In this study, we compared the performances of four different gas chromatography (GC) based microalgal fatty acid analysis methods that are typically applied to biorefinery research using wastewater-adapted microalgae. Compared with the HP-5-type non-polar column, WAX-type polar columns exhibited excellent abilities to quantitatively separate C16-C18 polyunsaturated fatty acids (PUFAs) from selected wastewater-adapted microalgae (Chlorella vulgaris, Ankistrodesmus gracilis and Scenedesmus quadricauda) isolates. GC-mass spectroscopy (MS) using the WAX-type polar column provided the strongest detection sensitivity among the tested methods by lowest detection limit, and GC-flame ionized detector (FID) with the same polar column exhibited nearly consistent results to GC-MS analysis. Our statistical comparison of microalgal fatty acid composition profiles generated using various GC methods, microalgal resources and culture media (wastewater, BG11 and nitrogen limitation) suggested that an appropriate GC method and algal resource choice are more important than the optimization of culture conditions to evaluate the applicability of microalgal biorefinery using wastewater resources.
The Renewable Fuel Standard (RFS2) under the Energy Independence and Security Act of 2007 requires 15.2 billion gallons of domestic alternative fuels per year by 2012, of which 2 billion gallons must be from advanced biofuel and emit 50% less life-cycle greenhouse gas (GHG) emissions than petroleum-based transportation fuels. Microalgal biodiesel, one type of advanced biofuel, has the qualities and potential to meet the RFS's requirement. A comparative life cycle assessment (LCA) of four microalgal biodiesel production conditions was investigated using a process LCA model with Monte Carlo simulation to assess global warming potential (GWP), eutrophication, ozone depletion and ecotoxicity potentials. The four conditions represent minimum and maximum production efficiencies and different sources of carbon dioxide and nutrient resources, i.e. synthetic and waste resources. The GWP results of the four CO2 microalgal biodiesel production conditions showed that none of the assumed production conditions meet the RFS's GHG requirement. The GWP results are sensitive to energy consumption in harvesting process. Other impacts such as eutrophication, ozone depletion and ecotoxicity potentials, are sensitive to percent lipid content of microalgae, service lifetime of PBRs and quantity of hexane in extraction process, respectively. Net energy ratio and other emissions should be included in future RFS for a more sustainable fuel.
The green alga Chlamydomonas reinhardtii has the ability to produce clean and renewable molecular hydrogen through the biophotolysis of water. Hydrogen production takes place under anaerobic conditions, which may be imposed metabolically by depriving the algae of sulphur. Sulphur-deprivation typically requires the spatial and temporal separation of the algal growth and hydrogen production stages. This would typically require separate photobioreactors for each stage as well as a costly and energy intensive medium exchange technique such as centrifugation, making the process difficult to scale up.
The aim of this paper is to show how these two stages are able to take place in a single reactor and hence eliminate the need for a separation step and for an additional reactor. To achieve this we have investigated the sulphate and acetate consumption and uptake rates during algal growth under different illumination conditions. The experiment has been repeated in various photobioreactor geometries in order to determine a reactor-independent relationship between the algal growth and nutrient consumption kinetics. Using this relationship, the initial sulphur and acetate concentrations of the algal medium have been optimised so that these nutrients run out at the exact moment when the maximum algal cell density is reached. This nutrient control method allows a fully-grown algal culture to enter spontaneous hydrogen production mode, eliminating the need for a medium separation technique and for an additional photobioreactor.
Hydrogen production rates and yields were measured by membrane-inlet mass spectrometry (MIMS) in a novel photobioreactor designed specifically to facilitate the green algal hydrogen production process. The nutrient control method of sulphur-deprivation has proven to be superior to the traditional methods of centrifugation and dilution. Hydrogen production by nutrient control reached a maximum rate of 1.30 ml/l/h and a yield of 112.7 ml/l, compared to maximum rates of 0.18 ml/l/h and 1.11 ml/l/h, and yields of 28.0 ml/l and 102.7 ml/l for the dilution and centrifugation methods, respectively. Nutrient control has been identified as the method of choice for green algal hydrogen production.
