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Microalgae cultures have emerged as a promising strategy in diverse areas, ranging from wastewater treatment to biofuel production, thus contributing to the search for carbon neutrality. These photosynthetic organisms can utilize the resources present in wastewater and fix atmospheric CO 2 to produce biomass with high energy potential. In this study, the removal efficiency of Polycyclic Aromatic Hydrocarbons (PAHs), CO 2 fixation and lipid content in the biomass produced from microalgae grown in airlift photobioreactor were evaluated. Four mesoscale cultures were carried out: Control (Seawater + Conway medium), Treatment A (Oil Produced Water + Poultry Effluent Water), Treatment B (Poultry Effluent Water + Seawater) and Treatment C (Oil Produced Water, Seawater and nutrients). The impact of biostimulation, through the addition of nutrients, on PAHs removal efficiency (up to 90%), CO 2 fixation rate (up to 0.20 g L -1 d -1 ) and the composition of the generated biomass was observed. Primarily, the addition of nitrates to the culture medium impacted CO 2 fixation rate of the microalgae. In addition, a direct correlation was observed between PAHs removal and lipid accumulation in the biomass, up to 36% in dry weight, demonstrating microalgae's ability to take advantage of the organic carbon (PAHs) present in the culture medium to generate lipid-rich biomass. The concentration of polysaccharides in the biomass obtained did not exceed 12% on a dry weight basis, and the Higher Heating Value (HHV) ranged between 17 and 21 MJ kg -1 . Finally, the potential of generating hydrogen through pyrolysis was highlighted, taking advantage of the characteristics of biomass as a conversion route to produce biofuels. These results show that microalgae are effective in wastewater treatment and have great potential in producing biofuels, thus contributing to the transition towards more sustainable energy sources and climate change mitigation., 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 Inc. All rights reserved.)

Microalgae can promote antibiotic removal, which has attracted growing attention. However, its synergistic removal performance with bacteria in antibiotic pollutants is still poorly understood. In this study, firstly, we selected two green algae (Dictyosphaerium sp. and Chlorella sp.) and exposed them to Enrofloxacin (ENR) to observe their extracellular polysaccharides (EPS) concentration dynamic and the removal of antibiotics. Secondly, EPS was extracted and added to in situ lake water (no algae) to investigate its combined effect with bacteria. The results indicate that both Dictyosphaerium sp. and Chlorella sp. exhibited high tolerance to ENR stress. When the biomass of microalgae was low, ENR could significantly stimulate algae to produce EPS. The removal rates of Dictyosphaerium sp. and Chlorella sp. were 15.8% and 10.5%, respectively. The addition of EPS can both alter the microbial community structure in the lake water and promote the removal of ENR. The LEfSe analysis showed that there were significant differences in the microbial marker taxa, which promoted the increase of special functional bacteria for decomposing ENR, between the EPS-added group and the control group. The EPS of Dictyosphaerium sp. increased the abundance of Moraxellaceae and Spirosomaceae, while the EPS of Chlorella sp. increased the abundance of Sphingomonadaceae and Microbacteriaceae. Under the synergistic effect, Chlorella sp. achieved a maximum removal rate of 24.2%, while Dictyosphaerium sp. achieved a maximum removal rate of 28.9%. Our study provides new insights into the removal performance and mechanism of antibiotics by freshwater microalgae in water bodies and contribute to the development of more effective water treatment strategies., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The present study evaluated the effects of heavy metals, viz., lead, mercury, and cadmium, on growth, chlorophyll a, b, c, carotenoids, and PUFA content of marine microalgae Chlorella sp. and Cylindrotheca fusiformis. At 96-h exposure, the IC 50 values for Hg 2+ , Pb 2+ , and Cd 2+ were 0.85 mg/L, 2.4 mg/L, and 5.3 mg/L respectively, in Chlorella sp. In C. fusiformis, IC 50 values for Hg 2+ , Pb 2+ , and Cd 2+ were 0.5 mg/L, 1.2 mg/L, and 3 mg/L respectively. The pigment contents of both microalgae were significantly affected upon heavy metal exposure. In Chlorella sp. and C. fusiformis, the exposed concentrations of Hg 2+ averagely decreased the PUFA content by 76.34% and 78.68%, respectively. Similarly, Pb 2+ -exposed concentrations resulted in 54.50% and 82.64% average reductions in PUFA content of Chlorella sp. and C. fusiformis, respectively. Cd 2+ -exposed concentrations showed 32.58% and 40.54% average reduction in PUFA content of Chlorella sp. and C. fusiformis, respectively. Among the environmental stress conditions, the dark treatment has increased total PUFA content by 6.63% in Chlorella sp. and 3.92% in C. fusiformis. It was observed that the 50% nitrogen starvation (two-stage) significantly improved the PUFA production from 26.47 ± 6.55% to 40.92 ± 10.74% in Chlorella sp. and from 11.23 ± 5.01 to 32.8 ± 14.17% in C. fusiformis. The toxicity for both microalgae was followed in the order Hg 2+  > Pb 2+  > Cd 2+ . Among the two species, Chlorella sp. has shown a high tolerance to heavy metals and can be effectively utilized in PUFA production., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

The efficient management and treatment of pharmaceutical industry wastewater (PIWW) have become a serious environmental issue due to its high toxicity. To overcome this problem, the present study deals with the phycoremediation of PIWW using Chlorella vulgaris microalga isolated from the Ganga River at Haridwar, India. For this, response surface methodology (RSM) and artificial neural network (ANN) tools were used to identify the best reduction of total phosphorus (TP) and total Kjeldahl's nitrogen (TKN) based pollutants along with the lipid production efficiency of C. vulgaris. Three different concentrations of pharmaceutical wastewater (0, 50, and 100%), operating temperatures (20, 25, and 30 °C), and light intensity (2000, 3000, and 4000 lx) were used to design the phycoremediation experiments having 6:18 h of dark/light period and reactor functional volume of 15L. Findings revealed that C. vulgaris was good enough to remove maximum TP (90.35%), TKN (83.55%) along 20.88% of lipid yield at 25.62 °C temperature, 60.73% PIWW concentration, and 4000 lx of light intensity, respectively. Based on the model performance and validation results, ANN showed more accuracy as compared to the RSM tool. Therefore, the findings of this study showed that C. vulgaris is capable of treating PIWW efficiently along with significant production of lipid content which can further be used in various applications including biofuel production., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Microalgae are powerful source for nutritionally valuable components as proteins, carbohydrates and especially unsaturated fatty acids. Microalgae may be employed in pharmaceutical, food, cosmetic, health industries, and biofuels. In this study for looking at high-level unsaturated fatty acids species, from 31 strains, by comparing growth curves, the best strain with a high growth rate and lipid content was selected by red Nile staining. It was determined by molecular identification that this strain belongs to the genus Chlorella sp. and is deposited into the Agricultural Biotechnology Research Institute of Iran Culture collection with culture collection number ABRIICC 30,041. Biomass analysis after growth optimization by response surface methodology showed that the selected strain had a specific growth rate of 0.216 ± 0.008 d -1 , biomass productivity of 142.58 ± 4.41 mg/Ld, and lipid content of 13.9 ± 0.26% with a high level of unsaturated fatty acids of 53.15%. It also included 51.3 ± 0.53% protein with a very high quality essential amino acids of 40.36%, the most lysine (8.77%) and arginine (13.31%) has been reported until now, and 26.9 ± 0.23% carbohydrates in photoautotroph condition. By MTT assay, there is no effect of cytotoxicity. This research introduces a potent native strain comparable with commercial strains that can be a hopeful source for food supplements and valuable bioactive ingredients in functional foods., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Microalgal technology is still economically unattractive due to the high cost associated with microalgal cultivation and biomass recovery from conventional suspension cultures. Biofilm-based cultivation is a promising alternative for higher biomass yield and cheap/easy biomass harvesting opportunities. Additionally, using anaerobic digestate food effluent (ADFE) as a nutrient source reduces the cultivation cost and achieves ADFE treatment as an added value. However, the search for locally available, inexpensive, and efficient support materials is still open to research. This study evaluates the potential of commercially available, low-cost papers as support material for biofilm cultivation of Chlorella sp. and treatment of ADFE. Among the four papers screened for microalgal attachment, quill board paper performed better in higher biomass yield and stability throughout the study period. The attached growth study was done in a modular food container vessel, using anaerobic digestate food effluent (ADFE) as a nutrient source and a basal medium as a control. The microalgae grew well on the support material with higher biomass yield and productivity of 108.64 g(DW) m -2 and 9.96 g (DW) m -2 d -1 , respectively, in the ADFE medium compared with 85.87 g (DW) m -2 and 4.99 g (DW) m -2 d -1 , respectively in the basal medium. Chlorophyll, a fluorescence (ChlF) probe, showed that cell density in the biofilm significantly changes the photosynthetic apparatus of the algae, with evidence of stress observed as the culture progressed. Also, efficient nutrient removal from the ADFE medium was achieved in the 100 %, 85 %, and 40.2 % ratios for ammoniacal nitrogen, phosphate, and chemical oxygen demand (COD). Therefore, using quill board paper as carrier material for microalgal cultivation offers promising advantages, including high biomass production, easy biomass harvesting (by scrapping or rolling the biomass with the paper), and efficient effluent treatment., 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 The Authors. Published by Elsevier B.V. All rights reserved.)

