Statistical evaluation and modeling of cheap substrate-based cultivation medium of Chlorella vulgaris to enhance microalgae lipid as new potential feedstock for biolubricant

Chlorella vulgaris (C. vulgaris) microalga was investigated as a new potential feedstock for the production of biodegradable lubricant. In order to enhance microalgae lipid for biolubricant production, mixotrophic growth of C. vulgaris was optimized using statistical analysis of Plackett–Burman (P-B) and response surface methodology (RSM). A cheap substrate-based medium of molasses and corn steep liquor (CSL) was used instead of expensive mineral salts to reduce the total cost of microalgae production. The effects of molasses and CSL concentration (cheap substrates) and light intensity on the growth of microalgae and their lipid content were analyzed and modeled. Designed models by RSM showed good compatibility with a 95% confidence level when compared to the cultivation system. According to the models, optimal cultivation conditions were obtained with biomass productivity of 0.123 g L^?1 day^?1 and lipid dry weight of 0.64 g L^?1 as 35% of dry weight of C. vulgaris. The extracted microalgae lipid presented useful fatty acid for biolubricant production with viscosities of 42.00 cSt at 40°C and 8.500 cSt at 100°C, viscosity index of 185, flash point of 185°C, and pour point of ?6°C. These properties showed that microalgae lipid could be used as potential feedstock for biolubricant production.     

Comparative Analyses on the Bioactive Compounds and in Vitro Antioxidant Capacity of Tea Infusions Prepared from Selected Medicinal Fruits

This study was conducted to analyze the bioactive compounds and in vitro antioxidant capacity of tea infusions prepared from whole and ground medicinal fruits, including gardenia, jujube, magnolia, quince, and wolfberries. The dried medicinal fruit samples were ground, and then passed through a 60‐mesh sieve (pore size, 250 μm). Hot water (80 °C) infusions of whole and ground fruits were examined. In average of both whole and ground tea infusions, the maximum bioactive compounds were found in gardenia (β‐carotene, lycopene, and vitamin C), magnolia (total chlorophyll and anthocyanin), quince (flavonoid), and wolfberries (phenolic), and the maximum antioxidant capacity was found in quince (ABTS and DPPH) and wolfberries (NSA). Whole fruit tea infusions showed a higher brightness than the ground fruit tea infusions. The total chlorophyll, anthocyanin, β‐carotene, lycopene, phenolic, flavonoid, and vitamin C contents were found to be significantly (p≤0.001) higher in the ground fruit tea infusions than in the whole fruit tea infusions; additionally, the ground fruit tea infusions had a higher antioxidant capacity especially ABTS, DPPH and NSA. Therefore, the ground fruit tea infusions appeared to be more powerful with regard to the contents of bioactive compounds and antioxidant capacities than the whole fruit tea infusions.     

Accumulation of anthocyanin in callus cultures of red-pod okra [<Emphasis Type="Italic">Abelmoschus esculentus</Emphasis> (L.) Hongjiao] in response to light and nitrogen levels

Nitrogen and light are critical determinants of biomass accumulation and secondary metabolite production under in vitro culture conditions. In this study, we analyzed the effects of varied concentrations of total nitrogen in Murashige and Skoog (MS) medium and light intensity on the production of biomass, anthocyanin pigments, and bioactive antioxidants in callus cultures of Abelmoschus esculentus cv. ‘Hongjiao’. Maximum callus biomass accumulation (3 g FW) was achieved when calluses were cultured on MS medium containing 60 mM nitrogen under 40 μmol m^??2 s^??1 light intensity. In contrast, maximum values of total anthocyanin accumulation (TA; 7.3 CV/g FW), total phenolic content (TP; 12.07 mg/100 g FW), total flavonoid content (TF; 2.47?±?0.15 mg/100 g FW), and total antioxidant activity (TAA; 56.10 μmol Trolox/g FW) were observed when calluses were cultured on MS medium containing 40 mM total nitrogen under 80 μmol m^??2 s^??1 light intensity. In addition, callus grown under same culture condition exhibited high flavonoid content along with increased phenolic content and antioxidant activity. High performance liquid chromatography (HPLC) was performed for qualitative and quantity analysis of callus cultures. Most of the pigments from the callus extracts were identical with pod anthocyanins, and appeared on the ODS-column HPLC with lower concentration than the main pigments of the pod tissues. These findings indicate that callus cultures of red-pod okra represent a potential source of bioactive compounds with antioxidant properties for industrial applications.     

