Research into the development of renewable and sustainable fuels has been a major concern during last decades. Microalgae, as a potential resource, have gained great attention for energy purposes. In this context, anaerobic digestion seems to be the most direct energy generation process. Nevertheless, the efficiency of this process is hampered due to the hard cell wall of some microalgae. In order to enhance its anaerobic biodegradability, the present research investigated the effect of thermal pretreatment at two temperatures (70 and 90 °C) applied to Scenedesmus biomass. No differences were detected in terms of organic matter or ammonium release upon the two tested temperatures. Nevertheless, a different fact was observed for their anaerobic biodegradability. While raw and pretreated at 70 °C microalgae attained 22–24% anaerobic biodegradability, microalgae pretreated at 90 °C achieved anaerobic biodegradability of 48%. Even though similar profiles were obtained for both temperatures along the pretreatment period, the damage caused in the cell wall at 90 °C seemed to be greater and rendered this substrate readily degradable for anaerobic digestion.
A photobioreactor was designed to evaluate the performance of anewly isolated thermo-tolerant microalga Desmodesmus sp. F2 in municipal wastewater under tropical outdoor conditions. The environmental parameters, levels of nutrients, and growth rates were monitored during the cultivations to elucidate the factors that contributed to accelerated growth after lag phase.Cultures bubbled with CO2-air had about 20% higher yields than the air-bubbled culture, and 2% of CO2 at a flux rate of 5 L/min was sufficient to reach this increased yield. In the cultures bubbled with CO2-air, the microalgal cells preferentially utilized ammonium and nitrate, while the air-bubbledculture made greater useof ammonium and organic nitrogen. In conclusion, the factors required for microalga Desmodesmus sp. F2toachieve accelerated growth in tropical outdoor conditions include (1) 2% CO2 bubbling; (2) a level of ammonium higher than 100 μM; and (3) a level of nitrate higher than 400 μM.
The advantages and drawbacks of dynamic filtration are discussed and currently available industrial filtration modules are presented. Since membrane shear rates are the key factor governing their performance, three equations are given to calculate the shear rates of various modules, with disks rotating near fixed membranes, rotating membranes on a single shaft and vibrating membranes such as in the VSEP. Recent applications taken from the literature confirm the large gains relatively to crossflow filtration in permeate flux and membrane selectivity, owing to large reductions in cake formation and concentration polarization. One of the advantages of this technology is that, with rotating membranes, it gives a choice between increasing the flux by factor of 3–5 as compared to crossflow filtration by using high rotation speeds or obtaining the same flux at low speed, but with a large energy saving. The power consumed by vibrations in large industrial VSEP units is small, owing to the use of resonance frequency.
Filtration separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was studied using a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane. Coagulation using chitosan effectively removed turbidity at >100 mg l−1 chitosan. The membrane filtration flux at 1 bar was increased with chitosan dose. The filtered cake at the end of filtration tests peaked in solid content at 100 mg l−1 chitosan, reaching 30.5% w/w, about 50% higher than that of the original suspension. Coagulation using 100 mg l−1 chitosan followed by PTFE membrane filtration at 1 bar is a feasible process to harvest C.vulgaris from the algal froth.
Cultivating microalgae at industrial scale for biodiesel production required substantial amount of mineral fertilizer, typically nitrogen and phosphorus. In fact, the production of mineral fertilizer implies the usage of energy and fossil fuels resulting to unsustainable practise in a long term. On the other hand, organic fertilizer which is derived from food waste, biomass or manure also contains high value of nutrients that can support microalgae growth. Hence, in the present study, the potential of using organic fertilizer as an alternative nutrient source to cultivate Chlorella vulgaris was investigated. Under the supplement of organic nutrients, it was found that C. vulgaris grown favourably under the following conditions: initial nitrate content of 26.67 mg/L, 24 h of continuous illumination and pH of 5. Nevertheless, slow growth rate was observed when cultivating C. vulgaris under open environment; a reduction of 27% was recorded in comparison with controlled environment. On the other hand, it was possible to reutilize the water to re-cultivate C. vulgaris. This observation reflects the high adaptability of C. vulgaris towards the surrounding environment and suitability to be grown under outdoor conditions. Total lipid of 18.1% from C. vulgaris biomass was successfully extracted and the fatty acids methyl ester profile was proven to be suitable for making biodiesel.
