Microalgae have been suggested as a promising feedstock for producing biofuel because of their potential of lipid production. In this study, a first principles ODE model for microalgae growth and neutral lipid synthesis which is proposed by Surisetty et al. is investigated for the purpose of maximizing the rate of microalgae growth and the amount of neutral lipid. The model has 6 states and 12 parameters and follows the assumption of Droop model which explains the growth as a two-step phenomenon; the uptake of nutrients is first occurred in the cell, and then use of intracellular nutrient to support cell's growth. In this study, optimal experimental design (OED) using D- optimality criterion is performed to compute the system input profile and find optimal parameters of the model. Sensitivity analysis is also performed to determine which parameters have a negligible effect on the model predictions.
This work introduces a systematic method for the economic and environmental analysis and design of new technologies applied to the 3rd generation (from microalgae) biodiesel production process. The evaluation method is based on the integrated use of process simulation techniques with economic and environmental models. The approach is applied to a new technology introduced by some of the authors, where the glycerol produced in the transesterification is used as carbon source for microalgae growth. Firstly, a state of the art biodiesel production plant in the process simulator it is modelled and the economical and environmental performance is computed. Then, the new technology is introduced and its performance are compared. The method presented is very useful for decision-makers in order to evaluate the inclusion of new technologies to improve the chemical process operation and topological designs.
Microalgae, which hold great potential for carbon neutral biofuels production, is regarded as one of the most viable options to serve as sustainable feedstock for biodiesel production. This paper analyses two processes for biodiesel production from microalgae (Chlorella Protothecoides). The analysis showed that the energy efficiency of the supercritical transesterification process is 52.85% with the most energy (75.55%) used in the separation step of the process. The alkali-catalysed process has 49.67% energy efficiency with 35.25% used in the biodiesel purification step. The supercritical process requires higher capital cost, the alkali-catalysed process requires slightly higher production cost due to higher number of unit operations and processing steps. It was found that technically, the non-catalytic supercritical transesterification method has higher energy efficiency, but the unit price of the biodiesel is slightly lower via the alkali-catalysed transesterification method.
We report on the application of Laser-Induced Breakdown Spectroscopy (LIBS) to the determination of elements distinctive in terms of their biological significance (such as potassium, magnesium, calcium, and sodium) and to the monitoring of accumulation of potentially toxic heavy metal ions in living microorganisms (algae), in order to trace e.g. the influence of environmental exposure and other cultivation and biological factors having an impact on them. Algae cells were suspended in liquid media or presented in a form of adherent cell mass on a surface (biofilm) and, consequently, characterized using their spectra. In our feasibility study we used three different experimental arrangements employing double-pulse LIBS technique in order to improve on analytical selectivity and sensitivity for potential industrial biotechnology applications, e.g. for monitoring of mass production of commercial biofuels, utilization in the food industry and control of the removal of heavy metal ions from industrial waste waters.
A novel photobioreactor was developed with a total volume of 30 m3 which required merely 100 m3 of land footprint. The bioreactor was capable of utilizing CO2 in the flue gas of a power plant as the carbon source for the growth of a freshwater alga, Spirulina platensis, mitigating the greenhouse effect caused by the same amount of CO2 discharge. Results of the study indicated that the photobioreactor was capable of fixing 2,234kg of CO2 per annum. Upon deducting the energy consumption of operating the bioreactor unit, the estimated amount of CO2 to be fixed by a scaled-up reactor would be 74 tons ha-1 year-1. In addition, the study proved that protein-free polysaccharides of S. platensis could induce the production of pro-IL-1 and IL-1 proteins through the mediation of ERK, JNK, and p38 MAPKs pathways. As a consequence, immunogenic activities of the macrophage cells were enhanced.
Energy is the most important necessity for human existence on the earth. Limited crude petroleum resources and increasing awareness regarding the environmental impacts of fossil fuels are driving the search for new energy sources and alternative fuels. Biodiesel is a fuel which is renewable, biodegradable, environmentally friendly, and non-toxic in nature and has attracted considerable attention during the past decades. The costs of feedstock and the production process are two major hurdles to large-scale biodiesel production in particular. Various technologies have been developed to reduce the production cost. This paper attempts to extensively review microwave-assisted technology for biodiesel production. Additionally, different types of feedstocks for biodiesel production have been summarized in this paper. It is concluded that the microwave-assisted technique reduces the reaction time significantly in comparison with conventional methods. In addition, a high quality biodiesel can be obtained from microwave-assisted transesterification of different kinds of oils. Finally, the energy payback for 1kg biodiesel produced by microwave-assisted technology is calculated in this paper and it indicated that the system is sustainable. Therefore it can be a suitable method of decreasing the cost of biodiesel and can also help the commercialization of this fuel.
