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

Experimental Scale-Up and Technoeconomic Assessment of Low-Grade Glycerol Purification from Waste-Based Biorefinery

The purification of waste-derived crude glycerol to the 2000 g scale is presented to provide a consolidated proof of concept. Starting from unprecedented low-quality glycerol from a second-generation biodiesel plant, currently disposed of at cost, a series of physiochemical steps are implemented to improve glycerol purity and recovery under relevant conditions. The study is carried out on two samples with initial purities of 38-57 wt % and ash contents of up to 16 wt %. Under the optimal process conditions, glycerol exhibits a remarkable increase to 85 wt % purity while preserving the overall glycerol recovery of the process of up to 71%. Among different purification steps, neutralization contributes to increasing the purity to 69 wt % while the remaining water and methanol evaporation have further increased the purity to >80 wt %. The adsorption step shows the smallest increase in glycerol purity despite it being required to decolorize and deodorize the final product. The developed process is further designed for industrial-scale application using Aspen Plus for a plant size of 1630 kg/h of purified glycerol which could achieve 82 wt % final purity and a maximum recovery of 77%. In addition, the process yields 315 kg/h of salable byproduct salts suitable as fertilizer and an overall CO2 emission of 0.70 ton per ton of purified glycerol mainly due to the unrecovered feedstock and solvent combustion. As a result, the proposed process implementation could generate positive revenues with a cost of the final products of €19.2 per ton.

Performance of production of polyhydroxyalkanoates from food waste fermentation with Rhodopseudomonas palustris

The use of waste as a carbon source can significantly reduce the cost of production of Polyhydroxyalkanoates (PHAs). In this study, an acidified hydrolysate solution derived from food waste (FW) was used as a carbon source for the synthesis of PHAs by Rhodopseudomonas palustris (R. palustris) and optimized the process parameters. The results showed that the PHAs yield reached 48.62% under optimal conditions (an incubation time of 30 days, volatile fatty acids (VFAs) in substrate concentration of 2202.21 mg⋅L^-1, an initial pH of 8.0, and inoculum concentration of 15%). The fraction of VFAs affects the composition of PHAs, R. palustris first uses VFAs with an even number of carbons to synthesize poly(3-hydroxybutyrate)(3HB), and later uses VFAs with an odd number of carbons to synthesize poly-3-hydroxyvalerate (3HV). Pathways for the synthesis of PHAs by R. palustris were inferred. R. palustris is a strain with the potential to synthesize PHAs.

The effect of light emission spectrum on biohydrogen production by Rhodopseudomonas palustris

Photofermentative hydrogen production has gained increasing attention as a source of green energy. To make such photofermentation processes economically competitive, operating costs need to be reduced, possibly through outdoor operation. Because photofermentation processes are light dependent, the emission spectrum and intensity of light both have a significant influence on the hydrogen production and merit investigation. This study investigates the effect of light sources on the hydrogen production and growth of Rhodopseudomonas palustris, comparing the organism's productivity under longer-wavelength light and light mimicking sunlight. Hydrogen production is enhanced under longer-wavelength light, producing 26.8% (± 7.3%) more hydrogen as compared to under light mimicking that of sunlight; however, R. palustris is still able to produce a considerable volume of hydrogen under light with a spectrum mimicking that of sunlight, providing a promising avenue for future research.

The effect of diurnal light cycles on biohydrogen production in a thermosiphon photobioreactor

Hydrogen production via microbial photofermentation shows great promise as a method for sustainable hydrogen production; however, operating costs associated with photofermentative hydrogen production need to be reduced. Costs can be reduced using a passive circulation system like the thermosiphon photobioreactor, and by operating it under natural sunlight. In this study, an automated system was implemented to investigate the effect of diurnal light cycles on the hydrogen productivity and growth of Rhodopseudomonas palustris and on the operation of a thermosiphon photobioreactor, under controlled conditions. Diurnal light cycles, simulating daylight times, were found to reduce hydrogen production in the thermosiphon photobioreactor demonstrating a low maximum production rate of 0.015 mol m^-3 h^-1 (± 0.002 mol m^-3 h^-1) as compared to 0.180 mol m^-3 h^-1 (± 0.0003 mol m^-3 h^-1) under continuous illumination. Glycerol consumption as well as hydrogen yield also decreased under diurnal light cycles. Nonetheless, hydrogen production in a thermosiphon photobioreactor under outdoor conditions was demonstrated as possible avenue for further investigation.