Crystallized silver nanoparticles (SNPs) have been biosynthesized by Spirulina platensis in an aqueous system. An aqueous solution of silver ions was treated with a live biomass of Spirulina platensis for the formation of SNPs. These nanoparticles showed an absorption peak at 430 nm in the UV-visible spectrum, corresponding to the plasmon resonance of SNPs. The transmission electron micrographs of nanoparticles in an aqueous solution showed the production of SNPs (average size of most particles: ∼12 nm) by Spirulina platensis. The X-Ray Diffraction (XRD) spectrum of the nanoparticles confirmed the formation of metallic silver, and the average size of the crystallite was estimated from the peak profile by the Scherrer method. The synthesized SNPs had an average size of 11.6 nm
As energy prices climb there is an increasing interest in alternative, renewable energy sources. One possible source of renewable bio-fuel is algae. This research uses a multi-year, Monte Carlo financial feasibility model to estimate the costs of production and chance of economic success for commercial size algal biofuel facilities in the Southwest. Capital and operating costs and productivity information from Davis et al. were used to develop parameters to define and simulate two types of algae production systems; open pond and photo-bioreactor (PBR).
The financial feasibility of PBRs is substantially lower than for open ponds. In the base case, average total costs of production for lipids, including financial costs, were $12.73/gal and $31.61/gal for open ponds and PBRs, respectively. The chance of economic success for the base situation was zero for both open ponds and PBRs. The financial feasibility analysis showed that the only way to achieve a 95% probability of economic success in the PBR system was to reduce CAPEX by 80% or more and OPEX by 90% or more. For the open pond system there were several options that could return a 95% or greater chance of economic success, for example, reducing CAPEX by 60% and OPEX by 90%.
Process variables affecting harvesting efficiency of Nannochloris oculata by AlCl3 flocculation such as, cell density, ionic strength, coagulant dosage, media pH, and cell surface charge were investigated. Initial cell density and coagulant dosage had a significant effect on the removal efficiency; however, levels of ionic strength tested were not significant. Best flocculation conditions of investigated variables were: 0.0016 ng of AlCl3/cell, 3.0 × 107 cell/mL, and pH 5.3. Removal efficiency at optimum conditions and salt concentrations of: 0, 15, and 30 g/L NaCl was 96, 98, and 97 %, respectively. Low cell density cultures ∼106 cell/mL, required five times greater AlCl3 dosage to achieve the same removal efficiency. Destabilization of algal cultures using 0.0032 ng of AlCl3/cell was observed by reducing the zeta potential to −22 mV. Acidification with HCl for conducting flocculation at pH 5.3 could be a significant cost burden unless is mitigated by selecting a low-buffering-capacity media.
The current interest in microalgae as a sustainable source of next generation biofuels and other valuable substances is driving exploration of their use as unique biotechnological production systems. To design and optimise appropriate production strategies, the behaviour of particular microalgal species should be well characterised under different culture conditions. Thus, flow cytometric (FCM) methods, which are already well established in environmental and toxicological studies of microalgae, are also useful for analysing the physiological state of microalgae, and have the potential to contribute to the rapid development of feasible bioprocesses. These methods are commonly based on the examination of intrinsic features of individual cells within a population (such as autofluorescence or size). Cells possessing the desired physiological or morphological features, which are detectable with or without fluorescent staining, are counted or isolated (sorted) using an FCM device. The options for implementation of FCM in the development of biotechnological processes detailed in this review are (i) analysing the chemical composition of biomass, (ii) monitoring cellular enzyme activity and cell viability, and (iii) sorting cells to isolate those overproducing the target compound or for the preparation of axenic cultures.
