Raceway pond cultivation of a marine microalga of Indian origin for biomass and lipid production: A case study

Engineering highly productive cyanobacteria towards carbon negative emissions technologies

Cyanobacteria are a diverse and ecologically important group of photosynthetic prokaryotes that contribute significantly to the global carbon cycle through the capture of CO2 as biomass. Cyanobacterial biotechnology could play a key role in a sustainable bioeconomy through negative emissions technologies (NETs), such as carbon sequestration or bioproduction. However, the primary issues of low productivities and high infrastructure costs currently limit the commercialisation of such applications. The isolation of several fast-growing strains and recent advancements in molecular biology tools now offer promising new avenues for improving yields, including metabolic engineering approaches guided by high-throughput screening and metabolic models. Furthermore, emerging research on engineering coculture communities could help to develop more robust culturing systems to support broader NET applications.

Biomass, photosynthetic activity, and biomolecule composition in Chlorella fusca (Chlorophyta) cultured in a raceway pond operated under greenhouse conditions

Raceways are widely used as microalgae culture systems due to their low cost, but they are not the best option for biomass yield. Understanding in situ photosynthetic performance can be a first step to increase their biomass productivity. This study aimed at comparing the real time photosynthetic activity in a greenhouse raceway culture (250L) with discrete measurements under laboratory conditions. We evaluated the photophysiology and biochemical composition of Chlorella fusca culture up to 120h. In situ photosynthetic activity was continuously monitored and compared to discrete ex situ measurements; biochemical compounds were measured daily. The results showed a final biomass density of 0.45gL^-1 (5 days - 120h) and an increase of the electron transport rate (ETR) up to 48h but decreased thereafter. When the relative ETR was estimated considering the absorption coefficient (a) positive correlations of this parameter with photosynthetic capacity, cell density, biomass, biocompounds and antioxidant activity were obtained, whereas no correlation was detected without considering a. In situ photosynthesis monitoring showed higher absolute maximal ETR (10 - 160 μmol m^-3s^-1) than discrete ex situ measurements. We demonstrated the importance of considering the light absorption coefficient for expressing photosynthetic capacity and showed that C. fusca can produce, in the short-term, bioactive compounds that are correlated to photosynthetic conditions.

Application of Arthrospira platensis for Medicinal Purposes and the Food Industry: A Review of the Literature

Arthrospira platensis is a filamentous cyanobacterium of the class Cyanophyceae and is the most cultivated photosynthetic prokaryote. It is used in the pharmaceutical sector, medicine and the food industry. It has a rich micro- and macro-element composition, containing proteins, lipids, carbohydrates, essential amino acids, polyunsaturated fatty acids, minerals and raw fibers. It is a commonly used ingredient in food products and nutritional supplements. The wide range of biologically active components determines its diverse pharmacological properties (antioxidant, antidiabetic, antimicrobial, antineoplastic, antitumor, anti-inflammatory, photoprotective, antiviral, etc.). This review summarizes research related to the taxonomy, distribution and chemical composition of Arthrospira platensis as well as its potential application in the food and pharmaceutical industries. Attention is drawn to its various medical applications as an antidiabetic and antiobesity agent, with hepatoprotective, antitumor, antimicrobial and antiviral effects as well as regulatory effects on neurodegenerative diseases.

Microalgae cultivation in wastewater from agricultural industries to benefit next generation of bioremediation: a bibliometric analysis

The aim of this study was to provide a bibliometric analysis and mapping of existing scientific papers, focusing on microalgae cultivation coupled with biomass production and bioremediation of wastewater from agricultural industries, including cassava, dairy, and coffee. Using the Web of Science (WoS) database for the period 1996-2021, a search was performed using a keyword strategy, aiming at segregating the papers in groups. For the first search step, the keywords "wastewater treatment", AND "microalgae", AND "cassava" OR "dairy" OR "coffee" were used, resulting in 59 papers. For the second step, the keywords "wastewater treatment" AND "biomass productivity" AND "microalgae" AND "economic viability" OR "environmental impacts" were used, which resulted in 34 articles. In these papers, keywords such as "carbon dioxide biofixation" and "removal of nutrients by the production of biomass by microalgae" followed by "environmental and economic impacts" were highlighted. Some of these papers presented an analysis of the economic feasibility of the process, which reveal the state-of-the-art setup required to make the cultivation of microalgae economically viable. Researches focusing on the efficiency of microalgae biomass harvesting are needed to improve the integration of microalgae production in industrial eco-parks using wastewater to achieve the global goal of bioremediation and clean alternatives for renewable energy generation.