Intensification of Hydrogen Production by a Co-culture of Syntrophomonas wolfei and Rhodopseudomonas palustris Employing High Concentrations of Butyrate as a Substrate

The purpose of this study is to present an effective form of developing a sequential dark (DF) and photo (PF) fermentation using volatile fatty acids (VFAs) and nitrogen compounds as bonding components between both metabolic networks of microbial growing in each fermentation. A simultaneous (co-)culture of Syntrophomonas wolfei (with its ability to consume butyrate and produce acetate) and Rhodopseudomonas palustris (that can use the produced acetate as a carbon source) performed a syntrophic metabolism. The former bacteria consumed the acetate/butyrate mixture reducing the butyrate concentration below 2.0 g/L, permitting Rhodopseudomonas palustris to produce hydrogen. Considering that the inoculum composition (Syntrophomonas wolfei/Rhodopseudomonas palustris) and the nitrogen source (yeast extract) define the microbial biomass specific productivity and the butyrate consumption, a response surface methodology defined the best inoculum design and yeast extract (YE) yielding to the highest biomass concentration of 1.1 g/L after 380.00 h. A second culture process (without a nitrogen source) showed the biomass produced in the previous culture process yields to produce a total cumulated hydrogen concentration of 3.4 mmol. This value was not obtained previously with the pure strain Rhodopseudomonas palustris if the culture medium contained butyrate concentration above 2.0 g/L, representing a contribution to the sequential fermentation scheme based on DF and PF.

Modelling and testing of a light reflector system for the enhancement of biohydrogen production in a thermosiphon photobioreactor

One of the main factors affecting hydrogen production and growth of photofermentative microorganisms is light; low light penetration and utilization are significant bottlenecks in photofermentative hydrogen production systems. In this study, light distribution in a thermosiphon photobioreactor operated with Rhodopseudomonas palustris was investigated. Radiation fields were modelled and simulated using computational fluid dynamics (ANSYS® Fluent, 2019 R2) and a reflector system was evaluated for the enhancement of light distribution in a thermosiphon photobioreactor. The effect of the reflector system was investigated experimentally in terms of hydrogen production, carbon substrate consumption and biomass circulation in the reactor. With the addition of the reflector system, hydrogen production was increased by 48% while glycerol consumption was increased from approximately 24% to 32%. After 336 h, the concentration of R. palustris cells still in suspension ranged from 0.13 to 0.18 g∙L^-1, with no discernible difference in concentration between the systems with and without reflectors. Collectively, the reflector system was shown to be a viable option in enhancing light distribution in photobioreactors, with an associated increase in both hydrogen production as well as glycerol consumption.

A Thermosiphon Photobioreactor for Photofermentative Hydrogen Production by Rhodopseudomonas palustris

A thermosiphon photobioreactor (TPBR) can potentially be used for biohydrogen production, circumventing the requirement for external mixing energy inputs. In this study, a TPBR is evaluated for photofermentative hydrogen production by Rhodopseudomonas palustris (R. palustris). Experiments were conducted in a TPBR, and response surface methodology (RSM), varying biomass concentration, and light intensity and temperature were employed to determine the operating conditions for the enhancement of both hydrogen production as well as biomass suspension. Biomass concentration was found to have had the most pronounced effect on both hydrogen production as well as biomass suspension. RSM models predicted maximum specific hydrogen production rates of 0.17 mol m⁻³h⁻¹ and 0.21 mmol g_CDW⁻¹h⁻¹ at R. palustris concentrations of 1.21 and 0.4 g L⁻¹, respectively. The experimentally measured hydrogen yield was in the range of 45 to 77% (±3.8%), and the glycerol consumption was 8 to 19% (±0.48). At a biomass concentration of 0.40 g L⁻¹, the highest percentage of biomass (72.3%), was predicted to remain in suspension in the TPBR. Collectively, the proposed novel photobioreactor was shown to produce hydrogen as well as passively circulate biomass.

