Enhanced biomass production, lipid yield and sedimentation efficiency by iron ion

Biodiesel production potential of microalgae, cultivated in acid mine drainage and livestock wastewater

The adaptability and biofuel production potential of two strains of microalgae isolated and cultivated in livestock wastewater effluent (LWE) with acid mine drainage (AMD) were investigated. The isolated strains of microalgae from samples obtained from LWE and AMD, two microalgal strains (Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17) were selected based on their growth rate and lipid productivity. The dry cell weight of Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17 after 20 days of cultivation in AMD increased from 0.05 to 0.59 g/L and from 0.05 to 0.55 g/L, respectively. These findings revealed a significant accumulation of fatty acids with increasing AMD content. Nephroselmis sp. KGE2 in LWE with 5% AMD demonstrated a higher growth rate (0.59 ± 0.03 g/L) and fatty acid production (401.5 ± 47.3 mg/L) than Autodesmus obliquus KGE17 with 5% AMD. Additionally, Nephroselmis sp. KGE2 had C16-C18 fatty acid content (92.4%) in LWE with AMD. Biodiesel produced from Nephroselmis sp. KGE2 had a higher cetane number (52.31) and iodine value (88.26 g I₂/100 g oil). Consequently, Nephroselmis sp. KGE2 can be considered a potential candidate for biodiesel production using AMD as an iron source.

Novel approach for the management of acid mine drainage (AMD) for the recovery of heavy metals along with lipid production by Chlorella vulgaris

The treatment of acid mine drainage (AMD) is of paramount importance for environmental sustainability. A two-stage process involving AMD remediation and simultaneous lipid production represents a highly efficient approach with zero-waste generation. Alkaline (NaOH) treatment of AMD at pH 8.0, 10.0, and 12.0 had significantly reduced metal loads (copper (Cu), cobalt (Co), chromium (Cr), cadmium (Cd), nickel (Ni), and zinc (Zn)) compared to the acidic pH range (4.0 and 6.0). The concentration levels of sulfates (SO₄ = 4520 mg/L), iron (Fe = 788 mg/L), aluminum (Al = 310 mg/L), and manganese (Mn = 19.4) were reduced to 2971 mg/L, 10.3 mg/L, 16.4 mg/L, and 1.3 mg/L, respectively at pH value 8.0. AMD with a pH value of 8.0 was later chosen as an ideal medium to favor the lipid accumulation by Chlorella vulgaris. Algal biomass was increasing to 5.5 g/L from 0.6 g/L of AMD-based medium within 15 days of cultivation. The FTIR and SEM-EDS studies revealed significant morphological changes in the microbial cell wall. The metals might positively impact lipid production in microalgae, where lipid yield achieved 0.18 g/g of glucose with lipid content of 0.35 g/g of biomass. The fatty acid profile presented 53.4% of saturated fatty acid content with a cetane value of 60.7. Thus, the efficiency of C. vulgaris was demonstrated with AMD treatment proving it to be a good candidate for bioenergy production.

Selenite as a Lipid Inductor in Marine Microalga Dunaliella tertiolecta: Comparison of One-Stage and Two-Stage Cultivation Strategies

Microalgae have emerged as one of the most promising alternative sources of biofuels due to their high lipid accumulation ability. High lipid content is of pivotal importance for biodiesel production. In order to obtain high lipid content, modifications of culture conditions and development of an efficient lipid induction method are called for. In the present study, the possibility of using selenium in a form of sodium selenite as a lipid inductor in marine microalga Dunaliella tertiolecta was investigated during one- and two-stage cultivation modes. The effects of selenite on algal growth, pigment content, oxidative stress, and neutral lipid content were determined during both cultivation modes. The results revealed that the two-stage cultivation on 10.00-40.00 mg L-1 of selenite resulted in up to twofold higher algal cell density compared to the one-stage cultivation. Selenite concentrations from 2.50 to 20.00 mg L-1 increased lipid peroxidation during both cultivation modes, emphasizing the selenite-induced oxidative stress accompanied by the increased lipid accumulation in microalgae cells. During one- and two-stage cultivation on 20.00 mg L-1 of selenite, lipid content increased 2.39- and 5.73-fold at days 9 and 14 of cultivation, respectively. Moreover, the highest obtained neutral lipid content during the two-stage cultivation was 5.40-fold higher than lipid content obtained during the one-stage cultivation. Collectively, these results suggest that the two-stage cultivation strategy, initiated with optimal culture conditions for biomass production and followed by the addition of selenite as a stress inductor, can be successfully deployed to enhance the lipid content in D. tertiolecta.

