Search

In this study, the performance of dielectric barrier discharge (DBD) with the aerated condition at discharge voltages of 15, 20, and 25 kV on the production of biogas; CH4, H2, CO, and CO2 and the removal of COD and BOD from POME were investigated. The experimental results showed that the aerated condition with a rate of 2.5 L/min at a high voltage (25 kV) produced CH4, CO, and CO2 that was 9.4, 21.5, and 19.6 times higher than the non-aerated one, respectively. The maximum cumulative volume of CH4, H2, CO, and CO2 was 95.4 ± 8.92, 0.94 ± 0.71, 3.06 ± 0.73, and 2.45 ± 0.35 mL/mg COD, respectively, under the aerated condition at 25 kV and the experimental data fit well with the polynomial regression (R2 > 95) for the initial biogas production. The decrease in COD and BOD was greatly affected by the high discharge voltage under the aerated condition, resulting in a high removal rate. These findings suggest that good performance was observed when the DBD was integrated with the aerated condition under the optimum discharge voltage. The study can give information on the optimum condition in a laboratory scale to produce CH4, H2, CO, and CO2, as well as the reduction of organic pollutants from POME.

The correlation between lightning and several weather parameters (rainfall, humidity, air temperature, and wind) in Padang from 2016 to 2020 was statistically analyzed. Lightning data and weather parameters were obtained from two electric field mills (EFMs) and the meteorology, climatology, and geophysics agency (BMKG), Indonesia. The study results show that the highest lightning occurred in November during the wet season. The correlation coefficient between lightning and rainfall during the wet and dry seasons was 0.52 and 0.26, respectively. Furthermore, the correlation coefficient of lightning with humidity, air temperature, and wind during the wet and dry seasons was 0.25, 0.06, 0.15, and -0.45, 0.25, -0.02, respectively. These results indicate a strong relationship between lightning and rainfall during the wet season; rainfall is the only primary variable in lightning frequency.

Rainwater is a potential source of drinking water, but has various components of dissolved organic matter (DOM). DOM is a reservoir of potential hazards in drinking water. Therefore, a new method is required to purify rainwater as a drinking water source in terms of DOM aspects. A radio-frequency (RF) treatment system is introduced here to purify source water with a small possibility of contamination. RF is generated by applying a frequency of 1.5 MHz through a glass reactor with a diameter of 2 mm which is wrapped by a 2 mm copper wire. The results demonstrate that UV260 value and dissolved organic carbon (DOC) are reduced during RF treatment. DOC was reduced by a lower amount compared to UV260, suggesting the partial transformation of bio-refractory DOM. A fluorescence excitation-emission matrix showed that humic-like substances in rainwater were reduced faster than protein-like ones, indicating that humic-like substances are susceptible to reduction by RF treatment. The results offer information on the use of RF treatment in a rainwater purification process for the production of drinking water.

Lightning discharges can produce electromagnetic fields, light and thunder (shock waves). Thunder can be defined as the acoustic emission associated with all impulsive processes in cloud-to-ground (CG) and intra-cloud (IC) flashes, including M-component type processes. The acoustic signature of thunder can be used to better understand some of the properties of the lightning channel. Acoustic signatures generated by lightning flashes have been analyzed in the time domain in many previous studies for the quantitative identification of thunder features. To strengthen the previous findings, the acoustic signal frequency of a close flash and a distant flash were analyzed using the Fast Fourier Transform (FFT), the Short-time Fourier Transform (STFT), and instantaneous frequency. The results showed that there were differences between the frequencies of both flashes. The frequency of the acoustic signal of the close flash was higher than that of the distant flash. The frequency ranges of the acoustic signals of the close flash and the distant flash were 300 to 700 Hz and 100 to 400 Hz, respectively.

