Chieh-Lun Cheng

Biohydrogen production from lignocellulosic feedstock.

Due to the recent energy crisis and rising concern over climate change, the development of clean alternative energy sources is of significant interest. Biohydrogen produced from cellulosic feedstock, such as second generation feedstock (lignocellulosic biomass) and third generation feedstock (carbohydrate-rich microalgae), is a promising candidate as a clean, CO2-neutral, non-polluting and high efficiency energy carrier to meet the future needs. This article reviews state-of-the-art technology on lignocellulosic biohydrogen production in terms of feedstock pretreatment, saccharification strategy, and fermentation technology. Future developments of integrated biohydrogen processes leading to efficient waste reduction, low CO2 emission and high overall hydrogen yield is discussed.

Investigation of magnetizing inrush current in transformers. I. Numerical simulation

A simple method for simulating magnetizing inrush currents in power transformers using real-time measurements is proposed. The method is based on a simplified model for representing the inrush current under different loading conditions. A digital simulation method using a PC-AT microcomputer is also proposed. Transformer operating conditions, including transformer loading power factors, switching-on angles, and remanent flux, are included. The simulation result show very good agreement with experiment results. >

High yield bio-butanol production by solvent-producing bacterial microflora.

Highly efficient butanol-producing bacterial microflora were isolated from hydrogen-producing sludge of a sewage treatment plant. Based on denaturing gradient gel electrophoresis (DGGE) analysis and 16s rDNA comparison, four strains from the butanol-producing microflora were identified as Clostridium saccharoperbutylacetonicum, Clostridium butylicum, Clostridium beijernckii, and Clostridium acetobutylicum. The effects of glucose, FeSO(4) · 7H(2)O and yeast extract concentrations on the butanol production by the mixture culture were investigated on batch mode. The medium composition for bio-butanol production was optimized using the Box-Behnken design and response surface methodology (RSM). The maximum butanol production rate (0.25 ± 0.02 g/L-h) and concentration (12.4 g/L) were obtained under the condition of glucose concentration, 60 g/L; FeSO(4) · 7H(2)O, 0.516 g/L; yeast extract concentration, 5.13 g/L. Addition of 6.0 g/L butyric acid significantly increased the butanol titer to 17.51 ± 0.49 g/L. Pressurized fermentation strategy (employed with a 5L fermentor) further enhanced the butanol concentration to 21.35 g/L, along with a maximum butanol rate of 1.25 g/L-h.

Investigation of magnetizing inrush current in transformers. II. Harmonic analysis

For pt.I see ibid., vol.8, no.1, p.246-54. Simulation data for the magnetizing inrush current generated by power transformers, obtained in part one, are used for harmonic analysis. The simulation results show very good agreement with experiment results. The relationship of the harmonics to all parameters is discussed. The results establish a guideline for eliminating harmonics due to inrush current, and provide reference for system design. >

Recovery of high-value metals from geothermal sites by biosorption and bioaccumulation

Generation of geothermal energy is associated with a significant amount of geothermal fluids, which may be abundant in high-value metals, such as lithium, cesium, rubidium, and other precious and rare earth metals. The recovery of high-value metals from geothermal fluids would thus have both economic and environmental benefits. The conventional technologies applied to achieve this are mostly physicochemical, which may be energy intensive, pose the risk of secondary pollution whilst being inefficient in recovering metals from dilute solutions. Biological methods, based on biosorption or bioaccumulation, have recently emerged as alternative approaches, as they are more environmentally friendly, cost effective, and suitable for treating wastewater with dilute metal contents. This article provides a comprehensive review of the related biological technologies used to recover the high-value metals present in geothermal fluids as well as critical discussion on the key issues that are often used to evaluate the effectiveness of those methods.

Enhancing butanol production with Clostridium pasteurianum CH4 using sequential glucose–glycerol addition and simultaneous dual-substrate cultivation strategies

Adding butyrate significantly enhanced butanol production from glycerol with Clostridium pasteurianum CH4, which predominantly produces butyrate (instead of butanol) when grown on glucose. Hence, the butyrate produced from assimilating glucose can be used to stimulate butanol production from glycerol under dual-substrate cultivation with glucose and glycerol. This proposed butanol production process was conducted by employing sequential or simultaneous addition of the two substrates. The latter approach exhibited better carbon source utilization and butanol production efficiencies. Under the optimal glucose to glycerol ratio (20 g L(-1) to 60 g L(-1)), the simultaneous dual-substrate strategy obtained maximum butanol titer, productivity and yield of 13.3 g L(-1), 0.28 g L(-1) h(-1), and 0.38 mol butanol/mol glycerol, respectively. Moreover, bagasse and crude glycerol as dual-substrates were also converted into butanol efficiently with a maximum butanol concentration, productivity and yield of 11.8 g L(-1), 0.14 g L(-1) h(-1), and 0.33 mol butanol/mol glycerol, respectively.

Characterization of cellulolytic enzymes and bioH2 production from anaerobic thermophilic Clostridium sp. TCW1

A thermophilic anaerobic bacterium Clostridium sp. TCW1 was isolated from dairy cow dung and was used to produce hydrogen from cellulosic feedstock. Extracellular cellulolytic enzymes produced from TCW1 strain were identified as endoglucanases (45, 53 and 70 kDa), exoglucanase (70 kDa), xylanases (53 and 60 kDa), and β-glucosidase (45 kDa). The endoglucanase and xylanase were more abundant. The optimal conditions for H2 production and enzyme production of the TCW1 strain were the same (60 °C, initial pH 7, agitation rate of 200 rpm). Ten cellulosic feedstock, including pure or natural cellulosic materials, were used as feedstock for hydrogen production by Clostridium strain TCW1 under optimal culture conditions. Using filter paper at 5.0 g/L resulted in the most effective hydrogen production performance, achieving a H2 production rate and yield of 57.7 ml/h/L and 2.03 mol H2/mol hexose, respectively. Production of cellulolytic enzyme activities was positively correlated with the efficiency of dark-H2 fermentation.

Transient model and simulation in three-phase three-limb transformers

When a three-phase three-limb power transformer, whose primary windings are Y-connected with isolated neutral, is energized or reclosed by asynchronous closure of the circuit breaker poles, the transient voltage at the still disconnected transformer terminal and the transient current flowing from the connected windings may reach considerably high values. This can cause serious damage to equipment connected to the transformer. This transient phenomenon is closely related to the switching sequence of the circuit breaker poles, switching-on angles, remanent flux and the magnetic saturation characteristics of the transformers iron core. This paper presents a simple and effective method to predict the transient phenomenon of power transformers. The proposed method formulates a model to represent the transient under various operating conditions. Simulations and experiments are both demonstrated to support the proposed method. >

Hysteresis characteristic analysis of transformer under different excitations using real time measurement

A simplified method for the analysis of hysteresis characteristics in a transformer under nonsinusoidal excitation is discussed. The nonsinusoidal sin m (wt) waveforms are used in the experiments. The hysteresis analysis is treated as a shape identification problem and is solved using the piecewise curve fitting technique. The proposed method uses a real-time data acquisition system, for measurement data and calculates hysteresis loop and loss directly from those data. Expressions for the hysteresis loop and energy loss using the proposed method are shown to agree well with analog measurements. The discrepancy between these two methods is less than 0.65%. >