Autotrophic Microalgae Research Articles

Effect of carbon dots supplementation in Chlorella vulgaris biomass production and its composition

Microalgae cultures have an excellent ability to capture CO2 and produce high, medium, and low valuable biocompounds such as proteins, carbohydrates, lipids, pigments, and polyhydroxyalkanoates; those compounds have shown excellent properties in the pharmaceutical, cosmetic, food, and medical industries. Recently, the supplementation of carbon dots (CDs) in autotrophic microalgae cultures has been explored as a new strategy to increase light capture and improve photoluminescence, which in turn enhances biomass growth and biocompounds production. In this work, we synthesized CDs through a simple carbonization method using orange juice as a natural precursor. The green synthesized CDs were analyzed in detail through characterization techniques such as Fourier-transform infrared spectroscopy (FTIR), UV–visible, fluorescence spectroscopy, and ζ potential analysis. Moreover, CDs were added to Chlorella vulgaris to analyze the response under different photoperiod cycles and CDs dosages. The optimal results were obtained with the addition of 0.5 mg l−1 of CDs under a photoperiod cycle of 16 h:8 h (light:dark). In these conditions, a maximum biomass production of 2.12 g l−1 was observed, which represents an enhancement of 112% and 17% in comparison to the control samples under the photoperiod of 12 h:12 h and 16 h:8 h (light/dark), respectively. Furthermore, the production of lipids, proteins, and carbohydrates was significantly increased to 249 mg g−1, 285 mg g−1, and 217 mg g−1 dry weight, respectively. These results suggest that the addition of CDs enhances cell growth and increases the production of lipids and proteins, being a strategy with great potential for the food and pharmaceutical industries.

Direct extracellular electron transfer for high electricity production by a new type of marine microalgae Nannochloropsis sp. HDY2

A growing number of autotrophic microalgae have been found to have extracellular electron transfer (EET) capabilities. However, the mechanism and function of EET pathway in microalgae have not thoroughly investigated. This study presents evidence of direct extracellular electron transfer (DEET) for impressive electricity production by a new type of marine microalgae Nannochloropsis sp. HDY2 in the single and double-chamber photosynthetic microbial fuel cells (PFMCs). The electricity generation of Nannochloropsis sp. is strongly inhibited by photosynthetic inhibitors, suggesting that electrons involved in the extracellular electron transfer (EET) of Nannochloropsis sp. are derived from photosynthesis. The results of dialysis bag and supernatant experiments suggest that Nannochloropsis sp. produce electricity by DEET. The lack of typical redox peaks in cyclic voltammetry (CV) analysis and the appearance of extracellular filamentous component (EFC) around cells support this finding. Under high light conditions, the chlorophyll a and carotenoid content of Nannochloropsis sp. rapidly decreased while the fatty acid synthesis and electricity generation increased, suggesting that the DEET pathway play an active role in the resistance to photooxidation of Nannochloropsis sp. This study provides the first evidence that Nannochloropsis has the capability of performing EET and sheds new light on the positive role of DEET on the environmental adaptation of Nannochloropsis.

Nitrogen use efficiency of microalgae application in wheat compared to mineral fertilizer

AbstractBackgroundWastewater from sewage treatment plants contains high levels of nutrients, which can be used for plant nutrition. Classical wastewater treatment plants use complex microbial consortia of autotrophic and heterotrophic microorganisms for biological wastewater treatment. Certain autotrophic microalgae (e.g., species of the genera Chlorella, Scenedesmus, and Pediastrum) accumulate nutrients from wastewater very effectively.AimsWe investigated the potential of microalgae biomass obtained from a prototype wastewater treatment plant as a source of nutrients for crops, focusing on nitrogen.MethodsWe provided wheat plants with different levels of algae biomass equivalent to 60, 120, and 180 kg N per hectare or with mineral fertilizer (N, P, and K) equivalent to the amounts contained in the algal biomass. Physiological and phenotypic traits were measured during growth, including vegetation indices, photosynthetic performance, growth, and nitrogen use efficiency (NUE). In addition, the adundances of Bacteria, Archaea and fungi and genes of ammonium oxidizing Bacteria and Archaea were determined in the rhizosphere of differently fertilized plants.ResultsMicroalgal application at fertilizer levels of 120 and 180 kg N ha–1 showed significantly improved physiological performance, growth, yield and nutrient uptake compared to the unfertilized control. Nevertheless, their yields and NUE were lower than with the application of equal amounts of mineral fertilization, while the adundance of rhizosphere microbes and ammonia‐oxidizing microorganisms were not significantly affected.ConclusionsMicroalgae from wastewater treatments form a suitable source of organic fertilizer for wheat plants with only moderate reductions in N use efficiency compared to mineral fertilizer.