Conventionally, microalgal lipid extraction uses volatile organic compounds as an extraction solvent. However, these solvents are harmful to human and environmental health. Therefore, this study evaluated the feasibility of alternative green solvents, namely, ethanol, dimethyl carbonate (DMC), cyclopentyl methyl ether (CPME), and 2-methyltetrahydrofuran (2-MeTHF) in lipid extraction from Chlorella sp. via ultrasound-assisted extraction (UAE). This study indicated that extraction parameters, such as ethanol-to-2-MeTHF ratio, solvent-to-biomass ratio, temperature, and time, significantly affected the crude lipid yield (P < 0.05). The highest crude lipid yield of 25.05 ± 0.924% was achieved using ethanol-2-MeTHF mixture (2:1, v/v) with a solvent-to-biomass ratio of 20:1 (v/w) at 60 °C for 25 min accompanying 100 W and 40 kHz. Ethanol-2-MeTHF-extracted lipids showed dominance in linoleic acid, α-linolenic acid, and palmitic acid. Overall this findings supported UAE using ethanol and 2-MeTHF as extraction solvents is a promising green alternative to conventional solvent extraction of lipids from microalgae., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

This study explores the challenges facing microalgae biofuel production, specifically low lipid content and difficulties with algal cell harvesting. The purpose of the research is to investigate the effect of seawater content and nanoparticle concentration on freshwater microalgae growth and biofuel production. The principal results of the study show that increasing the proportion of seawater and nanoparticles enhances the lipid content and cell diameter of microalgae, while excessive concentrations of nanoparticles and low seawater content lead to reduced microalgae growth. Furthermore, an optimal cell diameter was identified at a nanoparticle concentration of 150 mg/L. The study also reveals that increasing seawater content can decrease zeta potential and increase chlorophyll a content due to the concentration of dissolved organic matter. Increasing the seawater content from 0% to 25% decreased zeta potential by 1% owing to the instability and aggregation of the cells. Chlorophyll a for the 0% seawater was 0.55 which is increased to 1.32 only due to the increase in the seawater content. This significant increase is due to the concentration of dissolved organic matter in seawater. Additionally, the presence of seawater positively affects microalgae metabolic activity and biochar yield. The findings of this study offer valuable insights into the potential for optimizing microalgae biofuel production. The use of seawater and nanoparticles has shown promise in enhancing microalgae growth and biofuel yield, and the results of this study underscore the scientific value of exploring the role of seawater and nanoparticles in microalgae biofuel production. Further research in this area has the potential to significantly contribute to the development of sustainable energy solutions., 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 Inc. All rights reserved.)

Microalgae cultivation in swine wastewater (SW) allows the removal of nutrients and biomass production. However, SW is known for its Cu contamination, and its effects on algae cultivation systems such as high-rate algal ponds (HRAPs) are poorly understood. This gap in the literature limits the proposition of adequate concentrations of Cu to optimise SW treatment and resource recovery in HRAPs. For this assessment, 12 HRAPs installed outdoors were operated with 800 L of SW with different Cu concentrations (0.1-4.0 mg/L). Cu's interferences on the growth and composition of biomass and nutrient removal from SW were investigated through mass balance and experimental modelling. The results showed that the concentration of 1.0 mg Cu/L stimulated microalgae growth, and above 3.0 mg Cu/L caused inhibition accompanied by an accumulation of H 2 O 2 . Furthermore, Cu affected the contents of lipids and carotenoids observed in the biomass; the highest concentration was observed in the control (16%) and 0.5 mg Cu/L (1.6 mg/g), respectively. An innovative result was verified for nutrient removal, in which increased Cu concentration reduced the N-NH 4 removal rate. In contrast, the soluble P removal rate was enhanced by 2.0 mg Cu/L. Removal of soluble Cu in treated SW reached 91%. However, the action of microalgae in this process was not associated with assimilation but with a pH increase resulting from photosynthesis. A preliminary evaluation of economic viability showed that the commercialisation of biomass considering the concentration of carotenoids obtained in HRAPs with 0.5 mg Cu/L could be economically attractive. In conclusion, Cu affected the different parameters evaluated in this study in a complex way. This can help managers consort nutrient removal, biomass production, and resource recovery, providing information for possible industrial exploitation of the generated bioproducts.+ removal rate. In contrast, the soluble P removal rate was enhanced by 2.0 mg Cu/L. Removal of soluble Cu in treated SW reached 91%. However, the action of microalgae in this process was not associated with assimilation but with a pH increase resulting from photosynthesis. A preliminary evaluation of economic viability showed that the commercialisation of biomass considering the concentration of carotenoids obtained in HRAPs with 0.5 mg Cu/L could be economically attractive. In conclusion, Cu affected the different parameters evaluated in this study in a complex way. This can help managers consort nutrient removal, biomass production, and resource recovery, providing information for possible industrial exploitation of the generated bioproducts., 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.)

Cancer is the leading cause of death worldwide. Drug resistance and relapse after current standard treatments frequently occur; thus, alternative and effective treatments are required. Algae and cyanobacteria are abundant organisms that serve as bioresources of nutrients/metabolites, which are attractive sources of numerous bioactive compounds for drug discovery. In the present study, we, therefore, investigated anti-cancer activities of crude polysaccharide and ethanolic extracts from Chlorella sp., Sargassum spp., and Spirulina sp. against cell lines of five top-leading cancers including lung cancer (A549), cervical cancer (Hela), breast cancer (MCF7), hepatocellular carcinoma (Huh7), and cholangiocarcinoma (CCA; KKU213A). Only ethanolic extracts of Chlorella sp. showed consistent inhibition of growth of all cancer cell types. CCA was the most sensitive to Chlorella sp. ethanolic extract with CC50 of 277.4, 400.5, and 313.4 µg/mL for KKU055, KKU100, and KKU213A cells, respectively. Flow cytometric analysis demonstrated that CCA cell death was triggered via apoptosis pathway in accompany with lowering procaspase-3, -8, and -9 and increasing caspase enzymatic activity in addition to reducing anti-apoptosis Bcl-2 protein. Interestingly, the treatment of the extract at 400 µg/mL greatly inhibited the AKT/mTOR survival signaling as evidenced by significant reduction of phosphorylated-AKT and phosphorylated-mTOR proteins. The presence of reported bioactive compounds, gallic acid, and lutein, were confirmed in Chlorella sp. extract by high-performance liquid chromatography. Gallic acid and lutein treatment caused a significant reduction of KKU055, KKU100, and KKU213A cell viability. This study demonstrated the anti-cancer effect of Chlorella sp. ethanolic extract to promote cancer cell death via inhibition of AKT/mTOR pathway., Competing Interests: Conflict of interest statement All authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results., (Copyright © 2023 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

To elucidate the impacts of culture temperature on nutrient removal efficiency of Pyropia-processing wastewater (PPW) and microalgal biomass production, Chlorella sp. C2 was employed and cultivated in raw PPW under different temperatures. Results showed that, after incubating for 7 days, higher biomass (0.50 g/L) and total lipids (21.84 %) were attained at 35 °C. The maximal chemical oxygen demand (COD), phycobiliprotein, total nitrogen and total phosphorus removal rates were observed at 30-35 °C and separately reached 62.41 %, 92.61 %, 92.19 % and 98.33 %. Interestingly, COD removal efficiencies of Chlorella cells, cultivated for 3, 5 and 7 days at 30-35 °C, 15-25 °C and 10 °C respectively, could reach >75 % with assistance from 60-80 mg/L chitosan. Meanwhile, the clarification efficiency of chitosan on algal cells reached >95 %. It suggests that Chlorella strain cultured at altered temperatures could efficiently remove PPW nutrients assisted by moderate chitosan, simultaneously achieving the rapid harvest of microalgae., 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.)