Bahan keramik dan polimer banyak digunakan sebagai isolator dalam transmisi daya tegangan tinggi. Isolator cenderung mengalami kegagalan saat cuaca mendung (kelembaban tinggi) dan kondisi lingkungan seperti dekat pantai atau dekat pabrik semen. Kegagalan terjadi ketika permukaan isolator terkontaminasi oleh garam laut atau debu semen yang menyebabkan peluahan sebagian (PD). PD dan arus bocor dapat terjadi karena kontaminasi isolator menyebabkan kualitas isolasi menurun. Untuk mengatasi kegagalan isolator, metode ANFIS diusulkan sebagai prakiraan kondisi isolator secara non-kontak. Disamping alat pengujian memakai metoda baru juga dapat mengukur tingkat kebocoran isolasi. Oleh karena itu, perlu mengumpulkan data seperti voltase input, PD, arus bocor dan gambar termal isolator dalam dua kondisi berbeda yang bersih dan terkontaminasi pada tahap percobaan. Gambar termal ditangkap oleh kamera inframerah dan arus bocor dibaca melalui komputer pribadi (PC). Data-data ini digunakan sebagai input dalam pelatihan Jaringan Syaraf Tiruan (JST) dalam metode ANFIS. Lebih lanjut, metode ini menginterpretasikan data terukur dari isolator yang perlu dikategorikan sebagai Aman (p ≤ 0,5 dan / atau IB < 25 mA), Perlu Pemeliharaan (p > 0,5 ÷ ≤ 0,67 dan / atau IB (25 ÷ 33,5) mA) atau Berbahaya (p > 0,67 ÷ ≤ 0,83 dan / atau IB (33,5 ÷ 41) mA). Aplikasi akhir dari sistem dapat menjadi alat non-kontak untuk memprakirakan kondisi isolator keramik dan polimer yang digunakan oleh teknisi di lapangan.

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.

Partial-discharge is a symptom of high voltage insulation aging, which is a small voltage pulse with high frequency and superposition with high voltage sources that have low frequencies. To find out the existence of this signal, it needs a reliable measurement technique to avoid misinterpretation. This paper presents a technique for measuring partial discharge with an induction method. The sensor used is circular twin loops. The first loop passes through a partial discharge signal, and the second induction receiver produces an induced voltage signal. Various sizes of loop diameters are designed with dimensions 3.2, 4.7, 8.9, and 11.4 cm to look for sensor sensitivity. The performance sensor is analyzed by reading the sensitivity test to the input given with 50-ohm oscilloscope impedance. From the measurement results, the higher the diameter of the sensor loop has good sensitivity.

Inductively coupled plasma system was used in drinking water treatment system to kill the microorganisms in water such as total coliforms (TC), fecal coliforms (FC) and other coliforms (OC) from river water. The aim of this study was to investigate the effect of flowrate on removal efficiency (RE), death rate, and death yield and energy consumption of bacteria's. The frequency of the system was set at 4.6 MHz. The results show that the removal efficiencies and death rate of TC, FC and OC decreased with increasing flowrate. Compared to FC, the first-order reactions of TC and OC were lower in the following order: FC > OC > TC. The death yield of TC and OC significantly increased when the removal efficiency increased. The electromagnetic flux varied from 19.44 to 20.55 W/cm2 and the energy consumption was 0.26, 0.32, and 0.67 with flow rate at 20, 10 and 5 mL/minute, respectively. These results are very necessary to improve drinking water treatment.

Pathogenic bacteria, such as total coliforms (TC), fecal coliforms (FC) and other coliforms (OC), were removed from groundwater by inductively coupled plasma system treatment in continuous flow experiments. The objective of this study is to investigate the effect of flowrate and frequency on the behavior of microorganisms in drinking water treatment using inductively coupled plasma system (ICPS). The results showed that after 120 minutes of ICPS treatment, the removal efficiency with respect to TC, FC and OC decreased with increasing flowrate. The removal efficiency of FC was achieved at 100% in all runs. Compared to FC, the removal efficiencies with respect to TC and FC were lower than those with respect to TC and OC in the following order: FC >OC> TC. The disinfection yield of TC and OC significantly increased when the removal efficiency increased. The electromagnetic flux varied from 8.08±0.46 to 10.54±0.19 W/cm2. The results in the present work can be used to design a new technology for drinking water treatment to remove all pathogenic bacteria without using hazardous chemicals.

