Bioconversion technologies of crude glycerol to value added industrial products

Crude glycerol that is produced as the by-product from biodiesel, has to be effectively utilized to contribute to the viability of biodiesel. Crude glycerol in large amounts can pose a threat to the environment. Therefore, there is a need to convert this crude glycerol into valued added products using biotechnological processes, which brings new revenue to biodiesel producers. Crude glycerol can serve as a feedstock for biopolymers, poly unsaturated fatty acids, ethanol, hydrogen and n-butanol production and as a raw material for different value added industrial products. Hence, in this review we have presented different bioconversion technologies of glycerol to value added industrial products.

Lipid production by the oleaginous yeast Yarrowia lipolytica using industrial by-products under different culture conditions

BACKGROUND

Microbial lipid production using renewable feedstock shows great promise for the biodiesel industry.

RESULTS

In this study, the ability of a lipid-engineered Yarrowia lipolytica strain JMY4086 to produce lipids using molasses and crude glycerol under different oxygenation conditions and at different inoculum densities was evaluated in fed-batch cultures. The greatest lipid content, 31% of CDW, was obtained using a low-density inoculum, a constant agitation rate of 800 rpm, and an oxygenation rate of 1.5 L/min. When the strain was cultured for 450 h in a chemostat containing a nitrogen-limited medium (dilution rate of 0.01 h(-1); 250 g/L crude glycerol), volumetric lipid productivity was 0.43 g/L/h and biomass yield was 60 g CDW/L. The coefficient of lipid yield to glycerol consumption (Y L/gly) and the coefficient of lipid yield to biomass yield (Y L/X ) were equal to 0.1 and 0.4, respectively.

CONCLUSIONS

These results indicate that lipids may be produced using renewable feedstock, thus providing a means of decreasing the cost of biodiesel production. Furthermore, using molasses for biomass production and recycling glycerol from the biodiesel industry should allow biolipids to be sustainably produced.

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.

Robust succinic acid production from crude glycerol using engineered Yarrowia lipolytica

BACKGROUND

Integrating waste management with fuels and chemical production is considered to address the food waste problem and oil crisis. Approximately, 600 million tonnes crude glycerol is produced from the biodiesel industry annually, which is a top renewable feedstock for succinic acid production. To meet the increasing demand for succinic acid production, the development of more efficient and cost-effective production methods is urgently needed. Herein, we have proposed a new strategy for integration of both biodiesel and SA production in a biorefinery unit by construction of an aerobic yeast Yarrowia lipolytica with a deletion in the gene coding succinate dehydrogenase subunit 5.

RESULTS

Robust succinic acid production by an engineered yeast Y. lipolytica from crude glycerol without pre-treatment was demonstrated. Diversion of metabolic flow from tricarboxylic acid cycle led to the success in generating a succinic acid producer Y. lipolytica PGC01003. The fermentation media and conditions were optimized, which resulted in 43 g L(-1) succinic acid production from crude glycerol. Using the fed-batch strategy in 2.5 L fermenter, up to 160 g L(-1) SA was yielded, indicating the great industrial potential.

CONCLUSIONS

Inactivation of SDH5 in Y. lipolytica Po1f led to succinic acid accumulation and secretion significantly. To our best knowledge, this is the highest titer obtained in fermentation on succinic acid production. In addition, the performance of batch and fed-batch fermentation showed high tolerance and yield on biodiesel by-product crude glycerol. All these results indicated that PGC01003 is a promising microbial factorial cell for the highly efficient strategy solving the environmental problem in connection with the production of value-added product.