Microalgae act as the entrance of polybrominated diphenyl ethers (PBDEs) from abiotic to biotic environments, which controlled the environmental fate of PBDEs in aquatic environments. Combing with typical coastal environmental characteristics including extracellular polymer substances (EPS) enrichment, light limitation and nitrogen starvation, the changes of adsorption and absorption kinetics of BDE-47 by Chlorella sp. and the role of EPS therein were investigated. The results quantified the adsorption and absorption kinetics of BDE-47 by Chlorella sp. cells and fitted it by the Lagergren pseudo first order model. Furthermore, we found the adsorption and absorption kinetics could be changed by the above mentioned environmental factors. To be specific, the total BDE-47 adsorption amounts per microalgal cell were increased as the increase of ambient EPS (proteins or carbohydrates), attributing to the increase of soluble (SL)-EPS contents; increased total BDE-47 adsorption amounts but decreased absorption rates were found under light limitation and nitrogen starvation, which were attributed to increased bound (B)-EPS contents and protein/carbohydrates (P/C) ratios therein, respectively. Therefore, our study elucidated the adsorption and absorption kinetics of PBDEs by microalgae could be influenced by ambient environmental changes, clarified the roles of SL-EPS, B-EPS contents and P/C ratios, providing a solid basis for evaluating the environmental fate of PBDEs in the marine environments., 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 Inc. All rights reserved.)

The intolerance of high CO 2 in the exhaust gas is the "bottleneck" limiting the wide application of microalgae for CO 2 biosequestration. Around this topic, we selected high-CO 2 -tolerant (LAMB 33 and 31) and nontolerant (LAMB 122) Chlorella strains to study their different energy metabolisms and cytoplasmic pH regulations in response to high CO 2 . Under 40 % CO 2 , LAMB 33 and 31 both showed elevated ATP synthesis, accelerated ATP consumption and fast cytoplasmic pH regulation while exhibiting different acclimating strategies therein: chloroplast acclimations were reflected by high chlorophyll contents in 33 but photosystem transitions in 31; faster mitochondrial acclimations occurred in 33 than in 31; cellular organic carbon mainly flowed to monosaccharide synthesis for 33 but to monosaccharide and protein synthesis for 31; and cytoplasmic pH regulation was attributed to V-ATPase in 31 but not in 33. All the above metabolic processes gradually collapsed in 122, leading to growth inhibition. Our study identified different metabolic acclimation strategies among Chlorella strains to high CO 2 and provided new traits for breeding microalgae for CO 2 biosequestration., 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.)

Polybrominated diphenyl ethers (PBDEs) are toxic to marine organisms including the major primary producer phytoplankton, while the toxic mechanisms haven't yet been fully clarified. Therefore, we comprehensively studied the toxic mechanisms of BDE-47 on the marine chlorophyte Chlorella sp., with a focus on the role of cellular oxidative stress. The results indicate that BDE-47 stress resulted in the inhibition of population growth as well as cell death and programmed cell death. The antioxidant system was activated in both low and high BDE-47 treatments, but only microalgal cells in the high BDE-47 treatment showed cellular oxidative stress. By adding ROS inhibitor, the relief of photosynthetic inhibition, Ca 2+ overproduction and cell death was found. Therefore, we conclude that photosynthetic damage, cell death and cellular oxidative stress were the major mechanisms of BDE-47 toxicity to Chlorella sp., and that cellular oxidative stress played an important role in mediating the other mechanisms., (Copyright © 2021. Published by Elsevier Ltd.)

Microalgae biomass is a viable feedstock for a wide range of industries. Recently, there has also been interest in the ability of microalgae biomass applications for biofuel production. In the meantime, the cultivation of microalgae biomass requires high energy costs, and the application of microalgae for technical purposes is still problematic. A significant part of the cost of biomass arises from the nutrients used for cultivation. Chemical compounds included in the microalgae cultivation media can be replaced by suitable wastes containing nitrogen, phosphorus, and other elements. This could reduce the microalgae biomass cultivation price and allow cheaper biomass to be used for biofuel production. The aim of this work was to comprehensively investigate and optimize the growth process of microalgae using liquid waste (liquid waste after biogas production from sewage sludge and distillers' grain) as a source of nitrogen and phosphorus, and technical glycerol as a carbon source. It was found that higher levels of waste in the cultivation media were found to inhibit the accumulation of microalgal biomass, with the optimum level corresponding to a nitrogen concentration of 0.08 g/L. The influence of technical glycerol from biodiesel production on the yield of microalgal biomass was investigated, and it was found that the addition of 6% glycerol allows an increase in the concentration of microalgal biomass in the cultivation media, from 18.1 to 20.6%.

Considering the momentous cost drivers in energy efficient algal biorefinery processes, a green alternative in extracting lipid from microalgae is anticipated. Switchable solvent system using tertiary amines namely DMBA (Dimethylbenzylamine), DMCHA (Dimethylcyclohexylamine), and DIPEA (Diisopropylethylamine) for lipid extraction from wet hypersaline microalgae was investigated in this study. Interestingly, present study showed that at 1:1 (v/v of fresh DMBA solvent: microalgal biomass), and for 1 h extraction time, the lipid yield was 41.9, 26.6, and 33.3% for Chlorella sp. NITT 05, Chlorella sp. NITT 02, and Picochlorum sp. NITT 04, respectively and for recovered DMBA solvent, at 1:1 (v/v) and for 1 h extraction time, the lipid yield was 40.8, 25.97, and 32%, respectively. Similarly, lipid extraction using DMCHA solvent for Chlorella sp. NITT 05, Chlorella sp. NITT 02, and Picochlorum sp. NITT 04 at 1:1 (v/v of solvent: microalgal biomass) and 1 h extraction time showed 34.28, 24.24 and 23.33% lipids, respectively for fresh solvent and 34.01, 24.24 and 23.18% for recovered solvent respectively; while DIPEA was not competent in lipid extraction from three tested microalgae. FAME profile revealed the presence of saturated fatty acids as 43.04%, 40.98%, 38.45% and monounsaturated fatty acids as 28.38%, 27.05%, 23.3% for Chlorella sp. NITT05, Picochlorum sp. NITT04, Chlorella sp. NITT02, respectively. This study attributes Chlorella sp. NITT05 and Picochlorum sp. NITT04 to be ideal algal species for biodiesel production., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Open sewage contaminated channel wastewater (OSCCW) has high pollutant loads, responsible for eutrophication, when mixed with various channels of urban communities. But, these pollutants can be converted and recovered into useful end products with the help of algal species. In this study, two species of Chlorella (C. vulgaris and C. pyrenoidosa) were selected and investigated for the production of algal biomass and nutrient removal efficiencies with 50% concentration of OSCCW, in a comparative way at lab-scale. Chlorella sp. cultivated in OSCCW have removed nitrate (76.9-78.8%) and phosphate (67.6-79.7%) whereas COD (72.4-76.2%) and BOD (62.3-72.4%) respectively. Correlation analysis was investigated between physico-chemical parameters and biochemical profile of both species to analyze the positive and negative correlation between two variables. The bio-chemical profile and biomass productivity of both species of Chlorella were observed well on the basis of productivity of biomass (60.1, 56.5 mg/l/d), carbohydrate (15.71, 8.82 mg/l/d), protein (11.21, 15.82 mg/l/d), lipid (20.8, 17.5 mg/l/d) and chlorophyll (0.78, 0.67 mg/l/d) in OSCCW. The maximum lipid content (34.6%) was obtained with C. pyrenoidosa as compared to C. vulgaris. Findings also support that OSCCW is well-off with nutrient resources, which can be suitable alternative for algal biomass production and remediated wastewater can be used for animal and fish farming type activities., (Copyright © 2021 Elsevier B.V. All rights reserved.)

