Large-scale Cultivation Of Microalgae Research Articles

Improved microalgae growth and lipid production in anaerobic digestate with ultraviolet radiation pretreatment

Inappropriate sterilization strategies inhibit microalgal growth when culturing microalgae with anaerobic digestate. This study aimed to scientifically select a low-cost disinfection pretreatment of anaerobic digestate for large-scale microalgae cultivations. In this work, three different methods, including autoclaving, ultraviolet or NaClO treatments, were employed to sterilize the municipal anaerobic digestate. Scenedesmus quadricauda was then cultured in diluted liquid digestate for the simultaneous lipid production and nutrient removal. The results indicated that the growth of S. quadricauda was inhibited after NaClO treatment due to the residual free chlorine. The 15-min ultraviolet effectively mitigated microbial contamination and increasing nutrient availability, enhancing the electron transport of microalgal photosynthesis. After 6-days cultivation, the microalgal biomass concentration of the ultraviolet group was 1.09 g/L, comparable to that of the autoclaving group (1.15 g/L). High nutrient removal efficiency was observed: COD (93.30 %), NH4+-N (92.56 %), TN (85.82 %) and TP (95.12 %). Moreover, S. quadricauda outcompeted the indigenous microorganisms, contributing to its dominance in the culture system of ultraviolet group. The facultative anaerobe Comamonadaceae and aerobes Moraxellaceae, rather than strict anaerobe Paludibacteraceae and Bacteroidetes_vadinHA17, played vital roles in synergistic removal of contaminants by bacteria and algae. The potential competition for nitrogen and phosphorus by bacteria contributed to the ultraviolet group having the greatest lipid content (48.19 %). Therefore, this work suggested using 15-min ultraviolet treatment for anaerobic digestate in large-scale microalgae cultivation.

Isolation and identification of Chlorella sorokiniana HDMA-16 and its cultivation potential in flax retting wastewater

The utilization of microalgae for wastewater treatment presents a promising and cost-effective solution due to their ability to remove pollutants while simultaneously synthesizing biomass from wastewater nutrients. This research identified a novel strain of Chlorella sorokiniana and investigated its growth ability in flax retting wastewater (FRW), as well as its potential for FRW treatment. Chlorella sorokiniana HDMA-16 was inoculated into FRW, both with and without additional nutrient supplementation. The biomass, lipid content, and fatty acid profile of Chlorella sorokiniana HDMA-16 were determined, along with the changes in total nitrogen (TN), ammonia nitrogen (NH4+-N), total phosphorus (TP), and chemical oxygen demand (COD) in FRW. The results revealed that Chlorella sorokiniana HDMA-16 exhibited moderate growth in FRW without the need for additional nutrients. The strain achieved maximum biomass and lipid productivity levels of 785.7 mg L−1 and 151.5 RFU L−1 d−1. The lipid produced by Chlorella sorokiniana HDMA-16 displayed a favorable fatty acid profile, making the strain a potential candidate for the synthesis of by-products such as biodiesel. The removal rates of NH4+-N, TP, and COD in FRW reached a maximum of 26.86 %, 99.59 %, and 29.39 %. This study is significant in that it shows that the newly discovered Chlorella sorokiniana HDMA-16 can thrive in FRW and effectively remove pollutants. These findings provide a novel approach for FRW treatment and the large-scale cultivation of microalgae, offering promising prospects for sustainable wastewater treatment and microalgae-based industries.

