The supercritical water gasification (SCWG) of biomass for H(2) production is analyzed in terms of process development and energetic self-sustainability. The conceptual design of a plant is proposed and the SCWG process involving several substrates (glycerol, microalgae, sewage sludge, grape marc, phenol) is simulated by means of AspenPlus™. The influence of various parameters - biomass concentration and typology, reaction pressure and temperature - is analyzed. The process accounts for the possibility of exploiting the mechanical energy of compressed syngas (later burned to sustain the SCWG reaction) through expansion in turbines, while purified H(2) is fed to fuel cells. Results show that the SCWG reaction can be energetically self-sustained if minimum feed biomass concentrations of 15-25% are adopted. Interestingly, the H(2) yields are found to be maximal at similar feed concentrations. Finally, an energy balance is performed showing that the whole process could provide a net power of about 150kW(e)/(1000kg(feed)/h).
A green microalgae strain, Chlorococcum sp. was obtained from tropical freshwater in Indonesia. The effects of pH on growth, effects of salt, carbon dioxide level, nitrate, acetate, and photoperiod on biomass and lipid production were studied. The fatty acids composition was also investigated. This study shows that the strain had an optimum pH value for growth ranging from pH 8.0 to 8.5. The biomass concentration and lipid content were influenced by different concentrations of salt, CO(2) and nitrate. The lipid productivity ranged from 2 to 90.8mgL(-1)d(-1) in different mediums. The highest biomass concentration and total lipid content achieved were 1.75gL(-1) and 56% of dry weight, respectively. Moreover, the major fatty acid methyl esters were C16:0, C18:1, C18:2 and C18:3. The high lipid content and the fatty acid composition make the strain Chlorococcum sp. a potential resource for food, cosmetics and biodiesel
This study aims to understand the underlying reasons for the poor flotation response of marine microalgae. The flotation performance and hydrophobicity of a freshwater microalga (Chlorella sp. BR2) were compared to those of a marine microalga (Tetraselmis sp. M8) at different salinities in the presence of a cationic collector, tetradecyl trimethylammonium bromide. It was found that microalgal hydrophobicity played a more important role than salinity in determining the flotation performance
Microalgae have been considered as a promising feedstock for biofuels and greenhouse gas reduction. A low-cost harvesting technology without secondary contamination for down-stream extraction is a key requirement to make algal biofuel commercially viable. A novel harvesting method using ammonia as a flocculant to make the algal biomass settable was devised and studied. Another major advantage of this approach is that the ammonia added will be reused as fertilizer in the subsequent cultures. The results indicated that ammonia-induced flocculation led to more than 99% removal of algae at 12h. The OD(600) of algae growing in the ammonia-enriched flocculation medium treated with heating and CO(2) was 2 times than that of initial after 6days. These results suggested that this flocculation method was efficient, convenient and allowed the reuse of the flocculated medium, therefore providing an option for economic harvesting and cultivation of microalgae.
A novel green microalgae strain from Lake Fuxian has been isolated and identified as a potential feedstock for biodiesel production. The novel strain was named Monoraphidium sp. FXY-10 based on its morphological and genomic characterization. The lipid productivities, fatty acid profiles, and microalgae recovery efficiency (η(a)) of FXY-10 were investigated and compared under autotrophic and heterotrophic conditions. FXY-10 under autotrophic conditions exhibited a higher cellular lipid content (56.8%) than those under heterotrophic conditions (37.56%). However, FXY-10 growing under heterotrophic conditions exhibited more than 20-fold increase in lipid productivity compared with that under autotrophic conditions (148.74mgL(-1)d(-1) versus 6.88mgL(-1)d(-1)). Moreover, higher saturated and monounsaturated fatty acids (77.5%) of FXY-10 was obtained under heterotrophic culture conditions, suggesting its potential as a biodiesel feedstock. Gravity sedimentation was proposed as the harvesting biomass method based on the 97.9% microalgae recovery efficiency of heterotrophic cells after settling for 24h.
