Chlorella Minutissima Research Articles

Holistic approach for sequential transesterification and pyrolysis of microalgal biomass: Kinetic and thermodynamic analysis of pyrolysis using model-free and model-based approaches

Due to the renewability and sustainability, biofuels derived from algae are considered as competitive substitutes for fossil fuels. Present study investigated a holistic approach for sequential transesterification and pyrolysis of microalgal biomass, i.e. Chlorella minutissima. This study explores the complete utilization of algal biomass through sequential chemical (transesterification) and thermochemical (pyrolysis) processes. First, the lipids were extracted and converted to eco-friendly biodiesel using catalytic route. Then lipid-extracted microalgae were pyrolyzed via thermogravimetric analyzer at four heating rates, namely 5, 10, 20 and 30 °C/min. The model-free isoconversional Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), and Vyazovkin models were used to analyze the kinetics and thermodynamics of algal pyrolysis. The activation energy obtained for the pyrolysis of Chlorella minutissima utilizing KAS, FWO and Vyazovkin were 146.78, 148.86, 147.11 kJ/mol, respectively. Positive ΔH values from KAS, FWO, and Vyazovkin show an endothermic nature of the process. The mean ΔH was found to be 142.81, 143.97, and 142.82 kJ/mol, while the ΔG was 151.9, 152.20, and 161.40 kJ/mol, respectively for KAS, FWO, and Vyazovkin approaches, at 10 °C/min heating rate. Importantly, this study also revealed that the phase interfacial model was the most appropriate model to represent the degradation process using Coats-Redfern method at 5 oC

Leveraging the dynamics of microalgal CO2 capture to estimate the maximum inherent photosynthetic potential

AbstractBACKGROUNDNatural photosynthesis, utilizing intelligent molecular machinery to harness sunlight, stands as the benchmark for efficient energy generation. Despite its high quantum efficiency compared to synthetic methods, challenges persist due to dynamic nutritional and light requirements in plant, microalgae, and cyanobacteria‐driven processes. Reported microalgae CO2 uptake rates rely on biomass dry cell weight measurement after certain incubation period and systematic study of required CO2 concentrations for optimal photobioreactor operation remaining unexplored. This research is thus aimed at evaluating the critical dissolved CO2 (Ccrit ∙ CO2) concentration and specific CO2 uptake rates (SCUR) of Chlorella minutissima (CM) culture in the presence of surplus light and other nutrients by online monitoring and measuring the dynamic CO2 uptake rates which will help in maintaining the optimal rate of CO2 delivery for continuous cultivation of microalgae while minimizing the escape of CO2.RESULTSDissolved Ccrit ∙ CO2 was determined to be in the range of 16–20 mg/L, and the maximum SCUR in BBM (Bold Basal Medium) was found to be 0.73 mg CO2 (mg dcw ∙ h)−1. Interestingly, this SCUR value is nearly three times greater than that of the most efficient in vitro artificial photosynthetic novel pathway reported so far.CONCLUSIONFrom the calculated SCUR values, it may be noted that 9.6 g of biomass can be obtained from 1 g of microalgal inoculum in a day, thereby setting a benchmark for the scientists working in the areas of bioprocess engineering, synthetic biology, and metabolic engineering to comply. © 2024 Society of Chemical Industry (SCI).

Deciphering the effect of Chlorella minutissima incorporation in gluten-free millet cookies: Physical and functional properties

The current study provides insight into the utilization of protein-rich microalgal strain with anti-oxidant and antidiabetic potentials i.e., Chlorella minutissima, for the development of millet-based cookies. The studied microalgal strain has been very less explored for functional food properties and this is the first study to report its usage as an ingredient in the millet-based cookies, providing a therapeutic solution for diabetic patients. In this study, 1 %, 2 %, and 6 % dried biomass of C. minutissima were incorporated in the preparation of millet cookies and tested for various functional properties. The rheological study on millet cookie dough incorporated with C. minutissima showed viscoelastic behaviour depicting its underlying interactions and strength which were positively correlated with the physical property (hardness) of the cookies. The increased concentration of C. minutissima increased the protein content up to 2 % and significantly increased the total phenolic content (6.41 mg GAE g sample−1) of the cookie samples. Besides, this increased incorporation showed better in vitro digestibility of cookies (69.60 %) and expected glycaemic index (35.03). The study signifies the application of C. minutissima-based millet cookies in food industries, which aim to develop their product range for not only health cautious populations but also for diabetes patients.

