Batch stage study of lipid production from crude glycerol derived from yellow grease or animal fats through microalgal fermentation

A co-fermentation strategy with wood hydrolysate and crude glycerol to enhance the lipid accumulation in Rhodosporidium toruloides-1588

Wood hydrolysate has been regarded as sustainable and renewable substrate to produce microbial lipids, a potential feedstock for the biodiesel industry. Moreover, the major by-product of biofuel industries is crude glycerol but its implementation as a carbon source is still constrained due to the presence of impurities resulting in low biomass production and low lipid titer. Thus, this study investigates the effect of different carbon ratios of hydrolysate and crude glycerol on R. toruloides-1588. Hydrolysate to crude glycerol ratio of 60:40 resulted in maximum lipid accumulation of 49% (w/w), more than 90% of sugars and glycerol consumption. Further, scale-up to bench-scale fermenter resulted in 12% higher lipid accumulation (56.3% w/w, 0.15 g/L∙h) in 50% less time than flask fermentation. Hence, the ability of R. toruloides-1588 to flourish on different carbohydrates and accumulate high lipid content will be beneficial for the further development of biorefinery industries.

Heterotrophic Cultivation of the Cyanobacterium Pseudanabaena sp. on Forest Biomass Hydrolysates toward Sustainable Biodiesel Production

Environmental pollution, greenhouse gas emissions, depletion of fossil fuels, and a growing population have sparked a search for new and renewable energy sources such as biodiesel. The use of waste or residues as substrates for microbial growth can favor the implementation of a biorefinery concept with reduced environmental footprint. Cyanobacteria constitute microorganisms with enhanced ability to use industrial effluents, wastewaters, forest residues for growth, and concomitant production of added-value compounds. In this study, a recently isolated cyanobacterium strain of Pseudanabaena sp. was cultivated on hydrolysates from pretreated forest biomass (silver birch and Norway spruce), and the production of biodiesel-grade lipids was assessed. Optimizing carbon source concentration and the (C/N) carbon-to-nitrogen ratio resulted in 66.45% w/w lipid content when microalgae were grown on glucose, compared to 62.95% and 63.79% w/w when grown on spruce and birch hydrolysate, respectively. Importantly, the lipid profile was suitable for the production of high-quality biodiesel. The present study demonstrates how this new cyanobacterial strain could be used as a biofactory, converting residual resources into green biofuel.

Liquid wastes as a renewable feedstock for yeast biodiesel production: Opportunities and challenges

Microbial lipids (bacterial, yeast, or algal) production and its utilization as a feedstock for biodiesel production in a sustainable and economical way along with waste degradation is a promising technology. Oleaginous yeasts have demonstrated multiple advantages over algae and bacteria such as high lipid yields, lipid similarity to vegetable oil, and requirement of lesser area for cultivation. Oleaginous yeasts grown on lignocellulosic solid waste as renewable feedstocks have been widely reported and reviewed. Recently, industrial effluents and other liquid wastes have been evaluated as feedstocks for biodiesel production from oleaginous yeasts. The idea of the utilization of wastewater for the growth of oleaginous yeasts for simultaneous wastewater treatment and lipid production is gaining attention among researchers. However, the detailed knowledge on the economic aspects of different process involved during the conversion of oleaginous yeast into lipids hinders its large-scale application. Therefore, this review aims to provide an overview of yeast-derived biodiesel production by utilizing industrial effluents and other liquid wastes as feedstocks. Various technologies for biomass harvesting, lipid extraction and the economic aspects specifically focused on yeast biodiesel production were also analyzed and reported in this review. The utilization of liquid wastes and the incorporation of cost-efficient harvesting and lipid extraction strategy would facilitate large-scale commercialization of biodiesel production from oleaginous yeasts in near future.

Poly(ε-L-lysine) and poly(L-diaminopropionic acid) co-produced from spent mushroom substrate fermentation: potential use as food preservatives

Poly(ε-L-lysine) and poly(L-diaminopropionic acid) are valuable homopoly (amino acids) with antimicrobial properties and mainly produced in submerged fermentation. In this study, we investigated their co-production using waste biomass and spent mushroom substrate in solid-state fermentation. Simultaneous production of poly(L-diaminopropionic acid) and poly(ε-L-lysine) was achieved in a single fermentation process using pearl oyster mushroom residues as substrate, with the supplement of glycerol and corn steep liquor. After optimization of the fermentation parameters, the maximum yield of poly(ε-L-lysine) and poly(L-diaminopropionic acid) reached 51.4 mg/g substrate and 25.4 mg/g substrate, respectively. The optimal fermentation conditions were 70% initial moisture content, pH of 6.5, 30°C and an inoculum size of 14%. Furthermore, the fermentation time was reduced from 8 days to 6 days using repeated-batch solid-state fermentation. Finally, the antimicrobial effects of poly(L-diaminopropionic acid) and poly(ε-L-lysine) were evaluated in freshly pressed grape juice, which indicated tremendous potential of this mixture in its use as biological preservative.

