Hydrolysis of Golenkinia sp. biomass using Amberlyst 36 and nitric acid as catalysts

Production of levulinic acid from macroalgae by hydrothermal conversion with ionic resin catalyst

Gracilaria verrucosa is red algae (Rhodophyta) that is particularly significant because of its potential for bioenergy production as a sustainable and environmentally friendly marine bioresource. This study focuses on the production of levulinic acid from G. verrucosa using hydrothermal conversion with an ionic resin Purolite CT269DR as the catalyst. By optimization of the conversion condition, a 30.3 % (22.58 g/L) yield of levulinic acid (LA) (based on carbohydrate content) was obtained at 200 °C for 90 min with 12.5 % biomass and 50 % catalyst loading of biomass quantity. Simultaneously, formic acid yielded 14.0 % (10.42 g/L). The LA yield increased with increasing combined severity (CS) levels under tested ranges. Furthermore, the relationship between CS and LA synthesis was effectively fitted to the nonlinear sigmoidal equation. However, as the yield of sugar decreased, LA yield was linearly increased. Thus, the use of ionic resin as a heterogeneous catalyst presents significant potential for the manufacture of platform chemicals, specifically LA, through the conversion of renewable marine macroalgae.

Heuristic Optimization of Culture Conditions for Stimulating Hyper-Accumulation of Biomass and Lipid in Golenkinia SDEC-16

Overproduction of biomass and hyper-accumulation of lipids endow microalgae with promising characteristics to realize the cost-effective potential of advanced bioenergy. This study sought to heuristically optimize the culture conditions on a rarely reported Golenkinia sp. The results indicate that Golenkinia SDEC-16 can withstand the strong light intensity and grow in a modified BG11 medium. The optimal culture conditions for the favorable tradeoff between biomass and lipid accumulation were suggested as follows, 25,000 lux of light intensity, 9 mM of initial nitrogen concentration, and 20 mM of initial sodium chloride concentration. Under these conditions, the biomass concentration and productivity reached 6.65 g/L and 545 mg/L/d, and the synchronous lipid content and productivity reached 54.38% and 296.39 mg/L/d. Hypersalinity significantly promoted lipid contents at the cost of biomass and resulted in an increase of cell size but loss of spines of Golenkinia SDEC-16. The results shed new light on optimizing biomass and lipid productivity.

Hydrolysis of Lipid-Extracted Chlorella vulgaris by Simultaneous Use of Solid and Liquid Acids

Microalgal biomass was hydrolyzed using a solid acid catalyst with the aid of liquid acid. The use of solid acid as the main catalyst instead of liquid acid was to omit subsequent neutralization and/or desalination steps, which are commonly required in using the resulting hydrolysates for microbial fermentation. The hydrolysis of 10 g/L of lipid-extracted Chlorella vulgaris containing 12.2% carbohydrates using 7.6 g/L Amberlyst 36 and 0.0075 N nitric acid at 150°C resulted in 1.08 g/L of mono-sugars with a yield of 88.5%. For hydrolysis of higher concentrations of the biomass over 10 g/L, the amount of Amberlyst 36 needed to be increased in proportion to the biomass concentration to maintain similar levels of hydrolysis performance. Increasing the solid acid concentration protected the surface of the solid acid from being severely covered by cell debris during the reaction. A hydrolysate of lipid-extracted C. vulgaris 50 g/L was used, with no post-treatment of desalination, for the cultivation of Klebsiella oxytoca producing 2,3-butanediol. Cell growth in the hydrolysate was found to be almost the same as in the conventional medium with the same monosaccharide composition, confirming its fermentation compatibility. It was noticeable that the yield of 2,3-butanediol with the hydrolysate was observed to be 2.6 times higher than that with the conventional medium. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2729, 2019.

Valorization of lignocellulosic fibres of paper waste into levulinic acid using solid and aqueous Brønsted acid

This study aims to produce levulinic acid (LA) from paper towel waste in environment-friendly and economically feasible conditions, and evaluate the difference using solid and aqueous Brønsted acids. Direct dehydration of glucose to LA required sufficiently strong Brønsted acidity, where Amberlyst 36 demonstrated rapid production of approximately 30Cmol% of LA in 20min. However, the maximum yield of LA was limited by mass transfer. In contrast, the yield of LA gradually increased to over 40Cmol% in 1M H₂SO₄ at 150°C in 60min. The SEM images revealed the conversion in dilute acids under microwave at 150°C resulting in swelling structures of cellulose, which were similar to the pre-treatment process with concentrated acids. Further increase in reaction temperature to 200°C significantly shortened the reaction time from 60 to 2.5min, which saved the energy cost as revealed in preliminary cost analysis.

Engineering of Klebsiella oxytoca for production of 2,3-butanediol via simultaneous utilization of sugars from a Golenkinia sp. hydrolysate

The Klebsiella oxytoca was engineered to produce 2,3-butanediol (2,3-BDO) simultaneously utilizing glucose and galactose obtained from a Golenkinia sp. hydrolysate. For efficient uptake of galactose at a high concentration of glucose, Escherichia coli galactose permease (GalP) was introduced, and the expression of galP under a weak-strength promoter resulted in simultaneous consumption of galactose and glucose. Next, to improve the sugar consumption, a gene encoding methylglyoxal synthase (MgsA) known as an inhibitor of multisugar metabolism was deleted, and the mgsA-null mutant showed much faster consumption of both sugars than the wild-type strain did. Finally, we demonstrated that the engineered K. oxytoca could utilize sugar extracts from a Golenkinia sp. hydrolysate and successfully produces 2,3-BDO.