Optimizing culture conditions for heterotrophic-assisted photoautotrophic biofilm growth of Chlorella vulgaris to simultaneously improve microalgae biomass and lipid productivity

Hydrogel-based photobioreactor for Solid-State cultivation of Chlorella vulgaris

Solid-state cultivation is a promising technology for algal biomass production, achieving high productivities without the need for dewatering. However, such systems have suffered from high evaporation, and capital costs. Here is described a hydrogel photobioreactor (hPBR) with the aim of reducing water demand in solid-state cultivations. Two designs are described with "Design A" offering better humidity control overgrowth conditions. A biomass productivity of 2.41gm-2d-1, and 2.87gm-2d-1 when using physically crosslinked poly(vinyl alcohol) (pPVA) and chemically crosslinked PVA (cPVA) respectively were achieved with Chlorella vulgaris with a water demand around 0.44 kg g-1 of biomass. Over the 23 days of growth, the lipid content increased from 18.9 % to 56.6 % and 13.8 % to 43.2 % for pPVA and cPVA respectively, and the chlorophyll content decreased by more than 81 %. However, cell viability stayed high at over 98 % and surface coverage analysis showed good coverage of the gel surface.

Optimizing Chlorella vulgaris Cultivation to Enhance Biomass and Lutein Production

Lutein is widely used in medicine, health care, and food processing due to its antioxidant effects; however, it is difficult for the traditional extraction of lutein using marigolds to meet the increasing market demand for lutein. To achieve high-efficiency lutein production, we investigated the effects of different conditions on the biomass accumulation and lutein yield of Chlorella vulgaris. The optimized cultivation conditions include mixotrophic cultivation using sodium nitrate as a nitrogen source, maintaining a total-organic-carbon-to-total-nitrogen ratio of 12:1, a total-nitrogen-to-total-phosphorus ratio of 10:1, and lighting duration of 24 h. The results of the study indicated that under these specific conditions, Chlorella vulgaris attained a final biomass concentration, biomass productivity, and growth yield of 6.08 g·L-1, 1.00 g·L-1·d-1, and 1.67 g biomass/g TOC, respectively. Additionally, the concentrations of total chlorophyll, carotenoid, lutein, and protein reached 139.20 mg·L-1, 31.87 mg·L-1, 15.02 mg·L-1, and 2.17 g·L-1, respectively, and the content of lutein reached 2.47 mg·g-1. This study supplies a theoretical basis for the industrial application of lutein production using Chlorella vulgaris.

Microalgal-bacterial consortia for the treatment of livestock wastewater: Removal of pollutants, interaction mechanisms, influencing factors, and prospects for application

The livestock sector is responsible for a significant amount of wastewater globally. The microalgal-bacterial consortium (MBC) treatment has gained increasing attention as it is able to eliminate pollutants to yield value-added microalgal products. This review offers a critical discussion of the source of pollutants from livestock wastewater and the environmental impact of these pollutants. It also discusses the interactions between microalgae and bacteria in treatment systems and natural habitats in detail. The effects on MBC on the removal of various pollutants (conventional and emerging) are highlighted, focusing specifically on analysis of the removal mechanisms. Notably, the various influencing factors are classified into internal, external, and operating factors, and the mutual feedback relationships between them and the target (removal efficiency and biomass) have been thoroughly analysed. Finally, a wastewater recycling treatment model based on MBC is proposed for the construction of a green livestock farm, and the application value of various microalgal products has been analysed. The overall aim was to indicate that the use of MBC can provide cost-effective and eco-friendly approaches for the treatment of livestock wastewater, thereby advancing the path toward a promising microalgal-bacterial-based technology.

