Scenedesmus Obliquus Research Articles

Harvesting freshwater microalgae with natural polymer flocculants

This study revealed the differences in harvesting performance and potential mechanisms of four natural flocculants - Chitosan, Tanfloc, Cationic starch, Moringa oleifera - on microalgae cells and explored the potential of four flocculants for harvesting microalgae. Influence of dosage, culture pH, cell density and algal organic matter (AOM) on harvesting using four flocculants were compared. The effects of the flocculants on cell viability and the reusability of separated medium were also investigated. The results demonstrated that the optimal dosages of Chitosan/Tanfloc/Cationic starch for harvesting Chlorella vulgaris and Scenedesmus obliquus were much lower than Moringa oleifera. Chitosan/Tanfloc/Cationic starch and Moringa oleifera improved microalgae harvesting through electrostatic binding and bridging, respectively. The harvesting of other flocculants were affected by culture pH except for Moringa oleifera. Nevertheless, as biomass concentration increased from ~0.3 g L−1 to ~1.5 g L−1, the optimal dosage of Moringa oleifera increased significantly, which was about 20–100 times than other flocculants. AOM could interfere all harvesting processes to varying degrees. Moreover, the flocs formed from Chitosan/Tanfloc/Cationic starch were smaller but more compacted compared to Moringa oleifera, thus possessing a better dewatering functionality. The harvesting process of four flocculants did not affect cell viability or lead to the loss of cell extractions including lipid, carbohydrates and protein. In addition to Chitosan, the medium separated from the other flocculants after harvesting could be recycled for next cultivation, reducing costs of microalgae cultivation. Amongst four natural flocculants, Tanfloc displayed >98% high harvesting efficiency with low dosages (30 mg L−1 for Chlorella vulgaris and 20 mg L−1 for Scenedesmus obliquus). It could effectively harvest microalgae in a wide pH range (pH 4.0–9.0) and showed a good dewatering potential. More importantly, the lowest harvesting cost of the four flocculants facilitates its application for large-scale harvesting. We therefore recommend Tanfloc for microalgae harvesting of the four flocculants.

Regulation of malate-pyruvate pathway unifies the adequate provision of metabolic carbon precursors and NADPH in Tetradesmus obliquus

Metabolic engineering has been hailed as a promising tool to impart oil productivity in fast-growing microalgae, thereby generating industry-suitable strains. However, complex regulatory networks in lipogenesis hampered the success to unify the abundance of metabolic carbon precursors and reducing equivalents towards lipogenesis. To obviate the biological bottlenecks, we attempted to rewire the pyruvate pathway, which could enhance the supply of NADPH by heterologously overexpressing a malic enzyme from the oleaginous diatom Phaeodactylum tricornutum (PtME) in fast-growing microalga Tetradesmus obliquus (previously known as Scenedesmus obliquus). PtME overexpression did not impair physiological properties and upheld lipogenesis by facilitating the adequate provision of CO2 and NADPH, respectively, through malate decarboxylation. The malate-pyruvate pathway played a role in elevating lipid content by 2.4-fold via coupling the carbon precursors and reducing equivalents. The malic enzyme activity increased by 9.9-fold, thereby elevated lipogenic NADPH. Together, these data exemplify the crucial role of PtME in pyruvate cycle for amalgamating the provision of metabolic carbon precursors and NADPH towards lipid accumulation and lay a strong foundation for metabolic engineering in algal industrialization.

A novel microalgal biofilm reactor using walnut shell as substratum for microalgae biofilm cultivation and lipid accumulation

Microalgae are a potential candidate for biofuels, but the high cost and low biomass yield hinder the scale-up application of microalgae. In this study, a novel walnut shell based self-permeating biofilm reactor (WSPBR) was proposed for cultivation of Chlorella vulgaris (C. vulgaris) and Scenedesmus obliquus (S. obliquus). Major influencing factors such as walnut shell size, light intensity and CO2 concentration were studied in detail. The results showed that CO2 can enhance the storage of metabolic products in microalgal cells. Thermodynamics analysis indicated that C. vulgaris and S. obliquus were likely to adhere on the surface of walnut shells. S. obliquus and C. vulgaris biomass reached the maximum values of 97.43 and 70.49 g m−2, respectively, corresponding to the walnut shell size of 0.8–1.2 mm, light intensity of 150 μmol m−2 s−1 and CO2 concentration of 2%. The lipid contents of these microalgal cells were 34.32% and 28.94%, respectively. These results indicated that WSPBR was an efficient system for microalgae cultivation as feedstock for biofuels.