Heavy metals removal from wastewater using extracellular polymeric substances produced by Cloacibacterium normanense in wastewater sludge supplemented with crude glycerol and study of extracellular polymeric substances extraction by different methods

Extracellular polymeric substances synthesis by Cloacibacterium was affected by different concentrations of glycerol in the medium. The concentration of EPS in 72h fermentation was increased from 13g/L with no external carbon supplementation to 21.3±0.7g/L with 2% (w/v) crude glycerol addition. Physical and chemical extraction methods (heating, centrifugation and ethylene diamine tetra-acetic acid (EDTA)) were used in this study and their performance to extract EPS was compared. A significant variation in concentration of extracted B-EPS (broth-EPS) by heating (20.8±0.5g/L) and centrifugation (21.3±0.7g/L) extraction methods was not observed. However, in case of extraction with EDTA (5g/L), the B-EPS concentration extracted was 25.5±0.9g/L, which exhibited high flocculation activity of 95.3±0.5% at optimum dose of 23.1mgB-EPS/gkaolin. Moreover, Ni removal efficiency of 80% from primary treated wastewater was achieved using 35mg/L of B-EPS extracted by centrifugation method.

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.

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.

Aseptic production of citric and isocitric acid from crude glycerol by genetically modified Yarrowia lipolytica

The unconventional yeast Yarrowia lipolytica is known for its capacity to produce citric or isocitric acid from glycerol. In this study a reduction of production cost was achieved by using cheap crude glycerol and conducting the production at pH 3 to prevent bacterial contamination. In this study a Y. lipolytica strain overexpressing Gut1 and Gut2 was used. For the modified strain, crude glycerol proved to be an excellent substrate for production of citric/isocitric acids in aseptic conditions, as the final concentration of these compounds reached 75.9 ± 1.8 g L^-1 after 7 days of batch production. Interestingly, the concentration of isocitric acid was 42.5 ± 2.4 g L^-1, which is one of the highest concentrations of isocitric acid obtained from a waste substrate. In summary, these data show that organic acids can be efficiently produced by the yeast Y. lipolytica from crude glycerol without any prior purification in aseptic conditions.

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.

Two-step sequential liquefaction of lignocellulosic biomass by crude glycerol for the production of polyols and polyurethane foams

A two-step sequential biomass liquefaction process was developed to produce bio-based polyols and polyurethane (PU) foams using crude glycerol as a liquefaction solvent. The first step, acid-catalyzed liquefaction, was highly effective in liquefying biomass, while the second step, base-catalyzed liquefaction, featured extensive condensation reactions. By using the developed two-step liquefaction process, the polyols produced from lignocellulosic biomass and crude glycerol containing 26-40% organic impurities showed hydroxyl numbers ranging from 536 to 936mgKOH/g, viscosities from 20.6 to 28.0Pas, and molecular weights (Mw) from 444 to 769g/mol. The PU foams produced had densities ranging from 0.04 to 0.05g/cm(3), compressive strengths from 223 to 420kPa, and thermal conductivities from 32.2 to 38.9mW/mK. Polyols and PU foams produced from the two-step liquefaction process had improved properties over their analogs derived from a one-step biomass liquefaction by crude glycerol process catalyzed by acid or base.

Valorisation of crude glycerol to value-added products: Perspectives of process technology, economics and environmental issues

The enormous production of glycerol, a waste stream from biodiesel industries, as a low-value product has been causing a threat to both the environment and the economy. Therefore, it needs to be transformed effectively and efficiently into valued products for contributing positively towards the biodiesel economy. It can either be converted directly into competent chemicals or can be used as a feedstock/precursor for deriving valuable derivatives. In this review article, a technical evaluation has been stirred up, various factors and technologies used for producing value-added products from crude glycerol, Environmental and economic aspects of different conversion routes, cost factors and challenges of integration of the different routes for biorefinery have been reviewed and elaborated. There are tremendous environmental benefits in the conversion of crude glycerol via the biochemical route, the product and residue become eco-friendly. However, chemical conversions are faster processes, and economically viable if environmental aspects are partially ignored.

