification and improvement of strains that are used for coal-fired flue gas. Methods such as genetic engineering, random mutagenesis, and adaptive evolution have the potential to facilitate photosynthesis, improve growth rate and reduce CO 2 emission., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In order to evaluate light penetration and its influence on microalgae growth in a raceway pond with alternatively permutated conic baffles (RWP-APCB), 3D numerical simulation of light penetration was performed using computational fluid dynamics in an optimized flow field composed of microalgae cells, CO 2 bubbles and culture medium. Results showed that light intensity in the culture medium attenuated faster in accordance with solution depth, with increased microalgae cell concentration, increased bubble volume fraction and decreased CO 2 bubble diameter. Light zone fraction (i.e. ratio of light zone length to solution depth) increased with promoted incident irradiation. It was found that around 75% of microalgae cells were distributed in light zone and non-photochemical quenching coefficient of microalgae decreased by 32% in RWP-APCB. This resulted in a 16% increase of the Chlorella pyrenoidosa biomass growth rate, to 0.36 g/L/d., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

To reduce bubble diameter and enhance mass transfer, a novel jet-aerated tangential swirling-flow plate photobioreactor was developed that improves the growth rate of microalgae. In this system, the circulating microalgal solution enters a jet aerator that takes up 15% CO 2 by vacuum suction and then injects into a plate photobioreactor through four centrally symmetric nozzles. Each jetflow is tangent to a tangential circle, driving vertical vortex movement of the surrounding microalgal solution, which markedly reduced the bubble diameter and enhanced mass transfer. The mass transfer coefficient was enhanced by decreasing the nozzle number (n) and increasing the ratio of tangential circle diameter to plate photobioreactor equivalent diameter (d/D). The average bubble diameter decreased by 80.2% to 0.37 mm and the mass transfer coefficient increased 4.6 times to 48.9 h -1 when n was 4 and d/D was 0.34. Finally, the optimized system increased the biomass dry weight of microalgae by 49.4%., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this work, self-rotary propellers (SRPs) with clockwise/counterclockwise blades were investigated to create spiral flow fields without external power to strengthen gas-liquid mixing and promote microalgal growth in an open raceway pond. The rotational flow around the propellers and spiral flow between the propellers generated extensive wall shear stress in three dimensions. Four-clockwise blades on the propellers exerted better mixing than three-counterclockwise blades. The bubble generation diameter was reduced by 69% and the mass transfer coefficient increased by 49% when the propeller diameter was increased from 32 to 60 mm. The photochemical efficiency (φPS II ) of Arthrospira platensis cells was enhanced by 25%, while the helix pitch and trichome lengths were enlarged by 7-16%. Self-rotary propellers (60 mm diameter) with four-clockwise blades enhanced the growth rate of A. platensis biomass by 35% compared to that in an unmodified raceway pond without propellers., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A CO 2 microbubbles dissolver (CMD) was developed to facilitate dissolving inorganic carbon and strengthening mass transfer in a horizontal tubular photo-bioreactor system (HTPBRS), which enhanced microalgae biomass productivity with flue gas containing 15% CO 2 . The influence of pump power on the bubble formation and mixing effect was found to be more obvious than that of gas flow rate. Ceramic shell aerator was more favorable for reducing bubble diameter and enhancing mass transfer than traditional rubber strip aerator. Bubble formation time decreased by 53.4% and mixing time decreased by 68.9% in response to the increased pump power. When the base area ratio of ceramic shell aerator to dissolver in the HTPBRS increased, bubble formation time decreased by 19.6% and mass transfer coefficient increased by 80.9%. The biomass yield of microalgae Chlorella PY-ZU1 with ceramic shell aerator was 30% higher than that with rubber strip aerator in the HTPBRS., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

