Mixotrophic cultivation of microalgae to enhance the quality of lipid for biodiesel application: effects of scale of cultivation and light spectrum on reduction of α-linolenic acid.

The research on microalgal biodiesel is focused not only on getting the highest lipid productivity but also desired quality of lipid. The experiments were initially conducted on flask scale (1L) using acetate carbon source at different concentrations viz. 0.5, 2, 3 and 4 g L-1. The optimum concentration of acetate was considered for further experiments in two airlift photobioreactors (10 L) equipped separately with red and white LED lights. The Feasibility Index (FI) was derived to analyze the scalability of mixotrophic cultivation based on net carbon fixation in biomass per consumption of total organic carbon. The experimental strategy under mixotrophic mode of cultivation lowered the α-linolenic acid content of lipid by 60-80% as compared to autotrophic cultivation for Scenedesmus abundans species and yielded the highest biomass and lipid productivities, 59 ± 2 and 17 ± 1.8 mg L-1 day-1, respectively. The TOC, nitrate, and phosphate reduction rates were 74.6 ± 3.0, 11.5 ± 1.4, 9.6 ± 2.4 mg L-1 day-1, respectively. The significant change was observed in lipid compositions due to the scale, mode of cultivation, and light spectra. As compared to phototrophic cultivation, biodiesel obtained under mixotrophic cultivation only met standard biodiesel properties. The FI data showed that the mixotrophic cultivation was feasible on moderate concentrations of acetate (2-3 g L-1).

Fermentation of de-oiled algal biomass by Lactobacillus casei for production of lactic acid.

De-oiled algal biomass (algal cake) generated as waste byproduct during algal biodiesel production is a promising fermentable substrate for co-production of value-added chemicals in biorefinery systems. We explored the ability of Lactobacillus casei 12A to ferment algal cake for co-production of lactic acid. Carbohydrate and amino acid availability were determined to be limiting nutritional requirements for growth and lactic acid production by L. casei. These nutritional requirements were effectively addressed through enzymatic hydrolysis of the algal cake material using α-amylase, cellulase (endo-1,4-ß-D-glucanase), and pepsin. Results confirm fermentation of algal cake for production of value-added chemicals is a promising avenue for increasing the overall cost competiveness of the algal biodiesel production process.

Biodiesel Production from Chlorella protothecoides Oil by Microwave-Assisted Transesterification.

In this study, biodiesel production from microalgal oil by microwave-assisted transesterification was carried out to investigate its efficiency. Transesterification reactions were performed by using Chlorella protothecoides oil as feedstock, methanol, and potassium hydroxide as the catalyst. Methanol:oil ratio, reaction time and catalyst:oil ratio were investigated as process parameters affected methyl ester yield. 9:1 methanol/oil molar ratio, 1.5% KOH catalyst/oil ratio and 10 min were optimum values for the highest fatty acid methyl ester yield.

Enhancement of extraplastidic oil synthesis in Chlamydomonas reinhardtii using a type-2 diacylglycerol acyltransferase with a phosphorus starvation-inducible promoter.

When cultivated under stress conditions, many plants and algae accumulate oil. The unicellular green microalga Chlamydomonas reinhardtii accumulates neutral lipids (triacylglycerols; TAGs) during nutrient stress conditions. Temporal changes in TAG levels in nitrogen (N)- and phosphorus (P)-starved cells were examined to compare the effects of nutrient depletion on TAG accumulation in C. reinhardtii. TAG accumulation and fatty acid composition were substantially changed depending on the cultivation stage before nutrient starvation. Profiles of TAG accumulation also differed between N and P starvation. Logarithmic-growth-phase cells diluted into fresh medium showed substantial TAG accumulation with both N and P deprivation. N deprivation induced formation of oil droplets concomitant with the breakdown of thylakoid membranes. In contrast, P deprivation substantially induced accumulation of oil droplets in the cytosol and maintaining thylakoid membranes. As a consequence, P limitation accumulated more TAG both per cell and per culture medium under these conditions. To enhance oil accumulation under P deprivation, we constructed a P deprivation-dependent overexpressor of a Chlamydomonas type-2 diacylglycerol acyl-CoA acyltransferase (DGTT4) using a sulphoquinovosyldiacylglycerol 2 (SQD2) promoter, which was up-regulated during P starvation. The transformant strongly enhanced TAG accumulation with a slight increase in 18 : 1 content, which is a preferred substrate of DGTT4. These results demonstrated enhanced TAG accumulation using a P starvation-inducible promoter.