Optimization of prodigiosin production by Serratia marcescens using crude glycerol and enhancing production using gamma radiation

Prodigiosin is a red pigment produced by Serratia marcescens. Prodigiosin is regarded as a promising drug owing to its reported characteristics of possessing anti-microbial, anti-cancer, and immunosuppressive activity. A factorial design was applied to generate a set of 32 experimental combinations to study the optimal conditions for pigment production using crude glycerol obtained from local biodiesel facility as carbon source for the growth of Serratia marcescens. The maximum production (870 unit/cell) was achieved at 22 °C, at pH 9 with the addition of 1% (w/v) peptone and 109 cell/ml inoculum size after 6 days of incubation. Gamma radiation at dose 200 Gy was capable of doubling the production of the pigment using the optimized conditions and manipulating production temperature. Our results indicate that we have designed an economic medium supporting enhanced Serratia marcescens MN5 prodigiosin production giving an added value for crude glycerol obtained from biodiesel industry.

Enhanced malic acid production from glycerol with high-cell density Ustilago trichophora TZ1 cultivations

BACKGROUND

In order to establish a cost-efficient biodiesel biorefinery, valorization of its main by-product, crude glycerol, is imperative. Recently, Ustilago trichophora TZ1 was found to efficiently produce malic acid from glycerol. By adaptive laboratory evolution and medium optimization, titer and rate could be improved significantly.

RESULTS

Here we report on the investigation of this strain in fed-batch bioreactors. With pH controlled at 6.5 (automatic NaOH addition), a titer of 142 ± 1 g L(-1) produced at an overall rate of 0.54 ± 0.00 g L(-1) h(-1) was reached by optimizing the initial concentrations of ammonium and glycerol. Combining the potential of bioreactors and CaCO3 as buffer system, we were able to increase the overall production rate to 0.74 ± 0.06 g L(-1) h(-1) with a maximum production rate of 1.94 ± 0.32 g L(-1) reaching a titer of 195 ± 15 g L(-1). The initial purification strategy resulted in 90 % pure calcium malate as solid component. Notably, the fermentation is not influenced by an increased temperature of up to 37 °C, which reduces the energy required for cooling. However, direct acid production is not favored as at a lowered pH value of pH 4.5 the malic acid titer decreased to only 9 ± 1 g L(-1). When using crude glycerol as substrate, only the product to substrate yield is decreased. The results are discussed in the context of valorizing glycerol with Ustilaginaceae.

CONCLUSIONS

Combining these results reveals the potential of U. trichophora TZ1 to become an industrially applicable production host for malic acid from biodiesel-derived glycerol, thus making the overall biodiesel production process economically and ecologically more feasible.

Biorefining of by-product streams from sunflower-based biodiesel production plants for integrated synthesis of microbial oil and value-added co-products

This study focuses on the valorisation of crude glycerol and sunflower meal (SFM) from conventional biodiesel production plants for the separation of value-added co-products (antioxidant-rich extracts and protein isolate) and for enhancing biodiesel production through microbial oil synthesis. Microbial oil production was evaluated using three oleaginous yeast strains (Rhodosporidium toruloides, Lipomyces starkeyi and Cryptococcus curvatus) cultivated on crude glycerol and nutrient-rich hydrolysates derived from either whole SFM or SFM fractions that remained after separation of value-added co-products. Fed-batch bioreactor cultures with R. toruloides led to the production of 37.4gL(-1) of total dry weight with a microbial oil content of 51.3% (ww(-1)) when a biorefinery concept based on SFM fractionation was employed. The estimated biodiesel properties conformed with the limits set by the EN 14214 and ASTM D 6751 standards. The estimated cold filter plugging point (7.3-8.6°C) of the lipids produced by R. toruloides is closer to that of biodiesel derived from palm oil.