Evaluating Ammonia Toxicity and Growth Kinetics of Four Different Microalgae Species.

Although wastewater with high ammonia concentration is an ideal alternative environment for microalgae cultivation, high ammonia concentrations are toxic to microalgae and inhibit microalgae growth. In this study, the ammonia responses of four widely used microalgae species were investigated. Chlorella vulgaris, Chlorella minutissima, Chlamydomonas reinhardtii and Arthrospira platensis were grown in batch reactors maintained at seven different NH4Cl concentrations at a constant pH of 8. Growth and nitrogen removal kinetics were monitored. IC50 values for the mentioned species were found as 34.82 mg-FA/L, 30.17 mg-FA/L, 27.2 mg-FA/L and 44.44 mg-FA/L, respectively, while specific growth rates for different ammonia concentrations ranged between 0.148 and 1.271 d-1. C. vulgaris demonstrated the highest biomass growth under an ammonia concentration of 1700.95 mg/L. The highest removal of nitrogen was observed for A. platensis with an efficiency of 99.1%. The results showed that all tested species could grow without inhibition in ammonia levels comparable to those found in municipal wastewater. Furthermore, it has been concluded that species C. vulgaris and A. platensis can tolerate high ammonia levels similar to those found in high strength wastewaters.

Hematite Nanoparticle Mediated Enhancement of Chlorella minutissima Lipid Productivity for Sustainable Biodiesel Production

This study aims to enhance lipid and biofuel productivity from Chlorella minutissima with hematite (α-Fe2O3) nanoparticles (IONPs) as a growth stimulant. The IONPs were synthesized using chemical method and characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray (EDX) analysis to confirm their structure and composition. The experimental setup involved inoculating various concentrations of IONPs (10, 20, and 30 mg·L−1) into the microalgal BG-11 growth medium to evaluate their impact on microalgal growth and biodiesel production. Results of this study showed that a concentration of 10 mg·L−1 of IONPs significantly increased the biomass concentration to 508.1 mg·L−1 over a 20-day cultivation period, achieving the highest biomass production rate of 31.7 mg·L−1·d−1 at this concentration. The lipid extracted from the microalgal biomass was subsequently transesterified into biodiesel. Key biodiesel properties, such as cetane number, calorific value, density, and viscosity, were measured to assess fuel quality. The findings demonstrate that incorporating hematite nanoparticles into the microalgal growth medium can significantly boost both lipid content and overall growth, thereby improving biodiesel production. This study suggests that the use of α-Fe2O3 nanoparticles presents a promising approach for scalable and sustainable biofuel production from microalgae.

Elucidating the adaptive response and enhanced lipid production of Chlorella minutissima under Cr (VI) stress

The exponential surge in industrialization and urbanization witnessed in recent decades has alarmingly escalated the levels of hazardous pollutants, instigating profound apprehensions regarding environmental safety. In particular, the bioamplification of heavy metals like hexavalent chromium [Cr (VI)] being a prominent example, has not only imposed severe repercussions on human health but has also wrought havoc within the intricate balance of the ecological framework. Rectifying Cr (VI) via bioremediation agents exemplified as microalgae, emerges as an environmentally harmonious strategy. The present study delves into the intricate mechanisms underpinning the adaptive responses of a freshwater microalga, Chlorella minutissima, in the face of Cr (VI) stress. Evidencing exceptional tolerance to Cr (VI) induced stress, this microalga manifested an IC50 value of ~10 ppm while evidencing an astounding removal efficiency of ~89 %. This heightened assimilation of Cr (VI) by the microalgal cells concomitantly accompanied ~1.6 fold rise in total lipid content. The fostered levels of stress metabolites and antioxidant enzymes indicate the activation of defense mechanism to mitigate Cr (VI) induced oxidative damage. Microalgae employ reduction mechanism converting toxic Cr (VI) into the less deleterious Cr (III) where Cr2O3 and CrO (OH) were found to be the prominent species; while Cr (VI) primarily existed as CrO42−. The present study provided a detailed understanding of C. minutissima towards stress tolerance and enhanced lipid production mechanisms incited by chromium exposure.

