Characterization of crude glycerol from biodiesel plants

Modelling the long-term dynamics and inhibitory effects of crude glycerol impurities in a methanogenic and sulfidogenic UASB bioreactor

The performance of Upflow Anaerobic Sludge Blanket (UASB) bioreactors treating sulfate (SO42-) -rich effluents depends on multiple factors, including microbial interactions and operational conditions. The high complexity of these systems necessitates the use of mathematical modelling tools to better understand the process and predict the long-term impacts of various operational variables. In this work, a mathematical model describing the long-term operation of a sulfate-fed 2.5 L UASB reactor was developed, calibrated and validated. Crude glycerol was used as electron donor to achieve sulfate reduction. The hydraulic model of the UASB was described as a set of CSTRs in series to represent its plug flow-like behavior. The kinetic model included 8 fermentation processes using glycerol as the primary electron source, 5 sulfate-reduction processes using organic and inorganic electron sources, and 2 methanogenic processes. The model tackled the long-term accumulation of the impurities coming from the crude glycerol solution, namely slime -like-substances (SLS), and their inhibitory effects over the three different trophic groups: fermenters, sulfate-reducers and methanogens. A sensitivity analysis and calibration of the most relevant parameters was performed using the experimental data from 280 days of continuous operation of a lab-scale UASB. Volatile suspended solids (VSS), carbon (C) and sulfur (S) species profiles as well as microbial dynamics from initial methanogenic conditions to non-methanogenic conditions due to SLS impact were properly predicted by the model under steady-state feeding conditions. Furthermore, the model was validated using another independent set of data under dynamic-feeding conditions, containing 6 different phases with varying HRT, inlet sulfate and organic carbon concentrations. After successfully validating the model, a scenario analysis was conducted to evaluate two case studies, with different inlet sources: crude glycerol with varying SLS concentrations and pure glycerine (SLS-free). The results of the simulations suggest that heterotrophic SR have greater long-term resistance to the inhibitory effects of SLS, compared to methanogens. Methane production increased with higher C and S loading rates, and the balance between sulfate reduction efficiency and COD removal was optimal at a C/S ratio of 1.6 g C g S-1.

Delineating Catalyst Deactivation Mechanisms in Electrocatalytic Glycerol Oxidation toward Biodiesel Wastewater/CO2 Co-valorization

Biodiesel plays a key role in achieving economy-wide decarbonization but its production discharges significant amounts of CO2 and glycerol-laden wastewater. Given the increasing abundance of biodiesel wastewater and low redox potential of glycerol, coupling the glycerol oxidation reaction (GOR) with CO2 electrolysis has emerged as an attractive strategy to achieve sustainable wastewater management, CO2 utilization, and green chemical synthesis in a single unit process. Despite the need for highly stable catalysts, few studies have examined electrocatalyst deactivation in environmental waste streams. Here, we present a first-of-a-kind diagnostic study that investigates nickel (Ni) catalyst stability during the GOR in synthetic biodiesel wastewaters. A current decline of 99.7% was observed within 24 h of operation. This coincided with an 80% decrease in surface active Ni(II)/Ni(III) concentrations, 190-fold increases in interfacial impedance, and the appearance of electrode C-bonds that suggested surface coverage by GOR reactants and intermediates was likely a main contributor to loss in catalytic activity. Analyses in more complex electrolytes containing methanol and oleate suggested the emergence of distinct deactivation mechanisms through restricted NiOOH formation. Altogether, this study details several previously unreported catalyst deactivation mechanisms. These findings can ultimately help inform future catalyst design toward more practical and sustainable waste valorization.

Cupriavidus necator as a model organism for CO2-based biotechnology

Cupriavidus necator H16 is a chemolithoautotrophic model organism that can grow in a simple mineral medium supplemented with the gases H2, O2 and CO2. This unique metabolic capability makes it a promising organism for sustainable biotechnology applications such as the production of bioplastics, single cell proteins and bulk chemicals from renewable resources. However, gas fermentation, particularly with explosive gas mixtures like H2 and O2, poses considerable technical and safety challenges. Effective control of gas mixtures, pressurized environments, mass transfer from gas to liquid and gas solubility is essential to ensure both reproducibility and safety in bioprocessing systems. This chapter describes a detailed methodology for the cultivation of C. necator across various micro, small- and medium-scale setups, while emphasizing safety protocols. The chapter also outlines analytical techniques for the quantification of polyhydroxybutyrate (PHB), single cell protein and isopropanol as product examples for gas fermentation.

High-Yield Production of Polyhydroxybutyrate and Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from Crude Glycerol by a Newly Isolated Burkholderia Species Oh_219

Crude glycerol (CG), a major biodiesel production by-product, is the focus of ongoing research to convert it into polyhydroxyalkanoate (PHA). However, few bacterial strains are capable of efficiently achieving this conversion. Here, 10 PHA-producing strains were isolated from various media. Among them, Burkholderia sp. Oh_219 exhibited the highest polyhydroxybutyrate (PHB) production from glycerol and was therefore characterized further. Burkholderia sp. Oh_219 demonstrated significant tolerance to major growth inhibitors in CG and metabolized the fatty acids present as impurities in CG. Furthermore, the Oh_219 strain was genetically engineered using phaCBP-M-CPF4 and phaJPa to enable the fatty acid-based production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), a component of CG. The resulting strain produced PHBHHx containing 1.0-1.3 mol% of 3HHx from CG. Further supplementation with capric and lauric acids increased the 3HHx molar fraction to 9.7% and 18%, respectively. In a 5 L fermenter, the Oh_219 strain produced 15.3 g/L PHB from 29.6 g/L biomass using a two-stage fermentation system. This is the highest yield reported for PHA production from glycerol by Burkholderia spp. Additionally, PHB produced from CG had a lower melting point than that from pure glycerol and fructose. Taken together, Burkholderia sp. Oh_219 is a promising new candidate strain for producing PHA from CG.