Valorization of waste glycerol for the production of poly (3-hydroxybutyrate) and poly (3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by Cupriavidus necator and extraction in a sustainable manner

Glycerol is a by-product of many industrial processes and huge amounts of it are generated in the form of waste, thereby necessitating a search for the method of its disposal. An interesting solution is the valorization of crude glycerol into value added product such as polyhydroxyalkanoates (PHAs). The feasibility of producing PHAs by Cupriavidus necator was evaluated using crude glycerol (WG). Various cultivation strategies were designed for the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer by adding different organic acids as precursors at different concentrations levels. Batch cultivation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production showed accumulation of 6.76g/L biomass containing 4.84g/L copolymer on WG with a maximum 3-hydroxyvalerate content of 24.6mol%. PHAs extraction using a non-toxic and recyclable solvent, 1,2 propylene carbonate, showed the highest recovery yield (90%) and purity (93%) at 120°C temperature and 30min incubation. This is the first report on jatropha based glycerol valorization for poly(3-hydroxybutyrate-co-3-hydroxyvalerate) production coupled with extraction using non-toxic solvent.

Effect of crude glycerol impurities on lipid preparation by Rhodosporidium toruloides yeast 32489

Crude glycerol (byproduct of biodiesel preparation) was utilised as the carbon source to produce lipid using oleaginous yeast Rhodosporidium toruloides 32489. Under the same conditions, lipid production with crude glycerol was higher than those produced with glucose and pure glycerol. The effects of 4 main impurities in crude glycerol (methyl oleate, sodium oleate, NaCl and methanol) on lipid production were investigated. Compared with utilising pure glycerol, addition of methyl oleate, sodium oleate, and NaCl impurities increased lipid production by 47.0%, 68.0% and 64.0%, respectively, while methanol decreased lipid production by 17.7%. However, when methanol was mixed with other impurities, its inhibition effect was alleviated due to the promoting effect of other impurities. Hence, crude glycerol could be used as a renewable and low-cost carbon source to replace pure glucose or glycerol for lipid preparation.

Green and sustainable succinic acid production from crude glycerol by engineered Yarrowia lipolytica via agricultural residue based in situ fibrous bed bioreactor

In situ fibrous bed bioreactor (isFBB) for efficient succinic acid (SA) production by Yarrowia lipolytica was firstly developed in our former study. In this study, agricultural residues including wheat straw, corn stalk and sugarcane bagasse were investigated for the improvement of isFBB, and sugarcane bagasse was demonstrated to be the best immobilization material. With crude glycerol as the sole carbon source, optimization for isFBB batch fermentation was carried out. Under the optimal conditions of 20g sugarcane bagasse as immobilization material, 120gL^-1 crude glycerol as carbon source and 4Lmin^-1 of aeration rate, the resultant SA concentration was 53.6gL^-1 with an average productivity of 1.45gL^-1h^-1 and a SA yield of 0.45gg^-1. By feeding crude glycerol, SA titer up to 209.7gL^-1 was obtained from fed batch fermentation, which was the highest value that ever reported.

Characterizing and contrasting the microbial ecology of laboratory and full-scale EBPR systems cultured on synthetic and real wastewaters

The anthropogenic discharge of phosphorus (P) into surface waters can induce the proliferation of cyanobacteria and algae, which can negatively impact water quality. Enhanced biological P removal (EBPR) is an engineered process that can be employed to efficiently remove significant quantities of P from wastewater. Within this engineered system, the mixed microbial consortium (MMC) becomes enriched with polyphosphate accumulating organisms (PAOs). To date much knowledge has been developed on PAOs, and the EBPR process is generally well understood; nonetheless, the engineered process remains underutilized. In this study, investigations were conducted using qPCR and Illumina MiSeq to assess the impacts of wastewater (synthetic vs. real) on EBPR microbial ecology. While a strong relationship was demonstrated between EBPR metrics (P:C; influent VFA:P) and excellent P removal across diverse EBPR systems and MMCs, no such correlations existed with the specific MMCs. Moreover, MMCs exhibited distinct clusters based on substrate, and qPCR results based on the putative PAO Accumulibacter did not correlate with BLASTN eubacterial results for either Accumulibacter or Rhodocyclaceae. More critically, PAO-based sequences aligned poorly with Accumulibacter for both eubacterial and PAO primer sets, which strongly suggests that the conventional PAO primers applied in FISH and qPCR analysis do not sufficiently target the putative PAO Accumulibacter. In particular, negligible alignment was observed for PAO amplicons obtained from a MMC performing excellent EBPR on crude glycerol (an atypical substrate). A synthetic wastewater-based MMC exhibited the best observed BLASTN match of the PAO amplicons, raising concerns about the potential relevance in using synthetic substrates in the study of EBPR.