Knocking Out Chloroplastic Aldolases/Rubisco Lysine Methyltransferase Enhances Biomass Accumulation in Nannochloropsis oceanica under High-Light Stress

Rubisco large-subunit methyltransferase (LSMT), a SET-domain protein lysine methyltransferase, catalyzes the formation of trimethyl-lysine in the large subunit of Rubisco or in fructose-1,6-bisphosphate aldolases (FBAs). Rubisco and FBAs are both vital proteins involved in CO2 fixation in chloroplasts; however, the physiological effect of their trimethylation remains unknown. In Nannochloropsis oceanica, a homolog of LSMT (NoLSMT) is found. Phylogenetic analysis indicates that NoLSMT and other algae LSMTs are clustered in a basal position, suggesting that algal species are the origin of LSMT. As NoLSMT lacks the His-Ala/ProTrp triad, it is predicted to have FBAs as its substrate instead of Rubisco. The 18-20% reduced abundance of FBA methylation in NoLSMT-defective mutants further confirms this observation. Moreover, this gene (nolsmt) can be induced by low-CO2 conditions. Intriguingly, NoLSMT-knockout N. oceanica mutants exhibit a 9.7-13.8% increase in dry weight and enhanced growth, which is attributed to the alleviation of photoinhibition under high-light stress. This suggests that the elimination of FBA trimethylation facilitates carbon fixation under high-light stress conditions. These findings have implications in engineering carbon fixation to improve microalgae biomass production.

Improving biomass yields of microalgae biofilm by coculturing two microalgae species via forming biofilms with uniform microstructures and small cell-clusters

Microalgae coculture has the potential to promote microalgae biofilm growth. Herein, three two-species cocultured biofilms were studied by determining biomass yields and detailed microstructure parameters, including porosity, average pore length, average cluster length, etc. It was found that biomass yields could reduce by 21-53 % when biofilm porosities decreased from about 35 % to 20 %; while at similar porosities (∼20 %), biomass yields of cocultured biofilms increased by 37 % when they possessed uniform microstructure and small cell-clusters (pores and clusters of 1 ∼ 10 μm accounted for 96 % and 68 %, respectively). By analyzing morphologies and surface properties of cells, it was found that cells with small size, spherical shape, and reduced surface polymers could hinder the cell-clusters formation, thereby promoting biomass yields. The study provides new insights into choosing cocultured microalgae species for improving the biomass yield of biofilm via manipulating biofilm microstructures.

The effect of light intensity on microalgae biofilm structures and physiology under continuous illumination

The interest by biofilm-based microalgae technologies has increased lately due to productivity improvement, energy consumption reduction and easy harvesting. However, the effect of light, one key factor for system's operation, received less attention than for planktonic cultures. This work assessed the impact of Photon Flux Density (PFD) on Chlorella vulgaris biofilm dynamics (structure, physiology, activity). Microalgae biofilms were cultivated in a flow-cell system with PFD from 100 to 500 [Formula: see text]. In the first stage of biofilm development, uniform cell distribution was observed on the substratum exposed to 100 [Formula: see text] while cell clusters were formed under 500 [Formula: see text]. Though similar specific growth rate in exponential phase (ca. 0.3 [Formula: see text]) was obtained under all light intensities, biofilm cells at 500 [Formula: see text] seem to be ultimately photoinhibited (lower final cell density). Data confirm that Chlorella vulgaris showed a remarkable capability to cope with high light. This was marked for sessile cells at 300 [Formula: see text], which reduce very rapidly (in 2 days) their chlorophyll-a content, most probably to reduce photodamage, while maintaining a high final cell density. Besides cellular physiological adjustments, our data demonstrate that cellular spatial organization is light-dependent.

