Microalgae-based biorefinery--from biofuels to natural products

Spirulina platensis biomass composition is influenced by the light availability and harvest phase in raceway ponds

The behavior of cyanobacteria and its potential use for biofuel production in scale-up conditions is a topic of growing importance. The aim of our work is to study the effects of illumination, stirring, and different growth phases on the cultivation of the cyanobacteria Spirulina platensis in 10 L raceways. The cultivations were carried out in a greenhouse under measured, but not controlled, illumination and in agitated raceways with stirring speeds varying from 0.1 to 0.4 m s^-1, using culture media with nutrient depletion. At the end of the stationary phase (SP) and decline of culture, the biomass was harvested and used to determine the chemical composition. The stirring rate and the growing phase influenced the carbohydrate concentration. In both phases of cultivation, compared to high-speed stirring, stirring at lower speeds produced fewer carbohydrates in the culture. Biomass grown until the end of the SP with a stirring speed of 0.35 m s^-1 had a carbohydrate content of 72%, which is very high compared to that reported in the literature.

Enhanced Lipid Production in Chlamydomonas reinhardtii by Co-culturing With Azotobacter chroococcum

The green algae, Chlamydomonas reinhardtii, is one of the model species used to study lipid production, although research has focused on nitrogen-deficient cultures, that inhibit the development of biomass by C. reinhardtii and limit lipid production. In this study, Azotobacter chroococcum was added to the algal culture to improve lipid accumulation and productivity of C. reinhardtii. The maximum lipid content and production of C. reinhardtii in the co-culture were 65.85% and 387.76 mg/L, respectively, which were 2.3 and 5.9 times the control's levels of 29.11% and 65.99 mg/L, respectively. The maximum lipid productivity of C. reinhardtii in the co-culture was 141.86 mg/(L·day), which was 19.4 times the control's levels of 7.33 mg/(L·day). These increases were attributed to the enhanced growth and biomass and the change in the activity of enzymes related to lipid regulation (ACCase, DGAT, and PDAT). Compared to the conventional strategy of nitrogen deprivation, A. chroococcum added to the culture of C. reinhardtii resulted in higher lipid accumulation and activity, greater efficiency in the conversion of proteins to lipids, higher biomass, and increased growth of C. reinhardtii. Therefore, using A. chroococcum to improve the growth and biomass of C. reinhardtii is an efficient, rapid, and economically viable strategy for enhancing lipid production in C. reinhardtii.

Multilateral approach on enhancing economic viability of lipid production from microalgae: A review

Microalgae have been rising as a feedstock for biofuel in response to the energy crisis. Due to a high lipid content, composed of fatty acids favorable for the biodiesel production, microalgae are still being investigated as an alternative to biodiesel. Environmental factors and process conditions can alternate the quality and the quantity of lipid produced by microalgae, which can be critical for the overall production of biodiesel. To maximize both the lipid content and the biomass productivity, it is necessary to start with robust algal strains and optimal physio-chemical properties of the culture environment in combination with a novel culture system. These accumulative approaches for cost reduction can take algal process one step closer in achieving the economic feasibility.

Media Screening for Obtaining Haematococcus pluvialis Red Motile Macrozooids Rich in Astaxanthin and Fatty Acids

Astaxanthin from Haematococcus pluvialis is commercially produced in a two-stage process, involving green vegetative (macrozooid) and red aplanospore stages. This approach has been scaled up to an industrial process but constraints limit its commercial success and profitability, including: contamination issues, high pigment extraction costs, requirements for high light levels and photo-bleaching in the red stage. However, in addition to the aplanospore stage, this alga can produce astaxanthin in vegetative palmelloid and motile macrozooid cells. In this study, a two-stage process utilising different media in the green stage, with subsequent re-suspension in medium without nitrate was employed to optimise the formation of red motile macrozooids. Optimal growth in the green phase was obtained on cultivation under mixotrophic conditions in EG:JM media followed by re-suspension in medium without nitrate resulting in red motile macrozooids with an astaxanthin content of 2.74% (78.4% of total carotenoids) and a lipid content of 35.3% (rich in unsaturated fatty acids. It is envisaged that the red motile macrozooids could be harvested and fed as a whole-cell product directly in the animal feed and aquaculture sectors, or used as a blend of carotenoids and polyunsaturated fatty acids (PUFAs) in nutraceutical products.