The crude polysaccharides of Laminaria japonica (LP) were extracted with the optimal conditions as follows: raw materials to water 1:50 (w/v), extraction temperature 60 °C and extraction time 60 min. Trypsinase (6 U/ml) in combination with sevag reagent was beneficial to the removal of proteins from crude LP. Three fractions of LP1, LP2 and LP3 were obtained from the crude LP by using a final concentration of 40%, 60% and 80% ethanol to precipitate in turn. The three fractions showed obvious differences in monosaccharide compositions, molecular weight distribution, viscosity, IR spectroscopy and glycosyl linkages. In comparison with the control group, crude LP at a dose of 400 mg/Kg/day caused a reduction in total serum cholesterol, triglyceridest, high density lipoprotein-cholesterol and low density lipoprotein-cholesterol in serum by 80.6%, 63.4%, 43.8% and 79.8%, respectively. Moreover, crude LP exhibited good potential of enhancing antioxidant enzyme activities in serum of atherosclerosis mice.
Zeaxanthin is a type of xanthophyll found in carotenoids, which is produced as a food supplement frequently used for human retinal protection. These works investigated growth rate and harvest of the sea water algal species of Nannochloropsis oculata (N. oculata) by in-door and out-door cultivations; stirred ultrasonic acetone extraction of zeaxanthin from; employed column fractionation to obtain zeaxanthin-rich elution; and then coupled it with supercritical carbon dioxide anti-solvent (SAS) precipitation to generate the highly pure submicron-sized zeaxanthin. The ultrasonic extract contained 38.2 mg/g of zeaxanthin and then the column elution fractionation increased the zeaxanthin content to 41% (410.3 mg/g) with a recovery of 82.3%. The SAS precipitation at 215 bar, 50 °C for 24 min of injection time enhanced the zeaxanthin content to 58% (582.4 mg/g) with a recovery of 67.2%. Experimental results showed that the amount of zeaxanthin increased with total SAS time and feed concentration had an effect of enlarging the precipitates due to agglomeration and accumulation. The SAS precipitation of the column purified algal solution demonstrated a production of micro/nano-sized lamellar particulates that contained high amounts of zeaxanthin.
Microalgae are currently receiving strong consideration as an advanced biofuel feedstock because of their theoretically high yield (gal/acre/year) in comparison to terrestrial vegetable oil feedstocks. Microalgal lipids can be readily converted into a variety of biofuels including fatty acid methyl esters (i.e. biodiesel) via transesterification or alkanes via hydroprocessing. In contrast to paraffinic fuels whose properties can be tailored for a specific application, the properties of algal methyl ester biodiesel are directly related to the fatty acid composition of the algal lipids. Several microalgae species that are suitable for large scale cultivation such as those in the genus Nannochloropsis produce lipids that contain long chain-polyunsaturated fatty acids (LC-PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These constituents have high value as co-products but are problematic in terms of biodiesel properties such as ignition quality and oxidative stability. The objective of this study was to examine the effect of varying levels of EPA and DHA on algal methyl ester fuel properties. Oxidative stability, Cetane Number, density, viscosity, bulk modulus, cloud point and cold filter plugging point were measured for algal methyl esters produced from various microalgae feedstocks as well as model algal methyl ester compounds formulated to match the fatty acid composition of Nannochloropsis sp., Nannochloropsis oculata and Isochrysis galbana subjected to varying levels of removal of EPA and DHA. The results suggest that removal of 50 to 80% of the LC-PUFA from Nannochloropsis-based methyl esters would be sufficient for meeting existing specifications for oxidative stability. However, higher levels of LC-PUFA removal from Nannochloropsis-based methyl esters would be required to produce fuels with acceptable Cetane Number. The removal of EPA and DHA was shown to have a detrimental effect on cold flow properties since the algal methyl esters are also high in fully saturated fatty acid content.