Strain, cell density, and nutrient condition affect patterns of diurnal vertical migration and superoxide production in a red-tide alga.

A red tide occurs when cell densities of autotrophic microalgae and some heterotrophic protists increase dramatically and thereby change the color of the sea. Red tides sometimes have negative impacts on human activities, such as fisheries and tourism. Most red-tide flagellates display diurnal vertical migration (DVM) in which cells normally migrate upward during the day and downward at night. This behavior promotes active growth, due to the effective acquisition of nutrients and light, as well as population density increase and cell aggregation. However, the factors and their interactions influencing DVM remain to be clarified, such that no algorithm exists that can precisely simulate the DVM pattern and the development of a red tide in the field. Chattonella marina complex (hereafter Chattonella) is a representative microalga of harmful red tides and some previous studies has suggested that Chattonella's DVM plays important roles in development of a red tide. Chattonella can produce a large amount of superoxide (•O2 -), which is responsible for the regulation of various physiological processes as well as its toxicity against microorganisms and animals. In the present study, we examined the effects of strain, growth phase, cell density, and nutrient deficiency on the pattern of DVM. In addition, we also measured the •O2 - level in most experiments to assess the relationship between DVM and •O2 - production. Some strains displayed clear DVM, whereas others aggregated at the surface all day in a fixed condition. Strains' DVM patterns did not show a relationship with •O2 - production. Moreover, the DVM became less clear at high cell density and in nitrogen- or phosphorus-depleted conditions. Although a previous study reported that the •O2 - production rate increased during the light period and decreased during the dark period, regardless of cell density, the diurnal pattern of •O2 - became less clear at a higher cell density in a Chattonella strain used in the present study. Our findings indicate that DVM and •O2 - production by a Chattonella population composed of various strains can change across developmental phases and environmental conditions. This characteristic may produce adaptability in species and increase the chances of a massive population increase.

Conceptual Design of an Autotrophic Multi-Strain Microalgae-Based Biorefinery: Preliminary Techno-Economic and Life Cycle Assessments

Microalgae represent a promising solution in addressing the impacts associated with the current agricultural and manufacturing practices which are causing irreparable environmental damage. Microalgae have considerable biosynthetic potential, being a rich source of lipids, proteins, and high-value compounds. Under the scope of the H2020-BBI MULTI-STR3AM project, an innovative large-scale production system of valuable commodities for the food, feed, and fragrance sectors is being developed on the basis of microalgae, reducing costs, increasing the scale of production, and boosting value chain sustainability. In this work, we aimed to create a process model that can mimic an industrial plant to estimate mass and energy balances, optimize scheduling, and calculate production costs for a large-scale plant. Three autotrophic microalgae strains (Nannochloropsis sp., Dunaliella sp. and Spirulina sp.) were considered for this assessment, as well as the use of locally sourced CO2 (flue gas). The developed process model is a useful tool for obtaining the data required for techno-economic analysis (TEA) and life cycle assessment (LCA) of industrial biorefinery-based processes. Nannochloropsis sp. was the most economic option, whereas Dunaliella sp. was the most expensive strain to produce due to its lower productivity. Preliminary environmental assessments of the climate change impact category revealed that water recirculation and the use of flue gas could lead to values of 5.6, 10.6, and 9.2 kgCO2eq·kgAFDW−1 for Nannochloropsis sp., Dunaliella sp., and Spirulina sp., respectively, with electricity and NaCl as the main contributors. The obtained data allow for the quantification of the production costs and environmental impacts of the microalgal biomass fractions produced, which will be fundamental for future comparison studies and in determining if they are higher or lower than those of the replaced products. The process model developed in this work provides a useful tool for the evaluation and optimization of large-scale microalgae production systems.