This study aimed to evaluate the simultaneous interferences of Cu and Zn found in swine wastewater (SW) in the development of microalgae considering real conditions of cultivation in high rate algal ponds (HRAPs). Ten HRAPs on a pilot scale were fed with SW with different mixtures of Cu (0.5-3.0 mg/L) and Zn (5.0-25.0 mg/L). The interferences of these metals in removing nutrients (N-NH 4 and soluble phosphorus (Ps)) from the SW were determined. In addition, this study evaluated the effects on biomass growth and biochemical composition. Chlorella sp. was dominant in all HRAPs and the condition that potentiated its growth occurred in medium containing 1.8 mg Cu/L + 15.0 mg Zn/L, while higher concentrations conferred inhibition. Only Cu compromised the removal rates of N-NH + while the effects of Zn were not significant. Contrary, Zn interfered with Ps removal rates, but the impact of Cu was not significant. The greatest Cu applications increased the protein levels by biomass (50.5-55.2 %). Carbohydrate accumulation was favored by conditions that inhibited the development of microalgae due to either limitation or excess of metals. Copper and Zn compromised the levels of lipids, and the control treatment had the highest content (24.5 %). The presence of Cu and Zn changed the dynamics of HRAPs regarding nutrient removal, productivity, and biochemical composition of the biomass.4 + while the effects of Zn were not significant. Contrary, Zn interfered with Ps removal rates, but the impact of Cu was not significant. The greatest Cu applications increased the protein levels by biomass (50.5-55.2 %). Carbohydrate accumulation was favored by conditions that inhibited the development of microalgae due to either limitation or excess of metals. Copper and Zn compromised the levels of lipids, and the control treatment had the highest content (24.5 %). The presence of Cu and Zn changed the dynamics of HRAPs regarding nutrient removal, productivity, and biochemical composition of the biomass., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The integration of treatment of wastewater from agro-based industries with microalgae cultivation can reduce costs associated with cultivation while treating wastewater to meet the discharge limits for chemical quality of irrigation in agriculture and to obtain biofertilizers. Rose Oil Processing Effluent (ROPE) can be utilized as a growth medium for Chlorella sp. and thus can be used for biofertilizer production. The present study is aimed at determining the feasibility of the cultivation of Chlorella sp. in ROPE using a tubular photobioreactor with a capacity of 50 L and a raceway to treat ROPE while consuming less energy. The optimum mixing ratio ([ROPE/(ROPE + Bold Basal Medium (BBM)] × 100) was determined as 50% using 2-L Erlenmeyer flasks based on the COD removal efficiency. Better removal efficiencies with regard to COD, BOD 5 , NH 4 + -N, and NO 3 - -N were obtained from the raceway compared to the tubular photobioreactor. The effluents from both systems met the chemical quality of irrigation water. The results of the biomasses harvested from both systems in macro and microelements revealed that they have a potential as a biofertilizer in agriculture. The energetic analysis of the ROPE treatment using the tubular photobioreactor and raceway showed that the raceway system had a better net energy ratio while consuming less energy and producing more energy during cultivation. Overall, the raceway appeared to be a better option to treat ROPE with production of biofertilizer and irrigation water quality while consuming less energy., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Microalgae are known as renewable, potential, and sustainable feedstocks for biofuel production. The present work investigated the efficient valorization of green microalgae Chlorella sp. to produce sugars and 5-hydroxymethylfurfural (5-HMF) using thermochemical conversion with a metal-salt (ferric sulfate) as catalyst using a statistical approach and two-step conversion. A statistical approach with a Box-Behnken design was introduced to optimize the conversion for producing sugars. As a result of optimization, 86.46% sugar yield (68.32% glucose yield) was achieved under the condition of 5% biomass and 0.6 g-catalyst/g-biomass at 155 °C and 40 min. Two-step thermochemical conversion was introduced to produce 5-HMF from microalgae. In the first step, sugars were produced from the above optimum condition; in the second step, sugar hydrolysates were converted into 5-HMF by thermochemical conversion without an additional catalyst. In two-step conversion, the maximum 5-HMF yield (37.23%) was achieved at 170 °C and 60 min from the sugar hydrolysate of microalgae obtained from the first-step thermochemical conversion with ferric sulfate. In conclusion, the microalgae as biomass and ferric sulfate as catalyst have availability and the potential to produce biosugars and platform chemicals., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The successful cultivation of microalgae in wastewater establishes a waste to profit scenario as it combines treatment of a waste stream with production of valuable end-products. Here, growth and nutrient removal efficiency of three different locally isolated microalgal cultures (Chlorella sp., Scenedesmus sp., and a mixed consortium) cultivated in anaerobically digested municipal centrate (ADMC) and anaerobically digested abattoir effluent (ADAE) was evaluated. No significant differences (P > 0.05) in specific growth rate and biomass productivity were recorded between Chlorella monocultures and the mixed culture grown in both effluents. Scenedesmus sp. monocultures was found incapable of growth in both ADMC and ADAE throughout the cultivation period resulting in the collapse of cultures and no further measurements on the growth, biomass production and nutrient removal efficiency of this alga in both effluent. F q ´/F m ´ values which represent the immediate photo-physiological status of microalgae found to be negatively inhibited when Scenedesmus sp. was grown in both effluents throughout the cultivation period. F q ´/F m ´ values of Chlorella sp. monocultures and the mixed cultures recovered back to normal (≈0.6) after an initial drop. Ammonium removal rates was found to be significantly higher (≈2 folds) for Chlorella sp. monocultures grown in both ADMC and ADAE when compared to the mixed cultures. Nonetheless, no significant differences were observed in the removal of phosphate for both cultures in the different effluents. The total protein and carbohydrate content of the biomass produced was similar for both microalgae cultures grown using ADAE and ADMC. However, chlorophyll a and total carotenoids content were found to be higher (P < 0.05) for the cultures grown in ADAE than ADMC. Overall, Chlorella sp. monoculture was the most efficient option for treating both ADMC and ADAE while simultaneously generating protein rich biomass (up to 49%) that can be potentially exploited as aquaculture feedstock., 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 © 2021 Elsevier B.V. All rights reserved.)

High CO 2 acclimation for microalgae has attracted large research attention owing to the usefulness of microalgae in bio-sequestration of CO 2 from the emission source. In this study, one high CO 2 tolerant (LAMB 31) and non-tolerant (LAMB 122) Chlorella sp. strains were transferred from air to 40% CO 2 , during which four time points were chosen for comparative transcriptome analysis. Gene changes started in the lag phase (T1) of population growth with more genes (7889) upregulated in LAMB 31 than in LAMB 122 (1092). Further function enrichments indicated: In LAMB 31, up-regulation of genes in cyclic electron transportation, F-type ATPase and Calvin cycle were associated with the enhancement of carbon fixation abilities; upregulation of genes in phosphorylation together with V-ATPase, which contributed to cytoplasmatic pH stability; Lastly, enhancement of carbon metabolisms including TCA cycle and glycolysis accelerated the consumption of cellular organic carbon. Most of the genes in these pathways and processes showed downregulation in LAMB 122. This study disclosed the most complete transcriptional molecular mechanisms of Chlorella sp. responding to high CO 2 by combining CO 2 fixation, transportation, and metabolic processes. The results provided valuable genetic information for future screening and breeding of microalgae with high-CO 2 tolerance for more efficient CO 2 bio-sequestration., 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.)