From waste management to circular economy: Leveraging thermophiles for sustainable growth and global resource optimization

Waste of any origin is one of the most serious global and man-made concerns of our day. It causes climate change, environmental degradation, and human health problems. Proper waste management practices, including waste reduction, safe handling, and appropriate treatment, are essential to mitigate these consequences. It is thus essential to implement effective waste management strategies that reduce waste at the source, promote recycling and reuse, and safely dispose of waste. Transitioning to a circular economy with policies involving governments, industries, and individuals is essential for sustainable growth and waste management. The review focuses on diverse kinds of environmental waste sources around the world, such as residential, industrial, commercial, municipal services, electronic wastes, wastewater sewerage, and agricultural wastes, and their challenges in efficiently valorizing them into useful products. It highlights the need for rational waste management, circularity, and sustainable growth, and the potential of a circular economy to address these challenges. The article has explored the role of thermophilic microbes in the bioremediation of waste. Thermophiles known for their thermostability and thermostable enzymes, have emerged to have diverse applications in biotechnology and various industrial processes. Several approaches have been explored to unlock the potential of thermophiles in achieving the objective of establishing a zero-carbon sustainable bio-economy and minimizing waste generation. Various thermophiles have demonstrated substantial potential in addressing different waste challenges. The review findings affirm that thermophilic microbes have emerged as pivotal and indispensable candidates for harnessing and valorizing a range of environmental wastes into valuable products, thereby fostering the bio-circular economy.

A cellulose monolithic stir bar for sorptive extraction of glycerol from biodiesel

This work presents an eco-friendly approach for determining free glycerol in biodiesel samples, using a cellulose monolith stir bar in the sorptive extraction method with analysis by high-performance liquid chromatography and a refractive index detector. The cellulose monolith was produced from cellulose acetate by non-solvent-induced phase separation and subsequent alkaline deacetylation. The cellulose monolith presented a hierarchically porous structure, with 68% porosity and almost total deacetylation, with morphological and polarity characteristics that favor an efficient extraction of free glycerol from biodiesel. The sorptive extraction method using a cellulose monolith stir bar was optimized, obtaining a total extraction time of 30 min at 70 °C, using ultrapure water as the desorption solvent, and extraction of free glycerol of 93.6 ± 2.3%. The proposed method showed selectivity in free glycerol extraction, with limits of detection and quantification of 6.60 × 10-5% w/w and 2.18 × 10-4% w/w, respectively. Compared with the official reference method, the proposed one presented similar precision and accuracy, with few manipulations and any reagent/solvents. Furthermore, it is compatible with the principles of green chemistry and can be considered an eco-friendly method for determining free glycerol in biodiesel.

Conversion of Post-Refining Waste MONG to Gaseous Fuel in a Rotary Gasifier

Biodiesel manufacturing frequently employs sustainable materials like soybeans, microorganisms, palm extract, jatropha plant, and recycled frying oils. The expansion of biodiesel manufacturing has escalated the volume of waste byproducts, encompassing glycerin and non-glycerin organic matter (MONG), jointly known as raw glycerin. MONG is characterized by a low calorific value, a high autoignition temperature, and significant viscosity at room temperature. As a waste product, it negatively affects the natural environment due to the lack of viable disposal methods. Hence, there is a need for its conversion into high-calorific gaseous fuel with significantly less environmental impact. One of the methods for converting MONG into gaseous fuel is the pyrolysis process. This study describes the pyrolytic conversion of MONG conducted on a test stand consisting of a rotating chamber with a shell filled with liquid lead as a heating medium. Based on the measurements and balance calculations, the amount of heat required to preserve the autothermal process was determined. The calorific value and composition of the pyrolytic gas were measured, revealing that 70% of the gas involves compounds characterized by a high calorific value. As a result, the calorific value of dry, purified gas equals 35.07 MJ/kg. A life cycle assessment has been conducted, in order to determine if the produced gaseous fuel matches sustainable development criteria. MONG-based gas is a sustainable replacement of, e.g., natural gas, lignite, or hard coal; however, it allows us to avoid 233–416 kg/h CO2 emissions per 1 MWt of heat.

Anaerobic co-digestion of microalgal biomass, sugarcane vinasse, and residual glycerol from biodiesel using simplex-centroid mixture design: methane potential, synergic effect, and microbial diversity

Microalgal biomass (MB) is a promising feedstock for bioenergy production. Nonetheless, the cell recalcitrance and the low C/N ratio limit the methane yield during anaerobic digestion. As an alternative to overcome these challenges, MB co-digestion with different feedstocks has been proposed. Thus, this study evaluated the anaerobic co-digestion (AcoD) of MB cultivated in wastewater with sugarcane vinasse (VIN) and residual glycerol from biodiesel production (GLY). Batch tests were conducted using augmented simplex-centroid mixture design to investigate the impact of AcoD on methane production (SMP), synergistic effects, and the influence on microbial community. When compared to MB digestion, 150 NmL CH4.g-1VS, binary and ternary AcoD achieved SMP increases from 120 to 337%. The combination of 16.7:16.7:66.7 (MB:VIN:GLY) showed the highest SMP for a ternary mixture (631 NmL CH4.g-1VS). Optimal synergies ranged from 1.3 to 1.4 and were primarily found for the MB:GLY AcoD. Acetoclastic Methanosaeta genus was predominant, regardless the combination between substrates. Despite the largest SMP obtained from the MB:GLY AcoD, other ternary mixtures were also highly synergetic and therefore had strong potential as a strategic renewable energy source.

