Ecological Effects of Benzyl Chloride on Different Korean Aquatic Indigenous Species Using an Artificial Stream Mesocosm Simulating a Chemical Spill

In this study, an artificial stream mesocosm consisting of a head tank, faster-flowing riffle section, gravel section, pool section, lower-run section, and tail tank was installed to simulate a chemical spill in a river. The responses of freshwater periphyton algae, crustacea (Moina macrocopa), freshwater worm (Limnodrilus hoffmeisteri), benthic midge (Glyptotendipes tokunagai), and fish (Zacco platypus and Aphyocypris chinensis) were observed after exposure to benzyl chloride (classified as an accident preparedness substance, APS) at concentrations of 1, 2, and 4 µL/L for 22.5 h. Higher concentrations increased the inhibition (photosynthetic efficiency decrease) of periphyton algae and the mortality of M. macrocopa, whereas the reproduction of the female cladoceran decreased in the 4 µL/L treatment. Mortality of fish did not occur or was lower (≤20%) at all concentrations; however, toxic symptoms were observed for some time after chemical exposure termination and later, symptoms receded. G. tokunagai mortality increased at all concentrations except the control after seven days, and no significant toxic effects were observed in L. hoffmeisteri. The hazardous concentration of benzyl chloride was calculated as 94 µg/L. This study showed the different sensitivities of each species to benzyl chloride. The findings can assist in environmental risk assessment of APSs after chemical spills to protect Korean aquatic species.

Bacteriological Analysis of Water of Kathmandu Valley

Introduction: Water is indispensible for human existence. Water pollution is the most serious environmentalquality issue all over the world, yet the people are less aware and give little emphasis on the vital connectionbetween water and health. Drinking water of most communities and municipalities in Nepal is obtained fromsurface sources, rivers, streams, ponds and lakes. Most of these sources of water are likely to pollute withdomestic and industrial wastes and many types of microorganisms present in water causes various types ofinfectious diseases. Therefore, we intend to Þ nd the bacteriological water quality of Kathmandu valley.Methods: A total of 200 water samples collected from different sources (over head tank, well and tube wells,taps, springs through spouts and household Þ lter) from different parts of Kathmandu Valley were subjected forbacteriological analysis by MPN (3 sets 3 tubes) method. Presence of fecal coliform was detected by Eijkmantest.Result: Out of total 200 water samples, 130 (65.0%) were unsatisfactory, 19 (9.5%) were intermediate(suspicious), 30 (15.0%) were satisfactory and remaining 21(10.5%) were excellent. Of the unsatisfactorywater samples subjected to Eijkman test, 22.0% of overhead tank, 30.0% of ground water, 30.0% of pipedtap water, 40.0% of natural tap (spout) and none of the household Þ lter water showed fecal coliforms. Watercontamination rate was higher during summer than in winter season.Conclusion: It is concluded that most of the water sources of Kathmandu valley are bacteriologicallyunsatisfactory for drinking.doi: http://dx.doi.org/10.3126/mjsbh.v12i2.12919

An Experimental Investigation of Merging Buoyant Jets in a Crossflow

Merging buoyant jets discharged in a crossflow were investigated experimentally using a unique visualization technique. Salt water jets were discharged from a constant head tank while being towed in an inverted position at desired rates through stagnant receiving water. Visualization of the jet cross section was produced by using fluorescent dye and a vertical slit light source. The results were photographed as a sequence of instantaneous cross sections taken by a motor-driven camera. Maximum heights, widths, and the vertical cross sections of the deflected jets were determined for different ratios of crossflow velocity to discharge velocity, number of discharge jets and discharge nozzle line orientation. Horseshoe shaped cross sections were observed in the cases of a single jet and multiple jets where the crossflow velocity was parallel to the line of discharge ports, but the horseshoe pattern was not clear when the cross flow was perpendicular to the line of multiple jets. The wake behind the multiple jets in the crossflow exhibited a distinct trailing vortex sheet.

Occurrence of Gas-Bubble Disease in Three Species of Bivalve Molluscs

Gas-bubble disease was observed in adult oysters and hard clams held in heated running sea water during the winter. Heating the cold sea water in closed heat exchangers caused it to become supersaturated with atmospheric gases. Exposure of the animals to this water caused the formation of gas-filled conchiolin blisters on the valves of the oysters. Bubbles of gas were observed in the gill filaments of the oysters and clams and in the mantle tissue of the oysters. Any method, such as the use of baffles or an aerated head tank, that reduces the dissolved gas concentration in the water will help prevent the disease.

Subcooled Swirl-Flow Boiling and Burnout With Electrically Heated Twisted Tapes and Zero Wall Flux

A series of swirl-flow tests was conducted in which all of the heat was generated in twisted-tape swirl generators. This is in contrast to past ORNL swirl-flow tests with twisted tapes, in which ∼99 percent of the heat was generated in the metallic tube wall. In the present study, water from a constant-head tank flowed by gravity at 5 to 8 fps through a vertical 0.27-in.-ID glass tube ∼13 in. long, in which was located a resistance-heated, 16-mil-thick A-nickel tape. Tape-twist ratios were varied from 2.7 to ∞ inside tube diameters/180-deg twist, inlet water temperatures from 63 to 173 F, and heat fluxes from 0.21 × 106 to 1.20 × 106 Btu/hr·ft2. The water head above the top of the tube was held at 30.7 in. In all cases, the critical wall superheat increased with decrease of tape-twist ratio, whereas the critical heat fluxes for the twisted tapes fell between 93 percent and 122 percent of those for flat tapes, maximizing in all cases at a tape-twist ratio of 7 to 10. It is postulated that the deleterious effect of centripetal acceleration with this geometry, which tends to hold the vapor on the heated surface, is compensated in the swirl-flow entrance region by inertial impingement of the liquid onto the tape surface, and along the remainder of the length by a double-vortex secondary flow pattern in the plane normal to the tube wall. The power density of a swirl-flow tube assembly may therefore be significantly increased by generating heat in the twisted tape as well as in the tube wall.