Pretreatment and enzymatic hydrolysis optimization of lignocellulosic biomass for ethanol, xylitol, and phenylacetylcarbinol co-production using Candida magnoliae

Cellulosic bioethanol production generally has a higher operating cost due to relatively expensive pretreatment strategies and low efficiency of enzymatic hydrolysis. The production of other high-value chemicals such as xylitol and phenylacetylcarbinol (PAC) is, thus, necessary to offset the cost and promote economic viability. The optimal conditions of diluted sulfuric acid pretreatment under boiling water at 95°C and subsequent enzymatic hydrolysis steps for sugarcane bagasse (SCB), rice straw (RS), and corn cob (CC) were optimized using the response surface methodology via a central composite design to simplify the process on the large-scale production. The optimal pretreatment conditions (diluted sulfuric acid concentration (% w/v), treatment time (min)) for SCB (3.36, 113), RS (3.77, 109), and CC (3.89, 112) and the optimal enzymatic hydrolysis conditions (pretreated solid concentration (% w/v), hydrolysis time (h)) for SCB (12.1, 93), RS (10.9, 61), and CC (12.0, 90) were achieved. CC xylose-rich and CC glucose-rich hydrolysates obtained from the respective optimal condition of pretreatment and enzymatic hydrolysis steps were used for xylitol and ethanol production. The statistically significant highest (p ≤ 0.05) xylitol and ethanol yields were 65% ± 1% and 86% ± 2% using Candida magnoliae TISTR 5664. C. magnoliae could statistically significantly degrade (p ≤ 0.05) the inhibitors previously formed during the pretreatment step, including up to 97% w/w hydroxymethylfurfural, 76% w/w furfural, and completely degraded acetic acid during the xylitol production. This study was the first report using the mixed whole cells harvested from xylitol and ethanol production as a biocatalyst in PAC biotransformation under a two-phase emulsion system (vegetable oil/1 M phosphate (Pi) buffer). PAC concentration could be improved by 2-fold compared to a single-phase emulsion system using only 1 M Pi buffer

Increasing Efficiency of Dye-sensitized Solar Cells through Co-sensitization of Organic Dyes LEG4 and DN-F10 as Light Absorber

Organic dyes LEG4/DN-F10 as efficient co-sensitized dye system were introduced in dye- sensitized solar cell. With attribution of broaden spectral absorption, the LEG4/DN-F10 co-sensitized dye system could improve the photovoltaic performance of devices in combination with Co(II/III) electrolyte. The photo-transition energy gap of LEG4/DN-F10 system is 1.81 eV. In the present work, power conversion efficiency (PCE) of 4.47% were achieved for device based on LEG4/DN-F10 with short circuit current density, Jsc of 6.87 mA/cm2, Voc of 0.76 V and FF of 56.78 while PCE of device with single dye are 3.41% for LEG4 dye and 3.76% for DN-F10 dye. The co-sensitization is a simple and effective strategy to improve the photovoltaic performance of the device. Further optimization steps are needed to enhance power conversion efficiency and it is under way

Enhanced Photovoltaic Performance of Dye-Sensitized Solar Cells via Electrochemically Deposited TiO2 Compact Underlayer

The TiO2 compact layers produced by the electrochemical deposition method were employed as blocking underlayer in dye-sensitized solar cells (DSSCs). The galvanostatic deposition method was utilized to deposit TiO2 compact layer (TiO2-CL) onto FTO substrates from acidic titanium (III) chloride electrolytic solution. The formation-TiO2 compact layers were affirmed by X-ray diffraction (XRD). The transparency of TiO2 compact layer was examined by UV-vis absorption spectroscopy. The present work mainly investigated the effect of TiO2-CL incorporation on the photovoltaic performance of the DSSCs where the photosensitizer is LEG4 organic dye and the redox mediator is CoII/CoIII based electrolyte. Incorporation of TiO2-CL between transparent FTO electrode and meso-TiO2 could increase efficiency of a device with an obvious increase in short circuit current density. The power conversion efficiency is 4.3% and 3.5% of the devices with and without TiO2-CL

Production of Phenylacetylcarbinol via Biotransformation Using the Co-Culture of <i>Candida tropicalis</i> TISTR 5306 and <i>Saccharomyces cerevisiae</i> TISTR 5606 as the Biocatalyst

Phenylacetylcarbinol (PAC) is a precursor for the synthesis of several pharmaceuticals, including ephedrine, pseudoephedrine, and norephedrine. PAC is commonly produced through biotransformation using microbial pyruvate decarboxylase (PDC) in the form of frozen–thawed whole cells. However, the lack of microorganisms capable of high PDC activity is the main factor in the production of PAC. In addition, researchers are also looking for ways to utilize agro-industrial residues as an inexpensive carbon source through an integrated biorefinery approach in which sugars can be utilized for bioethanol production and frozen–thawed whole cells for PAC synthesis. In the present study, Candida tropicalis, Saccharomyces cerevisiae, and the co-culture of both strains were compared for their biomass and ethanol concentrations, as well as for their volumetric and specific PDC activities when cultivated in a sugarcane bagasse (SCB) hydrolysate medium (SCBHM). The co-culture that resulted in a higher level of PAC (8.65 ± 0.08 mM) with 26.4 ± 0.9 g L−1 ethanol production was chosen for further experiments. Biomass production was scaled up to 100 L and the kinetic parameters were studied. The biomass harvested from the bioreactor was utilized as frozen–thawed whole cells for the selection of an initial pyruvate (Pyr)-to-benzaldehyde (Bz) concentration ([Pyr]/[Bz]) ratio suitable for the PAC biotransformation in a single-phase emulsion system. The initial [Pyr]/[Bz] at 100/120 mM resulted in higher PAC levels with 10.5 ± 0.2 mM when compared to 200/240 mM (8.60 ± 0.01 mM). A subsequent two-phase emulsion system with Pyr in the aqueous phase, Bz in the organic phase, and frozen–thawed whole cells of the co-culture as the biocatalyst produced a 1.46-fold higher PAC level when compared to a single-phase emulsion system. In addition, the cost analysis strategy indicated preliminary costs of USD 0.82 and 1.01/kg PAC for the single-phase and two-phase emulsion systems, respectively. The results of the present study suggested that the co-culture of C. tropicalis and S. cerevisiae can effectively produce bioethanol and PAC from SCB and would decrease the overall production cost on an industrial scale utilizing the two-phase emulsion system with the proposed multiple-pass strategy