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Interplays between microalgae and clay minerals enhance biologically mediated flocculation, thereby affecting the sedimentation and transportation of suspended particulate matter (SPM) in water and benthic environments. This interaction forms larger flocs with a higher settling velocity and enhances SPM sinking. The aim of this study was to investigate the flocculation kinetics of microalgae and clay in suspension and to elucidate the mechanisms associated with such interactions. Standard jar test experiments were conducted using various mixtures of kaolinite and microalgal samples from batch cultures (Chlorella vulgaris) to estimate biologically mediated flocculation kinetics. The organic matter (OM) composition secreted by the microalgae was characterized using a liquid chromatography - organic carbon detection system, and quantitative analysis of transparent exopolymer particles was conducted separately. A two-class flocculation kinetic model, based on the interaction between flocculi and flocs, was also adopted to quantitatively analyze the experimental data from flocculation. Results from the flocculation kinetic tests and OM analyses, in association with other data analyses (i.e., floc size distribution and flocculation kinetic model), showed that flocculation increased with OM concentration during the growth phase (10-20 d). However, on day 23 during the early stationary phase, flocculation kinetics started decreasing and substantially declined on day 30, even though the amount of OM (mainly biopolymers) continued to increase. Our results indicate that an adequate quantity of biopolymers produced by the microalgal cells in the growth phase enhanced floc-to-floc attachment and hence flocculation kinetics. In contrast, an excessive quantity of biopolymers and humic substances in the stationary phase enhanced the formation of polymeric backbone structures and flocculation via scavenging particles but simultaneously increased steric stabilization with the production of a large number of fragmented particles., 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. The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: We wish to confirm that there are no known conflicts of interest associated with this manuscript., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

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

Cryopreservation is an efficient method used to preserve microorganisms for long periods of time, such as up to 30 years, without changes in genetic and physiological characteristics. As cyanobacteria and microalgae are usually maintained as both axenic and xenic cultures, knowledge of co-cultured bacteria and changes in their community structure is important for the successful maintenance of microbial culture collections. In this study, research on the changes in co-cultured bacterial community structure during cyanobacterial cryopreservation were investigated using three different experimental groups by next generation sequencing (NGS): 1) cultured Trichormus variabilis without cryopreservation (control group), 2) cultured T. variabilis after cryopreservation in 10% dimethyl sulfoxide (Me 2 SO) for 14 days (cryo-cell group), and 3) cultured T. variabilis after cryopreservation in 10% Me 2 SO for 14 days within alginate beads (cryo-bead group). The results showed that the abundance of Sphingomonas and Hydrogenophaga (belonging to phylum Proteobacteria) was significantly increased in the cryo-bead group (Sphingomonas, control: 0.25%, cryo-cell: 1.32%, cryo-bead: 41.70%; Hydrogenophaga, control: 5.47%, cryo-cell: 5.24%, cryo-bead: 12.32%). However, the abundance of the phylum Bacteroidetes was significantly decreased in the cryo-bead group compared to that in the other groups (control: 26.29%, cryo-cell: 38.84%, cryo-bead: 11.43%). Bacterial diversity was generally reduced after cryopreservation in the cryo-bead group, where the overgrowth of a few unique bacteria was observed in the co-cultured bacterial community. These results imply that changes in the co-cultured bacterial community during preservation should be considered as an important factor for the development of methods for cyanobacterial cryopreservation., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Exposure to particulate matter causes skin aging. In the present study, we investigated the effect of an algae-derived phenolic compound, dieckol (DK), against Chinese particulate matter (CPM)-stimulated aging in vitro in human dermal fibroblasts (HDF cells) and in vivo in zebrafish. DK effectively protected HDF cells against CPM-induced oxidative stress by scavenging intracellular reactive oxygen species. Moreover, DK significantly improved collagen synthesis and inhibited intracellular collagenase activity in CPM-stimulated HDF cells. In addition, DK remarkably reduced the expression of pro-inflammatory cytokines and matrix metalloproteinases via regulating the nuclear factor kappa B, activator protein 1, and mitogen-activated protein kinases signaling pathways in CPM-stimulated HDF cells. Furthermore, the in vivo test results demonstrated that DK effectively improved the survival rate of CPM-stimulated zebrafish via suppressing oxidative stress and inflammatory response. In conclusion, this study suggests that DK is a potential anti-aging compound that can be used as a therapeutic agent to improve CPM-induced skin aging, or as an ingredient to develop a cosmetic or medicine in the cosmeceutical and pharmaceutical industries., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study investigated the feasibility of using photoheterotrophic microalga, Desmodesmus armatus SCK, for removal of cesium (Cs + ) followed by recovery process using magnetic nanoparticles. The comparison of three microalgae results indicated that D. armatus SCK removed the most Cs + at both 25 °C and 10 °C. The results also revealed that the use of microalga grown in potassium (K + )-starved condition improves the accumulation of Cs + . Heterotrophic mode with addition of volatile fatty acids (VFAs), especially acetic acids (HAc), also enhanced removal of Cs + by K + -starved D. armatus SCK; maximum removal efficiency of Cs + was almost 2-fold higher than that of cells grown without organic carbon source. The Cs + taken up by this microalga was efficiently harvested using magnetic nanoparticles, polydiallyldimethylammonium (PDDA)-FeO 3 . Finally, this strain eliminated more than 99% of radioactive 137 Cs from solutions of 10, 100, and 1000 Bq mL -1 . Therefore, use of K + -starved microalga, D. armatus SCK, with VFAs could be promising means to remove the Cs from the liquid wastes., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

