Microalgae-based Biodiesel Production Research Articles

Combining fermentation broth with spent water recycling for microalgae cultivation: nutrient reutilization, biodiesel production and techno-economic simulation

This study presents an innovative and promising technology, Water Cycling Combined Fermentation Broth (WC2FB), which offers a sustainable solution to significantly reduce the costs associated with microalgae-based biodiesel production. The innovative approach involves utilising food waste as a nutrient source, supplemented by recycled water after microalgae harvesting, with the goal of improving the viability of industrial biofuel production. The results of nutrient removal efficiency demonstrated that the addition of 15% fermentation broth to the microalgal suspension efficiently utilised volatile fatty acids, resulting in a significant increase in lipid content. Additionally, biocomponent analysis confirmed that the WC2FB mode did not compromise the desirable properties of biodiesel. Through techno-economic simulations, we predicted a 90% probability of achieving net present value (NPV) at a selling price of $5/kg. Finally, we recommended that directing future efforts be directly towards the development of culture devices, low-cost bioflocculation methods, and biorefinery extraction to further advance biodiesel production.

Bio-Nanoparticles Mediated Transesterification of Algal Biomass for Biodiesel Production

Immense use of fossil fuels leads to various environmental issues, including greenhouse gas emissions, reduced oil reserves, increased energy costs, global climate changes, etc. These challenges can be tackled by using alternative renewable fuels such as biodiesel. Many studies reported that biodiesel production from microalgae biomass is an environment-friendly and energy-efficient approach, with significantly improved fuel quality in terms of density, calorific value and viscosity. Biodiesel is produced using the transesterification process and the most sustainable method is utilizing enzymes for transesterification. Lipase is an enzyme with excellent catalytic activity, specificity, enantio-selectivity, compatibility and stability and hence it is applied in microalgae biodiesel production. But, difficulty in enzymatic recovery, high enzyme cost and minimal reaction rate are some of its drawbacks that have to be addressed. In this aspect, the nanotechnological approach of lipase immobilization in producing microalgae biodiesel is a promising way to increase production yield and it is due to the adsorption efficiency, economic benefit, recyclability, crystallinity, durability, stability, environmental friendliness and catalytic performance of the bio-nanoparticles used. Through increasing post-harvest biomass yield, absorption of CO2 and photosynthesis in the photobioreactor, the use of nanoparticle immobilized lipase during the generation of biodiesel from microalgae has the potential to also remove feedstock availability constraints. This review article discusses the production of microalgae biodiesel, and effect of nanoparticles and immobilized lipase nanoparticles on biodiesel production. The advantages of using lipase nanoparticles and the challenges in introducing the immobilized lipase on nanoparticles in large-scale microalgae biodiesel production are also discussed. Reducing the water and land use, energy and nutrient footprints of integrated algae-based operations must be the main goal of larger-scale experiments as well as ongoing research and development in order to expedite the adoption of microalgae-based biodiesel production. Also, the cost-effectiveness and large-scale availability of nanoparticles and the impact of lipase nanoparticles on engine performance should be analyzed for commercialization of microalgae biodiesel.

A review on biodiesel production from microalgae: Influencing parameters and recent advanced technologies.

Microalgae are the important part of carbon cycle in the nature, and they could utilize the carbon resource in water and soil efficiently. The abilities of microalgae to mitigate CO2 emission and produce oil with a high productivity have been proven. Hence, this third-generation biodiesel should be popularized. This review firstly introduce the basic characteristics and application fields of microalgae. Then, the influencing parameters and recent advanced technologies for the microalgae biodiesel production have been discussed. In influencing parameters for biodiesel production section, the factors of microalgae cultivation, lipid accumulation, microalgae harvesting, and lipid extraction have been summarized. In recent advanced technologies for biodiesel production section, the microalgae cultivation systems, lipid induction technologies, microalgae harvesting technologies, and lipid extraction technologies have been reviewed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.

Mixotrophic Cultivation of Microalgae Using Biogas as the Substrate.