Bioactive properties of hydroalcoholic extract from Origanum onites L. as affected by glycerol incorporation

In the current study, the effect of glycerol -as a green solvent- addition into solvent mixture (50:50 ethanol:distilled water), on some biofunctional properties of Origanum onites L. was investigated. Response surface methodology (RSM) was used to detect the optimum conditions for the extraction process. Three variables namely glycerol concentration (X₁: 1–9 g), extraction temperature (X₂: 25–75 °C) and time (X₃:10–30 min) were selected and also total phenolic content, total flavonoid content, antioxidant capacity and antiradical activity of O. onites extracts were determined. Analysis of variance (ANOVA) showed that glycerol incorporation significantly increased the total phenolic content and antioxidant activity (p < 0.05) of the samples. Maximum levels to obtain the highest bioactive properties (highest total phenolic content and antioxidant activity) were determined as to be 9 g of glycerol addition for the extraction conditions as 45.4 °C and 75 min. This study reports the effect of glycerol on bioactive properties of O. onites and suggests that glycerol can be used to produce hydroalcoholic extracts having higher bioactivity from Origanum genus.     

Effects of the timing of a culture temperature reduction on the comprehensive metabolite profiles of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis>

This study investigated the effects of different temperature conditions on the comprehensive metabolite profiles of Chlorella vulgaris using gas chromatography–mass spectrometry coupled with multivariate statistical analysis. C. vulgaris cells cultivated at 20 °C were transferred to 10 °C incubators at different time points of cultivation [days 0 (TR0D), 7 (TR7D), and 14 (TR14D)], then they were cultivated at 10 °C until harvesting at day 21 to compare the growth and comprehensive metabolite profiles with those cultivated under a constant cultivation temperature of 20 °C (T20). There was no significant difference in algal cell growth between cultivation under the T20 and temperature reduction (TR) conditions. Algal fatty-acid profiles under TR were different from those of the T20 condition. Specifically, the contents of octadecanoic acid (C18:0), octadecenoic acid (C18:1), hexadecadienoic acid (C16:2), and octadecadienoic acid (C18:2) increased the most under TR0D. The relative levels of metabolites such as β-alanine, glutamine, glycine, isoleucine, proline, valine, and myo-inositol, which act as osmolytes, and bioactive compounds such as neophytadiene and ascorbic acid were increased under TR conditions on day 21. Among the metabolites, the contents of neophytadiene and ascorbic acid were further investigated, and the content of ascorbic acid was highest on day 14 under the TR7D condition, while the content of neophytadiene was highest on day 21 under the TR0D and TR14D condition. Therefore, we suggest that a TR from 20 to 10 °C could enhance the production in C. vulgaris cultures of bioactive fatty acids such as C18:1, C16:2, and C18:2 (TR0D), organic osmolytes such as β-alanine, glutamine, glycine, isoleucine, proline, valine, and myo-inositol (TR conditions), ascorbic acid (TR7D), and neophytadiene (TR0D and TR14D).     

Pressurized extraction of unsaturated fatty acids and carotenoids from wet Chlorella vulgaris and Phaeodactylum tricornutum biomass using subcritical liquids

The objective of this study was to investigate the extraction of lipids, for example, mono‐ and polyunsaturated fatty acids (PUFA) as well as carotenoids, from wet microalgae biomass using pressurized subcritical extraction solvents, which meet the requirements of food and feed applications. To demonstrate the effect of the solvent and temperature on the lipid yield, we chose two microalgae species, viz. Chlorella vulgaris and Phaeodactylum tricornutum, differing in their biochemical composition fundamentally. In case of P. tricornutum, ethanol showed the highest fatty acid yield of 85.9% w/w. In addition to eicosapentaenoic acid (EPA), the ethanolic extracts contained exceptional amounts of fucoxanthin (up to 26.1 mg/g d. w.), which can be beneficial to protect unsaturated fatty acids from oxidation processes and in terms of human nutrition. For C. vulgaris, a fatty acid yield of 76.5% w/w was achieved from wet biomass using ethyl acetate at 150°C. In general, an increase in the extraction temperature up to 150°C was found to be important in terms of fatty acid yield when extracting wet microalgae biomass. The results suggest that it is possible to efficiently extract both fatty acids and carotenoids from wet microalgae by selecting suitable solvents and thus circumvent energy‐intensive drying of the biomass.     