We evaluated the potential sequestration of cesium (Cs + ) by microalgae under heterotrophic growth conditions in an attempt to ultimately develop a system for treatment of radioactive wastewater. Thus, we examined the effects of initial Cs + concentration (100-500 μM), pH (5-9), K + and Na + concentrations (0-20 mg/L), and different organic carbon sources (acetate, glycerol, glucose) on Cs + removal. Our initial comparison of nine microalgae indicated that Desmodesmus armatus SCK had removed the most Cs + under various environmental conditions. Addition of organic substrates significantly enhanced Cs + uptake by D. armatus, even in the presence of a competitive cation (K + ). We also applied magnetic nanoparticles coated with a cationic polymer (polyethylenimine) to separate 137 Cs-containing microalgal biomass under a magnetic field. Our technique of combining bioaccumulation and magnetic separation successfully removed more than 90% of the radioactive 137 Cs from an aqueous medium. These results clearly demonstrate that the method described here is a promising bioremediation technique for treatment of radioactive liquid waste.

The successful production of microalgal biomass requires the precise coordination of many different steps. Cell harvesting is a central process in all methods currently used for the production of microalgal biomass. Therefore, improving the harvesting process itself, and using a harvesting method that is compatible with adjacent steps, is necessary to prevent problems that may occur during downstream processing. This study examined the potential of the cationic biopolymer ε-poly-L-lysine (ε-PLL) for use in the harvest of microalgae (Chlorella ellipsoidea). The effects of ε-PLL concentration and mixing intensity on flocculation efficiency and operating costs were determined. We found that ε-PLL was not toxic to microalgal cells at concentrations of up to 25 mg/L, based on the photosystem II quantum yield. A recovery rate of 95% was achieved using 19 mg/L ε-PLL, and the estimated harvest cost was 20 US$/ton of harvested biomass. Moreover, ε-PLL displayed antimicrobial properties, leaving the harvested biomass intact and pure. Therefore, the use of ε-PLL-induced flocculation appears to be an attractive option when harvesting microalgal biomass for use as low- and high-value commodities for humans or animals.

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

Novel carbon-based solid acid catalysts were synthesized through a sustainable route from lipid-extracted microalgal residue of Dunaliella tertiolecta , for biodiesel production. Two carbon-based solid acid catalysts were prepared by surface modification of bio-char with sulfuric acid (H₂SO₄) and sulfuryl chloride (SO₂Cl₂), respectively. The treated catalysts were characterized and their catalytic activities were evaluated by esterification of oleic acid. The esterification catalytic activity of the SO₂Cl₂-treated bio-char was higher (11.5 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) than that of commercial catalyst silica-supported Nafion SAC-13 (2.3 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) and H₂SO₄-treated bio-char (5.7 mmol Prod.∙h⁻¹∙g Cat. ⁻¹). Reusability of the catalysts was examined. The catalytic activity of the SO₂Cl₂-modified catalyst was sustained from the second run after the initial activity dropped after the first run and kept the same activity until the fifth run. It was higher than that of first-used Nafion. These experimental results demonstrate that catalysts from lipid-extracted algae have great potential for the economic and environment-friendly production of biodiesel.

Lipids in microalgae are energy-rich compounds and considered as an attractive feedstock for biodiesel production. To redirect carbon flux from competing pathways to the fatty acid synthesis pathway of Tetraselmis sp., we used three types of chemical inhibitors that can block the starch synthesis pathway or photorespiration, under nitrogen-sufficient and nitrogen-deficient conditions. The starch synthesis pathway in chloroplasts and the cytosol can be inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 1,2-cyclohexane diamine tetraacetic acid (CDTA), respectively. Degradation of glycine into ammonia during photorespiration was blocked by aminooxyacetate (AOA) to maintain biomass concentration. Inhibition of starch synthesis pathways in the cytosol by CDTA increased fatty acid productivity by 27% under nitrogen deficiency, whereas the blocking of photorespiration in mitochondria by AOA was increased by 35% under nitrogen-sufficient conditions. The results of this study indicate that blocking starch or photorespiration pathways may redirect the carbon flux to fatty acid synthesis.

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