Engineered Paper-Based Cell Culture Platforms

Paper is used in various applications in biomedical research including diagnostics, separations, and cell cultures. Paper can be conveniently engineered due to its tunable and flexible nature, and is amenable to high-throughput sample preparation and analysis. Paper-based platforms are used to culture primary cells, tumor cells, patient biopsies, stem cells, fibroblasts, osteoblasts, immune cells, bacteria, fungi, and plant cells. These platforms are compatible with standard analytical assays that are typically used to monitor cell behavior. Due to its thickness and porous nature, there are no mass transport limitations to/from the cells in paper scaffolds. It is possible to pattern paper in different scales (micrometer to centimeter), generate modular configurations in 3D, fabricate multicellular and compartmentalized tissue mimetics for clinical applications, and recover cells from the scaffolds for further analysis. 3D paper constructs can provide physiologically relevant tissue models for personalized medicine. Layer-by layer strategies to assemble tissue-like structures from low-cost and biocompatible paper-based materials offer unique opportunities that include understanding fundamental biology, developing disease models, and assembling different tissues for organ-on-paper applications. Paper-based platforms can also be used for origami-inspired tissue engineering. This work provides an overview of recent progress in engineered paper-based biomaterials and platforms to culture and analyze cells.

Formulation and utilisation of spent anaerobic digestate fluids for the growth and product formation of single cell algal cultures in heterotrophic and autotrophic conditions

Spent anaerobically digested effluents of agricultural origin were collected and treated using membrane filtration to achieve three-large particle free-nutrient streams of N:P ratios of 16.53, 3.78 and 14.22. Three algal species were grown on these streams, achieving good levels of bioremediation of digester fluids simultaneously with biomass and associated end product formation. Nannochloropsis oceanica and Scenedesmus quadricuada, where proven highly effective in remediating the streams achieving ammonia and phosphate reduction over 60% while for Schizochytrium limacinum SR21 these serve as an ideal production medium for lipids and biomass reaching 16.70w/w% and 1.42gL^-1 correspondingly. These processes thus provide treatment of sludge, avoiding the disposal problems by land spreading. The solid components are nutrient depleted but rich in organic matter as a soil enhancer, while the fluids rich in nutrients can be efficiently utilised for growth to generate high value materials of microalgae facilitating water reclamation.

Spirulina platensis is more efficient than Chlorella homosphaera in carbohydrate productivity

This study aimed to compare the production of biomass with high carbohydrate content by Spirulina platensis LEB 52 and Chlorella homosphaera microalgae. The cultivation of C. homosphaera and S. platensis LEB 52 was performed in standard medium diluted at 50%, and glucose was added as a source of organic carbon for mixotrophic metabolism. The sodium nitrate concentration was increased and the nitrogen components were reduced in the media to induce the synthesis of carbohydrates. C. homosphaera and S. platensis LEB 52 produced 16.32 and 116 mg L^-1 of carbohydrates per day, respectively, when cultivated with 50% less nitrogen and 20% and 10% more sodium chloride, compared with the control. Glucose addition was an essential factor for microalgal growth, resulting in biomass increases of up to 2.79- and 3.45-fold for C. homosphaera and S. platensis LEB 52, respectively. Spirulina presented better characteristics than Chlorella with regard to the capacities of growth and carbohydrate synthesis.