Performance and optimization studies of oil extraction from Nannochloropsis spp. and Scenedesmus obliquus

The amount of water removed from harvested algae and the required quantity of solvent for efficient oil recovery impact the overall economic viability of transforming algae to bioenergy. Thus, in this study, the effect of total solids (TS) content and solvent-to-biomass ratio on oil recovery from Nannochloropsis oculata and Nannochloropsis salina (both referred to in this work as Nannocloropsis spp. and representative of marine species of algae) and Scenedesmus obliquus (a freshwater specie) was studied using modified Bligh & Dyer (B-D) method and Soxhlet extraction (with either hexane or ethanol as solvent). Adopting the modified B-D method, a maximum oil content exists between 10 and 20 wt% TS. Oil recovered with ethanol (with no pretreatment) and hexane (on acid hydrolyzed algae) with thimble increases with both TS (varied from 10 to 20 wt%) and solvent-to-biomass ratio (varied from 10 to 25). Conversely, oil yield increases with solvent-to-biomass ratio but reduces with TS due to enhanced mixing and mass transfer, increase in partition coefficient of lipids during downstream separation at lower TS, and implementation of hexane extraction without thimble. Hexane extraction was subsequently performed on acid hydrolyzed algae in a scale-up model and a 98% performance was achieved while about 60% of algal oil at the optimum data point was transformed to biodiesel with no significant impact by the solvent-to-biomass ratio or scale-up. Ethanol recovers mostly polar lipids and potentially forms an azeotrope with water which makes green diesel production less favorable and solvent recoverability challenging, respectively while the use of a large quantity of chloroform is unsafe. Thus, ethanol extraction and modified Bligh-Dyer methods were not performed in the scale-up model. Results from the application of our techno-economic analysis (TEA) model indicate that predicted sale price of Hydrotreated Algal Oil (HTAO) at each of the oil extraction data points decreases with increase in the oil content of algae, using a base case of 10000 barrel per day of HTAO with credits from animal feed and nutraceutical production. At the optimum data point, the predicted sale price of HTAO is $8.59 per gallon.

Development of a new method for simultaneous extraction of chlorophylls and carotenoids from microalgal biomass

There are still limitations in the pigment extraction methods used in microalgae biomass, especially for laboratory scale. This work aimed to develop a simple method for simultaneous extraction of chlorophylls and carotenoids from the microalgae Spirulina sp. and Scenedesmus obliquus. The extraction was performed using a methanol/chloroform (2:1 v/v) mixture with different homogenization times (30, 60 and 120 min); after exhaustive extraction with chloroform, acetone, ethyl acetate, and ethanol were tested and compared with the reference maceration method (MM). Satisfactory recovery values, mostly between 101.1 and 124.2%, were obtained with 30 min of homogenization and extraction with ethanol after chloroform (PM30E). In general, the chlorophyll and carotenoid profiles obtained by the PM30E presented fewer isomers and possible degradation compounds. PM30E showed a reduction of about five times the volume of organic solvents and was four times faster than the MM. In addition, this method provided greater analytical frequency and security for the analyst, since PM30E is performed in a closed system of mechanical homogenization.

Treatment of clean in place (CIP) wastewater using microalgae: Nutrient upcycling and value-added byproducts production