Investigating the impact of n-heptane (C7H16) and nanoparticles (TiO2) on diesel-microalgae biodiesel blend in CI diesel engines.

Recent global challenges encompass profound environmental pollution and the depletion of finite fuel resources. In this study, the biodiesel used in the mixture was derived from Azolla pinnata microalgae oil through a trans-esterification reaction chosen for its high oil concentration. During the initial phase of the experiment, varying volumes of biodiesel (5%, 10%, and 15%) and n-heptane (5%, 10%, and 15%) were introduced to diesel to form a ternary fuel blend. The experimental outcome shows that an n-heptane and biodiesel mixture of 10% by volume would produce the best results. Next, experiments were carried out by incorporating 10, 40, and 80 ppm titanium oxide (TiO2) nanoparticles (NPs) in a recommended ternary fuel blend. The experimental investigation showed that D80A10H10TNP40 (diesel 80% + biodiesel 10% + n-heptane 10% + TiO2 40 ppm) caused a 7.21% increase in brake thermal efficiency (BTE) with a decrease in brake specific fuel consumption (BSFC) and brake specific energy consumption (BSEC) by 9.58% and 10%, respectively, compared to (diesel 80% + biodiesel 20%) D80A20. D80A10H10TNP40 exhibits lower emissions, with a significant reduction of 11.29% and 20.96% in carbon monoxide (CO) and unburnt hydrocarbons (UBHC), respectively. Nitrogen oxide (NOX) and smoke emissions were reduced by 3.3% and 11.13%, respectively, compared to D80A10H10. Furthermore, D80A10H10TNP40 demonstrated enhanced combustion properties, comprising a significant rise of 4.39% in-cylinder pressure (CP), 35.29% in heat release rate (HRR), and 25.05% in the rate of pressure rise (RPR). The findings of this investigation indicate that D80A10H10TNP40 exhibits enhanced efficiency, emission, and combustion properties compared to the D80A20 fuel.

Performance and exhaust emission characteristics investigation of compression ignition engine fuelled with microalgae biodiesel and its diesel blends.

Biofuels extracted from plant biomass can be used as fuel in CI engines to lower a hazardous atmospheric pollutant and mitigate climate risks. Furthermore, its implementation is hampered by inevitable obstacles such as feedstocks and the crop area required for their cultivation, leading to a lack of agricultural land for the expansion of food yields. Despite this, microalgae have been discovered to be the most competent and unwavering source of biodiesel due to their distinguishing characteristics of being non-eatable and requiring no cropland for cultivation. The objectives of this paper was to look into the potential of a novel, formerly underappreciated biodiesel from microalgae species which could be used as a fuel substitute. Transesterification is being used to extract the biodiesel. Microalgae are blended with petroleum diesel in percentage to create microalgae blends (MAB) as needed for experimentation. The impact of biodiesel on performance as well as exhaust emission attributes of a 1-cylinder diesel engine was experimentally studied. Compared to petroleum diesel, different blend of microalgae biodiesel showed a decline in torque and hence brake power, resulting in an average fall of 7.14 % in brake thermal efficiency and 11.54 % increase in brake-specific fuel consumption. There were wide differences in exhaust emission characteristics, including carbon monoxide and hydrocarbon, as the blend ratio in diesel increased. Moreover, nitrogen oxides and carbon dioxides increase in all algae biodiesel blends, but they are still within the acceptable range of petroleum diesel.

Efficient Production of Polyhydroxyalkanoate Through Halophilic Bacteria Utilizing Algal Biodiesel Waste Residue.

The objective of the current work was to investigate the potential of halophilic bacterial isolates for efficient utilization of crude glycerol from algal biodiesel waste into polyhydroxyalkanoates (PHAs) a green plastic. Screening of the isolates was directly done in algal biodiesel waste residue containing solid agar plates supplemented with Nile red. Crude glycerol is a biodiesel waste whose bioconversion into value-added products provides an alternative for efficient management with dual benefit. For the scale-up studies of PHAs, Halomonas spp. especially H. daqingensis was observed as a potential candidate growing well in 3% Algal biodiesel waste residue (ABWR), 5% NaCl supplementation at 35°C within 48 h of incubation. Maximum Cell dry weight (CDW) of 0.362 ± 0.001 g and 0.236 ± 0.003 g PHA was obtained with H. daqingensis when grown in the fermentor with 0.5 vvm air flow rate and 200 rpm containing 3% ABWR supplemented with 5% NaCl at 35°C incubation temperature for 48 h. ABWR can serve as a sole substrate for PHA production at an industrial scale serving two approaches: getting rid of the biodiesel industrial waste containing high amount of glycerol besides using waste replacing commercial substrate thereby reducing the cost of the product.