Mixotrophic culture of Chaetoceros sp. and the synergistic carbon and energy metabolism

This research studied the metabolic mechanism of the mixotrophic Chaetoceros sp. The results showed this alga had the highest cell density and growth rate of 47.72 × 105 cells mL-1 and 0.41 d-1, respectively, with a maximum dry weight of 2.90 g/L, when compared to photoautotrophic and photoheterotrophic modes. Compared to photoheterotrophy, transcriptomics results showed the Rubisco, PGK, and GAPDH related genes were separately up-regulated by 1.03, 2.36, and 1.36 times in CBB cycle in mixotrophic mode, suggesting intermediate metabolites of EMP and PPP can enter the chloroplast via transporter proteins, or membrane permeation, and feedback inhibition regulates the reduction of multiple reactions in CBB cycle. Chaetoceros sp. achieves high biomass by utilizing ATP and carbon structures from EMP and PPP pathways, and the addition of NaHCO3 leads to an up-regulation of CBB cycle for the mixotrophic alga, resulting in higher biomass compared to the photoheterotrophic mode.

Commercial paper as a promising carrier for biofilm cultivation of Chlorella sp. for the treatment of anaerobic digestate food effluent (ADFE): Effect on the photosynthetic efficiency

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

Enhancing catalytic activity and pore structure of metal-organic framework-808 via ligand competition for biodiesel production from microalgal lipids at reduced temperatures

Catalysts with hierarchical porous structures and increased active defects play a crucial role in catalyzing the conversion of microalgae lipids. However, the template methods used for pore expansion and the acidification process employed to enhance activity are cumbersome and prone to deactivation. It is necessary to propose a simple and versatile synthetic approach to overcome these challenges. By modulating N,N-dimethylformamide basicity with formic acid, MOF-808 exhibited enhanced coordination of benzene-1,3,5-tricarboxylic acid to Zr-clusters, creating three types of functional defects. These defects increased pore size from 1.63 nm to 5.34 nm and enhanced catalyst acidity by 22.8%, while maintaining high porosity. The active catalytic sites were confirmed to be defect sites (exposed Zr4+) through density functional theory. Compared to regular MOF-808, catalyst MOF-808-3/1 shows enhanced hierarchical porosity and increased acidity, enabling efficient conversions at reduced reaction temperature (100 °C) and pressure (352 kPa) compared to 200 °C and 4036 kPa, respectively.

Advancements of microalgal upstream technologies: Bioengineering and application aspects in the paradigm of circular bioeconomy

Sustainable energy transition has brought the attention towards microalgae utilization as potential feedstock due to its tremendous capabilities over its predecessors for generating more energy with reduced carbon footprint. However, the commercialization of microalgae feedstock remains debatable due to the various factors and considerations taken into scaling-up the conventional microalgal upstream processes. This review provides a state-of-the-art assessment over the recent developments of available and existing microalgal upstream cultivation systems catered for maximum biomass production. The key growth parameters and main cultivation modes necessary for optimized microalgal growth conditions along with the fundamental aspects were also reviewed and evaluated comprehensively. In addition, the advancements and strategies towards potential scale-up of the microalgal cultivation technologies were highlighted to provide insights for further development into the upstream processes aimed at sustainable circular bioeconomy.

Biotechnologies for bulk production of microalgal biomass: from mass cultivation to dried biomass acquisition

Microalgal biomass represents a sustainable bioresource for various applications, such as food, nutraceuticals, pharmaceuticals, feed, and other bio-based products. For decades, its mass production has attracted widespread attention and interest. The process of microalgal biomass production involves several techniques, mainly cultivation, harvesting, drying, and pollution control. These techniques are often designed and optimized to meet optimal growth conditions for microalgae and to produce high-quality biomass at acceptable cost. Importantly, mass production techniques are important for producing a commercial product in sufficient amounts. However, it should not be overlooked that microalgal biotechnology still faces challenges, in particular the high cost of production, the lack of knowledge about biological contaminants and the challenge of loss of active ingredients during biomass production. These issues involve the research and development of low-cost, standardized, industrial-scale production equipment and the optimization of production processes, as well as the urgent need to increase the research on biological contaminants and microalgal active ingredients. This review systematically examines the global development of microalgal biotechnology for biomass production, with emphasis on the techniques of cultivation, harvesting, drying and control of biological contaminants, and discusses the challenges and strategies to further improve quality and reduce costs. Moreover, the current status of biomass production of some biotechnologically important species has been summarized, and the importance of improving microalgae-related standards for their commercial applications is noted.