Rhodopseudomonas palustris: A biotechnology chassis

Rhodopseudomonas palustris is an attractive option for biotechnical applications and industrial engineering due to its metabolic versatility and its ability to catabolize a wide variety of feedstocks and convert them to several high-value products. Given its adaptable metabolism, R. palustris has been studied and applied in an extensive variety of applications such as examining metabolic tradeoffs for environmental perturbations, biodegradation of aromatic compounds, environmental remediation, biofuel production, agricultural biostimulation, and bioelectricity production. This review provides a holistic summary of the commercial applications for R. palustris as a biotechnology chassis and suggests future perspectives for research and engineering.

Characteristics and Application of Rhodopseudomonas palustris as a Microbial Cell Factory

Rhodopseudomonas palustris, a purple nonsulfur bacterium, is a bacterium with the properties of extraordinary metabolic versatility, carbon source diversity and metabolite diversity. Due to its biodetoxification and biodegradation properties, R. palustris has been traditionally applied in wastewater treatment and bioremediation. R. palustris is rich in various metabolites, contributing to its application in agriculture, aquaculture and livestock breeding as additives. In recent years, R. palustris has been engineered as a microbial cell factory to produce valuable chemicals, especially photofermentation of hydrogen. The outstanding property of R. palustris as a microbial cell factory is its ability to use a diversity of carbon sources. R. palustris is capable of CO₂ fixation, contributing to photoautotrophic conversion of CO₂ into valuable chemicals. R. palustris can assimilate short-chain organic acids and crude glycerol from industrial and agricultural wastewater. Lignocellulosic biomass hydrolysates can also be degraded by R. palustris. Utilization of these feedstocks can reduce the industry cost and is beneficial for environment. Applications of R. palustris for biopolymers and their building blocks production, and biofuels production are discussed. Afterward, some novel applications in microbial fuel cells, microbial electrosynthesis and photocatalytic synthesis are summarized. The challenges of the application of R. palustris are analyzed, and possible solutions are suggested.

Microalgal Biorefinery Concepts’ Developments for Biofuel and Bioproducts: Current Perspective and Bottlenecks

Microalgae have received much interest as a biofuel feedstock. However, the economic feasibility of biofuel production from microalgae does not satisfy capital investors. Apart from the biofuels, it is necessary to produce high-value co-products from microalgae fraction to satisfy the economic aspects of microalgae biorefinery. In addition, microalgae-based wastewater treatment is considered as an alternative for the conventional wastewater treatment in terms of energy consumption, which is suitable for microalgae biorefinery approaches. The energy consumption of a microalgae wastewater treatment system (0.2 kW/h/m³) was reduced 10 times when compared to the conventional wastewater treatment system (to 2 kW/h/m³). Microalgae are rich in various biomolecules such as carbohydrates, proteins, lipids, pigments, vitamins, and antioxidants; all these valuable products can be utilized by nutritional, pharmaceutical, and cosmetic industries. There are several bottlenecks associated with microalgae biorefinery. Hence, it is essential to promote the sustainability of microalgal biorefinery with innovative ideas to produce biofuel with high-value products. This review attempted to bring out the trends and promising solutions to realize microalgal production of multiple products at an industrial scale. New perspectives and current challenges are discussed for the development of algal biorefinery concepts.

Improvement of the Crude Glycerol Purification Process Derived from Biodiesel Production Waste Sources through Computational Modeling

Considering waste as a possible new resource for useful purposes is one of the strategies included in the circular economy principles. In fact, industrial processes are seen as great contributors to the formation of waste streams. With the aim to attain more sustainable and resilient systems, in this study, a process flow chart was elaborated in an Aspen Plus computer simulator, to obtain the production of pure glycerol from crude glycerol (a by-product of biodiesel production). This process occurs through fractional vacuum distillation, the methanol recovery route in the deacidification process and the removal of methanol from the reaction medium. The separation stages of the crude glycerol implemented enabled a degree of purification of 99.77%, meeting the specifications of the pharmaceutical use. The developed model allowed for the optimization of the purification process, raising by 40% the mass flow rate of pure glycerol. A conclusion could be drawn that the use of crude glycerol is an excellent option for the development of new products with greater added-value, contributing to the zero waste principles and to the circular economy.