Crude petroleum oil spills are among the most important organic contaminations. While the separated oils accumulated on the surface water are relatively easily removed, the emulsified portions are more difficult to remove and pose significant threats to the environment. Bioremediation using bacteria has proven to be an effective method, but the biomass produced in this case does not have any significant remunerative value. In this work, microalgae were proposed to combine emulsified oil remediation process with the potential of microalgae as a biofuel feedstock, thus enhancing the economic and environmental benefits of the process. A freshwater strain of Chlorella vulgaris was grown in water containing different concentrations of emulsified crude oil at different temperatures. The specific growth rate (μ max ) of the microalgae for each initial oil concentration was determined and was found to increase with the increase in initial oil concentration. For example, at 30°C, the specific growth rate, μ increased from 0.477 to 0.784 per day as the oil concentration increased from 57 to 222 mg/L. At 30°C, the effect of substrate concentration agreed with that of the microalgae growth, whereas at 40°C, the drop in oil concentration decreased with the increase in concentration. The results were fitted to a modified Monod kinetics model that used specific interfacial area as the influential substrate instead of the actual concentration. The results of this study clearly show the potential of using microalgae for emulsified oil remediation at relatively high concentrations., (© 2020 American Institute of Chemical Engineers.)

Pyropia-processing wastewater (PPW) contains diverse organic nutrients and causes environmental pollution. To explore the nutrient removal efficiency and growth performance of Chlorella sp. on PPW, the cultures were conducted in different culture substrates. Results showed that, after 7 days of incubation, the removal rates of total nitrogen (TN), total phosphorus (TP) and phycobiliprotein (PP) all reached more than 90% by cultivating Chlorella sp. C2 and C. sorokiniana F-275 in PPW. The chemical oxygen demand (COD) removal efficiencies could be over 50%. Meanwhile, the increments of biomass in two tested Chlorella strains were 1.39 and 4.89 times higher than those of BG11 and BBM substrates and the increases in lipid productivity were 1.34 and 10.18- fold, respectively. The C18:3 fatty acid proportions were markedly reduced by 27.89% and 29.10%. These results suggest that Chlorella sp. could efficiently reduce various nutrients in PPW and simultaneously accumulate higher biomass with higher biodiesel characteristics., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Bioconversion of food waste into value-added products is a promising way to tackle the global food waste management problem. In this study, a novel valorisation strategy for bioenergy and lutein production via microalgal fermentation was investigated. Significant amount of glucose was recovered from enzymatic hydrolysis of food waste. The resultant hydrolysate was then utilised as culture medium in mixotrophic cultivation of Chlorella sp. to obtain high levels of lipid and lutein, whose accumulation patterns were consistent with molecular analyses. The resultant algal lipid derived from microalgal biomass using food hydrolysate was at high quality in terms of biodiesel properties. Further, in semi-continuous fermentation, the average algal biomass was 6.1 g L -1 with 2.5 g L -1 lipid and 38.5 mg L -1 lutein using hydrolysate with an initial glucose concentration of 10 g L -1 . Meanwhile, the resultant algal biomass was 6.9 g L -1 with 1.8 g L -1 lipid and 63.0 mg L -1 lutein using hydrolysate with an initial glucose concentration of 20 g L -1 , which suggests food waste hydrolysate could trigger algal products preferences. The experimental results of this study suggested the potential of microalgae as a platform for bioconversion of food waste into high-value products, especially sustainable bioenergy., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Functional diversity/distinctness measure based trait has been proved to be a robust indicator to summarize the description of community structures and to assess water quality in different types of aquatic environment. In this study, for identifying the shielding effect of microalgae against protozoan grazing, a nine-day survey was conducted by exposing protozoan communities to a series of concentration gradients (10 0 (control), 10 4 , 10 5 , 10 6 and 10 7  cells ml -1 ) of two microalgae, respectively. Our results showed clear resistance of two test microalgae against protozoan grazing in five treatments. The functional distinctness measures commonly represented a decreasing trend along the gradient of concentrations of both microalgae. Ellipse tests based on the paired functional distinctness indices revealed that community functioning represented an uptrend departure from the expected pattern with the concentrations of both microalgae increase. Therefore, we suggest that the functional distinctness measures might be a reliable approach to detect the ecological effect of microalgae against protozoan grazing., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Microalgae has huge potential towards biological nutrient removal, but the challenges are remains in maximizing the biomass yield and so nutrient/pollutant removal efficiency. In this study, a response surface methodology-central composite design was applied to investigate the significant process variables (temperature, light intensity, inoculum density and light period) and its interaction effect on biomass yield of effluent acclimatized microalgae Nannochloropsis oculata, Chlorella vulgaris and Chlorella sorokiniana in ozone pre-treated tannery effluent (OPTE). At optimum culture condition N. oculata, C. vulgaris, and C. sorokiniana have yielded 0.67 g/L, 0.85 g/L, and 1.06 g/L biomass. Besides, correlation and regression analysis revealed the strong correlation between microalgal growth and nutrient removal rate. Among the species, C. sorokiniana has shown better remediation potential, at 27.5 °C, 150 μmol m -2 s -1 light intensity, 30% (v/v) inoculum, 16 h light period with the specific growth rate of 0.559 day -1 and nutrient/pollutant removal efficiency of 90% C, 90% N, 100% P, 82% COD, and 100% chromium. But, N. oculata has revealed the better lipid accumulation potential (40%) in OPTE. Thus, the present study established the appropriate strains and conditions required for OPTE treatment along with the value-added biomass production in large scale., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

To test the hypothesis that rotifers release one or more chemical microalgal growth inhibitors in addition to devouring the microalgal cells, the effects of different concentrations of filtered, bacteria-free, rotifer culture filtrate (RCF) on the growth and physiological parameters of Chlorella sp., and the response of Chlorella sp. at different starting cell densities to 10% RCF, were studied. The results show that RCF significantly decreased Chlorella cell densities during the incubation, suggesting that rotifers release some chemical(s) that inhibit microalgal cell growth. Chlorella cell densities decreased with increasing RCF concentration. Increasing the initial cell density of Chlorella dispersed the inhibitory chemical(s) present in 10% RCF over more cells, reducing their effect. The results confirm that the action of the chemical(s) released by rotifers on microalgal cell growth was dependent on both the RCF concentration and the exposure time. They also demonstrate that ≥10% RCF significantly inhibited photosynthesis and respiration, which would account for some of the decreased Chlorella cell growth in the presence of RCF. Calculations based on the data indicate that the rotifer-derived chemical(s) released hourly from each rotifer inhibits growth by 45.5 microalgal cells in addition to the rotifer predation, with a 48 h LC 50 value of 18.8% RCF. Based on these results, fresh medium instead of the old culture medium was contaminated by the rotifers., (© 2020 Phycological Society of America.)

The present research investigates potential of microalgae isolated from sewage treatment plant to utilize sodium bicarbonate as carbon source for CO 2 sequestration and biodiesel production. Eight algal isolates were isolated from waste water of sewage treatment plant, Amity University Haryana, India. The most potent algal isolates were identified and characterized on the basis of growth and lipid content. The efficient isolates ASW1 and ASW2 were identified as Chlorella sp. and Arthronema sp. by 18srRNA and 16srRNA sequencing method. In both isolates, maximum growth was observed under 20-W fluorescent bulb (3500 flux light intensity) with continuous light cycle of 24 h at pH 9.0 and 25 °C on the 20th day of incubation period. CO 2 utilization efficiency of both algal isolates were observed in terms of total CO 2 consumption rate. Under optimized culture conditions, total lipid content and lipid yield was higher in Arthronema sp. (180 mg l -1 ; 32.14%) as compared to Chlorella sp. (98 mg l -1 ; 29.6%) in 50 mM NaHCO 3 . Transesterified lipids were analysed by GC-MS. The fatty acid methyl ester profile of Arthronema sp. was 34.42% saturated and 65.58% unsaturated fatty acid. Chlorella sp. produces 29.80% saturated and 70.20% unsaturated fatty acid. In both isolates, C16 and C18 fatty acids dominated, which is a promising component for biodiesel. Graphical abstract.