Inhibition mechanism and biological recycling utilization of microalgae culture aging solution

During the process of recovering microalgae culture media, the culture media will age and inhibit the growth of microalgae. When the culture media was reused for the third time, the maximum biomass of Spirulina platensis FACHB-439 was only 56.13% of the fresh culture media. But the inhibitors in the aging solution are not known. In this study, the growth inhibition mechanism of Spirulina platensis aging solution was clarified through the identification of target organic matter by cyclic culture experiment and ion chromatography. The results showed that the growth inhibitors in the aging solution were polysaccharides, mainly including fucose and rhamnose. Further reverse addition experiments confirmed that polysaccharide inhibitors would increase with the increase of repeated use of the culture media. By inhibiting the synthesis of photosynthetic pigments in microalgae, they could cause oxidative damage and membrane peroxidation of microalgae cells, resulting in stress on the growth of microalgae. At the same time, this study established a purification method for reusing aging solution of heterologous microalgae (Chlorella sp. L166) to obtain high lipid and high carbohydrate biomass energy. The results showed that the biomass of Chlorella sp. L166 in the first circulating aging solution of S.platensis FACHB-439 increased by 25%, the carbon utilization rate reached 21.36%, the lipid content per cell increased by 1.61 times, and the carbohydrate content increased by 86.71%. This work is helpful to solve the problem that aging of culture media inhibits carbon sequestration efficiency and biomass yield of microalgae in large-scale production of microalgae. And the results of this study have achieved high utilization rate of water resource for large-scale cultivation of microalgae, which is conducive to realize the scale development of microalgae biotechnology.

A comprehensive universal model framework of microalgae growth dynamics for photobioreactor scaling-up design and optimization

Scaling up microalgae cultivation for large-scale utilization is challenging. To solve this problem and to optimize energy conversion by predicting and regulating the microalgae growth process, a universal and integrated numerical model framework for PBR design and optimization was developed. The model integrates computational fluid dynamics, light transfer, and microalgae growth sub-models, and supports aeration and stirring (dynamic mesh) for mixing. In this work, the model was first used to optimize culture conditions such as stir rate and light intensity, and then verified them experimentally. The model estimated the growth curve and growth rate of microalgae with an average error of 4.59% and a maximum error of 7.14%, respectively. The model can capture the growth kinetics of microalgae under large-scale conditions, and provide guidance for large-scale microalgae cultivation. Besides, we obtained that the traditional viewpoint of the dynamic illumination strategy is not exact and some PBR improvements for enhancing mixing and illumination were suggested.

Feasibility of growing microalgae on wastewaters collected from a vinegar plant for, concurrently, nutrient removal and biomass production

In this work, feasibility of using winemaking wastewater (WW), vinegar wastewater (VW), and pickle wastewater (PW) to cultivate microalgae was investigated. Results showed that the three wastewaters possessed different nutrient profiles due to their various sources, and VW was much richer in nutrients than WW and PW. The maximum biomass concentrations of 0.73, 2.45, and 0.64 g L−1 were observed when Chlorella vulgaris was cultivated in WW, VW, and PW, respectively, suggesting that VW was a potential algal culture medium. Moreover, four algal strains could grow well on VW, but biomass production and nutrient removal of C. vulgaris were significantly higher than that of the other three strains, indicating that this alga was a promising algal strain for VW treatment. Furtherly, initial cell density was optimized for improving nutrients removal and biomass production. The maximum biomass concentration and productivity of 2.83 g L−1 and 349.8 mg L−1 d−1, and TN, TP, and COD removal efficiencies of 80.02, 64.38, and 77.10 %, respectively, were obtained when initial cell density was 0.4 g L−1. Initial cell density had little impact on the algal chemical composition, but availability and concentration of nutrients and algal species exhibited remarkable influences on the chemical compositions of microalgae cultivated in these wastewaters. These findings not only verified the feasibility of using vinegar production wastewaters to cultivate microalgae, but also paved a way for large-scale microalgae cultivation using the wastewaters.

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.

