The interest in microorganisms to produce microbial lipids at large-scale processes has increased during the last decades. Rhodosporidium toruloides-1588 could be an efficient option for its ability to simultaneously utilize five- and six-carbon sugars. Nevertheless, one of the most important characteristics that any strain needs to be considered or used at an industrial scale is its capacity to grow in substrates with high sugar concentrations. In this study, the effect of high sugar concentrations and the effect of ammonium sulfate were tested on R. toruloides-1588 and its capacity to grow and accumulate lipids using undetoxified wood hydrolysates. Batch fermentations showed a catabolic repression effect on R. toruloides-1588 growth at sugar concentrations of 120 g/L. The maximum lipid accumulation was 8.2 g/L with palmitic, stearic, oleic, linoleic, and lignoceric acids as predominant fatty acids in the produced lipids. Furthermore, R. toruloides-1588 was able to utilize up to 80% of the total xylose content. Additionally, this study is the first to report the effect of using high xylose concentrations on the growth, sugar utilization, and lipid accumulation by R. toruloides-1588.

The interest in microbial lipids has recently increased because of their wide use to produce several value-added compounds in the biofuel, pharmaceutical and food industries. Oleaginous yeast such as Rhodosporidium toruloides could be an efficient option because of its ability to consume five-carbon sugars, high lipid accumulation, and tolerance to toxic compounds such as furans, phenolic compounds, and organic acids. The present study aims to investigate the effect of different initial sugar ratios, in combination with different carbon/nitrogen ratios, and the use of dibasic sodium phosphate (Na2HPO4) as an inducer on cell biomass production, sugar consumption, and lipid accumulation by Rhodosporidium toruloides-1588. The investigation showed a maximum lipid accumulation of 5.35 gL-1 (0.28 g of lipids/g of sugar) under the culture conditions of initial glucose: xylose ratio of 1:1, C/N ratio of 70, and Na2HPO4 concentration of 1.05 gL-1. The predominant lipids composition was palmitic, stearic, oleic, and linoleic acids which could be used as a suitable feedstock for biofuel production. Additionally, under the optimal conditions (initial glucose: xylose ratio of 1:1, 1.19 gL-1 of Na2HPO4 and C/N ratio of 70.50) an increase of 10.5% and 7.5% in lipid accumulation was observed, compared with control treatments (glucose and xylose, respectively). In addition, the study shows the ability of R. toruloides-1588 to tolerate inhibitors, a feature that could be a promising alternative to increase the feasibility of the microbial lipid production process using undetoxified wood hydrolysate as a sustainable culture media.

Lignocellulosic biomass has been identified as a renewable and sustainable feedstock to produce liquid hydrolysates as a suitable substrate to produce a variety of compounds through biochemical processes. Nevertheless, the main challenge to using this substrate is the hydrolysis needed to release fermentable sugars. This pretreatment leads to the production of microbial toxic compounds such as furans, phenols and organic acids. In this work, an oleaginous yeast, R. toruloides NRRL 1588, was used to study its ability to degrade inhibitors in C5 and C6 wood hydrolysates obtained from forestry residues. The study showed that R. toruloides NRRL 1588 can grow, accumulate lipids, and degrade up to 8.01 mgL−1 h−1 of furfural, 5.63 mgL−1 h−1 of 5-hydroxy methyl furfural, 1.70 mgL−1 h−1 of levulinic acid, 1.15 mgL−1 h−1 of syringaldehyde, 0.67 mgL−1 h−1 of vanillin, and 1.03 mgL−1 h−1 of vanillic acid. This work confirms the robustness of R. toruloides NRRL 1588 when grows in wood hydrolysates containing inhibitory compounds.

AbstractNi‐Co bimetallic and Ni or Co monometallic catalysts prepared for CO2 reforming of methane were tested with the stimulated biogas containing steam, CO2, CH4, H2, and CO. A mix of the prepared CO2 reforming catalyst and a commercial steam reforming catalyst was used in hopes of maximizing the CO2 conversion. Both CO2 reforming and steam reforming of CH4 occurred over the prepared Ni‐Co bimetallic and Ni or Co monometallic catalysts when the feed contained steam. However, CO2 reforming did not occur on the commercial steam reforming catalyst. There was a critical steam content limit above which the catalyst facilitated no more CO2 conversion but net CO2 production for steam reforming and water‐gas shift became the dominant reactions in the system. The Ni‐Co bimetallic catalyst can convert more than 70% of CO2 in a biogas feed that contains ~33 mol% of CH4, 21.5 mol% of CO2, 12 mol% of H2O, 3.5 mol% of H2, and 30 mol% of N2. The H2/CO ratio of the produced syngas was in the range of 1.8‐2. X‐ray absorption spectroscopy of the spent catalysts revealed that the metallic sites of Ni‐Co bimetallic, Ni and Co monometallic catalysts after the steam reforming of methane reaction with equimolar feed (CH4:H2O:N2 = 1:1:1) experienced severe oxidation, which led to the catalytic deactivation.