Direct transesterification of microalgae after pulsed electric field treatment

AbstractBACKGROUNDLipid extraction is a major bottleneck for the commercialization of microalgae due to energy costs involved during solvent recycling. Direct transesterification offers the possibility to bypass the extraction step by immediately converting the lipids to fatty acid methyl esters (FAMEs). In this study, the efficiency of direct transesterification after pulsed electric field (PEF) treatment was evaluated. Freshly harvested Auxenochlorella protothecoides (A. protothecoides), cultivated either autotrophically or mixotrophically, was subjected to PEF. Two treatment energies were tested, 0.25 and 1.5 MJ kgdw−1, and results were compared with those for conventional two‐step transesterification.RESULTSFor autotrophically grown A. protothecoides, the percentage of the total FAMEs recovered from untreated biomass and microalgae treated with 0.25 MJ kgdw−1 was 30% for both cases, while for 1.5 MJ kgdw−1 it was 65%. A 24 h incubation step between PEF treatment and direct transesterification significantly improved the results. Untreated biomass remained stable with 30% of FAMEs, while with both treatment energies a 97% FAME recovery was achieved. However, for mixotrophic A. protothecoides the process was not as effective. Approximately 30% of FAMEs were recovered for all three conditions immediately after PEF with only a marginal increase after incubation. The reason for this different behavior of the two cultivation modes is unknown and under investigation.CONCLUSIONSOverall, the synergy between PEF and direct transesterification was proven to have potential, in particular for autotrophic microalgae. Its implementation and further optimization in a biorefinery therefore merit further attention. © 2022 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Usage of source separated urine for the biodiesel production from algal biomass

Urine is one of the most significant side-stream of domestic wastewater and this highly concentrated wastewater can be used as a growth medium for microalgae for the purpose of biodiesel production. In this study, autotrophic microalgae cultivation was achieved with changing dilutions of 5%, 10%, 20% and 40% (v/v). The highest biomass production was carried out with 5% of urine including medium as 1 g/L after the three sets of acclimation with increasing volumes. At the beginning of the microalgae cultivation, biomass productivity and nutrient accumulation was considerably low. However, biomass productivity was doubled after the acclimation studies with 23% of lipid content. During the cultivation ammonium nitrogen was treated more than 90% and the phosphorus removal was maximum 58%. Fatty acids and methyl esters (FAME) content of the biomass oil was showed the high quality of biodiesel production was possible with 33.01 ± 1.02% of saturated fatty acids and 86.62 ± 3.29% of C16-C18 fatty acids. Urine has high potential to be used for microalgae cultivation and the biodiesel production.

Iron-dependent mutualism between Chlorella sorokiniana and Ralstonia pickettii forms the basis for a sustainable bioremediation system

Phototrophic communities of autotrophic microalgae and heterotrophic bacteria perform complex tasks of nutrient acquisition and tackling environmental stress but remain underexplored as a basis for the bioremediation of emerging pollutants. In industrial monoculture designs, poor iron uptake by microalgae limits their productivity and biotechnological efficacy. Iron supplementation is expensive and ineffective because iron remains insoluble in an aqueous medium and is biologically unavailable. However, microalgae develop complex interkingdom associations with siderophore-producing bacteria that help solubilize iron and increase its bioavailability. Using dye degradation as a model, we combined environmental isolations and synthetic ecology as a workflow to design a simplified microbial community based on iron and carbon exchange. We established a mutualism between the previously non-associated alga Chlorella sorokiniana and siderophore-producing bacterium Ralstonia pickettii. Siderophore-mediated increase in iron bioavailability alleviated Fe stress for algae and increased the reductive iron uptake mechanism and bioremediation potential. In exchange, C. sorokiniana produced galactose, glucose, and mannose as major extracellular monosaccharides, supporting bacterial growth. We propose that extracellular iron reduction by ferrireductase is crucial for azoreductase-mediated dye degradation in microalgae. These results demonstrate that iron bioavailability, often overlooked in cultivation, governs microalgal growth, enzymatic processes, and bioremediation potential. Our results suggest that phototrophic communities with an active association for iron and carbon exchange have the potential to overcome challenges associated with micronutrient availability, while scaling up bioremediation designs.

