{'fraction_non_alphanumeric': 0.030911318443125058, 'fraction_numerical': 0.02261803788521346, 'mean_word_length': 4.602956705385427, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
EFFECTS OF COAXIAL DIELECTRIC BARRIER DISCHARGE ON WATER TREATMENT AT DIFFERENT SITES OF KATHMANDU VALLEY, NEPAL

The research work reports the results concerning the effects of ozone produced by dielectric barrier discharge (DBD) in well, river and industrial wastewater. The dielectric barrier discharge (DBD) unit was developed to produce highly oxidizing ozone molecules, hydrogen peroxide and hydroxyl radicals for the treatment of water. The discharge was produced by applying AC high voltage (up to 10 kV peak-to-peaks) source of frequency 26 kHz across annular electrodes. The well and wastewater samples were collected from 5 different places of Kathmandu district, Nepal. Various physical, chemical and micro-biological parameters such as pH, Electrical Conductivity (EC), Dissolved Oxygen (DO), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Total Coliform were analysed before and after ozonation. Our results showed that pH of water after treatment changed slightly with respect to pH of untreated water. There was slight change in conductivity of water from the different sources after treatment by ozone. DO of all samples increased significantly after ozonation. It was found that BOD and COD of all samples decreased significantly after ozonation. Concentration of ferrous ion (Fe 2+ ) decreased after ozonation. There was significant decrease in Total Coliform after treatment.


Introduction
Wastewater consists of large numbers of biological pollutants, living micro-organisms, bacteria, protozoa, fungi and many other contaminants (Mohamed E. et al., 2013). Water becomes polluted due to various human activities such as direct release of solid and liquid waste of industries and domestic sewage wastewater into rivers and lakes; excessive use of chemical fertilizers, pesticides and insecticides pollutes water while it rains. This causes increase in water crisis and environmental deterioration (Bhatta R. et al., 2015).
The increasing pace of urbanization and population growth continues to affect the quality of drinking water. The increasing consumption of water and discharge of wastewater has been resulted with the growing population and rising economy, which causes huge pollution (Omosa I. B. et al., 2012). Water pollution causes reduction in available freshwater, and affects human health and ecosystem also (Armstrong A. 2009 There are various methods for the treatment of wastewater. Conventional wastewater purification methods include decontamination agents like chlorine, chlorine dioxide or by using ultraviolet radiation and hydrogen peroxide (Droste R. 1996).
Chemical treatment processes for the purification of wastewater are expensive, and the final products might be as toxic as primary substances. On the other hand, biological treatment is effective to remove a wide range of pollutants, but it may change temperature, pH values and the characters of the pollutants. According to latest studies, one of the emerging technologies for wastewater treatment is advanced oxidation processes (AOPs) (Glaze W. H. et al., 1987). The COD and BOD levels are reduced, and both organic and oxidizable inorganic components are removed by the use of oxidants produced from advanced oxidation processes. AOPs can completely oxidize organic materials to carbon dioxide and water. For water purification using AOPs, ozone produced by dielectric barrier discharge (DBD) has been proved effective. The area of water purification by ozone synthesis is an industrially accepted application of electric discharges (Bubnov A. G. et al., 2004; Chang M. B. and Wu S. J. 1997; Eliasson B. et al., 1987). In plasma technology such as DBD; ions, high-reactive short-lived oxygen and nitrogen radicals, ozone, H + , etc are generated from air or atmospheric oxygen. These reactive particles which are generated during discharge react rapidly with dissolved pollutants in water due to their high reactivity and reduce the contaminants in water. Therefore, AOPs are commonly used techniques for water purification (Quyen N. T. et al., 2017). DBD cold plasma is alternative to conventional disinfectant methods in water treatment due to its efficient antibacterial activity at a short period of time (Razuqi N.S. et al., 2017).
The dissociation of oxygen molecules takes place when air is passed through the DBD under the influence of high energy electrons within the inter electrode space. The atomic oxygen combines with another oxygen molecule to form ozone. When ozone is passed through water the chemical or biological properties of water may change.
Ozone, thus produced, is released into the water where it oxidizes various organic and inorganic chemicals present in water and converts them into simpler form which gets easily decomposed in the nature (