Valorization of Spent Escherichia coli Media Using Green Microalgae Chlamydomonas reinhardtii and Feedstock Production

The coupling of Chlamydomonas reinhardtii biomass production for nutrients removal of Escherichia coli anaerobic broth (EAB) is thought to be an economically feasible option for the cultivation of microalgae. The feasibility of growing microalgae in using EAB high in nutrients for the production of more biomass was examined. EAB comprised of nutrient-abundant effluents, which can be used to produce microalgae biomass and remove environment pollutant simultaneously. In this study, C. reinhardtii 21gr (cc1690) was cultivated in different diluted E. coli anaerobic broth supplemented with trace elements under mixotrophic and heterotrophic conditions. The results showed that C. reinhardtii grown in 1×, 1/2×, 1/5× and 1/10×E. coli anaerobic broth under mixotrophic conditions exhibited specific growth rates of 2.71, 2.68, 1.45, and 1.13 day^-1, and biomass production of 201.9, 184.2, 175.5, and 163.8 mg L^-1, respectively. Under heterotrophic conditions, the specific growth rates were 1.80, 1.86, 1.75, and 1.02 day^-1, and biomass production were 45.6, 29.4, 15.8, and 12.1 mg L^-1, respectively. The removal efficiency of chemical oxygen demand, total-nitrogen and total-phosphorus from 1×E. coli anaerobic broth was 21.51, 22.41, and 15.53%. Moreover, the dry biomass had relatively high carbohydrate (44.3%) and lipid content (18.7%). Therefore, this study provides an environmentally sustainable as well economical method for biomass production in promising model microalgae and subsequently paves the way for industrial use.

Effect of salinity stress on growth, lipid productivity, fatty acid composition, and biodiesel properties in Acutodesmus obliquus and Chlorella vulgaris

Two microalgae strains including Chlorella vulgaris and Acutodesmus obliquus were grown on BG11 medium with salinity stress ranging from 0.06 to 0.4 M NaCl. Highest lipid content in C. vulgaris and A. obliquus was 49 and 43% in BG11 amended with 0.4 M NaCl. The microalgal strains C. vulgaris and A. obliquus grow better at 0.06 M NaCl concentration than control condition. At 0.06 M NaCl, improved dry biomass content in C. vulgaris and A. obliquus was 0.92 and 0.68 gL^-1, respectively. Stress biomarkers like reactive oxygen species, antioxidant enzyme catalase, and ascorbate peroxidase were also lowest at 0.06 M NaCl concentration revealing that both the microalgal strains are well acclimatized at 0.06 M NaCl concentration. The fatty acid composition of the investigated microalgal strains was also improved by increased NaCl concentration. At 0.4 M NaCl, palmitic acid (37%), oleic acid (15.5%), and linoleic acid (20%) were the dominant fatty acids in C. vulgaris while palmitic acid (54%) and stearic acid (26.6%) were major fatty acids found in A. obliquus. Fatty acid profiling of C. vulgaris and A. obliquus significantly varied with salinity concentration. Therefore, the study showed that salt stress is an effective stress that could increase not only the lipid content but also improved the fatty acid composition which could make C. vulgaris and A. obliquus potential strains for biodiesel production.

Microalgae biorefinery: High value products perspectives

Microalgae have received much interest as a biofuel feedstock in response to the uprising energy crisis, climate change and depletion of natural sources. Development of microalgal biofuels from microalgae does not satisfy the economic feasibility of overwhelming capital investments and operations. Hence, high-value co-products have been produced through the extraction of a fraction of algae to improve the economics of a microalgae biorefinery. Examples of these high-value products are pigments, proteins, lipids, carbohydrates, vitamins and anti-oxidants, with applications in cosmetics, nutritional and pharmaceuticals industries. To promote the sustainability of this process, an innovative microalgae biorefinery structure is implemented through the production of multiple products in the form of high value products and biofuel. This review presents the current challenges in the extraction of high value products from microalgae and its integration in the biorefinery. The economic potential assessment of microalgae biorefinery was evaluated to highlight the feasibility of the process.