Controlling of two destructive zooplanktonic predators in Chlorella mass culture with surfactants

BACKGROUND

Predatory flagellates and ciliates are two common bio-contaminants which frequently cause biomass losses in Chlorella mass culture. Efficient and targeted ways are required to control these contaminations in Chlorella mass cultivation aiming for biofuel production especially.

RESULTS

Five surfactants were tested for its ability to control bio-contaminations in Chlorella culture. All five surfactants were able to eliminate the contaminants at a proper concentration. Particularly the minimal effective concentrations of sodium dodecyl benzene sulfonate (SDBS) to completely eliminate Poterioochromonas sp. and Hemiurosomoida sp. were 8 and 10 mg L^-1, respectively, yet the photosynthesis and viability of Chlorella was not significantly affected. These results were further validated in Chlorella mass cultures in 5, 20, and 200 m² raceway ponds.

CONCLUSIONS

A chemical method using 10 mg L^-1 SDBS as pesticide to control predatory flagellate or ciliate contamination in Chlorella mass culture was proposed. The method helps for a sustained microalgae biomass production and utilization, especially for biofuel production.

Influence of Nitrogen to Phosphorus Ratio and CO2 Concentration on Lipids Accumulation of Scenedesmus dimorphus for Bioenergy Production and CO2 Biofixation

The potential of Scenedesmus dimorphus microalgae for CO₂ biofixation and lipid biosynthesis for bioenergy applications was evaluated in this study. Batch experiments were conducted using synthetic tertiary municipal wastewater samples at several nitrogen to phosphorus (NP) ratios (1 : 1 to 8 : 1) and CO₂ concentrations (∼0%, 2%, 4%, and 6% CO₂ in supplied air). Scenedesmus dimorphus was cultivated for 25 days and the growth is highly dependent on the CO₂ concentration and the NP ratio. An NP ratio of 2 : 1 produces a biomass yield of 733 mg/L when the microalga culture was supplied with air enriched with 2% CO₂ . The maximum CO₂ biofixation rate of 49.6 mg L^-1  d^-1 is at an NP ratio of 8 : 1 with 4% CO₂ . A colorimetric technique depending on sulpho-phospho-vanillin (SPV) was utilized for the determination of the intracellular lipid content. The highest lipid content of 31.6% as the dry weight of the biomass is at an NP ratio of 1 : 1 and 6% CO₂ . These results indicate that supplementation of suitable CO₂ with favorable NP ratio has a considerable effect on lipid accumulation in the microalgae Scenedesmus dimorphus biomass.

Application of Heterogeneous Catalysts for Biodiesel Production from Microalgal Oil—A Review

The depletion of fossil fuel reserves and increased environmental concerns related to fossil fuel production and combustion has forced the global communities to search for renewable fuels. In this regard, microalgae-based biodiesel has been considered as one of the interesting alternatives. Biodiesel production from the cultivation of microalgae is eco-friendly and sustainable. Moreover, microalgae have several advantages over other bioenergy sources, including their good photosynthetic capacity and faster growth rates. The productivity of microalgae per unit land area is also significantly higher than that of terrestrial plants. The produced microalgae biomass is rich with high quality lipids, which can be converted into biodiesel by transesterification reactions. Generally, the transesterification reactions are carried out in the presence of a homogeneous or heterogeneous catalyst. The homogeneous catalysts have many disadvantages, including their single use, slow reaction rate and saponification issues due to the presence of fatty acids in the feedstock. The acidic nature of the homogeneous catalysts also causes equipment corrosion. On the other hand, the heterogeneous catalysts offer several advantages, including their reusability, higher reaction rate and selectivity, easy product/catalyst separation and low cost. Due to these facts, the development of solid phase transesterification catalysts have been receiving growing interest. The present review is focused on the use of heterogeneous catalysts for biodiesel production from microalgal oil as a reliable feedstock with a comparison to other available feedstocks. It also highlights optimal reaction conditions for maximum biodiesel yields, reusability of the solid catalysts, cost, and environmental impact. The superior lipid content of microalgae and the efficient concurrent esterification and transesterification of the solid acid−base catalysts can offer new advancements in biodiesel production.