Glycerol as a substrate for actinobacteria of biotechnological interest: Advantages and perspectives in circular economy systems

Actinobacteria represent a ubiquitous group of microorganisms widely distributed in ecosystems. They have diverse physiological and metabolic properties, including the production of extracellular enzymes and a variety of secondary bioactive metabolites, such as antibiotics, immunosuppressants, and other compounds of industrial interest. Therefore, actinobacteria have been used for biotechnological purposes for more than three decades. The development of a biotechnological process requires the evaluation of its cost/benefit ratio, including the search for economic and efficient substrates for microorganisms development. Biodiesel is a clean, renewable, quality and economically viable source of energy, which also contributes to the conservation of the environment. Crude glycerol is the main by-product of biodiesel production and has many properties, so it has a commercial value that can be used to finance the biofuel production process. Actinobacteria can use glycerol as a source of carbon and energy, either pure o crude. A circular economy system aims to eliminate waste and pollution, keep products and materials in use, and regenerate natural systems. Although these principles are not yet met, some approaches are being made in this direction; the transformation of crude glycerol by actinobacteria is a process with great potential to be scaled on an industrial level. This review discusses the reports on glycerol as a promising source of carbon and energy for obtaining biomass and high-added value products by actinobacteria. Also, the factors influencing the biomass and secondary metabolites production in bioreactors are analyzed, and the tools available to overcome those that generate the main problems are discussed.

Two-Stage Anaerobic Codigestion of Crude Glycerol and Micro-Algal Biomass for Biohydrogen and Methane Production by Anaerobic Sludge Consortium

Optimization of factors affecting biohydrogen production from the codigestion of crude glycerol and microalgal biomass by anaerobic sludge consortium was conducted. The experiments were designed by a response surface methodology with central composite design. The factors affecting the production of hydrogen were the concentrations of crude glycerol, microalgal biomass, and inoculum. The maximum hydrogen production (655.1 mL-H2/L) was achieved with 13.83 g/L crude glycerol, 23.1 g-VS/L microalgal biomass, and 10.3% (v/v) inoculum. The hydrogenic effluents obtained under low, high, and optimal conditions were further used as substrates for methane production. Methane production rates and methane yield of 868.7 mL-CH4/L and 2.95 mL-CH4/L-h were attained with the effluent produced under optimum conditions. The use of crude glycerol and microalgal biomass as cosubstrates had an antagonistic effect on biohydrogen production and a synergistic effect on methane fermentation. The two-stage process provided a more attractive solution, with a total energy of 1.27 kJ/g-VSadded, than the one-stage process.

Bioremediation of Crude Glycerol by a Sustainable Organic-Microbe Hybrid System

Klebsiella pneumoniae with crude glycerol-utilizing and hydrogen (H₂)-producing abilities was successfully isolated from return activated sludge from Shatin Sewage Treatment Works. The H₂ production strategy used in this study was optimized with crude glycerol concentrations, and 1,020 μmol of H₂ was generated in 3 h. An organic–microbe hybrid system was constructed with metal-free hydrothermal carbonation carbon (HTCC) microspheres to enhance the H₂ production under visible light (VL) irradiation. Under optimized VL intensity and HTCC concentration, an elevation of 35.3% in H₂ production can be obtained. Electron scavenger study revealed that the photogenerated electrons (e^–) from HTCC contributed to the additional H₂ production. The variation in intercellular intermediates, enzymatic activity, and reducing equivalents also suggested that the photogenerated e^– interacted with K. pneumoniae cells to direct the metabolic flux toward H₂ production. This study demonstrated the feasibility of using an organic–microbe hybrid system as a waste-to-energy technology.