Production of microbial oils by the oleaginous yeast Rhodotorula graminis S1/2R in a medium based on agro-industrial by-products

Biodiesel generated by transesterification of triglycerides from renewable sources is a clean form of energy that is currently used in many countries in blends with petrodiesel. It is mainly produced from food-grade vegetable oils obtained from oleaginous crops. High prices of these oils have made the sustainability of biodiesel production questionable. The use of nonedible feedstocks, such as intracellular triglycerides accumulated by oleaginous yeasts, appears as a feasible alternative. However, it has been demonstrated that an economically sustainable production of yeast oil could only be possible if low-cost media based on industrial subproducts, or wastes are used. In this work, we propose intracellular lipids production by a previously selected oleaginous yeast strain in a medium composed only by sugar cane vinasse and crude glycerol. Different culture strategies were studied. The highest biomass and lipid yields were obtained when the yeast R. graminis S1/2R was cultivated in batch without control of dissolved oxygen. The fatty acid methyl esters obtained under these conditions met the specification of international biodiesel standards.

Glycerol waste to value added products and its potential applications

The rapid industrial and economic development runs on fossil fuel and other energy sources. Limited oil reserves, environmental issues, and high transportation costs lead towards carbon unbiased renewable and sustainable fuel. Compared to other carbon-based fuels, biodiesel is attracted worldwide as a biofuel for the reduction of global dependence on fossil fuels and the greenhouse effect. During biodiesel production, approximately 10% of glycerol is formed in the transesterification process in a biodiesel plant. The ditching of crude glycerol is important as it contains salt, free fatty acids, and methanol that cause contamination of soil and creates environmental challenges for researchers. However, the excessive cost of crude glycerol refining and market capacity encourage the biodiesel industries for developing a new idea for utilising and produced extra sources of income and treat biodiesel waste. This review focuses on the significance of crude glycerol in the value-added utilisation and conversion to bioethanol by a fermentation process and describes the opportunities of glycerol in various applications.

Graphic abstract

Use of Biofuel Industry Wastes as Alternative Nutrient Sources for DHA-Yielding Schizochytrium limacinum Production

The simultaneous use of crude glycerol and effluent from anaerobic digestate, both wastes derived from the biofuel industry, were tested in the frame of circular economy concept, as potential low-cost nutrient sources for the cultivation of rich in docosahexaenoic acid (DHA) oil microalgae strain Schizochytrium limacinum SR21. Initially, the optimal carbon and nitrogen concentration levels for high S. limacinum biomass and lipids production were determined, in a culture media containing conventional, high cost, organic nitrogen sources (yeast extract and peptone), micronutrients and crude glycerol at varying concentrations. Then, the effect of a culture media composed of crude glycerol (as carbon source) and effluent digestate at varying proportions on biomass productivity, lipid accumulation, proximate composition, carbon assimilation and fatty acid content were determined. It was shown that the biomass and total lipid content increased considerably with varying effluent concentrations reaching 49.2 g L−1 at 48% (v/v) of effluent concentration, while the lipid yield at the same effluent concentration reached 10.15 g L−1, compared to 17.0 g L−1 dry biomass and 10.2 g L−1 lipid yield when yeast extract and peptone medium with micronutrients was used. Compared to the control treatment, the above production was obtained with 48% less inorganic salts, which are needed for the preparation of the artificial sea water. It was shown that Schizochytrium limacinum SR21 was able to remediate 40% of the total organic carbon content of the biofuel wastes, while DHA productivity remained at low levels with saturated fatty acids comprising the main fraction of total fatty acid content. The results of the present study suggest that the simultaneous use of two waste streams from the biofuel industry can serve as potential nutrient sources for the growth of Schizochytrium limacinum SR21, replacing the high cost organic nutrients and up to one half the required artificial sea water salts, but upregulation of DHA productivity through optimization of the abiotic environment is necessary for industrial application, including aqua feed production.