Hibberdia magna (Chrysophyceae): a promising freshwater fucoxanthin and polyunsaturated fatty acid producer

BackgroundAlgae are prominent producers of carotenoids and polyunsaturated fatty acids which are greatly prized in the food and pharmaceutic industry. Fucoxanthin represents a notable high-value carotenoid produced exclusively by algae. Its benefits range far beyond just antioxidant activity and include cancer prevention, anti-diabetes, anti-obesity, and many other positive effects. Accordingly, large-scale microalgae cultivation to produce fucoxanthin and polyunsaturated fatty acids is still under intensive development in the commercial and academic sectors. Industrially exploitable strains are predominantly derived from marine species while comparable freshwater fucoxanthin producers have yet to be explored.ResultsIn this study, we searched for freshwater fucoxanthin producers among photoautotrophic flagellates including members of the class Chrysophyceae. The initial screening turned our attention to the chrysophyte alga Hibberdia magna. We performed a comprehensive cultivation experiments using a temperature × light cross-gradient to assess the impact of these conditions on the target compounds productivity. Here we present the observations that H. magna simultaneously produces fucoxanthin (max. 1.2% dry biomass) and polyunsaturated fatty acids (max. ~ 9.9% dry biomass) and is accessible to routine cultivation in lab-scale conditions. The highest biomass yields were 3.73 g L−1 accompanied by maximal volumetric productivity of 0.54 g L−1 d−1 which are comparable values to marine microalgae fucoxanthin producers in phototrophic mode. H. magna demonstrated different optimal conditions for biomass, fucoxanthin, and fatty acid accumulation. While maximal fucoxanthin productivities were obtained in dim light and moderate temperatures (23 °C× 80 µmol m−2 s−1), the highest PUFA and overall biomass productivities were found in low temperature and high light (17–20 °C × 320–480 µmol m−2 s−1). Thus, a smart biotechnology setup should be designed to fully utilize H. magna biotechnological potential.ConclusionsOur research brings pioneer insight into the biotechnology potential of freshwater autotrophic flagellates and highlights their ability to produce high-value compounds. Freshwater fucoxanthin-producing species are of special importance as the use of sea-water-based media may increase cultivation costs and prohibits inland microalgae production.

Microalgal Growth and Nutrient Removal Efficiency in Non-Sterilised Primary Domestic Wastewater

Microalgae biomass can produce high quantities of biochemicals that can be used in various applications such as biodiesel, biogas, and aquaculture feed. The potential of sterilizing wastewater for microalgae-based wastewater treatment on a lab scale is well introduced. However, the operation cost for large-scale microalgae cultivation in wastewater treatment plants is high if using sterilising wastewater as the growth medium. The present study aimed to evaluate the growth of Scenedesmus sp., Chlorococcum aquaticum, Ankistrodesmus augustus, and Haematococcus pluvialis in non-sterilised domestic wastewater and their potential for pollutant removal in wastewater. The microalgae were cultivated in different concentrations of non-sterilised domestic wastewater, collected from a primary wastewater plant of a national sewerage company in Malaysia. Each species’ capacity for growth and the removal of pollutants were assessed. The results showed that the cell density, maximum biomass productivity, and biomass concentration of H. pluvialis, Scenedesmus sp., and C. aquaticum in 100% wastewater were significantly higher than the standard medium. Higher biomass concentration was obtained from H. pluvialis and C. aquaticum in 100% wastewater (815 g/L and 775.83 mg/L); nevertheless, Scenedesmus sp. in 100% wastewater yielded the highest specific growth rate (0.798 d−1) and the maximum biomass productivity (99.33 mg/L/day). Scenedesmus sp. in 100% wastewater also achieved better removal efficiency of total nitrogen (TN), total phosphorus (TP), and ammonia (N-NH4) with more than 90%. All tested microalgae species successfully remove nitrogen, ammonium, and phosphorus and reach the concentration limits set by the Department of the Environment, Malaysia. This study demonstrated that microalgae can grow well in non-sterilised domestic wastewater while simultaneously removing nitrogen and phosphorus effectively.