Microstructure-Property Relationship of Polyurethane Foams Modified with Baltic Sea Biomass: Microcomputed Tomography vs. Scanning Electron Microscopy

In this paper, novel rigid polyurethane foams modified with Baltic Sea biomass were compared with traditional petro-based polyurethane foam as reference sample. A special attention was focused on complex studies of microstructure, which was visualized and measured in 3D with high-resolution microcomputed tomography (microCT) and, as commonly applied for this purpose, scanning electron microscopy (SEM). The impact of pore volume, area, shape and orientation on appearance density and thermal insulation properties of polyurethane foams was determined. The results presented in the paper confirm that microcomputed tomography is a useful tool for relatively quick estimation of polyurethane foams’ microstructure, what is crucial especially in the case of thermal insulation materials.

Investigation of fermentation conditions of biodiesel by-products for high production of β-farnesene by an engineered Escherichia coli

Recently, the research on conversion of biodiesel by-products to high value-added products has received much attention, due to the adverse effects of large accumulations of biodiesel by-products caused by the rapid increase in biodiesel production. Herein, this study investigated the utilization of by-products crude glycerol (CG-1 and CG-2) from two different industrial methods of biodiesel production and the favorable fermentation conditions for the high yield of β-farnesene by an engineered Escherichia coli F4, which harbored an optimized mevalonate pathway. Through analyzing by-products' components and fermentation performance, we found that CG-2 did not contain harmful impurities such as methanol and black solid impurities, and the β-farnesene production was up to 2.7 g/L from CG-2, which was similar to that from pure glycerol (2.5 g/L) and higher than that (2.21 g/L) from CG-1. Therefore, CG-2 was more suitable for β-farnesene production than CG-1, which might provide a reference for choosing a more suitable method on practical biodiesel production. Afterward, a variety of important fermentation conditions were explored using CG-2 as a substrate in shaken flasks. Under the optimal conditions (including induced cell density 1.0, initial cell density 0.25, temperature after induction 33 °C, initial medium pH 6.5), the yield of β-farnesene from CG-2 reached 10.31 g/L in a 5-L bioreactor, which was 2.8-fold higher than initial conditions in shake flasks and was the highest yield of β-farnesene produced from biodiesel by-products by fermentation as well. The recommended fermentation conditions in this work will provide a valuable reference for the industrial production of β-farnesene utilizing biodiesel by-products.

Production of Biodiesel from Castor Oil: A Review

An attractive alternative to the use of fossil fuels is biodiesel, which can be obtained from a variety of feedstock through different transesterification systems such as ultrasound, microwave, biological, chemical, among others. The efficient and cost-effective biodiesel production depends on several parameters such as free fatty acid content in the feedstock, transesterification reaction efficiency, alcohol:oil ratio, catalysts type, and several parameters during the production process. However, biodiesel production from vegetable oils is under development, causing the final price of biodiesel to be higher than diesel derived from petroleum. An alternative to decrease the production costs will be the use of economical feedstocks and simple production processes. Castor oil is an excellent raw material in terms of price and quality, but especially this non-edible vegetable oil does not have any issues or compromise food security. Recently, the use of castor oil has attracted attention for producing and optimizing biodiesel production, due to high content of ricinoleic fatty acid and the possibility to esterify with only methanol, which assures low production costs. Additionally, biodiesel from castor oil has different advantages over conventional diesel. Some of them are biodegradable, non-toxic, renewable, they can be used alone, low greenhouse gas emission, among others. This review discusses and analyzes different transesterification processes, technologies, as well as different technical aspects during biodiesel production using castor oil as a feedstock.

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.