This study focuses on a scale-up procedure considering two vital parameters light energy and mixing for microalgae cultivation, taking Chlamydomonas reinhardtii as the model microorganism. Applying two stage hydrogen production protocol to 1L flat type and 2.5L tank type photobioreactors hydrogen production was investigated with constant light energy and mixing time. The conditions that provide the shortest transfer time to anaerobic culture (light energy; 2.96kJs(-1)m(-3) and mixing time; 1min) and highest hydrogen production rate (light energy; 1.22kJs(-1)m(-3) and mixing time; 2.5min) are applied to 5L photobioreactor. The final hydrogen production for 5L system after 192h was measured as 195±10mL that is comparable with the other systems is a good validation for the scale-up procedure.
Microalgae are a promising feedstock for sustainable biofuel production. At present, however, there are a number of challenges that limit the economic viability of the process. Two of the major challenges are the non-uniform distribution of light in photobioreactors and the inefficiencies associated with traditional biomass processing. To address the latter limitation, a number of studies have demonstrated organisms that directly secrete fuels without requiring organism harvesting. In this paper, we demonstrate a novel optofluidic photobioreactor that can help address the light distribution challenge while being compatible with these chemical secreting organisms. Our approach is based on light delivery to surface bound photosynthetic organisms through the evanescent field of an optically excited slab waveguide. In addition to characterizing organism growth-rates in the system, we also show here, for the first time, that the photon usage efficiency of evanescent field illumination is comparable to the direct illumination used in traditional photobioreactors. We also show that the stackable nature of the slab waveguide approach could yield a 12-fold improvement in the volumetric productivity.
Carbonic anhydrase II (CA II) can catalyze the reversible hydration reaction of CO(2) at a maximum of 1.4 × 10(6) molecules of CO(2) per second. The crude intracellular enzyme extract containing CA II was derived from Chlorella vulgaris. A successful CO(2) capture experiment with the presence of calcium had been conducted on the premise that the temperature was conditioned at a scope of 30-40 °C, that the biocatalyst-nurtured algal growth period lasted 3 days, and that pH ranged from7.5 to 8.5. Ions of K(+), Na(+), Ca(2+), Co(2+), Cu(2+), Fe(3+), Mg(2+), Mn(2+), and Zn(2+) at 0.01, 0.1, and 0.5 M were found to exhibit no more than 30 % inhibition on the residual activity of the biocatalyst. It is reasonable to expect that calcification catalyzed by microalgae presents an alternative to geological carbon capture and sequestration through a chain of fundamental researches carried on under the guidance of sequestration technology.
Microalgae are regarded as a potential biomass source for biofuel purposes. With regard to bioethanol production, microalgae seem to overcome traditional substrate drawbacks. Enzymatic activities are responsible for carbon allocation and hence for carbohydrate profiles. Enzyme activities may be manipulated by metabolic engineering; however, this goal may also be achieved by controlling environmental conditions of the culture system. We outline the key-enzymes as well as the main operational conditions applied to microalgae growth (inorganic nutrient supplementation, irradiance and temperature) that affect carbohydrate synthesis on microalgae and cyanobacteria. Normally, harsh conditions are needed for such a goal and thus, arrested microalgae growth may occur. Potential strategies to avoid arrested growth, while enhancing carbohydrate accumulation, were also pointed out in this review.
In order to maximize microalgae biomass production and reduce its overall costs, it is important to optimize inoculum conditions based on its physical and physiological characteristics. Chlorella sorokiniana cultures inoculated with inoculum at three different physiological stages (lag, exponential, and stationary) diluted to the same optical density were cultivated for 12 days under three different CO(2) concentrations (0.038, 5, or 10 % CO(2) v/v) and growth pattern and biomass production was observed. Samples inoculated with lag phase inoculum supplied with 5 % CO(2) achieved the maximum biomass production, whereas samples supplied with 0.038 % CO(2) never reached exponential growth. The better growth of samples inoculated with lag phase inoculum was attributed to its increased number of cells compared to the other two inocula.
