•Upstream and downstream process in Chlorella vulgaris has been explored for microwave assisted sustainable biodiesel production.•92.53% harvesting efficiency was achieved by a combined method of ...flocculation and filtration.•84.03% yield obtained by acid-based catalyzed transesterification in microwave assisted reactor.•Microwave assisted transesterification was more efficient than conventional heating transesterification.•Chlorella vulgaris can produce 13.62ton/hectare/year biodiesel.
The present study explores the integrated approach for the sustainable production of biodiesel from Chlorella vulgaris microalgae. The microalgae were cultivated in 10m2 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 1H NMR, 13C NMR, FTIR and GC; however, fuel properties of biodiesel were also studied using specified test methods as per ASTM and EN standards.
•EtOAC is firstly used as a single reactant and co-solvent for in situ transesterification.•EtOAC hydrolysis yields the EtOH/EtOAC system without using a co-solvent.•EtOAC provides higher FAEE yield ...and saccharification than EtOH/chloroform.•97.8% FAEE yield occurs at 113.6°C with 4.06M H2SO4 and 6.67ml EtOAC/g dried algae.
This study addresses wet in situ transesterification of microalgae for the production of biodiesel by introducing ethyl acetate as both reactant and co-solvent. Ethyl acetate and acid catalyst are mixed with wet microalgae in one pot and the mixture is heated for simultaneous lipid extraction and transesterification. As a single reactant and co-solvent, ethyl acetate can provide higher FAEE yield and more saccharification of carbohydrates than the case of binary ethanol and chloroform as a reactant and a co-solvent. The optimal yield was 97.8wt% at 114°C and 4.06M catalyst with 6.67mlEtOAC/g dried algae based on experimental results and response surface methodology (RSM). This wet in situ transesterification of microalgae using ethyl acetate doesn’t require an additional co-solvent and it also promises more economic benefit as combining extraction and transesterification in a single process.
Nitrogen deprivation (N-deprivation) is a proven strategy for inducing triacylglyceride accumulation in microalgae. However, its effect on the physical properties of cells and subsequently on product ...recovery processes is relatively unknown. In this study, the effect of N-deprivation on the cell size, cell wall thickness, and mechanical strength of three microalgae was investigated. As determined by analysis of micrographs from transmission electron microscopy, the average cell size and cell wall thickness for N-deprived
Nannochloropsis
sp. and
Chlorococcum
sp. were ca. 25% greater than the N-replete cells, and 20 and 70% greater, respectively, for N-deprived
Chlorella
sp. The average Young’s modulus of N-deprived
Chlorococcum
sp. cells was estimated using atomic force microscopy to be 775 kPa; 30% greater than the N-replete population. Although statistically significant, these microstructural changes did not appear to affect the overall susceptibility of cells to mechanical rupture by high pressure homogenisation. This is important as it suggests that subjecting these microalgae to nitrogen starvation to accumulate lipids does not adversely affect the recovery of intracellular lipids.
Scaling up algal cultures to the very large volumes required for commercial production is a complex task and requires skilled and experienced personnel. First it is necessary to consider how to ...optimize the process of producing enough inoculum for the large ponds or photobioreactors in order to minimize the time and cost required. In order to minimize the need for re-inoculation from stock cultures it is also essential to manage the large-scale cultures to avoid significant contamination or collapse. The maintenance of long-term, stable, high-productivity, large-scale cultures, usually under prevailing outdoor conditions of variable irradiance, temperature and rainfall, presents additional challenges most of which are not seen in the constant environment experienced by small-scale laboratory cultures. Methods and protocols to deal with these can only be developed at the large-scale and they will mostly be specific for the alga being cultured, the culture system being used and the location of the production plant. A common feature of all large-scale operations known to us is that, over time (years), both productivity and reliability of the cultures improve as the operators gather experience in managing their cultures.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
•Long-term lethality test using Artemia franciscana discriminates PS NP toxicity.•Surface chemistry determines nanoplastics behaviour and impact on marine plankton.•PS-COOH are adsorbed on the ...microalgae and accumulated in brine shrimp.•PS-NH2 inhibits microalgal growth and causes mortality in brine shrimp larvae.•clap up-regulation indicates physiological alterations in brine shrimp larvae.
