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This study aimed to develop magnetic Fe3O4/sugarcane bagasse activated carbon composite for the adsorption of arsenic (III) from aqueous solutions. Activated carbon (AC) was prepared from sugarcane bagasse by chemical activation using H3PO4 as an activating agent at 400 °C. To enhance adsorption capacity for arsenic, the resultant AC was composited with Fe3O4 particles by facile one-pot hydrothermal treatment. This method involves mixing the AC with aqueous solution of iron (II) chloride tetrahydrate, polyvinyl pyrrolidone (PVP), and ethanol. Batch adsorption experiments were conducted for the adsorption of As (III) onto the composite. The effects of pH, adsorbent dosage, and contact time on the arsenic adsorption were studied. The result showed that the composite could remove the arsenic from the water far more effectively than the plain AC. The highest percentage of arsenic removal was found at pH at 8, adsorbent dose of 1.8 g/L, and contact time of 60 min. Langmuir and Freundlich adsorption isotherm was used to analyze the equilibrium experimental data. Langmuir model showed the best fit compared to the Freundlich model with a maximal capacity of 6.69 mg/g. These findings indicated that magnetic Fe3O4/sugarcane bagasse AC composite could be potentially applied for adsorptive removal of arsenic (III) from aqueous solutions.

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The hydrogeochemical and stable isotopes of water (δD and δ18O) were combined to investigate the deep groundwater recharge processes in the geologically complex intermountain basin (Kathmandu Valley). Results of the stable isotopic composition of the deep groundwater compared with global and local meteoric water lines and d-excess showed the deep groundwater as a meteoric water origin which is insignificantly affected by evaporation. The analysis suggests the deep groundwater was recharged during high rainfall periods (wet season). Additionally, the control of seasonal variation was absent in the deep groundwater and in the spring water samples. The large range of isotopic composition distribution was due to the altitude affect, whereas variations are from the various geological settings of the infiltration encountered during the recharge processes. The tri-linear diagram showed Na-K-HCO3 and Ca-Mg-HCO3 as the two major water types. The distribution of water types in this intermountain basin was found to be unique compared to other basins. Ionic concentration of the samples was found to be higher in the central part than in the periphery due to the ion exchange processes. This study determines the spatial distribution of various recharge processes that depends upon the environment during rainfall and the geological settings.

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: The increasing concentration of nitrogen compounds in the groundwater is of a growing concern in terms of human health and groundwater quality. Although an excess of nitrogen compounds in the groundwater of the Kathmandu Valley has been reported, the seasonal variations of the fate of the nitrogen compounds and their relationships to the subsurface sediments are unknown. In this study, spatially distributed shallow dug well samples were collected during both the dry and wet seasons of 2016, and the nitrogen compound, chloride (Cl−), and iron (Fe2+) concentrations were analyzed. Two shallow dug wells and one deep tube well were monitored monthly for 2 years. Although NH4-N concentrations were similar in the clay-dominated areas during both seasons (1 and 0.9 mg-N/L), they were lower in the gravel-dominated areas during wet season (1.8 > 0.6 mg-N/L). The NO3-N concentration differed depending upon the soil type which increased during the wet season (clay 4.9 < 13.6 mg-N/L and gravel 2.5 < 6.8 mg-N/L). The Fe2+ concentration, however, was low during the wet season (clay 2.7 > 0.4 mg/L and gravel 2.8 > 0.3 mg/L). Long-term analysis showed higher fluctuation of nitrogen compounds in the gravel-bearing areas than in the clay-bearing areas.

The fluvio lacustrine deposits of the Kathmandu Valley, Nepal are divided into four zones in terms of aquifer distribution. Deep confined aquifer in the south, GRI, medium depth interbedded aquifer, GRIT, shallow unconfined aquifer in the north, GRIII and an unconfined aquifer of thin sand and gravel deposit widely distributed on the surfaces of the terraces and other locations. Surface sediment deposits of fine to medium grain size referred to as surface gravel deposits, supply considerable quantity of water for residents of the valley through "Dharas" (stone spouts) and wells at superficial depths. The discharge is reported to double during monsoon period. General quality of water from these sources is considered good with some exceptions. For some years now, underground water source is believed to contribute about 40% of the city water supply. This is aggregated even further by pumping of the water in the private household with overdrafting going on for sometime. This overdrafting can be observed from the declining trend of the water levels in the tube wells. The total dynamic reserve of the valley is 12,730 m3/day. The average amount of infiltration from the rainfall is 17.2%. The discharge from "Dharas" adds to 1380 m3/day. Hence if the ground water is properly managed, overdrafting may not be necessary. Multipurpose projects specially in the northern zone should help induce artificial recharge. Otherwise, Kathmandu may face a potential disaster in the near future.