Polyol production from waste materials by genetically modified Yarrowia lipolytica

Sugar alcohols (polyols) are sweeteners with many industrial applications. In this study, a fermentation process of polyol production based on waste substrates - raw industrial molasses and crude glycerol - was tested. The yeast strain Yarrowia lipolytica Wratislavia K1 was genetically modified by overexpression of the Saccharomyces cerevisiae SUC2 gene and overexpression of the native GUT1 gene. This process allowed for sucrose utilization and rapid glycerol assimilation by the engineered strain. In this study, the obtained strain AIB pAD-UTGut1 produced 100.65±3.75g/l of polyols, with productivity of 1.09±0.9g/lh and yield of 0.67±0.2g/g. This is the first study describing efficient polyol production by the modified Y. lipolytica strain from industrial raw molasses and crude glycerol. By process optimization, we established conditions for abundant polyol synthesis from low-value substrates.

Assessing an effective feeding strategy to optimize crude glycerol utilization as sustainable carbon source for lipid accumulation in oleaginous yeasts

Background

Microbial lipids can represent a valuable alternative feedstock for biodiesel production in the context of a viable bio-based economy. This production can be driven by cultivating some oleaginous microorganisms on crude-glycerol, a 10 % (w/w) by-product produced during the transesterification process from oils into biodiesel. Despite attractive, the perspective is still economically unsustainable, mainly because impurities in crude glycerol can negatively affect microbial performances. In this view, the selection of the best cell factory, together with the development of a robust and effective production process are primary requirements.

Results

The present work compared crude versus pure glycerol as carbon sources for lipid production by three different oleaginous yeasts: Rhodosporidium toruloides (DSM 4444), Lipomyces starkeyi (DSM 70295) and Cryptococcus curvatus (DSM 70022). An efficient yet simple feeding strategy for avoiding the lag phase caused by growth on crude glycerol was developed, leading to high biomass and lipid production for all the tested yeasts. Flow-cytometry and fourier transform infrared (FTIR) microspectroscopy, supported by principal component analysis (PCA), were used as non-invasive and quick techniques to monitor, compare and analyze the lipid production over time. Gas chromatography (GC) analysis completed the quali-quantitative description. Under these operative conditions, the highest lipid content (up to 60.9 % wt/wt) was measured in R. toruloides, while L. starkeyi showed the fastest glycerol consumption rate (1.05 g L⁻¹ h⁻¹). Being productivity the most industrially relevant feature to be pursued, under the presented optimized conditions R. toruloides showed the best lipid productivity (0.13 and 0.15 g L⁻¹ h⁻¹ on pure and crude glycerol, respectively).

Conclusions

Here we demonstrated that the development of an efficient feeding strategy is sufficient in preventing the inhibitory effect of crude glycerol, and robust enough to ensure high lipid accumulation by three different oleaginous yeasts. Single cell and in situ analyses allowed depicting and comparing the transition between growth and lipid accumulation occurring differently for the three different yeasts. These data provide novel information that can be exploited for screening the best cell factory, moving towards a sustainable microbial biodiesel production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0467-x) contains supplementary material, which is available to authorized users.