A novel microporous fibrous-diaphragm aerator (FDA) was proposed to generate pressurized gas with check valve to penetrate through millions of micropores (6-126 μm) of expanded fibrous diaphragm on internal support, thus decreasing bubble generation diameter and increasing bubble residence time for improving microalgal growth with CO 2 fixation in a raceway pond. When installation angle of FDA internal support increased from 0° to 45°, bubble generation time and diameter first decreased (to valley bottoms of 4 ms and 0.45 mm at 22°) and then increased. Compared to traditional strip aerator, bubble generation time and diameter decreased by 50% and 60% through FDA with support installation angle of 22° and average pore diameter of 28 µm, while gas-solution mixing time decreased by 22% and mass transfer coefficient increased by 40%, leading to increased actual photochemical efficiency (by 80%) and increased biomass yield (by 38.5%) of Arthrospira cells with pure CO 2 aeration through FDA., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Computational fluid dynamics were employed to simulate microalgal cells movement with enhanced flash-light effects in a gaslift loop-current column photobioreactor (GLCP) with serial lantern-shaped draft tube (LDT). Clockwise and anticlockwise vortexes were formed in outer down-flow region of GLCP with LDT. The radial velocity, axial velocity, and turbulent kinetic energy of microalgal solution appeared periodical change around the lanterns. The average radial velocity showed a sixfold improvement from 0.003 m/s to 0.021 m/s, and average turbulent kinetic energy was enhanced by 18.2% from 22.5 × 10 -4  m 2 /s 2 to 26.6 × 10 -4  m 2 /s 2 , thus increasing light/dark cycle frequency by 54%. The light/dark cycle frequency increased first and then decreased with an increase of individual lantern height. The increased lantern number promoted the light/dark cycle frequency and light time ratio. Microalgal biomass yield in the GLCP with LDT was improved by 30%, and CO 2 fixation peak rate was promoted by 35%., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Double paddlewheels were proposed to generate cycle flow for increasing horizontal fluid velocity between dark and light zones in a flat plate photo-bioreactor, which strengthened the mass transfer and the mixing effect to improve microalgal growth with 15% CO 2 . Numerical fluid dynamics were used to simulate the cycle flow field with double paddlewheels. The local flow field measured with particle image velocimetry fitted well with the numerical simulation results. The horizontal fluid velocity in the photo-bioreactor was markedly increased from 5.8 × 10 -5  m/s to 0.45 m/s with the rotation of double paddlewheels, resulting in a decreased dark/light cycle period. Therefore, bubble formation time and diameter reduced by 24.4% and 27.4%, respectively. Meanwhile, solution mixing time reduced by 31.3% and mass transfer coefficient increased by 41.2%. The biomass yield of microalgae Nannochloropsis Oceanic increased by 127.1% with double paddlewheels under 15% CO 2 condition., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A novel serial lantern-shaped draft tube (LDT) that generates vortices is proposed to increase radial velocity between dark and light regions for improving CO 2 fixation with microalgae in a gas-lift circumflux column (GCC) photobioreactor. Clockwise vortices are generated in the downflow outerloop of the GCC photobioreactor with LDT. Radial velocity was improved from 1.50 to 4.35 × 10 -2  m/s, thereby decreased liquid cycle period between dark and light regions by 1.9 times. Mixing time decreased by 21%, and mass transfer coefficient increased by 26% with LDT. Liquid radial velocity in the downflow outerloop and mass transfer coefficient in the GCC photobioreactor both first increased and then decreased when single-lantern height was increased. Peak CO 2 fixation rate increased from 0.62 to 0.87 g/L/d, microalgal biomass yield increased by 50%. Removal efficiencies of pollutants (chemical oxygen demand, ammonium, tilmicosin, and ethinylestradiol) in wastewater were 62-90% with microalgae growth in GCC photobioreactor with LDT., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Alternatively permutated conic (APC) baffles were proposed to generate vertical and horizontal vortex flow to intensify mixing and mass transfer in a raceway pond. Both clockwise vortexes were generated before and after conic baffles in the main stream to increase perpendicular