This study was done at ligtning detection system in Padang. The systems was consist of 3 electric field sensors with synchronous satelite GPS. Time of arrival and sensors coordinate was taken from each sensors. This data was used to calculate ligtning location by Time of Arrival Linear Spherical method. Then the distances between lighting and sensor can be calculated. The distances will compared with electric field waveforms recorded at lightning sensor to testing validity our results. After validity, lightning current peak can be calculated. 8 of 20 data sample are valid with lowest lightning current peak is -1,001 kA dan highest value is -2,661 kA. Keywords : Lightning, Lightning Detection System, Time of Arrival Ligtning Current Peak. Abstrak Penelitian ini dilakukan pada sistem deteksi petir yang dibangun di kota Padang. Sistem terdiri dari 3 sensor medan listrik dan GPS yang tersinkronisasi. Perbedaan waktu datang dan koordinat sensor didapatkan dari masing-masing sensor. Data ini digunakan untuk mendapatkan lokasi kejadian petir dengan metode Time of Arrival Linear Spherical . Setelah lokasi petir didapatkan maka jarak antara stasiun dengan lokasi kejadian petir dapat diketahui. Jarak sensor dengan petir dibandingkan dengan parameter gelombang medan listrik yang terekam sehingga dapat diketahui validnya hasil perhitungan. Setelah hasil perhitungan valid maka arus puncak dapat ditentukan. Dari 20 data tersebut terdapat 8 data yang bentuk gelombang medan listriknya sesuai dengan jarak antara sensor dengan lokasi petir dengan arus puncak petir yang terendah berada pada nilai -1,001 kA dan tertinggi berada pada nilai -22,661 kA. Kata Kunci: Pembangkit Listrik Tenaga Hybrid, Diesel Generator, Photovoltaic Array, HOMER, Optimalisasi, TNPC

The disinfection performance of the radio frequency inductively coupled plasma (RFICP) system against Salmonella Typhi in water was examined using continuous flow experiments. The evaluation was based on disinfection efficiency, death rate constant, disinfection yield, and energy consumption. For all experiments the electromagnetic flux generated in the plasma reactor varied from 4 to 6 W/cm2. The disinfection efficiency and death rate constant of Salmonella Typhi decreased with the increase of the initial number of Salmonella Typhi bacteria. The disinfection yield increased from 784 to 1889 CFU/KWh and the energy consumption decreased from 0.28 to 0.07 KWh/L with the flowrate increasing from 5 to 20 mL/minute. The flowrate is an important parameter in predicting disinfection performance against pathogenic bacteria in water to design drinking water treatment plants.

Compact intracloud discharge (CID) pulses have strong radio frequency radiation, large amplitude and a short duration of several microseconds. There are two types of CIDs, namely positive and negative CID. CID electric field signatures appear without any detectable initial breakdown process. It is unclear how the CID discharge process is initiated in thunderclouds. In this study we analyzed the initiation process of positive and negative CIDs and compared them with initial electric field pulses in the preliminary breakdown process of normal intracloud (IC) lightning flashes. 28 positive and 103 negative CID electric field records were examined. The waveforms of the CID pulses were compared with the initial electric field pulses from the preliminary breakdown process. We found that the maximum parameter values of the positive CIDs were higher than those of the negative CIDs. Furthermore, the time features of the CID pulses were smaller than those of the initial electric field pulses from the preliminary breakdown of IC lightning.

Cloud-to-ground lightning flashes are among the most dangerous natural phenomena in the world. To reduce lightning hazards, it is needed to investigate the evolution of thunderstorm electrification before the first lightning strike by electric field measurement. Electric field measurement at ground level is used as a basis for lightning hazard warnings. Also, weather satellites can provide valuable information about the location of convective cells that can potentially become thunderstorms. In this study, the relationship between electric field changes at ground level and thunderstorms before the first lightning stroke to the ground was investigated. It was found that the first cloud-to-ground lightning flashes were always preceded by an atmospheric electrostatic field change at ground level by several hours.

This Antenna Sensor for partial discharge (PD) detection has been widely proven in Gas-Insulated Substation (GIS) monitoring. The electromagnetic wave produced from PD activity which occurs at a frequency of 300 MHz to 3000 MHz This paper present design of the long bowtie antenna. Its development from the original bowtie antenna to acquire more bandwidth. Simulation using the finite element method (FEM). bandwidth total long bowtie antenna design results in return loss (RL) value under −10 decibel (dB) is 870 MHz Dual frequency resonant on 900 MHz with RL value −19.98 dB and 2.21 GHz with RL value −20.981 dB.