Environmental friendly synthesis of TiO2-ZnO nanocomposite catalyst and silver nanomaterilas for the enhanced production of biodiesel from Ulva lactuca seaweed and potential antimicrobial properties against the microbial pathogens.

TiO2-ZnO heterogeneous catalytic system provides a good replacement of a homogeneous catalytic reaction due to its easier recovery. In this study, biodiesel was produced from Ulva lactuca seaweeds using TiO2-ZnO nanocomposite catalysts with particle size of ~12 nm. The size controlled TiO2-ZnO nanocomposite was characterized by powder XRD analysis and TEM. The result of that TiO2-ZnO catalyst is a promising catalyst for the production of biodiesel under mild reaction conditions and high yield of hydroxydecanoic acid conversion of 82.8%. The various conditions optimized for the higher conversion to FAME (15.8 ml of FAME) were 4 wt% catalysts at 4 h under 60 °C and further there is no increase of conversion to FAME above 60 °C-80 °C. The total product yield was calculated as 82.8% of conversion to FAME. The evaluated biodiesel was found to be up to the mark of ASTM standards. The silver nanoparticles (AgNPs) were synthesized by using leftover biomass of algae obtaining after lipid extraction of U.lactuca. AgNPs particle size was achieved as ~12 nm and was confirmed by UV-Visible spectroscopy, XRD and TEM analysis. Antibacterial activities of the synthesized AgNPs were analyzed and compared. The antibacterial activity was excellent against bacterial pathogens and treatment against P. vulgaris shows the maximum zone of inhibition (13.8 mm). The present work identified that the unutilized bioresource such as U.lactuca can be effectively utilized for biodiesel production so as to replace fossil fuel usage.

Ohmic heating pretreatment of algal slurry for production of biodiesel.

Suspensions of the model microalga Chlorella sp. TISTR 8990 were pretreated by ohmic heating to facilitate release of lipids from the cells in subsequent extraction and lipase-mediated transesterification to biodiesel. After ohmic pretreatment, the moist biomass was suspended in a system of water, hexane, methanol and immobilized lipase for extraction of lipids and simultaneous conversion to biodiesel. The ohmic pretreatment was optimized using an experimental design based on Taguchi method to provide treated biomass that maximized the biodiesel yield in subsequent extraction-transesterification operation. The experimental factors were the frequency of electric current (5-105 Hz), the processing temperature (50-70 °C), the algal biomass concentration in the slurry (algal fresh weight to water mass ratio of 1-3) and the incubation time (1-3 min). Extraction-transesterification of the pretreated biomass was carried out at 40 °C for 24 h using a reaction systems of a fixed composition (i.e. biomass, hexane, methanol, water and immobilized enzyme). Compared to control (i.e. untreated biomass), the ohmic pretreatment under optimal conditions (5 Hz current frequency, 70 °C, 1:2 mass ratio of biomass to water, incubation time of 2-min) increased the rate of subsequent transesterification by nearly 2-fold.

Photosynthetic light reactions increase total lipid accumulation in carbon-supplemented batch cultures of Chlorella vulgaris.

Microalgae are an attractive biofuel feedstock because of their high lipid to biomass ratios, lipid compositions that are suitable for biodiesel production, and the ability to grow on varied carbon sources. While algae can grow autotrophically, supplying an exogenous carbon source can increase growth rates and allow heterotrophic growth in the absence of light. Time course analyses of dextrose-supplemented Chlorella vulgaris batch cultures demonstrate that light availability directly influences growth rate, chlorophyll production, and total lipid accumulation. Parallel photomixotrophic and heterotrophic cultures grown to stationary phase reached the same amount of biomass, but total lipid content was higher for algae grown in the presence of light (an average of 1.90 mg/mL vs. 0.77 mg/mL over 5 days of stationary phase growth).

Extractive-transesterification of algal lipids under microwave irradiation with hexane as solvent.

This study describes the use of microwaves (MW) for enhanced extractive-transesterification of algal lipids from dry algal biomass (Chlorella sp.). Two different single-step extractive-transesterification methods under MW irradiation were evaluated: (1) with ethanol as solvent/reactant and sodium hydroxide catalyst; and (2) with ethanol as reactant and hexane as solvent (sodium hydroxide catalyst). Biodiesel (fatty-acid-ethyl-esters, FAEE) yields from these two methods were compared with the conventional Bligh and Dyer (BD) method which followed a two-step extraction-transesterification process. The maximum lipid yields for MW, MW with hexane and BD methods were 20.1%, 20.1%, and 13.9%, respectively; while the FAEE conversion of the algal lipids were 96.2%, 94.3%, and 78.1%, respectively. The algae-biomass:ethanol molar ratio of 1:250-500 and 2.0-2.5% catalyst with reaction times around 6min were determined as optimum conditions for both methods. This study confers that the single-step non-conventional methods can contribute to higher algal lipid and FAEE yields.

