Wen-Teng Wu

Cultivation of microalgae for oil production with a cultivation strategy of urea limitation

The microalgae, Chlorella sp., were cultivated in various culture modes to assess biomass and lipid productivity in this study. In the batch mode, the biomass concentrations and lipid content of Chlorella sp. cultivated in a medium containing 0.025-0.200 g L(-1) urea were 0.464-2.027 g L(-1) and 0.661-0.326 g g(-1), respectively. The maximum lipid productivity of 0.124 g d(-1)L(-1) occurred in a medium containing 0.100 g L(-1) urea. In the fed-batch cultivation, the highest lipid content was obtained by feeding 0.025 g L(-1) of urea during the stationary phase, but the lipid productivity was not significantly increased. However, a semi-continuous process was carried out by harvesting the culture and renewing urea at 0.025 g L(-1) each time when the cultivation achieved the early stationary phase. The maximum lipid productivity of 0.139 g d(-1)L(-1) in the semi-continuous culture was highest in comparison with those in the batch and fed-batch cultivations.

Hydrolysis of microalgae cell walls for production of reducing sugar and lipid extraction.

In this study, cell walls of microalgae were hydrolyzed for the production of reducing sugar by cellulase, which was immobilized onto an electrospun polyacrylonitrile (PAN) nanofibrous membrane. Since the nitrile groups of the PAN membrane were activated by the amidination reaction and covalent binding to the amino groups of the cellulase, electrospun PAN nanofibrous membranes with a high specific surface area were applied as supports for the immobilization. Under the optimal hydrolysis conditions, the immobilized cellulase performed its hydrolyzing conversion at 62%, and the hydrolysis yield remained at 40% after five times of reuse. Additionally, microalgal lipid extraction efficiency increased to around 56% from 32% dramatically after cell wall hydrolysis. These results demonstrate the efficacy and feasibility of the proposed applications in hydrolysis process followed with lipid extraction.

Effects of biomass weight and light intensity on the performance of photosynthetic microbial fuel cells with Spirulina platensis.

Microalgae Spirulina platensis were attached to the anode of a membrane-free and mediator-free microbial fuel cell (MFC) to produce electricity through the consumption of biochemical compounds inside the microalgae. An increase in open circuit voltage (OCV) was observed with decreasing light intensity and optimal biomass area density. The highest OCV observation for the MFC was 0.39 V in the dark with a biomass area density on the anode surface of 1.2 g cm(-2). Additionally, it was observed that the MFC with 0.75 g cm(-2) of biomass area density produced 1.64 mW m(-2) of electrical power in the dark, which is superior to the 0.132 mW m(-2) produced in the light. Which also means the MFC can be applied to generate electrical power under both day and night conditions.

Cultivation of Acetobacter xylinum for bacterial cellulose production in a modified airlift reactor.

Acetobacter xylinum for bacterial cellulose production was cultivated in a modified airlift reactor. Better results were obtained from the modified reactor than from a conventional bubble column. After 72 h of cultivation, the final concentration of bacterial cellulose was 7.72 g/l and the productivity was 0.107 g/l per h in the modified airlift reactor. The concentration of bacterial cellulose was about three times higher than that produced in the conventional bubble column. Moreover, the bacterial cellulose produced using the modified reactor formed a unique elliptical pellet (the average diameter was 10 mm), which is different from the fibrous form produced using the stirred‐tank reactor. The modified airlift reactor with the suspended bacterial cellulose in pellet form had a higher volumetric oxygen‐transfer coefficient and mixing capability than that with bacterial cellulose in fibrous form. The dissolved oxygen in the modified airlift reactor could be maintained above 35% throughout the cultivation.

Performance of airlift bioreactors with net draft tube

Abstract Mixing and oxygenation in tower-type bioreactors are typically driven by gas movement, and as a result, these bioreactors have lower shear force as well as lower power requirement than other mechanically driven ones and therefore are attractive for industrial applications. This paper reviews the performance of a special tower-type bioreactor, the airlift bioreactor with net draft tube, developed by us, in several microbial fermentation situations. This type of bioreactor is equipped with a wire-mesh draft tube, which results in better liquid circulation and larger gas–liquid interfacial areas, and therefore produces much higher mixing efficiency and oxygen transport capability. As our data showed, the performance of this type of bioreactor in terms of mixing and oxygenation is substantially higher than that achievable by bubble column and conventional airlift bioreactors. Results from microbial fermentation experiments using this type of bioreactor also give evidence of the feasibility and superiority of this particular design.