Culture of microalgae Chlorella minutissima for biodiesel feedstock production

Microalgae are among the most promising of non‐food based biomass fuel feedstock alternatives. Algal biofuels production is challenged by limited oil content, growth rate, and economical cultivation. To develop the optimum cultivation conditions for increasing biofuels feedstock production, the effect of light source, light intensity, photoperiod, and nitrogen starvation on the growth rate, cell density, and lipid content of Chlorella minutissima were studied. The fatty acid content and composition of Chlorella minutissima were also investigated under the above conditions. Fluorescent lights were more effective than red or white light‐emitting diodes for algal growth. Increasing light intensity resulted in more rapid algal growth, while increasing the period of light also significantly increased biomass productivity. Our results showed that the lipid and triacylglycerol content were increased under N starvation conditions. Thus, a two‐phase strategy with an initial nutrient‐sufficient reactor followed by a nutrient deprivation strategy could likely balance the desire for rapid and high biomass generation (124 mg/L) with a high oil content (50%) of Chlorella minutissima to maximize the total amount of oil produced for biodiesel production. Moreover, methyl palmitate (C16:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl linolenate (C18:3) are the major components of Chlorella minutissima derived FAME, and choice of light source, intensity, and N starvation impacted the FAME composition of Chlorella minutissima. The optimized cultivation conditions resulted in higher growth rate, cell density, and oil content, making Chlorella minutissima a potentially suitable organism for biodiesel feedstock production. Biotechnol. Bioeng. 2011;108: 2280–2287. © 2011 Wiley Periodicals, Inc.     

Physical stress for overproduction of biomass and flavonoids in cell suspension cultures of Boesenbergia rotunda

Flavonoid, a bioactive compound isolated from the rhizomes of Boesenbergia rotunda, exhibited antibiotic and anti-inflammatory properties and has also shown high inhibitory activity of dengue-2 virus protease. Several factors are responsible for the production of flavonoid in cell cultures. In the present study, the effects of initial inoculation volume, temperature and speed of agitation on cell growth, total and selected flavonoid in suspension cultures of B. rotunda were determined. High performance liquid chromatography analysis showed that a 2 % inoculation volume induced a significantly high accumulation of biomass and of flavonoid in the cells. The cells cultured at 25 °C showed significantly high biomass and selected flavonoid accumulation while differences in medium agitation significantly affected the yield of selected flavonoid.     

Quercetin in Lyotropic Liquid Crystalline Formulations: Physical, Chemical and Functional Stability

The purpose of this study was to develop a lyotropic liquid crystalline formulation using the emulsifier vitamin E TPGS and evaluate its behavior after incorporation of a flavonoid, quercetin. The physical (macro and microscopic), chemical (determination of quercetin content by the HPLC method) and functional (determination of quercetin antioxidant activity by DPPH^• assay) stability of the lamellar liquid crystalline formulation containing flavonoid was evaluated when stored at 4 ± 2 °C; 30 ± 2 °C/70 ± 5% RH (relative humidity) and 40 ± 2 °C/70 ± 5% RH during 12 months. The lamellar liquid crystalline structure of the formulation was maintained during the experiment, however chemical and functional stability results showed a great influence of the storage period in all conditions tested. A significant decrease in quercetin content (approximately 40%) was detected during the first month of storage and a similar significant loss in antioxidant activity was detected after 6 months. The remaining flavonoid content was unchanged during the final 6 months of the experimental period. The results suggest possible interactions between quercetin and the liquid crystalline formulation, which could inhibit or reduce the quercetin activity incorporated in the system. In conclusion, the present study demonstrated that incorporation of quercetin (1%) did not affect the liquid crystalline structure composed of vitamin E TPGS/IPM/PG–H₂O (1:1) at 63.75/21.25/15 (w/w/w). Nevertheless, of the total quercetin incorporated in the system only 60% was free to act as an antioxidant.     