Nanostructured Solid/Liquid Acid Catalysts for Glycerol Esterification: The Key to Convert Liability into Assets

Owing to the growing concerns about the dwindling fossil fuel reserves, increasing energy demand, and climate emergency, it is imperative to develop and deploy sustainable energy technologies to ensure future energy supply and to transition to the net-zero world. In this context, there is great potential in the biorefinery concept for supplying drop in biofuels in the form of biodiesel. Biodiesel as a fuel can certainly bridge the gap where electrification or the use of hydrogen is not feasible, for instance, in heavy vehicles and in the farm and marine transportation sectors. However, the biodiesel industry also generates a large amount of crude glycerol as the by-product. Due to the presence of several impurities, crude glycerol may not be a suitable feedstock for all high-value products derived from glycerol, but it fits well with glycerol esterification for producing glycerol acetins, which have numerous applications. This review critically looks at the processes using nanostructured solid/liquid acid catalysts for glycerol esterification, including the economic viability of the scale-up. The homogeneous catalysts reviewed herein include mineral acids and Brønsted acidic ionic liquids, such as SO3H-functionalized and heteropoly acid based ionic liquids. The heterogeneous catalysts reviewed herein include solid acid catalysts such as metal oxides, ion-exchange resins, zeolites, and supported heteropoly acid-based catalysts. Furthermore, the techno-economic analysis studies have shown the process to be highly profitable, confirming the viability of glycerol esterification as a potential tool for economic value addition to the biorefinery industry.

Anaerobic digestion of crude glycerol from biodiesel production for biogas generation: Process optimization and pilot scale operation

Anaerobic digestion of wastes and wastewater is a complex process that can be affected by many operational parameters. In this context, the purpose of the present study was to optimize biogas production using crude glycerol (GLY) generated in biodiesel production from waste cooking oil without pretreatment or nutrient supplementation. The study was divided into two parts: the first phase consisted of an experimental design based on central composite design (CCD) with two variables (food to microorganism (F/M) ratio and cycle time) at five levels (F/M of 0.20; 0.51; 1.02; 1.53 and 2.04 gCOD/gVS; tc of 3, 4, 5, 6, 7 days) focusing on optimizing the biogas production from crude GLY in lab-scale batch reactors (500 mL). The second phase was conducted on a pilot-scale biodigester (1.2 m3) based on the optimized variables obtained from the CCD. The optimized results showed that the F/M ratio of 2.04 gCOD/gVS and a cycle time (tc) of 6 days reached the highest specific methane production (SMP) of 46 LCH4/kgVS. However, the highest SMP of 14.7 LCH4/kgVSd was obtained during the operation of the pilot-scale biodigester for the optimized conditions of F/M ratio of 0.23 gCOD/gSV and a tc of 7 days. Therefore, pilot-scale biogas production from crude GLY was demonstrated to be feasible without the use of nutrients or GLY pretreatment at 0.15 LGLY/m3 d.

Glycerol carbonate synthesis via transesterification of enriched glycerol and dimethyl carbonate using a Li-incorporated MCM-41 framework

Waste crude glycerol was successfully enriched and utilized as an inexpensive source for producing value-added chemicals, such as glycerol carbonate (GC) - a valuable compound with extensive industrial applications. The Li/MCM-41 heterogeneous catalyst was synthesized and used for the transesterification of enriched glycerol and dimethyl carbonate (DMC) to produce GC. The catalyst's physicochemical properties were characterized using thermogravimetric, Hammett indicator, inductively coupled plasma-optical emission spectroscopy, nitrogen adsorption-desorption, X-ray diffractometry, scanning electron microscopy, and Fourier-transform infrared spectroscopy analyses. Reaction conditions were optimized using response surface methodology and analysis of variance, yielding an accurate quadratic model to predict the GC yield under different transesterification variables. The results revealed that 5%Li/MCM-41 served as the optimal catalyst, achieving the highest TOF of 4.72 h-1. The DMC: enriched glycerol molar ratio had the greatest impact on the GC yield, with an R2 = 0.9743 and adjusted R2 = 0.9502. The optimal GC yield (58.77%) with a final purity of 78% was attained at a 5.15 wt% catalyst loading relative to the initial amount of enriched glycerol, DMC: enriched glycerol molar ratio of 4.24 : 1, and a reaction temperature of 86 °C for 165 min. The 5%Li/MCM-41 heterogeneous catalyst could be reused for four cycles with a decreased GC yield from 58.77% to 45.72%. Thus, the Li/MCM-41 catalyst demonstrated a remarkable efficiency and potential as a heterogeneous catalyst for synthesizing GC. This method not only contributes to environmental sustainability by making use of a byproduct from biodiesel production but also aligns with the principles of a circular economy.

The effect of slime accumulated in a long-term operating UASB using crude glycerol to treat S-rich wastewater

An up-flow anaerobic sludge blanket (UASB) reactor targeting sulfate reduction was operated under a constant TOC/S-SO42- ratio of 1.5 ± 0.3 g C/g S for 639 days using crude glycerol as carbon source. A filamentous and fluffy flocculant material, namely slime-like substances (SLS), was gradually accumulated in the bioreactor after the cease of methanogenic activity. The accumulation of SLS was followed by a decrease in the removal efficiencies and a deterioration in the performance. Selected characteristics of SLS were investigated to explore the causes of its formation and the effect of SLS on the UASB performance. Results showed that glycerol fermentation and sulfate reduction processes taking place in the reactor were mainly accomplished in the bottom part of the UASB reactor, as the sludge concentration in the bottom was higher. The accumulation of SLS in the UASB reactor caused sludge flotation that further led to biomass washout, which decreased the sulfate and glycerol removal efficiencies. Batch activity tests performed with granular sludge (GS), slime-covered granular sludge (SCGS) and SLS showed that there was no difference between GS and SLS in the mechanism of glycerol fermentation and sulfate reduction. However, the specific sulfate reduction rate of GS was higher than that of SLS, while SLS showed a higher glycerol fermentation rate than that of GS. The different rates in GS and SLS were attributed to the higher relative abundances of fermentative microorganisms found in SLS and higher relative abundances of sulfate reducing bacteria (SRB) found in GS.