Simulations of radiative transfer within an air-lift photobioreactor (PBR) are demonstrated by coupling it to the fluid hydrodynamics and employing wavelength dependant properties for the participating media. The radiative properties of the algal media are determined by matching the numerical predictions against measurements of radiative intensity distributions. To assist towards the design, scale-up and optimization of such reactors, a parametric investigation of the relative importance of the angular resolution of the radiation calculations, scattering phase functions of the bubbles, air mass flow rate and the bubble size are investigated by examining the 3D distributions of radiation within the PBR. Two hundred and eighty eight solid angles in the finite volume (FV) formulation of the radiative transfer equation (RTE) provide an optimum combination of speed and accuracy in the resulting calculations. While scattering results in a more effective redistribution of the energy, the results from employing isotropic and forward-scattering phase functions for the bubbles are found to be similar. The importance of bubble scattering diminishes at algal concentrations (>0.5 g/L) where the radiation attenuation is dominated by the absorption coefficient of the algal media. While 1 μm sized bubbles more effectively redistribute the radiation downstream of the radiators compared to larger sized bubbles, the differences in the radiation profiles obtained from 10 μm and 100 μm-sized bubbles were small within this reactor. The radiation distributions are also influenced by the mass flow rate of air. The calculations demonstrate the need to rigorously account for the air flow rate, bubble size and the scattering effects of bubbles through fully coupled numerical solutions to the fluid flow and radiative transfer equations and provide some best practice guidelines for increasing the fidelity of radiation simulations in PBR’s.
A novel method for biodiesel production without the need of conventional catalyst such as potassium hydroxide and sulfuric acid was proposed in this study. In the presence of water, biodiesel can be produced by reacting methanol with feedstock oil under subcritical condition. When refined soybean oil was used, high biodiesel conversion (96.4%) can be achieved in a reasonable short time (4 h). The conversion was 92.6% when soybean oil with a water content of 9 wt.% was used. The possibility of using oils with high acid and water contents as feedstock was also investigated. Since no catalyst was employed, the process is simpler and more environmental friendly than traditional methods.
In recent decades, the world has been confronted with an energy crisis associated with irreversible depletion of traditional sources of fossil fuels, coupled with atmospheric accumulation of greenhouse gases that cause global warming. The urgent need to replace traditional fuels led to emergence of biodiesel and biohydrogen as interesting alternatives, both of which can be obtained via microalga-mediated routes.
Microalgae are ubiquitous eukaryotic microorganisms, characterized by a remarkable metabolic plasticity. Their oil productivities are much higher than those of higher terrestrial plants, and they do not require high quality agricultural land. Microalgae may indeed be cultivated in brackish and wastewaters that provide suitable nutrients (e.g. View the MathML source), at the expense of only sunlight and atmospheric CO2. On the other hand, metabolic engineering permits release of molecular hydrogen also via photosynthetic routes, which will easily be converted to electricity in fuel cells or mechanical power in explosion engines, with only water vapor as exhaust product in both cases.
However, large-scale implementation of microalga-based systems to manufacture biodiesel and biohydrogen has been economically constrained by their still poor volumetric efficiencies, which imply excessively high costs when compared with current petrofuel prices. Technological improvements are accordingly critical, both on the biocatalyst and the bioreactor levels. The current bottlenecks that have apparently precluded full industrial exploitation of microalgae cells are critically discussed here, viz. those derived from the scarce knowledge on the mechanisms that control regulation of gene expression, the reduced number of species subjected to successful genetic transformation, the relatively low cell density attainable, the poor efficiency in harvesting, and the difficulties in light capture and use.
Therefore, this paper provides an overview of the feasibility of microalgae for production of biofuels via synthesis of liquid endocellular metabolites (i.e. triglycerides) and gaseous extracellular ones (i.e. molecular hydrogen), and addresses technical and economic shortcomings and opportunities along the whole processing chain, at both microorganism and reactor levels.
Although algal biofuels possess great potential, profitable production is quite challenging. Much of this challenge is rooted in the thermodynamic constraints associated with producing fuels with high energy, low entropy, and high exergy from dispersed materials. In this study, a preliminary thermodynamic analysis is presented that calculates the energy, entropy, and exergy of the intermediate products for algal biocrude production. These values are also used in an initial attempt to characterize the thermodynamic efficiency of that system. The production pathway is simplified by assuming ideal solutions throughout. Results for the energy and exergy efficiencies, and the first-order energy and exergy return on investment, of the system are given.
