Abstract.A pulsed high voltage was used to remove microorganisms in drinking water. The effects of the pulsed high voltage on pH, conductivity, temperature and oxidation reduction potential (ORP) of the drinking water were investigated. The observed results show that the removal efficiency with respect to fecal coliforms and total coliforms increased with the increase of the pulsed high voltage. The removal efficiency for microorganisms such as fecal coliforms and total coliforms was in the range 25-100% and 44-100%, respectively, after the water was exposed to a pulsed high voltage of 5-10 kV for 60 minutes. An increase of the pulsed high voltage caused a decrease in the conductivity and ORP with operational time.

A radio-frequency plasma system (RF) was used to investigate the removal of microorganisms from water.Plasma generated by RF radiation can produce active compounds (H•, •OH, H2O2, O3, etc.) that have a highoxidation potential and can kill microorganisms present in water (fecal coliforms and total coliforms). Thefrequency of the plasma system was set to 3.0, 3.3 and 3.7 MHz and applied to river water for 60 minutes. Theresults show that in all runs, the pH of the water produced was in the range from 7.4 to 7.9. The removalefficiencies of fecal coliforms achieved were between 83.75 and 95% and were higher than the removalefficiencies of total coliforms, which were between 82.61 and 93.48%. Meanwhile, the death rate (kD) of fecalcoliforms wasfaster than that of total coliforms. Therefore, the removal of total coliforms is the key to removingmicroorganisms fromwater. RF plasma treatment can be used for treatment of drinking water to decreasemicroorganisms.

The characteristics of multiple stroke negative cloud to ground (CG) lightning flashes in Padang, Indonesia based on electric field recording were investigated. 100 negative CG lightning flashes containing 623 strokes, recorded from August to October 2014, were examined. It was observed that all first return strokes (RS) negative CG lightning flashes were preceded by preliminary breakdown pulses (PBPs). However, only 40% of the detecable PBP trains could be analyzed statistically on PBP train duration, PBP-RS separation, and PBP/RS ratio, while the detectable leader pulses was 69%. In addition, it was also found that the arithmetic mean (AM) and maximum number of strokes were 5.2 and 18, respectively. The AM and geometric mean (GM) interstroke interval were 55.34 and 34.71 ms, respectively. Furthermore, 2% of the subsequent return stroke (SRS) peak electric fields were larger than those of the first return stroke (RS). The AM and GM ratios of SRS/RS were 0.36 and 0.3, respectively.Keywords: negative cloud to ground, preliminary breakdown, leader, return stroke, interstroke interval, peak electric field ratio IntroductionNegative cloud to ground (CG) lightning flashes is the most common type of CG discharges and has thereafter studied by many authors. A CG lightning flash usually contains preliminary breakdown pulses (PBPs) in the cloud and downward stepped leader (SL) propagation followed by the first return stroke (RS). The characteristics of a negative CG could largely be determined by the magnitude of the so called lower positive charge regions (LPCR) [1][2][3][4]. A larger LPCR causes the direction of negative leader propagation to be predominantly horizontal, even though finally the stepped leader propagates toward the ground. Meanwhile, a smaller LPCR causes negative stepped leader propagation to be predominantly vertical [5][6]. The time separation between PBPs and RS is approximately several milliseconds to hundreds of milliseconds. The generated electric field signature differentiates these processes. Nag and Rakov [5] stated that in negative CG lightning flashes, PBPs may not be detected on the first return stroke when the magnitude of the LPCR is very small. They claimed that CG lightning flashes vary in detectable PBP percentage according to latitude. Higher latitudes have a higher percentage of detectable PBPs than lower latitudes. In contrast, many researchers have argued that the first return stroke always involves PBPs in all negative CG flashes [7][8][9]. Their studies revealed that the detectable PBP percentage does not depend on latitude. A PBP can be detected if the amplitude of the PBP is above the noise level of the environment and electric field change sensors. However, Marshall et al. [9] have stated that they "cannot be certain that detection of PBPs always equals 100%" for all latitudes. In a more recent study, Zhu et al. [10] found that PBP detectability is not only affected by the sensor noise level but also by storm type, RS peak current and observation distance. The diffe...

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Abstract. In the palm oil industry, open ponding, aerobic and anaerobic digestion, physicochemical treatment and membrane filtration are generally applied as conventional treatments of palm oil mill effluent (POME). In this study, a sand filtration-dielectric barrier discharge (DBD) system was investigated as an alternative process for treating POME. This system can reduce land usage, processing time and costs compared to conventional systems. The removal efficiency of chemical oxygen demand (COD), biological oxygen demand (BOD 5 ), and oil-grease in relation to the applied voltage were studied. Furthermore, the pH and temperature profiles were investigated. The obtained results indicate that the removal efficiency of COD, BOD 5 , and oil-grease increased with an increase of the applied voltage. The electrical energy consumption needed is about 10.56 kWh/L of POME.