Experimental Set up of DBD
The experimental setup used for ozone generation in this study is shown in Fig.1. The discharge from dielectric barrier was generated using high voltage (up to 10 kV peak-to-peaks) AC power supply operating at 26 kHz across annular electrodes. The electrode system used was coaxial cylindrical. The anode was connected to the central copper rod placed inside the glass tube, and cathode was connected to an aluminum sheet wrapped around a glass tube. The thickness of glass was 1.8 mm. The gas was passed inside the tube through the gap between the anode and the glass tube of 1.85 mm thickness. The concentration of ozone dissolved in water was determined by using the iodometric titration method. The concentration of ozone passed was 1.2 mg/l for 2 minutes treatment and 2.4mg/l for 3 minutes treatment. The specification of the DBD system is given below. Diameter of copper rod is 3.18 mm, and length of outer electrode and central electrode are 4.73 cm and 12.54 cm respectively. The thickness of dielectric (glass) is 1.8 mm, whereas internal diameter of glass used is 8.05 mm, and thickness of aluminum sheet is 0.14 mm.    Fig. 2 shows the pH analyses of untreated and treated water samples from five different sources. pH of untreated water samples from S 1 to S 5 were 6.6,7.3,7.8,10.7 and 6.6 respectively. For sample S 2 , pH was found to be 7.4 after 2 and 3 minute treatment while for S 3 , pH didn't change even after treatment. For other samples S 1 ,S 4 and S 5 ,pH were found to be 7.0,10.8 and 7.1 after 2 minutes treatment, and 7.3,10.9 and 7.6 after 3 minutes treatment showing a slight increase in pH after treatment. pH of water sample S 1 is found to be much close to the neutral value of 7 as compared to other samples .In the case of water sample S 3 , there is no change in pH before and after treatment. It was also observed that pH of treated water samples are within the WHO acceptable concentration range 6.5 to 8.5(World Health Organization, 2007) for drinking, except in water sample S 4 .

Conductivity Analysis (µS/cm)
The conductivity analyses of untreated and treated water samples are depicted in Fig.3.The conductivity of untreated water samples lies in between 600µS/cm to 1120µS/cm. The conductivity of water samples, which were treated for 2 minutes, lies in between580µS/cm to1060 µS/cm and those water samples, treated for 3 minutes lies in between 480µS/cm to1040 µS/cm. The conductivity of four samples decreased slightly after treatment and that of one sample didn't change even after treatment. It was also observed that there was no significant change in conductivity of water samples before and after treatment. Conductivity is directly related to the amount of salts dissolved in water, and ozonation does not contribute to addition of extra ions. It was observed that correlation coefficients between each pair of samples except S 4 were at least 0.62 to 0.97. It shows that the conductivity decreased in four samples in fairly same pattern. Fig. 4 shows DO of untreated and treated water samples. DO of the untreated water samples from S 1 to S 5 were 5.2, 6.0, 3.2, 6.4 and 6.1 respectively before treatment. After treatment with ozone for 2 minutes, DO values of water samples were found to be 5.6, 7.2, 4.0, 6.8 and 6.8 and after treatment for 3 minutes, the values were 6.4, 7.6, 4.4, 7.1 and 7.0 respectively. From the above data, it is clear that DO of all samples increased significantly after treatment with ozone. DO levels depend on the water and atmosphere interface, production through photosynthesis, consumption by plants, animals and decomposer organism in respiration. Minimum DO level required for protection of aquatic life is 5.8mg/l to 6.8 mg/l (Goel P. K. 2006). It was observed that correlation coefficients between samples S 1 and S 5 was 0.88 which is minimum and that of S 2 and S 3 was 1.00 which is maximum. It shows that DO increased in each sample in a consistent way.

Biological Oxygen Demand (BOD) Analysis (mg/L)
BOD is defined as the amount of oxygen required by the microorganism in stabilizing the biologically degradable organic matter under aerobic conditions. Fig. 5 shows BOD of untreated and treated water samples from different sources. BOD of sample S 1 was 16 before treatment, and it was reduced to 8 and 4 after treatment for 2 and 3 minutes respectively.   After treatment for 2 minutes, the total coliform reduced to nil in sample S 4 and after treatment for 3 minutes, the total coliform reduced to nil in samples S 1 and S 4. Total coliform should be 0 in drinking water. Total coliform of two samples was zero after treatment. These two water samples are drinkable after ozonation. The correlation coefficients between different samples were not calculated because the total coliform count was very high (above 1100) before treatment in two samples.

Conclusion
Results of ozonated water samples from different sources showed slight increase in pH after treatment. The conductivity of water samples changed slightly after treatment by ozone. Conductivity is directly related to the amount of salts dissolved in water, and ozonation does not contribute to addition of extra ions. DO of all samples increased significantly after ozonation. BOD and COD of water samples decreased significantly after ozonation. Remarkable effect on ferrous ion concentration was observed. Iron in its ferrous state has charge of 2 + . When ozone is passed through the solution containing ferrous salts, it contributes the oxygen atom that reacts with the Fe 2+ to give ferric salt and hence concentration of Fe 2+ decreases. There was significant reduction in the number of coliform bacteria. This showed that the ozonation process could be a useful method for reducing the microorganism present in water.