Spent mushroom substrate for a second cultivation cycle of Pleurotus mushrooms and dephenolization of agro-industrial wastewaters

Spent mushroom substrate (SMS) of Pleurotus ostreatus was supplemented with wheat bran and soybean flour and used as substrate for a new cultivation cycle of the oyster mushrooms Pleurotus ostreatus and Pleurotus pulmonarius. The bioconversion efficiency of mushrooms produced over substrate (BE%) used and the chemical composition of sporophores were evaluated. The concentration of mycelial mass, crude exopolysaccharide content and laccase enzyme activity were also determined at the supplemented SMS before inoculation, at 50% and 100% of colonization stages in the new cultivation and in the final re-utilized SMS. The laccase enzyme was extracted to examine SMS potential for the dephenolization of olive mill and winery wastewaters. Results showed that both Pleurotus species exhibited BE over 185%, demonstrating this bioprocess could represent a promising strategy to convert SMS into nutritional food. Data also indicate the strong positive impact that SMS could have in the solid wastes’ management and agribusiness enhancement.

A review on variation in crude glycerol composition, bio-valorization of crude and purified glycerol as carbon source for lipid production

Crude glycerol (CG) is a by-product formed during the trans-esterification reaction for biodiesel production. Although crude glycerol is considered a waste stream of the biodiesel industry, it can replace expensive carbon substrates required for lipid production by oleaginous micro-organisms. However, crude glycerol has several impurities, such as methanol, soap, triglycerides, fatty acids, salts and metals, which are created during the trans-esterification process and may affect the cellular metabolism involved in lipid synthesis. This review aims to critically present a variation in crude glycerol composition depending on trans-esterification process and impact of impurities present in the crude glycerol on the cell growth and lipid accumulation by oleaginous microbes. This study also draws comparison between purified and crude glycerol for lipid production. Several techniques for crude glycerol purification (chemical treatment, thermal treatment, membrane technology, ion-exchange chromatography and adsorption) have been presented and discussed with reference to cost and environmental effects.

Effect of Salt Addition upon the Production of Metabolic Compounds by Yarrowia lipolytica Cultivated on Biodiesel-Derived Glycerol Diluted with Olive-Mill Wastewaters

One of the major environmental problems is the highly toxic agro-industrial waste called olive mill wastewater (OMW), deriving from olive oil production. On the other hand, the continuous development of the biological liquid fuel industry (biodiesel and bioethanol) makes it mandatory the process and exploitation of their main by-products, crude glycerol. This study dealt with the biotechnological conversions of biodiesel-derived crude glycerol with the use of the non-conventional yeast Yarrowia lipolytica in media that had been diluted with OMWs. OMWs, employed as simultaneous liquid medium and substrate, is a new trend recently appearing in Industrial Biotechnology, where value-added metabolites could be produced with simultaneous partial detoxification (i.e. decolorization and phenol removal) of the used residue. In the present study, diluted OMWs (containing 2.0 g/L of total phenolic compounds) blended with 70.0 g/L crude glycerol were employed as substrates. Production of value-added compounds by Y. lipolytica strain ACA-YC 5031 was studied in nitrogen-limited media favoring the production of secondary metabolites (i.e. citric acid, polyols, microbial lipids, polysaccharides). Batch-flask cultures were carried out and the impact of the addition of different NaCl concentrations (1.0%, 3.0%, 5.0% w/w) added upon the biochemical behavior of the strain was studied. Remarkable biomass production was observed in all trials, while in the “blank” experiment (no OMWs and no salt added), the metabolism was shifted toward the synthesis of polyols (Σpolyols = mannitol + arabitol + erythritol > 20 g/L and maximum total citric acid-Cit (sum of citric and isocitric acid) = 10.5 g/L). Addition of OMWs resulted in Citmax = 32.7 g/L, while Σpolyols concentration dropped to <15 g/L. Addition of salt in the OMW-based media slightly reduced the produced biomass, while Cit production drastically increased, reaching a final value of 54.0 g/L (conversion yield of Cit produced per unit of glycerol consumed = 0.82 g/g) in the trial with addition of 5.0% NaCl. Finally, significant color and phenols removal were observed, evaluating the yeast as a decontamination medium for the OMW and a great candidate for the production of value-added compounds.