Metal-based nanoadditives for increasing biomass and biohydrogen production in microalgal cultures: A review

Microalgae have emerged as an interesting alternative for the generation of biofuels, including bioethanol, biodiesel, biomethane, biohydrogen and syngas. They are also used for the production of biofertilizers and other products of interest, while acting as a CO2 sink and favoring water purification by absorbing nutrients. However, the economic viability of large-scale microalgae cultivation for any of these purposes is not yet a reality. One of the main factors affecting this viability refers to the microalgae growing phase. In this scenario, nanoparticles, e.g. metallic, are emerging as possible alternatives to improve the cultivation and harvesting of microalgae. The addition of certain nanoadditives in microalgal cultures can improve light conversion in the photobioreactor, as well as CO2 absorption performance. However, the way in which these nanoparticles act or the concentration at which they maximize their positive effects on the culture are aspects that remain unclear. Thus, this paper critically reviews recent advances in nanoparticulate additives when they are used as a supplement in microalgae cultures, with the specific objective of improving biohydrogen production, but also analyzing their effect on algal growth, lipid accumulation and CO2 capture. The effects of nanoparticles on the selection of metabolic pathways of microalgae and their potential toxicity are also reviewed. The reported studies reveal that the toxicity of nanoadditives depends on their concentration, typology (chemical nature, particle size, crystalline structure) and species of microalgae. Furthermore, the supplementation of certain nanoparticles clearly increases the accumulation of intracellular compounds of interest and the growth of the algae. Additional studies should focus on aspects such as optimizing the dose of nanoparticles, designing strategies to minimize toxicity risks, or working with several additives simultaneously to create synergistic effects.

Microalgae enrichment for biomass harvesting and water reuse by ceramic microfiltration membranes

Harvesting and water reuse are two critical issues for large-scale microalgae cultivation. Using two representative microalgae species, namely C. vulgaris and Scenedesmus sp., this study evaluates the performance of a ceramic microfiltration membrane to extract clean water for reuse and pre-concentrate the microalgae solution for subsequent harvesting. The results show that fouling was specific to each individual microalgae species due to the difference in cell properties (e.g. size, shape, and cell membrane). Importantly, membrane fouling could be efficiently mitigated by aeration and regular backwashing without any chemical addition. Aeration reduced the transmembrane pressure when filtering C. vulgaris and Scenedesmus sp. by 56 and 38%, respectively. In long-term performance experiments, C. vulgaris showed considerable membrane fouling over time; by contrast, Scenedesmus sp. showed negligible fouling. The results reaffirmed that membrane filtration efficiency was microalgae species-specific. Permeate water reuse for growing another batch of microalgae was also demonstrated using both species. Results reported here suggest that ceramic microfiltration membrane can simultaneously enrich the microalgae solution and recycle permeated water for microalgae cultivation.

Photosynthetic Carbon Uptake Correlates with Cell Protein Content during Lipid Accumulation in the Microalga Chlorella vulgaris NIES 227

Large-scale microalgae cultivation for biofuel production is currently limited by the possibility of maintaining high microalgae yield and high lipid content, concomitantly. In this study, the physiological changes of Chlorella vulgaris NIES 227 during lipid accumulation under nutrient limitation was monitored in parallel with the photosynthetic capacity of the microalgae to fix carbon from the proxy of oxygen productivity. In the exponential growth phase, as the biomass composition did not vary significantly (approx. 53.6 ± 7.8% protein, 6.64 ± 3.73% total lipids, and 26.0 ± 9.2% total carbohydrates of the total biomass dry-weight), the growth capacity of the microalgae was preserved (with net O2 productivity remaining above (4.44 ± 0.93) × 10−7 g O2·µmol PAR−1). Under nutrient limitation, protein content decreased (minimum of approx. 18.6 ± 6.0%), and lipid content increased (lipid content up to 56.0 ± 0.8%). The physiological change of the microalgae was associated with a loss of photosynthetic activity, down to a minimum (1.27 ± 0.26) × 10−7 g O2·µmol PAR−1. The decrease in photosynthetic O2 productivity was evidenced to correlate to the cell internal-protein content (R2 = 0.632, p = 2.04 × 10−6, N = 25). This approach could serve to develop productivity models, with the aim of optimizing industrial processes.