Bio-conversion of organic wastes towards polyhydroxyalkanoates

The bio-manufacturing of products with substantial commercial value, particularly polyhydroxyalkanoates (PHA), using cost-effective carbon sources through microorganisms, has garnered heightened attention from both the scientific community and industry over the past few decades. Opting for industrial PHA production from various organic wastes, spanning industrial, agricultural, municipal, and food-based sources, emerges as a wiser choice. This strategy not only eases the burden of recycling organic waste and curbs environmental pollution but also trims down PHA production costs, rendering these materials more competitive in commercial markets. In addition, PHAs are a family of renewable, environmentally friendly, fully biodegradable and biocompatible polyesters with a multitude of applications. This review provides an overview of recent developments in PHA production from organic wastes. It covers the optimization of diverse metabolic pathways for producing various types of PHA from organic waste sources, pre-treatment and downstream processing for PHA using unrelated organic wastes, and challenges in industrial production of PHA using unrelated organic waste feedstocks and the challenges faced in industrial PHA production from organic wastes, along with potential solutions. Lastly, this study suggests underlying research endeavors aimed at further enhancing of the feasibility of industrial PHA production from organic wastes as an alternative to current petroleum-based plastics in the near future.

Simultaneous Lipid and Carotenoid Production via Rhodotorula paludigena CM33 Using Crude Glycerol as the Main Substrate: Pilot-Scale Experiments

Rhodotorula paludigena CM33 is an oleaginous yeast that has been demonstrated to accumulate substantial quantities of intracellular lipids and carotenoids. In this study, crude glycerol, a by-product of biodiesel production, was used as a carbon source to enhance the accumulation of lipids and carotenoids in the cells. The culture conditions were first optimized using response surface methodology, which revealed that the carotenoid concentration and lipid content improved when the concentration of crude glycerol was 40 g/L. Different fermentation conditions were also investigated: batch, repeated-batch, and fed-batch conditions in a 500 L fermenter. For fed-batch fermentation, the maximum concentrations of biomass, lipids, and carotenoids obtained were 46.32 g/L, 37.65%, and 713.80 mg/L, respectively. A chemical-free carotenoid extraction method was also optimized using high-pressure homogenization and a microfluidizer device. The carotenoids were found to be mostly beta-carotene, which was confirmed by HPLC (high pressure liquid chromatography), LC-MS (liquid chromatography-mass spectrometry), and NMR (nuclear magnetic resonance). The results of this study indicate that crude glycerol can be used as a substrate to produce carotenoids, resulting in enhanced value of this biodiesel by-product.

Fermentation of biodiesel-derived crude glycerol to 1,3-propanediol with bio-wastes as support matrices: Polynomial prediction model

Biodiesel production from used cooking oil is sustainable alternative, for bio-energy production. The process generates residual crude glycerol (RCG) as the major energy-rich waste which can be used to produce various bio-based chemicals like 1,3-propanediol (1,3-PDO) through biotechnological interventions. This RCG contains several impurities like methanol, soap, organic materials, salts non-transesterified fatty acids and metals in varied concentrations. These impurities significantly affect yield and productivity of the bio-process due to their marked microbial toxicity. In this work, previously isolated Clostridium butyricum L4 was immobilized on various abundantly available cheap bio-wastes (like rice straw, activated carbon and corn cob) to explore advantages offered and improve tolerance to various feed impurities. Amongst these, shredded rice straw was found most suitable candidate for immobilization and results in maximum improvement in 1,3-PDO production (18.4%) with highest porosity (89.28%), lowest bulk density (194.48Kg/m3), and highest cellular biofilm density (CFU/g-8.4 ×1010) amongst the three matrices. For practical purposes, recyclability was evaluated and it was concluded that even after reusing for five successive cycles the production retained to ∼82.4%. Subsequently, polynomial model was developed using 30 runs central composite factorial design experiments having coefficient of regression (R²) as 0.9520, in order to predict yields under different immobilization conditions for 1,3-PDO production. Plackett-Burman was employed (Accuracy= 99.17%) to screen significant toxic impurities. Based on statistical analysis six impurities were found to be significantly influential on PDO production in adverse manner. With negative coefficient of estimate (COE) varying in decreasing order: Linoleic acid >Oleic acid >Stearic acid >NaCl>K2SO4 >KCl. The study illustrates practical application for repurposing waste glycerol generated from biodiesel plants, thus developing improved agnostic process along with yield production models.

Modular Solar-to-Fuel Electrolysis at Low Cell Potentials Enabled by Glycerol Electrooxidation and a Bipolar Membrane Separator

Solar fuel generation through water electrolysis or electrochemical CO2 reduction is thermodynamically limited when it is paired with oxygen evolution reaction (OER). Glycerol electrooxidation reaction (GEOR) is an alternative anodic reaction with lower anodic electrochemical potential that utilizes a renewable coproduct produced during biodiesel synthesis. We show that GEOR on an Au-Pt-Bi ternary metal electrocatalyst in a model alkaline crude glycerol solution can provide significant cell potential reductions even when paired to reduction reactions in seawater and acidic catholytes via a bipolar membrane (BPM). We showed that the combination of GEOR and a BPM separator lowers the total cell potential by 1 V at an electrolysis current of 10.0 mA cm-2 versus an anode performing anode's OER when paired with hydrogen evolution and CO2 reduction cathodes. The observed voltage reduction was steady for periods of up to 80 h, with minimal glycerol crossover observed through the membrane. These results motivate new, high-performance cell designs for photoelectrochemical solar fuel integrated systems based on glycerol electrooxidation.