Bacterial cellulose production by Komagataeibacter hansenii using algae-based glucose

Bacterial cellulose (BC) is a homopolymer and it is distinguished from plant-based cellulose by its unique properties such as high purity, high crystallinity, high water-holding capacity, and good biocompatibility. Microalgae are unicellular, photosynthetic microorganisms and are known to have high protein, starch, and oil content. In this study, Chlorella vulgaris was evaluated as source of glucose for the production of BC. To increase the starch content of algae the effect of nutrient starvation (nitrogen and sulfur) and light deficiency were tested in a batch assay. The starch contents (%) were 5.27 ± 0.04, 7.14 ± 0.18, 5.00 ± 0.08, and 1.35 ± 0.04 for normal cultivation, nitrogen starvation, sulfur starvation, and dark cultivation conditions, respectively. The performance of enzymatic and acidic methods was compared for the starch hydrolysis. This study demonstrated for the first time that acid hydrolysate of algal starch can be used to substitute glucose in the fermentation medium of Komagataeibacter hansenii for BC production. Glucose was used as a control for BC production. BC production yields on dry weight basis were 1.104 ± 0.002 g/L and 1.202 ± 0.005 g/L from algae-based glucose and glucose, respectively. The characterization of both BCs produced from glucose and algae-based glucose was investigated by scanning electron microscopy and Fourier transform infrared spectroscopy. The results have shown that the structural characteristics of algae-based BC were comparable to those of glucose-based BC.

Recent insights into biohydrogen production by microalgae - From biophotolysis to dark fermentation

One of the best options to alleviate the problems associated with global warming and climate change is to reduce burning of fossil fuels and search for new alternative energy resources. In case of biodiesel and bioethanol production, the choice of feedstock and the process design influences the GHG emissions and appropriate methods need to be adapted. Hydrogen is a zero-carbon and energy dense alternative energy carrier with clean burning properties and biohydrogen production by microalgae can reduce production associated GHG emissions to a great extent. Biohydrogen can be produced through dark fermentation using sugars, starch, or cellulosic materials. Microalgae-based biohydrogen production is recently regarded as a promising pathway for biohydrogen production via photolysis or being a substrate for anaerobic fermentation. This review lists the methods of hydrogen production by microalgae. The enzymes involved and the factors affecting the biohydrogen production process are discussed. The bottlenecks in microalgae-based biohydrogen production are critically reviewed and future research areas in hydrogen production are presented.

Current lipid extraction methods are significantly enhanced adding a water treatment step in Chlorella protothecoides

Background

Microalgae have the potential to rapidly accumulate lipids of high interest for the food, cosmetics, pharmaceutical and energy (e.g. biodiesel) industries. However, current lipid extraction methods show efficiency limitation and until now, extraction protocols have not been fully optimized for specific lipid compounds. The present study thus presents a novel lipid extraction method, consisting in the addition of a water treatment of biomass between the two-stage solvent extraction steps of current extraction methods. The resulting modified method not only enhances lipid extraction efficiency, but also yields a higher triacylglycerols (TAG) ratio, which is highly desirable for biodiesel production.

Results

Modification of four existing methods using acetone, chloroform/methanol (Chl/Met), chloroform/methanol/H₂O (Chl/Met/H₂O) and dichloromethane/methanol (Dic/Met) showed respective lipid extraction yield enhancement of 72.3, 35.8, 60.3 and 60.9%. The modified acetone method resulted in the highest extraction yield, with 68.9 ± 0.2% DW total lipids. Extraction of TAG was particularly improved with the water treatment, especially for the Chl/Met/H₂O and Dic/Met methods. The acetone method with the water treatment led to the highest extraction level of TAG with 73.7 ± 7.3 µg/mg DW, which is 130.8 ± 10.6% higher than the maximum value obtained for the four classical methods (31.9 ± 4.6 µg/mg DW). Interestingly, the water treatment preferentially improved the extraction of intracellular fractions, i.e. TAG, sterols, and free fatty acids, compared to the lipid fractions of the cell membranes, which are constituted of phospholipids (PL), acetone mobile polar lipids and hydrocarbons. Finally, from the 32 fatty acids analyzed for both neutral lipids (NL) and polar lipids (PL) fractions, it is clear that the water treatment greatly improves NL-to-PL ratio for the four standard methods assessed.