In this study, the effects of these carbon sources on cell growth and lipid accumulation of Scenedesmus quadricauda were investigated. Results showed that Scenedesmus quadricauda could grow on photoautotrophic, heterotrophic and mixotrophic modes. The lipid yield of Scenedesmus quadricauda was much lower in the culture containing NaHCO3 as only carbon source, while CO2 and glucose concentration significantly influenced cell yield and lipid accumulation in photoautotrophic and heterotrophic culture, respectively. Furthermore, lipid content of Scenedesmus quadricauda in mixotrophic culture (33.1% of cell dry weight) was much higher than that in photoautotrophic and heterotrophic cultivation (14%-28%). Therefore, upon comparing these three trophic modes, present results revealed mixotrophy was the optimal culture method for Scenedesmus quadricauda to produce lipid. Besides, it was a feasible and promising strategy to culture Scenedesmus quadricauda using starch wastewater as raw material, which could reduce chemical oxygen demand (COD) of wastewater and the cost of biodiesel production.
An approach based on energy gain was utilized to optimize algal cultivation in bubble columns. Net energy gain was estimated considering the energy input for mixing and providing carbon dioxide, and the energy that can be generated from the lipids extracted from the algal biomass. Energy input for sparging was minimized based on the gas-to-culture volume ratio and energy output from lipid production was maximized based on nitrate and CO2 levels. Sparging at a gas-to-culture volume ratio of 0.18 min-1 with CO2-enrichment of 0.5% and initial nitrate concentration of 1 mM was optimal for improving net energy gain with Nannochloropsis salina. Sparging with CO2-enriched air of 0.5% along with nitrogen starvation resulted in 50% more lipid productivity than sparging with ambient air.
Global warming, high-energy demand and availability of new technologies are amongst the factors catalyzing the search for alternative sources of energy. Currently, there is renewed interest in obtaining energy from wastes hitherto meant for disposal. Increased costs of disposal and their attendant problems of heavy environmental loading are some aspects making the disposal option unattractive. These wastes are sources of energy and among the several sources of generating this energy are the waste-to-energy (WTE) categories with potentials for useable fuel production. The WTE materials are mainly used domestic waste oils (UDWOs), municipal solid waste (MSW), agricultural and industrial wastes. However, the latter wastes are not attractive as they consist of innumerable hazardous contaminants. The UDWOs are arguably a safe and cost effective source of useable fuel. Their conversion offers the merits of a reduction in greenhouse gas emission (GHG), enhancing fuel diversification and a qualitatively comparable energy output to fossil diesel fuels. Thus, UDWOs could significantly contribute towards achieving the 2020 and 2030 goals of substituting approximately 20% and 30% of petro-diesel with biofuels in US and EU, respectively. Moreover, attaining the forecasted annual production rate of 227 billion liters of biofuel by most active stakeholders in the biodiesel industry could be easily achieved.
This review aims to analyse the performance of biodiesel fuels obtained from UDWO and to demonstrate the suitability of applying these fuels as substitutes to mineral diesel in various industries. Benefits of UDWO as a biodiesel feedstock were as well highlighted.
Quantification of total lipids is a necessity for any study of lipid production by microalgae, especially given the current interest in microalgal carbon capture and biofuels. In this study, we employed a simple yet sensitive method to indirectly measure the lipids in microalgae by measuring the fatty acids (FA) after saponification. The fatty acids were reacted with triethanolamine-copper salts (TEA-Cu) and the ternary TEA-Cu-FA complex was detected at 260 nm using a UV-visible spectrometer without any colour developer. The results showed that this method could be used to analyse low levels of lipids in the range of nano-moles from as little as 1 mL of microalgal culture. Furthermore, the structure of the TEA-Cu-FA complex and related reaction process are proposed to better understand this assay. There is no special instrument required and the method is very reproducible. To the best of our knowledge, this is the first report of the use of UV absorbance of copper salts with FA as a method to estimate lipids in algal cultures. It will pave the way for a more convenient assay of lipids in microalgae and can readily be expanded for estimating lipids in other biological systems.