Biogas utilization through biotechnology represents a potential and novel technology. We propose the microalgal mixotrophic cultivation to convert biogas to microalgae-based biodiesel, in which methanotroph was co-cultured to convert CH4 to organic intermediate (and CO2) for microalgal mixotrophic growth. This study constructed a co-culture of Methylocystis bryophila (methanotroph) and Scenedesmus obliquus (microalgae) with biogas feeding. Compared with the single culture of S. obliquus, higher microalgal biomass but a lower chlorophyll concentration was observed. The organic metabolism-related genes were upregulated, verifying microalgal mixotrophic growth. The stoichiometric calculation of M. bryophila culture shows that M. bryophila tends to release organic matter rather than grow under a low O2 content. M. bryophila rarely grew under five different light intensities, indicating that M. bryophila acts as a biocatalyst in the co-culture. The organic intermediate released by methanotroph increased the maximum biomass of microalgal culture, accelerated nitrogen absorption, accumulated more monounsaturated fatty acids, and improved the adaptation to light. The co-culture of microalgae and methanotroph may provide new opportunities for microalgae-based biodiesel production using biogas as a substrate.

Comparison of heterotrophic and mixotrophic Chlorella pyrenoidosa cultivation for the growth and lipid accumulation through acetic acid as a carbon source

In order to overcome the bottleneck of the high cost of microalgae biodiesel production, biomass and lipid accumulation of microalga Chlorella pyrenoidosa feeding on the low-cost carbon source, acetic acid (AcA), were investigated. The results showed that C. pyrenoidosa had the ability of mixotrophy and heterotrophy, which could tolerate 50 g/L of AcA in the heterotrophy with the biomass concentration of 137.89 ± 2.03 mg/L. Under heterotrophic condition, the biomass productivity at logarithmic stage was positively correlated with the AcA dosage, and the maximum biomass productivity of 187.26 ± 3.61 mg/L/d was obtained at 10 g/L of AcA. Four AcA concentrations (6, 10, 20 and 30 g/L) were set to evaluate the effects of AcA on the growth and lipid accumulation of C. pyrenoidosa under heterotrophic and mixotrophic conditions. Heterotrophic mode at 10 g/L of AcA was demonstrated to be the most potential condition with the maximum biomass productivity of 134.91 ± 5.74 mg/L/d and the highest lipid productivity of 42.04 ± 0.21 mg/L/d, and the lipid production (44.03 ± 2.84 mg/L) was 15-fold higher than the control of BG-11 medium. In addition, C. pyrenoidosa achieved the highest nutrient removal efficiency (30.0% and 85.9% for total nitrogen and phosphorus, respectively) and the highest AcA assimilation efficiency (74.1%). This study highlighted a promising win-win method of AcA recycling and microalgae-based biodiesel production.

Dual nutrient heterogeneity modes in a continuous flow photobioreactor for optimum nitrogen assimilation to produce microalgal biodiesel

The impact of different nitrogen sources on the microalga, Chlorella vulgaris, was studied in a newly developed microalgal-bacterial photobioreactor via a dual nutrient heterogeneity mode. The mechanisms of nitrogen transformation and valorisation were unveiled, and subsequently, optimized via dual nutrient heterogeneity feeding modes comprising of various NH4+-N and NO3−-N concentrations. The nitrogen-assimilation mechanism from the microalgal-bacterial consortium was found to reduce microalgal growth inhibition, stemming at high NH4+-N concentrations. Accordingly, the total nitrogen removal efficiency was enhanced from 40.91% to 96.38% accompanied with maximum microalgal biomass production of up to 792 mg/L at a balanced or higher NH4+-N loading from mixed nitrogen environment. The harvested microalgal biomass contained high lipid accumulation of approximately 30% when fed with optimum NH4+-N and NO3−-N loadings at 60 and 58 mg/d, respectively. At this mixed nitrogen species loadings, high unsaturated fatty acid methyl esters (FAME) were attained. Indeed, the major FAME species (97%–100%) fell within the C16-18 range, signifying biodiesel characteristics conformity to the requirements for quality biodiesel application. Therefore, the dual heterogeneity modes of balanced NH4+-N and NO3−-N loadings into photobioreactor could offer effective microalgal nitrogen assimilation for sustainable wastewater treatment and microalgae-based biodiesel production simultaneously.