Optimization of heterotrophic cultivation of Chlorella sp. HS2 using screening, statistical assessment, and validation

The heterotrophic cultivation of microalgae has a number of notable advantages, which include allowing high culture density levels as well as enabling the production of biomass in consistent and predictable quantities. In this study, the full potential of Chlorella sp. HS2 is explored through optimization of the parameters for its heterotrophic cultivation. First, carbon and nitrogen sources were screened in PhotobioBox. Initial screening using the Plackett-Burman design (PBD) was then adopted and the concentrations of the major nutrients (glucose, sodium nitrate, and dipotassium phosphate) were optimized via response surface methodology (RSM) with a central composite design (CCD). Upon validation of the model via flask-scale cultivation, the optimized BG11 medium was found to result in a three-fold improvement in biomass amounts, from 5.85 to 18.13 g/L, in comparison to a non-optimized BG11 medium containing 72 g/L glucose. Scaling up the cultivation to a 5-L fermenter resulted in a greatly improved biomass concentration of 35.3 g/L owing to more efficient oxygenation of the culture. In addition, phosphorus feeding fermentation was employed in an effort to address early depletion of phosphate, and a maximum biomass concentration of 42.95 g/L was achieved, with biomass productivity of 5.37 g/L/D.

Consolidated bioprocessing of wastewater cocktail in an algal biorefinery for enhanced biomass, lipid and lutein production coupled with efficient CO2 capture: An advanced optimization approach

We present a holistic approach in establishing a successful green integrated bio-refinery system with improved biomass, lipid and lutein productivity, while remediating wastewater and sequestering CO₂ with potential biodiesel and healthcare applications. To achieve this we evaluated the effect of four process parameters: CO₂% supply; acetate concentration; poultry litter waste (PLW) concentration; and light intensity on cultivation of Chlorella minutissma following the Taguchi's design of experimental technique. A four factors, three levels orthogonal array was adopted to cultivate Chlorella minutissma in specially developed waste water medium. Effect of the process parameters on biomass productivity, CO₂ fixation rate, lipid content, lutein productivity and bioremediation capacity were determined. Results obtained from individual parametric combinations and Signal/Noise (S/N) ratio responses indicated S3 (5% CO₂, 100 mg L^-1 of acetate, 10 g L^-1 of poultry litter, and 15, 000 lux of light intensity) combination as the optimum cultivation condition. Following the S3 combination a significant enhancement in biomass productivity (292 mg L^-1 d^-1) with exceedingly high CO₂ fixation rate and photosynthetic efficiency (51.51 g L^-1 d^-1 of CO₂; P.E: 15.81%) was achieved. A maximum of 169.29 mg L^-1 d^-1 of lipid with a balanced distribution of saturated and unsaturated fatty acids conformed to the international standard for biodiesel was achieved. Additionally, 7.21 mg L^-1 d^-1 of lutein productivity was also accomplished within 7 day of cultivation, while remediating up to 93-90% of nitrogenous and phosphate substrates. Statistically, the results reinforced our findings with the S/N responses and experimental observations for a particular property.

Performance evaluation of an outdoor algal biorefinery for sustainable production of biomass, lipid and lutein valorizing flue-gas carbon dioxide and wastewater cocktail

We evaluated wastewater remediation and CO₂ utilization potential of Chlorella minutissima from flue gas in a raceway pond, while synthesizing lutein and lipid for potential healthcare and biofuel application. A mix of 20% kitchen waste, 10 g L^-1 of poultry litter waste and 5% flue gas was maintained while cultivating the microalga. Complete removal of nitrate, nitrite and ammonium, 85% carbon and 91% phosphorus was observed. An average areal biomass productivity of 4.06 ± 0.12 g m^-2 day^-1 with a specific growth rate of 0.34 ± 0.03 day^-1 was observed within 9 days. Biomass productivity of 6.21 ± 0.16 g m^-2 day^-1 with a specific growth rate of 0.34 ± 0.03 day^-1 was achieved during winter. Furthermore, lipid content with appropriate fatty acid composition 1.04:1 (saturation:unsaturation) increased from 25% to 58%. Additionally, lutein productivity of 1.2 ± 0.08 mgL^-1 day^-1, while utilizing 80.74 ± 0.07 mg L^-1 day^-1 of CO₂ from 5% flue gas was obtained.