Valorisation of crude glycerol in the production of liquefied lignin bio-polyols for polyurethane formulations

Bio-polyols, produced by liquefying lignin with polyhydric alcohols, offer a promising alternative to conventional polyols for polyurethane production. To enhance the sustainability on the production of these bio-polyols, this study proposes the use of crude glycerol and microwave-assisted liquefaction as substitutes for conventional methods and commercial glycerol. This approach reduces the energy requirements of the reaction while also adding value to this by-product. The synthesis of bio-polyols with suitable properties to produce elastic and rigid polyurethane was carried out using previously optimised reaction conditions. Organosolv lignins obtained from Eucalyptus globulus and Pinus radiata were employed, using polyethylene glycol and crude glycerol as solvents and sulphuric acid as a catalyst. Several parameters of the bio-polyols were analysed, including hydroxyl number (IOH), acid number (An), and functionality (f), suggesting that the bio-polyols were suitable for polyurethane synthesis. Bio-polyols formulated to produce rigid polyurethanes exhibited IOH values of 554 and 383 (mg KOH/g), An values of 1.91 and 4.21 (mg KOH/g), and functionalities of 4.16 and 3.14 for Eucalyptus globulus and Pinus radiata lignin. In the case of bio-polyols for elastic polyurethanes, the values were 228 and 173 (mg KOH/g) (IOH), 20.94 and 25.09 (mg KOH/g) (An), and functionalities of 3.51 and 2.08.

Magnesium Binding by Cyberlindnera jadinii Yeast in Media from Potato Wastewater and Glycerol

The aim of this study was to determine the magnesium-binding capacity of Cyberlindnera jadinii yeast in media prepared from potato wastewater and glycerol (after biodiesel production), supplemented with magnesium salt. The research was carried out in two stages. In the first, the ability to binding magnesium by yeast in media supplemented with various doses of this element was tested. In the second stage, after selecting the appropriate dose of magnesium, the culture was carried out in a bioreactor. The composition of the yeast biomass was also analysed in terms of lipids and protein content and amino acid composition. Studies have shown that this type of medium can be used as a culture medium for the growth of C. jadinii yeast. In the first stage of the study, the most magnesium (8.97 mg/gd.m.) was bound by yeast cells after 48 h of cultivation in a medium supplemented with the addition of magnesium at a dose of 2 g/L. In the second stage of the research, the highest magnesium content in the biomass (7.9 mg/gd.m.) was noted after 24 h of cultivation in the same medium. The lipid and protein contents in the biomass obtained after 24 h of cultivation in the bioreactor were 6.35 and 43.73%, respectively. The main fatty acids present in the yeast lipids were oleic acid (59.4%) and linoleic acid (8.6%). Analysis of the amino acid profile of the proteins showed the highest proportions were glutamic acid (13.7%) and aspartic acid (11%).

Dual functional WO3/BiVO4 heterostructures for efficient photoelectrochemical water splitting and glycerol degradation

Dual functional heterojunctions of tungsten oxide and bismuth vanadate (WO₃/BiVO₄) photoanodes are developed and their applications in photoelectrochemical (PEC) water splitting and mineralization of glycerol are demonstrated. The thin-film WO₃/BiVO₄ photoelectrode was fabricated by a facile hydrothermal method. The morphology, chemical composition, crystalline structure, chemical state, and optical absorption properties of the WO₃/BiVO₄ photoelectrodes were characterized systematically. The WO₃/BiVO₄ photoelectrode exhibits a good distribution of elements and a well-crystalline monoclinic WO₃ and monoclinic scheelite BiVO₄. The light-absorption spectrum of the WO₃/BiVO₄ photoelectrodes reveals a broad absorption band in the visible light region with a maximum absorption of around 520 nm. The dual functional WO₃/BiVO₄ photoelectrodes achieved a high photocurrent density of 6.85 mA cm^-2, which is 2.8 times higher than that of the pristine WO₃ photoelectrode in the presence of a mixture of 0.5 M Na₂SO₄ and 0.5 M glycerol electrolyte under AM 1.5 G (100 mW cm^-2) illumination. The superior PEC performance of the WO₃/BiVO₄ photoelectrode was attributed to the synergistic effects of the superior crystal structure, light absorption, and efficient charge separation. Simultaneously, glycerol plays an essential role in increasing the efficiency of hydrogen production by suppressing charge recombination in the water redox reaction. Moreover, the WO₃/BiVO₄ photoelectrode shows the total organic carbon (TOC) removal efficiency of glycerol at about 82% at 120 min. Notably, the WO₃/BiVO₄ photoelectrode can be a promising photoelectrode for simultaneous hydrogen production and mineralization of glycerol with a simple, economical, and environmentally friendly approach.

Preparation of niacinamide imprinted starch-based biomaterials for treating of hyperpigmentation

The aim of this study was to prepare niacinamide (NA) imprinted biomaterials for treating hyperpigmentation using mungbean starch (MS), PVA, and plasticizers (glycerol (GL) and citric acid (CA)). Biomaterials and NA were characterized by FE-SEM, FT-IR, and ¹H NMR. To evaluate the applicability of the NA imprinted biomaterials for a transdermal drug delivery system (TDDS), NA release experiment was conducted in different pH and temperature conditions. Results of NA release properties indicated that NA was released about 99 % rapidly in the initial 10 min. NA release in low pH and high temperature was also higher than that in high pH and low temperature. The determination of experimental conditions and the analysis of NA release results were achieved using response surface methodology (RSM). Results of NA release using artificial skin indicated that NA release from NA imprinted biomaterials was increased at a relatively steady rate for 90 min. To verify for treating hyperpigmentation of the prepared biomaterials, tyrosinase inhibitory and antioxidant inhibitory were performed. Results indicated that NA imprinted biomaterials with the addition of CA exhibited 55.8 % of tyrosinase inhibitory and 73.0 % of antioxidant inhibitory. In addition, their ability to inhibit melanin synthesis in B16F10 cells was evaluated.