ABSTRACT: Omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) provide significant health benefits and this has led to an increased consumption as dietary supplements. Omega-3 fatty acids EPA and DHA are found in animals, transgenic plants, fungi and many microorganisms but are typically extracted from fatty fish, putting additional pressures on global fish stocks. As primary producers, many marine microalgae are rich in EPA (C20:5) and DHA (C22:6) and present a promising source of omega-3 fatty acids. Several heterotrophic microalgae have been used as biofactories for omega-3 fatty acids commercially, but a strong interest in autotrophic microalgae has emerged in recent years as microalgae are being developed as biofuel crops. This paper provides an overview of microalgal biotechnology and production platforms for the development of omega-3 fatty acids EPA and DHA. It refers to implications in current biotechnological uses of microalgae as aquaculture feed and future biofuel crops and explores potential applications of metabolic engineering and selective breeding to accumulate large amounts of omega-3 fatty acids in autotrophic microalgae.
The main step of the production of L-aminoacids concentrates from microalgae is the enzymatic hydrolysis. This process has to be done at the optimum temperature and pH of the enzyme in order to obtain the maximum yield. In order to keep a constant pH, NaOH (1M) or H2SO4 (1M) are used, depending on the reaction step. When working with pH it is not possible to use the governing equations due to the complexity of the enzymatic hydrolysis. In this work, the modelling of pH is experimentally performed on a laboratory scale plant. Since the obtained model presents delay and uncertainty in the parameters, a Filtered Smith Predictor is proposed as control strategy. This control scheme has been tested in the real system. The Filtered Smith Predictor has reduced the Integral Absolute Error and the time for the solution addition in more than 25% and it has increased 5% the production of L-aminoacids compared to an on-off control, which is the controller most used in these processes.
A method for lactic acid production and lipid extraction from microalgae (Nannochloropsis salina) biomass was investigated. Microalgae biomass was acid (5% H2SO4) hydrolyzed at 120 ˚C for 1 h, and subsequently treated with hexane at 40 ˚C and 200 rpm to separate lipid from the hydrolysate. The sugar (glucose plus xylose) yield reached 64.3% and remained the same until the biomass loading of 15% (w/v) after which, it dropped. Lipid free hydrolysate was neutralized and used as fermentation medium for Lactobacillus pentosus for lactic acid production. Lactic acid yield reached 92.8% at sugar 3-25 g/l, 30 ˚C and shaking speed 150 rpm under anaerobic condition. The acid hydrolysis facilitated lipid extraction from microalgae biomass, and lipid yields with and without acid hydrolysis were 85.6 and 48.7%, respectively. Results suggest that the developed method can be successfully applied in lipid extraction and lactic acid production from microalgae biomass.
In this research, the mass transfer kinetics for the biosorption of synthetic dyes (acid blue 9 and FD&C red no. 40) by Spirulina platensis nanoparticles was analyzed under different experimental conditions. The external mass transfer model (EMTM) and the homogeneous solid diffusion model (HSDM) were employed to study the mass transfer kinetics and also to estimate the values of external mass transfer coefficient (kf) and intraparticle diffusion coefficient (Dint). The Biot number (Bi) was used to verify the importance of external mass transfer in relation to intraparticle diffusion. The values of external mass transfer coefficient (kf) ranged from 1.67 × 10−6 to 11.40 × 10−6 cm s−1 and the intraparticle diffusion coefficient (Dint) ranged from 0.70 × 10−14 to 4.30 × 10−14 cm2 s−1. The Biot numbers (0.53≤Bi≤10.33) showed that, for both dyes, the biosorption onto S. platensis nanoparticles was controlled simultaneously by external mass transfer and intraparticle diffusion.
The screening for high lipid producing microalgae is a crucial step to enable large scale cultivation of suitable microalgae as a means of alternative energy. The Bligh and Dyer method has been traditionally used for the determination of biofuel-related lipids. But, we found that this method also extracts chlorophyll, to result in significant over-estimation of biofuel-related lipid measures. In this work, we present and characterize a method to obviate the chlorophyll interference to biofuel-related lipid determination.