Development of a Circular Oriented Bioprocess for Microbial Oil Production Using Diversified Mixed Confectionery Side-Streams

Diversified mixed confectionery waste streams were utilized in a two-stage bioprocess to formulate a nutrient-rich fermentation media for microbial oil production. Solid-state fermentation was conducted for the production of crude enzyme consortia to be subsequently applied in hydrolytic reactions to break down starch, disaccharides, and proteins into monosaccharides, amino acids, and peptides. Crude hydrolysates were evaluated in bioconversion processes using the red yeast Rhodosporidium toruloides DSM 4444 both in batch and fed-batch mode. Under nitrogen-limiting conditions, during fed-batch cultures, the concentration of microbial lipids reached 16.6-17 g·L-1 with the intracellular content being more than 40% (w/w) in both hydrolysates applied. R. toruloides was able to metabolize mixed carbon sources without catabolite repression. The fatty acid profile of the produced lipids was altered based on the substrate employed in the bioconversion process. Microbial lipids were rich in polyunsaturated fatty acids, with oleic acid being the major fatty acid (61.7%, w/w). This study showed that mixed food side-streams could be valorized for the production of microbial oil with high unsaturation degree, pointing towards the potential to produce tailor-made lipids for specific food applications. Likewise, the proposed process conforms unequivocally to the principles of the circular economy, as the entire quantity of confectionery by-products are implemented to generate added-value compounds that will find applications in the same original industry, thus closing the loop.

Chemical and biological conversion of crude glycerol derived from waste cooking oil to biodiesel

In this study, crude, purified, and pure glycerol were used to cultivate Trichosporon oleaginosus for lipid production which was then used as feedstock of biodiesel production. The purified glycerol was obtained from crude glycerol by removing soap with addition of H₃PO₄ which converted soap to free fatty acids and then separated from the solution. The results showed that purified glycerol provided similar performance as pure glycerol in lipid accumulation; however, crude glycerol as carbon source had negatively impacted the lipid production of T. oleaginosus. Purified glycerol was later used to determine the optimal glycerol concentration for lipid production. The highest lipid yield 0.19g/g glycerol was obtained at 50g/L purified glycerol in which the biomass concentration and lipid content were 10.75g/L and 47% w/w, respectively. An energy gain of 4150.51MJ could be obtained with 1tonne of the crude glycerol employed for biodiesel production through the process proposed in this study. The biodiesel production cost estimated was 6.32US$/gal. Fatty acid profiles revealed that C16:0 and C18:1 were the major compounds of the biodiesel from the lipid produced by T. oleaginosus cultivated with crude and purified glycerol. The study found that purified glycerol was promising carbon source for biodiesel production.

Cultivation of Chlorella vulgaris in a pilot-scale photobioreactor using real centrate wastewater with waste glycerol for improving microalgae biomass production and wastewater nutrients removal

To improve nutrients removal from real centrate wastewater and enhance the microalgae biomass production, cultivation of Chlorella vulgaris in lab and a pilot-scale photobioreactor with waste glycerol was studied. The results showed the optimal concentration of the crude glycerol was 1.0gL^-1 with the maximum biomass productivity of 460mgL^-1d^-1 TVS, the maximum lipid content of 27%, the nutrient removal efficiency of all above 86%, due to more balanced C/N ratio. The synergistic relationship between the wastewater-borne bacteria and the microalgae had significant good influence on nutrient removal. In pilot-scale wastewater-based algae cultivation, with 1gL^-1 waste glycerol addition, the average biomass production of 16.7gm^-2d^-1, lipid content of 23.6%, and the removal of 2.4gm^-2d^-1 NH₄⁺-N, 2.7gm^-2d^-1 total nitrogen, 3.0gm^-2d^-1 total phosphorous, and 103.0gm^-2d^-1 of COD were attained for 34days semi-continuous mode.

Lipid production and characterization by Mortierella (Umbelopsis) isabellina cultivated on lignocellulosic sugars

AIMS

To study and characterize the lipids produced by Mortierella (Umbelopsis) isabellina, during its growth on mixtures of glucose and xylose.