Kinetic modeling of autotrophic microalgae mainline processes for sewage treatment in phosphorus-replete and -deplete culture conditions

A kinetic model of autotrophic microalgal growth in sewage was developed to determine the biokinetic processes involved, including carbon-, nitrogen- and phosphorus-limited microalgal growth, dependence on light intensity, temperature and pH, light attenuation and gas exchange to the atmosphere. A new feature was the differentiation between two metabolic pathways of phosphorus consumption according to the availability of extracellular phosphorus. Two scenarios were differentiated: phosphorus-replete and -deplete culture conditions. In the former, the microalgae absorbed phosphorus to grow and store polyphosphate. In the latter the microalgae used the stored polyphosphate as a phosphorus source for growth.Calibration and validation were performed with experimental data from a pilot-scale membrane photobioreactor (MPBR) fed with the permeate obtained from an anaerobic membrane bioreactor (AnMBR) pilot plant fed with real urban wastewater. 12 of the model parameters were calibrated. Despite the dynamics involved in the operating and environmental conditions, the model was able to reproduce the overall process performance with a single set of model parameters values. Four periods of different environmental and operational conditions were accurately simulated. Regarding the former, light and temperature ranged 10–406 μmol·m−2·s−1 and 19.7–32.1 °C, respectively. Concerning the later, the photobioreactors widths were 0.25 and 0.10 m, and the biomass and hydraulic retention times ranged 3–4.5 and 1.5–2.5 days, respectively. The validation of the model resulted in an overall correlation coefficient (R2) of 0.9954. The simulation results showed the potential of the model to predict the dynamics of the different components: the relative proportions of microalgae, nitrogen and phosphorus removal, polyphosphate storage and consumption, and soluble organic matter concentration, as well as the influence of environmental parameters on the microalgae's biokinetic processes. The proposed model could provide an effective tool for the industry to predict microalgae production and comply with the discharge limits in areas declared sensitive to eutrophication.

A fungal immobilization technique for efficient harvesting of oleaginous microalgae: Key parameter optimization, mechanism exploration and spent medium recycling

To confront with energy crisis, microalgae as the promising feedstock have a great potential in exploring renewable energy field, whereas the high costs related to medium preparation and biomass harvesting are the main bottleneck to hinder the development on a large scale. Though cultivation of filamentous fungi for microalgae harvesting is an efficient, sustainable and emerging method, and the studies on specific mechanisms and spent medium recycling for efficiency improvement as well as resource saving through a co-pelletization mode are urgently needed. Hence, in this study, the harvesting process of autotrophic microalgae Chlorella vulgaris by pre-cultured Aspergillus oryzae pellets was investigated systematically. The highest efficiency (99.23%) was obtained within 5 h under the optimized conditions of 30 °C, 130 rpm and fungi:algae ratio of 1:1 on a dry weight basis without demand for pH adjustment (initial value on 9.68). Charge neutralization was not the main mechanisms involved in fungi-algae aggregations, and the functional group changes on cell surfaces as well as secreted metabolites in medium could be mainly responsible for inducing the bioflocculation process. After harvesting, separated water could also effectively support microalgae re-growth. The biomass concentration in medium with 50% recycling was higher than that in fresh medium, while lipid content was increased from 24.37% to 33.97% in fully recycled medium. These results indicated that the pellet-assisted mode for algal harvesting is a promising way to promote biofuel production and resource recycling.

Treatment of gaseous effluent using a microalgae-based system

High level of greenhouse gases emission is provoking the global warming. Several approaches have been proposed to the development of renewable and clean technologies, such as the biological CO2 mitigation methods mediated by autotrophic microalgae. Desmodesmus subspicatus and Devons mix microalgae were used to biomass production from gases and volatile compounds of a treatment system for the steakhouse smoke using open and closed photobioreactors, optimizing by two factorial designs. The efficiency of carbon oxides removal was calculated and the microalgae biomass was characterized. Smoke and structural configuration of the system were the most significant variables to increase the biomass production. Also, it was observed that, although Devons microalgae mix presented a slower growth as compared to D. subspicatus, the carbon amount removal was indeed larger in the former. D. subspicatus in closed regime presented 1.63 g L−1 of dry biomass (733.32 mg m−3 of Chl-a), a value about six times higher than in open cultivation. Similar result was observed with the Devons mix, which 1.27 g L−1 of dry biomass (690 mg m−3 of Chl-a) in the closed system, a value about three times higher than in the open system. In relation to the biomass composition, the D. subspicatus and Devon’s mix were analyzed concerning to total lipids (6.77 and 23.23%), carbohydrates (28.17 and 27.60%) and proteins (35.3 and 31.9%). These results indicated that both biomasses are interesting sources of nutrients and could be applied to industrial purposes.