Coupling of myo-inositol with salinity regulates ethylene-induced microalgal lipid hyperproduction in molasses wastewater

With the goal of cost-effective and high-efficient microalgae-based biodiesel production, this study evaluated the feasibility of the joint strategy concerning myo-inositol (MI) and salinity stress on lipid productivity of Monoraphidium sp. QLY-1 in molasses wastewater (MW). The maximal lipid productivity (147.79 mg L−1 d−1) was obtained under combined 0.5 g L−1 MI and 10 g L−1 NaCl treatment, which was 1.40-fold higher than the control. Meanwhile, the nutrients removal from MW was markedly increased under MI-NaCl treatment. Moreover, exogenous MI upregulated key lipogenic genes' expressions, activated autophagic activity and ethylene (ET) signaling, and ultimately alleviated the salinity-induced damage via reactive oxygen species (ROS) signaling. Further pharmacologic experiment confirmed the indispensable role of ET in the lipogenesis progress under the combined treatment. These data demonstrated the combined salinity stress and MI treatment to be capable for lipid hyperproduction and wastewater nutrients removal, which contributes to practically integrating the microalgae cultivation with wastewater treatment.

Selection of oil extraction process from Chlorella species of microalgae by using multi-criteria decision analysis technique for biodiesel production

Abstract In the last few decades, the energy crisis has been one of the main concerns related to the lack of long-term petroleum-based reserves as primary energy resources. Biodiesel emerged as a promising alternative. Nowadays, it is produced from edible vegetable oil, thereby causing commodity prices and food security disruption. In this case, microalgae serve as a sustainable and renewable feedstock for their fast growth, high lipid content, and CO2 absorbing agent. Five processes are applied on the production of microalgae-based biodiesel, namely cultivation, harvesting, extraction, conversion, and refinement. There is currently limited study on technology selection on industrial-scale technology for oil extraction from Chlorella spp. of microalgae. Therefore, this study aims to review and select the most suitable technology using simple multi-attribute rating technique extended to ranking – multi-criteria decision analysis (SMARTER-MCDA). Preliminary studies showed that conventional organic solvent extraction (COE), ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), electric pulse extraction (EPE), supercritical fluid extraction (SFE), and hydrothermal liquefaction (HTL) were the most promising technologies. These technologies required a series of evaluations using SMARTER-MCDA with several criteria, including easy scalability, extraction productivity, energy input, additional compound, and environmental impact. The result ranking showed that MAE technology was selected as the most suitable technology for oil extraction from Chlorella spp.

Strategies to Produce Cost-Effective Third-Generation Biofuel From Microalgae

Third-generation biofuel produced from microalgae is a viable solution to global energy insecurity and climate change. Despite an annual current global algal biomass production of 38 million litres, commercialization confronts significant economic challenges. However, cost minimization strategies, particularly for microalgae cultivation, have largely been excluded from recent studies. Therefore, this review provides essential insights into the technologies and economics of cost minimization strategies for large-scale applications. Cultivation of microalgae through aquafarming, in wastewater, or for biogas upgrading, and co-production of value-added products (VAPs) such as photo-bioreactors, protein, astaxanthin, and exopolysaccharides can drastically reduce biodiesel production costs. For instance, the co-production of photo-bioreactors and astaxanthin can reduce the cost of biodiesel production from $3.90 to $0.54 per litre. Though many technical challenges need to be addressed, the economic analysis reveals that incorporating such cost-effective strategies can make the biorefinery concept feasible and profitable. The cost of producing microalgal biodiesel can be lowered to $0.73kg−1dry weight when cultivated in wastewater or $0.54L−1when co-produced with VAPs. Most importantly, access to co-product markets with higher VAPs needs to be encouraged as the global market for microalgae-based VAPs is estimated to rise to $53.43 billion in 2026. Therefore, policies that incentivize research and development, as well as the production and consumption of microalgae-based biodiesel, are important to reduce the large gap in production cost that persists between biodiesel and petroleum diesel.