Characterization of crude glycerol and glycerol pitch from palm-based residual biomass

Crude glycerol (CG) and glycerol pitch (GP) are highly alkaline residues from biodiesel and oleochemical plants, respectively, and have organic content which incurs high disposal cost and poses an environmental threat. Characterization of these residues for composition and properties could provide insight into their quality for proper disposal and can help the biodiesel industry to adopt more sustainable practices, such as reducing waste and improving the efficiency of the production process, hence minimizing the impact of the biodiesel supply chain to the environment. These data also allow the identification and exploration of new ways for their utilization and transformation into highly value-added products. In this study, we evaluated four CG samples (B, C, D, and E) and two GP samples (F and G) obtained from Malaysian palm oil refineries, and the results were compared with pure glycerol (A). Spectroscopic analysis was performed using FTIR, 1H-, and 13C-NMR. All samples had similar density to A (1.26 g/cm3), except for F (1.31 g/cm3), while the density for E and G could not be determined due to their physical states. The pH and viscosity largely varied in the range of 7.26-11.89 and 43-225 cSt, respectively. The glycerol content of CG (B, C, D, and E) was high and consistent (81.7-87.3%) whereas GP F and G had 71.5 and 63.9% glycerol content, respectively. Major contaminants in CG and GP were water and matter organic non-glycerol (MONG), respectively. The water, ash, soap, and salt content were considerably low, which varied from 3.4 to 14.1%, 3.9 to 13.0%, 0.1 to 5.7%, and 4.1 to 9.2% respectively. Thermal analysis of CG and GP exhibited four phases of decomposition attributed to the impurities compared to the single phase in A. All samples had calorific values lower than A (18.1 MJ/kg) between 9.0 and 17.7 MJ/kg. Based on the results, CG and GP have high glycerol content which reveals their potential to be used as feedstock in bioconversion and chemical or thermal treatment while impurities may be removed by pre-treatment if required. As palm oil is one of the main feedstocks for the oleochemical industry, this work underlines the importance of characterization of the residue generated to provide additional data and information on palm-based agricultural industry wastes, minimize the impact of palm oil supply chain on the environment, and explore its potential usage for value-addition.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13399-023-04003-4.

The reliance of glycerol utilization by Cupriavidus necator on CO2 fixation and improved glycerol catabolism

While crude glycerol is a cheap carbon source for industrial-scale cultivation of microorganisms, its application relies on fast growth and conversion. The biopolymer producing Cupriavidus necator H16 (synonym: Ralstonia eutropha H16) grows poorly on glycerol. The heterologous expression of glycerol facilitator glpF, glycerol kinase glpK, and glycerol dehydrogenase glpD from E. coli accelerated the growth considerably. The naturally occurring glycerol utilization is inhibited by low glycerol kinase activity. A limited heterotrophic growth promotes the dependency on autotrophic growth by carbon dioxide (CO₂) fixation and refixation. As mixotrophic growth occurs in the wildtype due to low consumption rates of glycerol, CO₂ fixation by the Calvin-Benson-Bassham (CBB) cycle is essential. The deletion of both cbbX copies encoding putative RuBisCO-activases (AAA + ATPase) resulted in a sharp slowdown of growth and glycerol consumption. Activase activity is necessary for functioning carboxylation by RuBisCO. Each of the two copies compensates for the loss of the other, as suggested by observed expression levels. The strong tendency towards autotrophy supports previous investigations of glycerol growth and emphasizes the versatility of the metabolism of C. necator H16. Mixotrophy with glycerol-utilization and CO₂ fixation with a high dependence on the CBB is automatically occurring unless transportation and degradation of glycerol are optimized. Parallel engineering of CO₂ fixation and glycerol degradation is suggested towards application for value-added production from crude glycerol. KEY POINTS: • Growth on glycerol is highly dependent on efficient carbon fixation via CBB cycle. • CbbX is essential for the efficiency of RuBisCO in C. necator H16. • Expression of glycerol degradation pathway enzymes accelerates glycerol utilization.

Characterisation of bacterial nanocellulose and nanostructured carbon produced from crude glycerol by Komagataeibacter sucrofermentans

Bacterial nanocellulose (BNC), which has tunable properties, is a precursor of nanostructured energy storage materials; however, the cost of BNC production is challenging. This study uses crude glycerol from the biodiesel industry as a carbon nutrient and first-time carbonised BNC from K. sucrofermentans that is applied in energy storage. From crude glycerol in static cultivation, 6.4 g L^-1 BNC was produced with a high crystallinity index (85%) and tensile properties in comparison to conventionally used pure carbon substrates. Carbon materials were derived from the BNC retained fibrous and crystalline features with disordered porous structures. The electrochemical properties of the carbon materials have a specific capacitance of 140 F g^-1. This study highlights the valorisation of waste glycerol from the biodiesel industry as a substrate for efficient BNC production and the energy storage potential of carbon derived from BNC as renewable energy materials.

Cutaneotrichosporon oleaginosus: A Versatile Whole-Cell Biocatalyst for the Production of Single-Cell Oil from Agro-Industrial Wastes

Cutaneotrichosporon oleaginosus is an oleaginous yeast with several favourable qualities: It is fast growing, accumulates high amounts of lipids and has a very broad substrate spectrum. Its resistance to hydrolysis by-products makes it a promising biocatalyst for custom tailored microbial oils. C. oleaginosus can accumulate up to 60 wt.% of its biomass as lipids. This species is able to grow by using several compounds as a substrate, such as acetic acid, biodiesel-derived glycerol, N-acetylglucosamine, lignocellulosic hydrolysates, wastepaper and other agro-industrial wastes. This review is focused on state-of-the-art innovative and sustainable biorefinery schemes involving this promising yeast and second- and third-generation biomasses. Moreover, this review offers a comprehensive and updated summary of process strategies, biomass pretreatments and fermentation conditions for enhancing lipid production by C. oleaginosus as a whole-cell biocatalyst. Finally, an overview of the main industrial applications of single-cell oil is reported together with future perspectives.