Modern Technologies for Converting Microalgae Biomass into Various Kinds of Biofuel

Searching for alternative sources of biomass as a raw material for bioenergy is currently an urgent fundamental and applied scientific problem. Microalgae, due to the peculiarities of their physiology, high productivity, and the potential to consume carbon dioxide from the atmosphere, are one of the examples of such sources. The article presents the results of long-term research conducted at the Moscow State University’s Laboratory of Renewable Energy Sources on developing a technology for large-scale cultivation of microalgae, methods for increasing their productivity in terms of biomass and target products (lipids and carbohydrates), and obtaining various types of biofuels from biomass (biodiesel, bio-oil, synthesis gas, methane, etc.). The possibility of associated wastewater treatment, CO2 utilization, and obtaining of valuable by-products in the industrial cultivation of microalgae is shown.

The Analysis on the Current Situation of the Utilization Mode of Microalgal Biomass Materials

In recent years, global warming caused by the greenhouse effect has become one of the greatest threats to mankind. This will have a serious impact on the environment and human body, such as land desertification, increase in ocean acidity, sea level rise, and increase in pests and diseases; affect people’s normal work and rest; and make people feel dizzy and nauseated. Excessive emissions of carbon dioxide (CO2), the main component of the greenhouse gas, have contributed to the continued rise in Earth’s temperature. Although the world is vigorously developing clean energy to reduce carbon emissions, it will not replace fossil fuels in the short term. The conversion of biomass into energy is the most important way of energy utilization. Biomass energy refers to the solar energy stored in biomass in the form of chemical energy and is the fourth major energy source after oil, coal, and natural gas. At present, biofuels have gone through three developmental stages, which can be divided into first-generation biofuels, second-generation biofuels, and third-generation biofuels according to the types of raw materials and development history. The first generation of biofuels produced from food crops, such as bioethanol derived from sucrose and starch, has already entered the energy market. However, because the first generation of biofuels uses food crops as raw materials, there is a phenomenon of “competing with people for food,” and it is difficult to achieve large-scale application. To avoid the problem of food shortages, second-generation biofuels produced from nonfood crops, such as wood fiber, have been developed. Microalgae biomass energy is favored by governments and scholars all over the world because of its unique advantages of fast reproduction speed and high oil content. The cultivation of microalgae does not occupy traditional farmland, and the marginal land such as mountains, oceans, and deserts can cultivate microalgae, or develop microalgae cultivation in the air through the innovation of microalgae photosynthetic reactors. When municipal wastewater, food industry wastewater, and aquaculture wastewater are used as the medium for large-scale cultivation of microalgae, and waste gas from biogas power generation, flue gas from coal power plants, and industrial waste gas from fermentation are used as the CO2 gas source for large-scale cultivation of microalgae, it can be further reduced. The comprehensive production cost of microalgae bioenergy plays a significant emission reduction effect. Combining the above advantages, the use of microalgae to produce first- or second-generation bioenergy has become a new research direction. This study focuses on the review of microalgal biomass in fuel, nonfuel, wastewater treatment, and fuel cell.

Development of fertilizer-based medium for the growth rate improvement of Chlorella sp. in the laboratory scale