Quorum Sensing as a Trigger That Improves Characteristics of Microbial Biocatalysts

Quorum sensing (QS) of various microorganisms (bacteria, fungi, microalgae) today attracts the attention of researchers mainly from the point of view of clarifying the biochemical basics of this general biological phenomenon, establishing chemical compounds that regulate it, and studying the mechanisms of its realization. Such information is primarily aimed at its use in solving environmental problems and the development of effective antimicrobial agents. This review is oriented on other aspects of the application of such knowledge; in particular, it discusses the role of QS in the elaboration of various prospective biocatalytic systems for different biotechnological processes carried out under aerobic and anaerobic conditions (synthesis of enzymes, polysaccharides, organic acids, etc.). Particular attention is paid to the biotechnological aspects of QS application and the use of biocatalysts, which have a heterogeneous microbial composition. The priorities of how to trigger a quorum response in immobilized cells to maintain their long-term productive and stable metabolic functioning are also discussed. There are several approaches that can be realized: increase in cell concentration, introduction of inductors for synthesis of QS-molecules, addition of QS-molecules, and provoking competition between the participants of heterogeneous biocatalysts, etc.).

Screening of microalgae species and evaluation of algal-lipid stimulation strategies for biodiesel production

Microalgae is considered an alternative source for biodiesel production producing renewable, sustainable and carbon-neutral energy. Microalgae property changes among species, which determines the efficiency of biodiesel production. Besides the lipid content evaluation, multi-principles (including high lipid productivity, high biomass yield, pollution resistance and desired fatty acid, etc.) for superior oil-producing species screening was proposed in this review and three microalgae species (Chlorella vulgaris, Scenedesmus obliquus and Mychonastes afer) with high bio-lipid producing prospect were screened out based on big data digging and analysis. The multilateral strategies for algal-lipid stimulating were also compared, among which, nutrient restriction, temperature control, heterotrophy and chemicals addition showed high potential in enhancing lipid accumulation; while electromagnetic field showed little effect. Interestingly, it was found that the lipid accumulation was more sensitive to nitrogen (N)-limitation other than phosphorus (P). Nutrient restriction, salinity stress etc. enhanced lipid accumulation by creating a stressed environment. Hence, optimum conditions (e.g. N:15-35 mg/L and P:4-16 mg/L) should be set to balance the lipid accumulation and biomass growth, and further guarantee the algal-lipid productivity. Otherwise, two-step cultivation could be applied during all the stressed stimulation. Different from lab study, effectiveness, operability and economy should be all considered for stimulation strategy selection. Nutrient restriction, temperature control and heterotrophy were highly feasible after the multidimensional evaluation.

Insight into the comprehensive effect of carbon dioxide, light intensity and glucose on heterotrophic-assisted phototrophic microalgae biofilm growth: A multifactorial kinetic model

Heterotrophic-assisted photoautotrophic microalgae biofilm cultivation was an alternative way to realize CO₂ reduction and wastewater treatment. Growth kinetics supplied a channel to better understand how the cultivation conditions affect microalgal growth and CO₂ reduction. However, the two growth modes (heterotroph and photoautotroph) have different needs for organic and inorganic nutrients. Thus, combining the threshold theory and multiplication theory, an integral multifactorial kinetic model that looking insight into the comprehensive effect of glucose, CO₂, light intensity, and nitrate was developed for heterotrophic-assisted photoautotrophic microalgae biofilm growth in this study. R² between model and experiment was 0.99. It predicted the maximum specific growth rate and maximum CO₂ consumption rate of heterotrophic-assisted photoautotrophic microalgae biofilm was 1.868 h^-1 and 1.02 h^-1, respectively. This model fully explained the influence of the main factors on microalgae biofilm growth and reasonably predicted the growth rate of microalgae biofilm under different growth conditions.

