Long term competition between sulfate-reducing and methane-producing bacteria for acetate in anaerobic biofilm

A long term competition between sulfate-reducing bacteria (SRB) and methane-producing bacteria (MPB) for acetate was investigated using a laboratory scale anaerobic fluidized bed. When the synthetic wastewater composed of acetate and sulfate was fed at a low organic loading rate, averages of the remaining acetate and sulfate concentrations were 1.7 mg Cl⁻¹ and 78.5 mg l⁻¹, respectively. During several months of this acetate limited operation the methane production rate as well as the microbial mass of MPB declined gradually, whereas the amount of reduced sulfate along with the microbial mass of SRB increased, which apparently indicates that SRB out-compete MPB in the biofilm at lower acetate concentrations. On the other hand, MPB were able to form a biofilm faster than SRB at higher acetate concentrations presumably due to MPB's higher ability to adhere carrier surfaces compared with SRB. Kinetic constants for both species in the biofilm were determined and compared with those reported for pure MPB and SRB cultures. Based on the kinetic mechanism of this competition, operational conditions which would support methanogenesis by suppressing sulfate reduction were identified.     

Gas–liquid two-phase flow in narrow horizontal annuli

Experimental data associated with the two-phase flow regimes, void fraction and pressure drop in horizontal, narrow, concentric annuli are presented. Two transparent test sections, one with inner and outer diameters of 6.6 and 8.6 mm, and an overall length of 46.0 cm; the other with 33.2 and 35.2 mm diameters and 43.0 cm length, respectively, were used. Near-atmospheric air and water constituted the gas and liquid phases, respectively. The gas and liquid superficial velocities were varied in the 0.02–57 and 0.1–6.1 m s⁻¹ ranges, respectively. The major two-phase flow patterns observed included bubbly, slug/plug, churn, stratified, and annular. Transitional regimes, where the characteristics of two distinct flow regimes could be observed in the test sections, included bubbly-plug, stratified-slug and annular-slug. The obtained flow regime maps were different than flow regime maps typical of large horizontal channels and microchannels with circular cross-sections. They were also different from the flow regimes in rectangular thin channels. The measured average void fractions for the two test sections were compared with predictions of several empirical correlations. Overall, a correlation proposed by Butterworth [Butterworth, D., 1975. A comparison of some void fraction relationships for co-current gas–liquid flow. Int. J. Multiphase Flow 1, 845–850] based on the results of Lockhart and Martinelli (1949) provided the most accurate prediction of the measured void fractions. The measured pressure drops were compared with predictions of several empirical correlations. The correlation of Friedel [Friedel, L., 1979. Improved friction pressure drop correlations for horizontal and vertical two-phase pipe flow. 3R Int. 18, 485–492] was found to provide the best overall agreement with the data.     

Rocket‐triggered lightning current waveforms in winter and investigation of extra‐fast current change

Since 1986, the authors have been taking part in triggered lightning experiments in winter, at Okushishiku, Ishikawa, for the purpose of observing the entire lightning current waveforms with coaxial shunt resistors and an electro‐optical measuring system. Extra‐fast current changes of the order of 1,000 kA/μs were recognized by sharp pulse records superposed on the positive current waveform obtained by a shunt resistor of relatively high residual inductance. This was not the case with a resistor of lower inductance. Furthermore, a positive lightning current waveform which looks like the composite result of bi‐polar discharges has been observed by an advanced measuring system of high performance. This paper deals with these current‐related topics of triggered lightning discharges, which will be analyzed hereafter in detail. © 1999 Scripta Technica, Electr Eng Jpn, 128(2): 18–23, 1999     

Characteristics of lightning surges observed at 77 kV substations

In order to improve power supply reliability, it is necessary to prevent lightning faults in transmission lines and substation apparatus. However, faults are caused occasionally in lower-voltage power systems, particularly at the 77 kV level. The governing factor for insulation strength of substation apparatus is the lightning impulse voltage, and it is necessary to know the voltage level and distribution in a substation caused by lightning surges in order to investigate rational insulation coordination. For this purpose, the authors measured lightning surges at two 77 kV conventional substations from 1990 to 1993. In this paper, the characteristics of induced lightning surges and back flashover lightning surges are described. Comparisons of related surge voltages at two substations, the power line phases in grounding faults, and the equivalent capacitance of the substations are also discussed.