With the increasing concerns for global climate change, a sustainable, efficient and renewable energy production from wastewater is imperative. In this study, a novel microbial carbon capture cell (MCC), is constructed for the first time by the introduction of immobilized microalgae (Chlorella vulgaris) into the cathode chamber of microbial fuel cells (MFCs) to fulfill the zero discharge of carbon dioxide. This process can achieve an 84.8% COD removal, and simultaneously the maximum power density can reach 2485.35 mW m−3 at a current density of 7.9 A m−3 and the Coulombic efficiency is 9.40%, which are 88% and 57.7% greater than that with suspended C. vulgaris, respectively. These enhancements in performance demonstrate the feasibility of an economical and effective approach for the simultaneous wastewater treatment, electricity generation and biodiesel production from microalgae.
In this work, an on-line process for pressurised hot water extraction (PHWE) of antioxidants from plants as well as drying of the extract in one step by particle formation based on the use of supercritical carbon dioxide (SC-CO2) has been developed. This process has been called WEPO®, water extraction and particle formation on-line. With this process, dried extracts from onion with the same composition of quercetin derivatives as non-dried extracts have been obtained as a fine powder with spherical particles from 250 nm to 4 μm in diameter. The major compounds present in the extract were quercetin-3,4′-diglucoside, quercetin-4′-glucoside and quercetin. An auxiliary inert gas (hot N2) was used to enhance the drying process. Parameters such as temperature (120 °C), SC-CO2 and N2 pressures (80 and 12.5 bar, respectively) and flow rate of SC-CO2 (10 ml/min), have been settled by trial-and-error in order to achieve a fine and constant spray formation. Water content, size and morphology, antioxidant capacity and quercetin content of the particles were studied to evaluate the efficiency of the WEPO process. Results were compared with the ones from extracts obtained by continuous flow PHWE followed by freeze-drying. Results showed that both processes gave similar results in terms of antioxidant capacity, concentration of quercetin derivatives and water content, while only WEPO was able to produce defined spherical particles smaller than 4 μm.
Lipid-extracted microalgal biomass residues (LMBRs) were treated using cellulase, neutrase and alcalase in a two-step process and the resulting hydrolysates were used as a source of nutrients for the cultivation of Chlorella vulgaris under non-aerated and aerated conditions for lipid production. Aeration was favorable for cell growth and lipid accumulation and a biomass of approximately 3.28 g L−1, lipid content of 35% and lipid productivity of 116 mg L−1 d−1 were obtained. Thus, the tested mode of LMBRs utilization was effective for nutrient recycling in microalgal biodiesel production.
This paper explores the use of a novel microalgae membrane photoreactor (mMR) to polish the effluent from an aerobic membrane bioreactor (MBR) fed with domestic wastewater. Four microalgae species Chlorella (Chlorella sp.), Chlorella vulgaris (C. vulgaris), Scenedesmus quadricauda (S. quadricauda) and Scenedesmus dimorphus (S. dimorphus) were isolated from the environment and tested in batch reactors fed with permeate from the aerobic MBR to evaluate the nutrient removal rates for each species. All four microalgae species were able to completely remove NH4 in the reactor within 3 days. The removal rates of NO3, NO2 and PO4 were between 43–54%, 83–95% and 70–92%, respectively after 3 days in the batch reactor. Subsequently, an MBR–mMR system was operated for 23 days. The mMR was able to remove on average 50% of NH4, 75% of NO2, 35% of NO3 and 60% of PO4 consistently from the MBR effluent under the conditions tested.
To identify the alteration of the membrane potential and the effect of carotenoid extracts from Chlorococcum humicola (C. humicola) on membrane bound ATPases and lipid peroxidation.
The total carotenoids were extracted from C. humicola. Four groups of Swiss albino mice were treated as control, Benzo(a)pyrene [B(a)P], total carotenoids, B(a)P + total carotenoids respectively for a period of 60 days. Membrane lipid peroxidation and ATPases (Total ATPases, Ca2+ – ATPases, Mg2+ – ATPases, Na+ K+- ATPase) were determined in lung, liver and erythrocyte samples.