The Roles of Cullins E3 Ubiquitin Ligases in the Lipid Biosynthesis of the Green Microalgae Chlamydomonas reinhardtii.

Microalgae-based biodiesel production has many advantages over crude oil extraction and refinement, thus attracting more and more concern. Protein ubiquitination is a crucial mechanism in eukaryotes to regulate physiological responses and cell development, which is highly related to algal biodiesel production. Cullins as the molecular base of cullin-RING E3 ubiquitin ligases (CRLs), which are the largest known class of ubiquitin ligases, control the life activities of eukaryotic cells. Here, three cullins (CrCULs) in the green microalgae Chlamydomonas reinhardtii were identified and characterized. To investigate the roles of CrCULs in lipid metabolism, the gene expression profiles of CrCULs under nutrition starvation were examined. Except for down-regulation under nitrogen starvation, the CrCUL3 gene was induced by sulfur and iron starvation. CrCUL2 seemed insensitive to nitrogen and sulfur starvation because it only had changes after treatment for eight days. CrCUL4 exhibited an expression peak after nitrogen starvation for two days but this declined with time. All CrCULs expressions significantly increased under iron deficiency at two and four days but decreased thereafter. The silencing of CrCUL2 and CrCUL4 expression using RNAi (RNA interference) resulted in biomass decline and lipids increase but an increase of 20% and 28% in lipid content after growth for 10 days, respectively. In CrCUL2 and CrCUL4 RNAi lines, the content of fatty acids, especially C16:0 and C18:0, notably increased as well. However, the lipid content and fatty acids of the CrCUL3 RNAi strain slightly changed. Moreover, the subcellular localization of CrCUL4 showed a nuclear distribution pattern. These results suggest CrCUL2 and CrCUL4 are regulators for lipid accumulation in C. reinhardtii. This study may offer an important complement of lipid biosynthesis in microalgae.

Effect of different iron sources on sustainable microalgae-based biodiesel production using Auxenochlorella protothecoides

In this study, iron sources and their optimum concentrations for high-quality biodiesel production were determined on Auxenochlorella protothecoides microalgae. Three iron compounds—ferrous sulfate, ferric ethylenediaminetetraacetic acid (EDTA), and ferric chloride—were assessed regarding concentration, specific growth rate, lipid, and lipid quality in relation to fatty acid methyl ester (FAME) composition of microalgal biomass. Auxenochlorella protothecoides demonstrated high resistivity to high concentrations of iron species, still showing an ability to grow in the presence of iron concentrations as high as 21.60 mM. The highest saturated fatty acid (SFA), at 78.5% of FAME, was observed at 1.15 mM ferric chloride, and the highest biomass generation was observed at 1.08 mM ferrous sulfate. In addition, biodiesel and diesel fuel qualities were satisfactory with microalgae cultivated at 0.2 and 14.4 mM ferrous sulfate, 7.19 mM ferric EDTA, and 0.07–21.58 mM ferric chloride concentrations. The former may be more practical, since the use of this iron compound gives the desired result in a broader range. Overall, it can be inferred that high-quality lipid and biodiesel production can be obtained by changing the concentrations and sources of iron compounds. • Different iron compounds had a stimulatory effect on microalgae-based biodiesel. • The highest saturated fatty acid (SFA) was obtained by 78.5 % at 1.15 mM ferric chloride. • The highest biomass was obtained at 1.08 mM ferrous sulfate. • Ferric chloride addition stimulated high-quality lipid.