velocity by 40.3% and vorticity magnitude by 1.7 times on vertical cross section. Self-rotary flow around conic baffles and vortex flow among conic baffles were generated to increase perpendicular velocity by 80.4% and vorticity magnitude by 4.2 times on horizontal cross section. The bubble generation time and diameter decreased by 25.5% and 38.7%, respectively, while bubble residence time increased by 84.3%. The solution mixing time decreased by 48.1% and mass transfer coefficient increased by 34.0% with optimized relative spacing (ε) and height (ω) of conic baffles. The biomass productivity of Spirulina increased by 39.6% under pure CO 2 with APC baffles in a raceway pond., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Four solid acid catalysts including graphene oxide (GO), sulfonated graphene oxide (SGO), sulfonated graphene (SG), and sulfonated active carbon (SAC) were used to convert lipids in wet microalgae into biodiesel. The physiochemical properties of the catalysts were characterized with scanning electron microscope, X-ray diffraction, and thermogravimetric analysis. SGO provided the highest conversion efficiency (84.6% of sulfuric acid) of lipids to fatty acid methyl esters (FAME). Whereas SAC converted few lipids into FAME. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that much higher hydrophilic hydroxyl content in SGO catalyst resulted in a considerable higher conversion efficiency of lipids to FAME than that (48.6%) catalyzed by SG, although SO 3 H groups (0.44mmol/g) in SGO were less than those (1.69mmol/g) in SG. Given its higher SO 3 H group content than GO (0.38mmol/g), SGO had higher conversion efficiency than GO (73.1%), when they had similar hydrophilic hydroxyl contents., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The response mechanisms of microalgal mutant Chlorella PY-ZU1 cells were investigated in their removal of antibiotic tilmicosin from wastewater under 15% CO 2 . Low concentrations (0.01-2mgL -1 ) of tilmicosin in wastewater stimulated the growth of microalgal cells, whereas high concentrations (5-50mgL -1 ) of tilmicosin significantly inhibited cell growth. When initial tilmicosin concentration increased from 0 to 50mgL -1 , fractal dimension of microalgal cells monotonically increased from 1.36 to 1.62 and cell size monotonically decreased from 4.86 to 3.75μm. In parallel, malondialdehyde content, which represented the degree of cellular oxidative damage, monotonically increased from 1.92×10 -7 to 7.07×10 -7 nmol cell -1 . Superoxide dismutase activity that represented cellular antioxidant capacity first increased from 2.59×10 -4 to the peak of 6.60×10 -4 U cell -1 , then gradually decreased to 2.39×10 -4 U cell -1 . The maximum tilmicosin removal efficiency of 99.8% by Chlorella PY-ZU1 was obtained at the initial tilmicosin concentration of 50mgL -1 ., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A water-circulating column photobioreactor (WCC-PBR) was developed to decrease bubble generation time and mixing time for growing microalgal biomass at low energy consumption. Bubble generation time was decreased by 60.4% and mixing time was decreased by 41.5% owing to an enhanced solution velocity with a water pump. Bubble residence time was decreased by 31.1% and mass transfer coefficient was decreased by 0.4% owing to a reduced distance between air aerator and solution surface. Microalgal growth rate was decreased by 12.7% from 128.9mg/Lday in an air-lifting column photobioreactor (ALC-PBR) to 112.6mg/Lday in a WCC-PBR because of the decrease in residence time of bubbles and an additional shear of cells in a water pump. However, total energy consumption of a WCC-PBR with an air compressor and a water pump was lower by 21.1% than that of an ALC-PBR with only an air compressor., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In order to produce biodiesel from lipids in wet microalgae with graphene oxide (GO) as solid acid catalyst, the effects on lipids conversion efficiencies of catalyst dosage, transesterification temperature, reaction time, methanol dosage and chloroform dosage were investigated. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that GO contained 0.997mmol SO 3 H groups per gram and high amounts of OH groups. Scanning electron microscopy showed that wet microalgae cells were adsorbed on hydrophilic GO surfaces covered with many OH groups. Lipids extracted by chloroform from microalgal cells were transformed into fatty acids methyl esters (FAMEs) through transesterification catalyzed by the acid centers (SO 3 H groups) in GO catalysts. The lipids conversion efficiency into FAMEs was 95.1% in microwave-assisted transesterification reactions of 5wt.