The characteristics of 77 electric field changes of positive cloud to ground (CG) flashes in the tropics of Indonesia were investigated. It was found that the arithmetic mean (AM) and geometric mean (GM) values for 0%–100% and 10%–90% rise time were 12.7 μs, 11.9 μs and 6.1 μs, 5.8 μs, respectively. The percentages of single, double, and triple strokes of lightning flashes were 83% (64 cases), 16% (12 cases), and 1% (1 case), respectively. The AM and GM of the interstroke intervals and the return stroke (RS) amplitude ratios were 163.9 ms, 0.29, and 13.3 ms, 0.26, respectively. Furthermore, it was also found that 7 (9%) of 77 positive CG flashes had double peak return stroke waveforms with AM and GM values for 0%–100% and 10%–90% rise time of subsequent return strokes that were 6.7 μs, 6.4 μs and 4.1 μs, 4 μs, respectively. We inferred that these double peaks are produced by two ground terminations with a time interval varying from 7 to 560 μs.

Lightning dischare can cause destruction to the struck object and the other object that feel electromagnetic field interference cause lightning. Lightning process associatedwith movement of charge so that can be observed by measurement magnetic field. Two loop magnetic antena (north/south loop perpendicular to west/east loop) use to determinethe direction of lightning flash. The principleis comparinheg t output voltage from each sensor. Each station will give angle valuestowardlightning. Lightning location will get from calculate intersection of three line lightning magnetic field with use Magnetic Direction Finding (MDF) method. From 275 lightning data with record we get 20 data that have same time. From 20 data we get 3 lightning data that produce pointlocation oflightning. Three angulation of lightning location than optimized, the result is a point of lightning location and we get site error from the angle of calculation result. Avarage percentation for station 1, station 2 and station 3 is 2,88 %, 2,58 %, 1,16 %. Keyword : lightning detection, magnetic direction finding (MDF), lighning location, site error. Abstrak Sambaran petir dapat menimbulkan kerusakan pada objek yang disambar maupun pada objek lain yang mengalami interferensi gelombang elektromagnetik. Proses petir berhubungan dengan pergerakan muatan, sehingga dapat diamati melalui pengukuran medan magnet. Dua loop antena medan magnet (loop utara/selatan tegak lurus terhadap loop timur/barat) dapat digunakan untuk menentukan arah lokasi petir. Setiap stasiun akan memberikan nilai sudut arah lokasi petir. Lokasi terjadinya petir dapat diperoleh dengan menghitung titik perpotongan jalur medan magnet petir dari 3 titik sensor, dengan menggunakan metode Magnetic Direction Finding (MDF). Dari 275 data petir yang terekam pada ketiga stasiun, diperoleh 20 data petir dengan waktu kejadian yang sama. Selanjutnya dari 20 data petir pada masing-masing stasiun dengan waktu kejadian yang sama tersebut diperoleh 3 data petir yang menghasilkan triangulasi lokasi petir. Triangulasi lokasi petir dioptimasi sehingga menghasilkan titik lokasi petir, maka diperoleh nilai persimpangan sudut ( site error ) dari sudut hasil perhitungan.Hasil perhitungan menunjukan stasiun 1 memiliki site error terbesar karena pengaruh topografi. Persentase site error rata – rata stasiun 1, stasiun 2 dan stasiun 3 adalah 2,88 %, 2,58 % dan 1,16 %. Kata kunci:deteksi petir,magnetic direction findings(MDF), lokasi petir,site error