Biological valorization of pure and crude glycerol into 1,3-propanediol using a novel isolate Lactobacillus brevis N1E9.3.3

The aim of the study was to evaluate a novel onsite enrichment approach to isolate a crude glycerol utilizing facultative anaerobic bacteria. An onsite enrichment in natural conditions resulted an isolate, Lactobacillus brevis N1E9.3.3, that can utilize glycerol and produce 1,3-propanediol with a yield of 0.89g1,3-PDO/gGlycerol and productivity of 0.78g1,3-PDO/l/h at pH-8.5 under anaerobic conditions. Batch fermentation experiments with glycerol-glucose co-fermentation strategy was carried out to evaluate the production of 1,3-propanediol and other byproducts. The effect of other carbon sources as co-substrate was also evaluated. At the optimized condition, 18.6g/l 1,3-propanediol was monitored when biodiesel industry generated crude glycerol and 2.5% glucose were used as the substrate.

Dark fermentative bioconversion of glycerol to hydrogen by Bacillus thuringiensis

Biodiesel manufacturing units discharge effluents rich in glycerol. The need is to convert crude glycerol (CG) into useful products such as hydrogen (H2). Under batch culture, Bacillusthuringiensis EGU45 adapted on pure glycerol (PG, 2% v/v) resulted in an H2 yield of 0.646 mol/mol glycerol consumed on minimal media (250 mL) supplemented with 1% ammonium nitrate at 37°C over 4 days. Here, H2 constituted 67% of the total biogas. Under continuous culture, at 2 days of hydraulic retention time, B. thuringiensis immobilized on ligno-cellulosic materials (banana leaves - BL, 10% v/v) resulted in a H2 yield of 0.386 mol/mol PG consumed. On CG, the maximal H2 yield of 0.393 mol/mol feed consumed was recorded. In brief, B. thuringiensis could transform CG, on limited resources - minimal medium with sodium nitrate, by immobilizing them on cheap and easily available biowaste, which makes it a suitable candidate for H2 production on a large scale.

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.

Biohydrogen production by co-fermentation of crude glycerol and apple pomace hydrolysate using co-culture of Enterobacter aerogenes and Clostridium butyricum

Co-substrate utilization of various wastes with complementary characteristics can provide a complete medium for higher hydrogen production. This study evaluated potential of apple pomace hydrolysate (APH) co-fermented with crude glycerol (CG) for increased H2 production and decreased by-products formation. The central composite design (CCD) along with response surface methodology (RSM) was used as tool for optimization and 15 g/L of CG, 5 g/L of APH and 15% (v/v) inoculum were found to be optimum to produce as high as 26.07 ± 1.57 mmol H2/L of medium. The p-value of 0.0017 indicated that APH at lower concentration had a significant effect on H2 production. By using CG as sole carbon source, reductive pathway of glycerol metabolism was favored with 19.46 mmol H2/L. However, with APH, oxidative pathway was favored with higher H2 production (26.07 ± 1.57 mmol/L) and decrease in reduced by-products (1,3-propanediol and ethanol) formation. APH inclusion enhanced H2 production, and decreased substrate inhibition.

Crude glycerol as feedstock for polyhydroxyalkanoates production by mixed microbial cultures

The increase in global biodiesel production makes imperative the development of sustainable processes for the use of its main by-product, crude glycerol. In this study the feasibility of polyhydroxyalkanoates (PHA) production by a mixed microbial community using crude glycerol as feedstock was investigated. The selected culture had the ability to consume both glycerol and methanol fraction present in the crude. However, glycerol seemed to be the only carbon source contributing for the two biopolymers stored: poly-3-hydroxybutyrate (PHB) and glucose biopolymer (GB). In this work the culture reached a maximum PHB content of 47% (cdw) and a productivity of 0.27 g X/L.d, with an aerobic mixed cultures and a real waste substrate with non-volatile fatty acids (VFA) organic matter. The overall PHA yield on total substrate obtained was in the middle range of those reported in literature. The fact that crude glycerol can be used to produce PHA without any pre-treatment step, makes the overall production process economically more competitive, reducing polymer final cost.