Enhancing biomass, lipid production, and nutrient utilization of the microalga Monoraphidium sp. QLZ-3 in walnut shell extracts supplemented with carbon dioxide

Microalgae are a promising biofuel resource, but their high cost and low productivity hinder their commercial applications. In the present study, Monoraphidium sp. QLZ-3 was cultivated in walnut shell extracts (WSE) supplemented with carbon dioxide (CO₂). Biomass was enhanced from 0.40 g L^-1 to 1.18 g L^-1, and lipid content reached 49.54% in WSE-12% CO₂ media. Biomass and lipid productivity reached 196.88 and 97.52 mg L^-1 d^-1, which were 1.33- and 1.57-fold higher than those of the control, respectively. The amount of carbohydrates increased, but the protein contents decreased. Furthermore, the application of CO₂ promoted nutrient and polyphenol absorption and upregulated the expression levels of lipid biosynthetic genes of this WSE-cultivated alga. These results indicated that coupling WSE and CO₂ could be an efficient strategy to enhance biofuel production by microalgae.

Influences of carbon and nitrogen sources and metal ions on the heterotrophic culture of Scenedesmus sp. LX1

In this study, the influences of organic carbon sources (OCS, including xylose, glucose, maltose, sucrose, and starch) and inorganic and organic nitrogen sources (INS, including ammonia chloride and sodium nitrate; ONS, including arginine, alanine, proline, and valine) and metal ions (including Na⁺, K⁺, Mn²⁺, Zn²⁺ and Cu²⁺) on the growth, lipid accumulation, and nitrogen and phosphorus (N&P) removal capabilities of oleaginous Scenedesmus sp. LX1 under heterotrophic conditions were investigated. The results showed that glucose was the only OCS for Scenedesmus sp. LX1 to grow well with specific growth rate of 0.935 days^-1, maximum biomass of 1.72 g L^-1, and largest removal rates of N&P and organic carbon reaching 72.228%, 93.034%, and 19.208%, respectively. After 11 days of cultivation, the maximal biomass reached in the group with starch or glucose while maximal lipid and triacylglycerol (TAG) yields reached in the groups with maltose and sucrose, respectively. Sodium nitrate was best nitrogen source as the largest algal density, maximal yields of lipids and TAGs, and highest N&P removal rates reached up to 1.105 × 10⁷ cells·mL^-1, 196.70 mg L^-1, 5.19 mg L^-1, 89.61% and 100%, respectively. Scenedesmus sp. LX1 was found to have great tolerance to Na⁺, K⁺, Mn²⁺, and Zn²⁺ while 0.5 mg L^-1 Cu²⁺ had a strong inhibition on growth and N&P removal rate of Scenedesmus sp. LX1. Concentration increasing of five metal ions all caused the yield increases of microalgal lipid and TAGs. Graphical abstract.

Synthesis and Optimization of Methyl Laurate Using Sulfonated Pyrrolidonium Ionic Liquid as a Catalyst

Methyl laurate was synthesized from lauric acid and methanol using Brønsted acid ionic liquids as catalysts, by an esterification reaction. The efficiencies of four different catalysts, 1-methylimidazolium hydrogen sulfate ([Hmim]HSO4), 2-pyrrolidonium hydrogen sulfate ([Hnhp]HSO4), 1-(3-sulfonic acid) propyl-2-pyrrolidonium hydrogen sulfate ([C3SO3Hnhp]HSO4) and H2SO4 were compared. The effect of the methanol/lauric acid molar ratio, reaction temperature, reaction time, and catalyst dosage on the lauric acid conversion was investigated by single-factor experiments. On the basis of single-factor experiments, the esterification of lauric acid and methanol was optimized using response surface methodology (RSM) based on central composite design (CCD). The results showed that the most effective catalyst was the ionic liquid [C3SO3Hnhp]HSO4. The optimal conditions were as follows: [C3SO3Hnhp]HSO4 dosage of 10 % (based on the mass of lauric acid), methanol/lauric acid molar ratio of 9:1, reaction time of 1 h and reaction temperature of 70 °C. Under these conditions, the lauric acid conversion reached 95.33 %. The catalytic activity of [C3SO3Hnhp]HSO4 still remained high after 5 cycles.

