A suspension of microcystis aeruginosa (30 μg L−1chlorophyll a) was circulated in a hydrodynamic cavitation device and ozone was introduced at the suction side of the pump. The removal of algae over 10 min using hydrodynamic cavitation alone and ozone alone is less than 15% and 35% respectively. The destruction of algae rises significantly from 24% in the absence of the orifice to 91% with the optimized orifice on 5 min of processing using hydrodynamic cavitation along with ozone (HC/O3) and the utilization of ozone increases from 32% to 61%. Interestingly, the suction process is more effective than the extrusion method (positive pressure) and the optimal bulk temperature for algal elimination was found to be 20 °C. Increasing the input concentration of ozone is favorable for the removal of algae but leads to a greater loss of ozone and a decrease in the utilization of ozone. Under the optimal conditions, the algal cells and chlorophyll a are completely destroyed in 10 min by use of the hybrid method.
Highly unsaturated fatty acids like EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid) and AA (arachidonic acid) are essential in the development, growth, and physiological activities of aquaculture organisms. Microalgae are important main sources of EPA and DHA. In this study, the effect of mixed microalgal diets on the growth and fatty acid profile of European oyster (Ostrea edulis) juveniles was determined. The juvenile oysters (3.80 ± 0.15 g; 8.33 ± 0.10 mm) were cultured in 15 L static tanks with three replicates for the following treatments or microalgal combinations: Chaetoceros muelleri and Isochrysis galbana (CHGRA/T.ISO); Tetraselmis striata and Thalassiosira weissfloggii (TETRA/ACTIN); and Nannochloropsis oculata and Pavlova lutheri (NANNO/PAV). Juvenile oysters were fed microalgal diets daily at 10% of their body weight. The culture conditions for the oysters were 31.1 ± 0.4 psu, 16.3 ± 0.2 °C, and 8.9 ± 0.3 ppm D.O. After 6 weeks of culturing the oysters, a very highly significant difference (P < 0.001) was found in the growth rate. The best growth rate (final weight = 9.73 ± 0.89 g; final shell length = 13.48 ± 0.35 mm) was observed in NANNO/PAV treatment. The lowest growth rate (6.15 ± 0.25 g; 10.47 ± 0.18 mm) was in TETRA/ACTIN diet. EPA, DHA, and AA values of oyster were significantly higher in NANNO/PAV treatment but lowest in TETRA/ACTIN treatment (P < 0.001). The best diet in culturing European oyster juveniles was the mixture of Nannochloropsis oculata and Pavlova lutheri by providing better growth rates and higher levels of PUFAs.
This paper develops a hedonic pricing model for post-extracted algae residue (PEAR), which can be used for assessing the economic feasibility of an algal production enterprise. Prices and nutritional characteristics of commonly employed livestock feed ingredients are used to estimate the value of PEAR based on its composition. We find that PEAR would have a value lower than that of soybean meal in recent years. The value of PEAR will vary substantially based on its characteristics. PEAR could have generated algal fuel co-product credits that in recent years would have ranged between $0.95 and $2.43 per gallon of fuel produced.
Algae biomass residue was co-digested with lipid-rich fat, oil, and grease waste (FOG) to evaluate the effect on methane yield and macronutrient degradation. Co-digestion of algae biomass residue and FOG, each at 50% of the organic loading, allowed for an increased loading rate up to 3g VS/Ld, resulting in a specific methane yield of 0.54 L CH(4)/g VSd and a volumetric reactor productivity of 1.62 L CH(4)/Ld. Lipids were the key contributor to methane yields, accounting for 68-83% of the total methane potential. Co-digestion with algae biomass residue fractions of 33%, 50%, and 67% all maintained lipid degradations of at least 60% when the organic loading rate was increased to 3g VS/Ld, while synergetic effects on carbohydrate and protein degradation were less evident with increased loading.
This investigation examined the effects of the inorganic carbon concentration (4, 0.8 and 0 g/L NaHCO(3)) on the carbon formation, nitrate utilization, growth and fatty acids compositions of Nannochloropsis oculata. The dissolved inorganic carbon (DIC) concentration in the three treatments decreased sharply during the first 6 days, and the percentage of dissolved organic carbon (DOC) (% of total organic carbon (TOC)) decreased with the depletion of the DIC. The NO(3)(-) assimilation of the algae was correlated with the DIC concentration. The algae in the highest DIC treatment had the highest specific grow rate (0.0843 d(-1)) (P<0.0001), and their biomass and fatty acid methyl esters (FAME) productivity were 84.00 and 9.69 mg/L/d, respectively (P<0.0001). Contents of C16 and C18 series (% of FAME) were high and the C16:0 increased with the decrease of C18:1 during the cultivation. The iodine value (IV) of the algae was low at the low DIC media.