In-vitro Cr (III) alleviation and the concurrent biochemical responses by Chlorella minutissima to establish its phycoremediation potential and biofuel prospects

Different microalgal species possess the proficiency of tolerating heavy metals and enhance certain metabolic processes under metal stress. This is a novel study on C. minutissima under Chromium (III) stress to determine the IC50 value for optimization, to evaluate its phycoremediation potential and biofuel prospects. Varied range of Chromium Sulfate (20-120 mg/L) exposure on C. minutissima presented an IC50 value of 83.78 mg/L and ICPMS data stated that C. minutissima was able to eliminate 96.5% of Cr (III) from the medium with a BCF value of 0.96 and a high TI value of 1.035, reflecting on the high Cr (III) resistance ability and remediation potential of the selected microalgal species. A higher biomass productivity was observed for stressed cells (17.92 mg/L/day) than control (15.42 mg/L/day). The lipid content and productivity in the metal treated cells was elevated (21.21% and 0.77 mg/L in control, 30.12% and 1.26 mg/L under stress, respectively) with simultaneous maintenance of growth and photosynthetic functions. GC-MS study indicated a rise in MUFA under Cr (III) stress. This study presents significant insights for further investigation in utilization of C. minutissima for integrated approaches toward Cr (III) bioremediation and biodiesel production.

Modifying the aquatic toxicity of Co3O4 nanoparticles in exposed microalgae by CTAB mediated synthesis

Besides unique physical and chemical properties, Cobalt oxide nanoparticles (Co3O4 NPs) are ecotoxic in nature that limits their industrial applications. The present work assesses the ecotoxic effects of Co3O4 NPs in aquatic environments. Chlorella minutissima (freshwater microalgae) and Tetraselmis suecica (marine microalgae) were used as aquatic test species. Two forms of Co3O4 NPs were used; one was synthesized with CTAB (COCTAB NPs) and the other without CTAB (CO NPs). NPs were synthesized with the chemical co-precipitation method and further characterized. The average crystallite size of CO NPs and COCTAB NPs were 12–18 nm and 22–28 nm respectively. Aggregation occurred with both NPs but the increased hydrodynamic size was measured with COCTAB NPs in BG 11 (1465 nm) and f/2 media (1951 nm). The interaction of COCTAB NPs with microalgae showed a lower % growth inhibition effect than CO NPs. The 72 h EC 50 (effective concentration of a chemical having 50% of its impact) of COCTAB NPs for C. minutissima (50.71 mg/L) and T. suecica (63.92 mg/L) was higher than the corresponding EC 50 of CO NPs. Further, % chlorophyll – a content and % LDH (lactate dehydrogenase) release retained less affected in microalgae treated with COCTAB NPs. FTIR spectra and Zeta potential revealed that the use of CTAB in CO3O4 NPs synthesis has lowered toxicity possibly by preventing the cellular attachment of NPs and its ionic dissolution. The increased hydrodynamic size and colloidal instability also restricted the NPs from binding with cells crossing membrane barrier and causing any internal damage.