Conclusion

Water treatment of biomass after the first solvent extraction step helps the subsequent release of intracellular lipids in the second extraction step, thus improving the global lipids extraction yield. In addition, the water treatment positively modifies the intracellular lipid class ratios of the final extract, in which TAG ratio is significantly increased without changes in the fatty acids composition. The novel method thus provides an efficient way to improve lipid extraction yield of existing methods, as well as selectively favoring TAG, a lipid of the upmost interest for biodiesel production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0633-9) contains supplementary material, which is available to authorized users.

A Holistic Approach to Managing Microalgae for Biofuel Applications

Microalgae contribute up to 60% of the oxygen content in the Earth’s atmosphere by absorbing carbon dioxide and releasing oxygen during photosynthesis. Microalgae are abundantly available in the natural environment, thanks to their ability to survive and grow rapidly under harsh and inhospitable conditions. Microalgal cultivation is environmentally friendly because the microalgal biomass can be utilized for the productions of biofuels, food and feed supplements, pharmaceuticals, nutraceuticals, and cosmetics. The cultivation of microalgal also can complement approaches like carbon dioxide sequestration and bioremediation of wastewaters, thereby addressing the serious environmental concerns. This review focuses on the factors affecting microalgal cultures, techniques adapted to obtain high-density microalgal cultures in photobioreactors, and the conversion of microalgal biomass into biofuels. The applications of microalgae in carbon dioxide sequestration and phycoremediation of wastewater are also discussed.

Automation of route identification and optimisation based on data-mining and chemical intuition

Data-mining of Reaxys and network analysis of the combined literature and in-house reactions set were used to generate multiple possible reaction routes to convert a bio-waste feedstock, limonene, into a pharmaceutical API, paracetamol. The network analysis of data provides a rich knowledge-base for generation of the initial reaction screening and development programme. Based on the literature and the in-house data, an overall flowsheet for the conversion of limonene to paracetamol was proposed. Each individual reaction–separation step in the sequence was simulated as a combination of the continuous flow and batch steps. The linear model generation methodology allowed us to identify the reaction steps requiring further chemical optimisation. The generated model can be used for global optimisation and generation of environmental and other performance indicators, such as cost indicators. However, the identified further challenge is to automate model generation to evolve optimal multi-step chemical routes and optimal process configurations.

From Current Algae Products to Future Biorefinery Practices: A Review

Microalgae are considered to be one of the most promising next generation bio-based/food feedstocks with a unique lipid composition, high protein content, and an almost unlimited amount of other bio-active molecules. High-value components such as the soluble proteins, (poly) unsaturated fatty acids, pigments, and carbohydrates can be used as an important ingredient for several markets, such as the food/feed/chemical/cosmetics and health industries. Although cultivation costs have decreased significantly in the last few decades, large microalgae production processes become economically viable if all complex compounds are optimally valorized in their functional state. To isolate these functional compounds from the biomass, cost-effective, mild, and energy-efficient biorefinery techniques need to be developed and applied. In this review we describe current microalgae biorefinery strategies and the derived products, followed by new technological developments and an outlook toward future products and the biorefinery philosophy.