CIP wastewater is one of the major wastewater streams from the food industry, and its treatment is generally expensive, requiring a large effort to reduce its typically high nitrogen (N), and phosphorus (P) contents. Microalgae-based wastewater treatment is increasingly explored as a more sustainable alternative to the conventional methods, due to the added benefit of nutrient upcycling and value-added biomass production. For the first time, four microalgae species were used to treat CIP wastewater high in N (565.5 mg NO3−-N/l) and P (98.0 mg PO43−-P/l). An intermittent biomass harvesting strategy was adopted in this study to enhance the purification of CIP water and redirection of nutrients into algal biomass. Over 93 days operation, N removal efficiency was 52.1 ± 2.9%, 54.8 ± 2.5%, 50.0 ± 2.3% and 48.3 ± 0.5%, and P removal efficiency was 65.5 ± 10.0%, 79.4 ± 6.1%, 61.8 ± 2.5% and 69.1 ± 7.7% for Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus obliquus and wastewater borne microalgae, respectively. After the first (acclimatization) and second growth cycles, cell growth and nutrient removal slowed down but increased again after adding trace nutrients, indicating the lack of trace elements after the first two growth cycles. In the fourth and fifth batch runs, both algal growth rate and nutrient removal rate decreased despite adding trace nutrients and/or increasing light intensity, this being a consequence of the excreted soluble algal products accumulating during long-term operation. S. obliquus had the highest protein concentration of 44.5 ± 9.8% DW, while C. vulgaris accumulated the highest total lipid content (15.6 ± 0.9%, DW). In this proof-of-concept study, the cultivation of microalgae in CIP wastewater with an intermittent harvest of the accumulated algal biomass is demonstrated and it outlines the potential of microalgae to sustainably treat effluents with extremely high nutrients concentration while producing the food-grade algae biomass.

Process Development for the Detoxification of Fermentation Inhibitors from Acid Pretreated Microalgae Hydrolysate.

The aim of this study was to remove 5-hydroxymethyl furfural (5-HMF) and furfural, known as fermentation inhibitors, in acid pretreated hydrolysates (APH) obtained from Scenedesmus obliquus using activated carbon. Microwave-assisted pretreatment was used to produce APH containing glucose, xylose, and fermentation inhibitors (5-HMF, furfural). The response surface methodology was applied to optimize key detoxification variables such as temperature (16.5–58.5 °C), time (0.5–5.5 h), and solid–liquid (S-L) ratio of activated carbon (0.6–7.4 w/v%). Three variables showed significant effects on the removal of fermentation inhibitors. The optimum detoxification conditions with the maximum removal of fermentation inhibitors and the minimum loss of sugars (glucose and xylose) were as follows: temperature of 36.6 °C, extraction time of 3.86 h, and S-L ratio of 3.3 w/v%. Under these conditions, removal of 5-HMF, furfural, and sugars were 71.6, 83.1, and 2.44%, respectively, which agreed closely with the predicted values. When the APH and detoxified APH were used for ethanol fermentation by S. cerevisiae, the ethanol produced was 38.5% and 84.5% of the theoretical yields, respectively, which confirmed that detoxification using activated carbon was effective in removing fermentation inhibitors and increasing fermentation yield without significant removal of fermentable sugars.

Pilot-scale biorefining of Scenedesmus obliquus for the production of lipids and proteins

The whole process of algae farming and biomass biorefining was evaluated on a pilot scale for the production of protein concentrate for poultry feeding and crude lipids. Scenedesmus obliquus was produced in open raceway ponds, and the cells were disrupted under low-pressure homogenization operating at 150 bar. Lipids were efficiently extracted using a hybrid multistage process based on a wet extraction using hexane and ethyl acetate, followed by dry extractions using hexane. The protein concentrate containing 43.1% of total proteins was recovered at low centrifugation of 400g and submitted to a desolventization process to remove residual hexane. The protein concentrate showed a similar composition of essential amino acids in comparison to soybean which is the main protein source used in feed formulation. Aspartic acid and glutamic acid were the main amino acids observed in the microalgal protein concentrate. As a feed supplement for broilers, the protein concentrate-based feed showed equal ingestion of the control, but the latter showed lower energy efficiency. The processing of 168 kg of wet biomass (14.8 kg on a dry weight basis) resulted in a production of 1.3 kg of crude lipids and 12.6 kg of protein concentrate, which corresponded to 93.7% of the total dry biomass.