Microalgae are unicellular photosynthetic microorganisms, ubiquitous in nature which can be found in freshwater, seawater, hypersaline lakes, even in deserts and arctic ecosystems. Chlorella sp. is a eukaryotic, unicellular, photosynthetic organism with a spherical shape of about 1 to 20 μm in diameter. In this study, the combination of commonly used Walne medium and commercial fertilizers (ZA, TSP and Urea) were proposed as a low-cost approach for the cultivation of Chlorella sp. in the laboratory basis. The modified commercial fertilizer medium formulation consisted of the combination of at least 5% of Walne with different proportion of ZA, TSP and Urea. The result indicated that the combination of 5% (v/v) Walne and 95% (v/v) urea was able to retain the algal growth as compared to the combination of Urea, TSP and ZA. The obtained specific growth for 5% (v/v) Walne and 95% (v/v) urea modified medium was 0.246 d-1 and biomass productivity resulted 28 mg/L/d, which was comparable with commonly used Walne medium. Therefore, urea was primarily considered as the most suitable nitrogen source to support the growth of Chlorella sp. in the laboratory basis. Furthermore, modified commercial fertilizer medium developed in this study could potentially substitute the enriched medium used in the laboratory for the outdoor large-scale cultivation of microalgae.

Production of valuable platform chemicals through microalgal routes utilizing waste streams

Ever rising human population leads to increased demand for fresh water, energy and food, which in turn results in upsurge of wastewater at both industrial and domestic level. These wastewaters are rich in organic and inorganic compounds which if remain untreated, are harmful to the environment. A number of methods have been used over the years for wastewater treatment but microalgae gained the attention because of their efficiency, rapid growth and potential to produce valuable bioactive compounds, biofuels, fertilizers etc. Though, large scale microalgae cultivation is still a challenge due to high nutrient and water requirement coupled with harvesting and downstream processing but nevertheless, integrated approach of wastewater treatment and biomass production is an opportunity to enhance the economic profitability. Thus, various complex wastewater sources used in integrated process of bioremediation and microalgae biomass generation for production of valuable chemicals including the challenges and advancements are addressed in this review.

Microalgal biomass quantification from the non-invasive technique of image processing through red\u2013green\u2013blue (RGB) analysis

Continuous monitoring of biomass concentration in microalgae cultures is essential and one of the most important parameters to measure in this field. This study aims at digital image processing in RGB and greyscale models, being a simple and low-cost method for cell estimation. Images obtained from different photobioreactors with wastewater and at different conditions for the cultivation of Chlorella vulgaris were analyzed. The results suggested that this technique is very effective under controlled lighting conditions, in contrast to photobioreactors placed outdoors and of different design, presenting a lower linearity. The accuracy of the method could be improved with a high-quality charge-coupled device (CCD) camera. The development of efficient methods to assess biomass concentration is an important and necessary step towards large-scale microalgae cultivation. The colour analysis technique has a great potential to meet the needs of monitoring cultures in a cost-effective and automated way using simple and cheap instruments.

How do microalgae in response to biological pollution treat in cultivation? A case study investigating microalgal defense against ciliate predator Euplotes vannus.

Microalgae have significant amounts of proteins, lipids, carotenoids, vitamins, minerals, and unique pigments. However, with the gradual expansion of microalgae cultivation, hostile biological pollution seriously restricted the large-scale microalgae cultivation and limited the exploitation of its biological resources. Moreover, protozoan poses the greatest threat to microalgae cultivation. Here, the relationship between six marine economic microalgae populations and their ciliate predator Euplotes vannus was examined. And four concentrations were designed for each type of microalgae to carry out the experiment. It was revealed that four species of microalgae inhibit the ciliate population growth at high density. Furthermore, the experiment which was the influence of microalgae at three different growth stages on the growth of the ciliates for these four kinds of high-density inhibitory microalgae was designed. The microalgae inhibitory effects were already exhibited at the end of the exponential growth phase, and it was significantly inhibited during the stationary growth phase. As the microalgae concentration increased, the inhibitory effect became more pronounced. This study provides fundamental data for screening protozoan-inhibiting microalgae and shows potential to be used in algae cultivation.