Immobilization of cellulase onto electrospun polyacrylonitrile (PAN) nanofibrous membranes and its application to the reducing sugar production from microalgae

This study demonstrates a method to prepare an immobilized cellulase by using an electrospun polyacrylonitrile (PAN) nanofibrous membrane as the support. To obtain an immobilized cellulase with high hydrolytic activity, the immobilization conditions including activation time, enzyme concentration, immobilization time, and temperature were optimized. Under those conditions, the immobilized cellulase possessed a protein loading of 30 mg/g-support and a specific activity of 3.2U/mg-protein. After immobilization, the enzymatic stability of cellulase against pH and thermal stresses was improved. Fourier transform infrared spectroscopy (FTIR) measurements also revealed that the cellulase was covalently bonded to the supports. The immobilized cellulase was then used to hydrolyze cell wall of microalgae for the production of reducing sugars. Analyses using response surface methodology (RSM) show that the hydrolysis yield was affected by the reaction temperature, pH, and substrate/cellulase mass ratio, and a hydrolysis yield of 60.86% could be obtained at 47.85°C, pH 5.82, and a substrate/cellulase mass ratio of 40 g-substrate/g-cellulase. This result suggests that the proposed scheme for the cellulase immobilization has great potential for the application to the reducing sugar production.

A novel approach for scaling-up a fermentation system

The present study explores a method for scaling-up a fermentation system. The method consists of two parts. The first part investigates the effects of the environmental state variables on cultivation. If a wide range of the state variables has no significant effect on yield or productivity, scaling-up is not an issue in the fermentation system. If only a small range of the state variables has no substantial impact on cultivation, then pulse or periodical change of the state variables would be employed to investigate the effects of the change on cultivation. To illustrate the proposed method of scale-up, Bacillus thuringiensis was cultivated for thuringiensin production with the pH value as the environmental state variable. Different pH values at 7.0 and 8.4 had a significant effect on both cell growth and thuringiensin production. Variation of pH value for a short period of time did not have a substantial effect on either cell growth or thuringiensin production.

Effect of shear stress on cultivation of Bacillus thuringiensis for thuringiensin production.

Abstract. Cultivation of Bacillus thuringiensis for thuringiensin production is a mixed-growth-associated system. Cultivation conditions should be different during the cell growth stage and production stage. In this study, agitation speed and aeration rate were varied during the exponential growth phase and stationary phase in order to investigate the effect of shear stress via agitation on cultivation of B. thuringiensis for thuringiensin production. It was found that shear stress had a significant effect on thuringiensin production during the stationary phase. By decreasing the agitation speed during the stationary phase, product formation was increased up to 43%.

Immobilization of lipase to chitosan beads using a natural cross-linker.

Abstract Genipin, a reagent of plant origin was used for the immobilization of lipase by cross‐linking to chitosan beads. The catalytic properties and operational and storage stabilities of the immobilized lipase were compared with the soluble lipase. Under optimum conditions, 198 µg protein was bound per g chitosan with a protein‐coupling yield of 35%. The hydrolytic activity was 10.8 U/g chitosan and the relative specific activity was 108%. The immobilized lipase showed better thermal and pH stabilities compared to the soluble form. The immobilized enzyme exhibited mass transfer limitations as reflected by a higher apparent Km value and a lower energy of activation. The immobilized enzyme retained about 74% of its initial activity after five hydrolytic cycles.

Synthesis of Mixed Esters of Ascorbic Acid Using Methyl Esters of Palm and Soybean Oils

Abstract Mixed esters of ascorbic acid were synthesized using methyl esters of palm and soybean oils as acyl donors, in acetone at 50°C, and catalyzed by Novozym 435. A conversion of 62% was obtained with palm oil methyl ester at an ascorbic acid to acyl donor molar ratio of 1∶4; the mixed ester contained 45.89% ascorbyl palmitate, 42.59% ascorbyl oleate and 10.1% ascorbyl linoleate. Acylation with soybean oil methyl ester resulted in 17% conversion, yielding a mixed ester containing 10.08% ascorbyl palmitate, 20.68% ascorbyl oleate, and 64.96% of ascorbyl linoleate. The mixed esters of ascorbic acid can find direct use in food and cosmetics.