The activity of total ATPase was found to be significantly increased in the B(a)P treated liver and lung tissue. Erythrocyte membrane also showed higher ATPase activity which was significantly reverted on total carotenoid treatment.
It can be concluded that the changes in membrane potential favour the functional deterioration of physiological system. The overall findings demonstrates that the animals post treated with carotenoid extract fromC. humicola may maintains the alterations in membrane bound ATPase and lipid peroxidation in tissues against the carcinogenic chemical and hence aid in establishing the membrane potential action. Therefore C. humicola can be further extended to exploits its possible application for various health benefits as neutraceuticals and food additives.
Carbon dioxide (CO2) is one of the most important contributors for the increase of the greenhouse effect. CO2 concentrations are increasing in the last decades mainly due to the increase of anthropogenic emissions. To reduce the effects caused by this environmental problem, several technologies were studied to capture CO2 from large emission source points: (i) absorption; (ii) adsorption; (iii) gas-separation membranes; and (iv) cryogenic distillation. The resulting streams with high CO2 concentrations are transported and stored in geological formations. However, these methodologies, known as carbon capture and storage (CCS) technologies, are considered as short-term solutions, as there are still concerns about the environmental sustainability of these processes.
A promising technology is the biological capture of CO2 using microalgae. These microorganisms can fix CO2 using solar energy with efficiency ten times greater than terrestrial plants. Moreover, the capture process using microalgae has the following advantages: (i) being an environmental sustainable method; (ii) using directly the solar energy; and (iii) co-producing high added value materials based on biomass, such as human food, animal feed mainly for aquaculture, cosmetics, medical drugs, fertilizers, biomolecules for specific applications and biofuels. Approaches for making CO2 fixation by microalgae economically competitive in comparison with CCS methodologies are discussed, which includes the type of bioreactors, the key process parameters, the gaseous effluents and wastewater treatment, the harvesting methods and the products extracted by microalgal biomass.
It is often difficult to compare publications assessing the sustainability of algal biomass as a feedstock for biofuels, due to differences in data aggregation, life cycle boundaries, technical and life cycle assumptions, environmental metrics considered, and use of experimental, modeled or assumed data. Input data for the algae cultivation stage was collected from published studies, focusing on microalgae production in open-air raceway ponds. Input data was normalized to a consistent functional unit, 1 kg of dry algal biomass. Environmental impacts were applied consistently to the different study inputs in order to eliminate this source of variation between the studies. Greenhouse gas emissions, fossil energy demand, and consumptive freshwater use were tabulated for the algal feedstock growth stage for open pond systems, and results were categorized (energy use, macronutrient fertilizers, and everything else) to compare the different studies in general terms. Environmental impacts for the cultivation of algal biomass in the considered reports varied by over two orders of magnitude. To illustrate impacts of variability in the cultivation stage on the ultimate environmental footprint of microalgae biofuels, algal oil harvesting, extraction and conversion to Green Jet Fuel was examined using the Renewable Jet Fuel process developed by Honeywell's UOP.
Lipids obtained from Chlorella protothecoides in heterotrophic cultivation are considered a suitable feedstock for biodiesel production. In this study, glucose fed-batch fermentation was performed to increase final biomass and lipid production. The biomass productivity and lipid productivity were 6.28 and 2.06 g/L day, respectively. Biomass/glucose conversion and the lipid/glucose conversion were 43.3% and 14.2%, respectively. Extraction of lipids from algae has been identified as a key bottleneck in bioprocessing operations. Supercritical carbon dioxide (SC-CO2) was applied for neutral lipids extraction and the SC-CO2 kinetics was investigated by the Goto et al. model. The modeling showed a good fit with experimental data. Additionally, neutral lipids extracted by SC-CO2 displayed a suitable fatty acid profile for biodiesel [mainly C18:1 (60.0%), C18:2 (18.7%) and C16:0 (11.5%)]. Our study demonstrated the ability to produce high levels of neutral lipids through heterotrophic algal culture and subsequent extraction of lipids with SC-CO2 method developed.