Enhancement of hydrolysis of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> by hydrochloric acid

Chlorella vulgaris is considered as one of the potential sources of biomass for bio-based products because it consists of large amounts of carbohydrates. In this study, hydrothermal acid hydrolysis with five different acids (hydrochloric acid, nitric acid, peracetic acid, phosphoric acid, and sulfuric acid) was carried out to produce fermentable sugars (glucose, galactose). The hydrothermal acid hydrolysis by hydrochloric acid showed the highest sugar production. C. vulgaris was hydrolyzed with various concentrations of hydrochloric acid [0.5–10 % (w/w)] and microalgal biomass [20–140 g/L (w/v)] at 121 °C for 20 min. Among the concentrations examined, 2 % hydrochloric acid with 100 g/L biomass yielded the highest conversion of carbohydrates (92.5 %) into reducing sugars. The hydrolysate thus produced from C. vulgaris was fermented using the yeast Brettanomyces custersii H1-603 and obtained bioethanol yield of 0.37 g/g of algal sugars.     

Effects of <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> extract on growth and antioxidant defense systems of two freshwater microalgae

Microalgae in genus Chlorella and Scenedesmus are common in aquatic ecosystems and are widely used for various studies on algal growth and applications. Macroalgae may play an important role for control of microalgal growth, attributable to their rich content of bioactive compounds. In this study, the brown seaweed Ascophyllum nodosum was extracted with 70% acetone and the extract was used to treat the green microalgae, Chlorella vulgaris and Scenedesmus sp. Cell density and chlorophyll a concentration were used as growth indexes to evaluate the effects of A. nodosum extract (ANE) on the microalgae. The ANE with concentrations > 1% exhibited significant capability of inhibition of the growth of microalgae by over 80%. On the contrary, 1% ANE caused varying degrees of acceleration of cell proliferation and chlorophyll a synthesis in C. vulgaris and Scenedesmus sp., respectively. Analysis of antioxidant activities of the enzymes superoxide dismutase (SOD) and catalase (CAT) revealed the impact of ANE on the antioxidant defense system of the microalgae. The SOD and CAT activities were significantly depressed by high concentrations (> 2%) ANE, while a slight increase of the enzyme activities was observed with 1% ANE at the early period, which could be correlated to the growth response. Therefore, the mechanism of microalgae control could be related to the interaction between the ANE and the antioxidant defense systems. Phlorotannins are proposed as the principal algistatic components in the ANE which could be utilized in controlling microalgae growth.     

Antioxidant responses of microalgal species to pyrene

The antioxidant response of four freshwater microalgal species, Chlorella vulgaris Beij., Scenedesmus platydiscus (G. M. Smith) Chod., Scenedesmus quadricauda(Turp.) Bréb., and Selenastrum capricornutum Printz without pyrene addition (control) and at two pyrene concentrations (0.1 and 1.0 mgL⁻¹) were investigated. Under the control condition, the values of the antioxidant parameters differed significantly among species and the difference was seemed not to be related to their susceptibility to pyrene. The antioxidant response to pyrene treatments also varied from species to species. Pyrene led to a significant increase in total glutathione (GSH) content in all species except C. vulgaris, a species did not exhibit any ability to metabolize pyrene. The glutathione-S-transferase (GST) activities also remained unchanged in pyrene treated C. vulgaris, increased greatly in S. platydiscus and Se. capricornutum (the two species with higher pyrene metabolism ability), but inhibited remarkably in S. quadricauda (the only species sensitive to pyrene toxicity). On the other hand, the glutathione reductase (GR) activities increased in C. vulgaris but remained at a similar level as the control in the other three species. The malondialdehyde (MDA) content, an indicator of lipid peroxidation, declined in S. quadricauda but showed no significant change in the other three species. The activities of glutathione peroxidase (GPX), superoxide dismutase (SOD) and catalase (CAT) in pyrene treated cells remained almost the same as the controls for all microalgal species. Results suggested that the alterations of antioxidant systems in microalgae might not be useful indicators of pyrene exposure but pyrene-enhanced GSH metabolism might be important in pyrene biotransformation.     