Three-dimensional tissue fabrication system by co-culture of microalgae and animal cells for production of thicker and healthy cultured food

"Cultured food" is focused worldwide as "the third stage in meat production system" after hunting and livestock farming, and a sustainable food production system. In this study, we attempted to fabricate a three-dimensional (3-D) tissue by co-cultivation of animal cells with photosynthetic autotrophic microalgae so as to produce thicker and healthy cultured foods. Metabolism and damage of co-cultured tissues fabricated by microalgae, Chlorella vulgaris (C. vulgaris), and C2C12 cells were compared to monoculture tissues fabricated by C2C12 animal cells alone. Although the metabolism of monoculture tissue showed anaerobic respiration (ratio of lactate production to glucose consumption, LG ratio: 2.01 ± 0.15), that of the co-culture tissue partially changed to efficient aerobic respiration (LG ratio: 1.58 ± 0.14). In addition, the amount of ammonia in the culture media decreased markedly by co-cultivation. The release of lactate dehydrogenase from the thicker tissue was one-seventh in the co-cultivation, showing improved tissue damage. The co-cultivation with microalgae improved the culture condition of thicker tissues, resulting in the fabrication/maintenance of 200-400 µm-thickness tissues. The co-cultured tissue fabricated by microalgae and animal cells was not only rich in nutrients but also enabled thicker tissue fabrication without tissue damage as compared to tissue fabricated by animal cells alone. This tissue fabrication system by co-culture of microalgae and animal cells will be a valuable tool for the production of thicker and healthy cultured food.

Better management practices for environmentally sustainable production of microalgae and algal biofuels

The commercialization of biofuels produced from microalgae is in its infancy; therefore, many resource-management practices and production processes are still flexible. The purpose of this paper is to guide development of supply chains toward more environmentally sustainable practices. We review current and projected technologies and practices for autotrophic microalgae cultivation that promote environmental sustainability. We develop a framework that leverages these studies to propose better management practices (BMPs) for water quality and quantity, biodiversity, or greenhouse gas emissions in concert with productivity and profitability considerations. Some proposed BMPs are linked to numerical environmental targets, such as percent reductions in nutrient loadings to streams, whereas others seek to avoid thresholds leading to adverse health or ecological effects. Still others involve using the best available technologies, developed iteratively through life-cycle and techno-economic analyses. Proposed BMPs for microalgae cultivation focus on water quality and quantity, as well as improving greenhouse gas (GHG) emissions to obtain advanced biofuel designation. BMPs must allow producers to meet productivity and profitability targets, as well as environmental targets. These example BMPs characterize the state of science and engineering; thus, they will change over time.

Comparative scoping study report for the extraction of microalgae oils from two subspecies of Chlorella vulgaris

Abstract The production of microalgae as a fatty acid oil resource for use in biofuels production is a widespread research topic at the lab scale. Microalgae contain a higher lipid content on a dry-weight basis compared to oilseeds such as soybeans. Additionally, the growth and cultivation cycle of microalgae is 15 days, in comparison to soybeans, for which the cycle occurs once or twice annually. However, to date, it has been uneconomical to produce microalgae oils in a world-scale facility due to limitations in cultivating microalgae at commercial scales. Recent developments suggest that the use of heterotrophic microalgae may be economically feasible for large-scale oil production. To assess this feasibility, a comparative scoping study was performed analysing the feasibility of an industrial-scale process plant for the growth and extraction of oil from microalgae. Processes were developed at the preliminary design level using heterotrophic subspecies and autotrophic subspecies of Chlorella vulgaris. AACE Class 4 cost estimates and economic analyses were performed. This study concludes that processes based on heterotrophic microalgae are more likely to reach economic feasibility than processes using autotrophic microalgae. However, a few barriers still remain to achieving free-market economic viability.