Refill drinking water is a source of public drinking water in Indonesia, but the quality is not guaranteed. less optimal means of water treatment to remove pollutants in Drinking Water Refill (AMIU), especially for raw water containing total coliforms and fecal coliforms cause AMIU quality is uncontrolled. The use of radio frequency plasma technology on AMIU processing system can be used as a solution. Induced plasma system by radio frequency in water can form the active compound. The active compounds will react to microorganisms and causing microorganisms be reduced. In testing wastewater 35,000 MPN (100 %), with plasma frequency of 3,3 MHz, the bacteria can degrade to 6 % and with frequency of 3,7 MHz bacteria can degrade to 0,07 %. 23.000 MPN testing river water (100 %), with plasma frequency of 3,3 MHz setting can degrade the bacteria to 9 % and with 3,7 MHz frequency setting can degrade the bacteria to 6 %. Keyword : plasma, radio frequency , total coliform, fecal coliform Abstrak Air minum isi ulang merupakan salah satu sumber air minum masyarakat di Indonesia, namun kualitasnya tidak terjamin. Kurang optimalnya alat pengolah air guna menghilangkan polutan produk pada Air Minum Isi Ulang (AMIU), terutama untuk air baku yang mengandung total coliforms maupun fecal coliforms menyebabkan kualitas AMIU tidak terkontrol dengan baik. Penggunaan teknologi plasma radio frekuensi pada sistem pengolahan AMIU bisa dijadikan solusi. Sistem plasma yang terinduksi melalui radio frekuensi pada air dapat membentuk senyawa aktif. Senyawa aktif ini akan bereaksi terhadap mikroorganisme dan menyebabkan mikroorganisme mati. Pada pengujian air limbah 350.000 MPN (100 %), dengan frekuensi plasma 3,3 MHz dapat mendegradasi bakteri sampai 6 % dan dengan settingan frekuensi 3,7 MHz dapat mendegradasi bakteri hingga 0,07 %. Pada pengujian air sungai 23.000 MPN (100 %), dengan settingan frekuensi plasma 3,3 MHz dapat mendegradasi bakteri hingga 9 % dan dengan settingan frekuensi 3,7 MHz dapat mendegradasi bakteri hinggaa 6 %. Kata kunci : plasma, radio frekuensi, total coliform, fecal coliform.

This paper mapped 200 locations of lightning strikes in West Sumatra province. Mapping the location of lightning strikes as part of Lightning Information System was designed with the method of Lightning Distribution (LD). To get the location of lightning strikes obtained from the calculation reflection of ionosphere method to determine the distance of a lightning strike from stations of lightning and methods of Magnetic Direction Finding (MDF) to get directions from the lightning strike. Direction data obtained processed to generate a lightning incident location, then that location will be displayed on Google Maps. After that in the process of Lightning Distribution method which is a form of lightning strike density mapping by using the "File Format" grid, where each grid was measured to be 1 x 1 km 2 called the Local Density Flash (LFD). If there are multiple point strikes on the grid will change the color that is on the map fit how many number of strikes on the grid which is a Probabilistic computation Flash Density (PFD). The depiction of the scale of danger lightning in the form of variations color changes at the point where the bolt of green color represents the minimum number density of lightning strikes that contains a single point and the red color represents the maximum number density of strikes which contains more than ten points strike. Based on the color distribution of lightning strikes and Payakumbuh Agam area has the highest rate of lightning strikes in the study period. Key words: reflection ionosphere, magnetic direction finding (MDF), lightning distribution, lightning information system, and google maps API. Abstrak Paper ini memetakan 200 lokasi sambaran petir di daerah Sumatera Barat. Pemetaan lokasi sambaran petir sebagai bagian dari Sistem Informasi Petir (SIP) dirancang dengan metode Lightning Distribution (LD). Lokasi sambaran petir diperoleh menggunakan metode refleksi ionosfer untuk mengetahui jarak sambaran petir dari stasiun pendeteksi petir dan metode Magnetic Direction Finding (MDF) untuk mendapatkan arah dari sambaran petir. Data arah kemudian diproses untuk menghasilkansuatulokasikejadianpetir, kemudian lokasitersebutakan ditampilkan pada Google Maps . Setelah itu di proses dengan metode Lightning Distribution yang merupakan bentuk pemetaan kerapatan sambaran petir dengan menggunakan “Format File grid”, dimana setiap grid diukur sebesar 1 x 1 km 2 yang disebut dengan Local Flash Density (LFD). Jika terdapat beberapa titik sambaran pada satu grid akan merubah warna yang ada pada peta sesuai seberapa banyak jumlah sambaran pada satu grid yang merupakan perhitungan Probabilistic Flash Density (PFD). Penggambaran besarnya skala bahaya petir berupa variasi perubahan warna pada titik sambaran dimana warna hijau mewakili jumlah minimum kerapatan sambaran yang berisikan satu titik sambaran dan warna merah mewakili jumlah maximum kerapatan sambaran yang berisikan lebih dari sepuluh titik sambaran. Berdasarkan warna distribusi sambaran petir daerah Kabupaten Agam dan Payakumbuh memiliki tingkat sambaran petir tertinggi pada periode penelitian ini. Kata kunci : refleksi ionosfer, magnetic direction finding (MDF), lightning distribution, sistem informasi petir, dangoogle maps API