Optimized extraction of neutral carbohydrates, crude lipids and photosynthetic pigments from the wet biomass of the microalga Scenedesmus obliquus BR003

The establishment of microalgae as a sustainable source of bioproducts requires a detailed evaluation of unit operations that compose a biorefinery. Biorefining of microalgal biomass is performed in sequence for obtaining a diversity of valuable compounds, but the optimum sequence of biorefining still under scrutiny. Herein, detailed modeling of unit operations was performed to enhance the extraction of neutral carbohydrates, crude lipids, and photosynthetic pigments from the wet biomass (slurry) of the microalga Scenedesmus obliquus BR003. Concentrated sulfuric acid hydrolysis resulted in an optimized extraction yield of 93% at temperature of 80 °C, 1.5 mol L−1 of sulfuric acid solution, and retention time of 120 s. Temperature and retention time were important parameters to increase the extraction of neutral carbohydrates using concentrated sulfuric acid. The efficiency of the multistage extraction of crude lipids was drastically decreased by high biomass-to-solvent ratios, and the use of proper mixing systems and longer mixing times increased the efficiency of this unit operation. The highest lipid content was achieved using orbital shaker (210.1 ± 10.9 mg g−1), retention time of 55 min, and biomass-to-solid ratio of 6.6% (w w−1). The extraction of chlorophylls a and b, and total carotenoids could be described by sigmoidal functions between the extraction yields and ratios of ethanol to the microalgal slurry, hence high levels of ethanol were required to efficiently extract them. The minimum ratio of ethanol to microalgae slurry necessary to efficiently extract photosynthetic pigments from the slurry of S. obliquus BR003 was 0.8:0.2 in volume, and this condition allowed the extraction resulted in extraction yields from 84 to 100%.

Microalgae Consortia for Post-treating Effluent of Anaerobic Digestion of Cattle Waste and Evaluation of Biochemical Composition of Biomass

The aim of this study is to cultivate Spirulina platensis and Scenedesmus obliquus microalgae in consortia using effluents of cattle waste anaerobic treatment in order to give possibilities to the production of microalgae biomass to biorefineries uses. The biomasses obtained were characterized to evaluate the potential for the production of biofuels and other bioproducts. The effluent was used in sterile and non-sterile conditions to better understand the influence of other microorganisms in N and P removal. The biomass obtained with the addition of 10% of sterile effluent in Zarrouk media (20%) presented 44.12 and 34.62% of carbohydrates, using Spirulina platensis in monoculture or the 50%/50% consortia of Spirulina and Scenedesmus, respectively, this biomass presenting the potential to be used to bioethanol production. Nitrogen and phosphorous removal were higher in non-sterile conditions and reached 92.7 and 49.66% of nitrogen and phosphorous removal, respectively, using the consortia and with the addition of 30% effluent in the media. The cultivation of microalgae in a consortium may be used to assist the treatment of water concurrently with the production of biomass to different applications.

Multi‐omics reveal the pathways involved in induced defensive colony formation of Tetradesmus obliquus in response to Daphnia grazing cues

AbstractInducible defenses occur in various taxa of prey organisms. Many phytoplankton species, including the freshwater Chlorophyta Tetradesmus spp., can form defensive morphs under the zooplankton‐released grazing cues. However, definite statements on the actual mechanisms of inducible defense in phytoplankton are quite deficient. In the present study, the defensive mechanism of Tetradesmus obliquus (formerly known as Scenedesmus obliquus) induced by Daphnia infochemicals was analyzed through multifaceted analyses integrating physiological and biochemical monitoring, transcriptomics, and metabolomics. Results showed that the upregulated genes encoding G protein‐coupled receptor and phospholipase C were involved in the perception and transduction of grazing cues, and the transcripts related to extracellular polysaccharides formation and transductions were upregulated. The results provided molecular evidence for the role of extracellular polysaccharides in colony formation. Increased lipid content revealed through metabolomics suggested higher investment in lipid biosynthesis within colonial cells, whereas the downregulation of ribosome‐related pathways indicated less allocation of energy and resources to protein biosynthesis. The significant increase in indole‐3‐acetic acid content indicated that growth was activated under grazing cues. This study provided essential information on the inducible defensive mechanism of Tetradesmus and direct evidence for the intracellular reallocation of resources and energy owing to the defensive colony formation, which had considerable implications for enriching the theory of inducible defenses at the molecular level.