Acetone, butanol, and ethanol (ABE) fermentation by Clostridium saccharoperbutylacetonicum N1-4 using wastewater algae biomass as a carbon source was demonstrated. Algae from the Logan City Wastewater Lagoon system grow naturally at high rates providing an abundant source of renewable algal biomass. Batch fermentations were performed with 10% algae as feedstock. Fermentation of acid/base pretreated algae produced 2.74 g/L of total ABE, as compared with 7.27 g/L from pretreated algae supplemented with 1% glucose. Additionally, 9.74 g/L of total ABE was produced when xylanase and cellulase enzymes were supplemented to the pretreated algae media. The 1% glucose supplement increased total ABE production approximately 160%, while supplementing with enzymes resulted in a 250% increase in total ABE production when compared to production from pretreated algae with no supplementation of extraneous sugar and enzymes. Additionally, supplementation of enzymes produced the highest total ABE production yield of 0.311 g/g and volumetric productivity of 0.102 g/Lh. The use of non-pretreated algae produced 0.73 g/L of total ABE. The ability to engineer novel methods to produce these high value products from an abundant and renewable feedstock such as algae could have significant implications in stimulating domestic energy economies.
This study demonstrates the utility of rare-earth metal triflate catalysts (i.e., Sc(OTf)(3) and In(OTf)(3)) in the (trans)esterification of oleic acid as well as the lipids contained within carbonized algal biomass using ethanol in the presence of water. Both catalysts are highly active between 200 and 235°C with an ethanol:fatty acid (EtOH:FA) molar ratio of 10-20:1 and showed a high tolerance for moisture. Lipids within hydrochars produced by reacting Chlorella protothecoides paste (25% solids) in high temperature water (220-250°C) were successfully converted into fatty acid ethyl esters (FAEE). The highest FAEE yields (85-98%) were obtained when hydrochars were reacted for 60 min at 215°C with about 11-13 mol% Sc(OTf)(3), a 17-19:1 EtOH:FA molar ratio, and without water. FAEE yields remained as high as 93% in the presence of 9 wt.% water. Our preliminary results warrant further work to optimize triflate-catalyzed in situ (trans)esterification at low catalyst and ethanol loadings.
Green microalgae have recently drawn attention as promising organisms for biofuel production; however, the question is whether they can grow sufficient biomass relative to limiting input factors to be economically feasible. We have explored this question by determining how much biomass the green microalga Chlorella vulgaris can produce in photobioreactors based on highly efficient light-emitting diodes (LEDs). First, growth results were improved under the less expensive light of 660-nm LEDs, developing them in the laboratory to meet the performance levels of the traditional but more expensive 680-nm LEDs by adaptive laboratory evolution (ALE). We then optimized several other key parameters, including input superficial gas velocity, CO(2) concentration, light distribution, and growth media in reference to nutrient stoichiometry. Biomass density thereby rose to approximately 20 grams dry-cell-weight (gDCW) per liter (L). Since the light supply was recognized as a limiting factor, illumination was augmented by optimization at systematic level, providing for a biomass productivity of up to 2.11 gDCW/L/day, with a light yield of 0.81 gDCW/Einstein. These figures, which represent the best results ever reported, point to new dimensions in the photoautotrophic performance of microalgal cultures.
In this study, 97 microalgal strains purchased from algae bank and 50 microalgal strains isolated from local waters in Minnesota were screened for their adaptability growing on a 20-fold diluted digested swine manure wastewater (DSMW). A pool of candidate strains well adapted to the DSMW was established through a high-throughput screening process. Two top-performing facultative heterotrophic strains with high growth rate (0.536 day(-1) for UMN 271 and 0.433 day(-1) for UMN 231) and one strain with high omega-3 unsaturated fatty acid (EPA, 3.75 % of total fatty acids for UMN 231) were selected. Subsequently, a sequential two-stage mixo-photoautotrophic culture strategy was developed for biofuel and animal feed production as well as simultaneous swine wastewater treatment using above two strains. The maximal biomass concentration and lipid content at the first and second stages reached 2.03 g/L and 23.0 %, and 0.83 g/L and 19.0 % for UMN 271 and UMN 231, respectively. The maximal nutrient removals for total phosphorus and ammonia after second-stage cultivation were 100 and 89.46 %, respectively. The experiments showed that this sequential two-stage cultivation process has great potential for economically viable and environmentally friendly production of both renewable biofuel and high-value animal feed and at the same time for animal wastewater treatment.