Among many challenges faced in the commercial cultivation of microalgae, low-cost water and nutrients availability is crucial. Our study aimed at testing and optimizing two agro-industrial co-products, dry-grind ethanol thin stillage (TS) and soy whey (SW), as nutrient feedstock for mixotrophic/heterotrophic microalgal cultivation. Heterotrophic growth of Chlorella vulgaris was first optimized in a Bioscreen turbidimeter and 250 mL Erlenmeyer flasks, then scaled up to a 6-L stirred bioreactor. Intracellular oil was extracted from dried microalgal biomass by ultrasonication and solvent extraction treatments for yield comparison, and fatty acid (FA) profile. Biomass yields (dry basis) from TS, SW and modified basal medium (MBM) after 4 days of incubation at mixotrophic conditions in the bioreactor were 9.8, 6.3 and 8.0 g.L− 1 with oil content at 43, 11, and 27% (w/w) respectively. FA profile of oil samples was found to vary and depend on growth media characteristics. C. vulgaris when grown on TS and MBM produced oil richer in linoleic and linolenic acids, respectively. This research highlights the potential of two agro-industrial co-products as microalgal growth media with consequent production of high-value microalgal oil and biomass.
Flue gases are a resource yet to be fully utilised in microalgal biotechnology, not only to moderate the anthropogenic effects on our climate, but also to steer microalgal resource management towards innovative applications of microalgal biomass compounds. These gases, both untreated and treated into current discharge standards, contain CO2, N2, H2O, O2, NOx, SOx, CxHy, CO, particulate matter, halogen acids and heavy metals. To better steer and engineer flue gas-fed microalgal cultures, all these compounds need to be considered. Therefore, here, we review (i) the chemical composition and treatment technologies of flue gas, (ii) the uptake pathways and removal of the different compounds in microalgae reactors, and (iii) the tolerance and effects on microalgae of all flue gas compounds. By emphasising the interactions between microalgae and flue gas compounds, we envisage new pathways for microalgal biomass valorisation such as enzyme production for environmental technology, novel biogas production and biosequestration of minerals. Furthermore, we highlight fundamental and applied research niches that merit further investigation.
The freshwater microalga Neochloris oleoabundans was used to study algal lipid production in enriched natural seawater, in order to assess its suitability as biodiesel feedstock. Optimal and nitrogen-stress (N-stress) conditions were analyzed. Under optimal conditions, the strain’s growth rate was 0.73 div day−1 and the biomass concentration was 1.5 g L−1, while it had a maximum lipid yield under N-stress conditions (lipid content: 26% of dry weigh and lipid productivity: 56 mg L−1 day−1). Lipid accumulation was mainly due to a significant increase of triacylglycerol content. Neutral lipids were characterized by a dominance of monounsaturated fatty acids and displayed a fatty acid profile that is suitable for biodiesel. This work offers an interesting alternative for sustainable microalgal oil synthesis for biodiesel production without using freshwater resources. However, further studies are necessary in order to optimize the lipid productivities required for commercial biodiesel production.
Nannochloropsis sp. F&M-M24 and Tetraselmis suecica F&M-M33 were cultivated outdoors in Green Wall Panels under nutrient deficiency to stimulate oil synthesis. Under nitrogen deprivation, Nannochloropsis attained average biomass and lipid productivities of 9.9 and 6.5 g m−2 day−1, respectively. Starved Tetraselmis cultures achieved a biomass productivity of about 7.6 g m−2 day−1 and a lipid productivity of 1.7 g m−2 day−1. Lipids represented 39.1% and 68.5% of non-starved and starved Nannochloropsis biomass, respectively. Starvation did not increase lipid content in Tetraselmis biomass. Important differences in lipid classes and in fatty acid composition were observed under the different cultivation conditions for both microalgae.