METHODS AND RESULTS

Glucose and xylose were utilized as carbon sources, solely or in blends, under nitrogen-limited conditions, in batch-flask trials (initial sugars at 80 g l^-1 ). Significant lipid production (maximum lipid 17·8 g l^-1 ; lipid in DCW 61·0% w/w; lipid on glucose consumed 0·23 g g^-1 ) occurred on glucose employed solely, while xylose concentration in the growth medium was conversely correlated with lipid accumulation. With increasing xylose concentrations into the blend, lipid storage decreased while xylitol in significant concentrations (up to 24 g l^-1 ) was produced. Irrespective of the sugar blend employed, significant quantities of endopolysaccharides were detected in the first growth steps (in the presence of nitrogen into the medium or barely after its disappearance) while lipids were stored thereafter. Neutral lipids, mainly composed of triacylglycerols, were the main microbial lipid fraction. Phospholipids were quantified both through fractionation and subsequent gravimetric determination and also through determination of phosphorus, and it seemed that the second method was more accurate. Phospholipids were mainly composed of phosphatidylcholine and another nonidentified compound presumably being phosphatidyldimethylethanolamine.

CONCLUSIONS

Mortierella isabellina is suitable to convert lignocellulosic sugars into lipids.

SIGNIFICANCE AND IMPACT OF THE STUDY

Differentiations between metabolism on xylose and glucose were reported. Moreover, this is one of the first reports indicating extensive analysis of microbial lipids produced by M. isabellina.

Recent advances in the production of value added chemicals and lipids utilizing biodiesel industry generated crude glycerol as a substrate - Metabolic aspects, challenges and possibilities: An overview

One of the major ecological concerns associated with biodiesel production is the generation of waste/crude glycerol during the trans-esterification process. Purification of this crude glycerol is not economically viable. In this context, the development of an efficient and economically viable strategy would be biotransformation reactions converting the biodiesel derived crude glycerol into value added chemicals. Hence the process ensures the sustainability and waste management in biodiesel industry, paving a path to integrated biorefineries. This review addresses a waste to wealth approach for utilization of crude glycerol in the production of value added chemicals, current trends, challenges, future perspectives, metabolic approaches and the genetic tools developed for the improved synthesis over wild type microorganisms were described.

Value-added processing of crude glycerol into chemicals and polymers

Crude glycerol is a low-value byproduct which is primarily obtained from the biodiesel production process. Its composition is significantly different from that of pure glycerol. Crude glycerol usually contains various impurities, such as water, methanol, soap, fatty acids, and fatty acid methyl esters. Considerable efforts have been devoted to finding applications for converting crude glycerol into high-value products, such as biofuels, chemicals, polymers, and animal feed, to improve the economic viability of the biodiesel industry and overcome environmental challenges associated with crude glycerol disposal. This article reviews recent advances of biological and chemical technologies for value-added processing of crude glycerol into chemicals and polymers, and provides strategies for addressing production challenges.

Cultivation of Chlorella vulgaris in wastewater with waste glycerol: Strategies for improving nutrients removal and enhancing lipid production

To improve nutrients removal from wastewater and enhance lipid production, cultivation of Chlorella vulgaris in wastewater with waste glycerol generated from biodiesel production using scum derived oil as feedstock was studied. The results showed that nutrients removal was improved and lipid production of C. vulgaris was enhanced with the addition of waste glycerol into wastewater to balance its C/N ratio. The optimal concentration of the pretreated glycerol for C. vulgaris was 10gL(-1) with biomass concentration of 2.92gL(-1), lipid productivity of 163mgL(-1)d(-1), and the removal of 100% ammonia and 95% of total nitrogen. Alkaline conditions prompted cell growth and lipid accumulation of C. vulgaris while stimulating nutrients removal. The application of the integration process can lower both wastewater treatment and biofuel feedstock costs.

Biorefinery for Glycerol Rich Biodiesel Industry Waste

The biodiesel industry has the potential to meet the fuel requirements in the future. A few inherent lacunae of this bioprocess are the effluent, which is 10 % of the actual product, and the fact that it is 85 % glycerol along with a few impurities. Biological treatments of wastes have been known as a dependable and economical direction of overseeing them and bring some value added products as well. A novel eco-biotechnological strategy employs metabolically diverse bacteria, which ensures higher reproducibility and economics. In this article, we have opined, which organisms and what bioproducts should be the focus, while exploiting glycerol as feed.