Sustainability and carbon neutralization trends in microalgae bioenergy production from wastewater treatment: A review

Reducing CO2 emissions using biomass is gaining popularity as an environmentally friendly strategy. Due to high growth rates, low production costs, and ability to withstand harsh conditions, microalgae have become quite popular. Microalgae may also undertake photosynthesis, converting CO2 and solar energy into sugar before becoming biomass, making them an excellent source of renewable and promising biofuels. CO2 sequestration and biofixation was utilized to compare the synthesis of biodiesel as a third-generation biofuel from various types of wastewater was also used as a source for the algal cultivation. This review article focuses on recent developments, research discoveries in the field of microalgal CO2 capture modification and the optimization of conversion efficiency. This review is intended to serve as a helpful and reference for the use of wastewater treatment with microalgae to collect CO2. The overarching objective of this study is to assist wastewater treatment systems in achieving carbon neutrality.

Optimisation of Biomass Production and Nutritional Value of Two Marine Diatoms (Bacillariophyceae), Skeletonema costatum and Chaetoceros calcitrans

Simple Summary

One of the key constraints that is associated with the production of microalgae biomass and products, is the low yields that are associated with high production costs in microalgae cultivation units. Therefore, the aim of the present work was to improve the biomass productivity of two high-value diatom species, Skeletonema costatum and Chaetoceros calcitrans. To do so, the culture medium that was supplied to the cultures was optimised in a stepwise process, regarding the nutrient’s silicate, nitrate, phosphorus, iron, and micronutrients. For both diatoms, the results that were obtained revealed a significant increase in biomass productivity as well as an improved biochemical profile regarding increased omega-3 fatty acids contents. With this work, the optimise culture media was established for each diatom, thus providing a strategy for lower production costs that were reflected in higher productivities with higher biomass quality. Ultimately this will help improve the application of S. costatum and C. calcitrans in the aquaculture and nutraceutical industries.

Abstract

S. costatum and C. calcitrans are two cosmopolitan high-value centric diatoms, with a rich nutritional profile. The following work optimised the culture medium of S. costatum and C. calcitrans cultures, respectively, in a stepwise process as follows: 2.4 mM and 1.2 mM of silicate, 4 mM of nitrate, 100 µM of phosphate, 20 and 80 µM iron, and 0.5 mL L⁻¹ of micronutrients. The results that were obtained revealed an increase in biomass productivity with a 1.8- and 3.2-fold increase in biomass that was produced by S. costatum and C. calcitrans, respectively. The biochemical profile showed an increase in high-value PUFAs such as 2.6-fold and 2.3-fold increase in EPA for S. costatum and C. calcitrans, respectively, whilst a 2.6-fold increase in DHA was detected in S. costatum cultures. The present work provides the basic tools for the industrial cultivation of S. costatum and C. calcitrans with enhanced productivity as well as improved biomass quality, two factors which are highly relevant for a more effective application of these diatoms to aquaculture and nutraceutical production.

Overexpression of fatty acid synthesis genes in Synechocystis sp. PCC 6803 with disrupted glycogen synthesis increases lipid production with further enhancement under copper induced oxidative stress

In the present study, fatty acid synthesis genes such as alpha and beta subunits of acetyl CoA carboxylase (accA and accD) were overexpressed in the glgC (Glucose-1-phosphate adenylyltransferase) knockout Synechocystis sp. PCC 6803. The biomass and lipid contents were evaluated in both the wild type and the engineered strains after copper treatment. The maximum lipid production of 0.981 g/L with the productivity of 81.75 mg/L/d was obtained from the copper treated ΔglgC + A-OX strain, which showed a 3.3-fold increase compared to the untreated wild type with satisfactory biodiesel properties. After copper treatment the knockout strain improved the unsaturated fatty acids level contributing to the increase of the saturated and mono-unsaturated ratio with improvement of the fuel quality. Copper induced oxidative stress also improved the photosynthetic pigments in engineered strains leading to increased tolerance against oxidative stress in the engineered strains. The copper treatment increased the antioxidant enzyme activities in the engineered strains especially in ΔglgC + A-OX strain. The carbon flux to lipid synthesis was enhanced by the engineered strains particularly with the knockout-overexpression strains. The Synechocystis sp. PCC 6803 engineered with ΔglgC + A-OX showed high potential for fuel production after the copper treatment.