Removal of contaminants by chlorella species: an effort towards sustainable remediation

According to the United Nations, Sustainable Development Goals (SDG) goal 6 and goal 14 seeks to ensure the sustainable management of water present over the earth for all. Urban cities saw a lot of expansion in terms of population and the number of industries established there. Water quality analysis becomes a huge requirement of today’s scenario due to the impurities present in water which harms the livelihood of society. Some of the hazardous impurities like heavy metals destruct the surroundings. In this study, the removal of heavy metals from wastewater with an efficient technique i.e. Bioremediation is represented with the analysis and evaluation of results recorded in the laboratory testing. Two samples were taken from two different sites which are being analyzed with the implementation methodology represented in the present article. The inclusion of the ANOVA model for the optimization of the outcome generated is evaluated and received the P-value and F-crit value. Two algae Chlorella Minutissima & Chlorella Singularis were evaluated based on their impurity removal efficiency as well an analysis of the biological treatment method over other chemical methods has been examined. The results were analyzed and represented in the form of a table as well and the variation in the value of WQP is shown in the form of graphs. The observation shows that the variation in WQP after the integration of algae lies under the permissible limit. Alkalinity is estimated in the range of 20–40 mg/l, Hardness lies in the range of 0–60mg/l, and pH comes approximately in a range of 6.5–8. The results of the ANOVA model is also depicted in graphical form highlighting the P-value and F-crit value of different result generated. Finally, the summary of the proposed work is illustrated with the challenges faced and future recommendations have been provided. Based on the evaluation, the framework is generated for the efficient technique used for heavy metal removal i.e. Bioremediation which provides a great advancement in the efficacy of removal of heavy metals.

Lutein from Microalgae: An Industrial Perspective of Its Production, Downstream Processing, and Market

Lutein, a yellow xanthophyll carotenoid, is increasingly recognized for its nutraceutical benefits, particularly in protecting the retina’s macula from age-related degeneration. Microalgae are a promising source of lutein, which can be a primary product or a coproduct in biorefineries. Certain microalgae exhibit lutein levels (up to 1.7%) surpassing those of common dietary sources like kale, spinach, and egg yolk (approximately 0.7–0.9%). Predominantly associated with photosystem II’s light-harvesting complex, lutein is crucial in photosynthesis and cellular defense. However, being quantitatively minor among cellular constituents, lutein necessitates specialized processing for efficient extraction. Although ubiquitous in microalgae, it is not as easily inducible as β-carotene and astaxanthin in Dunaliella salina and Haematococcus pluvialis, respectively. Currently, microalgal lutein production predominantly occurs at the bench scale, presenting challenges in scaling up. Factors like culture medium significantly influence biomass and lutein yields in industrial production, while downstream processing requires cost-effective, food-grade solvent extraction techniques. This review delves into contemporary methods and innovative progress in microalgal lutein production, emphasizing industrial-scale processes from biomass cultivation to final product formulation. A conceptual industrial process proposed in this review shows that two 10 m3 photobioreactors could produce 108 kg dry mass for Chlorella minutissima, which can be processed into approximately 616 g of lutein extract, or over 6000 capsules of finished nutraceutical daily. Despite lutein production via microalgae being in nascent stages at large scales, existing research provides a solid foundation for well-informed scale-up endeavors.

Microalgal synthesis of the biodiesel employing simultaneous extraction and esterification via heterogeneous catalyst

Within the realm of biorefinery, the third generation of biodiesel production relies on extracting oil from Algae to create renewable fuels. Algae cultivation can occur under precise laboratory conditions, making them a sustainable substitute for Fatty Acid Methyl Ester or biodiesel production. Through analysis of the simultaneous extraction and (trans)esterification process of Algae Chlorella Minutissima utilizing sulfated carbonaceous catalysts, scientists have discovered an efficient technique for producing biodiesel. Various parameters, such as catalyst loading, oil-to-methanol ratio, reaction temperature, and reaction time for FFA reduction and FAME yields, were studied and optimized. Results indicate that utilizing a 10 wt% catalyst loading and a 70:30 volumetric oil to methanol ratio can achieve 67.59 % FFA reduction and a biodiesel yield of 44 mL. This method of producing biodiesel can occur in a single-unit operation, leading to higher yields of renewable fuel at a reduced cost and energy consumption. Finally, the quality of the biodiesel produced met ASTM D6751 standards, confirming its suitability for use.