Energy balance of biofuel production from biological conversion of crude glycerol

Crude glycerol, a by-product of biodiesel production, has gained significant attention as a carbon source for biofuel production. This study evaluated the energy balance of biodiesel, hydrogen, biogas, and ethanol production from 3.48 million L of crude glycerol (80% w/v). The conversion efficiency (energy output divided by energy invested) was 1.16, 0.22, 0.27, and 0.40 for the production of biodiesel, hydrogen, biogas, and ethanol respectively. It was found that the use of crude glycerol for biodiesel production was an energy gain process, with a positive energy balance and conversion efficiency of greater than 1. The energy balance revealed a net energy gain of 5226 GJ per 1 million kg biodiesel produced. Production of hydrogen, biogas and ethanol from crude glycerol were energy loss processes. Therefore, the conversion of crude glycerol to lipids and subsequently to biodiesel is suggested to be a better option compared to hydrogen, biogas, or ethanol production with respect to energy balance.

Effects of oxygen transfer coefficient on dihydroxyacetone production from crude glycerol

The principal objective of this study was to evaluate the kinetics of dihydroxyacetone production by Gluconobacter frateurii CGMCC 5397 under different oxygen volumetric mass transfer coefficient (k_La) conditions in submerged bioreactors using biodiesel-derived crude glycerol as the carbon source. k_La is a key fermentation parameter for the production of dihydroxyacetone. Cultivations were conducted in baffled- and unbaffled-flask cultures (the k_La values were 24.32 h⁻¹ and 52.05 h⁻¹, respectively) and fed-batch cultures (the k_La values were held at 18.21 h⁻¹, 46.03 h⁻¹, and 82.14 h⁻¹) to achieve high dihydroxyacetone concentration and productivity. The results showed that a high k_La could dramatically increase dihydroxyacetone concentrations and productivities. The baffled-flask culture (with a k_La of 52.05 h⁻¹) favored glycerol utilization and dihydroxyacetone production, and a dihydroxyacetone concentration as high as 131.16 g/L was achieved. When the k_La was set to 82.14 h⁻¹ in the fed-batch culture, the dihydroxyacetone concentration, productivity and yield were 175.44 g/L, 7.96 g/L/h and 0.89 g/g, respectively, all of which were significantly higher than those in previous studies and will benefit dihydroxyacetone industrial production.

Reconstruction and analysis of the genome-scale metabolic model of schizochytrium limacinum SR21 for docosahexaenoic acid production

Background

Schizochytrium limacinum SR21 is a potential industrial strain for docosahexaenoic acid (DHA) production that contains more than 30–40 % DHA among its total fatty acids.

Methods

To resolve the DHA biosynthesis mechanism and improve DHA production at a systematic level, a genomescale metabolic model (GSMM), named iCY1170_DHA, which contains 1769 reactions, 1659 metabolites, and 1170 genes, was reconstructed.

Results

Based on genome annotation results and literature reports, a new DHA synthesis pathway based on a polyketide synthase (PKS) system was detected in S. limacinum. Similarly to conventional fatty acid synthesis, the biosynthesis of DHA via PKS requires abundant acetyl-CoA and NADPH. The in silico addition of malate and citrate led to increases of 24.5 % and 37.1 % in DHA production, respectively. Moreover, based on the results predicted by the model, six amino acids were shown to improve DHA production by experiment. Finally, 30 genes were identified as potential targets for DHA over-production using a Minimization of Metabolic Adjustment algorithm.

Conclusions

The reconstructed GSMM, iCY1170_DHA, could be used to elucidate the mechanism by which DHA is synthesized in S. limacinum and predict the requirements of abundant acetyl-CoA and NADPH for DHA production as well as the enhanced yields achieved via supplementation with six amino acids, malate, and citrate.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2042-y) contains supplementary material, which is available to authorized users.

The purification of crude glycerol derived from biodiesel manufacture and its use as a substrate by Rhodopseudomonas palustris to produce hydrogen

Crude glycerol (CG) from biodiesel production is often contaminated with several compounds, including saponified fatty acids (SFAs). Photofermentative growth of Rhodopseudomonas palustris on glycerol leads to hydrogen production; however, R. palustris is inhibited by SFAs. This study examines inhibition of R. palustris by SFAs, finding that, with increasing concentration of SFA, growth rate falls, reaching zero at an SFA concentration of 0.2 mM. Methods for purifying CG were examined, namely (i) treatment with ethanol and activated carbon, (ii) pH adjustment, (iii) solvent extraction, and (iv) precipitation of the fatty acids with calcium. The rates of growth and production of hydrogen were investigated using CG treated by these methods. It was found that treatment with activated carbon, pH reduction, and calcium precipitation reduced inhibition, while solvent extraction was effective only when used in conjunction with pH adjustment. These treatments allow crude glycerol to be used for hydrogen production by R. palustris.