Biodiesel production, through intensification and profitable distribution of fatty acid methyl esters by a microalgae-yeast co-culture, isolated from wastewater as a function of the nutrients’ composition of the culture media

Due to expensive culture realizations and low lipid yields, microalgae-based biodiesel production still lacks economic viability at an industrial-scale. Optimization of lipids and fatty acid methyl esters (FAMEs) distribution is a necessary condition to get sustainable microalgae biodiesel production. Nutritional sources (nitrogen, phosphorous, carbon and iron) influence the lipid accumulation and biomass production yield. The aim of this study is to get high-quality biodiesel by a microalgae-yeast co-culture based on the selection of culture media micronutrients’ distribution. A response surface-based combination of NaNO3, K2HPO4 and FeSO4*7H2O nutrients increases biomass and lipids accumulations. The obtained highest biomass and lipids contents are 1.68 gL−1 and 27.77%, respectively. Under the selected optimized micronutrients’ composition, high-saturated fatty acids are obtained if high ratio of N/P (6:1 and 11:1) and unsaturated fatty acid under N/P ratio of (9:1) are considered. These results suggest microalgae-yeast co-culturing under controlled N/P ratio in the culture medium produce desirable lipids distributions, yielding better biodiesel quality and equilibrium between biomass and lipids accumulation. The selected micronutrient combination (with the selected N/P ratio) leads to augment the lipids content which is transformed into biodiesel. Biodiesel quality (determined by cetane number, iodine value, cloud point, oxidation stability, viscosity), is evaluated considering microalgae lipids and FAMEs produced by transesterification process. Fourier transform infrared (FTIR) corroborates the lipids distribution, which can be used to produce high quality biodiesel. Gas chromatography (GC) verifies the production of desirable methyl esters (C16 and C18).

Molecular identification, biomass, and biochemical composition of the marine chlorophyte Chlorella sp. MF1 isolated from Suez Bay

BackgroundAn Egyptian indigenous unicellular green microalga was isolated from the coastal water of Suez Bay (N 29.92°, E 32.473°), Red Sea, Egypt. The molecular analysis based on 18S rRNA sequence showed that the gene sequence for this strain was highly similar (100% identity and 98% query cover) to different Chlorella strains isolated from different habitats. ResultsThe observed morphological characters together with the molecular phylogeny assigned the isolated microalga as Chlorella sp. MF1 with accession number KX228798. This isolated strain was cultivated for estimation of its growth and biochemical composition. The mean specific growth rate (μ) was 0.273 day−1. Both the biomass productivity and the cellular lipid content increased by increasing salinity of the growth medium, recording a maximum of 6.53 gDW l−1 and 20.17%, respectively, at salinity 40.4. Fourteen fatty acids were identified. The total saturated fatty acid percentage was 54.73% with stearic (C18:0), arachidic (C20:0), and palmitic acids (C16:0) as major components, while the total unsaturated fatty acid percentage was 45.27% with linoleic acid (C18:2c) and oleic acid (C18:1) as majors. ConclusionThis algal strain proved to be a potential newly introduced microalga as one of the most proper options available for microalgae-based biodiesel production. The proximate analysis showed the protein content at 39.85% and carbohydrate at 23.7%, indicating its accessibility to various purposes.

Comparative assessment of pretreatment strategies for production of microalgae-based biodiesel from locally isolated Chlorella homosphaera

The yield and quality of lipids extracted from microalgal biomass are critical factors in the production of microalgae-based biodiesel. The green microalga Chlorella homosphaera, isolated from Beira Lake, Colombo, Sri Lanka was employed in the present study to identify the effect of chlorophyll removal and cell disruption methods on lipid extraction yield, fatty acid methyl ester (FAME) profile and quality parameters of biodiesel; including cetane number (CN), iodine value (IV), degree of unsaturation (DU) and high heating value (HHV). In the first section of this study, chlorophyll was removed from dry microalgae biomass prior to lipid extraction. Through the analysis of FAME profiles, it was observed that chlorophyll removal yielded biodiesel of enhanced quality, albeit with a lipid loss of 44.2% relative to the control. In the second section of the study, mechanical cell disruption strategies including grinding, autoclaving, water bath heating and microwaving were employed to identify the most effective method to improve lipid recovery from chlorophyll-removed microalgae biomass. Autoclaving (121 °C, 20min sterilization time, total time 2h) was the most effective cell disruption technique of the methods tested, in terms of lipid extraction yield (39.80%) and also biodiesel quality. Moreover, it was observed that employing cell disruption subsequent to chlorophyll removal has a significant impact on the FAME profile of microalgae-based biodiesel, and consequently served to increase HHV and CN although IV and DU did not vary significantly.