Theoretical Models Constructed by Artificial Intelligence Algorithms for Enhanced Lipid Production: Decision Support Tools

Theoretical models that predict the lipid content of microalgae are an important tool for increasing lipid productivity. In this study, response surface methodology (RSM), RSM combined with artificial neural network (ANN), and RSM combined with ensemble learning algorithms (ELA) for regression were used to calculate the maximum lipid percentage (%) from Chlorella minutissima (C. minutissima). We defined one set of rules to achieve the highest lipid content and used trees.RandomTree (tRT) to simulate the process parameters under various conditions. Among the various models, results showed the optimum values of the root mean squared error (0.2156), mean absolute error (0.1167), and correlation coefficient (0.9961) in the tRT model. RSM combined with tRT estimated that the lipid percentage was 30.3% in wastewater (< 35%), lysozyme (≥ 3.5 U/mL), and chitinase (< 15 U/mL) concentrations, achieving the best model based on experimental data. The optimal values of wastewater concentration, chitinase, and lysozyme were 20% (v/v), 5 U/mL, and 10 U/mL, respectively. Also, the if-then rules obtained from tRT were also used to test the process parameters. The tRT model served as a powerful tool to obtain maximum lipid content. The final rankings of the performance of various algorithms were determined. Furthermore, the models developed can be used by the fuel industry to achieve cost-effective, large-scale production of lipid content and biodiesel.

Co-Culturing Microalgae with Roseobacter Clade Bacteria as a Strategy for Vibrionaceae Control in Microalgae-Enriched Artemia.

Bacterial communities associated with fish larvae are highly influenced by the microbiota of live prey used as feed (rotifers or Artemia), generally dominated by bacterial strains with a low degree of specialization and high growth rates, (e.g., Vibrionaceae), which can be detrimental to larvae. Co-cultivation of microalgae used in the enrichment of Artemia (e.g., Phaeodactylum tricornutum, or Chlorella minutissima) with Vibrio-antagonistic probiotics belonging to the Roseobacter clade bacteria (e.g., Phaeobacter spp. or Ruegeria spp.) was studied. The introduction of the probiotics did not affect microalgae growth or significantly modify the composition of bacterial communities associated with both microalgae, as revealed by DGGE analysis. The inoculation of P. tricornutum with Ruegeria ALR6 allowed the maintenance of the probiotic in the scale-up of the microalgae cultures, both in axenic and non-axenic conditions. Using Ruegeria-inoculated P. tricornutum cultures in the enrichment of Artemia reduced the total Vibrionaceae count in Artemia by 2 Log units, therefore preventing the introduction of opportunistic or pathogenic bacteria to fish larvae fed with them.

Effects of leachate concentration, carbon dioxide and aeration flow rate on chlorophyll and carotenoid productivity and bioremediation potential of the microalga Chlorella minutissima

The use of microalgae cultures to process effluents from industries, leachates, and tanneries, among others, quantified by the reduction of metallic materials in the medium and the reduction of chemical oxygen demand (COD), helps reduce the environmental impact caused by human development. In addition, with the growth of the culture, it is possible to produce a significant amount of chlorophyll, a carotenoid of high value in the cosmetics and food industries that are used as a natural pigment. In this context, this work presents a study conducted to verify the bioremediation and chlorophyll production potential of the cultivation of the microalgae Chlorella minutíssima, using the Taguchi method. The microalgae Chlorella minutissima has given good results in the bioremediation of leachate, as a mean reduction of 33% in COD was obtained, as well as a 92% reduction in the toxic components. In addition, statistical analysis revealed that the four process factors were significant factors for chlorophyll a, chlorophyll b and carotenoid productivity (p < 0.05). Finally, it was observed that the maximum chlorophyll a (111.9 ± 0.8 mg‧L−1‧d−1), chlorophyll b (66.1 ± 1.7 mg‧L−1‧d−1), and carotenoid (31.9 ± 0.03 mg‧L−1‧d−1) values obtained occurred in Experiment 8, which is closer to the ideal conditions identified by statistical analysis, revealing the effectiveness of the use of the Taguchi method for the design of experiments.