Zero-waste algal biorefinery for bioenergy and biochar: A green leap towards achieving energy and environmental sustainability

In spite of tremendous efforts and huge investments on resources, biodiesel from oleaginous microalgae has not yet become a commercially viable and sustainable alternative to petro-diesel. This is mainly because of the technological and economic challenges hovering around large scale cultivation and downstream processing of algae, water and land usage, stabilized production technology, market forces and government policies on alternative energy and carbon credits. This review attempts to capture and analyse the global trends and developments in the areas of biofuel and bio-product of microalgae and proposes possible strategies that can be adopted to produce biofuel, biochar and bio-products utilizing wastewater in a bio-refinery model. The strategies include "Zero waste discharge" concept with process integration, wherein microalgae is grown strategically using different wastewater combined with flue gas in cultivation system for simultaneous production of 'high-value-low-volume' product and 'low-value-high-volume' product with sharing of the remnant biomass to produce biochar. In addition, the CO₂ present in the atmosphere is captured and sequestered long term in the form of biochar would help to attain carbon negativity, while remediating wastewater and balancing energy requirements. Therefore, "Zero waste discharge" concept holds the potential to make the process a sustainable one, while gaining on the carbon credits.

Mass cultivation of Dunaliella salina in a flat plate photobioreactor and its effective harvesting

Mass cultivation of Dunaliella salina was standardized in a flat plate photobioreactor followed by a vertical flat plate photobioreactor. Maximum biomass productivity (14.95 ± 0.43 mgL^-1d^-1 dry cell weight) was achieved in the latter at inoculum concentration of OD_680nm = 0.1, 100 µmolm^-2s^-1 light illumination and 1.0 L min^-1 aeration. Semicontinuous operation with varying KNO₃ and NaHCO₃ concentrations resulted highest biomass productivity (17.85 ± 0.55 mgL^-1d^-1) at 0.50 mM NaHCO₃ and 15 mM KNO₃. However, maximum lipid (16.36 ± 1.18% dry cell weight) was achieved at 0.75 mM NaHCO₃ and 10 mM KNO₃. Flocculation studies employing potash alum, FeCl₃·6H₂O or pH showed harvesting efficiencies exceeding 90% in 0.75 mM potash alum or FeCl₃·6H₂O or pH 11, but they yielded low concentration factor (<5) and were detrimental (Fv/Fm < 0.50). A combination of 0.50 mM FeCl₃·6H₂O and pH 9 was found as most suitable flocculating strategy with maximum concentration factor (>14) and least damaging (Fv/Fm > 0.54).

Outdoor pilot-scale cultivation of Spirulina sp. LEB-18 in different geographic locations for evaluating its growth and chemical composition

This study evaluated whether outdoor cultivation of Spirulina sp. in different geographical locations affected its growth and biomass quality, with respect to the chemical composition, volatile compound and heavy metal content, and thermal stability. The positive effect of solar radiation and temperature on biomass productivity in Spirulina sp. cultivated in the northeast was directly related to its improved nutritional characteristics, which occurred with an increase in protein, phycocyanin, and polyunsaturated fatty acid (mainly γ-linolenic) content. The biomass produced in Northeast and South Brazil showed high thermal stability and had volatile compounds that could be used as biomarkers of Spirulina, and their parameters were within the limits of internationally recognized standards for food additives; hence, they have been considered safe foods. However, the growth of crops in south Brazil occurred at lower rates due to low temperatures and luminous intensities, indicative of the robustness of microalgae in relation to these parameters.

Past, current, and future research on microalga-derived biodiesel: a critical review and bibliometric analysis

Microalga-derived biodiesel plays a crucial role in the sustainable development of biodiesel in recent years. Literature related to microalga-derived biodiesel had an increasing trend with the expanding research outputs. Based on the Science Citation Index Expanded (SCI-Expanded) of the Web of Science, a bibliometric analysis was conducted to characterize the body of knowledge on microalga-derived biodiesel between 1993 and 2016. From the 30 most frequently used author keywords, the following research hotspots are extracted: lipid preparation from different microalga species, microalga-derived lipid and environmental applications, lipid-producing microalgae cultivation, microalgae growth reactor, and microalga harvest and lipid extraction. Other keywords, i.e., microalga mixotrophic cultivation, symbiotic system between microalga and other oleaginous yeast, microalga genetic engineering, and other applications of lipid-producing microalga are future focal points of research. Graphical abstract.