Increased lipid production by heterologous expression of AtWRI1 transcription factor in Nannochloropsis salina

BACKGROUND

Genetic engineering of microalgae is necessary to produce economically feasible strains for biofuel production. Current efforts are focused on the manipulation of individual metabolic genes, but the outcomes are not sufficiently stable and/or efficient for large-scale production of biofuels and other materials. Transcription factors (TFs) are emerging as good alternatives for engineering of microalgae, not only to increase production of biomaterials but to enhance stress tolerance. Here, we investigated an AP2 type TF Wrinkled1 in Arabidopsis (AtWRI1) known as a key regulator of lipid biosynthesis in plants, and applied it to industrial microalgae, Nannochloropsis salina.

RESULTS

We expressed AtWRI1 TF heterologously in N. salina, named NsAtWRI1, in an effort to re-enact its key regulatory function of lipid accumulation. Stable integration AtWRI1 was confirmed by RESDA PCR, and its expression was confirmed by Western blotting using the FLAG tag. Characterizations of transformants revealed that the neutral and total lipid contents were greater in NsAtWRI1 transformants than in WT under both normal and stress conditions from day 8. Especially, total lipid contents were 36.5 and 44.7% higher in NsAtWRI1 2-3 than in WT under normal and osmotic stress condition, respectively. FAME contents of NsAtWRI1 2-3 were also increased compared to WT. As a result, FAME yield of NsAtWRI1 2-3 was increased to 768 mg/L/day, which was 64% higher than that of WT under the normal condition. We identified candidates of AtWRI1-regulated genes by searching for the presence of the AW-box in promoter regions, among which lipid metabolic genes were further analyzed by qRT-PCR. Overall, qRT-PCR results on day 1 indicated that AtWRI1 down-regulated TAGL and DAGK, and up-regulated PPDK, LPL, LPGAT1, and PDH, resulting in enhanced lipid production in NsAtWRI1 transformants from early growth phase.

CONCLUSION

AtWRI1 TF regulated several genes involved in lipid synthesis in N. salina, resulting in enhancement of neutral lipid and FAME production. These findings suggest that heterologous expression of AtWRI1 TF can be utilized for efficient biofuel production in industrial microalgae.

Extractive disruption process integration using ultrasonication and an aqueous two-phase system for protein recovery from Chlorella sorokiniana

Microalgae emerge as the most promising protein sources for aquaculture industry. However, the commercial proteins production at low cost remains a challenge. The process of harnessing microalgal proteins involves several steps such as cell disruption, isolation and extraction. The discrete processes are generally complicated, time-consuming and costly. To date, the notion of integrating microalgal cell disruption and proteins recovery process into one step is yet to explore. Hence, this study aimed to investigate the feasibility of applying methanol/potassium ATPS in the integrated process for proteins recovery from Chlorella sorokiniana. Parameters such as salt types, salt concentrations, methanol concentrations, NaCl addition were optimized. The possibility of upscaling and the effectiveness of recycling the phase components were also studied. The results showed that ATPS formed by 30% (w/w) K₃PO₄ and 20% (w/w) methanol with 3% (w/w) NaCl addition was optimum for proteins recovery. In this system, the partition coefficient and yield were 7.28 and 84.23%, respectively. There were no significant differences in the partition coefficient and yield when the integrated process was upscaled to 100-fold. The recovered phase components can still be recycled effectively at fifth cycle. In conclusions, this method is simple, rapid, environmental friendly and could be implemented at large scale.

Magnetic fields as triggers of microalga growth: evaluation of its effect on Spirulina sp

This study aimed at evaluating the influence of magnetic field on the growth and biomass composition of Spirulina sp., cultivated in vertical tubular photobioreactors. Magnetic fields of 5, 30 and 60mT generated by electric current and ferrite magnets were applied at different lengths of time. The magnetic field of 30 and 60mT for 1hd(-1) stimulated the growth, thus leading to higher biomass concentration by comparison with the control culture. Increase in productivity, protein and carbohydrate contents were 105.1% (60mT for 1hd(-1)), 16.6% (60mT for 24hd(-1)) and 133.2% (30mT for 24hd(-1)), respectively. These values were higher than the ones of the control. Results showed that magnetic field may influence the growth of Spirulina sp., since it triggers a stimulating effect and can leads to twofold biomass concentration in equal cultivation time periods.