% GO catalyst at 90°C for 40min., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In this study, computational fluid dynamics (CFD) was used to systemically analyze the movement of algae in a vortex flow field produced by up-down chute baffles. The average cell light/dark (L/D) cycle period, vertical fluid velocity, fraction of time the algae was resides in light zone and the L/D cycle period were investigated under different paddlewheel speeds and microalgal concentrations. Results showed that the L/D cycle period decreased but the vertical fluid velocity increased when the up-down chute baffles were used. The L/D cycle period decreased by 24% (from 5.1s to 3.9s), and vertical fluid velocity increased by 75% when up-down chute baffles were used with paddlewheel speed of 30r/min. The probability of L/D cycle period of 3s increased by 52% from 0.29 to 0.44 with the up-down chute baffles. This led to approximately 22% increase in biomass yield without changing the paddlewheel speed., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Aquatic micro-algae can be used as feedstocks for gaseous biofuel production via biological fermentation. However, micro-algae usually have low C/N ratios, which are not advantageous for fermentation. In this study, carbon-rich macro-algae (Laminaria digitata) mixed with nitrogen-rich micro-algae (Chlorella pyrenoidosa and Nannochloropsis oceanica) were used to maintain a suitable C/N ratio of 20 for a two-stage process combining hydrogen and methane fermentation. Co-fermentation of L. digitata and micro-algae facilitated hydrolysis and acidogenesis, resulting in hydrogen yields of 94.5-97.0mL/gVS; these values were 15.5-18.5% higher than mono-fermentation using L. digitata. Through the second stage of methane co-fermentation, a large portion of energy remaining in the hydrogenogenic effluents was recovered in the form of biomethane. The two-stage batch co-fermentation markedly increased the energy conversion efficiencies (ECEs) from 4.6-6.6% during the hydrogen fermentation to 57.0-70.9% in the combined hydrogen and methane production., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A novel swing gas aerator was developed to generate small bubbles for improving the mass transfer coefficient and microalgal growth rate in a raceway pond. A high-speed photography system (HSP) was used to measure the bubble diameter and generation time, and online precise dissolved oxygen probes and pH probes were used to measure the mass transfer coefficient and mixing time. Bubble generation time and diameter decreased by 21% and 9%, respectively, when rubber gas aerators were swung in the microalgae solution. When water pump power and gas aeration rate increased in a raceway pond with swing gas aerators and oscillating baffles (SGAOB), bubble generation time and diameter decreased but solution velocity and mass transfer coefficient increased. The mass transfer coefficient increased by 25% and the solution velocity increased by 11% when SGAOB was used, and the microalgal biomass yield increased by 18%., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Novel horizontal tubes and triangular prism (HTTP) baffles that generate flow vortices were developed to increase solution velocity between dark and light areas and thus improve microalgal growth in a flat-panel photo-bioreactor. Solution velocity, mass-transfer coefficient, and mixing time were measured with a particle-imaging velocimeter, dissolved oxygen probes, and pH probes. The solution mass-transfer coefficient increased by 30% and mixing time decreased by 21% when the HTTP baffles were used. The solution velocity between dark and light areas increased from ∼0.9cm/s to ∼3.5cm/s, resulting in a decreased dark-light cycle period to one-fourth. This enhanced flashing light effect with the HTTP baffles dramatically increased microalgae biomass yield by 70% in the flat-panel photo-bioreactor., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