Spectral characterization and binding dynamics of bioactive compounds from Chlorella minutissima against α-glucosidase: An in vitro and in silico approach

Management of type-II diabetes through regulating the activity of α-glucosidase is a promising therapeutic approach. Here, bioassay-guided isolation of algal secondary metabolites (ASM) from microalgae (Chlorella minutissima) inhibiting α-glucosidase was explored. In this study, the purified column fractions (SIV-P2) of C. minutissima acetone extract obtained from flash chromatography exhibited α-glucosidase inhibition potential with the IC50 value of 1.61 mg mL−1, and the active fractions were dominated by terpenoids and alkaloids. Further, molecular dynamics simulations revealed that Lucidine B, an alkaloid compound possesses the least binding energy (BE) of −318 KJ mol−1 when compared to the standard drug acarbose (−216.781 KJ mol−1). Lucidine B formed a hydrogen bond with Glu408 which possibly induced cleft closure and prevented the substrate entry to the active site (non-competitive inhibition). The present study unveils that ASM could be exploited as a potential inhibitor of α-glucosidase and may be used for the alleviation of type-II diabetes.

Cultivation of Chlorella minutissima under a novel phosphate application strategy for biodiesel production: A pilot scale study

Microalgal biodiesel is considered as a carbon-neutral and renewable energy source for replacing/blending with petroleum-based diesel fuel. Selection of a microalgal species for its potential to produce biodiesel relies significantly on its acclimatization to grow in outdoor condition with high lipid productivity. The present investigation undertakes outdoor experiments in a raceway pond system involving a local isolate of green microalga, Chlorella minutissima, throughout varied seasonal changes and culture depth. The variations in climatic and cultural parameters were documented; the optimum culture depth of 30 cm was taken for further investigation. A novel cultivation approach incorporating the sequential addition of low-dose phosphate (LDSPA) projected a lipid productivity of 5.88 ton hectare−1 year−1, which was ∼40% higher than its batch culture counterpart, along with a 14-fold reduction in phosphate application. The biodiesel exhibited the dominance of saturated and monounsaturated fatty acid methyl esters, and the fuel qualities were confirmed to be within the stipulated limitations of European, American and Indian biodiesel standards, thus nominating C. minutissima as an attractive feedstock for generating high-quality biodiesel.

The potential of microalgal sources as coating materials: A case study for the development of biocompatible surgical sutures.

Sutures are considered as surgical materials that form excellent surfaces to integrate the postoperative parts of the body. These materials present suitable platforms for potential bacterial penetrations. Therefore, coating these biomedical materials with biocompatible compounds is seen as a potential approach to improve their properties while avoiding adverse effects. The aim of this study was to evaluate Arthrospira platensis, Haematacoccus pluvialis, Chlorella minutissima, Botyrococcus braunii, and Nostoc muscorum as potential surgical suture coating materials. Their crude extracts were absorbed into two different sutures as poly glycolic (90%)-co-lactic acid (10%) (PGLA) and poly dioxanone (PDO); then, their cytotoxic effects and antibacterial activities were examined. Both N. muscorum-coated sutures (PGLA and PDO) and A. platensis-coated (PGLA and PDO) sutures did not induce any toxic effect on L929 mouse fibroblast cells (>70% cell viability). The highest antibacterial activity against Staphylococcus aureus was achieved with N. muscorum-coated PGLA and A. platensis-coated PGLA at 11.18±0.54 mm and 9.52±1.15 mm, respectively. These sutures were examined by mechanical analysis, and found suitable according to ISO 10993-5. In comparison with the commercial antibacterial agent (chlorohexidine), the results proved that N. muscorum extract can be considered as the most promising suture coating material for the human applications.