Plastic pollution has been globally recognized as a critical issue for marine ecosystems and nanoplastics constitute one of the last unexplored areas to understand the magnitude of this threat. However, current difficulties in sampling and identifying nano-sized debris make hard to assess their occurrence in marine environment. Polystyrene nanoparticles (PS NPs) are largely used as nanoplastics in ecotoxicological studies and although acute exposures have been already investigated, long-term toxicity on marine organisms is unknown. Our study aims at evaluating the effects of 40nm PS anionic carboxylated (PS-COOH) and 50nm cationic amino-modified (PS-NH2) NPs in two planktonic species, the green microalga Dunaliella tertiolecta and the brine shrimp Artemia franciscana, respectively prey and predator. PS NP behaviour in exposure media was determined through DLS, while their toxicity to microalgae and brine shrimps evaluated through 72h growth inhibition test and 14 d long-term toxicity test respectively. Moreover, the expression of target genes (i.e. clap and cstb), having a role in brine shrimp larval growth and molting, was measured in 48h brine shrimp larvae. A different behaviour of the two PS NPs in exposure media as well as diverse toxicity to the two planktonic species was observed. PS-COOH formed micro-scale aggregates (Z-Average>1μm) and did not affect the growth of microalgae up to 50μg/ml or that of brine shrimps up to 10μg/ml. However, these negatively charged NPs were adsorbed on microalgae and accumulated (and excreted) in brine shrimps, suggesting a potential trophic transfer from prey to predator. On the opposite, PS-NH2-formed nano-scale aggregates (Z-Average<200nm), caused inhibition of algal growth (EC50=12.97μg/ml) and mortality in brine shrimps at 14 d (LC50=0.83μg/ml). Moreover, 1μg/ml PS-NH2 significantly induced clap and cstb genes, explaining the physiological alterations (e.g. increase in molting) previously observed in 48h larvae, but also suggesting an apoptotic pathway triggered by cathepsin L-like protease in brine shrimps upon PS-NH2 exposure. These findings provide a first insight into long-term toxicity of nanoplastics to marine plankton, underlining the role of the surface chemistry in determining the behaviour and effects of PS NPs, in terms of adsorption, growth inhibition, accumulation, gene modulation and mortality. The use of long-term end-point has been identified as valuable tool for assessing the impact of nanoplastics on marine planktonic species, being more predictable of real exposure scenarios for risk assessment purposes.
•The mechanism of cationic polymeric flocculation at elevated salinities has been revealed.•Polymeric charge is a key parameter influencing flocculation.•Polymeric coiling is not affecting ...flocculation in marine conditions.
A mechanistic study was performed to evaluate the effect of salinity on cationic polymeric flocculants, that are used for the harvesting of microalgae. The polyacrylamide Synthofloc 5080H and the polysaccharide Chitosan were employed for the flocculation of Neochloris oleoabundans. In seawater conditions, a maximum biomass recovery of 66% was obtained with a dosage of 90mg/L Chitosan. This recovery was approximately 25% lower compared to Synthofloc 5080H reaching recoveries greater than 90% with dosages of 30mg/L. Although different recoveries were obtained with both flocculants, the polymers exhibit a similar apparent polymer length, as was evaluated from viscosity measurements. While both flocculants exhibit similar polymer lengths in increasing salinity, the zeta potential differs. This indicates that polymeric charge dominates flocculation. With increased salinity, the effectivity of cationic polymeric flocculants decreases due to a reduction in cationic charge. This mechanism was confirmed through a SEM analysis and additional experiments using flocculants with various charge densities.
This investigation utilized sugarcane bagasse aqueous extract (SBAE), a nontoxic, cost-effective medium to boost triacylglycerol (TAG) accumulation in novel fresh water microalgal isolate
Scenedesmus
...sp. IITRIND2. Maximum lipid productivity of 112 ± 5.2 mg/L/day was recorded in microalgae grown in SBAE compared to modified BBM (26 ± 3 %). Carotenoid to chlorophyll ratio was 12.5 ± 2 % higher than in photoautotrophic control, indicating an increase in photosystem II activity, thereby increasing growth rate. Fatty acid methyl ester (FAME) profile revealed presence of C14:0 (2.29 %), C16:0 (15.99 %), C16:2 (4.05 %), C18:0 (3.41 %), C18:1 (41.55 %), C18:2 (12.41), and C20:0 (1.21 %) as the major fatty acids. Cetane number (64.03), cold filter plugging property (−1.05 °C), and oxidative stability (12.03 h) indicated quality biodiesel abiding by ASTM D6751 and EN 14214 fuel standards. Results consolidate the candidature of novel freshwater microalgal isolate
Scenedesmus
sp. IITRIND2 cultivated in SBAE, aqueous extract made from copious, agricultural waste sugarcane bagasse to increase the lipid productivity, and could further be utilized for cost-effective biodiesel production.