A novel oscillating gas aerator combined with an oscillating baffle was proposed to generate smaller aeration bubbles and enhance solution mass transfer, which can improve microalgal growth in a raceway pond. A high-speed photography system (HSP) was used to measure bubble diameter and generation time, and online precise dissolved oxygen probes and pH probes were used to measure mass-transfer coefficient and mixing time. Bubble diameter and generation time decreased with decreased aeration gas rate, decreased orifice diameter, and increased water velocity in the oscillating gas aerator. The optimized oscillating gas aerator decreased bubble diameter and generation time by 25% and 58%, respectively, compared with a horizontal tubular gas aerator. Using an oscillating gas aerator and an oscillating baffle in a raceway pond increased the solution mass-transfer coefficient by 15% and decreased mixing time by 32%; consequently, microalgal biomass yield increased by 19%., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In order to produce biodiesel from microalgae cultured with abundant seawater, Chlorella sp. was mutated with (137)Se-γ ray irradiation and domesticated with f/2 seawater culture medium (salinity=3 wt.%) under 15 vol.% CO2 stress. Biomass yield of the mutant increased by 25% compared with wild species and lipid content increased to 54.9%. When nitrogen and phosphorus concentrations in the initial substrate increased, the increased propagation speed of the mutant resulted in decreased cell diameter by 26.6% and decreased cell wall thickness by 69.7%. The dramatically increased biomass yield of the mutant with sufficient initial substrate and relative nitrogen starvation in the later growth period with continuous 15 vol.% CO2 led to an increased lipid yield of 1.0 g/L. The long-chain unsaturated fatty acids increased, whereas short-chain saturated fatty acids decreased., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Unicellular green microalgae Haematococcus pluvialis was mutated with (60)Co-γ irradiation to promote growth rate and increase astaxanthin yield under high concentration of CO2 stress. The average specific growth rate of H. pluvialis mutated with 4000 Gy γ-ray irradiation was increased by 15% compared with the original strain with air aeration. The mutant grew best with 6% CO2 (the maximum specific growth rate was 0.60/d) when it was cultured with high concentrations of CO2 (2-10%). The peak biomass productivity (0.16 g/L/d) of the mutant cultured with 6% CO2 was 82% higher than that of the mutant with air. The astaxanthin yield and lipid content of the mutant induced with 6% CO2 and high light (108 μmol photons m(-2) s(-1)) increased to 46.0mg/L and 45.9%, which were 2.4 and 1.3 times higher than those of the wild-type strain, respectively., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The aeration gas was broken into smaller bubbles with enhanced local solution velocity to improve CO2 fixation with microalgae in raceway ponds with up-down chute baffles. A high-speed photography system and online precise pH probes were used to measure bubble generation and residence times, which were affected by paddlewheel speed, aerator orifice diameter, gas flow rate, and solution depth. Bubble generation time (from gas reaching aerator orifice surface to completely escaping from the aerator) decreased because of the enhanced local solution velocity, whereas bubble residence time increased because of the vortex flow field produced by up-down chute baffles. Bubble generation time decreased by 27% and bubble residence time increased by 27% when paddlewheel speed was 10r/min with an aeration gas rate of 0.03vvm. The decreased generation time and increased residence time of aeration bubbles promoted microalgae biomass yield by 29% in optimized flow fields in raceway ponds., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The polarities of the cytoplasm and reactants were measured through dielectric spectroscopy, contact angle test, NMR, and FTIR to investigate the mechanisms underlying acid-catalyzed lipid transesterification in wet microalgal cells subjected to microwave irradiation. Organics with apolar functional groups in the cytoplasm decreased the contact angle of methanol against triglyceride by 13.92°, which subsequently increased transesterification efficiency by 2.4 times. The microalgal biomass, given its higher hydrophilicity index of 1.96 than lipids, was more accessible to hydrophilic alcohols, which subsequently promoted transesterification. Water in the cytoplasm promoted the dielectric constant of methanol and increased the contact angle of methanol against triglyceride by 20.51°, which subsequently decreased