Utilization of biodiesel by-product as substrate for high-production of β-farnesene via relatively balanced mevalonate pathway in Escherichia coli

Farnesene has been identified as suitable jet fuel substitutes and metabolic engineering for microbial production of farnesene is an alternative and attractive route. In this study, due to accumulation of toxic intermediate isopentenyl pyrophosphate (IPP), an engineered Escherichia coli strain harboring heterologous mevalonate pathway produced only 4.11mg/L β-farnesene. Through higher-level expression of isopentenyl diphosphate isomerase and farnesyl diphosphate synthase to minimize the accumulated IPP, another engineered strain with relatively balanced mevalonate pathway was constructed and had the highest production of β-farnesene to date (8.74g/L) by Escherichia coli in a lab bioreactor. Furthermore, this is the first report on utilization of biodiesel by-product (simple purification) as substrate for high-production of β-farnesene by the engineered strain optimized and β-farnesene concentration reached 2.83g/L in a lab bioreactor. Therefore, the engineered strain optimized could be used as a platform host for high-production of other terpenoids using biodiesel by-product as substrate.

Recent Developments in Polyurethane Foams Containing Low-Cost and Pro-Ecological Modifiers

Diversity of the polyurethane (PU) foams applications cause that investigation of the relationships between their structure and properties is currently very popular topic among the many research institutions and companies. At the turn of the last years many scientific papers about PU foams and their composites were published. The one of the main trends in research in this field is related to the reduction of production costs of PU foams. This aim can be successfully achieved through the incorporation of raw materials of natural origin or the utilization of waste materials. This work reviews the progress and recent developments in area of PU foams containing low-cost and pro-ecological modifiers, such as crude glycerol, liquefied biomass, ground tire rubber, etc.

Optimization of biohydrogen yield produced by bacterial consortia using residual glycerin from biodiesel production

The aims of this study were to simplify the fermentation medium and to optimize the conditions of dark fermentation of residual glycerin to produce biohydrogen. It was possible to remove all micronutrients of fermentation medium and improve biohydrogen production by applying residual glycerin as feedstock. After statistical analysis of the following parameters pH, glycerin concentration and volatile suspended solids, the values of 5.5; 0.5g.L(-1) and 8.7g.L(-1), respectively, were defined as optimum condition for this process. It generated 2.44molH2/molglycerin, an expressive result when compared to previous results reported in literature and considering that theoretical yield of H2 from glycerol in dark fermentation process is 3molH2/molglycerol. This study allowed the improvement of yield and productivity by 68% and 67%, respectively.

Economical fermentation media for the production of a whole cell catalyst for the treatment of Cr(VI)-containing wastewaters

The biotechnology sector is continually seeking sustainable and more economical bioprocesses. Fermentation media produced with cheap components or wastes reduce production costs. Moreover, if wastes are used, they contribute to avoid environmental pollution. In this work, microbial growth media based on molasses or acidified glycerol as carbon sources and fertilizer as nitrogen source were tested for the production of a whole-cell catalyst that could be used in Cr(VI)-containing wastewater treatments. Results showed that the highest biomass production yield was obtained with a medium containing acidified glycerol 5% v/v and fertilizer 0.6% v/v. The biomass produced using this medium was immobilized in calcium alginate beads and used as catalyst in the biotransformation of Cr(VI) into Cr(III). The catalyst could be efficiently used for 5 reduction cycles of 40mg/l Cr(VI) each. Cr(III) retention assays were performed to determine whether Cr(III) could be retained by the catalyst avoiding its solubilization in the supernatants. The retention capacity of the catalyst at 32°C and pH 3.0 was 3mg Cr(III)/g. Both an alternative and economical fermentation medium is here proposed for the optimization of Cr(VI)-containing wastewater treatment.

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.

Potential Application of Biohydrogen Production Liquid Waste as Phosphate Solubilizing Agent-A Study Using Soybean Plants

With CO2 free emission and a gravimetric energy density higher than gasoline, diesel, biodiesel, and bioethanol, biohydrogen is a promising green renewable energy carrier. During fermentative hydrogen production, 60-70 % of the feedstock is converted to different by-products, dominated by organic acids. In the present investigation, a simple approach for value addition of hydrogen production liquid waste (HPLW) containing these compounds has been demonstrated. In soil, organic acids produced by phosphate solubilizing bacteria chelate the cations of insoluble inorganic phosphates (e.g., Ca3 (PO4)2) and make the phosphorus available to the plants. Organic acid-rich HPLW, therefore, has been evaluated as soil phosphate solubilizer. Application of HPLW as soil phosphate solubilizer was found to improve the phosphorus uptake of soybean plants by 2.18- to 2.74-folds. Additionally, 33-100 % increase in seed germination rate was also observed. Therefore, HPLW has the potential to be an alternative for phosphate solubilizing biofertilizers available in the market. Moreover, the strategy can be useful for phytoremediation of phosphorus-rich soil.

