Development of an attached growth reactor for NH4-N removal at a drinking water supply system in Kathmandu Valley, Nepal.

Higher concentrations of ammonium (NH(4)-N) and iron (Fe) than a standard for drinking are typical characteristics of groundwater in the study area. To remove NH(4)-N and Fe, the drinking water supply system in this study consists of a series of treatment units (i.e., aeration and sedimentation, filtration, and chlorination); however, NH(4)-N in treated water is higher than a standard for drinking (i.e., <1.5 mg NH(4)-N/L). The objective of this study, therefore, is to develop an attached growth system containing a fiber carrier for reducing NH(4)-N concentration within a safe level in the treated water. To avoid the need of air supply for nitrification, groundwater was continuously dripped through the reactor. It made the system simple operation and energy efficient. Effects of reactor design (reactor length and carrier area) were studied to achieve a high NH(4)-N removal efficiency. In accordance with raw groundwater characteristics in the area, effects of low inorganic carbon (IC) and phosphate (PO(4)-P) and high Fe on the removal efficiency were also investigated. The results showed a significant increase in NH(4)-N removal efficiency with reactor length and carrier area. A low IC and PO(4)-P had no effect on NH(4)-N removal, whereas a high Fe decreased the efficiency significantly. The first 550 days operation of a pilot-scale reactor installed in the drinking water supply system showed a gradual increase in the efficiency, reaching to 95-100%, and stability in the performance even with increased flow rate from 210 to 860 L/day. The high efficiency of the present work was indicated because only less than 1 mg of NH(4)-N/L was left over in the treated water.

Localization of aquaporin-2, renal morphology and urine composition in the bottlenose dolphin and the Baird's beaked whale.

This study examined the distribution pattern of aquaporin-2 (AQP2), relative medullary thickness (RMT) and urine properties in the bottlenose dolphin Tursiops truncatus and Baird's beaked whale Berardius bairdii. Immunohistochemical studies revealed that AQP2 was localized in the collecting tubules/ducts of both species' renicules, as in terrestrial mammals. The collecting ducts with AQP2 were thinner and arranged more densely in the dolphin than in the whale. RMT values in the renicule were moderate in both species, but were significantly higher in the dolphin (6.0 +/- 0.9) than the whale (4.9 +/- 0.7). Urine of the bottlenose dolphin is comparatively concentrated (osmolality: 1715.7 +/- 279.4 mOsm kg(-1), Na(+): 490.1 +/- 87.9 mmol l(-1), Cl(-): 402.7 +/- 79.6 mmol l(-1), K(+): 80.7 +/- 25.8 mmol l(-1), urea nitrogen: 703.5 +/- 253.9 mmol l(-1)), while urine of the dead Baird's beaked whale is less concentrated (osmolality: 837.5 +/- 293.8 mOsm kg(-1), Na(+): 192.9 +/- 81.5 mmol l(-1), Cl(-): 159.9 +/- 71.4 mmol l(-1), K(+): 44.3 +/- 29.5 mmol l(-1), urea nitrogen: 270.7 +/- 120.3 mmol l(-1)). These data suggest it is possible that the differences in these renal morphological features may be related in some way to the difference in urine composition between the species, although further studies are necessary.