The summary finding is that the first-order energy return on investment in the best case considered could be as high as 520, as compared to 1.7 × 10−3 in the experimental unit under development. While this analysis shows that significant improvement may be possible, the ultimate thermodynamic efficiency of algal biofuels likely lies closer to the moderate case examined here, which yielded a first-order energy return on investment of 10. For perspective, the first-order energy return on investment for oil and gas production has been estimated in the literature to be ∼35.
To evaluate the in vitro antioxidant capacity of a Chlorella marina (Butcher, 1952).
Samples were tested for the total phenolic content, antioxidant activity, deoxy ribose radical scavenging activity and reducing power.
The methanolic extract was found to have high levels of phenolic (0.647±0.052 mg GAE/g), when compared to diethyl ether and hexane. The diethyl ether extract exhibited higher antioxidant potential as (0.816±0.366 mg AscAE/ g), higher percentage of deoxy ribose radical scavenging activity (0.399±0.004) and reducing power (2.814±0.014).
The phenolic compounds were not a major contributor to the antioxidant capacities of these microalgae. This was very different from many other plant species like fruits, vegetables and medicinal plants. The microalgae could contain different antioxidant compounds from other plants.
Microalgae are a source of renewable oil for liquid fuels. However, costs for dewatering/drying, extraction, and processing have limited commercial scale production of biodiesel from algal biomass. A wet lipid extraction procedure was developed that was capable of extracting 79% of transesterifiable lipids from wet algal biomass (84% moisture) via acid and base hydrolysis (90 °C and ambient pressures), and 76% of those extracted lipids were isolated, by further processing, and converted to FAMEs. Furthermore, the procedure was capable of removing chlorophyll contamination of the algal lipid extract through precipitation. In addition, the procedure generated side streams that serve as feedstocks for microbial conversion to additional bioproducts. The capability of the procedure to extract lipids from wet algal biomass, to reduce/remove chlorophyll contamination, to potentially reduce organic solvent demand, and to generate feedstocks for high-value bioproducts presents opportunities to reduce costs of scaling up algal lipid extraction for biodiesel production.
A switchable hydrophilicity solvent (SHS) was studied for its effectiveness at extracting lipids from freeze-dried samples of Botryococcus braunii microalgae. The SHS N,N-dimethylcyclohexylamine extracted up to 22 wt.% crude lipid relative to the freeze-dried cell weight. The solvent was removed from the extract with water saturated with carbon dioxide at atmospheric pressure and recovered from the water upon de-carbonation of the mixture. Liquid chromatography–mass spectrometry (LC–MS) showed that the extracted lipids contained high concentrations of long chain tri-, di- and mono-acylglycerols, no phospholipids, and only 4–8% of residual solvent. Unlike extractions with conventional organic solvents, this new method requires neither distillation nor the use of volatile, flammable or chlorinated organic solvents.
This paper illustrates the Ultrasound Assisted Extraction (UAE) of β-carotene from Spirulina platensis. Various parameters such as extraction time, solvent type, biomass to solvent ratio, temperature, electrical acoustic intensity, length of the probe tip dipped into the solvent, duty cycle and pre treatment effect were explored for the extraction of β-carotene. From economic point of view, the optimal conditions for the extraction of β-carotene from Spirulina were 1.5 g Spirulina (2 min pre soaked in methanol) in 50 ml n-heptane at 30 °C temperature, 167 W/cm2 electrical acoustic intensity and 61.5% duty cycle for 8 min with probe tip length of 0.5 cm dipped into the extracting solvent from the surface. The maximum extraction achieved under the above mentioned optimum parameters was 47.10%. The pre-treatment time showed a promising effect on the yield as pre-treating the biomass with methanol for 2 min before ultrasonication showed 12 times increase in extraction yield of β-carotene.
Growth parameters and biochemical composition of the green microalga Chlorella vulgaris cultivated under different mixotrophic conditions were determined and compared to those obtained from a photoautotrophic control culture. Mixotrophic microalgae showed higher specific growth rate, final biomass concentration and productivities of lipids, starch and proteins than microalgae cultivated under photoautotrophic conditions. Moreover, supplementation of the inorganic culture medium with hydrolyzed cheese whey powder solution led to a significant improvement in microalgal biomass production and carbohydrate utilization when compared with the culture enriched with a mixture of pure glucose and galactose, due to the presence of growth promoting nutrients in cheese whey. Mixotrophic cultivation of C. vulgaris using the main dairy industry by-product could be considered a feasible alternative to reduce the costs of microalgal biomass production, since it does not require the addition of expensive carbohydrates to the culture medium.
Microalgae are microorganisms that can fix CO2 by using the energy from the sun and transforming it into organic molecules such as lipids (i.e. feedstock for biodiesel production). Microfiltration is a promising method to be considered in the harvesting step. In this study, two antifouling methods were tested in order to minimize permeability decrease over time, at low trans-membrane pressure filtration.