Monoraphidium sp. HDMA-20 is a new potential source of α-linolenic acid and eicosatetraenoic acid

BACKGROUND

ω-3 polyunsaturated fatty acids (PUFAs) are synthesized from α-Linolenic acid (ALA, C18:3ω3) and play important roles in anti-inflammatory and antioxidant responses in mammal cells. ALA is an essential fatty acid which cannot be produced within the human body and must be acquired through diet. The purpose of this study was to evaluate the potential of a novel microalgal strain (HDMA-20) as a source of ω-3 PUFAs including ALA and eicosatetraenoic acid (ETA, C20:4ω3).

METHOD

Phylogenetic Neighbor-Joining analysis based on 18S ribosomal DNA sequence was used to identify the microalga strain HDMA-20. Autotrophic condition was chosen to cultivate HDMA-20 to reduce the cultivation cost. GC-MS was used to determine the fatty acid composition of HDMA-20 lipid.

RESULTS

A microalgal strain (HDMA-20) from Lake Chengfeng (Daqing, Heilongjiang province, China) was found to accumulate high content of ω-3 PUFAs (63.4% of total lipid), with ALA and eicosatetraenoic acid (ETA, C20:4ω3) accounting for 35.4 and 9.6% of total lipid, respectively. Phylogenetic analysis based on 18S ribosomal DNA sequences suggested that the HDMA-20 belonged to genus Monoraphidium (Selenastraceae, Sphaeropleales) and its 18S rDNA sequence information turned out to be new molecular record of Monoraphidium species. The biomass productivity and lipid content of HDMA-20 were also investigated under autotrophic condition. The biomass productivity of HDMA-20 reached 36.3 mg L^- 1 day^- 1, and the lipid contents was 22.6% of dry weight.

CONCLUSION

HDMA-20 not only represent an additional source of ALA, but also a totally new source of ETA. The high content of ω-3 PUFAs, especially ALA, of HDMA-20, makes it suitable as a source of nutrition supplements for human health. In addition, HDMA-20 exhibited good properties in growth and lipid accumulation, implying its potential for cost-effective ω-3 PUFAs production in future.

Isolation of a novel strain of Monoraphidium sp. and characterization of its potential for α-linolenic acid and biodiesel production

α-Linolenic acid (ALA) is an essential fatty acid which cannot be synthesized de novo in mammals and must be ingested regularly in the diet. In this study, a microalgal strain named HDMA-11 was isolated from Lake Ming, China, and was found to accumulate a high ALA content (39.2% of total lipids). Phylogenetic neighbor-joining analysis indicated that HDMA-11 belongs to the genus Monoraphidium (Selenastraceae, Sphaeropleales) and its 18S ribosomal DNA sequence seemed to be a new molecular record of a Monoraphidium species. The fatty acid profiles, biomass productivity and lipid content of HDMA-11 were also investigated in autotrophic conditions. The high levels of polyunsaturated fatty acids in HDMA-11, especially ALA, make it suitable as a source of nutritional supplementation for human health. Furthermore, HDMA-11 exhibited good properties for biodiesel production, characterized by high lipid content (28.5% of dry weight), moderate biomass productivity (31.5 mg L^-1 day^-1) and a promising lipid profile.

Enhancement of Biomass and Lipid Productivities of Water Surface-Floating Microalgae by Chemical Mutagenesis

Water surface-floating microalgae have great potential for biofuel applications due to the ease of the harvesting process, which is one of the most problematic steps in conventional microalgal biofuel production. We have collected promising water surface-floating microalgae and characterized their capacity for biomass and lipid production. In this study, we performed chemical mutagenesis of two water surface-floating microalgae to elevate productivity. Floating microalgal strains AVFF007 and FFG039 (tentatively identified as Botryosphaerella sp. and Chlorococcum sp., respectively) were exposed to ethyl methane sulfonate (EMS) or 1-methyl-3-nitro-1-nitrosoguanidine (MNNG), and pale green mutants (PMs) were obtained. The most promising FFG039 PM formed robust biofilms on the surface of the culture medium, similar to those formed by wild type strains, and it exhibited 1.7-fold and 1.9-fold higher biomass and lipid productivities than those of the wild type. This study indicates that the chemical mutation strategy improves the lipid productivity of water surface-floating microalgae without inhibiting biofilm formation and floating ability.