Impurities of crude glycerol and their effect on metabolite production

Glycerol is a valuable raw material for the production of industrially useful metabolites. Among many promising applications for the use of glycerol is its bioconversion to high value-added compounds, such as 1,3-propanediol (1,3-PD), succinate, ethanol, propionate, and hydrogen, through microbial fermentation. Another method of waste material utilization is the application of crude glycerol in blends with other wastes (e.g., tomato waste hydrolysate). However, crude glycerol, a by-product of biodiesel production, has many impurities which can limit the yield of metabolites. In this mini-review we summarize the effects of crude glycerol impurities on various microbial fermentations and give an overview of the metabolites that can be synthesized by a number of prokaryotic and eukaryotic microorganisms when cultivated on glycerol.

Characterization of a new zeaxanthin producing strain of Chlorella saccharophila isolated from New Zealand marine waters

A fast growing strain of Chlorella saccharophila was isolated from the marine water of New Zealand and grown in heterotrophic conditions using glucose or glycerol as a carbon source. Biomass production was found to be higher in culture fed with glucose (2.14±0.08 g L(-1)) as compared to glycerol (0.378±0.04 g L(-1)). Lipid accumulation was similar for both carbon sources, at approximately 22% of dry cell weight. However, carotenoid yield was higher with glycerol (0.406±0.0125 mg g(-1)) than with glucose (0.21±0.034 mg g(-1)). Further optimization of the growth of the isolate gave maximal carotenoid production of 16.39±1.19 mg g(-1) total carotenoid, containing 11.32±0.64 mg g(-1) zeaxanthin and 5.07±0.55 mg g(-1) β-carotene. Comparison of various chemical and physical carotenoid extraction methods showed that ultrasonication was required for maximum extraction yields. The new strain has potential for biofuel, with carotenoid co-production.

Improvement of docosahexaenoic acid production on glycerol by Schizochytrium sp. S31 with constantly high oxygen transfer coefficient

Volumetric mass transfer coefficient (kLa) is a key fermentation parameter for the production of docosahexaenoic acid (DHA) from glycerol by Schizochytrium sp. S31. In order to elucidate the effects of kLa on the fermentations, both baffled and unbaffled flask cultures and fed-batch cultures were developed in present work. The results showed that high kLa could effectively increase the DHA concentration, DHA productivity and conversion yield (Yx/s, g/g). When kLa was set at 1802 ± 105 h(-1) in the fed-batch culture, DHA concentration was achieved at 28.93 g/L, DHA productivity at 301 mg/L/h and Yx/s at 0.44 ± 0.02 g/g, all of which were significantly higher than those in the previous similar studies.

Fatty acid shifts and metabolic activity changes of Schizochytrium sp. S31 cultured on glycerol

DHA production by Schizochytrium sp. S31 was studied in batch cultures on glycerol with stepwise dissolved oxygen strategy. Three growth stages were identified as cell growth, lipid accumulation and lipid turnover. It was revealed that fatty acid (FA) shifts during the three growth stages involved the activity changes of glycerol kinase (GK), FAD(+)-dependent glycerol-3-phosphate dehydrogenase (FAD(+)-G-3-PDH), malic enzyme (ME), ATP citrate lyase (ACL) and NAD(+)-dependent isocitrate dehydrogenase (NAD(+)-ICDH). Glycerol dissimilation in Schizochytrium sp. S31 was suggested via a phosphorylation by GK and a following oxidation by FAD(+)-G-3-PDH. Lipid accumulation of this strain was a growth-associated process, but the assimilable nitrogen depletion enhanced the accumulation of lipids. The exhaustion of glycerol induced the lipid turnover stage, where the short chain fatty acids were preferentially degraded and converted into lipid-free biomass (Xf) which was correlated to the increase of DHA content in biomass.

Value-added uses for crude glycerol--a byproduct of biodiesel production

Biodiesel is a promising alternative, and renewable, fuel. As its production increases, so does production of the principle co-product, crude glycerol. The effective utilization of crude glycerol will contribute to the viability of biodiesel. In this review, composition and quality factors of crude glycerol are discussed. The value-added utilization opportunities of crude glycerol are reviewed. The majority of crude glycerol is used as feedstock for production of other value-added chemicals, followed by animal feeds.