transesterification efficiency by 72.6%. The inhibitory effect of water on transesterification weakened with the prolonged carbon lengths of the alcohols because of decreased polarity. Microwave decreased the electric constants of alcohols and reduced the polarity difference between alcohols and lipids, thereby improving transesterification efficiency., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The pore structures and surface morphological characteristics of Nannochloropsis sp. cells with arsenic adsorption were initially investigated by N2-adsorption analysis and scanning electronic microscopy. Functional groups of cells were analysed by Fourier-transform infrared spectrometry and X-ray photoelectron spectroscopy. Total surface area of microalgal cells increased from 0.54 m(2)/g to 1.80 m(2)/g upon arsenic adsorption. The external cell surface area increased. More wrinkles and measles-like granules formed on the surfaces as a result of arsenic toxicity. Arsenic ions blocked cell pores and decreased the average pore diameter and total pore volume. Ether cross-linked structures in the algaenan layer of cell walls were disrupted as the percentage of C-O functional groups decreased. These functional groups underwent complexation reactions with arsenic ions. Accumulation of polyunsaturated fatty acids decreased because of oxidative stresses induced by arsenic. The increase in generation of short-chain saturated fatty acids was favourable for the production of quality biodiesel., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Instant catapult steam explosion (ICSE) was employed to disrupt wet microalgal cells for efficient lipid extraction. Physicochemical properties of exploded cells were investigated through SEM, TEM, FTIR, and TGA. The exploded cells increased in fractal dimension (1.53-1.65) when preheat time was prolonged from 0 min to 5 min and in surface pore area when steam pressure was increased. Meanwhile, the exploded cells decreased in mean size (1.69-1.44 μm) when the filling ratio of wet microalgal biomass in the preheat chamber decreased (75-12.5%). Flash evaporation and volume expansion exploded the cell walls and released the cytoplasm of the microalgal cells. These phenomena decreased the carbohydrate content and increased the lipid content in the exploded biomass. However, ICSE treatment did not change the lipid compositions in the microalgal cells. Using isopropanol as a cosolvent significantly increased the yield of lipids extracted with hexane from the exploded wet microalgal biomass., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Novel up-down chute baffles that sequentially generate clockwise and anticlockwise liquid vortexes were developed to increase vertical liquid velocity between the bottom dark area and the top light area in a raceway pond. The vertical liquid velocity, mixing time, and mass transfer coefficient were measured as functions of paddlewheel speed and air aeration rate by using a particle imaging velocimeter, pH probes, and dissolved oxygen probes. The up-down chute baffles decreased the liquid mixing time and increased the mass transfer coefficient by 41% and 25%, respectively. Besides, the vertical liquid velocity increased from ∼0.5cm/s to ∼6.1cm/s. As a result, the dark-light cycle period was reduced to 1/12. This enhanced flashing light effect with up-down chute baffles increased biomass yield by 32.6% in the same raceway pond., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

CO2 fixation between microalgal biomass and culture solution and the weight ratio of biomass consumption at nighttime to biomass growth at daytime were compared in an open raceway pond aerated with flue gas from a coal-fired power plant. Average daytime sunlight intensity and solution temperature were optimized to improve microalgal growth rate and to enhance the efficiency of CO2 fixation. When the average daytime solution temperature increased from 12 to 26°C, the rate of biomass consumption due to microalgal respiration at nighttime increased from 6.0 to 7.9g/m(2)/d, which was approximately 25% of the biomass growth rate at daytime. Furthermore, when the average daytime sunlight intensity increased from 39,900 to 88,300lux, CO2 fixation rate in the microalgal biomass increased from 18.4 to 40.7g/m(2)/d, which was approximately 1/3 of CO2 removal rate from flue gas by the microalgal culture system., (Copyright © 2015 Elsevier Ltd. All rights reserved.)