Modeling and improving arrayed microalgal biofilm attached culture system

A microalgal biofilm-attached-system is an alternative cultivation method, that offers potential advantages of improved biomass productivity, efficient harvesting, and water saving. These biofilm systems have been widely tested and utilized for microalgal biomass production and wastewater treatment. This research a microalgal growth model for the biofilm attached culture system has been developed and experimentally validated, both, in single and arrayed biofilm systems. It has been shown that the model has the capability to accurately describe microalgae growth. Moreover, via the model simulation, it was observed that system structural parameters, light dilution rate, and light intensity significantly affected the culture performance. The limitations, and improvement aspects of the model, are also discussed in this study. To our knowledge, this is the first time that a mathematical model for an arrayed-biofilm-attached-system has been developed and validated. This model will certainly be helpful in the design, improvement, optimization, and evaluation of the biofilm-attached-systems.

Thermoresponsive Surfaces Grafted by Shrinkable Hydrogel Poly(N-isopropylacrylamide) for Controlling Microalgae Cells Adhesion during Biofilm Cultivation

Microalgae is a promising candidate for reducing greenhouse gas and producing renewable biofuels. For microalgae biofilm cultivation, a strong adhesion ability of microalgae cells onto the surface is a prerequisite to resist the fluid shear stress, while strong adhesion is not of benefit to the biofilm harvesting process. To solve this dilemma, a thermoresponsive surface (TMRS) with lower critical solution temperature of 33 °C was made by grafting N-isopropylacrylamide onto a silicate glass slide. The wettability of the TMRS changed from hydrophilic (contact angle of 59.4°) to hydrophobic (contact angle of 91.6°) when the temperature rose from 15 to 35 °C, resulting in the increase of adhesion energy of the TMRS to Chlorella vulgaris cells by 135.6%. The experiments showed that the cells were more likely to attach onto the TMRS at the higher temperature of 35 °C owing to the surface microstructures generated by the hydrogel layer shrinkage, which is similar in size to the microalgae cells. And the cell coverage rate on TMRS increased by 32% compared to the original glass surface. Conversely, the cells separate easily from the TMRS at a lower temperature of 15 °C, and the cell adhesion density was reduced by 19% due to hydrogel layer swelling to a relatively flat surface.

Lipid and biodiesel production by cultivation isolated strain Chlorella sorokiniana pa.91 and Chlorella vulgaris in dairy wastewater treatment plant effluents

The present study provided a comparison of two species of microalgae growth in dairy wastewater treatment plant effluents. In optimum conditions their operation to biomass production, lipid accumulation and fatty acids methyl ester composition so as to biodiesel production is studied. For the first time, the not sterilized effluents of dairy wastewater treatment plant was used as the culture mediums of native microalgae, Chlorella sorokiniana strain pa.91, and another one Chlorella vulgaris. They were cultured under 5 light intensity levels so as to find optimum conditions to observed high biomass and lipid production. At the optimum light intensity the composition of fatty acids methyl ester in their lipids was analyzed by GC-MS. The light intensity of 7500 Lux was obtained as the optimum for both microalgae to produce high biomass. The biomass productivity of C. sorokiniana pa.91 and C. vulgaris in preliminary treated effluent at this light intensity was obtained 0.233 and 0.214 g L^-1 day^-1, respectively. This parameter in secondary treated effluent was achieved 0.185 and 0.166 g L^-1 day^-1, respectively. Moreover, the highest lipid content of their biomass was observed at the light intensity of 2500 Lux. At this light intensity and at the preliminary effluent the maximum lipid content of C. sorokiniana pa.91 and C. vulgaris was observed 31% and 34%, respectively and at the secondary one it was obtained 35% and 36.67%, respectively. Based on the results, the fatty acids composition in the lipids of microalgae C. sorokiniana pa.91 and C. vulgaris cultured in both effluents had the high amount of cetane number which is really useful for high quality biodiesel production. Also, the other valuable properties which produce the high quality biodiesel were the obtained amounts of CFPP and CP which shown a high performance potential biodiesel even at low temperatures. This feature was obtained, on the grounds that the unsaturated fatty acid was obtained more than saturated fatty acid. The nutrients-rich media of dairy wastewater effluents were applicable to growth both microalgae and useful biomass production, lipid accumulation and fatty acids profiling. Furthermore, the compounds of fatty acids had the best conditions to biodiesel production especially in cold weather areas.