An increasing number of investors is looking at algae as a viable source of biofuels, beside cultivation for human/animal feeding or to extract high-value chemicals and pharmaceuticals. However, present biomass productivities are far below theoretical estimations implying that a large part of the available photosynthetically active radiation is not used in photosynthesis. Light utilization inefficiency and rapid light attenuation within a mass culture due to high pigment optical density of wild type strains have been proposed as major limiting factors reducing solar-to-biomass conversion efficiency. Analysis of growth yields of mutants with reduced light-harvesting antennae and/or reduced overall pigment concentration per cell, generated by either mutagenesis or genetic engineering, could help understanding limiting factors for biomass accumulation in photobioreactor. Meanwhile, studies on photo-acclimation can provide additional information on the average status of algal cells in a photobioreactor to be used in modelling-based predictions. Identifying limiting factors in solar-to-biomass conversion efficiency is the first step for planning strategies of genetic improvement and domestication of algae to finally fill the gap between theoretical and industrial photosynthetic productivity.
In order to comply with criteria of green chemistry concepts and sustainability, a new procedure has been performed for solvent-free ultrasound-assisted extraction (UAE) to extract lipids from fresh Nannochloropsis oculata biomass. Through response surface methodology (RSM) parameters affecting the oil recovery were optimized. Optimum conditions for oil extraction were estimated as follows: i) 1000W ultrasonic power, ii) 30min extraction time and iii) biomass dry weight content at 5%. Yields were calculated by the total fatty acids methyl esters amounts analyzed by GC-FID-MS. The maximum oil recovery was around 0.21%. This value was compared with the one obtained with the conventional extraction method (Bligh and Dyer). Furthermore, effect of temperature on the yield was also investigated. The overall results show an innovative and effective extraction method adapted for microalgae oil recovery, without using solvent and with an enable scaling up.
The three-phase extraction process of olive oil yields highly contaminated wastewater (OMW). This waste is frequently dumped untreated either onto soil or into water sources. The biodegradation of this wastewater by the biomass production of microalgae was studied. The experiments were performed in stirred batch tank reactors on a laboratory scale using Scenedesmus obliquus, microalga tolerant to phenolic compounds. The culture medium was prepared with 2.5%, 5%, 10% and 20% OMW (v/v) in water. The experimental conditions were pH = 7.0, T = 298 K, 350 rpm and aeration 1 (v/v)/min with continuous illumination at an intensity of 298 μE m−2 s−1. Four additional comparative cultures were carried out: (1) 5% OMW without fat matter (WF); (2) 5% OMW pretreated with active carbon (WC); (3) synthetic mineral medium (RL); and (4) urban wastewater from the secondary treatment (UW). The maximum specific growth rates for the different cultures were μm = 0.037 ± 0.003 h−1 (10% OMW), μm = 0.04 ± 0.002 h−1 (WC), μm = 0.049 ± 0.001 h−1 (WF), μm = 0.048 ± 0.0 h−1 (RL) and μm = 0.052 ± 0.012 h−1 (UW). These results indicate that the fat content in the OMW and its dark colour are the main inhibitors factors of the growth of S. obliquus.
The aim of this work was to investigate anaerobic digestibility of algal bioethanol residue from saccharification and fermentation processes. A series of batch anaerobic digestion tests using saccharification and fermentation residue showed that the maximum methane yields of saccharification residue and fermentation residue were 239 L/kg VS (Volatile Solids) and 283 L/kg VS (Volatile Solids), respectively. Energy recovered by anaerobic digestion of the residue was 2.24 times higher than that from the ethanol produced in the main process. 5-HMF (5-hydroxymethylfurfural), a saccharification byproduct, could retard methanogenesis at over 3 g/L however, the inhibition was prevented by increasing cell biomass concentration. Anaerobic digestion of residue has the potential to enhance bioenergy recovery and environmental sustainability of algal bioethanol production.