The need to implement an efficient biomass fractionation and full utilization based on the concept of "biorefinery" for a viable economic utilization of microalgae

In the present work, microalgae strains, such as Scenedesmus obliquus and Phaeodactylum tricornutum grown in indoor/outdoor photobioreactors (PBRs) and in open ponds (this is the first study on such strains cultivated in the local Southern Italy climatic conditions), were fully analyzed for their protein content, carbohydrates, lipids, and fatty acid profile in order to assess their potential use for the production of biofuels, chemicals, and omega-3, and as animal feed and human food. They are compared with Nannochloropsis sp. (commercial sample) which was fully analyzed in our laboratory and Chlorella (literature data). An economic evaluation was carried out, demonstrating that the cultivation of microalgae for the production of only biofuels will not match the economic standards. Conversely, if chemicals are also produced applying the biorefinery concept and using wastewater as a source of nutrients, it will be possible to have a good positive return from microalgae.

Co-production of carbonic anhydrase and phycobiliproteins by Spirulina sp. and Synechococcus nidulans

The aim of this work was to study the co-production of the carbonic anhydrase, C-phycocyanin and allophycocyanin during cyanobacteria growth. Spirulina sp. LEB 18 demonstrated a high potential for simultaneously obtaining the three products, achieving a carbonic anhydrase (CA) productivity of 0.97U/L/d and the highest C-phycocyanin (PC, 5.9μg/mL/d) and allophycocyanin (APC, 4.3μg/mL/d) productivities. In the extraction study, high extraction yields were obtained from Spirulina using an ultrasonic homogenizer (CA: 25.5U/g; PC: 90mg/g; APC: 70mg/g). From the same biomass, it was possible to obtain three biomolecules that present high industrial value.

Waste biorefinery models towards sustainable circular bioeconomy: Critical review and future perspectives

Increased urbanization worldwide has resulted in a substantial increase in energy and material consumption as well as anthropogenic waste generation. The main source for our current needs is petroleum refinery, which have grave impact over energy-environment nexus. Therefore, production of bioenergy and biomaterials have significant potential to contribute and need to meet the ever increasing demand. In this perspective, a biorefinery concept visualizes negative-valued waste as a potential renewable feedstock. This review illustrates different bioprocess based technological models that will pave sustainable avenues for the development of biobased society. The proposed models hypothesize closed loop approach wherein waste is valorised through a cascade of various biotechnological processes addressing circular economy. Biorefinery offers a sustainable green option to utilize waste and to produce a gamut of marketable bioproducts and bioenergy on par to petro-chemical refinery.

Knowledge management in a waste based biorefinery in the QbD paradigm

Shifting resource base from fossil feedstock to renewable raw materials for production of chemical products has opened up an area of novel applications of industrial biotechnology-based process tools. This review aims to provide a concise and focused discussion on recent advances in knowledge management to facilitate efficient and optimal operation of a biorefinery. Application of quality by design (QbD) and process analytical technology (PAT) as tools for knowledge creation and management at different levels has been highlighted. Role of process integration, government policies, knowledge exchange through collaboration, and use of databases and computational tools have also been touched upon.

Biosynthesis of silver nanoparticle and its application in cell wall disruption to release carbohydrate and lipid from C. vulgaris for biofuel production

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The AgNP was successfully synthesised from soil isolated bacterium Bacillus subtilis.

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The synthesised AgNPs were confirmed by UV-Spec, FTIR, TEM and XRD.

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The AgNPs were successfully treated microalga to disrupt its cell wall to release lipids and carbohydrates.

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The cell wall damages evidenced by LDH assay and SEM.