From crude industrial waste glycerol to biopropene via Ru-mediated hydrodeoxygenation in ionic liquids

The catalytic conversion of crude glycerol to biopropene was investigated. A bifunctional Ru-ionic liquid system showed a high tolerance for common crude glycerol impurities like water, salts and methanol. After optimizing both dehydration and olefin selectivity, a 82% biopropene yield (94% selectivity) was obtained directly from industrial waste glycerol.

The Model System Saccharomyces cerevisiae Versus Emerging Non-Model Yeasts for the Production of Biofuels

Microorganisms are effective platforms for the production of a variety of chemicals including biofuels, commodity chemicals, polymers and other natural products. However, deep cellular understanding is required for improvement of current biofuel cell factories to truly transform the Bioeconomy. Modifications in microbial metabolic pathways and increased resistance to various types of stress caused by the production of these chemicals are crucial in the generation of robust and efficient production hosts. Recent advances in systems and synthetic biology provide new tools for metabolic engineering to design strategies and construct optimal biocatalysts for the sustainable production of desired chemicals, especially in the case of ethanol and fatty acid production. Yeast is an efficient producer of bioethanol and most of the available synthetic biology tools have been developed for the industrial yeast Saccharomyces cerevisiae. Non-conventional yeast systems have several advantageous characteristics that are not easily engineered such as ethanol tolerance, low pH tolerance, thermotolerance, inhibitor tolerance, genetic diversity and so forth. Currently, synthetic biology is still in its initial steps for studies in non-conventional yeasts such as Yarrowia lipolytica, Kluyveromyces marxianus, Issatchenkia orientalis and Pichia pastoris. Therefore, the development and application of advanced synthetic engineering tools must also focus on these underexploited, non-conventional yeast species. Herein, we review the basic synthetic biology tools that can be applied to the standard S. cerevisiae model strain, as well as those that have been developed for non-conventional yeasts. In addition, we will discuss the recent advances employed to develop non-conventional yeast strains that are efficient for the production of a variety of chemicals through the use of metabolic engineering and synthetic biology.

Thermo-Mechanical Properties of a Wood Fiber Insulation Board Using a Bio-Based Adhesive as a Binder

The goal of the present study was to develop a low-density thermal insulation board using wood fibers and a bio-based adhesive as a binder, which was prepared from a crude glycerol and citric acid mixture. The physical and mechanical properties of insulation boards manufactured using two ratios of crude glycerol and citric acid (1:0.66 and 1:1 mol/mol) and two adhesive contents (14% and 20%) were evaluated. The results show that the insulation boards with a range of density between 332 to 338 kg m−3 present thermal conductivity values between 0.064 W/m-K and 0.066 W/m-K. The effect of adhesive content was very significant for certain mechanical properties (tensile strength perpendicular to surface and compressive strength). The tensile strength (internal bond) increased between 20% and 36% with the increased adhesive content. In contrast, the compressive strength decreased between 7% and 15%. The thermo-mechanical properties obtained of insulation boards such as thermal conductivity, traverse strength, tensile strength parallel and perpendicular to surface, and compressive strength are in accordance with the requirements of the American Society for Testing and Materials C208-12 standard for different uses. The results confirm the potential of crude glycerol and citric acid mixture to be used as an adhesive in the wood fiber insulation boards’ manufacturing for sustainability purposes.

Development of novel strategies for higher fermentative biohydrogen recovery along with novel metabolites from organic wastes: The present state of the art

Depletion of fossil fuels and environmental concern has compelled us to search for alternative fuel. Hydrogen is considered as a dream fuel as it has high energy content (142 kJ g^-1 ) and is not chemically bound to carbon. At present, fossil fuel-based methods for producing hydrogen require high-energy input, which makes the processes expensive. The major processes for biohydrogen production are biophotolysis, microbial electrolysis, dark fermentation, and photofermentation. Fermentative hydrogen production has the additional advantages of potentially using various waste streams from different industries as feedstock. Novel strategies to enhance the productivity of fermentative hydrogen production include optimization in pretreatment methods, integrated fermentation systems (sequential and combined fermentation), use of nanoparticles as additives, metabolic engineering of microorganisms, improving the light utilization efficiency, developing more efficient photobioreactors, etc. More focus has been given to produce biohydrogen in a biorefinery approach in which, along with hydrogen gas, other metabolites (ethanol, butyric acid, 1,3-propanediol, etc.) are also produced, which have direct/indirect industrial applications. In present review, various emerging technologies that highlight biohydrogen production methods as effective and sustainable methods on a large scale have been critically reviewed. The possible future developments are also outlined.

Valorization of Biodiesel Byproduct Crude Glycerol for the Production of Bioenergy and Biochemicals

The rapid growth of global biodiesel production requires simultaneous effective utilization of glycerol obtained as a by-product of the transesterification process. Accumulation of the byproduct glycerol from biodiesel industries can lead to considerable environment issues. Hence, there is extensive research focus on the transformation of crude glycerol into value-added products. This paper makes an overview of the nature of crude glycerol and ongoing research on its conversion to value-added products. Both chemical and biological routes of glycerol valorization will be presented. Details of crude glycerol conversion into microbial lipid and subsequent products will also be highlighted.