Biodiesel from microalgae provides a promising alternative for biofuel production. Microalgae can be produced under three major cultivation modes, namely photoautotrophic cultivation, heterotrophic ...cultivation, and mixotrophic cultivation. Potentials and practices of biodiesel production from microalgae have been demonstrated mostly focusing on photoautotrophic cultivation; mixotrophic cultivation of microalgae for biodiesel production has rarely been reviewed. This paper summarizes the mechanisms and virtues of mixotrophic microalgae cultivation through comparison with other major cultivation modes. Influencing factors of microalgal biodiesel production under mixotrophic cultivation are presented, development of combining microalgal biodiesel production with wastewater treatment is especially reviewed, and bottlenecks and strategies for future commercial production are also identified.
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•Well to pump environmental assessment of two thermochemical processing pathways.•NER of 1.23 and GHG emissions of −11.4g CO2-eq (MJ)−1 for HTL pathway.•HTL represents promising ...conversion pathway based on use of wet biomass.•NER of 2.27 and GHG emissions of 210g CO2-eq (MJ)−1 for pyrolysis pathway.•Pyrolysis pathway: drying microalgae feedstock dominates environmental impact.
Microalgae is being investigated as a renewable transportation fuel feedstock based on various advantages that include high annual yields, utilization of poor quality land, does not compete with food, and can be integrated with various waste streams. This study focuses on directly assessing the environmental impact of two different thermochemical conversion technologies for the microalgae-to-biofuel process through life cycle assessment. A system boundary of “well to pump” (WTP) is defined and includes sub-process models of the growth, dewatering, thermochemical bio-oil recovery, bio-oil stabilization, conversion to renewable diesel, and transport to the pump. Models were validated with experimental and literature data and are representative of an industrial-scale microalgae-to-biofuel process. Two different thermochemical bio-oil conversion systems are modeled and compared on a systems level, hydrothermal liquefaction (HTL) and pyrolysis. The environmental impact of the two pathways were quantified on the metrics of net energy ratio (NER), defined here as energy consumed over energy produced, and greenhouse gas (GHG) emissions. Results for WTP biofuel production through the HTL pathway were determined to be 1.23 for the NER and GHG emissions of −11.4g CO2-eq (MJ renewable diesel)−1. Biofuel production through the pyrolysis pathway results in a NER of 2.27 and GHG emissions of 210g CO2-eq (MJ renewable diesel)−1. The large environmental impact associated with the pyrolysis pathway is attributed to feedstock drying requirements and combustion of co-products to improve system energetics. Discussion focuses on a detailed breakdown of the overall process energetics and GHGs, impact of modeling at laboratory-scale compared to industrial-scale, environmental impact sensitivity to systems engineering input parameters for future focused research and development, and a comparison of results to literature.
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•Novel silica nanoplates (NPLs) were synthesized under mild hydrothermal conditions.•The NPLs exhibit uniform anisotropic nanostructures of highly crystalline α-quartz.•Ultrathin NPLs ...disrupt the rigid and thick cell wall of microalga H. pluvialis.•The NPLs mediate the solvent extraction (~99%) of astaxanthin from algal biomass.•NPLs are a promising tool for energy saving and efficient algal biorefinery.
A facile template-free hydrothermal method was successfully developed for the controlled synthesis of ultrathin α-quartz nanoplates (NPLs) for the first time. Analyses of the α-quartz NPLs revealed the characteristic anisotropic nanostructures of highly crystalline α-quartz with an average lateral size and thickness of 1.14 ± 0.32 μm and 7.7 ± 0.6 nm, respectively. Importantly, efficient extraction of highly valuable chemicals such as astaxanthin (ATX) from the microalgal cells of Haematococcus pluvialis (H. pluvialis) was accomplished by lacerating the cell walls using the ultrathin α-quartz NPLs under mild ultrasonication. The incorporation of α-quartz NPLs enhanced the ATX extraction efficiency significantly (99%, 18.0 ± 0.6 mg ATX/g cell) when coupled with 5 min of ultrasonication. The dosage of α-quartz NPLs (800.0 mg/L) for maximum ATX extraction was reduced substantially to only 8% of the nanomaterial dose used in the extraction controls. The enhanced extraction efficiency and dosage were explained by the role of the structural anisotropy of α-quartz NPLs in multiple phase separation-extraction processes. This work provides a novel, facile, and economical route for the synthesis of uniform ultrathin nanoplates, offering a new material for the highly efficient harvesting of chemical products from various microalgal biorefinery processes.
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