Constraints to commercialization of algal fuels.

Production of algal crude oil has been achieved in various pilot scale facilities, but whether algal fuels can be produced in sufficient quantity to meaningfully displace petroleum fuels, has been largely overlooked. Limitations to commercialization of algal fuels need to be understood and addressed for any future commercialization. This review identifies the major constraints to commercialization of transport fuels from microalgae. Algae derived fuels are expensive compared to petroleum derived fuels, but this could change. Unfortunately, improved economics of production are not sufficient for an environmentally sustainable production, or its large scale feasibility. A low-cost point supply of concentrated carbon dioxide colocated with the other essential resources is necessary for producing algal fuels. An insufficiency of concentrated carbon dioxide is actually a major impediment to any substantial production of algal fuels. Sustainability of production requires the development of an ability to almost fully recycle the phosphorous and nitrogen nutrients that are necessary for algae culture. Development of a nitrogen biofixation ability to support production of algal fuels ought to be an important long term objective. At sufficiently large scale, a limited supply of freshwater will pose a significant limitation to production even if marine algae are used. Processes for recovering energy from the algal biomass left after the extraction of oil, are required for achieving a net positive energy balance in the algal fuel oil. The near term outlook for widespread use of algal fuels appears bleak, but fuels for niche applications such as in aviation may be likely in the medium term. Genetic and metabolic engineering of microalgae to boost production of fuel oil and ease its recovery, are essential for commercialization of algal fuels. Algae will need to be genetically modified for improved photosynthetic efficiency in the long term.

Algal biofuels: challenges and opportunities.

Biodiesel production using microalgae is attractive in a number of respects. Here a number of pros and cons to using microalgae for biofuels production are reviewed. Algal cultivation can be carried out using non-arable land and non-potable water with simple nutrient supply. In addition, algal biomass productivities are much higher than those of vascular plants and the extractable content of lipids that can be usefully converted to biodiesel, triacylglycerols (TAGs) can be much higher than that of the oil seeds now used for first generation biodiesel. On the other hand, practical, cost-effective production of biofuels from microalgae requires that a number of obstacles be overcome. These include the development of low-cost, effective growth systems, efficient and energy saving harvesting techniques, and methods for oil extraction and conversion that are environmentally benign and cost-effective. Promising recent advances in these areas are highlighted.

Induction of lipids and resultant FAME profiles of microalgae from coastal waters of Pearl River Delta.

This article presents a study on identification, cultivation and characterisation of microalgal strains from the coastal waters of the Pearl River Delta in Guangdong, China. Thirty-seven identified strains belong to the families: Chlorellaceae, Scotiellocystoidaceae, Scenedesmaceae,Selenastraceae,Micractiniaceae, Coccomyxaceae, Trebouxiaceae and Chlorococcaceae. Of isolated strains, Hindakia PKUAC 169 was selected for lipid induction using two methods: nitrogen starvation and salt stress. After derivatisation of algal lipids through in situ transesterification, lipid profiles of the alga under the two methods were analysed. The results have shown that both lipid yield and fatty acid profiles vary with the methods. Of the two tested methods of inducing lipid production, salt stress yielded three-fold higher lipid productivity than nitrogen starvation. The lipids are predominantly composed of C14-C18 fatty acids, which are favourable for biodiesel production. Moreover, the content of polyunsaturated fatty acids was below the limit of 12% set by EN14214 biodiesel standard.

Functional study of diacylglycerol acyltransferase type 2 family in Chlamydomonas reinhardtii.

Algal triacylglycerol biosynthesis is of increasing interest for potential biodiesel production. A model microalga, Chlamydomonas, has multiple isoforms of diacylglycerol acyltransferase type 2 (DGTT) catalyzing the final step of triacylglycerol biosynthesis; however, the functions of the isoforms are poorly understood. Here, we performed heterologous complementation assay of Chlamydomonas DGTT1 to 4 in a yeast mutant defective in triacylglycerol biosynthesis. DGTT1, 2 and 3 but not 4 complemented the phenotype, including triacylglycerol levels. Interestingly, complementation by DGTT2 increased triacylglycerol content by 9-fold.