Effects of Fe3O4 nanoparticle fabrication and surface modification on Chlorella sp. harvesting efficiency

Harvesting is a critical step in microalgae-based biodiesel production. Oleaginous microalgae harvesting by magnetic nanomaterials has gained attention because of the advantages of higher efficiency, lower cost, and convenient operation. In the present study, Fe3O4 magnetic nanoparticles (MNPs) were fabricated using two different methods (chemical coprecipitation and thermal decomposition), modified with amino acid using three different approaches (ultrasonic, long-time mixing, and “one-step” approaches), and utilized for oleaginous microalgae Chlorella sp. HQ harvesting. The results showed that the Fe3O4 MNPs synthesized by the chemical coprecipitation method achieved superior performance when considering both harvesting efficiency and fabrication cost. For the amino-acid modification, the one-step approach outcompeted the other approaches. At a dosage of 200 mg/L, the optimized Fe3O4@Arginine MNPs could achieve a harvesting efficiency of 95% with a low cost of only 347 USD/t of harvested algal biomass. Both the amino-acid content on the NPs and the number of amino groups in the amino acid molecules played a role in improving the harvesting performance.

Microalgae biodiesel production: a solution to increasing energy demands in Turkey

The transportation sector in Turkey, as in other parts of the world, has gained rapid momentum because of population growth and increased industrialization. The energy demand met using combustion of fossil fuels, such as gasoline and diesel, is the main issue to be assessed; however, because Turkey has a limited petroleum reservoir, > 70% of its fossil fuel is imported from foreign suppliers. In other words, Turkey’s economy is largely dependent on these countries for their fossil fuel commodities. Thus, not only would the production of microalgae-based biodiesel for Turkey’s transportation sector prevent global environmental disasters by limiting the use of unsustainable fossil fuels, thereby mitigating emissions (which have escalated over the past century), but it could also be the answer to Turkey’s increasing energy demand. The aim of this review is to use a snapshot of the energy demand not only in Turkey but throughout the entire world to assess the development of biodiesel sources, biodiesel policies, and biodiesel strategies in Turkey, and to provide a review of the technology involved in microalgae-based biodiesel production. With this study, energy solutions are provided to alleviate dependence on foreign-based energy resources by using new technologies to produce sustainable biodiesel fuel.

Efficient algal biodiesel production with an optimal harvest condition obtained via response surface methodology

Microalgae-based biodiesel production has gained immense attention owing to its eco-friendly nature; however, harvesting small-sized microalgal cells for commercialization is difficult. Previous studies have reported that illumination with blue light significantly increased the cell size, whereas illumination with red light resulted in small-sized cells with active divisions. Based on these findings, we attempted to establish a novel strategy for harvesting microalgal biomass by simultaneously illuminating them with blue light and treating them with chitosan. The results suggested that the optimal harvest condition using the combination of blue light and chitosan significantly differed from that using the combination of red light and chitosan. By altering the cell size through LED illumination during the chitosan-based harvest process, competitive biomass was harvested without hampering lipid production. Particularly, C 16: 0 fatty acid obtained via the chitosan-based harvest was increased from 17.96% under red LED to 20.67% under blue LED, thus rendering the highest overall lipid yield under blue LED. Therefore, we have developed a strategy for improved microalgal biomass harvesting based on the illumination of cells with blue light in conjunction with chitosan treatment.