Effect of inorganic carbon limitation on the conversion of organic carbon to total fatty acids by Monodus subterraneus

Traditional autotrophic microalgae exhibit low rates of organic carbon assimilation and conversion to useful compounds when switching to mixotrophic or heterotrophic growth. The goal of this study was to investigate the effect of inorganic carbon limitation on the efficiency of organic carbon (glycerol) assimilation and conversion to total fatty acids (TFAs) or the long-chain polyunsaturated fatty acid eicosapentaenoic acid (EPA). An oleaginous Monodus subterraneus was selected and six cultivation conditions were set, including Autotrophy-no aeration, Autotrophy-aeration, Mixotrophy-no aeration, Mixotrophy-no aeration & no Na2CO3, Mixotrophy-aeration, and Heterotrophy. The results showed M. subterraneus could utilize glycerol and grow under mixotrophic condition, while it was not occurred under heterotrophy. Superiority of mixotrophy to autotrophy on biomass productivity was more obvious under inorganic carbon limitation (no aeration or no Na2CO3) than inorganic carbon supply (aeration and existing Na2CO3 in the medium). CO2 limitation (no aeration) decreased content (of dry weight) and production (in medium) of TFAs, which was not evident in mixotrophy. CO2 limitation and inorganic carbon substrate stress largely improved the COD yield of TFAs and EPA under mixotrophic condition. TFA yield (%COD) under Mixotrophy-no aeration & no Na2CO3 was maximum (22.82%), and was almost two-fold higher than that under Mixotrophy-no aeration and nearly three-fold higher than that with Mixotrophy-aeration. EPA yield (% COD) under mixotrophy-no aeration & no Na2CO3 was maximum (6.58%). These results suggested that inorganic carbon limitation is a potentially useful method to enhance conversion of organic carbon to TFAs. Furthermore, the results suggest an application to obtain high value compounds (TFAs or EPA) combined with a high assimilation rate of waste glycerol from biodiesel and epichlorohydrin production by microalgae.

The effect of using different polar solvents on the stability of thermal extraction phycocyanin from Spirulina platensis

Spirulina platensis is one type of blue-green autotrophic microalgae which is included in the cyanobacteria class. Spirulina platensis microscopically, it looks like a thin thread (filament) in the form of a spiral. Phycocyanin, and phycobiliprotein are used in food, biotechnology, and the cosmetics industry because of their color and antioxidants. This goal of research is to provide information of the best polar solvents on the thermal stability of phycocyanin extract from Spirullina platensis. The research method used was the complete random design (CRD) method. The results of the concentration and purity of phycocyanin showed that the heating process using 80ºC for 60 minutes produced phycocyanin. The best polar solvent showe in etanol.

Evaluating differences in growth, photosynthetic efficiency, and transcriptome of Asterarcys sp. SCS-1881 under autotrophic, mixotrophic, and heterotrophic culturing conditions

Autotrophic microalgae can assimilate organic carbon sources for the growth of heterotrophy and mixotrophy. In particular, the physiological and biochemical response of different microalgae species on autotrophy, heterotrophy, and mixotrophy are quite different. The aim of the present study was to determine differences in growth, biochemical composition, photosynthetic characteristics, and metabolic pathway under autotrophic, heterotrophic and mixotrophic culture conditions in an oleaginous microalga, Asterarcys sp. SCS-1881. The results showed that Asterarcys sp. can use glucose for mixotrophic growth, but cannot under strict heterotrophic growth. Mixotrophic cultures can significantly increase the biomass concentration and cell count of Asterarcys sp. The microalga accumulated more protein under mixotrophic conditions, but more carbohydrates and total lipids under autotrophic conditions. The microalga under mixotrophic culture conditions showed significantly reduced pigment content, PSII activity, and photoprotective ability, but increased the activity of PSI when compared to those under autotrophic conditions. Under mixotrophic conditions, Asterarcys sp. also showed enhanced glycolysis, photosynthetic carbon fixation, and pentose phosphate pathway and thus more ATP, carbon skeleton structure, and NADPH. Additionally, the biosynthesis of triacylglycerol, carbohydrates, and pigments was reduced under mixotrophic conditions and the core protein complexes of PSI and PSII were attenuated. Similarly, photosynthetic electron transport and many other pathways related to protein synthesis were enhanced under mixotrophic conditions when compared to the microalga cultured under autotrophic conditions. These biochemical changes may work to co-operatively ensure a more efficient supply of energy and carbon skeleton for rapid growth of the microalga under mixotrophic conditions when compared to those raised under autotrophic conditions.