The Effect of Nutrients Mixture on The Biomass and Lipid Production from Microalgae Botryococcus braunii Mutated by UV-C Rays

Nutrient is one of the most important factors in the growth of microalgae. This research was conducted to study the effect of nutrient mixture on the biomass and lipid production of Botryococcus braunii. Microalgae B. braunii was cultivated in the commercial nutrient medium of agricultural fertilizer combinations of ammonium sulphate (ZA), urea, and triple superphosphate (TSP). Before the cultivation process, B. braunii was exposed to UV-C rays (254 nm) for 3 minutes. The concentration and type of fertilizer as a nitrogen source divided into four types of mixtures, namely FM-1, FM-2, FM-3, and FM-4 were compared with Walne nutrients to study their effects on microalgae growth and lipids. FM-1 consisting of 150 mg/L of ZA, 7.5 mg/L of urea, and 25 mg/L of TSP led to the best growth for native and mutated microalgae strains compared to Walne nutrients and other nutrient mixtures. The mutated microalgae showed less growth than the native microalgae strains. However, the mutation process significantly increased the lipid content in the microalgae. In native microalgae strains, FM-4 consisting of 136.3 mg/L of urea and 50 mg/L of TSP produced the lowest lipid at 8.96%. After being exposed to UV-C rays, the lipids in FM-4 medium increased to 55.11%. The results show that the use of commercial fertilizers and exposure to UV-C rays on microalgae have high potential in preparing lipids as raw material for biodiesel which can be effectively applied in large-scale microalgae cultivation.

Media optimization design towards maximizing biomass production of Tetradesmus obliquus under mixotrophic conditions

Maximizing biomass production is a key factor in developing large-scale microalgae cultivation. One major aspect to address is the cultivation medium composition in regards to the process objective. In this study, the effect of eight important nutrients/factors (glucose, nitrate, phosphate, sulfate, magnesium, iron, manganese, and calcium) and their interactions were investigated on the biomass production of the microalgae Tetradesmus obliquus under mixotrophic conditions. The Taguchi method, a robust tool for experimental design optimization, was used to find the optimum media composition for biomass production, with only a few well-defined experimental sets. Using Taguchi's L18 orthogonal array resulted to a 4-fold enhancement in biomass yields, with a maximum of about 7.98 g/L. Nitrate exhibited the most significant effect. Iron and phosphate showed a strong influence on short-term cultivations (6 to 9 days), while glucose and calcium had more impact on long-term cultivations (15 days). The overall optimum experimental conditions were provided.

Secretomics: a biochemical footprinting tool for developing microalgal cultivation strategies.

Microalgae offer a promising source of biofuel and a wide array of high-value biomolecules. Large-scale cultivation of microalgae at low density poses a significant challenge in terms of water management. High-density microalgae cultivation, however, can be challenging due to biochemical changes associated with growth dynamics. Therefore, there is a need for a biomarker that can predict the optimum density for high biomass cultivation. A locally isolated microalga Cyanobacterium aponinum CCC734 was grown with optimized nitrogen and phosphorus in the ratio of 12:1 for sustained high biomass productivity. To understand density-associated bottlenecks secretome dynamics were monitored at biomass densities from 0.6 ± 0.1 to 7 ± 0.1g/L (2 to 22 OD) in batch mode. Liquid chromatography coupled with mass spectrometry identified 880 exometabolites in the supernatant of C. aponinum CCC734. The PCA analysis showed similarity between exometabolite profiles at low (4 and 8 OD) and mid (12 and 16 OD), whereas distinctly separate at high biomass concentrations (20 and 22 OD). Ten exometabolites were selected based on their role in influencing growth and are specifically present at low, mid, and high biomass concentrations. Taking cues from secretome dynamics, 5.0 ± 0.5g/L biomass concentration (16 OD) was optimal for C. aponinum CCC734 cultivation. Further validation was performed with a semi-turbidostat mode of cultivation for 29days with a volumetric productivity of 1.0 ± 0.2g/L/day. The secretomes-based footprinting tool is the first comprehensive growth study of exometabolite at the molecular level at variable biomass densities. This tool may be utilized in analyzing and directing microalgal cultivation strategies and reduction in overall operating costs.