Coccolithophorid algae (Haptophycea) are mainly marine unicellular phytoplankton. The coccolithophorids are of global interest as they can fix carbon by photosynthesis as well as in calcium carbonate (coccoliths). They are the largest carbon sinks and one of the largest primary producers on the planet. They can also produce high amounts of lipids which have a high potential application as a renewable fuel and alternative food source. This paper reviews current knowledge on coccolithophorid algae photosynthesis and calcification and their potential industrial applications.
Some species of microalgae have high lipid yields; however, all species of microalgae, with the only known exception of Botryococcus braunii, have their lipids located inside the cells. The toughness of cell walls and cell membranes of microalgae makes the lipids not readily available for extraction and means that cell disruption an energy intensive process. The cell disruption energy required may become a critical consideration in the production of low valued commodities such as biofuels.
This study provides an overview of microalgal cell disruption processes which are potentially suitable for large scale lipid extractions. The energy requirements of these processes were calculated and then compared with estimates of the theoretical minimum energy required for disruption.
The results show that the mechanical disruption methods considered were highly energy inefficient when conducted under laboratory conditions and required a specific energy consumption of at least 33 MJ kg−1 of dry biomass. Thus the specific energy consumption is greater than the energy recoverable from the microalgae and is also a factor of 105 greater than that the estimated minimum theoretical energy consumption. This result clearly shows that further research and innovation is required for the sustainable cell disruption and lipid extraction from microalgae.
Crossflow microfiltration (MF) was successfully implemented for harvesting microalgae suspensions from a culture medium. In this study, investigations were carried out to harvest Chlorella sp. using a cellulose acetate (CA) membrane. Electrophoretic mobility profile during the cultivation process showed a maximum electronegative value of − 2.56 ± 0.07 μmcm/Vs on the 9th day of the experiment which were taken as a fresh cultures in each cultivation process. The effects of hydrodynamic conditions on the permeation flux are also discussed. The results show that the permeate flux increases with an increasing crossflow velocity (CFV) and transmembrane pressure (TMP). The flux is higher when the pressure is high, suggesting that the resistance of the membranes to mass transfer increases; hence, the applied pressure (driving force) has to be increased to obtain a higher flux. Furthermore, an increase in the CFV leads to a higher shear velocity, which makes it more difficult for microalgae to be deposited on the membrane, thus giving a better flux. The analysis of various resistances encountered in membrane filtration which involves the resistance of membrane itself and cake as well as those due to pore blocking and concentration polarization was studied. The experimental results obtained here show that the cake resistance (Rc) played a more major role in the filtration rate than the resistance due to concentration polarization (Rcp) and pore blocking (Rb) under the conditions examined. An increase in the CFV and a decrease in the TMP result in a reduction in the cake layer formation.
The use of molecular methods to investigate microalgal communities of natural and engineered freshwater resources is in its infancy, with the majority of previous studies carried out by microscopy. Inefficient or differential DNA extraction of microalgal community members can lead to bias in downstream community analysis. Three commercially available DNA extraction kits have been tested on a range of pure culture freshwater algal species with diverse cell walls and mixed algal cultures taken from eutrophic waste stabilization ponds (WSP). DNA yield and quality were evaluated, along with DNA suitability for amplification of 18S rRNA gene fragments by polymerase chain reaction (PCR). QiagenDNeasy ® Blood and Tissue kit (QBT), was found to give the highest DNA yields and quality. Denaturant Gradient Gel Electrophoresis (DGGE) was used to assess the diversity of communities from which DNA was extracted. No significant differences were found among kits when assessing diversity. QBT is recommended for use with WSP samples, a conclusion confirmed by further testing on communities from two tropical WSP systems. The fixation of microalgal samples with ethanol prior to DNA extraction was found to reduce yields as well as diversity and is not recommended.