Microalgae are the fledging feedstocks yielding raw materials for the production of third generation biofuel. Assorted and conventional cell wall disruption techniques were helpful in extracting lipids and carbohydrates, nevertheless the disadvantages have led the biotechnologists to explore new process to lyse cell wall in a faster and an economical manner. Silver nanoparticles have the ability to break the cell wall of microalgae and release biomolecules effectively. Green synthesis of silver nanoparticles was performed using a novel bacterial isolate of Bacillus subtilis. Characterisation of nanosilver and its effect on cell wall lysis of microalgae were extensively analysed. Cell wall damage was confirmed by lactate dehydrogenase assay and visually by SEM analysis. This first piece of research work on direct use of nanoparticles for cell wall lysis would potentially be advantageous over its conventional approaches and a greener, cost effective and non laborious method for the production of biodiesel.

The isolation and identification of new microalgal strains producing oil and carotenoid simultaneously with biofuel potential

Taxonomy and phylogeny of twenty two microalgal isolates were examined using both universal and newly designed molecular primers. Among the isolates, Scenedesmus bijugus, Coelastrella sp., Auxenochlorella protothecoides, and Chlorella sp. were particularly promising in terms of producing lipids as measured by fatty acid methyl esters (FAME) analysis and significant concentration of carotenoids. A comparative experiment showed that S. bijugus and Chlorella sp. were the most promising candidates (L(-)(1)d(-)(1), with biomass) 174.77±6.75, 169.81±5.22mg, lipids 40.14±3.31, 39.72±3.89mg, lutein 0.47, 0.36mg, and astaxanthin 0.27, 0.18mg respectively. The fatty acids produced by these microalgal isolates were mainly palmitic, stearic, oleic, linoleic, and linolenic acid. The freshwater microalgal isolate S. bijugus be the most suitable isolate for producing biodiesel and carotenoids, due to high productivity of biomass, lipids, metabolites, and its suitable fatty acid profile.

Increase in the carbohydrate content of the microalgae Spirulina in culture by nutrient starvation and the addition of residues of whey protein concentrate

Non-renewable sources that will end with time are the largest part of world energy consumption, which emphasizes the necessity to develop renewable sources of energy. This necessity has created opportunities for the use of microalgae as a biofuel. The use of microalgae as a feedstock source for bioethanol production requires high yields of both biomass and carbohydrates. With mixotrophic cultures, wastewater can be used to culture algae. The aim of the study was to increase the carbohydrate content in the microalgae Spirulina with the additions of residues from the ultra and nanofiltration of whey protein. The nutrient deficit in the Zarrouk medium diluted to 20% and the addition of 2.5% of both residue types led to high carbohydrate productivity (60 mg L(-1) d(-1)). With these culture conditions, the increase in carbohydrate production in Spirulina indicated that the conditions were appropriate for use with microalgae as a feedstock in the production of bioethanol.

A Review on the Assessment of Stress Conditions for Simultaneous Production of Microalgal Lipids and Carotenoids

Microalgal species are potential resource of both biofuels and high-value metabolites, and their production is growth dependent. Growth parameters can be screened for the selection of novel microalgal species that produce molecules of interest. In this context our review confirms that, autotrophic and heterotrophic organisms have demonstrated a dual potential, namely the ability to produce lipids as well as value-added products (particularly carotenoids) under influence of various physico-chemical stresses on microalgae. Some species of microalgae can synthesize, besides some pigments, very-long-chain polyunsaturated fatty acids (VL-PUFA,>20C) such as docosahexaenoic acid and eicosapentaenoic acid, those have significant applications in food and health. Producing value-added by-products in addition to biofuels, fatty acid methyl esters (FAME), and lipids has the potential to improve microalgae-based biorefineries by employing either the autotrophic or the heterotrophic mode, which could be an offshoot of biotechnology. The review considers the potential of microalgae to produce a range of products and indicates future directions for developing suitable criteria for choosing novel isolates through bioprospecting large gene pool of microalga obtained from various habitats and climatic conditions.