The Perspective of Large-Scale Production of Algae Biodiesel

We have had high expectations for using algae biodiesel for many years, but the quantities of biodiesel currently produced from algae are tiny compared to the quantities of conventional diesel oil. Furthermore, no comprehensive analysis of the impact of all factors on the market production of algal biodiesel has been made so far. This paper aims to analyze the strengths, weaknesses, opportunities, and threats associated with algal biodiesel, to evaluate its production prospects for the biofuels market. The results of the analysis show that it is possible to increase the efficiency of algae biomass production further. However, because the production of this biodiesel is an energy-intensive process, the price of biodiesel is high. Opportunities for more economical production of algal biodiesel are seen in integration with other processes, such as wastewater treatment, but this does not ensure large-scale production. The impact of state policies and laws is significant in the future of algal biodiesel production. With increasingly stringent environmental requirements, electric cars are a significant threat to biodiesel production. By considering all the influencing factors, it is not expected that algal biodiesel will gain an essential place in the fuel market.

A comprehensive review on cultivation and harvesting of microalgae for biodiesel production: Environmental pollution control and future directions

Biodiesel is one of the best promising candidates in response to the energy crisis, since it has the capability to minimize most of the environmental problems. Microalgae, as the feedstock of third-generation biodiesel, are considered as one of the most sustainable resources. However, microalgae production for biodiesel feedstock on a large scale is still limited, because of the influences of lipid contents, biomass productivities, lipid extraction technologies, the water used in microalgae cultivation and processes of biomass harvesting. This paper firstly reviews the recent advances in microalgae cultivation and growth processes. Subsequently, current microalgae harvesting technologies are summarized and flocculation mechanisms are analyzed, while the characteristics that the ideal harvesting methods should have are summarized. This review also summarizes the environmental pollution control performances and the key challenges in future. The key suggestions and conclusions in the paper can offer a promising roadmap for the cost-effective biodiesel production.

Bioprocess operation strategies with mixotrophy/photoinduction to enhance lutein production of microalga Chlorella sorokiniana FZU60

This study isolated and identified the lutein-enriching microalga Chlorella sorokiniana FZU60. Different types of media and concentrations of sodium acetate and nitrate were evaluated to improve mixotrophic growth and lutein production. Highest lutein content, production, and productivity were obtained in BG11 medium with 1 g/L acetate and 0.75 g/L nitrate. Additionally, pulse feeding with 1 g/L acetate every 48 h led to the alternation between mixotrophy and photoinduction, resulting in a lutein production of 33.6 mg/L. Most notably, excellent lutein content (9.57 mg/g) and productivity (11.57 mg/L/d) were obtained using a new multi-operation integrated strategy, and the achieved levels exceed those reported in most related studies. This work demonstrates the synergistic integration of simple and effective strategies for the enhancement of lutein production in the indigenous microalga C. sorokiniana FZU60 and provides new insight into the highly efficient microalgae-based lutein production.