Polymer insulators tend to fail because of the climatic and environmental conditions. The failure occurs when the surface of insulator is contaminated by sea salt or cement dust which lead to partial discharge (PD). Leakage currents will increase by PD that causes deterioration of insulation. To predict the insulation failures, an adaptive neurofuzzy inference system (ANFIS) method using initial color detection processes are proposed to estimate the leakage currents based on the polymer insulator thermal images (infrared signature). In this study, the sodium chloride and kaolin are used as pollutants of the polymer insulator according to IEC 60507 standards. Then, the insulator is tested in the laboratory using AC high voltage applied at 18 kV where the temperature detection is controlled at 26° C and 70% RH (relative humidity). The percentage of colors (Red, Yellow, and Blue) from the thermal image is measured using the color detection method. Correspond to the color percentage, the ANFIS method predicts leakage currents from polymer insulators. Furthermore, this system interprets measured data from insulators that need to be categorized as Safe, Need Maintenance or Harmful. The final application of the system can be a non-contact tool to predict the polymer insulators used by technicians in the field.

The acoustic signals of thunder provide information on the lightning channel, such as frequency, power spectra density, and images. In this study, to analyze the frequency variation in acoustic signals of thunder and to reconstruct the 3D lightning channel imaging, the short time Fourier transform (STFT) and differential time of arrival (DTOA) methods were used. The results showed that the frequency for four microphones varied from 4.88 Hz to 175.78 Hz. Furthermore, the range of power spectra density values for the four microphones was between -0.59 dB/Hz and -28.31 dB/Hz. This system can reconstruct 3D lightning channel imaging.

This paper presents partial discharge (PD) measurement techniques using a commercial sensor, High-Frequency Current Transformer (HFCT). An Output signal from HFCT is read by a digital oscilloscope and compared with the reading of convensional that PD detector. When PD occurs, the signals detected using high impedance that has a long time of oscillations and cause the delay of next reading of PD signals. To avoid this issue, the time of oscillations must be reduced by installing a damper which is a resistor connected in parallel between the sensor and the oscilloscope. The result of the measurement shows that the damper has the same reading on peak values as read by the convensional PD detector.

This paper presents the development of Rogowski coil to detect the partial discharge. Rogowski coil sensor is composed of a ferrite core with a various number of turns which is 5, 10, 20 and 30 turns with a half circle and full circle configuration. The sensors need to be tested based on the number of the turns they have in reading the partial discharge signals. The sensor is connected to a digital measurement device such as a digital oscilloscope which has an input impedance of 50 ohms and 1 Mohm with a time frame duration greater than or equal to 20 ms. The reading comparison is not only between the proposed sensors but also with a commercial partial discharge sensor. The partial discharge signal is generated by a commercial charge calibrator. The measurement result shows that using low impedance lead to decreased noise but the reading is too small compared with using high impedance.

Preliminary breakdown (PB) pulses can represent the propagation path of lightning initiation and can be used to model the charge structure of a thundercloud. The characteristics of PB pulses from the lightning initiation process depend on the charge structure of the lightning cloud. This study presents the PB pulse morphology and charge structure of thunderclouds from hybrid intracloud–negative cloud-to-ground (hybrid IC-NCG) lightning in Padang, Indonesia. PB pulses were obtained from lightning radiation electric field observation. A total of 41 PB pulse waveforms of hybrid IC-NGC flashes were analyzed. Three types of PB pulse characteristics occurred in association with three different types of hybrid IC-NCG lightning morphologies. Hybrid IC-NCG lightning can be initiated from the main negative cloud charge to the upper positive cloud charge or vice-versa. The propagation direction of the initial PB pulse train of hybrid IC-NCG flashes is either upward or downward.