Many studies have demonstrated the effectiveness of algicidal compounds produced by macrophytes against microalgae. The aim of this study was to assess the algicidal activity of seven Moroccan macrophyte ethyl acetate extracts (MEA) to control harmful algal blooms (HABs). The response and sensitivity of prokaryotic toxic cyanobacteria (Microcystis aeruginosa) and eukaryotic microalgae (Chlorella sp.) were highlighted. The algicidal effect of MEA extracts against the two microalgae was assessed using both the paper disc diffusion and microdilution methods. This last was used in order to evaluate the minimum inhibitory concentrations (MIC) and minimum algicidal concentrations (MAC). Results showed that the growth of both microalgae was significantly inhibited by all MEA extracts. Myriophyllum spicatum organic extract shows the highest growth inhibition activity against M. aeruginosa (35.33 ± 1.53) and Chlorella sp. (30.33 ± 1.15 mm). This stronger inhibitory activity was confirmed by the low MIC (6.25, 12.5 mg/L) and MAC (6.25, 12.5 mg/L) values. Furthermore, results showed different sensitivity between the prokaryotic and eukaryotic microalgae into MEA extracts. Based on the MIC and MAC values, we can distinguish two groups of plants. The first one, including M. spicatum, Ranunculus aquatilis, and Enteromorpha sp., can be considered as a preferable anti-prokaryotic group with a stronger inhibitory activity on M. aeruginosa growth. The second group, constituted by Potamogeton natans, Nasturtium officinale, Elodea sp., and Ceratophyllum sp., has a preferable and stronger inhibitory effect against eukaryotic algae (Chlorella sp.). Overall the results reveal the potential algicidal activity of macrophytes and suggested that MEA extracts could play an important role in biocontrol of HABs.

This study investigated the extracellular polymeric substance (EPS) and enzyme extrusion of Chlorella sp. using seven carbon sources and two salinities for potential pollutant co-metabolism. Results indicated that the levels of biomass, EPS and enzymes of microalgae cultured with glucose and saccharose outcompeted other carbon sources. For pigment production, glycine received the highest chlorophyll and carotene, up to 10 mg/L. The EPS reached 30 mg/L, having doubled the amount of protein than carbohydrate. For superoxide dismutase and peroxidase enzymes, the highest concentrations were beyond 60 U/ml and 6 nmol/d.ml, respectively. This amount could be potentially used for degrading 40% ciprofloxacin of concentration 2000 µg/L. When increasing salinity from 0.1% to 3.5%, the concentrations of pigment, EPS and enzymes rose 3 to 30 times. These results highlighted that certain carbon sources and salinities could induce Chlorella sp. to produce EPS and enzymes for pollutant co-metabolism and also for revenue-raising potential., 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. Huu Hao Ngo, a co-author on this paper, is the Editor of Bioresource Technology. He was blinded to this paper during review, and the paper was independently handled by Ashok Pandey as editor., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Biohydrogen is a plausible alternative fuel solution for the contemporary issues regarding global warming and the steadily increasing greenhouse gas emissions, because of its high energy content and carbon-free combustion properties. Hydrogen does not exist in its natural state and the current hydrogen production technologies (steam methane reforming, water splitting) are energy-intensive, accompanied by a huge carbon footprint. Dark fermentative hydrogen production by anaerobic hydrogen-producing bacteria is a green, sustainable and emission-free pathway for hydrogen production. Microalgal biomass is considered as the third generation biofuel feedstock and is receiving academic and industrial research attention for its carbon sequestration abilities. This review discusses in detail about the pretreatment methods that could be adapted for microalgal biomass for effective biohydrogen production. Microalgal cell wall structure and the associated polymeric carbohydrates that offer certain recalcitrance are critically analyzed and future research perspectives are presented., 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.)

Thiamphenicol (TAP) is a typical medicament in animal husbandry and aquaculture for treating diverse infections. In this work, thiamphenicol biodegradation performance via microalgae was tested. The cultivation results showed that TAP could be biodegraded via the target algae. Chlorella sp. L38 presented strong adaptive ability to high concentration TAP. Biodegradation, biosorption and bioaccumulation were the dominant metabolic fates. Biodegradation contributed around 97% of the total removal efficiency at the TAP concentration of 46.2 mg·L -1 . The removal of TAP by Chlorella L38 and UTEX1602 agreed with the kinetic range of zero-order reaction, and the shortest half-lives were 3.2 d and 5.0 d. Based on the identification of metabolites, the metabolic pathway of TAP by microalgae was proposed, including chlorination, chlorine substitution, dehydration and hydroxylation. Therefore, biological treatment via microalgae has the potential for TAP purification., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Microalgae are rich in valuable biomolecules and grow on non-arable land with rapid growth rate, which has a host of new possibility as alternative protein sources. In the present study, extraction of proteins from Chlorella vulgaris via an efficient technique, Liquid Triphasic Flotation (LTF) system, was studied. The optimized conditions in LTF system were 70% v/v of t-butanol, 40% w/v of salt solution, 0.5% w/v of biomass, pH 5.54, 1:1 of salt to t-butanol solution, and 10 min of air flotation time to attain 87.23% of protein recovery and 56.72% of separation efficiency. Besides, the study on recycling t-butanol has demonstrated that only one run was sufficient to maintain the performance of system. The efficiency of LTF in extracting protein has performed better than just Three Phase Partitioning (TPP) system. LTF system is hence an effective protein extraction and purification method with minimum operation unit and processing time., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

As one of the most mature carbon capture technologies, thermal regeneration of rich CO 2 absorption solvent is a crucial challenge due to its high energy consumption (typically in the range of 3-6 MJ/kg CO 2 ). In this work, a concept of bio-regeneration was proposed using microalgae to convert bicarbonate (which is one of the dominant components in rich solution) into value-added biomass. To evaluate the performance of bio-regeneration, different rich solution (including NH 4 HCO 3 , KHCO 3 and NaHCO 3 ) were investigated. Experimental results indicated that NH 4 HCO 3 could be a promising bicarbonate carrier for the proposed absorption-microalgae hybrid process, which had a higher biomass productivity (55.36 mg·L -1 ·d -1 ) compared to KHCO 3 and NaHCO 3 and carbon sequestration capacity could be up to 158.3 mg·L -1 ·d -1 . Meanwhile, pH adjustment was an effective approach to further intensify the performance of hybrid process. As a result, bio-regeneration of solvents could be a promising alternative to the conventional thermal regeneration., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Algal phytoremediation represents a practical green solution for treating anaerobically digested piggery effluent (ADPE). The potential and viability of combining microalgae and macroalgae cultivation for the efficient treatment of ADPE were evaluated in this study. Bioprospecting the ability of different locally isolated macroalgae species illustrated the potential of Cladophora sp. to successfully grow and treat ADPE with up to 150 mg/L NH 4 + . When grown by itself, the microalgae consortium used in this study consisting of Chlorella sp. and Scenedesmus sp. was found to grow and treat undiluted ADPE (up to 525 mg/L NH 4 + and biomass productivity of (0.012 ± 0.0001) g/(L·day). Nevertheless, when combined together, despite the different cultivation systems (attached and non-attached) evaluated, microalgae and macroalgae were unable to co-exist together and treat ADPE as their respective growth were inversely related to each other due to direct competition for nutrients and available resources as well as the negative physical interaction between both algal groups.4 + ) with an average ammonium removal rate of 25 mg/(L·day) NH 4 + and biomass productivity of (0.012 ± 0.0001) g/(L·day). Nevertheless, when combined together, despite the different cultivation systems (attached and non-attached) evaluated, microalgae and macroalgae were unable to co-exist together and treat ADPE as their respective growth were inversely related to each other due to direct competition for nutrients and available resources as well as the negative physical interaction between both algal groups., (Copyright © 2019. Published by Elsevier B.V.)