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.

The effect of organic load and feed strategy on biohydrogen production in an AnSBBR treating glycerin-based wastewater

An anaerobic sequencing batch biofilm reactor (AnSBBR) with recirculation of the liquid phase (at 30 °C with 3.5 L of working volume and treating 1.5 L per cycle) treating pure glycerin-based wastewater was applied to biohydrogen production. The applied volumetric organic load (AVOL) ranged from 7.7 to 17.1 kgCOD m(-3) d(-1), combining different influent concentrations (3000, 4000 and 5000 mgCOD L(-1)) and cycle lengths (4 and 3 h). The feed strategy used was to maintain the feeding time equal to half of the cycle time. The increase in the influent concentration and the decrease in cycle length improved the molar yield and molar productivity of hydrogen. The highest productivity (100.8 molH2 m(-3) d(-1)) and highest yield of hydrogen per load removed (20.0 molH2 kgCOD(-1)) were reached when the reactor operated with an AVOL of 17.1 kgCOD m(-3) d(-1), with 68% of H2 and only 3% of CH4 in its biogas. It was also found that pretreatment of the sludge/inoculum does not influence the productivity/yield of the process and the use of crude industrial glycerin-based wastewater in relation to the pure glycerol-based wastewater substantially decreased the production and composition of the hydrogen produced.

Improved glycerol utilization by a triacylglycerol-producing Rhodococcus opacus strain for renewable fuels

BACKGROUND

Glycerol generated during renewable fuel production processes is potentially an attractive substrate for the production of value-added materials by fermentation. An engineered strain MITXM-61 of the oleaginous bacterium Rhodococcus opacus produces large amounts of intracellular triacylglycerols (TAGs) for lipid-based biofuels on high concentrations of glucose and xylose. However, on glycerol medium, MITXM-61 does not produce TAGs and grows poorly. The aim of the present work was to construct a TAG-producing R. opacus strain capable of high-cell-density cultivation at high glycerol concentrations.

RESULTS

An adaptive evolution strategy was applied to improve the conversion of glycerol to TAGs in R. opacus MITXM-61. An evolved strain, MITGM-173, grown on a defined medium with 16 g L(-1) glycerol, produced 2.3 g L(-1) of TAGs, corresponding to 40.4% of the cell dry weight (CDW) and 0.144 g g(-1) of TAG yield per glycerol consumed. MITGM-173 was able to grow on high concentrations (greater than 150 g L(-1)) of glycerol. Cultivated in a medium containing an initial concentration of 20 g L(-1) glycerol, 40 g L(-1) glucose, and 40 g L(-1) xylose, MITGM-173 was capable of simultaneously consuming the mixed substrates and yielding 13.6 g L(-1) of TAGs, representing 51.2% of the CDM. In addition, when 20 g L(-1) glycerol was pulse-loaded into the culture with 40 g L(-1) glucose and 40 g L(-1) xylose at the stationary growth phase, MITGM-173 produced 14.3 g L(-1) of TAGs corresponding to 51.1% of the CDW although residual glycerol in the culture was observed. The addition of 20 g L(-1) glycerol in the glucose/xylose mix resulted in a TAG yield per glycerol consumed of 0.170 g g(-1) on the initial addition and 0.279 g g(-1) on the pulse addition of glycerol.

CONCLUSION

We have generated a TAG-producing R. opacus MITGM-173 strain that shows significantly improved glycerol utilization in comparison to the parental strain. The present study demonstrates that the evolved R. opacus strain shows significant promise for developing a cost-effective bioprocess to generate advanced renewable fuels from mixed sugar feedstocks supplemented with glycerol.