Yung-Chung Lo's research while affiliated with National Cheng Kung University and other places

Microalgal biomass, known as the third generation feedstock for biofuels production, is currently being explored mainly for lipids and functional components. However, the potential of microalgal carbohydrates has not been evaluated. In this investigation, Chlorella vulgaris JSC-6 was used for carbohydrates production from CO2 and fatty acids under different cultivation strategies to meet the requirements of a CO2-neutral and clean fermentation system for biofuel production. Autotrophic cultivation resulted in better carbon assimilation and carbohydrate accumulation; about 1.4 g CO2 could be converted to 1 g biomass, of which 50% are carbohydrates. Assimilation of fatty acids in photoheterotrophic and mixotrophic modes was influenced by pH, and pH 7-7.5 supported butyrate and acetate assimilation. The maximum carbohydrate content (49.86%) was attained in mixotrophic mode, and the ratio of the simple sugars glucose-xylose-arabinose was 1:0.11:0.02. The higher glucose content makes the microalgal biomass a suitable feedstock for sugar-based fermentations.

This work aimed to study the efficiency of polyvinyl-alcohol-immobilized Actinobacillus succinogenes ATCC55618 for succinic acid (SA) production. Batch fermentation (pH 7, 45% CO2 gas at 0.04 vvm) using glucose (40 g L⁻¹) resulted in SA titer, 26.7 g L⁻¹; productivity, 3.33 g L⁻¹ h⁻¹; yield, 0.621 g g⁻1. Fed-batch mode with cyclic extrication of SA from the medium markedly enhanced the yield to 0.699 g g⁻¹ and concentration to 59.5 g L⁻¹. Batch fermentation using sugars derived from Chlorella vulgaris ESP-31 without yeast extract gave a SA productivity, concentration, and yield of 1.82 g L⁻¹ h⁻¹, 36.1 g L⁻¹, and 0.720 g g⁻1, respectively. Furthermore, continuous fermentation (at 6 h HRT) with microalgal sugar improved the productivity and yield to 3.53 g L⁻¹ h⁻¹ and 0.62 g g⁻¹, respectively, which is comparable to those obtained by using glucose. This study reports the highest productivity for SA fermentation using microalgae-derived sugars.

Biobutanol produced by acetone-biobutanol-ethanol (ABE) fermentation process has been revisited in the light of its use as “drop in” liquid biofuel to be blended with gasoline. In this study, renewable feedstock like rice straw, sugarcane bagasse and microalgal hydrolysate were used in ABE fermentation via separate hydrolysis and fermentation. Clostridium acetobutylicum ATCC 824 was used as the fermenting organism. Alkali pretreatment followed by enzymatic hydrolysis was used for rice straw and sugarcane bagasse. In batch fermentation, a biobutanol titer and yield of 9.10 g/L and 0.42 mol/mol glucose (0.17 g biobutanol/g glucose), respectively was obtained from rice straw, while sugarcane bagasse achieved a biobutanol titer and yield of 8.40 g/L and 0.40 mol/mol glucose (0.16 g biobutanol/g glucose), respectively. Higher microalgal biomass loading with 3% acid pretreatment severely inhibited fermentation performance. Unhydrolyzed microalgal biomass at a loading of 180 g/L in ABE fermentation resulted in 4.32 g/L biobutanol and 0.09 g biobutanol/g microalgae as yield. C. acetobutylicum was immobilized in polyvinyl alcohol (PVA) for improving the cell loading in fermentation and protect the cells from biobutanol toxicity. With rice straw hydrolysate as a feedstock and in the absence of yeast extract, a biobutanol titer, yield and productivity of 13.80 g/L, 0.90 g/L/h, and 0.58 mol biobutanol/mol glucose (0.23 g biobutanol/g glucose), respectively were obtained. Hence, rice straw is a potential feedstock for biobutanol production for fuel use.