Preliminary experiments were performed to find optimum conditions of transmembrane pressure, rotational speed and membrane pore size. Pilot experiments were carried out in the optimal conditions using microalgae obtained from the culture step and from a previous concentration process based on sedimentation. Fouling was significantly minimized, and the permeability plateau increased up to 600 L/h/m2/bar.
Three microalgae species were tested: Phaeodactylum tricornutum(Pht), Nannochloropsis gaditana (Nng) and Chaetoceros calcitrans (Chc).
An economic assessment was also performed, which demonstrated that dynamic filtration is economically more efficient than tangential cross-flow filtration.
Nannochloropsis oculata was grown in an outdoor bubble column photobioreactor. To obtain information about the behaviour of microalgae/photobioreactor system related to the CO2 net balance, an analysis of the pH profiles during microalgae growth was carried out. The use of the carbonate equilibrium chemistry and the overall CO2 volumetric mass transfer in the photobioreactor has permitted to obtain information of the CO2 losses/CO2 microalgae consumption ratios. The simplicity of the technique used (a pH probe) could extend the use of this methodology for the correct selection of the photobioreactor/microalgae parameters with the aim to maximize the [CO2 uptaken/(CO2 uptaken + CO2 stripped)] ratios.
Bioregenerative life support system (BLSS) is an artificial ecosystem providing life support for crewmen on space or ground mission in terms of biological unit components. It is critically important to maintain gases (O2 and CO2) concentrations in the system to robustly stabilize at nominal levels, nevertheless BLSS is a complex system, its control law could not be sufficiently and profoundly investigated merely by traditional approaches, i.e., prototype experiment and open-loop control. In our research, a closed integrative system (CIS) composed of lettuce, silkworm and microalgae was constructed as a specific prototype of BLSS, studying the gases dynamics in system and their closed-loop regulation and control adopting microalgae as a bioregenerative tool in combination with computer simulation. Firstly, a precise kinetic model of CIS was developed for fully describing the dynamic characteristics of gases concentrations by means of system dynamics and artificial neural network based on relevant ecological mechanisms and experimental data. Secondly, a closed-loop CIS with Linear-Quadratic Gaussian (LQG) servo controller was established depended on microalgae peculiarity, such as high growth rate, metabolism flexibility, controllability, and so on. Thirdly, the closed-loop CIS was optimized via predetermined gases dynamic responses to control inputs and digital simulation. Finally, the effectiveness of the closed-loop CIS was fully tested and accredited by real-time simulation. The result showed that the closed-loop CIS could effectively regulate the light intensity and aerating rate to stimulate or inhibit the growth of microalgae based on real-time measurements of gases concentrations, and indirectly control them to come back to their nominal levels with desired dynamic response performances after deviation from originally equilibrium points. Therefore, the closed-loop control of microalgae might greatly enhance the safety and reliability of BLSS operation.
This trial evaluated the effects of partial replacement of fishmeal protein by a defatted microalgae meal (DMM) in a shrimp diet. The DMM was a by-product of astaxanthin production from Haematococcus pluvialis and contained 40.3% crude protein (CP) and 0.9% crude lipid (CL). Test diets were prepared by using DMM (3, 6, 9 and 12% in a diet) to replace 12.5%, 25%, 37.5% or 50% of a fishmeal protein in a control diet (32.3% CP & 8.9% CL). All test diets had similar protein and lipid levels. Each diet was randomly assigned to four tanks (12 juvenile shrimp per tank) in an indoor flow through seawater laboratory. After an 8-week feeding trial, shrimp fed the diet with 12.5% of the fishmeal protein replaced showed a significantly higher growth rate and lower feed conversion ratio than the shrimp fed the control diet (P < 0.05). The other three DMM-added diets had a similar effect on the growth of shrimp as the control diet (P > 0.05). Shrimp fed the four DMM-added diets appeared redder and contained higher free and esterified astaxanthins than shrimp fed the control diet. The results indicated that DMM could be a valuable alternative protein and pigmentation ingredient in shrimp feed.
To find out an alternative of coal saving, a kind of microalgae, Chlorella vulgaris (C. vulgaris) which is widespread in fresh water was introduced into coal pyrolysis process. In this work, the pyrolysis experiments of C. vulgaris and coal blend (CCB) were carried out by TGA, and those of C. vulgaris and coal were also taken respectively as control groups. It was found that: the TG and DTG profiles of CCB were similar to C. vulgaris, but different from coal under various blending ratios; DTG profiles of CCB were different at several heating rates; interaction was observed between the solid phases of CCB; kinetic triplets were determined by the Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and master-plots method, respectively. The results provide a reference for further study on co-pyrolysis of microalgae and coal to a certain extent.