Exploration of upstream and downstream process for microwave assisted sustainable biodiesel production from microalgae Chlorella vulgaris

The present study explores the integrated approach for the sustainable production of biodiesel from Chlorella vulgaris microalgae. The microalgae were cultivated in 10m(2) open raceway pond at semi-continuous mode with optimum volumetric and areal production of 28.105kg/L/y and 71.51t/h/y, respectively. Alum was used as flocculent for harvesting the microalgae and optimized at different pH. Lipid was extracted using chloroform: methanol (2:1) and having 12.39% of FFA. Effect of various reaction conditions such as effect of catalyst, methanol:lipid ratio, reaction temperature and time on biodiesel yields were studied under microwave irradiation; and 84.01% of biodiesel yield was obtained under optimized reaction conditions. A comparison was also made between the biodiesel productions under conventional heating and microwave irradiation. The synthesized biodiesel was characterized by (1)H NMR, (13)C NMR, FTIR and GC; however, fuel properties of biodiesel were also studied using specified test methods as per ASTM and EN standards.

Modelling of oxygen-evolving-complex ionization dynamics for energy-efficient production of microalgal biomass, pigment and lipid with carbon capture: an engineering vision for a biorefinery

Development of an algal growth kinetics model, incorporating oxygen-evolving-complex ionization dynamics, for sustainable production of algal biomass, lipid, and chlorophyll (with associated carbon dioxide capture) in an algal biorefinery.

Rationally leveraging mixotrophic growth of microalgae in different photobioreactor configurations for reducing the carbon footprint of an algal biorefinery: a techno-economic perspective

Experimental set-up to study mixotrophy in Chlorella vulgaris.

Process design for augmentation and spectrofluorometric quantification of neutral lipid by judicious doping of pathway intermediate in the culture of marine Chlorella variabilis for biodiesel application

Over the past few years microalgae have emerged as the most promising feedstock for biodiesel production. However, enhancing lipid content remains a major scientific challenge. Many studies irrationally rely upon nitrogen starvation for improving lipid content at the cost of biomass. In this study, strategic enhancement of neutral lipid without compromising with biomass production was achieved in marine Chlorella variabilis by supplementing the culture with triacylglycerol pathway intermediate, citric acid (1 g L(-1) pure and 0.5 g L(-1) orange peel extract as a low cost substitute). The microalga accumulated 17% and 34% (on dry cell weight basis) more neutral lipid, when cultivated in with citric acid and orange peel extract as supplements respectively, without any adverse effect on growth. The medium supplemented with orange peel extract stimulated better growth than that supplemented with citric acid. Gas chromatography studies validated that both the supplemented media yielded desired fatty acid composition for biodiesel production.

Attached cultivation for improving the biomass productivity of Spirulina platensis

To improve cultivation efficiency for microalgae Spirulina platensis is related to increase its potential use as food source and as an effective alternative for CO2 fixation. The present work attempted to establish a technique, namely attached cultivation, for S. platensis. Laboratory experiments were made firstly to investigate optimal conditions on attached cultivation. The optimal conditions were found: 25 g m(-2) for initial inoculum density using electrostatic flocking cloth as substrata, light intensity lower than 200 μmol m(-2) s(-1), CO2 enriched air flow (0.5%) at a superficial aeration rate of 0.0056 m s(-1) in a NaHCO3-free Zarrouk medium. An outdoor attached cultivation bench-scale bioreactor was built and a 10d culture of S. platensis was carried out with daily harvesting. A high footprint areal biomass productivity of 60 g m(-2) d(-1) was obtained. The nutrition of S. platensis with attached cultivation is identical to that with conventional liquid cultivation.

Process integration for microalgal lutein and biodiesel production with concomitant flue gas CO2 sequestration: a biorefinery model for healthcare, energy and environment

An integrated green microalgal biorefinery was developed with a view to sequestering flue gas CO₂ and synthesizing lutein and lipid for potential environmental, healthcare and biofuel applications respectively.