Predicting microalgal biomass yield in outdoor raceway pond cultivation with the empirical modeling approach

Microalgae offer economic prospects in the industrial growth of bioenergetics. Although microalgae cultivation in open raceway ponds is manageable and cost-effective, dynamic environmental parameters can disrupt their growth cycles. Hence, models were developed to predict and optimize large-scale outdoor microalgal production, but many attempts failed to reproduce the predictive ability. This study aims to develop a prediction model for biomass yield in open raceway ponds by integrating two multivariate methods, viz. principal component analysis (PCA) and partial least squares (PLS) regression. The model was developed based on the cultural and environmental findings for cultivating a freshwater chlorophycean microalga Chlorella minutissima in open raceway ponds for two consecutive years. Results obtained from PCA revealed a strong correlation between solar intensity and temperature parameters, accounting for 91% of the variability in the resultant biomass yield. Consequently, PLS regression predictors for model fitting were solar intensity, temperature, relative humidity, and dissolved oxygen concentration. Findings from PLS model demonstrated predicted R2 value of 0.91. Further, the model was validated using the experimental data for the outdoor conditions from available literature and showed significant prediction efficiency up to 97%, with mean absolute errors in the range of 3–21%. Thus, the developed model has the potential to predict the microalgal biomass yield in outdoor raceway ponds accurately.

Kinetic modelling for prediction of biomass concentration of Chlorella minutissima in open raceway pond cultivation: A pilot-scale study

For large-scale microalgae cultivation, modelling can play a significant role in predicting and improving biomass generation. Existing kinetic models for outdoor cultivation have drawbacks of reproducibility due to the involvement of uncontrollable environmental factors such as solar intensity, air temperature, relative humidity, dilution rate, etc., affecting the dependent variables such as culture temperature, dissolved oxygen concentration and pH, regardless of the availability of adequate nutrients in the medium. Thus, a kinetic model was proposed here to predict the biomass concentration accurately for all the given variables in terms of specific growth rates. Chlorella minutissima was cultivated in open raceway ponds to calibrate the proposed model, and biomass concentration was estimated as a function of time along with the cultural and environmental variables. Sensitivity analysis demonstrated that the estimated biomass concentration was highly sensitive to the specific growth rate of solar intensity followed by the air temperature. The model was evaluated using C. minutissima experimental data, which exhibited a prediction efficiency of 99.5% with an R2 value of 0.96. Further, the model validation was performed with experimental data obtained for outdoor cultivation of Scenedesmus accuminatus, Tetradesmus obliquus, Chlorella variabilis, Scenedesmus acutus, and Chlorella pyrenoidosa from the available literature, which showed the mean absolute percentage errors of 0.38, 9.1, 7.38, 9.5, and 1.72%, respectively. It has also been observed that as the availability of input variables increases, the accuracy of biomass concentration prediction increases. Thus, this model is recommended for forecasting microalgal biomass production.

Chlorella minutissima-assisted silver nanoparticles synthesis and evaluation of its antibacterial activity.

The conventional methods of nanoparticles synthesis led to the production of highly toxic by-products and the use of toxic chemicals that are highly expensive in nature. Thus, the recent past has witnessed a surge in green synthesis of nanoparticles as a sustainable alternative. The present study outlines the biogenic silver nanoparticles (Ag-NPs) synthesis from an aqueous extract of Chlorella minutissima. The effect of certain parameters such as the reaction mixture's pH and precursor metal solution to algal extract ratios were explored and optimized. The UV spectrophotometric analysis of Ag-NPs gave surface plasmon response maximally at 426nm. The developed Ag-NPs were characterized using zeta potential, indicating their high stability (-21.2mV) with a mean diameter of 73.13nm. Results from field emission-scanning electron microscopy (FE-SEM) showed that the particles were spherical in shape. Ag-NPs synthesized using Chlorella minutissima extract could significantly inhibit the growth of both Gram-positive and Gram-negative bacterial species. The study highlights that using C. minutissima extract for Ag-NPs synthesis is a convenient and fast process for controlling the growth of Gram-positive as well as Gram-negative bacteria.