Biological CO<Subscript>2</Subscript> fixation using C<Emphasis Type="Italic">hlorella vulgaris</Emphasis> and its thermal characteristics through thermogravimetric analysis

The present research is focused on cultivation of microalgae strain Chlorella vulgaris for bio-fixation of CO₂ coupled with biomass production. In this regard, a single semi-batch vertical tubular photobioreactor and four similar photobioreactors in series have been employed. The concentration of CO₂ in the feed stream was varied from 2 to 12 % (v/v) by adjusting CO₂ to air ratio. The amount of CO₂ capture and algae growth were monitored by measuring decrease of CO₂ concentration in the gas phase, microalgal cell density, and algal biomass production rate. The results show that 4 % CO₂ gives maximum amount of biomass (0.9 g L^?1) and productivity (0.118 g L^?1 day^?1) of C. vulgaris in a single reactor. In series reactors, average productivity per reactor found to be 0.078 g L^?1 day^?1. The maximum CO₂ uptake for single reactor also found with 4 % CO_2, and it is around 0.2 g L^?1 day^?1. In series reactors, average CO₂ uptake is 0.13 g L^?1 day^?1 per reactor. TOC analysis shows that the carbon content of the produced biomass is around 40.67 % of total weight. The thermochemical characteristics of the cultivated C. vulgaris samples were analyzed in the presence of air. All samples burn above 200 °C and the combustion rate become faster at around 600 °C. Almost 98 wt% of the produced biomass is combustible in this range.     

Systematic investigation of biomass and lipid productivity by microalgae in photobioreactors for biodiesel application

We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterizing their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the “light-limited” regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25-37% of DW), while the highest TAG content was found in C. vulgaris (11-14% of DW). These two species showed similar TAG productivities.     

Influence of drying methods over in vitro antitumoral effects of exopolysaccharides produced by Agaricus blazei LPB 03 on submerged fermentation

Agaricus blazei is a mushroom that belongs to the Brazilian biodiversity and is considered as an important producer of bioactive compounds beneficial to human health. Studies have demonstrated that these compounds present immuno-modulatory, antioxidant and antitumor properties. In order to compare the most used method for fungal polysaccharide drying, lyophilization with other industrial-scale methods, the aim of this work was to submit A. blazei LPB 03 polysaccharide extracts to vaucum, spray and freeze drying, and evaluate the maintenance of its antitumoral effects in vitro. Exopolysaccharides produced by A. blazei LPB 03 on submerged fermentation were extracted with ethanol and submitted to drying processes. The efficiency represents the water content that was removed during the drying process. The resultant dried products showed water content around 3% and water activity less than 0.380, preventing therefore the growth of microorganisms and reactions of chemical degradation. Exopolysaccharide extracts dried by vacuum and spray dryer did not showed any significant cytotoxic effect on cell viability of Wistar mice macrophages. Content of total sugars and protein decrease after drying, nevertheless, 20 mg/ml of exopolysaccharides dried by spray dryer reached 33% of inhibition rate over Ehrlich tumor cells in vitro.     

Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1 % (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2 % (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 μmol m^?2s^?1 for Chlorella sp. (22.5 %) and S. obliquus R8 (23.7 %) and 80 μmol m^?2s^?1 for C. vulgaris CCAP211/11B (20.1 %) and B. braunii FC124 (34.9 %).     

Comparison of the culture and harvesting of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> and <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> for the removal of pharmaceuticals from water

The objective of this work was to assess and compare the removal efficiency of paracetamol and salicylic acid from aqueous medium by a microalgae-based treatment, using either Chlorella vulgaris or Tetradesmus obliquus. Moreover, considering microalgae application in wastewater treatment, the influence of these pharmaceuticals in the algal nutrient removal capacity was evaluated. The removal of paracetamol by T. obliquus (>40 %) was larger than by C. vulgaris (>21 %) in batch culture, and this was also observed for salicylic acid (>93 % by T. obliquus and >25 % by C. vulgaris). Both strains removed nutrients (phosphate and nitrate) almost completely by the end of the batch culture, but T. obliquus showed the highest efficiency at the steady state conditions of the semicontinuous culture. In spite of this, under the flocculants here tested, the efficiency in the recovery of biomass was much higher for C. vulgaris. These results highlight the importance of strain selection in the application of microalgae for wastewater treatment and, particularly, for the removal of pharmaceuticals.     