Strategy study on enhancing lipid productivity of filamentous oleaginous microalgae Tribonema

Filamentous microalgae Tribonema is promising for biodiesel production in terms of high lipid content, easy harvesting and good contamination tolerance. As high lipid productivity is a key basis, several methods including different culture medium, phosphorus, iron and CO2 inductions were tested to enhance lipid productivity in Tribonema minus. T. minus subjected to BG11-freshwater medium achieved a favorable lipid productivity of 216.18mgL(-1)d(-1), much higher than those in other culture medium (BG11-S, Kuhl, f/2, f, 2f, BBM, ASW and ES). Secondly, the optimal phosphorus, iron and CO2 concentrations for high lipid productivity of T. minus were obtained, respectively. Finally, the cells of T. minus grown in optimized BG11 medium containing 80mgL(-1) KH2PO4 and 6mgL(-1) FeC6H5O7·NH4OH with 2% CO2 achieved a lipid productivity of 384.67mgL(-1)d(-1), representing a 1.56-fold increase from the control. Therefore, the strategy to enhance lipid productivity of T. minus was successfully proposed.

Microalgae from the Selenastraceae as emerging candidates for biodiesel production: a mini review

Over the years, microalgae have been identified to be a potential source of commercially important products such as pigments, polysaccharides, polyunsaturated fatty acids and in particular, biofuels. Current demands for sustainable fuel sources and bioproducts has led to an extensive search for promising strains of microalgae for large scale cultivation. Prospective strains identified for these purposes were among others, mainly from the genera Hematococcus, Dunaliella, Botryococcus, Chlorella, Scenedesmus and Nannochloropsis. Recently, microalgae from the Selenastraceae emerged as potential candidates for biodiesel production. Strains from the Selenastraceae such as Monoraphidium sp. FXY-10, M. contortum SAG 47.80, Ankistrodesmus sp. SP2-15 and M. minutum were high biomass and lipid producers when cultivated under optimal conditions. A number of Selenastraceae strains were also reported to be suitable for cultivation in wastewater. This review highlights recent reports on potential strains from the Selenastraceae for biodiesel production and contrasts their biomass productivity, lipid productivity as well as fatty acid profile. Cultivation strategies employed to enhance their biomass and lipid productivity as well as to reduce feedstock cost are also discussed in this paper.

The synthetic effect on volatile fatty acid disinhibition and methane production enhancement by dosing FeCl3in a sludge thermophilic anaerobic digestion system

A dosage gradient of FeCl₃was adopted and 9.92 mg Fe per g DS was favorable for the disinhibition of VFAs in sludge thermophilic digestion system.

Bioflocculant production from untreated corn stover using Cellulosimicrobium cellulans L804 isolate and its application to harvesting microalgae

BACKGROUND

Microalgae are widely studied for biofuel production. Nevertheless, harvesting step of biomass is still a critical challenge. Bioflocculants have been applied in numerous applications including the low-cost harvest of microalgae. A major bottleneck for commercial application of bioflocculant is its high production cost. Lignocellulosic substrates are abundantly available. Hence, the hydrolyzates of rice stover and corn stover have been used as carbon source to produce the bioflocculant in previous studies. However, the hydrolyzates of biomass required the neutralization of pH before the downstream fermentation processes, and the toxic by-products produced during hydrolysis process inhibited the microbial activities in the subsequent fermentation processes and contaminated the bioflocculant product. Therefore, strains that can secrete plant cell-wall-degrading enzymes and simultaneously produce bioflocculants through directly degrading the lignocellulosic biomasses are of academic and practical interests.

RESULTS

A lignocellulose-degrading strain Cellulosimicrobium cellulans L804 was isolated in this study, which can produce the bioflocculant MBF-L804 using untreated biomasses, such as corn stover, corn cob, potato residues, and peanut shell. The effects of culture conditions including initial pH, carbon source, and nitrogen source on MBF-L804 production were analyzed. The results showed that over 80 % flocculating activity was achieved when the corn stover, corn cob, potato residues, and peanut shell were used as carbon sources and 4.75 g/L of MBF-L804 was achieved under the optimized condition: 20 g/L dry corn stover as carbon source, 3 g/L yeast extract as nitrogen source, pH 8.2. The bioflocculant MBF-L804 contained 68.6 % polysaccharides and 28.0 % proteins. The Gel permeation chromatography analysis indicated that the approximate molecular weight (MW) of MBF-L804 was 229 kDa. The feasibility of harvesting microalgae Chlamydomonas reinhardtii and Chlorella minutissima using MBF-L804 was evaluated. The highest flocculating efficiencies for C. reinhardtii and C. minutissima were 99.04 and 93.83 %, respectively.

CONCLUSIONS

This study shows for the first time that C. cellulans L804 can directly convert corn stover, corn cob, potato residues and peanut shell into the bioflocculants, which can be used to effectively harvest microalgae.