The life cycle impacts were assessed for an integrated microalgal biodiesel production system that facilitates energy- and nutrient- recovery through anaerobic digestion, and utilizes glycerol generated within the facility for additional heterotrophic biodiesel production. Results show that when external fossil energy inputs are lowered through process integration, the energy demand, global warming potential (GWP), and process water demand decrease significantly and become less sensitive to algal lipid content. When substitution allocation is used to assign additional credit for avoidance of fossil energy use (through utilization of recycled nutrients and biogas), GWP and water demand can, in fact, increase with increase in lipid content. Relative to stand-alone algal biofuel facilities, energy demand can be lowered by 3–14 GJ per ton of biodiesel through process integration. GWP of biodiesel from the integrated system can be lowered by up to 71% compared to petroleum fuel. Evaporative water loss was the primary water demand driver.
The prevalence of allergic diseases such as asthma, atopic dermatitis, and allergic rhinitis has increased during the last two decades and contributed a great deal to morbidity and an appreciable mortality in the world. Until now, few novel efficacious drugs have been discovered to treat, control or even cure these diseases with a low adverse-effect profile. Meanwhile, glucocorticoids are still the mainstay for the treatment of allergic disease. Therefore, it is necessary to isolate novel anti-allergic agents from natural resources. Recently, marine algae have received much attention as they are a valuable source of chemically diverse bioactive compounds with numerous health benefit effects. This review focuses on anti-allergic agents derived from marine algae and presents an overview of their pharmaceutical potential in the treatment of allergic disorders.
Electrogenic activity of photo-bioelectrocatalytic /photo-biological fuel cell (PhFC) was evaluated in a mixotrophic mode under anoxygenic microenvironment using photosynthetic consortia as biocatalyst. An acetate rich wastewater was used as anolyte for harnessing energy along with additional treatment. Mixotrophic operation facilitated good electrogenic activity and wastewater treatment associated with biomass growth. PhFC operation documented feasible microenvironment for the growth of photosynthetic bacteria compared to algae which was supported by pigment (total chlorophyll and bacteriochlorophyll) and diversity analysis. Pigment data also illustrated the association between bacterial and algal species. The synergistic interaction between anoxygenic and oxygenic photosynthesis was found to be suitable for PhFC operation. Light dependent deposition of electrons at electrode was relatively higher compared to dark dependent electron deposition under anoxygenic condition. PhFC documented for good volatile fatty acids removal by utilizing them as electron donor. Bioelectrochemical behavior of PhFC was evaluated by voltammetric and chronoamperometry analysis.
This study investigated nitrogen and phosphorus assimilation and lipid production of microalgae in industrial wastewater. Two native strains of freshwater microalgae were evaluated their biomass growth and lipid production in modified BBM medium. Chlamydomonas sp. TAI-2 had better biomass growth and higher lipid production than Desmodesmus sp.TAI-1. The optimal growth and lipid accumulation of Chlamydomonas sp. TAI-2 were tested under different nitrogen sources, nitrogen and CO2 concentrations and illumination period in modified BBM medium. The optimal CO2 aeration was 5% for Chlamydomonas sp. TAI-2 to achieve maximal lipid accumulation under continuous illumination. Using industrial wastewater as the medium, Chlamydomonas sp. TAI-2 could remove 100% NH4+-N (38.4 mg/L) and NO3−-N (3.1 mg/L) and 33% PO43−-P (44.7 mg/L) and accumulate the lipid up to 18.4%. Over 90% of total fatty acids were 14:0, 16:0, 16:1, 18:1, and 18:3 fatty acids, which could be utilized for biodiesel production.