A model for industrial top‐fired dry reforming of methane (DRM) and for combined dry reforming and steam reforming of methane was developed for the first time. The model calculates and gives predictions on the temperature profiles for fuel gas, tube walls, and process gas, as well as the process gas composition profiles over the length of the tubes. Radiative heat transfer is modeled by Hottel Zone method. Material and energy balances are solved numerically using Newton‐Raphson solver. Kinetic models for two different DRM catalysts are applied in the model for comparison. Simulation results show that water–gas shift reaction is important in DRM and addition of steam in the feed of process gas is beneficial for industrial production. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2060–2071, 2017

An integrated dark fermentation and microbial electrochemical cell (MEC) process was evaluated for hydrogen production from sugar beet juice. Different substrate to inoculum (S/X) ratios were tested for dark fermentation, and the maximum hydrogen yield was 13% of initial COD at the S/X ratio of 2 and 4 for dark fermentation. Hydrogen yield was 12% of initial COD in the MEC using fermentation liquid end products as substrate, and butyrate only accumulated in the MEC. The overall hydrogen production from the integrated biohydrogen process was 25% of initial COD (equivalent to 6molH2/molhexoseadded), and the energy recovery from sugar beet juice was 57% using the combined biohydrogen.

This study investigates the potential of using a novel integrated biohydrogen reactor clarifier system (IBRCS) for acetone–butanol–ethanol (ABE) production using a mixed culture at different organic loading rates (OLRs). The results of this study showed that using a setting tank after the fermenter and recycle the settled biomass to the fermenter is a practical option to achieve high biomass concentration in the fermenter and thus sustainable ABE fermentation in continuous mode. The average ABE concentrations of 2.3, 7.0, and 14.6gABE/L which were corresponding to ABE production rates of 0.4, 1.4, and 2.8gABE/Lreactorh were achieved at OLRs of 21, 64, and 128gCOD/Lreactord, respectively. The main volatile fatty acids components in the effluent were acetic, propionic, and butyric acids. Acetic acid was the predominant component in the OLR-1, while butyric acid was the predominant acid in OLRs 2 and 3.

The aim of this study was to assess the synergistic effects of co-fermentation of glucose, starch, and cellulose using anaerobic digester sludge (ADS) on the biohydrogen (H2) production and the associated microbial communities. Yields of H2 were 1.22, 1.00, and 0.15 mol H2/mol hexose-added in fermentation reactions containing glucose, starch, and cellulose as mono-substrates. The H2 yields were greater by an average of 27 ± 4% than expected in all the different co-substrate conditions, which affirmed that co-fermentation of different substrates improved the H2 potential. Glucose addition to starch and/or cellulose favored acetate synthesis, while cellulose degradation was associated with the propionate synthesis pathway. Illumina sequencing technology and bioinformatics analyses revealed operational taxonomic units (OTUs) in the Phyla Bacteroides, Chloroflexi, Firmicutes, Proteobacteria, Spirochaetes, Synergistes, and Thermotogae were common in mono- and co-substrate batches. However, OTUs in the Phyla Acidobacteria, Actinobacteria, and Bacteroidetesee were unique to only the co-substrate conditions.

A modified twin-screw extruder incorporated with a filtration device was used as a liquid/solid separator for xylose removal from steam exploded corncobs. A face centered central composite design was used to study the combined effects of various enzymatic hydrolysis process variables (enzyme loading, surfactant addition, and hydrolysis time) with two differently extruded corncobs (7% xylose removal, 80% xylose removal) on glucose conversion. The results showed that the extrusion process led to an increase in cellulose crystallinity, while structural changes could also be observed via SEM. A quadratic polynomial model was developed for predicting the glucose conversion and the fitted model provided an adequate approximation of the true response as verified by the analysis of variance (ANOVA).