In recent years, the not too distant exhaustion of fossil fuels is becoming apparent. Apart from this, the combustion of fossil fuels leads to environmental concerns, the emission of greenhouse gases and issues with global warming and health problems. Production of biodiesel from microalgae may represent an attractive solution to the above mentioned problems, and can offer a renewable source of fuel with fewer pollutants. This review presents a compilation of engineering challenges related to microalgae as a source of biodiesel. Advantages and current limitations for biodiesel production are discussed; some aspects of algae cells biology, with emphasis on cell wall composition, as it represents a barrier for fatty acid extraction and lipid droplets are also presented. In addition, recent advances in the different stages of the manufacturing process are included, starting from the strain selection and finishing in the processing of fatty acids into biodiesel.
Microalgae can be converted to an energy-dense bio-oil via pyrolysis; however, the relatively high nitrogen content of this bio-oil presents a challenge for its direct use as fuels. Therefore, hydrothermal pretreatment was employed to reduce the N content in Nannochloropsis oculata feedstock by removing proteins without requiring significant energy inputs. The effects of reaction conditions on the yield and composition of pretreated algae were investigated by varying the temperature (150-225°C) and reaction time (10-60min). Compared with untreated algae, pretreated samples had higher carbon contents and enhanced heating values under all reaction conditions and 6-42% lower N contents at 200-225°C for 30-60min. The pyrolytic bio-oil from pretreated algae contained less N-containing compounds than that from untreated samples and the bio-oil contained mainly (44.9% GC-MS peak area) long-chain fatty acids (C14-C18) which can be more readily converted into hydrocarbon fuels in the presence of simple catalysts.
The influence of monoethanolamine (MEA) as a CO(2) absorbent on photoautotrophic culture of CO(2)-fixing microalgae was investigated. When 300ppm MEA (4.92mM) was added to blank culture medium, the dissolved inorganic carbon and the molar absorption ratio increased to 51.0mg/L and 0.34 [Formula: see text] , respectively, which was an almost 6-fold increase in CO(2) solubility. When free MEA up to 300mg/L was added to a green alga Scenedesmus sp. culture that was supplied 5% (v/v) CO(2) at 0.1vvm, both cell growth rate and final cell density were enhanced compared to when no MEA was added. The cell growth rate reached 288.6mg/L/d, which was equivalent to 539.6mg-CO(2)/L/d as a CO(2)-fixation rate and enhancement of about 63.0% compared to not adding MEA. Chlorophyll-a content and nitrate consumption rate increased correspondingly. MEA doses higher than 400mg/L inhibited cell growth, probably due to toxicity of the carbamate intermediate.
Currently, microalgae draw much attention as a promising source of natural antioxidants to replace synthetic antioxidants for food applications. In this paper, the use of voltammetric techniques as a fast alternative for chemical assays to determine the antioxidant power of microalgal biomass is discussed. It was found that antioxidant activities determined by square wave voltammetry correlate well with the results from other established antioxidant assays, such as Trolox equivalent antioxidant capacity (R(2) = 0.737), ferric reducing antioxidant potential (R(2) = 0.729), and AAPH-induced oxidation of linoleic acid (R(2) = 0.566). Besides yielding quantitative data on the antioxidant activity, square wave voltammetry provides additional information on the antioxidant profile of microalgal biomass as the peak potentials of antioxidant components are determined. Consequently, square wave voltammetry can be used as a tool for optimizing the extraction processes to recover antioxidant components from microalgae.
Herein is described a green and original alternative procedure for the extraction of oil from microalgae. Extractions were carried out using terpenes obtained from renewable feedstocks as alternative solvents instead of hazardous petroleum solvents such as n-hexane. The described method is achieved in two steps using Soxhlet extraction followed by the elimination of the solvent from the medium using Clevenger distillation in the second step. Oils extracted from microalgae were compared in terms of qualitative and quantitative determination. No significant difference was obtained between each extract, allowing us to conclude that the proposed method is green, clean and efficient.