Testing the Waste Based Biorefinery Concept: Pilot Scale Cultivation of Microalgal Species on Spent Anaerobic Digestate Fluids

A waste based biorefinery approach has been tested. This has been investigated by culturing in a 800 L photobioreactor two autotrophic microalgae namely Nannochloropsis oceanica and Scenedesmus quadricauda utilising filtered spent anaerobic digestate fluids of N:P ratio 14.22 as substrate. Significant rates of bioremediation simultaneously with biomass and associated end product formation were achieved. Nitrogen and phosphorus of waste based media was decreased up to 90%. The biomass biochemical analysis of the microalgae when grown on the waste based formulated media demonstrated the comparable content of lipids and proteins with the species grown on f/2 media. Theoretical biomethane potential generation, should the algal cultures be placed in an anaerobic digester, was calculated at 0.58 L CH4 g−1 VS for N. oceanica and 0.48 L CH4 g−1 VS for S. quadricauda showing comparable results with other studies of different source of biomass.

Potential of Autotroph Microalgae (Spirulina plantentis) as Antimicrobial agent

Microalgae is a phytoplankton that has antimicrobial activity. From 20 blue-green microalgae species, 78% have antibacterial activity and 42% antifungal activity, but there are still many other microalgae species that have unknown their activities. One of the microalgae whose unknown antimicrobial potential is Spirulina plantentis. The purpose of this study was to determine the antimicrobial potential of autotrophic microalgae (Spirulina plantentis) which can be used as antimicrobial compounds from natural materials. This study used the agar diffusion method to see the antimicrobial activity of autotrophic microalgae. Microalgae suspension was tested their antimicrobial activities by using Staphylococcus aureus, Escherichia coli, and Candida albicans. The result shows that the MICs of Spirulina plantentis suspension against C. albicans, E. coli and S. aureus were 62.5 ppm, 125 ppm and 500 ppm. The MBCs against C. albicans, E. coli and S. aureus were 125 ppm, 250 ppm and 500 ppm. Antimicrobial activity of Spirulina plantentis suspension exhibited week against C. albicans and E. coli, but no antimicrobial activity against S. aureus. Spirulina plantentis produced inhibition zone against C. albicans by 3.9 mm at 125 ppm and 15.6 mm at 250 ppm, against S. aureus and E. coli by 1.4 mm at 500 ppm and 1.6 mm at 1000 ppm. Against E. coli by 8.55 mm at 500 ppm and 12 mm at 1000 ppm.

Utilization of <i> Schizochytrium mangrovei </i> PQ6 as feed for rotifer <i> Brachionus plicatilis </i> in rearing black sleeper’s larvae (<i>Bostrichthys sinensis</i>, Lacepede, 1881)

Schizochytrium mangrovei PQ6 contains many important polyunsaturated fatty acids, such as docosahexaenoic acid (DHA, C22: 6w-3), eicosahexaenoic acid (EPA, C20: 5w-3) and docosapentaenoic acid (DPA, C22: 5w-6). These fatty acids are essential for survival and growth of many marine fish larvae. In this paper, fresh biomass of S. mangrovei PQ6 was used for culturing rotifer Brachionus plicatilis. In the first formula (L1), rotifers were fed on baker’s yeast; in second formula (L2), rotifers were fed on mixed two microalgae, Nannochloropsis oculata and Chaetoceros gracilis; in the third formula (L3), rotifers were fed on S. mangrovei PQ6 biomass. The results indicated that S. mangrovei PQ6 biomass can replace baker’s yeast and autotrophic microalgae in feeding rotifers. Total lipid, total fatty acid and polyunsaturated fatty acid contents of rotifers fed on formula 3 (S. mangrovei PQ6) were higher than those within others. High polyunsaturated fatty acid (C ≥ 20) in omega-3 and 6 groups; DHA and DPA contents of rotifers fed on S. mangrovei PQ6 were the highest, accounting for 39.81% of total fatty acid; 41.95% and 8.24% polyunsaturated fatty acids, corresponding to 20.52; 12.15 and 2.4 mg/g of dried weight, respectively.The survival rate of black sleeper’s larvae was highest when they were fed on rotifers grown on L3 formula (51.20 ± 0.89%), followed by L2 formula (48.70 ± 2.67%) and the lowest with L1 formula (43.44 ± 1.54%) (P < 0.05). However, among three formulas, no significant difference was found in the growth of black sleeper’s larvae (P > 0.05). These results suggest that biomass of S. mangrovei PQ6 can replace traditional feed like autotrophic microalgae or baker’s yeast for biomass culture of the Brachionus plicatilis rotifer for rearing black sleeper’s larvae to enhance seed quality to meet demands of market.