Eco-friendly larvicide of Amphora coffeaeformis and Scenedesmus obliquus microalgae extracts against Culex pipiens

National and international organizations are working together with the World Health Organization to control vector-borne diseases. The extensive uses of synthetic insecticides have led to the development of insect resistance and cause adverse health effects on humans and ecosystem. The current study aimed to study the potential larvicidal activity of microalgae (Amphora coffeaeformis and Scenedesmus obliquus) against the mosquito Culex pipiens. Toxicity on rats and an eco-toxicology study using the Microtox® test was performed. Liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) showed that A. coffeaeformis and S. obliquus extracts have high concentrations of polyphenolic compounds and unsaturated fatty acids. Both A. coffeaeformis and S. obliquus extracts had larvicidal activity with different mechanisms of toxic action against C. pipiens and the LC50 was 513.63 and 855.66 μg mL−1 compared with 173.16 μg mL−1 of the insecticide lambda-cyhalothrin. From toxicological studies on male rats and acute toxicity on bacterial strain of Vibrio fischeri using Microtox toxicity test, the A. coffeaeformis extract can be considered non-toxic to experimental animals and eco-friendly. Therefore, these findings propose the prospect use extracts of microalgae such as A. coffeaeformis as a safe and eco-friendly larvicide against C. pipiens.

Phytoremediation of 137Cs, 60Co, 241Am, and 239Pu from aquatic solutions using Chlamydomonas reinhardtii, Scenedesmus obliquus, and Chlorella vulgaris

This work is focused on the phytoremediation of radionuclides using eukaryotic green microalgae Chlamydomonas reinhardtii, Scenedesmus obliquus, and Chlorella vulgaris. This study highlights the potential use of microalgae in the process of phytoremediation in polluted aquatic solutions due to the unique cellular mechanism of uptake of different radionuclides. The kinetics of radionuclide removal from the samples was described according to the first-order kinetics and expressed by the rate constant k and calculated for each microalga at the most suitable pH. The activity of 137Cs and 60Co was measured in the presence of S. obliquus or C. reinhardtii and the activity of 241Am and 239Pu was measured in the presence of C. vulgaris. A significant decrease of activity of 137Cs was observed using C. reinhardtii with a rate constant of 2.4 Bq min−1 and S. obliquus after 3 h of incubation at pH 7 with rate constant of 2.5 Bq min−1. Chlorella vulgaris was able after 3 h of incubation to remove 241Am and 239Pu up to 90 and 70% in aquatic solutions at pH 1.7 and pH 1.5, with rate constants of 4.4 mBq min−1 and 2.8 × 10−2 mBq min−1, respectively. Novelty statement Ecologically suitable methods for the decontamination of liquid radioactive waste or radioactively contaminated areas are becoming more and more important due to the pollution of the planet. We believe that phytoremediation of radionuclides using microalgae is one of the optimal ecological methods to decontamination of radioactive waste. Microalgae as unicellular organisms have a number of advantages over the other organisms used in bioremediation—high level of tolerance to the environment, fast growth rates, high tolerance to various pH levels, etc. In this study, we used 3 different strains of microalgae for phytoremediation of various radionuclides (137Cs, 60Co, 241Am, and 239Pu). This research was focused on ex situ phytoremediation of radionuclides using microalgae at various pH levels of radioactively contaminated solutions. Due to the ability of microalgae to adapt to sometimes even extreme pH values, this research may be interesting for many institutions and researchers dealing with more environmentally friendly methods of decontamination of radioactive waste.

Co-culture of bacteria and microalgae for treatment of high concentration biogas slurry

The co-culture of microalgae and specific bacteria is conducive for improving wastewater treatment efficiency. In this study, native bacterial strains isolated from pig biogas slurry were screened for effective biogas slurry treatment when co-cultured with different microalgae. Scenedesmus obliquus and Bacillus megaterium (So-B) co-culture was found more efficient in treating high concentration biogas slurry compared with the pure microalgae culture. When the C/N/P ratio in biogas slurry was 106/16/1 and the initial microalgae-bacteria inoculation ratio was 9:1, the co-culture attained the maximum chemical oxygen demand (COD), total phosphorus (TP) and ammonia nitrogen (NH4+-N) removal rates of 85.98 %, 81.03 % and 65.48 %, respectively. High C/N ratio was favorable for NH4+-N removal by the co-culture. In addition, co-culture with bacteria markedly increased the ratio of saturated/unsaturated fatty acids in microalgae. These results suggest that the co-culture could efficiently reduce various nutrients in biogas slurry and simultaneously accumulate biomass with higher biofuel characteristics.