Glucose and Nitrogen Amendments Can Mitigate Wastewater‐Borne Bacteria Competition Effect Against Algal Growth in Wastewater‐Based Systems

The reuse of wastewater is important for reducing costs involved with algal lipid production. However, nutrient limitations, wastewater‐borne microbes, and mixotrophic growth can significantly affect biomass yields and lipid/biomass ratios. This research compared the growth performances of both Chlorella vulgaris and Pseudokirchneriella subcapitata on domestic wastewater effluent. The experiments were conducted in the presence and absence of wastewater‐borne bacteria, while additionally assessing the impact of distinct nitrate and glucose supplementations. When compared to the sterilized controls, the presence of wastewater‐borne bacteria in the effluent reduced C. vulgaris and P. subcapitata total biomass production by 37% and 46%, respectively. In the corresponding treatments supplemented with glucose and nitrate, total biomass production increased by 12% and 61%, respectively. The highest biomass production of 1.11 and 0.72 g · L^?1 was, however, observed in the sterilized treatments with both glucose and nitrate supplementations for C. vulgaris and P. subcapitata, respectively. Lipid to biomass ratios were, on average, threefold higher when only nitrate was introduced in the sterilized treatments for both species (0.4 and 0.5, respectively). Therefore, the combination of nitrate and glucose supplementation is shown to be an important strategy for enhancing algal lipid and biomass production when those algae are grown in the presence of wastewater‐borne bacteria. On the other hand, in the absence of wastewater‐borne bacteria, only nitrate supplementation can significantly improve lipid/biomass ratios.     

Biomass,Lipid and Fatty Acid Production in Large-Scale Cultures of the Marine Macroalga Derbesia tenuissima (Chlorophyta)

Biomass productivity was quantified for the marine macroalga Derbesia tenuissima cultivated outdoors at seven stocking densities from 0.25 to 8 g L^?1 for 5 weeks. Total lipids and fatty acid quantity and quality was measured from samples that were freeze-dried, dried by oven (75 °C), food dehydrator (60 °C), or outdoor in the sun (40 °C) or shade (38 °C). Stocking densities of 0.25 to 2 g L^?1 yielded the highest biomass productivities (>20 g dry weight m^?2 day^?1) with no effect on total lipid quantity (11 %), or fatty acid quantity (5.3 %) or quality at any density tested. However, there was an interactive effect of stocking density and drying technique, with a decrease of up to 40 % in polyunsaturated fatty acids in sun-dried compared to freeze-dried biomass. Notably, while fatty acid and biomass productivity may be inseparable in macroalgae, cultivation conditions have a significant carryover effect in the post-harvest delivery of high-quality bio-oils.     

Thermophilic,anaerobic co-digestion of microalgal biomass and cellulose for H<Subscript>2</Subscript> production

Microalgal biomass has been a focus in the sustainable energy field, especially biodiesel production. The purpose of this study was to assess the feasibility of treating microalgal biomass and cellulose by anaerobic digestion for H₂ production. A microbial consortium, TC60, known to degrade cellulose and other plant polymers, was enriched on a mixture of cellulose and green microalgal biomass of Dunaliella tertiolecta, a marine species, or Chlorella vulgaris, a freshwater species. After five enrichment steps at 60°C, hydrogen yields increased at least 10% under all conditions. Anaerobic digestion of D. tertiolecta and cellulose by TC60 produced 7.7 mmol H₂/g volatile solids (VS) which were higher than the levels (2.9–4.2 mmol/g VS) obtained with cellulose and C. vulgaris biomass. Both microalgal slurries contained satellite prokaryotes. The C. vulgaris slurry, without TC60 inoculation, generated H₂ levels on par with that of TC60 on cellulose alone. The biomass-fed anaerobic digestion resulted in large shifts in short chain fatty acid concentrations and increased ammonium levels. Growth and H₂ production increased when TC60 was grown on a combination of D. tertiolecta and cellulose due to nutrients released from algal cells via lysis. The results indicated that satellite heterotrophs from C. vulgaris produced H₂ but the Chlorella biomass was not substantially degraded by TC60. To date, this is the first study to examine H₂ production by anaerobic digestion of microalgal biomass. The results indicate that H₂ production is feasible but higher yields could be achieved by optimization of the bioprocess conditions including biomass pretreatment.