Violaxanthin is a major carotenoid of microalgae Chlorella ellipsoidea and is also found in dark-green leafy vegetables, such as spinach. In this study, the anti-inflammatory effect of violaxanthin isolated from C. ellipsoidea was examined using lipopolysaccharide (LPS)-stimulated RAW 264.7 mouse macrophage cells. In addition, the anti-inflammatory activity and mechanism of action of purified violaxanthin was assessed using various assays, such as quantitative real-time polymerase chain reaction (PCR), Western blotting, and electrophoretic-mobility shift assay (EMSA). The results of this combined analysis revealed that violaxanthin significantly inhibited nitric oxide (NO) and the prostaglandin E2 (PGE2). Interestingly, violaxanthin effectively inhibited LPS-mediated nuclear factor-κB (NF-κB) p65 subunit translocation into the nucleus, suggesting that the violaxanthin anti-inflammatory activity may be based on inhibition of the NF-κB pathways. In conclusion, violaxanthin of C. ellipsoidea holds promise for use as a potential anti-inflammatory agent for either therapeutic or functional adjuvant purposes.
Application of photosynthetic micro-organisms, such as cyanobacteria and green algae, for the carbon neutral energy production raises the need for cost-efficient photobiological processes. Optimization of these processes requires permanent control of many independent and mutably dependent parameters, for which a continuous cultivation approach has significant advantages. As central factors like the cell density can be kept constant by turbidostatic control, light intensity and iron content with its strong impact on productivity can be optimized. Both are key parameters due to their strong dependence on photosynthetic activity. Here we introduce an engineered low-cost 5L flat-plate photobioreactor in combination with a simple and efficient optimization procedure for continuous photo-cultivation of microalgae. Based on direct determination of the growth rate at constant cell densities and the continuous measurement of O(2) evolution, stress conditions and their effect on the photosynthetic productivity can be directly observed.
The profiles of carotenoids and production of β-carotene by six eustigmatophytes, Eustigmatos magnus, Eustigmatos polyphem, Eustigmatos vischeri, Vischeria helvetica, Vischeria punctata and Vischeria stellata, grown in a bubble column photobioreactor were measured. All eustigmatophytes contained β-carotene, violaxanthin and vaucheriaxanthin as their major carotenoids and accumulated large amount of β-carotene, which accounted for over 50 % of total carotenoids. Maximum intracellular β-carotene contents ranged 1.5-3.5 % of dry wt and in V. stellata it reached 5.9 % dry wt, accompanied by a biomass dry wt >7.3 g/l, with the highest up to 9.8 g/l. These eustigmatophytes are thus promising producers of β-carotene.
Green microalgae for several decades have been produced for commercial exploitation, with applications ranging from health food for human consumption, aquaculture and animal feed, to coloring agents, cosmetics and others. Several products from green algae which are used today consist of secondary metabolites that can be extracted from the algal biomass. The best known examples are the carotenoids astaxanthin and β-carotene, which are used as coloring agents and for health-promoting purposes. Many species of green algae are able to produce valuable metabolites for different uses; examples are antioxidants, several different carotenoids, polyunsaturated fatty acids, vitamins, anticancer and antiviral drugs. In many cases, these substances are secondary metabolites that are produced when the algae are exposed to stress conditions linked to nutrient deprivation, light intensity, temperature, salinity and pH. In other cases, the metabolites have been detected in algae grown under optimal conditions, and little is known about optimization of the production of each product, or the effects of stress conditions on their production. Some green algae have shown the ability to produce significant amounts of hydrogen gas during sulfur deprivation, a process which is currently studied extensively worldwide. At the moment, the majority of research in this field has focused on the model organism, Chlamydomonas reinhardtii, but other species of green algae also have this ability. Currently there is little information available regarding the possibility for producing hydrogen and other valuable metabolites in the same process. This study aims to explore which stress conditions are known to induce the production of different valuable products in comparison to stress reactions leading to hydrogen production. Wild type species of green microalgae with known ability to produce high amounts of certain valuable metabolites are listed and linked to species with ability to produce hydrogen during general anaerobic conditions, and during sulfur deprivation. Species used today for commercial purposes are also described. This information is analyzed in order to form a basis for selection of wild type species for a future multi-step process, where hydrogen production from solar energy is combined with the production of valuable metabolites and other commercial uses of the algal biomass.