Enhancing methane yield from crude glycerol anaerobic digestion by coupling with ultrasound or A. niger/E. coli biodegradation

Anaerobic digestion of crude glycerol from biodiesel production is a feasible way for methane production. However, crude glycerol (CG) contains impurities, such as long-chain fatty acids (LCFA) that can inhibit methanogenic microorganisms. Ultrasound promotes the hydrolysis of LCFA and deagglomerates the microorganisms in biological flocs. Furthermore, Aspergillus niger and Escherichia coli produce lipases capable of degrading LCFA. This study aims at improving the methane yield from anaerobic digestion by coupling with ultrasound or E. coli/A. niger biodegradation. The effect of the different treatments was first assessed in a perfectly mixed batch reactor (PMBR), using diluted CG at concentrations of 0.2%, 1.7%, and 3.2% (v/v). Later, the best conditions were replicated in an upflow anaerobic sludge blanket (UASB) reactor to simulate full-scale practical applications. Experiments in the PMBR showed that ultrasound or A. niger biodegradation steps improved methane yield up to 11% for 0.2% CG and 99% for 1.7% CG, respectively. CG biodegradation by E. coli inhibited the subsequent anaerobic digestion for all concentrations tested. Using a UASB digester, ultrasonic treatment of CG led to an average increase of 29% in methane production. The application of ultrasound led to a lower accumulation of propionic acid in the digested material and increased biogas production. On the other hand, an average 77% increase in methane production was achieved using a preliminary CG biodegradation step by A. niger, when operated at a loading rate of 2.9 kg COD m^-3 day^-1. Under these conditions, an energy gain of 0.48 kWh day^-1, with the production of the 0.434 m³ CH₄ kg^-1 COD_removal and 0.573 m³ CH₄ kg^-1 VS, and a biogas quality of 73% in methane were obtained. The digested material was analyzed for the detection and quantification of added-value by-products in order to obtain a broad assessment of the CG valorization through anaerobic digestion. In some experiments, propionic and oxalic acid were detected. However, the accumulation of propionic caused the inhibition of the acetogenic and methanogenic microorganisms.

Catalytic Synthesis of Monoglycerides by Glycerolysis of Triglycerides

The synthesis of monoglycerides by the transesterification of triglycerides with glycerol was studied using zinc glycerolate as a heterogeneous catalyst.

The effect of the operating variables on the triglyceride conversion and monoglyceride yield was evaluated. The maximum values of triglyceride conversion and monoglyceride yield reached at 2-hour reaction time were 83 and 49 %, respectively. These values were obtained at 240 °C with 3 % catalyst loading and glycerol/oil molar ratio of 6. When the molar ratio of the reactants was increased, the triglyceride conversion and monoglyceride yield achieved an optimum value. This behavior was related with a competitive adsorption of the reagents.

It was possible to reuse the catalyst without significant changes in activity.

Biosorption of glycerol impurities from biodiesel production onto electrospun chitosan-based nanofibers: equilibrium and thermodynamic evaluations

The increase in biodiesel production has been leading to an excess amount of crude glycerol and, consequently, serious environmental issues. For this reason, electrospun chitosan-based nanofibers (CB-EN), composed by chitosan and poly(ethylene oxide) (PEO), were synthesized to apply in the biosorption of impurities from industrial glycerol. To evaluate the biosorption efficiency, the chitosan-based nanofiber was compared to other chitosan-based biosorbents (chitosan biopolymeric film and chitosan powder). The equilibrium and thermodynamic studies were successfully performed to comprehend the interaction mechanisms through the biosorption of glycerol pigments onto electrospun chitosan-based nanofibers. The temperature effect was evaluated by experimental equilibrium curves. Freundlich and BET models were used to estimate isotherm parameters. Gibbs free energy change, enthalpy change, entropy change, and isosteric heat of biosorption were quantified. The equilibrium curves showed that the highest equilibrium relative adsorption (340.7 g^-1) was reached at 60 °C. The BET model was the most suitable to represent the equilibrium behavior. The thermodynamic parameters indicated that the biosorption was spontaneous, exothermic, random, and energetic heterogeneous. Therefore, this work developed a green and efficient alternative to refine industrial glycerol. Graphical abstract Note: This data is mandatory. Please provide.

Biotreatment of landfill leachate by microalgae-bacteria consortium in sequencing batch mode and product utilization

Biotreatment of leachate by microalgae-bacteria in a sequencing batch mode using a photobioreactor was investigated. The microalgae-bacteria biomass initial concentration was maintained at 3:1 ratio. The increase in the initial concentration of the biomass in the 2^nd batch favoured biomass growth, doubling biomass productivity, compared to the 1^st batch. In both batches, N-NH₄ was completely removed from the leachate. In the 2^nd batch, the nitrate, COD and phenol removal efficiencies were above 90%. The relative toxicity reduced from 57.32 to 1.12% at the end of 2^nd batch. The fatty acids content (C16-18) varied from 85.47 to 87.65% for the 1^st batch and 86.72 to 87.69% for the 2nd batch. The crude glycerol content varied from 34.54 to 42.36% for the 1^st batch and 33.64 to 39.55% for the 2^nd batch. The coexistence of microalgae and bacteria played an important role in leachate treatment and biomass production for biorefinery purposes.

Recent Progress in Synthesis of Glycerol Carbonate and Evaluation of Its Plasticizing Properties

The state of the art on the glycerol carbonate (GC) synthesis has been updated since the last published reviews in 2012, 2013, and 2016. Three types of reactions continue to be studied: glycerolysis of urea, transcarbonation of DMC, DEC, or cyclic carbonates with glycerol and reaction using CO₂. Among these different routes, DMC and glycerol were selected as the raw materials for the GC synthesis in this work since the transcarbonation from these green reagents leads to high yields and selectivities, using mild conditions including a less energy consuming GC separation process. Catalytic conditions using Na₂CO₃ seem to be a good compromise to achieve a high yield of GC, leading to an easier purification step without GC distillation. Mild temperatures for the reaction (73–78°C) as well as a low waste amount confirmed by the E-factor calculation, are in favor of controlled costs. Plasticizing properties of synthesized GC were compared to the behaviors of a commercial plasticizer and natural dialkyl carbonates, for a colorless nail polish formulation. The resulting films subjected to mechanical and thermal stresses (DMA and Persoz pendulum) showed the high plasticizing effect of GC toward nitrocellulose based films, probably due to hydrogen bond interactions between GC and nitrocellulose. The GC efficiency gives the possibility to decrease the content of the plasticizer in the formulation. Glycerol carbonate can be thus considered as a biobased ingredient abiding by the green chemistry concepts, and safe enough to be used in an ecodesigned nail polish formulation.