Evaluation of green microalgae isolated from central and north coast of Sao Paulo as source of oil

Microalgae strains, newly isolated from freshwater in mangrove areas of Central and North Coasts of Sao Paulo State (Brazil), were evaluated regarding total protein and lipid content, and fatty acids profile. The biochemical composition was compared with that observed in strains obtained by UTEX Culture Collection (USA). Among seven identified green algae, Monoraphidium contortum (CCMA-UFSCar-701) presented the highest lipid content (43.60%), close to that observed in Botryococcus braunii (UTEX-2441; 48.85%). Protein content in isolated strains varied in the range of 13.90~23.60%. Finally, the most abundant fatty acids were palmitic acid (C16:0), oleic acid (C18:1), linoleic acid (C18:2), and y-linolenic acid (C18:3).Chlorella vulgaris (CCMA- UFSCar-704) may be highlighted for its high linoleic acid content (49%). On the other hand, Elakatothrix sp (CCMA- UFSCar-702) and Scenedesmus obliquus (UTEX-B2630) presented the highest content of oleic acid (41% and 43%, respectively), which is preferable for oils to be used as feedstock for biodiesel.

Phytochemical and biological studies of carotenoids in some microalgae (Dunaliella salina, Scenedesmus obliquus and Spirulina platensis)

In the current work, carotenoids of the three microalgae [Spirulina platensis (S. platensis), Scenedesmus obliquus (S. obliquus) and Dunaliella salina (D. salina )] were extracted, quantified and exposed to phytochemical and biological (cytotoxic, antiviral, antioxidant, and anticholinesterase) activities . Also, some stress conditions were applied to S. platensis and S. obliquus to raise their carotenoid content. D. salina was found to contain the highest percent of carotenoids (0.67%) followed by S. obliquus (0.64 %), then S. platensis (0.5%). Six carotenoids were detected and identified in S. platensis and S. obliquus while four carotenoids were detected in D. salina. Lutein, β -carotene and diatoxanthin were predominant in S. platensis while β -carotene, diatoxanthin and echinenone were predominant in D. salina. Furthermore, echinenone, diatoxanthin and anthraxanthin were predominant in S. obliquus. D. salina carotenoid fraction showed potent cytotoxic activity on hepatocellular carcinoma (HepG2), breast cancer (MCF-7) and colorectal cancer (HCT116) cell lines with an IC50 24.7, 66.4 and 46.7 µg/ml, respectively. Also, S. platensis carotenoid fraction showed a significant cytotoxic activity on HepG2, MCF7 and HCT116 cell lines with an IC50 31.1, 69.9 and 62 µg/ml, respectively. D. salina and S. platensis exhibited significant antioxidant activity using1, 1- diphenyl-2picryl-hydrazyl (DPPH) in a concentration dependent manner. Also, D. salina and S. obliquus inhibited the activity of acetylcholinesterase to 60.00 and 30.00% at 10 µg/ml dose, respectively. So, D. salina and S. platensis carotenoid fractions are recommended to be included in anticancer drug researches while D. salina and S. obliquus carotenoid fractions should have a consideration in the treatment of neuro- degeneration disease.

Hydroponic Farm Wastewater Treatment Using an Indigenous Consortium

Hydroponic farms produce wastewater that need to be treated before being released into the environment. A three-step screening process (microplate, batch, and semi-continuous flasks experiments) initially designed to select an efficient microalgae strain allowed the isolation of a consortium that naturally developed in the hydroponic farm wastewater. During the non-optimized semi-continuous experiments, the best performing microalgae strain, Scenedesmus obliquus UTEX393 and the wastewater-born consortium cultures achieved good average linear growth rate (0.186 and 0.198/d, respectively) and high average nitrogen removal rates (23.5 mgN/L/d and 21.9 mgN/L/d, respectively). Phosphorus removal was very high probably due to precipitation. An integrated process was designed to treat the hydroponic farm wastewater using the wastewater-born consortium. Despite relatively low coagulation efficiencies in the preliminary tests, when integrated in a continuous process, chitosan was efficient to harvest the naturally wastewater-born consortium. The process was also efficient for removing nitrate and phosphate in less than seven days (average removal of 98.2 and 87.1% for nitrate and phosphate, respectively). These very promising results will help to define a pre-industrial pilot process.