Bioethanol produced from lignocellulosic materials has been considered as one of the most promising fuels to replace fossil fuels. Immobilized yeasts or bacteria have been frequently used in continuous system due to its feasibility for repeated use with high biomass retention during the continuous process. In this study, continuous SHcF (separate hydrolysis and co-fermentation) and SScF (simultaneous saccharification and co-fermentation) were evaluated for ethanol production from alkaline pretreated sugarcane bagasse using Zymomonas mobilis (PVA immobilized cells) and Pichia stipitis (suspended cells). In SHcF fermentation, the ethanol yield and productivity of 0.36 g ethanol/g cellulose (corresponding to 70.65% of theoretical yield) and 1.868 g/L/h were achieved. In contrast, SScF system resulted in an ethanol yield of 0.414 g ethanol/g cellulose (corresponding to 81.17% of theoretical yield) and ethanol productivity of 0.705 g/L/h. The performance of the two systems are compared and discussed.

Lactic acid (LA) fermentation was conducted with suspended and immobilized cells of an isolated Lactobacillus plantarum 23 strain using various fermentation strategies. Glucose and an alternative, relatively inexpensive carbon source - the hydrolysate of microalga Chlorella vulgaris ESP-31, were used as the carbon source. Batch fermentation using immobilized cells of L. plantarum 23 could enhance LA titer and yield by 43% and 39%, respectively, when compared with the suspended culture. Fed-batch culture integrated with in situ LA removal via ion exchange raised LA productivity by 72% by overcoming product inhibition. The highest LA productivity from glucose with PVA immobilized cells was 14.22 g/L/h, achieved under continuous operation at 50% w/v loading of immobilized beads and hydraulic retention time (HRT) of 2 h. PVA immobilized L. plantarum 23 could also use microalgal hydrolysate as the renewable carbon source, and the highest LA productivity was 9.93 g/L/h under continuous fermentation at 4 h HRT.

Concentration of ethanol from the fermentation broth is an energy-intensive process. Very high gravity (VHG) process with modified polyvinyl alcohol-immobilized Zymomonas mobilis cells integrated with in situ bioethanol removal via vacuum membrane distillation (VMD) was proposed to mitigate product inhibition effects in VHG fermentation. The proposed VHG + VMD system, at 300 g/L glucose loading, produced 127.4 g/L (16.1% v/v) ethanol, at 63.7 g/L−h productivity and 84.9% glucose conversion rate, which is the highest in reported literature.

Biosorption has emerged as a promising alternative approach for treating wastewater with dilute metal contents in a green and cost effective way. In this study, extracellular proteins of an isolated thermophilic bacterium (Tepidimonas fonticaldi AT-A2) were used as biosorbent to recover precious metal (i.e., Au) from wastewater. The Au (III) adsorption capacity on the T. fonticaldi AT-A2 proteins was the highest when the pH was set at about 4.0 to 5.0. The adsorption capacity increased with increasing temperature from 15 to 70°C. Adsorption isotherm studies show that both Langmuir and Freundrich models could describe the adsorption equilibrium. The maximum adsorption capacity of Au (III) at 50°C and pH 5 could reach 9.7 mg Au/mg protein. The protein-based biosorbent was also used for the recovery of Au from a wastewater containing 15 mg/L of Au, achieving a high adsorption capacity of 1.45 mg Au/mg protein and a removal efficiency of 71%.

The scaling of geothermal wells arising from formation of calcium carbonate is one of the major problems associated with the utilization of geothermal energy. A novel eco-friendly biological-based approach for geothermal well descaling was proposed. Thermophilic bacterial strains were isolated from geothermal areas in Taiwan and were evaluated for their calcium adsorption efficiency under the extreme conditions. Among the eight strains isolated, Tepidimonas fonticaldi AT-A2 isolated from Antun Hot Spring, Hualien showed the highest calcium adsorption capacity. The calcium adsorbing activity of T. fonticaldi AT-A2 was mainly associated with the extracellular proteins and the maximum calcium adsorption capacity (1.94 g Ca/g protein) was obtained at pH 10, 150 °C and 1 atm pressure. This calcium adsorption efficiency is much higher than that of metallothioneins and other bacterial extracellular proteins. The excellent calcium adsorption efficiency of the AT-A2 proteins indicates the potential for their applications in biological geothermal well descaling.