Impact of impurities in biodiesel-derived crude glycerol on the fermentation by Clostridium pasteurianum ATCC 6013

During the production of biodiesel, crude glycerol is produced as a byproduct at 10% (w/w). Clostridium pasteurianum has the inherent potential to grow on glycerol and produce 1,3-propanediol and butanol as the major products. Growth and product yields on crude glycerol were reported to be slower and lower, respectively, in comparison to the results obtained from pure glycerol. In this study, we analyzed the effect of each impurity present in the biodiesel-derived crude glycerol on the growth and metabolism of glycerol by C. pasteurianum. The crude glycerol contains methanol, salts (in the form of potassium chloride or sulfate), and fatty acids that were not transesterified. Salt and methanol were found to have no negative effects on the growth and metabolism of the bacteria on glycerol. The fatty acid with a higher degree of unsaturation, linoleic acid, was found to have strong inhibitory effect on the utilization of glycerol by the bacteria. The fatty acid with lower or no degrees of unsaturation such as stearic and oleic acid were found to be less detrimental to substrate utilization. The removal of fatty acids from crude glycerol by acid precipitation resulted in a fermentation behavior that is comparable to the one on pure glycerol. These results show that the fatty acids in the crude glycerol have a negative effect by directly affecting the utilization of glycerol as the carbon source, and hence their removal from crude glycerol is an essential step towards the utilization of crude glycerol.

Use of glycerol for producing 1,3-dihydroxyacetone by Gluconobacter oxydans in an airlift bioreactor

1,3-Dihydroxyacetone can be produced by biotransformation of glycerol with glycerol dehydrogenase from Gluconobacter oxydans cells. Firstly, improvement the activity of glycerol dehydrogenase was carried out by medium optimization. The optimal medium for cell cultivation was composed of 5.6g/l yeast extract, 4.7 g/l glycerol, 42.1g/l mannitol, 0.5 g/l K(2)HPO(4), 0.5 g/l KH(2)PO(4), 0.1g/l MgSO(4)·7H(2)O, and 2.0 g/l CaCO(3) with the initial pH of 4.9. Secondly, an internal loop airlift bioreactor was applied for DHA production from glycerol by resting cells of G. oxydans ZJB09113. Furthermore, the effects of pH, aeration rate and cell content on DHA production and glycerol feeding strategy were investigated. 156.3 ± 7.8 g/l of maximal DHA concentration with 89.8±2.4% of conversion rate of glycerol to DHA was achieved after 72h of biotransformation using 10g/l resting cells at 30°C, pH 5.0 and 1.5vvm of aeration rate.

A simple and fast method for the production and characterization of methylic and ethylic biodiesels from tucum oil via an alkaline route

A simple, fast, and complete route for the production of methylic and ethylic biodiesel from tucum oil is described. Aliquots of the oil obtained directly from pressed tucum (pulp and almonds) were treated with potassium methoxide or ethoxide at 40°C for 40 min. The biodiesel form was removed from the reactor and washed with 0.1 M HCl aqueous solution. A simple distillation at 100°C was carried out in order to remove water and alcohol species from the biodiesel. The oxidative stability index was obtained for the tucum oil as well as the methylic and ethylic biodiesel at 6.13, 2.90, and 2.80 h, for storage times higher than 8 days. Quality control of the original oil and of the methylic and ethylic biodiesels, such as the amount of glycerin produced during the transesterification process, was accomplished by the TLC, GC-MS, and FT-IR techniques. The results obtained in this study indicate a potential biofuel production by simple treatment of tucum, an important Amazonian fruit.

Bioconversion of crude glycerol to glycolipids in Ustilago maydis

Ustilago maydis is known to produce glycolipid-type biosurfactants. Here, we show that U. maydis is able to efficiently convert biodiesel-derived crude glycerol to glycolipids. We have optimized the medium composition and environmental factors for bioconversion of crude glycerol to glycolipids. The synthetic medium (MinCG) contains 50 g L(-1) crude glycerol and 20.3 mg L(-1) ammonium citrate as the carbon and nitrogen sources, respectively. The supplementation of trace amount of amino acids, Group-B vitamins and precursors of glycolipids, mannose and erythritol, also improved the final yield. At pH 4.0 and 30°C, 32.1 g L(-1) total glycolipids was produced in a 8.2-day fed-batch bioprocess. Methanol at 2% or above severely inhibited cell growth and production of glycolipids. Our results suggest that U. maydis is an excellent host for the bioconversion of crude glycerol to value-added products.