The use of P25 TiO 2 NPs in consumer products, their release, and environmental accumulation will have harmful effects on the coastal ecosystems. The sensitivity to TiO 2 NPs may vary depending on the structural property and physiological mechanism of algal species. Therefore, the present study investigates the differences in sensitivity of two marine algae, Dunaliella salina and Chlorella sp., towards P25 TiO 2 NPs. Among the two species, Chlorella sp. was more sensitive to TiO 2 NPs than Dunaliella salina. The different working concentrations of TiO 2 NPs, 0.1, 1, and 10 mg L -1 , were selected based on the EC 50 value. The EC 50 value of TiO 2 NPs for Dunaliella salina was found to be 1.8 and 13.3 mg L -1 under UV-A and dark conditions, respectively. The EC 50 value of TiO 2 NPs for Chlorella sp. was found to be 1.6 and 5.0 mg L -1 under UV-A and dark conditions, respectively. The decrease in cell viability was significantly higher for Chlorella sp. compared to Dunaliella salina at all concentrations except 0.1 mg L -1 . The cellular viability data was in correlation with the oxidative stress markers such as total ROS and LPO. A concentration-dependent increase in ROS and lipid peroxidation was noted under UV-A exposure, which was higher in Chlorella sp. compared to Dunaliella salina. The decrease in the SOD activity with NP concentration was more in Dunaliella salina than Chlorella sp. under both conditions, whereas Chlorella sp. showed increased CAT activity with increasing concentration. The uptake of TiO 2 NPs was more in Chlorella sp. than Dunaliella salina.

Conventional flocculants, commonly used to improve harvesting efficiency, can contaminate the broth and cause microalgae not suitable for food or feed production. In the present study, Pleurotus ostreatus, an edible fungal strain, was developed to improve the harvesting efficiency of microalgae. The results show that Pleurotus ostreatus pellets cultured under 100 rpm agitation resulted in higher harvesting efficiency than pellets cultured under 0 rpm and 150 rpm agitation. Lower pH of the Chlorella sp. suspension resulted in higher harvesting efficiency. The maximum recovery efficiency reached 64.86% in 150 mins. The above process could be used to achieve low cost, flocculant-free harvesting of microalgae as feedstock for feed or food production., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Aiming at simplifying the harvesting procedure, reducing the production cost, and improving the quality of microalgae-based biodiesel, herein, a novel one-step method for oil-rich biomass production and harvesting was proposed by growing Chlorella sp. with Aspergillus sp. in molasses wastewater. Lipid content and fatty acid profile were measured to assess the suitability of microalgal-fungal biomass for biodiesel production. The results showed that the highest biomass yield (4.215 g/L) was obtained when the inoculation ratio of fungi and microalgae was 100. Activities of fungi positive impacted the decolorization of wastewater and the removal of suspended solids. Thus, co-cultivation system had better performance than mono-system of microalgae in the removal of nutrients in wastewater. Analysis of biomass compositions showed that compared with mono-system of microalgae, co-cultivation system produced biomass with higher lipid content (35.2%) and yield microbial cell oil with lower unsaturation degree, potentially increasing the quality of microbial-cell-lipid based biodiesel., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A green microalga Chlorella sp. isolated from marine environment was investigated for its potential to pretreat saline antibiotic wastewater containing amoxicillin (AMX). Through Biolog EcoPlate assay, the Chlorella sp. showed its unique carbon source metabolic patterns under autotrophic condition. In addition, the microalga could effectively remove AMX (>99%) under initial AMX concentrations ranging from 10 to 150 mg/L through a treatability test. In the continuous AMX treatment using a lab-scale membrane photobioreactor (MPBR), a stable AMX removal efficiency of 85.6 ± 3.8% was observed. Moreover, with the aid of a subsequent bacterial treatment, the microalgal-bacterial process (the Chlorella sp. pretreatment followed by either intertidal wetland sediment or activated sludge) can achieve simultaneous AMX removal of >99% and total organic carbon (TOC) removal of ∼80%. In general, the microalgal pretreatment showed its great potential in effective removal of antibiotic residues, which could greatly enhance the overall treatment efficiency of saline antibiotic wastewater., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

In this work, a novel harvesting strategy using ferrofluids coupled with flocculation as a magnetic directional harvesting system was developed, providing a fast and easy way to effectively collect microalgae with no further modifications made to the ferrofluids. With a ferrofluid dosage of 25mgL -1 , a high harvesting efficiency of 95-100% was achieved within 1min. In addition, we successfully performed a wastewater recycling strategy coupled with a microalgal ferrofluid-harvesting dynamic flow-through system to harvest biomass of Chlorella sp. MTF-7 which could achieve over 80% of the maximum level after three repeated recycling cultivations. This work demonstrated the use of an integrated microalgal ferrofluid-harvesting dynamic flow-through system to develop a simple and effective strategy to enhance microalgal harvesting efficiency, along with wastewater recycling, in a marine microalgal Chlorella sp. MTF-7., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The feasibility of the bioremediation of cadmium (Cd) using microalgal-biochar immobilized complex (MBIC) was investigated. Major operating parameters (e.g., pH, biosorbent dosage, initial Cd(II) concentration and microalgal-biochar ratio) were varied to compare the treatability of viable algae (Chlorella sp.), biochar and MBIC. The biosorption isotherms obtained by using algae or biochar were found to have satisfactory Langmuir predictions, while the best fitting adsorption isotherm model for MBIC was the Sips model. The maximum Cd(II) adsorption capacity of MBIC with a Chlorella sp.: biochar ratio of 2:3 (217.41mgg -1 ) was higher than that of Chlorella sp. (169.92mgg -1 ) or biochar (95.82mgg -1 ) alone. The pseudo-second-order model fitted the biosorption process of MBIC well (R 2 >0.999). Moreover, zeta potential, SEM and FTIR studies revealed that electrostatic attraction, ion exchange and surface complexation were the main mechanisms responsible for Cd removal when using MBIC., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Bioethanol is an excellent alternative for petrol and has long-term economic advantages over non-renewable liquid biofuels. Bioethanol can be produced from different biomass materials, and it is categorized into three generations by biomass. First generation bioethanol directly competes with food items while second generation bioethanol requires more land area and fertilizers. Bioethanol produced from algae comes under third generation bioethanol and has many advantages over first and second generation bioethanol. Algae have higher growth rates than plants and require less land area also they do not need additional fertilizers for their growth. Microalgae can fix atmospheric CO2 from the environment and assimilate it into lipid and carbohydrates which can be used as a substrate for biofuel production.  In this work, microalgae Chlorella sp. was cultivated at 28oC and light intensity of 25µmol m-2 s-1 and used as a source of starch for bioethanol production. Chlorella starch was hydrolyzed into fermentable sugars by amylases produced from Aspergillus niger NCIM 616 for bioethanol production by yeast Saccharomyces cerevisiae NCIM 3494. Mathematical modelling gave the insight to predict the experimental profiles of bioethanol production from algal biomass.  Microbial growth, reducing sugar consumption, and bioethanol production were described quantitatively by using Logistic, Pirt, and Luedeking-Piret equations respectively.  The equations used in modelling of the fermentation kinetics matched very well with the experimental profiles, thus concluding that ethanol production from algal starch hydrolysate was growth-associated under the evaluated conditions.

Exploring indigenous microalgae capable of producing significant amounts of neutral lipids through high-throughput screening is crucial for sustainable biodiesel production. In this study, 31 indigenous microalgal strains were isolated from diverse aquatic habitats in KwaZulu-Natal, South Africa. Eight superior lipid-producing strains were selected for further analysis, based on Nile red fluorescence microscopy screening. The microalgal isolates were identified to belong to the genera Chlorella, Neochloris and Chlamydomonas via morpho-taxonomic and molecular approach by 18S rRNA gene sequencing. Chlorella vulgaris PH2 had the highest specific growth rate (μ) and lowest doubling time of 0.24 day -1 and 2.89 ± 0.05 day -1 , respectively. Chlorella vulgaris T4 had the highest biomass productivity of 35.71 ± 0.03 mg L -1 day -1 . Chlorella vulgaris PH2 had the highest lipid content of 34.28 ± 0.47 and 38 ± 9.2% (dcw) as determined by gravimetric analysis and the sulfo-phospho-vanillin (SPV) method, respectively. Chlorella vulgaris PH2 exhibited a high content of saturated fatty acids, while Chlorella sp. T4 exhibited a high total content of saturated and monounsaturated fatty acids with a low content of polyunsaturated fatty acids. The preponderance of neutral lipids suggests that Chlorella sp. T4 is a suitable candidate for biomass feedstock for biodiesel production.