The impact of natural organic matter (NOM) and pathogenic bacteria in water are of great concern in water treatment due to their effect on human health. In this study, the ability to combine filtration with an inductively coupled plasma system (ICPS) to remove natural organic matter and pathogenic bacteria from water was investigated. UV260 adsorption, dissolved organic carbon (DOC) and excitation-emission matrices (EEMs) were used to evaluate the removal of NOM by the filtration-ICPS combination. The system was operated at two different flow rates, 100 and 150 ml/minute. Decreasing trend revealed for UV260 and DOC with the higher flow rate. Tryptophan-like substances generally found in water were taken as a measure of microbial activity. This preliminary research shows that the average removal efficiencies for fecal coliforms, total coliforms and salmonella were highest at a flow rate of 100 ml/minute. It can be concluded that the combined filtration-ICPS method is capable of removing NOM and pathogenic bacteria from water.

The processing of palm oil into crude palm oil (CPO) produced palm oil mill effluent (POME) as many as 2500 l/ton of CPO. POME contains Chemical Oxygen Demand (COD) average of 21,280 mg/l, Biochemical Oxygen Demand (BOD) average of 34,720 mg/l, fatty oils average of 3,075 mg/l and the average pH of 4. Wastewater treatment systems in the palm oil industry is the combination of physical processes such as sedimentation and biological processes, either anaerobic or aerobic. The weaknesses of conventional processing systems is a long processing time (10-90 days) and require extensive land area (± 6 times the total area of the factory). This study aims to provide an alternative method for POME treatment with plasma system through Dielectric Barrier Discharge (DBD). The results showed removal efficiency for COD, BOD and fatty are 53%, 55 % and 40 % with the processing time of 4 hours, respectively. Beside, consumed energy was 7.2 kWh/l for voltage application of 19 kV. Keywords: oil palm wastewater, DBD plasma, compounds organics, energy consumption Abstrak Proses pengolahan kelapa sawit menjadi minyak sawit mentah atau Crude Palm Oil (CPO) menghasilkan limbah cair sawit sebanyak 2500 l/ton CPO. Limbah cair kelapa sawit ini mengandung Chemical Oxygen Demand (COD) rata-rata sebesar 21.280 mg/l, Biochemical Oxygen Demand (BOD) rata-rata sebesar 34.720 mg/l, minyak lemak rata-rata sebesar 3.075 mg/l dan pH rata-rata sebesar 4. Sistem pengolahan limbah cair kelapa sawit di industri adalah dengan kombinasi proses fisik seperti sedimentasi dan proses biologi, baik secara anaerob atau aerob. Kelemahan dari sistem pengolahan konvensional adalah waktu pengolahan yang lama (10-90 hari) dan membutuhkan lahan yang sangat luas (± 6 kali dari luas areal pabrik). Penelitian ini bertujuan untuk memberikan alternatif pengolahan limbah cair kelapa sawit dengan sistem plasma melalui metoda Dielectric Barrier Discharge (DBD). Hasil penelitian menunjukan efisiensi penghilangan COD sebesar 53%, BOD sebesar 55% dan minyak lemak 40% dengan waktu pengolahan 4 (empat) jam. Konsumsi energi yang dibutuhkan 7,2 kWh/l untuk tegangan pembangkitan 19 kV. Keywords: oil palm wastewater, DBD plasma, compounds organics, energy consumption

In this study, we have examined electric field records from 10 thunderstorm days containing 13 positive narrow bipolar pulses (PNBPs). It was found that PNBP occurrences have a strong relationship with thunderstorm activities. The mechanism of the NBPs was very different from intracloud (IC) and cloud-to-ground (CG) flashes. We also found that the AM values of rise time, full width at maximum time, zero crossing time, overshoot time, pulse duration and overshoot to peak amplitude ratio of the PNBPs were 1.64 μs, 1.32 μs, 9.38 μβ, 15.06 μ« and 0.31 μs, respectively. The pulse duration range was from 8.45 to 29.06 μs. Comparison with values from previous studies reported by other researchers showed that the mentioned parameters had no strong relationship with latitude or geographic location.