Enhanced tolerance and resistance characteristics of Scenedesmus obliquus FACHB-12 with K3 carrier in cadmium polluted water

Microalgae have been recognized as a cost-effective biosorbent for heavy metal pollutants in wastewater, while microalgal biofilms exhibit significant potential in microalgae–water separation post-treatment. In this study, cadmium (II) removal mechanisms of suspended Scenedesmus obliquus FACHB-12 (isolated from southern China) and Scenedesmus obliquus biofilm with K3 carriers were investigated based on their cadmium removal efficiency, pigment content, and antioxidant activity. Scenedesmus obliquus biofilm achieved the highest cadmium (II) removal of 91.27% under 20 mg/L of cadmium stress compared to 87.49% by suspended Scenedesmus obliquus after three days. Under 10 mg/L of cadmium stress, photosynthetic pigments, extracellular polymeric substances, total protein, and antioxidant responses including superoxide dismutase, catalase, and glutathione were measured for both suspended and biofilm forms of Scenedesmus obliquus. During the cultivation process with cadmium solution, temporary inhibition of pigments was observed within the first 24 h and then recovered after two days of exposure to cadmium. Extracellular polymeric substance concentration increased significantly in the biofilm at 34.91 mg/g on the third day of exposure to 10 mg/L of cadmium compared to 22.52 mg/g for suspended Scenedesmus obliquus. Protein levels in both groups increased over time at similar concentrations at the end of the experiment. Antioxidant activity was enhanced during the absorption process, with higher activity observed in the biofilm group. The results suggested that Scenedesmus obliquus biofilm could provide higher cadmium removal efficiency with increased tolerance to cadmium content. This study provides insightful information on the response mechanism of Scenedesmus biofilms under heavy metal oxidative stress.

Effects of irradiance of red and blue:red LEDs on Scenedesmus obliquus M2-1 optimization of biomass and high added-value compounds

Microalgae have shown a great potential as a source of bioactive compounds, such lipidic compounds as fatty acids and carotenoids, with recognized benefit for human health. Their synthesis is directly affected by culturing conditions, but, as photosynthetic organisms, microalgae are greatly influenced by light, particularly light quality and irradiance, responsible for growth regulation and activation of biochemical pathways. Therefore, the aim of this work was to maximize biomass and high added-value compound productivity by Scenedesmus obliquus M2-1, using different light irradiances of two previously selected light sources for the production of antioxidant compounds: monochromatic red light (R) and a mixture of 40% of blue and 60% of red light (BR). Four irradiances (50, 100, 150, and 200 μmolphotons m−2 s−1) were accordingly evaluated for both light sources, upon productivity of biomass, fatty acids, carotenoids, and total antioxidant compounds. Changes in light quality and irradiance influenced these aforementioned productivities. Optimal condition for biomass productivity was 150 μmolphotons m−2 s−1, regardless light quality, for both sources. On the other hand, when the production targets carotenoids, polyunsaturated fatty acids, and/or total antioxidant capacity, the optimal condition was found to be at 200 μmolphotons m−2 s−1 under BR light.

Effect of algae (Scenedesmus obliquus) biomass pre-treatment on bio-oil production in hydrothermal liquefaction (HTL): Biochar and aqueous phase utilization studies.

Environmental concerns due to fossil fuel usage has turned the research interest towards biomass and bioenergy field. Renewable biomass such as microalgae provides numerous advantages as they can grow in wastewater; sequester carbon dioxide, economical and eco-friendly. In this study, effect of pretreatment of microalgae (Scenedesmus obliquus) biomass using post-hydrothermal liquefaction wastewater (PHWW) for bio-oil production through hydrothermal liquefaction at a temperature of 300°C was studied. Results showed liquefaction of pre-treated biomass yielded 48.53% bio-oil whereas 28.35% was resulted from biomass without pretreatment. The analysis of higher heating value of bio-oil showed that pretreated biomass oil has 36.19MJ.Kg-1 against non-pretreated biomass oil, which has 28.88MJ.Kg-1. Bio-oil (pretreated biomass) analysis revealed that 60% of compounds are in diesel and gasoline range with 58.09% of energy recovery. Bio-oil was rich in hydrocarbons of C7-C21 range with less oxygenated compounds. Carbon balance showed that an increase of 13% of carbon was sequestered in solid residue obtained from pretreated biomass and about 146% of increase also obtained in bio-oil.