While reverse osmosis (RO) is a promising technology for wastewater reclamation, RO concentrate (ROC) treatment and disposal are important issues to consider. Conventional chemical and physical treatment methods for ROC present certain limitations, such as relatively low nitrogen and phosphorus removal efficiencies as well as the requirement of an extra process for hardness removal. This study proposes a novel biological approach for simultaneous removal of nitrogen, phosphorus, and calcium (Ca(2+)) and magnesium (Mg(2+)) ions from the ROC of municipal wastewater treatment plants by microalgal cultivation and algal biomass production. Two microalgae strains, Chlorella sp. ZTY4 and Scenedesmus sp. LX1, were used for batch cultivation of 14-16 days. Both strains grew well in ROC with average biomass production of 318.7 mg/L and lipid contents up to 30.6%, and nitrogen and phosphorus could be effectively removed with efficiencies of up to 89.8% and 92.7%, respectively. Approximately 55.9%-83.7% Ca(2+) could be removed from the system using the cultured strains. Mg(2+) removal began when Ca(2+) precipitation ceased, and the removal efficiency of the ion could reach up to 56.0%. The most decisive factor influencing Ca(2+) and Mg(2+) removal was chemical precipitation with increases in pH caused by algal growth. The results of this study provide a new biological approach for removing nitrogen, phosphorous, and hardness from ROC. The results suggest that microalgal cultivation presents new opportunities for applying an algal process to ROC treatment. The proposed approach serves dual purposes of nutrient and hardness reduction and production of lipid rich micro-algal biomass., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

One of the buffers namely Tris (Tris-(hydroxymethyl)-amino methane) was used to increase the growth of microalgae by stabilizing the pH value in microalgae cultures. The objective of this research is to determine the growth rate and biomass productivity of Chlorella sp. with and without Tris addition. Both conditions function at various N:P ratios cultured in photobioreactors (carbon dioxide of 5%(v/v), light intensity of 3.3 Klux). Daily variations in nutrient removal (nitrogen and phosphorus), cell concentration, DO, temperature and pH were measured for data analysis. The results show that the largest yield of biomass was achieved at the N:P ratio of 15:1 with and without Tris. After cultivation lasting 92 h, the algae concentration at this ratio was 1250 mg L(-1) and 3568 mg L(-1) with and without Tris, respectively. This indicates that adding Tris to the photobioreactor greatly reduces algae biomass due to bacterial competition., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

In order to produce microalgal lipids that can be transformed to biodiesel fuel, one isolate with high lipid content was identified as Chlorella sp. Y8-1. The growth and lipid productivity of an isolated microalga Chlorella sp. Y8-1 were investigated under different cultivation conditions, including autotrophic growth (CO2, with light), heterotrophic growth (sucrose, without light) and mixotrophic growth (organic carbon sources and CO2, with light). Mixotrophic Chlorella sp. Y8-1 showed higher lipid content (35.5±4.2%) and higher lipid productivity (0.01 g/L/d) than Chlorella sp. Y8-1 cultivated under autotrophic and heterotrophic conditions on modified Walne medium. Fatty acid analysis of Chlorella sp. Y8-1 showed the major presence of palmitic acid (C16:0), oleic acid (C18:1), linoleic acid (C18:2) and linolenic acids (C18:3). The main fatty acid compositions of the Chlorella sp. Y8-1 are appropriate for biodiesel production., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Wastewater treatment with microalgae such as oxidation ditch algae reactor (ODAR) could reduce organic matter, however, the process might produce by-products that are toxic when dissolved in water. Effluent organic matter and algae organic matter are by-products of the microalgae process, that are released as well in ODAR system. The presence of these compounds in water can be a precursor for the formation of disinfection by-products (DBPs). The aim of this study is to determine the characteristics of effluent organic matter contained in domestic ODAR using the microalgae Chlorella sp. under variations of oxic and oxic-anoxic conditions. Novelty of this study is oxidation ditch combined with microalgae and the effect of aeration and intermittent aeration in the quality of wastewater effluent. Microalgae were applied in ODAR under oxic for 24 hours of aeration and oxic-anoxic through a brush aerator on for 7 hours and off for 3 hours with a ratio of waste volume to microalgae 1:1 with sampling time up to 5 hours. The results showed that BOD concentration tends to decrease up to 45% and 67% for oxic-anoxic and oxic, respectively. The UV254 value increased up to 110% and 147% for oxic-anoxic and oxic, respectively. Further, fluorescence excitation-emission matrix (FEEM) analysis identified the changing of four organic fractions as measured by the fluorescence regional index (FRI). The results indicate a decrease of aromatic protein-like significantly up to 62% and a decrease in soluble microbial products up to 30%. While humic acid-like and fulvic acid-like tends to increase by about 25-29% and 44-46%. [ABSTRACT FROM AUTHOR]

Chlorella has become one of the most studied and produced microalgae, with Spirulina among the hundreds of species since the beginning of microalgal biotechnology. The growth performance of microalgae and the biochemical composition of the biomass may also vary significantly by strain. Therefore, it is thought that searching for new strains from aquatic environments is important in providing the most suitable microalgae for production. An isolated strain from Daday Stream was cultured in the laboratory at Kastamonu University. BG-11 was used as a medium, and CO2 from the air was used as a carbon source in the experiments. The initial cell number was arranged to 1.0×106 cells mL-1, and the highest cell number was found on the 17th day as 40.52×106 cells mL-1. Chlorophyll a and carotenoids were determined at the end of the experiment and were found as 3.48±0.08 µg mL-1 and 1.16±0.02 µg mL-1, respectively. Total lipid amount and fatty acid composition analysis were also conducted at the end of the study. According to the analyses, the lipid content of Chlorella sp. was found to be 15.37±0.00% (w/w). SSFA (saturated fatty acid), SMUFA (monounsaturated fatty acid), and SPUFA (polyunsaturated fatty acid) ratios were calculated to be 31.30±1.21%, 4.99±0.34% and 63.71±2.65%, respectively. [ABSTRACT FROM AUTHOR]

Cold climate ecosystems hint the researchers to discover economically native cold-adapted strains, which can tolerate temperature fluctuations in outdoor large-scale cultivation for producing lipids as biofuel or for nutritional applications. Cheshmeh-Sabz Lake (Iran) was screened in winter. The lake water was sampled at 5 °C and three strains of Scenedesmus sp. (dominant in BG-11), Ankistrodesmus sp. (dominant in WC), and Chlorella sp. (dominant in BBM) were identified using molecular methods. Strains' growth parameters, lipid content, and lipid productivity were also investigated at 8 and 25 °C. Scenedesmus sp. had the most biomass productivity (~ 0.54 ± 0.001 g/L*d) with no significant difference at 8 and 25 °C and demonstrated the highest amount of lipid productivity at 25 °C (9.43 ± 1.05 g/L*d). Scenedesmus sp. produced the highest percentage of α-linolenic acid at 15 and 25 °C (10.96 ± 1.5% and 11.07 ± 0.31%, respectively) among the strains. There was no significant difference for palmitic acid content at 8, 15, and 25 °C (41.05 ± 5.2, 38.48 ± 4.25, and 39.82 ± 1.58% respectively). Biomass productivity decreased in Ankistrodesmus sp. and Chlorella sp. at 8 °C in comparison to that of 25 °C (~ 86% and ~ 34% decrease, respectively). Ankistrodesmus sp. produced the highest proportion of α-linolenic acid at 8 °C (9.98 ± 0.10%). The highest percentage of palmitic acid was observed in Chlorella at 25 °C (44.41 ± 7.56%). Based on the results, Scenedesmus sp. is the proper choice for outdoor cultivation at different seasons due to its relatively high biomass productivity and the specific growth rate in low and high temperatures (8 and 25 °C). [ABSTRACT FROM AUTHOR]