Optimization of microwave assisted lipid extraction from microalga Scenedesmus obliquus grown on municipal wastewater

Efficient cost effective lipid extraction from microalgae is a challenging topic for large scale production of microalgae-based biodiesel. In this study, a microwave-assisted lipid extraction process was applied to the oil-rich green microalga Scenedesmus obliquus grown on municipal wastewater. N-hexane/isopropanol solvent was used as alternative solvent. Optimal extraction parameters were determined as: operational temperature of 130 °C, extraction time of 0.25 h, solvent ratio of N-hexane/isopropanol of 3:2 (V:V), phase ratio of co-solvent/biomass was 50:1 (mL:g). Relative extraction rates of lipid and fatty acid methyl esters (FAMEs) achieved using microwave-assisted extraction (MAE) were 88.25% and 95.58%, respectively, which is higher than traditional water bath heating extraction process (WHE). In addition, compared with WHE, the apparent first order rate constant of MAE was enhanced by 18 times compared to traditional methods. Analysis using scanning electron microscopy indicated that disruption of the cell wall of Scenedesmus obliquus by microwave led to the enhancement of solvents’ penetration and lipid extraction.

Interactive effect of indole-3-acetic acid and diethyl aminoethyl hexanoate on the growth and fatty acid content of some microalgae for biodiesel production

Enhancement of microalgal growth and fatty acid production is essential for development of a microalgae-based biodiesel production platform. Three different microalgal species (Scenedesmus obliquus GU732418, Ourococcus multisporus GU732424 and Chlorella vulgaris FR751187) were individually cultivated in media containing both indole-3-acetic acid (IAA) and diethyl aminoethyl hexanoate (DAH) at concentrations of 10−8−10−4 M. Combined phytohormones (10−8 to 10−5 M) increased the growth of all three species compared to growth in media without phytohormones. IAA and DAH supported the maximum growth of S. obliquusi (38.12 × 106 cells mL−1) at 10−8 M, O. multisporus (85.89 × 106 cells mL−1) at 10−6 M, and C. vulgaris (4.09 × 106 cells mL−1) at 10−5 M. Addition of 10−7 M IAA and DAH also assisted the removal of Zn2+ (97%), K+ (88%) and Mg2+ (99%) from the media by S. obliquus. The highest removal of Zn2+, K+, and Mg2+ by C. vulgaris was achieved at 10−5 M IAA and DAH. Under all experimental conditions (10−8−10−4 M IAA and DAH) the amounts of poly-unsaturated fatty acids were significantly increased. Palmitic acid, linoleic acid and γ-linolenic acid were the major fatty acids, accounting for 11.75–21.55%, 2.55–6.73%, and 52.93–75.89% of the total fatty acid content, respectively. The fatty acids that accumulated in O. multisporus and C. vulgaris were found to be suitable for production of high quality biodiesel with characteristics equivalent to crop seed oil-derived biodiesel.

Molecular Identification and Comparative Evaluation of Tropical Marine Microalgae for Biodiesel Production.

Marine microalgae have emerged as important feedstock for liquid biofuel production. The identification of lipid-rich native microalgal species with high growth rate and optimal fatty acid profile and biodiesel properties is the most challenging step in microalgae-based biodiesel production. In this study, attempts have been made to bio-prospect the biodiesel production potential of marine and brackish water microalgal isolates from the west coast of India. A total of 14 microalgal species were isolated, identified using specific molecular markers and based on the lipid content; seven species with total lipid content above 20% of dry cell weight were selected for assessing biodiesel production potential in terms of lipid and biomass productivities, nile red fluorescence, fatty acid profile and biodiesel properties. On comparative analysis, the diatoms were proven to be promising based on the overall desirable properties for biodiesel production. The most potential strain Navicula phyllepta MACC8 with a total lipid content of 26.54 % of dry weight of biomass, the highest growth rate (0.58 day-1) and lipid and biomass productivities of 114 and 431 mgL-1 day-1, respectively, was rich in fatty acids mainly of C16:0, C16:1 and C18:0 in the neutral lipid fraction, the most favoured fatty acids for ideal biodiesel properties. The biodiesel properties met the requirements of fuel quality standards based on empirical estimation. The marine diatoms hold a great promise as feedstock for large-scale biodiesel production along with valuable by-products in a biorefinery perspective, after augmenting lipid and biomass production through biochemical and genetic engineering approaches.