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Aromatic organoarsenic compounds tend to transform into more mobile toxic inorganic arsenic via several processes, and can inadvertently spread toxic inorganic arsenic through the environment to water sources. To gain insight into the transformation mechanisms, we herein investigated how the process of para arsanilic acid (p-ASA) transformation works in detail on the surface of adsorbents by comparing it with phenylarsonic acid (PA) and aniline, which have similar chemical structures. In contrast to the values of 0.23 mmol g and 0.68 mmol g for PA and aniline, the maximum adsorption capacity was determined to be 0.40 mmol g for p-ASA at pH 4.0. The results of FTIR and XPS spectra supported the presence of a protonated amine, resulting in a suitable condition for the oxidation of p-ASA. Based on the combined results of UV-spectra and UPLC-Q-TOF-MS, we confirmed that the adsorbed p-ASA was first oxidized through the transfer of one electron from p-ASA on MnO surface to form a radical intermediate, which through further hydrolysis and coupling led to formation of benzoquinone and azophenylarsonic acid, which was identified as a major intermediate. After that, p-ASA radical intermediate was cleaved to form arsenite (III), and then further oxidized into arsenate (V) with the release of manganese (Mn) into solution, indicating a heterogeneous oxidation process.

Objectives: In order to evaluate the quality assurance of drinking water in Kathmandu valley, this study analyzed selected physiochemical and microbial parameters of treated water samples and compared with Nepal Drinking Water Quality Standards (NDWQS). Methods: Treated water samples were collected from all over the Kathmandu valley and analyzed in terms of physicochemical and microbiological parameters over the period of one year from July 2017 to July 2018. The physio-chemical parameters of water samples were performed according to standard methods for the examination of water and wastewater. The total coliforms were enumerated by standard membrane filtration technique. Results: We report that microbiological aspect of treated water was the major problem as 66% of the water samples crossed the guideline value for total coliform count. Above 92% of jar water samples, 77% of tanker water samples and 69% of filtered water samples had the total coliform count exceeding the NDWQS. Moreover, 20% of bottled water was contaminated by coliform bacteria. Iron and ammonia content were found to be higher than the guideline values in 16% and 21% of the total treated water samples respectively. Analyzing the types of treated water samples showed that 35% and 15% of tanker water samples had higher ammonia and iron content respectively, and the same parameters were higher in 23% and 19% in the filtered water samples respectively than the standard criteria recommended by NDWQS. Conclusion: The treated water samples exceed the standard values set by NDWQS and hence had poor quality. The presence of faecal pollution indicating coliform bacteria was the key problem for treated drinking water of Kathmandu valley. Therefore, monitoring and proper treatment of water should be conducted to prevent dissemination of waterborne diseases.

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Sixty (56.1%) water samples crossed the permissible limit of WHO guideline value in heterotrophic plate count and total coliform count each. Ten different genera of gram negative bacteria were recovered in which E. coli was predominant followed by Citrobacter spp., Shigella spp., Enterobacter spp., Providencia spp., Klebsiella spp., Salmonella spp., Pseudomonas spp., Proteus spp. and Edwardsiella spp. Higher the temperature of water sample, higher the bacterial growth was obtained (p= 0.002), and similarly higher level of free residual chlorine in water reduced the bacterial growth (p= 0.037) whereas increase or decrease of pH (p= 0.454), turbidity (p= 0.164) and conductivity (p= 0.969) did not affect the microbial growth. A negative correlation (r= -0.162) between heterotrophic plate count and free residual chlorine was observed, however, without statistical significance (p= 0.096). Similarly, a negative correlation (r= -0.383) between total Coliform count and free residual chlorine was observed with statistical significance (p= 0.001). In chlorine assay, all tested eight genera of gram negative bacteria were found to be chlorine resistant at 0.2 mg/l for a contact time of 30 minutes. Average time required for T99.9 (3-log) and T99.99 (4-log) reduction of viable isolates from initial population of 2×106 cells/ml were found to be less than 30 minutes and greater than 60 minutes respectively. Log inactivation of various bacterial isolates with chlorine concentration of 0.2 mg/l for a contact time of 30 minutes were found to be ranged from 3 to 3.5-log. Emergence of chlorine resistant organisms in drinking water probably demands alternate disinfection or mitigation strategy. Nepal Journal of Science and Technology Vol. 13, No. 1 (2012) 173-178 DOI: http://dx.doi.org/10.3126/njst.v13i1.7456

Microplastics are man-made pollutants which have been detected in surface water and groundwater. Research on microplastic concentration in aquatic environment is attracting scientists from developing countries, but in Nepal no information regarding microplastic in freshwater system is available. Therefore, this study investigates the presence and abundance of microplastic in lake surface water of Phewa Lake, the second largest lake in Nepal. The average concentration of microplastic for surface water was 2.96 ± 1.83 particles/L in winter (dry) season and 1.51 ± 0.62 particles/L in rainy (wet) season. Significant difference with t = 4.687 ( p < 0.01) in microplastic concentration was observed in two different seasons. Fibers (93.04% for winter and 96.69% for rainy season) were the commonly found microplastic type in lake water and transparent as the dominant color for the two seasons. Almost all the detected microplastic were found to be < 1 mm in size. Due to the small size of microplastic and unavailability of micro-Fourier transform infrared spectroscopy (μ-FTIR) and Raman spectroscopy in Nepal, polymer identification was not done. The findings from this study can provide a valuable baseline data on microplastics for the first time in Nepal’s freshwater lake environment. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-18301-9.